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FULLY S.O.R. £2.25 


Converts a DMM to read 
low value resistance @ 


All round protection fo 
your home, garage, shed gig 


9"770262" 361065 


WIRELESS VIDEO BUG KIT Transmits video and audio 
signals from a minature CCTV camera (included) to any 
standard television! Allthe components including a PP3 battery 
will fitinto a cigarette packet with the lens requiring ahole about 
3mm diameter. Supplied with telescopic aerial but a piece of 
wire about 4" long will still give a range of up to 100 metres. A 
single PP3 will probably give less than 1 hours operating time. 
£99 REF EP79. (probably not licensable!) 

GOT AN EXPENSIVE BIKE? You need one of our bottle 
alarms, they look like a standard water bottle, but open the top, 
insert a key to activate a motion sensor alarm built inside. Fits 
all standard bottle carriers, supplied with two keys. SALE 
PRICE £7.99 REF SA32. 

GOT AN EXPENSIVE ANYTHING? You need one of our 
cased vibration alarms, keyswitch operated, fully cased just fit 
it to anything from videos to caravans, provides a years 
protection from 1 PP3 battery, and protect it! UK made. SALE 
PRICE £4.99 REF SA33. 

DAMAGED ANSWER PHONES These are probably 
beyond repair so they are just£4.99 each. Mainly response 200 
machines. REF SA30. 

left to clear at £5 ref SA31. Condition unknown. 
COMPUTER DISC CLEAROUT We are left with a lot of 
software packs that need clearing so we are selling at disc 
value only! 50 discs for £4, thats just 8p each!!(our choice of 
discs) SALE PRICE £4 ref EP66 

Complete with fan etc and 200 watt power supply. SALE 
PRICE £9.95 ref EP67 

DELL PC POWER SUPPLIES 145 watt, +5,-5,+12,-12, 
150x150x85mm complete with switch, flyleadsand|EC socket. 
SALE PRICE £9.99 ref EP55 

1.44 DISC DRIVES Standard PC 3.5" drives but returns so 
they will need attention SALE PRICE £4.99 ref EP68 

1.2 DISC DRIVES Standard 5.25" drives but returns so they 
will need attention SALE PRICE £4.99 ref EP69 

PP3 NICADS New and unused but some storage marks. 
SALE PRICE £4.99 ref EP52 

SOLAR PANELS 3v output with two flyleads, 100x60 mm 
pack of 10 SALE PRICE £6.99 ref EP56 

DELL PC POWER SUPPLIES (Customer returns) 
Standard PC psu's complete with fly leads, case and fan, pack 
of two psus SALE PRICE £5 FOR TWO!! ref EP61 

GAS HOBS AND OVENS Brand new gas appliances, 
perfect for small flats etc. Basic 3 burner hob SALE PRICE 
£24.99 ref EP72. Basic small built in oven SALE PRICE £79 ref 

BITS AND BOBS We have a quantity of cased modems, 
multiplexers etc different specs but ideal strippers. SALE 
PRICE £4 each ref EP63 

RED EYE SECURITY PROTECTOR 1,000 watt outdoor 
PIR switch SALE PRICE £9.99 ref EP57 

ENERGY BANK KIT 100 6"x6" 6v 100mA panels, 100 
diodes, connection details etc. £69.95 ref EF112. 

CCTV CAMERA MODULES 46X70X29mm, 30 grams, 
12v 100mA. auto electronic shutter, 3.6mm F2 lens, CCIR, 
512x492 pixels, video output is 1v p-p (75 ohm). Works directly 
into a scart or video input on a tvor video. IR sensitive. £79.95 
ref EF 137. 

IR LAMP KIT Suitable for the above camera enables the 
camera to be used in total darkness! £5.99 ref EF 138. 
PASTELACCOUNTS SOFTWARE, does everything for 
all sizes of businesses, includes wordprocessor, report writer, 
windowing, networkable up to 10 stations, multiple cash books 
etc. 200 page comprehensive manual. 90 days free technical 
support (0345-326009 try before you buy!) Current retail price 
is £129, SALE PRICE £9.95 ref SA12. SAVE £120!!! 


C ITOH PRINTERS 80 col, 9 pin matrix, serial/parallel, 
NLQ/draft, 3 mth warranty, good condition, SALE PRICE £39 
ref SA14. 

REUSEABLE HEAT PACKS. Idealfor fishermen, outdoor 
enthusiasts elderly orinfirm, warming food, drinks etc, defrosting 
pipes etc.reuseable up to 10 times, lasts for up to 8 hours per 
go, 2,000wh energy, gets up to 90 degC. SALE PRICE £9.95 

A4 DTP MONITORS Brand new, 300 DPI. Complete with 
diagram but no interface details.(so you will have to work 
it out!) Bargain at just £7.99 each!!!! Ref EF185 

12V 2AMP LAPT OP psu's 110x55x40mm (includes standard 
IEC socket) and 2m lead with plug. 100-240v IP. SALE PRICE 
£6.99 REF SA15. 

times etc) up to 4 items (8A 240v each) with this kit. Complete 
with Software, relays, PCB etc. £25.99 Ref 95/26 
range UPS system providing protection for your computer 
system and valuablesoftware against mains power fluctuations 
and cuts.New and boxed, UK made Provides up to 5 mins 
running time in the event of complete power failure to allow you 
to run your system down correctly. SALE PRICE just £89.00. 
SOLAR PATH LIGHTS Lowenergy walklights powered by 
th sun! builtin PIR so they work when you walk past. Includes 
solar panel & rechargeable bat. SALE PRICE £19.9REF EP62 

BIG BROTHER PSU Cased PSU, 6v 2A output, 

2m o/p lead, 1.5m input lead, UK made,220v. SALE PRICE 
£4.99 REF EP7 


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 is a certificate enabling 

you to reproduce the manuals as much as you like! SALE 

RACAL MODEM BONANZA! 1 Racal MPS1223 1200/75 
modem, telephone lead, mains lead, manual and comms 
software, the cheapest way onto the net! all this for just £13 ref 

unbranded. We have sold 100,000+ so ok! Pack of 50 £24.99 
ref DEC16 

Smw LASER POINTER. Supplied in kit form, complete with 
power adjuster, 1-Smw, and beam divergence adjuster. Runs 
on 2AAA batteries. Produces thin red beam ideal for levels, gun 
sights, experiments etc. Cheapest in the UK! just £39.95 ref 

RADIO PAGERSBrand new, UK made pocket pagers 
clearance price is just £4.99 each 100x40x15mm packed with 
bits! Ref SEPS5. 

BULL TENS UNIT Fully built and tested TENS 
(Transcutaneous Electrical Nerve Stimulation) unit, complete 
with electrodes and full instructions. TENS is used for the relief 
of pain etc in up to 70% of sufferers. Drug free pain relief, safe 
and easy to use, can be used in conjunction with analgesics etc. 
£49 Ref TEN/1 

quality modern units,(like wyse 50,s) 2xRS232, 20 function 
keys, 50 thro to 38,400 baud, menu driven port, screen, cursor, 
and keyboard setup menus (18 menu's). £29 REF NOV4. 
into a basic VGA screen. Complete with built in psu, lead and 
s/ware.. Ideal for laptops or a cheap upgrade.Supplied in kit 
form for home assembly. SALE PRICE £25 REF SA34 
EMERGENCY LIGHTING UNIT Complete unit with 2 
double bulb floodlights, built in charger and auto switch. Fully 
cased. 6v 8AH lead acid req'd. (secondhand) £4 ref MAG4P11. 
of ultra thin 4 core insulated cable, 28lbs breaking strain, less 
than 1mm thick! Ideal alarms, intercoms, fishing, dolls house's 
etc. SALE PRICE £13.99 ref EP51 

cable, plug etc SALE PRICE JUST £4.99 REF SA28 
3.75A, +12@1.5A, -12@.4A. 230/110, cased, BM41012. £5.99 
ref AUG6P3. 

AUTO SUNCHARGER 155x300mm solar panel with diode 
and 3 metre lead fitted with a cigar plug. 12v 2watt. SALE 
PRICE £8.99 REF SA25. 


ECLATRON FLASH TUBE As used in police car flashing 
lights etc, full spec supplied, 60-100 flashes a min. SALE 
PRICE £6.99 REF SA15. 

24v AC S6WATT Cased power supply. New. SALE PRICE 
JUST £9.99 REF SA40 

anstraightfrom Her majesty's forces. SALE PRICE £44 REF 

MICRODRIVE STRIPPERS Small cased tape drives ideal 
for stripping, lots of useful goodies including a smart case, and 
lots of components. SALE PRICE JUST £4.99 FOR FIVE REF 

130mA solar cells, 4 LED's, wire, buzzer, switch plus 1 relay or 
motor.Superb value kit SALE PRICE JUST £4.99 REF SA27 

condition. Back anodised metal case. SALE PRICE £49 REF 

SWITCHED MODE PSU ex equip, 60w +5v @S5A, -5v@.5A, 
+12v@2A,-12v@.5A 120/220vcased 245x88x55mm | ECinput 
socket £6.99 REF MAG7P1 

PLUG IN ACORN PSU 19v AC 14w , £2.99 REF MAG3P10 
POWER SUPPLY fully cased with mains and o/p leads 17v 
DC 900m output. Bargain price £5.99 ref MAG6P9 



4.4A. on/offswuncased, selectable mains input, 145x100x45mm 

13.8V 1.9A psu cased with leads. Just £9.99 REF MAG10P3 
PPC MODEM CARDS. These are high spec plug in cards 
made for the Amstrad laptop computers. 2400 baud dial up unit 
complete with leads. Clearance price is £5 REF: MAGS5P1 
200 WATT INVERTER Converts 10-15v DC into either 110v 
or 240vVAC. Fully cased 115x36x 156mm, complete with heavy 
duty power lead, cigar plug, AC outlet socket.Auto overload 
shutdown, auto short circuit shut down, auto input over voltage 
shutdown, auto input under voltage shut down (with audible 
alarm), auto temp contro!, unit shuts down if overheated and 
soundsaudible alarm. Fused reversed polarity protected. output 
frequency within 2%, voltage within 10%. A well built unit at an 
keen price. Just £64.99 ref AUG65. 

us for the C5 motor but ok for any 12v motor up to 30A. 
Complete with PCB etc. A heat sink may be required. £17.00 

100m of 6 core cable, 100 cable clips, 2 line drivers with RS232 

and all connectors etc. Ideallow cost method of communicating 
between PC's over a long distance. Complete kit £8.99. 
ELECTRIC MOTOR KIT Comprehensive educational kit 
includes all you need to build an electric motor. £9.99 ref 

VIEWDATA SYSTEMS made by Phillips, complete with 
internal 1200/75 modem, keyboard, psu etc RGB and composite 
outputs, menu driven, autodialler etc. SALE PRICE £12.99 

AIR RIFLES .22 As used by the Chinese army for training 
puposes, so there is a lot about! £39.95 Ref EF78. 500 pellets 
£4.50 ref EF80. 

in to 13A socket with output lead. three types available, 9vdc 
150mA £1.50 ref SA19, 9vdc 200mA £2.00 ref SA20, 6.5vdc 
500mA £2 ref SA21. 

VIDEO SENDER UNIT. Transmits both audio and video 
signals from either a video camera, video recorder, TV or 
Computer etc to any standard TV set in a 100' range! (tune TV 
to a spare channel) 12vDC op. Price is£15 REF: MAG15 12v 
psu is £5 extra REF: MAGSP2 

*FM CORDLESS MICROPHONE Small hand held unit 
with a 500' range! 2 transmit power levels. Reqs PP3 9v battery. 
Tuneable to any FM receiver. Price is £15 REF: MAG15P1 
talkies with a range up to 2 km in open country. Units measure 
22x52x155mm. Including cases and earp'ces. 2xPP3 req'd. 
£30.00 pr.REF: MAG30 

295x 135x60mm, 4 drive connectors 1 mother board connector. 
150watt, 12vfan, iec inlet and on/off switch. SALE PRICE £7.99 
REF SA 22 

*FM TRANSMITTER KIT housed in a standard working 13A 
adapter!! the bug runs directly off the mains so lasts forever! 
why pay £700? or price is £15 REF: EF62 Transmits to any FM 
radio. (this is in kit form with full instructions. ) 

*FM BUG BUILT AND TESTED superior design to kit. 
Supplied to detective agencies. 9v battery req’d. £14 REF: 

COINSLOT MECHANISMS originally made to retail at £79 
each, these units are designed to convert an ordinary phone 
into a payphone. The units have the locks missing and 
sometimes broken hinges. However they can be adapted for 
their original use or used for something else?? SALE PRICE 
JUST £2.50 REF SA23 

GAT AIR PISTOL PACK Complete with pistol, darts and 
pellets £12.95 Ref EF82 extra pellets (500) £4.50 ref EF80. 
6"X12" AMORPHOUS SOLAR PANEL 12v 155x310mm 
130mA. SALE PRICE £4.99 REF SA24. 


£4.99 ref MAG5P13 ideal for experimenters! 30 m for £12.99 ref 






A Hand held personal Gamma and X Ray detec 
tor. This unit contains two Geiger Tubes, has a 4 

s 2 

digit LCD display with a Piezo speaker, giving a 
audio visual indication. The unit detects hig 
energy electromagnetic quanta with an energ 
from 30K eV to over 1.2M eV and a measuring 
range of 5-9999 UR/h or 10-99990 Nr/h. ref NOV18 

ISSN 0262 3617 EVERYDAY 



VOL. 24 No.9 SEPTEMBER 1995 The No. 1 Independent Magazine for Electronics, 
Technology and Computer Projects 


SIMPLE THEREMIN by Jake Rothman 674 
Making music by sleight of hand — pocket-sized instrument echoes 
the 1920s 

LOW RANGE OHMMETER ADAPTOR by Steve Knight — «684 
Allows a DVM to measure resistances below 12. Easy to calibrate 
Give all-round protection to your garden shed, garden furniture and home 
VANDATA by Peter Unwin | 706 
Constant “cockpit” display confirms caravan lights integrity while en-route 

Providing very quiet power for personal audio amplifiers 
of " ag 

INGENUITY UNLIMITED by Enthusiastic Readers 696 

The circuit showcase for readers’ designs 

We may not “surf the stripboard”’ but there’s other jargon to cope with! 
INTERFACE by Robert Penfold 717 
Hardware detecting Morse signals helps relieve the computer's task 

CAVE RADIO By Mike Bedford 721 
Can you help to improve cave safety through a better comms link? 

AMATEUR RADIO by Tony Smith G4FAI 736 

RAE classes; Special interest groups; News bulletin trouble spot 


Everyday news from the world of electronics 

NEW TECHNOLOGY UPDATE by lan Poole 682. 
The latest SiGe developments improve junction gains and speed 

FOX REPORT by Barry Fox 3 700 
The loss of the important Alan Blumlein archives would be scandalous 
Our range of educational videos 

Did you miss these? 

OHM SWEET OHM by Max Fidling 715 
Electro-plumbing the plants at Fidling Acres makes Piddles melon-choly! 
SHOPTALK with David Barrington 724 
Component buying for EPE projects 

A wide range of technical books available by mail order 

PCBs for EPE projects — some at knock-down prices! 


© Wimborne Publishing Ltd 1995. Copyright in all 

drawings, photographs and articles published in & R E E 

protected, and reproduction or imitations in whole GREENWELD SUMMER SALE CATALOGUE . 
or in part are expressly forbidden. between pages 700 /701 

_ Our October ’95 Issue will be published on Friday, Readers Service @ Editorial and Advertisement Departments 673 
1 September 1995. See page 663 for details. 

Everyday with Practical Electronics, September 1995 661 





AT 286 
40Mb HD + 3Mb Ram 

with battery backup is provided as standard. Supplied in good used 
condition complete with enhanced keyboard, 640k + 2Mb RAM, 
DOS 4.01 and 90 DAY Full Guarantee. Ready to Run ! 

Order as HIGRADE 286 OA/Z Y £149.00 (E) 


Optional Fitted extras: VGA graphics card 
1.4Mb 3%" floppy disk drive (instead of 1.2 Mb) 
NE2000 Ethernet (thick, thin or twisted) network card 


5%" from £22.95 - 3%" from £24.95 

Massive purchases of standard 5%" and 3%" drives enables us to 
present prime product at industry beating low prices! All units (unless 
Stated) are BRAND NEW or removed from often brand new equip- 
ment and are fully tested, aligned and shipped to you with a 90 day 
guarantee and operate from standard voltages and are of standard 
size. All are IBM-PC compatible (if 3/2" supported on your PC). 

3%" Panasonic JU363/4 720K or equivalent £24.95(B 
3%" Mitsubishi MF355C-L. 1.4 Meg. Laptops only * £36.95(B 
3%" Mitsubishi MF355C-D. 1.4 Meg. Non laptop £29.95(B 
5%" Teac FD-55GFR 1.2 Meg £29.95(B 
5%" BRAND NEW Mitsubishi MF501B 360K £22.95(B 
* Data cable included in price. 

Shugart 800/801 8" SS refurbished & tested £195.00(E 
Shugart 851 8" double sided refurbished & tested £250.00(E 
Mitsubishi M2894-63 8" double sided NEW £275.00(E 
Mitsubishi M2896-63-02U 8" DS slimline NEW £285.00(E 

Dual 8" drives with 2 mbyte capacity housed in a smart case with . 

built in power supply. Ideal as exterior drives! 


End of line purchase scoop! Brand new NEC D2246 8" 85 Mbyte 
of hard disk storage! Full industry standard SMD interface. Ultra 
hi speed data transfer and access time, replaces Fujitsu equivalent 

model. complete with manual. Only £299.00(E) 
3%" FUJI FK-309-26 20mb MFM I/F RFE £59.95(C 
3%" CONNER CP3024 20 mb IDE I/F (or equiv )RFE £69.95(C 
3%" CONNER CP3044 40mb IDE I/F (or equiv.)RFE £89.00(C 
3%" RODIME RO3057S 45mb SCSI I/F (Mac & Acorn) £99.00(C 
5%" MINISCRIBE 3425 20mb MFM I/F (or equiv.) RFE £49.95(C 
5%" SEAGATE ST-238R 30 mb RLL I/F Refurb £69.95(C 
5%" CDC 94205-51 40mb HH MFM I/F RFE tested £69.95(C 
8" FUJITSU M2322K 160Mb SMD I/F RFE tested £195.00(E) 

Hard disc controllers for MFM , IDE, SCSI, RLL etc. from £16.95 


Converts your colour monitor into a QUALITY COLOUR TV!! 



The TELEBOX consists of an attractive fully cased mains powered 
unit, containing all electronics ready to plug into a host of video moni- 
tors made by makers such as MICROVITEC, ATARI, SANYO, 
composite video output will also plug directly into most video 
recorders, allowing reception of TV channels not normally receivable 
on most television receivers* (TELEBOX MB). Push button controls 
on the front panel allow reception of 8 fully tuneable ‘off air’ UHF 
colour television channels. TELEBOX MB covers virtually all televi- 
sion frequencies VHF and UHF including the HYPERBAND as 
used by most cable TV operators. A composite video output is 
located on the rear panel for direct connection to most makes of 
monitor or desktop video ~ popes For complete compatibility - even 
. for monitors without sound - an integral 4 watt audio amplifier and 
low level Hi Fi audio output are provided as standard. 
TELEBOX ST for composite video input type monitors 
TELEBOX STL as ST but with integral speaker £37.50 
TELEBOX MB Multiband VHF-UHF-Cable- Hyperband.tuner £69.95 
For overseas PAL versions state 5.5 or 6mhz sound specification. 
“For cable / hyperband reception Telebox MB should be connected 
to cable type service. Shipping code on all Teleboxes is (B 


MITSUBISHI MMF-D6D12DL 60 x 25 mm 12v DC 
MITSUBISHI MMF-09B12DH 92x25mm12vDC £5.95 10/ £53 
PANCAKE 12-3.5 92 x 18 mm 12v DC £7.95 10 / £69 
EX-EQUIP 120 x 38mm AC fans - tested specify 110 or 240 v £6.95 
_ EX-EQUIP 80 x 38mm AC fans - tested specify 110.0r 240 v £5.95 
VERO rack mount 1U x 19" fan tray specify 110 or 240v £45.95 (8) 
IMHOF B26 1900 rack mnt 3U x 19" Blower 110/240v NEW £79.95 
Shipping on all fans (A). Blowers (B). 50,000 Fans Ex Stock CALL 



5,000,000 items EX STOCK 


£4.95 10 / £42 

Issue 13 Of Display News now available - send lar 



ri . BR cc > sree 2 PB apcial™ - ° 

e eee © ® e ee ___e§ Open Mon - Sat 9:00 - 5:30 Open Mon-Fri 9.00-5:30 

Be Sa tee ses SO" han iawened Dept EE. 32 Biggin Way 

Seco’ oe ° Secce M4 wee eae ee Upper Norwood 
Selhurst Park SR Rail Stations LONDON SE19 3XF 



ONLY £99.00 

A massive bulk purchase enables us to bring you a COMPLETE 
coy! to run colour PC DA ghd at an unheard of price! 
The Display Electronics PC99 system comprises of fully com- 
patible and expandable XT PC with 256k of RAM, 5%° k flop- 
py disk drive, 12" CGA colour monitor, standard 84 key key- 

oard, MS DOS and all connecting cables - just plug in and go 
!! Ideal students, schools or anybody wishing to learn the world of 
PC's on an ultra low budget. Don't miss this opportunity. 

Fully guaranteed for 90 ag Re as PCOSCOL £99.00 (E) 

Optional Fitted extras: 640k RAM 
2nd floppy drive, specify 5%" 360k or 3%" 720k £29.95 
Above prices for PC99 offer ONLY. 



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

com includi 
SVGA modes, BBC, COMMODORE (including 
Amiga 1200), ARCHIMEDES and APPLE. Man 
features: Etched faceplate, text switching and LO 
et eras yt 7h phe specification. Full 90 day warranty. 
in condition. . 
Orderasmits-svca Only £1396 
Tilt & Swivel Base £8.00 Leads for IBM PC £8.95 (A) 
External Cables for other £ CALL 

PHILIPS HCS35 ame style 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 amp and speaker for all audio visual uses. 
Will connect direct to Amiga and Atari BBC computers. Ideal for 
all monitoring / security applications with direct connection to 
most colour cameras. High quality with many features such as front 
concealed flap controls, VCR correction button etc. Good used 

condition - fully tested with a 90 day guarantee 
14" x H12%" x 15%" B. : Only £99 

Special Offer save £16.95 - Order TELEBOX ST & 
HCS35 together - giving you a quality colour TV & AV 

system for Only £122.50 (E) 
KME 10" en 4 definition. colour monitors. Nice tight 0.28" dot pitch 

for superb clarity and modern styling. Operates from ; ss 
any 15.625 khz sync RGB video source, with RGB 
analog and composite sync such as Atari,# 
Commodore Amiga, Acorn Archimedes & BBC. 3 
Measures only 13%" x 12" x 11". Only £125 (E) 
Good used condition. 90 vg! Pp seat 

KME 10" as above for PC standard £145.00 (E) 

PHILIPS HCS31 Ultra compact 9” colour video monitor with stan- 
dard composite 15.625 Khz video input via SCART socket. Ideal 
for all monitoring / security applications. High quality, ex-equipment 
fully tested with a 90 day guarantee (possible minor screen burns). 
In attractive square black plastic case Magar W10" x H10" x 
13%" D. Mains powered Limited Quantity - Only £79.00 (D) 

20" 22" and 26" AV SPECIALS 

Superbly made UK manufacture. PIL all solid state colour monitors, 
complete with composite video & optional sound inputs. 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 (F) 


Virtually every type of power 
supply you can imagine.Over 
10,000 Power Supplies Ex Stock 

Call for info / list. 
oy md oh OF 74 RO odd ood 

Zeta 3220-05 AO 4 pen HPGL RS232 fast drum plotter £1950 
3M VDA - Video Distribution Amps.1 in 32 out £375 
Trio 0-18 vdc bench PSU. 30 amps. New £470 
Fujitsu M3041 600 LPM band printer £1950 
VG Electronics 1035 TELETEXT Decoding Margin Meter £3750 

Andrews LARGE 3.1 m Satellite Dish + mount (For Voyager!) £950 
RED TOP IR Heat seeking missile (not armed !!) POA 

KNS EMC / Line interference tester NEW £1200 
Thuriby LA 160B logic analyser £375 
INTEL SBC 486/133SE Multibus 486 system. 8Mb Ram £1200 
GEC 1.5kw 115v 60hz power source £950 
Brush 2Kw 400 Hz 3 phase frequency converter £850 
Anton Pillar 75 kW 400 Hz 3.phase frequency converter POA 
Newton Derby 70 KW 400 Hz 3 phase frequency converter POA 
COMPONEDEX T1000 Portable TELEX tester NEW £250 

Sekonic SD-150H 18 channel digital Hybrid chart recorder £1995 
HP 7580A A1 8 pen HPGL high speed drum plotter £1850 
Computar MCA1613APC 16mm auto iris lenses 'C' mount 
Seaward PAT 2000 dual voltage computerised PAT tester 
Densei MUD 0185AH 1KVa UPS system with batts NEW £575 

e SA 

Allow approx 6 days 


DISTEL © The Original 
FREE On line Database 
Info on 1000's of items 

V21,V22, V22 BIS 
0181 679 1888 

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

Universities and Local Authorities - minimum account order £50. Cheques over £100 are subject to 10 working days clearance. Carriage 
aan (C)=£8.50, (D)=£12.00, (E)=£15.00, (F)=£18.00, (G)=CALL. for ing - faster CALL. 

nate pctions ws antic Chacperas reckons Ton CAS lovee cade ake 
notice. Orders subject to stock. Discounts for volume. Top CASH prices paid for surplus 

Surplus always 
wanted for cash! 
Superb quality 6 foot 40U 

Virtually New, Ultra Smart 
Less than Half Price! 

Top quality 19" rack cabinets made in UK by 
Optima Enclosures Ltd. Units feature 
designer, smoked acrylic lockable front door, 
full height lockable half louvered back door 
and 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 most versatile we have 
ever sold. Racks may be stacked side by side and therefore require 
only two side panels to stand singly or in bays 
Overall dimensions are: 77%" H x 32%" D x 22" W. Order as: 

OPT Rack 1 Complete with removable side panels. £335.00 (G) 

OPT Rack 2 Rack, Less side panels £225.00 (G) 

32U - High Quality - All steel cabinet 

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 
hinged for easy access and all are lockable with <% 
five secure 5 lever barrel locks. The front door & 
is constructed of double walled steel with a ES 
‘designer style’ smoked acrylic front panel to 
enable status indicators to be seen through the # 
anel, yet remain unobtrusive. Internally the rack & 
eatures full slotted reinforced vertical fixing mem- § 
bers to take the heaviest of 19” rack equip- 
ment. The two movable vertical fixing struts 
(extras available) are pre punched for standard 
‘cage nuts’. A mains distribution panel internal- 
ly mounted to the bottom rear, provides 8 IEC 3 # 5 
pin Euro sockets and 1 x 13 amp 3 pin switched ‘ Rs +: 
utility socket. Overall ventilation is provided by “&& 
fully louvered back door and double skinned top section 
with top and side louvres. 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 biue. External dimensions 64” H x 
25” D x 23%” W. 

Sold at LESS than a third of makers price !! 
A superb buy at only £195.00 

Over 1000 racks in all sizes 19" 22" & 24" 
3 to 44 U. Available from stock !! 

Call with your requirements. 

The ultimate in ‘Touch Screen Technology’ made by the experts - 
MicroTouch - but sold at a price below cost !! System consists of 
a flat translucent ogee laminated panel measuring 29.5 x 23.5 cm 
connected to a PCB with on board sophisticated electronics. From 
the board comes a standard serial RS232 or TTL output. The out- 
put continuously gives simple serial data containing positional X & Y 
co-ordinates as to where a finger is touching the panel - as the fin- 
ger moves, the data instantly changes. The X & Y information is 
given at an incredible matrix resolution of 1024 x 1024 positions 
over the screen size !!! So, no position, however small fails detec- 
tion. A host of available translation software enables direct con- 
nection to a PC for a myriad of applications including: control pan- 
els, pointing devices, POS systems, controllers for the disabled or 
computer un-trained etc etc Imagine using your finger in ‘Windows’ 
instead of a mouse !! (a driver is indeed available !) The applica- 
tions for this amazing product are only limited by your imagina- 
tion!! Supplied as a complete system including Controller, Power 
Supply and Data at an incredible price of only: £1 45.00 

RFE. Full Software Support Available - Fully Guaranteed . (B) 


INTEL 'ABOVE' Memory Expansion Board. Full length PC-XT 
and PC-AT compatible card with 2 Mbytes of memory on board. 
Card is fully selectable for Expanded or Extended (286 processor 
and above) memory. Full data and driver disk supplied. In good 
used condition fully tested and guaranteed. 
Windows compatible. Order as: ABOVE CARD. £59.95(a1) 
Half length 8 bit memory upgrade cards for PC AT XT expands 
memory either 256k or 512k in 64k steps. May also be used to fill 
in RAM above 640k DOS limit. Complete with data. 

Order as: XT RAM UG. 256k. £32.95 or 512k £38.95 (A1) 

1MB x9 SIMM 9 chip 120ns 

ont £19.50 (A1 
1 MB x9 SIMM 3 chip 80 ns £53.50 70ns £26.00 (A1 
1MBx9 SIMM9chip80ns £22.50 70ns £28.00 (A1 

4 MB 70ns 72 pin SIMM module only £125.00 (A1 
SPECIAL INTEL 486-DX33 CPU £79.99 (A1) 


EMERSON ACCUCARD UPS, brand new 8 Bit half length PC 
compatible card for all IBM XT/AT compatibles. Card provides DC 
power to all internal system components in the event of power sup- 
ply failure.The Accusaver software provided uses only 6k of base 

AM and automatically copies all system, expanded and video 
memory to the hard disk in the event of loss of power. When power 
is returned the machine is returned to the exact status when the 
power failed !! The unit features full self diagnostics on boot and is 

Normally £189.00 NOW! £69.00 or 2 for £120 @ 
- PACKED with bargains! 


0181 679 4414 

FAX 0181 679 1927 

Govemment, Schools, 
(A)=£3.00, (A1)=£4.00, 
shipping Scotland All goods supplied to our 

on a retum to base basis. All rights reserved to prices / specifications without prior 
rode, Al vedere eke act ontociged © Deaoiay Blocrerics 1008, EA OE 4 

Everyday with Practical Electronics, September 1995 

Build any one of six different projects on next month’s FREE P.C.B. 
Three projects will appear next month and three in the November issue. 

The projects are: 


Imagine an ordinary |.e.d. bargraph as a VU meter display. Now imagine it a 
hundred times larger, ten thousand times brighter, ten tungsten lights 
flashing, ascending, cascading, all in time with the music, and 
all driven from your normal hi-fi. It's all possible with 
the aid of the Ginormous VU Meter. Plus the 
power to impress your local ravers! 


A cheap and cheerful capacitance ‘‘meter’’. There is often a need to measure or confirm the 
value of an “unknown” capacitor or one on which the lettering has become obscured. Certain 
components of dubious origin appear to have non-standard markings and this makes them difficult to 
match up if ever they need to be replaced. The circuit to be described is probably the simplest which can 
be constructed which will find the value of a capacitor with reasonable accuracy. 

It will measure values from less than 10nF to 5000uF with an accuracy good enough to determine the 
nearest standard value of an “unknown” component. 

You may not spot them, but electronic tags are attached to ever-increasing types of merchandise in 
most High Street stores and shops. The detection techniques used are ingenious, ranging from 
multiple r.f. transceiving to magnetic pattern matching and harmonic frequency analysis. Any 
commodity, whether it's clothing, garden tools, library books or videos, to name but a few, is likely to 
trap the would-be thief. Understand the detection principles as explained by an engineer from a 
major company which makes the equipment. 

| wir PRACTICAL | 



Everyday with Practical Electronics, September 1995 


7 Teco: ROLL GUILE Lome, layout could not be easier" eh OPC 

Electronics World & Wireless World Jan 1995 ‘file export 
& SpiceAge 
DDE link! 

Quickroute 3.0 for Windows 3.1 has 

| | been designed from the start to be Wo k 3 () 
Yaa EE as easy to use as possible, without Ouic r O ut 4 ® 
“Gm Sacrificing the power professional 

Bae Engineers need to get the job done. , 
Ml Quickroute is available with Integrated Schematic and PCB 
(PT schematic capture, support for Design for Windows 3.1 
me Ousses & power rails, 1-8 layer 

@| auto-routing, SPICE file export, and 
jour new extended library pack. 
» Quickroute 3.0 PRO+ can also 
connect to the Windows simulation i Beaten . 
package SpiceAge using Windows newinrs aaa jas walaeae fox sooo va fess ‘ 
DDE. Contact POWERware for eee cae = feral lbae| : a 

m more details! oa Pr ” 
il | ay ee ae a a8: 

Seolieses PR 
i ae . 


utateteteetetetet Pttettetetettte ol Seteteteteetetetete eM etatetetete by eretatetetet OOO: | MERRRERRRERL EE” | ORME, tot) MEERRROOR RE. | MEARS RR ROR 

*Schematic & PCB Drawing *1/2 layer auto-router 
*Supports Windows printers/plotters *Full set of 
libraries *Clipboard support *Designer Special (manual 
on disk) also available. 

RT%e] 199 

*Schematic & PCB Design *Schematic Capture 
*Integrated Rats-Nest Generation *1-8 layer Auto-router 
(faster than Designer) *Net-List Export *Supports ; o 
Windows printers/plotters *CAD-CAM outputs. Busses and Power rails handled easily 
UEiale Cl fe)ey-1my (-} melasma ai@re 

Seceuy ee 33 
bbbabeh) Att 

TOL Tore 
| PPP > >>>P P>>D>Pi>>> 
= he S054 Bp 



ppp >> >> > p> >; 

zpezezzezezezece | 

PE Ht * 


246) £299 

As the PRO but also includes *Advanced Schematic Capture 
(Busses,Power rails,etc) *Larger Schematic & PCB Designs 
*Gerber file IMPORT for File Exchange *Extended libraries 
(CMOS,SMT,etc) *SPICE Export *SpiceAge DDE link. 

*Prices exclude P+P and V.A.T. VISA/MasterCard 
Accepted *Network versions available. 

view Bwn-s—— 
Ao) + 
re m 

Quickroute Systems Ltd, 14 Ley Lane, 
Marple Bridge, Stockport, SK6 5DD, U.K. 

Tel/Fax 0161 449 7101 DDE link to SpiceAge pastedtdl 
email Simulator with PRO+ vailabie. 

664 t Everyday with Practical Electronics, September 1995 


SYSTEM Evaluation Kits 
Programs 24, 28, 32 pin EPROMS, EE-PROMS, FLASH 

Radio Data Modules 

Data Transmitters & Receivers 

_| and Emulators as standard, quickly, reliably and at low same Day DispatchE 
cost. 173MHz, 418MHz & 433.92MHz 
| Expandable to cover virtually any programmable part . : 
including serial E2, PALS, GALS, EPLD's and Credit Card Orders Ta @@ 
microcontrollers from all manufacturers. Applications: 
DESIGN | Remote Controls 
Not a plug in card but connects to the PC serial or 1 | Wire-free Security | 
parallel port; it comes complete with powerful yet easy as Remote Monitoring 
to control software, cable and manual. : 
RF Computer links 
UK design, manufacture and support. Same day : 5 
dispatch, 12 month warranty. 10 day money back NEW! Transceiver evaluation kit. Includes: 
guarantee. , 2x Transceivers, test PCB with PIC micro, 
ASK FOR FREE INFORMATION PACK bit error rate, range & self test firmware 
— : OG) o zs batteries, antenna and carry case. £149.00 
MOP ELECTRONICS Ltd. | Aa ae Radio - Tech Limited 
Unit 2, Park Road Centre, Malmesbury, Wiltshire, SN16 OBX UK ‘T ~—-DISTRIBUTOR OF RADIOMETRIX PRODUCTS 
TEL. 01666 825146 FAX. 01666 825141 Overbridge House, Weald Hall Lane, Thornwood, Epping, Essex. CM16 6NB 
GERMANY 089/4602071; NORWAY 0702-17890; ITALY 02 92 10 3554 Sales 0181-368 8277 Fax 0181-361 3434, Admin 01992-576107 Fax 01992- -561994 

FRANCE (1); IRELAND 1-2800395; SWEDEN 08-590-32185; 


PA 400 *vPurier £1 39-99 Gite = 

@ INPUT 0:75V-1:2V @INPUT IMPEDANCE 47Kohms | 
@ OUTPUT POWER 2x 200 WATT MAX (4ohms) y 

@ FREQUENCY RESPONSE 14H2z-26kH2z (3db) 

@S/N RATIO 10db @ SEPARATION 70db 

@ DIMS 482mm/308mm/132mm 3U @ WEIGHT 8:4kg 


P y :‘ 700 BEEFY ei socers ONLY £204: Ls soaks 

W @ INPUT 0- ‘75V-1:2V VIA %" (6:-35mm) JACK SOCKETS RyCry 
sv @OUTPUT MAX 2 350W (4 ohms) VIA 3-PIN XLR FM L , 
@ OUTPUT RMS 2 x 230W iii i ‘ 
Ww @ SIZE 438mm (W) x 87mm (H) x 268mm (D) 2U @ WEIGHT 7. 65ke (3: 2She Booced 


(R) (C) 376 EDGWARE ROAD LONDON W21EB Tel: 0171-723 8432/0171-723 3462 Fax 0171-723 3467 
2 mins. from Edqware Road Tube Station. 

Everyday with Practical Electronics, September 1995 : , 665 



No. 1 for Kits 

Whether your requirement for surveillance equipment is amateur, professional or you are just fascinated by this unique area of 
electronics SUMA DESIGNS has a kit to fit the bill. We have been designing electronic surveillance equipment for over 12 years 
and you can be sure that all our kits are very well tried, tested and proven and come complete with full instructions, circuit 
diagrams, assembly details and all high quality components including fibreglass PCB. Unless otherwise stated all transmitters 
are tuneable and can be received on an ordinary VHF FM radio. 

Genuine SUMA kits available only direct from Suma Designs. Beware inferior imitations! 

UTX Ultra-miniature Room Transmitter 
Smallesi room transmitter kit in the world! Incredible 10mm x 20mm including: 

mic. 3-12V Operation: SOOM range, ii. s oi dec ssscisstaiviccssscescsoepeceesoececbanestvdoreares £16.45 
MTX Micro-miniature Room Transmitter 

Best-selling micro-miniature Room Transmitter 

Just 17mm x 17mm including mic. 3-12V operation. 1000 range..............ss00 £13.45 
STX High-performance Room Transmitter 

Hi performance transmitter with a buffered output stage for greater stability and range. 
Measures 22mm x 22mm including mic. 6-12V operation, 1500m range............. £15.45 
VT500 High-power Room Transmitter 

Powerful 250mW output providing excellent range and performance. Size 20mm x 
40mm. 9-12V operation. 3000M range..................cccccceccsssescssssetesscscecessscesseneeeevess £16.45 
VXT Voice Activated Transmitter | 

Triggers only when sounds are detected. Very low standby current. Variable sensitivity 
and delay with LED indicator. Size 20mm x 67mm. 9V operation. 1000m range...£19.45 

HVX400 Mains Powered Room Transmitter 

Connects directly to 240V AC supply for long-term monitoring. Size 30mm x 35mm. 
SOON TANGO icici CE aie hid tig sty iA pehcaatidc rhe aeee £19.45 
SCRX Subcarrier Scrambled Room Transmitter 

Scrambled output from this transmitter cannot be monitored without the SCDM decoder 

connected to the receiver. Size 20mm x 67mm. 9V operation. 1000m range............. £22.95 
SCLX Subcarrier Telephone Transmitter 

Connects to telephone line anywhere, requires no batteries. Output scrambled so 
requires-SCDM connected to receiver. Size 32mm x 37mm. 1000m range........... £23.95 
SCDM Subcarrier Decoder Unit for SCRX 

Connects to receiver earphone socket and provides decoded audio output to 
headphones. Size 32mm x 70mm. 9-12V Operation ..............cccceseesesesereeeeseseeseenes £22.95 

ATR2 Micro Size Telephone Recording Interface 

Connects between telephone line (anywhere) and cassette recorder. Switches tape 
automatically as phone is used. All conversations recorded. Size 16mm x 32mm. 
POWOTO PLOT TH oo isco cok ccsascc oiccseuss hssgadeiasnscocacsoohcssssopsleabvasbemsctuleceeqietbonses £13.45 

DerT. EE 

UTLX Ultra-miniature Telephone Transmitter 

Smallest telephone transmitter kit available. Incredible size of 10mm x 20mm! 
Connects to line (anywhere) and switches on and off with phone use. 

All conversation transmitted. Powered from line. 500m range.................60.. £15.95 

TLX700 Micro-miniature Telephone Transmitter 

Best-selling telephone transmitter. Being 20mm x 20mm it is easier to assemble than 
UTLX. Connects to line (anywhere) and switches on and off with phone use. All 
conversations transmitted. Powered from line. 1000m range ...................ce. £13.45 

STLX Hi Telephone Transmitter 

High performance transmitter with buffered output stage providing excellent stability 
and performance. Connects to line (anywhere) and switches on and off with phone use. 
All conversations transmitted. Powered from line. Size 22mm x 22mm. 

I ia aia cgsgs Gila ck cphesduitdid Lied opi doddndhsdcndavicccivicdcccadicvacdiien, £16.45 

TKX900 Signalling/Tracking Transmitter 

Transmits a continous stream of audio pulses with variable tone and rate. Ideal for 
signalling or tracking purposes. High power output giving range up to 3000m. Size 
PEE NTL Te CUNT 6s gnt cokes aacasvonee)sicds fucssideccsssdscvesdccccudteaiodae ndeiotoss £22.95 

CD400 Pocket Bug Detector/Locator 

LED and piezo bleeper pulse slowly, rate of pulse and pitch of tome increase as you 
approach signal. Gain control allows pinpointing of source. Size 45mm x 54mm. 9V 
TSE ASRS RP a Ree a aa ree AM Diba CRA Rae art SPR PORE od ARON Cao £30.95 

CD600 Professional Bug Detector/Locator 

Multicolour readout of signal strength with variable rate bleeper and variable sensitivity 
used to detect and locate hidden transmitters. Switch to AUDIO CONFORM mode to 
distinguish between localised bug transmission and normal legitimate signals such as 
pagers, cellular, taxis etc. Size 70mm x 100mm. 9V operation .................cccccccee £50.95 

QTX180 Crystal Controlled Room Transmitter 

Narrow band FM transmitter for the ultimate in privacy. Operates on 180 MHz and 
requires the use of a scanner receiver or our QRX180 kit (see catalogue). Size 
20mm x 67mm. 9V operation. 1000M range........... ee ccccceeeeetseeeeeeeeeeeeaeeeneeeeees £40.95 

QLX180 Crystal Controlled Telephone Transmitter : 
As per QTX180 but connects to telephone line to monitor both sides of conversat- 
tions. 20mm x 67mm. 9V operation. 1000M range..............ccccceeceeeseeeeesteetteeaeees £40.95 . 

| QSX180 Line Powered Crystal Controlled Phone Transmitter 

As per QLX180 but draws power requirements from line. No batteries required. Size 
SRTUIYK 7 TOUTE PAINS INN gins st se chicane cox copaesiaiecal pabcaciicnassiasecchenlatbstoadeesyetes £35.95 

QRX180 Crystal Controlled FM Receiver 

For monitoring any of the ‘Q’ range transmitters. High sensitivity unit. All RF section 
supplied as a pre-built and aligned module ready to connect on board so no difficulty 
setting up. Outpt to headphones. 60mm x 75mm. 9V operation ............... £60.95 

A build-up service is available on all our kits if required. 

UK customers please send cheques, POs or registered cash. Please add 
£1.50 per order for P&P. Goods despatched ASAP allowing for cheque 
Clearance. Overseas customers send sterling bank draft and add £5.00 per 
order for shipment. Credit card orders welcomed on 0827 714476. 


THE Wor«sHops, 95 MAIn ROAD, 

BD] RY [C7] RS 


01827 714476 



Everyday with Practical Electronics, September 1995 

Pico Releases PC 

Pico's Virtual Instrumentation enable you to use your 
computer as a variety of useful test and measurement 
instruments or as an advanced data logger. 


a F-]gen cl acm- [ale m-Ye) alr: acm-lacm-1e]e)e)i (tem Cole (=i tal-] ar- lm. el-(e1.¢-[8[= 
om akemanle)a=mce)aq(-t-m-lelele)amialere)anley-iele)iii ame) mere) ale) (:> @--1 G16] ©) 
fe} celer-lo lel a=t-MamOlalil.(-meg-lelidcelar-lmmellelemlammer-le-m-lere [Ul F-Jld(elamer-[gel-e Tete] Mote 
they simply plug into the PC's parallel or serial port, making Advanced data <a yew op oe 
them ideal for use with portable PC's. logging software. 

Time (hours) jo 

Call for your Guide on ‘Virtual Instrumentation’. RECLINE CREE R ERS EE 

NEW from Pico TC-08 thermocouple to PC Converter | — 
8 channel Thermocouple Interface 

@ Connects to your serial port - no power supply required. sina 
@ Supplied with PicoLog datalogging software 
for advanced temperature processing, min/max detection and alarm. 
@ 8 Thermocouple inputs (B,E,J,K,N,R,S and T types) —_—- | 
@ Resolution and accuracy dependant on thermocouple type. a 
For type K the resolution is better than 0.1°C . 

TC-08 £199 
TC-O08 + Calibration Certificate £224 

complete with PicoLog, software drivers and connecting cable. 
A range of thermocouple probes is available. 

SLA-16 & SLY-S2 Logic Analysers *#2O@€-/00 virtual instrument 

Pocket sized 16/32 channel Logic Analysers Dual Channel 12 bit resolution 

Connects to PC serial port. 
Up to 50MHz sampling. 

2 Digital Storage Scope 

@ Internal and external 


Spectrum Analyser 
Frequency Meter 
Chart Recorder 
Data Logger 

The ADC-100 offers both a high 
SL4-52 £349 sampling rate (100kHz) and a high 
with software, power resolution. It is ideal as a general 
supply and cables purpose test instrument either in the 
lab or in the field. Flexible input ranges 
(+200mV to +20V) allows the unit to 
connect directly to a wide variety of signals. 

2#DE-100 with PicoScope £199 
with PicoScope & PicoLog £219 

clock modes. 
8K Trace Buffer. 

SL-A4-16 £219 


1 Channel 8 bit 

@ Lowest cost in the Pico range The ADC-10 gives your computer a single channel of 
@ Up to 22kHz sampling analog input. Simply plug into the parallel port. 
@ 0 -5V input range 2#ADE-10 with PicoScope £49 

Carriage UK free, Overseas £9 Oscilloscope Probes (x1, x10) £10 PicoScope & PicoLog £59 



Pico Technology Ltd. Broadway House, 149-151 St Neots Rd, Hardwick, Cambridge. CB3 7QJ 
me Tel: (0)1954 - 211716 Fax: (0)1954 - 211880 E-mail: 100073.2365 

Phone or FAX for sales, ordering information, data sheets, technical support. All prices exclusive of VAT 

Everyday with Practical Electronics, September 1995 667 



If you are looking for a means of 
improving your knowledge of the 
basics of electronics then this 
software is for you. 


* Insulators, Conductors, Resistance * D.C. Circuits 
* Capacitance and Inductance * A.C. Series Circuits 
* A.C. Parallel Circuits * Reactance and Impedance 

* A.C. and D.C. Power * Frequency and Tuned Circuits 

* Using Numbers * Complex Numbers, Phase Angles 

* P.N. Junction Diode * Bi-polar and MOSFET Transistors 

* Operational Amplifiers * Logic Gates * Digital Number Systems 

* Combinational Logic * Flip Flops * Counters aad Shift Registers 

* Memory * Microcomputer operation 

Now an extended range of electronics topics with an 
improved graphics presentation, available to electronics 
hobbyists, students, schools, colleges, and used for training 
within industry throughout the UK and overseas. A fully 
interactive electronics program where the user selects from 
over 250 analogue and digital topics. Circuit diagrams, wave 
forms, phase angles, voltages and currents or logic states are 
shown, drawn to scale, in full colour. Formulae are given 
demonstrating all the calculation steps, exactly as in a 
textbook, using your input values. 

An ‘on screen’ electronics package including circuit theory 
to enable a learning through doing approach to encourage ex- 
perimentation. For the young student, mature hobbyist or the 
engineer that just needs to keep up-to-date in an easy and 
enjoyable way. 

Having reviewed a dozen, or more, educational software 
packages designed to “‘teach’’ electronics, I was more than a little 
sceptical when I first heard about Electronics Principles: there 
seemed to be little that could be done that has not been done 
elsewhere. When I started to use the package my views changed. 

Vout= Vin* 

Vout» Vin* 

Indeed, I was so impressed with it that 1 quickly came to the 

conclusion that readers should have an opportunity to try the 
package out for themselves! - MIKE TOOLEY B.A. Dean of 
Faculty of Technology, Brooklands Technical College. 

Complete package Still only £49 25 


An extended and improved version of the popular Toolbox software. 
Presents commonly used formulae in a way that makes calculations easier 
thus encouraging experimentation in circuit design. 3 

Covers D.C. Calculations from Ohm’s Law to Loading a Potential 

Divider; Further D.C. Calculations from Power Ratio Decibels to © 

Kirchhoff’s Laws; A.C. Calculations from Average Peak Current to Filters 
and Admittance; Capacitance Calculations from Values to RC Time 
Constants; Inductance Calculations from Values to Selectivity; Binary 
Calculations from Addition to 2’s Complement; Numbers and Phase 
Angles from Addition to Polar to Rectangular; Operational Amplifiers 
from Inverting Op.Amp to Op.Amp Differentiator. 

Test Data. Vin = 30volts : Rl = 1kohms : R2 = 1.5kohms : Load = 10kohms. 

Only £19.95. 

Vin = 30V 
Ri = 1k 
Re = 1.5k 
Vout = 18V 

Load = 10k 
regerty) [RL AZ| Load =1.3043k 

Loaded Yout=16.9811V 

Ri +R2 
Effect of connecting a load across RZ 

_ReijLoed _ 
Ril + (R2! Load) 

Fi = Theory. 


