Maplin Project Book 10 - World Radio History
32
Transcript of Maplin Project Book 10 - World Radio History
MAPLINPROJECTS
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renleb PROJECTS577210 &MOLARS
Project Book 1 Universal Timer. Programmablemains controller. Combo -Amplifier. 120WMOSFET power amp. Temperature Gauge.10°C - 100°C, LED readout. Pass The Bomb!Pass -The -Parcel with a difference. Six easy -to -build Projects on Vero -board. Car batt. monitor;Colour snap game; CMOS Logic Probe; PeakLevel meter; Games timer; Multi -colour pendant.Order As XAO1B (Maplin Project Book No. 1)Price 70p NV.
Project Book 2 Digital Multi -Train Controller.Controls up to 14 model trains. Home SecuritySystem. Six independent channels. Digital MPGMeter. With large LED display, a must for moreeconomical motoring.Order As XAO2C (Maplin Project Book No. 2)Price 70p NV.Project Book 3 ZX81 Keyboard. 43 keys, plugsdirectly into ZX81 with no soldering. Stereo 25WMOSFET Amp. 25W r.m.s per channel; Disc,Tape, Tuner & Aux. Radar Intruder detector.20 metres range, may be used with our securitysystem. Remote Control for Train Controller.Remote control by infra -red, radio or wire.Order As XAO3D (Maplin Project Book No. 3)Price 70p NV.
Project Book 4 Telephone Exchange. Up to 32extensions on 2 -wire lines. Remote Control forAmplifier. Volume, balance and tone controlledvia infra -red link. Frequency Counter. 8 digitDFM, 10Hz - 600MHz range. Ultrasonic IntruderDetector. Areas up to 400 square feet can becovered.Order As XAO4E (Maplin Project Book No. 41Price 70p NV.
Project Book 5 Modem. 300 baud transmissionspeed over normal telephone lines. Inverter.240V AC 60W from 12V car battery. ZX81 SoundGenerator. 3 tone generators fully controlledfrom BASIC. Central Heating Controller.Optimised performance with this advancedsystem. External Horn Timer. Exterior intruderalarm. Panic Button. Add on to our HomeSecurity System. Model Train Projects. Add on toour Multi -Train Controller. Interfacing Microprocessors. How to use parallel I 0 ports, withcircuits.Order As XAO5F (Maplin Project Book No. 5)Price 70p NV.
Project Book 6 VIC20 & ZX81 Talkbacks.Speech synthesis projects. Scratch Filter.
NIA Pt_ IN ',nu& t
II4V14.41.1A SYSTEM19 MOWN
4101.01 )411491111119.rrory Met NV
ISMIDAIF IOW "Mt
Tunable active circuit 'reclaims' scratchedrecords. Bridging Module. Converts two 75WMOSFET amps to one 400W full bridge amplifier.Moisture Meter. Finds damp in walls and floors.ZX81 TV Sound and Normal/Inverse Video. TVsound and inverse video direct. Four SimpleVeroboard Projects. Portable Stereo Amp; SineGenerator; Headphone Enhancer and StylusOrgan.Order As XAO6G (Maplin Project Book No. 61Price 70p NV.
Project Book 7 CMOS Crystal Calibrator.For amateur radio receiver calibration. DX'er'sAudio Processor. Improved sound from Comm-unications Receivers. Enlarger Timer.An accurate timer for the darkroom. SweepOscillator. Displays AF frequency response cn anoscilloscope screen. VIC20 and ZX81 Interfaces.RS232 compatableOrder As XAO7H (Maplin Project Book No. 71Price 70p NV.
Project Book 8 Spectrum Modem/RS232Interface. 2400 baud self contained operatingsystem. Synchime. Simulates bells, gongs andother chiming sounds. Dragon 32 RS232/ModemInterface. Plugs into ROM expansion port.Codelock. Programmable electronic lock. CMOSLogic Probe. Digital display shows logic states.Minilab Power Supply. Versatile unit for the testbench. Dragon 32 I/O Ports. Two 8 -bit ports.Doorbell for The Deaf. Flashing lamp attractsattention.Order As XAO8J (Maplin Project Book No. 81Price 70p NV.
Electronics Issue 9 Spectrum Keyboard. 47 fulltravel keys. VIC Extendiboard. Three expansionports, one switchable. Oric Talkback. Speechsynthesiser for the Oric 1. Infra -Red MovementDetector. 30 metres range outdoors. TDA7000FM Radio. Complete FM receiver on a chip. ZX81High Resolution Graphics. 256 x 192 fine pixeldisplay. Ten Projects! Personal Stereo DynamicNoise Limiter; Logic Pulser; ZX81 1K Extendi-RAM; TTL/RS232 Converter; Pseudo Stereo AMRadio; and more,Order As XAO9K (Maplin Magazine Volume 3Issue 9) Price 70p NV.
Project Book 10 Spectrum Easyload. Helpscassette loading with the Spectrum. 80m
' \\ \--\\MAPLIN ==.PROJECTS
:JK FOUR "
v..4.70;. vtis'
.e.
/NISt. MPG. STV eiliOLOINWPOOR WPM
e...E COSIKIKOMOIN 041.81
Receiver. Simple SSB direct conversion receiver.Fluorescent Tube Driver. 8W 12V for campingand caravanning. Auto-Waa. Automatic waa-waaeffects unit. Digi-Tel Expansion. Expands MaplinTelephone Exchange to 32 extensions. Oric 1Modem Interface. Adapts the Oric 1 to the MaplinModem. Dragon 32 Extendiport. Makes theDragon's cartridge socket more accessible.Order As XA1OL (Maplin Project Book No. 10)Price 70p NV.
Electronics Issue 11 Mapmix. Six channelaudio mixer. Xenon Tube Driver. Xenon flashtube module with strobe. Enlarger ExposureMeter. Simple inexpensive tool for the darkroom.8 Channel Fluid Detector. Checlucontrol fluidlevel in up to 8 containers. Servo & DriverModule. Servo mechanism with driver modulekit. Mk II Noise Reduction Unit. Improves signal,noise ratio of tape recordings. Cautious Ni-CadCharger. Controlled charging of ni-cad cells.Motherboard for The BBC Micro. Gives easyaccess to ports.Order As XA11M (Maplin Magazine Volume 3Issue 11) Price 70p NV.
Electronics Issue 12 RTTY Unit. The TU1000receives transmits Radio Teletype; connects tocomputer via RS232. Computadrum. Use yourcomputer as a drum synthesiser. Light Pen.Draw onto the TV screen or select menu options.PWM Motor Drive. Reversible model motordriver for 6V and 12V.Order As XA12N (Maplin Magazine Volume 3Issue 12) Price 70p NV.
Electronics Issue 13 Explosive Gas Alarm.Flammable gas detector. Flash Meter. Get yourexposure right when using your flash gun.Musical Announcer. A doorbell with a difference.Mains Controller. An add-on for the 8 -ChannelFluid detector.Order As XA13P (Maplin Magazine Volume 4Issue 13) Price 75p NV.Electronics Issue 14 Live Wire Detector.Invaluable aid for the handyman. Trundle. Theline follower robot as featured on Channel 4 Zero2. High quality 'turtle' robot. 4 -Channel PWMController. Digital control of motors and servos.Display Driver Module. How to use our LEDbargraph display ICs. Control -A -Train. Full inertiacontrol of model trains.Order As XA14Q (Maplin Magazine Volume 4Issue 141 Price 75p NV.
dlectir Aritia6THE MAPLIN MAGAZINE
PROJECT BOOK TENThis Project Book replaces issue 10 of 'Electronics'which is now out of print. Other issues of'Electronics' will also be replaced by Project
Books once they are out of print. For currentprices of kits, please consult the latest Maplinprice list, order as XFO8J, available free of charge.
PageHero Goes to School 2
Even a robot has to learn.Spectrum Easyload 4Enhance cassette loading of programs into your Sinclair SpectrumDragon 32 Extendiport 9
Extend the Dragon 32 cartridge slot.80m Amateur Receiver 10Direct conversion receiver for the 80m band.Oric 1 Maplin Modem Interface 15Open up a whole new world with your Oric 1.32 Line Digi-Tel Expansion 18Expansion details for the Maplin Digi-Tel Telephone Exchange.Auto-Waa Effects Unit 22Create waa-waa effects with this easy to build unit.2.8kW Power Controller 25Ideal for controlling electric drills, soldering irons, etc.Fluorescent Tube Driver 288 watt 12 volt circuit, ideal for camping, etc.
Editor Doug SimmonsProduction Manager Hugh MoirTechnical Editors Robert Kirsch,
Dave Goodman
CONTENTS
Art D;rectorTechnical Artists
Peter BlackmoreRoy SmithJohn Dudley
Published by Maplin Electronic Supplies Ltd.P.O. Box 3, Rayleigh, Essex
Typeset by Essex Process & Engraving Co.Printed by Mayhew McCrimmon Ltd.
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Copyright. All material is subject to world wide copyright protection, and reproduction or imitation in whole or part is expressly forbidden. All reasonable care is taken to
ensure accuracy in preparation of the magazine, but Maplin Electronic Supplies Ltd. cannot be held legally responsible for its contents. Where errors occur corrections will be
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(ip Copyright 1984 Maplin Electronic Supplies Limited.
There was a hushed air of expectat-ion in the school as David Snoad, Maplin'sNational Sales Manager called for Herothe Robot to bring himself onto the stage.David had just finished explaining to the400 pupils at Earls Hall Junior School inSouthend, how famous Hero is as a resultof his personal appearances on BBC TV's"60 Minutes" and "Pebble Mill At One"programmes and on chat shows onCentral, Anglia and Tyne Tees television.
"We want Hero!" the children shout-ed when the robot did not appear and avoice from off-stage said, "Please bequiet, I'm trying to sleep. And anyway,I'm feeling shy."
David became exasperated, "If youdon't come out, I'll pull your plug out!"
The children strained forward; thenaughty schoolboy image those fewwords had conjured, had already endear-ed Hero to them. And when Hero at lastpropelled himself onto the stage, hisdiminutive appearance - less than 1
metre high - further reinforced theiridentification with him.
Hero made a wide tour around thestage until David said, "Come here!" andthe robot at once turned, went up toDavid and stopped. The children weretotally convinced that Hero was movingand speaking entirely from decisionsmade within his own 'brain'. After allthere were no wires attached to him andthere was no visible aerial for remotecontrol.
It may come as quite a surprise toyou to learn that the children wereabsolutely correct. From the momentHero came onto the stage, everything hedid was as a result of instructions pre-programmed into his microprocessor'brain' and silicon chip memory. Therewas no remote control by radio, infra -redor anything else. Throughout the entire 2hour demonstration Hero did it all, all byhimself!
However, Hero did have his ownmicrophone which David placed besidehim. The robot then demonstrated themovements he can make, describingeach one: "I can move my arm"; "I canturn my head" and so on.
David invited six children onto the
stage to make up a panel to ask the robotquestions. The children sat on chairs,three on each side and the first questionwas, "What can you say?"
"Everything that has ever been said,or ever will be said," replied the robot.Hero demonstrated his ability to speakother languages as well then, by sayingsome French and Spanish phrases.
The next questioner asked, "How doyou spell coat?"
"K 0 T E," said Hero."That's not right!" said David."You asked me how I spell coat, not
how the dictionary spells it," said Hero.Not a very original joke, but the childrenenjoyed it. "Anyway, robots don't needcoats." And David then explained to thechildren how vital robots are for workingin areas where it would be dangerous orimpossible for humans to work due toexcessive heat for example.
"Hero will now show you how he canspell his name," said David, and placed in
front of the robot, but in the wrong order,the four letters of his name on largepieces of card. Without further intervent-ion, Hero moved the letters around. Atone point it looked as though he wasgoing to spell it incorrectly, but when hemoved the last letter it was right and thechildren applauded loudly.
