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Ke 
SNe” _IIAGAZINEFORELECTRONICS TECHNOLOGY & COMPUTER 


PROJECTS 






> 





VERSATILE 
CROPHONE/AUD 


PREAMPLIFIER 













Fe ietave a 






































‘CHANNEL 2:WIRE 
SMISSION SYSTEM 


Versatile two-way 
PIC-based design 


PIR LIGHT CHECKER 
false triggering 


EEPLUS 
New Technology Update 


Teach-In 2000 « Practically Speaking 
Ingenuity Unlimited +« Net Work 


http://www.epemag.wimborne.co.uk 








12v 18AN SEALED LEADACID BATTERIES, 
new and boxed, unused pack of 4 £39.95 
ref CYC7 or £15 each ref CYC6 


AUTOMATIC CHARGER Faortne above battenes, charges 
2 at once, charge level indicator circuitry, 6 hourcharge. £10 ref CYC8 


A new range of 12v to 


240v INVERTERS 

IV400S (400 watt) £89 

IV800S (800watt)£159 
IV1200S (1200 watt) £219 


ECG MACHINES ?/év 10AH BATTS/24V 8A TX Ex 
government ECG machines! Measures 390X320X120mm, onthe front 
are controls for scan speed, scan delay, scan mode, loads of connec- 
tions on the rear including video out etc. On the front panel are two DIN 
sockets for connecting the body sensors to. Sensors not included, 
Inside 2 x Gv 10AH lead acid batts ( not in good condition), pcb’s and 
a 8A? 24vtorroidial transformer (mains in). said as seen’ may have one 
or two broken knobs etc due to poor storage £15.99 ref VP2 


SODIUM LAMP SYSTEMS £75.70 compietesystem 


with 250w or 400watt SON-T Agro bulb, reflector with bulb holder and 
remote ballast and starter(uncased) all you need is wire. 250W 
system ref SLS1, 400W system SLS2. 


PCSUPPORT HANDBOOK the uttimatetechnical guide 
to building and maintaining PC’s. Over 460 A4 pages packed with 
technical data and diagrams just£10 refPCBK. If you want 4 copies 
for £33 ref PCBK2. Also available is a CD packed with diagnostic 
programmes to use with the book £5 ref PCBK1 


D SIZE NICADS Tagged, 1200mA, 1.2v pack of 4 for £6 ref 
CYC9 or as a pack of 24 for£22 ref CYC10 


D SIZE SEALED LEAD ACID BATTERIES 


2v 2.5ah rechargeable sealed lead acid battery made by Cyclon. 
60x45mrm (standard D size) supplied as a pack of 12 or 20 giving you 
options for battery configerations eg 12v at Sah, 24v at 2.5ah, 6v at 
10ah. These batteries are particularly useful in that you can arrange 
them in your project to optimise space etc (eg boat ballast etc) Pack 
of 12 £10 ref CYC4, pack of 20 £16 ref CYCS 


HYDROPONICS DO YOU GROW YOUR OWN? 


We have a full colour hydroponics catalogue availabie containing 
nutrients, pumps, fittings, enviromental control, light fittings, plants, 
test equipment etc Ring for your free copy. 


PC COMBINED UPS AND PSU treunithas atotal power 


of 292 watts, standard mother board connectors and 12 peripheral 
power leads for drives etc. Inside is 3 12v 7.2aH sealed lead acid 
batteries. Backup time is 8 mins at full load or 30 mins at half toad. 
Made inthe UK by Magnum, 110 or240vac input, +5vat35A, -Svat 5A, 
+12v at GA, -12v at 5A outputs. 170x260x220mm, new and boxed. 
£29.95 Ref PCUPS2 


ALTERNATIVE ENERGY CD, PACKED WITH 
HUNDREDS OF ALTERNATIVE ENERGY RE- 
LATED ARTICLES,PLANS AND INFORMATION 
ETC £14.50 REF CD56 

AERIAL PHOTOGRAPHY KIT This rocket comes with 


a built in camera! it flies up to 500 feet (150 m) turns over, and takes 
an aerial photograph of the ground below. The rocket then returns wih 
its film via its paracute. Takes 110 film. Supplied complete with 
everything including a launch pad and 3 motors (no film) £29.98 ref 
astro 


PROJECT BOXES another bargain for you are these smart 


ABS project boxes, smart two piece screw together case measuring 
approx 6"xS"x2" complete with panel mounted LED. Inside you will find 
loads of free bits, tape heads, motors, chips resistors, transistors etc. 
Pack of 20 £19.95 ref MD2 


TELEPHONES ust in this week is a huge delivery of tel- 


ephones, all brand new and boxed. Two piece construction - Ilum+- 
nated keypad, tone or pulse (switchable), recall, redial and pause, 
high/low and off ringer switch and quality construction. Off white colour 
and is supplied with a standard international lead (same as US or 
modems) if you wish to have a BT tead supplied to convert the phones 
theseare £1.55eachrefBTLX Phones£4.99 each ref PH2 10 off £30 
ref SS2 


3HP MAINS MOTORS Single phase 240v, brand new, 2 
pole, 340x180mm, 2850 rpm, builtin automatice reset overload protec- 
tor, keyed shaft (40x16mm)Made by Leeson. £99 each ref LEE1 


BUILD YOU OWN WINDFARM FROM SCRAP 
New publication gives step by step guide to building wind generators 
and propetlors. Armed with this publication and a good local scrap 
yard could make you self sufficient in electricity! £12 ref LOT81 


CHIEFTAN TANK DOUBLE LASERS9S WATT+3 
WATT+LASER OPTICS could be adapted for laser 


listener, long rangecomms etc Double beam units designed tofit inthe 
barrel ofa tank, each unit has 2 semi conductor lasers and motor drive 
units for alignement. 7 mile range, no circuit diagrams due to MOD, 
new price £50,000? us? £199. Each unit has two gallium Arsenide 
injection lasers, 1 x 9 watt, 1 x 3 watt, 900nm wavelength, 28vdc, 
600hz pulse freq. The units also contain a receiver to detect reflected 
signals from targets. £99 Ref LOT4. 


MAGNETIC CREDIT CARD READERS AND 
ENCODING MANUAL £9.95 Cased with flyieads, designed to 


read standard credit cards! complete with control elctronics PCB and 
manual! covering everything you could want to know about whats 
hidden in that magnetic strip on your card! just £9.95 ref BAR31 


SOLAR POWER LAB SPECIAL 2x6"x6" 6v 130maA 
cells, 4LED's, wire, buzzer, switch+ relay or motor. £7.98 REF SA27 


SOLAR NICAD CHARGERS 4x AAsize£9.99 ref6P476, 
2x C size £9 99 ref 6P477 





BRAND NEW MILITARY ISSUE DOSE ME- 


TERS current NATO issue Standard emergency services unit 
Used by most of the worids Military personel New and boxed Normal! 
retail price £400, BULLS bargain price just £E99The PORM 82 Misa 
portable, lightweight, water resistant gamma radiation survey meter 
to measure radiological dose rate in the range 0.1to 300 centigrays 
per hour in air. The Geiger Muller (G. M_) tube detecting unit is energy 
and polar response corrected. The radiation level is displayed on a 
Liquid Crystal Display. The microcomputer corrects for the non- 
linearity of the G.M. tube response. The instrument is powered by 
three international! C size battenes giving typically 400 hours opera- 
tian innormai conditions. The dose rate meter PORM 82M. designed 
and selected for the United Kingdom Government, has been fully 
evaluated to satisfy a wide range of environmental conditions and is 
nuclear hard. The construction enables the instrument to be easily 
decontaminated. The instrument ts designed for radiation surveys far 
post incident monitoring. Used in a mobile role, either carried by 
troops or in military vehicles for rapid deployment enabling radiation 
hot spots te be quickly located. Range 0 - 300 cGy/h in 0.1 cGyih 
increments. Over-range to 1500 cGy/n - indicates flashing 300. Accu- 
racy f20% of true dose rate +0 1 cGyih, 0- 100 cGy/h. [30% of truedose 
rate, 100 - 300 cGy/h. Energy Response 0.3 MeV to 3 MeV - within 
f20% (Ra 226). 80 Ke¥ to 300 KeV - within 140% (Ra 226). Detector 
Energy compensated Halogen quenched Geiger Muller Tube. Con- 
trois Cambined battery access and ON/ OFF switch. Batteries 3 
Intemational standard C ceils. Weight 560 arms. Operating Tempera- 
ture Range -30deg C to +60 degC. Indications High contrast 4 digit 
LCD. Battery tow indication Dose rate Rising/Falling £99 ref PDRM. 


Hydrogen fuel cellsOur new Hydrogen fuel cells are 1v 
at up tp 1A output, Hydrogen input, easily driven from a 
smal electrolosis assembly or from a hydrogen source, our 
demo model uses a solar pane! with the output leads in a 
glass of salt water to produce the hydrogen! Each cell is 
designed to be completely taken apart, put back together 
and expanded to what ever capacity you like, (upto 10watts 
and 12v per assembly. Cells cost£43 ref HFC11 


PHILIPS VP406 LASER DISC PLAYERS, scart 
OUTPUT, JUST PUT YOUR VIDEO DISK IN AND PRESS PLAY, 
STANDARD AUDIO AND VIDEO OUTPUTS, £14.95 REF VP406 


SMOKE ALARMS wsains powered, made by the famous 
Gent company, easy fit next to light fittings power point. Pack of 5 


£15 ref SS23, pack of 12£24 ref SS24 
4AH D SIZE NICADS pack of 4£10 ref 4AHPK 


SENDER KIT containsai! components to buiida A/V transmit- 
ter complete with case £35 ref VSXX2 


10 WATT SOLAR PANEL Amorphous siticon panel 


fitted in a anodized aluminium frame. Panel measures 3' by 1° with 
screw terminals for easy connection.. 3° x 1" solar panel £55 ref 
PAAGAS 


12VSOLAR POWERED WATER PUMP rerfectfor 


many 12v DC uses, from solar fountains to hydroponics! Smait and 
compact yet powerful. works direct from our 10 watt solar panel in 
bright sun. Max hd:l7 ft Max flow = 8 Lpm,1 .5A Ref AC8 £18.99 


SOLAR ENERGY BANK KIT 50x 6"x12” 6v solar 
panels(amorphous)+50 diodes £99 ref EF112 


PINHOLE CAMERA MODULE WITH AUDIO! 


Superb board camera with on board sound! extra small just 28mm 
square (including microphone) ideal for covert surveillance. Can be 
hidden inside anything , even a matchbox! Complete with 15 metre 
cable, psu and tv/ver connnectors. £49.95 ref CC6J 


SOLAR MOTORS Tiny motors which run quite happily on 


voltages from3-12vdc. Works on our 6v amorphous 6" panels and 
you can run therm from the sun! 32mm dia 20mm thick. £1.50 each 


WALKIE TALKIES 1 MILE RANGE £37/PAIR REF MAG30 

LIQUID CRYSTAL DISPLAY Bargain prices, 
40 character 1 line 154x16mm £6.00 ref SMC4011A 
YOUR HOME COULD BE SELFSUFFICENTIN 


ELECTRICITY Comprehensive plans with loads of info on 
designing systems, panels, contro! electronics etc £7 ref PV1 


AUTO SUNCHARGER 155x300mm solar pane! with diode 
and 3 metre lead and cigar plug. 12v 2w. £12.99 REF AUG10P3. 


SOLAR POWER LAB SPECIAL 2x6'x6"6v130maA 
cells, 4LED's, wre, buzzer, switch + relayormotor. £7.99 REF SA27 


SOLAR NICAD CHARGERS 4 AA size £9.99 ref 
6P476, 2xCsize £9.99 ref 6BP4A77 


MINATURE TOGGLE SWITCHES Tresetop quaiity 


Japanese panel mount toggle switches measure 35x13x1 2mm, are 
2 pote changeover and will switch 1A at 250vac, or 3 A at 125vac. 
Complete with mounting washers and nuts. Supplied as a boxof 100 
switches for £29.95 ref SWT35 or a bag of 15 for £4.99 ref SWT34 


VOICE CHANGERS hold one of these units over your 


phone mouth piece an you can adjust your voice using the controls 
on the unit! Battery operated £15 ref CC3 


BULL ELECTRICAL 


250 PORTLAND ROAD, HOVE, SUSSEX. 
BN3 5QT. (ESTABLISHED 50 YEARS). 


MAIL ORDER TERMS: CASH, PO OR CHEQUE 


WITH ORDER PLUS £4.00 P&P PLUS VAT. 


24 HOUR SERVICE £6.50 PLUS VAT. 
OVERSEAS ORDERS AT COST PLUS £3.50 


(ACCESS, VISA, SWITCH, AMERICAN EXPRESS) 


‘phone orders : 01273 203500 


FAX 01273 323077 
Sales@bull-electrical.com 





30 WATTS OF SOLAR POWER for just £69, 
4 panels each one 3'x1’ and producing 
8w, 13v. PACK OF FOUR £69 ref SOLX 

200 WATT INVERTERS plugs straight into your car 


cigarette lighter socket and is fitted with a 13A socket so you can run 
your mains operated devices from your car battery £49 95 ref SS66 


THE TRUTH MACHINE Tells if someone is tying by micro 


tremors in their voice, battery operated, works in general conversa- 
tion and on the ‘phone and TV as well! £42.49 ref TD3 


INFRARED FILMs: square piece of flexible infra red film that 


will only allow IR light through. Perfect for converting ordinary 
torches, lights, headlights etc ta infra red output only using standard 
light bulbs Easily cut to shape. 6" square £15 ref IRF2 

33 KILO LIFT MAGNE Tneodynium,32mm diameter with 
a fixing bolt on the back for easy mounting. Each magnet will lift 33 
kilos, 4 magnets bolted to a plate will lift an incredible 132 kilos! £15 


ref MAG33 Pack of 4 just £39 reg MAG33AA 
HYDROGEN FUELCELL PLANS. oadsofinformation 


on hydrogen storage and production. Practical plans to build a 
Hydrogen fuel cell (good workshop facilities required) £8 set ref FCP1 


STIRLING ENGINE PLANS interesting information pack 


covering al aspects of Stirling engines, pictures of home made 
engines made from an aerosol can running on acandle! £12 refSTIR2 


ENERGY SAVER PLUGS saves up to 15% electricity 
when used with fridges, motors up to 2A, light bulbs, soldering irons 
etc. £9 earef LOT71, 10 pack £69 refLOT72. 


12V OPERATED SMOKE BOMBS type 3 is a 12v 


trigger and 3 smoke cannisters, each cannister will fill a room ina 
very short space of time! £14.99 ref SB3. Type 2 is 20 smaller 
cannisters (suitable for mock equipment fires etc} and 1 trigger 
module for £29 refSB2 Type 1 isa 12vtngger and 20 large cannisters 
£49 ref SB1 


HIPOWER ZENON VARIABLE STROBES usetu' 


12v PCB fitted with hi power strobe tube and contro! electronics and 
speed contro! potentiometer. Perfect for interesting projects etc 
70x55mmn 1 2vdc operation. £6 earef FLS1, pack of 10 £49 ref FLS2 


NEW LASER POINTERS 4.5mw, 75 metre range, hand 
held unit runs ontwo AA battenes (supplied) 670nm. £29 ref DEC49J 
HOW TO PRODUCE 35 BOTTLES OF WHISKY 


FROM ASACK OF POTATOES Comprehensive 270 


page book covers ail aspects of spirit production fram everyday 
materials. Inciudes construction details of simple stilts £12 ref MS3 


NEW HIGH POWER MINI BUGwitna rangeofupto 800 


metres and a3 days use froma PP3 this is our top selling bug! less 
than 1" square and a 10m voice pickup range. £28 Ref LOT102 


IR LAMP KIT suitabie for cctv cameras, enables the camera 
to be used in total darkness! £6 ref EF 138 
INFRA RED POWERBEAM Handheld battery powered 


lamp, 4 inch reflector, gives out powerful pure infrared light! perfect for 
CCTV use, nightsights etc. £29 ref PB1. 


SUPER WIDEBAND RADAR DETECTOR cvetects 


both radar and laser , X K and KA bands, speed cameras, and all 
known speed detection systems. 360 degree coverage, front&r 
earwaveguides, 1.1"x2.7"x4.6" fits on visor or dash £149 


LOPTX Made by Samsung for colour TV £3 each ref SS52 
LAPTOP LCD SCREENS 240x175mm, £12 ref SS51 


WANT TO MAKE SOME MONEY? STUCK FOR 


AN IDEA? we have collated 140 business manuals that give 
you information on setting up different businesses, you peruse these 
at your leisure using the text editor on your PC. Also included ts the 
certificate enabling you to reproduce (and sel!) the manuals as much 
as you like! £14 ref EP74 


ELECTRONIC SPEED CONTROLLER KIT rortne 


above motoris£19 ref MAG17. Save £5 ifyou buythem both together, 
4 motor plus speed controller rrp is £41, offer price £36 ref MOTSA 


INFRA RED REMOTE CONTROLS maze for TV's but 
may have other uses pack of 100 £39 ref IREM 


RCB UNITS Inline IEC lead with fitted RC 
breaker. Installed in seconds. Pack of 3 
£9.98 ref LOT5A 


On our web sites you 
can 


1. Order online. 

2. Check your premium bonds. 

3. Enter our auction or build your own. 

4. Add E-commerce to your own site. 

5. Discover our software site, optical site, hydro- 
ponics site, holiday home exchange site, inkjet 
site, hotels site. 

6. View our web camera. 


7. Invest in our future. 


http://www.bullnet.co.uk 


YOUR HOME COULD BE SELF SUFFICENTIN 
ELECTRICITY Comprehensive plans with loads of info on 
designing systems, panels, control electronics etc £7 ref PV1 


AUTO SUNCHARGER 155x300mm solar panel with diode 
and 3 metre lead and cigar plug. 12v 2w. £12.99 REF 
AUG10P3. STEPPER MOTORS brand newstepper motors, 


4mm fixing holes with 47. 14mm fixing centres, 20mm shaft, 6.35mm 
diameter, Sv/pnase, 0.7A/phase, 1.8 deg step (200 step) Body 
56x36mm. £14.99 ea ref STEP6, pack of 4 for £49.95. PIC based 
variable speedcontroller kit £15 ref STEP7 


ISSN 0262 3617 
PROJECTS ... THEORY ... NEWS... 
COMMENTS ... POPULAR FEATURES ... 


VOL. 29. No. 5 MAY 2000 


Cover illustration by Jonathan Robertson 








ELECTRONICS TODAY INTERNATIONAL 


http:/Awww.epemag.wimborne.co.uk 








© Wimborne Publishing Ltd 2000. Copyright in all 
drawings, photographs and articles published in 
EVERYDAY PRACTICAL ELECTRONICS is fully pro- 


tected, and reproduction or imitations in whole or in — 


part are expressly forbidden. 


Our June 2000 issue will be published on Friday, 
5 May 2000. See page 323 for details 


Everyday Practical Electronics, May 2000 








Projects and Circuits 


VERSATILE MIC/AUDIO PREAMPLIFIER by Raymond Haigh 332 
New chip SSM2166 offers a.g.c., compression, limiting and noise reduction 
INGENUITY UNLIMITED hosted by Alan Winstanley 

Sensitive Hall Effect Switch; Infra-red Remote Tester; Auditory Illusion; 
Experimenter’s Power Supply 

LOW-COST CAPACITANCE METER by Robert Penfold 

An easy-build Starter Project that adds a useful tool to your workshop 
MULTI-CHANNEL TRANSMISSION SYSTEM - 1. by Andy Flind 
An 8 to 16-channel 2-wire signalling link with optional interface 

PIR LIGHT CHECKER by Terry de Vaux-Balbirnie 

Be trigger happy with your outdoor security light system! 


: 


2 8 § 


Series and ‘Features 


NET WORK - THE INTERNET PAGE surfed by Alan Winstanley 
Google Box; Free for All; Under the Surf; Looking Ahead 
TECHNOLOGY TIMELINES - 4. Computing - 1900 to 2000 
by Clive “Max” Maxfield and Alvin Brown 

Who, what, where and when -— the fascinating story of how technology 
developed in the last millennium 

NEW TECHNOLOGY UPDATE by Ian Poole 

Lower operating voltages speed microprocessor rates, but heat 
dissipation becomes more of a problem 

CIRCUIT SURGERY by Alan Winstanley and lan Bell 

Op.amps — outputs and short-circuit protection; Battery Flattery 
TEACH-IN 2000 - 7. Op.amps by John Becker 

Essential info for the electronics novice, with breadboard experiments 
and interactive computer simulations 

PRACTICALLY SPEAKING by Robert Penfold 

A novice’s guide to using stripboard 


Regulars and Services 


EDITORIAL | 

NEWS - Barry Fox highlights technology's leading edge 

Plus everyday news from the world of electronics 

BACK ISSUES Did you miss these? 

ELECTRONICS VIDEOS Our range of educational videos 
READOUT John Becker addresses general points arising 

CD-ROMS FOR ELECTRONICS 

Filters; Digital Works 3.0; Parts Gallery + Electronic Circuits and Components; 
Digital Electronics; Analogue Electronics; PiCtutor, Modular Circuit Design; 
see also Direct Book Service pages 

SHOPTALK with David Barrington 

The essential guide to component buying for EPE projects 


ELECTRONICS MANUALS 
Essential reference works for hobbyists, students and service engineers 


DIRECT BOOK SERVICE 

A wide range of technical books available by mail order, plus more CD-ROMs 
PRINTED CIRCUIT BOARD AND SOFTWARE SERVICE 

PCBs for EPE projects, plus EPE software 


ADVERTISERS INDEX 


FREE 
GIANT TECHNOLOGY TIMELINES CHART between pages 360/361 


Nees 88 


$8.88 8 


Readers Service @ Editorial and Advertisement Departments 331 


321 


-» $94 4 





Converts your colour monitor into a QUALITY COLOUR TV! 





MB). Push bution controls on the front panel allow reception of 8 fully 
channels. 


‘olf ai’ UHF colour television TELEBOX ME Covers vitualy af tle: 


oe ig airy pute For complete compatibility - even 
watt audio amplifier and low level Hi Fi audio output afe 
prea g as ee par new - fully guaranteed. 
TELEBOX ST for composite video input type monitors 
TELEBOX STL as ST but fitted with integral speaker 
TELEBOX MB Multiband VHF/UHF/Cable/Hyperband tuner £69.95 
For overseas PAL versions state 5.5 or 6 mHz sound specification. 
“For cable / hyperband signal reception Telebdox MB should be con- 
nected to.a cable type service. Shipping on all Telebox's, code (B) 


£36.95 
£39.50 


State of the art PAL (UK spec) UHF TV tuner module | 


with composite 1V pp video & NICAM hi fi stereo sound 
outputs. Micro electronics ail on one small PCB only 73 x 160 
="¥ §2 mm enable full tuning control via a simple 3 wire link to an 
IBM pc type computer. Supplied compiete with simple working pro- 
gram and documentation. Requires +12V & + 5V DC to operate. 
BRAND NEW - Order as MY00. Only £49.95 code (B) 
See www.distel.co.uk/data_my00.htm for picture + full details 


All units (unless stated) are BRAND NEW or removed from often . 


brand new orice and are fully tested, aligned and shipped to 
you with a full 90 day guarantee. Call er see our web site 
www.distel.co.uk for over 2000 unlisted drives for spares or repair. 


3%" Mitsubishi MF355C-L. 1.4 Meg. Laptops only £25.95(B) 
3%* Mitsubishi MF355C-D. 1.4 ve Non laptop £18.95(B) 
5%" Teac FD-55GFR 1.2 Meg (for iBM pc's) RFE £18.95(B8} 
5%" Teac FO-55F-03-U 720K 40/80 (for BBC's etc) RFE £29.95(B 
5%" BRAND NEW Mitsubishi MF5018 360K £22.95(8 


Table top case with int 


8” Shugart 800/801 8" 


ral PSU for HH 5%“ Floppy/HD £29.95(6 
S refurbished & tested £216.00(E 


8” Shugart 810 8° SS HH Brand New £195.00(E 
8” Shugart 851 8* double sided refurbished & tested £260.00(E 
8” Mitsubishi M2894-63 double sided NEW £295.00(E 
8" Mitsubishi M2896-63-02U DS slimline NEW Saas ~ 


Dual 8“ cased drives with integral power supply 2 Mb 


2%" TOSHIBA MK1002MAV 1.1Gb Japtop(12.5 mm H New £79.95 
2%* TOSHIBA MK2101MAN 2.16 Gb laptop (19 mm H) New £89.50 
2%" TOSHIBA MK4309MAT 4.3Gb laptop (8.2 mm H) New £105.00 
2%* TOSHIBAMK6409MAV 6.1Gb laptop (12.7 mm H}) New£190.00 
2%" to 3%" conversion kit for Pc’s, complete with connectors £14.95 
3¥" FUJI FK-309-26 20mb MEM I/F RFE 


3%" CONNER CP3024 20 mb IDE I/F (or pene RFE £59.95 
3%* CONNER CP3044 40 mb IDE VF {or equiv.) RFE £69.00 
3%" QUANTUM 40S Prodri ve 42mb SCSI I/F, New RFE £49.00 
51%" MINISCRIBE 3425 20mb MFM I/F (or equiv.) RFE £49.95 
5%* SEAGATE ST-238R 30 mb ALL (/F Refurb £69.95 
5%* CDC 94205-51 40mb HH MFM I/F RFE tested £69.95 
5%* HP 97548 850 Mb SCSI RFE tested £99.00 
5%" HP C3010 2 Gbyte SCS! differential RFE tested £195.00 
8° NEC 02246 85 Mb SMD interface. New £199.00 
8" FUJITSU M2322K 160Mb SMD I/F RFE tested £195.00 
8 FUJITSU M2392K 2 Gb SMD V/F RFE tested £345.00 


Many other drives in stock - Shipping on all drives is code (C1) 


MITS. a FA3445ETKL 14” industrial spec SVGA monitors £245 
FARNELL 0-60V DC @ 50 Am by bench Power Supplies £995 
FARNELL AP3080 0-30V DC @ 80 Amps, bench Suppy £1850 
1kW to 400 kW - 400 Hz 3; power sources - ex stock £POA 
IBM 8230 Type 1, Token ring base unit driver £760 
Wayne Kerr RA200 Audio frequency response analyser £2500 
IBM 53F5501 Token Ring ICS 20 port lobe modules £750 
{BM MAU Token ring distribution panel 8228-23-5050N £95 
AIM 501 Low distortion Oscillator 9Hz to 330Khz, IEEE £550 
ALLGON 8360.1 1805-1880 MHz hybrid power combiners £250 
Trend OSA 274 Data Analyser with G703(2M) 64 i/o £POA 


Marconi 6310 Programmabie 2 to 22 GHz sweep generator 
Marconi 2022C 10KHz-1GHz RF signal generator £ 
Marconi 2030 opt 03 10KHz-1.3 GHz signal generator, New 
HP1650B Logic Analyser £ 


HP3781A Pattern generator & HP3782A Error Detector £POA 
HP6621A Dual Programmable GPIB PSU 0-7 V 160 watts £1800 
HP6264 Rack mount variable 0-20V @ 20A metered PSU £675 
HP54121A DC to 22 GHz four channel test set £POA 
HP8130A opt 020 300 MHz pulse generator, GPIB etc £7900 
HP Ai, AO B pen HPGL high speed drum plotters - from £550 
HP DRAFTMASTER 1 8 pen high speed plotter £750 
EG+G Brookdeal 95035C Precision lock in amp £1800 
View Eng. Mod 1200 computerised inspection system £POA 
Sony DXC-3000A High quality CCD colour TV camera £995 
Keithley 590 CV capacitor / voltage analyser £POA 
Racal ICR40 dual 40 channe! voice recorder system £3750 
Fiskers 45KVA 3 ph On Line UPS - New batteries £9500 
Emerson AP130 2.5KVA industrial spec.UPS £2100 
Mann Tally MT645 aa speed line printer £2200 
intel SBC 486/433SE Multibus 486 system. BMb Ram £945 
Siemens K4400 64Kb to 140Mb demux analyser £2950 





Will connect direct to 


Ls 





OBSOLETE - SHORT SUPPLY - BULK 


10,000,000 items EX STOCK 


For MAJOR savincs 
CALL OR SEE OUR WEB SITE www.distel.co.uk 


One of the highest specification 
monitors you will ever see - 
At this price - Don’t miss it!! 


Mitsubishi FA3415ETKL 14" SVGA Multisyne colour monitor with fine 
,, 0.28 dot pitch tube and resolution of 1024 x 768. A 





modes, BBC, COMMODORE 
4 ARCHIMEDES and APPLE. 


ye faceplate, text and LOW! TION MPR 


Sahn ala at 


~ $pecification. Fully guaranteed, in EXCELLENT fittle 
Only £119 
included. y © MTSSvGA 


Extemal cables for other types of computers available - CALL 






Ex demo 17% 0.28 SVGA Mitsubishi Diamond Pro 
monitors, Full multisyne etc. 
Full 90 day guarantee. Only £199.00 (E) 


Just in - Microvitec 20" VGA (800 x 600 res.) colour monitors. 
Good SH condition - from £299 - CALL for info 


PHILIPS HCS35 (same ap ts as CM8833) attractively styled 14” 
colour monitor with both RGB and standard composite 15.625 
Khz video inputs via SCART socket and separate phono jacks. 
integral audio power a mp and speaker for all audio visual uses. 

Amiga and Atari BBC computers. ideal for ail 
video monitoring / security applications with direct connection 
to most colour cameras. High quality with many features such as 
tront concealed flap controls, VCR correction button etc. Good 


used condition - fully tested - quaranteed 
Dimensions: W14" : H12%" BS 5%" D Only £99. 00 (E) 


PHILIPS HCS31 Ultra compact 9" colour video monitor with stan- 
dard composite 15.625 Khz video input via SCART socket. Idea! 
for ail monitoring / security applications. High quality, ex-equipment 
fully tested & guaranteed (possible minor screen burns). In attrac- 
tive square black plastic case measuring W10* x H10" x 13%" D. 


240 V AC mains powered. Only £79.00 (0) 


KME 10" 15M100039 high definition colour monitors with 0. aiid dot 
pitch. Superb clarity and modern styling. cocccmewogee 
Operates from a a 15.625 khz sync RGB video gsc. 
source, with RGB analog and composite sync 3 
such as Atari, Commodore Amiga, Acorn #& 
Archimedes & BBC. Measures only 1 Me" x 12° x 


11". Good used condition. Only £125 (E) 
20" 22" and 26" AV SPECIALS 


Superbly made UK manufacture. PIL. all solid state colour monitors, 
complete with composite video & optional sound input. Attractive 
teak style case. Perfect for Schools, Shops, Disco, Clubs, etc.in 
EXCELLENT little used condition with full 90 day guarantee. 


20"....£135 22"....£155 26"....£185 (7 


We probably have the largest range of video monitors in 
Europe, All sizes and types from 4" to 42“ call for info. 





seat every type o 
upply you can imagi 
10, 000 Pawer Suppi lien 
Call or see our 


HP6030A 0-200V DC @ 17 Amps bench power su ply £1950 
intel SBC 486/125C08 Enhanced Muitibus (MSA) £1150 
Nikon HFX-11 (Ephiphot) exposure control unit £1450 
PHILIPS PM5518 pro. TV signal generator £1250 


Motorola VME Bus Boards & Components List. SAE / CALL £POA 


Trio 0-18 vdc linear, metered 30 amp bench PSU. New £550 
. Fujitsu M3041R 600 LPM high speed band printer £1950 
Fujitsu M3041D 600 LPM printer with network interface £1250 
Perkin Elmer 2998 infrared spectrophotometer £500 
Perkin Elmer 597 Infrared spectrophotometer £3500 
_ VG Electronics 1035 TELETEXT ing Margin Meter £3250 
LightBand 60 output high spec 2u rack mount Video VDA's £495 


Sekonic SD 150H 18.channel digital Hybrid Sait tos recorder £1995 
B&K 2633 Microphone pre amp £300 
Taylor Hobson Tallysurf amplifier / recorder £750 
ADC $S200 Carbon dioxide gas detector / monitor £1450 
BBC AM20/3 PPM Meter (Ernest Turmer) + drive electronics id 
ANRITSU 9654A Optical DC-2.5G/> waveform monitor £5650 

ANRITSU MS900181 0.6-1.7 uM optical spectrum analyser EPOA 


ANRITSU ML93A optical power méter £990 
ANRITSU Fibre optic characteristic test set £POA 
R&S FTDZ Dual sound unit £650 
R&S SBUF-E1 Vision modulator £775 
WILTRON 6630B 12.4 / 20GHz RF sweep generator £5750 
TEK 2445 150 MHz 4 trace oscilloscope £1250 
TEK 2465 300 Mhz 300 MHz oscilloscope rack mount £1955 


TEK TDS380 400Mhz digital realtime + disk drive, FFT etc £2900 


TEK TDS524A 500Mhz digital realtime + colour display etc £5100— 


HP3585A Opt 907 20Hz to 40 Mhz spectrum analyser £3950 
PHILIPS PW1730/10 6OKV XRAY generator & accessories LPOA 
CLAUDE LYONS 12A 240V single phase auto. volt. regs £325 
CLAUDE LYONS 100A 240/415V 3 phase auto. volt. regs £2900 


THIS en 'S SELECTION Amppry OUR VAST ve SUL STOCKS 








Surplus always 
i wanted for cash! 


Superb quality 6 foot 40U 
Virtually New, Ultra Smart 


Less than Half Price! 


- Top qualit y 19” rack cabinets made in UK by 
Optima Enctosures Ltd. Units feature 
designer, smoked acrylic lockable front door, 
full height fockable half iduvered back door 
and louvered removable side panels. Fully 
adjustable internal fixing struts, ready punched 
for any configuration of equipment mounting 
plus ready mounted integral 12 way 13 amp 
socket switched mains distribution strip make 
these racks some of the mast versatile we 

have ever sold. Racks may be stacked side by side and therefore 

tequire only two side panels to stand sin gly or in multiple bays. 

Overall dimensions are: 77%" H x 32%" D x 22" W. Order as: 

OPT Rack 1 Complete with removable side panels. £345.00 (G) 
OPT Rack 2 Rack, Less side panels £245.00 (G) 








Made by Eurocraft Enclosures Ltd to the highest possible spec, 
rack features all steel construction with removable 
side, front and back doors. Front and back doors are _<¢S>. 






hinged for easy access and ail are lockable with <a 
five secure 5 lever barrel locks. The front door Ess 
is constructed of double walled stee! with a 
‘designer style’ smoked acrylic front panel to} 
enable status indicators to be seen through the B 
panel, yet remain unobtrusive. internally the rack 
features fully slotted reinforced vertical fixing | 
members to take the heaviest of 19" rack 
equipment. The two movable vertical fixing struts 
{extras available) are pre punched for standard 
‘cage nuts’. A mains distribution panet internal- B= 
ly mounted to the bottom rear, provides 8 x IEC 3 A: 
pin Euro sockets and 1 x 13 amp 3 pin switched “Gx 
utility socket. Overall ventilation is provided by oe 

fully louvered back door and double skinned top section ~ 

with top and side iouvres. The top panel may be removed for fitting 
of integral fans to the sub plate etc. Other features include: fitted 
castors and floor levelers, prepunched utility panel at lower rear for 
cable / connector access etc. Supplied in excellent, slightly used 
condition with keys. Colour Royal blue. External dimensions 
mm=1625H x 635D x 603 W. ( 64" H x 25” D x 23%" W) 


Sold at LESS than a third of makers price f! 


A superb buy at only £245.00 @ 
42U version of the above only £345 - CALL 


A special bulk purchase from a cancelled export order brings you 
the most amazing savings on these ultra high spec 12v DC 14 Ah 
rechargeable batteries. Made by Hawker Energy Ltd, type SBS15 


™ featuring pure lead plates which offer a far superior shelf & guaran- 


teed 15 ead service life. Fully BT & BS6290 approved. Supplied 
BRAND NEW and boxed. Dimensions 200 wide, 137 high, 77 deep: 
M6 boit terminals. Fully guaranteed. Current makers price over £70 


eahOur Price £35 each « or 4 for £99 6 


Save £££E"s by choosing your next relay from our Massive Stocks 
covering types such as Military, Octal, Cradle, Hermetically Sealed, 
Continental, Contactors, Time Delay, Reed, Mercury Wetted, Solid 
State, Printed Circuit Mounting etc. , CALL or see our web site 
www.distel.co.uk for more information: Many obsolete types from 
stock. Save ££££"s 


Undoubdtedi h- miracle of modern technology & 
our special buying power ! A quality product fea- 
turing a fully cased COLOUR CCD camera at a 
give away price ! Unit features full fow tot sensing for 

use in fow light & high fight 
applications. MA 10 mm fixed. focus 
wide angle lens gives excellent focus 
and resolution trom close up to long 
range. The composite video output will 
connect to any composite monitor or TV 
(via SCART socket) and most video 
recorders. Unit runs from 12V DC so, 
ideal for security & portable applica- 
iii tions where mains power not available. 
Overall dimensions 66 mm wide x 117 deep x 43 high. Supplied 
BRAND NEW & fully guaranteed with user data, 100's of applica- 
tions including Security, Home Video, Web TV, Web Cams atc, etc. 


Web ref=LK33 ONLY £99.00 or 2 for £180.00 (e) 


NT4 WorkStation, complete with service pack 3 
and licence - OEM packaged. ONLY £89.00 ja) 
ENCARTA 95 - CDROM, Not the latest - but at this price | £7.95 
DOS 5.0 on 3%" disks with concise books c/w QBasic . £14.95 
Windows for Workgroups 3.11+ Dos 6.22 on 3.5" disks | £55.00 
Wordperfect 6 for DOS supplied on 3%" disks with manual £24.95 


shipping charges for software is.code B 


DISTEL on the web !! - Over 16,000,000 items from stock - www.distel.co.ak 


ALL MAIL TO 
Dept PE, 29/35 Osborne Rd 
Thornton Heath 


Surrey CR7 8PD 
Open Mon - Fri 9.00 - 5:30 








LONDON SHOP 


Open Mon - Sat 9:00 - §:30 | 
215 Whitehorse Lane 
South Norwood 
On 68A Bus Route 
Nr. Thornion Heath & 
Selhurst Park SR Raii Stations - 


DISTEL© 


Visit our web site 
| www.distel.co.uk 
| email = admin@distel. co.uk 







ALL @ ENQUIRIES 










FAX 0208 653 8888 


All prices for UK Mainland. UK customers add 17.5% VAT to TOTAL order amount. Minimum order £10. Bona Fide account orders accepted from Govemment, Schoot 


Universities and Local Authorities - 





of Sale and unless stated guaranteed for 90 days. All 
} to stock. Discounts for volume. Top CASH prices paid 


minenum account order £50. 


Cheques over £100 are subject to 10 working days clearance. Carriage charges (A}=£3.00, (A1}=£4.% 

errs | 26. (B}=£5.50, (C)=£8.50..(C-1) £12.50, (D)=£15.00, (E}=£ 18.00, (F}=£20.00, (G}eCALL. Allow approx 6 days for shipping - faster CALL. All goods supplied to our Standard Condition 

VISA Ea | 26 | 28 rantees on a retum to base basis. All rights reserved to change prices / specifications without prior notice. Orders subj. 
YEARS surplus goods. All trademarks, tradenames etc acknowledged. © Display Electronics 1999. E & O £. 07/99. 





CANUTE TIDE PREDICTOR po 













For several years the author experimented with writing computer 
software intended to produce results that matched those given in 
published tide tables, and which could ultimately form the basis for a 
low-power microprocessor controlled tide predictor (long before PICs 
came along). 

Eventually he became aware that official tide tables are compiled 
not just according to the geometries of the Earth-moon-sun 
system, but also in relation to local data compiled over 
generations. There was no hope, therefore, of developing a 
simple system that could match standard tide table 4 
accuracy. 

However, most people do not need the accuracy of 
Official tide tables. All they might be interest in, for example, 
is whether it is better to go to the beach in the morning or 
afternoon in order to find the tide at the preferred state of rise or fall. 

That is what the Canute Tide Predictor is aimed at achieving — to show on 
an l.c.d., a tide-state bargraph and high-low tide times accurate to within about an hour. The use of a PIC16F876 
microcontroller has allowed a very simple unit to be designed. 

Anyone who loves the sea, sandy beaches or rocky shore lines will find this design a useful guide when 
considering a quick trip to the coast. 


TECHNOLOGY TIMELINES — ATMOSPHERIC ELECTRICITY 


The ionised layers of the atmosphere extend from about 

THE FUTURE 40km to 200km (25 to 125 miles) above the Earth. This 

It's been interesting and fun looking back ionisation is caused by the “Solar Wind” passing the Earth 
over the last 100 years or so to see how we and leaves the upper atmosphere positively charged. 
got where we are — quite a staggered path, There is thus an electric field between the upper atmos- 
with all sorts of odd developments coming phere and the Earth and, given suitable instruments, this field 
together to produce major forward steps in can be detected as it results in a miniscule current through 
technology. Finally we get to peer into the the atmosphere. 
future, it’s not quite as exact an art as looking A potential of around 100 volts is often present just one 
back, but Max and Alvin are taking a stab at metre off the ground. In other words, there is often a potential 
it from their starting point at the forefront of of 200 volts or more between your nose and toes! Of course, 
technology in the USA. We may not need to nobody gets electrocuted because the resistance of the air 
wait long to see if what they predict actually is so high that only a very tiny current is present. And this is 
happens with the rate of development of new why the actual values are so difficult to measure. But they 
technology. can be measured quite easily and we will show you how. 


PLUS: ALL THE REGULAR FEATURES 





DON'T MISS AN 


2 FAA ISSUE - PLACE YOUR 
ON: ORDER NOW! 





Demand is bound to be high 


INCORPORATING ELECTRONICS TODAY INTERNATIONAL 


JUNE ISSUE ON SALE FRIDAY, MAY 5 





Everyday Practical Electronics, May 2000 323 


HOW DOES YOUR EQUIPMENT MEASURE UP? AT STEWART OF READING THERE’S ALWAYS ‘SCOPE’ FOR IMPROVEMENT! 


7] og =| OF YN Eo) 5 t : 


SINAD MEASUREMENTS 


for only Gg 


Ps MARCONI 893C 
AF POWER METER 
300u Watts-30 Watts; 20Hz-35kHz 
2:5 ohm-20 kilohms 
MARCONI 893C unused, boxed £100 
MARCONI 893B — to 10 Watts max. 
NO SINAD £30 


GOULD J3B 
SINE/SQ. OSCILLATOR 


SOLARTRON 7150 


DMM 6%- ~digit. TRUE R.M.S. High Accuracy IEEE 
HIGH QUALITY RACAL COUNTERS 


TEKTRONIX 244SA 
4-channel, 150MHz, 
delay sweep, 
cursors/readout 


S 


TEKTRONIX 475 
«x Dual trace, 200MHz, 
delay sweep 


400 


Low distortion 
Balanced metered 


MARCONI 2610 TRUE RMS VOLTMETER 
z NS Mer Attenuator 
Meter 


Digital LCD + 
5Hz to &> 


Analogue 
25MHz + D.C. Autoranging 


AVO 8 MK. 6 MULTIMETER 


& 
& 


In Ever-Ready Case 
with Leads and 
Batteries 


Other AVOs from 


GOODWILL GFC 8010G 
FREQUENCY COUNTER, Range 
1Hz-120MHz, 8-Digit Display, 15mV 
RMS Sensitivity Unused £75 


9904 Universal Timer Counter, 50MHz 
9916 Counter, 10Hz-520MHz 


RACAL TRUE RMS VOLTMETERS 
GOODWILL 
GVT427 DUAL CHANNEL A.C. 
MILLIVOLTMETER 
10mV 300V in 12 ranges 
Frequency 10Hz-1MHz 
Used £100 Unused £125 


RACAL/AIM 9343M LCR aoe 

Auto measurements of R, C, L, Q 

HUNTRON TRACKER Model 1000 

H.P. 5315A Universal Counter, 1GHz, 2-ch .. 
FLUKE 8050A DMM 412 digit 2A True RMS . .£75 
FLUKE 8010A DMM 3% digit 10A 

FLUKE 8012A DMM 3% digit 3A 


9300 5Hz-20MHz usable to 6OMHz, 10V-316V £95 
9300B Version £150 
9301/9302 RF Version to 1-5GHz .from £200-£300 


MARCONI TF2015 AM/FM sig gen, 10-520MHz . .£175 
RACAL 9008 Auto Mod Meter, 1-5MHz-2GHz ... .£200 
LEVELL TG200DMP RC Oscillator, 1Hz-1MHz . . . .£50 
Sine/Sq. Meter, battery operated (batts. not supplied) 

FARNELL LF1 Sine/Sq. scillator, 10Hz-1MHz . . . .£75 


110 WYKEHAM ROAD, READING, BERKS. RG6 1PL 
Telephone: (0118) 9268041. Fax: (0118) 9351696 
Callers welcome 9am-5.30pm Monday to Friday (other times by arrangement) 


























DISTANCE 
LEARNING COURSES in: 


Analogue and Digital Electronics, Fibre Optics, 
Fault Diagnosis, Mechanics, Mathematics and 
Programmable Logic Controllers leading to a 


BTEC PROFESSIONAL 
DEVELOPMENT CERTIFICATE 


© Suitable for beginners and 

those wishing to update their 
knowledge and practical skills 
Courses are very practical and 
delivered as self contained kits 

No travelling or college attendance 
Learning is at your own pace 

Each course can stand alone or be 
part of a modular study programme 
Tutor supported and BTEC certified 





o oe¢coc 6 












For information contact: 

NCT Ltd., P.O. Box 11 

Wendover, Bucks HP22 6XA 

Telephone 01296 624270; Fax 01296 625299 
Web: http://www.nct.ltd.uk 


324 


MARCONI 2022E 
a Syn AM/FM SIG GEN, 
. 10kHz-1-01GHz 
a Up to +10dBm_ output, 
Eiaee mod, I.c.d. display, 
eyboard entry, etc., 
small, lightweight. 


£525-£600-£750 


RADIO COMMUNICATIONS TEST SETS 
MARCONI 2955/29958 
MARCONI 2955A/2960 £2500 
MARCONI 2019 Synth AM/FM si <i gen, 80kKHz-1040MHz .. .£475 
H.P. 8657A Synth sig gen, 100kHz-1040MHz £2500 
H.P. 8656B Synth sig gen, 100kKHz-990MHz 
H.P. 8656A S gen, 100kKHz-990MHz 
GIGATRONIC 7100 sig gen, 10MHz-20GHz 
MARCONI 2017 AM/FM phase-locked sig gen, 
10kHz-1024MHz, good signal 
H.P. 86404 AM/FM sig gen, 500kKHz-1024MHz 
H.P. 8640A AM/FM sig gen, 500kHz-512MHz 
PHILIPS PM5328 sig gen, 100kHz-180MHz with 
200MHz, freq. counter, IEEE 
RACAL 9081 Synth AM/FM sig ge en, 5-520MHz 
H.P. 3325A Synth function gen, 21MHz 
MARCONI 6500 Ampitude A Analyser 
H.P. 4275A LCR Meter, 10kHz-10MHz 
H.P. 8903E Distortion Analyser 
WAYNE KERR 3245 Inductance Analyser 
H.P. 8112A Pulse Generator, 50MHz 


SPECTRUM ANALYSERS, 3 

H.P. 8562A 1kHz-22G' 
TEKTRONIX 492 SO 18GHz a: 
EATON/AILTECH 757 0-001-22GHz..............8 , .§£2500 
ADVANTEST R3261A 9kHz-2-6GHz, synthesised .. .. ‘ee 
H.P. 853A (Dig. Frame) with 8559A 100kHz-21GHz 3 ap 750 

H.P. 8558B with main frame, 100kHz-1500MHz ... .. ... £1250 
MARCONI 2382 100Hz-400MHz, high resolution ....¥. }.£2000 
B&K 2033R Signal Analyser 
ADVANTEST TR4131 10kHz-3-5GHz 
MARCONI 2370 30Hz-110MHz 
H.P. 141 SYSTEMS 
8553 1kHz-110MHz 
8554 500kHz-1250MHz 
8555 10MHz-18GHz 


UNUSED OSCILLOSCOPES 
TEKTRONIX TDS350 dual trace, 200MHz, 1GS/s ; 
TEKTRONIX TAS485 4-channel, 200MHz etc. .......... £11 
H.P. 54600B dual trace, 100MHz, 20MS/s 

OSCILLOSCOPES 

PHILIPS PM3092 2+2-ch., 200MHZz, delay, TB etc 
PHILIPS PM3082 2+2-ch., 100MHZz, delay etc £800 
TEKTRONIX TAS465 dual trace, 100MHz, delay etc. ...... £800 
TEKTRONIX 2645 4-ch., 300MHz, delay cursors . . £1250 
TEKTRONIX 2430 dual trace, 150MHz, 100MS/s, crsors etc. £800 
TEKTRONIX 2232 dual trace, 100MHz, 100MS/s, cursors etc.£800 
TEKTRONIX 2212 dual trace, 60MHz, 20MS/s, cursors etc. .£650 
TEKTRONIX 2210 dual trace, S0MHx, 20MS/s £450 
H.P. 54200A Digitising, 50MHz, 200MS/s 


PHALIPS PM3217 - Dual Trace 50MHz Dela 
VERY GOOD 
OSCILLOSCOPE 
Incl. 2 probes, pouch 


TEKTRONIX P6106A Probe, 250MHz readout, unused 





























DATRON AutoCal Multimeter, 5Y2-7¥2-digit, ben denp-es4 
rom 


MARCONI 2400 Frequency Counter, 20GHz 

H.P. 5350B Frequency Counter, 20GHz 

H.P. 5342A 10Hz-18GHz sip mo Counter 
FARNELL AP100/30 Power Su 

FARNELL AP70/30 Power S 

PHILIPS PM5418TN Colour 

PHILIPS PM5418TX1 Colour TV Pattern Generator 
B&K Accelerometer, type 4366 

H.P. 11692D Dual Directional Coupler, 2MHz-18GHz 
H.P. 11691D Dual Directional Coupler, 2MHz-18GHz 
TEKTRONIX P6109B Probe, 100MHz readout, unused 


& Front cover 


LL EVER 
| GOULD 0S1100 - <€> 
Dual Trace, 30MHz 


Delay. Very bright. Supplied with manual and two probes 
WELLER EC3100A 

Temperature controlled Soldering Station 
200°C-450°C. Unused 


8125 


1-5MHz-2GHz, 3- 5-digit l.c.d. 
display. Unused £400 


Kn e% 

TEKTRONIX 400 SERIES 
468 Digital Storage Dual Trace 100MHz Delay 
466 Analogue Storage Dual Trace 100MHz Delay 
485 Dual Trace 350MHz Delay Sweep 
475 Dual Trace 200MHz Delay Sweep 
465 Dual Trace 100MHz Delay Sweep 


Also available: 
FARNELL AMM2000 Auto Mod Meter, 10Hz-2:4GHz. Unused .. . 
MARCONI 2305 Mod Meter, 500kHz-2GHz 


Used Equipment — GUARANTEED. Manuals supplied 
This is a VERY SMALL SAMPLE OF STOCK. SAE or Telephone for lists. 
Please check availability before ordering. 

CARRIAGE all units £16. VAT to be added to Total of Goods and Carriage 








SQUIRES 
MODEL & CRAFT TOOLS 


Fluorescent Bench Magnifier. 
- With 22W circular daylight simulation tube. 
- 5" dia. glass lens, x1.75 magnification. 
- Spring balanced arms for universal positioning. 
Multi-angle table clamp. 
Robust metal construction. 
Code LA100 - Price £49.95 Post Free to UK addresses. 





Post, Telephone or Fax your orders to:- 
Squires, 100 London Road, Bognor Regis, 
West Sussex, PO21 1DD 

Tel 01243 842424 

Fax 01243 842525 
Shop Now Open 


EWROCARD. 


Everyday Practical Electronics, May 2000 


SURVEIL 


A rom he. ¢ 


lectroni rveillan -quipmen 


No.1 oplier 


SUMA DESIGNS has been supplying professional quality electronic surveillance equipment kits for over 20 years. Whether your 
requirement is hobbyist, amateur or professional you can be sure that you are buying from a company that knows the business. 
We ONLY sell surveillance products, no alarms, disco lights or computer bits. All of our kits are designed for self assembly and 
are well tried, tested and proven. All kits are supplied complete with top grade components, fibreglass PCB, full instructions, 
circuit diagrams and assembly details. Unless otherwise stated all transmitter kits are tuneable and can be received using an 


ordinary VHF FM radio. 


UTX Ulitra-miniature Room Transmitter 

At less than 1/2 the size of a postage stamp the UTX is the smallest room 
transmitter kit in the world! Incredible 10mm x 20mm including 
microphone, 3-12V operation. Range up to 500m _ .......... £13.95 


MTX Micro-miniature Room Transmitter 
Our best selling room transmitter kit. Just 17mm x 17mm including mic. 
Extremely sensitive. 3-12V operation. Range up to 1000m. . .£14.95 


STX High-performance Room Transmitter 

High performance transmitter with buffered output for greater stability and 
range. Measures just 22mm x 22mm including mic. 6-12V operation. 
RIGS UTP TSOOIA Sw lees cee o PLR £16.95 


VT500 High-power Room Transmitter 

Our most powerful room transmitter with around 250mW of output 
power. Excellent range and penetration. Size 20mm x 40mm, 6-12V 
pperation. Range up tO SOQOM:.:.. 6. eS ie oie bole g photons £17.95 


VXT Voice-activated Room Transmitter 

Triggers only when sounds are detected by on-board mic. Variable 
trigger sensitivity and on-time with LED trigger indicator. Very low 
standby current. Size 20mm x 67mm, 9V operation, range up to 
POI: 8 EE OES EE EVE SRE £21.95 


HVX400 Mains Powered Room Transmitter 
Connects directly to 240V AC supply. Ideal for long-term monitoring. Size 
30mm x 35mm, range up to 500m. ..... 1... ee ee ee ee £21.95 


SCRX Subcarrier Scrambled Room Transmitter 

To increase the security of the transmission the audio is subcarrier 
modulated. Receiver now requires the decoder module (SCDM) connected 
to allow monitoring. Size 20mm x 67mm, 9V operation, up to 1000m 
ARN oka cpa eek ety bh R54 edw neuen eee £24.95 


SCDM Subcarrier Decoder for SCRX 
Connects to earphone socket on receiver and provides decoded audio 
output to headphones. Size 32mm x 70mm, 9-12V operation. . .£27.95 





UTLX Ultra-miniature Telephone Transmitter , 

Smallest kit available. Connects onto telephone line, switches on and off 
automatically as phone is used. All conversations transmitted. Size 10mm x 
20mm, powered from line, up to 500m range. .......... ... £13.95 


TLX700 Micro-miniature Telephone Transmitter 
Best selling kit. Performance as UTLX but easier to assemble as PCB is 20mm 
PS i fad Gr ect 5.5 dba ag eee eos £14.95 


STLX High-performance Telephone Transmitter 

High-performance transmitter with buffered output for greater stability 
and range. Connects onto telephone line and switches on and off 
automatically as phone is used. Both sides of conversation transmitted 
up to 1000m. Powered from line. Size 22mm x 22mm...... £16.95 


TO ORDER: 

Post, fax or telephone your order direct to our sales office. Payment can be 
Credit card (Visa or Mastercard), Postal Order, cash (please send registered) or 
cheques. Kits despatched same day (cheques need clearing). All orders sent by 
recorded or registered post. Please add postage as follows: 

ORDER UP TO £30.00: To UK £2.50 To EUROPE £5.50 _ All other £7.50 
ORDERS OVER £30.00: To UK £3.65 To EUROPE £7.50 All others call 
Overseas customers please use credit cards or send sterling cheque 
or bank draft. 


SUMA 
DESIGNS 


Everyday Practical Electronics, May 2000 





Dept. EE, The Workshops, 95 Main Road, 
Baxterley, Warwickshire, CV9 2LE, U.K. 





PTS7 Automatic Telephone Recording Interface 

Connects between telephone line (anywhere) and normal cassette 
recorder. Automatically switches recorder on and off as phone is used. 
Both sides. of any conversation recorded. 9V operation, size 20mm x 
SHITE ST eS EO BAA So eas wee ape ee eae ale ae PG om £21.95 


CD400 Pocket Size Bug Detector/Locator 

LED and piezo bleeper pulse slowly. Pulse rate and tone pitch increase as 
Signal source is approached. Variable sensitivity allows pinpointing of signal 
source. 9V operation, size 45mm x 54mm. ...........00 000s £34.95 


CD600 Professional Bug Detector/Locator 

Multicolour bargraph LED readout of signal strength with variable rate 
bleeper and variable sensitivity allows pinpointing of any signal source. 
When found, unit is switched into AUDIO CONFIRM mode to distinguish 
between bugging devices and legitimate signals such as pagers, cellphones 
etc. Size 70mm x 100mm. 9V operation. .................. £59.95 





QTX180 Crystal Controlled Room Transmitter 

Narrow band FM crystal transmitter for ultimate in privacy. Output 
frequency 173.225 MHz. Designed for use with ORX180 receiver unit. Size 
20mm x 67mm, 9V operation, range up to 1000m 


QLX180 Crystal Controlled Telephone Transmitter 
Specifications as per QTX180 but connects onto telephone line to allow 
monitoring of both sides of conversations. ................ £44,95 


QSX180 Line Powered Crystal Telephone Transmitter 

Connects onto telephone line, switches on and off as phone is used. Power is 
drawn from line. Output, frequency 173.225 MHz. Designed for use with 
ORX180 receiver. Size 32mm x 37mm. Range up to 500m. ....... £39.95 


QRX180 Crystal Controlied FM Receiver 

Specifically designed for use with any of the SUMA ‘O’ range kits. High 
Sensitivity design. Complex RF front end section supplied as pre-built and 
aligned sub-assembly so no difficult setting up. Headphone output. PCB 
size 60mm x 75mm. 9V operation. ........... 0.000 eee eee £69.95 


TKX900 Signalling/Tracking Transmitter 

Transmits a continuous stream of audio bleeps. Variable pitch and bleep 
rate. Ideal for signalling, alarm or basic tracking uses. High power output. 
Size 25mm x 63mm, 9-12V operation, up to 2000m range. ... £23.95 


MBX-1 Hi-Fi Micro Broadcaster 

Connects to headphone socket of CD player, Walkman or Hi-Fi and 
broadcasts your favourite music around house and garden up to 250m. 
Size 27mm x 60mm, 9V operation. ............ 000 e eee eee £22.95 


DLTX/RX Radio Remote Switch System 
Two kits, transmitter sends a coded signal (256 selectable codes) when button 
pressed. Receiver detects signal, checks code and activates relay. Can be set to 
be momentary or toggle (on/off) operation. Range up to 100m, 9V operation 
on both units. TX 45mm x 45mm, RX 35mm x 90mm. 