Designed to complement the EPE Teach-In 
No. 7 publication, which contains a com- 
plete electronics course aimed at GCSE and ~ 
A Level students, this software can also 
be used as a stand alone learning package 
for everyone interested in electronics. From 
simple d.c. current flow and Ohm’s Law it 
covers the whole GCSE syllabus including 
a.c., semiconductors, op.amps, digital elec- 
tronics, radio and fibre optic communica- 
tions, digital numbering systems and goes on 
to look at microprocessor c.p.u.s, 6502 ad- 
dressing modes and instruction sets. It even 
produces a program listing, which can be 
saved or retrieved from hard disk, when any 
of the instructions from the listed instruction 
set are input, thus allowing the user to 
monitor the registers for each of the address- 
ing modes. 

The original version is now widely used in 
schools and colleges throughout the UK. 

An interactive, user friendly medium which 
assists learning in an enjoyable and interesting 

way. Only £39.95 


upgrades callus on 01376 514008 

GCSE MATHS now version 2.0 

A series of programs covering all the major topics 
required by the school syllabus. Designed to be 
user friendly enabling you to study or revise in 
what we believe is an interesting and enjoyable 
way. There are nearly one hundred and fifty menu 
driven screens with interactive graphics, enabling a 
“learning through doing’? approach to encourage 
experimentation. Now being used in many schools 

throughout the UK. 
Only £49.95 

These programs require a PC (or fully compatible system) running DOS or Windows with an 80286 or better processor 
and VGA (ideally colour) graphics. In addition you must have 4Mb of hard disk space, a high density (1-44Mb) floppy 
drive and at least 640K of RAM. We also recommend the use of a mouse. Site licences are available — please enquire. 

Available from 

EPT Educational Software, Pump House, Lockram Lane, Witham, Essex. UK. CM8 2B]. Tel: 01376 514008. 
Add £2 per order for UK post and packing. Make cheques payable to EPT Educational Software. 

Visa and Mastercard orders accepted — please give card number, expiry date and cardholders address if different from the delivery address. 
OVERSEAS ORDERS: Add £2.50 postage for countries in the E.E.C. Overseas readers, outside the E.E.C. countries add £3.50 for airmail postage. 

Everyday with Practical Electronics, September 1995 


Solar Cell, will give 100mA of free electricity, pack of 1, 
Order Ref: 631. 

Plastic Fan Blades, 3in. diameter, push-on spindle type, 
keep your motor cool, etc. Pack of 2, Order Ref: 638. 

PC Games in cases for remaking, pack of 6, Order Ref: 645. 
Piezo Noise Makers, standard size, pack of 2, Order Ref: 647. 
Ditto but mini, only 23mm across, Order Ref: 648. 

Covers, suit Piezo sounders etc, need 22mm hole, pack of 
6, Order Ref: 651. 

10A Micro Switches with screw terminals, mains voltage, 
pack of 2, Order Ref: 662. 

PCB Mounted Relay, 5V/6V coil, two changeover 5A con- 
tacts, pack of 1, Order Ref: 665. 

Controlled 4-Rocker Switch, 3 switches cannot be on 
unless the first master is on, suit 3kW blow heater, etc., 
pack of 1, Order Ref: 666. 

0-33 nF 1000V Caps, ideal to put in series with 115V 2-4W 
motors, pack of 4, Order Ref: 672. 

Copper Clad Panel, size 12in. x Qin. doproximately. make 
your own PCB or its strong enough to act as a chassis, 
pack of 1, Order Ref: 683. 

100M Coil of Connecting Wire, Order Ref: 685. 

12V Motor, extra efficient, will work with solar cells, pack of 

1, Order Ref: 687. 

Sub Min. Push-Switches, pack of 2, Order Ref: 688. 
Ceramic Beads, ideal insulation where heat or flame, pack 
of 100, Order Ref: 690. 

6in. Lengths of ‘Ain. Diameter Paxolin Tubing, make useful 
test prods, etc, pack of 3, Order Ref: 691. 

PCB Panel, part of micro TV, has EHT generator circuit, 
pack of 1, Order Ref: 692. 

1920 Vintage Resistors, you have probably never seen any 
quite like them, pack of 2, Order Ref: 695. 

440V A.C. Cap, 4 aluminium cased, pack of 1, Order 
Ref: 702. 

Power Supply Unit, output 9V 100mA D.C., pack of 1, Order 
Ref: 733. 

Foldover Type Telescopic Aerial, pack of 1, Order Ref: 747. 
AM/FM Tuning Capacitor, air spaced with “%in. spindle, 
pack of 1, Order Ref: 743. 

Multi-Voltage Transformer, gives 10V, 9V, 8V, 7V, 1%V or 
1V, pack of 1, Order Ref: 744. 

D.P.D.T. Rocker Switches for motor reversing, etc., pack of 
2, Order Ref: 745. 

Black Noise Transparent Speaker Mesh 12in. x Qin., pack 
of 4, Order Ref: 746. 

Lightest Touch Changeover Micro Switches, mains volt- 
age, pack of 2, Order Ref: 748. 

Pair Porcelain Insulators, pack of 4, suitable cabin aerials, 
etc., Order Ref: 749. 

Cased PSU, A.C. output, 15V 150mA and 9:8V 60mA, pack 
of 1, Order Ref: 751. 

3 Changeover Contact Relay with coil, suitable for 12V A.C. 
or 6V D.C., pack of 1, Order Ref: 753. 

Lever-Operated Micro Switches, ex-equipment, batch 
tested, any faulty would be replaced, pack of 10, Order 
Ref: 755. 

Project Box, size approximately 100mm x 75mm x 24mm, 
its lid is a metal heatsink, pack of 1, Order Ref: 759. 

Ex-BT Instrument in plastic case with carrying handle, has 
many useful parts, pack of 1, Order Ref: 760. 

Pick-Up Arm with diamond stylus, new and unused, pack of 
1, Order Ref: 764. 

Rubber Feet, fit corners of square chassis, pack of 20, 
Order Ref: 769. 

24V Bakelite Encased A.C. or D.C. Buzzer, pack of 1, Order 
Ref: 774. . 

Component Mounting Tag Strip, 14 tags each side, pack of 

~ 1, Order Ref: 779. 

Ya Meg Pots each fitted double-pole switch, pack of 2, 
Order Ref: 780. 

Thermostat for a refrigerator, pack of 1, Order Ref: 783. 
C/O Micro Switches operated by a wire control to spindle 
through side, pack of 2, Order Ref: 786. 

Multi-Tag Mains Panel, has 12 tags to take “%in. push-on 
connectors, pack of 1, Order Ref: 792. 

Reed Switch, flat instead of round so many more can be 
stacked in a small area, pack of 1, Order Ref: 796. 

Very Thin Drills (0-3mm), pack of 12, Order Ref: 797. 

Rocker Switches, spring-loaded with changeover 10A 
230V contacts, pack of 2, Order Ref: 800. 

Micro Switch, 10A changeover, operated by extra long 
(2in.) lever, pack of 1, Order Ref: 801 

Mains Circuit Breaker, 7A, pushbutton operated, not self- 
resetting, pack of 1, Order Ref: 802. 

In-Line Switch intended for electric blanket to give vari- 
able heat but obviously has other uses, pack of 1, Order 
Ref: 805. 

Plug for Car Lighter Sockets, each having internal fuse, 
pack of 2, Order Ref: 809. 

Main Transformer 12V-0V-12V, 6W, pack of 1, 
Ref: 811. 

10M of Mains Voltage Flex with screen and outer PVC in- 
sulation, Order Ref: 815. 

Computer Grade Capacitor, 10,000uf 15V, pack of 1, Order 
Ref: 816. 

13A Adaptor to take three plugs, fused, pack of 1, Order 
Ref: 819. 


-13A Adaptors to each take two plugs, pack of 2, Order 

Ref: 820. 

Mains Isolation Transformer 19W, pack of 1, 
Ref: 821. 

AM/FM Tuning Cap, airspaced and with “in. spindle, pack 
of 1, Order Ref: 827. 

0-01,.F 250V Mains Working Suppressor Caps, pack of 5, 
Order Ref: 836. 

Ring Main Junction Boxes, 13A, 230V, pack of 3, Order 
Ref: BD1. 

Flush Plate Light Switches, 5A white, pack of 2, Order 
Ref: BD5. . 

Octal Valve Bases, Paxolin, pack of 4, Order Ref: 12. 
Germanium Transistors, OC45 etc, pack of 50 assorted, 
Order Ref: 15. 

Light Sensitive Transistors, ref OCP70, pack of 2, Order 
Ref: 14. 

a. i ere Electrolytic, 5000uF, 10V, just 1, Order 
Ref: 1 

pon Crossover, for tweeter, 
woofer, just 1, Order Ref: 23. 

Key Switch, panel mounting with key, just 1, Order Ref: 31. 


mid-range and 

Multi Tester, 19 range, 20,000 opv, ex- 
British Telecom, reconditioned, complete 
with prods, £8.50, Order Ref: 8.5P3. Case 
also holds prods and small tools, £2 extra. 

12V 10A D.C. PSU, £9.50, Order: Ref: 9.5P1. 
With details of small conversion you have to 
make, Order Ref: 9.5P1 with details. 

Insulation Tester and Multimeter. You read 
insulation directly in megohms and the multi- 
meter section has A.C. volts, D.C. volts, 3 
ranges milliamps, Ohms and a 5A range. 
Only £7.50, Order Ref: 7.5P4. Case also holds 
test prods and small tools, £2 extra. 

Repairable Test Meter. We have some of 
these insulation testers which will not work 
on all ranges. They should be repairable, 
movement is OK. We will supply circuit dia- 
gram. Price £3, Order Ref: 3P176. 

Medicine Cupboard Alarm. Sounds off 
when door is opened, neatly cased, uses 9V 
battery, £3, Order Ref: 3P155. 

Water Level Alarm. Sounds off directly 
water reaches its adjustable sensor. Neatly 
cased, uses 9V battery, £3, Order Ref: 
3P156. : 

250W Light Dimmer. Fits in place of normal 
wall switch, £2, Order Ref: 2P380. 

Philips High Resolution 9in. Monitor. In 
metal frame, brand new, £15, Order Ref: 
15P 1. 

Order 10 of any one item or bargin pack 

and you will receive an extra one free. 

Quartz Clock Mechanism. With two sets of 
hands, one modern, one period, £3, Order 

Flashing Beacon. 12V Zenon tube cased 
and with amber coloured dome. Ready to 
fix to car roof, etc, £7.50, Order Ref: 7.5P13. 

2 Socket Mains Adaptor. Virtually unbreak- 
able. £2, Order Ref: 2P271. 

3-Core Extension Lead. Tough pvc covered, 
15M for £2, Order Ref: 2P 189. 

2-Core Extension Lead. For lights and many 
garden tools, 20M for £20, Order Ref: 2P20. 

Stereo Headphones. With moving coil in- 
serts, So superior sound, £1, Order Ref: 898. 

15W 8in. 8 Ohm Speaker and 3in. Tweeter. 
Made for Amstrad, £4, Order Ref: 4P57. 

12V Solenoid. 1’2in. long, extra powerful, 
£1. Order Ref: 232. 

Mains Fan PAPST, 15mm square, £8, Order 
Ref: 8P8. 

Horn Speaker. Horn diameter 5‘2in., 8 ohm, 

‘8W, £3, Order Ref: 3P82. 

25W Speaker with Tweeter. For 8 ohm or 4 
ohm, £7, Order Ref: 7P12. 

20W Goodmans Speaker. Sin. 4 ohm, £3, 
Order Ref: 3P 145. 

20W Goodmans 4 Ohm Tweeter. 
Order Ref: 1.5P9. 

Double Fan. Ideal for greenhouse or cooker 
hood, £10, Order Ref: 10P84. 

Helium Neon Laser. Philips full spec., £30, 
Order Ref: 30P1. 


“LCD Multi Tester — Model M3800. 32 ranges 

including 20A A.C. and D.C., £25, Order 
Ref: 25P14. 

63mm Axial Fan. 12V brushless, 9-bladed 
so really good air mover, with drive circuit 
details, £1, Order Ref: 919. 

2A Mains Filter/Peak Suppressor. 
mounting, £2, Order Ref: 2P315. 


Everyday with Practical Electronics, September 1995 


In Handle Mains On/Off Switches. Sometimes known as 
pistol grip switches, pack of 2, Order Ref: 839. 

Double-Pole Changeover Toggle Switches, ideal reversing 
easy motors, etc, pack of 2, Order Ref: 841. 

3M 2-Core Curly Lead, 5A, Order Ref: 846. 

1M 3-Core Curly Lead, 13A, Order Ref: 847. 

A.C. Shaded-Pole Mains Motor with base fixing plate, pack of 

1, Order Ref: 848. 

4in. Plastic Dial, fits flatted in. spindle, transparent so dial 
can be underneath, pack of 2, Order Ref: 851. 

2500 \F 12V Capacitors, pack of 5, Order Ref: 853. 

Delay Switch on B7G base, pack of 1, Order Ref: 854. 

3 Changeover Relay, 6V A.C.; 3V D.C., pack of 1, Order 
Ref: 859. 

3 Contact Micro Switches, operated with slightest touch, 
pack of 2, Order Ref: 861. 

Normally on V3 Micro Switch, pack of 4, Order Ref: 862. . 
Highvac Numicator Tube, highvac ref XN3, pack of 1, Order 
Ref: 865. 

Ditto but reference XN11, pack of 1, Order Ref: 866. 

Sub Min Normally-Off Micro Switch, pack of 1, Order Ref: 867. 
Sub Min Changeover Micro Switch, pack of 3, Order Ref: 868. 
Ex-GPO Telephone Dial, rotary type, pack. of 1, Order 
Ref: 904. 

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. 
Edge Type Push Switches, BCD system, pack of 2, Order 
Ref: 915. 

10M 4-Core Flex, suitable for telephone extension, Order 
Ref: 918. 

Old Type Kettle Element, 2-pin plug, pack of 1, Order Ret: 

6V 24W Headlamp Bulb, normal BC plug in cap, pack of 1, 

Order Ref: 928. 

40 Lamp Unit to make a figure or letter display, pack of 1, 

Order Ref: 930. 

10K Horizontal Preset Resistors, pack of 10, Order Ref: 931. 

1M 64-Way Ribbon Cable, Order Ref: 932. 

15V 320mA PSU, pack of 1, Order Ref: 934. 

15V + 15V 1-5VA Potted PCB Mains Ne teh SRY pack of 1, 

Order Ref: 937. 

16 Ohm 3in. Speakers, pack of 2, Order Ref: 962. 

Mains Relay with 15A changeover contacts, pack of 1, Order 

Ref: 965. 

In-Line Fuse Holders take 20mm fuse, just cut the flex and 

insert, pack of 4, Order Ref: 969. 

Oblong Panel Mounting Neons, pack of 4, Order Ref: 970. 

Copper Clad Panels, size 7in. x 4in., pack of 2, Order Ref: 973. 

Standard Sized Audio Plug adapted to take two 3mm plugs, 

pack of 1, Order Ref: 974. 

3-5mm Jack Plugs, pack of 10, Order Ref: 975. 

Drill Control Case, ready punched and with control logos, 

pack of 1, Order Ref: 979. 

Standard Size Old Type Wonder Plugs, pack of 10, Order 

Ref: 986. 

8 uF 350V Electrolytic, pack of 2, Order Ref: 987. 

15V 320mA PSU, pack of 1, Order Ref: 989. 

Screw-in Neon Bulbs, pack of 4, Order Ref: 990. 

Very Small Slide Switch, pack of 4, Order Ref: 992. 

50uF + 50uF 350V Working Electrolytics, pack of 2, Order 

Ref: 994. 

8700,\F 7V Working Electrolytic, pack of 1, Order Ref:996. 

1 Meg Preset Pots, pack of 4, Order Ref: 998. 

Spring-Loaded 20A Toggle Switch, pack of 2, Order Ref: 

White Project Box, 78mm x 115mm x 35mm, pack of 1, Order 
Ref: 1006. 

12in. Lengths Panolin Tubing, “in. diameter, pack of 2, Order 
Ref: 1008. 

Slidelock 15A Fuses, panel mounting, pack of 3, Order 
Ref: 1011. 

6V Solenoids, good length pull, pack of 2, Order Ref: 1012. 

Relay with 3 Sets of Changeover 8A Contacts, pack of 1,- 

24V A.C. or 12V D.C., Order Ref: 1016. 7 

White Toggle Switch, push-in spring retain type, pack of 4, 
Order Ref: 1019. 

2M Mains Leads, 2-core, black outer, pack of 4, Order 
Ref: 1020. 

2M Mains Leads, 3-core, black outer, pack of 3, Order 
Ref: 1021. 

Ferrite Slabs with coils, pack of 2, Order Ref: 1027. 

12V D.C. Polarised Relay, 2 changeover contacts, pack of 1, 
Order Ref: 1032. 

12 x 12 Paxolin Panel, medium thickness, pack of 1, Order 
Ref: 1033. 

Tunning Caps, solid DIA, for LW and MW, pack of 2, Order 
Ref: 37. 

Trimmer Caps, screw down type, 10 assorted, Order Ref: 38. 

1.F .Transformers, 465kHz, pack of 4, Order Ref: 40. 

IC Sockets for PCB, pack of 10, Order Ref: 54. 

6‘2in. 4 Ohm Speaker, pack of 1, Order Ref: 137. 

100K Stereo Pots, pack of 4, Order Ref: 143. 

Fuseholders, chassis mounting for 20mm fuses, pack of 5, 
Order Ref: 144. 

Sockets Covers, child protectors for twin 13A sockets, pack of 
4, Order Ref: 149. 

Ditto but for single 13A sockets, pack of 4, Order Ref: 150. 

Pot Cores, ferrite, 54mm x 18mm, pack of 2 pairs, Order 
Ref: 156. 

The above prices include VAT but please add £3 towards 
our packing and carriage if your order is under £25. Send 
cheque or phone and quote credit card number. 


Pilgrim Works (Dept. E.E.) 
Stairbridge Lane, Bolney, 

Sussex RH17 5PA 

Telephone: 01444 881965 
@UETom ee pa oliimelilela-mile 39) 



Et E-Cr i RO NEC. S 


t the latest MAGENTA DESIGN — highly 
I stable & sensitive — with uC control 

t of all timing functions and advanced ! KIT 856........ Spe a ci iS ages oat e ASS £28.00 ge cnee Gok eee 
I pulse separation techniques. | BAT DETECTOR ) I. PCB, all components & tube + 

I @ New circuit design 1994 
I @ High stability 
I drift cancelling 

I @ Easy to build 
i &use 

1 @ No ground 
effect, works 
in seawater 

@ Detects gold, 
silver, ferrous & 

y @ Efficient quartz controlled 
microcontroller pulse generation. 

g @ Full kit with headphones & all 

RUT B46 Bosrck: dices ss £63.95 
L 4 POWER SUPPLY 0-25V 2:5A 

Based on our MkI design and 

A versatile thermostat using a thermistor probe and Preserving all the features, 

having an l.c.d. display. MIN/MAX memories, -10 but now with switching 
to 110 degrees celsius, or can be set to read in pre-regulator for much 


Fahrenheit. Individually settable upper and lower 

switching temperatures allow close control, or alter- higher 
natively allow a wide ‘dead band’ to be set which meters 

can result in substantial energy savings when used Amps. Fully variable down to 

with domestic hot water systems. Ideal for green- 

house ventilation or heating control, aquaria, home Z€FO. Toroidal mains trans- 
brewing, etc. Mains powered, 10A SPCO relay out- former. Kit includes punched 

and printed case and all 

BA OF tsa ninsiccnean £29.95 _ parts. As featured in April 
orn 1994 EPE. An essential piece 

of equipment. 

KIT 845..,;..3306.. £64.95 
pact hand-held case. MOSFET output drives a ULTRASONIC PEsT SCAR ER 

put. Punched and printed case. 


A powerful 23kHz ultrasound generator in a com- 

special sealed transducer with intense pulses via 

a special tuned transformer. Sweeping frequency Keep pets/pests away from newly 
sown areas, fruit, vegetable and 
flower beds, children’s play areas, 
KUT 842. eeesttteerenre £22,596 patios etc. This project produces 
intense pulses of ultrasound 
which deter visiting animals. 

A really professional looking project. Kit is sup- @ KIT INCLUDES ALL 

curacy of 1%. Large clear 5 digit display and high @ EFFICIENT 100V 

output is designed to give maximum output with- 
out any special setting up. 


-plied with a punched and printed front panel, case, 
p.c.b. and all components. Quartz controlled ac- 

areed Sperenee. pag for ak — as =~ HF, ee TRANSDUCER OUTPUT @ UPTO 4 METRES 
and pF ranges give clear unambiguous read out o 
Ret taoatneer 4 a Capacitors from a few pF up TO HUMANS @ LOW CURRENT DRAIN 

SS ee eee ees CSS 9G: KUT ROE 2 ei os oie ei ccncskvy chespiatanadegsomctics £14.81 



indicate Volts and 

135 Hunter Street 
Staffs. DE14 2ST 


I A novel wind speed indicator with LED read-out. Kit comes I An innovative and exciting 
P.. TREASURE HUNTER complete with sensor cups, and weatherproof sensing head. Jj Project. Wave the wand through 
Mainspower unit £5.99 extra. 

up to 200 Megohms. 


efficiency. Panel 

A very popular project which picks up vibrationsby A\AOQTOR INTERFACE 

means of a contact probe and passes them on to a 
pair of headphones or an amplifier. Sounds from 
engines, watches, and speech travelling through 
walls can be amplified and heard clearly. Useful 
for mechanics, instrument engineers, and nosey 

HAMEG HM303 30 MHz 

Western Europe's best selling oscilloscope - now improved. 
It now features 30MHz bandwidth, triggering to 100MHz 
and 2mV/div sensitivity. 

Sharp bright display on 8 x 10cm screen with internal 
graticule. Special component tester built in’ - allows 
capacitors, resistors, transistors, diode, and many other 
components to be checked at a glance. 

As with its predecessor, the QUALITY OF THIS INSTRU- 
MENT IS OUTSTANDING. It is supported with a two year 
warranty covering parts and labour. If you are buying an 
oscilloscope, this is the one. It costs a fraction more than 
some others, but it is far far superior. Supplied with test 
probes, mains lead, and manual. 

£392. 00 t: £68. 60 VAT Includes FREE 

Next-day delivery 


An exciting project supplied with two 200 step motors, interface board, and easy 
to use P.C. software. 
Allows independent control of both motors - speed, direction, number of steps, @ 190mm SEARCH COIL 
and half/full step mode. Connects to: computer parallel port. Requires 12V 1 
D.C. supply and printer lead. 

RIT JRO £19.98 KIT 846 (with 2 motors) ....... £67.00 (Printer lead £5.00) 


The classic book by Tom Duncan used throughout 
schools. Very well illustrated, ideal first book for age 10 
on. No soldering. Uses an S.DEC breadboard. 

Book &Components £28.95, Book only £7.25 


An Usborne book, wonderfully illustrated in colour. Com- 
ponent pack allows 6 projects to. be built and kept. Sol- 
dering is necessary. Age 12 on, or younger with adult 
help. Book & Components £20.88, Book only £2.95 

A more advanced book to follow the others. No soldering. 
Circuits cover a wide range of interests. 

Book & Components £30.69, Book only. £2.95 

Superb new design. Regulated 
output, efficient circuit. 

All Prices 
include V.A.T. 
Add £3.00 per 


Tel 01283 565435 Fax 546932 EE159 order p &p 

—_—. % 


the air and your message appears. 
Programmable to hold any message 

instructions for message loading. 

An excellent circuit which reduces ultrasound frequencies between 20 and100kHz I KIT 8 49 £1 6. 99 
. the normal (human) audible range. Operating rather like a radio receiver the circuit go *\% * SO Twi sssseccsccsssesscssseses 
allows the listner to tune-in to the ultrasonic frequencies of interest. Listening to Bats 
is fascinating, and it is possible to identify various different types using this project. 1 2V E P R O M E RAS E R 
Other uses have been found in industry for vibration monitoring etc. 

KET 844. cic ct ees, £21.44 _ inless than 20 minutes. Operates from a 12V supply 

A safe low cost eraser for up to 4 EPROMS ata time 

(400mA). Used extensively for mobile work - up- 

1OOOV & 500V INSULATION  fencPcitations where mains supplies are not al 

T E ST E R lowed. Safety interlock prevents contact with UV. 

EELS OR ASS tees Ge £28.51 

Dual- MOSFET 25V 2.5A 
scale meter, compact case. Reads POWER SUPPLY 

High performance design has made this one of our 

Kit includes wound coil, cut-out classic kits. Two panel meters indicate Volts and 
case, meter scale. PCB & ALL Amps. Variable from 0-25 Volts and current limit 

control from 0-2:5A. Rugged power MOSFET out- 
put stage. Toroidal mains transformer. 

KET Be Boj. cies csesreee ROPE RN 4 US |: Res BP epee £56.82 


A reliable and neat electronic tester which checks 
insulation resistance of wiring and appliances etc., 
at 500 Volts. The unit is battery powered, simple 
and safe to operate. Leakage resistance of up to 
100 Megohms Can be read easily. A very popular 
college project. 

KIT 444. eee £22.37 

Digital lock with 12 key keypad. Entering a 
four digit code operates a 250V 16A relay. 
A special anti-tamper circuit permits the relay 
board to be mounted remotely. Ideal car immobi- 
liser, operates from 12V. Drilled case, brushed 
aluminium keypad. 

2S. | 8 ae peer oe See £19.86 



Magenta’s highly 
developed & 
acclaimed design. 
Quartz crystal 
controlled circuit 
MOSFET coil drive. 
D.C. coupled 


Full kit includes 
case & 



search coil. 


PUP t sie ccsecpneresasenesogs £45.95 

Ideal for robots, buggies, 
and many other mechanical 
projects. Min. plastic gearbox 
with 1.5-4.5V DC motor. 6 
ratios can be set up. 

Small type MGS....£4.77 | 


For computer control via standard 4 pole unipolar 

MD38 - miniature 48 steps per rev 
MD35'4 - standard 48 steps per rev 

Everyday with Practical Electronics, September 1995 

i An 1th wb Jb SD <2 A <2 <a 4 4» . 4a fh fb Ab, 4b 4h 4 4h 4b 4: ee a wAS li 


PICs are being used 
more and more because 

they allow complicated jobs 
to be done with a single chip. 
All the work is done by programming. 
One PIC replaces a board full of ICs. 
Saving time, space, power, and MONEY. 


STEP 1 — Buy the PIC-DATS 

Development & Training System - 
STEP 2- Follow May & June ‘95 EPE 
| Series — showing how to program 

for practical applications 

STEP 3- Start writing and testing 
yourown programs > 

PIC a traininc syste 


Sa oo 



A real-world application for a PIC microchip. This project can be made to do just 
what you chose by writing your own software. It can be programmed to work as 
a 4-Channel Light Chaser or a simple controller for domestic lighting. Zero volt 

crossing signal is provided and there is a 4x3 matrix keypad. (Less case). 


+ £3.00 p&p 
— (12V at 200mA) 
\ £8.99 

9-WAY £6.00 
25-WAY £7.00 

Motors and Controllers 

A range of kits and components for motion control and computer interfacing. Ideal for Design 
and Technical projects, and a whole range of up to the minute ‘Home Automation’ applications. 

Comstep PC Computer 
Interface and Driver board 

Drives two motors from PC With 2-200 
Step Motors 

parallel port. Supplied with 
comprehensive software. 
Needs 12Volt 1A supply. 

Kit 846 

Power Booster for Comstep 

Adds to Comstep and allows With MD24 

motors up to 4 Amps to be 

driven. Two boosters drive 

two motors from a single Comstep. Uses standard 
Comstep software. 

Kit 850 £39.95 

PC Communications Protocol 
for Comstep 

An interface board adding four switched inputs to 
the Comstep + All the code to ~svelop your 
applications. Files in C, BASIC, FORTRAN & 
ASSEMBLER + demo. 

Kit 851 

PC Joystick Interface for 

Software for operating Comstep from a standard 
PC Joystick. Allows two Axis control, with 
acceleration, speed, and X-Y position control. 
Stores co-ordinates. 

Kit 852 

Stand-Alone Stepping motor 

A Stand alone interface giving full control in 
all modes. Pushbutton opé:ztion with adjustable 
acceleration and speed. Ideai for demo and setting 
up. Then connect to computer port for full control. 

Kit 843... 

Versatile Stepping motor 


A Magenta design, gives Half and Full-Wave drive. 
Up to 1Amp and 24Volts. CMOS inputs — Drive 
from logic or computer port. Needs power supply. 

Kit 816 

Mini-Lab & Micro Lab 
Electronics Teach-In 7 

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. 

SMALL — MGS - £4.77 

Stepping Motors 

MD38...Mini 48 step...£8.65 | / 
MD35...Std 48 step...£12.98 | 
MD200...200 step...£16.80 
MD24...Large 200 step...£22.95 

More Information: 

All listed items come with data and instructions. 
For more information, including reprints of the 
appropriate magazine articles, send an SAE + 

£1.00 per kit — or phone and use 

Mastercard/Visa etc. 

As featured in EPE and now published as Teach-In 7. All parts 
are supplied by Magenta. Teach-I/n 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 Built Micro Lab —- £189.95 

Tel: 01283 565435 Fax: 01283 546932 All prices include VAT. Add £3.00 p&p. 

Everyday with Practical Electronics, September 1995 671 

AD847JN £6.50 SSM2143P £3.78 1IN5 / 
AD9696KN £7.73 TBAI20S £0.90 BAI57 £010 Sie ak SE tence ee 
ADEL2020AN £5.06 TBA800 £0.70 BAI58 £0.10  ACI27 So Boos hie EB 
ADM222AH_ £3.55 TBASIOS £0.68 BAI59 £0.10 ACI28 os Se es eee 
ADM232AAN £3.55 TBA820M £0.39 BY126 £0.13 ACI87 rive BCaae 25 rats BDXSae t's 
10 £1.49 BY127 £0.11 ACI188 I : 
M690AN £5.13 TDAII70S £1.83 BY133 £0.10 yee ee A ee et 
ADM690AN £5.13 Al £1.83 BYL £0.1 ACY17 £3.84 BC357 £0.25 BFI82 £0.31 
ADMOSIAN. £6.48 A2 fl. 28  AD149 £1.67 BC393 £0.73 BFI85 £0.31 
ADM699AN £3.58 TDA2030 fig AOL £040 ADIG? ek ote ie. Eris cee 
AMPO4EP £10,94 TDA20S0V £3.98 OA200 £0.10 BCIO7 £016 BCdG! £040 BFIOS" £019 
F04G : £3.11 OA202 £0.29 BCIO7B : ? 
CA741ICE £0.28 TLO6ICP £0.35 Zeners 2.7 to 33V init wan tee eta tee 
CAT4ICE £0.28. TLOSICP ; ts 2.7 to C108 £0.14 BC478 £0.32 BF244B £0.35 
CATATC £0.39 Cc £0.60 % wv £0.08 BC1O8A £0.14 BC479 £0.32 BF244C £0.35 
CA3059 £1.16 71 £0.48 ectifiers BCIOS Ol? BCsIe: Enos brass 33 
CA3080E £0.72 TLO72CP £0.68 Tb TR SOV £0.19 BCIO9C e017 BCs? «2030. «BESS? Ee 
CA3130E £0.98 74 £0.58 WO02 1.5A 200V £0.20 BCII4 £0.41 BCS) 03 Brass £038 
. £0. ¢ 2 , 
CA3189E £1.22 TLO82CP oy34 Woe ea 6p0V £0.22/ BCH TOs BCS]. See. ee ame 
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: 54 BR34 ; . 
4000 Series 74HC Series 74,542 £9.25  DG412DI £4.19 TLC272 0.88 A 6UOV £0'30 Bead f028 Herts £008  BFXES £034 
4000 £0.17 74HCO0. £0.16 74L847 £0.72  EL2020CN £4.99 TMPOIFP £5.60 BR62 6A 200V £0.70 BCI41 £027 BCS49C §010 BEYSO £039 
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4010 £023 acl : oe 74.85 £035 ICM7556 £0.98 ULN2803 £0.60 TIC106D £0.40 BC160 £0.28 BC560A nies BU20s that 
: C20 £0.28 £0.20 : : 4 : 
4012 £0.16 74H 27 £0.16 74L890 £0.44 ae Md ZN414Z £1.16 TIC126b £0.77 BCI7OB sole Bees) £001 SESTAN £140 
: 0 £02 0.35 , : O° : : , 
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weds Shas $01 : ; BCI78 £0.18 BCY7 
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pe E03 TAHCeS £0.24 748123 £031 LMBIINS £0.28 27128-20 £4.08 ‘Transistors 182 £0.11 Biss «| Ook eae 
pod 5408125 £030 318 1.28  27C128-20 £4.08 2NI613 £0.31 BCI82A £0.1 BDIsy goss ReaD EL SO 
ps £0 AC 107 £040 748126 £0.25  LM3I9N-14 £0.96 27256-2 £4.85, 2NI711 £0.26  BCI82B £0.08 BDIag £033 ie ft tp 
at23 aig HHHCI2 £033 748126 $02 319 0.96 27256 85 IN1893 ne C1828 £0.08 BDI38 £0.22 MJ2501 £1.60 
anes £021 TAHCI25 £0.24 7408133 £0.36. LM335Z £1.52 27C512 £3.95 2N2218A £0.28 BCIg21B £0.08 BDIad O38: TOI. ER 
ates 1s Tac 24 TACSI33 £0, LM335Z £1.52 anasic onthe 08 BDI40 £0.25 .MJLIOIS £2.11 
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9 anc 139 £0.31 Cavatay rar LM380N-14 £1.12 41256-10 £2.80 2N2905A — £0.25 Be SAL oo 8 D201 040 MPSAbe Enis 
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4042 £0.22 74HC162 £0.45 Siete? Soot EM733 £0.64 ADS74AJN £18.48 2N3 £0.50 BCI12L £0.08 or Oh Te £0.32 
£0.28 TAHC 16? £0.27 Jarsieo £0.48  LM/48CN-8 £0.31 7675 £20.88 2N3702 £0.09  BC212LB _—£0.08 Bpaaoc Eh IPaiA Eas 
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4047 £0.48 74HCI73 £032 74LS162 £0.44 ieee 2%) AD TSEN fae aNST0S ritts BCziA8 £0.08 BD244A £0.33 Tipsy” 20.48 
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4048 £0 28 duct? £07 7418163 £0.32 Liesl Oe Oe eR eos ONS? te BC213LC £0.08 BD244C £0.53 + TIP48 £0.62 
4050. £0.20 14HCI22 £0.45 74LS165 £048 [MR090N £1.76 ADI2EKN £2033 2N3772 gai: pea EDOs BDI £118 TpLa1 Bh 5 
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4053 E40 14NCAL E037 Tarstts £04 LM3915 £2.70  TLCS49IP £3.51 2N3820 £0.66  BC238C £0.09 tes oy eee | ee 
4054 £0.59 74HC243 £0.48 T4LSI75. £0. (M13600 —«£1'82.-ZN425E. «£5.94: 2N3904 ESE 0 IM g's A "a a a 8 = 
4055 £0.34 74HC244 £0.40 THLSI90 £060 Tuicg6ocN 2:16 ZN426E £3.03. 2N3905 £0.10 BC250A «£0.15 Spas) ay pias Ene 
pi £048 TAHCZES £0.40 7408192 £0.60 LMC6032IN £1.55 ZN427E £8.78  2N3 £0.10 BC251 £0.13 BDs3d hay Play Ena 
ey be EN 2S sar giy 034 LMC6042IN £1.82 ZN428E £5.94 2N4036 £0.34 BC252 £0.13 Hct mee) ae oh 
4066 £0.24 74HC253 £0.25 © TALSI83 £534 LP3IIN £0.74 ZN439E8 £7.13 2N5245 £0.80  BC2%6IB £0.24 a AM 9 RE Rd 
aoe! £196 T4HC3s? £23 T4LSI95 £024 TPAUN £14 Ne EB aNstoe fos? — BC26IB £0.24 BD536 ~=—- £0.65 ~—s TIP3055 £0.63 
ies D6 T4HCI39 BD) T4LSI96 024 TBIN £0.74 GUMS ety fos7  BC2628 £0.24 BD581 £0.62 VNIOKM £0.48 
ps A Se ER iy MAX202CPE £2.97 Regulators 2N5322 £0.57 — BC307 £0.10 BDe46 £0.52 ZTX300 £0. 
ped £017 TAH C322 £0.64 7408240 £0.32  MAX208CNG £6.99 7805 £0. N5 £0.11  BC308 £0.10 Bbede soa oresop fale 
piel £0.22 TAHC356 £045 J4L8241 £032  MAX220CPE £5.06 7808 £0.50 2N5551 £0.11  BC319C £0.13 Epes $033 eh 
pode SOT AHS £054 7408242 £0.32 | MAX222CPE £5.06 7812 £0.38 2N6107 £0.60 BC327 £0.10 BD707 foa3 SAMEDAY 
pe its £0.17 TANC367 £0.23 7408243 £0.30  MAX232CPE £2.58 7815 £0.38 2N6491 £1.58 §BC327-16 £0.10 BD708 £104 
ise eee ates cam Meee «Be MAX238CNG £6.88 7905 £0.31 2SB548 £0.30  BC328 £0.10 Re i oreazeinrameaen 
07) 017 T4HC3rA 0.40 TALS245 £0.60 MAX242CPE £551 Tg £038 Electrolytic Radi seg accor 
ia i eee oa e047. aD. ; : ectrolytic al Capacitors El 
pod. pes ae ee er 7415251 ahi MAX635ACP £4.99 7924 £0.38 eS l6v 25v 3v 100v 450v “mie ¢ napa <n wer 
4082 £021 74HC423 £0.37 7418257 £0.24 Melqgo £046 T8L08 fo33 10) = «£005 £006 £0 , os = Bene 
4085 £0.28 74HC553 £0.42 74LS258 £024 MEIa89 se me et = Beare ot = BRS 
4085 £0.28 74HC553 £042 TALSI58 £024 Mc3302 £0.56 78L12 £0.24 2.2 —- -- £0.05 £0.06 £031 22 -- -- £0.10 £0.10 £0.22 
4086 £0.26 74H1C563 £0.48 TéL-$3¢6 £0.14 MC3340p £1.60 78L15 £0.24 47 --  -- £0.05 £0.08 £039 47 -- -- £0.10 £0.10 --- 
4089 £055 74HC564 £0.48 T4877} £0.32 MCA5S8P £0.36 781.24 £0.39 10 £0.05 £0.05 £0.06 £0.08 £0.44 10 -- -—- £0.12 £0.12 £0.48 
| Ho Bis O45 Tee oe Mv: fo me 08 2 Oe Oe oe ms Be ae £0.13 £0.17 £1.06 
4094 £031 74HC574 £0.45 748365 £031 Mv6oIDP £2.97 7908 £0.28 47 £0.06 £0.06 £0.11 -- £0.98 47 £0.10 £0.11 £0.16 £0.20 --- 
4095 £0.56 74HC640 rite 7aLS367 © £0.21 531 £147 79L12 £0.28 100 £0.06 £0.09 £0.11 --- --- 100° = £0.10 £0.13-£021 — 
4099 £0.38 T4HC4017 sh.64 748374 £0.32 468 £134 ADM666AN £344 1000 £0.22 £029 -- -. 1000 £0.33 £0.40 £1.05 -- --- 
4502 £0.38 7444020 £035 748373. $0.4 NEsgon fo96  L200CV cia, 2m 2037 O37 —~ —.. — 7 pia — — 
4508 £1.40 74HC4049 £0.25 74L$378 £0.62 ei ee [387A £324 iin PCB Production Equi = 
. 2 : ; 
4510 £0. 74HC4050 £0.25 Ep gt oH NE592 £0.62 2 £2.30 ‘AW Carbon Film 5% E12 Series 1Q-10M Phoio-Resist Aerosol § na ro e447 
4512 £0.32 74HC4075 £0.27 74LS395 £0.26 setesan £0.80 OK £0.65 WY Carbon Fil im a ig pe ais 
4512 £0:32 74HC4075 £0.27 Taree) £062 NES5534N £0.60 LM323K £2.34 “WwW Carbon Film bid Series 1Q-10M PCB Plastic pe hong ol ray 200ml £3.12 
4514 £0.77 J4HC4078 £0.16 Aree £000 OPO7CN £1.42 LM334Z £1.35 £0.02 Each, £0.95 Developing / Etching Tray 1.35 
4515 £0.98 74HC4511 £0.64 74LS670 £04 OP27CN £090 LM338K —s £5.52. 4W Metal Film E24 Series 109-IM _ Plastic Tweezers £0.55 
4516 £0.31 74HC4514 £0.84 near ICs. OP7IGP £236 733 £0.29 £0.04 Each, £1.72 per Transfer Spatular (Alfac) £0.70 
4518 £0.44 74HCAS38 £0. AOSARIN,. Tee OPSOGP £3.11 LP2950CZ £2.97 Enclosed Piste m/ Vert. 100Q-1M0O Transfer Eraser (Ai (Alfac) £0.55 
4520 £0.43 74HC4543 £0.90 AD OO £5.40 OP9O7FP £2.43 REFOICP £3.44 0.15W £0.15 Each Small Knife with — bl £0.39 
4521 £0.62 741. ries ADSQDAN £452 OP113GP £3.44 REFO2CP £4.66 Skeleton Presets Horz / Vert. 100Q-1M0O = PCB Polishing Block £1.84 
4536 £0.40 74, $00 £0.25 ADSOZAN £4.52. OPITOGP £209 REFI2Z 1.28 0.1W £0.11 Each Clear Drafting Film, { Pe r Ad 44 
4527 £0.40 ASO OS ADGDOAN £9.88 OP177GP £1.89 REFI95GP £4.72 POTS '4” Shaft 25mm Dia 470Q - 2M2 aque Draftin in pe £0.46 
4528 £0.40 TAL SOF £079 ADEDSIN. £16.20 OP183GP £3.44 F25Z £1.22 Lin or Log £0.42 Each Ferric wt Chloride Pellets 25¢ 2508 ( (kt) £1.31 
4529 £0.44 741803 0.29 ADGSSIN £8.35 2 £5.60 REFSOZ £1.22 *Please State Value* Ferric Chloride Pellets 500g (1It) £2.47 
4532 £0.32 74804 £0.17 ADSHIN £825 Op2izrP £5.20 TLASICP £0145 DIL Socke Tin Plating Powder (Th) £12.93 
4534 £248. M4805 £014 ADCS2A0 tpg OP275GP £2.57 423 £1.55 8 Pin £0.07 14 Pin £0.11 UV Exposure Unit. details ay sane oat 31 
4541 £0.33 74.809 £0.14 AO OTIN ate OP290GP £5.40  1IN914 £0.06 28 Pin £0.22 40 Pin £0.25 also available Teamsters Developers. Tanks 
4595 £034 741811 £0.17 ADTO8IN £5.69 eee aes aor £0.06 Photo Resist _ - Glass Fibre Paper a 
3s@ #4) 74LSI2. $0.14 ADTIUN £151 Ohaoocp Fits IN4oo2 «£0.07 ‘Size (146mm) Single Double — Single ‘Double G45033inm 0 
4560 £1.18 74L813 £0.14 ADIIZIN £238 Opigrap £13.74 1N4003 £0.07 4x6 S158. “£109 41.20 £147 - 64x O5mum poe 
4566 £196 74.814 £0.25 ADIOSIN. £s94  OPA95 £8.69 4004 £0.07 6x 12” £4.62 £5.15 £3.46 £4.20 95x 127mm £1.50 
q372 £0.25 TALSl> = £0.14 ADTOTAN £8.69 PMIOI2GP £5.20 1N4005 £0.07 9x 12” £6.93 £7.77 £5.19 £6.36 95x 43lmm £4.80 
os SO Marea eid. ADBIIN. £6.73 C4136 £0. 1N4006 £0.08 10x 12” £8.87 £9.81 £6.78 £8.30 119 x 454mm £6.20 
$e, £970 74L822 £0.14 ADSIZAN £632 SAAI027 = £4.52. INOW? £0.08 12x 17" £9.09 £10.19 £6. 34 +Breadboard ¥ 
ne £010 4826 £0.14 ADBIZAN £881 SG3524N £1.08. 1N4148 £0.05 Glass Fi ; . 83 £8.34 81x 6) r £ 
109 £038 74827 £0.14. AD8I7AN £3.85 $63543 £6.88 IN4149 cone se ge ei lgem ys Copper Clad 175 x 42m £3.90 
40109 £058 74827 £0.14. ADBITAN £389 SL4go £4.12 1N5400 £0.09 160x 100mm _ £1.94 £2.20 £0.70 £0.74 173 x 67mm £3.96 
Oss 0G eye E14 ADS22AN £5.20 SL490 £4.05 1N5401 £0.09 203x1l4mm = = £2.52 £2.78 = ae 203 x 75mm with ! 
sols. £024 ate? £014. -ADS26AN £5.33 SSM2017P £3.38 1N5402 £0.10 220x 100mm = £2.58 £2.88 £1.00 £1.05 & mountin lat rer BO 
pte 056 TS3R £0.19. ADB29IN £6.41 SSM2131P £4.19 1N5404 £0.11 233x 220mm £5.67 £6.41 £2.38 £2.52 ey 
T4L$38 £0.19 ADBSOIN, £641 SSM2I4IP tii i i 233x 160mm £399 £441 £175 £139 No Minimum 
: ; 0.8mm Thick Photoresist Board Now In Stock _ Order Value 

SSM2 142P 

Everyday with Practical Electronics, September 1995 

——_———_— Eh a a ee ee ee eee eee een a ae a Se 

a ae 
r ss aT 


by Fax. 



Editorial Offices: 



Phone: Wimborne (01202) 881749 

Fax: (01202) 841692. DX: Wimborne 45314 

Due to the cost we cannot reply to orders or queries 

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

Advertisement Offices: 




Ever since Leon Theremin produced the first successful electronic instrument 
back in the 1920s the world has periodically reaffirmed its interest in his un- 
usual “‘musical’’ instrument which is played without physical contact. One 
thing is for sure, the sound of the Theremin is very unusual — whether most 
players can achieve something musical is another matter. 

With two of these devices in the office recently they have proved to be com- 
pulsive playthings for visitors. This simple design is, as far as we can tell, the 
only semiconductor design to be published as a full constructional project for 
many years (with the exception of a full frequency and volume controlled 
instrument, also by Jake Rothman, in Supplement 40 of our Modern Elec- 
tronics Manual, published recently). Construction of the Simple Theremin is 
reasonably straightforward, playing it is the difficult bit! This basic instrument 
will give you a taste for the weird world of Theremin music. If you are really 
hooked we intend to publish a more advanced design, with both pitch and 
volume control asa future project. 


Finally a word of warning; don’t build this project if any member of your 
family, especially the younger ones, is likely to get hooked. The effect of those 
learning the Theremin is equally as bad as those learning the violin! It is too 
early to tell if the ultimate sound will be worth the painful learning process, 
but somehow I doubt it. 

Borough, Wimborne, Dorset BH21 1PF. 

Tel: 01202 881749. Subscriptions start 
with the next available issue. We 
accept Access (MasterCard) or Visa. 


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OO to every- — 

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We are unable to offer any advice on the use, 
purchase, repair or modification of commercial 
equipment or the incorporation or modifica- 
tion of designs published in the magazine. 
We regret that we cannot provide data or 
answer queries on articles or projects that 
are more than five years old. Letters requir- 
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All reasonable precautions are taken to en- 
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We do not supply electronic components 
or kits for building the projects featured, these 
can be supplied by advertisers. 

We advise readers to check that all parts are 
still available before commencing any project 
ina back-dated issue. 

We regret that we cannot provide data, 
or answer queries, on projects that are 
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Although the proprietors and staff of EVERY- 
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the law before buying any transmitting or 
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from illegal use or ownership. The laws vary > 
from country to country; overseas readers 
should check local laws. 




Take a trip “Back to the Future” 

and discover the fascinating 
world of “music and magic” that is 

the Theremin 

ORGET inputting that formant data 

into your MIDI synthesis worksta- 

tion via the Qwerty user interface for 
a limited time window (enough of this 
techno-rubbish — Ed!) and get back to those 
eerie tones of the good old Theremin. 

It was Leon Theremin who _ first 
popularised electronic music with his 
electronic musical instrument the There- 
min. His creation certainly followed Arthur 
C. Clark’s assertion that good technology 
should appear like magic, since it was 
played with no physical contact. The 
“‘Thereminists” moved their hands in a 
controlled way around the antennas that 
controlled pitch and volume. 

A motionless body was essential for pitch 
stability, but this merely enhanced the 
theatrical effect and mystery. Along with 
its eerie sounds, the instrument’s strange- 
ness led the Theremin to be used on the 
soundtrack of many 1950s science fiction 
movies, such as The Day The Earth Stood 


The Theremin is surrounded by intrigue 
and legend and this was played upon a 
great deal in the Channel 4 documentary, 
presented shortly after Leon Theremin’s 
death in 1994. However, the role of a tech- 
nical magazine like EPE is to demystify 
such things and explain their operation. 



It is said that a lot has been discovered in 
electronics when things go wrong and this 
is very likely in the case of the Theremin, 
since the principle of the Theremin fre- 
quently arises by accident in electronics as 
a form of instability. 

A classic case occurs in radios where 
there is a loud whistle accompanying the 
desired programme. If the tuning control 
is adjusted the whistle usually changes 

pitch. Combining this with another com- 

mon fault, hand capacitance effects, the 
pitch will change if a hand is moved 
towards the receiver. 

It is very likely that the old regenerative 
wireless sets popular in the twenties which 
were prone to these defects, inspired 
Theremin to analyse and exploit the effect 
to make a musical instrument. So there 
is no real mystery, the Theremin is in 
fact just a glorified audible capacitance 



The basis of all Theremins is two high 
frequency oscillators, of almost identi- 
cal frequency, normally operating from 
0:-2MHz to 2MHz. One oscillator is fixed 
while the other is connected to a conductor 
which forms a variable capacitor with the 
player’s hand. As the hand is moved, a 
minute change in capacitance occurs (in the 
order of fractions of a picofarad (pF) 

Fig. 1. Black diagram for the basic Theremin, 


shifting the oscillator’s frequency by a 
correspondingly small amount. 

