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JUNE 1995 


hifi at a 

AA To PP3 Battery 

Save money on 
battery costs 
Smart Carbs 
Barry Fox investigates 7 
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& Computer Projects 


554 WORCESTER ST. - TEL: 01902 22039 

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 £12.99 each!!!! 
OPD MONITORS 9° mono monitor, fully cased complete with 
raster board, switched mode psu etc. CGA/TTL input (15way D), IEC 
mains. £15.99 ref DEC23. Price including kit to convert to composite 
monitor for CCTV use etc is £21.99 ref DEC24 

times etc) up to 4 items (8A 240v each) with this kit. Complete with 
Software, relays, PCB etc. £25.99 Ref 95/26 

COMPLETE PC 300 WATT UPS SYSTEM Top of the range 
UPS system providing protection for your computer system and 
valuable software 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 £119.00. 

RACAL MODEM BONANZA! 1 Racal MPS1223 1200/75 
modem, telephone lead, mainslead, manual and comms software, the 
cheapest way onto the net! all this for just £13 ref DEC13. 

HOW LOW ARE YOUR FLOPPIES? 3.5" (1.44) unbranded. 
We have sold 100,000+ so ok! Pack of 50 £24.99 ref DEC 16 
‘returns’ so they may have faults but look ok. Complete with new leads 
and leather case. Price for two meters & 1 case is £10 ref DEC89. 
Smw LASER POINTER. Supplied in kit form, complete with 
power adjuster, 1-Smw, and beam divergence adjuster. Runson2 AAA 
batteries. Produces thin red beam ideal forlevels, gun sights, expen- 
ments etc. Cheapest in the UK! just £39.95 ref DEC49 

SHOP WOBBLERS!Small assemblies designed to take D size 
batteries and ‘wobble’ cardboard model signs aboutin shop windows! 
£3.99 Ref SEP4P2. 

RADIO PAGERSBrand new, UK made pocket pagers dearance 
price is just £4.99 each 100x40x 15mm packed with bits! Ref SEP5. 
BULL TENS UNTT 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 modem 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. 

new controllers, adjustable from -50 deg C to +1,200 deg C using 
graduated dial, 2% accuracy, thermocouple input, longlife relay output 
,3A 240v o/p contacts. Perfect for exactly controlling a temperature, 
Nomai trade £50+, ours £15. Ref E5C2. 

ELECTRIC MOTOR BONANZA! 110x60mm.Brand new 
precision, cap start (or spin to start), virtually silent and features a 
moving outer case that acts as a fly wheel. Because of their unusual 
design we think that 2 of these in a tube with some homemade fan 
blades could form the basis for a wind tunnel etc. Clearance priceisjust 
£4.99 FORAPAIR! (note-these will have to be wired in senesfor 240v 
operation Ref NOV1. 

MOTOR NO 2 BARGAIN 110x90mm.Similar to the above 
motor but more suitable for mounting vertically (ie tumtable etc). Again 
you will have to wire 2in series for 240v use. Bargain priceisjust£4 99 

Minature adjustable timers, 4 pole c/o output 3A 240v, 
HY1230S, 12vDC adjustable from 0-30 secs. £9.99 
HY1210M, 12vDC adjustable from 0-10 mins. £9.99 
HY1260M, 12vDC adjustable from 0-60 mins. £9.99 
4 HY2460M, 24vAC adjustable from 0-60 mins. £5.99 
HY241S, 24vAC adjustable from O-1 secs. £5.99 
HY2460S, 24vAC adjustable from 0-60 secs, £5.99 
HY243H, 24vAC adjustable from O-3 hours. £8.99 
HY2401S, 240v adjustable from 0-1 secs. £9.99 
HY2405S, 240v adjustable from 0-5 secs. £9.99 
HY24060m, 240v adjustable from 0-60 mins. £12.99 
PC PAL VGA TO TV CONVERTER Converts a colour TV into 
a basic VGA screen. Complete with built in psu, lead and s/ware. 
£49.95. Ideal forlaptops or acheap upgrade. We also can supply this 
in kit form for home assembly at £34.95 ref EF 54. 

DRINKING BIRD Remember these? hook onto wine glass (sup- 
plied) and they drink, standup,drink, standup ETC! £4 each Ref EF 1 
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 MAG4P 11. 

GUIDED MISSILE WIRE. 4,200 metre reel of ultra thin 4 core 
insulated cable, 28lbs breaking strain, less than 1mm thick! Ideal 
alarms, intercoms, fishing, dolls house's etc. £14.99 ref MAG15P5 
300v PANEL METER 70X60X50MMM, AC, 90 degree scale. Good 
quality meter. £5.99 ref MAG 6P 14. Ideal for monitoring mains etc. 
ASTEC SWITCHED MODE PSU BM41012 Gives +5 @ 3.75A, 
+12@1.5A, -12@.4A. 230/110, cased, BM41012. £5.99 ref AUG6P3. 
TORRODIAL TX 30-0-30 480VA, Perfect for Mosfet amplifiers 
etc. 120mm dia 55mm thick. £18.99 ref APR19. 

AUTO SUNCHARGER 155x300mm solar panel with diode and 
3metrelead fitted with a cigar plug. 12v 2watt.£9.99 ea ref AUG10P3. 
FLOPPY DISCS DSDD Top quality 5.25" discs, these have been 
written to once and are unused. Pack of 20 is £4 ref AUG4P1. 
ECLATRON FLASH TUBE Asused in police car flashing lights 
etc, full spec supplied, 60-100 flashes a min. £9.99 ref APR10P5. 
24v AC S6WATT Cased power supply. New. £13.99 ref APR14. 
anstraightfrom Her majesty's forces. £50 ref MAG SOP3. 
STETHOSCOPE Fully functioning stethoscope, ideal for listening 
to hearts, pipes, motors etc. £6 ref MAR6P6. 

OUTDOOR SOLAR PATH LIGHT Captures sunlight during 

the day and automatically switches on a built inlamp at dusk. Complete 
with sealed lead acid battery etc £19.99 ref MAR20P1. 

ALARM VERSION Of above unit comes with built in alarm and pir 
to deter intruders. Good value at just £24.99 ref MAR25P4. 
CARETAKER VOLUMETREK Alam, will cover the whole of the 
ground floor against forcred entry. Includes mains power supply and 
integral battery backup. Powerful internal sounder, will take external bell 
if req'd. Retail £150+, ours? £49.99 ref MARSOP 1. 

TELEPHONE CABLE White 6 core 100m ree! complete with a 
pack of 100 ciips. Ideal ‘phone extns etc. £7.99 ref MAR8P3. 
MICRODRIVE STRIPPER Small cased tape drives ideal for 
stripping, lots of useful goodies including a smart case, and lots of 
components. £2 each ref JUN2P3. 

SOLAR POWER LAB SPECIAL You get TWO 6"x& 6v 130mA 
solar cells, 4 LED's, wire, buzzer, switch plus 1 relay or motor. Superb 
value kit just €5.99 REF: MAG6P8 

SOLID STATE RELAYS Will switch 25A mains. Input 3.5-26v DC 
57x43x2 1mm with terminal screws £3.99 REF MAG4P 10 
BUGGING TAPE RECORDER Small voice activated recorder, 
uses microcassette complete with headphones. £28.99 ref MAR29P 1. 
ULTRAMINI BUG ME 6mmx3.5mm made by AKG, .5-12velectret 
condenser. Cost £12 ea, Ours? just four for £9.99 REF MAG10P2. 
condition. Back anodised metal case. £79 each REF JUN79 
ANSWER PHONES Retums with 2 faults, we give you the bits for 
1 fault, you have to find the other yourself. BT Response 200's £18 ea 
REF MAG18P1. PSU £5 ref MAGS5P 12. 

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

PLUG IN PSU 9V 200mA DC £2.99 each REF MAG3P9 
PLUG IN ACORN PSU 19v AC 14w , £2.99 REF MAG3P 10 
POWER SUPPLY fully cased with mains and o/p leads 17v DC 
900mA output. Bargain price £5.99 ref MAG6P9 

ACORN ARCHIMEDES PSU +5v @ 4.4A. on/off sw uncased, 
selectable mains input, 145x100x45mm £7 REF MAG7P2 
GEIGER COUNTER KIT Low cost professional twin tube, com- 
plete with PCB and components. Now only £19 REF AUG19. 

Sv DC POWER SUPPLY Standard plugin type 150ma 9v DC with 
lead and DC power plug. price for two is £2.99 ref AUG3P4. 

AA NICAD PACK encapsulated pack of 8 AA nicad batteries 
(tagged) ex equip, 55x32x32mm. £3 a pack. REF MAG3P 11 

13.8V 1.9A psu cased with leads. Just £9.99 REF MAG10P3 
PPCMODEM CARDS. These are high spec plugin cards made for 
the Amstrad laptop computers. 2400 baud dial up unit complete with 
leads. Clearance price is £5 REF: MAG5P1 

hi spec satellite equipment but perfect for all sorts of remote control 
projects. Our clearance price is just £2 REF: MAG2 

200 WATT INVERTER Converts 10-15v DC into either 110v or 
240v AC. Fully cased 115x36x156mm, complete with heavy duty power 
lead, cigar plug, AC outlet socket.Auto overoad shutdown, auto short 
circuit shut down, auto input over voltage shutdown, auto input under 
voltage shut down (with audible alarm), auto temp control, unit shuts 
down if overheated and sounds audible alarm. Fused reversed polarity 
protected. output frequency within 2%, voltage within 10%. Aextremely 
well built unit at an excellent price. Just £64.99 ref AUG65. 
the C5 motor but ok for any 12v motor up to 30A. Complete with PCB 
etc. A heat sink may be required. £17.00 REF: MAG17 
MAINSCABLEPrecut black 2 core 2metre lengths ideal for repairs, 
projects etc. 50 metres for £1.99 ref AUG2P7. 

of 6 core cable, 100 cable dips, 2 line divers with RS232 interfaces 
and all connectors etc. Ideal low cost method of communicating be- 
tween PC's over along distance. Complete kit £8.99. 

MINI CYCLOPS PIR 52x62x40mm runs on PP3 battery complete 
with shrill sounder. Cheap protection at only £5.99 ref MAR6P4. 
ELECTRIC MOTOR KIT Comprehensive educational kitincludes 
all you need to build an electric motor. £9.99 ref MAR10P4. 
VIEWDATA SYSTEMS made by Phillips, complete with internal 
1200/75 modem, keyboard, psu etc RGB and composite outputs, menu 
driven, autodialler etc. £18 each Ref EF88. 

BOOMERANG High tech, patented poly propylene, 34cm wing 
span. Get out and get some exercise for £4.99 ref EF83 

AIR RIFLES .22As used by the Chinese army for training puposes, 
so there is a lot about! £39.95 Ref EF78. 500 pellets £4.50 ref EF80. 
PEANUT TREE Complete kit to grow your own peanuts! full 
instructions supplied. £3 Ref EF45. 

PLUG IN POWER SUPPLYS Plugs in to 13A socket with output 
lead. three types available, 9vdc 150mA £2 ref EF58, 9vdc 200mA 
£2.50 ref EF59, 6. S5vdc 500mA £3 ref EF61. 

VIDEO SENDER UNIT. Transmits both audio and video signals 
from either a video camera, video recorder, TV or Computer etcto any 
standard TV set in a 100' range! (tune TV toa spare channel) 12v DC 
op. Priceis £15 REF: MAG15 12v psu is £5 extra REF: MAG5P2 
“FM CORDLESS MICROPHONE Smaii hand held unit with a 
500' range! 2 transmit powerlevels. Reqs PP3 Sv battery. Tuneabie to 
any FM receiver. Piceis£15 REF: MAG15P1 

LOW COST WALKIE TALKIES Pair of battery operated units 
with a range of about 200’. Ideal for garden useor as an educational toy. 
Price is£8 a pair REF: MAG 8P1 2.x PP3 req'd. 

*MINATURE RADW TRANSCEIVERS A pair of walkie talkies 


- TEL: 01273 203500 © 

FAX: 01273 323077 

with a range of up to 2km in open country. Units measure 22x52x 155mm. 
Induding cases and earp'ces. 2xPP3 req'd. £30.00 pr.REF: MAG30 
COMPOSITE VIDEO KIT. Converts composite video into sepa 
rate H sync, V sync, and video. 12v DC. £8.00 REF: MAG8P2. 
LQ3600 PRINTER ASSEMBLIES Made by Amstrad they are 
entire mechanical printer assemblies including printhead, stepper mo- 
tors etc etc In fact everything bar the case and electronics, a good 
Stripper £5 REF: MAGSP3 cr 2 for£8 REF: MAG8P3 

LED PACK of 100 standard red 5m leds £5 REF MAG5P4 
UNIVERSAL PC POWER SUPPLY complete with flyleads, 
switch, fan etc. Two types available 150w at £15 REF:MAG15P2 
(23x23x23mm) and 200w at £20 REF: MAG20P3 (23x23x23mm) 
GYROSCOPE About 3° high and an excellent educational toy for all 
ages! Price with instruction booklet £6 Ref EF 15. 

FUTURE PC POWER SUPPLIES These are 295x135x60mm, 
4 drive connectors 1 mother board connector. 150watt, 12v fan, iec 
inlet and on/off switch. £12 Ref EF6. 

VENUS FLY TRAP KIT Grow your own carnivorous plant with this 
simple kit £3 ref EF 34. 

PC POWER SUPPLIES (returns) These are 140x150x90mm. o/ 
ps are +12,-12,+5 and -5v. Builtin 12v fan. These are retums so they 
may well need repairing! £3.50 each ref EF 42. 

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

*FM BUG KIT New design with PCB embedded coil for extra stability. 
Works to any FM radio. 9v battery req'd. £5 REF: MAGS5P5 

*FM BUG BUILT AND TESTED superior design to kit. Supplied 
to detective agencies. 9v battery req'd. £14 REF: MAG14 
TALKING COIN BOX STRIPPER orginally made to retail at£79 
each, these units are designed to convert an ordinary phone into a 
payphone. Theunits have the locks missing and sometimes broken 
hinges. However they can be adapted for their original use or used for 
something else?? Price is just £3 REF: MAG3P1 

TOP QUALITY SPEAKERS Made for Hi Fi televisions these are 
10 watt 4R Jap made 4° round with large shielded magnets. Good 
quality. £2 each REF: MAG2P4 or 4 for £6 REF: MAG6P2 
TWEETERS 2" diameter good quality tweeter 140R (ok with the 
above speaker) 2 for £2 REF: MAG2P5 or 4 for€3 REF: MAG3P4 
AT KEYBOARDS Made by Apricot these quality keyboards need 
justa small modtorunon any AT, they work perfectly but you will have 
to put up with 1 or 2 foreign keycaps! Price £6 REF: MAG6P3 
HEADPHONES Ex Virgin Atlantic. 8pairsfor€2 REF: MAG2P8 
DOS PACKS Microsoft version 3.3 or higher complete with all 
manuals or price just £5 REF: MAG5P8 Worth it just for the very 
comprehensive manual! §.25° only. 

GAS HOBS Brand new made by Optimus, basic three bumer suitable 
for small flat etc bargain price just £29.95 ref EF73. 

GAT AIR PISTOL PACK Complete with pistol, darts and peliets 
£12.95 Ref EF82 extra pellets (500) £4.50 ref EF80. 
CHRISTMAS TREE KIT Start growing it now! £3 ref EF53. 
DOS PACK Microsoft version 5 Original software but no manuals 
hence only £5.99. 3.5* only. 

PIR DETECTOR Made by famous UK alarm manufacturer these 
are hi spec, long range internal units. 12v operation. Slight marks on | 
case and unboxed (although brand new) £8 REF: MAG8P5 
MOBILE CAR PHONEE6.99 Weil almost! complete in carphone 
excluding the box of electronics normally hidden under seat. Can be 
made toilluminate with 12v also has built in light sensor so display only 
illuminates when dark. Totally convincing! REF: MAG6P6 

ALARM BEACONS Zenon strobe made to mount on an extemal 
bell box but could be used for caravans etc. 12v operation. Just connect § 
up and it flashes reguiany) £5 REF: MAG5P 11 

6"°X12" AMORPHOUS SOLAR PANEL 12v 155x310mm 
130mA. Bargain price just £5.99 ea REF MAG6P 12. 

FIBRE OPTIC CABLE BUMPER PACK 10 metres for £4.99 
ref MAG5P 13 ideal for experimenters! 30 m for £12.99 ref MAG13P1 § 
HEATSINKS (finned) T0220, designed tomount vertically on apeb | 
50x40x25mm you can have a pack of 4 for £1 ref JUN1P11. 
STROBE LIGHT KIT Adjustable from 1 hz right up to 60hz! 
(electronic asssembly kit with full instructions) £16 ref EF28. 

ROCK LIGHTS Unusual things these, two pieces of rock that glow f 
when rubbed together belived to cause raini€3 a pair Ref EF29. 


15mW, Helium neon, 3 switchable wavelengths 63um, 1.15um,3.39um 
(2 ofthem are infrared) 500: 1 polarizer built in so good for holography. 
Supplied complete with mains power supply. 790x65mm. Use with 





4 Hand held personal Gamma and X Ray detector. 

his unit contains two Geiger Tubes, has a 4 digit LCD 
display with a Piezo speaker, giving an audio visual 
ndication. The unit detects high energy electromag- 
netic quanta with an energy from 30K eV to over 1.2M 
eV and a measuring range of 5-9999 UR/h or 10-99990 

INr/h. Supplied complete with handbook.Ref. NOV 18. 

PROJE —_ ae poe 



The No. 1 Independent Magazine for Electronics, 
Technology and Computer Projects 

VOL. 24 No.6 JUNE 1995 


EPE HiFi VALVE AMPLIFIER -1 by Jake Rothman 434 
A brand new hybrid design that retains that unique ‘‘valve sound” 

NAME OF THE GAME —4 @¢ Star-Struck! ¢ Six-Shot Zapper 

¢ Wander Wands by Roy Bebbington 446 
Easy-build modules to enhance your quiz and party games 
PIC-DATS-2 4-Channel Light Chaser by Mark Stuart 465 
Take your PIC and create your very own light show. Demonstration project 
to show how easy it is to program your PICs 
AA TO PP3 CONVERTER by Robert Penfold 476 
Step up the power of your AA's with this low-cost d.c. to d.c. converter 
R.F. SIGNAL GENERATOR - 2 by Steve Knight 487 

Final construction of this high performance piece of test gear 


CIRCUIT SURGERY by Alan Winstanley 472 
Voxbox upgrade, diodes and current flow | 
by Mike Tooley B.A. 

Concluding article — Further reading extends the range of Electronics Workbench 
INTERFACE by Robert Penfold 4f4 
The page for computer enthusiasts — Model train control 

AMATEUR RADIO by Tony Smith G4FAI 500 

Hobby or Politics; No DXCC Status; Young Amateur of the Year; 
Story of the Key 


Everyday news from the world of electronics | 
The latest developments in memory storage 
OHM SWEET OHM by Max Fidling 453 
Max investigates strange ‘goings on” in the attic 
SMART CARDS by Barry Fox | | 454 
What they are, how they work, are they secure? 
BACK ISSUES Did you miss these? 460 
SHOPTALK with David Barrington | 478 
Component buying for EPE projects 
“yy Our range of educational videos | 
A wide range of technical books available by mail order 
PCBs for EPE projects 
Wimbo Publishing Ltd 1995. Copyright in all 
a and articles published in F R E E 

protected, and reproduction or imitations in whole THE BUDGETCD & TAPE CO. CATALOGUE 

or in part are expressly forbidden. Banded to UK copies 
Our July ’95 Issue will be published on Friday, Readers Service @ Editorial and Advertisement Departments 433 
2 June 1995. See page 423 for details. Cover photo: Alfred Pasieka/Science Photo Library 

Everyday with Practical Electronics, June 1995 | 421 


AT 286 

40Mb HD + 3Mb Ram 

LIMITED QUANTITY only of these 12Mhz HI GRADE 286 pee 
Made in the USA to an industrial specification, the system was 
designed for total reliability. The compact case houses the mother- 
board, PSU and EGA video card with single 5%" 1.2 Mb floppy disk 
drive & integral 40Mb hard disk drive to the front. Real time clock 
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 ONLY 14 to Run ! 

Order as HIGRADE 286 QAVZ $9.0 E) 
CALL ¥_ = I O90 

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%" 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 By 
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! £499.00(F) 


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 )JRFE £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 6} 
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 s pt 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 inte efi speaker 
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 60x 25mm 12vDC £4.95 10/£42 
MITSUBISHI MMF-09B12DH 92 x 25mm 12vDC = £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 or 240 v_ £5.95 
VERO rack mount 1U x 19" fan tra ay 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 


issue 13 Of Display 

Se 8 [eur 


News now available - send lar 

e e e 

e e@ee e e i 

a eee e @ e ® Open Mon - Sat 9: : Open Mon-Fri 9.00-5:30 

© @t ee” SG os 215 Whitehorse Lane Dept EE. 32 Biggin Way 

Seco 8 ° Secce es 8 {On 68A Bus Route Upper Norwood 
Selhurst Park SR Rail Stations LONDON SE19 3XF 

and Local Authorities - minimum 
eramumyeo] Grae Ons 550, (C)-EB50, ana (E}-£15 00, (asad (CALL Allow approx 
unless stated guaranteed for 90 days. All 
notice. sate es nf Pech rg mel an Top CASH prices 






ONLY £99.00 

A massive bulk purchase enables us to bring you a COMPLETE 
poacy to run colour PC system at an unheard of price! 
The Display Electronics PC99 youn comprises of fully com- 
patible and expandab le XT PC with 256k of RAM, 5%" 360k flop- 
py disk drive, 12" CGA colour monitor, standard 84 key key- 

oard, MS DOS and all connecting cables - just plug in and go 
I! 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 i es PCSOCOL £99.00 (E) 

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


One of the highest specification 
ate monitors you will ever see - 

At this price - Don’t miss it!! 

Mitsubishi di sede 14” SVGA Multisync monitor with fine 
0.28 dot pitch tube and guaranteed resolution of 1024 x 768. A 
. variety of inputs allows connection to a host of 
: computers fen Be PC's in CGA, EGA, VGA & 
: SVGA modes C, COMMODORE (including 
Amiga 1200), ARCHIMEDES and APPLE. Man 
features: Etched faceplate, text switching and LO 
Suni ire HEN ME ee Full 90 day warranty. 
u in ittle u ition 

P Orderasmirs-svGa Only £1396 
Tilt & Swivel Base £8.00 Leads for IBM PC £8.95 (A) 
External Cables for other com £ CALL 

PHILIPS HCS35 (same s ae 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 Sage 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 H1236° x 1544" 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" pel definition colour monitors. Nice tight 0.28" dot pitch 

for superb clarity and modern styling. Operates from ; 
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 day guarantee. 

KME 10" as above for PC EGA 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 Dh amg, 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) 


Mlaed Mas d every type of power 
ply you can imagine.Over 
000 Power Supplies Ex Stock 

Call for info / list. 


Zeta 3220-05 AO 4 pen HPGL RS232 fast drum plotter 


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 oe £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 

Thuriby LA 160B logic analyser 

INTEL SBC 486/133SE Multibus 486 system. 8Mb Ram 

GEC 1.5kw 115v 60hz power source £950 
Brush 2Kw 400 Hz 3 phase frequency converter £850 
Anton Pillar 75 kW 400 Hz 3 a frequency converter POA 

Newton Derby 70 KW 400 Hz 3 phase frequency converter 
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 £125 
Seaward PAT 2000 dual ke computerised PAT tester £585 
Densel MUD 0185AH 1KVa UPS system with batts NEW £575 

m account order £50. 

V21,V22, V22 BIS 
0181 679 1888 

i usin for fis Mainland. UK eat add 17.5% VAT yA TOTAL order amount. Minimum order £10. Bona Fide account orders accept 

Surplus always 
wanted for cash! 

Superb quality 6 foot 40U 
Virtually New, Ultra Smart 

Less than Half Price! 

Top qualit y 19" rack cabinets made in UK by 
Optima 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 Ess 
is constructed of double walled steel with a ES 
‘designer style’ smoked acrylic front panel to 
enable status indicators to be seen through the 
panel, yet remain unobtrusive. Internally the rack 
features 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 
pin Euro sockets and 1 x 13 amp 3 pin switched <a 
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 blue. 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 (a) 

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

OF TIM Wi dam celelamacrelelic-tiatsia) 


The ultimate in ‘Touch Screen Technology’ made by the experts - 
MicroTouch - but sold at a price below cost !! System consists of 
a flat translucent glass 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: 
RFE. Full Software Support Available - Fully Gunna 145.00 (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. ae ng be used to fill 
in RAM above 640k DOS limit. Complete with d 

Order as: XT RAM UG. 256k. £32.95 or 51 ok £38.95 (A1) 

1 MB x9 SIMM 9 chip 120ns onl 

Wy £19.50 (A1 
1MBx9 SIMM3chip80ns £23.50 70ns £26.00 (A1 
1MBx9 SIMMQchip80ns £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 
RAM 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 
supplied brand new, with full, ea instructions and manual. 

Normally £189.00 now! r€69 ‘00 or 2 for £120 « 

e SGE - PACKED with bargains! 

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


0181 678 4414 

FAX 0181 679 1927 

ed from 

Govemment, Schools, 
. Cheques over £100 are subject to 10 working days clearance. Carriage “sh ag (A)=£3.00, (A1)=£4.00, 
6 days for shipping - 
on a retum to base basis. Oe ee ee ee eee 
for surplus goods. All trademarks etc acknowledged. © Display 

faster CALL Scotland surcharge CALL All goods supplied to our 
tions without prior 
ics 1995.E& OE. 4/5 

Everyday with Practical Electronics, June 1995 


A reasonably accurate, inexpensive and easy 
to build anemometer. This unit employs 
an electric motor to dispense with 
complicated bearings, shafts 
and transducers. It will_ 
indicate windspeed 

from 10 to 75 m.p.h. 
onanl.e.d. bargraph | 
or moving dot readout. * 



Automatically opens and closes curtains at preset light levels. Can be used with almost 
any corded system. An infra-red remote control transmitter and receiver will also be 
described and the unit could be interfaced to a computer control system if so desired. 


| A professional quality ramp generator aimed at the intermediate to advanced 
constructor. This high quality design has a multitude of uses including: oscilloscope 
calibrator, plotter timebase, curve tracer, frequency response analyser and spectrum 

* Plus all the regular * Don’t miss out place 
features. an order with your 
: newsagent or take out a 
| subscription NOW! 




Everyday with Practical Electronics, June 1995 



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 
Smallest room transmitter kit in the world! Incredible 10mm x 20mm including: 
MIC. 3-12V Operation. 500M range............cccccsccessccsseesssecsssecssscsseecssersescsesens £16.45 

MTX Micro-miniature Room Transmitter 
Best-selling micro-miniature Room Transmitter 
Just 17mm x 17mm including mic. 3-12V operation. 1000m range..................... £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.............cccccccsscssscssesssssssescsesssssesssseseesens £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. 
STE FIM sccssadsscovuncectsyessoacnsg tind) Sood beasanbtevesiipsoss eohetis colach estdtdbidenbdesvvein cokeaghoaaeas £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 .............ccccccseccescseseseseesesees £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. 
POWEIOG FONT TING vnssisnsessincascivscsssscsasasavdnsensbossassanscuadanccbecotetooukdsotteisdeedenienteniseatioter £13.45 


individual Transmitter DLTX. 
Individual Receiver DURX earn 

favuurite music palate around t h 
-operstion 250 ts A 

Dept. 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 rangé..................... £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 £13.45 

STLX High-performance 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. 

LOO FRING assay as csstetnwciosyyasesacsesosanssanantoprsinns ceosadmvata capsnslin shy jonanoahaASodvvaaeesyabannees £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 
25MM X GSMM. OV Operation ...............ccccscesccscsscsscscscsscsscessscsscscsscsssscssesceseaveseess £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 
RINE iaiiiseccceirdecks haiseagastecrevsapaded vclcdannadlseaviaeniasnnensdedeoutempanes £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 cee £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............... cee ceeeeeeeeeeeeeseneeeeeeteeneeeeees £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.............eceeeeeeeeteeesteeeeeeees £40.95 

QSX180 Line Powered Crystal Controlled Phone Transmitter 

As per QLX180 but draws power requirements from line. No batteries required. Size 
SZ2MM X S7MM. RANGE SOOM............cesccrscsscsrsrcsssrbecsseeracerssssssesersscssestsrsccseseveserace £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 ...................00 £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 WorkKsHopPs, 95 Main ROAD, 




CV9 2LE 
01827 714476 



Everyday with Practical Electronics, June 1995 

_ EASY-PC, Schematic and PCB CAD 
Over 18,000 Installations — 
in 80 Countries World-wide! 

) \| ¢ Runs on:- PC/XT/AT/ 

286/ 386/ 486 with 
Hercules, CGA, EGA 
or VGA display and 
many DOS emulations. 

e Design:- Single sided, 
Double sided and 
Multi-layer (8) boards. 

e Provides full Surface 
Mount support. 

-e Standard output 
includes Dot Matrix / 
Laser / Ink-jet Printer, 
Pen Plotter, Photo- 
plotter and N.C. Drill. 

e Tech Support - free. 

e Superbly easy to use. 

- Options:-500 piece Surface Mount Symbol Library £48, 
1000 piece Symbol Library £38, Gerber Import facility £98. 

Electronic Designs Right First Time? 

Affordable Electronics CAD 

LAYAN: NEW, Electro-magnetic Layout 
Simulator. Includes the effects of the 
PCB LAYOUT into your simulation. 

Links to EASY-PC Professional XM and 
ANALYSER Ill Professional. 

STOCKIT: NEW, Comprehensive Stock £145.00 
Control program for the small or medium 
sized business 

Simulation ONLY £495 

: t VEER DIS Prefess iana ingar Circuit Siwiater 
; guration iprartes 00: —s ows 

F 1ke3€X7,0N2 Gesin: 10.000 Mite nd:300.000 Wis stens K-Scale:les. 

Bain (48) ex? Phase (*) 

= (ol 

EASY- PC Professional: From £195.00 
me, lie Schematic Capture and PCB CAD. 
Links to ANALYSER IIl and PULSAR. 
2 (OEM PULSAR / PULSAR Professional: From £98.00 

Digital Circuit Simulators 

ANALYSER Ill / ANALYSER Ill Professional: From £98.00 
Linear Analogue Circuit Simulators 

Z-MATCH for Windows: | £245.00] 
Smith Chart based problem solving program 
for R.F. Engineers 

FILTECH/ FILTECH Professional: From £145.00 
Active and Passive Filter design programs. 

EASY-PC: — £98.00 
Entry level PCB and Schematic CAD 

Prices exclude P&P and VAT. 

0.06 9.6 ws a6 Lal 
Plot:Gein Vector! Mee/fngle Grew fute fel.te:0 @ 


For full information, please write, phone or fax:- 

Number One Systems 

Telephone UK: 01480 461778 (7 lines) Fax: 01480 494042 International +44 1480 461778 

USA: Ref. EVD, 386 Foxborough Drive, Mountain View, CA 94041 
, Telephone/Fax: (415) 968-9306 


Everyday with Practical Electronics, June 1995. | | 425 

SUMMER 1995 


ulti Function 
EPROM Programmer 

The Summer ’95 edition has 280 pages packed 
with over 4000 products and now with news and 
features including a full construction project. 

» The computer section is greatly increased with new 
ranges of equipment and accessories for PCs including: 

-Mother boards, CPUs and SIMMs 
CD ROM drives and hard drives 
Sound cards, I/O cards, disc drive 
cards and video cards 
Mice, trackerballs and joysticks 
Power supplies and cases 

» Feature project for an EPROM programmer 

» New 20MHz ‘scope from Leader, training systems from 
Flight and an extended range of mobile phone batteries 
and accessories from Uniross 

» Latest addition from Velleman kits including a video 
digitiser card 

» 280 pages, 26 sections, over 4000 products from some 
of the worlds finest manufactures and suppliers 

» Available at most large newsagents, from 13th April, or 
directly from Cirkit 

» Send for your copy today! 

Cirkit Distribution Ltd 
Park Lane - Broxbourne - Hertfordshire - EN10 7NQ 
Telephone: 01992 448899 - Fax: 01992 471314 



174 Dalkeith Road, Edinburgh EH16 5DX * 0131 667 2611 

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: .00 
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. 

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. 
part vgs 1p each, £5.95 per 1000, £49.50 per 

High quality photo resist copper 
clad epoxy glass boards 

Dimensions single-sided double-sided 
3x4 inches £1.09 1.23 
4x8 inches ; £2.99 
6x12 inches : - 
12x12 inches 

AA (HP7) 500mAH 
AA 700mAH 

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 hours 
or 4Cs or Ds in 12 to 14 hours plus 1xPP3 y ry fe 
or 4 cells may be charged at a time) 

High power charger, as above but charges fee 
Cs and Ds in 5 hours; AAs, Cs and Ds mustbe 
charged in twos or fours £10.95 

Nickel Metal Hydryde AA cells, high capacity 

with no memory. If charged at 100mA and discharged 

at 250mA or less 1200mAH capacity (lower capacity 
for high discharge rates) £3.75 

Stick of 4, 42mm x 16mm NiCad batteries, 171mm x 
16mm dia., with red and black leads, 4-8V......£5.95 
ag, hed grade Capacitors with screw terminals, 
58000puF 60 £4.9 
115V AC, 80V DC Motor, 4mm x 22mm shaft, 
50mm dia. x 60mm long body (excluding shaft), 
it has a replaceable thermal fuse and brushes 
£4.95 each, £3.95 100+ 
7-segment common anode |.e.d. display, 12mm..45p 
LM337K TO3 case variable peauiater 1. 


GaAs F.E.T. low leakage current S8873 £12.95 

each, £9.95 10+, £7.95 100+ 
BS250 p-channel MOSFET 
BC559 transistor £3.95 per 100 
74LS05 Hex inverter £10.00 per 100 
Used 8748 Microcontroller £3.50 
SL952 UHF Limiting amplifier, LC 16 surface 

mounting package with data sheet 1 


x MAIL ORDER - generally by x 


Monday-Thursday 9.15 - 6.00 
Friday 9.15-5.00 
Saturday 9.30-5.00 

The supplier to use if you're looking 

£1.25 each; 90p 100 + 
10p 100+, 6p 1000 + 
Sinclair light gun terminated with a jack plug and 
PP3 clip gives a signal when pointed at 50Hz 
flickering light, with output waveform chart ..£3.95 
DC-DC converter, Reliability model, V12P5, 12V input 
5V 200mA out, 300V input to output isolation, with 
£4.95 each or pack of 10 - £39.50 
Hour counter used 7-digit 240V a.c. 50Hz...£1.45 
QWERTY keyboard, 58-key good quality 
switches, new 
Airpax A82903-C large stepping motor 14V 
7-5° step, 27 ohm, 68mm dia. body, 6.3mm 
£8.95 or £200.00 for a box of 30 
Polyester capacitors, box type, 22.5mm lead pitch 
O0-9unF 250V d.c. 18p each, 14p 100+ , 9p 1000 + 
1pF 250V d.c. 20p each, 15p 100 +, 10p 1000 + 
1uF 50V bipolar electrolytic axial leads, 15p each, 
7:5p 1000+ 
0-22u.F 250V polyester axial leads, 15p each, 
100+ 7-5p each 
Polypropylene 1,f 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 22u.F 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 
40uF 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, 270hm 2W, 68o0hm 2W 25p each, 
15p each 100+ 
we have a range of 0:25W, 0:5W, 1W and 2W 
solid carbon resistors — please send SAE for list 
P.C. 400W PSU (intel part 201035-001) with 
standard motherboard and 5 disk drive 
connectors, fan and mains inlet/outlet 
connectors on back and switch on the side (top 
» for tower case) dims. 212 x 149 x 149mm 
excluding switch, £26.00 each, £138.00 for 6 
MX180 Digital Multimeter 17 ranges, 1000V 
d.c. 750V a.c. 2Mohm 200mA transistor Hfe 9V 
and 1.5V battery test £12.95 
AMD 27256-3 EPROMS £2.00 each, £1.25 100 + 
DIP switch, 3PCO 12-pin (ERG SDC-3-023) 
60p each, 40p 100 + 
Disk Drive Boxes for a 5:25 disk drive, with room 
for a power supply, light-grey plastic 67mm x 
268mm x 247mm £7.95 or £49.50 for 10 
Handheld Ultrasonic remote contro! £3.95 
CV2486 gas relay 30mm x 10mm dia. with 
3 wire terminals, will also work as a neon 
20p each, £7.50 per 100 
All products advertised are new and unused unless 
otherwise stated. 

Wide range of CMOS TTL 74HC 74F Linear 
Transistors kits, rechargeable batteries, capacitors, 
tools etc. always in stock 

Please add £1.95 towards P&P. VAT included in all pri 


276-278 Chatsworth Road 
Chesterfield S40 2BH 
Access/Visa Orders: 

Tel: (01246) 211202 Fax: (01246) 550959 
Callers welcome 

Everyday with Practical Electronics, June 1995 



xcellent condition (less than a year old!) the unit is 
otally enclosed in a steel case 340x 152x 152mm... 
has an IEC mains inlet with suppressor fitted and 
on/off mains rocker switch, and all outputs are on 
jeads with power connectors. Now for the spec: 
Inputs: 100-120V @ 10A or 200-240V @ 
6A, Outputs +5V @ 40A; +12V @ 165A; -6V 
@ 1A; -12V @ 1A switchable on front panel. 
A 12Vde 120x120mm fan is fitted at the rear of 
= the case. Current distributor price of a unit of this 
“ilk would be around £400. Save 92% 

Oe Our Price £29.95 

Another fine selection of SMPSUs recently anived These are all ex: , but in 
order. All are 115/230 Vac input. Do not exceed maximum wattage 

X3216 33yF 250V size 25x16 6/£1.00 
X3191 100uF 160V size 40x25 3/£1.00 
X3189 100uF 400V size 31x25 DP 3.89. £2.00 
X3221 150uyF 385V sie 48x36 DP 3.88. £2.00 
X3190 470uF 350V size 51x30 DP 6.00. £3.00 


25820 The story behind these is that they were going to 
be sent to Metal Box shareholders to try and stave off a 
bid. However, before they could be posted, a takeover 
was announced - so now we've got them. The metal box 
measures 200x 135x45mm and is finished in an attractive 
blue and gold pattern. Inside, the tie is English made 
100% pure silk in royal blue (sample of material on re- 
quest) with a ci discreet logo (ideal if BM or MB are 

X6098 6V Constant cur- 
rent ni-cad charger for up 
to 4 1.2V cells. Red LED 
indicates charging at 
100mA and after 14 hrs, 
the green LED illuminates 

= =: and charging stops. 
T104BA 10m aerial reall 
Wind-on reel. Reel contains a builtin TV/radio splitter |25962 Astec SA70A-3400 70W unit. +5V8A: +12V 26966 Famell NOS5P210 55Wunit. +5V2.5A; +12V Great Value 
| Pere 1A £4.96 
£595. NOW £3.60 3.5A; -12V 1A; 5VO.7A. £14.95 
ee! LAB BIOTA, EAAOR. at £3.95 

25963 Hitron HSG40-31 40W unit +5V 3A: +12V 25967 Astec SA40-1304 44W unit. +5V 5A; +12V 
O5A; -12V0.5A. £14.96 2A; -12V0.2A £4.96 

Some ex-equip axial flow fans, all in good working order 
at substantial savings over new models. 

23866 Smallest fan we've seen! 42x42 by just 10mm 
thick! Made by Nitev, model TA150DC. Rated 12V DC 
0.11A Only £3.00 

X6016 Papst (mostly) 612L 60x60x25mm 12V de 
(6-15V) 0.7W fans. List is 27.47. 

Our price £3.00 

BO47E A 
specifically for car, truck and bus use with a coverage volume 
of 14m3. Removes unpleasant smells, airbome dust, 
bacteria, tobacco smoke, etc. Supplied with a double sided 
self adhesive pad. Power 12Vde 1.8W Dims: 110x65mm 
Price £2.95 

X9007 Superb BRAND NEW 200W Farnell PSU - 25968 Astec SA30-1305 30W unit. +5V 2A; +12V 
their list price over £200! +5V 285A; +24V 05a; 2A -12V0.3A £3.96 
+12V 3A; -12V 1A. £19.96 

Ring, wnte, fax or call in for our scintillating NEW 64 page Spring 
Supplement, listing stacks of surplus stock at super prices! 

Our 1995 Catalogue, 192 pages of regular stock is just £2 post paid. 

NEW! - The Budget CD & Tape Catalogue - 48 pages of tapes (mostly £ 1.99) and CDs (mostly £2.99) 
Much of our surplus stock is never included in these ads - the only way to be ‘in the know’ is to 
become a Subscriber. This pnvleged group of customers receive The Greenweld Guardian every 
month with details of all our new surplus stocks. Don’t miss the Bargains (and there are plenty) - 
become a Subscriber today! There’s a free prize draw every month, the occasional free gift and 
the odd competition, too. All for just £6 a year (E 10 o‘seas) - or become a GOLD Subscriber with 
the additional benefit of 5% discount on all goods* + half price postage for £12 (£20 o’seas) 

‘Not bulk or sale prices “not o’seas 


: XX9006 This PC is! The hard disk, floppy and all bnards have bee 
: taken out, leaving only a 12V fan, speaker, 6V lithium battery and 
' @ very nice totally enclosed 94 watt power supply with the fol 
: lowing spec: -12V@410mA; +12V@2A; +5V@ 2A So all we're 
: asking for this magnificent lump of machinery is just: £12.96 


X9009 Two part instrument case 445x330x 105mm in 
blue aluminium containing a multiplexer PCB 290x195mm 
with Z80B + 7 support chips, 27C512 and 8x41256- 
12DRAMs all in sockets; also 25+ LS chips, MHz xtal osc 
etc. There are also 10x32 way DIN sockets, 6 with 
matching plugs. Three cl have V24 visi: Lgl 2 
each containing 4x 1489 ICs and terminating in a ay ee 

socket. There’s a 5OW switch mode PSU, too - and a 1 2 os ORR Cee Mais Almanac. ; 
60x60x25mm 12V fan. What a lot you get! - all for just. Key Clip Art (5000 TIFF images), 

Phone Nos: SALES 01703 S56565. Technical 305000, Key Fonts, 
Accounts 231003; Fax (All depts) 236307; FaxOnDemand 236315" |Key Gourmet, 

*To obtain latest lists, info etc, just dial 01703 236315 from any fax machine and follow instructions. [MPC Vizard, 

Single prices in this advert include VAT; Quanti don't. 
P&P €4 per order (£9.50 next day). Min Credit Card Ba: Otfelel Sport Image - World Cup 1994, 
UFO (spooky), 

Orders welcome from Education - min 
accepted by cheque, PO, cash, book {Slob Zone 3D, 
: tokens, 

We're always looking for new 
parcels of surplus goods - send 
details to the address below 

YO10AC Cast steel miniature bench vice. 66mm i jaws 
open to GOmm. Two bolt fixing to bench. Red enamel 
finish. Dims 100x65x70mm. Only £4.95 

CSL20 Great offer on SCART leads! These are 1.5m 
long with all pins connected. Super Price! Just £2.00 


Just taken delivery of a great new collec- 
tion of software on CD-ROM. Prices start 
from £6.95 for individual disks, but there’s 
even a better deal on offer at present - 
11 CD-ROMs for just £29.95. 

This collection from Softkey includes the 
- following titles: 

CNN Newsroom, 

25964 Audix HM230S/Tact UDM100 professional 
dynamic mic with on/off switch and cardoid character- 
istics. 5m lead with XLR skt fitted mic end. Impressive 
spec! Supplied with clip and adaptor, individually boxed. 
List price £44.06. Our Price £19.95 



Reece ory, 

Z3873 Super Offer! A complete clock in a Geen I 
40x25mm module. IV operation with sleep & 
snooze, 24hr alarm, PM, colon and alarm ELECTRONIC 

indicators. Sim Slow setting contr 
5 display theaigghas shes selectable, a COMrOMNT> ft) have enormous stocks. We are |Game Empire (over 250 games) 

brightness control. Full info supplied. Alli this SWITCH Be pee fd Reda 6-5.30 Mon-Sat. Come | cond for our latest lists which gives full 

for 99p! 27D Park Road Southampton $015 3UQ_ |cetails of everything available! 

invoice charge £15. Payment 
witch, » Access, Visa, 
Connect. Our stores (over 10,000 sq _|“\te0 Cube and 

Everyday with Practical Electronics, June 1995 427 


ewes, RRR aa ee (oes pee) GED QemetStse Gey) GuaeA 
eam Gar aay Genea® Gare PSE GE Qeaarecsrs? Gece Ge 
— = — = = scm ee oe = os SOLAR CELL 2 voit 150mA max, size 60 x 100mm £1.35 each 5 for £6 
— ae 2a. 33 = a — 2 on == | BNC SOCKETS 50 ohm single hole fixing 50p each 10 for £4.00 
oo oman: ments oe ome = ~~ os » oom = os 
a oon oe com one — == - pay ow a bow 2 = MERCURY TILT SWITCH BREADBOARD 
ama - sh =-s on —  .« = = = = Standard on/off £1.00 each 173 X 65mm 840TP £5.25 each 
a=. cn bo: ae \om oom cms Ge =. -——- om — = 4 Contact (Directional) £1.50 each TEXTOOL ZIF SOCKET 
Sane Ls FEED SUENCS Gt SS SK. SA a CMS PIEZO VIBRATION SENSOR 28 pin zero insertion socket £5.95 each 

with data sheet £1.00 each 


PROJECT BOXES A range of high quality boxes moulded in black high impact ABS, 
easily drilled or punched to produce a professional looking end product 
L H 

EPROMS 27C256 - 30. Once programmed but never used eprom. Mounted on a 
plastic carrier, can easily be removed from the carrier or used with a low insertion 
force socket. 27C256 £1.00 each 6 for £5.00 
Suitable low insertion force socket 28 pin 

40p each 3 for £1.00 

Ly A ke at dap MULTITURN PRESETS 20mm RECT, 1K, 5K, 10K, 20K, 50K, 100K 1MO. 
. 40p each, 3 for £1.00 
Th cAI 57 «220.92 Gl aeubibionaiatons 100db PIEZO SOUNDER : : 
MB1 79 61 40 £1.36 0-12 Ohm 5W 30p each _ 2KHz note, 3-12V d.c. 40Ma, 45mm dia. x 26mm £1.76 each 
MB2 100 76 41 £1.47 0:10 Ohm 25W 80p each SOUND BOMB Two tone alarm sounder incorporating four piezo elements in white 
MB3 118 98 45 £1.71 1-00 Ohm 50W £1.00 each plastic box. 100db 12V D.C. £5.99 
MB4 216 130 85 £5.19 2:20 Ohm 50W £1.00 each MINIATURE HORN SIREN 100db two-tone Piezo siren 12V D.C. £5.17 
MB5 150 100 60 £2.35 3-9 Ohm 50W £1.00 each - VIBRATION SENSITIVE ALARM BOARD WITH PIEZO SOUNDER 
MB6 220 150 64 £3.95 10:00 Ohm 100W £2.00 each Originally a bike alarm. There is a short delay after activation then the piezo 
MB7 177 120 83 £3.42 2:2 kOhm 50W £1.00 each sounder operates for a preset period. £3.76 each 
MB8 150 80 50 £2.22 or the above alarm board with custom designed case, fixing clip and keyswitch £9.95 
All sizes are in millimetres INFRA-RED BREAK BEAM Transmitter and receiver p.c.b. with 2 lens assemblies. 
MICRO SWITCH roller arm operation spdt 40p each BULKLEDS | 12V d.c. supply. These are ex-installation units and are not guaranteed to be 
sali 60 sis 500 5mm round | FLOURESCENT LIGHT INVERTOR. Drives an 8 watt tuve directly from 6V d.c. Data 
p peach  spdt3 position c/off 70p each lied £4.50 h 
dpat 70peach _dpdt3 position c/off 80peach | REDLEDS | Suplie -50 eeac 

spdt 3 position c/off biased both ways 70p each £25.85 

dpat 3 position c/off biased one way 80p each 

spdt biased 60p each 



DIL RELAYS 5 volt dp/changeover 60p 10 for £5.00 SUB-MINIATURE TOGGLE SWITCHES 
12 volt dp/changeover 80p 10 for £6.00 P.C.B. Mounting 

RELAY 10 amp contacts sp/changeover 12 volt coil £1.20 each BO1 S.P. on 4 for £1.00 

CAR HORN RELAY in metal can with fixing lug, 
s/poleon10ampcontacts £1.00 each6 for £5.00 
20 AMP RELAY dp on 12 voit coil 
£1.50 each 4 for £5.00 
REED RELAY 12 volt . 50p each 10 for £4.00 
240 VOLT AC RELAY. 3-pole c/o 10 amp 
contacts £1.50 each 4 for £5.00 


1 amp 7805/7812/7815 all 33p each. 7905/7912/7915 all 39p each SPECIAL OFFER 

2 amp 78S05/78S212 54p each 
In white 

plug socket cover 
9pin 30p 30p 35p 
15pin 40p 40p 35p 
25pin 50p 50p 40p 

100mA 78L05/78412/78L15 all 26p each. 79L05/79L12/79L15 all 29p each 
Adjustable LM317T 70p each. LM723 29p each, L200 £1.28 each 
Transistors TIP2955 70p each, TIP 3055 70p each 

2N3053 29p each, 2N3055 70p each, 2N4403 28p each, 2N3819 40p each 

~MICRO IC’S - Z80A CPU £1.20; Z80A PIO £1.50; Z80B SIO-1 £4.00; 
SAB80C535-N £11.75; PCB80C31BH-16P £2.35. 

