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HIFI REVIEW Tandy's new CD with remote control player Fluke. First Family of DMMs. When accuracy, performance and value are important, professionals the world over look to Fluke - the first family of DMMs. Reliable Fluke-quality 3½- or 4½-digit DMMs fit every need - from design engineering to industrial troubleshooting. There's the low-cost 70 Series - the most DMM you can get for the money. The tough 20 Series - totally sealed and built to survive the dirtiest, grimiest, roughest jobs. The reliable 80208 Series - made to withstand the rigors of the field service environment. The precise 8060A Series the most powerful and complete test and measurement system available in~ handheld package. And, of course, the versatile Bench/Portables that carry on the Fluke tradition for precision and durability in lab-quality bench instruments. Fluke comes in first again with the world's largest selection of quality accessories to help extend the capabilities of your DMM even further. There's no need to look anywhere else. Uncompromising Fluke design and leading edge technology are the reasons why attempts at imitation will never fool the millions of professionals that accept nothing less than a Fluke. FROM THE WORLD LEADER IN DIGITAL MULTIMETERS. IFLU KEI ® E L MEASCO Instru m e nts P t 11. Ltd. Dealer enquiries welcome f aik to your local Elmeasco distributor about Fluke • A&.L.. John Pope Electrical (062) 80 6576 • J Blackwood & Sons (062) 80 5235 • George Brown (062) 80 4355 • ll.SJ:1!. Ames Agency 699 4524 • J Blackwood & Sons • George Brown 519 5855 Newcastle 69 6399 • Auto-Catt Industries 526 2222 • D.G.E. Systems (049) 69 1625 • W.F.Di xon (049) 69 5177 • Ebson 707 2 111 • Macelec (042) 29 1455 • Novacastrian Electronic Supply (049) 62 1358 • Obiat Ply Ltd 698 4776 • Petro•Ject 569 9655 • David Reid 267 1385 • Selectroparts 708 3244 • Geoff Wood 427 1676 • N.TERRITQRY J Blackwood & Son (089) 84 4255, 52 1788 • Thew & McCann (089) 84 4999 • O~NS~N£ 55Auslec (07) 854 1661 • G.Brown Group (07) 252 3876 • Petro-Ject (075) 91 4199 • St Lucia Electronics 52 7466 • Cliff t:le ronics 1 • Nortek (Townsville) (077)79 8600 • l. E.Boughen 3691277 • Fred Hoe & Sons 277 4311 • The Electronics Shop (075) 32 3632 • Thompson Instruments (Cairns) (070)51 2404 • S AUSTRALIA Protronics 212 3111 • Trio Electrix 212 6235 • Industrial Pyrometers 352 3688 • J Blackwood & Sons 46 0391 • Petro -Ject 363 1353 • TASMAWA George Harvey (003) 31 6533 (002) 34 2233 • VICTORIA Radio Parts 329 7888 • George Brown Electronics Group 878 81 11 • G.B. Telespares 328 4301 • A.W.M. Electrical Wholesalers • Petro-Ject 419 9377 • J Blackwood & Sons 542 4321 • Factory Controls (052) 78 8222 • Mektronics Co 690 4593 • Truscott Electronics 723 3094 • WAUSTRALIA Atkins Carlyle 481 1233 • Dobbie Instruments 276 8888 • Protronics 362 1044 -.... --- _,_ . ry _ , .. ____. ._.. _.- _,_,. -- = -------- ff_. ---__. · __. _,., ~ -I -" - -I ~ --_ VOLUME _, - -' _, , _1.- _ . .--__,_ _ .~ - -_,. . J -_,~ - -NUMBER 5 - ------.. ,_. __. _, ___.__. .,._. _. ~~ .. ..,- ~ - - ..J ..... _. -- -- _. - - --- _, I -. ...I, -I , --I A - - _, _,, ~ - _ ---I --- a ~ 'c"' MARCH 1988 ., _ _ ,.., _ _ _ A-~~-- --- - - - - A-- >T<~ .:::;,-:;, - - - ~ ..:::.. ...._ -::-:-·_ TANDY'S NEW CD-1500 is a mid- priced CD player that comes with remote control as standard. We tell you how it performs in our review starting page 16. FEATURES 6 New Life for Radio-Cassette Players by Homer Davidson 12 16 65 76 81 Simple service tips to bring back the good sound Vintage Radio: How it Began by John Hill From spark transmitters to the Audion Tandy's CD-1500 CD Player by Leo Simpson Mid-priced unit has remote control High, Low, Sink and Source by Leo Simpson What the jargon means The Evolution of Electric Railways by Bryan Maher Pt.5 - Electrics in Australia Digital Fundamentals, Pt.5 by Louis Frenzel Counters & shift registers DON'T PUT UP with interruptions from extension phones. When you pick up one telephone, this simple device automatically cuts the extension phones dead. Details page 18. PROJECTS TO BUILD 18 Line Grabber for Telephones by Greg Swain Pick up one phone & it cuts the others dead 26 Remote Switch For Car Burglar Alarms by John Clarke The transmitter attaches to your keyring 40 Endless Loop Tape Player by Greg Swain Use it as a novel doorbell 43 Technilab 301 Function Generator by David Whitby Useful test instrument doubles as a signal tracer 56 Old-Time Crystal Radio by John Hill Its performance will surprise you 60 Build Your Own Light Box by Leo Simpson Low cost & easy on the eyes PRESS THE BUTTON on a small keyring transmitter and this project will automatically turn your car's burglar alarm on and off. Construction begins on page 26 SPECIAL COLUMNS 50 Serviceman's Log by the original TV serviceman A baffling exercise 68 Amateur Radio by Garry Cratt Antennas for the VHF & UHF bands 72 The Way I See It by Neville Williams The quest for the ultimate in hifi sound is half the fun! DEPARTMENTS 2 Publisher's Letter 3 Mailbag 4 News & Views 15 Bookshelf 38 Circuit Notebook 88 Product Showcase 94 Ask Silicon Chip 96 Market Centre FANCY A BARKING doorbell? This endless loop tape player is the answer. It can also serve as a novel pre-recorded message system. See page 40. MARCH 1988 1 SILICON CHIP PUBLISHER'S LE't·t'ER Publisher & Editor-In-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Ro.bert Flynn Regular Contributors Neville Williams, FIREE, VK2XV Bryan Maher, M.E. B.Sc. Jim Yalden, VK2YGY Garry Cratt, VK2YBX Jim Lawler, MTETIA Photography Bob Donaldson Editorial Advisory Panel Philip Watson, MIREE, VK2ZPW Norman Marks Steve Payor, B.Sc. , B.E. SILICON CHIP is published 1 2 times a year by Silicon Chip Publications Pty Ltd. All material copyright (c) . No part of the contents of this publication. may be reproduced without prior written consent of the publisher. Kitset suppliers may not photostat articles without written permission of the publisher. Typesetting/makeup: Magazine Printers Pty Ltd, Waterloo, NSW 2017 . Printing: Macquarie Publications Pty Ltd, Dubbo, NSW 2830. Distribution: Network Distribution Company. Subscription rates are currently $42 per year (12 issues) . Out-. side Australia the cost is $62 per year surface mail or $1 20 per year air mail. Liability: Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Address all mail to: Silicon Chip Publications Pty Ltd, PO Box 139, Collaroy Beach , NSW 2097. Phone (02) 982 3935. ISSN 1030-2662 * Recommended and maximum Australian price only . 2 SILICON CHIP Tell us what you like and what you don't like Welcome to the March issue of SILICON CHIP which is the fifth since we started. Already, this magazine is gaining a considerable following as more people come to know about it. That is very gratifying but we'd like you to tell us how to improve SILICON CHIP. Too few people are telling us what they think. Quite a few readers have taken out a subscription and have pencilled a note on the coupon saying "top magazine" or some similar comment. Now this gives us a warm inner glow but it does not tell us which parts of the magazine you really like. Maybe there were some parts you didn't think much of. Or maybe there was an article that you disagreed with. Perhaps you thought that an article could have been improved or it omitted some useful information. Please give us this sort of feedback. We want your constructive criticism so that we can give you the highest editorial standard. So if you think that something in SILICON CHIP is good or could be improved or whatever, please jot down those thoughts in a letter and send it to us, straight away. Don't worry about whether your writing is neat or whether you use correct sentence structure. Just write to us. We'll get the message. This month's Mailbag carries a number of letters which give a good example of what we're talking about. These letters mention an article which appeared then proceed to tell us how it might have been improv- . ed or what it omitted. Good. We might not agree with everything that is written but we're not afraid to publish criticism if it is constructive. If you feel that we should cover a particular topic or describe a pet project of yours, please put in your request. We might not be able to do it but there's a much higher chance of us doing so if you write to us. And if you wish to see a controversial subject discussed in some detail, say in Neville Williams' column "The Way I See It", don't hesitate to write - there is a good chance that Neville will get stuck into it. There are several other ways you can contribute to SILICON CHIP. If you're really keen you might submit an ar\icle for publication. You might send in an idea for the Circuit Notebook pages. Or you might ask a question to be discussed in the " Ask Silicon Chip" pages. It's over to you. We'd love to hear from you. Leo Simpson SILICON CHIP, PO Box 139, Collaroy Beach 2097. MAILBAG Converter needs crowbar I only discovered SILICON CHIP by accident when looking over the book stand in the local newsagent. At first I didn't take much notice of it - just another electronics magazine, I thought - but when I noticed the two names up top, things suddenly clicked. Judging by the comments in "Mailbag" for January, your magazine looks like a winner. Also I would like to comment on your 24 to 12V converter in the December 1987 issue. I feel that the 12 volt output from the unit should have some sort of overvoltage protection. If Q3 goes short-circuit for any reason, the full 24 volts would be fed straight to any 12 volt equipment connected to it, so causing damage to the equipment. The fuses would no doubt blow but not before the equipment was damaged. A "crowbar" protector of some sort may be the best approach. P.W.Bell Glenorchy, Tas A crowbar could be simply incorporated into the circuit by connecting a 15V or 16V 20W zener diode across the 12V output. If an overvoltage condition did occur the zener might short circuit but it would also take out the 5-amp fuse and thus prevent damage to the equipment. A thousand issues My compliments on your new magazine. It's nice to see the familiar pens back at work again. All power to you and may this be the beginning of a thousand issues. Jim Lawler Hobart, Tas CD hyperbole I am becoming rather annoyed at the ridiculous amount of advertising garbage that is being associated with compact disc players. For example, an ad from one manufacturer boasts of a chassis built from materials such as Cosmal-Z alloy, lead, ferrite and alloy materials. Many companies are dishing out these "space-age breakthroughs". A few years back I read an audio magazine that claimed that a "remarkably audible improvement" could be obtained from CD players by using an aftermarket "disc stabiliser" to stop the disc from resonating. Now maybe I'm missing something but these sort of claims seem to be nothing short of pure hyperbole. If the CD itself is a circular spiral of pits representing 1 's or O's, the resultant bits for the data stream can only be either 1 or O and in any case, a Schmitt trigger would soon remove any discrepancies. If the radial and focussing servos are working properly, the data stream should be able to be decoded without any problems. Then there are the claims that three-spot lasers offer vast improvements over single spot systems. This had me intrigued since back in 1969 Philips were working on Videodisc players which used a three-spot system. Yet Philips, who pioneered the laser disc revolution, both video and audio, now use a single spot laser in all their CD players. The list goes on and on. I feel sorry for the poor innocent customer who has these claims rammed down his throat. Stephen McBride Townsville, Qld Vintage radio circuits Congratulations on your successful start with SILICON CHIP. You certainly have my support. For those people interested in restoring old radios, I have copies of the Australian Service Manuals covering Australian-made radio receivers from 1937 to 1946. I would be happy to supply copies of receiver circuits in return for two 3 7 cent stamps to cover copying and postage. In addition to the make and model, it would be helpful to know the year of manufacture, number and types of valves, and the wave bands available. J. Emery BulJ Creek, WA Wants beginner articles Congratulations on your new magazine. I'm enjoying the train series, as well as the rest. In fact, I haven't enjoyed reading an electronics magazine as much for years , and I started in 1958. I hope you will be able to write a significant number of your articles and projects aimed at the beginner. I think it is of great importance to encourage our young people as much as possible. I guess I'm particularly thinking of my son, who at eleven, is ready to tackle almost anything with the nearest screwdriver but who needs some encouragement to discover "how it works". W. Adams St. Lucia, Qld Further hazards of the MEN system I have a comment on the article "Your House Wiring Could Kill You", as published in the November 1987 issue. Where you suggest removal of the earth connection to clean it, you have not considered the neutral connection from the meters and frequency injection relay/time clock. In the event of high neutral circuit resistance between the house switchboard and the substation, the earth current from the clocks etc will flow back to the transformer via the earth connection (as you have accurately described). However, the meters cannot be isolated by the main switches. The only way to isolate this equipment and remove the neutral/earth current is to remove the county council's service fuses which, of course, is against the law. Another potential danger is where an installation remote from the substation has a high resistance main neutral connection. The current will then flow via the earth connection (as described in your article). For houses close to the substation, this earth current can then flow "back up" through their earth connections and into the main neutral conductor to reach the substation. The possibility then exists for an earth current to be measured when the main switches are off and the council service fuses are removed! Naturally a voltage will appear under these circumstances if the earth connection is removed for cleaning. I suggest that earth connection cleaning should only be performed by a licensed electrician because of the above possibilities. Footnote: I too have had trouble convincing a council that their neutral connections were not good. When finally investigated they found that the substation neutral connection had been burnt off completely! John Lean South Tamworth, NSW MARCH 1988 3 NEWS&VIEWS Australian TV manufacture ceases In January of this year, the Sanyo TV plant in Albury closed its doors and all the equipment was disposed off. This follows the closure of the Philips TV plant in Clayton in October last year. The closures are partly as a result of progressive tariff reductions on TV imports. We have very mixed feelings about the closures. While the tariff reductions will, in theory, lead to cheaper TV sets, it may BBC goes cold on stereo TV Five years ago, when Australia adopted the German developed method of stereo TV transmissions there was criticism in some circles. Some prominent engineers were disappointed that Australia had not selected the technically more elegant BBC digital stereo system. This has been a moot point over the intervening period as stereo TV has slowly grown in popularity. For those people with stereo TV receivers the sound quality is every bit as good as that from TV/FM stereo simulcasts. The only question is, when is the ABC going to adopt stereo TV? Late last year, it became clear that Australia had made the right be more expensive in the long term as parts for repairs become more difficult to obtain. The other factor to be considered is that TV sets will no longer be designed to suit the special requirements of the Australian market. In the future we will just be supplied with variants of "world" sets. It remains to be seen whether such sets perform as well as those designed for our market. decision. While it may have developed the more elegant system, the BBC has more or less abandoned its stereo TV system, leaving a number of TV and IC manufacturers in the lurch. Britain still may have stereo TV if the IBA and Britain's TV manufacturers have their way. In view of the BBC's decision, will the ABC now decide to adopt stereo TV broadcasts? It's about time they did. Black hole defeats heat seeking missiles Everyone has heard of heatseeking missiles which home in op the jet exhaust of fighter planes, no matter how much they dodge about. Now McDonnell Douglas engineers have come up with the Black Hole Infrared Suppression System which is currently in use on the US Apache helicopter. Engine exhuast is mixed with outside air and routed through a series of pipes before being expelled through finned nozzles. The result is that the exhaust is so cool that it is ignored by heat-seeking missiles. It is a pity they couldn't come up with a system to reduce the noise of helicopters as well. Currently, helicopters are the greatest source of aircraft noise nuisance above our cities. Radio service for Japanese tourists The projected start of Japanese language transmissions in major tourist locations throughout Australia have been slightly delayed. Originally scheduled to begin in February (see SILICON CHIP, January 1988 issue, page 11), they should be under way in Sydney by the time you read this issue. The transmssions are in narrowband FM on 151MHz. We are gratified to report that the transmitters being installed in locations around Australia are all designed and manufactured in this country. The receivers also have been designed in Australia but will be manufactured off-shore. Magnetic fields may be hazardous According to a recent report in IEEE Spectrum there is growing concern in the United States about low level magnetic fields. For some time there has been concern around the world about the health effects of high intensity electric fields, as radiated by high voltage power lines. Although no state has regulations on magnetic fields, six states have regulations regarding exposure to electric fields from high voltage power lines. Now attention is shifting to the 4 SILICON CHIP possible effects of low level magnetic fields and the National Cancer Institute is likely to start a large scale study of childhood leukemia and the possible part played by magnetic fields. At present no domestic electric appliance has been fingered as a source of magnetic field exposure although at least one US researcher is inclined to discourage the use of electric blankets by young children. Some researchers are cautioning that prolonged exposure to magnetic fields 'may' cause cancer. In Australia, most authorities warn against children using electric blankets anyhow but not for any risk of leukemia. Young children do not have well a developed ability to regulate their body temperature. If they are placed on electric blankets there is a strong risk that their body temperature will rise to dangerous limits. If not caught quickly, this can lead to convulsions and ultimately, death. The Singing Detective now available on LP Many readers will have no doubt watched the six part series of "The Singing Detective" which was televised by the ABC during December and January. The series was notable for its clever dialogue and the way in which old songs were reworked as the hallucinations of Philip Marlow; Marlow is a psychological case suffering from a horrible skin disease. In a touch of marketing brilliance, the ABC had the record of the music on sale before Christmas and many must have been sold, to thousands of keen viewers. Alas the music sounded better over the television than it does on a hifi system. No doubt the music has much more impact when backed up by the brilliant choreography of the show but the sound quality is marred, as the sleeve notes admit. · How much better might it have been if it had been re-mastered by Australia's noted specialist on old recordings, Robert Parker? And wouldn't it have been better still if it had been available on compact disc? Shonky fast nicad charger One of the shonkiest products we've seen to date came on the market late last year. It's a fast charger for nickel-cadmium batteries and specifically intended for recharging AA cells for radiocontrolled model cars and toys. Now the whole subject of fast charging nick.el cadmium batteries is a controversial one. Mostly the manufacturers and distributors of nicad cells don't want to know about it. They know that lots of cells are being fast-charged but they warn that cell life will be reduced. Our enquiries lead us to believe that fast charging is OK provided it is done carefully. The charger must have a timer or some means of sensing the cell voltage or cell temperature. If the cells are left on a high charge rate after they are fully charged they are certain to be ACS services project a big market This is the ACS adaptor module described in SILICON CHIP in January 1988. It can be fitted to just about any FM tuner. Since reporting in our January issue about the authorisation of ACS subcarrier transmissions for FM stations, thfh'e have been a number of interesting developments. Besides the ABC in Sydney, a number of other metropolitan stations have taken out or are in the process of applying for licences. In Sydney, 2MBS-FM is broadcasting stock exchange information (using a digitally encoded transmission) while 2SER-FM also has an ACS encoder installed and is in a position to start broadcasting. Stations in Brisbane and Perth also have encoders installed. The biggest market for ACS transmissions looks like being for racing information. We would assume that it will be a corndamaged. But with these provisos, fast charging is safe and practical. Well it is one thing to have a fast charger which controls the rate of charge and then disconnects the cells after a certain time or after a certain voltage has been reached. This latest product is something else. It just uses a 12V 120mA DC plugpack feeding an 8-cell holder. There is no current limiting other than the natural limit of the plugpack itself, no timer and no voltage cut out. In a word, it's crude. plementary service to that already available on Teletext. Early market projections give a potential demand as high as 100,000 receivers. And here is an interesting wrinkle. The Department of Transport and Communications will be charging the provider of ACS services a licence fee for each receiver in use. And you thought licence fees were a thing of the past. The catch is that ACS (Ancilliary Communications Service, known in the USA as SCA, Subsidiary Communications Authorisation) is a special service not intended for normal public service. Note: SILICON CHIP published an ACS decoder for FM tuners in the Januai:y issue. Now maybe the internal impedance of the AC plugpack will limit the current through the cells to a safe value but maybe it won't. The blister pack instructions tell you to charge the cells for three to four hours and they warn against over-charging. But what happens if you put them on charge in the afternoon and then forget them until the next day? We hate to think. We would be very wary about any charger that does not have a timer or some other cut-out system to stop charging. M ARCH 1988 5 By HOMER L. DAVIDSON NEW LIFE FOR RADIO-CASSE'I*I'E PLAYERS Ghetto-blas.ters and portable cassette players can sound awful after a few years. Here's how to bring back the good sound. Everything with moving parts runs down with age. When it comes to electronic equipment, the sound gets fuzzy and distorted, power drops off and so on. After a while you might be considering dropping the whole lot in the bin and then lashing out on a new one. But it doesn't have to be. You can resurrect most portable audio gear without being a servicing genius. Of all the gear that suffers the ravages of time and use, the portable "ghetto-blaster" suffers the most because it's always in harm's way. If it's not getting bounced, dropped, or fried in the boot of a car, it's getting beach sand in the tape drive and rain in the speakers. A few simple adjustments and repairs are often all 6 SILICON CHIP it takes to make sluggish portables come back to life. And keep in mind that a few simple repairs early enough can prevent an expensive repair later on. With the cost of servicing the way it is nowadays, it is better to do preventative maintenance now rather than having to discard it later on because a repair job is too expensive to be worthwhile. Here are a few easy-to-make repairs that can be done by just about anyone who can tell one end of a soldering iron from the other. Dead - Nothing Perhaps the most common fault in a portable player is that it will appear to be dead when you turn it on. Inspect the dial drum (4) and the plastic pulleys (1, 2 3) if tuning problems are encountered. If necessary, ' restring the dial-cord assembly. Make sure that the dial pointer moves in the correct direction as you rotate the tuning knob. Check the power supply's silicon diodes when there's no sound, or no tape movement. When tested with an ohmmeter, a leaky or shorted diode will indicate a low resistance measurement in both directions. This is often after a period of weeks or days when it hasn't been used. This is where your powers as a detective come into play. To determine if a portable stereo cassette player is dead only when connected to the mains power, try switching over to battery operation. Suspect a defective mains cord or plug if the unit operates on batteries but not from the mains power. Try another cord, if handy. Sometimes the power cord of your electric shaver will fit the two-pin mains socket on the player. Don't force it though as you may damage the socket. Check the continuity of the mains cord by testing it with the ohmmeter function of your analog or digital multimeter. If the cord tests OK, check the mains onoff switch. Often these are slide switches of dubious quality and their contacts become sloppy after a few years. If the switch is OK check the silicon diodes used in the power supply. Look for breaks or burn marks. You may find two or four diodes wired as a full-wave or bridge rectifier circuit. On a normal diode a low resistance should be found in only one direction. If 'the diode also shows a reading in the other direction (ie, with the test leads reversed), remove one end from the printed circuit board and repeat the test. If it still shows a reading in the reverse direction, the diode is leaky and should be replaced. the battery compartment and terminals, and from the printed circuit board. It is important to remove every trace of electrolyte because it really can cause serious corrosion damage. If this corrosion is allowed to go too far, the player will have to be tossed out. Clean up each battery contact with emery paper until they are sparkling clean. Before installing new batteries, polish their end caps to make sure they are thoroughly clean. Make sure that the polarity of each battery is correct, as you insert it. If the player doesn't operate with a new set of batteries, check the total voltage at the battery terminals with your DMM when the batteries are under load - ie, when the radio or tape player is turned on. If the batteries are new and the voltage is seriously down on what you'd expect, you may have a more serious fault in the player. If the player works but doesn't sound brilliant, Dead When Battery-Powered Make sure that the radio plays when mainspowered before checking for poor batteries. One dead or several weak batteries can prevent proper operation; the sound may distort or the tape may run at a lower-than-normal speed. Inspect the battery terminals for dirty or corroded contact areas. Sometimes, when the batteries are left in the player for a long time they will leak and seriously corrode the battery terminals. If the batteries have leaked, thoroughly clean all traces of battery electrolyte from A dirty play/record or function switch can cause motorboating and erratic or intermittent operation. Spray contact-cleaning fluid inside the switch area and work the switch back and forth a few times to clean the contacts. MARCH 1988 7 around the pulleys and back to the drum (using masking tape to hold the dial cord on the pulleys until finished). Attach the free end of the cord to the small spring sticking out of the drum. Then pull on the cord to slightly stretch the spring before securing the cord with a knot. Place a dab of glue on each end of the dial cord to prevent it from unraveling after you're certain that the drum is rotating in the right direction. Erratic Operation A loud popping noise, motorboating, or intermittent or erratic operation may be caused by a dirty function switch. A loud squealing noise may be heard when in the record or play mode of a cassette recorder if the function switch is dirty. To clean the switch, spray contact-cleaning fluid on the switch's contacts, then move the switch back and forth a few times to clean the contacts. Do the same with other dirty switch contacts, or a dirty (noisy) volume control. Slow speeds can be caused by a dry or worn rubber pressure roller (3), gummed spindles or drive motor (4, 5, 6), very dirty heads (1, 2), or a dry or gummed counter (7). maybe the batteries are due for replacement. Most portables will perform reasonably well provided the battery voltage is at least 75% of the nominal value. For example, if your portable has four 1.5V cells giving 6V, you can expect it to give reasonable sound down to about 4.5 volts. Below that it probably will still work but it will sound yuck. Replace the batteries. While on the subject of batteries, it is a good idea to use alkaline cells instead of carbon zinc batteries. Alkaline cells give longer life and their generally lower internal impedance can help the portable's amplifiers to deliver better sound quality. Keep The Dial Cord On Track Check for a broken dial cord, or a dial cord that's slipped off a pulley, when stations can't be tuned in or the dial pointer won't move. Remove the back or front cover to get at the dial-cord assembly. Most of the larger portable players can be inspected internally by removing several Phillips-head screws located in the back cover. Inspect the dial cord for a break or slippage. Sometimes the plastic dial-cord pulleys break loose from their plastic bearings and allow the dial cord to lie loose. Repair the pulley's plastic bearing by substituting a metal screw (use a small screw that fits inside the pulley area). To do that, first make a sketch of the dial-cord stringing, then remove the dial cord. While holding the damaged pulley in the correct position, apply heat from a soldering iron. When the plastic softens, press the screw into the plastic and let the assembly cool. Then restring the dial cord. To restring a broken dial cord, draw a rough sketch showing where the cord passes around each pulley and the drum that's attached to the tuning capacitor. Select a piece of dial cord 30cm longer than necessary and tie one end to the drum. Then route the cord 8 SILICON CHIP Slow Speeds Incorrect tape speed, or no tape movement at all, can be caused by tape that's wrapped itself around the , capstan drive shaft, or an old, dry capstan pressure roller, or a defective motor. Inspect for tape wrappage around the pressure roller or its bearing. Also inspect the capstan by rotating it with your fingers. Notice if the capstan/flywheel seems to drag, indicating dry or gummed bearings. Suspect a defective motor if the capstan appears to be free. Rotate the motor pulley with the cassette player turned on. Sometimes, a dead motor starts if this is done, indicating that its operation is intermittent. Measure the voltage at the motor's power supply terminals if the motor appears to be dead. No voltage indicates poor wire connections or a dirty off-on switch. If the motor proves defective, replace it with a unit having the exact same part number. A Good Cleaning A dirty tape head may produce weak volume, or a A dirty tape head can cause weak sound, distortion, or a noise in one or both channels. Check the erase head for excess oxide that may prevent full erasure of a previous recording. dead or noisy channel. Use a cotton bud saturated in alcohol to clean the record/replay head, erase head, capstan, and pressure roller. Deposited tape oxide appears brown or shiny-black in colour, so remove anything that resembles those colours from the pressure roller and tape-head surfaces. (Those parts usually can be cleaned through the front loading area). Clean off the oxide each week if the portable is operated continuously. A cleaning cassette can also be used to help keep the tape path clean. When the plastic cover is removed to make other repairs, clean up all oxide from the chassis and mechanical areas with a cleaning stick soaked in alcohol. A Loud Rushing Noise Suspect a broken tape-head lead, its connection, or an open tape head when a loud rushing noise is heard on either channel of the cassette player. Often, the tape-head wires will break off right at the connections. After you make the repair, make sure the tapehead cable is flexible and moves freely with the tape head. Check the tape-head windings for continuity by switching your DMM to the 2k-ohm range. Compare the measurements with the resistance readings of a tape head known to he in good condition. Usually, a stereo tape head will have four connections for two separate windings. Compare both stereo windings. They should be quite close in resistance. An infinite resistance reading indicates an open winding. A very low or zero resistance measurement may indicate leaky or shorted turns. Check the resistance between the head's high terminal and the chassis ground because it's possible to find leakage between the metal shell and a tape-head winding. Push or pull the tape-head terminals with the DMM leads attached. Sometimes an intermittent connection will show up when you do this. The continuity of the erase head may be tested in the same manner. Tape Spillout A loud, rough noise may be produced by an open-circuit tape head (1, 2) winding or because the wires have broken loose from the tape head terminals. Turn the volume up to determine if the noise is in one or both speakers. Often the dead or defective channel is indicated by the VU meters (if so equipped). Recordings that sound jumbled can be caused by a defective or dirty erase head. First, remove (clean) the oxide from the erase head and then try making another recording. Suspect an open erase head or circuit if the previous recording isn't erased. Make sure that you check the wiring connections at the rear of the erase head. Checking The Record/Play Head The record/play tape head can be checked with a DMM. First, inspect the tape head's connections, then make a low-ohm continuity test of the tape head. Tape drag or spillout can be caused by a dirty or worn pressure roller, an erratic or slow take-up reel, or a defective cassette. Most tape spillout problems are caused by erratic operation or non-rotation of the take-up reel. While drag causes wow and flutter - or gurgles [as if the tape were playing under water) spillage allows the tape to come out of the cassette and foul any of the rotating mechanisms. Whatever it gets into, the tape outside the cassette gets damaged permanently. Often, erratic operation is caused by dirt that has become sticky over a period of time. Clean up both reel spindles with alcohol and a cotton bud. Also, check the hub for gummed or dry bearings. To inspect the bearing area, remove the "C" washer at the top and pull the hub off. A single drop of oil on the bearing might help. Also, notice whether the take-up reel rotates smoothly. Other checks In some models, a spider ring inside the plastic turntable is rotated to a higher speed to apply more pressure to the take-up reel. Rotate the spider ring for greater pressure and check the take-up adjustment. Don't forget to check the rubber pressure roller for wear, or for any sticky substance that can cause tape MARCH 1988 9 spillout. A binding tape-counter assembly can cause tape drag (slower speed). Most important, don't assume that the cassette's shell is good because it looks good. A slight warp, unnoticed by a quick glance, can cause tape drag, spillout, or total lock-up. Intermittent AM or FM Go directly to the AM-FM selector switch when either band is erratic or intermittent. Often, a dirty AM-FM selector switch prevents FM stations from being tuned. Locate the switch and spray contactcleaner fluid inside the contact area. Spray into the end area of a slide-type band switch. Move the switch back and forth to work the cleaner into the contacts. Also, inspect the switch's terminal wires for broken or poorly-soldered connections. Intermittent Sound Intermittent sound can be caused by a defective speaker, earphone jack, or amplifier section. First, check for the intermittent sound on both radio and tape operation. If the sound is intermittent on both, suspect a defective speaker or amplifier. Connect an external speaker to determine if the radio's own speaker is intermittent. Suspect a defective earphone or jack cable when the sound is intermittent only for earphone operation. Flex the earphone cable to test for loose or broken wires. Inspect the male plug to check for possible poor contacts or broken internal connections. Check the female jack for poor wire connections. A bent, dirty, or shorting earphone jack can prevent speaker operation. Distorted Sound Weak and distorted sound may result from a faulty Tape pulling or spillout may be caused by a jammed or slow take-up reel or turntable. You should also suspect a broken belt or a drive pulley that isn't engaging the take-up reel. 10 SILICON CHIP If the sound is noisy or distorted, check for foreign objects poked into the speaker's cone (1 and 2). Also, check the speaker's terminals for poorly soldered connections. Always replace a defective speaker with one that's the same size and impedance. audio power amplifier integrated circuit or the speaker. Determine if distortion is only from one speaker channel. Inspect the body of the integrated circuit for indications of overheating. Keep in mind that a problem in the audio power amplifier can disable the entire audio section because the preamplifier, booster and output stage might be part of a single integrated circuit. Comparison voltage measurements can isolate a leaky or open power amplifier IC. If the radio or tape player uses two of the same kind of integrated circuit, measure the voltage on the same terminals of similar devices for comparative voltage measurements. If the voltages vary by a few volts or more, suspect a faulty IC. A channel may appear dead, weak, noisy or distorted if its speaker is defective. Exchange the wires of the suspected speaker with those of the other channel. You can even connect another speaker across the suspected one with test leads to determine if the speaker, earphone jack contacts, and the amplifier are working. In fact, a speaker with leads can be used to signal trace the sound from the audio power amplifier's output capacitor to the dead speaker. A distorted or noisy speaker may have foreign objects poked into, or adjacent to, the speaker's cone. Inspect the speaker's terminals for poorly soldered connections. Replace the defective unit with one that's the same size and has the same impedance. Before you replace the cover, check the dial-cord movement, clean the tape heads and switches, and possibly replace the batteries. Make certain the each lever or pushbutton of the cassette player is working. Clean up the whole cabinet with a common household window spray after replacing the covers. Replace all the knobs. If you have the equipment pressurised air in cans or from a compressor - spray a jet of air into the corners and brush out the dirt with a small paint brush. ·! c Adapted by arrangement from an original article which appeared in HANDS ON ELECTRONICS. Copyright (c) Gemsback Publications, USA. VOOD FOR CHIPS ..• WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR C TRIMPOT COVERS CARD EDGE CONNECTOR SPECIALS .~-~ Wouldn't it be handy if you could mount a rectangular multi-turn trimpot on a front panej? Well you can with a trimpot cover. Only $2.00 and you'll need a trimpot tool to adjust it with . This handy little gadget is just like a pen and has a blade at each end. One end is specially designed so it can't slip. Well worth $2.00 . IBM PRINTER CABLES Available in two lengths - 1.8m and 4m. Both have quality connectors each end. You couldn't make one for the price! 1. .95 4m 3 SHORTING LINKS Take your pick of these three 0.1" pitch Card Edge Connectors Genuine 3M brand IDC 50 way or Belgian made Franelco Wire Wrap in 62 or 86way An unrepeatable bargain at only $13.95 ear::h. ONLY $1.00 KEYBOARD SWITCHES Ideal for programming and test linking on circuit boards , these links have a standard 0.1" spacing . Contact is partially exposed for touching a probe on. Packet of ten $2.95. 23 PIN 'D' CONNECTORS j Building your own keyboard? Then here's the ideal switch . Single momentary make contact. Complete with ivory key cap. What a bargain at Only $1 .00 No it's not a misprint - there are now 23pin Dconnectors on some of the newer PC's. So if you're finding it hard to get plugs and sockets to match, Geoff of course has 'em. Male, Female and Backshell all the same price $3.50. TRIMMER CAPACITORS Miniature circular type only 6mm diameter and 5mm high. 8 types to choose from 2 to 16pF, 3 to 11pF, 3 to 225pF, 4.2 to 20pF, 5.2 to 30pF, 6.8 to 45pF, 10 to 120pF, 60 to 160pF. All $1.50. DIP SWITCHES Geoff carries a wide range of DIP switches including a rotary type . Ch ec k yo ur requirements : Conventional - 2way 60c, 4 way $1 .75, 6 way $2.30, 7 way $2.40, 8 way $2 ,50. Right Angle 8 way $4.00 Rotary 8 way $5.50 NATIONAL 32000 DESIGNER'S KIT Geoff has had to order two consignments of these kits in since we advertised them . They are only suitable for advanced computer hobbyists and professionals. Two versions - one with 32016, the other with a 32032. Both have a 32082 Memory Management Unit, a 32201 Timing Control Unit, a 32081 Floating Point Unit, 1 32202 Interrupt Control Unit and two "Tiny Development Systems" (TDS) PROMs. That's seven chips altogether. There's a massive pack of literature including a databook 40mm thick, a 20mm thick instruction set reference manual, a TDS user guide, a programming reference guide, application notes on UNIX , 32 bit architecture and even a PASCAL li sting to aid development of 32000 code using a PC. To top it all off there's an article reprint from the US on a UNIX co-processor for under $US400II These are definitely not for beginners but wha! a great buy - 32016 kit is just $132. The 32032 costs $180. (P&P $6.00 local or $ 15.00 airmail - it"s a big packl) Contact Geoff for all your semiconductor and IC requirements. Our range ts constantly expanding. Always remember to call "Wood for Chips!" MULTI-TURN DIALS If you use multi-turn potentiometers you need these beaut Dials 10 turn Digital Multi-Dial has three digit readout. One turn of the knob gives a count of 100. Resolution to one fifth of a digit graduations! Measures approx 45x25x25mm (inc knob). Incorporates lever action locking mechanism. $36.50. Circular Multi-Dials have 50 graduations with turns counter which goes up to fifteen turns . Available in two sizes 23mm and 46mm diameter. The smaller one 1s ideal for cramped panel layouts. 23mm $24.00 and 46mm $36.50. THUMBWHEEL SWITCHES ~ ~ Cl: 0 lL. Cl 0 ~ These are genuine C&K high quality. Avai lable in decimal or BCD format. PCB edge .connector or solde r leads on directly. Both types are $6.85 each . End plates are $3.80 a pa ir and screws are $1 .40 a pa ir. They com e in sizes dependi ng on num ber of wafers 1- 3 or 3 to 7. Please specify when ordering. ~ 8.30 to 5 Monday to Fnday 8.30 to 12 Sat. Mail Orders add $5.UO to cover postal charges. GEOFF WOOD ELECTRONICS P/L Q:: All prices INCLUDE sales tax. (02) 427 1676 D 0 lL. Cl 0 ~ Tax exemption c ertificates accepted ,1 llne value exceeds $10.00. BANKCARD, MASTERCARD. VISA, CHEQUES OR CASH CHEERFULLY ACCEPTED ==--fl.::::::oc::===== i •o ! ~.~.:"' INC IN NSW 229 Burns Bay Road (Corner Beatrice SI) Lane Cove West N.S.W. P.O.Box 671 , Lane Cove N.S.W.2066 Fax: (02) 428 5198 specialising in electronic components for the professional and hobbyist. The early days of radio were exciting times. Inventors leapfrogged each other with new developments and the art progressed to a science in a very short time. By JOHN HILL Some time ago I wrote a couple of articles on the subject of vintage radio. Both stories delved into the joys and tribulations of collecting and restoring old. valve radio sets. These articles were very well received by readers and it was pleasing to know that there were others doing what I'm doing. It doesn't matter how obscure one's hobbies may be, there are always others interested in the same things. So once again I pick up the pen to write about my restorations. This time my stories will be more detailed, and each article will deal with a specific aspect of collecting and restoring vintage radios. However, before commencing on this series of useful articles, I thought it appropriate to discuss briefly some of the more interesting developments that lead up to the science of radio a§! we know it. today. Many of the things that we now take for granted in this modern world of ours began life in such a crude way that it is quite amazing that they were ever considered useful. Radio had such a beginning. In the early days, spark transmitters and coherers were used solely for Morse code transmission and reception the equipment was incapable of transmitting or receiving speech or music. Early experiments Heinrich Hertz was the originator of the spark transmitter and, in 1888, discovered that signals could be transmitted to a receiver without the use of connecting wires. The equipment that Hertz used was extremely simple and very short ranged; in fact, the 12 SILICON CHIP transmission range was within the space of a single room! How often great discoveries have such humble beginnings. Although Hertz didn't know it at the time, he had discovered radio waves. These invisible waves were soon to be referred to as "Hertzian waves". Hertz' transmitter was simply a large Leyden jar (an early type of capacitor) connected in series with a coil of wire and a spark gap. When the charged capacitor discharged across the gap, radio waves were produced by the coil which acted as a transmission aerial. The receiver consisted of a similar coil connected to a considerably smaller gap. When the crude transmitter sparked, a corresponding spark was reproduced at the receiver gap. Now those early pioneers of radio were no fools. Hertz soon calculated the speed of his Hertzian waves and determined that they travelled at exactly the same speed as light which had already been determined with reasonable accuracy by 1849. The limiting factor of Hertz' equipment was that it would only work over very short distances of a few metres. If these Hertzian waves he had discovered were to be useful at all, it would require considerable improvement to both transmitter and receiver. The first receiver refinement was the development of the "coherer" in 1892. A number of inventors can lay claim to several versions of the device but the Frenchman Edouard Branly developed the type of coherer that Marconi successfully used in his early radio experiments. Compared to modern radio receivers, the coherer is incoming signal would automatically activate the decoherer and the recorder. Marconi Collecting and restoring vintage radio sets is a fascinating hobby. This old American Silvertone is missing most of its veneer but still has its original dial (complete with tuning eye) and all its original knobs. the ultimate in crudeness. It consisted basically of a small glass tube containing two metallic plugs (usually silver) that almost met in the middle, leaving about a one millimetre gap. In this small area was placed a mixture of zinc and silver filings (although Marconi used nickel and silver because it was more sensitive). When the coherer came under the influence of Hertzian waves, the filings in the gap would cohere (stick together, just as iron filings do when under the influence of a magnetic field). Unfortunately, the filings would stay that way after the signal ceased and the device had to be tapped with a pencil or like instrument to settle the filings ready for the next signal. The big coherer breakthrough came about when a Russian by the name of Popoff invented a device for "decohering" the coherer. Popoff's invention employed an electric bell-like mechanism that kept tapping the coherer. The coherer had the unique ability of being a conductor when cohered and a non-conductor when decohered. When properly set up with a battery and relays, it would operate telegraphic recorders such as a Morse sounder or a Morse inkE;ir. The latter instrument put the dots and dashes on a strip of paper. An This early two-valve receiver is the Marconiphone V2A, made around 1923. (Photo courtesy Orpheus Radio Museum, Ballarat). Guglielmo Marconi, an Italian, was the next person of importance on the radio scene and he is often given the credit for inventing radio communications. In actual fact, Marconi invented very little but had the happy knack of improving and adapting other people's inventions for his own benefit. In 1895, Marconi broke new ground with a successful transmission over two kilometres using Branly's coherer and Popoff's decoder. For this he was granted the first English patent for Wireless Telegraphy. Marconi soon improved his equipment and set a new record when messages were transmitted and received between two British warships that were some 20km apart. At the tender age of only 23 years Marconi formed, with the backing of some wealthy English businessmen, The Wireless Telegraph and Signal Company. A vintage Martin radio. The compartment below the control panel housed the receiver's batteries. (Photo courtesy Orpheus Radio Museum). In 1899, Marconi (again using someone else's ideas, in this case, Sir Oliver Lodge) incorporated tuned circuits in .his wireless equipment and patented the idea in 1900. This was a significant step forward as it helped reduce interstation interference. By this stage, the range of Marconi's radio was around 120 kilometres and wireless equipment was mainly used for ship to shore contact. An amateur radio enthusiast during those days could spend the night staring at the coherer of his homemade receiver, hoping to pick up a signal from a passing ship. Imagine the excitement he would experience if the filings in his coherer suddenly stood to attention as a signal was received. If he knew Morse code, he could even decipher the message. American contributions The Americans also contributed well to early radio, although they were a bit slow off the mark. Two of the MARCH 1988 13 Vintage Radio more prominent names on the other side of the Atlantic were Reginald Fessenden and Lee De Forest. Fessendon thought more along the lines of radio telephony as opposed to Marconi's radio telegraphy. To this end he dabbled with high frequency alternators in order to experiment with continuous wave transmissions. He also developed an electrolytic detector which actually rectified the incoming constant wave signals. De Forest also developed an electrolytic detector which caused much conflict between he and Fessendon. The electrolytic detector consisted of a small cup of dilute acid into which a silver wire was dipped. It was similar to the crystal and cat's whisker detector which was yet to be discovered. The electrolytic detector was far more sensitive than the coherer and had the ability to rectify incoming radio-frequency signals. Meanwhile, back across the Atlantic again, Englishman Ambrose Fleming had been experimenting with his two-element valve. He found that its diode characteristic could be used to rectify or detect radio signals. It is interesting to note that Edison had observed the one way characteristic of the diode (the Edison effect) some years previously, but it was Fleming who found a use for it. This Polle Royale is an American 5-tube battery set from the mid-1920s. It employed three tuning controls and a staggered valve arrangement. While De Forest, Fleming and Edison were of the same era and all experimented ,,vith crude diodes, they should not be thought of as inventors of the device. Observation of the Edison effect goes back a long way. In 1725, Duffay discovered that if one or two closely spaced insulated metal spheres was heated, a current carrying path was formed between them. So the thermionic diode goes back two and a half centuries. Edison's experiments centred around removing the dark coating that attached itself to the inside of his incandescent lamps. He figured that a plate inside the glass envelope could prevent that from happening. Strange that a hundred years later the same problem still exists in incandescent bulbs. The Audion The inclined basket coils in this glass covered custommade receiver indicates that it employs a Neutrodyne circuit. (Photo courtesy Orpheus Radio Museum). Fleming's diode was a glass envelope containing a filament (cathode) and a plate (anode). Those· unfamiliar with vacuum tube operation may appreciate an explanation of its function. The glowing filament emits electrons which form an electron cloud that hangs around the general proximity of the filament. However, if a positive charge is connected to the plate by means of a siza]Jle "B" battery, the plate draws the negatively charged electrons to it, hence the one way flow. The negative of the filament ("A") battery and the negative of the plate ("B") battery must be connected for this effect to take place. 14 SILICON CHIP Unfortunately, Fleming's moment of glory was somewhat short lived and insignificant compared to what Lee De Forest was developing at the time. De Forest's "Audion" valve was perhaps the greatest single development in the history of radio. De Forest's brilliant idea was to put a control grid (a spiral of fine wire) between the filament and the plate, thus making a 3-element valve. Varying the 9tate of the charge on the grid controls the electron flow from cathode to anode. When the grid is negatively charged it repells the electrons back towards the filament and, when positively charged, allows most of the electrons to pass through to the plate. . Therefore, slight signal variations on the grid of De Forest's three-element valve produced larger but proportional variations in the plate current. The Audion not only rectified radio frequency signals but it amplified them as well. It was later found that the new valve could also be used in oscillator circuits. De Forest's revolutionary discovery was a great step forward in the development of radio and a whole new era was about to start. This short history of radio will continue next month and will include the period that lead up to commercial broadcasting in the early 1920s. After that, we'll start collecting and restoring vintage radios. BOOKSHELF Servicing compact disc players Compact Disc Player Maintenance and Repair, by Gordon McComb and John Cook. Published 1987 by TAB Books Inc, Blue Ridge Summit, PA 17214. Soft covers, 235 x 188mm, 245 pages. ISBN 0-8306-2790-1. This is a general book which describes basically how a compact disc player works, how discs are made and simple maintenance. The complex detail required for fullscale repair of all types of compact disc machines cannot be included in a single book. The philosophy behind the information provided in the book is that most CD player faults are due to dirty switch contacts, broken connections, a dirty lens or disc problem. Major faults are best tackled by a repair centre. Even if you cannot repair the fault yourself, you will be far better placed to describe the fault to the repair organisation. There are ten chapters plus five appendices. Chapter 1 discusses the compact disc, its standards, encoding, manufacture and the types of players~ Chapter 2 describes how CD players work. This details the IBM PC & XT Reference Manual IBM PC & PC XT User's Reference Manual, by Gilbert Held. 2nd edition published 1987 by Hayden Books, Indianapolis, Indiana. Soft covers, 235 x 180mm, 479 pages. ISBN O 672 46427 6. Unlike most computer books, which concentrate on software, this manual also covers the hardware aspects of the IBM PC and XT. Chapter 1 kicks off with a detailed hardware overview of the two computers. The various customising options are also covered, along with mechanical and electronic basics such as focusing, digital-to-analog conversion and the controls. Chapter 3 covers CD specifications, including frequency response, signal-to-noise ratio, channel separation, phase, distortion, dynamic range and error correction. The next chapter discusses setting up the CD player for best performance. Chapter 5 is on tools and other equipment necessary for CD player maintenance. It discusses multimeters, logic probes and laser detectors. Cleaners and test discs are also covered and the text even tells you how to make your own error correction test disc. This section is an interesting concept but descriptions of several cards that can be plugged into the system expansion slots. The next chapter gives a detailed description of the system setup. It covers on-board memory expansion, shows how disc drives and adapter cards are installed and describes how the assembled system can be checked out. Chapter 3 concentrates of floppy dies and covers such topics as data storage, drive incompatibility and storage capacity. The remaining chapters deal with the software aspects of the IBM PCs, with detailed descriptions of DOS {Disc Operating System) and we won't give the game away in this review. The next chapter is on preventative maintenance and chapters 8 and 9 on troubleshooting. The troubleshooting chapter contains many flow charts to assist in locating the fault. A lot of it is the sort of commonsense servicing procedure that would be used for repairing any piece of audio equipment but it is nonetheless valid for all that. Finally, chapter 10 gives details on many popular CD players although some have not been sold in this country. There are a number of appendices too with Appendix E being the most interesting. It lists the specifications of a large number of CD players which are or have been available in the USA. Quite a few have not been sold in this country and, as might be expected, a great many current models are not listed because the book was compiled before they were released. Considering that there have been such large number of CD players sold, there is very little available on servicing these complex products. This book is very welcome for that reason. Our copy came from Dick Smith Electronics. (J.C.) the BASIC programming language. The chapter headings are as follows: The Disc Operating System, Fixed Disc Organisation, BASIC Overview, Basic BASIC, BASIC Commands, Advanced BASIC, Data File Operations, Text and Graphics Display Control, Batch Process-ing and Fixed Disc Operations, Audio and Data Communications, and Introduction to TopView. Finally, the book concludes with four appendices: ASCII Code Representation, Extended Character Codes, BASIC Error Messages, Programming Tips and Techniques. Our sample copy came direct from the publisher. {G.S.) MARCH 1988 15 HIFIREVIEW Tandy's CD-1500 remote controlled CD player Compact disc players continue to become cheaper, smaller and lighter. Typical of this trend is Tandy's latest CD player, the remote-controlled Realistic CD-1500. Reviewed by LEO SIMPSON Even though compact disc players have been with us now for five years we are still amazed at their inherent complexity. Yet each new model brings more refinements, whether in user facilities, simplification in manufacturing, or both. This latest CD player from Tandy is one of the smallest units on the market, apart from those specifically intended for portable or car use. It measures 370mm wide, 270mm from front to back and 73mm high and weighs just 2.9kg. Inevitably, it has an all-black finish; plastic front panel and a painted steel chassis and cover. The digital display is a very fine white vacuum fluorescent unit, not the rather coarse liquid crystal display depicted in the current Tandy catalog. The display indicates track, elapsed time and playing mode. It also has provision on the display for index information. Controls Playing controls are relatively simple although there are eleven pushbuttons in all. On the left is the power button and adjacent to the disc drawer is the open/close button. Underneath the display are buttons for Auto Space, Repeat Memory, and further to the right, Track/ ASMS, index forward and reverse. To the right of the display is the play/pause button and below that, the stop/clear button. On the back, the chassis is bare expect for a pair of RCA sockets The remote control is supplied as standard with the CD-1500 and duplicates most of the front panel controls. 16 SILICON CHIP and power cord entry. No headphone socket is fitted which is a pity really since we believe that many people these days wish to listen to their CDs direct on headphones, without the need of a separate amplifier. Inside the chassis, the CD-1500 is revealed as one of the simplest players we have seen. It has the smallest CD player mechanism, made largely from plastic and with a flexible multiway printed conductor strip coupling the digital signals to the large printed board. This accommodates four LSI (large scale integration) chips with one being a surface mount type. Other printed boards are provided for mains termination and the mains switch (near the power transformer) and the front panel display and pushbuttons. All told, it is hard to see how a CD player could be made simpler although future models will be just that; such is the march of progress. Playing it Pushing the open/close button on the CD-1500 extends the drawer ready to accept a disc. The drawer is different from most CD players in that it pushes a door flap down as it The interior of the Realistic CD1500 is neat and uncluttered and uses just four LSI chips. The player mechanism is made mainly from plastic. emerges, a difference which is not important but a difference nonetheless. Pushing the open/close button causes the disc drawer to go back into the player whereupon the number of tracks and total playing time are shown on the display. Alternatively, after placing the disc on the extended drawer, you can push the Play button to initiate playing immediately. You can push the disc drawer in by hand and it will withdraw by itself although the instruction manual warns against this. We deliberately did it a number of times to see if the mechanism would jam but it didn't. We think this is important because users will abuse players in this way in spite of any warning to the contrary. An interesting feature is the Auto-Space button. If this is pushed, a four-second interval is inserted at the end of each track. This can be handy if you are dubbing CDs to cassettes and wish to use the automatic music search facility now on a lot of cassette decks. The Memory button allows the playing order of the disc tracks to be programmed before playing starts. Up to 24 tracks can be programmed in this way. Pushing the Stop/Clear button clears the memory. The next facility, Track/ASMS, functions differently to that on other CD players. Pushing the lefthand button during play puts the Specifications Audio Frequency response Dynamic range Signal-to-noise ratio Harmonic distortion Separation Line output at 0dB 5Hz-20kHz, ± 1 dB 90dB 90dB .006% (at 1 kHz) 90dB 2V RMS Signal format Sampling frequency Quantisation Transmission 44.1 kHz 1 6 bit linear 4 .3218 Mb/s laser pickup back to the start of the track being played whereupon playing recommences. Further pushes put the pickup back to subsequent tracks. Pushing the righthand button moves the pickup to the start of the next track so that play starts there. So where does the ASMS (Automatic Search Music System) feature come in? The owner's manual does not explain it except to give the explanation just described. It certainly does not function in the way of Automatic Music Selection on a number of CD players we have seen whereby they will play the first ten seconds of each track until you stop it. From the foregoing, we think the ASMS designation is a misnomer. The Index buttons were similarly confusing. They function as skip forward or skip back buttons but at no time were we able to locate indexed points on discs using these buttons. Nor were index numbers ever displayed. The owner's manual makes no mention of the Index facility so we are inclined to the view that this feature was planned but left out in production models. One very worthwhile geature of the CD-1500 is the remote control handpiece. This duplicates the front panel controls with the exception of the power, open/close and auto space buttons. It has a range of about five metres and uses two penlight AA cells. Performance As the accompanying spec panel shows, the CD-1500 is pretty standard. It uses a single D-A converter and samples at the 44. lkHz rate. Our tests confirmed the specifications pretty closely. For example,, we measured harmonic distortion at lkHz and 0dB at 0.007% versus the specified figure of 0.006%. The small discrepancy is due to the residual 44. lkHz in the output which is about 83dB down. The frequency response is ruler flat over much of the range but has the usual small irregularities at the extreme top which is the result of the steep filtering used to remove the 44 . lkHz sampling artefacts. It also has the (inaudible) 24.lkHz beat which is present when you atcontinued on page 89 MARCH 1988 17 LINE G BER FOR TELEPHONES Don't put up with interruptions from extension phones. When you pick up the telephone, this simple circuit cuts the extension phone(s) dead. H ZHO~ ©3VAO£Z O!tl" By JOHN CLARKE & GREG SWAIN We all know what it's like to be in the middle of a phone call and have someone pick up an extension phone and start dialling. Or do you have young children in the household who like to mischievously listen in? Or maybe you operate a modem in parallel with your existing phone. Any interruption from an extension phone during transmission will result in garbled data, which is annoying to say the least. This simple circuit solves those problems. We've called it a "Line Grabber" because that's exactly what it does. When you pick up the phone it "grabs" the line and cuts the extension phones out. It makes it impossible for someone else to interrupt from an extension phone. 18 SILICON CHIP Any extension phone picked up while you have your phone off-hook will be completely dead and will remain so until your call is finished. If another phone is then picked up, that phone will then "grab" the line and all the other phones will be dead. As far as incoming phone calls are concerned, the same thing applies. The phones ring normally and if you pick up the phone first, you've got the call. The outside caller does not perceive any difference in the way the phone works though and nor will you, apart from the complete freedom from interruptions. The benefits are obvious: no more eavesdropping, no more unwanted dial tones or clicks on top of your conversation, and no more in- The single version is designed for installation inside the telephone, hut can also be built into a plastic case fitted with a telephone plug and socket. terruptions to data transmissions. With the Line Grabber, the phone line is exclusively yours until you hang up. Of course, if you want to transfer an incoming call to another extension that can still be done. Just hang up the phone you first took the call on and then pick up the extension - the incoming call will be there. A separate Line Grabber circuit must be built for each extension phone. That sounds messy but the circuit only uses a few cheap parts so the overall cost will not be high. We've produced two different versions so that you can choose the one that best suits your particular application. The first version consists of a single circuit built onto a small PCB. This version could be installed inside the telephone itself (one for each phone) and is used where the phones are plugged into different sockets. Alternatively, you could build this single Line Grabber into a zippy box, combined with a phone plug and socket. Either way, you will need two Line Grabber circuits for two telephones, three for three telephones, and so on. The second version has two Line Grabber circuits on a single PCB. This is housed in a small plastic case which is fitted with a telephone plug and two sockets. It is the logical choice where a telephone and a modem are operated in parallel from the same socket. Additional single Line Grabber circuits can then be installed inside other extension phones as required. Circuit details Fig.1 shows the circuit details for a two-telephone system. Each sec- The dual version has two Line Grabber circuits on a single printed circuit hoard. This is the version to go for where two telephones (or a telephone and a modem) are operated in parallel from the same socket. tion uses a bridge rectifier and an associated SCR (silicon controlled rectifier) to provide a DC and an AC path for the phone. Diodes Dl to D4 form the bridge rectifier for phone 1 while D6 to D9 form the rectifier for phone 2. Normally, when the phones are onhook, there is no DC path through either phone and therefore the two bridges and their associated SCRs are effectively out of circuit. Now let's take phone 1 off-hook. When this happens, a DC path is created through the phone. Current then flows via the bridge rectifier and SCRl and through the phone. This allows you to either answer an incoming call or dial for an outgoing call. Let's just look at that sequence in a little more detail. Normally, when a phone is on-hook, the voltage across the phone lines will be about 50V DC. When the phone is taken off-hook, DC voltage is applied via the bridge rectifier and LED 1 to the anode of SCRl. At the same time, current flows via the 100kQ resistor and zener diode D5 into the gate of SCRl. This gate current immediately causes SCRl to conduct and allows current to flow through the phone. So as far A 4x1N43R4 2 A/BN WHT 2 2 WHT WHT LINE IN 0.1 8250VACI PHONE 2 PHONE 1 GOBLUE mrn K AG PHONE LINE GRABBER KA G SC12·1·488 Fig.1: each section of the circuit uses a bridge rectifier and an SCR to provide a DC and an AC path for the phone. This diagram shows the details for a two-telephone system. MARCH 1988 19 -.~<.:..-~;,;-\,) PHONE ') , , C, '~ , ·,.co c ·; Fig. 2: parts layout for the single version of the Line Grabber. You will have to build one of these for each extension phone. The O.lµF capacitor is fitted to the first board only and is omitted from the rest. · 20 SILICON CHIP ··.•.,(.',\(. ) ;·,0:1 " ' ' c :.> 250VAC , · c, PHONE 2 Fig.3: follow this wiring diagram if you wish to build the dual version. It has two identical sections on the one PCB. The PCB for the dual version clips into the integral supports inside the case. The leads from the sockets and plug terminate on the back of the PCB. as phone 1 and the phone lines are concerned, everything is normal. There is an extra voltage drop across the bridge rectifier, LED 1 and SCRl of about 3.5V but that does not affect the operation of the phone. Now consider what happens when phone 2 is lifted? Normally, without the Line Grabber, someone would be able to listen in to your conversation on phone 1. However, with phone 1 off the hook, the voltage across the line is only about 10 to 12V. This means that no gate current can flow via 18V zener diode DlO to the gate of SCRZ and so there is no DC path to phone 2. C' As far as phone 2 is concerned, the line is dead. Phone 2 cannot be used until phone 1 is hung up. Similarly, if phone 2 is used first, it kills the line to phone 1. The LED associated with each SCR is illuminated when the associated phone grabs the line (because of current flow via the SCR). That sums up the operation of the Line Grabber as far as conventional telephones are concerned but there are still a few wrinkles to consider. What about electronic phones which always consume several microamps of DC when they are on-hook? The Line Grabber Fig.4: the Line Grabber circuit can also be built on Veroboard. Use an oversize drill to make the cuts in the copper tracks. caters for this situation by providing a DC path through the bridge rectifer, the l00kQ resistor, the zener diode and the 2.2kQ gate resistor of the SCR. This current is not sufficient to trigger the SCR but is does allow the circuitry in pushbutton phones to · function normally. The only remaining component to be explained is the 0.lµF 250VAC capacitor across the incoming line. This is intended to suppress transient voltages which could falsely trigger the SCRs. For example, if phone 1 is in use, a spike on the line could falsely trigger SCR2 if phone 2 happened to be off-hook. This would then place both phones on the line, which would defeat the purpose of the Line Grabber. While it won't be obvious from our circuit description above, an attractive feature of the Line Grabber is that it causes no loading of the phone lines when the phones are on-hook. This is good because it means you can build as many Line Grabbers as you want, without worrying about line loading. Building it First, you must decide which version you are going to build. If you build the dual version you will need the large printed circuit board which measures 60 x 46mm. The smaller version measures 38 x 46mm. Whichever board you use though, you will need the same case. We used a plastic jiffy box from Altronics r- PARTS LIST 1 PCB, code SC12-1 -488-1, 60 x 46mm (double version) 1 PCB, code SC12-1 -488-2, 38 x 46mm (single version) 1 plastic case, 83 x 54 x 28mm (Altronics Cat No H-0105) 1 telephone line plug 1 telephone line socket Semiconductors Fig.5: above are actual-size etching patterns for the two PCBs. =.-I~.{1{1 j.' Capacitors and Resistors f,/:J· PHONE LINE GRABBER PHONE 1 e e PHONE 2 Fig.6: full-size front panel artwork for the dual version. measuring 83 x 54 x 28mm (Cat No H-0105}. You can mount the phone sockets on the base of this box while the phone plug is wired to a flying lead. The PCB is wedged into the integral supports inside the case, as shown in the photo. The SCR is laid on its side as shown in the photos. The LED pokes out through a hole in the side of the case. You can also make the Line Grabber on Veroboard. We have shown a wiring layout for a single version, to fit in the same case. If you want the double version just build two on a wider section of Veroboard. Assembling the boards should present no problem at all. Just make sure that you observe correct 1 C106D silicon controlled rectifier 1 red light emitting diode 1 18V 400mW zener diode 4 1 N4004 silicon diodes 1 0.1 µ,F 250VAC metallised polycarbonate capacitor 1 1 OOkO 0.25W resistor 1 2.2k0 0.25W resistor 1 1000 0.25W resis tor Note: the above parts list is . for the single version only, unless noted. Grabbers you build you only need one 0.1µ,F 250VAC capacitor. When you're finished the board or boards, they need to be wired to the sockets and phone plug. The wiring is shown in the circuit diagram (Fig.1}. Checking it This is what the Veroboard version looks like. Take care - it's easy to make a mistake with Veroboard. polarity for the diodes, SCRs and LEDs. You can leave the LED[s) out if you wish. Just install a link in place of the 1000 resistor(s). Regardless of how many Line What About the Off-Hook Indicator? You may be wondering about the pros and cons of the Line Grabber as compared to the Off-Hook Indicator circuit published in the N~vemb~r 1987 issue of SILICON CHIP . The Line Grabber has advantages 1n that 1t is a simpler circuit and does not cause any loading of the phone lines . It also stops eavesdropping and you can build as many as you like. By comparison, the Off-Hook Indicator allows you to have more than one extension in use at a time, when you want to have a 3-way con~ers~tion . It also tells you when any extension is off the hook which 1s important. It is possible to check the circuit before you connect it to your phones. You'll need an adjustable DC power supply with an output of 20 volts or more. Connect the Line Grabber to the power supply in series with a limiting resistor of several hundred ohms. Polarity is not important because of the bridge rectifier. Initially, no current should flow. Now short the connections between pin 2 and pin 6 on the Line Grabber phone socket (for phone 1, if you've built a dual version). Wind up the supply voltage and observe that the LED is illuminated once the supply voltage rises above 18 volts. If the LED illuminates at quite low supply voltages it is possible that you have reversed the polarity of D5 (or DlO}, so that it is not working correctly as a zener diode. If current is flowing (you can continued on page 93 M A RCH 1988 21 Great Kit Projects To Build Many Just Released For 1988 Go Anywhere 240V Maine Power rrom your car or truck battery with theee fantaetlc DC to AC lnvertere A must for farming, camping, mining, boating, remote settlements and wherever else 240W power isn't available. 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I Build this circuit and you can turn your car's burglar alarm on and off by pressing the button on a small keyring transmitter. By JOHN CLARKE The main purpose of this project is to add a remote control facility to the Protector Car Alarm described in February. Basically, it lets you switch your car's burglar alarm on and off from outside the vehicle, simply by pushing the button on a small keyring transmitter. Apart from the obvious added convenience, remote control offers improved security (no need for hidden switches) and allows the elimination of entry and exit delays. All sensors can now be wired to the instant trip input to give instantaneous alarm response to any attempted break in. With this unit, you can customise your burglar alarm to suit your own needs, making it quite complex (as presented) or quite a lot simpler. For example, it gives you a choice of piezo alarm or siren to tell you when the alarm is turned on or off and it will also flash the car's traffic indicators briefly when the alarm is armed or disabled. The circuitry presented here could also be used as the basis for any single channel remote control application. It is simple to set up and very reliable. The accompanying panel lists the main features. As you can see, it's a very versatile circuit although the basic concept is fairly simple. ICl is a Motorola MC145026 trinary encoder. This uses a 9-bit trinary code. Trinary code is like binary code except is uses three logic states instead of two. The three trinary states used by this IC are high, low or open-circuit. Only one transmitter code word (one 9-bit word) is possible, as selected by the connections to the IC's nine address inputs, Al to A9. In keeping with the trinary states just mentioned, each of the nine address inputs can be connected to the + 12V rail, to ground or left unconnected. In our application, because of the particular decoder used in the receiver, the A9 input must be either connected to the + 12V rail or ground. The 9-bit code word is sent as a series of pulses from pin 15 of ICl. The frequency of the pulses is set by the two resistors and the capacitor connected to pins 11, 12 and 13. For our circuit, the frequency is about 2kHz. Transmitter Main Features The transmitter comprises a digital encoder integrated circuit (ICl) and a UHF oscillator operating at 304MHz. Fig.1 shows the details. • • • • • 11 • • • • • SILICON CHIP UHF transmitter and receiver on 304MHz Two versions of the handheld transmitter. Transmitter uses a single IC and one transistor. Single button to activate and disable alarm. 