\The oscillator outputs are then com- 
bined in a mixer as shown in Fig. 1 to 
produce a beat frequency as shown in 
Fig. 2. If the two original frequencies are 
close enough together, the beat frequency 
will be in the audio region. | 

Now here comes the clever bit: since the 
original frequencies are in the radio fre- 
quency (r.f.) region, it only requires a very 

. Small percentage shift to make a large dif- 

ference to the beat frequency, giving a sen- 
sitive instrument with a wide pitch range. 

The mixer output contains a lot of r-f. 
and is just like an a.m. radio signal. This 
then needs to be detected and filtered to 
obtain a clean audio signal. If the r-f. 
content is not removed the audio output 
amplifier may “overheat” and the signal 
may be radiated by the output wires caus- 
ing instability. 



Original Theremins built by RCA in the 
thirties were very large valve/wooden instru- 
ments with a vertical conductor for Pitch 
and a horizontal loop for Volume. (Basic 
Theremins, such as the one described here, 
do not usually have a volume control con- 
ductor.) The RCA’s Volume control was 
quite unusual since it had a negative control 
characteristic, in that no tone was emitted 
until the hand was removed. 

Since voltage controlled amplifiers were 
not effective at that time, the unique solu-. 
tion of varying the brightness of a di- 
rectly heated valve filament was used. This 
filament was fed with r.f. generated by an 
oscillator that could be damped via the 
control conductor. 


Fig. 2. Beat frequency output from the 
mixer stage. 

Everyday with Practical Electronics, September 1995 

SS —_——— ee ee ee ee eee ee ee ee eel. Cl el 

Original RCA Theremins were very 
highly developed pieces of electronics, 
having excellent stability and range. They 
have often been used in conjunction with 
an orchestra and can be considered true 
concert instruments. Of course this is 
reflected, along with their scarcity, in the 
price, which is in the order of £12,000. 



Being £11,980 cheaper than the RCA 
model, the design presented here is harder 
to play in tune because of a more com- 
pressed range, but when plugged into a 
loudspeaker with decent bass response and 
some sound processing gear, the results can 
be quite acceptable. 

To obtain a range comparable with the 
original necessitates the use of expensive 
specially made coils, whereas this design 
uses standard 100yH coils available from 
most of the main distributors. 


The complete circuit diagram of the 
Simple Theremin is shown in Fig. 3. The 
two oscillators are of the Colpitts con- 
figuration which avoids the need for a 
tapped coil by using two capacitors to form 
a “tapped” capacitance. This allows ordi- 
nary off-the-shelf inductors to be used. 

The frequency of the fixed oscillator, 
built around transistor TR1, is around 
1:33MHz. The variable frequency oscil- 
lator, built around TR2, is connected to the 
Pitch aerial (note that this is at positive 
potential since current can flow through 
coil L2). Trimming for ambient conditions 
is provided by trimmer capacitor VC1. 

Mixing of the two oscillator outputs 
is accomplished by transistor TR3. To 
prevent the oscillators locking together 
at low frequencies the mix resistors R9 
and R10 are of high value. Note R10 is 
about half the value of R9 to ensure the 
amplitude of the resulting waveform does 
not fall to zero at the dips of the beat 
frequency. This ensures there is always 









Two versions of the Simple Theremin, only the Pitch conductor shape has Daas 


some carrier frequency which reduces the 
distortion produced by the detector. 

The mixer stage is simply a collector 
biased common emitter stage. If a different 
transistor is used, resistor R11 may need 
altering to get lowest distortion. To prevent 
low frequency oscillation the mixer stage is 
decoupled by resistor R13 and capacitor 
C13. Note that the two oscillators have 
their own decoupling, provided by ceramic 
capacitors Cl and C6. 

Demodulation of the mixer output is 
provided by diode D2. Capacitor C14 is 
used to block the half-rail d.c. bias present 
on TR3 collector. To prevent a d.c. offset 
building up, diode D1 provides an equiv- 
alent d.c. path. 

First stage r.f. filtering to recover the 
audio is provided by capacitor C15. A 
second stage of r-f. filtering is provided by 
R15 and capacitor C16 before the signal is 
fed into load resistor R17. 

To prevent the Volume control VR1 
from scratching due to d.c., the signal is 
a.c. coupled via capacitor C20. Unusually 
for a Volume control, it is acceptable. for 
VRI to be a “‘linear” type, although a log. 
type gives a smoother change at low levels. 

A final stage of filtering, built around 
resistor R16 and capacitor C17, is applied 
just before the input to IC1, an LM386 
power amplifier i.c. The LM386 was chosen 
since it is less prone to r.f. oscillation than a 
lot of monolithic power amps and provides 
an adequate output of 250mW. 

A Zobel network consisting of resistor 
R18 and capacitor C21 is used to prevent 
any h.f. oscillation due to the voice-coil 
inductance of the loudspeaker. Capacitor 
C22 is used to block the half-rail d.c. 
bias voltage from entering the loudspeaker. 
Finally, decoupling for the power-amp is 
achieved by capacitor C18, with high fre- 
quency bypassing provided by C19. 

Fig. 3. Complete circuit diagram for the handheld Simple Theremin. 

Everyday with Practical Electronics, September 1995 



All the frequency determining capacitors 
should be zero temperature coefficient NPO 
ceramic, or better still, negative temperature 
coefficient, such as N150 ceramic types. The 
use of N150 capacitors helps compensate for 
the positive temperature coefficient of the 
ferrite cored inductors used. 

Most N1I50 ceramic capacitors can be 
identified by a band of orange paint across 
the top. However, aiming for high stability 
in a Theremin can be a pointless exercise 
since they will tend to drift according to air 
temperature, humidity and the proximity 
of any objects. 

All the other capacitors are used for 
coupling and decoupling and cheap poor- 
tolerance ceramics and electrolytics can be 

‘used. None of the resistors are critical and 
standard five per cent carbon-film types 
can be used. 

The transistors are cheap r.f. types as 
used in a.m. radios; it is possible to use Lf. 
types such as BC182s although it may be 
necessary to alter the value of the emitter 
components to get a clean sine wave. Al- 
though Schottky diodes are specified for 
the detector, old germanium types, such as 
the OA91, work almost as well. 


The Theremin printed circuit board 
(p.c.b.) topside component layout and full 
size underside copper foil master pattern 
are shown in Fig. 4. Construction should 
not present any problems provided the 
circuit is built on the recommended p.c.b. 
The board is available from the EPE PCB 
Service, code 952. 

To minimise the magnetic coupling be- 
tween the two oscillators the inductors L1 
and L2 are mounted on almost opposite 
corners of the p.c.b. They are also at 
right angles to each other, with L1 being 
horizontally mounted whereas L2 is in a 
vertical orientation. 


Back in the early eighties as a young 
electronics undergraduate one of my lec- 
turers said, “‘no more cornfields laddie”’ 


150k (2 off) 
33k (2 off) 
4k7 (3 off) 
5602 (2 off) 
12k (2 off) 

2k2 (2 off 
az (20f) = SHOP 
All 0:25W 5% carbon film TALK 

Capacitors Page 

C1, C6, 
C18, C21 

C2; CS; CY, 

C9, C15, 

C16,C17 10nceramic 20% (7 off) 
C3 27p ceramic 2% NPO or 


C4, C8, 

C12,C10 100p ceramic, NPO or 

N150 (4 off) 

C10 15p ceramic, NPO or 

C13,C20 47uradial elect. 10V 

C19,C22 220pradial‘elect. 10V 

VC1 10p Philips trimmer 

100n ceramic, 
+80 — 20% (4 off) 


This design is offered as a project for 
home construction only and no licence 
for commercial manufacture is implied. 

referring to a recently constructed mixer 
channel I had designed with all the resistors 
mounted vertically. However, no apologies 
are made for this being a “cornfield” 
design since it is the only way, apart from 
surface-mount techniques, the Theremin 
could be made pocket-sized without having 
to use one of those awful mini-jacks. Only 
full-size jack sockets are reliable enough, as 
users of Walkman type cassette players will 

— testify. 

Assembling the board should follow the 
normal rule of “lowest components first”’ 




LS Of¢P+ 



7 Voyel ged, @erext a 
guidance only 


D1, D2 BAT85 small signal 
Schottky diode (2 off) 
TR1, TR2, : 

TR3 BF195 npnsilicon rf. 
transistor (3 off) 
IC1 LM386 low voltage 

L1,L2 100uH axial inductor 
(2 off) 
B1 9V alkaline battery 
(PP3), with clip 
6-3mm (%in.) mono 
switched jack socket 
$1 S.p.s.t. min. toggle 
LSFs 8ohm 1-5in. diameter 
loudspeaker, with 
alnico magnet 
Plastic case, with battery compart- 
ment, size 105mm x 60mm x 28mm; 
printed circuit board available from EPE 
PCB Service, code 952; 8-pin d.i.l. 
socket; 10mm dia., 3mm shaft, collet 
knob plus end cap; single-ended solder 
pins (8 off); 16s.w.g. tinned cop- 
per wire, approx. 150mm length, for 
Pitch aerial; multistrand connecting 
wire; solder etc. ! 

Note that the p.c.b. design and circuit is 
copyright of Longwave Instruments and 
many not be manufactured by commer- 
cial companies. 

although this will contradict the other 
general rule of “resistors first’’ which can- 
not apply to vertical mount boards. It is a 
good idea to mount ICI in a socket and 
care should be taken bending the leads of 
the diodes and coils. The transistors are 
“lock fit” and so despite being of low 
profile, they can be fitted last, in accord- 
ance with good practice. 

Trimmer capacitor VCl MUST be 
mounted on the copper side of the board. 
This is quite a tricky soldering job 
necessitating a fine pointed iron, since the 

Fig. 4. Printed circuit board component layout and full size underside copper foil master pattern for the Simple Theremin. 
The size of the speaker cutout may need to be enlarged to suit the size of magnet on the speaker used. 


Everyday with Practical Electronics, September 1995 

ee ee a 
ee ee OY a CO a & & 4 44 4 BAe A Deh me A i» fh 4 a 4A uk A 

iron has to go under the component to 
reach the tags. When mounting the 
potentiometer VR1 it is essential that the 
tags are firmly bent over before being 
soldered, since the soldered joins on all 
p.c.b. mounted pots are subject to con- 
siderable mechanical stress. 


Being a compact unit, the drilling and 
mounting details are more critical than for 
most units. In particular the 2.5mm mount- 
ing holes for the p.c.b. are very tight, as is 
the actual size of the p.c.b. 

Some judicious filing of the board will 
be needed to ensure an accurate fit inside 
the case. This is best accomplished before 
the p.c.b. has been soldered up, since the 
trimmer capacitor is sensitive to dust and 

The loudspeaker is mounted with Evos- 
tik impact adhesive (the brown stuff). It 
is essential that the speaker used has a 
colmnar or alnico magnet, the more com- 
mon ferrite magnets will be too wide and 
will foul the components on the p.c.b. 

- Since the speaker does not have to 
handle the full range, a single hole sufficient 
to clear the voice coil will suffice. This 

g 18 mm 

Fig. 5. Case measurements and drilling details. 

provides protection without the need for a must be bent over to give a maximum 
covering grille. Fig. 5 shows the drilling clearance to be able to close the box. 

details for the box. 


There is very little wiring in the unit, it 
only being necessary for the battery 
clip, switch, output jack socket and 
loudspeaker. The full interwiring details 
are shown in Fig. 6. Note that the 
connecting tags for the jack socket SK! 



The trimmer capacitor mounted on the 
track side of the p.c.b. 




Whidden lititikktikdddlhtikdltimi lll) 





eV ee si Fig. 6. Interwiring between components mounted in the two sections of the small 
The completed p.c.b. is a tight fit in the case. The battery lead is secured to the battery compartment mounting/dividing 
case. strut as shown inset. 

Everyday with Practical Electronics, September 1995 677 






Fig. 7. Construction and mounting of 

the Pitch aerial. 

The aerial is made of 16s.w.g. tinned cop- 
per wire and is soldered between four solder 
pins as illustrated in Fig. 7 and photographs. 
For maximum strength it is best to insert the 
pins using a large soldering iron by heat- 
ing the pin up for a few seconds before 
firmly pushing it into the board with the bit. 
Using the standard pin insertion tool does 
not seem to work with glass fibre boards so 
the soldering iron technique was found to be 
the most effective approach. 


When testing the unit, the most common 
cause of no output is the oscillators being 
too far apart in frequency due to com- 
ponent tolerances. It should be possible to 
adjust VC1 so that the null point or ‘‘zero 
beat” should occur when its plates are half 

Above the null point the frequency 
should increase as the hand is brought 
nearer the “Pitch aerial’’. Interestingly, at 
the other side of the null point the fre- 
quency goes down. If the oscillator fre- 
quencies cannot be brought close enough 
with VC1 it will be necessary to pad-up 
either capacitor C10 or C3. 

Another cause of zero output is one of 
the oscillators not oscillating. This is most 
commonly due to an “open circuit” induc- 
tor, incorrect insertion of the transistor or 
solder bridges. 

If available, the oscillator output should 
be checked with a ’scope probe set to x 10 
to provide a degree of isolation. The output 
should be a good sine wave in the order of 
a few volts peak-to-peak, see Fig. 8. 


The audio output of the simple Theremin 
should also be a clean sine wave, since this 
is the standard ‘“‘Theremin sound’. Some 
circuits have a buzzy sound as a result of 
harmonics. This can sometimes give good 
results if sound processing is used. 

Positioning and interwiring between components mounted in the two halves of the 

case. Note the jack socket connecting tags have been bent down. 


0-5yS/ DIV diol 

Fig. 8 Oscillator output waveform 
taken with x10 probe. Voltage may be 
higher than battery voltage due to 

A harmonically rich sound can be 
achieved by clipping the waveform by over 
driving the mixer stage. Another method is 
to increase the coupling between the 
oscillators by reducing the value of the mix 
resistors, R9 and R10, or by encourag- 
ing magnetic coupling. This technique 
produces a ramp waveform as a result of 
the oscillators “‘pulling” each other. 

The original Theremins were designed to 
have a harmonic structure very similar to a 
violin. It is interesting that Leon achieved 
this by careful tweaking and listening, not 
having the advantage of oscilloscopes and 
spectrum analysers in those days. 

Playing or “conducting” the Theremin is accomplished by “waving” the hand(s) 

near the Pitch aerial. 


Do not expect to be able to play a tune 
on the Theremin immediately; they are 
very hard to play, even making the violin 
seem easy! One of the reasons for this, is 
the unusual control law which results in the 
rate of pitch change rapidly increasing as 
the hand gets nearer the “‘aerial”’. 

Secondly, the effective range of the pitch 
control is only a few inches and thirdly 
there is no tactile feedback. However, the 
unit is great for special effects and a tuneful 
rendition can be obtained if the instrument 
is sampled. 

For loudness control a guitar style 
volume pedal can be used. 

The Theremin will cause slight inter- 
ference to a.m. radios and will transmit its 
whistle at the low end of the MW band, 
where it should cause few problems since 
there are hardly any stations and the range 
of the interference is only a few feet. 

Traditionally, Theremins are played by 
moving a hand near the Pitch aerial. How- 
ever, with the Simple Theremin the unit can 
be handheld and moved against a fixed 
conducting object, such as a desk lamp. 

Interesting effects can be made when two 
Theremins are played against each other 
since they beat together and may also lock 
when the. aerials touch. Having suffered 
the effects of children having a ‘‘There- 
min war” it is suggested this is tried in a 
sound-proofed room! Generally, children 
love Theremins and they may be of some 
therapeutic value to the handicapped. 


Pitch to MIDI converters are now avail- 
able which greatly extend the possibilities 
for using Theremins. One advantage is 
that special software can be employed to 
make the instrument’s control characteris- 
tic easier to play, such as by increasing the . 
spacing between notes for example. There- 
min manufacturers Longwave Instruments 
are currently developing a pitch to MIDI 
converter. = 

1. ¥ PQ 

HART KITS give you the opportunity to build the 
very best engineered hifi equipment there is, 
designed by the leaders in their field, using the best 
components that are available. 

Every HART KIT is not just a new equipment ac- 
quisition but a valuable investment in knowledge, 
giving you guided hands-on experience of modern 
electronic techniques. 

In short HART is your ’friend in the trade’ giving 
you, as a knowledgeable constructor, access to bet- 
ter equipment at lower prices than the man in the 

You can buy the reprints and construction manual 
for any kit to see how easy it is to build your own 
equipment the HART way. The FULL cost can be 
credited against your subsequent kit purchase. 

Our list will give you full details of a// our Audio Kits, 
components and special offers. 


The Hart “Chiara 
Single-Ended Class “A” Headphone Amplifier. 

Most modern high fidelity amplifiers either do not 
have a headphone output facility, or this may not be 
up to the highest standard. 

The new Hart “Chiara” has been introduced as 
an add-on unit to remedy this situation, and will 

- provide two ultra high quality headphone outlets. 

This is the first unit in our 2000 Range of mod- 
ules to be introduced through the year. Housed in 
the neat, black finished, Hart Minibox it features 
the wide frequency response, low-distortion and 
“musicality” that one associates with designs from 
the renowned John Linsley Hood. 

Both outputs will drive any standard high quality 
headphones with an impedance greater than 30 
ohms and the unit is ideal for use with the Senn- 
heiser range. A signal link-through makes it easy to 
incorporate into your system and two extra out- 
puts, one at output level and one adjusted by the 
Volume control are available on the back panel. The 
high level output also makes a very useful long-line 
driver where remote mounted power amplifiers are 
used. Power requirements are very simple and can 
be provided by either of our new ‘‘Andante’”’ power 
supplies. Use the K3565 to drive the “Chiara”’ on its 
own, K3550 if driving other modules as well. 

Volume and Balance controls are provided and as 
befits any unit with serious aspirations to quality 
these are the ultra high quality Alps ‘‘Blue Velvet’’ 

Very easily built, even by beginners, since all 
components fit directly on the single printed circuit 
board and there is no conventional wiring what- 
soever. The kit has very detailed instructions, and 
even comes with a roll of Hart audiograde silver 
saider. It can also be supplied factory assembled 
and tested. 

Selling for less than the total cost of all the com- 
ponents, if they were bought separately, this unit 
represents incredible value for money and makes 
an attractive and harmonious addition to any hifi 

K2100 The total cost of a complete set of all com- 
ponents to build this unit is £126.37. Our special 
discount price for all parts bought together as a kit 

We faet gttcs elles foi s4as vcassaccentagnabaccosstieaswes steno £109.50 
K2100SA Series Audiophile, with extra selected 
components...............000 se ckbtagapeakacd soot ae Rakai £112.46 

Now available again and even better than before! 
Our famous triple purpose test cassette will help 
you set up your recorder for peak performance after 
fitting a new record/play head. This quality preci- 
sion Test Cassette is digitally mastered in real time 
to give you an accurate standard to set the head 
azimuth, Dolby/VU level and tape speed, all easily 
done without test equipment. 

TC1D Triple Purpose Test Cassette.................... £9.99 


4A 4 “ El ‘ ve 
And now, hot off the press, yet another classic 
from the pen of John Linsley Hood. Following the 
ongoing enormous success of his ‘‘Art of Linear 
Electronics” the latest offering is the all-new 
edition of ‘‘Audio Electronics’, now entirely 
re-written by the master himself. 
Underlying audio techniques and equipment is a 
world of electronics that determines the quality of 
sound. For anyone involved in designing, adapt- 
ing or using digital or analogue audio equipment 
understanding electronics leads to far greater 
control over the reproduced sound. 
The subjects covered include tape recording, 
tuners, power output stages, digital audio, test 
instruments and loudspeaker crossover systems. 
John’s lifetime of experience and personal in- 
novation in this field allow him to apply his gift of 
being so familiar with his subject that he can write 
clearly about it and make it both interesting and 
comprehensible to the reader. 
Containing 240 pages and over 250 line illustra- 
tions this new book represents great value for 
money at only £18.99 plus £2.50 postage. Send or 
telephone for your personal copy now. 

ALPS ‘GlucVeluct 

Precision Audio Controls 

To fulfil the need for ultra high quality controls we 
import a special range of precision audio pots in 
values to cover most quality amplifier applications. 
All in 2-gang stereo format, with 20mm long 6mm 
diam. steel shafts, except for the 50K Log which is 
25mm x 6mm. Overall size of the manual pot is 27W 
x 24H x 27Deep, motorised versions are 72:-4mm 
Deep from the mounting face. Mounting bush for 
both types is 8mm diameter. 

Now you can throw out those noisy ill-matched 
carbon pots and replace with the real hi-fi com- 
ponents only used selectively in the very top flight of 
World class amplifiers. The improvement in track 
accuracy and matching really is incredible giving 
better tonal balance between channels and rock 
solid image stability. 

The motorised versions use a 5V DC motor coupled 
to the normal control shaft with a friction clutch so 
that the control can be operated manually or electri- 
cally. The idea of having electrically operated pots 
may seem odd, archaic even, but it is in fact the only 
way that remote control can be applied to any serious 
Hi-Fi system without loss of quality. The values 
chosen are the most suitable available for a low loss 
passive volume and balance control system, allow- 
ing armchair control of these two functions. 

Our prices represent such super value for pots of 
this quality due to large purchases for our own kits. 


PAM VO AAI iisiiseiis dp ski ica sinctdcasdavasabentibias £15.67 
2-Gang 10K, 50K or 100K Log. ............cceeeeeeees £16.40 
2-Gang 10K Special Balance, zero crosstalk and 
BOTS COTS COG iii ois sasisccstccsdenscancdeccnssctbaddaahe £17.48 

2-Gang 20K Log Volume Control £26.20 
2-Gang 10K RD Special Balance, zero crosstalk and 

less than 10% loss in centre position.....,......... £26.98 
999R 2/4 R/P 1OOMH..............ccecececseeeseeeees Geeta £16.84 

We have a few erase heads to suit which can only 
be supplied when 2 R/P heads are purchased £36.80 


DEM1 Mains Powered Tape Head 
Demagentizer, prevents noise on playback 

due to residual head magentisation................... £4.08 
DEM115 Electronic, Cassette Type, 
GOT VUI TINE oi cialis cscs sgnescs vavnsnhdadaccntevepecnsssbaboaed £8.61 

Send or ‘phone for your copy of our FREE List of these and many other Kits & Components. Enquiries from Overseas 
customers are equally welcome, but PLEASE send 2 IRCs if you want a list sent surface post, or 5 for Airmail. 
Ordering is easy. Just write or telephone your requirements to sample the friendly and efficient HART 
service. Payment by cheque, cash or credit card. A telephoned order with your credit card number will 

get your order on its way to you THAT DAY. 

Please add part cost of carriage and insurance as follows:-INLAND Orders up to £20 - £1.50, 

Orders over £20 - £3.50. 

Express Courier, next working day £10. 

OVERSEAS - Please see the ordering information with our lists. 


(01691) 652894 

Everyday with Practical Electronics, September 1995 




The HART K1450 Magnetic pickup preamplifier kit 
features a totally discrete component implementa- 
tion with a specially designed low input impedance 
front end and the superior sound of the Shunt Feed- 
back circuitry. High quality components fitting to an 
advanced double-sided printed circuit board make 
this a product at the leading edge of technology that 
you will be proud to own. Nevertheless with our step 
by step instructions it is very easy and satisfying to 
assemble. The higher current consumption of this 
unit means that it is best powered by our new 
Andante Audio Power Supply, itself an advanced 
piece of technology in a matching case. This sup- 
plies the superbly smoothed and stabilised supply 
lines needed by any sensitive preamplifer and fea- 
tures a fully potted Hi-grade toroidal transformer 
along with a special limited shift earth system for 
hum free operation. The K1450 is suitable for all - 
moving coil and moving magent transducers this 
unit is especially recommended for, and will extract 
the very best from the modern generation of low 
output high quality moving Coil transducers. 

K1450 Kit, complete with all parts ready to 
assemble inside the fully finished 228mm x 134mm x 
63mm case. Kit includes full, easy to follow, 
assembly instructions as well as the Hart Guide to 
PCB Construction, we even throw in enough Hart 
Audiograde Silver Solder to construct your kit! 

ebb apdbABAUS Bie arta prcaces Wide cosa pues cosine ole se leceushincsseancanted £111.58 

K1450SA Series Audiophile version with selected. 

COMMITEE ois 86.00 boii chesatoseuaben beet £133.94 


Do your tapes lack treble? A worn head could be the 
problem. For top performance cassette recorder 
heads should be replaced every 1,500 hours. Fitting 
one of our high quality replacement heads could 
restore performance to better than new! Standard 
inductances and mountings make fitting easy on 
nearly all machines (Sony are special dimensions, 
we do not stock) and our TC1 Test Cassette helps 
you set the azimuth spot on. As we are the actual 
importers you get prime parts at lower prices, com- 
pare our prices with other suppliers and see! All our 
heads are suitable for use with any Dolby system 
and are normally available ex-stock. We also stock 
a wide range of special heads for home construc- 
tion and industrial users. 

HC80 NEW RANGE High Beta Permalloy Stereo 
head. Modern space saver design for easy fitting 
and lower cost. Suitable for chrome, metal and 
ferric tapes, truly a universal replacement head for 
everything from hi-fi decks to car players and at an 

incredible price tOO!...............ccecceeeeeeseceeseeseeees £11.70 
HRP373 Downstream monitor combi head...... £62.59 
HQ551A 4-Track R/ £8.75 
HQ551S Sony Mount 4-Tr. R/P......0....c0cccceeeeee £14.90 
HQR560 Rotary Base 12:5mm R/PY/E................ £21.90 
HQR570 Rotary Base 15mm R/P/E................... £22.59 
HQR580 Rotary Base 12:5mm R/P.................... £14.29 
HART Classical CD’s. 

Top quality, Full Digital (DDD), over 100 titles from 
only £1.99! Ring or send for your list! 


We stock a good range of books of interest to the 
electronics and audio enthusiast, including many 
reprinted classics from the valve era. Some were in 
last months advertisement, but see our list for the 
full range. 

New this month is the GEC Valve designs book at 
£18.95, and the VTL Book, a modern look at valve 
designs, £17.95. 


New diamond-coated X-ray needle gun attacks malignancy from within 
— by Hazel Cavendish 

DVANCED electronic technology has 

found a way of attacking cancer 
cells from the inside of a tumour rather 
than by passing high-energy beams 
through a patient’s body. It is the first 
time this has been done successfully. 

A remarkable electronic gun invented 
in America — at present on its British 
trials in the treatment of brain tumours 
in a British Hospital — fires electrons 
along a 10cm-long needle to irradiate 
and kill a mass of cancerous cells in 
a single treatment lasting only half an 

The Photoelectron Corporation in 
Maine, USA has spent the last six 
years developing electron-beam sys- 
tems, based on highly innovative 
technology which originated in the 
R&D centre of another American 

company, the Thermo Electron 
Corporation. Their president, Peter 
Nomikos, set out to merge the 

disciplines of physics with radiosur- 
gery to create a radical new approach 
to the therapeutic treatment of 
malignant tumours. The result was the 
development of an effective X-ray 
system which could minimize or 
eliminate tissue damage during radia- 
tion treatment. — 


The first trials involving patients with 
brain tumours have proved highly en- 
couraging. In 14 patients treated at 
the Massachusetts General Hospital in 
Maine, and four other major US hospi- 
tals, tumour growth was halted and 
cancer cells killed in nearly all the cases. 
Tumour growth recurred in only three 
patients, and those cases occurred at the 
tumour margin where the radiation dose 
was minimal. In the second phase of 
trials the peripheral dose was increased 
with successful results. 

Most tumours were irradiated for less 
than 30 minutes, and the procedure 
was well tolerated by all the patients, 
who suffered no trauma or ensuing 
complications from the treatment, and 
were generally discharged from hospital 
within 24 hours. Trials are now in 
progress at the Royal Free Hospital in 


The most remarkable feature of the 
battery-powered gun is its 100mm- 
long diamond-coated needle which 
accelerates electrons towards the cen- 
tre of the tumour. The electrons collide 
with a tungsten target which results in 


The new electronically controlled X-ray gun can be focussed 

to a precise region within a tumour. 

a uniform distribution of X-rays 
around the target area. Precisely 
regulated X-ray photons emitted in a 
spherically symmetric or asymmetric 
pattern ensure that the entire tumour 
is engaged. The 33mm-wide gun can 
be inserted in the same track used to 
take a biopsy of a brain tumour. .The 
advantage is that all this is taking place 
within the tumour, and because the 
rays are absorbed in the tumour tissue 
there are none left by the time they 
reach its edge to cause damage to 
healthy tissue. 

torture instrument, this apparatus can 
save lives and is attached to the head 
ensuring absolute stability of the X-ray 
needle gun mounted on it. 




the Nor- 
folk and Nor- 
wich Hospi- 
tal’s Radiotherapy 
Department and is 
involved in the 
trials, comments 
that ‘“The use of 
the diamond- 
coated needle is 
significart, as 
diamonds provide 
an inert material 

there is no 
interaction -— 
chemical or 

otherwise -— with 
the brain tissue 
that it passes 
through to reach 
the tumour.” 

Explaining the 
use of electromag- 
netic fields within 
the gun to steer the 
X-rays, he said 
‘“‘You have to control the path of the 
electrons so they hit the right part of the 
target with absolute accuracy.” The 
gun’s ability to match the radiation field 
to the shape and size of a tumour offers a 
precision and flexibility never before 
experienced in brain operations. 

The new technique of treating brain 
cancer appears to compare favourably 
with existing treatments. It may replace 
the linear accelerator and gamma knife. 


Major advantages over therapy with 
radioactive implants are also cited, the 
latter normally requiring much longer 
treatment times, usually several days. 
The new device also scores in that its 
X-ray output remains constant with 
time. Additionally, it eliminates dif- 
ficulties in handling and disposing of 
radioactive materials and the need to 
shield personnel. 

The cost of the equipment to calibrate 
and run the device is said to be in the 
region of £330,000 — a sum ten times less 
than existing brain cancer treatment sys- 
tems with their inherent disadvantages to 
skin and tissue. “Our goal is to make 
life easier for people with cancer by al- 
leviating their suffering and reducing the 
cost of cancer treatments,” says Peter 
Nomikos. His company is now working 
on a reconfiguration of the device to treat 
other cancers. 

Everyday with Practical Electronics, September 1995 

a. at 

-measures together 

museums and the 


LECTRONICS has had a major 
F impact on our world view. Many 

features of the electronics tech- 
nology with which we are familiar 
have their origins in the hidden 
world of defence electronics, during 
the Second World War and _ the 
military tensions of. the following 
decades. Understanding the history of 
defence electronics and its relationship 
with domestic electronics therefore 
plays a vital part in understanding 
contemporary history. The new Centre 
for the History of Defence Electronics 
(CHiDE) has been established in the 
Department of Conservation Sciences 
at Bournemouth University to promote 
this understanding. 

The broad aim of the Centre is to 
contribute to the study and public 
awareness of the history of electronics 
and through this to the _ public 
understanding of science. Initially the 
Centre will concentrate on_ radar, 
sonar, com- 
munications, and 
electronic counter- 

with their wider 
social conse- 

Innovative ap- 
proaches in the 
field of history, 

public dissemina- 
tion of science and 
technology will be 
drawn together to 
provide systematic 
coverage of a field 

which has absorbed a major part of 
UK expenditure on research and 
development. | 

The Centre will place technical his- 
tory in both a social and military context 
and show how science and technology 
impacts on ordinary people. 

A Virtual Museum will be created on 
the Internet (this should go “‘live”’ 
during August) and an interactive CD, 
providing easy access to the Centre’s 
resources both for the public and for 
scholars. It will contain an index to 
relevant sources at other locations, 
allowing the Centre to become a natural 
focus for researchers in this field. The 
latest database technology will store 
and retrieve material that includes 
documentary, pictorial and oral ar- 
chives. The Virtual Museum will feed 
into schools and libraries to promote 
better public understanding of science 
and assist in the teaching of technology. 

Recollections of those involved in 
technical developments will be ob- 

‘tained by the Centre by means 

of recorded interviews to maximise 

retention of their unique experiences 
which would otherwise be lost through 
the passage of time. 

Research will be conducted on speci- 
fic topics in the history of electronics. 
The Centre will also pursue three 
major research themes based on the 
developments and evaluation of the use 
of oral and autobiographical records in 
the communication of technical his-. 
tory; multimedia interactive tools for 
the representation of technical con- © 
cepts; multimedia interactive tools for 
the representation of socio technical 

The University is looking for both 
financial and practical support for this 
project. If you feel you can help in any 
way, from typing a manuscript to spon- 
soring research, please contact either Dr 
John Beavis (Director of the Centre) or 

- Brian James (Manager of the Centre) 

at Department of Conservation Serv- 
ices, Bournemouth University, Poole, 
Dorset BH12 5BB. Tel: 01202 595178 
Fax: 01202 595255, Internet: consci@ 

Blenheim fitted veith Air Interception MK1/V (supplied by Douglas Fisher FRPS ) 


Although security firms talk glibly 
about burglar alarms which connect 
direct to the local police station, this is 
in fact not true. But it is easy to 
understand how misconceptions arise. 

When | phoned the Home Office for 
comment, the Home Office referred me 
to the Metropolitan Police Press Office 
at Scotland Yard. They told me that 
there was only one person in Scot- 
land Yard who could talk about burglar 
alarms and he would phone me back 
“if he has time’’. Weeks later | had still 
heard nothing further. Fortunately the 
Crime Prevention Officer at my local 
police station was more helpful. 

Burglar alarms which automatically 
dial a telephone number are con- 
nected to a central control station, 
funded and often shared by several of 
the major alarm companies. When 
the phone rings at the central sta- 
tion, the controller first phones the 
householder (whose private phone 
number is kept on file) to check 
whether it is a false alarm. If there is 
no reply, then the alarm is taken to 
be genuine. The control centre then 
notifies the police. 

The police then, in theory at least, 
rush to the scene of the crime and 
check for any sign of forced entry. If 

there is no sign of forced entry, the 
call is registered as a ‘false alarm”. 
The police have no powers to enter 
premises unless there are clear signs 
that a burglar has been inside. 

If the householder has delegated 
someone as key holder, for instance a 
neighbour, then the key holder can 
open the premises to let the police in. 

There is a penalty for too many false 
alarms. Only four are allowed in any 
twelve month period, and an excessive 
number earns a ban on police assis- 
tance for three months. 

So anyone fitting an electronic alarm 
should do everything possible to en- 
sure that it is not tripped by household 
pets, vibration from heavy lorries or 
extreme changes in the weather. 

Barry Fox 

Faster PIC 

Microchip’s new PIC17C43 is the fastest 
8-bit microcontroller available, achiev- 
ing 160 nanosecond instruction times at 
25MHz. This high-performance RISC- 
based microcontroller is a cost. effec- 
tive alternative to more expensive 16-bit 
microcontrollers and dedicated digital 
signal processors. 

“The: PICT/Cas : “inctudes:::a 
4K x 16 one-time-programmable EPROM 
memory, and 454 bytes of user RAM. 
On-chip peripherals include: the fastest 

Everyday with Practical Electronics, September 1995 

PWM outputs in the industry, fast capture 
inputs, a serial communications interface 
(USART), and a sophisticated watchdog 
timer with its own RC oscillator. 

The PIC17C43_ provides the ideal 
upgrade path for Microchip’s high-end 
PIC17C42 and mid-range PICI6CXX 
users. Pin-for-pin plug compatible with the 
PIC17C42, the PIC17C43 allows users to 
plug the device into the same space on their 
printed circuit board and run PICI7C42 
software with few changes. 

For further information, contact 
Arizona Microchip Technology Ltd., Unit 
6, The Courtyard, Meadowbank, Furlong 
Road, Bourne End, Bucks, SL8 S5AJ. Tel: 
(01628) 851077, Fax: (01628) 850259. 


R.A.E. and MORSE courses are starting 
again at Wombourne, as follows: 

R.A.E. classes on Mondays, 7.00-9.00 
p.m. commencing 18 September. 

Morse classes on Thursdays, 7.00-9.00 
pm. commencing 21 September. 

Morse students are taken from begin; 
ner’'s groups to new format 12 w.p.m. 
Morse Test level. The tutors have been 
running these courses for many years 
with a remarkably high success rate. 

Enrolment is on 11 and 12 September 
at: Wombourne Youth and Community 
Centre, Church Road, Wombourne, 
Wolverhampton WV5 QEZ. Details from 
Brian Fereday on 01902 820826. 


: T ‘ ; i 

N RECENT years there have been many 
Fecsorts in the electronics press about a 
new silicon/germanium technology. Some 
reports claim that it will be the most 
significant development in semiconductor 
technology for many years. Others say that 
it will never live up to the extravagant 
claims made for it, and that it will be just 
another “‘flash in the pan’’. 

The new technology uses both silicon 
and germanium (SiGe) in the structure in a 
way that improves both the gain and 
frequency response of the transistors. With 
current silicon technology it offers an im- 
provement in speed of about two and a half 

This means that it is fast enough to 
take on gallium arsenide on this factor 
alone. However it is much cheaper. to use 
than gallium arsenide, involving relatively 
slight modifications to the existing silicon 
processes. This gives it the additional ad- 
vantage of being able to use existing plant 
and not require large amounts of invest- 
ment to set up a new process line. 

These advantages make the new technol- 
ogy ideal to cater for the new boom in 
telecommunications. Cellular phones could 
use SiGe integrated circuits to provide. all 
their functions, from r.f. signal handling 
down to all the control and processing 
required in the phone. This would bring 
down the cost of this form of communica- 
tion even further. 

The idea behind the technology has 
been understood for some years: It is 
based around a hetero-junction bipolar 
transistor (h.b.t.) Normally transistors use 
what is called a homo-junction, or one 
made from the same type of material e.g. 
silicon/silicon. By adding a second material 
it is possible to create a hetero-junction, 
and this creates its own electric field within 
the structure. 

The improvement in performance can 
be explained in terms of the band-gap. 
Germanium has a smaller band-gap than 
silicon, and introducing a small amount of 
germanium decreases the band-gap in the 
transistor. This increases the number of 
electrons available and hence improves the 

The internal electric field also helps the 
electron mobility, reducing the time for the 
electrons to travel across the junction. It is 
this effect which gives the improvement in 
the frequency response of the devices. 

Whilst’ silicon and germanium have the 
same shaped crystal structure there ig a 
difference between the lattice spacing be- 
tween the two materials. The silicon is 
about 96 per cent that of the germanium. 
This means that if there was a junction 
between the two materials the mismatch 



are no “flash in the pan!”’ 

would cause strains to be set up resulting 
in defects at the junction, preventing the 
devices from operating. 

To overcome the problem a silicon ger- 
manium alloy having a spacing half way 
between the two substances was developed 
and used. This enables a junction to be 
made from silicon and the alloy. Although 
some stress remains in the structure it is 
much reduced and with new techniques and 
careful manufacture no defects are formed. 

The exact proportions of silicon and 
germanium in the alloy have to be carefully 
chosen. Increasing the amount of ger- 
manium improves’ the performance, but 
increases the likelihood of defects. Now the 
balance seems to have been reached using 
about 30 per cent germanium, and the 
remainder silicon. 

One of the major advantages of the tech- 
nology is that it is compatible with most of 
today’s processes enabling the new devices 
to be made with very few modifications to 
existing plant. In fact it is not just the 
improvements in specification which make 
this development so important. It is the 
fact that they can be achieved by slightly 
modifying an existing process and using 
existing equipment. 

One method of manufacture uses an 
ultra high vacuum chemical vapour deposi- 
tion (UHV/CVD) process. Normal chemi- 
cal vapour deposition processes operate 
at temperatures which would damage the 
structure. By using the new process lower 
temperatures can be used. 

The UHV/CVD stage uses a mixture of 
the two semiconductors and leaves a thin 
and very accurately controlled layer of 
atoms on top of the silicon substrate. This 
is the basis of the hetero-structure used in 
the devices. 

_In other experiments techniques includ- 
ing molecular beam epitaxy have been 
used. This too operates in an ultra high 
vacuum, which is required to keep the 
temperatures down. 


When the first devices were manufac- 
tured in early 1990 they achieved speeds 
which were about twice as fast as any- 
thing that was possible with silicon. Now 
with the technology improving, further 
advancements are being made and the 

technology is moving still further ahead of 

silicon. Speeds of over 100GHz have been 
reported even now, with higher cut-off 
frequencies promised for the future. 

Apart from speed, these devices offer a 
high level of gain. Devices operating at 
around 3GHz have been shown to have a 
gain of over 20dB. Coupled to this they can 

lan Poole investigates the possibilities of the latest 
developments in SiGe technology and finds that they 

enable circuits to operate with a high level 
of efficiency. 

This aspect is a great bonus for anyone 
designing portable equipment where bat- 
tery consumption is of crucial importance. 
Often radio frequency circuits consume 
large amounts of current so that they can 
reach the gain and frequency requirements. 
If the SiGe devices can improve on the 
existing technologies then this will give 
them a considerable advantage. 

A further advantage of SiGe devices is 
that they offer a good noise figure. One of 
the limiting factors in any radio receiver 
design is the amount of noise generated by 
the front end circuits. att 

At the frequencies where these devices will 
be used the noise generated internally by the 
set will far outweigh any noise picked up by 
the aerial. This means that any noise gener- 
ated in these stages can have the effect of 
masking out the weaker signals. 

. Improved noise figure devices will enable 
more effective circuits to be designed, en- 
suring that the noise generated within 
the set is kept to an absolute minimum. 
Currently noise figures of 0-6dB are being 
achieved at frequencies around 2GHz. 

There are many advantages to using SiGe 
technology, but there are still a few draw- 
backs associated with it. One of the major 
worries is associated with its reliability. 

Even with the new alloy there is a strain 
set up within the crystal structure. This 
may give rise to long term failures, espe- 
cially if the equipment is operated at 
elevated temperatures. To find out whether 
this is a problem a number of investiga- 
tions are being performed. 

Another difficulty is the low operating 
voltages which it will sustain. The technol- 
ogy has a low breakdown voltage and this 
limits many aspects of operation. There 
is a trend towards ever decreasing supply 
voltages in the digital areas, and this will 
present no problem. In fact 3-3V is now 
becoming the new standard especially for 
battery powered portable equipment. 

However, there are still a number of 
areas where higher voltages are needed. 
This is particularly true for transmitting 
amplifiers where they are needed to ensure 
that the required power levels can be 
attained. It is in this area that SiGe devices 
are lacking. Even if they are kept within 
their limits whilst operating into a good 
aerial, if this is removed then damage will 
almost certainly result. 

Enormous possibilities exist for SiGe 
devices. Work is progressing to overcome 
many of the limitations, and it is to be 
expected that real improvements will be 
seen in the next few years. 

Everyday with Practical Electronics, September 1995 



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~ Constructional Project 



Increase the accuracy of low 
value resistance readings on 

your DVM. 

T IS sometimes necessary to find the 

value of a resistor or, more particularly 

perhaps, the resistance of a length of 
wire, or a small coil, or a current meter 
shunt, where the actual resistance lies 
below ten ohms and may well be a fraction 
of an ohm. 

This is where a low range ohm-meter is 
useful. Such an ohmmeter is also very 
handy for checking the resistance of 
printed circuit board tracks, especially 
where the tracks have to carry appreciable 
currents, and soldered connections. where 
an extremely small resistance should be 


If reasonable accuracy in the measure- 
ment of a low resistance is needed it is wise 
not to depend upon analogue ohmmeters 
unless these have been specifically designed 
to have a low-resistance range. Ordinary 
analogue multimeters of good quality such 
as the Avometer used on the lowest resis- 
tance range will certainly provide an in- 
dication of values below ten ohms. 

However, once the test resistance falls be- 
tween the scale divisions or gets below one 
ohm, the eye is forced to judge the position 
of the pointer against a fraction of the scale 
length that is devoid of identifying lines. 

For example, the author needed to find 
the value of a shunt resistor which was 
known to be approximately 0-7Q; on the 
Avometer he had to judge the value indica- 
tion on a blank section of the scale which 
was about 5mm long and represented zero 
to one ohm, see Fig. 1. 

After taking the test lead resistance into 
consideration and allowing (again by eye) 
for the scale non-linearity, the reading 
looked to be somewhere about 0-7Q, but it 
could well have been anything from 0-6Q to 
0-8Q, clearly a hit and miss measurement. 

For those who now wonder about using 
a digital meter, the answer is that a similar 
problem can arise in general purpose 
instruments in spite of their much superior 
resolution over analogue meters. For 



Fig. 1. Low ohms scaling of typical 
analogue multimeter. 

instance, a 3-5-digit display type of digital 
meter with a basic 199-9 indication on its 
lowest resistance range is_ perfectably 
readable down to an ohm or so without too 
much questioning. When going below an 
ohm, though, some doubt can creep in. 

As an example, a reading of 000-5 on the 
2002 range does not mean that the test 

resistance ‘is exactly 0-5Q; its value could | 
well lie between 0:-45Q and 0-55Q, and the 
display may often be found to flicker be- 
tween readings of 000-4 and 000-5 or 000-5 
and 000-6 on such occasions. Using the 
digital instrument on the author’s shunt 
resistor simply gave such a result, and once 
again the actual value could have been 
between 0:65Q and 0-75Q. This was no 
improvement on the guess-work associated 
with the Avometer. 

Using a very accurate bridge the author 
actually found the resistor to be 0-737Q, 
but it was while pondering on the points 
discussed above that he got an idea for a 
simple adaptor which could be used with a 
digital meter to provide more reasonable 
accuracy of this sort. 


Of course, it is possible to measure the 
current through, and the voltage across 
an unknown resistor and then use Ohm’s 
law to calculate the value. This is a bit 
troublesome since a large current is needed 
to produce a measureable voltage drop. 
The problem is then simply switched from 
the ability to read a small resistance ac- 
curately to that of measuring a small volt- 
age accurately. 

Everyday with Practical Electronics, September 1995 















Fig. 2. Full circuit diagram for the Low Range Ohmmeter Adaptor. 

With the very simple adaptor described 
here, an existing 3-5-digit DVM used in the 
millivolt mode can be made to read be- 
tween zero and 10Q in two ranges: 0 to 
1Q and 0 to 10Q with two (and possibly 
three) decimal place indication. Using this 
adaptor, the shunt resistor value was found 
to be 0-73(4)Q within the stated accuracy 
of the voltage range used and that of the 
calibration resistor used. 

The full circuit diagram for the Low 
Range Ohmmeter Adaptor is shown in Fig. 
2, where its simplicity is immediately ap- 
parent. The source of power supply is a 
single 1-SV cell and only a single transistor 
is needed, plus a few resistors and diodes 
and a couple of multi-turn potentiometers, 
all readily available and inexpensive. 

Transistor TR1 is a constant current gen- 
erator producing a known current through 
the test resistor Rx. The voltage developed 
across the test resistor is then measured 
by an external DVM which is switched to 
the 200mV range. Thus, unless Ohm’s law 
has been deceiving us all these years, this 
voltage will be directly proportional to the 
value of the test resistance since the current 
is constant. 

The level of the current is set for the two 
ranges, 192 and 10Q respectively by adjust- 
ment of the multi-turn potentiometers VR1 
and VR2. Multi-turns are used since the or- 



Fig. 3. Printed circuit board , 
component layout and full size 

copper foil master track pattern. 
This board is available from the 
EPE PCB Service, code 926. 

dinary carbon rotary types are insufficiently 
“smooth” to be able to adjust with any ac- 
curacy, especially on the 1Q range. 

Once these are set up, no further atten- 
tion is needed until the battery voltage has 
changed sufficiently to affect the readings. 
A couple of “trimmer”’ holes are provided 
in the case lid so that small correcting ad- 
justment can be made to the multi-turn 
pots each time the adaptor is used. When 
drilling the case lid, position these trim 
holes so that they are directly above the 
multi-turn screwheads. 

The on-off switch S1 is a push-to-make 
button type. This type is used because in 
operation it is pressed only when a reading 
is being taken and so prevents the adaptor 
from being inadvertently left on after use, 
the current drain from the cell being quite 


The adaptor is built on a small printed 
circuit board which is shown in Fig. 3. 
There should be no problems in making 
this up, just make sure of the orientations 
of the transistor and diodes, with the usual 

Everyday with Practical Electronics, September 1995 


R1 10 5% or better 
R2 120 5% or better FALK 
R3 10 1%orbetter Page — 

R4 1 1% or better 
All resistors metal film or better 

VR1 10 0:75in multi-turn 
VR2 100 0:75in multi-turn (20 
turns or more) 

D1,D2 1N4148 signal diode (2 off) 
TR1 BFY52 npntransistor 


S1 push-to-make momentary 

action switch 

$2 S.p.s.t. min. toggle switch 

Printed circuit board available from 
EPE PCB Service, code 926; plastic box 
85mm x 56mm x 40mm; single AA size 
cell holder with tag ends; 4mm screw 
terminal post (2 off); solder tag (2 off); 
connecting wire; solder. 

Approx cost 
guidance only 

+ a 6, 

care in soldering. When completed, this - 
board slips vertically into the internal wall 
grooving at one end of the small case. 

There is nothing critical about position- 
ing things inside the case, except that the 
access holes to the potentiometers should 
be correctly placed. The switch wire lengths 
are not important but keep the two test ter- 
minal leads as short as you possibly can 
without any tightness or straining. 

The test terminals, TP1 and TP2, should 

be of the all metal types so that the test 

resistor can be clamped firmly and closely 
to them. Avoid terminal plugs and sockets 
as these can introduce small but significant 
resistance. Terminals could, alternatively 
be made using a couple of 2BA screws 
about one inch in length, with nuts and 
washers as appropriate. 

The cut-out pattern for the lid com- 
ponents and the lettering legends are 
shown in Fig. 4. If you use an alternative 
case there should be no problem in placing 
the parts in roughly the same positions. 
The simple cell is an AA type battery 
clipped into a conventional holder (with 
tags) which is glued or screwed to the base 
of the case. Because of spacing require- 
ments with the small listed case, mount the 
cell holder diagonally. 