The children on stage began to getfidgety and David asked Hero to tell himif any child moved when his back wasturned. When David spoke to one of thetwo groups on the stage, a boy on theother side slowly raised his leg.
"Something moved!" said Hero to thedelight of the audience. This pantomimesequence had all the children rockingwith laughter.
When Hero demonstrated his abilityto sing, his rendition of Jingle Bells, withwhich the whole school joined in, earnedhim a school choir badge which he is stillvery proud of.
Finally, Hero was asked what hewould like for Christmas. "A cuddly toy,"he replied.
"You're just an old softy at heart,"said David.
2
Mario Lawton of Class 1E wrote, "Iliked it when Hero refused to come onand when he spelt his name. His singingis very nice, but mine is better. I hope helikes his choir badge. I hoped that wecould touch him. Love Mario."
Rebecca Hindle of Class 2K wrote, "Iliked Hero very much because he mademe laugh. I liked Hero when he put theletters in the right place. He's very clever.I also liked it when the boy told a jokeand he laughed, but Hero wouldn't stoplaughing. I think Hero is cute."
And Hero replied, "Robots needlove and cuddles too, just like humans."
"What's the time?" asked one of thechildren. Hero gave the correct time fromhis internal real-time clock which runscontinuously.
The realisation that the presentationhad lasted nearly two hours and that itwas nearly time for lunch, led to the robotgoing into his grand finale, a rendition ofOld MacDonald Had A Robot - "..with aready here and a ready there. Here aready, there a ready, everywhere aready, ready..."
Letters to NeroThe children clapped loud and long.
They had thoroughly enjoyed themselvesand learned a lot as well. As they wereleaving the hall, one little girl askedDavid in a very serious tone if Hero had agirlfriend. "He didn't have a girlfriendbefore today," said David, "but he's madefriends with lots of nice little girls thismorning."
In the afternoon, the children watch-ed a film about industrial robots whichhad been kindly loaned to us by the FordMotor Company. Afterwards, each class,unbeknown to David, wrote him a letterand here are some of the best ones.
Nicola Squibb wrote, "I enjoyedevery moment of the show; it wasfantastic the way Hero was controlled. Ithought the way his arm worked was veryunusual. I liked his singing a lot and Ithought he was a very clever robot, butthe next time he spells coat, he shouldlook it up in a dictionary first."
The mysterious Andrew W. wrote, "Ilike the things that Hero can do. I woulc.like to have a robot like Hero. I hope hebeing a good boy."
Graham Newell of Class 3J wrote."Hero was a bit rude at first, but he wasjust joking. My favourite bit was when hewas joking and telling fibs to you when hewas asked a question."
But our favourite letter cf all camefrom Sarah Staplton of Class 2B whowrote, "We enjoyed Hero being here andwe enjoyed his singing. I think he's veryclever to do all he did for us. Do you keephim at home or is he just your friend?"
Continued on page 6.
SPECTRUMEASYLOAD
* Connects between Micro and Recorder.* Battery Powered - No Bus Connections.* Save and Load Indication.* Mic Output for Second Recorder.* Charging From Spectrum P.S.U.
Much has been written about cassetteloading and saving problems associatedwith Sinclair Micro's, which tend to showthat difficulties of one sort or another arebeing experienced. Many low cost re-corders suffer from poor high frequencyresponse which can sometimes be imp-roved by careful re -alignment of therecord/playback head. Systems withrecord level AGC can fluctuate if thesignal level is too high producing largelow -frequency transients and attenuatedharmonics, none of which leads toreliable operation!
The rule, therefore is always to usegood quality recorders and data cass-ettes whenever possible if problems areto be minimised, but even so one partic-ular nuisance still exists. When makinga cassette recording, input signals can be'monitored' from the ear socket. On mostrecorders, either a small percentage ofsignal is taken from the mic input directlyor via signal processing circuitry, allow-ing the user to listen in with an ear -piecewhen recording and is fine for normaluse. However, the Spectrum 'ear' and4
by Dave Goodman'mic' ports are effectively coupled to-gether, through internal circuitry, andwith both sockets connected to a record-er, a closed loop is generated. The resultof this is signal feedback similar to thehowl heard when microphones areplaced too close to amplifier loudspeakers, and data is corrupted or lostaltogether. One recommended method toprevent this from happening is to removethe ear lead when saving, or mic leadwhen loading programs and trust that theappropriate connections are made eachtime this is done. After a while wear andtear takes its toll; plug leads can pull outand sockets become loose, returning theoriginal reliability problem. An imp-rovement would be to place a change-over switch between recorder and microwhich selects either ear or mic leadsseparately.
Simple Save, Easy LoadFigure 3, block diagram, shows the
basic switching method employed in themodule with both mic and ear signalpaths disconnected via SWA and SWB.
When a signal is output from the Spect-rum mic socket, SWB operates (Figure3B) completing a path to the recorder micsocket and preventing SWA from operat-ing. The ear connection is thus isolatedbetween recorder and micro. Similarlysignals present at the recorder ear socket(Figure 3C) are detected and SWAoperates completing a path to theSpectrum ear socket and preventing SWBfrom operating. Save or Load monitorsdetect signal directions and operateswitches appropriate to the requiredroute automatically.
Circuit DescriptionData output from the Spectrum is
high-pass filtered by Cl, RI and R3 toreduce the amplitude of low frequencysignals. IC IB imposes AGC on the signalkeeping the level constant for goodrecording quality. At the start of aSpectrum save routine, a short headertone is sent allowing the recorder AGC tostabilise. This tone is of higher frequencythan the serial data train and being highimpedance, from source, can suffer
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attenuation, causing incorrect AGC sett-ings. IC 1B therefore maintains a const-ant amplitude on all composite datasignals. IC2D is normally closed (Bilateralswitch) and IC4 amplifies the incomingsignal for charging C. TR1 conducts,operating LED1 (indicating that 'save'mode is selected) and IC3D output goeslow. IC3C operates switch IC2C and theprocessed signal is further amplified byIC4C to pass at a low impedance to therecorder mic (input) socket. To preventthe monitor signal from activating IC2B,IC2A is held open while IC2C is closedand the return path is thus disconnected.Providing that the recorder is set torecord, data signals are stored on tapeuntil the save routine has completed andno further signals are present; wherebyLED1 is extinguished, switch IC2C isopened and IC2A is cicsed.
When loading frorr tape, IC1A AGCamplifier determines a suitable signallevel for driving the Spectrum ear input.A minimum input level of 0.4V is requiredFrom the recorder, which corresponds to
5
MAPLIN GB57M ISS 1
Figure 2. PCB Layout and overlaya low volume setting, although higherlevels up to 3V will make little difference.IC4B amplifies the signal and produces avoltage across 010, TR2 conducts operat-ing LED2 (LOAD mode selected) andIC3A output goes low. IC3B closes switchIC2B whereby the data signal is furtheramplified to approx. 4V by IC5. RV2 canbe used for trimming the amplitude to suitindividual Spectrum input requirements.IC2D is held open, while IC2B is closed,thus breaking the loop as before. Withloading completed, LED2 extinguishes,IC2B opens and switch IC2D closes. Inboth save and load modes, capacitors C9and 010 discharge slowly with theabsence of data signals ensuring a smalldelay before releasing the bilateralswitches. Occasionally short gaps appearbetween data streams, which wouldcause IC4B or IC4D to break the signalpath, resulting in lost data, so a delay isnecessary for preventing this action.
P.S.UPower is supplied to the module
from a PP3 battery which delivers 9V at10mA. Si in the 'ON' position connects 9Vto LED3 and potential divider R29, R30.Three voltage rails of +4.5V, -4.5V andOV are generated for supplying the IC's,but only in the 'ON' mode. If a recharge-able type nicad (HW31J) is used, thenperiodic recharging is available using theSpectrum power supply connected to6
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SKT1. LED4, R34 and Si in the 'charge'position set a 10mA charge rate for thebattery and only Spectrum power packsshould be used for this purpose.
ConstructionUse 24 gauge BTC to fabricate 17
links required for insertion into thePCB (see Figure 4). Place each link over aline printed on the legend and push flatdown into the PCB. Carefully bend andinsert diodes DI and D2 then Zenerdiodes D3 and D4. In all cases, positionthe bar -end printed around one end ofthe component body, to line up with thebar on the legend, as these componentsmust be fitted correctly. Resistors RI toR34 can next be bent to shape and fittedinto the PCB. Solder all components to thetrack pads and cut off excess wire ends.Fit IC's 1 to 5, RV1, RV2, and TR1, TR2(referring to Figure 4). When insertingcapacitors Cl and 2 (Polycarb's) treateach connection lead carefully as theyare easily broken. If breakage doesoccur, it is possible to re -solder theseleads to the body edge, but is notadvisable. Mount PC electrolytics C3 to12; the longest lead is +V and theshortest lead (minus sign on body) is -V.Note that these components stand vert-ical with the base flat onto the PCB.Again, solder the remaining componentsin place, remove excess wires and fit 9Veropins, pin 1 to 9, from the track side.Press them home with the soldering ironand solder in place. Insert SKT1 andpress down onto the board. Solder inposition. Finally wire the battery clip with+ve (red lead) to `BAT+' and -ve (blacklead) to 'BAT -'. Terminal pins are notrequired for these connections so solderdirect into the PCB.
Clean the tracks and joints withsolvent or thinners and a brush tofacilitate inspection. Ensure all joints aresound with no shorts apparent betweenpads etc, then recheck assembly andcomponents.
Case & Final AssemblyIf mounting the project into a box
(Verobox LLO8J) then Figure 5 showsrecommended drilling and mounting arr-angements. LEDS 1 to 4 are mounteddirectly onto the PCB and bent at rightangles so they may protrude through themetal side plate. When using holders,push them into each hole from the outsidebefore inserting the LED. Switch Si alsomounts onto this panel and the threeterminals are wired directly to each pinimmediately behind on the PCB. 3.5mmsockets SKT2 to 6 are mounted on theopposite panel. Snip off the bottomcontact (Figure 4) before fitting and wireto each pin as shown. The -ve returnconnection is commoned to each socketand terminated on pin 6. Pins 1 to 5 arewired to the centre terminals on eachsocket only. Place SI in the 'Charge'position which is left when viewed fromthe front and connect the battery. Justenough room between PCB and box hasbeen allowed to accomodate the PP3battery or a rechargeable version.
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current checks. The first check requiresthe meter being connected betweenbattery +V terminal and +ve clipterminal. Set the meter to current rangeand switch Si to the ON (right) positior,.LED 3 illuminates and the supply currentshould be 10 to 12mA. Now insert aSpectrum PSU into SKT 1 and turn switch
Si from 'ON' to 'Charge'. LED 3 goes outand LED 4 illuminates with a chargecLrrent reading between 7 and 10mA.Remove the PSU plug and LED 4
extinguishes with zero current reading.Switch to 'ON' position again, removemeter and reconnect the battery clip.
Set the meter to Volts range andconnect the -ye lead to battery -ve.Ewitch to ON and check quiescent stateof Bilateral switches IC2 as follows: -102 pin 5 and pin 6 = OV (low), IC2 pin 12and pin 13 = 9V (high).
Next check the op -amp supply railsare correct by removing the meternegative lead and reconnecting to OV.The most convenient place to find the OVconnection is on the link betweenresistors R17 and R2C. Place the meterpositive lead on IC5 pin 7 and check for+4.5V. Also check for -4.5V on IC5 pin
4. Note that the exact readings aredependant on the battery voltage andcould be between 4.3 and 4.8V.
These general checks give a goodindication that all is well so far. If any, orall readings do not correspond to thevalues given, assume a fault exists and gono further until the problem is cleared.IC's and PC electrolytic capacitors areoften inserted wrongly and are worth re-checking. Set both RV1 and RV2 with
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their wipers to halfway position. Connectthe cassette recorder ear socket toSKT5, Tape 1 Ear 0/P, and switch on themodule. Play back a pre-recorded pro-gram and adjust the volume control toabout 'lard travel. LED2 will illuminateuntil either data disappears or therecorder is turned off. Repeat the testwith recorder ear connected to moduleSKT2, Spectrum mic, and check LED1only illuminates.
