everyday lectron cs - world radio history

EVERYDAYMIMILECTRON CS

and computer PROJECTSAPRIL 1984 90p

A WIDE SPECTRUM

QUASI STEREOQUIZ MASTER II FUSE /DIODE CHECKER

MULTIPURPOSE INTERFACE FOR COMPUTERSplus

DATA ACQUISITION & CONTROL SYSTEM FORBBC MICRO, PET, VIC-20 & COMMODORE 64

Australia $1.50 New Zealand $1.75 Malaysia $4.95

electrontze AUTO-1ELECTRON1C PRODUCTSKITS OR READY BUILT

I TOTAL ENERGY DISCHARGE 1ELECTRONIC IGNITION

IS

YOUR CARAS GOOD AS IT COULD BE ?* Is it EASY TO START in the cold and the damp? Total Energy

Discharge will give the most powerful spark and maintain full outputeven with a near flat battery.

* Is it ECONOMICAL or does it "go off" between services as theignition performance deteriorates? Total Energy Discharge givesmuch more output and maintains it from service to service.

* Has it PEAK PERFORMANCE or is it flat at high and low revs.where the ignition output is marginal? Total Energy Discharge givesa more powerful spark from idle to the engines maximum (even with8 cylinders).

* Is the PERFORMANCE SMOOTH. The more powerful spark ofTotal Energy Discharge eliminates the "near misfires" whilst anelectronic filter smoothes out the effects of contact bounce etc.

* Do the PLUGS and POINTS always need changing to bring theengine back to its best? Total Energy Discharge eliminates contactarcing and erosion by removing the heavy electrical load. The timingstays "spot on" and the contact condition doesn t affect theperformance either. Larger plug gaps can be used, even wet orbadly fouled plugs can be fired with this system.

* TOTAL ENERGY DISCHARGE is a unique system and the mostpowerful on the market - 3 1/2 times the power of inductive systems -3 1/2 times the energy and 3 times the duration of ordinary capacitivesystems. These are the facts:Performance at only 6 volts (max. supply 16 volts)SPARK POWER - 140W, SPARK ENERGY - 36miSPARK DURATION - 5000, STORED ENERGY 135m..iLOADED OUTPUT VOLTAGE

50pF load - ,

tiOrtik#141900it - 26k VWe challenge any manufac 04fish better performancefigures. Before you buy any er make, ask for the facts, itsprobably only an inductive system. But if an inductive system iswhat you really want, we'll still give you a good deal.

* All ELECTRONIZE electronic ignitions feature:EASY FITTING, STANDARD/ELECTRONIC CHANGEOVERSWITCH, STATIC TIMING LIGHT and DESIGNED INRELIABILITY (14 years experience and a 3 year guarantee).

* IN KIT FORM it provides a top performance system at less than halfthe price of comparable ready built units.The kit includes: pre -drilledfibreglass PCB, pre -wound and varnished ferrite transformer, highquality 2uF discharge capacitor, case, easy to follow instructions,solder and everything needed to build and fit to your car. All youneed is a soldering iron and a few basic tools.

ilLost NEW CARS already have electronic ignition. Update YOUR CAlld

ritECTRONIZEELECTRONIC CAR ALARM

HOW SAFE IS YOUR CAR ?More and more cars are stolen each week and even a steering lockseems little help. But a car thief will avoid a car that will cause himtrouble and attract attention. If your car has a good alarm system -well there are plenty of other cars to choose from.

LOOK AT THE PROTECTION AN ELECTRONIZE ALARMCAN GIVE* MINIATURE KEY PLUG A minia

ring and is coded to your paru* 2025 INDIVIDUAL COMB

1% tolerance resistors, both tip

to your key

and togetherontains two

give 2025 different combinations.* ATTRACTS MAXIMUM ATTENTION This alarm system not only

intermittently sounds the horn, but also flashes the headlight andprevents the engine being started.

* 60 SECOND ALARM PERIOD Once triggered the alarm will soundfor 60 seconds, unless cancelled bx the key plug, before resettingready to be triggered again.

* 30 SECOND EXIT DELAY The system is armed by pressing a smallbutton on a dashboard mounted control panel. This starts a 30Second delto,, period during whIlitithe owner can open and closedoors without triggering the alarm.

* 10 SECOND ENTRY DELAY When a door is opened a 10 seconddelay operates to allow the owner to disarm the system with thecoded key plug. Latching circuits are used and once triggered thealarm can only be cancelled by the key plug.

* L.E.D. FUNCTION INDICATOR An LED is included in thedashboard unit and indicates the systems operating state. The LEDlights continuously to show the system is armed and in the exit delaycondition. A flashing LED indicates that the alarm has been triggeredand is in the entry delay condition.

* ACCESSORY LOOP - BONNET/BOOT SWITCH - IGNITIONTRIGGER These operate three separate circuits and will trigger thealarm immediately, regardless of entry and exit delays.

* SAFETY INTERLOCK The system cannot be armed by accidentwhen the engine is running and the car is in motion.

* LOW SUPPLY CURRENT CMOS IC's and low power operationalamplifiers achieve a normal operating current of only 2.5 mA.

* IN KIT FORM It provides a high level of protection at a really lowcost. The kit includes everything needed, the case, fibreglass PCB,random selection resistors to set the code and full set of componentsetc. In fact everything down to the last washer plus easy to followinstructions. A

fill in the coupon and send to:

ELECTROMIE DESIGN Dept C Magnus Rd

Please Supply: pi Send More InformationTOTAL ENERGY DISCHARGE (6 or 12 volt negative earth)

D.I.Y. parts kit £1,540 £14.95

n Assembled ready to fit £2810 £19.95(positive earth unit £22.951

TVVIN OUTPUT for cars and motor cycles with dual ignition

Twin, D.I.Y. parts kit £24-:55 £22.95

r7 Twin, Assembled ready to fit £36-.45 £29.95

CAR ALARM (12 volt negative eanhlD.I.Y. parts kit £24c56 £19.95

LLi Assembled ready to fit £U185 £29.95

Wilnecote Tamworth B77 5BY tel 0827 281000

SPECIAL OFFER. Buy one electronic ignition kit plusone alarm kit for £30.85 or assembled units for £44.65.Goods must be purchased at the same time.

I enclose cheque/postal order OR debit my Access/Visa card

IllllllllllllllllVISA

Name

Address

Code

Please Add £1.00 P&P(UK) Per Unit Prices Include VAT

EVERYDAY

VOL. 13 NO. 4 APRIL 1984

ELECTRONICSrat=PROJECTS . . . THEORY . . . NEWS . . .

COMMENT ... POPULAR FEATURES ...

EE -T-

With effect from April 1, he EE Editorial offices will belocated at:Westover House, West Quay Road, Poole, Dorset.See page 257 for further details.

IPC Magazines Limited 1984. Copyright in alldrawings, photographs and articles published inEVERYDAY ELECTRONICS is fully protected, andreproduction or imitations in whole or in part areexpressly forbidden.

PROJECTSAUDIO SINEWAVE SWEEP GENERATORby R. E. LiddiardFor amplifier performance checksFUSE/DIODE CHECKER by L. A. PrivettBlack Box Project Rapid continuity and polarity indicationDATA ACQUISITION SYSTEMby J. Adams and G. M. FeatherQUIZ -MASTER II by S. LyonsDetermines who -hit- the button first in panel gamesMULTIPURPOSE INTERFACE FOR COMPUTERSby M. P. HorseyEight channel control from the Micro User PortQUASI -STEREO ADAPTOR by R. A. PenfoldAdds stereo effect to TV soundTIMER MODULE FOR CENTRAL HEATING SYSTEMSby S. IbbsAccurate interval timer for fuel economy

SERIESTEACH -IN 84 by George HyltonPart 7: Waveforms and DistortionMICROCOMPUTER INTERFACING TECHNIQUESby J. Adams and G. M. FeatherPart 10: Data monitoring, acquisition and control processesWHY NARROW BAND F.M.? by E. A. RuleModulation systems compared

FEATURESEDITORIAL Home Entertainment: A Wider ViewSHOPTALK by Dave BarringtonProduct news and component buyingREADERS' LETTERSYour news and viewsSOFTWARE SERVICECOUNTER INTELLIGENCE by Paul YoungA retailer commentsFOR YOUR ENTERTAINMENT by Barry FoxMole Proof: Cashless SocietyEVERYDAY NEWSWhat's happening in the world of electronicsRADIO WORLD by Pat Hawker G3VAReliability; Radio Callsigns; CB ChangesPLEASE TAKE NOTEGames Scoreboard; Oric Port Board

CIRCUIT EXCHANGEA forum for readers' ideas

NEW PRODUCTSFacts and photos of instruments, equipments and toolsSQUARE ONEBeginners' Page: CapacitorsPRINTED CIRCUIT BOARD SERVICE

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232

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Our May 1984 issue will be published on Thursday,April 19. See page 259 for details. Readers' Services Editorial and Advertisement Departments 225

Everyday Electronics, April 1984 217

YOUR CAREER ..YOUR FUTURE ..YOUR OWN BUSINESS..

THIS IS THE AGE-OF ELECTROthe worldt fastest growth industry...

There is a world wide demand for designers/engineers and for men to service and maintain all theon the market today - industrial - commercial and domestic. No unemployment in this walk ofAlso the most exciting of all hobbies - especially if you know the basic essentials of the subjecA few hours a week for less than a year - and the knowledge will be yours... .We have had over 40 years of experience in training men and women successfu ly in this subject.

Our new style course will enableanyone to have a real understandingof electronics by a modern, practicaland visual method. No previousknowledge is required, no maths, andan absolute minumum of theory.

You learn by the practical way ineasy steps, mastering all the essentialsof your hobby or to start, or further, acareer in electronics or as a self-employed servicing engineer.

All the training can be carried out inthe comfort of your own home and atyour own pace. A tutor is available towhom you can write personally at anytime, for advice or help during yourwork. A Certificate is given at the endof every course.

You will do the following: Build a modern oscilloscope Recognise and handle current electronic

components Read, draw and understand circuit diagrams Carry out 40 experiments on basic

electronic circuits used in modernequipment using the oscilloscope

Build and use digital electronic circuitsand current solid state 'chips'

Learn how to test and service every typeof electronic device used in industry andcommerce today. Servicing of radio, T.V.,Hi-Fi, VCR and microprocessor/computerequipment.

OUR HOBBY

ICS !

electronic equipmentlife!

SE I

Radio &Electronics School[ CACC British Natunial ,Berks.RG1 1BR

COLOUR BROCHURE

I

I

I

IPOST NOW

Please send your brochure without any obligation to I am interested in:

COURSE IN ELECTRONICS

NAME as described above IRADIO AMATEUR LICENCEMICROPROCESSORS I

ADDRESSOTHER SUBJECTS Iplease state below

I

OR TELEPHONE US

BLOCK CAPS PLEASE 0734 51 51 5 ORC

owYrcunK us22758

EE/4/841(24TELEXHR SERVICE) CACC I

School Reading,Berks.EG-1 1BRJ

218 Everyday Electronics, April 1984

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Heathkit IFS A PLEASURE TO BUILDBring the enjoyment back into your hobbywith a kit from Heathkit. The beautifullyillustrated documentation and step-by-step instructions make building a Heathkita relaxing, absorbing pleasure! Every kitincludes a constructors' guide coveringsoldering and component identificationwhich makes construction straightforwardeven for a beginner.The Heathkit range contains many kitsideal for beginners as well asamateur radio kits, computer-ised weather stations, ahighly sophisticatedrobot, a 16 -bit computerkit and a range of home(or classroom) learningcourses that haveeasy -to -under-stand texts andillustrations, in sect-ions so that you canprogress at your ownpace, whilst the hands-on experiments ensurelong-term retention ofthe material covered.

You'll find Heathkits available for Amateur RadioGear Car Test Equipment Kits For The Home Self -Instruction Courses Computer Kits Test

Instrument Kits Kits For Weather Measurements.

All the most popular kits and educational productsare fully detailed in the 1984 Maplin catalogue (seeoutside back cover of this magazine for details) or

for the full list of Heathkit products send 50p forthe Heathkit International Cataloguecomplete with a UK price list of allitems.

All Heathkit products available inthe UK from:

Maplin ElectronicSupplies Ltd.P.O. Box 3, Rayleigh,Essex, SS6 8LR.Tel: (0702) 552911.(For shop addresses see back cover.)

PRACTICAL DESIGN GUIDES

A Guide to Printed Circuit Board DesignCharles HamiltonPrinted circuit boards can look, and sometimes are, extremely complicated. The high density ofcomponents on modern boards combined with the mass tracking can deter the would-bedesigner. This new book strips away the aura of mystique surrounding PCB design. A practicalbook covering design methods and practice currently employed in the modern drawing office, itdescribes a logical step by step approach to PCB design. Fully illustrated throughout, the book isan invaluable guide and practical aid to the young or inexperienced designer in the drawingoffice.

Softcover 104 pages 216 x 138 mm Illustrated 0 408 01398 2 £7.50 March 1984

The Art of Micro DesignA A BerkThe Art of Micro Design has been written for engineers, technicians and students looking for apractical guide to the design of microprocessor -based systems. It presents down-to-earthinformation to allow the reader to begin immediate design of anything using microprocessors,from control systems to large computers. Throughout the book the emphasis is on hardware,and the practical 'cookbook' style of presenting information reflects the author's many years ofmicro systems design.

Softcover 320 pages 216 x 138 mm Illustrated 0 408 01403 2 13.95 1984

Available from your nearest bookseller

q Butterworths Borough Green, Sevenoaks, Kent TN1 5 8PH


BI-PAK BARGAINSMINIATURE TOOLS FOR HOBBYISTS

00

Miniature round nose side cutters -insulated handles 41inch length. OrderNo: Y043.

Miniature long nose pliers --insulated handles 51inch length.

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Miniature bend nose pliers -insulated handles 51inchlength. Order No: Y045

Miniature end nippers -insulated handles 41inchlength. Order No: Y046.

Miniature snipe nose plierswith side cutter and serratedjaws - insulated handles 5inchlength. Order No: Y042 ALL AT 1.25

moth

FLEXEY DRIVER

A flexible shaft screwdriver for thoseawkward to get at screws Overalllength 8 linch. Order No: FS -1 Flatblade 4mm FS -2 Cross point no. 1 fliteach.

eSEMSCO----

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VALUE PACKSMy Description Price300 Assorted Resistors Mixed Types £1.00300 Carbon Resistors 14 Watt Pre -Formed MOO200150b Watt Resistors 100 ohm -1M Mixed £1.00200 Assorted Capacitors All Types ELM200 Ceramic Caps Miniature - Mixed £100100 Mixed Ceramics Disc 1pf - 56pf £120100 Mixed Ceramic Disc. 68pf - .0150 £1.00100 Assorted Polyester/Polystyrene Caps f1.0060 C280 Type Caps Metal Foil Mixed £1.00

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20 Pcs. 1 - 2 & 4 mm Plugs & SocketsMatching Sizes £1.00

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TECASBOTYThe Electronic Components and Semi-conductor Bargain of the Year! This collectionof Components & Semiconductors for the

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REGULATEDVARIABLEStabilisedPOWER SUPPLYVariable Irom 230 volts and 0 2 Amps. Sot includes -I VPS30 Module. I - 25 volt 2 amp transformer.I 0-50v 2" Panel Meter. 1 - 0-2 amp 2" Panel Meter.I 470 ohm wirewound potentiometer. 1 457 ohm

rebound potentiometer. Wiring Diagram

included. Order No. VPS30 KIT f20.MINIATURE FM TRANSMITTER

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8 Bit MICROPROCESSORNational INS8080AN 40 Pin OIL N Channel SiliconGATE MOS TECHNOLOGY As used in NationalsN8080 Micro Computer Family

Instruction Cycle Time 2 uSSupplied with functionalBlock Diagram

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MULTITESTERS

I 000 opy Including test leads la Battery

AC volts - 0-15-150-500-1,000

DC yetis 0 15-150-500 1000

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0/No 1322.0UR PRICE f6.50 ONLY

5T21 SCREWDRIVER SET6 precision screwdrivers in hinged plasticcase. Sizes - 00, 1.4, 2, 24, 2.9 and3.8mm £1.75

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5T41 TOOL SET5 precision instruments in hinged plasticcase. Crosspoint (Philips) screwdrivers - HOand HI Hex key wrenches. - 1.5, 2 and2.5mm £1.75

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ELECTRONIC SIREN 12v DCRed plastic case with adjustable fixingbracket Emits high-pitched wailing noteof varying pitch - 100 cycles per minute.Dims - 90mm (dia.) 60mm (depth). Power- 12v DC.

Our Price: £5.50

BRAND NEW LCDDISPLAY MULTITESTERRE 188mLCD 10 MEGOHM INPUT IMPEDANCE31 digit '16 ranges plus hFE test facihty forPNP and NPN transistors 'Auto zero, autopolarity Single-handed, pushbutton operation 5*Over range indication 12.5mm 8 -inch) large zLCD readout 'Diode check 'Fast circuitprotection 'Test leads, battery and instructions 01included. trye

Max indication 1999 or -1999Polarity indication Negative only

Positive readings appearwithout sign

Input Impedance 10 MegohmsZero adjust AutomaticSampling time 250 milliseconds

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-. OUR GREAT NEW 1984 CATALOGUEPresented with a Professional Approach and Appeal to ALL who requireQuality Electronic Components, Semiconductors and other AccessoriesALL at realistic prices. There are no wasted pages of uselessinformation so often included in Catalogues published nowadays.Just solid facts i.e. price, description and individual features of whatwe have available. But remember, BI-PAK's policy has always beento sell quality components at competitive prices and THAT WESTILL DO.

We hold vast stocks "in stock" for fast immediate delivery, allitems in our Catalogue are available ex stock. The Catalogueis designed for use with our 24 hours "ansaphone" serviceand the Visa/Access credit cards, which we accept over thetelephone.To receive your NEW 1984 BI-PAK Catalogue, send 75p

PLUS 25p p&p to: -

SIREN ALARM MODULEAmerican Police type screamer poweredfrom any 12 volt supply into 4 or 8 ohmspeaker. Ideal for car burglar alarm,

freezer breakdown and other securitypurposes. 5pniatt, 12v max.

£3.85Order No.

BP124.

The Third andFourth Hand .. .

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MW398 NI -CAD CHARGERUniversal Nr-Cad battery charger. All plasticcase with lift up lid Charge/Test switch. LEDIndicators at each of the five charging points.

Charges - Power -PP3 I9V) 220-240V ACU12 (1-5V penlite) Dims -U11 (1-5V "C") 210 x 100 x 50mmU2 (1 5V "Cr) £6.95

POWER SUPPLY OUR PRICE £3.25Power supply fits directly into 13 amp socketFused for safety. Polarity reversing socket.Voltage switch. Lead with multi plugInput - 240V AC 50HZ, Output - 3, 4, 5, 6,

7 5, 9 & 12V DC Rating - 300 ma MW88

Send your orders to Dept EE4 BI-PAK PO BOX 6 WARE. HERTSSHOP AT 3 BALDOCK ST. WARE, HERTS

TERMS CASH WITH ORDER. SAME DAY DESPATCH. ACCESS.BARCLAYCARD ALSO ACCEPTED. TEL. (09201 3182. GIRO 388 7006

ADD 15% VAT AND 75p PER ORDER POSTAGE AND PACKING

TRIACS - PLASTIC4 AMP - 400v - 10202 - TAG 13661 OFF 10 OFF 50 OFF 100 OFF

40p £3.75 £17.50 E30.008 AMP 400v -10202 - TAG 42560p £5.75 £27.50 E50.00

VOLTAGE REGULATORS T0220Positive +7805 - 40p7812 - 40p7815 - 40p7824 - 40p

Negative +7905 - 50p7912 - 50p7915 - 50p7924 - 50p

Use your credit card. Ring us on Ware 3182NOW and get your order even faster Goodsnormally sent 2nd Class MailRemember you must add VAT at 15% to yourTotal orderPostage add 75p per Total order

Multicore makes solderThe Five Core AdvantageOnly Multicore wire solders have a 5 -core, or 4 -coreflux construction. The 5 -cores identify noncorrosive fluxes; the 4 -core, water solublefluxes.If you were to slice through a section ofMulticore cored solder you would seeseparate round cores of flux symmetricallyarranged around its perimeter. Only athin wall of solder separates the fluxcores from the surface.What are the advantages of theMulticore construction?1. Because the flux is peripherally

arranged it will react and flowfaster.

2. Flux voids are eliminatedwith Multicore. That's whyyou can depend on con-tinuity of the flux stream forcomplete wetting . . . everytime.

3. Because wetting is faster, complete and uniform,you use less solder and transmit less heat to thejoint area. With Multicore Solders, you get thehighest purity metals, vigorous fluxing action anda wire solder that meets all applicable Internationalstandards.

Ersin MulticoreContains 5 cores of non-corrosive flux.Uses: For all electrical joints.Handy Pack: Size 19A 60/40tin/lead 1.22mm dia£1.50 RRPTool Box Reel: Size 3 60/40tin/lead 1.6mm dia£4.37

Multicore SavbitIncreases the life of yoursoldering bit by 10 times.Uses: For all electrical work.Reduces copper errosion.Handy Pack: Size 5 1.2mmdia £1.38 RRP.Tool Box Reel: Size 121.2mm dia £4.37

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EVERYDAY

ELECTRONICSand computer PROJECTS

VOL. 13 No. 4 APRIL 1984

EditorF. E. BENNETT

Assistant EditorB. W. TERRELL B.Sc.

Production and News EditorD. G. BARRINGTON

Projects EditorG. P. HODGSON

Technical Sub -EditorR. A. HOOPER

Art EditorR. F. PALMER

Assistant Art EditorP. A. LOATES

Technical IllustratorD. J. GOODING Tech. (CEO

SecretaryJACQUELINE DOIDGE

Editorial OfficesKING'S REACH TOWERSTAMFORD STREETLONDON SE1 9LSPhone: 01-261 6873

Advertisement ManagerD. W. B. TILLEARDPhone: 01-261 6676

SecretaryCHRISTINE POCKNELL

Sales ExecutiveA. TONGEPhone: 01-261 6819

RepresentativeR. WILLETTPhone: 01-261 6865

Classified SupervisorB. BLAKEPhone: 01-261 5897

Make -Up and Copy DepartmentPhone: 01-261 6615

Advertisement OfficesKING'S REACH TOWERSTAMFORD STREETLONDON SE1 9LS

HOME ENTERTAINMENT: A WIDER VIEWCOME changes or new developments seem patently obvious after the eventJ and make one wonder why they were not thought of before. The homeentertainment scene currently provides a couple of such cases.

For a first example, consider the time it has taken for the combined TVand audio system to appear. Except for rare and expensive up-market ver-sions, the television set has maintained a separate and independent existence;its makers apparently confident that limitations imposed by minisculespeakers were more than adequately compensated for by the alluring colourpictures it could display.

Another example is the coolness shown by set makers towards any wideruse of the TV as a monitor or display unit for other forms of signal input.

But things have been changing. First video games, then microcomputersand video recorders, and now just around the corner is cable TV and thedirect broadcast satellite. Set manufacturers are at last showing signs of ap-preciating this changing situation and are introducing facilities for auxiliaryinputs to their latest models. And now finally the bringing together of visualand sound systems within a single rack or cabinet assembly has beenrealised-and by a British company, we are pleased to note. Fidelitylaunched their AVS1600 hi fi rack system with 16in colour TV last monthand are to be congratulated on being the first in this field.

This development serves also to bring attention to the progress made inelectronic engineering and manufacture in the consumer products' area,which is no less impressive than in the professional and defence electronicsareas. Quite remarkable is the close packing of high technology that is com-monly achieved today in electronic products. Moreover, hand in hand withminiaturisation of components goes a high standard of reliability.

To be honest, these two important aspects of contemporary electronics gounheeded by the vast majority of consumers who use and depend upon theseproducts. But to the technically minded, and especially those brought up onvalves or familiar at least with the early transistor days, the transformation isremarkable. Sudden breakdowns are no longer commonplace. Even with themost complex products, such as TV receivers, calls upon the service engineerare rare and when they do occur the service engineer's task is relatively sim-ple and speedily performed, usually involving the substitution of a module orcircuit board. (Component reliability is in fact discussed by Pat Hawker inthis month's Radio World.)

The home constructor cannot expect to match the degree of close -packingnow routine in factory produced equipments. But he does enjoy the benefitsof greater reliability that is inherent in modern components, and this mustmake his hobby all the more satisfying and worthwhile. And, howevercomprehensive the electronic conglomerations that appear on the domesticmarket may become, it is fair to assume there will always remain needsand opportunities for extending further their usefulness by peripheral andauxiliary units designed and built at home.

Readers' EnquiriesWe cannot undertake to answer readers' letters requesting modifications,

designs or information on commercial equipment or subjects not publishedby us. All letters requiring a personal reply should be accompanied by astamped self-addressed envelope.

We cannot undertake to engage in discussions on the telephone.

Component SuppliesReaders should note that we do not supply electronic components for

building the projects featured in EVERYDAY ELECTRONICS, but theserequirements can be met by our advertisers.

All reasonable precautions are taken to ensure that the advice and datagiven to readers are reliable. We cannot, however, guarantee it and wecannot accept legal responsibility for it. Prices quoted are those currentas we go to press.

Back IssuesCertain back issues of EVERYDAY ELECTRONICS are available world-

wide price 1 .00 inclusive of postage and packing per copy. Enquirieswith remittance should be sent to Post Sales Department, IPC MagazinesLtd., Lavington House, 25 Lavington Street, London SE1 OPF. In the eventof non -availability remittances will be returned.

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AUDIO SINEWAVESWEEP GENERATOR

BY R. E. LIDDIARD

THE requirement for low distortion sinewaves for use in audio equipment is

well-known. Testing the performance ofan amplifier, for example, demands thatthe signals used be of particularly goodquality. In some applications sweep gen-erators are required-audio frequencyspectrum analysers being one example,and freedom from harmonics is oftenvery important. Designing low distortionsine -wave sweep generators using con-ventional components is both cumber-some and expensive, frequently involvingseveral voltage controlled filter stages.

This article introduces a new device-an opto-coupled resistor-and describesan inexpensive, but excellent perfor-mance, audio frequency sinewave sweepgenerator/oscillator.

WIEN BRIDGE OSCILLATORSA basic Wein Bridge Oscillator is

shown in Fig. I. Oscillations areproduced in this circuit when the gain inthe amplifier exactly compensates for thelosses in the RC feedback circuit and theinput is in -phase with the output. (Phaseis the amount that a.c. current and a.c.voltage are "out of step" with each other.)In Fig. 1 this occurs when the phasechange from C2 R2 is the same as thephase change from Cl R I. If C2 = Cland R2 = R I these phase changes areonly equal when the frequency

fand the gain of the amplifier is exactly 3.

If the gain is greater than 3, the outputwill increase until it reaches the supplyvoltage, when "clipping" will occur. If thegain is less than 3, the output will simplydie away, so we use a thermistor circuit tocontrol the gain automatically. If theoutput from the amplifier rises, theaverage current through the thermistorRTH rises and so does its temperature.This reduces its resistance and lowers thegain of the amplifier again, giving just thecontrol we need.

LOW DISTORTION CIRCUITDistortion in this type of circuit is

about 0.02 per cent and this is mostly dueto non-linearities in the amplifier as thevoltage on both its inputs swing up anddown over a range one-third of the out-put. By using two amplifier stages, withone input on each stage connected toearth, this "common -mode" non -linearitycan be eliminated and distortion reducedto around 0.001 per cent. Such a circuitis shown in Fig. 2.

In this case, sinusoidal oscillations aremaintained when the output of op -ampA I is just greater or equal to twice theoutput of op -amp A2, and the outputs areexactly out -of -phase. Automatic gaincontrol is still achieved by means of athermistor circuit, though its operationhas been reversed.

Frequency can be altered either bychanging the values of R or by changingthe values of C. Traditionally double -ganged potentiometers have been used tochange R.

DESIGNING A SWEEPGENERATOR

Modifying the circuit of Fig. 2 toproduce a sweep generator presents twoproblems:

Firstly, whatever components are usedto replace the resistances R, they mustrespond equally and simultaneously toexternal control. Any tracking error be-tween the two resistive elements willresult in "bounce"-fluctuations inoutput amplitude as the frequency ischanged.

Secondly, the resistances of the devicesmust be strictly linear, that means thesame both forward and reverse biased,

C2 R2

OUTPUT

Fig. 1. Basic Wein Bridge Oscillator. Fig. 2. Low distortion a.f. sinewave oscillator.


otherwise distortion will occur. This latterproblem tends to eliminate all directionalcomponents such as diodes and tran-sistors, but leaves one device which hasgood resistive properties at suitable signallevels-the light dependent resistor(I.d.r.).

OPTO-COUPLED RESISTORSBy physically connecting a light depen-

dent resistor (I.d.r.) to a light emittingdiode (l.e.d.), as in Fig. 3, a truly bi-directional "opto-coupled resistor" isformed, whose resistance is inverselyproportional to control current (or con-versely, whose conductance is propor-tional to control current) as shown inFig. 4.

Different combinations of l.e.d. andI.d.r. will produce different "slopes"because of physical differences in con-struction and variations in internal per-formance, but the characteristics remainessentially linear. These can be matchedby means of external components asillustrated in Fig. 5.

Rx is a high value resistance appliedacross the output of one of the I.d.r.s tocompensate for differences in resistanceat low control currents. VRy is used toovercome the variation of light outputs ofdifferent I.e.d.s and different transfercharacteristics of l.e.d./l.d.r. combina-tions. Good matching can be achieved inthis way over a 1000:1 range of resis-tance. In the Sweep Generator describedbelow, Rx was found to be unnecessary.

Such opto-coupled resistors are suit-able for use in any application where anexternal control of resistance is required,provided the current through the I.d.r. isnot too small, when noise levels maybecome prohibitive. Multiple devices canbe constructed and matched by "casca-ding" opto-coupled resistors as shown inFig. 6. Note that the control circuit iscompletely isolated from the resistancecircuits, which are also isolated from eachother.

Fig. 4. Opto-coupled resistorcharacteristics.

Fig. 5. Matchingcircuit for twoopto-coupledresistors.

Fig. 6. Multipleopto-coupledresistors incascade.

LIGHTDEPENDENTRESISTOR LED L DR

GLUE .=-111. 1 a17(LDR) r -

LIGHTS 111EMITTING

(LED)DIODE

1

PCC

1 1 1

OCR

Fig. 3. Opto-coupled resistor (OCR): (a) physical arrange-ment of light dependent resistor (I.d.r.) and light emittingdiode (l.e.d.); (b) circuit symbol.

+VE

SMALL 'DARKCONDUCTANCE"

OCR1

D PCC

OCR2

()DPCC

OCR1

OCR2


VRI

tookfl

MAX

91C1

MINVR2

1001(0

TPF

ITRIGGERI

01

1N914

tCI = LF 347IC2= 1458C

D2

IC1 PIN 4IC2 PIN 8

D3

1N914 161914

IC1 PINGIC2 PIN C

a

22011 -

I aI OS

L

OCR1

OCR 2

PCC1

RPY51341

_J

1C52200pF

3

2PCC2

RPY58A

IC2

C6

2200pF

Fig. 7. The full circuit diagram for the Audio Sinewave Sweep Generator.

AUDIO SINEWAVE SWEEPGENERATOR CIRCUIT

The full circuit for the Audio Sine -wave Sweep Generator is shown in Fig. 7.The Wien Bridge oscillator as describedabove, is formed by IC2, OCR I, OCR2,VR4, C5, C6, R2 and RTH1.

IC la and IC lb set the maximum andminimum voltages applied to the bufferIC1c which supplies the OCRs throughDI to D3 and VR4, so effectively VR1and VR2 set the maximum and minimumfrequencies respectively.

The FREQUENCY/RATE control, VR3,permits the selection of any frequencybetween these limits in MANUAL mode anddetermines the sweep rate in SWEEPmode-the sweep rate being set by therate at which C3 is charged. C3 can beincreased or decreased if slower or fasterranges of sweep rate are required, and forthis reason C3 has been mounted on theback of the facia panel, not the printedcircuit board.

The circuit is designed to sweep fromhigh frequency to low (the delay at thestart of a sweep as RTH 1 takes effect ismuch reduced at higher frequency) but byre -adjusting VR1 and VR2 and reversingthe polarity of C3, a sweep from low tohigh frequency can be produced.

SI provides MANUAL/SWEEP selectionand S2 is the sweep TRIGGER. A socket isprovided at the input of IC1c forEXTERNAL frequency control and lendsitself to phase -locked loop techniques ifrequired.

At the output of the oscillator a bufferis provided in IC Id with VR5 as a LEVELcontrol, but loads less than lkS2 shouldbe avoided.

A 9V plus 9V power supply isprovided by two PP9 batteries, BI, B2.

SPECIFICATIONOperating Modes: Manual or SweepDistortion: <0.002% at 1 kHzFrequency Range: 20Hz to 20kHz (but see text)Output Amplitude: OV to 5V r.m.s. (OV to 14V peak -to -peak)Buffered Output Stage. Suits loads of greater than 1kS2 impedanceExternal Frequency Control is also provided

COMPONENTS1Vg.6Resistors

R1 10okf2R2 11(1/R3 1001d2R4 1 MOR5All 1W carbon ±5%

PotentiometersVR1,2 100k0 miniature

horizontal skeletonpreset (2 off)

VR3 470k0 linear, standardspindle

VR4 22012 miniaturehorizontal skeleton preset

VR5 101(0 linear, standardspindle

CapacitorsClC2C3C4C5C6C7C8

1µF 100V elect.1µF 100V elect.100µF 25V elect.1µF 100V elect.2200pF polystyrene2200pF polystyrene470µF 16V elect.470µF 16V elect.

SemiconductorsD1,2,3 1N 914 diode (3 off)D4,5 light emitting diode,

square (overall 6.4mmx 3.8mm), yellow (2 off)

D6

IC1

IC2

SwitchesS1S2

SocketsSK 1SK2

SK3

light emitting diode5mm dia., red, withclipLF347 quad op -amp,14 -pin d.i.l.1458C dual op -amp,8 -pin d.i.l.