Calibration is quite simple, but care is 
needed on the 19 range. You will need 
two accurate test or calibration resistors 
of 1Q and 10Q in value at a minimum one 
per cent tolerance, but better if you can 
get them. If you happen to have a stan- 
dard resistance box (the author has an old 
ex-Army one which contains a total of 
100Q which can be adjusted in precise 
0-192 steps) each range can be thoroughly 
checked with the best possible accuracy. 

Set both multi-turn potentiometers, VR1 
and VR2, to about mid-travel, set the 
Range switch to 10Q and clamp an 
accurate 10Q calibration resistor firmly 
across the test terminals. Now connect 
your digital meter, switched to the 200mV 


d.c. range, across the test resistor (lead 
length here is not important). Although 
the 200mV range of the DVM is being 
used, it is only used as far as the 100mV 
point. The reading obtained then cor- 
responds to the unknown resistance value 
from 0 to 109. Now adjust preset VR2 to 
give this 100mV meter reading while 
pressing the button switch. The reading 
(although strictly in millivolts) corresponds 
to a resistance value of 10Q. 

You can check the linearity of the scale 
by connecting one or more intermediate 
values of resistance to the test terminals. 
The positioning of the decimal points for 
any reading has, of course, to be mentally 
adjusted to suit the scaling. 

Repeat the above procedure on the 1Q 
range, using your accurate 1Q calibration 
resistor at the test terminals, and this time 
adjusting preset VRI to give a reading of 
100mV, which will now represent a 12 
resistance value. A reading of, say, 47-5mV 
would therefore indicate a resistance of 

It is a bit trickier to set the DVM exactly 
to 100mY on this smallest range than it is 
on the larger. This comes about because of 
slight fluctuation in the otherwise constant 
current from transistor TR1 and the finite 
resolution of preset VR1. A flickering of 
the last decimal place in this case within the 
range 000-2 does not impede the usefulness 
of the adaptor, particularly if the calibra- 
tion resistor is not better than a one per 
cent type. 


Some DVMs have a lowest d.c. range of 
400mV. These can still be used, adjusting 
the multi-turn presets to provide a full scale 
at the 100mV point. 


Fig. 4. Layout and drilling details for the case. 

There is no reason why an analogue 
meter, possibly with an f.s.d. of 100A to 
500n.A cannot be used in place of a DVM. 
However, a lot depends upon the internal 
resistance and it is possible that anything 
above a few hundred ohms may not enable 
f.s.d. to be obtained. 

If you have a meter with a lowest range 
of 100mV, it is worthwhile doing a bit 
of experimenting with it. By using a larger 
case, such a meter could be built into 
it, so making up a compact low range 


Everyday with Practical Electronics, September 1995 


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The National College of Technology offer a range of 
packaged learning short courses for study at home or in 
an industrial training environment which carry modular 
BTEC awards leading to a higher BTEC certificate. Study 
can commence at any time and at any level enabling you 
to create a study routine to fit around existing commit- 
ments. Courses on offer include: 

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Digital Electronics 
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Tutor support and BTEC certification are available as 

| options with no travelling or college attendance re- 

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lecturettes, PCB’s, instruments, tools, components and 
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Everyday with Practical Electronics, September 1995 


Constructional Project 




All-round protection for the garden 
shed, garden furniture, garage and 

e home. 

OUSE break-ins have been a problem 

for a long time, but in recent years 

the problem of theft from gardens, 
garden sheds and garages has escalated 

This is probably partly due to the fact 
that a garden shed may be quite easy to 
break into and therefore offer an oppor- 
tunity for the thief where there is a low risk 
of being caught. Furthermore, the average 
garden shed is now home to a great many 
expensive items such as mountain bikes, 
lawnmowers, power tools, etc. 

The total value of the items in many 
cases may well exceed a thousand pounds. 
Thieves know this, and they also know that 
they can sell such items quickly for “easy 
money’. Many readers will relate to this 
problem from bitter personal experience — 


as does the author, which is how the idea 
for this project came about. 

The design is mains powered but a 
rechargeable battery is used as a backup if 
the mains fails or if any of the wires are 
cut. The battery and the siren are housed 
outside in a standard alarm bell-box. If 
someone tries to tamper with the bell-box 
the siren will sound. An internal buzzer is 
included. The basic sensor system is in the 
form of a balanced resistive loop, al- 
though provision has been made for pas- 
sive infra-red (PIR) sensors to be used as 


The basic operation of the alarm is 
shown in the block diagram in Fig. 1. 
It comprises internal and external sensor 


circuits, both partly interlinked. Consider- 
ing the internal section of the alarm first, in 
which PIR sensors can be used, when the 
keyswitch is opened there is a 30 second 
delay before the alarm becomes active. 
This allows the householder to switch the 
alarm on and leave the house without it 
being triggered. 

If, after this delay, one of the sensors is 
triggered, there is a 15 seconds delay before 
the alarm is set off, which should allow 
enough time for the householder to switch 
the alarm off after re-entering the house. If 
the external siren is set off, it continues to 
sound for 20 minutes before being auto- 
matically switched off. 

For the external alarm, a resistive wire 
loop is used as the sensor. The operation 
of this circuit is controlled by a switch. 
When the switch is opened, there is a delay 
of approximately seven minutes before the 
alarm becomes active. This allows plenty 
of time to switch on the alarm, leave the 
house, take the car out of the garage, and 
so on, before the alarm becomes active. 



Everyday with Practical Electronics, September 1995 

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mem hb hie 

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Fig. 2. How the resistive loop might be routed. The options are limitless. 

After this period, if the alarm is tripped, 
the buzzer inside the house will sound, but 
there will be a delay of about two minutes 
before the external siren sounds. 

There several advantages to configuring 

the alarm in this way. First of all, it allows 

time to put the car back in the garage, enter 
the house and switch off the alarm before 
the external siren sounds thereby “crying 
wolf’ to the displeasure of neighbours. 

Also, if someone raids the garden shed in 
the middle of the night, the internal buzzer 
will go off immediately, but the thief will 
not know that he has been rumbled. There 
is then a choice: switch off the alarm and 
telephone the police, hoping they will ar- 
rive before the thief disappears with the 
best power drill. Alternatively, the alarm 
could be left on, allowing the external 
siren to sound, which would hopefully 
encourage the thief to make a hasty retreat. 

All delay times can be changed during 


The internal section of the alarm is in- 
tended to be used with commercially avail- 
able PIR sensors. These can be powered 
from the alarm’s 13-8V power supply. The 
sensors contain normally-closed relay con- 
tacts and any number of sensors can be 
wired in series! Using this type of sensor 
offers the minimum fuss since there is little 
wiring. Microswitches, magnetic. switches 
or pressure pads and the like could be used 

Externally, bell wire is used to form the 
resistive loop around the garden shed, 

garden bench, garage and tools, etc., as 
shown in Fig. 2. Taking the example of the 
garden shed, microswitches or magnetic 
switches can be fitted to the doors (mag- 
netic switches are usually better since they 
tolerate more play). 

If the shed window is large enough to 
need. protecting, conductive tape could be 
used, or a fine piece of wire stretched across 
it, supported by nails. If the window is 
broken, the wire will break, opening the 

For individual items that need to be 
protected but remain accessible to the 

Fig. 3. Power supply and decoupling capacitor details. 

Everyday with Practical Electronics, September 1995 

owner, the garden bench for example, a 
phono line plug and socket pair can be 
inserted into the loop. The loop can then be 
passed through one of the bars in the 
bench. Each connector pair has a resistor 
wired into it. 

The resistive loop forms one arm of a 
potential divider, the resultant potential 
being fed to a “windowed” comparator. In 
conventional loop alarms, the loop is a 
short circuit and the alarm will only trip if 
the loop is opened. This type of system 

could easily be disabled if a shorting link is 

made across the cable. 

In the system described here, if the 
loop is opened, shorted or its resistance 
changed, the potential at the sensing com- 
parator will change and the comparator 
will trip. Using this technique, almost any 
item can be protected. It is very difficult to 
bypass this type of loop. 

With the prototype, the bell wire was laid 
under the garden path, a spade being used 
to prise up the slabs just enough to tuck 
the wire underneath. This meant that no 
part of the wire could be seen, which was 
desirable though not completely necessary. 

There is no reason why the wire should 
not be suspended overhead, or laid under 
a hedge, for example. However, it would 
be a good idea to protect sensitive areas of 
the wire by passing it through a length of 
thin-bore plumbing pipe, or similar. This 
would prevent the local rabbit population 
from chewing through the loop during the 


The circuit diagram for the mains 
operated power supply used in the alarm 
system is shown in Fig. 3. The secondary 
a.c. voltage from transformer T1 is bridge 


Fig. 4. Circuit diagram for the main part of the alarm sytem. 

rectified by REC1, smoothed by capacitors 
Cl and C2, and regulated down to 15V d.c. 
by IC1. Diodes D1 and D2 then drop this 
voltage down to approximately 13-8V, a 
voltage chosen because it is the recom- 
mended float charging voltage for the lead 
acid back-up battery. 

Since spikes could appear on the sup- 
ply line, which could possibly trigger the 
alarm, a voltage dependent resistor, VDR1 
is included. This is an 18V device which 
reduces spike levels should they occur, 

Unplugging the connector looped 
around the garden bench will auto- 
matically set off the active alarm. 


thereby reducing the possibility of a false 

The siren used in the system draws about 
300mA when operating. Depending on the 
type used, the PIR sensors could draw up 
to 40mA each. The float charging current 
for the battery is about 10mA. 

Using a 15V 12VA transformer, the max- 
° % ° ° 
imum output current available is a little 

over 0:5A, which should be adequate for 

most systems. 

Also shown in Fig. 3 are the decoupling 
capacitors placed across the i.c. power sup- 
ply pins. The capacitors help to reduce 
noise and to stabilise the voltage across the 
devices whilst they are switching. 


The circuit diagram for the main part 
of the alarm system is shown in Fig. 4. 
Taking the internal section of the alarm 
first, with the keyswitch S3 in the OFF 
state, input pin 6 of Schmitt NAND gate 
ICSb is held low via resistor R19. Regard- 
less of the logic level on the other input, pin 
5, the gate’s output at pin 4 will be high, 
thereby holding the JK bistable IC6b reset 
via its pin 12. In this state, the condition of 
the sensors has no effect. 

When the keyswitch is switched to the 
ON state, enabling the alarm, capacitor 
C17 starts to charge up via resistor R20. 
After around 30 seconds, when C17 has 
charged up sufficiently, ICSb pin 4 goes 
low, removing the reset signal from IC6b. 
This timing forms the exit delay to allow 
the house to be left after the alarm is 

switched on. Light emitting diode (l.e.d.) 
D10 is turned on when the circuit is active, 
resistor R21 limiting the current drawn. 

After this exit delay, if any of the sensor 
switches (S2a, S2b etc.) are opened, input 
pin 13 of Schmitt NAND gate ICS5a will 
rapidly rise from logic 0 (low) to logic 1 
(high). Since ICSa pin 12 is already held 
high via resistor R20, ICSa output pin 
11 will go low and, via inverter IC4f, 
send a positive-going clock pulse to IC6b. 
Capacitor C16 is included to provide filter- 
ing of the loop line to protect against minor 
noise levels, 

The clock pulse triggers the bistable such 
that its Q output pin 14 goes low, which in 
turn causes NAND gate ICSc output pin 3 
to go high (ICSc pin 1 is already held high 
at this time). Capacitor C18 now starts to 
charge up via resistor R22. After about 15 
seconds, when C18 has been charged suffi- 
ciently, the output of Schmitt inverter IC4d 
will go low. This timing forms the entry 
delay so that the alarm can be switched off 
after re-entering the house. 

When output pin 4 of inverter IC4d goes 
low (an action which causes the siren to 
sound), reset pin 11 of counter IC7 also 
goes low, so enabling the counter. The 
counter is now clocked via its pin 10 by the 
output signals from the astable multi- 
vibrator formed around Schmitt NAND 
gate ICSd. Resistor R24 and capacitor C19 
set the clock frequency to a little less than 
1Hz. (Decreasing the value of either com- 
ponent will increase the frequency.) 

Once enabled, counter IC7 counts 1024 
pulses and then its output Q11, pin 1, goes 

Everyday with Practical Electronics, September 1995 

=m mth om 

she me Me ee 

high. Inverted by IC4e, output Q11 now 
causes bistable IC6b to be reset via ICSb. 
This action propagates through the circuit, 
resetting counter IC7, and also turning off 
the siren control line. 

When [CSc output pin 3 goes low, 
capacitor C18 is rapidly discharged via 
diode D8, so there is no delay in the alarm 
switching off. The clock frequency as 

described provides a siren sounding time of 

around 20 minutes. With the counter once 
again reset, the alarm is reprimed and 
ready to be triggered if a sensor is tripped. 


Still referring to Fig. 4, the outdoor sec- 
tion of the alarm works as follows: 

Resistor R2 and Zener diode D4 set a 
10V reference voltage. Via the chain of 
resistors RS to R7, this voltage is divided 
down to provide 5:5V at the non-inverting 
input of op.amp IC2a (pin 3) and 4-5V at 
the inverting input of op.amp IC2b (pin 6). 
Both op.amps are configured as “win- 
dowed’’ comparators, in this instance, the 
“window” being the 1V differential be- 
tween the 4:SV and 5-5V reference voltages. 

The external loop total resistance is 
designated as R4 in the dotted box to the 
top left of Fig. 4. Between them, resistance 
R4 and preset variable resistor VR1 form a 
potential divider, whose junction voltage 
(at test point TP1) is set for approximately 
5V. Via resistor R3, this voltage is applied 
equally to IC2a pin 2 and IC2b pin 5S. 

Feedback resistors R8 and R9 provide 
hysteresis for the two comparators so as to 
ensure a clean switching action. Decou- 

‘pling capacitors C10 to Cl2 are used to 

reduce the possibility of false triggering by 
noise signals. 

With the potential at TP! set for SV, the 
outputs of both comparators are both close 
to the positive supply line voltage, provid- 
ing a logic | level to the inputs of Schmitt 
NAND gate [C3a. 

If the resistance of the sensor loop is 
increased, the voltage at TP1 will drop. 
Should it go below 4-5V, comparator IC2b 
will be triggered and its output go low. 
Similarly, if the loop resistance decreases, 
the voltage at TP1 will rise. If it rises above 
5:5V the output of comparator IC2a will 
go low. 

If either comparator output is triggered 
low, IC3a pin 4 will go high, applying the 

same level to pin 12 of Schmitt NAND 
gate IC3c. Resistor R10, capacitor C13 and 
diode D5 are included to reduce the pos- 
sibility of a false alarm. Provided that this 
end of the circuit is active, the high output 
of I1C3a will propagate through IC3c and 
IC4b providing a positive-going clock sig- 
nal to pin 3 of bistable [Céa. ! 

When triggered by the clock pulse, 
output Q of IC6a goes high, turning on 
transistor TR1 via resistor R15. As a 
result, buzzer WD1 is activated. Addition- 
ally, capacitor C15 starts to charge up via 
resistor R14. After about 105 seconds, or 
so, the output from Schmitt inverter IC4c 
goes low, causing the output from NAND 
gate ICSc to go high. From this point on, 
the operation of the circuit is exactly the 
same as for the internal section of the 
alarm. Diode D7 speeds up the discharg- 
ing of C15 at the end of the 20 minutes 

The delay caused by the combination of 
R14/C15 and R22/C18 gives a total delay 
time of about two minutes between the 
sounding of the internal buzzer and the 
sounding of the external siren. 

Activation of this part of the circuit is 
controlled by switch S1. With S1 in the 
OFF condition, the two inputs to Schmitt 
NAND gate {C3b are held low via resis- 
tor R12. When this circuit section is first 
switched on by S1, capacitor C14 starts to 
charge up through resistor R11. Then, after 
about seven minutes, IC3b output pin 3 
goes low, and via inverter IC4a, takes IC3c 
pin 13 and IC3d pin 8 high. This period 
provides the required exit delay. 

At the end of the delay, IC3d output pin 
10 goes low, removing the Reset level from 
bistable IC6a pin 4. After this, if the loop 
resistance changes enough to trip either of 
the comparators, the output of IC4b will 
go high, triggering IC6a. 


The circuit diagram for the siren driver 
is shown in Fig. 5. This uses a win- 
dowed comparator in the same way as the 
loop sensor, formed here around op.amps 
IC8a and IC8b. The reference voltages are 
provided by the potential divider formed 
by resistors R26, R28 and R30. The alarm 
signal voltage is brought to the junction of 
resistors R27 and R29 (test point TP2). It 
is then fed via R27 equally to the two 

Fig. 5. Circuit diagram for the siren driver. 

Everyday with Practical Electronics, September 1995 

The siren, its sub-assembly board and 
back-up battery may be mounted in the 
same housing. 

op.amps. Capacitor C20 mops-up minor 
noise signals. 

If the wire between the main alarm cir- 
cuit and the siren driver is tampered with, 
or if the alarm signal line goes low (from 
IC4d via R23) due to one of the sensors 
being tripped, the voltage at TP2 changes. 
One or other of the comparators (depend- 
ing on the polarity of the voltage change) 
then trips and its output goes high, turn- 
ing on MOSFET TR2 and so sounding the 
siren, WD2. Diodes D11 and D12 prevent 
conflict between the two op.amp outputs. 
Resistor R31 provides a discharge path for 
TR2’s gate capacitance. 

This section of the alarm, together with 
the lead acid battery, is housed externally 
in a bell-box. The fuse protects the battery 
from short circuit should the wire from the 
main alarm circuit to the bell-box be cut. 

Resistor R25 couples the power rail back 
to l.e.d. D9 in the main circuit. Together 
with l.e.d. D3 of the power supply, this 
gives a positive indication that the supply 
rail throughout the alarm system is heal- 
thy. On the front of the bell-box l.e.d. D13 
gives a visual indication to passers-by that 
the bell-box is not empty! When the siren 
sounds, l.e.d. D14, which is also on the 
front of the bell-box, flashes thereby giving | 
a visual fix on where the noise of the siren is 
coming from. 

Diode D15 reduces the voltage across 
l.e.d. D14 to around 10V. The latter’s max- 
imum working voltage is 12V so the 13.8V 
supply could destroy it if D15 was omitted. 

Should someone try to remove the lid- 
retaining screw from the bell-box, micro- 
switch S4 will close, so changing the volt- 
age at TP2 and setting off the alarm. 


The various delays incorporated into the 
alarm were designed for a specific user and 
these delays may not meet the requirements 
of all readers. Table. 1 shows which com- 
ponents are responsible for the delays and 
can be used to calculate component values 
for other timings. 

All quoted delays are approximate, 
especially the seven minute one, since 


capacitor tolerances are quite wide and the 
higher capacitor values have larger leakage 
currents. Furthermore, the exact delay is 
dependent on the logic threshold of the 
Schmitt trigger gates, a level which 
may vary between devices from different 
manufacturers and between production 

=~=N<xF<ccuwmwMDOVvOZEr Rei _ LOAM. w > 



joints for the main alarm circutts. 



The 20 minutes siren sounding delay 
can be changed in two ways: one of the 
other counter outputs could be used in- 
stead of output Q11, or the clock fre- 
quency generated by ICSd could changed. 
Smaller values of either resistor R24 or 
capacitor C19 will result in shorter delay 
times. | 

15 16 

67 8 9 10 1112 B14 

Fig. 6. Topside component layout and underside stripboard track cuts and solder 


The alarm system is constructed on two 
pieces of 0-1 inch grid stripboard. Com- 
ponent layout, soldering points and track 
cutting details for the main circuit are 
shown in Fig. 6. Similar details for the siren 
driver circuit are given in Fig. 7. . 

There are many track cuts to be made 
and it is probably best if they are cut after 
assembling the components. Beware not to 
exert too much pressure on the stripboard 
when making the cuts — it is fragile and 
could break, especially when several cuts 
are in line. The use of a proper track cut- 
ting tool is recommended. Make sure that 
the tracks are cut cleanly and that there are 
no whiskers of copper left dangling loose. 

Assembly of the components can be 
carried out in any order you feel content 
with, ideally starting with the lowest profile 
components. Remember to include all of 
the link wires shown. The use of i.c. sockets 
is strongly recommended. 

Take care over the polarities and 
orientations of the electrolytic capacitors 
and semiconductors. Treat all the i.c.s as 
CMOS devices, taking the usual precau- 
tions to discharge static electricity from 
your body before handling them. Follow- 
ing assembly, thoroughly check that sol- 
dered joints are satisfactorily made and 
that the components are indeed correctly 

123 465 6 7 8 9 10111213 14 15 16 17 
AC OOM@@0808G00eCCOD 
BOMO0MO000000000 8008 
cl 000080000 €H@00 8 
DO oO®O0G@00CM0eG80000 
FOO0000 @@ 0000080000 
Ge @0008 00800 8@00 
KO 0MF00000000000000 
LO @O) @0@00008000808 


Fig. 7. Stripboard assembly details for 
the siren driver circuit. 

Everyday with Practical Electronics, September 1995 

ey ‘iy eae a 


Resistors 15, ; SOP 
R3, R6, Rov, "” TALK 

R28,R31 10k (5off) Page 
R4 4k7 (see text) 

R5, R7, R15, 

R23, R29 47k (5 off) 
R8, RO 1M (2 off) 
R10, R17 100k (2 off) 
R11 3M9 
R12,R18,R19 10Q (3 off) 
R13,R21,R25 1k2 (3 off) 
R14, R24 3M3 (2 off) 

R16 4k7 

R20 1M5 

R22 470k 

R26, R30 22k (2 off) 

VDR1 18V voltage 
dependent resistor 

VR1 100k multi-turn preset 

C1 2200n elect. 25V 
C2 to C12, 
C16, C20, C21 100n (14 off) 
C13, C19 1p elect. 63V (2 off) 

C14 100p elect. 16V 
C15,C17,C18 33p elect 16V (2 off) 

D1,D2 1N4001 diode (2 off) 
D3, D6, 
D10 _ l.e.d., red (3 off) 
D4 BZY88C 10V Zener diode 
D5, D7, 
D8, D11, 
D1i2  1N4148 signal diode (5 off) 
D9 l.e.d., yellow, 10mm, 
rectangular plus holder 
D13 l.e.d., green, 10mm, 
rectangular plus holder 
D14 l.e.d., red, flashing, 10mm, 
rectangular plus holder 
D15 BZY88C 3V9 Zener diode 
TR1 BC108 npn transistor 
TR2 BUZ10 MOSFET n-channel 
power transistor 
IC1 7815 voltage regulator 
IC2,1C8 LM385 dual op.amp (2 off) 
IC3,1C5 4093 quad 2-input Schmitt 
NAND gate 
1C4 40106 hex Schmitt inverter 
IC6 4027 dual JK bistable 
IC7 4040 12-stage counter 
REC1 50V 1A bridge rectifier 

T1 15V-OV 15V-OV, 12VA 
mains transformer 
250mA 20mm fuse and 
panel mounting fuseholder 
1A 20mm fuse and 
p.c.b. mounting holder 
buzzer (see text) 
siren (see text) 
dual light switch (see text) 
see text 
s.p.d.t. keyswitch 
S.p.c.0. Microswitch 
see text 
8-pin phono line socket 
8-pin DIN chassis socket 
8-pin phono line plug 
8-pin DIN line plug 
Stripboard, 0-1 inch matrix 19 holes x 
16 strips, stripboard 0-1 inch matix 45 
holes x 40 strips; diecast metal box 
190mm x 108mm x 60mm; 12V lead 
acid battery; commercial detectors as 
appropriate (see text); bell-box to suit; 
connecting cable; wire; solder, etc. 


y Voy el gey. aext t 
guidance only 

Table 1. Delay Times. 

Delay Calculation Time 
House Exit 0-6 x R20 x C17 Seconds 0-6 x 15M x 33 = 30 Seconds 
House Entry R22 x C18 Seconds 470k x 33 = 15:5 Seconds 
Loop Exit 1:1xR11xC14Secondsfor 1:1x3:-9Mx100y = 429 Seconds 

large C with high leakage 

= 7 Minutes 

0-6 x R11 x C14 Seconds for 
small C with low leakage 

Loop Entry 

The main alarm circuit board should be 
housed in a suitable metal -box which 
provides screening. Holes should be drilled 
to suit the l.e.d.s, keyswitch, mains cable 
and the DIN socket used to connect to the 
rest of the system. | 

Holes should also be drilled to mount the 
transformer and, if required, to allow the 
box to be mounted on the wall. Holes are 
needed as well to allow the buzzer to be 
heard. The main stripboard can be used as 
template for the positions of the holes for 
the spacers on which the board is mounted. 

Once all the holes have been drilled and 
filed as required, the front panel can be 
finished off. The front panel can be sprayed 
using car touch-up paint, for example. 
Rub-down lettering can be used to provide 
suitable legends on the front panel, then 
spraying it with a clear protective lacquer. 

The board, transformer and the rest of 
the hardware can now be fitted to box and 
wired up as shown in Fig. 8. The Live and 
Neutral wires of the mains cable can be 
soldered directly to the transformer ter- 
minals. The Earth wire should be secured 
to the case using a solder tag. A locking 
cable grommet should be used to secure the 
cable to the case. 


Everyday with Practical Electronics, September 1995 

R14 x-.C15 Seconds 
+ House Entry Delay 

3°3M x 33 + 15-5 Seconds 
= 108 + 15:5 = 123-5 Seconds 
= 2 Minutes 

If the suggested transformer is used the 
two secondary windings should be wired in 
parallel (as shown) to provide the required 
output current. _ 

An insulating bush and washer should be 
used when mounting the voltage regulator 
to the case. The latter provides heat sinking 
for the regulator. 


With the prototype, a conveniently 
located domestic wall-mounted switch, 
normally used to control an outside light, 
was modified for use as switch Sl. The 
original single-switch unit was removed 
and replaced with a double-switch unit. 
One switch was used to control the 
light as before, the other was used as S1. 
The switch must be the changeover 

A hole was drilled into the switch plate 
to suit l.e.d. D6. Ensure that the l.e.d. can- 
not be dislodged and come into contact 
with the mains wiring of the light switch. 

If preferred, S1 could be an ordinary 
s.p.d.t. toggle switch located in the main 
alarm box. 


Fig. 8. Wiring details for the control box. = ~_ 


The main alarm box can be located in 
any convenient position. The prototype 
was located in the cupboard containing the 
household mains fusebox and the alarm 
was wired directly into this. 

The siren drive board was housed in a 
ready-made bell-box along with the backup 
battery, siren and anti-tamper switch S4. 
Holes can be drilled to take spacers on 
which the circuit board can be mounted. It 
would be a good idea to spray the board 
with protective coating since it is likely to 
be exposed to damp conditions outside. 

The siren was bolted to appropriate 
mounting holes in the box and the battery 
was placed on the shelf provided. An 
existing hole was used for mounting switch 
S4. Two holes were drilled in the front of 
the box to take l.e.d.s D13 and D14. 

The inside of the bell-box should be 
wired as per Fig. 9, but leaving the siren 
and switch S4 disconnected. The box can 
be fitted to the side of the house, using a 
masonry drill to drill holes into which 
Rawlplugs, or similar, can be inserted. The 
bell-box can then be secured to these. 

Referring to the interconnection diagram 
of Fig. 10, the cable for the DIN plug 
should be routed from the main alarm unit 
up to the roof space where it can be wired 
into an 8-way junction box. Four-core 


cable is used to connect between. the junc- 
tion box and the bell-box. 

Using a suitable masonry drill, the wire 
could be passed from the bell-box straight 
through the wall into the roof space and 
then to the junction box. If this is not pos- 
sible, the wire should be routed through the 
eaves as unobtrusively as possible. 

Similar cable can be used to connect PIR 
sensors, although care should be taken to 
avoid running this cable parallel to mains 
wiring. Bell wire for the sensor loop can 
be brought straight into the roof space and 
connected up in the junction box. Once the 


wiring has been completed the unit can be 
tested. After which the front of the bell-box 
can be secured. 


When testing, beware that mains volt- 
ages are present. Extreme care should be 
taken. If in any doubt, consult a qualified 

Before powering up the alarm, the resis- 
tance across the d.c. supply lines should be 
checked. This should be in excess of six 
kilohms (6k). If it differs greatly check the 
position and orientation of all components 
and ensure that all the tracks are correctly 

With the keyswitch (S3) and switch S1 
turned off, switch on the mains supply. The 
three l.e.d.s D3, D9 and D13 should light, 
and there should be no sound from the 
buzzer. Check that the power supply is 
delivering an output of 13-8V at the junc- 
tion of D2 and VDRI1. 7 

With the external loop complete — no 
doors open, etc. — measure the voltage at 
test point TP1. Adjust preset VR1 until a 
reading of SV is obtained. Check that the 
voltage on IC3 pin 12 is zero (logic 0). 
The voltage on IC6 pin 4 should be high 
(13-8V). Open switch S1 and verify that 
l.e.d. D6 lights and that IC6 pin 4 goes to 
logic 0 after around seven minutes. 

Open and then close the resistive loop 
and verify that the internal buzzer sounds 
immediately and the alarm signal line (at 
TP2) goes low about two minutes later. It 
might be a good idea to muffle the buzzer 
during this test! 

Open the loop once more and verify that 
again the buzzer starts to sound. Switch off 
S1 — the buzzer should stop and l.e.d. D6 
should turn off. 

Connect the external siren and then 
switch on keyswitch $3. Check that 1.e.d. 
D10 turns on and that IC6 pin 12 goes low 
about 30 seconds later. Trip one of the 
sensors and ensure that after 15 seconds the 
external siren sounds and that l.e.d. D14 
flashes. Switching off the keyswitch should 


Fig. 9. Wiring details for the bell(siren)- box. 

Everyday with Practical Electronics, September 1995 


turn off the siren, D10 and D14. Switch off 
the mains power and verify that l.e.d. D3 
goes out. 

Anti-tamper switch S4 can now be con- 
nected, at which juncture the siren will 
sound! Ignoring the noise, fit the front 
panel to the bell-box. Once the main screw 
is firmly screwed in the siren should be- 
come silent. 

Note that it is unwise to connect or 
disconnect the DIN connector whilst the 
alarm is powered up since this may upset 
the CMOS i.c.s. 

The alarm can now be put into per- 
manent operation. 


The author’s alarm has been in operation | BELL BOX 
for many months and fortunately there has : 
been no attempted break-in during that | 
time. There was a false alarm during this | | 
period but this was found to be due to 

excessive play in one of the doors of the 
garden shed. The author thus assumes that 


the system is extremely reliable, which is an | 
important feature — too many false alarms | 
would destroy the perceived effectiveness of SUPPLY | 
the system. 
If the internal buzzer is found to be too | 7 
quiet it could be replaced by a buzzer Fig. 10. Suggested system interconnection details. 

located outside the main alarm box, 
replacing the 8-pin connector by a 13-pin 

type. Two of the spare pins on the 
replacement connector can be used to take 
the buzzer wires through the box. The 
current consumption of any buzzer should 
not exceed 100mA. 

Usually in alarm systems a strobe light is 
used instead of a flashing l.e.d. The lat- 
ter was chosen here because it was much 
cheaper than a strobe light, although still 
surprisingly effective. However, if a strobe 
light is preferred in place of l.e.d. D14, it 
Should be wired in parallel to the siren. 
In this case both D14 and D15 can be 

The system caf be easily adapted to in- 
clude a panic switch. The normally closed 
contacts of this switch could be wired into 
the loop, or the normally open contacts 
could be wired between the alarm signal 
line and the OV line. Similarly, the unit 
could be expanded to include a fire alarm 
by using a smoke alarm having relay con- 
tacts which should be wired in the same 
way as suggested for the panic switch. O 


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The binders are finished in hard wearing royal blue p.v.c. with the 
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The price is £5.95 plus £3.50 post and packing. If you order more than 
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Everyday with Practical Electronics, September 1995 

Our regular round-up of readers’ own circuits. We 
pay between £10-£50 for all material published, 
depending on length and technical merit. We're 
looking for novel applications and circuit tips, not 
simply mechanical or electrical ideas. Ideas must 
be the reader's own work and 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 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, 

Tone Burst Generator 
= forcine symc. controll 

HE device shown in the circuit design 

Fig. 1 was designed initially for cine 
work, to create a tape containing tone 
bursts at a rate of between 18 to 24 times 
a second. It has flexible input and out- 
put arrangements and can no doubt be 
adapted to other electronic applications, 
perhaps as a gated signal injector or tone 

The design is based around two square 
wave oscillators, each formed from a pair 
of NAND gates. IClc and ICld together 
form an audio oscillator which operates 
as follows: 

Assuming that both inputs to IClc are 
low, the output (pin 10) will be high. ICld 
inverts this to low, causing capacitor C2 
to charge through resistor R6. When the 

junction of R6/C2 rises to half the sup- 
ply rail, pin 10 swings low and conse- 
quently ICld output goes high, causing 
C2 to start discharging through resistor 
R6. The outputs eventually change state 
again, this process continuing at an audio 

The other generator ICla and ICI1b 
operates in a similar fashion, but at a 
lower rate which can be adjusted with 
preset potentiometer VR1. Resistors R1 
and RS5 pull down the oscillator inputs to 
OV which inhibits their operation. 

Normally, the output of the lower- 
frequency generator gates the audio fre- 
quency generator. However, by inserting a 
jack plug into socket SK1, this connection 
is broken. The user can then control the 
operation of the unit by providing a high 
gate signal into the jack socket; connec- 
tion “A” will gate the slow stage whilst 
connection “*B”’ controls the audio stage. 

PIN 14 


SK1, 2 = STEREO 3-Smm JACK 



3-Smm JACK 


BH21 1PF. They could earn you some real cash! 

The output of the lower frequency gate 
is also brought out to SK2. Depending 
on the connection, you can either create 
an active high arrangement (connection 
“C’’) or a “‘pull down’”’ function (connec- 
tion “‘D’’) where a suitable load maybe 
returned to either the negative or positive 
rail respectively. 

Socket SK3 offers a high impedance 
tone output for recording or monitoring 
with a crystal earpiece. Transistor TR3 
offers a visual indication, via l.e.d. D2, 
that tones are being produced. 

In the prototype, l.e.d. D2 was used to 
strobe perforated tape having 18 holes 
per 3-75” (18 holes per second). Preset 
VRI1 was then trimmed until the holes 
appeared static, when the unit was then 
known to be running at exactly 18 pulses 
per second. 

Chris Brown, 
Witham, Essex. 

Cc . 

Fig. 1. Circuit diagram for the Tone Burst Generator. 


Everyday with Practical Electronics, September 1995 

Doorchime Disabler 
= ring tlhe clhamges 

RIGINALLY designed for the “Goods 

Inwards”’ bell of a retail outlet, the 
adaptable circuit of Fig. 2 could be used 
as a domestic doorbell to prevent the 
nuisance caused by a caller pressing the 
bell-push excessively. The circuit consists 
of a piezoelectric sounder acting as a door 
chime, along with a modified bell push- 
switch. The proposed system functions 
with existing twin-core bell wire, if already 

In operation, a green I.e.d. D4 mounted 
on the bell pushswitch itself, illuminates 
after the switch has been pressed. A pulsing 
bleep tone then sounds for approximately 
80 seconds, during which time any fur- 
ther operations of the pushswitch have no 


At the end of this period, the system 
resets and the green l.e.d. is extinguished. 
Alternatively the system can be reset using 
a separate “manual” pushswitch mounted 

In Fig. 2, in the reset condition the green 
l.e.d. diode D4 together with diode D5 
are reverse biased. On closing the bell 
pushswitch §2, D3 is forward biased which 
pulls IC3b output (pin 11) high. 

Pin three of IC2 is now clocked which 
takes its Q output (pin 1) high. This is 
inverted by IC3c whose pin 4 is now low. 
This is complemented by pin 3 of IC3d 
which is now high. Hence l.e.d. D4 be- 
comes forward biased and illuminates, with 
resistor R5 limiting the current. 

An astable formed by IC3a is now 
enabled, clocking the ripple counter IC1. 
Transistor TR1 is energised by the Q7 
output (pin 6) of the 4020 and completes 

the circuit to the piezo sounder WD1 
which pulses and the red l.e.d. D1 flashes. 
When Q14 (pin 3) of the counter reaches 
logic 1, IC1 and IC2 are reset via diode 

A “manual” reset can be forced by clos- 
ing pushswitch S1, diode D2 preventing 
current sinking into the Q14 output. Resis- 
tor R3 prevents false resetting. 

The prototype was powered by a 
PP3 battery. Quiescent current was im- 
measurably small when reset, rising to 
9mA when triggered. For best effect, l.e.d. 
D1 should be a Superbright red type and 
the green device D4 a low current type, 
mounted out of direct sunlight near the bell 

David Geary, 

a k 


LA 1N4148 

Fig. 2. Circuit diagram for the Doorchime Disabler. 

Solar-Driven Battery Recharger 

= another bright idea! 

AVING a 12V solar panel to hand, and 

being interested in renewable energy 
sources, I designed the simple circuit 
shown in Fig. 3 to enable my solar panel 
to be adapted to recharge a set of four 
nickel-cadmium (NiCad) batteries. I have 
found it especially valuable when camp- 
ing, as it kept a lamp and radio powered 
successfully. : 

The circuit is based around a con- 
stant-current source powered by the 12V 
200mA solar array B5. The supply voltage 
seems to vary from 12V to 15V when 
charging. This is used to power a constant 
current source based around transistor 

The four rectifiers Dl to D4 each 
develop approximately 0-7V across them 
when conducting, or roughly 2-8V in 
total. The base-emitter junction of TR1 
loses 0:7V of this and the remaining 2-1V 
appears across resistor R2. 

A constant current of 30mA therefore 
flows through R2. I subsequently added 

the l.e.d. D6 which illuminates directly 
from the potential across R2 and draws a — 

further 10mA or so. 

A total charging current of 40mA there- 
fore flows through the four recharge- 
able batteries (B1 to B4), and l.e.d. D6 
illuminates: when the rechargeable bat- 
teries are inserted correctly. The addi- 
tional diode D5 prevents the batteries 
from discharging back into the solar panel 
when the sun goes in. The transistor and 
rectifiers chosen, happened to be available 
but substitute types would be fine. 

David Dawson AMIEE BSc., 

Everyday with Practical Electronics, September 1995 

Fig. 3. Circuit diagram for a solar- 
driven battery charger. 


HE circuit diagram of Fig. 4 will check 

the continuity of cables, connectors etc. 
as well as testing the function of light-emit- 
ting diodes (l.e.d.s). 

Transistors TR3 and TR4 with as- 
sociated components together form a 
transistor astable multivibrator. The piezo 
sounder WD1 will generate an audible tone 
when the astable operates. 

Transistors TR1 and TR2 act as a switch 
to energise the audio oscillator. When 
continuity exists between sockets SK3 and 
SK4, the transistor switch completes the 
supply to the astable which will drive the 
piezo sounder. An l.e.d. test facility is 
available via SK1 and SK2, with resistor 
R1 limiting the forward current to about 

The circuit can be powered from a 9V 
' PP3 battery. No on-off switch is required 
because only a tiny leakage current flows 
when the circuit is not in use. 

E.W. Fair, 

Stoke-on-Trent, Staffs. 

Rapid Crystal Checker 
= GOrmoO-go indicator 

Y CIRCUIT diagram shown in Fig. 5 

will oscillate with almost any crystal 
or ceramic resonator. Oscillation is indi- 
cated by an l.e.d., which is much more 
economical than a meter. X1 is the quartz 
crystal or resonator under test, and if the 
circuit does not oscillate then the collector- 

Continuity and L.E.D. Tester - wires buzz off? 

Fig. 4. Circuit diagram for the Continuity and L.E.D. Tester. 

or similar which decouples the l.e.d. to 
prevent it from quenching oscillation. 

The components shown were “‘junk box”’ 
items, and in practice any silicon transistor 
should work satisfactorily. The l.e.d. was a - 
2000mced high intensity type which gave a 
good level of light output at very low‘cur- 
rents. R.F. precautions are required when 
constructing the circuit, ensuring leads are 
as short as possible otherwise they can act 
as a tuned circuit. 

emitter voltage across transistor TR1 is 
insufficient to illuminate the l.e.d. D1. The 
diode D2 is a germanium type AA119 

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Fig. 5. Rapid Crystal Checker circuit 

Battery Charger Current Control = take 

Di - D4 SOV PIV 6A 
Table. 1. 

PL1 Charge 
connected Current 
to: (A) 
SK1 6:2 
SK2 4:5 
SK3 3:0 
SK4 1:6 
SK5 1:0 

Fig. 6. Battery Charger Current Control 
circuit diagram. 

UDGET mass-produced car battery chargers do not often have 

any form of charge current control. Whilst this isn’t a problem 
for ordinary trickle charging, when trying to re-charge a very flat 
battery, heavy currents flow and it may be desirable to limit the 
charge current in order to reduce the load on the transformer within 
the charger. Fig. 6 depicts a very simple means of selecting the charge 
current. The design is suitable for battery chargers rated up to SA. 

The circuit uses silicon rectifiers as voltage droppers to reduce the 
voltage applied across the car battery. Each rectifier drops approxi- 
mately 0:7V when fully conducting. It was found that four rectifiers 
in series gave sufficient control for normal use with my battery 
charger, but more could be added if needed. 

The appropriate number of rectifiers is selected by inserting PL1, a 
4mm wander plug, into the appropriate 4mm sockets SK1 to SKS. 
Table. 1 summarises the results obtained with a nominal 4“Amp 
charger. Readers’ actual results will depend on the battery’s state of 
charge and the output from the charger itself. 

The rectifiers should be well ventilated and heavy duty cable 
MUST be used for interconnections. I suggest 50 PIV 6A rectifiers 
(e.g. Maplin P600A or similar), each fitted with a high profile TOS 
lobe-finned heatsink. 

P.C. Cole, Devonport, Plymouth. 

Everyday with Practical Electronics, September 1995 

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Blumlein Archives Scandal? 

Every month or'so | get asked the same 
question. Whatever happened about the 
Alan Blumlein archives? 

The short answer is nothing. The long 
answer is likely to go down in electronics 
history as a national scandal. Future gen- 
erations will look back and ask how 
anyone allowed it to happen. Believe me 
a lot of individuals tried to prevent it. But 
the self-styled “biographer’’ risks going 
down in history as the man who buried 
the reputation of arguably the most bril- 
liant electronics engineer this country 
ever produced. The UK’s IEE, the Institu- 
tion of Electronics and Electrical En- 
gineers, also risks going down in history 
as the one official body which could have 
done something to rescue the archive but 
chickened out. 

While at EMI's Central Research 
Laboratories in the 1930s Alan Blumlein 
invented film and disc stereo recording 
and a host of electronic circuits, for 
instance for measurement, high voltage 
control and telephone equalisation. He 
was a key figure in the teams which built 
the 405 line all-electronic TV system and 
then went on to develop the H2S (Home 
Sweet Home) map radars which helped 
Britain win the War. He was awarded 128 
patents before he was killed on June 7 
1942. The Halifax bomber testing his 

H2S radar system crashed near the River 

Wye at Goodrich in Herefordshire. 
Because he was a hands-on researcher, 
Blumlein was aboard. 

Biographical Concern 

Francis Thomson of Watford started 
collecting original papers in 1972, 
promising to write a biography. He was 
encouraged by Blumlein’s son, Simon. 
Thomson has never produced _ the 
biography but still holds all the papers 
which people sent in response to 
published calls. He has ducked questions 
on progress and what will happen to the 
papers. Simon Blumlein has grown 
increasingly concerned. 

Early in 1991, Thomson again started 
asking magazines and journals to pub- 
lish appeals for yet more biographical 
material. Those editors who knew what 
happened, or more accurately not hap- 
pened since 1972, treated his call with 
suspicion. Others, for instance, 7e/ev/- 
sion, the journal of the Royal Television 
Society, and Nature, the science profes- 
sion’s journal of record, published the 
fresh appeals. BBC Radio even broadcast 
Thomson's plea. 

Later (23 January 1992) Wature took 
the unprecedented step of publishing a 



by Barry Fox 

note warning readers that it had “since 
come to light that Mr Thomson is unable 
to produce evidence of work on such a 
book, that he has declined to make the 
material already collected available to 
others and that readers would be ill- 
advised to accede to his request for 
biographical material” . 

In May 1991, knowing that third party 
honest broker attempts at guaranteeing 
the iong term security of Thomson’s col- 
lected papers had failed, | formally re- 
quested that the IEE investigate the biog- 
rapher’s behaviour. | drew attention to 
Thomson's use of IEE membership when 
publishing further appeals for material. | 
made very clear that my motive, in asking 
the IEE to investigate the behaviour of 
one of its members, was to safeguard the 
material collected. 

“Whatever happened about 
the Alan Blumlein archives? 

“This historical material is too 
important to risk losing." 

It took the IEE over a year, and many 
nags from me, to come to a decision (in 
late June 1992). By coincidence this 
came shortly after the fiftieth anniversary 
of Blumlein’s death. Neatly summing up 
what the lack of a biography on Blumlein 
means, the 7/mes report of the memorial 
ceremony did not even mention Alan 
Blumlein by name. 

The IEE’s decision was to take no 
action. The reasons given were marked 
“Confidential” and the IEE refused my 
requests to lift this restriction. How- 
ever the IEE has stated, without seal 
of confidence, that ‘‘the investigating 
panel received assurances from Mr 
Thomson that the archival material he 
has collected will be safeguarded and 
(the panel) has no reason to doubt this 

Because | had previously raised the 
question of the Blumlein archive with 
the Royal Society, | asked the Royal 
Society if it had any news to tell us. The 
Royal Society's librarian, Sheila Edwards, 

“Lam happy to confirm that | have been 
in correspondence with Mr Thomson, 
and that the Officers of the Society have 
agreed to accept Mr Thomson’s generous 
offer to donate his collection of Blumlein 
papers to the Society”’. 

Royal Society Secrecy 
The Royal Society’s rules decree that 
papers are kept secret until forty years 

after the death of the subject. As Alan 

Blumlein died over fifty years ago, this 
means that the Blumlein papers will be 
available as soon as the Royal Society 
has them. 

Unfortunately the promise of seeing the 

’ Blumlein papers safe in the library of the 

Royal Society proved to be a false dawn. 

At first the Royal Society would say 
only that it was ‘‘still negotiating with 
Mr Thomson”. At a seminar held at the 
IEE in October 1992, | answered a ques- 
tion on archiving progress with the sug- 
gestion that those who are concerned 
should phone the Royal Society and ask 
for themselves. 

This suggestion did not, however, ap- 
peal to the IEE. The Institution’s Assistant 
Secretary, Philip Secker, rose from the 
audience at the Savoy Hill meeting and 
warned that to make such approaches 
would be “‘counter productive’ because 
“negotiations are at a delicate stage”’. 

Honouring this request | left it several 
years before contacting the Royal Society 
again. The time seemed right when | 
heard that the new Centre for the History 
of Defence Electronics at Bournemouth 
University refers to Blumlein’s work. New 
generations will be wondering why there 
is no biography they can read. 

In early July | phoned the Royal 
Society Library to ask if it had ever 
received the Blumlein archives. 

“It doesn't ring any bells’, a librarian 
told me, coming back later to add 
that “there is no entry in the archive 

Head Librarian Sheila Edwards then 
confirmed the bad news. ‘Nothing has 

“| must admit | wasn’t surprised’, she 

IEE Responsibility 

The ball is now firmly back in the IEE’s 
court. The Institution said previously that 
it Saw no reason to doubt the assurance 
given by Francis Thomson that the col- 
lected papers would be safely archived. 
But after three full years this has still not 
happened. | suggest it is now the clear 
responsibility of the IEE to approach 
Francis Thomson and ask for the promise 
to be honoured. 

This historical material is too important 
to risk losing. | have written to the 
Secretary of the IEE to ask for the Institu- 
tion’s attributable view on Francis Thom- 
son's apparent failure to do what he 
promised three years ago. 

Everyday with Practical Electronics, September 1995 


A range of videos designed to provide instruction on electronics theory. Each video gives a sound introduction and ground- 
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Everyday with Practical Electronics, September 1995 


‘S$ Seeks 
: ye 

HEN recently making attempts to 
connect my PC to the ‘‘super- 
highway”, | was struck by the immense 
amount of jargon associated with this 
aspect of computing. It seems to be 
quite normal for books on the subject 
to be about 50 per cent glossary! 

Much of this terminology is essential, 
as a great deal of repetition would 
otherwise be needed, with the same 
explanations and descriptions cropping 
up time and time again. On the other 
hand, it is probably fair to say that 
many aspects of modern technol- 
ogy are riddled with an excess of 
terminology, and a lot of genuine 

Fortunately, electronics is rather less 
loaded down with gobbledygook than 
many other aspects of modern technol- 
ogy. As yet we do not “surf the strip- 
board’’. There is still a certain amount 
of necessary terminology for beginners 
(““‘newbies?” — Robert's phrase not ours 
— Ed) to deal with. This month we will 
consider some of the terms that tend to 
confound newcomers to the hobby. 


Potentiometers are available’ in 
logarithmic and linear varieties. In 
components lists and catalogues these 
are normally just referred to as “‘log.” 
and ‘‘lin.”” types respectively. There 
are also anti-logarithmic (‘‘antilog.”’) 
potentiometers, but these are not 
widely available and are little used in 

What is the difference between log. 
and lin. potentiometers, and what hap- 
pens if you use the wrong type? 

A normal potentiometer is a control 
that is mounted on the front panel of a 
project. It is a form of ‘‘variable resis- 
tor’’ which has three tags. Two of these 
connect to opposite ends of a resistive 
track, usually made of carbon, and 
the third connects to a “wiper” con- 
tact that can be positioned anywhere 
along the resistive track by adjusting 
the spindle. 

If a potentiometer has a value of 
100k, then the resistance between the 
two track terminals will be approxi- 
mately 100k (kilohms). If the wiper is 
set at a central setting, there will be 
about 50k between the wiper terminal 
and each track terminal — see Fig. 1a. If 
the wiper is moved so that it is about 
25 per cent along the track, there will 
be about 25k between the wiper and 
one track terminal, and about 75k be- 
tween the wiper and the other track 
terminal (Fig. 1b). 




by Robert Penfold 

At least, this will be the case if the 
potentiometer is a //near type. If it is a 
logarithmic type the two sections of 

the track will have very different values. 

with the wiper at a central setting. 