40-metre transmitter range. Trinary digital coding wiMl 13,122 codes for security. Multi-optioned receiver (build it as you want it). Relay switch-on and off for any burglar alarm. Momentary traffic indicator flashing for alarm set. Piezo alarm or siren for audible indication of alarm set. Pushing the Transmit button (S1) causes the IC to deliver the coded word from pin 15. This is used to key the UHF oscillator Ql on and off at a rate of 2kHz. When pin 15 is high ( + 12V), Ql oscillates. Ql is a BFR91A, a surface mounting transistor intended for use in UHF and microwave amplifiers. Inductor L1 and the 2-6pF capacitor The Remote Switch can be teamed with the Protector Alarm, or with any commercial alarm. The small keyring transmitter is in the foreground. form a tuned circuit load for the collector of Ql. Its base is grounded (to AC signals) by a 4 70pF capacitor. Stray capacitance between the emitter and collector of Ql provides positive feedback which causes it to oscillate, at 304MHz. To increase the oscillator's output, the emitter degeneration resistor is bypassed with a 1.5pF capacitor, which is critical in value. The size of this capacitor cannot be too large since it would reduce the positive feedback and thereby stop oscillation. The transmitter is powered from a 12V lighter battery (VR22, EL12, GP23 or equivalent). Actually, the circuit could be made to work at voltages down to 4.5V but the selected battery is the one best suited for the job since it is so compact. The battery is bypassed by a 0. lµF capacitor located near IC1 and by a 0.047µF capacitor near the tuned circuit for Ql. When S1 is closed the current drawn by the circuit is a few milliamps, the exact figure depending on the code word selected at Al to A9. The current through LED 1 is about 7mA. When S1 is open, the current drain is less than 200 nanoamps (0.2 microamps). The transmitter can be built into one of two cases which are small enough to be attached to a key ring. T m: 16 ..I.. 1 LOW 14 IC1 MC145026 47k 15 10k 470pFl .,. 13 12 TE 11 .,. t ENCODING OPTIONS 100k .0022 220k + E TYPE MARKING .,. L1 : 32mm OF 0.71mm TINNED COPPER WIRE FOR SMALL VERSION. LARGER VERSION USES PCB TRACKS. toN LARGE VERSION ONLY UHF REMOTE ALARM SWITCH TRANSMITTER SCD3·1·28B Fig.1: the transmitter uses an MC145026 trinary encoder IC to key UHF oscillator Qt on and off. A1-A9 are connected to give the address code (see text). We'll talk about these later in the section on construction. Receiver The receiver circuit is shown in Fig.2. It consists of four sections: an RF input amplifier and detector (Ql and Q2), a tuned 2kHz amplifier (IC1), decoder IC2, and optional relay driver circuitry. The transmitted signal is picked up by the antenna which is loaded MARCH 1988 27 This view shows the UHF switch receiver installed in the same case as the Protector Car Burglar Alarm described in February. Connections between the two PCBs are via PCB-mounting terminal blocks (see Fig. 12). by inductor L1. The signal is then coupled via a .001µF capacitor to the base of Qt , which is an RF amplifier with a tuned collector load. Signal from the collector of Qt is fed from a voltage divider consisting of a 2.7pF and a 22pF capacitor to self-oscillating detector stage QZ. This operates on the principle that whenever signal is received the circuit oscillates at 304MHz, but when the signal is not received, the circuit is quiescent. The detected signal from QZ is extracted from the 0.001µF capacitor connected to its base. This capacitor bypasses the 304MHz signal but not the ZkHz pulse modulation which is superimposed on the signal fed to the antenna. This ZkHz pulse signal is ACcoupled via a 2.2µF capacitor to ICta, an inverting op amp with a gain of about 470. ICtb is a Schmitt trigger. It squares up the amplified signal from ICla before feeding it to ICZ, the trinary decoder. ICZ is a MC:::145028 decoder which is compatible with the MC145026 used in the transmitter 28 SILICON CHIP circuit. It is set up to respond only to the unique code word sent by the transmitter. This is done by connecting the address inputs Al to A9 in exactly the same way as for IC1 in the transmitter. When IC2 detects a correct code from the transmitter, the output at pin 11 goes high and charges the 2.2µF capacitor at the input of IC3a via the 2.2k0 resistor and diode Dl. It takes about 5ms before the output of Schmitt trigger IC3a goes low. When transmission ceases, the output of ICZ goes low and the 2.2µF capacitor discharges via the 470k0 resistor. This takes about one second after which the output of IC3a goes high again. This delay is to prevent false triggering. Just how the circuit operates from this point on depends on how you build it. For example, you could decide to use it to momentarily close relay RLY1 every time the transmitter button was pushed. To accomplish this, connect link LK1 (following IC3a), leave out link LK2 and omit IC4, IC5, Q4 and all the associated components. If you do this, pins 8 and 9 of IC3 should be connected to pin 7. Every time the transmitter button is pressed, the resulting momentary low output from IC3a causes IC3d to go momentarily high and turn on transistor Q3. This closes relay RLY1 for one second. Alternatively, you can go for a more complex circuit function by omitting link LK1 and installing link LKZ instead. Now, with ICZ detecting the valid code and the resultant pulse delayed and squared up by IC3a, a further pulse inversion takes place in IC3b, before the signal is fed to the clock input of IC4a, a D-type flipflop. This is connected to change states when it receives a clock pulse. The Q-bar output of IC4a connects to the input of IC3d via link LKZ. IC3d drives transistor Q3 when its output is high and this in turn operates RL Yt. Thus, relay RLY1 closes at the first push of the transmitter button and opens with the second push on the button. This function could be used to turn any commercial burglar alarm on and off. Audible options IC5 is a CMOS 555 timer connected as a monostable (ie, con- 4.m . . - - - - -....- - - + - - -....-'JW,-----------..------~>------..---- ANTENNA +8V .01J 4.7M 10k F16 L2 22pF L1 +4 3.3pF 10 10k.,. .,. + 16VWJ .,. .001! .,. L1 : 190mm OF 0.63mm ENAMELLED COPPER WIRE. 15T ON 3.2mm FORMER L2 : 65mm OF 0.71mm TINNED COPPER WIRE. 1.5T ON 5mm FORMER. F16 FERRITE SCREW CORE. 8V + 100 16VWJ .,. 9 INPUT ..----1--+12v I 05 1N4002 LK1 : MOMENTARY RELAY 1 LK2 : ON/OFF RELAY 1 2x1~ioo2 RELAY 1 ...+-M-+-011 RIGHT D1 1N4148 2.2k OUTPUT LK1 06-11>-----..,.09 LK2 .---+----+12v _ _ _..__ _ _ ___,_ _ _ _ _ +8V 02 1N4148 100k PIEZO SIREN VR1 1M 12 47k .022I .001 .,. IC5 TLC555 10 +12V 180k .,. .,. 0.1+ .,. PIEZO TRANSDUCER 13 10 +12V COMMON 470k 11 + 2.2 16VW+ DECODING OPTIONS INDICATORS 214 100k Z01 33V 1W 100 16VW + 1_ 00k _ IC3b CHASsIsn.:1- - - . . __ _ _...._ _ _ _ _- 1 . - - . - .0471 1/E! PLASTIC f1 lmUT 1 s-··.6: i'"'"' m + 8V r - - - - - - - - 0 7 DISABLE TYPE Q1 50 BELOW GNO 3 CK s 4013 IC4a 2.2k ii2 R 7 4 8V 11 16VW 470k SC03·H88 + .011 10 16VW "-4.._._._,......,_.-tiF-Q& OFF Q 12 11 CK .,. .,. UHF REMOTE ALARM SWITCH RECEIVER D4 1N4148 14 IC4b 13 9D R 10 s 8 .,. 03 1N4148 '----li-tll--+---Q 8 ON Fig.2: the receiver circuit can be built so that relay 1 provides momentary or on/off switching. MARCH 1988 29 . •' TRANSMITTER ~TINPLATE 15mm x 5mm SCOJ-1-288-3 TINPLATE /15mm x 5mm ~ '-------4.---' ~ 4 x 1mm x 6mm WIRE STAKES Fig.3: battery clip detail for the small transmitter. Fig.5: parts layout for the small transmitter PCB. The S1 switch contacts are made from tinned copper wire. nected to deliver one pulse when it is triggered). When the output of IC3a goes low (when a transmission occurs), pin 2 of IC5 is pulled low and the output at pin 3 goes high, for about 120 milliseconds. The timing is mainly determined by the 0.22µF capacitor at pins 6 and 7 and the lMO trimpot and lOOkO resistor connected to the + 8V line. The timing is modified by the 100k0 resistor connected to pin 5 from the Q output of IC4a. Pin 5 controls the threshold voltage of the comparators within the IC. When the Q output of IC4a is high, pin 5 is pulled higher than its nominal setting (2/3 Vee) and the PLASTIC SUTTON ~-;::::::::>=====b TINPLATE 16mm x 5mm SCREW ANO NUT 1.5mm OIA. x 3mm Fig.4: the switch for the small transmitter is made from ·a piece of tinplate and a small plastic button. Fig.6: to code the transmitter each A1-A8 input is connected to the high rail, the low rail, or left open circuit. A9 must be connected high or low. timing period becomes longer. When Q of IC4a is low, pin 5 is pulled lower and the timing period becomes shorter. Pin 3 of IC5 drives transistor Q4 to turn on the piezo siren. Because the voltage on pin 5 of IC5 is controlled by the Q output of IC4a, the siren emits a short burst of sound when IC4a is clocked to the off state and a longer burst when IC4a is clocked to the on state. Pin 3 of IC5 is also connected to pin 9 of IC3c. When pin 3 of IC5 is high, IC3c oscillates and drives the piezo transducer. This is a lower cost alternative to the piezo siren driven by Q4. Traffic indicator option Relay RLY2 is also driven by Q4 via diode D6. It has a 2200µF capacitor connected across it and this is charged via D6, Q4 and the 120 resistor. The resistor limits the initial surge current while the 2200µF capacitor is used to keep the relay energised for about a second after Q4 turns off. The contacts of relay RL Y2 are arranged so that they can switch on the vehicle indicators for a short time to provide visual indication of a received signal. Diodes D7 and D8 isolate the left and right indicators. IC4b is clocked by the pin 3 output of IC5 while its D input, pin 9, is connected to the Q-bar output of IC4a via a delay network consisting of the 2.2k0 resistor and O.OlµF capacitor. The delay ensures that IC4b is clocked with data from Qbar of IC4a before it changes state. The Q outputs of IC4b follow the Q outputs of IC4a and are used to provide on and off signalling for the Protector Alarm described in the February 1988 issue. The Q output connects via diode D3 to the on input of the Protector alarm, while the Q-bar output is capacitively coupled to the off input. This provides a short pulse which is sufficient to switch off the alarm circuit. A further output from the. Q-bar output is used to provide the Disable control. This can be used to disable an ultrasonic movement detector which we hope to describe in a future issue. Power for the circuit comes mainly from a 7808 3-terminal regulator. This isolates the sensitive circuitry from the 12V automotive electrical system. A 33V zener diode protects the input of the regulator from any voltage spikes on the 12V line. Construction Fitting the parts in the Jaycar case is bit of a challenge but it can be done if the parts are 'squashed' down on the PCB. The pen points to the two switch contacts which are made from looped tinned copper wire. 30 SILICON CHIP As noted above, the handheld transmitter may be built in one of two cases, one from Dick Smith Electronics and one from Jaycar Electronics. We have designed two transmitter boards to suit the two cases. The larger of the two cases is from Dick Smith Electronics. It measures 31 x 58 x 17mm (DSE Cat No H-2497). The printed board to I 12V J + Fig.7: alternative transmitter PCB for the DSE case. The .0022uF capacitor lies flat across the IC (see photo). Fig.8: Al-A9 address pins for the alternative transmitter. Make sure the transmitter code matches the receiver. The larger of the two transmitters is still compact enough to fit your keyring. The two transmitters look different but their circuits are the same. Coil L1 is part of the PCB pattern for the larger version, while the smaller version uses a wire loop. Power comes from a 12V lighter battery. suit it measures 46 x 33m (SC code 3-1-288-2). The case from Jaycar is smaller, measuring 34 x 43 x 13mm (Jaycar Cat No HB-6072). The board to suit measures 30 x 30mm (SC code 3-1-288-3). While the Jaycar case is notably smaller, it has the disadvantage that a switch and battery clips are not available and will have to be made. Nor can the LED indicator be fitted into it. The Dick Smith case is supplied with battery clips and a commercial switch can be used. Construction of the transmitter in the Dick Smith case should be straightforward. The smaller transmitter is more difficult to construct due to the necessity to make the switch and battery clips. We made the battery clips for ours from pieces of tinplate 15mm long by 5mm wide. They are each soldered to two wire stakes on the PCB. This is shown in Fig.3. The switch is also made using tinplate. It is secured to the lid of the case using a screw and nut. A small plastic button is glued to the tinplate as shown in Fig.4. Contacts for the switch are mounted on the PCB using tinned copper wire loops. These are raised about 4mm above the PCB surface but some adjustment in height may be necessary to provide a satisfactory switch action. The component layout for the smaller transmitter board is shown in Fig.5. The smaller transmitter PCB requires a 5.5mm hole to clear the screw pillar in the lid and a 5mm hole for the transistor. Before assembling components on the PCB, check that the PCB will fit within the case. You may need to file off the corners of the PCB so that it will follow the internal corner radius of the case. Install the IC with pin 1 towards the battery clip side of the PCB. The transistor is mounted on the underside of the PCB. Tin the PCB tracks with solder before soldering the transistor leads in place. The remaining components are not so easily installed. None of the parts can sit more than 6mm above the PCB surface to avoid fouling the lid of the case. To achieve this low profile, the resistors are mounted end on and bent over so that they lie close to the PCB. The smaller capacitors can be mounted upright, however the larger ceramic capacitors should be bent over. The 0.0022µF greencap should be mounted side on. The trimmer capacitor can be mounted in the normal fashion. The 11 inductor is made using 32mm of 0.71mm diameter wire looped and laid flat on the PCB as shown in Fig.5. The larger transmitter version in the Dick Smith case uses the SC03-1-288-2 PCB. Components for this PCB can be installed as shown in Fig.7. The battery clips are pre-shaped and are simply inserted into the PCB and soldered on the underside. Now install the IC and link. Some MARCH 1988 31 Receiver ANTENNA INPUT Fig.9: parts layout for the receiver PCB. For momentary relay switching, install LK1 and omit LK2, IC4, IC5, Q4 and associated parts. Also, connect pins 8 and 9 of IC3 to pin 7. For latched contacts, omit LK1 and install LK2 and all parts. L2 FORMATION DIMENSIONS IN MILLIMETRES Fig.10: L2 is wound using 0.71mm tinned copper wire. resistors are mounted flat on the PCB while others are mounted end on as shown on the overlay. All the capacitors are mounted flush against the PCB except the .0022µF greencap which is bent to lie flat over the top of the IC. The switch is mounted so that the flat side of the switch body is towards the battery terminal end of the PCB. The LED is mounted 11mm above the PCB surface. The transistor is mounted on the underside of the PCB. Tin the PCB tracks with solder before finally soldering the transistor pins in place. Fig.11: connect the A1-A9 receiver inputs to exactly match the transmitter code. A1-A8 can be high, low or open circuit; A9 must be tied high or low. 32 SILICON CHIP The UHF receiver is built on a PCB coded 03-1-288-1 and measuring 132 x 87mm. It can be installed in a plastic utility case measuring 159 x 96 x 51mm or, if you have made the Protector Burglar Alarm, you can build it into the same case. Begin construction of the receiver by installing all the low profile components such as the resistors, links, diodes, and ICs. When installing the links, decide whether relay RLYl is to be wired with momentary or on/off operation and install either link 1 or link 2 accordingly. Fig.9 shows the receiver board with all parts installed. We assume that many readers will build versions with some of the options omitted. If this is the case, examine the layout diagram carefully to determine what parts can be left out. The BFR91 transistors are mounted on the underside of the PCB. Before mounting and soldering each of these transistors, tin the tracks with solder. This makes it easier to solder each transistor into place. L1 is made using a 190mm length of 0.63mm enamelled copper wire wound around a 3.2mm (1/8-inch) drill bit. Wind on 15 turns and strip the insulation from the ends with a sharp knife before soldering it to the PCB. 12 is wound on a 5mm plastic former which is fitted into the PCB so that it is a tight fit. The winding details are shown in Fig.10. Don't forget to screw in the F16 ferrite core. Continue construction by installing the capacitors, relays, remaining transistors, the 3-terminal regulator and the insulated terminal block. Take care with the orientation of the electrolytic capacitors and transistors. The antenna is simply a 300mm length of hookup wire soldered to the antenna input pad on the board (see Fig.9). The receiver can be mounted in its own case using PCB standoffs. A Scotchcal label measuring 90 x 153mm is secured to the front panel. The artwork is shown in Fig.13. Alternatively, the PCB can be PROTECTOR ALARM : 1,2 + 12V TO VEHICLE BATTERY e 3 TO BATTERY BACKUP VIA 3A FUSE-- - - - -- - -- - -•40N - - - 5 OFF 6 POWER GROUND ....- IGNITION COIL e e 7 VEHICLE BATTERY e 8 IGNITION e 9 INSTANT e 10 DELAY a, GND 5A ALARM CONTACTS 4, DASHBOARD FLASHER PIEZO SIREN 1 ,----------------+-12-V14-......,.._----, - ~ -~•m,s PIEZO TRANSDUCER 13 - - : - - PIEZO SIREN 12 ~ INDICATORS R~~~~ : ~ ~ -1------:: COM MON 9 ON 8 DISABLE 7 . . . . _ OFF 6 NORMALLY CLOSED 5 NORMALLY OPEN 4 COMMON 3 UHF REMOTE ALARM SWITCH + 12V 2 GROUND 1 ALTERNATIVE CONNECTION e-!- -..., --- TO "DISABLE" ON e ULTRASONIC DETECTOR e I e : ::::"---Jf----f:2:'.Jr--;::n±-_--=.IJ:::;--....... 1 CHASSIS Fig.12: here's how to wire the UHF remote switch to the Protector car alarm. The piezo transducer can be omitted if you have fitted the piezo siren. mounted in the Protector alarm case as shown in one of the photographs. It is mounted on 15mm standoffs at the terminal end of the PCB and supported using Ushaped brackets at the opposite end. Fig.12 shows how the UHF remote switch is wired to the Protector car alarm. The remaining connections to the Protector alarm are as shown in the February issue. Testing and alignment Both the transmitter and receiver must be coded before they can be tested. Figs.6, 8 and 11 show the Al to A9 code inputs on the copper side of the PCB for two transmitters and the receiver respectively. Note that the receiver code must exactly match the transmitter code, otherwise the unit won't work. Initially, to allow testing, we recommend that only the A9 input of the transmitter and receiver be coded. This input must be bridged to either the high or low rails (it must not be left open circuit). The transmitter frequency must This fully-optioned receiver board features on/off switching for relay 1. The second relay (top right) provides the traffic indicator option. be set to 304MHz by using a frequency meter. Temporarily connect pin 15 of ICl to the positive rail. This will set the oscillator in operation. Now hold the transmitter near the input of the frequency meter and adjust the trimmer capacitor for a reading of 304MHz. In some cases it may be necessary to connect a coil of wire between the inM ARCH 1988 33 r: :-J C L: PIEZO TRANSDUCER PIEZO SIREN RIGHT INDICATORS [ LEFT COMMON ON DISABLE OFF NORMALLY CLOSED NORMALLY OPEN COMMON +12V GROUND UHF REMOTE ALARM SWITCH Fig.13: actual size reproduction of the front panel artwork. I SC03-1·288·2 Flg.14: etching pattern for the larger transmitter PCB. Fig.15: etching pattern for the small transmitter PCB. Fig.16 (right): etching pattern for the receiver 34 SILICON CHIP r 14 13 12 11 10 9 8 7 6 ~ 2 1 PARTS LIST Transmitter 1 transmitter case (Jaycar Cat. HB6072, 34 x 43 x 13mm; or DSE Cat. H-2497, 31 x 58 x 17mm) 1 PCB, code SC03-1-288-3, 30 x 30mm (for Jaycar case); or SC03-1-288-2, 46 x 33mm (for DSE case) 1 PC-mounting pushbutton switch, DSE Cat. S-1 200 (for DSE case) 1 3mm LED (for DSE case) 1 50mm x 5mm tinplate (for Jaycar case) 1 5mm x 4mm plastic button (for Jaycar case) 1 1.5mm dia x 3mm screw plus nut (for Jaycar case) 1 12V lighter battery (VR22, EL 12, GP23 or equivalent) 32mm 0.71mm tinned copper wire (for L 1, Jaycar case) Semiconductors 1 BFR91 NPN lJHF transistor 1 MC145026 trinary encoder Capacitors 1 0.1 µ.F miniature polyester 1 .04 7 µ.F ceramic 1 2200pF metallised polyester (greencap) 1 4 70pF ceramic 1 1.5pF ceramic 1 2-6pF ceramic trimmer Resistors (0.25W, 5%) 1 X 220k0, 1 X 100k0, 1 X put and ground of the frequency meter to obtain a satisfactory reading. Once the frequency has been set, remove the temporary connection to pin 15. Now connect the receiver to a 12V power supply. Apply power and check that the output of the regulator is at + 8V. Next, connect a multimeter set to read DC volts between test point TPl and ground. Apply power and wait 10 seconds for the 2.2µ.F capacitor at the base of Q2 to charge. Adjust the slug in L2 for maximum signal when the transmitter switch is pressed (ie, for maximum reading on the DMM). You may need to progressively move the transmitter away from the receiver 47k0, 1 x 1 OkO, 1 x 1.5k0 (if LED is required), 1 x 1 kO Receiver 1 plastic utility case, 159 x 96 X 51 * 1 Scotchcal front panel, 1 53 x 90mm* 1 printed circuit board, code SC3-1-288-1, 133 x 87 1 1 0-way PC-mounting insulated screw terminal block 1 4-way PC-mounting insulated screw terminal block 2 1 2V SPOT relays* 1 piezo transducer* 1 piezo siren* Semiconductors 1 MC145028 trinary decoder 1 TL062 low power dual op amp 1 4013 dual D flipflop* 1 4093 quad NANO gate 1 7808 3-terminal 8V regulator 1 TLC555 CMOS timer* 2 BFR91 NPN UHF transistors 1 BC337 NPN transistor* 1 B0681 NPN Darlington transistor* 3 1 N4002 1 A diodes* 4 1 N4148, 1 N914 diodes 1 33V 1W zener diode Capacitors 1 2200µ.F 16VW PC electrolytic* 2 100µ,F 16VW PC electrolytic and repeat the adjustment for L2 to obtain the setting for maximum sensitivity. Once adjusted, the receiver should be respond to a transmission by activating relays RLYl and RL Y2 (if fitted). Relay RL Y2 should close on receipt of a transmission and remain closed for about one second. Connecting a piezo transducer between terminals 13 and 14 or a piezo siren between terminals 12 and 14 will then provide the audible indicator for the receiver. A short burst of sound will be heard during the off transmission and a longer burst of sound during the on transmission. Trimpot VRl adjusts the lengths of these tone bursts. 3 1 Oµ.F 16VW PC electrolytic 2 2.2µ.F 16VW PC electrolytic 1 1µ.F 1 6VW PC electrolytic 1 0.22µ.F PC electrolytic 2 0.1 µ.F metallised polyester 1 O. 04 7 µ.F metallised polyester 1 0.022µ.F metallised polyester 1 0.01 µ.F metallised polyester 1 0 .01 µ.F ceramic 1 0 .001 µ.F metallised polyester 4 0 .001 µ.F ceramic 1 22pF ceramic 1 3.3pF ceramic 1 2. 7pF ceramic 1 2.2pF ceramic Inductors and wires L 1 190mm 0 .62mm enamelled copper wire L2 65mm 0 .71mm tinned copper wire, 5mm former DSE cat L-1010, F16 ferrite screw core L3 3 .3µ.H 300mm 1 mm solid core insulated wire (for the antenna) Resistors (0.25W, 5%) 2 x 4.7MO, 3 x 470k0, 1 x 180k0, 1 x 150k0, 6 x 1 OOkO, 2 x 47k0, 1 X 39k0, 1 X 22k0, 1 X 18kQ, 6 x 1 OkQ, 2 x 2.2k0, 1 x 1 kQ, 1 X 4 70Q, 1 X 270Q, 1 X 12n, 1 x 4.7n, 1 x 1Mn miniature vertical trimpot * optional text). components (see Coding The receiver and transmitter can now be coded using selected high, low or open circuit connections to Al to A8. Each Al to AB input can be bridged to the high rail, the low rail or left open circuit. For example, you could bridge Al to the high rail, A2 to the low rail, leave A3 open circuit, bridge A4 high and so on. It's a good idea to write your selected code down on a piece of paper before actually making the necessary connections. Make sure that the receiver and transmitter coding are identical. Finally, drip some molten candle wax into the screw core of L2 to prevent it from moving and thus detuning the receiver. It M ARCH 1988 35 Easy Serial Links RS232 Breakout Box Parallel Switch Box Male/Male Gender Bender. Adapts female serial cables without resoldering or reconnecting. All 25 pins wired pin to pin. Simply plug in twin male D825 sockets. Cat X-3565 Just what you need for modems or any serial applications. D825 male to female. Pin 1 is permanently wired, all others are open with wire links supplied . Perfect for making up special serial cables. Cat X-3568 No more cable changing! The parallel switch box can save you heaps of time. Lets you run one printer and two computers or even two printers and one computer. Just plug it in and it does the s27so 80286 ·Mother Board Your own 'Baby AT'! Use it with our do-ityourself kit or your own custom computer. Provision for 256K, 512K, 640K or 1024K RAM, selectable 6,8, 10 & 12MHz speeds, 8 inpuVoutput slots, IBM PC/AT compatibility, Award BIOS and much more! Cat X-1000 s499 Serial Switch Box RS232 Permanent Jumper Box Female/Female Gender Bender The same as above but with twin female sockets permanently wired. Makes cable connections quick and hassle free! Cat X-3566 Lighbling Fast or NLQ. Super fast 135cps dot matrix printer for home or office use. Just what you need for letters, graphics ... all your printing requirements. The DSE 135 Printer, great value and exceptionaj quality. Correspondence, invoicing, reports, designs, graphs ... anything. Cat X-3225 s This one's similar to the breakout box but the connections are made internally and soldered for permanent applications. All 25 pins are open with wire links supplied. Cat X-3569 s995 ;g;' ,. • What a pain in the .... , they never give you more than one serial port! What's more, there's so many serial applications. Well, we've solved the problem. The serial switch box lets you connect two devices to your serial port. A modem and a mouse, two modems, a printer and a .... whatever you like. Cat X-3573 s59es 80 Column Printer Stand Takes the foul-ups out of printing. Keeps your printer and paper working NEATLY together and gives you the time to go about your work while the printing's being done. Saves space and time. Cat X-3811 s39es CPU Floor Stand Lets you store your CPU 011 it's side out of harms way. Great when space is at a premium! With more space on your desk you'll most likely end up with less mess - now that seems sensible. Cat X-3810 132 Column Printer Stand When you need to use the larger format paper then this is the printer stand for you. Just like the 80 column stand. Helps eliminate paper jams by storing and taking-up paper during printing. Cat X-3812 s49es ~ The ultimate modem at just the right price! The Bit Blitzer 12E with selectable full duplex 1200/1200 or 300/300 baud, auto answer, auto dial, auto disconnect, Hayes AT command set compatibility and more. Fully keyboard controllable, so it's easy to operate. Cat X-3306 JUST Now with Viatel With the Bit Blitzer 123E you get all the advanced features of the 12E PLUS the advantage of 1200ll5 baud Viatel operation. At this great low ~ Q , l / ~'"' ~ ,_,,., Order by phone: 24 hour .despatch through DSXpress. Call TOLL FREE (008)22 6610 (Sydney Area, call 888 2105) s399 .. s499 DICl<<at>.sMITH ELECTRONICS PTY LTD I ~ Make your own PCB'S with... DATAK Pos/Neg Film Refills Tinit - Tin Plate Powder Circuit-Fix It Assorted Marks Pack contains enough dry developer, fi xer and wash to process up to 15 5" X 6" film Great for control panels, meters, dial plates, etc. 6 sheets of transfers including letters in black, gold and white. Cat N-5750 s1195 $9995 ----------!! !l!lilil l l'! '_ .. 60 MHz CRO Probes You'd expect to pay $$$ more for a CRO Probe with this versatility. With x 1/x 10 switch, coax CRO connector, IC adaptor, spring clip, wandering earth, BNC adaptor and more! Cat 0-1247 The ER-17 filter is just what you need for any pos/neg work. Keep it clean and dust free and you'll have it for years cat N-571 1 Just about everything you'll need for pcb work .. Hundreds of transfers. 5 sizes of d_oughnuts, square p_ ads, 16-12 pm DIP, T092trans1storsandm.ore! 1095 · 0 Cat N-5766 5 1995 t·· Burnisher ~ _.,,., t ~ . Negative Resist Developer Yellow Pos/Neg Filter · Assorted PCB Transfers $ 11 ., >>. - t l ..····.· ,., ;;· ·,:,"·J··· ' ·~ The Complete PCB Kit All the chemicals you need to create your own professional pcb's! Use the kit to make your own artwork or use magazine art, use the patented Pos-Neg process to make photo ne~ative, sensitize and expose blank copper, develop and etch - its all made easy! Save time and money wi)h Datak PCB Kit ER-4. cat N-5700 sheets cat N ~ 59.09 5 A solvent that will develop negative acting photo resist. In handy 483ml container. Cat N-5905 '<1 s1195 .'\\'\~ j \ ~\ · .. .,. ~1 ER-71 Neg_ative Photo Resist Assorted Targets A liquid cinnimate resist in bottle with pump sprayer for easy application. Covers 4000 sq mm. ;;Sas , , S0995 pair Safe~ Yellow 3.5 Digit Multimeter 300ohm Plug This is one of our be.st selling 3.5 digit Multimeters - it's no wonder when you see the features! Includes Tr, diode, continuity PLUS battery checker. Checks current to 10A and resistance to 200 megs. Cat 0-1445 2 x 40 fluoro starters. Keep a pack handy and you won't be left in the dark. Cat P-5625 s1 !!O 3.5 Digit with Capacitance Checker Similar to our safety yellow Q-1445 only this has a capacitance checker and goes to 20 megohms resistance. Resolution is great and it has a fast 300ms cycle time and fuse protected meter. Cat 0-1465 ~ESS DICK SMI TH ELECTRON/CS EXPRESS ORDER SER VIC E Plug to suit ribbon cable for TV antenna. Cat P-2082 s120 Fluoro Starter Pack 24 Hour Timer 3.5 Digit with Temperature An LCD that's ready for work. With many more ranges than you'd expect at the price including full AC/DC current up to 10A. It also checks diodes and continuity and has overload protection on all ranges. Cat 0-1511 Sl 15 Order by phone: 24 hour despatch through DSXpress. Calf TOLL FREE (008)22 6610 (Sydney Area, call 888 2105) Mounts on wall or skirting. With 75 ohm connector for coax. Cat P-2044 s495 ~ Great security device! Lets you time lights, appliances, etc to switch on and off automatically. cat P-5701 300ohm Wall connector Plug and socket for wall mounted 300 ohm ribbon cable connection. s39 95 Power Point Safety Tester s· Cat P-2080 ~ d t J 1 imp 1e an easy O use. uSt P ug it into the power point and the light pattern indicates any faults. 52as cat P-5390 ~ s7ss ----~,- ----------- DICK0 SMITH ELECT PT Y LTD Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Adjustable Load for Power Supplies When designing power supplies, a variable load is needed to determine the current capacity. You could use a large power rheostat (a variable wirewound resistor) but these are now very expensive and hard to obtain. And a rheostat's capacity to dissipate power depends on what proportion of the element you use. If you use half a rheostat's resistance element, it will only be able to dissipate half its rated power. So if you use a rheostat right at the bottom of its resistance range, the small portion of the element in use will tend to seriously overheat. The solution to this problem is to use a power transistor mounted on a large heatsink. By connecting the collector and emitter of the power Handy Hints Hint #1: Do you make your own printed circuit boards? The first step is to thoroughly clean and dry the copper surface prior to coating it with photo-resist. To obtain a dust-free surface, do not use paper towels as they often shed lint. Instead, dry the surface with a hair-dryer. This gives an absolutely clean, dust-free surface. Hint #2: In many circuits, fuses are desirable but they can take up quite a lot of space on small circuit boards. In quite a few applications though, a small resistor will do the same job and take up a lot less space. Values below 10 ohms and with a rating of 0.25W are the ones to go for. They will provide current limiting and fusing for currents of several hundred milliamps. As a bonus, resistors are much cheaper than fuses and are more readily available. 38 SILICON CHIP +12vo------Q1 8D681 + OVU---41---------tt-----41""-0 transistor to the DC power source to be measured, the amount of load current can be easily adjusted by varying the base current drive to the transistor. Our circuit uses the readily available 2N3055 (Q2) as the power transistor and a BD681 Darlington (Ql) as the source of base current. VR1 varies the base current to Ql and hence varies the current drawn from the supply. The amount of power able to be dissipated by the 2N3055 depends on the size and effectiveness of its heatsink. With a reasonably large heatsink, it should be possible to dissipate about 40 watts. The maximum current drawn from the power supply can be found by dividing the dissipation (say 40 watts) by the voltage between collector and emitter. For 20 volts between collector and emitter, the load can draw 2 amps. Note: the circuit is suitable as a DC load only. It will not work on AC without being modified. Updated Synchroscope for Frequency Comparison This is the frequency comparator to beat all frequency comparators. While some designs use four LEDs in a circle (see page 63, November 1987) to produce a rotating display, this circuit drives 16 LEDs to produce a far more visually satisfying effect. Two 74121 monostables (IC1 and IC2) are used to generate short (30 nanosecond) pulses to be fed to a 74193 up/down 4-bit counter. The output of this counter is fed to a 74154 binary 1-of-16 decoder which drives the 16 LEDs. Ordinary 74-series TTL integrated circuits have been specified here as this is essentially a "junk-box " project but 74LS types may be used instead. The circuit may also be adapted to use a 7442 1-of-10 decoder and a 74192 up-down counter. Further, a 74123 dual monostable could be used but it does not have a Schmitt trigger "B" input like the 74121. The 74121's "B" input has typical switching thresholds of + 1.35V and + 1.55V. An input sensitivity of 200mV peak-peak could be obtained by simply biasing the input to + 1.45V with a pull-down resistor. However, the resulting input impedance would be quite low. To overcome that, the accompanying JFET input stage has been included which should be satisfactory for most applications. In some cases the 1k0 drain load resistor may need to be increased if the FET has a low Idss. $30 to Steve Payor, Kogarah Bay, NSW. Precision Reset for Microprocessors CRO Probe Modification If you are using an oscilloscope probe in a sensitive circuit such as a high gain audio preamplifier or power amplifier, off a resistor it can cause problems. The probe's capacitance and attach it to the probe can be sufficient to cause a tip as shown in power amplifier to exhibit low the accompanying illevel instability. lustration. The resistor The way to effectively isolates the probe avoid this capacitance from the problem is to clip the leads --1ok RESISTOR sensitive circuit being measured. Usually a value of between 1k0 and 10k0 will suffice. The technique can also be useful when measuring RF or high speed logic circuits. ,----------+VDD MICROPROCESSOR - - - - - - - ~ - - -VSS Most designers of dedicated microprocessor equipment use a simple RC network for resetting when the supply voltage is low. This usually works without trouble but it can lead to problems in some cases. A more precise method involves using the Seiko S-8054HN voltage detector. This 3-terminal device in a T0-92 package uses a window comparator which delivers a logic low (OV) at its open drain output whenever the supply voltage is in the precise range from 3.8 to 4.2 volts DC. Other applications include level discrimination, power failure indicator and charging monitor. The Seiko S-8054HN is available directly from VSI Electronics (Aust) Pty Ltd. Phone (02) 439 8622. Help! Save Us From Circuit Burnout! We know we're brilliant. You've said so yourselves. But we know that there are lots of ingenious circuits lanquishing out there in readers' brain cells. So bung 'em into us and we'll publish them in their full glory. You'll not only make some money but you'll also save us from the dreadful "circuit burnout s~~drom~ which happens to anyone who has to generate too many c1rcu1t ideas in too short a time . We'll pay up to $50 for a really good circuit. So transfer your circuit to paper and send it SILICON CHIP, PO Box 139, Collaroy Beach NSW 2097 . ' +5V + .01J 1J .01J .01I 1k ':" 16 1f 5B UT 1 ':' IC3 74193 ':' +5V 4 .011 14 UT 2 9 RT IC2 74121 5B .,. .,. .,. A QB 2 2 B QC 6 21 C QD 7 20 D 2 15 314 4 13 11 510 IC4 74154 DOWN ~ a QA 3 0 17 1 16 .,. u ..J l--3ons 15 1 61 62 18 19 12 +5V .,. B 74121 .01 ,H t~CECr-1 10M ':' ., 60D VIEWEDFROM BELOW MARCH 1988 39 Endless loop tape Fancy a barking doorbell? Or how about a novel pre-recorded message system for a shop display, or for the home? This endless loop tape recorder is the answer. By GREG SWAIN Initially, we didn't quite know what to do with this intriguing little gadget. After all, what possible use is a tape recorder that can only play for 20 seconds before repeating itself? Then we began to think of all sorts of applications. In addition to those already mentioned, it could be used for pre-recorded announcements over a PA system, as an appointments reminder, or as a convenient message system for family members. It could even be used to store telephone numbers, or just as a source of amusement. If you want a really novel doorbell, this unit will do the job. You could record a message telling your guests that the barbeque is around the back, or you could record the spine-chilling sound of a slobbering, salivating dog. Mind you, the effect would be lost when the caller took his finger off the button. (One of our staff members, who shall mercifully remain nameless, decided to do an imitation of a furious canine and performed with great gusto while holding down the record button. It was very effective too although the effect was not quite what he intended. We all broke up whenever it was played back). A pre-assembled tape recorder module from Jaycar Electronics forms the basis of the unit. Instead of the familiar cassette mechanism, it uses a continuous tape loop with only one spool. The tape is wound in a couple of layers on the outside of the spool and is withdrawn from +v---•.il.\!!!.---------------. S1 R-P RECORO/ PLAYBACK an SPEAKER .,. MICROPHONE ELECTRET .,. 22D + 1DVWJ 47Dll + sotw : MOTOR ERASE .,. ENDLESS LOOP TAPE PLAYER SC1-1-488 Fig.1: the circuit for the endless loop tape player. IC1 provides signal amplification while IC2 is for motor speed control. 