5mm rnd red/yellow/green/amber 10p each 12 for £1.00 any mix 
5mm rnd high brightness red/green 20p each 6 for £1.00 any mix 
5mm rnd flashing red 60p each, yellow/green 70p each 
5mm rnd bi-colour 35p each, tri-colour 45p each 
LED mounted in chrome bezel red, yellow or green 30p each, 4 for £1 
LED mounted in a black bezel red only 25p each, 5 for £1.00 
PLASTIC BEZEL for 5mm rnd leds 10 for 40p 
High brightness bi-colour |.e.d., rectangular, red/green, two leads 40p each 

High quality probe precision temperature sensor. Mounted in a plastic covered probe 
with a 1 meter coiled lead. Temp. range — 40 to 150°C. Resistance at: 150°C 188.3 ohms; 
25°C 10.0 kohm and at — 40°C 336.5 kohm. The original price of these probes was over 

high impact ABS 
50 x 70 x 25mm 
60p each 10 for £5.00 

£24.00. OUR PRICE £3.76 with data 

10 or 20 minute bell cut off + ve or — ve trigger” timed relay contacts. £4.96 

Single zone alarm control unit built into a domestic light switch box. Ideal for home, 
caravan, boat, garage, shed etc. 

Facilities: - Normally closed loop for pir sensors, door/window contacts etc. Normally 
open loop for pressure mats. 24-hour loop for personal attack button Visual indication 
that the system is operational. Automatic SIREN 

bllletad rs rib op Ne _ 12 volt de for external use 115db 


Brand new passive infra-red sensor, measures only 

33mmMW x 24mmH x 29mmD. Logic level output. Full data 

and application notes supplied. 


Type 1. Measures 130 x 70 x 50mm with walk test led, relay i i 

and tamper protection. 12 volt dc supply required £6.50 each 
Type 2. As above but a smaller unit 90 x 75 x 50mm £8.50 each 
Type 3. Ceiling mounting passive, infra red sensor 360° detection, 12V d.c. supply relay 
output, tamper circuit and pulse count option. Data supplied. £11.75 each 

Please note: There may be variations in the size : 
of the above passive infra red sensors depend- oceans ane 
ing on stock at the time of ordering. But the unit  €1.10 each 
will certainly be within the stated sizes. JUNCTION BOX 


hite 6 
DUAL TECH SENSOR Microwave and passive eowe 
infra-red combined. Separate ied indication for each function. Measures 120 x 75 x 
50mm. 12 volt d.c. supply, Relay output. Tamper protection. £21.15 each 


PCB CCD CAMERA. Mounted in a plastic dome. 
12V d.c. supply. Composite video output. Fitted 
with a 2-9mm lens. Mono. 0:5 lux. £98.70 


BO2 D.P. on 3 for £1.00 

BO3 3x D.P. 3 pos, centre off 

BOO4 DIL SWITCHES 4-way S.P. on 3 for £1.00 

BOOS DIL SWITCHES 8-way S.P. on 2 for £1.00 

BOO6 DIL SWITCHES 12-way 90° sp on 2 for £1.00 


BOO8 1 x CAPACITOR 1 FARAD 5.5 VOLT 20mm dia. x 7mm high 

BOOS INSTRUMENT KNOBS (0.25” SHAFT) High quality grey plastic knob, collet 
fixing 15mm dia, 5 for £1.00 

BO10 as above but 29mm dia, 3 for £1.00 

BO11 4x MAGNETIC EARPIECE 8 ohm with 3.5mm plug 



BO14 8x2 PIN DIN PLUGS screw terminal connection 

BO15 2x LIGHT DEPENDENT RESISTOR Less than 200 ohms in daylight, greater 
than 10 megohms in darkness 

BO16 1x KEYPAD 20-key in 5 x 4 matrix bubble type switch contacts 

BO17 2x PIEZO BUZZERS approx 3 to 20 volt d.c. 

BO18 5 x 78M12 VOLTAGE REGULATORS positive 12V 500mA 

BO19 4x TLO82CP bi-fet op-amps 

BO20 20 x ASSORTED LEDS full spec. various shapes and sizes 

BO21 3x INFRA-RED DIODE TX/RX PAIRS made by Honeywell(no info) 

BO22 4 x CONSTANT CURRENT LED 5mm round, red 2-18V d.c. or a.c. nominal 

BO23 50 x IN4148 diode 


BO25 5x DIACS 

BO26 3 BDX33C 10 amp 100V npn transistor 

BO27 12 x 2N3702 Transisto: 

BO28 12 x 2N3904 Transistor 

BO29 12 x BC337 Transistor 

BO31 2x MAN6610 2 digit 0.6” 7 segment display Com anode, amber 

BO32 3x PHONO TO PHONO LEAD 63cm long 

BO33 15 x RECTANGULAR RED LEDs 6 x 6 x 2mm stackable 

BO34 1x PHOTO SENSITIVE SCR mounted on a PCB, data sheet supplied 

BO35 4x IEC Panel Mounting Mains Plug Snap fix 


BO37 5 LENGTHS OF HEATSHRINK SLEEVING 8mm dia. 400mm long 


BO39 15 x MONOLITHIC CERAMIC CAPACITORS 0.1 mfd 63V, in a dil package 

BO40 25 x ASSORTED ELECTROLYTIC CAPACITORS PCB mounting useful values 


BO42 6x 3-S5mm LINE JACK SOCKETS (mono) 

BO43 6 x3-5mm JACK PLUG (mono) 

BO44 8 x 35mm CHASSIS SOCKET (mono) 

BO45 2x TRIACS 800 volt 8 amp 

BO46 12 x BC213L Transistor 


BO48 15 x MIN CERMET TRIMMER POTS (good range of values) 

BO49 1x PCB WITH TWO LARGE LEDS 15mm square, one red and one green 

BO50 1x 12V DC RELAY 4-pole c/o with plug in base 

BO51 4x LM324 quad op-amps 

BOS2 4x 555 Timer 

BO53 5x741o0p-amp . 

. BOS4 25 x IN4001 diode 

BO55 20 x IN4007 diode 


BO57 1x DACO8 Digital to analogue convertor with data 

BO60 3x C106D Thyristor 

BO61 5 x 78M05 VOLTAGE REGULATORS positive 5 volt 500mA 

BO64 7 CMOS 4001B IC’s 

BO65 6 CMOS 4011B IC’s 



Please use order code when ordering the bargain packs. 
Please make cheques and postal orders payable to Mailtech. 
All prices include VAT. Please add £1.00 postage to all orders. 
Telephone enquiries between 10a.m. and 5 p.m. 
Tuesday to Thursday. 

Fax and answerphone at other times on 0158 474475. 

Dept EE, Maiultech 
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J ale) os-Jali a= ase od) Ph 

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LON Me celine Ati mile b mel el am C212) elalelalomy (Ulaalelzi maul meat: late [=m co 

01584 831475 

Everyday with Practical Electronics, June 1995 


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 ““Chcara 

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 
solder. 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 

Mi sctiphacaeiauiecs soiwirrcsdessiaienastesinias eeivesasuestiesaeanes £109.50 
K2100SA Series Audiophile, with extra selected 
COMPOMNENMS...............ccceceeeessssesssseseeeeeeeeeeeeeeaaees £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 

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 ‘GlucVeluet 

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. 


OT IY cess savissiesssssoiscdcananamrnraningcoase £15.67 
2-Gang 10K, 50K or 100K Log. ............ceeeeeeeees £16.40 
2-Gang 10K Special Balance, zero crosstalk and 
DTT CT NR essisccsiisiaseisccsemssuaseiiecctitanincees £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 
BOOM 274 RIP TOOMI. .2.....00scecavenssvescoscevenssosssasees £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, 
CTT BE so iiccisins doscareneanesecnnteentninticaesnksgonnine £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. 

get your order on its way to you THAT DAY. 


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 

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. 

Everyday with Practical Electronics, June 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! 

Sa ce eh wena staan aaa Phased aaagia £111.58 

K1450SA Series Audiophile version with selected 

NIT iiss vosssiaseesctxinaeccsuecnciceinisorsonions £133.94 


LER Sitacrnr 

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!............. ce ceeeeeeeeeeeeeeeeeees £11.70 
HRP373 Downstream monitor combi head...... £62.59 
HQ551A 4-Track R/P............ccccceccccccesssseeeeeeeeeeeees £8.75 
HQ551S Sony Mount 4-Tr. R/P............cceeeeeeeeeee £14.90 
*HQR560 Rotary Base 12-5mm R/P/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. 

(01691) 652894) uKjecvar ed 


a ees | 

Man ae ety 


I The latest MAGENTA DESIGN - highly # 
I stable & sensitive — with uC control 
I of all timing functions and advanced I 


135 Hunter Street 
Staffs. DE14 2ST 

Output, efficient circuit. 

1000V & 500V INSULATION Fspacewriter 

Superb new design. Regulated 

Dual- y UP to 16 digits long. Comes pre-loaded 
scale meter, compact case. Reads 

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

Tel 01283 565435 Fax 546932 EE156 order p &p 

An innovative and exciting — 
project. Wave the wand through “™ie 
the air and your message appears. “™™ 
Programmable to hold any message 

with “MERRY XMAS". Kit includes 

I pulse separation techniques. up to 200 Megohms ee, 
I @ New circuit design 1994 i Kit includes wound coil, cut-out PKIT ° ” 
, Si ntalssiaierieees £16.99 
 @ High stability i case, meter scale, PCB & ALL on oe on on on on on on on a a 
I drift cancelling i COMPORSITS. 12V EPROM ERASER 
I @ Easy to build ! SUL. Ete EoD trips tan 20 sinines Oyeteies fem a2) ppl 
& use i 400mA). Used extensively for mobile work - up- 
I ®No ground i M OS FET M k| | VAR IAB LE B EN C H perl ae sia ‘he fleld a Ales adic: 
tional situations where mains supplies are not al- 
1 effect, works | POWE R S U P P LY Q- 25V _ DA. lowed. Safety interlock prevents coniact with UV. 
1 in seawater y Based on caeoitige ge kt and KIT 790 £28.51 
preserving all the features,  «§-_ «sty, NE Mette ‘ 
; e oe but now with switching MOSFET 25V 2.5A 
f pre-regulator for much POWER SUPPLY 
i non-terrous I higher efficiency. Panel High performance design has made this one of our 
i metals | meters indicate Volts and classic kits. Two panel meters indicate Volts and 
| @ Efficient quartz controlled g Amps. Fully variable down to SoRelaan Lek Rugged power MOSFET ay 
microcontroller pulse generation. y Zer0. Toroidal mains trans- put stage. Toroidal mains transformer. 
j @ Fullkitwith headphones & all fone". Kt includes punched KIT 769...seccecsccecsseeeesees £56.82 
I parts. As featured in April. INSULATION TESTER 
LKiT 847. ol Oeigebgr aa ol ...£63. 954 1994 EPE. An essential piece A reliable and neat electronic tester which checks 
of equipment. hgh ag able of oe and abl a 
at olts. The unit is battery powered, simple 
DIGITAL LCD TH ER MOSTAT KIT 845 jiiieieowwes £64.95 and safe to operate. Leakage Lh Si of up to 

A versatile thermostat using a thermistor probe and 

having an I.c.d. display. MIN/MAX memories, -10 ULTRASONIC PEsT SCARER 

to 110 degrees celsius, or can be set to read in 

Fahrenheit. Individually settable upper and lower Keep pets/pests away from newly 
sown areas, fruit, vegetable and 
can result in substantial energy savings when used flower beds, children’s play areas, 
patios etc. This project produces 
brewing, etc. Mains powered, 10A SPCO relay out- Intense pulses of ultrasound 
which deter visiting animals. 


pact hand-held case. MOSFET output drives a @ COMPLETELY INAUDIBLE 


output is designed to give maximum output with- KIT Ref. 812..........ccccccccccccccceceeeeeeeeeeeeseeeeseees 


An exciting project supplied with two 200 step motors, interface board, and easy MOSFET coil drive. 
to use P.C. software. 
Allows independent control of both motors — speed, direction, number of steps, amplification. 

A really professional looking project. Kit is sup- and half/full step mode. Connects to computer parallel port. Requires 12V 1A Full kit includes 

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

with domestic hot water systems. Ideal for green- 
house ventilation or heating control, aquaria, home 

put. Punched and printed case. 

RUT B41 jo cisstsrtiemtaidenath woo 


A powerful 23kHz ultrasound generator in a com- 

special sealed transducer with intense pulses via 
a special tuned transformer. Sweeping frequency 

Out any special setting up. 

BET BE seicvscsnesternivees £22.56 







lO-ZOMr xr} 



£14.81 Magenta’s highly 

100 Megohms can be read easily. A very popular 
college project. 

KIT 444... eaeieues £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. 

KIT 840... eee £19.86 


developed & 
acclaimed design. 
Quartz crystal 
controlled circuit 

D.C. coupled 

plied with a punched and printed front panel, case, D.C. supply and printer lead. PCB handle 
.c.b. and all components. Quartz controlled ac- , ' ' HEADPHONES 
sielen of 1%. bares clear 5 digit display and high KIT 846 (with 2 motors) ....... £67.00 (Printerlead £5.00) case & : 
speed operation. Ideal for beginners — as the pF, hF search coil. @ EFFICIENT 
and pF ranges give clear unambiguous read out of ION ISER CMOS DESIGN 

marked and unmarked capacitors from a few pF up_ A highly efficient mains powered Negative lon Generator that clears the air by 
neutralising excess positive ions. Many claimed health benefits due to the ioniser 

KIT 493 £39 95 removing dust and pollen from the air and clearing smoke particles. Costs virtually 
EN A eee e estes eesessseeseesess sh UYU = nothing to run and is completely safe in operation. Uses five point emitters. 

Abo GF 2 dixiasecuestisnieonasmei eels eee eee £17.75 

to thousands of pF. 


A very popular project which picks up vibrations by 
means of a contact probe and passes them on to a BAT D ETECTO R 

pair of headphones or an amplifier. Sounds from An excellent circuit which reduces ultrasound frequencies between 20 and 100 kHz 



engines, watches, and speech travelling through to the normal (human) audible range. Operating rather like a radio receiver the circuit 
walls can be amplified and heard clearly. Useful allows the listner to tune-in to the ultrasonic frequencies of interest. Listening to Bats @ 190mm SEARCH COIL 

for mechanics, instrument engineers, and nosey _ is fascinating, and it is possible to identify various different types using this project. @ NO ‘GROUND EFFECT’ 


Other uses have been found in industry for vibration monitoring etc. 

BET 290) vrcsssvavnautdateenecy. CIO 96. AT Aitken nclnieemieievat £21.44 KIT 815 

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. OT £68. 60 VAT Includes FREE 

Next-day delivery 



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 

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, June 1 995 


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. 

7 TET FE ETT Oe nr 




Saving time, space, power, and MONEY. Wz 


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 
your own programs 


A real-world application for a PIC microchip. This project can be made 

to do just what you chose if you write your own software. OR works as 
a 4-Channel hard fired — zero volt switching — Light Chaser. Kit includes 
programmed PIC, software disk and all components (less case). 

AL ere 



(12V at 200mA) 


9-WAY £6.00 
25-WAY £7. £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 whale 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. 

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. 

MOE BO ss icicearssesiascs 

PC Communications Protocol 
for Comstep 

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

Kit 851 

Mini-Lab & Micro Lab 
Electronics Teach-In 7 

As featured in EPE and now published as Teach-In 7. All parts 
are supplied by Magenta. Teach-/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 

PC Joystick Interface for 

Software for operating Comstep fess 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 operation with adjustable 
acceleration and speed. Ideal for demo and setting 
up. Then connect to computer port for full control. 

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. 

Tel: 01283 565435 Fax: 01283546932 —_Allprices include VAT. Add £3.00 p&p. 

Everyday with Practical Electronics, June 1995 

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. 




74HC4002 £0.16 
74HC4017 £0.64 
74HC4020, £0.35 
74HC4040 £0.45 
74HC4049 £0.25. 
74HC4050 £0.25 
74HC4060 £0.39 
74HC4075 £0.27 
74HC4078 £0.16 
74HC4511 £0.64 
74HC45 14 £0.84 
74HC4538 £0.41 
74HC4543 £0.90 

74LS Series 
74LSO00 = £0.25 
74LSO1 £0.14 
74LS02 £0.29 
74LS03 £0.29 
74LS04 £0.14 
74LS05 £0.14 
74LS08 £0.23 
74LS09 £0.14 
74LS10 £0.14 
74LS11 £0.17 
74LS12 £0.14 
74LS13 £0.14 
74LS14 £0.25" 
74LS15 £0.14 
74LS20 £0.16 
74LS21 £0.14 
74LS22 £0.14 
74LS26 £0.14 
74LS27 ~—- £0.14 
74LS30 £0.14 
74LS32 £0.14 
74LS37 = £0.14 
74LS38 £0.19 
74LS40 = £0.14 
T4LS42 £0.25 

ESR Electronic Com 





AD9696KN £12.45 
FSCS Be £4.54 
ADM222AH _ £3.55 
ADM232AAN £3.55 
ADM485JN — £2.57 
ADM690AN_ £4.59 
ADM69IAN_ £5.91 
ADM695AN _ £5.91 
ADM699AN £3.19 
AMPO4FP £21.02 
BUFO4GP £10.02 
CA741CE £0.28 
CA747CE £0.39 
CA3046 £0.37 
CA3059 £1.16 
CA3080E £0.72 
CA3130E £0.98 
CA3140E £0.56 
CA3189E £1.22 
CA3240E £1.12 
DG211CJ £1.49 
DG212CJ £1.55 
DG411DJ £3.11, 
DG412DJ £4.19 
EL2020CN £4.99 
EL2030CN £5.67 
ICL7 106 £2.80 
ICL7611 £1.16 
ICL7621 £1.70 
ICL8038 £5.25 
ICM7555 £0.43 
ICM7556 £0.98 
LI65V £2.63 
L272M £1.89 
L293E £4.32 
L297 £6.37 
L298 £6.99 
LF347N £0.86 
LF351N £0.43 
LF353N £0.42 
LF356 £0.84 
LM301A £0.25 
LM308N £0.42 
LM311N-8 £0.28 

318 £1.28 
LM319N-14 £0.96 
M324 £0.35 
LM335Z £1.52 
LM339N £0.24 
LM348N £0.31 
LM358N £0.27 
LM377 £2.57 
LM380N-14 = £1.12 
LM381N £2.70 
LM382 £2.30 
LM386 £0.79 
LM387 £1.60 
LM392N £0.79 
LM393N £0.28 
LM709T £0.79 
LM733 £0.64 
LM748CN-8 = £0.31 
LMS579CP £3.38 
LM 1458 £0.26 
LM 1881 £4.00 
LM2917N8 ~— £3.20 
LM3900N £0.72 
LM3909N £1.76 
LM3911 £2.56 
LM3914 £2.70 
LM3915 £2.70 
LM 13600 £1.82 
LMC660CN = £2.16 
LMC6032IN = £1.55 
LMC6042IN £1.82 
LP311N £0.74 
LP324N £0.74 
LP339N £0.73 
MAX202CPE £2.97 
MAX208CNG £6.99 
MAX220CPE £5.06 
MAX222CPE £5.06 
MAX232CPE £3.71 
MAX238CNG £6.88 
MAX242CPE £5.51 
MAX631ACP £4.99 
MAX635ACP £4.99 
C1488 £0.46 
MC1489 £0.46 
MC3302 £0.56 
MC3340P £1.60 
MC4558P £0.36 
MVS00DP £2.63 
MV60!1DP £2.97 
NES531 £1.47 
NESS55N £0.25 
NES56N £0.36 
NE565 £1.84 
NES66N £1.12 
NES67N £0.39 
NES71N £2.47 
NE592 £0.58 
NE5532N £0.80 
NE5534N £0.60 
OP07CN £1.42 
OP27CN £2.49 
OP77GP £3.12 
OP90GP £4.14 
OP97FP £4.02 
OP113GP £4.04 
OP176GP £2.30 
OP177GP £2.49 
OP183GP £3.78 
OP200GP £6.81 
OP213FP £6.38 
OP275GP £2.84 
OP282GP £2.63 
OP283GP £5.81 
OP290GP £6.24 
OP295GP £5.54 
OP297GP £7.56 
OP467GP £15.90 
OP495GP £10.44 
PMIO12GP =e £6.38 
RC4136 £0.90 
SAA1027 £4.52 
SG3524N £1.08 
SG3543 £6.88 
SL486 £2.63 
SL490 £2.63 
SSM2017P —s £3.38 
SSM2131P £4.87 
SSM2141P £5.94 
SSM2142P £6.08 

ponents. Credit Card Orders Acce 

pted. NO Surchar 

SSM2143P —- £4.99_ 1N5407 £0.14  2SB548 £0.30 BC328 £0.10 ; 
TBA120S £0.90 1N5408 £0.15 2SD1730 £1.44 BC328-16 £0.10 BD ries 
TBA800 £0.70 BAI57 £0.10  AC126 £0.44 BC337 £0.10 BDX33C £0.49 
TBA810S £0.68 BAIS58 £0.10 ACI27 £0.50 BC337-25 £0.10 BDX34C £0.50 
TBA820M —‘ £0.39 BAI59 £0.10 ACI28 £0.28 BC338 £0.10 BDX53C_ £0.47 
TDA1024 £1.49 BY126 £0.13 ACI87 £0.48 BC338-25 £0.10 BDX54C _ £0.50 
TDAII70S £1.83 BY127 £0.11 ACI88 £0.48 BC348B. £0.14 —BFI80 £0.31 
TDA2002 £1.04 BY133 £0.10 ACYI7 £3.84 BC357 £0.25. — BF 182 £0.31 
TDA3030.—«ET'18. OASO for; | ABIl. © S0ee: peahiC. Eh BRise Seat 
TDA2050V £3.98 OA9I £0.10  ADI62 £0.92 BC441 £040 BFI94B £0.19 
TEASII5 £3.11 OA200 £0.10 | BCIO7 £0.16 BC461 £0.40  BFI95 £0.19 
TLO61CP £0.35 OA202 £0.29 BCIO7B £0.15 BC463 £0.29 BF244 £0.35 
HOSEN £092 4m 008 «BCIEA | eatia bree oe BME BS 
ae 4 m . s BA bo 
TLO7ICP £0.48 1.3W £0.14 BCIO8C £0.16 BC490 £0.24 BF257 £0.33 
TLO72CP £0.68 Bridge Rectifiers BC109 £0.17 BCS16 £0.22  BF259 £0.33 
TLO74CN £0.58 W005 1.5A 50V £0.19 BCIO9C £0.17 BC517 £0.20. BF337 £0.36 
TLO8! £0.33 WO02 1.5A 200V £0.20 BCII4 £0.41 BC527 £0.20 BF355 £0.3 
TLO82CP £0.54 WO4 1.5A 400V £0.22 BCII5 £0.41 BC528 £0.20 BF423 £0.13 
TLO84CN £0.63 W06 1.5A 600V £0.22 BCII6 £0.41 BCS537 £0.20  BF451 £0.19 
TL494CN £1.49 WO08 1.5A 800V £0.27 BCII8 £0.41 BC5S46B £0.08  BF459 £0.33 
TL7705ACP £1.62 WO101.5A IkV £0.24 BC132 £0.36 BC546C £0.08  BF469 £0.36 
TLC271 £0.54 BR32 3A 200V £0.36 BC134 £0.36 BC547B £0.09 BFX29 £0.29 
TLC272 £0.88 BR34 3A 400V £0.40 BC135 £0.36 BC547C £0.09 BFX84 £03! 
TMPOIFP £7.25 BR36 3A 600V £0.44 BCI40 £0.25 BCS48C £0.08 BFX85 £0.32 
U257B £1.28 BR62 6A 200V £0.70 BCI4I £0.27 BC549C £0.10 BFYS5O £0.29 
U267B 1.28 BR68 6A 800V £0.74 BC142 £0.31 BCS550C £0.10 BFY51 £0.26 
UA2240CN £2.30 1004 10A 400V £1.39 BCI43 £0.34 BC556A £0.08 BFY52 £0.28 
ULN2003 £0.52 2502 25A 200V £1.68 BCI49 £0.21 BCS557B £0.08  BSI07 £0.21 
ULNIOS «£120 Thyristora  Belsy, = Seis. Beasge «feck BS 0 
ULN2803 £0.60 PON2AA £0.30 BCI59 £0.12 BC559C £0.08  BUI26 "33 
ZN409CE £1.89 TIC106D £0.40  BC160 £0.28 BCS60A £0.09 BU205 £1.41 
ZN414Z £1.16 TICII6D £0.66 BCI70 £0.16 BCS560B £0.09  BU208A_ £1.24 
Nite’ > aha eee” |B Bere =. a Bue Be 
5 riac \ i ‘Zz Py : 
EPROM’s ie ZDLOSDA £0.42 BCI71B £0.16 BC639 = £0.21 BUSO8A = £1.42 
2732 £484 TIC26D £0.73 BCIT3B O13 Bev 70 £031 era tt 74 
2764-25 £4.20 BTAO08-600B £0.99  BCI77 £0.18 BCY71 £0.20 BU806 £1.06 
27C64-25 £3.44 TIC236D £0.96 BCI78 £0.18 BCY72 £0.20 BUTIIA £1.33 
$3820 £408 DBS 32V. £0.20. Balto, © SRL? BDineP 686 BUTMAF £133 
27C 128-20 £4.08 Transistors BC182 £0.08 BDI36 £0.21 IRF540 £1.60 
27256-20 £4.85 2NI1613 £0.31 BC182A £0.11 BD137 £0.23 IRF740 £1.80 
27€256-20 £3.95 2NI711 £0.26  BCI82B £0.08 BDI38 £0.22 MJ2501 £1.60 
270512 £3.95 3N1893 £0 «BC I82L £0.08 BDI39 £0.23 + MJ3001_~—-£1.80 
RAM ine amotio Pee BC182LB £0.08 BD140 £0.25 MJIIOIS £2.11 
6116-10 £1.53 2N2222A = £0.18 BCISSL_ Ss EDOR Biles. fons | Mubue fod 
6264-10 £3.06 2N2646 £0.86 BC1I83LB £0.08 BD166 £0.35  MJE350 £0.42 
41256-10 £2.80 2N2904A £0.25  BCI84 £0.08 BDI87 £0.39  MPSAOS £0.14 
62256-10 £5.35 eo ree BCI84L £0.08 BD201 £0.40 MPSA06 £0.12 
3142568 £688 2N2007A £020 Besb§c 072 Bbse 040 apsawe Eee 
A/D Converters 2N2926 £0.16 = BC206B £0.72 BD204. £0.40. + MRF475_— ‘£7.28 
Data Acquisition 2N3053 £0.27 BC207B £0.74 BD222 £0.58 290C "2 
AD430AN" £29.62, 2N3054 £0.90 C208 £0.72 BD225 fa) TIP30C 3 
ADSS7JN £8.75. 2N3055 £0.62  BC209A £0.72 BD232 £038 TIP3IC £0.34 
ADS74AJN £20.66 2N3439 £0.62 BC212 £0.08 BD237 £0.32  TIP32C £0.32 
AD767JN £22.44 2N3440 £0.50 = BC212L £0.08 BD238 £0.32 TIP33C £0.72 
AD775JN = £21.54. 2N3702 £0.09 BC?212LB £0.08 BD?: £0.37 TIP4IA £0.48 
AD7226KN £25.69 2N3703 £0.10 BC213 £0.08 BD243B £050 TIP42C £0.38 
AD7528JN_ £14.28 2N3704 £0.10 BC213 £0.08 BD244A £053  TIP47 £0.48 
AD7545AKN £15.18 2N3705 £0.10 BC213LC ‘£0.08 BD244C £0.53  TIP48 £0.62 
AD7581JN £26.99 2N3706 £0.10  BC214 £0.08 BD245C £1.18  TIPSO £0.53 
AD7828KN £26.76 2N3771 £1.44 9 BC214L £0.08 BD246 £1.18 TIPI21 £0.35 
AD7845JN £18.06 2N3772 £1.51 = BC225 £0.15 BD246C £1.18 TIPI22 £0.40 
ICL7109CPL £7.75  2N3773 £1.79 BC237B £0.09 BD283 £0.61 TIPI25 £0.37 
TLCS49IP = £3.51 =. 2N3819 £0.39 = BC238B £0.09 BD284 £0.61 TIPI27 £0.40 
42 £5.94 2N3820 £0.66  BC238C £0.09 BD400 £0.79 TIPI32 £0.46 
ZN426E £3.03 2N3904 £0.10 BC239C £0.10 BD441 £0.41 TIPI37 £0.46 
ZN427E £8.78  2N3905 £0.10  BC250A £0.15 BD442 £041 TIPI42 £1.08 
N428 £5.94 2N3906 £0.10  BC251 £0.13 BDS34. = £0.47.—s TIPI47.~—s £1.12 
ZN439E8 £7.13 2N4036 £0.34 BC252 £0.13. BD535 £0.50 TIP2955 £063 
245 £0.80 rel Ly. ‘ 305 63 
- ve vi £7.02 areas 2 a BC261B £0.24 BD536 £0.65  TIP3055 ~—-£0.63 
Regulators —-2N5321_—=— £0.57 BC267B «£030 BDS07 «£092 VNGOARD ETS 
5322 £0.57 3 59 : 
780; er ane He at BC307 £0.10 BD646 £0.52 ZTX300 £0.16 
He BRM Bg moe Bee RED 
7905 £0.31 2N6491 £1.58  BC327-16 £0.10 BD708 £1.04 
7915 £0.38 Electrolytic Radial Capacitors Electrolytic Axial Capacitors 
7924 £0.38 pF lov 25v 63v_ 100v 450v F l6v 25v 63v 100v 450v 
781.05 £0.25 O47 -- £0.05 £0.07 bai oa eS es ee 
78L08 £0.31 10  --- - £0.05 £0.06 £0.15 1.0 ---  -- £0.10 £0.10 £0.19 
781.12 £0.24 2.2 -- -- £0.05 £0.06 £0.18 2.2 --  -- £0.10 £0.10 £0.22 
781.15 £0.24 4.7 --  -=- £0.05 £0.08 --- 47 -- £0.09 £0.10 £0.10 £0.34 
78124 £0.26 10 £0.05 £0.05 £0.06 £0.08 £0.44 10 --  -- £0.12 £0.12 £0.48 
7905 £0.28 22 £0.05 £0.05 £0.09 --- —--- 99 --- £0.09 £0.13 £0.17 £1.06 
7908 £0.28 47 £0.06 £0.06 £0.11 --- — --- 47 £0.10 £0.11 £0.16 £0.20 --- 
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Everyday with Practical Electronics, June 1995 




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Editorial Offices: 



Phone: Wimborne (01202) 881749 

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Due to the cost we cannot reply to orders or queries 

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Advertisement Offices: 


VOL. 24 No. 6 JUNE ’95 


Wandering around an Antiques Fair over the Easter weekend, my attention was 
captured by a working Bakelite cased radio, an unusual, rather ugly, design with 
pushbutton tuning — it was obviously from the early Fifties and turned out to be of 
American origin (115V a.c.). The most interesting feature was the price — just over 
£200! I am told that some early radios, those made by Marconi in the very early days of 
radio, can cost thousands of pounds. | 

I started to wonder if any item of modern equipment might command such interest in 
forty years’ time. It seems doubtful that many of our present day products could 
be refurbished to full working order as any custom chips, microcontrollers and pro- 
grammed memory would be difficult to reproduce. However, if you look at some 
mundane items which are now becoming collectable, it makes you wonder if we should 
be hoarding personal cassette players, radios, etc. No doubt the most interesting work- 
ing designs of such things will become collectors items, possibly made more valuable 
because of the difficulty in repairing them in the future. 


Jake Rothman, who has designed our EPE HiFi Valve Amplifier admits to having a 
weakness for old transistor radios, of the type that Bush put out in the Seventies. Jake 
has bought and restored a number of these and is threatening us with an article on how 
it’s done — anyone interested? I guess we should all start collecting and restoring now 
SO we can retire on the proceeds in years to come! Incidentally we expect to publish a 
High Voltage Capacitor Reformer project next month — very useful to anyone refur- 
bishing valve equipment. 

The specialist knowledge and ingenuity needed to refurbish items using “blown” 
chips can, of course, be gained by the hobbyist and, providing a replacement “blank”’ 
chip is available, it is not beyond the ability of the enthusiast to write new software 
froma knowledge of the operation and circuitry of the original product and thus blow 
a new device. 

Our PIC-DATS (last month) and follow up PIC Light Chaser articles will give you an 
excellent start in this rewarding operation. So, perhaps we should also be hoarding 
some of the most popular programmable chips for future use too! 


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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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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 
in a back-dated issue. 

We regret that we cannot provide data or 
answer queries on projects that are more 
than five years old. 

Although the proprietors and staff of EVERY- 
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from illegal use or ownership. The laws vary 
from country to country; overseas readers 
should check local laws. 


Constructional Project 




Riding on the wave of the “valve revival”, 
Jake presents his own design so that 
constructors can create the valve sound, 
without suffering “antique CGealer” prices! 

e39OW rms. into 8 ohms ¢ 20OHZ to 2OKHz, +O0:20dB 

e /nput Sens. SO0OMYV for full output ¢ less than O:1% 

t.h.d. at TSW into 8 ohms e¢ Hybrid design for minimum 
valve count ¢ Monoblock design (two required for Sberao! 
e Optimised for use withCDe 

HiFi Valve Amplifier. Designed to 

sound at least as good as the Quad II 
power-amp described in the February 1994 

The design is not a rehashed 1950s 
circuit. It is based around a brand new 
hybrid topology combining the positive 
attributes of vacuum and solid-state tech- 
nologies. This amp enables the valve sound 
to be obtained without suffering ‘‘antique 
dealer”’ prices. 


In terms of “pounds-per-watt” valve 
amplifiers cost around five to twenty times 
more than equivalent power solid-state 
designs, so why use valves? The answer 
lies in the type of distortion produced, 
generally valve type distortion sounds sub- 
jectively better, even if it is much higher on 
the ‘‘spec sheet.” 

Audio distortion is a complex subject, in- 
evitably intertwined with psychoacoustics. 
The human ear produces its own distortion 
which tends to increase smoothly with level 
and comprises mainly low-order harmonics. 

It does not seem surprising therefore that 
studies have shown distortions very dis- 
similar to this are much more noticeable, 
humans may prefer to hear distortions they 
are familiar with! Unfortunately the dis- 
tortions produced by standard Class-AB 
solid-state designs are almost the opposite 
to that of the human hearing, tending to 

Hi at last, is the promised EPE 

suffer increasing distortion at low-levels 

and hard clipping at overload. 
Often distortion is at a minimum 
just before clipping and the harmonics 


produced tend to be high and of an 

odd-order such as 5th and 7th. This tends 

to manifest itself as a lack of clarity in 
the top end and low-level reverberation. 
Characteristic distortion curves for the two 
different technologies are shown in Fig. 1 
and Fig. 2. 



234567 9 







More astute readers may have realised 
that the transistor amplifier distortion 
curve in Fig. 1 is very similar to that 
produced by digital recording media. CDs 



20Hz 20k 



SOW 60W 

| Fig. 1. Solid-state distortion — Class-AB 

Everyday with Practical Electronics, June 1995 

exhibit a distortion rise at low levels simply 
because there are fewer bits to convey the 

One could be excused for thinking this 
means there is no point in using a valve 
amplifier with CDs. There is — because for 

some unknown reason, the distortion curve 

of the valve amplifier seems to hide that of 
the CD player and make the system sound 

What matters is the overall distortion 
pattern (with regard to harmonics and 
level) and the frequency response of the 
complete hi-fi system. This effect of hi-fi 
components complementing each other is 
known as synergy. This effect has also been 
used in studios for many years, where valve 

condenser microphones and guitar proces- | 

sors are common place, complementing 
digital recording and sampling. A few years 
ago a CD player was introduced that had 
valves following the DAC! 


Another aspect to amplifier sound is the 
use of negative feedback. Feedback is 

necessary to reduce distortion and flatten 

frequency response. 

Where a lot of feedback is used clip- 
ping tends to be much harder and sudden. 
The distortion harmonics although much 
reduced, are pushed up to higher orders. 
Soft clipping or gradual overload is subjec- 
tively less unpleasant and is akin to the 
effect of hitting a string or soundboard 

There is a school of thought in hi-fi that 
believes that any feedback is bad. This aim 
is very difficult to achieve in practice, since 
the only amplifying devices linear enough 

to not need feedback are a select few triode | 


Generally speaking the less linear an 
amplifying device is, the more feedback is 
required. Phase shift limits the amount of 
feedback that can be applied before oscil- 
lation occurs. Valve amplifiers generally 
employ coupling capacitors and output 
transformers which limit the amount of 
feedback to a maximum of around 20dB 
(open-loop gain reduced by ~ 10). 



PERL Tie ith Wars tl aia 


The output impedance of valve 
amplifiers is generally higher than 
transistor amps because of the smaller 
amount of negative feedback used, the high 
output impedance of valves themselves and 
the resistance in the transformer windings. 
A high output impedance means that the 
loudspeaker damping factor is lower, often 
giving the impression of better bass. 

This often makes small closed-box 
speakers sound better. The BBC designed 
LS3/5a is such a design and is often seen 
partnered with Quads (synergy again). 

Table 1 compares the linearity of various 
output devices. It is interesting to note that 
MOSFETs are the least linear, it even says 
in the Hitachi data book that a MOSFET 
output stage produces ten times more dis- 
tortion than a comparable bipolar stage. 

Fortunately, MOSFETs have such a 
high bandwidth that massive amounts of 
negative feedback can be used to give 
acceptable distortion. 


Another reason for the good sound of 
valve amplifiers is not that they use valves 
per se, but that they are usually Class-A 
designs. Class-A amplifiers run at full 
power even with no signal, with the 
output devices never out of conduc- 
tion throughout the whole cycle. This 
means there is no low-level or crossover 

Valves are very effective at dissipating 
heat so it is simple to run them in Class-A. 
With solid-state devices massive heatsinks 
and thermal stabilisation are needed, so 
Class-A is rarely used. 


The block diagram of the EPE HiFi 
Valve Amplifier, with an op.amp based 
phase-splitter followed by a triode driver 
stage feeding an ultra-linear EL34 output 
stage, is shown in Fig. 3. The ultra-linear 
output stage is based on the Mullard 5-20 

Table. 1: Linear comparison of output devices 



Beam Tetrode 
(in ultra-linear mode) 


Most linear, least distortion, lowest efficiency. e.g. 

Slightly more distortion but almost as efficient as 
pentodes. e.g. 6L6, KT66, EL34, 5881. Used in 5-20 

and Williamson design. 

(in ultra-linear mode) 


Used in Leak Stereo 20. Distortion between triode 
and pentode. e.g. EL84 

Good for guitar amps. Third harmonic distortion 

predominates. e.g. Vox AC30 using EL84s. 

Bipolar Transistor 

Cheapest. Difficult to use in Class-A due to thermal 

runaway risk. Most efficient. e.g. 2N3055. 


Most reliable, best h.f. response but least linear. e.g. 

2SK135 and 2SJ50. 


THD 4 AT 10W 

20Hz 1k : 20k 



Fig. 2. Typical valve distrotion — Class-A. 

Everyday with Practical Electronics, June 1995 


A phase-splitter is always necessary in 
push-pull valve amplifiers because com- 
plementary valves are not available. All 
valves are like n.p.n. devices, so unless 
someone can invent a positron emitting 
electrode using some kind of anti-matter, 
the p.n.p. valve is a long way off. 

Single-ended vs 
Push-pull operation 
Single-ended valve amplifier designs do 
not need a phase-splitter at all and have a 
nicer sound because the second harmonic 
distortion is not cancelled, which can leave 
remaining third harmonics exposed, as 
with push-pull amplifiers. The drawback 

_ with the single-ended approach is that the 

output transformer is a pig to design — 
because there is a net d.c. current flow. 

In push-pull, the d.c. current flows of 
both output valves are in opposite direc- 
tions cancelling any generated steady-state 
flux in the transformer core. In single- 
ended designs a gap is required in the core 
to prevent saturation which makes good 
inductance figures hard to achieve. 

The end result is that single-ended output 
transformers start at four times the price of 
an equivalent push-pull type. If cost is no 
object, single-ended triode designs give the 


nicest sound, but a push-pull ultra-linear 
amp gives most of the attributes of valve 
sound for the lowest cost. 


The op.amp phase-splitter was chosen 
because it is more stable, avoiding the drift 
that occurs with valve based designs. Since 
it operates at low levels, it operates in 
Class-A and clips long after the output 
valves clip, avoiding any solid-state type 
sonic signatures. It also provides a low 
impedance balanced input of the type used 
in top studio technology to avoid hum 
pick-up (most valve amplifier inputs are 
very high impedance and unbalanced). 

Since the amplifier is intended to be used 
with CD players, which almost invariably 
use 5532 op.amp i.c.s in their output fil- 
ters, it is felt from an engineering point of 
view that one extra will not be perceived. 
Incidentally, 80 per cent of top selling al- 
bums are mixed on SSLs which use at least 
thirty 5534s in the signal path. 

A pair of differential op.amp. stages 
with their inputs wired in parallel anti- 
phase form the basis of the phase-splitter. 
This configuration was popularised by Ted 
Fletcher of the Alice mixer company to 
obtain an equal impedance on both inputs, 
since the standard single differential amp 
has unequal impedances, which impairs the 
common mode rejection ratio. The circuit 
also gives additional anti-phase output 
making it ideal for use as a phase-splitter. 


Looking at the phase-splitter circuit in 

more detail, the full circuit diagram of the 

EPE HiFi Valve Amplifier is shown in Fig. 
4. The phase-splitter circuit has a gain of 
four times, sufficient to fully drive the 
valves, but not so high that it clips with full 
CD level signals. 

To ensure maximum headroom the rail 
voltage is 33V to 36V. The differential 
stages are band limited to 40kHz by 
capacitors C3 and CS. These also serve to 
prevent r.f. breakthrough. 

Both op.amps are biased to half-rail 

(16:5V) for single-rail operation. This 

necessitates the use of blocking capacitors 
Cl and C4 at the input and C7 and C8 at 
the output. 


An ECC83 triode valve (V1) is used to 
amplify the outputs of the op.amps to over 
25V r.m.s. to fully drive the output stage. 
Using a 400V h.t., anode resistors R26 
and R29 and cathode resistors R15/R16 
and R11/R12, the ECC83 sections deliver 
almost their maximum gain of around 50 


o> PY Ta Pee ee Ke | ; 
Bis / 

Fig. 3. Block diagram of the EPE HiFi Valve Amp/ifier. 

To prevent oscillation the grids (pins 2 
and 7) are fed by stopper resistors R25 and 
R28. The grids are held at OV potential by 
pull-down resistors R24 and R27. Negative 
feedback is applied in a balanced fashion 
from the output transformer secondary to 
cathode resistors R16 and R12. 

To make up the total 2-2 kilohm cathode 
resistance required for correct biasing at 
2V, two kilohm resistors R15 and R11 are 
included in series with R16 and R12. These 
resistors are bypassed by capacitors Cll 
and C9 to ensure maximum open-loop 

Finally, the output of the driver valves 
are fed via capacitors C15 and C17 to the 
output stage. Since the ECC83 anodes 
(pins 1 and 6) sit at 205V it is essential 
that low-leakage 400V capacitors, such as 
polycarbonate or polypropylene, be used 

The ECC83 valve was chosen for its high 
gain and availability. More adventurous 
constructors may wish to use a _ higher 
power valve such as the 6SL7, or better still 
the 12BH7, to get lower distortion. 


A pair of EL34 valves (V2, V3) in the 
standard Mullard ultra-linear configura- 
tion will give around 20W at 0-8 per cent 
total harmonic distortion (t.h.d.) open- 
loop. The valves operate in pure Class-A 
up to around 15W and after that point the 
system operates to some extent in Class-B 
and this is given the classification AB1. 

This project is NOT for beginners 

Not only is there mains voltage in this amplifier, there is. 
also 450V h.t. which is even more dangerous because it 

is d.c., which means that muscles may ‘‘freeze” 


use well insulated probes when testing and always check if 

switched off. 

It should be pointed out that the I.e.d. 


is extinguished 
when the h.t. fuse has blown, this means that the bleeding 
function is also disabled and the capacitors could still be 
holding a lethal charge. The same applies if the amplifier is 
operated with the phase-splitter board removed. 

The maximum output power just before 
clipping into 8 ohms is 24W r.m.s. Only 
when the amp is driven beyond clipping 
are the valves pushed to full cut-off. This 
point is visible on the ‘scope and it 
looks like a crossover kink in the middle 
of the waveform when the amp 1s clipped 

When this occurs the output valves are 
being driven into “grid current”. Grid cur- 
rent flows when the grid is driven more 
positive than the cathode, causing it to 
act like an anode picking up some of the 
electron stream. In the case of the EL34 the 
cathode voltage is around 32V so the input 
voltage would have to exceed this figure to 
give rise to grid current. 

Grid current can cause problems in that 
it tends to charge up the coupling 
capacitors which, because of their long 
time constant in association with the 
discharge paths, can cause slow shifts in the 
d.c. bias. This can manifest itself as 
“speaker pumping” when the amp is driven 
hard with pulsed signals. 

To prevent parasitic oscillations, resis- 
tors R35 and R31 are used as grid stoppers 
on the control grids of the output valves. 
Resistors R34 and R30 hold V2 and V3 
grids (pin 5) at ground potential. Their 
value is the highest allowable to reduce 
loading on the driver stage. 

The ultra-linear taps on the output trans- 
former are connected via resistors R37 and 
R33 to the suppressor grids, pin 4. These 
help maintain linearity at high levels and 
are also wired close to the valve socket to 
help act as grid stoppers. 


The cathode resistors R32 and R36 have 
to dissipate high power and thus MUST be 
a high power type. These resistors generate 
the necessary bias for the output valves by 
making the cathode positive with respect 
to the grid, which has the same effect as 
making the grid negative with respect to 
the cathode. 

Indeed, some amplifiers employ a 
separate negative power supply for the grid 
bias. This system of biasing is called “‘fixed 
bias” as opposed to cathode bias and can 
be used to obtain higher continuous power 

Everyday with Practical Electronics, June 1995 


30W r.m.s. into 4 ohms 
24W r.m.s. into 8 ohms 
I7W r.m.s. into 15 ohms 

300mV r.m.s. for full output 
20Hz to 20kHz, +0-2dB 

less than 0-1% T.H.D. at IS5W into 8 ohms 
in midband. 

0-25% at 50Hz mostly 
second and third 

Power Output: 

Input Sensitivity: 
Frequency Response: 

Power Consumption: 95W 
Signal-to-Noise/Hum Ratio: — |00dB 

For pulsed type music signals found in 
hi-fi applications however, the power ad- 
vantage is insignificant and so only tends to 
be found in guitar amps. It is also less reli- 
able since if the bias power rail should go 
down, the direct grounding of the cathodes 
would allow a huge current to flow through 
the output valves and transformer, possibly 
resulting in expensive failures. 