The result obtained from measure- 
ments taken on a “real life’’ 100k 
logarithmic potentiometer is shown in 
Fig. 1c. The total track resistance is 
clearly more than 100k, but is within 
the 20 per cent tolerance rating of most 

Of more importance is the disparate 
resistance in each half of the track. One 
half has about ten times the resistance 
of the other half! Results would be 
much the same for an anti-logarithmic 
potentiometer, but the two resistances 
would be swapped over. 

a potentiometer of the wrong type 
is satisfactory only as a temporary 
measure if there are supply difficulties 
with the right component, but. is 
something that should otherwise be 

Readers occasionally complain that 
components lists do not spec- 
ify whether ‘preset’ potentiometers 
should have logarithmic or linear laws. 
In most component catalogues, even. 
the larger ones, you will not find 
logarithmic presets listed. Unless stated 
otherwise, preset resistors can safely be 
assumed to be linear types. 


What is the difference between a 
polarised capacitor and an electrolytic 
capacitor? Although these are some- 
times taken to be different terms for 
the same thing, they are not quite 
the same. An electrolytic capacitor is 
an example of a polarised capacitor, 
but not all polarised capacitors are 
electrolytics. : 

The only polarised non-electrolytic 
type in common use is the tantalum 
variety, which are also known as tan- 
talum “‘beads”, due to their bead-like 
shape. — 

Unlike ordinary capacitors, polarised 
types must be connected into circuit 
the right way round. Printed circuit 
mounting types are marked with “+” 

Fig. 1(a) and (b). A linear potentiometer produces the resistances one would 
expect; (c) a logarithmic potentiometer is very lop-sided. 


Linear potentiometers are used for 
the vast majority of applications, such 
as tone controls, temperature controls 
on electronic thermostats, and so on. 
Logarithmic types are designed for use 
as volume controls, and are used for 
little else. If a linear potentiometer iis 
used as a volume control, advancing 
the volume from zero produces a large 
increase in volume initially, with large 
changes in the setting of the control 
having little effect thereafter. 

This is not due to a fault in the 
potentiometer, but is more to do with 
the way the human hearing mechanism 
works. As sounds become louder, our 
hearing effectively becomes less sensi- 

‘tive. A logarithmic potentiometer is 

designed to counteract this compres- 
sion effect, and give what appears to 
be more even variations in volume as 
the control is adjusted. 

A project will work after a fashion if 
you use potentiometers of the wrong 
type. The control will have odd charac- 
teristics though, making it difficult to 
use the equipment properly. Using 

4a Lad 

and “— 
Printed circuit mounting capacitors 
are also known as just ‘“PC” capacitors, 
and “radial capacitors. These terms 
can be applied to practically any com- 
ponent that is intended for vertical 
mounting on a printed circuit board. 
The other standard form for 
Capacitors is the axial variety. These are 
tubular components having a leadout 
wire at each end, and intended for 
horizontal mounting. In other words, 
components that look rather like 
resistors, but are usually somewhat 

signs to indicate their 

larger than normal 0-:25W resistors. 

The term “axial’’ can be applied to 
any component of this general form. 
Axial capacitors normally have “+” - 
and (or) ““—” markings, plus an iden- 
tation around the body near the posi- 
tive leadout wire. 


Using a non-polarised capacitor in 
place of a polarised type is all right from 
the electrical point of view, but is not 
likely to be very practical. Non- 

Everyday with Practical Electronics, September 1995 _ 

polarised capacitors are generally 
much larger than polarised types 
having similar values, and are also 
much more expensive. 

Using a polarised component in 
place of a non-polarised type is 
definitely not advisable. A polarised 
capacitor only functions properly if it is 
subjected to a d.c. signal of the correct 
polarity, and a suitable signal may not 
be present. Also, polarised capacitors 
tend to be much lower in quality than 
non-polarised types. 

It is not a good idea to use an 
electrolytic capacitor where a tantalum 
type is called for. Tantalum capacitors 
are superior to the average electrolytic 
type in several respects. 

They generally have’ closer 
tolerances, lower leakage currents, and 
work better at high frequencies. There 
are a few high grade and relatively 
expensive electrolytics which might 
give good results when used in place of 
a tantalum type, but it is advisable to err 
on the side of caution and use the 
specified type of capacitor. 


Switches are often described as 
something like ‘’s.p.d.t.” in com- 
ponents lists and component 
catalogues. Abbreviations such as this 
tend to cause a certain amount of 
consternation amongst beginners, but 
there are only four of them, and they 
are really quite easy to understand. 

These are the meanings of the four 

S.p.s.t. single-pole single-throw 

s.p.d.t. single-pole double-throw 

d.p.s.t. double-pole single-throw 
d.p.d.t. double-pole double-throw 

A single-throw switch is a simple 
on/off type. A double-throw switch is 
one which provides what is more com- 
monly called a “changeover” action. 
In other words, there are three tags, 
and the middle (moving) one connects 
through to one or other of the other 
two tags, depending on the setting of 
the switch. 

A single-pole switch has just one 
set of contacts. a double-pole type 
has two sets, and is effectively two 
switches operated in unison. 

The circuit symbols for the four types 
of switch, and how these relate to 
practical switches, is shown in Fig. 2. 
The tag arrangements shown are the 
most common ones, but they are not 
truly universal. With any switch it is not 

a bad idea to check what connects to 

where using a continuity tester (i.e. 
multimeter set to Ohms range), rather 
than jumping to conclusions. 

In component catalogues you may 
find that some types of switch are only 
available as s.p.s.t. and d.p.d.t. types. 
This rationalisation is possible because 
a d.p.d.t. switch can be used as a 
d.p.s.t. or s.p.d.t. type. , 

Simply ignore tags ‘’d”’, ‘‘e’”’, and ‘‘f”’, 
and the other three contacts provide a 
s.p.d.t. switch. Ignore tags ‘’c”’ and “’f,”’ 
and the other four provide a d.p.s.t. 

Although toggle switches are well 
known to those who build electronic 
projects, few newcomers to the hobby 

Fig. 2. Circuit symbols and most common tag arrangements for the four basic types 

of switch. 

seem to have heard of “toggle” 
switches before. They are just switches 
that are operated via small levers. 
Believe it or not, the lever of a toggle 
switch is called a “‘dolly”’. 

With relay contacts and switches 
you may sometimes encounter the ab- 
breviations ‘‘n.c."” and ‘‘n.o.”, which 
stand for ‘normally closed” and “‘nor- 
mally open’. These terms are used to 
describe single-throw switches that are 
biased to one position. 

For example, a pushbutton switch 
that has contacts which close when it 
is Operated, and open again when it is 
released, is a normally open switch. 
A normally closed switch is the op- 
posite of this, with the contacts open- 
ing when the switch is operated, and 
closing when it is released. 


The word ‘“‘choke’’ seems to be 
rather less used now than it was in 
the past. Even some relatively ex- 
perienced constructors seem to be 
puzzled by references to this type of 

It is merely an alternative name for 
an inductor, and it is mainly used 
when referring to small inductors for 
use in radio frequency equipment (rf. 
chokes). It is occasionally applied to 
larger inductors, such as those used in 
mains interference suppressors. 

D.|.L. stands for ‘‘dual-in-line’, and it 
is a term normally applied to integrated 

Everyday with Practical Electronics, September 1995 


Starting in FPE November issue: 
An enticing new series explaining in 
simple steps how a multitude of circuits 
can be designed from very simple 
building blocks. 

Don’t miss “/EACGH-IN *96’’ 
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circuits. These mostly have two rows of 
pins spaced 0:3 inches apart, or 0:6 
inches in the case of large devices 
having more than about 22 pins. Pin 
spacing is 0:1 inches. The term ‘‘d.i.I.” 
can be applied to any component that 
has two lines of pins, such as banks 

. Of miniature printed circuit mount- 

ing switches, and integrated circuit 
holders. . 

There are also s.i.l. (single-in-line) 
components which have a single row 
of pins, but these are relatively rare. The 
only common examples are banks of 
resistors, and integrated circuits that 
are designed to handle high powers. At 
one time there were also q.i.l. (quad- 
in-line) integrated circuits, but this 
type of encapsulation now seems to be 
obsolete. . 

When ordering integrated circuits 
you do not normally need to specify a 
d.i.l. or (where appropriate) s.i.l. en- 
capsulation. Most integrated circuits 
are available from manufacturers in a 
variety of case styles, including various 
surface mount types. In general, com- 
ponent retailers only offer the plastic 
s.i.l. or d.i.l. version of a device. 

If two versions are available, the 
article concerned should clearly state 
which version is required. In most 
cases the type numbers will be slightly 
different anyway, with the suffix 
usually indicating the case style (‘‘CP”’ 
for a plastic d.i.l. encapsulation for 






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is also available — see order form. Alternatively, indexes are published in the December issue for that year. Where we 
are unable to provide a back issue a photostat of any one article (or-one part of a series) can be purchased for the 

same price. 


PROJECTS 6 Tee” "Venable "Bench 
Power Supply e EPE Soundac PC sound 
output board e CCD TV Camera, Part 2/Frame 
Grab e Impulse Clock Master Unit e Telephone 
Ring Detector. 

FEATURES e Best of British, Part 1 e 

Calculation Corner, Part 4 e Electronics 

Workbench Review e Free Wall Chart — 
Electronics Formulae 2. 

PROJECTS e Simple TENS Unit 
(transcutaneous pain relief) ® 

Capacitance/Inductance Meter e L.E.D. Matrix 
Message Display, Part 1 e Stereo Noise Gate e 
Dual Stepping Motor Driver for PCs. 
FEATURES e Calculation Corner, Part 5 e 
Best of British, Part 2. 

PROJECTS ® Mictocontiotler PI. Treasure 
Hunter e Digital Water Meter e Microproces- 
sor Smart Switch e Advanced TENS Unit 
(transcutaneous pain relief) e L.E.D. Matrix 
Message Display, Part 2. 

FEATURES e Best of British, Part 3 e Cal- 
culation Corner, Part 6. 

PROJ ECTS « @ Yaxbox Voice Raoul Board 
e Simple NiCad Charger e Watering Wizard 
(automatic garden watering)e- Pocket Print 
Timer e Stereo HiFi Controller, Part 1. 
FEATURES e Best of British, Part 4 e Cal- 
culation Corner, Part 7. 

Al Mc OL 

PROJECTS ® Experimentat fi Noise Cancelling 
Unit e Dancing Fountains, Part 1 e Charged- 
Up (PC battery tip) e 6802 Development 
Board @e TV Camera Update e Stereo HiFi 
Controller, Part 2. 

FEATURES e Calculation Corner, Part 8 e 
Best of British, Part 5 e I'll Be Seeing You 
(multimedia communications) 

PROJECTS e Protector Plus Car Alarm e 
Greenhouse Watering System e Experimental 
Seismograph, Part 1 @ Three-Channel Lamp 
Controller e Dancing Fountains, Part 2. 
FEATURES e Calculation Corner, Part 9 e 
The Invisible Force (magnetic force). 

Clock e 
Visual/Audio Guitar Tuner e Hobby Power 
Supply e Audio Auxiplexer e Experimental 
Seismograph, Part 2. 

FEATURES e Electronics from the Ground 
Up, Part 1 with Free PC Software e Calculation 
Corner, Part 10. 

PROJECTS e Digilogue — 


PROJECTS. e 1 000V/S00V iheutaticn Tadier 
e Video Modules, Part 1 (Simple Fader, Im- 
proved Fader, Video Enhancer) e Active Guitar 
Tone Control e Power Controller e TV Off-er. 
FEATURES e Electronics from the Ground 
wai tid Zz e Consumer ElecHonics Show. 

PROJECTS. @ eanentier Wand ¢ ®  EPE Fruit 
Machine e Universal Digital Code Lock e Video 
Modules, Part 2 (Horizontal Wiper, Vertical 
Wiper, Audio Mixer) e Rodent Repeller. 
FEATURES e Electronics from the Ground 
Up, Part 3 e Embedded Controllers e Index for 
Volume 23. 

PROJECTS e . Magnetic Field Detector e 
Moving Display Metronome e Model Railway 
Track Cleaner e Beating the Christmas Lights e 
EPE Fruit Machine, Part 2 eVideo Modules, 
Part 3 (Dynamic Noise Limiter, System Mains 
Power Supply). 

FEATURES e Electronics from the Ground 
Up, Part 4 e Electromagnetic Compatibility e 
etna 5 | Wransitors. 

PROJECTS e 12V 35W PA Rae e 
Foot-Operated Drill Controller e The Ultimate 
Screen Saver e MIDI Pedal Board e Model 
Railway Signals. 

FEATURES e Electronics from the Ground 
Up, Part 5 e Transformerless Power Supplies e 
MARCH S 0 Review. 

PROJECTS e » Multi- Bursa Thernhestat ® 
Name of the Game-1 Counterspell e Sound 
Activated Switch e Audio Amplifier e Light 
Beam Communicator. 

FEATURES e Electronics from the Ground 
Up, Part 6 e Understanding PIC Micro- 
controllers e Visio Graphics Software Review. 

FREE Multi- Project PCB with this issue. 


PROJECTS ® National 
e Auto-Battery Charger e Light-Activated 
Switch e Switch On/Off Timer e Continuity 
Tester e Name of the Game-2 Counterspin. 
FEATURES e Electronics from the Ground 
Up, Part 7 e Circuit Surgery e The Hard Cell 
wseneihe ie gales 

MAY 95 

PROJECTS Ce 1 (PIC Develop- 
ment and Training System) e R.F. Signal 

Generator - 1 @ DI Pedal e Club Vote 

Totaliser e Name of the Game-3, On Your 
Marks and Games Timer. 
FEATURES e Electronics from the Ground 
Up, Part 8 e Las oes Show eeniea 

PROJECTS ¢ a PIC- DATS- 2 (PIC controlled 
4-Channel Light Chaser) e EPE HiFi Valve 
Amplifier — 1 @ R.F. Signal Generator — 2 e AA 
to PP3 Converter e Name of the Game - 4, 
Star-Struck!, Six-Shot Light Zapper, Wander 

FEATURES e Electronics from the Ground 
sia Part 9 e Smart Cards. 

PROJ ECTS e Windicator e Curtain Winder e 
Ramp Generator — 1 e High Voltage Capacitor 
Reformer e EPE HiFi Valve Amplifier — 2 
FEATURES e Bridge Rectification Enhanced 
6 we Unlimited. 

PROJECTS ® Solar Seeker ® . Personal Prac- 
tice Amplifier e Infra-Red Remote Control Unit 
e Versatile Microcontrolled 3-Digit Timer e 
Ramp Generator — 2. 

FEATURES e Static e Circuit Surgery. 

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Everyday with Practical Electronics, September 1995 


SUMMER 1995 





The Summer ’95 edition has 280 pages packed 
with over 4000 products and now with news and 
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Constructional Project 



Tow and know! Make sure your 
caravan or trailer is stillon tow 
with its multiple lighting network 
intact and functional, and 
understand more about high 
current monitoring. 

system designed to interface between 

a towcar and a caravan. It should be 
suitable for most cars with 12V, negative 
earth electrical systems, and any Caravan 
or Trailer that has on-board battery 

There are two parts to Vandata, a Boot 
unit, and a smaller Dash Display unit 
which has light emitting diodes on a remote 
ribbon cable extension to permit mounting 
in a restricted space. 

In addition to indicating the correct 
operation of all exterior lights and in- 
dicators (except Reverse), it confirms that 
the caravan refrigerator has been set to 
12V operation. 

It is not an Alarm system, but a con- 

VY scm is a repeater and monitor 

stant monitor giving a pre-journey “cock- 

pit check” and reassurance en route. 


Many points were considered in the 
design. Reliability was paramount — in some 
instances, the unit might only be required 
for a few hours on a handful of days each 
year. It must impose a low load on the 
existing wiring, so that normal in-car fault 
indicating circuits are not confused. The 
voltage repeaters and current detectors 
should introduce no appreciable loss, and 
the complete unit when not in actual use 
should ideally consume no current. 

Any modification to the caravan must be 
of a very minor nature and not render it 
incapable of being towed by any nron- 
equipped vehicle. Conversely, the equip- 
ment should permit any caravan to be 
towed, although the full facilities offered by 
the unit may not then be fully realised. 


When considering what form the Van- 
data design should take, the author first 
examined what he could achieve using 
modern semiconductor technology. Mat- 
ters were not straightforward! 

In the field of automobile electrics, 
many major changes have taken place in 
the past few years, but one of the more 
subtle is the increasing use of sealed, or 
semi-sealed batteries, together with very 


high current output alternators. This has 
resulted in many manufacturers applying 
to the system a lower charging voltage 
with closer control. 

The Continentals in particular often 
work in the 13-6V to 14-2V bracket, i.e. 
virtually toleranced around the accepted 
voltage at which lead-acid batteries can be 
left on permanent charge. Low-voltage, 
high-current circuits such as those with 
which we are dealing have a rather 
intrusive associated problem, namely volt- 
age drop. With a starting voltage of, for 
example, 13-9V it is quite difficult to ensure 
a 12:6V supply at the back-end of a 
caravan, let alone insert additional elec- 
tronics whilst in transit! 

This ruled out the use of emitter-follower 
devices in the Vandata design, the inherent 
0:7V base-emitter drop being unacceptable. 
Power MOSFETs have a very low satura- 
tion voltage when used in common-source 
mode, but in common-drain, source-fol- 
lower mode they suffer from an even less 
acceptable gate-source limit. Although pnp 
power MOSFETs work beautifully in com- 
mon-source mode and feeding from the 
positive supply, they require additional cir- 
cuitry in the form of inverting drivers, and 
are frightfully expensive. 

Everyday with Practical Electronics, September 1995 


A fairly recent arrival on the component 
market, certainly as far as the home con- 
structor is‘ concerned, is the High Side 
Power Driver. This type of device provides 
an interface between low power control 
logic and high current loads. From a first 
study it has everything one could ask for in 
the Vandata application, and a prototype 
was constructed using VN0O5 and VN20 
devices. Several problems soon became 

For the design in mind, nine devices were 
required together with additional circuitry 
where change-over functions were planned. 
The in-built load detection apa would 
have been useful had the loads been single, 

but apart from the fridge, all the loads were © 

multiple. / 
For example, many caravans have one or 

more low wattage side repeaters in addition— 

to the 21W direction indicators. The high- 
density 5-pin lead-outs would have made 
a double-sided p.c.b. virtually essential 
when planning input and output tracks 
of between 3A and 10A capacity. To- 
gether with the need to heatsink all nine 
devices, the budget ran at double that for 
electromechanical relays. 

Similarly, load-detector i.c. UL2455 ap- 
peared to be the logical choice for current 
detection, and would have been ideal had 
the loads been in the range of 5W to 25W, 
as would be the case within the caravan 
itself. However, to detect, for example, two 
21W Stop lights required a “‘sense”’ resistor 
of the order of only six milliohms. Any 
higher loads would require “‘cable drop” 

sensing, i.e. outside the unit. 

Furthermore, an automobile can be a 
rather hazardous environment for semi- 
conductor devices: reversed batteries, open 
circuit batteries causing abnormal alter- 

nator output, and (you had better 
believe it!) 24V batteries used for 
jump-starts are but a few of the 

problems to be considered. 


However, the author had six reed relay 
switches left over from a burglar alarm 
design completed some 12 years ago. Con- 
sequently, needing to monitor so many 
amps, he decided to see how they would 
behave as current detectors. 

Although their specifications look wider 
than the proverbial barn door — 20 to 40 
amp-turns (AT) for make, and 8 to 25 AT 
for break — in the near perfect inductance 
of a few turns of heavy gauge copper wire, 
they behave far better than could have been 
hoped. Not only did they perform almost 
identically, but a further supply purchased 
this year were indistinguishable from the 
twelve year old “‘spares”’. 

Tests using a simple coil of 16 s.w.g. 
enamelled wire, single layered on a 9/64in. 
former around a reed switch, gave reliable 
“make” at 12 AT, making it straightforward 
to determine the coils required. The caravan 
fridge, a single load of approximately 8A 
(100W) presented no problem, nor did the 
detection of the presence or absence of one 
21W bulb out of two, as represented by the 
Stop and Fog lamp circuits. 

The failure of one 21W bulb when in 
parallel with a 5W one, as represented by the 
right and left indicators with a side repeater 
light fitted, was also reliably detected. In 
fact, the relays performed every bit as well in 
this application as the semiconductor circuit. 

Furthermore, when not in actual use a 
relay design need not be connected across 
the car battery supply, and so draws no 
quiescent current. Also, open-circuit relay 
contacts are largely self-protecting. 


The Riding light load presented an en- 
tirely different problem. Whereas the lamp 
circuits already mentioned are fairly stan- 
dard for a large number of caravans, the 
low wattage of the individual bulbs and the 
variable mix of wattages involved in the 
riding circuits made the loss of one bulb 

Caravan input connections § are 
separated into left and right hand sides. 
The front and rear bulbs are 5W each, but 
the number plate may be illuminated by 
one or two bulbs of either 3W or S5W, 
usually fed from the left. In addition, 
many makes are fitted with SW white/red 
repeaters on the sides. Some rear clusters 
also incorporate two 5W rear Riding 
lights on each side, in line with current 
automobile practice. 

The total number of Riding lights on 
different caravans can vary, some having 
eight, others might have five, for example. 
Then it was discovered that four bulbs of 
one make drew more current than five 
equally rated bulbs of another. Obviously it 

‘would be an extremely complex task to 

design a current monitor to cope with such 
varied lighting circumstances. 

It was decided, therefore, to settle for a 
straightforward “Circuit Fail” limit of ap- 
proximately 2A to the left and right circuits 
combined. A compromise perhaps, but one 
which should suit all caravans. A small ele- 
ment of customising was not to be ruled out, 
but the basic remit was first and foremost a 
“fit and forget” unit, with doubtful indica- 
tions being worse than none. 


Already it had ‘been decided that no 
cockpit monitoring was required for lights 

which are visible in the driver’s rear view 
mirrors. Reversing lights remained the only 
circuit left to be considered. 

Only recently have caravans started to 
appear with reversing lamps in the rear 
clusters, but it is by no means universal 
and some manufacturers only fit them 
on certain models. The author does not 
have them on his caravan, using instead 
an audible bleeper fitted under its rear, 
operated by the selection of reverse gear, 
an arrangement which requires no visual 

Consequently, Vandata has _ been 
designed without provision for monitoring 
reversing lights. If they do become 
mandatory, the author suggests that two 
Xenon strobe lights and either a bleeper or 
a recorded message would satisfy all parties 
— perhaps a good use for the EPE Voxbox 
of July 1994? 


Details of the connections to the two 
interfacing plug/socket units, usually 
situated adjacent to the towball, are shown 
in Table 1. The connectors are mechani- 
cally identical, only a different arrange- 
ment of “pins” and “tubes” prevents them 
being interconnected. The 12S connector 
(““Supplementary’’) is white (or grey) and 
the 12N (““Norma!’’) is black. 

Note that the 12N terminals 5 and 7 give 
separate access to the left and right riding 
lights of the caravan. As far as the author 
is aware, only cars produced in Germany 
have this facility fitted as standard. The 
Vandata unit only offers combined control 
of these two terminals. 

In order that the Vandata unit is only 

operative when a caravan is coupled, and 
also as proof to the driver that it IS 
electrically coupled, it is required that 
connector 12S/7 (black), currently unallo- 
cated, is coupled to the caravan’s bat- 
tery charging circuit via connector 12S/2 
(blue). As a short term measure, this 
could be done at the 12S plug, but is > 
best accomplished at the junction/fuse box, 
usually in one of the front lockers, where 
the 12S cable terminates and the interior 
caravan wiring takes over. 

If the connection between these two wires 
is made at the caravan side of the fuses, two 
functions may be achieved. Firstly, a check 
is automatically made on the charging 
voltage reaching the battery circuit (a bat- 
tery does not have to be fitted). Secondly, 
the link may be anything from a few 
centimetres of wire to several metres, in 
which case it can be used to convey some 
additional item of information to the car 
driver: the author has fitted a magnetic 
switch adjacent to the caravan handbrake 
mechanism, only closed when the hand 
brake is fully off. He used to have a habit of 
driving away with the brakes not fully 

Conventionally, 12S/4 and 12S/2 are 
separately wired: 12S/4 directly from the 
car battery and 12S/2 via a split-charge 
relay which also feeds, through separate 
contacts, the fridge connection on 12S/6. 
The author is unfamiliar with the device, 
never having used one, but understands 
that the recommended circuit is prone to 
several pitfalls, such as the fridge operating 
itself from the caravan battery if the com- 
mon supply fuse blows, and the caravan 
battery discharging into the car starting 
circuit if the relay cannot be operated from 
the alternator. 

Table 1.12N and 12S connector wiring. 

12N Terminal 

L-IND 1 
Rear Fog 

Earth (return) 

R-Side/Tail/Number plate 
Stop Lights 



Colour Code 12S 
Yellow Reversing Lights 
Blue Batt. Charge 
White Earth 
Green Int. Lights 
Brown Not used 
Red 3 Refrigerator 
Black Not used 

Everyday with Practical Electronics, September 1995 



Fig. 1. Circuit diagram details for the current sensing system of Vandata. 

The author has always used a diode in 
the caravan charge/lighting circuit, pre- 
viously a high-current germanium type (a 
rare bird these days), but changing to a 
‘Schottky diode as soon as their advantages 
became apparent. These include a lower 
‘Vr than conventional silicon diodes, par- 
ticularly at less than rated current, and a 
robust ability to withstand surges. With 
such a diode in circuit there is no possibility 
of any reverse feed from the caravan 
battery and connector 12S/2/4 can be com- 
moned in the Vandata unit. 




Generally speaking, from hereon connec- 
tions to the terminal blocks TB1 and TB2 
will be referred to by their destination 
(towing) socket numbers, 12S and 12N 
respectively. This enables the same tests 
quoted to be carried out on the terminal 
blocks and the car sockets when fully wired 

Thus a reference to 12S/1, for example, 
will refer to terminal block TB1 pin 1 when 

testing the unit in the workshop, but will 
refer to the car socket 12S pin 1 connec- 
tion if testing at that end is required. Sim- 
ilarly, 12N/1/2/4 refers to terminal block 
TB2 pins 1, 2 and 4 as well as the same pins 
of connector 12N. 

Referring to the circuit diagram in 
Fig. 1, the car battery and associated 
charging circuits supply power to the 
Boot Unit via connector TB3 pins | to 4. 
This is a permanent connection, but no 
current will flow in the quiescent state. 
When the caravan 12S plug is mated with 

Everyday with Practical Electronics, September 1995 

its connector, usually adjacent to the 
towing hitch, the car’s +12V supply is 
fed to the caravan battery terminals via 
Schottky diode D8. 

Charging of the caravan battery will only 
take place when the car alternator (i.e. the 
engine) is running. The diode prevents any 
chance of the caravan battery supply- 
ing current to the car. By virtue of a 
wired addition to the caravan already 
mentioned, and irrespective of whether a 
caravan battery is actually fitted, this sup- 
ply is returned to the car and Boot Unit 
by connector 12S/7. Diode D7 protects 
against caravan battery reversal. 

The returned supply, only present when 
the caravan is actually coupled, powers the 
supervisory circuit in the Boot Unit and 
supplies the dashboard mounted Display 
Unit via socket SK1. It also operates relays 
RLAI1 and RLA2. The relays provide the 
optional facility to disconnect the towing 
vehicle’s rear fog and reversing lights when 
actually towing, to prevent a disconcert- 
ing glare reflected from the front of the 

The caravan’s rear fog and reversing 
lights (if the latter are fitted) will be 
operated irrespective of whether this op- 
tion is invoked by the car supplies being 
redirected from inputs TB3/11 and TB3/12 
to connections 12N/2 and 12S/1. 

When the alternator is running, the 
charge output is applied to TB3/5 and 
operates RLA3 supplying current to the 
fridge, (connections 12S/6 and 12S/5). 

It should be noted that the electrical 
systems of certain cars, notably those 
of French manufacture, do not always 
produce this additional voltage output, and 
RLA3 must therefore be operated from 
another source. Relays RLA4 to RLA7 are 
each operated, individually or in combina- 
tion, when the car’s right indicator (R-Ind), 
left indicator (L-Ind), footbrake (Stop) and 
side/rear (Riding) lights are respectively 

These inputs are on TB3 pins 7 to 10 with 
the corresponding relayed outputs on 
connector 12N pins 1, 4, 6 and 5/7. Diodes 
D1 to D6 limit back e.m.f. from the relay 
solenoids. All relayed outputs are fused, 
and although the fuse ratings may seem 

somewhat high, 
they are there to 
protect printed 
circuit tracks and 

Table 2. Consequential truth table for IC1 

Q2 Q1 7 Qo 

cableforms, reduce CONDITION INPUT OUTPUT 
fire risks and STATE STATES 
introduce as little IC1 powered All low 0 0 0 
voltage drop as 
possible. Fridge On D1 high 0 0 1 
Fog lights D2 high 0 1 0 
REED Stop lights D3 high 0 1 1 
R-Ind D4 high 1 0 0 
Reed relays 
RLA8 to RLAI3 L-Ind D5 high 1 0 1 

have their coils 
inserted in the 
current paths of the outputs to be 
monitored. Satisfactory loading of any 
selected circuit operates the associated reed 
switch. The switches have one side 
commoned to the +12V supply from the 
caravan. When either or several of these 
relays are operated, the switches connect 
the inputs of IC] (normally grounded by 
resistors R20 to R26) to a logic | level. 

Component IC1 is an 8-bit to BCD (bi- 
nary coded decimal) priority encoder, with 
only inputs D1 to D5 used. Table 2 shows 
how the inputs are interpreted, the outputs 
QO to Q2 répresenting the address of the 
highest active input, irrespective of the state 
of the other inputs. This action is used so 
that only one condition or state, and there- 
fore indication, is displayed by the dash- 
board unit. 

The selection of Riding lights (TB3/10 
and RLA7) also powers IC2, via resistor 
R3. Capacitor C3 provides local decou- 
pling and diode D9 a measure of over- 
voltage protection. 

IC2 is a quad 2-input NAND gate of 
which two gates, IC2b and IC2c, are con- 
figured as a square-wave oscillator running 
at about 1Hz. The oscillator is normally 
inhibited by a third gate, IC2a, inverting 
the logic 1 applied to its pins 5 and 6 by the 
contacts of RLA13. Oscillation frequency 
is set by resistor R5 and capacitor C4. 

In the event of insufficient or no current 
in the RLA13 coil, its contacts will not 
close and so IC2a has its inputs biased 
low via resistor R2. The high output from 
IC2a thus allows IC2b/c to oscillate. The 

Fig. 2. Display unit circuit diagram details. 

Everyday with Practical Electronics, September 1995 


output from IC2c, buffered and inverted 
by IC2d and transistor TRI, modulates 
the voltage on the D1 input of IC] (pin 
11) provided by the fridge current detec- 
tor RLA8, resistors Rl and R8 being the 
effective components. 

Note that IC2d output pin 10 is low in 
both the unpowered and inhibited states. 
TR1 is required so that IC1 pin 11 is unaf- 
fected when IC1 is not powered. Outputs 
QO, Q1, Q2 are taken to SK1 terminals 1, 
4/5 and 2 respectively. 

It could be argued that R-Ind should 
have a higher priority than L-Ind, but 
this is of no significance since they are 
not selectable simultaneously, both having 
equal status. In the event of Hazard selec- 
tion, both rear indicators will flash cor- 
rectly, although the supervisory indication 
will be L-Ind. 

Normal driving, day or night, will be with 
IC1 output QO high. In the event of Riding 
light failure, it will alternate high and low. 


The overall Display Indication strategy 
can best be appreciated after considering 
the circuit diagram of the Display Unit 
itself, as shown in Fig. 2. The Display Unit 
is powered from the Boot Unit, via a DIN- 
to-DIN cable between sockets SK1 and 

SK2, and therefore is only powered when 

the caravan connection is complete. The 
BCD outputs from IC1 of the Boot Unit in 
Fig. 2 are applied to pins 10, 13 and 12 


| 3 Ne be si iw as 5 a TTS ne es TepPRE. ae Rey 5 dessa : i 
siti ' 4 ny As : 


Fig. 3. Component 
| positioning details 
| for both printed circuit 
| boards of the 
Vandata unit. 
SI iy R 
| 2 
| @ 
| 2 
| @ 
| @ SK1 
| @ 
| @ 
e 7 ; 
| @ @ 
@ @ 
| @ @ 
| @ 
| eC) 
@ . 
| —— - «ha HSS: 0:9mm SLEEVED 
ret. 1 : , , LINK WIRE | 
| | : 
! ° 710 : | Everyday with Practical Electronics, September 1995 

(in increasing order of significance) of the 
BCD to decimal decoder IC3. All of the 
inputs are normally held low, including the 
unused pin 11, by resistors R9 to R12. 
With all inputs low, output QO (pin 3) is 
held high. 

Subsequent input code changes will 
cause the appropriate outputs Q1 to QS to 
go high, only one output being active at a 
time. The outputs are coupled via hex 
buffer IC4 to operate the tricolour light 

emitting diodes (I.e.d.s) D18 and D19 via a 

series of resistors/diodes. Readers may spot 
that diode D12 is not really necessary, but 
it simplifies the calculation for resistor R15! 

The display combinations available are 
shown in Table 3. The centre column des- 
cribes the output states of IC3 and the 
component path from IC4. 


Details of the component and track lay- 
outs for the Boot Unit and Display Unit 
printed circuit boards (p.c.b.s) are shown in 
Fig. 3 and Fig. 4. These boards are avail- 
able from the EPE PCB Service, codes 953 
and 954, respectively. 

The large copper areas on the Boot Unit 
p.c.b., and the gauge of some component 
pins make a soldering iron of reasonable 
wattage essential, the author suggests 45W 

First, carefully cut off the small section of 

_ the Display p.c.b. which holds the l.e:d.s. 

Next, fit the Boot Unit link wires, noting 
that some should be of heavier duty wire 
and that some must be sleeved. All small 
components can now be soldered in. All the 
i.c.s are CMOS devices and the normal 
precautions should be taken, ensuring that 
you discharge static electricity from your- 
self before handling them, by touching a 
grounded item first, for example. The use 
of sockets for the i.c.s. is recommended. 

Schottky diode D8 is in a DO220a case 
and should be mounted flat to the board on 
its heatsink. 


The winding of the reed relay coils needs 
a little care and patience. Coils for RLA9 
to RLA13 use 0-9mm (20 s.w.g.) enamelled 
copper wire, close wound on a 4mm former 
(drill shank), then slid onto an 18mm 
length of plastic tubular drinking straw and 
doped up with 5-minute epoxy. Fig. 5 
shows the final shaping. RLA9 and RLA12 
require six full turns, RLA13 eight full 
turns, and RLA10 and RLAI1 eleven full 


Table 3. Connector condition, signal state/routing and display indications 

1 Caravan connected output 0 (pin 3) high 
Engine Off R14, D10, R17, D18 (red) D18 amber 
R14,D11, R18, D18 (green) 
2 Engine running output 1 (pin 14) high None 
Fridge On not used 
3 Riding Fail Alternate Cond 1/Cond 2 D18 Flashing 
4 Fog lights output 2 (pin 2) High D1i8 + D19 
R13, D15, R17, D18 (red) red 
R13, D16, R16, D19 (red) (Low intensity) 
5 Stop lights Output 3 (pin 15) High D18 + D19 
D13, R16, D19 (red) red 
D14, R17, D18 (red) (High intensity) 
6 R-Ind Output 4 (pin 1) Dl8 green. 
D17, R18, D18 (green) (High intensity) 
7 L-Ind Output 5 (pin 6) high D19 green 
D12, R15, D19 (green) (High intensity) 

turns. The reed switches themselves are sli 
into the tube of the coil assembly. 

Relay RLA8 spans a different board 
spacing to the others, and should be wound 
using 1:25mm (18 s.w.g.) enamelled wire; 
3-5 turns are required, spaced by a single 
turn thickness. The two ends of the coils 
should be thoroughly cleaned and pre- 
tinned before fitting to avoid any pos- 
sibility of a bad joint, since the coils are 
part of the high current paths. 

If specific requirements make it desirable 
to modify any of the reed relay coils, it must 
be born in mind that the back of a caravan is 
a long way from the test bench. Variable 
voltages under different load conditions, 
lamps from alternative manufacturers with 
different consumption, installation varia- 
tions, cable resistance (and inductance), and 
thermal inertia, i.e. filaments remaining hot 

from a previous operation make it prudent 
to have a minimum current/turns product of 
about 17. 

The reed switches should be soldered di- 
rectly to the turret pins, not wrapped, and 
positioned centrally within the coils. 


The Boot Unit box should be employed 
“upside-down’’, the p.c.b. mounted in the 
white half. The p.c.b. needs rectangles 
removed from each corner to make it fit. 
Cut slots in the box to suit the board 
mounted connectors. 

With the Display Unit box, a slot should 
be cut to allow the ribbon cable to pass 
through to the two tricolour l.e.d.s. on their 
small board. Cable length will depend on 
the installation requirements. 

The interconnecting braided cable be- 
tween the two units, from SK1 to SK2, uses 
the same DIN plugs at each end. To enable 
the lead to work any way round they 
should be wired “mirror image’’, i.e. 1-3, 
2-2, 3-1, 4-5. On both p.c.b.s, SK 1 and SK2 
pins 4 and 5 are common. The braiding 
connects the metal shells of the sockets as a 
screened Earth connection. To ensure satis- 
factory Earthing, link the two half shells 
with a short length of soldered braid. 

Everyday with Practical Electronics, September 1995 




R1,R19 20k (2 off) 
R2 47k 
R3 3302 TALK 
R4, R6, R7, Page 
R9to R12 100k (7 off) 
R5 470k 
R8 10k 
R13 4k7 

R14toR18 1k2 (5 off) 
R20to R27 100k x8 resistor module 
All 0:25W 5% carbon film or better 


47, elect. 63V (3 off) 
10n polyester 63V (2 off) 
C4 -,  1ppolyester 63V 

100p elect. 16V 


D1 to D7 1N4003 rectifier diode 
(7 off) 

D8 MBR2045 Schottky 

DY 12V 1W Zener diode 

D10to D17 BAX16 signal diode or 
similar (8 off) 

D18,D19 © tricolourl.e.d. (2 off) 

TR1 BC108 npn transistor, or 

_ similar 

1C1 4532B 8-bit priority 

IC2 4011B quad 2-input 
NAND gate 

IC3 4028B BCD to decimal 

IC4 4050B hex buffer 


RLA1, RLA2, 
RLA4 to 

RLA7 s.p.c.o. 12V 10A p.c.b. 

mounting relay (6 off) 

RLA3 s.p.c.o. 12V 16A p.c.b. 
mounting relay 
RLA8 to 
RLA13 reed relay switches 
(6 off) (see text) 
FS1, FS2, 
FS4 to FS7 10A 20mm fuse (6 off) 
FS3 25A 1-25in fuse 
TB1 12-way p.c.b. mounting 
screw terminal block 
TB2 3-way p.c.b. mounting 
screw terminal block 
TB3,TB4 8-wayp.c.b. mounting 
screw terminal block 
(2 off) 
SK1,SK2 = 5-pin DIN p.c.b. 

mounting socket (2 off) 

Printed circuit boards for Boot and 
Display unit (pair) available from the 
EPE PCB service, code 953 and 954; 
14-pin d.i.l. socket; 16-pin d.i.l. socket 
(3 off); turret pins for reed switches 
(12 off); dual-tone case for Boot Unit 
205mm x 140mm x 40mm; case for 
Display unit 110mm x 56mm x 22mm; 
p.c.b. mounting fuse clips, 20mm (6 
off); p.c.b. mounting fuse clips, 1:25in 
(2 off); 4-way braided cable, length to 
suit; 5-way ribbon cable, length to suit; 
7-way cable, length to suit; slotted heat 
sink for diode D8, 19mm x 17mm x 
20.5mm; 5-pin DIN line plugs (2 off); 
18 s.w.g. and 20 s.w.g. enamelled cop- 
per wire for coils (see text); intercon- 
necting link wire; solder etc. 

Approx cost £457 

excl. cables 

guidance only 

SR rscich tabi 

ie Yah 5 ‘ " 
se ns 
fe te: 

Fig. 5. Details of how the coils are wound. 

Close-up detail of two of the coils 
wound around their reed switches with 
a plastic former in between. 


When installed, the unit will, in all 
probability be rather inaccessible, and the 
high currents involved may easily damage 
a faulty board. A short time spent on 
some straightforward checks is therefore 
worthwhile. After cleaning the boards 
(I.P.A. or Meths) give them a thorough 
visual inspection. Dry joints are a par- 
ticular problem with heavy-gauge pins 
and wire. 

Connect a low current 12V supply di- 
rectly to the Display board, 0V to the 
Earthy end of one of resistors R9 to R12, 
and +VE to pin 1 of the DIN socket. 
Diode D18 should light, amber. With these 
connections retained, momentarily make 
the connections between the + 12V supply 
and the following pins of socket SK2, and 
check that the results are as shown: 

Pin3 No l.e.d.s on 

Pin 4 Both l.e.d.s red, low 

Pins3and4_ Bothl.e.d.s red, high 

Pin 2 D18 green, high brightness 

Pins2and3 D19green, high brightness 


Connect the two boards together using 
the DIN-to-DIN lead. Examination of the 
track of the Boot p.c.b. will show that there 
is no continuity between the Input Earth 
(TB3/6) and the Output Earths, TB4/3, 
12S/3A and 12N/3A. Damage to p.c.b. 
tracks may result if Earth return currents 
flow in other than their intended paths. The 
above mentioned connections should there- 
fore be taken, independently, to the nega- 
tive side (OV) of the 12V supply. 

Now connect a +12V_ supply to 
TB3/1/2/3/4. If the source is not protected, 
the use of an in-line fuse of about 5A is a 
wise precaution, The units should draw 
no current at this time and no lL.e.d.s 
should light. | 

Everyday with Practical Electronics, September 1995 

With a multimeter set to the appropriate 
mode and range check the following con- 

nections and results: 

TB3/12 to TB4/2 continuity 

TB3/11 to TB4/1 continuity 

TB3/12 to 12S/1 open circuit 
TB3/11 to 12N/2 open circuit 
12S/1/5/6/7 no voltage” 
12N/1/2/4/5/6/7 no voltage” 

(*with respect to common negative) 

Temporarily connect 12S/2 to 12S/7 and 

establish that: 

Relays RLAI and RLA2 operate 
(audible click); D18 lights amber. 

Check now: 
TB3/12 to 12S/1 continuity 
TB3/11 to 12N/2 continuity 
TB3/12 to TB4/2 open circuit 
TB3/11 to TB4/1 open circuit 

A selection of short croc-clip to croc-clip 
jump leads will prove most useful for the 

following tests: 


+ 12V to TB3/5 +12V at 12S/5/6 
+12V to TB3/7 +12V at12N/1 
+12V to TB3/8 +12V at 12N/4 
+12V to TB3/9 +12V at 12N/6 
+12V to TB3/10 +12V at 12N/5/7 

Audible indication of relay operation 
should be heard at each test. 



Temporarily link a bridge wire between 
the mounting pins of the reed switches as 

follows: / 
RLA8 D18 extinguishes 
RLA8, RLAY D18, D19 Low 
brightness red 
RLA12 D18, D19 High 
brightness red 
RLA8, RLA12, 
RLA11 D19 High 
brightness green 
RLA8, RLA12, 
RLA10 D18 High 
brightness green 
RLA10 and 
RLA12 unbridged D18, D19 off 
+12V to TB3/10 D18 flashes 

RLA13 contacts bridged D18 off 


> —_- 

Table 4. Loaded testing checks and results. 

Fridge 21.+ 21 12S/6 TB3/5 No change 
add 21 12S/6 TB3/5 D18, D19 off 
Fog light 21 12N/2 TB3/11 D18 amber 
add5+ 5 12N/2 TB3/11 D18, D19 red 
Stop 21 12N/6 TB3/9 D18 amber 
add5 + 5 12N/6 TB3/9 D18,D19 red 
L-ind 5 12N/1 TB3/7 D18 amber 
add5+ 5 12N/1 TB3/7 D19 green 
R-Ind 5 12N/4 TB3/8 D18 amber 
add5+ 5 12N/4 TB3/8 D18 green 
Riding 5 12N/5 TB3/10 D18 flashing 
add 21 12N/5 TB3/10 D18, D19 off 
5 3 12N/7 TB3/10 D18 flashing 
add 21 12N/7 TB3/10 D18, D19 off 
Final Riding check — RLA8 contacts bridged: D18, D19 off 

If the supervisory tests all prove to be 
satisfactory, then it is very unlikely that 
any fault exists. 


Further tests to check the sensitivity of 
the reed relay coils and switches can now 
be made. Car bulbs are the best source of 
high wattage test loads, a selection of SW 
and 21W being necessary. 

Testing now requires either a regulated 
power supply capable of delivering 12:6V 
at up to 20A, or a 12V car battery. A bat- 
tery charger is not suitable. 

Maintain the Earth connections and con- 
nect the + 12V supply to TB3/1/2/3/4. En- 
sure 12S/2 is linked to 12S/7. D18 should 
light amber. 

Connect the loads as detailed in Table 4 
using several bulbs in parallel where shown. 
The bulbs are connected between the 
designated load connection and OV (Earth). 
Remove the bulbs after each path is proved 
to be satisfactory. Note: bulbs get HOT! 

At this stage it may be worth considering 
customising RLA13. If the unit is to be used 
exclusively for one caravan only, then the 
exact number of bulbs and total wattage of 
the Riding lights will be known and the 
number of coil turns can be re-evaluated. As 
commented on earlier, though, be aware that 
bulbs from different manufacturers may 
draw different currents even though they 
nominally have the same wattage. 


The manufacturer’s recommendations 
on such matters as disconnection of the 
battery before undertaking any electrical 
work should be studied, particularly where 
alarms, immobilisers and processor-con- 
trolled engine management systems are 


Only general advice can be given about 
siting the Boot Unit because of the variety 
of vehicles into which it may be fitted. It 
should be within the boot or rear area 
of the vehicle which provides the shortest 
cable run to the ball hitch, or to the bracket 
on which the 12S: and 12N sockets are 
fitted. Keep the two runs of 7-core cable as 
short as possible. 

If the muting facility available on Fog 
and Reversing lights (either or both) is 
required’ then these feeds must be lo- 
cated, cut and reconnected to TB4. Any 
existing split-charge relays or supplemen- 
tary indicator relays used in a previous 
installation should be removed. 


If efficient operation of the fridge and 
caravan lights is to be achieved, voltage 
drop must be kept to a minimum. The four 
Earth points of the Boot unit should be 
taken to the nearest manufacturer’s Earth 
point(s) using 28 x 0:3mm cable (offcuts 
of 12S white), and soundly terminated 
(TB3/6, TB4/3, 12S/3A and 12N/3A). 


Under some circumstances, the current 
into the unit can be up to 15A, increasing 
to 18A if fog lights become necessary, plus 
a further SA to 6A if an indicator and 
the stop lights are invoked. The following 
cable facts become relevant: 

For a length of up to four metres, the 
maximum currnt recommended in either 35 
x Q0-3mm or 19 x 0:lmm cable is 5A, 
rising to 10A if the run is two metres 
or less, even though the nominal rating 
of either is 21A, with a resistance of 
0-0075 ohms/metre. Therefore, a minimum 
of three runs of such cable should be 
adequate for most installations, assuming 
the run to be under four metres. 

However, a highly suitable cable is cur- 
rently available (see Shop Talk) which is 
primarily intended for in-car hi-fi installa- 
tions (NOT suitable for starter motors!) 
but perfect for this application. 

It consists of 700 strands of 0:12mm cop- 
per, giving a cross section area of 8 sq. 
mm. Theoretically this gives a rating of 
80A, but more importantly a resistance of 
only 0:002/metre. Connection to this is best 
made by several pigtails of say 21 x 0-3 or 
28 x 0:3 (off-cuts of 12S 7-core) soldered 

and taped at each end. Connector TB3 
accepts four such pigtails. 


Connection to the battery positive line 
should be via a 25A fuse. Any cable runs 
must be clear of moving parts, sharp edges 
etc., and should be secured at regular 
intervals. The author’s vehicle has plastic 
trunking from front to rear under the floor, 
which makes an ideal path for such cables. 

The “‘Charge”’ connection also needs to 
be run to the engine compartment. Any 
sensible cable (9 x 0:3mm) is suitable, and 
may well be run alongside the power cable. 
It should be connected to the supplemen- 
tary output of the alternator. Some expan- 
sion may be required here, in view of more 
“subtle changes” the automobile industry 
are springing on the unsuspecting. 

The so called “Ignition Warning Light” 
is usually connected between the ignition 
switch and the supplementary low current 
output on the alternator. When the ignition 
is switched on, the battery circuit is com- 
pleted through the lamp and the effec- 
tive ground of the idle alternator. When 
the alternator starts producing current, this 
“backs-off’ the battery supply, and the lamp 
goes out. It is this low current source that is 
conventionally used to provide the current 
to operate the fridge relay, so that this load 
is not in circuit unless the engine is running. 

Unfortunately, as mentioned above, 
certain manufacturers, Ducellier, Valeo, 
SEV Marschal, Paris-Rhone and possibly 
others, produce alternators with a “‘Simu- 
lated Warning Light’ connection in place 
of the one previously mentioned. This 
consists of (effectively) a transistor, nor- 
mally biased on when the alternator is idle, 
but cut off when the alternator is generat- 
ing. The effect on the warning light is the 
same, but obviously it is no longer a source 
that can be used in the same way. 

Note that the makes mentioned do not 
automatically imply a “‘Simulated”’ output. 
Only examination can ensure a positive 
identification. (Beware of measuring the 
leakage through the warning bulb itself!) 