4 -pole, 3 -way rotarysingle -pole, on/off pushbutton

jack socket 3.5mm,terminal post, red, with4mm top socketterminal post, black,with 4mm top socket

MiscellaneousB 1,2 9V battery, PP9 (2 off)PCC1,2 light dependent

resistor, RPY58A (2 off)thermistor, R53RTH1

Battery clips for PP9 (2); colletknob black, 15mm collet cap grey,15mm collet nut cover; d.i.l.socket, 8 -pin; d.i.l. socket 14 -pin;p.c.b.; Veropins 1mm; Verobox212 or similar plastics case, size153mm wide, 84mm deep,59mm high.


RI HI

R2

142

IC2b

EE

R3 R4

VR5

10k11 1000 'MD SK2

LEVEL!

IC 'OUTPUT I

3

5K3

1

R5

221ra

06

S1b

C7

4708F

`ca

Sic I

0

Bi9v

1829V

PRINTED CIRCUIT BOARDA diagram of the printed circuit board

is shown in Fig. 8. The layout has beendesigned to accommodate the closeproximity of S 1 when using a Veroboxtype 212.

110-0--rm1

EE

43 84°4-°6 lawJF

.--to

.o

O

TeLILI-Law-T"83 Rd

OC7

.7M113-7.<02 .74MILIFID3

+®0)RI

140* -

O) \ C20 C81

POSITIONOFS1

S

VR1 VR2

C6

VR4

RTH1

OCR2 OCR1--a

PCC26''' 4 4 '-'1.PCC1

CS

RETAININGLINK

Da 05 L. -k

VEROPINS Q- 0

Fig. 8. Printed circuit board for the Audio Sinewave Sweep Generator.


© ®0 10ICt BI-VE IC2 TC2

PIN I B2+VE RIICI

PINS 8,9 81 +VE

®CI,C8 ICI PIN 5-VE B2-VE C4 -VEPIN 5 R3 PIN 7

11111 1111111111 f

C3

Fig. 9. Facia panel (rear view) showing panel mounted components and wiring to p.c.b.

Drill a in hole in the p.c.b., asshown, to accommodate leads from thebattery to Si and the earth terminal SK3.Fit Veropins-where indicated. Thesewill facilitate the interwiring to the off -board components.

Solder the l.e.d.s in position first, tak-ing care to ensure the correct polarity.

Glue the l.d.r.s to the l.e.d.s using aclear adhesive and solder the I.d.r. leadsin position. When the glue has set, paintthe l.e.d./1.d.r. combinations with severalcoats of black paint. It is vital that all ex-ternal light is excluded from these devices.

Solder the remaining components asshown and solder the retaining link inposition over the thermistor using in-sulated wire. NOTE: this link also formspart of the circuit. Finally check that thep.c.b. is free from short circuits betweenthe tracks, and insert the i.c.s.

Mount components onto the faciapanel and wire up in accordance withFig. 9.

SETTING UPStarting with all presets and poten-

tiometers in the mid -position, and Si setto MANUAL, adjust VR1 and VR2 untiloscillations are produced. If the oscilla-tions are fluctuating, adjust VR4 until aconstant amplitude sine wave is heard.With VR3 set alternately to maximumand minimum, adjust VR1 and VR2respectively to set the desired range offrequencies.

At this stage it is useful to check thatthe output is not affected by the presenceof a bright light. If any change is detected,apply another coat of paint to the opto-coupled resistors and repeat the setting -up procedure.

OPERATIONIn MANUAL mode, the Audio Sinewave

Sweep Generator provides low distortionsine waves between 20Hz and 20kHz. InSWEEP mode the entire audio spectrumcan be swept in 20 seconds with nodetectable "bounce". Faster sweep rates

+VE

16

10 14 I2.8kHz

IC4060

13 6 4kHz

15 3 2 kHz

1 800Hz

2 400Hz

3 200Hz

R = /MD33pF

XL . 50x216 Hz3.2768MHz

CRYSTALEARPHONE

0

SINEWAVEGENERATOR

OUTPUT

-VE

Fig. 10. Circuit of a crystal oscillator and frequency divider suitable for calibration purposes.

can be readily achieved by reducing thevalue of C3.

Amplitudes up to 16V peak -to -peakare produced without clipping.

CALIBRATIONA simple, yet accurate method of

calibrating the sine -wave generator canbe performed using the circuit in Fig. 10.This consists of a crystal oscillator andfrequency divider using a single chip-aCMOS 4060. A range of accurate fre-

quencies are provided as shown in thediagram. Any supply voltage between 5Vand 15V can be used.

To calibrate the sine -wave generatorswitch S1 to MANUAL and adjust theFREQUENCY/RATE until the same tone isheard when compared with the crystaloscillator. Although the crystal oscillatorproduces square waves, it is quite easy tomatch the tones using this circuit.

If required, a calibration scale can beadded to the FREQUENCY/RATE control.


SHOPTALKCatalogue Received

The latest edition of the excellentGreenweld 1984/5 ComponentsCatalogue has been increased to 84pages and includes many new lines.

The biggest increase appears to bein the "Connector" section, where theincreasing demands of the computerinterfacing requirements has resultedin a new family of special edge connec-tors and multi -cable "artery" leads.These include RS232 and Centronicsconnectors.

Other additions include an expandedrange of audio modules and semicon-ductors.

All prices are quoted on the pageand include VAT. Also, there are five20p "Big G" discount vouchers on theinside back cover. These areredeemable with purchases on thebasis of: one voucher accepted withany order over £4; thereafter onevoucher for every £3 worth of goodsordered up to a maximum of fivevouchers.

Copies of the Greenweld 1984/5Components Catalogue cost £1 (70pplus postage), or 70p to callers to theirshop. Mail orders for copies should besent to Greenweld Electronics Ltd.,Dept. EE, 443 Millbrook Road,Southampton, SO1 OHX.

MothercardTalking of the increasing demands

from readers for "inter -active" modules

ZX Expansion boardsfrom Velleman

BY DAVE BARRINGTON

to make the home computer more ver-satile and practical, Velleman (UK)have developed a range of plug-inboards for the Sinclair ZX machines.

Resulting from customers' enquirieswanting to expand the features of theirsystems, they have introduced an inter-face system consisting of a specificmotherboard for each type of com-puter, and interface cards that can beplugged onto the motherboards.

It is possible, using the variouscards, to add to each system thefollowing features: Eight open collectoroutputs (25V/50mA); code K2609.Analogue -to -Digital conversion, 8 -bitprecision, 5.1V full-scale; code K2610.Eight opto coupler inputs; code K261 1.A Centronics parallel printer interface;code K2614. Digital -to -Analogue con-version, 8 -bit precision, 1.02V full-scale.

The motherboards for the ZX81 andthe ZX Spectrum are available now,offering space for four interface cards.They are provided with a 23 -pole edgeconnector at the back, giving thefacility to connect the ZX printer or tostack more motherboards one after theother.

Power is taken from the computer's9V d.c. supply or from an external un-regulated 9V to 12V d.c. power source,depending on the consumption and thenumber of interface cards used.

For details and prices write to:Velleman (UK) Ltd., Dept. EE, POBox 30, St. Leonards-on-Sea, EastSussex TN37 7NL.

CONSTRUCTIONAL PROJECTS

Multipurpose Interface for ComputersThe mains transformer used in the

Multipurpose Interface for Computersproject was purchased from RS Compon-ents. This is from their 20VA range andcarries the stock number: 207-582.

The two 9V 11A secondary windingsare wired in parallel to give the required 9V2.2A rating.

The 2A circuit breaker CBI is also listedby RS Components under the "sub-miniature" range and should be ordered asstock number: 335-996.

If this project is to be built on the EEp.c.b., the relay used should be of the typespecified: RS 349-658. This is to agreewith the allocation of mounting holes andsolder pads on the board. If other relays areused then suitable leads can be taken fromthe board to the relay mounting tags.

It must be pointed out that RS Compon-ents will not supply to the general publicand the above components will have to beordered through your local recognised com-ponent supplier.

The 16 -pin quad opto-isolator is stockedby Bi-Pak and is designated ILQ74 andshould be ordered as: Code 1517. It is alsoavailable from Rapid and TK Electronics.

Microcomputer Interfacing TechniquesThe ADC 0817 40 -pin 16 -channel 8 -bit

analogue -to -digital i.c. used in the Data Ac-quisition and Control Data Board appearsto be only available from Cricklewood Elec-tronics Ltd.

Timer Module for Central HeatingSystems

The choice of relay for the Timer Modulefor Central Heating Systems is not criticaland is dependent on the power require-ments of the appliance being controlled. Arelay with a coil resistance of between 180to 500 ohms, with mains rated contactsshould be suitable.

For a wider choice of relay, it is possibleto wire two sets of contacts on a double -pole changeover type in parallel to enable itto handle higher currents. The relay can bemounted to the side of the board and leadstaken from the board to the relay contacttags.

Audio Sinewave Sweep GeneratorThe bead thermistor type RA53 used in

the Audio Sinewave Sweep Generator isstocked (No. 151-1141 by RS Components.It is also listed by Greenweld and Maplin astype R53. This thermistor is rated 51(0 at20°C and has a minimum resistance of800.

The "square" I.e.d.s are now stocked bymost advertisers. However, the light depen-dent resistor, type RPY58A, is currentlyonly listed by Maplin (code: HBO9K (LDRRPY58A) and Cricklewood Electronics.

Quasi -StereoThe dual operational amplifier i.c., type

1458C, used in the Quasi -Stereo projectappears to be only listed by Enfield Elec-tronics, Greenweld and Maplin.

An alternative device, with identicaltechnical specification, is the µA747C.However, this is a 14 -pin device and wouldnecessitate changing the printed circuitboard layout to cater for the different pin-ning of this i.c.

We cannot foresee any component buy-ing problems for the Quizmaster II and theFuse and Diode Checker-the second inour "Black Box" projects.


A Black Box Project

FUSE /DIODE CHEF-rHIS simple circuit is for quick testing

I of fuses that are not visably checkablesuch as those found in 13A plugtops.Because of its oscillating action, it willalso test diodes and give an indication asto which end is the cathode.

CIRCUIT DESCRIPTIONThe circuit diagram of the Diode/Fuse

Checker is shown in Fig. 1. The design isbased around the cmos 4011 input NANDgate. Two NAND gates (IC la and IC lb)are used to form a bistable multivibrator(as in last month's Black Box circuit)using RI, R2 and Cl. This in turn feedstwo more NAND gates, one of whichinverts the signal of the other.

The output of IC lc goes to a touchplate, the output of the other gate (IC Id)goes to the two 1.e.d.s connected inverselyback to back and then on to the othertouch plate. Because of the oscillatingfunction of the circuit, the polarity acrossthe two plates alternate, so that if a shortconnects the two plates together (such asa fuse), then current will first flowas shown in Fig. 2a illuminating DI,current will then flow in the oppositedirection as in Fig. 2b, illuminating D2.

This will continue while there is a con-nection across the plates. If the fuse hasblown, then no current can flow eitherway and neither l.e.d. will light.

DIODE CHECKERIf a diode is connected across the

plates, then current will flow only in onedirection, illuminating the appropriatel.e.d. (as in Fig. 2c) and if the I.e.d. ispositioned accordingly, it will show thecathode end (k) of the diode under test, ifthat diode is functioning.

If the diode has gone short circuit, bothl.e.d.s will light (as for the fuse) and if it isopen circuit, neither will come on.

ALL DESIGNS FEATURED INTHE BLACK BOX SERIES WILLUSE THE SAME BLACKPLASTICS CASE AND SAMESIZE PIECE OF STRIPBOARD

CONSTRUCTIONThe circuit is built on a piece of strip -

board 24 holes by 10 strips and thelayout is shown in Fig. 3. The case is thesame black plastic case, 80 x 61 x41mm, as used in all Black Box projects.

Mount the i.c. socket first, followed bythe links, resistors and capacitors. Asmall piece of copper was used as the twotouch plates (see photo), as it was easy tosolder to the back of them. Alternatively,brass could be used or even another pieceof stripboard.

Drill the four holes in the lid of the box,solder the wires to the plate and glue theplates to the lid after passing the cablesthrough the appropriate holes, usingepoxy resin or something similar. Whilethis is setting, prepare the cutout for theswitch and then fix this in the box.

Connect up all the cables to the boardand switch, and also to the l.e.d.s andtouch plates. Fit the i.c. into the holder,taking usual precautions for cmos. Theboard was held in the box with double -sided tape, and foam was used to stop thebattery shaking about.

TESTINGSwitch the unit on, short out the two

touch plates with a piece of wire and bothl.e.d.s should light up (you should just beable to see them oscillating). Place aknown, good diode across the plates(such as a 1N4001) after taking away thepiece of wire and one 1.e.d. will light upcorresponding to the cathode end (k) of

Rt470k0

EE

the diode. If the other end is illuminatedthen swap the connections to each 1.e.d.around. If, however both I.e.d.s light upor not at all, then the diode is either shortcircuited or open circuited.

Please note: due to the simplicity ofthis circuit, diodes with an averageforward current of less than 10mA (suchas AA144) or diodes with less than apeak reverse voltage of 7V (such as aBA104 or BA117) should not be usedwith the Diode/Fuse Checker, as damageto the diode may result.

Fig. 1. Circuit diagram of the Fuse/Diode Checker.

0-033pF

IC1.1011

ICIPIN IL

ICIPIN 7

St

ION/OFF

DI

TIL220

TOUCHPLATES

D2

9

81 g9V


ICER BY L. A. PRIVETT

(b)

(c)

D1

Fig. 2. (a) and (b) show the current path when testing a good fuse. Note that bothI.e.d.s light alternately. (c) shows the current flow when a good diode is placedacross the touch plates lighting only one I.e.d.

81x 0 0 0 0 0

+VEO

o

B1 0-VE

cio0 R2

0 01/4

sir o

1-510 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1

1

1I1.

D2 kI 1

D1 a

IliTOUCH

oo oo 00 0000000 o oo o

IPLATE

w

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 C 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 C 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Fig. 3. The stripboard layout of the Fuse/Diode Checker. To complete the wiring, theother touch plate is connected to Dlk/D2a.

View inside the finished model. A piece offoam holds the board and battery in placewhen closed.

COMPONENTS

ResistorsR1,2 470k0 12 off)

CapacitorC1 0.0331.1F polyester

SemiconductorsD1,2 TIL220 5mm red I.e.d.

12 off)IC1 4011 cmos quad 2 -input

NAND gate

MiscellaneousS1 d.p.d.t. miniature slide switchB1 9V PP3 batteryBlack plastic case, 80 x 61 x41mm; 0.1in matrix stripboard,10 strips by 24 holes; battery clip;14 -pin i.c. socket; wire; piece ofcopper sheet, 40 x 40mm (fortouch plates); double -sided tape;small piece of foam rubber.


TEACH-. N

3 5

THE oscillators we've made so far havebeen of a type that generates

something approximating to squarewaves (Fig. 7.1). Any repeatingwaveform which is not a sine wave con-tains harmonics (multiples of the basicfrequency). These affect the tonal qualityof the sound heard when the wave is usedto energise a loudspeaker or earphone.Square waves have a timbre reminiscentof organs or reed instruments.

EXPERIMENT 7.1

PHASE SHIFT OSCILLATORA pure sine wave makes a rather

smooth -sounding note. To demonstratethis, build the oscillator shown in Fig. 7.2.This is a phase -shift oscillator. You'llremember that when talking about op -amps I explained how what is meant to benegative feedback can become positiveand cause oscillation. The phase -shiftoscillator exploits this.

Normally, if the collector output of asingle -stage transistor amplifier is fedback to the base, feedback is negative andthe circuit is stable. (This is the basis ofthe auto -bias technique.) In a phase -shiftoscillator, CR "time constant" compo-nents are inserted in the negative feed-back path to provide enough time delayto provoke oscillation at one particularfrequency.

With the values of R and C shown, os-cillation is at an audio frequency. At lowsettings of VR1, oscillation stops, becausethe fed -back signals are too attenuated.

Set VR1 so that the circuit just os-cillates. You'll find that the sound has thepure quality I mentioned.

If you set VR1 very carefully to apoint where the circuit just fails to os-cillate you'll find that any sudden upset,like disconnecting then re -connecting thebattery, produces a bell -like "ting".

298

C

29D

E

1829E19 G

A TWELVE -PART HOME STUDY COURSE IN THEPRINCIPLES AND PRACTICE OF ELECTRONICCIRCUITS. ESSENTIALLY PRACTICAL, EACH PARTINCLUDES EXPERIMENTS TO DEMONSTRATE ANDPROVE THE THEORY.USE OF A PROPRIETARY BREADBOARDELIMINATES NEED FOR SOLDERING AND MAKESASSEMBLY OF CIRCUITS SIMPLE.THE IDEAL INTRODUCTION TO THE SUBJECT FORNEWCOMERS. ALSO A USEFUL REFRESHERCOURSE FOR OTHERS.

By GEORGE HYLTON

OW MuffaMIXClj

xl

R1 10kfl

'\/.\At

TIME --Jo.--

+9V

TR1BC107B

Fig. 7.3 (right). EBBOcomponent layout forFig. 7.2.

R2IMI1

C1

lOnFC2

lUnF

R33.3k12

B1 +ye

1 r,A o A

2 8 103 o- 9R1 5 7 9

1,-- ED -

C3IOnF

VRI10kI1

1

R3

F

BI -ye

0

OV

1

Fig. 7.1. Square wave.

Fig. 7.2 (left). Phaseshift oscillator circuit.

12

X1

CRYSTALEARPHONE


The explanation is that the sharpchange of voltage caused by suddenlyconnecting the battery generates frequen-cies, some of which are close to the os-cillation frequency. The circuit tries tokeep these circulating. It can't, but theydie away slowly, turning what wouldnormally be a click into a "ting". Thisprocess, called ringing, can occur inbadly -designed negative feedback am-plifiers and in filters with sharp cut-offs.

At high settings of VR1 the tonesounds harsher. Some other noise seemsto creep in. The pure sine wave of thejust -oscillating circuit is now distorted.

OVERLOADWhat causes the distortion? Well,

there is a limit to the size of sine wavewhich your circuit can generate. SupposeTR 1 collector voltage (VcE) is 4V. If theoscillation makes the collector currentincrease, this voltage falls (because R Idrops more volts).

At some low collector voltage TR 1ceases to function as an amplifier. Let'ssay this is 0.1V. Then driving the baseharder has no effect: the collector voltagejust stays at 0.1V. The result is that, atthe collector, what should have been asine wave gets its negative voltage peaksflattened (Fig. 7.4).

When the collector current is driventoo far the other way, a similar over-loading effect happens. A negative driveto the base reduces Ic. But Ic can't bereduced below zero. Once the zero point(Ic = 0) is reached, further negative basedrive has no effect. The collector currentis cut off and that's that. Under these con-ditions there is no voltage drop in R1 andVCE is the same as Vcc.

0

0L>

-1

U

A AirOUTPUT

Fig. 7.4. Peak clipping: collector voltage waveform when the positive peaks ofthe input signal are too large.

OUT

PI

P2

OUTPUTCURRENT

INPUTVOLTAGE

Fig. 7.5. How the non-linear charac-teristic of a transistor producesdistortion.

OUTPUT

IN

I INPUT

Fig. 7.6. A linear transfer charac-teristic gives distortionless ampli-fication.

NON-LINEAR TRANSFERThis form of peak clipping or limiting

is a common sort of distortion. It is easilycured by reducing the signal level. There

is another common kind of distortionwhich is harder to deal with. It occurswhen a transistor is voltage -driven.

Changing the base voltage (VBE) of abipolar transistor makes the collectorcurrent vary as shown in Fig. 7.5. Theimportant point about this graph is that itis curved. (In the case of field-effect tran-sistors, the shape of the curve is ratherdifferent but it is still a curve rather than astraight line.)

This is unfortunate. In audio amplifierswe want the output waveform to be afaithful enlargement of the input. With acurved input -versus -output graph (oftencalled a transfer characteristic) this kindof fidelity is impossible. If we bias thetransistor to a working point such as P1and apply a sine -wave input voltage asshown, the output current wave is distor-ted. The negative -going parts of the inputwave have less effect on Ic than thepositive -going parts.

What can be done about it? Onepossibility is to operate at point P2 wherethe characteristic is less bent. This meansbiasing the transistor to a greater d.c.collector current.

CURRENT DRIVEWhat is needed is a straight-line

transfer characteristic, like Fig. 7.6. Sucha linear characteristic gives zero distor-tion. It so happens that the relationshipbetween base current and collector


current is linear. So if a bipolar transistorcan be current -driven rather than voltage -driven, distortion is minimised.

Current drive means that the signalmust come from a source whose im-pedance is very much greater than theinput impedance of the transistor. Unfor-tunately, the input stage of an amplifierusually can't be current -driven because,for lowest noise, a bipolar transistor hasto be voltage -driven. The only usefuldistortion -reducing trick left is negativefeedback. Distortion is reduced as thefeedback reduces the gain.

EXPERIMENT 7.2

Fig. 7.7. Experiment to show heat effects.

TEMPERATURE EFFECTSSet up the circuit of Fig. 7.7. (Work

out your own EBBO layout.) R2 dropsIV for every 10mA of collector current.Set the collector current to 30mA (3V).Switch off the battery for five minutes.Switch on again and observe the voltagereading. It increases slowly, indicating anincrease in collector current.

This is the result of the transistor war-ming up internally. Let's confirm thattransistors are affected by heat by warm-ing this one externally. Switch off. Leavefor five minutes to cool. Remove R2 butleave the meter in place.

Switch on. Set VR1 to give any con-venient meter reading. Squeeze the caseof TR 1 between finger and thumb, takingcare not to touch the leadout wires. Aftersqueezing for a while the meter readingincreases, as your body heat travels to theactive semiconductor material inside thecase.

ENERGY CONVERSIONWhere did the heat come from in the

first experiment, when we weren't holdingthe transistor? It was generated inside thetransistor. When current flows through aresistor, the resistor warms up. The elec-trical energy is turned into thermalenergy.

A transistor is not a resistor, but to thebattery it looks rather like one. When 9V

drives 1mA through any circuit, to the 9Vsource the circuit looks like 9k0. If thecircuit is a transistor then the warm-ing effect is just the same.

In our first experiment (R2 in place)the current was set high to increase theheating effect. The amount of heatreleased in a resistor depends on thecurrent, naturally. But the current de-pends on the voltage. Take 10 and applyIV: 1A flows. Apply 2V and 2A flows.The amount of heat released depends onboth voltage and current.

To be precise, it depends on voltagetimes current. So if 1V and lA gives oneunit of heating, 2V and 2A give, not twobut four units. The units are in fact watts,and watts (W) are the measure of the rateat which energy is being expended. So 2Vx 2A = 4W.

THERMAL RUNAWAYInternal heating can be dangerous.

Make a transistor too hot and it dies.The danger is great in "power am-

plifiers", that is, amplifiers which haveto deliver considerable power (to loud-speakers, for example).

Your finger -and -thumb experimentshows that a warm bipolar transistorpasses more current. It therefore con-sumes more power. But this in turn raisesthe internal temperature, and this makesthe transistor pass more current . . . andconsume more power . . . and get hotter. . . and hotter . . . and hotter. The circuit"runs away".

So why haven't all our transistorsdestroyed themselves by thermalrunaway? Two reasons. First, there hasalways been enough resistance in the wayto limit the current to something safe.Take Fig. 7.7. Here there is 1000. Even ifthe full 9V were applied to 1000 thecurrent would only be 90mA. In fact, thetransistor can't get hot enough to pass90mA, because the more volts lost in R2the less volts across the transistor. At90mA, the voltage across TR I would bezero; so, no heating. The most heating oc-curs when the current is 45mA and thevoltage across TR1 and R2 is the same(4.5 V).

The power being expended in each ofthem is then 4.5V x 45mA. Volts timesmilliamps gives the power in milliwatts(mW); 1000mW = 1W.

COOLINGThe other reason why our transistors

haven't destroyed themselves is that theyare cooled by the air around them and byradiating heat. These cooling processesget more efficient as the transistor getshotter. For once, nature is on our side.

But only up to a point. There is a limitto the rate at which heat can be removed.The on* practicable way of increasingthe cooling rate is to clamp the transistorto a metal plate. The plate provides alarger escape area for the heat.

Small transistors can't be helped muchby such a heatsink because the internal

heat has to get to the outside case of thedevice from the hidden semiconductormaterial inside. It can't do this instan-taneously; the heat has to cross thethermal barrier between semiconductorand case.

But our transistors are designed onlyfor low -power operation. High -powertransistors are mounted on metal platesor studs which can be bolted to heatsinks.

Heatsinks are often made ofaluminium, with fins to increase the sur-face area, as on a radiator, andblackened. A heatsink is described interms of the amount by which its tem-perature rises when 1W is being dis-sipated. Thus a heatsink may bedescribed as "3°C/W". In this case, if itwere clamped to a transistor dissipating3W its temperature would rise by 9°C.

POWER IN A.C. CIRCUITSPower is volts times current. The

meaning of voltage and current in a d.c.circuit is quite clear. But in a.c. circuitsvoltage and current are constantly chang-ing. How do you measure power in thiscase?

The principle is to measure the a.c.quantities in a way that makes themdirectly comparable with d.c. An a.c.meter "reads" an a.c. current whoseheating effect, when it flows through aresistor, is the same as d.c. of equalstrength.

To make a.c. and d.c. equivalent in thisway, the quantities have to be what arecalled r.m.s. currents and voltages. R.m.s.("root mean square") refers to themathematical basis for the equivalence.

Multimeters with a.c. scales aremarked in r.m.s. voltage or current. Un-fortunately, meters are liars. They reallymeasure another kind of a.c., average -value a.c., which is much easier tomeasure than r.m.s. So your metermeasures average -value a.c. but its scalesare marked in r.m.s.

The meter reads correctly only if thea.c. currents and voltages have wave-forms which are sine waves. With otherwave shapes the meter reading is wrong.True r.m.s. meters do exist, but they areexpensive.

AUDIO POWERFortunately, the errors are usually not

too enormous. All the same, they exist.To make life easier when talking aboutaudio power, equipment makers usuallyquote values for sine -wave signals. (Realspeech and music are not of sine waveform.)

Amplifier specifications often don'tquote r.m.s. power but peak power, whichis greater and makes the figures lookgood. Peak power is also more relevant todistortion. As we've seen, an "overload"type of distortion happens when an am-plifier can't handle the peak signal. So anamplifier's peak power rating says howmuch it can deliver round about the pointwhere peak clipping begins. See page 238


CHECK YOURPROGRESSQuestions on Teach-ln 84 Part 7Answers next monthQ7.1 A transistor has a collector

load resistor of 1000. Thesupply voltage (Vcc) is 10V.

(a) What is the maximumcurrent that can flow in theload?(b) What is then the loadpower dissipation?(c) What is the transistorpower dissipation? (i.e.,collector volts times collec-tor current).(d) What are the condi-tions in this type of circuitfor maximum power dis-sipation in the transistor?(e) What are then thecollector voltage (VcE) andcurrent?(f) If the transistor has hFE= 100 what base current isrequired in condition (e)?

Q7.2 In transistor data, the tem-perature rise due to internalheating is described in termsof a "thermal resistance" RTHbetween the collector -basejunction and the case ormounting stud of the tran-

sistor; for example, if RTH(junction to case) = 10°C/VVand the transistor is dis-sipating 2W, the junctiontemperature is 20°C higherthan the case temperature.

(a) If the maximum safejunction temperature is150°C and the transistor ison a heatsink which holdsits case at 50°C, what isthe maximum power whichcan safely be dissipated inthe transistor?(b) If the ambient tem-perature around the heat -sink is 25°C, what must bethe thermal resistancebetween heatsink and air?,

Q7.3 In audio power stages likeFig. 7.10, the peak loadcurrent is half Vcc divided byRL. (This occurs when onetransistor is "cut off" and theother is "hard on" with its VCE= 0.) The peak load power isthen (Vcc/2) times the loadcurrent, which in turn is(Vcc/2)/R L.

(a) If Vcc = 20V and RL =40 what is the peakpower?(b) What is the peakpower if Vcc is raised to40V?

(c) If the r.m.s. (sine wave)power is half the peakpower, how can it becalculated in terms of Vccand RL?

ANSWERS TO PART 606.1 (a) pnp.

(b) The circuit is similar toFig. 6.9 except that TR1 ispnp. The input voltage is fixedat 4.5V by R1 and R2. Themeter is replaced by R3.Negative feedback forces Vxto be equal to Vy. This makesthe voltage across R3 be4.5V, so the emitter current is4-5mA.(c) 4.5mA approx., since lc isnearly the same as IE.(d) If R4 were 11(12 it woulddrop 4.5V. But there is a dropof 4.5V in R3. Together thesewould use up all the supplyvoltage, leaving nothing tooperate TR1 .(e) None. Vy is still Vcc/2.(f) 3mA. (Vy and Vx become3V.)

LETTERSTeach -In BuzzSir-I have a problem; In your Experiment4.4 (see Teach In '84-January issue) I

constructed the circuit according to theschematic (Fig. 4.10) using Veroboard andit didn't work. No buzz. I then noticed thatthe EBBO layout was different, so I rewiredaccordingly. Still no buzz.

By experimenting I found that if I left theVR1 as shown on the EBBO layout, butconnected the earpiece to the TR1 input in-stead of to earth, I did get a buzz, whichvaried (in volume) with the setting of theVR1, but there was no change in frequency.The system worked equally well if either the(a) or (b) connections of the potentiometer(VR1) were totally disconnected. And in allcases the system worked better (louder) ifthe 1 OkS2V was replaced by 1001d/potentiometer.

Evidently I am doing something wrong,and as I am consciencientiously (9 workingthrough all the experiments and progresschecks, I would be very glad if you wouldplease tell me where I am going wrong.

R. W. Seymour -LeeNewbury,

Berks.

Sorry about the error in Fig. 4.11. Theend of VR1 marked "a" should be connec-ted to C2 and the earphone Xl, as shown inthe corrected version of Fig. 4.11 givenhere.

However, this is not the only problem inyour case. I deduce from the symptomswhich you describe that your output cou-pling capacitor C2 is faulty. It has gone"open". The result is that no ac. can getthrough it, hence no oscillation.

The reason why your last circuit did os-cillate is that the earpiece itself is (elec-trically) a capacitance; in your circuit it cou-ples the output of the amplifier back to theinput. Your 1001(0 potentiometer acts as a

BI-ye

B

C

ci

F

5 bCI 0-

RI

"volume control" by bypassing some of theoutput current to "earth." As the sliderapproaches "a" the volume then falls (andeventually oscillation ceases).

Thank you for drawing the problem of thedrawings to my attention.-George Hylton.

5 11 13 15 17

8 10 12 14-a-c-u B 0-0R2 g 7 26;411 13

4 5- ' TR2 10 12- ---0 Dq 11 C2E 0-

c b 17F 3-

1

3 5 R4f TRI11

e

A

19

18 20a --a n19

II ,XI

CRYSTALEARPHONE


DISTORTION VERSUSDISSIPATION

We've seen (Fig. 7.5) that for low dis-tortion a transistor should operate with afairly large standing collector current.That's fine for a pre -amplifier or the low -signal -level parts of a power amplifier.But for the output stage, where signalvoltages and currents are highest, highstanding current is bad from the powerdissipation point of view.

Suppose, for example, that the tran-sistor in Fig. 7.8 has to deliver maximumpower to a 100 load. The condition forthis is that Vcc is shared equally betweenload and transistor. In this example, the100 load drops 10V so the current is 1A.The transistor also runs at 10V, IA so its"collector dissipation" is 10W. The tran-sistor dissipates IOW whether or notthere is any signal present.

This is a warm and wasteful mode ofoperation. For economy, it would bepreferable if the transistor were switchedoff when there is no signal. Then, when asignal arrives, it should be switched onjust enough to handle this particularstrength of signal without overloading.

PUSH-PULLSuch an amplifier can be built. It is

called a "sliding bias" amplifier. But youare unlikely to come across one. There isanother way of achieving the same objec-tive which works better. It's called push-pull working.

The principle is illustrated in Fig. 7.9.Here RL is the load to which power mustbe delivered. There are two batteries. V 1is twice the voltage of V2.

Suppose VR1 is a linear -law "pot".With the slider at the half -way point, halfof V 1 is tapped off: 10V. No currentflows in RL because the "tapped off 10Vis opposed and cancelled by V2.

If the slider is now moved up, towards(a), more of V 1 is tapped off. This over-comes V2 and current flows downwardsthrough RL. When the slider reaches (a),the net voltage applied to RL is VI - V2.This is lOy in our case (20V - 10V) soIA flows in RL and the power is 10W.

Now move the slider back to the mid-point of VR 1, then on downwards. Belowthe midpoint, the tapped -off portion of VIis less than 10V. So V2 overcomes it.Current flows from V2 into the slider andupwards through RL. With the slider at(b), the full 10V of V2 is applied to RL.Current is now lA and power 10W.

By moving the slider up and down pastthe midpoint, current can be made to flowfirst one way then the other throughRL. In other words, the arrangementgenerates a.c. If RL were a loudspeaker,and the slider were waggled up and downat an audio frequency, sound would beemitted. The peak power would be 10W.

This mode of operation is called push-pull working. To make it practical, wefirst replace V2 with a capacitance C 1(Fig. 7.9b). With the slider at the mid -

VR1

81

VI(20V)

T

V2 (10V)

VR1

:B1V1 (20V)

RL -(1011)

b

+ II I82

bRL

(Ion)

(a) (b) (c)

Fig. 7.9. "Thought experiments" to Illustrate push-pull operation. (a) Two -batterycircuit. (b) How a capacitor can replace one battery. (c) Two -resistance version of (b)which is easier to transistorise.

+10V

+20V

RL(/011)

TR1

Fig. 7.8. Rudimentarypower amplifier.

+VCC (20V)

b

+ at.P61 TR1COMe

CI+1

b

6giTe

TR2

4111M

1' TR1(npn)

e+

1

C2

1."4

+vcc

TR2(pnp)

RL000)

(a) (b)

Fig. 7.10. Two versions of a push-pull power stage. (a) Singlepolarity transistors with two signals in anti -phase. (b) Comple-mentary transistors with single signal.

point C 1 charges to 10V. Move it up, andmore current flows into C 1. Move itdown towards (b) and C 1 discharges,current flowing out. RL receives to-and-fro currents as before.

The next step is taken purely because apotentiometer like VR1 can't be imitateddirectly by transistors. But an equivalentcan (Fig. 7.9c). Here VR1 increases asVR2 decreases and vice -versa. Thevoltage at their junction moves up anddown exactly as before.

