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Are nicad batteries a pollution problem? u~s1s' --------...'--'-'--c1RO"'c~"'i-!'];■;M•J,SERVICING - HIFI - Hands-Free Speakerphone - :J;MlliNf-:J High Performance In Your Shirt Pocketl 3 1/2 digit LCD Display Ranes Max Res Accuracy Vdc Vac Ade 100µV 1mV 100µA 10mA 100µA 10mA 0.1 f.! 200mV-1kV 2V-750V 200mA 10A Aac 200mA 10A Ohms 2oon-2Mn Display also has Low Battery & Over-Range Indication 0.5% +1dig 0.75%+5dig 0.75%+ 1dig 1.5%+5dig 1%+5dig 2%+?dig 0.75%+ 1dig Built In Diode Check, Lo-Power Ohms & Continuity Test Beeper Memory Function for Relative Readings (DM6235 & DM6335) Autoranging Manual Ranging Over-Ride (DM6235 & DM6335) One Year Warran Hold Reading Function (DM6335) 10A Range Automatic Current Limiting Overload Protected to 1000Vdc/750Vac l0MQ Input Impedance Look At The Low Pricesl Prices include 9V Battery and High Quality Silicon Rubber Test Leads with Screw-On Alligator Clips Gotta Gatta GoldStar Dealer enquiries welcome. Call (02)736 2243 Recommended prices only including Sales Tax $88.80 $99.60 DM6135 Autoranging 3 1/2 digit 1OA ac/dc DM6235 As above with Memory function and Range Hold DM6335 As above with Data Hold $118 • 80 You've Gotta Getts Goldstar from: M.L John Pope Electrical (062) 80 6576 • J Blackwood & Sons (062) 80 5235 • George Brown (062) 80 4355 J Blackwood & Sons• George Brown 5 t 9 5855 Newcastle 69 6399 • Auto-Can Industries 526 2222 • D.G.E. Syslems (049) 69 1625 • W. F.Dixon (049) 69 5177 • Ebsen 707 2111 • Macelec (042) 29 1455 • Novacastrian Electronic Supply (049) 62 1358 • Obiat Pty Ltd 698 4776 • Petro-Ject 569 9655 • David Reid 267 1385 • Digital 709 6511 • Geoff Wood 427 1676 N.TERRIIORY J Blackwood & Son (089) 84 4255, 52 1788 • Thew & Mccann (089) 84 4999 QUEENSLAND Auslec (07) 854 1661 • G. Brown Gro up (07) 252 3876 • Petro-Ject (075) 91 4199 • St Lucia Electronics 52 7466 • Cliff Electronics 341 4655 • LE.Boughan 3691277 • The Electronics Shop (075) 32 3632 • Thompson Instruments (Cairns) (070)51 2404 • Nortek (Townsville)(077) 79 8600 S AUSTRALIA Protronics 212 3111 • Trio Electrix 212 6235 • Industrial Pyrometers 352 3688 • J Blackwood & Sons 46 039 1 • Petro-Ject 363 1353 TASMANIA George Harvey (003) 31 6533 (002) 34 2233 VICTORIA Radio Parts 329 7888 • George Brown Electronics Group 878 8111 • G. B. Telespares 328 4301 • A.W.M. Electrical Wholesalers• Pelro-Ject 419 9377 • J Blackwood & Sons 542 4321 • Factory Controls (052) 78 822 • Mektronics Co 690 4593 • Truscon Electronics 723 3094 W AUSTRALIA Atkins Carlyle 481 1233 • Debbie Instruments 276 8888 • Protronics 362 1044 N.s.w. Ames Agency 699 4524 • SEPTEMBER 1 988 HERE'S A HANDS-FREE TELEPHONE that anyone can afford. It's easy to build and uses a special chip from Motorola for really top performance. Details page 14. FEATURES 8 Sony's Mind-Blowing 8mm Video Gear by Leo Simpson Digital stereo sound plus stunning picture quality 58 Motorola's MC34018 Speakerphone IC by Leo Simpson Test circuit, pin functions & internal details 66 Digital Fundamentals, Pt.10 by Louis Frenzel Programming microcomputers 82 What is Negative Feedback? by Bryan Maher Pt.4: How feedback reduces distortion 88 The Evolution of Electric Railways by Bryan Maher Pt.11: The Queensland 25kV AC suburban system PROJECTS TO BUILD 14 Build a Hands-Free Speakerphone by John Clarke SONY'S NEW 8MM VIDEO GEAR is simply stunning. With PCM digital stereo sound and brilliant picture quality, it will change your perception of the 8mm format. Our report starts on page 8. Uses a special chip for top performance 30 Electronic Fish Bite Detector by Branco Justic Attaches to your rod, buzzes when a fish bites 46 High Performance AC Millivoltmeter by Leo Simpson Pt.2: We show you how to build it 60 The Incredible Vader Voice by Darth Junior Let's you imitate the dastardly Darth SPECIAL COLUMNS Vintage Radio by John Hill Checking and replacing the resistors 22 The Way I See It by Neville Williams Could we end up drinking nickel cadmium cocktails? 38 Serviceman's Log by the original TV serviceman Helping the old folk at home 84 Amateur Radio by Garry Cratt Switchmode charger for gel batteries 4 IT WASN'T MOISTURE that caused the dew light to come on in a customer's VCR but our intrepid serviceman solved the problem anyway. His adventures start on page 38. DEPARTMENTS 2 Publisher's Letter 3 Mailbag 34 Circuit Notebook 93 Subscriptions 95 Product Showcase 100 102 103 104 Ask Silicon Chip Back Issues Notes & Errata Market Centre THIS FISH BITE DETECTOR attaches to your fishing rod and is just the shot for night-time fishing. When a fish bites, it sounds a low-level piezo buzzer and flashes a LED. See page 30. SILICON CHIP Publisher & Editor-In-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Advertising Manager Paul Buchtmann Regular Contributors Neville Williams, FIREE, VK2XV Bryan Maher, M.E. B.Sc. Jim Yalden, VK2YGY Garry Cratt, VK2YBX Jim Lawler, MTETIA John Hill David Whitby Photography Bob Donaldson Editorial Advisory Panel Philip Watson, 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: Masterprint Pty Ltd, Dubbo, NSW 2830. Distribution: Network Distribution Company. Subscription rates are currently · $42 per year (12 issues) . Outside Australia the cost is $62 per year surface mail or $120 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 PUBLISHER'S LE'l-l'ER From the electronic shutter to high-definition TV This month we have reviewed a fancy 8mm video system from Sony which includes a camcorder and a VCR with PCM stereo sound editing facilities. In the brief time we had to familiarise ourselves with the equipment we were very impressed with its performance and innovative features. But while both the camcorder and VCR abound with new features , the aspect which most fascinated us was the electronic shutter. For anyone who has even a smattering of knowl,edge of the workings of a TV camera, the concept of an electronic shutter which can operate at 1/l00oth of a second or faster is truly incredible. Such a concept is not feasible with conventional video camera picture tubes. It has been made possible by the new solid state cameras which use CCD (charge coupled device) imaging circuits. In these cameras, the picture from the lens system is focussed directly onto the integrated circuit which is scanned electronically to extract the video signal. In just a few years, CCD cameras have surpassed conventional cameras in their overall performance, picture quality, light sensitivity and now with the addition of "electronic shutters". Many ENG (electronic news-gathering) cameras used by televison stations now have a couple of shutter speeds, typically to 111000th of a second although the Sony camcorder reviewed in this issue runs as high as 114000th of a second. As we point out in the review, there is no shutter as such. The CCD is merely allowed to build up charge on its picture elements for a much briefer time than the normal 20 milliseconds. So for a 1/4000 sec shutter speed, the CCD is " open" for only 250 microseconds. The latest CCD imagers have the capability of a 64µs shutter speed (1/15,625 sec). What this means is that cameras using these imagers will have the potential for really high speed photography, much faster than even exotic film cameras can achieve. Combine that with the much higher picture resolution now possible and near-future developments in high-definition television (HDTV) and you have to conclude that the death knell of movie film is not far off. In the future , when you go to the movies, you will see HDTV tapes, not film. How long will it be before these developments take place? It will be probably ten years or more before HDTV theatres become commonplace. In the meantime, have a look at the picture quality available from the latest 8mm video camcorders when shown on a direct video monitor. It is surprisingly good. Leo Simpson MAILBAG Fan of the Serviceman I have been reading SILICON CHIP since the first issue in November 1987. Although I am a novice to electronics I am enjoying most of the articles. In particular, I find the Serviceman's Log delightful. The reason for buying the first issue was to read the suggestions about converting car stereos and your article encouraged me to do so. The only expensive part was the power supply (Electrophone DC, 13.8V approx. $70) which also serves me well for other jobs. I am also looking forward to reading more of the series on Vintage Radio as a logical approach to learning about radio electronics and its evolution. Could you perhaps help me to find the circuit for a Kreisler CH-7 of 1948 vintage which I recently picked up in almost mint condition. Everything works except for the MW range. H. Luedecke 9 Starkey Street Killarney Heights, NSW Key parts for High Energy Ignition in stock We have experienced a large number of requests for the key parts for the High Energy Ignition project published in the May and June issues of SILICON CHIP. As a result, we will now be carrying permanent stock of the MJ10012 Darlington transistor and the MC3334P IC. We wish you continued success with this brilliant magazine. David Hall Electronics Shop 5, Woodridge Centrepoint Woodridge, Qld Query on drawing symbols I have been overseas for some time and was amazed and delighted to see your fresh new magazine with old(!) familiar names on the staff. Just one observation I would like to make. Since 1968 there has been an Australian Standard for electronic symbols. This has been taught in T AFE colleges since that time and is used by industry. There also appears to be an electronics magazine standard and many symbols used - eg, resistors, diodes, capacitors, trans- former windings and relay coils - do not follow the Australian standard. The Australian Standard, which dosely follows the International Standard, is easy to draw, neater and I feel, more easily recognised than the symbols you are using. A fresh new magazine should use the Australian Standard symbols which have been carefully thought out, agreed to by industry and accepted and taught by every TAFE college in Australia. Apart from this I feel your magazine is great. J. L. Lowe Heatherbrae, NSW We are aware of the Australian Standard for electronic symbols but we elected not to use it because we feel that it is not as intuitively easy to understand as ours. For example, we regard the rectangle symbol used for resistors in the Australian Standard as meaningless; it could stand for virtually any component which comes in a cylindrical package. Similarly, the lack of clear polarity symbols (ie, + and signs) on the capacitor symbols does not aid understanding of circuits. We could go on but the point is made. Fuel cut-off solenoid for cars I refer to Circuit Notebook in the July 1988 issue of SILICON CHIP regarding the fuel cut-off solenoid for cars. The author makes a note about cars fitted with electric fuel pumps not requiring a cut-off solenoid. However, I understand some aftermarket electric fuel pumps are designed for free-flow operation in the event of pump failure. It may be worthwhile checking the pump if you are following the author's suggestion of switching the supply to the pump. J. Dunn Yass, NSW Discrete components still play a major role For starters I think your magazine is great. I am in the RAAF working on very complex UHF transceivers and after reading your "Publisher's Letter" in the July 1988 issue, I was hap1.?Y to find that your policy towards electronics other than microprocessors is a very good one. People SILICON CHIP, PO Box 139, Collaroy Beach 2097. should realise that discrete components still play a major role in hitech equipment. I find your magazine very easy to read but one point I would like to bring up is the continuation of an article from the front of the magazine to a page right up the back. I look forward to more great issues. A. Cross Point Cook, Vic More hazards in electrical wiring Further to your excellent article entitled ''Your House Wiring Could Kill You" and subsequent correspondence, I wish to relate three examples which confirm your opinion for the need to improve the attitude to safety standards, with electric power wiring. The first example occurred during the early 1960s when a new building for a scientific research establishment was erected on an isolated site about 15km from a large country town. This required an overhead power line and transformer to be installed by the local electricity council. Later, when some electronic equipment was being installed by technicians from the scientific group, a lot of problems occurred with the equipment burning out. On checking the 240V AC mains supply, using several different ''true RMS'' meters, a steady reading of 280V AC was recorded, thus explaining the problem. When this abnormal voltage was discussed with the local council electrician who had installed the transformer, his only reaction was to say, "Youse meters are all wrong". Eventually, after raising the problem with more senior council staff, the fault was rectified. The second example concerns a neighbour, a recently retired senior Electrical Inspector, who had installed four additional GPOs (general purpose outlets, meaning power points) in his caravan. I was asked to repair a small appliance in his caravan and whilst checking, I was surprised to find that 240V AC was still on throughout the appliance, even though the GPO was switched off! Continued on page 72 SEPTEMBER1988 3 VINTAGE RADIO By JOHN HILL Checking & replacing resistors Although generally more reliable than capacitors, resistors also cause their share of problems in old valve radio receivers. They should all be carefully checked and, if necessary, replaced as part of the restoration process. Resistors, both fixed and variable, are common components in valve radios. The big difference between resistors in vintage radios and those in modern circuits is size. Modern resistors are much smaller due to greatly improved manufacturing techniques. Old fixed resistors can be quite troublesome and a problem that is frequently encountered is that they go high. In other words, what might have been a 250kfl resistor 40 years ago could well be a 0.5Mfl resistor today. But although some resistors may have gone high, most will measure within their original tolerance or very close to it. Those old resistors were manufactured with a tolerance of ± 20%, which gives sufficient latitude for most of them to fall into the "near enough" category. However, some resistors appear to be less stable than others and these can sometimes rise well beyond tolerance to double their original value. Odd ones may go even higher. Naturally, such resistors should be replaced if a radio set is to operate at anything near its normal performance level. When restoring an old radio, it is advisable to individually check each resistor with an ohmmeter. Such a check out will detect a lot of potential problems. It will also quickly locate any burnt out resistors. It is a simple matter to read the colour code so as to determine a resistor's original value, then check with an ohmmeter to see if the measured value is somewhere near where it should be. You will find that most resistors will check out near enough but every now and then one will appear to be way off value. While the resistor may indeed be faulty, the most likely reason for the screwball reading is that the resistor is still connected into the circuit. In-circuit tests work OK most of the time in valve radios but occasionally, other resistances or the influence of leaky capacitors may completely upset the reading. Any resistors that fall into this category should be disconnected at one end and tested again. This will usually show that the resistor is quite serviceable but if the reading is still off-value, the resistor should be replaced. Strictly speaking, all resistors should be checked out of circuit but such a procedure is not always convenient and mostly unnecessary. My advice is that you only disconnect the suspect ones. Colour coding Early resistors were quite large and their resistance value was clearly marked. Colour coding of resistor values didn't become common until around the mid 1930s. 4 SILICON CHIP Some mention should be made at this stage regarding the colour coding of resistors, as the majority of resistors found in valve radios use a different scheme to that currently in use. The colours have the same values as for modern resistors but the arrangement of the colours is different. • . ::i Rheostats (or variable resistors) were used in early battery radios to regulate the filament voltage. These units are typically quite robust and seldom require replacement. Tapped wirewound resistors were common in valve sets from the early to mid-1930s. They often give trouble at the taps due to poor contacts. A typical wirewound potentiometer from the 1930s. These can give trouble due to dust and dirt in the works. A careful clean followed by a spray with WD40 will usually restore the pot to as-new condition. The wiper arm requires periodic lubrication. Replacing resistors This is a typical body, end and dot resistor. The colours have the same code as for modern-day resistors but are read differently. The body colour represents the first figure of the reading, the end colour represents the second figure, and the dot represents the multiplier in powers of 10. Some resistors will have a band instead of a dot to indicate the multiplier. The old system of identification was knows as the ''body, end and dot" method and the colours are read in that order. The body colour represents the first figure of the reading, the end colour represents the second figure, and the dot colour is the multiplier in powers of 10. So the actual colour code remains unaltered - it is only the order of reading that is different with these old style resistors. Prior to the body, end and dot system, fixed resistors were clearly labelled with either a paper sticker or the resistance value was painted onto them. Early radios up to about the mid-1930s had this type of resistor identification but colour coded resistors took over from about that time. But regardless of how a resistor is labelled, the important thing is to determine its original value. This is necessary if the resistor is to be checked or replaced. Replacing a resistor is a bit like replacing a capacitor (see last month's issue). Once the old component has been unsoldered, it is extremely easy to lose track of where it came from. A better method of replacing resistors is to cut them out with side cutters, leaving the old wire leads in place to mark where the component came from. This practice is a good procedure to adopt for it prevents mistakes. Like other radio components, each resistor has a job to do and just one burnt out device can stop the set from working or cause a serious malfunction. A burnt out resistor is a fairly common complaint in valve radios. SEPTEMBER 1988 5 A burnt out resistor is a fairly common problem in valve radios and generally occurs when some other component (eg, a capacitor) breaks down. a burnt out section can be quickly detected with the aid of an ohmmeter. When restoring a set with a tapped wirewound resistor, it is a good idea to measure the resistance of each section and pencil its value on the underside of the chassis. If the resistor gives trouble at any time, either all or part of the resistor can be built up by adding separate wirewound resistors of the appropriate values. Pencilling bits of information under the chassis is a great reminder for those with lousy memories. Any resistors that can no longer be identified by their colour code should be disconnected, their resistance measured and once again, the resistance value pencilled onto the chassis. It's anyone's guess what the resistor value should be if it has burnt out and only someone well experienced in valve radio repairs would know what to replace it with. Not everyone has a circuit for each of the sets in his collection. Potentiometers A noisy pot can often be cured by spraying WD40 or similar cleaning fluid onto the carbon track. For early pots, the dust cover must first be removed for the treatment to be effective. There are a number of reasons for a resistor burning out and some of the more likely causes would be poor or faulty internal connections to the lead out wires, corrosion due to moisture, and overloading beyond its wattage rating. The latter problem can be caused by other components breaking down. For example, a leaky high-voltage paper capacitor could well be the cause of a resistor giving trouble. When this is the case, replacing the resistor is only half the cure. That's just one reason why it's a good idea 6 SILICON CHIP to replace all paper and electrolytic capacitors when restoring an old valve radio. It may take a little extra time but will result in the restoration being far more reliable and trouble-free. Wirewound resistors Another type of resistor that was fairly common in early radios is the large wirewound type that had a number of tappings along its length. These resistors can give trouble at the tap connections and can also burn out if overloaded. A bad tap or Variable resistors, such as potentiometers and rheostats, can also present the vintage restorer with a few problems. Rheostats hardly warrant a mention as they were only used in ancient battery receivers to control the filament voltage. These units were made very large and robust and should require little maintenance other than a good clean (eg, with WD40). On the other hand, potentiometers cause the vintage radio restorer quite a few worries and one common problem with them is excessive noise when the pot shaft is rotated. Volume controls frequently give trouble in this regard and in bad cases, there may even be dead spots where the sound is completely cut off. Many of the early superhets had wirewound potentiometers for volume controls and these can cause a few headaches when the fine wire wears through and creates an open circuit. Finding a suitable wirewound replacement can be difficult but you can use a secondhand pot that is in good condition. The replacement will need to It's not hard to see why this carbon pot was giving trouble. Excessive power dissipation, probably due to an external component failure, has "cooked" the carbon track. Pots in this condition must be replaced with an equivalent type. A good multimeter is essential for checking resistor values. When restoring a vintage radio, it is a good idea to check the value of every resistor in the circuit as a matter of course. be cleaned and lubricated if it is to work smoothly. However, many early wirewound pots seem to be wirewound not because they needed to be, but because that was the way they made them back then. What that statement really means is that in most cases (but not all), a carbon pot of similar value can be used quite successfully. But if the substitute belches smoke when the set is turned on, then you will know that a wirewound replacement is really needed in that particular application. If in doubt about using a carbon pot, install a milliamp meter in the circuit in series with the pot. If no more than lOmA flows through the pot, then everything should be OK. Most old wirewound pots give trouble because of dust and dirt in the works. They are completely open at the back and an accumulation of dust can stop them from working. These potentiometers need a good clean up and should be fitted with some form of dust proofing if they are to continue to work smoothly. An effective dust cover can be improvised by attaching a small plastic bag to the back of the pot. Sticky tape or even string will hold it in place. If you are good at sheet metal work, perhaps a neat metal can could be fitted instead. Either way, a dust cover on an open pot is a good idea. A noisy carbon pot can easily be cured by replacing it with a new one although that is often easier said than done. Modern potentiometers can be either too short in the shaft or of the splined metric type. An extension can overcome these problems. However, a new component is not always required and quite often a clean and lube job will get a noisy pot working smoothly again. The first step is to remove the pot from the chassis and clean it externally. Once this has been done, you can prise off the metal dust cover from the back of the pot and inspect it carefully for internal damage. If everything is OK, spray lightly inside with WD40 or similar. Finally, flick out the excess fluid and replace the dust cap. A drop of oil on the pot shaft may help free up the movement if it's a bit stiff. This procedure works quite well but is only effective if the dust cover is removed. There is little hope of the spray penetrating the working parts of the pot with the cover in place, although some late model radios have pots with an opening that allows the spray (and dust) to enter. If this rejuvenation process fails to give satisfactory results, then the pot will have to replaced. That just about covers most of the important aspects of resistors as far as vintage radio restoration is concerned. One final comment should be made, though. When replacing resistors, remember to always use a component of similar (or greater) wattage, otherwise the resistor will quickly burn out. This applies to both carbon and wirewound types. Next month's vintage radio topic is on high tension supplies. ~ SEPTEMBER 1988 7 VIDEO REVIEW SONY'S MJND-BLOWING 81VIM VIDEO GEAR Recently we had a chance to review a line-up of Sony's top 8mm video equipment, the V200E video camcorder and the EV-S800 video recorder. Both have PCM digital sound but picture quality is the real attraction. In a word, it is stunning. By LEO SIMPSON It was the "jog" control on the remote control of the EV-S800 VCR which started me off on this review. It's a facility for controlling the slow motion playback, similar to that found on broadcast VTRs for editing. Not only is it good for video editing, it is also great for searching the PCM digital sound tracks which store up to 6 hours of high quality stereo sound. Having lined up an EV-S800 for review, we agreed to have a look at Sony's V200E camcorder and KX-14CPI Trinitron video monitor at the same time. And having accepted this other video gear, the direction of the review was bound to change, for the V200E is not just another 8mm video camera with a few more facilities. It is much more than that. Most people are probably now familiar with the 8mm video cassette format and the very capable 8mm camcorders produced by Sony and some other manufacturers. They have very good picture quality, especially so since they come in such a small format. But the advent of the Sony V200E is likely to change peoples' perception of the 8mm format. This camera is no longer a miniature and offers facilities and performance more like a professional ENG (stands for Electronic News Gathering) camera than a domestic unit. Let's say right at the outset that we are not going to fully describe the operating facilities of the V200E. That is impossible within the constraints of a normal review. After all the instruction manual has 76 pages and the service manual runs to more than 160 pages. So we can only touch on the highlights. Camera features The highlights are pretty staggering. The V200E is a complete 8mm camera and recorder and the first one with digital PCM (pulse code modulation) stereo sound as well as the normal FM mono sound track. It comes with a stereo microphone, six-to-one zoom lens with macro, automatic iris (same as the aperture control on a still camera), automatic focus, six electronic shutter speeds up to 1/400oth of a second, automatic white balance, date and titling facilities, fade control, audio line input metering and level controls, audio dubbing, narration microphone and on and on and on. Twenty years ago, the concept of such a camera would have been out of this world. After all, at that time (1968) TV studio cameras had only just become available with zoom Sony's EV-S800 8mm VCR offers comprehensive editing and slow motion facilities with its "jog" control, seen at the righthand side of the unit. The EV-S800 will also record and playback up to 18 hours of digital PCM stereo sound. 8 SILICON CHIP --;' ri¾ziti'':> '!¥.i,,., . 