40 SILICON CHIP player PARTS LIST 1 ED-1 000R endless loop tape unit (available from Jaycar) 1 plastic case, 159 x 96 x 54mm (Altronics Cat No H-0201 or equivalent) 1 Scotchcal front-panel label, 154 x 90mm (optional) 1 50mm diameter 811 loudspeaker 1 4-way AA battery holder 4 AA batteries (preferably alkaline) 1 battery clip to suit holder 1 momentary pushbutton switch 1 pushbutton cap (to suit changeover switch) 1 electret microphone We built the tape module into a plastic zippy case, along with a battery power supply. The speaker, microphone and run switch were fitted to the front panel. Miscellaneous Screened cable, hookup wire, scrap aluminium for battery clamp, self-tapping screws the bottom layer. Apart from that, the rest of the transport mechanism is fairly standard with a capstan, pinch roller and belt-drive from the motor. A spring-loaded multipole pushbutton switch on the side of the module provides the changeover from playback to the record mode. Whenever power is applied the unit is automatically in the playback mode. Putting the module into playback is a good way of finding out what "endless" means; it goes on and on and on. All that is need to make it work is an electret microphone insert, a small 811 loudspeaker and a source of DC which may be anywhere between 4.5 and 6 volts. This power can be derived from batteries or a 4.5V DC mains plugpack. How it works Fig.1 shows the circuit of the ED-1000 endless loop tape recorder. Most of the work is done by ICl which provides all the necessary signal amplification. This view shows the parts layout inside the case. The tape module is secured to one end of the case by two self-tapping screws. In the playback mode , ICl amplifies the signal from the record/playback head and drives the loudspeaker via a 100µ,F capacitor. In the record mode, it amplifies the signal from the electret microphone and drives the record/playback head via a parallel 33k11 resistor and .022µ,F capacitor. This network provides a modest degree of treble boost for the recorded signal. A 5-pole 2-position slide switch, referred to above, is used to switch the circuit between record and replay. In the record position, DC MARCH 1988 41 Above: follow this labelled photograph when hooking up the external connections to the tape player PCB. Note that the electret microphone should be wired using shielded cable. At right is a close-up of the player module showing the endless tape-loop mechanism and the record and replay heads. bias is supplied to the erase head via a 4700 resistor and to the record/playback head via a 22k0 resistor. IC2 (KA2402) and its associated components are used for motor speed control. Construction The above circuit details have been induded so that you'll know r. where to hook the external components. We mounted the tape mechanism in a plastic case measuring 159 x 96 x 54mm. The loudspeaker, electret microphone and switch are all mounted on the lid of the case, while the tape unit is secured to the base using self-tapping screws. Start construction by drilling two holes in the base that align with the • ENDLESS LOOP TAPE PLAYER L: 42 • plastic posts on the bottom of the tape unit. Clean up the holes with an oversize drill bit, then drill and ream a 16mm hole in the end of the case to allow finger access to the record switch. The lid of the case should have holes drilled for the speaker grille, the microphone and the power switch. Attach the Scotchcal art- • • • • ••••• • • • • RUN Fig.2: here is an actual-size reproduction of the front panel artwork. SILICON CHIP .:J Jiu.ii.a·this versatile test instrument Techni]ab 301 function generator This versatile test instrument packs a 10Hz-110kHz function generator, a power supply, and an audio amplifier and loudspeaker into one compact package. By DAVID WHITBY If your funds don't extend to a workshop full of exotic test gear, this multi-function test instrument is for you. It features a function generator, power supply and audio amplifier all in one package, and is ideal for testing prototype circuits and for service work. We think that it will more than earn its keep in many small workshops and labs. The idea behind the Technila b 301 was to provide a versatile test instrument at an affordable price. This has been achieved with a very clever circuit that uses just three low-cost ICs and a couple of 3-terminal regulators. As well as keeping the cost low, this also makes the unit extremely easy to build. There are many potential applications for the instrument. Here are just a few: (1) Audio servicing: you can use the unit as a signal tracer for servicing audio circuits. A signal injected from the function generator can be traced by the built-in amplifier and loudspeaker. (2) Loudspeaker testing: by connecting the generator output to the amplifier, you can ·use the unit for frequency response testing of loudspeakers or amplifiers. (3) Variable frequency code practice oscillator: a Morse key connected between the generator output and the amplifier input is all The Technilah 301 is housed in a grey plastic case with red front-panel lettering. It can generate sine, triangle and square waves from 10Hz to 110kHz. that's required to make a Morse code practice oscillator. (4) Power supply: the unit provides both ± 6V regulated and ± 15V filtered supply rails for powering prototype circuits. Other voltages can be derived from these rails by means of external voltage regulation circuits (eg, zener diodes or 3-terminal regulators). The instrument can provide up to 200mA which is sufficient for most small projects using op amps or logic ICs. Perhaps the most important feature of the Technilab 301 is the built-in function generator. A function generator is useful for checking out audio and logic circuits. Despite the very simple circuit employed, the Technilab is capable of providing sine, triangle and square waveforms with frequency continuously variable from lOHz to 1 lOkHz over four ranges. MARCH 1988 43 FREQUENCY VR1 1M LIN. 100k +6V 82pF VR5 10k H~ .~. .OOl X100 ~ .01 33k +6V x10 Sla 0.1 K Slb 1k RANGE l ':' 1-4) AXED OUTPllT .I1IL 4069 IC1a 1 LE01 15pF 39k 0 2 .It. 100k \I\ 10 S2a S2b 220k 40 400 mV/DIV S3b 1M +6V D1 1N4002 OFF SINE • SYMMETRY VR7 10k +15V HOM ON 0 I -~ +6V 02 1N4002 _;~ ~;_, OV 03 1N4002 S3a 12VAC INPUT OUTPUT OUTPUT VR8 1k UN REG AMPLIFIER IN iov ~1 .1 7806 ':' ":' +15V • LUME 100pFI -6V REG ,. i:k LOG . . GND 7906 -15V NOM 06 1N4002 IN TECHNILAB 301 Fig.1: the function generator circuit is based on CMOS hex inverters IC1 and IC2, while IC3 is the audio amplifier stage. D1, D2 and the two 3-terminal regulators provide the ± 15V and the ± 6V power supply rails. The output level is also continuously variable (from 0-4V over three ranges). And, as a bonus, there is a separate 6V p-p square wave output which is completely independent of the level set. This feature allows reliable external oscilloscope triggering and/or frequency measurements, regardless of the level being fed into the test circuit. The output from the generator is made available on small binding post terminals on the front panel. It can then be fed directly to the circuit under test or to the in-built 44 SILICON CHIP. audio amplifier. The amplifier can deliver 1W into an 80 load and connecting an external lead via the 3.5mm OUT socket automatically disconnects the internal loudspeaker. How it works Take a look now at the circuit details in Fig.1. This can be split into three sections: a function generator based on CMOS hex inverters ICl and IC2; a power supply stage built around two 3-terminal regulators; and an audio amplifier stage based on IC3. We'll consider the function generator circuitry first. ICla is connected as an integrator with four switched capacitors from input to output. These capacitors ar e selected by Sla and provide the four decades of frequency range. IClb and IClc together form a Schmitt trigger. This is fed from the output of ICla via one of the trimpots VR2-VR5 , as selected by Slb. The output of IClc is then fed back to the input of ICla via a lkD resistor and the main frequency control (VRl) to form a surprisingly *MOUNTED ON UNDERSIDE OF BOARD 12VAC INPUT Fig.2: install the parts on the PCB as shown in this diagram. Note that the 3-terminal regulators, the 4700µF filter capacitors and the loudspeaker are . mounted on the back of the board. Take care with component polarity. simple but stable 4-decade oscillator with both triangle (pin 1) and square wave (pin 6) outputs. The four trimpots (VR2-VR5) 11llow adjustment of each frequency decade to match the dial calibration. Inverter stage ICld buffers the output of IClc to provide the fixed 6V p-p square wave output. Additionally, the square wave output of IClc is fed direct to switch S2a and to S2a via a 39k0 attenuator. The triangle wave is derived from pin 2 of ICla and applied to buffer/amplifier stage ICle which is wired in linear mode. After that, the signal is fed to a shaping network (33pF // 18kn) and then fed to S2a. Similarly, the sinewave output is produced by driving the triangle wave into soft limiting stage IClf which is also wired in linear mode. VR6 and VR7 provide adjustment for level and symmetry to produce a rough approximation of a sinewave. Switch S2a selects the appropriate waveform and feeds it to an output stage consisting of six 4069 inverters (IC2a-IC2f) wired in parallel. This stage is used in linear mode in the first three switch positions for sine, triangle and square waves and provides a 4V p-p signal to the output attenuator. In the fourth switch position, the 27kn feedback resistor is switched out and IC2 inverts the output of IClc to provide a 6V p-p square wave to the attenuator network. The 6V p-p variable output is useful for driving digital circuits operating from 6V supply rails and Specifications Waveform functions Frequency range Output level Output impedance Amplifier power output Power supply rails Maximum supply current Sine, triangle and square wave 1 OHz-11 OkHz 0-4V p-p continuously variable on sine, triangle and square wave, 0-6V p-p continuously variable on square wave, 6V p-p fixed square wave output 600 ohms 1W into 8 ohms ± 15V unregulated, ± 6V regulated 200mA also has faster switching times, especially on the highest frequency range. Note: this output is independent of the 6V p-p fixed square wave output from ICld. The signal from the 4069 output stage is AC-coupled via a 470µF capacitor to the attenuator network. This network consists of a lkn pot, fixed 9.lkO and lOOkO resistors, and switch S3b. Depending on the setting of the pot, the output impedance will be no more than about 6000. The audio amplifier circuitry is about as simple as you can get and is based on an LM380 audio IC. This has a power output of 1W into 80, a gain of about 10 and a frequency response from 30Hz to 30kHz (-3dB). Starting at the input, a O. lµF ceramic capacitor couples the incoming signal to 500kn pot VR9 which functions as a volume control. From there, the signal is coupled via another O. lµF capacitor to the pin 2 input and also to the pin 6 input via a 220k0 resistor and parallel 33pF capacitor. The 220k0 limits the gain, while the 33pF capacitor determines the upper frequency rolloff. The amplified output signal appears at pin 8 and is fed to the loudspeaker via a 470µF capacitor and series 4. 70 resistor which provides short-circuit protection. The series 4.70 resistor and O. lµF capacitor across the output form a Zobel network which ensures stability of the amplifier. Power for the circuit is derived from a 12V AC plugpack transformer. Dl and Cl half-wave rectify the incoming AC to provide a nominal + 15V rail, while DZ and C2 provide a nominal - 15V rail. Note: these rails will be closer to + 18V and - 18V under no-load conditions. Finally, regulated ± 6V rails are derived using 7806 and 7906 3-terminal regulators. Diodes D3-D6 protect the supply against reverse polarity connection to external voltages (eg, charged capacitors). Construction A complete kit of parts for this project is available from Technikit Electronics (see panel). To make MARCH 1988 45 PARTS LIST 1 plastic case with silkscreened front panel (predrilled) 1 carrying handle 3 knobs 1 PCB, code Technilab 301, 146 x 86mm 1 8 n loudspeaker with attached pedastal 1 0 threaded brass spacers 3 2-pole 4-position slide switches 1 3.5mm DC power socket 1 3 .5mm switched line socket Semiconductors Above shows the completed PCB, ready for installation in the case. Note the threaded spacers and screws which form the 10 binding post terminals. 2 4069 hex inverter ICs 1 LM380N audio amplifier IC 1 7806 +6V 3-terminal regulator 1 7906 -6V 3-terminal regulator 6 1 N4002 or 1 N4004 diodes Capacitors A small pedastal is used to support the loudspeaker on the back of the board. Note that the PC pattern has been modified to eliminate the wire link. construction really easy, the case comes pre-drilled with the speaker grille already fitted to the rear panel. The front panel features red screen printing on a dark grey background for a professional finish. All the components, except for the power input jack, are mounted on a printed circuit board [PCB) measuring 146 x 86mm. The three pots, along with the 3-terminal regulators, 4700µ,F filter capacitors and the loudspeaker, are mounted on the back of the board, with all other parts mounted on the front. Begin assembly by installing all the parts on the front of the PCB as 46 SILICON CHIP shown in Fig.2. You can install the parts in any order you wish but make sure that the ICs, diodes and electrolytic capacitors are correctly oriented. The three electrolytics used (2 x 470µ,F and 1 x 10µ,F) are all RB types and should be installed with their bodies flat against the PCB [see Fig.2). To do this, bend the leads of each capacitor at right angles before mounting it on the PCB. The power indicator J;..ED should be stood off the board by about 8mm [the long lead is the anode). Ten terminals must also be mounted on the board for the 2 4700µ,F 25VW axial electrolytics 2 4 70µ,F 16VW PC electrolytic 1 1 Oµ,F 16VW PC electrolytic 5 0 .1µ,F ceramic 1 0.1 µ,F greencap 1 .01 µ,F green cap 1 .001 µ,F greencap 1 1OOpF ceramic 1 82pF NPO ceramic 2 33pF ceramic 1 1 5pF ceramic Resistors (0.25W, 5%) 1 x 1 MO, 3 x 220k0, 3 x 1 OOkO, 1 X 39k0, 1 X 33k0, 3 X 27k0, 1 x 22k0, 1 x 18k0, 1 X 9.1 kO, 2 x 1k0, 1 x470, 2 x4.70, 1 x 1MO trimpot, 1 x 500k0 log potentiometer, 6 x 1 OkO trimpots, 1 x 1 kO linear potentiometer various inputs and outputs. These consist initially of 25mm nickelplated screws which are fastened to the PCB by means of 12mm tapped brass spacers. The ends of the screws are later passed through the front panel and fitted with washers, nuts and plated knurled knobs to finish the terminals. Check that the three 4-position slide switches are pushed down firmly onto the PCB before soldering. The loudspeaker socket is installed with its earth terminal towards the bottom of the PCB. You can now install the parts on the frequency control on the x1, x10 and xlO0 ranges. The x1k range begins at l0kHz, so how much of this range you hear will depend on your hearing. Finally, use your multimeter to check the supply voltages. The ± 6V rails should be very close to their nominal values for loads up to 200mA (within 5%). The ±15V rails should vary from around ± 18V at no load down to a minimum of ± 14V with a l00mA load. Calibration The loudspeaker, 3-terminal regulators, and 4700µF capacitors are mounted on the back of the PCB. The regulators are kept cool by finned heatsinks. the rear of the PCB. The pots go in first. Bend their leads at right angles so that they mate with their respective pads on the board. Secure the pots from the front of the board with the washers and nuts provided before soldering the terminals. Note that the pots are all different values so be sure to use the correct pot at each location. Next, solder 35mm lengths of hookup wire to each of the speaker output pads on the back of the PCB. The two 4700µF capacitors can now be mounted, followed by the 6V regulators. Bolt small TO-220 style heatsinks to the 6V regulators as shown in the photograph. Make sure that these don't short with the leads from the 4700µF electrolytics. The loudspeaker supplied with the kit comes with a "pedestal" attached to its magnet (see photo). This pedestal consists of a fibre disc, a 12mm threaded spacer and a screw. The whole assembly is simply mounted on the back of the PCB and secured from the front using a nut. You can now complete the wiring by attaching the speaker leads and by connecting leads from the PCB AC-input pads to the 3.5mm socket on the rear of the case. Testing A final check of component orientation and placement is advisable before switching on. When you are satisfied that everything is correct, apply power and check that the LED comes on. Now turn the gain full on and touch the amplifier input terminal - you should hear a healthy "blurt" from the speaker. If everything is OK so far, set the output level to 40 x 5, select the square waveform, and connect a wire link between the generator output and amplifier input terminals. You should now hear tones from the loudspeaker as you vary Where to buy the kit A kit of parts for this project is available from Technikit Electronics. The kit includes all parts and comes with a pre-drilled case and a silkscreened front panel. Price: $69 .50 plus $6 .50 p&p ($8 .50 to NZ) . Add $1 0. 00 for the 1 2V AC plugpack transformer. Payment may be made by cheque or Bankcard/Mastercard number with mail order, or by Bankcard/Mastercard number for telephone order. Send your order to: Technikit Electronics, 654 Calder Hwy, Keilor, Vic. 3036. Phone (03) 336 7840. The Technilab 301 is also available in fully built-up form. Contact Technikit Electronics for further details . Calibration involves adjusting the six preset pots (VR2-VR7) along one edge of the PCB. For non-critical applications, these can all be set to mid-travel. The dial calibrations will then be accurate to ± 10% and you will get quite a reasonable sinewave. To accurately calibrate the instrument, you will need a digital frequency meter (eg, the 1GHz DFM described in SILICON CHIP from Nov.87 to Jan.88). The procedure is as follows: (1). connect the DFM to the generator output terminals; (2). set the output to maximum on square wave and set the main frequency dial to 110; (3). set the frequency range to xl and adjust trimpot VR2 so that the DFM reads 110Hz; (4). adjust VR3 on the xlO range for a reading of 1 lO0Hz, VR4 on the xlO0 range for a reading of 11kHz, and VR5 on the xlk range for a reading of 1 lOkHz. An oscilloscope is required to accurately set the sinewave shape. Set the output frequency to lkHz, then adjust VR7 (symmetry) so that the positive and negative peaks are as close as possible to the same shape. After that, it's simply a matter of adjusting VR6 (sine level) for smooth rounding of the sinewave peaks. Don't go too far or you will flatten the peaks too much. Once calibration has been completed, the PCB can be fitted to the front panel and secured by fitting nuts and washers to the terminals. Complete the terminals by fitting the round knurled nuts, then screw the handle to the rear panel. Finally, fit the front panel assembly to the case and secure it using the four corner screws. ~ MARCH 1988 47 YVAH JAY~AHJAY~AHJAY~AHJAYLAHJAYLAHJAYLAHJAYLAHJATLAHJAY~AHJAYVAHJATVAHJATVAHJAlVAHJA TVAHJATVAHJATVAHJATVAHJATVAHJA TVAH JATVAHJA T~ YCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCARJAYC YCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCARJAYC. YCAR YCAR YCAR YCAR YCAR YCAR YCAR YCAR YCAR YCAR YCAR YCAR YCAR .... YCAR r LOW COST UTILITY TIMER rLOW DISTORTION AUDIO OSCILLATOR YCAR Ref: EA Feb 1988 YCAR Ref: EA Dec 1986 Whether you wish your egg soft but not too soft, or whether YCAR At last it's available, the metered version of our auudio oscillator. Compares wtth the very YCAR you want to add the time factor to a game ofTrtvtal Pursuit, best laboratory standard sine wave equipment available. YCAR this utility timer Is Ideal. Cat KA-1677 YCAR Complete ktt ,J \.. '!'CAR "Cat. KA-1697 "I YCAR YCAR SUPER SIMPLE MODEM YCAR rTRANSISTOR, FET AND Ref: AEM Sept 1986 YCAR YCAR Due to customer demand, we have decided to Introduce this Into our range. It's very cheap ZENER TESTER YCAR and It works well. Kit Is suppl1ed with RS232 female connector and all other parts except YCAR power pack. which Is extra $13.95 (Cat MP-3020) Ref: EA Feb 1988 YCAR Revamped version of an oldie. Checks transistors, fets and \.. Cat KM -3046 YCAR zencrs as well as checking transistor breakdown voltages. YCAR YCAR Great for the workbench, and also for showing how '!'CAR semiconductor devices operate. Complete kit Includes box, r LOW OHMS ADAPTOR FOR DMM's YCAR meter, transformer and all parts. 'l'CAR Ref: Silicon Chip Feb 1988 -...cat. KA· 1698 ,J YCAR Another handy kit from SC which utlllses your digital multlmeter. YCAR .... Cat. KC-5023 '!'CAR ~ ELEPHONEINTERCOM YCAR "I Ref: ETI Feb 1988 '!'CAR rMODEM END OF FILE INDICATOR '!'CAR Use 2 old telephones to make an intercom. Kit includes 'l'CAR power supply, filter capacitors, box and all parts. Ref: Silicon Chip Feb 1988 YCAR PC board and all parts supplied Including switch. • CaL KE-4731 '!'CAR Cat KC-5024 YCAR "YCAR YCAR rDOOR MINDER ULTIMATE CAR BURGLAR ALARM 'l'CAR YCAR Ref: Silicon Chip Feb '88 Ref: Sllcon Chip Feb '88 'l'CAR 9V power supply New gcnerat1on door opener alarm. Includes flashing light switch, back-up battery and lgn1tlon ldller. '!'CAR Cat MP-3010 $18.50 Cat KC-5020 YCAR Cat KC-5021 Extras - Siren Horn Cat. LA-5700 $26.50Screamer Plezo Cat. LA-5255 $17.95 ~ 'l'CAR '!'CAR 'l'CAR Push Button Wall Mount 'l'CAR 6V 2400 rpm Cassette 500mW <at> 6V Audio Ampli'l'CAR '!'CAR Phone with AM/FM Radio! Player Motor fier under $4! 'l'CAR Scoop purchase prical An AM/FM radio w~h good tone that YCAR That's right! A SIX TRANSISTOR 112 watt amp for the cost YCAR mounts on the wall (kitchen or garage ideal). When the SCOOP BUY! of two hamburgers I It has a two transistor tape preamp which 'l'CAR phone is answered the music mutes out. You can even put This motor measuring 38 dia and 35mm long (plus shall is NAB equalised and a 4 transistor power amp. It has '!'CAR the music on the line if you need to put the caller on hold I 10mm long) has high torque, modest current consumption. facilities to take line level inputs. The (irregularly shaped) '!'CAR (Requires 3 x AAA batteries nOI supplied). '!'CAR It is ideal as a cassette deck replacement motor. It is very board measures roughly 110(L) x 48(W)mm. Each amp Cat. YT-7072 YCAR high in qual~y - the molor itself is rubber mounted into an comes with complete schematic and conneclion diagram. (2 '!'CAR outer case, with screened power leads. required for stereo). STAGGERING VALUE '!'CAR Ideal also for toys, robotics, etc. Cat. AA-0290 YCAR Cat. YM-2702 {CAR $39.95 {CAR {CAR fCAR '!'CAR 10+ 95e ea ,, {CAR fCAR CATALOGUE $165.00 $21.95 $55.00 $85.00 $29.95 $ ... $59.95 $37.50 9 9 5 $79.50 ONLY $1.00 ea $3.95 ea ,,,,,,.,.,- / 1 CAR {CAR ,CAR {CAR ICAR {CAR fCAR {CAR {CAR fCAR {CAR {CAR {CAR fCAR (CAR (CAR fCAR fCAR 1 CAR 'CAR tCAR 'CAR 'CAR 1 CAR 'CAR 'CAR 'CAR 'CAR ' CAR 'CAR 'CAR 'CAR 'CAR 'CAR 'CAR 'CAR HAS THE JAYCAR CATALOGUE (that was inserted in this magazine) GONE MISSING? GET YOUR COPY FROM: ANY.JAYCAR STORE• FREE 'CAR 'CAR 'CAR WITH ELECTRONICS AUSTRALIA AND SILICON CHIP 'CAR 'CAR MARCH ISSUE OR SEND $2 TO PO BOX 185 CONCORD 'CAR 'CAR 2137 AND WE'LL POST ONE TO YOU. 'CAR 'CAR 'CAR 'CAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYC, 'CAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYC, 'CAR JAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCARJAYC 'CAR . . . _ ~ , - , . ,u_,.,..._._,.,. u..uru n uvl"&..e .LA..l.l.C..A.. IAVl"'AO 1 ~ IA\ll"A..C..JA.ll/"AD IA\ll"A..Q .1.A.Yt"'AP I AVCAQ IOYCA.A IAVr.AA IAVr.AA IAVr.AA IAV("AQ IAVl"AD IAVf'AO IAVr .Jr\ T l..,., 1-\ n .JM. T VM.n Wl'\ T \J M.rl Wl'\ll,,,.,l'\ll ,JI"\[ v .... ,, ,.,,... , ....,,... , '..,,.. , ....,, " ' ... . , ' ..... .... - ·. ' ..., , • . • - · .. ... , ••• -· •• - · •. • - · . . -· . -· JAYCAR JAYCARJ AYCAR JAYCARJAYCARJAYCAR,IAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCAR J JAYCARJAYCAR JAY CARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYC~RJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCAR. JAY( JAYC JAYC JAYC JAYC JAYC JAY( JAY( JAYC JAY( JAYC JAY( JAY( JAYC JAYC JAY( A very well-known Australian manufacturer of modems came to us with a problem. They h~rt ~ smallish number of their No.1 selling Intelligent Modems left from their final productioo run. JAY C (The product was being discontinued because their upgraded 1988 model intelligent modem is fitted in a smaller more attractive case. JAV( They were anxious to clear the old stock to make way for the new. To be frank, however, there is a snag even though It is in reality a very small snag. What is it? , ,\Y( HAYES COMPATIBILITY. 'Hayes' command protocol is used by the Intelligent modems to communicate with each other. The problem is that this intelligent modem only uses a subset of . AV( the Hayes command protocol. (This can be likened to IBM 'Clone'-type computers. Most are not 100% IBM software compatible. They work well anyway). AYC Mind you, the above is only a problem ff you were, say a bank or large corporation trying to use this modem to receive information at high speed from their intelligent modems I . ..\V( ..,t\V ( BUT ff you use It as an ORIGINATE modem i.e. as a house user/hobbyist etc., it is perfect! WE GUARANTEE THAT. .,,\V( This is a wonderful opponunhy to buy a high speed (1200 baud FULL DUPLEX) modem with auto dial/auto answer FOR THE PRICE OF A LOW SPEED DUMB MODEM I ..,,\V( REMEMBER the only drawback is that it will not ALWAYS work with 'sman' software but will always work In the terminal/Viatel mode. j:., y( We have purchased this product FAR BELOW manufacturers factory cost. Massive savings are being passed on. This price is 112 the price shown in our 1987 catalogue I A condition of ., AYC purchase was that we did not reveal the manufacturer's name, but you can always make an Average guess I ..,AV { SPECIFICATIONS:• Speeds 300 baud full duplex 1200/75 limited full duplex 1200 baud full duplex (option)• Data Standards .AYC .,WC CCITT V21, CCITT V23, Bell 103, CCITT V22 (option) Bell 212 (option)• Interface CCITT V24 (RS232) • Data Format ; AY C Asynchronous• Diagnostics Analogue and digital \oopback • Filtering Dighal, no adjustment crystal locked • Power 240V AC . AYC 12 wans • Transmit Level -10d8M/600 ohms• Receive Senshivity-40dBM • Receiver Tolerance ±16Hz , AYC • Modulation Frequency shift keying Phase shift keying (with V22 option)• V21/V22/V23 (1200/ 1200 option fitted) . A V( Cat. XC-4834 ; AV( CELEBRATION INTELLIGENT MODEM PRICE SLASHED!! SAVE OVt:R 50% WAS $699 NOW ONLY JAV( $349 .AYr . AYC LED and HOLD ER FOR PCB MOUNTI 10mm DIRECT IMPORT SAVES YOU MONEY 10mm LEDs - NOW AT AFFORDABLE PRICES Red Cat. ZD-1956 Green Cat. ZD-1957 Yellow Cat. ZD-1958 Orange Cat. ZD-1959 (NEW) · . These are basically a 5mm LED mounted in a plastic houstng specifically designed for PCB mounting. Available tn the 4 standard colours. Red Cat. ZD-1780 Green Cat. ZD-1781 Yellow Cat. ZD-I782 C range Cat. ZD-1783 ~ 232 !S9m-n1 I ~ I~__)_ rL ~ Ll - r l15mm) I I 020'' rci.smm1 , J .~ .100.. {2.54mm l 10 up 42~ 350 [8 9 mm-, - -,--~ 1as . ALL THE SAME PRIC 48 <: ea WAS $1.95 ea NOW $1.50 ea 1 J I+ ' -~ {3.2mm•O 5mm , rs,m,o, (5.0mm·0 Smml ,AYr JAYI JAY : JAY! .AYI ..,AYr JAY1 , AY· , AY JAY JAY JAY JAY , AY . AY .JAY ,JAY .,AY ,, AY ,. AY ,,J AY .JAY ,AY .AV cAY , AV .AV . AV J AY ; AY . AY 10 up $1.30 ea .AY LOWER PRICES ON ULTRA BRIGHT LEDS DIRECT IMPORT SAVES YOU MONEY (ALLRED) WAS 200mCd Cat. ZD-1790 99t 500mCd Cat. ZD-1792 $3.75 10 up 70~ $2.50 10 up 90t ~i% ••t---A••···· JA\ '!~ ~ !~ ~ ////////////////////////////////////////////~////////////////////////////////////////////////////////////////////////~///////////////////////1; fr~~~,~ ~ ~SYDNEY - CITY ~ 1 ~ ~ ~CONCORD •· I ~ % ....._~. . . .,_,....,..,.;::...;:;,aJ~HURSTVILLE % % . _ • ~., ,.-_,., I 1 ~ CARLINGFORD . % - ~ ~ o ~ · ·· / i\ '\ !MasterCard.! _ '· ·.. i • , '·--··x .. _ / _ ~ ••-■■■ll■il ~ VISA AMERICAN ~--••■ EXJ>Aess ~ <at>:'«ff~ , eo,rr """"G $5 $10 $25 $SO $9.99 $24.99 $49.99 $99 _99 s ~GORE HILL 1/, . 2.00 $3.751/,BURANDA $ 4.50 % $G.SO~ OLD ~ HEAD ~ 115 117YorkSt.(02)2671614Mon-Fri 8.30 - 5.30 Thurs 8.30 pm - Sat 9 - 12 Cnr.Carlingford&PennantHillsRd(02)8724444Mon-Fr, 9 - 5.30 Thurs 8.30 pm- Sat 9- 2pm ~ ~ ~ 115ParramattaRd(02)7453077Mon-FriB.30-5.30-SatB.30-12 121ForastRd(02)5707oooMon-Fri9-5.30Thurs8.30pm-Sat9-12 '"'~"""' ~ ~ ~ l!1 ~ ~,,,,_,oo,., 1"1 oDmo- Mon-Fri 9 - 5.30 Sat 9 - 4pm 144LoganRd(07)3930777Mon-Fn9-~30Thurs830-Sat9-12 ~ ~ ~ ~ OVEA$100 $10.001/, MELBOURNE-CITY Shop2,45ABeckattSt c,ty(03) 6632030 ROAD FREIGHT Mon-Fri9-5.30Fri8.30-Sat9-12 1/, IN A~~iR~t1~Ri 350 1/,SPRINGVALE VIC ~~wdku{<at>r{q«'~- MAIL v1l Ry;~otrP Parramatta Road Concord2137 (02) 747 2022 Telex72293 FACSIM I LE (02) 744 0767 MAIL ORDERS p O Bo, 185 ~ A, ~ A\ ~ A\ ~ !~ ~ A\ ~ A' ~!; ~ ,, ~ A'. ~ AA' // ~ :: Concord 2137 HOTLINE (O ) 2 7471888 FOR ORDERS ONLY TOLLFREE ~ , ~!, (OO 8 ) O22888 ~ A' .ffij H~~ J"-~~---(g~{q({{«~t; 887-889SpringvaleRoadMulgrave(03)5471022 9 0 0 Ncfiro°ERd ~ OFFICE 12 JAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCAf JAYCAR JAYCARJAYCAR JAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCAf JAYCAR JAYCARJAYCAR JAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCARJAYCAR JAYCAF • A baffling exercise It was the Count of Monte Cristo who, prompted by his creator Alexander Dumas, made the profound observation that, "Only he who has known the greatest sorrow can know the greatest joy." After battling with a particularly stubborn video recorder recently, I felt the same way. Fortunately, my first story did not cause all that much frustration. It concerns a Toshiba colour TV set; a model C-1416, 33cm set of some five years vintage. The job started out as a fairly routine assignment but caused some head scratching at one stage. It started off with a phone call from a new customer who, after describing the make and model of the set, complained simply that it had stopped. I tried a few discreet questions to get some idea of what I might be up against, but quickly realised that this wasn't getting anywhere; the set had stopped and that, as far as the customer was concerned, was all there was to it. All I could do was suggest that he bring it into the shop. So it was that he turned up at the shop a couple of days later and sat the Toshiba on the counter. I plugged it in while he was there and confirmed that, at least as far as he was concerned, the set was totally dead; no picture, no raster, no sound. But it wasn't totally dead to my ears, because I could hear the power supply hiccuping away merrily, suggesting an overload which it didn't like. I am not very familiar with this particular set but there were a couple of points in my favour; I had a service manual and, when I came to work on it, I found it a lot easier to get at than many designs I could mention. The circuit was well laid out and easy to follow, and appeared to be a fairly conventional arrangement. As I said, it all looked fairly straightforward. Likely suspects With symptoms like this the two areas I first suspect are the power supply and the horizontal output stage. The power supply was fairly typical; a switchmode arrangement running from a bridge rectifier connected directly to the mains. Much the same applied to the horizontal output stage; a horizontal driver transistor, Q402 (2SC2482), driving __ PIN 1, LOT T461 .JLf\_ ......,. / 890VP-P C464 560pf C463 .0022 2kV Fig.1: horizontal output stage of the Toshiba model C-1416 TV set. Note the protective resistor and diode built into the 2SD896 transistor. 50 SILICON CHIP the horizontal output stage (Q404) via a transformer (T401). The horizontal output stage was a 2SD869, a transistor with built-in protection (ie, a resistor from the emitter to base and a diode from collector to base). The main HT rail was shown as 114V, which was applied to pin 3 of the horizontal output transformer, then from pin 1 to the collector of the aforementioned 2SO869. That much digested I decided to measure the HT rail, which can often provide a clue as to the likely culprit. It turned out to be well down, around 50V, and I mentally filed this figure for future reference. At this stage it was a toss-up whether to move to the right of the circuit, towards the horizontal stage, or to the left towards the power supply. Fully aware that Murphy would be lurking around the corner, to make sure that which ever way I went would be the wrong way, I took a punt on the output stage. Well it seemed that Murphy must have slipped out for a cup of Irish coffee, because that was the right decision. In greater detail I simply disconnected the output transistor. These transistors are not the easiest to test, since they tend to show a low resistance from collector to base, regardless of polarity, due to the protective diode. Similarly they show a low value resistance, ranging from about 400 to 900 according to type, between base and emitter. Granted, one can allow for these characteristics but it is usually easier to simply fit a new transistor. But, before fitting a new one, I switched the set on with the original one removed. I wasn't quite sure what kind of a HT reading I would get, but I hoped it would come up to something near normal, if the transistor had been faulty. On the other hand, there was a risk that it might go high and trigger any over-voltage protective circuitry. Once again, it seemed that I had done the right thing because the HT rail came up almost spot on the circuit value. It seemed that it was my lucky day; I should have the job knocked over in short order. All I had to do was fit a new transistor and we should be up and running. It must have been around this time that Murphy finished his coffee and came back on duty. I switched the set on, full of confidence, only to find that it was in exactly the same condition as before; power supply hiccuping and low HT rail. Somewhat taken aback, I reached for the CRO leads and made a quick check of the signal from the driver stage, through the driver transformer, and to the base of the output stage. As nearly as I could tell, allowing for the reduced rail voltage, this section appeared to be functioning. At that point the only logical thing I could think to do was to take the new transistor out, check the HT rail and power supply behaviour again, and try to decide what to do next. And that operation produced surprise number two the rail voltage had risen, but not all the way; it was now sitting at around 75V. What the heck was going on? Smoke signals I double checked the connections to the transistor, confirmed that they were correct, and began looking for any other silly mistake I might have made. I found nothing, but had left the set running during those few minutes. Suddenly my nose told me that something was getting hot somewhere and a few seconds later I pinpointed the source. A thin curl of smoke was rising from a capacitor which forms part of the output stage assembly; C464, a 560pF, 2kV unit connected between the collector and the emitter of the output transistor. It was a blue plastic encapsulated unit which had suddenly developed a brown spot that grew larger as I watched it. Well, that was the breakthrough. I pulled the capacitor out and then, before refitting the output transistor, turned the set on and checked the HT rail again. And this time it came up just above the nominated value, exactly as it had done the first time. Which I reckoned proved the point. At a more practical level I needed a replacement capacitor. My stocks didn't run to an exact replacement, but I did find a 560pF unit with a 3kV rating. This was fitted, the original output transistor wired back in, and the set given another try. And this time everything worked; the set gave forth sound, the HT rail came up spot on, and a first class picture appeared as the set warmed up. So that was that and the set was duly returned to a happy customer. But it is worth speculating on what caused the sequence of events just related. Fairly obviously, the capacitor was faulty all along, being unable to withstand the peak level of nearly 900V generated by the output stage, and pulled the HT rail down accordingly. But with the output stage removed no such voltage was generated, and all it had to withstand was the 114V from the HT rail. Initially, at least, it was able to do this but it must have been on the point of breaking down completely. My test run with the replacement transistor must have been the last straw; by the time I tested the set without the output stage for the second time, it was breaking down at 114V and went up in smoke. Which is all very satisfying from a technical point of view, but most of my diagnosis was wasted; a few more minutes running on the bench would have produced the curl of MARCH 1988 51 SERVICEMAN'S LOG smoke and revealed the fault with no effort on my part. That's the luck of the game and it had a happy ending anyway. A failure to erase My next story involves a much more frustrating experience. It concerns a Sanyo beta video recorder, type VTC 5005, that belonged to a regular customer. The first intimation of the trouble came via a phone call from the lady of the house. The fault was rather unusual in that the machine would record the video signal satisfactorily but, on odd occasions, would fail to record the sound or erase any previous sound track. She went on to enquire whether this was a common fault, whether I knew what would cause it, and, of course, was it going to be expensive to fix. I had to reply that it was a fault I had not encountered before, that I could only assess the likely cause in broad terms, and that it was almost impossible to estimate the cost. However, I did promise not to let costs get out of hand without consulting her. In the meantime I suggested that she bring the set in. So the lady turned up at the shop a couple of days later with the machine and, commendably, she had thought to bring a faulty tape with it. In the event it didn't help a great deal, except to confirm the symptoms she had described, but even that was useful and I wish all my customers could be so thoughtful. I tried the machine while she was there, but I need hardly add that it behaved perfectly. This surprised neither of us. I have not had much experience with this machine, but I do have a manual and I fished this out immediately. In particular I concentrated on the section designated "VD-1 Audio Circuit"; the section which handles the audio signal taking it from the record/replay head, or feeding it to it, as required - and which also incorporates the bias and erase oscillator. It was this latter which interested me most because it was this function that was failing somewhere along the line. But exactly where was the real question. It could be in the oscillator itself, it could be the erase head, or it could be the flexible lead and plug and socket which connects the head to the board. The record/replay head seemed an unlikely suspect, in that there had been no replay problems as such. And if the bias line to this head had failed somewhere on the board I would have expected that the system would still erase, but fail to record anything but a weak and distorted signal. So the odds were strongly in favour of a failure within the erase circuit, or failure of the oscillator itself. :~-. ,. ~ ...-......,.~ 1\-\~'s ~E LUC.Ko~ "Me: GAME. & \T ~~b F\ l'\A1)P'f e.rJl>\NG ~N'(W~'l ... 52 SILICON CHIP ~~ But I needed to be sure. And when you think about it, this isn't an easy function to monitor. Simply letting the machine run in the record mode is of little value, since any failure will not be apparent until the tape is replayed, by which time the fault will most probably have vanished. But, in any case, the time involved in such an approach would be quite unacceptable. As depicted on the accompanying circuit the erase/bias oscillator (near the bottom) consists of transistor Q2007, transformer T2001, and a few minor components. The secondary of T2001 feeds the erase head directly from pin 5, and supplies the bias for the record head from pin 6, via C2027 and tab pot VR2003. The erase head is connected via plug and socket S2002 and the record/replay head via S2001. Fortunately, the circuitry involved is fairly easy to reach. In fact the audio circuit, as shown separately in the manual, is really a part of the complete video/audio board, and the print side of this is directly accessible when the main covers are removed. After that, removal of a few screws permits the board to be swung up, giving access to the component side. For a start I set the machine up in the record mode and connected the CRO to the active terminal of the erase head, this being about the most convenient access point. This confirmed that the oscillator was functioning, at least for the present, so I decided to leave it running in this way, while I went on with other jobs, simply glancing at the CRO from time to time to check what was happening. Initially, this approach paid off. After it had been running for some time I checked the CRO and realised that the erase signal had vanished. Unfortunately, before I could make any further tests the system came good. I wasn't too worried at this stage; I blissfully imagined that, since the fault was obviously in a mood to happen spontaneously, a little prodding, freezing, or heating would encourage its reappearance. I should have known better. I tried every trick in the book; I froze every component likely to be involv- .