By substituting transistors for VR 1and VR2, and controlling their effectiveresistances by applying signals to theirbases, the circuit becomes an audiopower amplifier. Peak power to RL isIOW.

TRANSISTOR PUSH-PULLOne possible scheme is shown in

Fig. 7.10a. Here, the signal voltage isduplicated. One copy, Vs I, drives TR1.The other copy, Vs2, drives TR2, butwith the reverse polarity.

When the voltages are as shown, TR1is turned on. Current flows from Vcc+via TR 1 into C 1, so RL gets a downwardcurrent. The actual amount depends onhow hard TR1 is turned on, and thisdepends on the signal amplitude.Meanwhile, TR2 is held off. No collectorcurrent can flow as base is negative.

When the next audio half -cycle occurs,the signal polarity reverses. TR 1 is nowheld off but TR2 turned on. C I dis-charges through TR2, giving an upwardcurrent through RL. If there is no signal,TR I and TR2 are both off.

BIASThe arrangement has one drawback.

Since a transistor passes no collectorcurrent until VBE reaches around 0.6V,audio signals less than 0.6V are ignored.The result is bad distortion.

To avoid this, TR1 and TR2 must begiven enough bias to turn them on slightlyin the absence of a signal. Even a smallpositive signal can then turn a transistoron further.

COMPLEMENTARY OUTPUTSTAGE

The Fig. 7.10a arrangement is oftenused in high -power amplifiers. But for lowand medium power circuit (b), Fig. 7.10b,is commoner. Its advantage is that onlyone signal (Vsl) is needed. The arrange-ment makes use of the fact that a positivesignal turns an npn transistor on, but apnp transistor off.

When Vs 1 polarity is as shown, TR1 isturned on and delivers a current to C2and RL. When the polarity reverses, thenegative signal turns TR 1 off but TR2 on,and RL gets a reverse current as before.

In the no -signal condition, both tran-sistors are off. But in practical circuitsthey are given enough bias to turn themon slightly in the absence of a signal.

With both circuits, when the signal islarge, TR1 handles the positive halfcycles and TR2 the negative ones. Forsmall signals the standing bias makesboth transistors operative.

Next month: Power In General


INTELLIGENCECOlRBY PAUL YOUNG

UnsurpassedThe introduction of the home micro-

computer has produced a curiousdichotomy and in the short term view, theelectronics hobby has suffered. Those whostarted constructing them, soon found theywere more fascinating to play with, worsestill, many teenagers who were almost cer-tain candidates for the electronics hobbywere being wooed on to the homecomputer by advertising and televisioncoverage.

The other day, I happened to visit a largestationer's in London and the first thing thatmet my eyes was several shelves full ofhome computers. I think they might havehad more success, assuming they were try-ing to attract the casual buyer, if they hadavoided such arcane language. The largenotice saying "128 Kilobytes of RAM"would be meaningless to the tyro, whereas,"Produces 130,000 characters or 20,000words" might give him some idea what itwas all about.

Well, they are here to stay and I suppose

I shall be told, "If you can't beat 'em, joinem", though it goes against the grain forsome of us more mature chaps. It wastherefore, with great interest, that I readwhat the Right Honorable Tony Benn hadto say on the subject, in one of the"nationals".

"This technology represents as great anadvance in the communications arts as didthe printing press, the television, radio-ortelephone and tape recorders". He goes onto say, "It is for typing-simple typing-that the machine has proved itself to beunsurpassed, offering to my shaky two -fingered typing an undreamed of capacityto produce perfect copy without, as before,consuming more bottles of Tippex thanmugs of tea."

Positive ChargeI was interested to see in the February

issue Of EVERYDAY ELECTRONICS a construc-tional article on a Negative Ion Generator. Ihave been exchanging letters on the subject

of the benefit of negative Ions with a

knowledgeable reader.We were discussing when the air was

more likely to be charged with an excess ofpositive Ions. During thunderstorms, ofcourse, but he said there was also a theorythat people living under high voltage elec-tric pylons suffer in this way although nosatisfactory conclusion has been arrived at.

It made me wonder if the average colourtelevision produces positive Ions. As acorollary, has anyone produced a meterthat would show the amount of positive ornegative Ions in a room.

I suppose an Electroscope might be theanswer, Readers' views on this would bemost welcome.

Finally, here is a way of testing yourIoniser that I can personally vouch for. Viewthe end of the pin in total darkness and atiny blue corona will be visible round thetip. It is very small, and a magnifying glasswould be helpful.

I don't know whether it will work withfive pins and it might be better to make thetest after the first pin is placed in position.

EVERYDAY ELECTROMICSSOFTWARE SERVICE

The EE Software Service provides an easyand reliable means of program entry for ourcomputer -based projects. All programshave been tested by us and consist of twogood quality copies of the working programon cassette tape. Certain program listingsare also available.

All prices include VAT, postage and pack-ing. Remittances should be sent to Every-day Electronics Software Service, EditorialOffices, Westover House, West Quay Road,Poole, Dorset BH15 1JG. Cheques shouldbe crossed and made payable to IPCMagazines Ltd.

PROJECT TITLECASSETTE

CODECASSETTE

COSTLISTINGCODE

LISTINGCOST

ZX81 SPEED COMPUTING SYSTEM(Feb 83) T001 £2.95 L001 £2.95

REAL-TIME CLOCK (Apple II) (May 83) T002 £2.95 L002 £2.95REAL-TIME CLOCK (BBC Micro) T003 £2.95 L003 £2.95

(May 83)EPROM PROGRAMMER (TRS-80 & T004 £3.95 N/A -

GENIE) (June 83(*STORAGE 'SCOPE INTERFACE (BBC

Micro) (Aug 83) T005 £2.95 -ELECTRO-CARDIOGRAPH (BBC

Micro) (Jan 84) T006 £2.95 - -EPROM PROGRAMMER/ROM CARD

(ZX81)** (Feb 841 T007 £3.95

Includes Command List with examples."Includes Keyboard Overlay.


MICROCOMPUTERINTERFACING TECHNIQUES

INCLUDING MANY USEFUL CONSTRUCTIONAL PROJECTSPART TEN: DATA ACQUISITION AND CONTROL

BY J. ADAMS B.Sc, M.Sc. & G. M . FEATHER B.Sc.

N the previous articles the techniques ofI I/O control and the monitoring ofanalogue quantities from the real worldhave been treated separately.

In many actual applications it isnecessary to take corrective action on thebasis of comparisons made betweenreadings of physical parameters and theirprescribed values. For example, analoguevoltages developed from separate tem-perature probes, could be converted intodigital values monitored by the micro-computer and compared with pre -deter-mined values allotted for the particularapplication.

If this comparison shows that correc-tion is desirable then appropriate signalscould be sent to individual output devicescontrolled by the microcomputer so thatthe necessary correction could beachieved.

Such a system allows the repetitiousmonitoring of analogue quantities overlong periods of time and this allied with aprecise control in response to thesemeasurements will obviate human error.

In addition, if transient events aremonitored using the system, the speed ofthe microcomputer allows an almostinstantaneous response. It should beapparent that the considerable flexibilityand undoubted accuracy of such systemsoffer many advantages over manualsystems.

CLOSED -LOOP SYSTEM

This month's project in the series isa closed -loop feedback control system.Information obtained from a 16 -channelanalogue -to -digital converter is fed backto the microcomputer so that it can con-trol seven separate output devices to com-pensate for the effect of external changes.

This method is, of course, more crudethan a closed -loop system including fullproportional control (employing perhapsa DAC) but it is cheaper and easier toimplement.

In practice a degree of pseudo -proportional control can often beachieved by the subsequent on -and -offswitching of appropriate devices and thiscan be further improved by anticipatoryon -off control. In such control systemsthe devices are actuated before themeasured physical parameters reach theirthreshold values. This approach reduces

oscillations of the monitored quantities of"hunting" as it is generally termed.

It is a relatively straightforward matterto write the requisite software with ap-propriate anticipation values included toprevent this occurring.

APPLICATIONSThere are many applications for such

regulatory control systems. Two obvious

and useful applications-in the house andin the greenhouse-are outlined below.

HOUSE ENERGYMANAGEMENT SYSTEM

The main shortcoming of conventionalcentral heating control systems is the in-herent lack of flexibility. This is exem-plified by the continuous reprogramming

ANALOGUEINPUTS -

ADDRESSBUS

02

RAW

CHANNEL SELECT\

16CHANNEL

MUX

LATCH ENABLE

xS AMP.

CHANNEL SELECT

ADC

LATCH ENABLE

ADDRESSDECODE

DS

DATA DO - 06 -IN

DATALATCH

RELAYDRIVER

DATA TOUSER PORT

STARTCONVERSION

OUTPUTENABLE

Fig. 10.1. Block diagram giving system overview.

OUTPUTS


of the clock needed, for example, everyweekend. If measurements of individualroom temperatures are collatedperiodically together with the temperatureof the water and perhaps the external airtemperature, then the appropriate outputresponses can be triggered to provide aclosed -looped feedback control system.

GREENHOUSE MANAGEMENTSYSTEM

A similar closed -looped proceduremay be adopted in a greenhouse manage-ment system. "Dry" temperature probescan be used to send information to themicrocomputer so that air and soil tem-peratures can be monitored efficiently.

If "wet" temperature probes are alsoused, then the relative humidity can alsobe computed. The ambient light condi-tions may also be measured and assessed.

Suitable software controlled responsesto complete the feedback loop includeusing output signals to switch a heater onor off, controlling a ventilator fan orperhaps opening or closing blinds.

SYSTEM OVERVIEWThe reader should by now be fully ver-

sant with the techniques of analogue dataacquisition using an ADC and the controlof external devices, as these have beenfully dealt with earlier in this series.

Fig. 10.1 shows the individual inputand output sections of a closed -loopmicrcomputer control system.

INPUT SECTIONThe input section can handle

simultaneously up to sixteen channels ofanalogue data from appropriatetransducers. All channels have a fullrange sensitivity of IV and are unipolar.The input impedance of each is approx-imately 101(0.

Digital data from this section istransferred to the microcomputer via itsuser port, the ADC and channel multi-plexing operation being also fashionedfrom this port. Simple transducers, fortemperature and light intensity, aredescribed briefly at the end of the article.

OUTPUT SECTIONSeven individually controllable outputs

are provided which can operate a 5Vrelay situated at the device to be con-trolled. The output board is driven fromthe extension bus, suitable address busdecoding and data bus latching circuitrybeing included.

POWER SUPPLYThe power supply includedis quite

conventional circuitry to develop the+7.5V supplies for the analogue signalamplifier on the input board and +5V forall the TTL supplies and the output relaydrivers.

COMPONENTS

ResistorsR1-8 10k0 x 8 commoned (2 off)R9-16R17 30k0R18 7.5k0R19-26 1001(12 (8 off)R27 1k0R28,29 2200 (2 off)All -kW carbon ±5% unless specified otherwise

CapacitorsCl 1000pF ceramic plateC2,3 0.1µF polyester type C280C4,5 1000µF 25V elect. axial (2 off)C6 0. 1µF polyester type C280

SemiconductorsD1 BZX61 5.6V Zener 1.3WD2-5 W005 1 A 50V bridge rectifierD6,7 BZX61 C7V5 7.5V 1.3W Zener (2 off)ICI 741 op -ampIC2 ADC 0817 16 -channel multiplexed A -to -D converter i.c.IC3 74LSO4 low power Schottky TTL hex inverterIC4 74LSI33 low power Schottky TTL 13 -input NANDIC5 74LS27 low power Schottky TTL triple 3 -input NORIC6 74LSO4 low power Schottky TTL hex inverterIC7 74LS273 low power Schottky TTL octal latchIC8 ULN2001 7 -stage Darlington driver i.c.IC9 7805 +5V 1A voltage regulator

£50

SeeMiscellaneous

S1 miniature on -off toggleFS1 1.25A anti -surge 20mm fuse 41:1LP 1 panel mounting mains neonT1 mains primary/two 0-9V 330mA secondaries page 231TB 1,2 12 -way barrier strips (2 off)TB3 5 -way barrier stripsVR1 10k0 miniature horizontal carbon skeleton presetPrinted circuit boards: Input board, single -sided size 135 x 100mm, EE PCBService, Order code,8404-02; Output board, single -sided size 135 x 100mm, EEPCB Service, Order code 8404-03; Power supply board, single -sided size 100 x57mm, EE PCB Service, Order code 8404-04; 20mm panel mounting fuseholder; aluminium case, vinyl covered top size 275 x 153 x 75mm approx.; 6BAfixings, soldertag and board spacers; p.v.c. covered stranded connecting wire; 1 1 -

way ribbon cable; 23 -way ribbon cable; single -sided Veropins (73 off); 22 s.w.g.tinned copper wire; d.i.l. i.c. sockets: 40 -pin (1 off), 20 -pin (1 off), 16 -pin (2 off),14 -pin (3 off), 8 -pin (1 off); 3 -core mains cable; cable clamp and grommet formains cable.


'12' oo

ANALOGUEINPUTS

CHANNELNo.

TBI/1'0' a.

'1' a' 2

RI -R1610k13

IC3PIN 14 19

38

'Z' 073

9

'3 oo4

'4'5 Ic

5'6 Ia,

'6' oo

7' oo

'8' co

171

'10° au

'11'

71

10

12

40

-/V\A"-1--

T82/1

2

3

8

9

'13' CO

'14' c

'15' or)

OV -

10

3

11

TB3or

01BZX 51

55V

12

14

18

VR110k11

7 +

IC1741

a

R17

30k0

15

R18

17VCC

+V REF

CH. 0

37

EOC

C

CH.1 ALE

CH.2 IC2 OEADC 0817

CH.3

CH.4

CH 5

CH.6

CH.7

CH.8

CH.9

CH.I0

CH.11

CH.I2

CH.13

CH.14

CH.15

COMP IN

AN.COMMON

-VCC -V REF

DATABUS

MSB

LSB

CHANNELADDRESS

C

B

CLK

7.5k0

20 23

ic3,7aLsoc

IC?PI N1 7

R19 C R20IOND 10010

R21

1001d2

R22

MicaRZ3

/00kaR24

100141

P83

32

21 C82

31 P7

30 P6

29 P5

28 Pd

27 P3

26 P2

25 P1

2

3

3

35

3

22

R25

1004

IC3a "3-W\r-e-1716Cl

woopF

2

OV

0

0cr

Fig. 10.2. Circuit diagram of the input section of the Data Acquisition System (DAS).

THE INPUT SECTIONCIRCUITRY

Fig. 10.2 shows the complete circuit ofthe input board section of the system.

The ADC 0817 (1C2) is a 16 -channel8 -bit successive approximation typeanalogue -to -digital (ADC) and isprovided with tri-state output lines. Themaximum input range for each analoguechannel is dependent upon the referencevoltage used and is, in this case, +5V.

This is rather higher than the usualrange of transducer output circuitry andan operational amplifier, IC 1, is includedbetween the output of the multiplexer(channel selector) and the input to theADC section of the device.

No on -chip clock is provided with theADC 0817. The necessary clock signalsare generated by IC3 which is wired as asimple astable circuit.

The maximum clock frequency for theADC 0817 is quoted by the manufac-turers as being 640kHz, but in this

application a much lower clock is per-missible and a frequency of approxi-mately 30kHz is employed.

The 16 -channel multiplexer section ofthe ADC 0817 requires a 4 -bit addresscode and this is routed from the user portvia the four least significant lines of the8 -bit port configured for output. Thisoperation precedes the start conversionsignal and the address is latched into themultiplexer hence holding the selectedchannel whilst conversion takes place.This procedure is explained in more detailin the software section.

THE OUTPUT SECTIONCIRCUITRY

As previously mentioned, the outputsection of the circuitry interfaces directlywith the extension bus. Readers of lastmonth's article will realise that addressbus decoding is necessary to provide thedevice select signal for the data bus latch.

Fig. 10.3 shows the complete circuit ofthe output section circuitry. IC4, IC5 andIC6 provide decoding for up to twelve ad-dress bus lines along with the 02 clocksignal, I/O and R/W lines. The number oflines actually used depends upon themicrocomputer as detailed last month.Note that any unused inputs to the74LS133 thirteen input NAND gate shouldbe pulled up to logic 1 by direct connec-tion to +5V.

The arrangement of this decoding cir-cuitry and the number of lines used de-pends upon the microcomputer used andis identical to that featured in the outputport design feature detailed in lastmonth's article. In order to avoid un-necessary repetition, readers are referredto that article for further details.

When a valid address is detected bythe circuit and the I/O and R/W controlbus lines are low, data present on DO toD6 is latched into IC7, the 74LS273 octallatch.


L.

CO

CO

A8BAr'6A0

C 0

1

R27

1k12 IC4 PIN 16ICS 86 PINS 14

Fi LINKS

6

2

4 3

AS 2

A7 15

SPARE

SPARE 10

SPARESPARE012

13

12

14

.110few

LU

D3

(a

02

IC4

1C4.74L513 3ICS = 741_527

IC6. 74L504

3

01

04 13

D5 it

17

OV

IC5 & 6 PINS 7I C4. PIN B

OS

IC7

(cc

74 L5273

GNI)

2

12

15

16

.C20.4JF

C3

0 IJF

EE

IC8ULN2001

Fig. 10.3. Circuit diagram of the output section of the DAS.

The Q outputs of this drive the sevenstage Darlington transistor array, IC8.Each output of this is capable ofswitching up to 500mA and can be usedto actuate a switch located at the par-ticular device to be controlled.

It should be noted, however, that theuse of relays can induce spurious signalson the buses. One practical solution tothis problem is to use optically isolatedzero -crossing solid-state switches. Theseallow the switching of perhaps a heaterwhen the mains voltage is at the zero -point of its cycle.

POWER SUPPLY CIRCUITRYThe power supply for the system is

relatively conventional and Fig. 10.4should be consulted.

The 240V a.c. mains is placed acrossthe primary of T1 via S 1 the on -offswitch. Power on is indicated by mainsneon, LP I.

B2 /500+5V

00 OUT 3

1

1700 OUT 2

2 800OUT 1

13 900OUT 0

14

15

1°00 OUT 4

Boo our s

16 21200OUT 6

EE

Fig. 10.4. Power supplycircuitry for the DAS.

IN IC97805

R29

f000pF 22011

R28

220(1

rj7C5+ 1000pF

D6BZYB8

7-5V

COM

OUT

iC6

a

D7BZYB8

a 7-5V

0 ipF

Ov


18V appears across the centre tappedsecondary of Ti. The bridge rectifier (D1to D4) provides full -wave rectification togive pulsating d.c. of peak value, about+13V. C3 smooths the +ve peaks to feed

IC9. Negative peaks are smoothed by C4.The ADC and other digital sections of

the circuity require the usual +5V supply,which is provided for by the 7805 voltageregulator, IC9. The 741 operational am -

plifier is operated at +7.5V. The currentrequirement is very small and these sup-plies are derived from the Zener diodes,D6 and D7, and associated dropperresistors R28 and R29.

DATAACQUISITIOMSYSTEMINPUT BOARD

The three sections of the system areeach constructed on separate printed cir-cuit boards.

The actual -size master p.c.b. patternfor the ADC input board is shown in Fig.10.5. This board is available from the EEPCB Service, Order code 8404-02. Thelayout of the components on the boardtopside is given in Fig. 10.6.

Assemble the components as shownpaying attention to the polarity of D 1.Resistors R11 to R27 are a little unusualin appearance to those normally found inEE. These are s.i.l. packaged (single -in -line) and contain eight equal valueresistors all "commoned" at one end.This gives nine s.i.l. pins. These packagesmust be assembled the correct wayround. There is a small white dot abovethe "common" pin.

In the prototype the leads to the boardwere soldered directly to the board. Itmay be better to use Veropins for each ofthese connections, as then the boardsmay be positioned in the case, and in-terwired, and to the case mounted com-ponents in situ.

Sockets were used to hold all i.c.s(except IC9), and we recommend thatconstructors do likewise. Do not reset thei.c.s in their sockets until the system hasbeen fully wired up.

OUTPUT BOARDThe printed circuit board master pat-

tern actual -size, for the Output board isshown in Fig. 10.7, with the componentlayout on the p.c.b. topside given inFig. 10.8.

The p.c.b. is available from the EEPCB Service, Order code 8404-03.Assemble the board as indicated. UseVeropins for all cable connection points.

The completedDAS "Input'board.

The fully assem-bled DAS "Out-put" board.


0

CI

INPUT BOARD

0m110

111%

a 0 00

0 00 0

1 0E00040 "

EE8404-02

Fig. 10.5. Actual -size master pattern for the DAS input section. This board is available from the EE PCBService, Order code 8404-02.

-7 5V @.75V@

5V®OVC)

C82 0)P0 0P1 C)P2 0P3

P4 0P5 0P6 @P7 0

PEI3

ov*

-1111-R25

I

-C 1C

C

COMMON

R9 -R16

RI -RS

COMMON

VR1

C) 0V15

0 14013@ 120 11

10

@98

0.70.6O.50403OO 2

Fig. 10.6. Layout of the components on the topside of the "Input" board.


OUTPUT BOARD

1.0NEMO*00 Ellmn**011onoymoilemames=om=

11211.1 ONMENNE*

EE8404-03

0

Fig 10.7. Actual -size master pattern for the DAS "Output". This board is available from the EE PCB Service,Order code 8404-03.

D60504D30D2

Di*D0

-Lc'r'*

0-111-E-40aCiz_

-4n*02® IC 7

0-00--AF --0

A7* (3- - - -0A6 (i) 0A5* C R27

11

AG C

A3* E ]A 2

A

40*

IC4C

C

C

3

lib@

ay®C3

IC5

C

4.!

C 106

C

C

*6*5

3 *4ICS

3 *001

2

* 3 5V

Dv 5V*

Fig. 10.8. Layout of the components on the topside of the "Output" board.


POWER SUPPLY

0

Fig. 10.9. The actual -size master p.c.b. pattern for the power supply board for theDAS. This board is available from the EE PCB Service, Order code 8404-04.

n,0

®

ovC)

D 2-D5

IC9

1/P

METAL TAGOP

0Co M

R29 28

k

07 D6

a

I 0a

C6

00000OV OV 5V .7.5V -7.5V

Fig. 10.10. The layout of the components on the topside of the DAS powersupply board.

Plan view of the prototype DAS with lid removed from case.

Rear panel of the prototype DAS.

SOFTWAREThe techniques involved for the

software Microcomputer Data Acquisi-tion and Control System have beencovered in earlier articles. A possiblesequence of operations is outlinedbelow:1. Disable tri-state by taking the appro-priate output line from the microcom-puter (to pin 21 of the ADC) to logiczero.

2. Disable address -latch by taking theappropriate output signal line from themicrocomputer (to pin 32 of the ADC)to logic zero.

3. Configure the user port for output bysetting all bits in the appropriate datadirection register for the port.4. Select ADC channel required (0-1 5).5. Route channel selected (to pins 36,35, 34, 33 of the ADC) using the fourleast significant lines of user portpreviously configured for output.6. Enable address -latch by sendinglogic one output signal to pin 32 of theADC.7. Initiate conversion by sending theaddress -latch 'line to logic zero thusallowing a negative going pulse toreach the start conversion pin (16) ofthe ADC.8. Wait for the conversion to be com-pleted (not necessary if using BASIC).9. Configure user port for input byclearing all bits in the appropriate datadirection register.10. Enable the tri-state by taking theappropriate output signal line to logicone.1 1 . Read the value presented to theuser port via lines 31 to 24 from theADC.12. Disable the tri-state by taking theappropriate output signal line to logiczero.13. Configure the user port again foroutput by setting the requisite bits inthe data direction register.14. Compare digital result obtainedfrom ADC with allotted value.15. Turn on or off appropriate outputcontrol device on extension bus.16. GOTO step 4.


CASE REAR PANEL

TB3

TO MICRO USER PORT

ai SLOTS

TO MICRO EXPANSION POR

FS1 FROM 240VA.C.MAINS

INPUT BOARD

OUTPUT BOARD

PRIMARYh"----1 240V OV-

9V V

POWER SUPPLYBOARD

IF "

0 0 10 1 4 5 6 7 8 10 1 12 13 14 15+ V 0 1 2 3

0ANALOGUE INPUT CHANNEL N° OUTPUTS

CASE FRONT PANEL

Fig. 10.11. Position of components and circuit boards for the complete DASwith full interwiring details.

Shows the front panel of the prototype DAS.

LP1

A

S1

POWER SUPPLYMost of the power supply components

are mounted on a p.c.b. The actual -sizemaster p.c.b. pattern is given in Fig. 10.9.This board is available from the EE PCBService, Order code 8404-04.

Assemble the components on the top-side of the board according to Fig. 10.10paying attention to the orientation of thediodes, electrolytic capacitors and IC9.

INTERWIRINGPrepare the case and fit all the compo-

nents. Mount the three p.c.b.s on suitableheight spacers above the base of the caseand interwire and connect to the casemounted components as shown in Fig.10.11.

The ends of the ribbon cables shouldbe suitably terminated to mate with themicro in use. Insert all i.c.s paying atten-tion to polarity. Label the case as shownin the photographs.Next month:Vehicle Control with the Micro


ENTERTAINMENTBY BARRY FOX

Mole ProofEarlier this year there was considerable

cufuffle about the leakage of secret Govern-ment documents. Leaking of course, hasbeen much, much easier since the readyavailability of Xerox copy machines in the60s.

Before the advent of copying machines itwas very hard to copy a document quicklyand unobtrusively. Although spy films stillshow the hero or villain snapping away witha miniature camera, this is stretchingcredibility.

As anyone who has ever tried to takeclose-up shots with a camera will know,there are any number of pitfalls. Focussingis critical, especially if the light level is lowand the camera aperture wide open. Youneed a very steady hand, or a tripod, toavoid camera shake. It is all too easy to gethighlights, with the light source reflectedfrom the surface of the paper.

"Wet" photo copy machines made thingseasier. But they were slow to use and therewas the added problem of how to get rid ofthe throw away wet negative sheet thatcame out of the machine along with thepositive copy. It's no joke, if you are a molecopying a hundred -page document, to tryto get rid of a hundred sheets of paper sod-den with chemical developer!

Although the original Xerography inven-tion, made by Chester Carlson, dates backto before the war, it was not until the 60sthat Rank Xerox made plain paper copyinga part of office routine. It wasn't long beforepeople with secret documents, startedworrying about unauthorised copying. SoRank -Xerox invented and patented, a

system of making documents uncopyable.There is a high intensity light in a

Xerocopy machine and if the paper beingcopied contains a coloured fluorescentmaterial this light is absorbed at onewavelength and re -emitted at another. Thisdazzles the copier by swamping the imagecontrast.

Secret MessageOn early Xerox copying machines, the

813 and 3600, it was possible to make amessage secure simply by writing it onpaper with red or orange fluorescentcolouring. The original message is perfectlylegible, but completely uncopyable.

The Xerox anti -copy patent specified thebest type of dyes to use in aerosol sprays.But in the 70s, Rank -Xerox came out with anew generation of machine, for instance,the 4000, which could produce superblyclear copies of dye -masked messages thatbaffled the older machines.

All modern Xerox machines contain daz-zle proof optics. So they can make clearcopies of virtually any messages that canbe read by the human eye. Paradoxically, ifGovernment departments were to use oldermachines, they would be able to make adocument secure by dye masking.

Some of the early machines are in factavailable, for outright purchase. They arereconditioned models taken out of rentalservice. So if anyone wants to make theiroffice mole proof, they need only buy an oldmachine and some sprays of fluorescentdye.

Radio MoleThe hunt for Government moles remin-

ded me of something that happened when Iwas in the Air Force, during the last fewmonths of National Service. We were learn-ing to service high power radio transmit-ters. The only way to check the transmitterwas to tune it to the transmission frequencyand run the valves up to full power. But theoutput stages would blow up if there wasno aerial.

Obviously stray radio transmissions froma workshop on an RAF base could haveinterfered with important communications.So the workshop transmitter could beeither connected to a real aerial, or a stringof light bulbs that served as a dummyaerial.

One day, one conscript unplugged thedummy aerial and plugged in the real one.He then broadcast a "Mayday" emergencysignal. All across England air-sea rescuewas mobilised and they soon pin -pointedthe Wiltshire air base.

The military police on the airbase swiftlypin -pointed the workshop most likely tohouse the guilty man. All but two peopledenied knowledge of the incident. Theremaining two pleaded innocence butblamed each other. The military police,fearing questions in Parliament about unfaircollective punishment, couldn't lock upboth airmen. The police tried for days to ex-tract an admission of guilt. But they failedand both suspects walked free.

We never did know which one of the twohad done the deed.

Cashless SocietyThe cashless society is coming. Some

cash and credit cards carry a magneticallycoded identity strip. The next generation ofcards are quite literally miniature com-puters.

It is not generally known that theCardphone public telephone boxes, whichare being installed by British Telecomaround Britain, use a holographic techni-que. You buy a card, that looks like a creditcard, which lets you make a limited numberof "free" phone -calls when you push it intoa slot in the telephone box. As you makethe calls, an I.c.d. shows how the units arebeing used up.

It would be possible to base the phone -card system on magnetic technology, eras-ing areas of magnetism, one at a time, aholographic card is much rrfore secure.However, the phonecard system, whichcomes from the Swiss company Landis andGyr, relies on the optical phenomenon

whereby light shone on an ultra -fine patternwill create interference effects, like fringinground a grating or colours from oil onwater.

PhonecardThe Phonecard, which is made of plastic

and looks like a credit card, has a track inthe surface which contains a series of in-dividual holograms.

Each one produces a characteristic pat-tern of light and shade when illuminated bya strong lamp.

This light and shade pattern is sensed byphoto cells which switch the telephone on.As each unit of telephone time is used up,the holograms are destroyed, one by one,by a sharply focussed heat beam. If youlook carefully at a Phonecard you can seethe track along the top surface, with tinybumps where units have been burned out.

On the continent, especially France, theyare experimenting with an even more exotickind of card, appropriately christened the"Smart Card". Again, this looks like a

plastic credit card, but it contains anastonishing array of electronics.

Buried inside the plastic there is a micro-processor, and several levels of memory.Some levels are readily accessible to give areadout of the card serial number. Someare accessible only when the micro-processor is interrogated by another com-puter.

For instance, the card can be used in-stead of cheques, with each cash with-drawal or payment subtracted from a creditbalance programmed into the card'smemory. The Smart Card is in effect anelectronic wallet.

Current cards have a memory of 8K bits,which is sufficient capacity for 200separate banking transactions. SeveralFrench cities, including Lyon, have shopsand telephones equipped with computerunits which can interrogate Smart Cards sothat they function instead of cash.

Paper SecurityIn theory the cashless society makes life

safer and easier for everyone. But in prac-tice this isn't necessarily so.

A friend of mine has been trying for overa month to subscribe to one of the newvideo systems that lets you do banking andshopping by a telephone line hooked up toa home computer. The delays have all beencaused by office bureaucrats fumbling thepaper work.

Exotic cash cards can only be secure ifthey rely on the user keying in a secretpassword or code number. But all too manypeople write their secret word or numberon their card, or on a piece of paper whichthey keep in the same wallet as the card.So security is gone!

Thanks to the cashless society, it's possi-ble to order goods, services and theatretickets by telephone or video screen, usingthe number of your credit card. But oftenpeople who use credit cards throw awaythe copy receipt which they are given whenthey have used the card in a shop orrestaurant. These receipts give the cardnumber, the owner's name and signature.So once again security is jeopardised.

Your cash will never be 100 per centsafe, even in a cashless society. We shallalways need paper, if only to keep a recordof electronic transactions. And, of course,pen and paper is the only system thatworks when there's a power cut!


CV

EXECUTE WHEN DID CABLED?

WHO WAS T -P 7 MOON?14C.

rE MICROCHIP?

111ASTER1V-'TELEVISION : BY S. LYONS WHAT YEAR. WA

DISCOVERED NEW ZEALAND? WHY DO BIRDS MIGR

DETERMINE who is first on the buttonin panel games with the Quiz -Master

H. For up to eight players, each with ahand-held response control, the unit givesboth audible and visual indication of thefastest to press, upon which, all otherresponse units are disabled.

The design has provision for up toeight response units to be used, each con-nected to the main control unit by 5 -pinDIN plugs on leads to 5 -pin DIN sockets.

The circuit of the Quiz -Master II is intwo parts, the response units, and themain control unit. It is the function of thelatter to determine who pressed first, andisolate all other response units. Theresponse unit consists of a switch,resistor, and an I.e.d.

RESPONSE UNIT CIRCUITThe response unit circuit is shown in

Fig. I. L.e.d. DI is not physically connec-ted to switch Si (except by the zero voltsline) and is driven by the main controlunit, and will only light up if its switchclosure has been accepted as a validresponse (that is, if it was pushed first).

Switch SI is a non -latching push -to -make type, and is used to generate a TTLlogic I when open and logic 0 whenclosed. The required voltage level is set byresistor R 1.

Fig. 1. Response unit circuit diagram.

S1

PLI

EE2

01

TIL220

S

S

All this is housed in a small, plasticbox. To link it to the main control unit,individual twin screened cable is used,terminated with a 5 -pin DIN plug.

MAIN CONTROL UNITFig. 3 shows the circuit diagram of the

main control unit. The heart of the circuitis IC 1, a 74LS373 octal transparentlatch. The inputs of this device are fedfrom the switches of the response units,and the outputs are fed to three logicgates. Two of these gates are used toproduce the signals for the indicators, theother is an 8 -input NAND gate.

This gate produces the necessary latchsignal for IC1, and also the signal to con-trol the piezo-electric buzzer. Note thatthere is an inverter gate immediately afterthe NAND gate output; this is to producethe correct logic level for IC6.

The RESET signal is produced by S2and R2. S2 is a non -latching push -to -break switch. The logic levels generatedby these components are logic 1 when theswitch is pressed, and logic 0 when notpressed. The signal is oRed with the inver-ted output of IC5 to produce the latchenable signal fed to pin 11, IC 1.

When a response unit has beenpressed, it sends a logic 0 to an input of

IC I. If no other unit has been pressedbefore it, the output associated with thisinput will also be at logic 0, all otheroutputs at logic 1. This will cause theoutput of IC5 to go to logic 1.

Inverter IC4e inverts this to logic 0 todrive the buzzer, and to change the out-put of IC6 from logic 1 to logic 0. Thiswill latch the outputs of IC 1, in effect,freezing the state of it, preventing anyother response unit operating. To resetthe unit, a logic 1 is required on the otherinput of IC6, produced by S2.