1 . · - · - - -~ . . " Sony's top 8mm camcorder, the CCD-V200E, has 8:1 zoom and macro lens, auto-focus, auto-iris, auto white balance and six electronic shutter speeds to 114000th of a second. It also has PCM digital stereo sound. lens (before that they had three differing lenses on a rota ting turret). Now we have a camera recorder which offers not just zoom lens but a great deal more. As soon as you see the V200E you realise it is a completely different kettle of fish to other 8mm or VHS-C camcorders. This is a much larger and heavier camera, designed to rest on your shoulder rather than be operated with one hand. It has a proper shoulder rest, an adjustable pistol grip and a fully adjustable eye piece (adjustable for both focus and left or right eye use). Just to give you an idea of its size, it weighs 3.3kg with battery and cassette in place and with the pistol grip fully extended, for tall, gangly people like the Editor-in-Chief, it measures 500mm from front to back. But in spite of its larger size and weight, it is more comfortable to operate for longer periods than smaller camcorders which require single-handed operation. You can shoot in virtually any lighting conditions without the need for auxiliary spot lamps. The CCD (charge-coupled device) image sensor will work from 100,000 lux (bright sunlight) down to 5 lux (candle light) although for noise free pictures, video lights are recommended if the ambient light is less than 300 lux. The resolution of the V200E's CCD imager is the same as Sony's V90E camera but better than other 8mm cameras. It has a total of 439,000 pixels (picture elements) versus 291,000 for Sony's other 8mm camcorders. The zoom capability is dramatic. With a range of 8 to 1, it is about the maximum that is practical for a handheld camera when the maximum telephoto setting is used. The infrared auto focus also works very well in most situations, even when panning on a moving object. It can be tricked though, when you are shooting through a window and a number of other situations spelled out in the instruction manual. Electronic shutter The V200E has an electronic shutter which operates as fast as 1/4000 sec. By comparison, some ENG cameras can go to 1/1000 sec. Now the concept of a video camera having any sort of a shutter at all goes against the grain but here is one which has six electronic shutter speeds. How does it work? Well, there is no mechanical shutter as such, nor is the basic frame rate of 25 pictures per second changed. But the way in which the image is scanned is different. All the picture elements are scanned 50 times a second and fed to a field store. The field store data is then processed to give a conventional video signal with 50 fields a second. By manipulating voltages on the CCD imager, it is possible to change the time over which the image is SEPTEMBER 1988 9 Another view of the V200E camcorder, with its control handle folded away. The viewfinder can be adjusted for left 01 right eye use. The unit has a stereo mic out front and a narration mic on the side, below the viewfinder. stored. In effect, instead of letting the CCD imager record the varying light conditions during each 20 millisecond field period, the image is "frozen" after the designated shutter interval (1/120, 1/250, 1/500, 1/2000 and 1/4000 sec) but then scanned at the normal line and field speeds. As the heading on this review suggests, this is pretty mindblowing stuff. The high speed shutter makes little difference to the picture during normal playback but it greatly reduces or eliminates blurring of fast moving objects during slow motion replay or when displaying still pictures. By the same token, it also reduces blurring when panning on fast moving objects. The electronic shutter really makes use of the excellent sensitivity of the CCD imagers in these new cameras. As you might expect, selecting a higher shutter speed causes the iris to open up to compensate. It is quite fascinating to look into the camera lens while changing the shutter speed - sure enough, the iris closes or opens up immediately. Picture quality Well, what about the picture quality? It is absolutely tops. More objectively, it probably isn't quite up to the standard offered by the 10 SILICON CHIP broadcast ENG cameras with their higher resolution three chip CCD imagers (with light splitting into red, green and blue via dichroic mirrors) but it is not far off it. We viewed it both via the V200E's recorder and via the EV-S800 VCR, feeding direct video to the Trinitron monitor. Feeding the signal to an ordinary TV set via the V200E's or the EV-S800's UHF modulator inevitably causes some degradation. In fact, the ultimate picture quality of the V200E when displayed via a normal TV is not much better than that of a standard 8mm camcorder. It is really wasted in this situation. So much so that we can imagine many buyers of the V200E investing in a Trinitron video monitor too, to get the very best picture. For pictures of moving objects, the V200E really does excel. I took a series of shots of my daughter on her bicycle. She started off in the distance and as she came past, I panned to keep her in the viewfinder. Shutter speed was 1/250 sec. On replay, there was not a trace of the blurring you normally expect when panning. Even the bicycle spokes could be clearly seen (rotating in the right direction too). And on slow motion, the background was pin sharp instead of the blur you expect with panned shots. Marvellous. At this point we should compare the picture quality on playback from the V200E and EV-S800 VCR. On the V200E it is good, as we've already said, but on the EV-S800 it is even better. Hence our comparison to ENG camera quality earlier. On the EV-SB00, the picture is brighter and even more detailed. On still pictures it is brilliant. Whereas the V200E has a reasonably noise-free still play, the EV-S800 is perfect, with not a whisker of noise. By the way, both camcorder and VCR have adjusting facilities to remove jitter from the still playback mode but again, in the final result, the EV-SB00 is better. You'd expect it to be too, for the EV-SB00 is a fullblown VCR with all the bells and whistles. PCM stereo sound To be really blunt about it, the PCM digital stereo sound facility on the V200E probably won't be used to maximum effect in most applications. It gives wonderfully clean stereo sound to back up the hifi pictures but that is it. Sure, you could dub the sound from compact discs onto the tape and get very little degradation but we don't think most users will bother. They'll just want the V200E for its picture capability. We could be wrong on this point but that was our reaction. Who would buy the V200E anyhow? It is not a cheap piece of gear relative to other 8mm cameras but in terms of absolute performance and facilities it is a bargain. We see it as having wide commercial and professional use. For sports coaches, nature photographers, estate agents, and many others, it would be invaluable. The EV-S800 recorder This deck was the initial attraction in this review and it ended up being over-shadowed by the camcorder. That's unfortunate because the EV-S800 is a top piece of gear. We've already talked about the excellent picture quality, made possible by its newly developed 4-head drum. It has advanced luminance processing circuitry giving a claimed 5.4MHz bandwidth and higher white-clip level (220% ). It also has PCM digital multi stereo sound. This takes a little explaining. It is not just an alternative to VHS or Beta hifi systems in that it gives high quality stereo sound. It is much more. VHS and Beta hifi systems are effectively a dual FM carrier recorded underneath the analog video signal on the tape. Digital PCM sound is another technique entirely. The stereo sound signals are sampled at 31.5kHz, quantised and then stored on the tape in the gaps between successive picture scans. This is similar to the technique used for the transmission of BMAC TV signals from Aussat. Again, pretty mind-blowing stuff. In the multi PCM mode, the EV-S800 becomes a sound-only recorder, able to record up to six pairs of stereo signals on the track. To do this, each helical scan of the tape by the video head stores six blocks of PCM signals, in the space normally occupied by the video signal. So there are not six pairs of conventional tracks in the normal sense but six blocks of signals. When the heads read off the signal for a stereo pair, they have to be switched at the right time in each scan. The technique means that up to 18 hours of high quality stereo sound can be stored. That is what you call dense recording. You can select the tracks to be played by using the program controls on the deck or its remote con- The 8mm video cassette is about the same size as an audio cassette and just as easy to handle. It employs specially formulated metal tape. trol. Interestingly, in the the PCM multi replay mode, the function of the jog/shuttle dial on the VCR differs from that on the remote control. You can use the jog dial on the VCR to change tracks but you can't do that on the remote control-you have to use the program + and buttons instead. In fact, becoming acquainted with all the control functions on this deck would take quite some time. As an editing machine, to handle cassettes from a camcorder, it certainly has flexible facilities although we did not have anywhere The infrared remote control for the EV-S800 does just about everything except watch the program for you. near enough time to see what they could do. It took us long enough just to become familiar with the conventional VCR record and playback facilities and those to do with the PCM sound. It really is quite a complex package: Incidentally, while the V200E camcorder's video-cum-PCM signal can be replayed by the EV-S800 and other 8mm video PCM VCRs, the V200E cannot replay PCM multi stereo sound recordings. Well, how do we sum up this lineup of video gear from Sony? Clearly, it is at the leading edge of video technology and in some respects offers facilities and performance not yet available on broadcast standard video equipment. For anyone interested in producing and looking at videotapes which are clearly superior to conventional video equipment, this is the way to go. It is quite unsettling to go back to viewing ordinary TV, knowing what is possible from 8mm video. Recommended retail prices for the Sony equipment are as follows: V200E camcorder $4999.00; EV-S800 PCM stereo VCR, $3199.00; and the KX-14CPI monitor, $1299.00. For further information, contact your local Sony dealer or Sony (Australia) Pty Ltd, 33-39 Talavera Road, North Ryde, NSW 2113. Phone (02} 887 6666. ~ SEPTEMBER 1988 11 -IN ORDER ANOPENTO W $1000 IN OUR 1,000,000TH FUN WAY KIT! THE VALUE OF We'e cetebrating the incredible success of our "Fun Way Into Electronics"' series, with the one millionth Fun Way kit due to be sold any day! Inside that millionth kit is a surprise: a voucher which can be exchanged for goods worth $1000 in any Dick Smith Electronics store. Thafs right: anything you like, to the value of $10001 It could be any kit from the Fun Way Into Electronics range, or any of~ Fun Way packs. And ifs out there right now (we_ don't even know_ where.-. 11 could be in any of our stores or the OSXpress Marl Order Center), Just wa1t1ng for someone to come along and pick it up or order it. What a bonus that person willgell •~ ~ ' ~t • WARNING! THE SHOP The workshop. tfie shack, the Barga·In Labels toolbox ' ' whatever, with these Solvent Non corrosive, low toxicity, idea for all sorts of -•. __! electronic clean ing --.·applications. Cal N- 1040 ._ _ i Your switch and relay contacts will love itl ff h Cl ~c1ng, reduces wP.ar. s7so cat N-1042 \su:~:~ PCB Laffluer , P -rotects pcb s ram tarnishing, damage. . Solder-through covering .,,m,.,.,,., S825 00 Ca!N-1045 ' ' r - 7 Now Hear These. .. gr.::.::/Lub i ' xpenmen ors . . circU1 developers ... eng,neers .. : why mess around with the pile of components on the bench; make your prototypes on breadboards - saves a lot of ~ -- time in the long runl 4 styles to .. · choose from : Mini: 80 x 60mm, 58 groups of five connected terminal points. cat P-4614 pas/neg , 3 phases, earth, etc. 18 metre rolls, 19mm wide. Colours: Green/Yellow N-1359 Orange N-1360 Red N-1361 Black N-1362 Brown N-1363 Blue N-1364 All One Price: 95c/roll OLDER ON! ick of running out of solder : uy in bulk - -it lasts and lasts nd ___ You'll save money, too! wo gauges, both 200g rolls. .71mm (22g) at N-1623 .25 (17g) at N-1619 ~ r,,1' 3 ,•: 95 ea: Positions Poles Cal No 6 S-6302 2 4 S-6303 3 3 S-6304 4 2 S-6305 5 2 S-6306 6 1 S-6312 12 And The Big Guns (With Big Savings!): 2495 ■ BOX AND s·"E' KW s 11s runs stratight off mains. Very popular bezel. Cat S-3550 S 135 ■ • Now With Alum·In1·um AndPIas1·1c LI'•dSI There's only one genuine Zippy box: it's the one with the deep ribbed sides and the genuine Dick Smith Electronics catalogue number moulded into the bottom. Don't be fooled by cheap imitations; insist on the one, the only genuine Zippy Box_ --- ~ exclusive to Dick Smitl!,,;AJ', , I1 ~ Electronics. ""'' . · , Here's a handy one: a special scoop purchase so you know you'll $ave on the normal price! Mains plug-pack with a 6V DC, 400mA secondary- perfect for all those low voltage projects! Cat M- 9548 Think what you'd normally pay! Our price: $6 95 ' ■ Dual Colour: both red and green LEDs in one bezel. Great.when two state 1nd1cat1on required. Cat s-353 o s41s S1095 I Giant: As above, but 128 groups_ Save On Phones. 178 x 67mm. Cat P-4615 s395 Earpieces and Phones at bargain pnces: With terminals: 256 groups, +, - Save $3 on inside ear mini & earth terminals too. s3ft95 phones. Quality, yet very tiny. Cat P4616 · ;,-· And a panel 128 groups, with terminals and front panel for mountinf pots, switches etc. 7 5 Cat P-4G Want QUI CK' GRABA ZIPPY POWER? . Both ea Mini Neon: Tiny size, contains neon only (requires series R). High visibility. Cat S-3552 Onlys225 each! Was 7 This month -, DC or AC. Looks great! Red: Cal S-3510 Green : Ca!S-3512 No More $195 B·1rdsnests•. E · t · -1 240V Neon Internal resistor - Water displacer, penetrates to free stuck nuts & bolts, , _ etc. Also protects against • :::corrosion_ cat N-1065 .:-= •_ COLOURED INSULATION 'APE TOO K , T All the colours you need to mark 5 Now If you need a bezel, look no further. There are some reall y bright ideas in this lot of quality bezels _ Mini LED: 2 colours, our most A big 290 x 220 x 45mm case with popular_ Low drain (20mA <at> internal divider containing multiple 2V), high visibility. $4 secti ons. cat H-2596 Red: Cat S-3528 95 Green : Cat S-3529 ' ~995 - s1595 W · ~ --_- __ as 75 . See The Light? - Air Duster s7so s3·95 ea -==s1so ea ·,e.c ■"'"'" ""''"'•ms,.,, r - s329 High brightness, requires 12V Give dirt, dust etc a high pressure blast - inert gas won't' corrode or damage, great 10 tight cornersl Cal N-1050 The Dick Smith range of quality rotary switches has been a little hard to come by recently .. but they're back! We now have good stocks of all styles. Single Tilt Drawer They're stackable: just keep on Similar to left, but this has one adding as many modules as you drawer on an axle which allows require. And if you add them this tilting forward cat H-2581 month, you'll save! 2 drawers per unit. Cat H-2580 r"'·"~~, . , I _ • $4, ., _ 1 Sup.erb quality hi-fi speakers you II be proud to own - and hear.I 3 way with massive_300mm woofer, 120mm midrange and ~ 65mm tweeter. Overall size 385X300 x 725mm. 65W power CTIIOC"' handling, attractive teak "woodgrain" fini sh with black gnlle. -,,_-- Cat A-9500 Both: • Permagard -2- Drawer Modular Introductory offer: $1.00 OFF! Now Only s~ • _-: u ·· Permit numbers applied for at time of going to press in NSW, Victoria, ACT and NT. Check out these parts drawers: they're great for resistors, capacitors, semis, fish hooks, etc, etc, etc. Watch out: there are over 80 labels here in just about everything imaginable - warn ings, voltage, AC, DC, fuses, etc, etc. etc, al l on an adhesive backed mylar base: just cut out the ones you want & stick ·em where you want. And at only $2.95 that's fantastic value_ Cat N-5759 ~ IT COULD BE YOU! Somewhere to PUT IT ALL BACK IN STOCK'■ I. value plus service aids. · Cleamng IT MUST BE WON. Cat C-4135 95 Now .S6.95 Were Save $5 on hghtwe1ght earphones. ~~tml~ei!t1th on/off switch. ss. Were $29.95 Now Other Plugpacks: 9V <at> 200mA (Cat M-9514) $11.95 3/6/9V <at> 200mA (Cat M-9525) Small (UBS): 28 x 54 x 83mm Cat H-2855 Large (UB1): so x 90 x 150mm Cat H-2855 S2:'5li $1.95 $>.!15$3.45 Medium (U83): 41 x 68 x 130mm Giant (UB2): 60 x 113 x Cal H-2855 196mm Cat H-2855 $24.95 w.,o-$2.95 S&;l!O $4.95 S16.95 3/4.5!6f7.5/9/12V<at> 300mA (Cat M-9526) $17.95 12V AC <at> 500mA (Cat M-9555) S29.95 16V AC <at> 900mA (Cat M-9567) $14.95 WHY WON'T IT SELL? Portasol Pro! What do you do when you're out of reach of a power point. Use a Portasol, of course - the butane powered gas soldering iron that goes where you go. You know the portasol: here's the PRO model' The complete kit includes: • Portasol PRO Gas Iron • Four tips including hot knife and blow torch • Tip Cleaning Sponge• All in a heavy duty plastic 95 case which doubles as an iron stand! Cat T- 1374 Spare tips to suit: 5 Standard soldering tip Cat T-1375 Blowtorch tip - for really applying the heatl. Good for (carefully') shrinking Hot Kni fe tip (ideal for working in plastics, etc) heatshrink. Cat T-1377 simply replaces soldering iron tip. Cat T-1376 $79 12SS S1295 S1295 It would have to be one of the handiest devices anyone working with aud io could ever own. It instantly checks cables for go/ no go in RCA, Cannon & 6.5mm - without having to worry about meters, etc. But it didn't sell. So we've slashed the price to way below cost to clear ·em out. OK, we lose - but YOU REAP THE BENEFIT of our mistakel Cat 0- 1532 SHOULD BE WAY OVER $60 .. . NOW WAY BELOW COST AT s1995 Now available at 60 stores: • NSW• Albury 218399• Bankstown Square 707 4888• Blacktown6 71 7722• Bondi Junction 387 1444 • Brook vale (Warringah Mall) 905 0441 • Campbelltown (046)27 2199 • Chatswood Chase 411 1955 • Chullora 642 8922 • Gore Hill 439 5311 • Gosford 25 0235 • Hornsby 477 6633 • Liverpool 600 9888 • Maitland 33 7866 • Miranda 525 2 722 • • • • • • • • • Newcastle 611896 • North Ryde88 3855 • Parramatta 689 2188 • Penrith (047)32 3400 • Railway Square 211 3777 Sydney City 267 9111 • Tamworth 66 1711 • Wollongong 28 3800 • ACT• Fyshwick 80 4944 • VIC • Ballarat 31 5433 Bendigo 43 0388 • Box Hill 890 0699 • Coburg 383 4455 • Dandenong 794 9377 • East Brighton 592 2366 Essendon 379 7444 • Footscray 689 2055 • Frankston 783 9144 • Geelong 43 8804 • Melbourne City 326 6088 Richmond 4281614 • Ringwood 879 5338 • Springvale 547 0522 • QLD • Brisbane City 229 9377• Buranda 3916233 Cairns 311 515 • Chermside 359 625 5 • Redbank 288 5599 • Rockhampton 27 9644 • Southport 32 9863 Toowoomba 38 4300 • Townsvtlle 72 5722 • Undefwood 341 0844 •SA• Adelaide City 232 1200 • Beverley 3471900 St. Marys 277 8977 • Elizabeth 255 6099 • Enfield 260 6088 •WA• Cannington 451 8666 • Fremantle 335 9733 orth Perth 328 6944 • Perth Citv 481 3261 • TAS • Hobart 31 0800 •NT• Stuart Park 81 1977 NOW AVAILABLE AT ALL STORES - OR CALL TOLL FREE: (008) 22 6610 FOR HOME DELIVERY! Hands Up if you can Spell... YOU WON'T CHOKE ON THESE PRICES! Project call for an RF choke? Check out our great range from a miniscule 1 uH and everything in between' All one low. low price : $115 each (even cheaper in quanitity 1) 82uH L-1793 1uH L-1 759 100uH L-1795 1.SuH L-1 761 2.2uH L-1 763 150uH L-1 799 3.3uH L-1 765 220uH L-I803 4.7uH L-1767 330uH L-1 807 470uH L-I8I 1 6.0uH L-1769 560uH L-1 813 8.2uH L-1771 10uH L- 1773 820uH L-I8t7 1mH L-1 820 15~H L-1775 1.5mH L-1822 22uH L-1779 33uH L-1783 2.SmH L-1824 5mH L-t826 47uH L- t787 69uH L-1791 All $1.15 ea 10 up 95C ea HARDWARE TOGO! You know what it's like: you're building that masterpiece and your junk box has run out of ... ! Keep the junk box filled without breakinQ the bank with our value-plus range of hardware: here's a small selection - Radio Theory Handbook At last! An Aussie book for amateurs - or amateurs to be. Almost 350 pages, compares very favourably with ARRL etc - but it's $10 cheaper! Written to DoTaC syllabus. Cat 8-4002 Keep your hand up if you can spell with 100% accuracy I The Franklin Spellmaster will turn even the world's worst speller into a superspeller - if you can say the word, you can spell it! Features: • 80,000 word dictionary • Advanced searching and deduction • Inbuilt games and word-finding features • All in the palm of your hand 1 It's better than a dictionary (you don't need to know how the word is spelt!), better than a computer with a spelling checker (it's portable). Sensashunal? No, sensational! Cal Y-7305 Meters & Scopes: Experiments with EPROMs How to use Test What they are, how they work Equipment and, of course, experiments How often have you wondered how to get the best from a CAO. Or dipper. Or even a multimeter? Wonder no more: it's here! Cat B-5000 AND projects to build involving or for treatment of EPROMsincluding ,,,..__ ..,,,, burners. EPRQ-• Cat 8-5001 -~ s1!195 ' AND OLD FRIENDS REVISITED... Transistor Equivalents Basic Electronics Theory WIA Novice Electronics Probably the most useful book a hobbyist could have (after the Dick Smith Catalogue, of course!) It's been out of stock lor a while so grab one now. A whopper! 666 pages crammed full of everything you've ever wanted to know about electronics and then some. Ideal .!!:!.m~v._ .. reference work. CatB-1615 want to get an amateur licence? Start with the Novice Licence and work up: this book will get you that licence. 136 pages, very good value for money. Cal 8-2317 5695 Euc°r1i~,~ ,.. 1'~ s2995 Soldering to batteries is a big no-no. Finish off that project with one of these superb battery holders from Dick Smith Electronics. 1 x "D" Cell Cat P-6101 70c 4 x "C" Cells Cat P-6104 90c 4 x "AA" Cells, Long Cat P-6114 75c 4 x "AA" Cells, Squat Cat P-6124 70c 6 x "AA" Cells, Squat Cat P-6116 95c S695 -J '\J HOLD IT! save on Big Feet! 2mm square self-adhesive feet - no need to drill holes. Use on commercial gear, too, to prevent scratches! Pack of 4. Cat H-1749 Was $1.95 pk, Now 5 150 50coff Connectors 4Sc! Cable Clamps: More Savings A nilly two-part cable clamp offering high security. Heavy duty, pack of five. Cat H-1970 Was$1.95 Now Only 5 145 WHY USE BAKELITE PCB? Fibreglass has all the advantages: stronger, higher resistivity, better temperature handling, better "abuse" handling ... these days, there's no reason to keep using bakelite PCB (but if you really want it, we have it!). Especially when you look at the low, low prices of our fibreglass PCB blanks. (Want to etch your own PCB's? Check out the range of DATAK PCB making matenals at any Dick Smith store!) Fibreglass blanks: Size Cat No Sounds Good To You Quality Mangavox Speakers for replacement in existing enclosures or building new desions. Compare the value, compare the prices, Use components? There's only one way to buy them: in bulk. compare the savmgsf You 'll make savings of up to 50% and more by buying Dick Smith bulk component packs. No rubbish - just prime spec, guaranteed new components. 10IN WOOFER Cat C-2052 =--- 100 Premium LEDs The no-solder way to join cables: Just place them in the connector, squeeze with pliers and: presto! Pack of 2 Cat H-6720 Was95C, Now Only PACKS: THE SMART WAY TO BUY YOUR COMPONENTS! Price 6x3 (150x75) H-5540 $3,45 6x6 (150x150) H-5545 $4,95 6x-12 (150x75) H-5550 $15.95 Who'd want 100 LEDs? Anyone who wants more than 40 or so! Because the last half are effectively FREE! You never know when you'll need them! Cat Z-4084$ ~ 1995 t;;,0°/ ~~ -E-"j -. Normally $39.95 Now 529 95 0 0 5 8 IN WOOFER Cat C-2054 Normally $29.95 Now 5 1!195 Why use carbons when 1% metal films are so cheap - especially in a bulk pack. 300 Computer-selected values between 10 Ohms & 1 meg. Cat R-7015 SAVE OVER $6 5 1495 55 Electrolytics Normally $29.95 Now 5 SOMEWHERE OVER THE RAINBOW YOU'LL SAVE Rainbow cable is by far the most economic way of buying hookup wire: '/ou've always got the number o conductors you need (up to 12!), and you can peel off as much or as little as you like! And if you buy it by the roll (100m) you'll save even more than nonmal off our bulk price! $1.90 per metre, Normally $1 .71 per metre in bulk rolls; THIS MONTH ONLY $1.50 8IN TWIN CONE Cat C-2082 300 1/4W 1% RESISTORS 8 x "AA" Cells, Squat Cat P-6128 S1 .20 10 x "AA" Cells, Squat Cat P-6130 $1 .45 "216" (9V) Snap Cat P-6216 25c "216" Chassis/PCB holder ' Cat P-6220 $2.95 LIMITED STOCKS 19 95 per metre in bulk (1 OOm) rolls. COMPUTER CORNER Cables, Too ... We have a huge range of ready- made computer cables or the cable, and plugs & The cheapest around - but there's Need a floppy disk drive? We sockets to make up your own no loss of quality! Superb "Alps" have both popular formats in Here are just two examples: keyswitches for reliability, ideal half height drives, ready to slot Centronics Printer Cable: for most IBM compatible into your computer. computers. Cat X-3821 360K (Ideal for adding to an AT standard Centronics plug on end, 25 pin D the other. As to give XT compatibihty) used on most computers & Cat X-8012 printers. Cat X-8614 101 Key Keyboard Aoppy Drives Incredibly handy, because you can usually substitute a close value electro in a circuit if you haven't got the right one! 55 single ended (RB) types. Cat R-7030 =...,.,....,,, S229 52495 S Data Cable: Shielded 269 55 Core core cable with drain wire, BIG SAVINGS OVER ONE-OFF 1.2Mb (standard "AT" type drive) Cat X-2200 ************************* HERE COMES CHRISTMAS! Have you got your coloured lights all ready for Christmas - it's only a few weeks away (bet that scared the pants off youl). Chnstrnas (and any other) parties take on a whole new atmosphere with the right lights - and here are the ri ght lights: Par 38 Heavy Duty R95 Light Duty Pressed Glass Reflector Globes $10.95 ea $6.95 ea Yellow S-3850 Yellow S-3851 Red S-3852 Red S-3853 Blue S-3854 Blue S-3855 Green S-3856 Green S-3857 Edison Screw Lampholder to Suit: cat P-5620$7.95 ea Gender Benders 8 , It's always the same; Murphy's Cable Corollary applies ; if you have two cables to join, both will havr male (or female) plugs or sockets! Gender Benders fix that probl em: standard 25pin "D''. Male to Male x-~oo5 MAJOR DICK SMITH ELECTRONICS AUTHORISED STOCKISTS: • NSW • An11idala: Sound Components 72 4981 • Ballina: Ballina Electronics 86 7022 • Bowral: F.R.H. Electrical 61 1861 • Broken Hill: Hobbies & Electronics 88 4098 • Char~stown: Newlronics 43 9600 • Coffs Hartlour: Gotts Harbour Electronics 52 5684 • Dubbo: Chris's Hi-Fi 82 8711 • Forster: Forster Village Electronics 54 5006 • Glen Innes: John Sommerlad Electronics 32 3661 • Griffith: Miatronics 62 4534 • lnvorell: Lyn Willing Electronics 221821 • Lismore: Decro Electronics Services 21 4137 • Moree: Moree Electronics52 3458• Mlldgee: Headware 72 3895 • Nowra: Nowra Electronics 214979 • Wagga: Phi llips Electronics 21 6558• VIC • Morwell: Morwell Electronics 34 6133 • Shepparton: Phillips Electronics Ply. Ltd. 21 9497 • Warrnambool: Marrtronics 62 9870 •OLD• Bundaberg: Bob Elkin Electronics 72 1785 • Kingaro1: Holmes Today Electronics 62 1658 • Kawana: Splitec 94 7349 • Mackar: Stevens Electronics 511723 • Mlf'lborough: Keller Electronics 21 4559 •SA• Mt Galllbier: Hutchessons Communications Centre 25 0400 •WA• Albanr Micro Electronics 41 2077 • Geraldton: Batavia Lighting & Electrical 23 1842 • Karnl~a: Dave's Oscitronics 85 4836 • TAS • Devonport: A.I. Electronics & Hobbies 24 8322 Female X-3566 to Female Each: s12ll6 ■-,, ,·. ·••• Id! . periect for running in buildings for computer LANs, terminals, etc. Cat W-2040 5 85 5 65 1 l /m or in 100m rolls. tm Don't Forget Our Range Of Disks, Ribbons, Plugs, Sockets, Etc Etc Etc Here's a hands-free telephone that anyone can afford. With the Speakerphone you can have relaxing conversations without the need to hold the phone to your ear. And if you are put on "hold" you can continue with your work while you wait. By LEO SIMPSON & JOHN CLARKE How would you like to be able to talk on the telephone with your hands completely free? Well, now you can. If you are taking down details over the phone there is no need to "crook your neck" to hold the phone on your shoulder while you write. And if you are talking to friends or relatives, other people with you can listen in or join in the conversation - it's like listening to the radio, except that you can talk back! Imagine the freedom of being able to talk on the phone while you move around the room, do your exercise routines, lie in bed, or carry on virtually any activity, all without touching the phone itself. And if you 14 SILICON CHIP are put on "hold" it is great to be able to carry on with other activities without being glued to the phone. For long distance calls to your relatives or friends, the Speakerphone can be a real money-saver since all members of your household can listen in or participate in the conversation instead of each family member waiting for his or her "turn". Well it sounds marvellous, doesn't it? And it is. We predict that in a few years' time, virtually every household will have one, such is the ease and convenience of its use. Of course, you can buy a phone with a loudspeaking facility right now but they're not cheap, at around $250 or more. Features The Speakerphone does not replace your existing telephone but operates in parallel with it. To make a phone call, you dial from your existing Telecom phone in the normal way. Having established contact, you then switch over to the Speakerphone and "hang up" the Telecom phone. To answer an incoming call you can pick up your Telecom phone and speak and then switch over to the Speakerphone or you can switch on the Speakerphone directly and answer immediately. If you don't tell the person at the other end, it is likely that they will not know you are using it - it's that good. For the hard of hearing Should you wish to have a more private conversation but still have your hands free, you can use a standard pair of stereo headphones to ELECTRET MICROPHONE MICROPHONE AMPLIFIER MC34018 BUFFER 9 TRANSMIT ATTENUATOR 4 TRANSMIT LEVEL DETECTOR . SIGNAUNOISE DETECTOR TRANSMIT/ RECEIVE COMPARATOR ATTENUATOR CONTROL SIDETONE NETWORK RECEIVE LEVEL DETECTOR PEAK LIMITER 15 SPEAKER TRANSMIT OUTPUT RECEIVE ATTENUATOR 27 RECEIVE INPUT SPEAKER AMPUAER REGULATOR HOOK ~ 16 DC INPUT TELEPHONE LINE 24 18 ':' -!- 0 RECEIVE VOLUME CONTROL Fig.1: block diagram of the MC34018 speakerphone IC. It contains all the amplifiers, attenuators and control circuits necessary to produce a high-quality hands-free telephone. listen to the other party. If you or someone in your household is partially deaf, the Speakerphone can be a real boon. With the headphones plugged in it acts as a very effective and comfortable telephone amplifier. For elderly people too it could be very convenient, especially if they have arthritis and cannot easily hold the phone. In fact, the more we used the prototype Speakerphone, the more enthusiastic we became. It is hard to understand why commercial versions of this product have not been marketed years ago. The Speakerphone is housed in a small plastic case containing a loudspeaker and sensitive electret microphone. It has two switches, one to connect or disconnect it from the phone lines and one to mute the microphone. There is also a volume control for the loudspeaker and a stereo headphone socket. No batteries or mains power connection is required, since the Speakerphone is powered directly from the phone lines. To connect the Speakerphone you need an approved Telecom parallel adaptor socket. No other modifications are required. Motorola's MC34018 Check to see whether or not your microphone is sealed at the back. If it isn't, sleeve the microphone body with a 15mm length of heatshrink tubing, then seal the back with a doh of plasticine. What makes the Speakerphone possible is Motorola's MC34018, called, funnily enough, a voiceswitched speakerphone circuit. The MC34018 chip contains all the amplifiers, attenuators and control functions necessary to produce a high quality hands-free telephone (see Fig .1 ). It includes a microphone prea-mplifier, a small power amplifier for the loudspeaker, transmit and receive attenuators, a background noise monitoring system and automatic gain controls for the transmit and receive sound levels. The intended applications for the MC34018 are for domestic speakerphones, intercoms and automotive telephones. It can be used in conjunction with other telephone integrated circuits which incorporate SEPTEMBER 1988 15 PARTS LIST 1 PCB, code SC12-1-0988-1, 122 x 126mm 1 plastic instrument case, 155 x 1 59 x 65mm (Jaycar HB-5913 or equivalent) 1 front panel label, 146 x 59mm 1 Arlec 45035 or Ferguson MT-620 6000 1: 1 isolating transformer 1 1 20mm loudspeaker (see text) 1 6.5mm stereo headphone panel socket 1 20k0 linear potentiometer 2 SPOT toggle switches 1 electret microphone insert 1 knob 1 small grommet 2 metres of two core telephone wire 1 telephone plug 1 telephone double adaptor (Altronics P-0995 or equivalent) Capacitors 1 1 OOOµF 1 6VW PC electrolytic 4 4 7 µF 1 6VW PC electrolytic 1 1 OµF 16VW PC electrolytic 3 4. 7 µF 1 6VW PC electrolytic 3 1µF 1 6VW PC electrolytic 4 O. 1µF metallised polyester 4 0.068µF metallised polyester 1 0 .047µF 250VAC 2 0. 04 7µF metallised polyester 4 0.01 µF metallised polyester 2 O.004 7 µF metallised polyester 1 0.001 µF metallised polyester Resistors (0.25W, 5%) 2 x 2.2MO, 1 x 1 MO, 2 x 470k0, 1 X 220k0, 1 X 200k0, 1 X 100k0, 1 x 91k0, 1 X 68k0, 3 X 47k0, 1 X 33k0, 1 x 30k0, 1 X 27k0, 2 x 22k0, 1 X 18k0, 1 X 15k0, 1 X 10k0, 1 x8.2k0, 1 x 6.8k0, 3 x 4 . 7k0, 1 x 4.3k0, 1 x 3.3k0, 2 X 2 .2k0, 1 X 4700, 1 X 2700, 1 X 270, 1 X 220 Semiconductors 1 4 7 1 MC34018P speakerphone IC BC548 NPN transistors 1N4007 1A diodes 7.5V 400mW zener diode dialling functions or it can be used on its own, as in the circuit published here. Fig.1 is a block diagram showing the functions performed by the MC34018 integrated circuit, together with the additional functions needed for a complete Speakerphone. When all the external componentry is taken into account it adds up to a fairly complex circuit, although most of the extra parts are low in cost. Before we discuss the complete circuit, the concept of conventional phones and the Speakerphone should be described. Simplex and duplex In a conventional telephone system the transmit (microphone) and receive (earpiece) signals are carried over two wires and then converted to a four-wire system inside the phone itself by a hybrid transformer (also known as an "induction coil"). So inside the phone there are two wires for the 16 SILICON CHIP Miscellaneous Rainbow cable, solder, dob of plasticine or blue tack, PC stakes, self tapping screws. microphone circuit and two for the earpiece. As well as separating the microphone and earpiece circuits, the hybrid transformer also provides a degree of "sidetone". Sidetone is the process whereby some of the microphone signal is deliberately fed into the earpiece; it gives the person speaking an idea of how loud he (or she) should speak. In this way, sidetone compensates for the varying losses of long or short lines. Without sidetone, the line will sound "dead". Apart from the ins and outs of sidetone, the conventional telephone has the advantage of being a true "duplex" system, meaning that both parties can talk at the same time! Most radio communications systems, by contrast, are simplex, so only one party can talk at a time. The Speakerphone too, is ·a simplex system. In normal conversation, with polite persons using the Speakerphone, only one person speaks at a time. If you're rude though, and talk very loud, you can override the person at the other end. The MC34018 operates on the principle of comparing the transmit and receive signals to determine which is stronger and then switching into that mode. It also contains circuitry to discriminate between noise and speech in both the transmit and receive modes so that it is not triggered by noise. How it works Let's now have a look at the complete circuit diagram of Fig.2. Rather than describe each and every function of the 28-pin MC34018, we'll assume that you will refer to the data on the IC elsewhere in this issue. At the lefthand side of the circuit is an electret microphone. This is biased from the VB line ( + 2.9V at pin 21) using a 2.2kO resistor. The microphone signal is then coupled via a 0.lµF capacitor to pin 9, the microphone amplifier input. This has a gain of 34dB (50 times) and feeds the Signal/Noise Detector and Transmit Attenuator. The Signal/Noise Detector (see Fig.1) discriminates between speech signals and those due to ordinary background noise (which may originate from computer fans, air-conditioning, etc). If the signal from the microphone is speech, a logic signal is fed to the attenuator control which says "pass the signal through the Transmit Attenuator" to the Transmit Output, at pin 4. But another logic function is involved. The Transmit Level Detector, pin 5, monitors the Transmit Output at pin 4 and its output signal is fed to the Transmit/Receive comparator. This controls whether the circuit is switched into the transmit or receive mode. So when the Transmit Attenuator is at maximum gain (ie, mic signals passing through), the Receive Attenuator is at maximum attenuation (ie, fully off). They are never both on or both off. If the signal at the transmit end is due to background noise, the Speakerphone will normally be in receive mode. Switching times between receive HOOK FERGUSON MT620, ARLEC 45035 T1 >--oA(2) 06 .047 250VAC .01 07, 220k 68k B (6) 01 BC548 15k .01 .068 .01 .,. 