To prevent localised negative feed- 
back stopping the output valves being 
fully driven, the cathode resistors are 
bypassed with electrolytic capacitors C16 
and C18. Proponents of fixed bias would 
no doubt argue that the elimination of 
these electrolytics would be beneficial. 
However, as with all electrolytics used in 
audio signal positions, if the value is made 
big enough (so no signal voltage appears 

the capacitor) 
and there is a 
positive bias voltage 
across it, no distortion will occur. 

It is possible to use a single cathode resis- 
tor and capacitor common to both valves, 
as used in the Quad, but this is a false 
economy since it means matched valves 
then have to be used. 


Around 20dB of negative feedback is 
included around the amplifier, mainly to 
extend the frequency response, lower dis- 
tortion to below around 0-1 per cent and 
help mitigate the effects of any valve mis- 
matching. The feedback is taken from the 
output transformer secondary and applied 
in a balanced form to the driver stage 

Fig. 4.. Circuit diagram for the Phase-spiltter and power output stages for the HiFi Valve Amplifier. Note that capacitor C22 and 

resistor R43 are optional, see text. 

Everyday with Practical Electronics, June 1995 


where it is developed across R12 and 
R16, the unbypassed cathode resistors in 
_ the driver stage. It was not considered 
desirable to include the op.amp in the 
overall feedback loop, since this would 
have made the open-loop gain too high, 
resulting in hard clipping. 

The level of feedback is set by resistors 
R14 and R18, with optional low frequency 
compensation provided by the RC net- 
works comprising resistors R13 and R17 
and capacitors C10 and C12. The total 
feedback resistance must not be reduced 
below one kilohm or there is a risk of low 
frequency instability setting in. 

High frequency compensation was not 
found to be necessary, but it could easily be 
included using the p.c.b. positions occupied 
by R14, C10, R17 and C12. Another op- 
tion is afforded by C22 and R43 which 
allow a little high frequency boost to be 
included if desired. Note that these com- 
ponents are such a rare option that there 
are no holes for them on the p.c.b., they 
will have to be soldered across the ends of 
resistors R14 and R18. 

The open-loop frequency response of the 
amplifier, which exhibits —1dB points at 
30Hz and 15kHz, is shown in Fig. 5. With 
negative feedback the response is flat from 
20Hz to 20kHz as shown in Fig. 6. 

The feedback network can be used to 
provide a degree of frequency response 
manipulation to compensate for speaker 
deficiencies etc. Fig. 7 shows such a curve 
where a little boost at 50Hz and 12kHz has 

been applied to give a better balance with a 

pair of small bookshelf speakers. 

In this case capacitors C10 and C12 were 
made 470n while C22 was 6n8 and R43 was 
given a value of 1-6 kilohms. To avoid ex- 

cessive lift at extreme I.f., the phase-splitter 

input coupling capacitors Cl and C4 were 
reduced to lpF. 


It was mainly the power requirements of 
valves compared to transistors that led to 
their demise in the 1960s. The power con- 
sumption of this amplifier is very high, with 
21W (3-3A at 6:3V) being used for heater 
power alone. The h.t. current is 140mA at 

(277) eo} C3 extern 

430V or 60W, giving a total of around 95W 
including transformer losses! This is even 
when the amplifier is just idling since it is 
basically Class-A. 

The complete power supply circuit 
diagram, based around Maplin’s “High 
Power Valve Mains Transformer’’, is given 
in Fig. 8. This transformer was used in 
Maplin’s valve amp design to power two 
stereo channels. In the authors opinion it 
ran much too hot for long-term reliability, 
so in this design, an individual transformer 
should be used for each channel. This 
allows the amplifiers to be constructed as 
monoblocks (two for stereo), simplifying 
“earth loop” and crosstalk considerations. 

Original power supplies for valve 
amplifiers used valve rectifiers and 
smoothing chokes. A valve rectifier was 
abandoned in favour of silicon since they 
are expensive, wear out like any valve and 
consume extra heater power. Another 
advantage of the silicon rectifier is that it is 
easy to use as a bridge. 

Most valve rectifiers are of the double 
diode type which needs a centre-tapped 

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Fig. 5. Graph showing the open-loop frequency response at 15V rm.s. into 8 ohms. 


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200 500 1k 2k 5k 10k 20k 40k ae if 
mverntattyo (me Co Co Cy Coq co =e) ae ae 

Fig. 7. Graph showing the closed-loop with response equalisation. 

Everyday with Practical Electronics, June 1995 

secondary on the power transformer with 
twice the voltage. A silicon bridge saves 
money on the mains transformer and 
makes it more reliable because the voltage 
Stress is lower. 

However, there is a problem with solid- 
state rectifiers and that is their immediate 
turn-on, whereas a valve rectifier slowly 
warms up and applies the h.t. voltage to 
the circuit gradually. The slow turn-on 
characteristic of valve rectifiers protects 
capacitors from destructive surges, but 
more importantly, prevents cathode strip- 
ping in the valves where the full h.t. is 
present but the cathode has not yet warmed 
up. The mechanism involved is fairly com- 
plex but is basically due to the electrons 
being pulled from the barium oxide coating 
on the cathode, resulting in reduced emis- 
sion in the long term. 

To minimise the problem of cathode 
stripping, a Brimistor (R42) is. used. This is 
a special type of thermal resistor (thermis- 
tor) formerly made by Brimar and later 
STC, which has a high resistance when cold 
which reduces to a low value when hot. 

The type used in this design is the CZ6, 
which has a resistance of four kilohms cold 
and 300 ohms hot. This is not as good as 
the valve rectifier which is an open circuit 
when cold, but it certainly helps. 

If the thermistor cannot be obtained, a 
Standby switch is an alternative. It is even 
possible to wire a valve rectifier, such as a 
GZ37, in series with the bridge rectifier 
with both sections connected in parallel. 

This would then still obviate the need for a 

centre-tapped secondary. 

In the days when electrolytic smoothing 
capacitors were only available up to 16yF, 
additional smoothing was needed and this 
was achieved by using a smoothing choke. 
Unfortunately, with the passing of time, 
Capacitance has become a much cheaper 
commodity, while the cost of inductors has 
increased in line with inflation, 

Since it is now possible to buy standard 
smoothing caps up to 220uF, we can dis- 
pense with the choke and use resistance in 
its place. In this case, the Brimistor forms 
the resistive smoothing element and a surge 
resistor R39 protects the first smoothing 
capacitor and the rectifier from the switch- 
on surge. Note that the first capacitor C21 
must be a 500V type because the no load 
voltage at turn-on is around 480V. 

For safety the chassis is Earthed directly 
to the mains earth, while the “signal earth”’ 
is only connected to the mains earth via 
resistor R41 to prevent ground loops. The 

Fig. 8. Circuit diagram for the amplifier Power Sup, 

SRE IE yee PRPs) 

‘ F 
Pe eee ee Bee Pe ies 

‘ P| rr ‘ * 7 a ® Vik a oe 

4 A Rey a Phas on 

“star” earth point for the amplifier is 
formed from a thick piece of tinned copper 
wire strapped between the two smoothing 
capacitors C20 and C21. To avoid the 
charging current pulses causing buzzing, 


ply section. 

the output of the rectifier is wired directly — 

to the terminals of C21. 

Further smoothing and decoupling for 
the driver stage is provided by R38 and 
C19. Since the driver stage only consumes 
around 1-8mA, this rail can be used to 
power external pre-amps etc. if desired. 
Resistor R38 will have to be reduced 
accordingly to compensate for the extra 
current drawn. 


All the heaters are run on a.c. straight 
off the mains transformer T2. D.C. heater 
power is not needed since all the valves run 
at relatively high signal levels. 

The heater winding is centre-tapped to 
ground (OV) which reduces hum, by 

balancing any residual electron emission. 

from the heaters. 



The relatively low voltage of 33V to 36V 
needed for the op.amps was a bit of a 
headache, in that almost 400V needed to be 
dropped. This meant that around five watts 
needed to be dissipated in a “dropper 
resistor”. This would normally be con- 
sidered unacceptable in an efficient solid- 
State design, but where the output valves 
are dissipating around 75W, this seemed to 
be only a minor problem. 

In the end, the dropper resistor solved two” 

additional problems: it provided a bleeder 
resistor function for the h.t. rail, prevent- 
ing shock risk from residual charge in the 
smoothing caps. Secondly, by placing an 
l.e.d. in series, a reliable power indicator was 
provided, which also showed when the h.t. 
rail had discharged (see Fig. 4). | 

The dropper resistor is composed of 
three 10 kilohm 2W resistors R21, R22 
and R23. However, the board will accom- 
modate a single wirewound type if this can 
be obtained. A more reliable choice would 
be a metal-clad type bolted to the chassis to 
aid cooling. : 

A simple Zener diode regulator (DS) 
holds the rail voltage at 36V and capacitor 
C14 filters out any ripple and Zener noise. 
The half-rail bias for the op.amp is derived 
by resistor R19 and R20 wired as a poten- 
tial divider. Decoupling of the bias is 
provided by capacitor C13. , 

Everyday with Practical Electronics, June 1 995 


very reliable. . 
The driver anode load resistors are un- 


Components are under much greater 
temperature stress in valve equipment. 
Electrolytic capacitors tend to dry out, 
especially the small ones used for cathode 
bypasses and coupling because they have a 
large surface area-to-volume ratio. 

Fortunately, the smaller cathode 
electrolytics can easily be replaced by solid 
electrolyte types, such as solid tantalum 
and solid aluminium _ types. 
aluminium types (made by Philips and 

Rifa) are even more reliable than tantalum. 

The high wattage resistors are under con- 
siderable stress and metal-oxide types such 
as Vishay FP] and FP2 are recommended 
for the film types. For the wirewound resis- 
tors, Welwyn W22 series vitreous types are 

der high voltage stress and physically small 
resistors, such as Maplin’s 0-6W commer- 
cial rating (0-25W industrial rating) metal- 
film types, will not be robust enough. Use a 
full-size industrially rated type such as the 
0-5W metal-film types. Resistors mounted 
on tag strips are under greater lead-pull 
stress than resistors mounted 
with the support of a p.c.b., 
so full-sized types are recom- 
mended here also. 



Cheap valves from Eastern Europe usually work well, Chinese tubes 
do not seem to last as long. Using original Mullard types is not cost 
effective because of inflated collector’ prices. The EL34B is slightly 
stronger than the EL34S. 


Traditional chassis construction is used for the bulk of the amplifier 
(many TV service engineers discovered that power output valves soon 
burnt their way through printed circuit boards!) However, a p.c.b. is 
used for the op.amp phase-splitter and feedback components in view of 


R1, R4, R5, R6, RY, R10 100k (6 off) See 
R2,R3,R7,R8,R19,R20 22k (6off) SOP 

R11,R15 2k (2 off) 
R12, R16 200 (20) LZALK 
_ R13, R17 4k3 (2 off) Page 
R14, R18 1k2 (2 off) © 
R43 . 1k2 optional 
All 0:-25W 1% metal film (for p.c.b.) 
R24,R27 — 1M (2 off) 
R25, R28, R31, R35: 2k2 (4 off) 
R26, R29 220k (2 off) 
R30, R34 680k (2 off) 
R40 12 (depends on lamp LP1 current) 
All full-size 0-5W 1% metal film . 
R33, R37, R41 1k (3 off) 
R38 18k 
All 1W 5% carbon film or 2% metal oxide FP1 
R21, R22, R23 10k (3 off) (can be replaced with 
single 33k 7W WW) 
All 2W 5% carbon film or 2% metal oxide FP2 
R32, R36 470 (2 off) 
R39 68 
All 7W 5% wirewound Welwyn W22 
R42 CZ6 Brimistor (thermistor) — see text 
C1, C4 47, axial tantalum, 20V (2 off) 
C2, C3,C5,C6 10p polystyrene 2:5% (4 off) 
C7,C8 . 470n 5mm polyester 10% (2 off) 
C9, C11 33 tantalum or solid aluminium, 10V (2 off) 
C10, C12 22 polyester 20%, 63V (2 off) 
C13 4u7 tantalum bead, 25V ; 
C14 1000p radial elect. 35V 
C15, C17 470n 400V axial polycarbonate or 
polypropylene, 10% Wima MKB3 
(see text) (2 off) 
C16, C18 68p axial solid aluminium (type 123), 40V (2 off) 
C19 47, 450V axial 
C20 68p to 220 450V 
C21 68pu to 220 500V 
C22 6n8 polyester (eq. option) 
C23 330n polyester 
V1 ECC83 triode 
V2, V3 EL34 beam tetrode (2 off) 
D1 to D4 BYX84 or 1N4007 1000V p.i.v. 1A rec. diode (4 off) 
D5 36V or 33V 400mW Zener diode 
D6 5mm red diffused I.e.d. 20mA 
IC1 NE5532N dual low noise op.amp 
T1 Valve output transformer, primary anode-to-anode impedance 6k6 
T2 240V a.c. mains transformer, with 350V 250mA secondary and 6:3V 
7:5V centre-tapped valve heater winding 
SK1 | filtered mains IEC socket 
S1 d.p.d.t. mains toggle switch, with indicator lamp 
FS1 3A cartridge fuse, with panel fuseholder 
FS2 315mA quick-blow 20mm fuse, with panel fuseholder 

Diecast box, size 273mm x 172mm x 51mm; printed circuit board (phase-splitter) avail- 
able from EPE PCB Service, code 941; 8-pin d.i.I. socket; chassis-mounted B9A valve 
holder; chassis-mount octal valve holder (2 off); 3-pin XLR chassis socket; loudspeaker 
terminals; |.e.d. holder; 2-pin Molex assembley (4 off); 3-pin Molex assembly (2 off); 
6-way tag strip, plus two “earth” mounting tags; 2-way tag strip, plus three “earth” 
mounting tags; capacitor clips (2 off); small cable ties (3 off); stick-down plastic cable tie 
mounts (3 off); p.c.b. mounting pillars plus bolts (4 off); multistrand connecting wire, 
7/0:1 for Molex connectors; 3-core mains lead; mains wire 7/0-2 for valve heaters; ap- 
prox. 250mm length twin-screened cable; 102mm length 16 s.w.g. tinned copper wire; 
102mm 22 s.w.g. tinned copper wire; one metre silicone sleeving; M4 nuts, bolts and 
washers (8 off); M3 nuts, bolts and washers (9 off); screw locking compound; solder etc. 

Approx cost £ y | 7 | O 
guidance only 

Fig. 9. Phase-splitter printed circuit 
board component layout and full size 
underside copper foil master. 

Before we undertake the traditional task 
of “‘chassis bashing” associated with valve 
work, we can first tackle the more familiar 
operation of constructing the printed cir- 
cuit board (p.c.b.). The top side component 
layout and full size underside copper foil 
master pattern are shown in Fig. 9. This 
board is available from the EPE PCB Serv- 
ice, code 941. 

Commence construction of the Phase- 
splitter p.c.b. by mounting components in 
height order starting with resistors first, but 
leave the semiconductors until last. Be 
especially careful to get the polarities of the 
electrolytic capacitors, Zener diode and the 
op.amp i.c. the right way round on the 

The dropper resistors R21, R22 and 
R23 should be soldered in a clamped 
fashion onto the track by firmly bending 
the lead over. This is because components 
that “run” hot put additional thermal 
stress on the soldered joints. The resistors 
should also be spaced away from the p.c.b. 
by ceramic beads, if possible, to prevent 

Make sure that the straight pin p.c.b. 
connectors are soldered on the board with 

440 Everyday with Practical Electronics, June 1995 

g 25mm 




P.C.B. J 3m 
DRIVER e , 75 



Chassis layout dimensions and drilling 
details, with the position of all the com- 
ponents having been worked out to ease 
the wiring, minimise hum and prevent un- 
desirable coupling, are shown in Fig. 10. 
One of the basic considerations to minimise 
hum is that the two transformers have been 
placed as far apart as possible with their 

- cores at right angles to each other. Another 
is that the low-level part of the circuit, the 
phase-splitter, has been placed as far away 
as possible from the power transformer. 

The smoothing electrolytics are away 
from the drying heat of the output valves 
and the output wiring is kept separate from 
the input wiring by running each on op- 
posite sides of the case. Since it is desirable 
for aesthetic reasons to have all the con- 
necting leads coming out of the rear of the 
chassis the main input lead has to be a 
screened cable, since it runs near the power 
supply electrolytics. 

SWITCH 016mm 



Next Month: We conclude with all 
the interwiring and final testing. 

Fig. 10. Chassis top, front and rear component layout, 
details and dimensions. 

their locating “friction lock’? headers cor- 

rectly positioned, see Fig. 9. The make up 
of the interconnecting plugs is shown next 

Once the Phase-spilitter board has been 
constructed it should be put to one side un- 
til the diecast box chassis drilling has been pales hasan 
completed. board showing the 
component layout. 
CHASSIS Note the high 
CONSTRUCTION wattage resistors 
A diecast box is used for the chassis be- are stood on-end 

cause they have nice looking rounded edges and have ceramic 
and are easy to drill. Do not use steel for beads keeping the 
the chassis since this will spread the mag- resistor bodies 
netic field of the mains transformer around. clear of the p.c.b. 

Everyday with Practical Electronics, June 1995 . | 44] 

A roundup of the latest 
Everyday News from the 



Virtual reality and I.c.d. holography combine to meet the need for 

RGENT need for a method of 

training “keyhole surgeons” in 
conducting laser operations has 
opened up a world of medi- 
cal opportunity to Professor Bob 
Stone’s Virtual Reality (VR) team at 
Salford. He has recently taken on 
the role of Director of Virtual Reality 
Studies for the North of England 
Wolfson Centre for Minimally 
Invasive Therapy, and heads the VR 
Division of Intelligent Systems 
Solutions (formerly known as 
Advanced Robotics Research). 

In recent months the media has 
drawn attention to public anxiety 
about key-hole surgery, leading to a 
call for action in improving the 
training of surgeons graduating 
from conventional open surgery to 
the more remote techniques of laser 


Because live animal-based training 
is prohibited by UK _ regulations, 
primary key-hole surgical experience 
is presently fostered through the 
remote handling of ‘‘dolly mixtures”, 
grapes, raw chicken tissue, plastic 
tubing and foam-mounted balloons. 
It is now realised that provision 
of even a basic virtual human 
simulator will help to develop speci- 
fic surgical skills. 

VR has the potential to reproduce 
the natural and fluidic characteris- 
tics of human anatomy, requiring 
only a_ re-setting of the host 
computer, once a training session 
has been completed. Professor Stone 
says the use of their techniques 
will provide the “flight simulator” 
qualities surgeons are demanding 
- the ability to generate cost- 
effective what-if scenarios, such 
as insufflation failures, anatomical 
ambiguities, patient distress and 
instrument failure. 

With support from the Department 
of Health and the Wolfson Founda- 
tion, a project was initiated at 
Salford University integrating the 
skills and talents of a number of 
academic and small company teams 
from throughout the UK, backed by 
know-how from the VR team. In the 
early part of the project the team 
observed and recorded the work of 
the surgeon by visiting operating 
theatres and using video and digital 


training keyhole surgeons 

— by Hazel Cavendish 

Laparoscopic Cholecystectomy opera- 
tion in progress. Courtesy of University 
of Manchester. 

During extensive discussions with 
practising and trainee surgeons they 
learned that medics would not accept 
any form of head-mounted displays. 
These were deemed unacceptable for 
image quality, in-theatre communica- 
tion, ergonomic and hygiene reasons. 
There was a 50-50 split in opinions 
as to the need for stereoscopic view- 
ing and the importance of tactile and 
force feedback. 

Some surgeons claimed that vision 
was the overriding sense; others in- 
sisted that a simulator would have 
to include a reasonable representa- 
tion of such features as elasticity, 
instrument constraints within the 
body cavity, and varying degrees of 
movement ‘‘viscosity’”’. 


It was necessary to adopt a dis- 
play technology which did not re- 
quire any form of head or face- 
mounted peripheral to achieve the 
necessary stereoscopic effect. A solu- 
tion was offered by the Richmond 
Holographics autostereoscopic dis- 
play system which uses conventional 
le.d.s combined with Holographic 
Optical Elements (HOEs). 

HOEs are devices made _ using 
similar techniques to those used 

for making holograms, and are 
recordings of the interference pat- 
tern which results when two or more 
laser beams intersect. Unlike ordi- 
nary holograms, they do not contain 
an image: instead they are used to 
bend, focus and otherwise mod- 
ulate light in unusual and _ fre- 
quently complex ways, with optical 
properties that cannot be achieved 
with conventional optics. 

The use of special HOEs make it 
easy to fabricate a display which 
directs light from one image into one 
of the viewer's eyes and light from a 
second image into the other eye. 
Both images can be displayed on one 
l.c.d. The HOE permits the display to 
compensate for viewer movement; 
binocular fusion occurs to produce a 
three-dimensional whole image. The 
Richmond Holographics system will 
allow Wolfson Centre researchers to 
evaluate the necessity for three- 
dimensional endoscopy. 

In due course the VR system means 
that a practice operation will be able 
to be carried out in the same way as 
a real one, but instead of a living 
patient on the operating table, the 
surgeon will have an electronic box 
in which to insert his instruments. 
Then, as in a conventional keyhole 
operation, surgery will be performed 
by looking at a TV monitor. 


Yet Professor Stone declares there 
is still an uphill battle: “Surgeons 
and the medical fraternity in the UK 
generally look upon VR and related 
technologies with sceptical eyes,” he 
says. “Also, for some reason (and 
with one notable exception), the 
larger VR hardware and software 
companies in Britain seem to have 
written-off the medical area as being 
a non-lucrative market. 

At present, the cost of VR tech- 
nologies is totally unjustifiable for 
medical training; up to £150,000 
for the computing platform alone. 
Nevertheless, rapid advances are 
being made in the development 
of much cheaper, high-performance 
graphics processors for PC _ plat- 
forms. It is highly likely that com- 
puters delivering the performance 
required by the medical fraternity 
will become available at a more 
realistic in-hospital price within two 
to four years. 

Everyday with Practical Electronics, June 1995 

emai iy an Ser Rae ae et <eampaacin —- 
) Pht peas [Ey Tey \ 

4 * hte ah dat Nie tia, 
Warne a2 RATES 


CADPAK and PROPAK for Windows have recently been 
introduced into the Labcentre range of software products. 
CADPAK for Windows includes both schematic drawing and 
p.c.b. drafting tools but as an entry level product, there is no 
netlist link between them. CADPAK is especially suited to 
hobby, educational and small scale schematic and p.c.b. design. 
PROPAK for Windows adds netlist based integration, auto- 
matic power plan generation and a powerful auto-router. 

Both of these packages for Windows are based on well proven 
existing Labcenter products (which run from DOS). At the same 
time, the new products make full use of Windows features such 
as on-line help. PROPAK autorouting runs as a true 32-bit 
application — making it faster than 16-bit products. 

CADPAK and PROPAK for Windows are priced at £149 and 
£495 respectively. Contact Labcenter Electronics, 53-55 Main 
St., Grassington, N. Yorks BD23 SAA. Tel: 01756 753440, Fax: 
01756 752857 for more details of these products and upgrades 

from existing Labcenter products. 



The Amateur Radio, Electronics and 
Computer Club (AREC Club) of Malta 
are organising an ‘‘on the air’ activity to 
mark Victory in Europe Day. The call 
sign is QH50VE and operation, on a 24 
hour basis, will continue during May 
6th, 7th and 8th. Frequencies, subject 
to interference and propagation, will 
be 3:775MHz, 7:044MHz, 14:225MHz, 
21-25MHz and 28:55MHz SSB. 

AREC Club, PO Box 114, Valletta 
CMROI Malta. 


CLPK have joined forces again with 
Sharward Promotions (the Shows and 
Exhibitions Division of Sharward Serv- 
ices) to undertake the organisation of The 
East Coast Amateur Radio and Com- 
puter Rally, which this year will be 
held on August Bank Holiday Sunday, 
27th August. The venue is the Clacton 
Leisure Centre, Vista Road, Clacton-on- 
Sea, Essex. 

Major suppliers and manufacturers of 
radio equipment, computers and com- 
puter software, accessories, antennas and 
secondhand gear will be at the Rally. 
There will also be a “Bring and Buy” sale. 

The show runs from 10.30 a.m. to 4.00 
p.m., with the bar and cafeteria available 
from 11.00 a.m. There is a Free car park. 

For further details please contact the 
organisers: Sharward Promotions, Upland 
Centre, 2 Upland Rd., Ipswich IP4 SBT. 
Tel: 01473 272002, Fax: 01473 272008. 

Also organised by the same company is 
the Ipswich Computer Show, Saturday 
May 20, 10 am. to 4 p.m. At Willis 


A digital answerphone which can also store faxes, 
operate as a high speed modem and automatically Ole Bae 
forward messages is now available from Andest Ltd. er ei 

The Virtual PA (V.PA) can be accessed from 
anywhere in the world to retrieve voice messages 
or redirect faxes to any fax machine. The 
standard unit contains |Mbyte of memory, 
enough to store 20 minutes of voice or | 

approximately 50 fax pages, but this can be 
expanded to 8Mbytes if needed. 
The unit can be easily programmed using 

the built in five button key pad and lLce.d. _ 
screen or it can be linked to a PC. The stan- 
dard version operates at 2400bps for data and > 

19200bps for fax and costs £399. 

Contact Andest Ltd., Chancery Court, Lincoln 
01494 429309, Fax: 
Bulletin Board — Fax Back Service: 

Rd., High Wycombe. Tel: 
01494 538598, 
01494 510560. 

Carroon Sports and Social Club, The 
Street, Rushmere St. Andrew, Ipswich. 


The 38th Longleat Amateur Radio Rally 
is at Longleat House (not the Safari Park) 
on Sunday 25th June from 9.30 a.m. to 5 
p.m. Further information from Gordon 
Lindsay GOKGL, 66 Jubilee Crescent, 
Mangotsfield, Bristol. Tel/Fax: 0117 940 


The fourth National Vintage Com- 
munications Fair will take place in the 
Pavilions Hall of the NEC in Birmin- 
gham on Sunday, May 14 and _ will 
feature thousands of rare and _ collec- 
table vintage technology items with spe- 
cial emphasis on early radios, television 
receivers, gramophones, telephones and 
classic 1950s hi-fi. In attendance will be 
over 300 specialist dealers from the UK, the 
Continent and the USA. For the seasoned 
collector, it’s the event of the year. 

The fair is presented annually by the 
Sound and Vision Yearbook which is a 
comprehensive reference guidebook to over 
one hundred sound and vision collect- 
ing hobbies from Amateur Radio through 
Classic Audio, Theatre, Cinema and other 
Organs/TV and Radio Related Collectables 
etc., to Vintage Wireless. For early arrivals 
at this year’s Fair, the £5 admission price 
includes — while stocks last — a free copy of 
the latest edition of the Yearbook. 

More information and copies of. this 
fascinating little Yearbook (£3.50 post free) 
are available from Sunrise Press, 2-4 Brook 
St., Bampton, Devon EX16 9LY. Tel: 
01398 331532. 

Everyday with Practical Electronics, June 1995 


A pilot scheme to help more secon- 

dary schools get on-line to Internet 

was recently launched by Tim Eggar, 
Minister for Industry and Energy with 
£250,000 of DTI backing. 

“We are working with the 
information technology and com- 
munications industries who are 
going to ‘adopt’ local schools, 
providing equipment, line connec- 
tion and training. Industry will be 
contributing about £350,000, over 
half the total cost. DTI will provide a 
help desk and project management, 
and will ensure that suitable 
educational material is available,” 
said Mr. Eggar. 

“The companies are close to iden- 
tifying the 50 schools who will 
participate in the project. These are 
either near the companies’ own 
plants or are amongst those who 
have been ringing asking to be 

“If the pilot stage is a success, 
and if enough schools sign up to 
the initiative, then the scheme will 
be extended with DTI committing 
another £750,000 for a full pro- 
gramme in 1996.” 

The companies involved have 
come together to form a ‘National 
Information Infrastructure (NII) Task 
Force’. Based on the Federation of 
the Electronics Industry, these 
companies include GPT, IBM, and 
Lucas Systems as well as a number 
of smaller companies such as 
Softwright Systems, the independent . 
software company. 

lan Taylor, the DTI Technology 
Minister responsible for coordinating 
multimedia matters, has recently 
established a Multimedia Industry 
Advisory Group. “The Group will 
monitor progress of the Online 
project’, said Mr Taylor, ‘‘and assess 
its contributions to education. 

“We are aware of concerns about 
information on the Internet. It will 
obviously be important to provide 
adequate protection against un- 
desirable material, and this issue is 
under consideration by members of 
the Schools Online Project.” 


New Technology 

lan Poole investigates the intense development of flash and 
ferro-electric memories which promises enhanced | 
endurance, speed and density, while cavities replace gutters 
in research to improve silicon purity. 

EMORIES are one of the most impor- 
Mien areas for development at the 
moment. There has been phenomenal 
growth in the sales of computers over the 
last ten years. This has resulted in a greater 
need for smaller and more _ portable 
systems, which in turn has meant that the 
requirements being placed on memories are 

becoming even greater. 

One development to hit the market in 
recent years has been the flash memory. 
This provides many improvements over 
other memories which are available at the 
moment because the technology consumes 
less power and has a very high density. 

Some manufacturers are even using these 
memories to make replacements for disk 
drives. Although they are more expensive 
than a standard disk drive they offer the 
advantage of being far more robust, and 
much smaller. 

There are many other uses for these 
devices and as a result a large number of 
manufacturers are entering the market. 
This increased competition has forced the 
development of these devices ahead. Intel 
now manufacture a 16Mbit device and no 
doubt other companies will follow suit in 
due time. 

Another area of development of flash 
memories is in increasing their life time. 
The memories have a limited number of 
write/erase cycles and some of the first 
devices to hit the market only had a lifetime 
of about a thousand cycles or so. Now 
development has improved their perfor- 
mance quite considerably and most devices 
will offer an endurance of 100,000 cycles, 
and there is a growing trend for figures of 
1,000,000 cycles to be quoted. 

Obviously cost is an important factor. 
Current flash devices are roughly three 
times the cost of an equivalent EPROM. 
This reduces sales and Intel are currently 
working towards making flash the cheapest 
form of memory on the market. This will 
ensure that it is in a commanding position 
for the next few years. 

Ferro-Electric | 

Despite the enormous interest in flash 
technology and the great amount of 
coverage it is receiving in the electronics 
press it is not the only new memory 
technology about. Over ten years ago a 
company called Ramtron put forwards the 
idea for a ferro-electric memory. Now they 
have over forty patents granted for the idea 
and a number of others pending. 

Supporters of this type of memory des- 
cribe it as the ideal solution for portable 


equipment. It combines many of the fea- 
tures required by today’s designers. It is 
very low power, high density, high speed, 
and offers an almost unlimited number of 
write/erase cycles. 

The technology uses the property of 
certain crystals in which magnetic dipoles 
align in different directions according to 
the electric field which is applied. When the 
electric field is removed the dipoles stay in 
place and the data is stored almost per- 
manently. The other advantage of ferro- 
electric memories 1s that the life of the cells 
is measured in hundreds of millions of 
write/erase cycles instead of around a mil- 
lion for flash memories. 

Another advantage is that their power 
requirement is around ten times less than 
an equivalent flash memory. This is a dis- 
tinct advantage for portable applications 
where many of these memories are likely to 
be used. | 




Fig. 1. A cell in a “ferro-electric’ 


Despite these advantages, ferro-electrics 
still have a way to go before they catch up 
with flash. One of the main areas where 
they are behind is in their density. It is 
expected that the first 256K devices will be 
made this year and there are rumoured to 
be plans for |!Mbit memories sometime in 
the future, although no dates are known. 
This is a far cry from the 16Mbit flash 
devices which are currently being manufac- 
tured by Intel. Nevertheless ferro-electric 
development is forging ahead. 

For the long term, ferro-electrics ap- 
pear to provide many exciting possibilities. 
However, the technology is still very much 
in its infancy and we will have to wait a few 
more years to see if they come up with the 

One of the key features which has 
enabled today’s semiconductor technology 
to progress as far as it has is the purity of 
the semiconductors. The main reason why 

f.e.t.s were not introduced any earlier was 
simply the fact that it was not possible to 
produce silicon which was pure enough to 
enable them to work reliably. 

Now with feature sizes many orders of 
magnitude smaller and much more strin- 
gent demands being placed on the device 
performances, semiconductor material of 
the highest grade has to be used. Often 
when yields fall and devices do not come 
up to their specification the reason 1s 
that the base semiconductor was not pure 
enough. Even very low levels of impurity 
can have a marked effect. 

In preparation of the basic silicon for 
semiconductor crystals a technique known 
as zone refining is used. This removes most 
of the impurities, but even though this 
method has been improved it is still not 
always capable of reducing impurity levels 
by the degrees necessary. | 

Impurities can be wide ranging, and a 
scheme called “guttering” is commonly 
used to reduce their levels. To perform this 
an unused portion of the wafer, normally 
the back or underside is roughened using a 
coarse etch. This breaks up the crystal 
lattice creating many sites for the im- 
purities to lodge as metal silicides. As the 
chosen portion of the wafer is unused they 
can remain here without any ill effects on 
the remainder of the chip. 

The process works reasonably well but as 
demands on the purity of silicon increase, 
it is not sufficient for many of the latest 
processes. It does not remove all the im- 
purities and the silicides sometimes form 
in areas where they are not wanted. Cop- 
per, one of the most troublesome impurities 
can be reduced to much lower levels by a 
process in which some microscopic cavities 
are created just below the surface of the 

The cavities are formed by implanting 
helium atoms into the wafer. The wafer is 
then heated forcing out the helium atoms 
but leaving microscopic cavities or voids 
which have nanometre dimensions. These 
serve to trap the copper by forming areas 
where the copper atoms can migrate. Once 
the copper atoms have migrated into the 
voids they become bonded to the silicon. 
As in the guttering process the voids are 
formed in areas of the silicon not used for 
the active circuitry. 

The use of these voids has a number of 
advantages. Once within the voids the cop- 
per is held more firmly than if guttering 
had been used. In fact the voids are stable 
to temperatures over 1100°C; sufficiently 
far above most of the temperatures which 
would be needed in any of the subsequent 
processes. In addition to this the voids are 
capable of holding a relatively large num- 
ber of copper atoms, making the process 
useful when impurity levels are high. 

Everyday with Practical Electronics, June 1995 

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Ter Name of the Game is a series of electronics 

PART 4 = 

displays, new games employing electronic word-making, 
and games of skill. 

In the final part this month, we aim for the stars with both 
Star-Struck! and Six-Shot Light Zapper, and find hidden at- 
traction with a touch of wander-lust. | 

projects based on party games or TV quiz games. 
Featuring something old, something new, there are 
electronic versions of popular, well-established TV games 
such as Countdown and Catchword with alphanumeric 

bows, 4 

tri-colour light emitting diodes (l.e.d.s) 

at its points is mounted on a board. To 
its sides are two smaller stars, one painted 
red and: one painted green. The smaller 
stars are the targets and their six points are 
fitted with pushbutton switches. 

Initially, the central star displays three red 
l.e.d.s.and three green ones. During play, the 
red and green contestants stand in front of 
the board and simultaneously throw soft 
rubber balls at the pushbuttons of their star. 
As each switch is hit, the l.e.d. at the same 
point on the large star changes colour ac- which star has been struck. The 

N this game, a large star displaying six 

aim is to make all six l.e.d.s change to the 

same colour: a red team contestant aims to 
get an all-red star, and his green opponent 
aims to get an all-green one. 


The tri-colour l.e.d.s are activated by six 
bistable (flip-flop) circuits, which can be 
reset by a central pushbutton switch on 

- each.of the target stars to display three red 

l.e.d.s.and three green ones. This switch 
also offers a bonus target during play to 
enable a player to pee a three l.e.d.s at 
once. } 

In the heat of battle, it may not be ob- 
vious when ‘one player has succeeded in 
turningzyall six l.e.d.s on to the same colour, 
especially if one (or more) of the l.e.d.s 
is almost immediately. reversed by the op- 
ponent. A. useful addition is an optional 

“‘six-light indicator” buzzer circuit, which 
sounds.immediately l.e.d.s are displayed as 
either-all red or all green. The buzzer sig- 
nals the end of the round, or the end of the 
game if there are only two contestants. 

As seen in Fig. 1, the Star-Struck! circuit 
mainly consists of the six identical bistable 

- multivibrators, or flip-flops as they are 


commonly called. As the name implies, a 
eee has.two stable but opposite output 
: states:’ when. one output is high, the other is 
~ low and vice versa. Each time a bistable is 
suitably triggered, its outputs change to 
their opposite states. 


For the purposes of this game, two 
switches are used to trigger each bis- 
table, and a tri-colour l.e.d. indicates its 
output states. Although bi-colour l.e.d.s 
are available, in this circuit the author 
found that tri-colour |.e.d.s were easier to 
use because of their common cathodes. 
The author also preferred to use flip-flops 
designed around transistors rather than 
using integrated circuit flip-flops. (Desig- 
ner’s “spares” boxes often have discrete 
components which can be used in place of 
more sophisticated devices!) 


Taking the circuit formed around tran- 
sistors TRI, TR2, and their associated 
components as an example, the operation 
of a transistorised flip-flop is as follows: 
At power switch-on, depending on cir- 
cuit parameters, component tolerances etc., 
one of the transistors will switch on in 
preference to the other. If TRI is on, 

current from resistor R1 flows from its 

collector (c) to its emitter (e) and then 
through the “red” anode (a) to the cathode 
(k) of l.e.d. D1, so turning it on. 

The collector of TRI is connected via 
resistor R2 to the base (b) of TR2. Thus, 
when the collector of TR1 is low so too is the 
base of TR2, consequently the latter transis- 
tor is held off, and its associated l.e.d. D1 

“green” is inactive. In this stable state of the 
flip-flop, pressing switch S8, which takes the 
base of TR2 to the OV line, will have no 
effect as the base is already low. 

Pressing switch S1, however, will now. 
take the base of TR1 low, so switching off 
this transistor. As a result, l.e.d. D1 (red) is 
turned off. The collector of transistor TR1 
is now held high and current passes via 
resistors Rl and R2 to the base of TR2, so 
turning on both it and its associated l.e.d. 
D1 (green). 

The operation of the other five flip- 
flops (TR3/TR4, TR5/TR6, TR7/TR8, 
TR9/TRIO and TR11/TR12) is basically 
identical to that of flip-flop TR1/TR2. The 
three flip-flops around TR1 to TR6 are 
considered as “Green’s”’ flip-flops, whilst 
‘“‘Red’s”’ are those around TR7 to TRI12. 
Both groups of flip-flops can be reset to 
their “home” colours by switches S7 and 
S14 respectively. 

Everyday with Practical Electronics, June 1995 



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S Fig. 2. Topside component layout and underside stripboard 
“ __ track cuts and solder joints for the Star-Struck! game. 

Saas, 3 
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Assembled stripboard modules for Star-Struck! and its opp- 
tional buzzer circuit mounted on the back of the target board. 

Everyday with Practical Electronics, June 1995 447 

Fig. 3. Wiring details for the components mounted directly on the Star- Struck! target board. 

Pressing the “Reset Green” switch S7 
takes to ground the bases of TR1, TR3 and 
TRS, via diodes D7, D8 and D9. This 
action bypasses switches S1, S2 and S3 but 
has a similar effect to pressing all three 
together, causing the three flip-flops to 
switch to the state in which the green l.e.d.s 
of D1, D2 and D3 are turned on. Pressing 
the “Reset Red’ switch S14 has a similar 
effect on the other three flip-flops, turning 
on the red l.e.d.s of D4, DS and D6. 


The Star-Struck! game was built on a 
sheet of 3-ply plywood measuring 1Sin. x 
24in. (381mm xX 610mm), but the base 
material and its size can be varied ac- 
cording to individual requirements. For 
stability, and to protect the components 


Resistors SOP 

R1, R4, R5, R8, TALK 

R9, R12, R13, 

R16, R17, R20, ro 

R21. R24 1k (12 off) 
R2, R3, R6, R7, 

R10, R11, R14, 

R15, R18, R19. 

R22. R23 10k (12 off) 
All 0.25W 5% carbon film. 

Dito D6 _l.e.d., tri-colour (6 off) 
D7toD12 1N4148 signal diode 
(6 off) 
TR1 to 


BC109 or similar npn 
transistor (12 off) 

4068B 8-input NAND 
gate (2 off) (see text) 


S1 to 

$14 s.p. push-to-make switches 
(14 off — see text) 

$15 S.p.s.t. min. toggle switch 

WD1 piezo buzzer (see text) 

Stripboard O-1lin. pitch (see text); 
plywood panel (see text); wood battens 
for frame (see text); R6 size 1-5V cells 
(6 off) and battery box; single-core and 
stranded connecting wire; solder, etc. 


excl. wood 

Approx cost 
guidance only 


Rear view of the Star-Struck/ target board showing all the components and wiring 

In their relative positions. 

behind it, the board was edged by 5/8in. 
(16mm) square battens. Holes should be 
drilled in the board to suit the switches, 
l.e.d.s and the buzzer. The l.e.d.s can be 
mounted via a row of three small holes 
drilled for their lead-out wires. 

The author constructed his game elec- 
tronics on two pieces of stripboard, one for 
the circuit of the six flip-flops and one 
for the buzzer circuit. The flip-flops were 
constructed on a piece of 0-lin. pitch 
stripboard (24 strips x 24 holes), com- 
ponent layout assembly details for which 
are shown in Fig. 2. Note that the transis- 
tors need their pins to be re-orientated so 
that they correspond with the notations on 
the stripboard layout. 


Connections _ be- 
tween the _l.e.d.s 
and the pushbutton 
switches of the stars 
are best made using 
rigid wire which, 
providing care in 
positioning it is 
observed, need not be 
insulated.. Connections 
back to the stripboard 
should then be made 
using stranded and 

insulated flexible wires. Details of the 
interwiring are shown in Fig. 3. 

Be sure to thoroughly check the com- 
pleted assemblies, looking out for missed 
track cuts, badly soldered joints and 
wrongly orientated components. 

When choosing the rubber balls, make 
sure that they are sufficiently firm to coun- 
teract the contact pressure of the pushbut- 
ton switches. Avoid balls which may be so 
hard as to damage the switches and 1.e.d.s. 


The circuit diagram for the optional 
“‘six-light’’ buzzer is shown in Fig. 4. The 
circuit is used to announce that all lights 

Fig. 4. Buzzer circuit for Star- Struck! 

Everyday with Practical Electronics, June 1995 

of one colour have been switched on. The 
circuit consists of two 8-input NAND 
gates, IC1 and IC2, one for each colour, 
both feeding to the same non-polarised 
piezo sounder, WD1. Six inputs of gate 
IC1 are connected to each of the collectors 
of the odd-numbered transistors, and six 
inputs of gate IC2 are connected to each 
of the collectors of the even-numbered 
transistors. The two spare inputs of each 
gate (pins 11 and 12) are connected to the 
+ 9V line. 

During the game, when neither contest- 
ant has gained all six l.e.d.s on, the out- 
put pins 13 of both NAND gates will be 
high and no current will flow through the 
buzzer WD1. As soon as one contestant 
gains all six l.e.d.s on, all eight inputs of the 
relevant gate will be high and current will 
flow through the buzzer into the still-low 
output of the other gate. Consequently, the 
buzzer will buzz! : 

Usually, when the buzzer sounds the 
display will immediately show which 
contestant’s colour dominates. In a fast 
moving game, though, it is possible that 
balls may continue to hit the switches 
immediately after the buzzer has sounded 
and it may be unclear as who really is the 
winner. To avoid potential aggravation 
between players, the circuit could be 
modified so that each gate is fitted with its 
own buzzer, each possibly having a 
different tone, or being mounted far 

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Fig. 5. Stripboard assembly details for the Star-Struck! buzzer circuit. 

enough apart so that direction will verify 
the winner’s identity. In this case one lead 
of each buzzer is connected to pin 13 of its 
relevant gate, and the other lead is taken 
to the +9V line. This technique may also 
be used if readers have difficulty locating 
non-polarised buzzers. 

Construction of the buzzer circuit was 
made on a piece of 0-linch pitch stripboard 
measuring 20 strips <x 15 holes. The as- 
sembly layout details for this board are 

shown in Fig. 5. Both circuits may, of 
course, be assembled on a single piece of 
stripboard. Be sure, though, to cut the 
tracks between the two circuits. 

It is preferable that sockets should be 
used for the two CMOS NAND gates, 
IC1 and IC2. The current consumption of 
the piezo sounder WD1 should not exceed 
10mA, the maximum output current 
available from the CMOS 4068 NAND 


Throwing light on the war-games count-down. 

HIS project is basically a_ light 

gun that can be used for games 

either having light-dependent resis- 
tors (I.d.r.s) as targets or that can be 
adapted for them. For instance, the 
Star-Struck! project previously described 
could be easily modified to use l.d.r.s 
instead of the pushbutton targets; 1.e. the 
targets would be “beamed” instead of 
“struck”. In this case, because of the 
spread of the light beam, it would be better 
to space out the |.d.r.s to make the game 
more skilful by having to re-aim. 

Other ideas for using this zapper are 
referred to later. The idea of aiming a light 
beam to fire at a target is particularly 
appealing as light rays travel in straight 
lines. However, there are a few fundamen- 
tal technical points to take into considera- 
tion to make the project worthwhile. 


The better the focus of the light beam, the 
greater the skill required to strike the target. 
If a diffused light beam is used to direct on to 
the target I.d.r. then the intensity may not 
be sufficient to activate whatever sensor is 

Everyday with Practical Electronics, June 1995 


used, e.g. to trigger the bistable in the Star- 
Struck! project. Also, as less skill is required 
the game will lose its appeal. A suitable lens 
is therefore essential to narrow the beam of 
light. The easiest way is probably to press 
into service an old spotlight torch, just using 
its bulb and lens holder. 


In the interests of skill, it is important 
that the trigger action is controlled. Using 
an ordinary torch as a light gun has other 
drawbacks as well as its diffused area of 
light. After switching on, it is all too easy 
to locate the target by using the beam to 
correct the angle — what might be called 
“spraying the target’. 

For this reason, when triggered the light 
gun should ideally give one flash for a 
fixed period independent of the length of 
time for which the trigger is pressed. The 
light gun described here gives a fixed 
flash of about 0-5 seconds, but the circuit 
parameters can be changed to suit in- 
dividual requirements. If you’re a John 
Wayne and quick on the trigger, then 
split-second timing is a must! | 

To make the game competitive all 

marksmen and markswomen need to have 

the same number of “shots in their 
lockers”, and to hold with tradition, this 
light gun has been designed as a six- 
shooter. It gives a visual indication of the 
number of shots fired and will not fire any 
more shots after the sixth, unless the 
Reload switch is pressed. 


Circuit diagram details for the Six-shot 
Light Zapper are shown in Fig.1. To obtain 
six, and only six pulses all of the same 
length when the light gun is fired, the 
circuit employs a 555 timer (IC1) in monos- 
table mode and a 4017 decade counter 
(IC2) limited to seven outputs. 

Referring to timer ICI, output pin 3, 
discharge pin 7 and threshold pin 6 are 
normally pulled low internally and timing 
capacitor Cl is held discharged. When the 
Fire pushbutton switch S2 is pressed, logic 
0 is applied from IC2 output pin 5 to IC] 
input pin 2, and as a result IC] output 


Fig. 1. Circuit diagram details for the Six-Shot Light Zapper. 

pin 3 is triggered high. The monostable is 
now in its unstable state. 

Capacitor C1 now starts to charge up via 
resistor Rl. When Cl has charged to ap- 
proximately two-thirds of the supply volt- 
age, IC] pin 6 and pin 7 are triggered 
low. This discharges C1 again and also sets 
IC1 output pin 3 to its low state. IC1 has 
now been returned to its stable state and is 
ready to receive the next trigger pulse. 

The stated values for capacitor Cl and 
resistor R1 give an output pulse length 

BC 109 




R1 100k 
R2 ~5k6 

R3,R6 10k (2 off) 

R4 120k TALK 
R5,R7 1k (2 off) age 

All 0.25W 5% carbon film. 