RESPONSE DISPLAYA visual indication of which response

unit initiated the above effect is displayedon both the master control unit's frontpanel, and on the appropriate responseunit. The signal to drive the l.e.d.s comesfrom the outputs of IC 1, via an inverter.The inverter is used as an inverting buffer,one for each l.e.d., two per output line.The I.e.d. is extinguished when the unit isreset.

POWER SUPPLYThe power supply unit is quite simple

(see Fig. 2), using a standard 5Vmonolithic voltage regulator integrated

Fig. 2. Circuit diagram of the power supply section.

rL FS1

53a

500mA

240V

AC.MAINS

NSib

IN

EE

5V

OV


circuit (IC7). This is the only devicewhich requires heatsinking, bolting it tothe case with a mica washer between itand the case should be fine. A few holesor slots to allow air to circulate inside thecase would be helpful.

The rest of the circuit is straight-forward, the illuminated mains switch S3on both "live" and "neutral" lines ofmains, with a 500mA fuse FS 1 in the liveline placed before the switch. Thetransformer T1 has two secondarywindings of OV to 6V each at 250mA,wired in parallel. The bridge rectifier is astandard readily available 50V, lA type.

CONSTRUCTIONMAIN CIRCUIT BOARD

With the exception of the I.e.d.s andthe buzzer, all the components are moun-ted on the circuit board. The circuit takes

IC X 111[31(11121111L1111:1111011 2 4 4 2

POW6Pt ar111

Fig. 3. Complete circuit diagram of the Quiz -Master II main control unit.

51<1

SK21

IC2-7PIN I4 100nF

3

4

51(3

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dal

51

13

14

7

18

ICI7a LS 373

TOOnF urOnF TOOnF TOnF T00nFC2 C3 C4 C5 INC6

5 2

6 3

9 4

12

15

5

6

16 11

19

11

10o<3

SK5

)1

SK7

) I

2*<10

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IC2-7PINS 7

8 9 13 9 3 13 3VyVVer \Cy \IC2/ Nivpr), o

8 12 8 4 t2

a 4,0, a 44 _'1/4 a 44 a 44 a 4/4 a

TIL 220

IC612

2

13

EE

IC2,3,4,7. 74LSO4IC5 . 74L530106 = 74L532

DI140

52

+5V

IRESETI

ov


TABLE 1

A- +12V A

B-S K8/2C-S K7/2D-S K6/2E-S K5/2F-SK1 /2G-S K2/2H-S K3/2J-S K4/2K-D5aL-D8aM -S K2/4N-D3aO-WD1P-S K7/4Q-S K8/4R-D9aS-S K1 /4T-D7aU-S K6/4V-D2aW-S K5/4X-D6aY-S K4/4 wZ-D4aAA-S K3/4 ur

BB-OVCC-WD1 R

0P

M

KJ

N0

FE

N

C

1 2 3 4 5

Ao 0 0 0 0 0 0 00Bo6CDoE

0C

eH

oJ

) 0000000

1 2 3 4 5

15 20

0 0 0 0 0 0 0 0 0 0 0

00000.

10 15

25 30 35 40 45

ooooo 000S0000000000

X

AA

0.0 0 0000 000 00000000 000000

20 25 30 35 40 45

50

50

0 0 000 00 00 0 0 0 0 0 00 00 0 0 00 000 o 000 0 000 ooo o0000 oo 0000000000 o ooooo o oo 00000 oo oo 000000 000000000000o 0000 0000000o0000000000 0 oo oo o o oo 000000 oek ooo000.000..0.0.00000.000.000.0000.0.00.00 0.000 00

0000000000000000000000000000000000000 .00.0 .000 0000000000 00000 000 00000 00000000000 00 000 000 0000000000 00000 000 0 00 00000 00000 0000 0 00 o0 00000 000000000000 000 0000000 0000 00 0 05 0 000000 0 0000 00 00 0 00 00 00 00000000 00 0 0 O 0000 000 00000 0 0000 0 00 0 0 00000000000 00000 00 00 0000 00 0 00 0 0 0 00 0 0 000 000000 000000 0 0 0 00 0 000 O 000 00 0 0 0 0 0 0 0 0 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 o 00 0000 0505000 000 0 0 000 0000 0 0 00 00 00 0 0 05 00 000 0000 0 0000 0 00 0 000000 0000000000 00 0 050 00000 0 00000 ooo o ooooooooooooooClooooo 0000 00000o oo ooo 00 0gooo o ooo o 0oO

oc000 o000o 0 0 00o o o 0 o 0 0 0000 00000.00 00000 0. 0 oo 0 00 00.0000000.0.0000.00 .0. o 000 . ..0 00.0.0000000000000o 0 0 oo 00 oo 00 0 o 00000oo00000000oo0 oo0 o o oo 0 o oo o o0000 oo 0 0 0 0 0 0 0 0 0 0 0. 0 0 0 ooo o ooo o ooo 0. 0 0 0000000000S0000000000000.0000000005000000 00005S555

52

Fig. 4. The component layout and trackside view of the main control unit stripboard assembly. Note that the wires to case -mountedcomponents are lettered (A, B, C and so on) and the destinations of these wires are given in Table 1 (above left). For clarity, thedecoupling capacitors, Cl to C6, have been omitted from this view, but should be soldered across the power supply pins of the i.c.s (onthe trackside, if necessary). Note also the links under IC2,3 and 4 and that some links use the same holes in the board.


4

5 -PINDIN PLUG

PL1

Fig. 5. The assembly of theresponse unit (one ofeight), can be seen in thisdiagram. Approximately3m of cable is used foreach.

the form of a stripboard. The componentlayout and trackside view are shown inFig. 4.

Although TTL i.c.s are used, socketsare used in the construction to allow easyreplacement of faulty chips. As TTL isused, decoupling capacitors are requiredto be mounted close to the i.c.s. It is ad-vised that the sockets are soldered in first,followed by the capacitors, so as not toforget them. The rest of the componentsare then fitted in as normal.

The connectors for the response unitscan be fitted into the aluminium case,along with the other case -mounted items,such as mains switch, reset switch, fuseholder and l.e.d.s. Once fitted, they canbe wired up to the circuit board.

COMPONENTS

ResistorsR1 1kS2 (8 off)

RESPONSE UNIT (8 off)

SemiconductorsD1 TIL220 5mm red I.e.d. (8 off)

MiscellaneousS1 non -latching push -to -make switch (8 off)PL1 5 -pin 240° DIN plug (8 off)Twin screened cable (approximately 24m); plastic case, 70 x 50 x 25mm(8 off)

ResistorR2

CapacitorsC1-6C7C8C9

MAIN CONTROL UNIT

1k0

0.11.1F ceramic (6 off)2204F 16V elect.220nF polyester C280470nF polyester C280

SemiconductorsIC1 74LS373 TTL octal latchIC2-4,7 74LSO4 TTL hex inverter )4 off)IC5 74LS30 -r-ri.. 8 -input NAND gateIC6 74LS32 rn_ quad 2 -input OR gateIC8 7805 5V, 1A regulatorD2-9 TIL220 5mm red I.e.d. (8 off)D10-13 W005, 1A, 50V bridge rectifier

MiscellaneousS2S3/LP1SK1-8WD1FS1

non -latching push -to -make switchmains switch with integral neon indicator5 -pin 240° DIN socket (8 off)piezo-electric buzzer500mA 20mm quick blow fuse

T1 OV-6V, OV-6V 250mA mains transformerAluminium case, 250 x 110 x 80mm; 20 -pin di!. holder; 14 -pin d.i.l. holder (6off); wire; mica insulating mounting kit (for IC8); chassis fuse holder for 20mmfuse; O.1 in matrix stripboard, 24 strips by 50 holes.


102

77

aUIZ-MASTER II CASE DETAILS

0

245

OM'10 121

DIA DIA

102

0

O

53

016 DIA

66.5

19-S

18

S2D9 D8 D7 D6 D5 04 D3 D20 00000000

60 IOH

48

SKI SK2 SK3 SK4 SKS 5K6 SK7 5K8000000029.5

0

ALL DIMENSION IN mm

Fig. 6. Drilling details and case -mounted component positions for the Quiz -Master II case. This case is a two-part chassis type and caneither be fabricated or a box of similar dimensions can be purchased. The top diagram shows the end panel of the bottom half withholes for the mains cable and fuse holder. Note all hole sizes must be checked with components to be used.


(Above). The rear viewof the Quiz -Master II

showing the DIN

sockets with oneresponse unit pluggedin.

(Left). The internal wir-ing of one of theresponse units.

(Below). The twohalves of the chassiscase separated to showthe internal wiring ofthe main control unit.Note the prototype unituses a proprietarypower supply unitrather than the unitdescribed in the text.

The power supply is constructed on aseparate board, and is straightforward tobuild. The only thing to remember is tomake sure the voltage regulator is facingthe right way, to allow it to be bolted tothe case. Two wires for both the 5V railand OV rail emerge from the p.s.u. This isto provide five volts to both the circuit,and the response units via SK 1 to SK8.

As the prototype unit uses aproprietary power supply module, noconstruction drawing has been given.However, it can be seen from the circuitdiagram (Fig. 2) that it is a fairly simpleassembly made on a piece of stripboard.

The transformer and IC8 (via a micawasher and insulating bush) should bescrewed to the case and the bridge rec-tifier and capacitors soldered to the smallpiece of board. Wires are then taken tothe main board, sockets and l.e.d.s.

The response units are easy to con-struct, as no circuit board is needed. Allcomponents are mounted on the switch.Three holes are required in the box hous-ing the components, one for the switch,one for the l.e.d., and the other for thecable to leave the box. See Fig. 5.

TESTINGBefore any i.c.s are inserted on the

main board, it is advisable to check thatthe power supply is in order. Althoughrri_, are quite hardy little bugs, they donot like their power rails swapped over.This can be done with a multimeter on the10V range. The correct voltage should be5 V.

Next, the inputs to ICI should bechecked. The voltage on these inputsshould be 5V when the switch is open,dropping to OV on pressing the switch.With no i.c.s installed, no I.e.d.s shouldlight. If any light, there is a solder bridgesomewhere on the board.

Once all i.c. sockets have been checkedfor power, switch the unit off and insertthe i.c.s, making sure they are the correctway round. Now switch on. If the buzzersounds, press RESET. Assuming that noi.c. is faulty, and no solder bridges remainundetected, the buzzer should stop, andno I.e.d. will light. Press a response unit'sbutton. The buzzer should sound, andtwo I.e.d.s will light up; one on theresponse unit pressed, and the other onthe main control board. Now pressanother response unit. It should have noeffect.

OPERATIONTo operate the unit in a quiz, each con-

testant should be given a response unit,plugged into the back of the main controlunit. Any number of units up to eightmay be plugged in, unused response unitsneed not be plugged in. Switch on, andpress RESET. This may not be necessary,but is a good habit. Now proceed with thequestions. After a response unit has beenactivated, it can be reset, whilst theanswer is given ready for the next ques-tion. At the end of a session, switch offand remove the response units.


EVERYDAYnews from the world o

HOME and AWAY WINSUNDERSEA LINKS

A£7.25 million contract for the world's first international opticalfibre undersea cable was signed recently by Sir George Jefferson,

Chairman of British Telecom.It was for a 122km cable, linking the UK and Belgium, to be made in

Britain by the submarine systems division of Standard Telephones andCables. Sir Kenneth Corfield, STC's Chairman, signed the contract forthe company.

The contract award means that, in two year's time, phone calls, com-puter data and messages will travel between Britain and continentalEurope as pulses of laser light along tiny strands of ultra pure glass asthin as a human hair.

The investment is shared between four countries. Half will be held byBritish Telecom International, and the balance by three Europeantelecommunications administrations-the Deutsche Bundespost ofWest Germany, the Belgian RTT and the Netherlands PTT.

The cable, capable of carrying nearly 12,000 phone callssimultaneously, will be laid by British Telecom's cableship HMS Alertin the spring of 1985. It will be buried to protect it against damage byshipping, in particular by trawling activities.

The new optical fibre cable willoperate in digital form, at speeds of upto 280 million bits (binary digits) asecond (Mbit/s). Digital operationuses on -off impulses to carry a varietyof information technology services, aswell as speech, along the same pathmore efficiently than present-dayanalogue transmission.

It offers considerable savings intransmission costs by using the ad-vanced form of optical fibre operationknown as singlemode transmission.This enables a single ray of laser lightto travel great distances along thefibre before regeneration at a repeater.

Technical NoteThe new UK -Belgium cable, the

fifth system between the two coun-tries, will contain three pairs of fibres.Each pair will work at 280Mbit/s-a

capacity of 3,840 64kbit/s circuits,giving a total cable capacity of 11,520circuits.

The system will use long -wavelength (1,300nm) singlemodetransmission. It will contain three sub-merged repeaters, each containingthree both -way optical regenerators.They will be installed at approxi-mately 30km intervals, to give a totalsystem length between terminal sta-tions of 122km.

British Telecom notched upanother major world first in opticalfibre communications.

In this latest achievement, theysuccessfully brought into service theworld's first 140Mbitls commercialoptical fibre link, using singlemodetransmission, between Luton andMilton Keynes.

FUTURE OPTICAL FIBRE SUBMARINE CABLE4.000 telephone circuits per fibre per 12,000 coasts per cable

C.: 6- r = -MODERN COAXIAL SUBMARINE CABLE4,000 telephone circuits

for UK

WORLD'S FIRST INTERNATIONAL UNDERSEAOPTICAL FIBRE CABLE

ROYAL PETThe microcomputer manufacturer, Commodore BusinessMachines (UK) Ltd, has become the first manufacturing com-pany to be granted the Royal Warrant of Appointment by HerMajesty The Queen for computer business systems.

General Manager of Commodore UK, Mr HowardStan worth, said: "As a high technology company with a grow-ing manufacturing and ancillary supplier base in the UK, weare delighted and honoured to receive the Royal Warrant ofAppointment to Her Majesty The Queen."


electronics

ALL-ROUND HOMEENTERTAINMENT CENTRE- FIDELITY SCORES A FIRST

VISUAL and audio home entertainment from one integrated system. Ithad to happen of course, and to London -based Fidelity go the

honours for being first in this field.The Audio Visual System 1600 announced in February incorporates

a I6 -in colour TV, a 3 -waveband tuner, a belt driven record player, astereo cassette deck, a 24 watt amplifier (12 watt per channel) andcomes with matching loudspeakers and a remote control.

The television has an optional spatial sound which electronicallyseparates the sound to create a stereo effect through the floor standingspeakers. The television can function as a video monitor for use withhome computers and video equipment. Either can be plugged directlyinto the 21 -pin Euro connector monitor socket at the rear of the systemto give crisper computer graphics and sharper reproductions on videorecordings. Fidelity is looking ahead, for this monitor socket will ad-ditionally suit cable and satellite systems of the future.

The expected inclusive retail price is around £400.Stereo (from tape, record or radio) and TV can be operated at the

same time, with video sound being available via headphones. Thus all

the family needs seem to be catered for by this stylish rack equipmentwith hinged glass door. The floor standing speakers are finished in adark rosewood effect.

Whether as a second set for the larger household, a natural for theteenager's room or a perfectly adequate main entertainment centre forthe smaller home - the AVS 1600 seems sure of a warm welcome bythe British public.

EE 0

The London based editorial team. (Left to right) Derek Gooding, Brian Terrell, Dick Hooper, Fred Bennett,Jackie Doidge, Peter Loates, Roy Palmer, Graham Hodgson and Dave Barrington.

From the dizzy heights of the 21st floor, King'sReach Tower, with panoramic views of Westminsterand the meandering Thames in old London Town,Everyday Electronics moves to the 2nd Flooroffices by the quayside at Poole Harbour in Dorset,with an elevation a mere masthead above sea level.

As from next month Everyday Electronicseditorial department will be based at Poole, Dorset.The editorial team currently producing our com-panion magazine Practical Electronics in Poole, willthen be responsible also for Everyday Electronics.

Mike Kenward, Editor of Practical Electronicswill be editor of both magazines. As many readerswill know, Mike was assistant editor of EverydayElectronics from its launch in 1971 until 1977. Hetook over as editor of Practical Electronics fromFred Bennett when PE moved from London.

The existing PE editorial team will be augmentedto meet this new situation. Dave Barrington willmove from London to take up the post of AssistantEditor/Production. Fred Bennett, present editor ofEveryday Electronics, will be Consultant Editor andwill remain based in London.

All other members of the present EE team areseeking pastures new.

ADVERTISEMENT DEPARTMENTEarlier this year Advertisement Manager Roy

Smith handed over to David Tilleard who now hasoverall responsibility for both titles. He is assistedby Richard Willett who continues as AdvertisementRepresentative for Everyday Electronics.

EDITORIAL TEAMOf the present EE editorial team Brian Terrell

and Peter Loates are "founder members", workingon this publication continuously since issue numberone. In 1977 the following transferred to EE: DavidBarrington and Derek Gooding (ex -Practical Elec-tronics); and Roy Palmer (ex -PracticalHouseholder). More recent recruits are: JackieDoidge, Graham Hodgson and Richard Hooper.

The disbanding of this team has been a con-siderable wrench to all concerned and particularlyso for the longer serving members. The old teamnow bid farewell to their readers and hand over totheir colleagues at Poole confident that readers'needs and interests will be in safe hands.


RADIOWORLD

l/111\"4141.1..

MUM 2/111111W11111111111111111111M1111111111111111WMIN WIWI/ IMO/\WIMP WI/ mu,-wry mu/ yr

BY PAT HAWKER G3VA

ReliabilityOver the years we have come to expect a

great improvement in the reliability of con-sumer electronics of all types. Perhaps themost dramatic has been in colour televisionreceivers; with an improvement of from anaverage of about four faults per year, withthe early dual -standard sets, to an averageof only about one fault in three years incurrent models.

Murphy's Law unfortunately seems tomean that there are still a few "rogue"models that keep service engineers busy. Arecent Which? report, however, suggeststhat the differences between brands areunlikely to be big enough to worry about-regardless of whether manufactured inEurope, or Japan the country that a decadeago did so much to improve the reliability ofmass-produced equipment.

Today, relatively few faults are due tobasic electronic circuit design, whilesemiconductor devices do not have theinherent failure mechanism of thediminishing cathode emission of thermionicdevices. Though it should not be forgottenthat for such specialised applications assubmerged cable repeaters, the Post Officeat their research centre at Dollis Hill in the1960s developed valves designed toprovide continuous operation for at least 20years.

Although semiconductor devices do notwear out, this does not mean they are im-mortal. Their working lives can be broughtto a sudden end by over -voltage transients,although good circuit design can provideprotection against these events. Protectioncircuits may not themselves always provesatisfactory and for some professionalequipment it may be necessary to ask "dowe need a protection circuit for the protec-tion circuit?"

Dust -free manufacture of materials isone of the major reasons for improvedreliability. But semiconductors can still failor change characteristics from suchmechanisms as electro-migration; that is,the movement of aluminium atoms along aconductor caused by collisions with theconducting electrons to the extent whereeventually this results in an open -circuit.

Also there is dielectric breakdown; forexample, due to defects in the very thingate insulator regions of metal oxidesemiconductors, and that old enemy corro-sion, due to absorbed moisture on the chipsurfaces. Contamination of materials duringmanufacture; for example, oil contamina-tion from machines may not show up formonths or years.

Q -FaxFor over a decade electronic device

manufacturers have aimed at what they call"zero defects" and published life -test data,

though these figures may be averaged overdifferent factories in different parts of theworld, and have to be viewed with caution.

The UK's largest manufacturer of elec-tronic components, Mullard Ltd., hasrecently introduced in its factories a Q -Fax("quality facts") system to keep the work-force informed on results, defects andtargets. A 380 -page teletext -type Q -Faxsystem has been installed at Simonstone,Lancashire where component parts forcolour picture tubes are made. A rotatingsequence of six -pages is displayedautomatically, but staff are encouraged tocall-up any of the pages.

After three months' operation, Mullardclaim the system, by improving com-munication between management and theshopfloor, is resulting in a steady decreasein component defects. The idea raises theage-old question, does this type of informa-tion technology have lasting effects oncethe novelty has worn off?

I recall one major Japanese manufac-turer has another approach. Workers areencouraged regularly to beat -up with sticksdummies representing the management!

In the end it all comes down to findingways in which people can be encouraged toexercise continuous care and skill over longperiods-and to ensure that dust -free reallymeans dust free.

Radio CallsignsIt is now some 50 years since every radio

broadcasting station on the medium- orlong -wave bands had its own callsign. Forinstance, 2MT for the Writtle experimentalstation; 2L0 for London; 6ZY for Man-chester and 5XX for the Daventry long -wave station.

This practice was dropped in Europe inthe early 1930s, but continues, even today,in the USA, with many thousands of three -or four-letter callsigns (each beginning W orK) and with suffixes AM for amplitude-

- CB ChangesThe new conditions attached to British CB

licences since 1 February seem unlikely tohave any major effect on this service, par-ticularly since there does not seem to be mucheffort devoted to enforcing the regulations orto checking on whether only the 280,000licence holders are using 27MHz transmitters.though there have been a lot of prosecutions.

No new licences will be issued to anyoneunder 14 years, but there is no restriction onyounger people using transmitters undersupervision. It will be possible to use home -constructed aerials with loading coils in themore effective position two-thirds of the wayup the element.

modulated medium -wave stations; FM forthe VHF frequency -modulated stations; andTV for television stations.

With so many stations on the air it is notsurprising that the owners value greatlycallsigns that are easy to remember. Par-ticularly those that identify with city ornetwork such as WNBC and WNYC.

Callsigns are issued by the Federal Com-munications Commission (FCC) thoughthe call -letters are often suggested by theapplicants. As part of the current "de-regulation" process FCC has made it clearthat it no longer expects to be involved inthe call -letter disputes that arise.

The FCC will no longer officially insistthat all call -letters should be in "goodtaste", although FCC's Mass Media Bureaustaff have warned the commissioners that itwould not be proper for an agency of thefederal government to issue "clearlyobscene or indecent" callsigns. The com-missioners however believe that if a com-munity objects to a callsign it can "makeits displeasure known to the station or theadvertiser".

In the days when the Post Office used toissue amateur radio callsigns there were anumber of three -letter combinations listedas "not to be issued". Even so, I can thinkof one or two people who were saddledwith embarrassingly explicit callsigns!

Legal TransceiversThe Department of Trade and Industry

have recently confirmed to the R.S.G.B.that the installation and use by short-wavelisteners of two-way transceivers is not incontravention of the existing WirelessTelegraphy Acts. This is provided, of course,that the equipment is used only to receivesound radio broadcasts from authorisedbroadcasting stations or to receivetransmissions from licensed amateur radiostations.

This ruling shows how difficult it is tobring prosecutions for "pirate" operation ofunlicensed transmitting equipment underthe existing law since it is necessary alwaysto prove use of the equipment. Whetherthis will remain true when the currentTelecommunications Bill (including the PartVI amendments to the Wireless TelegraphyActs), is enacted, is an interesting questionsince this would seem to make possibleprosecution of persons in control of or inpossession of specified equipment.

There is also, of course, the point thatmany people buy equipment while they areh.f. listeners with the genuine intention ofusing the transmitting facilities only whenthey obtain a licence. But for some thetemptation proves too great!

The ban on the playing of music andre -broadcasting radio programmes has alwaysexisted but is now made more explicit. Thelicence now highlights the recommendationthat Channel 9 should be used only for callsrequesting assitance and other emergencies.

What may produce greater changes notonly in "pirate" CB but also "pirate" broad-casting and pirating on h.f. and on amateurbands is the Telecommunications Bill when (orif) it finally reaches the Statute Book, follow-ing the delay caused by the General Electionand the political controversy about privatisa-tion of British Telecom.


N000EXPERIMENTERSPSU...All serious constructors require a reliable power supply. Thisunit fits the bill admirably with a switchable output rangingfrom 2-12V in steps of 1V. A novel feature is the use of apower op/amp which provides the output current up to amaximum of 325mA. The output is short-circuit protectedand is accurate to within 0.1 V.

VARICAP AM RADIOIn this a.m. receiver the principle of the variable capacitancediode is employed as the tuning medium. The full medium -wave hand is covered, the output is designed for a crystalearphone.

SIMPLE LOOP/BURGLAR ALARM

This battery operated alarm system has been designed around the wireloop principle often seen in shops to protect easily stolen articles such asradios. The design does, however, have many other uses since the alarmsounds for a preset period once the loop is broken.

EVERYDAY

ELECTRONICSand computer PROJECTS

MAY 1984 ISSUE ON SALE FRIDAY, APRIL 19


MULTIPURPOSEIHTERFACE FOR

cornPUTERS

M. P. HORSEY

SOFTWARE APPLICATIONS FOR MODEL RAILWAYCONTROL USING THE RM380Z AND VIC-20

HE unit described here is designed toI interface to the user port or parallel

printer port of a micro. Details of its usewith the Research Machines 380Zcomputer-popular in schools-and theVIC-20 are given. The circuit is expectedto work with most other machines, sinceit uses the standard data outputs as re-quired by a parallel interface printer.

The unit has eight separate channels tocontrol eight devices. It was built with amodel railway in mind, and channels oneto four will sink 100mA-suitable forl.e.d.s, or small bleepers, and so on.

Channels five and six will sink 500mAto 1A, depending on the heatsink used onthe power transistors. These outputs willdrive small motors in train -sets, robots,and the like. Channels seven and eighthave relay outputs, and provide a varietyof uses, including controlling the polarityof the motor outputs, to enable the motorto reverse.

The unit will therefore power twotrains, forward and reverse, and providefour more low current outputs for signalsand other accessories.

Considerable economies may be madeif fewer outputs are required. For exam-

ple, for just one train, only the compo-nents associated with channels five andseven will be needed. The simpleprograms included, will enable the speedand direction of a train to be computercontrolled, via channels five and seven.

OPTICAL ISOLATIONThe interface power supply is totally

isolated from the computer data andpower outputs by means of an opticalisolator chip. This ensures that should a

disaster occur to the interface, the com-puter cannot be damaged. Each l.e.d. inthe interface chip requires a sink currentinto the computer of about 7mA. Thuswith all computer data outputs low, amaximum current of 56mA is requiredfrom the 5 -volt supply from the com-puter.

COMPUTER DATA OUTPUTSThe eight data outputs are normally

numbered 0 to 7. This may cause someconfusion since channel 1 will be drivenfrom data 0, channel 2 from data 1, andso on to channel 8 from data 7.

Each computer data output is nor-mally low (that is, nearly OV). Whena suitable number is POKEd to theappropriate address, the required dataoutput will go high (nearly 5V), and thisin turn switches on the chosen outputfrom the interface.

SOFTWARE CONTROLThe combination of data outputs re-

quired, is controlled by POKEing asuitable number, determined in thefollowing way:

The number POKEd must be conver-ted into an 8 -bit binary number. If theright-hand bit is a zero, then DO will below. If the right-hand bit is a one, then DOwill be high. If the next bit is a zero, thenD I will be low. The examples in Table 1should clarify the situation.

In a computer program, the commandPOKE A,B is used to POKE the numberB (as described above), into address A.Different computers will require differentaddresses for A, and some computersmay employ an alternative to the com-mand POKE (for example, the BBC com-puter).

CIRCUIT DIAGRAMThe complete circuit diagram is given

in Fig. I.Each of the eight channels work in a

similar way. Consider channel 1. WhenDO is low (nearly OV), current from thecomputer 5 -volt supply will flow viacurrent limiting resistor R I, through theinternal l.e.d. in the quad opto isolatorchip ICI, and into DO. Channel 1 internalphoto -transistor will turn on, and thevoltage at the base of transistor TR 1 will

Table 1. POKEing data into the port.

POKEdnumber

(decimal)

Equivalentbinary

number

Data outputs

D7 D6 D5 D4 D3 D2 D1 DO

01

23

166480

00000000000000010000001000000011000100000100000001010000

lowlowlowlowlowlowlow

lowlowlowlowlowhihi


lowlowlowlow

hilow

hi



lowlow

hihi

lowlowlow

lowhi

lowhi

lowlowlow


be near zero. Thus TR I will be turned offand no current will flow into its collector.

If the decimal number 1 (binary00000001) is POKEd to the computerport, then DO will go high (nearly 5V),and no current will flow through the 1.e.d.The internal photo -transistor will turn off,and the voltage at the base of TR1 willrise-due to the current flowing throughresistor R9. Transistor TR 1 will thereforeturn on, and current will flow from the12 -volt supply, through the load connec-ted to OUTPUT 1.

Channels 1 to 4 work in an identicalway. Channels 5 and 6 are similar, exceptthat the emitter of the BC 184L transistoris connected to the base of the powertransistor type TIP4 I A. Thus a muchlarger current can be controlled.

Channels 7 and 8 drive relays, whichcan in turn control a variety of options-even mains circuits if suitable precautionsare taken.

Diodes D I to D8 protect their respec-tive transistors against any back-e.m.f.voltage spikes caused by inductive loadssuch as motors and relays.

SHORT CIRCUITSIt should be noted that a 2 -amp ther-

mal circuit breaker, CB 1, is included inthe design. This is rather large for modelrailways, and in this application, a lowercurrent circuit breaker may be considereddesirable. Alternatively, the circuit couldbe powered from a train -set controller, inwhich case the cut-out switch on the con-troller will provide the necessary protec-tion.

POWER SUPPLYA fairly conventional power supply cir-

cuit is included, and a transformer can beselected to suit the current requirements

Fig. 1. Complete circuit diagram of the Microcomputer Interface.

!di IL074

RI .170l1 11

00

02 470(1 31

41 k

02

C3

04

,4 4

a

2V

541/18

TR18118.11.

RIO1040

94148

I4. 2

TR2

1114148

TR3Brim_

12

411

04194148

4( la 1 eel71

I 1/k

1C2 11074

2

R6 4700

R7 4700

61 k

TR48C1841

56

14

85712011

TR5911841

194148

TR6

'OA

RIBon

TR7BC1841

414

TR8TIP41A

Oka44148 IK1r °

TR9911841

CO3 +

4CC)} OUTPUT 2

5 cA

OUTPUT 3

7

00Boo} OUTPUT/

9 0!).

OUTPUT S

cctco

OUTPUT 6:200

TB2

RLAI WN.C.RL.A2 d1.0.

RIBS

RIB 4 03.0.

RlB1 N.C.

RLB2 .

A 0 CX:Y

R183

RLE14

IXY

"L5

COMPONENTSResistors

R1-8 4700 (8 off)R9-16 10k12 (8 off)R17,18 12052 2W (2 off)All +W carbon ±5% except wherestated otherwise

CapacitorsCl 0.1µF polyester type

C280C2 4700µF 25V elect. axial

See

SemiconductorsIC1,2 ILQ74 quad opto-

isolator (16 -pin d.i.l.)(2 off)

TR1-5,7, BC184Lnpn silicon9,10 (8 off)

TR6,8 TIP41A npn silicon(2 off)

D1-8 1N4148 or 1N4001(8 off)

D9-12 WO 05 1A 50V diodebridge

MiscellaneousT1 mains primary/9V 2.2A

secondaryS1 on/off toggle mainsCB 1 2A circuit breakerLP1 panel mounting mains

neonFS1 1A 20mmR LA,B 12V d.c. 205 coil with

double -pole change-over contacts(RS 349-658) (2 off)

TB 1,2 12 -way 2A screwterminal blocks(2 off)

Printed circuit board: single -sided 100 x 160mm, EE PCBService, Order code 8404-01;plastic case 215 x 130 x 83mm;3 -core mains cable; rubber grom-met; mains cable gripper; 6BA fix-ings and 10mm long spacers; i.c.sockets, 16 -pin (2 off), p.v.c.covered connecting wire; multi -core cable (9 -way); plug to suitcomputer port; 20mm panelmounting fuseholder.

Tapage 231

Approx. costGuidance only E26

CBI 2AZ.9V

O

SI


O 0

O 0

EE 8 4 04 -01

O 0

Fig. 2. The actual -size master pattern for the Multipurpose Interface p.c.b. This board is available from the EE PCB Service,Order code 8404-01.

DO-DI

-9V A.G. RL4

RLA2

ti

111111[1111111111111111111

C2

11

RLA

Cl

,

C

RLA3RLBI

RLA4RLB2

RLB

Of1111111'sCOIL

0,"

C

0

CI

(-)110

a

RLB3

RL84

a06

D5

IRS TR7 TR9 TRIO IC2e

- III 1111 11,

b b b bI lirD6

f0;i1 f0/ il i ::TRB TR6 IP RS 16 DIF4

R13 R14 D7 RIS 08 R16

D4 R12 03 R11 02 R1O DI R9 I D3

:1'1

IIWTr02

Ill

D1

ICI

6I 1

Rd R3k k k k

I

b b b°I

c,4 cib ci c I PORT (INPUTS)I DO TO COMPUTER

e e e le ift i 11171-5V1R4 TR3 TR2 TR1

R17 R18

O 11.2111,4 TB//611 TB2/8 ITAIO TI1/12 ITBI/1\ IBM()

TB2/I 182/3 TB /5 TB2/7 TB2/9 TB2/1I TB1/11 TBI/9I-OUTPUT 7 OUTPUTSOUT 6 --I-OUT 5-1

1,40P.`:44WAVILVW7

0.6.34M;

R8

RI

IT81/8 MI/61181/4 TBI/2

TI31/7 181/5 TBI/3 TB /IOUT 4 OUT 3 OUT 2 OUT I

D7

.."111F05

Fig. 3. The layout of the components on the topside of the p.c.b. with full interwiring details to case mounted components andcomputer output port.


envisaged. Note that the 9 -volts a.c.transformer output is raised to nearly 13 -volts d.c. when connected to a bridgerectifier (D9 to D 12) and smoothingcapacitor C2, but the maximum a.c.current is reduced by a factor of x 0.62.Thus if the two 9 -volt windings of thetransformer listed are connected inparallel the maximum a.c. current is2.2A. This is reduced to a maximum of2A using the thermal cut-out switch in-dicated, but the maximum d.c. currentavailable is 2A x 0.62 = 1.24A.

CONSTRUCTIONThe prototype was constructed using a

printed circuit board measuring 160 x100mm. The actual -size master p.c.b.pattern is shown in Fig. 2. Provision hasbeen made for all eight channels. If lessare required omit the relevant compon-ents. This board is available from the EEPCB Service, Order code 8404-01. Beginby drilling the holes required to anchorthe p.c.b. to the case.