SEND 2 x 1st CLASS STAMPS FOR OUR 2000 KIT CATALOGUE 
CONTAINING FULL DETAILS OF THESE AND OTHER KITS. 
A BUILD-UP SERVICE IS AVAILABLE ON ALL OF OUR KITS, 
DETAILS IN CATALOGUE. 
Please note: Some of our part numbers are being unscrupulously used by 
other companies selling kits eg. MTX, VXT. DO NOT BE MISLEAD! These are 
NOT GENUINE SUMA KITS which are only available direct from us or our 
appointed distributors. 
If you wish to collect kits direct from our office 
PLEASE TELEPHONE 


TEL/FAX: 01827 714476 
(24 HOUR ORDERLINE} 


LY he 


oo > 


LE. -Ly NEw T 


8 CAVANS WAY, 
BINLEY INDUSTRIAL 
ESTATE. 
COVENTRY CV3 2SF 
Tel: 01203 650702 
Fax: 01203 650773 
Mobile: 0860 400683 


(Premises situated close to Eastern-by-pass in Coventry with easy access 
to M1, M6, M40, M42, M45 and M69) 


OSCILLOSCOPES 
























Beckman 9020 — 20MHZz — Dual Channel .........csc.cccccscsscsscsscscsscescsasssceccssesscscececacencsscssceseescadencsarsucseses £150 
Gould OS 245A/250/255/300/3000/3351/4000 .. -from £125 
Hewlett Packard 180A/180C/181A/182C ....... -from £150 
Hewlett Packard 1740A, 1741A, 1744A, 100MHz Dual Channel .from £300 
Hewlett Packard 54100D — 1GHz mf, se sdssssanasnes gre tisapiseaca eet .-£1250 
Hewlett Packard 54200A — 50MHZ DigitiZing............. eee eeccccescsscecsesscsscecscescsssscssesssncecancatsasansasenseenaeees £500 
Hewlett Packard 54201A — 300MHz Digitizing.................. .-..£1250 
Hewlett Packard 54512B — 300MHz — 1 GS/s 4-Channel ... ....£2250 
Hewlett Packard 54501A — 100MHz — 100 Ms/s 4-Channnel ............ccccccssccscssessescescssessessessessesseseeacees £1250 
Hitachi V152F/V302B/V302F/V353F/V550B/V650F ............ from £105 
Hitachi V650F — 60MHz Dual Channel ......... ccc ccc eeeeeeeee ...£200 
Hitachi V1100A — 100MHz 4-Channel ...............ccceseeceseeeees ...£900 
Intron 2020 — 20MHz Digital Storage (NEW) .............:ccccccescssssssscscssssesscsssersesessvsccavecsasscsacassasessacerenenses £450 
Iwatsu SS5710/SS5702 — 20MHZ ..........c cc cecccccsceesseeeeceeseees from £125 
Meguro — MSO 1270A — 20 MHz Digital Storage (NEW) ..........cccccccccccscsscsessesescecscsssssecesseecsenscaaeceseees £450 
Lecroy 9304 AM — 200MHz - 100 Ms/s 4-Channel .......... 3000 
Lecroy 9450A — 300MHz/400 Ms/s D.S.O. 2-Channel ..... £2250 
Philips PM 3055 — 50MHz Dual Timebase ................ccccscecessssesescscecscsecsescsusevavscecssssscacseavassneesacacensnss £450 
Philips PM 3211/PM 3212/PM 3214/PM 3217/PM 3234/PM 3240. 3243/ 

PM 3244/PM 3261/PM 3262/PM 3263/PM 3540 o.oo........cccccccccccscccscscesssssssesecesescssesesesaesersnees from £125 
Philips PM 3295A — 400MHz Dual Chantel ..............cccccccccccsssesceccsccsscsssscsevsccaccsssaseacsucsscsussccaceaseaceuse £1600 
Philips PM 3335 — 50MHz/20 Ms/s D.S.O. 2-Channel .........cccccccccsccsscssssessseccsccscenssassccesesccacsasessesceeeess £950 
Tektronix 455 — 50MHz Dual Channel ..............cccccceccccscsscsscsscsssscessceccsssessessecacasesssussucsscsucsacsecesecensueee £200 
Tektronix 464/466 — 100MHz Analogue Storage .......... .from £300 
Tektronix 465/465B — 100MHz Dual Channel ........... .from £300 
TEATOMMX 4BB — 1DOMHZ D.S.O. ..ccsrSecesqiivescossscscossosvesssasessconegscnedesencceosecesavqupstviesseduececchdsevesadsdveo dee’ £500 
Tektronix TAS 475 — 100MHZ — 4-Channnel ...0......c.cccccccsccesesssssesscsccsscseavstcsecsesasssscasesesucsecsueeeseeeeseeeees £995 
Tektronix 475/475A — 200MHz/250MHz Dual Channel .from £400 
Tektronix 485 — 350MHZ — 2-Channel .............c:cscccsssssssssssssssscsssescsssssscesecssssseessessceccssccsseesessccesseceeeces £750 
Tektronix 2211 — Digital Storage — 50MHz .... ..£800 
Tektronix 2213 — 60MHz Dual Channel ...... ..£350 


Tektronix 2215 — 60MHz Dual Trace ........... 
Tektronix 2220 — 60MHz Dual Channel D.S.O. .. 

Tektronix 2221 — 60MHz Digital Storage 2-Channel . 
Tektronix 2225 — 50MHz Dual Channel .................... 


Tektronix 2235 — 100MHz Dual trace .................... ...£600 
Tektronix 2335 — Dual Trace 100MHz (portable) ... ..£600 
Tektronix 2440 — 300MHz/500 Ms/s D.S.O. 2-Channel .£2500 
Tektronix 2445 — 150MHz — 4-Channel+ DMM ................ ..£900 
Tektronix 2445A — 100MHz — 4-Channel .............ccccceeeeeeeseeeee ..£900 
Tektronix 2476B — 400MHz — 4-Channel ........... cece ceeecesesesceceeeseeeee ....£6500 
Tektronix 5403 — 60MHz — 2 or 4-Channel ...........ccccccccccccesssccessccessseeeees .from £150 
Tektronix 7313, 7603, 7623, 7633 — 100MHz 4-Channel ................c0ccc000 .from £225 
Tektronix 7704 — 250MHZ 4-Channel ........ccccccccsccccscccssscecesssccesacecseseee ... from £350 
Tektronix 7904 — 500MHZ ou... .cccecccccssscccsscccecssscecseseccessseceseeesensees .from £400 


HITACHI V212 — 20MHz DUAL TRACE 
HITACHI V222 - 20MHz DUAL TRACE + ALTERNATE MAGNIFY ... 


SPECTRUM ANALYSERS 

















Ando AC8211 — Spectrum Analyser 1*7GHZ ...........cccccsssccssccsssccssscssscesessssscsscesseesceeseseceessessasensesanece £1995 
Anritsu MS62B — 10KHZ-1700MHZ ............cccsscsscssesscsssssesesseescssessessseesesecesessessussuseseessessessescneasssees £1995 
Anritsu MS3401A + MS3401B — (10H2Z-30MHZ) 0.0.0.0... ccececcsscssesseesscesessscseeeseeseesseesenssees £3500 + £3995 
Anritsu MS610B — 10KH2-2GHZ — (Mint) oo... cece ctceseeseesecseeseessesessessesseseseeseeseeseesecsessuseesenereenees £4500 
Anritsu MS710F — 100kHz-23GHz Spectrum Analyser ..........ccccescsccssssesscssessceecsessesecsceseeeeeceneeeenees £5500 
Avcom PSAG5S — 1000MHZ — portable oo... cc cceccscssessessesscsseeeecsseceesceseseesecseseneeecesseeseteeseeeesesens £850 
Hameg 8028/8038 — Spectrum Analyser/T mre Pe + 100MHZ OscilloSCope...........ce cece cece £1000 
Hewlett Packard 182R with 8559A (GOMHz-216 2) csudvabdvesasveudsiadedsscsbase teegaipaads hausssasunscsapncbaraaeasahee) £2750 
Hewlett Packard 182T + 8558B — 0:1 to 1500MHZ 0.0... ccceessessesseseecsccssesetessessscesesssenseaseeeeness £1250 
Hewlett Packard 853A + 8558B — 0-1 to 1500MHZ occ ccccscsscssessssecsscnsessssesseessseesesecucereseersees £2250 
Hewlett Packard 3562A Dual Channel Dynamic Sig. Analyser ..............:cccsccessesseseesseseseeeeerseeeeees £5750 
Howlett Packard SGBQA = SHZ-SOKHZ ...........csssccccasensssoogernosensgcssdesaqssvancusssevsacasecinposbshevboobtsecsnddighsnasezs £800 
Hewlett Packard 3582A — 0-:02H2-25-6kHz (Dual Channel) ....... cc cccccseessessseesseseeseenseseenseseceseeeenees £2000 
Hewlett Packard 3585A — 20HZ-40MHZ ...........cccccecccesseeneseteeseessessesscesceesssscensesseeseeesensesaeesseseseneees £4000 
Hewlett Packard 8569B — (0°01 to 22GHZ) ...........:ccsssssnscsesssscctencesesssssssssaseasccesscsesscceccasescsecnsceses £4250 
Hewlett Packard 85046A — 'S’ Parameter Test Set 0.0.0... cccsectesssesctsessessesssseesssscssceecaseseeseeneneeeee £2500 
Hewlett Packard 8753A — Network Analyser o............ccccccsesssessssssesccseesssessessensteesennessenseceeees from £3000 
Hewlett Packard 8753B — Network Analyser ..............c.cccccssccssesecesenseeseesssesseeeceesesesecseseeseenenes from £4500 
PERO BIE SGINE: 2, 0n350cccdhvoveiny <sctdoconcrasosindesvedenquecnsdtnaploguosvagh btonsLipasngskaivcacatenaelgsrasosnpseqveceiages £2000 
Meguro MSA 4901 — 1-300GHZ (AS NEW) oo... eee ceecsecsseseentesessccsscsescessessesseneesseaeeesesceasessesaeeseeas £750 
Miro TIBA 4092 — 1-1GHz (AS. NEW). ...0:sercsccsssorcdecanstnevesnastshinnspodbnnasiqnavepesnpespeatiahisenssansiccnnysioons £1000 
Rohde & Schwarz — SWOB 5 Polyskop 0°1-1300MHZ o.........ccccccccsccsessesseseescescesssseesesssereeeeteneeeees £1500 
Takeda Riken 4132 — 1-O0GHz Spectrum Analyser... cccccscsssccscrsetsessessescesseeteecesseeeseesseneteseatenes £2100 
Tektronix 7L18 with mainframe (1-5-60Ghz with external Mixers) ............cccescecseesessceeseseeseeseeteesens £2000 
Tektronix 495P — 100HZ-1-8GHZ programmable 0.0.0... ccccsscsscesecncesesenesstersseseseceseeseenseneeasseesee £4500 
Tektronix 496P — 1kHz-1-8GHz Spectrum Analyser ...........ccccccccssecsccssessessessceeeseeeseesasesesneeeatenseeeees £4250 
MISCELLANEOUS 
Adret 740A — 100kHz-1120MHz Synthesised Signal Generator .............cccsscescesscerseetsesseenseeeseeeeeea £800 
Anritsu MG 3601A Signal Generator 0:1-1040MHZ ............cccccsscccsscssseceessecsseesseecseeeseeersesteesseeeeneeees £1250 
Anritsu ME 462B DF/3 Transmission Analyser ...............cccccscccsseceseccseseseceseseseecseceaeceeeceeesensenseseneeere £2500 
Anritsu MG 645B Signal Generator 0°05-1050MHZ ............ccsssssssssscsseessscssssegsesseeessssseceeceassasseeaceneees £750 
Boontoh 92C A/F Millivoitmeter ..............:.sseccsccsssssssssssssecessscersstsccesessenssestecssrsesesseesssacersseseveeseseseneass £195 
BOONTON OBA True RMS VORMOtOL vicccsscsssssssccsscssasasssssoscsssescssscsssesesrscassnedssanserecccconsncsetseceansuitexeniacesee £195 
Dranetz 626 — AC/DC — Multifunction Amalyser 0.0... .ccceccceccsssseecessssecesseseceesseeeesseeseseceeeseceeeeeeeees £500 
ElP- 331 — Frequency Counter 1SGHZ .....:..cccccsssssconssssnncsesccazersnsssuecssecsnscesicsinesacquasenssenssslacesattseassoeses £450 
EIP 545 — Frequency Counter 18GHZ 0.0... ecceccssecessseeeesseeesseeeessseeeeceeseeceaeeesseseeneseneeseseeeceseeees £1250 
EIP 575 — Fraquenicy Couriter 18GHZ ........cccescesssccssesedvscsesosoncsepategoiosencontesnsenepiscpnspeahoossssdagsaensasstsdane £1450 
Eltek SMPS — Power Supply 6GOV-3OV ..0..... cee cecccesecsseecssceeseeseneseeeeeecesseeeseesaseeseesueceaeseeeesssereeneeeaueees £350 
Farnell TSV-70 MKII Power Supply (70V — 5A or 35V — 10A) . ...£200 
Farnell DSG-1 Synthesised Signal Generator .... £125 
Farnell AP 30250A Power Supply 3V — 250A .... ....£1750 
Feedback PFG 605 Power Function Generator ............ccceeeccsseceeesssceceseseeesecsseeeeenaeeceesusesesseeneenaeeeees £150 
Fluke 5100A — Calibrator ...........0....ccccceeeeeee ....£1950 
GN ELMI EPR31 PCM Signalling Recorder ..... £2000 
Guildline 9152 — T12 Battery Standard Cell .... ..£550 
Hewlett Packard 1630D — Logic Analyser (43 Channels) ..............ccccccssecsssscceeecesseeenseeensecesseeseneeeeeeees £500 
Hewlett Packard 16500A/B and C — Fitted with 16510A/1651A/161530A/16531A 
sO AN AIVGON aio 5e25cs05 cy 2ecesizccsivsestaccudazecasasccsapyeaneeyaseTeucianssassssdoussadisasesceavepusiacasensustinetinsvesd from £2000 
Hewlett Packard 331A — Distortion AmalySer ...............ccccccsseesereeeenseecensesseecsneeeenaeessaeeeseeeseeeeseeererseses £300 
Hewlett Packard 333A — Distortion Analyser 00.0.0... ccccsessessseseesecsseesesenseeeensesasenseeeesenesssssasensensaeens £300 
Hewlett Packard 334A — Distortion Analyser ..............ccccccssseceseeeseseeeseeesesecessaeeesseeesseessneeesaeeenteeeeeeeees £300 
Hewlett Packard 3325A — 21MHz Synthesiser/Function Generator ...............cccccccessseecsssteeseesteeeeeeeeees £900 
Hewlett Packard 3335A — Synthesised Signal Generator (200HZ-81 MHZ) ............c:ceeesseeseeteeeeeeees £2750 
Hewlett Packard 3336C — Synthesised Signal Generator (10HZ-21MHZ) ...........ccscesscssseeseseseeseeeeeees £800 
Hewlett Packard 3455A — 6’ Digit Multimeter (AUtoCal) 0.0.0.0. eecseeeceeseeeeeeeneeeeesseceseeeceeeeseeeeenee £500 
Hewlett Packard 3456A — Digital Voltmeter ...............ccccscccssssecsssseesseeceseeeeseeeseeseeeecseeeseseeeeseceaeeeees £600 
Hewlett Packard 3488A — HP — 1B Switch Control Unit (various Plug-ins available) ................. £550 
Hewlett Packard 35600A — Dual Channel Dynamic Signal Analyser ..............c:.ccccsssessesseesenecnesnereee £3750 
Hewlett Packard 3586A — Selective Level Meter ...............ccececessseessecsseeseneeecseescceeeeseesesseseeseeenseeseees £800 
Hewlett Packard 3711A/3712A/3791B/3793B — Microwave Link Analyser .............::csesesesccesseeee £1500 
Hewlett Packard 3746A — Selective Measuring Set .0...........ccecsssccssssesssecceseeeseeeesseeeseeeesseeeeeeeeeeeeeens £500 
Hewlett Packard 3776A — PCM Terminal Test Set ...............cccscessccssecsecesseeeeeeseesseeseeseatesseeeseeceeeeees £1000 
Hewlett Packard 3779A/3779C — Primary Mux AnalySer ............c:ccccseccessseecsssessseceseeeesseceeeeeeeees from £400 
Hewlett Packard 3784A — Digital Transmission Analyser ..............c:cccsscssccesssessscsseeseessecereeeseseeseeees £5000 


326 




















Hewlett Packard 3785A — Jitter Generator + RECeIVEL................ccccccecessescssescecescscatescsssecsesvecssesesenaces £1250 
Hewlett Packard 37900D — ene Test Set (No. 7 and ISDN) .. ...£4250 
Hewlett Packard P382A — Variable AttenuatOr ................ccccccecescsscssecescscssesssesescscscscecsesscavscavacseaeasenees £250 
Hewlett Packard 4192A — LF Impedance Analyser ................. ...£6500 
Hewlett Packard 4262A — Digita LCE WGUGT iced. occacesccvesetssecsesascsatsacscssassiacctuanseaaatenanctiRab ton £950 
Hewlett Packard 4342A — ‘Q’ Meter ................cccescseseesseseeeeees .i £600 
Hewlett Packard 435A or B Power Meter (with 8481A/8484<A) ....... from £400 
Hewlett Packard 436A and 437B — Power Meter and Sensor ............ from £900 
Hewlett Packard 4948A — (TIMS) Transmission Impairment M/Set ...............:c0:cccccesevecsesseeseesscenes *.£1000 
Hewlett Packard 4972A — Lan Protocol Analyser ...........c:ccccccscessescesccscsscesceseescsccsecsscsesseseesensudpeauesh £1250 
Hewlett Packard 5183 — Waveform ReCOrdel ...............:cccccsssecessessscsscesssscsecsscecceceeeseseensesssneecenee ...£1250 
Hewlett Packard 5238A — Frequency Counter 100MHZ ..............cccccsccccesssssssescessescessesscsessseesencuapevsenne £250 
Hewlett Packard 5314A — (NEW) 100MHz Universal Counter ...............c:cccccsccsccsssscescsscessesceseeereeevanes £250 
Hewlett Packard 5316A — Universal Counter (IEEE) ...............ccsccsccsssssssessseseceeseccsseseeeasessesserseseeseen 400 
Hewlett Packard 5335A — 200MHz by Performance Systems Counter .............ccccscessseseeseesseeeenes £600 
Hewlett Packard 5324A — Microwave Frequency Counter (500MHz-18GHz) Opts 143 ...........600... £800 
Hewlett Packard 5359A — High Resolution Time Synthesiser .................cccccccccccessssesesseseessseseeseenanee £2950 
Hewlett Packard 5370B — Universal Timer/Counter ..................:cccccccsssescescessescsscessesseacsacseceareeceveusese £2000 
Hewlett Packard 5384A — 225MHz Frequency Counter ................cccccseesesssscescsesseescecsecseescacsecavecsuseusse £500 
Hewlett Packard 5385A — Frequency Counter — 1GHz — (HP1B) with OPTS 001/003/004/005 ........ £750 
Hewlett Packard 6033A — Power Supply eile (20V — 30A) . 
Hewlett Packard 6253A — Power Supply 20V — 3A Twin ................:000 4 
Hewlett Packard 6255A — Power Supply 40V — 1-5A Twin ............. ohasgenes 
HEWLETT PACKARD 6261B 

Power Supply 20V — 50A £350 Discount for Quantities 
Hewlett Packard 6264B — Power Supply (0-20V, 0-25A) ............c:ccccscccscescceecssvescseeeseussecsecseeeceautarsees £300 
Hewlett Packard 6266B — Power Supply 40V — 5A o.oo... ccc eccesccsscescesesecsssceccsscsecessussecsecseceesaseaees £220 
Hewlett Packard 6271B — Power Supply 60V — 3A 0000... ccccccccesccesccccecescessccsecseceseeaseseaseseeneceseeee £225 
Hewlett Packard 6624A — Quad Power Supply ......................+. ...£2000 
Hewlett Packard 6632A — Power cupey RR 6 OAD ica iccnsnscdacsaenscacemaintsdanedinietixauaynneaseminnte £800 
Hewlett Packard 6652A — 20V — 25A System P.S.U. o.oo... ecceessesscescssccsecsscssssucneesccascsscaccsesacscsuceesees £750 
Hewlett Packard 7475A — 6 Pen Plotter ...............ccccccccccscesscessecsessesecssccsscesusessseseceuscsucnaduasnesesaeeeenaeees £250 
Hewlett Packard 7550A — 8 Pen Plotter .0.............cc cc ccceccsscssecessceseceeesesssesscssceeesesetscecsuseusesseacvececensanere £350 
Hewlett Packard 778D — Coax Dual Directional Coupler ...............ccccccccccsscescescssceecssceesescsceassessveeeeneers £600 
Hewlett Packard 8015A — 50MHz Pulse Generator ..................:cccccscessesccsscsscseceecescseceucsesessceesencessesase £500 
Hewlett Packard 8165A — 50MHz Programmable Signal Source .......... ...£1250 
Hewlett Packard 8180A — Data Generator .0.0......... cece ceeceesceesceeeeeeee ...£1500 
Hewlett Packard 8182A — Data Analyser ...................cccccccccsseseeceeeceseceseesseees ...£1500 
Hewlett Packard 8350B — Sweep Oscillator Mainframe (various plug-in options available) . ...£2500 
Hewlett Packard 83554A — Wave Source Module 26°5 to 40GHZ ...........0..ccccececeseesseeseessseeees ...£3500 
Hewlett Packard 83555A — Millimeter - Wave Source Module 33-50GHz .... ...£4250 
Hewlett Packard 8405A — Vector Voltmeter ...............ccccccecssescesscescesecseeseesssceceescsccescaucsecaeeaseceuscenss £350 
Hewlett Packard 8620C — Sweep Oscillator Mainframe ...............ccccccsccsees from £250 
Hewlett Packard 8640B — Signal Generator it OMHZ + 1OZEMINZ) a scseiersicrsssccdsncersatarpeses .... from £850 
Hewlett Packard 8642A — Signal Generator (0-01 to 1050MHz) High Performance Synthesiser ....£6500 
Hewlett Packard 8656A — Synthesised Signal Generator (Q9QOMHZ) ................cccccccscseserscesepeceesensreeees £850 
Hewlett Packard 8656B — Synthesised Signal Generator .................ccccesceseeeseeees £1450 
Hewlett Packard 8657A — Signal Generator (100kHz-1040MH2) ...........0:.....0.. ...£1900 
Hewlett Packard 8660D — Synthesised Signal Generator (10kH2-2600MHz) .. £3250 
Hewlett Packard 8750A — Storage Normalliser ...............:.c:cccccsessessessessescssenseseesescaderessessessecatenseeseees £295 
Hewlett Packard 8756A — Scalar Network Analyser ...... ...£1500 
Hewlett Packard 8757A — Scalar Network Analyser .. . £2250 
Hewlett Packard 8901A — Modulation Analyser.......... £1000 
Hewlett Packard 8901B — Modulation Analyser ......... ...£2000 
Hewlett Packard 8903E — Distortion Analyser.................... ...£1600 
Hewlett Packard 8903B — Distortion Analyser (Mint) .....................06 ...£1500 
Hewlett Packard 8920A — R/F Comms Test Set ................ccccccesceeseceeeeseeeeeeees ...£2500 
Hewlett Packard 8922B/G/H — Raadio Comms Test Sets (G.S.M.) ..........ccccccscesseesereees .from £8000 
Hewlett Packard 8958A — Cellular Radio Interface .................ccccccccsceessesscessccessesesensceeccnscesceeeesceassass £1000 
Keytek MZ-15/EC — Minizap 15kV Hand-Held ESD Simulator ................c:cccccccsecssessessessessesseeseceeeee £1750 
Krohn-Hite 2200 — Lin/Log Sweep Generator .......... cc ecccsecesscsscessecsscessececessccseesseceseesssceeseeseuseusecnees £995 
Kroh-Hite 4024A — Oscillator ......... cece cccccsecssecssseseeeseessecseecsseesssesesesesesesesessscsscessesssseuscacenssesacenseseaes £250 
Krohn-Hite 5200 — Sweep, Function Generator ..............cccccccssscesssccessecessesesecssnsseseecsnsesssessescsesenseaees £350 
Krohn-Hite 6500 — Phase Meter oo... cece ceecsecesecsseccsssessccecessceseceseecseecseesseeceessusssecesesseseceesenss £250 
LOE ST TD —DISIOITION MOtOL ......:.....ccseccccrsssscsssosssssrvscccssesccssessensossccssacsesacoesesscssscoecesesssscssescoess £350 
Leader 3216 — Signal Generator (100kKHz-140kHz) AM/FM/CW with built-in FM stereo 

modulator (cnt, wabsaasscybscisbisasdoussassodavansssbonnsdvasaasaseaisdassssseesusnsecsueudvasxseoseiveosveedseaueyschoesasssncaiseosusadeen® £995 
Marconi 1066B — Demultiplexer and Frame Alignment Monitor (n@W) .............c.cccccecccesseeceesssseseserees £POA 
Marconi 2019 — 80kHz-1040MHz Synthesised — GONOPEOS ai dincsssenissessvanscesecsadssssvesssecassasseveseees £750 
Marconi 2019A — 80kHz-1040MHz Synthesised Signal Generator ..............cccceeccsceeeeeeseeseeseeeeeenee £1000 
ION es i LIM PAUNORIROE (IIGW) cocci ccoqscsersecssneseivepesocenssscsscsesssscessssoventcavavssescapescseceoseovaqesoose £POA 
Marconi 2185 — 1-5GHz id orbhlfaaad POURIOE (IW) s5sssiscsssacissciarsmsceiveaiessinmaicunidanemuaents £POA 
SNE ED “ACCRA GION FADUOF ...sisccacpcnsccscssscvscsssssssssisccandsiensnssssscsecoesosesdoqodesnaeseoossesbeesecsachecsdaceoes £1750 
Marconi 2337A — Automatic Distortion Meter 00.0.0... ccccccseseesecseesscecsseessecsesseseescscseecseseeeeneeeeees £150 
SNE nT TIE FAMED VORINIOL .....c2scssesssaccasscosscsessonsonesensvsessesoncrsneososssesossasouetengpeusososencessasaesens £700 
Maroonl.2071 — Data Comme Analyaer ..:........cciccsccsssiscccssrsssssssssssscssscsscsnscssssssssesscgsscasesssesnesssedesasosons £500 
SERTROT BOGS ~ FGI COMMS TOBE Sot .........srsersscssscsserssccsssenscrsssssesccesesccsnsesscccersasconssossnseacsscesceas £2000 
Marconi 6310 — Sweep Generator — Programmable — new (2-20GHZ) ............cccecsccescessesseeeeeeeseenee £3500 
Marconi 6950/6960 — Power Meter & S@NSOF .............cccccscscsecessecesssccessecsseceeseeesseeesssesecssaneeees from £500 
Marconi 6960 — Power Meter & S@NSOF oo... ec cceceeesecssecsseessecsscscsssssccsaeeseeesseceesensereceneees from £950 
Marconi 893 — A/F Power Meter .............ccccccccccsecssseeseseeessssesseeccseeceseeseseccseeceseeesnetesssesetseeessaeensecaeees £250 
PURE PREG TS RAPEE FUNICLION GONGTEION ....:scccccscccssscsssssssssssncascssssessossesssnsssesessgnsassnscsossensscssearscssenecs £400 
Or 5 at: ST UUNOE (08.F 1.0), ) vizinessapepsisnancesasisasiedesansscsnssdnninnasansissvunnsadeensessiuwieataviexmunmass £800 
Philips 5518 — Synthesised Function Generator ............cccceecsssecceesssessessescsesesesesseteesseesessesennaeeses £1500 
PD EES i 40 PRION) CADET RI occessciccsssssesssecoccsscssavesnssscnnssossissssossasssasssssensescetccesesseensesnsoas £350 
Philips PM5716 — 50MHz Pulse Generator .......... ccc ccecesessteecsessscesseessecceeeesesescnesseseseecsssaeesesaeeneeneees £525 
Prema 4000 — 61% Digit Multimeter (NEW) .0......... ce cceeccseceseeesteeeesseecsneceseeecseeccaeeseterescsseeeeenseeea £350 
Quartzlock 2A — Off-Air Frequency Standard ............ccccccccssccsccssseceseeccseecsesesssecenseecsecseeeesseeeseeeaeers £200 
PN TOE = SDE FIDRUBNCVGOUNMIOS, nciccsccsdsccccccesscnscrspscecssncssscdsosccnsdassedshsocsscnsdcubsSensnensqisiesserneds £700 
Racal 6111/6151 — GSM Radio Comms Test Set 0... ccccsccscctsccsscssesseesssesssesesseesssssessnescseseacaneeees £POA 
Racal Dana 9081/9082 — Synthesised Signal Generator 520MHZ............ eee cetteeeteetteeeeeeee from £400 
Racal Dana 9084 — Synthesised Signal Generator 104MHZ..............cccecseeseeeeeseeteneeteteseseeneneenteeeeeney £450 
Racal 9301A — True RMS R/F Multivolimeter............ ccc eeecesecesesecesecessscseseneeseseseeceesseesseseesesssaeennes £300 
Racal Dana 9302A — R/F Multivoltmeter (NeW VErSION) .........cceceesesseesseseecesenescssenssseesrsessessesesssueees £375 
Racal Dana 9303 — R/F Level Meter & Head .........ieciccccsssseestesssesesssssscsssesescesssssesscrsscesseesnteceseneeaess £650 
Racal Dana 9917 — UHF Frequency Meter 560MHZ ..........c cece eseesecteetecteseseneseeeeeseseseeseseeseseeasenseeens £175 
Rohde & Schwarz LFM2 — 60MHz Group Delay Sweep Generator... ccc cescereeseeeepereeneetseensenees £950 
Rohde & Schwarz CMTA 94 — GSM Radio Comms Analyser ...........cccscccssssessssectecasessersrsseeesseesssens £6995 
Schaffner NSG 203A — Line Voltage Variation Simulator .........cc cece ceeteceescetedenscneceeredeesseseesennna £750 
Schaffner NSG 222A — Interference Simulator oo... cece eetcideeceseseseeseenessacsessecsagecenecssereeessennees £700 
Schaffner NSG 223 — Interference Generator ices cctsecsescsseessascstensesasessensseseuanseecddscenennderees £700 
Schlumberger 2720 — 1250MHz Frequency Counter .......... ccc cceeecneceeseseeqessessessersedeesecueessesecusecauese £400 
Schlumberger 4031 — 1GHz Radio Comms Test Set ........... cc ccccecscsessetrestecseessscssesteeseeseanessseeeeenes £4995 
Schiumberger Stabilock 4040 — Radio Comms Test Set ......... cece ceeeeeeeeseeeeetassteeeteseeeeeseeeseeey £1995 
Schiumberger 7060/7065/7075 — Multimeters ................cescsesssssseneseseneeneseneneceneeetesneneneneeanenees from £350 
Stanford Research DS 340 — 15MHz Synthesised Function (NEW) and Arbitrary 

SRNR 5 5.2 aa fisay dcnen oes setatsangesiecssdeatocansghogscoadenatilonvadebevassudsbesustaiatdbssseindiaicesssavidie £1200 
Systron Donner 6030 — Microwave Frequency Counter (26:5GHZ) ............ccescetesneneceeeteeeneeeneeeeey £1995 
Tektronix AM503 + TM501 + P6302 — Current Probe Amplifier..............ccccesseeceetenteeeenesseneenecnensenens £995 
Tektronix PG506 + TG501 + SG503 + TM503 — Oscilloscope Calibrator ...........cceeccssseseesetseeeeeees £1995 
EIN OTT = CHD UV ACOE 6. osiisssnk se ssessicesceteceneasecesoensesedcovedversedeiisesevedsersaucéevosessstesceansesssoouecsaees £1150 
Tektronix 1240 — Logic Analyser ............:.cccecccccsseeceessecesssesecsseeesessneecssseecseeeceseeecestecessesenneeseneeensaceeeres £500 
Tektronix 141A — PAL Test Signal Gemerator ............ cc ccceccsescesscesenecsecessessesssseesesseesseecsesessseserseeeses £250 
Tektronix AA5001 & TM5006 M/F — Programmable Distortion Analyser ..............:cccccsesseeeesseeeeees £1995 
Tektronix TM5003 + AFG 5101 — Arbitrary Function Generator ............::ccccsssssccsscecceeesssssecssereneesees £1500 
Tektronix — Plug-ins — many available such as SC504, SW503, SG502, 

PG508, FG504, FG503, TG501, TR503 + many MOFe ....... eee cccessseeeseneeessneeestsneesseeeneessneeaeees £POA 
Time 9811 — Programmable Resistance 0.0.0... cceseeesseeeesseeesssseesesseeesseeeesseesenaeesessesessesssneseeeeeeness 
THO DRRH = VONMIO CANNON oii isc cccccicscdisccssscdsecsssssecarscosacecoossncessacsasseasasedeeencscsazesbbsgansonatenarssaveneesose 
Valhalla Scientific — 2724 Programmable Resistance Standard ................:cesseesseeesseeesseesseeeeeeeens 
Wandel & Goltermann PFJ-8 — Error/Jitter Test Seto... ccc cecsecestecceseeeeseeesesseseseeeseeeeesseeeenee 
Wandel & Goltermann PCM4 (+ Options) ..............:ccceccesseeseecnsecenseessesseeeeeseseeeesasesseeesesensesereenaeenes 
Wandel & Goltermann MU30 — Test Point Scanner 00.0... eee ceeeceseceneceeeeseneeeeaeeeeeesaeteaeeeneeaeenses 
Waryree Kerr. 4225: = LCR Bridge «........csccssscsssssssrssscccsssscsscscssscsnsoscsnseesccsescessnnessesesscesnasescessssssnrsossseesee 
Wavetek 171 — Synthesised Function Generator ...............cescccsesseeeeseeeeeeneeesesneeeceneeeeseeesseeseaeeeesenaes 
Wavetek 172B — Programmable Signal Source (0:0001HZ-13MHZ) .............c:ecscessseesessscesreeeeseeees 
Wavetek 184 — Sweep Generator — 5MHZ ........ cee eeeeceneeeeseeceeeesneeeescecereeeeseeesseeeseeerseeseseasseseseaseneseas 
Wavetek 3010 — 1-1GHz Signal Generator ........ eee csceeseeesneescnneceseeessesseeeenseeseeeesseseseseeeeneseaesense 
Wiltron 6409 — RF Analysers . MH2Z-2GHZ) ...........ssscccosssscesescecessserectenes sie 
Wiltron 6620S — Programmable Sweep Generator (3-6GHz-6-5GHz) 





Wiltron 6747-20 — yee Seng: sneha Synthesiser (10MHz-20GHz) .... a 
Yokogowa 3655 — Analysing RECOrder 00.0.0... cee ecsseeesceecseeeeseeeessecesseceseeeeneeessuecseesseeeseseneesseesnneeers 


MANY MORE ITEMS AVAILABLE - 
SEND LARGE SAE FOR LIST OF EQUIPMENT 
ALL EQUIPMENT IS USED — 


WITH 30 DAYS GUARANTEE. 
PLEASE CHECK FOR AVAILABILITY BEFORE ORDERING — 
CARRIAGE & VAT TO BE ADDED TO ALL GOODS 





Everyday Practical Electronics, May 2000 | 


The science lab in a PC 





‘Experiments | Ideas for ‘DrDAQ 


2 yaw ary iniginsind ix; WAG sad writting syge 2 








« Flickering Lights. Use a tigds sense UGS eat tube hohts, computer manitors a WG TY Sereeng 

» Gaewm Chorus. Use ty He: th teas Ors be * MORSE the dav chor 

« Sound waveforms, Us 

WESTIN, SaghING os 
rage DY 






aa " PLW Graph 


y. 134 8 Bourn SOURS 10640 85.275 
. Sound insulation. Us Se O SG SHINTO VAL og Light {CHI} 






ret 


AS 
Sound waveforms of musical instrumer 









Ligne insulation. Exooviment with diierant 

bits of insist m fisnie tye ics the 

* Acid Base Titration. ficnitor t 

+ Acid Rain. Measure the ph w 

» Exothermic Reactions. a 

» Endothermic Reactions. 1 en 

« Day and Might Mt tex ape ‘yee io 

« Fermentation of Grass Cuttings. ? Megsur 

Foe Fruit Power. Make a frud dattery. Experime 

Capacitor chasyetdischarge. Experiment 60 

infra red remote controts. Use a piety aii 

ot a Output of s solar ceil, What fistors affect 
t e Meat insulation. vvrap test ty nes in cifferee 

; a ea cy Sica teas an aff: 50 

Ee was the COE 

be Heat Loss Through Windows. Custoure 


[ 


> 

j 

3 } 

Light decay tinverse Square hava}, fies fi 80} 
} 

? 






70 






‘sia tome { 
3 + a | : 
re] | ay 
at ae | ed Ea 
eae & eee | { 
4 lL areee 


The DrDAQ is a low cost data logger from Pico Technology. 
It is supplied ready to use with all cables, software and 
example science experiments. 





DrDAQ represents a breakthrough in data logging. Simply 
plug DrDAQ into any Windows PC, run the supplied software 
and you are ready to collect and display data. DrDAQ draws 
its power from the parallel port, so no batteries or power 
supplies are required. 


beck axpesmands, please gat in tock, idiow this Jed: for mare intoroating.) 






























Output 







Voltage 


Resistance 






Light level 









Temperature 







Microphone 
External sensors 


Very low cost 
Built in sensors for light, sound (level and 
waveforms) and temperature 

Use DrDAQ to capture fast signals (eg 
sound waveforms) 

Outputs for control experiments 
Supplied with both PicoScope 


(oscilloscope) and PicoLog (data logging) 
software 










Transform your PC.... Into an 
vok-Tod | | Lok-Tore) ol Mmm] el-Lea nde atm: Var: I hVA-1- & 


relaremaaleridianl=1a>) ame 





The Pico Technology range of PC based oscilloscopes offer performance | lt es 
only previously available on the most expensive ‘benchtop' scopes. By | be. 


intergrating several instruments into one unit, they are both flexible and cost f= ~~ | : 


effective. 


Connection to a PC gives these virtual instruments the edge over traditional 
oscilloscopes: the ability to print and save waveforms is just one example. _ 
Units are supplied with PicoScope for Windows which is powerful, yet simple * acacia 


to use, with comprehensive on line help. 





Applications 
Features Vv Video 
W A fraction of the cost of comparable benchtop scopes v Automotive 
Vv Oscilloscope and data logging software supplied v Audio 


v Electronics design 
Vv Fault finding — 
v Education a ~~ y 


v Prices from £69 (excl VAT) 
v Up to 100 MS/s sampling, 50 MHz spectrum analyser 





Tel: 01480 396395, Fax: 01480 396296, E:mail: 








GENT 


ELECTRON I 
MAIL ORDER ONLY e CALLERS BY APPOINTMENT 


C$ 


EPE MICROCONTROLLER! 


PI. TREASURE HUNTER! 
The latest MAGENTA DESIGN - highly , 
stable & sensitive — with I.C. control f 
I of all timing functions and advanced 


r-- 


EUROCARD 


EE213 135 Hunter Street, Burton-on-Trent, Staffs. DE14 2ST 
Tel 01283 565435 Fax 546932 

~ http://www.magenta2000.co.uk 
E-mail: sales@magenta2000.co.uk 


LT D___§AIl Prices include V.A.T. Add £3.00 per order p&p. £6.99 next day 





PIC PIPE DESCALER 


e SIMPLE TO BUILD @ SWEPT 
@ HIGH POWER OUTPUT FREQUENCY 
e AUDIO & VISUAL MONITORING 


An affordable circuit which sweeps 





TEACH-IN 















I pulse separation techniques. I the incoming water supply with = =§=»_—»_——— epee, 
, 5 variable frequency electromagnetic 

@ High stability signals. May reduce scale formation, ==» seseneeemeeeeneen 
I drift cancelling i I dissolve existing scale and improve 
le Easy to build g lathering ability by altering the way 
, 2 use , salts in the water behave. 

Kit includes case, PC.B, coupling 
Ie No ground I coil and all components. ar 
1 effect, works g High coil current ensures maximum | : a 
1 in seawater : effect. L.E.D. monitor : , . . 
' | ) KIT 868 ......... £22.95 POWER UNIT.........£3.99 
i fe Detects gold, I 
| f silver, ferrous & J MICRO PEsT 
! “ non-ferrous 3 
1° Efficient quartz controlled , padi iges a my! wee 
P microcontroller pulse generation. I special fries to give fandom 
py © Full kit with headphones & all y delay and pulse time. Easy to 
, hardware § build reliable circuit. Keeps pets/ 
pests away from newly sown areas, 
KIT 847... cla cll hak ...£63. 954 play areas, etc. Uses power source 


from 9 to 24 volts. 


e RANDOM PULSES 
e HIGH POWER 
e DUAL OPTION 


PORTABLE ULTRASONIC 
PEsT SCARER 


A powerful 23kHz ultrasound generator in 





Plug-in power supply £4.99 , 


; ee ee et RST BOF vis volctisaierisvebiadinisaesus £19.99 

side <sngrs via a special tuned transformer. K i T + S L A V E U N IT seseeee eee eee . 3 2 5 0 
weeping frequency output is designed to 

give maximum output without any special WINDICATOR 

eerung up: A novel wind speed indicator with LED readout. Kit comes 

KIT 842........ eueeneazaunees £22.56 complete with sensor cups, and weatherproof sensing 


head. Mains power unit £5.99 extra. 





KEE B56 fins ectnorestete ei vatgenphersnti textos £28.00 
* TENS UNIT * 
y DUAL OUTPUT TENS UNIT 
_— ent As featured in March ‘97 issue. {_#spare 


Magenta have prepared a FULL KIT for this 
excellent new project. All components, PCB, 
hardware and electrodes are included. 
Designed for simple assembly and testing and 
providing high level dual output drive. 


KIT 866.... Full kit including four electrodes £32.90 


1000V & 500V INSULATION 
TESTER 


Superb new design. Regulated 
output, efficient circuit. Dual- 
scale meter, compact case. 
Reads up to 200 Megohms. 

Kit includes wound coil, cut-out 
case, meter scale, PCB & ALL 
components. 


IT BES, ccisscidaieesetns £32.95 


EPE 


£6.50 


DC Motor/Gearboxes 


Our Popular and Versatile DC 
motor/Gearbox sets. 

Ideal for Models, Robots, 
Buggies etc. 1-5 to 4-5V 
Multi ratio gearbox 
gives wide range of speeds. 


LARGE TYPE — MGL £6.95 
SMALL — MGS — £4.77 





Stepping Motors 
MD38...Mini 48 step...£8.65 


MD35...Std 48 step...£9.99 
MD200...200 step...£12.99 
MD24...Large 200 step...£22.95 





MOSFET Mkil VARIABLE BENCH 
POWER SUPPLY 0-25V 2:5A._ 





2000 


Full set of top quality NEW 
components for this educational 
series. All parts as specified by 
EPE. Kit includes breadboard, 
wire, croc clips, pins and _ all 
components for experiments, as 


listed in Introduction to Part 1. 
“Batteries and tools not included. 





TEACH-IN 2000 — 
KIT 879 £44.95 


MULTIMETER £14.45 








ISPACEWRITER %& 


An innovative and exciting Ya 
project. Wave the wand through asl 
the air and your message appears. my 
Programmable to hold any message *y 
g uP to 16 digits long. Comes pre-loaded 
A with’ “MERRY XMAS". Kit includes 
§ PCB, all components & tube plus 
i instructions for message loading. 


ET BAS cis sieecsindcseewaivs £1 a 
= mn Hm EE EE Ee Ee ee a 
12V EPROM ERASER 
A safe low cost eraser for up to 4 EPROMS at a time 
in less than 20 minutes. Operates from a 12V supply 
(400mA). Used extensively for mobile work — up- 
dating equipment in the field etc. Also in educa- 
tional situations where mains supplies are not al- 
lowed. Safety interlock prevents contact with UV. 


RE 20 veissicvessticernenienades £29.90 


SUPER BAT 
DETECTOR 


1 WATT O/P, BUILT IN 
SPEAKER, COMPACT CASE 
20kHz-140kHz 
NEW DESIGN WITH 40kHz MIC. 


A new circuit using a ‘full bridge’ audio. 
amplifier i.c., internal We. -. 
speaker, and head- Bi ee 
phone/tape socket. The Yo" asiatae 
latest sensitive transducer, -¥" 

and ‘double balanced mixer’ per 
give a stable, high peformance  — 
superheterodyne design. 


Il 0: txeciseusnqrnneeniass £24.99 
ALSO AVAILABLE Built & Tested ....£39.99 






| ULTRASONIC PEsT SCARER 


Keep pets/pests away from 


newl sown areas, fruit, 
ee oS ae et oe PROJECT Venetabie and flower beds, 
rales aa Ne va ee Pl children’s play areas, patios 
cores _ ON Cs etc. This project produces 


switching pre-regulator for | 
much higher efficiency. Panel 
meters indicate Volts and 
Amps. Fully variable down to 
zero. Toroidal mains trans- 
former. Kit includes punched 
and printed case and. all 
parts. As featured in April 
1994 EPE. An essential piece 
of equipment. 


328 


Programmed PICs for 
all* EPE Projects 
16C84/16F84/16C71 
All £5.90 each 
PIC16F877 now in stock 
C1 0 inc. VAT & postage 


(“some projects are 
copyright) 





Kit No. 845... .£64.95 


intense pulses of ultrasound 
which deter visiting animals. 
e KIT INCLUDES ALL 
COMPONENTS, PCB & CASE 
@ EFFICIENT 100V , 
TRANSDUCER OUTPUT e UP TO 4 METRES 
@ COMPLETELY INAUDIBLE RANGE 
TO HUMANS @ LOW CURRENT DRAIN 


PE Oh Ue ecaneiananteerntasacineteceasg exearsiansncel £15.00 


PEsT _ 
SCARER ¢ 


~ZOUP Dire 





Everyday Practical Electronics, May 2000 


SIMPLE PIC PROGRAMMER - 
INCREDIBLE LOW PRICE! Kit 857 £12.99 


INCLUDES 1-PIC16F84. CHIP Power Supply £3.99 





EPE PIC Tutorial 


At Last! A Real, Practical, Hands-On Series 


@ Learn Programming from scratch using PIC16F84 









SOFTWARE DISK, LEAD 
CONNECTOR, PROFESSIONAL EXTRA CHIPS: 
PC BOARD & INSTRUCTIONS PIC 16F84 £4.84 





© Start by lighting I.e.d.s and do 30 tutorials to Sound 
n ion, Data Displ n ri 
@ PIC TUTOR Board with Switches, I.e.d.s, and on board 









Based on February ‘96 EPE. Magenta designed PCB and kit. 
PCB with ‘Reset’ switch, Program switch, 5V regulator and 
test L.E.D.s, and connection points for access to all A and B 
port pins. 


PIC16C84 LCD DISPLAY DRIVER 
INCLUDES 1-PIC16F84 Kit 360 £19.99 


WITH DEMO PROGRAM ——= 
SOFTWARE DISK, PCB, Power Supply £3.99 
INSTRUCTIONS AND | FULL PROGRAM SOURCE . 
16-CHARACTER 2-LINE | CODE SUPPLIED — DEVELOP 
LCD DISPLAY YOUR OWN APPLICATION! 


Another super PIC project from Magenta. Supplied with PCB, 
industry standard 2-LINE x 16-character display, data, all 
components, and software to include in your own programs. 
Ideal develpment base for meters, terminals, calculators, 
counters, timers — Just waiting for your application! 


PIC16F84 MAINS POWER 4-CHANNEL 


CONTROLLER & LIGHT CHASER 


WITH PROGRAMMED 16F84 AND DISK WITH 

SOURCE CODE IN MPASM Mew focnsnsn File bis 

ZERO VOLT SWITCHING chaser cotware GAEIEIC 

MULTIPLE CHASE PATTERNS J and pre-programmed 

OPTO ISOLATED PIC16F84 chip. Easily 

5 AMP OUTPUTS Be oe acnt Seeders 

PR AmMGN eo | Huacamtin 
‘ ted’ so that it 

e HARD FIRED TRIACS be fllowadaasin 


Kit 855 £39. 95 LOTS OF OTHER APPLICATIONS 
PIC TOOLKIT V1 


@ PROGRAMS PIC16C84 and 16F84 e ACCEPTS TASM AND MPASM CODE 
Full kit includes PIC16F84 chip, top quality p.c.b. printed with component 
layout, turned pin PIC socket, all components and software* 

*Needs QBASIC or QUICKBASIC 


KIT 871... £13.99. Built and tested £21.99 


Ph = ALL PARTS FOR SERIES INCLUDING PCBs, 
IZZ PROGRAMMED CHIP. CD-ROM AND DISPLAYS 


MAIN BOARD - FULL KIT£131.95 BUILT £149.95 
(/O PORT KIT £16.99 BUILT 

Esl: SE Meee aN s Mets £12.49 POWER SUPPLY ..£3.99 
8-BIT SWITCH/LATCH £7.95 INT. MODULE .£10.45 


68000 Pexiuceat” N 
@ NEW PCB DESIGN ; . £99.95 


@ 8 MHz 68000 16-BIT BUS ~ @ ON BOARD 


PO 5V REGULATOR 
@ PIT AND I/O PORT OPTIONS oe @ PSU £6.99 
@ |2C PORT OPTIONS 7 : rei @ SERIAL LEAD £3.99 


Mini-Lab & Micro Lab 
Electronics Teach a? 7 


As featured in EPE and now 
published as Teach-lIn 7. All 
parts 

are supplied by Magenta. 
Teach-In 7 is £3.95 from us or 
EPE 

Full Mini Lab Kit — £119.95 — 
Power supply extra — £22.55 
Full Micro Lab Kit — £155.95 


eer ee Eee All pricesinclude VAT. Add £3.00 p&p. Next Day £6.99 
Tel: 01283 565435 Fax: 01283 546932 E-mail: sales@magenta2000.co.uk 








PIC TUTOR BOARD KIT 
Includes: PIC16F84 Chip, TOP Quality PCB printed with 
Component Layout and all components* (*not ZIF 
Socket or Displays). Included with the Magenta Kit is a 
disk with Test and Demonstration routines. 

KIT 870 ...... £27.95, Built & Tested. ...... £42.95 
Optional: Power Supply — £3.99, ZIF Socket — £9.99 

LCD Display ................. £7.99 LED Display .............. £6.99 
Reprints Mar/Apr/May 98 — £3.00 set 3 


PIC TOOLKIT V2 __ 


e@ SUPER UPGRADE FROM V1 e 18, 28 AND 40-PIN CHIPS 

@ READ, WRITE, ASSEMBLE & DISASSEMBLE PICS 

e SIMPLE POWER SUPPLY OPTIONS 5-20V 

@ ALL SWITCHING UNDER SOFTWARE CONTROL 

@ MAGENTA DESIGNED PCB HAS TERMINAL PINS AND OSCILLATOR 
CONNECTIONS FOR-ALL CHIPS 

e INCLUDES SOFTWARE AND PIC CHIP 


KIT 878 .. . £22.99 with 16F84.. 


SUPER PIC PROGRAMMER 


READS, PROGRAMS, AND VERIFIES 
WINDOWS® SOFTWARE 
PIC16C6X, 7X, AND 8X 

USES ANY PC PARALLEL PORT 
USES STANDARD MICROCHIP e@ HEX FILES 
OPTIONAL DISASSEMBLER SOFTWARE (EXTRA) 
PCB, LEAD, ALL COMPONENTS, TURNED PIN 
SOCKETS FOR 18, 28, AND 40 PIN ICs. 


INFORMATION =A Power Supply £3.99 



















. £29.99 with 16F877 




















SUPERB PRODUCT AT AN 


DISASSEMBLER 
UNBEATABLE LOW PRICE. SOFTWARE £11.75 









PIC STEPPING MOTOR DRIVER 
Kit 863 £18.99 


FULL SOURCE CODE SUPPLIED. 
INSTRUCTIONS ALSO USE FOR DRIVING OTHER 
AND MOTOR. POWER DEVICES e.g. SOLENOIDS. 


Another NEW Magenta PIC project. Drives any 4-phase unipolar motor — up 
to 24V and 1A. Kit includes all components and 48 step motor. Chip is 

pre-programmed with demo software, then write your own, and re- program 
the same chip! Circuit accepts inputs from switches etc and drives motor in 
response. Also runs standard demo sequence from memory. 


8-CHANNEL DATA LOGGER 


As featured in Aug./Sept. ‘99 EPE. Full kit with Magenta 
redesigned PCB - LCD fits directly on board. Use as Data 

Logger or as a test bed for many other 16F877 projects. Kit 
includes programmed chip, 8 EEPROMs, PCB, case and all components. 


KIT 877 £49.95 inc. 8 x 256K EEPROMS 





INCLUDES: PCB, 
PIC16F84 WITH 

DEMO PROGRAM, 
SOFTWARE DISK, 






























Everyday Practical Electronics, May 2000 329 

















































































































& Boxes & Cases Equipment Wire 
Ww Many more sizes available Black, Brown, Red, Orange, 
- ie Yellow, Green, Blue, Purple, 
BE A ae €, Grey & White. Per 100m 
a ‘oe Solid 1/0.6mm £2.67 
wZ BNC Plug 502 Solder £0.99 Miniature Round ti Stranded 7/0.2mm £2.44 
£0 BNC Plug 502 Crimp £0.68 250mA 125V 28 x 10mm tba ° Electroni 
GE FREER EES G0 (ome MmnaNeN a omens pe = 
U rim on Latching Pus eneral Pur a . 
OE BNC Chassis Socket £0.81 BlackPIM £0.23 75x 56x 25mm £0.99 3mm White 900med £2.13 
EQ Fug Cu £0.26 Yellow PIM £093 (ieazcgamm £1.13 smmGreen led £0.09 
=aV ug - Crim , ellow , x 57 x 22mm 
Be, TNC ¥lug 508 Solder £1.24 Green PTM £0.23 79x61x 40mm. «170 3mm YelowLled | = £0.1 
Y INC Plug 502 Crimp £0.85 Blue PIM £0.23 100 x 76x 41 g1-79 sam frrange Led.” .° 50.10 
BZ INC Pg 750 Solder E140 White PIM £093 118% 98x 45mm «£2.98 3mm Blue med £1.04 
“Oo TNC Plug 75Q Grip £1.16 Non Latching Push to Break 150 x 100 x 60mm £2.77 p Heth Whit 200) d £069 
ee UHF Plug 5mm Cable £0.63 Black PTB £0.24 150 x 80 x 50mm £2.72 . White 1100tr d £205 
UHF Plug 11mm Cable£0.75 Standard Square..-.. Diecast Aluminium BmmRed led £0.08 
= cca go i Te COME Set RT 
iad NASSIS OKT- RN at, cal whet, Sou.* (haa ‘76 5mm Yelow Led £0.08 
Extensive ran RF con- 1A 250V : 112 x 62 x 31mm £4.18 y ‘ 
wal ARE ae : 5mm O Led £0.10 
om nectors:in stock, inc.FME, 39 x ISMM a ea 120 x 65 x 40mm S461" BM ange Le : 
SMA, Mini UHF & N Type. 12mm @ Mouritiig Hole 150 x 80 x 50 £4.09. grin Bye Samed = 51 04 
cite OS erudeale eh Non Latching Push to Make 121 x 95 x 81mm ene 08 Bm Blue io0ncd — ELO4 
“ ac wo Piece Aluminium : 
10 Way Transistion £0. Ff Red PTM £0.60 133x70x37mm £2.08 2MMRed Flashing £0.44 
14 Way Transistion £0 pee... Blue PTM £0.60 102 x 102 x 37m £1.94 2mm Green Flashing £0.50 
16 Way Transistion Colours Red, Black’”Green, White PTM £060 102x70x 37mm «£1.81 2mm Fellow Ene oh oa 
3 way iad iptite Blue, White or Yellow Loteting “push On sage et 102 6S Fr aall I a 5mm Tri-Colour Led £0.28 
G oa: 2mm Solder Plugs £0.18 3 °CF era 
Spr Biba, BRE ag War pransision £025 3mm Chassis Sackets £026 Red BSS 98103 x 20mm £2.79 Odeo ed Cathode 20.78 
ep Bitos = Sot] 50 Way Transistion 4mm Plugs Screw £0.38 White £0.65 203 152x 76mm — £4.84 OF Rea AT, BB 
18 Pin DIL 0.3” 60.12 Large Range of Connee- 4mm Stackable Plugs £0.40 Recker Switches 193 * 102 . nm eS > 0.3” Red C.Anode 0.78 
20 Pin DIL 0.3” £0.12 tors available - contact 4mm Shrouded Plugs £0.74 n re 152 x 102 % 7émin £437 Infra Red Devices 
5A Pin DIL 0.6” £0.12 our sales department 4mm Chassis Sockets £0.24 6A 250V Solder Tags Stecl/Aluminiu ‘#2 3mm IR Emitter £0.23 
28 Pin DIL 0.6” £0.13 for full details 4mm Binding Posts £0.46 SPST 21x 14x 16mm £0.69 py pape ge pote 5mm IR Emitter £0.39 
40 Pin DIL 0.6” £0.19 33mm Crocodile Clips £0.10 DPDT 21 x 24 x 22mm £0.96 Alo ie ba: b FOP, 3mm Photo-Transistor £0.26 
Sas 2 Soe Me DC Low Voltage __.. SPST - Amber Neon £1.02 203x127x5lmm £5.04 435 Opto: Coupler £0.58 
” MANNS aot nda to- £0. 
gee bins . peae A. 15A 250V Push on Tags 14x 63x5/mm £3.04 4N39 Obto-Coubler £0.45 
20 Pin DIL 0.3” £028  Selder Bucket DC Plug 0.7ID 2.350D £0.47 Spst30x 11x 22mm £0.58 Wire & Cable 6N135 Opto-Coupler £1.30 
24 Pin DIL 0.6” £0.35 9 Way Male Plu £0.24 Hc Plug 13ID 340D £0:32 ats ao x 25x22mm£1.12 Ribbon Cable 6N136 Opto-Coupler £0.85 
28 Pin DIL 0.6 £0.39 9 Way Female Socket £0.24 DE Plug 1.7ID 400D £0.47 Hlumin Price per 300mm (1 ft) 6N137 Opto-Coupler £0.90 
40 Pin DIL 0.6” £0.64 15 Way Male Plug £0.36 HE Plug 17ID 4:750D £0.47 13e 250V Push on Tags 10 Way Grey Ribbon £0.10 6N138 Opto-Coupler £1.30 
ZIF Socket 15 Way Female Socket £0.39 DE Plus 21ID 50OD £0.25 opot 30xl4mm Red £0.84 16 Way Grey Ribbon £0.17 6N139 Opto-Coupler £0.90 
Universal ZIF DIL Sockets 15 Way H.D. Plu £0.48 DE Plus 25ID SOOD £024 REST 30x25mm Amber£1.40 20 Way Grey Ribbon £0.24 CNY17-1 QO-Coupler £0.47 
| Way 0 3.0.6" £5.78 18 Way HD. Soc et £0.64 Dé Plug 31D S30D £0.46 DPST 30x25mm Green£1.40 26 Way Grey Rippon e022 CNY! a -Coupler 3 
28 Way 0.3-0.6" £6.75 23 Way Male Plug 0.44 DC Line Socket 2.1mm £0.57 Relays ay, Grey Ribbon £0. iehel stab, ea 
Sway OR0S, £747 23 Wey came g ooh 20 BC tne Socket 2mm £0.48 CE Mowning «ap 20 Way Srey pon £052 ors Beto-turer £09 
ay 0.3-0.6" assis Skt 2.1mm £0. : 35 $0 Way Grey Ribbon. £0.64 ISQ- -Coupler £1. 
25 Wa Female Skt £0.37 DC Chassis Skt 25mm £0.41 1A 24Vdc DPDT 12V £2.00 ay Ure ! on fi | Q 74 Opto-Cou ler £1.52 
Fates shots, ibe inten owmtog We ain GA aBBVee  V'UET Hy,” 198) Reamaled Gemper Wee Sah Scal 
T05 Base socket” £0.24 SOY ef 08 ee) «© BATIOV SPDT 12V £0.58 560g reels availabl ORPI2ZLDR £0.88 
ase Socket . 9 Way Female Socket £0.93 | i 5A 110V SPDT 6V £0:72 74 1g Fes ie ai @ le exoy : 
IDC Cable Sockets 15 Way Male Plug 32 ee SA 1IOVSPDT12V £0.72 128WGEnamelled £097 Crystals 
coal Nich femaigcecosl Rd RUG Ber ay, Faze Ie SWS Enameled £827 BPS Smal Can 
| 25 Way Female Socket£1:13 3 pin IEC Line Socket £1.08 BA240V DPDT 6y. £1.76 ZOSWGEnamelled £0.97 He/so egg, 097 
oe Riaht Analed PCB ; 22 SWG Enamelled £1.01 
‘ g gie 3 Pin IEC Line Plu £1.78 5A 240V DPDT 12V ‘£1.76 24SWGE lled £1.12 1.8432MHZ £1.08 
10 Way Socke £0.25 3 Pin Chassis Socket £0.55 JOA 240VSPDT6V_ £1.25 52 8Wwe&Enamelled £1.14 2-OMHZ £1.01 
14 Way Socket £0.35 3 Pin Chassis Plug £0.72 10A 240V SPDT 12V £1.44 58SwWGEnamelled £1.22 2-4576MHz £0.84 
16 Way Socket —-£0.37 8 Way Bulgin <<, 10A 240V SPDT 24 £1.44 25 8WE Enamelled E124 3. 2768MMz £0.51 
a Wey poets! oO. fe~ || Computer Accessories 32SWGEnamelled £1.25 Urry elas pt 
34 Way Socket £039 2WayMale Plug | £0.33 O' | Adaptors | ae ew Enameled = £127 4OMHz £0.41 
SbWey Socket £080. 19 Way Mole Plyg £0.39 J | 38 SWG Enameled £1.55 7 13az0oMre «EO.AI 
; 15 Way Female Socket £0.39 8 Pin Line Plug P551 £4.08 RAMS 4 49152M £0.41 
IDC Cable Plugs 15 ay Socket £0.58 8 Pin Cha is Sk 4 9 Tinned Copper re 0 2 ; 
NEW 23 Way Male Plo £5 8 Pin Chassis Skt P552 £1.3 Per 50g (20z) Reel 60M £0.41 
10 Way Plug £0.58 25 Way Female O ket £0.51 Tog le ea, 9M Gender Changer £2.18 500g reels available 73 Z ‘Al 
14 Way Plu £0.64 ‘Switches 9F Gender Changer £2.29 14 SW Tinned £0.97 2-3728MHz £0.41 
16. War Plug £068 5 Wen coco ere, £0.29 : 25M Gender Changer £2.60 16 SWG Tinned £0.97 BOMHZ, £0.49 
20 Way Plug £0.72 9 Way Cover - Black £0.3 Z5F Gender Changer £2.89 18 sWG Tinned £0.97 10.0MHz £0.38 
26 Way Plug £0.76 15 Way Cover - Grey £0.32 Male - 25 Female £1.90 20 SWG Tinned £1.01 1 -OMHz £0.40 
34 Way Plug £0.88 23 Way Cover - Grey £0.38 Sub-Miniafure 9 Female -25 Male £1.90 22 SWG Tinne £1.01 110592MH 60:4] 
40 Way Plug £1.00 23 Way Cover - Black £0.38 3A 125V 1A 250V 9M - 6 Mini Din Male £2.40 24 SWG Tinned £1.03 12.0MH + 0:4] 
50 Way Plug £1.22 25 Way Cover - Gre £0.34 2mm @ Mounting Hole 9F - 6 Mini Din Female £2.40 26 SWG Tinned £1.03 14.7456MH 60:4] 
PCB Box “sities an. «OB Way Cover. Black £037 SPST. 5x 10mm £0.58 5M Din - 6F Mini Din £2.08 24 SWG Tinned £1.03 +2 : 
Headers SPDT 5 x 10mm £0.60 5F Din - 6M Minj Din LS. OMHZ aot 
9to9 Cover/Case £0.80 SPDT C/OFf 0 : 20.0MHz £0.42 
25 to 25 Cover / Case £0.84 SPD 5x 10mm £0.81 Testers / Patch Boxes 
ee 9 to 25 Cover/ Case £0.80 DRDT 9.2 x 10mm £0.66 Mini Tester7 LEDs £4.72 [eeeeeereeeaamema ae 
audia.¢ Miniature Check Tester 18 LEDs £6.32 | EPE PROJECTS 
0 Way Straight e onnectors a Lip A min eee Enhanced + Switches pee | Teach-in 2000 & EPE 
traight il » 6.2mm ounting Hole umper Box M- ; cgi ih Gs Sin Gt ome ee P 
g Wer Stag : B® sor aim BRN, 2 a, | rrolecte 
tA eee ; : remnant 
4 2.5mm Jack Plu £0.25 SPDT c/off 8x 13mm £0.60 S732 Surge Dectecttr 65°43 | /each-in 2000 Hardware & Tools Pack 
2.5mm Line Soc et £0.16 SPDT c/o Biased 2 way£0.97 Mains Surge Protector£1 1 99 Normal £42.34 Pack Price £33.87 
2.5mm Chassis Socket £0.20 SPDT ¢/o Biased 1 way£l.04 4Ga g Surge Block £1 5.50 | Teach-in 2000 Components Pack(1) 
3.2mm Mono Flug. yaa DPDT I2k Tamm | £0.72 Loads & Cables Normal £21.03 Pack Price £16.82 
pin Mona ine okt S014 DPDT c/off 12 x 13mm £0.80 Teach-in 2000 Components Pack(2) 
5 Bm Sleres Plog £034 ooRt he aed ‘ wee 2 Normal £16.91 Pack Price £14. 13 
3.5mm Stereo Line Skt £0.37 Stemndes YR Full details on our Web site 
3.5mm Stereo Chassis £0.34 10A 250V Push on terminals 7 - 
oe ised Plug Sock oer: 2mm @ Mounting Hole 2) ————— 
Mt Mone pine Socket £h-32 SPST 18 x 30mm £1.28 1.5m Printer Lead £3.40 
y" Stereo Plug se £0.40 SPDT Soft 18% 30mm é| oh 0 renee a ERIS 
’" Stereo Line Socket £0.38 DPDT 21 x 30mm £1.65 Serial Printer 25M-9F £4.50 






¥,"” Stereo Chassis Skt 
NEUTRIK Speanon Plug 
ono Series 















Red Line Plu £0.20 
: Black Line Plug £0.20 
; Yellow Line Plug £0.20 
; White Line Plug £0.20 
y i : Red Line Socket £0.20 
40 Way Straight £0.92 Black Line Socket £0.20 
50 Way Straight £1.27 Yellow Line Socket £0.20 
Way 90° £0.46 White Line Socket 0.20 
14 Way 90 £0.48 Red Chassis Socket £0.20 
: Black Chassis Socket £0.2 
Gold Plated Plug Red £0.6 
Gold Plated Plug Black£0.66 
metal — 












nooee 


XLR Series - 


ager 


3 Pin Line Plu 

3 Pin Line Socket 
3 Pin Chassis Plu 
3 Pin Chassis Socket 
Neutrik Line Plu 
Neutrik Line Socket 
Neutrik Chassis plug. 

N k Ch S £2.32 






















DPDT c/off 21 x 30mm £1.68 


Slide Switches 


Miniature 
300mA 125V 


7 x 15mm Mounting Hole 
£0.20 


DPDT 7x23 
Standard 
1A 125V 


mm 






5.5 x 12mm Mounting Hole 
£0.25 


DPDT 12x 35mm 


QO DPDT c/o 12 x 35mm 


Rotary Switches 






SE 3 


¢ 150mA 250V 


£0.27 


Make before Break 22mm @ 


9.8mm @ 
1 Pole 12 Way 
2 Pole 6 Way 
3 Pole 4 Way 
4 Pole 3 Wa 






Mounting Hole 





serial Printer 25M-25F £4.45 

Null Modem Leads 

9 Female-9 Female £3.16 

25 Female- 25 Female £4.63 
emale - emale £3.18 

ee to 9&25F £5.52 


odem s 
25Male to 9Female 


£4.08 
25Male to 25Female £4.75 
PC Link Leads 
pterlin’ 25M to 25M. £4.38 
Patch Lead 
25Male to 25Male £4.50 
36Male to 36Male £2.60 

nternal Leads 

ORPY Ree A/B £3.00 
Hard Disk 2xIDE £1.65 


Power 54-2 x 5% 
Power 5%-2 x 3% 


Power 5%4-3%,5% £2.24 
Networ nq 

BNC T Piece FMF £1.71 
BNC T Piece FFF £2.40 
BNC Coupler F £0.95 
BNC Coupler M 1.6 


£1.65 
BNC Ratchet Crimper£17.44 
50Q BNC Terminator £1.24 
Thinnet Cable perm £0.39 


A 3% digit multimeter. 
with 19 ran 


Range ® Fuse Protection * Auto- ® 
matic Polarity & Zero ® This digi- * 
tal multimeter comes with leads 

battery and manual. © Dims 126 x 70 x 24mm 


Technical books & CD ROMs 

Data Table & Equivalent charts from ECA ——— 
Characteristics, pin outs, equivalents & selector 
tables for semiconductors are_available as . %& 
paper books or on CD ROM. Demo version #4 
of the CD ROMs & full details of the complete 

range are available from our web site. 