08 1N4007 1M .., 470k .,. .001 .,. .068 4.7k 0.1 ___ .06.,8_......, m 5 1 4.7k .068 3.3k 10 27 13 XD1 TXI 0.1 RU V 16 ,.__ _ _ _ _ _ ____.ITXO HEADPHONES +2.9V - .,. VOLUME VR1 20k ~ 21 VB 1 16VW 47 + 16VWI _+ 17 6C IC1 MC3401B 24 VLC SK 15 + 2 , 1:ff 47 / - 16VW 22k SPEAKER RS .,. RTX 2 91k *Rl+RS RR 1 30k = 25rl 18k B EO VIEWED FROM BELOW ... SPEAKERPHONE SC12·1 ·0988·1 Fig.2: the two key components in the circuit are the isolation transformer and the MC34018 speakerphone IC. The circuit is powered from the telephone lines via the isolation transformer (ie, no external supply is required). and transmit modes are very short although there is seldom any evidence of clicks. The transmit and receive attenuators also take care of differences in voice levels so tHat people who shout do not overload the system while there is plenty of gain for people who speak softly. The Transmit Output signal at pin 4 is fed to filter and buffer stages consisting of Ql, Q2 and Q3. Ql is a high-pass filter with a gain of unity. Ql 's output signal is fed to the Transmit Level Detector at pin 5, as already mentioned, and also to the emitter of Q2 which operates as a grounded base stage. Q2's collector output couples directly to the base of Q3 which has little gain but operates as a phase splitter. SEPTEMBER 1988 17 The PCB assembly is secured to integral pillars on the base of the case using four self-tapping screws. We soldered the MC34018 directly to the board but you can use a 28-pin IC socket if you wish. r- ~~~ ~=•D'-~:-7 !o :r,~~ -. -. . . 0 0 !J 18 SILICON CHIP Fig.3 (left): save money by using this full-size pattern to etch your own printed circuit board. Q3's collector output drives the line transformer Tl while its emitter output provides a sidetone signal via the .068µ,F capacitor. The receive signal from the phone line is coupled into the high pass filter consisting of Q4 via the 15k0 resistor. Its emitter output couples into the receive input, pin 27, and the receive level detector, pin 7, on the MC34018. Note that the sidetone signal from Q3 couples into the input of Q4, the receive input buffer. This signal is there to cancel the transmit signal which would otherwise be coupled into the receive input. As such, it is not really a sidetone circuit, is it? After passing through the internal attenuators, the receive signal is fed to the Speaker Amplifier (see Fig.1) which has a fixed gain of 34dB. The signal level is set by the DC volume control input, at pin 4. The amplifier is capable of delivering up to 100 milliwatts on an intermittent basis, into a 250 speaker. Because 250 loudspeakers are Special Note While the Speakerphone is designed to conform with Australian Telecom standards, any unit built from the design featured here will not be a legal installation as far as Telecom is concerned. To be legally connected, the Speakerphone or any other phone device must be tested and approved by Telecom and must carry a Telecom permit sticker. not readily obtainable, our circuit uses a low-profile but efficient 40 car radio speaker and so it is fed· via a 220 resistor. The isolating transformer The function of transformer Tl is not immediately clear from the circuit since it does not provide complete isolation of the circuit from the phone lines. It has two isolating functions. First, it allows DC from the phone lines to be fed into the circuit via the primary and thence via the diode bridge, Dl to D4. Thus DC is fed to the circuit without any loading of the transmit and receive signals. Second, the transformer isolates the low voltage DC rail for the circuit from the incoming phone lines. The low voltage DC for the circuit is clamped to 7.5V by zener diode D5 and then fed to pin 16 of the IC. An internal regulator then produces a fixed + 5.4V for the other internal circuit functions. Diodes D6, D7 and D8 plus the .OlµF capacitor across the 4.7k0 collector load resistor for Q3 pre. vent excessive transmit signals. The .047µF capacitor across the phone lines suppresses large transient spikes. There ate two switches in the circuit. St connects the circuit to the phone line. S2 mutes the electret microphone by shorting its output signal, when you want to talk without the party at the other end, hearing anything. It's handy if you want to blow your nose while the other person is speaking. A set of stereo headphones may be connected. When the headphones are plugged in, the speaker 0 - 6 B , HEADPHONES SPEAKER r'\ ELECTRET MICROPHONE Fig.4: install the parts on the board as shown here but don't install the IC until after the initial circuit checks detailed in the text have been made. The telephone cable enters through a grommeted hole in the rear panel and loops through two holes in the PCB. is disconnected. The series 2700 resistor limits the signal fed to the headphones. Construction The Speakerphone is housed in a standard plastic instrument case measuring 155mm wide, 159mm deep and 66mm high (Jaycar Cat. No. HB5913). Most of the circuitry inside it is mounted on a PCB measuring 122 x 126mm and coded SC12-1-0988-1. Assembly is a straightforward matter of installing the components and soldering them into the board, assembling the hardware into the case and then completing the internal wiring. Fig.4 shows the wiring details. Start by installing all the small components on the board. Note that a number of the capacitors adjacent to the IC may need to be laid over on their sides, to clear the loudspeaker magnet. These capacitors can be seen in the internal photograph of the unit. When all the small components including the four transistors have been soldered into place, solder in the transformer. The recommended types are the Ferguson MT-620 and the Arlec 45035. These are 6000 1: 1 isolating transformers normally used in Telecom approved modems. Do not install the IC yet. Initial circuit checks Connect a power supply, capable of delivering between 25 and 50 volts DC to the circuit via a 5600 5 watt resistor to the board inputs marked 1 and 3, adjacent to the SEPTEMBER 1988 19 The Speakerphone is simply plugged into a standard double adaptor plug in parallel with your existing telephone. You can buy the double adaptor plug from parts retailers and hardware stores. transformer (see Fig.3}. Check that the voltage across the zener diode D5 is close to + 7.5 volts. The same voltage should appear at the collectors of Ql and Q4. When that check has been performed, the MC34018 can be inserted and carefully soldered into place. Use a 28-pin socket if you wish. We did not bother. The rest of the circuitry should now be completed. You can use PC stakes to make the wiring easier or you can just solder short lengths of hook-up wire directly to the board and then solder the other ends to the switches and other off-board parts. The PCB is secured to integral pillars on the base of the case using four self-tapping screws. Installing the microphone The electret microphone may require special care to install, depending on whether it is fully sealed at the back or not. Ours wasn't so there was a problem with sound from the speaker inside the case getting into the back of the microphone and partially muting the circuit. To cure this problem we first sleeved the microphone with a 15mm length of heatshrink tubing and then pushed the whole assembly irito a close-fitting hole in the plastic front panel. After soldering on the two wires, we filled the sleeving at the back of the microphone with plasticine. The loudspeaker should be as large as possible while still being capable of being fitted into the case. We used a 40 speaker intended for use with car radios. It has a nominal diameter of 120mm and a front-to-back dimension of 35mm. With all the wiring complete, reconnect the DC power supply as before, via a 5600 5W resistor. Check the voltages again. The voltage at pin 16 of the IC should be close to + 6V while at pin 21, + 2.9V should be present. If these checks are positive, the unit is ready to be connected in parallel with your existing phone. You will need a double adaptor phone socket and a phone plug. Connect the wires from the Speakerphone to pins 2 and 6. Plug the unit into the phone lines in parallel with your phone. With S1 in the off position, no DC voltage should be present across D5. You should be able to use your existing phone in the normal way. With S1 in the On position and the standard phone "on hook" you should hear dial tone from the speaker. Check that the loudness can be varied with the volume control. Now switch off the Speakerphone and make a phone call in the normal way. When you're ready, switch over to the Speakerphone and hang up the other phone. You can now sit back and enjoy a "hands-free" conversation. ~ 7 SPEAKERPHONE OFF MUTE 0 0 0 0 ON VOLUME L 20 SILICON CHIP 0 HEADPHONES _J Fig.5: this is a full-size reproduction of the front panel artwork. wpoD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS . . WOOD FOR C ~ i5 Cl: 0 I.I.. 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BANKCARD, MASTERCARD, VISA, CHEQUES OR CASH CHEERFULLY ACCEPTED :i:: ·THE WAY I SEE IT By NEVILLE WILLIAMS Could we end up drinking nickel-cadmium cocktails? Faced with an unserviceable nicad battery, most of us simply drop it into the garbage bin. But according to a recent report, we 're not doing the right thing. If nicad cells are let loose in the environment, we run the risk of getting our own back in some as yet unspecified form. A really galvanising drink, maybe! This rather alarming scenario flows from a recent TV interview with visiting environmentalist, Canadian born Dr Suzuki, as relayed to me by a reader from Parramatta, NSW. I imagine that quite a few others may have seen it and wondered what it was all about. Here's what the Parramatta reader had to say: Dear Mr. Williams, I was quite taken recently, by an interview with Dr David Suzuki on the TV Midday show. I am not an avid environmentalist but the sheer common sense of what he had to say could not be ignored. The bottom line was simply that, if our children are not very different from us, it will be a poor look-out both for them and the planet that they will have to share on a global basis. Because of my involvement with electronics, I was particularly interested in his observations about nickel cadmium batteries. They are now used in very large quantities and when no longer serviceable, normally end up in the garbage bin. In reality, they mostly end up in a tip, along with tons of other household garbage, where they presumably break down and release their 22 SILICON CHIP chemical contents into the water table. Dr Suzuki says that the batteries should be returned and recycled to avoid polluting the environment. I gathered that this is already mandatory in Sweden, with nicad batteries being available mainly on a new-for-old replacement basis. The curious thing is that similar concern does not seem to have been ref1ected in any of the articles I have seen about such batteries. There are all manner of instructions and arguments about how they should be maintained but never a word about how they should be disposed of. By coincidence, but perhaps alerted by Dr Suzuki's concern for the environment, I came across an issue of the English magazine "New Scientist" for Feb. 25, 1988 which featured an article entitled "Electricity: a public hazard in private hands". While the writer of the article was concerned about the implications of privatising Britain's electricity supply industry, what comes through loud and clear is the enormous problem of protecting the environment of a sma11ish, heavily populated nation from pollution by the by- products of power generation, ranging from nuclear waste and acid rain to the logistic difficulties of decommissioning obsolete fossilfuelled and nuclear power stations. Faced with the two extremes, nicad batteries on the one hand, and nuclear power stations on the other, I got to thinking about a few things in between, like alleged radiation from power lines and even the electric blankets on which many of us have been sleeping during the past winter. Maybe electricity isn't quite the "clean" energy source that it was on(l;e cracked up to be! T. A. (Parramatta, NSW). If T.A. professes not to be an avid environmentalist, I certainly claim no special expertise in this area either, preferring to be seen simply as a technical columnist reacting to a reader's letter. However, if the reader's concern and my observations cause further light to be shed on the subject, that's what this column is all about. Considered in isolation, his reference to electricity as a notquite-so-clean energy source tends to distort the thinking that follows, viz: if the use of electricity can be shown to have undesirable consequences, we should question its use and seek some other (Utopian?) option free from environmental effects. Endemic to homo sapiens The fact is that human beings have an impact on the environment by their very existence and, if the TV series Nature of Australia is to Energy and the environment Oil lamps and candles were the only sources of light available until the beginning of the present century, when gas was first introduced . Its adoption met with great opposition and lecturers in all parts of the country proclaimed the direful effects that would follow its employment. The antagonistic feeling thus aroused may be compared to the strong prejudice previously evinced against its parent, coal, as a fuel. Two hundred years ago, the citizens of London petitioned Parliament to forbid the burning of be believed (June 11, 1988), that observation applies no less to the Aboriginal race that roamed our continent before the Europeans arrived. The end effect of any one human activity has to be judged in relative rather than absolute terms. All practical energy sources, it would seem, involve some social and environmental consequences and our overall objective should be to reach decisions that will avoid or minimise those that appear to be most destructive. As a lad, I lived in a country village where initially, a couple of hundred people relied on the surrounding bush for timber, bark, firewood and the occasional variation in diet. It was natural and convenient to do so but one didn't need to be a sage to appreciate the impact and the limitations of a communal bush-based existence, even on that small scale. Many years later (1968) I was being shown around Manchester, in the UK and noticed a particular building that appeared to have been painted in a deep, flat black. But it hadn't! While other buildings had been progressively steamcleaned during the previous decade, that one had been deliberately left in its original state as an eloquent reminder of what the entire city had been like after centuries of domestic coal fires and fossil fuelled industry and transport. Nor was Manchester as they saw it in 1885 coal in the city " on account of its stench". But the threatened failure of the wood supply helped them to forget their objections, and coal soon became the principal source of artificial heat, as it has since become our chief means of obtaining light. Although gas represents a vast improvement on previous modes of illumination, we are far from being altogether satisfied with it. It often contains impurities which are not only prejudicial to health but are most destructive to property. We want something purer and unique; it was typical of many such centres in Britain's industrial heartland. Against that sort of background and my further memories of the one-time environment of Sydney's Eveleigh railway loco sheds, it is not hard to accept that our forefathers really did look forward to electricity as the environmentally clean energy source to which T. A. refers. Just in case you think that, in saying this, I'm simply romancing in print, break off here and read the contents of the accompanying panel, abstracted from "Science For All", compiled by Robert Brown MA, PhD, FLS, FRGS, for Cassell & Co, circa 1885. The panel contains an extract from an article by T. C. Hepworth entitled: The Light of the Future. Batteries - a hazard? But that aside, what's all this about nickel-cadmium batteries? As with T. A., the proposition advanced by Dr Suzuki was new to me. I could not remember the matter ever having been raised. Searching for clues, I checked through all the textbooks I could lay my hands on, but in vain. The construction of nicad cells was explained, along with their characteristics, charge requirements, behaviour, etc; users were warned not to toss them in a fire , for fear of explosion, or to carry them loose in a pocket, in case they might be more wholesome. How common it is to hear the remark "I must examine this or that by daylight before I can judge of it". Is not this an acknowledgment that our present resources are not equal to our requirements? That gas will be immediately supplanted is improbable; but we hope that the day is not distant when some better means of illumination is vouchsafed to us. Many circumstances have taught us to look for this boon to the magic power called "electricity". From "Science for All", 1885. shorted by keys, etc. and overheat. But I found not a single word about not dumping them with the rubbish. Norman Marks, on the Advisory Panel of this magazine, could not recall anything either but he remembered a Danish camera technician telling him that, in his country, all batteries were subject to new-for-old replacement. He was under the impression that similar arrangements applied in Japan and that in the USA there was an obligation to return mercury cells. Whether or not the emphasis, in each case, was on the environment or reclamation was not clear. Norman also made the point that cadmium had been named as a health risk, when included in alloys used for hard soldering in poorly ventilated situations. Oyster beds in Western Australia had allegedly been contaminated by naturally occurring cadmium and, many years ago, a welder in a major Australian radio factory had been reported killed by toxic cadmium fumes when processing heavily plated chassis. Phil Watson, a former confrere who has read and written more articles about batteries than anyone else I've met, could remember no warnings about discarding batteries of any kind, not even the otherwise touchy lithium cells. In his opinion, the concentration of chemicals from randomly discarded cells would be negligible and certainly less than it might be if SEPTEMBER 1988 23 THE WAY I SEE IT - CTD cells were returned to collection points and then discarded in bulk by people who failed to follow through. Last but not least, I checked with the Eveready Batteries Division of Union Carbide. After consultation with company cognoscenti, a spokesman rang back to say that, while they published instructions about handling and using the various kinds of cells, they had never had reason to make any statements about their ultimate disposal. Yes, they were concerned about environmental effects but as a company, they were unaware of any documented reason for the apprehension attributed to Dr Suzuki. They were quite happy for me to publish their statement and would certainly examine any evidence that might emerge as a result. And there I propose to leave the particular matter for the time being, to give readers the opportunity to react. If there's a body of evidence out there, in English, Swedish, Danish, Japanese or any other language, that has escaped attention in this country, who better than SILICON CHIP readers to bring it to our attention? Electric blankets & whatnots As for T. A.'s reference to unspecified radiation effects from power lines and the possible consequences of sleeping on switched-on electric blankets, that projects us into a highly speculative area. There are accepted industrial guidelines, procedures and practices for those directly involved in work on active high voltage power lines and equipment. Whether the risk of exposure to significant electrostatic or electromagnetic fields extends to hikers or to cattle grazing beneath major power lines is questionable. It is even more so in respect to the distribution cables passing your front door. They may be unsightly but currently accepted wisdom is that they are not a health hazard. Electric blankets, electric footwarmers, mittens and shawls are also assumed to be safe, as far as potential radiation effects are concerned. Even so, they are not without their critics - some for obscure physiological reasons, others because they're a bit wary about electricity, anyway. Personally, having put up with my share of ice cold sheets as a country kid, I'm partial nowadays to a nice warm bed. But I don't deliberately leave the electric blanket on all night. There's no point in exposing oneself to even a hypothetical risk if a doona on top makes it unnecessary. As for electric booties, mittens and shawls, I guess that, for those who suffer from (physically) cold feet, cold hands and arthritic backs, the choice between tangible comfort and an intangible, hypothetical risk, has something to do with the quality of life! Those huge power stations Finally, there's the article in New Scientist mentioned by T. A. and concerned with the contemplated privatisation of Britain's power generation industry. Author Roger Milne points out that, during the past decade, the power industry has been a major contributor to two massive environmental headaches - nuclear waste and acid rain, the latter resulting from millions of tonnes of sulphur dioxide and oxides of nitrogen belching, every year, from the stacks of fossil (mainly coal) fired power stations. This in addition to the direct environmental issues involving the location of large new power sta- tions of any kind, and the unsightly associated network of cables and towers. Projections indicate that Britain, already facing a crisis with intermediate level nuclear waste, will have nowhere left to store low level waste by the turn of the century. What's more, if it manages to control gas emissions from coal fired stations, the FGD (flue gas desulphurisation) equipment will have necessitated limestone quarrying as a raw material, and dumping facilities for the by-product, gypsum, both on a scale that will produce their own environmental confrontations. Can private industry cope with problems of this order and, beyond that again, can it cope with insurance and the financial implications of a nuclear accident in the light of what happened at Chernobyl? The way I see it, exchanges about the environment are not simply arguments that we win or lose. A certain point of view may prevail at any given time but the real problem doesn't go away. We can't forever ignore the environment, despoiling our forests and digging up ever more raw materials, while dumping reclaimable substances and chemicals into council sludge pits - there to be lost forever. Or leaving until tomorrow, action that should be taken today! Whatever we may think of particular statements by Dr Suzuki and other environmentalists, their overall theme is valid and it is high time that we all started thinking that way, without leaving the responsibility for changing attitude either to government or to private enterprise. Turning back the calendar By way of a complete change in subject matter, reader J. R. from Southport, Qld, supports my lament in the June issue under the heading: Those power distribution cables passing your front door may be unsightly but currently accepted wisdom is that they ore not a health hazard. 24 SILICON CHIP "For all practical purposes, Mr Fixit has had his day"! He says, however, that while most popularpriced domestic appliances are designed as throw-away units, repairable appliances made in Europe can still be obtained - for about double the price. For example, he has a modern English-made kettle, which can be repaired easily and for which spare parts are readily available. As for electric can openers, he reminds me that some models had a small grinding wheel at the back for sharpening knives. Before discarding them, he says, check to see whether it can be used for sharpening small drills and removing burrs from small metalwork. But I rather gather that, in J. R's mind, there's only a fine line between manufacturers who produce non-repairable appliances and outright "rip-off merchants". This because, in his letter, he proceeds directly from one subject to the other. I extract (with some abbreviation): The first criminal radio con man came to my notice in 1926. His equipment comprised a bogus diploma in wireless engineering, a receipt book and a small suitcase containing a few tools, a duster and a couple of valves in cartons. Starting around 10am, after the husbands had left for work, he would pick on a suburban street and call at the first house that had an aerial in the back yard. Putting on his best smile, he would usually manage to get inside (without obligation) to look at the radio, usually a neutrodyne or a regenerative TRF using 201-A or 199 type valves. He would lift the lid and "test" the set, unobtrusively keeping a finger on the fixed plates of a tuning condenser to detune the signal. Then he would switch off, replace one of the valves with a "new" one from a carton, convince the lady that reception was now much better, carefully dust the set, collect the money and move on down the street. He usually managed to "repair" about six receivers a day, ending up with the proceeds and, of course, still having two "new" valves left over to carry on with. Several weeks and many suburbs later, police put an end to his career as a "wireless engineer" but they were unable to return either the money or the correct valves to the original owners. Strangely, while retaining quite a few memories of the mid-1920s, none of my own recollections have to do with deliberate rip-off merchants. Maybe the limited number of wireless sets in the country and the technical awareness of most of their owners didn't leave too much room for dishonest initiative. About Guglielmo Marconi But J. R. isn't done yet. Still referring to electronic con men and ripoff merchants, which "trade on the gullible public who know less than they do" he says (and here I quote his letter exactly): These characters have been with us since wireless began. Marconi was the first of them. He managed to get himself credited with having invented wireless communication. Actually he invented very little but he was a great organiser, with an excellent grasp as a business man. Actually, the first man who visualised the idea of wireless communication was Faraday, some 50 yecirs before Marconi. Faraday mentioned it in his notes. Various other scientists were instrumental in inventing something connected with wireless. Lodge invented a coherer. Tuning coils had already been invented and Hertz had produced a spark gap transmitter. What Marconi did was to put all these ideas together into a practical and commercial form. Wow, that's telling 'em! Personally, I have always thought of Marconi as an inventor-cumentrepreneur but as an outright ripoff merchant, no. However, prompted by J. R.'s allegation, I reached down a copy of the book Guglielmo Marconi by David Gunston, one of the series The Great Nobel Prizes, published in 1970 and distributed by Heron Books. It's been on my shelf for years in its handsome leather binding and I had long since forgotten the details of its content. But thumbing through the book, it would seem to be a warts-and-all biography which certainly does not ignore the fact that the history of wireless is an unfolding story, with many scientists and inventors picking up and expanding upon the work of others. One chapter in the book is entitled "Those who paved the way" and this is followed by brief biographies of Michael Faraday, Joseph Henry, Samuel Morse, Sir Charles Wheatstone, James Maxwell, Karl Braun, Sir Oliver Lodge, Reginald Fessenden, Lee De Forest, and Edwin Armstrong. In the final chapter the author says: "Apart from the immensity of Marconi's achievements in his own right, what cannot be over-stressed is the impetus that his achievements in his own right gave to others ... men like De Forest, Franklin and Fleming were encouraged by Marconi's own breakthroughs to develop and add to their own particular lines of thought..." Far be it from me to base a conclusion on a thumb-through of a single biography but I do wonder about the biographer's summation above and J. R's own observations: "He was a great organiser, with an excellent grasp as a businessman" and "What Marconi did was to put all these ideas together into a practical and commercial form". The way I see it, far from confirming him as a con man, the above statements wouldn't read too badly as an epitaph! ~ 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 SEPTEMBER 1988 25 Cat Desc!iption AA-0380 AA-0382 AC-1600 AC-1678 AC-1958 AA-2019 AA-2024 AA-2025 AA-2026 AA-2060 AA-2091 AS-3017 AS-3050 AS-3182 AS-3303 AM-4103 AM-4110 AM-4180 AM-4210 AM-4212 AV-6!1:!5 AV-6532 BS-0404 Jaybrik &NI amp module Jaybrik 100W amp module Head demagnetis« 240V ~ker switch -5 pairs o/st.. eo ..ase head Headphone - light high quality Professional style headfoone Headphone AM/FM ra o Headg;one - fold up type Spea er mounting brkts • pai' Car radio ;rit - sp-iJ base 7x515ohmcarra ospkr Pilow~k,. 