The advice currently being offered by 
Caravan Associations for conventional 
fridge/charge relay connections in these 
circumstances is to operate the relay from 
the ignition switch. This means that the 
fridge is in operation if ignition is selected 
for any one of many car accessories, it also 

Everyday with Practical Electronics, September 1995 

means that the caravan battery is already 
-in parallel before cranking commences. 
Without the protection of a suitable diode, 
very high currents could flow in conductors 
not designed for starter motor supplies! 
Vandata is ideal under these conditions, 
since the Schottky diode (D8) prevents 
the latter and more serious of the two 
problems. Dash indications remain as des- 
cribed, except that D18 (amber) should 
extinguish at “Ignition On” instead of 
when charging commences. : 


The Display unit has been designed with 
a ribbon cable extension to the two l.e.d.s 
so that space for the complete box is not 
required immediately behind the fascia. 
The l.e.d.s should be fitted in any suitable 
position on the dash board or centre 
console where they can be seen at a glance, 
and the plastic box tucked away into any 
available nearby space. 

Hee RE Parcs THe TS ae eae 
PA 8 EES ged Vig? RE) ak 1 NY pds 

By PE I Be 

The DIN-to-DIN cable also needs to 
be run from the boot to the rear of the 
dash area, concealed under the carpet and 
trims. Because of the design variety of 
vehicles, it is difficult to be more speci- 
fic. On completion, one quick check is 
worth while: if a temporary short is ap- 
plied between 12S/2 and 12S/7 at the cou- 
pling connector the right hand l.e.d. D18 
should light amber. 


There are two improvements that can be 
made to conventional caravan wiring. The 
fridge, operating on 12V, draws between 
7A and 10A, depending on size and type. 
All this current is allocated to one connec- 
tor 12S/6 and one conductor. Voltage drop 
and impaired efficiency are inevitable in 
such a connection, and yet there is connec- 
tor 12S/5 adjacent to it, unallocated and 
unused. The Vandata unit commons these 
two connections, so that anyone wishing to 

join them (at the locker fuse box) will im- 
prove the fridge efficiency. 

The second tip concerns the Earth 
wiring. Both connector 12S/3 and 12N/3 
are designated as Earth connections. Both 
are sourced at the car chassis, yet very few 
manufacturers actually wire them together 
in the caravan. Apart from being electri- 
cally sloppy, this is a complete waste of 
good copper. The 12N Earth wire returns 
for much of the time only the occasional 
indicator or brake light currents, but if 
commoned at the caravan it can help to 
reduce the voltage drop in the 12S Earth 
from the steady fridge load. It also paves 
the way for simple refinements. For 
example, operating any of the exterior 
lights from the caravan battery. 

However, the important point is that the 
only basic modification actually required 
for the satisfactory operation of Vandata is 
the strap, or loop from 12S/2 (blue) to 
12S/7 (black), somewhere caravan-side of 
the plug. O 

Ohm Sweet Ohm 

Max Fidling 

Salad days 

The glorious summer weather always 
tempts me away from the workshop and 
my attention turns to the garden here at 
Fidling Acres. Standing proudly in one 
corner of the plot is my beloved glasshouse, 
by now a veritable production line of juicy 
red tomatoes! You would think that there 
was little scope to spice up my horticultural 
hobby with the addition of a few electronic 
gadgets, but you’d be wrong ... and my 
four-legged fiend Piddles, a member of the 
animal species Felinus Cleverdickus Maxi- 
mus, still does his best as usual to thwart 
my latest project! 

Pondering this, my mind set to the task 
of inventing a way to keep my greenhouse 
well supplied with water — especially as 
holiday time loomed and my greenhouse 
would need to look after itself for a spell! 
Having given the tomato plants a lavish 
watering with the garden hose, I retired 
to the workshop to examine the prospects 
of automating the watering, while Piddles 
played around near the garden sprinkler 
which was aimed carefully at the melon 
patch nearby — strange because he loathed 
water! - 

I sought a way of automatically monitor- 
ing the dampness of the tomato plants, and 
turning on the water supply at the ap- 
propriate moment. I did have a further 
incentive because I wanted to cock a snook 
at my neighbours, and prove just how in- 
genious and self sufficient we Fidlings are! I 
could be the envy of my friends at the local 
horticultural society, too! 

Setting to work in the ’shop, I leafed 

through my pile of yellowing magazines, 
in search of inspiration. In one of my 
overflowing boxes of bits I had gathered 
together a motley collection of washing 
machine spares, including quite a few water 
‘solenoid valves which I recall I had plun- 
dered from a defunct dishwasher. I always 
stored such stuff carefully away, since you 
never knew when it would come in useful, 
so I had tons of bits stored in old biscuit 
tins which were rusting away gradually on 
the shelves. 

The solenoid valves were 240V 
mains operated, which deterred me 
not a jot. A simple solid-state 
moisture sensor, based on a rain 
alarm design I found in a 
magazine, was adapted to 
power the solenoid valve via 
an old Octal-base mains © 
relay. A probe was as- 
sembled from a pointed 
piece of stripboard offcut. 

The valve turned on like a 
good ’un when the resistance 
of the probe fell below a certain 
level. Good! Bridging the copper 
Strips with water (I used my soldering iron 
sponge) switched the valve off with a loud 

Gleefully, I fitted the gizmo into an 
aluminium box, replete with a _ large 
bakelite control knob to enable me to set 
the watering level precisely (well, sort of 
precisely). The prototype was then fitted 
into the greenhouse, high up out of harm’s 
way. A water supply was laid on and a 
variety of valves, all heavily swathed in 
gaffer tape, was installed via a web of green 


Over the next week or so the system 
gradually became more elaborate. Very 
cleverly, I thought, I added an extra circuit 
which enabled the garden sprinkler to turn 
on automatically and water the melon 
patch outside! I had prodded a moisture 
probe into the greenhouse soil, and another 
one in the melon patch. 

Soon the system settled down so that 
the tomato plants received an automatic 
supply of water when the going got hot. I 
could almost hear them slurping it up in 
appreciation! Things were not so good in 
the melon patch nearby, though. Wilting 
leaves told me that the plumtious plants 
were not getting in on the act, and 
melons like nothing more than water — 
lots of it! 

Piddles had become accustomed to the 
sight of the tangle of wiring and hosepipe, 

_ Everyday with Practical Electronics, September 1995 

this certainly hadn’t prevented him from 
indulging in his daily mousing, and 
one morning he was rummaging around 
amongst the melon patch, much to my 
chagrin, while I was twiddling with the 
electronics in the greenhouse, trying to 
coax the sprinkler system into operation. 
I'd suspected that one of the solenoid 
valves was misbehaving, so after some 
ferreting in the workshop I'd searched out 

Meanwhile, out of the corner of my eye I 
could see the tail of a certain moggie scoot- 
ing amongst the melons erratically, like a 
submarine’s periscope searching urgently 
fora kill. A plan formed... 

Quickly fitting the hosepipe to the re- 
placement valve and screwing the box back 
together, I switched on the mains supply 
and the water again, not wanting to miss 
this golden opportunity. With a flourish, 
I twirled the bakelite knob on the con- 
troller deftly and the solenoid valve clicked 

Water sputtered out of the sprinkler out- 
side as the melons began to bask in the 
glorious water. The cat’s tail drooped, a 
head popped up and then Piddles realising 
what I’d done, shot out of the melon 
patch at a grand rate of knots! A soggy 
moggie indeed! If only I’'d got my Polaroid, 
the picture would have had pride of place 
above the bench! 

One of my better days. 


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Everyday with Practical Electronics, September 1995 

All Trademarks Acknowledged 

AST month’s Interface article described 

the “Hamcomm 3.0” shareware pro- 
gram for decoding c.w., RTTY, etc. using 
a PC. The simple interface circuit des- 
cribed in that article relies upon the 
computer to handle just about every- 
thing. The interface does little more than 
amplify and clip the audio output from the 
receiver so that it can drive an input line 
of an RS232C port. 

The interface described in the previous 
article is slightly more sophisticated than 
most interfaces of this genre, and it 
provides some audio filtering. However, it 
still leaves the vast majority of the signal 
processing to the computer. | 

Tone Decoder 

Although “Hamcomm 3.0” is able to work 
well with a simple interface, it also has the 
ability to operate in conjunction with a 
“proper” external decoder. In the case of a 
c.w. decoder this simply has to take the CTS 
line of the serial port high when a tone is 
detected, or low when no tone is present. A 
practical tone decoder normally uses the 
arrangement shown in the block diagram of 

Fig. 1. 



Robert Penfold 

maintain sufficiently accurate tuning. There 
can also be problems with ringing effects in 
the filtering. 

A practical system usually has a 
bandwidth of a few hundred hertz. This is 
sufficient to prevent the decoder from 
responding to signals on adjacent channels, 
but is not so narrow as to make the decoder 

difficult to use. 

The filtering in the tone decoder is un- 
necessary if the receiver has a_ built-in 
c.w. filter. However, few communications 
receivers seem to have a cw. filter as 
standard, and where available as an add-on 
it tends to be extremely expensive. 

The output from the filter is fed to a rec- 
tifier and smoothing circuit. This produces a 
positive d.c. voltage that is roughly propor- 
tional to the strength of the output signal 
from the filter. A strong d.c. bias is therefore 
produced when the c.w. tone is present, but 
only a weak signal is produced when it is 

A level detector is driven from the output 
of the smoothing circuit, and its threshold 
level is set between the tone and no-tone 
output potentials of the smoothing circuit. 

Rect. & Level 
Smoothing Detector 

: Fig. 1. Block diagram for a basic c.w. tone decoder. 

The input signal is first fed to a buffer 
amplifier which ensures that the next stage 
is fed from an adequately low source 
impedance. The buffer stage is followed by 
a bandpass filter which has a narrow 
bandwidth. A c.w. signal consists of just a 
single tone, and it can therefore be 
accommodated by a bandwidth of just a few 

In practice it is essential to use a wider 
bandwidth as it is otherwise virtually impos- 
sible to tune in a signal properly, and to 

Its output therefore goes high when a tone 
is present, and low when it is not, giving the 
required tone decoding. 

In practice the threshold level has to be 
something of a compromise. Setting it 
just above the normal noise threshold 
gives good sensitivity, but leaves the 
unit vulnerable to triggering from QRM 
or any bursts of increased background 
noise. A higher threshold level results in 
lower sensitivity, but gives better overall 

1C1,3 = LF441CN 
IC2 = LF442CN 

C8 D2 

330n OA91 

Fig. 2. The c.w. tone decoder circuit diagram. 

Everyday with Practical Electronics, September 1995 

JK2 Phone 

Twin Peaks 

The circuit diagram for a simple tone 
decoder for use with “Hamcomm 3.0” is 
shown in Fig. 2. IC1 acts as a straightfor- 
ward non-inverting buffer stage at the input, 
and this feeds into a two stage bandpass 
filter based on IC2. 

The two halves of the filter are essen- 
tially the same, but the filter resistors in the 
second stage (R6 and R8) are slightly lower 
in value than those in the first stage (R2 and 
R4). This gives ‘slightly different centre fre- 
quencies, and an overall response that it 
slightly broadened. 

The approximate frequency response of 
the filter is shown in Fig. 3. As can be seen 
from this, the bandwidth is still reasonably 
narrow, and the operating frequencies of 
the two stages are not far enough apart to 
produce dual peaks. 

The overall centre frequency is at a little 
over 1kHz. The frequency response of the 
filter is something less than phenomenal, but 
it is quite good for a simple filter, and it 
produces good results. | 

The rectifier and smoothing circuit is 
a conventional half-wave type based on 
diodes D1 and D2. The time constant of 
resistor R11 and capacitor C9 must be long 
enough to give a large amount of smooth- 
ing, but short enough to avoid “smearing” 
of the c.w. signal. A time constant of about 
50ms seems to give optimum results. 

A voltage comparator, IC3 forms the basis 
of the level detector. The output from the 
smoothing circuit is connected to IC3’s in- 
verting input, and its non-inverting input is 
biased slightly positive of the central OV 
supply rail. 

The output of IC3 is normally high, but it 
goes low when the output voltage from 
the smoothing circuit exceeds the reference 
level at the non-inverting input. Note that 
this requires “Hamcomm 3.0” to be set to 
the “Reverse” keying mode. Resistor R14 
introduces some hysteresis which helps to 
give “clean” switching from one state to the 



200 300 400 600 1k 

Fig. 3. The approximate frequency response of the bandpass filter. 

other when there is a lot of noise on the 
input signal. 

The value of resistor R13 sets the 
threshold level of IC3. Higher values give 
higher threshold levels, and lower values 
give lower threshold voltages. 

The specified value gave good results - 
when the decoder was used with the “REC” — 

output of a Yaesu FRG-8800 receiver, but 

with other receivers it would probably be _ 
worthwhile experimenting with different 

values. It might be worth replacing resistor 
R13 with a 10k preset to enable the 
threshold level to be easily trimmed for 
optimum results. 

The circuit is powered from the RTS and 
DTR outputs of the PC serial port. Diodes 
D3 to Dé form a bridge rectifier that ensures 
that the circuit is provided. with supplies of 
the correct polarities. This gives nominal 
plus and minus 12V supplies, but the loaded 
supply voltage is likely to be somewhat less 
than this. 

All three integrated circuits are low cur- 
rent types, which ensure that the loaded 
supply voltages are still perfectly adequate. 
The total current consumption of the circuit 
is only a milliamp or so. It is likely that 
the circuit will not function properly using 
ordinary operational amplifiers such as the 
LF351N and LF353N. 

In Tune 

For the decoder to work well it is essential 
that stations are tuned in accurately. As 
pointed out in last month's Interface article, 
“Hamcomm 3.0” has some sophisticated 
built-in tuning aids. Unfortunately, these are 
inoperative when an external tone decoder 
is used. 

It is possible to get around this by includ- 
ing a simple interface as well as a tone 
decoder. This is possible because a simple 
interface and a tone decoder use different 
inputs of the serial port (DSR and CTS 

The circuit diagram for a simple add-on 
interface for the tone decoder is shown in 
Fig. 4. This is just an open loop clipping 
amplifier. In use it was found to be not 
quite as useful as hoped. 


The main problem 
is that the _pro- 
gram cannot work 
using the simple 
interface and _ the 
tone decoder simul- 
» taneously. This re- 
quires some manipula- 
tion of the program 
kings when switch- 
ing from tuning to 
reception, and vice 
versa, although the 
program’s macro fea- 
ture could probably | 
make this process 
much quicker. 

A more effective 
way of obtaining 
accurate tuning is to’ 
monitor the output 
from the filter using 
a crystal earphone 
connected to socket 
JK2. This enables the 
receiver's tuning to be 
set “by ear” for the 
strongest signal. Note 
that only a= crys- 
tal earphone can be 
driven from JK2, and 
that there is  insuffi- 
cient drive current 
available for other types of headphone and 

IC4 = LF441CN 

Gnd -12V 

Fig. 4. Circuit for the add-on simple 


Construction of the interface is quite 
straightforward, and the general layout is 
not critical. Stripboard construction is per- 

_fectly adequate. Take due care when con- 

necting diodes D1 and D2 as these are 
germanium diodes, and they are more 
vulnerable to heat damage than silicon 

Connection details for 25-pin and 9-pin 
PC serial ports are provided in Fig. 5. In 
either case the connections are made to 
the computer via a female D-connector. 

When using the interface remember to 
select “CW” from the “Mode” menu, 
together with “External Converter” and 
“Reverse” modes from the “Keying” 
menu. The external interface seems to 
give improved results when there are 
problems with QRM or general back- 
ground noise. This is not to say that 
perfect decoding is always obtained. 

Using an external decoder does not 
overcome problems with the software 

O00C OO 9000000 


Fig. 5. Connections for 25 -pin and 9-pin serial ports. 

producing frequent ‘garbage’ when 
decoding Morse code that has ragged 
timing. With a signal that is reasonably 
free from fading, and also has quite good 
timing accuracy, the system does produce 
copy that is reasonably error-free. 

An advantage of using an external tone 
decoder is that it is far less demanding on 
the computer. This method should there- 
fore work perfectly well with practically 
any PC, including something as basic as 
an XT type. 

The “Hamcomm 3.0” program is available 
from The PDSL, Dept EPE, Winscombe 
House, Beacon Road, Crowborough, 
Sussex, TN6 1UL (Tel. 01892 663298, Fax 
01892 661149). 

Everyday with Practical Electronics, September 1995 

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Everyday with Practical Electronics, August 1995 

Special Feature 



Going underground with Earth Current 
Communications - an area where there is plenty 
of scope for the electronics experimenter. 

Help explore the secrets of below ground 
communications and make cave exploration safer. 

gained for when visiting a new kilometre long extension to 

Ogof Daren Cilau in the Brecon Beacons was experienced 
by South Wales caver Matt Ward. It was on his way back towards 
the entrance that a large rock dropped in a narrow section of passage 
just ahead of Matt and cut him off from the rest of his party. The 
alarm was raised and thanks to the sterling efforts of the Gwent 
Cave Rescue Team he was eventually freed from his confinement, 
remarkably not much worse for his two-day captivity. 

The advance rescue team decided to lay a field telephone, nor- 
mally a reliable choice, especially in unfamiliar territory like these 
new passages. However, the telephone did not perform well and 
there was never a successful link end-to-end. This was because the 
cable became torn apart in the arduous entrance passages. 

The alternative communications technology was to use a Cave 
Radio, known locally as the ‘““Ogofone” (ogof means cave in 
Welsh), and developed by Bob Williams and Ian Todd. This 
equipment was taken underground at quite a late stage in the 
incident whilst another group took the corresponding surface set 
to the precise spot on the hillside directly above the rock fall. From 
here the surface people had a line of sight back to the surface 
controller and could talk to him on a v.h.f. handset. Within five 
minutes they were also talking to the underground team through 
100 metres of solid rock via the Ogofone, albeit too late to be of 
any help in the actual rescue. This illustrates how the lack of 
effective communications can often hinder cave rescue teams. 

Community Contribution 

World-wide, very few people are developing cave communica- 
tion equipment. However, this lack of interest in the electronic side 
of potholing is not indicative of the popularity of caving as a sport 
— in the UK alone, there are an estimated 125,000 trips under- 
ground every year. The unfortunate consequences of this are the 
number of rescues. In 1994, the 15 rescue groups of the British 
Cave Rescue Council were called out to a total of 48 caving inci- 
dents involving 112 people. Sadly, five of these people didn’t make 
it safely back to the surface. 

What this means is that there’s significant scope for innovation, 
and large numbers of people are potential beneficiaries of new 
developments in this area. If you take up the gauntlet, and decide 
to get involved in underground communication, therefore, you 
could make a significant contribution to the caving community. 

Cave Radio 

Orchestrating rescues is surely the most important use of cave 
radios and is probably the main motivation for people working 
in this area. Perhaps it’s difficult to quantify the benefit of effec- 
tive communications in emergencies, but there are certainly people 
walking about today who owe their lives to cave radios. 

f LUCKY escape and a longer stay underground than he bar- 

Everyday with Practical Electronics, September 1995 

However, the cave rescue organisations are not the only poten- 
tial users of cave radios. We could envisage, for example, the use of 
cave radios to prevent accidents, rather than just helping when 
they do occur. A caving party in touch with the surface, for in- 
stance, could be warned of impending wet weather and so make 
their exit before being trapped by rising water. 

At the moment, cave radios are too expensive for this to be 
viable, but it must surely be the ultimate aim. However, even if 
widespread availability isn’t currently a practical proposition, cave 
radios are used outside the rescue groups, primarily by cave sur- 
veyors, cave scientists, and, of course, those engaged in research 
and development of cave communications. 


Let us step back over a decade. For many years it had been 
known that the water thundering into the mighty shaft of Gaping 
Gill in the Yorkshire Dales, emerged some time later from the 
mouth of Ingleborough Cave, some two miles distant. However, 
after almost a hundred and fifty years of exploration, no connect- 
ing passage had ever been found. The complex surveys of both 
systems showed a number of points in Gaping Gill apparently 
close to points in Ingleborough Cave, but exactly which point 
should cavers explore to find the elusive link passage? 

Since the surveyed points at the far extremities of both systems 
were likely to be in error, this search could have taken forever. 
Then, in 1983, technology came to the rescue in the form of the 
“‘Molefone”’, developed by Bob Mackin. Operating on 87kHz, and 
providing voice communication, this cave radio could also be used 
to pinpoint an underground transmitter from the surface. By provid- 
ing additional fixed survey points in this way, the survey accuracy 

‘was improved and the likely break-through point identified. The 

link-up expedition was planned with military precision, TV crews 
and reporters alerted, and the through trip is now history. 

More recently, the use of microprocessor-controlled data loggers 
has made scientists more productive, but frequent underground 
trips were still necessary to extract the collected data. Clearly the 
ultimate solution is to interface the data logger to a cave radio. 
Now, using a laptop computer interfaced to a cave radio on the 
surface, data can be uploaded via a telemetry link. 

Cave Fadio Principles 

Intuitively, most people wouldn’t expect radios to work down 
caves. After all, a few metres of soil and pre-stressed concrete is 
enough to blank out car radios in under-passes. In practice, if you 
were to take an ordinary transistor radio a hundred metres under- 
ground, you’d be unlikely to hear anything at all. However, if your 
radio receiver operated in the lower part of the I.f. band, you’d be 
able to hear MSF, the National Physics Laboratory’s standard 
time and frequency station, coming in loud and clear on 60kHz. 

The reason for this surprising result is that the absorption of 
radio waves by rock depends on the frequency, with low fre- 


quencies being the most efficient at penetrating the ground. With- 
out going into all the theory, it is suffice to say that to achieve 
communication to a depth of a couple of hundred metres — the 
maximum depth of most British caves — radios tend to operate in 
the 800Hz to 150kHz region. 

Now, the standard radio antenna, against which the efficiency 
of other antennas is compared, is called a dipole and is half a 
wavelength long. OK receiving antennas don’t have to be half or 
even a quarter wavelength long, and telescopic car antennas are 
indeed far shorter than this at MW and LW. However, the receiv- 
ing antenna is only one part of the system. The transmitting an- 
tenna responsible for radiating the BBC Radio 4 LW signal is of 
significant proportions as you'll know if you’ve driven past the 
transmitting site at Droitwitch. The fact is that if both transmitting 
and receiving antennas are significantly shorter than quarter of a 
wavelength, then the overall system would be grossly inefficient. 

Returning to our typical cave radio frequencies, and converting 
to wavelengths, we get a range of about 2km to 400km, so, we 
would have to surmise that small portable cave radios are imprac- 
tical. Huge antennas would be required yet caves are not renowned 
for their spaciousness. 

All that has been said so far relates to “‘conventional’ radio, 
communication by the transfer of power through free space by 
electromagnetic radiation. However, as an alternative to normal 
radio, which employs the so called “‘far field’’, “near field” com- 
munication can be used. 

Much closer than half a wavelength from the transmitting an- 
tenna, localised magnetic and electrostatic fields exist and can be 
received by induction or capacitive coupling, respectively. The 
near magnetic field, referred to as the “induction field” looks 
particularly promising since it can be generated effectively using 
small loop antennas. 

The induction field is not suitable for long distance communica- 
tion since it decays with the cube of distance, but it is eminently 
suitable for cave radios, since it is rarely further than a few 
hundred metres from a cave to the surface. The technique 
employed by cave radios, therefore, is referred to as low frequency 
induction. Fig. 1 illustrates the principle of conventional cave 
radio, and you'll notice the familiar “bar magnet’’ field lines 
associated with inductive communications. 

Earth Current Signalling 

Take a microphone and audio amplifier, feed the output into a 
step-up transformer, and connect the transformer secondary to a 
pair of copper rods driven into the ground a few metres apart. 
Now connect the input of another audio amplifier to two more 
ground rods a couple of hundred metres away. Attach a pair of 
headphones and you'll find that anything spoken into the distant 
microphone will be clearly audible. 

t eX 
Re ® 

Surface signals being received underground using an induc- 

tive loop “aerial.” : 
Our heading picture shows caver Rob Gill setting and test- 
ing a surface hybrid earth/current baseband transmitting rg. 



Fig. 1. Conventional Cave Radios operate by low frequency 
(Lf) induction. This can be viewed as akin to the opera- 
tion of a transformer but with very loose coupling between 
primary and secondary windings. 

This technique is called “earth current signalling’’, and was first 
demonstrated over 100 years ago. Shortly afterwards, Marconi 
developed radio and so this early form of wireless (in the most 
literal sense of the word) communications was never developed, 
except briefly for use on the front line during WW1. 

Earth current signalling has continued to fascinate electronics 
enthusiasts though, and articles have regularly appeared in the 
amateur electronics press. Its popularity probably lies in the fact 
that an operating licence is not required, but it is doubtful that 
many people have found any genuine applications for it. 

However, earth current signalling is potentially valuable, specifi- 
cally in the area of cave communication. Furthermore, it provides 
plenty of scope for experimentation. First let’s take a look at some 
background information. 

As with virtually any communication system, experimenters 
with earth current signalling will soon find that the signal strength 
decreases as the distance between the transmitter rods and the 
receiver rods is increased. Another familiar result is that com- 
munications efficiency can be improved by increasing the separa- 
tion between the two transmitter rods and/or between the two 
receiver rods. 

Of course, all this is what would, intuitively, be expected and is 
readily explained by assuming that the ground is a two-dimen- 
sional network of resistors and that communication is achieved by 
conduction. What most experimenters don’t consider, however, 
is that the earth isn’t two-dimensional, it also has depth. So, 
if you take the receiving set-up down a cave, and knock the 
ground rods into the floor of a cave passage you will be able to 
achieve communication through the earth. In Fig. 2, earth current 
communications is shown modelled as a 3-D resistor network with 
a surface transmitter being received both on the surface and in a 
cave passage. 

The other thing most earth current experimenters don’t realise 
is that conduction isn’t the only possible communication model. 
When an alternating current passes through the earth, a magnetic 
field will be generated, so we could argue that the receiver operates 

Fig. 2. Earth current communication can be remodelled by 
considering the earth as a rectangular grid of resistors. How- 
ever the earth also has depth, so a signal injected on the 
surface can be received in a cave. 

Everyday with Practical Electronics, September 1995 


by detecting this magnetic field. For a conventional set-up, this is 
probably splitting hairs, but if true, there will be other means by 
which the signal could be detected. 

We’ve already seen that cave radios operate by magnetic induc- 
tion, so if an earth current signal does generate a magnetic field, it 
should be possible to detect it using an induction receiver. Simi- 
larly, an earth current receiving rig should be able to receive an 
inductively generated signal. A number of people are now starting 
to experiment with hybrid earth current/induction radio systems 
for rescue use and have shown that the technique is viable. The 
main advantage over pure induction cave radios is that the surface 
party can achieve coverage over a wide underground area with one 
widely spaced pair of rods. Using conventional cave radios, at 
maximum depth, the surface party has to track the underground 
party across the surface to maintain contact. This, in fact, is one of 
the main reasons that cave radios are not used universally during 
rescues in horizontally extensive caves such as that in Daren Cilau 
mentioned earlier. 

Fig. 3. The current flow in the earth, resulting from inject- 
ing a signal into ground rods, forms a series of huge under- 
ground loops. Just like an induction transmitter, a magnetic 
field is therefore generated and can be received underground 
using an induction loop. 

Note that the field pattern differs from the familiar “bar 
magnet” pattern associated with an induction loop transmit- 
ter due to the combined effect of multiple “loops.” 

In Fig. 3, we see a hybrid system in action. Here, an earth 
current transmitter is being received inductively underground. It 
should, perhaps, be pointed out that the magnetic field lines are 
different from those in Fig. 1 because the current path makes up an 
infinite number of underground loops, all contributing to the 
overall field pattern. 

So far one important fact has been glossed over. The earth 
current system outlined in this section operates at “‘audio fre- 
quencies’. In technical jargon it is a baseband system. You'll 
remember, however, that the Molefone referred to earlier operated 
at 87kHz, as does the Ogofone. 

Certainly cave radios can operate at baseband, and this was, 

in fact, the first technique employed. However, in the interests of - 

reduced power consumption, reduced antenna mass, and increased 
efficiency, these were soon replaced by carrier-based designs. Of 
course, earth current systems could also operate above the audio 
band and this would indeed be necessary for inter-operation with 
cave radios. 

Experimental Suggestions 

In this section, some areas where the constructor could get in- 
volved in experimenting with earth current communication un- 
derground will be suggested. However, first some very important 
safety guidelines must be highlighted. It would be irresponsible to 
entice inexperienced people into caves without adequate supervi- 
sion. After all, the main aim in writing this article is to help make 
caving safer, so it would be wholly inappropriate if the end result 
was to generate “‘customers”’ for the cave rescue groups. 

It is probably stating the obvious but potholes provide oppor- 
tunity for getting lost, getting stuck, being crushed by falling rocks, 
falling down pitches, drowning, and suffering hypothermia. How- 
ever, if you’re sensible, a trip underground is not especially dan- 
gerous, and most of these hazards can be virtually eliminated. 

First and foremost, if you’re not a caver, being sensible means 
only going underground in the company of people with caving 
experience. One approach would be to make contact with a lo- 
cal caving club, although you'll probably find that most of the 
members won’t share your enthusiasm for electronics. More ap- 
propriate, given your motivation for going underground, would be 

Everyday with Practical Electronics, September 1995 

to make contact with the Cave Radio & Electronics Group of the 
British Cave Research Association. Details are provided near the 
end of this article. 

One other introductory comment before we get down to business 
— licensing. The author chose to offer this article to Everyday 
with Practical Electronics rather than an amateur radio magazine 
because: it concerns an area where non-licensed electronics en- 
thusiasts can take part on the same footing as radio amateurs. 

Although you need a licence to experiment with inductive com- 
munication, the I.f. band is not covered by the amateur radio 
licence in the UK, so everyone would have to work under a Test 
and Development licence. With earth current communications, 
however, you probably don’t need a licence at all, though the 
situation is far from clear. Certainly it has always been assumed 
that earth current work doesn’t require a licence. 

However, since the use of low frequency inductive communica- 
tion is controlled in the UK, and since we are now admitting to the 
fact that an earth current does generate an induction field, would 
the Radiocommunications Agency (RA) now take a different view? 
So long as you work at baseband, there should be no problem. 
If you were to experiment at 87kHz in order to interact with an 
induction radio, on the other hand, it would be wise to check it out 
with the RA first. 

Practical Work 

So, warnings and preparatory comments out of the way, what 
practical experiments on underground earth current communica- 
tions could you carry out? First of all, let’s make it clear that no 
pratical circuits are going to be presented here. Quite a lot can be 
done with off-the-shelf equipment, and even when custom equip- 
ment is required, very simple circuits can often be used. 

For example, to generate a baseband earth current, all you need 
is a source of an audio signal — a cassette recorder or microphone 
for example, a standard audio amplifier, a step-up transformer and 
a pair of ground rods. The underground induction receiver can 
also be very simple. 

In the system demonstrated to the author, the receiver was based 
on an old transistor radio. All the r.f. circuitry had been bypassed, 
so that the ferrite rod antenna was connected directly to the audio 
amplifier. This is by no means an optimum receiver, but even with 
this simple set-up, quite a lot can be learned. 

A number of avenues for experimentation come to mind. For ex- 
ample, how well does a single pair of ground rods “flood” a cave 
system with an induction field? Does one pair of rods fire most of the 
signal at right angles to the line between the rods, as dipole antennas 
do, or does it give an omnidirectional field pattern? If we get direc- 
tional coverage, can the situation be improved by using extra rods? 

We know that signal strength can be improved by increasing the 
spacing between the ground rods, but there are clearly practical 
limits to the separation between them. So, what other methods 
could be used to improve efficiency? Is it best to use longer rods, or 
thicker rods? It has been suggested that better than either of these 
options is to replace each rod with a hexagonal array of rods — but 
does this work in practice? 

What has just been described are preliminary but nevertheless 
important experiments. To go beyond this initial stage, however, 
you'll probably need to improve the receiver. As with all induction 
radios, you'll find that there i is a pay-off between antenna size and 

In general, the easiest way to improve the performance of a loop 
is to increase its cross-sectional area, although large diameter 
loops are obviously not suitable for use in small cave passages. For 
this reason, ferrite rods are sometimes used to increase the an- 
tenna’s effectiveness. Another means by which loops can be made 
much more efficient is to tune them to resonance, but for speech 
communication, the Q-factor mustn’t be so high as to reduce the 
bandwidth below 3kHz. 

Interference radiated from overhead mains cables on 50Hz and 
multiples thereof, is another problem, even in the remote areas 
where most of the UK’s caves are located. To get maximum per- 

formance out of baseband systems, therefore, notch filters would 
probably be required. 

As already indicated, the ultimate aim with earth current com- 
munications must be to obtain interpretability with 1.f. induction 
radios. Since these are relatively sophisticated SSB transceivers, 
however, this does require a modicum of experience in conven- 
tional r.f. circuit design. 

However, one other area for experimentation does come to 
mind. You’ll remember that in the section “Cave Radio’, it was 
suggested that if all cavers were to carry radios, they could be 
warned of impending bad weather and so many rescues could be 
obviated. Although two-way cave radios offering speech com- 
munication will probably always be too expensive for this, there is 
an alternative. Each underground party carries a cheap compact 



receiver which can detect an induction field on a specific audio 
frequency. On receipt of this signal an alarm is sounded. 

Slightly more sophisticated, we could envisage a unit which 
reacted to perhaps three different audio frequencies and il- 
luminated one of three different coloured l.e.d.s. These could be 
interpreted in various ways, perhaps “get out of there’, “‘get out of 
there quickly”, and “all clear’’, for example. 

With a conventional cave radio transmitter, this system may not 
be workable. Communication is in one direction only, so unless the 
underground party keeps exactly to a pre-arranged schedule, the 
surface party won’t know exactly where they are. Since induction- 
to-induction systems require reasonably accurate alignment of 
transmitting and receiving loops at maximum range, this wouldn’t 
provide the reliable warning mechanism which is required. How- 
ever, if an “earth current transmitter” is able to saturate the cave 
system with signal, then it would be eminently suitable. 

The Cave Radio & Electronics 


Hopefully this article has given you some food for thought and it 
is the author’s hope that some readers might decide to do some 
experimentation in this area. The major motivation for developing 
cave communications equipment is surely to help the cave rescue 
organisations, so it would be a shame if the experimenter were to 
develop something but didn’t have the opportunity for their work 
to be publicised. 

The Cave Radio & Electronics Group (CREG) of the British 
Cave Research Association (BCRA) is the UK’s body dedicated 

equipment for use in caving. Through a quarterly Journal, which 
covers a wide range of topics, the CREG acts as a clearing house 
for the dissemination of news and ideas, in addition to publishing 
practical circuits. Also of potential interest to readers, field 
meetings are held twice a year around the country and provide an 
opportunity to share ideas in a practical way. 

You'll also notice from the short bibliography, that the CREG 
has already published many practical and theoretical articles relat- 
ing to induction radio and earth current communications. If you 
do intend to start experimenting in this area, it might be an idea to 
take a look at these articles — they could save you from “‘re-invent- 
ing the wheel”. For details of membership of CREG please send 
a stamped, self-addressed envelope to Mike Bedford at 4 Holme 
House, Oakworth, Keighley, W. Yorks. BD22 0QY. 0 


Venturing Underground with VLF Radio, Mike Bedford, Radio Communications, 

Vol. 71, No. 1 (January 1995). 
An introduction to LF induction radio for caving. Describes the use of cave 
radios for radio-location and gives practical circuits for an 874Hz transmitter 
and receiver. 

An Introduction to Earth-Current Communications, David Gibson, CREG 

Journal 17 (September 1994), 
A mainly theoretical introduction to earth current for use in cave com- 
munication. Also discusses earth current/induction hybrid systems. Quite 

bon Current/Induction Field Experiments, Rob Gill, CREG Journal 19 (March 
Description of experiments to show the viability of hybrid earth 
current/induction field systems as postulated by David Gibson in his article 

to the development of communication and other electronic 


Simple Theremin 

The small handheld box for the Simple 
Theremin came from Rapid Electronics 
(qf 07206 751166), code 30-0270. The 
printed circuit board is a tight-fit in the case 
and the edges may need “rubbing down” 
slightly to fit. 

Other handheld cases could be used and 
most of our component advertisers should 
be able to offer a suitable alternative. If 
another case is used it should be plastic and 
not metal, since this will adversely affect the 
range of the instrument. 

We understand that the BR195 lock- 
fit transistors and the 100yH_ induc- 
tors are available at a ‘surplus’ price 
from Greenweld Electronics (qi 07703 
236363). The specified miniature poten- 
tiometer seems to be fairly expensive and 
will take some finding locally. The only 
listing we have found is from Farnell 
Electronic Services (4 07279 626777) 
and is carried under the Bourn 50 series 

should carry stocks of the Philips type 
trimmer capacitor and can usually be found 
listed as a ‘film dielectric’ trimmer. The 
38mm diameter loudspeaker, with an “al- 
nico’ magnet, is another part which should 
be widely available. It is most important that 
a speaker with an alnico or colmar magnet 
be used, as the popular ‘’ferrite’’ magnet 
type will be too large for the p.c.b. 

The low K metalised or ceramic plate 
capacitors should be generally available 
and not cause too much concern. They are 
certainly currently listed by Cirkit (4 
01992 448899). 

If readers do experience difficulty in 
locating parts for the Simp/e Theremin, kits 
and complete units are available from 
Longwave Instruments, Dept EPE, 
23 Ashley Lane, Hordle, Lymington, 
Hants $041 OGB. (4p 07425 610849). 
Ready made, the Simple Theremin costs 
£49.99 and a full specification Theremin is 
available for the sum of £350. A MIDI 
converter unit will be marketed by them 

- The printed circuit board for the Simple 

Theremin is available from the EPE PCB 


Most of our component advertisers 

id TALK 

with David Barrington 

Service, code 952 (see page 735). 

Comprehensive Security System 

Some of the items called up for the 
Comprehensive Security System may prove 
elusive to locate locally. 

If you take up the PIR sensor option 
you will find prices vary quite considerably 
and it might be well worthwhile shopping 
around. A sensor is currently being listed by 
Bull Electrical(qp 07273 203500) for 
the sum of £8 (code Mag8P5) and also by 
Mailtech (iP 07584 831475) from £6.50 
to £11.75 each. Before ordering check that 
they have relay outputs. 

The small buzzer (code KU56L), 
keyswitch (CJ94C) and the “staccato” 
electronic siren (YZO3D) were all pur- 
chased from Maplin. The 12VA mains 
transformer also came from the same 
source, order code DM28F. 

An empty alarm bell box, alarm sticker 
and the 12V 2AHr. lead acid battery were 
purchased from Electrovalue (qP 07784 
442253). \Ne understand that the range 
has changed recently. The 7- channel 
MOSFET was also purchased from the 
same source. 

The bell wire and the domestic dual light 
switch, although not listed in their adver- 
tisements, are stocked by Bull Electrical 
(see above) and J&N Factors (q@P 07444 

Quite a large number of our advertiser 
stock security/intruder switches, micro- 
switches and pressure mat switches, all at 
fairly reasonable prices in comparison to 
“superstores ’’. 

Low-Range Ohmmeter Adaptor 

There should be no problems when 
shopping for components for the Low- 
Range Ohmmeter Adaptor. 

The multi-turn potentiometers are 
usually the cermet type and the most 
common range usually comes in anything 
from 18-turns to about 25-turns. The only 
point to watchout for is that they will fit on 
the p.c.b., although there is a _ certain 
amount of ‘play’ in the connecting wires. 

The other points to watchout for are: the 
“test” terminals must be all metal types, 

and that the pushbutton test switch is a 
low-profile type so that it does not short 
‘ing any components in the small plastic 
The small printed circuit board is avail- 
able from the FPE PCB Service, code 926. 


- One or two “special’’ components for the 
Vandata project need highlighting as they 
many not be available from local suppliers. 

We shall start off by tackling the relays. 
Although it is quite possible to use other 
relays, it is suggested that the ones speci- 
fied be used as others many not fit on the 
printed circuit board. 

The 10A mains relay is listed by Maplin 
as their “Ultra Miniature High Power’ type, 
code YX97F. They also supplied the 16A 
(12V 170 ohm coil) Automotive type relay, 
code JM26D (16A/12V car relay). 

The reed relay switches are RS. 
components and are available from 
Electromail (qi 07536 204 555), their 
mail order outlet. The code number to quote 
is 338-147. 

The MBR2045 Schottky diode, 5mm 
multicolour |.e.d.s and a suitable slotted 
heatsink all came from Maplin. Codes 
GX350, YH75S and FL58N. The heatsink 
could be fabricated from 40mm x 20mm 
aluminium plate. 

The turret pins for mounting the reed 
relays were ordered from the above com- 
pany, code JMO4E (two packs required). 
The screw-terminal locks and 18s.w.g. and 
20s.w.g. enalled wire. should be available 

If you wish to use identical cases, these 
were ordered from Maplin, codes LLOSF for 
the boot unit and KC93B for the display 

The two printed circuit boards for the 
Vandata are available from the EPE PCB 
Service, codes 953 (Boot) and 954 (Dis- 
play) respectively. 

Finally, as there are high currents as- 
sociated with ‘‘car electrics”, any additional 
inter-linking wires should be rated identi- 
cally to the existing coupling cables that 
many need “breaking” into. These should 
be available from any good caravan and car 
accessory shops or garages specialising in 
caravan spares. 

Hum-Free Battery Eliminator 

We cannot foresee that any component 
buying problems are likely to occur for 
readers wishing to construct the Hum-Free 
Battery Eliminator project. 

Everyday with Practical Electronics, September 1995 


The essential 
reference work 

_ © Easy-to-use format 
a ® Clear and simple layout 
Be Comprehensive subject range 
® Regular Supplements 
®@ Sturdy ring-binder 
® Projects to build 
®@ Components checklists 
@ Extensive data tables 
® Detailed supply information 
® Ready-to-transfer PCBs 
.® Detailed assembly instructions 
@ Professionally written 

The revised edition of The Modern Electronics | ESSENTIAL DATA: Extensive tables on diodes, transistors, 
Base Manual contains practical, easy-to-follow _ thy"istors and triacs, digital and linear i.c:s, 

‘ microprocessors. 
information on the following subjects: The Manual also has an extensive Glossary, and covers 

BASIC PRINCIPLES: Symbols, components and their Safety, Specialist Vocabulary with Abbreviations and 
characteristics, active and passive component circuits, power § Suppliers. The most comprehensive reference work ever 
supplies, acoustics and electroacoustics, the workshop, _ produced at a price you can afford, the revised edition of THE 
principles of metrology, measuring instruments, digital MODERN ELECTRONICS MANUAL provides you with all the 
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_ Everyday with Practical Electronics, August 1995 

Constructional Project 




Musicians may hum the tune, 

OWARDS the end of the article describ- 

ing the guitarists’ Personal Practice 

Amplifier (last month), brief mention 
was made of using it with a mains power 
adaptor. Earthing of the negative rail was 
recommended to increase safety and reduce 
hum, but at the time this had not been tried 
with the prototype. At least, not with one 
of the little plug-in mains adaptors that are 
so common nowadays. 


The musician for whom this project was 
designed took it home, boxed it up and 
wired it very neatly, added a 20mA l.e.d. 
power indicator, and installed a partly- 
charged PP3 NiCad battery. Readers can 
guess how long that lasted, probably not 
even for the first riff! 

Next, he fitted a switched power socket 
for a 9V 300mA plug-in adaptor. Result: 
hum. Lots and lots of hum! So the author’s 
phone rang again, and soon the unit was 
back on the bench for investigation. 

The construction of mains adaptors 
varies with make and use. Some contain 
just a transformer to produce a low-voltage 
a.c. output, but general-purpose types 
usually have a transformer, rectifier and 
perhaps a decoupling capacitor to generate 
a dc. supply. Most have no active 
regulation and so the output voltage varies 
with load. 

Mains adaptors have to provide the spec- 
ified voltage at full load. At lesser loads 
they produce higher voltages, often up to 
the peak value of the sinewave from the 
transformer — nearly 50 per cent higher. 
There is generally some a.c. ripple on the 
output, which at light loads often has an 
unpleasant “‘sawtooth” waveform because 
the capacitor is charged only at the peaks 
of each cycle. 

It can be difficult to earth the output of 
one of these adaptors as they normally 
use the “double insulated” approach to 
provide an isolated output. The earth pin is 
often just a plastic dummy provided only 
to open the protection cover in the mains 


but never amplifiers and PSUs! 


The difficulty with using a mains adaptor 
with the Practice Amplifier centred upon 
the TDA2822 output amplifier. Firstly, this 
becomes more sensitive at higher sup- 
ply voltages. With around 12V from the 
(nominally) 9V plug-in unit, much noise 
and instability became apparent. Secondly, 
the TDA2822 does not appreciate supply 
rail hum. ? 

Ripple from the adaptor supply was 
measured at just 0-1V r.m.s., but this was 
still enough to render the amplifier quite 
unusable. Disconnecting the leads from the 
volume control and shorting them to their 
screens made no difference, confirming that 
the hum was entering via the power sup- 
ply. More decoupling proved unhelpful. A 
1000uF capacitor applied close to the chip 
supply pins had no effect. 


A means of reducing the adaptor sup- 
ply voltage and ripple was clearly needed 
to solve the problem. One method tested 

was an active ripple suppressor. Whilst this 
was not the solution eventually adopted, it 
worked quite well. The circuit is shown in 
Fig. 1 for readers who might like to experi- 
ment with it. It works as follows: 

Resistor R1 is chosen so that about 
five milliamps flows through diodes D1 
and D2. The voltage drop across these 
is about 1-2V, providing a voltage with 
“headroom” beneath the ripple for the 
active part of the circuit. This still has the 
full ripple imposed on it so it is smoothed 
by resistor-R2 and capacitor Cl, and then 





Fig. 1. Active ripple rejection circuit. 

Everyday with Practical Electronics, September 1995 

buffered by transistors TR1 and TR2 con- 
nected as a complementary Darlington 

With the component values shown, the 
ripple is reduced to less than one per cent. 
It works quite well and could provide a 
cheap and simple solution. The diodes 
reduce the voltage a little, as does the 
base-emitter drop of transistor TR1. The 
total loss is about 2V. : | 

However, the circuit does not actually 
regulate the output voltage and may not be 
suitable for use with some adaptors. Nor 
does it solve the problem of earthing the 
output, and, due to the way power socket 
switches are constructed, it could not easily 
be housed inside the amplifier’s case. Con- 
nection somewhere in the lead between 
supply and project would be required. 


Consequently, to achieve reliable and 
repeatable results, it was decided to design 
a regulated supply with a much higher 
performance than found in most commer- 
cial units. The full circuit diagram for this 
is shown in Fig. 2. ; 

Transformer T1 is a 250mA type with 
12V-0-12V secondary windings. Diodes D1 
and D2 perform full-wave voltage rectifica- 
tion, with capacitor C3 providing d.c. 
voltage smoothing. The two small-value 
capacitors Cl and C2 reduce noise gener- 
ated by the diode switching. Regulator IC] 
is an LM317T, an adjustable output volt- 
age type. In Fig. 2, the values of resistors 
Rl, R2 and R3 determine the output 
voltage, set here to 9V. 

Capacitor C6 provides additional output 
decoupling, although the regulator itself 
removes nearly all the ripple. The circuit 
to be supplied will also normally have its 
own decoupling. Capacitors C4 and C5 
are required to ensure regulator stability. 
The output of this circuit is a stable d.c. 
voltage of the correct value regardless of 
load (within the limits of the transformer) 
and virtually free of ripple and noise, a 
huge improvement over most commercial 

Since the circuit is connected to the 
mains with a standard three-pin plug, it is 
simple to earth any point of the output as 
required, either negative or positive rail. 
Even if a “floating” output is required, the 
transformer metalwork can be earthed, 
which again helps to reduce noise. 


A little additional information may be 
useful for constructors who would like 

to know a bit more about the LM317T . 

regulator chip, and perhaps set a different 
output voltage. The regulator is a 3A 

3 2 7 


Fig. 3. Pinouts for the LM317T voltage 

Ni eta dae Sa soya i ar a i re 


Fig. 2. Complete circuit diagram for the Hum-free Battery Eliminator. 

device in a TO220 package, as shown in 
Fig. 3. 

There is also a 100mA version available 
ina TO92 package for low-power applica- 
tions. Both devices can accept input volt- 
ages up to 40V but need a minimum of 3V 
difference between input and output pins. 
However, with high differential voltages 
across the chip, a watch must be kept on 
its heat djssipation. Additionally, a mini- 
mum load of 5mA should be taken from 
the output at all times, although this 
can conveniently be drawn by the voltage 
determining network. 

The output voltage is determined by the 
ratio of two resistances in a feedback net- 
work, as shown in Fig. 4. The usual for- 
mula given for determining the resistance 
values is Vout = 1:25 x (1 + R2/R1) volts, 
but the author prefers a slightly different 
approach. Essentially, the chip operates by 
maintaining a constant 1-:25V between the 
output and “adjust” pins. This means that 
a 220 ohm resistor (R1) between output 
and ‘“‘adjust” will draw 1-25/220 milliamps, 
slightly more than the SmA minimum load. 
required, leaving only the value of R2 to be 

Fig. 4. Simple voltage regulator circult. 

The voltage across resistor R2 is clearly 
the required voltage less 1.25V, whilst the 
current which will pass through R2 is that 
from R1 plus 50pA. The S0pA is the cur- 
rent which flows from the ‘“‘adjust’” pin, 
ignored in original formula. With the cur- 
rent and required voltage figures known, 
the necessary resistance can be easily calcu- 
lated from R = V/I. The precise resistance 
value can be obtained by using appropriate 
resistors in series or parallel, or by using a 
preset potentiometer. . 

It should be noted that the potential be- 
tween output and “adjust” may not be ex- 
actly 1-25V, in fact the data sheets quote 
1:2V to 1-3V, a variation of about four per 

(Further information about the LM317T 
was given in EPE October 1994 issue, page 
796. Ed.) 

Everyday with Practical Electronics, September 1995 



Using a printed circuit board for a cir- 
cuit as simple as this seemed to the author 
to be “overkill”. Instead, most of the com- 
ponents are mounted on a small piece of 
0-1 inch grid stripboard having 14 strips by 
18 holes, as shown in Fig. 5. 

Ss A ee ee a ee 7) 



O000000000 0000000 

Fig. 5. Stripboard layout and track details 
for the Hum-free Battery Eliminator. 