-----------------------------------■ ..---------il----> R2001 C2009 L?K I AUDIO IN I GNO 0 -L?µ/16 I R "'8al I >- a: "'"' 52001 -- H ... 2 : R-iN~EAD R-P HEAD 02001 2so1011 SWITCHING Q2002 2501011 SWITCHING u "'"' 2~ 3-- h I a- 20 22K R203', ~ Q.1 (0) a/ ?: I (8 -L) Q2003 2SC945 SWITCHING -T ,R r2001 ~~µ" i2 03? 02006 2SC2603 SWITCHING c~~ '"''N' REC/ PLAY OUTPUT LEVEL (0-2) ' -v TP2001 ,02 1 I --- ,..,____-+____,·,~~<. >"' R2036" 8.2K ijg o,- ~ iL u a: r P12002 R2039 R2038 'OK 10K - 02004 2SA1016 SWITCHING g~io1 2SD43B ------------------------------------ Fig.2: relevant section of the audio circuit of the Sanyo VTC 5005 VCR. Note the erase head plug at bottom left. ed and blasted the whole area with a hair dryer. I tugged the leads, wriggled the plugs and sockets, and prodded every component with everything short of a sledgehammer. Nothing produced the slightest hint of a fault. Had I not known better, I would have been prepared to swear that there was absolutely nothing wrong. All I could do now was to continue the tests as before. And this I did, for several hours each day for the next couple of weeks. But not once did the CRO pattern so much as flicker, even though I repeated some of the previous brute force tactics from time to time. It was a stalemate. I would have been happy to leave things set up for as long as was necessary, but this would hardly suit the customer. In fact they had already made a couple of polite enquiries and I sensed that they were becoming impatient. Among other things, I realised that they used the machine more for playing prerecorded tapes from the video shop than for recording off-air programs. The upshot was that I explained to them what I had discovered so far [which wasn't really very much) and that, until the machine elected to fail again - which it appeared to be stubbornly refusing to do at this stage - there was very little chance that I could make any progress. So it was agreed that they take the machine away and make such use of it as they could, until such time as the fault worsened. Weeks went by, then several months, before I saw them again. Then the lady contacted me with a completely different problem and I took the opportunity to enquire about the recorder. "Oh, it's going fine", she replied, "whatever you did seems to have fixed it." I know the feeling: after that length of time I could almost kid myself that I had done something to fix it; almost, but not quite. Deep down I knew it was only a matter of time before the gremlin would strike again. But more months went by and a couple of discreet checks on my part produced the same answer, "It's going fine. " Then came the day when the lady was on the phone with a tale of woe. "The recorder is really playing up now. It is almost impossible to record anything." This was the best news I had heard about the machine so far and my enthusiasm probably showed when I suggested she bring it in immediately. She lost no time in responding. Before disturbing anything I loaded a tape into the machine and made a brief test recording. Sure enough, the fault was there. So, very gently, I removed the covers and connected one of the CRO probes to the active lead at the audio erase head. This confirmed that the fault was still present and I reached for the second CRO probe with the idea of checking progressively along the board. At which point the system suddenly came good and there was no more I could do until it decided to play up again. Fortunately I didn't have to wait very long. When it failed this time I very gently removed the necessary screws and lifted the MARCH 1988 53 SERVICEMAN'S LOG board so as to provide access to the component side. This didn't disturb anything and the fault remained. I reached for the second CRO probe and approached the print side of the board in the vicinity of the two pins which mate with socket S2002, and which carries the leads to the erase head. By just touching the board, and before I could make an electrical connection, I cleared the fault. Suspect plug and socket I immediately suspected the plug and socket assembly, and this seemed to be confirmed when I wriggled the lead and the plug and found that, by stressing the assembly in a certain way, I could make the fault come and go. At last it looked as though I was getting somewhere. In this setup the plug on the lead is actually the female connection, the male contacts being two pins soldered into the board. I was specially suspicious of the female contacts, particularly where they made contact with the cable. This is a crimped connection and it is not 54 SILICON CHIP unusual to find the crimping does not penetrate the insulation properly, resulting in an intermittent connection. Removing contacts from plugs of this type is a little tricky. They are held in by a small tongue or barb punched into the contact, and which is depressed when the contact is inserted into the plug. It springs up when the contact is fully inserted and effectively locks it in place. To remove these I use a long, thin, pointed probe with which to TETIA CORNER Thorn 9904 (Q Chassis) Symptom: No luminance . Sound and colour OK. A normal picture appears briefly if the set is switched on again quickly after switching off. 12V rail reads high at 15.5V. Cure: D231 (EQA01-12S) 12V zener diode open circu it. This diode sets the 1 2V rail and the higher voltage when it fails blanks the video output from IC201 . depress the tongue and thus allow the contact to be withdrawn from the back of the plug. With both contacts out I examined them carefully. As far as I could see they were quite OK, but I also checked them with an ohmmeter. Again they seemed faultless, even when the wires were vigorously tugged and wriggled. Nevertheless, I put them through my own "extra crimping" process. This involves applying pressure to the stem of the contact, in the valley where it is supposed to punch through the cable insulation. To do this, I use a pair of cutters, with one blade lying the length of the valley. I know it sounds drastic, and it certainly looks risky, but it is merely a matter of applying a judicious amount of pressure. And it does work. But it didn't help much in this case. I re-assembled the plug, fitted it back on the board and gave the whole setup another wriggle test. It behaved exactly as before; pressure on the plug or tension on the cable could make the fault come or go. And, since I felt that I had cleared the plug, the next likely suspect was the pair of pins on the board. Conned I examined the joints where these pins were soldered to the board, even though I had already been over them once before, but could see nothing suspicious. Nevertheless I resoldered them, just to make sure. But this achieved nothing either and I was forced to the conclusion that there was probably nothing wrong with the plug, socket, and cable assembly; that I had been conned by their sensitivity to pressure. And I had been conned in more ways than one. It had seemed so obvious that this was where the fault lay that I hadn't even bothered to make the other obvious check which I had set out to make at the beginning; whether the oscillator itself continued to function when the waveform vanished from the erase head. I quickly made amends, connecting the second CRO probe directly to the oscillator circuit. Then I wriggled the plug and socket assembly again, created the fault, and established that it was the oscillator that was failing, not the circuit to the head, in spite of the symptoms. That much established, the next likely possibility seemed to be a faulty component in the oscillator circuit and, by now, I would have been quite happy to replace every component in this part of the circuit if it produced a quick cure. After all, there was only one transistor and a handful of resistors and capacitors. The transformer, T2001, was about the only special item. But before taking that drastic step I decided on another freeze, heat, and bash routine. After all, the thing was much more touchy now than it had been when I tried this before, and it might just work. And so I set to, with the machine in the record mode, both CRO probes connected, and the fault condition evident, this having been achieved by much wriggling of the aforementioned erase head plug. I drew a blank with the freezer, and similarly with the heating, so I reached for the sledge-hammer actually the butt end of an insulated alignment tool - and began prodding. Nothing happened until I came to C2029, a 100µ,F 16V electrolytic, when the lightest touch caused the oscillator to come good. Which was very encouraging, except that no amount of additional prodding, freezing, or heating of this component could reverse the procedure. So what did it mean? Was the capacitor faulty, or was this another furphy like the erase head plug where, apparently, vibration and pressure was being transmitted to the fault somewhere nearby on the board? In any event, it seemed logical to remove the capacitor, check it as thoroughly as possible and, if any suspicion remained, replace it. But it didn't come to that because, as I unsoldered one of the lugs, the solder came away much too readily and I was convinced that I had uncovered a dry joint, one that had defied my visual inspection. Closer inspection of the lug confirmed my suspicion. It had been tinned during manufacture but I was convinced that the solder on ... the board had never really "wet" it. Most likely it was a "cold" joint; one where the temperature of the lug had never reached the melting point of the solder. I measured the capacitor as a matter of course, and it was well within tolerance. I cleaned the lug, tinned it again, put it back on the board, and made sure it was well and truly soldered to the pattern. Then I checked the whole system again. I wasn't really surprised when it came good immediately, because it had done that many times. But I was gratified to find that wriggling the erase plug no longer had any effect. Considering how touchy it had been before, I felt it was very significant. But there was more to it than that. The capacitor's position on the board was slap alongside the two pins which mated with the erase plug. So wriggling the plug could easily have aggravated a dry joint at the capacitor lug. I ran the machine for several hours a day for a week or so after that, and it never missed a beat. Of course it had done that before too, so I couldn't be one hundred percent sure that I had fixed it. The only thing I felt sure about was that I had found a dry joint, even if the only evidence I had was my own observation when I unsoldered it. And so the machine was returned to the customer, with a strong emphasis on the need to contact me immediately should the fault show again. Thafwas several months ago and a couple of check calls have confirmed that there has been absolutely no sign of the fault. Only time will tell though. I'm keeping my fingers crossed. ~ RCS Radio Pty Ltd is the only company which manufactures and sells every PCB & front panel published in SILICON CHIP, ETI and EA. 651 Forest Road, Bexley, NSW 2207 Phone (02) 587 3491 for instant prices 4-HOUR TURNAROUND SERVICE MARCH 1988 55 OLD-'I'I M f. CRYSTAL DXing with a crystal set can be a lot of fun. This old-time crystal radio comes as a kit and delivers a performance that will surprise you. By JOHN HILL The story of this old-time crystal radio begins in the Victorian city of Ballarat. Like many towns these days, Ballarat is chasing its share of the tourist dollar and offers many first-class attractions for the tourist to see. The latest addition to Ballarat's sights is something that should be of interest to SILICON CHIP readers, especially those old enough to remember the early days of radio. Ballarat now boasts the Orpheus Radio Museum which is full of 56 SILICON CHIP fascinating electronic relics from the past. However, the premises are not used solely as a museum. In a separate factory area at the rear, museum owner Richard Wilson has a workforce of approximately 20 employees producing computer equipment and other hi-tech electronic gear under sub-contract, as well as their own products marketed under the "Atron" tradename. An unusual aspect of the 10 business is the production of vintage radio kits which are sold through the museum and by mail order. These kits include a 1-valve receiver, a 2-valve receiver and a "Super Crystal Set". Both of the valve radios are battery-operated "reaction" types. The crystal set The Super Crystal Set is of particular interest and is based on an early Navy circuit which is most efficient. I have built this set and its performance is so good I had difficulty in believing the station call signs I heard. Any crystal set that can separate about 15 stations and pull in interstate transmissions at listenable volume is a mighty fine design. I might add that this remarkable performance was possible even with a local 5kW station only 6km away. Without that local station, the t::o------c ,11 I ~ E .__---~· # START ) S1 CJ HIGH Z PHONES I T EARTH SUPER CRYSTAl SET Fig.1: unlike other crystal sets, this design has two separate tuning circuits with variable inductive coupling (via L2). Result - greatly improved station selectivity. ◄ The Super Crystal Set control panel is well laid out. Black bakelite , brass fittings and gold lettering give the receiver an authentic vintage radio appearance. Super Crytal Set would perform even better. Personally, I relate rather well to crystal sets, for it wa s these simple receivers that fostered my interest in radio some 40 years ago. I built them in all shapes and sizes, including some in matchbo xes. However, I was always restricted to one station listening. As I lived in Bendigo at the time, 3BO was all I ever heard on any of my crystal sets. My crystal sets were set up in my bedroom and I would often go to bed early and lay in the dark with the headphones on and listen for hours. I did a lot of listening to crystal sets simply because they were all I could afford at the time. Yes, I have very fond memories of my home made crystal receivers. Getting back to the Super Crystal Set again: it is available in kit fo rm and is very well presented. The kit is complete and comes with a bra ss stud switch, a headphone jack, and every nut, bolt and washer - in short, the lot! The front panel and baseboard are pre-drilled so tha t the set goes together with a minimum of fuss. This end of the set tunes the radio frequencies before the signal is fed to the detector. The small tuning capacitor at right is the author's modification Spiderweb coils Construction of the Super Crystal Set is quite intricate and it takes a good many hours to build. It requires the winding of thr ee The detector end of the set is fairly conventional. The small white spider web coil is the "swinging" coupler that varies the coupling between the two sections of the receiver. M ARCH 1988 5:7 Crystal sets require high impedance headphones hut you can also use low impedance phones provided you use a matching transformer. Shown is an old STC headset. This has an impedance of 2000 ohms and is guaranteed to put callouses on your ears within one hour. "spiderweb" coils, two of which are tapped. One coil is of the "swinging'' variety and is used to vary the coupling between the two stages of the receiver. These two separate stages in the receiver require further explanation. Most crystal sets have a single tapped coil and a tuning capacitor to select the stations. Such a set-up usually gives very broad tuning and if there are a number of strong local stations, as is the case in capital cities, then the set may not be selective enough to separate each signal without interference. The Super Crystal Set is not like this. It has two separate tuning circuits that are connected by a variable inductive coupling which also helps to make the receiver very selective. In other words, the set has a tuned radio frequency (RF) stage before the detector, with the two stages inductively coupled by a high-frequency transformer (the swinging spiderweb coil). Such a circuit design has a dramatic effect on selectivity, with very little loss in volume. Tuning the Super Crystal Set is a two-handed job since each circuit must be tuned separately (no fancy ganged capacitors back in the good ol' days)! The RF circuit is tuned with a brass stud switch, while the detector circuit is tuned with a variable capacitor. The brass stud switch is connected to the aerial coil which is tapped every eight turns. This eight turn tapping set-up proved to be interesting in the set that I built. Some stations were received at equal volume on two adjoining studs, indicating that the true resonance point of the coil was midway between the studs. I reasoned that a bit of fine tuning could perhaps make this excellent receiver even better. To eliminate this slight error, a small variable capacitor was added to the radio frequency circuit in order to smooth out the courseness of the 8-turn tappings. The addition of this capacitor was so successful it almost doubled the number of stations received. Note: this small capacitor is not included in the kit and w_a s strictly my own experimental modification. If you wish, you can do exactly the same. The variable capacitor is shown by the broken line on the circuit diagram (Fig .1). The general appearance of the Super Crystal Set is most pleasing to the eye. The kit has been designed in keeping with the early radio scene and all fittings are made of brass and black Bakelite. The assembled components are mounted on a stained and polished baseboard. Gold lettering on the front panel adds the finishing touch to a well-presented product. Lacquering of the baseboard is the or.ly preparation required by the constructor before assembly. No cat's whisker Anyone familiar with crystal sets will recall how tedious it was to This back view shows the complexity of this particular crystal set. Quite a few hours are required to assemble the kit. 58 SILICON CHIP find a "good spot" on the crystal and how easy it was to bump the cat's whisker off that good spot once it was found. The Super Crystal Set solves that problem by using a fixed detector which takes the form of a good-quality ger- manium diode. Mounting the diode inside a fibre tube makes it look a little more authentic. Actually, the gold-bonded diode is the secret to the set's success. If a real crystal detector were used, it would reduce the receiver's sensitivity. One novel aspect of a crystal set is the fact that it costs absolutely nothing to run, as it utilises the radio frequency energy that's picked up by aerial. Of course, the aerial must be long enough to collect sufficient energy to operate the set. A suitable aerial should be in the vicinity of 30 metres long and as high as it can be conveniently strung. An earth connection is also a must for good crystal set reception. My aerial is a single strand wire that is approximately 25 metres long and six metres high. Such an aerial is only average in crystal set terms, but the reception I obtain is the best I've ever experienced. On a good night I can pick up two Adelaide stations (5AN and 5CL), two Melbourne stations (310 and 3AR), one Sydney station (2BL), and one Queensland station (4QD). The latter is about 1,500km, as the crow flies, from my home in Maryborough, Central Victoria. If anyone had told me that a crystal set could do that prior to my building the Super Crystal Set, I wouldn't have believed them. The Super Crystal Set is well named it really does give super results! Headphones The sound reproduction from the set is also surprisingly good and the tonal quality quite acceptable through either my Brown or STC headphones. Although phones such as these are designed for maximum sensitivity rather than hifi reproduction, they aren't too bad to listen to . Crystal set headphones need to be of high impedance - around 2000 ohms. If high-impedance phones are not available, low impedance phones can be matched up to a crystal set by using an old speaker transformer. These gives the advantage of more comfortable listen- ing with better tone, but a slight drop in volume is apparent. A small speaker transformer, complete with box, plug and socket is available as an optional extra if required. Those who wish to build the Super Crystal Set can do so regardless of what type of headphones they have. In these days of computerised hitech everything, it makes a pleasant change to build a good oldfashioned crystal set. There's something about going back to basics that's hard to explain. The cost of this particular piece of nostalgia is $89.50 for the kit and $5.00 for packaging and postage. Yes, I know you could buy quite a good transistor radio for that amount, but I doubt if you would have as much fun with it. Believe me, DXing with a good crystal set is pretty exciting stuff! Footnote: the Super Crystal Set is available from Ballarat Electronic Supplies, 5 Ripen St, Ballarat, Vic 3350. Phone (053) 31 1947 . Build This Old-T1Dle Crystal Set Suppliers of * R A D · I O ~ vintage wireless kits and wireless parts. RSD B98 Ballarat, 3352. Ph. (053) 34 2513 Send for a free catalogue today! WHEN NEXT IN BALLARAT DON'T MISS THE ORPHEUS RADIO MUSEUM CNR. RING RD. & WESTERN HWY. BALLARAT OPEN 7 DAYS A WEEK 10am - 5pm MARCH 1988 59 How- Do you design your own printed circuit layouts? That being the case, you need a good light box. This one is cheap, easy on the eyes and easy to build. By LEO SIMPSON At SILICON CHIP we needed a good light box. We design our printed circuit boards using Bishop tapes so we needed a light box for that. And we needed a light box for checking our wiring and overlay diagrams and for marking up all the photographs for page layouts. When we came to look at commercially available light boxes though, there were few that met our requirements. There were plenty of large commercial units, intended for use in photocomposing rooms and so on 60 SILICON CHIP and some intended for doctors' and dentists' surgeries, but few that were reasonably compact and cool and comfortable to work on. None were cheap. Most, if not all, used frosted float glass as the working surface. We did not want these. Glass light boxes often break and therefore can be a real hazard to anyone working with them. Frosted glass is expensive and inconvenient to replace too, so that was another reason not to use it. Hence, we decided to design and build our own. We are presenting the details here for anyone who needs a similar unit and who is able to handle a saw and screwdriver. The total cost is less than $70, if you buy all new materials. Essentially, all that is required is a suitably shaped box, painted white inside and fitted with an 18 or 20 watt fluorescent light batten. On top is mounted a sheet of white translucent Perspex. And that is all there is to it. · We even saved ourselves the trouble of painting it by using white Melamine-coated particle board, 16mm thick. This was cut to size, screwed together and the job was half done. We spent more time shopping for the materials than actually putting it together. To make it easy to work on, particularly if you are taping up a printed board design, we made the box with a sloping top, angled at 15° to the horizontal. At the front , to build a light box the box tapers down to 38mm, so it is quite comfortable to work on. Tools required You can get by with the very minimum of tools for this project. In fact you could manage the whole job using hand tools. To make it easier though, you will need an electric drill and a circular saw, preferably with a tungsten-carbide tipped blade. The assembly process consists of cutting the Melamine-surfaced particle board to size, drilling the holes for the screws, power cord entry and ventilators and then simply screwing it together. Glueing the box together is not practical, since the Melamine surfaces won't take glue. The first task is cut the various pieces to size. We dimensioned the box to suit a standard 18 or 20 watt fluorescent batten (batten is the term used to describe the whole fitting, including the tube) with a few millimetres clearance at each end. Just to be sure though, measure your batten before you mark up the sheet for cutting it would be most frustrating to find you had made the box too small. The top edges of the front and back pieces of the box should be chamfered to match the 15° slope of the sides. This is easily achieved by setting the baseplate of the circular saw to the correct 15° setting. With care in your saw work, all the pieces should fit together squarely with little need for work with a plane or rasp. To ensure you achieve straight cuts, use a straight edge as a guide for your circular saw. The idea is to clamp a thin straight-edged length of timber to the particle board and use it as a guide for the saw. Don't forget to drill the various holes for the power cord and ventilation. We used kitchen cupboard vents which fit in a 28mm (actually 1-1/8 inch) hole. You will need a hole saw or a Speedibore (an auger 18W FLUORESCENT LIGHT BATTEN BOLTED TO REAR »F - - - - BOX WITH TWO 5mm DIA. x 35mm SCREWS AND NUTS. SPACE BATTEN FROM REAR OF BOX BY ONE NUT THICKNESS. HOLES A: 28mm DIA. TO ACCEPT CUPBOARD VENTILATORS 8: 10mm DIA. MAINS CORD ENTRY C: 6mm DIA. REAR 130x613 A i / --1 BASE 312x613 i 130 J CHAMFER TOP EDGES OF FRONT AND REAR TO SAME ANGLE AS SIDES (15'). ASSEMBLE BOX WITH 40mm COUNTERSUNK PARTICLE BOARD SCREWS. COVER SCREW HEADS WITH DRESS CAPS. MATERIAL: 16mm PARTICLE BOARD COATED WITH WHITE MELAMIME ON BOTH SIDES. COVER EXPOSED EDGES WITH IRON-ON EDGE STRIP. COVER TOP OF BOX WITH 360x645 PIECE OF WHITE TRANSLUCENT 5mm ACRYLIC SHEET. DIMENSIONS IN MILLIMETRES LIGHT BOX 4 rv 38 Fig.1: we made our light box from 16mm-thick Melamime-coated particle board. The dimensions shown suit a standard 20W fluorescent batten but we suggest that you check the length of your batten before marking the sheet for cutting. MARCH 1988 61 The fluorescent batten is fitted to the rear of the case to give an even spread of light. Kitchen cupboard vents are used to cover the ventilation holes. bit made for electric drills) to drill these holes. When drilling these holes, drill through until the bit just breaks through the surface and then finish the hole by drilling through from the other side. This stops you making a mess of the hole and possibly tearing the Melamine surface. Finish off the sawn surfaces with a rasp or sanding block before going to the next step, which is to make the rightangle butt joints to assemble the box. The various sections are then screwed together. We used Chipboard screws (Bg x 40mm, countersunk, made by W.A. Deutscher) which have a coarse thread for good holding power. Underneath each screw head we placed the countersunk plastic washer for a white Snap Cap (decorative screw caps made by Furnco ). Alternatively, you can use Furnco Directors, which are particle board screws which are supplied with their own decorative caps. Either way, there is no need to coutertsink the screw heads into the particle board. We used fourteen screws (and decorative caps) to assemble the box. To finish off all the exposed edges of the particle board, use an iron-on Melamine edging tape (Armaflex-GL) and then trim to fit using a sharp utility knife. Now fit four rubber feet to the underside of the box so that it does not scratch or move around on the table. The next step is to fit the Perspex top. Assuming that you have made the box to the same size as our drawing, the Perspex sheet should be 360 x 645mm. We used some 3mm thick sheet we had on hand but we suggest 4.5mm material as a better choice as it will be more rigid. You can get Perspex cut to size from glass suppliers or you can go to a specialist outlet such as Cadillac Plastics in Sydney. We attached the Perspex to be top of the box using four countersunk head self tappers, 20mm long. Drill and countersink the screw holes before you remove the protective paper coating from both sides of the Perspex. Having fitted the Perspex, remove it again so the fluorescent light fitting can be installed. Remove the tube and the top cover from the batten and place it in the box as shown. Mark the positions of the mounting holes at both ends and drill the box for 5mm diameter Close-up view of the batten wiring. The mains cord should be anchored with a clamp and its leads connected to the 3-way terminal block. 62 SILICON CHIP screws. Before securing the batten, fit the cord entry hole with a junction box grommet. Secure the fluorescent batten with two 5mm screws and nuts, with one nut used on each screw to space the batten away from the rear surface of the box. You may think that a more even spread of illumination could be obtained by moving the batten more towards the centre-line of the box but we found that it gives a hot bright strip across the middle which is unsatisfactory. Now connect a 3-core mains power cord fitted with a 3-pin plug. These battens are fitted internally with a 3-way insulated terminal block for this purpose. The centre terminal is connected to the earth wire. The cord should also be anchored with a clamp. Now the cover and tube can be fitted to the batten and power applied to test it. We didn't bother to fit a mains switch on the box, by the way, as it seemed superfluous. Now fit the snap vents. Of course you don't really have to fit these but the vent holes look a bit grotty without them. You could also fit a handle to each end, to make it easier to lift. And that completes the light box. Let there be light. ~ LIST OF MATERIALS 1 sheet of 1 6mm Melamine surfaced particle board 1 18-watt fluorescent batten, including tube 1 3-core power flex and 3-pin plug 1 4 40mm x 8 gauge Chipboard screws (or Furnco Directors) 1 4 Furnco white Snap Caps size 8/8 (not necessary if Furnco Directors are used) 4 20mm x 1 0 gauge countersunk head selftapping screws · 4 rubber feet 2 5mm 20mm long screws, with nuts and washers 5 kitchen cupboard vents 1 sheet of white 4.5mm or 6mm Perspex, 360 x 645mm Miscellaneous Iron-on Melamine edging tape (Armaflex G-L) THE ELECTRON/CS MAGAZINE FOR THE ENTHUSIAST WE INVITE BECOME You To A SUPPORTER We believe that electronics is a fascinating pursuit, and the most useful hobby that anyone can have, particularly for a young person in school. Anyone with a good grounding in electronics is better prepared to meet the challenge of today's and tomorrow's technology. Because we believed that many more people should come to know about and enjoy electronics, we decided to start a new magazine expressly for electronics enthusiasts, whether they be nervous beginners or seasoned veterans. We called it SILICON CHIP, a name which focuses on the very basis of today's electronics technology. We started SILICON CHIP as an independent magazine completely free from the influence of any existing publishing company, because we wanted to establish the highest possible standards for accuracy and attention to detail. Our team is very small: founders Leo Simpson and Greg Swain, plus full time staff members John Clarke and Bob Flynn. SILICON CHIP has now been on sale for five months and has been very well received. Even at this early stage, you, the readers, have clearly indicated that SILICON CHIP is the most entertaining and best produced electronics magazine in Australia. Considering the hard work in getting started, it has been a very gratifying response. But we want to make SILICON CHIP even better. To do this, we need the resources to employ more people; we need the services of technical illustrators, writers, designers and other creative people. This is the only way that we can be sure of attaining the highest possible editorial standard. We know this is what you want. Your letters tell us. But we can only do this with your enthusiastic support. Already, many hundreds of readers have taken out subscriptions to give SILICON CHIP a solid start but we we would like to have thousands more. If you haven't already done so, please give us your vote by becoming a subscriber. By doing so, you will be ensuring the future of an entertaining, informative and independent SILICON CHIP magazine. Regular Features * * * * Constructional Projects For The Enthusiast HiFi Review Digital Electronics Course Circuit Notebook Vintage Radio Junk Mail * * * * The Serviceman's Log Amateur Radio, by Garry Cratt, VK2YBX The Way I See It, by Neville Willams Book Reviews Most magazines sell their subscriber list to mail order companies, to earn extra income. We will not do this. We will lose some money by adopting this policy but we believe that your privacy is paramount. BECOME A SUPPORTER BY FILLING OUT THE POST AGE FREE SUBSCRIPTION COUPON OVERLEAF MARCH ► 1988 63 FREEPOST SUBSCRIPTION COUPON BACK ISSUES To: Freepost 25, Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097, Australia. NO POSTAGE STAMP REQUIRED IN AUSTRALIA NAME (Mr/Mrs/Ms] ................ ................................................................... . STREET ............................... ............................................... ..... ................... . SUBURB/TOWN ........................................................ ..POSTCODE ............ . Subscription cost: 1 year (12 issues) 2 years (24 issues) Within Australia □ $42 □ $84 Overseas surface mail □ $62 □ $124 Overseas air mail □ $120 □ $240 Enclosed is my cheque or money order for $ ........ ... or please debit my D Bankcard D Visa Card No .. .. .................. ... ........ ..... ... ....... .......... ... ........................... ............ ... Signature .................................................. Card expiry date ...... ./ ...... ./ ...... . Subscription to commence in ................................................................. •• •· • GIFT 1 to: NAME (Mr/Mrs/Ms]........ .... ................. .......... ....... .. ... ........... .. ... ..... ...... .... .. Issue Highlights November 1987: Car Stereo in Your Home; 1GHz Frequency Meter; Capacitance Adapter for DMMs; Off-Hook Indicator for Phones; Your House Wiring Could Kill You . December 1987: 1 00W Power Amplifier Module ; Passive lnfrared Sensor for Burglar Alarms ; Universal Speed Control and Lamp Dimmer; 24V to 12V DC Converter. January 1988: 4-bay Bowtie UHF Antenna; Dual Tracking Power Supply; Custom Phone Ringer; Subcarrier Adapter for FM Tuners. February 1988: 200 Watt Stereo Power Amplifier; Deluxe Car Burglar Alarm; End of File Indicator for Modems; Simple Door Minder; Low Ohms Adapter for Multimeters. Price: $5 .00 each (incl. p&p). Fill out the coupon on page 7 5 (or a photostat copy or letter) and send it to: Silicon Chip Publications, PO Box 139, Collaroy Beach 2097 . STREET .. .... ................ .... ...... ....... ........................................... .. ....... ...... ...... SUBURB/TOWN ..... .. ......... .................. ....... ........ .. ....... POSTCODE ............ . Subscription cost: 1 year (12 issues] 2 years (24 issues] Within Australia □ $42 □ $84 Overseas surface mail □ $62 □ $124 Overseas air mail □ $120 □ $240 Enclosed is my cheque or money order for $ ..... ..... . or please debit my D Bankcard D Visa Card No .... ....... .... ...................... ......... .... ......... .... ..... ....... ...... .............. .... ... . Signature ............ ............ .... ...................... Card expiry date ... ..../ ...... ./ .. .... . Subscription to commence in ........................................... .................. ••••••• ·• GIFT 2 to: NAME (Mr/Mrs/Ms].... ......... ......... ........... .... ............. ... .......... .. ..... .... .... ... .. . STREET ........ ....... ...... ................. ... .................... .... ...... ........ .. ...... ......... ...... . SUBURB/TOWN ....... .... .. .......... ... .. ....... .. .......... .... ....... POSTCODE .... ....... .. Subscription cost: 1 year (12 issues] 2 years (24 issues] Within Australia D $42 □ $84 Overseas surface mail □ $62 □ $124 Overseas air mail □ $120 □ $240 Enclosed is my cheque or money order for $ ... ........ or please debit my D Bankcard D Visa Card No ...... ........... .... ........... ... ........... ... ........... ..... ... .. ........................... .... .. Signature ............... .............................. .....Card expiry date ... ... ./ .. .... ./ ... .. .. Subscription to commence in ......... ....... .............. .. ...... .... ..... ...... ................ . Note: photocopy this coupon if you don't wish to cut the magazine, or include the relevant details in a letter. 64 SILICON CHIP ~ / ::X -/ , LIMITED NUMBERS OF BACK ISSUES ARE AVAILABLE SO DON'T DELAY Electronic jargon explained ffigh, low, sink and source: What do they mean? We use the terms high, low, sink and source frequently in the circuit descriptions for Silicon Chip projects. Let's take a closer look at these terms. To the electronics novice and perhaps even to the more experienced, these terms can cause considerable confusion. High and low are terms frequently employed when describing logic and switching circuitry but they can also be used when describing analog circuitry, particularly comparators. Consider Fig.1 which is the triangular symbol used for an operational amplifier. It is usually drawn with two inputs (inverting and non-inverting) and one output. If the op amp is biased for normal linear operation, its output pin will usually "sit" at about half the voltage between the positive and negative supply pins. In the case of op amps with ± 15V supplies, this means that the output will "sit" at close to 0V when no signal is present. When the op amp is fed with a large DC input signal the chances are that its output will go "high" or "low" depending on the polarity of the input signal and the configuration of the circuit. By high or low, we mean that the op amp output is driven as high or low as it can go. In most op amps running with ± 15V rails, the output will go to about + 13V when driven high and about - 13V when driven low. In a comparator, which is an op amp specially designed for sensing whether a signal is above or below set thresholds, the output can go higher, typically almost to the positive and negative supply rails, provided it is lightly loaded. In CMOS logic circuits which are specially designed for switching and normally run from a single DC rail, the outputs will always sit at virtually the positive rail or at 0V, except during the time that they are changing "state". There is a proviso though; they must be lightly loaded. If an electronic device is more heavily loaded, its output voltage will not go as high or as low as it can when it is lightly loaded. The reason is that typical op amps and logic circuits do not behave like ideal voltage sources. They are Fig. 1 OPAMP -V - V Fig. 2 COMPARATOR +v +L J) Vrel. -V When the output of an op amp is high, it will deliver current to its external load, as in Fig.3. This depicts current lo flowing out of the op amp and through the load to the 0V line. The op amp is therefore said to "source" current. On the other hand, when the op amp output is low, current will flow through the load from the 0V line and back into the op amp, as depicted in Fig.4. Here, the op amp is said to "sink" current. By the way, we're talking about conventional current flow here, from positive to negative. Most op amps can source just as much current as they can sink but some can sink a lot more than they can source. Take for example the LM324 op amp. This device can operate from a single supply and it has a number of special features which make it a very handy in a lot of applications. However, it cannot source as much current as it can sink. Similarly, consider the LM3900 which is a quad Norton op amp. (The term Norton means that its inputs are current controlled rather than voltage controlled). Each op amp in the LM3900 package can continued on page 93 lo + IN "sink". +V +v + strictly limited in the amount of current they can deliver. And that brings us to the terms "source" and f ig. 3 CURRENT SOURCE -1 + .,. -v Fig. 4 "!" ~URRENT SINK MARCH 1988 65 Transistor Nipper Pliers Is your tool kit well equipped? Great for working on pcb boards. Sharp, precision made, long life cutting edge. Stainless steel with 95mm body, spring return and 9mm blades. CatT-3205 The Ultimate Portable Iron Service-people, technicians, hobbyists... anyone who needs a quick, reliable soldering iron in a flash. Portasol, the pocket sized butane powered soldering iron. Gives the equivalent of 10-60 watts in seconds. Refills via any standard butane lighter charge pack. 