5 x 8 P w'p-oof speak,. HI quality earphone for 1V's Mic scr"" adap 1/4'-3/8" male Two mrcr: attaclment PA~ • p-olessional 30 watt PA amp 100wattPAam~ Vldeoswik:hl~ Lead 5 PIN • 5 IN rewrse Book • intro Aul:> solid stalll Bk - Soul of CPM Bk - Printer connections bt>le Bk - Macintosh program tech Bk - C p-og tech for MAC Bk - Computer conn solved Bk - Basic elect technology Bk - Basic elect ;rid DC circ Cassetles lo use wll'I BS0452 Bk - Und,.standi~ microproc Bk - Und,.st Digi electronics Bk - H'book elect tables & form Bk-CableTV Bk - 8080/8085 s/ware design Bk - Microcomp for bus'n app Bk - Crash course - digital lllch Bk - Intro Apple MAC Bk - Fhe optics exp~oj Bk - Semi gen ptxp r ce Bk - HO# to read schematics Bk - Comp car alJdio Bk • Data Comm, Netw & sys Bk - Advanced Urix prog guide Bk • Natlonal Htid products Mos memory - lional 1o· passive radiator 12" passive radiator 8" 2<11'1 4 ohm laser twntc spkr PA box I:> slit 8' spkr X'over - 3 way 400Hzt4.5kHz Spkr Mnt lu9" pk 6 p,.spex sheet 150 X 100mm 12 way PCB mnt sctfM term Metal cron ..s for spkr box86 lnstru case 90x125x190 lnstru case 140x175x220 lnstru case 145x115x21 O lnstru case 200x90x220 Weatherproof outdoor case Plasticdra--= Plasticdra-H'sink brkt 4 x T03 PCB 300x300mm d/slde l'lin Musicolor 4 kit Trans & FET 186181' kit Sullwoof,. mosfet amp kit COAM stereo decoder kit Aallrnast.. wakaround kit Aailmaster conroler kit Railrnaster clesel sound kit Railrnaster steam SOllld kit ~•f)i conrol railmaSler kit fNo/1 olrn moslet amp mod CDattenual:>rklt Video fader kit AM.fM IJne, remote cont kit CDadapta- kit Photo timer - clgllal kit Tt.rbotime,- kit Audio oscilator low dist kit 8 ch;ri 1/R tr;rismit kit IA receiv,. (std) kit IA receiv,. (add on) kit SOW moslet amp kit 12<11'1 mosfet amp kit RTTY enooder kit Car alarm current drop kil Audio d' . ind kit 64 Pkt r!ro11 Bal line driv.. kit RS-true-232 Interface kit Uo salellte decoder kit BS-0406 BS-0412 BS-0416 BS-0420 BS-0422 BS-0450 BS-0452 BS-0453 BS-0456 BS-0458 BS-0550 BS-0560 BS-0590 BS-0602 BS-0703 BS-0714 BS-0720 BS-0725 BS-0730 BS-0732 BS-0733 BS-0737 BN-4040 BN-4045 CA-2180 CA-2190 CE-2324 CB-2360 CX-2618 HP-1225 HK-3110 HM-3182 HM-3822 HB-5480 HB-5481 HB-5482 HB-5483 HB-6060 HB-6300 HB-6301 HH-8500 HP-9524 KA-1010 KA-1225 KA-1452 KA-1555 KA-1559 KA-1560 KA-1561 KA-1562 KA-1563 KA-1622 KA-1624 KA-1626 KA-1636 KA-1645 KA-1674 KA-1679 KA-1680 KA-1684 KA-1685 KA-1686 KM-3010 KM-3012 KM-3016 KM-3048 KM-3054 KM-3058 KM-3060 KM-3062 KM-3063 Normal p-ice 99.00 125.00 14.95 63.95 7.95 24.95 22.95 39.95 9.95 79.00 12.95 12.50 12.95 42.95 6.99 1.95 9.95 135.00 229.00 469.00 39.95 7.95 19.95 39.95 29.95 44.50 37.95 37.95 39.95 39.95 26.50 27.95 27.95 34.95 21.00 24.95 15.95 34.95 21.95 26.95 34.95 27.50 19.95 75.00 42.00 17.95 17.95 36.50 47.50 19.95 26.50 8.95 0.49 2.95 4.25 2.50 25.95 31.95 31.95 31.95 29.95 5.50 5.50 2.50 9.95 125.00 26.50 125.00 26.50 13.95 109.95 22.50 22.50 21.95 99.50 9.95 24.95 99.50 18.00 89.95 29.95 139.00 45.00 127.95 55.00 59.50 79.50 32.50 49.50 14.50 59.95 99.50 24.95 55.00 Sale p-ice 69.00 95.00 8.95 45.00 4.95 13.95 12.95 19.95 4.95 49.00 6.95 6.00 7.95 27.95 3.99 0.85 2.95 89.00 150.00 340.00 19.95 3.50 9.95 19.95 16.95 22.00 17.95 17.95 18.95 18.95 13.50 14.95 14.95 17.95 10.00 10.00 7.95 18.95 11.95 13.95 19.95 12.95 9.95 35.00 21.00 10.00 10.00 16.50 20.00 12.95 16.50 4.95 0.20 1.75 2.00 1.40 14.50 17.00 17.00 18.00 16.50 2.85 2.85 1.00 5.00 85.00 15.50 95.00 13.50 6.50 79.00 9.50 9.50 11.95 55.00 5.00 12.95 69.50 9.95 55.00 19.95 85.00 22.50 75.00 25.00 29.50 45.00 19.50 32.50 10.00 42.50 50.00 12.50 29.50 Cat Desc!iption KM-3066 KE-4000 KE-4002 KE-4012 KE-4013 KE-4202 KE-4204 KE-4678 KE-4708 KE-4720 KE-4726 KE-4731 KE-4732 KC-5011 KC-5014 KC-5018 KC-5020 KC-5022 KC-5024 KC-5025 KJ-6692 KJ.S694 KJ-6695 KS-8103 KS-8107 KS-8108 KS-8126 KS-8127 KS-8129 LF-1200 LF-1300 LT-3015 LT-3063 LT-3064 LT-3120 LT-3150 LT-3166 LT-3170 LT-3190 LM-3845 LA-5010 LA-5062 LA-5064 LA-5073 LA-5270 MM-1800 MT-3800 MS-4005 1'&0125 PS-0196 PP-0684 PS-0866 PS-0903 pp.0992 PP-0994 PP-0996 PM-2700 PA-3512 PA-3516 PA-3658 PA-3670 PA-3672 P~6510 Pl-6513 P~6515 P~6519 PH-9234 QM-3510 OM-3512 OM-3520 QP~105 OC-7160 OC-7114 OC-7125 RP-3806 RP-3814 RP-3831 RG-5179 RG-5183 AG-5185 RG-5195 RG-5198 RC-5400 AC-5450 RE~241 AZ-6625 RZ-6627 RZ-6646 AZ~ AZ-6681 AZ-6682 ST-0569 SP-0702 SP-0800 VHF rec for wealhe! set kit Buzz board kit Electronic siren kit 12V flasher kit Microwave oven det kit ETl5000 preamp kit ETl5000 graphic ~ kit ETl340 car alarm kit DI box kit Di ilal sampler kit T=one screamer kit Telephone intarcom kit Baby mind,. kit OH hoolt indicator kit Subcarrier adaptor kit SOW amp module kit Door mind,. kit Dual track plsupPI): kit Modem end-fie-Ind kit Line grabber - telephone kit Solar power 150 in 1 exp Electronics 60 in 1 exp Electronics 120 in 1 exp Transistor l861er kit Electronic lice kit PCl#er Sl,wl~ .5112V kit NiCad batt rger kit Siren l<it Sinple Trner kit RF choke alllln 10-100MHz Whlsle fi ter · Jabel FM band rejection filter Telescope raclo ;ritema Telescope raclo ;ritenna Carav;ri UHF,VHF,FM am,,j/ TV ;rit Ghostbust,. UHF, HF VHF metro ant TV Gutt,. gr_, TV ant ~tslnan TV ;rit eh 4&5 eo modulator LVM2A34 Miri burglar alarm Alarm emergency PitiJtton Glass break detector Rolle! shutter contact 4' 12V alarm bell Teleoom transformer T~e ne T/F experimental IEC mains filer 8 amp 3.5mm line ski, red, mono 6.5mm line sk~ Slereo, metal BNC line female crinp 37D ri!1Jt ;rigle socket 50 way Centronics type ski IDC he 16 way rt angle ecoo IDC he 34 way rt angle econ IDC he 50 way rt angle ecoo 3 pin line plug & skt Adaptor mic conniRCA ski Adaptor mic conn.6.Smm ski Adaptor ~n DIN -reverse Adaptor 2.1 skV1.3 pig Adaptor DC 2.5 skV1 .3 pig 8t,n wlw IC sk1 1 pin w/w/lC skt 22 pin w/w IC ski 24 ~ w/w IC ekt gold 21 batt PC mount holder Magrifier round, econ Magrifier bifoca"1igll Microscope 30X i ght BloodKcessure monitor Litle ofessor-Texas Cala.lator • comput,. style Solar cala.lator desk/pocket 1K log switch pot SOK log switch • pot 5K radio on/off vol swik:h 3.3uF 63~leencap 4. 7uF 250 polycarbonate 5.6uF 100V ~bonate 0.1uF 400V E polyest,. Predsion 1&2% cap pack CSA5 300K resonator Decooling ~ 0.02uF 14 ~n 2200uF 35V B electro 0.33A 35V RT !ant mi spec 0.68A 35V RT tanl ml spec 6.8uF 35V AT tant mil spec 150uF 20Vmil spec tant AT 22uF 35V mi spec tanl AT 47uF 20V ml spec tan! AT Swi mini SPOT C/off spring P.tiutton sw 1OA,□on or p/olf Paddle switch S DT gr~ fr:'" Normal p-ice 99.00 5.50 5.90 9.95 17.95 399.00 219.00 79.50 42.50 119.00 29.95 59.95 34.95 12.95 22.95 32.95 37.50 99.95 9.95 19.95 39.95 32.50 42.50 15.50 10.95 13.95 17.95 8.95 11.95 1.00 23.95 7.95 8.95 9.95 99.00 109.50 39.95 32.50 59.95 12.95 29.50 3.85 5.95 37.50 14.95 30.00 2.00 29.95 0.65 2.25 2.20 11.95 5.00 3.50 5.50 7.95 1.50 1.95 1.95 7.95 2.20 2.20 1.00 2.50 2.50 4.95 3.75 14.95 27.95 24.95 129.50 29.95 15.99 17.95 2.95 2.95 2.25 2.25 5.50 5.50 0.85 12.50 3.95 1.50 2.50 0.50 0.50 0.65 0.75 0.85 0.95 5.50 3.95 2.95 Sale p-ice 59.00 3.00 4.00 4.50 9.95 300.00 159.00 45.00 26.50 75.00 17.50 37.50 20.00 6.50 11.50 18.95 19.95 67.50 5.50 12.95 25.00 16.00 26.50 8.50 6.00 5.95 8.50 3.95 5.95 0.50 12.00 3.50 5.00 5.00 49.00 69.50 25.00 22.50 29.95 5.95 9.95 1.00 2.95 19.95 9.50 15.00 0.50 15.00 0.20 1.00 1.00 5.00 2.00 2.00 3.00 5.00 0.75 0.50 0.50 2.50 1.20 1.20 0.30 1.00 0.50 1.50 2.00 7.00 15.00 12.00 85.00 20.00 9.00 11.00 0.50 0.50 0.75 0.75 2.00 2.00 0.10 5.00 1.50 0.20 1.00 0.05 0.05 0.10 0.10 0.10 0.15 2.00 1.25 1.00 Cat Description SZ-2040 SC-2282 SL-2571 SL-2625 SL-2626 SL-2760 SY-4067 TS-1390 TS-1391 TS-1392 TS-1393 TS-1476 TH-1768 TH-1795 TH-1835 TH-1842 TH-1844 TH-1950 TH-1952 TH-1954 TH-1955 WM-4518 WS-5510 WS-5512 WS-5514 WS-5516 WS-5518 WS-5520 XC-0110 XC-0122 XC-0130 XW-0250 XW-0390 XW-0392 XW-0395 XM-0600 XA-1030 XV-2210 XM-4500 XS-4840 XC-5016 XC-5020 XC-5050 XS-7000 YT-6540 YT-7070 ZD-1931 ZD-1932 ZD-1980 ZT-2245 ZL-3170 ZL-3370 ZC-4032 ZC-4034 ZC-4035 ZC-4500 ZC-4517 ZC-4557 ZC-4580 ZC-4581 ZS-5810 ZS-5853 ll.-8072 Fuse puller Circuit break DP with switch 6V large green bezel 12V orange bezel 12V green bezel Fluro lamp/torch 3 x C cell 24V PCB relay SPOT 3A Weller tip CT5 BB8 2.4mm Well,. tip CT5 CC8 3.2mm Well,. tip CT5 DD8 5mm Wen,. ~ CT5 EE8 6.4mm Adcola esold,. pen !or E024 Nibbling tool • Kingcralt Cable De goo National inspection i!1Jt Pearl catch Tapered reamer 5-20mm Art knife with 25 blades Utilitykrife-small Uility krife - medi1111 - saw Touch knife - pocket type 24 w:,rainbow cable - metre Hea ink IJbe pack - asst Heatshrink IJbe 3.5mm 2 mt Heatshrink IJbe 5mm 2 mt Heatshrink IJbe 7mm 2 mt Heatshrink IJbe 10mm 2 mt Heatshrink IJbe 12mm 2 mt Pendul1111 driv.. Melodfu module 12 ~s Twlnk e little star m e Quartz clock/compass Digl alarm dock wil'I temp Temperalure alarm dock travel Car dittal LED alarm clock Brake amp Hash,. Elami junior robot Teledek 2000 Viatel unit Green screen 12" monitor Multicom 2 software I.O plus 2 card PC/XT Multi 1,0 board PC/XT 1SOW power supply PCIXT Centronics printer switch Sid block for phones Porsche 928 telephone PC817 1 X optocoople! 4 pin PC837 3 x optoc~12 pin LED/CDS cell opto 1:>r MJ3000 T03 darl flN UM170LEDdriver LM370 IC 4032 Triple serial adder 4034 8 Slg tri-st llli bulll'g 4035 4 bll shift register 4500 lndust cont unit 4517 dual 64 bit stal shfte 45571-64btvar-ing shftre 4580 4 x 4 mutiport regsr 4581 4bltalu 7410 triple input NANO gate 7453 exp 4 wide 2 Iii' ;ri!of CDP1822 Normal p-ice 3.95 5.95 1.20 1.95 1.95 19.95 1.95 4.95 4.95 4.95 4.95 79.95 19.95 14.50 23.95 6.50 15.95 9.95 2.99 14.95 1.99 4.95 3.50 3.50 3.95 3.50 3.50 3.50 14.95 14.95 3.95 5.95 27.95 29.95 24.50 12.95 99.00 129.00 229.50 149.50 139.00 199.00 159.00 99.00 34.95 49.95 1.20 2.00 3.00 10.00 4.20 1.00 3.50 2.95 1.50 7.95 5.50 8.50 10.50 4.50 0.25 1.20 11.50 Sale price 1.75 2.50 0.20 0,40 0.40 12.00 0.40 0.50 0.50 0.50 0.50 55.00 12.50 7.50 13.95 3.50 9.95 5.50 1.75 7.95 1.20 2.50 2.00 1.20 1.30 1.30 1.40 1.70 4.95 5.95 1.50 2.95 14.95 18.95 10.00 6.95 69.00 79.00 139.50 79.50 79.00 109.00 100.00 65.00 22.50 29.95 0.40 0.50 0.50 2.00 1.00 0.20 1.50 1.00 0.50 4.00 1.50 3.75 4.50 2.00 0.05 0.40 2.00 SPRINGVALE OPEN 'TII., 2pm SATURDAY TURN YOUR SURPLUS STOCK INTO CASH!! Jaycar will purchase your surplus stocks of components and equipment. We arc continually on the lookout for sources of prime quality merchandise. CALL GARY JOHNSTON OR BRUCE ROUTLEY TODAY ON (02) 747 2022 SENSATIONAL SCOOP PURCHASE! ~ Enjoy a "SOUNDTRACKER 1" Video Processing centre for less than 1/3 the cost of recent retail. The Soundtracker 1 Is a U.S. made video graphic equaliser, mono to stereo digital synthesiser and noise reduction unit. It goes between your VCR and audio amp to enable you to apporach that cinema sound of the movie theatre! It has a 5 band graphic to lrrprove Bass, treble, muddy mlds, etc. It has a noise gate to help reduce annoying tape hiss and It will synthesise a STEREO signal as well I It also works with stereo VCR's. They were on the market for around $379 and at that price were a FLOP. So Jaycar bought the Importers stock at a way below cost end-of-financial year price. The result is that you (once again) get a fantastic BELOW COST bargain. You can grab one of these at a never-to-be-repeated prcle of $99.95. NEW MODEL NOW AVAILABLE with DUAL TRANSDUCERS Special Introductory Price ONLY $39.95 Cat. YS-5512 Single Unit still available SAVE $10 on catalogue price Only$29.95 Cat. YS-5510 12V CAR ANALOGUE CLOCK MOVEMENT MASSIVE SCOOP PURCHASE! Grab a quartz crystal car clock with a set of automotive style hands at a price that will astonish you I Once again our suppliers huge loss Is your gain I Convert that broken unreliable or Inaccurate mechanical clock In your car to space age precision I Made In West Germany by VDO, the module measures roughly 45 x 38 x 40 deep. The compact size virtually ensures that It will flt in any space! Quantity strictly limltedl Probe Cases SAVE $10 ON LOGIC TESTER Now direct i!ll)Orted, we can pass on the savings to you. Will test all logic families (TTL, LS, CMOS, ate) SPECIFICATIONS Input lrllJ9dance: DC4-16V Working Voltage: Input Overload Protection: Current ConsurllJlion: Max 32mA at SV Supply Voltage Protection: Frequency Reponse: Max20M Hz Operating Te111'.)81'ature: Response Pulse Width: Longer than 25nsec Cat. QP-2210 $12.95 Min 1M ohm ±250VDC/AC ±SOVDC/AC ·20+70"C _B/ifl6lt ~ WAS $39.95 NOW $29.95 Cat. XC-0108 Cat. HB-6400 Telephone Diverter NEWMODEL ONLY $9.95 This professional quality product will automatically transfer incoming calls to another telephone number. Your business will not lose any important calls if you move, as incoming calls can be diverted to your new office address. Two telephone lines are required while the YT-6510 Is not Telecom approved It Is a very well made product. A 7.5V AC adaptor lsprovlded. Q Cat. YT-6510 WAL.KMAN SAVE $3 SPEAKERS $~ Pair of micro mini stereo speakers. Ideal for Walkman type radios, players. Cat.M-2050 ONLY $219 $15.95 pair Loudspeaker P.A. Bin Enclosure Designs Book AVTEK AUTOANSWER MODEM SALE WAS $349 SPECIAL SAVE $149 $14.95 Fane Acoustics UK, makers of speakers for the likes of Pink Floyd, David Bowie, Genesis, Iron Maiden ale. have produced an absolutely fantastic book on P.A. bin designs. The book begins with construction Info In general, I.e. what materials to use, how to join timber, how to brace the cabinets, sealing, lining, wiring, crossovers, impedance matching, etc. The second section Includes 22 separate detailed designs for: reflex cabinets, horns, wedge monitors, folded horns, w bins etc. Designs accommodate 1O", 12", 15" and 18' speaker components. This book Is cram packed with information. Save a fortune and build high power P.A. bins for yourself and friends. Cat. BF-4150 NEW'88 Cat. XC-4322 rn;w.rr<at> Jj)<at>filrn lR'.flID©l<at> lR'.flfilftrn~ Wfill ~<at>rr IIDfilrr[!IDfirn 1 · Another scoop purchase. This time a quality, high performance 4 amp 240V PCB mount mains filter. The schematic and pinout of the filter Is printed on the top of the 45(L)x28(W)x 16.S(H)mm potted plastic case, The unit has all of the major electricity authority approvals (German, US, Canadian, etc) marked on It as well. It has twin series chokes (2 x 1mH) MKT and MKP quality mains caps as shunts. As a filter It Is very effective. This product sells to OEM's In OOO's for about $19. Due to the enormous loss that the distressed manufacturer made when selling the goods to us you will pay almost half this one offll The quantity Is limited and It Is a once only olfer. OEM's. We can supply this to you at a great pricel Call nowl Cat MS-4008 $9.95 10 up $8.95 ea fJEf}j LOW COST CAPACITANCE METER VADER VOICE Ref: EA August 1988 Turn your analogue or digital multirreter into a direct reading capacitance meter. Will read a capacitor in the range from 3.3pF to 2000uF Ref: Silicon Chip August 1988 Change your voice to sound like Darth Vader from Star Wars. Full kit Including box, mic insert and speaker Cat. KC-5039 $16.95 Ref: EA Feb 1984 A would-be thief starts the car, It goes a few metres WIRELESS DOORBELL Ref: SIiicon Chip August 1988 What a great idea A wireless doorbell with the option to have as many sounders as your house requires. Transmitter Is mounted In a UBS Jiffy box with a pushbutton switch which mounts outside your front door. Powered by a 9V battery. Receiver mounts in plastic box and requires a 12V DC plugpack, our MP-3006 will do $14.95. Use as many receivers as you require. TRANSMITTER KIT Ignition Killer KC-5036 LOW COST 50MHz 4 DIGIT DIGITAL FREQUENCY METER Ref: EA May 1986 A low cost but highly sensitive, high impedance input unit measuring to well over 50MHz. All parts mount on the one PCB. The Jaycar kit includes case, front panel and all specnied parts. $23.50 $99 $16.95 and stops. He imrrediately cranks the engine and ff fires but stops again moments later. This could continue indefinitely. The Jaycar kit contains specffied original CDrfl)onents, instructions and 2 BONUS alarm stickers. Cat. KA-1536 "SCREACHER" CAR ALARM $42.50 Scare the pants off would be thieves with this great kit! • Fits under dash • Alarm goes off Inside car • Unbearable sound Cat. KA-1675 A JAYCAR/SILICON CHIP EXCLUSIVE KIT PLASMA DISCHARGE DISPLAY Ref: SIiicon Chip August 1988 Jaycar and Silicon Chip have combined to produce a low cost but spectacular plasma discharge display. Al the heart of the kit Is an exclusive rare-earth gas chamber specially made for this kit. This gas chamber Is specifically designed to produce a spectacular red, violet and orange continuously moving light show. It's like nothing on earth I You will absolutely amaze your friends and family. The Jaycar kit ol this project includes the rare-earth chamber, mounting plinth, EHT transformer and inverter electronics. A 2-3 arrp 12V DC power supply is required. (A battery charger Is ideal) . You can have this exclusive kit, complete for the amazing low price of only $2991 Call In to one of our stores for a derrol Cat. KC-5035 SAVE $3 ONLY $29.50 Discolite Kit , ,,,,._ ..- / $159.:;Q Ref: Silicon Chip July 1988 Build your own light show. More features than the Musicolor. New design. The Jaycar kit Includes punched and screened front panel, punched and anodised rear panel and all specified parts. Cat. KC-5032 STUDIO 200 HI FI PREAMP KIT Ref: Silicon Chip June/July 1988 The new Studio 200 PrearTl) offers excellent specfflcatlons and features for a very moderate price. Main Features • Very low noise on inputs - less than many CD players Cat. KC-5033 • Very low harrronic and intermodulation distortion • Up to 7 stereo program sources can be connected • Tape rronltor loop • Separate hiQh ~uallty headph~ne amp $229.00 ELECTRIC FENCE CONTROLLER Ref: EA December 1985 • Needs no auto coil • Uses special output transformer • L86s current drain and higher performance Cat. KA-1680 Protector Car Alarm Ref: Silicon Chip Feb 1988 About every feature you could ever want in a car alarm. See our 1988 catalogue for full details. Cat. KC-5021 $59.50 $79.50 Kill those clicks and pops from next doors vacuum cleaner or lawn edger etc. Kit Includes 240V socket and plug, PCB, all CDrfl)Onents and hardware. Remote Control (NEW FULL KIT) Ref: Silicon Chip March 1988 We are now selling this kit in a full form version. Kit includes all corrponents except box for receiver, piezo siren and piezo transducer and battery for transmitter.. These Items are available separately: Transducer Cat. AB-3440 $2.75; Piezo Cat. LA-5255 $17.95; Battery (pkt 2) Cat. SB-2420 $3.75 $39.95 TROBOSCOPIC TUNE Ref : EA July 1988 This simple circuit provides crystal-locked accuracy for tuning virtually any musical Instrument. It also doubles as a stable frequency reference if you prefer to tune up by ear. Kit includes box and all parts. Cat. KA-1705 $79.50 5000 POWER AMP "BLACK MONOLITH" RE-BORN WITH TOPOLOGY MODULES Jaycar proudly re-introduces the fantastic 5000 series power amplifier with the new 'state-of-the-art' Topology Power Modules. Get the upgraded module performance for the same price as the old 5000 arrp. Cat. KE-4200 $ 499.00 Extras not Included in kit Back 1.4> battery Cat. SB-2480 $22.50 Piezo siren Cat. LA-5255 $17.95 12 volt siren Cat. LA-5700 $26.50 Ref: EA Feb 1987 Will supply from Oto ±21.5 volts at currents up to 2 amps. Also features overload protection, a fused +5V<at> 1A output and metering. Cat. KA-1682 Ref: Silicon Chip May/June 1988 A high energy ignition system which uses the cars existing ignition coil and points. Unit has extended dwell and is compatible with both our Hall Effect and Opto Sensors. In fact, all components to interface both these are now Included free in the TAI kit. Complete kit with diecast box and all components and interface components. Cat. KC-5030 $129.95 $49.95 OPTION 1 Playmaster 60/60 Blueprint amp kit BREAKERLESS(HALLEFFECTI SPARKRITE SYSTEM $369 Ref: Silicon Chip June 1988 A professionally engineered electronic ('breakerless") contact breaker system. Yes, only Jaycar has a complete Hall Effect triggerhead assembly This set Is designed to flt most European and Japanese cars. In fact, It will also flt many Australian cars fitted with Lucas, Bosch, Motorcralt, AC Delco, or Autollte electrics. If you wish you can check first by sending a SAE for a car/distributor list. Cat. KJ-6655 $99.95 OPTION 2 SIEMENS HALL EFFECT CONVERSION Playmaster AM./FM Tuner Kit $599 Ref: Silicon Chip June 1988 If you have a car that will not take the very comprehensive KJ-6655 Hall type breaker point set, then this device is for you. German made Siemens HKZ-101 Hall Effect switch. Interface components included in TAI kit. Cat. ZD-1980 $34.95 8" White Cone Woofer QUARTZ CRYSTAL CLOCK MOVEMENT NEWMODELEXTRA FEATURES SAME PRICE ~~[ffi<at>~ □ [N] • VERY COMPACT• POWERED BY 1.5V AA BATTERY THAT LASTS FOR ONE YEAR • ±15 SECOND/MONTH ACCURACY• NEW MODEL• BONUS METAL HOOK TO HOLD CLOCK ON WALL • BONUS ON/OFF SWITCH Fit your own custom clock face. Great for novel applications such as fitting to pictures, boxes, photographs, etc. SUPPLIED WITH 3 SETS OF HANDS Cat. XC-0100 ~ 1 ll=i!!!!!!!!!_ _.,. ~ ~ $31.95 D D D 0 a D D 0 0 8 SECTOR BURGLAR ALARM KIT Jaycar Soldering kit Cat. TS-1850 D NORMALLY $26.95 SPECIAL $19.95 each $12.95 Designed for general purpose soldering. This kit includes a 30 watt 240V soldering iron and quallty metal stand with sponge, a length of solder and a roll of solderwick. D Best looking and sounding 8" woofer we've ever seen for the price. White cone, large magnet 10oz, roll surround Power Handling: 30 watts rms Resonant Freq.: 45Hz Freq. Response: 45 - 5000Hz Impedance: 8 ohm Sensitivity: 96dB Cat.CW-2111 - --c:::. !1.:-_ ,.. _...::===:=! Ref: EA Jan/Feb 1985 Costs far less than commercial equivalents. We don't know of an 8 sector unit for under $4001 Kit contains PCB, all components switches, power lead, 4 alarm stickers, horn speaker and case. Option: Gel battery 1.2Ah Cat. SB-2480 Cat. KA-1582 $169 • 1 HEAD OFFICE MAIL ORDERS 115 Parramatta Road Concord 2137 P.O. Box 185 Concord 21,37 HOTLINE (02) 7471888 Telephone (02) 747 2022 Telex 72293 FACSIMILE (02) 744 0767 ;LI ~ ,I '~~' MAIL ORDER VIA YOUR SYDNEY-CITY 117 YorkSt.(02)2671614 - VISA Mon-Fri 8.30 · 5.30 Thurs 8.30 pm· Sat 9 · 12 CARLINGFORD Cnr. Carlingford & Pennant Hills Rd (02) 872 4444. , · I M ____ a _ s t e. r C a ~- Mon-Fri 9 • 5.30 Thurs 8.30 pm• Sat 9 - 2pm -CONCORD rd. HURSTVILLE 115ParramattaRd(02)7453077Mon-Fri 8.30 · 5.30 • Sat 8.30 · 12 121 Forest Rd (02) 570 7000. Mon-Fri 9 • 5.30 Thurs 8.30 pm - Sat 9 • 12 POST & PACKING $9.99 $ 2.00 $10 $24.99 $ 3.75 $25 $49.99 $ 4.50 $50 S99. 99 S 6.50 OVER $100 $10.00 $5 FOR ORDERS ONLY TOLLFREE (008) 022 888 ff ROAD FREIGHT ANYWHERE IN AUSTRALIA $13.50 GORE HILL 188 Pacific Hwy cnr Bellevue Ave (02) 439 4799. Mon-Fri 9 • 5.30 Sat 9 - 4pm BURANDAOLD 144 Logan Rd (07) 393 0777. Mon-Fri 9 - 5.30 Thurs 8.30 • Sat 9 · 12 MELBOURNE-CITY Shop 2, 45 A'Beckett St City (03) 663 2030 Mon-Fri 9 - 5.30 Fri 8.30. Sat 9 - 12 SPRINGVALE VIC 887-889 Springvale Road Mulgrave (03) 547 1022 NrCnr. Dandenong Road Mon-Fri 9 · 5.30 Fri 8.30 · Sat9 -12 :<~~. 1-,, :;. :1 "..;li·:·=. ~~~~ ·• ·7 .~ . . ·1, • • . . PARTS LIST 1 PCB, code OE42F (from Oatley Electronics) 1 165mm length of 32mm 0. D. plastic conduit 2 end caps to suit conduit 1 momentary-contact pushbutton switch 1 battery holder (to suit 1 2V lighter battery) 1 12V lighter battery (VR22, EL 12, GP23 or equivalent) 1 piezoelectric disc transducer 1 12V piezo buzzer 6 PC stakes Semiconductors 1 2N5484 FET (must be specially selected - see text) 1 BC559 PNP transistor 1 4069 hex inverter IC 7 1N41 48 silicon diodes 1 5mm red LED Capacitors 6 1OµF 16VW LL electrolytics 2 0.1 µF monolithics 2 680pF ceramics Resistors (0.25W, 5%) 1 x 2.2M0, 3 x 1MO, 2 x 270k{l, 1 x 100k0, 3x3.3k0, 1 x4700, 1 x SOT (R6 - see text), 1 x 1 Mn trimpot Miscellaneous Threaded rod, nuts, hookup wire, solder etc. Where to buy the parts: a complete kit of parts for this project is available from Oatley Electronics, 5 Lansdowne Pde (PO Box 89), Oatley, NSW 2223. Telephone (02) 570 4985. The price is $24.95 plus $2.50 p&p. Note: copyright for the PCB artwork associated with this project is retained by Oatley Electronics. 30 SILICON CHIP FISH Bfl'f. DETECTOR Attach this simple unit to your fishing rod and you'll get an audible and visual warning when a fish is biting. This self-contained unit is easy to build and is simply secured to your fishing rod. It works by detecting rod vibration whenever a fish bites. No connection is made to the line and it has no on affect on normal rod and reel operations. When a fish bites, it flashes a LED and momentarily sounds a low-level piezo buzzer. As any fisherman knows, if you want to detect every fish bite you have to continuously hold the rod and "feel" the line. Alternatively, if the rod is placed in a rod holder which is embedded in sand, you have to continuously stare at the rod in order to detect a fish bite. This can become a little boring if the fish are only biting occasionally. The big advantage of the Fish Bite Detector is that it eliminates continuous "rod staring" or "rod R4 470{} D5 2x1N4148 0 B EOC GS 0 VIEWED FROM BELOW *SELECT ON TEST FISH BITE DETECTOR Fig.1: a piezoelectric transducer is used to detect vibrations and trigger the alarm. When vibrations are detected, Q1 and Q2 conduct, pin 6 of IC1c switches low, and the outputs of IC1d, e & f switch high to drive the LED and piezo buzzer. holding". And it solves the problem of using several rods at once, particularly at night. Some fishing reels are equipped with mechanisms that make a noise when a fish has taken the bait and is "on the run". However, these are generally quite insensitive and are only useful if the fish has well and truly hooked itself. By contrast, the project presented here is very sensitive and will respond to any decent nibble. And there's a sensitivity control that you can adjust to suit the size of the fish! Vibration detector As mentioned above, this unit works by detecting vibrations. More specifically, it detects rapid vibrations which are characteristic of a fish bite but does not respond to low frequency vibrations. This makes the unit insensitive to slow drags on the fishing line due to normal wave movements. To make the unit waterproof, the circuit is built into a 165mm x 32mm O.D. piece of plastic conduit which is fitted with end caps. The only external control is a pushbutton on/off switch which is fitted to one end. It alternately switches the power on or off with each successive operation. Power on/off indication is provided by the internal piezo buzzer. This emits a brief tone when the unit is turned on and gives a longer tone when the unit is switched off. Power consumption when the unit is switched off is negligible and is less than 2µ,A when the unit is on. This rises to a few milliamps when the unit is triggered, but this is for a short time only and has little effect on battery life. How it works Fig.1 shows the circuit details. It uses a piezoelectric transducer to detect vibrations and trigger the alarm. Let's take a broad look at the circuit operation first, before launching into a more detailed explanation. Alternate power on/off switching is provided by inverter stages ICla and ICl b, in conjunction with pushbutton switch S1. When the output of !Cl b is high, the amplifier consisting of stages Ql and QZ is on and it amplifies signals from the piezoelectric transducer. This stage then triggers a switching cir- cuit made up of gates IClc, ICld, ICle and IC1f, which in turn drive the piezo buzzer and the indicator LED. In greater detail, ICla and IClb are used to toggle the supply to Ql and QZ with alternate presses of S1. What happens is that the output (pin 4) of IClb simply assumes a logic level which is the inverse of that present on Cl when S1 is pressed. There's just one wrinkle here: there must be sufficient time (about 3 seconds) between presses of the pushbutton to allow Cl to charge or discharge via Rl. Let's say that initially pin 4 of IClb is low. This means that pin 1 of ICla will also be low, Cl will be discharged, and pins 2 and 4 will be high. If S1 is now briefly pressed, pin 3 will be pulled low and pins 4 and 1 will switch high. Pin 4 now supplies power to Ql and QZ via decoupling stage R4 (4700) and C4 (10µ,F). PIEZO TRANSDUCE / ~ Fig.2: you'll find the values for the various part numbers marked on the circuit diagram at the top of this page. Note that the resistors and diodes are all mounted end-on to conserve space. Use PC stakes to terminate external wiring connections. SEPTEMBER1988 31 The piezoelectric disc is made into a vibration detector by attaching a threaded rod and nut assembly close to the rim. The bottom rear edge of the disc is soldered to the earth track on the PCB. The circuit now latches in this condition and so Cl charges via Rl to the positive supply rail. If Sl is now pressed again, pin 3 of ICl b will be pulled low and thus pins 4 and 1 will switch low. Cl then discharges via Rl into pin 1 of ICla, ready for the next cycle. The piezoelectric disc is made into a vibration detector by attaching a threaded rod and nut assembly close to the rim. When vibration occurs, the piezo element is physically distorted and it generates an output voltage. This signal is then coupled via VRl to the gate of FET stage Ql. VRl is used to set the sensitivity while Dl and DZ prevent excessive voltage from being applied to the FET. The FET amplifier stage (Ql) is biased close to its cut-off point due to the high value of source resistance employed (R7 = lMD). Because FETs have such a wide spread in their parameters, a suitable FET and matching source resistor is selected on test (S.O.T.) and supplied as part of the kit. Transistor QZ forms an amplifier stage which is biased below cut-off by R6 (which is also specially selected). This means that QZ's collector normally sits at OV. However, if vibrations are detected, Ql and QZ conduct and QZ's collector rises to almost the full supply voltage. When this happens, the pin 6 output of IClc switches low and discharges capacitor CB (0. lµF) via diode D7. Thus, the outputs of paralleled inverter stages ICld, ICle and IClf switch high and drive the buzzer and LED indicator (the latter via current limiting resistor Rl2). Rl l and CB set the indicator time constant to around 0.2 seconds. As soon as vibrations cease, the output of IClc switches high again and CB charges via Rl l (2.ZMD). When the voltage on CB exceeds the inverter thresholds, their outputs switch low again and turn off the buzzer and LED indicator. Diodes D5 and D6 form an OR gate which isolates the indicator circuitry from the power supply switching circuitry. As we've already seen, the unit is turned on when S1 is pressed and pin 4 of ICl b switches high. To provide power on indication, this high is applied to a time constant circuit consisting of C3 and R5 to produce a 30ms pulse. This 30ms pulse is then applied to pin 5 of IClc via D5 but we still get a 0.2s indication period due to the Rl 1-CB time constant. Thus, the piezo buzzer sounds (and the LED lights) for 0.2 seconds whenever the unit is turned on. When the unit is turned off, pin 2 of ICla switches high and this signal is applied to a time constant circuit consisting of CZ and R3. This produces a 2.7-second pulse which is then coupled to pin 5 of IClc via D6. The piezo buzzer now sounds Keep all parts clear of the threaded rod and nut assembly to avoid upsetting the sensitivity of the piezoelectric transducer. We used a socket for IC1 but this can be considered optional. The piezo buzzer is connected to the PCB via PC stakes. 32 SILICON CHIP A SMALL PIECE OF FOAM RUBBER PREVENTS THE PIEZOELECTRIC DISC ASSEMBLY FROM TOUCHING THE PLASTIC AND STOPS MOVEMENT OF B SEVERAL SMALL HOLES ENABLE SOUND TO ESCAPE SHORT LENGT OF RIGID WIRE PREVENTS THE PIEZOELECTRIC DISC ASSEMBLY FROM TOUCHING THE SWITCH Testing Fig.3: how it all goes together. A small piece of foam rubber should be included as shown to stop the piezoelectric disc assembly from touching the case. The rigid wire stop prevents sideways movement of the board. Great care should be exercised when soldering the lead from the PCB to the front of the disc as it's easy to damage the thin metallic layer. Note the adjacent rigid wire stop soldered to the underside of the PCB. for the relatively long period of 2.7 seconds to tell you that the unit has turned off. Construction A kit of parts for this project is available from Oatley Electronics (see parts list). The kit is supplied complete and includes the printed circuit board (PCB), all on-board components, the piezo transducer, and the plastic conduit case. Fig.2 shows how the parts are mounted on the PCB. Install the parts as shown but leave the piezoelectric disc assembly off the board for the time being. Note that many of the parts are mounted endon to save space. Be sure to double-check the orientation of all polarised parts, as it's easy to make a mistake here. These parts include the diodes, transistors, IC, electrolytic cap- other end that goes to the disc. Note that the thin metallic layer lifts off easily with excessive heat. Do not try to tin this layer or apply heat directly with the soldering iron. The best procedure is to simply heat the back of the tinned lead with a soldering iron while holding it in contact with the disc. acitors, the LED, battery holder and the piezo buzzer. The piezo buzzer is supported on one end of the board by two PC stakes while two short pieces of tinned copper wire connect · the battery holder terminals to the PCB. Avoid using excessive heat and be careful not to bend the disc when working on the piezoelectric disc assembly. The first step is to solder the disc to the edge of the PCB as shown in one of the photographs. Tin both the edge of the disc and the relevant PCB track before soldering them together. The screw and nut can now be soldered to the top of the disc (see photo). Finally, a short length of hookup wire is used to connect the thin metallic layer on the disc to the input connection on the PCB. To do this, first connect one end of the lead to the PCB, then tin the Testing is no big deal. You simply set VRl (the sensitivity control) to its mid-setting and install the battery. If everything is OK, you will be greeted by a 2.7-second beep as the battery is installed. Pressing the pushbutton switch should now turn the unit on with an accompanying short beep. That same short beep should now occur each time vibration is detected. You will find that the unit is extremely sensitive just touching the PCB or the table on which the unit is resting should be enough to "set it off". VRl can now be set for the desired sensitivity. In practice, the sensitivity can be set quite high, because fish bites create a series of pulses that are quite distinct from false triggers. Final installation Fig.3 shows how the unit is installed in the plastic case. You will have to drill holes in the end caps to mount the LED and the pushbutton switch. In addition, a couple of small holes should be drilled adjacent to the LED to allow sound to escape from the piezo buzzer. Before sliding the assembly home, it is a good idea to slip a rubber band around the battery and the PCB to stop the battery from falling out of its holder. Also, a short length of rigid wire should be soldered to the earth pattern of the PCB (adjacent to the piezo transducer) so that the PCB assembly can not slide too far forward and foul the switch terminals. A couple of stout rubber bands or a hose clamp can be used to attach the Fish Bite Detector to your fishing rod. You will find that the unit will work quite well if attached about one-third of the way up the rod stem. ~ SEPTEMBER1988 33 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. National Semiconductor's LM12 150 watt op amp For many years monolithic power amplifiers have been regarded as devices of dubious reliability and so they often were, even when of quite low rating. In recent years though, monolithic power amplifiers have become available in ever increasing ratings. Now, National Semiconductor has topped them all with the release of its LM12 150 watt operational amplifier. Housed in a standard TO-3 metal encapsulation, with four leads instead of the normal two, the LM12 is capable of delivering up to ± 35 volts at up to ± 10 amps while operating from balanced supply rails of ± 40 volts DC. This enables it to deliver 150 watts into a 40 load with less than .01 % harmonic distortion. Furthermore, the LM12 has a phenomenal peak dissipation capability of 800 watts which allows it to to handle difficult reactive loads such as transducers, actuators or small motors, without derating. The LM12 in not only an inherently rugged device but also has comprehensive overload protection, including: • input protection; • controlled turn on; • thermal limiting; • over-voltage protection; • output current limiting; • dynamic safe-area protection. The LM12 delivers up to ± 10A output current at any output voltage swing yet is completely protected against overloads, including .