Full details of UK, European or World- 
wide Order information on our web site. 


tte 














































































Ss 


Editorial Offices: 
EVERYDAY PRACTICAL ELECTRONICS EDITORIAL 
ALLEN HOUSE, EAST BOROUGH, WIMBORNE 


le DORSET BH21 1PF 








FRE .] MAGAZINE FOR ELECTRONICS TECHNOLOGY & COMPUTER PROUECTS 


Phone: Wimborne (01202) 881749 

Fax: (01202) 841692. 

E-mail: editorial @ epemag.wimborne.co.uk 

Web Site: http://www.epemag.wimborne.co.uk 

Online Edition www.epemag.com 

See notes on Readers’ Enquiries below — we regret lengthy 
technical enquiries cannot be answered over the telephone. 


Advertisement Offices: 


EVERYDAY PRACTICAL ELECTRONICS ADVERTISEMENTS 
MILL LODGE, MILL LANE 


VOL. 29 No. 5 MAY 2000 


CHIPPER 

Every so often a new chip comes along that looks like it will be very popular for 
a wide range of applications, just such a chip forms the basis of our main cover 
subject this month — the Versatile Microphone/Audio Preamplifier. The problem 
with specialised chips of this nature is that sometimes they don’t stay in produc- 
tion for a long period and, for hobbyists, who seem to like to build projects years 
after they have been published, this can obviously cause headaches. It’s why we 
advise readers to check that all components are still available before commencing 
any project in a back dated issue. Whilst it is sometimes possible to find old chips 
(particularly via the internet) they are often highly priced and obviously supplies 
do eventually get exhausted. 

We do, however, have high hopes that this chip will be around for some time as 
it appears to have been designed to cover a very wide range of applications, includ- 
ing use for microphone inputs to PCs. This fact alone will ensure high demand and 
therefore longevity, should it be taken up by the computer manufacturers. Let’s 
hope it is. However, that in itself does not entirely get us out of the woods — the PC 
makers will no doubt use a surface mount device which does not necessarily guar- 
antee continuing availability of the d.i.. version. Once development has taken 
place, the industrial requirement for d.1.1. versions often falls dramatically so they 
can sometimes be discontinued. | 


NO WAY 

I suppose the answer is to build it now and hope for the best. There seems to be 
no way of knowing which chips will hang around and also no way of knowing of 
all the chips that have been discontinued. We usually only find this out when read- 
ers ring us with buying problems. Thankfully we can often help them out, but we 
have an ever increasing list of past projects that are no longer viable because of 
obsolete components. Unfortunately it is not a problem we expect to improve as 
time goes by. 





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purchased from retail magazine outlets around the 
world. An Internet on-line version can be purchased 
from www.epemag.com 





o 5 ee 
oe st 


Everyday Practical Electronics, 





May 2000 


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READERS’ ENQUIRIES 

E-mail: techdept @ epemag.wimborne.co.uk 
We are unable to offer any advice on the use, 
purchase, repair or modification of commercial 
equipment or the incorporation or modification 
of designs published in the magazine. We 
regret that we cannot provide data or answer 
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antee it and we cannot accept legal responsi- 
bility for it. 


COMPONENT SUPPLIES 

We do not supply electronic components or 
kits for building the projects featured, these 
can be supplied by advertisers (see Shoptalk). 
We advise readers to check that all parts are 
still available before commencing any project 
in a back-dated issue. 


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E-mail: adverts @ epemag.wimborne.co.uk 
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EVERYDAY PRACTICAL ELECTRONICS take 
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zine and its Publishers cannot give any under- 
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The Publishers regret that under no circum- 
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complaints should first address them to the 
advertiser. 


TRANSMITTERS/BUGS/TELEPHONE 
EQUIPMENT 

We advise readers that certain items of radio 
transmitting and telephone equipment which 
may be advertised in our pages cannot be 
legally used in the UK. Readers should check 
the law before buying any transmitting or 
telephone equipment as a fine, confiscation of 
equipment and/or imprisonment can result 
from illegal use or ownership. The laws vary 
from country to country; readers should check 
local laws. 


331 


Constructional Project 





VERSATILE 
MICc/AUDIO 
PREAMPLIFIER 


RAYMOND HAIGH 





Use one of the latest chips on the 
block to produce an audio pre-amp, 
with a.g.c., compression, limiting and 


noise reduction. 


NTENDED primarily as a means of pro- 

cessing microphone inputs to comput- 

ers, the SSM2166P integrated circuit 
(manufactured by Analog Devices) has a 
wider range of possible applications. 
Public address and surveillance systems 
immediately spring to mind, and the device 
will be of particular interest to radio enthu- 
siasts, especially now that the popular 
Plessey 6270 i.c. mic/pre-amp, with voice 
gain, is no longer available. 

This article describes how the new i.c. 
can be used for a variety of signal inputs, 
and additional circuitry is given for readers 
who require a signal-strength meter. 


THE CHIP 


The various amplifying and control 
stages built into the SSM2166 chip are 
shown in Fig.1. , 


_ Signal inputs are buffered by op.amp A, 
internally connected to a rectifier stage, B, 
which produces a d.c. voltage which varies 
in proportion to signal strength. | 

After processing by the control circuit, 
C, the d.c. voltage is used to fix the large 
and small signal gain of a second 
op.amp, D. 


AMPLIFIERS 

The input impedance of buffer amplifier, 
A, is 180 kilohms (180k) and its gain can 
be set, by external feedback resistors, 
between OdB and 20dB. There is a standing 
d.c. voltage on the input, and a blocking 
capacitor must be used. 

The input and output impedances of the 
controlled amplifier, D, are 1k, and 75 
ohms, respectively. A standing d.c. voltage 
necessitates the 
use of a blocking 
capacitor at the 
output. 


SIGNAL OUTPUT 





Provision is made for setting the nomi- 
nal gain of the controlled stage between 
OdB and 20dB, but a.g.c. action will 
increase amplification, at the lowest signal 
levels, to as much as 60dB. The output can 
be muted. 

Interestingly, the noise generated by the 
controlled stage is designed to be at a min- 
imum when its gain is at a maximum, and 
this significantly improves the overall 
signal-to-noise ratio of the system. 


RECTIFIER 


The circuit of the rectifier, or level detec- 
tor stage (B), has been specially developed 
for this application. It produces a d.c. con- 
trol voltage which is proportional to the log 
of the true r.m.s. value of the input signal. 

The speed at which the control voltage 
responds to changes in signal level, or the 
“attack time’’, can be controlled by the user. 
Response to high-level changes is automati- 
cally speeded up by the i.c. in order to min- 
imise the duration of any overload. 


CONTROL CIRCUIT 


The control circuit (C) enables the user 
to programme the performance of the i.c. in 
a very comprehensive way, and the amount 
of signal compression can be set between 
zero and 60dB. 


LIMITING IS IMPOSED IN THIS REGION IN 
ORDER TO HOLD THE OUTPUT BELOW A 
PRE-DETERMINED LEVEL 


CONTROLLED 


BUFFER AMPLIFIER 


AMPLIFIER 


THRESHOLD OF 
LIMITING SET. y= 
BY VR4 , 


IN THIS REGION GAIN REDUCES AS 
SIGNAL STRENGTH INCREASES IN 
ORDER TO COMPRESS THE DYNAMIC 


TRUE R.M.S. RANGE. COMPRESSION IS SET BY VR3 


LEVEL 
DETECTOR 


CONTROL 
CIRCUITRY 


IN THIS REGION GAIN REDUCES AS 

SIGNAL STRENGTH REDUCES IN 

ORDER TO PREVENT HIGH-LEVEL 

AMPLIFICATION OF NOISE UNDER 
THRESHOLD NO-SIGNAL CONDITIONS 
SET BY VR2 





SIGNAL INPUT 





Fig.1. Internal block schematic for the SSM2166P micro- eae 
phone preamplifier, with variable compression and noise Fig.2. Relationship between limiting, compression and 
gating. downward expansion or “squelch”. 


332 | | Everyday Practical Electronics, May 2000 


Signal limiting can also be applied to 
prevent the occasional transient exceeding 
the desired maximum output. It can be set 
at outputs ranging from 30mV to IV. 
Above this threshold, the maximum com- 
pression ratio of 15:1 is applied. 

The response of the system to very low 
level inputs can be reduced in order to 
prevent the amplification of noise under 
no-signal conditions. The threshold of 
this downward expansion (the lower the 
signal the less it is amplified), can be set 
at inputs of between 250uV and 20mV. 

Provision is made for the device to be 
placed in a “power-down” or stand-by 
mode, and this feature will be of particular 
interest when it is used in sophisticated 
surveillance systems. In this state, current 
consumption is reduced to around 10uA 
and the input and output ports assume a 
high impedance. 

User programmable control circuitry, 
coupled with the complex rectifier or level 
detector, contribute significantly to the 
chip’s performance. The relationship 
between the noise reduction, compression 
and limiting functions is displayed in 
Fig.2. 


RATINGS 


No doubt with computer circuit 
compatibility in mind, the SSM2166 is 
designed for a 5V supply. The absolute 
maximum supply voltage is 10V. 
Current consumption is approximately 
10mA. 

The maximum input to the buffer is 1V, 
and the maximum output from the con- 
trolled amplifier is 1-4V rm.s. for 1 per 
cent total harmonic distortion. Frequency 
response extends well into the rf. 
spectrum. 

Static discharges can damage the i.c., 
and the usual precautions (discharging the 
body) should be taken when handling and 
connecting it into circuit. 


AUDIO IN (0 ELECTRET MICROPHONES AND 
INPUTS REQUIRING A D.C. BLOCKING CAPACITOR 


AUDIO IN (2) DYNAMIC (MOVING COIL) MICROPHONES 


The SSM2166P. is embedded in a 14- 


‘pin, dual-in-line package, and the suffix 


“Pp” refers to the standard-size version. 
This is the type most likely to be stocked 


‘by suppliers. However, surface-mount 


types are also manufactured: these carry 
the suffix “S’’. 


CIRCUIT DETAILS 


The full circuit diagram for the Versatile 
Mic/Audio Preamplifier, incorporating a 
signal strength meter, is given in Fig.3. 
Provision for controlling so many func- 
tions results in a plethora of preset poten- 
tiometer controls. However, they do enable 


the signal processing to be tailored to indi-' 


vidual requirements, and their adjustment 
is not critical or difficult. A summary of 
their various functions is set out in Table 1. 


IC1 
SSM2166P 


COMPRESSIO! 


SIGNAL | 
\LEVEL | 





Preset VR1 permits adjustment of the 
input signal level to prevent overload and 
to optimise the performance of the circuit. 
Its value is appropriate for moving coil and 
electret microphones, and for audio signals 
derived from most transistor circuits. 
Keeping the value below 5 kilohms 
increases the stability margin of IC1. 

Power can be supplied to an electret 
microphone’s integral f.e.t. (field-effect- 
transistor) buffer via resistor Rl, and Cl 
acts as a d.c. blocking capacitor. The input 
arrangements for alternative microphones 
and other signal sources are discussed at 
greater length later. 

The input signal to IC1 is applied to the 
non-inverting (+) input of the buffer ampli- 
fier stage (Pin 7 — see Fig.1) via blocking 
capacitor C2. This i.c. has an extended 





Fig.3. Complete circuit diagram for the Versatile Mic/Audio Preamplifier. 


Everyday Practical Electronics, May 2000 


333 


frequency response and C3 introduces a 
measure of roll-off above 20kHz or so, 
again in the interests of stability. 


BUFFER GAIN 

The gain of the buffer amplifier is set at 
6dB by resistors R2 and R3, and this is 
likely to be sufficient for most purposes. 
Gain can be increased to a maximum of 
20dB by decreasing R3 to about 1-2 
kilohms. Adding this to the gain of the 
controlled amplifier results in an overall 
system gain, when signals are too small to 
initiate compression, of 80dB. 

This is a great deal of amplification in a 
small package, and particular care must be 
taken with the screening and routing of 
input and output leads, and the connections 
to a shared power supply, if instability is to 
be avoided. Separate ground, or OV leads, 
from signal source circuitry, the preampli- 
fier, and the power amplifier, should be run 
to a common point at the power supply. 
The screening braid of signal cables should 
be connected to ground at the preamplifier 
end only. 


If desired, the gain of the buffer can be © 


set at unity by deleting R3 and inserting a 
wire link in place of resistor R2 (to connect 
pin 5 and pin 6). Blocking capacitor C4 
maintains the correct d.c. conditions. 


CONTROLLED 
AMPLIFIER 


The output from the buffer stage (pin 5) 
is connected, via d.c. blocking capacitor 
CS to the non-inverting (+) input (pin 3) of 
the controlled amplifier stage. A capacitor 
of identical value, C6, at pin 4 connects the 
inverting (—) input to ground (OV). (This 
connection makes any electrical noise on 
the ground rail appear as a common mode 
signal to the controlled amplifier and the 
differential input circuitry rejects it). 

The nominal gain of the controlled 
amplifier can be set, by preset VRS, 
between unity and 20dB. Resistor R6 
ensures that the gain does not fall below 
unity. 

Switched muting can be achieved by 
grounding pin 2 via a 330 ohm resistor (the 
switch should be located at the ground or 
OV rail end). Switch clicks can be sup- 
pressed by connecting a 10nF capacitor 
between pin 2 and ground. 

The i.c. can be put in stand-by mode by 
disconnecting pin 12 from ground and con- 
necting it, via a 100 kilohms resistor, to the 
+5V rail. Provision has not been made for 
muting or powering-down on the p.c.b. 

The processed output is taken from pin 
13 and connected, via d.c. blocking capac- 
itor C9, to preset VR6. This enables the 
output signal level to be adjusted to suit the 
input sensitivity of the power amplifier. 


ATTACK TIME 


The response or “attack” time of the . 


a.g.c. system can be controlled by adjust- 
ing the value of the rectifier reservoir 
capacitor C7. The i.c. manufacturer sug- 
gests a value within the range 2-2uF to 
47uF, with smaller capacitors being suit- 
able for music and the larger for speech. 

Too low a value will result in “pump- 
ing” effects, with background noise “rush- 
ing up” between bursts of speech. This will 
become increasingly apparent as the com- 
pression ratio is raised. 


334 


Table 1: Preset Control Functions 


Function i 
Set input signal level: clockwise to increase. 


Set threshold of downward expansion (squelch): 


clockwise to lower. 

Set compression: clockwise to increase. 
Set threshold of signal limiting: 
clockwise to lower. 

Set gain of controlled amplifier: 
clockwise to increase. 

Set output signal level: clockwise to increase. 
Set signal strength meter pointer at full scale 
(when strongest signal being processed): 
clockwise gives clockwise pointer movement. 


Pre-set Value 
VR1 4k7 
VR2 1M 
VR3 100k 
VR4 47k 
VR5 22k 
VR6 10k 
VR7 10k 
VR8 10k 


Set signal strength meter pointer at zero 


(under no-signal conditions): clockwise gives 
clockwise pointer movement. 


COMPONENTS 


Conversely, too high a value will exces- 
sively slow the response of the system to 
changes in signal level. The 22~F compo- 
nent specified for C7 has been found to 
work well with both speech and music 
inputs. 

The attack time is controlled mainly by 
the value of C7, but the much longer 
“decay”’ time is dependant upon this capac- 
itor and the internal control circuit. Fast 
attack and slow decay help to reduce the 
pumping effect, which seems far less pro- 
nounced with this i.c. than with simpler 
audio a.g.c. systems. 


COMPRESSION 


The amount of compression is deter- 
mined by preset VR3, which connects pin 
10 to ground. There is no compression with 
the potentiometer set to zero. When its 
resistance is at maximum, a 60dB change 
in input level (above the downward expan- 
sion or squelch threshold) changes the out- 
put by less than 6dB. 

The onset of limiting is controlled by 
preset VR4. Setting this potentiometer to 
maximum resistance fixes it at 30mV. With 
VR4 at minimum resistance, it is around 
1V r.m.s. Above the threshold of limiting, a 
15:1 compression ratio is imposed, irre- 
spective of the setting of compression con- 
trol VR3. 


NOISE REDUCTION 


Preset potentiometer VR2 sets the 
threshold below which downward expan- 
sion (gain reduces as the signals become 
weaker) is applied. With maximum resis- 
tance, downward expansion starts at signal 
levels in the region of 250uV. Turned to 
zero resistance, the threshold is raised to 
around 20mV. 

Gain rises to a maximum under no-sig- 
nal conditions with all conventional a.g.c. 
systems, and the amplification of external 
and internally generated noise produces a 
loud and tiresome hiss in the speaker or 
‘phones. The i.c.’s noise reduction facility, 
which operates as a “squelch”’ control, is 
very effective in overcoming this. It can 
reduce output noise below the level of 
audibility when signal levels fall to zero. 

With any squelch system, a need to 
resolve very weak signals overlaid by noise 
compromises the usefulness of the feature. 
Radio enthusiasts with a particular interest 
in it could mount VR2 as a panel control so 
that the threshold could be adjusted to suit 
reception conditions. 


Resistors 


1k (4off) See 


10k (2 off) S/-|OP 
TALK 
page 


2M2 

(See 
Table 2) 

15k 

4k7 


All 0-25W 5% carbon film 
Potentiometers 


VR1 
- VR2 
VR3 
VR4 
VR5 


VR6, VR7, 
VR8 


Capacitors 


4k7 enclosed carbon 
preset, horizontal 
1M enclosed carbon 
preset, horizontal 
100k enclosed carbon 
preset, horizontal 
47k enclosed carbon 
preset, horizontal 
22k enclosed carbon 
preset, horizontal 


10k enclosed carbon 
preset, horizontal (3 off) 


4u7 radial elect. 10V 
(3 off) 

100n ceramic (2 off) 

10n ceramic. 

1u radial elect. 10V 
(2 off) 

22u radial elect. 

470u radial elect. 


Semiconductors 


TR1 


IC1 


IC2 


BC547 npn low power 
transistor (or similar 
i.e. BC239, BC548) 

SSM2166 microphone 
preamp (Analog 
Devices) 

LM78LO5ACZ +5V 
100mA voltage 
regulator 


Miscellaneous 


ME1 


50uA to 1mA f.s.d. 
moving coil meter 
(see text) 


Printed circuit board available from the 
EPE PCB Service, code 260; 14-pin d.i.l. 
socket; screened cable; multistrand con- 
necting wire; solder pins; solder etc. 


yVo)e) ge) em Orex-y i 
Guidance Only 


Everyday Practical Electronics, May 2000 


£17 


excluding meter 





POWER SUPPLY 


The maximum safe supply voltage is 
10V, and it should be noted that, under a 
light load, a fresh 9V alkaline battery will 
usually deliver a higher voltage than this. 

However, in order to ensure the correct 
operation of the device, and provide a high 
degree of isolation from other equipment 
sharing the same power supply, a 5V 
100mA voltage regulator, IC2, is included 
in the circuit. This enables supplies with 
outputs ranging from 8V to 18V (or more, 
depending on IC2 rating) to be used. 

Bypass capacitors C8 and C10 shunt the 
noise in the regulator output to ground. 
Note that C8 is essential to the stability of 
IC1 and it must be located as close as pos- 
sible to pin 14, even when the unit is bat- 
tery powered. 


SIGNAL STRENGTH 
METER 


Some readers, especially those wishing 
to incorporate the unit into a radio receiver, 
may welcome the provision of a signal 
strength meter. This is included in the cir- 
cuit diagram of Fig.1 and consists of tran- 
sistor TR1, meter MEI and associated 
components. 

The a.g.c. control voltage appears on pin 
8 of IC1. It ranges from 290mV under no- 
signal conditions to approximately 720mV 
with high level inputs. 

Transistor TR1, configured as a d.c. 
amplifier, ensures that IC1’s a.g.c. line is 
only lightly loaded, even when a ImA 
meter is used. It forms one arm of a bridge 
circuit, the other three being its collector 
load, R9, and the potential divider chain 
comprising preset VR8 and resistor R10. 
The bridge is balanced, and the meter set at 
zero under no-signal conditions, by preset 
potentiometer VR8. 

When a signal is being processed, the 
rising a.g.c. voltage on the base (b) of TR1 
increases its collector current and, hence, 
the voltage drop across resistor R9. This 
unbalances the bridge and drives the meter 
pointer over. Preset VR7 adjusts the sensi- 
tivity of the meter so that the pointer can be 
set just short of full-scale deflection (f.s.d.) 
when registering a strong signal. 

The circuit can be made to accommodate 
meters with full-scale deflections ranging 
from 50uA to I1mA by adjusting the value 
of resistor R8. This resistor controls the 
flow of current through the base-emitter 
junction of transistor TR1, and values to 
suit a range of meter f.s.d.s are given in 
Table 2. Bias resistor R7 provides a mea- 
sure of negative feedback which helps to 
stabilise the operation of the circuit. 

Almost any small-signal npn transistor 
should prove suitable for TR1, and a 
2N5827 or 2N5828 could be used in addi- 
tion to the types listed in the Components 
list. These devices have different case 
styles and the base connections must be 
checked. 


Table 2: Signal Strength Meter 
(Values of R8 for different meter 





sensitivities) 
Meter fsd. R8 
50uA 1M 
100uA 470k 
500uA 100k 
imA 47k 





CONSTRUCTION 


All the components, with the exception 
of the meter ME1, are asembled on a small, 
single-sided, printed circuit board (p.c.b.). 
The topside component layout, together 
with a full-size underside copper foil mas- 
ter pattern, is shown in Fig.4. This board is 
available from the EPE PCB Service, code 
260. 

Commence construction in the usual 
way by mounting the smallest components 
first working up to the largest, but fit IC1, 
IC2 and TRI last (see earlier comments 


POWER SUPPLY 
NEGATIVE +8V TO +18V 


UNDERSIDE 
VIEW 


ebc 


BC547 
BC239 
BC548 . 


UNDERSIDE 
VIEW 


IN 
COM 
_OUT 


LM78LO5ACZ 





about the static sensitive nature of IC1). A 
holder for IC1 will facilitate substitution 
checking. Solder pins, inserted at the lead- 
out points, will ease the task of off-board 
wiring. 


SPOT-CHECKS 


When all the components have been 
soldered in position on the p.c.b., double- 
check the orientation of electrolytic capac- 
itors, the i.c.s and the transistor. Also, 
check the p.c.b. for bridged tracks and poor 
solder joints. 


THRESHOLD 
OF LIMITING 


SIGNAL OUT 
BAROTR 


E 
A\ 
N 


SIGNAL 
STRENGTH 
METER 


Fig.4. Printed circuit board component layout, interwiring details and full size under- 


side copper foil master. 


Everyday Practical Electronics, May 2000 


335 


' HIGH IMPEDANCE 
E 


Fig.5. The line-powered buffer stage built into electret micro- 
phones can also be used for ceramic and crystal types. (Most 
f.e.t.s will function in this circuit with the source grounded, elimi- 
nating the need for the source resistor and bypass capacitor.) 


Next, with IC1 “out of circuit’’, connect 
a supply voltage of between 7V and 9V 
and check that the output from regulator 
IC2 is producing 5V. A fault in this device, 
or its wrong connection, could result in the 
destruction of IC1 when higher voltages 
are applied. 

Once all is well, place IC1 in its socket 
(checking orientation), connect, via 
screened cable, a signal source and a power 
amplifier. Adjust the various preset poten- 
tiometers until the processing meets your 
requirements. All preset functions are sum- 
marised in Table 1 for ease of reference. 


MICROPHONES 


The unit works well with dynamic (mov- 
ing coil), electret, crystal and ceramic 
' microphones. Screened cable must, of 
course, be used to connect any type of 
microphone to the preamplifier. 

Very high quality studio microphones 
can be insensitive and require balanced 
feeders to minimise hum pick-up. The pre- 
amplifier described here is configured for 
unbalanced inputs, and is not likely to be 
suitable, as it stands, for microphones of 
this kind. | 

A few words about the various types of 
signal input may prove helpful. 


Dynamic Microphones 

Dynamic microphones are manufactured 
with impedances ranging from 50 ohms to 
600 ohms. Output tends to be greatest with 
the higher impedance units. 

This type of microphone should be con- 
nected to Input 2 (i.e., directly across pre- 
set VR1), and the wire link must be 
removed to isolate resistor R1 from the 5V 
rail. 


Electret Microphones 

Electret microphones are a modern devel- 
opment of the capacitor microphone (a per- 
manently charged diaphragm, the electret, 
eliminates the need for an external charging 
voltage). The output from the actual unit is 
low and at a high impedance, so these micro- 
phones have an integral f.e.t. buffer. The 
drain load for the internal f.e.t. is provided at 
the amplifier end of the cable (resistor R1 in 
Fig.3), to facilitate line powering. 

Electret microphones must be connected 
to Input 1, and the wire link must be in 
place to connect resistor R1 to the supply 
rail. The 1 kilohm drain load (R1), fed 
from the 5V supply, should ensure the 


336 





optimum performance 
of most microphones 
of this kind. 


Crystal and 
Ceramic 
Microphones 


Crystal and ceramic 
microphones rely upon 
the piezo-electric effect 





to produce a signal Layout of components on the completed circuit board. The 
voltage. The vibrating “Signal Strength Meter’ components, except the meter, have 


diaphragm 
stresses in a wafer of 

crystal, often Rochelle salt, or in a barium 
titanate element in the case of ceramic 
units. 

These microphones should be connected 
to Input 2. They have a high impedance, 
and feeding them into preset VR1 will 
reduce their response to low audio frequen- 
cies. Low frequency roll-off is, however, 
desirable for communications work, and 
more is said about this later. 

The use of long connecting cables will 
attenuate the signal but have little effect on 
frequency response (cable capacitance is 
modest compared to the self-capacitance of 
these microphones, which can be as high as 
30nF). 

If an extended frequency response is 
required from microphones of this type, the 
use of an external, line-powered, f.e.t. 
buffer, as built into electret microphones, is 
recommended. This will also prevent sig- 
nal losses when long cables are used. 

A suitable circuit diagram is given in 
Fig.5 and the circuit can be built inside the 
microphone case. When this arrangement 
is adopted, resistor R1 must, of course, be 
connected to the supply rail, and the signal 
must be fed to Input 1. 


RADIO RECEIVERS 


Audio derived a.g.c. is often incorporat- 
ed into direct conversion radio receivers. 
Even simple superhets can benefit from 
this form of control (sometimes a conven- 
tional r.f. derived system is not very effec- 
tive when amateur single-side-band signals 
are being processed). 

Direct conversion and regenerative 
receivers will require a single transistor 
audio amplifier, after the product detector 
or regenerative detector, in order to ensure 
sufficient signal voltage for the SSM2166P. 
The output from the detector stage in most 
superhets will be more than adequate. 


induces Deen included on the board (bottom right). 


Radio receivers should be connected to 
Input 1, and the wire link removed. The 
orientation of electrolytic capacitor C1 will 
usually be correct when the receiver has a 
negative ground or OV rail. 

However, some diode detectors in super- 
hets are configured to provide an output 
which is negative going with respect to 
ground (to suit the receiver’s a.g.c. circuit). 
The polarity of C1 will need to be reversed 
when equipment of this kind is connected. 


SIGNAL PROCESSING 


The preamplifier’s frequency response is 
reasonably flat from below 100Hz to more 
than 20kHz. Speech clarity, especially 
under noisy conditions, can be improved 
by “rolling off” frequencies below 300Hz 
and above 3000Hz, and active or passive 
band-pass filters are often used for this 
purpose. 

A big improvement can, however, be 
made by modifying some of the coupling 
and bypass components in the preamplifier. 
Constructors wishing to limit the frequen- 
cy response in this way should reduce the 
value of capacitor C9, to 47nF (a Mylar or 
ceramic capacitor is then suitable). This 
will attenuate the lower frequencies. 

Wiring a 220nF ceramic capacitor across 
preset VR1 will attenuate the higher fre- 
quencies. Although extremely simple, 
these measures are quite effective. [] 


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above. 30A15 £13.95 

@ TELEPHONE LINE RELAY SWITCH Turn on/off 4 
relays over your phone line from anywhere in the world. 4- 
digit security code. Line protection circuitry built-in (non- 
approved). PCB 78x105mm. 3086KT £39.95 

@ PC DATA ACQUISITION/CONTROL UNIT Use your 
PC to monitor physical variables (e.g. pressure, tem- 
perature, light, weight, switch state, movement, relays, 
etc.), process the information & use results to control 
physical devices like motors, sirens, relays, servo & 
stepper motors. Inputs: 16 digital & 11 analogue. 
Outputs: 8 digital & 1 analogue. Plastic case with print- 
ed front/rear panels, software utilities, programming 
examples & all components (except sensors & cable) 
provided. 12VDC. 3093KT £79.95 

@ PIC 16C71 FOUR SERVO MOTOR DRIVER 
Simultaneously control up to 4 servo motors. Software & 
all components (except servos/control pots) supplied. 
5VDC. PCB 50x70mm. 3102KT £14.95 










a oe re ee 


EILLANC 


High performance surveillance bugs. Room transmitters supplied with sensitive electret microphone & battery holder/clip. All trans- 
mitters can be received on an ordinary VHF/FM radio between 88-108MH7z. Available in Kit Form (KT).or Assembled & Tested (AS). 


ROOM SURVEILLANCE 

@ MTX - MINIATURE 3V TRANSMITTER 

Easy to build & guaranteed to transmit 300m @ 3V. Long bat- 
tery life. 3-5V operation. Only 45x18mm. @ 3007KT £5.95 
AS3007.£10.95 

MRTX - MINIATURE 9V TRANSMITTER 

Our best selling bug. Super sensitive, high power - 500m range 
@ 9V (over 1km with 18V supply and better aerial). 45x19mm. 
3018KT £6.95 AS3018 £11.95 

HPTX - HIGH POWER TRANSMITTER 

High performance, 2 stage 
transmitter gives greater 
stability & higher quality 
reception. 1000m range 6- § 
12V DC operation. Size 
70x15mm. 3032KT £8.95 
AS3032 £17.95 

@ MMTX - MICRO-MINIATURE 9V TRANSMITTER 

The ultimate bug for its size, performance and price. Just 
15x25mm. 500m range @ 9V. Good stability. 6-18V operation. 
3051KT £7.95 AS3051 £13.95 

@ VTX - VOICE ACTIVATED TRANSMITTER 

Operates only when sounds detected. Low standby current. 
Variable trigger sensitivity. 500m range. Peaking circuit sup- 
plied for maximum RF output. On/off switch. 6V operation. Only 
63x38mm. 3028KT £9.95 AS3028 £22.95 

HARD-WIRED BUG/TWO STATION INTERCOM 

Each station has its own amplifier, speaker and mic. Can be 
set up as either a hard-wired bug or two-station intercom. 10m 
x 2-core cable supplied. 9V operation. 3021KT £13.95 (kit 
form on 

@ TRVS - TAPE RECORDER VOX SWITCH 

Used to automatically operate a tape recorder (not supplied) 
via its REMOTE socket when sounds are detected. All conver- 
sations recorded. Adjustable sensitivity & turn-off delay. 
115x19mm. 3013KT £7.95 AS3013 £19.95 





@ STEREO VU METER shows peak music power 
using 2 rows of 10 LED’s (mixed green & red) 
moving bar display. 0-30db. 3089KT £10.95 

@ AM RADIO KIT 1 Tuned Radio Frequency front- 
end, single chip AM radio IC & 2 stages of audio 
amplification. All components inc. speaker provid- 
ed. PCB 32x102mm. 3063KT £9.95 

@ DRILL SPEED CONTROLLER Adjust the speed 
of your electric drill according to the job at hand. 
Suitable for 240V AC mains powered drills up to 
700W power. PCB: 48mm x 65mm. Box provided. 
6074KT £17.90 

@ 3 INPUT MONO MIXER Independent level con- 
trol for each input and separate bass/treble controls. 
Input sensitivity: 240mV. 18V DC. PCB: 60mm x 
185mm 1052KT £16.95 

@ ELECTRONIC SIREN 5 Watt. Impressive 5W 
power output. Suitable for alarm systems, car, 
motorbikes, etc. Output frequency 1-2kHz. 6-12V 
DC. PCB: 37mm x 71mm. Siren not provided 
1003KT £5.95 

@ NEGATIVE\POSITIVE ION GENERATOR 
Standard Cockcroft-Walton multiplier circuit. Mains 
voltage experience required. 3057KT £9.95 


30-in-ONE 


Great introduction to electronics. Ideal for the budding elec- : 


Electronic Projects Lab 


tronics expert! Build a radio, burglar alarm, water detector, 
morse code practice circuit, simple computer circuits, and 


er 9 2 KOE 
SESTESE 


much'more! NO soldering, tools or previous electronics 
knowledge required. Circuits can be built and unassembled 
repeatedly. Comprehensive 68-page manual with explana- 
tions, schematics and assembly diagrams. Suitable for age 


10+. Excellent for schools. Requires 2 x AA batteries. 


ONLY £14.95 (phone for bulk discounts). 


@ PC SERIAL PORT ISOLATED I/O BOARD 
Provides eight 240VAC/10A relay outputs & 4 opti- 
cally isolated inputs. Designed for use in various con- 
trol & sensing applications e.g. load switching, exter- 
nal switch input sensing, contact closure & external 
voltage sensing. Controlled via serial port & a termi- 
nal emulator program (built into Windows). Can be 
used with ANY computer/operating system. Plastic 
case with printed front/rear panels & all components 
(except cable) provided. 3108KT £49.95 

@ UNIPOLAR STEPPER MOTOR DRIVER for any 
5/6/8 lead motor. Fast/slow & single step rates. 
Direction contro! & on/off switch. Wave, 2-phase & 
half-wave step modes. 4 LED indicators. PCB 
50x65mm. 3109KT £14.95 

@ PC CONTROLLED STEPPER MOTOR DRIVER 
Control two unipolar stepper motors (3A max. each) 
via PC printer port. Wave, 2-phase & half-wave step 
modes. Software accepts 4 digital inputs from exter- 
nal switches & will single step motors. PCB fits in D- 
shell case provided. 3113KT £16.95 

@ 12-BIT PC DATA ACQUISITION/CONTROL UNIT 
Similar to kit 3093 above but uses a 12 bit Analogue- 
to-Digital Converter (ADC) with internal analogue mul- 
tiplexor. Reads 8 single ended channels or 4 differen- 
tial inputs or a mixture of both. Analogue inputs read 0- 
4V. Four TTL/CMOS compatible digital input/outputs. 
ADC conversion time <10uS. Software (C, QB & Win), 
extended D shell case & all components (except sen- 
sors & cable) provided. 3118KT £47.95 

@ LIQUID LEVEL SENSOR/RAIN ALARM Will indi- 
cate fluid levels or simply the presence of fluid. Relay 
output to control a pump to add/remove water when it 
reaches a certain level. 1080KT £6.95 

@ UNIVERSAL TIMER Seven crystal controlled tim- 
ing operations in:steps of 0.1s from 0.1-6553.6s or 1 
second steps from 0.1-65536s. Allows 4 signal input 
types from push button to electrically isolated volt- 
age switching sources. On-board relay will switch 
240V/5A. Box, software & all components provided. 
PCB 56 x 97mm. 3054KT £24.95 





@ LED DICE Classic intro to electronics & circuit 
analysis. 7 LED’s simulate dice roll, slow down & land 
on a number at random. 555 IC circuit. 3003KT £7.95 
@ STAIRWAY TO HEAVEN Tests hand-eye co-ordination. 
Press switch when green segment of LED lights to climb 
the stairway - miss & start again! Good intro to several 
basic circuits. 3005KT £7.95 

@ ROULETTE LED ‘Ball’ spins round the wheel, 
slows down & drops into a slot. 10 LED’s. Good intro 
to CMOS decade counters & Op-Amps. 3006KT 
£9.95 

@ DUAL LED DICE PIC 16C54 circuit performs sim- 
ilar function to 3003KT above but two dice. Good 
intro to micro-controllers. 3071KT £11.95 

@ 9V XENON TUBE FLASHER Transformer circuit 
steps up 9V battery to flash a 25mm Xenon tube. 
Adjustable flash rate (0-25-2 Sec’s). 3022KT £10.95 
@ LED FLASHER 1 5 ultra bright red LED’s flash in 
7 selectable patterns. 3037MKT £4.50 


@ LED FLASHER 2 Similar to above but flash in 


sequence or randomly. Ideal for model railways. 
3052MKT £4.50 

@ INTRODUCTION TO PIC PROGRAMMING. 
Learn programming from scratch. Programming 
hardware, a P16F84 chip and a two-part, practical, 
hands-on tutorial series are provided. 3081KT 
£21.95 

@ SERIAL PIC PROGRAMMER for all 8/18/28/40 
pin DIP serial programmed PICs. 3rd party software 
supplied expires after 21 days (costs US$25 to reg- 
ister). 3096KT £14.95 

@ ‘PICALL’ SERIAL & PARALLEL PIC PRO- 
GRAMMER for all 8/18/28/40 pin DIP parallel AND 
serial PICs. Includes fully functional & registered 
software (DOS, W3.1, W95/8). 3117KT £54.95 

@ ATMEL 89Cx051 PROGRAMMER Simple-to-use 
yet powerful programmer for the Atmel 89C1051, 
89C2051 & 89C4051 uC’s. Programmer does NOT 
require special software other than a terminal emu- 
lator program (built into Windows). Can be used with 
ANY computer/operating system. 3121KT £34.95 


TELEPHONE SURVEILLANCE 

@ MTTX - MINIATURE TELEPHONE TRANSMITTER 
Attaches anywhere to phone line. Transmits only when phone 
is used! Tune-in your radio and hear both parties. 300m range. 
Uses line as aerial & power source. 20x45mm. 3016KT £7.95 
AS3016 £13.95 

@ TRI - TELEPHONE RECORDING INTERFACE 
Automatically record all conversations. Connects between 
phone line & tape recorder (not supplied). Operates recorders 
with 1.5-12V battery systems. Powered from line. 50x33mm. 
3033KT £7.95 AS3033 £16.95 

@ TPA - TELEPHONE PICK-UP AMPLIFIER/WIRELESS 
PHONE BUG 

Place pick-up coil on the phone line or near phone earpiece 
and hear both sides of the conversation. 3055KT £10.95 
AS3055 £19.95 

@ 1 WATT FM TRANSMITTER Easy to construct. Delivers a 
Crisp, clear signal. Two-stage circuit. Kit includes microphone 
and requires a simple open dipole aerial. 8-30VDC. PCB 
42x45mm. 1009KT £14.95 

@ 4 WATT FM TRANSMITTER Comprises three RF 
stages and an audio preamplifier stage. Piezoelectric 
microphone supplied or you can use a separate pream- 
plifier circuit. Antenna can be an open dipole or Ground 
Plane. Ideal project for those who wish to get started in 
the fascinating world of FM broadcasting and want a 
good basic circuit to experiment with. 12-18VDC. PCB 
44x146mm. 1028KT. £23.95 

@ 15 WATT FM TRANSMITTER (PRE-ASSEMBLED & 
TESTED) Four transistor based stages with Philips BLY 
88 in final stage. 15 Watts RF power on the air. 88- 
108MHz. Accepts open dipole, Ground Plane, 5/8, J, or 
YAGI configuration antennas. 12-18VDC. PCB 
70x220mm. SWS meter needed for alignment. 1021KT 
£69.95 

@ SIMILAR TO ABOVE BUT 25W Output. 1028KT £79.95 















a ee ee ee 






















nm en ee Se eee 










@ 3V/1-5V TO 9V BATTERY CONVERTER Replace | 


expensive 9V batteries with economic 1.5V batter- 
ies. IC based circuit steps up 1 or 2 ‘AA’ batteries to 
give 9V/18mA. 3035KT £4.95 

@ STABILISED POWER SUPPLY 3-30V/2.5A Ideal 
for hobbyist & professional laboratory. Very reliable 
& versatile design at an extremely reasonable price. 
Short circuit protection. Variable DC voltages (3- 
30V). Rated output 2.5 Amps. Large heatsink sup- 
plied. You just supply a 24VAC/3A transformer. PCB 
55x112mm. Mains operation. 1007KT £17.50. 
Custom Designed Box 2007 £34.95 

@ STABILISED POWER SUPPLY 2-30V/5A As kit 
1007 above but rated at 5Amp. Requires a 
24VAC/5A transformer. 1096KT £29.95. Custom 
Designed Box 2096 £34.95 

@ RFI POWER SUPPLY Designed to power RF 
transmitters/receivers. Blocks high frequencies & 
eliminates problems like noise, overheating, stand- 
ing waves, etc. Output: 12-14VDC/3A. 
Thermal/short circuit protection & electronic stabili- 
sation. You just supply a 18VAC/3A transformer. 
PCB 72x82mm. 1171KT £24.95 

@ MOTORBIKE ALARM Uses a reliable vibration sen- 
sor (adjustable sensitivity) to detect movement of the 
bike to trigger the alarm & switch the output relay to 
which a siren, bikes horn, indicators or other warning 
device can be attached. Auto-reset. 6-12VDC. PCB 
57x64mm. 1011KT £11.95 Box £5.95 f 

@ CAR ALARM SYSTEM Protect your car from 
theft. Features vibration sensor, courtesy/boot light 
voltage drop sensor and bonnet/boot earth switch 
sensor. Entry/exit delays, auto-reset and adjustable 
alarm duration. 6-12V DC. PCB: 47mm x 55mm 
1019KT £11.95 Box £6.50 

@ LIGHT ALARM Protect your valuables. Alarm 
sounds if circuit detects smallest amount of light. 
Place in cash box etc. 3008KT £4.50 


2 oe ee ee Ce 


a eee eee ee 


@ PIEZO SCREAMER 110dB of ear piercing | 


noise. Fits in box with 2 x 35mm piezo elements 
built into their own resonant cavity. Use as an 


mo 


alarm siren or just for fun! 6-9VDC. 3015KT £9.95 | 


@ COMBINATION LOCK Versatile electronic lock 
comprising main circuit & separate keypad for 
remote opening of lock. Relay supplied. 3029KT 
£9.95 

@ ULTRASONIC MOVEMENT DETECTOR Crystal 
locked detector frequency for stability & reliability. PCB 
75x40mm houses all components. 4-7m range. 
Adjustable sensitivity. Output will drive external 
relay/circuits. 9VDC. 3049KT £12.95 

PIR DETECTOR MODULE 3-lead assembled unit 
just 25x35mm as used in commercial burglar alarm 
systems. 3076KT £7.95 


@ INFRARED SECURITY BEAM When the invisi- | 


ble IR beam is broken a relay is tripped that can be 
used to sound a bell or alarm. 25 metre range. 
Mains rated relays provided. 12VDC operation. 
3130KT £11.95 

@ FUNCTION GENERATOR Quad Op-Amp oscilla- 
tor & wave shaper circuit generates audio range 
square waves (6Hz-6KHz), triangle & pseudo sine 
outputs. 9VDC. 3023KT £3.95 


7 a ee ee 


' 


@ LOGIC PROBE tests CMOS & TTL circuits & | 


detects fast pulses. Visual & audio indication of 


logic state. Full instructions supplied. 3024KT | 


£6.95 

@ SQUARE WAVE OSCILLATOR Generates 
square waves at 6 preset frequencies in factors of 
10 from 1Hz-100KHz. Visual output indicator. 5- 
18VDC. Box provided. 3111KT £7.95 

@ PC DRIVEN POCKET SAMPLER/DATA LOG- 
GER Analogue voltage sampler records voltages 
up to 2V or 20V over periods from milli-seconds to 
months. Can also be used as a simple digital 
scope to examine audio & other signals up to 
about 5KHz. Software & D-shell case provided. 
3112KT £19.95 

@ 20 MHz FUNCTION GENERATOR Square, tri- 
angular and sine: waveform up to 20MHz over 3 
ranges using ‘coarse’ and ‘fine’ frequency adjust- 
ment controls. Adjustable output from 0-2V p-p. A 
TTL output is also provided for connection to a 
frequency meter. Uses MAX038 IC. Plastic case 
with printed front/rear panels & all components 
provided. 7-12VAC. 3101KT £49.95 





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Everyday Practical Electronics, May 2000 


A roundup of the latest Everyday 


News from the world of 


electronics 








BACK TO THE FUTURE WITH MILLIPEDES 


Millipedes may help bring back punched card technology for PC data 


TEAM of researchers from IBM’s labo- 
ratory in Zurich recently revealed their 
road map for the future of data storage. 
One surprise is that punched cards are due 
for a comeback, but around a million times 
smaller than they were the first time round. 
The real density of hard disk recorders is 
now increasing at 120 per cent per year, 
thanks to IBM’s 1988 discovery of GMR, 
the giant magneto-resistive material which 
was ready for commercial exploitation two 
years ago and is now used in 70 per cent of 
all hard drive read heads — either made by 
IBM or under licence. 

GMR is a multi-layer sandwich of mag- 
netic and non-magnetic materials which 
show dramatic changes of resistance in a 
changing magnetic field. This makes the 
read head ten times more sensitive, and so 
lets it detect smaller magnetic domains. 


-Hard Drive Density 

Currently hard drives can record around 
20 Gigabits of data for every square inch 
(6.45cm*) of surface area and 35 
Gbit/sq.inch, drives are already working in 
the lab. The likely practical limit looks like 
being 100Gbit. At this density the individ- 
ual magnetic domains are so small and 
close that they affect each other, making 
storage unreliable. Before this limit is 
reached, the current method of recording a 
signal, with a miniature inductive head, 
will have become unworkable. 

IBM’s Magneto-electronics team leader, 
Dr Stuart Parkin, believes that in two years 
time hard drives will have to use vertical, 
instead of horizontal, recording. For VR 
the domains are switched by a field which 
aligns the magnetic particles through the 
disk coating. 

IBM’s Microdrive, the hard drive no big- 
ger than a large postage stamp, currently 
stores 340 Megabytes, or nearly 900 still 
pictures from a video camera. The next 
Microdrives will hold 1GB. By compari- 
son an 8MB Compact Flash card holds 
around 20 pictures. 

So what happens when disk drives run 
out of space? Dr Bernard Meyerson, 
IBM’s Director of Telecommunications 
Technology, dismisses the idea that optical 
disk can take over from magnetic hard 
disks. 

“IBM has worked for years on optical 
storage, including disks with several lay- 
ers to increase density. But there is a 
basic limiting factor — the wavelength of 
light’. 


Millipede Tips 
Big Blue’s Blue Sky research efforts are 
now concentrated on an extraordinary new 


storage. Barry Fox reports. 


technology called Millipede. A silicon 
chip, the size of a finger nail, is made with 
a matrix of 1024 tiny cantilever arms, each 
with a sharp tip, around Inm in size. When 
the tips are moved, by feeding current to 
activate drive coils, they press down on a 
spinning plastic film disk to create tiny 
indentations. These can then be read by 
sensor tips. 

The fundamental science on Atomic Force 
Microscopy was done in 1980, and won a 
Nobel Prize for IBM’s Dr Gerd Binnig in 
1986. The first laboratory demonstrations 
are now nearly ready. “It’s back for the 
future”, says Gerd Binnig, alluding to the 
original punch card, developed in the last 
century for census data processing and then 
used by early computers. 

But whereas original punch cards had 
permanent perforations, the new Millipede 
recording material can be erased, by heat- 
ing the plastic to re-flow depressed areas. 
The chip moves across the surface, in a 
scanning raster, writing 1GB of data in a 
3mm x 3mm area. 

The write/read system must be kept 






PICs and related products. 


Everyday Practical Electronics, May 2000 


MICROCHIP HANDBOOK 


MANY of you will already have found how useful Microchip’s Embedded Control 
Handbook can be when writing PIC microcontroller software. The latest update to this 
book has been released and provides a comprehensive reference tool for anyone using 


The 848-page updated handbook provides current application notes, technical briefs 
and reference designs which have been written and published since the previous edition. 
The book can be obtained through any authorised Microchip representative. The mater- 
ial is also available individually on Microchip’s website at www.microchip.com. 

It is interesting to note from another Microchip press release that the organisation is 
offering a comprehensive University Programme within the UK, designed to help univer- 
sity professors give their engineering students a hands-on understanding of PICs and 
related products. Details can be found via www.microchip.com/university. 

Microchip’s UK HQ is at Microchip House, 505 Eskdale Road, Winnersh Triangle, 
Wokingham, Berks RG41 5TU. Tel: 0118 921 5858. Fax: 0118 921 5835. 


surgically clean, but the techniques used to 
keep hard drives clean are applicable. Air 
is continually blown over the surface, 
through very fine filters. 


Tunnelling Ram 

There are also new developments com- 
ing in Random Access Memory. Current 
RAM needs power to retain data. TMJ 
(tunnelling magnetic junction)-RAM 
retains data even when the power is 
switched off. So it works like flash memo- 
ry, but with much higher capacity, and 
much lower power needed for writing. 
With Magnetic RAM a PC could boot up 
within seconds. 

The system relies on the ability to 
detect and control the spin parameters of 
electrons in ferromagnetic materials. 
Switching at low power is possible 
because of the quantum physics phenom- 
enon known as tunnelling, whereby if 
enough electrons confront a_ barrier, 
some will pass through, even though 
their energy state is theoretically too low 
to allow it. 
















339 

















E-mail: admin @ greenweld.co.uk. 


Greenweld Catalogue 


YOU will be glad to hear that Greenweld have reopened. Chris Knight tells us that after 
many months of work they have finally got the business going again. You will probably 
recall that the original Greenweld Electronics ceased trading last year, but the remaining 
stock was astutely bought by Chris and Tim Knight and Geoffrey Carter. 

The trio have a scientific background and wide business experience, along with inter- 
ests ranging from computers to cars and robots to recycling. 

We are pleased to have received the new Greenweld catalogue, the first under the new 
ownership and management team. The catalogue lists many ranges of the types of com- 
ponent that anyone involved in electronics is likely to need, not only resistors, capacitors, 
potentiometers, logic i.c.s, |.c.d.s and so on, but also items such as meters and tools, 
hardware and surplus stocks, and there is a selection of books as well. 

Good wishes to Greenweld from us all at EPE. 

For more information, contact Greenweld Ltd., Dept EPE, PO Box 144, Hoddesdon, 
Herts, EN11 OZG. Tel: 01277 811042. Fax: 01277 812419. Web: www.greenweld.co.uk. 





MILLENNIUM TIME CAPSULE 


THE Millennium Time Capsule is a major 
national project in celebration of the new 
millennium. Businesses, schools, clubs 
and the general public are invited to take 
part in this. prestigious event and to send a 
personal message to future generations. 
The Millennium time capsule will be 
buried for 200 years. Inside, contributors 
will have their own box containing what- 
ever they wish to include. Photographs, 
videos, books, tapes, letters — the list is as 
long as your imagination. 

The time capsule will be the largest 
ever constructed, providing a snapshot of 
the UK at the end of the millennium. But 
it will also be a very personal record. 
Every contributor will be sent certifica- 
tion, identifying their box within the cap- 
sule. In this way individual boxes can be 
passed down from generation to genera- 
tion and inherited by our descendants in 
the year 2200. 

The massive site will house thousands of 
time capsules from people from all over 
Britain and abroad. Time capsules can be 
sent to the project throughout the year 
2000. The site will be sealed in 2001 and 
shall remain buried for 200 years. A trust 
is being established to ensure the site is 
excavated in 2200. Anyone can take part 
by filling a time capsule pack and sending 
it back to the project. Each pack contains a 
time capsule measuring 340mm x 250mm 
x 80mm, along with specialised folders 
and envelopes which help to preserve the 
items within it. 


Records of the project, including the 


participants and location of the site shall 
be kept with The International Time 
Capsule Society in Atlanta, key regional 
record repositories in Britain and within 
the records of the project itself. 

The location of the site will be 
announced later this year. 

Everyone who takes part receives a cer- 
tificate giving them legal title to their time 
capsule and its contents, allowing them to 
leave their legacy to future generations. 

Packs can be ordered by sending a cheque 
for £41 made payable to: The Millennium 
Time Capsule Project and sent with the par- 
ticipants name and address to: The 
Millennium Time Capsule Project, PO Box 
736, Newcastle upon Tyne NE99 1LQ. Tel: 
0191 261 6784. Fax: 0191 232 1274. E-mail: 
editorial @ millennium-timecapsule.com. 


340 


Alternatively, packs can be ordered 
through the website at: www.millennium- 
timecapsule.com. 

Why not tell us, for possible inclusion in 
Readout, what you are sending or would 
like to have sent if the capsules had been 
large enough? Replies may be serious or 
humorous (but at least loosely connected 
with electronics)! 


~ WIND POWER 


A BOOK called Windpower Workshop: 
Building your own wind turbine, has been 
written by Hugh Piggott, the technical con- 
sultant to the BBC 1 docusoap Castaway 
2000, in which the castaways rely on 
renewable energy for their power needs. 

Hugh has lived for 25 years on a similar 
island and runs his own wind turbine com- 
pany. His book is based-on his knowledge 
of wind power harnessing and is aimed at 
helping budding survivalists, hobby engi- 
neers, self-sufficiency hopefuls and stu- 
dents of renewable energy to learn more 
about wind power. 

The book is priced £10 + £1.75 p&p, 
and available by mail order from the 
Centre for Alternative Technology, 
Machynlleth, Powys SY20 9AZ. Tel: 
01654 702400. Fax: 01654 702782. 
E-mail: |media@catinfo.demon.co.uk. 
Web: www.cat.org.uk. 






















RADIO BYGONES WEB SITE 


HAVE you browsed the web site of our sister publication Radio Bygones? This bi-monthly 
magazine is aimed at anyone with an interest in vintage radios and is only available via sub- 
scription. The RB web site can be accessed via www.radiobygones.co.uk. Through it you 
can take out a subscription to RB, use the “small ads” section and use the Message Board. 
You can also contact AB via E-mail at radiobygones @wimborne.co.uk. More information 
is given in the AB advert elsewhere in this issue. 

The AB Bulletin Board is for the benefit of not only RB readers, but visitors to the web- 
site as well. Via the Board, you can post questions, chat about magazine-related topics 
and to discuss views, nostalgia, information and tips. Editorially, RB does not offer a per- 
sonal follow-up to readers’ queries posted on the Board. However, you are always wel- 
come to contact RB via EPE HQ if you would like Editorial replies, or if you would like 
your offerings to be considered for publication in AB itself. 

We must deny, though, the humorous(?) suggestion of Webmaster Alan Winstanley, 
that you need a Long Wave computer to use the site! 

Alan, of course, will be familiar to you as Circuit Surgeon, Net Work Surfer, Ingenuity 
Unlimiter, and indeed Webmaster of the EPE site. Should you be looking for a superbly 
designed website of your own, Alan’s company Amaryllis Design is a Web Design Bureau 
well-capable of producing an excellent result for you. Contact can be made via 
arw @amaryllis.co.uk, whilst the site itself is at www.amaryllis.co.uk. 


Three Counties Radio 
& Computer Rally 


SUNDAY 21 May 2000. By popular 
demand following the 1999 rally, the 
Three Counties annual radio and. computer 
rally is to be staged a week before. the 
Spring Bank holiday. It will be held at the 
Perdiswell Leisure Centre, Bilford Road, 
Worcester. 

For those not familiar with the venue, 
the following facilities are available: full 
restaurant services from 7 a.m., licensed 
bar from 11 a.m., all traders in two adja- 
cent halls, easy access to the halls which 
are at ground level, free parking for 900 
cars and coaches. 