Next, assemble the p.c.b. according toFig. 3.

Solder in the i.c. holders, wire links andresistors, noting that resistors R17 andR 18 are 2 watt types.

The diodes must be fitted with thecorrect polarity (that is, the right wayround), and care must be taken with theBC184L transistors, to ensure that theleads are correctly orientated. If BC 184(without the L) transistors are used, notethat the leads will be in a different order.

The fully assembled p.c.b. ready for wiring up.

The power transistors may be fitted tothe circuit board as shown, and no heat -sink is necessary if small model railwaymotors are driven. For larger currents,heatsinks should be secured to the metalplates of the transistors.

Alternatively, the power transistorsmay be fastened to a sheet of metal (orthe case-if made of metal), and flexiblewires used to connect them to the p.c.b. Ifboth transistors share one heatsink, usemica washers and insulating bushes.

The relays specified will fit directly to

the p.c.b. Other relays may be used withdifferent pin -outs. These would be moun-ted off -board and connected to the boardusing flexible wires.

CASEA sturdy plastic box measuring 215 x

130 x 83mm was used to house the inter-face and power supply. Drill thenecessary holes for the mains lead, fuse,mains switch, cut-out switch, neon andtransformer. Drill holes in the lid of thecase for mounting the stripboard, and

CBI

OV

SECONDARY

TO 260VA.C. MAINS

Fig. 4. Interwiring of the case mounted components fitted in position.


Shows the case mounted components fitted and interwired.

MODEL RAILWAY CONTROLSOFTWARE FOR RM380Z

10 REM"TRAIN5"RML380Z20 LET P=&FBFF:Q=030 PUT12:GRAPH40 PLOT 30,55,"T R A I N"50 PLOT 30,52,"*********.60 PLOT 0,40,"You may select the followin9:"70 PLOT 10,34,"F:forward R: reverse 8: stop80 PLOT 22,28,"Speed:type 1 to 9"90 PLOT 0,22,"100 PLOT 0,16,"Present Conditions:"110 PLOT 5,10,"Direction:"120 PLOT 50,10,"Speed:"130 PLOT 0,2,"140 IF 8$=""THEN LET B$="STOPPED"150 IF 0=0 THEN A=0160 LET C$=STR$(A)170 PLOT 27,10,8$180 PLOT 62,10,C$190 REM TRAIN RUNNING LOOP200 LET A$=GET$(0)210 IF 0$<>""THEN GOTO 310220 IF A>8 THEN 270230 FOR X=1 TO 10-A240 IF B$="REVERSE" THEN POKE P,64 ELSE POKE P,0250 NEXT X260 IF A<1 THEN 200270 FOR X=1 TO A280 POKE P,Q290 NEXT X300 GOTO 200310 REM SELECT DIRECTION & SPEED320 IF A$="F"OR A$="f"THEN 3$="FORWARD":LET Q=16330 IF A$="R"OR A$="r"THEN B$="REVERSE":LET Q=80340 IF 0$="S"OR A$="s"THEN B$="STOPPED":LET 0=0350 LET A=VAL(A$)360 GOTO 150

Table 2. User port pin assignments

AM 380Z VIC-20

Pin no. Function

5 DOO6 D027 D048 D069 +5V

18 DO119 D0320 D0521 D07

Pin no. Function

2 +5VC DO

D D1E D2F D3H 04J D5K D6L D7

MODEL RAILWAY CONTROLSOFTWARE FOR VIC-20

13 REM ***************1 REM 4441 4441

2 REM *44 ADAPTED *44:3 REM #$* *444 REM 0* FOR THE 44*5 REM 44* *4*5 REM 4411 VIC20 41**

7 REM 4* 448 REM *4 BY J.HALL 4*9 REM +4 Ye*

10 REM*********#*.114.15 POKE37138,25520 LETP=37136:0=030 PRINT"D"'POKE36879,15740 PRINT"401 TRAIN"50 PRIATA *iti*#+"

60 PRINT"MA YOU MAY SELECT THE70 PRINT"AAM M F = NFORWARD"72 PRINT"A M P = NREVERSE"75 PRINT"A S S= NSTOPPED"80 PRINT"XM SPEED =85 FORY=0T08000,NEXT90 FORT=38T0150POKE35881,T:NEXT95 POKE35879,29100 PRINT"UMPPRESENT CONDITIONS "

105 PRINT" ZIPS****** 141P114+44*"110 PRINT"AWINDIRECTION:"120 PRINT"ADMil SPEED:"130 FORT=1601-038STEP-1:POKE36881,T:NEXT140 IFB$=""THENLETBWM5TOPPED"150 IFO=OTHENA=0160 LETC$=STR$(A)170 PRINT"MSQMOMSPDSMNIPMSS$180 PRINT-00101KKOSIOMMIMOMPIPPMS. 05.190 REM ++TRAIN LOOP**200 OETA$210 IFF4(>""THENGOT0310220 IFF08THEN270230 FORX=17010-A240 POKEP,V250 NEXT260 IFA<1THEN200270 FORX=1TOA280 POKEP,0290 NEXTX300 GOT0200310 REM 444SELECT***$20 IFF4="F"THENB$="IFORWARD":9=16:V=0330 IFA$="R"THENB$="UREVERSE":0=80:V=64340 IFA5.="S"THENB$="NSTOPPED":LETO=0:V=0350 LETA=VAL(A$)360 0070150

READY.

A FoLLowiNoJr


The assembled unitshowing terminal blocks

in position on the prototype.

terminal blocks, and holes for thecomputer lead, and output connections.Connect the data input cable to a suitableconnector to mate with the socket on thecomputer. Fig. 5 in conjunction withTable 2 gives details.

Care must be taken with the clearancebetween the p.c.b. components and thetransformer. For added safety, thetransformer was mounted with its mainsconnections the opposite side from thep.c.b.

OUTPUT TERMINAL BLOCKSTake care to use wire capable of carry-

ing the required current to the outputterminal blocks. The connections tochannel 7 (relay 1) are shown to permitforward/reverse motion of a motor drivenfrom channel 5. This enables the interfaceto be used with the programs listed below.

MOTOR CONTROLThe speed of the motor may be con-

trolled by rapid switching on and off ofthe appropriate power transistor, andproviding the program loop which con-trols this is quite short, the resultsachieved can be very good. The directionis controlled by a relay, such that if therelay is switched off, the motor directionis forward, but if the relay is turned on,the motor direction is reversed.

COMPUTER PROGRAM FORMODEL RAILWAY

The variable P is used to select theappropriate output address, and Q is thenumber to be POKEd to that address.

The program plots some instructions onthe TV monitor, and indicates the presentconditions (that is, what the train shouldbe doing).

Care has been taken to keep the speedcontrol loop short, to ensure smooth run-ning.

Another precaution is, that if the direc-tion is changed from FORWARD toREVERSE (or vice versa) the speeddrops to zero and has to be typed again.This ensures that the motor is not undulystrained.

SETTING UP AND TESTINGDouble check construction and inter -

wiring. Do not connect the interface tothe computer at this stage.

To test the interface, begin byswitching on the power supply. Connect avoltmeter to the +12V line (+ve terminalof C2), and connect its negative lead tooutput 1. The voltmeter should readabout 12 volts. Repeat this procedure foroutputs 2 to 6. Observe the relays; theyshould be on, that is, the n.o. contactsshould be closed.

If further testing is desired-beforeconnecting to the computer, a 5 or 6 voltsupply may be connected to the +5V sup-ply line, and the negative of the supplyconnected in turn to each data input. Avoltmeter connected as before shouldindicate a zero reading when the ap-propriate data input is negative.

Finally, switch off the interface unit,and connect it to the computer. Switch onthe computer and interface. The initialdata output will be zero (binary00000000). Thus each output should be

"off". This may be checked with avoltmeter connected as before.

With the Research Machines 380Zcomputer, typing the BASIC command:POKE&FBFF,1 should produce thebinary number 00000001 to be output,and hence DO will go high, causing thevoltmeter on output 1 to read 12 volts.POKE&FBFF,2 will cause the next out-put to switch on, POKE&FBFF,4 thenext, then 8,16,32,64,128 will cause out-puts 3 to 8 to switch on respectively.

Finally, try out the program listed witha small motor or model train. Designingmore complex programs to use with theinterface is where the fun really begins.

CONNECTING TO THE VIC-20Like the Research Machines 380Z, the

VIC-20 computer also provides the re-quired data outputs, but at address37136. The VIC-20 also requires thenumber 255 to be POKEd at address37138, in order to set the lines as outputs.

Bearing this in mind, the VIC-20 maybe connected to the interface unit using a2 x 12 -way 0.156in p.c. edge connector,the connector should be wired to suit thesocket shown in Fig. 5 and Table 2.

Converting the train program for usewith the VIC-20, required numerousmodifications, as this computer has noPLOT or PRINT@ command. The largedisplay characters also required programmodification to display the required infor-mation.

The finished program does performexactly the same task as the onedesigned for the Research Machines380Z computer.

Fia. 5. Location and pin numbering of suitable outlet sockets on the RM380Z and VIC-20 micros.

1 2 3 4 56789 10 11 12

A BCDEFHJ KLMN


URING the past few years prior to theD establishment of a Citizen's Bandradio service in the UK, there was muchdebate concerning the best modulationsystem for such a service. Many argu-ments were put forward either in favouror against single sideband (s.s.b.), fre-quency modulation (f.m.), or amplitudemodulation (a.m.), depending on personalviewpoints. The system that was finallychosen for CB radio was narrow bandfrequency modulation (n.b.f.m.).

In this article we shall now take acloser look at this mode of transmissionand compare it with a.m. in the context ofamateur radio, CB radio and point-to-point communications. Broadcasting hascertain special requirements and features,and does not come into the present dis-cussion.

First we must consider the major dif-ference between the two systems and thatis in regard to the actual method ofmodulation of the carrier wave. Fig. 1

shows an a.m. signal which consists ofthe modulating audio signal and r.f.carrier being added together in a way thatcauses the amplitude of the carrier tochange. As the audio and carrier frequen-cies are different there will be phase dif-ferences between them and when the twosignals are in -phase their amplitudes willadd, and when they are out -of -phase theiramplitudes will subtract, thus producingthe amplitude modulated carrier wave inFig. 1(c). Note that the actual frequencyof the carrier wave is constant.

With the f.m. system, the modulatingaudio is added to the carrier in such away that its frequency varies but its am-plitude remains constant. Fig. 2 showshow this occurs. This change in fre-quency is called the deviation of thecarrier and is the equal to the modulationof the a.m. carrier wave.

OVER MODULATIONNow with the a.m. system it is possible

to over -modulate the carrier, Fig. 3 showswhat happens. If the amplitude of theaudio modulating signal is greater thanthe amplitude of the carrier it will still in-crease the overall amplitude when theyare in -phase but as it cannot reduce thecarrier to less than zero when they areout -of -phase the carrier is "cut off" forthe duration of the time that the audio istrying to take the carrier below zero. Thisresults in severe distortion of the carrierand "splatter" into nearby channels adja-cent to the transmitter frequency.

In theory it is not possible to over -modulate an f.m. carrier as when theaudio modulating signal is increased inamplitude it simply causes a larger shift inthe frequency of the carrier. This wouldat first seem to be the answer to manyproblems, but, in practice there are otherfactors which set the limit to how muchdeviation can be applied.

First the actual tuned circuits of thetransmitter will limit the amount of devia-tion. These have to have a response that

is even, over the total amount of fre-quency shift, otherwise as the signal shiftstowards the edge of the selectivity of thetuned circuits there will be a reduction inthe output, Fig. 4. This would mean thatamplitude modulation was being in-troduced. Therefore the total deviationmust be kept to within the capabilities ofthe transmitter tuned circuits (and aerial)bandwidths.

RECEIVER BANDWIDTHAlso there is the question of receiver

bandwidth. If the deviation of thetransmitter is greater than the receiverbandwidth then the signal would passoutside the receiver passband and be lost,or at the very least again have amplitudevariations added to it (Fig. 4). For normalamateur and CB equipment this max-imum deviation is limited to around 5kHzand this is equal to the 100 per centmodulation of the a.m. system. Withoutgoing into the technical reasons, this alsomeans that a similar number of stationscan be spaced into a given frequencyband. A wider deviation would reduce thenumber of f.m. stations in a given band.

DETECTION SYSTEMSThe next major difference between the

two signals is in the detection system usedin the receivers. The a.m. detector has torespond to amplitude changes in the in-coming signal and this means that it will

Fig. 1. Amplitude modulation, showinghow the two signals are added in- orout -of -phase to produce the finalmodulated carrier.

lo)

(b)

(c)

1

Fig. 2. Frequency modulation. Note that thefinal carrier is constant in AMPLITUDE.

411111,

11F 11111F

Fig. 3. Over -modulated carrier wave.Note the gaps in the carrier where themodulating signal has tried to reducethe amplitude below zero.


NOISE PULSES

I

NOISE PULSES

R.F. STAGE

R.F. STAGE

I.F. STAGE

i11,111!

LINEARAMPLIFIER

RESULTANT OUTPUT AMPLITUDE

LIMITERSTAGE

(a)

DETECTOR

RECOVEREDAUDIO PLUSNOISE

APAMPLITUDE PULSESREMOVED BYLIMITER

SATURATED LEAMPLIFIER

MAX.

MIN.

THIS PART OF INPUT SIGNAL ISOUTSIDE THE PASS BANDOF THE TUNED CIRCUIT

CONSTANT AMPLITUDEINPUT SIGNAL

(b)

DISCRIMINATOR

AUDIO 0/P

RECOVEREDAUDIO NONOISE -

AUDIO 0/P

Fig. 5 (above). Showing how noise pulses areremoved by the f.m. limiter stage and prevented frombeing passed on to the output. On a.m. the detectorresponds to noise pulses as if it were a normal am-plitude modulated signal and passes them on to theoutput.

Fig. 4 (left). Showing how a signal of constant am-plitude, but frequency shifted due to modulation, canbe moved outside the tuned circuit's passband andcause resulting amplitude modulation of the signal.

also respond to amplitude interferencesuch as, car ignition systems, switching,motor commutators, and so on.

The f.m. detector is designed to res-pond to changes in frequency of the in-coming carrier and can be made insen-sitive to amplitude changes. Therefore itis far less likely to respond to amplitudesources of interference like car ignition.This at once makes it a better system foruse in mobile installations, as it isautomatically immune to impulse noises,and is many hundreds of times betterthan the a.m. system.

Fig. 5 shows a carrier with impulsenoise on it and how it passes through thetwo types of receiver.

SIGNAL AMPLIFICATIONThe next main difference between the

two types of receiver is the way the stagesamplify the signal. With the a.m. system,the changes in amplitude must be pre-served and this means that any amplify-ing stage must not distort the signal. Inorder for this to happen arrangementsmust be made to reduce the amplificationon strong signals so that the stages arenot overloaded. This automatic gain con-trol (a.g.c.) is an important design featureof all a.m. receivers.

On f.m. we are not concerned with am-plitude variations but only the changes infrequency, and in fact the stages can beallowed to saturate and this will preventamplitude changes from reaching the f.m.detector, further improving the immunityto impulse noises and the like. It also sim-plifies the design of the amplifying stages.A further advantage is that once satura-tion (limiting) has been reached the audiooutput from the receiver is constant.

On a.m., if you are listening to a weakstation with the volume control turned upand a strong local comes on, you will getdeafened! On f.m. both signals would bethe same volume-although in practiceonly the stronger one would be heard, dueto the capture effect (more about thislater).

Fig. 6 shows a typical input outputcurve of an f.m. receiver. Note the rapidreduction in noise as the signal strengthincreases. Compare with the a.m. curveFig. 7.

A good f.m. receiver will be designedso that even very weak signals fullysaturate (limit) the i.f. amplifier stages,which in practice means that all signalswill be at the same output volumeirrespective of their actual strength. Thisis why changing the transmitter power

has no effect whatever on the receivedsignal once it is strong enough to reachthe limiting level, unlike a.m. where in-creasing the transmitter power willproduce a change in output at thereceiver.

CAPTURE EFFECTWith a f.m. receiver the detector or, to

give it its proper name, the discriminatorwill "capture" a signal which is on thesame frequency but stronger. The betterthe receiver, the less difference there willbe between the two signals in strengthbefore the receiver captures the stronger.

For example, if you are listening to saya fixed station of a given strength and amobile station is on the same frequency,at first you will only hear the fixed sta-tion. Then quite suddenly as the mobilestation comes into range its signal willbecome slightly stronger than the fixedstations and the receiver will "capture it".The result is a sudden switch from onestation to the other. The better thereceiver the more abrupt the change -overwill be. There is no warning, it just hap-pens. This is unlike a.m. where you canhear the weaker signal building up under-neath the stronger until it is strong


0

Cg 20

t 40

0<60

80

AUDIO OUTPUT

NOISE LEVEL

I I 1

0 1 10 100 1000 10,000R.F. INPUT SIGNAL IN MICROVOLTS

Fig. 6. Typical f.m. receiver input/output response.

0

Pa 20

a.a.

'5 40

00

60

80

NOISE LEVEL

I I I I I

0 I 10 100 1000 10,000R.F. INPUT SIGNAL IN MICROVOLTS

Fig. 7. Typical a.m. receiver output/input response. Responseswill vary from design to design with the better receivers havinga more constant output and quicker reduction in noise.However, on a.m. there is not an equivalent effect to the "cap-ture" effect of f.m.

enough to cause severe interferencebefore taking over.

This is one of the reasons why it ispossible to "break in" on an a.m. contactbut not an f.m. one. If you tried to breakin on an f.m. contact you would just notbe heard unless your signal was strongenough to be captured by the receiver.

RESIDUAL NOISENow this capture effect also applies to

noise. When the signal you are trying toreceive drops below the residual noiselevel the receiver will capture the noise inthe same way as it would a strongersignal. The result is that f.m. signalswhich are getting weaker will suddenlydisappear into the noise, whereas on a.m.you can often "copy" them right downinto and sometimes even below theresidual noise level. At this thresholdpoint an increase in f.m. transmitter7

power can make an improvement inreception which is quite dramatic due tothe receiver again capturing the strongersignal.

On the a.m. system an increase insignal of 3dB (double power) will notmake much practical difference to thereceived signal although of course it willimprove it to some extent. On f.m. thesame change in power at the capturepoint can make all the difference betweena signal being 100 per cent copy and notbeing heard at all, assuming of coursethat the receiver has a good capture ratio.

CAPTURE RATIOThis is normally quoted in dBs and the

smaller the figure the better. The figurequoted is the difference in power requiredbetween two signals on the same fre-quency before the receiver will capturethe stronger.

For example, if the receiver is quotedas having a 3dB capture ratio then onesignal would have to be twice the powerof the other. If the receiver was quoted as0.5dB (modern hi-fi stereo receiversachieve this) then the power change isonly 1.12 times. Note here that we arereferring to received power and nottransmitter power.

The effect of this "capturing" of thestronger signal is why it is possible forf.m. stations that are in different localitiesto have "nets" on the same frequencywithout mutual interference. On a.m.there would be a hetrodyne whistle in thebackground all the time.

Next month we shall consider some ofthe actual circuits used and their dif-ferences, as between the f.m. and a.m.systems.

PRACTICAL.iioNics

FREE:LOGIC DESIGN CARD

PROJECTSSIMPLE POWER SUPPLY UNITLOGIC SIGNAL GENERATORSUSTAIN UNITEPROM DUPLICATOR

PLUSSPECIAL TEST GEAR BUYERS' GUIDEMULTIMETERS

MAY ISSUE ON SALEFRIDAY, APRIL 6

PLEASE TAKE NOTEGames Scoreboard(January 1984)

The first paragraph on page 44should read:

"If for example, S4 was set toposition '2' and S3 set to position '5',on the 25th pulse from the lowfrequency oscillator, the inputs . ."

The original text had inadvertentlytransposed the references to switchesS3 and S4.

The last sentence in the firstparagraph of page 45 states incorrectlythat 4066 quad bilateral switches (IC9to IC12) are opened by taking thecontrol pins to logic high when in factthe opposite is true, that is, a logic highon the control pin closes the switch.

Teach -In 84(January 1984)

Experiment 4.4, diagram Fig. 4.11.The end of potentiometer VR I marked"a" should be connected to capacitorC2 and the earphone X1 at point E17.See page 237.

Microcomputer InterfacingTechniques Part 8(February 1984)

Oric Port Board. There is an errorin the circuit diagram, Fig. 8.6, andthe component layout Fig. 8.9. In bothdiagrams the signal line labelled "I/Opin 5" should be labelled "I/O ControlPin 6".


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L _I


1

QUASI -STEREOBY R.A.PENFOLD

TELEVISION sound is often criticised asbeing of a rather poor technical

quality, but this is not strictly true as thef.m. sound channel used in the UK tele-vision system is capable of providingquite a high level of fidelity with goodbandwidth, signal-to-noise ratio, and lowdistortion.

Television sets generally have a com-paratively poor sound quality due to therather simple output stages and smallloudspeakers which do not equal those ofeven low cost hi-fi systems.

These days many television sets havean earphone or tape socket which can becoupled to a hi-fi amplifier and speakersto give a considerable improvement in theaudio quality. However, the televisionsound channel provides only a

monophonic signal (with no immediateprospect of stereo being introduced), andthis can lead to disappointing results.

QUASI -STEREO EFFECTWith a monophonic signal coupled to

both channels of a stereo system thesound produced seems to emanate frommid -way between the two loudspeakersand a stereo image is obviously not ob-tained. This can sound rather as if thesound is being fed to the listener along atunnel and results may actually bepreferable if only one stereo channel is fedwith the input signal.

There is no way of producing a truestereo signal from a mono one, but there

Fig. 1 a. In -phase signals.

are various ways of producing a quasi -stereo effect. Rather than producing aproper stereo image processors of thistype, spread out the sound between thetwo loudspeakers so that more spaciousand realistic results are obtained.

FILTERING SYSTEMThe most common method of syn-

thesising a pseudo -stereo signal from amono input is to use a simple system offiltering, where the lower middle and bassfrequencies are fed into one channel withthe upper middle and treble frequenciesbeing fed into the other channel.

The two filters used to split the signalare designed to give no overall change inthe frequency response of the system.High frequency sounds are on one side ofthe sound stage, low frequency soundsare on the opposite side and middlefrequencies are in the central image area.

This system can sometimes work well,but a major drawback is the inbalance inthe signal-to-noise ratio of the two chan-nels that is produced. One channel is fedwith the high frequency sounds andtherefore has most of the background"hiss" and a poor signal-to-noise ratio,while the other channel has most of thishiss filtered out and therefore has a verygood signal-to-noise ratio.

This problem can be overcome usingmore complex filtering with two com-plementary filters having several peaksand troughs in their frequency response

being used, but quite complex circuits areneeded to completely eliminate theproblem using this method.

PHASE CHANGESA less well-known method of produc-

ing a quasi -stereo signal is to use phasechanges to spread out the pseudo -stereoimage. As this method does not alter thefrequency response of either channelthere is no problem at all with an in -balance of the signal-to-noise ratios of thetwo channels and quite a good quasi -stereo effect can be obtained using thismethod.

In order to produce a good stereo im-age it is essential for the signals fed to theloudspeakers to be in -phase, like the twosignals in the oscillograph shown in Fig.la. In other words the two signals mustrise and fall in amplitude together, andmust be of the same polarity. Further-more, the two loudspeakers must be con-nected with the same phase so that asignal in both channels causes the speakerdiaphragms to move backwards andforwards together, and not one dia-phragm to move forwards while the othertravels backwards.

Signals in both stereo channels thenproduce a central image, or one slightlyoffset from the centre of the sound stage,depending on the relative strength of thesignal in each channel.

The most simple method of producinga quasi -stereo effect using a phasing

Fig. 1 b. Out -of -phase signals.


technique is to simply reverse the connec-tions to one loudspeaker so that the in -phase relationship of the two channels(and thus the central image as well) aredestroyed. The sounds then seem tocome, as they actually do, from the twoloudspeakers. An obvious limitation ofthis system is that no central image at allis obtained and a less obvious one is thatbass frequencies tend to be phased -outand there is consequently a noticeableloss of bass performance.

Much better results are obtained usinga phase shift circuit in one channel so thatthe two channels are in -phase at somefrequencies, out -of -phase at certain fre-quencies (as in Fig. lb) and somewherebetween these two extremes at other fre-quencies (as in Fig lc). This produces acentral image at frequencies where anin -phase relationship is produced and thesides of the quasi -stereo image at frequen-cies where the phase difference betweenthe two channels is substantial.

Fig. 2. Basic phase -shift network.

PHASE SHIFTERPhase shifting without introducing any

changes in frequency response can be ob-tained using a simple circuit based on anoperational amplifier and Fig. 2 showsthe standard configuration.

At low frequencies Ca has a very highimpedance in relation to the resistance ofR,, and Ca therefore has no significant

Fig. 1 c. Randomly -phased signals.

effect on the circuit. The operational am-plifier then acts as a simple inverting am-plifier with R. biasing the non -invertinginput to the central OV supply rail, and Raplus Rb normally having the same value,so that unity voltage gain is obtained.

At high frequencies Ca has a low im-pedance and effectively couples the inputsignal direct to the non -inverting input ofthe operational amplifier. Although atfirst sight it might seem that the couplingto the non -inverting input would cancelout the basic unity gain inverting am-plifier function of the circuit and produceno output, this is not the case. Ra and Rbset the voltage gain from the non -inverting input to the output at two times,but this is reduced to unity by the coupl-ing of the inverting input.

Thus the circuit acts as an inverter atlow frequencies, gives no phase change athigh frequencies and produces inter-mediate degrees of phase change betweenthese two extremes. Unity voltage gain isobtained at all frequencies.

CIRCUIT DESCRIPTIONThe full circuit diagram of the Quasi -

Stereo Adaptor is shown in Fig. 3. ICI isused as a simple buffer amplifier and thisensures that the first phase -shift circuit isfed from a suitably low source im-pedance. R1, R2 and CI are used toproduce a centre -tapping on the supplywhich is used to bias the non -invertinginput of ICI (and the other operationalamplifiers used in the circuit).

One output is taken from the output ofthe buffer amplifier, and this signal under-goes no phase change.

The output of the buffer amplifier isalso fed to a series of four phase -shift cir-cuits of the type described above. At lowfrequencies there is no overall phase shiftthrough these four circuits since the inver-sion through the first phase shifter is can-celled out by the inversion through thesecond stage and the inversions throughstages three and four also cancel out eachother.

COMPONENTS

ResistorsR1,2 4.7k0 (2 off)R3 56k0R4,5,7,8,

10,11,13, 14 181(0 (8 off)

R6,9,12,15 100k0 (4 off)

All IW carbon ±5%

Capacitors4.7µF 63V axial elect.

C2 1µF 63V radial elect.C3,8 10µF 16V radial elect.

(2 off)C4-7 1 nF polycarbonate

(4 off)C9 100µF 10V radial elect.C10 100nF polyester

SemiconductorsIC1 741C op -ampIC2,3 1458C dual op -amp

(2 off)

gehopTalk

page 231

MiscellaneousSi rotary on/off switchB1 9V PP6 batterySK1,2,3 phono sockets (3 off)

Printed circuit board: single -sided, size 105 x 48mm, EE PCBService, Order code 8404-01;case, 133 x 102 x 38mm(AB 10); Veropins; battery connec-tor; connecting wire.

Approx. costGuidance only £8


SI

Rt

4.7k17

R3

5610

R2C1

47pF4 NI

EE

0C310}1F

SK2(OUT 11

R5

1816

R6

/00/a7

IICI PIN 7

1C2,1C3 PIN 8

R8

/8/d7

R9

10011

1C1,1C2,1C3 PIN

ICI =761C1C2,1C3 =1458

RIP

78kil

R12

100101

C9

T00pF

R14

18k12

R1S

100/6

TION/OFF1

CIO

100nF

8119V

Fig. 3. Complete circuit diagram for the Quasi -Stereo Adaptor.

This is an important factor as it givesin -phase signals at bass frequencies andavoids the cancelling effect mentionedearlier and its attendant loss of bassresponse.

FREQUENCY INCREASEAs the input frequency is gradually in-

creased the degree of phase shift throughthe circuit increases as well, until thesignals become out -of -phase at frequen-cies around 700Hz. Increasing the inputfrequency further gives a greater phaseshift so that the signals gradually moveback into phase again, and then back intoantiphase at about 4kHz.

At still higher frequencies the signalsmove back into phase again, but at thispoint the maximum phase shift of the cir-cuit is achieved and a further increase infrequency does not produce a furtherchange in phase shift.

The circuit, thus, gives outputs that arein -phase at high frequencies, low frequen-cies and a narrow band of frequencies, ata little over 1kHz, with antiphase outputsbeing produced at frequencies at around700Hz and 4kHz. In practice this seemsto give good results without either thesides or centre of the sound stagebeing excessively strong and dominantand certainly seems to give a much morespacious sound than straightforwardmonophonic reproduction.

POWER SUPPLYA 9 -volt supply at a current drain of

only about 4mA is required, and this isobtained from a PP6 size battery. Theunit only has one control, and this ismerely on/off switch S1. The maximuminput level that can be handled withoutclipping and severe distortion occurring isaround 2V r.m.s. which is more than ade-quate. Although the processed signal

passes through five operational am-plifiers, these are all used with only unityvoltages gain and the noise and distortionlevels of the unit are therefore negligible.

CONSTRUCTIONCASE

An aluminium box measuring about133 x 102 x 38mm makes a neat hous-ing for this project, but there are a num-ber of cases of a similar size that arereadily available and any of these shouldsuffice. A metal case is a better choicethan a plastic one for this applicationthough, since a metal case will providescreening and should eliminate any slightpick-up of mains hum or similar inter-ference.

The overall layout of the unit is quitesimple and straightforward. Phonosockets are used for SK 1 to SK3 on theprototype, but these can be changed forany type of audio connector that will bemore convenient in use.

The copper track pattern and compo-nent layout of the printed circuit board(105 x 48mm) are reproduced actual -sizein Fig. 4. Construction of the boardshould be perfectly straightforwardprovided the appropriate types ofcapacitor specified in the components list(or a physically similar alternative) areused. Veropins are used on the board atpoints where connections to B1, S1, orthe sockets will be made.

The finished printed circuit board ismounted on the base panel of the caseusing 12.5mm 6BA bolts, and 6.35mmspacers to keep the underside of theboard clear of the metal case. The finalwiring is then completed and it is notessential to use screened cable to makethe connections from the componentpanel to the sockets.

Note, the printed circuit board isavailable from the EE PCB Service,Order code 8404-01.

IN USEAn important point to note is that the

unit should only be used with a televisionset that has an output socket of somekind, which should come from the audiostages of the set via an isolation circuit sothat there is no risk of obtaining an elec-tric shock. Simply taking an audio outputfrom across the loudspeaker of a televi-sion receiver is not satisfactory since oneof the output leads would almost certainlyconnect direct to one side of the mainsand this would be extremely dangerousindeed.

The input signal is coupled to SK 1 andthe outputs from SK2 and SK3 arecoupled to the inputs of the amplifier. Theprototype is used with the phase -shift cir-cuits in the left-hand channel, but it doesnot really matter which channel is theordinary mono signal and which is thephase shifted one. The effect is much thesame either way.

It is possible to use the unit withsources other than a television receiverand it can be used with a video cassetterecorder, for example, or if f.m. stereoreception is very noisy it may be advan-tageous to switch to mono in order to ob-tain a much lower noise level and then usethe adaptor to give a quasi -stereo effect.

The effect of the adaptor is mostnoticeable when a signal having a largenumber of frequency components spreadacross the whole audio spectrum isprocessed, such as a piece of orchestralmusic or applause from a large audience.The sound stage should then clearly ex-tend from one loudspeaker to the otherwith a reasonably strong central imageand not just the sound seeming toemanate from the two loudspeakers. 0


LC)

+C1 R3

SKI

F° 8011S%o o

E E 8404-07o

Fig. 4. The master p.c.b. (full-size) for the Quasi -Stereo Adaptor

E

I R6

R5

1c

Roc

SK2

C5

1C2

'R10

R7

R12

R9

SK 3

OC7 R151f

QUASI -STEREOADAPTOR

S1

Fig. 5. Component layout onthe topside of the printed cir-cuit board with wiring to thefront and rear panels.

B1

-Ve

The completed Quasi -StereoAdaptor with the case"shroud" removed showingpositioning of the printedcircuit board and battery.

R8/11 &OM*1 R13

010

Everyday Electronics, April 1984273

TIMER MODULEFOR

CENTRAL HEATING SYSTEMS

1-HERE are many occasions when anI accurate interval -timer is extremely

useful in the home and elsewhere. Thissimple -to -build module was originallydesigned to control a central -heatingsystem, but details are given to show howits use can be extended far beyond this.

Most central heating systems have amanual/auto switch, the normal arrange-ment being a switch in the live line toeither bypass or go via the clockmechanism (see Fig. 1). It is all too easyto switch it to manual, for example, toheat up the water, and then forget to turnit back, so that money is wasted with thesystem being on too long.

Thus an easy way of providing controwould be to insert a timing module between points A and B in the diagram,

CLOCKCONTROL

AUTO

LIVE A /DOFF

I MANUAL

TIMERMODULEE

Fig. 1. Manual/Auto switching of atypical system with positioning of TimerModule indicated.

8 CENTRALHEATING

which would automatically bypass theswitch and clock for a predeterminedlength of time. Such a circuit would notaffect the normal Auto/Manual operationof the heating. The project described herehas a push to start button, and a push-button to abort the timing sequence atany time. It also contains a range switch,the prototype being set to 40 minutes(low) and 80 minutes (high), to cater forhot water or radiators, respectively.

CIRCUIT DESCRIPTIONThe first design used a 555 in a simple

monostable circuit, but experimentsshowed that the large electrolyticcapacitors needed for long timing periodscould not be depended upon to give therequired repeatable accuracy. The solu-tion was to use an oscillator clocking abinary ripple counter, the 4020, the fre-quency of the oscillator being adjustable.