In case of confusion the Spectrumconnections are EAR = SKT3 and MIC =SKT2. Recorder connections are EAR =SKT5 and MIC = SKT4. SKT6 presents aprocessed output from SKT5 for conn-ection to a mic input on a secondrecorder and may be used for makingback up copies of your own programs.
Final testing involves the addition oftwo connecting cables, terminated bothends with 3.5mm plugs. Connect both
mic and ear Spectrum ports to SKT2and SKT3 on the module. Connect the twonew cables (see parts list) from therecorder mic and ear sockets to SKT4and SKT5 on the module, switch on andtry loading a program. Adjust eitherrecorder volume or RV2 as necessary ifproblems are encountered. When savingprograms, RV1 can be adjusted ifplayback levels are too low or noisy, butthe half travel setting should be adequate.
SPECTRUM EASYLOAD PARTS LIST SEMICONDUCTORS
RESISTORS:- All 0.4W 1% Metal FilmR1,2 180kR3-8 inc. 4k7R9,10 51RR11,12 100kR13,14 1k5R15,16,17 47kR18-21 inc. 470k
2
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(M1OOK)(M1K5)(M47K)
(M470K)
D1,2D3,4TR1,2IC1IC2IC3IC4ICS
1N4:48BZY88C6V8BC548LM 13700N40668E40938E3403uA741C(8 pin)
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R22 150k (M150K) MISCELLANEOUS
R23,24,25 10k 3 (M 10K) LEDs -4 inc. Minied Red 4 (WL32K)R26 22k (M22K) Si SPDT Ultra Min Toggle (FH980)R27,28 2k2 2 (M2K2) SKT1 PC Mtg Power Skt (RK37S)
R29,30 lk 2 (M1K) SKT2-6 inc. 3.5 Jack Skt 5 (HF82D)R31 82k (M82K) Milled Clips 4 (YY39N)R32 18k (M18K) PP3 clip (HF28F)R33 39k (M39K) Vercpin 2141 1pkt (FL21X)
R34 100R (M100R) Spectrum Easyload PCB (GB57M)RV1,2 47k Hor Sub -min Preset 2 (WR60Q) OPTIONAL
CAPACITORS Case (LL08J)
C1,2 100nF Polycarbonate 2 (WW41U) Plugpack 0 2 (RW28F)
C3,4,5 10uF 35V PC Electrolytic 3 (FF04E)C6,7,8,12 2u2F 63V PC Electrolytic 4 (FFO2C) A Complete Kit of pans (excluding Case and Plugpak Q) is available.C9,10,11 100uF 10V PC Electrolytic 3 (FF1OL) Order As LK39N (Spectrum Easyload Kit)
HERO GOES TO SCHOOL Continued from page 3.
So how was it all done. Well the factis that Shakin' Stevens has got nothing onDavid Snoad! The trigger needed tomake Hero say the next line of his pre-programmed speech was in fact Davidsurreptitiously moving his leg into thedetection range of Hero's ultrasonicrange -finder. Everything was, of course,carefully rehearsed and the children onthe stage only asked the questions theyhad been told to ask.
Robots Are AmHero's entrance routine and the part
where he spelt his name was achieved byhaving controlled him directly to makeeach move before the show. Whencontrolled in this way from his 'teachingpendant', he remembers everything andcan repeat it absolutely precisely as oftenas required.
When the children from Earls HallSchool come up against robots, as theyundoubtedly will during their workinglives, they will not see them as giantdaunting machines that are incompre-hensible and unapproachable. They willalways remember that enchanting littlerobot they met as children and will beable to interact with robots without anyqualms or fears.
As far-sighted headmaster BobShaw, who had organised the show said,"Few such demonstrations have comm-
anded such a high level of interest. As ameans of demystifying the robot, theevent was a great success. The school'sone microcomputer allows each pupil atotal of ten minutes hands-on experiencea term. The robot is, however, ideallysuited for group involvement."
We would just like to say thanks toall the children and teachers at Earls HallSchool, who made the day such fun for usas well, and the letters were a lovely ideathat we all enjoyed very much. Hero sayshe'd love to be owned by any of thechildren he met that morning. "I'm reallyvery easy to look after," he says, "all youhave to do is plug me in to the mainswhen I say, 'Low battery'!"
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This simple to build projecteffectively brings the Dragon 32cartridge socket to a more accessibleposition. As Dragon project builders willno doubt be aware, a great deal ofperipheral device circuitry becomesinaccessible once inserted into thecartridge opening, thus making testingand troubleshooting somewhat difficult!
The Extendiport allows two (2 x 20way) socket extensions, or one socketand one open PCB edge connector to beavailable for use by external devices. Forthe sake of simplicity, no buffering or CEswitching has been fitted, so greatattention must be paid when soldering onthe board. There are forty track pins tobe inserted from the top side; push themdown to the track before soldering toensure full penetration through the PCB.Solder both sides carefully and check forshort circuits. A 2 x 20 way socket can befitted to the top if required and/or to theedge connector to suit requirements.Again carefully solder all terminals andcheck for shorts. Two rubber feet can befitted to side 1 with 2 x 4BA bolts and nuts.This will ensure a good fit into the Dragonsocket and avoid excess movement andstrain.
Once construction has been com-pleted, it will be well worthwhilechecking adjacent terminals for shorts,using a suitable ohm -meter or continuitytester. The Dragon's Address, Data andControl lines are not internally bufferedand damage to the processor will result ifany PCB faults are not found beforeinserting the Extendiport - thereforemeticulous attention should be paid to theconstruction of this project.
PARTS LISTPrinted Circuit BoardPC Edge Conn 2 x 20 wayTrack PinsCabinet FeetBolt 4BA V,"Nut 4BA
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Plimareur1Peceiver* Direct conversion design* Excellent introduction to amateur radio* Single-sideband and CW operation* Straightforward construction* Alignment without test gear
The cost of amateur radio equipmentis generally quite high these days, andthis tends to give newcomers to thehobby the impression that amateur bandtransmissions can only be received usinga vast array of the latest in ready-madegear. In fact quite good results can beachieved on the short wave amateurbands using relatively simple home -constructed equipment. Conditions onthe short wave bands are, to say the least,rather difficult these days, principally dueto the overcrowding and high outputpower of many commercial transmitters.Even using sophisticated receivingequipment a reasonable amount of skill isrequired in order to obtain good results,and when using a simple receiver theamount of patience and skill needed isthat much greater. However, provided itis used carefully and sensibly, a simplereceiver of the type described here canprovide creditable results and a lot of fun.
In order to make the finished set aseasy as possible to set up ready for use asingle band direct conversion design hasbeen adopted. The band chosen is 8010
metres, which in the U.K. extends from 3.5to 3.8MHz (the upper limit is 4MHz in theU.S.A. and some other countries). This isadmittedly not the best band for longdistance reception, and one of the highfrequency bands would be better in thisrespect. On the other hand, it will providereception of European stations after dark,with stations from further afield beingreceived when conditions are favourable(North American stations have beenreceived using the prototype). During thedaytime there will often be transmissionsfrom British amateurs, and there isunlikely to be a total lack of stations forlong. The high frequency bands,especially now the current sunspot cycleis nearing its minimum, tend to be 'dead'for much of the time, and are notcurrently an attractive proposition for asingle band receiver.
Single SidebandTuning an amateur band transmiss-
ion properly tends to be rather moredifficult than tuning in an ordinary AMbroadcast station. The reason for this is
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the widespread use of SSB (singlesideband) as the transmission mode. Thisis a form of AM transmission, but it is verydifferent from the reception point of view.With an ordinary AM signal a smalltuning error will probably give no morethan a slight loss of audio quality, andmight be totally unnoticeable. With anSSB transmission even a very small tuningerror is usually sufficient to render theaudio output completely unintelligible. Itis not essential to understand the basicsof SSB and the way it is resolved by thisreceiver, but it should certainly help tomake the set easier to use, making thetuning of a station a less 'hit and miss'affair.
Probably the most convenient way oflooking at an SSB transmission is to thinkof it as an audio frequency signal wherethe frequencies have all been raised by acertain amount to bring them into theradio frequency range. For example, iffrequencies at 1kHz, 2kHz and 3.5kHzwere to be fed into an SSB transmitteroperating at 3.7MHz, the RF output fre-quencies would be at 3.701MHz (3.7MHz
+ 1kHz), 3.702MHz (3.7MHz + 2kHz), and3.7035MHz (3.7MHz + 3.5kHz), bearingin mind that 1kHz is equal to 0.001MHz.The strengths of the RF output signals areproportional to the strengths of the corr-esponding audio input signals. Of course,with a voice input to the transmitter theaudio signal would be comprised of amultitude of audio frequencies, and itwould be changing from one instant tothe next. However, the principle ofoperation remains unchanged, and with acomplex audio input a correspondinglycomplex RF output is generated.
In practice there are actually twotypes of SSB, lower sideband (LSB) andupper sideband (USB). With the systemdescribed above the RF output signalsare higher in frequency than the basic3.7MHz transmission frequency, and thisis upper sideband. With lower sidebandthe output frequencies are below thebasic transmission frequency, or in theexample given above this would give out-puts at 3.699MHz (3.7MHz - lkHz),3.698MHz (3.7MHz - 2kHz), & 3.6965MHz(3.7MHz - 3.5kHz). Figure 1 shows theseexamples in diagrammatic form, andshould help to clarify things.
In addition to SSB, the other maintransmission mode used by amateurs onthe short wave bands is CW (continouswave), which is a form of Morse Codetransmission. It consists just of keying aradio frequency signal on and off, andthis type of transmission can be resolvedby any SSB receiver.
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Figure 2. Block diagram of the Direct Conversion Receiver.
Direct ConversionThe most simple type of receiver
which is suitable for single sidebandreception is the direct conversion type,and it is a receiver of this kind which isfeatured here. Direct conversion receiversuse the heterodyne effect to reverse thetransmission process, and shift the receivedradio frequency signals back down to theoriginal audio frequencies. Figure 2
shows the receiver in block diagramform, and this helps to explain the way inwhich incoming signals are processed.
Signals from the aerial are coupledto a tuned circuit which acts as a passivebandpass filter. This eliminates mostsignals that are well outside the frequencyrange that is of interest, but there are stilla great many signals present at the outputof the filter, and it does not significantlyaid the selectivity of the set. Its purpose isto cut down the number of signals fed tothe rest of the receiver to manageableproportions.
The product detector and RF oscilla-tor stages are responsible for demodulat-ing received signals. The output of theproduct detector contains all the inputfrequencies, plus the sum and differencefrequer.cies. In this application it is thedifference frequency that is of importance,as it is :his that constitutes the demodulated
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audio output. For example, if a 3.7MHzSSB transmission is to be received, theRF oscillator must be set to operate at3.7MHz. An audio input to the transmittera: (say) 1kHz would give an RF output ateither 3.701MHz or 3.699MHz, dependingon whether the signal is an uppersideband type or a lower sideband one.In either case the difference between the3.7MHz operating frequency of the RFoscillator and the signal frequency will be1kHz (3.701MHz - 3.7MHz = 1kHz and3.7MHz - 3.699MHz = 1kHz
Provided the oscillator is tuned to thecorrect frequency, any audio inputfrequency at the transmitter will beconverted back to the same audiofrequency by this heterodyne process atthe receiver. However, if the oscillator isnot at quite the right frequency, all theaudio output frequencies will be wrong. Iftie oscillator is placed slightly too faraway from the SSB signal the differencefrequencies are increased, as are theaudio output frequencies. Due to theincrease in the pitch of the audio outputthis is popularly known as the 'DonaldDuck' effect. If the oscillator frequency istaken too close to the SSB transmission,the opposite occurs, with a lowering inthe pitch of the audio signal. Theoscillator frequency has to be placed justbelow an upper sideband signal, or justabove a lower sideband signal. If it isplaced on the wrong side, the high audiofrequencies become low frequencies,and the low audio frequencies becomenigh ones. This inversion of the signal'scrambles' it completely so that theJverall pitch is about right, but probablynot a single word would be understand-able. This is easily corrected by simply:uning through the transmission, and thenwith the oscillator positioned on the rightside, the tuning is adjusted for an outputof the correct pitch. In practice there isalways going to be a small error in thepitch of the output signal, and there is noway of determining what is precisely thecorrect pitch anyway. It is therefore amatter of adjusting the tuning to producethe audio pitch that sounds best.