C1 4u7 axial elect. 10V 
C2 10n disc ceramic 

TR1 BC109 n.p.n. transistor 
D1 l.e.d. yellow 

3mm or 5mm 

D2 to D7 |.e.d. red 3mm or 5mm 
(6 off) 

IC1 555 timer 

IC2 4017BE decade 


$1,S2 s.p. push-make switch (2 off) 

S3 s.p.s.t. min. toggle switch 

Plastic box to suit torch used (see 
text), 6V torch assembly (see text); 
stripboard 0.1 inch pitch (11 strips x 
25 holes); 6V battery; connecting wire, 
solder, etc. 

Approx cost 
(COLUM el 

ot £6, 

excl torch and case 

of about 0.5 seconds. To reduce the pulse 
length, reduce the value of either, or both, 
of these components. 

Between them, capacitor C2 and resistors 
R2 and R4 shape the short initial trigger 



Fig. 2. Stripboard component layout, wiring and track cutting details for the Six- 

Shot Light Zapper. 

Everyday with Practical Electronics, June 1995 

/nterior detail of the assembled and cased Six-Shot Light Zapper. 

pulse required by IC2 when the Fire switch 
S2 is pressed. In this way, the flash has the 
same duration no matter how long S2 is 
held down. (The trigger pulse to IC] must 
be shorter than the output pulse timing.) 
Resistor R4 in parallel with C2 provides a 
discharge path across it, allowing S2 to be 
rapidly re-fired. 

This fixed-length output pulse from IC] 
pin 3 serves two purposes: via resistor RS it 
provides a “‘one-shot”’ base current to tran- 
sistor TR1, turning it on and so lighting 
lamp LP! for the duration of the pulse. 
Secondly, it triggers decade counter IC2 via 
its clock input pin 14. Each of the first 
seven outputs of IC2 is connected to a light 
emitting diode (l.e.d.), D1 to D7. 

Each time the Fire switch S2 is pressed, 
the resulting output pulse from ICI se- 
quentially triggers high the outputs of IC2 
in turn, causing the respective l.e.d. to be 
switched on. As each output goes high, 
the preceding one goes low. The display 
thus advances from D1 (Loaded position) 
through to D7 (Reload position). Resistor 
R7 limits the current through the l.e.d.s. 

The Reload |.e.d. D7 is turned on by the 
logic 1 on IC2 output pin 5 when trig- 
gered after the sixth shot. Simultaneously, 
switch S2 pin 1 is held at logic 1 by IC2 
pin 5 and so the switch cannot generate a 
negative-going pulse with which to trigger 
timer IC1. A further connection is taken 
from IC2 pin 5 to IC2 clock enable pin 13. 
The high logic on this pin now holds the 
counter inhibited and |.e.d. D7 stays on. 

Counter IC2 remains inhibited until the 
Reload switch S1 is pressed, an action 
which connects the +9V rail to IC2 reset 
pin.15, so resetting the counter to zero. The 
now-active ‘“‘zero” output on [C2 pin 3 
lights the “Loaded” |.e.d. D1 making the 

circuit ready for the next six shots. 


The circuit is built on a piece of 0-1 inch 
pitch stripboard which carries IC], [C2 
and their associated components. The 
layout of the two sides of the stripboard 
showing components, connections, track 
cuts and solder points. are shown in Fig.2. 
Normal precautions to protect the 1.c.s 
from static’ should be observed and d.i.l. 
sockets for them are recommended. The 
i.c.s themselves should’ be fitted last 
after the wiring and soldering has been 
thoroughly checked. 

With a little ingenuity, the light zapper 
could look like a futuristic space-gun com- 
plete with sights. In the prototype, as 
shown in the photograph, the bulb-holder 
and lens of a 6V torch were fitted to one 
end of. a small plastic case. The seven 
l.e.d.s were mounted in line on the front 
panel, together with the On/off and Reload 
switches, $3 and S1. The Fire switch S2 was 
mounted below the lens at the end of the 
box, in a convenient position for the trigger 

Although the photo shows the case to 
have a sloped front, in reality, any case 
shape or size will do provided it can have 
the torch assembly and small stripboard 
mounted in it. The layout of the front panel 
is not critical. The panel can be labelled 
with rub-down lettering and protected un- 
der a clear plastic cover. 

The quiescent current is only about 
10mA, but the bulb used will dictate the 
current consumed during the flash period. 
Suitable 6V mz.e.s. bulbs are readily 
available with a current consumption of 
only 40mA. The use of a lower voltage bulb 
is not recommended. The unit should be 
powered by a 6V battery, preferably a 
long-life type. It may be powered by a 9V 
battery if the bulb voltage rating is 
increased accordingly. 


As a suggestion for a game with the 
Six-Shot Light Zapper, a very simple target 
could be made by wiring-up just one of the 
“Star-Struck!”’ project’s bistable circuits 
(see its Fig.l), e.g. TRI, TR2 and as- 
sociated components. Each of the pushbut- 
ton switches S1 and S8 should be re- 
placed by a light dependent resistor (I.d.r.). 
The l.d.r.s can then be used as targets. 
To encourage re-aiming, these should be 
widely spaced either side of a tri-colour 

An interesting variation on this idea is to 
make individual ‘“‘zapper targets” that can 
be attached to a gaming participant like 
a badge. The Aim of the Game, so to 
speak, is for people in a team to get zapped! 
For instance, in subdued lighting the Light 
Zapper can be aimed by a member of one 
team at the red glows of six opponents, 
each wearing an l.e.d. and an 1.d.r., aiming 
to change the glows to green (or vice versa). 
There are endless possibilities, but a sug- 
gested circuit for another zapper target is 
given in Fig.3. 

This circuit is a further variation on the 
Star-Struck! bistable. Here switch SI] is 
replaced by an I.d.r. (R5), switch S2 is the 
same as S8 in the original circuit. Tri- 
colour l.e.d. D1 has its twin anodes (a) 

Fig. 3. Suggested circuit for a “Target 

Close-up details of the stripboard assembly of the Six-Shot Light Zapper. 

Everyday with Practical Electronics, June 1995 


en - 

@ [e) 









BC 109 

Fig. 4. Stripboard layout details for the “Target Badge” circuit. The inset shows a 

possible “Badge” layout. 

connected respectively to the collectors of 
transistors TR1 and TR2. As before, the 
common cathode (k) is grounded. 

To start the game, switch S2 is pressed to 
bring on the red l.e.d. within D1. When 
I.d.r. RS is “‘zapped” by a correctly aimed 
Light Zapper, the bistable changes output 
states, so switching off the red l.e.d. and 

switching on the green one. The starting 
and “‘zapping” colours can be changed by 
swapping over the two anode connections 
of D1. 

The suggested stripboard layout for the 
small circuit is shown in Fig.4. There are 
no track cuts required on this board. Be 
sure to observe the correct polarities of 

R1,R4 = 1k (2 off) 
-R2,R3 = 3k3 (2 off) 
R5 ORP12 
(or similar) 





D1 l.e.d. tri-colour 
TR2 BC109 (2 off) 

S.p.s.t. min. slide switch 
s.p. push-make switch 
Stripboard O-1in. pitch (7 strips x 16 
holes), rigid badge material (see text). 


led. D1 and transistors TRI and TR2. 
A suggested ‘Target Badge” layout and 
its wiring detail is shown in Fig. 4. The 
badge can be made from any rigid material 
sized to your choice. This sub-circuit can be 
powered by a 9V battery. 

Approx cost 
guidance only 


A simply wanderful way to keep the party colourful. 

ANDER WANDS can be used to 
“break the ice” at children’s 
parties. No, they are not pick-axes: 
they look like small white batons which 
arriving guests will be curious to find out 
what they are. They serve as a talking point 
and are something to hold in the hand, but 

in fact they are much more than that! 


Each Wander Wand comprises a length 
of plastic tubing which contains a bi-colour 
light emitting diode (l.e.d.) at one end, two 
small batteries, a reed switch, a current 
limiting resistor, and a permanent mag- 

net. The circuit diagram of the Wander | 

Wand tube is shown in Fig.1. Its equiv- 
alent schematic physical layout is shown in 

In Fig. 1, resistor R1 limits the current 
through the bi-colour l.e.d. D1. The stated 
value for Rl, 150 ohms, gives an l.e.d. 
current of about 20mA. When the magnet 

of another Wander Wand is held near reed 
switch S1, the switch contacts close and 
one of the two l.e.d.s within D1 is turned 
on. With the battery polarity connected as 


shown, current will flow through the red 

Turning the battery polarity round the 
other way will cause the current to flow 
through the green l.e.d. Alternatively, the 
l.e.d. polarity can be changed at the con- 
structional stage. When the l.e.d. is not 
energised, it is impossible to tell whether it 
is connected for a red or a green display. 


The plastic case for the Wander Wand 

Fig. 1. Circuit diagram for the Wander 

can vary in shape or size, largely depending 
on the type of batteries used. The author’s 
prototype, which was powered by two 
AAA-size batteries, was cut from a length 
of white, half-inch diameter plastic tubing 
of a type obtainable at most d.i.y. stores. 

As shown in Fig. 2, the batteries were 
held under tension from their negative end 
by a small spring soldered: to the point of a 
drawing pin pushed through a small slice of 
dowel. Similarly, dowelling and a drawing 
pin were also used for the positive battery 

The AAA-size batteries were a fairly 
tight fit in the tube, but there was sufficient 
space for a single length of enamelled 
copper wire to link the far end of the two 
batteries via resistor R1 to one side of the 
l.e.d. The point of the drawing pin, from 
the positive end of the batteries, was sol- 
dered to one terminal of the reed switch. 
The other reed. switch terminal was sol- 
dered to the other side of the l.e.d. 

The two legs of the l.e.d. were fed 
through two small holes drilled in another 
piece of dowel, which was a push-fit in the 
end of the tube. Finally, a small bar magnet 
was located in the other end and secured by 
a fourth piece of dowel. 

Everyday with Practical Electronics, June 1995 



i gaat 

1 ‘ 

carbon film TALK 


D1 __i.e.d. bi-colour (red/green) 

S1 reed switch 
Battery, AAA-size (2 off); plastic tube 
(see text); dowelling; small spring; 
drawing pin (2 off); small bar magnet; 

connecting wire; solder etc. 

excl. batteries 


There are countless ways in which the 
Wander Wands can be used. Here are some 
of the more obvious ones: 

On arrival, guests can be armed with a 
wand and first of all establish to which 

Approx cost 

guidance only 

Max Fidling 

Plumb Crazy 

Being a bit of a do-it-yourselfer, there’s 
not much in the Fidling household which 
has escaped the attention of my handyman 
activities. Not content with my multi-pur- 
pose screwdriver set which has seen me 

through many a scrape, I recently added - 

a set of pliers and wire cutters which I 
spotted on a market stall. 

I think it was possibly the colour of the 
hot-dipped plastic handles which most 
attracted me to them, since I like to colour 
co-ordinate everything like the profes- 
sionals do, and generally impress my 
friends. If they do actually “‘ply” or cut 
wire, then that’s a bit of a bonus as far as 
I’m concerned! As I was to discover, much 
to my dismay, they neither plied nor cut... 
I’d hoped for much better at £1.49 the pair. 

One spring morning I happened to be 
ferreting around in the attic, in the general 
vicinity of the cold water tank. Strange 
rusty-looking ring-like patterns had started 
to appear in the freshly applied white emul- 
sion of the ceiling down below, and I had 
been summoned to investigate. If I hadn’t 
recently painted the ceiling, I pondered, it 
would probably not have happened, and 
obviously my five litres of vinyl silk had 
tempted fate too far. 

The attic is the one place I know where 
Piddles won’t enter (pity, because we have 
a mouse or two and so the moggie could do 
some good for a change) so he was sat 
at the bottom of the step ladder peering 
up into the loft entrance and waiting for 
events to unfurl. 

Staring through the gloom using my 
faltering plastic torch, I soon saw the 
problem — the water tank’s level had risen 
too far and so it had started to drain 
through the overflow pipe. This pipe had 

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team colour they belong: touch the l.e.d. 
(reed switch) end of one wand against the 
magnet end of another wand and it will 
glow either red or green, as appropriate. 

Wands can also be used as batons in team > 

games and relay races, e.g. a baton must 
first be made to glow before the next team 
member can proceed. 

Charts or lists of questions placed 
around the room are useful as party 
starters, e.g. magazine clippings of famous 
personalities to identify, adverts to recog- 
nise, etc. These can have a magnet secreted 
somewhere behind them: point to the right 
answer and the wand will glow to score a 
point for that team colour. 

A quiz board could even have its own 

recently been refitted by yours truly after I 
thought I would try my hand at plumbing. 
No problem except that sadly, the overflow 
itself had, er, a slight gap where I’d joined it 
-to another pipe, and so water was dribbling 
out and ruining the ceiling below! 

Back at the workshop, I started thumb- 
ing through my comprehensive library of 
ancient electronics magazines, looking for 
inspiration. I had in mind a water level 
alarm or moisture detector which could 
warn me when the water tank level was 
getting too high. 

Not the most earth-shattering applica- 
tion of electronics, but one which even 
I should be able to implement without 
doing too much damage! Anyway, having 
repaired the paintwork I was still in “hot 
water” with the Boss so I needed to make a 
few smart moves, so eventually I designed a 
simple unit which was a conglomeration of 
several published designs. 

A foot too far 

I'd pressed a 555 timer chip into service, 
since I always had these littered around the 
place. Using an old telephone earpiece as a 
loudspeaker, an audio oscillator was soon 
soldered together on some stripboard, run- 
ning from some old pen-cell batteries. Add 
a transistor switch and two old wire coat 
hangers with a terminal block, and voila! 

When the two coat hangers were dipped 
into water, a mechanical hum emanated 
from the earpiece, not dissimilar to a 
G.P.O. dialling tone, actually. It wasn’t 
quite loud enough, so I adopted plan B 
which was to jack up the supply voltage 
until either something blew up or threshold 
of pain sound level was reached, whichever 
came first... 

Everyday with Practical Electronics, June 1995 

Fig. 2. How the Wander Wand components are assembled inside the tube. 

_ Wands will come to mind once several have 


indicator display, using the same circuit as 
shown in Fig. 1. In this case, the magnet 
end of the wand would be used to activate 
the reed switch, or switches if several cir- 
cuits are used. 

A firm favourite at parties is searching 
for treasure on a large map. Small mag- 
nets can be secreted behind the map at 
strategic places. Copies of the treasure map 
can be distributed with clues to help players 
search out and sense these hidden magnets. 
An adult can keep a tally of the number 
of green or red wands activated when the 
treasure is located. 

No doubt other games with Wander 


been built. 

Piddles accompanied me back to the step 
ladder and I clambered up into the at- 
tic, carrying my latest brainchild, with its 
battery hanging loosely on the end of a 
PP3 clip. I perched precariously astride two 
rafters, and started to beaver away happily, 
humming a tune. Unfortunately, the wire 
coat hanger “‘probes”’ proved too long and 
so I needed to bend them to shape and 
shorten them to just-above-water level. 

Looking in my toolbox, my eyes lighted 
on my new chromium-plated Pliers & Wire 
Cutter Set (Qty. # 2 pcs.”’, as it said on the 
pack) so now would be the acid test. Grab- 
bing the wire cutters, I set about the wire 
coat hangers gleefully, with all the skill of 
an electronics hobbyist who’s also not very 
good at plumbing. 

Much to my dismay, the quality of 
the old wire coat hangers seemed to ex- 
cel that of the wire cutters, as one jaw 
pinged off, ricocheted off the wooden roof 
beams and plopped into the water tank! 
This rather caught me by surprise and I 
pirouetted deftly before temporarily losing 
my balance — worse was yet to come as I 
accidentally raised one foot and shoved it 
straight through the newly re-painted ceil- 
ing below! Now I really was in deep water! 
Typically, through the gaping hole I could 
see a certain cat peering up at me, tail 
swishing and looking not at all surprised. 


re ae aged 

Special Report 



What they are, how they work, where they are going, are they 
secure? Before long most of us will be using Smart Cards of one type 
or another, in this feature Barry looks at the present and future 
Smart Card scene paying particular attention to security. 

HE Smart Card or cashless society is coming. Westminster 

Bank is testing Mondex, a system that replaces traditional 
magnetic stripe credit cards with an electronic purse that looks 
like a stripe card but incorporates a microprocessor chip and 
memory to store and process cash data. 

Shell petrol stations have stopped giving drivers paper 
tokens for Air Miles (without telling us how to convert them 
into travel) and giving us smart cards which store 
electronic Air Miles (unfortunately still without telling us what 
exactly to do with them). The government’s plans for health 
and idendity cards all rely on smart card technology. 

Smart Move 

British Telecom will soon start converting all its payphones 
from optical to smart card working. This is a massive com- 
mitment. BT introduced the optical phonecard in 1981 and 
now has a network of 35,000 card phones. “We have taken 
the technology as far as we can go’, says Les King of BT. 
‘Moving to smart card technology gives us freedom for future 

All existing optical card phones will be replaced with smart 
card readers and new payphones will be designed to read 
smart cards as well as credit cards. The cards will not be 
rechargeable and BT has “no plans yet” to collect old cards 
and recycle them. 

The new phone cards will cost customers the same as ex- 
isting cards even though it is far more expensive to produce 
smart cards than optical cards. But the volume in which BT 
will buy smart cards (from Gemplus and GPT) to sell through 
50,000 retail outlets across the UK, will drive the manufactur- 
ing costs down to similar levels. 

Magnetic cards will not disappear overnight, but they are 
likely to be used only where the data is secured by a mag- 
netic watermark or vetted by online checking every time the 
card is used. For added security the two technologies may be 

All this paves the way for a cashless society, where electronic 
credits are transferred instead of cash. Because smart cards 
have a far greater memory capacity than magnetic cards, an 
“electronic purse” can double as an identity card. Inevitably 
there will be objections from those who see it as an intrusion 
into personal liberty and privacy. Criminals will see it as an 
opportunity to earn even more from fraud. For hackers the 
smart card society represents a new challenge. 

To, get a handle on the debate, it pays to understand the 
technologies involved. 

The use of plastic cards as a replacement for cash dates back 
to the early 50s when the Diners’ Club and American Express 
Company in the US started to issue members with cards which 
vouched for their creditworthiness. European banks started 


issuing cards in the 60s, with Barclaycard and Visa from 
Barclays, and Access from Lloyds, National Westminster and 
the Midland banks. 

The banks then started installing ATMs (automatic teller 
machines), popularly known as “‘hole-in-the-wall” cash dis- 
pensers. This followed a technical specification set by ISO the 
International Organisation for Standardisation (this is correct 
full name, not International Standards Organisation). The 
ISO 7810 series of standards ensure that any card with a 
magnetic stripe can physically be read by any check-out till or 
ATM, anywhere in the world. 


The banks have traditionally refused to discuss any aspect 
of security, on the grounds that it helps criminals. But with 
even the bankers’ own trade body, the Association for Pay- 
ment Clearing Services (APACS), generating publicity for the 
wildfire spread of card fraud, it is clear that criminals already 
know all they need to know about card technology. Prisoners 
in jail pass on the secrets, and at least one DIY manual on card 
fraud has been circulated. The banks are now reluctant to dis- 
cuss security because they do not want to trigger a rush of 
claims from customers who say they have lost money through 
technology loopholes. 

The stripe on a magnetic card is divided into three parallel 
tracks, like a three channel stereo sound recording. Tracks one 
and two contain data, written or pre-recorded on the card 
prior to issue. The data on track one is more tightly packed (at 
210 bits/inch) than the data on track two (at 75 bits/inch). 
Track three stores data at the same density as track 1, but 

At the Mondex Centre in S windon s shopping centre, 
cardholders can transfer funds from their bank account 
directly “into” their Mondex card using special BT phones. 

Everyday with Practical Electronics, June 1995 

allows the card reader to record data on the card as well as 
read it. 

The banks use mainly track two, which is in the centre of the 
stripe. Track three is used to carry a number which checks 
against the personal identification number or PIN, which only 
the legitimate owner of the card should know. Critics of bank 
security argue that up until two years ago, it was possible 
for anyone with expert knowledge, for instance an ex-bank 
employee, to decode the PIN from a stolen card (much as it is 
possible to decode a driver’s sex and birth date from the 
innocent-looking number a the top of their driving licence) 
and then use the PIN IT to draw cash from an ATM. 

The banks’ formal line is that this is, and always has been, 
impossible, and that there has never been sufficient code on a 
card to allow extraction of the full PIN. The banks claim that 
the PIN can only be derived from data which is securely stored 
by the bank. 

Although some members of staff will have access to PIN 
data, the banks’ policy is to restrict the number of staff with 
access to a carefully selected few. The source of any breach of 
security can immediately be narrowed to a very small group of 
employees. The theory then is that this group will work to- 
gether to identify any one of their members who has stolen 

But critics say that service engineers working with ATMs, 
and system progammers working on the bank’s computers, 
may have access to PIN data. 

Skirn KHlead 

Because all magnetic cards follow the ISO standard, anyone 
can easily obtain blanks. They are given away by Super- 
markets and Petrol Stations, for customer loyalty schemes. 
Any data on the card is just wiped off with an ordinary 
magnet. Criminals can then buy the card readers and writers 
which are sold for legitimate business use. 

It is not even necessary to know how to decode a PIN from 
supposedly secret data. An expert witness in a recent card 
fraud case told a Court in Suffolk how he had personally 
manufactured a card, using data obtained from a discarded 
ATM transaction slip and a PIN observed over the card 
owner’s shoulders. 

Although many ATMs have now stopped printing out card 
details, fraudsters have in the past used binoculars to col- 
lect PINs, and then matched them by time of transaction to 
discarded slips. More recently criminals have stolen PINs 
at mock auctions, by persuading cardholders to swipe them 
through a reader, and enter their PINs into a keypad with 
hidden memory. 

There are also several ways to transfer owner identification 
data from a borrowed or stolen card to a blank. If two mag- 
netic tapes are sandwiched together and pressed with a hot 
iron, the magnetic pattern on one will transfer to the other. But 
the more elegant solution is to use a device called a “skimmer” 
which any electronics enthusiast can build from standard com- 
ponents, costing only a few pounds. 

A skimmer has two magnetic heads, like those in a tape 
recorder. One head can read the magnetic field from a card 
and the other can generate a magnetic field and so write to a 
card. The two heads are connected together by an amplifier. 

Two cards, one original and one blank, are laid side-by-side 
on the surface of the skimmer and then by hand moved as a 
pair over the two heads. As the read head picks up data from 
the original card, the record head writes it to the blank card. 
Skimming a card takes literally seconds, and produces a per- 
fect copy of the original. 

Audit Trail 

There is no need for today’s cards to be so insecure. The ISO 
standard allows for the reader to write to the third track and 
_ So record a code which identifies the last ATM at which the 
card was used. When the card is next used, this code is read by 
the ATM before a new code is written. This gives the bank 
the chance to build an audit trail of where a card has been 
used and should thus let the bank know immediately whether 
disputed transactions have been made by a customer’s own 

Everyday with Practical Electronics, June 1995 

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card, or a skimmed copy. 

The banks have been cagey about discussing this valuable 
security check. One explanation could be that the audit trail 
will in some cases prove that the bank’s security has been 

- breached; another is that some banks have been slow to invest 

in the system modifications needed to exploit the track three 
write option. 

Although Mercury uses magnetic cards for its payphones, a 
clever system of on-line checking stops people playing the ob- 
vious trick and using a skimmer to add new units to an expired 
card. When the caller puts a card in a Mercury payphone, 
the system checks its previous usage with an on-line database, 
and rejects any card that has mysteriously increased in value 
instead of decreasing. A similar system could, if the banks 
wished to implement it, sound an alarm as soon as anyone 
tried to use a stolen card inan ATM. : 

Hot Nurnber | 

Although the banks have now tried to make cards more 
secure by embossing a hologram patch in the surface, en- 
terprising criminals have now found a way round this trick 
too. They collect stolen cards and use- heat or solvents to 
flatten out the embossed details of the legitimate owner. Then 
they use an embossing tool to imprint details of a new owner. 
These details are readily available from credit card transaction 
slip copies and carbons which owners discard or which res- 
taurants,and shops throw in their dustbins. 

Criminals without their own embossing tools can now 
simply telephone orders to the new wave of copy shops in the 
Far East which make cards to order. The legitimate card 
owner only finds out that their card has been copied when they 
get their next bill. | 

These cards need not even have valid magnetic data in their 
stripes. The magnetic stripe on legitimate cards often wears, or 
becomes de-magnetized, so staff in shops and restaurants are 
not surprised to find that some customers’ cards refuse to work 
in a reader. Even if they phone for approval, the embossed 
details on the card will be correct so the transaction will be 

In the early 90s APACS had found that 75 per cent of all 
card fraud was taking place at the point of sale. Criminals do 
not waste time buying groceries, or cinema tickets, with stolen 
cards, they use them to buy VCRs, camcorders and computers 
which can quickly be re-sold for cash. 

One trick is to swipe a stolen card through a credit card 
payphone and see if it is accepted. If it is, then the card is not 
yet registered as “hot” and can safely be used in a shop. A new 
variation on this trick is for people who run shady premium 
service phone lines (like sex lines) to run up bills on stolen 
cards by dialing the service and leave the phone off the hook. 
BT then has to pay the service a percentage of the charged 

The pocket size Mondex card reader. 

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Cardowners are often their own worst enemies. When 
choosing a PIN, people take a simple number, like a birthdate, 
to make it easier to remember. The first thing a thief with a 
stolen wallet does is look for a note of the owners’s birthday 
and try it with any credit cards. Some cardholders choose a 
long number but then, because they cannot remember it, write 
it on a piece of paper in the same wallet, or even the back of 
the card. 

Two years ago, at a conference organised by trade body the 
Radio, Electrical and Television Retailers Association, John 
Carnegie-Brown, of Barclays Merchant Services, told dealers 
‘The cost of putting photographs on cards is greater than the 
fraud it eliminates. We do not feel we can cope with it at this 
time”. But TSB and The Royal Bank of Scotland think it is 
worthwhile and have now been using photo-cards. 

Biometric Technique 
The major banks are more interested in biometric tech- 

niques. The card stores a template which it checks against the 

carrier. In its simplest form this template can be a passport 
photograph, which is checked against a video image shot at 
the checkpoint. 

Every human eye has a characteristic pattern of blood ves- 
sels in the retina. The card can store a map of this pattern 
which is checked by asking the cardholder to peer into the 
lens on a video camera at the check point. Although suitable 
for the military, eye checks at the Supermarket would not be 

The card can also store a voice print, which logs the fre- 
quency content of the holder’s speech. But this is unreliable. A 
common cold changes the human voice drastically. 

Electronically sensing signatures is more attractive, and the. 

new generation of Personal Digital Assitants, like Apple’s 
Newton, are already designed to convert handwriting into 
electronic signals. But signatures vary, not just from day to 
day but from hour to hour. Rolls Royce and the British 
Technology Group have separately worked out their own 
ways of tracking these changes, but even the cleverest technol- 
ogy cannot cope when shoppers have to sign on a crowded 
counter at an awkward angle. 

Surprisingly the best bet may prove to be the most secure 
identification system of all, finger printing. At the point of sale, 
cardholders put their fingers on a pad, which optically scans 
the tips of the fingers with a laser, similar to the scanners now 
widely used to read bar codes on Supermarket goods. 

Low key market research by the banks suggests that only 
around two per cent of cardholders have strong objections, 
preferring finger printing to loss of money through fraud. But 
the few people who do object, do so vehemently. They also 
object to the idea of being photographed, or having their sig- 
natures electronically recorded. So no bank will dare make 
biometric identification mandatory. Also, manual workers of- 
ten have unreadable fingerprints. 

Two airports in New York, Newark and JFK, are now test- 
ing a hand geometry system. The card stores a map of the 
holder’s hand size and shape, and compares this with a reading 
taken at the check point. 


Magnetic cards cannot store enough data to encode a signa- 

ture, or fingerprint, or any other biometric data. Standard 
memory capacity is only around 200 characters, spread over 
the three tracks. There are two solutions, Smart Cards with 
built-in computer chip memories and Optical Cards which 
store data like a stationary compact disc. 

The Drexler Corporation of California leads in optical card 

technology. The card writer houses a laser which burns lines of 
five micrometre pits into a thin metal coating on the card. 
These pits are then read by a lower powered laser which scans 
the surface, sensing the changes in reflection caused by the pits. 

Precision mechanics move the card backwards and forwards 
under the laser optics. The optics must step sideways across 
the card in increments of around 10 micrometres to create a 
horizontal grid of several thousand parallel tracks across the 
card width. Together these tracks can hold up to six megabytes 


PE a IT TE I ee OT, ETS a Oe erg Em } 

of data in digital code, equivalent to four high density com- 
puter floppy discs. 

The optical card is relative cheap (under $5 in bulk). It is 
secure in that data cannot be altered or copied or read. But if 
the card surface is scuffed it may become unreadable. And the 
reader must be expensive, costing several hundred dollars. 

British Telecom has been testing Drexler cards as a means of 
storing medical records for expectant mothers attending the 
West London and Chelsea and Westminster Hospitals in Lon- 
don. US Government agencies are now using optical megabyte 
cards for storing sensitive information. 

French Innovatron 

The favourite technology for the future, however, remains 
the Smart or IC (integrated circuit) card which was invented 
and patented by French journalist Roland Moreno and his 
company Innovatron, in the early 70s. Innovatron then 
licensed Bull, Schlumberger and Philips to develop working 
cards. The difficulty of building a microprocessor and solid 
state memory into a credit card which is only 0-76mm thick 
and is sufficiently flexible to be sat on, should not be 

The French government has backed smart card technology, 
seeing it as a national asset and means of modernising the 
country’s telephone and banking systems. Since 1992 all bank 
cards in France have been smart. The ISO 7816 series of stan- 
dards ensures compatibility between cards and readers. 

The very latest card reader terminal from the in ventors of 
Smart Cards, Innovatron of Paris, France. 

Cost is kept down because not all cards are stats smart. 
The standard card contains an 8-bit microprocessor, and then 
a wide range of memory options. This has let designers launch 
new systems with cards which use the bare essentials of 
memory and intelligence, then use more intelligence and 
memory as the system demands it. 

This is what has happened with satellite broadcaster BSkyB. 
The scrambling system for the movie channels. uses a smart 
card to authorise decoding, Each new issue of cards has been 
progressively smarter, and more expensive, as hackers have 
discovered new ways of breaching the security of the entry 
level system. 

Memory capacity ranges from 1 to 64 kilobytes, in a mix of 
ROM (Read Only Memory) and EPROM (Electrically Pro- 
grammable Read Only Memory) which is pre-programmed to 
store the control codes for the microprocessor, RAM (Ran- 
dom Access Memory) which acts as a temporary buffer when 
the card is powered by a reader and EEPROM (Electrically 
Erasable Programmable Read Only Memory) which stores 
data written into the card by the reader, without the need for 
battery back-up. 

Smart IC cards fall into two broad types: thiode with a 
cluster of electrical contacts which make direct connection 
with mating contacts in the reader, and contactless cards 
which rely on wireless communication. 

Contact cards are cheap, now costing a dollar or so each in 
bulk, with the reader hardware costing only a few dollars 

Everyday with Practical Electronics, June 1995 

more. Contact cards are only suitable for use where the card 
remains in the reader most of the time e.g. in a satellite 
decoder, and there is no risk of the contacts getting too dirty 
for the contacts in the reader to wipe clean. 

Where cards are intended to be carried by the owner, 
dropped in the mud, and used in a variety of readers to pay for 
goods or services, they must work without contacts. The 
connection is then made by radio link. The reader emits a 
signal which the card converts into power and uses to transmit 
data back tothe reader. 

Travel Cards 

The power and frequency of the reader’s signal determine 
the range of operation. For some applications, short range 
connection is essential, for instance to prevent one passenger’s 
travel card paying for another passenger’s journey. British 
company GEC is making the contactless cards which London 
Transport is now trialling on buses working in Harrow, North 
London. The same technology is used in Manchester. 

The Harrow test involves contactless cards on nineteen bus 
routes. London Transport has equipped 200 vehicles with 
smart card readers and around 25,000 passengers are now 
regularly using cards to pay for journeys. The cards work like 
ordinary travel cards, but store time information to give free 
travel for a week or a month. When passengers get on a bus 
they wipe the card over a reader. If the time has expired, a light 
warns the driver. | 

If the trials are successful LT plans to extend the system 
throughout London’s bus network, and use the same cards to 
pay for station car parking and buy from vending machines. 

Although middle-aged passengers still fumble, school- | 

children no longer bother even to take the cards out of their 
pockets. They just brush their jacket pocket against the reader. 

LT has had to delay the second phase of its trial, which 
expands the scheme to stored-value fare cards. These will work 
like an electronic purse, storing £10 worth of travel units which 
the reader sucks out in return for a ticket. Around 200 shops in 
Harrow already have the equipment needed to re-charge cards 
in return for cash. | 

LT blames “mundane” reasons for the delay. The first cards 
were not strong enough. Whereas people treat their credit 
cards carefully, they put travel tickets in a back pocket and sit 
on them. Also bus gearboxes often vibrate when waiting at a 
bus stop. This has been fooling the reader. When this happens 
the travel cards can be be checked visually, like ordinary cards. 
But the purse cards only work electronically. 

Similar trials are underway in Bolton. If successful the 
Greater Manchester Transport Executive will extend the 
scheme county-wide to buses, trains and trams, with pas- 
sengers able to use the same cards to buy goods. 

Some 2500 people are now using smart cards on 120 of 

Bolton’s buses. The Greater Manchester Passenger Transport 

Authority plans to extend the scheme across the whole county, 
over the next three years. The GMPTA cards already work as 
electronic purses, storing a number of flat rate concessionary 
fare payments. Each time a passenger uses a card the reader 
sucks out another 30p. Cardholders can then go to re-chargers 
installed at Supermarkets, Schools and Bolton Town Hall to 
pay cash for an electronic top-up. 

“The main complaint’, say the organisers “is from people 
who get on buses which do not yet have a card reader”’. 

The long-term plan is to encourage local shopkeepers, and 
sandwich bars, to install readers and so let cardholders pay for 
goods with their travel cards. 

Call for SIM 

The new digital cellphones now available for Mercury’s 
One-to-One and Hutchison’s Orange networks (and on 
Cellnet and Vodafone’s new GSM services) rely on similar (but 
sometimes cut-down) cards called Subscriber Identification 
Modules. Without a SIM, the cellphone cannot be used to 
make or receive calls. Once the SIM is plugged in, the phone 
springs to life, making calls which are billed to the 
SIM-owner’s account. 

The card also stores a library list of the telephone numbers 
which the subscriber most frequently calls. If an Orange sub- 

Everyday with Practical Electronics, June 1995 


On entering the bus, passengers wipe their “contactless” 
card across the reader and the driver verifies a valid card. 
scriber gives Hutchison a written list of numbers, an operator 
will key them into a transmitter which sends them to the phone 
where they are stored in the SIM. When the SIM is plugged 
into another cellphone it can immediately read the library list 
of numbers, make calls on the SIM-owner’s account and 
receive calls dialled to the SIM-owner’s number. If a cellphone 
goes wrong, the owner just slots the SIM in a replacement, 
which behaves just as if it were the original. 


French payphones use smartcards, 70 million of them a year, 
even though telephone services in most other countries cut 
overheads by using cheap magnetic or holographic cards from 
which credits are erased or burned away by the payphone 
reader. . 

Most French salaries are paid by the month into a bank. So 
virtually everyone has a bank account. In France all cards are 
debit cards, and the Groupe Cartes Banqueres (comparable to 
the Association for Payment Clearing Services in the UK) rep- 
resents all the banks which issue the cards, and runs a scheme 
whereby each bank honours: every other banks cards for all 
transactions. Any French national using a bank card must 
now use a smart card. This has cut fraud inside France to 
almost non-existent levels. 

The GCB estimates are that at least half this fraud occurred 
because the electronic point of sale, EPOS, equipment worked 
“off line”. It collected information on all transactions during 
the day and sent it to the bank for processing at night. 

All 21 million bank cards in France are now smart. Direct 
‘on line” connections with the banks let the EPOS terminals © 
check a smartcard’s validity, against a personal identification 
number or PIN entered by the customer, in under two seconds. 
If the PIN does not match the card, the reader displays a mes- 
sage to the shop staff, telling them to pick up and keep the | 
card. Soon the readers will be able to send a signal into a 
suspect card to make it useless. 

The only fraud on French cards now is abroad, where 
people travel to other countries where there are no smart card 
readers, and use the cards like conventional credit cards. This 

is possible because French smart cards also have magnetic 

stripes like ordinary credit cards. 

Smart World 

AT and T, Bull, Hitachi, Mitsubishi, Motorola, Philips, 
Schlumberger, Siemens and Thomson now all make smartcard 
chips and cards. Most countries are running tests to find out 
what else the technology can do, and how reliable they are. | 

A test in Helsinki lets travellers use the same smart card to 
pay for bus or taxi travel. Dublin Bus is testing contact cards 
as part of a research project funded by the European Com- 
mission. The same card can be used in Irish car parks and 

The Japanese Government is storing the medical records of 
300 mothers and young children on smart cards, in Awaji Is- 
land, Hyogo Prefecture. The British Department of Health is 
compare different card types for storing patients’ medical 

etails. : 

In the US President Clinton’s plans for health care and the 
electronic delivery of benefits to replace food stamp coupons 
has excited companies which smell the market potential. The 


State of Wyoming looks likely to be the first to experiment 
with smart card health records. Hughes Aircraft will soon 
start transmitting digitally coded TV entertainment, direct into 
North American homes by satellite. Viewers will need a smart 
card to decode the signal. 

In the UK, Wessex Water has been testing smart cards in the 
city of Bath. The householder has a Water Card and charges 
it with cash credits at a local shop or water company office. 
When the card is slotted into a household meter, it opens the 
valve to pass water to the value of the credits. The intelligence 
of the card lets it run up a small debt if the credits run out over 
a Bank Holiday weekend. When the householder next pays to 
top up the card the debt is settled at the same time. 

British Gas has developed a similar system, called Quan- 
tum, for charging its customers for gas. The householder slots 
a card into the Quantum meter to load it with credits and 
pass gas. At the same time the meter loads information about 
the householder’s gas use into the card. When the cardholder 
takes it to a retailer, a card reader displays an estimate of how 
much it will cost to charge up the card for another month 
of similar use. At the same time the reader can relay a mes- 

sage from the meter which warns the retailer if the meter has. 

been tampered with. The meter also sucks enough extra credits 
from the card to pay the quarterly standing charge. 

At least fifteen countries around the world, including 
Denmark, Switzerland and Taiwan are planning or testing 
electronic purse systems which rely on the extra storage 
capacity and intelligence of a smart card to control cash 
debits and credits. Britain’s National Westminster Bank has 
proposed the most ambitious scheme of all, Mondex. 

Ambitious Mondex 

‘Mondex will allow two cardholders to exchange cash units 
directly, without clearance through a central control system, 
just as if they were five pound notes. As one purse at a shop 
check-out gains credits, another, from a customer’s wallet, 
loses them. The cardholder can then fill up the card again by 
slotting it into an automatic teller machine which delivers 
electronic credits instead of cash, while debiting the holder’s 
bank account. The credits can also be sucked into the card 
down a telephone line by calling the bank. Or the credits can 
be sent down the line into someone else’s card. 

Because the Mondex card stores cash credits, anyone can 
use it to make a purchase from any shop which has a Mondex 
reader. So losing the card is the same as losing cash. Security 
comes with an electronic wallet, like a pocket organiser, which 
locks the card’s memory with a PIN. 

The Mondex ecard will be loaded with credits at an ATM or 
by connection to a phone line. So Mondex immediately be- 
comes a target for criminals who will want to get money out of 
a card without it losing value, or get money into a card with- 
out debiting an account, or make copies of cards to spend the 
same money several times over. Westminster’s security experts 
are confident that Mondex will resist these attacks. 


Liberty, formerly the National Council for Civil Liberties, 
has so far lobbied successfully against the Government’s plans 
to use smart cards as a weapon against football hooliganism. 
The idea, which came from Margaret Thatcher while she was 
Prime Minister, was for football grounds to install turnstiles 
that opened only when a spectator waved a valid smart card. 
The card would store identity details along with any black 
mark for bad behaviour. 
_ The organisation was particularly worried because the 
cards would have to be contactless, to work reliably in all 
weathers, and after dropping into the mud. So a powerful 
reader could have secretly interrogated a card while still in 
the owner’s pocket. Although Liberty’s policies and position 
come across as rather muddled, the organisation does have a 
loud voice. 1 

Says Atiya Lockwood, of Liberty, ““We don’t mind cards for 
specific uses. But we don’t want to see too much information 
stored on one card, because then it becomes an identity card. 
You may be quite happy for a doctor to get details of your 
medication or allergies from a card, but you would not want 
your doctor to be able to read about your criminal record from 
the same card.” 

Watermark | 
Thorn EMI’s Central Research Laboratories has been 
watching the collapse of confidence in magnetic card 
technology, and the trend to smart cards, with special 
interest. It is now 25 years since CRL developed a method of 
watermarking magnetic tape. The original intention was to 
distinguish between original and pirate music recordings, but 
the record industry was not interested. In 1978 Swedish 
banks started using the system to distinguish between 
genuine and copy magnetic bank cards. Since 1980, every 
banking transaction in Sweden has been unambigiously tied 
to the card used for that transaction. But outside Sweden 

no-one was interested. 

‘The idea was too early for its time’, says Hugh Tarrant, 
Managing Director of Thorn Secure Science International, a 
new company formed in Swindon to make watermarked tape 
which card makers bond to ISO cards. 

Tarrant has watched the explosion of fraud on all types 
of magnetic card change attitudes. In 1986 South Korea 
adopted watermarking to stop an explosion of fraud when 
people found out how to clone telephone cards. The same 
system is used in Australia to control poker gaming by phone 
line and by the House of Commons, Windsor Castle and the 
Ministry of Defence to control access to secure areas. The 

- door locks are triggered by magnetic cards that look for the 

watermark and reject any counterfeit copy. TSSI now sells 
enough tape for a thousand million bank, phone and identity 
cards each year. 

In addition to the standard three ISO tracks. watermarked 
magnetic cards have an extra track, numbered zero, nearest 
the edge of the card. So a watermarked card is recognisable by 
its wider than usual magnetic stripe. 

TSSI reveals that at least one major bank tried and rejected 
the system ten years ago, even though the price of watermark- 
ing is only around 10 US cents per card. Card fraud was then 
still a rarity. 

The National Westminster and Barclays banks have since 
last October been quietly running consumer tests in Nor- 
thampton, with Visa International, now the largest consumer 
payment system. The two banks have each issued 15,000 
watermarked cards and a Safeway store and 12 ATMs have 
been equipped with readers which can trap anyone attempting 
to use a copy card. 

Hugh Tarrant has an interesting view of the future. He 
acknowledges that magnetic cards can never have enough 
memory capacity to serve as electronic purses. But he also 
believes that smart card technology will prove a lot less secure 
than some of its proponents promise. 

“But a system that combines both watermarked magnetic 
stripe and an embedded chip, would give a mix of analogue, 
chemical and digital technology.” says Tarrant. ““Now that 
would be the most secure system of all’’. L 

Everyday with Practical Electronics, June 1995 

Pico Re 

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. 

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purpose test instrument either in the 
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Everyday with Practical Electronics, June 1995 

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We can supply back issues of EPE by post, most issues from the past five years are available. An index for each year 
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. 


nightlight) e@ Timer and NiCad Capacity 

Autolight cnuronnatec 
Checker @ 250W/600W Inverter and 
Uninterruptable Power Supply, Part 2 e 
Multi-Purpose Audio System, Part 4 e Pond 
Heater Thermostat. 

FEATURES e Safety First, Part 2 e Calcula- 
tion Corner, Part 1 @ Electronics Testing and 
Fault Diagnosis, Course Review. 

PROJECTS e Whistle Controlled Light 

Switch e Reviving the Valve Sound 
(rebuilding the Quad II power amp) e 
Introduction to Microcontrollers — Timeout e 

Battery To Mains Inverter and Uninterruptable 

Power Supply, Part 3 e Multi-Purpose Audio 
System, Part 5. 

FEATURES e Calculation Corner, Part 2 e 
Safety First, Part 3 @ European International 
Audio & Video Fair. 

Immobiliser e 

PROJ ECTS e Smart-Key 
Audio/R.F. Monitor e CCD TV Camera, Part 1 
e Visual Doorbell e Three- Phase Generator. 
FEATURES e Safety First, Part 4 e Calcula- 
tion Corner, Part 3 e Free Wall Chart — Elec- 
tronics Formulae 1. 

PROJECTS e MOSFET Variable 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 @ ‘Simple TENS nis 
(transcutaneous pain relief) Py 
Capacitance/Inductance Meter e L.E.D. Matrix 
Message Display, Part 1 e Stereo Noise Gate @ 
Dual Stepping Motor Driver for PCs. 
FEATURES e Calculation Corner, Part 5 e 
Best of British, Part 2. 

PROJECTS e Microcontroller P.!. 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 @ Cal- 
culation Corner, Part 6. 

PROJECTS « e Voxbox Voice Recording 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. 


eerie e Experimental 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 
Shik elle COMIN URES CE, 

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). 

PROJECTS e Digilogue 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. 

nsulation Tester 

PROJECTS ® 1000V/500 
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 

wa Part 2 e ) Consumer Electronics Show 

PROJECTS e Spacewriter Wand e 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 
Gheeking Usa 

PROJECTS e 12V 35W PA Amplifier 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 
Quickroute 3.0 peau 

PROJECTS e Multi-Purpose Thermostat e 
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 

Lottery Predictor 

PROJECTS e 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 
Sea Telephones). 

ment and Training System) e R.F. Signal 
Generator e MIDI 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 Vegas Show Report. 

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The revised edition of the Modern Electronics Base REPAIRS AND MAINTENANCE: Basic circuit operation 
Manual contains practical, easy-to-follow information for radio, television, audio/hi-fi, telephones, computers. 
on the following subjects: 

. ESSENTIAL DATA: Extensive tables on diodes, 
BASIC PRINCIPLES: Symbols, components and their transistors, thyristors and triacs, digital and linear 
characteristics, active and passive component circuits, i.c.S, microprocessors. 
power supplies, acoustics and electroacoustics, the 
workshop, principles of metrology, measuring EXTENSIVE GLOSSARY: Should you come across a 
instruments, digital electronics, analogue electronics, technical word, phrase or abbreviation you're not 
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CIRCUITS TO BUILD: There’s nothing to beat the is Manual and you ll find a comprehensive definition 

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principles to circuit-building, the Modern Electronics The Manual also covers Safety, Specialist 
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appropriate diagrams, how to assemble radios, The most comprehensive reference work ever 
loudspeakers, amplifiers, car projects, computer produced at a price you can afford, the revised edition 
interfaces, measuring instruments, workshop of THE MODERN ELECTRONICS MANUAL provides you 
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Revised Edition of Basic Work: Now contains over 1,000 pages of information. 

Regular Supplements: Approximately 160-page Supplements of additional information which are forwarded to you 
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Part 2 

Highlighting the PIC microcontroller, Mark Stuart 
channels your attention onto how its elegant 
development system can be used CO good effect. 

N Part One of the PIC-DATS article last 

month, the PIC microcontroller was in- 

troduced and the principles of its use 
and programming described. This second 
part follows on, introducing the practical 
operation of the PIC-DATS system and 
demonstrating its use in the development of 
a typical hardware project. 

The project chosen is a 4-Channel Light 
Chaser controller. The main reason for the 
choice is that such a project demonstrates 
how to read switch (digital) and poten- 
tiometer (analogue) inputs, and how to 
control low voltage and mains power 
devices. The programming described in- 
volves timing loops and demonstrates 
timed control of the outputs, which is 
necessary for “Zero Volt Switching” of the 
mains power devices. 


Although the originally intended use of 
the project is as a Light Chaser, it can 
also be used for many other general pur- 
pose applications where computer con- 
trol of mains powered devices is needed. 
For example, random switching of house 
lights and appliances for security purposes, 
central heating control and greenhouse 
watering systems. 