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Electron ics & Hobbies 24 83 22 • Launceston: Wilts Electronics 31 5688 •NT• Alice Springs: Farmer Electronics 52 2967 ;~~:r~;~~.;~~~~~~: ~~~~o~i~~~:~i'!t~~~~::·H~~:.~ri!:/~~J!~~~i~~ld~ J;:~:~:~r:m~~~::n1~~;i~~g7~ f;4~i~r:~h~~-~~i~~/e~~ 1 AMATEUR RADIO By GARRY CRATT, VK2YBX Antennas for the VHF & UHF bands One of the most difficult decisions the amateur is faced with today is the choice of antenna to use. This article sets out to explain the advantages and disadvantages of the various types of antennas available. One of the most commonly held beliefs is that antennas should be judged on gain alone, and that an antenna with high gain is better than one with low gain. But that's not all there is to it. Antenna gain is closely related to antenna directivity, which in turn is closely related to the radiation pattern. A high gain antenna may be unsuitable in some cases if, for example, it radiates energy in the wrong direction. In fact, it is the ability of an antenna to radiate most of the energy fed to it in a particular direction (and minimum radiation in other directions) that provides power gain. The general direction of maximum radiation when the radiation pattern is plotted is called the major lobe. The areas of lower radiation levels (as no antenna is perfectly directional) are called minor lobes. The term front to back ratio is also commonly used in discussions on antennas. This is simply the ratio of the power radiated in the preferred direction to the power radiated in the opposite direction - see Fig.1. The power gain is the ratio of the maximum radiation signal in a given direction to the maximum radiation signal produced by a theoretical reference antenna with the same power input. This theoretical reference antenna is . w -' z < w d ffi > RELATIVE POWER (uW) Fig. 2: graph showing how the angle of radiation decreases as the antenna approaches one wavelength. A lower angle of radiation gives greater gain. 68 SILICON CHIP MAJOR LOBE ~NORf LOBES Fig.I: the general direction of maximum radiation is called the major.lobe, while the areas of lower radiation are the minor lobes. Fig.3: dimensions for a discone antenna to cover 140-450MHz. The disc can be solid aluminium while the cone can be wire mesh. known as an isotropic radiator, which is a hypothetical, lossless omnidirectional antenna. In practice, antenna gain measurements are normally made in comparison to a single half-wave dipole. Because the radiation pattern of a half-wave dipole is somewhat imperfect, its power gain compared with the theoretical isotropic radiator has been mathematically calculated at 2.15dB. This means that the gain oI a practical antenna can be referred to an isotropic radiator by adding ~ COAX \::!f__c_oA_x_~ Fig.4: a vertical collinear antenna can be made by joining pieces of coaxial cable (see text). The antenna can be centre-fed or end-fed. 2.15dB to the measured gain against a half-wave dipole. All this is easy to visualise when applied to a directional antenna such as a yagi, quad etc, but takes a little more explanation when applied to omnidirectional vertical antennas. Beca u s e it is used as th e reference, it follows that a halfwave dipole has a unity gain. If we take a vertical half-wave dipole and replace its lower half with a groundplane, the image of the vertical quarter-wave radiator is reflected in the groundplane. As a result, the groundplane antenna produces similar results to a halfwave dipole. There are many other factors, too detailed to explain here, that also come into play. Suffice to say, the qua rter wave radiator is groundplane dependent, and incapable of substantial gain. In order to obtain usable gain from a vertical antenna, we need to compress the major lobes so that they have a low angle of radiation compared to the horizontal plane see Fig.2 . In fact useful gain in this type of antenna is closely related to a low angle of radiation. VHF vertical gain antennas, for example, may comprise two half wave dipoles fed in phase etc, and use compression of the major lobes to obtain a low angle of radiation. Such an antenna is called a collinear. that of a quarter wavelength radiator. Fig.3 shows the dimensions for both disc and cone to cover the frequency band from 140-450MHz. Discones are sold commercially by Emtronics, Vicom, Dick Smith Electronics, etc. Vertical collinears Vertical collinear antennas can be easily fabricated by using coaxial cable.of either 75-ohm or 50-ohm impedance. This type of antenna is made from a series of lengths of coa xial cabl e , each a halfwavelength long and fed in phase. The elements are joined together with the outer braid and centre conductors transposed at each connection. Fig.4 shows the details. COAXIAL CA■L■ SP■Cll'ICATIONS Cable No The discohe, so called because it comprises a metal or mesh cone, is a broadband vertically polarised antenna which acts as a wideband impedance matching transformer, coupling the 50-ohm input to the higher impedance of free space. The radiation pattern is similar to Nomi1111I Imp Zo(j) "-L Cable Outoide Diam 1MHz A - (d■ /1-) Velocity Factor 10MHz 100MHz c-ltanc:e RG-5/U RG-5 ■ /U RG-IA/U RG-IA/U RG-9/U RG-9■ /U RG-10A/U RG•11A/U RG-12A/U RG-13A/U RG•14A/U R(l-11/U RG•17A/U RG-11A/U RG,19A/U RG 20A/U RG,21 A/U RG-29/U RG-34A/U 0 RG-34 ■ /U RG-35A/U RG 54A/U RG-55/U RG,SSA/U RG-51/U RG-51C/U RG,59A/U RG-59■ /U RG,82A/U RG-74A/U RG-13/U RG-171/U RG-213/U RG-211/U RG, 220/U 52.5 50.0 75.0 50.0 51 .0 50.0 50.0 75.0 75.0 75.0 50.0 52.0 50.0 50.0 50.0 50.0 50.0 53.5 75 0 75.0 75.0 58.0 53.5 50.0 53.5 50.0 75.0 75.0 93.0 50.0 35.0 50.0 50.0 50.0 50.0 8.45 8.45 8.45 10.3 10.66 10.8 12.06 10.3 12.06 10.8 13.85 18 22.1 24 28.4 30.35 4.7 4.6 16 18 24 6.35 5.2 5.4 4.95 4.95 6.15 6.15 6.15 15.6 10.3 2.0 10.3 22.1 28.4 Maximum Operating (pF/10011) Voltage 1 - H • 3000MHz (mm) 0 The discone antenna Thus the sections are assembled by soldering the centre conductor of the first section to the braid of the second section and vice versa. The gain, bandwidth and radiation pattern are all governed by the number of elements used. Bandwidth can be roughly calculated as: BW = 2f/(3n + 1) where f is the operating frequency and n is the number of elements. For example, a 16 element array operating at 438MHz will have a bandwidth of 438MHz x 2 -:- 49 = 17.9MHz bandwidth. The entire array can be secured inside a piece of PVC conduit. Alternatively, the junctions of the elements can be sealed with weatherproof insulation tape or heatshrink tubing. Using PVC conduit will cause the centre frequency to be pulled low, so it is best to start construction by cutting a length of coaxial ea ble to an electrical half-wavelength (using the formula 150/f(MHz) = half wavelength (metres). Once this has been done, strip back the PVC sheath 15mm at both en d s , separate the outer braid, then twist the braid conductors together and tin them with solder. (rms ) 0.21 0.16 0.21 0.16 0.16 0.175 0.16 0.18 0.18 0.18 0. 12 0.1 0.066 0.066 0.04 0.04 1.4 0.33 0.065 0.07 0.18 0.36 0.36 0.33 0.42 0.34 0.25 0.10 0.23 2.6 0.16 0.066 0.04 0.77 0.66 0.78 0.55 0.57 0.81 0.55 0.7 0.66 0.66 0.41 0.4 0.225 0.225 0.17 0.17 4.4 1.2 0.29 0.3 0.235 0.74 1.3 1.3 1.25 1.4 1.10 1.10 0.85 0.38 0.8 5.8 0.6 0.2 0.2 2.9 2.4 2.9 2.0 2.0 2.1 2.0 2.3 2.3 2.3 1.4 1.2 0.8 0.8 0.68 0.68 13.0 4.4 1.3 1.4 0.85 3.1 4.8 4.8 4.65 4.9 3.40 3.40 2.70 1.5 2.8 13.8 1.9 1.0 0.7 11.5 8.8 11.2 8.0 7.3 9.0 8.0 7.8 8.0 8.0 .5 8.7 3.4 3.4 3 3.5 43.0 16.0 3.0 5.8 3.5 11 .5 17.0 17.0 17.5 24.0 12.0 12.0 8.6 6.0 9.6 46 8.0 4.4 3.6 22.0 16.7 21.0 16.5 15.5 18.0 16.5 16.5 16.5 16.5 12.0 16.0 8.5 8.5 7.7 7.7 85.0 30.0 12.5 8:6 21.5 32.0 32.0 37.5 45.0 26.0 18 .11 .5 24.0 76 0.659 0.659 0.659 0.659 0.659 0.659 0.659 0.66 0.659 0.659 0.659 0.67 0.659 0.659 0.659 0.659 0.659 0.659 0.659 0.66 0.659 0.659 0.659 0.659 0.659 0.659 0.659 0.66 0.84 0.659 0.66 0.665 0.66 0.66 0.66 28.5 29.5 20.0 30.5 30.0 30.5 30.5 20.5 20.5 20.5 30.0 29.5 30.0 30.5 30.5 30.5 30.0 28.5 20.5 21 .5 20.5 26.5 28.5 29.5 28.5 30.0 20.5 21.0 13.5 30.0 44.0 27.9 29.5 29.5 29.5 3000 3000 2700 4000 4000 4000 4000 5000 4000 4000 5500 6000 11000 11 000 14000 14000 2700 1900 5200 6500 10000 3000 1900 1900 1900 1900 2300 2300 750 5500 2000 5000 11000 14000 Table 1: coaxial cable specifications. Use low-loss cable for long runs and check that the impedance is correct. (Courtesy Dick Smith Electr onics). MA RCH 1988 69 MAST s (a) STACKING IN THE SAME PLANE (b) STACKING IN PARALLEL PLANES Fig. 5: additional antenna system gain can be achieved by stacking in either the same plane or parallel planes. Our diagram shows two vertically-polarised antennas, but horizontally-polarised antennas may also be stacked. Next, strip 5mm of dielectric from the centre conductor and tin the centre conductor. You can now check the resonant frequency of this length of cable with a grid dip oscillator (GDO). This is done by shorting the braid and centre conductor at one end of the element, and coupling the GDO to the other end. Because the formula used to calculate the half-wave section does not take into account the velocity factor of the cable, it is normal for the cable to be too long at first. It can be made to resonate at the correct frequency by progressively reducing its length by trial and error. An advantage of the coaxial collinear is that it is an easily reproduced design. Because of this, it is used by many commercial antenna manufacturers. Cables and connectors Having selected a suitable antenna, care must be taken to maximise the available antenna system performance by selecting a suitable feedline. As can be seen from Table 1, the main factor with which we are concerned is attenuation. The difference in attenuation between, say, RG-58C/U and RG-213 over a length of 30 metres at a frequency of 100MHz is 3dB. Clearly, for long coaxial runs, we need to select a cable with low loss. For mobile installations, where the length of 70 SILICON CHIP coaxial cable used is less than three or four metres, the loss incurred by using a smaller diameter cable is a worthwhile tradeoff compared to the ease of installation. Of course, the selection of cable is also determined by price. Lowloss cable can be expensive, particularly for UHF work. Connectors also form an important part of any antenna system, particularly at VHF and UHF. Of prime importance is the impedance of the connector, which is largely determined by the physical construction and design. The materials used in manufacture are also important, particularly the dielectric insulation. An inferior connector will create an impedance mismatch, causing a high SWR (standing wave ratio). It may also have a high insertion loss, thereby further reducing antenna system performance. Connectors should be chosen carefully, as there are many inferior types available which are quite unsuitable for RF work and which should really be limited to video use. Many connectors are also available in both 50-ohm and 75-ohm variations, so it is important to choose the correct type. or vertically polarised antennas. By stacking yagi antennas (or any derivative of a yagi), between 5/8 wavelength and 1-1/4 wavelengths apart, an additional 2.5 to 3dB of gain can be realised. Stacked antennas must be fed in phase, and because a typical VHF or UHF yagi is a 50-ohm device, a matching transformer must be used. To feed the two antennas in phase they must be fed in parallel. This means that to obtain a reasonable match to 50-ohm feedline, we must transform the impedance of each antenna to 100 ohms, so that the two antennas in parallel have an impedance of 50 ohms. This is easily achieved by using a coaxial line transformer, made from 75-ohm coaxial cable. The formula used to calculate this is as follows: Zs = Zq x Zq/Zl where Zq is the impedance of the matching transformer, Zl is the feed impedance, and Zs is the required antenna impedance for parallel operation. If we substitute figures from the above example, we get: 100 = Zq x Zq/50 Thus, Zq x Zq = 5000, so Zq = 70.7 ohms. In practice 75-ohm cable presents a minimal mismatch. Because each antenna must be fed with one of these coaxial transformers, the physical construction should look like Fig.6. Note also that each impedance transformer must be a single quarter wavelength in length, or an odd multiple of a quarter wavelength. With that background, you LINES PARALLELED ' ----50r! TAIL Stacking antennas Additional antenna gain can be achieved by stacking two identical, directional antennas, in either the same plane or in parallel planes. This applies equally to horizontally TO MAIN FEEDLINE Fig.6: phasing harness for stacked antennas. Each section must be an odd multiple of a quarter wavelength. should now find it easier to select an antenna for a particular application. Let's take a look at a few examples. Base station operation For maximum directivity, either horizontally or vertically, a yagi antenna is a good choice. A rotator will then enable 360° operation. For omnidirectional operation, a five-eighths wavelength antenna could be used provided a good groundplane is available. If no suitable ground plane is available, a vertical collinear antenna could be used instead. Note that a suitable location is required for good omnidirectional operation (eg, the top of a hill). The discone anternia is suitable for omnidirectional operation on a variety of VHF & UHF frequencies, provided that 3dBd gain (dBd means gain referred to a dipole) is acceptable. For directional operation on a variety of VHF & UHF frequencies, a log periodic antenna can be used with a rotator. Mobile operation The size of the antenna and the mounting method on your vehicle are the two main considerations here. As virtually all mobile applications require vertical polarisation and omnidirectional operation, the choice of antennas can be reduced to the following: (1). Quarter-wave whip - generally requires drilling a hole in the middle of the car's roof for best results. Advantages: (a) physically short; (b) relatively high angle of radiation which gives better results in city or hilly locations, particularly at UHF. Has marginal gain of ldBi. (2). Five-eighths vertical - requires a ground plane as above, but has a low angle of radiation, providing better gain than a quarter wave whip (almost 3dBi). Offers good performance on flat terrain (but probably worse in hilly terrain). (3). Half-wave radiator - ground independent and so can be easily gutter mounted. Has ldB of gain over a quarter-wave whip. (4). Two half-wave radiators end fed - ground independent, improved gain (almost 5.2dBi), but SAFETY WATCH Lt Safety Watch will be an occasional feature in SILICON CHIP drawing attention to issues of electrical s afety in the workshop and home. VCRs and water don't mix Vases of flowers should never be placed on top of TV set or near a video cassette recorder. If the vase is knocked over, the water could do a lot of damage to the internal circuitry of the TV or VCR and may even cause the picture tube to crack. Worse, if splashed water comes into contact with mains wiring inside the VCR, it could create a path between the mains and chassis. Because most VCRs are double-insulated (ie, they only have a two-core power flex), any leakage between the mains and chassis could mean that the VCR exterior is live and lethal. Moral: keep all vases, drinks and other containers of liquid away from your VCR and TV set. Keep it well away from your stereo equipment too. sign of deterioration. They're not cheap but then neither is a fire in the kitchen. Safety with the iron Hazardous power cords We recently came across a power cord fitted to a vertical grille which had shorted at the point where the cord entered the grille base. When the sheath was removed from the cord, the insulation surrounding each of the three leads was found to be badly perished. The short occurred between Active and Neutral. When more closely examined, the outer rubber sheath of the cord was noted to be shiny from continued exposure to grease and had tell-tale signs of cracking and perishing where the cord entered the moulded 3-pin plug. Moral: carefully examine power cords used for frypans and vertical grilles. Such cords are prone to perishing because of their exposure to grease and cooking oil. Replace the cord at the first Avoid placing appliances on stove tops. This is what can happen. Some people put their electric iron on the stove to cool off before it is put away in a cupboard. This photo shows what happened when the iron was dislodged slightly, onto an adjacent hotplate which had been inadvertently left on. As you can see, a great deal of damage was done to the iron in only a few seconds. The iron had to be replaced. Moral: if you put your iron on the stove to cool down, place it well away from the hotplates. Better still, leave it on the ironing board to cool down and then put it way. continued on page 93 M ARCH 1988 71 THE WAY I SEE IT By NEVILLE WILLIAMS The quest for the ultimate in hifi sound is half the fun! As I hung up the phone recently, after a lengthy conversation with an old-time hifi enthusiast, I was more than ever convinced by the obvious: that, for such a person, hifi would be nowhere near as interesting, fascinating, or challenging if there wasn't the possibility of improving the sound even slightly! Back in the 78rpm era, there was virtually unlimited scope for improvement. The discs themselves carried a substantial content of distortion and noise, such that a prime objective was to suppress both in some way, without unacceptably compromising the wanted signal. With the appearance of microgroove recordings in the fifties, the search was on for styli, cartridges and pickup arms that combined suitably low mass with user-ruggedness. It was a combination that didn't come easily - any more than did affordable wow-free, rumble-free playback turntables. As the signal source gradually improved, attention was diverted to amplifiers and loudspeaker systems, leading to a boom in the British hifi industry, with famous brand names like Acos, BAKER, Goodmans, Leak, QUAD, Rogers, Wharfedale, &c. I doubt that there ever could be another batch of enthusiasts more varied, more interesting or more dedicated than the founders of that particular group of companies. By the sixties, tape emerged as a rival for disc and stereo had ap72 SILICON CHIP peared, so the entire evolutionary process had to be updated and repeated: groove geometry, styli, pickups, turntables, amplifiers, loudspeakers and even the layout of the listening room itself. To use the old cliche, there never was a dull moment; never a period when enthusiasts could relax, secure in the knowledge that they could settle back and enjoy the ultimate. There was always some other aspect to explore, some new challenge appearing on the horizon. Running out of challenge? It's certainly been that way for as long as I can remember, but what of the future? Surely, as hifi sound equipment gets better and better, there must come a time when technology has overtaken our needs and, more specifically, our own physical limitations. Will the fascination of hifi sound diminish by half when equipment can be installed, used and largely forgotten, except when it malfunctions; like power, water, refrigeration and plumbing systems? The now-retired enthusiast, who triggered off this whole line of thought with his phone call, has been collecting cherished recordings for as long as I can remember and fussing over them like a mother hen. From constant listening, he knows their every last quiver and quaver. A few years back, unsettled by the prospect of the compact disc revolution, he sought my assurance that it made sense for him to stay with his present collection and equipment, rather than trade it for a fraction of its original worth and re-invest in CDs. Knowing his age and background, I agreed with his proposition. This time around, after the opening pleasantries, he hit me with the question: "How good is the top-ofthe line Shure cartridge?" The purchase price mentioned was around $600. I answered in a general way, based on my recollection of a very favourable review of the V-15 type V-MR which had been published some time ago. It seemed to me that anyone who had acquired and carefully set up a Shure cartridge at that price level should have little to worry about, bearing in mind the performance parameters applicable to phono players. But there was more to come: "How good are the Australian Garrott replacement styli? The makers claim a much better contour and polish than the standard commercial equivalent". My answer was along the lines that the Garrott brothers had been working with styli for many years and, by now, they ought to be pretty good at it! But whether a new Gar- rott stylus would actually sound better or last longer than a new Shure stylus in a Shure cartridge, I was not in a position to say. His next question was a doublebarrelled effort: "Having in mind the cost of a new stylus, what do you think of the idea of putting the money towards the purchase of a new Garrott cartridge? And, if the Garrott was really as good as the makers claimed, would the difference justify the hassle of having to set up the arm to suit it?" I could offer no definitive answer because I had never been through the particular exercise. "Well, who can I ask?", he said. "It's not sufficient simply to talk to the companies concerned, because they have a vested interest. Hifi dealers have their own pet lines. Magazines review cartridges from time to time but they rarely do a comparative anlysis. Who would know the answer to my questions?" It was about then that I realised that I hadn't been witness to an argument about phono cartridges for quite a long time. Vinyl disc enthusiasts still have their preferences and strongly held opinions but they make the headlines much less frequently than once they did; and they certainly feature less in conversation where audio engineers gather. Even in the strongholds of conservatism, compact disc is now plainly winning acceptance as the best way to store and reproduce sound, with the vinyl disc system being relegated to a lesser role - by its very nature technically inferior, no matter how good the particular stylus and cartridge. What about a listening test? When I talked along these lines, my enthusiast friend suddenly had another bright idea. What if he bought a new Garrott cartridge complete and, if it could be arranged, have me over to share in a comparative listening test to decide which offered the best sound? I declined, on the basis that at my age, I did not consider myself able to offer a definitive subjective opinion on ultimate sound quality. Yes, I was well able to appreciate the difference between good and not-so-good sound, and I had been active in the game long enough to know whether other people's statements and opinions made good technical sense. But, in this situation, I would not be comparing good and not-so-good sound but trying to pick possible subtle differences between two very good cartridges, involving the portion of the spectrum which I could no longer hear to advantage, if at all. "But I'm the same age as you and I reckon my hearing's still pretty good", he said. To which I could only reply: "For your sake, I hope it is, but it would make you very much an exception to the rule". "On the other hand, if your hearing is merely average for your age, you may well be worrying about subtleties to no good purpose, and at considerable cost". And that's about where we left it - in practical terms, a rather futile conversation. A few days later, he rang to say that he had checked his hearing with a frequency disc in his collection and could still hear lOkHz. "Good", I said, "but did you leave the volume control set for the complete run?" No he hadn't, he'd "cheated a fair bit!" With a normal level response, he would probably be lucky to hear anything above about BkHz. He went on to say that another retired friend had insisted that a trained listener could hear more than the average person, despite what a frequency check might show - an idea that I, for one, would be delighted to see proven. But my own experience and observation would suggest that, while such a person may indeed be very perceptive with what faculty he has, he would still be missing out on the top end of the audio spectrum. He would be in much the same position as a short-sighted projectionist, trying to adjust to critical focus - without his spectacles! Back to the introduction Having equipped himself with a wow-free, hum-free, vibration-free turntable, a good arm and either one of two top-line cartridges, my enthusiast friend may well have reached the stage where there is no real point in doing anything beyond maintaining what he already has. Problems? ... and you don't have our 112 page catalogue ... you've got real problems! ARISTA ... your one-stop problem solver. Audio leads ... Batteries ... Chargers ... Battery holders ... Cables ... Car accessories ... CD accessories ... Converters ... "Cutec" ... Earphones .. . Fuses ... Headphones .. . Intercoms ... Knobs .. . Microphones and accessories ... Mixers ... Multimeters ... Plugs/Sockets, etc ... Plug adaptors ... Power packs and leads ... PA ... Disc and Tape care ... Security equipment ... Signal modifiers ... Solderless terminals ... Storage boxes ... Switches ... Telephone and TV accessories .. . Tools and Technical aids .. . Video accessories ... Wiring accessories ... You name it and we're bound to have it ...Try us ... NOW! Get your catalogue ... it'll solve a whole lot of your problems! Just send $2 + 50c p&h and your return address to: ARIST~ ELECTRONICS PTY LTD PO BOX 191, LIDCOMBE, NSW 2141 MARCH 1988 73 An apparent lack of intestinal fortitude! Dear Mr Williams, I read with interest your comments regarding the repair of electronic equipment, the delays and the lack of service and spares encountered. I wonder, however, why you bother to write about it when you are obviously supporting this policy. Yes, you . You claim to be fair by not naming the companies who are not prepared to supply service or spares, thus denying consumers answers to the questions they ask before buying equipment. Certainly you do not know all the companies that are not supplying service but you certainly know at least some of them and should have the intestinal fortitude to , name those against whom you have evidence, rather than making sweeping generalisations against all. Having been in the industry, you know that no managing director will provide adequate fund alloca, tions to the service department unless he perceives that lack of service is costing his company sales. Ask any salesperson about service and you will be assured that service is perfect, regardless of the actual situation, so to whom can the customer turn for unbiased information? If you want to see what effect exposure of company shortcomings has, I suggest you subscribe to the ACA magazine, " Choice". There you will find (to the best of their ability) a reasonable report on many consumer items. It is noticeable that appliances that don't perform well are named, and often disappear from the retailers' shelves. The same concept, of course, applies to service and spares. The other thought that occurs to me is that the companies you have not named could be advertisers or possible suppliers to the magazine for, after all, how fair is it to name Tandy or Hills as being good organisations, whilst refusing to name the bad ones? D.T., (Traralgon, Vic). Keep the records spotless (as he does), check the arm and turntable regularly, check and replace the stylus as necessary and that's about the end of it. If he did decide to change over to compact disc, he could just about forget about maintenance, as well! Again, assuming that his amplifier is to full modern specifications, it is difficult to see why he would need another one, advertising claims notwithstanding. That leaves his loudspeakers as the one area where he might find reason to invest in something different, because loudspeakers do vary a lot in the their subjective impact. Imagine it: one more step to take and most of the fascination, speculation and challenge of hifi would have vanished. Or would it? • With compact disc, we had a storage and playback medium with a vanishingly small amount of noise and distortion. • With digital audio tape in immediate view, we would be able to record and play back a nearperfect signal. • We had practical, affordable amplifiers to match. • We had drift-free, lowdistortion FM-stereo tuners, some with AM-stereo as a bonus. • We'd never had a wider or better choice of loudspeakers. Maybe, I said, as people realised that they had access to nearperfect equipment, some of the fascination, speculation and challenge that had characterised hifi for 60 years (since the term was first used) would begin to taper off. As you might expect, Leo did not agree at all. He stated that while compact disc players were pretty good they were still being refined and improved by the manufacturers. And there were presently 1 " The search continues Talking over this theme with Leo Simpson, I suggested as a try-on that, for all practical purposes, hifi " perfection" may well be in sight. 74 SILICON CHIP very few amplifiers which truly matched the standards offered by CD players. Nor were speakers anywhere close to the standards offered by even mediocre amplifiers of twenty years ago. When loudspeakers commonly offered a frequency response flat to within ± 2dB, we might be getting somewhere. Nor were most tuners all that marvellous. With a few exceptions most FM tuners would be hard put to deliver a stereo signal-to-noise ratio of much better than 70dB. Most would be hard put to reproduce a stereo signal with less than 0.5% harmonic distortion. And even if they could do these things, the FM transmitters couldn't! And that was without mentioning the enormous differences between the acoustics of the concert hall and those of the average listening room. Really, we've only just started on this problem. In fact, Leo disagreed totally with my proposition. He says that hifi may be good but anyone who thinks that "things have gone just about as far as they can go" is no longer really interested in hifi. Pretty strong words indeed! When pressed, I'd have to agree. Now matter how good the specifications of present equipment, or by how much they appear to surpass our aural capability, there'll still be plenty of room for improvements. That's what hifi is all about! Back to electronic servicing On reading the letter in the accompanying panel from D.T. in Traralgon, Vic, my immediate impression was that he would make an excellent mob orator, his message replete with sweeping statements, and uninterrupted by pauses for reflection. How my criticism of present-day servicing attitudes and standards, with its emphasis on unacceptable delays, can be construed as "supporting the policy" escapes me. I "bothered" to raise the subject in the November issue for reasons quite specifically stated at the beginning of the article and, in so doing, I just happened to be telling the truth! Faced with a number of unsatisfactory servicing situations, as detailed, I made a number of inquiries (also detailed) in an effort to establish whether my disturbing experience was unusual or typical. Unfortunately, the indicators pointed strongly to the latter, with the problem being industry wide, rather than confined to a few offending manufacturers. Sorry D.T. but, on that basis, I stand by my statement in the December issue that it would have been unfair to single out for criticism typical companies which had come to my attention, either directly, or in casual conversation. There is a considerable difference between disturbing observations and the sort of evidence necessary to justify black-listing in a magazine. In that same November article, the editor inserted a panel (p.17) suggesting that "there must be another side" to this "rather uncomplimentary" picture and inviting contrary opinion from companies and readers. To date, no-one has complained of injustice, the overwhelming response being support for the original article, as presented. D.T. makes an issue of a managerial link between back-up service, customer goodwill, and Did you sales. He seems not to have noticed that, under the heading "Spare parts problem" (Nov. p.16), I assume the existence of such a link and go on to suggest important economic reasons why the traditional relationship has been distorted to the disadvantage of back-up service. Since making that observation, the Australian dollar has slipped yet further from 100 to around 90 yen. Perhaps D.T. should also re-read the last couple of columns on page 17 of the same issue. Far from abandoning readers to · the glib assurance of "any salesperson" about "perfect service", the article seeks to alert them to that very possibility. I quote: "Don't assume that your friendly emporium will take over your service worries, because they have been so nice to you in other ways. Check out the warranty, read the fine print, and discover exactly what's involved. What is the warranty period and what does it cover ... " D.T. then suggests that I/we should investigate and report on products and services in the manner of Choice magazine. He has completely missed the point that Choice is a special kind of • miss I.so Simpson and Greg 5waln Pffl!S!IIII••• magazine, supplied only to people who, by virtue of their subscription, become members of the Australian Consumers Association. In effect, they constitute a private group funding research reports, which they alone receive in the form of a monthly journal. It exists purely for that purpose and relies on membership fees to cover the cost of administration, research and publication. In short, Choice operates on a completely different legal basis to publications like SILICON CHIP, which is available to anyone who cares to buy a copy from the newsagent. For all such magazines and newspapers, comment on products and services is an optional small segment of the editorial content, commanding an equally small segment of the budget and subject to the normal legal constraints relating to "publication". The "logic " of D.T's final paragraph intrigues me: If you have reason to commend someone, it is only fair to balance it with a condemnation of somebody else. If you fail to do so, you probably have an ulterior motive - like needing their support as an advertiser. Thanks for the vote of confidence! ~ these issues? Issue Highlights November 1 98 7: Car Stereo in V our Home; 1 GHz Frequency Meter; Capacitance · Adaptor for DMMs; Off-hook Indicator for Phones. December 1 98 7: 1 00W PmNer Amplifier Module; Passive lnfrared Sensor for Burglar Alarms; Universal Speed Please send me a back issue for □ December 1987 D January 1988 Enclosed is my cheque or money order for $ ........ or please debit my D November 1987 Control and Lamp Dimmer; 24 V to 12 V DC Converter. D Bankcard Ja~uary 1988: 4-bay BmNtie UHF Antenna; Dual Tracking PmNer Supply; Custom Phone D Visa Name ....... .. .... ...... ..... .... ........ ... .. ... ...... ...... ......... ... ........ ... ..... ........ Address ... .. .. .... ..... ......... ........ .... ... .... ..... .... ............... ... ...... .. ... ..... . Suburb/town ..... ........... ... ..... ........ .. .. .. .... ..... ..... Postcode.. ... .. ... .. ... . Card No............ ... ..... ...... .. ........... ...... ..... .................. .... ........... .. .. . Signature ... .. .... ... .. .. ... ..... .... ............. Card expiry date .. ... . ./ ....... / ...... . L ________________________ Ringer; Subcarrier Adapator for FM tuners. Price: $5.00 each (incl. p&p). Fill out the coupon at left (or a photostat copy) and send it to: S1ucoN CHIP, PO Box 139, i_ _ _ _ _ _ _ _Beach, ___ _ __ Collaroy 2097. MARCH 1988 75 Introduced in 1927, this wooden electric passenger car was one of many which ran on the Sydney metropolitan system up until the late 1960s. (Bryan Maher photo). 