The oscillator is formed around twogates of a cmos 4011 quad 2 -input NANDgate, and the output is fed into the inputpin 10 of the 4020. See circuit diagram,

Fig. 2. At switch -on, a brief reset pulse isfed by C2 and R2 to the 4020 reset (pin11) to ensure that all the outputs are low.This is achieved because at the instant ofswitch -on, C2 acts like a short circuit, butvery quickly charges up, and then R2pulls the pin down to OV to enablecounting to commence.

The low output at either pin 1 or 2(selected via S1) is inverted by anothergate of the 4011 (IC1c) to provide a highlevel at the base of the transistor TR1,which turns on and energises the relayplaced as a collector load. One set of con-tacts short out the push -to -make switch,so that the supply line is established andretained when the start button is released,

whilst the other set of contacts is connec-ted between points A and B (Fig. 1) toprovide the live line to the central heating.

The pins of the 4020 go high and lowin a very specific sequence after apredetermined number of input pulses;pin 1 after 4096 pulses and pin 2 after8192, and so on until eventually the selec-ted pin goes high, causing the base of thetransistor to go low, turning off the relay.This opens both sets of contacts, thus dis-connecting the supply to the circuit andthe live to the central heating. S2 is in-cluded so that the timing sequence can becancelled at any time. It is a push -to -break, and disconnects the relay coil fromthe supply line, turning the whole unit off.

PINS 12,13 614CCI

ICI= 4011

ICla IC1b5

0.3 r 0-

680kI1

16

4111-Z. MR VD D

V R I

Ma

lc -10 714 F

PIN 7 ICI

t

R2

0 I,

CK 1C24020 2 SWI012 *II

100k.O

03

DIT1L 220

ICk8

)0R4 )Oka

2

205 I F*

TBC109R1

LO120

EL A-1

RL A-2

DV

to

Fig. 2 (above). The oscillator circuit diagram and (below) suggested power supply circuits forthe Timer Module. S3 is the start button and S2 aborts the timing cycle.

1C3

12V

EE

12V


SUPPLYThe power lead is taken from the sup-

ply to the central heating, after the fusefor safety reasons, and is transformed byT1, rectified by the diodes and smoothedby C3 before being regulated by the 7812(IC3). An l.e.d. and a current limitingresistor is connected to another of the4020 outputs to provide a flashing indica-tion that the circuit is operating, but thisis purely optional and may be omitted ifdesired.

CIRCUIT BOARDThere should be no problems

associated with construction; however,readers are reminded that parts of the cir-cuit are at mains potential, so great careis obviously essential. It is advisable to

COMPONENTS

ResistorsR1R2R3R4

680k0100k0330010kS2

See

CapacitorsCl 0.47µF polyesterC2 0.1pF polyesterC3 330pF 25V elect.C4 10pF 16V single elect.

page 231

SemiconductorsD1-4 1N4001 (4 off-see

text)D5 TIL220 5mm red I.e.d.TR1 BC109 npn siliconIC1 4011 cmos quad 2 -input

NAND gateIC2 4020 cmos 14 -stage

binary ripple counter1C3 7812 12V, 1A regulator

MiscellaneousVR 1 1 MO miniature

horizontal presetT1 12V (or 12V -0-12V see

text) 100mA mainstransformer

RLA-2 miniature 12V relay,2050 coil with d.p.d.t.mains rated contacts

Si s.p.d.t. miniature toggleS2 push -to -break

momentary actionS3 push -to -make

momentary actionPrinted circuit board: single -sidedsize 90 x 65mm, EE PCB Service,Order code 8404-05; case to suit;mains lead; soldertag; equipmentwire; mounting hardware.

Approx. costGuidance only .E1 4

use a p.c.b. and a suggested design forone is given in Fig. 3. Mount the compo-nents, taking care to observe the polarityof the diodes and capacitor, and theorientation of the i.c.s, transistor andregulator. See Fig. 4.

The transformer can be either a12V -0-12V centre -tapped type, in whichcase the diodes D2 and D5 are omitted,and the centre tapping is connected toOV, or a 0-12V transformer, which willneed all four diodes as a bridge rectifier.

The relay was soldered to the board asshown, and small lengths of wire usedto make the necessary connections. En-sure that the relay contacts are capable ofcarrying the required current, if necessaryby connecting more than one set of con-tacts in parallel.

S3 has a pair of normally open (N/O)contacts wired across it, and the other setof N/O contacts will eventually be con-nected between points A and B, but it isbest to calibrate the unit first. Monitor pin4 of IC2 and adjust VR1. The time takenfor pin 2 to go high will be time taken for

pin 4 of IC 1 to change from one state tothe other, times 128. For example, if itchanges state every 37.5 seconds, pin 2will go high after 80 minutes (pin 1 after40 minutes). The other contacts can nowbe wired in.

The module can be mounted in anyconvenient sized box (earthed if metal isused), with two leads running from it viagrommets or strain relief bushes. Onelead provides the mains supply to themodule, the other runs from the relay toA and B. The transformer is bolted insidethe case, with the mains earth lead con-nected to a soldertag.

CONCLUSIONSpare pads have been provided on the

p.c.b., and looking at the waveformdiagram it can be seen that if, for exam-ple, pin 2 of IC2 goes high after 60minutes, pin 3 does not change state untiltwo hours have passed, whilst pin 15changes state every 15 minutes. For thoseconstructors who would like to, S I can be

Fig. 3. Full-size printed circuit master pattern for the Timer Module.7-53-1

O DI

0/P

t* COM

a k IC3'.:TL I/Pci,METAL TAG

D2 D3

k a

k a

05 4

a 11

C341+

R30 0 0 0 11

0 0 0 0 0R2 C2

4/411:1.-. ( .)°

...

ICI

I-1 LI LI I-1 LI

jSi(POLE)Fig. 4. Layout of components on the topside of the p.c.b. If the 12V -0-12V transformer is used, D2 and D5 are omitted and the C.T. terminalis used.

0411.11-.R4

e

ti

..:

RLA

oi

TRI


Table 1

pin no. pulses needed to switchoutput on

9 2' (2)7 24 (16)5 25 (32)4 26 (64)6 2' (128)

13 28 (256)12 29 (512)14 210 (1024)15 211 (2048)

1 212 (4096)2 213 (8192)3 214(16384)

changed for a 4 -way rotary switch toselect any of these outputs, and indeed ifRI were removed and two leads run to a

Fig. 5. Waveform diagram for some of the pins of the 4020 binary counter i.c.

two megohm linear pot, a four range taking the longest time, so if two pins, forvariable timer (very useful in the kitchen) example, 12 and 14 were chosen, againwould be provided, with VR I acting as a with a pot replacing the fixed resistor RI,minimum time adjustment control. a two range darkroom timer could be

The table shown gives the sequence of constructed.pins on IC2, each one going high after With a little imagination, the moduletwice the period of its predecessor, pin 3 can form the basis of several very useful

projects, and it is hoped that the abovesuggestions have provided food forthought. If used for the central heating,there is no reason why the pushbuttonsshould not be mounted remotely in thekitchen, making the unit even more con-venient to use. 0

an astable, or some other potentially un- closed, and either a logic I or 0 when thesymmetrical "odds determinator", heads switch is open.and tails counts the power line frequency The output of the first J.K. flip-flop isso that both the length of time the push used to cycle the second J.K. which isbutton is held down and the phase of the connected as a binary divider. One of itspower at the instant the push button is outputs drives the HEADS indicator anddepressed combine to provide a truly ran- the other drives the TAILS lamp. Tran-dom 50-50 long term result. sistors TR3 and TR4 provide sufficient

In the first J.K. flip-flop only the direct power for the flip-flop outputs to drive theinputs (CLEAR and PRESET) are used lamps. When S1 is closed both lampsso that the circuit squares up and follows cycle on and off 30 times a second, athe power line frequency as long as Si is speed much faster than the eye can followclosed. Transistors RI and R2 alternately to discourage cheating.set and reset the flip-flop immediately Hamid Reza Nameri,after each sequential power line zero Tehran,crossing. The Q output of the first J.K. is Iran.a noise -free squarewave when S1 is

CIRCUITEXCHANGEHEADS AND TAILS

THISproject is ideal for school

laboratories as a probabilitydemonstrator or study aid.

The simple circuit diagram shown usesa -r-rt, i.c. and four low-cost transistors.The visual readout of the second flip-flopindicates heads or tails. Rather than using DI

k a

ICIPIN 5

R3ICI =MC7476

lki)

SCI =C20 IgF 475F

C3 .....C40.01 pF

iNaooi

D2

C1.41

cc

cc8

R6 e

9 CLEAR II

3I0

WI15 , IC1b

CK TR3 TR4 +

1540012500pF

1 0

ICla 12

2N5139R70.,\AA,

255139

bCK

PRESET11(12

16K.) a 7 19847b1

2

!HEADS' 0 [TAILS'R2

LPI LP2

iknRI

IFLIPIR4 SI .II.

1512

e 01 12

TR2255139

R5

PAYTR12N5139 ICI

PIN 13

WV1k0

FS1

2A

240VA.C.

MAINS


CIRCUITEXCHANGE

This is the spot where readers pass on to fellow enthusiasts usefuland interesting circuits they have themselves devised. Payment ismade for all circuits published in this feature. Contributions shouldbe accompanied by a letter stating that the circuit idea offered iswholly or in significant part the original work of the sender and thatit has not been offered for publication elsewhere.

51

/OM

ICIR2 PIN 14

lOkfl

10N1

'OFF I

A ICla2

5

6

IC1b

SOLENOID

TR1IRF 330

Cl

110 33/JF

1102151

R3

271,12

C2

15920

15920a

a

D4

ICI= 4093

ICIPIN 7

1

PULSE GENERATORTHE purpose of this circuit is tomeasure the time period for which the

solenoid is energised. This is done bygenerating a positive pulse for everyoperation of the on/off switch. Thesepulses are fed to a timer counter set tosingle line count. With the on pulse thetimer starts to count and on the off pulsethe timer stops and displays the period.

When the on/off switch is switched tothe on position the output from gate 1

becomes positive, the f.e.t. TR I is gatedand the solenoid becomes energised.Capacitor C I and resistor R3 differen-tiate this voltage and produce a pulsewhose length is Cl x R3 = time. DiodeD3 conducts this pulse to gate 4 via gate3 which gives a double inversion so thatthe pulse maintains the same polarity butis buffered from the circuit. This pulse isused to gate (start) the timer.

As the output from gate I becomespositive the output from gate 2 decays ina negative direction. This negative pulse isfed to the common rail via C2 and D2.

0 334.4F

R4

27k!2

a

1S920

D215920

+ Ve

SWITCH FUNCTION

0v

PULSE GENERATED ATJUNCTION C1 R3

PULSE GENERATED ATJUNCTION C2 R4

PULSE TRAIN SEENAT TIMER

12

13

R5

IMO

Etc

TRUTH TABLE(GATES IC1a84b)

A B 0 (Tli

0 0

0 0

8

9

IC ld

- ON

-.4

OFF

10

1 -ye

TIMER

CeR=0.3344F x 271411=89mS

OV

When the on/off switch is switched tothe off position the output states of gates1 and 2 will reverse (RI, R2 and gates 1,2 are a simple debounce circuit). Gate 2will generate a positive -going pulse whoseduration is C2 x R4 which will be fed tothe timer via D4 and gates 3 and 4 whichwill stop the counter.

The negative pulse generated at gate 1will be fed to the common rail via Cl andD I. The time displayed on the timer willbe the duration for which the solenoid hasbeen energised.

D. R. Fownes,Wolverhampton.


TRANSISTORTESTER

HE latest addition to theI Osborne Electronics 4000

series of hand-held test units is themodel 4500 Transistor Tester.

Completely self-contained, theunit is claimed to simplify and .speed the task of checking the pnjunctions of discrete semiconduc-tors whether in or out of circuit.

The checking of pnp or npntransistors, diodes and open orshort circuit junctions are instan-tly identified by a series of I.e.d.swhich indicate the junction status.This is carried out by connectingtwo test probes across the junc-tion to be checked.

Further information isavailable direct from:

Osborne Electronics,Dept EE, Binstead Road,

Ryde, Isle of Wight.

CLEAN SWEEPT HE introduction of their newI VHS VCR head cleaner,

which may be used wet or dry, isannounced by Bib Audio/VideoProducts. Bib claim that thiscleaner is the safest and easiest touse cleaner yet devised.

Developed in the BibLaboratories, they claim manyspecial features for the cleaner.The most significant being thetype of non-abrasive cleaningtape, which is a special spunbonded polyester made to theirown specification.

Another feature is theautomatic way in which thecorrect amount of fluid is appliedto the cleaning tape. The fluid isreleased by pressing a button forone second on the side of thecassette housing, which feeds thefluid into a chamber throughwhich the cleaning tape passes,eliminating the chance ofapplying too much or too little.

This ensures that the wholetape travel path, including tapeheads, drum, guides, audio heads

and capstan are cleaned in onesimple operation. The cleaningtime takes only 10 seconds.

It is recommended that thecleaning tape is never re -woundas each cleaning operationpresents a new portion of cleaningtape to the heads and avoids the"re -playing" of accumulatedcontaminants. The cleaner willlast for 35 cleanings, or fouryears' average use.

Bib recommend "PreventiveVideo Maintenance" as the key togood quality pictures. VCR headsshould be cleaned regularly after40 to 50 hours' playing time, asoxide particles and dustaccumulate. These all stick totape heads, drum and guides andother parts causing "snow" in thepicture, poor tape handling andeven tape damage.

Attractively packed in a

descriptive carton, this newcleaner has a recommended retailprice of £9.98 including VAT.

Bib Audio/Video Products Ltd,Dept EE, Kelsey House,

Wood Lane End,Hemel Hempstead HP2 4RQ.

SUPER SAVER

How often do you turn on theimmersion heater for a quick

boost, then forget to turn it offagain? To prevent this wastage,and to help older people who maynot feel comfortable using aprogrammable timer, Superswitchhave introduced a simple run-back timer control.

Operating on the same princi-ple as many kitchen timers, butdesigned so that it is capable ofswitching the immersion heaterload, Superswitch's 1512 con-troller is claimed to be easy to useand understand.

With the two -position switch at"timed", the dial is set to the timerequired; anything from a fewminutes to two hours. The con-troller then counts down to zero.At any time, you are able to seehow much time is left to run, orturn the dial forward or back, toadjust the length of time the im-mersion heater will remain on.

The Superswitch 1512 Immer-sion Heater Controller is expectedto sell for around £20. Furtherinformation and local stockistsaddresses may be obtained from:

Superswitch Electric AppliancesLtd., Dept EE,

7 Station Trading Estate,Camberley, Surrey GUI 7 9A H.

Aulamokallybens von4,4400lupe 4 path,uNlieut loaohroghaunful residue..

0 Can he 4111417.0.44,.1.. dy.

364Ily ruu,aboanau.. No awry relli or

nplowereant Dom,Lowyfer 35

a...0,0 0. 40u.row" ovum,.


SaARoneFORBEGI\NERS

APACITORS come in a bewilderingC range of types and sizes mainlybecause, unlike resistors, it is impossibleto devise a single method of constructionthat will yield a sufficiently wide range ofvalues and working voltages.

A capacitor consists of two plates ofconductive material separated by an in-sulator or dielectric. It is the combinationof materials for these two elements thatcauses the confusion. Besides its value, acapacitor also has a working voltage andtolerance. If either of these are important,they are specified in the components list.

Another major division is polarisedand non -polarised capacitors. Generallythe polarised types are large in value andmust be connected up correctly. Withinthe above parameters, a capacitor is oftenchosen because of its size and stability.

This being the case, it means thatvirtually any capacitor with the samevalue and the same, or higher, voltagerating will work in a given circuit andthis should be borne in mind whenexperimenting with spare or surpluscomponents.

NON -POLARISEDCAPACITORS

Polyester capacitors are widely usedand cover the middle range ofcapacitances and the typical range isfrom 0.01µF to 2.0µF. Polyestercapacitors are available in tubular, tabletand block forms and have a tolerance of10 and 20 per cent. The normal workingvoltage is up to 400V d.c.

A miniature dipped case type oftenreferred to as a C280 is shown in Table 1.This type of capacitor is wax treated andcovered with a hard lacquer. The variouscoloured bands represent the value of thecapacitor, using a similar code to theresistor one. The two top bands give thefirst two digits and the third themultiplier. A fourth band gives toleranceand the fifth the working voltage.

The smallest capacitors are theceramic type and range from 18pF to0.1µF (see Fig. 1). These capacitors haveclose tolerance, low loss and highstability.

A wide range of polystyrene capacitorsare available in the range 10pF to 0.10.Thus they cover very nearly the same

r

CAPACITORCOLOURCODE

TANTALUM SERIES C280microfarads (pF) picofarads(pF)

Band (ring) 1st 2nd Spot 3rdColour band band (Multiplier) band

BLACK

BROWN

RED

ORANGE

YELLOW

GREEN

BLUE

VIOLET

GREY

WHITE

PINK

SPOT

1st 2nd 3rd band 4th 5thband band (Multiplier) band band

0 1 10y 0 1 201.

1 1 10 1 1 10

2 2 100 2 2 100

3 3 3 3 1000

4 4 6 3V 4 4 10000

5 5 16V 5 5 100000 51.

6 6 20V 6 6 1000000

7 7 7 7 0.01

8 0 01 25V 8 8 0001

9 9 0001 3V 9 9 101.

35V

1st BAND

2nd BAND

- 3rd BAND

REDSPOT

1st

2nd

3rd

TANTALUM TYPES

1st BAND2nd BAND3rd BAND4th BAND5th BAND

100V

250V

400V

SERIES C280

Table 1 : The capacitor colour coding for tantalum and series C280 capacitors.

Fig. 1. A diagram showing the various shapes of commonly used capacitors.

range as ceramics. They have a betterelectrical performance than the ceramicsand are available with close tolerancessuch as 5, 2 i and 1 per cent.

However, polystyrene capacitors arerather more expensive and are only usedwhere there special characteristics areessential. Polystyrene capacitors aretubular in shape and rather more bulkythan ceramics. They can be used as ageneral purpose low value type wheretolerance is not so important.

ELECTROLYTICSElectrolytic or polarised capacitors are

a special case. They provide quite a largevalue of capacitance, but must beconnected the right way round in thecircuit. They are made with specificworking voltages, which must not beexceeded in practice.

It is however, permissible to use themat a lower voltage than the stated working

voltage. Electrolytics are available as"double -ended" types with the connectingleads emerging from either end; also as"single -ended" types with both leads atthe same end of the component. Double -ended types, as shown in Fig. 1, arerecommended for general purpose use.

Aluminium electrolytic capacitors.


Printed circuit boards for certain EE con-structional projects are now available fromthe EE PCB Service, see list. These arefabricated in glass -fibre, and are fully drilledand roller tinned. All prices include VAT andpostage and packing. Remittances shouldbe sent to: EE PCB Service, Everyday Elec-tronics Editorial Offices, Westover House,West Quay Road, Poole, Dorset BH15 1JG.Cheques should be crossed and madepayable to IPC Magazines Ltd.

We regret that the ordering codes for theAugust projects have been incorrectlyquoted in the Sept -Oct issues. Correctcodes are given here.

Please note that when ordering it is im-portant to give project title as well as ordercode. Please print name and address inBlock Caps.

Readers ordering both p.c.b.s and soft-ware cassettes may send a single cheque/PO for the combined amounts listed.

Readers are advised to check withprices appearing in current issue beforeordering.

PROJECT TITLE Order Code Cost

Eprom Programmer, TRS-80 (June 83) 8306-01 £9.31Eprom Programmer, Genie (June 83) 8306-02 £9.31Eprom Programmer, TRS-80 & Genie (June 83) 8306-03 £1.98

User Port Input/Output M.I.T. Part 1 (July 83) 8307-01 £4.82User Port Control M.I.T. Part 1 (July 83) 8307-02 £5.17

Storage 'Scope Interface, BBC Micro (Aug 83( 8308-01 £3.20Car Intruder Alarm (Aug 83) 8308-02 £5.15High Power Interface M.I.T. Part 2 (Aug 83) 8308-03 £5.08Pedestrian Crossing Simulation M.I.T. Part 2 (Aug 83) 8308-04 £3.56Electronic Die (Aug 83) 8308-05 £4.56

High Speed A -to -D Converter M.I.T. Part 3 (Sept 83) 8309-01 £4.53Signal Conditioning Amplifier M.I.T. Part 3 (Sept 83) 8309-02 £4.48Stylus Organ (Sept 83) 8309-03 £6.84Distress Beacon (Sept 83) *8309-04 £5.36Distress Beacon Pocket Version (Sept 83) 8309-05 £3.98

D -to -A Converter M.I.T. Part 4 (Oct 83) 8310-01 £5.77High Power DAC Driver M.I.T. Part 4 (Oct 83) 8310-02 £5.13Electronic Pendulum (Oct 83) 8310-03 £5.43

TTL/Power Interface for Stepper Motor M.I.T. Part 5 (Nov 83) 8311-01 £5.46Stepper Motor Manual Controller M.I.T. Part 5 (Nov 83) 8311-02 £5.70Digital Gauss Meter (Nov 83) 8311-03 £4.45Speech Synthesiser for BBC Micro (Nov 83) 8311-04 £3.93Car On/Off Touch Switch (Nov 83) 8311-05 £3.1 1

4 -Channel High Speed ADC (Analogue) M./.T. Part 6 (Dec 83) 8312-01 £5.724 -Channel High Speed ADC (Digital) M.I.T. Part 6 (Dec 83) 8312-02 £5.29TRS-80 Twin Cassette Interface (Dec 83) 8312-03/09 £7.43Environmental Data Recorder (Dec 83) 8312-04 £7.24Touch Operated Die (Dot matrix) (Dec 83) 8312-05/06 £4.34Touch Operated Die (7 -segment) (Dec 83) 8312-05/07 £4.34Continuity Tester (Dec 83) 8312-08 £3.41

Central Heating Pump Delay (Jan 84) 8401-01 £3.33Biological Amplifier M.I.T. Part 7 (Jan 84) 8401-02 £6.27Temp. Measurement and Control System for ZX Computers

(Jan 84)Analogue Thermometer Unit 8401-03 £2.35Analogue -to -Digital Unit 8401-04 £2.56

Games Scoreboard (Jan 84) 8401-06/07 £9.60

Eprom Programmer/ROM Card for ZX81 (Feb 84) **8402-01 £7.84Oric Port Board M./.T. Part 8 (Feb 84) 8402-02 £9.56Negative Ion Generator (Feb 84) *8402-03 £8.95Temp. Measurement and Control System for ZX Computers

(Feb 84)Relay Driver Unit 8402-04 £3.52

Latched Output Port M.I.T. Part 9 (Mar 84) 8403-01 £5.30Buffered Input Port M.I.T. Part 9 (Mar 84) 8403-02 £4.80VIC-20 Extension Port Connector M.I.T. Part 9 (Mar 84) 8403-03 £4.42Commodore 64 Extension Port Connector M.I.T. Part 9 (Mar 84) 8403-04 £4.71Digital Multimeter Add -On for BBC Micro (Mar 84) 8403-05 £4.63

Multipurpose Interface for Computers 8404-01 £5.72Data Acquisition "Input" M.1.T. Part 10 (Apr 84) 8404-02 £5.20Data Acquisition "Output" M.I.T. Part 10 (Apr 84) 8404-03 £5.20Data Acquisition "PSU" M.I.T. Part 10 (Apr 84) 8404-04 £3.09Timer Module (Apr 84) 8404-05 £3.58A.F. Sweep Generator (Apr 84) 8404-06 £3.55Quasi Stereo Adaptor (Apr 84) 8404-07 £3.56

*Set of four boards. **Calibrated with C1, VR1 and IC3 fitted.M.I.T-Microcomputer Interfacing Techniques, 12 -Part Series.


Install your ownlatt611111 system and save

using built andtested modules

A COMPLETE INTRUDER ALARMEASILY ASSEMBLED ULTRASONIC UNIT CK 5063

Requires no installation. Easily assembled usingour professionally built and tested modules.

Adjustable range up to 25ft Built -to entrance Et exit delay Built 1ntimed alarm Key operated switch - Off. Test and Operate Provision for an extension speaker Fully self-contained Uses US 5063. PSL 1865 Key Switch 3901.

3' Speaker 3515

Now you can assemble a really effective tnt, uder alarm at this low price using tried and tested Riscompmodules Supplied with full instructions the kit contains everything necessary to provide an effectivewarning system for your house or flat. With a built-in LED indicator and test position the unit is easily set-up requiring no Installation. It may simply be placed on a cupboard or desk. Movement within its rangewill then cause the built-in siren to produce a penetrating 90dbs of sound, or even 110db s with anadditional speaker. All parts included and supplied with full instructions for ease of assemblySire 200 180. 70mm Order as Ce 5063

DIGITAL ULTRASONIC DETECTOR

US 5063

3 levels of discrinenaiton against Usealarms

Crystal control for greater stability Adjustable range up to 25ft. Built-in delays 12V operationThis advanced new module uses digital signalprocessing to provide the highest level ofsensitivity whilst discriminating against potentialfalse alarm conditions. The module has a built-inexit delay and timed alarm period. together withselectable entrance delay. plus many moreoutstanding features.

ULTRASONIC MODULE

US 4012

£10.95 +V.A.T. Adjustable range from 5-25ft.This popular low cost ultrasonic detector isalready used in a wider range of applications fromadnider detectors to automatic light switches anddoor opening equipment, featuring 2 LEDrodtcators for ease of setting up.

INFRA -RED SYSTEM

IR 1470 only £25.61 +V.A.T.

Consisting of separate transmitter and receiverboth of which are housed in attractive moulded

moduthe system provides an invisiblelated beam over distances of up to 50ft

operating a relay when the beam is broken.Intended for use in security systems, but alsodeal for photographic and measurementapplications. Sine 80 by 50 by 35mm.

POWER SUPPLY Et RELAY UNIT

PS 4012Provides stabilised 12V output at 95mA andcontains a relay with 3 amp contacts. The unit isdesigned to operate with up to 2 ultrasonic unitsor 1 infra -red unit 18 1470. Price E4.25

SIREN MODULE SI. 157Produces a loud penetrating sliding tone which.when coupled to a suitable horn speaker.produces S.P.L. s of 110dbs at 2 metres.Operating from 9-15V. Price E2.95 + 11.)11.

51/2" HORN SPEAKER HS 588This weather-proof horn speaker providesextremely high sound pressure levels II 10dbsat 2 metres) when used with the CA 1250, PS1865 or SL 157 P11. E4.95 VAT.

3-POS. KEY SWITCH 3901Single pole, 3-pos. key switch intended for use

Pwith the CA 1250 Price E3.43 + V.AT.lease allow 7 da - for delive

ALARM CONTROL UNIT

CA 1250

Price £19.95 +

The head of any alarm system is the control unit.The CA 1250 offers every possible feature thatis likely to be required when constructing a

system whether a highly soPhiSticatedinstallation or simply controlling a singlemagnetic switch on the front door. Eluilt-tn electronic siren drives 2 loud speakersProvides exit and entrance delays together

with fixed alarm time Battery back-up with trickle charging facilityOperates with magnetic switches. pressuer

pads. ultrasonic or L R. unitsAntetamper and panic facilityStabilised output voltage2 operating modes full alarrn/antetamper

and nic facilitySc rewpa connections for ease of installationSeparate relay contacts for external loads '

Test loop facility

SIREN b POWER SUPPLY MODULEPSL

only

E9.95+ V.A.T.

Acomplete siren and power supply module eft ichts capable of providing sound levels of 110dbsat 2 metres when used with a horn speaker. Inaddition, the unit provides a stabilised 12V outputup to 100mA A switching relay is also includedso that the unit may be used in Conjunction withthe US 5063 to form a complete alarm.

HARDWARE KIT

HW 1250

only£9.50

+

This attractive case is designed to house thecontrol unit CA 1250, together with theappropriate LED indicators and key switchSupplied with the necessary mounting pillars andpunched front panel. the unit is given a

professional appearance by an adhesive silkscreened label. Size 200 by 180 by 70mm

ULTRASONIC MODULEENCLOSURE

-40

only£2.95

+ V.AT.

Suitable metal enclosure for housing an individualultrasonic module type US 5063 or US 4012Supplied with the necessary mounting pillars andscrews etc. For US 5063 order SC 5063. forUS 4012 order SC 4012

Add 15%. VAT to all pricesAdd 50p post Er packing to all ordersUnits on demonstrationShop hours 9.00 to 5.30 p.m.Closed WednesdaySaturday 9.00 to 1.00 p.m.SAE with all enquiriesOrder by telephone or post

usingyour credit card 1.ft

RiSCOMP LiMiTEDDept EE721 Duke Street,Princes Risborough,Bucks. HP17 OATPrinces Risborough (084 44) 6326

Once againfor thisseries.Our experiencefrom stockPrice for

TEACH-INsupplying

- as we have

means yourprice, so

£18.95 inc

84a complete set of parts

done for all previous

kit can be suppliedorder with confidence.post and VAT.

GREENWELD isever popular series

in this fieldat the best possible

complete kit is only

STORE CLEARANCE!!We've bought so much surplus recently

# our stores are bulging at the seams! Inorder to clear some space, were onceagain offering "Bargain Parcels" whichhave proved very popular in the past.* They contain resistors, capacitors,switches, panels with transistors andIC's, screws and various hardware + allthe odd bits and pieces which haveaccumulated over the years. Eachparcel weighs 10Ibs and costs just£8.00.

MOTORIZED GEARBOXThese units are as used in acomputerized tank, and offer theexperimenter in robotics theopportunity to buy the electro- PRECISION PCB DRILLmechanical parts required in building Small size, 35mm dia x 165mm long.remote controlled vehicles. The unit 12V operation. Supplied with collett +has 2 x 3V motors, linked by a tmm bit 6000RPM. Only £7.50.magnetic clutch, thus enabling turning

PACKS! PACKS! PACKS!of the vehicle, and a gearbox containedwithin the black ABS housing, reducing K517 Transistor Pack. 50 assorted fullthe final drive speed to approx 50rpm. spec marked plastic devices PNPData is supplied with the unit showing TPN RF AF. Type numbersvarious options on driving the motors include BC114, 117, 172, 182, 183,etc. £5.95. Suitable wheels also 198, 239, 251, 214, 225, 320,available: 3 W' Dia plastic with blue tyre, BF198, 255, 394, 2N3904 etc etc.drilled to push -fit on spindle. 2 for £1.30 Retail cost E7+. Special low(limited qty). 3' dia aluminium disc price 275p3mm thick, drilled to push -fit onspindle. 2 for 68p. K523 Resistor Pack. 1000 - yes, 1000 1

SEAT BELT ALARMand I watt 5% hi -stab carbon filmresistors with pre -formed leads

Originally for sale at £8.95, these well for PCB mounting. Enormousmade units 70x 50x 25mm provide range of preferred values from aboth audible and visual alarms. Uses 2 few ohms to a several megohms.IC's, P82720 transducer, etc. Available Only 250p. 5000 £10; 20,000 £36.ready built, with circuit and instructionsfor just £3.95. Also available as a kit, K520 Switch Pack. 20 different assortedPCB + all components, box, wire, etc, switches - rocker, slide, push,together with instructions. Only £2.95. rotary, toggle, micro etc. Amazing

RIBBON CABLE value at only 200p

Special purchase of multicoloured 14 K522 Copper clad board. All pieces tooway ribbon cable - 40p/metre; 50m small for our etching kits. Mostly£18; 100m £32.00; 250m £65.00. double sided fibreglass. 250g

(approx 110 sq ins) for 200pTTL PANELS K541 It's back!! Our most popular packPanels with assorted TTL inc LS types. ever - Vero offcuts. This has beenBig variety. 20 chips £1.00; 100 chips

£4.00; 1000 chips £30.00. restricted for some time, but wehave now built up a reasonablestock and can once again offer

"THE SENSIBLE 64" 100 sq ins of vero copper dadDavid Highmores new book on the offcuts, average size 403".Commodore 64 now available. E5.95. Offered at around I the price of

new board 320p

THE 1984 K530 100 Assorted polyester caps - all

GREENWELD new modern components, radialand axial leads. All values from

CATALOGUE 0.01 to 1uf at voltages from 63 to

NOW AVAILABLE!! 1000!! Super value at 395p

It's Bigger, Brighter, Better, more K503 100 assorted wirewoundcomponents than ever before. With resistors, 1W -12W. Wide range ofeach copy there's discount vouchers, values 2.00Bargain List, Wholesale Discount List,Bulk Buyers List, Order Form and NICAD CHARGERSReply Paid Envelope. All for ust £1.00! Versatile unit for charging AA, C, D andOrder now for early delivery' PP3 batteries. Charge/test switch, LED

indicators at each of the 5 chargingCOMPUTER GAMES points. Mains powered. 210 x 100 x

Z901 Can you follow the flashing light/ 50mm £7.95.Model A124. Unit plugs directly into

pulsating tone sequence of this famous 13A socket, and will charge up to 4 AAgame? Supplied as a fully working PCB cells at a time. Only £4.80.with speaker (no case) plus fullinstructions. Only £4.95 NI -CAD BATTERIES

AA size 99p each; C size 199p; D size2902 Probably the most popular 220p; PP3 size 395p.electronic game on the market - basedon the old fashioned pencil and paper STABILIZED PSU PANELbattleship game, this computerized A199. A versatile stabilized powerversion has brought it bang up to date! supply with both voltage (2-30V) andWe supply a ready built PCB containing current (20mA-2A1 fully variable. Many76477 sound effect chip, TMS1000 uses inc bench PSU, Nicad charger,micro -processor chip, R's, C's etc. gen. purpose testing. Panel ready built,Offered for its component value only tested and calibrated. £7.75. Suitable(board may be cracked or chipped, it's transformer and pots E6.00. Full dataonly £1.95. Instructions and circuit, 30p. supplied.

GREENWELDGoods normally despatched of post.by return

443D Millbrook Road Southampton SO1 OHXOur shop has enormous stocks of Tel (0703) 772501components and is open from ALL PRICES INCLUDE VAT;9-5.30 Mon -Sat. Come & see us!! JUST ADD 60p P&P


Put the thrilkipuwerbacktutuyew pregrams with

K! ...UNTILONE DAY HE DISCOVERED

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THIS ISGOSH!A -MAZE -I0

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INTROVERTEDMIDNIGHT HACKER.