It can also be modified to provide low 
voltage control outputs for operating 
model motors, solenoids, and_ other 
motion control devices. Inputs from other 
types of sensor may also be applied 
instead of switches, allowing a wide range 
of “stand alone” applications to be 

The design is such that program develop- 
ment and simulation can be done without 
any mains voltage being applied. There 
is also total mains isolation so that the 
system may also be operated and fur- 
ther developed with mains power applied, 
provided due care is taken. 

As the main purpose of this article 
is to cover PIC programming and the 
PIC-DATS system, the description of the 
hardware and construction of the project 
will be kept to a minimum. The circuitry is 
all on a single printed circuit board (p.c.b.), 
but any mechanical construction, casing, 
etc. is left to the user. 


The circuit diagram for the complete 
4-Channel Light Chaser is shown in Fig. 1. 
The circuit is divided into two parts: the 
Mains Power section, and the low voltage 
Control section. Between the two circuits 
there is complete electrical isolation. 

Mains power is controlled by four triacs, 
CSRI to CSR4. These devices can switch 
up to 600 volts and five amps (provided 
they are fitted with heatsinks and there 
is adequate ventilation). Each channel is 
provided with a fuse, which will protect 
the circuit in the event of an overload or 
“short”. It is unlikely that the fuse will 
protect the triac, however, as the short time 
it takes to blow a triac is a lot less than the 
time needed to blow a fuse. 

The triacs are switched on by applying a 
voltage between their MT1 and Gate (g) 
terminals. This voltage is supplied by trans- 
former T2, rectified by REC2 and smoothed 
by capacitor C6. Although it is a low volt- 
age, one side must be connected to Mains 
Live (so that current can flow between MTI1 
and Gate) and so it MUST be treated as 

Everyday with Practical Electronics, June | 995 

Mains Voltage. Resistor R18 is used to link 
the low voltage supply to the Mains. 

Gate voltage is applied to the triacs via 
opto-isolators IC2 to IC5. Each opto- 
isolator has a phototransistor at its output 
and an l.e.d. at its input. Light from the l.e.d. 
makes the phototransistor conduct. Resistor 
R14 limits the gate current to CSRI, and 
R19 reduces the sensitivity of the triac to 
spurious electrical pulses and interference 
that may be carried on the incoming mains 
supply. Resistors R15 to R17, and R20 to 
R22 do the same for the other triacs. 

A separate fuse, FS1, is provided in the 
supply to the two mains transformers. 

As the only path through the opto- 
isolators is for light, there is no electrical 
connection, and so the input l.e.d.s are free 
of mains voltage. 


The Control section of the circuit is 
powered by a second mains transformer, 
T1. The low voltage output is rectified by 
REC! and smoothed by Capacitor Cl. 
Diode D1 is added so that an unsmoothed 




RBI fe 


Vb PIC 16C54 



Fig. 1. Circuit diagram for the complete PIC-DATS 4-Channel Light Chaser. 

output 1s available from which mains zero 
crossing points can be derived. 

The smoothed output is taken via resis- 
tor R4 to Zener diode D4. This provides a 
reference voltage for the base of transis- 
tor TRI, which acts as a voltage regulator 
producing 6:25V on its emitter. Resistor 
R3 provides current limiting and short cir- 
cuit protection, providing a stable limited 
power source and making it almost impos- 
sible to damage ICI even if it is fitted 
backwards. Capacitor C2 provides decou- 
pling to maintain a clean supply when IC] 
draws pulses of current. . 

ICI is a PICI6C54 microcontroller. Its 
4-bit Input/Output (I/O) Port RA is used to 
drive the opto-isolator l.e.d.s via current 
limiting resistors R6 to RY and monitor 
l.e.d.s DS to D8. 

The 8-bit I/O Port RB is used for the 
remaining functions. Port RBO senses the 
setting of potentiometer VRI, using it 
along with resistor RIO and capacitor C5 
as a simple analogue to digital converter 
(ADC) circuit. Port RB7 picks up pulses 
from the collector of TR2, which is turned 


off briefly when the unsmoothed full wave 
rectified supply from REC! falls to zero at 
each mains “zero crossing” point. 

Ports RBI to RB6 are used to read the 
keypad which consists of 12 individual 
switches arranged in a matrix of three 
columns of four rows. This arrangement 
allows 12 switches to be read individually by 
only seven connections. Unfortunately, only 
six are available in this circuit, and so it has 
been necessary to use a trick and add diodes 
D2 and D3. These diodes give the top row of 
switches (g) pull-up lines from d and e 
simultaneously. This allows them to be 
distinguished from the other keys which pull 
up only one line at a time. | 

The drawback to this method is that it 
can give false Row g outputs if keys are 
pressed simultaneously in Row d and Row 
e, but this is not a problem when only 
single keys are expected to be pressed. 
Resistors R11 to R13 pull down Ports RB1 
to RB3 so that when the keypad is not 
pressed all three read as logic zeros. 

All of the microcontroller operation ts 
carried out at a speed determined by the 

on-chip clock oscillator. The frequency is 
determined by resonator or crystal X1. C3 
and C4 provide the correct capacitive load- 
ing for the oscillator circuit. 


The circuit is built on a single printed 
circuit board, which is available from the 
EPE PCB Service, code 942. This board 
can be assembled to different levels. as 
required. For basic program development 
it 1S necessary only to fit the components 
around ICI. 

The opto-isolators can be omitted if their 
pins | and 2 are shorted together to provide 
a current path to light l.e.d.s DS to D8. The 
power supply section T1, D4 etc. can also be 
omitted, and instead of mains power, a 6V 
battery (easily provided by four AA cells ina 
holder) can be connected across C2. 

Leave resistor R5 in position so that Port 
RB7 is always pulled up to a logic | level. 
This is the ideal set-up whilst first ex- 
perimenting as it is completely safe and 
allows simple programs to be checked with 
ease. The battery may also be used if the 

Everyday with Practical Electronics, June 1995 

power supply section has been assembled, 
provided the mains input is unplugged. 

All of the components are fitted as shown 
on the component layout drawing in Fig. 2. 
DO NOT use sockets for opto-isolators 
IC2 to ICS as the distance between the 
socket pins is less than that between the 

pins of the opto-isolators and would reduce | 

the clearance distance below that required 
for safe isolation. Opto-isolators are reli- 
able anyway, and so there 1s no reason to 
have them in sockets — but do make sure 
before soldering that they are fitted the 
right way round! 

The socket for IC] can be a turned pin 
type or an ordinary one. Turned’ pin sock- 
ets are more durable. 

Assembly of the mains side of the circuit 
is conventional. Use a nut and bolt to hold 
each triac tab down to the board, and take 
care to keep all of the soldering tidy to 
avoid accidental track bridges. 

Insulated wire links are needed to join 
the Mains Neutral connections across to 
all of the output terminals. These should 
be made with 16/0-2 wire insulated with 

It helps alignment when fitting the 

Everyday with Practical Electronics, June 1995 

Fig. 2. Component layout and full size copper foil track master for the PIC- DATS 4- Channel Light Chaser. 

fuseholders if a fuse is clipped into them 
before soldering. 7 


It is essential to make checks for solder 
bridges, dry joints, and incorrectly fitted 
components before applying power to the 
board. If battery power is being used, con- 
nect a 6V supply across capacitor C2. This 
is best done by soldering a pair of 7/0-2 
connecting wires to the track side of the 
board where the pins of C2 are fitted. Do 
not yet insert IC]. 

Using a short length of connecting wire, 



R1 100k 
R2 47k 
R3 47 
R4,R10_ 1k (2 off) 
toR13 10k (4 off) 
R6 to RO 150 (4 off) 
R17 —- 820 (4 off) 
R18 10 
R22 470 (4 off). 

Potentiometer | 
VR1.—_:. 470k rotary carbon lin. 

~C1,C6 - 220y radial elect. 16V 
(2 off) 
~€2 > = 47 radial elect. 10V 
C3,C4 33p 2.5mm ceramic (2 off) 
C5 see text 

. Semiconductors 
- D1 ©» : 1N4001 rectifier diode 
D2,,D3  1N4148 signal diode (2 off) | 
D4 6V8 400mW Zener diode 
D5 to D8 3mm red l.e.d., standard 

REC2 W005 bridge rectifier (2 off) 
TR1, TR2 BC183 npn transistor 

(2 off) 
CSR1 to 
CSR4 TAG M29 triac, isolated tab 
1C1 ~P1IC16C54 microcontroller 

: (see text) 
IC2 to 

“1C5 CNY17-3 opto-isolator 
/ (4 off) 


X1 _. 4MHz crystal or resonator 

FS1 250mA fuse, 20mm 

FS2 to 

FS5 3A fuse, 20mm (4 off) 

T1,T2 11V0-8VA transformer, 

p.c.b. mounting, Magenta 
TX0811 (2 off) 

Printed Circuit board, available from 
the EPE PCB Service, code 942; 20mm 
fuse clips, p.c.b. mounting (5 off); 3- 
way terminal. block, p.c.b. mounting, 
mains rated (5 off); mains connectors, 
to suit application (5 off); case, to 
suit.application (see text); 18-way d.i.l. 
socket; insulating pillars and screws (4 
off); keypad, 4 x 3 matrix; connecting 

cable; wire; solder, etc. 

link pin 5 of the i.c. socket in turn to pins 1, 
2, 17, and 18. This should light the cor- 
responding l.e.d.s D5 to D8 and will be ac- 
tivating the opto-isolators if they have been 
fitted. If the l.e.d.s do not light, check their 
polarity, and that of the opto-isolators. 

If a fully built mains powered circuit 1s 
being built, the above battery test can still 
be used before applying the mains. 


If you are competent to use the mains 
powered version, it is strongly recommended 
that the p.c.b. is screwed down to a substan- 
tial piece of wood before testing. This holds 

Approx cost 
guidance only 



keying logic. 

it in place, and takes away the temptation 
to pick it up with bare hands. Use an in- 
sulated test bench, and plug in to a cir- 
cuit powered via an RCCB (residual current 
circuit breaker). An RCCB is essential for 
this and other electronics work using mains 
power and greatly reduces any hazard. 

Once mains power is applied, check the 
regulated supply from the emitter of TRI, 
which should be close to 6:25V. Check the 
operation of l.e.d.s DS to D8 as before, and 

that the triacs are being triggered when the ~ 

l.e.d.s are lit. This is best done using a low 
wattage lamp as a load on each output. 

Once this has been done, and power has 
been switched off, the circuit is ready for 
the PIC chip to be inserted. First, though, it 
has to be programmed! _ 


_ The PIC program can range from simple 
to very complicated. To make an easy in- 
troduction, the PIC-DATS will first be used 
with some very simple examples, starting 
with a program to turn on just one of the 
outputs in response to the pressing of one 
key on the keypad. 

The program will then be extended in 
several small stages until a simple light 
sequencing program is developed. This pro- 

cedure will have supplied the basic tools - 

further programming development is left to 
the individual to exercise his or her mind. 
Those new to PICs will be surprised at the 
ease with which simple working programs 
can be written, and how simple steps can be 
combined into larger programs. 

All of the programs shown, and some 
more complicated ones, are supplied on the 
disk referred to last month, and in this 
month’s Shop Talk. 


The outputs from the PIC SIM system, 
described last month, are connected to a 
40-way IDC plug on the end of the board. 
Most of the connections are not used, but it 
is difficult to fit individual wires, and so a 
300mm length of 40-way rainbow (colour 
coded) ribbon cable should be used. The 
pins required are: 


39 Ground Target pin 5 
40 | Ground Target pin 5 
"15 PORT RBO Target pin 6 
17 PORT RBI Target pin 7 
19 PORT RB2 Target pin 8 
21 PORT RB3 Target pin 9 
22 PORT RB4 Target pin 10 
20 PORT RB5 

Target pin 11 

Fig. 3. Ke eypad connections and 





COL 2 
ROW 1 
COL 1 
ROW 4 
COL3 _ 
ROW 3. 
ROW 2 


18 PORT RB6 Target pin 12 
16 PORT RB7 Target pin 13 
p&e, PORT RCO Target pin 17 
25 PORT RCI Target pin 18 
Zt PORT RC2 Target pin | 
29 PORT RC3 Target pin 2 

Port RC is being used since Port RA is 
not available on the PIC-DATS. It is, how- 
ever, a simple matter to change over when 
programming the final chip so that Port 
RA is used. 

The ends of the ribbon cable must now 
be connected to the Light Chaser board. As 
this board is the one for which the final’ 
code is being developed, it is referred to 
as the “target system’. The lead connect- 
ing the PIC-DATS to the target system is 
known as the “‘probe connecting lead” and 
the connector used to make contact with 
the socket of IC1 is the “target probe’’. 

The ideal means of connecting the rib- 
bon cable to the socket of ICI is to use an 
18-way d.i.l. (dual-in-line) header which is 
an IDC connector whose pins plug directly 
into an 18-way 1.c. socket. | 

There is a difficulty with this, though: the 
ribbon cable from the PIC-DATS is not in 
the correct order: to fit directly. To overcome 
this, either solder the wires individually to 
the d.i.1. header pins, taking care not to melt 
the plastic connector body, or fit a separate 
ribbon cable into the d.i.l. header and make 
individual soldered and sleeved joints be- 
tween the appropriate wires. 

Alternative probe arrangements are pos- 
sible, including the simple but effective 
method of soldering the ribbon cable di- 
rectly to the track side of the p.c.b. under- 
neath the socket for IC1. If this method is 
used, take care to unplug the 40-way 

Everyday with Practical Electronics, June 1995 

connector from the PIC-DATS when the 
time comes to fit a programmed PIC into 
the socket. 

For the PIC-DATS simulation control of 
this target circuit, DO NOT connect the 
PIC-DATS control cable to pins 3, 4, 14, 15 
or 16 of the socket for IC1. 

Once the target probe connections are 
made, and have been double checked, plug 
in the 40-way connector, connect the PIC- 
DATS power supply and power up the 
target system using a 6V battery. 


One of the best aspects of the PIC- 
DATS software is the way it is able to 
switch to and from the Text Editor and 
Cross Assembler programs. To achieve 
this it is necessary to edit a simple file 
called PICSIM.INI which indicates the 
directories and paths through which to 
access the two programs. 

The file can be changed easily if neces- 
sary using a word-processor. If the PIC- 
DATS program has been loaded in the 
standard way, and assuming it is to be run 
from a hard disk on drive C, the first line 
will read: 


The second line is the path to the Text 
Editor. The prototype was developed using 
a word-processor package called PCWrite 
which uses the command ED.EXE to start. 
It is located in a directory called PCW1. 
The second line reads: 


Users who only have floppy disk drives 
will need to make alternative entries, but 
provided the disk capacity is sufficient the 
system can be run successfully. It is useful 

to have a compact word-processor as the | 

programs need to be written in very simple 
ASCII code. | 

Assuming the software has been cor- 
rectly loaded and the serial lead is 
connected between’ connector PL2 and 
the computer, enter the PIC directory, 
and run PICSIM5X. Remember to enter 
PICSIMSX 2 if the serial lead has been 
connected to the COM 2 port of the PC 
instead of COM 1. 

If all is well, the PIC-DATS will sign on 
and the COMMAND prompt will appear. 
If not, check the lead and power supply. If 
necessary switch off the PIC-DATS power, 
and then switch on again to reset. 

Once in Command mode, experiment 
with some commands to see their effect. 
The manual supplied with the software 
gives full details of each command, and 
only the bare essentials are provided here: 






indicates where the next line of code should be loaded 

loads the value 00 to W, which is the working register 

copies the value in W to the Port RC control register - which 
determines whether the port bits are inputs or aes loading 
00 sets all Port RC bits to output 




1FF | 

the value 00 into Port RC setting all lines LOW 

loads the value FF into W 

the value FF into Port RC setting all lines HIGH 

the PIC back to the first line so that the program loops 

indicates where the next line of code should go. 

located at 1FF. This is the first thing the PIC reads and so it 
immediately jumps to START which is at address 00 and begins 
running the instructions from there 

Listing 2. Explanation of the commands used in Listing 7. 

Key B_ switches alternately between 
decimal and hex numbering. Hex is the 
more usual system for programming and 
should be selected. 

Key M switches through the range of 
processors covered. Select 16C54. 

Key P steps through the available reg- 
ister file pages, this should be set for page 0. 

Key W allows the watchdog timer to be 
enabled - the watchdog timer is an inde- 
pendent counter that automatically resets 
the PIC if the program runs away due to an 
unforeseen programming bug. Its use can 
be complicated, and it is not necessary in 

_the current application so set function W to 

The other commands are either obvious, 
such as Q for Quit, or are better explained 
by example as programming proceeds. 


As with all types of programming, there 
are rules that must be obeyed, and com- 
mands that will only be recognised in the 
correct places. The MPASM Cross As- 
sembler that is being used is not unfriendly, 
but cannot work if it does not understand 
the programmer’s intentions. The easiest 
way to start is to modify a known working 
program - some simple examples of which 
are supplied on the software disk. 

The first lines in a PIC program are to 
tell the MPASM Cross Assembler program 
which type of PIC the program is for, 
which numbering system is being used 
(Hex, Decimal, Binary etc.) and where to 
locate the code in memory. 

A simple program which sets Port RC to 
operate as an output port and then switch 
the eight outputs alternately between logic 
0 and logic 1 is shown in Listing 1. 

This file, PICA1.ASM, is included on the 

software disk, but should be typed in as 
an exercise to show how the system works. 

;LOAD W WITH 00 (BINARY 00000000) 
;LOAD W WITH FF (BINARY 11111111) 


Listing 1. PICA1.ASM. simple program which sets Port RC to operate as an output 


Everyday with Practical Electronics, June 1995 

The name of the file in which the re-typed 
program is stored is not important, but it 
must have the suffix **.ASM” (pronounced 
“dot A-S-M’’) and be in pure ASCII code, 
that is, it must not contain any printer con- 
trol or other non-text codes. Most word- 
processors are able to work in this mode 
without difficulty. 

Take note of the columns used for the 
various statements in the .ASM file, in par- 
ticular the way that the label “START”. 
begins in column one. Note also the semi- 
colons (;) which indicate that the following 
words on that line are comments. 

Line by line the program works as des- — 
cribed in Listing 2. 

The two ORG statements are very im- 
portant as they determine the starting ad- 
dress (ORiGin) for the code. The main 
part of the code starts from 0000, but the 
PIC16C54 always starts at 01FF following 
switch on or Reset so a simple command is 
written and inserted directing the PIC to 
the label START for its next instruction. 

The use of a label allows a particular 
piece of code to be found by the program 
no matter where it is in the memory. 
START could be at location 0OOFC and the 
program would still find it correctly. Note 
also that the word BANANA or any other 
word (apart from a few reserved words 
such as LIST that would cause confusion) 
made from up to six letters and numbers, 
could be used instead of START. 

The .ASM program cannot be run directly 
as it is, but must first be “Assembled” into 
the correct form to be loaded into the PIC 
chip. This is done by the MPASM.EXE pro- 
gram. It takes the .ASM file and produces 
two other main files, one is a listing file (suf- 
fix .LST) which contains all of the original 
information and adds the addresses and PIC 
instruction codes. a 

The other is the code file for program- 
ming into the PIC processor (suffix .HEX). 
If there are errors in the original .ASM file 
which cannot be converted into code, a 
third file is produced with the suffix .ERR 
containing details of each error and the 
reason it cannot be interpreted. 

The listing file generated from the ASM 
file in Listing 1 is shown in Listing 3. It 
contains in columns one and two details of 
the location and contents of the code that 
would be loaded into the PIC processor. 
For example, memory location 0000 will 
contain the code 0CO00, and so on. 

These codes are the “‘machine code” 
equivalents of the statements entered in the 
.ASM file. The listing file also shows the 
amount of memory used, the date and time 
of assembly and a table of labels and their 
addresses. If errors have been made in the 
.ASM file, these will be shown in the 

LST file with details that help with their 


To write a .ASM file from the PIC-DATS 
software environment, press E and then 
The PICA1.LST file: | select the file from the list provided. If a 
new file is to be written press ‘“‘Esc”’ and the 
text editor program will start up as usual. 
When the file is complete, save in the usual 

MPASM 01.02 Released C:\PICA\PICA 4-16-1995 20:20:10 

scene , way and exit. A single keypress will then 
To run the cross assembler, press XA and 
0001 PROCESSOR 16C55 select the .ASM file from the menu. The 
shui sighncdaglpaengi 4 ws 3 ~MPASM program will run, and report any 
pon BEDE ERA Ree errors. A single keypress will again return 
wane to the PIC-DATS. If there are errors, press 
0007 tes Bae ié E and enter the file name with suffix .ERR 
0008 ;LOAD W WITH 00 (BINARY 00000000) to see the error report. Alternatively, enter 
0009 ;COPY W INTO TRIS C SET PORT C AS O/P. a .LST suffix and find the errors in the 
0010 ;COPY W INTO PORT C TO SET ALL Os listing file. The error explanations and their 
0011 sLOAD W WITH FF (BINARY ATL41111) solutions are often simple, but the more 
phe ee complicated ones will need some thought 
0014 and reference to the PIC data sheets (sup- 
0015 | | plied with the PIC-DATS kit). 
0016 F  ;RESET ADDRESS Once the code is correct, return to the 
0017 ;GO TO START POINT : PIC-DATS program and use the L com- 
0018 | mand to load the assembled .HEX file from 
0019 ) the menu. 
0020 : 
MPASM 01.02 Released C:\PICA\PICA 4-16-1995 20:20:10 STEPPED 
eee Now the real fun begins! Assuming the 
SYMBOL TABLE | target system is connected to the PIC- 
| DATS and powered, the code can be 
LABEL stepped through one instruction at a time 
. using the S command. As the state of the 
ereee | I/O ports is changed, the l.e.d.s on the 

target system will turn on and off. Note 
that in this circuit, the l.e.d.s are turned on 
by a logic 0 and off by a logic 1. 
0000 : Press Q to end the single stepping, and 
| then press T. The program will now run on 
, pe its own and the l.e.d.s will appear to be 
0180 : constantly lit, although they are actually 
vate s flashing on and off very quickly. The speed 
at which the program is now running is 
much slower than the final speed of the PIC 
teres « | device. This is because the PC computer 
Warnings : . has to operate the PIC-DATS via a serial 
Messages : link, and update the screen after each in- 
struction. For testing programs, however, 
it is fast enough, provided there are no time 

MEMORY USAGE MAP ("X" = Used, " = Unused) 

All other memory blocks unused. 

Listing 3. The Listing file generated for the program in Listing 7. 
The .HEX file is much shorter, and 

is practically unreadable except by the PROCESSOR 16C55 
PIC programming software. Thus the 
PICA1.HEX file would read: RADIX HEX 

:08000000000C07002700F FOCB3 ‘TITLE “PICA_B.ASM" 


0203 FEOOO00AF3 . LIST 

:00000001 FF | 

, , ORG 

This file contains the code that will - | 
be loaded into the PIC when it is pro- MOVLW ;LOAD W WITH 00 (BINARY 00000000) 
grammed, and other information giving the TRIS ;COPY W INTO TRIS C SET PORT C AS O/P 
memory locations to be used, and a check- MOVWF ;COPY W INTO PORT C TO SET ALL Os 
Ee ee ee eee ae ae MOVLW) _B"11111110" ;LOAD CHASE PATTERN 1 INTO W 
detected as it is downloaded. MOVWF 0X07 ;COPY W INTO PORT C TO SET OUTPUTS 

Program .ASM files can be written with MOVWF 0X07 ;COPY W INTO PORT C TO SET OUTPUTS 
enceadn Many tea aces ty MOVLW B"11111011" LOAD CHASE PATTERN 3 INTO W 


running MPASM.EXE to produce .LST : : 
and .HEX files (and a .ERR file if there are MOVLW B"11110111" ;LOAD CHASE PATTERN 4 INTO W 
errors). This arrangement can be used MOVWF 0X07 ;COPY W INTO PORT C TO SET OUTPUTS 
without PIC-DATS itself and is useful for 
checking program ideas and learning the GOTO CHASE ;LOOP BACK TO BEGINNING OF CHASE 
basic rules for the .ASM files. ae a suxate auberes 

The PIC-DATS system is much more ef- nine ee G6 Te. EELEE DORE 
fective for code development, however, as it END 

allows the code to be run and developed in 
hardware as well as software. Provided the 
PICSIM.INI file has been set up correctly, 
the PIC-DATS program allows easy access Listing 4. Program listing for PICA. B.ASM, which generates a simple chase light- 
to and from the text editor and assembler. ing sequence. . 

470 Everyday with Practical Electronics, June 1995 



ORG 0x00 

MOVLW 0x00 
TRIS 07 

MOVLW BB" 10001111" 
TRIS 06 

SWCOL1 0X06,4 



;LOAD W WITH 00 (BINARY 00000000) 


;LOAD W WITH 00 | 









Listing 5. Program to read the hash key and operate Channel 7 L.e.d. 

critical applications, or long delay loops 
which will cause tedious boredom! 

Modify the .ASM file so that OXFI is 
loaded instead of OXFF, run the XA 
program again, then press L to reload, and 
again repeatedly press S to single step 
through the new code. This time only one 
of the four l.e.d.s will turn on and off. Try 
other changes, possibly including some 
deliberate errors and see the codes gener- 

ated in the .ERR file. 


The codes such as MOVLW are instruc- 
tions that the PIC16CS54 carries out. There 
are only 33 of these, but as almost one mil- 
lion can be executed in one second (using a 
4MHz clock speed), they can be made into 
powerful combinations. 

This article is intended only to illustrate 
some of the basic options so that the 
PIC-DATS system can be operated, and 
code can be written, assembled, corrected 
(debugged) and run. The real work of 
learning the instructions, their limitations 
and applications, is down to the user. 

Having produced a program which turns 
the outputs on and off, its development 
into one which produces a simple chase 
sequence is relatively simple, as is il- 
lustrated by the program PICA_B.ASM, 
shown in Listing 4. 

The listing file .LST is not printed here to 
save space, but it can be produced by run- 
ning MPASM as before. 

_A program which reads the # (hash) key 
on the unit’s keypad and then switches the 
Channel | l.e.d as necessary is illustrated 
by PICA_C.ASM, shown in Listing 5. 

This uses BSF and BCF instructions to 
set (make logic 1) and clear (make logic 0), 
respectively. It also uses the BTFSS in- 
struction, which tests the state of an I/O 
port line and skips one instruction if the 
I/O line is set to logic 1. 

By following these examples, and those 
on the software disk, it will be possible to 

increasingly understand the nature of the 
programs and how they are built up. With 
the PIC-DATS system it is possible to ex- 
periment with the whole range of instruc- 
tions and so build up a working knowledge 
in anefficient and easy manner. 

The other keys on the unit’s keypad are 
read in a similar way, as is the Zero Volt 
Crossing signal. The reading of the set- 
ting of potentiometer VR1 is more compli- 
cated, however. This is done by first setting 
Port RBO as an output port and charging 
capacitor CS to + 5V, the logic | level. RBO 
is then programmed as an input port and 
read by the software. At first it reads a logic 
1 as CS is fully charged, but gradually CS 
discharges at a rate determined by VRI 
until RBO reads as logic 0. The time for this 
to happen indicates the setting of VR1. 

In the Chaser Lights application, the 
time is used directly to set the chase speed, 
but the setting of VRI1 could be used 
for other purposes in different programs. 
This process is only a simple and not 

very accurate analogue to digital converter. 

(ADC), but it’s cheap! 


The PIC-DATS system comes with a 
built-in programmer. This allows the code 
which has been developed, or any other 
-HEX code files, to be programmed into 
any of the chips in the PIC16CSx family of 

The low-cost versions of the PIC16CSx: 
chips are fully enclosed plastic devices and 
although they contain EPROM, cannot be 
erased. This makes them One Time Pro- 
grammable devices (OTP). However, an 
alternative UV-Erasable type is available, 
and it is highly recommended that at least 
one of these is obtained. Such devices are 
not very expensive and are essential for 
serious programming where the cost of 
wasted OTPs. with out-of-date programs 
could soon build up. (It should be noted 
that the PIC-DATS system cannot pro- 

Everyday with Practical Electronics, June 1995 

gram the PIC16C84 electronically erasable 
(EEPROM) devices.) 

To operate the programming part of 
PIC-DATS, first Quit the PICSIMSX pro- 
gram, and run the PICPROG program. As 
with PICSIMS5X if Com 2 port is being 
used, it is necessary to type PICPROG 2. 

Once running, the PICPROG program 
produces a screen display which has a num- 
ber of self explanatory functions which can 
be selected by mouse or cursor keys. The 
commands can be explored one by one to 
see their effect (without using the “pro- 
gram” option). | 

There are several “CONFIGURATION” 
settings to be made. These allow the type of 
oscillator to be set up — normally select XT 
for 4MHz crystal or resonator operation, 
and the Watchdog timer to be Enabled or 
Disabled — set this to Disable. 

The Code Protection option, if selected, 

‘makes it impossible for the code to be read 

out of the chip once it. has been pro- 
grammed. It is an important security fea- 
ture, but when code is being developed it is 
useful to Disable the protection so that the 
code can be checked and identified. It is 
possible to Enable just the Code Protection 
later on, once a prototype has been tested. 

Before using the PIC-DATS as a pro- 
grammer it 1s essential to disconnect any 
other hardware by removing the 40-way 
IDC header connector. This must be done 
before inserting any devices into the pro- 
gramming sockets. 


To program a PIC chip, first insert the 
device into the appropriate socket - taking 
care to put it the right way round. Then set 
up the required configuration and select the 
wanted file. The file is found in the same 
way that PICSIMS5X finds its files and so is 
dependant upon the correct setting of the 
INI file. 

The device being programmed is not 
powered until the program or read com- 
mands have been entered. Up until then the 
socket is “cold” and the chip can be 
inserted or removed without danger of 

- damage (provided normal anti-static han- 

dling precautions are observed). 
Downloading the program into the chip 

is fast and is indicated by an l.e.d. (D2) 

next to the programming sockets. The 
screen display shows the result of the 

When program downloading has been 
completed, make sure the target system is 
switched off, and plug in the programmed 
PIC device. Switch on, and if all is well the 
hardware will come to life and operate as a 
stand alone system. 

After many years experience in the use of 
microcontrollers, it still delights (and some- 
times surprises!) the author when a Target 
System suddenly takes on its own new per- 
sonality and springs to life. 

It is hoped that this same satisfaction will 
be achieved by all readers who are prepared 
to put in the necessary time and effort. 


In Fig. 4 last month the pin notations for 
transistors TR! and TR3 should read in 
order of b, c, e (top to bottom). 

See Shop Talk page for details on how 
to obtain a complete kit, the software 
programs and pre-programmed PIC 
-microcontroller for this project. 


Regular Clinic 




Our two-way “Surgery” of readers’ questions and comments looks at a “‘mes- 

sage reminder” function for the popular Voxbox project. We also take the lid 

off diode terminals with some typical diode applications. Finally, the Surgery 
gets wired and goes on the Internet! | 

ELCOME to this month’s Circuit 

Surgery, our two-way column full 
of advice, hints and general info. to 
share amongst the readership. Let’s dip 
straight into the post-bag with this en- 
quiry from Barry Timms of Vermillion, 
South Dakota, USA who posed a couple 
of questions to the Surgery. 

Voxbox Upgrade 

I have two technical questions and 
would be grateful if you could supply a 
response to both. Firstly, concerning the 
Voxbox project of July 1994. It’s men- 
tioned that the addition of an l.e.d. to the 
circuit could indicate that a message is 
stored. I’m building this project and 
wondered if you could tell me where to 
connect the l.e.d. to provide this function. 

Secondly, could you clarify why you 
designate the terminals of a standard 
diode the way you do? I know that the 
polarities of most diodes and small 
rectifiers are indicated by a band marked 
around the cathode (k). Current flows 
through the diode from anode to cathode, 
but most textbook definitions of the 
cathode and anode electrodes seem to me 
to imply that current actually flows in the 
opposite direction! 

Your Voxbox ‘Message Waiting” 
Indicator query first. This highly 
popular project was designed jointly 
by GEC-Plessey Telecomms engineers 
*Guy Dance and Jeremy Austin as their 
excellent contribution to the Technology 
in Action Day event, which aims to 
encourage engineering disciplines in 
British schools. 

To recap, Voxbox is a fully solid-state 
recording unit which stores up to 20 
seconds’ worth of speech — a kind of 
talking memo pad! It uses the ISD1016 
(16 seconds) or the ISD1020 (20 seconds) 
integrated circuit at its heart: the latter 
has a lower frequency sampling rate, so 
reproduction isn’t quite as good. 

The idea of a “jogger” l.e.d. to warn 
that a message is stored, might appeal to 
those who’ve already built this project. 
The authors’ initial idea for an l.e.d. 
reminder was to simply use an on- 



Fig. 1. Voxbox “Message Waiting” indicator modification. 


ae eS 

(Courtesy Guy Dance and Jeremy Austin). 

off switch and an le.d., arranged to 
illuminate when the switch was in the 
“on” position. 

What they had in mind was that the 
user would record a message and switch 
on the l.e.d. as a reminder to others to 
play it back. The recipient switches it 
off again after inwardly digesting the 
Voxbox’s pithy comments! 

A high-efficiency |.e.d. could be used 
to reduce current consumption. Alterna- 
tively, you could try building a separate 
l.e.d. flasher circuit based on something 
like the LM3909 custom.|.e.d. oscillator 
chip, driven by a separate 1-5V cell for 

Our project designers have  sub- 
sequently proposed an “automatic” 

version which illuminates an l.e.d. when 
you record a message, and extinguishing 
it after it’s been listened to. They 
suggested using a single D-type latch for 
this idea, see Fig. 1. The logic state of the 
record buttons is loaded into the latch 
when the “End of Message” (EOM) 
pulse is generated. In record mode, the 
EOM signal is initiated by the release of 
the Record button. 

An RC network adds a short delay in 
the signal to allow the latch to catch the 
record signal. Thus, starting the record- 
ing mode will clock a Logic 0 into 

the latch and light the l.e.d., playback 
clocks a Logic 1 and extinguishes it 
again. The authors tried this idea and it 
seems to work OK, they say, but it’s 
only intended for single messages since 
the l.e.d. indicator circuit obviously 
resets itself as soon as the first message 
is played back. 

Looking at the mechanical side, the 
constructor could use half of a 74HC74 
dual D-type flip-flop to implement this 
idea. The ‘“‘extra’”’ chip can be grafted 
into the circuit by mounting it on, say, a 
small piece of stripboard and simply sol- 
dering the connections over to the main 
p.c.b. using hook-up wire to connect to 
the copper track side. 

It’s best to link any unused inputs (e.g. 
on the unused half of the logic chip) to 
OV for safety, rather than leave them 
floating. Again, try a_ high-efficiency 
l.e.d. for improved performance. In- 
cidentally, the Voxbox printed circuit 
board is available from the EPE PCB 
Service, Code 885 £6.90 — see our PCB 
page elsewhere in this issue. My thanks 
to Guy and Jeremy for helping out. 

*Guy was recently presented with a special 
award at the Young Engineers Awards to 

‘Industry in recognition of the active support and 

help he has given to the Young Engineers Club at 
Poole Grammar School. 

Everyday with Practical Electronics, June | 995 

Conventional current 
flows from positive to 
neaative potentials 

~ Electrons flow the 
reverse direction, in real 

Fig. 2. Conventional current and 
electron flow. 

Darned Diodes! 

Turning to Barry’s second question 
on diode markings, this highlights a 
common dilemma facing those involved 
with other science disciplines such as 
physics or chemistry. Just which way 
does electric current flow? 

Consider a battery powered flashlight 
bulb, see Fig. 2. You can be forgiven for 
thinking that electric current flows from 
positive to negative. You might, how- 
ever, be aware that in real life, current 
actually flows the other way, from the 
negative to the positive terminal of the 

Perhaps the pioneers seemed to as- 
sume from “Day One” that current 
flowed from the positive to negative 
poles. This has left us with a problem — 
the fact that what happens in our circuit 
diagrams is exactly the reverse of what a 
chemist or a physicist would expect! 

Without delving too deeply into the 
physics, we now know that electrons hold 
a negative charge, and so they will flow 
out of the negative terminal and through 
the bulb towards the positive terminal (to 
which negative electrons are attracted). 
So, electric current flows towards the 
most positively-charged electrode, in real 
life. We call this “true life’ current 
electron flow. 

In our own context, though, it’s only 
in such disciplines as atomic physics or 
electrochemistry that we would start to 
worry about real-time electron flow. 
Everybody in electronics still talks 
generally in what we call “conventional 
current flow” terms, where old-fashioned 
conventions have it that current is 
deemed to flow from positive to negative 
potentials. In other words, we’re all 
fooling ourselves in electronics because 
in reality, electrons flow in the opposite 
direction, but this doesn’t affect our use 
of components or our understanding of 
electronics at all. 

Stop Press! Mr. Timms subsequently 
advised by Internet (see later) that he’d 
succeeded with the Voxbox add-on as 

illustrated. He replaced the l.e.d. with 
a flashing type to achieve a noticeable 
visual signal for the message recipient. 

One interesting way of looking at this 

is to compare the semiconductor diode » 

and also its thermionic valve (vacuum 
tube) predecessor, see Fig. 3. In the case 
of an old-fashioned thermionic diode 
valve — probably easier to understand 
than a semiconductor one — what hap- 
pens is that when heat is applied to the 
cathode by the heater filament, negative 
electrons “boil off’ the cathode. These 
free electrons will be attracted towards 
the anode if a suitable positive “bias 
voltage”’ is applied to the anode: then, an 

electron flow is carried from cathode to 

anode. However, by tradition we would 
deem the conventional current to be flow- 
ing through the valve the other way, 
from anode to cathode. 

True life 
electron flow in 

a valve - 
electrons travel 
from cathode to 



On your marks... 

Our standard markings for diodes and 
rectifiers are summarised in Fig. 4. 
Nearly always, the cathode is readily 
identifiable by a band or stripe at the 
cathode lead-out. 

Occasionally, you see diodes marked 
with a series of stripes — a real nuisance if 
you're not familiar with them! A com- 
mon striped component is the faithful 
1N4148 diode, which may arrive colour- 
coded Yellow/ Brown/ Yellow/ Grey. 
This actually borrows from the resistor 
colour code for “4148” and the first 
yellow stripe indicates the cathode. 

As an aside, when I was putting 
the finishing touches to a _ construc- 

current flows 
through a diode 
from anode to 


Fig. 3. Current flow through a thermionic diode valve and a semiconductor diode. 

Any semiconductor physics book will 
tell you in more detail how current 
is carried by “holes” and electrons 
gathered within a semiconductor diode 
device, and how to bias them into 
operation correctly. As you probably 
know, it’s necessary for the anode to be 
about 0-6V more positive than the 
cathode, before (conventional!) current 
can flow through a silicon diode at all. 

Which way, and how, to mark the 
terminals of a diode, is perhaps a bit 
subjective. At one time — years ago now — 
we did mark the cathode terminal with a 
+ symbol, but now we letter each pin- 
out with “a” and “k’’, to help the novice 
to remember which terminal is which. 
Perhaps it was too confusing when the 
cathode was marked as positive — since 
the direction of conventional current 
flow implies that this is the “negative” 


Typical diode 


Yellow Brown Yellow Grey | 



Schematic symbol 

kK a 

Fig. 4. Diode identification diagram. 

Everyday with Practical Electronics, June 1995 

tional project — actually a prototype 
‘“Windicator’’ Wind Speed Indicator (to 
appear next month — Ed.) — one 
light-emitting diode resolutely refused to 
light. It turned out that the lLe.d. (a 
standard 0-2in. type) had in fact been 
moulded wrongly, and the cathode 
identifying “notch” was actually next to 
the anode! Has that ever happened to 
any reader? 

If you come across an unusual l.e.d. | 
such as a special-shape type, you can 
often identify the cathode by peering 
through the body of the l.e.d. and ex- 
amining the l.e.d. chip assembly (if its 
body is transparent). You'll see that the 
light-emitting chip is mounted onto a 
tiny saucer-shaped reflector. The lead 
connected to this is the cathode. Look 
even closer, and you'll possibly just see a 
very fine wire jumping from the anode 
termination over to the l.e.d. chip in the 

Clip Joint 

Yes, my sub-titles get worse. My 
thanks to Mr. Charles Hill of Carmar- 
then, Wales who dropped us a line with 
the following question, again concerning 
the application of diodes. Mr. Hill 
sketched a typical demodulator circuit as 
depicted in Fig. 5. 

I often see a reverse-connected diode 
used in a circuit but don’t quite understand 
why it’s necessary. I assume that the diode 
D1 is a form of rectifier, but why the 
reverse-biased diode D2. Could you shed 
some light on this, please? 

Certainly — thanks for the letter. 
Everyone will have seen a diode reverse- 
connected across an inductive load such 
as a relay. This acts against the reverse 
voltage spike (“back e.m.f.”’) generated — 
by the relay coil when it switches out of 
circuit. | 

The pulse can easily be several hundred 
volts instantaneous peak, which will 


AC Input 

Fig. 5. Diode demodulator circuit. 

destroy any sensitive semiconductors on 
the same circuit, so the diode shunts this 
away before any harm can arise. 
Anyone who followed our Teach-In 
series (featuring the Mini Lab and Micro 
Lab) might recall the back e.m.f. graphs 
we managed to capture on a storage 
C.R.O. (oscilloscope) and print out 
(Teach In ’93, December 1992 issue 
showed a peak 300V reverse voltage 
generated by a 12V relay!) 

In your circuit, Mr. Hill, diode D1 will 
rectify the signal and if the input sig- 
nal then falls below OV the ‘“‘redundant’”’ 
diode D2 will swing into action. The 
OV rail is then in effect more positive 
than the signal voltage, so eventually the 
diode will become forward biased and 
clip the signal away. 

Obviously this can only happen once a 
sufficient forward voltage has _ been 
reached. It might be included just 

+V supply 

Fig. 6. CMOS Input protection diodes. 

as a Safety pre- 
caution to prevent 
any transistors or 
i.c.s from receiving 
a reversed input 
voltage, or there 
could be a par- 
ticular need to clip 
or detect the signal 


this way.. | 
Exactly the 
same protection 

utilised by CMOS 
i.c. manufacturers. 
Constructors will 
be aware of 
the well-known 
dangers of excess 
static electricity 
accumulation, since this can damage 
CMOS circuits, the electrostatic 
discharge punching a hole straight into 
the metal-oxide silicon chip and 
permanently killing it (I recently killed a 
small MOSFET this way, when I forget 
to use the anti-static wrist strap!). CMOS 
circuits mainly incorporate an input 
protection diode circuit on the input 
circuit which guards against excess 
electrostatic voltages. 

For example, two diodes may be used 

in an arrangement which I simplified in 

Fig. 6. D1 would conduct if the input 
voltage exceeds the supply rail, whilst D2 
will shunt away any input voltages which 
fall below the OV rail. Under normal 
circumstances, neither diode would con- 
duct. They’re not foolproof “‘catch-alls’’, 
though, and you still need the usual anti- 
static precautions. 

alan@ Internet 

As I type this month’s column into 
my PC, ready to download the 
article to ““Headquarters’’, I’m pleased 
to announce the introduction of a 
new E-mail/Internet connection. This 
will be especially welcomed by many 
of our overseas readers. Now anyone 
with an E-mail connection can post 
queries to Circuit Surgery via the 

You need a PC (or Mac, Amiga, 
Archimedes, etc.) which is fitted with a 
suitably compatible modem (these are 
dropping in price all the time: a decent 
BABT-Approved 14:4K type is less 

principle 18: 

than £100 now) and a connection to an 

ordinary phone line. Users need to sign 

up with a service provider if they don’t 
already have access via a workplace, 
college or University. There are several 
providers available in the UK and 
many more across Europe and the 
United States. Preferably choose one 
having a dial-in hub in your “local” 
phone area, so you only pay for cheap 
local rate calls. 

Circuit Surgery is playing its modest 
part on the Internet, helping out with 
queries posted into various electronics 
UseNet newsgroups: these are open 
discussion areas where anyone can chip 
in with information, in answer to a query 
or comment. It’s often a rewarding 
experience — recently a simple query 
brought forth replies and friendly help 
and advice from folks at the USS. 
Johnson Space Center (NASA), not to 
mention Hewlett Packard, IBM and 
several Universities around the world! 
For our own part, for example, we 
solved an electronics query in Canada 
and received an enthusiastic “thank 
you” from a highly delighted student 
over there! 

Here’s the bit you’ve maybe been 
waiting for: you can now E-mail Circuit 
Surgery on 
Whilst the speed of your message may 
be instantaneous (almost), please don’t 
expect an immediate reply from your 
hard-pressed scribe, who does his best! 
Watch this space for news of future 

If you have any queries or questions 

which you would like us to investigate, 
or any advice, hints and tips which you 
think other readers would appreciate, 
you can now contact Circuit Surgery 
by writing to: Alan Winstanley, 
Circuit Surgery, Wimborne Publishing 
Ltd., Allen House, East Borough, 
Wimborne, Dorset, BH21 IPF; or by 
E-mail/Internet, as above. 
_ The usual conditions apply — as al- 
ways, we cannot guarantee an individual 
reply unless material is to be published in 
this column though we'll always try our 
best to help. 

Next time: an investigation of a preci- 
sion rectifier with no forward voltage 
drop! Also, more news from our Internet 
feed. See you soon! 



Please reserve/deliver a copy of Everyday with 

Practical Electronics for me each month. 
Everyday with Practical Electronics is published on the first Friday of each month and distributed by Seymour. 

Make sure of your copy of EPE each month — cut out or photostat this form, fill it in and hand it to your newsagent. 


Name and Address 

Everyday with Practical Electronics, June 1995 

Electronics World & Wireless World Jan 1995 

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Everyday with Practical Electronics, June 1995 475 

Constructional Project 



A low voltage d.c.-to-d.c. converter — 

that provides a 9GV output from one 

or two AA cells. 
HE humble PP3 battery has for many 

} years been a popular method of 

powering electronic projects. It repre- 
sents a safe means of powering small 
electronic gadgets, and at one time it 
also represented a very inexpensive way 
of powering circuits that required only 
modest amounts of current (up to about 

Whereas electronic gadgets have tended 
to become more complex but relatively in- 
expensive over the last twenty years or so, 
the batteries to power them have become 
ever more expensive. In “real terms’’ bat- 
teries are probably no more expensive now 
than they were in the past, but relative to 
the devices they power, most batteries are 
now much more expensive. | 

This has led to circuit designers looking 
for lower cost methods of providing bat- 
tery power. This has resulted in the in- 
creased use of AA (HP7) size cells in 
electronic gadgets. 

Many radio sets, personal stereos, etc. 
now use low voltage circuits powered from 
two or three AA size cells. AA batteries 
provide a given amount of power much 
more cheaply than PP3s, or any of the 
other 9V layer type batteries. 

In terms of amp/hour capacity an AA 
size cell typically has about five times more 
capacity than a PP3 battery, but at one 
sixth of the output voltage. A single AA 
cell therefore has slightly less capacity than 
a PP3 size battery, but is generally about 75 
per cent to 80 per cent cheaper than an 
equivalent PP3 battery. 


Where it is practical, simply designing 
circuits to operate on low supply voltages is 
the best method. This is not always pos- 
sible though, and circuits must then be 
powered from a 9V battery, or a 9V supply 
derived from a 1-5V or 3V battery via a 
step-up circuit. This second method incurs 
the additional cost of the d.c. to d.c. 
converter circuit which provides the boost 
from 1:5V/3V to 9V, but due to the reduced 
running costs this additional outlay should 
be more than recouped in the medium 
There are a number of small switching 
regulator integrated circuits which, on the 
face of it, would be ideal for this ap- 
plication. However, a careful look at the 
specifications of some common switching 


weep Ae. > 

regulator chips reveals that few are capable 
of operating with an input voltage as low 
as 3V, and none can operate with an input 
voltage of around 1V to 1-5V. Fortunately, 
there are now a few switching regulator 
devices that are specifically designed for 
operation with an input provided by one or 
two 1-5V batteries. 


The step-up regulator featured here is 
based on the LT1073CN8 switch mode 
regulator chip. It will operate with a 1:5V 
supply provided by a single AA cell, or a 
3V supply provided by two AA cells in 

The circuit is exactly the same in either 
case, with the regulator action of the device 
ensuring that the output voltage remains at 
about 9V regardless of which input voltage 
is used. The circuit will operate with output 
currents of up to about 15mA or so, even if 
the power source is only a single cell. 