-----------------------------v+ j 13 60µ 14! 1m R16 I '014 shorts from the output to the positive or negative supply rail. The device is also normally stable with resistive, inductive and small capacitive loads. Large capacitive loads can be handled safely with a suitable decoupling network at the output. The dynamic safe-area protection is provided by instantaneous peak-temperature limiting within the power transistor array; if the chip gets too hot, it shuts down until the temperature returns to a safe level. In practice, if the device case temperature rises above 150°C, the device shuts down until the temperature drops to 145°C. Should the supply voltage exceed ratings or drop below 15V, the op amp shuts down completely. Absolute maximum supply voltage is 100 volts total. The LM12 is internally compensated for amplifier configurations with gain down to unity. Small signal bandwidth (for a unity gain amp stage) is typically 700kHz and maximum slew rate is 9V per microsecond. Internal circuit 02 '015 R5 4k • output clomps: hrE "I Fig.1: internal circuit of the LM12 op amp. Q1-Q4 form differential input pairs while Q10-Q13 form a class-AH output stage. 34 SILICON CHIP Fig.1 shows the internal circuit of the LM12, excluding the active protection circuitry. It is a conventional operational amplifier circuit with a differential input provided by Q1, Q2, Q3 and Q4. The loads of Q3 and Q4 are provided by a current mirror consisting of Q5 and Q6. The output of Q6 is buffered by emitter follower QB and then fed to the driver stage Q9 and thence to the class-AB output stage consisting of Q10, Q11, Q12 and Q13. Bias stabilisation for the output stage is provided by R1 1k common ground point/-:- Fig.2: basic power amplifier ·configuration. With careful layout, harmonic distortion should be less than .01 % . Note the external clamp diodes (D1 and D2} diodes D4 to D7. Q14 and Q15 function as the output clamp diodes. Fig.2 shows a suggested circuit for the LM12 for a power amplifier application. Balanced supply rails are required and they should be well bypassed right at the op amp supply pins with good quality electrolytic capacitors of at least 20µ,F. For low frequency distortion, the capacitors should be 470µ,F or more. External output clamp diodes are included in the circuit even though the LM12 has internal output diodes of its own, as noted above. The reason for the clamp diodes is that if the amplifier goes into safearea limiting (ie, switches off its output drive) when driving an inductive load, the stored energy in the load will be released as a spike voltage back into the amplifier's output. Without the clamp diodes Fig.3: the voltage swing delivered to the load can be doubled by using a bridge configuration. ·Output clamping to the supply rails is provided by the bridge rectifier (note: supply connections not shown} Fig.4: unlike the circuit of Fig.3, this bridge configuration allows one side of the load to be connected to earth the output transistors can be punched through. External clamp diodes are specified because the internal diodes are limited in the amount of current they can pass. The circuit of Fig.2 has an output decoupling network consisting of a 4µ,H inductor and 2.20 resistor which ensures stability with large capacitive loading. Depending on lead dress of input, output and supply leads, the circuit can deliver up to 150 watts into a 40 load with less than .01 % harmonic distortion at lkHz. We have confirmed this performance in a "breadboard" circuit in our workshop. However, to guarantee the full 150 watts capability, the top-specced LM12C version must be used. While it is presently an expensive device, it would be ideal as the basis for a public address amplifier. Fig.3 shows a bridge circuit using two LM12 devices. This enables the voltage swing delivered to the load to be doubled. Al is connected as an inverting amplifier with a gain of 10 while A2 is connected as a noninverting amplifier with the same gain. The four diodes in the bridge configuration are the external clamp diodes needed for each LM12. (Note: supply connections to the LM12s are not shown). A limitation of the standard bridge connection is that both sides of the load are a hove earth potential. This can be fixed with the circuit of Fig.4 which allows one of the LM12 outputs to be tied directly to earth. One side of the load is therfore tied to earth. To make it work, the circuit must be run from floating supplies; ie, the centre-tap continued next page Fig.5: this circuit shows how two amplifiers can be cascaded to double the output swing Fig.6: discrete power transistors (Ql-Q4} can be used to increase the output drive for even higher power SEPTEMBER 1988 35 R1• Problems? ... and you don -'t have our .120page catalogue . .. R2• 10k 10k I _ R2V1N OUT - A1 A6 • PRECISION RESISTORS Fig.7: this circuit provides an output current proportional to the input voltage. Current drive is sometimes preferred for servo motors because is provides more loop stability of the supply rails cannot be connected to earth. (A similar circuit configuration using discrete transistors is employed in both channels of the Amcron MA-1200 power amplifier reviewed in the July 1988 issue of At last . .. a TRADE catalogue for the consumer ARISTA ... your one-stop problem solver. Video plugs and sockets ... Video extension speakers . .. Video flyleads ... Video RF interference filters . . . Video splitters ... Indoor antennas ... Video switching units . . . Down converters . . . Video speaker controllers . . . Video camera lights ... Video tape rewinders .. . Video cine adaptors ... Video head cleaners . .. Video splicing kits . . . Video storage cases . . . Video dust covers . . . Video leads ... Searl plug leads . . . Video dubbing kits . . . Video headphones ... Video shotgun and wireless microphone systems . . . Pre-amplifiers with video inputs ... Video camera stands . . . Just about anything you want. ... Try us ... NOW! Get your catalogue FREE from your local ARISTA dealer or send $2.50 P&H and your return address to: ARIST~ ELECTRONICS PTY LTD PO BOX 191, LIDCOMBE, NSW 2141 36 SILICON CHIP SILICON CHIP). As an alternative to Fig.4, two LM12s can be cascaded, as shown in Fig.5. In this circuit, Al drives the centre-tap of the balanced supply rails for amplifier A2. Thus the output swings of Al and A2 are added and one side of the load is tied to earth. The advantage of this circuit over the bridge configurations of Figs.3 and 4 is that the outputs can be cascaded over several stages, although each successive amplifier stage requires separate floating supply rails (ie, not referenced to earth). More and more power For even higher power, discrete power transistors can be used to increase the output drive to ± 90V at ± 10A, as shown in Fig.6. In this circuit, Ql, QZ, Q3 and Q4 operate as voltage followers with positive Fig.9: this configuration gives parallel operation without the need for a buffer amplifier as in Fig.8. Fig.8: output currents up to 20A can be obtained by using an LM144 op amp to drive two LM12s connected in parallel and negative reference voltages provided by the 39V zener diodes, D3 and D4. The LM12 drives the common connection of the two reference diodes and thus modulates its own supply rails. This enables Al to deliver a much higher output swing while still limiting its absolute supply voltage to about ± 38 volts. The LM12 can be used as a current driver, as shown in the circuit of Fig. 7. This provides an output current directly proportional to the input voltage. Current drive is sometimes preferred for servo motors because it provides more loop stability. The feedback resistors, Rl to R6, need to be matched to within .01 % . Parallel operation If more than ± 10A output is required, LM12s can be connected in parallel, as shown in the circuit of Fig.8. This employs an LM144 high voltage op amp to drive two LM12s which are connected as voltage followers. Feedback is applied from the commoned 0. Hl output resistors back to the inverting input of the LM144. Note that the supply voltage to the LM144 must be limited to ± 36 volts DC. An alternative to Fig.8 is shown in Fig.9 where A2 is connected as a current follower across R4, the output resistor for A1. Thus A2 acts as a slave to A2 and the output current is shared between the two devices. Note: most of this information has been extracted from application literature on the LM12, as featured in Volume 1 of the National Semiconductor Linear Databook, 1988. ~ MO D EM S foi dfu~tiafia Don't buy imported • unsupported The Avtek advantage Australian designed Australian manufactured Australian supported MEGAMODEMS 12/123 The Avtek Megamodems provide Australia's best value communications products. with a range of fully automatic, autodialling modems. Megamodems are suitable for data transfer from personal computers. terminals, mainframes and mini host computers and for all videotex services such as Viatel. The use of the latest technology has enabled us to make the Megamodem more compact and reliable than any other modem. Price is very competitive and reflects efficiencies incorporated in the design. The Megamodems are locally designed and built. SeNice, support and specialist R&D for the Megamodem range is all based in Australia. Available either as a standalone RS232 model or as a plug in 1/2 card for IBM PCs and compatibles. The · Megamodem range of modems are Telecom authorised. Automatic Dlal, Answer, and Disconnect: The Megamodems will automatically answer an incoming call and connect the computer to the line. When originating a call it will then dial out the required number and auto-connect to the computer at the other end. It will then ''hang-up" at the end of a communications session. Both pulse and tone dialling are supported. The modem is compatible with new Telecom exchanges and modern PABXs and can handle high speed tone dialling. Fully Hayes AT Smartmodem Compatible: The Megamodems are industry standard "HAYESSMARTMODEM "compatible which means they can take advantage of all the communications facilities of packages such as Crosstalk. Open Access. Symphony and Multicom. All communications parameters such as baud rate, parity and number of stop bits are set up automatically by the software and the Megamodem. Using appropriate software data can be sent and received while the Megamodem is unattended. Specifications Data Standards Data Rates CCITTV2l. Bell 103, CCITT V22 Bell 212. (123 model only CCITT V23) 300/300. 1200/1200 (123 model only 1200/75, 75/ 1200) MAIL ORDER WELCOME VISA ■- BUY DIRECT FROM THE MANUFACTURER Model 12 & PC12 $375nctax Model 123 & PC123 $449nctax t ~ ! VTEK L / ~ Box 284 Pymble 2073 Telephone (02) 888 5333 Facsimile (02) 887 2839 Helping the old folk at home Pride of place this month goes to a story from my Tasmanian colleague, J.L. Apart from technicalities, it has a high human interest, serving to remind us that, TV program knockers aside, there are many people for whom this is the only form of entertainment available. Technically, J.L. 's story emphasises the problems created by the need to expand an antenna distribution system as the demand for outlets grows. Anyway, this how J.L. tells it. "Got a light mate?" The sepulchral voice boomed out of the darkness in the ceiling space over the old people's home at Taroona, south of Hobart. I had been called in to add a new outlet to the 60-odd outlets already connected to the home's TV antenna system. The last thing I expected was to be asked for a light amid the dust and fluff between the rafters. The enquiry came from a Telecom technician who was looking for a phone line terminal board. I had often come across phone lines among the power and antenna NURSE'S LOUNGE KITCHEN CHAPEL ➔-~ o-4 ·nl ➔ OINING ROOM Basic layout RESIDENT'S LOUNGE 2 -WAY SPLITTER --<> TV OUTLETS 4- AY SPLITTER I <$>-o ~ I I D SPLITTER [> AMPLIFIER ◊ OROPTAPS ADMINISTRATION BLOCK HOSPITAL ANO RESIDENTIAL WEST WING Fig.1: general layout of the retirement home installation. It is not possible to show each individual T and outlet, but the order and value of T's shown is typical. Note the splitter feeding the nurses' lounge. 38 STLICON CHIP wires but I couldn't help regarding the terminal panels. The best I could do was lend him my lantern so that he could continue his search in greater comfort. He surprised me by revealing that Telecom employees don't rate a torch or lantern as part of their normal kit. They have to draw one from store and he had not done so because he didn't realise that he would be working in the ceiling. This is probably the most surprising encounter I have had since I inherited the installation. I have had many other encounters over the years, some uplifting and some tragic but all of them interesting. I was called to the home for the first time when the system consisted of about 40 outlets. Since then I have added another 20 and another 20 need to be added before every room has an outlet. It is quite an installation. The home is made up of two residential wings which form two parallel sides of a rectangle. What is called the west wing is a single storey building which houses the hospital and some 25 residential rooms. The east wing is a double storey building of about 46 rooms. An administration block forms the third side of the rectangle and a chapel, residents' lounge, dining room and kitchen, the fourth side. The system began soon after the home was completed, not long after TV started in southern Tasmania. But as with many new buildings, little thought was given to the provision of either telephone or TV services, and both facilities have had to be added piecemeal over the years. It seems that the story began when a local doctor's mother moved into the home, and found it impossible to receive satisfactory TV About this time the firm that had installed and maintained the system was sold. The new firm cut out all domestic service and the home authorities had to find a new firm to serve their needs. I was the third or fourth technician offered the contract but it appears that I was the only one game enough to take it on. (I sometimes wonder if "thick" should be substituted for "game"). Although I have cursed the job at times, particularly on hot summer days in the stifling atmosphere under the roof, I still think it is one of my more interesting occupations and I'll be very sorry when age makes me give it up. Anyway, that's the background to the story; now for some technical and physical details. ~ ~ <G>~~~ SOME OF -rH~ -RE.SIDE:"1\S WeRE. GE1\\NG VJORM'-t' 'P\G,u~e:.s •.... signals with an indoor antenna in her room. So her son had an antenna installed for her. When her fellow residents saw the lovely picture she was getting they all wanted an antenna. But the home authorities, quite understandably, didn't want a forest of antennas on the roof. So a well known and respected TV service firm was called in to install a system that would accommodate any resident prepared to pay for an outlet. The heart of the system was a distribution amplifier near the antenna, of about 25dB gain. From this a long trunk was run the length of the east wing with "T" taps for each subscriber. A "T" tap (or simply a "T") is designed to isolate each set from the line and minimise local oscillator and similar interference to other sets. It has a relatively high loss between the line and the set (side loss) and a minimum through loss to the remainder of the line. Typical figures would range from 30dB side loss with 0.2dB through loss to 12dB side loss for 1.5dB through loss. Knowing what value of T to use in each part of the system is a vital aspect of distribution engineering. The original system worked well for the first 12 to 15 residents in the east wing but more outlets were soon needed and the hospital and west wing residents also wanted outlets. The much longer run was clearly beyond the capacity of the existing amplifier. The solution was to fit a larger, 30dB, amplifier at the antenna end and move the existing amplifier to the other end of the east wing trunk. From here another trunk was taken through the administration block to the west wing and a new network begun. Wormy pictures The 30dB amplifier had been fitted at the antenna end not long before I took over the system, and some of the residents close to it were getting wormy pictures. This was not surprising, since some of them had 80dBu or more at their outlets. At this point it might be wise to digress briefly to discuss distribution network terms and standards. TV signal strengths can be most conveniently expressed directly in decibels (dB), provided this is done relative to some accepted reference. By using decibels, gains and losses can be easily added and subtracted, rather than resorting to the complicated multiplication and division needed if other values are used. The reference used in this application is 1 microvolt (lµ V), expressed as dBu. Most modern TV sets require 1 millivolt (lmV) or 1000µ V for a good stable, snow free picture. On the basis of the lµ V reference, lmV is + 60dBu. Most sets would work, after a fashion, down to 50dBu, but 40dBu would result in a very snowy picture. At 30dBu there would be more snow than picture and a 20dBu signal would probably be unrecognisable as a TV picture. In the other direction, most sets can cope with 70 or 75dBu. Their AGC (automatic gain control) SEPTEMBER 1988 39 SERVICEMAN'S LOG should be able to take care of such levels. But at 80dBu and above the AGC cannot always cope and wriggly patterns on the screen are the result. My aim was to provide 60dBu at each outlet. This was most conveniently done by starting with a high level signal and reducing it as required at each outlet with an appropriately rated T. In this installation the antenna was delivering about 65dBu to the amplifier, which was raising the level by 30dB to around 95dBu. Thus, sets close to the amplifier were being overloaded, even after the losses in the first string of T's. The original system had used 16dB and 12dB side loss T's, which had been OK with the old 25dB amplifier, but were not good enough with the new, more powerful amplifier. My problem was how to reduce the level to the first 20 rooms without the expense of replacing all the T's down the line with ones having higher side loss values. The first step was to split the amplifier output into two trunks, using a four way splitter with the two unused splits terminated. A twoway splitter causes a 3.5dB loss in each leg and a four-way splitter about 7dB. Thus I was able to in- troduce a 7dB loss into each trunk before I had to worry about changing any of the T's. In addition, I have 4dB in reserve which I can reclaim at any time by changing to a two-way splitter. Then I took about 10 rooms closest to the amplifier and connected them through new 30dB and 26dB T's. This solved the overload problem for this group and left only a few troublesome sets on the other trunk running to the second amplifier. These were cured on a temporary basis by fitting attenuators at the outlets. Later, a more permanent cure was made . when new outlets nearby justified the installation of more appropriately rated T's. Nurses' lounge I was handed a sticky problem at one stage when I was asked to extend the system out of the west wing, along a covered walkway and into a nurses' lounge some 40 metres beyond the end of the west wing trunk. I removed the termination from the last T (the last T must always be terminated), and ran an extension to the lounge, feeding the new outlet from a terminated 12dB T. But when I connected a TV set to this outlet there wasn't enough signal for a satisfactory picture. It was too long a run from the last amplifier, there were too many T's in the cable, and the 12dB in the final T was the last straw. To solve this problem I tried a different approach. I went back to the start of the new run and replaced the last T with a 2-way splitter, and removed the Tat the end of the new run; ie, in the nurses' lounge. This meant that there was now a 3dB loss to the new run, but no 12dB loss at its far end, since the T had been removed from this position. This meant a gain of at least 9dB, but actually a bit more because the T at the end of the old run would have introduced at least ldB through loss into the new run. Thus the nurses' set should have been at least 10dB better off and the end result, a first class picture, would seem to confirm this. But was I l 11 40 SILICON CHIP I tempting fate in terms of isolation, particularly from either of the sets on the splitter back into previous sets on the line? Yes, I was breaking the rules. A splitter typically provides around 22dB of isolation between the two sets it is feeding, but only about 3.5dB between either of these sets and the line into the splitter. So, while there was little chance of interference between the two sets, there was a risk that either one could interfere with other sets on the main line. But I was lucky; I have had no problems or complaints. Putting new outlets into an old building often presents real difficulties and taxes both my ingenuity and physical endurance. I often need to be in the roof and on an outside wall at the same time. And you can't nail a cable to an aluminium window frame. Most of the cables are brought out under the eaves and down the outside walls. This isn't an ideal situation - I would prefer to run them inside the wall cavity. Unfortunately this is impractical in most old buildings and impossible in twostorey ones. So I run them as inconspicuously as possible on the outside walls. Civil engineering One particular outlet will stay long in my memory. It was into a downstairs room of the two-storey block, with steeply sloping ground outside the window. The first problem was to provide a stable, level base for the ladder. This took over half an hour of civil engineering, involving quite a bit earth moving and the use of bricks and planks to create a retaining wall. (This ladder base is now a garden bed; another feather in my multitalented cap!) When I put my ladder against the wall I found that, fully extended to eight metres, it only just reached the top of the upstairs window. If it slipped, I would go through the glass. So I had to modify the top of the ladder with a plank held in place with G-clamps. This worked, but I felt decidedly unsafe perched so far above ground. After all this preparation it was up the ladder, drill a hole, down the ladder, grab the coax, up the ladder, push the coax through the hole, down the ladder, into the building, up the stairs, into the ceiling, and search for the end of the cable. Alas, the low pitch of the roof prevented me from getting closer than three metres from the coil of cable, clearly visible under the eaves. I had the idea that moving a few tiles might give me enough freedom to push the cable into a more accessible position. But my ladder wasn't long enough and I could only stand on the top rung, with my chin on the guttering, wondering how I might move those tiles only inches from my nose. Then I had the first really good idea I'd had all day. I came down the ladder (again), got into the van and drove into town to buy a 4-metre length of 3mm mild steel rod. With the end of the rod bent into a small hook I effectively had an arm four metres long and could easily reach the cable - without having to move tiles or buy a longer ladder! The rest of that job was an anticlimax, although there was still a lot of up and down the ladder while I fixed the cable to the wall. But my elderly client was ecstatic when she saw the "lovely pictures" and her delight made all the hassles seem worthwhile. As I mentioned at the beginning I've had both happy and sad contacts on this job. One of the sad ones was a dear old lady who was so crippled with arthritis that she couldn't press the buttons on her TV remote control unit. And I complain because it sometimes hurts me to hold a screwdriver! Other clients have died before they got full value from my work. Then I have had others (metaphorically) leaping over chairs in delight at the birth of a great-greatgrandchild. Although most of my clients at the home are, in a sense, really there just waiting to die, they are almost all a happy and nice-tobe-with crowd. One old chap likes to help me, even though he has trouble picking up cable clips, one at a time. Well, that's J.L.'s story, and I found it most interesting. The only comment I would offer concerns the lack of problems with the splitter. The most likely cause of interference between sets on the same antenna system is where the local oscillator frequency of a set on a lower frequency channel falls within the video band of a higher channel. Granted, there are other possibilities, involving harmonics etc, but this is the major problem. I'm not sure about all the channels in this area. The best reference I can find lists channels 2 and 6 in Hobart, and a channel 8 translator in Taroona. By my calculations, SEPTEMBER1988 41 SERVICEMAN'S LOG ~ ~ -- · ~7 MRS '-Nl>l'Altf' ( DOt.S~'i ~NOIN WHA1 Mt.iAfftORIG more likely to be a component fault, probably the dew sensor itself. I suggested he bring it in for me to check. So he turned up a couple of days later with the machine and I connected it to a monitor and turned it on while he was there. The dew light came on as predicted and, since the weather had been fine and dry during those few days, there seemed little doubt that it was a false alarm. I warned him that if it was a faulty dew sensor there might be some delay, since I had no replacements in stock. He indicated that there was no great hurry. At the first opportunity I pulled the covers off to have a closer look. And it was then that I observed the second fault; as soon as power was applied the video head drum commenced turning, which was definitely not normal. I pushed a cassette into the carrier and it accepted it and put it down on the deck. But that was as far as it would go; pressing the play button .produced no response - which wasn't really surprising. Two faults or one? none of these would qualify as likely to either cause or suffer from such interference. But other localities may not be so fortunate , particularly those within range of two different TV transmission centres. For example, a combination of channels 2 and 5 would be suspect, while channels 6 and 10 clashed badly on the NSW north coast some years ago, to the point where channel 10 had to be changed to channel 11. And these are only two possibilities. Faulty dew sensor From my own bench this month I have a story about a puzzling dew sensor fault in a National NV-370 video recorder. In fact, there were two faults, seemingly unrelated, but 42 SILICON CHIP the dew sensor fault was the one which alerted the owner, and the only one that he knew about. The story started with a phone call from the owner - a new customer - who explained that he had been away on holidays for a few weeks and that, on switching on the recorder when he returned home, the dew light warning appeared. Since there had been a bout of wet weather while he was away, he simply left the machine turned on for a few hours, expecting that the condition would correct itself. When this did not happen, he rang me to ask whether it was reasonable to expect that there would be any moisture left in the machine after this treatment. I said it seemed unlikely and that it was So, did I have two separate faults or was it one fault producing two apparently unrelated symptoms? I decided to pursue the dew sensor fault first, clarify that situation, then take it from there. The dew sensor in this machine is mounted on a small sub-assembly bracket mounted on the rear right hand corner of the deck. The accompanying exploded view of this corner shows the bracket (item 69), the dew sensor (67), the loading motor connection board, VJB00A54, to which the dew sensor is connected, and sundry minor components. Dew sensors are strange beasts. As I have found on previous occasions, they are basically resistors which increase in value in humid conditions. (Don't ask me how they work!) On this basis, an open circuit or high resistance dew sensor would simulate a high humidity situation. And the logical way to test for such a condition would be to short out the dew sensor, at least in theory. In practice, in this machine, it y-/ _/ ✓ 68 ELECTRONIC COM ONENTS We stock a wide range of electronic parts '7 .. • 1 ~· 11 • For service • For Hobby • For Transmitters • For Receivers Also in stock: ~D/:}__·1! Valves for Transmitters - 6146, 8950, 4X150, 6JS6, 811 and many others. Valves for receivers, made by Rhode & Schwarz, Siemens & Collins. R-388, R-390(A}, R392 and more . Fig.2: exploded view showing the dew sensor bracket (69), the dew sensor (67), and the loading motor connection board, VJB00A54. The relevant corner of the main chassis is also shown. wasn't all that simple. While the exploded view (Fig.2) may give the impression that it should be easy to get at, this is not so when everything is in its proper place. The best I could do was release the bracket and tilt it at an angle which allowed me to get a pair of sharp pointed test prods onto the sensor terminals to provide a patch. This had no effect, which seemed to rule out the sensor as the faulty component and to support the idea that it was a common fault creating both symptoms. At this stage, pressure of more urgent jobs and the need to think about the problem prompted me to put the job aside for a few hours. In fact, it was the next day before I turned it on again, only to find that the fault had vanished; the dew Mail order welcome D. Dauner Electronics 51 Georges Crescent, Georges Hall 2198, NSW Phone: (02) 724 6982 Telex 178 401 TV TECHNICIANS & SERVICE COMPANYS Have your PHILIPS