OURN BUG'S GOT

TO BE IN HERE

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BIG Kstylish, unusual, obnoxious and irritatingly

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BIG K On sale 15th March


E.E. PROJECT KITS MAGENTA TEACH IN 84Full Kits inc. PCBs, or veroboard, hard-ware, electronics, cases (unless stated).Less batteries.If you do not have the issue of E.E. whichincludes the project - you will need toorder the instruction reprint as an extra --50p each. Reprints available separately50p each L p&p 508.

DIGITAL MULTIMETER add on for BBC MicroMar. B4 £2498NI -CAD BATTERY CHARGER Mar. 84 £9.85REVERSING BLIPPER Mar. 84 £6.78D.I.N. LEAD TESTER Mar. 84 £8.32PIPE FINDER Mar 84 £3.60LOW POWER STEREO AMP Mar. 84 £27.88IONISER Feb 84 E23.98EPROM PROGRAMMER IZX811 Feb 84 £14.48SIGNAL TRACER Feb 84 £13.35CAR LIGHTS WARNING Feb 84 £3.76GUITAR TUNER Jan 84 £17.73BIOLOGICAL AMPLIFIER Jan 84 E19.16CONTINUITY TESTER Dec 83 £9.99CHILDREN'S DISCO LIGHTS Dec 83 E8.42NOVEL EGG TIMER Dec 83 inc. case £1024SPEECH SYNTHESIZER FOR THE BBC MICRONov 83 less cable - sockets £2198MULTIMOD Nov 83 E16.98LONG RANGE CAMERA/FLASHGUN TRIGGERNov 83 £13.50HOME INTERCOM less link wire Oct. 83E14.38IMMERSION HEATER TELL -TALE Oct 8319.98TEMPERATURE TRANSDUCER AMP Oct.83 E14.87SHORT WAVE RADIO less 'phones, Oct.83 £25.63Mono headphones extra £3.36DIGITAL TO ANALOGUE BOARD Oct. 83119.98less cable, case & connectorHIGH POWER DAC DRIVER BOARD Oct. 83 lesscase £12.52A TO D CONVERTER FOR RM3802 Sept. 83 incplug £35.98HIGH SPEED A TO D CONVERTER Sept 83 lesscable & connector £27.98SIGNAL CONDITIONING AMP Sept 83 nocase £8.98STORAGE 'SCOPE INTERFACE FOR BBC MI-CRO Aug 83 less software £15.38PEDESTRIAN CROSSING SIMULATIONBOARD Aug 83 no case £10.29HIGH POWER INTERFACE BOARD Aug 83 nocase £10.38CAR INTRUDER ALARM Aug 83 £16.98TRI BOOST GUITAR TONE CONTROLLER July83 E8.35USER PORT I/O BOARD less cable -Wes E10.49USER PORT CONTROL BOARD July 83 lesscable plug £25.14BINARY BANDIT GAME July 83 less case £998EPROM PROGRAMMER Jun. 83 less software,TRS80 £44.99 Genie £45.73ENVELOPE SHAPER Jun. 83 less case £12.33REAL TIME CLOCK May 83 less software and

cases.Apple II E33.98 BBC £39.59 less power plugMODEL TRAIN CONTROLLER May 83 E27.17GUITAR HEADPHONE AMPLIFIER May 83E7.92MW PERSONAL RADIO less case. May 83 092MOISTURE DETECTOR May 83 E5.46CAR RADIO POWER BOOSTER April 83£11.99FUNCTION GENERATOR April 83 £45.98FLANGER SOUND EFFECTS April 83 E24.17NOVELTY EGG TIMER April 83 less case £5.48ZX SPECTRUM AMPLIFIER April 83DUAL POWER SUPPLY March 83BUZZ OFF March 83SPEECH PROCESSOR Feb. 83PUSH BIKE ALARM Feb. 83DOUBLE DICE Jan. 83ELECTRONIC V/I METER Dec. 82ZX TAPE CONTROL Nov. 82SINE WAVE GEN Oct. 82G P. PRE -AMP Oct. 82LIGHTS ON ALERT Oct. 82CONTINUITY CHECKER Sept. 82SOUND SPLITTER Sept. 82SOUND RECOMBINER Sept 82SCREEN WASH DELAY Sept 82CB ROGER BLEEPER Aug. 82

£9.87E59.38£4.51 's

* * * *,£11.66 " FUN WITH ELECTRONICS£11.73 Enjoyable introduction to electronics. Full of£11.90 * very clear full colour pictures and easy to followE12.52 text. Ideal for all beginners - children andE7.13 JP adults. Only basic tools needed. 64 full colour

E16.11 pages cover all aspects - soldering - fault£6.09 * finding - components !identification and how£4.68 they work).15.47 or Also full details of how to build 6 projects -

£17.35 burglar alarm, radio, games, etc. Requires Sol -£4.07 dering - 4 pages clearly show you how.£4.93 * COMPONENTS SUPPLIED ALLOW ALL£932 PROJECTS TO BE BUILT AND KEPT.

CAMERA OR FLASH GUN TRIGGER Mar. 82E13.85 less tripod bushes

POCKET TIMER Mar. 82 E4.10GUITAR TUNER Mar. 82 117.19SIMPLE STABILISED POWER SUPPLY Jan. 82

£26.98MINI EGG TIMER. Jan. 82. £4.40SIREN MODULE Jan. 82 less speaker E6.10MODEL TRAIN CHUFFER Jan 82 E8.98SIMPLE INFRA RED REMOTE CONTROLNov 81 £18.70EXPERIMENTER CRYSTAL SET Nov. 81 lessaerial £6.60Headphones E3.36 extraCAPACITANCE METER Oct. 81 125.81SUSTAIN UNIT Oct. 81 E13.99'POPULAR DESIGNS' Oct. 81 £00.00TAPE NOISE LIMITER £498HEADS AND TAILS GAME £2.75CONTINUITY TESTER £4.48PHOTO FLASH SLAVE £3.80FUZZ BOX £7.98SOIL MOISTURE UNIT - £6.39ICE ALARM £8.700-12V POWER SUPPLY Sept. 81 119.48CMOS CAR SECURITY ALARM Sept. 81 £9.95CMOS DIE Sept. 81 £8.80CMOS METRONOME Aug. 81 E8.99COMBINATION LOCK July 81 less case 121.58LIGHTS REMINDER AND IGNITION LOCATORE.E. May 81 E6.26SOIL MOISTURE INDICATOR E.E. May 81 £4.49GUITAR HEADPHONE AMP E.E. May 81 E4.66PHONE BELL REPEATER/BABY ALARM May81 £6.15INTERCOM April 81 124.43SIMPLE TRANSISTOR & DIODE TESTERS Mar.81 Ohmeter version E 2 .22Led version £2.98LED DICE Mar. 81 E9.35MODULATED TONE DOORBELL Mar, 81 £7.352 NOTE DOOR CHIME Dec. 80 E11.35LIVE WIRE GAME Dec. 80 £12.87GUITAR PRACTICE AMPLIFIER Nov. 80E14.10 less case. Standard case extra E3.88SOUND TO LIGHT Nov. 80 3 channel £23.40TRANSISTOR TESTER Nov. 80 £12.80AUDIO EFFECTS UNIT FOR WEIRD SOUNDSOct 80 £14.40IRON HEAT CONTROL Oct. 80 £6.30TTL LOGIC PROBE Sept. 80 E5.68ZENER DIODE TESTER Jun. 80 £7.30LIGHTS WARNING SYSTEM May 80 £5.20BATTERY VOLTAGE MONITOR May 80 15.66CABLE & PIPE LOCATOR less coil former Mar80 £4.61KITCHEN TIMER Mar. 80 E16.20MICRO MUSIC BOX Feb. 80 £17.86Case extra £3.60SLIDE/TAPE SYNCHRONISER Feb 80 113.50MORSE PRACTICE OSCILLATOR Feb. 80 £498SPRING LINE REVERB UNIT Jan 80 £27.20UNIBOARD BURGLAR ALARM Dec. 79 £6.70DARKROOM TIMER July 79 £3.20ELECTRONIC CANARY Jun. 79 £690TRANSISTOR TESTER Apr. 79 £598MICROCHIME DOORBELL Feb. 79 £1798FUSE CHECKER Sept. 78 E2.54SOUND TO LIGHT Sept. 78 19.20CAR BATTERY STATE INDICATOR less caseSept. 78 E2.29R.F. SIGNAL GENERATOR Sept. 78 E31.20IN SITU TRANSISTOR TESTER Jun. 78 E7.50FLASHMETER less calc & diffuser May78 £16.50WEIRD SOUND EFFECTS GENERATOR Mar.78 E6.20AUDIO VISUAL METRONOME Jan. 78 £6.58ELECTRONIC TOUCH SWITCH Jan. 78 E2.99RAPID DIODE CHECK Jan. 78 £3.15PHONE/DOORBELL REPEATER July 77 E820ELECTRONIC DICE Mar. 77 £6.24

* * * * * *

2 -WAY INTERCOM July 82 no case 14.52 * Supplied less batteries & cases.ELECTRONIC PITCH PIPE July 82 15.40 FUN WITH ELECTRONICS.REFLEX TESTER July 82 ET" * COMPONENT PACK £1648SEAT BELT REMINDER Jun 82 £4.10 BOOK EXTRA £125EGG TIMER June 82 £5.44 * Book available separately *CAR LED VOLTMETER less case. May 82E3.18V C 0 SOUND EFFECTS UNIT Apr. 82 E12.71 * * * * * * * * * * * * * *

* *

*

MORE KITS ANDCOMPONENTSIN OUR LISTS

ELECTRONICSCATALOGUE

Illustrations, descriptions, circuits all in -FREE PRICE LIST

Price list included with

producteluded. Up-to-date price list enclosed. All pro -

orders or send sae (9 x 4) ducts are stock lines for fast delivery.CONTAINS LOTS MORE

KITS, PCDs & Send 80p in stamps or add 80p to order.COMPONENTS Free to Schools/Colleges requested on official

letterhead.

MAGENTA ELECTRONICS LTD.

EE15, 135 HUNTER ST., Add Sop p&p to orders.

BURTON -ON -TRENTall rs

Prices include VAT.[(-114./.11,1.1A1:1;1:21;

STAFFS, DE14 2ST. Sae all enquiries.Official orders welcome.MAIL ORDER ONLY. OVERSEAS: Payment must be sterling.

0283 65435, Mon -Fri 9-5. IRISH REPUBLIC and BFPO. UK PRICES.Access/Barclaycard (Visa) by EUROPE. UK PRICES plus 10%.phone or post. ELSEWHERE, write for quote.24 hr Answerphone for credit card orders.

Ikea eh ........,

* NEW SERIES - ALL COMPONENTS IN STOCK NOW FOR *1* FAST DELIVERY. All top quality components as specified by ** Everyday Electronics. Our kit comes complete with FREE ** COMPONENT IDENTIFICATION SHEET. Follow this edu- *

cational series and learn about electronics - Start today.* MAGENTA'S TEACH IN KIT INCLUDES ALL OF THESE TOP *

QUALITY ITEMS: resistors, pot, capacitors, semiconductors, ** varicap diode, leds, ferrite rod, sockets, crystal earpiece, termi-* nal blocks, wire and of course 2 breadboards. PLUS A FREE* COPY OF OUR CATALOGUE & PRICE LIST. AVAILABLE NOW* - TEACH IN 84 KIT. £18.98 inc VAT. P +P 50p. Send now for ** fast delivery. Reprints of previously published parts 50p each. ** Official school/college orders welcome.* * * * * * * * * * ** * * * * * * * * * * * * * * *

SOLDERING/TOOLSANTEX X5 SOLDERING IRON 25W £629SOLDERING IRON STAND £2.18SPARE BITS. Small, standard, large, £1.04each. For X5 -X25SOLDER. Handy size El .38SOLDER CARTON £2.50DESOLDER BRAID 69pHEAT SINK TWEEZERS 35pDESOLDER PUMP £6.48HOW TO SOLDER LEAFLET 13pLOW COST CUTTERS £1.69LOW COST LONG NOSE PLIERS £1.68WIRE STRIPPERS & CUTTERS £2.88

PRECISION PETITE12V PCB DRILL £12.80DRILL STAND E8.78VERO SPOT FACE CUTTER £1.76PIN INSERTION TOOL £2.52VEROPINS Ipk of 1001 0.1" 65pMULTIMETER TYPE 1 (1.000 opvl £595CROCODILE CLIP TEST LEAD SET. 10 leadswith 20 clips E1.15RESISTOR COLOUR CODE CALCULATOR 23pCONNECTING WIRE PACK TYPE ED. 11colours 40pILLUMINATED MAGNIFIERS

Small 2" dia. 15 wag) 0.32Large 3" dia. 14 magi £2.52

CORE TRIM TOOL 39pPRESET TRIM TOOL 60pFREEZER AEROSOL £1.59CONTACT CLEANER AEROSOL E1.45ELECOLIT CONDUCTIVE PAINT £4.99PVC TAPE tRGB) 3 reels E39pSCREWDRIVER SET E1.98POCKET TOOL SET E3.98DENTISTS INSPECTION MIRROR £2.85JEWELLERS EYEGLASS £1.50PLASTIC TWEEZERS 69p

MULTIMETER TYPE 2. O'N360TR) 20K o.p.vwith transistor tester. E14.99AC - DC volts. DC current. 4 very useful resis-tance ranges. We've used it and we like it.

4' / HELPING HANDS JIG £6.65Heavy base. Six ball andsocket joints allow infinitegariation of clips through360°. Has 2j" diameter 12.5magnifier attached), usedand recommended by ourstaff.

PAIR OF PROBES WITH LEADS Icc) 77p0 MAX PUNCHES

3/8"£2.98; 1/2"13.06; 5/8" £3.17; 3/43.24.

Speakers Mm 8 ohm 87p; 64 ohm 89p; 80 ohm90pCrystal earpiece 57pMagnetic earpiece 19pStethoscope attachment 69pMono headphones E3.36Stereo headphones £5 49Telephone pickup coil 68pMin buzzer 6V 75p 12V 72p.Euro breadboard5 Dec breadboardBimboard breadboardVerobloc breadboard

£6.20E3.98E6.98£5.88

BOOKS:

50 Simple L.E.D. CircuitsHow to Make Walkie-TalkiesProjects in Opto-ElectronicsElectronic Projects for BeginnersElectronic Security Devices50 Circuits Using 7400 Series IC'sSecond Book of CMOS IC ProjectsElectronic Household ProjectsRadio Control for BeginnersElectronic Synthesiser ProjectsHow to Identify Unmarked IC's 65pInternational Diode Equivalents Guide £225Handbook of Integrated Circuits (IC's) Equiv.& Substitutes E1.95Beginners Guide to Building ElectronicProjects E1.95Second Book of Transistor Equivalents andSubstitutes f 1 .75How to Build Your Own Solid StateOscilloscope £1.95Semiconductor Data Book Newnes £6.95Basic Electronics. Theory and practice E8.98Burgular Alarm Systems £5.55Electronics. Build and Learn £3.90Electronic Projects in Music £3.90Electronic Projects in Photography f3 90

A Practical Introduction to Digital IC's £1 75How to design and Make Your Own PCB's

£1.95E1.50E7.95£1.95E1.95E1.95V .75E1.50El 75£1.75E1.75

PCB etching kit2X81 edge connectorFerrite rod 5 inchPP3 clips 10p PP9 clips 11p.2 Station intercornmIC Sockets 8 pin 16p; 14 pin 17pTraditional Style BellPublic Address Mic 50KMic Insert CrystalCassette MicPillow SpeakerHorn Speaker 8 ohm

£6.48£2.25

59p

£10.5316 pin 18p

£1.95£4.95

45pf 1.29p

E1.40£698

Microprocessors for Hobbyists E4 75Electronic Test Equipment ConstructionBP75 £1.75Electronic Projects for Home Security £3.90Questions and Answers Electronics £2.7020 Solid State Projects Car and Garage E4.80110 Electronic Alarm Projects E5.9852 Projects using IC741 £1.25IC555 Projects £195Electronic Music Projects £1 75Practical Construction of Pre -Amps, ToneControls, Filters -t- Atten. £1.95Radio Control For Beginners £1.75Mobile Disco Handbook E1.35More books in our price list

ADVENTURES WITHMICROELECTRONICS

Similar to 'Electronics' below. UsesI.C.s. Includes dice, electronic organ,doorbell, reaction timer, radio etc.Based on Bimboard 1 bread board.Adventures with Microelectronics £3.20Component pack £34.64 less battery.

ADVENTURES WITH ELECTRONICS tY.,7:.7,An easy to follow book suitable for all ages. Ideal for beginners. No soldering, uses an S -Dec Breadboard. Gives clear instructions with lots of pictures. 16 projects - includingthree radios, siren, metronome, organ, intercom, timer, etc. Helps you learn aboutelectronic components and how circuits work. Component pack includes an S -Decbreadboard and all the components for the projects.Adventures with Electronics £2.85. Component pack £20.98 less battery.


PREVIOUSLY ADVERTISEDSTILL AVAILABLETape punch and readerBench isolating transformer 250 watt .

BOAC in-flight stereo unitDrill assortment 4 each 25 sizes between 25mm & 2.5mmBattery condition tester, less boxNicad chargers, mainsFlourescent inventor 13 watt from 12vTen digit stitch pad-pb phone etc.Uniselector 2 pole 25 wayWater valve mains operatedCounter 6 digit mains operatedditto 12v zesettableDouble glazing clear PVC sheet, 23:" wide -per running ft.Locking mechanism with 2 keysMagnetic ClutchMouth operated suck or blow switchSolenoid with slug 8 12v battery op.ditto 230v mainsTimer Omron STP NH 110v AC CoilKey switch with 2 keys dp mainsAir valve mains operatedLatching relay mains operatedDry film lubricant aerosol can ..Coin op switch, cased with coin tray

£22 50£7.75E1.50

E11.50E1.75E0 75E3 50

El 95Ea 60E2 50El 15£345£0.15El 15Ea 50£2 30El 82E2 30E6 90El 75E3 75E3 50£0.65£4.60

8 POWERFUL MODELMOTORS(all different)for robots, meccanos, drills,remote control planes, boats,etc. £2.95.

arc

laai,aietaINK

Complete kit of parts for a three channel sound to light unitcontrolling over 2000 watts of lighting. Use this at home if youwish but it is plenty rugged enough for disco work. The unit ishoused in an attractive two tone metal case and has controls foreach channel, and a master on/off. The audio input and outputare by %" sockets and three panel mounting fuse holders providethyristor protection. A four pin plug and socket facilitate ease ofconnecting lamps. Special price is £14.95 in kit form or £25.00assembled and tested.

12 volt MOTOR BY SMITHSMade for use in cars, etc. these are serieswound and they become morepowerful as load increases. Size3'4" long by 3" dia. They havea good length of Yz" spindle -Price £3.45.Ditto, but double ended E4.25.Ditto, but permanent magnet £3.75.

EXTRA POWERFUL 12v MOTORProbably develops up to hp. so it could be used to power ago-kart or to drive a compressor, etc. £7.95 t- £1.50 post.

THERMOSTAT ASSORTMENT10 different thermostats. 7 bi-metal types and 3 liquid types.There are the current stets which will open the switch to protecidevices against overload, short circuits, etc., or when fitted sayin front of the element of a blow heater, the heat would tripthe star if the blower fuses; appliance stats, one for high temp-eratures, others adjustable over a range of temperatures whichcould include 0 - 100°C. There is also a thermostatic pod whichcan be immersed, an oven stet, a calibrated boiler stat, finally a,'iCe seat which, fitted to our waterproof heater element, up in thiiloft could protect your pipes from freezing. Separately, thesethermostats could cost around £15.00 - however, you can havethe parcel for E2.50.

MINI MONO AMP on pc.b., size 4"x 2" (app.(Fitted volume control and a hole for a tone con-trol should you require it. The amplifierhas three transistors and we estim-ate the output to be 3W rms.More technical data will be includ-ed with the amp. Brand new,perfect condition, offered at the verylow price of £1.15 each, or 10 for £10.00.

- BARGAIN OF THE YEAR -The AMSTRAD Stereo Tuner.This ready assembled unit is the ideal tuner for a musiccentre or an amplifier, it can also be quickly made into apersonal stereo radio - easy to carry about and which willgive you superb reception.

Other uses are as a "get you to sleep radio", you could eventake it with you to use in the lounge when the rest of thefamily want to view programmes in which you are notinterested. You can listen to some music instead.

Some of the features are: long wave band 115 - 270 KHz,medium wave band 525 - 1650KHz, FM band 87 -108MHz, mono, stereo & AFC switchable, tuning meterto give you spot on stereo tuning, optional LED wave bandindicator, fully assembled and fully aligned. Full wiringup data showing you how to connect to amplifier or head-phones and details of suitable FM aerial (note ferrite rodaerial is included for medium and long wave bands. Allmade up on very compact board.

Offered at a fraction of its cost: only £6.00£1.50 poet insurance.

THIS MONTH'S SNIPII you order 4 Amstrad Stereo Tuners, as described inbottom left-hand column, you can have them for£20.00 Including post. Offer closes April 30th.

REVERSIBLE MOTOR with control gear Made by thefamous Framco Company this robust motor is aPProx 7Vr" long, 3/A"dia. 3/8" shaft. Very powerful, almost impossible to stop. Ideal foroperating stage curtains, doors, ventilators, etc. Even garage doors ifproperly balanced. Offered complete with control gear as follows:1 Framco motor with gear box 1 push to start switch1 manual reversing & on/off switch 2 limit stop switches1 circuit diag. of connections ONLY £19.50 r- postage E2.50.

FOR SOMEONE SPECIALWhy not make your greeting card play a tune? It could play'Happy Birthday'. 'Merry Christmas, 'Wedding March', etc, or'Home Sweet Home', etc. Wafer thin 3 part assemblies, formaking cards musical. Mini microchip speaker and battery withswitch that operates as the card is opened. Please state tune whenordering. Complete, ready to work £1.25.

JOYSTICKWHY PAY £10 OR MORE - Make yourself a Joystick -full details were given in Dec/Jan 'Sinclair Projects'. We willsupply complete kit for £2.30. Although designed for theSpectrum or 2081 it is equally suitable for any home computer.

TELEPHONE ITEMSPlug and Wall socket 4 pin or 5 pin E3 45Plugs only 4 pin or 5 Pin El 15Modern desk telephone E7 50Heavy black old type E5 50External bell unit E6 50Bell ringing power unit Ea 50Pick up coil ............. £1.15STABILISED POWER SUPPLY (Mains Input)By LAMDA IUSAI - Ideal for computer add-ons, d.c. output.Regulated for line volts and load current. Voltage regulation .1%with input variations up to 20% - load regulation 1% from noload to full load - or full load to no load. Complete in heavy dutycase - Models available: 5v 9A £23. 12v 1.5AE13.25. 15v - 1.2A E13.25. 24v 2A £23.

PRESTEL UNIT - brand new and complete except far 7plug in IC's - Price: £19.75r £2.00 p&p.Note: British Tele.com may notconnect this equip.ment as there is nomanufacturer toguarantee it, howeverit is well worth buyingfor its immense breakdownvalue - sold originally at over £150.

25A ELECTRICAL PROGRAMMERLearn in your sleep: Have radio playing andkettle boiling as you wake - switch on lights toward off intruders - have a warm house to comehome to. You can do all these and more. By afamous maker with 25 amp on/off switch.Independent 60 minute memory logger.

beautiful unit at £2.50.

FROZEN PIPES. Can be avoided by winding our heating cablaround them - 15 mtrsconnected to mains costs only about 10p perweek to run. Hundreds of other uses as it is waterproof and veryflexible. Resistance 60 ohms/rnetre. Price 28p/metre or 15 m for £3 9524 HOUR TIME SWITCH Made for control of RandallCentral Heating Boilers these give 2 on/offs per 24 hrs. Equallysuitable for control of immersion heaters of heating systems. £4.60.

50 THINGS YOU CAN MAKEThings you can make include Multi range meter, Lowohms tester, A.C. amps meter. Alarm clock, Solderingiron minder, Two way telephone. Memory jogger, Liveline tester, Continuity checker, etc. etc., and you will stillhave hundreds of parts for future projects. Our 10Kgparcel contains not less than 1,000 items - panel meters,timers, thermal trips, relays, switches, motors, drills, taps,and dies, tools, thermostats, coils, condensers, resistors,neons, earphone/microphones, nrcad charger, power unit,multi -turn pots and notes on the 50 projects.

YOURS FOR ONLY £11.50 plus £3.00 post.

MINI -MULTI TESTER Deluxe pocket size precision mov-ing coil instrument, Jewelled bearings .2000 o.p.v.mirrored scale.11 instant range measures: DC volts 10, 50, 250, 1000.

AC volts 10, 50, 250, 1000.DC amps 0 - 100 mA.

Continuity and resistance 0 - 1 meg ohmsin two ranges. Complete with test prodsand instruction book showing how tomeasure capacity and inductance as well.Unbelievable value at only £6.75 60p

post and insurance.

FREE Amps range kit to enableyou to read DC current from 0 10 amps, directly on the 0 - 10scale. It's free if you purchasequickly, but if you already own aMini -Tester and would like one,send £2.50.

J. BULL (Electrical) Ltd.(Dept. HE). 34 - 36 AMERICA LANE,

HAYWARDS HEATH, SUSSEX RH16 30U.Established30 YEARS

MAIL ORDER TERMS: Cash, P.O. or cheque with order. Orders under£12 add 60p service charge. Monthly account orders accepted fromschools and public companies. Access & B/card orders accepted day ornight. Haywards Heath (0444) 454563. Bulk orders: phone for quote.Shop open 9.00 - 5.30, mon to Fri, not Saturday.

STORE CLOSING SALEAll stocks must go from one of our big warehouses. 10,000,000items, everything from AERIALS to ZENER will be cleared atfantastically low prices if you are a manufacturer you can saveyourself a fortune send for our Sale List, not for small buyers asminimum order £100.

EXTRACTOR FANS - MAINS OPERATEDWoods extractor.

5" - E5.75, Post E1.25.6" - £6.95, Post E1.25.

5" Plannair extractor£6.50. Post £1.25.

4"x 4" Muffin 115v.£4.50, Post 75p.

4"x 4" Muffin 230v.E5.75. Post 75p.

All the above ex -computer,those below are unused.4" x 4" £8.50. Post 75p.9" American made

£11.50. post £2.00.Tangential Blower 10 x 3air outlet, dual speed

£4.60. Post E1.50.

TANGENTIAL BLOW HEATERby British Solartron, asused in best blow heaters.2Kw approx 9" wide £5.95,3Kw either 9" or 12" wide(your choice) £6.95 com-plete with 'cold' half' and'full' heat switch. safetycut out and connection dig.Please add post £1.50 for 1 or £2.30 for two.

2.5 Kw KIT Still available £4.95+ £1.50 post.

1MINIATURE WAFER SWITCHES2 pole, 2 way -- 4 pole, 2 way - 3 pole, 3 way -4 pole, 3 way - 2 pole, 4 way - 3 pole, 4 way -2 pole, 6 way - 1 pole, 12 way.All at 25p each or 10 for £2.00

BLEEP TONE These work off 12v and have an unusual andpleasant bleep 69p each.

CONNECTING WIRE PACK 48 lengths of connectingvvire, each 1 metre long and differently colour coded, a must forthose difficult interconnecting jobs. 85p the lot.

RED LEDS to for 69p. mo for £5.75. 1000 for £52.

IN LINE SIMM ERSTAT Ideal heat controller for solderingiron and many other hand-held appliances. E2.30. 10 for £17.25.

VENNER TIME SWITCHMains operated with 20 amp switch, oneon and one off per 24 hrs. repeats dailyautomatically correcting for the lengthen-ing or shortening day. An expensive timeswitch but you can have it for only £2.95.These are without case but we can supplya plastic case - £1.75 or metal case - £2.95.Also available is adaptor kit to convertthis into a normal 24 hr. time switchbut with the added advantage of up to12 on/offs per 24 hrs. This makes an

ideal controller for the immersion heater.Price of adaptor kit is E2.30.

IONISER KITRefresh your home, office, shop, work room, etc. with anegative ION generator. Makes you feel better and workharder - a complete mains operated kit, case included.

611.95 plus £2.00 post.

OTHER POPULAR PROJECTSShort Wave Set - covers all the short wave bands usingplug-in coils. Kit complete . . . .....R C Bridge Kit3 Channel Sound to Light - with fully prepared metal caseDitto - made upBig Ear, listen through wallsRobot controller - receiver/transmitterIgnition kit - helps starting, saves petrol, improvesperformanceSilent sentinel Ultra Sonic Transmitter and receiverCar Light 'left on' alarmSecret switch - fools friends and enemies alike .

3 - 30v Variable Power Supply2 Short & Medium wave Crystal Radio3v to 16v Mains Power Supply KitLight Chaser . . - three modes .

Mullard Unilex HiFi stereo amplifier with speakersRadio stethoscope - fault finding aidMug stop - emits piercing squarkMorse Trainer - complete with keyDrill control kitDrill control kit - made upInterrupted beam kitTransmitter surveillance kitRadio MikeFM receiver kit - for surveillance or normal FMSeat Belt reminderCar Starter Charger KitSoil heater for plants and seedsInsulation Tester - electronic meggerBattery shaver or fluorescent from 12vMatchbox Radio - receives Medium WaveMixer Pre -amp - disco special with caseAerial Rotator - mains operatedAerial direction indicator40 watt amp - hifi 20hz - 20kHzMicrovolt multiplier - measure very low currents withordinary multitesterPure Sine Wave GeneratorLinear Power output meter115 Watt Amplifier 5Hz 25kHzPower supply for 115 watt ampsStereo Bass Booster, most items

E14.50

E9 95£14.95£25 00

£9 50£9 50

£13 95£9.50E3 50£1.95

£1380E3 99E1 95

E17.50£16.75

Ea 80E2 50£299£3 95E6 95£2 50£2 30£6 90E3.50£3 00

E15 50£1650

E7 95£6 90E2 95

£1600E29 50

E5 50E9 50

£3 95E5 75

E11 50£13 50

£8 50£8 95

Frivi0-,raua

PRI111%.Are you bewildered by the choice of Soft-ware Programs on the market?Not sure what Program you really need,what it does or where to get it?

sonwage INDEXIs your answer

The most comprehensive magazine listing of Soft-ware programs for the eight leading Microcomputers. BBC COMMODORE 64 DRAGON VIC 20 ORIC ATARI 400/800 SPECTRUM ZX81


Software Index takes the headache out ofchoosing the programs suited to your Micro.

For people involved in electronics andspecialist programs, Software Index willprovide the information you need and be avaluable time -saving guide.Games, education, business and personalmanagement are also covered.

DON'T LET SOFTWARE GIVE YOUA HARD TIME, GET THE USERGUIDE TO MICROCOMPUTER

Microcomp

SOFTWARE-

uter Software

User Guide to

sorovaReman

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285

Miscellaneous EVERYDAYCOPPERFOIL

TAPEA NEW CONCEPT FOR

LOW VOLTAGE PROJECTSThin self-adhesive pure Copperfoil tape. A newconcept for low voltage projects (up to 24 voltsAC/DC) with a current carrying capacity of over5 amps.

Ideal for bus bar supplies, prototype boards,burglar alarms etc, etc. The possibilities areendless.

5/32"wide x 36 yard rolls @ £2.95 per roll plus40p post and packing per order or send SAEfor Data Sheet and sample.

COPPERFOIL ENTERPRISES,Dept. EE, 141 Lyndhurst Drive,Hornchurch, Essex RM1 1 1JP.

ELECTRONICSARNE WITHOUT0

Build electroniccircuits without solderon a Roden S -Dec.This has built-incontacts and holes intowhich you plug your components.Suitable for all ages. Can be usedtime after time. Ideal gift forstudents or experimenters.Full instructions and 2 circuitdiagrams with each S -Dec.Send cheque or P.O. to -Rodeo Mamas, Dep EE n6,-;High March, Daventry.Northants, Nail 40E. .11. ZiZi including p & p

ORIC-1 EPROM PROGRAMMER. Full hardwareand software plans of a low-cost unit which programs,stimulates and duplicates Eproms on your 48K Oric.Price £2.50 from HOWELL & COLLINS. 43 Cross-ways, Crawley, Sussex RH1 0 1QT.

For SaleVARIABLE VOLTAGE POWER SUPPLY 0-15v1.5A. 14 in working order with built in voltmeter andoverload protection £13.50 + £3.00 p&p. S.A.E.lists. S.H.E. 5, St. Josephs Park, Ballycruttle, Down-patrick BT30 7EN.

SecurityBURGLAR ALARM EQUIPMENT. Free catalogue.C.W.A.S. Ltd., 0274-308920. Showrooms open 9-5,Mon -Sat.

ELECTRONICI,and computer PROJECIReach effectively and economically to -days enthusiasts anxious toknow of your products and services through our semi -display andclassified pages. Semi -display spaces may be booked at £7-80 persingle column centimetre (minimum 2.5cm). The prepaid rate for classifiedadvertisements is 33 pence per word (minimum 12 words), box number60p extra All cheques, postal orders, etc., to be made payable to

SECURITYAlarm Systems

FREE COMPREHENSIVE CATALOGUE!

LOWEST DISCOUNT PRICES HIGHEST QUALITY EQUIPMENT FREE DIY DESIGN GUIDE FULLY ILLUSTRATED MICROCHIP CIRCUITRY QUICK DESPATCH SERVICE FULL INSTRUCTIONS

SEND SAE OR PHONE

C-TEC SECURITY, Dept EE,60 Market St, Wigan WN1 1HX.Telephone (0942) 42444

Receivers & Components

ELECTRONIC COMPONENTS MERSEYSIDE,Myca Electronics, 2 Victoria Place, Seacombe Ferry,Wallasey L44 6NR. 051-638 8647.

AERIAL BOOSTERSNext to the set fitting

04511/G -UHF TV, gain about 20dbs, Tunable over the completeUHF TV band. PRICE E8.70.BII-VHF/FM RADIO, gain about 14dbs, when on the offposition connects the aerial direct to the radio. 0.70.All Boosters we make work off a PP3/006p/Ef22 type batteryor fly to I8v DC. P&P 30p PER ORDER.

ELECTRONIC MAILOROER, 62 Bridge St, Ramsbottom,Lance BLO 9AG. Tel (0706821 3036

AccessNisa Cards Welcome SAE Leaflets

COMPONENTS & EQUIPMENT - 1984 Catalogue70p + 20p P&P. Callers: 18 Victoria Road,TAMWORTH. 369 Alumrock Road, BIRMING-HAM. 103 Coventry Street, KIDDERMINSTER.Express Mail Order Service. LIGHTNINGELECTRONICS, PO Box 8, Tamwonh, Staffs.