Bear in mind though, that the voltage 
step-up is obtained at the expense of a 
current step-down. Using a 1-:5V input 

there is a voltage step-up by a factor of six. 

When the input voltage falls somewhat 

due to ageing of the battery, the output — 

voltage is maintained at about 9V due to 
the regulator action of the circuit. This 
gives an actual voltage step-up by a fac- 
tor of about seven. Due to losses through 
the circuit the input current is likely to be 
closer to ten times the output current. 

An output current of 15mA could there- 
fore result in an input current of around 
150mA, which would not give a very long 
operating life from even a “high power” 
AA battery. For output currents of more 
than about 7mA it is better to use two AA 
cells in series to provide an input poten- 
tial of 3V (and a current step-down of 
only about five times), or to use a higher 
capacity cell such as a C-type or D-type. 


A d.c. voltage step-up is effectively 
achieved by converting the input signal to 
an a.c. type, feeding it through a step-up 
transformer, and then rectifying the output 
of the transformer to obtain a boosted d.c. 
output voltage. In most practical d.c. to 
d.c. converters the input signal is converted 

to what is really a “chopped’’ d.c. signal 

rather than a true a.c. type, and the step-up 

is often provided by a simple inductor 
rather than some form of transformer. 
There is no obvious way in which a 
simple inductor can provide a voltage 
step-up, but it is actually possible. The 
point to bear in mind here is that a high 
reverse voltage is generated across an in- 
ductor if the current flowing through it is 
suddenly removed. This is caused by the 
rapidly decaying magnetic lines of force 
moving through the turns of wire on the 
inductor. It is the same effect that causes a 
high voltage to be produced across a relay 
coil when it is de-energised, necessitating 
the use of a protection diode. 

Fig. 1. 

Basic step-up switch mode 
circuit diagram. | 

The reverse voltage generated can be 
many times higher than the forward volt- 
age used to energise the inductor, and 
a tenfold step-up is easily produced. Of 
course, you do not get something for 
nothing, and like a voltage step-up through 
a transformer, the boost in voltage is 
gained at the expense of reduced output 


The basic configuration for a switch 
mode power supply that provides a voltage 
step-up is shown in-Fig. 1. Transistor TR1 
is the electronic switch, and the control 
signal is normally a squarewave signal, or 
something not too far removed from a 
squarewave signal. 

The operating frequency of the circuit is 
generally much higher than the 50Hz mains 
frequency, and is typically about 20kHz. 
This relatively high operating frequency 
makes it easier to obtain high efficiency, 
and also enables a small inductor to be 

However, the inductor must be a type in- 
tended for operation at about 20kHz. An 
r.f. choke will not give a worthwhile level of 
performance, and neither will an inductor 
intended for operation at the 50Hz mains 

Everyday with Practical Electronics, June 1995 

When transistor TR1 is switched on, 
inductor LI is effectively short circuited 
across the input supply, and the current 
flowing through LI rapidly rises. A high 
reverse voltage is generated across L1] when 
TRI switches off. The left hand terminal of 
L1 is then negative, and the right hand 
terminal is positive. The voltage across L1 
is therefore in series with the input supply, 
and is added to it. 

With TR1 being repeatedly switched on 
and off at high speed, a rapid succession of 
high voltage pulses are generated at the 
collector (c) of TR1. These are fed to Cl, 
which is a smoothing capacitor at the out- 
put of the circuit. Diode D1 couples the 
voltage pulses to Cl, but it also ensures 
that TR1 does not short circuit the output 
during its “‘on”’ periods. 



circuits that will work efficiently at such a 
low voltage. 

Despite this the LT1073CN8 will operate 
with good efficiency at supply voltages as 
low as one volt. Consequently, it will work 
properly using a single 1:5V cell as the 
power source. 

Furthermore, it will continue to work 
properly even when the battery is nearing 
exhaustion, and its actual output voltage 
is only about 1:2V. Cl is a decoupling 
capacitor on the input supply to IC1. 

The regulator (IC1) has: built-in current 
limiting at the input, and there is provision 
for a discrete current limiting resistor be- 
tween pins | and 2. This facility is not used 
in this circuit though. 

Pins 3 and 4 connect to the electronic 
switch, which is driven by an internal oscil- 

Fig. 2. Complete diagram for the AA to PP3 Converter. 

With this basic configuration the output 
voltage is dependent on a number of 
factors, such as the input voltage, the 
switching frequency, and the precise 
characteristics of inductor L1. Practical 
switch mode power supplies are almost 
invariably based on integrated circuits 
which include a regulator circuit that 
provides a more predictable output 

Regulator R1 is a load resistor, and it is 
not an essential part of the basic step-up 
circuit. It is required with many practical 
switch mode power supplies in order to 
ensure that there is always sufficient out- 
put current to keep the series regulator 
working properly. Often this resistance 1s 
provided by a feedback circuit, which is 
likely to be part of the internal circuit in the 
case of a fixed voltage regulator. 



The full circuit diagram for the AA To 
PP3 Converter is shown in Fig. 2. Bl 
is shown as being a 1:5V battery but, 
as explained previously, the circuit will 
work just as well with a 3V supply. Sl 
is the On/Off switch of the unit in which 
the converter is used, and the addition of 
the converter will obviously necessitate 
rewiring of this switch. 

The on/off switch could simply be left on 
the output side of the unit, since the quies- 
cent current consumption of the circuit is 
under 200nA. However, this would result 
in some reduction in battery life, and it is 
safer to have the circuit switched off when 
it is not in use. 

The LT1073CN8 device used for IC1 is a 
switch mode regulator which is specifically 
designed for this application. It is difficult 
to produce semiconductor circuits that will 
work at all on supply voltages as low as 
1:-5V, and even more difficult to produce 

lator circuit at frequency of between 15kHz 
and 23kHz. Inductor L1 and diode D1 are 
the equivalents of L1 and D1 in Fig. f. 

In order to obtain good efficiency it is 
important that D1 is a high speed device, 
and that it has a low forward voltage drop. 
A Schottky rectifier diode is therefore used 
for Dl. 

The circuit will work using an ordinary 
rectifier such as a 1N4002, but with greatly 
reduced efficiency. On the face of it, a 
Schottky signal diode would be adequate in 
this circuit, as it is only operating with low 
output currents. In practice though, a 
Schottky rectifier such as the 1N5822 gives 
significantly better efficiency. 


R1 390k 
R2 10k * » 
-0:25W 5% carbon film 

C1 47, radial elect. 16V 
GZ 100, axial elect. 10V 

D1 1N5822 Schottky rec. diode 
11 LT1073CN8 switch.mode 
d.c. to d.c. adj. regulator: 

L1 100pH min. radial inductors: 
S1 min. s.p.s.t. toggle-switch 
(see text) 
B1 1-5V or 3V battery (see text) 
Stripboard 0-1in. matrix, size 22 -holes 
X°14 copper strips; 8-pin d.i.f socket; 
battery holder; single-sided solder pins; 
multistrand connecting wire; case to 
choice; solder etc. ps 

Approx cost 
guidance only 



Smoothing of the output signal 18 
provided by capacitor C2. A value of 
100uF is more than adequate as the 
maximum output current is quite low, and 
the ripple frequency is relatively high. 
Resistors Rl and R2 provide a:load:across 
the output under quiescent conditions, and 
they are also the feedback network for the 
regulator circuit. 

The output voltage is typically a little un- 
der 9V with the specified values, but there 
will obviously be some variation in the out- 
put voltage from one unit to another due'to 
the component tolerances. If necessary, the 
output voltage can be boosted slightly: by 
increasing the value of resistor R1 to 430 

The built-in regulator is very efficient, 
and variations in output loading have very 

Layout of components on the stripboard. The extra board space at the top 1s so that 
/t can easily be mounted, on spacers, in a small plastic box. 

Everyday with Practical Electronics, June 1995 


The complete 
Converter circuit 
board. Note the use of a 
.c. socket for the d.c. to d.c. 
adjustable regulator. 

- zranimoaoonse > 


Fig. 3. Stripboard component layout and interwiring. The only breaks 
required in the underside copper tracks are between the i.c. pins at points J14 

little effect on the output voltage. In fact 
the output voltage is more stable than that 
from a real PP3 battery. 


‘This simple circuit is easily built on a 
small piece of stripboard, and a suitable 
topside component layout and the four un- 
derside breaks in the copper strips is shown 
in Fig. 3. This layout is based on a board 
which has 22 holes by 14 copper strips. 


ee ee 



Construction of the board is not difficult, 
but there are a few points which must be 
borne in mind. . 

The 1N5822 rectifier diode used for D1 
has exceptionally heavy gauge leadout wires. 
These are presumably designed to aid a very 
low voltage drop when the device is used 
at high currents, but they simply make the 
component a bit awkward to deal with in 
this case. D1’s leadout wires are too thick to 
go through the holes in the stripboard! 

One possible solution would be to en- 
large the appropriate two holes, but it was 
found easier to fit these holes with single- 
sided pins, and then connect D1 to the pins. 
This does not give particularly neat results, 
but it works well, and is risk-free. 

The choice of component for IC] must 
be a plain LT1073CN8, and not an 
LT1073CN8-5 (which has a fixed output 
potential of SV). IC1 is not a static sensitive 
component, but it is not a particularly 
cheap type either. Therefore, it is strongly 
recommended that an i.c. holder be used 
for this component. 

It is also recommended that only the 
specified inductor be used for L1 (see Shop 
Talk). The circuit should operate well using 
any 100uH inductor that is suitable for 
operation at around 20kHz and has a 
reasonably low resistance, but the circuit 
has only been tested using the specified 
component. Also, other types might not fit 
well into this component layout. Do not 
overlook the three short link-wires. 


The AA battery or batteries fit into a 
plastic holder. It is probably best to use 
a holder that has solder tags rather than a 
PP3 style connector. This is due to the fact 
that the circuit seems to stall at switch-on 
unless the resistance between the battery 
and the circuit board is kept very low. 

Soldered connections avoid the risk of 
poor connections between the battery 
holder and the battery clip. The terminals 
which connect to the battery or batteries 
must be kept reasonably clean and free 
from corrosion. 

This device should work well with most 
projects that require a 9V supply at no 
more than a few milliamps. It is less than 
ideal for use with radio equipment though, 
or any sensitive circuits that could be 
adversely affected by the signal that is 
inevitably radiated due to the switching 
action of the step-up circuit. O 

EPE Valve HiFi Amplifier 

_It is most important that constructors 
undertaking the EPE Valve HiFi Amplifier 
adhere to the correct ratings of the resistors 
listed in the components box. Brimistors are 
now considered obsolete technology and 
are not now generally available. However, 
Brian J. Reed (4 0787 393 9055) can, we 
understand, supply them at a surplus price. 

Due to their weight, the mains 
and valve output transformers are best 
ordered/purchased from your _ nearest 
Maplin shop to save on the postage costs. 
These transformers were specially wound 
by Danbury Electronics (DB424 and 
DB425) for Maplin, codes DM54J (Valve 
Mains) and DM35H (O/P Trans.). 

The “chassis” diecast box and solid 
aluminium capacitors were purchased from 
Farnell Electronic Services (07279 
626777). Solid aluminium capacitors are 
also stocked by many of our component 
advertisers. Electro Supplies (@P 0767 
477 9272) can supply high voltage 

The purchase of the valves can be a bit 
tricky as prices will depend on where you 
make your purchase and it is probably wise 
to ring round our advertisers, such as Green- 
weld, Cirkit, Mauritron, ESR, Bull and M&B 
Electrical. One of the cheapest appears to be 
Colomor (4 0787 743 0899). Ham radio 
rallies are also a good source, but don’t buy 


with David Barrington 

from specialist HiFi suppliers unless you 
have a large trust fund. 

The Phase- Splitter p.c.b. is available from 
the EPE PCB Service, code 941. 

PIC-DATS 4-Channel Light Chaser | 

A full kit of parts for the 4-Channe/ Light 
Chaser, PIC-DATS demonstration project, 
is available from Magenta Electronics, 
Dept. EPE, 135 Hunter Street, Burton- 
on-Trent, Staffs., DE14 2ST. 

The kit (code 855) includes the p.c.b., 
a “one time programmable” PIC chip and 
a disk containing all necessary software. 
The cost of the kit is £39.95 (less case), 
plus £3 for post and carriage. Also available 
separately is the disk containing the basic 
software and development programs for the 
sum of £3.99, including p&p. 

The printed circuit board is available from 
the EPE PCB Service, code 942. 

R.F. Signal Generator 

Several components needed for the A.F. 
Signal Generator can be classed as special 
items and may not be available locally. 

The first and probably most expensive 
of these is the Jackson type-O twin- 
gang air-spaced tuning capacitor. This is 
available from Maplin (code FF40T) or 

‘Electrovalue, (4 07784 442253), code 

5250/2. The epicyclic reduction drive unit 
and pointer were purchased from Maplin, 
codes RX42V and HB47B respectively. 

The presets should be as specified or 
they will not fit on the p.c.b. These were 
obtained through Electromail, (4 07536. 
204555), code 186-750. The neon LP1 
was also ordered from the same source and 
is the ‘‘slim-line” type, code 576-614. 

The only listing we have found for the 
high frequency f.e.t. type 2N5486 has also 
been Electromail, code 641-910. The 3VA 
mains transformer has twin 15V_ secon- 
daries and came from the above source, 
code 210-796. 

Capacitor C19 MUST be a type rated for 
continuous operation across the mains sup- 
ply. These are usually classified as class-X 
or class-Y types and are stocked by most 
component suppliers. 

The p.c.b.s are available from the FPE 
PCB Service, code 936 (R.F./Mod.) and 
937a/b (Coil and Power Supply — pair). 

AA to PP3 Converter 

For best results it is recommended that 
only the specified components be used in 
the AA to PP3 Converter project. 

The switch mode adjustable voltage 
regulator 1C1 must be a plain LT1073CN8, 
and not one with a suffix-5 added to the 
type number. This device was purchased 
from Electromail (@® 07536 204555), 
code 265-364. 

It is important that the 1N5822 Schottky 
rectifier diode be used in this circuit. This 
was purchased from Maplin, code GX30H. 
The circuit will work with an.ordinary rec- 
tifier diode, such as the 1N4002, but with 
greatly reduced efficiency. 

The 100uH radial inductor is listed by 
Maplin code AH32K and Electromail, code 

Everyday with Practical Electronics, June 1995 


If you are looking for a means of 
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basics of electronics then this 
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Everyday with Practical Electronics, June 1995 479 


Mike Tooley, BA 

Part 9 

provide you with a comprehensive and up-to-date 
introduction to the world of electronics. The series is 
based on Electronics Workbench, a remarkable software 
package that lets you use your PC to build and test a wide 

E LECTRONICS from the Ground Up is designed to 

range of circuits. 

In this final instalment we round-off the series by taking a 
brief look back at the earlier parts and suggesting some 
further reading for those wishing to explore the full poten- 
tial of Electronics Workbench. 

Back issues of earlier parts of this series are available — 

see Back Issues page. 


Part One of Electronics from the Ground 
Up provided you with a brief introduction to 
electricity and electronics. Its five practical 
assignments aimed to familiarize you with 
the techniques for constructing simple 
circuits and making measurements with 
the basic test instruments provided in 
Electronics Workbench (EWB). 

Part Two dealt with d.c. and a.c. circuits 
and also described the use of the oscillo- 
scope for measuring waveforms. This part 
also introduced capacitors and inductors 
and their use in a.c. and d.c. circuits. 

Semiconductor diodes were introduced 
in Part Three. We investigated the be- 
haviour of half-wave and full-wave rectifiers 
and developed these into complete power 
supply circuits incorporating smoothing 
and voltage regulation. 

5 V/biv 
loc] © 



2. V/Div  & 

Fig. 9.1 Push-pull output stage from Electronics Workbench: 150 Circuits. 


Transistors featured in Part Four where 
we also introduced the concept of gain 
and amplification. Understanding transistor 
operation is crucial to understanding most 
analogue circuits and it is worth revisiting 
this part if you intend to work with transistor 
circuits in the future (note that, to keep 
things simple, we did not cover field effect 

Integrated circuit operational amplifiers 
were explained in Part Five. We looked at a 
variety of circuit applications for opera- 
tional amplifiers (op.amps) and showed 
how it was possible to design circuits to 
provide specific amounts of gain as well as 
an accurately defined frequency response. 

Oscillators were described in Part Six 
where we investigated the behaviour of 
a variety of oscillator circuits including 
sinusoidal, pulse and square-wave types. 
Part Seven was devoted to logic gates, 
digital circuits, truth tables and Boolean 
algebra. Finally, Part Eight featured bis- 
table elements and we illustrated their use 
in counters and shift registers. These last 
two parts are essential for those intending 
to work primarily with digital circuits. | 


Readers wishing to explore electronics 
further will be pleased to know that EWB 
is well supported with three books that 
provide information on extending the use 
of the package. Each book is supported 
with a disk containing circuit files for 
loading into EWB. 

Everyday with Practical Electronics, June 1995 

oan | |e 

FRequency [120 iL Hz By 

puTy cycLe [50 



Fig. 9.2 Notch filter from Electronics 
Workbench: 150 Circuits (note the Bode 
Plotter display clearly shows the notch in 
the frequency response characteristic). 


ence _FJE] @ 

1.68ms/div = 




Electronics Workbench: 150 Circuits (pub- 
lished by Interactive, ISBN 0-921862-24-5) 
contains 150 of the most frequently-used 
electronic circuits. The book contains a typi- 
cal screen shot of each circuit as supplied on 
the accompanying floppy disk. Test equip- 
ment settings and displays also feature as 
does a brief written explanation of each circuit 
together with some further suggestions for 
experimentation. In many respects, this book 
begins where Electronics from the Ground 
Up ends and provides enormous scope for 
further experimentation. 

If you are interested in servicing or fault- 
finding, Troubleshooting with Electronics 
_ Workbench by Don Browning (published 

_by Interactive, ISBN 0-921862-27-X) is just 
for you! This book contains more than 
00 ready-to-use circuits and assignments. 
However, unlike Electronics Workbench: 
150 Circuits, the circuit files in this book 
are not working! Instead, you are left to 
determine the cause of the fault using the 
test equipment exactly as you would on 

Electronics Workbench: 150 Circuits. 
ISBN 0-921862-24-5. 

Everyday with Practical Electronics, June 1995 

Troubleshooting with Electronics 
Workbench. ISBN 0-921862-27-X. 

a real circuit. Troubleshooting with Elec- 
tronics Workbench introduces the learner 
to troubleshooting techniques and, most 
important, it develops the logical thinking 
process that results in rapid and efficient 
fault finding. 

Finally, Electronics Workbench: Practi- 
cal Teaching Ideas by Allan Souder (pub- 
lished by Interactive, ISBN 0-921862-22-9) 

contains a teacher’s perspective on the use 

of EWB in the classroom. Allan Souder 
shares his experiences with readers in the 
form of exercises, exarhples and assign- 
ments. Teachers will find this a particularly 
useful book as it shows how several im- 
portant principles and concepts can be 
brought to life with the aid of EWB. 

If you intend to make further use of EWB 
you should seriously consider upgrading to 

the full package. The full package will 
provide you with a full range of test 

equipment (including Bode Plotter and 
Logic Converter that were not included in 
the cut-down version) and an unlimited 
Parts Bin. The package also comes with 
some additional support materials, “on- 
line” help, and an excellent User’s Guide 
which includes tutorials, a reference sec- 
tion and troubleshooting information. A 

Electronics Workbench: Practical Teach- 
ing Ideas: ISBN 0-921862-22-9. 


Ph ei I 


File Edit Circuit Window Help 

ce 6.2 2.94 [2.2.6 





|Two-stage common-emitter amplifier. 

Overall voltage gain (approx) = 115 

For vin of 20 my (p-p) at 1808Hz., vout is 2.3v(p-p) 

| oe 
=[ Wultineter 

Faure .3yv 





Low 3dB frequency = 100Hz. 

Fig. 9.3 Fault-finding a two-stage common-emitter amplifier with Troubleshooting with Electronics Workbench. 

“Quick Reference Card” is also supplied. 
You can use this to get started, or simply 
keep it by you for reference. 

Interactive demonstrations are included 
on the disk that comes with the package. 
These examples give you a quick overview 
of EWB and show you how to build and test 
circuits. Sample circuits (also supplied on 

pr 3.3 KOHM 

256 OHM 

3.262 VOLT 


the disk) include approximately 20 typical 
analogue and digital circuits. You can ex- 
amine, test and modify them or use them 
as building blocks for your own circuits. 
Tutorials are included within the User’s 
Guide. These are invaluable for those who 
may be unfamiliar with a graphical user 
interface or who may have had little or 

no experience of building and testing 
electronic circuits. For registered users, 
there is the User Support “help-line”. A 
Bulletin Board Service (BBS) is also avail- 
able to provide the latest product informa- 
tion. Users can leave questions for answer 
via the BBS and circuits may be down or 
up-loaded for sharing with other users. 

| a, FOL 

$608 OHM 

478 OHM 

256 9) 

Yd | ey EY 



| Parts [Gl 

| | 

Fig. 9.4 An example of Thevenin’s Theorem in Electronics Workbench: Practical Teaching Ideas. | 

Everyday with Practical Electronics, June 1995 

The full version of EWB offers a wide 
choice of printing facilities. You can print 
the current display (exactly as it appears on 
your computer's screen) or print out circuit 
descriptions, component lists, parameters 
associated with the component models, 
circuit diagrams, and test equipment dis- 

plays. You can also convert your display | 

into a PCX file for loading into one of 
many popular paint, graphics, CAD ‘or DTP 

Finally, it is important to note that the full 
version of EWB is copy protected and must 
be uninstalled if you wish to move the 
software to a different platform. However, if 
you want to use EWB at two different 
locations (for example, at work and at 
home), you need not delete all of the EWB 
files when uninstalling, just the authoriza- 
tion code. 


One of the questions asked by several 
readers relates to what else you can do with 
EWB once you have finished using it as a 
learning aid. One ‘of the advantages of 
the package as far as the hobbyist and 

i te . ‘ ~ — =~ 

Fig. 9.5 Answer to last month’s Brain Teaser. 

enthusiast is concerned is that it permits 

breadboarding of circuits before laying 

them out for final prototype construction. 

There are several stages to this process: 

1. Sketch the basic circuit design and 
identify component values 

2. Select the required components from 
the Parts Bin and place them within the 
breadboard area 

3. Change the component values (from 
their default values to those that you 

4. Select the appropriate models for the 
active components used in the circuit 

5. Connect the circuit 

6. Select the instruments that you require 
to test the circuit (often you will start 
with the multi-range meter in order to 
check supplies and bias voltages, etc.) 

7. Place the test instruments on the 
breadboard and select appropriate 

8. Refine the circuit layout (i.e., move the 
components and test instruments so 
that the symbols, component legends, 
and wiring all fit neatly and logically 
within the breadboard area) 

clear] | 

Ei] « 

9. Test the circuit and, where neces- 
sary modify component values as 

10. Evaluate the circuit and check against 

11. Print out the circuit diagram and com- 
ponents list (don’t forget to save the 
circuit for future reference!). 

Answer to last month’s Brain Teaser 

Last month’s Brain Teaser involved the 
design of a logic circuit arrangement that 
would generate a waveform with a ratio of 
high to low period of 7:1. Fig. 9.5 shows the 
solution arrived at using the full version of 
EWB together with the logic analyser display 
(the output waveform is the lowest trace). 



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@ S/N RATIO 10db @ SEPARATION 70db 

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



P A 700 marae 8 

W @ INPUT 0: ‘75V-1-2V VIA 4" (6-35mm) JACK SOCKETS 
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sk @ OUTPUT MAX 2x 350W (4 ohms) VIA 3-PIN XLR FM} 

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2 mins. from Edgware Road Tube Station. 
' Everyday with Practical Electronics, June 1995 483 

Robert Penfold 

‘ pear 
A COMPUTER operated model train con- 
troller of the pulsed variety can be 
quite a complex set up. Such a system can 
be based on a conventional pulse width 
modulation (p.w.m.) controller, with the 
control voltage being provided from an 
output port of the computer via a digi- 
tal to analogue converter. This involves 
quite a lot of hardware, and is relatively 
expensive, but it does have a significant 

The speed of the train is controlled by 
simply outputting suitable values to the 
output port. High values give fast speeds, 
and low values give slow speeds or stop 
the model train. This method of control is 
not particularly taxing on the computer, 

which can therefore be a slow machine | 

running a slow programming language. 

The demands on the computer are so low — 

that there will still be plenty of computing 
time left for other tasks, such as controll- 
ing signals, or providing some sort of 
graphics display. 

On The Pulse 

There is an alternative approach that re- 
quires far less hardware, and this is to use a 
software routine to generate a suitable pulse 
signal on a digital output line. The signal is 
then used to drive the train via an amplifier 
and a buffer stage. This method is quite 
simple to implement in theory, since the 
pulsed output signal is an extremely simple 

To drive the train at half power a 
squarewave signal is used. With its one-to- 
one mark-space ratio the. average output 
voltage squarewave is half the supply 
potential. Using a higher mark-space ratio 
gives an output signal that is high for a 
greater proportion of the time. This gives a 
higher average output voltage, and more 
power is fed to the motor in the train. Using 
a lower mark-space ratio give a lower 
average output voltage, and less power to 
the motor in the engine. 

Although one might reasonably expect 
the pulsed signal to interfere with the 

correct operation of the motor, this does not 

actually happen. In fact a pulsed signal gives 

better low speed performance, with less 

likelihood of stalling. Pulsed control also 
gives more realistic starting, with no jump- 

starts. Very low pulse speeds must be. 

avoided as they would result in the motor 
operating intermittently. 

High pulse rates are also unsuitable, as 
they can result in strong radio frequency 
interference being radiated from the tracks. 
Also, the motor provides a highly inductive 
load which-could have a high impedance at 
high frequencies. This would give an in- 
adequate current flow. In practice, any fre- 
quency from around 50Hz to 500Hz or so is 
usually satisfactory. 


In days gone by, this software based 
method was not possible using an ordinary 
BASIC language due to the slow operating 
speed of an interpreted BASIC. Producing 
an output signal having a suitable range of 
mark-space ratios was possible, but not at a 
high enough frequency to give good results. 

However, modern computers are much 
faster than the 8-bit machines of about ten — 

years ago. A few experiments using a 
33MHz 80386 based PC running GW 
BASIC and Q BASIC programs showed that 

it is possible to obtain quite good results 

using a software generated pulse signal. 
Results should be at least as good using a 
faster PC, but it might not be worthwhile 
using anything less than an 80386SX based 
PC running at about 20 or 25MHz. 


To R1 2 R3 

Port 10k 1k5 


a pala PAT FO PR RAE MART RY. Tae 

the reference level, and the output of ICI 

goes low. Transistor TRI is an emitter 

follower buffer stage at the output of IC1. : 
This is a high gain power Darlington device, 
and although the drive current from IC1 is" 
only a few milliamps, TR1 can drive the 
motor with output currents of up to two 
amps. Resistor R4 provides TR1 with a load 
resistance when the output of the controller 
is left unconnected. Diodes D1 and D2 
suppress any high voltage transients that 
are generated across the inductive load 
provided by a small d.c. motor. 

Switch S1 is the forward/reverse switch, 
and this can be a set of d.p.d.t. relay contacts 
if direction control via the computer is re- 
quired. Fig. 2 shows the circuit diagram for a 

suitable relay driver. The relay can be any 12 

Fig. 1. Circuit diagram for the pulsed controller interface. 


The circuit diagram for the pulsed con- 
troller interface is shown in Fig. 1. IC1 is an 
operational amplifier, but in this circuit it is 

used as a voltage comparator. IC1 must be 

a device that can operate properly with 
low input voltages. The NE5534P (and 
NE5534AN) are suitable, but most other 

operational amplifiers will not work in this 


Resistors R2 and R3 provide a reference ; 

potential of between 1:5 and two volts to 
ICI’s non-inverting input. In other words, a 
voltage that is between the valid logic 0 and 
logic 1 levels. IC1’s non-inverting input is 
fed from the digital output of the computer. 
Obviously any latching output will do, but 
it will be assumed here that the interface is 
driven from D0 of printer port one (LPT 1). 

When the digital output is high, ICI’s © 

non-inverting input is taken above the 
reference level, and the output of IC1 goes 
high. When the digital output is low, ICI’s 

‘non-inverting input (pin 3) is taken below 

volt type which has a coil resistance of 
about 250 ohms or more, and d.p.d.t. con- 
tacts of adequate rating. Again, this circuit 
can be driven from any latching digital out- 
put, but we will proceed on the assump- 
tion that it is driven from the “Initialise” 



Fig. 2. Direction control relay driver. 

Everyday with Practical Electronics, June 1995 

Fig. 3. Printer port connections for the pulsed train controller. 

output of LPT1. Fig. 3 provides details of 
the connections to the printer port for both 

the pulse controller interface and the relay 


Both circuits require a 15 volt supply 
which must be reasonably stable and ripple- 
free. The maximum output voltage from the 
controller is about 12 volts due to the 
voltage losses introduced by IC1 and TR1. 
For small gauge trains a maximum supply 
current of one amp is adequate, and the 
mains power supply circuit of Fig. 4 can then 
be used. Transformer T1 should have a 
secondary rating of at least two amps, and 
FS1 should be an “anti-surge” or “time- 
delay” fuse. 

The same circuit can be used for larger 
gauge locomotives that require up to two 
amps, but transformer T1 must then have a 
secondary rating of at least four amps, and 
fuse FSI should have a rating of two 
amps. Also, diodes D1 to D4 should be 
1N5402 rectifiers, and IC1 should be a 
78S15 regulator (which is available from 
RS/Electromail). The normal safety precau- 
tions should be observed when building 
and using the power supply. Beginners 
‘should not undertake construction of a 
mains powered circuit such as this. 

Transistor TR1 and regulator IC1 in the 
power supply must be fitted with heatsinks. 
For a one amp controller a couple of bolt-on 
heatsinks having a rating of about 10 or 12 
degrees Centigrade per watt will suffice. For 
a two amp version it would be advisable 
to use larger heatsinks having a rating of 
about six to seven degrees Centigrade per 
watt. Note that the heat-tab of TR1 con- 
nects internally to its collector terminal. The 
heat-tab of the voltage regulator connects 
internally to its common terminal. 

The GW BASIC/Q BASIC program 
shown in the software listing provides speed 

control, and direction control as well if the | 

relay driver circuit is included in the 

The first part of the program simply clears 
the screen and provides on-screen instruc- 
tions on how to control the program. 
Lines from 90 to 160 produce the output 
_ waveform on output Do of the printer port. 
Two FOR... NEXT delay loops set the high 
and low output times. The number of loops 
performed in each of these, and hence the 
mark and space times, are controlled by 
variables “M” and “S”. They are each given 
an initial value of 50, giving a one-to-one 
mark-space ratio. Other values can be used 
at lines 90 and 100, but the two values must 
total 100. 

The GOTO in- 
struction at line 190 
continuously loops 
the relevant part 
of the program. 
However, lines 170 
and 180 detect key 
presses, and take the 
program into the 

at line 200. If the 
“A’ key is pressed, 
‘M” is increased by 
one, and “S” is 
decreased by one, giving increased output 
power. Pressing the “B” key has the 
opposite effect, with “M” being decre- 
mented by one, and “S” being incremented 
by one. This produces reduced output 
powe:. . . 

Operating the “E” key brings the pro- 
gram to a halt at line 220. Lines 230 and 
240 provide forward/reverse switching if 
the relay driver circuit is included: These 
lines detect presses of the “R” and “F” keys 

respectively, and set the “Initialise” output — 

high or low. The purpose of lines 250 to 280 
is to keep the values of “M” and “S” within 
acceptable limits. 

Although the hardware and software are 
both pretty basic, the system provides 
excellent control, with smooth acceleration 
and deceleration. Results would probably be 
a bit slow and jerky using a slow PC. Using 
a fast 80486 or Pentium based PC it might 
be necessary to use higher values in the 
FOR ... NEXT loops. Otherwise accelera- 
tion and deceleration might be too rapid. At 
minimum power the motor is not com- 
pletely switched off, and it is still fed with 
very brief pulses. The power fed. to the 
motor should be far too low to be of any 
practical significance though. 

_ nfo 

240V AC 

subroutine _ starting. 

Software listing for generating pulses 
for Model Train Controlling. 


20 OUT &H378, 0 

30 CLS 






90 M=50 | 

100 S = 50 

110 OUT &H378, 1 

120 FOR HIGH = 1TOM 


140 OUT &H378, 0 

150 FORLOW = 1TOS 


170 A$ = INKEY$ 

180 IF LEN(A$) = 1 THEN GOSUB 200 
190 GOTO 110 

200 IF ASC(A$) = 97 THENM = M+ 1 

205 IF ASC(A$) = 97 THENS = S — 1 

210 IF ASC(A$) = 98 THENS = S + 1 

215 IF ASC(A$) = 98 THENM = M — 1 

220 IF ASC(A$) = 101 THEN END 

230 IF ASC(A$) = 114 THEN OUT 

240 IF ASC(A$) = 102 THEN OUT 

250 IFM > 100 THENM = 100 

260 IFM < 1THENM = 1 

270 IFS > 100 THENS = 100 

280 IFS < 1THENS = 1 

290 RETURN | 

Fig. 4 (below). Circuit diagram for the 
15 V mains power supply unit. 

ICt = vA7815 
Di to D4 = 1N4002 




This ring binder uses a special system to allow the issues to be easily removed and 
reinserted without any damage. A nylon strip slips over each issue and this passes over 
the four rings in the binder, thus holding the magazine in place. 

The binders are finished in hard wearing royal blue p.v.c. with the magazine logo in 
gold on the spine. They will keep your issues neat and tidy but allow you to remove them 
for use easily. ) 

The price is £5.95 plus £3.50 post and packing. If you order more than one binder add 
£1 postage for each binder after the initial £3.50 postage charge, (for overseas readers 
the postage is £6:00 each to everywhere except Australia and Papua New Guinea which 
costs £10.50 each). 

Send your payment in £'s sterling cheque or PO (Overseas readers send £ sterling 
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We also accept credit card payments. Mastercard (Access) or Visa (minimum credit 
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Everyday with Practical Electronics, June 1995 7 | 485 

-“s mini 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 
teal bare Se 2 watts!. £14. 10 Kit no 

FM/AM Scanast, well not quite you have 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. 

2 z 4 P4 ¥ £, Sto 
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 Near cree sdiiotabis ini 
sitivity, preset alarm time, auto reset. Could be 
connected to bikes horn etc. £14.10 Kit no 1011 

0-5 minute timer, adjustable from 0 to 5 mins, will 
switch up to 2A mains. Perfect for alarms, photo- 
graphiclaboratoriesetc. 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 
built up form only. £92.82 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 radar ideal as a movement detector 

" with arange of about 10 metres, automate your cat 

flap! 12v operation so ideal for cars, caravans etc. 
£16.45 Kit 1049. 

Liquid level detector useful for detecting fluid 
levels in tanks, fishponds, baths or as arain or leak 
alarm. Will switch 2A mains. £5.87 Kit no 1081. 

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 generator, produces sinusoidal, 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 youto 
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 1036. 


> D-v 
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 callrelay, useful dtenteatvaieeins 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 automatic charging rates, 
visual indication of battery state, ideal for alarm 
systems, emergency lighting etc. 100mA 12vdc. 
£14.10 Kit no 1095. 

Car alarm system, works on voltage drop and/or 
vibration, entry and exit delays plus adjustable 
alarm duration. Good for cars, caravansetc. £14.10 
Kit no 1019, 

Portable alarm sy stem, based on a mercury 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. 

BS avo7 

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. _ 

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. C an 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. 
a contr or motors up 

to 30A! (you may need a heatsink for 30A) £19.97. 
omposite converts composite signals 

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 experiments £5.87. 

5. Electronic accupuncture kit, may help with 
migrane, poor circulation, backache etc. £8.22. 

6. Wecttyine apparatus kit, produces a weak 
adjustable high tension of 80-300v from a 9v bat- 
tery, ideal for catching worms etc! £9.40. 

b Adapter bug kit, contains everything you need 
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 required. 

8. Nicad charger kit automatic charger for cells 
from 1.2v to 15v, 7 settings 50600mA, transformer 
required 18-20v 600mA. £9.40. 

JEU. Tnverter kits, produce 240vactrom a 12vdc 
supply, two versions are available a 15w one at 

£14.10, and an 80w version at £23.50. 

ay to order... 
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 
post and packing. 

Everyday with Practical Electronics, June 1995 

Constructional Project = 



A high performance, relatively 
low cost design that covers the 
range T15MHz to SOMHz in three 

switched bands. 

O FAR we have described the Sig- 
nal Generator circuits, fabrication of 
the component mounting chassis and 
construction of the three p.c.b.s. We have 
also covered the drilling of the front panel 
and the mounting of the completed rf. 
board, together with the coil bracket, on 
the large L-shaped mounting chassis. 
Before we move on to mounting the 
power supply board on the case rear panel 
and conclude with the calibration, we should 
like to refer back to the front panel drilling 
details (Fig. 9) given last month. The dis- 
tance measurement from the /eft-hand edge 
to holes ““D”’, the chassis mounting holes, 
should be 22mm and not 12:5mm as shown. 


The power supply unit is fitted to the 
back panel of the case. This panel, like the 
front one, can be completely removed to 
make life easier, and the positioning and 
fixing of the board is a simple job. Provi- 
sion is also made here for the entry of the 
mains cable and the fuseholder FS1. 

Holes for these should be drilled to 
suit the components you have; the mains 
lead can be brought directly through a 
grommeted hole, but must be adequately 
anchored down on the inner surface. If you 
use an appropriate plug and socket system, 
such anchoring is unnecessary. 

Again, you have the choice here. Fig. 17 
shows the board position, interwiring and 
suitable places for the fuseholder and 
mains lead entry points. 


Some of the panel components, switches 
S1, S2 and S3, and the output poten- 
tiometer VR3 are mounted on the rear 
mounting chassis. The remaining pieces, 
two 4mm sockets, the BNC output connec- 
tor and the neon indicator LP1 go onto the 
front panel proper. 

When the panels are finally brought 
together, these front panel parts project 
through the corresponding holes in the rear 
mounting panel for internal connections to 
be made later. This is where accurate 
alignment of the holes is vital, but any 
slight deviations can be corrected with a 
round file. 

What follows now applies to those con- - 
structors who are using the printed scale 

provided (see Fig. 15); this should be. ac- 
curate enough for general purpose use as- 

suming that the coils have been carefully. 

wound to specification. For those purists 
who would wish to do their own calibration, 

suitable methods will be givenlateron. =. 
Mount first of all those parts which goon 
the rear back mounting panel: switches S1, 

S2 and $3 and the output control VR3. The 
rotary switches have small locating lugs 
which when used will prevent the switch 
bodies rotating in use. 

It is wise (but not absolutely essential) to 

use this facility by drilling 3mm (’s") holes 
positioned about 10mm (*s”) from the cen- 
tre of the main fixing hole as Fig. 13 il- 

lustrates; when the switches are fitted, these 

holes should accept the locating lug snugly. 
Using these holes also prevents unneces- 
sary over-tightening of the locking nuts. 

Part 2 == 


Now, for the time being, wire up in- 
ternally the coil outlets to switch Sl, 
adjusting the wire lengths as necessary 
(but not tight); bring two leads from the 
poles of this switch down to the two 
nearest solder pin points on the main 
board (P6 and P7), and connect the ‘‘tag”’ 
common connection from the coil board 
to the appropriate pin (P5) on the main 
p.c.b. (see Fig. 17). 


Fig. 13. To stop the rotary switches 
rotating during use their locating lugs 
are secured in small holes SOpICA 
their main fixing holes. 

The input and output sockets are mounted on the front panel and protrude through 
holes in the L-shaped mounting chassis so that they can be wired to the Function 
switch and the R.F. Level contro/ potentiometer. Note the capacitors wired directly 
between the switch tags and the 4mm sockets. 

Everyday with Practical Electronics, June 1995 





Fig. 14. Oscilloscope display of the output as unmodulated 
and as modulated carrier. In the modulated case the high 


frequency signal Is not seen as individual waves. 

Connect also two leads from the power 
supply unit to the r.f. board input pins 
P4 and P8, making sure of the correct 
polarity. This then completes the tem- 
porary wire-up needed for test and calibra- 
tion purposes. 

Keep the power unit in the background 
by using longish connections; you cannot 
then touch it accidentally when doing the 
checks. In this condition, both testing and 
calibration can be completed before the 
front panel and its components are fitted to 
the rear mounting chassis. 

Due to the presence of mains voltages on 
the power supply p.c.b., and also from 
the mains input socket and fuseholder on 
the back panel, extreme care MUST be 
taken when testing and calibrating the sub- 
assemblies. In fact, apart from “keeping the 
power panel in the background”’, it might be 
wise to also put it in a temporary box for 
additional safety. 


For comprehensive testing of the R.F. 
Signal Generator you will need, as men- 
tioned earlier, a voltmeter (digital or 
analogue), an oscilloscope and, if you are 
doing your own calibration later on, a 
frequency meter. 

Set the preset potentiometers VR1 and 
VR2 to mid-travel, close the tuning 
capacitor gang, set the Frequency Range 
switch S1 to the lowest frequency range, 
(fully anticlockwise), and have a voltmeter 
ready. Switch on the power supply unit and 
check the following voltages at the main 
board points indicated: 

P4: About 18V (if below 16V reduce 
R18 in value slightly) 

Across diode D1: 15V+0-5V 

Across diode D3: 7:5V +0-5V 

P5; About 4V +0-5V 

P10 (collector of TR2): 13V+1V 

Interpret these measurements’ with 
respect to the tolerances of the Zener 

diodes for example; very small differences 

outside of the ranges given can be ignored. 

If the voltages seem satisfactory and 
there is no sign of discontent from any of 
the board components, connect the oscillo- 
scope to the output point pin P9 and switch 
to a fast timebase; there should be a 
continuous sinewave output as shown in 
Fig. 14. If necessary, adjust preset VR2 
carefully to ensure that there is no visible 
distortion of the output waveform. 

Check now on all three positions of 
Range switch S1 and all rotations of the 
tuning capacitor. There will probably be 
small variations in the amplitude of the 
waveform throughout these checks but the 
oscillation should not collapse. 


The amplitude on the upper range par- 
ticularly may well be seen to diminish as 
the tuning is adjusted, but this is most 
likely to be due to the falling response 
of the oscilloscope to frequencies above 
some 20MHz. If you can use the scope to 
measure the wave amplitude, this should be 
about 3V peak-to-peak (1:07V r.m.s.). 

Now connect together, with a short piece 
of wire, the points PJ and P2. This will 
enable the 500Hz oscillator/modulator sec- 
tion. Check with the scope switched to a 
relatively slow timebase that there is a 
sinusoidal output at the collector of TRS, 
point P3. This wave should be about 
4V amplitude peak-to-peak (1-4V r.m.s.) 
and approximately 500Hz in frequency, 
though the exact value is not important; 
more important is that there should be no 

Transfer the scope to the output P9 again 
and with the same timebase setting adjust 
preset VR1 carefully to give you a mod- 
ulated output signal rather as shown in 
Fig. 14b. VR1 controls the depth of modul- 

Lettering and layout of components on the front panel of the 
completed R.F. Signal Generator. 

ation and any “unbalance’ or distortion 
in the modulation envelope. You should 
finish up with about 30 per cent modula- 
tion depth as the figure indicates but again, 
within reason, this is not a critical point. 

If all the above checks are satisfactory, 
the tuning scale can now be fitted (if this is 
your choice) before the final assembly con- 
struction is undertaken. 


There are three choices available here 
regarding the calibration of the R.F. Signal 
Generator: you can use the ready prepared 
scale, shown in Fig. 15; you can prepare 
your own scale in the same form; or you 
can use a frequency meter connected to 
the generator and forgo the central paper 
scale altogether. In this last case, as men- 
tioned earlier, the scale cutout will have 
been omitted from the front panel. 

If you use the ready prepared scale, 
its actual accuracy will essentially depend 

The positioning of the power supply p.c.b. fuseholder and mains input socket must 
be located on the case rear panel such that they do not short out on the coil board 
when they are finally brought together in the case. | 

Everyday with Practical Electronics, June 1995 

Fig. 16. How the scale is situated rela- 
tive to the position of the ball-drive 
flange and spindle. 

upon the care taken over the winding of the 
coils. The tuning capacitor may also con- 
tribute some slight error to the tracking but 
this will be small in the worst case, and the 
accuracy obtained will almost certainly be 

_ attributable to the inductances. 

To check on this point, three sets of the 
coils were constructed and the error against 
the scale calibration done with the first set 
did not amount to more than about one 
millimetre of scale position with the other 
two. Averaged out, this does not make 
the calibration worse than +3 per cent 
which is comparable with commercial in- 
struments in the lower price ranges. 

If you decide to use this scale (Fig. 15), 
don’t cut the copy from the magazine as 
there will be a tendency for the back print 
to show through when it is. glued in posi- 
tion. Get a photocopy made on to a piece 
of good quality paper, and trim this to the 
outline indicated in the diagram. 

Glue the scale (or edge tape it carefully) 
to the face of the rear, front panel mount- 
ing chassis so that the circular cut-out is 
positioned centrally to the projecting ball- 
drive flange and the bottom scale line in 
effect passes “‘through”’ the centre of the 
drive spindle. Fig. 16 should make these 
points clear. 

Next, cut the Perspex pointer to 57mm 
(2%") in overall length and screw it with 
a couple of short 8BA screws to the 
flange face. Unlock the rear gang spindle 
grubscrews so that the ball-drive does not 
rotate the gang (vanes), close the gang 
fully, and turn the ball-drive until the 
pointer cursor line is exactly in coin- 
cidence with the bottom scale line on the 
right-hand side. 

Fig. 16. 

Now retighten the gang spindle grub 
screws and check that the pointer travels 
over the scale without rubbing against it 
and finishes up along the bottom scale line 
of the left-hand side. There may be a slight 
overshoot here but ignore this as there is a 
“dead” patch over a few degrees when the 
capacitor vanes are fully disengaged. 


The completion of the work is now in 
sight (did I hear somebody somewhere 
make a comment?) but first the front panel 
has to be finished off with the appropriate 
legends and the fixing of a piece of Perspex 
or other transparent material over the scale 

Before lettering, the front panel may be 
sprayed a light colour, say, white or very 
pale blue, if black letters are used, and 
black or a dark blue if white letters are 
used. If the panel is not unduly marked 
from the hole cutting earlier, it may be left 
in its natural brushed aluminium finish. In 
all cases, make quite sure that the surface is 
free of grease. 

The required front panel marking, using 
rub-off lettering and assuming that the 
specified control knob sizes are used, can 


settee ate 

p aheratet alee 

The tuning scale 1s glued or taped to the face of the mounting 
chassis centrally above the ball-drive spindle — see opposite and 

be seen in the photographs. The size of the 
letters should not be more than 8-point 
(2mm) as room is at a premium on this 
panel, but you can decide for yourself if 
you feel that in some places a 10-point 
(2-5mm) or larger style might be more 
attractive or help legibility. When the let- 
tering is completed a thin coat of protective 
lacquer will make the legends resistant to 

It now remains to glue a piece of thin 
Perspex, say, 2mm ('16") thickness (or any 
other transparent sheet) over the scale 
cutout; this, of course, goes behind the 
front panel. This sheet will need a clearance 
hole for the drive spindle and an overlap of 
about 6mm ('’4") at the top and sides; it 
should not overlap at the bottom edge by 
more than 3mm ('’8”) or it might foul the 
4mm socket located below it. These points 
can best be judged when you are doing the 
work rather than my pouring out long 
sermons of explanation. 


The final assembly is quite straightfor- 
ward. The remaining panel components, 
neon indicator LPl, the BNC output 
socket and the two 4mm sockets can now 

The ball-drive links the tuning capacitor to the front panel tuning cursor and knob. 
One of the two spindle grub-screws can be clearly seen. 

Everyday with Practical Electronics, June 1995 


be fitted to the front panel and this in turn 
secured to the rear panel piece. 

Trim off the switch spindles to a 
projecting length to suit the knobs used 
(about 10mm (*s”) is suitable), fit the knobs 
with the correct orientation to match the 
panel markings where necessary, and 
finally check that everything turns or 
switches without scraping against the panel 
or the frequency scale. 