The reception of CW transmission isfar less critical, and it is just a matter oftuning the oscillator close to the trans-mission frequency so that the differencefrequency provides an audio output. Thepitch is relatively unimportant, and youcan adjust the tuning control for any audio
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frequency you like. With a simple receiverof the type featured here it does notnormally matter which side of the CWsignal the oscillator signal is placed,although it may sometimes be found thatone side suffers less from adjacentchannel interference than the other.
Apart from the audio signal, the sumsignal and the input frequencies arepresent at the output of the productdetector. These are easily removedthough, as they are all radio frequencysignals, and a simple passive filter is allthat is needed to do this. An amateurband receiver requires a high level ofoverall gain, and with a direct conversionreceiver the bulk of the gain is generallyprovided by the audio stages. Two highgain audio amplifiers are thereforeincluded in the unit. A lowpass filter isfitted between these stages, and it is anactive 18dB per octave type. The purposeof the filter is to cut down adjacentchannel interference, and it is this filterwhich provides most of the receiver'sselectivity.
Most low frequency band receivershave the tuning provided by ordinaryvariable capacitors, but in this casevariable capacitance (varicap) diodes areused. In order to obtain good stability thetuning voltage is obtained from a regulatedsupply. In this application there is notechnical advantage in using varicaptuning, and this method is used merelybecause it is less expensive than usingvariable capacitors of suitably highquality.
The CircuitFigure 3 shows the full circuit
diagram of the receiver. The mainwinding of T1, together with the capacit-ance provided by C2 and tuning diodeDI, forms the input tuned circuit. Theaerial signal is fed to the low impedancecoupling winding on Ti via C22 and RFattenuator RV1. The latter can be used toreduce the aerial signal if the receiver isoverloaded. C22 helps to prevent audiosignals from being picked up at the inputof the circuit.
TR I and TR2 are used in a simpleproduct detector configuration. Somemore sophisticated circuits were tried,but although the least expensive and mostsimple, this one gave the best results. The
oscillator uses TR4 as a source followerstage with frequency selective positivefeedback provided by T2. In order toobtain a large enough capacitance swingusing BA102 varicap diodes. It is necess-ary to use two of these wired in parallel(D2 and D3). This permits coverage of thefull 3.5 to 4.0MHz band.
R17 plus D4 provide a stabilisedsupply of 6.8 volts for the tuning circuit.RV4 is the main tuning control, and RV3,which provides only a limited tuningrange, is used for fine tuning. Trackingbetween the RF and oscillator is notperfect, but as the frequency rangecovered is quite small, and the bandwidthof Ti is quite large, this does notsignificantly degrade the performance ofthe set.
To
LI and C6 provide RF filtering at theoutput of the product detector, and theremaining audio signal is coupled to thevolume control, RV2. TR3 is used as thebasis of the first audio amplifier which is astraightforward high gain commonemitter stage. The output of TR3 is takento the lowpass filter which is a conven-tional third order design having a cutofffrequency of about 3.5kHz. ICI is used asthe unity gain buffer stage for the filter.
The second audio amplifier stageuses operational amplifier IC2 as a non -inverting amplifier having a voltage gainof about 220 times. C23 aids the stabilityof the circuit. The output of the set isintended for use with medium or highimpedance headphones, although it alsoseems to work quite well with inexpens-ive low impedance types, or even with acrystal earphone.
Power is obtained from six HP7batteries connected in series, or anyother 9 volt battery of fairly high capacity.As the current consumption of thereceiver is about 8 to 9 milliarnps the useof a small 9V battery is not recommended.
ConstructionMost of the components are mounted
on the printed circuit board. Details of thecircuit board and wiring are given inFigure 4.
Start by fitting resistors, capacitors,and the two inductors (LI and L2). Then fitthe semiconductor devices, taking care toconnect each one the right way round. IC1and IC2 are both inexpensive types and it
12
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is probably not worthwhile using socketsfor these. T1 and T2 are designed as plug-in coils (which fit a B9A valvehclder)rather than for printed circuit mounting.Despite this they can be mounted directon the board without too much difficulty.The only problem that might arise isgetting solder to flow over the pinsproperly, and to avoid difficulty it isadvisable to clean the pins prior to fittingand connecting the coils. This is easilydone using fine sandpaper or by scrapingthe pins with the blade of a penknife. Forpacking purposes the coils are suppliedwith their cores fully screwed down, but innormal use the cores will need to be
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unscrewed somewhat. They should there-fore be sat so that about 10 millimetres ofmetal screwthread protrudes from the topof each cne.
It will be easier to make theconnections to the off -board componentsif Veropins are fitted to the board at theappropriate places.
A metal instrument case whichmeasures about 250 by 150 by 75mmmakes an ideal housing for this project,although it could be fitted into a somewhatsmaller case if desired. The five controlsand the headphone socket are mountedon the front panel, and the general layoutcan be seen from the photographs. It is
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advisable to adhere to this layout as thefinal wiring up of the unit will then beeasier. The aerial and earth sockets aremounted on the rear panel of the case.
The printed circuit board is mountedon the base panel, or if :he specified case:s used, it is mounted on the aluminiumchassis supplied with the case. It should
positioned so that the componentsmounted on the front panel are roughlyaligned with the part of 1he board to whichthey will be connected. Spacers are usedever the mounting bolts to keep theconnections on the underside of the boardclear of the metal case or chassis. Finally,the battery clip is wired to the board and
13
the remaining wiring is added usingordinary multistrand connecting wire.
If the unit is powered from six HP7cells these must be fitted into a plasticbattery holder. Connections to the holderare made via an ordinary PP3 style batteryclip. Alternatively, the receiver can bepowered by a large 9 volt battery such asa PP7 or PP9, but note that these use thelarger type of battery connector.
Aerial and EarthIt is not essential to use a very long
aerial, and quite good results should beobtained using 10 or 20 metres of wirepositioned as high as possible. It is alsonot essential to use proper aerial wire, andfairly heavy duty PVC covered connectingwire or about 18 swg enamelled copperwire should be perfectly satisfactory. Inthe long term it would be advisable toinstall the aerial properly, but initially amake -shift arrangement is perfectly satis-factory and it gives you the opportunity todetermine what gives the best results. Ashort indoor aerial is far less than ideal,especially for a low frequency short waveband such as 80 metres. Apart from givingrelatively weak reception, an aerial of thistype is more prone to pick up interferencefrom television sets etc.
An earth connection can provide asubstantial improvement in results on the80 metre band, but, nevertheless, good
results can be obtained without oneprovided a reasonably efficient aerial isused. If you do wish to use an earth, thiscan consist of a length of metal rod or pipepushed into the ground and connected toSK2 of the receiver via a piece of wirewhich should be as short as possible. Donot use the mains earth. Apart from thesafety aspect, this would almost certainlyintroduce mains "hum" into the receiver.
Adjustment and UseWith the set installed and switched
on, and with both RV1 and RV2 welladvanced, by adjusting tuning controlRV4 it will probably be possible to tune ina few stations of some kind. It should thenbe possible to adjust the core of T1 topeak the sensitivity of the receiver.Assuming that a suitable RF signalgenerator is not available, the only way toset the core of T2 for the correctfrequency coverage is to use trial anderror. This is a matter of searching for 80metre amateur transmissions by adjustingRV4 and the core of T2, and then givingT2's core any setting which brings allthese stations within the coverage of RV4.It is probably best to make the finaladjustment after dark, and preferably atthe weekend, as this is when the band islikely to be most heavily used. In general,the lower half of the band is used for CWtransmissions, and the upper half is usedfor SSB. Remember to adjust the core of
T1 for peak performance once the coreof T2 has been given its final setting. Thebandwidth of Ti is quite wide, and thesetting of its core is not too critical.
As explained earlier, tuning in anSSB signal properly is quite tricky, butwith a little practice it is something that iseasily mastered. Very careful tuning isrequired in order to bring the audiooutput to the correct pitch, and the finaltuning is much easier using fine tuningcontrol RV3. With RV1 fully advanced theproduct detector may become overload-ed, leading to the breakthrough ofbroadcast stations or other transmissions.It is obvious when this happens since thetuning controls will have no effect on asignal of this type. The breakthrough canbe eliminated by backing off RV 1somewhat. With a receiver of this type itis generally better to have the volumecontrol well advanced and the RFattenuator control advanced no furtherthan necessary.
Amateur stations use callsigns, andthe first one or two letters of the callsigndenote the country in which the station isoperating. All British callsigns start withthe letter "G", and plenty of these shouldbe heard on 80 metres. There should alsobe no shortage of other Europeanstations, such as West Germany (DM/DL)and the USSR (U). Stations in the USA (W)may be heard in the early hours of themorning.
PARTS LIST FOR 80M RECEIVER
RESISTORS All 0.4W 1% Metal Film unless specified. SEMICONDUCTORSR1,16 100k 2 (M100K) IC1,2 uA741C (8 pin DIL) 2 (QL22Y)R2 560k (M560K) TR1,2,3 BC549 3 (0015R)R3, I5 2k2 2 (M2K2) TR4 BF244 (QF16S)R4 IMO (M1M) D1,2,3 MV2108 3 (QY81C)R5 47R (M47R) D4 BZY38C6V8 (QH I OL)R6 1M5 Valk 5% Carbon film (B1M5)R7 3k9 (M3K9) MISCELLANEOUSR8-10 10k 3 (MIOK) L I 1mH Choke (WH47B)R11 390R (M390R) L2 10uH Choke (W H350)R12 220k (M220K) TI Trars Coil 3T Blue (HX77J)R13 lkO (M1K) T2 Trars Coil 3T Red (HX78K)R14 4k7 (M4K7) Si SPST Ultra Min Toggle (FH97F)R17 560R (M560R) SK 1 2mrr. Socket Red (HF47B)R18 15k (M15K) SK2 2mn Socket Black (HF44X)RV1,3 Pot lin 4k7 2 (FWO1B) JK I 1/4" Jack Socket Brk (HF90X)RV2 Pot log 4k7 (FW21X) Printed Circuit Board (GBS9P)RV4 Pot lin 100k (FWO5F) Verc'pin 2145 1pkt (FL24B)
Knob K7B 2 (YX02C)CAPACITORS Knob K7C 2 (YX03D)CI,15,16,21 100uF 10V PC Electrolytic 4 (FF 10L) 9V Battery Holder (HQ01B)C2 22pF Ceramic (WX48C) PP3 slip (HF28F)C3 560pF Ceramic (VVX65V) B1 (HP7 Batteries 6 reqd)C4 100nF Polyester (BX76H) WILE lm (BLOOA)C5,9,10,17 4n7 Mylar 4 (WW 17T)C6,23 lOnF Polyester 2 (BX70M) OPTIONALC7 luF 63V Axial Electrolytic (FB12N) Case Blue Type 233 (XY48C)C8 220nF Polyester (BX78K) Bolt 6BA x 1/2" 1 Pkt (BFO6G)C11 15nF Polyester (BX71N) Nut 6BA 1 Pkt (BFI8U)C12 1nF Mylar (WWISR) Spar 6BA x 1/4" 1 Pkt (FW34M)C13,20 luF 100V PC Electrolytic 2 (FFOIB)C14 47uF 25V PC Electrolytic (FFO8J)C18 33pF Ceramic (WXSOE)C19 390pF Ceramic (WX63T) A kit of parts (exchiding case, fittings & batteries) is available.C22 220pF Ceramic (WX60Q) Order As LK41U.