The organisers point out that, being close 
to the City Centre, wives and children can 
spend a pleasant day in Historic Worcester, 
sight seeing, shopping or a boat trip on the 
river Severn (we’d like to ask why wives and 
children should be shuttled off — we are sure 
they are just as interested in what the rally 
has to offer as the rest of us are!). 

For more details contact William E. 
Cotton G4PQZ, tel/fax: 01905 773181 (for 
fax please ring first). 


Farnell’s Catalogue 


NO longer need you complain that “the 
Farnell catalogue is great but it’s just too 
big”! This renowned supplier is separating 
its catalogue into six books, split by 
product. It will be available from April. 

Farnell say that this allows emphasis to 
be placed on their core product strengths, 
market the full range, provide the “ulti- 
mate one stop shop” and to focus on new 
products three times a year instead of 
twice, as at present. 

From the summer edition onwards, 
colour pages will also be made available 
for suppliers to advertise their products in 
these books. 

Farnell’s catalogue always has been a 
“must”? to have in your electronics work- 
shop. This change of binding will surely be 
welcomed. Don’t forget, also, that Farnell 
have product data on CD-ROM as well. 

For more information contact Farnell, 
Canal Road, Leeds LS12 2TU. Tel: 0113 
263 6311. Fax: 0113 263 3411. Web: 
www.farnell.com. 





Everyday Practical Electronics, May 2000 


‘The FED PIC C Compiler - Rapid, Efficient, High level development 


FED PIC C Compiler — Version 3.0 now available 


e@ Supports all 14-bit core PIC’s — 12C67x, 16C55x, 


16C6x, 16C7x, 16C8x, 16C87x, etc. 
Will produce code for MPLAB 


LEARN to Program PIC’s in C with FED! — 
With the FED introductory manual: 
“Learn to program PIC’s with FED PIC C” 


Suitable for complete beginners to PIC’s or to the 
C programming language 
e Leads through example 
@ Introduces simple C programs, then covers 
variables and casting, pointers, structures 
and unions, functions, etc. 
All examples will run fully within the simulator, 
or on the FED 16F84 and 16F877 
development boards 
Covers use of interrupts and programming for 
real time applications 
Hints and tips on good programming practice 
with the PIC 
Full examples of debugging using FED PIC C 
are included 
Included FREE on our PIC C Compiler CD 
ROM, or available in paper copy 
Available only to existing or new customers 
for our C Compiler. 


Prices (reductions for PICDESIM/WIZPIC users) 
C Compiler with all manuals on CD ROM £60. CD ROM with printed manuals £75. 
Upgrade — PICDESIM/WIZPIC users £45.00 CD ROM. 
“Learn to program PIC’s with FED PIC C”— £7.50. 


Designed to ANSI C Standards 


Complete development environment includes 
Editor, assembler, simulator, waveform analyser 
and terminal emulator (see screenshot below) 


Libraries include serial interfaces, 12C, LCD, 
keypads, delays, string handling, hardware etc. 


Simulator runs up to 10 times faster than 
MPLAB, allows inputs to be defined, multiple 
breakpoint types, single stepping, step over etc. 


Prices fully inclusive 


EE, 
STRELEN 


PIC Serial Programmer 
(Left) 


Handles serially programmed 
PIC devices in a 40-pin multi- 
width ZIF socket. 16C55X, 
16C6X, 16C7X, 16C8x, 16F8X, 
120508, 12C509, 16C72XPIC 
14000, 16F87X, etc. 
Also In-Circuit programming. 
Operates on PC serial port 
Price: £45/kit 

£50/built & tested 


PIC Introductory — Programs 8 & 18 pin devices : 16C505, 
16C55X, 16C61, 16C62X, 16C71, 16C71X, 16C8X, 16F8X, 
12C508/9, 12C671/2 etc. £25/kit. 


AVR — AVR - 1200,2313,4144,8515, 8535, 4434 etc. in ZIF. 4-5V 
battery powered. Price : £40 for the kit or £45 built & tested. 


All our Programmers operate on PC serial interface. No hard to 
handle parallel cable swapping ! Programmers supplied with 
instructions, + Windows 3.1/95/98/NT software. 

Upgrade programmers from our web site ! 


Forest Electronic Developments 
60 Walkford Road, Christchurch, Dorset, BH23 5QG. 


E-mail — info @fored.co.uk, or sales @ fored.co.uk 
Web Site — http://www.fored.co.uk 
01425-274068 (Voice/Fax) 

Prices are fully inclusive. Add £3.00 for P&P and handling to each order. 
Cheques/POs payable to Forest Electronic Developments, or phone with 
credit card details. 


\WVATVATA Kel asle mere m 01.4 


> 


alite 


Everyday Practical Electronics, May 2000 


PIC Visual Development. 


e Rapid Application Development 
for the PIC microcontroller 

e Drag and drop your software 
component selections on to 
your design 


Included components support timers, serial inter- 
faces, 12C, LCD, 7-Seg displays, keypads, switches, 
port controls, and many more. 

Connect software components to PIC pins by point & 
click using the mouse 

Set parameters for each component from drop down 
list boxes, check boxes, or text entry 

Links your code automatically into library events (e.g. 
Button Pressed, Byte Received etc) 

Up to 10 times faster than MPLAB 

Supports all 14-bit core PIC’s -12C67x, 16C55x, 
16C6x, 16C7x, 16C8x, 16C87x etc. 


Cost — CD-ROM with Data sheets and application notes — 
£35.00, Floppy version £30.00. 


Fully supported by WIZPIC, 
PICDESIM, the serial programmer 
and our C Compiler. 


16F877-04 
16F877-20 


EUROCARD 


£5.50 
£6.00 





341 


Our regular round-up of readers’ own circuits. We pay 
between £10 and £50 for all material published, depending 
on length and technical merit. We're looking for novel 
*6/ applications and circuit tips, not simply mechanical or 

# electrical ideas. Ideas must be the reader's own work and 


-§>e42) not have been submitted for publication elsewhere. 





The circuits shown have NOT been proven by us. Ingenuity 
Unlimited is open to ALL abilities, but items for 
consideration in this column should preferably be typed or 
word-processed, with a brief circuit description (between 
100 and 500 words maximum) and full circuit diagram 
showing all relevant component values. Please draw all 
circuit schematics as clearly as possible. 

Send your circuit ideas to: Alan Winstanley, Ingenuity 
Unlimited, Wimborne Publishing Ltd., Allen House, East 
Borough, Wimborne, Dorset BS21 1PF. 

They could earn you some real cash and a prize! 
















WIN A PICO PC BASED 


OSCILLOSCOPE 
@ 50MSPS Dual Channel Storage Oscilloscope 
@ 25MHz Spectrum Analyser 
® Multimeter @ Frequency Meter 
@ Signal Generator 
If you have a novel circuit idea which would be 
of use to other readers then a Pico Technology 
PC based oscilloscope could be yours. 
Every six months, Pico Technology will be 
awarding an ADC200-50 digital storage 
oscilloscope for the best IU submission. In 
addition, two single channel ADC-40s will be 
presented to the runners-up. 





Sensitive Hall Effect Switch — )'ce! tiae Meld 


Us the UGN3503U linear Hall 
Effect sensor with a dual op.amp 
allows the construction of a simple 
but extremely sensitive Hall Effect 
switch that could prove useful in 
many applications. A circuit diagram 
for just such a switch is shown in Fig. 
1. The Hall Effect device is ICI, 
which has just three terminals, for 
positive and negative supplies and 
the output. A regulated 5V supply is 
suggested for most applications. 

With a 5V supply and in the 
absence of a magnetic field, the 
output from IC1 is about 2:5V. On 
the approach of a magnet, the out- 
put will rise or fall, depending on 
the magnetic field’s polarity. With a 
5V supply, the AD8532 is an excel- 
lent choice for the dual op.amp IC2 
as it is designed for this supply volt- 
age, has rail-to-rail inputs and outputs and, 
being a CMOS component, has very high 
input impedances. In addition it can supply 
up to 250mA of output current. 

The first op.amp, IC2a, is used as a non- 
inverting amplifier with a voltage gain of about 
20 to amplify the output of IC1 to more useful 
levels. Because a.c. coupling via capacitor Cl 
is used for the input, resistor R3 sets the work- 
ing point to half the supply. This is necessary to 





Fig.1. Sensitive Hall Effect Switch circuit diagram. 


avoid drift in the Hall Effect sensor IC1. The 
high value of R3 allows the circuit to operate at 
very low frequencies, down to less than 1Hz. 
The second op.amp IC2b is connected as a 
comparator with hysteresis set by resistors R7 
and R8 to about 500mV to ensure a rapid, 
bounce-free switching action. 

With the values shown this circuit can 
detect the approach of a small bar magnet of 
the type commonly used for operating reed 


switches, at a range of about 25mm. 
Sensitivity could be adjusted by 
altering the gain of the amplifier 
stage or the hysteresis. Note that the 
strength of a magnetic field falls in 
proportion to the square of the dis- 
tance from its source. 

The polarity of the output change 
from IC1 depends on the polarity of 
the magnetic field. When the face 
bearing the device markings is 
approached by a North pole the out- 
put voltage falls, whilst the approach 
of a South pole will make it rise. The 
sensor is said to be capable of oper- 
ating up to 23kHz, so for most prac- 
tical applications the upper speed 
limit will not be an issue! 

It is also possible to place a mag- 
net behind the sensor so that the flux 
passing through it will change on the 
approach of a ferrous, but not necessarily 
magnetic, object. Applications of this type 
might include sensing passing steel gear- 
wheel teeth, or the movement of a steel lever. 

Since the current consumption of IC1 is 
about 9mA this circuit is unsuitable for 
micropower applications but it should find 
plenty of uses where power consumption is 
not critical. , 

Andy Flind, Taunton, Somerset. 








Infra-Red Remote 
Tester - Sounds Goodl 


N Infra-Red Remote Control Tester, 

which gives both an audio and visual 
indication that a remote control is function- 
ing, is shown in Fig.2. Its operation is as fol- 
lows: D1 is a reverse biased photodiode, 
which forms an infra-red detector. Its output 
is buffered by ICla and then enters a pulse 
stretcher comprising capacitor C2, resistor 
R2 and IC1b. 

The pulse stretcher enables even the short- 
est of pulse trains to trigger the following 
oscillator. Diode D3 is a low current red l.e.d. 
which sinks into the output of IC1b and pro- 
vides the visual indication. 

An oscillator is formed of IC1c and IC1d, 
which drives a piezo disc element X1. This is 
connected across [Cle (rather than more con- 
ventionally to OV) to provide a louder output. 
Oscillation is stopped by the normally high 
output from IC1b via diode D2. When an IR 


342 


pulse train is detected, IC1b goes low and the 


input to ICld sees only a high impedance 
from the diode and oscillation starts. The 
input of gate IC1f is grounded for stability. 


NOT USED 





The circuit runs from a 9V PP3, and the 
standby current of a little under 2uA means 
there is no real need for an on/off switch. 

Matthew Waite, Leeds. 


ICie 


4049BE 


+t >- 


X1 
PIEZO DISC 


Fig.2. Circuit diagram for an Infra-Red Remote Tester. 


Everyday Practical Electronics, May 2000 


ae a 





Auditory Ilusion - Revved-up *phomes 


circuit pictured in Fig. 3 is a classic 
auditory illusion which has puzzled psy- 
chologists and neuroscientists for decades. A 
two-tone “siren” plays into stereo head- 
phones. The tones are separated by one 
octave, and alternate at roughly 4Hz. 
However, the siren is played out of phase 
into each headphone. If all were well, each 
ear would perceive a two-tone siren: in actual 





fact, the mind perceives a two-tone “ping- 
pong” effect, which jumps from ear to ear. 

What has the mind done with the missing 
tones? Further, if one reverses the~ head- 
phones, the tones jump back to where they 
were before! | 

Two oscillators, formed from ICla and 
IClc, are fed to quad bilateral switch IC2, 
which, with IC1d, is wired as an electronic 


d.p.d.t. relay. Oscillator IC1b switches the 
“relay” at roughly 4Hz, so causing the two 
oscillators to play the two-tone siren out of 
phase. 

Preset VR1 is adjusted so that oscillator 
1Cla is one octave higher than oscillator 
1Clc. The output can be fed to high-imped- 
ance headphones, or an amplifier as the effect 
is the same when loudspeakers are used. 


Rev. Thomas Scarborough, 
Fresnaye, Cape Town, South Africa. 


OUTPUT TO 
HIGH-IMPEDANCE 
HEADPHONES OR 
AMPLIFIER 


Fig.3. Experimental Auditory Illusion circuit diagram. 





Experimenter’s Power Supply - Varialblle States 


CIRCUIT for a handy Variable Power Supply 
which will meet the needs of many elec- 
tronics hobbyists is shown in Fig.4. It provides 
OV to 25V at up to 250mA. The error amplifier 
within a 723-type voltage regulator chip (IC3) 
cannot function with rail-to-rail input and there- 
fore a precision, shunt reference, TL431C (IC2) 
biases pin 5 of the 723 regulator to +2-50V. 
The regulator’s inverting input (pin 4) sees 
a set point potential from potentiometer VR1 
which can swing either above or below this 





level. Hence the output voltage, attenuated by 
the 10k and 100k resistors R5 and R6 is 
forced to extend from 0V (CCW) to +25V 
(CW) to track the +2-50V reference. 

An external TIP29C power transistor TR1 
extends the current limit to 250mA and is off- 
set by a second programmable Zener diode 
IC4 at pin 10 of the 723 regulator. This volt- 
age difference plus two Vpr drops gives suf- 
ficient headroom at pin 13 for the amplifier 
stage when Vout = 0. 


The 723’s internal Zener diode at pin 9 was 
not used, as the 6:2V requires a larger source 
from the transformer at maximum output, 25V. 
Even with this precaution it is possible to exceed 
the 723’s absolute maximum voltage at pins 11 
and 12: therefore, a three terminal regulator, 
78LOSACZ (IC1) was added to maintain 30V. 

As constructed, a single mains transformer 
with two, isolated 12VA windings allowed 
dual, floating d.c. sources of OV to 25V mag- 
nitude, a convenience if both positive and 
negative voltages or their sum is desired. 

John A. Haas, Fort Collins, CO. USA. 


TL431C 


REF 
a 
k 


78LO5ACZ 


Fig.4. Experimenter’s Power Supply circuit using the 723 variable voltage regulator. 


Everyday Practical Electronics, May 2000 


343 





Starter Project 











METER 





LOW-COST 
CAPACITANCE 


ROBERT PENFOLD 


A simple starter project that will let you 


get the measure of most Capacitors. 


Five switched ranges: 


TYPICAL multimeter can measure 
voltage, current and resistance over 
wide range of values, and usually 


has a few “tricks up its sleeve’’ such as con- 
tinuity tester and transistor checker facili- 


ties. Some multimeters have capacitance — 


measuring ranges, but this feature remains 
something of a rarity. This is a pity, because 
anyone undertaking electronic faultfinding 
will soon need to check suspect capacitors 
and a ready-made capacitance meter is an 
expensive item of equipment. 

The unit featured here offers a low-cost 
solution to the problem of testing capaci- 
tors. It is an analogue capacitance meter 
that has five switched ranges with full-scale 
values of InF; 10nF; 100nF; IF; and 
10uF. It cannot measure very high or low 
value components, but it is suitable for test- 
ing the vast majority of capacitors used in 
everyday electronics. 


SYSTEM OPERATION 

The block diagram for the Low-Cost 
Capacitance Meter is shown in Fig.1. Like 
most simple capacitance meter designs, 
this unit is based on a 


344 


7NF to 1QuF 


monostable circuit. When triggered by an 
input pulse a monostable produces an output 
pulse having a duration that is controlled by 
a CR network. In this case the monostable is 
triggered manually using a pushbutton 
switch each time a reading is required. 

The resistor in the timing network is one 
of five resistors selected via a switch, and 
these resistors provide the unit with its five 
ranges. The capacitor in the CR network is 
the capacitor under test. 

The duration of the 
output pulse is propor- 
tional to the values of 
both components in the 
CR network. If a InF 
Capacitor produces. an 
output pulse of one 
millisecond in dura- 
tion, components hav- 
ing values of 2:2nF and 
4-7nF would respec- 
tively produce pulse 
lengths of 2:2ms and 
4-7ms. 


MONOSTABLE 


CAPACITOR 


Fig. 1. 








Schematic 
Capacitance Meter. 











Each output pulse must be converted 
into a voltage that is proportional to the 
pulse duration. A moving coil panel meter 
can then read this voltage, and with every- 
thing set up correctly it will provide accu- 
rate capacitance readings. 

If we extend the example given previ- 
ously, with a potential of one volt per mil- 
lisecond being produced, a meter having a 
full-scale value of 10V would actually read 
0 to 10nF. This time-to-voltage conversion 
is actually quite simple to achieve, and is 
provided by a constant current generator 
and a charge storage capacitor. 

When charged via a resistor the potential 
across the capacitor does not rise in a linear 
fashion. As the charge potential increases, 


CURRENT 
GENERATOR 


BUFFER 
AMPLIFIER 


block diagram for the Low-Cost 


the voltage across the resistor falls, giving a 
steadily reducing charge current. The volt- 
age therefore increases at an ever-decreas- 
ing rate (inverse exponentially). 

A current regulator avoids this problem 
by ensuring that the charge current does not 
vary with time, giving a linear rise in the 
charge voltage. The circuit therefore pro- 
vides the required conversion from capaci- 
tance to voltage, but it is important that 
loading on the storage capacitor is kept to a 
minimum. 

Tapping off a significant current could 
adversely affect the linearity of the circuit 
and would also result in readings rapidly 
decaying to zero. The meter is, therefore, 
driven via a buffer amplifier that has a very 
high input impedance. Once a reading has 
been taken and noted, operating the Reset 
switch discharges the storage capacitor and 
returns the reading to zero so that a new 
reading can be taken. 


Everyday Practical Electronics, May 2000 


CIRCUIT OPERATION 


The complete circuit diagram for the 
Low-Cost Capacitance Meter project 
appears in Fig.2. The monostable is based 
on a low-power 555 timer (IC1) used in the 
standard monostable configuration. 

Apart from the fact it gives much longer 
battery life, a low-power 555 is a better 
choice for this type of circuit due its lower 
self-capacitance. This produces much bet- 
ter accuracy on the InF range, and a stan- 
dard 555 is therefore not recommended for 
use in this circuit. 

Switch S1 sets the Range and R1 to R5 
are the five timing resistors. Resistors R1 
to R5 respectively provide the 1nF, 10nF, 
100nF, 1uwF, and 10uF ranges. 

One slight flaw in the 555 for this applica- 
tion is that it will only act.as a pulse stretcher 
and not as a pulse shortener. In other words, 
the output pulse will not end at the appropri- 
ate time if the input pulse is still present. 


If it were used to directly trigger IC1, 
the input pulse from pushbutton switch S2 
would invariably be far too long. A simple 
_CR circuit is therefore used to ensure that 
IC1 will always receive a very short trigger 
pulse, regardless of how long Measure 
switch S2 is pressed. 

Resistor R6 holds the trigger input of 
IC1 (pin 2) high under standby conditions, 
but it is briefly pulsed low when S2 is 
operated and capacitor C2 charges via R6. 
When S2 is released, resistor R7 dis- 
charges C2 so that the unit is ready to trig- 
ger again the next time S2 is operated. 
Resistor R7 has been given a very high 
value so that the discharge time of C2 is 
long enough to prevent spurious triggering 
if S2 does not operate “cleanly”. Most 
mechanical switches suffer from contact 
bounce, and without this debouncing it is 
likely that retriggering would occur practi- 
cally every time S2 was released. 

Under standby conditions the output at 
pin 3 of IC1 is low, and both transistor TR1 
and TR2 are switched off. Consequently, 
only insignificant leakage currents flow 
into the charge storage capacitor C3. An 
output pulse from IC1 switches on TRI, 
which in turn activates TR2. 

Transistor TR2 is connected as a con- 
ventional constant current generator, and 
the value of resistor R10 controls the 


output current. This is around 115uA with 
the specified value. Transistors TR1 and 
TR2 switch off again at the end of the pulse 
from IC1, and the charge voltage on C3 is 
then read by the voltmeter circuit based on 
panel meter ME1. | . 


METER CIRCUIT 

Operational amplifier (op.amp) IC2 is 
used as the buffer amplifier, and the PMOS 
input stage of this device ensures that there 
is no significant loading on the “charge” 
capacitor C3. The input resistance of IC2 is 
actually over one million megohms. 

However, the voltage on C3 will gradu- 
ally leak away through various paths, 
including C3’s own leakage resistance. The 
reading should remain accurate for at least 
a minute or two, and in most cases it will 
not change noticeably for several minutes. 
There will certainly be plenty of time for a 
reading to be taken before any significant 
drift occurs. 


ST +V 


TS555CN 
OUT 


DISCH. 


THRES. 
TRIG. 
GND 





Resistors 
R1 10M 1% 

metal film 

1M 1% 
metal film 

100k 1% 
metal film 

10k 1% metal film 

~ 1k 1% metal film 


4k7 (2 off) | 
ap off) See 


Potentiometer 
VR1 47k min enclosed or 
skeleton preset, 
horizontal 


Capacitors 
C1 100n ceramic 
C2 150p ceramic plate 
C3 220n polyester 


Everyday Practical Electronics, May 2000 


sk — SHOP 


5k6 


10k TALK 


10Q 
39k — 


All 0-25W 5% carbon film, except where 
specified 


Briefly operating Reset switch S3 dis- 
charges C3 and zeros the meter so that 
another reading can be taken. Resistor R12 
limits the discharge current to a level that 
ensures the contacts of S3 have a long 


- operating life. The rate of discharge is still 


so high that it appears to be instant. | 
Preset VR1 enables the sensitivity of the 


~ voltmeter ME1 to be adjusted, and in prac- 


tice this is adjusted so that the required 


- full-scale values are obtained. In order to 


ensure good accuracy on all five ranges it 
is essential for range resistors R1 to R5 to 
be close tolerance (one or two percent) 
components. 

There is no overload protection circuit for 
the meter, but this protection is effectively 
built into the design. The circuit driving the 
meter is only capable of producing minor 
overloads, and is incapable of inflicting any 
damage. The current consumption of the cir- 
cuit is only about 3mA, and a PP3 size bat-: 
tery is adequate to power the unit. ; 


[CAPACITANCE | 


Vo) eo) ge) eam Orel t e 1 P. 
Guidance Only 


excluding batt., case, meter 


Semiconductors 
D1, D2 1N4148 signal diode (2 off) 
TR1 BC549 npn transistor 
TR2 <5 BC559 pnp transistor 
IC1 TS555CN low power timer 
IC2 CA3140E PMOS op.amp 


Miscellaneous | 
7 : 100uA moving coil panel 
meter : 

SK1 . 2mm socket, red 

SK2 = ~— 2mm socket, black 

S1 12-way single-pole rotary 
switch (set for 5-way 
operation) (see text) 

pushbutton switch, 
push-to-make (2 off) 

S4 S.p.s.t. min toggle switch 

B1 battery (PP3 size), with 

connector leads 


$2,S3 


Metal instrument case (or type to 
choice), size 150mm x 100mm x 75mm; 
stripboard 0-1-inch matrix, size 34 holes. 
by 21 copper strips; 8-pin d.i.l. socket (2 
off); control knob; calibration capacitor 
(see text); test leads (see text); connect- 
ing wire; solder pins; solder, etc. 





345 





SI: 
vii 
ea 


$2 


n 
ca 
7) 
S 


FUN VOMNM|}®ITIr-~ CAT ZSZovVdSV,MVHAC 


5 
@ 





25 
0 Oo 
Oo ®@ 
coe) 
owe) 
e 


Fig.3. Stripboard component layout, interwiring and details of breaks required in 


underside copper tracks. 


CONSTRUCTION 


The Low-Cost Capacitance Meter is 
built up on a small piece of stripboard hav- 
ing 34 holes by 21 copper strips. The top- 
side component layout, underside details 
and interwiring to off-board components is 
shown in Fig.3. 

As this board is not of a standard size, a 
piece will have to be cut from a large board 
using a small hacksaw. Cut along rows of 
holes rather than between them, and 
smooth any rough edges produced using a 
file. Then drill the two 3mm diameter 
mounting holes in the board and make the 
17 breaks in the copper strips. There is a 
special tool for making the breaks in the 
copper strips, but a handheld twist drill bit 
of around 5mm dia. does the job very well. 

The circuit board is now ready for the 
components, linkwires and solder pins to 
be added. The CA3140E used for IC2 has a 
PMOS input stage that is vulnerable to 


damage from static charges, and the appro- — 


priate handling precautions must therefore 
be taken when dealing with this i.c. 

It should be fitted to the board via a hold- 
er, but it should not be plugged into place 
until the unit is otherwise finished, and the 
board and wiring double-checked for any 
errors. It should be left in its anti-static 


346 


packing until then. Try to handle the device 
as little as possible when fitting it in its 1.c. 
socket, and keep well away from any likely 
sources of static electricity such as televi- 
sions sets and computer monitors. 

Although the TS555CN timer used for 
IC1 is not static-sensitive it is still a good 
idea to fit it in an i.c. socket. Be careful to 
fit IC1 the right way around because it has 
the opposite orientation to normal, with pin 
one at the bottom. This chip could easily be 
destroyed if it is fitted the wrong way 
around. 

In all other respects construction of the 
board is fairly straightforward. The 
linkwires can be made from the trimmings 
from resistor leadouts or 22 s.w.g. tinned 
copper wire. In order to fit into this layout 
properly capacitor C3 should be a printed 
circuit mounting component having 7-5mm 
(0-3-inch) lead spacing. Be careful to fit the 
diodes and transistors with the correct ori- 
entation. Note that transistors TR1 and TR2 
have opposite orientations. 


RANGE RESISTORS 


The five range resistors (R1 to R5) are 
mounted directly on the Range rotary 
switch S1, which helps to minimise stray 
capacitance and pick up of electrical noise. 


4 Lowore ] 


CAPACITANCE 





Mount the Range resistors directly on 
the switch tags before switch is fitted in 
the case. 


This aids good accuracy, especially on the 
InF range. It is best to mount the resistors 
on S1 before this switch is fitted in the case. 

Fitting the resistors is made much easier 
if the switch is stuck to the workbench 
using Plasticine or Bostik Blu-Tack. 
Provided the tags and the ends of the lead- 
outs are tinned with solder it should then be 
quite easy to build this sub-assembly. 

Try to complete the soldered joints rea- 
sonably swiftly so that the resistors do not 
overheat. It takes quite a lot of heat to 
destroy resistors, but relatively small 
amounts can impair their accuracy. 


CASING UP 


A medium size metal instrument case is 
probably the best choice for a project of 
this type, but a plastic box is also suitable. 
The exact layout is not critical, but mount 
SK1 and SK2 close together. 


Everyday Practical Electronics, May 2000 


Many capacitors will then connect 
directly into the sockets without too much 
difficulty, but a set of test leads will also be 
needed to accommodate some capacitors. 
All that is required are two insulated leads 
about 100mm long. Each lead is fitted with 
a 2mm plug at one end and a small croco- 
dile clip at the other. 

Fitting the meter on the front panel is 
potentially awkward because a large round 
cutout is required. For most meters a cutout 
of 38mm dia. is required, but it is advisable 
to check this point by actually measuring 
the diameter of the meter’s rear section. 
DIY superstores sell adjustable hole cutters 
that will do the job quickly and easily, or 
the cutout can be made using a coping saw, 
Abrafile, etc. 

Four 3mm dia. holes are required for the 
meter’s threaded mounting rods. Marking 
the positions of these is quite easy as they 
are usually at the corners of a square hav- 
ing 32mm sides, and the same centre as the 
main cutout. Once again though, it would 
be prudent to check this by making mea- 
surements on the meter prior to drilling the 
holes. 

The circuit board is mounted on the base 
panel of the case towards the left-hand side 
of the unit, leaving sufficient space for the 
battery to the right of the board. The com- 
ponent panel is mounted using either 6BA 
or metric M2-5 bolts, and spacers or nuts 
are used to ensure that the underside of the 


board is held well clear of the case bottom. 
To complete the unit the hard wiring is 
added. This offers nothing out of the ordi- 
nary, but be careful to connect the battery 
clip and meter ME1 with the correct 
polarity. 


CALIBRATION 


Preset potentiometer (wired as a “vari- 
able resistor”) VR1 must be given the cor- 
rect setting in order to obtain good accura- 
cy from the unit, and a close tolerance 
capacitor is needed for calibration. For 
optimum accuracy this capacitor should 
have a value equal to the full-scale value of 
the range used during calibration. 

In theory it does not matter which range 
is used when calibrating the unit, but in 
practice either the 1nF or 10nF range has to 
be used. Suitable capacitors for the other 
ranges are either unavailable or extremely 
expensive. 

The 10nF range is the better choice as 
the small self-capacitance of IC1 is less 
significant on this range, although this fac- 
tor seems to have very little affect on accu- 
racy. Probably the best option is to calibrate 
the unit on the 10nF range using a 10nF 
polystyrene capacitor having a tolerance of 
one percent. 

It is possible that a large reading will be 
produced on the meter when the unit is first 
switched on, but pressing Reset switch S3 
should reset the meter to zero. If it is not 


possible to zero the meter properly, switch 
off at once and recheck the entire wiring, 
etc. 

If all is well, set preset VR1 at maximum 
resistance (adjusted full clockwise). Then 
with the unit set to the correct range and the 
calibration capacitor connected to SK1 and 
SK2, operate pushswitch S2. This should 
produce a strong deflection of the meter, 
and VR1 is then adjusted for precisely full- 
scale reading on meter MEI. The unit 
should then provide accurate readings on 
all five ranges. 


IN USE 


The Meter is suitable for use with 
polarised capacitors such as electrolytic 
and tantalum types. However, it is essential 
that they are connected to SK1 and SK2 
with the correct polarity. The positive (+) 
lead connects to SK1 and the negative lead 
connects to SK2. 

Especially when using the InF and 10nF 
ranges, avoid touching the lead that con- 
nects to SK1 when a reading is being taken. 
Otherwise electrical noise might be intro- 
duced into the system producing inaccurate 
results, 

Avoid connecting a charged capacitor to 
this or any other capacitance meter, since 
doing so could result in damage to the 
semiconductors in the meter circuit. If in 
doubt always discharge a capacitor before 
testing it. [+] 





Layout of components inside the metal case of the completed Low-Cost Capacitance Meter. The circuit board is mounted to one 
side to leave space for the battery. 


Everyday Practical Electronics, May 2000 


347 





SURFING THE INTERNET =a 


NET WORK 
ALAN WINSTANLEY 


Google Box 
— readers will have noticed that I recently placed a 
Google search engine in the 100 per cent revalidated Net 
Work A-Z page on our web site, containing many of the exist- 
ing links I have highlighted in the past. Google is hugely fast and 
easy to use. Instead of trying to index every known web site, 
Google actually indexes on the basis of all the other links made 
to those same web sites. The search engine makes the reasonable 
assumption that the better a web site is, the greater the number 
of links pointing to that site. More importantly, Google keeps a 
cache of stored web pages, so that even if a web site is taken 
down there is still a possibility that you can retrieve the content 
from Google’s cache. Give it a try. 

In March 2000 Net Work I outlined the evolution of Alta Vista, 
Digital Equipment’s leading search engine and portal site which 
was acquired by computer manufacturer Compaq in early 1998. 
There is no doubt that Alta Vista is a first-rate search engine, 
offering further options to non-English users courtesy of its 
Babel Fish language translator. Alta Vista continues to roll out 
across Europe, starting out in Germany almost a year ago, fol- 
lowed by Sweden and more recently the UK in December 1999. 
The Californian-based company then launched into France and 
the Netherlands last month. 


Free for all 

In early March Alta Vista UK took the wind out of the sails of 
cable operator NTL (www.askntl.com) as well as British Telecom, 
by announcing its new free Internet access service for UK users. In 
fact it isn’t entirely free — there will be a one-off set-up charge of 
anything up to £50 being reported, and an annual cost of say £20. 
The new service, to be called AltaVista0800, will be rolled out at a 
rate of 90,000 users per month starting in June 2000. 

In the USA and Canada, a service called AltaVista Free 
Access has been available since August 1999 (see 
www.microay.com), offering completely free Internet access to 
its users. There are no set-up or subscription charges at all. 
Instead, AltaVista Free Access employs a “Micro Portal’? — a 
window on the user’s computer screen which contains rotating 
adverts and other customisable content. The technology behind 
this is provided by 1IstUp.com, a US developer specialising in 
advert-supported dial-up accounts. The advertising window must 
always remain open to enjoy free Internet access, which is a 
powerful incentive for many consumers already conditioned to 
banner ads., to remain loyal. 

In the UK, by using an 0800 access number, subscribers are 
relieved of the worry of the cost of the phone call, though obvi- 
ously they still have to pay line rental charges. Alta Vista UK’s 
new service will not allow a permanent 24x7 connection to the 
Internet, because it will time out after five minutes of inactivity. 
Furthermore, any attempt to “ping”? an open connection with a 
keep-alive utility such as WakeUp will be treated as an abuse 
presumably leading to withdrawal of the service. 


Under the Surf 


The new service announced by Alta Vista UK wrong-footed 
British Telecom into declaring its own revised plan for unmetered 
access. BT previously suggested its SurfTime package (see Net 
Work Feb ’00) could cost anything up to £35 a month for always-on 
access. I showed how this was five times more than a user in Dallas, 
Texas who pays just $12 (£7 a month) after loyalty discounts, with 
local Internet and voice calls thrown in for free. 

In light of Alta Vista UK’s new 0800 package, BT was forced into 
firming up its own position. They make much of the fact that their 
SurfTime option will be available to businesses as well as home 


348 





users, and they are attempting to cater for users’ differing habits, 
given that many users are obviously at work during the day and only 
access the Internet during evenings and weekends. The cheapest 
option that BT now proposes is for occasional users, paying 1 pence 
per minute daytimes, 0-6 pence evenings and 0-5 pence weekends, 
on top of line rental at £9.26 per month. 

As usual, BT’s press release is not entirely straightforward, 
partly because they hint at an all-inclusive cost for Internet 
access by bundling in rental figures plus an estimate of monthly 
ISP charges. For a service fee of £5.99 a month excluding rental, 
BT customers can choose the evening and weekend package 
which allows for unmetered access plus up to 80 minutes’ voice 
calls. BT’s always-on package is likely to cost £19.99 per month 
plus rental for home users and £29.74 exc. VAT (inc. rental) for 
business users. 

Realising that the rates will be scrutinised by an increasingly 
impatient audience, BT has gone to extraordinary lengths to 
emphasise how competitive they say their dial-up Internet pack- 
ages are in comparison with similar ones in the USA. 

The rates won’t be available to end users until June 2000, and 
there is a further complication: BT SurfTime will require users 
to access their preferred ISP by using an 0844 04 number. If your 
preferred ISP doesn’t offer one, then you can’t use the SurfTime 
package. More problems in store include the fact that no whole- 
sale pricing had been offered, therefore no other service provider 
(e.g. Freeserve) would be able to compete by re-selling BT 
SurfTime. 

As if BT’s convoluted phone tariffs aren’t enough, don’t forget 
the offerings over at BT Internet (www.btinternet.com), the telco’s 
Internet Service Provider arm. Unmetered 0800 evening and week- 
end access is now available at a new lower rate of £9.99 a month or 
£109.98 p.a., and as a sign of their eagerness to help novices getting 
to grips with the Internet, BT have actually increased the cost of 
support calls to 50 pence a minute up from local rate. 


Looking Ahead 


The UK Internet market remains as volatile as ever, and fur- 
ther sweeping changes are probable over the next 12 to 18 
months before the market finally settles down. For Freeserve, the 
18-month old pioneer of the free ISP model, interesting times 
are ahead. As with all free ISPs, Freeserve makes its revenue 
from that all-important slice of the cost of the BT 0845 phone 
call, plus advertising and the cost of providing technical support. 

Consumers tend not to have much loyalty towards their ISP 
and if they suddenly decide to jump ship from the free ISPs and 
move to a service such as AltaVista0800, preferring to pay an 
annual fee for free unlimited calls, this is bound to have a pro- 
found impact on Freeserve which charges nothing as an ISP but 
makes you pay for the calls instead. It is hard to know what will 
happen to those free ISPs that also bundle your domain name 
and technical support in with the deal. 

It is not as though any of these free ISPs can levy even a small 
monthly fee, as they don’t have any billing mechanism in place. 
Freeserve’s latest move involves offering free Internet access, 
provided customers make £10 of calls per month routed through 
Energis, its parent telco. However, BT is now spending the inter- 
vening months rolling out the interconnect components, and 
ISPs which adopt the 0844 SurfTime tariff are expected to be 
able to charge their subscription fees to their customer using the 
user’s BT phone bill. When there are new offers springing up all 
the time, it makes sense not to commit to a long-term agreement 
until all the players have made their moves. 

You can E-mail me at alan@epemag.demon.co.uk. My web 
site is at http://homepages.tcp.co.uk/~alanwin. 


Everyday Practical Electronics, May 2000 


CONTROL & ROBOTICS 


Hivelaom aksiauii cli 





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Stamps from £25 (single quantities), 
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Special Feature 








CLIVE “MAX” MAXFIELD AND ALVIN BROWN 


TECHNOLOGY (ag 
TIMELINES | 


PART 4 - COMPUTING 1900-1999 





Boldly going behind the beyond, behind which no-one 
has boldly gone behind, beyond, before! 


purpose of this series is to review 

; how we came to be where we are today 

(technology-wise), and where we look 

like ending up tomorrow. In Part 1 we cast 

our gaze into the depths of time to consider 

the state-of-the-art in electronics, communi- 

cations, and computing leading up to 

11:59pm on 31 December 1899, as the world 
was poised to enter the 20th Century. 

Parts 2 and 3 covered fundamental elec- 
tronics and communications in the 20th 
Century, respectively. Now, in Part 4 we 
consider some of the key discoveries in 
computing that occurred during the 20th 
Century. These developments have set the 
scene for what is to come as we plunge 
forth into the third millennium. But before 
we Start, let’s first consider logic diagrams 
and logic machines, which usually receive 
little mention... 


LOGIC AND LOGIC 
DIAGRAMS 


With the exception of Charles Babbage’s 
proposal for a mechanical computer called 
the Analytical Engine in 1832, very little 
thought was given to computing prior to 
1900. Instead, effort was focused on simple 
mechanical calculators, and also on varia- 
tions of another mechanism put forward in 
1882 by Babbage called a Difference 
Engine, which could be used to generate 
certain mathematical tables. 

However, this is not to say that nothing 
of interest (computing-wise) was taking 
place, because there were a number of 
developments that would prove to be 
extremely interesting to computer scientists 
in the 20th Century. 

First of all, the self-taught British math- 
ematician George Boole published two key 


papers in 1847 and 1854. These papers 


described how logical expressions could be 
represented in a mathematical form that is 
now known as Boolean Algebra. What 
Boole was trying to do was to create a 
mathematical technique that could be used 
to represent and rigorously test logical and 
philosophical arguments. 

We can only imagine what he would 
have thought had he realised that his new 


350 


mathematics would find application in 
designing digital computers 100 years in 
his future. But we digress... 


LOGIC WONDERLAND 


In 1881, a lecturer in logic and ethics at 
John Hopkins University called Allan 
Marquand invented a graphical technique 
of representing logical problems using 
squares and rectangles. Marquand’s efforts 
set a number of people to pondering, 
including the Reverend Charles Lutwidge 
Dodgson, who published his own diagram- 
matic technique in a book called The Game 
of Logic in 1886. (The Reverend is better 
known to most of us as Lewis Carroll, the 
author of Alice’s Adventures in 
Wonderland.) 

In the early 1890s, yet another approach 
was put forward by the English logician 
John Venn, who was extremely impressed 
by Boole’s work. Unlike earlier graphical 
techniques, Venn’s diagrams were based on 
the use of circles and ellipses, which could 
be employed to represent Boolean 
equations. 

The rectangles and 
squares of Marquand 
and Carroll eventually 
led to Maurice 
Karnaugh inventing a 
graphical technique 
for both representing 
and minimising 
Boolean expressions 
in the 1950s. These 
techniques were to 
become tremendously 
useful to designers of 
digital logic, and 
Karnaugh maps and 
Venn Diagrams are 





time. Perhaps the earliest example is a set 
of concentric, nested discs revolving 
around a central axis as proposed by the 
Spanish theologian Ramon Lull in 1274. 
Each disc contained a number of different 
words or symbols, which could be com- 
bined in different ways by rotating the 
disks. 

Lull’s disks were followed by a variety 
of other techniques over the centuries, most 
of which we would now consider to be 
“half-baked” on a good day. 

The world’s first real logic machine (that 
is, one that could actually be used to solve 
simple logic problems, as opposed to Lull’s 
which tended to create more problems than 
it solved) was invented in the late 1700s by 
the British scientist and statesman Charles 
Stanhope (third Earl of Stanhope). 

This device, the Stanhope Demonstrator, 
was a small box with a window in the top, 
along with two different coloured slides 
that the user pushed into slots in the sides. 
Although this doesn’t sound like much it 
was a Start, but Stanhope wouldn’t publish 





both still taught and Stanhope Square Demonstrator, late 18th century. Courtesy 


used to this day. 


LOGIC 
MACHINES 


In addition to speculating about logic, it 
should come as no surprise to learn that 
people have been experimenting with so- 
called “logic machines’ for quite some 


Science Museum/Science and Society Picture Library. 


any details and instructed his friends not to 
say anything about what he was doing. 

In fact, it wasn’t until around sixty years 
after his death that the Earl’s notes and one 
of his devices fell into the hands of the 
Reverend Robert Harley, who subsequently 


Everyday Practical Electronics, May 2000 





Stanhope’s calculating machine, 1777. Courtesy Science Museum/Science and Society Picture 
Library. 


published an article on the Stanhope 
Demonstrator in 1879. 

Stanhope also invented a circular 
demonstrator and a mechanical calculating 
machine. : 


LOGIC PIANOS 


Working on a somewhat different 
approach was the British logician and 
economist William Stanley Jevons, who, in 
1869, produced the earliest model of his 
famous Jevons’ Logic Machine. This device 
is notable because it was the first machine 
that could solve a logical problem faster 
than that problem could be solved without 
using the machine! 

Jevons was an aficionado of Boolean 
logic, and his solution was something of a 
cross between a logical abacus and a piano 
(in fact it was sometimes referred to as a 
“Logic Piano”). This device, which was 
about a metre (three feet) tall, consisted of 
keys, levers and pulleys, along with letters 
that could be either visible or hidden. When 
the operator pressed keys representing log- 
ical operations, the appropriate letters 
appeared to reveal the result. 

The next real advance in logic machines 
was made by Allan Marquand, whom we 
previously met in connection with his work 
on logic diagrams. In 1881, by means of the 
ingenious use of rods, levers, and springs, 
Marquand extended Jevons’ work to pro- 
duce the Marquand Logic Machine. Like 





Jevons’ device, Marquand’s machine could 
only handle four variables, but it was 
smaller and significantly more intuitive to 
use 


ROCKET-POWERED 
FRISBEES 


Things continued to develop apace. In 
1936, the American psychologist Benjamin 
Burack from Chicago constructed what 
was probably the world’s first electrical 
logic machine. Burack’s device used light 
bulbs to display the logical relationships 
between a collection of switches, but for 
some reason he didn’t publish anything 
about his work until 1949. 

In fact, the connection between Boolean 
algebra and circuits based on switches had 
been recognized as early as 1886 by an 
educator called Charles Pierce. However, 
nothing substantial happened in this area 
until 1938, at which time the American 
engineer Claude E. Shannon published an 
article based on his master’s thesis at MIT. 

Shannon’s thesis has been described as: 
“Possibly the most important Master’s the- 
sis of the twentieth century.”’ In his paper, 
which was widely circulated, Shannon 
showed how Boole’s concepts of TRUE 
and FALSE could be used to represent the 
functions of switches in electronic circuits. 
(Shannon is also credited with the inven- 
tion of the rocket-powered Frisbee, and is 
famous for riding down the corridors at 
Bell Laboratories on a 
unicycle while simul- 
taneously juggling 
four balls.) 

Following 
Shannon’s paper, a 
substantial amount of 
attention was focused 
on developing electron- 
ic logic machines. 
Unfortunately, interest 
in special-purpose 
logic machines waned 
in the 1940s with the 
advent of general-pur- 
pose computers, which 
proved to be much 
more powerful and for 


Monroe’s “Full Automatic” calculating machine, 1922, the which programs could 
first machine to offer fully automatic multiplication and divi- be written to handle 


Sion. Courtesy Science Museum/Science and Society Picture Library. 


Everyday Practical Electronics, May 2000 


formal logic. 


TIMELINES 


1274: Spain. Theologian Ramon Lull 
proposes a “logic machine” consisting 
of a set of concentric, nested disks. 

1777: Charles Stanhope invents a 
mechanical calculating machine. 

Late 1700s: Charles Stanhope 
invents the Stanhope Demonstrator. 

1822: England. Charles Babbage 
starts to build a mechanical calculating 
machine — the Difference Engine. 

1832: England. Charles Babbage 
conceives the first mechancial computer 
— the Analytical Engine. 

1847: England. George Boole pub- 
lishes his first ideas on symbolic logic. 

1869: William Stanley Jevons invents 
the Logic Piano. 

1881: Alan Marquand invents a 
graphical technique of representing 
logic problems. 

1886: Reverend Charles Lutwidge 
Dodgson (Lewis Carroll) publishes a 
diagramatic technique for logic repre- 
sentation in The Game of Logic. 

1890s: John Venn proposes logic rep- 
resentation using circles and ellipses. 

1925: America. Scientist, engineer 
and politician Vannevar Bush designs an 
analogue computer called the Product 
Intergraph. 

1930: America. Vannevar Bush 
designs an analogue computer called a 
Differential Analyzer. 

1936: America. Efficiency expert 
August Dvorak patents his layout for 
keys on a typewriter called the Dvorak 
Keyboard. 

1936: America. Psychologist Benja- 
min Burack constructs the first electrical 
logic machine (but he didn’t publish 
anything about it until 1949). 

1937: America. George Robert 
Stibitz, a scientist at Bell Labs, builds a 
simple digital calculator machine based 
on relays called the Model K. 

1937: England. Graduate student Alan 
Turing (of Colossus fame) writes his 
ground-breaking paper On Computable 
Numbers with an Application to the 
Entscheidungsproblem. 

1937: England. Alan Turing invents a 
theoretical (thought experiment) com- 
puter called the Turing Machine. 

1938: America. Claude E. Shannon 
publishes an article (based on his mas- 
ter’s thesis at MIT) that showed how 
Boolean algebra could be used to design 
digital circuits. 

1938: Germany. Konrad Zuse finish- 
es the construction of the first working 
mechanical digital computer (the Z1). 

1939: America. George Robert 
Stibitz builds a digital calculator called 
the Complex Number Calculator. 

1939: America. John Vincent 
Atanasoff (and Clifford Berry) may or 
may not have constructed the first truly 
electronic special-purpose digital com- 
puter called the ABC (but it did not 
work until 1942). 

1940: America. George Robert 
Stibitz performs first example of remote 
computing between New York and New 
Hampshire. 


351 





Ha 


by Vannevar Bush. Courtesy Science Museum/Science and Society 


Picture Library. 


ELECTROMECHANICAL 
COMPUTERS 


In 1927, with the assistance of two col- 
leagues at MIT, the American scientist, 
engineer and politician Vannevar Bush 
designed an analogue computer that could 
solve simple equations. This device, which 
Bush dubbed a Product Intergraph, was 
subsequently built by one of his students. 

Bush continued to develop his ideas and, 
in 1930, built a bigger version, which he 
called a Differential Analyzer. The 
Differential Analyzer was based on the use of 
mechanical integrators that could be inter- 
connected in any desired manner. To provide 
amplification, Bush employed torque ampli- 
fiers, which were based on the same princi- 
ple as a ship’s capstan. The final device used 
its integrators, torque amplifiers, drive belts, 
shafts, and gears to measure movements and 
distances (not dissimilar in concept to an 
automatic slide rule). 

Although Bush’s first Differential 
Analyzer was driven by electric motors, its 
internal operations were purely mechani- 
cal. In 1935 Bush developed a second 
version, in which the gears were shifted 
electro-mechanically and which employed 
paper tapes to carry instructions and to set 
up the gears. 

In our age, when computers can be 
constructed the size of postage stamps, it is 
difficult to visualize the scale of the prob- 
lems that these early pioneers faced. To 


352 


Harvard Mark I, the first large-scale a 


utomatic digital computer. Courtesy of IBM. 





provide some sense of 
perspective, Bush’s 
second Differential 
Analyzer weighed in 
at a whopping 100 
tons! In addition to all 
of the mechanical ele- 
ments, it contained 
2000 vacuum tubes, 
thousands of relays, 
150 motors, and 
approximately 200 
miles of wire. 

As well as being a 
major achievement in 
its own right, the 
Differential Analyzer 
was also significant 

ecause it focused 
attention on analogue 
computing techniques, 
and therefore detract- 
ed from the investigation and development 
of digital solutions for quite some time. 


FLASHLIGHT BULBS 
AND TIN CANS 


However, not everyone was enamoured 
by analogue computing. In 1937, George 
Robert Stibitz, a scientist at Bell 
Laboratories built a digital machine based 
on relays, flashlight bulbs and metal strips 
cut from tin-cans, which he called the 
Model K (because most of it was construct- 
ed on his kitchen table). 

Stibitz’s machine, worked on the princi- 
ple that if two relays were activated they 
caused a third relay to become active, 
where this third relay represented the. sum 
of the operation. For example, if the two 
relays representing the numbers 3 and 6 
were activated, this would activate another 
relay representing the number 9. (A replica 
of the Model K is on display at the 
Smithsonian.) 

Stibitz went on to create a machine 
called the Complex Number Calculator, 
which, although not tremendously sophisti- 
cated by today’s standards, was an impor- 
tant step along the way. In 1940, Stibitz 
performed a spectacular demonstration at a 
meeting in New Hampshire. 

Leaving his computer in New York City, 
he took a teleprinter to the meeting and pro- 
ceeded to connect it to his computer via 
telephone. In the first example of remote 











TIMELINES 


1941: Germany. Konrad Zuse finish- 
es the first true relay-based general-pur- 
pose digital computer (the Z3). 

1942: Germany. Between 1942 and 
1943 Konrad Zuse builds the Z1 and Z2 
computers for the Henschel aircraft 
company. 

1942: Germany, Between 1942 and 
1945/6 Konrad Zuse develops the ideas 
for a high-level computer programming 
language called Plankakul. 

1943: England. Alan Turing and team 
build a special-purpose electronic (vac- 
uum tube) computer called Colossus. 

1944; America. Howard Aiken and 
team finish building an electromechani- 
cal computer called the Harvard Mark I 
(also known as the IBM ASCC). 


1945: America. Hungarian/American 
mathematician Johann (John) Von 
Neumann publishes a paper entitled 
First Draft of a report on the EDVAC. 


1946: America. John William 
Mauchly, J. Presper Eckert and team 
finish building a general-purpose elec- 
tronic computer called ENIAC. 

1948: America. Work starts on the 
first commercial computer, UNIVAC 1. 

1948: America. First commercial 
computer, UNIVAC 1, is completed. 

1949; England, Cambridge 
University. Small experimental comput- 
er called EDSAC performs its first 
calculation. 

1949: England. EDSAC computer 
uses first assembler called Initial 
Orders. 





computing, Stibitz astounded the attendees 
by allowing them to pose problems which 
were entered on the teleprinter; within a 
short time the teleprinter presented the 
answers generated by the computer. 


HARVARD MARK | 


Many consider that the modern computer 
era commenced with the first large-scale 
automatic digital computer, which was 
developed between 1939 and 1944. This 
device, the brainchild of a Harvard graduate, 
Howard H. Aiken, was officially known as 
the IBM automatic sequence controlled 
calculator (ASCC), but is more commonly 
referred to as the Harvard Mark I. 

The Mark I was constructed out of 
switches, relays, rotating shafts, and clutch- 
es, and was described as sounding like a 
“roomful of ladies knitting.’ The machine 
contained more than 750,000 components, 
was 50 feet long, 8 feet tall (15-2m x 2-4m), 
and weighed approximately five tons 
(5080kg)! 

Although the Mark I is considered to be 
the first digital computer, its architecture 
was significantly different from modern 
machines. The device consisted of many 
calculators which worked on parts of the 
same problem under the guidance of a sin- 
gle control unit. 

Instructions were read in on paper tape, 
data was provided separately on punched 
cards, and the device could only perform 
operations in the sequence in which they 
were received. This machine was based on 
numbers that were 23 digits wide — it could 


Everyday Practical Electronics, May 2000 


add or subtract two of these numbers in 
three-tenths of a second, multiply them in 
four seconds, and. divide them in ten 
seconds. 


KONRAD ZUSE 

In. the aftermath of World War II, it was 
discovered that a program controlled calcu- 
lator called the Z3 had been completed in 
Germany in 1941, which means that the Z3 
pre-dated the Harvard Mark I. The Z3’s 
architect was a German engineer called 
Konrad Zuse, who developed his first 
machine, the Z1, in his parents’ living room 
in Berlin in 1938. 


ces 


of Horst Zuse. 


Although based on relays, the Z3 was 
very sophisticated for its time; for example, 
it utilized the binary number system and 
could handle floating-point arithmetic. 
(Zuse had considered employing vacuum 
tubes, but he decided to use relays because 
they were more readily available and 
also because he feared that tubes were 
unreliable). 

In 1943, Zuse started work on a general- 
purpose relay computer called the Z4. 
Sadly, the original Z3 was destroyed by 
bombing in 1944 and therefore didn’t sur- 
vive the war (although a new Z3 was recon- 
structed in the 1960s). However, the Z4 did 
survive — in a cave in the Bavarian Alps — 
and by 1950 it was up and running in a 
Zurich bank. 

It is interesting to note that paper was in 
short supply in Germany during the war, so 
instead of using paper tape, Zuse was 
obliged to punch holes in old movie film to 
store his programs and data. We may only 
speculate as to the films Zuse used for his 
hole-punching activities; for example, were 
any first-edition Marlene Dietrich classics 
on the list? (Marlene Dietrich fell out of 
favour with the Hitler regime when she 
emigrated to America in the early 1930s, 
but copies of her films would still have 
been around during the war.) 

Zuse was an amazing man who was well 
ahead of his time. In fact there isn’t enough 
space to do him justice in this article, but 
you can find a “world-exclusive” feature 
article on Zuse at the EPE Online web site 
at www.epemag.com. This article, which 


Everyday Practical Electronics, May 2000 





Rebuilt version of Konrad Zuse’s ZI computer. The original 
was built in his parent's living room in Berlin in 1938. Courtesy 


was written by Konrad’s eldest son, Horst 
Zuse, contains over 100 photographs from 
Horst’s private collection, many of which 
have never been published before! 


FIRST ELECTRONIC 
COMPUTERS 


We now turn our attention to an 
American mathematician and physicist, 
John Vincent Atanasoff, who has the 
dubious honour of being known as the 
man who either did or did not construct 
the first truly electronic special-purpose 
digital computer. 

A lecturer at Iowa State College (now 
Iowa State University), 
Atanasoff was dis- 
gruntled with the 
cumbersome and time- 
consuming process of 
solving complex equa- 
tions by hand. 
Working alongside 
one of his graduate 
students (the brilliant 
Clifford Berry), 
Atanasoff commenced 
work on an electronic 
computer in early 
1939, and had a proto- 
type machine by the 
autumn of that year. 

In the process of 
creating the device, 
Atanasoff and Berry 
evolved a number of 
ingenious and unique 
features. For example, 
one of the biggest 
problems for comput- 
er designers of the 
time was to be able to 
store numbers for use 
in the machine’s calculations. 

Atanasoff’s design utilized capacitors to 
store electrical charge that could represent 
numbers in the form of logic Os and logic 
ls. The capacitors were mounted in rotat- 
ing bakelite cylinders, which had metal 


bands on their outer surface. These cylin- 
ders, each approximately 12 inches tall and 
8 inches in diameter (30cm x 20cm), could 
store thirty binary numbers, which could be 
read off the metal bands as the cylinders 
rotated. 

Input data was presented to the machine 
in the form of punched cards, while inter- 
mediate results could be stored on other 
cards. Once again, Atanasoff’s solution to 
storing intermediate results was quite inter- 
esting — he used sparks to burn small spots 
onto the cards. The presence or absence of 
these spots could be automatically deter- 
mined by the machine later, because the 
electrical resistance of a carbonized spot 
varied from that of the blank card. 

Some references report that Atanasoff 
and Berry had a fully working model of 
their machine by 1942. However, while 
some observers agreed that the machine 
was completed and did work, others report- 
ed that it was almost completed and would 
have worked, while still others stated that it 
was just a collection of parts that never 
worked. So unless more definitive evidence 
comes to light, it’s a case of: “You pays 
your money and you takes your choice’. 


GENIUSES AND 
ECCENTRICS 


Many of the people who designed the 
early computers were both geniuses and 
eccentrics of the first order, and the English 
mathematician Alan Turing was _ first 
among equals. In 1937, while a graduate 
student, Turing wrote his ground-breaking 
paper On Computable Numbers with an 
Application to the Entscheidungsproblem. 

Since Turing did not have access to a real 
computer (not unreasonably as they didn’t 
exist at the time), he invented his own as an 
abstract “paper exercise’’. This theoretical 
model, which became known as a Turing 
Machine, was both simple and elegant, and 
subsequently inspired many “thought 
experiments’. 

During World War II, Turing worked as a 
cryptographer, decoding codes and cyphers 





“Enigma” codes during WWII. Courtesy Science Museum/Science and Society Picture Library. 


353 


at one of the British government’s top- 
secret establishments located at Bletchley 
Park. During this time Turing was a key 
player in the breaking of the German’s 
now-famous code generated by their 
Enigma machine. However, in addition to 
Enigma, the Germans had another cypher 
that was employed for their ultra-top-secret 
communications. This cypher, which was 
vastly more complicated that Enigma, was 
generated by a machine called a 
Geheimfernschreiber (secret telegraph), 
which the allies referred to as the “Fish”. 

In January 1943, along with a number of 
colleagues, Turing began to construct an elec- 
tronic machine to decode the 
Geheimfernschreiber cypher. This machine, 
which they dubbed Colossus, comprised 
1,800 vacuum tubes and was completed and 
working by December of the same year! 

By any standards Colossus was one of 
the world’s earliest working programmable 
electronic digital computers. But it was a 
special-purpose machine that was really 
only suited to a narrow range of tasks (for 
example, it was not capable of performing 
decimal multiplications). Having said this, 
although Colossus was built as a special- 
purpose computer, it did prove flexible 
enough to be programmed to execute a 
variety of different routines. 


ENIAC AND EDVAC 


By the mid-1940s, the majority of com- 
puters were being built using vacuum tubes 
rather than switches and relays. Although 
vacuum tubes were fragile, expensive and 
used a lot of power, they were much faster 
than relays (and much quieter). If we 
ignore Atanasoff’s machine and Colossus, 
then the first true general-purpose electron- 
ic computer was the electronic numerical 
integrator and computer (ENIAC), which 
was constructed at the University of 
Pennsylvania between 1943 and 1946. 

ENIAC, which was the brainchild of 
John William Mauchly and J. Presper 
Eckert Jr., was a monster — it was 10 feet 
(3m) tall, occupied 1,000 square feet 
(300m2) of floor-space, weighed in at 
approximately 30 tons (30480kg), and used 
more than 70,000 resistors, 10,000 capaci- 
tors, 6,000 switches, and 18,000 vacuum 
tubes. The final machine required 150 kilo- 
watts of power, which was enough to light 
a small town. 

One of the greatest problems with com- 
puters built from vacuum tubes was relia- 
bility; 90 per cent of ENIAC’s down-time 
was attributed to locating and replacing 





Electronic vacuum tubes, 1946, which replaced electric relays and made opera- 


burnt-out tubes. Records from 1952 show 
that approximately 19,000 vacuum tubes 
had to be replaced in that year alone, which 
averages out to about 50 tubes a day! 

In August 1944, Mauchly and Eckert 
proposed the building of another machine 
called the electronic discrete variable 
automatic computer (EDVAC). This new 
machine was intended to feature many 
improvements over ENIAC, including a 
new form of memory based on pulses of 
sound racing through mercury delay 
lines. 


FIRST DRAFT 


In June 1944, the Hungarian-American 
mathematician Johann (John) von 
Neumann first became aware of ENIAC. 
Von Neumann, who was a consultant on the 
Manhattan Project, immediately recog- 
nized the role that could be played by a 
computer like ENIAC in solving the vast 
arrays of complex equations involved in 
designing atomic weapons. 

Von Neumann was tremendously excited 
by ENIAC and quickly became a consul- 
tant to both the ENIAC and EDVAC pro- 
jects. In June 1945, he published a paper 
entitled First Draft of a report on the 
EDVAC, in which he presented all of the 
basic elements of a_ stored-program 
computer: 


Saeatetatetatatatshttel 








@ A control unit, which could interpret 
an instruction retrieved from the memory 
and select alternative courses of action 
based on the results of previous opera- 
tions. 