There is one important point to mention 
here which can save you spending more 
than you have to. The Lorlin switches and 
the output level potentiometer are avail- 
able with ain. (6-35mm) or 6mm spindles 
and if you use collet knobs as given in the 
parts list, make certain that you order the 
right size to suit the spindles you have. 

Also, some switches have a flat on the 
spindle to accommodate grub screw fixing, 
but if such a method is used here, the orien- 
tation of the switches must be such that the 
knob pointer marks match up to those on 
the front panel. If you use collet type knobs 
this problem does not arise, hence it is ad- 
visable to get the 6mm spindle types as well 
as minus the flat. 


The internal connections can now be 
made from the main board to the various 
panel sockets and switches; these are leads 
from board points PJ, P2 and P3 to Mod. 
Function switch S2 with returns by way of 
capacitor C9, C10/R17 to the 4mm sock- 
ets; a lead from point P9 to the output 
R.F. Level potentiometer VR3 and a short 
length of screened lead down to the BNC 
output socket with a return to the main 
board “‘earth’’ line at P//. The placing of 
these wires is not critical but keep them as 
neat as possible. 

The front panel can now be slid into the 
base part of the case; the back panel with 
the power supply board can be similarly 
placed in position and connections made 
for the positive and negative rails to board 
points P4 and P5 respectively. The mains 
lead is taken by way of the fuse FS1 to the 
On-Off switch $3 and returned to the trans- 
former input pads on the power supply 

The box top can now be finally screwed 
into position. A short appendix follows for 
those who wish to do their own calibra- 
tion or use a Frequency Meter directly for 

Own Calibration 

If you decide to do your own scale 
calibration, this can be carried out in one 
of two ways: either against a radio receiver 

which has a.m. medium and shortwave 
bands (a good communications receiver is 
really best for this purpose), or against a 
Frequency Counter which goes up as far as 
30MHz as a minimum. 

The first method, used with care, enables 
the work to be done with a fair degree 
of accuracy; the second methcd enables 
the calibration over the whole three ranges 
to be accomplished with a high degree of 

If you prefer to do away with a scale 
altogether, you can connect the Frequency 
Counter (or a suitable module) as your 
readout. As mentioned in the text, this 
method provides complete accuracy and 
saves the metal work needed for the front 
panel scale cutout. We will briefly examine 
these methods in turn. 




If you are to calibrate your own scale 
you will need a blank copy of the scale 
based on Fig. 15 and a “half” pointer. This 
latter if fabricated from a second Perspex 
pointer as given in the parts list and sawing 
it (with great care!) to the shape shown in 
Fig. 18. 

The cursor line now forms a calibration 
‘edge’ when the half pointer is fitted over 
the scale blank. A well pointed pencil can 

Fig. 18. Adapting a pointer for calibra- 
tion purposes. 



SK2 ©) SK1 @ 




Fig. 17. The front and rear panels lard flat to show the interwiring and main 

circuit board connecting points. Positioning of the power supply board, 
mains input socket and fuse are fairly critical as they could possibly foul the 
coil board when the sections are brought together in the case. 

Everyday with Practical Electronics, June 1995 

The top cover removed from the completed R.F. Signal Generator to show the 
compact arrangement of component boards inside the case. 

then make the various scale frequency 
positions by operating along this edge 
which effectively indicates the true cursor 
line when the full-size pointer is later fitted 
as described in the text. 

You will, of course, transfer the pencilled 
scale on to a fresh piece of paper using ink 
and rub-off numbering to complete your 
final scale. 


You will need a receiver which covers the 
frequency range 1-SMHz to 30MHz or 
wavelengths from 200m to 10m. These 
ranges will be found on the shortwave 
bands and possibly the bottom end of the 
medium wave band. 

A few inches of unscreened wire on the 
end of the r.f. output cable placed close to 
the receiver’s ferrite rod or the aerial input 

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point will radiate enough to be picked 
up by the receiver; only sufficient output 

should be used to hear the 500Hz modula- . 

tion adequately on the receiver speaker or 
phones. Too much will lead to confusing 
harmonics or swamping of the true tuning 

Starting with the lowest frequency 
range, which is about 1-4MHz to 2-4MHz 
(215m to 125m), set the receiver to 
1-S5MHz (200m) and tune the R.F. Signal 
Generator through the band until its 
output is detected by the receiver. This 
point is now marked on the scale. The 
1-6MHz point is then found in the same 
way, and so on. 

In this way all three bands can be 
calibrated at the main frequency points and 
marking between these added by eye. It has 
to be admitted that this method is tedious 
and the accuracy only fair, but for general 

purposes is possibly.good enough. 

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The use of a Frequency Counter for 
calibration purposes gives very good ac- 
curacy when transferred to the scale using 
the half-pointer method. 

The counter can be fed from the r.f. out- 
put socket or from point P/O on the main 
board; if you use this point, disconnect 
capacitor C14 or the signal level at the 
higher frequencies may not be adequate 
enough for the counter input. This point is 
actually useful if you build in a counter 
module in place of the scale. 

Switch to UNMOD. on the Function 
switch so that an unmodulated output is 
obtained for the counter. Tune the Signal 
Generator to give as exact readings as you 

-can hold on the counter (it is difficult to be 

absolutely precise); then at the frequencies © 
1-SMHz, 1-55MHz, 1:6MHz etc. calibrate 
the scale for the lowest range and repeat 
at convenient intervals for the other two 

This is the method that was used to 
draw up the scale of Fig. 15. If you are not 
using that scale as such but calibrating 
you own, you will find it a convenient 
guide to work to. 


This project is one involving a lot of 
careful workmanship, with quite a bit of 
thought given to each stage of construc- 
tion. Describing its construction has also 
not been easy, but hopefully the article 
has given enough information to make a 
worthwhile instrument. O 

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can switch mains up to 5A so could be footswitch if 
fitted in pattress. Order Ref: 263. 

50 x Mixed Silicon Diodes. Order Ref: 293. 

1 x 6 Digit Mains Operated Counter. Standard size but 
counts in even numbers. Order Ref: 28. 

2 x 6V Operated Reed Relays. One normally on, other 
normally closed. Order Ref: 48. 

1 x Cabinet Lock. With two keys. Order Ref: 55. 

6%" 82 5 Watt Speaker. Order Ref: 824. 

1 x Shaded-Pole Mains Motor. %” stack, so quite 
powerful. Order Ref: 85. 

2 x 5 Aluminium Fan Blades. Could be fitted to the 
above motor. Order Ref: 86. 

1x Case, 3%" x 2%” x 1%” with 13A socket pins. 
Order Ref: 845. 

4 x Luminous Rocker Switches. 10A mains. Order 
Ref: 793. 

4 x Different Standard V3 Microswitches. Order 
Ref: 340. 

4x Different Sub Min Microswitches. Order Ref: 313. 

iain ee Mere aaa r 
¥ perah wn Hee Why, ae f 
ca brane. * e % 



i ee See 

ey Vier Vi exe? Waele) = 

British Telecom Multimter. It is a 20,000 OPV with a full 
vision scale, nicely cased, measuring approximately 6” x 
4" x 2%" deep. Has six D.C. volt ranges up to 250V, five 
A.C. ranges up to 1000V, five D.C. current ranges up to 
1A and three resistance ranges, one low resistance, one 
medium and the other up to one Megohm. All ranges are 
selected by one central control switch. Price complete 
with leads £8.50, Order Ref: 8.5P3. Carrying case with 
handle available and space for small tools, £2 extra. 

Infra Red Controller. Made for Thorn TV sets but suitable 
for other control purposes. Fully built and ready to operate, 
real bargain, £21, Order Ref: 2P304. 

Hall Effect. Give positive or negative pulses when magnet 
passes over it. Mounted on small PCB, 2 for £1, Order Ref: 1032. 
Digital Multi-Tester. 30 range, model no. 3800, normal 
price £40, our price £25, Order Ref: 25P14. Brand new and 

Water Pump with spindle for operation by portable drill, £5, 
Order Ref: 5P240. 

Mains Klaxon Type Alarm. Very loud output but adjustable. 
Completely encased, shelf or wall mounting, £5, Order 
Ref: 5P226. 

Speed Controller for 12V DC Motors. Suitable for motors 
with horse powers up to one third and drawing currents 
up to 30A. Gives very good control of speed. Uses MOS- 
FETS and is based on a well tried circuit which appeared in 
the Mode! Engineer some time ago. The complete kit with 
case and on/off switch, price £18. Order Ref: 18P8. 

Figure-8 Flex. Figure-8 flat white pvc lead, flexible with 
‘ cores. Ideal for speaker extensions and bell 
circuits. Also adequately insulated for mains lighting. 
50m coil, £2. Order Ref: 2P345. 12m coil, £1. Order Ref: 1014. 
Friedland Underdome Bell. Their ref: 792, a loud ringer but 
very neat, 3” diameter, complete with wall fixing screws, 
£5. Order Ref: 5P232. 

Flashing Beacon. ideal as a warning light, the fire 
alarm, etc. Zenon tube produces intense pulse of 

light. Operates from 12V DC and is supplied complete 
with mounting base. Price £7.50, Order Ref: 7.5P13. 

12V 10A Switch Mode Power Supply. For only £9.50 and a 
little bit of work because you have to convert our 135W 
PSU. Modifications are relatively simple — we supply 
instructions. Simply order PSU Ref: 9.5P2 and request 
modification details, price still £9.50 

Medicine Cupboard Alarm. Or it could be used to warn 
when any cupboard door is opened. The light shining on 
the unit makes the bell ring. Completely built and neatly 
cased, requires only a battery, £3. Order Ref: 3P155. 

Don’t Let it Overflow! Be it bath, sink, cellar, sump or any 
other thing that could flood. This device will tell you when 
the water has risen to the pre-set level. Adjustable over 
quite a useful range. Neatly cased for wall mounting, ready 
to work when battery fitted, £3. Order Ref: 3P156. 

Very Powerful Mains Motor. With extra long (2%”) shafts 
extending out each side. Makes it ideal for a reversing 
arrangement for, as you know, shaded-pole motors are not 
reversible, £3. Order Ref: 3P157. 

45A Double-Pole Mains Switch. Mounted on a 6” x 3%” 
aluminium plate, beautifully finished in gold, with pilot 
light. Top quality, made by MEM, £2. Order Ref: 2P316. 
Lamp Dimmer. Suitable for up to 250W, on standard plate 
so fits directly in place of existing switch. Coloured red, 
blue, yellow or green but will take emulsion paint, £2 each, 
Order Ref: 2P380. 

LCD 3‘ Digit Panel Meter 
This is a multi-range voltmeter/ammeter using the 

A-D converter chip 7106 to provide five ranges each of 
volts and amps. Supplied with full data sheet. Special 
snip price of £12. Order Ref: 12P 19. 

12V/24V DC Solenoid. The construction of this is such that | 

it will push or pull. With 24V this is terrifically powerful but 
is still quite good at 12V, £1. Order Ref: 877. 

Don’t Stand Out In The Cold. Our 12m telephone extension 
lead has a flat BT socket one end and flat BT plug other 
end, £2. Order Ref: 2P338. 

20 W 5” 4 Ohm Speaker. Mounted on baffle with front grille, 
£3, Order Ref: 3P145. Matching 4 ohm 20W tweeter on 
separate baffle, £1.50. Order Ref: 1.5P9. 

Telephone Extension Wire, 4-core correctly colour coded, 
intended for permanent extensions, 25m coil, £2, Order 
Ref: 2P339. 

High Power Switch Mode PSU, Normal mains input, three 
outputs: +12V at 4A, +5A at 16A and —12V at ‘RA. 
Completely enclosed in plated steel case. Brand new. Our 
special offer price of £9.50, Order Ref: 9.5P 1. 

Philips 9”° High Resolution Monitor. Black and white in 
metal frame for easy mounting. Brand new, still in maker’s 
packing, offered at less than price of tube alone, only £15. 
Order Ref: 15P1. 

3%” Rubber Grommets for insulation through panel. Packet 
of 100, £1, Order Ref: 181. 

Mains Transformer 6V-0V-6V 6VA, £1, Order Ref: 330. 
Ceramic Wave Change Switch, 12-pole, 3-way with %” 

~ spindle, £1, Order Ref: 303. 

Luminous Rocker Switches. Packet of 3, £1, Order Ref: 373. 
Cased Mains Power Supply with leads, ideal to operate 
doorbell, £1, Order Ref: 102. 

High Current A.C. Mains Relay. This has a 230V coil and 
changeover switch rated at 15A with PCB mounting with 
clear plastic cover, £1, Order Ref: 965. 

Ultra Thin Drills, actually 0.3mm. To buy these regular 
costs a fortune. However, these are packed in half dozens 
and the price to you is £1 per pack. Order Ref: 797B. 

You Can Stand On It! Made to house GPO telephone equip- 
ment,.this box is extremely tough and would be ideal for 
keeping your small tools in. Internal size approx. 10%” 
x 4%" x 6” high. Complete with carrying strap, price £2. 
Order Ref: 2P283B. 

Ultrasonic Transducers. Two metal cased units, one trans- 
mits, one receives. Built to operate around 40kHz. Price 
£1.50 the pair. Order Ref: 1.5P/4. 

Power Supply with Extras. Mains input is fused and filtered 
and the 12V DC output is voltage regulated. Intended for 
high class equipment, this is mounted on a PCB and, also 
mounted on the board, but easily removed, are two 12V 
relays and Piezo sounder, £3. Order Ref: 3P80B. 

Mains 230V Fan. Best make ‘“‘PAPST’’, 412” square, metal 
blades, £8. Order Ref: 8P8. 

Everyday with Practical Electronics, June 1995. 

sy Naferui, bwey.Vie) sj = 

2MW Laser. Helium neon by Philips, full spec. £30. Order Ref: 
30P1. Power supply for this in kit form with case is £15, Order 
Ref: 15P 16, or in larger case to house tube as well £18, Order 
Ref: 18P2. The larger unit, made up, tested and ready to use, 
complete with laser tube £69, Order Ref: 69P1. 

12V 8ohm speaker, only £1.50 and waterproof. 

Solar Charger. Holds 4AA NiCads and recharges these in 
eight hours, in very neat plastic case £6. Order Ref: 6P3. 
Ferrite Aerial Rod. 8” long %” diameter, made by Mullard. 
Complete with two coils, 2 for £1, Order Ref: 832P. 
Air-Spaced Trimmer Caps. 2-20pF, ideal for precision 
tuning UHF circuits, 4 for £1, Order Ref: 818B. 

Modem Amstrad FM240. As new condition but customer 
return, So you may need to fault find, £6, Order Ref: 6P34. 
Amstrad Power Unit. 13-5V at 1:9A or 12V at 2A encased 
and with leads and output plug, normal mains input, £6. 

-Order Ref: 6P23. 

80W Mains Transformer. Two available, good quality, both 
with normal primaries and upright mounting, one is 20V 
4A, Order Ref: 3P106, the other 40V 2A, Order Ref: 3P107, 
only £3 each. 

Project Box. Size approx. 8” x 4” x 4%” metal, sprayed grey, | 

louvred ends for ventilation otherwise undrilled. Made for 

.GPO so best quality, only £3 each. Order Ref: 3P74. 

Sintinel Component Board. Amongst hundreds of other 
parts, this has 15 ICs, all plug-in so do not need desolder- 
ing. Cost well over £100, yours for £4. Order Ref: 4P67. 
Sinclair 9V 2-1A Power Supply. Made to operate the 138K 
Spectrum Plus 2, cased with input and output leads. 
Originally listed at around £15, are brand new, our price is 
only £3. Order Ref: 3P 151. 

15W 8 Ohm 8” Speaker & 3” Tweeter. Made for a discon- 
tinued high quality music centre, gives real hi-fi and only 
£4 per pair. Order Ref: 4P57. 

Water Pump. Very powerful, mains operated, £10. Order 
Ref: 10P74. 

0-1mA Full Vision Panel Meter. 2%” square, scaled 0-100 
but scale easily removed for re-writing, £1, each. Order 
Ref: 756. 

Amstrad Keyboard Model KB5. This is a most comprehen- 
sive keyboard, having over 100 keys including, of course, 
full numerical and qwerty. Brand new, still in maker's 
packing, £5. Order Ref. 5P202. 

Unusual Solenoid. Solenoids normally have to be ener- 
gised to pull in and hold the core, this is a disadvantage 
where the appliance is left on for most of the time. We now 
have magnetic solenoids which hold the core until a volt- 
age is applied to release it. £2. Order Ref: 2P327. 

Mains Filter. Resin impregnated, nicely cased, p.c.b. 
mounting, £2, Order Ref: 2P315. 

0V-20V DC Panel Meter. This is a nice size 65mm sq. It is 
ideal if you are making a voltage variable instrument or 
battery charger. Price £3, Order Ref: 3P188. 

Another 12V-0V-12V Transformer is a 50VA and is suitable 
for dropping through the chassis or as it is fitted with four 
pillars it can be mounted above the chassis. Also should 
you want a 12V 4A transformer then this one should be 

quite suitable, you use just one half of the secondary. Price 

£3.50, Order Ref: 3.5P7. 

15W 8” 8 Ohm Speaker and 3” Tweeter. Amstrad, made 

for their high quality music centre, £4 per pair, Order 

Ref: 4P57. 

Insulation Tester with Multimter. Internally generates volt- 

ages which enables you to read insulation directly in 

megohms. The multimeter has four ranges, AC/DC volts, 3 

ranges milliamps, 3 ranges resistance and 5 amp range. 

These instruments are ex-British Telecom tut in very good 

condition, tested and guaranteed OK, probably cost at 

least £50, yours for only £7.50 with leads, carrying case £2 

extra, Order Ref: 7.5P4. 

We Have Some of the above testers but slightly faulty, not 

working on all ranges, should be repairable, we supply 

diagram, £3, Order Ref: 3P176. 

Clock Module. 2” LCD display, requires 1.5V battery, goes 

back to zero when switched off so ideal for timing opera- 

tions, £2, Order Ref: 2P307. 

Field Telephones. Ex-GPO, reconditioned, just join 

together with almost any length twin wire, £15 each, Order 

Ref: 15P62. 

Heavy Duty Time Switch (Smiths). Will switch on up to 

100A, ex-electricty board, reconditioned, £10, Order Ref: 

10P 14. 

Lead Lamp. Ideal for motorists, normal handgrip and 

hainging hook, takes 60W bulb protected by glass cover. 

£4. Order Ref: 4P31. 

Ultrasonic Car or House Alarm. Operates from its own bat- 

tery, nicely cased, is reasonably loud and can be coupled 

to external horn, £10, Order Ref: 10P76. 

Clock Module. 2” LCD display, requires 1-5V battery, goes 

back to zero when switched off so ideal for timing opera- 

tions, £2, Order Ref: 2P307. 

Quartz Clock Mechanisms. Complete with 2 sets of hands, 

—_ or period, made up ready to work, £3, Order Ref: 

12V-6V Reducer. Plugs into car socket to work radio, etc. 

£2, Order Ref: 2P318. 

Prices include VAT. Send cheque/postal order 
or ring and quote credit card number. 
Add £3 post and packing. 

Orders over £25 post free. 


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

Sussex RH17 5PA 

Telephone: 01444 881965 
OE Xomr-baeleim@elalela(cmila-39) 
oF: 1 (=) c- Cole Wa fol Ulalot-| arm a fer-lom 
Hove, Sussex. 




@ A powerful set of basic functions, 
statements, and operators — over 230 in 

set of basic instructions this complete. 
@ Advanced statistics functions 
enabling computations on up to 15 
independent variables. 

@ Recursive subprograms and user 
defined functions. 

@ A keyboard that can be easily 
customised for your specific application. 
@ HP-!L Interface pre-installed to 

commands, Interface to HP-1L, HP-1B, 


all — many larger computers don’t havea _ 


These are second users systems, ex NHS, 
are fully tested and working but have no 
programming (THAT IS UP TO YOU). 

Bar-code Reader..................cccceeeeeees £12.95 

A.C. Power Supply 
(Works from batteries normally) 

Perce reccceescecseeeeesess 

Complete kit of HP71B, Bar-code Reader 
and power supply..............::ccceseeee £39.50 

Unit 41, InShops, Wellington Centre 


As easy to use as a calculator ; 
but as powerful as a READER 
Smart wand 

TRACP eS ey BPE pe ae 


PPA Cie ee Spree 
+ A ° “« , 
s » 

‘Unit 15, Craven Way feauaeags Est., Newosarket Suffolk. CB8 0AP 



— Automatically Telephone: (01638) 662989 Facsimile: (01683) 660799 
decodes all major 220/240V ANY Two Secondaries 
bar-code standards. Price Dimensions 

70 x 35mm 
80 x 45mm 
90 x 35mm 
90 x 45mm 
110x 45mm 
110 x 50mm 
110 x 60mm 
140 x 60mm 
140 x 70mm 
125 x 65mm 
160 x 70mm 


Prices include VAT & Carriage 
For further information and quantity discounts, contact Michael Dornan 

200 Signal diodes 1N4148 
75 Rectifier Diodes 1N4001 

BC327 Transistors 

@ An advanced internal file system for Keyboard Overlay.............ccccccseeees £1.00 Phone: 01638 662989 Fax: 01638 660799 
storing programs and data — The HP71 (Limited quantities) 

has continuous memory — when you (Unkown Program — Memory 

turn the computer offit retains Modules (2 different types). iain £3.00 

programs and data. (Limited quantities) 

SMM red 1.€.0.8.........ccceeceeeeeeeeeeneeeees 
Asstd. high brightness I.e.d.s.......... 

create a system that can print, plot, shee ese VAT — Rectifier Diodes 1N4007 Axial |.e.d.s (Diode package) 
store, retrieve and display information. Delivery Next day £3.00) Rectifier Diodes 1N5401 Asstd. 7-segment displays 
Control or read instruments or speak to (Currently selling in US for over £500!) bec Lael oe Lideneseieadseenaaet £1.00 tog il dependant resistors 
other computers, 5000 bytes/sec. sstd. Zener Diodes sstd. IF transformers 

Built in ROM includes 46 separate INTERCONNECTIONS LTD ts og St ee Asstd. coil formers 

Asstd. RF chokes (inductors) 

Asstd. connectors edge.,d.i.I., sil etc 
Asstd. d.i.l. sockets up to 40-pin 

RS232C, GPIO or series 80. Includes Aldershot, Hants, GU11 SDB 

BC328 Transistors 

| connection cables. Tel: (01252) 341900 Fax: (01293) 822786 BC337 Transistors Asstd. disc ceramic capacitors 
. - BC478 Transistors Asstd. capacitors 1nF to 1pF 
| Please rush me ‘Please debit credit card BC546 Transistors Asstd electrolytic capacitors 
BC547 Transistors 4P3W MBB min. rotary switches 
im HP71 B Powerful Calc/Computer @ £29.95 No. eee eer eeeeeeceeeeccssceveees Exp eee eeeeeeeenes BC548 Transistors Min. SP/CO slide switches.. 
| [_] Bar-code Reader (@ £12.95 ania BC549 Transistors 1” glass reed switches 
| na eee eS eee BC550 Transistors 4N7 mini axial capacitors 
O willed 4 2 eta PI OGS io cisstintsussicisisieinimvcuiataladectie BC557 Transistors 24-pin d.i.|. wire wrap i.c. Skts. ........ 
CJ Keyboard overlay @ £1.00 BC558 Transistors 12V motorised volume control 50k...£1. 
M dul F311 | EE BC559 Transistors Grommets 6-3mm id, 9-5mm od 
OJ emory module (@ BC640 Transistors c/f %W 5% resistors any one 
[_]Complete kit of HP7IB, Bar-code Reader (vrrrrrcrtrrereererrseeeeeeeessseeeeeeessteneeeeetereeeees ; value, E24, range 1R to 10M 
and Power @ 
d Power Supply @ £39.50 . * etebcheaiaataacneten POStcOde -..cccsscsesseesee i Prices include VAT, postage £1.25. Stamp for Lists 
Total payment £........... + £3 delivery =£........... TE sinicicdcisdimndnces oman ENG904 Transistors ye 

288 Abbeydale Road. Sheffield $7 1FL 
Phone (0114) 2552886 Fax (0114) 2500689 

78M08 8V 500mA Pos Regulators... 
79M08 8V 500mA Neg Regulators....£1.00 
5MM red 1.€.0.8.............cccceeesseeee cece £1.00 

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. 

* Back annotation (linked to schematic), » . . 
— * ower; memory and signal autorouter - £50 

ate aaa te 

eron resolution. an 

AGES sc sa PSR Os DR 2 
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Published by Everyday Electronics in association 
with Magenta Electronics. / 

Contains twenty of the best projects from previous 
issues of EE each backed with a kit of components. The 
projects are: Seashell Sea Synthesiser, 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 Fre- 

quency Meter, Infra Red Alarm, EE Equaliser loniser, Bat 
Detector, Acoustic Probe, Mains Tester 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 Generator. 

128 pages (A4 size) £2.45 



Mike Tooley BA (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 regist- 
ering for assessment, etc. Starting with basic terminol- 
ogy, integrated circuits, logic families and numbering 
systems the text builds in stages, with revision and 
assessments built in, up to programming, languages, 
flow charts, etc. The course is ideal for the newcomer to 

the subject. 
Order code TI-88/89 £2.45 

80 pages (A4 size) 

Everyday with Practical Electronics Books 


(Published by Everyday with Practical Electronics) 
Mike Tooley BA f 

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 circuits. 

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 thinking behind design, assembly, construction, 
testing and evaluation, together with suggested ‘‘mods” 
to meet individual needs. The practical projects have 
each been designed to stand on their own as complete 
items of equipment. P.C.B.s for all the modules and 
projects are available by mail order. 

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. 

136 pages (A4 size) £3.45 

TEACH-IN No. 7 plus FREE Software 



(Published by Everyday with Practical 

Alan Winstanley and Keith Dye 

The highly acclaimed Teach-/n series, which included 
the construction and use of the Mini Lab and Micro 
Lab test and development units, has been put together 
in book form. Additionally EPT Educational Software — 

. have developed a GCSE Electronics software program to 

compliment the course and a FREE DISC covering the 
first two parts of the course is included with the book. 

An interesting and thorough tutorial series aimed 
specifically 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 then this is for you. 
If you are teaching electronics or technology you 
must make sure you see it. Jeach-/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 interest- 
ing way: you will both see and hear the electron in 
action! The Micro Lab microprocessor add-on system 
will appeal to higher level students and those develop- 
ing microprocessor projects. 

152 pages (A4 size) £3.95 

Computers and Computing 

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). 

114 pages £4.95 

FOR YOU (covers version 6.2) 
N. Kantanis & P. R. M. Oliver 
This book was written with the busy person in mind and, 
as such, it has an underlying structure based on ‘‘what you 
need to know first, appears first’’. Nonetheless, the book 
has also been designed to be circular, which means that 
you don't have to start at the beginning and go to the end. 
The book explains: How to write customised batch 
files which allow you to display what you want on your 
screen, and in the form and order you want it, instead 
of being forced to use the DOS prompt on a blank 
screen. How to design and set up a fast interactive 
and professional fooking menu system, so that you or 
anyone else can run utility applications or commercial 
software packages easily. How the ANSI.SYS display 
and keyboard commands can be used to position the 
cursor on any part of the screen, change the inten- 
sity of the displayed characters or change their colour. 
How the Edit screen editor or the Edlin line editor can 
be used to enter ESCape (ANSI.SYS) commands into 
simple ASCII files to allow control of both your screen 
display and your printer. How to control the opera- 
tion of the two main types of printers in use today, 
Epson compatible dot matrix and HP compatible laser 
printers. How to use several routines, such as moving 
and finding files, protecting files from accidental erasure, 

a simplified backup process, a screen saver, and a disc 
cataloguing system. 

The Debug program and how it can be used to create, 
see and change the contents of any file, including those 
of programs written in assembler code. This includes 
how to find your way around the names and tasks of the 
CPU registers and the meeting of some simple assembler 

(olmel-lanetele loa 1 sans) £4.95 

182 pages 


lan R. Sinclair 

In this book, you'll find out what a CD ROM is, how it 
works, and why it is such a perfect add-on for a PC, 
allowing you to buy programmes, text, graphics and 
sound on a CD. It also describes the installation of a CD 
ROM drive and a sound card, pointing out the common 
problems that arise, and then shows how to use them to 
create a complete multimedia presentation that contains 
text, photos, a soundtrack with your own voice re- 
corded as a commentary, even animation and edited 

video footage. 

184 pages 


N. Kantaris 

This guide is written with the non-expert, busy person 

-in mind and, as such, it has an underlying structure 

based on ‘what you need to know first, appears first’’. 
Nevertheless, the guide is also designed to be circular, 
which means that you don't have to start at the begin- 
ning and go to the end. The more experienced user can 
start from any section. 

The guide covers versions 3.0, 3.1 and 3.2 of both 
PC-DOS and MS-DOS as implemented by IBM and 
other manufacturers of ‘‘compatible’’ microcomputers. 

64 pages Order code BP232 £2.95 

Everyday with Practical Electronics, June 1995 


R.A. Penfold 

If you require a microcomputer for business applications, 
or a high quality home computer, an IBM PC or com- 
patible is often the obvious choice. They are competi- 
tively priced, and are backed up by an enormous range 
of applications programs, hardware add-ons, etc. The 
main difficulty for the uninitiated is deciding on the 
specification that will best suit his or her needs. PCs 
range from simple systems of limited capabilities up to 
complex systems that can happily run applications that 
would have been considered beyond the abilities of 
a microcomputer not so long ago. It would be very 
easy to choose a PC system that is inadequate to run 
your applications efficiently, or one which goes beyond 
your needs and consequently represents poor value for 

This book explains PC specifications in detail, and the 
subjects covered include the following: Differences 
between types of PC (XT, AT, 80386, etc); Maths 
co-processors; Input devices (keyboards, mice, and 
digitisers); Memory, including both expanded (EMS) 
and extended RAM; RAM disks and disk caches; Floppy 
disk drive formats and compatibility; Hard disk drives 
(including interleave factors and access times); Display 
adaptors, including all standard PC types (CGA, Her- 
cules, Super VGA, etc); Contains everything you need to 
know if you can’t tell your EMS from your EGA! 

104 pages - @ Order code BP282 £4.95 


R.A. & J. W. Penfold 

Obtain a vast increase in running speed by writing pro- 
grams for 6800 based micros such as the Commodore, 
Amiga, Atari ST range or Apple Macintosh range etc., in 
assembly language. It is not as difficult as one might 
think and this book covers the fundamentals. 

112 pages £2.95 


Testing and 

Test Gear . 

cov Dick be RAR ak a uy Se 

Audio and Music 


R. A. Penfold | 

This book explains the basic function of an oscilloscope, 
gives a detailed explanation of all the standard controls, 
and provides advice on buying. A separate chapter deals 
with using an oscilloscope for fault finding on linear and 
logic circuits, plenty of example waveforms help to il- 
lustrate the control functions and the effects of various 
fault conditions. The function and use of various other 
pieces of test equipment are also covered, including sig- 
nal generators, logic probes, logic pulsers, and crystal 

Order code BP267 £3.50 

104 pages 


R. A. Penfold 

The Musical Instrument Digital Interface (MIDI) is sur- 
rounded by a great deal of misunderstanding, and many of 
the user manuals that accompany MIDI equipment are 
quite incomprehensible to the reader. 

The Practical MIDI Handbook is aimed primarily at 
musicians, enthusiasts and technicians who want to 
exploit the vast capabilities of MIDI, but who have no 
previous knowledge of electronics or computing. The 
majority of the book is devoted to an explanation of what 
MIDI can do and how to exploit it to the full, with practical 
advice on connecting up a MIDI system and getting it to 
work, as well as deciphering the technical information in 
those manuals. 

128 pages £6.95 

(olazel-taerelelon a On key 

Theory and Reference 


R.A. Penfold 

Provides an inexpensive single source of easily located 
information that the amateur electronics enthusiast is likely 
to need for the day-to-day pursuance of this fascinat- 
ing hobby. Covers common component colour codes. 
Detai's the characteristics and pinouts of many popular 
semiconductor devices, including various types of logic 
i.c.s, Operational amplifiers, transistors, FETs, unijunc- 
tions, diodes, rectifiers, SCRs, diacs, triacs, regulators and 
SMDs, etc. Illustrates many useful types of circuits, such 
as timers and oscillators, audio amplifiers and filters, as 
well as including a separate section on power supplies. 
Also contains a multitude of other useful data. 

88 pages £4.95 
F. A. Wilson 

Explains in crystal clear terms the absolute fundamentals 
behind electricity and electronics. Really helps you to dis- 
cover and understand the subject, perhaps for the first time 

Have you ever: Wondered about the true link between 
electricity and magnetism? Felt you could never under- 
stand the work of Einstein, Newton, Boltzmann, Planck 
and other early scientists? Just accepted that an electron is 
like a little black ball? Got mixed up with e.m.f. and p.d.? 
Thought the idea of holes in semiconductors is a bit much? 

Then help is at hand with this inexpensive book, in as 
simple a way as possible and without too much, complex 
mathematics and formulae. 

244 pages Temporarily out of print 
G. H. Olsen 

Electronic devices surround us on all sides and their num- 
bers are increasing without mercy. Ours is the problem 
therefore in keeping up with this relentless expansion. 
Unfortunately we cannot know it all and most of us do not 
wish to afford the cost of large reference books which 
explain many concepts in fair detail. Here is an answer, an 
inexpensive reference guide which explains briefly (but 
we hope, well) many of the underlying electronics features 
of practical devices, most of which, to a certain extent, 
control our lives. 

This book is in effect more than just a dictionary of prac- 
tical electronics terms, it goes a stage further in also getting 

down to fundamentals. Accordingly the number of terms 

may be limited but the explanations of the many which are 
included are designed to leave the reader more competent 
and satisfied — and this is without the use of complicated 

‘mathematics which often on first reading can be confus- 


For those who also wish to get right down to the root of 
the matter, there is a second volume entitled A Reference 
Guide to Basic Electronics Terms (BP286), each of the 
books referring to its companion as necessary. 

A reference guide for practically everybody concerned 
with electronics. 


432 pages Order code BP287 


Owen Bishop 

This book describes over 60 modular electronic circuits, 
how they work, how to build them, and how to use them. 
The modules may be wired together to make hundreds of 
different electronic systems, both analogue and digital. To 
show the reader how to begin building systems from mod- 
ules, a selection of over 25 electronic systems are des- 
cribed in detail, covering such widely differing applica- 
tions as timing, home security, measurement, audio (in- 
cusing a simple radio receiver), games and remote con- 

200 pages Temporarily out of print 

Project Building 


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. ' 
Order code BP110 £2.95 

96 pages | 

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. 

80 pages Order code BP121 £2.50 


R. A. Penfold 

The purpose of this book is to provide practical information 
to help the reader sort out the bewildering array of com- 
ponents currently on offer. An advanced knowledge of the 
theory of electronics is not needed, and this book is not 
intended to be a course in electronic theory. The main aim 


is to explain the differences between components of the 
same basic type (e.g. carbon, carbon film, metal film, and 
wire-wound resistors) so that the right component for a 
given application can be selected. A wide range of com- 
ponents are included, with the emphasis firmly on those 
components that are used a great deal in projects for the 
home constructor. 

166 pages £3.95 

(Ol ael-)mexele (sm si oasis) 

ee pa C.G.1.A., C.Eng., F.1.E.E., F.1.E.R.E., 

Especially written for those who wish to participate in 
the intricacies of electronics more through practical con- 
struction than by theoretical study. It is designed for all 
ages upwards from the day one can read intelligently and 

handle simple tools. 
Order code BP92 £1.75 

80 pages 


See the first page of books - ELECTRONICS TEACH-IN 
No. 6 — for full details. 


Published by Everyday Electronics in association 
with Magenta Electronics. 

See the first page of books for full details. 


V. Capel 
This book explores the various features, good points and 
snags of speaker designs. It examines the whys and 
wherefores so that the reader can understand the 
principles involved and so make an informed choice of 
design, or even design loudspeaker enclosures for him or 
herself. Crossover units are also explained, the various 
types, how they work, the distortions they produce and 
how to avoid them. Finally there is a step-by-step 
description of the construction of the Kapellmeister 
loudspeaker enclosure. 


148 pages Order code BP256 


V. Capel 

Feedback is the bane of all public address systems. 
While feedback cannot be completely eliminated, many 
things can be done to reduce it to a level at which it is no 
longer a problem. 

Much of the trouble is often the hall itself, not 
the equipment, but there is a simple and practical 
way of greatly improving acoustics. Some microphones 
are prone to feedback while others are not. Certain 
loudspeaker systems are much better than others, and 
the way the units are positioned can produce or reduce 
feedback. All these matters are fully explored as well as 
electronic aids such as equalizers, frequency-shifters 
and notch filters. 

The special requirements of live group concerts are 
considered, and also the related problem of instability 
that is sometimes encountered with large set-ups. We 
even take a look at some unsuccessful attempts to cure 
feedback so as to save readers wasted time and effort 
duplicating them. 

Also included is the circuit and layout of an inexpen- 
sive but highly successful twin-notch filter, and how to 

operate it. 
(Olzel-larerelel=m ston ne) £3.95 

92 pages 


R.A. Penfold 

This book provides circuits and background informa- 
tion for a range of preamplifiers, p!us tone controls, 
filters, mixers, etc. The use of modern low noise opera- 
tional amplifiers and a specialist high performance audio 
preamplifier i.c. results in circuits that have excellent 
performance, but which are still quite simple. All the 
Circuits featured can be built at quite low cost (just a few 
pounds in most cases). 

The preamplifier circuits featured include: Microphone 
preamplifiers (low impendance, high impedance, and 
crystal). Magnetic cartridge pick-up preamplifiers 
with R.I.A.A. equalisation. Crystal/ceramic pick-up 
preamplifier. Guitar pick-up preamplifier. Tape head 
preamplifier (for use with compact cassette systems). 

Other circuits include: Audio limiter to prevent over- 
loading of power amplifiers. Passive tone controls. Ac- 
tive tone controls. PA filters (highpass and lowpass). 
Scratch and rumble filters. Loudness filter. Audio mixers. 
Volume and balance controls. 


92 pages Order code BP309 

R.A. Penfold 

Computers are playing an increasingly important part in 
the world of music, and the days when computerised 
music was strictly for the fanatical few are long gone. | 

If you are more used to the black and white keys of a 
synth keyboard than the QWERTY keyboard of a com- 
puter, you may be understandably confused by the jar- 
gon and terminology bandied about by computer buffs. 
But fear not, setting up and using a computer-based 
acy making system is not as difficult as you might 

This book will help you learn the basics of computing, 
running applications programs, wiring up a MIDI sys- 
tem and using the system to good effect, in fact just 
about everything you need to know about hardware and 
the programs, with no previous knowledge of computing 
needed or assumed. This book will help you to choose the 
right components for a system to suit your personal needs, 
and equip you to exploit that system fully. 

174 pages (Oydelclmerolelen a OnkOy, £8.95 


R.A. Penfold 

This book contains a collection of guitar effects and some 
general purpose effects units, many of which are suitable 
for beginners to project building. An introductory chapter 
gives guidance on construction. 

Each project has an introduction, an explanation of how 
it works, a circuit diagram, complete instructions on strip- 
board layout and assembly, as well as notes on setting 
up and using the units. Contents include: Guitar tuner; 
Guitar preamplifier; Guitar headphone amplifier; Soft dis- 
tortion unit; Compressor; Envelope waa waa; Phaser; Dual 
tracking effects unit; Noise gate/expander; Treble booster; 
Dynamic treble booster; Envelope modifier; Tremelo unit; 

box. ; 
Order code PC110 £8.95 

110 pages 

R. A. Penfold 

Practical constructional details of how to build a num- 
ber of audio power amplifiers ranging from about 50 to 
300/400 watts r.m.s. Includes MOSFET and bipolar tran- 

sistor designs. 
Order code BP277 £3.95 

96 pages 

Everyday with Practical Electronics, June 1995 


Owen Bishop 

This book deals with the subject in a non-mathematical 
way. It reviews the main types of filter, explaining in simple 
terms how each type works and how it is used. 

The book also presents a dozen filter-based projects with 
applications in and around the home or in the constructor’s 
workshop. These include a number of audio projects such 
as a rythm sequencer and a multi-voiced electronic organ. 

Concluding the book is a practical step-by-step guide to 
designing simple filters for a wide range of purposes, with 
Circuit diagrams and worked examples. 

88 pages Order code BP299 £4.95 


R. M. Marston . 

One hundred and forty useful alarm circuits, of a variety of 

types, are shown in this volume. The operating principle of 

each one is explained in concise but comprehensive terms, 

and brief construction notes are given where necessary. 
Aimed at the practical design engineer, technician and 

experimenter, as well as the electronics student and 

Order code NE11 £13.95 

124 pages 


lan R. Sinclair 

This book, intended for enthusiasts, students and tech- 

nicians, seeks to establish a firm foundation in digital 

electronics by treating the topics of gates and flip-flops 
thoroughly and from the beginning. 

Topics such as Boolean algebra and Karnaugh mapping 
are explained, demonstrated and used extensively, and 
more attention is paid to the subject of synchronous 
counters than to the simple but less important ripple 

No background other than a basic- knowledge of elec- 
tronics is assumed, and the more theoretical topics are 

explained from the beginning, as also are many working - 

practices. The book concludes with an explanation of 
microprocessor techniques as applied to digital logic. 

200 pages £8.95 

Robert Penfold 

Robots and robotics offer one of the most interesting areas 
for the electronics hobbyist to experiment in. Today the 
mechanical side of robots is not too difficult, as there are 


R. A. Penfold 

This book describes a number of electronic circuits, most of 
which are quite simple, which can be used to enhance the 
performance of most short wave radio systems. 

The circuits covered include:— An aerial tuning unit; A 
simple active aerial; An add-on b.f.o. for portable sets; 
Awavetrap to combat signals on spurious responses; An 
audio notch filter; A parametric equaliser; C.W. and S.S.B. 
audio filters; Simple noise limiters; A speech processor; A 
volume expander. 

Other useful circuits include a crystal oscillator, and 
RTTY/C.W. tone decoder, and a RTTY serial to parallel 
converter. A full range of interesting and useful circuits for 

short wave enthusiasts. 
Order code BP304 £3.95 

92 pages 


1. D. Poole 

Amateur radio is a unique and fascinating hobby which has 

attracted thousands of people since it began at the turn of the 
century. \ 

’ This book gives the newcomer a comprehensive and easy 

~ to understand guide through the subject so that the reader 

can gain the most from the hobby. It then remains an essen- 

tial reference volume to be used time and again. Topics 

covered include the basic aspects of the hobby, such as 

operating procedures, jargon and setting up a station. Tech- 

nical topics covered include propagation, receivers, transmit- 

ters and aerials etc. 

150 pages «£3.50 
R. A. Penfold 

The subject of aerials is vast but in this book the author has 
considered practical aerial designs, including active, loop 
and ferrite aerials which give good performances and are 
relatively simple and inexpensive to build. The complex 
theory and mathematics of aerial design have been avoided. 
Also included are constructional details of a number of 
aerial accessories including a pre-selector, attenuator, filters 
and a tuning unit. 
96 pages £2.50 

R. A. Penfold 
Short wave radio is a fascinating hobby, but one that seems 
to be regarded by many as an expensive pastime these days. 
In fact it is possible to pursue this hobby for a minimal 
monetary outlay if you are prepared to undertake a bit of 
d.i.y., and the receivers described in this book can all be built 
at low cost. All the sets are easy to construct, full wiring 
diagrams etc. are provided, and they are suitable for complete 
beginners. The receivers only require simple aerials, and do 
not need any complex alignment or other difficult setting up 

The topics covered in this book include: The broadcast 
bands and their characteristics; The amateur bands and their 

(Orel) merele (sm ot a hele) 


Circuits and Design — 

robotics kit and a wide range of mechanical components 
available. The microcontroller is not too much of a problem 
either, since the software need not be terribly complex and 
many inexpensive home computers are well suited to the 

The main stumbling block for most would-be robot 
builders is the electronics to interface the computer to the 

motors, and the sensors which provide feedback from the - 

robot to the computer. The purpose of this book is to 
explain and provide some relatively simple electronic 
circuits which bridge this gap. 

92 pages Order code BP1/9] £2.95 

lan R. Sinclair 
This book covers the often neglected topic of electronic 
power supplies. All types of supplies that are used for elec- 
tronics purposes are covered in detail, starting with cells 
and batteries and extending by way of rectified supplies 
and linear stabilisers to modern switch-mode systems, i.c. 
switch-mode regulators, DC-DC converters and inverters. 
The devices, their operating principles and typical cir- 
cuits are all dealt with in detail. The action of rectifiers 
and the reservoir capacitor is emphasised, and the subject 
of stabilisation is covered. The book includes some useful 
formulae for assessing the likely hum level of a conven- 
tional rectifier reservoir supply. 

136 pages Order code PC108 £7.95 
R. N. Soar . 

Contains 50 interesting and useful circuits and applica- 
tions, covering many different branches of electronics, 
using one of the most inexpensive and freely available 
components — the light-emitting diode (LED). Also in- 
cludes circuits for the 707 common anode display. 

64 pages Order code BP42 £1.95 
BOOK 2 50 more |l.e.d. circuits. 

50 pages £1.95 

A. Penfold 

Written to help you create and experiment with your own 
electronic designs by combining and using the various 
standard “building block” circuits provided. Where ap- 
plicable, advice on how to alter the circuit parameters is 

The circuits covered in this book are mainly concerned 
with analogue signal processing and include: Audio 

Radio, TV. Satellite 

characteristics; The propagation of radio signals; Simple 
aerials; Making an earth connection; Short wave crystal set; 
Simple t.r.f. receivers; Single sideband reception; Direct 
conversion receiver. 

Contains everything you need to know in order to get 
started in this absorbing hobby. 

88 pages Order code BP275 £3.95 


A. Pickford 

Communications and broadcast satellites are normally inac- 
cessible to individuals unless they are actively involved in 
their technicalities by working for organisations such as 
British Telecom, the various space agencies or military 
bodies. Even those who possess a satellite television receiver 
system do not participate in the technical aspects of these 
highly technological systems. 

There are a large number of amateur communicatians 
satellites in orbit around the world, traversing the globe 
continuously and they can be tracked and their signals 
received with relatively inexpensive equipment. This equip- 
ment can be connected to a home computer such as the BBC 
ee or IBM compatible PCs, for the decoding of received 

Everyday with Practical Electronics, June 1995 

amplifiers (op.amp and bipolar transistors); audio power 
amplifiers; d.c. amplifiers; highpass, lowpass, bandpass 
and notch filters; tone controls; voltage controlled 
amplifiers and filters; triggers and voltage comparators; 
gates and electronic switching; bargraphs; mixers; phase 
shifters, current mirrors, hold circuits, etc. 

Over 150 circuits are provided, which it is hoped will be 
useful to all those involved in circuit design and applica- 
tion, be they professionals, students or hobbyists. 

182 pages £4.95 
R.A. Penfold 

This book will help you to create and experiment with 
your own electronic designs by combining and using 
the various standard ‘“‘building blocks” circuits provided. 
Where applicable, advice on how to alter the circuit 
parameters is provided. 

The circuits covered are mainly concerned with signal 

_ generation, power supplies, and digital electronics. 

The topics covered in this book include: 555 oscillators; 
sinewave oscillators; function generators; CMOS oscil- 

,lators; voltage controlled oscillators; radio frequency oscil- 

lators; 555 monostables; CMOS monostables; TTL monos- 
tables; precision long timers; power supply and regulator 
Circuits; negative supply generators and voltage boosters; 
digital dividers; decoders, etc; counters and display drivers; 
D/A and A/D converters; opto-isolators, flip/flops, noise 
generators, tone decoders, etc. ; 

Over 170 circuits are provided, which it is hoped will be 
useful to all those involved in circuit design and applica- 
tion, be they professionals, students or hobbyists. 