ORDER FORM PLEASE WRITE IN BLOCK CAPITALS

Please insert the advertisement below in the next availble issue of Everyday Electronicsfor Insertions. I enclose Cheque/P.O. for f(Cheques and Postal Orders should be crossed Lloyds Bank Ltd. and made payable to Everyday Electronics)

NAME

ADDRESS

EVERYDAY ELECTRONICS

Classified Advertisement Dept., Room 2612,King's Reach Tower, Stamford Street, London SE1 9LSTelephone 01-261 5942

Rate:33p per word, minimum 12 words. Box No. 60p extra.

Company registered in England. Registered No 53626 Registered Office: King's Reach Tower, Stamford Street, London SEt 9LS

BUMPER BOX OF BITSWOW!!! We've got so many components in stock, wecan't possibly list them all!!! - So buy a box, in it you'llfind resistors, capacitors, displays, switches, panelswith transistors, diodes, IC's etc, coils, pots and soon. All modern parts- guaranteed at least 1000 items,minimum weight 10Ibs. ONLY £8.50.

PSU PANELStabilized 5v, variable ±0.5V. Regulation 1% Max. cur-rent 2A. Will take AC I/P up to 15V, or DC I/P up to 24V.Panel 140 x 35mm contains all components exceptseries reg. transistor which is mounted separately.PCB stand-offs, included ONLY £3.95. Heatsink 75p;transformer £5.00.

RESISTOR PACKAll sorts - everything from ith to 10W. Carbon, Film,W/W, Oxide, PCB, etc. 2000 resistors - yes, 2000!!! Foronly f4.95.

SWITCH PACKSlide (up to 9 wayl, push button banks, push types- atotal of 50 switches for only £3.95.

All prices include VAT and Post/Packing.Send SAE for latest lists.

ELECTRONICS WORLD r!1d Dews Road, Salisbury, Wilts, SP2 7SN

S.A.E. ELECTRO, mechanical catalogue of kits andhits. 200 quality components £2.25 inclusive. E.M.S.15 Windmill Gardens, Whixall, Whitchurch,Shropshire.

500 SMALL COMPONENTS including TTL transis-tors £2.50, 7lbs or 10Ibs assorted components £5.00/£6.50. Fifty 74 series I.Cs on panel £2.20. Post Paid.J. W. BLANSHARD, 2 Barnfield Crescent, SaleCheshire, M33 1NL.

TURN YOUR SURPLUS capacitors, transistors etc.,into cash. Contact Coles Harding & Co., 103 SouthBrink Wisbech, Cambs. 0945-584188. Immediatesettlement.

Courses

CONQUER THE CHIP-master modem electronicsthe practical way by seeing and doing in your ownhome. Write for your free colour brochure now toBRITISH NATIONAL RADIO & ELECTRON-ICS SCHOOL, Dept C3, Reading, Berks RG I I BR.

Service Sheets

FULL SIZE SERVICE SHEETS £2 + lsae; CTV/MusC £3 + lsae. Repair/circs almost any named TV/VCR £9.50. Isae free quotations for manuals, sheets- free mag inc. service sheet. T.I.S.E.E. 76 ChurchStreet, Larkhall, Lanarks - Phone 0698 883334.

BELL'S TELEVISION SERVICE for service sheetson Radio, TV etc. £1.50 plus S.A.E. Service Manualson Colour TV and Video Recorders, prices onrequest. S.A.E. with enquiries to: BTS, 190 King'sRoad, Harrogate, N. Yorkshire. Tel: 0423 55885.


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511, .1 iillialillaliIiiil MIINO*Val -101111Mii

110011.UMW i MOOS6.60.411, 110/100111011."*. rill"....,or .OarOW

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AT YOUR SERVICEEveryday Electronics and Computer Projects and crossed "Lloyds BankLtd." Treasury notes should always be sent registered post Advertise-ments, together with remittance, should be sent to the Classified Adver-tisement Department Everyday Electronics and Computer Projects, Room2612, IPC Magazines Limited, King's Reach Tower, Stamford St, LondonSE1 9LS. (Telephone 01-261 5942).

Bimconsoles - Metal Browntog

base, BIMBOARDSPrototype with plug-in breadboards.

Part No. ABEfeite

Component support brackets suppliedBIM 2601 178 51 210 38.5 70 10.96 with all except EurobreadboardBIM 2602 280BIM 2603 381

51

51

210210

38.538.5

7070

12.1914.10 Number of

BIM 2604 483 51 210 38.5 70 16.01 Type Contact PointsBIM 2605 480 51 261 38.5 70 17.85 Eurobreadboard 500 6.25BIM 2701 178 76 210 38.5 70 11.52 Eurobreadboard PCB 500 0.75BIM 2702 280 102 210 38.5 70 13.40 Bimboard 1 550 6.55BIM 2703 381 102 210 385 70 14.86 Bimbusstnp 80 250BIM 2704 483 102 210 385 70 16.97 Bimboerd PCB 630 1.44

Bimboard Layout Pad 0.46MP Urobreadboard 1422 17/5

Bimconsoles - ABS Black or Grey base Bimboard Designer 77.00

with Grey Aluminium topBIM 6005 105 55.5 143 315 37.5BIM 6006 170 55.5 143 31.5 37.5BIM 6007 170 81.8 218 31.5 538

2.25

2.8°D3.85

ESIDE

L A PLAN

All prices inc VAT Add 60p per order on Bimboards, £2.30 perorder on Bimconsoles for p&p. SAE for full list. Mail Order only.

BIMSALESDept EE4, 48a Station Road, Cheadle Hulme, Cheadle,

Cheshire, SK8 7AB. Tel: 061 485 6667.

baker,* BAKER *GROUP P.A. DISCOAMPLIFIERS post £2150 watt Output. 4 input Miner150 wan Output. Slave 500I 50+ I50w Stereo. 300w Mono150w P.A. Vocal. 8 inputs. High/Low100 wan Valve Model 4 inputs60 wan Valve Model, 4 inputs.60 watt Mobile 240v AC and

BAKER LOUDSPEAKERSType ModelHi-Fi MajorHi-Fi SuperbDisco/P.A. Group 45Hi-Fi WooferHi-Fi AuditoriumEU F AuditoriumDisco/P.A. DG75Disco/P.A. DG I00P.A. Group 100P.A. Disco 100

BAKER DISCO SYSTEMS150 Watts twm turntables.slide controls Complete 1330

,. ..._......... ......

, 1 3

' . .0 0 0 0-** ow *pre -amp. Illustrated £99

my, Input 3 Speaker Outputs 080Slave 500 mv. Inputs £125

Mixer Echo Socket £1295 Outputs. Heavy duty 1125

Low imp and 100v line output ...L69I 2v DC. 4-8-16 ohm+100v fine ...L89

Post £2 eachSloe Watts Ohms Price12in 30 4/8/16 £16.00I2M 30 8/16 £26.0012in 45 4/8/16 £16.0012in 80 8 £25.0012in 45 8/16 £24.00I5in 60 8/16 £37.0012M 75 4/8/16 £20.0012in 100 8/16 £26.0015in 100£.35.001510 100 8/16 135.00

Carriage £30twin speakers, headphones. microphone,

or Console only £105.

RCS SOUND TO LIGHT CONTROLLER KITPrinted circuit. Cabinet. 3 channels. 1,000 watts each. Will operate fromhome Hi-Fi or Disco. £19. Post £1 or Ready Built £27.Coloured Disco Bulbs 100w ES or BC 12.20 pp f 1.50 for 6.

LOW VOLTAGE MAINS TRANSFORMERS 4550 post paid9 volt 3 amp; 12 volt 3 amp; 16 volt 2 amp; 20 volt 1 amp; 30 volt liamp; 30 volt 5 amp + 17-0-17 volt tamp; 35 volt 2 amp; 20440-60 voltI amp; 12-0-12 volt 2 amp; 20-0-20 volt I amp; 25-0-25 volt 2 amp.

ALUMINIUM CHASSIS 18 s.iv.g. Uodrilled, 4 sides, riveted comers:6 x 4 x ain. 41.75; 8 x 6 x ain. £2.20; 10 x 7 x ain. £2.75;14 0 9 x 2lin. 13.60; 16 X 6 x 2.4in. £3; 12 x 3 x 24in. 11.80;12 0 8 x 24in. 13.20; 16 x 10 0 ain. 13.80.ALI ANGLE BRACKET 6 x i x lin. 30p.ALUMINIUM PANELS 18 sm.g. 12 a 12in. 41.80; 14 x Yin. £1.75;6 x 4in. 55p; 12 x 8in. £1.30; ici x Tin. 96p; 8 x 6in. 90p; 14 x 3m.72p; 12 x Sin. 90p; 16 X 10in. £2.10; 16 X 6in. £1.30.ALUMINIUM BOXES. MANY OTHER SIZES IN STOCK.4 x 21 x 2UL MOO; 3 x 2 x tin. 80p; 6 x 4 x tin. 11.60; 8x6x3 in.12.50; 12 x 5 x 3M. E2.75; 6 x 4 x 3M. £1.00; 10 x 7 x 3M. £3.

HIGH VOLTAGE ELECTROLYT1CS 32+32/350V 50p20/500V 75p 8+8/500V . El 32+32/500V £232/350V 45p 8+16/450V . 75p 125/500V £232/500V 95p 16+ 16/350V . 75p 16+ 32 +32/500V 12

SINGLE PLAY DECKS. Post U.Make Model Cartridge PriceBSR P170 Ceramic £20GARRARD 6200 Ceramic £22BSR P182 Ceramic £26BSR P232 Magnetic £28AUTOCHANGER BSR Ceramic 020

RADIO COMPONENT SPECIALISTSDept 4, 337, WHITEHORSE ROAD, CROYDON

SURREY, U.K. TEL: 01-684 1665I ACCESSI 'VISA'

Post 65p Minimum. Callers Welcomelists 32p Same day despatch. Closed Wed

BRITAIN'S No. 1. PRACTICAL MOTORING MAGAZINE

APRIL ISSUE

Practical

FOR 0.13. HOME IMPROVEMENTS

APRIL ISSUE

FREE GIFT FREE GIFTLITTLE CHEF MAP 20 FISCHER W&LLPLUGS

bailieOWEXTRAIEXTRA Home Plus

This colour magazine

extra is free with P Motoristand P. Householder.

SPECIAL

FEATURESGADGETS

FOR THE HOME. RAISING THE

READIES,WINTER RAVAGES

REPAIRED.a

Dorit miss out on these BUMPER ISSUES ON SALE NOW!


T.V. SOUND TUNERSERIES It BUILT AND TESTED Complete with case. £26.50 +£2,00 p&p.

In the cut-throat world ofconsumer electronics, oneof the questions designersapparently ponder overis "Will anyone notice ifwe save money by chopp-ing this out?" In thedomestic TV set, one of thefirst casualties seems to bethe sound quality. Small speakersand no tone controls are common Also available with built-in headphone

and all this is really quite sad, as theamp. ONLY £32.50 + £2.00 p&p.

TV companies do their best to transmit tna highest quality sound. Given this background acompact and independent TV tuner that connects direct to your Hi-Fi is a must for qualityreproduction. The unit is mains -operated.This TV SOUND TUNER offers full UHF coverage with 5 pre -selected tuning controls. It canalso be used in conjunction with your video recorder. Dimensions: 10%"x7%"x215".E.T.I. kit version of above without chassis, case and hardware. £16.20 plus E1.50 p&p.

PRACTICAL ELECTRONICS STE EO CASSETTERECORDER KIT WITHCOMPLETECASE

ONLY £34.50 plus £2..75 p&p. NOISE REDUCTION SYSTEM. AUTOSTOP. TAPE COUNTER. SWITCHABLEE.Q. INDEPENDENT LEVEL CONTROLS. TWIN V.U. METER. WOW & FLUTTER0.1%. RECORD/PLAYBACK I.C. WITHELECTRONIC SWITCHING. FULLYVARIABLE RECORDING BIAS FORACCURATE MATCHING OF 'ALL TYPES.Kit includes tape transport mechanism, ready punched and backprinted quality circuit board and all electronic parts. ie. semiconductors,resistors, capacitors, hardware, top cover, printed scale and mains transformer.You only supply solder & hook-up wire. Featured in April P.E. reprint 50p. Free with kit.

BSR RECORD DECKSAuto -Changer model takes upto 6 records with manual over-ride. Supplied with stereoceramic cartridge.

£12.95 plus E1.75 p&p.

3 speed, auto, vet -down; withauto return. Fitted with vis-cous damped cue, tubular alu-minium counter -weighted arm,fitted with ceramic head. Ideallysuited for home or disco use.£17.50 plus £1.75 p&p.

Manual single play record deckwith auto return and cueinglever. Fitted with stereo cera-mic cartridge 2 speeds with 45rpm spindle adaptor ideallysuited for home or disco.13"x11" approx.£14.95 plus £1.75 p&p.

125W HIGH POWERAMP MODULESThe power amp kit is a module for highpower applications - disco units, guitar amplif-iers, public address systems and even highpower domestic systems. The unit is protectedagainst short circuiting of the load and is safein an open circuit condition. A large safetymargin exists by use of generously rated com-ponents, result, a high powered rugged unit.The PC board is back printed, etched andready to drill for ease of construction and thealuminium chassis is preformed and ready touse. Supplied with all parts, circuit diagramsand instructions.Accessories: Stereo mains power supply kit withtrans. £10.500 f2p&p. Mono: £7.50 + £2p&p.

SPECIAL OFFER! Replacement st. cassettetape heads. E1.80 ea. Add 50p p&p to order.Philips st. mag. cartridge. £3.95 + 60p p&p.PLINTH to suit BSR Record Player Deck(with cover). Size 16%"x 14%"x 2%". Coversize: £14%"x 13 %"x 3%". Due to fragilenature, Buyer collect only. Price: £8.95.

STEREO TUSPECIAL

OFFER!

£13.95+£2.50 p&p.

ER KIT

This easy to build 3 band stereo AM/FMtuner kit is designed in conjunction withP.E. (July '811. For ease of construction andalignment it incorporates three Mullard mod-ules and an I.C. IF System. Front scale size10%"x2%" approx. Complete with diagramand instructions.

SPECIFICATIONS: 1111111111Max. output power (RMS): 125 W. Operatingvoltage (DCI: 50 - 80 max. Loads: 4 - 16 ohm.Frequency response measured @ 100 watts:25Hz - 20KHz. Sensitivity for 100w: 400mV@ 47K. Typical T.H.D. @ 50 watts, 4 ohms:0.1%. Dimensions: 205x90 and 190x36mm.

KIT £10.50 BUILT £14.25411.15 p&p. +E1.15 p&p.

HI-FI SPEAKER BARGAINSAUDAX 8" SPEAKER £5.95+ £2.20 p&p.High quality 40 watts RMSbass/mid. Ideal for eitherHiFi or Disco use this speakerfeatures an aluminium voicecoil and a heavy 70mm dia.magnet. Freq. Res.: 20Hzto 7kHz. Imp.: 8 ohms.

AUDAX 40W FERRO -FLUIDHI-FI TWEETER Freq. res.,5KHz 22KHz. Imp.: 8 ohms.60mm sq. £5.50 + 60p p&p.

GOODMANS TWEETERS 8 ohmsoft dome radiator tweeter (3%"sq)for use in systems up to 40W.£3.95 ea + £1 p&p. £6.95 pr +£1.50.

MONO MIXER AMPIdeal forhalls andclubs.

£45.00+ £2 p&p.50 Watt, six individually mixed inputs for 2pickups (Cer. or magi, 2 moving coil micro-phones and 2 auxiliary for tape tuner, organsetc. Eight slider controls -6 for level and 2for master bass and treble, 4 extra treblecontrols for mic. and aux. inputs. Size:13%"x6%"x 3%" app. Power output 50 WRMS (cont.) for use with 4 to 8 ohmspeakers. Attractive black vinyl case withmatching fascia and knobs. Ready to use.

All mail to: 21A HIGH ST, ACTON W3 6NG.Callers: Mon - Sat 9.30 - 5.30. Half day Wed.Access phone orders on 01-992 8430.Noes Goods despatched to U.K. postai addresses onlyAll items sublet[ to availability. Prices correct et30/11/83 and subject to change without notice.Please allow 14 working days 1rom receipt of orderfor despatch. RTVC Limited reserve the right to up.date their products without notice. All enquiries sendS.A.E. Telephone or mail orders by ACCESS welcome

CALLERS TO: 323 EDGWARE ROAD,LONDON W2. Telephone: 01-723 8432.15 minutes walk from Edgware Road Tube Station)Now open 6 days a week 9 - 5.30. Prices include VAT.

R La

INDEX TOADVERTISERSBib Audio 222, 223Big K 282Bimsales 287Bi-Pak 221BK Electronics Cover IIIB.N.R.E.S. 218Butterworths 220Bull J. 284

Copperfoil Ltd 286C-Tec Security 286

Electronics Mail Order 286Electronics World 286Electronize Design Cover IIElectrovalue 223Enfield Electronics 224

Global Specialties Corporation 269Greenweld Electronics 281

Homeplus 287

ICS Intertext 223

Magenta Electronics 283Maplin Electronics Cover IV, 220

Radio Component Specialists 287R & TVC 288Rapid Electronics 219Riscomp Ltd 281Roden Products 286

Software Index 285

T.K. Electronics 222

Published approximately the third Friday of each month by IPC Magazines Ltd., Kings Reach Tower, Stamford St., London SE1 9LS. Printed in England by Chapel River Press, Andover, Hants.Sole Agents for Australia and New Zealand -Gordon and Gotch (A/Sia) Ltd. South Africa -Central News Agency Ltd. Subscriptions: Inland £12.00, Overseas E13.00 per annum payable to IPCServices, Oakfield House, Perrymount Road, Haywards Heath, Sussex. Everyday Electronics is sold subject to the following conditions namely that it shall not, without the written consent of thePublishers first given, be lent, resold, hired out or otherwise disposed of by way of Trade at more than the recommended selling price shown on cover, and that it shall not be lent, resold, or hiredout or otherwise disposed of in a mutilated condition or in any unauthorised cover by way of Trade, or affixed to or as part of any publication or advertising, literary or pictorial matter whatsoever.

TYPE'A'

TYPE 'C'

TYPE 'E

1'1 MULLARD SPEAKER KITSPurposefully designed 40 watt R.M.S. end Xwatt R.M.S. 8 ohm speaker systems recentlydeveloped by MULLARD'S specialist team inBelgium. Kits comprise Mallard woofer 18" or5"l with foam surround and aluminium voice coil.Mallard 3" high power domed tweeter. B.K.E.built and tested crossover based on Mullardcircuit, combining low loss components, glassfibre board and recessed loudspeaker terminals.SUPERB SOUNDS AT LOW COST. Kits suppliedin polystyrene packs complete with instructions.8" 40W system - recommended cabinet size 240x 216 x 445mmPrice E14.90 each + 12.00 P Et P.5" 30W system - recommended cabinet size160 x 175 x 295mmPrice E13.90 each + E1.50 P 8 P.

Designer approved flat pack cabinet kits.including grill fabric. Can be finished with iron onveneer or self adhesive vinyl etc.8" system cabinet kit E8.00 each a 12.50 P Er P.5' system cabinet kit E7.00 each . E2.00 P Er P.

STEREO CASSETTE TAPEDECK MODULEComprising of a top panel and tape mechanism coupled toa record/play back printed board assembly. Supplied asone complete unit for horizontal installation into cabinet orconsole of own choice. These units are brand new, readybuilt and tested.Features: Three digit tape counter. Autostop. Six pianotype keys, record, rewind, fast forward. play, stop andeject. Automatic record level control. Main inputs plussecondary inputs for stereo microphones. InputSensitivity: 10OrnV to 2V. Input Impedance: 68K.Output level: 400mV to both left and right handchannels. Output Impedance: 10K. Signal to noiseratio: 45d8. Wow and flutter: 0.1%. Power Supplyrequirements: 18V DC at 300mA. Connections: Theleft and right hand stereo inputs and outputs are viaindividual screened leads, all terminated with phono plugs1phono sockets provided). Dimensions: Top Panel 5 iin

11Iin Clearance required under top panel 21in.Supplied complete with circuit diagram and connectingdiagram. Anractive black and silver finish.Price 128.70 + E2.50 postage and packing.Supplementary parts for 18V D.C. power supply(transformer, bridge rectifier and smoothing capacitor)E3.50.

LOUDSPEAKERS POWER RANGETHREE QUALITY POWER LOUD-SPEAKERSI15' 12" and 8" See 'Photo).Ideal for both Hi-Fi and Disco applica-tions. All units have attractive cast alu-minium (ground finish) fixing escutcheons.Specification and Prices.15" 100 watt R.M.S. Impedance 8 ohms.50 oz. magnet. 2" aluminium voice coil. Res.Freq. 20 Hz. Freq. Resp. to 2.5KHz. Sens.97dB. Price: £34.00 each + C3.00 P&P12" 100 watt R.M.S. Impedance 8 ohms.50oz, magnet. 2" aluminium voice coil. Res.Freq. 25Hz. Freq Resp. to 4 KHz. Sens.95dB. Price £26.00 each + £3.00 P&P.

50 watt R.M.S. Impedance 8 ohms. 20oz. magnet. 1'z" aluminium voice coil. Res.Freq. 40Hz. Freq. Resp to 6 KHz. Sens.92dB. Black Cone. Price: £9.50 each. Alsoavailable with black protective grille Price.£9.99 each. P8P C1,50.

85 watt R.M.S. McKENZIE C1285GP (LEAD GUITAR, KEYBOARD, DISCO) 2'aluminium voice coil. aluminium centre dome. 8 ohm imp., Res. Freq. 45Hz., Freq.Resp. to 6.5kHz., Sens, 98dB. Price £24.00 + £3 carriage.12" 35 watt R.M.S. McKENZIE C12815TC (PA., DISCO) 2" aluminium voice coil. Twincone. 8 ohm. imp., Res. Free 45HZ., Freq. Resp. to 1 4KHz. PriceE24.00+ C3 carriage_15" 150 watt R.M.S. McKENZIE C15 (BASS GUITAR. P.A.) 3" aluminium voice coil.Die cast chassis. 8 ohm imp, Res. Freq. 40Hz., Freq. Resp. to 4KHz. Price £49 +£4

,carriage. Cabinets fixings in stock S.A.E.

PIEZO ELECTRIC TWEETERS MOTOROLAJoin the Piezo revolution. The low dynamic mass (no voice coil) of aPiezo tweeter produces an improved transient response with a lowerdistortion level than ordinary dynamic tweeters. As a crossover is notrequired these units can be added to existing speaker systems of upto 100 watts (more if 2 put in series). FREE EXPLANATORY LEAFLETSSUPPLIED WITH EACH TWEETER.

TYPE 'A'IKSN2036A13" round with protectivewire mesh, ideal for bookshelf and mediumsized Hi-fi speakers. Price £4.29 each.TYPE 'B' (KSN1005AI 3 ", " super horn. Forgeneral purpose speakers, disco and P.A.systems etc. Price £4.99 each.TYPE 'C' IKSN6016Al2- . 5" wide dispersionhorn. For quality Hi'fi systems and qualitydiscos etc. Price £5.99 each.TYPE 'D' IKSN1025A) 2" - 6" wide dispersionhorn. Upper frequency response retainedextending down to mid range 12KHz1. Suitablefor high quality Hi-fi systems and qualitydiscos. Price £7.99 each.TYPE 'E' (KSN1038A13%" horn tweeter with

TYPE 'D" attractive silver finish trim. Suitable for Hi-fimonitor systems etc. Price £4.99 each.TYPE 'F' 1KSN1057A) Cased version of type'E'. Free standing satellite tweeter. Perfectadd on tweeter for conventional loudspeakersystems. Price 510.75 eachP&P 30p ea. (or SAE for Piezo leaflets).

TYPE 'F" B.K. ELECTRONICS

(RP 12 LOUDSPEAKERThe very best in quality

and value.Ported tuned cabinet in hard-wearing black vynide with protec-tive corners and carry handle. Builtand tested, employing 12in Britishdriver and Piezo tweeter. Spec 100watts RMS; 8 ohms; 45Hz-2OKHz;Size: 20in x 15in x 12in; Weight30 pounds.

Price: 63.00 each£120 per pair

Carriage: £5 each £7 per pair

BK ELECTRONICSPrompt Deliveries

VAT inclusive

prices

Audio Equipment

Test Equipment

by

Thandar

and

Leader

HOBBY KITS. Proven designs including glassfibre printed circuit board and high qualitycomponents complete with instructions.

FM MICROTRANSMITTE R (BUG) 90/105MHz with very sensi-live microphone. Range 100/300 metres. 57 x 46 x 14mm (9 volt)Price: £7.99pDIGITALTHERMOMETER -9.9 C to +99.9C. LED display. Com-plete with sensor. 70 x 70 mm (9 volt) Price: £27.60p3 WATT FM TRANSMITTER 3 WATT 85/115MHz varicap con-trolled. professional performance. Range up to 3 miles 35 x 84 x 12mm (12 volt) Price: £12.490SINGLE CHANNEL RADIO CONTROLLED TRANSMITTER/RECEIVER 27MHZ Range up to 500 metres. Double coded mod-ulation. Receiver output operates relay with 2amp/240 voltcontacts. Ideal for many applications. Receiver 90 x 70 x 22 mm 9/12 volt) Price: £16.49 Transmitter 80 x 50 x 15 mm (9/12 volt)Price £10.29 P&P All Kits + 75p each. S.A.E. for complete list.

BSR P256 TURNTABLEP256 turntable chassis S shaped tone arm Belt driven Aluminium platter Precision calibrated counter balance Antiskate (bias device) Damped cueing lever 240 volt AC operation (Hz) Cut outtemplate supplied Completely manual arm.This deck has a completely manual arm and isdesigned primarily for disco and studio usewhere all the advantages of a manual arm are

required.Price £32.35 each. C2.50 P&P.

el POWER AMPLIFIERMODULE

READY BUILT

40111110%;00444404

New model.Improved specification

3 watt FMTransmitter

NEW OM P100 Mk.11 POWER AMPLIFIERMODULE Power Amplifier Module completewith integral heat sink, toroidal transformerpower supply and glass fibre p.c.b. assembly.Incorporates drive circuit to powerLED Vu meter. New improved specificationmakes this amplifier ideal for P.A.. Instrumentaland Hi-Fi applications.SPECIFICATIONOutput Power:- 110 watts R.M.S.Loads:- Open and short circuit proof 4/16ohms.Frequency Response:- 15Hz - 30KHz -3dB.T.H.D.:- 0.01%.S.N.R. (Unweighted):- -118dB t3.5dBSensitivity for Max Output:- 500mV @ 10K.Size:- 360 x 115 x 72 mm Price:- £31.99 +£2.50 P&P. Vu Meter Price:- £8.50 + 50p P&P.

MOSFET versions available up to 300W. R.M.S.

HOME PROTECTION SYSTEMBetter to be 'Alarmed' then terrified.Thandar's famous 'Minder' Burglar Alarm System.Superior microwave principle. Supplied as three units.complete with interconnection cable. FULLYGUARANTEED.Control Unit - Houses microwave radar unit. rangeup to 15 metres adjustable by sensitivity control.!Three position, key operated facia switch - off - test- armed. 30 second exit and entry delay.Indoor alarm - Electronic swept freq. siren.104dB output.Outdoor Alarm - Electronic swept freq. siren, 98dBoutput. Housed in a tamper -proof heavy duty metalcase.Both the control unit and outdoor alarm contain re-chargeable batteries which provide full protectionduring mains failure. Power requirement 200/260 VoltAC 50/60Hz. Expandable with door sensors, panicbuttons etc. Complete with instructions

SAVE £128 usti,rl price £22885

BKE's PRICE E99.p&p£4SAE tor Colour brochure

STEREO DISCO MIXER with 7 band graphicequaliser and 10 segment L.E.D. Vu Meters. Manyoutstanding features.5 Inputs with individual fader controls:-2 Mag. turntable, 2 Aux. plus Mic. with talk -overswitch. Headphone monitor. Master output controlwith Hi -Low outputs. Compatible with our OMPPower Amplifiers.Size: 360 x 200 x 120 mm. Supply 240V/50Hz AC.

READYBUILT

STEREO

DISCO MIXER

UNIT 5, COMET WAY, SOUTHEND-ON-SEA, ESSEX, SS2 6TR* SAE for current lists. * Official orders welcome. * All prices include VAT. * Sales Counter. *

* All items packed where applicable in special energy absorbing PU foam. * Please phone 0702 527572 *

Full -travel, full size

KEYBOARD )Simply plugs intoexpansion port on your

SPECTRU 1

* Single -key selection of all major multi -key functions.* Plugs directly into Spectrum expansion port and

extends port for other peripherals.* Can accept Atari -type joysticks (optional extra).* Absolutely no soldering or dismantling of Spectrum.* Available in kit -form or ready -built.The kit is sold in three parts - the Keyboard Main Kit which allowsyou to make your own arrangements for connection to theSpectrum - the Adaptor Kit which contains the extension boardand socket for the expansion port and the cable between the

KIT pm.3995READY-BUILT

E44.95extension board and the keyboard -and the Case Kit which includes all thenecessary mounting hardware.

Order As LK29G (Keyboard Main Kit) Price £28.50LK30H (Adaptor Kit) Price £6.50XG35Q (Case) Price £4.95

Full construction details in Projects Book.9.

Also available ready -built for direct connection and including case.Order As XG36P (Spectrum Keyboard) Price £44.95

Maplin's Fantastic ProjectsFull details in our project books. Price70p each.

In Book 1 (XAO1B) 120W rmsMOSFET Combo -AmplifierUniversal Timer with 18 program timesand 4 outputs Temperature Gauge Six Vero Projects.

In Book 2 (XAO2C) Home SecuritySystem Train Controller for 14 trainson one circuit Stopwatch withmultiple modes Miles -per -GallonMeter.

In Book 3 (XAO3D) ZX81 Keyboardwith electronics Stereo 25WMOSFET Amplifier Doppler RadarIntruder Detector Remote Controlfor Train Controller.

In Book 4 (XAO4E) TelephoneExchange for 16 extensionsFrequency Counter 10Hz to 600 MHz Ultrasonic Intruder Detector I/O Portfor ZX81 Car Burglar AlarmRemote Contol for 25W Stereo Amp.

In Book 5 (XAO5F) Modem toEuropean standard 100W 240V AC

MAPLINPROJECTS

-----Inverter Sounds Generator for ZX81 Central Heating Controller PanicButton for Home Security System Model Train Projects Timer forExternal Sounder,

In Book 6 (XAO6G) SpeechSynthesiser for ZX81 & VIC20 Module to Bridge two of our MOSFETamps to make a 350W Amp ZX81Sound on your TV Scratch Filter Damp. Meter Four Simple Projects

In Book 7 (XAO7H) Modem (RS232)Interface for ZX81NIC20 DigitalEnlarger Timer/Controller DXersAudio Processor Sweep Oscillator CMOS Crystal Calibrator.

1984CATALOGUE

A massive 480 big pages ofdescription, pictures and dataand now with prices on the page.The new Maplin catalogue is theone book no constructor shouldbe without. Now includes newHeathkit section. On sale in allbranches of W.H. Smith. Price£1.35 - It's incredible value formoney. Or send £1.65 (includingp & p) to our mail-order address.

Great ProjectsFrom MAW

Our book "Best of E&MMProjects Vol. 1" brings together21 fascinating and novel pro-jects from E&MM's first Year.

Projects include HarmonyGenerator, Guitar Tuner, Hexa-drum, Syntom, Auto Swell,Partylite, Car Aerial Booster,MOS-FET Amp and othermusical, hi-fi and car projects.Order As XH61R. Price £1.

rPost this coupon now for your copy of the 1984catalogue. Price £1.35 + 30p post and packaging.If you live outside the U.K. send £2.20 or 11International Reply Coupons. I enclose £1.65

Name

L EE/4/84

In Book 8 (XAO8J) Modem (RS232)Interface for Dragon and Spectrum Synchime I/O Ports for Dragon Electronic Lock Minilab PowerSupply Logic Probe Doorbell forthe Deaf.

In Book 9 (XAO9K) Keyboard withelectronics for ZX Spectrum Infra -Red Intruder Detector Multi meter toFrequency Meter Converter FM

Radio with no alignment Hi -ResGraphics for ZX81 SpeechSynthesiser for Oric VICExtendiboard ZX81 ExtendiRAM Dynamic Noise Limiter for PersonalCassette Players TTL Levels toModem/RS232 Converter LogicPulser Psuedo-Stereo AM Radio Ni-Cad Charger Timer Adder-Subtractor Syndrums' Interface Microphone Pre -Amp Limiter.

THE MAPLIN MODEM KITExchange programswith friends, leave orread messages fromthe various Billboardservices, talk tocomputer bureaux, orplace orders andcheck stock levelson Maplin's Cashtelservice. A Maplin Modem will bring a whole newcomputer and vastly increase its potential.Now you can exchange data with any other computer using a 300baud European standard (CCITT) modem and because the MaplinModem uses this standard, you could talk to any one of tens ofthousands of existing users.Some computers need an interface and we have kits for the ZX81,VIC20/Commodore 64, Dragon and Spectrum and shortly Atari,whilst the BBC needs only a short program which is listed inProjects Book 8.A Maplin Modem will add a new dimension to your hobby.Order As LW99H (Modem Kit) excluding case. Price £39.95.

YK62S (Modem Case) Price £9.95.Full construction details in Projects Book 5.

world to your

mroun ELECTRONICSUPPLIES LTD

Mail Order. P.O. Box 3, Rayleigh, Essex SS6 8LR. Tel: Southend(0702) 552911 Shops at: 159-161 King Street, Hammersmith,London W6. Tel: 01-748-0926. 8 Oxford Road, Manchester. Tel: 061-236-0281. Lynton Square, Perry Barr, Birmingham. Tel: 021-356-7292. 282-284 London Road, Westcliff-on-Sea, Essex. Tel: 0702554000. 46-48 Bevois Valley Road, Southampton. Tel: 0703 25831.All shops closed all day Monday.All prices include VAT and carriage. Please add 50p handling chargeto orders under £5 total value (except catalogue).

Despatch by retort, of post whew youus available

everyday lectron cs - world radio history

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