The key point made by the paper was 
that the computer could modify its own 
programs, in much the same way as was 
originally suggested by Charles Babbage in 
the 1830s. The computer structure resulting 
from the criteria presented in this paper is 
popularly known as a von Neumann 
Machine, and virtually all digital comput- 
ers from that time forward have been based 
on this architecture. 

Unfortunately, although the conceptual 
design for EDVAC was completed by 1946, 
several key members left the project to pur- 
sue their own careers, and the machine did 
not become fully operational until 1952. 
When it was finally completed, EDVAC 
contained approximately 4,000 vacuum 
tubes and 10,000 crystal diodes. A 1956 
report shows that EDVAC’s average error- 
free up-time was approximately eight 
hours. 


EDSAC TO UNIVAC 


In light of its late completion, some 
would dispute EDVAC’s claim-to-fame as 
the first stored-program computer. A small 


One small section of the receiver unit for ENIAC. Another photo of ENIAC was 


shown in Part 2. Courtesy Science Museum/Science and Society Picture Library. 


@ A memory containing both data and 
instructions. Also to allow both data and 
instruction memory locations to be read 
from, and written to, in any desired order. 

@ A calculating unit capable of per- 
forming both arithmetic and logical opera- 
tions on the data. 


tional programs that could multiply two 10-digit numbers 40 times per second. 


Courtesy of IBM. 


354 





experimental machine based on the 
EDVAC concept consisting of 32 words of 
memory and a 5-instruction command set 
was operating at Manchester University, 
England, by June 1948. 

Another machine called EDSAC 
(Electronic Delay Storage Automatic 
Calculator) performed its first calculation 
at Cambridge University, England, in May 
1949. EDSAC contained 3,000 vacuum 
tubes and used mercury delay lines for 
memory. Programs were input using paper 
tape and output results were passed to a 
teleprinter. 

Additionally, EDSAC is credited as 
using one of the first assemblers called 
Initial Orders, which allowed it to be pro- 
grammed symbolically instead of using 
machine code. Last but not least, the first 
commercially available computer, UNI- 
VAC I (Universal Automatic Computer), 
was also based on the EDVAC design. 
Work started on UNIVAC I in 1948, and the 
first unit was delivered in 1951, which 
therefore predates EDVAC’s becoming 
fully operational. 


Everyday Practical Electronics, May 2000 





| Magnetic core memory store. Logic 0 and 1 depended on the polarity of the 





magnetised field for each bead. Courtesy of IBM. 


MAGNETIC CORE 


STORES 
One of the biggest problems faced by 


early computer designers was the lack of 
small, efficient memories. In Germany 
Konrad Zuse experimented with purely 
mechanical memories (which were surpris- 
ingly reliable), whilst other engineers 
worked with a variety of esoteric tech- 
niques, including the phosphorescent effect 
in storage oscilloscopes, and mercury delay 
lines as discussed earlier. 

Around 1950, Jay Forrester at MIT came 
up with the idea of using ferromagnetic 
beads (“cores”) threaded onto wires to 
store logic Os and 1s (depending on which 
way they were magnetized). Although 
unwieldy by today’s standards, these core 
stores were incredibly useful at that time, 
and they paved the way for bigger and 
better computers. 

Of course, the advent of the transistor 
was revolutionary in computing circles, 
because each transistor could replace a vac- 
uum tube that was 100s of times larger, 
consumed 100s of times more power, and 
was 100s of times less reliable. 

However, transistors by themselves did 
not oust core stores. This was due to the 
fact that storing one bit of data required a 
single core only 1mm or less in diameter, 
but storing the same bit would require 
between four and six transistors. Thus, it 
was not until the invention of the integrated 
circuit that useful semiconductor memory 
devices started to appear in the early 1970s. 
(The development of vacuum tubes, tran- 
sistors, and integrated circuits were dis- 
cussed in Part 2.) , 


FIRST 
MICROPROCESSORS 


In 1970, the Japanese calculator compa- 
ny Busicom approached Intel with a 
request to design a set of twelve integrated 
circuits for use in a new calculator. The task 


Everyday Practical Electronics, May 2000 


was presented to one Marcian “Ted” Hoff, 
a man who could foresee a somewhat bleak 
and never-ending role for himself design- 
ing sets of special-purpose integrated cir- 
cuits for one-of-a-kind tasks. 

However, during his early ruminations 
on the project, Hoff realized that rather 
than design the special-purpose devices 
requested by Busicom, he could create a 
single integrated circuit with the attributes 
of a simple-minded, stripped-down, gener- 
al-purpose computer processor. 

The result of Hoff’s inspiration was the 
world’s first microprocessor, the 4004, 
where the ‘4’s were used to indicate that the 
device had a 4-bit data path (there is a 
photo in Part 2). The 4004 was part of a 
four-chip system which also consisted of a 
256-byte ROM, a 32-bit RAM, and a 10-bit 
shift register. 

The 4004 itself contained approximately 
2,300 transistors and could execute 60,000 
operations per second. The advantage (as 
far as Hoff was concerned) was that by sim- 
ply changing the external program, the 
same device could be used for a multitude 
of future projects. 

In November 1972, Intel introduced the 
8008, which was essentially an 8-bit ver- 
sion of the 4004. The 8008 contained 
approximately 3,300 transistors and was 
the first microprocessor to be supported by 
a high-level language compiler called 
PL/M. The 8008 was followed by the 4040, 
which extended the 4004’s capabilities by 
adding logical and compare instructions, 
and by supporting subroutine nesting using 
a small internal stack. 

However, the 4004, 4040, and 8008 were 
all designed for specific applications, and it 
was not until April 1974 that Intel presented 
the first true general-purpose microprocessor, 
the 8080. This 8-bit device, which contained 
around 4,500 transistors and could perform 
200,000 operations per second, was destined 
for fame as the central processor of many of 
the early home computers. 


TIMELINES 


1949; America. MIT’s first real-time 
computer, Whirlwind. 

1950: America. Jay Forrester at MIT 
invents magnetic core store. 

1951: America. Computers are sold 
commercially. 

1952: America. John William 
Mauchly, J. Presper Eckert and team 
finish building a general-purpose 
(stored program) electronic computer 
called EDVAC. 

1956: America. John Backus and 
team at IBM introduce the first widely 
used high-level computer language, 
FORTRAN. 

1956: America. John McCarthy 
develops a computer language called 
LISP for artificial intelligence 
applications. 

1956: America. MANIAC 1 is the 
first computer program to beat a human 
in a game (a simplified version of 
chess). : 

1957: America. IBM 610 Auto-Point 
computer is introduced. 

1958: America. Computer data is 
transmitted over regular telephone 
circuits. 

1959: America. COBOL computer 
language is introduced for business 
applications. 

1961: Time-sharing computing is 
developed. 

1963: In America, the LINC com- 
puter was designed at MIT. 

1965: John Kemeny and Thomas 
Kurtz develop the BASIC computer 
programming language. 

1968: First Static RAM i.c. reaches 
the market. 

1970: First floppy disk (8.5 inch?) is 
used for storing computer data. 

1970: America. Ethernet developed at 
Palo Alto Research centre by Bob 
Metcalfe and David Boggs. 

1971: America. Datapoint 2200 com- 
puter introduced by CTC. 

1971; CTC’s Kenbak-1 Computer is 
introduced. 

1971: America. Ted Hoff designs 
(and Intel releases) the first computer- 
on-a-chip, the 4004 microprocessor. 

1971: Niklaus Wirth develops PAS- 
CAL computer language (named after 
Blaise Pascal). 

1972: November, America. Intel 
introduce the 8008 microprocessor. 

1973: America. Xerox Alto Computer 
is introduced. 

1973: May, France. 8008-based 
Micral microcomputer is introduced. 

1973: June, the term microcomputer 
first appears in print in reference to the 
8008-based Micral microcomputer. 

1973: America. Scelbi Computer 
Consulting Company introduce the 
Scelbi-8H microcomputer-based do-it- 
yourself computer kit. 

1973: PDP-8 becomes the first popu- 
lar microcomputer. 

1974: America. Intel introduce the 
8080 microprocessor. 

1974: August, America. Motorola 
introduce the 6800 microprocessor. 


355 


Following the 8080, the microprocessor 
field exploded with devices such as the 
6800 from Motorola in August 1974, the 
6502 from MOS Technology in 1975, and 
the Z80 from Zilog in 1976 (to name but a 
few). 

Unfortunately, documenting all of the 
different microprocessors would require a 
book in its own right, so we won’t even 
attempt the task here. Instead, we’ll create 
a cunning diversion that will allow us to 
leap gracefully into the next topic . .. Good 
grief! Did you see what just flew past your 
window? 


FIRST PERSONAL 
COMPUTERS (PCs) 


Given that the 8008 was not introduced 
until November 1972, the resulting flurry 
of activity was quite impressive. Only six 
months later, in May 1973, the first com- 
puter based on a microprocessor was 
designed and built in France. 

Unfortunately the 8008-based Micral, as 
this device was known, did not prove 
tremendously successful in America. 
However, in June of that year, the term 
“microcomputer”’ first appeared in print in 
reference to the Micral. 

In the same mid-1973 time-frame, the 
Scelbi Computer Consulting Company 
presented the 8008-based Scelbi-8H micro- 
computer, which was the first microproces- 
sor-based computer kit to hit the market 
(the Micral wasn’t a kit — it was only avail- 
able in fully assembled form). The Scelbi- 
8H was advertised at $565 and came 
equipped with 1Kbyte of RAM. 

In June 1974, Radio Electronics maga- 
zine published an article by Jonathan Titus 
on building a microcomputer called the 
Mark-8, which, like the Micral and the 
Scelbi-8H, was based on the 8008 micro- 
processor. The Mark-8 received a lot of 
attention from hobbyists, and a number of 
user groups sprang up around the US to 
share hints and tips and disseminate 
information. 


LAUNDROMATS IN 
ALBUQUERQUE 


Around the same time that Jonathan 
Titus was penning his article on the Mark- 
8, a man called Ed Roberts was pondering 
the future of his failing calculator company 
known as MITS (which was next door to a 
laundromat in Albuquerque, New Mexico). 
Roberts decided to take a gamble with what 
little funds remained available to him, and 
he started to design a computer called the 
Altair 8800 (the name “Altair” originated 
in one of the early episodes of Star Trek). 





Altair 8800b microcomputer, 
Museum/Science and Society Picture Library. 


356 


1975. Courtesy Science 


Roberts based his system on the newly- 
released 8080 microprocessor, and the 
resulting do-it-yourself kit was advertised 
in Popular Electronics magazine in January 
1975 for the then unheard-of price of $439. 
In fact, when the first unit shipped in April 
of that year, the price had fallen to an amaz- 
ingly low $375. 

Even though it only contained a miserly 
256 bytes of RAM and the only way to pro- 
gram it was by means of a switch panel, the 
Altair 8800 proved to be a tremendous suc- 
cess. (These kits were supplied with a steel 
cabinet sufficient to withstand most natural 
disasters, which is why a remarkable num- 
ber of them continue to lurk in their 
owner’s garages to this day.) 


BASIC GATES 

Also in April 1975, Bill Gates and Paul 
Allen founded Microsoft (which was to 
achieve a certain notoriety over the coming 
years), and in July of that year, MITS 
announced the availability of BASIC 2.0 on 
the Altair 8800. This BASIC interpreter, 
which was written by Gates and Allen, was 
the first reasonably high-level computer 
language program to be made available on 
a home computer — MITS sold 2,000 sys- 
tems that year, which certainly made Ed 
Roberts a happy camper, while Microsoft 
had taken its first tentative step on the path 
toward world domination. 

In June 1975, MOS Technology intro- 
duced their 6502 microprocessor for only 
$25 (an Intel 8080 would deplete your bank 
account by about $150 at that time). A short 
time later, MOS Technology announced their 
6502-based KIM-1 microcomputer, which 
boasted 2K bytes of ROM (for the monitor 


program), 1Kbyte of RAM, an octal keypad, 


a flashing l.e.d. display, and a cassette 
recorder for storing programs. This unit, 
which was only available in fully-assembled 
form, was initially priced at $245, but this 
soon fell to an astoundingly low $170. 

The introduction of new microcomputers 
proceeded apace. Sometime after the KIM- 
1 became available, the Sphere Corporation 
introduced its Sphere 1 kit, which com- 
prised a 6800 microprocessor, 4K bytes of 
RAM, a QWERTY keyboard, and a video 
interface (but no monitor) for $650. 


JOBS AND WOZNIAK 

In March 1976, two guys called Steve 
Wozniak and Steve Jobs (who had been fired 
with enthusiasm by the Altair 8800) finished 
work on a home-grown 6502-based comput- 
er which they called the Apple 1 (a few 
weeks later they formed the Apple Computer 
Company on April Fools day). 

Although it was not 
tremendously sophisti- 
cated, the Apple 1 
attracted __ sufficient 
interest for them to cre- 
ate the Apple II, which 
many believe to be the 
first personal computer 


able and usable. The 
Apple II, — which 
became available in 
April 1977 for $1,300, 
comprised 16K bytes 
of ROM, 4K bytes of 
RAM, a keyboard and 
a colour display. 





that was both afford- | 


TIMELINES | 

1974: June, America. Radio 
Electronics magazine publish an article by 
Jonathan (Jon) Titus on building an 8008- 
based microcomputer called the Mark-8. 

1975: America. MOS Technology 
introduce the 6502 microprocessor. 

1975: January, America, Ed Roberts 
and his MITs company introduce the 
8080-based Altair 8800 microcomputer. 

1975: April, America. Bill Gates and 
Paul Allen found Microsoft. 

1975: July, America. Microsoft 
release BASIC 2.0 for the Altair 8800 
microcomputer. | 

1975: America. MOS Technology 
introduce the 6502-based KIM-1 micro- 
computer. 

1975: America. Sphere Corporation 
introduce the 6800-based Sphere 1 

_ microcomputer. 

1975: America. Microcomputer in kit 
form reaches US home market. 

1976: America. Zilog introduce the 
Z80 microprocessor. 

1976: March, America. Steve 
Wozniak and Steve Jobs introduce the 
6502-based Apple 1: microcomputer. 

1976: April Ist, America. Steve 
Wozniak and Steve Jobs form the Apple 
computer company. 

1977: April, America. Apple intro- 
duces the Apple II microcomputer. 

1977: April, America. Commodore 
Business Machines present their 6502- 
based Commodore PET microcomputer. 

1977: August, America. Tandy/Radio 
Shack announce their Z80-based TRS- 
80 microcomputer. 

1978: America. Apple introduce the 
first hard disk drive for use with porven: 
al computers. 

1979: America, the first true commer- 
cial microcomputer program, the 
VisiCalc spreadsheet, is available for the 
Apple II. 

1979; ADA programming language is 
named after Augusta Ada Lovelace 
(now credited as being the first comput- 
er programmer). 

1981: America. First IBM PC is 
launched. 

1981: America. First mouse pointing 
device is introduced. 

1981: First laptop computer is intro- 
duced. 

1983: Apple’s Lisa is the first person- 
al computer to use a mouse and pull- 
down menus. 

1983: Time magazine names the 
computer as Man Of The Year. 

1984: 1MB memory chips intro- 
duced. | , 

1985: CD-ROMs are used ‘to: store 
computer data for the first time. 


Apple was one of the great early success 
stories — in 1977 they had an income of 
$700,000 (which was quite a lot of money 
in those days), and just one year later this 
had soared tenfold to $7 million! (which 
was a great deal of money in those days). 

Also in April 1977, Commodore 
Business Machines presented their 6502- 
based Commodore PET, which contained 
14K bytes of ROM, 4K bytes of RAM, a 
keyboard, a display and a cassette tape 
drive for only $600. Similarly, in August of 


Everyday Practical Electronics, May 2000 





A Commodore PET 32K computer, 


that year, Tandy/Radio Shack announced 
their Z80-based TRS-80, comprising 4K 
bytes of ROM, 4K bytes of RAM, a key- 
board and a cassette tape drive for $600. 


WOT! NO SOFTWARE? 


One point that may seem strange today is 
that there were practically no programs avail- 
able for these early machines (apart from the 
programs written by the users themselves). In 
fact, it wasn’t until late in 1978 that commer- 
cial software began to appear. 

Possibly the most significant tool of that 
time was the VisiCalc spreadsheet pro- 
gram, which was written for the Apple II 
by a student at the Harvard Business 
School and which appeared in 1979. It is 
difficult to overstate the impact of this pro- 
gram, but it is estimated that over a quarter 
of the Apple machines sold in 1979 were 
purchased by businesses solely for the pur- 
pose of running VisiCalc. In addition to 
making Apple very happy, the success of 
VisiCalc spurred the development of other 
applications such as word processors. 

When home computers first began to 
appear, existing manufacturers of large 
computers tended to regard them with dis- 
dain (“It’s just a fad. .. it will never catch 
on’’). However, it wasn’t too long before 
the sound of money changing hands began 


. eee aa 


during the Cold War. Courtesy of IBM. 


Everyday Practical Electronics, May 2000 


1979. Cassette 
recorders provided external data storage. Courtesy John Becker. 





Two of the ballistic track monitors of Sage, the massive US 
military computer that helped defend the Western World 


to awaken their interest. In 1981, IBM 
launched their first PC for $1,365, which, 
if nothing else, sent a very powerful signal 
to the world that personal computers were 
here to stay. 

The advent of the general-purpose micro- 
processor heralded a new era in computing — 
microcomputer systems small enough to fit 
on a desk could be endowed with more pro- 
cessing power than monsters weighing tens 
of tons only a decade before. The effects of 


‘ these developments are still unfolding, but it 


is not excessive to say that digital computing 
and the personal computer have changed the 
world more significantly than almost any 
other human invention, and many observers 
believe that we’ve only just begun our jour- 
ney into the unknown! 


EVER SO HUMBLE 


We crave your indulgence and ask you 
to accept our humblest apologies for all of 
the things we had to leave out. Surely com- 
puter languages like FORTRAN, COBOL, 
BASIC, C, LISP, FORTH and .. . (the list 
goes on) deserve a mention? How could 
we neglect microcomputers such as the 
PDP and VAX from Digital Equipment 
Corporation (DEC) that had such an 
impact on the industry? Are operating sys- 
tems like VMS, UNIX, and Windows to be 






1949. 


(DEC), 1977 


personal computer. 


QUOTABLE QUOTES 


“Computers in the future may weigh no more than 1-5 tons.” 
Popular Mechanics, forecasting the relentless march of science, 


“1 think there is a world market for about five computers.” Thomas 
Watson, Chairman of IBM, 1943. 

“I have travelled the length and breadth of this country and talked 
with the best people, and I can assure you that data processing is a 
fad that won’t last out the year.” The editor in charge of business 
books for Prentice Hall, 1957. 

“There is no reason for any individual to have a computer in their 
home.”” Ken Olson, President of Digital Equipment Corporation 


“So we went to Atari and said, ‘Hey, we’ve got this amazing thing, 
even built with some of your parts, and what do you think about fund- 
ing us? Or we’ll give it to you. We just want to do it. Pay our salary, 
we’ll come work for you.’ And they said, ‘No.’ So then we went to 
Hewlett-Packard, and they said, ‘Hey, we don’t need you. You haven’t 
got through college yet.’’ Apple Computer Inc. founder Steve Jobs on 
attempts to get Atari and HP interested in his and Steve Wozniak’s 


“640K of memory ought to be enough for anybody.”’ Bill Gates, 
CEO of Microsoft, 1981. 





which all PC-compatibles must emulate. Courtesy of IBM. 


ignored? What about behemoths like 
SAGE (which consumed a million watts of 
power) and CRAY Supercomputers? 

The problem is that one could go on for- 
ever, so we chose to restrict ourselves only 
to those topics that we felt were particular- 
ly germane to this series. As usual you may 
of course disagree (or you may simply 
crave more once this series is finished), in 
which. case please feel free to vent your 
feelings by inundating the Editor with your 
letters and E-mails. 


ACKNOWLEDGEMENT 

Portions of this article were abstracted 
from our book, Bebop BYTES Back (An 
Unconventional Guide to Computers), with 
the kind permission of its publisher, Doone 
Publications. (Bebop BYTES Back is avail- 
able from the EPE Direct Book Service — 
see page 394 — Ed.) 


NEXT MONTH 

In the fifth and final instalment of this 
series we shall gird up our loins and pon- 
tificate on the future. Where do you think 
the technology roller-coaster will take us in 
the next 10, 100 or 1000 years? Start pon- 
dering now and see if you agree with us in 
next month’s exciting issue — same time ... 
same place ... same channel! 
























357 








T is a commonly known fact that micro- 

processor clock speeds are increasing all 
the time. Only a few years ago clock 
speeds of 1GHz were thought to be many 
years away. Now a number of manufactur- 
ers have offerings with speeds around 
1GHz that will shortly hit the marketplace. 
IBM have a 64-bit Power PC chip. 
Compaq, have their 1GHz Alpha, and Intel 
a version of a Pentium III. These devices 
have been able to achieve their speed as a 
result of a number of developments that 
have been undertaken in many research 
institutes and development areas. 

All of the devices have geometries that 
are less than 0-2 microns, and this means 
that the operating voltages are low. For 
example the Alpha operates on a voltage of 
1-65 volts. Not only is this low voltage 
required because of the low breakdown 
voltages associated with the minute 
geometries, but it also reduces the power 
consumption. 


Power consumption is an increasing 
problem as demonstrated by the fact that 
even modest Pentium chips require cool- 
ing. However when it is realised that 
IBM’s 64-bit PowerPC uses 19 million 
transistors it is hardly surprising that very 
significant amounts of heat are dissipated. 
Some of the new chips now under develop- 
ment dissipate levels of heat well in excess 
of 50 watts, and the trend of increasing 
levels of power dissipation is likely to con- 
tinue. With the increasing levels of power 
dissipation, thermal control of chips is an 
integral part of the design and it is every bit 
as important and challenging as the electri- 
cal performance. 

It is interesting to note that when the first 
bipolar integrated circuits were introduced, 
limits of around 20 transistors were 
thought to be the limit of integration as a 
result of thermal considerations. The intro- 
duction of CMOS techniques enabled a 
quantum leap to be made in the levels of 
integration and the trend towards ever-larg- 
er i.c.s has increased since then. 

More recently, the reduction of supply 
voltage has been of assistance as the ther- 
mal boundaries have been approached, 
because power levels are proportional to 
the square of the voltage. Even so other 
effects prevent the picture from being quite 
so rosy. The design of the transistors in the 
chip has to be altered to enable them to 
operate at low voltages. One of the results 
of this is that they become far more leaky 
and this effect means that they consume 
power even when they are switched off. 


Temperature rises 


To ensure the highest speed of operation, 
devices should be operated at a low 


358 


New Technology 





Whilst lower operating voltages enable microproces- 
sors to run faster, the problem of heat dissipation 
becomes more significant. lan Poole reports. 


temperature. The unwanted additional 
power consumption from the leaky transis- 
tors raises the temperature and this reduces 
the electron mobility because of the 
increased number of collisions that occur 
as the electrons move around the crystal 
lattice. 

Accordingly, it makes the methods and 
techniques used for heat extraction from 
the i.c. a point of major importance if 
speeds are to increase at the current rate. A 
company named Kryotech is already mar- 
keting a chip that is cooled, increasing its 
performance by a half again. To the same 
end, IBM are optimising the performance 
of their basic silicon designs for low tem- 
perature operation with a view to this 
being one of the ways forward for the 
future. 

However, even though speed generally 
increases with cooling, it also increases the 
threshold voltage for the individual 
devices, and this in turn increases the level 
of leakage and partially offsets any gains 
that are made. This is one of the factors 
that makes optimising the design for low 
temperature operation so important. By 
choosing the optimum level of threshold 
voltage, the maximum use can be made of 
any cooling that is used. 


There are a number of ways in which 
heat can be extracted from the chips. One 
method is to use a system that is effective- 
ly a small-scale version of a domestic 
refrigerator. These systems are very suc- 
cessful, being already employed in a num- 
ber of high end products and they are able 
to cool chips down to a temperature of 
around —50°C. 

Whilst this can give significant advan- 
tages in performance, lower temperatures 
can provide even greater improvements. To 
achieve this there are a number of methods 
that can be adopted. The most popular idea 
is that of thermo-electric heat pumps. 
These do not involve the same level of 
mechanical hardware and are accordingly 
less expensive. They can also be interfaced 
to the basic chip more easily, and can actu- 
ally be made as part of the same assembly. 

However, the basic Peltier devices, 
although attractive at first sight, leak too 
much heat back into the chip, and as a 
result they are not as efficient as they are 
required to be for this function. 
Fortunately, new work undertaken at the 
Massachusetts Institute of Technology has 
resulted in the production of new materials 
and structures that give far more effective 
and efficient solutions. 

The requirement is to be able to remove 
a considerable amount of heat from a 
small area. One of the new solutions 
using a thin film semiconductor heat 


pump can extract as much as 100 watts 
per square centimetre. With further work 
it is expected that these devices could be 
built into the basic chip package, provid- 
ing a very convenient, efficient and 
reliable method of extracting heat from 
the devices. 


Packages 


Whilst heat is a major problem that is 
being overcome, new package technolo- 
gy is also part of the solution. Long gone 
are the days when dual-in-line packages 
were able to meet most requirements. 
Even the quad flat packs are not suitable, 
and in addition to this, equipment manu- 
facturers dislike them because they are 
easily damaged. Flip chip packages 
where the silicon is directly bonded to 
the package are able to give performance 
improvements. This gives a _ speed 
increase as a result of its lower resistance 
and RC delays as well as giving a physi- 
cally shorter connection. 

Further improvements have been made 
by adopting a system that enables the 
critical leads to be kept as short as possi- 
ble. Although this technique requires the 
addition of an extra layer of metalisation 
and a complete re-layout of the chip, it 
provides an increase that although small 
still helps to increase the overall speed of 
operation. 

A further increase in performance is 
achieved by using a dielectric with a low 
value. In turn this reduces the levels of 
Capacitance and cross talk, which were 
large enough to slow down the speed of 
operation. The material chosen for this is 
silicon oxyfluoride (SiOF). 


Summary 


Although different manufacturers use 
different techniques to give the new high- 
er clock speeds, the overall pattern is 
clear, and it is likely that in a few years 
time they will all be used as standard. 
Many of them give minor improvements 
on their own, but when used with the 
other techniques they enable a significant 
improvement in performance to be 
achieved in the chip as a whole. This 
demonstrates the fact that is commonly 
true in technology that a variety of 
improvements are required to give the 
overall improvement in performance. 


CHIP LINKS 


Are you aware that the EPE website 
(www.epemag.wimborne.co.uk) 


has links to several semiconductor 
manufacturers’ sites from which data 
sheets can be downloaded? 





Everyday Practical Electronics, May 2000 





Write your PIC programs in BASIC! - No STAMP REQUIRED! 


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» True compiler provides faster program execution and longer programs =. 2 PiCmicro. ai 2s 

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e More user variables 
e Peek and Poke instructions to access any PiCmicro register from BASIC The PicBasic Pro Compiler gives you direct access to all of the PICmicro registers - /O ports, A/D converters, hardwarr 
e Serial speeds to 9600 baud . serial ports, etc. - easily and in BASIC. It automatically takes care of the page boundaries and RAM banks. It even 
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°9 ) The PicBasic Pro Compiler is a DOS command line application (it also works in Windows) and runs on PC compatible 


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PICmicros. PBC converts your basic language these programs into hex or binary files that pic 1 6F 62x, 8x, 87x, PIC] 7Cx« and PIC18Cx« microcontrollers and works with most PICmicro programmers, includin 
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programs can be compiled into PICmicro code and programmed directly into a 
PiCmicro, eliminating the need for a BASIC Stamp module. These programs execute MUCN Version 2.3 of the PicBasic Pro Compiler adds support for the 16-bit core PIC] 8Cx« microcontrollers. If you are a 
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Built-in LCD support 
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I2C instructions to access more external devices including serial EEPROMs 

More variable space (processor dependent) 

In-line assembler and Call support 

MPASM / ICE compatibilty 

Use in DOS or Windows 

Supports PIC] 2C67x, 12CE67x, 14C000, 16C55x, xx, 7x, 84, 92x, 16CE62x, 16F62x, 8x, 87x, 


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The PicBasic Compiler allows variables from BO - B79 and WO - W39 when used with 
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Constructional Project 





ANDY FLIND 

















Part One 








A PIC-based 8 to 16-Channe!l 2-wire on-off signalling 
communication link. An add-on Interface (next month) will 
extend possible options to internal private telephone and 


intercom systems. 


HIS project provides up to sixteen 

channels of on-off signalling com- 

munication through just a single pair 
of wires, in one direction or in both direc- 
tions simultaneously. In a one-way system 
the Transmitter may be powered through 
the same pair of wires which allows the 
monitoring of up to sixteen inputs from 
locations having no local power supplies. 
An interfacing option (next month) 
enables operation through audio circuits, 
such as private internal telephone and 
intercom systems. 

Although ideal for remote signalling and 
alarm system monitoring, other possible 
applications could include such things as 
environmental monitoring, model railway 
controls and switching for advanced light- 
ing or display systems. The versatility of 
using circuit modules, and the ways in 
which they can be connected together, 
means that possible applications are limited 
only by the constructor’s own imagination. 


HOSPITAL CALL 


Like many designs, this one began with 
a request from a friend, who on this occa- 
sion is the volunteer engineer for the local 
“Hospital Radio’. Although operated by 
amateurs this service manages to maintain 
impressively high operating standards. 

At present a new studio is being con- 
structed at some distance from their exist- 
ing one and for a while they will be oper- 
ating these simultaneously, often with a 
D.J. working in both. To make this possi- 
ble a number of signalling channels are 
required for functions such as indicating 
when a microphone is in use. Security 
monitoring channels are also needed since 
the original studio is housed in a 
“Portacabin” and has suffered from 
attempted break-ins. 

The request, then, was for the provision of 
sixteen “on-off” signalling channels to oper- 
ate through a single circuit from the hospi- 
tal’s internal telephone system. Plus, the 
icing on the designer’s cake, it was required 
to operate simultaneously in both directions. 


360 


TAKE YOUR PIC 


Initial thoughts were that the task could 
be carried out easily with a suitably pro- 
grammed PIC. Whilst the programming 
proved far from easy, it eventually resulted 
in the extremely versatile system 
described here. 

It can operate to the original specifica- 
tion with sixteen channels in each direc- 
tion through a circuit capable only of 
handling low-level audio signals, but, as 
described, it can also be used in several 
other ways to suit less demanding applica- 
tions. It can have either eight or sixteen 
channels, in one or both directions, and in 
some cases the Transmitter may be 





The 
Transmitter board. 


te 


powered through the signalling wires 
which can sometimes be very useful. 
Later upgrading of a system is also sim- 
ple, as the second eight channels can be 
added by simply plugging in extra PICs. 
This is a project offering lots of possible 
options for tailoring the configuration to 
suit the individual constructor’s needs. 


SENDING A SIGNAL 


The method of signal transmission used 
is relatively simple. A total of sixteen 
“clock”’ pulses are sent and for each there 
is a following “signal” pulse if the associ- 
ated input is active. Part of the resulting 
waveform is shown in Fig.1. 





ate = 
ts ae poe zs 3 a 


three modules: Receiver board; Interface (next month) and, foreground, 


Everyday Practical Electronics, May 2000 








It can be seen that the pulses are nega- 
tive-going, with a positive quiescent state 
which allows the signalling line to serve as 
the transmitter power supply if required. 
The basic timing of each pulse is 0-Sms 
low, 0-5ms high, so that if all the switches 
are active the sequence becomes a burst of 
1kHz tone, a suitable frequency for trans- 
mission through an audio circuit. 

Squarewaves with a_ peak-to-peak 
amplitude of 5V are not suitable for tele- 
phone circuits however, as stray coupling 
into adjacent circuits in the cables is likely 
to cause interference to other users. The 
original intention was to “smooth” and 
attenuate the waveform with passive low- 
pass filtering and restore it at the far end 
with a comparator but this idea failed since 
telephone circuits usually carry only a.c. 
signals due to coupling transformers and 
capacitors. 

The average d.c. content of the wave- 
form produced by this project varies with 
the number of active inputs and the result- 
ing variation of the average level at the far 
end of an a.c. coupled circuit made it 
impossible to adjust the comparator for 
reliable operation. A solution was eventu- 
ally found for this problem, the principle 
of which is shown in Fig.2. 


CLOCK DATA 
PULSE PULSE 


INPUT INPUT 
OFF ACTIVE 


OUTPUT 


(A) 





Fig.2. Waveform generation. 


Two outputs from the PIC (RA2 and 
RA3) are connected through a pair of 1 
kilohm (1k) resistors and the output is 
taken from. their junction. The quiescent 
state consists of one output high (positive) 
and one low (negative) so that the output is 
half the supply voltage. A “signal pulse”’ 
consists of making both outputs low, fol- 
lowed by a return to the quiescent state, 
then both outputs high, then back to one 
high, one low. 

This results in the waveform shown at 
Fig.2a, which is much better for transmis- 
sion through an a.c. circuit. Furthermore, if 
the “low” and “high” states occupy around 
61 per cent of the total period the energy 
content will be similar to that of a cycle of 
sinewave. When passed through a suitable 
low-pass filter this produces a very good 
approximation of a sinewave as shown in 
Fig.2b, far more suited to telephone circuits. 

In passing, it’s worth mentioning that 
with a 5V supply the current “wasted” by 
the two resistors in the quiescent state is 


Everyday Practical Electronics, May 2000 


INITIALISE: 
ALL PORT B AS INPUT 
WITH WEAK PULL-UPS ON 


DELAY - 5ms OR 10m 


HAS LINE BEEN 
INACTIVE FOR MORE 
THAN 1:8ms? 


MUTE THE LOCAL RECEIVER 


GET IC2s INPUT STATES 
AND STORE IN REGISTER SW2 


GET OWN INPUT STATES AND 
STORE IN REGISTER SW1 


TRANSMIT CLOCK PULSE fF 


IS FIRST INPUT 
STATE LOW? 


DELAY FOR 
DURATION 
OF PULSE 


TRANSMIT PULSE 


Fig.3. Flow diagram for the first 
Transmitter PIC, IC. 


only 2-5mA as they present a series resis- 
tance of 2 kilohms, whilst the output 
impedance is only 500 ohms as for this 
they are effectively in parallel. 


BI-DIRECTIONAL 
OPERATION 


Achieving bi-directional operation was 
more difficult. In telephony there are 
“two-to-four-wire’’ converter circuits 
which split the conventional two wires into 
separate transmit and receive pairs. They 
work by coupling the circuit to the receiv- 
er through an impedance of some kind, 
often just a resistor, and injecting an 
inverted form of the locally transmitted 
signal into the receiver to cancel the bit of 
it that comes through this impedance. 

Success with this type of circuit 
assumes that the transmission path will 
have a known and constant impedance, 
both resistive and reactive, and attempts to 
use it with the proposed telephone circuit 
failed miserably. Eventually a software 
solution was found in which each trans- 
mitter checks the line for silence before 
transmitting and mutes the local receiver 
before doing so. Two such transmitters can 
be made to synchronise to each other and 
take turns to transmit. 

The PIC16F84 can have internal “weak 
pull-up”’ resistors applied to the eight bits 
of port B when these are configured as 
inputs, removing the necessity to provide 
them externally. Each input can then be as 
simple as just a switch pulling it to ground 
if required. 


INITIALISE: 
PORT A BIT 2 INPUT 
ALL PORT B AS INPUT 
WITH WEAK PULL-UPS ON 


IS PORT A 
BIT 2 LOW? 


GET PORT B STATES 
STORE IN FILE SW1 


IS PORT A 
BIT 2 HIGH? 


MAKE PORT A BIT 2 OUTPUT 


SET PORT ABIT 2 HIGH 


IS FIRST BIT 
OF SW1 LOW? 


SET PORT ABIT 2 LOW 


DELAY FOR 100yus 


REPEAT FOR REMAINING 
SEVEN BITS OF SW1 


MAKE PORT A BIT 2 AN INPUT 





Fig.4. Flow diagram for the second 
Transmitter PIC, IC2. 


A single PIC can only provide eight 
such inputs however, and this project 
required sixteen. Since these i.c.s are now 
available at a cost of less than £2 from 
some suppliers, the quickest and cheapest 
way to obtain a further eight inputs is from 
a second PIC which transmits its inputs 
serially to the first upon request. 


SOFTWARE 
OPERATION 


An outline of the software operation for 
the first PIC, IC1, in the Transmitter cir- 
cuit is shown in the flow diagram Fig.3. 
The initial setting up includes configuring 


_all of port B as inputs. with active weak 


pull-ups. 

This is followed by a brief delay. It is 
unlikely but quite possible that both trans- 
mitters in a bi-directional system might 
check the line, find it inactive and transmit 
together in perfect synchronisation. The 
use of a slightly different delay in each 
transmitter will quickly break such a pat- 
tern to ensure correct operation. Five and 
ten milliseconds are the values used for 
this. 

Following the delay the PIC monitors 
the line for a period of inactivity greater 
than 1-8ms, after which it mutes the input 
to the local receiver, collects the input 
states from the second PIC, IC2, and stores 
them in a register named SW2, and then 
stores its own input states in register SW1. 
It then transmits the first clock “pulse”’ as 
described earlier and checks the first bit of 
SW1. If this is clear, corresponding to an 


361 


active input, a second pulse is transmitted. 
If it is set, the input was inactive so a delay 
lasting the period of a pulse is called. 

This action is repeated for the remaining 
seven bits of SW1 followed by the eight bits 
of SW2, the whole process taking precisely 
32ms. After this the program returns to the 
start and the entire sequence is repeated. 

A flow diagram of the Transmitter soft- 
ware for IC2 is shown in Fig.4. 





Fig.5. Communication between two 
PICs. 


x ou START 








INITIALISE 
ss ALLPORT BAS OUTPUT 


go” \S INPUT TO 
- PORTA 
Ma BIT 2 Low? 


fs CLEAR INPUT FILES 
ff swi and sw2 





WAT 1008 


¥ IS INPUT TO 
<< PORT A 
MBIT 2 LOW? 


| walt 500us 


IS INPUT TO 
4 PORT A 
QL BIT 2 HIGH? 


IS INPUT TO 
a BIT 2 HIGH? 


| | seTFIRST BIT OF Swi 


fs wart ims 


REPEAT FOR REMAINING SEVEN BITS 
OF SW1 AND EIGHT BITS OF SW2 





IS PORT A 
BIT 4 LOW? 


Fig.6. Flow diagram for the Receiver. 


362 





PIC-TO-PIC 


From time to time readers have asked 
how communication between PICs can be 
achieved so a detailed description of the 
method used may be helpful. In this circuit 
two PIC connections (RAI and RA2) are 
linked as shown in Fig.5. A 1k resistor is 
used in case both pins become outputs 
simultaneously, although this should never 
be the case. 

Initially, both connections are config- 
ured as inputs and the 10k resistor pulls 
them both high. When ICI requires data 
from IC2 it’s pin becomes an output and is 
pulsed low for about 400us before return- 
ing to the input state. 

Meanwhile, IC2 has been waiting for 
the low pulse. On seeing this it stores its 
input states in a register and waits for the 
input to return to the high state. When this 
happens it makes its pin an output and 
sends the eight input states serially at 
intervals of 100us. Following this the pin 
returns to the input state and the program 
returns to the start to wait for the next 
pulse from IC1. 

In the meanatime, 50us after restoring 
its connection to input, IC1 commences 
taking eight readings from it at 100us 


- intervals and storing the results in register 


SW2. The whole process takes just over a 
millisecond and is easy to implement, both 
in hardware and software. This is serial 
communication at its simplest and more 
sophisticated methods are obviously pos- 
sible but it provides a starting point for 
anyone wanting to connect two or more 
PICs together. 

One advantage of this method is that for 
eight-channel operation IC2 can be omit- 
ted. IC1 will still request the information 
but will “see’’ eight inactive inputs as each 
time it reads the pin it will see a high state 
set by the 10k resistor. 


RECEIVER SOFTWARE 


Continuing with the Receiver, the flow 
diagram for this is shown in Fig.6. The 
program begins by looking for a falling 
edge in the input signal from the line. 


When it locates one it clears the two input. 


registers named SW1 and SW2 which will 
contain the sixteen switch states. 

It then waits for 100us, which should 
take it into the low portion of a pulse if this 
was the origin of the edge. It checks the 
input is still low, if not it returns to the pro- 
gram start. Otherwise, it waits for 500us 
and checks that the input is now high, as it 
will be if a pulse is present. Again, if it 
isn’t the program returns to the start. 

After another 500us, which takes it to 
the point where the input will be low or 
high depending on the input state being 
transmitted, it samples the state of the 
line and stores it in the first bit of regis- 
ter SW1. A further delay of Ims takes it 
to the next clock pulse, where the 
process is repeated until all sixteen puls- 
es have been checked and their associat- 
ed data bits read. 

Both low and high states of all sixteen 
clock pulses are checked and if any are 
missing the program immediately returns 
to the start. This provides rapid synchroni- 
sation to the transmitter and good protec- 
tion against data corruption as a complete 
valid sequence must be received before 
output takes place. 


Assuming a complete sequence is 
received, the program now checks the 
input to port A bit 4. This is wired “high” 
for IC1 and “low” for IC2, so the PIC 
knows which socket it is in and sends the 
appropriate eight bits of data to port B, 
SW1 in the case of IC1 and SW2 for IC2. 

In contrast to the Transmitter there is no 
communication between the two i.c.s 
which both simply check and store all six- 
teen bits and output the appropriate set. 
This allows them to use identical software 
and, as with the Transmitter, if just eight 
channels are required the second i.c. can 
be simply omitted. 

An examination of the software of this 
project will reveal that it is written in 
straightforward “top-down” style with 
most repetitive operations simply repeated 
the appropriate number of times in prefer- 
ence to using loop techniques. This tends 
to improve reliability and is easy to follow, 
even though it is more tedious to write. 


TRANSMITTER 
CIRCUIT 


As with many PIC projects, the circuits 
are relatively simple as so much of the 
work is done by the software. The only 
complexity is in the Transmitter where the 
various methods of use make some of the 
components optional. 

These options will be explained in more 
detail next month. For now the simplest 
method will be described so that construc- 
tion and testing can be carried out. 

The full circuit diagram of the 
Transmitter is shown in Fig.7. The two 
16F84 PICs, IC1 and IC2, share a common 
clock using the oscillator of IC1 with a 
4MHz crystal X1 and capacitors Cl and 
C2. 

Both IC1 and [C2 have all eight inputs 
of port B pulled high internally so these 
are simply brought out to pins to which 
external connections can be made. The 
communication between them is through 
resistor R7 with pull-up resistor R8. A dig- 
ital output is taken from IC1 port A bit 2 
(at pin 1), which is normally high and goes 
low for clock and data pulses. 

The sensing and muting function, only 
required for synchronised bi-directional 
use, is performed with port A bit 1 (at pin 
18) and operates as follows. When used in 
this way the signal is coupled to the local 
receiver through a 10k resistor, and the 
sense/mute pin is also connected to the 
receiver side of this resistor. 

Initially it is an input, and listens for a 
continuous “high”’ signal to confirm that 
the other transmitter is not sending. Once 
this is detected it is converted to an output 
and set high for the duration of transmis- 
sion, so the local receiver effectively sees 
a continuous inactive line. Where this 
facility is not required, resistor R2 holds 
this pin high so that transmission will take 
place anyway. 

Other optional bits are resistors R3 and 
R4 which are only required if the unit is 
used with the Interface circuit to be 
described next month, and resistors R1, 
RS, transistor TR1 and diode D1, are need- 
ed if it is to be powered through a 2-wire 
connection from the distant Receiver. 

The principle here is that one of the two 
wires is a common ground (OV), or nega- 
tive, whilst the other is energised from 


Everyday Practical Electronics, May 2000 


IC1 


PIC16F84 


IC2 


PIC16F84 





Fig.7. Full circuit diagram for the Transmitter section. Note the items marked with an asterisk are optional — see text. 


+5V through a 220 ohm resistor (an option 
in the Receiver) and charges capacitor C4 
via diode D1 whilst the line is high. Then 
C4 supplies the circuit whilst the line is 
pulled low for pulses by transistor TR1. 
Finally, there is an optional on-board 
5V supply regulator, IC3. In most cases 
the Transmitter will be supplied with +5V 
from a Receiver, either local for a bi-direc- 
tional system or remote. However, if an 
application requires that it should be self- 
powered for any reason, regulator IC3 can 
be fitted together with input decoupling 
capacitors C6 and C7. In most cases these 
three components will not be needed. 


+5V OUTPUT 


MCLR 
IC1 


PIC16F84 RA4 


Also, of course, where only eight channels 
are needed IC2 may be omitted. 


RECEIVER CIRCUIT 


The Receiver circuit diagram shown in 
Fig.8 is even simpler. As with the 
Transmitter, the two PIC16F84s, IC1 and 
IC2, share a common 4MHz crystal clock. 
However, there is no communication 
between them. Instead the input signal is 
connected to RA2 (at pin 1) of both PICs. 

Each of the sixteen outputs is provided 
with a resistor supplying an l.e.d (light- 
emitting diode). These can be omitted if 
not required although they are useful when 


VDD 


MCLR 


IC2 


Rp7 PICt6FS4 


testing. For clarity only one resistor and 
one l.e.d. is shown for each i.c. in Fig.8, 
since the others are identical. 

The supply regulator IC3 is a robust 1A 
type mounted on a small heatsink as is has 
to supply the l.e.d.s and probably also 
some output circuits and a Transmitter. 
The only optional component is resistor 
R10 which is needed if 2-wire operation 
with the Transmitter powered from the 
line is intended. 


CONSTRUCTION 


Construction of this project is 
straightforward. The Transmitter and 





Fig.8. Complete circuit diagram for the Receiver section of the Multi-Channel Transmission System. 


Everyday Practical Electronics, May 2000 


363 


Receiver circuits, that make up the 
Multi-channel Transmission System, are 
both built up on single-sided printed cir- 
cuit boards (p.c.b.s). These boards are 
available from the EPE PCB Service, 
codes 264 (Trans.) and 265 (Rec.). The 
Interface p.c.b. (next month) is also 
available, code 266. 

Starting with the Receiver all the com- 
ponents except resistor R10, just above 
IC1, should be fitted as shown in Fig.9. 
The use of d.i.l. sockets is recommended 
for the two PICs, IC1 and IC2. 

Solder pins are suggested for the exter- 
nal connections as these will then be more 
robust and can be made from the compo- 
nent side of the board. A degree of force is 


sometimes required to insert such pins so 
it may be best to fit them first. 

The l.e.d.s, which should be 2mA types, 
and their associated resistors are optional. 
Where fitted it is not too difficult to bend 
their leads in the required manner, and a 
little “Blu-Tack’’ may be helpful for hold- 
ing them in position during soldering. 

Not mentioned so far is the plug PL1. A 
requirement for the original application 
was a means of rapid connection and 
removal for testing and service purposes 
so 20-way IDC header plugs were includ- 
ed in the design. These are retained in this 
project but can be omitted if not required. 

The two PICs should not be inserted yet. 
An initial test is to supply the completed 


OV (GND) 


wish — see text. 


Resistors 
R1 to R8& 
R11 to 


R9,R19 


Capacitors 
C1, C2, 
C3, C5, 


Receiver board with +9V to +12V which 
should result in a supply current of about 
4-8mA whilst the regulated output of +5V 
should be available from the solder pin, 
marked +5V, just above IC1. 


TRANSMITTER 


If the above test is satisfactory construc- 
tion can continue with the Transmitter 
p.c.b., the component layout, together with 
a full size copper foil master, is shown in 
Fig.10. All the optional components 
should be omitted at this stage and the two 
PICs should not be inserted. 

Once the board has been completed, it is 
worth checking initially by powering it with 
a 5V supply taken from the Receiver. It 





Complete Receiver module, including the I.e.d.s. The |.e.d.s, 
together with their associated resistors, can be omitted if you 


COMPONENTS 


RECEIVER 


R18 68022 (16 off) 

4k7 (2 off) 
*R10 2202 

All 0-6W 1% metal film type 


22p resin-dipped ceramic (2 off) 
100n resin-dipped ceramic (3 off) 
C4 10u radial elect. 63V 

C7, 470u radial elect. 25V 


Semiconductors 
D1toD16 red |.e.d., 2mA type (16 off) 
IC1, IC2 PIC16F84 pre-programmed microcontroller 
(2 off) 
IC3 7805 5V 1A voltage regulator. 


Miscellaneous: 
X1 4M#z crystal 
PL1 20-way IDC header plug 


_ Printed circuit board available from the EPE PCB Service, 
code 265 (Rec.); 18-pin d.i.l. socket (2 off); small heatsink for 
IC3; multistrand connecting wire; solder pins; solder etc. 

Note: Resistor R10, marked with an asterisk, is optional — 
see text. 





Vo} e) ge) em Orel) | 
Guidance Only 


Fig.9. Receiver printed circuit board component layout and 
full size copper foil master pattern. 





364 Everyday Practical Electronics, May 2000 


COMPONENTS 


TRANSMITTER 
Resistors 


ik(30f) TALK 
R 10k 
All 0-6W 1% metal film 


Capacitors 
C1, C2, 22p resin-dipped 
ceramic (2 off) 
C3, C5, 100n resin-dipped 
*C6 ceramic (3 off) 
C4, 10u radial elect. 63V 
*C7 100u radial elect. 25V 


Semiconductors 
1N4148 signal diode 
"TAT; BC184L npn transistor 
IC1,1C2, PIC16F84 
pre-programmed 
microcontroller (2 off) 
IC3, 78L05 5V 100mA 
voltage regulator. 


Miscellaneous 
X1 4MHz crystal 
PL1 20-way IDC header plug 


Printed circuit board available from 
the EPEPCB Service, code 264 
(Trans.); 18-pin d.i.|. socket (2 off); solder 
pins; multistrand connecting wire; solder 
etc. 

Note: All components marked with an 
asterisk (*) are optional — see text. 


£16 


should draw virtually no current at all since 
the only components bridging the supply are 
the three decoupling capacitors. However, 
short circuits do occasionally occur in con- 
struction and electrolytics have been known 
to be fitted the wrong way round! 


TESTING 

If all seems well IC1, programmed with 
TXIC1_5 (5ms delay) or TXIC1_10 
(10ms delay) software, can be inserted. 
This should raise the supply current to 
about 2mA and the average voltage mea- 
sured with a meter at Output 2 should be 
about 4V, indicating that IC1 is operating 
and transmitting an appropriate pulse 
sequence. 

Next, a PIC programmed with receiver 
RX software should be inserted into the 
Receiver board at IC1 position and a con- 
nection made from Output 2 of the 
Transmitter to “IN” of the Receiver as 
shown in Fig.11. Connecting any of the 
first eight inputs (1 to 8) to ground (OV) 
should now illuminate the corresponding 
output l.e.d.s on the Receiver or take the 
appropriate outputs high if the l.e.d.s are 

not fitted. 

Finally, if all sixteen channels are 
required, a second PIC with RX software 
can be fitted to the Receiver and one with 
TXIC2 software to the transmitter, after 
which the remaining eight channels (9 to 
16) can be tested. The two boards are now 
operational and ready for use. 


Vo) eo) (eo) mm Orel) | 
Guidance Only 





Everyday Practical Electronics, May 2000 


OUTPUT 3 


SENSE 
‘/MUTE 


OUTPUT 2 


OUTPUT 1 


COMMON 


+5 VOLTS 


GND (OV) 


+12 VOLTS 


16 COMMON 





Fig.10. Printed circuit board topside component layout and full size undersided 
copper foil master pattern for the Transmitter. 


RESOURCES 

Software for the Multi-Channel 
Transmission System Transmitter and 
Receiver modules is available on a PC- 
compatible 3:5 inch disk from the 
Editorial Office, code EPE Disk 3 (a 
nominal handling charge is levied). 
Alternatively, it may be downloaed Free 
from the EPE Web site. | 

Ready-programmed PICs are also avail- 
able and full details, including the above 


TRANSMITTER 


OUTPUT 3 
SENSE/MUTE 
OUTPUT 2 
OUTPUT 1 
COMMON 


options, can be found in the Shoptalk page 
in this issue. 

Next Month: Details of the various 
ways in which these units can be used will 
be given, together with the construction of 
an Interface board for use with internal 
telephone circuits or similar long lines. 
This is effective in reducing or eliminating 
the radiated interference sometimes 
caused by high-level digital signals in 
transmission circuits. 


SUPPLY 
+12V 
OV 


Fig.11. Test set-up for checking out the two p.c.b.s. 





365 








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VT201 54 minutes. Part One; D.C. Circuits. 
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Everyday Practical Electronics, May 2000 


John Becker addresses some 


of the general points readers 
have raised. Have you anything 
interesting to say? 
Drop us a line! 


WIN A DIGITAL 
MULTIMETER 


A 31/5 digit pocket-sized I.c.d. multime- 


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Every month we will give a Digital 
Multimeter to the author of the best 
Readout letter. 





exceeded a critical limit # 


Sci oscillated 


and, as it was usually coupled to the aerial, # 


- became a transmitter. This had di 
sequences as many receivers il 
- hood would be swamp 


_ those with critically adinsted reaction controls Me 


_ also burst into oscillation. 


The BBC Handbook for 1929 ho warnings - 


about the problem, leaflets were issued by the 


Post Office (then the wireless licensing : 


authority) and cartoons on the su 
appeared in- Punch. (In_ 3929 the 
Handbook carried circt 


potential listeners to. construct recenes). - 


_ People were branded as bad ap ie if age ay 
- were suspected of os¢ cing ng. 
_anrf. amplifier stage 


_ the oscillating circuit was no longer rdiecly 


Ot  Tecreadi to the aerial. 


by the radiation and . a : 
of the Titanic. Possibly there is a copy. at 
oe Amberley. es 


: ae advertising oe t 


A book | worth reading _ is Sure 


: Regenerative Receivers by JR. ‘Whitehead, S 
. Cen Press, 


‘1950, (Dr : 
man so the book is 
rds aircraft equipment.) 
Guy s ole ie Patent Atto 
. Plaistow, Bilinges 


oe nk you Gu, most interesting informa 


nak the: posted were. Mone on and “si 
| bandwidth limitation was a aug advan: A 


= anh Seniiation was 5 ewfieaat 
_ The oscillation caused by positi 
_ back in circuits using “leaky grid’’ ¢ 


4 was rectified Ma the aed aavng the fe valve : like-mi 


PIC LOCATIONS 0 TO 3 

Dear EPE, 

PIC Toolkit Mk 2 (May-June ’99) forces the 
addition of a JMP to location 0005 at the Reset 
Vector and loads any HEX file from location 
$0004 onwards, despite the HEX file address 
information. Similarly, the decode routine 
used during disassembly totally ignores ANY 
CODE in locations $0000 to $0003 inclusive. 

Note that it is common for an interrupt routine 
code block to start at 0004 and continue through 
0005 until the end of the routine. It is also com- 
mon for other code such as Subroutines to start 
at 0005, the Reset vector being a JMP to the rel- 
evant location. 

Peter Balcombe, 
via the Net 


Everyday Practical Electronics, May 2000 


S and you can ‘find for ‘vin a about it eae the . 


ev nore in this issue. y yo 


well, at ‘wweradiobygones ‘ 
a lows a to “chat” with 





The reason for Toolkit not allowing pro- 
grammed access to locations O to 3 is historical, 
having adopted the convention used in the 
Simple PIC16C84 Programmer of Feb ’96, as 
designed by Derren Crome. The same question 
was subsequently raised by readers and we have 
replied in various ways since then. The following 
is Derren’s original reply: 

When the PIC is put into programming mode, 
it sets its internal counter to $0000, which is the 
reset vector address. It was decided to have the 
program set this to $0005, which is the begin- 
ning of the program memory address space. 

Addresses $0001 to $0003 are not of use to the 
user. Address $0004 is the interrupt vector which 
is set by the first line in the assembly code. The 
user program starts at $0005. 


PIC16F87x PROBLEMS 


Dear EPE, 

I have been experimenting with the new PICs 
(876 and ’877) and Toolkit Mk2 hardware and 
software, mostly using a 3-2768MHz crystal 
clock rate. 

I have problems with Port C bits 0 and 1 as 
outputs at relatively fast state changes. With 
“slow” switching, e.g. using your TKTEST4 
program, all seems OK. However, if I halve the 
COUNTs to speed up switching, the bit CO 
Square wave becomes erratic and the bit Cl 
square wave gets somewhat noisy. If I output $00 
and $FF to all ports in a rapid loop, these two bits 
are a mess, while all other bits, on Port C (and 


Ports A, B, D and E) are OK. 


I am setting PAGEO and PAGE! OK using 
both bits RPO and RP1, and I have even tried 
ensuring that TIMER] is off by setting file T1 
CON to all zeros. I assume the problem is some- 
thing to do with the multi-functional nature of 
these two bits, and most likely to do with 
TIMER1. 

I have examined the PIC datasheet and recent 
issues of EPE but I am foxed. I note in the 8- 
Channel Data Logger (Aug-Sep ’99), that you use 
these two bits for push-button input, which is slow 
(and not output), so maybe you have not seen this 
problem yet. Can you offer any help, please? 

TK2 is great! Thanks for adding recognition 
of TABs for spaces. You asked for suggestions 
for other facilities: are you able to add two use- 
ful functions to the assembler (functions which 
TASM supports), I think many people would 
find they make for clearer programs: 

(a) simple addition in statements, e.g.: 

HIGHBIT EQU %10000000 

RETLW ‘P’ 

RETLW ‘T’ 

RETLW ‘C’ + HIGHBIT ;end of string ‘x’ of 
total ‘n’ strings 

I use this for a useful l.c.d. text driver, with top 
bit set for end of each string, filtered off before 
displaying. It currently causes an error in TK2. 

(b) Multiple components to a #DEFINE state- 
ment, e.g.: 

EQUs for STATUS, RPO, RP1, then: 

#DEFINE SETRPO BSF STATUS,RPO 

#DEFINE CLRRP1 BCF STATUS,RP1 

#DEFINE PAGE! SETRPO\CLRRP1 etc. (at 
the moment this only codes one statement.) 

Could you please pass on my appreciation to 
all your staff for an excellent magazine and a 
very useful web-site. I find all the PIC stuff 
extremely clear and very useful. 

Incidentally, my first introduction to electronics 
was ETI magazine, back in the mid-seventies. 
Since then I have built RAM and I/O boards and 
data loggers for the NASCOM (Z80), the North 
Star Horizon (Z80 and S100 bus), the dear old BBC 
(6520) and all the IBM PCs from 1981 to date, 
within both my professional work and my hobby. 

Roger D. Redman, via the Net 


I’ve not come up against your Port C problem. 


‘Are you sure that your PIC is fully healthy? I 


have seen erratic waveforms on other devices 
when part of them has died for some reason. Buy 
another PIC and try the program on it. 

Both your TK suggestions seem useful. Thank 
you Roger. Perhaps one day... ! 


369 


PATENTLY DIFFICULT 

Dear EPE, 

I have designed a microprocessor-based PC 
Card for the ISA bus, but no one wants to know. 
I have tried over 40 UK manufacturers that were 
specifically selected to do the job of buying the 
manufacturing rights of my card, and have con- 
tacted a telecoms company here as my card uses 
Distinctive Ring Patterns from them, but not one 
of them has had the decency to reply. 

Are all UK-based inventors of electronic 
devices treated, this pathetic way all the time? Or 
is there someone you know out there who would 
be interested in manufacturing my card? I am 
made to feel that I am insignificant, a has been, a 
nobody. 

You would not believe the amount of E-mail 
and snail-mail I have sent out, but, nothing what- 
soever has come back. I am so depressed with it 
all. I think the question is, after the Patent, what 
now ? 

I would be ever so grateful to you and your 
colleagues if you could publish this and your 
reply, as I feel it would benefit other UK 
Electronics Inventors in the same situation. 

Jim Delaney, Sheffield 


Jim’s plea was E-mailed to our Online Editor, 
Alan, who offered the following extremely prac- 
tical reply: 


I’ve worked on both sides of the desk, both 
designing a wide variety of products as a devel- 
opment manager and also receiving proposals 
from outside designers hoping that my company 
would take on their idea. It happens all the time, 
and it’s surprising how badly presented the appli- 
cant’s case can be. Not every manufacturer 
would be as sympathetic to the aspiring designer 
as I was, so first impressions count, and a crisp 
business-like approach can only help as well as 
setting you above all the other (amateur) appli- 
cations vying for the same spot. 

However, I was one of the few who would 
always spare a little time to look at an external 
idea, but my next problem would be selling the 
merits of the idea to the senior management. If a 
designer couldn’t sell the concept to me, I had no 
hope selling it up the ladder. 

Often designers had no idea of the investments 
needed in tooling, production and distribution 
either. No basic market research, no sales projec- 
tions, no budgeting — a design without such ini- 
tial marketing research really would need to set 
the world alight. James Dyson found out the hard 
way and persevered, now everyone buys his vac- 
uum cleaners (even me!). The Black & Decker 
Lawnraker and their WorkMate bench are two 
more examples of products designed by amateur 
designers. The Bayliss wind-up radio is another. 

In my career in product development, I have 
only come across one really switched-on profes- 
sional-looking designer (a real “ideas man’’) 
who presented a very powerful case, with good 
quality prototypes and lots of ideas that forced us 
to sit up and listen. He was immensely enthusi- 
astic and positive, and had really thought of 
everything and had come up with some very cute 
answers. 