'l'H E EVOLUTION OF ELECTRIC RAILWAYS As in other countries, Australia had some experience with electric traction before the turn of the century. However, it was not till much later that extensive electrification took place. By BRYAN MAHER suburbs. Expanding gradually, the Railways Department built and operated a large system of high voltage feeders from their power stations to many country towns and cities. They used 33kV lines from Newcastle to the Hunter River Valley and up the north coast towards Grafton; 66kV lines fr om Sydney to the Blue Mountains; and also Australia's first intercity power line interconnector, the 66kV line built in 1942 to join Newcastle and Sydney. One of the spans of that Newcastle-Sydney interconnector was a record 960 metres long, across the Hawkesbury River. This particular span was believed to be the longest power line span on wooden poles in the wo r ld . Originally built using 19-strand 10 gauge cadmium-copper conductors, that span with a 61-metre sag in the middle had each phase supported by a pyramid structure made of three 18 metre wooden poles sunk 4.3 metres into the rocky hilltop. The whole 66kV line fro m Hamilton substation in Newcastle to St. Leonards substation in Sydney was designed to carry 200 amperes, and at full current 6000 The absolute first electric traction of any type in Australia was an electric tramway using a direct current overhead trolley wire system in Sydney, from Waverley to Bondi Junction. This came into operation on 9th November, 1890. Direct current supply was generated by the New South Wales Railways at an installation a small distance away in the direction of Randwick. That little DC generator near Randwick marked the first entry into t h e electr icity generating business by the New South Railways, starting an enterprise which continued to grow for the following seventy years. The Railways Department during that time not only generated all power used by electric trams, trains, stations, yard lighting, workshops and signals in the Newcastle, Sydney and Blue Mountains districts, but also supplied, owned and operated at Newcastle the largest electric and hydraulic coal loading wharf system on the Pacific Ocean. Furthermore, in that period, the New South W ales Ra il ways operated 50Hz and 25Hz coal burning power stations at Ultimo and White Bay in Sydney and at Zara Street in Newcastle, and for a long time owned some of the largest synchronous motors in Australia 10MW in Newcastle and 30MW in Sydney. During that time, the Zara Street plant also supplied 90 percent of all power used in Newcastle and its - -_ ELECTRICS IN AUSTRALIA 76 PART 5 S ILICON CHIP volts was lost over the length by resistive losses. This was the first time in Australia that two large cities had their power systems synchronised and joined. Victorian Electrics Melbourne became the first Australian city to boast electric suburban trains, in 1918. Some wooden carriages, previously steam-hauled, were converted to electric traction by the fitting of pantographs, control gear and new bogies containing electric motors. Overhead wiring construction was proceeding on a number of suburban lines and the first electric train, from Sandringham to Essendon, ran in 1919. Construction of AC-DC substations and overhead conductors above the tracks continued and Melbourne's 1500 volt DC electric suburban railway system eventually grew very large. Australia's early use of electric locomotives was confined to the coalfields in the eastern corner of Victoria where the very considerable brown coal deposits are mined by the open cut method. The first electrically hauled coal train ran in 1923. The Melbourne Electric Tramway system has, since quite early days, been working with the railways in shifting millions of commuters. Nowadays, this system is the only extensive electric tramway system remaining in Australia. A shining example to the rest of Australia, Melbourne has extended the tracks and purchased many new tramcars. The up-to-date "Z" class, of which 215 new cars have been put into service over a ten year period, are now being augmented by the latest order of 52 modern "A" class trams. In 1985, a $100-million contract was let by Melbourne's Metropolitan Transport Authority for the supply of 130 Articulated Light Rail Vehicles for use on long tram routes and later on two converted railway routes. These advanced vehicles consist of two cars sharing three bogies. Propulsion is by two 600 volt DC 195kW AEG traction motors. These can speed the 32.5 tonne vehicle with its 182 passengers along at a brisk 72km/h. The modern control system uses Grand old Locomotive No 1, the first steam loco in NSW. This beautifully restored loco is on permanent display in the Sydney Powerhouse Museum. (SRA photo). AEG thyristor DC-to-DC chopper circuits. Melbourne showed the world that construction of 1500 volt DC underground railways was still alive and well by opening their City Loop Line in 1981. Circling the City from Spencer Street Station via Flagstaff, Museum and Parliament Stations to Flinders Street or outer suburbs, this new line takes passengers within walking distance of their city workplace, easing street traffic congestion. Adelaide's longest surviving electric tramway, the famous fast Glenelg Tram has always been an example to Australia of the quickest way to move people. And the people of Brisbane were for many years served well by an electric tramway installation which reached the peak of its importance about 1930. Sadly, Brisbane eventually followed the lead of many other cities and scrapped all electric trams in favour of diesel buses. Newcastle and Sydney To appreciate the early story in Newcastle and Sydney we have to keep in mind the intimate relationship in New South Wales between the railways, tramways, power stations and coal loading wharves. These were all administered by the Department of Railways. Electric tramway systems had been expanding since their beginning in 1890, long before electric trains appeared. Newcastle was originally founded because a certain British Army lieutenant saw coal protruding out of the ground between Cooks Hill and Merewether while he was out chasing escaped convicts. With a working railway from Newcastle tci East Maitland from 1857, the discovery of large deposits of Australia's best gas-coal over an area from Walls end to Cessnock opened the possibility of an export market as a permanent boost to the colony's finances. Seizing the opportunity, the New South Wales Railways built the largest coal loading wharves in the country on an unused expanse of low-lying land known as Bullock Island on the north side of Newcastle harbour. Initially, five hydraulic coal loading cranes were installed, later extended to thirteen. Before the turn of the century, and for many decades after, Newcastle was the greatest coal loading port on the Pacific Ocean. So many sailing ships called at the port that while awaiting loading they were tied up three deep over miles of wharves. MARCH 1988 77 This was one of the 500 horsepower 6.6kV motors which drove the centrifugal pumps for the hydraulic cranes. These were used for coal loading at Newcastle. (Bryan Maher photo). To handle all the coal trains, the New South Wales Railways built the largest railway yard in the Southern Hemisphere. Complete with four weighbridges the whole installation, including storage and loading yards, was seven kilometres long. Running through five suburbs, the storage section reached sixty tracks wide, capable of taking 200 fully-loaded trains. Coal loading The hydraulic cranes installed for coal loading used water as the working fluid at a pressure 700 psi. The original steam-driven pumps were augmented in 1914 by two electric motor driven 3-cylinder piston pumps. The 600 volt DC 200 kilowatt compound motors were designed to start and stop automatically to keep up the supply of high pressure water as required by the cranes. Much later, in 1943, a fourteenstage centrifugal water pump driven by a double-ended 500hp (373kW) three phase 6600 volt induction motor was added to augment the hydraulic system. About 1914, the coal loading facility received a boost with the addition of seven huge electric cranes each weighing 240 tonnes and capable of lifting 15 tonnes. These were equipped with twin 75kW hoist motors and 56 kilowatts each for the travel and slew motors, on 600 volts DC. The Bullock Island 600 volts DC system grew in useage and was inter c onne cte d to the growing Newcastle suburban electric tramway system. To provide the required 600 volt direct current for all these loads, a 600 volt 3000 amp DC rotary converter was installed in the substation. Also provided were 300 lead-acid cells, each big enough to have a bath in. These constituted a 600 volt battery capable of providing 1000 amps of load current for hours (sometimes all night) if and when the AC supply or the substation were shut down. A rotary converter resembles a large DC generator with commutator and brushes but with the addition of tappings from some armature coils. These taps are connected to slip rings and are fed with AC, usually 6-phase, supplied from a 3-phase transformer. The converter runs at a synchronous speed determined by the AC frequency and the number of armature poles while DC output is delivered from the commutator and brushes. It is an efficient and compact machine, superior to an AC motor driving a separate DC generator. Because rotary converters work better with low frequency AC, all NSW Railways power stations generated 25Hz 6600 volt AC for traction supply, and separately generated 50Hz 11,000 volt AC for lighting and other loads. A very strange machine A 33-class loco shunts long lines of coal wagons at the Newcastle loading docks in the 1940s. The hydraulic cranes can be seen in the background. (Bryan Maher photo). 78 SILICON CHIP Other Newcastle tramway substations, each containing two 25Hz AC to 600V DC rotary converters, were built at Hunter Street and Hamilton. This latter substation supplied 600 volts DC to Newcastle's southern and western suburbs, the most distant being Wallsend, 13km from the city. Con- "to shoot through like a Bondi Tram." Electric trolley buses were introduced on a limited scale in Sydney near Town Hall and in the suburbs of Kogarah, Rockdale and Brighton-Le-Sands. These clever machines used two trolley poles contacting both a positive 600 volt and a zero potential overhead contact wire. Capable of being steered on any part of the road, these rubber-tyred vehicles called at the kerb for passengers and their quiet operation and fast acceleration distinguished them from diesel buses. At crossovers and junctions the construction of the oppositepotential parallel trolley wires was quite a headache. The Balmain beautie An earlier motor used to drive hydraulic accumulators at the Newcastle dockyards. Installed in 1914, it ran on 600V drawing 386 amps. (Bryan Maher photo). diderable voltage drop occurred along the long 600 volt feeder cables. To compensate for this voltage drop a rather strange machine called a Direct Current Series Generator was added at the Hamilton substation. This generator was driven at constant speed by a 3-phase AC motor. Now a series DC generator (ie, a DC generator with its field coils in series with its own armature) has a very strange and somewhat unstable voltage/current characteristic. When driven at constant speed such a generator's output voltage is more or less proportional to its own load current. If we draw no current from it, this generator will generate almost no voltage at all. If we draw a small current from it the machine will generate a small voltage and if we draw a large current, this same machine will generate a large voltage. Now that series generator was itself placed in series with the 600 volt feeder supplying trams which were out at the end of the W allsend line. With the rotary converters generating a constant 600 volts, the series generator added extra volts proportional to tram current, extra volts intended to be just equal to the voltage drop along the cable, so that the correct 600 volts always appeared at the other end. In peak hours, when trams at the end of the line could take as much as 500 amps, up to 300 volts was added to the system 600 volts, making 900 volts in all at the substation end. If we now subtract the 300-volt drop along the long cable due to its resistance, we get 600 volts out in the distant suburb, so the tram and passengers were all happy. Do you believe it? Yes, it really did exist. Theoretically minded readers will see it as a case of a positive resistance (the feeder cable) being cancelled by an equal negative resistance [the series generator) of - 0.6 ohms. Wow! Sydney electric tramway Meantime, back in Sydney, the electric tramway system was growing too. It also ran on 600 volts DC and a similar system of rotary converters in DC substations was built at strategic points of the suburban system. But whereas Newcastle trams were propelled by two motors, one in each bogie, many Sydney tramcars were equipped with four motors, to cope with the hilly terrain. These gave good acceleration on level streets and led to the world-famous Australianism Many Sydney harbourside streets feature a "steep-drop-tothe-water" but do readers recall the remarkable installation once used to allow trams to safely-descend the hill to Balmain Wharf arid then make the very steep ascent back up again? The tram's traction power and rail adhesion were insufficient for this short steep climb. Therefore, below the road, right under the tram tracks, was constructed a tunnel on the same slope as the road. In the tunnel was laid a standard gauge rail track upon which ran a heavy four wheel truck weighing about 12 tonnes. Up above, on the tram track, was mounted a strong but light four wheel truck. These two trucks were tied together by a long heavy steel cable, the steel cable passing over a pulley mounted just below the road surface at the top of the hill. You can work out what happened, can't you? Left to themselves, the two trucks rested with the heavy truck in the tunnel at the bottom of the hill, and the light truck sitting all alone on the tram track in the middle of the street at the top of the hill, held by the steel cable. So any attempt to push the light truck downwards on the tram track meant pulling the heavy truck up the track in the tunnel below. Of course the tunnel and the heavy truck in it were completely hidden from view. All that was visible was that silly looking light truck MARCH 1988 79 To provide a 600V DC supply for the Newcastle dockyards, a 3000 amp rotary converter was installed, in conjunction with a 600V battery capable of supplying 1000 amps. The small motor on the shaft was used for starting. in the middle of the road. Just imagine it. Along comes a d·ouble tram wanting to go down the hill to the wharf. It stops at the top of the hill and slowly nudges forward till it meets the light truck sitting on the track in front of it. The tram then drives forward, pushing the light truck down the hill and in so doing pulls the heavy truck in the tunnel to the top of the hill. Meanwhile, at the wharf, a Sydney ferry arrives and disgorges hundreds of weary city workers. All climb aboard the double tram which then starts up the hill, traction motors working hard and with the light truck now pushing from behind because of the weight of the heavy truck in the tunnel. The combined effort of tram's motors and the truck push is sufficient to haul the tram and its 200 tired passengers to top of hill. Success. Sadly, Sydney decided (followed by Newcastle) to scrap all 600 volt DC electric trams, to be replaced by 80 SILICON CHIP diesel buses. All tram tracks, overhead wiring and substations had to be demolished. The destruction, begun in the mid 1940s, pleased some and disturbed others who saw electric trams as the quickest way to move large crowds at important public events. Two clever machines The Railways also used the 600 volt DC system to supply cranes in the large railway workshops at Everleigh and Chullora in Sydney. A similiar system supplied cranes in the Newcastle area at Cardiff Locomotive Workshops, Honeysuckle Point Rail Shops, and the Bullock Island coal loading depot. So at least some 600 volt DC rotary converters survived for a few more years. Because Cardiff Workshops were built out of Newcastle, too far out to be supplied at 6600 volts AC 25Hz, use was made of the 33kV 50Hz AC ring main from Hamilton- Cardiff-Maitland. This presented a design difficulty for the Cardiff 600 volt DC substation as rotary converters suffer bad commutation and brush arcing if run on 50Hz supply. To solve this problem, a pair of very clever machines called Motor Converters were installed, each rated to deliver 600 volts at 500 amps DC. These machines had an AC stator winding supplied with 2200 volts 5GHz 3-phase AC. This induced currents in the rotor by ordinary induction motor action except that the rotor ran at exactly half synchronous speed. This resulted in rotor currents being half frequency, ie 25Hz. The stator was extended to carry a set of DC compound field coils and the long rotor had a commutator connected to all rotor windings at that end. DC output was collected from the commutator by brushes in the same manner as rotary converters. With only 25Hz currents in the rotor, commutation was perfect in these machines. It can be shown that half the output energy was derived by motor generator action and half by rotary converter action, and that the efficiency was higher than a straight motor generator but lower than a simple rotary converter. Advances in coal loading The State Rail Authority in 1961 moved out of the coal loading business at Newcastle, that industry being taken over by the Port of Newcastle (part of the Maritime Services Board). Two of the electric coal loading cranes, Nos.12 and 13, with their 29-metre high jibs were retained for loading of general cargo, while all other cranes were removed. All coal loading is now performed by fast belt convevors, capable of delivering up to 10,000 tonnes per hour. The new wharves are suitable for ships up to 229,000 tonnes and 15.5 metres draught. Of the once-remarkable hydraulic crane system, all has passed into history except the handsome solid stone Hydraulic Power House building, listed by the National Trust. Next month we will have a close look at some DC electric railways. ' ~ -·T-1 I • , t ' ·.$ . -:: +~::• ., ' ¥••--ey a• ~ . •• • •Y•~==•~-Y'') ? I ' . l ··-·· }'-··. » ••\•• ! Having looked at the va:ri<>~s :type$ of Jlipf\ops, ~~,r~.}}O'r -~ ea~I,~O-!~okjhto, s':s~e~tia['~~ic •·J ,· J ... "'·' t· · . j _cq-.~~~s~ '1E;I"e ·-w~ -~~s~~;i:yer !!ow ~!!J:~I'Y c;ou,1:1.~ersT,,: and shift registers worlc~ · · · · · . ' . · - .. ;l=t . ,. 0 ""'· . b. i_~ t4,~; 'i:, 1 - ! ,. ' ~ -1· ~ «-. 'Q&, ,. LESSON 5: COUNTERS & SHIFT REGISTERS ,,· >··· By Louis E. Frenzel, Jr. · · ··--~~nt· ® '$, :< f The two basic types of logic circuits are combinational circuits and sequential circuits. Combinational circuits are made up of logic gates connected in a special way. The outputs are a function of the inputs and how the gates are interconnected. Sequential circuits are made up of both gates and flipflops. The flipflops are the primary components as they are used to store binary states. Those states can be changed by input signals to form new states. Sequential logic circuits are designed to perform a variety of storage and timing operations. A sequential logic circuit can retain a binary word or manipulate it in various ways. Sequential circuits can also perform many different kinds of timing and sequencing operations. The two most commonly used sequential logic circuits are counters and shift registers. Virtually every digital circuit contains a counter or a shift register of some type. Binary Counters A binary counter is a series of JK flipflops which counts the number of input pulses that appear at the PARALLEL COUNTER OUTPUT A(LSB) COUNT 8 J --~·r IN K T c K ii RESET OR CLEAR Fig. 1: a 4-bit binary counter. All J and K flipflops are connected to binary 1 (high). Each flipflop toggles on the trailing edge of a clock waveform applied to input T. ' ! ' t input to the first flipflop. The counter stores the sum of input pulses as a binary number. To determine the number of input pulses applied to the counter, you simply look at the flipflop outputs and read the binary number stored there. Many digital circuits require that you keep track of the number of pulses that occur at a given point in the circuit. A counter is used for this purpose. Fig.1 shows a logic diagram of a simple 4-bit binary counter with the JK flipflop outputs designated as A, B, C and D. Each flipflop output is connected to the clock or toggle (T) input of the next flipflop in the series. This is referred to as cascading. The pulses to be counted are applied to the toggle input of flipflop A. All J and K inputs are assumed to be at binary 1 (high). Another important connection shown in Fig.1 is that all the clear (C) or reset inputs to the JK flipflops are connected together to form a common reset line. A binary O applied to the reset line will clear the flipflops so that the binary number stored in the counter is zero (0000). We can read off the binary number stored in the counter by looking at the logic states of the normal flipflop outputs. These are read from right to left, or DCBA. The A bit is the LSB (least significant bit) and the D bit is the MSB (most significant bit). Now let's see how the counter operates. Assume that we are using JK flipflops that change state when the clock input switches from 1 to 0. We call this the trailing edge or the negative-going transition of the input pulse. Now assume that an input pulse occurs that switches from high to low. This causes flipflop A to toggle from the binary Oto the binary 1 state. Looking at the flipflop outputs and reading them in the DCBA order, we see that the binary number stored in the MARCH 1988 81 NUMBER OF INPUT PULSES 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 C B A 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 0 1 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Fig.2: truth table for a 4-bit binary counter. counter is 0001. This is the binary reading for the decimal number 1. So one input pulse has occurred. When the second input pulse occurs, flipflop A is toggled again. This time it switches from the 1 to 0 state. As its state changes, the A output switches from high to low. That in turn causes flipflop B to toggle and set, its normal output going from O to 1. The transition appears at the clock input to the C flipflop, but the flipflop ignores low to high transitions. If we now look at the counter outputs, we see that the number stored there is 0010 or the binary equivalent of decimal 2. Two input pulses have now occurred. If you continue to apply input pulses to the counter, one flipflop will simply toggle the next in sequence and the binary number stored in the counter will increase by one for each input pulse that occurs. When this happens, we say that the counter is being incremented. The counter counts up from O to the maximum value that the counter is capable of holding. Fig.2 shows the truth table of the 4-bit binary counter. Note that the decimal number of input pulses applied to the counter corresponds to the binary value displayed by the outputs. This is true only if the counter has been reset prior to counting. An important point to note is that when fifteen input pulses have occurred, the binary number stored is 1111. When the 16th input pulse occurs, flipflop A toggles to 0. This in turn toggles B to 0, which in turn toggles C to 0, which toggles D to 0. The binary number PULSES TO BE COUNTED 1I 2I 3I 4 I 5I 6 I 7I 8 II 9 10I 11l 12I 13l 14I 15I A I 1 C 0 0 0 I I I--- 1 1 1 1 1 1 I o 0 0 1 ...o_"-o_...o_o=----=-o__,o..._..::.o__,o'-'! 1 1 1 Fig.3: input and output waveforms for a 4-bit binary counter. 82 SILICON CHIP 0 1 ~ I I 0 1 1 1 1 1 ·now indicated in the counter is 0000. This is equivalent to the initial reset state described earlier. In other words, the number 16 is too large for the counter to store. So once a 4-bit counter counts to 15, the next input pulse simply returns it to zero and it starts again. Fig.3 shows the input and output waveforms for the 4-bit binary counter as 16 input pulses are applied. Those timing waveforms illustrate all possible states of the counter. You may want to trace through the logic diagram of the counter and correlate each of the pulses shown in the timing diagram with each flipflop. This will ensure that you understand how each flipflop changes state on the high-to-low transition of each input pulse. Counting to Higher Values To count to larger numbers, all you do is add more flipflops to the counting chain. Each additional flipflop lengthens the binary word of the counter by one bit, thereby doubling its maximum count capability. The total number of states that a counter can assume is 2N where N is the number of flipflops. With four flipflops, the total number of states is 24 = 2 x 2 x 2 x 2 = 16. Those states are O (0000) through 15 (1111). You can determine the maximum count capability of the counter with the simple formula shown below: M = 2N - 1 where M = maximum count number and N = number of flipflops. With four flipflops, the maximum count capability is: M = 24 - 1 = 15 A 5-bit counter has a maximum count capability of 31. A 6-bit counter can count to 63, a 7-bit counter to 127, an 8-bit counter to 255, a 12-bit counter to 4095 and so on. ' A binary counter can also be used as a frequency divider. Take a look at the waveforms shown in Fig.3. Recall that a JK flipflop acts as a divide-by-2 circuit. As you can see in Fig.3, the output of the first flipflop has a period that is twice the period of the input pulses being counted. This means that the output of flipflop A is half that of the input frequency. Now look at the output of flipflop B. Again, you can see that its frequency is half that of flipflop A's output. A similar relationship exists in the remaining waveforms. The output frequency of flipflop B is onefourth that of the input to flipflop A. The outputs of flipflops C and D are one-eighth and one-sixteenth of the input frequency respectively. The frequency division factor of a binary counter is simply 2. With four flipflops, the frequency division factor is 16. A binary counter with eight flipflops will divide an input frequency by: 28 = 2 X 2 X 2 X 2 X 2 X 2 X 2 X 2 = 256 Thus, if a 6.4MHz input signal is applied to the 4-bit binary counter, the output of flipflop D will be 6.4 16 = 0.4MHz or 400kHz. Preset Counters The term preset means to put a flipflop into one state or the other prior to another operation taking Fig.6: count sequence of a 4-bit down counter. INPUT PULSE 1 1 1 1 1 1 1 1 0 0 0 0 0 0 1 2 3 COUNT .4 IN K C 5 6 7 8 ii 9 10 11 12 13 14 15 Fig.4: flipflop preset circuitry. place. Presetting a counter simply 1!1eans load~ng a binary number into the counter pnor to the mput pulses being applied. In many applicat~ons, the preset can simply be a clear or reset operation. If this was not done, the binary numbers stored in the co~nter would have no meaning unless you knew the bmary number stored in the counter beforehand. It's not too hard to see that it's a lot simpler to clear the counter first so that the binary number stored in the counter exactly represents the number of input pulses that occurred. On the other hand, there are applications where it is desirable to begin counting at some predetermined number. This is done with preset circuitry that takes advantage of the asynchronous set (S) and clear (C) inputs of the JK flipflops. A typical circuit for one flipflop is shown in Fig.4. If you would like to preset the flipflop to binary 1, you apply a binary 1 to the preset input _at gate fi-:-· Then you apply a binary 1 to the LOAD mput. This forces the output of gate A low and the output of gate B high, The result is that the asynchronous set input of the flipflop causes it to store a binary 1. Applying a binary O to the preset input and then switching LOAD from low to high will cause the flipflop to be reset or store a binary 0. . When all flipflops in the counter have the preset circuitry shown, then a parallel binary number can be applied to the counter and loaded into it prior to beginning the count operation. To show how that presetting works, assume that the 4-bit binary counter described previously has preset circuitry. Suppose that we apply the binary number 1010 to the preset inputs and load it into the counter. The counter outputs DCBA will read 1010 (decimal 10). Then assume that input pulses occur. If four input pulses occur, the counter is incremented to 1110 (ie, to decimal 14). Down Counters The binary counter described previously is an up counter as each input pulse increments the binary IN Fig.5: a 4-bit binary down counter. OUTPUTS C B 0 1 1 1 1 0 1 1 1 1 0 0 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 A 1 1 0 1 1 0 0 0 1 1 1 0 1 0 0 0 INPUT PULSES A B 1 C 1 1 Io 0 0 o I Io 1 I 0 0 I I 0 1 1 1 Io 01 0 0 0 0 0 0 01 Fig.7: input and output waveforms for a 4-bit down counter. number stored in the flipflop. That is, as each input pulse occurs, one is added to the count. It is also possible to construct a down counter so that the binary number in the counter is decremented by one as each input pulse occurs. As a result, down counters count backwards. For example, if a 4-bit binary down counter were preset to 1111, sequential input pulses would decrement it to 1110, 1101, 1100, etc. Some digital applications require this capability. Fig.5 shows how to connect four JK flipflops to form a down counter. Again the flipflops are cascaded by connecting the output of one flipflop to the clock (T) input of the next in series. The main difference here is that we connect the complement output of each flipflop to the clock input of the next. However, we still monitor the normal flipflop outputs to determine the count stored there. With this arrangement, the count sequence shown in Fig.6 is obtained. The table shows the counter starting with the maximum count stored in the flip flops (1111 ). When the count is decremented to zero, the next input pulse simply flips the counter back to its maximum count value of 1111. The cycle then repeats. Down counting is illustrated in the timing waveforms of Fig.7. Those output waveforms are the ones that occur at the normal flipflop outputs. Since the complement flipflop outputs are not shown, it is more difficult to trace the operation of that counter. If you'd like to see how each input pulse causes the toggling and triggering of each flipflop in sequence, simply draw the complement signals to each of the MARCH 1988 83 A IN T COUNT CONTROL Fig.8: a 4-bit binary up/down counter. When the count control signal is high (binary 1), the circuit is an up counter. When the count control signal is low, the circuit is a down counter. waveforms in Fig.7 before doing a pulse-by-pulse analysis. Keep in mind that a down counter can also include preset circuitry so that it may begin decrementing from some particular value. By adding some logic circuitry to the counter you can make it count up or down. This is illustrated in Fig.8. An up/down COUNT CONTROL line is added to determine the direction of counting. If a binary 1 is applied to that input, the counter will count up. This binary 1 enables all of the A gates and it causes the normal flipflop outputs to pass through the gates to the clock (T) inputs of the next flipflop in sequence. If the up/down control line is made binary 0, the B gates are enabled by the inverter and the A gates are inhibited. This causes the complement outputs to be passed through to the clock inputs. The counter then counts down. While binary counters can easily be made up of in' 192, ' L192,'LS192 ( 13) BO RR OW ! 12J CAR RY O UTPUT OUTPUT dividual flipflops and gates, that is rarely done anymore. The integrated-circuit manufacturers have already constructed binary counters in a variety of configurations, usually in multiples of four or eight bits. TTL, CMOS and ECL ICs are available, including those with presetting, down counting, etc. A Typical IC Counter One of the most-used IC counters is the 4-bit MSI device shown in Fig.9. The device is a 4-bit binary up/down counter with presetting. In other words, it incorporates all the features we discussed previously. The counter has four outputs and four parallel data lines are used for applying a preset input. The loadinput line causes the parallel binary word applied to the data inputs to be loaded into the flipflops. The counter also has a clear line for resetting it to zero. Instead of having a single count input like the up/down counter discussed previously, this device has two inputs. To decrement the counter, you apply input pulses to the down-count input. To increment the counter, you apply pulses to the up-count input. Carry and Borrow c~~~~ .o:<•:c._ 1 - - - I > <>-+ttt-1-t-t---+t---, UP !SJ COUNT DA TA 19) INPUT D The carry and borrow outputs have not been discussed previously. These are used when counters are cascaded. The carry output is produced by an AND gate that looks at the normal flipflop outputs. It detects when the counter content is 1111 which is the maximum value. The next input pulse will cause it to return to zero. When this happens, the carry output generates a pulse which is applied to the next counter in series, so that the overflow will be recorded. The borrow output is used for cascading counters in a down count application. The borrow output signal is generated by an AND gate that monitors the complement outputs of the flipflops. When the counter is decremented to 0000, the borrow output signal is generated and applied to the down count input of the next counter in series. With those signals, multiple counters can be cascaded to form binary counters with lengths of 8, 12, 16, 20 or any other multiples of 4 bits. BCD Counters Fig.9: schematic diagram for the Texas Instruments 74192 4-bit binary up/down counter. 84 SILICON CHIP While such counters are useful, there are many situations where it is desirable to use a decimal-like representation. To cope with this problem, some special binary codes have been developed. The most popular of those is binary coded decimal (BCD). BCD is BCD DECIMAL D C 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 0 0 0 0 1 1 B A 0 0 0 0 1 1 1 1 0 1 1 0 0 1 1 1 0 1 0 1 0 0 0 0 0 1 Fig.10: decimal to binary-codeddecimal (BCD) equivalents. 0 still a binary code in that decimal values are represented with binary numbers but only the decimal numbers 0 to 9 are used. The BCD code is shown in Fig.10. Decimal numbers are represented by 4-bit BCD numbers, one for each digit. For example, the number 729 in BCD is 0111 0010 1001. By using flipflops and gates it is possible to construct a BCD counter - that is, one that counts by tens. It has 10 states, 0 to 9. Such a counter is called a BCD counter, decimal or decade counter; you see one in Fig.11. Notice that the first three flipflops are cascaded in a standard 4-bit binary counter with the normal output connected to the clock input of the next flipflop in the chain. The last flipflop, on the other hand, has its clock (T) input connected to the normal output of the A flipflop. Note that the signal controlling the J input on the D flipflop is dervived from an AND gate that monitors flipflops Band C. Note also that the complement output of the D flipflop is fed back to the J input of the B flipflop. The result of all these unusual interconnections is that the counter has only ten states instead of the usual 16 for a 4-bit counter. The counter counts in the BCD sequence previously described in Fig.10. The waveforms generated by the BCD counter are shown in Fig.12. The counter counts from 0 (0000) to 9 (1001) in the normal sequence. When the tenth input pulse is received [trailing edge), the counter returns to 0 and the sequence repeats. While it's possible to construct a BCD counter from individual gates and flipflops, there's no need to bother since such devices are available as single integrated circuits. Most of these feature a master clear or reset line and many feature both presetting and up/down counting capabilities. To count values higher than 9, BCD counters may be cascaded as shown in Fig.13. The first BCD counter then counts in units of Oto 9. After 10 input pulses occur, the MSB output of the first counter (ie, the D output) triggers the next counter in sequence. The second IN .I. 1 A o o oI ............... _ co OO 0 0 1 1 1 ...~o~o_l_o 0 0 0 0~ I Fig.12: input and output waveforms for a BCD counter. counter represents the tens decade and is incremented every 10 input pulses. The tens counter in turn drives the hundreds counter. Additional counters can be added for thousands, tens of thousands, hundreds of thousands and so on. To read the content of the counter, you observe the BCD codes at the counter outputs. For example, the number stored in the counter shown is 853. Note that in reading the output of a BCD counter, the 4-bit groups are separated from each other. The output is three 4-bit BCD numbers (1000 0101 0011). Just as you can use binary counters for frequency division so can you use BCD counters for that application. The circuit shown in Fig.13 will produce frequency division by some multiple of 10. The first BCD counter will divide the input frequency by 10 (ie, its D output will be one-tenth the frequency of the input). The second counter will produce division by 100 while the third will produce division by 1000. Both binary and BCD counters can be used in counting and frequency dividing applications at very high frequencies. Standard TTL MSI counters can achieve speeds upward of 50MHz while Schottky TTL counters can achieve speeds up to 125MHz. CMOS counters have a much lower limit of approximately 25MHz, but progress is being made in extending this. ECL counters are available for frequencies up to 2GHz. Shi£t Registers Another sequential circuit made up of flipflops is the shift register. Like a counter, multiple flipflops are used to store a binary word. However, the flipflops are interconnected in such a way that incrementing and LEAST 1100 SIGNIFCANT A B C D DIGIT (LSD) COUNT IN Fig.11: schematic diagram for a BCD counter. All unused J and K inputs are connected to binary 1 (high). 0 II 1 1 0 1 0 A B C D BCD COUNTER BCD COUNTER UNITS TENS MOST SIGNIFICANT DIGIT (MSD) HUNDREDS Fig.13: cascaded BCD counters MARCH 1988 85 IN SHIFT (CLOCK) Fig.14: logic diagram for a 4-bit shift register. decrementing counting operations are not achieved. Instead, the connections are such that the binary word stored in the counter is shifted either to the right or to the left. In other words, as each clock pulse occurs, the bit stored in one flipflop is shifted into the flipflop next to it. A common 4-bit shift register is illustrated in Fig.14. All the clock (T) inputs are connected together to a single line. The normal and complement outputs of one flipflop are connected to the J and K inputs respectively of the next flipflop in sequence. A single input line is used for entering data into the shift register a bit at a time. Shift registers are used to deal with serial data words. A serial pulse train, that occurs in synchronism with the shift clock pulses, applied to the input will be entered into the shift register a bit at a time. This is illustrated in simplified form in Fig.15. The individual blocks represent each of the flipflops in the shift register. All the flipflops are initially reset. When the first clock pulse occurs, the first bit in the serial pulse train at the input will be shifted into the first flipflop. A binary O is shifted out of the D flipflop. As each shift clock pulse occurs, the next bit is shifted into the register. The first bit moves over to flipflop B to accommodate the new input bit. After four clock pulses have occurred, the entire serial word is then contained in the shift register, as shown. Holding the input line at zero and applying four additional shift pulses will cause the binary number stored in the shift register to be shifted out a bit at a time, thereby generating a serial output word. The process is illustrated in Fig.16. As you can see, the shift register can be used to accept, store and generate serial binary data words. One of the most common applications for a shift 1101 register is serial-to-parallel data conversion. A serial data word can be shifted into the shift register. If the outputs of the individual flipflops are available, then that word will appear as a parallel data word as shown in Fig.17 A. If the flipflops in the shift register have presetting circuitry similar to that described earlier for binary counters, then the register can be loaded with a parallel binary number. Once the shift register is preset with the parallel number, shift pulses will shift the word out a bit at a time. This creates a serial version of the parallel input word. Thus, the shift register accomplishes parallel-to-serial data conversion as shown in Fig .17B. Like counters, shift registers are available as prepackaged circuits in a variety of forms. MSI devices with four and eight bits are common. Those feature preset, clear, shift right, or shift right and left. Larger shift registers can be created by simply cascading 4 - and 8-bit devices. For example, a 32-bit shift register can be created by cascading four 8-bit devices. Very large LSI shift registers are also available for special applications. For example, a 256-bit MOS shift register is available for memory applications. Such a register is not used to store a single 256-bit word. Instead, it is used to store many smaller words. For example, a 256-bit shift register can store 256 -;- 8 = 32 bytes. Those bytes are retained in the shift register flipflops end to end as illustrated in Fig.18. The data is entered serially and read out serially. Because there are so many flipflops, parallel output is not feasible. Fig.19 shows a circuit for using the 256-bit shift register as a memory. The gates at the input of the shift register are used for entering serial data when it is desired to store a byte and for data recirculation. When clock pulses are applied to a shift register, data that is shifted out is generally lost. However, it doesn't have to be. By taking the serial output of the shift register and feeding it back into the shift register input, the serial word will be restored at the input as it is read out. This is accomplished with gates A and Cat the input to the shift register. The CONTROL line is used to select whether new serial data is to be stored or whether recirculation is to be accomplished. When the CONTROL input is high, the shift register lolololol ORIGINAL STATE Fig.15: how serial data is entered into a shift register. o-1 oI oI111 1o, 11lol1lololoo 2ND 2ND o-1 oI oI o1, 1, o, 1l1lol1lolooo 3RD 3RD 1,1,101110000 4TH 86 . SILICON CHIP Fig.16: how serial data is removed from a shift register. o-!o I olo lo 11011 4TH 1 A 0 1 0 RECIRCULATE mJ 101ololojojoj ORIGINAL STATE AFTER 4 SHIFT PULSES 256•BIT SHIFT REGISTER Bffl ORIGINAL STATE 0 1 1 SERIAL OUT ~ AFTER PRESET Wr90~0110 0 0 1 1 0 CLOCK Fig.17: shift register applications for (A) serial-toparallel conversion and (B) parallel-to-serial conversion. IN ---i BYTE BYTE BYTE 31 30 29 I 1 BYTE ADDRESS o=D---ouT BYTE BYTE BYTE 2 1 0 Fig.18: a 256-bit shift register used as a serial memory to store 32 bits of data. will recirculate. Serial data output is fed to gate A which is enabled by the control line. This passes through OR gate C to the shift register input. During this time, any new serial data is ignored by gate B which is inhibited by the inverter operated by the CONTROL line. To enter new data, the CONTROL line is set to binary 0. This enables gate B and inhibits gate A. No recirculation will take place. However, as the shift pulses are applied, the new serial byte to be stored will be shifted in a bit at a time. To keep track of where the different bytes are stored in the shift register memory, the circuit in Fig.19: a 256 bit shift register used as a memory bank. Fig.19 uses a 3-bit binary counter and a 5-bit binary counter. The 5-bit binary counter is a word counter and its output is a 5-bit binary word we call the address. Remember we said that it is possible to store 32 bytes in a 256-bit shift register. We label those bytes byte O to byte 31. The 5-bit counter has a maximum count capability of 31, therefore, the address appearing at the output of the counter designates which byte appears to the far right of the shift register, ready to be shifted out. The 3-bit binary counter is used to count clock pulses. This 8-state counter counts to eight for each byte stored or read out. Reproduced from Hands-On Electronics by arrangement. Gernsback Publications, USA. ~ © SHORT QUIZ ON DIGITAL FUNDAMENTALS 1 . A 4-bit binary up counter is preset to 001 0. Seven input pulses occur. The decimal value of the counter content is: c. 9 a. 2 d. 11 b. 7 2 . The maximum number of states that a 6-bit counter can represent is _ _ _ _ _ __ _ __ 3. The maximum number count capability of a 7-bit counter is ___________ _ _ __ 4. A 3-bit binary counter is cascaded with a BCD counter. An input frequency of 400kHz is applied to the circuit. The output frequency is _ _ _ kHz. 5. How many BCD counters does it take to represent the number 1 9, 900? a. 2 c. 4 b. 3 d. 5 6. A 4-bit binary down counter is preset to 0011 . Six input pulses occur. The binary value of the counter content is: a. 0011 c. 1010 b. 0110 d. 1101 7. Clearing a counter or shift register means the same as presetting it to _____ _ _ _ __ LESSON 5 8 . The maximum count of a 4-bit BCD counter is: a. 1000 c. 101 O b. 1001 d. 1111 9. Counters and shift registers are a type of _ _ logic circuit. 