The stripboard should be carefully cut 
and filed to fit into the slots at the sides of 
the suggested case. There are two track cuts 
to be made in the board, and three link 

One of the links appears to connect to a 
strip that goes nowhere else. In fact, as the 
“adjust” pin is a point where noise might 
enter the circuit, the strips to either side of 
the one connected to “‘adjust” are also con- 
nected to the negative rail to help guard 
against this. 

Little needs to be said regarding con- 
struction, save that three of the 100n 
capacitors (C1, C2 and C5) have their leads 
bent outwards and this should be done 
with care as they are fragile. Testing con- 
sists of simply connecting up the com- 
ponents, thoroughly checking the assembly 
when complete, attaching a meter and 
applying power. However, be extremely 
careful as mains voltages are present around 
the transformer. If in any doubt, consult a 
qualified electrician. 


Fig. 6. Connections between board, transformer and regulator. 

In the unlikely event of problems, the cir- 
cuit could be supplied with 12V d.c. from a 
current-limited supply in place of the trans- 
former whilst trouble-shooting takes place. 


Connections between board, transformer 
and regulator are shown in Fig. 6. The 
regulator is bolted to a small piece of 
aluminium which is wedged into the end of 
the case behind the pillars to which the lid is 
screwed. The heatsink tab on the regulator is 
internally connected to the output pin, so it 
should NOT be allowed to come into con- 
tact with any other part of the circuit. 

The mains earth lead does not have to be 
connected to the negative rail. It can be 
connected to positive or, where a double- 
insulated transformer is used (the type with 
separate bobbins for primary and secon- 
dary windings), it could be omitted al- 
together. (If a metal case is used, the case 
MUST be connected to the Earth lead.) 
All three arrangements were tried with the 
Practice Amplifier and none produced any 
audible hum. An l.e.d. could be added to 
indicate that the unit is operating. 


There are many ways in which this power 
supply can be housed. The prototype was 
fitted into an ABS plastic box with in- 
ternal dimensions of 49-Smm x 99-5mm x 
40mm. Although the prototype shown in 
the photograph was built with a mains plug 
on a short lead, another was constructed as 
a plug-in unit, with the plug fixed directly 
to the case. This was awkward to wire 
though, and is not really recommended. 

EVERYDAY(| -—s—sx'—sit 


Cases with moulded plugs are available, 
but the problem with these is that the Earth 
pin is usually a plastic dummy. With some 
types it might be possible to remove this 
and replace it with a metal pin taken from 
an ordinary plug. 

Ripple from this battery eliminator is 
practically unmeasurable, and _ voltage 
regulation from zero to 250mA is better 
than one per cent. It has completely 
eliminated the Practice Amplifier problem 
experienced by the author’s musician 
friend. With the volume control fully up 
there is no audible hum. 

The unit may well prove beneficial for 
use with other equipment having problems 
with mains power supplies, and could also 

| enclose payment of £ 
payable to Everyday with Practical Electronics 


R1,R2 2k7 (2 off) 
R3 2202 
All 0:25W 5% carbon 
film or better 




C1, C2, 
C4,C5 100n ceramic (4 off) 
C3 10001 radial elect. 35V 
C6 100u radial elect. 25V 

D1,D2 1N4001 rectifier diode 
1C1 LM317T adjustable positive 
voltage regulator, 3A 


T1 12V-0-12V 250mA mains 


Plastic ABS case, 49:5mm x 99:5mm 
x 40mm (internal measurements); 0-1 
inch stripboard, 14 strips < 18 holes; 
2-pin output socket — to suit applica- 
tion; mains plug and cable; connecting 

wire, solder, etc. 

be used as a bench power supply for 
test equipment, etc. It runs cooler than 
many commercial units, a two-hour test at 
270mA produced only comfortable hand- 
warmth, mostly from the transformer. 

Approx cost 
guidance only 

(cheque/PO in € sterling only), 

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Everyday with Practical Electronics, September 1995 

High quality stepping motor kits (all including 
stepping motors) ‘Comstep’ independent control of 
2 stepping motors by PC (Via the Parallel Port) with 
2 motors and software. 

; Kit £67.00; ready built £99.00 

Software support and 4-digital inputs kit 

Power interface 4A kit £36.00, power interface 8A 
kit, £46.00 

Stepper kit 4 (manual control) includes 200 step 
stepping motor and control circuit £23.00 

We are now stocking a range of stepping motors and 
kits to drive them — please ask for the stepping motor 
‘data sheet for full information. 

Inverter toroidal transformers 225VA 10:5-0-10-5V 
primary 0-260-285V secondary £29.95 
LEDs 3mm or 5mm red or green 7p each; yellow 
11p each. 
Cable Ties 1p each, £5.95 per 1000, £49.50 per 

High quality photo resist copper 
clad epoxy glass boards 
Dimensions single-sided double-sided 
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4x8 inches £2.75 £2.99 

6x12 inches £6.20 = 
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AA (HP7) 500mAH £0.99 
C 2AH with solder tags 
D 4AH with solder tags 
1/2AA with solder tags 
AAA (HP16) 180mAH 
AA 500mAH with solder tags 
C (HP11) 1:8AH 
D (HP2) 1:2AH 
PP3 8:4V 110mAH 
Sub C with solder tags 
1/3 AA with tags (Philips CTV) 
Standard Charger, charges 4 AA cells in 5 hou 

or 4Cs or Ds in 12 to 14 hours plus 1xPP3 (1, 2,3 

or 4 cells may be charged at a time) £5.95 
High power charger, as above but charges the 

s and Ds in 5 hours; AAs, Cs and Ds mustbe 

charged in twos or fours £10.95 
Nickel Metal Hydryde AA cells, high capacity 
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at 250mA or less 1200mAH capacity (lower capacity 
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Stick of 4, 42mm x 16mm NiCad batteries,171mm x 
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Computer grade capacitors with screw terminals, 
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7-segment common anode |.e.d. display, 1 ae oe 
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BS250 p-channel MOSFET 45p 
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SL952 UHF Limiting amplifier, LC 16 surface 
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Airpax A82903-C large stepping motor 14V 
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Polyester capacitors, box type, 22.5mm lead pitch 
0-9 F 250V d.c. 18p each, 14p 100 +, 9p 1000 + 
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100+ 7:-5p each 
Polypropylene 1 pf 400V d.c. (Wima MKP10) 
27.5mm pitch, 32 x 29 x 17mm case, 75p each, 
60p 100+ 
Philips 123 series solid aluminium axial leads, 
33yF 10V and 2.2uF 40V 40p each, 25p 100 + 
Philips 108 series long life 22uF 63V axial 
30p each, 15p 1000 + 
Multilayer AVX ceramic capacitors, all 5mm 
pitch, 100V 100pF, 150pF, 220pF, 10,000pF 
(10n) 10p each, 5p 100+, 3.5p 1000 + 
500pF compression trimmer p 
40.F 370V a.c. motor start capacitor (dialectrol type 
containing no p.c.b.s)...........£5.95 or £49.50 for 10 
Solid carbon resistors, very low inductance, ideal 
for r.f. circuits, 270ohm 2W, 680hm 2W 25p each, 
15p each 100+ 
we have a range of 0:25W, 0-5W, 1W and 2W 
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P.C. 400W PSU (intel part 201035-001) with 
standard motherboard and 5 disk drive 
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MX180 Digital Multimeter 17 ranges, 1000V 
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SCART to SCART leads, all pins connected, 

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TV on/off switches, from £1.95, most types. 

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Miniature Tool Kit, comprises: side-cutters 
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Varta, p.c.b. mounting rechargeable batteries, 
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Indoor amplified antenna, wide band, 

UHF/VHF, £11.95 plus £3, p&p. 

SAA301 OP £3.40; TDA3651SI £1.10; 
TDA3654 £1.89; TDA3651A £2.85; 
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£2.28; TDA3050, £3.90; TDA3653 £3.43; 
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3564 £4.59; TDA4500 £3.43; TDA8180 
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CONNECTORS: Phono to Phono couplers, 40p 
each; Phono plugs, red or black, 50p each; 
Phono sockets, red or black, 50p each. 
poy Js gees Cassette Head Cleaning Splicing 
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35mm Scotch camera film, 24 exposure film, plus 
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Latest type quick fit Satellite dishes, Black Mesh 
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SPECIAL OFFER, Astra 1D upgrade ADX plus 
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NOKIA LNB FSS 1:3dB max, motorised system, 

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Periswitch SCART switching box, automatically 
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Multi-media kit, dual speed CD ROM, motorised, 
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Everyday with Practical Electronics, September 1995 

High quality electronic surveillance kite that give excellent 
performance. Room transmitters are supplied with 
sensitive electret microphones & battery holders/clips. All 
transmitters can be received on an ordinary VHF FM radio. 

Easy to build & guaranteed 

to transmit 500 metres - over 1000m 

possible with higher voltage & better aerial. 
3-9V operation. Only 45x18mm. 3007-KT. £4.95 

MRTX - Miniature 9V Room Transmitter 
Our best selling ‘bug’. Super sensitive, high power - 
1000m range (2 miles possible with 18V supply & better 
aerial!). 9-18V operation. Just 45x19mm. 3018-KT, £5.95 

HPTX - High Power Room Transmitter 

High performance, 2 stage transmitter gives greater 
stability & high quality reception. 1000m 

range with 9V battery. 6-12V 
operation. On/ off switch. Size 
70x15mm. 3032-KT. £6.95 

VTX - Voice Activated Transmitter 
Activates only when sounds are detected. Low standby 
current conserves battery power. Adjustable sensitivity & 
tum-off delay. 6V operation. Size 63x38mm. Powerful 2 
stage transmitter. 1000m range. 3028-KT. £8.95 

TRI - Telephone Interface 
Connects between phone line and cassette recorder. 
Automatically switches on tape when phone is used. 
Records all conversations. Powered from line. -Size 
48x32mm. 3033-KT. £6.25 

TRVS - Tape Recorder Vox Switch 
Very sensitive, voice activated switch - automatically turns 
on cassette recorder when sounds are detected. 
Adjustable sensitivity and turn-off delay. Size 115x19mm 
including sensitive electret mic. 3013-KT. £7.50 

MTTX - Miniature Telephone Transmitter 
Attaches anywhere to phone line. 

Transmits only when phone is 

used! Uses phone line as 

aerial & power source. 500m 

range. 45x15mm. 3016-KT. £4.95 

Ultrasonic Movement Detector 
Xtal controlied oscillator, detector 
circuits & pair of edge mounted 
Ultrasonic transducers on single 
board just 75x40mm. Detection 
range from 4-7m with adjustable 
sensitivity. Red LED indicator. Outputs to drive extemal 
relay or circuits. 9V DC operation. 3049-KT. £14.95 

5 LED Sequence Flasher 
5 LED's flash in sequence. On/off push switch controls 
flashing sequence. Ideal for model railways. Very small 
COB PCB 15x8mm with spare supplied. Intro to electronics 
in today’s toys & games. 3V operation. 3052-KT £3.95 

Roulette LED 
10 LED's simulate bail rotating around 
the “wheel”. Press “Roll” button & “ball” 
runs at max. rate; release & “ball” siows 
down & drops into slot. Adjustable ball 
speed. Illustrates principles of a Voltage 
1S ll Controlled Oscillator built using CMOS 
decade counter & Op-Amp. 9V powered. 3006-KT. £11.50 

Combination Lock 
Versatile 9 key combination lock. Complete with separate 
Keypad for remote installation from main circuit. Lock 
automatically resets. 120VAC/10A relay supplied. 9-12V 
operation. 3029-KT. £10.95 

Intro To Audio Power Amps 
Build your own fully working Class AB amplifier. Get hands- 
on learning about Bootstrapping, Cross-over Distortion, 
Complementary Pairs, & Push-Pull outputs. Detailed 
explanation given. Delivers several watts of power to the 8 
Ohm speaker supplied. 3048-KT. £10.95 

One Chip AM Radio 
Complete AM radio on a PCB. Tuned radio frequency front- 
end, AM Radio IC amplifier & detector and two stages of 
amplification of the audio signal into the speaker provided. 
All components supplied. Coil pre-wound. Excellent intro to 
modern mini-sized AM radio electronics. 3063-KT. £10.95 

Blowing, Level Crossing Bell, Chugging 
& “Clickety-Clack”. 2.5-6V operation. 
il) COB PCB 29x16mm. Speaker supplied. 
2 boards can be joined to produce a 
sequence of sounds. SG1. £4.95 


Our range of HIGH QUALITY project kite are supplied with all components, top quality fibre glase PCB's & 
comprehensive instructions. Send 2 x 1st clase stamps for our latest catalogue containing over 100 kits 
& publications. b<IMail order only. Please ADD £1.50 P. & P. per order & make cheques/PO0's payable to: 


(Oey 0) oun od od ot POLAT OE Sere lUlolaliarelereiie 


Hertfordshire CM23 2PA 


As easy to use as a calculator 
but as powerful as a , 

@ A powerful set of basic functions, 
statements, and operators — over 230 in 
all— many larger computers don’t have a 
set of basic instructions this complete. 
@ Advanced statistics functions 
enabling computations on up to 15 
independent variables. 

@ Recursive subprograms and user 
defined functions. 

@ An advanced internal file system for 
storing programs and data — The HP71 
has continuous memory — when you 
turn the computer off it retains 
programs and data. 

@ A keyboard that can be easily 
customised for your specific application. 
@ HP-1L Interface pre-installed to 
create a system that can print, plot, 
store, retrieve and display information. 
Control or read instruments or speak to 
other computers, 5000 bytes/sec. 

Built in ROM includes 46 separate 
commands, Interface to HP-1L, HP-1B, 
RS232C, GPIO or series 80. Includes 


Smart wand 

— Automatically 
recognises and 
decodes all major 
bar-code standards. 

Buy 2 kits for £59.00 

These are second users systems, ex NHS, 
are fully tested and working but have no 
programming (THAT IS UP TO YOU). . 

WAT Pi scsicrcst ech cditipabiataees aoaaee £29.95 
Bar-code Reader,.....0..cccccecscecseccecese £12.95 
A.C. Power Supplly..............:ccc000008- £4.95 
(Works from batteries normally) 
Keyboard Overlay...........sccseseeseees £1.00 
(Limited quantities) 
(Unknown Program) Memory 
oe i Bee IES i Ge pa ee £3.00 
Complete kit of HP71B, Bar-code Reader 
and power supply...............000 se0-£39.50 
(Prices include VAT/Delivery within 
7 days, £3.00 for UK) 
(Currently selling in US for over US$500!) 

Unit 51, InShops, Wellington Centre 
Aldershot, Hants,GU11 5DB | 

connection cableSy Tel: (01252) 341900 Fax: (01293) 822786 

Please rush me Please debit credit card 

[_] HP71B Powerful Cale/Computer @ £29.95 No. .ooocecccccccccccccceccecue. an 

[_] Bar-code Reader @ £12.95 PONG Sick sedcescds es cocesinns 

indvek Supply @ £498 Es ees 

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[]Memory module @ £3.00. 00000 = *srrssrresssrsseseesseereseeevsneetneetasennnenun 

[_]Complete kit of HP71 B, Bar-code Reader POPPI ECCI ITT rrr Tri Tirir Terie Tirirrr rere eer errr 
and Power Suppty @ 899.90". gc Ea eae ei 

Total payment £........... + £3 delivery =£........... EEL: vagvitgaicaniabetd ase 

We accept Mastercard, Visa, Cheques or money orders — please post the above form to us, 
or Fax it, or Telephone with a verbal credit card order. 


«4 imini FM transmitter, very high gain preamp, 
supplied complete with FET electret microphone. 
Designed to cover 88-108 Mhz but it is easy to 
change it to cover 63-130Mhz. Works with a com- 
mon 9v (PP3) battery. 0.2W RF. £8.22 Kit no 1001. 

Electronic siren kit with an impressive 5 watt 
power output. Ideal for car/bike alarms etc. 6- 
12vdc, max current 1A, tone frequency 1.2khz. 
£7.05 Kit no 1003. 

3-30v Power supply, variable, stabilized power 
supply for laboratory use. Shortcircuit protected, 
suitable for professional or amateur applications. 
24v 3A transformer is also needed to complete the 
kit. £16.45 Kit 1007. 

Powerful 1 watt FM transmitter supplied com- 
plete with piezoelectric microphone. 8-30vdc. At 
25-S0v sic will get nearly 2 watts!. £14.10 Kit no 

FM/AM Scanner, well not quite you here to turn 
the knob yourself but you will hear things on this 
radio (even TV) that you would not hear on an 
ordinary radio!. Receiver covers 50-160Mhz both 
AM and FM. Built in 5 watt amplifier. £17.62 Kit 
no 1013. 

Mosquito repeller, modern way to keep midges at 
bay! Runs for about a month on a 1.5v battery. 
£8.22 Kit no 1015. 

3 channel wireless sound to light system, mains 
operated, separate sensitivity adjustment for each 
channel, 1,200 watt power handling. Microphone 
included. £16.45 Kit no 1014. 

Motorbike/cycle trembler alarm, adjustable sen- 
sitivity, preset alarm time, auto reset. Could be 
connected to bikes horn etc. £14.10 Kit no 1011 

gees 's. 

0-5 minute timer, adjustable from 0 to 5 mins, will 
switch up to 2A mains. Perfect for alarms, photo- 
graphiclaboratories etc. 12vdc. £8.22 Kit no 1020. 


4 watt FM transmitter, small but powerful trans- 
mitter, 3 RF stages, microphone and an audio 
preamp include in kit. £23.50 Kit no 1028. 

25 watt FM transmitter 4 RF stages, preamp 
required (our kit 1068 is suitable). Due to the 
complexity of the transmitter it is supplied in 
ne up form only. £92. it Kit no 1031. 

Strobe light, adjustable frequency from 1- to 60 Hz. 
(alot faster than conventional strobes) mains op- 
erated. £18.80 Kit no 1037. 

Ultrasonic velar ideal : as a movement detector 
with ar ange of about 10 metres, automate your cat 
flap! 12v operation so ideal for cars, caravans etc. 
£16.45 Kit 1049. 

Liquid le level detector useful for lpipciing fluid 

levels in tanks, fishponds, baths or as arain or leak 

alarm. Will switch 2A mains, £5.87 Kit no 1081. 
ayes ees et 

Combination lock 9 key, easily programmable, 
will switch 2A mains. Complete with keypad. 9v 
operation. £11.75 Kit1114. __ 

Phone bug detector, this device will warn you if 
somebody is eavesdropping on your phone line. 
£7.05 Kit no 1130. 

Robot voice, interesting circuit that distorts your 
voice! adjustable, answer the phone with a differ- 
ent voice! 12vdc £10.57 Kit no 1131. 

Telephone bug, small bug powered by the tel- 
ephone line, starts transmitting as soon as the 
handset is picked up! £9.40 Kit no 1135. 

function; generster, i me ceased, saw tooth 
and square waves adjustable from 20hz-20khz, 
separate level controls for each shape. Will pro- 
duce all 3 together. 24vac £17.62 Kit no 1008. 

3 Channel light chaser, 800 watts per channel, 
speed and direction controls supplied with 12 leds 
and mains triacs, so you can use mains light bulbs 
if you want. 9-15vdc £19.97 Kit no 1026. 

12v flourescent. A useful kit that will enable you to 
light 4° flourescent tubes from your car battery! 
(you will also need a 9v 2A transformer, not sup- 
plied) £9.40 Kit no 1069. 

VOX switch, sound activated switch ideal for turn- 
ing tape recorders on and off when sounds are 
heard. Makes the tape last alot longer! adjustable 
sensitivity, built in delay. £9.40 Kit 1073. 

Incar sound to light, Put some atmosphere in your 
car with this mini 3 channel sound to light. Each 
channel has 6 led's. £11.75 Kit no 1086. 


‘ D—-Vv 
7 watt HI FI power amplifier useful, powerful, 
ideal for intercomms, audio systems, car use etc. 
12-18vdc 500mA. £8.22 Kit No 1025. 

Phone call relay, useful i doelis Oatainietien arelay 
when ever the ‘phone rings, could be used to 
operate more bells or signalling lights etc. Will 
switch mains at 2A. £11.75 Kit no 1122. 

Lead acid charger, two mubbandiie ihaeies rates, 
visual indication of battery state, ideal for alarm 
systems, emergency lighting etc. 100mA 12vdc. 
£14.10 Kit no 1095. 

Car alarm system, wakes a on ss colina dre and/or 
vibration, entry and exit delays plus adjustable 
alarm duration. Good for cars, caravansetc. £14.10 
Kit no 1019, 

Portable alarm system, based on amercury switch. 
The alarm continues to sound until the unit is 
disabled by the owner. Buzzer included. £12.92 
Kit no 1150. 

Preamp mixer, 3 input mono mixer, separate bass 
and treble controls plus independent level con- 
trols. 18vdc, input sens 150mv. 100mA. £17.62 
Kit no 1052. i 

Mini metal detector, suitable for locating pipes in 
walls etc, range 15-20 cm, complete with case. 9v 
operation. £9.40 Kit no 1022. 

3] Peo : 
800 watt single channel sound to light kit, mains 

operated, add rhythm to your party for only £9.40 
Kit no 1006. 

Sound effects generator, produce sounds ranging 
from bird chips to sirens, complete with speaker, 
add sound effects to your projects for just £10.57 
Kit no 1045. 

Pi. , J 
Guitar preamp with tone controls, small enough to 
fit inside any guitar, based on TL082 IC, 9-12vdc, 
50mA. £9.40 Kit no 1091. 

15 watt FM transmitter, 4 stage high power, 
preamp required. 12-18vdc. Can use either ground 
plane, open dipole, or Y agi. Supplied in built form 
only at £81.07 Kit 1021. 

Telephone amplifier, Very sensitive amplifier 
which uses a ‘phone pickup coil (supplied) will let 
you follow a conversation without holding the 
phone. £12.92 Kit no 1059. 
contr: or motors up 
to 30A! (you may need a heatsink for 30A) £19.97. 
omposite converts compo 
into separ ate Hsync Vsync and video £9.40. 
3. Geiger counter kit, contains everything you 
need to build a working counter £22.32. 
4. Solar energy kit, contains a solar panel, motor, 
buzzer and cable for e nts £5.87. 
5 c¢ accupuncture may 
migrane, r circulation, backache etc. £8.22. 
6. Feceiving apparatus kit, produces a weak 
adjustable high tension of 80-300v from a 9v bat- 
tery, ideal for catching worms etc! £9.40. 
apter bug co i$ eV ig you 
to build a professional bug built inside a standard 
13A mains adapter! the bug is mains powered so 
it operates all the time the adapter is plugged in. 
Price is £16.45 for the complete kit including 
adapter. Hand tools and glue ae 
8. Nicad charger kit automatic charger for ce 
from 1.2v to 15v, 7 settings 50600mA, transformer 
required 18-20v 600mA. £9.40. 
JEU. Inverter kits, produce 240vactrom a 12vdc 
supply, two versions are available a 15w one at 
£14.10, and an 80w version at £23.50. 

hone to order. Beer 
Remember to add £1.50 p&p. 
By phone with a credit card. 
By post with either a cheque, 
postal order or credit card details. 
By fax with credit casd details. 

TEL 01273 771156 

FAX 01273 206875 
Overseas orders please add £3.50 

Everyday with Practical Electronics, September 1995 

is Ek SECS LON eh 
\" yee ete 




Mike Tooley B.A. (published by Everyday 

A complete course that can lead successful readers to the 
award of a City and Guilds Certificate in Introductory 
Microprocessors (726/303). The book contains every- 
thing you need to know including full details on register- 
ing for assessment, etc. 

Sections cover Microcomputer Systems, Microproces- 
sors, Memories, Input/Output, Interfacing and Program- 
ming. There are various practical assignments and eight 
Data Pages covering popular microprocessors. 

And excellent introduction to the subject even for those 
who do not wish to take the City and Guilds assessment. 

80 pages £2.45 



(published by Everyday with Practical Electronics) 

' Mike Tooley B.A. 

This book is designed for the beginner and experienced 
reader alike, and aims to dispel some of the mystique 
associated with the design of electronic circuits. It shows 
how even the relative newcomer to electronics can, with 
the right approach, design and realise quite complex 

Fourteen individual p.c.b. modules are described which, 
with various detailed modifications, should allow anyone 
to design and construct a very wide range of different 
projects. Nine ‘hands-on’ complete DIY projects have 
also been included so readers can follow the think- 
ing behind design, assembly, construction, testing and 
evaluation, together with suggested “mods” to meet 
individual needs. 

The subjects covered in each chapter of the book are: 
Introduction and Power Supplies; Small Signal Amplifiers; 
Power Amplifiers; Oscillators; Logic Circuits; Timers; 
Radio; Power Control; Optoelectronics. 

The nine complete constructional projects are: Ver- 
satile Bench Power Supply; Simple Intercom; Bench 
Amplifier/Signal Tracer; Waveform Generator; Electronic 
Die; Pulse Generator; Radio Receiver; Disco Lights Con- 
troller; Optical Communications Link. bin 

136 pages 

(published by Everyday with Practical Electronics) 
Alan Winstanley and Keith Dye B. Eng(Tech)AMIEE 
This highly acclaimed EPE Teach-in series, which in- 
cluded the construction and use of the Mini Laband 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 DISKC 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 learning aids bring electronics 
to life in an enjoyable and interesting way: you will both 
see and hear the electron in action! The Micro Lab 

fs Caves 


microprocessor add-on system will appeal to higher level 
students and those developing microprocessor projects. 

160 pages £3.95 


(published by Everyday Electronics in association 
with Magenta Electronics) 

Contains twenty projects from previous issues of FE each 
backed with a kit of components. The projects are: 
Seashell Sea Synthesizer, EE Treasure Hunter, Mini Strobe. 
Digital Capacitance Meter, Three- Channel Sound to Light, 
BBC 16K sideways RAM, Simple Short Wave Radio, 
Insulation. Tester, Stepper Motor Interface, Eprom Eraser, 
200MHz Digital Frequency Meter, Infra Red Alarm, 
EE Equaliser, loniser, Bat Detector, Acoustic Probe, 
Mainstester and Fuse Finder, Light Rider —- (Lapel Badge, 
Disco Lights, Chaser Light), Musical Doorbell, Function 
Generator, Tilt Alarm, 10W Audio Amplifier, EE Buccaneer 
Induction Balance Metal Detector, BBC Midi Interface, 
Variable Bench Power Supply, Pet Scarer, Audio Signal 

128 pages £2.45 



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 com- 
ponents that are readily available, and they are easy to 
construct. Full construction details are provided, includ- 
ing stripboard layouts and wiring diagrams. Where ap- 
propriate, simple setting up procedures are described in 
detail; no test equipment is needed. 

The projects covered in this book include: Four chan- 
nel 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 (Oldelslmerelel-m st iels) £4.95 


1. D. Poole 

The aim of this book is to give guidance on the deci- 
sions which have to be made when setting up any 
amateur radio or short wave listening station. Often the 
experience 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 

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. see 

86 pages Order code BP300 

Everyday with Practical Electronics, September 1995 


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. esp 

72 pages Ol cell morelelom oi aks) 

Joe Pritchard G1IUQW 

Part One covers the ‘‘science”’ side of the subject, going 
from a few simple electrical ‘‘first principles”, through a 
brief treatment of radio transmission methods to simple 
receivers. The emphasis is on practical receiver designs 
and how to build and modify them, with several circuits in 
the book. 

Part Two covers the use of sets, what can be heard, 
the various bands, propagation, identification of stations, 
sources of information, QSLing of stations and listening 
to amateurs. Some computer techniques, such as com- 
puter Morse decoding and radio teletype decoding are also 

224 pages £15.95 



R. A. Penfold 

Included in this book are a collection of the most popular 
types of project which, we feel sure, will provide many 
designs to interest all electronics enthusiasts. All the cir- 
cuits utilise modern, inexpensive and freely available com- 
ponents. The 27 projects selected cover a very wide range 
and are divided into four basic areas: Radio Projects, Audio 
Projects, Household Projects and Test Instruments. An in- 
teresting addition to the library of both the beginner and 
more advanced constructor. pas 

135 pages Order code BP49 

R.A. Penfold 
This book describes in detail how to construct some simple 
and inexpensive but extremely useful, pieces of test equip- 
ment. Stripboard layouts are provided for all designs, to- 
gether with wiring diagrams where appropriate, 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 £2.95 

R. A. Penfold 

Deals with the simple methods of copying printed cir- 
cuit 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. pare 

80 pages Order code BP121 


R. A. Penfold 

We have all built projects only to find that they did not 
work correctly, or at all, when first switched on. The aim 
of this book is to help the reader overcome just these 
problems by indicating how and where to start looking for 
many of the common faults that can occur when building 
up projects. 

96 pages Temporarily out of print 


R. A. Penfold 

The purpose of this book is to provide the reader with a 
wide range of preamplifier and power amplifier designs 
that will, itis hoped, cover most normal requirements. 

The preamplifier circuits include low noise microphone 
and RIAA types, a tape head preamplifier, a guitar 
preamplifier and various tone controls. The power 
amplifier designs range from low power battery operation 
to 100W MOSFET types and also include a 12 volt bridge 
amplifier capable of giving up to 18W output. 

All the circuits are relatively easy to construct using the 
p.c.b. or stripboard designs given. Where necessary any 
setting-up procedures are described, but in most cases no 
setting-up or test gear is required in order to successfully 

complete the project. 
100 pages (oleelelmerelel =a =) on Wa £2.95. 

See ELECTRONICS TEACH IN No. 6 above left. 



Third Edition 

lan Sinclair 

A completely updated and revised third edition of this 
popular title. It still contains a carefully selected collection 
of standard circuits, rules-of-thumb, and design data for 
professional engineers, students and enthusiasts involved 
in radio and electronics, but is now over one hundred 
pages bigger. 

The book covers many areas not available elsewhere in 
such a handy volume, and this new edition now includes 
chapters on: Microprocessors and Microprocessor 
Systems: Instruction Registers, Clocking, Memory, Read- 
Write Memory, Buses, Reading and Writing Actions, 
Three-state Control, Control Bus, Timing and Bus Control, 
PC Register and Addressing, Addressing Methods, 
Interrupts, Inputs and Outputs, Ports, Keyboard Interfac- 
ing, Video Interfacing. Digital-Analogue conversions: 
Analogue-to- Digital Conversion, Sampling and Conver- 
sion, Digital-to-Analogue Conversion, Current Addition 
Methods, Conversion Problems, Bitstream Methods, 
Computer Plug-in Boards. Computer Aids in Elec- 
tronics: The Computer, Linear Circuit and Nodes, PCB 
Layouts, Circuit Diagrams, Public Domain Software 
Library. Hardware Components and Practical Work: 
Hardware, Video connectors, Control Knobs and switches, 
Cabinets and cases, Packages for semiconductors, In- 
tegrated circuit packages, Constructing circuits, Surface 
mounting, Testing and trouble-shooting, Practical work on 
microprocessing equipment, Instruments for digital servic- 
ing work, Logic analysers. 

Other chapters cover Passive Components, Active Dis- 
crete Components, Discrete Component Circuits, Linear 
ICs, Digital ICs, Transferring Digital Data and Computer 

Aids in Electronics. 
(Ol del-)merele(sm)\ ial Bs) £14.95 

338 pages 


R. A. Penfold 

This book is primarily intended as a follow-up to BP239, 
(see below), and should also be of value to anyone who 
already understands the basics of voltage testing and 
simple component testing. By using the techniques des- 
cribed in Chapter 1 you can test and analyse the perfor- 
mance of a range of components with just a multimeter 
(plus a very few inexpensive components in some cases). 
Some useful quick check methods are also covered. 

While a multimeter is supremely versatile, it does have 
its limitations. The simple add-ons described in Chapter 2 
extended the capabilities of a multimeter to make it even 
more useful. 

84 pages £2.95 

Order code BP265) 

Steve Money 

The principles of operation of the various types of test 
instrument are explained in simple terms with a minimum 
of mathematical analysis. The book covers analogue and 
digital meters, bridges, oscilloscopes, signal generators, 
counters, timers and frequency measurement. The practi- 
cal uses of the instruments are also examined. 

Everything from Audio Oscillators, through R, C & L 
measurements (and a whole lot more) to Waveform Gen- 
erators and testing Zeners. 

206 pages Order code PC109 £8.95 

F. A. Wilson, C.G.1.A., C.Eng., F.1.E.E., F.1.E.R.E., 
The wonders of electronics multiply unceasingly and 
electronic devices are creeping relentlessly into all walks of 
modern life. As with most professions, ours too has a 
language of its own, ever expanding and now encompass- 
ing several thousands of terms. This book picks out and 
explains some of the more important fundamental terms 
(over 700), making the explanations as easy to understand 
as can be expected of a complicated subject and avoiding 
high-level mathematics. 

Through its system of references, each term is backed up 
by a list of other relevant or more fundamental terms so 
that a chosen subject can be studied to any depth required. 

472 pages Order code BP286 £5.95 

R. A. Penfold 

This book is primarily aimed at beginners and those of 
limited experience of electronics. Chapter 1 covers the 
basics of analogue and digital multimeters, discussing the 
relative merits and the limitations of the two types. In 
Chapter 2 various methods of component checking are 
described, including tests for transistors, thyristors, resis- 
tors, capacitors and diodes. Circuit testing is covered in 
Chapter 3, with subjects such as voltage, current and 
continuity checks being discussed. : 

In the main little or no previous knowledge or experience 
is assumed. Using these simple component and circuit 
testing techniques the reader should be able to confidently 
tackle servicing of most electronic projects. 
96 pages Order code BP239 £2.95 

R.A. Penfold 
é The first chapter gives full constructional details of a cir-. 

cuit demonstrator unit that is used in subsequent chapters | 

to introduce common electronic components — resistors, 

capacitors, transformers, diodes, transistors, thyristors, fets 

and op.amps. Later chapters go on to describe how these 
components are built up into useful circuits, oscillators, 
multivibrators, bistables and logic circuits. 

At every stage in the book there are practical tests and 
experiments that you can carry out on the demonstrator 
unit to investigate the points described and to help you 
understand the principles involved. You will soon be able 
to go on to more complex circuits and tackle fault finding 
logically in other circuit you build. : 


120 pages Order code PC103 




F. A. Wilson, C.G.1.A., C.Eng., F.1.E.E., F.1.E.R.E., 

Bridges the gap between complicated technical theory, and 

“cut-and-tried” methods which may bring success in design 
but leave the experimenter unfulfilled. A strong practical bias 
— tedious and higher mathematics have been avoided where 
possible and many tables have been included. 

The book is divided into six basic sections: Units and 
Constants, Direct-Current Circuits, Passive Components, 
Alternating-Current Circuits, Networks and Theorems, 
Measurements. — 

256 pages Order code £3.95 

Geoff Phillips 

The author has used his 30 years experience in industry 
to draw together the basic information that is constantly 
demanded. Facts, formulae, data and charts are presented 
to help the engineer when designing, developing, evaluat- 
ing, fault finding and repairing electronic circuits. The 
result is this handy workmate volume: a memory aid, tutor 
and reference source which is recommended to all elec- 
tronics engineers, students and technicians. 

Have you ever wished for a concise and comprehen- 
sive guide to electronics concepts and rules of thumb? 
Have you ever been unable to source a component, or 
choose between two alternatives for a particular applica- 
tion? How much time do you spend searching for basic 
facts or manufacturer's specifications? This book is the 
answer, it covers resistors, capacitors, inductors, semicon- 
ductors, logic circuits, EMC, audio, electronics and music, 
telephones, electronics in lighting, thermal considerations, 
connections, reference data. 


158 pages Order code NE20 2 



A. Michaels 

Helps the reader to find possible substitutes for a popular 
selection of European. American and Japanese transistors. 
Also shows material type, polarity, manufacturer and use. 
320 pages £3.9 

(oymelslaerele ism oi atste) 


(Second Edition) 

lan Sinclair 

Digital recording methods have existed for many years and 
have become familiar to the professional recording en- 
gineer, 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 principles 
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 
methods are explained, but the mathematical background 
and theory is avoided, other than to state the end product. 
128 pages Order code PC102 £7.95 


F. A. Wilson, C.G.1.A., C.Eng., F.1.E.E., F.1.E.R.E., 

Analysis of the sound wave and an explanation of acousti- 
cal quantities. prepare the way. These are followed by a 
study of the mechanism of hearing and examination of the 
various sounds we hear. A look at room acoustics with 
a subsequent chapter on microphones and loudspeakers 
then sets the scene for the main chapter on audio systems 
— amplifiers, oscillators, disc and magnetic recording and 

Ol gels) aerelel-m 3 ame £3.95 


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 Order code BP358 £4.95 


electronic music. 

320 pages 



F. A. Wilson 

Marconi first bridged the Atlantic with radio waves, then of 
a mere 200 kilohertz. Since then for communication we 
have moved up the frequency scale through megahertz 

- and microwaves and are now probing light waves. Ac- 

cordingly no self-respecting electronics engineer can af- 
ford not to be conversant with light and its uses in elec- 
tronics since development of opto-electronic devices and 
communication systems is proceeding at a truly explosive 

This book is not for the expert but neither is it for the 
completely uninitiated. It is assumed the reader has some 
basic knowledge of electronics. After dealing with sub- 
jects like Fundamamentals, Waves and Particles and The 
Nature of Light such things as Emitters, Detectors and Dis- 
plays are discussed. Chapter 7 details four different types 
of Lasers before concluding with a chapter on Fibre Op- 

161 pages Ol aelsimerele(sm si attots) £4.95 
Owen Bishop 

This book is a comprehensive ready-reference manual for 
electronics enthusiasts of all levels, be they hobbyists, 
students or professionals. A helpful major section covers 
the main kinds of component, including surface-mounted 
devices. For each sort, it lists the most useful and readily 
available types, complete with details of their electronic 
characteristics, pin-outs and other essential information. 
Basic electronic units are defined, backed up by a 
compendium of the most often required formulae, fully 
explained. There are five more extensive sections devoted 
to circuit design, covering analogue, digital, radio, display, 
and power supply circuits. Over 150 practical circuit 
diagrams cover a broad range of functions. The reader is 
shown how to adapt these basic designs to a variety of 
applications. Many of the circuit descriptions include 
step-by-step instructions for using most of the standard 
types of integrated circuit such as operational amplifiers, 
comparators, filters, voltage converters and switched- 
mode power supply devices, as well as the principal logic 

circuits. ; 
328 pages £4.95 


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 

104 pages Order code PC111 £6.95 



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- 
ponents. The projects covered include: Waa-Waa Units; 
Distortion 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 


102 pages Ole l- 3 arerele ism = 3 aaclole: 


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 con- 
structing cabinets, wiring up, when and where to use 
wadding, and when not:-to, what fittings are available, 
finishing, 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 


164 pages Order code BP297 

Everyday with Practical Electronics, September 1995 


Owen Bishop 

Remote control systems lend themselves to a modular ap- 
proach. This makes it possible for a wide range of sys- 
tems, from the simplest to the most complex, to be built up 
from a number of relatively simple modules. The author has 
tried to ensure that, as far as possible, the circuit mod- 
ules in this book are compatible with one another. They 
can be linked together in many different configurations to 
produce remote control systems tailored to switch a table 
lamp on and off, or to operate an industrial robot, this book 
should provide the circuit you require. 

240 pages Order code BP240 £3.95 

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 Order code 160 £2.50 


Fourth Edition. lan Sinclair 

Contains all of the everyday information that anyone work- 
ing in electronics will need. 

It provides a practical and comprehensive collection of 
circuits, rules of thumb and design data for professional 
engineers, students and enthusaists, and therefore enough 
background to allow the understanding and development 
of a range of basic circuits. 

Contents: Passive components, Active discrete com- 
ponents, Discrete component circuits, Sensing com- 
ponents, 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. 

440 pages £12.99 
R. M. Marston 

A vast range of audio and audio- associated i.c.s are readily 
available for use by amateur and professional design 
engineers and technicians. This manual is a guide to the 
most popular and useful of these devices, with over 240 
diagrams. It deals with i.c.s such as low frequency linear 
amplifiers, dual pre-amplifiers, audio power amplifiers, 
charge coupled device delay lines, bar-graph display 
drivers, and power supply regulators, and shows how to 
use these devices in circuits ranging from simple signal 
conditioners and filters to complex graphic equalizers, 
stereo amplifier systems, and echo/reverb delay lines etc. 

168 pages £13.95 


R. N. Soar 

Contains 50 interesting and useful circuits and applications, 
covering many different branches of electronics, using one of 
the most simple and inexpensive of components — the diode. 
Includes the use of germanium and silicon signal diodes, 
silicon rectifier diodes and Zener diodes, etc. 

64 pages Order code BP36 £1.95 

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 Jogic 
i.c.s in practical applications. 
119 pages OME Le £4.95 


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 principles 
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 univer- 
sally recognised type numbers. se 

182 pages Ole lclmorelelcm)\s a kes 


R. A. Penfold 

The first part of this book covers standard operational 
amplifer based ‘building blocks” (integrator, precision 
rectifier, function generator, amplifiers, etc), and considers 
the ways in which modern devices can be used to give 
superior performance in each one. The second part des- 
cribes 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 controllers, opto- 

isolator audio link, audio millivolt meter, temperature 
monitor, low distortion audio signal generator, simple 
video fader, and many more. 

120 pages £4.95 


R. M. Marston 

Written for the professional engineer, student or en- 
thusiast. It describes the basic principles and characteris- 
tics of these devices and includes over 200 circuits. 

All the circuits have been designed, built and fully 
evaluated by the author; all use inexpensive and interna- 
tionally available devices. 


187 pages Oyaeleimerelel em) ot 2 


R. M. Marston 

This manual is concerned mainly with waveform generator 
techniques and circuits. Waveform generators are used 
somewhere or other in most types of electronic equipment, 
and thus form one of the most widely used classes of 
circuit. They may be designed to produce outputs with 
sine, square, triangle, ramp, pulse, staircase, or a variety of 
other forms. The generators may produce modulated or 
unmodulated outputs, and the outputs may be of single or 
multiple form. 

Waveform generator circuits may be built using transis- 
tors, op.amps, standard digital i.c.s, or dedicated waveform 
or “function” generator i.c.s. 

The manual is divided into eleven chapters, and presents 
over 300 practical circuits, diagrams and tables. The sub- 
jects covered include: Basic principles; Sine wave gener- 
ators; Square wave generators; Pulse generator circuits; 
“Timer i.c."’ generator circuits; Triangle and sawtooth gen- 
erators; Multi-waveform generation; Waveform synthesizer 
i.c.s; Special waveform generators; Phaselocked loop cir- 
cuits; Miscellaneous “555” circuits. 


267 pages Order code NE18 



R. A. Penfold 

Once you know how, PC interfacing is less involved than 
interfacing many eight-bit machines, which have tended 
to use some unusual interfacing methods. 

This book gives you: A detailed description of the lines 
present on the PC expansion bus. A detailed discussion 
of the physical characteristics of PC expansion cards. The 
1/O map and details of the areas where your add-on can 
be fitted. A discussion of address decoding techniques. 
Practical address decoder circuits. Simple TTL 8-bit input 
and output ports. Details of using the 8255 parallel inter- 
face adaptor. Digital to analogue converter circuits. In fact 
everything you need to know in order to produce success- 

ful PC add-ons. 
80 pages £3.95 


D. Weale 

This book is for anyone intending to buy an IBM com- 
patible computer system, whether it is their first system or 
a replacement. There are sections on hardware, applica- 
tion and systems programs, and how to actually make your 
choice as well as sections on the law, ergonomics and a 
glossary of common terms. The text contains many useful 
tips and some warnings (which could save much effort 
and expense). After having read this book you should have 
a better idea of what is suitable for your needs, how to 
obtain it and how to ensure that the system is operated 
with the minimum of difficulty. 

144 pages Order code BP323 £4.95 

Everyday with Practical Electronics, September 1995 

AND COMPATIBLES (Revised Edition) 

R. A. Penfold 

Not only are PC and compatible computers very expan- 
dable, but before long most users actually wish to take 
advantage of that expandability and start upgrading their 
PC system. Some aspects of PC upgrading can be a bit 
confusing, but this book provides advice and guidance on 
the popular forms of internal PC expansion, and should 
help to make things reasonably straightforward and pain- 
less. Little knowledge of computing is assumed. The only 
assumption is that you can operate a standard PC of some 
kind (PC, PC XT, PC AT, or an 80386 based PC). 

The subjects covered include: PC overview; Memory 
upgrades; Adding a hard disk drive; Adding a floppy disk 
drive; Display adaptors and monitors; Fitting a maths 
co-processor; Keyboards; Ports; Mice and digitisers; 
Maintenance (including preventative maintenance) and 
Repairs, and the increasingly popular subject of d.i.y. PCs. 

196 pages £5.95 


F. A. Wilson, C.G.1.A., C.ENG., F.1.E.E., F.1.E.R.E., 
Another book on BASIC but with a difference. This one 
does not skip through the whole of the subject and thereby 
leave many would-be programmers floundering but in- 
stead concentrates on introducing the technique by look- 
ing in depth at the most frequently used and more easily 
understood computer instructions. For all new and poten- 
tial micro users. 

192 pages £2.95 


Mike Tooley BA 

The revised and enlarged third edition contains a new 
chapter on servicing 68000 based microcomputers. It has 
been updated throughout and includes many new photos 
and diagrams. It is essential for anyone concerned with 
the maintenance of personal computer equipment or 
peripherals, whether professional service technician, stu- 
dent or enthusiast. 

240 pages Order code NE15 £25 


N. Kantaris 

If you are a PC user and want to get the most out of your 
computer in terms of efficiency and productivity, then you 
must learn the intricacies of its MS-DOS operating system. 
With this book you will learn to do just that in the shortest 
and most effective way. 

The book explains: The enhancements to be found in 
MS-DOS version 5, over previous versions of the operat- 
ing system. How the DOS operating system is structured 
so that you can understand what happens when you first 
switch on your computer. How directories and subdirec- 
tories can be employed to structure your hard disk for 
maximum efficiency. How to use the DOS Shell program 
(a menu-driven graphical interface) to perform various 
house-keeping operations on your disk. How to manage 
disk files, and how to use the MS-DOS Editor to fully 
configure your system by writing your own CONFIG.SYS 
and AUTOEXEC.BAT files. How to optimise your system 
by either increasing its conventional memory or increasing 
its speed. How to write batch files to automate the opera- 
tion of your system. 

A summary of all DOS commands, illustrated with ex- 
amples, is given in the penultimate chapter, which turns it 
into a useful reference guide. 

124 pages £4.95 


PCB Designer 

For Windows 3.1 

Annan nnngy NON ARAN ARAN AE 

J ie rae 
it ; Ee 
& a : 


Looking for the price? 

PCB Designer - [c:\pcb\samplel.pcb] 

| File Edit Board Text Snap Window Help 

Runs on any PC running Windows 3.1 in standard or 
enhanced mode with 2MB RAM 
Will work with any Windows supported printer and monitor 

ang meen 

a ee’ 

x & & 
12 +4 3 
3 rem 2g 

It's just £49.00 all inclusive! §-— ao ~am 
...NO postage... vY Produce Single or Double sided PCBs. 
...10 additional charges for Y Print out to any Windows supported printer. 
overseas orders. | ¥ Toolbar for rapid access to commonly used 
Dealers and distributors _ components. 
wanted. ¥Y Helpful prompts on screen as you work. 
v Pad, track & IC sizes fully customisable. 
¥ Nocharges for technical support. 
¥ Snap-to grid sizes 0.1", 0.05" 0.025" and 
- ¥ SMT pads and other pad shapes. = (3 )=siuupan 

Internet Lui) 
A working demo is available via 

gl cae 

22 Tavistock Drive, Belmont, Hereford, HR2 7XIN 

_ 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. Remitances should be sent to The PCB Serv- 
ice, Everyday with Practical Electronics, Allen House, East Borough, 
Wimborne, Dorset BH21 1PF. Cheques should be crossed and made payable to 
Everyday with Practical Electronics (Payment in £ sterling only). 
NOTE: While 95% of our boards are held in stock and are dispatched 
within seven days of receipt of order, please allow a maximum of 28 days 
for delivery — overseas readers allow extra if ordered by surface mail. 
Back numbers or photostats of articles are available if required — see the 
Back Issues page for details. 
Please check price and availability in the latest issue. 

Boards can only be supplied on a payment with order basis. 


We have a few p.c.b.s left from past projects 

these are being offered at the knock down £7 00 
price of £1.00 each — no matter what size s 

they are (some of these boards are EACH 
worth over £10.00 each) while stocks last. inc. VAT 
This price includes VAT and UK post — and p&p 
overseas orders please add 50p postage (or £1 
per board for airmail postage). 

Tea Tune Thermostat 609; Suntan Timer 610; Time Switch 614; 
Doorbell Delay 616; Midi Pedal 639, Midi Merge 640; Audio Lead 
Tester 641; Music on Hold 646; Power Supply 25V 700mA 656; 
Stereo Noise Generator 681; Amstrad Speech Synthesiser 689; 
Hand Tally, main board 699 and display board 700; Ghost Waker 
703; Amstrad PCW Sound Generator 715; Automatic Light Control 
— PSU board 747 and logic board 748; Modular Disco Lights — 
Simple Chaser 745 — Masterlink 752 — Dimmer Interface 765 — 
VU Sound Module 767 — Superchaser 771 — Supersweep 772; 
UV Exposure Unit 768; Bicycle Alarm 773; Knockerbox 775; 
Auto Nightlight 779; Mind Machine — Programmer Board 780; 
Transistor Checker 781; Micro-Sense Alarm 783; Telesound 784; 
Programmable Timer, 785; Auto Garage Light 786; Economy Seven 
Timer, 788; Sonic Continuity Tester, 789; Telephone Ringer, 790; 
Experimental Weighing Scale, 792; 12V Drill Charger/PSU (both © 
boards), 793. 

Any of the above for just £1 each inc. VAT and p&p. 
Back numbers or photostats of articles are available see the 
Back Issues page for details. 