A personal meeting sold us on the concepts. 
He had all the ideas and we were prepared to 
develop the product and tool up for mass pro- 
duction, which is what we did (for a special type 
of tool kit). It would also be true that, sometimes, 
manufacturers just don’t know what they’re 
looking at and are being very short-sighted, so 
you have no hope with such firms. 

Manufacturers usually have their own agenda 
with their own products currently on the drawing 
board (CAD screen anyway), so to take on an 
external design could mean dumping one of their 
own in-house designs. There would need to be a 
very good reason to do that. 

In the case of electronics, there is also the 
development cost involved with making the 
product EMC compatible and gaining CE- 
approval. Maybe the fact it’s an ISA card rather 
than, say, PCI might also detract from it, I could- 
n’t say. I believe that ISA is being phased out in 


370 


the PC2000 spec., though of course ISA slots 
will be around on legacy systems for some time 
to come. 

It’s only worth patenting if you can afford the 
legal costs of fighting an infringement. A pend- 
ing patent enables designers to go with an NDA 
instead and then try to sell All Rights. I think it’s 
not just the treatment of inventors which is the 
problem, more likely it’s the pressure the manu- 
facturers are already under with their own prod- 
uct lines. They get too wrapped up in their own 
problems to want to go looking for more! But a 
forward-thinking and progressive company (e.g. 
Black & Decker) will listen to outside ideas, if 
only to get the feel for an idea that may subse- 
quently be proposed to their competitors. 

You should ask yourself whether it’s worth 
sub-contracting the production yourself, and 
maybe get a small batch made and sell direct if 
you have to (e.g. on a web site). CE approval is 
your next hurdle, then give a few samples away 
and get the market talking about it. If you can 
make a big enough nuisance of yourself in the 
marketplace, it could then be that someone will 
buy the rights. Just make sure you are fully pro- 
tected with design rights. There are plenty of 
good electronic engineers who can CAD up a 
board and polish off its development. 

Try looking at James Dyson’s web site 
(www.dyson.com/co.uk), there used to be an 
inventor’s resource there. There is also an alt. 
newsgroup for inventors where I’m sure you'll 
get more help. Also you could try a local 
University — an example in my case would be the 
new Product Design & Development Centre 
based at the University of Hull, with whom I’m 
working. 

I’m sorry I can’t be of more assistance but 
hope the above helps — good luck! 

Alan Winstanley 


REGEN RECEIVER AND F.E.T.s 

Dear EPE, 

I am writing to you as a subscriber to EPE and 
an electronics construction enthusiast for some 
35 years. First, thank you for the superb series of 
articles on R.F. Design by Raymond Haigh, cul- 
minating in the High Performance Receiver 
(March ’00), which I have decided to construct. 

I am not “new” to construction, having built 
over 23 receivers for short waves over the years, 
designing and producing my own p.c.b.s for 
these receivers. 

It is the power gain of the 2N3819 f.e.t.s used 
in Raymond Haigh’s design that I wish to query. 
The problem is that many component suppliers 
use the same manufacturer for 2N3819s and the 
spread in characteristics of these devices may 
affect the receiver’s performance. In my own 
designs I use BF244 and BF245. Your comments 
are requested. 

John B. Dickinson, Tamworth, Staffs 


John Dickinson gave a lot more information in 
his letter and sent an example 2N3819. We for- 
warded everything to Raymond Haigh, who 
replied: 


Thank you for letting me read Mr Dickinson’s 
interesting and helpful letter. I should be grateful 
if you would thank him for having taken so much 
trouble and for his very kind remarks about my 
recent series of articles. I would offer the follow- 
ing observations: 

He is, of course, quite correct in pointing out 
the wide spread in f.e.t. characteristics. He is also 
correct when he says that the specifications for 
the BF244 and BF245 are tighter than the speci- 
fication for the 2N3819. Referring to the tables 
published in Farnell’s catalogue, the transconduc 
tance spread for the BF244 and BF245 is 3 to 
6-5mA/V, whilst the spread for the 2N3819 is 
slightly greater at 2 to 6-SmA/V. 

Unfortunately, the BF244 and BF245 may not 
be readily available outside Europe, and regard 
must be had to the world-wide circulation of 
EPE. Because of this, I will have to continue 
specifying the ubiquitous 2N3819. 

I have built about six versions of the circuit 


using this transistor as a drain bend detector. 
They all worked well with the component values 
quoted and without any selection of the 
2N3819s. 

I have, however, explored this question. The 
outcome of the trial was as follows: 

(a) Thirty-three 2N3819 transistors were con- 
nected into circuit and provision made for moni- 
toring the audio output voltage. Of these, 23 
performed in a completely satisfactory way, 
three were marginally better than the rest, and 
seven performed badly, or would not work at all, 
unless the detector source resistor was increased 
in value. The transistor kindly supplied by Mr 
Dickinson was one of those which would not 
work at all. 

(b) When the source bias resistor (R5) was 
increased to 15k, all 33 specimens of the 2N3819 
performed in a completely satisfactory way. 
With the source bias resistor increased, several 
specimens of 2SK168, MPF102, TIS14 and J310 
(about twenty transistors in total) all worked well 
in the circuit also. 

(c) The few transistors which were marginally 
better than the rest gave a very slightly higher 
output with the specified 4k7 source resistor. It 
would seem my earlier endeavours to milk the 
last drop of performance from the circuit had 
revealed this. It is unfortunate that I made a 
chance selection of transistors which would 
work with this source bias resistor. Had I not 
done so I would have discovered that the circuit 
would not suit devices at the other extreme of the 
characteristic spread. 

(d) Working and non-working devices in the 
test were distributed across a random selection of 
the products of different manufacturers. 
Presumably, therefore, the problem is primarily 
one of characteristic spreads rather than manu- 
facturing differences. However, as suggested by 
Mr Dickinson, there could well be a tendency for 
some manufacturer’s transistors to drift towards 
a particular extreme of the tolerance range. 

(e) I suggest that the value of TR2 source bias 
resistor, R5, be increased to 15k to ensure that all 
specimens of 2N3819 are operated in the non- 
linear region of their characteristic curve. With 
this value for the source resistor, most other 
j.f.e.t.s, including the 2SK88, MPF102 and J310 
should also work well. 

Raymond Haigh, Doncaster, S. Yorks 


BINARY CONVERSION 

Dear EPE, 

Your Teach-In 2000 Part 6 (Logic gates, 
Binary and Hex) brought to mind a system of 
converting decimal to binary I learnt many years 
ago. 

Dredging through my personal memory-bank 
and with many false starts, the system is to 
divide the number to be converted by 2 continu- 
ously, ignoring any remainder. Every time the 
number is odd, put a dash (—) beside it. If it is 
even put “o’’. The top “—”’ or “o” is the least sig- 
nificant figure and the bottom one most signifi- 
cant. For example, decimal 3353 is converted as 
follows: 

3353 - 
1676 0 
838 o 
419 - 
209 — 
104 o 
52 0 
26 oO 
13 - 
6 o 
a- w 
i. ee 

Turn the paper through 90 degrees so that the 
most significant figure is to the left then read off 
the binary code. Thus decimal 3353 equals 
110100011001 binary. 

This method is probably well-known in the 
“Trade”’ but it might be new to some readers. 

Harry Nairn, Ashtead, Surrey 


It’s certainly new to me as well Harry. It’s a 
form of long division, of course. Many thanks. 


Everyday Practical Electronics, May 2000 





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371 


Everyday Practical Electronics are pleased to be able to offer all readers these 


ELECTRONICS CD-ROMS 


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A 


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Interested in programming PIC microcontrollers? Learn with PiCtutor by John Becker 


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Constructional Project 


TERRY DE VAUX-BALBIRNIE 


Be trigger happy with your outdoor 
security light system. 


ASSIVE infra-red (PIR) lamps, of the 

type which may be bought in any 

DIY store, are now very popular 
with householders. Mounted on an outside 
wall, they may be used to improve securi- 
ty or simply to illuminate dark areas when 
a member of the family passes by. 


JUST PASSING 
THROUGH 


These lamps are designed to switch on 
for a certain time when someone walks in 
the detection field. This extends fan- 
shaped from a “window” in the front of 
the detector. In simple units, the operating 
time is fixed at manufacture. However, it is 
more usual to provide a control which may 
be used to adjust it over a certain range. 

Normally, the lamps operate only when 
the ambient light falls below a certain level 
so that they will not switch on during day- 
light hours. Again, the point at which this 
happens is often adjustable using a control 
on the unit. 

The working part of a PIR lamp is a sen- 
sor which detects the infra-red radiation 
which is naturally emitted by a warm 
body. The detector may be contained in a 
separate unit connected remotely to the 


374 


lamp. In most DIY units, however, it is 
attached to the lamp itself because this 
makes for simpler installation. 

When a warm object moves in the sen- 
sitive zone, a signal is given which, after 
processing, operates a relay and switches 
on a filament bulb. In the larger security- 
type lamp, the bulb will be a halogen unit 
of some 150W to 500W rating. Smaller 
PIR lamps use an ordinary 60W household 
bulb. 


BLOWING IN THE 
WIND 


When the PIR unit is properly installed, 
the lamp does its job well and rarely caus- 
es problems. However, when it is not prop- 
erly set up it may be activated by animals 
such as dogs and cats passing by. 

Any warm object moving in (and espe- 
cially across) the detection field is likely to 
cause the unit to trigger — even warm air 
from a nearby central heating flue. Tree 
branches and other objects moving in the 
wind sometimes activate it — presumably 
because they reflect infra-red from some- 
where else. 

Any cause of false triggering may be 
difficult to track down. It can occur even 


















when the user has taken every precaution 
detailed in the installation guide. After 
supposedly “‘correct’’ setting-up, there 1s 
often a tendency towards occasional false 
triggering. This will require further adjust- 
ment on a “trial and error” basis to elimi- 
nate it completely. 

Most PIR lamps have a “‘test’’ facility 
which enables them to operate in daylight 
and this helps with the initial adjustment 
process. However, it will miss any false 
triggering which happens only occasional- 
ly. There could be considerable difficulty 
when the lamp is mounted in a position 
which cannot be seen from the house. 

Normally, the only way to check for 
correct operation would be to stand out- 
side and watch it for a long period of time! 
Unnecessary operation of the lamp can be 
a nuisance to neighbours as well as 
wasting electricity and reducing the life of 
the bulb. With this PIR Light Checker, 
however, you can leave the monitoring to 
automatic electronics! 


CLOCKED 


This self-contained battery-operated 
unit will automatically monitor a PIR lamp 
over a period of several hours overnight. 
An Le.d. (light-emitting diode) display 
registers the number of times it has been 
triggered, up to nine. If the count exceeds 
this, the display will return to zero but the 
decimal point will light up. This shows the 
“overflow” — that is, a number greater than 
nine. When the unit is switched off then on 
again, the count is reset to zero, ready for 
a further test. 

By adjusting the aim and sensitivity 
control on the lamp (if one exists), re-sit- 
ing and cutting away foliage as necessary, 
any improvement can be easily monitored. 
Multiple causes of false triggering may 
then be eliminated one by one over a peri- 
od of a few days. Note that if the unit is 
used to monitor the lamp overnight, it will 
record an extra count at dawn and this will 
need to be subtracted from the total. 

This circuit is only suitable for use at 
night with the PIR lamp in “normal” 
mode. There must be no other bright 
sources of light nearby which could result 
in false counts. 


BATTERY SAVING 


The circuit is housed in a small plastic 
box. This. has a seven-segment l.e.d. dis- 
play showing through a hole in the lid. 
There are also two switches (see photo- 
graph). One of these is simply an on-off 
switch while the other activates the 


Everyday Practical Electronics, May 2000 


display. This latter switch is operated only when a reading needs 
to be taken and so saves battery power. A hole in the side of the 
box allows light from the lamp being monitored to reach a sensor 
on the printed circuit board (p.c.b.) inside. 

The unit draws power from a 6V battery pack consisting of four 
AA-size alkaline cells. Under standby conditions, the current 
requirement of the prototype unit is some 400uA. 

When the display is operated, the current rises to a value which 
depends on the number being displayed. This is because each digit 
is formed by lighting up the appropriate segments in the display. 
The most current-hungry case is when the number “8” is involved 
(since this uses all seven segments) together with the “over-flow”’ 
decimal point. 

Since each segment and the decimal point require 12mA 
approximately, the total current will be about 100mA. However, 
this will only be needed for a few seconds during each test and, as 
stated earlier, it is the “worst” case. In practice, the battery pack 
should last for at least a year under normal conditions. 


HOW IT WORKS 

The full circuit diagram for the PIR Light Checker’ is shown in 
Fig.1. Power is derived from a 6V battery pack (4 x 1-5V cell) B1 via 
on-off switch S2 and diode D1. The diode prevents possible damage 
if the supply were to be connected in the opposite sense. If this were 
done, the diode would be reverse-biased so no current would flow. 

It will be found that the actual nominal supply voltage is 
5:3V taking into account the forward voltage drop of the diode 
(0-7V approximately). Capacitor C8 charges up almost instant- 
ly and helps to provide a smooth and stable supply. 

The light sensing section of the circuit is centred on IC1 and asso- 
ciated components. The light detector itself is a light-dependent 


COMPONENTS 


56k 
R2 sub-min light-dependent resistor 
(I.d.r.)., dark resistance 5MQ 
approx. (See text) 
470k (2 off) See 


Resistors 
R1 


R3, R4 


eR SHOP 
TALK 
page 


R9 to R11 1M (5 off) 
R8,R19 2M2 (2 off) 
R12 to R18, 
R20 2702 (8 off) 
All 0-25W 5% carbon film, except R2. 


Potentiometer 
VR1 2M2 min. enclosed carbon preset, horiz. 


Capacitors ) 
C1 47n metallised polyester, 2.5mm pitch 
100n metallised polyester, 2.5mm pitch 


100n metallised polyester, 5mm pitch (4 off) 
1u radial elect, 63V. 
220u radial elect, 10V 


Semiconductors 
D1 1N4001 1A 50V rectifier diode 
TR1 2N3903 npn transistor 
IC1 ICL7611 micropower op.amp 
IC2 ICM7556IPD dual CMOS timer 
IC3 40110B decade up/down counter 


Miscellaneous 
x1 7-segment, common cathode, I.e.d. display, 
12-7mm 
$1 min. S.p.s.t. push-to-make or biased toggle switch 
S2 min. s.p.s.t. toggle switch 


Printed circuit board available from the EPE PCB Service, code 
263; 8-pin d.i.l. socket; 14-pin d.i.l. socket; 16-pin d.i.l. socket; 
1-5V AA-size alkaline cell (4 off) and holder; plastic case, 138mm 
x 76mm x 38mm internal; p.c.b. support (2 off); connecting wire; 


solder, etc. 


excluding battery pack 


7. Vo) eo} ce) om Oxel-y 
CTU [oF Talor-m Ola iY 





Everyday Practical Electronics, May 2000 


GND 


5 
E 
a 
Lo) 
es 


EN EN 





Fig.1. Complete circuit diagram for the PIR Light Checker. 


375 


resistor (I.d.r.), R2. The resistance of this 
device rises as the illumination of its sensi- 
tive surface falls. 

The l.d.r. works in conjunction with 
fixed resistor R1 and preset potentiometer 
VRI1 to form a potential divider connected 
across the supply. Thus, as the resistance 
of the I.d.r. increases, the voltage across it 
will rise. This voltage will therefore be 
greater when the I.d.r. is dark than when it 
is illuminated. The actual “dark” and 
“light” voltages can be varied within cer- 
tain limits by adjusting VR1. 

The voltage appearing across the I.d.r. is 
applied to the inverting input (pin 2) of 
operational amplifier (op.amp) IC1. The 
non-inverting input (pin 3) is connected to 
the mid-point of a further potential divider 
consisting of fixed resistors R3 and R4. 
Since these have the same value, the volt- 
age here will be equal to one-half that of 
the supply — that is, 2-6V approximately. 


A BIT DIM 


With preset VR1 suitably adjusted, 


under dim conditions the voltage at the’ 


op.amp inverting input will exceed that at 
the non-inverting one, so the device will be 
off with the output (pin 6) low. When the 
l.d.r. is sufficiently illuminated, the condi- 
tions will reverse with the inverting input 
voltage falling below the non-inverting 
one. The op.amp will then switch on and 
output pin 6 will go high. Resistor R5 
applies some positive feedback to the sys- 
tem which sharpens the switching action at 
the critical light level. 

Transistor TR1 inverts the output state of 
the op.amp. When the output is high, cur- 
rent flows into TR1 base (b) through cur- 
rent-limiting resistor R6. This switches the 
transistor on and its collector (c) goes low. 
When the op.amp output is low, no current 
will enter the base and the transistor will 
remain off. The collector will then take on a 
high logic state via load resistor R7. The 
state of the collector is therefore in the 
opposite sense to that of the op.amp output. 


MONOSTABLE 


Transistor TR1’s collector is connected 
to the trigger input (pin 6) of a monostable 
based on IC2a, which is one half of dual 
integrated circuit timer, [C2. 

When TRI collector goes from high to 
low (that is, the I.d.r. is illuminated), the 
trigger input receives a low pulse through 

capacitor C1. The monostable output (pin 

5) then goes high for a time dependent on 
the values of resistor R10 and capacitor 
C4. With the values specified, the timed 
period is 0-1s, approximately. 

While the op.amp output remains low 
(the I.d.r. dimly illuminated), the high state 
of TR1’s collector has no effect. In fact, in 
the absence of a low pulse, [C2a trigger 
input is kept high through resistor R9 and 
this prevents possible false triggering. 
Capacitor C3 decouples this section of the 
circuit. 

At the instant of powering-up, capacitor 
C2 keeps IC2a reset input (pin 4) low and 
this disables the monostable. The capaci- 
tor soon charges up through resistor R8, 
pin 4 goes high and the monostable then 
functions normally. The purpose of this is 
to allow time for the power supply to set- 
tle down to a steady state since, otherwise, 
the monostable could self-trigger and a 
false count would be registered. 


376 





Fig.2. The seven segments of the dis- 
play are indentified by letters (a to g). 


COUNTING PULSES 


When the monostable outputs a pulse, 
this is transferred to the “clock up” input 
(pin 9) of counter and 7-segment driver 
IC3. This registers the number of pulses 


received and decodes the result into a form 


which will directly drive the 7-segment 
l.e.d. display X1. 

The seven segments of the l.e.d. display 
are identified by letters a to g as shown in 
Fig.2. Note that the unit used in this circuit 
is a common cathode type. In this, all the 
l.e.d. cathodes (including that of the deci- 
mal point) are connected together and 
taken to pin 3 (GND). 

Each segment requires a current-limit- 
ing resistor (R12 to R18) as with a con- 
ventional l.e.d. With the value specified, 
each one will draw 12mA approximately 
when using a new battery. 

The display, however, will do nothing 
until push-to-make “Display”’ switch S1 is 


operated. This allows current to flow 
through any active segments and complete 
the circuit via pin 3 to the OV line. With S1 
in the off state, no current is drawn by the 
display. 

At the instant of switching on, IC3’s 
reset input (pin 5) is maintained in a high 
state while capacitor C5 charges up 
through R11. During this time, the counter 
is reset so the display will always begin at 
zero. After a short time, C5 will charge 
sufficiently, pin 5 will go low and the 
counter will function normally. Capacitor 
C6 decouples this section of the circuit. 

When the count passes from 9 to 0, 
IC3’s carry output, pin 10, goes low 
momentarily. This would normally be used 
to feed the clock input of a second 
counter/driver i.c. and a further display 
would provide a readout up to 99. 

To save costs only one counter and dis- 
play are used in this circuit. However, the 
low pulse provides the “overflow”’ indica- 
tion by operating the decimal point. This 
uses IC2b (the second section of dual 
timer IC2). It is configured as a form of 
latch by making the threshold and dis- 
charge inputs (pin 12 and pin 13) low. 

Thus, once triggered by making pin 8 
low for an instant, the output (pin 9) will 
go high and remain high until the supply is 
interrupted. The output feeds the decimal 
point via curvent-limiting resistor R20. 


CONSTRUCTION 

The PIR Light Checker circuit is built 
on a single-sided printed circuit board 
(p.c.b.). The topside component layout and 
underside copper foil master pattern are 
shown in Fig.3. This board is available 
from the EPE PCB Service, code 263. 

In the prototype, one corner of the p.c.b. 
had to be cut off to avoid a bush in the box, 





The p.c.b. removed from the case lid to show wiring to the display and on/off 
toggle switches. The display switch needs to be a “biased” off type. Note the 
7-segment display chip must be the highest component on the p.c.b. 


Everyday Practical Electronics, May 2000 


see photograph. Begin construction by 
drilling the two fixing holes and soldering 
the three i.c. sockets and four link wires 
into place. 

Omit display X1 for the moment. Note 
that it must end up as the highest compo- 
nent on the p.c.b. Checks should be made 
at intervals during the other assembly by 
inserting it into its holes in the p.c.b. (but 
do not solder it yet). | 

Follow with all resistors (including pre- 
set VR1 but not I.d.r. R2). Note that many 
of the resistors are mounted vertically (see 
photo). 

Solder electrolytic capacitors C5 and 
C8 in position taking care over their polar- 
ity. If they are not of the sub-miniature 
type, it may be necessary to mount them 
flat on the p.c.b. so that they will not be 
higher than the display. 





Close-up of circuit board showing the 
leads of the l.d.r. carefully bent at 
right-angles to the p.c.b. to align with 
‘light window” in side of case. 


Cut the I.d.r. leads to a length of about 
10mm and solder them to the R2 position 
on the p.c.b. Bend them through right- 
angles so that the “window’”’ points to the 
left. Note that the specified |.d.r. is a sub- 
miniature type having a body diameter of 
Smm approximately. If one of these is not 
readily available, it would be possible to 
use a standard ORP12 device, but some 
adjustment may be needed to the end leads 
to prevent the body getting in the way of 
anything else. 

Add the diode and transistor to the 
p.c.b., taking care over their orientation. 
The flat face of transistor TR1 should face 
to the right as viewed in Fig.3. 

Solder the display to the p.c.b. (with the 
decimal point at bottom right, as shown in 
the photo) using minimum heat from the 
soldering iron to prevent possible damage. 

Solder 10cm pieces of light-duty strand- 
ed connecting wire to the points labelled 
+6V and S1. Solder the negative (black) 
battery connector lead to the OV point. 
Adjust VR1 to approximately mid-track 
position. 


TESTING 
Immediately before handling the pins of 
IC1, IC2 and IC3, touch something which 
is “earthed” (such as a metal water tap). 
This will remove any static charge which 
may be present on the body. Insert the i.c.s 
in their sockets with the correct orientation. 


Everyday Practical Electronics, May 2000 


Vp PRO DR SIE. Ca ee git b 
4 Ys Get RRS 


la 



























BATTERY —VE 





BATTERY +VE 






Fig.3. Printed circuit board component layout, full size underside copper foil master 
pattern and wiring to the two off-board switches. 


Before mounting the p.c.b. in its case, 
perform a basic check so that any minor 
problems may be resolved more easily. 

To do this, bare the end few millimetres 
of the wires for display switch S1 and con- 
nect them together. Similarly, bare the end 
of the +6V wire. Insert the cells for battery 
B1 into their holder and apply the connec- 
tor. Twist the battery connector positive 
(red) wire to the +6V wire from the p.c.b. 

The display should light up and read zero. 
The decimal point should also be off. If it 


‘ shows some other number, or the decimal 


point is on, the connection was probably not 





done “cleanly”, so disconnect the battery, 
wait for 30 seconds and try again! 

Cover the l.d.r. with the hand then 
remove it to allow light to reach its win- 
dow. The display should advance to a 
count of 1. If this does not work, it is like- 
ly that the I.d.r. has not been properly cov- 
ered. Try working in a dark cupboard and 
open the door slightly to give the flash of 
light. If this still does not work, re-adjust 
preset VR1 and try again. 

By allowing repeated flashes of light to 
reach the l.d.r., the counter should incre- 
ment to 9 and the next flash should return 


% 





Layout of components on the completed circuit board. Note, one corner of the 


board has been trimmed off so it will fit in the case 


377 





it to zero. However, the decimal point 
should now be seen to be lit up. If you 
wish to reset the display, you will need to 
wait for up to thirty seconds between dis- 
connecting the battery and re-connecting it 
again. 


ENCLOSURE 


If all is well, the p.c.b. may now be 
mounted in the box. Note that when using 
the specified unit, everything may be 
attached to the lid section. This method 
places least strain on the battery connect- 
ing wires. 

First, disconnect the positive supply 
wire and detach the battery connector. 
Decide on positions for the p.c.b., battery 
pack and switches, checking that there is 
sufficient space for everything to fit. 
Arrange for the 1.d.r. to lie between 5mm 
and 10mm from the side of the box. 

In the prototype, a miniature toggle 
switch with “make” contacts was used for 
the on-off switch and a matching biased 
toggle switch was used for the display. A 
biased switch is one which springs back to 
the off position when pressure is removed 
from the actuating lever. It is best to use 
either a biased toggle switch or a push-to- 
make switch to activate the display so that 
it cannot be left on accidentally. 

Mark through the p.c.b. fixing holes. 
Measure the position of the display and 
mark around its outline. Mark also the 
position directly in line with the I.d.r. win- 
dow and VR1 on the top. Mark the posi- 
tion of the switches. Remove the p.c.b. and 
drill all these holes. 

The hole for the l.d.r. should have a 


diameter of approximately 4mm (about © 


twice as large if the ORP12 type I.d.r. is 
used). The hole above the preset VR1 posi- 
tion should be large enough to allow it to 
be adjusted using a thin screwdriver or 
trimming tool. 

The easiest way to make the hole for the 
display is to drill small holes within its 
outline then remove the plastic using a 
small hacksaw blade, or sharp chisel. 


















the-art just a few short years ago... 


and return it to: 


Tel 01202 881749. Fax 01202 841692. 
Web:www.radiobygones.co.uk 


378 


Radio_ 
Bygones 


WHETHER your interest is in domestic radio and TV or in amateur radio, in 
military, aeronautical or marine communications, in radar and radio navigation, in 
instruments, in broadcasting, in audio and recording, or in professional radio 
systems fixed or mobile, RADIO BYGONES is the magazine for you. 


ARTICLES on restoration and repair, history, circuit techniques, personalities, 
reminiscences and just plain nostalgia — you'll find them all. Plus features on 
museums and private collections and a full-colour photo-feature in every issue. 
It's MOSTLY about valves, of course, but ‘solid-state' — whether of the coherer and 
spark-gap variety or early transistors — also has a place. 


FROM THE DAYS of Maxwell, Hertz, Lodge and Marconi to what was the state-of- 





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Completed PIR Light Checker front panel layout. The display cutout has been 
backed with a piece of translucent filter material. 


Finally, smooth the edges up to the line 
using a small file. 

Attach the p.c.b. temporarily using 
nylon fixings and with short plastic stand- 
off insulators on the bolt shanks. Adjust 
the length of the stand-off insulators so 
that the display will end up 1mm approxi- 
mately below the inside face of the box. 
When satisfied, re-attach the p.c.b. 

Check that the I.d.r. window lies direct- 
ly in line with the hole drilled for it. If not, 
adjust the position of its end leads so that 
it is. Attach the switches. Secure the bat- 
tery pack using a small bracket or adhesive 
pads. Refer to Fig.3 and complete the 
internal wiring. 

In the prototype, a piece of red plastic 
filter was glued over the display hole on 
the inside of the box. This gives a profes- 
sional appearance and also improves the 
contrast of the display. If a piece of real 
filter is not available, perhaps suitable 
material could be obtained from a sweet 
wrapper or something similar. 


The leading magazine 
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enthusiasts 


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INTO SERVICE 


With switch S2 off, connect the battery 
and attach the lid. Find a suitable place for 
the unit so that light from the PIR lamp 
will reach the l.d.r. directly through the 
hole in the side of the box. The fact that 
the I.d.r. is some distance behind the hole 
makes the response directional. This is 
useful because it tends to discriminate 
against other sources of light which could 
result in false counting. 

Make some tests at night. For initial tri- 
als, you may find it helpful to use an elas- 
tic band or p.v.c. tape to hold the display 
switch (S1) on, so that the count may be 
observed over a period of time. Remember 
that this wastes the batteries so don’t do it 
for too long. 

Adjust preset VR1 for best effect. 
Remember to protect the unit against rain 
entering if this is a possibility. 

No more disturbed neighbours with this 
“Trigger Happy”’ circuit! CJ 





(_] Two years (12 issues) 


Note: Minimum credit card 
payment is £5 


Gi edi aus eC Rip UR SE OS OUR ALE SOE lok doe ke Sow ies we Sree 


eee 28 Se € OS P aC Se BaP CHO we HPS eee eee eas 8 eo Hs AP © 


2th ke Seve ck es 6 @ a 5) © @. 9 er- 6) 0-9 6 Op SE @ 21D © mw U8. O78 fd 6-0 0 8 8. G8 


Everyday Practical Electronics, May 2000 


£1 BARGAIN PACKS 


- List No. 3 


‘1 item per pack unless otherwise stated. 





30A PORCELAIN FUSE HOLDERS. Make your own fuse 
board. Pack of 4. Order Ref: 82. 

4U5V 150mA D.C. POWER SUPPLY. Mains operated, fully 
enclosed so quite safe. Order Ref: 104. 

CROCODILE CLIPS. Small size, 10 each red and black. Order 
Ref: 116. 

PLASTIC HEADED CABLE CLIPS. Nail in type, several sizes. 
Pack of 50. Order Ref: 123. 

MES BATTEN HOLDERS. Pack of 4. Order Ref: 126. 


2 CIRCUIT MICRO SWITCHES (Licon). pack of 4. Order Ref: : 


157. 

13A SWITCH SOCKET. Quite standard. Order Ref: 164. 

30A PANEL MOUNTING TOGGLE SWITCH. Double pole. 
Order Ref: 166. 

3/8 RUBBER GROMMETS. Pack of 10. Order Ref: 181. 

BC LAMP HOLDER ADAPTORS. Pack of 4. Order Ref: 191. 
SUPERIOR TYPE PUSH SWITCHES. Make your own 
keyboard. Pack of 8. Order Ref: 201. 

MAINS TRANSFORMER 8V-0V-8V «A. Order Ref: 212. 

SUB MIN TOGGLE SWITCHES. Pack of 3. Order Ref: 214. 
HIGH POWER 3in. SPEAKER (11W 8o0hm). Order Ref: 246. 
MEDIUM WAVE PERMEABILITY TUNER. It's almost a 
complete radio with circuit. Order Ref: 2247. 
SCREW DOWN TERMINALS with through panel insulators. 
Pack of 4. Order Ref: 264. 

L.C.D. CLOCK DISPLAY. «in. figures. Order Ref: 329. 
PUSH-ON LONG SHAFTER KNOBS for in. spindle. Pack of 10. 
Order Ref: 339. 

EX-GPO SPEAKER INSERTS. Ref 4T. Pack of 2. Order Ref: 
352. 

SUB MIN I.F. TRANSFORMERS. Just right if you want coil 
formers. Pack of 50. Order Ref: 360. 

24V 200mA P.S.U. Order Ref: 393. 

HEATING ELEMENT. Mains voltage 100W, brass encased. 
Order Ref: 8. 

MAINS INTERFERENCE SUPPRESSOR. Order Ref: 21. 
ROCKER SWITCHES. 10A mains voltage. Pack of 3. Order Ref: 
41. : 


MINI UNI SELECTOR with diagram for electronic jig-saw. Order 
Ref: 56. 
APPLIANCE THERMOSTATS. Adjustable up to 15A. Pack of 2. 
Order Ref: 65. 
MAINS MOTOR with gearbox giving 1 rev per 24 hours. Order 
Ref: 89. 
ROUND POINTER KNOBS for flatted in. spindles. Pack of 10. 
Order Ref: 295. 
CERAMIC WAVE CHANGE SWITCH. 122-pole, 3-way with in. 
spindle. Order Ref: 303. 
PLASTIC STETHOSETS. Take crystal or magnetic inserts. 
Pack of 2. Order Ref: 331. 
PRE-SET RESISTORS. Various types and values. Pack of 20. 
Order Ref: 332. 
CAR TYPE ROCKER SWITCHES. Assorted, pack of 6. Order 
Ref: 333. 
REVERSING SWITCH. 20A double pole or 40A single pole. 
Order Ref: 343. 
SKIRTED CONTROL KNOBS. Engraved 0-10, pack of 4. Order 
Ref: 355. 
LUMINOUS PUSH-ON PUSH-OFF SWITCHES. Pack of 3. 
Order Ref: 373. 
MAINS TRANSFORMER OPERATED NICAD CHARGER. 
Cased with leads. Order Ref: 385. 
CLOCKWORK MOTORS. Run for one hour. Order Ref: 389. 
SLIDE SWITCHES. Single pole changeover. Pack of 10. Order 
Ref: 1053. Z ' 
2-CORE MAINS LEAD. Black, 2m long. Pack of 4. Order Ref: 
1020. 
DITTO 3 core, black. Pack of 3. Order Ref: 1021. 
HEAD CLEANER. For your video or tape, complete with brush. 
Order Ref: 1026. 
PAXOLIN PANEL. Approximately 12in. x 12in. Order Ref: 1033. 
CLOCKWORK MOTOR. Suitable up to 6 hours. Order Ref: 
1038. | 
TRANSISTOR DRIVER TRANSFORMER. Maker's ref. no. 
LT44, impedance ratio 20k ohm to 1k ohm, centre tapped, 50p. 
Order Ref: 1/23R4. 
TUBULAR ELECTROLYTIC CAP. Twin 200pF at 275V. Order 
Ref: 1046. 
HIGH CURRENT RELAY. 12V D.C. or 24V A.C., operates 
changeover contacts. Order Ref: 1026. 
FIGURE 8 FLEX. Ideal speaker lead, 12m. Order Ref: 1024. 
6V SOLENOID with good strong pull. Pack of 2. Order Ref: 
1012. 


oa ELECTROLYTICS. 150pF at 200V. Pack of 3. Order 

ef: 993. 

MINI RELAY. 5V, coil size 50mm x 15mm x 15mm with closing 

5A contacts. Pack of 2. Order Ref: D41. 

MINI RELAY with 5V coil, size 26mm x 19mm x 17mm, 2 sets 

changeover contacts. Just one. Order Ref: D42. 

— RODS. 3/8in. diameter, 8in. long. Pack of 3. Order Ref: 
53. 

ROTARY SWITCH. 9-pole, 6-way. Pack of 2. Order Ref: D54. 

2-CORE CURLY LEAD. 5A, 2m. Order Ref: 846. 

3-CORE CURLY LEAD. 13A, 1m. Order Ref: 847. 

DELAY SWITCH. on B7G base. Order Ref: 854. 

3 CHANGEOVER RELAY. 6V A.C., 3V D.C. Order Ref: 859. 

3 CONTACT MICRO SWITCHES, operated with slightest touch. 

Pack of 2. Order Ref: 861. 

a NUMICATOR TUBE. Highvac ref XN3. Order Ref: 
5. 

DITTO but reference XN11. Order Ref: 866. 

QUARTZ LINEAR HEATING TUBES. 306W but 110V so would 

have to be joined in series. Pack of 2. Order Ref: 907. 

2IN. ROUND LOUDSPEAKERS. 50A coil. Pack of 2. Order Ref: 

908. 


25M 4-CORE CABLE. Suitable for telephone extension. Order 
Ref: 918. 





RECHARGEABLE 12V JELLY ACID BATTER- 
IES. Yuasa 12V 2.3AH. These are 7in. long, 
3in. high and 1¥in. wide with robust terminals 


- protruding through the top. Price £3.50 or 5 for 


£15. Order Ref: 3.5P11. 

DITTO, but 12V 18AH. This is 7in. long, 7in. 
high and 3in. wide. Brand new with 12 months 
guarantee, price £12.50 or pack of 4 for £48, 
including VAT and carriage. Order Ref: 12.5P3. 
Note — This battery will start a car and is ideal 
for golf trolleys, etc. 

CHARGER for these batteries and other 
sealed lead acid batteries, £5. Order Ref: 
5P269. 

RECHARGEABLE NICAD BATTERIES. AA 
size, 25p each, which is a real bargain consid- 
ering many firms charge as much as £2 each. 
These are in packs of 10, coupled together 
with an output lead so are a 12V unit but easi- 
ly divideable into 2 x 6V or 10 x 1-2V. £2.50 per 
pack, 10 packs for £25 including carriage. 
Order Ref: 2.5P34. 

ANSWER-PHONE UNIT. Brand new, suitable 
for connection to any BT line, has been cur- 
rently sold for around £25. You can have one at 
£12. Order Ref: 12P38. 

LIGHT ALARM. A circuit for this appears in the 
February issue, however, we have a rather less 
complicated model already made up and in a 
nice case, price only £3. Order Ref: 3P155. 
ULTRA VIOLET VIEWING UNIT. This is a very 
neat metal enclosure about the size of a 6in. 
cube. The lamp and control gear are in the top 
compartment and an open space with a plat- 
form below allows you to inspect paper or 
other objects under the UV light. Intended for 
230V mains operation. Price £12. Order 
Ref:12P35. 

TWIN 13A SWITCHED SOCKET. Standard in 
all respects and complete with fixing screws. 
White, standard size and suitable for flush 
mounting or in a surface box. Price £1.50. 
Order Ref: 1.5P61. 

VERY POWERFUL BATTERY MOTORS. Were 
intended to operate portable screwdrivers. 
Approximately 2%in. long, 1¥%in. in diameter, 
with a good length of spindle. Will operate with 
considerable power off any voltage between 6 
and 12 D.C. Price £2. Order Ref:2P456. 
Quantity discount 25% for 100. 

BIG 12V TRANSFORMER. It is 55VA so that is 
over 4A which is normal working, intermittantly 
it would be a much higher amperage. Beautiful 
transformer, well made and very well insulated, 
terminals are in a plastic frame so can’t be 
accidentally touched. Price £3.50. Order Ref: 
3.5P20. 

SOUND SWITCH. Can be operated by clap- 
ping hands, shouting or almost any other 
noise. Ready to work but needs casing. Price 
only £3. Order Ref: 3P246. 


1MA PANEL METER. Approximately 80mm x 
55mm, front engraved 0-100. Price £1.50 each. 
Order Ref: 1/16R2. 

VERY THIN DRILLS. 12 assorted sizes vary 
between 0-6mm and 1-6mm. Price £1. Order 
Ref: 128. 

EVEN THINNER DRILLS. 12 that’ vary 
between 0-1 and 0-5mm. Price £1. Order 
Ref:129. 

D.C. MOTOR WITH GEARBOX. Size 60mm 
long, 30mm diameter. Very powerful, operates 
off any voltage between 6 and 24 D.C. Speed 
at 6V is 200 rpm, speed controller available. 
Special price £3 each. Order Ref: 3P108. 
FLASHING BEACON. Ideal for putting on a 
van, a tractor or any vehicle that should always 
be seen. Uses a Xenon tube and has an amber 
coloured dome. Separate fixing base is includ- 
ed so unit can be put away if desirable. Price 
£5. Order Ref: 5P267. 

MOTOR SPEED CONTROLLER. These are 
suitable for D.C. motors for voltage up to 12 
and any power up to 1/6 h.p. They reduce the 
speed by intermittent full voltage pulses so 
there should be no loss of power. In kit form 
these are £12. Order Ref: 12P34. Or made up 
and tested, £20. Order Ref: 20P39. 

MOST USEFUL POWER SUPPLY. Rated at 
19V 1A, this plugs into a 13A socket, is really 
nicely boxed. £2. Order Ref: 2P733. 

BT TELEPHONE EXTENSION WIRE. This is 
proper heavy duty cable for running around the 


skirting board when you want to make a per- © 


manent extension. 4 cores properly colour 
coded, 25m length. Only £1. Order Ref:1067. 





SMART HIGH QUALITY ELECTRONIC KITS 


CAT. NO. DESCRIPTION PRICE 
£ 
1005 Touch Switch 2.87 
1010 5-input stereo mixer with monitor output 19.31 
1016 Loudspeaker protection unit 3.22 
1023 Dynamic head preamp 2.50 
1024 Microphone preamplifier 2.07 
1025 7 watt hi-fi power amplifier 2.53 
1026 Running lights 4.60 
1027 NiC.cad battery charger 3.91 
1030 © Light dimmer 2.53 
1039 Stereo VU meter 4.60 
1042 AF generator 250Hz-16kHz 1.70 
1043 Loudness stereo unit 3.22 
1047 ° Sound switch 5.29 
1048 Electronic thermostat 3.68 
1050 3-input hi-fi stereo preamplifier 12.42 
1052 3-input mono mixer 6.21 
1053 Electronic metronome 3.22 
1054 4-input instrument mixer ee 
1057 Cassette head preamplifier 3.22 
1059 Telephone amplifier 4.60 
1062 5V 0-5A stabilised supply for TTL 2.30 
1064 12V 0-5A stabilised supply 3.22 
1067 Stereo VU meter with leads 9.20 
1068 18V 0-5A stabilised power supply 2.53 
1070 Hi-fi preamplifier 7.47 
1071 4-input selector 6.90 
1080 Liquid level sensor, rain alarm 2.30 
1082 Car voltmeter with l.e.d.s 7.36 
1083 Video signal amplifier 2.76 
1085 DC converter 12V to 6V or 7-5V or 9V 2.53 
1086 Music to light for your car 4.60 
1093 Windscreen wiper controller 3.68 
1094 Home alarm system 12.42 
1098 Digital thermometer with |.c.d. display 11.50 
1101 Dollar tester 4.60 
1102 Stereo VU meter with 14 I.e.d.s 6.67 
1106 Thermometer with |.e.d.s 6.90 
1107 Electronics to help win the pools 3.68 
1112 Loudspeaker protection with delay 4.60 
1115 Courtesy light delay 2.07 
1118 Time switch with triac 0-10 mins 4.14 
1122 Telephone call relay 3.68 
1123 Morse code generator 1.84 
1126 Microphone preamplifier 4.60 
1127 Microphone tone control 4.60 
1128a Power flasher 12V d.c. 2.53 
1133 Stereo sound to light 5.26 


TOROIDAL MAINS TRANSFORMERS 
All with 220V/240V primary winding 

24V + 24V at 25VA would give 25V at 1A or 50V at %A, 
price £3. Order Ref: 3P245. 
0-7V 40VA has a main winding 7V at 5A and a secondary 
winding 12V at 1A, price £3. Order Ref: 3P238. 
35V at 80VA , price £5. Order Ref: 
0-110V + 0-110V at 120VA would give you 110V at just 
over 1A or 220V at A, price £8. Order Ref: 8PG3. 
0-35V + 0-35V at 150VA would give 35V at 4A or 70V at 
2A, price £8. Order Ref: 8PGQ. 
0-35V + 0-35V at 220VA would give 35V at 6A or 70V at 
3%A, price £10. Order Ref: 10PG4. : 
0-110V + 0-110V at 220V would give 110V at 2A or 220V 
at 1A, price £12. Order Ref: 12PG5. 
0-110V + 0-110V at 500VA would give 110V at 5A or 220V 
at nearly 3A, price £25. Order Ref: 25PG8. 


SUPER WOOFERS 


A 10in. 4ohm with power rating of 250W music and normal 
150W. Normal selling price for this is £55 + VAT, you can 
buy at £29 including VAT and 
carriage. Order Ref: 29P7. 
The second one is an 8in. 
4ohm, 200W music, 200W 
normal, again by Challenger, 
price £18. Order Ref: 18P9. 
Deduct 10% from these 
prices if you order in pairs or 
can collect. These are all 
brand new in maker's pack- 
ing. 





TERMS 


Send cash, PO, cheque or quote credit card number — 
orders under £25 add £3.50 service charge. 


J & N FACTORS 
Pilgrim Works (Dept.E.E.) 


Stairbridge Lane, Bolney 
Sussex RH17 5PA 





Telephone: 01444 881965 


Regular Clinic 


ALAN WINSTANLEY 


and IAN BELL 

































Our circuit surgeons provide more advice to help with reader’s problems and 
conclude their mini-series investigating the inner workings of operational 
amplifiers, looking at output stages and short-circuit protection. 


We month we round off our explo- 
ration of the op.amp by looking at the 
level shifter circuits which are used to get 
the d.c. bias levels correct in different 
stages of an op.amp. We outline typical 
short-circuit protection techniques and 
also output stages, which are power 
amplifiers that share some of the features 
of basic audio power amplifier output 
stages. Some of the principles we'll 
outline also apply to designs which use 
discrete transistors instead of integrated 
circuits. 


Shifty Circuits 

No coupling capacitors can be used 
between stages within op.amps — they 
have to work with d.c. and very low fre- 
quency inputs. Biasing is easy in multi- 
stage capacitively-coupled amplifiers 
because the biasing of each stage is isolat- 
ed by the coupling capacitor. 

In an op.amp, life is not so simple. We 
might, for example, have one stage with 
an output whose signal varies around a 
bias point of half the positive supply, 
which has to be connected to a stage that 
needs a signal which varies around 0V 
(ground) instead. Therefore what we 
would need to do is “shift’’ the d.c. bias 
level of a signal. 

Ideally, a circuit for this purpose should 
provide a stable shift in d.c. level without 
introducing noise, it should not attenuate 
the signal, and should allow the designer 
to select any level shift required (within 
reason). We could achieve a shift using a 
two-resistor potential divider, but this 
attenuates the signal. We could use a 
Zener diode to provide a voltage drop, but 
these are noisy. We could use diode volt- 
age drops, but these only come in steps of 
about 0-6V per diode used. 

The circuit in Fig.la acts as a level 
shifter, changing the d.c. level from V;, to 
Vout Without significant attenuation of the 
signal. The current source (see Circuit 
Surgery, May and June ’99) provides a 
current J that flows through R to give a 
fixed voltage drop of JR. The voltage drop 
is fixed (it does not depend on the signal) 
because the current source produces the 


380 


same current even if the voltage across it 
varies due to the signal. 

The total fixed voltage drop from V;, to 
Vout also includes the Vgp voltage of the 
transistor, which will also not vary a great 
deal as the signal varies. Thus the circuit 
shifts the d.c. level of the signal down by 
UR+ Vor) volts. 


Out of the Op.Amp 

An op.amp output stage must be capable 
of supplying sufficient current to the exter- 
nal load (i.e. out of the chip on which the 
op.amp is fabricated). In order to do this it 
must have low output resistance and pro- 
vide power gain. It does not have to pro- 
vide voltage gain as this is done by earlier 
stages. 








Fig. 1c. Basic push-pull amplifier. 


The output stage is a power amplifier — 
a term that conjures images of circuits 
which deliver many watts of power. This 
does not have to be the case — it is the fact 
that power gain is provided rather than 
the amount of power available that mat- 
ters. However, there are, of course, high 
power op.amps and the op.amp output cir- 
cuits share features with some types of 
audio power amplifier. 

The well-known emitter follower cir- 
cuit (Fig. 1b) has a voltage gain of just less 
than unity, high input resistance and low 
output resistance. So it can deliver a rela- 
tively high-current version of a “weak’”’ 
voltage signal. The circuit is called an 
emitter follower because the signal volt- 
age at the emitter, which is where the load 
is connected, “follows” (is the same as) 
the voltage at the base. The absolute volt- 
age at the emitter is one Vpp drop (about 


—— OUTPUT 


\ --7- INPUT 
\ 





Fig.2. Sinewave with crossover 
distortion. 


Everyday Practical Electronics, May 2000 


0-6 to 0-7V) lower than the base voltage, but this is just a shift in 
d.c. level. 

Our emitter follower circuit of Fig.1b has the right kind of prop- 
erties for an op. amp output stage, but is not suitable as it stands 
because we require the load to be connected to ground and the out- 
put signal to be both positive and negative. In this circuit the tran- 
sistor would turn off with negative input voltages, so we would 
only amplify half the signal! 

To overcome this, two emitter-followers are used in what is 
known as a push-pull amplifier (see Fig.1c). This type of circuit is 
also referred to as a class-B amplifier because each output transis- 
tor conducts for one-half of the waveform cycle. Transistors in 
class-A amplifiers conduct for the whole cycle, and in class-C for 
less than half. 

The basic push-pull output stage suffers from a problem called 
crossover-distortion. Only one transistor can be on at any time, 
that is: if V;, > Vgg then TR1 is conducting, and if V;, <—Vpp then 
TR2 is conducting instead. However, this means that for small 
inputs, neither transistor is on: if -Vpr < Vi, < Vp then TR1 and 
TR2 are both off. 

So signals, or parts of signals, in this range are not amplified, 
which leads to distortion of the output. Fig.2 shows a sinewave 
input to a basic push-pull amplifier (dotted line) and the resulting 
distorted output (solid line). Although this circuit is not suitable 
for op.amps it may be of use in other applications where the 
distortion does not matter, for example in a basic motor control 
circuit. 


Crossover Distortion 

To overcome crossover distortion, the output transistors are 
biased so that with no signal present they are both just on the point 
of conduction. Then when Vj; = 0 both transistors are just con- 
ducting, when Vj, > 0 TR1 conducts and TR2 is off, and when Vyy 
< 0 TR2 conducts and TR1 is off. 

This can be achieved using two diodes, or two transistors con- 
nected as diodes, to provide the 2 x Vpp difference in bias voltage 
required between the transistors’ bases (see Fig.3). The diodes are 


biased with the current required to give the correct Vpp value by 


means of a current source. 

As the input signal varies the diodes maintain a constant 2 x Vpr 
difference between the two base voltages. The actual base voltages 
will vary with the signal, but the difference between them is fixed 
by this biasing arrangement. 

The diodes are ideally at the same temperature as the output tran- 
sistors so that changes in their voltage drop with temperature tracks 
those of the output transistor. This applies on op.amp i.c.s and for 
discrete component power amplifiers using this type of circuit. 


Short Circuits 

The push-pull amplifier is likely to be damaged if its output is 
short-circuited to ground, due to excessive collector current in the 
conducting transistor. A short-circuit protection arrangement may 
be added to overcome this problem. The protection circuit moni- 
tors the current flowing in the output and turns off the output tran- 
sistor if the current exceeds some pre-defined limit. The current 
detection is usually achieved by using a small resistor in the out- 
put signal path, and a transistor to switch off the output (see Fig.4); 
the output current causes a voltage drop across the resistor. 

A protection transistor switches on when the resistor voltage 
reaches about 0-6V to 0-7V. The protection transistor is connected 
so that when it is on, it effectively short circuits the input to the 
power transistors, so they have no signal to amplify. The protection 
resistor values, R,; and Rp» may be chosen using Rp; = Rp = 
Vbe trp / Imax where Vberrp: is the turn-on voltage of | the protec- 
tion transistor (typically 0-6V to 0-7V) and I,,., is the maximum out- 
put current, i.e. the current at which the protection kicks in. This 
kind of protection circuit is what enables op.amps to have the “‘infi- 
nite output short circuit duration” quoted on many data sheets. 


Audio Power Amp 

The circuit shown in Fig.5 is a discrete component version of the 
circuit in Fig.4, which could form the basis of an audio power 
amplifier output stage. Resistors are used instead of the current 
sources ubiquitous in i.c. circuits. 

Biasing is achieved using what is known as a Vgp multiplier and 
is manually adjustable using preset VR1I to give the required 
quiescent current for the circuit (the degree to which the output 
transistors are “just on’’ with no signal). The Vpg multiplier circuit 
consists of TR,, preset VR1 and resistor R2. The voltage V,,,, is 


4 


Everyday Practical Electronics, May 2000 





Fig.3. Output transistors biased to prevent crossover 
distortion. The diodes may be implemented using transistor 
base-emitter junctions. 





Fig.4. Output stage with protection circuit (protection 
components are shown using bold lines). 





Fig.5. Audio power amplifier using similar configuration to 
op.amp output stage. 


381 


effectively fixed by virtue of the fact that 
TR,’s Vpr voltage does not vary much, 
resulting in a fixed voltage across R2 and 
hence a fixed current through it. 

If the preset VR1 and resistor R2 are 
chosen so that their current is much larger 
than TR,’s base current then we can 
assume all of the current in R2 also flows 
in VR1. Thus the total dropped across VR1 
and R2 (i.e. Vp;a;) is equal to Vgp multi- 
plied by the ratio of the total resistance of 
VRI1 and R2 to the value of R2, i.e. 


Vpias = Vag (VRI + R2) 
R2 


We hope that our discussion on the 
op.amp over the past few months has 
given you some insight into what is 
inside these chips that get used in so 
many constructor’s projects. Of course, 
there is a lot more to the circuitry of 
modern op.amps than we have space to 
discuss in this series — as a browse 
through the schematics in manufacturers’ 
data sheets will reveal. 

Hopefully, however, you would also be 
able to recognise at least some of the 
basic sub-circuits (e.g. differential 


have shown in your own designs - let us 
know if you do. Jan Bell. 


Battery Flattery 


Briefly on the subject of troubleshooting 
lead acid chargers, Mr Alister Bottomley 
wrote: “Am I correct in assuming that in 
order to charge a 12V lead acid battery it 
must receive a voltage greater than 12V 
across it — the greater the voltage the 
greater the charging current? 

My battery charger has _ suddenly 
reduced its output to 11-7V as measured 
on its “high” tapping. I can’t find any 
losses or problems in the circuit.” 

A lead acid battery requires something 
like 2:2V per cell or higher constant volt- 
age to charge. A higher voltage could be 
used but the battery life will be shortened, 
and it is true that the greater the applied 
voltage, the greater the charge current will 
be. Current gradually reduces to a trickle 
as the battery charges up. 

The reason you are measuring a strange 
d.c. voltage is because it isn’t a smooth 
level d.c. voltage you are actually testing. 
Ordinary car battery chargers have a rec- 
tified d.c. output which is unsmoothed. 
However, your multimeter will want to 


An electronics mains power supply uses 
a smoothing or “reservoir” capacitor to 
iron out the ripple, to produce a higher 
peak value and much smoother d.c. volt- 
age. The capacitor then charges to the 
peak value of the rectified d.c. sinewave. 
In fact, it’s the car battery itself which acts 
as a giant smoothing capacitor across the 
supply. Hooking this across the battery 
charger means that the voltage seen across 
the battery will then increase. 

Also, your test equipment may actually 
cause you to misinterpret the result, and 
sometimes the very use of test equipment 
can affect the operation of the circuit as 
well. Constructors gradually learn to com- 
pensate for this with experience. 


CIRCUIT THERAPY 


Circuit Surgery is your column. If you 
have any queries or comments, please 
write to: Alan Winstanley, Circuit Surgery, 
Wimborne Publishing Ltd., Allen House, 
East Borough, Wimborne, Dorset, BH21 
1PF, United Kingdom. E-mail 


alan@epemag.demon.co.uk. Please indi- 


cate if your query is not for publication. A 
personal reply cannot always 

be guaranteed but we will try 

to publish representative 

answers in this column. 





read a pure d.c. voltage, or it will read an 
r.m.s. voltage on its a.c. range instead. 
An oscilloscope would highlight the 
problem. 


amplifier) in these schematics, even if 
there are one or two extra transistors 
present. We also hope that some of you 
might find other uses for the circuits we 





Details and prices for all of this month’s printed circuit boards can be 
found on page 397. 


PLEASE TAKE NOTE 


with David Barrington 


Micro-PiCscope April ‘00 
Unfortunately, a digit was missed from the order code of the orange box 
and it should be: 281-6841. We apologise for this error. 


FRUSTRATED! 


Looking for ICs TRANSISTORs? 
A phone call to us could get a result. We 
offer an extensive range and with a world- 
wide database at our fingertips, we are 
able to source even more. We specialise in 
devices with the following prefix (to name 
but a few). 





Versatile Mic/Audio Preamplifier 

Todate, we have only traced two sources for the SSM2166P microphone 
preamplifier ic. used in the Versatile Mic/Audio Preamplifier project. It is 
currently listed by Maplin (www.maplin.co.uk), code GS39N and also car- 
ried by Farnell (@ 0113 263 6311 or www.farnell.com), code 114-7249. 

If you are going to include the Signal Strength Meter option, the actual 
selection of the moving coil meter is left to individual choice, hence the 
small table giving resistor values for meter movements ranging from 50uA 
up to 1mA. Many of our component advertisers should be able to offer a 
suitable small panel meter. 



















Low-Cost Capacitance Meter 

The only item that needs highlighting when buying parts for the Low-Cost 
Capacitance Meter, this month’s Starter Project, is the timer i-c. 

A low-power version of the 555 timer must be used in this project as, due 
to its low self-capacitance, it gives better accuracy on the 1nF range. 
Therefore, use the TS555 timer instead of the standard NE version. The 
low-power version should be widely stocked and readily available. 

Once again, the meter is left to individual choice as prices seem to vary 
quite considerably. The model uses a 100uA movement obtained from 
Maplin (www.maplin.co.uk), code RW92A. 

The 12-way single-pole rotary range switch is a Lorlin type which has an 
adjustable rotation limiting “end-stop” which should be set to 5-ways. This 
was also purchased from the above, code FF73Q. 


Multi-Channel Transmission System 

Most of the components called up for the Multi-Channel Transmission 
System should be stock items, even unprogrammed PIC16F84s are now 
widely available. 

The author is able to supply ready-programmed PIC16F84s. You will 
need to order at least two microcontrollers, one Transmitter (Tx) and one 
Receiver (Rx). We understand that the first two will cost £6 each and any 
additional PICs £5 each, inclusive of postage (overseas add £1 per order 
for postage). Orders should be sent to: Andy Flind, 22 Holway Hill, 
Taunton, Somerset, TA1 2HB. Payments should be made out to A. Flind. 
For those who wish to program their own PICs, the software is available 
from the Editorial Offices on a 3-5in. PC-compatible disk, see PCB Service 
page 397. It is also available free via the EPE web site: ftp://epemag.wim- 
borne.co.uk/pubs/PICS/multichannel. 


PIR Light Checker mE a 
Nearly all the components needed to build the PIR Light Checker project 
should be obtainable from your usual local supplier. The miniature light- 
dependent resistor (I.d.r.) and the 7-segment, common cathode, display 
both came from Maplin (www.maplin.co.uk), codes AZ83E and FR41U 
respectively. You can, of course, use the good old ORP12 I.d.r. 





We can also offer equivalents (at customers’ risk) 
We also stock a full range of other electronic components 
Mail, phone, Fax Credit Card orders and callers welcome 


Connect 


382 Everyday Practical Electronics, May 2000 








Learn The Easy Way! 





Experimenting with PIC Microcontrollers 
This Third release in our “Experimenting with.....” series concentrates on the PIC16F84 and 
PIC16C711 microcontrollers, and consists of the book, a programmer/experimental module, 
and an integrated suite of programmes to run on a PC. 

The book with its abundance of flow diagrams and circuit diagrams is the heart of the sys- 
tem, and the software is the brains. A text editor with word processing power is the keystone 
supporting the assembler, disassembler, simulator, and programming software. As the text 
is typed in the assembler works in the background testing each line so that errors are imme- 
diately highlighted. When the typing is done the simulator can be used to single step or run 
the programme. Boxes pop up showing the contents of registers and the result of any text 
written to a standard 2 line by 16 character display. If it works correctly plug the program- 
mer/experimental module onto the end of your printer lead and test it using a real live PIC. 
All operations work directly from the assembler text in the editor. 

The 24 experiments assume no prior programming or electronic experience. These are alll 
performed using the programmer/experimental module which is already wired with LEDs, 
push buttons, and an alphanumeric liquid crystal display. Flashing LEDs, text display, real 
time clock, period timer, beeps and music, including a rendition of Beethoven’s Fur Elise. 
Then there are two projects to work through; building a sinewave generator covering 0.2Hz 
to 20kHz in five ranges, and investigating measurement of the power taken by domestic 
appliances. In the space of 24 experiments, two projects and 56 exercises the system works 
through from absolute beginner to experienced engineer level. 


Programming PICs 


The assembler understands normal PIC 
terminology. This has two distinct advan- 
tages for beginners over the usual sys- 
tem; it is not necessary to start pro- 
grammes with a list of definitions, and 


Assembler 
The first book Experimenting with PC 
Computers with its kit is the easiest way 
ever to learn assembly language program- 
ming, simple circuit design and interfacing 
to a PIC. If you have enough intelligence to 
understand t he English language and you 
can operate a PC computer then you have 
all the necessary background knowledge. 
Flashing LEDs, digital to analogue con- 
verters, simple oscilloscope, charging 
curves, temperature graphs and audio 


digitising. 
C & C++ 

The second book Experimenting with 
C&C++ Programmes uses a_ similar 
approach. It teaches the user to pro- 
gramme by using C to drive the simple 
hardware circuits built using the materials . 
supplied in the kit of parts. The experi- 
mental circuits build up to a storage 
oscilloscope using relatively simple C 
techniques to construct a programme that 
is by no means simple. When approached 
in this way C is only marginally more diffi- 
cult than BASIC and infinitely more power- 
ful. C programmers are always in demand. 
Ideal for absolute beginners and experi- 
enced programmers. 