192 pages Order code BP322 £4.95 
E.A. Parr 

This book has been written as a designer's guide covering 
many operational amplifiers, serving both as a source book 
of circuits and a reference book for design calculations. 
The approach has been made as non-mathematical as pos- 

160 pages £2.95 

R.A. Penfold 

‘This book first covers the basics of simple logic circuits 

in general, and then progresses to specific TTL logic in- 
tegrated circuits. The devices covered include gates, os- 
cillators, timers, flip/flops, dividers, and decoder circuits. 
Some practical circuits are used to illustrate the use of TTL 
devices in the ‘real world” 

142 pages £4.95 

This book describes several currently available systems, 
their connection to an appropriate computer and how they 

can be operated with suitable software. 

102 pages (Olmelelmeorelelen =) oss10) £3.95 


P. Shore 

Provides the casual listener, amateur radio DXer and the 
professional radio monitor with an essential reference 
work designed to guide him or her around the ever 
more complex radio bands. This new edition has been 
completely revised and rewritten and incorporates much 
more information which is divided into the following 

Listening to Short Wave Radio; Choosing a Short 
Wave Radio Receiver; How to Use the IRSG; Abbrevia- 
tions; County Codes; Worldwide Short Wave Radio Sta- 
tions; European, Middle Eastern and African Long Wave 
Radio Stations; European, Near and Middle Eastern and 
African Medium Wave Radio Stations; Canadian Medium 
Wave Radio Stations; USA Medium Wave Radio Stations; 
Broadcasts in English; Programmes for DXers and Short 
Wave Listeners; UK FM Radio Stations; Time Differences 
From GMT; Wavelength/Frequency Conversion. 

226 pages £5.95 


: CRICKLEWOOD £ Ie ctronics 
Very Interesting CATALOGUE 



TV & VIDEO SPARES (inc Video Heads) 
IN CAR AUDIO+SPEAKERS (inc Bass tubes) 


& much much much more (over 10,000 lines). 

Pay by PO, Cheque, Credit Card or tape Coins to Paper __ 
Please send me ......copies of the 1995 Cricklewood Catalogue. 
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 

PCB Designer 

For Windows 3. 1 

PCB Desit 


Looking for the price? 
It's just £49.00 all inclusive! postage... additional charges for 
overseas orders. : 
Dealers and distributors 



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A working demo is available via anonymous SF TP from as /pub/i ibmpc/windows/pcbdemo/pcbdemo. Zip 


Produce Single or Double sided PCBs. 

Print out to amy Windows supported printer. 
Toolbar for rapid access to commonly used 

Helpful prompts on screen as you work. 
Pad, track & IC sizes fully customisable. 
No charges for technical support. 

Snap-to grid sizes 0.1", 0.05" 0.025" and 

SMT pads and other pad shapes. 
Prints at the resolution of your printer - much 
igher than the screen shot shown here. 





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 property 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 £2.50) 
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 
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 electrical components at competitive prices. 

Send an SAE for price lists. . 

149 The Vale, Acton W3 7HR 

Tel: 0181 932 0144 
Fax: 0181 932 0145 

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 

- [c:\pcb\samplel.pcb] 
Eat aoe lest eh Window eee 



e-mail enquiries can be addressed to Be" 

Niche Software (UK) et 

22 Tavistock Drive, Belmont, Hereford, HR2 7XN 


Phone (01432) 355 414 

Everyday with Practical Electronics, June 1995 

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 now 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. 


Bike Odometer (pair of boards) mil 
Amstrad PCW A to D Converter (double-sided 
Experimental Electronic Pipe a 

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 
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 
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 
Whistle Controlled Light Switch 
Battery to Mains Inverter — U.P.S. charger board 

Three Phase Generator 

Visual Doorbell 

CCD TV Camera — Control Board 
(double-sided, plated-through-hole) 

Telephone Ring Detector 
CCD TV Camera 
Combined Video, Test & Ext Plug Boards 866a/e 
Frame Grab Control — 867 
(double-sided plated-through-hole) oe 
EPE Sound DAC PC Sound Board 868 
MOSFET Variable Bench Power Supply | 869 

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 3 
L.E.D. Matrix Message Display Unit 
PC Interface 
Microprocessor Smartswitch 
Microcontroller P.I. 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 

Everyday with Practical Electronics, June 1995 

Dancing Fountains - 2 oa 
PC-Compatible Interface (double-side 

Automatic Greenhouse Watering System 
Seismograph — 1 Sensor/Filter 

3-Channel Lamp Controller 

Seismograph — 2 Boeaecal 
PC-Compatible Interface (double-side 
Visual/Audio Guitar Tuner : 

Digilogue Clock — 

Hobby Power Supply 

Audio Auxiplexer 
Control Board 

Power Controller 

1000V/500V Insulation Tester 

Active Guitar Tone Control 

TV Off-er = (pair) 908/909 

Video Modules—1 Simple Fader 910 
Improved Fader 911 
Video Enhancer 912 

Rodent Repeller 

EPE Fruit Machine 

Video Modules -2 Horizontal Wiper 
Vertical Wiper 
4-Channel Audio Mixer 

Spacewriter Wand 

Universal Digital Code Lock 

Video Modules — | JAN'95 | 
3 Dynamic Noise Limiter 

System Mains Power Supply 
Magnetic Field Detector 

Model Railway Track Cleaner 

Moving Display Metronome 

The Ultimate Screen Saver 
Foot-Operated Drill Controller 
Model Railway Signals 

12V 35W PA Amplifier 

Multi- Purpose Thermostat 
Multi- Project PCB 
Sound-Activated Switch 
Audio Amplifier 
Light Beam Communicator (2 boards required) 
Multi- Project PCB 
Light-Activated Switch 
Switch On/Off Timer 
Continuity Tester 
Auto Battery Charger 
National Lottery Predictor 
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 


Order Code _ Project Quantity Price 

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Please supply name and address of cardholder if different from the address shown 
Ce Hee He eH eee eee Eee ee eee ee ee ee ee ee ee ee ee 




Tony Smith G4FAL__ 


In 1992, an amateur station with the 
callsign 1B1NCC came on the air from 
the Turkish Republic of Northern Cyprus 
(TRNC) and worked several thousand 
other amateur stations worldwide. En- 
thusiasts in the TRNC had been promot- 
ing amateur radio and some UK-licensed 
amateurs. donated transmitting equip- 
ment to help get the station established. 

1B1NCC was subject to extensive and 
deliberate interference from other sta- 
tions, mostly in Cyprus and Greece, and 
the Ministry of Communications of the 
Republic of Cyprus issued a statement 
asking that “under no_ circumstances 
should contact be made with this station”. 

Since that time, 1B1NCC has become 
the club station of the TRNC Amateur 
Radio Society and four more stations, 
with suffixes AA, AB, AC and AD (Class 
A) and one in Class B, 1B2AA, have 
come on the air. 

The situation described arises from the 
division of Cyprus, following the Turkish 
invasion of 1974, which has been the 
subject of several United Nations resolu- 
tions calling for a peaceful solution to the 
problem and the re-creation of a united 

Northern Cyprus has been unable to 
join the United Nations or its agencies, 
including the International Telecom- 
munications Union (ITU), and the only 
country that recognises it is Turkey. 
Because it is not recognised by the ITU 
there is no legal callsign series for TRNC 
to use so it has taken the 1B prefix from 
the non-allocated list of ITU callsigns 
beginning with 1 or 0. 

Although their stations have no in- 
ternational status, the TRNC ARS has 
persuaded its own government to amend 
its Radio & Telegraphy Act to cover 
amateur radio operation. The regulations 
are based on CEPT licensing require- 
ments and IARU band plans, and 
licences are issued to any TRNC national 
who passes an amateur radio examina- 
tion and a Morse test. Temporary licences 
are also issued to foreign nationals 
equivalent to their home licences. 

The Cyprus Amateur Radio Society 
protested to the Executive Committee of 
the International Amateur Radio Union, 
Region 1, about the operation of amateur 
radio stations in Northern Cyprus. The EC 
expressed the opinion that the ITU 
regulations should be adhered to and 
that IARU Societies should inform their 
members that amateur radio stations 
should not contact stations with prefixes 
not issued by the ITU. 


In the USA, the DX Advisory Com- 
mittee of the American Radio Relay 
League (ARRL) rejected a proposal that 
the TRNC be granted separate country 
status for DXCC purposes. Such status, if 


approved, would have enabled contacts 
with stations in Northern Cyprus to count 
for scoring in the prestigious DXCC 
Award programme, and in most contests, 
irrespective of the furore about them. 

The TRNC ARS says that no stations 
have refused to work them because of 
the IARU recommendation, and that they 
take particular care to keep all of their 
contacts strictly non-political and relative 
to amateur matters. 

The fact remains, however, that at 
present amateur stations in Northern 
Cyprus do not conform with international 
regulations, and the IARU has recom- 
mended that other amateur stations 
should not contact them. 

The situation is complicated by the fact 
that radio amateurs are proud of their 
ability to communicate with each other on 
non-controversial matters irrespective of 
differences between their political masters. 
Some countries occasionally forbid con- 
tacts with specified other countries, but 

even at the height of the cold war it was 

possible to have friendly personal contacts 
between East and West. 

The controversy over the TRNC 
amateur stations is clearly a symbol of the 
deep differences between Greek and 
Turkish Cypriots and there seems little 
possibility of amateur radio contacts 
between them. Amongst the rest of the 
world’s amateur radio community there 
are divided opinions. 

Some do take note of the the views of 
the IARU and will not work TRNC sta- 
tions. Others, because there has been 
no formal prohibition, feel they should 
be free to talk to either party without 
hindrance. Much as we would like to 
think otherwise, amateur radio is not 
immune to the stresses of international 
politics after all! 

Details of the Young Amateur of the 
Year Award 1995 have been announced 
by the Radiocommunications Agency. It 
is offered by the Agency in conjunction 

with the Radio Society of Great Britain 

and is open to anyone under 18 who has 
an interest in radio. 

' Applicants need not be _ licensed 
amateurs but the following areas of 
activity will be taken into account 
when assessing their applications. DIY 
radio construction; operation of radio; 
community service (e.g., assisting in 
emergency communications); encourag- 
ing others (e.g., through the amateur 
radio novice licence scheme), and school 

The prize for the most outstanding 
achievement between 1st August 1994 

and 31st July 1995 will be £300 cash 

and the runner-up will receive £50. There 
may well be additional prizes for both 
winners provided by the radiocom- 
munications industry. Both winners will 

aE AE hn ANB oe RUS he eee bee eh dee oe alle rape 

SNaataaiaisaia nacuetatsatitoencaadeenmieaeie a 
“ 5 4 ae sae 

also be invited to visit the Agency's 
Radio Monitoring Station at Baldock in 
Hertfordshire. | 

Further details can be obtained from the 
Radio Society of Great Britain, Lambda 
House, Cranborne Road, Potters Bar, Herts 
EN6 3JE, to whom applications should be 
sent not later than 31st July 1995. 


Many radio amateurs, and others, col- : 
lect Morse keys. It is a fascinating hobby 
since the keys come in a variety of types, 
ranging from simple hand keys to modern 
complex electronic keyers. In some cases 
they go back long before radio, to the 
time when the electric telegraph, using a 
single wire and an earth return, was the 
“wonder of the age” spanning continents 
with ease. 

Of interest to established collectors, and 
to those just thinking about starting, 
Morsum Magnificat, the Morse Magazine 
has just published “7he Story of the Key”. 
a reprint from the magazine of an 
authoritative six part series by Louise 
Moreau W3WRE. This covers. the 
development of the key, beginning with 
Alfred Vail’s “Correspondent”, used on 
Samuel F.B. Morse’s triumphant Baltimore 
to Washington demonstration of 1844. 

It outlines the first attempts to in- 
crease sending speed (and at the same 
time alleviate ‘‘telegrapher’s paralysis’’ or 
“glass arm’) leading to the ‘Double 
Speed Key”, or ‘’Sideswiper’’ of 1888. It 
goes on to tell the amazing story of the 
Vibroplex semi-automatic key, which first 
appeared in 1904, involving legal battles 
by the company with its many imitators 
and the eventual “licensing” of the so- 
called ‘‘bastard bugs” to permit their use 

Finally it tells how, with the advent 
of wireless, the landline straight key was 
adapted for “‘spark’’ use, and was later 
modified again when the power of the 
spark was no longer a problem. 

The book also includes an alphabetical 

list of American Telegraph Instrument 
Makers from 1837 to 1900, with their 
addresses, dates of operation and a broad 
indication of the types of instruments 
they produced. 
- Originally intended for existing readers 
of Morsum Magnificat, the final result is a 
book which will have a much wider ap- 
peal. With over 75 indexed photographs 
of the keys described in the text, coupled 
with the information available in the list 
of makers, it will be an invaluable and en- 
tertaining source of reference for both key 
collectors and today’s key users. 

“The Story of the Key” has 60 pages x 
A5 soft-cover format. It is obtainable by 
post direct from G. C. Arnold Partners, 
9 Wetherby Close, Broadstone, Dorset 
BH18 8JB, price £3.95 post free (UK), or 
£4.25 overseas by surface mail. Please 
mention EPEwhen ordering a copy. 

- Everyday with Practical Electronics, June 1995 

r- a AR Lil OM as ical READ 

Nee ee 

aT NT eat kT) Xcamelt Tel[e RO) RUTSTS19IME MARCONI 2440 Microwave Counter 20GHz 
MTemMolsorel cei ATL GROOLT RAGA coco. Frequency Counter SOMHZ-1:5CH2 LE 

| , MARCONI 2435 Digital Frequency Meter 2GHz 

RACAL 1998 Freq, Counter 1:3GHz (options GPIB & High St 
Available from £200 - PLUG-INS SOLD SEPERATELY RACAL/DANA 1991 Universal Counter/Timer 160MHz 9 dig 
TEKTRONIX 2465 4 Channel 3 

MARCONI 2437 Universal Counter /Timer DC -100MHz 8 dig 
Delay Sweep Cursors.......€4750 } Racal 9916 Frequency Counter 10HZ-520MHZ 

TEKTRONIX 2246A 4.Channel 100MHz Cursors } pied ete... pie RACAL 9906A Universal Counter Timer 10Hz-200MHZ. 

TEKTRONIX 2245A.4 Channel 100MHz Cursors etc. ... £1000 BLACK STAR Meteor 100 Frequency Counter 100MHz 

TEKTRONIX 485 Dual Trace 350MHz Delay Sweep... DATRON 1081 1081 7: "5 digit Autocal Multimeter/True RMS 


PHILIPS PM2534 Multi Function DMM 3'-6' digit GPIB/IEEE 

SOLARTRON 7065 6 digit Microprocessor Voltmeter 
AC/DC/Ohms/Auto.. ; 

SOLARTRON 7150 67-37 digit OMM with IEEE 

SOLARTRON 7045 4’ digit Multimeter Volts/Amps/Ohms.... 

THANDAR 1504 4°. digit True RMS Multimeter with Adapt 

WILTRON 560 Scaler Networ' k Analyser with Detectors 

H.P.5005A Signature Multimeter 

RACAL /Dana 9104 RF Power Meter 1MHz-1GH2; 40mW-300W 

AVO.CT160 Valve Tester:(Valve Data not included) 

PHILIPS PM5565 Waveform Monitor 

TRIO CS1566A Dual Trace 20MHZ... PHILIPS PM6307 Wow and Flutter Meter 

CROTECH 3132 Dual Trace 20MHZ £150 
TAC VES ual rae 00D toragelCusors As. £1900 MET SBA ae 

PHILIPS PM3305 4 Trace 35MHz Digital Storage... 
GOULD 0S4000 Dual Trace 10M Digital Storage sila Shpenronidel by beer 
TEKTRONIX 464 Dual Trace 100MHz Ana Stora RADFORD LDMS2 Low Distortion Measuring Set... 
H.P.1741A Dual Trace 100MHz Analogue Storage a KEMO Dual Variable Filter VBF/3 012-1 
THIS IS JUST A SAMPLE - MANY OTHERS AVAILABLE RACAL Instrumentation Recorder type Store 40N 
EATON/AILTECH 380k11 Synthesized Sig sallncatascancin RACAL Instrumentation Recorder type Store 7DS. £500 
with PM3602 AM/FM Phase Mod... veaeeevel?.O H.P. 4275A Multi Freq LCR Component veter with Test Fixtures. £3500 
HP. 8656A Synthesized AM/FM Sig. Gen. 100kHz-990MHZ.... H.P.4264A LCR Meter with Test Fixture 16061A. 
- MARCONI 2019 Synthesized AM/FM Sig Gen 80kHz-1040M MARCONI TF2700 Universal Bridge, Battery Oa 
MARCONI 2022 Am/FM Sig. Gen. 10kHz-1000MHz f WAYNE KERR B424 Digital Component Meter LCR 
MARCONI 2018 Synthesized AM/FM Sig Gen BOkHz- 520MHZ. H.P. 1630D 43 Channels: ; 
HP. 8013B Pulse Gen. 1Hz-5OMHz 

AT LAST. A comprehensive; easy to follow 

guide to building short range transmitters 
and surveillance devices. Packed with 

useful information and circuits. | 

* Only £3.95 inc p&p. 

(Some of the circuits iricluded cannot be used legally in the UK) 

All kits come with pre-drilled PCBs and high spec. ICG 

MICRO FM TRANSMITTER (a). 1km range, 80-100MHz itt 
preset inc. mic., very small (2x 3cm) | “~“Y €6.95 | 
MICRO FM TRANSMITTER (b). Variable mic. sens., tunable 90-110MHz. | 
1km range £7.95 
FM TRACKER. Transmits an audio tone for direction finding, tracking etc. 
80-110MHz £8.50 
ULTRA MINIATURE FM TRANSMITTER. Runs off watch battery (inc), only 
1x2cm, 200mtrs range. 80-100MHz £8.95 
FM RECEIVER (a). Tiny high quality FM-radio. Will drive headphones 
direct (not inc) £10.90 
FM RECEIVER (b). As (a) but with 3 watt audio output and tuning LED £1 3.50 
CRYSTAL RADIO. Includes tuner, earphone, ferrite aerial, etc. ‘£7.50. |): 
AM RADIO. Single chip radio for headphones (not inc.) £8.90 

15 WATT General purpose upgrade 
40 WATT High quality, HD 0-:003%, switch 
on mute ideal for compact disc 
150 WATT Rugged and powerful MOSFET | 
design. PA/sound systems 

GENERAL PURPOSE PREAMP. Variable gain 9-25V:40mV max in 
ULTRA LOW NOISE. For high quality mixers, mics etc 9-25V 
ACTIVE TONE. 12dB c/b bass and treble with variable gain 
7 BAND EQ. 150Hz-18kHz for EQ units and-tone control, 
includes on-board preamp and pots. Variable gain 
NOISE GATE. Dynamic noise reduction system. Variable input 
and cut off level. Will accept instruments, tape decks etc £15.95 
MUSIC KITS. Full range of on-board units for guitars and other instruments. 
Tone boosters, active circuits, delay lines, transducers. Send for list. 

Prices include P&P. Mail Order Only. Make cheques and postal orders payable to: 

a Woodhouse Street. 

BECKMAN 9020 Dual Trace 20MHz Delay Sweep 
HAMEG 412 Dual Trace 20MHz Delay Sweep. 
IWATSU SS5702 Dual Trace 20MHz 

HP. 6268 0-40V: 0-30A.... 
FARNELL H30/100 0-30V; 0-100A. Metered... 
THURLBY PL320QMD 0-30V; 0-2A Twice Digiita 
£250 | THURLBY PL320 0-30V; 0-2A Digiital 
| FARNELL E350 0-350V;0-200mA Metered... 
BRANDENBURG Model 472R +/-2kV Metered 


ape es eres Sony Digital Delay Kit 

HAMEG OSCILLOSCOPE HMO Dual Trace 6OMiz Delay Sweep Only 
HAMEG OSOLLOSCOPE HM303 Dual Trace 30MM Comp Tester.” £382 £24.95 
IFRA7750 Synthesized 1GHz.... £4000 Allother models availabl gh pti rant £655 
4 ; 0 m avaliable — all OSC! 5 
HP 8565A O01SCHZ-22GHZ._ | Ee 

APOLLO 10 100MHz Counter Timer Ratio/Period/Time int. etc. 
APOLLO 100 100Mbz (as above re tao functions) 

H.P. 8495B Attenuator DC- A8GHZ. 0dB-110B in 1dB Steps 

HATFIELD 2105 Attenuator 50 on AUDIO POWER AMPS 
DX TDR1 502 .occsorocnmne 



HP. 141T with 8554B & 85528 SOOkHz-125 
HP. 141T with 8553B & 85524 1kHz-110M 
HP.141T Main Frames Only. Good Tubes 
MARCONI T2370. 30H2-10MHZ 

JUPITOR 500 FUNCTION GEN. 01H2-500kHz si 
All other Black Star equipment available. 


= ot  Gusrentced. Manuals supplied if possible. 
This is a VERY SMALL SAMPLE OF STOCK. SAE or telephone for lists. Please check availability before 
ordering. CARRIAGE all units £16. VAT to be added to Total of Goods and Carriage. 
eee aes 


= Ty ‘a 
Tel: 01734 268041 Fax: 01734 351696 Callers welcome 9am to 5.30pm MON-FRI (UNTIL 8pm THURS) Leeds 


Surplus Precision Medical Unit, internally in excel- 

lent condition. Designed primarily. to eject a precise 

INPUT 220V/240V AC 50/60 controllable amount of fluid from a medical syringe 

OUTPUT 0V-260V (latter not supplied). Contains the following remov- 

Price P&P | able BN plait ee ee Eee gees 4 

: ; EPR scap Precision otor wit 
O-5KVA 2 5 amp max £31.90 : £6.00 300:1 Gearbox and optical encoder coupled to a 
(£44.53 inc VAT) precision threaded drive mechanism. Mains supply 
1KVA 5 amp max 

2KVA 10 amp max 
3KVA 15 amp max 



Tel: 0181 984 0831 

Amstrad, Toshiba, from £5. Satellite Finder Kit, Meter etc. £29.99. 
Ferguson, Philips, ITT, Sony from £10. Marconi Blue Cap, ex-rental, £5 plus £2 
Universal Remote Control, operates TV, Video, post & carr. 

Satellite, with Teletext buttons, £16.99 or Amstrad Compact Black Cap. LNB, voltage 
non-Text £10.99. switching, 1dB, special price £23.95 plus £2 

£41.15 £7.00 | with 6 x 1.5V Ni-Cad AA cells back-up. L.C.D. 
(£56.58 inc VAT) | Digital readout 17mm high with legends. Audible 
£59. ch. 78 Say) ree These are sold for the dismantling of the exceptional 
. c quality components. Regret NO cncure available. 
£78.65 £8.50 Ridiculously low price: £20.00 + £4.00 p&p 

5 (£102.40 inc VAT) (£28.20 inc VAT). : jae post &carr. 
5KVA 25 amp max £139.15 . 5 KVA ISOLATION TRANSFORMER We repair Philips hand sets, £5.00. Satellite dishes, Black Mesh 60cm, £25.99 plus 
(Plus Carriage) | As New Ex-Equipment, fully shrouded, Line Noise Pinch Rollers from £2.99. £5 post & carr. 

Buy direct from the Importers. Keenest prices in the country | Suppression, Ultra Isolation Transformer with Video Fig.-8 Mains Lead, Feletinken type, £1., SPECIAL OFFER, satellite owners upgrade to 

110V-240V Auto transfer either cased with American socket and 
mains lead or open frame type. Available for immediate delivery. 


Write/Phone your enquiries 

4ft 40 watt £14.00 (callers only) (£16.45 inc VAT) 
2ft 20 watt £9.00 (callers only) (£10.58 inc VAT) 
12in 8 watt £4.80+ 75p p&p (£6.52 inc VAT) 
Yin 6 watt £3.96 + 50p p&p (£5.24 inc VAT) 
6in 4 watt £3.96 + 50p p&p (£5.24 inc VAT) 

terminal covers and knock-out cable entries. 
Primary 120V/240V, Secondary 120V/240V, 
50/60Hz, 0-O05pF Capacitance. Size, L 37cm x W 
19cm x.H 16cm, Weight 42 kilos. Price £120 + 
VAT. Ex-warehouse. Carriage on request. 

New Manuf. Surplus Skeleton Blower suitable for 
mounting inside an enclosure to cool equipment. 
Overall size 130 x 110 x 85mm. Outlet 80 x 35mm. 
Impellor 60mm dia. x 60mm long. Price £14.10 inc 
p&p & VAT. 

Brand new 220V/240V AC/DC SEW-TRIC 2 lead Brush 
Motor. Size L. 100mm x H. 70mm x W. 55mm. Spindle % 

R.F. Video leads, 50p. 
SCART to SCART leads, £1 75. 

SCART to SCART leads, all pins connected, 


Aerial R.F. cable, RG62, 30p per mtr. 
Aerial R.F. male plugs, 30p each. 

TV on/off switches, from £1.95, most types. 
Halogen Lamps, 240V S500W, for outdoor 

floodilamps, £1 

Miniature Tool Kit, comprises: side-cutters knife, 


screwdrivers, £7.00. 

Varta, p.c.b. mounting rechargeable batteries, 
oval type Ni-Cad. Suitable for CMOS and 

Astra TD with our ADX frequency extender, 
£25.99. Can be used with standard or 
enhanced LNB. 

Satellite cable, high quality copper screen, 30p 
mtr., 100 mtr. roll £27 plus £5 post & carr. 

F. Connectors, 40p each. 

MASPRO LNB FSS, 1:3dB max., £13.33. 

NOKIA LNB FSS 1:3, £11.99. 

NOKIA Feed Horns, for offset antenna, £8. 

NOKIA Electromagnetic, Polarizers, £10. While 

stocks fast. 
Head Cleaners, £2.99. 

NMOS systems, 2:4V 100nAH, 99p. 

Ferguson TX90 tube bases, £2. 

Ferguson TX100 SCART panels, £2. 

Indoor amplified antenna, wide band, UH F/VHF. 
£11.99 plus £3, post & carr. 

Philips K30 colour brightness controls, front 
draw etc. £2. 

TV Loudspeakers, 6”x4”, 16 ohms, £1.50 each. 

Power Supply AC adapters, universal 300mA, 
£4.99, 750mA, £7.99 

Philips Krypton Torches, £1 50. 

Philips Television G11 line output panel, 
complete, £5 plus £2, post & carr. 

Philips Soldering lron, 240V, 25W, £5.99. 

Voltage Regulators, LM340T, 44p. 

1.C.s: SAA3010P £3.40; TDA3651 SI £1.10; 
TDA3654 £1.89; TDA3651A £2.85; 
TDA3562A £2.85; TDA2600 £5.73; 
TDA2578 £3.43; TDA2579 £2.86; TDA2030 
£2.28; TDA3653 £3.43; TDA3651 £2.29; 
TDA3562 £3.44; TDA 3564 £4.59; TDA4500 
£3.43; TDA8180 £5.48; TDA8190 £3.43; 
TDA8361, £19.99; STK4793 £9.00. 

DIODES: Type RH1, £2.00. 

£1.75; BU11AF 55p; BC327 10p; BC337 
10p; BC338 10p; BC548 10p; BC549 10p. 

5p; 1 50V 5p; 2:2y SOV 6p; 4:7 25V 10p; 
47 100V 20p; 470p 25V boyy ni 63V 60p; 

2,200 40V 60p; 3,300 25V 80 

Amstrad Universal remote controls, £6.00. 

Periswitch SCART switching box, 
automatically switches between VCR, 
Satellite and TV. Expensive unit! Originally 
priced at £99.95. OUR PRICE £9.99. These 
units require an additional 12V d.c. adaptor 
at £4.99 and 3 SCART leads at £6. Technical 
details on request. £4 post &carr. 

CONNECTORS: Phono to Phono couplers, 
40p each; Phono plugs, red or black, 50p 
each; Phono sockets, red or black, 50p each. 
Philips Audio Cassette Head Cleaning 
Splicing Kit, £2. 
High quality loudspeaker cable, 50p per mtr. 
Servicing Sprays £3.00 most types. 
Ceramic Type Pulse Capacitors, 20 for £1. 
Ferguson surround sound extension TV speakers, 
with stand, £25 a pair, plus £5 post & carr. ; 
PYE Stereo Cassette/Radio, FM/AM, New, 
Boxed, £25.99 plus £5 post & carr. ’ 


This is just a small sample of components 
available, please phone with your requirements. 
Please add £1.00 postage & packing, 
except where stated otherwise. 

No VAT charged. 

For either 6in, 9in or 12in tubes £6.05 + £1.40 p&p 
(£8.75 inc VAT) | 71 RPM 20lb/inch torque reversable 115V AC input 
The above Tubes are suitable for Forged Bank Note detec- including capacitor and transformer for 240V AC 
tion, security marking etc. operation. Price inc VAT and p&p £27.73. 
Other Wavelengths of U.V. TUBE available please. tele- “SOLID STATE EHT UNIT | 

phone your enquiries. Input 230V/240V AC, Output approx 15KV. 
400 WATT UV LAMP _— Producing 10mm spark. Built-in 10 sec timer. | 
Only £38.00+ £4.00 p&p (£49.35 inc VAT) Easily modified for 20 sec, 30 sec to continuous. 
160 WATT SELF-BALLASTED Designed for boiler ignition. Dozens of uses in the 

BLACK LIGHT MERCURY BULB field of physics and electronics, e.g. supplying 
Available with E.S. fitting. neon or argon tubes etc. Price less case 

Price inc VAT & p&p £25.55 £8.50 + £2.40 p&p (£12.81 inc VAT) NMS. 

500 GPH 15ft head 3 amp £19.98 Build your own EPROM ERASURE for a fraction of 
1750 GPH 15ft head 9 amp £34.55 the price of a made-up unit. Kit of parts less case 
Also now available: includes 12in 8 watt 2537 Angst Tube Ballast unit, pair 
24V D.C. 1750 GPH 15ft head of bi-pin leads, neon indicator, on/off switch, safety 
5 amp £35.55 microswitch and circuit £15.00 + £2.00 p&p 
All designed to be used submerged. (£19.98 inc VAT) 
IGHT STROBE KIT Pye 15 amp changeover lever microswitch, ‘ens $171. 
Decne tox Discd Theeirical uadeee Brand new. Price 5 for £7.05 inc VAT & p&p. 
Approx 16-joules. Adjustable speed £50.00+ £3.00 p&p WASHING MACHINE WATER PUMP 
(£62.28 inc VAT) Brand new 240V AC fan cooled.. Can be used for a 
Case and reflector £24.00+ £3.00 p&p (£31.73 inc. VAT). | variety of purposes. Inlet 1%in., outlet 1in. dia. Price 
SAE for further details including Hy-Light and] includes p&p. & VAT. £11.20 each or 2 for £20. 50 
inciustrat Strobe Kits. inclusive. 


TEL: 0181-995 1560 FAX: 0181 -995 0549 Ample 

in. dia. x Tin. long. Price £14.10 inc p&p & VAT. 

Showroom open 

Everyday with Practical Electronics, June 1995 501 



Everyday with Practical Electronics reaches nearly 

twice as many UK readers as any other indepen- 

dent monthly hobby electronics magazine, our 
audited sales figures prove it. We have been the 
leading independent monthly magazine in this 
market for the last ten years 

If you want your advertisements to be seen by the largest readership’ at the most economical price our classified and 
semi-display pages offer the best value. The prepaid rate for semi-display space is £8 (+ VAT) per single column centimetre 
(minimum 2.5cm). The prepaid rate for classified adverts is 30p (+ VAT) per word (minimum 12 words). 

All cheques, postal orders, etc., to be made payable to Everyday with Practical Electronics. VAT must be added. Advertise- 
ments, together with remittance, should be sent to Everyday with Practical Electronics Advertisements, Holland Wood House, 
Church Lane, Great Holland, Essex CO13 OJS. Phone/Fax (01255) 850596. 

For rates and information on display and classified advertising please contact our Advertisement Manager, Peter Mew as above. 


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: 


71 Gainsford Road, Southampton SO19 7AW. 


2SA, 2SB, 2SC, 
2SJ, 2SK, SAA, 

TEL: (69) 741 0300 
65) 749 1048 

705 Sims Drive #03-09 
Shun Li Industrial Complex, 
Singapore 1438. 

‘ ha | Pe mt ‘4k @) 
cluding sensitive electret mic., tuneable 70-115MHz, 

500m range. KIT £5.95. ASSEMBLED £9.95. 

powered from line, transmits all conversations, 500m 
9 iii aailliis KIT £5.95. ASSEMBLED 

Supplied with all components & high quality PCB's. Prices 
include P&P. Send 2 x 1st class stamps for our kits and 
publications catalgoue. Cheques/P.O.’s payable to: 


(Dept. EPE) Unit 14 Sunningdale 

Bishops Storttord Herts CIVIZ3 2PA 



3000 items at competitive prices! 

_ Batteries e Buzzers e Cable e Displays 
Capacitors e Cases e Connectors e LDR 
CMOS e Crystals e Data switches e Diodes 

Displays e Fuses elntegrated circuits 
Knobs e LEDs e Loudspeakers e Relays 
Resistors e Solder equipment e Switches 
Transformers e Transistors @ Triacs e etc 

For your copy, send your name and 
address, with 50p (stamp) towards 
cost of carriage to: 


42 Elm Grove, Southsea, Hants PO5 1JG 




O.N.C., O.N.D. and H.N.C. 
Next course commences 

Monday 18th September 1995 

Me) ]21e)\ 44 ons -10)\ | (essa exe) a a =e] = 
TEL: 0171-373 8721 


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 : 
Operates from , » ees = VAT 
cae a be + Post and 

ree we Sin, ay insurance £4 


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. 
ne or send your wants list for quote 


exists to help electronics enthusiasts by 

personal contact and through a quarterly 

For membership details, write to the 


Mr. J. F. Davies, 70 Ash Road, Cuddington, 

Northwich, Cheshire CW8 2PB. 
Space donated by Everyday with Practical Electronics 

This 22cm space in 
Everyday with 
Practical Electronics 
Would ONLY cost you 

£20 «var 


Annual subscription rates (1995): 

UK £24.00. 
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money prices. S.A.E. for FREE catalogue. 
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PLDs AND EPROMS copied or pro- 
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channels, 64 levels, 127 presets, assembled 
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60 WATT AMPLIFIERS, £5.00, SOV module 
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sories, tools, etc. Free lists from Spiral Solutions 
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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 7QL. 

prices you can afford. Very low cost (sometimes 
free) tooling. Small quantities speciality. 01685 
(Aberdare) 874763. 

many items equipment, kits and instruments 
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Electronics [_] | TV, Video & Hi-Fi Servicing 

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SPECIAL OFFER = for limited period only 

CHOOSE 8 x £1 packs FREE with every 15 purchased 
SP1 15 x 5mm Red Leds SP42 200 x Mixed 0.25W C.F. resistors 

SP2 15 x 5mm Green Leds SP47 5 x Min. push button switches 
SP3 12 x 5mm Yellow Leds SP102 20 x 8pin DIL sockets 

SP4 10 x 5mm Amber Leds SP103 15 x 14pin DIL sockets 

SP6 15 x 3mm Red Leds SP104 15 x 16 pin DIL sockets 

SP10 100 x 1N4148 diodes SP112 5 x Cmos 4093 

SP11 30 x 1N4001 diodes SP118 2 x Cmos 4047 

SP12 30 x 1N4002 diodes SP125 10 x 1000/16V radial elect caps 
SP18 20 x BC182 transistors SP130 100 x Mixed 0.5W C.F. resistors 
SP19 20 x BC183 transistors SP135 6x Min. slide switches 

SP20 20 x BC184 transistors SP137. 4 x W005 bridge rectifiers 
SP21 20 x BC212 transistors SP138 20 x 2-2/50V rad elect caps 
SP22 20 x BC214 transistors SP142 2x Cmos 4017 

SP23 20 x BC549 transistors SP147 = 5 x Stripboard 9 strips/25 holes 
SP28 5 x Cmos 4011 SP151 4 x 8mm RedLeds 

SP29 4 x Cmos 4013 SP156 3 x Stripboard 14 strips/27 holes 
SP33 5 x Cmos 4081 SP165 2 x LF351 0p.amps 

SP36 25 x 10/25V radial elect caps SP173 10 x 220/25V rad elect caps 
SP37 15 x 100/35V radial elect caps SP175 20 x 1/63V rad elect caps 

SP40 15 x BC237 transistors SP183 20 x BC547 transistors 

Catalogue £1 or FREE with first order. 
P&P £1.25 per order. NO VAT. 
Orders to: Sherwood Electronics, 

7 Williamson St., Mansfield, Notts. NG19 6TD. 

RP3 5 each value — total 365 £2.60 
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1000 popular values £5.30 

Everyday with Practical Electronics, June 1995 

STE ee 

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Certificated Supported 

NA T / 


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- 
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vocational training contain workbooks, audio cassette 
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certification, there is probably a distance learning course 
ready for you. Write or telephone for details to: 
National College of Technology 
NCT Ltd., PO Box 11 
Wendover, Bucks 
Tel: (01296) 624270 


Mixed metal/carbon film resistors “sW E12 series 10 ohms to 1 Megonm.............:ce 
Carbon Film resistors %W 5% E24 series 0.51 R to 1OMO 

PPPoE eee eee eR COOP CCCC Creer eee ees 

100 off per value — 75p. even hundreds ag value totalling 1000 ............ cece £6.00p 
Metal Film resistors %W 10R to 1 MO 5% E12 series — 1 4p. 1% E24 series ...........:ccceeees 2p 
Mixed metal/carbon film resistors ZW E24 series 1RO to 10MO .........ccccccsseneeeeeeeeeees 1’Ap 

1 watt mixed metal/Carbon Film 5% E12 series 4R7 to 10 MeQON Is ............ccseceeseesseeees 5p 
Linear Carbon pre-sets 100mW and %W 100R to 2M2 EG Ser i@S .........seseceeeeteteeeeeeentees . 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 
Mylar (polyester) capacitors 100V working E12 series vertical mountin 

1000p to 8200p - 3p. .01 to .068 - 4p. 0.1 - 5p. 0.12, 0.15, 0.22 - 6p. 0.47/50V - 8p 

Submin ceramic plate capacitors 100V w 

2 btn mountings. E12 series 

2% 1.8pf to 47pf - 3p. 2% 56pf to 330pf - 4p. 10% 39OP-4700p ........ ec eeecsssseseereeteeeeeees 4p 
Disc/plate ceramics 50V E12 series 1PO to 1000P, E6 Series 1500P to 47000P............... 2p 
Polystyrene capacitors 63V working E12 series long axial wires 

10pf to 820pf - 5p. 1000pf to 10,000pf - 6p. 12,000PF ....... eee eee eeeeeeeeteeteteeeeeeeeeees 7p 
741 Op Amp - 20p. 555 Timer — 20p. LM3900 ....0... ce ccecessceeeseseeeessssesessecaseeeseeseeeseeeeees 80p 
CMOS 4001 - 20p. 4011 - 22p. 4017 — 40p. 4069UB unbuffered «0.0.00... cc eeeeteeeeeees 20p 

DIL holders, 8-pin 9p; 14-, 16-, 18-pin 12p; 24-pin 18p; 28-pin 20p; 40-pin 25p. 

1/50, 2.2/50, 4.7/50, 10/25, he ke abasiptasusaias 

22/16, 22/25, 22/50, 33/16, 47/ 
100/16, 100/25 7p; 100/50 

DIODES (piv/amps 


1A + or — 5V, 8V, 12V, 15V, 18V & 24V - 55p. 100mMA. 5.8, 12, 15, V + oes 30p 

ps) , 
75/25mA 1N4148 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 40O0MW - 6p. 1 Walt... ee ceeceeeeeteeeteeeneeeeeneeees 10p 

Battery snaps for PP3 - 7p for PP9.................. 

L.E.D.’s 3mm. & 5mm. Red, Green, Yellow - 10p. Grommets 3mm - 2p. 5mm..............645 2p 
Red flashing L.E.D.’s require 9-12V supply Only, SMM .........ccceeeeeeeeteeteeteeteeeeeetteeeenenees 50p 

Mains indicator neons with 220k reSiStOF .............:ccsecccseeeeneeeeeeeeeeeeees serararnncasbaictay ueaies 10p 
20mm fuses 100mA to 5A. O. blow 6p.A/surge 10p. Holders, chassis, mounting ............ 6p 
High speed pc drill 0.8, 1.0, 1.3, 1.5, 2.0mm - 40p. Machines 12V dC ...........:ccceee £15.00 

HELPING HANDS 6 ball joints and 2 croc clips to hold awkward jODS ............:se £4.50 
AA/HP7 Nicad rechargeable cells 90p each. Universal charger unit ...............:cseeees £6.50 
AA/HP7 zinc/carbon batteries in packs of 4 

Glass reed switches with single pole make contacts - 8p. Magnets ..............:cccseceereees 

0.1” Stripboard 2%” x 1” 9 rows 25 holes - 25p. 34 x 2%” 24 rows 37 holes ............5 70p 
Jack plugs 2.5 & 3.5m — 14p; Sockets Panel Mtg. 2.5 & 3.5... ccccceeteeesteeeeneeees 10p 
Ear pieces 2.5 & 3.5mm, dynamic — 20p; 3.5mM CryStal..........cceccceeeseeteeteeeteeeeeeetaaes £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. 

15 Amstrad Games. ...............+. 
15 Spectrum Games ............... 

£1 PAC 
50 BC547A; 20 BS107; 20 BSS92; 
10 2N2907A; 20 2N5086; 
50 2N5551; 3 BD145; 10 BD237; 
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 21-1OMHz 
crystals; 10 811 MHZ filters; 50 6-way 
i.c. skts.; 50 14-way d.i.p. hors; 
20 TO18 heatsinks; 20 TO5 heatsinks; 
200 TO5 mounting pads; 200 TO18 
mountings pads; 2 10092 LOPT Tx; 
5 12-way terminal blocks; 10 silver 
control knobs; 10 95V V.D.R.;312V 
counters; 25 3:5mm jack plugs; 
10 PCB MT microswitch; 10 6-way 
d.i.|. switch; 10-1 pole 3-way rotary 
switch; 25 slide switches; 5 3A 250V 
power toggle switch; 50 4-7uF 25V 
caps; 15 2200uF 25V caps; 
10 0-047uF suppresion caps; 
25 neons; 10 1p,.F 250V polyesters. 

5%” to 3%” floppy converter 

lead £1.50 ea 
STC p.s.u. 240V Input; 5V 6A 

Output, (converts to 12V 3A, 

details supplied).................. £5 
Temperature probes, with 

apes sae, crtraniretenaied £3.95" 
Universal Timer (10 min. delay and_, 

20 min. cut-off functions) ..£3.95 | 
12V 400mW Zeners, ....... 100 off £1 
3AMP mains filters............ . 
40 Character x 1-line dot 

matrix display.................. 
Car Dashboard Display (show 

lights, indicators, doors, 

on picture of car)................. , 
4-digit clock display............... £2.50 
4-digit I.c.d. with 7211 driver..£3.50" 
17-digit v.f. display.........0.00.... £2.95" 
Giant 2-digit v.f. display......... 
12V stepper motors, 48 steps 

per rev., 7-3° step angle....... 


Cee ee eeeseeseneseseeseseseeeeese 

250 off mixed electrolytic 

BG: cis vnteintcnitten ae ; 
250 off polyester caps............£4.95 | 
1000 off mixed resistors “W..£4.95 | 
100 off phono plugs............... £2.95 

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 ............6.000 £12.50 
Do not add VAT. Postage 30p (free over £5). Stamp for list. 


127 Chesterfield Rd., Sheffield S8ORN Tel: 01742 557771 Return posting 

50 off mixed terminal blocks..£2.50 
25 off buzzers & sounders...... 

25 off mixed relays................. 

50 off mixed switches............. 

250 off i.c. sockets.................. 

1000 off Ceramic cap.s............ 

5 off 3V Lithium memory 

5V SPCO S.I.L. reed relay........ 
12V Piezoelectric Sounders...... 
DIL Switches 3/4/6 and 
3:5mm jack plugs............... 
100 off Zener diodes, mixed........ 
21 -piece mini screwdriver set. £3.95" 
Universal test lead kit.............. £3.95" 
10 crocodile clip leads............ 
20 off mixed R.F. Filters, 
Crystals, etc. ...cccccceceeeeeee £4.95" 
100m P.V.C. sleeving.............. . 

Q0V0310, £10*; QQV0320A, £10": 
QQV0640A, £20*; ECC 82, £3"; 
ECH 81, £2*: PCL 805, £3": 

ORP 11, £3; ORP 40, £3; CV 4004, 
4005, 4006, 4007, 4014, 4020, 
4024, 4043, 4055, 4064, 5042, 
5080, ALL £5 each”. 

We also buy all forms of electronic 
components, p.s.u’s, disk drives etc. 
Lists to below address. 

DY=) 0) an =e =n O0 OF \N/ 1 od ot a ok Om 
sé Bl @reyar-s ec] olism averclem 
St. lves, Huntingdon, 
Cambs PE17 6EO 
Tel/Fax: 01480 300819 

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, 

Millions of quality components 
at lowest ever prices! 

Plus Tools, Watches, Fancy Goods, Toys. 
Mail order UK only. 

All inclusive prices — 
NO VAT to add on. 
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 


NLR. BARDWELL...cccsscccssscccoseccsseccsseccsssecessscsesscessseees 494 
B.K. ELECTRONICS ccc cccsccccseccsseccsssecsssecssseesees Cover (iii) 
BRIAN J. REED.u.ccccccscccsssccsssccssecsssecsssccsssccsssessseessensees 504 
BULL ELECTRICAL ...c.cccsccccsscccsseccssecsecsseesseesees Cover (ii) 
CHATWIN GUITARS (SCG),...ccccsscccssseccssscccsseecessseeeee 501 
CIRKIT DISTRIBUTION.....cccccsccccssscccsseccssseccssseesesseeen 426 
COMPAC ELECTRONICS.....ccscccsssecsssecscsesssessseesseeee 501 
COMPELEC....ccsccccsseccssecssseccssecsssesssscssssessssecssesseceseesves 504 
COOKE INTERNATIONAL. ....ccccccssccccsssecsssecsssssesesseeee 503 
CRICKLEWOOD ELECTRONICS. .......cccccccssecsseesseeee 498 
CR SUPPLY COMPANY. .....cccsscccsssscsssesssseccssecssesssees 504 
DIRECT CCTV. ..cccccscccssseccsssecsssecssuccsssccsssecsseessessnecsseen 498 
DISPLAY ELECTRONICS. .....cccsccccsssscssseccsseesseesseessees 422 
EPT EDUCATIONAL SOFTWARE ......cccssecccsssessssseeses 479 
ESR ELECTRONIC COMPONENTS.......--ssescssseesssees 432 
EXPRESS COMPONENTS. .....cccssccssseccsseccssssccsssecenseee 486 
FRASER ELECTRONICS. .....ccccccsscccsssescssseccsssseesssseeees502 
GATS ELECTRONICS .....cccccsseccssscccsssccssseccssssccssseccessee 498 
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Phone/Fax: (01255) 850596 

For Editorial address and phone numbers see page 433. 

Colchester, Essex. Distributed by Seymour, Windsor House, 1270 London Road, Norbury, London SW16 4DH. Sole Agents for Australia and New Zealand—Gordon & Gotch (Asi 

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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 MXFS900 £449.15 

BARS awe 

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98 de cats Bre #2: : ap 
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* Xa. DIO NANIOR e 2 or. 
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KR ern. eae bad 

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 

SSA ae a a cranes Sok Babe eran nn So 

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 120mm 

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. 

\s > 

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 + 
Bridged Mono 
400 WATTS (200 + 
Bridged Mono 

& * Stereo, bridgable mono * Choice of 
high & low level inputs * L & R level 
controls * Remote on-off * Speaker & 
thermal protection. 

125) Stereo, 250W 

200) Stereo, 400W 

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 500mV, 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 5}00mV, 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 5}00mV, 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 97dB. PRICE £32.71 + £2.00 P&P 

RES. FREQ. 71Hz, FREQ. RESP. TO 7KHz, SENS97<dB. 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 99dB. 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 97cdB. 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 



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10) OM eKo)[o] 1] dl f= et (40 ll of foia- 
with hundreds of Brand New 
Products at Super Low Prices. 

Available from all branches of WH SMITH, John Menzies in Scot 
ONLY, Eason & Son in N. Ireland ONLY, and Maplin stores nationv 

The Maplin Electronics 1995 Catalogue — OUT OF THIS WO