¥Y Prints at the resolution of your printer - much 

anonymous FTP from as /pub/ibmpc/windows/pcbdemo/ 
e-mail enquiries can be addressed to 

Phone (01432) 355 414 

Digital Servo Interface 

Tie Pulser 

CCD Reverb Unit 

Switch- Mode Power Supply 

UV Exposure Timer 

Cricket Game 
Quick Prom 

Gas Alarm 800 £5.47 
Dual Metronome 801 £6.74 
Ultrasonic Tape Measure 802 £6.06 
Quicktest 803 £4.82 

Traffic Lights System £5.04 

Mini Lab 95. 
EPE Altimet (Altimeter) 
Personal Stereo Amplifier 

Universal Infra-Red Remote Control () Xeuey 
Combination Switch 
Christmas Lights Colour Spectrum 

TV/UHF Aerial Amp (double-sided) 
Continuously Variable Balanced Power Supply 
Emergency Lighting Unit 

Car Elecric Window Enhancer 
Simplifly Atari STFM Interface 

Personal Stereo Amp. Add-On 

Electronic Fire 
Mind Machine MkII — Signal Generator 

Ventilation Fan Timer 
Universal Data Logger 

Mind Machine MkIl - Magic Lights 
Superhet Radio Control Receiver 
Guitar Preamp and Distortion Unit 
Linear Clock — Timing Board 
Display Board 
Universal Alarm Module 

Electronic Snooker Scoreboard 832 

Mind Machine MkIl 
— Computer Interface 

Xenon Strobe 

Electronic Gong 

Micro Lab — p.c.b., EPROM, PAL and booklet 

Everyday with Practical Electronics, September 1995 

Bike Odometer (pair of boards) ee 
Amstrad PCW A to D Converter (double-side 
Experimental Electronic Pipe Descaler 
Sound Activated Camera Trigger 

L.E.D. Sandglass 
Main and Display boards 
Kettle Alert: 
Linear Power Supply (double-sided) 
Multi-Purpose Audio System 
Six Channel Stereo Mixer 

Multi-Purpose Audio System 
Microphone Pre-Amp module 
RIAA Pre-Amp module 

20 Metre Receiver 

Multi-Purpose Audio System | DEC’93 | 
Tone Control and 1W Stereo Amplifier 
Tone Control 
1W Stereo Amplifier 

Three-Way Christmas Tree Lights Flasher 

Auto Alarm 

250W/600W Battery to Mains Inverter 

Multi-Purpose Audio System | JAN'94 | 
10W + 10W Stereo Power Amplifier 
Power Supply 
Pond Heater Thermostat 
Timer/NiCad Capacity Checker 

Multi- Purpose Audio System 
Balanced Microphone Preamplifier 

Balanced Microphone Power Supply 859 
Whistle Controlled Light Switch 860 
Battery to Mains Inverter — U.P.S. charger board 862 
Three Phase Generator 861 
Visual Doorbell 863 

CCD TV Camera — Control Board 
(double-sided, plated-through-hole) 

Telephone Ring Detector 
CCD TV Camera 
Combined Video, Test & Ext Plug Boards 
Frame Grab Control 
(double-sided plated-through-hole) 
EPE Sound DAC PC Sound Board 
MOSFET Variable Bench Power Supply 

L.E.D. Matrix Message Display Unit 
Display Board ; 
CPU Board 
Stereo Noise Gate 
Simple TENS Unit 
Capacitance/Inductance Meter 

Advanced TENS Unit 
Digital Water Meter — Scaler 

L.E.D. Matrix Message Display Unit 


PC Interface 
Microprocessor Smartswitch 
Microcontroller P.|. Treasure Hunter 

Print Timer 
Watering Wizard 

‘Simple NiCad Charger 


Stereo HiFi Controller — 1 Power Supply 

Stereo HiFi Controller — 2 
Main Board 
Expansion/Display Boards (pair) 
Dancing Fountains — 1 
Pump Controller 
6802 Microprocessor Development Board 

Dancing Fountains — 2 nak 
PC-Compatible Interface (double-sided 

Automatic Greenhouse Watering System 
Seismograph — 1 Sensor/Filter 

— Clock/Mixer 
3-Channel Lamp Controller 

Seismograph — 2 mae 
PC-Compatible Interface (double-sided 
Visual/Audio Guitar Tuner 7 

Digilogue Clock 
Hobby Power Supply 
Audio Auxiplexer 
Control Board 

Power Controller 
1000V/500V Insulation Tester 
Active Guitar Tone Control 

TV Off-er = (pair) 

Video Modules—1 Simple Fader 
Improved Fader 
Video Enhancer 



Everyday with Practical Electronics, September 1995 

Rodent Repeller 
EPE Fruit Machine 
Video Modules -2 Horizontal Wiper 

Vertical Wiper 

4-Channel Audio Mixer 
Spacewriter Wand 

Universal Digital Code Lock 
Video Modules — 

3 Dynamic Noise Limiter 
System Mains Power Supply 
Magnetic Field Detector 
Model Railway Track Cleaner 
Moving Display Metronome 

The Ultimate Screen Saver 927 
Foot-Operated Drill Controller 928 
Model Railway Signals 929 
12V 35W PA Amplifier 930 
Multi-Purpose Thermostat 931 £6.30 
Multi-Project PCB 932 £3.00 
Sound-Activated Switch 
Audio Amplifier 
Light Beam Communicator (2 boards required) 
Multi-Project PCB 932 £3.00 
Light-Activated Switch 
Switch On/Off Timer 
Continuity Tester 
Auto Battery Charger 934 £5.36 
National Lottery Predictor 935 £5.34 

R.F. Signal Generator 
Coil & Power Supply (pair) 

MIDI Pedal 

Club Vote Totaliser 

PIC-DATS Development System 

(double-sided p.t.h.) 
EPE HiFi Valve Amplifier — 

Phase splitter 
PIC-DATS 4 -channel Light Chaser 

HV Capacitor Reformer 
Ramp Generator 
Logic Board (double-sided p.t.h.) & Analogue 
board (pair) 
Automatic Curtain Winder 

Microcontrolled 3-Digit Timer 




IR Remote Control — Transmitter 948 
— Receiver 949 
Personal Practice Amplifier 950 

Low-Range Ohmmeter Adaptor 
Simple Theremin 


Boot Control Unit 

Display Unit 


Order Code Project Quantity Price 

Bait ooh i aio (cheque/PO in £ sterling only) to: 
Everyday with it 

Practical Electronics 

Access (MasterCard) or Visa No. 
Minimum order for credit cards £5 

STOTUIR, 5s ii seeritdaticc ess Aten eta ces Card Exp. Dates. 2c din ce 

Be ee ee a ce eer eek tate See eek te ee eee ee eee te ee ee ee ee 

Please supply name and address of cardholder if different from the address shown 




Tony Smith G4FAL 


Classes for the radio amateurs’ ex- 
amination (RAE) restart in September. 
These are for the full RAE which leads to 
a Class B (VHF and UHF only) amateur 
radio licence or a Class A (all bands) 
licence. To obtain the latter, applicants 
must also pass a 12 words per minute 
Morse test. 

The Novice examination (NRAE) is 
simpler, and has a shorter period of study, 
leading to the Novice B or A licence (the 
latter with a 5wpm Morse requirement). 
Most of what follows relates to the 
full RAE, and there will be more about 
Novice entry in a later column. 

The RAE has a multiple choice format, 
and is in two parts. Part one covers the 
radio regulations, transmitter interference 
and electromagnetic compatibility. Part 
two covers operating procedures and 
practices; electrical theory; solid state 
devices; receivers; transmitters; propaga- 
tion and antennas; and measurements. 

This need not be too daunting for those 
set on becoming a radio amateur. | knew 
little about radio before | took an RAE 
course, but enthusiasm for my new- 
found interest carried me through to a 
good result. Anyone who already has 
some knowledge of and a interest in 
electronics would have an even better 
chance of passing with flying colours. 


The course for the RAE usually runs 
over one academic year. The exams are 
held in December and May at technical 
colleges, evening institutes, local radio 
clubs and schools across the UK. Those 
who make good progress often take the 
December exam and if unsuccessful try 
again the following May. 

In the four year period ending May 
1994, 18,190 candidates took the RAE 
and 12,561 passed, a success rate of 69 
per cent. To give an idea of how many 
people currently participate in amateur 
radio, there were 61,291 licenses on 
issue in the UK at the end of March 
1995. These comprised 32,715 Class A 
licences, 26,465 Class B, 188 Novice A, 
and 1,923 Novice B. 

These figures exclude the many en- 
thusiasts studying for the exams at any 
one time. There are also thousands of 
shortwave listeners who listen to amateur 
radio as well as other radio services. 
Many of these SWLs also have a good 
understanding of amateur radio but do 
not feel the need to obtain a transmitting 


Amateur radio is a hobby for all. You 
can get a licence to immerse yourself in 
one or more different aspects of radio 
communication. With the appropriate 
licence you can use a microphone to talk 

to people in this country or round the 


world. You can even talk to astronauts on 
shuttle flights or in orbiting satellites. 

_ With acquired skills, you can communi- 
cate using Morse code, computers, 
teleprinters or television. With the ap- 
propriate equipment, you can reflect your 
signals to their destination via the 
ionosphere, repeaters, satellites, meteor 
showers, the aurora borealis, or the 

You can experiment with antennas or 
ancillary equipment to improve the per- 
formance of your station; or modify your 
rig if you wish. You can build your own 
transmitter or receiver, or you can invent 
and try out some new form of improved 
radio communication — if you can con- 
vince the authorities of its potential value! 

Again depending on the licence you 
hold, you can transmit and receive over 
a wide range of authorised frequencies, 
from HF to microwaves. 


You can join special activity groups 
such as RAYNET, which trains con- 
tinuously and, when required, provides 
valuable communications facilities for the 
emergency services. 

There are contest groups, expedition 
groups, and special groups for virtually 
all amateur radio interests, as well as 
others whose members are linked by 
a common interest outside the hobby. 
There are such groups or clubs for rail- 
waymen, police, Esperantists, ex- and 
current members of the armed services, 
and many others. In a more general sense 
there are local radio clubs across the 
country, which are usually very pleased 
to welcome newcomers to the hobby. 

A national society, the Radio Society of 
Great Britain (RSGB), provides a wide 
range of services to its members, includ- 
ing amonthly journal Radio Communica- 
tion. \t also publishes or sells a large 
range of specialist books catering for 
every branch of the hobby from beginner 
to advanced level. 

Within the hobby there are many other 
publications available from home and 
abroad, magazines, books, and club jour- 
nals, again catering for just about every 


The Radiocommunications Agency has 
a free booklet, “How to Become a Radio 
Amateur", obtainable by ‘phoning 0171 
215 2352. Copies of the examination syl- 
labus (price £2.00 post free), plus free 
sample questions, can be obtained from 
The City & Guilds of London Institute, 
46 Britannia Street, London WC1X ORG. 
Quote Subject 773 for the NRAE, and 
Subject 765 for the RAE. 

The RSGB will provide more infor- 
mation about all types of entry into 
amateur radio on request, and has a 
number of useful publications for RAE 

and NRAE students. Their address is: 
Lambda House, Cranborne Road, Potters 
Bar, Herts EN6 3JE. Tel: 01707 659015. 

| should point out that, apart from 
classes, there are RAE correspondence 
courses available, while some students 
successfully devise their own “course”, 
simply using books to learn or revise the 
subject as appropriate. 

If you have been thinking about becom- 
ing a radio amateur, now is the time to 
arrange a September start on a course of 
study for the RAE. Get the information 
mentioned above, sign up for a course, 
and good luck! | look forward to meeting 
you on the air in the not too distant future! 


Having written enthusiastically about 
the attractions of amateur radio, I'm now 
turning to one of its trouble spots. Many 
countries permit their national radio 
societies to broadcast amateur radio 
news bulletins and where these are 
limited, as with the RSGB_ weekly 
broadcasts, there are usually few inter- 
ference problems. 

In the USA, however, not only does the 
national society, ARRL, broadcast bul- 
letins daily but other organisations do 
also. This has led to an enormous row, 
with some broadcasters accused of inter- 
fering with ongoing contacts when they 
come on the air. 

In particular, there is a row about the 
broadcasts of the International Amateur 
Radio Network (IARN). Stations broad- 
casting bulletins do not have allocated 
frequencies, and are expected to check 
that a frequency is clear before using it, 
just like any other amateur station. | 

Unfortunately, [ARN and other bulletin 
stations believe (wrongly) that by pub- 
lishing a schedule in advance they may 
operate on a specific frequency regard- 
less of channel occupancy. Frustrated 
amateurs dispossessed from such fre- 
quencies have retaliated by interfering 
with the bulletins. The broadcasters have 
responded by holding what they see as 
“their’’ frequencies for long periods with 
extended broadcasts, and tempers have 
been running high. 

In an effort to alleviate the level of 
anger and retaliation now on the hf. 
bands, one amateur, Fred Maia W5Y1I, has 
proposed to the US licensing authority 
(the FCC) that all news bulletins and 
code practice transmissions be moved to 
frequencies above 30MHz. 

The ARRL have reacted strongly to this 
suggestion. Their own broadcasts do not 
cause problems, and they object to the 
idea of losing their highly valued news 
bulletins and Morse practice transmis- 
sions from the h.f. bands. 

The FCC has received many comments 
for and against the idea of such a move. It 
will be interesting to see how the matter 
is resolved. 

Everyday with Practical Electronics, September 1995 



This super quality CCD camera 
can be connected into your existing 
TV or video using the AV channel 
and can be used for discrete — 

surveillance or observing your Droherey externally using a suitable weatherproof 
housing. Can accommodate lighting levels ranging from daylight to street 
lighting using its built in electronic shutter. Excellent when using with an infra 
red source, Built in wide angle fixed focus lens the camera has a resolution of 380 
TVL. Can be housed inside an empty floodlight case, (extra). 

Special offer price of only: £79.95 Plus VAT (P&P £3.50) 
For full range of CCTV products send SAE to: 

Direct CCTV Ltd., Dept. PE27., Unit 6, Carrick Court, Forrest Grove 
Business Park, Middlesbrough, TS2 10E. 

TIMER KIT. Controls 4 outputs at preset times over a 7 day cycle. 
LED display. Easily programmed via keyboard. £65.95 
ELECTRONIC LOCK KIT. Over 38,000 possible combinations. 
Alarm sounds after 3-9 failed. guesses ‘and locks out keyboard for 
preset time. £25.50 
SUPER SENSITIVE FM MICROBUG. Runs off a 9V battery, fits 
in a match box, listen in on any FM radio. £10.25 
STROBE KIT. Can be triggered by external voltage e.g. loudspeaker 
or as a slave flash for photographic purposes. £21.85 

Plus many many more. Including all TK Kits. 

For full details send your SAE. now. 

We have a full range of electronic components at competitive prices. 

Send an SAE for price lists. 
NEW BOOK! Beginner’s Guide To the Internet. 88pp £5 Inc. 

G AT S 149 The Vale, Acton W3 7HR 

Tel: 0181 932 0144 
ELECTRONICS Fax: 0181 932 0145 

15 Amstrad Games................. 50 off mixed terminal blocks..£2.50 

15 Spectrum Games ............... £5.00" 25 off buzzers & sounders......£3.50* 
£1 PACKS 25 off mixed £4.95* 
50 BCS4 7A: 2085) G 20 BSS92; 50 off mixed switches............. £7.50" 
250 off i.c. SoCKetS.........0.0c0000. .95* 
50 2N5551;3BD145;10BD237; | too0gH Germic cape Ey BO" 

10 BD239A; 5 BFW43; 10 BFX30; 

3 BSX59; 10 VN2010-L; 20 ZTX304; 
20 ZTX311; 20 ZTX510; 20 ZTX551; 
5 5V d.i.l. relays; 10 21:10MHz 
crystals; 10 811 MHZ filters; 50 6-way 
i.c. skts.; 50 14-way d.i.p. hors; 

20 TO18 heatsinks; 20 TOS heatsinks; 
200 TO5 mounting pads; 200 TO18 
mountings pads; 2 1002 LOPT Tx; 

5 12-way terminal blocks; 10 silver 
control knobs; 10 95V V.D.R.;3 12V 
counters; 25 3:5mm jack plugs; 

10 PCB MT microswitch; 10 6-way 
d.i.1. switch; 10-1 pole 3-way rotary 
switch; 25 slide switches; 5 3A 250V 
power toggle switch; 50 4:7u.F 25V 
caps; 15 2200uF 25V caps; 

5 off 3V Lithium memory 

back-up batteries................. £2.00* 
100 off 2200uF 25V caps.......£6.00* 
3lb mixed component pack......£4.95 
Jumbo component pack.............. £10 
Crystal oscillators 10/12MHz..£1 ea 
5V DPCO DILL. relay.:.......... 60p ea” 
5V SPCO S.I.L. reed relay.......40p ea” 
12V Piezoelectric Sounders......50p ea 
DIL Switches 3/4/6 and ~ 

3:5mm jack plugs..... Sinicesioni 10 for £1* 
100 off Zener diodes, mixed........ £2* 

10 0:047F suppresion Caps; 1 0 crocodile clip leads wiadebneene .£3.50* 

25 neons; 10 1,F 250V polyesters. or wl ty R.F. Filters, i 
oo eee FYStONS OIG sik ous cl sces £4.95 

5%" to 3%" floppy rorerter 100m P.V.C. sleeving............. £4.50" 

MIN os son cs bans oko sceennicas 1.50 ea* 
STC p.s.u. 240V Input; 5V 6A 
Output, (converts to 12V 3A, 

QQV0310, £10"; ;,QQV0320A, £10"; 

details supplied)........ sabsehaetes £5.95 | QOV0640A, £20", ECC 82, £3": 
Temperature probes, with eon ECH 81, £2*: PCL 805, £3°: 
EEN Gre ERED, Sek aR 5 

ORP 11, £3; ORP 40, £3; CV 4004, 

Universal Timer (10 min. delay and 4005, 4006, 4007, 4014, 4020, 

1A AOOrR Zoe tions) £3.98. | 4024, 4043, 4055, 4064, 5042, 
— mains filters............ £1.00 ea” | 5080, ALL £5 each”. 
40 Character x 1-line dot 

matrix display.................. £4.95 ea” QUANTITY DISCOUNTS 

We also buy all forms of electronic 
é components, p.s.u’s, disk drives etc. 

Lists to below address. 


| DY=Yo) at ot en OU O)AY/ 0 od <a am ok Om 
14 Constable Road, 

Car Dashboard Display (shows 

lights, indicators, doors, 

on picture of car)................. £4.95 
4-digit clock display............... £2.50° 
4-digit l.c.d. with 7211 driver..£3. 50° 
17-digit v.f. display................. £2.95" 
Giant 2-digit v.f. display......... £2.95" 
12V stepper motors, 48 steps 

per rev., 7:3° step angle.......£3.95* 
250 off mixed electrolytic 

CMG fica nn oan £4.95* 
250 off polyester caps............ £4.95" St. Ives, Huntingdon, 
1000 off mixed resistors %4W..£4. 95° Cambs PE176EQ 
100 off phono plugs............... £2.95" Tel/Fax: 01480 300819 

Everyday with Practical Electronics, September 1995 

JCG Electronic projects 






MICRO FM (a). 1km range transmitter, 80-100MHz 

preset, received on any FM radio. Includes FET mic. 
2x3cm PC \ 
MICRO FM (b). Variable mic. sensitivity. Tuneable 
80-110MHz. 1km range, 2x 3-5 cm PCB £7.95 
ULTRA MINI FM. 200mtrs range. 80-100MHz, runs off 
watch battery (inc), only 1x 2em PCB 


dynamic noise gate with variable effect and level €15.95 
AU19 ANALOGUE DELAY. “Bucket brigade’ delay line. 
Variable clock frequency for producing double track and 

gs echoeffects etc. Delay times from2-5to5ims £18.50 

AU20 CONTROL OSC. Low fequency oscillator to 
modulate the analogue delay line for Flanging, 
Chorus and other effects 

AU21 fat DIGITAL DELAYS. 200ms and 800ms digital 


finding, tracking etc. 80-110MHz 
FM RECEIVER (a). Small high quality FM receiver. 
Covers standard FM broadcast bands. Will drive 
headphones (not inc) £10.90 
FM RECEIVER (b). As (a) but with 3 watt audio power amp 
and tuning LED €1 
CRYSTAL RADIO. Great introduction to radio 
electronics. Includes tuner, ferrite aerial and 
earphone £7.50 
AM RADIO. Single chip radio for use with headphones, 
(not inc.) or an external amplifier £8.90 
I.R. REMOTE CONTROL. Single channel for lights, 
garage doors etc. Transmitter - £6.95 
Receiver (with mains relay) = - £9.50 
Single channel, XTAL controlled Transmitter - £9.50 
Receiver (with mains relay) - £15.45 
MICRO TRANSMITTER GUIDE. Packed with useful 
Circuits and info - How to build surveillance devices, 
short range TX's etc. i £3.95 

applications where low noise isn’t a priority - guitar 

‘anole rate from 25kHz-50kHz variable delay time, 

200ms - £20.40, 800ms - £24.95 

P2 15 WATT. General purpose upgrade. Uses TDA2030. 
24V single rail with heatsink £9.95 

3.50 3 40 WATT. High quality power amp for compact disc 

and other demanding applications. Switch on mute, 
thermal/short protection. Distortion less than 0:003% 
27V + with heatsink £15.50 
P4 150 WATT. Rugged and powerful MOSFET design, 
excellent response and reliability, 50V+ with heatsink. 
ideal for guitar amps. PA or sound system £22.95 


Most of the kits in this section are designed to be small 
enough to be installed inside instruments, but can easily 
be adapted for other applications such as Effects Pedals 
TL10 VOLUME BOOSTER. Compact circuit for low 
output pickups £3.95 
TL11 OVERDRIVE: Will provide enough clean “<— to 
overdrive any guitar amp. Variable £7.95 
TL12 DISTORTION. Smooth distortion and sustain. 
Variable €7 
TL20 HI BOOST. Variable high frequency booster 

amps etc. 9V-15V, variable gain and high output €4.20 or guitar or bass 

AU11 LOW NOISE PREAMP for more critical input stages. 
Ideal for mixers etc. 9V-15V, variable gain £4.50 
Standard. Uses an NE5534 i.c. 9V-15V, variable 

gain £5.99 
AU13 SMALL SIGNAL. Single FET preamp for boosting low 
Output piezo pickups or acoustic transducers £3.90 
AU14 SMALL SIG + EQ. An AU13 with a simple 
three-band passive EQ circuit. Designed for 

piezo pu's £6.90 
AU15 SINGLE TRANSISTOR. Low noise preamp for 
electric guitars etc. Preset gain. BC184L £3.90 
AU16 ACTIVE TONE CONTROL. 12dB cut and boost, 
bass and treble with preamp. Includes pots. £8.95 
AU17 7-BAND EQ board for graphic/toner control 
applications. Pots included £12.95 

TL21 LOW BOOST. Variable low frequency t booster 

for guitar or bass 

TL22 MID BOOST. Variable mid-range booster for guitar 
and bass. Can also produce Wah Wah effects  €6.75 
TL23 GUITAR ACTIVE TONE. Fully active tone controls 
for guitar. Includes control pots. €12.95 
TL24 BASS ACTIVE TONE. As above but for bass 

guitar £12.95 
TL25 HALL EFFECT WAH WAH. Tuneable band pass 

filter, controlled by the proximity of a magnet to a hall 
effect sensor. Makes for a smooth filter sweep without 
the noise associated with potentiometer arrangements 
(pedal assembly not included) €10.75 
TL26 HALL EFFECT VOLUME. Circuitry for making a 
high quality volume pedal (pedal assembly not 


CRICKLEWOOD Flectronics 

Very Interesting 



b heque, Credit Card or tap 

copies of the 1995 Cricklewood Catalogue. 

— send me 


TV & VIDEO SPARES (inc Video Heads) 

IN CAR AUDIO+SPEAKERS (inc Bass tubes) 


& much much much more (over 10,000 lines). 

Coins to Pap 

I enclose £2.50 per copy (UK & Europe). £5.00 overseas 

Cricklewood Electronics Ltd, 40-42 Cricklewood Broadway 
London NW2 SET Tel 0181 450 0995 Fax 0181 208 1441 




Everyday with Practical Electronics reaches nearly 
twice as many UK readers as any other indepen- 
dent monthly hobby electronics magazine, our 
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1 to 24 volts up to % amp. 1 to 20 volts up to 1 amp. 1 to 16 volts up to 1% 
amps d.c. Fully stabilised. Twin panel meters for instant voltage and cur- 
rent readings. Overload protection inc. 
Fully variable. f4 5 
pag from VAT 
Va. + Post and 
Compact unit. F 
Size 9x 5% x 3in. i insurance £4 
NEW MODEL. Up to 38volts d.c. at 6 amps. 10 amps peak. Fully variable 
Twin panel meters. Size 14% x 11 x 4%in. 96 inc VAT. Carr £6. 
SURREY, U.K. Tel: 0181-684 1665 
-» Lots of transformers, high volt caps, values, speakers, in stock. 


exists to help electronics 
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For membership details, write to the 

Mr. J. F. Davies, 70 Ash Road, 
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Cheshire CW8 2PB. 

Space donated by Everyday with Practical Electronics 

HND in Telecommunications 
Degree in Electronics 

The Division of Electronics offers a two 
year BTEC HND in Communications 
Engineering (Telecommunications). 

A third year of study leads to a B.Eng. 
Degree in Electronics. 
Mature students are welcome. 

For more information phone 
01254 292348 and ask for Sam Jones 



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a ee 
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O.N.C., O.N.D. and H.N.C. 

Next course commences 
Monday 18th September 1995 

Me) 510) 14 ons -10)\ | (orsnele) mm =e] = 
TEL: 0171-373 8721 


All you will ever need to know about Bugs. Over 
40 Bug circuits for every application. Telephone, 
High Power, Crystal Controlled, and UHF Bugs 
and many pages of useful information. Many 
previously unavailable circuits. This is the very 
latest book, and the “ONLY” book of its kind 
in the UK. A valuable asset for the hobbyist 
and professional. Introductory offer price only 
£9.95 inc. P&P. 
For immediate despatch, send cheque or P.O.’s payable to: 

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send s.a.e. to B. M. Ansbro, 38 Poynings 
Drive, Hove, Sussex BN3 8GR, or phone 
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money prices. S.A.E. for FREE catalogue. 
SIR-KIT Electronics, 70 Oxford Road, 
Clacton, CO15 3TE. 

PLDs AND EPROMS copied or pro- 
grammed. We supply logic devices/convert 
discrete logic to PLDs. Also PCBs designed. 
Send for details to PO Box 1561 Bath (01225 

VALVE ENTHUSIASTS: Capacitors and 
other parts in stock. For free advice/lists 
please ring, Geoff Davies (Radio), Tel: 01788 

and above, polyester, polypropylene and 
electrolytic. Geoff Davies (Radio), Tel: 01788 

channels, 64 levels, 127 presets, assembled 
and tested. Requires 20V AC supply and 
case. Cheques for £59, made payable to 
Technology Direct, 27 Hartland Grove, 
Priestfield, Middlesbrough, Cleveland TS3 

German quality, £69.50 post paid. Also 
complete He-Ne Laser systems from £85.00. 
Telephone 01925 575848 for details. 
Cheques or PO to, English Scientific, 12 
Orford Avenue, Warrington, Cheshire, WA2 

prices you can afford. Very low cost 
(sometimes free) Tooling. Small quantities 
speciality. 01685 (Aberdare) 874763. 

PIC CHIP PROGRAMMER. Low cost solu- 
tion, uses PC printer port, full constructional 
details, plus all software and examples, £20. I. 
Bailey, 15 Mount Road, Fleetwood FY7 6EZ. 
Tel: 01253 875148. 

COMPLETE GUIDE to building a P.C. 
details send SAE, D. Bryan, MAYEP, 19 Acie 
Gdns., Bulwell, Nottingham NG6 8NY. — 

SERVICE. Prototype and _ Production. 
Artwork raised from magazines or draft 
designs at low cost. PCB’s also designed from 
schematics. Production assembly also under- 
taken: For details send to P. Agar, 36 
Woodcot Avenue, Belfast, BTS 5JA or phone 
01232 473533 (7 days). 

COMPUTERS. Complete Home Study 
Course. Includes 20 comprehensive lessons, 
separate reference manual, fault finding 
charts, diagnostic software and more. Only 
£24.95. Tel: 01633 280216. 

Everyday with Practical Electronics, September 1995 

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This course provides a strong education in 
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Over the past 100 years more than 10 million students throughout the world have found it worth 
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i Mr/Mrs/Miss/Ms 

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Study for a successful career in Electronic 
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Establishing a new University 

Everyday with Practical Electronics, September 1995 

Deane Road, Bolton, Lancashire, BL3 5AB. Telephone 01204 528851. Fax 01204 399074 


Millions of quality components 
at lowest ever prices! 

Plus Tools, Watches, Fancy Goods, Toys. 
Mail order UK only. 

200 Signal diodes 1N4148 é SMM £Od 1.€.0.8........cccceetecseeeeeeeeeees 
75 Rectifier Diodes 1N4001 J Asstd. high brightness |.e.d.s.......... 
Rectifier Diodes 1N4007 ' Axial |.e.d.s (Diode/package) £ 
Rectifier Diodes 1N5401 Asstd. 7-segment displays 
NE555 Timer 1.C.S.................0000c00000 ORP12 light dependant resistors 
Asstd. Zener Diodes Asstd. IF transformers 
BC212L Transistors Asstd. coil former: 
BC213L Transistors Asstd. RF chokes Tinductors) 
BC327 Transistors Asstd.,connectors edge,d.i.l., sil etc 
8C328 Transistors Asstd. d.i.|. sockets up to 40-pin 
BC337 Transistors Asstd. disc ceramic capacitors 
BC478 Transistors Asstd. capacitors 1nF to 1pF 
BC546 Transistors Asstd electrolytic capacitors 
BC547 Transistors 4P3W MBB min. rotary switches 
BC548 Transistors Min. SP/CO slide switches 
BCS549 Transistors 1” glass reed switches 
BC550 Transistors 4N7 mini axial capacitors 
‘C557 Transistors 24-pin d.i.|. wire wrap i.c. skts. ........ 
BC5568 Transistors 12V motorised volume control 50k...£1. 
BC559 Transistors Grommets 6-3mm id, 9-5mm od 
BC640 Transistors c/f %W 5% resistors any one 
MPSA42 Transistors value, E24, range 1R to 10M 
MPSAQ2 Transistors 
2N3702 Transistors 
2N3904 Transistors 
78L12 12V 100mA Pos Regulators... 
79M08 BV 500mA Neg Regulators.... 
5MM £Od 1.€.0.58.............ccccceseceeceeeeees 


All inclusive prices — 
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Send 43p stamped self addressed label or 

envelope for catalogue/clearance list. 
At least 2,100 offers to amaze you. 

Brian J Reed 
6 Queensmead Avenue, East Ewell 
Epsom, Surrey KT17 3EQ 
Tel: 0181-393 9055 


Ce ee ee ee ee ee ee 


eek ek ek ek ek ek dk otk 

Prices include VAT. postage £1.25. Stamp for Lists 
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Phone (0114) 2552886 Fax (0114) 2500689 

Rs" SSSSRSSRSeeeseeysseseRsa 


TO IOI Ot tok 
Special packs £1 each — : 
choose 1 x £1 pack FREE with 10 purchased 


SP1 15 x 5mm Red Leds SP41 20 x Mixed transistors N . R . BAR DWE LL OPE EOUOeCEeOCrerrerrere reer errr rr errr err iter rere rrr ere 740 
SP2 15 x 5mm Green Leds SP42 200 x Mixed 0.25W C.F. resistors 

SP3 12 x 5mm Yellow Leds SP43 2 x LM1458 SeeCeeeeeeeeeeeeeaeeeee eee eee eee eee eee eee eee 

SP4 10 x 5mm Amber Leds SP47 5 x Min.pushbuttonswitches $f @ | £=OD.KR, ELEC LTRUNIUCS 2... ccc ccc ccc ccccccecceucuce 

SP6 15 x 3mm Red Leds SP49 5 x 5 metres stranded wire 

SP7 12 x 3mm Green Leds SP102 20x 8pinDiLsockets j= $f Fh fF BONER EUIIN TIND EDD UL Di ccccccscscnscsccccesscccecensessseessecseeseeees 

SP10 100 x 1N4148 diodes SP103 15 x 14pin DIL sockets 

SP11 30 x 1N4001 diodes SP104 15x 16pinDiLsockets «§-_—»_ fT EM RPMIN, J. FREED sesseeeeeeseecneseensettersnsnnenecnnnnseseeeseesananens +! 

SPi2 30 x 1N4002 diodes spins Sx 7aisoo == |) BULL ELECTRICAL ..........--00.0+0-4-- 5 ssided eats bsantey Cover (ii) 
x transistors 1 15 x 557 transistors 

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x transistors 115 x 10mm Red Leds 

$P20 20 x BC184 transistors SP11§ 3 x 10mm Red Leds _ | TWIN GUITARS (SCG)... ceccceseccsseseseeeeeeeeeeeee 737 

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x transistors 125 10 x 1000/16V radial elect caps 

SP28 5 x Cmos 4011 SP128 100 x Cable ties (small) | COM PAC ELECTRONICS SCC CREECH eee ee ee 729 

SP36 25 x 10/25V radial elect caps SP130 100 x Mixed 0.5W C.F. resistors nd. gg esac ca cahesweblonseniiivcithoaes 

SP37 15 x 100/35V radial elect caps SP133 20 x 1N4004 diodes 

SP39 10 x 470/16V radial elect caps SP147 5x Stripboard9strips/25holes jé§o§f # fF SVUZAUZINE TIN EO PUINAALTUPINAFAL, nce ccecececensscnenneceneceecseencueees 

SP40 15 x BC237 transistors SP156 3 x Stripboard 14 strips/27 holes 

RESISTOR PACKS — 0.25W C.Film Catalogue £1 inc. P&P or FREE with first 

RP3 5 each value — total 365 < £2.60 order. P&P £1.25 per order. NO VAT. CR SU PPLY COM PANY Se eee eee eee eee eee eee eee eee eee eee eee eee eee 

RP7 10 each value _ total 730 £3.95 Orders to: Sherwood Electronics, D | R ECT C CTV COP e meee reese eeereee eee neeEeEseeeeEEeEEeeeeeETEESeeseEeSeeeED 

RP10 — 1000 popular values £5.30 7 Williamson St., Mansfield, Notts. NG19 6TD. 

| EPT EDUCATIONAL SOFTWARE cececccssccccssssvescsccocsses 
, a - ~ ESR ELECTRONIC COMPONENTG.......................... 672 
Patra “ranpormccikeer sheng = Pte! sar a ala ha aa I EXPRESS COMPONENTG............... ee ne Be ane 730 

100 off per value — 75p. even hundreds per value totalling 1000........... Pinvesniacedserdaes £6.00p 
Metal Film resistors %4W 10R to 1 MO 5% E12 series — 1 4p. 1% E24 series ..............:00000 2p 
Mixed metal/carbon film resistors 44W E24 series 1RO to TOMO .........cccccceeceeeseeseeeseees 1%4p 
1 watt mixed metal/Carbon Film 5% E12 series 4R7 to 10 Megohis ..............ssserereseseees 5p 
Linear Carbon pre-sets 100mW and %W 100R to 2M2 E6 series .............. phephvaaspesseogescnotss 7p 
Miniature polyster capacitors 250V working for vertical mounting 

.015, .022, .033, .047, .068-4p. 0.1 - 5p. 0.12, 0.15, 0.22 - 6p. 0.47 - 8p. 0.68 - 8p. 1.0 - 12p 

CPA wo Clee PETRIE UC ois csenissessscrsenseasennpenceonrsapenabetesibns 


PPE TEER ORION TIONS... occ ccssccsscsccssscconseserssasenesiesneces 

Mylar (polyester) capacitors 1 V working E12 series vertical mountin 

10bop te 8200p - 3p .01 to aaa me we y cles < 0.22 - oe ag oe - a ape nae se 669 
ubmin ceramic piate capacitors w vertical mountings. 

2% 1.8pf to 47pf - 3p. 2% S6pf to 330pf - 4p. 10% 390-4700 «.......seessseseusersessenssesssen 4p GE Weber d FURR ha cncianscvesvonsssreputenetibanconceedhslaganendes 729 

Disc/plate ceramics Eov oe eories ve * ; Goon E6 wecbnge 1 apt led apa tah ae 2p ate csc acwocigny elounieccothgcteiiacken! 699 
olystyrene capacitors working series long axial w 

10p\ to 820pf - 5p. 1000pf to 10,000pf - Bp. 12,000 PE rennin Ip MAGENTA ELECTRONICS... ccccseseeeeeeeeees 670/671 

741 Op Amp - 20p. 555 Timer —20p. LM3900 ........csssssscsssssssseescesssssseceesssnsnssesensneteesneestes 80p MAPLIN ELECTRONIGG........................-.00..0-. Cover (iv) 

CMOS 4001 - 20p. 4011 - 22p. 4017 — 40p. 4069UB unbuffered ............cssssscccsseeeseees 20p 439 

DIL holders, 8-pin 9p; 14-, 16-, 18-pin 12p; 24-pin 18p; 28-pin 20p; 40-pin 25p. 

BPS re EI LENT ae TUT inscscistk tee cite hea bushinrnnorcaesentavnssccasecocovevenasvescessageonsers 5p 
22/16, 22/25, 22/50, 33/ . hy PPE Ge Er TET OE oii iitbcasa diseases ink acho sanctus cconencugeasbanings 6p 


Sete eeeeeeesseeeeeeeseeeeeseeeeeeeeee 
PreePeCCET OT OCCCerrrerrr rrr ite) 

Kcbedeccedevecessccepecceicccdecescnscceccceccoecevence CW BD Mm FRR Re we SF Fe SE SEW HSS HSse ee sG ee SOOT SHeHHTKAeSasesssseseeaeseoaenesseee 

47/10, 2 

1A + , 5V, 8V, 1 hy 15V, 18V & 24V - 55p. 100mA. 5.8, 12, 15, Vit occ eeeeeeeeeees 30p 
DIODES (piv/amps 

refzemAs N4148 2p. 800/1A 1N4006 4%p. 400/3A 1N5404 14p. 115/15mA OA91 .. 8p 
100/1A 1N4002 3%p. 1000/1A 1N4007 5p. 60/1.5A S1M1 5p. 100/1A bridge .......... 25p 
400/1A 1N4004 4p. 1250/1A BY 127 10p. 30/150mA OA47 gold bonded .................. 18p 
Zener diodes E24 series 3V3 to 33V 400MW - Gp. 1 Walt ..........ceeereeeeeteeteeeees aco aera 10p 
Battery snaps for PP3 - 7p for PPS ...........ccccscscessssssseeseenstsestsasrensessesesacsseaseenssnesnsssseesenseees 12p 
L.E.D.’s 3mm. & 5mm. Red, Green, Yellow - 10p. Grommets 3mm - 2p. 5mm..............065 2p 
Red flashing L.E.D.’s require 9-12V supply only, SMM ..........cceeserensreretsestseseserersseneens 50p 
Mains indicator neons with 220k resistor ............ccccccccscecessesseeeeeeeeeeeeseeersenseeeetseeeseeeneeenes 10p 

NE hoes ao ias casei escavcssyenisvencnsseasvesazasebnnee chess 

Omm fuses 100mA to 5A. O. blow 6p.A/surge 10p. Holders, chassis, mounting ............ 6p 
High speed pe drill 0.8,, 1.8, 2.0mm - 40p: Machines 12V de nm £15.00 SHERWOOD ELECTRONICS... eeeeeeeseeeteeee 
HELPI G HANDS 6 ball joints and 2 croc clips to hold awkward jobs ................0.06 £4.50 

AA/HP7 Nicad rechargeable cells 90p each. Universal charger unit £6.50 
AA/HP7 zinc/carbon batteries in packs Of 4 ............:ccceseesetceseeteeeteeeeeeneeeeeeens £1.10 per pack 
Glass reed switches with single pole make contacts - 8p. Magnets ...............:cceseeeeee 20p 
0.1” Stripboard 2%" x 1” 9 rows 25 holes - 25p. 3% x 2%” 24 rows 37 holes ................. 70p 
Jack plugs 2.5 & 3.5m - 14p; Sockets Panel Mtg. 2.5 & 3.51M..........cccceeeeeeeeseseeeneeteereess 10p 
Ear pieces 2.5 & 3.5mm, dynamic — 20p; 3.5mm Crystal...........cceceeseeeseeeseeneeeteeeeeeeees £1.50 
Multi cored solder, 22G - 8p yard, 18G — 14p yard. 
BC107/8/9 - 12p. BC547/8/9 - 8p. BC557/8/9 - 8p. BC182, 182L, BC183, 183L, 
BC184, 184L, BC212, 212L - 10p. 
BC327, 337, 337L - 12p. BC727, 737 - 12p. BD135/6/7/8/9 - 25p. BCY70 - 18p. 
BFY50/51/52°- 20p. 
BFX88 - 15p, 2N3055 - 55p, TIP31, 32 - 30p, TIP41, 42 - 40p. BU208A - £1.50, BF195, 197 - 12p 
lonisers with seven year guarantee, 240V AC, list price £16.95 or more ................... £12.50 
Do not add VAT. Postage 30p (free over £5). Stamp for list. 


127 Chesterfield Rd., Sheffield S8ORN Tel: 01742557771 Return posting 


Phone/Fax: (01255) 850596 

For Editorial address and phone numbers see page 673. 

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 Benham & Co. Ltd, 
Colchester, Essex. Distributed by Seymour, Windsor House, 1270 London Road, Norbury, London SW16 4DH. Sole Agents for Australia and New Zealand-Gordon & Gotch (Asia) Ltd., South 
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Wimborne, Dorset BH2! 1PF. EVERYDAY with PRACTICAL ELECTRONICS is sold subject 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. 


FOUR MODELS:- MXF200 (100W + 100W) MXF400 (200W + 200W) 

MXF600 (300W + 300W) MXF900 (450W + 450W) 
FEATURES: xIndependent power supplies with two toroidal transformers * Twin L.E.D. Vu meters * 
Level controls * Illuminated on/off switch * XLR connectors * 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. 


SIZES:- MXF200 W19"xH3"2" (2U)xD11” 
MXF400 W19"xH5"4" (3U)xD12” 
MXF600 W19"xH5"4” (3U)xD13” 
MXF900 W19"xH5%4” (3U)xD14%.4” 
PRICES:-MXF200 £175.00 MXF400 £233.85 
MXF600 £329.00 MXF900 £449.15 

Advanced 3-Way Stereo Active Cross-Over, 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 250/500/800Hz, Mid-Top 1.8/3/5KHz, all at 24dB per octave. Bass invert switches 
on each bass channel. Nominal 775mV input/output. Fully compatible with OMP rack amplifier and modules. 

Price £117.44 + £5.00 P&P 

* sealed & arched ttle 

STEREO DISCO MIXER with 2 x 7 band 
L & R graphic equalisers with bar graph 
FEATURES:- including Echo with repeat & 
speed control, DJ Mic with talk-over 
| switch, 6 Channels with individual faders 
plus cross fade, Cue Headphone Monitor. 8 
Sound Effects. Useful combination of the 
following inputs:- 3 turntables (mag), 3 
mics, 5 Line for CD, Tape, Video etc. 

Price £144.99 + £5.00 P&P 

SIZE: 482 x 240: x 1 S0nini 

Join the Piezo revolution! The low dynamic mass (no voice coil) of a Piezo tweeter produces an improved 
transient response with a lower distortion level than ordinary dynamic tweeters. As a crossover is not required 
these units can be added to existing speaker systems of up to 100 watts (more if two are put in series. FREE 

, TYPE ‘A’ (KSN1036A) 3” round with protective wire mesh. Ideal for 
bookshelf and medium sized Hi-Fi apeakers. Price £4.90 + 50p P&P. 
TYPE ‘B’ (KSN1005A) 3'." super horn for general purpose speakers, 
disco and P.A. systems etc. Price £5.99 + 50p P&P. 

TYPE ‘C’ (KSN1016A) 2”x5” wide dispersion horn for quality Hi-Fi sys- 
» tems and quality discos etc. Price £6.99 + 50p P&P. 

TYPE ‘D’ (KSN1025A) 2”x6" wide dispersion horn. Upper frequency 
response retained extending down to mid-range (2KHz). Suitable for high 
quality Hi-Fi systems and quality discos. Price £9.99 + 50p P&P. 

TYPE ‘E’ (KSN1038A) 3%.” horn tweeter with attractive silver finish trim. 
Suitable for Hi-Fi monitor systems etc. Price £5.99 + 50p P&P. 

LEVEL CONTROL Combines, on a recessed mounting plate, level control 
and cabinet input jack socket. 85x85mm. Price £4.10 + 50p P&P. 

A new range of quality loudspeakers, designed to take advantage of the latest 
speaker technology and enclosure designs. Both models utilize studio quality 
12” 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. 


ibl FC 12-100WATTS (100dB) PRICE £159.00 PER PAIR 
ibl FC 12-200WATTS (100dB) PRICE £175.00 PER PAIR 

Delivery £6.00 per pair 

150 WATTS (75 + 75) Stereo, 150W 
Bridged Mono 
250 WATTS (125 + 125) Stereo, 250W 
Bridged Mono 
; 400 WATTS (200 + 200) Stereo, 400W 

« Bridged Mono 
> Features: 
* Stereo, bridgable mono * Choice of 
high & low level inputs * L & R level 
controls * Remote on-off * Speaker & 
thermal protection. 

PRICES: 150W £49.99 250W £99.99 
400W £109.95 P&P £2.00 EACH 



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, integral heat sink, glass fibre P.C.B. and 
drive circuits to power a compatible Vu meter. All models are open and short circuit proof. 


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 5}00mV, S.N.R. 
-110 dB. Size 300 x 123 x 60mm. 
PRICE £40.85 + £3.50 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. 
-110 dB. Size 300 x 155 x 100mm. 

PRICE £64.35 + £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. 
-110 dB. Size 330 x 175 x 100mm. 

PRICE £81.75 + £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. 
-110 dB, Fan Cooled, D.C. Loudspeaker Protection, 2 
Second Anti-Thump Delay. Size 385 x 210 x 105mm. 
PRICE £132.85 + £5.00 P&P 

OMP/MF 1000 Mos-Fet Output power 1000 watts 
R.M.S. into 2 ohms, 725 watts R.M.S. 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. -110 dB, Fan 
Cooled, D.C. Loudspeaker Protection, 2 Second 
Anti-Thump Delay. Size 422 x 300 x 125mm. 

PRICE £259.00 + £12.00 P&P 




McKenzie and Fane Loudspeakers are also available. 



RES. FREQ. 72Hz, FREQ. RESP. TO 4KHz, SENS 97<cB. PRICE £32.71 + £2.00 P&P 

RES. FREQ. 71Hz, FREQ. RESP. TO 7KHz, SENS97dB. PRICE £33.74 + £2.50 P&P 
RES. FREQ. 65Hz, FREQ. RESP. TO 3.5KHz, SENS 99dB. PRICE £43.47 + £2.50 P&P 
RES.FREQ. 49Hz, FREQ. RESP. TO 6KHz, SENS 100dB. PRICE £35.64 + £3.50 P&P 
MONITOR. RES. FREQ 42Hz, FREQ. RESP. TO 10KHz, SENS 98dB. PRICE £36.67 + £3.50 P&P 

RES. FREQ. 58Hz, FREQ. RESP. TO 6KHz, SENS 98dB. PRICE £46.71 + £3.50 P&P 
RES. FREQ. 47Hz, FREQ. RESP. TO 5KHz, SENS 103dB. PRICE £70.19 + £3.50 P&P 

RES. FREQ. 46Hz, FREQ. RESP. TO 5KHz, SENS 99cB. PRICE £50.72 + £4.00 P&P 

RES. FREQ. 39Hz, FREQ. RESP. TO 3KHz, SENS 103dB. PRICE £73.34 + £4.00 P&P 

ALL EARBENDER UNITS 8 OHMS (Except EB8-50 & EB10-50 which are dual impedance tapped @ 4 & 8 ohm) 


RES. FREQ. 40Hz, FREQ. RESP. TO 7KHz SENS 97dB. PRICE €8.90 + £2.00 P&P 

RES. FREQ. 40Hz, FREQ. RESP. TO 5KHz, SENS. 99dB. PRICE £13.65 + £2.50 P&P 
10” 100WATT EB10-100 BASS, HI-FI, STUDIO. 


RES. FREQ. 26Hz, FREQ. RESP. TO 3 KHz, SENS 93dB. PRICE £42.12 + £3.50 P&P 

RES. FREQ. 63Hz, FREQ. RESP. TO 20KHz, SENS 92dB. 

RES. FREQ. 38Hz, FREQ. RESP. TO 20KHz, SENS 94dB. 

RES. FREQ. 40Hz, FREQ. RESP. TO 18KHz, SENS 89dB. PRICE £12.99 + £1.50 P&P 

RES. FREQ. 35Hz, FREQ. RESP. TO 12KHz, SENS 98dB. PRICE £16.49 + £2.00 P&P 

PRICE £30.39 + £3.50 P&P 

PRICE £9.99 + £1.50 P&P 

PRICE £10.99 + 1.50 P&P 



PRICE £14.85 + £1.00 P&P 


PRICE £8.80 + £1.00 P&P 



righter and Better Value 
than ever before. Over 1180 Full 
Colour pages with hundreds of Brand 
New Products at Super Low Prices 

on sale from 1st September = _ rex 

Ast BuAgabe A. 

from all branches of WHSMITH and other major retail outlets. 
Order by post including P & P £3.45 

01702 554161 

Belfast 357-359 Lisburn Road. Birmingham Sutton New Road, Erdington. Bradford 28 Valley Road, Hamm Strasse. Brighton 65 London Road. Bristol 302 Gloucester Road. 
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The Forbes Building, Linthorpe Road. Milton Keynes Unit 2, Office World Building, Snowdon Drive, Winterhill. Newcastle-upon-Tyne Unit 4, Allison Court (The Metro Centre), Gateshead 
Northampton 139 St. James Road. Nottingham 86-88 Lower Parliament Street. Portsmouth 98-100 Kingston Road. Preston Unit 1, Corporation Street. Reading 129-131 Oxford Road. 
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Stockport 259-261 Wellington Road South. Stoke-on-Trent 39-45 London Road. Plus many NEW stores opening soon. Tel: (01702) 552911 for details of your nearest store.