The Kits 
The kits contain the prototyping board, 
lead assemblies, components and pro- 
gramming software to do all the experi- 
ments. The ‘made up’ kits are supplied 
ready to start the first experiment. The 
‘unmade’ kits require the prototyping board 
and leads to be assembled and soldered 
before you can start. The ‘top up’ kit CP2t 
is for readers who have purchased a kit to 
go with the first book, and contains all the 
components and programming software 
but not the prototyping board or leads. The 
kits do not include the book. 


Hardware required 
All three systems assume you have a PC 
(386 or better) and a printer lead. 





Mail Order Form 
Please make your cheque/PO payable to Brunning Software and send with this form to 
Brunning Software, 138 The Street, Little Clacton, Clacton-on-sea, Essex, CO16 9LS. 
Your order will be processed as soon as your cheque arrives. Despatch is usually the 
| same day. Software supplied on 3-5in. HD discs. The kits do not include the book. 






the assembler recognises errors such as Please supply: fp 
call intcon because it knows that INT- Book Experimenting with PCs (Maplin code NV68)....... £23.99 .... Gi, ; 
CON is a register not a subroutine name. Kit 1a ‘made up’ and ready to start (Not from Maplin) ..... £46.00 .... a 


The programmer module itself is a fine 
example of what can be achieved with 
PIC microcontrollers. It uses its own PIC 
to control the timing and voltages 
required to programme the test PIC. The 
programming is performed and verified 
at normal 5 volts, then verified again with 
+10% volts applied to ensure that the 
device is programmed with a good mar- 
gin and not poised on the edge of failure. 
The system is optimised for the 
PIC16F84 and PIC16C771 and will pro- 
gramme similar PICs (83, 710, 71, 620, 
621 etc). 

The module is supplied with a test PIC 
fitted, and requires two PP3 batteries 
which are not supplied. 


Brunning Software 





Name 





Mail order address: 






Everyday Practical Electronics, May 2000 


Kit lu ‘unmade’ needs assembling (Maplin code NV67) 
Book Experimenting with C & C++ (Maplin code NW47) 
Kit CP2a ‘made up’ and ready to start (Not from Maplin) . . 
Kit CP2u ‘unmade’ needs assembling (Maplin code NW48) .£39.99 .... 
Kit CP2t ‘top up’ to add to Kit 1 (Maplin code NW49)..... £2299 .v... 
Book Experimenting with PIC Microcontrollers .......... £25199 .... 
PIC Programmer/experimental module & software ........ £64.00 . 


UK postage: Free for orders above £30 otherwise add £3 per sae: 
Prices include VAT where applicable 


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138 The Street, Little Clacton, Clacton-on-sea, 
Essex, CO16 9LS. Tel: 01255 862308 


383 


EPE/ET! Tutorial Series 


TEACH-IN 2000 





Part Seven - Op.amps 





Over the previous six parts of Teach-Iln 2000, which we 
know you have been greatly enjoying, we have covered 
passive components and several digital logic circuits. Via 
the interactive computer programs and the simple inter- 
face you assembled, you have also been able to observe 
the various waveforms generated by the experimental 
breadboard circuits, showing how a few electronic com- 
ponents can be connected to achieve interesting results. 


JOHN BECKER 








fighter seh 
Hi 


We now move on from the “interesting” to the “practical”, 
in terms of describing active components which can be 
used to amplify and otherwise modify the waveforms 
generated. It is op.amps we now examine, those simple 
robust components that feature so frequently in audio 
and other analogue circuits. This month we demonstrate 
their basic nature, next month we get you experimenting 
with some useful applications. 


tronic component in the analogue 

designer’s armoury is the opera- 
tional amplifier. Better known, perhaps, by 
its abbreviated name of op.amp (or op-amp, 
or even opamp) this family of devices 
seemingly has more applications than there 
are designers who use it! 

In this month’s Tutorial we illustrate 
some of the op.amp’s major features as 
an amplifier. In next month’s Tutorial we 
follow on by going into a bit more sim- 
ple experimental detail, discussing what 
else op.amps can do, and getting you to 
try it. 


FIRST DEMONSTRATION 


From your components stock, select one 
of the 8-pin dual-in-line (d.il.) devices 
labelled LM358, call it IC4. Now assemble 
your breadboard according to Fig.7.1. Any 
previous components in the area illustrated 
should be removed (all your counting and 
logic gate experiments from last month 
have already served their purpose, we 
hope!). Leave the oscillator components 
intact for now. 

The equivalent circuit diagram and the 
component values are shown in Fig.7.2. 

Connect the oscillator waveform from 
the junction of capacitor C1 and IC1a pin 1 
(see Fig.4.3 of Part 4) to the point marked 
“D.C. INPUT’. Use a 
crocodile-clipped link. +6V O 

Ignore the points 
shelled “Buffer “| °°" oe 
Input” and “Buffer + 
Output’, their purpose Ac air er 
will be discussed later 
on in the Tutorial. 

The oscillator 
should have diodes 
D2 and D3 included; 
its capacitor C1 value 
should be 100uF. Set 


Pisic' the most important elec- 


384 


(SEE TEXT) BUFFER BUFFER 


OUTPUT INPUT 


AC. D.C. OUTPUT 
INPUT = INPUT 
(SEE TEXT) 





Fig.7.1 Breadboard layout for the first 
op.amp experiments. 





Fig.7.2. Circuit diagram associated with Fig.7.1. 





Breadboard showing the components 
for the first op.amp experiments, part 
of IC1 is just seen at the left. 


the frequency control VR1’s wiper to 
midway, so that the generated waveform 
will be roughly triangular. 

Set each of the Fig.7.1 presets (VR2 to 
VR4) so that their wipers (moving con- 
tacts) are also in a midway position, pro- 
viding approximately equal resistance to 
either side of the wiper. 

Referring to Fig.5.6 of Part 5, connect 
IC4 pin 1 to the input to the analogue-to- 
digital converter (IC2 pin 2), and then con- 
nect IC2’s output to IN1 of the computer 
interface section. Run the Analogue Input 
Waveform Display program. 

Connect up your battery to the bread- 
board (as you’ve done a good few times 
before — is the battery power still OK?) and 
observe the computer screen displaying the 
triangular waveform being generated by 
ICla and associated components. 


Everyday Practical Electronics, May 2000 


‘ 
a 
: ee 


VARIABLE AMPLITUDE 


We are now going to ask you to make 
various adjustments on the op.amp’s three 
presets and observe the screen responses. 
We shall discuss what you observe in due 
course. First, carefully adjust the wiper 
position of VR4 until the waveform is 
roughly central on the screen. 

Next, slowly adjust the wiper of VR3 in 
a clockwise direction (to the “right””) while 
observing the screen. This action increases 
the resistance between the wiper and the 
end connected to IC4 pin 1, the op.amp’s 
output. 

It will no doubt interest you to see that 
the vertical size of the waveform increases, 
in other words, its amplitude increases the 
further you adjust VR3. The limit will be 
reached when you cannot turn the wiper 
any further. The amplitude will now be 
about twice that you started with. 

Note, though, how the waveform’s rela- 
tive position on the screen probably 
changes as you rotate VR3. Carefully 
adjust the wiper of VR4 to set the wave- 
form back to a mid-screen position if it 
does. 

Now rotate VR3’s wiper anticlockwise. 
The waveform amplitude will be seen to 
decrease, and once the wiper goes beyond 
the midway position, the waveform ampli- 
tude will begin to fall below that at which it 
started. The waveform is now said to have 
been attenuated. 

Towards the far end of the anticlockwise 
rotation the waveform should be seen just 
as a straightish horizontal line. 

Set VR3’s wiper to its fully clockwise 
position and leave it there. 


PEAK FLATTENING 


Turn your attention now to preset VR2. 
First rotate it clockwise, to increase the 
effective resistance between its wiper and 
IC4 pin 2, one of the op.amp’s two inputs. 
Note how an increase in resistance here 
causes a decrease in the waveform 
amplitude. 

Next adjust VR2’s wiper anticlockwise. 
Once it goes beyond the original midway 
position, note how rapidly the waveform 
amplitude increases. You may also notice a 
change in the waveform’s frequency (fewer 
cycles per screen-full!). Note also that its 
top and bottom peaks become flattened the 
more that VR2’s resistance is decreased. 
The peaks are unlikely to be evenly flat- 
tened, however. Carefully adjust VR4 until 
they become more equal. 

As you further rotate VR2’s wiper, you 
will eventually see a waveform somewhat 
resembling a square wave instead of a tri- 
angle. Adjusting VR4 will change the 
waveform’s mark-space ratio (discussed in 
Part 4). Before VR2 reaches its minimum 
resistance, and with VR4 set too much to 
either side of midway, the oscillator might 
stop functioning. 


WAVEFORM INVERSION 


That’s the first set of observations — on to 
the next. Return all three op.amp wipers 
(VR2 to VR4) to a midway position. If the 
oscillator had indeed ceased functioning, 
this action should restart it. If it doesn’t, 
briefly disconnect the power and then 
reconnect it. 

Adjust IC1’s preset VR1 so that a rising- 
ramp waveform is seen (ramps were 


Everyday Practical Electronics, May 2000 



















The op.amp type (LM358) used in this 
Teach-In is manufactured using a struc- 
ture called bipolar. In essence, this uses 
many transistors internally interconnect- 
ed on the op.amp chip and which require 
current to flow through them. In most 
cases the current is not great, but can still 
place a load on the circuit which is being 
fed into the op.amp inputs. 

Another type of op.amp manufactur- 
ing process uses the ffeld effect transistor 
(f.e.t.) technique. F.E.T. devices operate 
on a different principle to those used in 
bipolar devices and respond to the volt- 
age (field) on their inputs rather than 
through their inputs. These devices, 


discussed in Part 5). Leave all presets as 
they are and connect the ADC input to the 
input of ICla (pin 1). Look back at the 
screen. Whereas you had a rising ramp a 
few moments ago, you should now see a 
falling ramp — curiouser and curiouser! 
Time, then, to discuss your findings in 
relation to an op.amp’s basic nature. 


BASIC OP.AMP NATURE 


In essence, an op.amp is a two-input sin- 
gle-output device which has the capability 
of greatly amplifying a voltage difference 
between its two inputs. For this reason, it 
can be called a differential amplifier. 
Within limits, the amplification is accord- 
ing to a linear relationship. (You will recall 
that we discussed linear relationships when 
we discussed potentiometers in Part 3.) For 
each unit of change at the input, an equiva- 
lent but linearly amplified increase will 
result at the output. 

For some purposes (but not all) the 
amount of amplification (gain) available is 


far too great to be of use — it can be several . 


hundred thousand times for some op.amps. 
However, there is a simple technique that 
can be used to restrict the amplification to a 
more manageable level. 

In Fig.7.3 is shown the basic symbol for 
an op.amp (no longer cluttered as it is 
Fig.7.2). The symbol shows that one input 
is marked as inverting (—), and the other as 
non-inverting (+). The different input 
modes have great significance to the way in 
which the op.amp can be used and 
controlled. 

Note that the “—’’ and “+” symbols have 
nothing to do with power supply connec- 
tions, they merely symbolise the inverting 
and non-inverting nature of the respective 
input. 


INVERTING INPUT 
OUTPUT 


NON-INVERTING INPUT (+ 





Fig.7.3. Op.amp symbol and connec- 
tion names. 


INPUT TO OUTPUT 


First, suppose that both inputs have the 
same voltage level applied to them. 
Because there is no difference between the 
voltages, the output will be held at the same 
voltage. If the voltage on the non-inverting 


PANEL 7.1. OPAMP MANUFACTURING 
CONSTRUCTION 








therefore, do not draw current from the 
circuit feeding into them and so place no 
load on them. : 

All the circuits discussed in this Zeach- 
In part could probably have f.e.t. 
op.amps used instead of the bipolar 
LM358. Such devices include TLO62, 
TLO72 and TLO82. 

Component suppliers’ catalogues and 
manufacturers’ data sheets should be 
consulted for information about the dif- 
ferent op.amp types available. Internet 
access to various manufacturers web 
sites and data sheets can be gained via 
the EPE web site at www.epemag.wim- 
borne.co.uk. 









input rises fractionally above that on the 
inverting input, the output voltage will try 
to rise by the same amount amplified (mul- 
tiplied) by the gain factor (of, say, 
100,000). 

Conversely, should the voltage on the 
non-inverted input fall below that on the 
inverted input, so the output will try to fall 
by an equivalently amplified amount. 

Obviously, a similar effect will occur, 
but in the opposite direction, if it is the 
inverting input voltage that changes while 
the non-inverting input voltage remains 
constant. 


NEGATIVE FEEDBACK 


Consider, though, what happens if part 
of the output voltage is fed back to the 
inverting input, see Fig.7.4. Feedback into 
this input (via resistor R2 in this case) is 
known as negative feedback. The output 
will try to swing in the direction prompted 
by the relative voltage difference across the 
two inputs, but the effect will be dimin- 
ished according to the amount of that 
change which is fed back to counteract it. 


OUTPUT 





Fig.7.4. Feeding back part of the 
output voltage to the inverting input. 


The output might be trying to change by 
100,000 times, but the feedback might be set 
for 99,990 times. The net difference is thus 
only 10. Therefore, the effective amplifica- 
tion is only 10 times that of the difference 
originally fed into the two inputs. The gain is 
thus said to have a value of 10. 

More ‘strictly, when the signal is being 
applied to the inverting input, the gain 
should be said to be —10 (minus 10) 
because of the inversion. For the most part 
here, though, we shall just refer to the gain 
as a positive value. 

Low gain values are of much better use if 
you want to just slightly raise the amplitude 
of a waveform, as you have just done with 
the triangle waveform. In fact, when you 
first adjusted preset VR3 to its maximum 


385 


resistance, the gain you gave to the wave- 
form was about 2, i.e. you doubled the 
waveform amplitude. So let’s explain the 
mechanism which is used in the circuit of 
Fig.7.2 to control the signal gain. 


CONTROLLING GAIN 


First, assume that the waveform being 
sent to the inverting input of IC4 via preset 
VR2 is alternating about a midway voltage 
level. Let’s say the midway level is at 3V 
(half the voltage applied to the full circuit, 
as supplied by your 6V battery). 

Your initial adjustment of preset VR4 
applied just about the same midway voltage 
(which we refer to as the bias) to the non- 
inverting input (you will recall that you 
were asked to originally set its wiper to a 
midway position). This action roughly bal- 
anced the two inputs at the midway voltage. 
The changes in voltage caused by the trian- 
gle waveform’s swing thus became evenly 
balanced as seen across the two op.amp 
inputs. 


The voltage being fed into the inverting | 


input, however, passes through the resis- 
tance offered by preset VR2. On its own 
that resistance has no appreciable affect on 
the voltage actually reaching the input. 
Preset VR3, though, is connected so that it 
feeds back part of the output voltage to the 
inverting input. Jointly, the effect of both 
resistances, VR2 and VR3, determines the 
amount of negative feedback that occurs. 
Respectively, they are the equivalent of R1 
and R2 in Fig.7.4. 

If both resistances are equal, then the 
negative feedback amount is the same as 
the basic input amount, but inverted. The 
result is that the voltage actually “‘seen’’ at 
the inverting input is the input voltage 
minus the feedback voltage, i.e. nil! At 
least, that would be the case if you ignored 
the non-inverting input. 

But you can’t and don’t. The internal cir- 
cuitry of the op.amp effectively adds this 
input’s voltage (3V in this case) to the volt- 
age on the other input. Thus both inputs 
end up with the same voltage on them! 
Confirm this point using your meter to 
monitor the voltage on op.amp pins 2 and 
3, and that from IC1a pin 1. 

What’s the good of that? you might ask. 
Well, there’s a lot! In order to achieve that 
balance between inputs, the output has had 
to change its voltage level. And that’s what 
we are interested in, the change in output 
level in response to a change in input level. 


BALANCING ACT 


In the above equal resistance example 
(VR2 = VR3), the output changes by the 
same amount as the input, but in the oppo- 
site direction. An input change of 1V 
upwards, for instance, causes an output 
voltage change of 1V downwards. 

If, though, VR3 resistance is twice that 
of VR2 resistance, twice. the amount of 
feedback is required in order to achieve the 
balance at the op.amp _ inputs. 
Consequently, a 1V input change results 
in a 2V output change in the opposite 
direction. 

Similarly, if VR3 resistance is half that 
of VR2 resistance, then the output change 
required to achieve balance is only half that 
fed into VR1. Thus, a 1V input rise will 
cause a 0-5V output fall. 

Indeed you have already proved the truth 


386 





SINGLE 


741 (VARIOUS PREFIXES) BIPOLAR 
NE531 BIPOLAR 

TLO61 F.E.T. 
TLO71 F.E.T. 
TLO81 F.E.T. 


8 +VE 





7 OUTPUTB 
6 INPUT B (—) 
5 INPUT B (+) 






EXAMPLES 
LM358 BIPOLAR 
NE5532 BIPOLAR 
1458 (VARIOUS PREFIXES) BIPOLAR 
TLO62 F.E.T. 
TLO72 F.E.T. 
TLO82 F.E.T. 


















| Of these statements when observing the 

affect of changing the values of VR2 and 
VR3. You have proved both signal 
gain (amplification) and signal reduction 
(attenuation). 


INVERTING GAIN FORMULA 


There is a simple formula which defines — 


the gain in relation to the value of the 
inverting input resistance (call it R1, as in 
Fig.7.4) and the negative feedback resis- 
tance (call it R2): 


Gain = R2/R1 


Thus if R2 is 100kQ and R1 is 10kQ the 
gain is 100k/10k = 10. The output signal 
will be ten times greater than that coming 
in through R1 (within certain limits, as dis- 
cussed ina moment). | 

Similarly, if R2 is 10kQ and R1 is 
100k then the gain will be 10k/100k = 
0-1. The output signal will then be 0-1 (one 
tenth) of the input signal. 


VIRTUAL EARTH 


There is a term used to describe the 
effect seen at the inverting input when there 
is a balance of voltage directly at the two 
inputs when feedback is employed — virtu- 
al earth. It is not a “true”’ earth in the sense 
that applies when referring to the common 
or OV line of a circuit, but nonetheless it is 
one into which voltages can be fed via 
resistances from many sources without 
causing a change in the virtual earth 




















OUTPUT A 
INPUT A (—) 
INPUT A (++) 














OUTPUT B 










EXAMPLES 
324 (VARIOUS PREFIXES) BIPOLAR 
TLO64 F.E.T. 
TLO74 F.E.T. 










sbssitssitositscissstssizsikesis sists sits etsitesstsase esses ire 


feedback conditions, only adjusting the 


voltage level on the non-inverting input 
will cause a change in level on the inverting 
input, this occurring due to the op.amp’s 
internal circuitry, as said earlier. 

Note that a virtual earth condition does 
not exist if negative feedback is not 
employed. 


WAVEFORM CLIPPING 


What we have not yet accounted for is 
the “flattening” of the waveform peaks as 
the gain is increased beyond a certain point. 
The term given to this effect is clipping. 

The clipping has two possible causes. 
First, the op.amp is powered at a particular 
voltage, 6V (or thereabouts) in your exper- 
iments. Reason must tell you that the 
op.amp cannot output a voltage greater 
than its power supply. 

In a perfect op.amp, the output voltage 
would be capable of swinging fully 
between the two power line levels, OV and 
6V in this case. The flattening occurs when 
the swing can increase no _ further, 
irrespective of the amount of amplification 
available. } 

There are, indeed, some more-spe- 
cialised op.amps manufactured whose out- 
puts can swing almost completely between 
the power line levels. The term given is that 
they have a rail-to-rail output capability, 
where rail means power-rail (power-line). 

Most general purpose op.amps, though, 
do not have rail-to-rail output. Most will 


Everyday Practical Electronics, May 2000 













Most op.amps are designed to be run 
from a dual-rail power supply, i.e. one 
having positive, negative and zero 
(ground) output voltage rails, typically 
+15V but may not’be as high as this with 
some devices. 

As we deliberately demonstrate in this 


from a power supply having only positive 
and OV (ground) connections. In this 
case the middle rail voltage is provided 
by using the voltage at the centre of an 
equally-divided potential divider (as used 
in the demos). 





only swing within limits somewhat less 
than the power rail range. The actual range 
depends on the op.amp type, the voltage 
that it is being powered at, and the amount 
of current that is being drawn from its out- 
put by the load into which it is feeding. 
Under no-load conditions, the LM358 you 
are using here has a typical swing of about 
0-5V to 3-8V for a 5V power supply. 


INPUT CAPACITOR 


Earlier, we drew your attention to the 
likelihood that, when the gain was being 
adjusted, the waveform position seen on 
screen would change as well as amplitude. 
This is in part due to the fact that the trian- 
gular waveform tapped from [Cla pin 1 
may not be swinging about an exact mid- 
way voltage level. 

Consequently, any d.c. voltage differ- 
ence between the waveform’s midway level 
and that set by VR4 is amplified by the 
op.amp, causing the vertical shift observed. 

There is a very easy cure for this — to 
stop the d.c. level from the oscillator reach- 
ing the op.amp, just allowing the a.c. volt- 
age change through. 

In Teach-In Part 2 we discussed capaci- 
tors in terms of their ability to be charged 
and discharged through a resistance. We 
displayed it via one of the computer demos 
and gave formulae for it. 

Capacitors have another attribute, the 
ability to stop direct current (d.c.) passing 
through them whilst allowing alternating 
current (a.c.) to pass through. We shall dis- 
cuss this ability more fully in a future 
Teach-In part, but for the moment accept 
this as a fact. But bear in mind that future 
discussions will point out that this ability is 
governed by the capacitance value and the 
load resistance into which the “output” side 
of the capacitor is fed. Two other terms 
come into use in that discussion, differenti- 
ation and integration. 


A.C. COUPLING 


So let’s prove the point even though we 
don’t explain it. Remove the oscillator con- 
nection from the “D.C. Input” point on 
your breadboard and connect it to the “A.C. 
Input”’ point. This now provides the input 
path with what is known as a.c. coupling 
(as opposed to d.c. coupling, which has 
been the situation so far). 

Run the same group of adjustments 
using op.amp presets VR2 to VR4 as you 
did earlier and observe the screen results. 

You should find that once VR4 has been 
set midway, there should be no vertical 
shift of the waveform as you adjust gain, 
just the amplitude change. 


Everyday Practical Electronics, May 2000 


PANEL 7.3. OPAMP POWER LINES 


Teach-In, op.amps can also be powered © 





Note that whilst in theory all op.amp 
circuits shown in this Teach-In part can 
be powered from dual-rail supplies, on 
no account should dual-rail supplies | 
be used if the circuit is to be connected | 
to the ADC device or to a computer. 
Additional circuitry would be required in 
order to permit computer connection. 
Failure to observe this could seriously 
harm the ADC and/or computer. 

For optimum stability of an op.amp 
circuit, the power supply should be 
regulated at fixed voltage levels. Power 
supplies will be discussed in Part 9. | 


There is, though, a 
much more _ pro- 
nounced effect that 
you may observe, that 
of a reduction in oscil- 
lator frequency with 
the additional capaci- 
tor in circuit. Further- 
more, the frequency 
and shape of the wave- 
form are likely to 
vary when adjusting 
op.amp preset VR2. 

The effect is due to 
the oscillator now see- 
ing two capacitors in 
parallel, its own Cl, 
and C2 of the op.amp 
circuit. The effective 
value of the latter is 
also changed by the 
amount of resistance it 
sees from VR2. 

We have a cure for 
this as well! 


SIGNAL 
BUFFERING 


There is a scenario 
that we have. not yet 
explored, that of feed- 
ing a voltage into the 
non-inverting input, 
and merely feeding the 


types draw none at all, see Panel 7.1). They 
are said to have high impedance inputs, 
where impedance can loosely be described 
as resistance. 

In the earlier experiments, capacitor C2 
caused a frequency change at the oscillator 
because the current/voltage flowing 
through the resistance provided by VR1 
was being partly diverted into C2. If we 
insert a unity gain op.amp to isolate (buffer) 
the charging process for C1 from the effect 
of C2, then the oscillator frequency will be 
unaffected by the presence of C2. 

The circuit diagram for this simple 
improvement is shown in Fig.7.6. Here we 
now use the second half of the dual op.amp, 
IC4b, to provide the unity gain buffer stage 
and then feed its output into the amplifier 
stage around [C4a, still via C2 and VR2. 


Ri = 27 


i GRIN = ReeRE 7 oy : 
| BIASR4/(RS<R4 362.50 | | 





output straight back Interactive computer display illustrating an inverting 


into the inverting input, Op.amp Circuit. 
but without any addi- 

tional voltage or current being fed into that 
input. Such a circuit is shown in Fig.7.5. 


OUTPUT 
INPUT 


Fig.7.5. Unity gain op.amp buffer. 


The interesting thing about this circuit is 
that the total negative feedback ensures that 
the voltage applied to the non-inverting 
input receives neither amplification nor 
attenuation at the output. Whatever change 
there is on this input is exactly followed by 
the output, and in the same direction. In this 
configuration, the circuit is known as a 
unity gain amplifier, i.e. the gain is 1. The 
circuit is also said to function as a buffer. 

What is now worth noting is that inputs 
to op.amps draw very little current (some 


Referring back to the breadboard layout 
in Fig.7.1, connect the oscillator output 
from [Cla pin 1 to the point labelled 
“Buffer Input’? and connect “Buffer 
Output” to “A.C. Input”. Ensure that the 
small link between columns 25 and 26 of 
row G is inserted. 

Having made the changes, observe that 
the frequency is now unaffected by the 
presence of the amplifying stage. 


SIGNAL NON-INVERSION 


We have not fully discussed the fact the 
waveform being output from [C4a is an 
upside down (inverted) version of that gen- 
erated by the oscillator. There are occasions 
when this inversion might be undesirable, 
in d.c. voltage amplification, for example. 

As another example, in audio amplifica- 
tion involving many _ simultaneously 
processed sources, signals must often 
remain the “right-way-up”’ with respect to 
each in order to maintain their correct rela- 
tionships. Failure to do so could have 


387 


severely detrimental effects on the overall 
sound quality. It could even result in two 
signals cancelling each other (a principle 
we shall demonstrate next month). . 

One way that we can maintain the cor- 
rect phase relationship, as it is known in 
waveform processing, is to use the amplifi- 
er stage in its non-inverting mode rather 
than its inverting mode. We can still pro- 
vide the same amount of amplification. 


NON-INVERSION CIRCUIT 


First we need to connect the signal to the 
non-inverting input of the op.amp. We must 
then provide the correct midway bias volt- 
age to the inverting input. It is, though, this 
input that is still responsible for partly con- 
trolling the negative feedback, and thus the 
gain. Consequently, the resistance of the 
bias setting control must also be taken into 
account. 

There are several approaches to this 
problem. We shall just take an option that is 
easy to implement with the breadboard lay- 
out we are already using. The circuit is 
shown in Fig.7.7. Change the breadboard 
layout to that shown in Fig.7.8. 

The signal is still being fed in via capac- 
itor C2 in order to isolate the amplification 
from the affects of the d.c. bias that might 





Fig.7.7. Non-inverting op.amp amplifier circuit. 


exist from the oscillator. However, we must 
provide the op.amp side of C2 with a dis- 
charge path, as supplied via preset VR4. 


OUTPUT 


Fig.7.8 and photo. Breadboard layout for Fig.7.7, note that the second half of IC4 


& VR2 and VR3, but 





Note that in the “real 
world”, the discharge 
resistance value in rela- 
tion to the value of 
capacitor C2 affects the 
frequency range that 
can be correctly han- 
dled (to be discussed 
when we examine inte- 
gration in a later part of [ff 
the series), and should [# 
be chosen accordingly. |ff 
For the sake of this 
demo, however, we’ll 
ignore such niceties — 
the relationship is OK 
for what are trying to 
show. 

We retain presets 
have to provide a sec- op.amp circul. 
ond midway bias volt- 
age into the now 
“loose” wiper of VR2. This is provided by 
the voltage divider formed by resistors R3 
and R4. At their junction is added a capac- 
itor (C3) to “smooth” the voltage here, 
which could otherwise vary significantly 
with the changing signal levels in the feed- 
back path. 

As we discussed 
when considering volt- 
age dividers feeding 
into another resistance 
(Part 1), the resistance 
of R3 and R4 should be 
equal in order to pro- 
vide the midway volt- 
age, but also of a value 
about ten times less 
than the load resistance 
(effectively VR2 in this 
case). A value of 4k7Q 
has been chosen on the 
assumption that VR2 is 
set about midway 
(about 47kQ). Fine 
adjustment of the mid- 
way level can be made 
using preset VR4. 

Note that the wrong figure was published 
for Fig.1.12 of Part 1. The correct figure, 
which illustrates a voltage divider feeding 
into another resistance (R,,,), is shown now 
as Fig.7.9. 

The circuit in Fig.7.7 does not invert the 
signal output. Examine the output at IC4 





is now required to be connected into the circuit. 


388 








JELTS  NURERALS = § 
ALUE CHANGEABLE WHEN 


Interactive computer screen illustrating a non-inverting 


pin 1 as shown on your screen (via the 
ADC) and confirm that it is the same way 
up as the original. Now that you have a 
buffer amp in circuit, you can monitor the 
basic oscillator waveform from its output 
(IC4 pin 7). 


NON-INVERSION GAIN 


Earlier we defined the formula for calcu- 
lating inversion gain as: 


R2/R1 


where R1 and R2 represented the 
inverting input and feedback resistances 
respectively. 

Using the inversion configuration, signal 
attenuation can be achieved as well as 


_ amplification. 


For the non-inverting amplifier, the low- 
est level of signal amplification is 1 (unity), 
attenuation can never be_ achieved. 
Consequently, the gain calculation 
becomes feedback resistance (R2) divided 
by inverting input resistance (R1), as 
before, but a value of 1 is then added: 


Gain = (R2/R1)+1 


You will probably spot that if R2 has a 
value of zero, then the unity gain condition 
exists, irrespective of the value of R1. 


D.C. AMPLIFICATION 


For the last several paragraphs we have 
concentrated heavily on an op.amp’s abili- 
ty to amplify waveforms (i.e. a.c. signals). 
You may not have recognised it, but you 


Fig.7.9. Why a meter (represented by 
resistance R,,, affects the voltage read- 
ing at resistor junctions. Corrected 
Fig.1.12 for Part 1. 


Everyday Practical Electronics, May 2000 


have already proved that the op.amp is 
equally suited to amplifying d.c. levels. 
When you were initially experimenting 
with the relationships of the three presets in 
Fig.7.2, you needed to adjust VR4 in order to 


compensate for the d.c. bias coming from the 


oscillator. You may have noticed that the 


adjustment became more sensitive when the 


gain was set high by either VR2 or VR3. 

This was entirely due to the d.c. bias 
from the oscillator and VR4 being ampli- 
fied. At that time the d.c. amplification was 
undesirable. There are, though, many occa- 
sions in which a d.c. level needs to be 
amplified in order to be useful. 


One example that comes to mind is the 
way in which the thermistor (heat sensor) 


and light dependent resistor (I.d.r.) you 
were encouraged to try as part of various 
oscillator experiments could be used (Part 
3). We’ ll examine how voltage change with 
temperature or light intensity can be moni- 
tored on your multimeter and computer 
screen as part of next month’s Tutorial. 


D.C. STABILITY 


We must comment now, however, that 
amplifying d.c. voltage is not necessarily as 
easy as one might like. We have said that 
the values of electronic components can 
change with temperature, indeed the ther- 
mistor is an exaggerated example of this 
(but intended to do so beneficially). 

Unfortunately, op.amp circuits are no 
exception to this rule. Not only can the 
components which are used in conjunction 
with op.amps have their values changed 
according to temperature, but so too can the 
characteristics of the op.amp itself. 

The subject is actually too complicated 
to fully discuss or demonstrate as part of 
Teach-In, but it is something of which you 
should be aware. There are many circuit 
techniques by which the problem can be 
overcome, and more sophisticated (and 
expensive) op.amps in which the situation 
is less pronounced. 


TEMPERATURE DRIFT 


A particular example of an op.amp’s 
temperature dependency affects the d.c. 
output relative to the input. In a d.c. ampli- 
fication circuit you can set up a bias level 
on one input in order to bring it closer to 
the d.c. level on the other input (i.e. narrow 
the differential voltage between the two). 
The resulting d.c. output level, however, 
may only hold true at the temperature at 
which the adjustment is made. 

As the ambient (surrounding) temperature 
changes, so the d.c. output level can change, 
even though the voltage difference on the 
two inputs seemingly remains the same. 
Such a change is known as temperature drift. 
It will be far more pronounced at higher 
amplification settings. Typical temperature 
drift values are usually quoted in component 
data sheets, often in the form of graphs. 

You should also be aware that an op.amp 
can heat up internally when the current into 
or out of its output increases, and that this 
will affect its characteristics. 

For a.c. amplification (waveforms fed in 
and out via capacitors), though, tempera- 
ture drift is seldom of any significance. 


COMPUTER DEMOS 


We suggest that you now run two of the 
op.amp demo programs which interactively 


Everyday Practical Electronics, May 2000 


PANEL 7.4. RESISTANCE VALUES 


The question of what decade ranges 
the resistance values should be chosen 
from for op.amp’ designs is a-slightly 
tricky one. You will recognise that a uni- 
form potential divider, for instance, can 
be made up from any two equal resis- 
tance values. So, should the values each 
be 1Q, 10kQ or even 10M? 

We have to say first that only a text 
book heavily dedicated to op.amps can 
really give definitive answers. There are, 
though, some basic considerations which 
it is appropriate to mention here: 

One consideration is that power econ- 
omy should always be at the forefront of 
any designer’s mind. Since power con- 
sumption is less with higher value resis- 
tors, this does not favour very low 
resistances for the divider. 

We have already said that a divider’s 
resistance should ideally be .at least ten 
times less than the load into which it 
feeds. When the divider is feeding into 
the non-inverting input simply as bias, its 
resistance can therefore be comparatively 
high. When it is providing bias to the 
inverting input of a feedback circuit, the 
load is provided by the effective input 
resistance and so the divider resistance 
should be chosen with respect to that. 

The input resistance is chosen in rela- 
tion to the gain required and the resulting 
value of the feedback resistor. One mat- 
ter to consider here is that the gain of an 
amplifier (as opposed to a comparator) is 
usually best kept below about 200, and 
preferably below 100. 

In d.c. amplification circuits, another 
factor to be considered is that (again, 
ideally) both op.amp inputs should 


have equal current flow, and the resis-_ 


tances should be chosen to meet this 
condition. 


illustrate the functioning of inverting and 
non-inverting op.amp circuits. 

From the main menu select Op.amps — 
Menu, this will bring up another screen 
from which five op.amp demo programs 
can be selected. The two we suggest you 
play with now are Simple Inverting Amp 
and Simple Non-Inverting Amp. We shall 
discuss the other three options next 
month. 

The inverting demo _ illustrates - an 
op.amp’s response to an a.c. coupled input 
triangle waveform in respect of different 
resistance values. Resistors R1 and R2 con- 
trol the gain, while R3 and R4 change the 
bias on the non-inverting input. : 

The non-inverting demo also inputs an 
a.c. coupled triangle waveform. Resistors 
R1 and R2 control the gain. R4 has a fixed 
unspecified value; it is the “bleed”’ resistor 
required following input capacitor C3, The 
bias voltage applied via R4 can be changed. 

Signal input amplitude and frequency rate 
(Cycle Count) can also be changed. The 
power supply voltage is fixed at +5V/OV. 
Note that the demo op.amp has been given 
output min/max limits of 1V and 4V. 

The controls are stated on screen, press 
the appropriate keys to activate the function 
to be changed. Note the varying conditions 
under which the output signal can become 
clipped. You can press the <PAUSE> key to 


In choosing gain setting values, and 
those of the dividers, it should be borne 
in mind that very high values of resis- 
tance are prone to causing the circuit to 
pick up signals from external electrical 
sources, such as mains “hum’’, motor- 
bike ignition, frequency radiation from 
TV or computer monitors, etc. 

Additionally, the relationship between 
signal capacitors and resistors affects the 
frequency response of the circuit as a 
whole. Some of this capacitance can be 
due to that which exists in the op.amp 
itself, as well as the proximity of one 
printed circuit board track to another. 

With some op.amps a further problem 
is that if the load they feed into has quite 
a low resistance, distortion of the output 
can occur if the feedback resistance is too 
high. 

Asa very rough guide, however, the 
ranges of input and feedback resistances 
are usually best kept between about 1kQ 
and 1MQ, but it does depend on the cir- 
cumstances. It is then usually best if the 
values are chosen from the “common- 
place’’ decade multiples, such as those in 
the E12 range (see Part 1): 1, 1.2, 1.5, 1.8, 
2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8 and 8.2. 

To help you become more conversant . 
with what resistance values can be cho- 
sen for different op.amp circuits, study 
the published circuits of other electronics 
designers. 

Finally, despite this list of considera- 
tions, for general experimentation 
op.amps are really easy devices to use 
successfully. You can play around with 
component values to your heart’s content 
with an excellent chance of achieving 
results, even if not perfect. Furthermore, 
op.amps are such hardy devices that you 
are highly unlikely to ever kill one! 





stop the waveform scrolling, then press any 
other key to restart scrolling. 


NEXT MONTH 

This seems a convenient point at which 
to end this month’s Tutorial. We do not 
have room for an Experimental section as 
such, this has been moved forward to next 
month and becomes Tutorial Part.8. 

In reality, Part 7 and Part 8 are both a 
mixture of Tutorial and Experimental. 
What we discuss in Part 8, though, is all 
based on the. characteristics we have been 
describing here in Part 7, and illustrates 


‘some interesting ways in which op.amps 


can be used. 


MORE SOFTWARE 
Version VI.I of the Teach-in 2000 soft- 
- ware is now available on disk and from our 
website (www.epemag.wimborne.co.uk). 
The software includes all the previous pro- 
grams (some slightly updated) plus all 


those needed to see you through to the 
end of the series. 

Copy all the files on to your computer 
(having unzipped them first). When asked if 
you wish to overwrite ae dave files, say 
yes to all. 





389 


PRACTICALLY SPEAKING 





Robert Penfold looks at the Techniques of Actually Doing It! 


I IS SAID that the simplest inventions 
are the best ones, and, for the elec- 
tronics hobbyist, stripboard possibly 
ranks alongside sliced bread and the 
wheel in the best inventions stakes. 

Stripboard is a proprietary printed 
circuit board that is noted for its versa- 
tility. For most projects it represents the 
only practical alternative to using a cus- 
tom printed circuit board (p.c.b.). 

A project based on a custom board is 
actually the best choice for a complete 
beginner due to the relatively foolproof 
nature of these boards. However, many 
small and medium sized projects are 
based on stripboards, and newcomers 
to the hobby soon find themselves 
using this method of construction. 

Although stripboard is not quite as 
straightforward to use as custom 
p.c.b.s, it is not really that difficult to use 
either. There are a few traps waiting for 
the unwary, but once you are aware of 
the pitfalls it is not too difficult to obtain 
perfect results almost every time. 


Right Pitch 

So what exactly is stripboard? It is 
based.on a board about 1-6mm thick 
that is made from an insulating materi- 
al. Presumably the colour of the board 
varies from one manufacturer to anoth- 
er, but it seems to be supplied in a vari- 
ety of yellow-brown colours from almost 
white to virtually black. 

The board is drilled with one-milli- 
metre diameter holes on a _ regular 
matrix. In the past it was possible to 
obtain stripboards with the holes 
spaced at 0-1-inch, 0-15-inch, or 0-2- 
inch intervals, but these days only 0-1- 
inch boards are readily available. It is 
only 0-1-inch pitch boards that are of 
any real use with modern projects, 
because many components will not fit 
onto 0-15-inch or 0-2-inch boards. 

One side of stripboard is plain, while 
the other side has copper strips run- 
ning along the rows of holes. It is, of 
course, from these copper strips that 
the stripboard name is derived. Many 
people still refer to this material by the 
old proprietary name of “Veroboard”. 

Like an ordinary single-sided printed 
circuit board, the components are 
mounted on the plain side. The leadout 
wires are trimmed short on the other 
side and soldered to the copper strips, 
which then carry the connections from 
one component to another. Fig.1 shows 


the plain and copper sides of two - 


scraps of stripboard. 


Brittle Experience 

With a custom p.c.b. there is usually 
no preparation required. When you are 
ready to start construction you simply 
begin fitting the component to the 
board. With stripboard a small amount 
of work is needed before the board is 
ready to accept the components, and 
the normal first step is to cut out a 


390 


board of the required 
size. 

As pointed out 
previously, _ strip- 
board comes ina 
range yellow-brown 
colours, reflecting a 
range of materials 
used in the board. 
Some of these mate- 


rials are tougher 
than others, but 
most _ stripboards 


seem to be slightly 
brittle. It is best to err 
on the side of cau- 
tion and assume that 
all these boards are 
brittle, and exercise , : 

due care when working on them. Use 


the “hammer and tongs” approach and 


you may well end up with three or four 
small boards instead of one large one! 

Over the years various suggestions 
have been made for quick and easy 
ways of cutting stripboard to size using 
implements such as glass and tile cut- 
ters. The problem with these methods 
is that they work well with some makes 
of stripboard, but can produce disas- 
trous results with others. 

The only truly reliable method found 
so far is to carefully cut along rows of 
holes using a hacksaw. Due to the 
close spacing of the holes and width of 
the blade it is not practical to cut 
between rows. Cutting along rows of 
holes inevitably produces some very 
rough edges, but these are easily filed 
to a neat finish using a flat file. 

The finished board might slot into 
place in the case, but it is more likely 
that it will be bolted in place. Any 
mounting holes should be drilled at this 
stage using an ordinary HSS twist drill. 
Use a piece of scrap timber, chipboard, 
etc. underneath the board, and: use 
only moderate pressure. This should 
give good “clean” holes and avoid any 
cracking around them. 

When drilling any form of copper 
laminate board it is best to drill 
the board with the copper side 
uppermost, as there is. other- 
wise a risk of the copper being 
torn away from the board. 





The article describing the pro- 
ject should include a diagram 
that clearly shows the positions 
of the breaks, as in the example 
of Fig.2. Double-check the posi- 





Fig.1. Stripboard only has the copper strips on one side 


tion of each break before actually mak- 
ing it. If a mistake should be made it is 
possible to solder a small piece of wire 
over the break, but more than the occa- 
sional repair will give scrappy looking 
results and poor reliability. 

A special strip-cutting tool is avail- 
able, and it is often referred to as a 
“spot face cutter” in component. cata- 
logues. This is basically just a drill style 
Cutting tool fitted in a handle. In order to 
cut a strip the point of the tool is placed 
in position and the handle is given a 


- couple of rotations while applying mod- 


erate pressure (Fig.3). 

If you will be producing anything 
more than the occasional stripboard 
project it is certainly worthwhile buying 
this tool. Initially you may prefer to use 
a handheld twist drill bit of about 5mm 
in diameter, which will do the job quite 
well. | 

Either way, make quite sure that the 
strips are cut right across their full 
width. Very fine residual tracks of cop- 
per can be difficult to see with the 
naked eye, so it is worth checking the 


board with the aid of a magnifier. 


@®ooes oso @ 

o0oo0o00c08:08062€U600l8U8 

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o 0o0o 90980 090 

000 8 8 8 GB 
» Big Breaks | © © o o Go o « @ of 
With anything but the most FESS S Seeger 
simple of projects it is necessary 
to make some breaks in the 
copper strips. Without any cuts 
each strip can only carry one set 
of interconnections, but by 
pieces, it can carry three sets of 
connections. ra a ) 


Although you need to make sure that 
the strips are cut properly, do not go to 
the other extreme and practically drill 
through the board. With a large number 











Fig.2. The underside view of the board will 
clearly show the positions of any breaks 
required in the copper strips. 


Everyday Practical Electronics, May 2000 


_ of breaks this would seriously weaken 
it. Brush away any copper shavings as 
these could otherwise cause short 
circuits. 


Moving In 

At this stage the board is ready — 
the components to be added. This is 
one respect in which stripboard is 
rather more awkward than a custom 
printed circuit board. With a p.c.b. there 
is one hole per leadout wire or pin, but 
with stripboard less than 10 percent of 
the holes are normally used. 


Mistakes with component placement | 
are more easily made, and when they — 


do occur they can be difficult to spot. To 
compensate for this it is necessary to 
proceed more carefully and to double- 
check the positioning before fitting and 
soldering each component in place. 

Having to remove and refit a small 
component occasionally is not a major 
disaster, but getting a multi-pin compo- 
nent, such as an integrated circuit (i.c.), 
in the wrong place can be more difficult 
to deal with. Removing this type of 
component requires proper desolder- 
ing equipment and risks damaging the 
board. 





Fig.3. Using the special tool provides 
the easiest way of making breaks in the 
copper tracks. 


Getting a large number of compo- 
nents shifted out of position is time 
consuming to correct, and all the sol- 
dering and desoldering could take its 
toll on the board. It is much better to 
proceed carefully and get things right 
first time. 


On Your Marks 

Stripboard layout diagrams often 
have letters to identify the copper strips 
and numbers to identify the columns of 
holes, as in the dummy layout diagram 
of Fig.4. Many constructors find it use- 
ful to mark the board itself with these 
letters and numbers, so that they can 
quickly and easily match any point on 
the board with its equivalent point on 
the diagram. 

A fine point fibre-tip pen is required, 
as there is not a great deal of space 
available for the labels. Also, it needs to 
be a type that is capable of writing on 
glass and other non-porous surfaces. 
Otherwise it will not mark the board 
properly, or the labels will rub off the 
first time you handle the board. | 


Everyday Practical Electronics, May 2000 


It is difficult to mark numbers for all 
the columns of holes, but navigating 
your way around the board should still 


be easy if only every fifth or tenth col- | 


umn is labelled. Similarly, it is only nec- 
essary to label every other copper strip, 
or even every fourth or fifth strip. 

Do not make the classic mistake of 
getting the orientation of the board 
wrong so that all the components are fit- 
ted in the wrong places. There are usual- 
ly mounting holes that make the correct 
orientation obvious, but the diagrams for 
the two sides of the board normally have 
a marker that indicates the same corner 
of the board in both views. This is includ- 
ed in Fig.2 and Fig.4, and leaves no 
excuse for getting it wrong. 


Missing Link 

With the preliminaries out of the way, 
assembling a component panel is 
much the same whether it is based on 
stripboard or a p.c.b. There are a cou- 
ple of differences though, one of which 
is the higher number of /ink-wires 
encountered when building projects 
based on stripboard. 

The copper tracks of a custom p.c.b. 
can weave all round the board if neces- 
sary, but this is clearly not possible with 
stripboard. Link-wires provide a means 
of compensating for the lack of versatil- 
ity in the track pattern, and enable con- 
nections to run from any given point on 
the board to any other point. Virtually 
every stripboard layout has at least a 
few link-wires, and the larger boards 
can have dozens of them. 

The usual way of fitting link-wires is 
to preform a piece of wire to fit into the 
layout in much the same way as resis- 
tors and axial capacitors are fitted. The 
ends of the wires are then trimmed to 
length and soldered to the board in the 
usual way. 

An alternative method is: to cut a 
piece of wire that is slightly over-length 
and then solder one end of it to one of 
the holes in the board. Next thread the 
other end of the wire through the sec- 
ond hole and pull it tight using a small 
pair of pliers. Finally trim the wire and 
solder it to the board. 

The trimmings from resistor leadout 
wires are ideal for short link-wires, but 
for longer wires 22s.w.g. or 24s.w.g. (or 
about 0-6mm dia.) tinned copper wire is 
needed. Where a layout has a lot of 
link-wires be sure to meticulously 
check that every link has been fitted to 
the board. 


Corner he duster eBESS 


123 45 6 7 8 9 10 111213 1415 16 17 18 19 20 21 22 23 24 


eoeootooooceoeoeaoaeeseeeeeeeeaeast ee 8 
° ° 
O ———Mounting holes» (C) ° 


OTN 


|e 
A an 


SK1 SK2 


ocgoocoo 0000800 





Fig.4. An example stripboard layout diagram. 








Fig.5. Removing some excess flux ren- 
dered this solder bridge fairly obvious. 


There is no need to insulate short 
links, but with wires of around 25mm or 
more in length there is a slight risk of 
short circuits occurring, particularly 
where there are several wires running 
side by side. In this case, it is advisable 
to fit the longer link-wires with pieces of 
p.v.c. Sleeving. 


Building Bridges 

The second potential problem with 
stripboard is accidental short. circuits 
due to solder splashes and excess sol- 
der on joints. This can be a problem 
with any form of printed circuit board, 
but it tends to be more problematic with 


‘Stripboard due to the very narrow gap 


between one track and the next. There 
is actually only about 0-3mm between 
adjacent tracks. 

Usually it is fairly obvious when 
excess solder bridges two tracks, and 
remedial action can be taken straight 
away. Small amounts of excess solder 
can usually be wiped away with the bit 
of the soldering iron, but large amounts 
should be removed using a desoldering 
pump. The affected joint or joints can 
then be carefully remade. 

The real problems are caused by the 
tiny trails of solder that are barely visi- 
ble. In fact, they are sometimes buried 
under excess flux and can only be seen 
if the board is cleaned (Fig.5). 

Having completed a stripboard it is 
definitely advisable to clean the copper 
side of the board and thoroughly check 
it for solder bridges. Cleaning fluids for 
removing excess flux are available, but 
simply scrubbing the board vigorously 
with something like an old toothbrush 
seems to do an equally good job. 

Any reasonably powerful magnify- 
ing glass will provide a good close-up 
view of the board, but something like 

an 8x or 10x loupe is best. These 

are primarily intended for viewing 

slides and they are available from 

most camera shops. The cheap- 

est of loupes is adequate for this 
Si! application. 

If a stripboard refuses to work for 
no apparent reason it is worthwhile 
making some checks using a con- 
tinuity tester. Check that there are — 
no short circuits between adjacent 
copper strips or across any breaks 

pi- in the strips. Usually, once you 
know a short circuit is there it will 
miraculously appear when the 
board is given another visual 
check! 


391 


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projects that are easily constructed from readily available 
components. Stripboard layouts and wiring diagrams are 
provided for each project. The projects covered include: 
constant voltage controller; pulsed controller; pushbutton 
pulsed controller; pulsed controller with simulated inertia, 
momentum and braking; automatic signals; steam whistle 
sound effect; two-tone horn sound effect; automatic two- 
tone horn effect; automatic chuffer. 

The final chapter covers the increasingly popular sub- 
ject of using a computer to control a model railway layout, 
including circuits for computer-based controllers and sig- 


nalling systems. 
Order code BP384 £4.99 


151 pages 

A PRACTICAL INTRODUCTION TO SURFACE 

MOUNT DEVICES 

Bill Mooney 

This book takes you from the simplest possible starting 
point to a high level of competence in handworking with 
surface mount devices (SMD’s). The wider subject of SM 
technology is also introduced, so giving a feeling for its 
depth and fascination. 

Subjects such as p.c.b. design, chip control, soldering 
techniques and specialist tools for SM are fully explained 
and developed as the book progresses. Some useful con- 
structional projects are also included. 

Whilst the book is mainly intended as an introduction, it 
is also an invaluable reference book, and the browser 
should find it engrossing. 


120 pages Order code BP411 £4.99 


394 





PROJECT CONSTRUCTION 


_-EPE BOOKS 





TEACH-IN No. 7. plus FREE SOFTWARE 
ANALOGUE AND DIGITAL ELECTRONICS COURSE 
| eet by gokbe lA Practical Electronics) 

lan Winstanley and Keith Dye B.Eng(Tech)AMIEE 
This highly acclaimed EPE Teach-/n series, which included 
the construction and use of the Mini Lab and Micro Lab 
test and development units, has been put together in 
book form. Additionally, EPT Educational Software have 
developed a GCSE Electronics software program to com- 
pliment the course and a FREE DISK covering the first two 
parts of the course is included with the book. 

An interesting and thorough tutorial series aimed speci- 
fically at the novice or complete beginner in electronics. 
The series is designed to support those undertaking either 
GCSE Electronics or GCE Advanced Levels, and starts 
with fundamental principles. 

If you are taking electronics or technology at school 
or college, this book is for you. If you just want to 
learn the basics of electronics or technology you must 
make sure you see it. Teach-/n No. 7 will be invaluable 
if you are considering a career in electronics or even 
if you are already training in one. The Mini Lab and 
software enable the construction and testing of both 
demonstration and development circuits. These learn- 
ing aids bring electronics to life in an enjoyable and 
interesting way: you will both see and hear the electron 
in action! The Micro Lab microprocessor add-on system 
will appeal to higher level students and those develop- 
ing microprocessor projects. 


160 pages £3.95 


FAULT-FINDING ELECTRONIC PROJECTS 
R. A. Penfold 
Starting with mechanical faults such as dry joints, 
short-circuits etc, coverage includes linear circuits, using a 
meter to make voltage checks, signal tracing techniques 
and fault finding on logic circuits. The final chapter covers 
ways of testing a wide range of electronic components, 
such as resistors, capacitors, operational amplifiers, 
diodes, transistors, SCRs and triacs, with the aid of only a 
limited amount of test equipment. 

The construction and use of a Tristate Continuity Tester, 
a Signal Tracer, a Logic Probe and a CMOS Tester are also 


included. 

136 pages £4.99 
TEST EQUIPMENT CONSTRUCTION 

R. A. Penfold 


This book describes in detail how to construct some 
simple and inexpensive but extremely useful, pieces of 
test equipment. Stripboard layouts are provided for 
all designs, together with wiring diagrams where ap- 
propriate, plus notes on construction and use. 
The following designs are included:— 
AF Generator, Capacitance Meter, Test Bench Amplifier, 
AF Frequency Meter, Audio Mullivoltmeter, Analogue 
Probe, High Resistance Voltmeter, CMOS Probe, Transis- 
tor Tester, TTL Probe. 
The designs are suitable for both newcomers and more 
experienced hobbyists. 
104 pages £3.99 






Order code BP248 


HOW TO DESIGN AND MAKE YOUR OWN PC.B.s 

R. A. Penfold 

Deals with the simple methods of copying printed circuit 
board designs from magazines and books, and covers 
all aspects of simple p.c.b. construction including photo- 
graphic methods and designing your own p.c.b.s. 


66 pages Order code BP121 £3.99 


ELECTRONIC PROJECT BUILDING FOR BEGINNERS 
R. A. Penfold 
This book is for complete beginners to electronic project 
building. It provides a complete introduction to the practical 
side of this fascinating hobby, including the following topics: 
Component identification, and buying the right parts; 
Resistor colour codes, capacitor value markings, etc; Advice 
on buying the right tools for the job; Soldering, with advice 
on how to produce good joints and avoid “dry” joints; 
Making easy work of the hard wiring; Construction methods, 
including stripboard, custom printed circuit boards, plain 
matrix board, surface mount boards and wire-wrapping; 
Finishing off, and adding panel labels; Getting “problem” 
rojects to work, including simple methods of fault-finding; 
n fact everything you need to know in order to get started in 
this absorbing and creative hobby. 


135 pages £4.95 














The books listed have been 
selected by Everyday Practi- 
cal Electronics editorial staff 
as being of special interest 
‘to everyone involved in elec- 
tronics and computing. They 
are supplied by mail order 
to your door. Full ordering 
details are given on the last 
book page. 


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RADIO / TV 


VIDEO 





ELECTRONIC PROJECTS FOR VIDEO 

ENTHUSIASTS 

R. A. Penfold 

This book provides a number of practical designs for 
video accessories that will help you get the best results 
from your camcorder and VCR. All the projects use 
inexpensive components that are readily available, and 
they are easy to construct. Full construction details are 
provided, including stripboard layouts and wiring dia- 
grams. Where appropriate, simple setting up procedures 
are described in detail; no test equipment is needed. 

The projects covered in this book include: Four channel 
audio mixer, Four channel stereo mixer, Dynamic noise 
limiter (DNL), Automatic audio fader, Video faders, Video 
wipers, Video crispener, Mains power supply unit. 


109 pages £4.95 


a ee UP AN AMATEUR RADIO STATION 

. D. Poole 

The aim of this book is to give guidance on the decisions 
which have to be made when setting up any amateur 
radio or short wave listening station. Often the ex- 
perience which is needed is learned by one’s mistakes, 
however, this can be expensive. To help overcome this, 
guidance is given on many aspects of setting up and 
running an efficient station. It then proceeds to the 
steps that need to be taken in gaining a full transmitting 
licence. 

Topics covered include: The equipment that is 
needed; Setting up the shack; Which aerials to use; 
Methods of construction; Preparing for the licence. 

An essential addition to the library of all those taking 
their first steps in amateur radio. 


86 pages £3.95 
EXPERIMENTAL ANTENNA TOPICS 
H. C. Wright 


Although nearly a century has passed since Marconi’s first 
demonstration or radio communication, there is still re- 
search and experiment to be carried out in the field of 
antenna design and behaviour. 

The aim of the experimenter will be to make a 
measurement or confirm a principle, and this can be done 
with relatively fragile, short-life apparatus. Because of this, 
devices described in this book make liberal use of 
cardboard, cooking foil, plastic bottles, cat food tins, etc. 
These materials are, in general, cheap to obtain and easily 
worked with simple tools, encouraging the trial-and-error 
philosophy which leads to innovation and discovery. 

Although primarily a practical book with text closely 
supported by diagrams, some formulae which can be 
used by straightforward substitution and some simple 
graphs have also been included. 


72 pages £3.50 


= kenny INDOOR AND WINDOW AERIALS 

. M. No 

Many people live in flats and apartments or other types of 
accommodation where outdoor aerials are prohibited, or 
a lack of garden space etc. prevents aerials from being 
erected. This does not mean you have to forgo shortwave 
listening, for even a 20-foot length of wire stretched out 
along the skirting board of a room can produce accept- 
able results. However, with some additional effort and ex- 
perimentation one may well be able to improve perfor- 
mance further. 

This concise book tells the story, and shows the reader 
how to construct and use 25 indoor and window aerials that 
the author has proven to be sure performers. 

Much information is also given on shortwave bands, aerial 
directivity, time zones, dimensions etc. 


SO pages £1.75 


Everyday Practical Electronics, May 2000 





TWO EXCITING BOOKS 


Specially imported by EPE 


Bebop To The 
Boolean Boogie 
By Clive (call me Max) Maxfield 
ORDER CODE BEB1 £24.95. 


An Unconventional Guide to Electronics 
Fundamentals, Components and Processes 


The Foreword by Pete Waddell, Editor, Printed Circuit Design, reads: 


“Personally, | think that the title of this tome alone (hmmm, a movie?) . 


should provide some input as to what you can expect. But, for those 


who require a bit more: be forewarned, dear reader, you will probably 


learn far more than you could hope: to expect from Bebop 
to the Boolean Boogie, just because of the unique approach 
Max has to technical material. The author will guide you from 
| the basics through a minefield 
of potentially boring theoretical 
mish-mash, to a Nirvana. of 
understanding. You will not suf- 
fer that fate familiar to every 
reader: re-reading paragraphs 
over and over wondering what 
in the world the author was 
trying to say. For a limey, Max 
shoots amazingly well and from 
the hip, but in a way that 
will keep you interested and 
poe amused. If you are not vigilant, 
you may not only learn some- 
_ thing, but you may even enjoy 
| the process. The only further 
| advice | can give is to ‘expect 
the unexpected’.” } 
) This book gives the “big pic- 
, ture” of digital electronics. This 
indepth, highly readable, up-to-the-minute guide shows you how 
electronic 
transistors operate, how printed circuit boards are fabricated, and 
what the innards of memory ICs look like. You'll also gain a working 
knowledge of Boolean Algebra and Karnaugh Maps, and understand 


B<eBOpP 


0) Ge 
BOGE / 





what Reed-Muller logic is and how it’s used. And there’s much, 


MUCH more (including a recipe for a truly great seafood gumbo). 
Hundreds of carefully drawn illustrations clearly show the impor- 
tant points of each topic. The author's tongue-in-cheek British humor 


makes it a delight to read, but this is a REAL technical book, ex- - 


tremely detailed and accurate. A bbe reference for your own shelf, 
and also an ideal gift for a friend or family member who wants to 
understand what it is you do all day. ... 


By importing these books ourselves we have managed to 
make them available in the UK at an exceptional price. 





evices work and how they’re made. You'll discover how ~ 


Audio and Music 


Bebop Bytes Back 


By Clive’*Max’” Maxfield and 
Alvin Brown 
ORDER CODE BEB2 £29.95 
An Unconventional Guide To Computers 


Plus FREE CD-ROM which includes: Fully Functional 
Internet-Ready Virtual Computer with Interactive Labs 


The Foreword by Lee Felsenstein reads: 


“1, The more time you spend with this book and its accompany- 
ing CD-ROM, the more you'll get out of it. Skimming through it 
won't take you where you want to go. Paying serious attention, on 
the other hand, will teach you more about computers than you can 
imagine. (You might also see a few beautiful sunrises.) 

2. The labs work on two levels: on and under the surface. When 
you're performing the labs Shei 
you'll need to look for pat- # | 
terns that build up from in- 
dividual events. .. 