14
* Build this inexpensive project anduse your Oric with the Maplin Modem
by Robert PenfoldFor a home-computer in its price
range, the Oric 1 has a respectable rangeof interfaces, but unfortunately it does nothave an RS232C or RS423 serial interface,and it cannot be directly linked to thevery popular Maplin Modem project.However, the Oric 1 does have an expan-sion port which provides the full control,data, and address buses, and a relativelysimple circuit is all that is needed to inter-face this to the Maplin Modem.
It is an interface of this type whichforms the subject of this article, and theunit is a sort of "stripped down" RS232Cinterface. The Maplin Modem does notuse any of the RS232C handshake lines(clear to send, data terminal ready, etc.),and so none of these are implemented inthis interface. Also, the RS232C systemuses signal levels of -12 and + 12 voltsrather than the more usual 0 and 5 volts.The Oric 1 provides only one voltage of+5 volts, and the maximum currentavailable is only about 100 milliamps. Inorder to provide full RS232C output levelsit would therefore be necessary to have aseparate mains power supply unit for theinterface. Fortunately the Maplin Modemhas both standard RS232C and TTLinputs/outputs. Thus there is no difficulty
in driving it from this interface which ispowered from the Oric 1, and whichsends/receives standard TTL logic levels.This simplifies the circuit and avoids theneed for a separate power supply, but itshould be realised by users of theinterface that it is unlikely to operateproperly if used with RS232C equipmentunless suitable level shifting circuitry isadded (such as the Maplin TTL/RS232CConverter project).
The CircuitFigure 1 shows the full circuit
diagram of the Oric 1 Modem Interface.The Oric 1 48K machine has a vacant areaof memcry between #BFEO and #BFFF,but it is not unused in the normal sense.The Oric 1 48K machine uses 64K RAMchips, and the full 64K address range ofits 6502 microprocessor is thereforeoccupied. The ROM containing theoperating system and the BASIC inter-preter is used to program part of theRAM, and the remaining 48K (approx-imately) is available for program storage.The address range from #BFEO to #BFFFis unused in the sense that it is not in thesection of the RAM normally used forprogram storage, and it is not used by the
111=1311131
3ASIC interpreter or operating systemeither. There is RAM at this addressrange though, and it car. only be used forinput/output devices if the RAM isdisabled. This address range is totallyunused in the 16K Oric i incidentally.
The address decoding is providedby IC1 and 1C2. As only a singleinput/output device is used in theinterface, only partial address decodingis required. IC1 is a 3 :o 8 line decoderwhich is used to decode Al2 to A15. Al2is connected to the positive chip enableinput of IC1, while the other 3 lines arefed to the normal inputs of IC1. IC2 is aneight input NAND gate, and this is used todecode address lines A4 to Al 1. Theoutput at pin 8 goes Low when all theinputs are high. Pin 8 cf IC1 is used todrive one of the negative chip enableinputs of IC1. Output 5 of IC1 (pin 10)goes low when A14 is low, but the other11 decoded address lines are high, andthis corresponds to the required address
15
SKT 1 +5V0
A15 0
414 0A13 0
Al2 0
2
3
A110
A100A90A80A70A60 -
A50A40
MAP 0
I/O CONO
ROMDIG 0
DO 0D1 0D20D30D40D 5&O 60
070A00
RIWO020
IC21
2
co
IC1
10
5
IC5loonF Pin 14
OV
3
4
5
6
11
12
0
r-
14
22
21
20
19
18
17
16
15
11
13
14
0 V
6850
C1
6
8
10
12
3
4
+ 5V
5
IC5a1
2
IC5b74LS08
)6
IC5Pin?
Olnput
()Output
0 Ground
4
n.c.
8
R1
100k
4
23
IC3
OV 0
Figure 1. Circuit diagram
range of #BFFO to #BFFF.The negative output pulse from IC1,
when any address in the specified rangeis accessed, is used to operate the 'MAP',`ROMDIS', and 'I/O Control' inputs of the
IC4
7555
2 6
R V1
1M
R21M
C2100pF
Oric 1. The result of this is that internalcircuits of the machine, which mightotherwise place an output onto the databus at the same time as the modeminterface, are disabled when the interface
34
0
MAPLINGB55K ISS 1
1
.
1
1
is being addressed. In particular, theRAM at the relevant address range iseffectively eliminated, and the interface isfree to place data onto the data bus.
A 6850 ACIA (asynchronous comm-unications interface adaptor) is used toconvert the parallel output from the databus into the correct serial format for theMaplin Modem and CASHTEL. It alsoconverts the serial output of the modeminto parallel data which is fed back ontothe Oric's data bus. The negative chipselect input at pin 9 of the 6850 (IC3) isdriven from the output of the addressdecoder. The data carrier detect input ofIC3 is not needed in this application, andis therefore tied to the negative supplyrail to permit normal operation of IC3.The 6850 has clear to send and request tosend handshake lines at pins 24 and 5respectively, but as explained earlier,these are not needed for use with theMaplin modem. Accordingly, these pinsare left unconnected. The serial datainput and output terminals are connectedto the input and output of the interface viaAND gates of IC5, and these are used togive compatibility with standard TTLinput/output levels.
Clock OscillatorThe 6850 has separate transmitter
and receiver clock inputs, but in this casethe transmission and reception rates arethe same at 300 baud, and these twoinputs are driven in parallel. The 6850does not have a built-in divide by n circuitto enable the system clock to be used asthe transmit/receive clock. Special baudrate generator chips are available, andthese are basically a crystal oscillator anddivider circuit. A simple and inexpensive
IC1
...==11.
^1:7-
IC2
MAPLINGB55K
AIC3
1
ICS
= 11111,
Cl1111
41IC4 RV1
C2
Figure 2. PCB layout and overlay16
alternative for an application such as thiswhere only a single, fairly low baud rateis needed, is to use an ordinary C -Roscillator. In this case a straight -forward7555 astable circuit is utilised, and RV1 isadjusted to give the correct operatingfrequency. Under software control the6850 can have a clock frequency at 1, 16,or 64 times the baud rate. In practice it isbest to have the clock frequency at 16 or64 times the baud rate as the clock is thenautomatically synchronised with incom-ing data. In this circuit the clock oscillatoroperates at 4.8kHz and the 6850 is set tothe divide by 16 mode to give 300 baudoperation.
Although the 6850 has four registers,it has only one register select input (pin11). This is driven from address line A0,and the port therefore occupies address-es #BFFO (49136 decimal) and #BFF1(49137 decimal). In fact accessing anyaddress from #BFF0 to #BFFF willoperate one or other of these registers,but the base addresses given are theobvious ones to use. Only two addressesare needed for the four registers as twoare read only registers, and the other twoare write only types. The table belowshows the four registers available andhow they are accessed:-ADDRESS READ WRITE49136 Status Register Control Register49137 Receive RegisterTransmit Register
Of course, the 6850 is fed from theread/write line of the computer so that theappropriate register at each address isconnected through to the data bus. The6850 needs a timing signal at its 'Enable'input, and this is provided by the Oric'sclock signal. Although the Oric 1 uses ahigh speed version of the 6502 micro-processor, the system clock operates at1MHz, and a standard 6850 is perfectlyadequate for use with this machine.
ConstructionDetails of the printed circuit board
are provided in Figure 2. Start by fittingthe resistors, capacitors, and the linkwires. The latter are made from about 24swg tinned copper wire, or pieces ofwire trimmed from resistor and capacitorleadouts will do if no suitable wire is tohand. Provided these wires are keptquite taut it is not necessary to addinsulation to any of them.
Next the integrated circuits are fittedto the board. Although IC4 is a CMOS
device it does not require any specialanti-static handling precautions. IC3 is aMOS device, and is a relatively expensivecomponent. It is therefore worthwhileusing a (24 pin DIL) IC socket for thisdevice, even if the others are connecteddirectly to the board. Also, do not fit IC3into its socket until the unit is in otherrespects complete, and leave it in theanti -static packaging until that time. Notethat IC3 has the opposite orientation tothe other four integrated circuits.
The board is connected to the Oric'sexpansion port via a length of 34 -wayribbon cable and a 34 -way IDC socket. Itis advisable to obtain the socket andcable ready connected (they are supp-lied thus in the kit). The IDC socket fitsthe expansion port of the Oric 1 and thefree end of the cable connects to theboard. Be careful to connect the cable tothe board the right way round (consultthe expansion port connection diagramon page 151 of the Oric 1 manual). Beforeconnecting the cable, strip a smallamount cf insulation from the end of eachlead and tin it with solder. :t should thenbe quite easy to connect the leads to theboard, one by one, being careful not toget any leads crossed over. An alternat-ive to direct connection is to use two 17 -way Min:con connectors.
In UseConnect the interface to the Oric's
expansion port before switching on theOric. Once switched on the computershould function normally - switch off atonce and recheck the interface if it doesnot.
The accompanying program (figure3) enables the interface to be used withthe Maplin modem and CASHTEL. Wheninitially testing the unit try running thisprogram with the input & output of theinterface connected together. Characterstyped on the keyboard should appear onthe screen, but this should not happen ifthe link from the output to the input of the
10 POKE 49136,320 POKE 49136,2130 CLS40 IF (PEEK(49136)AND I)= 1
THEN PRINT CHR$(PEEK(49137));50 IN$ = KEY$60 IF 1N$<,""THEN POKE 49137,ASC(IN$)70 GOTO 40
Figure 3. Program listing
ORIC MAPLIN MODEM INTERFACE PARTS LIST
interface is cut.The 6850 does not have a reset input,
but is instead reset under softwarecontrol by writing a value of 3 to thecontrol register (i.e. POKE 49136,3). Thecontrol register is also used to select therequired word format, after a masterreset has been performed. There areeight word formats available, as detailedn the table provided below.
VALUE WORD FORMAT POKED
1 7 bits, 2 stop bits, even parity5 7 bits, 2 stop bits, odd parity9 7 bits, 1 stop bit, even parity13 7 bits, 1 stop bit, odd parity17 8 bits, 2 stop bits21 8 bits, 1 stop bit25 8 bits, 1 stop bit, even parity29 8 bits, 1 stop bit, odd parity
Deducting one from these values sets the6850 to the divide by 64 mode, andreduces the baud rate to 75. TheCASHTEL system requires 8 data bits andone stop bit, and 21 is the value to be?OKEd to the control register. However,when accessing other systems it might benecessary to use a different word formatand the corresponding control number.
The ASCII codes of characters to betransmitted are written on the transmitregister at address 49137. Bit 1 of thestatus register can be read to determine if:he transmit register is empty, and readyto receive the next character, but this isnormally unnecessary if the keyboard is:he source of the transmitted characters,due to the relatively slow rate at whichcharacters will be supplied to theinterface. The receive data register fullflag is at bit 0 of the status register, and itis normally necessary to check this andonly read the receive register when anew character has been received. Other-wise multiple readings of each characterwill occur. The receive register full flag isautomatically reset when the receiveregister is read.
Those who require full informationon the 6850 should consult the relevantdata sheet (which is available fromMaplin price 40p).
Initially RV1 should be set at abouthalf resistance, but it will probably benecessary to trim this component slightlybefore precisely the right baud rate isobtained and the interface operatesproperly with the CASHTEL system, etc.