10. List four ways that data can be entered, stored and read out of a shift register . a. c. b. d. ANSWERS ino repas 'U! 1a1reJed ·p ino 1a11eJed 'U! 1epas ·o lno 1a11eJed 'U! 1a11eJed ·q ino 1epas 'u! 1epas ·e ·o L 1e11uanbas ·6 (6 1ewpap) LOO L ·q ·g OJaZ 'L .( LO L L '0 L L L ' L L L L '0000 ' LOOO 'O LOO Oj S8W!l X!S pa1uawaJoap S! L LOO) . LOLL ·p ·(1!6!P lpea JOJ Ja\unoo 0:)8 auo) g ·p 'ZH)j9 = 08 ~ ZH)jQQv ·o L Aq Ja\unoo 088 a41 pue g /4q sap!A!P Ja\unoo 11q•£ a41 'ZH)f9 LG L = L - (G X G X G X G X G X G X G) = L - LG v9 = G x G x G x G x G x G = gG 6 = L + G = L + 0 LOO JO '. 6 ·o MARCH 1988 ·g ·g ·v '8 ·G .L 87 Bearcat BCB00XLT Scanning Receiver from Uniden Designed for the US market, the Bearcat BCB00XLT scanning receiver should be of considerable interest to communications enthusiasts. Here we review its main features. While most scanner enthusiasts recognise the name Uniden, few realise that this is also the manufacturer behind the wellknown Bearcat brand of scanning receivers. The BCB00XLT is top-ofthe-line in the Bearcat range, mainly because if its ability to receive the new cellular telephone frequencies. But the BCB00XLT has other attributes that make it special in Australia. The only version available here is the US model which means that it covers important communications bands not normally covered by scanners made specifically for the Australian market (see Table 1). As such, the Bearcat BCB00XLT 88 SILICON CHIP should be of interest to amateur radio operators, pilots, mariners, commercial users, satellite enthusiasts, UHF CBers and scanner enthusiasts alike. It covers four amateur radio bands, commercial VHF and UHF bands, the aviation band, and both PAMTS and cellular telephone frequencies. As with other scanners now on the market, the unit includes microprocessor control. It has 40 memories which can be linked or programmed separately, allowing two banks of dedicated service frequencies to be scanned. This means that you can scan all 40 channels or elect to scan channels 1-20 or 21-40. The keyboard is easy to use and is laid out in two sections to allow programming and operation. The program section allows the direct selection of any of 40 stored frequencies, while the operations section provides for channel lockout, direct channel access, automatic search, scanning, priority override and delay functions. The frequency and operating mode are displayed on a 9-digit green fluorescent display. Perhaps one of the more interesting features is the priority override. This allows the user to monitor transmissions on one channel while actually listening to another. What happens is that the priority feature samples the frequency on channel 1 every three seconds. If a signal is detected on this channel when sampled, the receiver then remains tuned in to it until the transmission ceases. The scanner then reverts to the previous mode of operation. Band (MHz) Sensitivity (12dB SINAD) Channel Steps 29-30 30-50 50-54 118-135.975 136-144 144-148 148-174 0.3µV 0 .3µV 0.3µV 0.8µV 0.3µV 0.3µV 0 .3µV 5kHz 5kHz 5kHz 5kHz 5kHz 5kHz 5kHz 406-420 0 .5µV 12.5kHz 420-450 450-470 0.5µV 0.5µV 12.5kHz 12.5kHz 470-512 0 .5µV 12.5kHz 806-912 0 .7µV 12.5kHz Supplied with the 800XLT are two antennas, one for the VHF/UHF bands (telescopic) and the other for the 800-900MHz band. These attach to sockets on the top and rear panels. Alternatively, an external antenna can be used for better reception of weak or noisy signals. Because the 800XLT scanner is a US version, it does have a couple of minor drawbacks. First, the squelch controls operates in reverse; ie, you rotate it anticlockwise to mute the receiver. Second, the scanner has a key marked Service continued from page 17 10-metre amateur Cordless phones 6-metre amateur AM aircraft Polar orbiting satellites 2-metre amateur VHF commercial; VHF marine UHF low band commercial 7 0cm amateur Ul-iF commercial; police rescue helicopter UHF CB; PAMTS mobile phones Cellular telephones "WX" which is designed to scan local weather stations in the US (162.4MHz-162 .55MHz). Unfortunately, this feature is of no use in Australia. But, apart from these quibbles and the fact that the unit is only available for 12V DC operation, the BC800XLT is well worth consideration by those with an interest in VHF and UHF communications. It is priced at $749 and is available from Santronic Corporation, 345 Princess Highway, Rockdale 2216. Phone 599 3355. (Garry Cratt). Spot light for video film-making Most recent model domestic video cameras are usable in quite low values of light, down to only 5 or 6 lux in some cases. But to really give the best results, with bright colours, they need lots of light. This video accessory light from Arista gives plenty of that. It consists of a lightweight holder with a quartz halogen lamp which can be attached to most video cameras via a bracket. Four "barn doors" on the lamp housing allow the beam to be controlled. The unit is powered from a 12V gel battery which is held in a shoulder pack and weighs Hifi Review 2.75kg. The unit comes with a charger. For further information, contact Arista Electronics Pty Ltd, 57 Vore Street, Silverwater, NSW 2141. Phone (02) 648 3488. tempt to measure distortion at 20kHz. In other words, the performance is well up to standard for a medium-priced CD player. The CD-1500 also went through our usual tests for tracking and error correction and showed up well. Nor is it fazed by physical shock to the case and it is better in this respect than a number of more expensive players. In summary, the Realistic CD-1500 is a good machine which performs well and has most of the facilities which most people want. The only drawback is that, considering it is basically a no-frills player with remote control, it is a touch dear. To be fair though, it is backed up by the largest electronic retail network in the country with a service record second to none. That being the case, it is worth paying a premium for the CD-1500. It is priced at $529.00. You can hear it at any Tandy store. ~ Tape Player continued from page 42 work first so that it can be used as a drilling template (optional). A small clamp made from scrap aluminium was used to hold the batteries in position and is secured to one end of the case using a screw and nut. It's now simply a matter of mounting the parts and completing the wiring as shown in the coded photograph. The electret microphone should be wired using shielded cable, while the remaining wiring can be light-duty hookup wire. Be sure to connect the battery leads the right way around. To test the unit, first press the run button and check that the tape motor runs. If it does, you can now record a message by pressing the run and record buttons at the same time while speaking into the microphone. Check that the message plays back and repeats if the run button is held down. Finally, you can add a volume control by connecting a 5000 potentiometer in series with the speaker. Connect the amplifier output to one side of the pot and connect the loudspeaker to the pot ·wiper. .~ MARCH 1988 89 NEWPRODUCTS-CTD National Series 32000 Designer Kit For those in the computing business, all the interest has moved into the 32-bit arena, with microprocessors such as the National 32000 series. To help the development process, a Designer Kit has been made available at a very reasonable price. The NS32000 32-bit family series of ICs are designed for high performance applications such as in CAD workstations, multi-tasking, multiuser systems, robotics and artificial intelligence. The power of this series of microcomputers brings super mini and mainframe power to a desktop or personal computer. The design is optimised to use high level languages (HLL) such as C, Pascal and FORTRAN 77 while operating with UNIX. National's designer kit is a very economical way to obtain the major integrated circuits plus documentation and software for a complete 32-bit microcomputer. ICs supplied with the designer kit are the NS32032 central processing unit (CPU), an NS32081 floating point unit (FPU), an NS32082 '?'A National D semlconduct.nr Series 32000 Desi• . . gtlerKit Fir,stin ~~Bit Microprocessors 90 SILICON CHIP memory management unit (MMU), an NS32201 timing control unit (TCU) and NS32202 interrupt control unit (ICU). In addition, a set of four PROMs programmed with the Tiny Development System (IDS) and a PAL (programmable array logic) address decoding IC are supplied. These components can be built onto a printed circuit board with the addition of extra memory, logic and peripheral components, to complete the 32-bit microcomputer. A full circuit diagram is given for the computer and copious information is provided to enable construction of the PCB. A suitable PCB can be obtained by sending US $129.95 to Computer Talk in the USA, using the order form included with the kit. Once complete, the computer PCB can be connected to an IBM PC/AT COMt port. The PC terminal and keyboard are then used for the transfer of files between the designer kit and PC/AT using the IDSCOM software utility supplied on disc with the kit. A Tiny Development System (IDS) enables generation of 32000 executable code. The TDS features include writing, editing assembly, debugging and execution of source code programs. Architecture Architecture for the Series 32000 products is very clean, even though the floating point arithmetic and memory management could not be incorporated onto the same chip as the CPU. The CPU has an optimum number, size and scope of registers. There are eight 32-bit general purpose registers and eight 32-bit floating point data registers. The memory management unit is intended for implementing demand paged virtual memory. At any point in time a program sees an addressing space of up to 16 megabytes. The design reduces bus interference between direct memory access, multiple CPUs and graphics by reducing memory bus traffic. It does this by maximising information in each transfer and eliminates transfers by keeping information where it is needed. Overall, the powerful instruction set, 32-bit bus and complete family of chip sets available plus the ability to operate HLL and UNIX make up a very advanced machine. Undoubtably, the National Series 32000 microprocessor chip sets will be widely used in the future. The Series 32000 Designer Kit is available for just $180 including tax from Geoff Wood Electronics Pty Ltd, 220 Burns Bay Road, Lane Cove West, NSW 2066. Phone (02) 427 1676 . . Velleman kits from Eagle Electronics Made in Belgium, the Velleman range of electronic kits is very comprehensive and encompasses projects such as a microprocessor universal timer, electronic ignition, electronic thermometer, a motor speed control, a light computer and a Centronics interface. Each kit is well presented and packaged. We had a look at a sample kit, the Stereo VU LED meter, K-1798 which is based on two Siemens UAA170 ICs together with two 741 op amps. The kit is packaged in a see-through plastic box and uses a well finished screen-printed, tinned and solder-masked printed board. The LEDs are mounted behind a screen-printed panel which could be part of the front panel of a mixer or similar piece of audio equipment. For further information on the Velleman range, contact Eagle Electronics Pty Ltd, 54 Unley Road, Unley, South Australia. Phone (08) 271 2885 . The LogicBridge. A new concept in handheld logic analysers. The LogicBridge 136 is a dedicated logic instrument for those involved in the design, repair or maintenance of digital electronic circuits and equipment. It is handheld and battery powered . While it performs like an intelligent 3 channel logic probe. it is also able to store waveiorms like a logic analyser. Waveforms can be viewed and measured on a custom LED display. Stored waveforms can later be serially transferred to a personal computer for further analysis. Being a dedicated logic instrument, the LogicBridge has a range of speci al digital debugging and indentification faci lities. As well , an audio output may be used for triggering and waveform identification . With over 10,000 units sold in the U.S. alone. it is the ideal unit for the workshop or the field technici an alike. SHOWROOM SALES 86 Parramatta Road Camperdown 2050 VIC OLD WA Radio Parts Group. Melbourne. Phone 329 7888 Bailee Systems. Brisbane. Phone 369 5900 Nortek. Townsv1lle Phone 79 8600 H1nco Engineering . Perth. Phone 381 4477 ACT SA TAS Phone· (0215193933 Fax 10215501378 Electronic Components. Fyshw1ck Phone 47 3688 !nt"I Commurncat1ons Systems. Por1 Adelaide Phone 47 3688 George Harvey Electronics. Hobart Phone 34 2233 MARCH 1988 91 NEWPRODUCTS-CTD 20MHz oscilloscope from GW Instruments One of the lowest cost oscilloscopes presently available is the GOS-522 20MHz dual trace model from GW Instruments. It has a 15-cm rectangular tube with internal graticule. Accelerating potential is approximately 2.2kV. Additional features offered by the GOS-522 include vertical mode triggering, auto trigger level lock and variable hold-off. The auto trigger facility is handy for triggering from waveforms where the DC offset level is varying while the variable hold-off feature is useful when monitoring digital and video waveforms with irregular or uneven duty cycle. Signal shot Sideways printing and all that As versatile as the the average BO-column dot matrix printer is, there are many things it just won't do or won't do without a hell of a lot of programming. For example, say you're printing out a big spreadsheet or a family tree (something we know you do every week or so). The only way to print it out is to do it sideways. Now there is a software package which allows your IBM PC and dot matrix printer to do it. It also allows a wide variety of fonts, as well as the full IBM character set. Note: as well as the standard 80-odd ASCII characters on the keyboard, the IBM also has provision for the Greek alphabet, maths symbols and graphics characters. The new program also allows printing enhancements to programs such as W ordstar which do not normally allow you to use all the fonts available on your printer (without customising Wordstar, that is). Called Printworks, the new software is also available in a version to suit laser printers. Contact PC Extras, GO3 The Watertower, Redfern Hill. Phone (02) 319 2155. Effective new strippers from Arista Small oven for printed circuit boards An oven for curing the resist on PC prototypes is the latest in a line of equipment from Sesame Electronics for making PCBs in small quantities. The unit has an electric heating element, a dial thermostat, and a timer. The PCB, which can be any size up to 250 x 200mm, rests on a wire tray inside the oven. For further information contact Sesame Electronics Pty Ltd, PO Box 452, Prahan, Vic 3181. Telephone (03) 527 8807. 92 SILICON CHIP Arista have two new wire strippers in their range of tools for the technician and enthusiast. One model, the CS 500, is for stripping coax cables, (cable types RG58 and RG59) while the other, a brutallooking but effective beast, the CS 100, is for stripping single and multi-strand wires. For further information, contact your Arista stockist or Arista Elec- Line Grabber for Phones sweep mode is also available. The GOS-522 has a genuine 20MHz bandwidth and has a 20 nanosecond/division sweep range to make timing measurements at high frequencies much easier. For further information on the GOS-522 contact your GW Instruments stockist or the Australian distributor, Emona Instruments, 86 Parramatta Road, Camperdown, NSW 2000. Phone (02) 519 3933. check this by measuring the voltage across the limiting resistor) but the LED is not illuminated, it is likely that the LED is installed the wrong way around. If you can't get the LED to illuminate for supply voltages above 20 volts, try shorting out the SCR. This will indicate whether the SCR and its associated components are faulty or not. Repeat these tests for your other Line Grabbers. You should be sure that they are working correctly before you connect them to the phone lines. A further wrinlcle There is another variation of the Line Grabber you could use if you Amateur Radio tronics Pty Ltd, 5 7 Vore Street, Silverwater, NSW 2141. Phone (02) 648 3488. continued from page 21 wanted to be clever. Say you had a phone which you use a lot and you don't want to fit the Line Grabber to it. That's OK. All you do is fit Line Grabbers to all the other extensions but not to your phone. This will allow your phone to grab the line at any time but if another extension is picked up before yours, you can still listen in. That could be useful in situations when another extension answers a call intended for you. ~ Acknowledgement: we thank Arista Electronics Pty Ltd for giving us the idea for this project. They will have a commercial version available shortly. Antennas physically long. Suitable only for UHF due to physical instability. Next month, we'll describe a few practical antennas that you can build yourself. Corrections In Table 1 on p.77, January 1988, the location of the VK4RAT transmitter should have been listed as Townsville (not Brisbane). Also, the vision input signal should read 426.25MHz (not 444.25MHz). Would readers also please note that the address of the Sydney ATV continued from page 71 Group is now 24 Larra St, Guildford, 2161, NSW. The repeater operates from 6.30-9pm on Mondays, Tuesdays and Thursdays, and from 12-5pm on Saturdays and Sundays. We thank the two readers who contacted us with the above information. Finally, the author would like to acknowledge the following amateurs who provided information on amateur TV for the January issue: VK2BTV, VK2ZZO, VK2AAK, VK3PC, VK3BFG, VK5AWA and VK5KG ~ High, Low, Sink & Source Strobe warning light This self-contained Xenon strobe light can be used as a warning beacon on boats or cars, as an attention-getter for shop displays, as a Christmas or party decoration, or as an external indicator for a domestic burglar alarm. It runs from 12V DC, battery or mains plugpack, and draws about 150mA. Flash rate is about two per second. The screw-on lens cap is available in red, orange or blue. The unit is weatherproof and has a screw mounting base. It retails for $35 from Arista outlets. source up to about 18 milliamps but depending on the output voltage it can sink only about one milliamp. Some logic circuits can sink a lot more current than they can source. The prime examples of this aTe TTL (transistor-transistor logic) devices which can typically sink about 25mA, or a lot more in the case of Schottky devices, when their outputs are low (ie, close to 0V) but can source virtually no current when their outputs are high (5V). These examples of devices which have unequal source and sink current capability invariably have output stages which are essentially non-symmetrical. In some cases, they may have open-collector out- continued from page 65 puts which means that they can sink quite a lot of current but can source no current at all unless they have an external "pull-up" resistor to pull their outputs high. Finally, before we leave this discussion, there is another definition of high and low which is relevant to comparators and logic circuitry. A signal is said to be high if it is high enough to cause a comparator or logic gate to change state. In this definition, high means above the positive threshold of the device's input. For example, in a logic circuit running at 15V, high may be any voltage above + 7.5V. Similarly, low many be any voltage below + 7.5V. ~ MARCH 1988 93 ASK SIUCON CHIP Got a technical problem? Can't understand a piece of jargon or some electronic principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Capacitance Adapter for DMMs I am writing regarding the Capacitance Adapter for DMMs described in the November issue of SILICON CHIP. I purchased the kit from Altronics in Perth and after building it, tested the unit on the "pF " range with a lOOOpF capacitor. I found it did not read accurately and only reached 857pF. I was not able to correct this situation with the LOW adjust trimpot VR1. I found the only way to get a correct reading was to remove the 120kQ resistor in series with VR1 and replace it with a link. It now reads accurately on all ranges. Could you please tell me why I had to remove this resistor? (K.A., Kambalda West, WA). • The immediate explanation for the need to remove the 120kQ resistor is that the upper and lower input signal thresholds of the 74HC132 NAND Schmitt trigger are outside the tolerances catered for by our circuit. In fact , on the face of it, the thresholds are much further apart than we catered for. When we looked at various manufacturers' data again, prompted by your letter, we note that the range of hysteresis values (difference between upper and lower threshold voltages) is more than four to one for a supply voltage of 5 volts. For example, at one extreme of manufacturing tolerance, a 74HC132 could have an upper threshold of about 3.5 volts and a lower threshold of 1 volt, giving a hysteresis of 2.5 volts (ie, the difference). At the other extreme, a 74HC132 could have an upper threshold of 2.5 volts and a lower threshold of 1. 9 volts, giving a hysteresis value of 0.6 volts. If you divide 2.5 by 0.6 you get a value of a little over 4, as we quoted above. When such a NAND Schmitt trig94 SILICON CHIP ger is used in the oscillator circuit of the Capacitance Adapter (see ICla), the likely range of the frequency it will produce, without adjustment, is about 4.5 to one. This is because the charging and discharging of the .047 µF capacitor is an exponential function. Without going into the maths of the oscillator function, it's looks as though we goofed rather badly doesn't it? After all, the combination of 100kn trimpot and 120kn fixed resistor only gives a range of 1.83:1 (220kn divided by 120k0) does it not? We can see all our readers nodding in agreement. ...------+sv 74HC132 VRl 100k This is the oscillator circuit of the Capacitance Adapter featured in the November 1987 issue. Wide tolerance limits on hysteresis for the gate inputs mean that the frequency can vary by more than 4.5:1 before adjustment. But before we get out the sackcloth and ashes, one other factor should be considered. All the upper and lower threshold levels in the four gates of a particular 74C132 should be roughly equal, should they not? Therefore, even though the oscillator frequency of IC la can be expected to vary over a wide range, before adjustment, oscillator IClc can be expected to more or less "track" ICla. Similarly, the switching levels of IClb can be expected to vary as much as the other two gates. Therefore, the range of adjust- ment we have provided for the oscillator of ICla should have been enough to cater for variations between the gates of particular 74C132 devices. Unfortunately though, manufacturers do not give any clues as to the expected variation between gates of individual devices. We are in the dark on that topic. So the bottom line is, we are not sure why you had to replace the 120kn resistor with a link. It should not have been necessary to remove it completely. In fact, if a lOOOpF capacitor was giving a maximum reading of 85 7pF as you claim, then it should have been possible to get sufficient range of adjustment by replacing the 120kQ resistor with a value of 82kQ. Clearly though, your experience suggests that a greater range of adjustment is necessary. We will therefore play it safe and suggest to the suppliers for this kit that they change the 100kQ trimpot VR1 to 200kQ and the 120kQ resistor to 47kQ. This will give an overall frequency adjustment range of 5.25:1. Infrared sensor for driveway monitor I wish to construct an infrared sensor to mount under the eaves at the front of my house, to detect people approaching up the driveway and to turn on an outside light. Would the passive infrared sensor for burglar alarms as described in your December 1987 issue be adaptable to this function? Also could it be disabled during daylight? (W.D., Mt Waverley, Vic). • Yep. The PIR sensor described in December should be just what the doctor ordered. You could disable it during daylight hours by using a light dependant resistor (ORP12 or similar) connected between pin 2 of IC4 and the + 12V line. Note that if you intend to use a How to dim fluorescent lights I built the Speedi-Watt dimmer descibed in the December 1987 issue of SILICON CHIP and I have tried it out as a dimmer for a 20 watt fluorescent lamp fitting. Unfortunately, it will only dim over a very limited range below which it flickers badly. Also, the lamp will not start if the dimmer is wound down before power is applied. What do I have to do to make the circuit dim reliably? (B.L., Curl Curl, NSW). • Fluorescent lamps do not like being dimmed, as you have found. It is possible but the circuit gets complicated by the need for a transformer. When a fluorescent lamp is operated at full mains voltage the filament electrodes at each end of the tube run quite warm and so provide plenty of electrons to maintain the discharge. If you use a dimmer, the normal discharge current is reduced and so the filaments become cooler. The way around this is to maintain the filaments at a constant temperature by running them from a transformer with two separate low voltage windings, one for each end of the tube. The transformer should have two 6V windings and should be connected to the mains so that its primary voltage is independent of the setting of the dimmer. The cirmains spotlight, the relay should have contacts rated for 240V AC. Transistor replacement for amplifier I am interested in your 100W module as published in the December 1987 issue. It would seem an ideal replacement for a Millbank Electronics amplifier I have under repair for a friend. This particular amplifier failed and in the process one BDY7 4 power transistor failed on each side. I have repaired the main board but have been unable to source any BDY74 power transistors. C4 .01 25DVAC This circuit shows how the Speedi-Watt Dimmer published in the December 1987 issue can be adapted to dim fluorescent lamps. cuit is shown in the accompanying panel. Note that it uses the SpeediW att dimmer featured in the December 1987 issue of SILICON CHIP. This will allow the tube to be dimmed over a much greater range but even so it is best to start it with full voltage applied and then to dim down. Companies that make fluorescent ballasts generally make these dimmer filament transformers. To buy them you will have to contact a lighting supplier. Note that there is one other trap to the circuit. It needs a rapid start tube and rapid start ballast; ie, the conventional starter and ballast is dispensed with. In effect, this means that the lamp fitting has to be completely re-wired. The only bits you get to re-use are the metalwork and the "tombstones". Furthermore, rapid start tubes are becoming harder to get, as are most of the older tubes with a diameter of 3 7mm. On the other hand, you may find that a 20W or 18W tube will start fairly easily, despite the fact that it is not a rapid start type. The truth is that dimming fluorescent lamps is a pain which is why it is not done on a commercial basis very frequently. It can be done with a high frequency "electronic" ballast, but that is another story. Your 100W module does seem an ideal repalcement, however the transformer in the Millbank amplifier delivers ± 55 volts DC under quiescent conditions, with full power consumption being 220VA. Could I use your 100W module to slot straight in or would I have to reduce the voltage output of the supply? The output of the Millbank amplifier can either be taken direct from the output stages into an an load or via an output transformer. The output transformer is wired in parallel with the direct output and can be configured for two separate 50V supplies or a single 100V supply. I would presume the primary of the output transformer to be an impedance. So again, could I use your 100W module? (J.B., Broadmeadows, Vic). • According to our references, the BDY7 4 is a 115 W silicon power transistor with a collector voltage rating of 150V and a current rating of 15 amps. It was originally sourced by Philips and Mullard. With those ratings, it should be easy to obtain a suitable replacement. We suggest the 2N3773, sourced by RCA and Motorola, or the Motorola MJ15003. Both these have higher power ratings than the BDY74 and the latter transistor is available continued on page 96 MARCH 1988 95 CEl.1'1' Cash in your sqrplus gear. Advertise it here in Silicon Chip. Advertising rates for this page: Classified ads - $7.00 for up to 15 words plus 40 cents for each additional word; Display ads (casual rate) - $20 per column centimetre (max. 10cm). Closing date: five weeks prior to month of sale. If you use a PO Box number, you must include your permanent address and phone number for our files. We cannot accept ads submitted without this information. To run your own classified ad, put one word on each of the lines below and send this form with your payment to: Silicon Chip Classifieds, PO Box 139, Collaroy Beach, NSW 2097. PLEASE PRINT EACH WORD SEPARATELY, IN BLOCK LETTERS 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ($7.00) 16 ($7.40) 17 ($7.80) 18 ($8.20) 19 ($8.60) 20 ($9.00) Advertisers Index Our advertisers are vital to t.he success of SILICON CHIP. Please give them your support. Altronics .. .. ... ....... .. ... ....... 22-25 Arista Electronics .... .. ... ... .. .. ... 73 Ballarat Electronic Supplies ..... 59 Dick Smith Electronics .. .. .. 36,37, 66,67 Elmeasco .... ........ .. .. ... .. .. .... . IFC Emona Instruments ...... .. .... .. .. 91 Geoff Wood Electronics ..... .. .. . 11 Jaycar Electronics .. .. .. ...... 48,49 RCS Radio .. .... .. ........ .... ....... . 55 Tandy Electronics .. .............. . IBC VSI Electronics ................... OBC PC Boards 21 ($9.40) 22 ($9.80) 23 ($10.20) 24 ($10.60) 25 ($11.00) Name ... ...... ....... .. ... ......... ... ...... .......... .... .. ... ...... ... •··· ···•· ··· ··· ··· ···· ···· ······ ····· ··•· Address ... ... ........ ..... ................ ..... ...... .. .............. ... ..... .. .. . . Suburb/Town ..... ........ .. ....... ....... ....... .... ..... .... ....... .. ....... . ... Postcode ... .... .... ..... . Enclosed is my cheque or money order for $ ........ .. ...... .. ... .. ..... ....... or please debit my Bankcard □ Visa □ Card No ...... .. .......... .. .... ........ ... ..... ..... ..... ....... .... ... . Signature .. ............... ... .. ..... ..... .. ........... ..... Ask Silicon Chip continued from page 95 from stores such as Jaycar, Dick Smith Electronics and Altronics. The above really answers your question in full but your letter does raise a few points of interest. First, as noted in these pages last month, the 100W module described in December 1987 will not run safely with supply voltages much above its nominal ± 40V DC. Second, it is not really intended for driving an output transformer. To do so, it would require flyback diodes (such as 1N5404) across each output transistor (ie, each diode reverse biased). The diodes safely damp any spikes which would otherwise be generated by the transformer's inductance when the amplifier is driven into clipping (or if the protection circuits operate). The amplifier should also incorporate a trimpot adjustment to minimise any residual DC output 96 SILICON CHIP voltage which would cause direct current to flow in the transformer. By the way, we suspect that the output transformers in your Millbank amplifier are autotransformers which can be configured for 50V or 100V lines. This means that your amplifier is mainly intended for public address applications. The 100V (or 50V) output is intended for driving lots of small speakers in parallel with its own step down transformer. The idea is to keep on adding speakers, of say 5-watt rating, until the amplifier is fully loaded. Thus, a 200W amplifier with 100V lines could drive 40 5 watt speakers. If readers are interested in a 100W public address amplifier with suitable microphone and mixing facilities, we would like to know about it. If there is enough interest, we'll do it. ~ Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207 . Phone (02) 587 3491 . • Jemal Products, 5 Forge St, Kewdale, WA 6105. Phone (09) 451 8726 . Notes & Corrections Capacitance Adapter for DMMs, Nov. 1987: to give more range of calibration adjustment, trimpot VRl should be changed to 200k0 and the associated 120k0 resistor reduced to 47k0. 24V to 12V Converter, Dec. 1987: the wiring diagram on page 31 shows the lOOJLF capacitor (associated with D9) incorrectly polarised. The circuit diagram on page 30 is correct. To provide crowbar overvoltage protection in the event of a circuit mishap, connect a 15V 5W or 20W zener diode across the 13.6V output. The zener's anode should connect to the positive output terminal. If the output voltage exceeds 15V the zener will conduct heavily and blow the fuse. The zener may also fuse and become short-circuit. Note: Jaycar Electronics can supply a 15V 5W zener diode, type 1N5352B, which would be suitable for this application. ~~JI PARTS CLEARANCE SALE Computer Connections Archer Enclosures 4000/TTL Digital ICs 3 - 1. Subminiature Connector Hood. 276-1529 Reg4.99 .•.... ... .. ...... Sale! 1.29 2. Experimenter's PC Board. 276-170 Reg5.95 .• • ••..•.....••.. Sale!2.49 3. Plug in Board with RS-232 Port. 276-187 Reg 3.99 ................. Sale! 1.99 DualType.276-2413 Reg2.99 .. Sale!49< Decade Counter/Divider. 276-2417 Reg 3.99 ...... .. ...•.• • • Sale! 79< Quad Bilateral Switch. 276-2466 Reg 2.99 •••..•.••.•• •• .. Sale! 49• Quad NANO Gate. 216- 1801 Reg 1.89 ........... .... . Sale! 29< 4. Utility Box. With cooling vents. 270-9520 Reg 11.95 ......... Sale! 7 .95 5. Economy Case. 210-222 Reg5.95 ... . .. . ........ Sale!3.95 6. Box & PC Combos. 5.4x8.4x 3.5cm. 210-ZBJ Reg6.95 .... . ...... Sale! 4.95 7. lx6x3.2cm. 270-284 Reg 7 .95 Sale! 5.95 High Quality Relays Compacitor/Film/ Circuits Tantalums & Trimmers "'~ 7. Micro-Mini SPOT. With 12V DC coil. 275.241 Reg3.49 .. .. . ........ Sale! 2.49 8. SPST Reed. 5V DC coil. 275.m Reg 2.99 ................. Sale! 1.99 12VDCcoil.m-m Reg2.99 ... Sale! 1.99 9. Mini SPOT. With leads. 215-004 Reg4.29 .........••••.... Sale! 2.99 16 □ 18 19 - <at> ~ a -a 20 21 27 ~ 10 4.7 10 3300 II 220 II 470 II 1000 II 4.7 12 .01 13 .01 16. Trim Gasket. 270-036 Reg 1.99 .......... Sale!5' 17. IC Test Probe Adapter. 270-335 Reg 1.99 .... Sale! 49' 18. Switch Panel. 275-705 Reg 1.49 ......... Sale! 99' 19. On/Off Switch. Label plates. 275-320 Reg99' ... .. .. . . . Sale! 10' 20. Replacement Lamp . Flange. 272-1125 Reg 1.09 ......... Sale! 29' 21. Bayonet. 272-1155 Reg 99' ..... ... .. Sale!29' 22. Neon. 272-1102 Reg 1.29 ......... Sale! 49' 23. 6 Volt Bulbs. 272-341 Reg 2.49 . ........ Sale!99' =·. I,-. • 28 35 35 16 16 16 35 Cat.No. Reg Sale 272- 1012 272- 102 1 272-956 272-957 272-958 272-1024 272-1065 272-1051 .99 1.49 .99 1.09 1.19 .79 1.29 .99 .29 1.99 .29 .29 .29 .29 .49 .29 uf WVDC Car. :So. Reg Sale H 0. 1 .47 1.0 2.2 10 272-1432 272-1 -1 ll 272-1 -1 34 272- 1415 272- 1-116 272- 1-117 .99 .99 .99 1.09 1.29 .49 .49 .49 .59 .69 22 35 15 15 15 16 16 Fi~ Va lu e- WVDC Cat. No. Reg Sal(' 15 3 t o l OpF I 500 I 10 272-1 Jl8 1.-19 .99 " H H 14 1-1 to 60 rF 272-11 4 0 1.-19 2.49 .i9 .99 Fuse Holder 240V 5 Amp Thermal Circuit Breaker. 210-96,,1 Reg7.95 Sale! 1.99 24. 3PDT Centre-Off. rn-661 Reg6.95 .............. Sale!4.95 25. Submini Toggles. 275-326 Reg4.29 .............. Sale! 2.29 SPOT Centre-Off. 275.325 Reg4.99 ...... ........ Sale!2.99 26. Heavy Duty Slide Switch. 275-275 Reg 2.49 .............. Sale! 1.49 29 Er -r.andy It Fig 14 24 Reg5 .95 .. . . .................. Sale!95• 28. Connector. Type CF-56. 278-223 Reg 2.29 ...................... Sale! 49• 29. Connector. PAL chassis socket. 278-9604 Reg 2.99 ................. ..... Sale! 59' PAL chassis plug.278-960, Reg 2.99 ... Sale! 59• 30. Bushing. For RG59, RG58, RG62 cable. 218-1643 Reg79• ...•••••••......... Sale!9• ELEeTR8NleS WVDC Switches 27. Adapter. Female 'F' to BNC male. 21a-z5 1 ' uf Extras ~ 17 Fig 20K Turn Trim Pot. 271-1-1,, Reg 2. 79 . . . . .... Sale! 79 ' Hook Up Wire Packs Colnur Gq m Ydlow Bllll· l l)O 10 10 Ca i. Ntl. R,:i.:: Sall· 278-9633 7,9; 2.9i \()() 278-963 -t 7.9; 2.95 AC Circuit Breaker Rated 2 amps, 120V AC. With 120 seconds at 1. 7 5 amps, 60 seconds at 2 amps. ZiL'-9ll L' Reg 3.29 . . Sale! 1.99 f}'~~.,, 31. 8-Pin Mike Plug. 21H25 Reg4.99. Sale! 3.99 32. Accepts Phono Plug. ZH-lL'6 Reg4.49 ..................... Sale! 3.99 33. Chass Sock, 4' Pins. 21-1-%1-1 Reg 2.29 ........ . .... ........ Sale! l .49 34. Dual Phono Jacks. 21-1-112 Reg 1.99 ........ .. ........... Sale! 1.49 35. lnline Plugs, 5 Pins. 27-1-%Zi Reg 2.49 ........ .. ....... . ... Sale! 1.49 Hurry! Limited Quantities - Stocks Will Not Last At These Prices. With Over 350 Tandy Stores and Dealers Nationwide - There's One Near You. Prices Apply at all Tandy Stores and Participating Dealers.