VARICAP TUNERS (ELC2060) Repaired or Exchanged ONLY $17.oo ea TEN or MORE $15.oo Quick service 3 Months Warranty Send Faulty Tuners Cheques and money orders + P&P 8 ~ cs-~Awo,, - · WC\RN\NG AP~RE.D. $2.00 to: -:r.v.TUNERs) 216 Canterbury Road, Revesby 2212, Sydney Australia Phone: (02) 77 4 1154 SEPTEMBER 1988 43 SERVICEMAN'S LOG P1512 1 2 3 4 5 6 CAPSTAN FG LED GND LOADING <at> t- 1 LOADING (f;l) l+I SENSOR LED DEW SENSOR BP1512 BP1512 BP1512 BP1512 BP1512 BP1512 - I 2 3 4 5 6 Pl515 I TO LOADING MOTDRI I 2 LOADING LOADING<at> Fig.3: interconnection board, VJB00A54, and the dew sensor. Note the panels indicating the various plug connections. light was out and the drum had stopped turning. I loaded a tape and it played without hesitation; everything was back to normal. So there was the further complication that the fault was intermittent. And, as if to prove the point, the next time I turned it on, the fault had returned. Racking my brains for an inspiration I remembered that the mode select switch is something of a problem child on the National NV-450 and, while I had never had any such problems with the NV-370, it uses the same switch. I had such a switch on hand and, since there are only four leads and a minimum of mechanical work involved, it was a fairly simple job to swap them. Unfortunately it proved to be a false trail; it made no difference. So where to now? Delving back into the manual I began concentrating on the previously mentioned loading motor connection board to which the dew sensor is connected. The pattern of it is reproduced here and, as can be seen, it is little more than an interconnection device between various sections of the machine, which are fed into it via four plugs, P1512, 1513, 1514 and 1515. The sections connected to three of the plugs are shown in the panels alongside the board pattern; P1513 goes to the sensor LED, Pl514 to the 44 SILICON CHIP capstan motor, and P1515 to the loading motor, all three then being re-routed via P1512. (Incidentally, notice how the common Asian confusion between the letters "L" and "R" has crept into the designation of pin 1 in the P1513 panel). It was while I was studying this board pattern and the various interconnections, seeking inspiration, that I noticed a possible common factor. The wide copper track, surrounding a blank circle near the centre of the board and branching in two directions, is a chassis connection using the mounting screw (413 on the exploded diagram Fig.2) to complete the c.onnection. This pattern provides two chassis connections; one for the TETIA TV TIP General Electric TC53L2. Symptoms: Horizontal shakes of a few lines at a time . Occasionally shuts down with a loud screech . If kept running with an external power supply, the screech can be modified by tapping the line output board. Cure: TR704 (2SC1 722) line driver transistor intermittent internal open circuit. The transistor seems to be insensitive to direct tapping but responds to vibration through its connecting pins. dew sensor and one for the capstan motor. Could this be the common factor, assuming that a malfunction in the capstan motor circuit could ultimately be reflected in the false operation of the drum motor? While such interaction between the two motor circuits seemed somewhat tenuous, I was clutching at straws. But there was one other factor. Somewhere in my memory chip something stirred; a vague recollection of a "shop talk" session with a group of colleagues during which someone had mentioned a set of weird symptoms created by a faulty chassis connection in a National machine. I hadn't paid much attention at the time - not enough, obviously - but then, someone else was telling me about another equally interesting fault. All these thoughts went through my mind in much less time than it takes to tell - and they all pointed in the one direction; the mounting screw, 413. I reached over and applied gentle pressure to the board. And that was it; the dew light went out and the drum stopped turning. I reached for a Phillips screwdriver and tried tightening the offending screw. It was very tight and moved only a fraction of a turn, but that was enough to effect a more permanent cure; enough to let me play a tape and generally confirm that everything was working as it should. But I wasn't prepared to trust that screw. I pulled the board out and soldered a length of lead to the copper pattern near the mounting screw. Then I replaced the board and anchored the lead securely under a nearby screw. Since then I have learned that a mod sheet has recently been issued concerning this problem, and recommending that a separate lead be fitted along the lines I have just described. Now they tell me! One other point. I realise now that all my effort to short out the dew sensor was wasted; it was already disconnected at the chassis end, so the test was meaningless. Had I shorted it to chassis I would probably have solved the problem a lot quicker. Now I tell me! •~ 23 PIN "D" CONNECTORS 08-23 Male . . . $3.50 08-23 Female . . . . . . . $3.50 08-23 8ackshell . . . . . . . $3.50 VARIAC'S . . . VARIABLE TRANSFORMERS 240 Volt AC input. Output terminals are 4mm captive head type with separate earth connector 3 MODELS AVAILABLE • 0-250 volt<at> 5 amp $174 • 0-270 volt <at> 7 amp . $205 This handy little dispenser allows you to number all your cable needs • Complete with numbers from O to 9, make up any combination as you like $26.50 RS-232 PATCH BOX • Complete with ONLY $15.oo D89 to D825 ADAPTORS • 9 pin PLUG to 25 pin SKT. CAS 23 . . . . . $10.95 • 9 pin SKT. to 25 pin PLUG. Dil\lG 'I'I If. AC LIVOL'I'M f.~fER B Because the AC Millivoltmeter can measure audio signals down into the microvolt region it must be carefully constructed to minimise crosstalk and feedback in its high gain circuitry. Special measures must also be taken to avoid common mode signals and earth loops. By LEO SIMPSON & BOB FLYNN As far as our new AC Millivoltmeter is concerned, building the high gain circuitry is only half the job. Correct installation and wiring inside the case is critical if the proper performance is to be obtained. Earthing and layout of the wiring inside the case is especially critical. Taking short cuts in this area will result in an instrument which gives unreliable or even nonsensical results. Do the job properly and you'll have a measuring instrument of which you can be proud. We had to build several pro- totypes of this instrument and try out many variations in the wiring before we could be sure that we had a layout which would give correct results under a wide range of measurement conditions. That is not to say that putting the AC Millivoltmeter together is going to be a difficult job; it isn't. But if you vary the wiring layout or the components you are asking for trouble. Let's mention some of the critical areas of the instrument before we go on to detail the construction: • Insulated BNC sockets for the signal input and CRO output; • Wiring and layout of the mode switch; • Termination of the various shielded cables; • Metal shields around the Input Attenuator S1 and Noise Switch S4; • Mains and power supply wiring; • Transformer orientation. Some component substitutions are permissible though and we'll list those as we progress through the article. Assembly procedure To simplify the description, we'll assume that you have purchased a complete kit of all parts, including pre-punched metalwork and a screen-printed or Dynamark front panel. We'll also assume that you have a meter movement with the correct scale. To date though, only Dick Smith Electronics have indicated that they will supply the complete kit. Other kitsellers may come to the party at a later date. If you're not buying a complete kit but have opted to build your own from scratch you'll need to refer to the parts list and to a panel in this article which tells where you can buy some of the special parts needed. Assuming that you have the complete kit laid out in front of you, we suggest you start by building the power supply into the case. Then you can move on to assembling the main board, wiring the switches and finally the wiring inside the case. Power supply Both BNC sockets on the AC Millivoltmeter are insulated from the case even though the entire "earthy" side of the circuit is connected to case. Note the two voltage scales and dB scales on the meter. 46 SILICON CHIP The power supply is a version of our Universal Power Supply Board presented in last month's issue. It uses a 30V centre-tapped transformer (Altronics M-2855) and a bridge rectifier. We understand that the kit supplied by Dick Smith Electronics will use a 2851 15V 0 0 0 INPUT SEE SEPARATE DIAGRAM FGft 11, 13, S4 AHB S5 EONNECTIONI Fig.1: the overall wiring for the AC Millivoltmeter. Note that no part of the circuit, except for the transformer core, is connected to the mains earth. And there is only one connection from the circuit to the case, at the solder lug on the top righthand corner of the board. SEPTEMBER 1988 47 This view of the power supply inside the rear panel of the case shows how the transformer is angled to minimise hum. Note the all-plastic mains switch and heatshrinlc sleeving on the contacts. THREE WAFERS, EACH SINGLE POLE 12 POSITION CLICKER PLATE SINGLE POLE, 12 POSITION WAFER CLICKER PLATE SHIELD PLATE I { \ S1 \._ S3 TWO WAFERS, EACH SINGLE POLE 12 POSITION CLICKER PLATE CLICKER PLATE SHIELD PLATE I \ TWO POLE., S POSITION WAFER \ S5 S4 LORLIN ELECTRONICS MINIATURE ROTARY SWITCHES TYPE RA DIMENSIONS IN MILLIMETRES Fig.2: this diagram shows the wafer arrangement on the four rotary switches. Note that all switches must have make-before-break (shorting) contacts. transformer (as made by Ferguson and others) with two half wave rectifiers. Our wiring diagram shows the former version. Watch the polarity of the diodes and electrolytic capacitors when wiring up the power supply board. Note that the pinouts for the positive and negative 3-terminal 48 SILICON CHIP regulators are not the same. Don't get confused and swap them over or install them the wrong way around; they won't like it. Use PC stakes or pins for the AC input and DC output connections to the board. It makes connections easier. The power supply board and transformer are installed inside the rear panel of the case. The board is mounted using screws and tapped spacers which may be of metal or an insulating material such as Nylon. The transformer must be isolated from the case. This is done using tapped insulating pillars, 10mm long. The mains cord earth is terminated to a solder lug which is secured by one of the transformer mounting screws. The mains earth does not connect to the case itself but does run over to the Earthing switch, S6. The mains switch must be rated at 250VAC and be of all-plastic construction, such as made by Swann. Do not use a miniature toggle switch for this task. (Note: the Swann switch was not specified in the parts list published last month). By installing the transformer on pillars and using an all-plastic switch, the mains wiring will be done to double-insulation standards. This is necessary because neither the circuitry nor the case is connected back to earth. This is done to ensure that earth loops do not occur when measurements are being performed with earthed equipment. Note that the transformer is oriented at an angle of about 30° to the base of the case. This is to minimise hum injection into the circuitry. The Active (brown) wire of the mains cord is connected directly to one terminal of the mains switch while the centre terminal of the switch is connected to one of the transformer primary wires, via a 2-way insulating terminal block. The other terminal of the insulating block terminates the neutral wire from the mains cord and the other primary wire from the transformer primary. Both terminals of the mains switch should be sleeved with heatshrink tubing to prevent any possibility of contact with the AC mains. When the power supply is complete you can turn it on and check the ± 15V outputs from the 3-terminal regulators. That done, tie the mains wires to the insulating terminal block together with a ALL WAFERS VIEWED FROM REAR WAFER NEAREST CLICKER PLATE WAFER REMOTE FROM CLICKER PLATE ® WAFER NEAREST CLICKER PLATE 0 Switches MIDDLE WAFER M WAFER REMOTE FROM CLICKER PLATE Fig.3: this diagram shows how the wafers for S1, S3, S4 and S5 are wired. All resistors on S1 and S4 are 1% metal film types. The letter coding for the various wires corresponds with points shown in the wiring diagram, Fig.1. small Nylon cable tie. This is to reduce the possibility of any of the mains wiring from coming adrift inside the case. As a final step in the power supply construction, cut and shape a suitable piece of Presspahn or Elephantide (Bakelised canvas or Kraft paper) to sit under the mains terminal block and to cover all the mains wiring. We have left this out of our prototype so that the mains wiring could be photographed. If you can't obtain Presspahn (it is hard to get) use a piece of plastic icecream container cut and glued to shape (use M.E.K. or A.C.C. glue). Main circuit board Most of the AC Millivoltmeter's circuitry, with the exception of components wired to switches, is mounted on the main circuit board. This measures 193 x 98mm. We circuits. At one end of the board there are two long wire links. These should be run with insulated single strand wire, to avoid the possibility of shorts. Note that the Set Level pot is a 16mm diameter PC mounting type. It has been specified because of the limited space on the front panel. Be careful with the orientation of the electrolytic capacitors and ICs. There are three 50µF non-polarised electros and these can be installed either way around. Note that all the ICs are oriented in the same direction. When the board is finished, carefully inspect it and then put it aside. have used miniature capacitors (monolithic and miniature metallised types) throughout the circuit in our prototype but the board has been designed so that it will also accept the more conventional greencaps (metallised polyester). Capacitor tolerances are not critical in the circuit; the ± 10% tolerance of greencaps is adequate. Resistors are another matter. We have specified 1 % tolerance metal film resistors throughout, partly to obtain precise values and partly for their low noise. Don't substitute carbon film types. PC pins or stakes should be used for all external connections to the board. Doing it without PC pins is not practical. We suggest you install the PC pins, wire links, resistors and diodes first, followed by the capacitors and then the integrated While the switching in the AC Millivoltmeter is fairly complex, there is not a great deal of wiring. It must be done in the right order though. All the resistors on the Input Attenuator switch St and those on the Noise switch S4 can be wired onto the switches before they are installed. S1 is a single wafer switch and all the attenuator resistors are installed around it as shown in the wiring diagram of Fig.3. You can also refer to the relevant photos. S3 is a triple-wafer switch with intermediate shield plates between the wafers. Do not even think about using a conventional single-wafer 3-pole switch in this application; the crosstalk between the sections of the switch will make the circuit unstable. You must use the triplewafer switch specified. S5, the Filter switch, is a 2-pole 3-position type and while we used one from Lorlin, you could save a few dollars by using one which is readily available · from kitset suppliers. However, our wiring diagram depicts the Lorlin switch types throughout. You should solder all the connecting wires to the Mode and Filter switches before they are installed. At this stage you should be ready to install some of the hardware in the case. This includes the two insulated BNC connectors, toggle switch S6, pushbutton switch S2 and then the main printed circuit board. The board is installed with SEPTEMBER 1988 49 This view shows most of the main board, along with Input Attenuator S1 and the Noise switch S4. Note the two wafers for S4 and the tagstrip for the 11,tF input coupling capacitor. four 5mm spacers and secured with screws and nuts. Now install the Mode and Filter switches and make all the connections from them to the printed board. Run a short length of shielded cable from the CRO output socket to the adjacent points on the board. Note that the shield is not connected at the socket end. Instead, the shield solder lug connection of the BNC socket runs over to the centre lug of the Earthing switch, S6. One side of this switch is then wired to the earthing lug on the transformer while the other terminal goes to the 0V connection on the power supply board. Switch shields S1 and S4, the Input Attenuator and Noise switches, are surrounded by a metal shield to prevent crosstalk from other parts of the Actual size artwork for the meter scale. 50 SILICON CHIP circuitry. The cutting and folding diagrams for these shields are shown in Fig.4. They can be made from thin aluminium or tinplate. The shields are held in place by the switches themselves. The input BNC socket has its centre pin directly connected to the lµF 200V blocking capacitor. The other end of the capacitor is supported on an isolated tagstrip (ie, it should not short to the shield). The outer shield solder lug of the BNC socket connects to the main input earth for the board, adjacent to the pushbutton, S2. The wire runs through a hole in the shield, right under the socket, then drops down in the corner, loops around the pushbutton switch and then terminates on the main earth point. This point also terminates the shield side of the short coax cable from the Input Attenuator, S1. Note that this shielded ea ble takes the shortest possible route, via a hole in the surrounding shield, adjacent to the BNC socket. The wire from the middle wafer of S3 (S3b) to S4b runs via a hole in the relevant shield. The wires from S4a to the printed board should be twisted together. A 1000 resistor runs from one side of the pushbutton switch to a point adjacent to the signal input on the earth. The side of the pushbutton is wired direct to the input point. Both the resistor and connecting wire should be kept as short and direct as possible. The meter movement may now be installed in the case and wired into circuit. Note the polarity markings ( + and - symbols) stamped on the meter. We found it necessary to reduce the basic sensitivity of our prototype meter by connecting a 2.2k0 resistor across it. This is visible in the photos but not shown on the wiring diagram. This won't be necessary with the final circuit. Finish the wiring by connecting the three supply wires from the power board to main board. These should be twisted together with the wire to the Earthing switch, S6. Set-up and calibration Do not apply power yet. First check with your multimeter that the earth pin of the 3-pin power plug connects to the transformer core but to no other part in the circuit. With the Earthing switch in the "Float" position, the shield section of the CRO output BNC socket should connect to the mains earth. With the Earthing switch in the "Case" position, the shield section of the CRO socket should connect to the case. Again using your multimeter (switched to a low "Ohms" range) check that the outer shield of the Input BNC socket connects to the case. Some readers may think that this means the socket does not have to be insulated but it does. Now apply power and check that the ± 15V supply rails connect to the DC inputs on the mains board. Then using the OV input as a reference point, check that + 15V is present at pin 7 of ICs 1, 2, 3, 4, 6 and 8 and at pin 8 of IC5 and IC8. Check also that - 15V is present at pin 4 of all eight ICs. Offset voltages The next step is to check the output voltage of each op amp. Pin 6 of ICl can be expected to be less than ,1 00 00 00 0 I ,1 ~ 0 l! Actual size artwork for the main board of the AC Millivoltmeter. ± 100mV but it will vary depending on the setting of the Input Attenuator. Similarly, pin 6 of IC3 and IC4 should be less than ± lOOmV, depending on the setting of the Noise switch, S4; with S4 at - 30dB and the Input Attenuator at lmV, pin 6 of IC3 can go to - 1.3V or more Pin 6 of IC2 can be expected to be less than ± 100mV when the Mode switch S3 is in the "Volts" setting but will go to as much as - 5V or more when S3 is in the SEPTEMBER1988 51 This top view shows the connections from the power supply board to the main board. Note the wire from the main board OV point to the Earthing switch for the CRO output socket. Calibration 205 10 20 I ~ 37 0 ~ ~ ~ "' N ... ~ "'"' :::, C !!! ~ BEND UP ."' 51 21 45 45 4 ~ 0. :::, C !!! f I: 52 :1·,~1- 44 54 SILICON CHIP "'"' "'"' "Noise" setting, and depending on the setting of the Noise switch S4. To check IC5a, the Filter switch S5 must be in the "20Hz-20kHz" setting and the output voltage at pin 1 can be expected to be within ± lOmV. The same applies for pin 7 of IC5 although the setting of S5 does not matter for this measurement. (The reason S5 must be in the "20Hz to 20kHz" setting to measure pin 1 of IC5 is that the input of IC5a, pin 3, is not biased for the other switch settings; ie, "Flat" and "A Wt"). Pin 6 of IC6 should be within ± lOmV, regardless of switch settings. The same applies to pin 6 of ICB. Pin 7 of IC7a can be expected to be around - 130mV while pin 1 of IC7a should ideally be less than ± lmV. If it is not, there is likely to be a slight deflection of the meter movement. If there is an offset of several millivolts, it may be necessary to adjust the 6.2k11 resistor at pin 3. We did not have to do this on the two prototypes we built. HOLES : A : 3.2mm DIA. B: 5mm DIA. C: 10mm DIA. O: 19mm DIA. DIMENSIONS IN MILLIMETRES Fig.4: these are the dimensional and bending details for the metal shields to go around the Input Attenuator and Noise switches. To calibrate the AC Millivoltmeter, you will need a lkHz sinewave oscillator with a known amplitude output, preferably 1V RMS or more. Set the Mode switch to "Volts", the Input Attenuator to 1V and the Filter switch to "A Wt". Feed a lkHz sinewave of 1 V RMS amplitude into the input and adjust trimpot VR4 for full scale deflecction of the meter. Then move the Filter switch to the "20Hz to 20kHz" setting and adjust VR3 for full scale deflection of the meter. Then move the Filter switch to the "Flat" setting and adjust VR2 for full scale deflection. That completes the calibration procedure. If you have wide range sinewave oscillator with a calibrated attenuator, you can now check the frequency response and accuracy of the attenuators associated with S1 and S4. To verify the Noise Floor of the instrument, first put the lid on the case and secure all the fastening screws. Short the BNC input socket with a shorting plug or a piece of wire held in place with a small Special Parts If you're not purchasing a complete kit from Dick Smith Electronics or one of the other suppliers, there are number of parts which may be not readily available from your local supplier. The case for the prototype came from the Australian Transistor Company in Melbourne; phone (03) 898 2933. The Lorlin switches came from C & K Electronics (Aust) Pty Ltd; phone (02) 635 0799. The front panel, meter scale and printed boards are available from ACS Radio Pty Ltd, phone (02) 587 3491 or Jemal Products, phone (09) 350 5555. In New Zealand, contact Marday Services, Auckland, phone 88 5730 . All the op amps should be readily available with the possible exception of the OP27. This can be obtained from Geoff Wood · Electronics, phone (02) 427 1676. Cl) "'ea (..) + + 0 cc (..) cc w w I~ I- ..J 0 -> - . .J ..J ea ...I ea • • "C crocodile clip. Any noisy transformers or computers should be as far away as possible. Set the Earthing switch to "Float". Set the Input Attenuator to lmV, the Mode switch to "Noise", the Set Level control fully anticlockwise and the Filter switch to "Flat". Wind down the Noise switch until a pointer deflection towards the top of the scale is obtained. This should occur on the - 50dB Noise range. Press the Noise pushbutton and the reading should drop down scale to about - 3. This corresponds to a reading of - 55dB with respect to lmV. While still holding the pushbutton down, move the Filter switch to the "20-Z0kHz" setting. The reading then drops by lldB. It should now be about - 4 on the - 60dB range. Finally, move the Filter switch to the "A Wt" setting. The reading should then drop to about - 7 on the - 60dB range, with the Noise pushbutton still depressed. Note that it is normal for the meter pointer to flick up scale when switching Noise ranges below - 30dB. ~ ea "C 0 N I I.LI Cl) c5 z ~· • ea "C I • ea "C ..,, 0 I 0 ~ "C 0 i Cl) cc + :!i:! • .lll: I.LI : ; : . :i cc .:i ::c 0 • ea• 0 It) I • N_ ea + cc ea "C 0 <C et "C 0 ID ...I I W> 1-L.L.I Cl) L.U ...I > M > 0 ... > 0 ... • • • ... • • e M > I::::, Cl.. 3: + =• • •> • • ... > >•e > ... ... > e E 0 0 E 0 M E z I.LI c,; 0 Cl) :E - • g;?• Cl) ...I • + !l = > M 0 I- ::, L Cl) "' "ci 0 > 0 M > 0 + Cl.. 3: + Cl)~ L.U f:3:E ~ ccccO Cl..c::,Z LL + _J This is the actual size front panel artwork. Artwork for the power supply board was shown on page 48 of the July 1988 issue. SEPTEMBER 1988 53 :11J££JBIJ.B.R::mm1.1111e1: : Bl1BBll:l'BS:'':'::::11B.: ::119:J&I:'::':''.'''.: =: : : . ·,:.:.;.:-: ,-------------------------------.., I I I Why Waste Your time With Other Suppliers Altronics Can Deliver Any Of The Quality Products Just Phone Your Order Toll Free 1 To You Tomorrow I J kO ' D On 008 999 007 I a~/ Direit~~e II Country Clients Please Allow Addit ional 48-72 Hours I 1 I I . ~------------------------------- croprocessor Co tro Clips On To S etecto Invisible from outside your vehlcle - this fantastic high spec Radar Detector Detects X and K Band Radar up lo an Amazing 13KM This super compact "Sunvisor clip on " Microeye Detector is virtually invisible from the outside of most vehicles at normal eye t)eiaht hence its very unlikely yours would attract the attention a thief (or the Gendarmes for that matter) However, please remember that use of Radar Detectors is not permitted in some states. 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Quite simply GaAs diodes increase the sensitivity of the Microeye Vector.•Using the latest digital processing technology the unit will filter out and ignore emissions from 80% of poorly designed Radar Detectors that emit microwaves . • Simply plugs into your cigarette lighter socket. • Clips onto sunvisor • Detects Mobile Radar Equ ipment. • Highway/ City Modes switch allows monitoring of City or Highway conditions. Ultra High Power Capacity Polypropylene Basa Drivers Save 25% Thll Month 12" (300mm) Model 100 Watts continuous input 150 Watts intermittent input Impedance 8 Ohm Sensitivity 93db Weight 3620gm 99 C Accessories Included:- Visor bracket • Velcro • Cigarette lighter plug . 21 Day Money Back Guarantee . • Our incredible ALC Mic is one of the most exciting products for '88. Wireless Mics suffer from overmodulation distortion with too higher input sound level making them unsuitable for high grade vocal entertainment use of ALC (Automatic Level compressor) fixes all this. • Cardiod-Uni Directional Pick-up pattern• Freq.Res.: 30Hz-15KHz • Carrier Frequency.Adjust Range : ithin +lMHz, 88-108MHz. Built-in Antenna Then ■re the Genuine Grain Oriented Toroid Transformers •• used In Electronlc Australla Projects Toroidal Power Transformers Why • Toroid? • Sm eller size and weight to meet modern "Slimline" requ irements . • Low electricall y induced noi se demanded Normally $129.00 Ama Super Bargain Save $50 Fantastic Negative Ion enera or There have been volumes written about the benefits of negative ions combating air pollution, cigarette smoke etc. can be very beneficial to Asthma sufferers. Our great little Rover generates billions of ions per second! 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This fantastic Ultrasonic cleaner can earn its cost a hundred times over in cleaning Computer Connectors, PCB's, Switches, Relays, Jewellery, Glasses, Watches etc. How Does It Work? The Pin Point Ultrasonic Cleaner uses a transducer generator to produce millions of activated microscopic cleansing bubbles, which blow dirt, grease & grime off surfaces, and deep into cracks and hoies. This personal ultrasonic cleaner won't scratch precious jewellery or glass. Comparison studies made by hospitals, commercial businesses and industry show ultrasonic cleaning proves better and safer than any conventional method. But don't take our word for it. Test the Pin Point Ultrasonic cleaner yourself. Pop your dirty watches, glasses, connectors etc. into the cleaners stainless steel basin, add a cup of tap water, and three minutes later see the difference. The results are instantly revealing. SPECIFICATIONS Power Supply : 240V 50Hz Power Consumption : 300mA Frequency : 40 +/-2KHz Dimensions: 224 x 114 x 124mm Capacity : 570ml Weight: 1kg Body Materlal: ABS Plastic Tank Material: Stainless Steel (SUS 304) On/Off : 3 Minute Auto Timer. Amazing Price Breakthrough * Free $50 Probe Set Dual Trace 20MHz Oacllloacope Thi• all new CRO must be the beat valued quality Oacllloacope In Auatrallal i t:l~~~1f~IiitI~iilil~g~~~~1~~11I Q 0120 also features a ' Hold Off' control for seeing the front end of the input wave form. .. It ::~!~~~~~~~~~:~rt;t~?J~~a;c~~a:;i~h;~-~~n.ak~~t1~Y~:~d~/fl~esign : !: ~~~~rr~l~~~~~:f :i~~l~~!&g~£~~aef}~¥s;~;rtirt~~~free .•••••••••••••1••••••• • AconvenientX-Y operation modeallowsphasedifference f;t::,~-, ::::::;:;:::::::::::::! measurements between two waveforms. 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HM I lllll __....; This new addition to the LABTECH range will astound you with its high :;,;,:;:;,~:~ih::~:::,~;::~:.:::~"'.:~;~::,:~:.~•o<<h,,w,,, t:f! perlo,m }/}}If/{ :••···••:•••:1 :••:· Q 1530 s499 .• •-~_:'._~i1•_:,_: : •: 1;_:_. :·111: ·1•■:-:-·-■•111■.■a·_ ·- • • _·aii::=a ,== !: : : : : ·•··-·-··:·::~ --:::::~:~:t=·=·=·•·=·=·•·•=:•:•:•:;(:::;~,:}; :-:•:•:-:.:,::;_:::;:::;::::::❖:•:❖:-:-:-:-:-:; ···:::::.; :•:•:•, ......::::::::::: :::::;:~:::::::~:::::;:;:;:;:~:~t . . ·:: ·:. =:::;~;~;~:.::::fil:.:,:❖:: ·-·-:::::-.-,.,•,·-·: ::::=:=:;:&%:=::::::::: - - · ·m1111. 11i1:•:·.nlili,1111.1-mj:·::iii:::::111:\11,·:::·;::::::;:i:. :.:' ·:.; ,. , Great Kit Projects To Build Many Just Released For 1988 Ja~~~~~t~~ell Universal High Power Ampllfler Module (See SC Oec'87) High power rugged reliable design featuring low distortion and inbuilt speaker protection All components, including output transistors mount on a single PCB. Suitable for high quality guitar amp, public address or in a high fidelity stereo amplifier. Kit includes angled heatsink bracket, main heatsink and unlike other kit suppliers, the in-built Polyswitch for loudspeaker protection. 5140 s69 100W 150W Ver1lon K Ver1lon K 5150 s This unit contains all necessary components to complete:-• A Phono Pre-Amp with RIAA freq. response• A tape Pre-amp with NAB response• A microphone Pre-amp with either 40 55 or 80db of gain.• Or a Pre-amp for just about anything! Power 10-40V DC High 100db Ripple t--Re-;e-ct-io_~_5_5_1o_S_1_8_ ._5_0________ijij!ii!lll!l!:!lii::jj: Active Direct Injection Box (See EA Oct'87) High Energy Ignition System (See Slllcon Chip May'88) Extends the life of plugs & points, increases power & improves fuel economy. Suits 4,6 & 8 cylinder engines. Install one into your car & start saving$$$ from the very ~r:;:: s43 .50 5805 Line FIiter & Conditioner <"" EA Ju1y·11 --------,159.50 :~'!'ft!~~•~~;s be~l~i~a::w K The Discolite Flashes party lights on and off in beat with music from ~~ul~ga~~~~~~els controlled by 4 separate audio channels • Forward, reverse and auto-reversing chaser patterns• Simultaneous strobe on all four channels • ' Alternating light patterns • Music modulation available on chaser, strobe & alternate patterns• Inbuilt microphone for beat triggering or audio modulation of lights• Direct inputs for beat triggering or audio modulation of lights • Sensitivity control • presettable sensitivity levels for each channel • Front panel LEDs mimic light display. Great For Parties, Shop displays and special lighting effects. those annoying clicks & pops on your stereo & TV when the 6040 1:!:!/:!!/:///!//::: C'•'?'