RESISTORS:- All 0.4W 1% Metal Film IC3 MG6850P (WQ48C)RI 100k (M100K) IC4 ICM7555 (YH63T)R2 1M (M1M) ICS 74LS08 (YFO6G)RV1 Hor S -Mm Preset 1M (WR64U)
MISCELLANEOUSCAPACITORS SKI 34 -way DC Socket & Cable (BK96E)Cl 1001iF Disc Ceramic (BX03D) Veropins 2145 1 pkt (FL24B)C2 100pF Ceramic (WX56L) Printed Circuit Board (GB55K)
24 -way DIL Socket (BL2OW)
SEMICONDUCTORSIC1 74LS138 (YF53H) A kit of all :he above parts is available.IC2 74LS30 (YF2OW) Order As LK4OT (Oric Modem I/F Kit)
17
32 -LINEEXPANSIONfor the Maplin Digi-Tel Telephone Exchange* Expansion board for up to 32 extensions* No call can be interrupted or overheard by another caller* Standard 2 -wire connection to all telephones* All phones powered by the 2 -wire line* Mains connection required only at the exchange* May be used with standard British Telecom phones* Up to 16 telephones may be in use at any one time
by Robert KirschIntroduction
This article describes the additionsto the 16 line Digi-Tel TelephoneExchange (described in the September/November 1982 edition of 'Electronics'and Maplin Project Book Four) to enablea furthur 16 lines to be added thusincreasing the total capacity to 32 lines.The expansion board is the same size asthe 16 line mother board and may bemounted above or below it; most of theinterconnecting wires coming from theleft hand side of both boards. There aresix additional connections between thetwo boards, details of which are shown inFigure 3b.
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Figure 2. Expansion motherboard circuit
19
Wire pins 1-57 to pins 1-57on expansion board. 11 to 1 etcl.
Motherboard
1
1_57i
Extensions
1 Cr-r-0---.)
32 17
5
Transformer T1
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See seperate wiringfor pins 58 - 63
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59 i61 630 0 0 0 0 0
58 60 62
CCB boards 'ELC boards PSU
Figure 3a. Wiring diagram
The expansion board can beequipped with up to 4 E.L.C. cards and upto 4 C.C.B. cards, in the same manner asthe 16 line exchange, depending on thenumber of additional extensions requir-ed. A modified P.S.U. card is used thatdoes not include the components for the100V ringing as this is fed, along with alltiming pulses etc. from the 16 line board.
Numbering SchemeThe relationship between the exten-
sion system number, and the numberdialled to obtain that extension isreprinted in figure 3c.
CircuitSee Figures 1,2 & 4. The principle of
operation is the same as that described inPart 1 but, as in this case the 4 C.C.B.cards on the 16 line board must haveaccess to the new 16 extensions, 4
additional CP switches (IC's 1-4) areprovided. The 4 C.C.B. cards on theexpansion board, switch to any of the 32lines using the 8 CP switches (IC's 5-12).A calling extension is switched to a freeC.C.B. card by one of the 4 CP switches(IC's 13-16). All control of output CPswitches is accomplished by the EPROMlogic on the 16 line board and for thisreason both EPROM address arid datalines are extended between the twoboards.
When extensions 17-32 are dialledon the 16 line Digi-Tel, the EPROM (M4YELLOW) connects the call to NU tone,therefore a new EPROK-(M5 BROWN) isprovided in the expansion kit, which hasthe correct codes for routing to the new20
Expansion board
SystemExtensionNumber
SystemNumber Extension Number
Dialled Number Dialled1 21 19 392 22 20 303 23 21 414 .......... ...... ....... 24 22 425 25 23 436 26 24 447 27 25 458 28 26 469 ......... ................ 29 47
10 20 28 4811 31 29 4912 32 30 4013 33 31 5114 34 32 5215 35 Aux 1 816 ..... ....... ......... 36 Aux 2 .......... 917 37 Aux 3 018 38
Figure 3c. Number conversion table
Vo
59t-1.1C4
6
117
60R26
62 0
10 000.58 63D -
Till 0
Motherboard
105
Expansion board
58 59 60 61 62 63
Figure 3b. Additional inter -board wiring
extensions. Both boards have 3 auxiliaryoutputs. These may be used independ-ently or both sets may be connected inparallel, the busy tone being returned if asecond board tries to switch to a circuitalready in use.
ConstructionRefer to P.C.B. legends, parts lists
and Figures 3a & 3b. The board isconstructed in the same way as the 16 lineone, not forgetting to solder on both sidesof the board components marked with aring on the legend. D.I.L. sockets shouldbe used for all CP switch IC's (IC1-17)and these components should not beinserted until the construction has beencompleted and all P.S.U. voltages havebeen checked.
FS1
0 aE
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2
3
21
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DI
I 22
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C2T2 200uF
I/P
Earthtag
Figure 4. Modified PSU circuit
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C/P
ICl
P213k
R34k3
IIP
IC2
0/P +154
017
TP2 14815
u m C3N m100nF C4 aim
100nF
EXPANSION BOARD PARTS LISTRESISTORS: All 0.4W Metal FilmR1-20,25 27,29-31,3710kR21-23,26,28,32-36 100kR24 2M2
CAPACITORSC1-4
26 MIOK)10 ( vl 100K)1 (M2M2)
100uF 25V PC Electrolytic 4 (-2711M)
SEMICONDUCTORSD1-65 1N4148D66IC1-17IC18IC19-21TR1-3
MISCELLANEOUS
BZY88C 12V45100BE4081BE40106BEBC548
P.C. Board8 way P.C. TerminalEdge Connector 124Edge Connector Fool GEdge Connector Foot HDIL Socket 16 pinTrack Pir,Veropin 2145Bolt 6BA x 1/2"Nut 6BAWasher 6BA
ADDITIONAL PARTSTI
FI
OPTIONAL
Toroidal Transformer 24V 24VSafuseholder 20Fuse A'S 2ATerminal Block 5ATag 2BAC6A Mains WhiteWire 3202 WhiteRibbon Cable 30 wayEPROM 2716.1v15
P.B. TelephoneP.B. Telephone4 -wire Phone Cable
65 (QL80B)QH16S)
17 (QQ51F)W48C)
3 (C W64U)3 (QB73Q)
(GB35Q)5 (RK38R)9 (FL85G)9 (FL9IY)9 (FL92A)17 (BL19V)6 pkts (FL82D)1 pkt tFL24B)2 pkts (3F06G)2 pkts (BF18U)2 pkts (BF22Y)
1 pkt2m2m2m
11K86T,(1)(96E)
IIAR2OW)( HFO IB)
(BF27E)(XR04E)(XR37S)(XR67X)(QY600)
Set of 4 (XG19V)As req (MG18U)As req (XR66W)
04 Common
04 Ringing
0 OEM
18
19
7
12 813 I
0TP5 8 & 9 I
POWER SUPPLY PARTS LISTRESIST DRS: All 0.4W 1/ Metal FilmR2 13kR3 4k3
CAPACITORSC2 2200aF 40V Axial ElectrolyticC3,4 100nF Polyester
SEMICONDUCTORSD1,2 IN5401IC 1 uA78GU1CIC2 uA7815UC
MISCELLANEOUSP.C. BoardHeatsmk 4YBolt SBA x /2"Nut 6BAWasaer 6BA.Track PinsVerc pin 2145
(M13K)(M4K3)
(FB91Y)2 (BX76H)
2 (QL82D)(W079L)
(QL33L)
(GBO7H)(FL41U)
1 okt (BFO6G)1 pkt (BF18U)1 okt (BF22Y)1 pkt (FL82D)1 okt (FL24B)
A kit is available containing ail the parts in the above 3 113t5, excluding07tional parts.
Order As LI(37S (Digi-Tel 32 -Line Expansi ma Kit)
21
O
4.;"'4.4i,v;".V:
Ns.
There are several ways of producingthe well known and much used waa-waaeffect, but in each case the basic effect isgenerated using some form of bandpassfilter which is swept up and down over allor part of the audio band. This boosts afairly narrow and continuously changingband of frequencies, and it is mainly theconsequent variations in the relativestrengths of harmonics in the processedsignal that give the effect.
The difference between the varioustypes of waa-waa effects units is the wayin which the filter frequency is varied,and there are three main types. The mostsimple of these is where the filter is con-trolled manually using a foot -pedal. Theother two types operate the filter auto-matically, one using an oscillator tosweep the filter in a cyclic manner, andthe other using a sort of envelope gener-ator to move the filter frequency in sym-pathy with the strength of the processedsignal.
This auto-waa unit is of the thirdtype, and this form of waa unit has theadvantage of being very easy to usewhile giving an excellent range of effects.With this design it is possible to adjust theminimum filter frequency to practicallyany audio frequency, and a sweep depthcontrol is also included. Another usefulfeature of the unit is a resonance controlwhich enables the bandwidth of the filterto be adjusted. The filter is actually a12dB per octave lowpass type, but pos-itive feedback is used to give a peak inthe response just above the cutoff fre-quency, and this type of filter probablygives the best waa effect. With the reson-ance control fully backed -off the filter22
...
vv
by Robert Penfold
Automatic nofoot pedal needed
Very low powerconsumption
Wide range ofmusical effects
InBuffer
Resonance/-
Amplifier
Two stageVCF
Out-0Frequency
Sweeprange
Rectifier ActiveLPF
Figure 1. Block diagramoperates as a straight forward 12dB peroctave lowpass type, and the unit thengives a more subtle but useful effect.
O
Block DiagramThe block diagram of Figure 1, helps
to explain the general way in which thecircuit functions.
A buffer stage at the input gives thecircuit a reasonably high input imped-ance and provides a suitably low driveimpedance for the subsequent stage.Some of the output from the buffer stageis fed through a two stage voltage con-trolled filter (VCF) and then to the output.The rest of the output from the bufferstage is fed to an amplifier, and theamplified signal is then rectified toproduce a DC control voltage for theflter. The operating frequency of thefilter is roughly proportional to thecontrol voltage, and the DC output fromthe rectifier is roughly proportional to theamplitude of the input signal. As the amp-litude of the input signal rises and falls theoperating frequency of the filter is there-fore moved up and down in the requiredmanner. The sweep range control isincluded between the rectifier and theVCF, and the base frequency control isalso included in this part of the unit.
For this system to work properly it isessential for the control voltage to be anaccurate reflection of the input level, andit must have fast attack and decay timesso that it accurately tracks the inputsignal. On the .other hand, the output fromthe rectifier must be well smoothed toprevent audio signals being fed to thecontrol input of the filter and producingdistortion products. In this design the useof a three stage active filter instead of asingle smoothing capacitor gives fastattack and decay times with no significantbreakthrough at audio frequencies.
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Figure 2. Circuit diagram
The CircuitThe circuit is based on an LM13700N
dual transconductance amplifier, as canbe seen by refering to the circuit diagramof Figure 2.
IC 1 is used as the buffer amplifier atthe input of the unit, and this provides thecircuit with an input impedance of over100 kibhms. C3 couples some of IC1 soutput tc the VCF which uses both trans -conductance amplifiers and buffer ampli-fiers of the LM13700N, IC2.
With RV2 set at minimum resistancethe oirctit operates as a straight forward12dB per octave lowpass filter with R8and R9 setting the nominal voltage gain ofthe circuit at unity at pass frequencies.The frequency at which the roll -off com-mences is determined by the values offilter capacitors C5 and C6, and the gainof the amplifiers (which is in turndependent on the bias current fed to pins1 and .6). The cutoff frequency can there-fore be varied by means of a controlcurrent, or a control voltage if a resistor isadded in series with the control inputs sothat the current flow is roughly pro-portional to the input voltage. The filter'scutoff frequency can be varied manuallyusing RV4 which supplies a variablecontrol voltage - R23 is the seriesresistor. The cutoff frequer.cy can be setanywhere within the audio range. If SI isclosed, a strong bias current is fed to thefilter regardless of the setting of RV4 sothat the cutoff frequency is set above theupper limit of the audio band and thefiltering is effectively removed. Ir. prac-tice Si is a foot operated switch and itenables the waa effect to be easilyswitched in and out.