3.. When you're done, 
you won't look any different. 

ou won't get a trophy ora 
certificate to hang on your 
wall. You'll have some 
knowledge, and some skill, 
and you'll be ready to 
find more knowledge and 
develop more skill. Much of 
this will be recognisable 
only to someone who has 
the same knowledge and hy 
skill.” Fully Functional Internet| 

This follow-on to Bebop [itenermetelus 
to the Boolean Boogie. is a ® s 
multimedia extravaganza 
of information about how 
computers work. It picks 
up where “Bebop I” left off, guiding you through the 
fascinating world of computer design... and you'll have a few 
chuckles, if not belly laughs, along the way. In addition to over 
200 megabytes of mega-cool multimedia, the accompanying 
CD-ROM (for Windows 95 machines only) contains a virtual 
microcomputer, simulating the motherboard and _ standard 
computer peripherals in an extremely realistic manner. In 
addition to a wealth of technical information, myriad nuggets of 
trivia, and hundreds of carefully drawn illustrations, the book 
contains a set of lab experiments for the virtual microcomputer 


An Unconventional Guide to 
Computers 





that let you recreate the experiences of early computer 


pioneers... | 
lf you're the slightest bit interested in the inner workings of 
computers, then don’t dare to miss this one! 


POSTAGE 





VALVE & TRANSISTOR AUDIO 
AMPLIFIERS 
John Linsley Hood . 
This is John Linsley Hood’s greatest work yet, describing 
the milestones that have marked the development. of 
audio. amplifiers since the earliest days to the latest 
systems. Including classic amps with valves at their heart 
and exciting new designs using the latest components, 
this book is the complete world guide to audio amp 
design. 
Contents: Active components; Valves or vacuum tubes; 
Solid-state devices; Passive components; Inductors and 
transformers; Capacitors, Resistors, Switches and electri- 
cal contacts; Voltage amplifier stages using valves; 
Valve audio amplifier layouts; Negative feedback; Valve 
operated power amplifiers; Solid state voltage amplifiers; 
Early solid-state audio amplifiers; Contemporary power 


amplifier designs; Preamplifiers; Power supplies (PSUs); — 


Index. 
250 pages £19.99 
AUDIO AMPLIFIER PROJECTS 


R. A. Penfold 


A wide range of useful audio amplifier projects, each project - 


features a circuit diagram, an explanation of the circuit 
operation and a stripboard layout diagram. All construc- 
tional details are provided along with a shopping list of 
components, and none of the designs requires the use 
of any test equipment in order to set up properly. All 
the projects are designed for straightforward assembly on 
simple circuit boards. 


Everyday Practical Electronics, May 2000 


Circuits include: High impedance mic preamp, Low 
impedance mic preamp, Crystal mic preamp, Guitar and GP 
preamplifier, Scratch and rumble filter, RIAA preamplifier, 
Tape preamplifier, Audio limiter, Bass and treble tone 
controls, Loudness filter, Loudness control, Simple graphic 
equaliser, Basic audio mixer, Small (300mW) audio power 
amp, 6 watt audio power amp, 20/32 watt power amp and 
power supply, Dynamic noise limiter. . 

A must for audio enthusiasts with more sense than 


money! 

116 pages £9.95 
MAKING MUSIC WITH DIGITAL AUDIO 

lan Waugh ; 


In this practical and clearly-written book, lan Waugh explains 
all aspects of the subject from digital audio basics to putting 
together a system to suit your own music requirements. 
Using the minimum of technical language, the book explains 
exactly what BN need to know about: Sound and digital 
audio, Basic digital recording principles, Sample rates and 
resolutions, Consumer sound cards and dedicated digital 
audio cards. 

On a practical level you will learn about: sample edit- 
ing, digital multi-tracking, digital FX processing, integrat- 
ing MIDI and digital audio, using sample CDs, mastering 
to DAT and direct to CD, digital audio and Multimedia. . 

This book is for every musician who wants to be a part 
of the most important development in music since the 
invention of the b aicdge dino It’s affordable, it’s flexible, 
it’s powerful and it’s here now! It’s digital and it’s the 
future of music making. 


256 pages £14.95 








You only pay 


£1°50 


per order 
(UK postage) 


NO MATTER HOW 
MANY BOOKS 
YOU ORDER 


Overseas Readers see 
ORDERING DETAILS on the 
next page for overseas 
postage prices 












395 


CIRCUITS AND DESIGN 





AN INTRODUCTION TO PIC MICROCONTROLLERS 
Robert Penfold 
Designing your own PIC based projects may seem a 


daunting task, but it is really not too difficult providing you 


have some previous experience of electronics. The PIC 
processors have plenty of useful features, but they are still 
reasonably simple and straightforward to use. This book 
should contain everything you need to know. 


Topics covered include: the PIC register set; numbering , 
systems; bitwise operations and rotation; the PIC instruction. © 


set; using interrupts; using the analogue to digital converter; 


clock circuits; using the real time clock counter (RTCC); 


using subroutines; driving seven segment displays. 
166 pages 


PRACTICAL OSCILLATOR CIRCUITS 
A. Flind 


Extensive coverage is given to circuits using capacitors and 
resistors to control frequency. Designs: using CMOS, timer: © 


i.c.s and op.amps are all described in detail, with a special 
chapter on “waveform generator” i.c.s. Reliable “white” and 
“pink” noise generator circuits are also included. 

Various circuits using inductors and capacitors are 
covered, with emphasis on stable low frequency gener- 
ation. Some of these are amazingly simple, but are still 
very useful signal sources. 

Crystal oscillators have their own chapter. Many of the 
circuits shown are readily available special i.c.s for 
simplicity and reliability, and -offer several output fre- 
quencies. Finally, complete constructional details are 
given for an audio sinewave generator. 


133 pages Order code BP393 £4.99 


PRACTICAL ELECTRONIC CONTROL PROJECTS 

Owen Bishop 

Explains electronic control theory in simple, non- 
mathematical terms and is illustrated by 30 practical 
designs suitable for the student or hobbyist to build. 
Shows how to use sensors as input to the control system, 
and how to provide output to lamps, heaters, solenoids, 
relays and motors. 


Computer based control is explained by practical 


examples that can be run on a PC. For stand-alone 
systems, the projects use microcontrollers, such 
as the inexpensive and easy-to-use Stamp BASIC 
_microcontroller. These projects are chosen to introduce 
and demonstrate as many aspects as possible of -the 
programming language and techniques. 


198 pages Order code BP377 Eiges 


PRACTICAL ELECTRONICS HANDBOOK - 

Fourth Edition. lan Sinclair 

Contains all of the everyday information that anyone 
working in electronics will need. 


It provides a practical and comprehensive collection 


of circuits, rules of thumb and design data for profes- 
sional engineers, students and enthusaists, and there- 
fore enough background to allow the understanding and 
development of a range of basic circuits. 


_440 pages 


Order code BP394 £5.99 





£5.99 - 


Contents: Passive components, Active discrete 
components, Discrete component circuits, Sensing 


components, Linear |.C.s, Digital |.C.s, Microprocessors 


and microprocessor systems, Transferring digital data, 
Digital-analogue conversions, Computer aids_ in 


electronics, Hardware components and practical work, 


Standard metric wire table, Bibliography, The HEX scale, 


Index. 
Order code NE21 £14.99 


_. COIL DESIGN AND CONSTRUCTIONAL MANUAL 


B. B. Babani 

A complete book for the home constructor on “how to 
make” RF, IF, audio. and power coils, chokes and trans- 
formers. Practically every possible type is discussed and 
calculations necessary are given and explained in detail. 
Although this book is now twenty years old, with the 


exception of toroids and-pulse transformers little has 
changed in coil design since it was written. 


96 pages £3.99 
OPTOELECTRONICS CIRCUITS MANUAL 
R. M. Marston 


A useful single-volume guide to the optoelectronics 
device user, specifically aimed at the practical design 
engineer, technician, and the experimenter, as well as the 
electronics student. and amateur. It deals with the subject 


in an easy-to-read; down-to-earth, and non-mathematical . 


yet comprehensive manner, explaining the basic prin- 
ciples and characteristics of the best known devices, and 


‘presenting the reader with many practical applications 


and over 200 circuits. Most of the i.c.s and other devices 
used are inexpensive and readily available types, with 
universally recognised type numbers. 


182 pages B Order code NE14, £14.99 


INTRODUCTION TO DIGITAL AUDIO 
(Second Edition) 
lan Sinclair 


_ Digital recording methods have existed for many years 


and have become familiar to the professional recording 


‘engineer, but the compact disc (CD) was the first device to 


bring audio methods into the home. The next step is the 
appearance of digital audio tape (DAT) equipment. 
All this development has involved methods and circuits 


that are totally ‘alien to the technician or keen amateur 


who has previously worked with audio circuits. The prin- 
ciples and practices of digital audio owe little or nothing 
to the traditional linear circuits of the past, and are much 
more comprehensible to today’s computer engineer than 
the older generation of audio engineers. 

This book is intended to bridge the gap of understand- 
ing for the technician and enthusiast. The principles and 





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AUDIO AND MUSIC 


OPERATIONAL AMPLIFIER USER’S HANDBOOK 

R. A. Penfold 

The first part of this book covers standard operational 
amplifer based “building blocks” (integrator, precision 
rectifier, function generator, amplifiers, etc), and con- 
siders the ways in which modern devices can be used 
to give superior performance in each one. The second 
part describes a number of practical circuits that exploit 
modern operational amplifiers, such as high slew-rate, 
ultra low noise, and low input offset devices. The projects 
include: Low noise tape preamplifier, low noise RIAA 
preamplifier, audio power amplifiers, d.c. power con- 
trollers, opto-isolator audio. link, audio millivolt meter, 
temperature monitor, low distortion audio signal gener- 
ator, simple video fader, and many more. 


120 pages Order code BP335 £4.95 


A BEGINNERS GUIDE TO CMOS DIGITAL ICs 

R. A. Penfold 

Getting started with logic circuits can be difficult, since 
many of the fundamental concepts of digital design tend 
to seem rather abstract, and remote from obviously useful 
applications. This book covers the basic theory of digital 
electronics and the use of CMOS integrated circuits, but 
does not lose sight of the fact that digital electronics has 
numerous “real world” applications. 

The topics covered in this book include: the basic con- 
cepts of logic circuits; the functions of gates, inverters and 
other logic “building blocks”; CMOS logic i.c. characteris- 
tics, and their advantages in practical circuit design; oscil- 
lators and monostables (timers); flip/flops, binary dividers 
and binary counters; decade counters and display drivers. 

The emphasis is on a practical treatment of the subject, 
and all the circuits are based on “real” CMOS devices. A 
number of the circuits demonstrate the use of CMOS logic 
i.c.s in practical applications. 


119 pages Order code BP333 £4.95 


methods are explained, but the mathematical background 
and theory is avoided, other than to state the end product. 


128 pages £7.95 
PROJECTS FOR THE ELECTRIC GUITAR 
J. Chatwin 


This book is for anyone interested in the electric guitar. It 
explains how the electronic functions of the instrument 
work together, and includes information on the various 
pickups and transducers that can be fitted. There are com- 
plete circuit diagrams for the major types of instrument, 
as well as a selection of wiring modifications and pickup 
switching circuits. These can be used to help you create 
your own custom wiring. 

Along with the electric guitar, sections are also in- 
cluded relating to acoustic instruments. The function of 
specialised piezoelectric pickups is explained and there 
are detailed instructions on how to make your own 
contact and bridge transducers. The projects range from 
simple preamps and tone boosters, to complete active 
controls and equaliser units. 


92 pages £4.95 
MIDI SURVIVAL GUIDE 
Vic Lennard 


Whether you’re a beginner or a seasoned pro, the MIDI 
Survival Guide shows you the way. No maths, no MIDI 
theory, just practical advice on starting up, setting up 
and ending up with a working MIDI system. 

Over 40 cabling diagrams. Connect synths, sound 
modules, sequencers, drum machines and multitracks. 
How to budget and buy secondhand. Using switch, 
thru and merger boxes. Transfer songs between 
different sequencers. Get the best out of General MIDI. 
Understand MIDI implementation charts. No MIDI 
theory. 


104 pages Temporarily out of print 


PRACTICAL ELECTRONIC MUSICAL 
EFFECTS UNITS 
R. A. Penfold 
This book provides practical circuits for a number of 
electronic musical effects units. All can be built at rela- 
tively low cost, and use standard, readily available com- 
a The projects covered include: Waa-Waa Units; 
istortion Units; Phaser; Guitar Envelope Shaper; 
Compressor; Tremolo Unit; Metal Effects Unit; Bass 
and Treble Boosters; Graphic Equaliser; Parametric 
Equaliser. The projects cover a range of complexities, 
but most are well within the capabilities of the average 
electronics hobbyist. None of them require the use of 
test equipment and several are suitable for near 


beginners. 
102 pages £4.95 


LOUDSPEAKERS FOR MUSICIANS 
Vivan Capel 
This book contains all that a working musician needs to 
know about loudspeakers; the different types, how they 
work, the most suitable for different instruments, for 
cabaret work, and for vocals. It gives tips on construct- 
ing cabinets, wiring up, when and where to use wad- 
ding, and when not to, what fittings are available, finish- 
ing, how to ensure they travel well, how to connect 
multi-speaker arrays and much more. 

Ten practical enclosure designs with plans and com- 
ments are given in the last chapter, but by the time 
you've read that far you should be able to design your 


own! 
164 pages Order code BP297 £4.99 


Everyday Practical Electronics, May 2000 


PROJECT TITLE — | Order Code 
Musical Sundial JUNE’99 £9.51 
PC Audio Frequency Meter _ £8.79 
P| 
12V Battery Tester 


Intruder Deterrent 


Printed circuit boards for certain EPE constructional projects are available from the 
PCB Service, see list. These are fabricated in glass fibre, and are fully drilled and 
roller tinned. All prices include VAT and postage and packing. Add £1 per board for 
airmail outside of Europe. Remittances should be sent to The PCB Service, 
Everyday Practical Electronics, Allen House, East Borough, Wimborne, Dorset . 

BH21 1PF. Tel: 01202 881749; Fax 01202 841692 (NOTE, we cannot reply toover- J Sound Activated Switch _ 

seas orders or queries by Fax); E-mail: orders@epemag.wimborne.co.uk. peezer Alarm Multi-project PCB SEPT'OO IMP eat 
Cheques should be crossed and made payable to Everyday Practical Electronics Variable Dual Power Suppl 


(Payment in £ sterling only). 7 7 OCT’99 7 0 
NOTE: While 95% of our boards are held in stock and are dispatched within och tiaie: me °7 88 
seven days of receipt of order, please allow a maximum of 28 days for delivery | %!nteriorLamp Delay == p 53.00 
— overseas readers allow extra if ordered by surface mail. Mains Cable Locator (Multi-project PCB 


%& 8-Channel Analogue Data Logger 
Buffer Amplifier (Oscillators Pt 2) 
Magnetic Field Detective 


Back numbers or photostats of articles are available if required — see the Back Vibralarm NOV’99 Sie ren 
ang ae ge FGnornoos Spat ar cs | 
Please check price and availability in the latest issue. &Ginormous Stopwatch — Part 2~ DEC’99 

Boards can only be supplied on a payment with order basis. — Giant Display 247 £7.85 


Serial Port Converter 248 £3.96 
249 £4.44 


Scratch Blanker JAN’00 *- eee £4.83 
Flashing Snowman (Multi-project PCB £3.00 


% Video Cleaner FEB’00 £5.63 
Find It £4.20 
*& Teach-in 2000 — Part 4 £4.52 


PROJECT TITLE Order Code 


Remote Control Finder olou m:y4 168 £6.32 
Rechargeable Handlamp 169 £6.23 
& PIC Water Descaler 170 £6.90 
% EPE Time Machine NOV’97 171 £8.34 






































Auto-Dim Bedlight 172 £6.63 ; 

Portable 12V PSU/Charger 173 e861" 1B  pecorcraive facehyp: oce’scr }] £5.49 
Car Immobiliser DEC 97 % EPE Icebreaker — PCB257, programmed 

Safe and Sound (Security Bleeper 17 £7.32 PIC16F877 and floppy disc Set Only |£22.99 
Surface Thermometer JAN’98 ing W S 

Disco Lights Flasher 178 £8.30 %& Micro-PiCscope 

Waa-Waa Pedal (Multi-project PCB) FEB’98 932 £3.00 | Garage Link 


% Virtual Scope — Digital Board 
Analogue Board (per board) 

%& Water Wizard 

Kissometer 

% EPE PIC Tutorial 

The Handy Thing (Double-Sided) 

Lighting-Up Reminder 

% Audio System Remote Controller —- PSU 

Main Board 


Transmitter 
Receiver 
ic/Audi 
PIR Light Checker 
% Multi-Channel Transmission System 
Transmitter 
Receiver 
Interface 


EPE SOFTWARE 


Software programs for EPE projects marked with an asterisk « are available on 3.5 
inch PC-compatible disks or free from our Internet site. Six disks are available: PIC 
Tutorial (Mar-May ‘98 issues); PIC Toolkit Mk2 (May-Jun ‘99 issues); EPE Disk 1 
(Apr ‘95-Dec ‘98 issues); EPE Disk 2 (Jan-Dec ‘99). EPE Disk 3 (Jan ‘00 issue to 
current cover date); EPE Teach-in 2000. The disks are obtainable from the EPE 
PCB Service at £2.75 each (UK) to cover our admin costs (the software itself is 
free). Overseas (each): £3.35 surface mail, £4.35 each airmail. All files can be 
downloaded free from our Internet FTP site: ftp://ftp.epemag.wimborne.co.uk. 



















Simple Metal Detector 
(Multi-project PCB) 
Single or Dual-Tracking Power Supply 

% RC-Meter 














ight . 
Stereo Tone Control plus 20W Stereo Amplifier 
Tone Control 
20W Amplifier 

& Dice Lott 
EPE Mood Changer 
*AT89C2051/1051 Programmer 
Main Board 
Test Board 
& Reaction Timer Software onl 
%& PIC 16x84 Toolkit 
% Greenhouse Computer 
Control Board 
PSU Board 
Float Charger 
Lightbulb Saver 
Personal Stereo Amplifier 
(Multi-project PCB) 
% Greenhouse Radio Link 
& PIC Altimeter 
Voice Processor 
% Digiserv R/C Expander 
IR Remote Control — Transmitter 
— Receiver 

PIC Tape Measure 
Electronic Thermostat — T-Stat 
PhizzyB 

A-—PCB B-CD-ROM C- Prog. Microcontroller 
15-Way IR Remote Control 

Switch Matrix 
15-Way Rec/Decoder 
Damp Stat 
Handheld Function Generator 
% Fading Christmas Lights 
PhizzyB I/O Board (4-section 
Twinkle Twinkle Reaction Game 
% EPE Mind PiCkler 
PhizzyB |/O Board (4-section) 
Alternative Courtesy Lig * 
Light Alarm 
*Wireless Monitoring System Transmitter 
Receiver 

& PIC MIDI Sustain Pedal _ Software onl 
% Wireless Monitoring System-2 

F.M. Trans/Rec Adaptors 
% Time and Date Generator 
Auto Cupboard Light 
Smoke Absorber 
lroning Board Saver 
Voice Record/Playback Module 
Mechanical Radio (pair) 
& Versatile Event Counter 
PIC Toolkit Mk2 









JUNE’98 














JULY’98 






AUG’98 













EPE PRINTED CIRCUIT 
BOARD SERVICE 


Order Code _— Project Quantity Price 


SEPT’98 


























IGBITVG ns ccutyjataiocsevarcocvcanaee 






INGORE i etaln vapseorsinsasisinbod nymistiesticeseeinseocesesadecuotbons 






























| enclose payment of £.............63. 


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a aoe Remote Control NOTE: You can order p.c.b.s via our Internet site on a secure server: 
Receiver http://www.epemag.wimborne.co.uk 






, 397 Everyday Practical Electronics, May 2000 


CLASSIFIED 


Everyday Practical Electronics reaches twice as 
many UK readers as any other independent monthly 
hobby electronics magazine, our audited sales 


figures prove it. We have been the leading 
independent monthly magazine in this market for the 
last fifteen years. 





lf you want your advertisements to be seen by the largest readership at the most economical price our classified and semi-display 
pages offer the best value. The prepaid rate for semi-display space is £8 (+VAT) per single column centimetre (minimum 2-5cm). 
The prepaid rate for classified adverts is 30p (+VAT) per word (minimum 12 words). 


All cheques, postal orders, etc., to be made payable to Everyday Practical Electronics. VAT must be added. Advertisements, together 
with remittance, should be sent to Everyday Practical Electronics Advertisements, Mill Lodge, Mill Lane, Thorpe-le-Soken, Essex CO16 


OED. Phone/Fax (01255) 861161. 


For rates and information on display and classified advertising please contact our Advertisement Manager, Peter Mew as above. 





RCS VARIABLE VOLTAGE D.C. BENCH POWER SUPPLY 
Up to 20 volts d.c. at 1 amp continuous, 1-5 amps peak, 
fully variable from i : 
Voltage and eee P45 VAT 
Current meters , 

foreasy read- [a = Fost £4 
Out. 240 volt &.c. isimenmmnnansninsnnnnannNNNE: 
input. Fully smoothed, size 23cmx14cmx8cm. 


RADIO COMPONENT SPECIALISTS 


f= 4 337 WHITEHORSEROAD, CROYDON “trea” 
1544 SURREY, CRO 2HS. Tel: 0181-684 1665 
Lots of transformers, high volt caps, valves, output transformers, speakers, in stock. 
Phone or send your wants list for quote. 








NOW AVAILABLE WITH 


y a =} =} 128K AND 512K — 024 


ALSO SPECTRUM 
AND QL. PARTS 


W. N. RICHARDSON & CO. 
PHONE/FAX 01494 8713196 
RAVENSMEAD, CHALFONT ST PETER, 
BUCKS, SL9 ONB 


















TIS - Midlinbank Farm 
Ryeland, Strathaven ML10 6RD 
Manuals on anything electronic 
Circuits — VCR £8, CTV £6 
Service Manuals from £10 
Repair Manuals from £5 
P&P any order £2.50 
Write, or ring 01357 440280 for full details 
of our lending service and FREE quote for 
any data 


BTEC ELECTRONICS 
TECHNICIAN TRAINING 


GNVQ ADVANCED ENGINEERING 
(ELECTRONIC) — PART-TIME 
HND ELECTRONICS — FULL-TIME 
B.Eng FOUNDATION — FULL-TIME 
Next course commences 
Monday 18th September 2000 


FULL PROSPECTUS FROM 


Mo) \| be) mm on 8 -10)\| (ex more) mm =e] = 
(Dept EPE) 20 PENYWERN ROAD 
EARLS COURT, LONDON SW5 9SU 
TEL: 0171-373 8721 















THE BRITISH AMATEUR 
ELECTRONICS CLUB 


exists to help electronics enthusiasts by 
personal contact and through a quarterly 
Newsletter. 
For membership details, write to the 
Secretary: 
Mr. M. P. Moses, 

5 Park View, Cwmaman, 
Aberdare CF44 6PP 
Space donated by 
Everyday Practical Electronics 


398 


Miscellaneous 





® Circuits developed from concept to schematic 
to PCB layout to prototype. 

¢ Prototype and small qty. PCB manufacture 

© Assistance with design and development. 


Contact R. Tanfield for further details 


Circuitinnovate@cs.com 











S Circuit 24 Leasmires Avenue 


l 7 Easingwold, York 
Innovations Fs)svor 


PRINTED CIRCUIT BOARDS - QUICK 
SERVICE. Prototype and production artwork 
raised from magazines or draft designs at low 


cost. PCBs designed from schematics. 
Production assembly, wiring and software pro- 
gramming. For details contact Patrick at Agar 
Circuits, Unit 5, East Belfast Enterprise Park, 
308 Albertbridge Road, Belfast, BTS 4GX. 
Phone 028 9073 8897, Fax 028 9073 1802, 
E-mail agar @ argonet.co.uk. 

PCB MANUFACTURING -~ SERVICE. 
Affordable PCB production from CAD or 
magazines (fibre glass single-sided only). For 
detailed information and cost, write to: Mr. Belt, 
5 Velden Way, Mill Road, Market Rasen, Lincs 
LN8 3HD (including a sae). 

HEAR TWEAKS’ PINGS-WHISTLES. 
Unique Receiver Design; Self-A Envelope. PO 
Box 694, St Helier, JE4 9PZ, Jersey CI. 
PROTOTYPE PRINTED CIRCUIT 
BOARDS one offs and quantities, for details 
send s.a.e. to B. M. Ansbro, 38 Poynings Drive, 
Hove, Sussex BN3 8GR, or phone Brighton 
883871, fax 01273 706670. 

G.C.S.E. ELECTRONIC KITS, at pocket 
money prices. S.A.E. for FREE catalogue. SIR- 
KIT Electronics, 52 Severn Road, Clacton, 
CO15 3RB. 





sub-directories: 
PIC-project source code files: /pub/PICS 


EPE text files: /pub/docs 
Basic Soldering Guide: solder.txt 


New readers and subscribers info: epe_info.txt 

Newsgroups or Usenet users advice: usenet.txt 
Ni-Cad discussion: nicadfaq.zip and nicad2.zip 
Writing for EPE advice: write4us.txt 








web-based forum! 


EPE FTP site: ftp://ftp.epemag.wimborne.co.uk 


Access the FTP site by typing the above into your web browser, or by setting 
up an FTP session using appropriate FTP software, then go into quoted 


PIC projects each have their own folder; navigate to the correct folder and open it, then fetch all the 
files contained within. Do not try to download the folder itself! 


EPE TENS Unit user advice: tens.doc and tens.txt 
Ingenuity Unlimited submission guidance: ing_unlt.txt 


On-line readers! Try the EPE Chat Zone -— a virtually 
real-time Internet “discussion board” in a simple to use 


http:/Awww.epemag.wimborne.co.uk/wwwboard 
Or buy EPE Online: www.epemag.com 


VALVE ENTHUSIASTS: Capacitors and 
other parts in stock. For free advice/lists 
please ring, Geoff Davies (Radio), Tel. 01788 
574774. 

100W and 250W SOLID STATE POWER 
AMPLIFIERS, power supplies, active crossovers 
and stepped attenuator p.c.b.s, kits or A&T mod- 
ules. PCBs are professional grade with solder 
mask and component location silkscreen. We also 
supply a wide range of top quality audiophile 
active and passive components, specialising in the 
latest high performance Japanese transistors and 
UK lateral power MOSFETs. Write for a free cat- 
alogue. Mail order only. White Noise, 11 Station 
Road, Bearsden, Glasgow G61 4AW. Tel: 0141 | 
942 2460. 

SCOPEMETER, Philips/Fluke PM97 50MHz 
dual trace, digital storage oscilloscope and digi- 
tal multimeter. Complete with probe set, leads, 
charger, user manual and hardcase. Mint condi- 
tion, never used, £525 ovno. Wisbech 01945 
7005 14. 

PCBs AND PRE-PROGRAMMED PIC 
CHIPS and required components lists. Noughts 
and Crosses and Draughts games — play PIC 
chip. Shopping list reminder, has parallel printer 
port. Timer — 4 settings: 4, 10, 20, 30 minutes, 
auto power off. Radio Tx, Rx — sends 4-bit data 
switches, 4 relays — optional. A. Morell, 12 
Boscobel Road, Winchester, SO22 6RY. 

VISIT OUR WEB SITE AT http://www.par- 
tridgeelectronics.co.uk for components, valves, 
i.c.s, transistors, surplus bargains, audio equip- 
ment etc., or phone 01268 793256. 

FREE PROTOTYPE PRINTED CIRCUIT 
BOARDS! Free prototype p.c.b. with quantity 
orders. Call Patrick on 028 9073 8897 for details. 
Agar Circuits, Unit 5, East Belfast Enterprise Park, 
308 Albertbridge Road, Belfast BTS 4GX. 





















Ensure you set your FTP 
software to ASCII transfer 
when fetching text files, or 
they may be unreadable. 


Note that any file which ends 






in .zip needs unzipping 
before use. Unzip utilities can 
be downloaded from: 
http://www.winzip.com or 
http://www.pkware.com 














Everyday Practical Electronics, May 2000 


TRAIN TODAY FOR A BETTER FUTURE 


Electrical Contracting & Installation 
Electrical Engineering 

C&G/ICS Basic Electronic Engineering 
C&G/ICS Basic Mechanical Engineering 
TV and Video Servicing 

Radio and Hi-Fi Servicing 

Refrigeration Heating & Air Conditioning 
Motorcycle Maintenance 





Now you can get the skills and qualifications you need for 
career success with an ICS Home Study Course. Learn in the 
comfort of your own home at the pace and times that suit you. 
ICS is the world's largest, most experienced home study 
school. Over the past 100 years ICS have helped nearly 10 
million people to improve their job prospects. Find out how we 
can help YOU. Post or phone today for FREE INFORMATION 
on the course of your choice 





















Or write to: International Correspondence Schools, FREEPOST 882, 8 Elliot Place, 
Clydeway Skypark, Glasgow, G3 8BR. Tel: 0500 581 557 or Tel/Fax: Dublin 285 2533. 


eee 
Please send me my Free Information on your Electronics Courses. 


Mir/Mrs/M Miss 
BLOCK CAPITALS PLEASE Date of Birth / / / 
EOIN ES ERNE RARE SS SG 


Occupation Tel. No. 


From time to time, we permit other carefully screened organisations to write to you about 0400 
products and services. If you would prefer not to hear from such organisations please tick box 1 Dept. ZEEE 07 





























a B24 


hk ag SZ 
OPERATING & SERVICE MANUALS 


SUPPLIER OF QUALITY USED 
TEST INSTRUMENTS 


Unit Four, Fordingbridge Site, Barnham, 
Bognor Regis, West Sussex, PO22 OHD, UK 
Tel: (+44) 01243 545111/2. Fax: (+44) 01243 542457 
FREE MONTHLY MAIL ORDER CATALOGUE 


As T- oblate M\\ianawmerele) «ct lal mere) ia] 
E-mail: info@cooke-int.com 


Unit Four, Fordingbridge Site, Bamham, 
Bognor Regis, West Sussex, PO22 OHD, UK 
Tel: (+44) 01243 545111/2. Fax: (+44) 01243 542457 
FREE MONTHLY MAIL ORDER CATALOGUE 


Web: http:\\www.cooke-int.com 
E-mail: info@cooke-int.com 





Detailed Instructions with Schematics 
High Quality Screen Printed PCBs 
High Quality Components 


Transmitters from 0-05W to 35W 
FM Stereo Coders 

Audio Compressor Limiters 
Antennas 

RF Power Amps 


1W Professional PLL FM Transmitter for Licenced Use in the UK 


evant field ahiiie tmanes dilih Visit our Website at http://www.veronica.co.uk 
ACCEPT MAJOR CREDIT CARDS 


Tel 01274 883434 Fax 01274 428665 
email info @ veronica.co.uk 
Unit 5/6 1A Sandbeds/Albert Rd Queensbury BRADFORD BD13 1AA 


100 
75 


Signal Diodes 1N4148 

Rectifier Diodes 1N4001 

Rectifier Diodes 1N4007 

W01 Bridge Rectifiers 

555 Timer |.C.s 

741 Op Amps 

Assorted Zener Diodes 400mW 
Assorted 7-segment Displays 

5mm I.e.d.s, red, green or yellow 
3mm l.e.d.s, met poy or yellow 
Axial |.e.d.s, 2mcd red Diode Package 
Asstd. High Brightness |.e.d.s, var cols . 
BC182L Transistors 

BC212L Transistors 

BC237 Transistors 

BC327 Transistors 

BC328 Transistors 

BC547 Transistors 

BC548 Transistors 

BC549 Transistors 

BC557 Transistors 

BC558 Transistors 

BC559 Transistors 

2N3904 Transistors 

inf 50V wkg Axial Capacitors 
4N7 50V wkg Axial Capacitors 
1uf 250V encapsulat 

cased capacitors 

Asstd capacitors electrolytic- 
Asstd. capacitors 1nF to 1uF 


8888888838888 


> +> BB th > Pp bp > Mt i yin ip hn iD 


S88 888888888ses8e88s8888s8888 


A WA 


Asstd. disc ceramic capacitors £1.00 
Asstd. Skel Presets (sm, stand, cermet) £1.00 
Asstd. RF chokes (inductors) £1.00 
Asstd. grommets £1.00 
Asstd. solder tags, p/conns, terminals .£1.00 
Asstd. crystals — plug in £1. 
Asstd. coil formers 

Asstd. dil switches 

Miniature slide switches sp/co 

Standard slide switches dp/dt .00 
Asstd. beads (ceramic, teflon, fish spine) £1.00 
Asstd. small stand offs, throughs etc .£1.00 
Asstd. dil sockets up to 40 way 

TV coax plugs, plastic 

Small spring loaded terminals 

metres very thin connecting wire, red . . 
lin. glass reed switches 

Magnetic ear pips with lead and plug 
Any one value '/4W 5% cf resistors ran 
1R to 10M 


8 


+ sss se se 


f 
8& 88888 


=—o 


E-mail sales @ Bardwells.co.uk 
Web site: http:/www.bardwells.co.uk 





Everyday Practical Electronics, May 2000 


SEND FOR 
FREE CATALOGUE 
















































PERFECT FOR NOVICE FIRSTTIME — FY KIT & B38 0-18 MIN. TIMER L.E.D. & SPEAKER £5.50 
BUILDERS IN ELECTRONICS INSTRUCTIONS B39 TOY THERAMIN MUSIC £6.80 
X1  24IC MK484 M.W. RADIO £10.00 B40 AMPLIFIED RE PROBE + METER £10.50 
X3_ 1-0 + TRAN M.W. RADIO £10.00 B41 TRANSMITTER R.F INDICATOR £4.80 
X5  MK484 + 2030 M>W> RADIO £18.00 B43 AUDIO NOISE GENERATOR £10.00 
X7  MK484 TUNER M.W. NO AMP £6.00 B45 GENERAL 3-TRANSISTOR AMP £5.50 
X8  S.W.HAM RECEIVER £13.50 B46 LM386 AMPLIFIER GENERAL £5.50 
B2 BASIC CRYSTAL SET AMPLIFIED £10.00 B48 COMMON PRE-AMP RADIO £5.50 
X9  SW.HAM RADIO £17.50 B49 PEST SCARERHIGH PITCH £12.00 
B4 WORKSHOP AMPLIFIER £10.00 B50 VARIABLE FREQ. OSCILLATOR £5.50 
X10 S.W. TUNER HAM £10.00 B51 AUTOMATIC NIGHT LIGHT £5.50 
X11 §. METER £10.50 B52 FROST ALARM £5.80 
B44 SIMPLEH.F MW. ATU £7.50 B53 PRESSURE MAT & ALARM £13.50 
B8  S.W. TUNER GENERAL £10.00 B54 GUITARTUNER £9.50 
C1 BASIC CRYSTAL SET M.W. £6.50 B55 TOUCH ALARM £5.80 
B61 MW SIGNAL BOOSTER £12.50 B56 SIMPLE LIGHT METER £13.50 
BQ FAKE CAR ALARM FLASHER £5.00 B57_L.E.D. CONTINUITY METER £4.50 
B10 2L.E.D. FLASHER £4.80 B58 SOUND-OPERATED SWITCH £6.50 
B11 LOW VOLTS L.E.D. ALARM 9V-12V £5.00 BS58A 8 FLASHING L.E.Ds £6.80 
B12 LIE DETECTOR WITH METER £10.00 B59 TBA820M AUDIO AMP £10.50 
B13 TOY ORGAN £6.50 B60 TDA2030 AUDIO AMP £9.50 
B14. METRONOME I.C. CONTROL £5.00 B62 ELECTRONIC DICE GAME £8.50 
B15 TOUCH SWITCH £5.00 B63 ADVANCED THERAMIN-MUSIC £10.50 
B16 HEADS OR TAILS GAME £5.00 B64 TOUCH DELAY LAMP £5.50 
B17 SIREN £4.80 B65 FISHERMAN'S ROD BITE ALARM £5.00 
B18 RAIN DETECTOR £4.80 B66 BEAMBREAK DETECTOR ALARM £8.00 
B19 CONTINUITY TESTER £4.50 B67 __LATCHING BURGLAR ALARM £7.50 
B20 MORSE CODE OSCILLATOR £4.80 B68 LIGHT-OPERATED RELAY £7.50 
B21 BURGLAR ALARML.E.D.&SPEAKER £5.00 B69 MICROPHONE PRE-AMP £7.50 
B22 LOOP SECURITY ALARM £5.00 B70 MAGNETIC ALARM - MODELS £7.50 
B23 VIBRATION ALARM £4.80 B72 BATH ORWATER BUTT ALARM £6.80 
B24 METAL DETECTOR + METER £14.00 B73 0-18 VOLT POWER SUPPLY UNIT £6.80 
B25 HAND TREMOR GAME £4.80 B74 FM. BUG POWER SUPPLY OV-9V £6.50 
B26 RAIN SYNTHESISER - NOISE £10.50 B75 1 TRANSISTOR EM. BUG £6.50 
B27 AUTO LIGHT DARK INDICATOR £4.80 B76 2TRANSISTOR FM. BUG £7.50 
B28 ADJ. LOW LIGHT INDICATOR £4.80 

B29 DARK ACTIVATED L.E.D. FLASHER £4.80 







LOOK! NEW VALVE RADIO KITS 









Bas! CAR ELECTRIC PROSE 4 

3) Ki VALVEPSUFOROURKITS £20.00 
B32 SIGNAL INJECTOR £4.50 ‘ 
B33 MOISTURE METER -L.E.D. £4.80 K2 ONE VALVER M.W. & S.W. £17.50 
B34 _L.E.D. TRANSISTOR TESTER NPN £450 kK TWO VALVERMW.&S.W. £25.00 
EAS DIODE TESTEn— Le. £4.50 4.“ ONE VALVE AMPLIFIER £12.00 


L.E.D. TRANSISTOR TESTER PNP £4.50 
IC 555 TESTER - L.E.D. K5 BATTERY 1-VALVER S.W. £15.00 


MAKE POSTAL ORDERS/CHEQUES PAYABLE TO DAVID JOHNS AND SEND TO: 
37 GOSBECKS ROAD, COLCHESTER, ESSEX CO2 9JR 


UK POST AND PACKING £3 — ALLOW 14 DAYS DELIVERY 
WORLDWIDE POST AND PACKING £5 


01206 523123 é 
http:/Awww.davidjohns.f9.co.uk 






















Black and White Pin Hole Board Cameras 
with Audio. Cameras in P.I.R., Radios, 
Clocks, Briefcases etc. Transmitting 
Cameras with Receiver (Wireless). 
Cameras as above with colour. 
Audio Surveillance Kits and Ready Built 
Units, Bug Detector etc. 


Please phone 0181 203 6008 for free catalogue. 
Fax 0181 201 5359 
www.uspy.com 
New DTI approved Video Transmitters and Receivers (Wireless) 
Major credit cards now taken 


Ideal for TEACH-IN 2000 


Built-in transistor test socket 
and diode test position. 
DC volts 200mV to 1000V. 
AC volts 200V to 750V. 
DC current 200mA to 10A. 
Resistance 200 ohms to 
2000K ohms. 


Special offer to EPE readers 
incl. VAT 


399 


SHERWOOD See 


- FREE COMPONENTS 


Bit 10 x £1 Special Packs and choose another one FREE 


SP1 15 x 5mm Red LEDs SP131 2 x TLO71 Op.Amps 
SP2 12 x 5mm Green LEDs SP133 20x 1N4004 diodes 
SP3 12 x 5mm Yellow LEDs SP134 15x 1N4007 diodes 
SP6 15 x 3mm Red LEDs SP135 6 x Min. slide switches 
SP7 12 x 3mm Green LEDs SP136 3 x BFY50 transistors 
SP10 100 x 1N4148 diodes SP137 4 x W005 1-5A bridge rectifiers 
SP11 30 x 1N4001 diodes SP138 20x 2-2/63V radial elect. caps. 
SP12 30 x 1N4002 diodes SP140 3 x W04 1-5A bridge rectifiers 
SP18 20 x BC 182 transistors SP142 2 x CMOS 4017 
SP20 20 x BC184 transistors SP143 5 Pairs min. crocodile clips 
SP21 20 x BC212 transistors (Red & Black) 
SP23 20 x BC549 transistors SP145 6 x ZTX300 transistors 
SP24 4 x CMOS 4001 SP146 10x 2N3704 transistors 
SP25 4 x 555 timers SP147 5 x Stripboard 9 strips x 
SP26 4 x 741 Op.Amps 25 holes 
SP28 4 x CMOS 4011 SP151 4 x 8mm Red LEDs 
SP29 3 x CMOS 4013 SP152 4 x 8mm Green LEDs 
SP31 4 x CMOS 4071 SP153 4 x 8mm Yellow LEDs 
SP34 20 x 1N914 diodes SP154 15 x BC548 transistors 
SP36 25 x 10/25V radial elect.caps. ~- SP156 3 x Stripboard, 14 strips x 
SP37 15 x 100/35V radial elect. caps. 27 holes 
SP39 10 x 470/16V radial elect.caps. SP160 10x 2N3904 transistors 
SP40 15 x BC237 transistors SP161 10x 2N3906 transistors 
SP41 20 x Mixed transistors SP165 2 x LF351 Op.Amps 
SP42 200 x Mixed 0-25W C.F. resistors SP167 6 x BC107 transistors 
SP47 5 x Min. PB switches SP168 6x BC108 transistors 
SP102 20x 8-pin DIL sockets SP175 20x 1/63V radial elect. caps. 
SP103 15x 14-pin DIL sockets SP177. 10x 1A 20mm quick blow fuses 
SP104 15x 16-pin DIL sockets SP182 20x 4-7/63V radial elect. caps. 
SP105 4 x 74LS00 SP183 20x BC547 transistors 
SP109 15 x BC557 transistors SP187 15x BC239 transistors 
SP112 4 x CMOS 4093 SP191 3 x CMOS 4023 
SP114 5 x ZTX500 transistors SP192 3 x CMOS 4066 
SP115 3 x 10mm Red LEDs SP193 20x BC213 transistors 
SP116 3 x 10mm Green LEDs SP194 8 x OA90 diodes 
SP118 2 x CMOS 4047 SP195 3 x 10mm Yellow LEDs 
SP120 3 x 74LS93 SP197 6 x 20 pin DIL sockets 
SP124 20x Assorted ceramic disc caps SP198 5 x 24 pin DIL sockets 
SP130 100 x Mixed 0-5W C.F. resistors 

yA i]t] EOF: 1 ¢-]felelU(-maley m= \\c-l1t-]e] (=a am 


inc. P&P or FREE with first order. 
P&P £1.25 per order. NO VAT 
Orders to: 
Sherwood Electronics, 
7 Williamson St., Mansfield, 
Notts. NG19 6TD. 


RESISTOR PACKS -— C.Film 
5 each value — total 3650-25W £2.85 
10 each value — total 730 0-25W £4.10 
1000 popular values 0-25W . 
5 each value-total 365 0-5W 
10 each value-total 730 0-5W 
1000 popular values 0-5W £8.15 


Watch Slides on TV. 


Make videos of your slides. Digitise your slides 
(using a video capture card) 

“Liesgang diatv’ automatic slide viewer with built in 
high quality colour TV camera. It has a composite 
video output to a phono plug (SCART & BNC adap- 
tors are available). They are in very good condition 
with few signs of use. 

£91.91 + VAT = £108.00 


Board cameras all with 512 x 582 pixels 8-5mm 1/3 inch sensor and Siiemposie video 
out. All need to be housed in your own enclosure and have fragile exposed surface 
mount parts. They all require a power supply of between 10V and 12V DC 150mA. 
47MIR size 60 x 36 x 27mm with 6 infra red LEDs (gives the same illumination as a 
small torch but is not visible to the human eye) £37.00 + VAT = £43.48 

30MP size 32 x 32 x 14mm spy camera with a fixed focus pin hole lens for hiding 
behind a very small hole £35.00 + VAT = £41.13 

40MC size 39 x 38 x 27mm camera for ‘C’ mount lens these give a much sharper 
image than with the smaller lenses £32.00 + VAT = £37.60 

Economy C mount lenses all fixed focus & fixed iris 

VSL1220F 12mm F1.6 12 x 15 degrees viewing angle £15.97 + VAT £18.76 
VSL4022F 4mm F1-22 63 x 47 degrees viewing angle £17.65 + VAT £20.74 
VSL6022F 6mm F1.22 42 x 32 degrees viewing angle £19.05 + VAT £22.38 
VSL8020F 8mm F1.22 32 x 24 degrees viewing angle £19.90 + VAT £23.38 


Better quality C Mount lenses 
VSL1614F 16mm _F1-6 30 x 24 degrees viewing angle £26.43 + VAT £31.06 
VWL813M 8mm F1.3 with iris 56 x 42 degrees viewing angle £77.45 + VAT = £91.00 
1206 surface mount resistors E12 values 10 ohm to 1M ohm 
100 of 1 value £1.00+ VAT 1000 of 1 value £5.00 + VAT 
866 battery pack originally intended to be ai 
used with an orbitel mobile telephone it con- 
tains 10 1-6Ah sub C batteries (42 x 22 dia. 
the size usually used in cordless screw- 
drivers etc.) the pack is new and unused 
and can be broken open quite easily 
£7.46 + VAT = £8.77 


Please add £1.66 + vat = £1.95 postage & packing per order 


JPG Electronics 


276-278 Chatsworth Road, Chesterfield, S40 2BH. 
Tel 01246 211202 Fax 01246 550959 
Mastercard/Visa/Switch 7 
Callers welcome 9.30 a.m. to 5.30 p.m. Monday to Saturday 








thousands of an item is available. (Payment is returned if sold out. 


Millions of quality components 
at lowest ever prices! 
Plus anything from bankruptcy — theft recovery 
— frustrated orders — over productions etc. 
Send 50p stamped self-addressed label or 


envelope for clearance lists. 
Brian J Reed 
6 Queensmead Avenue, East Ewell, 
Epsom, Surrey KT17 3EQ 
Tel: 07775 945386 or 0208 393 9055 
Mall Order UK only. 


Lists are updated and only 40 are sent out every 2 weeks. This 
normally ensures that orders can be fulfilled where only a few 



















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COOKE INTERNATIONAL 

CROWNHILL ASSOCIATES 

DAVID JOHNS 

DISPLAY ELECTRONICS 

EPT EDUCATIONAL SOFTWARE 

ESR ELECTRONIC COMPONENTS 
FOREST ELECTRONIC DEVELOPMENTS 


J&N FACTORS 

JPG ELECTRONICS 
LABCENTER ELECTRONICS 
LEADING EDGE TECHNOLOGY 
MAGENTA ELECTRONICS 
MILFORD INSTRUMENTS 
NATIONAL COLLEGE OF TECHNOLOGY 
PICO TECHNOLOGY 

QUASAR ELECTRONICS 
SERVICE TRADING CO 
SHERWOOD ELECTRONICS 
SLM (MODEL) ENGINEERS 
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STEWART OF READING 

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ADVERTISEMENT MANAGER: PETER J. MEW 


ADVERTISEMENT OFFICES: 
EVERYDAY PRACTICAL ELECTRONICS, ADVERTISEMENTS, 


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For Editorial address and phone numbers see page 331 


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Published on approximately the first Friday of each month by Wimborne Publishing Ltd., Allen House, East Borough, Wimborne, Dorset BH21 1PF. Printed in England by Wiltshire (Bristol) Printers Ltd., Bristol, 
BS20 9XP. Distributed by COMAG Magazine Marketing, Tavistock Rd., West Drayton, UB7 7QE. Subscriptions INLAND £26.50 and OVERSEAS £32.50 standard air service (£50 express airmail) payable to 

“Everyday Practical Electronics”, Subs Dept, Allen House, East Borough, Wimborne, Dorset BH21 1PF. E-mail: subs @epemag. wimborne.co.uk. EVERYDAY PRACTICAL ELECTRONICS/ET1 is sold sub- 
ject to the following conditions, namely that it shall not, without the written consent of the Publishers first having been given, be lent, resold, hired out or otherwise disposed of by way of Trade at more than the 
recommended selling price shown on the cover, and that it shall not be lent, resold, hired out or otherwise disposed of in a mutilated condition or in any unauthorised cover by way of Trade or affixed to or as 


part of any publication or advertising, literary or pictorial matter whatsoever. 








THE RENOWED MXF SERIES OF POWER AMPLIFIERS 
FOUR MODELS:- MXF200 ( 100W + 100W ) MXF400 (200W + 200W) 
MXF600 (300W + 300W) MXF900 (450W + 450W) 

ALL POWER RATINGS ARE R.M.S. INTO 4 OHMS, WITH BOTH CHANNELS DRIVEN 


FEATURES: * Independent power supplies with two toroidal transformers * Twin L.E.D. Vu Meters 
* Level controls * Illuminated on/off switch * Jack/XLR inputs * Speakon outputs * Standard 775mV 
inputs * Open and short circuit proof * Latest Mos-Fets for stress free power delivery into virtually any 
load * High slew rate * Very low distortion * Aluminium cases * MXF600 & MXF900 fan cooled with D.C. 
loudspeaker and thermal protection. 


USED THE WORLD OVER IN CLUBS, PUBS, CINEMAS, DISCOS ETC 


MXF200 W19” Di1” 3” (2U) 

Sizes:  MXF400 W19" D12” HS” (3U) 
“  MXF600 W19” D13”—-H52” (3U) 
MXF900 W19” D142” H52” (3U) 





MXF400 £233.85 


MXF900 £449.15 
SPECIALIST CARRIER DEL. £12.50 EACH 


PRICES:- MXF200 £175.00 
MXF600 £329.00 





BASS X MID ATOP BASS/MID XTOP ASSX_MID/TOP 
CONFIGURED 3 WAY 2 WAY BASS/MID COMBINED = 2 WAY MID/TOP COMBINED 
FEATURES: 


Advanced 3-Way Stereo Active Cross-Over (switchable two way), housed in a 19” x 1U case. Each channel 
has three level controls: Bass, Mid & Top. The removable front fascia allows access to the programmable DIL 
switches to adjust the cross-over frequency: Bass-Mid 125/250/500Hz, Mid-Top 1.8/3/5Hz, all at 24dB per 
octave. The 2/3 way selector switches are also accessed by removing the front fascia. Each stereo channel 
can be configured separately. Bass Invert Switches are incorporated on each channel. Nominal 775mV 
input/output. Fully compatible with OMP Rack Amplifier and Modules. 


PRICE:- £117.44 + £5.00 P&P 


The 12 and 16 Channel SPM Series Of Studio Quality Mixers 
Are Ideal For Fixed Installation Stage And Mobile 


* 48v PHANTOM POWER 
* BUILT IN POWER SUPPLY 
* 230V AC/50Hz 

* PEAK INPUT LEVEL LEDS : : 
* PRE FADE LISTEN (PFL) a 
* SUB MASTER OUTPUT 

* COMBINED XLR/ % JACK 
* 60mm FADERS * CH.MUTE 
* 2 STEREO AUX.SEND/RETURNS 
* CONSTANT PAN CONTROL 

* 3 BAND EQ WITH MID SWEEP 
* HEADPHONE/CONTROL ROOM O/P 
* CD/TAPE INPUTS & OUTPUTS ° 
* BALANCED INPUTS & OUTPUTS 
* BUS ASSIGN SWITCH 


* MONITOR SEND ices:. SPM1202 4MONO MIC/LINE.4STEREO INPUTS £299.00 FREE 
“ SPM1602 8MONO MIC/LINE.4STEREO INPUTS £399.00 UK P&P 













* 4 STEREO INPUT 
CHANNELS 

* 2 DJ MIC INPUT 
CHANNELS 


* 2X7 BAND GRAPHIC 
EQUALISERS 


* HEADPHONE 
! MONITOR WITH PFL 

| * ASSIGNABLE 
CROSSFADE 

_  .... — * DIGITAL ECHO 

STEREO DISCO MIXER WITH:- *2X7 GRAPHIC EQUALISERS *2 MONO MIC INPUTS *DJ MIC 
WITH FADER, TALKOVER AND VOICE CHANGER *4 STEREO CHANNELS WITH _ INDIVIDUAL 
FADERS AND ASSIGNABLE CROSSFADE *CHANNELS SWITCHABLE, TURNTABLE (MAG 
CARTRIDGE), CD, LINE, TAPE, ETC. *ECHO WITH BALANCE, REPEAT AND DELAY 
* HEADPHONE MONITOR WITH PREFADE LISTEN *CHOICE OF 6 SOUND EFFECTS *STEREO 
MONO SWITCH *2 X LED VU METERS *MASTER FADER * OUTPUT 775mV 


* SIZE:- 482X240X115mm *POWER:- 230V AC 50/60Hz.PRICE:- £169.00 + £5.00 P&P 
CYBERWAVE FMM 1000 “ee r 


* IDEAL FOR:- LIVE BANDS, PUBLIC ADDRESS & KARAOKE ETC. 
* ON/STANDBY/OFF SWITCH MOUNTED ON MIC BARREL FOR EASE OF USE ,.. 
* 100 HOURS BATTERY RUNNING TIME. 1 PP3 (NOT SUPPLIED) &, 
* SINGLE CHANNEL RF MICROPHONE 174.23 OR 174.56MHz 
* MAINS ADAPTOR FOR RECEIVER SUPPLIED * FM LOCK INDICATOR 
& VOL CONTROL ON RECEIVER. PRICE:- £119.99 FREE UK P&P 








A new range of quality loudspeakers, designed to take 

advantage of the latest loudspeaker technology and 

enclosure designs. All models utilize high quality studio 
cast aluminium loudspeakers with factory fitted grilles, wide dispersion constant 
directivity horns, extruded aluminium corner protection and steel ball corners, 
complimented with heavy duty black covering. The enclosures are fitted as standard 
with top hats for optional loudspeaker stands. The FC15-300 incorporates a large 
16 X 6 inch horn. All cabinets are fitted with the latest Speakon’ connectors 
for your convenience and safety. Five models to choose from. 








PLEASE NOTE:- POWER RATINGS 
QUOTED ARE IN WATTS R.M.S. FOR 
EACH INDIVIDUAL CABINET. 

ALL ENCLOSURES ARE 8 OHM. 
15=15 inch speaker 
12=12 inch speaker sae 

ibl FC15-300 WATTS Freq Range 35Hz-20KHz, Sens 101dB, Size H695 W502 D415mm 

PRICE:- £299.00 per pair 
ibl FC12-300 WATTS Freq Range 45Hz-20KHz, Sens 96dB, Size H600 W405 D300mm 
PRICE:- £249.00 tt pair 
ibl FC12-200 WATTS Freq Range 40Hz-20KHz, Sens 97dB, Size H600 W405 D300mm 
PRICE:- £199.00 per pair 
ibl FC12-100 WATTS Freq Range 45Hz-20KHz, Sens 100dB, Size H546 W380 D300mm 
PRICE:- £179.00 per pair 
ibl WM12-200 WATTS Freq Range 40Hz-20KHz, Sens 97dB, Size H418 W600 D385mm 
PRICE:- £125.00 EACH 
SPECIALIST CARRIER DEL:- £12.50 per pair, Wedge Monitor £7.00 each 


Optional Metal Stands PRICE:- £49.00 per pair Delivery:- £6.00 


COLOSSUS POWER 


VERY HIGH POWER LOUDSPEAKERS 
THE COLOSSUS RANGE OF LOUDSPEAKERS POTN, 
ARE DESIGNED FOR USE IN SUPERIOR HIGH 
POWER OUTPUT SYSTEMS. ALL MODELS ARE 8 OHM 

COLOSSUS 12MB:-* 12 INCH * 450WATT R.M.S. 

* 900 WATTS PEAK * Sens 98 dB.* Res Freq.55 Hz. 

* Frequency Range 40 Hz-3.5KHzPRICE £129.00 

COLOSSUS 15XB:-* 15 INCH * 600WATTS R.M.S. 

* 1200 WATTS PEAK * Sens 99 dB * Res Freq.35 Hz. 

* Frequency Range 30 Hz-1.0KHz PRICE £159.00 


COLOSSUS 18XB:-* 18 INCH * 600WATTS R.M.S. 
* 1200 WATTS PEAK *Sens 100dB.* Res Freq.30 Hz. 
* Frequency Range 27 Hz-1.0Kz PRICE £183.00 

ALL MODELS ARE DELIVERED CARRIAGE FREE(UK ONLY) 


DOA-ZOZ mMoHoms 














SUPPLIED READY 
BUILT AND TESTED 
These modules now enjoy a world-wide reputation for quality, reliability and performance at a realistic price. Four 
models are available to suit the needs of the professional and hobby market i.e. Industry, Leisure, Instrumental and 
Hi-Fi etc. When comparing prices, NOTE that all models include toroidal power supply, integralheat sink, glass fibre 
P.C.B. and drive circuits to power a compatible Vu meter. All models are open and short circuit proof. 


PURCHASED BY PROFESSIONAL USERS 
OMP/MF 100 Mos-Fet Output power 110 watts 
R.M.S. into 4 ohms, frequency response 1Hz - 100KHz - 
3dB, Damping Factor >300, Slew Rate 45V/uS, T.H.D 
typical 0.002%, Input Sensitivity 500mV, S.N.R. - 
110dB. Size 300 x 123 x 60mm. 

PRICE:- £42.85 + £4.00 P&P 


OMP/MF 200 Mos-Fet Output power 200 watts 
R.M.S. into 4 ohms, frequency response 1Hz - 100KHz 
-3dB, Damping Factor >300, Slew Rate 50V/uS, T.H.D. 
typical 0.001%, Input Sensitivity 500mV, S.N.R. -110dB. 
Size 300 x 155 x 100mm. 


PRICE:- £66.35 + £4.00 P&P 


OMP/MF 300 Mos-Fet Output power 300 watts 
R.M.S. into 4 ohms, frequency response 1Hz - 100KHz 
-3dB, Damping Factor >300, Slew Rate 60V/uS, T.H.D. 
» typical 0.001%, Input Sensitivity 500mV, S.N.R. -110dB. 
Size 330 x 175 x 100mm. 


PRICE:- £83.75 + £5.00 P&P 


OMP/MF 450 Mos-Fet Output power 450 watts 
R.M.S. into 4 ohms, frequency response 1Hz - 100KHz 
-3dB, Damping Factor >300, Slew Rate 75V/uS, 
T.H.D. typical 0.001%, Input Sensitivity 500mV, S.N.R. 
-110dB, Fan Cooled, D.C. Loudspeaker Protection, 2 
Second Anti- Thump Delay. Size 385 x 210 x 105mm. 
PRICE:- £135.85 +£6.00 P&P 


OMP/MF 1000 Mos-Fet Output power 1000 watts 
R.M.S. into 2 ohms, 725 watts R.MS. into 4 ohms, 
frequency response 1Hz - 100KHz -3dB, Damping 
Factor >300, Slew Rate 75V/uS, T.H.D. typical 
0.002%, Input Sensitivity 500mV, S.N.R. -110dB, Fan 
Cooled, D.C. Loudspeaker Protection, 2 Second 
Anti-Thump Delay. Size 422 x 300 x 125mm. 
PRICE:- £261.00 + £12.00 P&P 


NOTE: MOS-FET MODULES ARE AVAILABLE IN TWO VERSIONS: 
STANDARD - INPUT SENS 500mV, BAND WIDTH 100KHz. O 

PEC (PROFESSIONAL EQUIPMENT COMPATIBLE) - INPUT SENS 
775mV, BAND WIDTH 50KHz. ORDER STANDARD OR PEC 





ULES 








CD-ROM 


Students and Hobbyists the 
complete package for 
£49.95* ($82.17) normally £99.95* 


Colleges and universities including 
unlimited user site licence. 


£299.95* normally £595.95* 
L_j Electronics. Electrical and Mathematics Principles V6 pelea Mi ae ecm eB e aN! On ten “Pea on 
cal Sonor. Ope im “Digtel Messue Mico PIC® Toobor Indew Hep — * +VAT if applicable 
| : Postage FREE 


i. nt | Tools & Equipment | Ics| 
__ Categ! e¥ DC VOLTAGE: Loading a Voltage Divider. 


Boolean & DeMc 


Load = 10k 
R2 fi) Load =3.1973k 


DC VOLTAGE: Loading a Voltage Divider 


‘Unloaded output. 
Effect of connecting Vout = 30x sy ee = 9591837 = 3.5918 
a load across R2. ‘Loaded output.’ 


“4 Vout = 30 x 397.273 


we 


ha ens eee en ee a sea Please telephone or visit 


=. Resistor Colour Codes 


New Av = ay xB] 4 ee our website for a list of 
Effective Input = Input voltage - (A = HRY gee eee ererneY OVer rele) aarciia Menu 
New Output voltage = Input voltag | | som Own : 
it selections. Yalow =4- Bande] to3 = numesical value, fouth = mies o 
© Green =5 umber of nought's. For values < 10chms. Fourth band is 
PO eeeuetaremeeia 
eptsoft limited. Pump House, Lockram Lane, “Electronics Principles is a well thought out Yellow, Violet, Black. Red = 47kOhme 
Witham, Essex. UK. CM8 2Bu. and comprehensive program that is also “Caluet Souk 
I=) OM RCW Ac MoM (0001s il at=).0m Olt AGM @lel0 101610 easy to install and stable in operation. | tet oe 
info@eptsoft.com www.eptsoft.com hiorclam eXomaele)(o]Alcrelatsrel\yalacrere)anlaalciale (cre nm ee 
Switch, Delta, Visa and MasterCard payments Robert Penfold. Everyday Practical _eceememem J 
accepted - please give card number and expiry Electronics magazine. | 


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