•'•'•:,:,:, JJ(JJ 't r/::<at>} •·•·····•·•·•···•·· t \({ ~~di~f~o~:i;~s;::v:~;~:~~uter crashes from power . spikes & glitches.Altronics " \ customised version housed • I in strong sturdy Jiffy box nickel sprayed for EMI shielding. K - 30 ·••··•'•·•·•·•· I'{}( 39 50 $ · ■ ..:··.::": '.:. ,•·.::· ~ - ,: · 0 : : i ). ·.:· · •: ·.: ,_... ,: · · .. ;w;;Jiat'flI:'..f} 0 ::·w~t<~r>~· .•: ,~ / · - - - The Screecher The Protector Car Alarm (SN EA Aug'86) 110db Modulated Tone Now our top selling Car Alarm. Two Sensor inputs-Normally open and normally closed enable simple connection to door, bonnet, Boot light, switches etc. (SIiicon Chip Feb'88) Save Over $100 On An Equivalent Commercial System Feature■: Internal & External Sirens • Dash lamp flasher • Battery back 11 up• Delayed & Non delayed inputs• Ignition killer• Easy to build & install. =----------------------------Super Low Price on Famous EA 8 Sector Alarm Svstem Kit (See EA Mag.Jan ·asj FHluree: • Alarm has 8 separate input circuits - 8 sectors can be monitored independently. • Each input circuit is provided with an indicator LED and a sector On/ Off switch . • Individual sector isolation allows the user to have some areas of the premises habited while others remain protected e.g. Inside Off/Outside On. • Inputs accept both normally closed and normally open sensors. • Two inputs provided with an entry delay between 10-75 seconds). Internal trip wc1rning buuer-alerts owner/ occupant of pending alarm operationgreat for the "forgetful" amoungst us. This buzzer is pre-settable between 5 end 55 seconds prior to Alarm. • Unique circuit detects automatically when any N/0 or N/ C loops are either open circuit or dead short. e.g. aomeon• trying to brtdge rffd 1wltche1 etc. • Switched output can be used to send a silent alarm through an auto-dialler circuit or similar. I r::c:n 1 (without Back Up Battery) (12V 1.2AH Backup Battery) 1:11 :111::1:1 S 5065 " ::::gr> 14310 s129.oo Bench Top Power Supply 3-30V to 1 amp Max.with variable current llmlt FEATURES: * Output 3 to 30V at 1A • Short circuit protected• Load switching• Current limiting . Dual scale meter • Housed in our Delu xe "ABS" instrument case . SPECIFICATIONS: • Output Voltage - 3 to 30V • Output Current - Oto 1 amp (fully variable)• Load Regulation - Better than 0 .2% from Oto fu ll load • Output Ripple-Less than 2mV RMS. ::::::::: K 3210 s79.oo I S149.50 S24.95 24V To 12V DC (SIiicon Chip Dec'87) Laboratory Power Supply Enables 12V appliances like stereos, 2 way radios, CB's etc. to operate from a 24 V battery. • Operates from 18V- 30V. Output is 13.6V at 5 amps. K 3255 K3300 3-5 Volta at up to 5 Amps $ 195 Designed by Electronics Australia, this supply has been one of our most popular kits. Our version incorporates refinements and is now housed in an attractive , tough "ABS" instrument case. This all new compact version has been made possible by the use of a highefficiency Toroid Power Transformer. So you win four ways• less heat, less weight - Greatly enhanced appearance and easier to build Remember the Allronlca Kit 11 fully drllled and punched. · s59 .00 Manufacturers, Contractors and Bulk Users Please Contact Our Wholesale Sales Dept. Sydney (NSW Only) Colin Fobister 436 0422 Perth 09 328 2199 174 Roe St. Perth W.A. 6000 PHONE TOLL FREE 008 999 007 Perth Metro & After Hours (09) 328 1599 ALL MAIL ORDERS P.O. Box 8350 Perth Mail Exchange W.A.6000 AL TRONICS RESELLERS Chances are there is an Altronics Reseller right near you - check this list or phone us for details of the nearest dealer. Pleaae Note: Resellers have to pay the cost of freight and insurance and therefore the prices charged by individual Dealers may vary slightly from this Catalogue - in many cases, however, Dealer prices will still represent a significant cost saving from prices charged by Altronics Competitors. Don't forget our E1pre11 Mall and Phone Order Service - for the coat of e loc ■ I call, Bankcard, Visa or Maatercard holder ■ can phone order for a■ me day deapatch . STANDARD DELIVERY & PACKING CHARGE $4.00 to 1Kg $7 over 1Kg AUSTRALIA WIDE - We process your order the day received and despatch via. Australia Post. Allow approx 7 days from day you post order to when you receive goods $7.00 OVERNIGHT JETSERVICE - We process your order the day received and despatch via. Overnight JelNrvlce Courter for delivery next day Country areas please allow additional 24-48 hours. Weight limit 3Kgs (3Kgs covers 95% of Orders) . $10.00 HEAVY HEAVY SERVICE - All orders of 10Kgs or more must travel Express Road - Please allow 7 days for delivery. INSURANCE - As with virtually every other Australian supplier, we send goods at consignees risk. Should you require comprehensive insurance cover against loss or damage please add 1% to order value (minimum charge $1 ) . .When phone ordering please request "Insurance" TOLL FREE PHONE ORDER - Bankcard.Visa, Mastercard Holders can phone order toll free up to 6pm Eastern Standard Time. Remember with our Overnight JelNrvlc• we deliver next day. COUNTRY ALBANY BP Electronics ■ 412681 ESPERANCE Esperance Communications 713344 QERALDTON K .B .Electronics & Marine 212176 KALGOORLIE Todays Electronics ■ 212777 KARRATHA Daves Oscitronic 854836 MANDURAH Lance Rock Retravision 351246 WYALKATCHEM D & J Pease 811132 NT ALICE SPRINGS Ascom Electronics 521713 Farmer Electronics 522967 ACT CANBERRA Bennett Commercial Electronics 805359 Scientronics 548334 VICTORIA CITY All Electronic Components 6623506 SOUTH MELBOURNE Winscott Trading 6995740 SU BUR BAN CHELTENHAM Talking Electronics 5842386 CROYDEN Truscott Electronics ■ 7233,860 PRESTON Preston Electronics 4840191 COUNTRY BENDIGO KC Johnson ■ 411411 MORWELL Morwell Electronics 346133 QUEENSLAND CITY Delsound P/L 8396155 SUBURBAN FORTITUDE VALLEY Economic Electronics 2523762 WOODRIDGE David Hall Electronics 8082777 COUNTRY CAIRNS Electronic World ■ 518555 BUNDABERG Bob Elkins Electronics 721785 GLADSTONE Supertronics 724321 MACKAY Phi ltronics ■ 578855 ROCKHAMPTONAccess Electronics (East St.) 221058 Electron World 278988 TOOWOOMBA Hunts Electronics ■ 329677 TOWNSVILLE Solex ■ 722015 SA CITY Electronic Comp & Equip. 2125999 Force Electronic ■ 2125505 SUBURBAN BRIGHTON Force Electronics ■ 3770512 CHRISTIES BEACH Force Electronics ■ 3823366 ENFIELD Force Electronics ■ 3496340 FINDON Force Electronics ■ 3471188 COUNTRY MT.QAMBIER South East Electronics 250034 WHYALLA Eyre Electronics ■ 454764 TASMANIA HOBART George Harvey ■ 342233 LAUNCESTON George Harvey ■ 316533 Nichols Radio TV 316171 NSW CITY David Reid Electronics ■ 2671385 CARINGHAH Hicom Unitronics 5247878 LEWISHAM PrePak Electronics 5699770 SMITHFIELD Chantronics 6097218 COUNTRY COFFS HARBOUR Coifs Habour Electronics 525684 GOSFORD Tomorrows Electronics ■ 247246 NELSON BAY Nelson Bay Electronics 813685 NEWCASTLE Novocastrian Elect.Supplies ■ 621358 NOWRA Ewing Electronics■ 218412 RAYMOND TERRACE Alback Electronics 873419 WINDSOR M & E Electronics 775935 WOLLONGONG Newtek Electronics ■ 271620 WA Blue Ribbon OHier■ are highlighted with a ■. ii ········•~ These Dealers generally carry a comprehensive range of Altronic products and kits or will order any required item for you. Abridged data for the MC34018 Speakerphone IC Elsewhere in this issue we have published the complete circuit of the Speakerphone, based on Motorola's MC34018. This 28-pin device can be used in conjunction with a conventional telephone and dialler IC such as the MC34014 or used on its own. By Leo Simpson The MC34018 contains most of the circuitry necessary to produce a high-quality speakerphone. Included in the IC are an amplifier for an electret microphone, an audio power amplifier capable of delivering up to 100 milliwatts to a 250 loudspeaker, a monitoring system for background noise and an attenuation system which responds to the relative levels of the transmit and receive signals as well as the background level. The receive sound level from the speaker is adjustable via a DC control input. A test circuit showing the key internal details of the MC34018 is depicted in Fig, 1. Most of the external components shown on this circuit are included in our circuit for the Speakerphone elsewhere in thi~ magazine. A table showing the function of each of the 28 pins is shown on the facing page. The key functions of the MC34018 revolve around the Transmit and Receive Attenuators, the Attenuator Control and the Transmit/Receive Comparator. Also important are the Transmit and The MC34018 comes in a 28-pin package and is ideal for use in speakerphones, intercom systems and automotive telephones. Receive Level Detectors. The Transmit/Receive Comparator is effective only in the Transmit mode while the Volume control (VLC, pin 24) is effective only in the Receive mode. The input impedance of the Transmit and Receive Attenuators is typically 5k0 and the maximum input signal Fig.1: this test circuit shows the key internal functions of the MC34018. It uses logarithmic amplifiers for the transmit and receive level detection. This enables it to handle a very wide dynamic range. 58 SILICON CHIP PIN DESCRIPTION Pin Name Description Pin Name Description 1 RR A resistor to ground provides a reference current for the transmit and receive attenuators. 2 RTX A resistor to ground determines the nominal gain of the transmit attenuator. The transmit channel gain is inversely proportional to the RTX resistance. 3 TXI Input to the transmit attenuator. Input resistance is nominally 5k0. 4 TXO Output of the transmit attenuator. The TXO output signal drives the input of the transmit level detector, as well as the external circuit which drives the telephone line. 5 TU Input of the transmit level detector. An external resistor AC coupled to the TU pin sets the detection level. Decreasing this resistor increases the sensitivity to transmit channel signals. 6 TLO Output of the transmit level detector. The external resistor and capacitor set the time the comparator will hold the system in the transmit mode after speech ceases. 7 RU Input of the receive level detector. An external resistor AC coupled to the RU pin sets the detection level. Decreasing this resistor increases the sensitivity to receive channel signals. 8 RLO 9 MCI Output of the receive level detector. The external resistor and capacitor set the time the comparator will hold the system in _the receive mode after the receive signal ceases. Microphone amplifier input. Input impedance is nominally 10k0 and the DC bias v,oltage is approximately equal to VB. 17 AGC cs Digital chip select input. When at a Logic "0" ( < 0. 7V) the Vee regulator is enabled. When at a Logic "1 " ( > 1.6V), the chip is in the standby mode drawing 0 .5mA. An open CS pin is a Logic " 0". Input impedance is nominally 140k0. The input voltage should not exceed 11 V. . 19 SKI Input to the speaker amplifier. Input impedance is nominally 20k0. 20 Vee A 5.4V regulated output which powers all circuits except the speaker amplifier output stage. Vee can be used to power external circuitry such as a microprocessor (3.0mA max). A filter capacitor is required. The MC34018 can be powered by a separate regulated supply by connecting V+ and Ve~ a voltage between 4.5V and 6.5V while maintaining at a Logic "1 ". 21 VB An output voltage equal to approximately Vee/2 which serves as an analog ground for the speakerphone system. Up to 1 .5mA of external load current may be sourced from VB. Output impedance is 2500. A filter capacitor is required . 18 22 Gnd Ground pin for the IC (except the speaker amplifier) . 23 XDC Transmit detector output. A resistor and capacitor at this pin hold the system in the transmit mode during pauses between words or phrases. When the XDC pin voltage decays to ground, the attenuators switch from the transmit mode to the idle mode. The internal resistor at XDC is nominally 2.6k0. 24 VLC Volume control input. Connecting this pin to the slider of a variable resistor provides receive mode volume control. The VLC pin voltage should be less than or equal to VB. 25 ACF Attenuator control filter . A capacitor connected to this pin reduces noise transients as the attenuator control switches level of attenuation. 26 RXO Output of the receive attenuator. Normally this pin is AC coupled to the input of the speaker amplifier. 27 RXI Input of the receive attenuator. Input resistance is nominally 5k0. 28 RRX A resistor to ground determines the nominal gain of the receive attenuator. The receive channel gain is directly proportional to the RR resistancce. 10 MCO Microphone amplifier output. The mic amp gain is internally set at 34dB (50 V/V). 11 CP1 A parallel resistor and capacitor connected between this pin and Vee holds a voltage corresponding to the background noise level. The transmit detector compares the CP1 voltage with the speech signal from CP2. 12 CP2 A capacitor at this pin peak detects the speech signals for comparison with the background noise level held at CP1. 13 XDI Input to the transmit detector system. The microphone amplifier output is AC coupled to the XDI pin through an external resistor. 14 SKG High current ground pin for the speaker amp output stage . The SKG voltage should be within 10mV of the ground voltage at pin 22. 15 SKO Speaker amplifier output. The SKO pin will source and sink up to 1O0mA when AC-coupled to the speaker. The speaker amp gain is Internally set at 34dB (50 V/V). 16 v+ Input DC supply voltage . V+ can be powered from Tip and Ring if an AC decoupling inductor is used to prevent loading AC line signals. The required V+ voltage is 6.0 to 11 V (7 .5V nominal) at 7 .0 mA. before the onset of distortion is about 700 millivolts peak-to-peak. The Transmit and Receive Level Detectors are logarithmic amplifiers (depicted with diodes in their feedback networks) which can handle a wide range of signals, thus allowing a wide range of signal levels. The outputs of the amplifiers are rectified and the filter components at pin 6 (TLO: Transmit Level Detector Output) and pin 8 (RLO: Receive Level Detector Out- A capacitor from this pin to VB stabilises the speaker amp gain control loop and additionally controls the attack and decay time of this circuit. The gain control loop limits the speaker amp input to prevent clipping at SKO. The internal resistance at the AGC pin is nominally 11 0k0 . put) are set to provide a fast risetime and slow decay. Also included are on-chip voltage regulators for both internal and external circuitry, thus allowing linepowered operation (ie, no separate power supply required). Comprehensive data and design information on the MC34018 are available in the Motorola Telecommunications Device Data Handbook. ~ P SUFFIX PLASTIC PACKAGE CASE 7 10·02 28 • FN SUFFIX PLC C-28 CASE 776 -0 1 The MC34018 is made in two packages but will only be available over the counter in the DIL case. SEPTEMBER1988 59 ER VOICE Are you a fan of Star Wars? Come on now, almost everyone is. Now you can sound like Darth Vader or a number of other diabolical characters from the nether regions of the galaxy. By DARTH JUNIOR Possibly, you just might not see the reason for building such a handy space-war accessory. If this is the case we will not waste valuable magazine space explaining why such a unit is desirable. It should be self-evident to anyone who has ever seen the Star War movies. Apart from its obvious everyday utility, the Vader Voice is cheap and easy to build. It is housed in a small plastic box with an electret microphone on one side and a tiny speaker on the other. There is a press-to-talk switch which you press when you want to talk - truly amazing. And, should you ever want to be heard with your own everyday boring voice, there is a toggle to switch CH PPER MICROPHONE from Vader to Normal. We doubt whether anyone would want to use it but we put it in to make it more complicated to use. After all, you don't want everyone figuring out how to use it more after than one sitting. The circuit Fig.1 shows the block diagram for the Vader Voice. A microphone feeds an amplifier which drives the following chopper circuit. The chopper switches between the amplified microphone signal and ground at a rate set by the 3.5kHz oscillator. The output signal from the chopper is then fed to a low pass filter. This removes the residual 3.5kHz signals from the LOW-PASS FILTER LOUDSPEAKER A r"XJ r"XJ AMPLIAER x15 'v 0 POWER AMPLIAER 3.5kHz OSCILLATOR Fig.1: how it works. The signal from the microphone is amplified and drives a chopper circuit which is switched by a 3.5lcHz oscillator. The output from the chopper is then filtered, amplified and fed to a loudspeaker. 60 SILICON CHIP resultant waveform before it is fed to the power amplifier and loudspeaker. Fig.2 illustrates how the circuit works. Waveform A is the signal from the microphone after passing through the first amplifier while waveform B is from the 3.5kHz oscillator. Waveform C shows how the audio signal is chopped at 3.5kHz while waveform Dis the output from the low pass filter. Note tliat waveform D is quite different to the original waveform A. Fig.3 is the full circuit diagram. It employs just two integrated circuits: a 4051 CMOS multiplexer which provides the switching function and an LM324 quad op amp. The rest of the circuit comprises two transistors plus the resistors and capacitors. The microphone is an electret type which is supplied via a 10k0 resistor. Signal from the electret microphone is fed via a .0033µF capacitor to the input of ICla which is connected as a non-inverting amplifier with a gain of 15 (set by the 470k0 and 33k0 feedback resistors). A 220pF capacitor across the 470k0 feedback resistor rolls the signal off above about 1.5kHz. Because of the gradual rolloff rate of this filtering, the signal is only reduced by half at 3kHz. ICla is biased at half the 9V supply, via the 470k0 resistor connected to pin 10 and the two 180k0 voltage divider resistors. This "half supply" voltage is decoupled with a lOµF capacitor and is used to bias pin 3 of IClc and pin 13 of IC2. IClb is connected as a Schmitt trigger oscillator. It has positive feedback via a 470k0 resistor from the output at pin 7 to the noninverting input at pin 5. Pin 5 also has a 470k0 resistor to ground and one to the positive supply. This means that when the output of the amplifier is high, the voltage at the non-inverting input is about 6V and when low the input is at about 3V. This establishes the upper and lower thresholds for the Schmitt trigger. The oscillator works as follows. The .0022µF capacitor at the inverting input is charged via the 100k0 resistor when the op amp output is high (ie, + 9V) and discharged when the op amp output is low (OV). When the capacitor voltage rises above 6V the output of the op amp A TIME -TIME Fig.2: these waveforms illustrate the circuit operation. Waveform A is the signal from the microphone, waveform B the signal from the 3.5kHz oscillator and waveform C is the audio signal chopped at 3.5kHz. Waveform Dis the signal from the low pass filter. suddenly flicks low and the capacitor then begins to discharge via the 100k0 resistor. When the capacitor is discharged to 3V, the op amp then flicks high and the capacitor starts to charge up again. The result of this continuing cycle is a square wave at the output of op amp ICl b at a frequency of about 3.5kHz. This waveform is us- 1k .----..-'WV.-.....- - - - - - - - - - - - - - - - - - - + - - - - - - . - - + - - - - + 9 V .01 3kHz LOW-PASS Al TER 1 2 5 .015 15 16 22k 14 1 +4.5V IC2 4051 13 O ELECTRET MICROPHONE 3 C 470k 11 A 220pF 6 7 0 12 .,. +9V POWER +9V + 220 16VW+ 01 BC337 S1~ T ...._ 9V : -i B ELJc VIEWED FROM BELOW 100k .,. .,. .,. VADER VOICE ·1 220 16VW B sn LOUDSPEAKER .00221 SCOB-1-0888-1 Fig.3: the circuit is basically a conventional amplifier with the addition of a chopper which operates at 3.5kHz. IC2 is the chopper and is controlled by IClb which works as a 3.5kHz oscillator. SEPTEMBER 1988 61 I° 0 ~ VADER VOICE i NORMAU PRESS VADER ON L:. 0 0 ..:J Fig.5: the PCB pattern and front panel artwork are shown here full scale. The metallised polyester capacitors should lie flat across the PCB so that there is room to squeeze the battery inside the case. The board sits upside down in the case, on top of the integral slide pillars. ed to toggle IC2, at pin 11. IC2 is connected as a single-pole switch which is toggled by the square wave signal fed to pin 11. The output of the switch, pin 3, is thus connected alternately to the audio signal, at pin 14, or the "half supply" point, at pin 13. This effectively chops up the incoming waveform. Switch S2 disables ICl b as an oscillator and forces its output high (when closed). This causes IC2 to 62 SILICON CHIP provide a normal straight through signal path for the audio signal. The output from IC2 feeds a third order 3kHz low pass filter formed by IClc and the ancillary components. This provides a steep rolloff of signals above 3kHz at a rate of 18dB/octave. The filtered signal is fed directly to ICla which drives a pair of complementary symmetry transistors, Ql and QZ, to form a minimum component amplifier. 100% feedback around the amplifier helps minimise the inevitable crossover distortion. The output transistors drive an sn loudspeaker via a 220µ,F capacitor. Overall, the circuit has been devised to give very low current drain and so a standard 9V battery (Eveready 216 or equivalent) should last quite well. To further conserve the battery, power switch Sl is a momentary contact pushbutton the press-to-talk switch mentioned earlier. Construction The Vader Voice is housed in a plastic case measuring 83 x 54 x PARTS LIST The 32mm loudspeaker is mounted on the back panel. The speaker shown is from IRH but virtually any miniature 80 loudspeaker could be used. 31mm. Most of the components are mounted on a small printed board measuring 50 x 63mm and coded SCOB-1-0888-1. Begin construction with the PCB. Insert and solder in the low profile components such as the resistors, ICs and links. Make sure that the ICs are correctly oriented as shown on the overlay diagram of Fig.4. Now the transistors can be soldered in as well as the capacitors. The electrolytic capacitors must be oriented correctly as shown and the filter capacitors (.015µF, .01µF and .001µF) plus the .0022µF oscillator capacitor should lie flat across the PCB so that there is room to squeeze the battery into the case. You can now run the wire connections to the switches, microphone, loudspeaker and battery. Holes need to be drilled in the lid of the case for the switches and microphone. For the loudspeaker, two 1mm holes need to be drilled for its terminals. Our prototype used a 32mm 80 loudspeaker supplied by IRH Components. (Cat. No. KSS-3108). It mounts directly onto the case and is retained by the two terminals at the rear. Finally, connect the battery and check that the circuit works. If a feedback howl occurs, try swapping the connections to the loudspeaker. The PCB is designed to mount upside down and sit on top of the integral slide pillars. 1 plastic case, 83 x 54 x 31mm 1 PCB, SC08-1 -0888-1 , 50 x 63mm 1 Scotchcal front panel, 50 x 79mm 1 32mm 80 loudspeaker (IRH KSS-3108) 1 electret microphone 1 9V 216 battery and clip lead 1 SPOT toggle switch 1 SPOT momentary action pushbutton switch Semiconductors 1 LM324 quad op amp 1 4051 1 to 8 analog multiplexer/demultiplexer 1 BC327 PNP transistor 1 BC337 NPN transistor Capacitors 2 220µF 16VW PC electrolytic When speaking into the microphone, the volume level can be adjusted by talking closer or further from the microphone. Alternatively, if a larger speaker is used, it may be necessary to provide a volume control in the form of a 1k0 potentiometer connected in series with the output. Alternatively, you could dispense with the loudspeaker altogether and couple the output from the 1 4 7 µF 1 6VW PC electrolytic 1 1 OµF 16VW PC electrolytic 1 O. 1µF metallised polyester (greencap) 1 0.015µF metallised polyester 1 0.01-µF metallised polyester 1 0.0033µF metallised polyester 1 0.0022µF metallised polyester 1 0.001 µF metallised polyester 1 220pF ceramic or polystyrene Resistors (0.25W, 5%) 5 X 470k0, 2 X 180k0, 1 X 1 OOkO, 1 x 47k0, 1 x 33k0, 1 x 22k0, 4 x 1 OkO, 1 x 1 kO Miscellaneous Solder, tinned copper wire, 250mm twin hookup wire. filter, IC1c, to the line input of a public address amplifier or cassette deck, if you wanted to record your Vader Voice. We'll leave it to you to think up the possibilities. Troubleshooting If your Vader Voice doesn't work at switch-on, you can start checking it out by meauring the supply continued on page 98 SEPTEMBER 1988 63 IT? WHYB BUILD IT YOURSELF & $AVE! Building your own saves you money - especially at the low, low prices of our amateur & related kits this month (see below). But there's more reasons to "roll your own" than just to save money... • • • • • You'll keep (or maybe regain?) those construction skills you had back in the good ol' days - when all there was available was to do it yourself. In these days of "black boxes" it's to easy to lose those important - perhaps elementary - skills such as soldering technique, component dress, wiring, even component identification! You'll be able to enter those "home brew" competitions that used to be so much a part of our hobby. Today they're all but forgotten in many instances. You'll get the piece of gear - test equipment, transceiver, amplifier, whatever, far sooner than having to wait until you've saved for it. Perhaps most importantly of all, you'll be proud to say "I built it myself!" BIG SAVINGS THIS MONTH ON AMATEUR & RELATED KITS: UHF Amateur Transceiver UHFWattmater The ideal way to get onto 70cm. Cat K-6300 Was $249.95 The inexpensive way to keep your VHF Wattmeter is easy to build, a 70cm station up to scratch. Cat K-6312 must for your 2m station. Cat K-6316 Was $49.95 THIS MONTH: Was $49.95 THIS MONTH: 10 to 14dB gain on all HF bands · expect around 150W PEP or so from on all bar 28 (3dB lower). 2m Amateur Transceiver . . was $379 THIS MONTH: THIS MONTH: 199 5 40/BOCH Upgrade Kit for UHF Transcerver Or A Power Meter? s3995 Doubles the number of channels you can access. cat K-6301 Was $12.95 THIS MONTH: 5 Why not make a pigeon pair? Covers full 2m band . . . a great "big time" project for novices (needs fair level of technical skill). cat K-6308 70cm Preamp Was $249.95 THIS MONTH: 595 Not just for the kit transceiver: get a few more dB out of any commercial receiver too - and cheap! Cat K-6306 Was $21.95 THIS MONTH: sges s199 99 THIS MONTH: 49 5 299 100 W On SIX Too , • All-mode amp needs only 6W drive for 100W out. Includes carrier operated relay. Cat K-6349 95 was $329 THIS MONTH: 5279 And A New DIY SW Receiver: ~overs 500kHz of HF, with 30W PEP output. As supplied covers 80 metres, upgrade kits below give you other bands. Cat K-6330 Need A Supply? Was $399 THIS MONTH: • Features 3 bands from 0.48 to 17.12MHz, a great "start-up" kit (great for school projects). Now available in limited quantities in all DSE stores. Cat K-6355 s99 Matching 13.8V power supply for VHF or UHF transceiver. cat K-6310 s3995 Extra oomph out, too: 50W ish from 2W drive! includes carrier detecting switching. Cat K-6307 Was $279.00 Perfect for the kit - or handheld, etc. 100W out from 15W in (40W from 2W). Cat K-6313 THIS MONTH: 5 199 Was $299 THIS MONTH: 5249 LIMITED QUANTITIES OF THESE KITS AVAILABLt AT ALL DICK SMITH ELECTRONICS STORES OR PHONE YOUR ORDER DIRECT 10 I ~f.~ . ,<\tte~uate 1t! The 50 ohm attenua~or ~It gives you up to 63dB attenuation m 1dB steps from 50 to 500MHz. Cat K-6323 Was $79.95 5 ltF Transceiver Slashed, Too! UHF Power Amp I And Just In Casa You Have Too Much ... ~a7:~~ft Like its 70cm brother, it will put some SIG into your signal! Cat K-6311 was $129.00 THIS MONTH: Was $49 -95 THIS M0NTH: How About A linear? I s3995 2m GaAsFET Preamp UHF GaAsFET Preamp When you really want performance, try this beauty! 13dB gain, includes full tx/rx switching. Cat K-6309 Was $129.00 THIS MONTH: 5 100W+ Of HF Muscle ll,i~'ftT:UO:J~r:1 299 5 Upgrade kits to suit Haff Price: 40 metre K-6332 20 metre K-6333 15 metre K-6334 10 metre K-6335 Were $39.95 each ... THIS MONTH: 5 1995 ea. HURRY - SOME STOCKS LIMITED! Hands-Free Phone Studfinder You could spend hundreds of dollars on a hands-free phone. If you've ever hammered a nail into a wall - and missed the Vader Voice Shades of Star Wars! The kids'II have a ball with this one: just speak into it and your voice comes out just like Darth Vader's! Nifty little kit, complete in one zippy box. Cat K-3510 Or you could build this kit. Simple, effective-and cheap! Use in conjunction with existing phone for full two-way handsfree conversation. Cat K-3100 As SBBn In 'Silicon Chip' stud - this one's for you! Easy to build (one night project) is perfect for the home toolbox. (Sorry, it cannot detect the other type of stud!) Cat K-2723 As seen in 'Electronics Australia' s39gs $ As seen in 'Silicon Chip' s299s Guitar Practice Amplifier Short form kit.(PCB components only - you decide which !!~2A ~p~~!!rk!!.eb,!Xcian or hobbyist. Fully metered, extremely easy to build and very versatile. Cat K-3461 & case you want to put it in) ~iving a neat little 8 watt amplifier for guitar and similar practice. Cat K-3548 As seen in · Australian Electronics Monthly' s1995 As seen in · Australian Electronics Monlhly$1 Remember the twin 25 of a decade ago? We made countless thousands of kits! Here's the up-to-date model: EA's new 3030 Amplifier. Easy to build, an ideal project for schools, tech colleges, etc - or just the hobbyist who wants a hi-spec kit at a low-spec price. • 30W per channel • 0.025% distortion at 30W • -76d8 (phono) and -91dB (line) noise figure 09 ...,., ' : Our Kit Policy . . . : * * * * ** * ** ,,-s '," "- ************************************************** ** * * ** * 1995 EA's new 30/30 Amplifier Perfect Beginner's Project! ,., ,":_ ' ... ,. <'\-....,..,u;~ ' ~- -~ ........ ~ ' . . __ ... ., ,_, ,__,,, Where we advertise a kit from an electronics magazine, it is our firm policy to have that kit in our stores no later than the fifteenth day of the month of issue of the appropriate magazine (usually we do much better than that!) It's part ofourcommittment to the hobbyists and enthusiasts of Australia and New Zealand. We want you to : We've made up a special kit for this amplifier which includes have the latest kits, at the best possible prices, and as soon as possible. all the "expensive" and hard-to-get bits - the power amplifier IC's, the transformer, the silk-screened & punched front panel O~ca~tonally, we re_let down: an o~dball component that has.to come from th_e ot~er side of the world; a and the printed circuit board. shtppmgordock stnke that delays vital parts; perhaps a magazme that changes ,ts mmd about the month of * . publication (or even about the design of the project!). The other components (such as the passive components. pots, etc) are normal stock lines at your nearest Dick Smith Ifwe let you down by nothavmg!he k1t you wantm the store when we veprom,sed ,t, weapolog,se. We hope Electronics store (or you may even have many of them in your you'll understand that we're domg our very best to fix the problem - but th ey're not always that 'fixable'. junk boxl) Cat K-5100 Don't forget that there are 'rain checks' available in all stores to ensure that you don't miss out when the * ·· stock arrives - you'll get it for the price advertised and written on the rain check. As seen in 'Electronics Australia' . ** Special 'Short Form' Kit·. * . * * . . . * * * . . . * Short form kit $ Dick Smith Electronics. : as described above: , . . . , 9995 k************************************************* Relative field Strength Meter At Last! Recently Released Kits At time of going to press, there were good stocks of these in our stores. But don't blink . 1fi¥D11 M (GAr.', • t ~1' . M'<<!'< • ! Nicad Charger \' l Discolight Move over, Musicolor: Discolite is here. It's the latest in colour organs, with chaser, audio chaser, etc etc. You want a light show? Discolite is what you want! Cat K-3150 As seen In ·smcon Chip' l 5 Megafast! What you read is what you 9et charge 7.2V r/c model type Nicads quickly, but safely: about 15 to 20 minutes, without risk of overcharge. Cat K-3477 As seen In 'Silicon Chip' s45 Line Filter/ Conditioner s39ss s199 Budget Supply 165 !~!~~~~de~y~~!!~!