The filter is actually a state -variabletype with bandpass filtering available atthe output of IC2a, but this output is
unused in this application. Instead, a formof bandpass filtering is obtained at theoutput of IC2b by adjusting RV2 for.ncreased resistance so that the feedbackover IC2a is decreased. This gives aboost in gain, but only over a narrownand of frequencies immediately belowthe cutoff frequency. This form of filteringgives the required bocst over a narrowband of frequencies, but it gives normal:unity) voltage gain at frequencies below:his band. As a result of this there is noattenuation of the fundamental frequen-cies in the processed s.gnal, and it is forthis reason that this type of filtering giveswhat is generally accepted as a betterwaa effect than conventional bandpassfiltering.
A certain amount of the output fromIC1 is taken via preset attenuator RV1,and then amplified by TR I which is usedas a straight forward high gain commonemitter amplifier. The amplified signal isrectified by DI and then applied to theinput of the active filter which is based onIC3. This is a conventional three stagecircuit apart from the fact that R17 biasesthe input of the filter to earth and the filteronly handles positive half cycles. ACA3130T is used in the IC3 positionbecause this has a CMOS output stagewhich enables its output to go within afew millivolts of the negative supply rail.Most operational amplifiers, such as thestandard 741C device, have a minimumoutput voltage of about 2 or 3 volts whichis far too high to give acceptable resultsin this circuit. Another advantage of theCA3130T is that it has an extremely highinput impedance, and due to the highvalue of filter resistors R18 to R20 this isessential. The filter resistors have beengiven such a high value in order to enablethe low cutoff frequency of about 10 Hertzto be achieved using reasonably low filter
23
uo
V
RI C3
R2
C4
nSK1S2
B1
0 0 0
(101-4-32,0d cpc\LlIr
1..agrEoc__1.1\oorroici=4-1,0980,10
Figure 3. Legend, artwork and wiring diagram
capacitor values. This cutoff frequencygives more than adequate attack anddecay times but ensures that there is nosigificant ripple on the DC output signal.
The output of IC3 is coupled to thecontrol input of the VCF by way of D2,R22, and RV3. The latter acts as the mod-ulation depth control. D2 is needed toprevent any interaction between thedepth and frequency controls.
As the circuit has a current con-sumption of only about 4.5 milliamps asmall (PP3 size) 9 volt battery can be usedas the power source and will give manyhours of operation.
ConstructionFull details of the printed circuit
board are provided in Figure 3. Theresistors, capacitors, and single link wireare soldered in place first, followed bythe semiconductor devices. IC3 has aMOS input stage and should therefore befitted in place last of all, while taking theusual MOS handling precautions. DI andD2 are germanium diodes which aremore susceptible to damage by heat thansilicon devices. Appropriate care not tooverheat these components should betaken when they are being soldered tothe board. It is helpful to fit Veropins at24
places where connections to off -boardcomponents will eventually be made.
For this type of project a very toughcase is required, and one which screensthe circuit from electrical noise is also anasset. A diecast aluminium box is ideal,and the printed circuit board has beendesigned to fit a 150 by 80 by 50mm caseof this type. The two sockets and threepotentiometers are mounted on the frontpanel (which is one of the 150 by 50mmsides of the case), and Si is mountedcentrally on the top panel. S2 is a pair ofmake contacts on SKI and the unit istherefore automatically switched on andoff when a jack plug is plugged into andremoved from SKI. An ordinary on/offswitch could be used if preferred, but itwould be difficult to accomodate this onthe rather crowded front panel, and thesuggested method is probably the mostpractical solution. Incidentally, thismethod of on/off switching is often usedfor musical effects units.
Next the hard -wiring is added, asshown in the wiring diagram of Figure 3.This is all quite straight forward andshould not give any problems. Finally, theprinted circuit board is fitted into the setof guide rails nearest the rear of the unitwith the component side facing forwards.
There is plenty of space for the battery tothe rear of SKI, and a piece of foammaterial can be used to keep the batteryin place.
AdjustmentThe only preset control is RV I which
must be adjusted to suit the input signallevel. If it is set too far in a clockwisedirection the filter frequency will tend togo to its highest level even when the inputsignal has fallen well below its peaklevel. If it is set too far in the oppositedirection the filter frequency will bevirtually static at the level set using RV4.A suitable setting for RV1 is found byempirical means, and is any setting thatproduces a good waa effect with the filterfrequency sweeping up and down insympathy with volume of the processedsignal. The unit can handle a low levelsingal from (say) a low output guitar pick-up, or a high level signal from a highoutput pick-up, keyboard instrument, orany similar signal source.However a verylow level signal, such as the output from amicrophone, would require a certainamount of preamplification.
Results are likely to be best with RV2well backed off, RV4 set for a base fre-uency around the middle of the audio
Continued on page 27
JA)-ek :B:3 PQJ1 vrd\10111:1;1
b 1N1 rilLP :1"
* Controls up to 12 Amps at 240VAC* 99% Power Transfer* R.F.I. Suppression* Simple Constructionby Dave Goodman
By utilising the PC12 thick film IC thisPower Controller can handle loads up to2.8kW - much greater than most,reasonably priced, commercially avail-able units. Voltage levels are continuous-ly variable from 240V down to between 2and 20V, this final level being dependenton the load applied, up to a maximum of12 amps. The unit is therefore suitable forcontrolling lamps, electric drills, solder-ing irons, bar type electric fires and manyother electrical items. The module maybe incorporated into a complete project,to provide a self-contained powercontroller, as described later in thisarticle. Alternatively it may be used tosuit a particular application.
Circuit Descriptionici is a thick film hybrid device with
an integral heat sink mounting plate,requiring RV1 for varying the conductionphase angle between 160 and 0 degrees.The Triac is turned on after an applied acwaveform has passed through zero voltsand it remains on until, after passingthrough its peak, the waveform againreaches zero thus turning the triac offagain. This process is repeated duringthe next half -cycle as shown in Figure 1.Triacs differ from thyristors in that theyare able to conduct during positive andnegative half cycles (effectively aswitched diode). This means that fullcycle control and hence 99% powertransfer is available at maximum current.
Full power is available with RV1 setfully clockwise i.e. minimum resistance(see circuit diagram, Figure 2). Increas-ing resistance between output pin 2 andcontrol input pin 1 determines the phaseangle or position along the waveformwhere IC1 will turn on. At maximumresistance the phase angle is in directopposition and no power is delivered, butthis action must not be compared withthat of a mechanical switch, as full mainspotential is available with no loadconnected.
Due to the fast switching action ofIC1, harmonics are generated especially
I AI
WA=ov
1r:=,r20mS
IB
ConductionPhase 160°
ICI
off
oft
off
off
CO
o.
ConductionPhase 45°
Figure Triac conduction waveformsat 50% power setting. These harmonicsare exter.ded up into the RI% range andare radia:ed along the connecting cablesand into the air producing R.F.interference and a loud buzz in audioequipment! Not only is R.F.I. anannoyance, it must meet Department ofTrade and Industry requirements, so L.C.
41*
filtering of the harmonics is performed byCl, C2 and RFC1 to 4. Four 3 amp chokeshandle the 12A maximum currentavailability, offering a low impedance at30Hz and a high impedance to high'requency signals. A neon lamp NImdicates permanently when mains isapplied without a load, but will not be onif fuse FS1 blows. With a load connected,NI indicates fully at maximum power anddims progressively as power levels are:educed by RV1 down to a minimum.
PCB ConstructionInsert all five Veropins (P1-5) into the
holes marked with a circle. (see Figure 3,pcb artwork and legend) push the pinheads firmly down to the board andsolder in place. Mount the four chokes(RFC1-4) and the suppressor caps Cl andC2, solder these components in placeand remove excess wire ends. It isimportant to push all components downon to the board so that they cannot bemoved about and cannot break awayfrom their positions. Remove the nut andwasher from RV1 and insert into theboard from the component side. Asshown in Figure 5, two terminals aresoldered to pins 4 and 5 and the third isnot used and may be cut off or bent away.
25
Replace both washer and nut on RV1 andtighten up to the PCB.
IC1 pins 1, 2 and 3 are inserted andsoldered from the track side of the PCBand IC1 is set approximately 12mm awayfrom the board (see Figure 5). Theheatsink bracket is completely isolatedand can be connected to mains earthwithout problem. Note that IC1 must bebolted onto a suitable heatsink and foruse with high load currents, the heatsinkwill need to be rated at between 3' and4`C per Watt.
Box Drillingand Assembly
The parts list gives details of asuitable box, neon lamp, fuse holder, 13Aswitched socket and miscellania. Figure 4shows drilling instructions for the box;there are twelve holes to be drilled. Tomake life easier the PCB could be used asa template (before assembly of course!)by placing it inside the box and markingeach hole with a pencil or scriber. Thesame applies to the socket pattress. Aftermarking out, drill all required holes,noting that holes type 'b' requirecountersinking on the outside of the box.
With reference to Figure 5, fitgrommets into the 13mm holes and placethe socket pattress over the holesmarked 'a', insert half -inch x 4BA counter-sunk screws into both holes and securethe top one only with a 4BA nut andwasher. Spread a thin layer of heatsinkcompound over IC1 mounting plate andplace over the bottom screw. Fit a 4BAsolder tag in place and secure theassembly with a 4BA nut. Remove the
mock nut from the neon lamp Ni beforeserting it into the I 1mm hole; this alsoplies to the fuse holder which is placed
gut a 14mm hole. Refit both locknuts andtighten down. Insert 1 inch x 6BA counter-sunk screws into the four holes marked'b', and slide a spacing collar over eachone. The assembled PCB is positionedover these screws with the spindle of RV1protruding through the 7mm hole. Securethe PCB with 4 x 6BA nuts and washers.
WARNING240V
RFC1
RFC2
RFC3
RFC4
IC1
1 2 3
I-
I-
RV1
Figure 2. Circuit diagram
All dimsin mm
55
to
4'b' Holes3.5mm 0Cskto suit6BA scr
125
hole 4.3mm 0Csk to suit 4BAscrew
Ta'Holes 0 4.3mm110
Figure 4. Case drilling details
01
C2
Cl
N1
FS1
03CC
CDz
DANGER LIVE
0
Hole13mm 0
7,
Holemm 0
Hole
X14mm 0
Hole\\ 7mm 0
Wiring DetailsRefer to Figure 5. Strip away approx.
18 inches of insulating sheath from oneend of the 13A connecting cable. Passthis end through the top grommet into thebox and clamp in place with a 5/16 inch 'P'clip and I/2 inch x 4BA countersunkscrew, nut and washer. Measure and cutthe live (brown) wire and solder it to aterminal on FS1. Use three inches ofbrown wire and join the other FS1terminal to PCB pin 1. Connect anotherwire length between one terminal of Niand pin 2. Solder the remaining 5 to 6inches to PCB pin 3 and feed through thegrommet for connection to SKT1. Both theblue and green/yellow wires from thecable should now be cut to approx. 8inches long and placed through thegrommet.
Solder one end of neutral (blue) wireto the unused terminal of Ni and solderone end of the earth (green/yellow) wireto the 4BA tag on IC1. Thread both wiresthrough the grommet to SKT I. Thereshould now be five wires protrudingthrough the box: 1 brown, 2 blue and 2green/yellow. Terminate both blue wiresto terminal N (neutral), both green/yellowwires to terminal E (earth) and the Brownwire to terminal L (live) on the switched
0
0
MAPLIN GB51F
Figure 3. Artwork and legend26
0MAPLIN POWER PCB GB51F ISS.2
socket SKT1, then secure to the pattresswith both screws provided. Finally cut offRV1 spindle half an inch above the boxand fit a control knob. Insert a 10A 11/4"fuse into FS1 holder and bolt on thebottom box cover.
Testing and UseConnect the 13A cable to the mains
supply and switch on. Ni should light up,but note that varying RV1 will slightlyalter the light output of Ni. Unscrew theterminal post in FS1 and let it pop up -do not remove it - and Ni will go out.Retighten the terminal post. If you have abedside or table lamp available plug itinto SKT1, ensuring that its own switch ison! Turn SKT1 switch off and RV1 fullyanti -clockwise. Ni should be illuminateduntil SKT1 is switched on, whereupon itwill go out. Slowly turn RV1 clockwise.Neon Ni will gradually brighten, as willthe test lamp. Do not worry if a quiet buzzis heard with RV1 at maximum - this isquite normal.
Problems can be encountered whencontrolling inductive loads such as pumpmotors. Changing the power factorcauses the triac to fire intermittently andheavy currents will be passed, which mayblow FS1, even for a small load. Finally,remember that the switch on SKT1 onlydisconnects output power to the load anddoes not remove mains supply from theunit. Therefore keep loose wires, fingersetc. away from the PCB as full mains ispresent and potentially dangerous!
FS1
r1:13
1, N.
6BA fixings
P Clip
4BA fixings
Figure 5. Assembly and wiring
Continued on inside back cover.
AUTO-WAA Continued from page 24.band, and RV3 set for a medium to highmodulation depth. However, a littleexperimentation will soon show whatsettings give the best effects with aparticular instrument. Bear in mind thatsetting RV4 for a low base frequencycould result in fundamental frequenciesin the processed signal being substant-
ialy boosted as the filter sweeps throughthem, and with a high level input over-loading with attendant distortion couldresult. There is also a danger of over-loading the equipment fed from the out-put of the unit, and the best effect tends tobe obtained with the filter sweeping overmedium and high frequencies anyway.
PARTS LIST FOR AUTO-WAA SEMICONDUCTORSD1,2 0A91 2 (QH72P)
RESISTORS:- All 0.4W I% Metal Film unless otherwi se sta:ed. TRI BC109C (QB33L)R1,2 220k 2 (M220K) ICI uA 741C (f -pin DIL) (QL22Y)R3.4,10,14,16 4k7 S (M4K7) IC2 LM:3700N (YH64U)R5,7,12,13 1k0 4 (M1K) IC3 CA3130T (QH28F)R6,11R8.9,22R15R17,21,23R18,19,20RV1RV2RV3RV4
101( 2
22k 3
1M8 Carbon film W100k 3
IMO 3
10k Hor Sub -min Preset220k Pot Lin470k Pot Lin47k Pot Lin
(MIOK)(M22K)(B1M8)
(M100K)(MIM)
(WR58N)(FWO6G)(FWO7H)(YWO4E)
MISCELLANEOUSSKI DPDT Jack SocketSK2 Jack Socket OpenSI Press Toe E.w 1S2 (Part of SKI)
Printed Circuit BoardKnob K7B 3
Wire 1 pktBattery Cli; (PP3 Clip)
(BW80B)(HF91Y)(FH92A)
(GB54J)(YX02C)(BLOOA)(HF28F)
Veropins 2:45 I pkt (FL24B)CAPACITORSCl 220nF Polycarbonate (WW45Y) OPTIONAL
C2,3 2u2 63V PC Electrolytic 2 i:FFO2C) Battery 9V ?P3 Nicad (HW31J)
C4.14 100hiF 10V PC Electrolytic 2 (FF 10L) Case (LH73Q)
C5,6 330pF Ceramic 2 (WX62S) CaliMet Feet 1 pkt (FW I9V)
C7 10uF 35V PC Electrolytic (FF04E) 16 Pin DIL Socket (BL19V)
C8 luF 100V PC Electrolytic (FFO1B) 8 Pin DIL Socket (BL17T)
C9 100nF Polycarbonate (WW41U) Bolt 4BA V," 1 pkt (BFO2C)
C10 22nF Polycarbonate (WW33L) Nut 4BA 1 pkt (BF 17T)
C11 47nF Polycarbonate (WW37S)C12 3n3 Polycarbonate (WW25C) A kit of parts (excluding optional items) is available.C13 100pF Ceramic (WX56L) Order As LK36P (Auto Waa Kit)
27
8W
PrBy Dave Goodman
es
Fluorescent lights have manyadvantages over incandescent lampswhen used out of doors especially whenlimited power resources are available.Heat output is very low, reducing the riskof fire especially in tents and an averagefamily car battery could supply sufficientpower for up to 15 hours continuous use.Light output radiates from the length ofthe tube, not from one focussed pointmaking diffusers and reflectors unnec-essary, and being much kinder on theeyes. Unfortunately there is one problemwith fluorescent tubes: high voltages arerequired to 'Strike and run them, so amethod of driving many hundreds of voltsfrom a 12 volt source must be employed.Our fluorescent tube driver meets therequirements and provides a system atmuch lower cost than commerciallyavailable units.
Circuit DescriptionWhen power is applied, TR1 is
turned on hard via RI and L2. LI isenergised and passes a high currentwhich induces a pulse in L2 and turns TR1off for the duration of the pulse. Nocurrent flows through L 1 at this time andL2 offers a low impedance path from RIto TR1 base thus turning it on again. Dueto this alternating field a large voltage isdeveloped across LI - around 100 volts- and step-up winding L3 generatesseveral hundred volts, enough to strikethe fluorescent tube. The load nowremains constant across L3 and theoscillation frequency is maintained bytime constant R1 and C2.
Under normal load running condit-ions a 50kHz square wave at 250 voltsshould be present across pins 5 and 6. Incase of reversed battery connections, DIprevents damage to both TR1 and batteryfrom occurring, and it will not passcurrent under these conditions. CIdecouples the supply rails and preventsRF transmission from long battery -leadcables (see circuit diagram, Figure 1).28
..........
e
* Ideal for Camping, Caravans and Boats* Runs from 12V Battery Supply* High Efficiency Light Output
4 tgo:,404*
TransformerConstruction
Three separate windings are requir-ed, see Figure 2, these being:Secondary L3: 200 turns of 34swg (0.3mm)
E/C wireSecondary L2: 15 turns of 34swg (0.3mm)
E/C wirePrimary LI: 30 turns of 24swg (0.6mm)
E/C wireWind L3 first on the bobbin (Figure 2a) bytinning the E/C wire and soldering it to
D1 1N4001
Figure 1. Circuit diagram
finish windingdirection
startfinish
start
anchor pin
Ass---- finish
start
Figure 2. Construction of T1
the terminal L3 start. Wrap each turnclose to the previous one and build up inlayers. Approximately 30 to 32 turns canbe made across the former, so six layersshould be built up as neatly as possible.Terminate L3 finish as before and insulatethe windings with a single layer of PVCinsulating tape wrapped tightly aroundthe coil. Next wind L2 (Figure 2b) startingand terminating on the opposite twobobbin pins (3rd one not used). Again,spread all 15 turns tightly across theprevious coil L3 - eight turns across and7 turns back. Finally, wind LI straight ontop of L2 (Figure 2c). Leaving two inchesof spare wire, wind two layers, 15
across and 15 back again leaving two
inches of spare wire. Wrap three turns ofPVC tape tightly around LI to prevent itfrom unwinding and drop into onesection of T 1. Fit the remaining sectionover the bobbin and secure both halveswith metal clips clamped over each end.Before fitting onto the pcb make sure thewindings of L2 and L3 have beensoldered correctly to their bobbin pinsand remove any excess solder whichmay prevent insertion into the board.
PCB ConstructionRefer to the parts list and Figure 3.
Mount the capacitors C2,3 and resistorRI. Insert diode DI correctly to thelegend on the PCB to ensure correctpolarity. Next insert Veropins 1 to 6.
Position the vaned heatsink and mountTR1 (Figure 4) making sure that the leadsof TR1 go through the board and tightenthe nut and bolt. Insert CI, which ispolarised, and finally fit T1. LI is solderedto pins 3 and 4 and the two wire endsshould be scraped to remove the enamelbefore tinning. Solder components andcut-off all excess leads.
Using the ModuleConnect an ammeter in series with
pin number 1 and + 12 volt supply; supplycommon or -ye goes to pin 2. Set theammeter scale to allow a reading of 1
amp or more and apply power. A highpitch whistling may be heard, with acurrent reading of 0.4 to 0.5A. If thereading is IA or more, switch off andreverse LI connections to pins 3 and 4
C2
-0Figure 3. PCB legend
and check again. Remove power andconnect an 8W 12 inch fluorescent tubeacross pins 5 and 6. The tube willprobably have two starter terminals ateach end (four altogether). Join each pairtogether before connection to the pcb.Keep all connections short and insulatebare terminals to prevent the risk ofshock. Remember high voltages arepresent here and could be dangerous,even with limited current availability!
Apply power again and the tubeshould glow dimly, then after a second ortwo light up completely. Check currentreading is approximately 0.5A. No whistl-ing should be audible and the tube shouldnot flicker, but if this is not so, tryreversing LI connections to pins 3 & 4 orreverse tube connections to pins 5 and 6.
The inverter can drive two tubes in
TUBE DRIVER PARTS LISTRESISTORS:- 143W 5% Carbon FilmRI 1k5 (See text)
CAPACITORSC1C2C3
100uF 25V PC ElectrolyticlOnF Carbonate4n7F Ceramic
SEMICONDUCTORSDI 1N4001TR1 BD711
MISCELLANEOUSLI 30 Turns x 24swg E.C.W.L2 15 Turns x 34swg E.C.W.L3 200 Turns x 34swg E.C.W.Ti Ferrite Pot Core Type 3
Bobbin Type 3Clip Type 324swg Enamelled Copper Wire34swg Enamelled Copper WireMounting KitHeatsinkVeropin 2145Tube Driver P.C.B.6BA x tin Bolt6BA Nut12V 8W fluorescent Tube
(S1K5)
(FF11M)(WW29G)(WX76H)
(QL73Q)(WH1SR)
(HX09K)(H)C1OL)
2 (HX11M)1 reel (BL28F)1 reel (BL42V)
(WR23A)(FL58N)
1 pkt (FL24B)(GB52G)
1 pkt (BFO6G)1 pkt (BF18U)
(LQ11M)
A complete kit of parts is available.Order As LK35Q (Tube Driver Kit)
Nut
PlasticWasher
Air,- TR1'Mr Es 1
I 41e-- MWIacsaher
Heatsink
V /NV Axxvev
.. Bolt
Figure 4. Mounting thetransformer and heatsink
PCB
series (not parallel), at slightly reducedlight output levels and the supply currentwill rise by 100mA or so when doing this.Resistor RI can be increased up to 2k toreduce light output (and supply current)or taken down to 470R for increased lightoutput, with supply current up to 1A. Withthe specified value for RI, tube lifeexpectancy should be high and theprototype has been running for a greatmany hours without problem.
For housing the tube, clear plasticp: ping as used on water tank overflowsetc. can be utilised and fitted to a smallplastic box containing the inverter. Themodule could then be potted for safetyand a cork fitted into the open end of thepipe.
Continued from page 27.
POWER CONTROLLER PARTS USTRESISTORSRVI 220k Lin Pot
CAPACITORSCl lOnF VS Cap 250V ACC2 100nF VS Cap 250V AC
SEMICONDUCTORSIC1 PC12R
MISCELLANEOUSRFC1-4 inc RF Supp Choke 3A
Power P.C.B.Veropin 2141
NI Pan Neon RedFSI 11/4" Fuse 10A
Safuseholder 11/4"SKT1 Single Switched Socket
Surface Pattress 29mm SingleGrommet Large6BA x 1" Countersunk Screw4BA x 1/2" Countersunk Screw6BA x 1/2" Spacer4BA Tag6BA Washer4BA Washer6BA Nut4BA NutKnob K213A HD Mains Cable
OPTIONALCase DCM5006
(FWO6G)
(FF53H)(FF56L)
(QY38R)
4 (HWO6G)(GB5 IF)
1 pkt (FL21X)(RX83E)(WR16S)(RX97F)(HL71N)(YB15R)
2 (FW60Q)1 pkt (BF I3P)1 pkt (BFIOL)1 pkt (FW35Q)1 pkt (BF28F)1 pkt (BF22Y)1 pkt (BF21X)1 pkt (BFI8U)1 pkt (BF17T)
(HB24B)As req (XRIOL)
(LH74R)
A complete kit of parts (excluding case) is available.Order As LK34M (Power Controller Kit)
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