~~ Power Strobotuner Accurately and professionally tune virtually any musical instrument with this fully self-contained and portable kit. If you're into music, get into this! Cat K-3550 s37,__ As seen in 'Electronics Australia' economical! cat K-3460 $ · Australian Electronics Monthly' Chair/Tilt Alarm Nifty little alarm circuit designed to go off on movement (more precisely, change of angle). It's a great way to protect perambulatory property participating in purloining, pillaging, pilfering, pinching or plundering. Cat K-3248 As S88R in · Australi11 Electronics Monthly' A low-cost variable supply that's ideal for beginners (no need to mess around with mains - it can be powered from a battery if you wish or any other AC or DC source). No metering, no :~1:e:~: _§,jj s1195 . ~~--------- Commercial line filters cost a fortune: build your own for a lot less. Filters out HF noise, spikes, etc and gives over-voltage protection. Cat K-3080 As SBBn in 'Electronics Australia' turn your amplifier on (or if it goes into ampllficus cactus). Protect your valuable speakers with this easy-to-build and easy-to-fit kit. Cat K-4008 Here's one for the antenna installers, TV techs, etc. Checked out the price of a FSM lately? Build this instead for an xteenth the cost! Gives good relative indication, works on VHF & UHF, and even gives out video signal. Battery/mains operated. Cat K-6329 As seen in 'Electronics Australia' Mini Mixer Here's a great oeginners project - with specs that make it good enough for serious use. 4 input mixer suits mics, guitar, etc - very simple to make. Cat K-3039 6250 -~~' ·~ As seen In · Australian Electronics Monthly' DIGITAL FUNDAMENTALS Microprocessors don't do anything until they are programmed. Our final chapter in the series takes a look at programming basics. LESSON 10: PROGRAMMING MICROCOMPUTERS By Louis E. Frenzel MICROCOMPUTERS BY THEMSELVES DON'T do very much. They are simply a collection of electronic circuits and other hardware waiting for directions which tell them what to do. Those directions come from the programs that cause the microcomputer circuits to perform in a specific way. Once given a program, the microcomputer will accomplish some useful work. All the programs that computers use are referred to as software. In this final lesson, we discuss the basic process of creating the software that will make the microcomputer do something worthwhile. More specifically, we will show you how to write some simple programs using the microcomputer's instruction set. · Microcomputers have, for the most part, replaced large complex collections of smaller SSI and MSI integrated circuits. By programming a microprocessor, you can cause it to perform all of those basic operations which are usually carried out by individual gates and flipflops wired in many different configurations. Microprocessors can be programmed to perform arithmetic operations, logical operations such as AND, OR and NOT, counting, shifting, comparing, and many other standard digital functions. We will show you how to accomplish many of those basic operations in this lesson. Introduction to Programming Programming is the process of converting a problem to be solved into a form that the microcomputer can interpret. During that process, a program is created. Recall that a program is a sequential list of microcomputer instructions that tell how to accomplish some specific result. Programming is basically a two-step process. The 66 SILICON CHIP first step is problem solving where you define the work to be done and develop a solution. The second step is called coding. That is the process of converting your problem into a specific computer language. In this case, that language is the specific instruction set of the microcomputer. You will hear it called machine language. Following the work we started in Lesson 9, we will use the instruction set of the type 6800/6502 microprocessors. Problem Solving The first step in programming is to clearly define the problem. That is where you ask yourself what it is that you are trying to do. The best way to begin the process is to write down a general statement of what you are trying to accomplish. Anything else you can do to explain or illustrate the problem will also be helpful to you in coming up with a solution. For example, draw yourself a picture using blocks that might show the flow of the problem from one step to the next. If necessary, make charts and tables or lists that specifically state what needs to be done. Keep in mind a picture of the basic computing process, which involves input data of some kind that is then processed to create some useful new output data. Defining the available inputs and the desired outputs will help you understand exactly what processing must take place. Next, analyse all of the material you have collected. That will result in your coming up with an algorithm. An algorithm is a detailed step-by-step procedure for solving the problem. It could be a basic algebra statement or formula to compute. Otherwise, it might be even more like a recipe with individual steps to be accomplished one after another. Fig.1: a flowchart is useful for describing the problem to be solved. This one is for determining the larger of two numbers, A and B. START ACC A CONDITION CODE REGISTER (CCR) ACCUMULATORS{' • INSTRUCTION REGISTER (OP CODE) ACC B ,...L===== NEGATIVE ZERO ---CARRY PROGRAM COUNTER STACK POINTER NO (A>B) INDEX REGISTER Fig.2: this is the basic register organisation in the 6800 microprocessor. Note that there are two accumulators. STORE B STORE A But to refresh your memory, let's take a brief look at the architecture of the device and the formats of the instructions. STOP One way to illustrate the problem you are trying to solve and test is to draw yourself a flow chart. That is a graphical description of the problem using standard symbols. Fig.1 illustrates the solving of a typical problem. The oval symbols represent start and stop conditions. The rectangular boxes state specific processing operations to be carried out on your data. The diamond-shaped figure represents a decision, which usually asks a question with a "yes" or "no" answer. Work your way through the problem in Fig.1 to be sure that you understand how it works. Coding Once your problem is well-defined and your algorithm is available, you can begin writing the program. That is the process of creating a sequential list of the microprocessor's instructions. When you finish coding the program, you should check it over carefully for errors. Programming is a very time-consuming and tedious process and it is extremely easy to make a mistake. You may goof in thinking through your algorithm and there may be some faulty logic that you will not discover until you test the program. Or you may simply make a coding error, leaving out an instruction or entering an incorrect op code or address. In any case, attempt to get out all the bugs. Next, you will load the program into the microcomputer and test it. If everything is satisfactory, the computer will run the program and will give the desired results. If not, you will need to do some debugging. Debugging is typically standard procedure, particularly for large, complex programs. Short programs can usually be written and run the first time without error. But big programs, using hundreds or even thousands of instructions, generally require hours of debugging to make them work properly. · As stated earlier, we will use the architecture and instructions of the 6800 and 6502 microprocessors. Architecture Fig.2 shows the general layout of the 6800 microprocessor. Note that it has two 8-bit accumulators labelled ACC A and ACC B. An 8-bit instruction register holds the op code, and an 8-bit condition code register (CCR) indicates CPU status. Also included is a program counter, a stack pointer and an index register. Those are 16-bit registers. We won't show the block diagram of the 6502 since it is basically similar in its organisation. The main difference is that the 6502 has only a single accumulator (A), but it does have two index registers labelled X and Y. The instruction sets are also similar and we will use instructions that are common to both. In operation, the microprocessor fetches instructions which are in the memory, puts them into the instruction register, then decodes and interprets them. The logic in the microprocessor then causes the circuitry to carry out the designated operations. Most of those operations take place on data that is in the accumulator. Data may be brought in from the memory and stored in the accumulator, then used in some arithmetic or logic operation with the result stored in the accumulator. That result can then be transferred to a storage location in memory. Once an instruction is executed, the next instruction in sequence in memory is then fetched and executed. The process continues until the end of the program is reached. Condition Codes As the program instructions are executed, various conditions are monitored and the results are stored in the flipflops of the condition-code register (CCR). Those flipflops are also known as status flags. Some of the more common conditions monitored include carry (C), zero (Z), and negative (N). For example, the carry bit is set to binary 1 in the condition-code register if the result of an addition in the accumulator causes a carry to be generated out of the most-significant-bit (MSB) position. SEPTEMBER 1988 67 OP CODE ADDRESS OR DATA OP CODE 1/2 OF ADDRESS Attit~1s { ~--------f 1/2 OF ADDRESS Fig.3: a 2-byte instruction puts the complete address or data in one memory location. A 3-byte instruction puts only half the address in a memory location. BINARY HEXADECIMAL 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 0 1 2 3 4 5 6 7 8 9 A B C D E F Fig.4: binary to hexadecimal conversion. The binary number 10001011 is the equivalent of hex 8B. The zero bit in the condition-code register is set if the result of some operation in the accumulator is zero. Should some arithmetic, logic, or other operation result in the accumulator containing all zeros, the zero flipflop is set to binary 1. In a similar way, the negative or N flag of the condition-code register will be set to binary 1 if the result of an arithmetic operation produces a negative result. A negative result is indicated by the most significant bit of the accumulator [bit 7) being a binary 1. The condition-code bits can then be monitored so that decisions can be made by special jump and branch instructions. We will illustrate these in the programs to come. Instruction Format An instruction for the microprocessor consists of one, two or three bytes stored in memory. Some simple instructions contain only an 8-bit op code that designates an operation to be performed. Some instructions require two bytes, as shown in Fig.3a. The first byte is the op code that tells the microprocessor what is to be done. The second byte usually contains an address that designates where the data to be operated upon is stored. Alternatively, the second byte may also contain the data itself to be used in the operation. A three-byte instruction [shown in Fig.3b) contains an op code in the first byte; the remaining two bytes contain the upper and lower halves of a 16-bit address, which usually designates the location where the data to be operated on is stored. The instructions, of course, are nothing more than binary numbers. However, programmers don't work with binary. It is too difficult to remember all those ls and 0s. Most programmers who write programs in 68 SILICON CHIP machine language typically use hexadecimal [hex) notation. This is the process of replacing each 4-bit binary group of numbers with its equivalent hexadecimal symbol. · The hexadecimal symbols include the digits 0 through 9 and the letters A through F. Fig.4 shows the designations. To express a given binary number in hex, simply replace each 4-bit group with its equivalent hex digit. For example, the binary number 10001011 in hexadecimal is 8B. This happens to be the op code for the ADD instruction in the 6800. All of the instruction op codes have a specific hexadecimal designation. In addition, the addresses are also expressed in hex notation. To keep things simple in this lesson, we are going to use our own special notation. We will use a simple three or four-letter mnemonic designation for each instruction and express memory locations and data in terms of decimal numbers. We will also limit ourselves to the use of two-byte instructions. Simple Example The simple program shown below is designed to add two numbers together and store their sum. Let's step through the program one instruction at a time so that you can see how to read it. LOCATION MEMORY INSTRUCTION ADDRESS OR DATA 0 LDAA 1 7 2 ADD 8 STAA 3 4 5 6 1 8 9 9 HALT 25 19 44 (SUM) The first instruction in location 0, LDAA, loads accumulator A with the number stored in memory location 7. That is designated by the second byte of the instruction in location 1. Looking down the program, you can see that in memory location 7 is the number 25. That first instruction brings the number 25 into accumulator A. The next instruction in location 2 is ADD. This instruction tells the computer to add the number stored at the memory location designated by the second byte of the instruction [in location 3) to the number contained in accumulator A. As you can see, the number 19 is stored in location 8. The sum, 44, will be stored in the accumulator. The third instruction in location 4, STAA, says to store the accumulator in location 9. That is, the sum in the accumulator will now be stored in the memory location designated by the second byte of the instruction in memory location 5. The address stored there is 9. Therefore, the sum will be stored in that location. The program ends at that point. Now that you have the format in mind, let's take a look at a number of sample programs that show how to do useful functions. In each example we will show a programming listing and explain what is happening. We will introduce new instructions in each sample, but those will be explained as we go along. Arithmetic Operations MEMORY LOCATION c-------~ INSTRUCTION ADDRESS OR DATA 0 LDAA Let's code the program 1 18 described by the flow chart 2 SUBA 3 19 in Fig.1. The purpose of the 4 BMI program is to determine 12 5 6 LDAA which of two numbers, A and 7 18 B, is larger. Our algorithm is 8 STAA 9 2D to subtract B from A, then to 10 JMP 11 test to see if the difference is 22 12 LOAA positive or negative. If the 13 19 14 STAA difference is positive, then A 15 20 is larger than B. If the dif16 JMP 17 22 ference is negative, B is 18 A= 14 larger than A. The program 19 B = 17 20 LARGER= 17 concludes by storing the 21 larger of the two numbers in 22 HALT texta designated memory location. The program for solving the problem is illustrated at the top of this page. The first instruction, LDAA, loads the first number A stored in memory location 18 into accumulator A. The second instruction subtracts number B stored in location 19 from number A. The difference between the two numbers is stored back in the accumulator. If A is 14 and Bis 17, the result in the accumulator is -3. The next instruction is a branch-if-minus (BMI) instruction. This is a decision-making instruction that may change the sequence of program execution if a certain condition occurs. In this case, the instruction tests the negative flipflop in the condition code register. Recall that various flipflops in the condition code register are set or reset depending upon the outcome of the execution of the various instructions. If the subtraction results in a positive result in the accumulator, then the negative flipflop in the condition code register is set to binary 0. If the subtraction operation results in a negative value, then the negative flipflop is set to binary 1. The branch if minus instruction looks at the negative flipflop to determine what action to take. If the subtraction operation results in a positive value, no branch occurs. The next instruction in sequence after the BMI instruction is executed as would normally be the case. Therefore, A is the larger of the two numbers. The LDAA instruction in location 6 causes that number to be loaded into the accumulator. The next instruction, STAA, stores that number in the designated memory location. Next, the JMP instruction causes an unconditional jump to occur. The program counter is loaded with the address part of the JMP instruction in location 11. Therefore, the CPU resumes executing at location 22. A HALT at that location ends the program. (Note: in this article, a HALT instruction is used to stop a program. In truth, there is no such instruction in the 6800 or 6502 . It is used here to simplify the discussion. In practice, other more complex techniques beyond the scope of this article are used). r MAIN PROGRAM I I I I INSTRUCTIONS JUMP TO SUBROUTINE - ' • SUBROUTINE I I ~ I I I ~ -- -- - RETURN I l. r J I I I JUMP TO SUBROUTINE _ _ _ _ _ _ _ _ _ ..JI Fig.5: a small program which will be used many times by the main program can be stored as a subroutine, to which the main program jumps (and returns) when it's needed. If the result of the subtraction is a negative number, as it is in this example, then the BMI instruction detects it and causes the program to branch to a memory address designated in the second byte of the BMI instruction in location 6. In other words, the usual next instruction in sequence is not executed. The BMI instruction causes the program counter to be loaded with the address designated in the BMI instruction, in this case 12. This indicates that the larger of the two numbers is B. Therefore, the instruction at 12, an LDAA, causes the B to be loaded into the accumulator. The STAA instruction stores the result in the memory location designated for the larger number. The JMP instruction then causes the program to jump to the designated memory location, in this case 22. At that point, the program ends. Subroutines Most simple 8-bit microprocessors such as the 6800 and 6502 can only perform simple arithmetic operations such as add and subtract. But many times the problem to be solved requires more complex math, such as multiplication, division, square root or some other operation. The microprocessors can perform these operations, but they must be programmed to do so. A special program is written to perform one of these math operations. Whenever the main program needs to perform, say, a multiplication, it will branch to or call this special multiplication program, perform the desired operation, and then return to the main program sequence. This is illustrated in Fig.5 . Such programs, which may be referenced several times by the main program, are called subroutines. A subroutine is simply a specialised segment of computer code that does some specific task. Rather than write that sequence of code each time it is needed, the code is written once. Then special inSEPTEMBER 1988 69 START (PARTIAL PRODUCT) chosen here is simple and is easy to understand. Since the microprocessor can add and subtract, naturally the subroutine must use these instructions. One way to perform multiplication is by repeated addition. For example, if you wish to multiply 5 by 3, you can accomplish it by simply adding 5 three times. This is what our program will do. Add to Multiply LOOP N STOP Fig.6: as this flowchart shows, multiplication is done by repeated addition. structions are used by the main program to call the subroutine, use it, then return to the main program. A jump to subroutine instruction [JSR) calls up the subroutine. This instruction's address tells where the subroutine is located. When a JSR is executed, the contents of the program counter are stored in the stack. That allows the CPU to pick up where it left off when the subroutine has been executed. At the end of the subroutine is a return-fromsubroutine instruction (RTS). It retrieves the address in the stack and loads it into the program counter. The main program then resumes executing. The program we want to illustrate here is a subroutine for performing multiplication. It will illustrate the concept of a subroutine and how higherlevel math functions are programmed using the microprocessor instruction set. There are a number of ways to produce multiplication in a microprocessor. The algorithm we have 70 SILICON CHIP Recall that in multiplication, there are usually two quantities involved. One number is called the multiplicand while the other is called the multiplier. The answer or solution to the multiplication results in a new value called the product. In the microprocessor we will set aside three memory locations to store those three values. The flow chart outlining the multiplication is shown in Fig.6. Basically, the process is to add the multiplicand for the number of times specified by the multiplier. In the program, we designate the location where the final product will be stored. During the multiplication process, the partial product obtained each time the multiplicand is added is stored in that location. Initially, the partial product is zero. Then, each time we pass through the program, the multiplicand is added to it and then restored. Each time the multiplicand is added, the multiplier is loaded into the accumulator and one is subtracted from it. That tells us that the multiplicand has been added one time. We then reduce the multiplier by 1 and restore it. We then check to see if the multiplier is zero. Naturally, if it is zero, then the multiplicand has been added the correct number of times. If not, then the program goes back and repeats the same sequence. Note in the flow chart the use of a decision block designated Is multiplier zero? If the answer is yes, then the correct product is available for use. If the multiplier is not zero, the answer is no and the procedure begins again. That forms a program loop. A loop in programming terms simply means that a particular sequence of instructions is repeated a number of times as required by the algorithm. A loop is implemented with a decision making branch or jump instruction. The code for the problem is given below. Let's walk through it step-by-step to be sure you understand the process. The first instruction, CLR, clears the memory location designated by the second byte to be cleared to zero. As you can see, that clears memory location 20 where the partial product is to be stored. The next instruction, LDAA, causes the partial product to be loaded into the accumulator. Of course, it is zero at this time. The next instruction, ADD, causes the multiplicand in location 18 to be added to the accumulator. The result in this case is simply the multiplicand itself. The next instruction, STAA, causes the contents of the accumulator to be stored back into location 20, the partial product. Next, the LDAA instruction in location 9 causes the multiplier in location 19 to be loaded into the accumulator. The DECA instruction then decrements it. MEMORY LOCATION 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 INSTRUCTION ADDRESS OR DATA CLR 20 LDAA 20 ADO 18 STAA 20 LOAA 19 OECA STAA 19 BNE 3 RTS MULTIPUCAND MULTIPLIER PRODUCT (PARTIAL PRODUCT) That instruction simply causes 1 to be subtracted from the contents of the accumulator. To decrement means to subtract one. The multiplier has now been reduced by 1, indicating that the multiplicand has been added once. We restore the reduced multiplier in location 19. Next, a BNE (branch if not equal to zero) instruction is executed. That instruction looks at the decremented multiplier in the accumulator and attempts to determine if its value is equal to zero. If it is not equal to zero, then it causes the normal program sequence to be abandoned. A branch occurs to the memory location designated in the second byte of the BNE instruction. In this case, the branch occurs back to memory location 3. This causes the instructions stored between locations 3 and 13 to be re-executed. The process, therefore, is repeated. The multiplicand is added again to the partial product and the result is restored. The multiplier is loaded and decremented by 1 and restored. Again, the BNE checks for any zero result. If none occurs, then a backwards loop is again performed. At some point, however, the multiplier will be reduced to zero. At that point the BNE instruction detects the zero so no branch or loop occurs. The next instruction in sequence at location 16 is executed. That is a return from subroutine (RTS) instruction. In a subroutine, the final instruction is called a return from subroutine. The instruction simply retrieves the content of the program counter which was previously stored in the stack by the jump to subroutine instruction that caused the subroutine to be called. At that point, the main program resumes. cumulator while the other is stored in a memory location that will be referenced by the AND instruction. The AND instruction is designated ANDA which means to AND the contents of accumulator A with the contents of the memory location designated in the instruction. The corresponding bits in the two 8-bit words will be ANDed together with the logical result being stored back in that same bit position in the accumulator (see Fig.7). The individual bits being operated on are independent of one another and do not affect adjacent bits. Because of this, you can perform various individual bit manipulations within a word if desired. OR operations can also be performed with the ORA instruction. The EXCLUSIVE OR function is performed with the EORA instruction. As for performing the NOT function, a special instruction called complement [COM) is used. Here a word is loaded into the accumulator and the COM instruction is executed. The result is that each bit in the word is complemented; that is, ls are changed to Os and Os changed to ls. With those basic logic functions, virtually any Boolean operation can be implemented with short subroutines. An example of a useful logical operation is to use the AND instruction to perform masking. Masking is the process of blocking out or eliminating a bit or groups of bits from a binary word. When the bits are eliminated, they are effectively set to or replaced by binary Os. To mask bits from a given word, that word is first stored in the accumulator. Then, a special mask word in some memory location is ANDed with it. To eliminate the desired bits from the word, the corresponding bits in the mask are set to binary 0. Those bits to be retained are ANDed with binary ls in the mask word. Here's an example: A - BINARY WORD 11001100 B - MASK WORD 00111100 C - RESULT OF ANDING 00001100 The truth table for the basic AND function is given below as a refresher. 8 C 0 1 0 1 0 0 0 1 The simple program below illustrates the use of the AND instruction for masking. The purpose of the program is to convert ASCII characters into standard BCD numbers. Logical Operations As we indicated, a microprocessor can also perform logical operations such as AND, OR and NOT. It can even perform more complex operations such as EX-. CLUSIVE OR. The 6800 and 6502 microprocessors, for example, have instructions for those operations. The instructions operate on all of the bits in the accumulator rather than one bit at a time. For example, to perform an AND operation between two binary numbers, one of them is stored in the ac- A 0 0 1 1 MEMORY LOCATION INSTRUCTION ADDRESS OR DATA 0 1 2 3 4 LDAA 5 6 7 8 9 10 8 ANDA 9 STAA 10 HALT 00111001 (ASCn CODE FOR 9) 00001111 (MASK WORD) 00001001 (BCD RESULT} ASCII Code Recall that ASCII is the 8-bit code widely used for communications between computers and peripheral SEPTEMBER 1988 71 ACCUMULATOR __ MEMORY _LOC&_J:ION Fig.7: the AND instruction is designated ANDA which means to AND the contents of accumulator A with the contents of the memory location designated in the instruction. devices or in data communications. A special 8-bit code is given to upper and lower case letters of the alphabet, numbers, punctuation marks and special symbols. The ASCII codes for the numbers 0 to 9 turn out to be the standard 4-bit BCD codes for those numbers plus a special 4-bit code preceding it, in this case 0011. For example, the BCD number for 5 is 0101. The ASCII version, therefore, is 00110101. In order to use ASCII numbers in arithmetic operations, they must first be converted into their BCD equivalents. A simple way of doing that is to strip off the first four bits, leaving the 4-bit BCD code. That can Mailbag - SILICON CHIP Implementing Counters A microprocessor can also be used to perform counting functions. For example, by using the interrupt feature of a microprocessor, external pulse trains can be counted. The pulses to be counted are simply applied to the interrupt input of the microprocessor. continued from page 3 This was because: (a) the additional switches installed in the caravan were only single pole instead of double pole; and (b) the inlet socket on the caravan had been incorrectly wired at the factory, even though it was clearly marked "A" and "N" on the appropriate terminals. Prominently displayed in the caravan was a sign to the effect that all electrical wiring had been inspected and passed. It had been used like this for many years. On the table was an old toaster with hinged sides, so it was surprising that no-ori.e had· been zapped. After this initial wiring fault was corrected, the single-pole switches were replaced with doublepole types. The third example was reported in another magazine many years ago. As I recall, a young child was killed because the electrician who wired the house had incorrectly installed a combination GPO with a coax TV socket. The insulating shroud over the back of the coax socket had been omitted and, as a result, the outer braid of the coax cable had come into contact with the Active terminal. This caused the metal roof and downpipes of the house to become live at 240V AC. The downpipes finished about 15cm above ground 72 be done with a masking code of 00001111. The first four zeros will be ANDed with the 0011 portion of the ASCII code we wish to eliminate. ANDing those digits with zero will cause the logical result to be 0000. The four bit BCD portion of the code we wish to retain will be ANDed with the 1111 portion of the mask word. ANDing bits with binary 1 's will simply reproduce those bits. In the program above, the ASCII number has been previously stored in memory location 8. That number is now brought into the accumulator with the first instruction, LDAA. Next, the ANDA instruction is executed. The mask word is stored in location 9. That number is ANDed with the contents of the accumulator. The result appears in the accumulator. In this case, the ASCII number 9 is converted to its BCD equivalent, 00001001. That number is then stored in location 10 by the STAA instruction. Then the program halts. level and when the child touched the downpipe, a fatal shock was received. This house wiring had also been inspected and passed. In conclusion, I should say that noone is perfect but as you pointed out, there is room for improvement in the electrical trade, especially with regard to council electricians and inspectors. M. C. Laybutt Ainslie, ACT Good mix of projects Congratulations on a very good magazine. It is well ahead of all the other electronics magazines in the marketplace. Electronics and other journalists have a privileged position as far as keeping up with new products and technology. Notice I did not say that it is an easy job. They cannot really be effective without keeping abreast. Manufacturers and suppliers make it easier by supplying literature, demos, samples etc in the hope of getting press releases published. Compare this with the engineer who chose to go into industry, say into designing power supplies. Now let's reduce his field of vision further by saying switching power supplies. Only those suppliers that have corn- ponents that go into switching supplies send him data - and then only half of those because he is, unlike the magazines, unknown to many. His principal job is to design new power supplies but a large proportion would consist of other items, such as investigating why a particular design fails for customer A but not for customer B. Or marketing may say they can get an order for 100 units if you can increase the output voltage by a couple of volts or increase the output current by lO0mA. Such tasks are often made worse because he was not the original designer. And of course there's the paperwork like writing engineering change instructions to manufacturing. This engineer doesn't have a chance of knowing about memory mapping of microprocessors or 100 other things. Changing the subject, magazine articles are not sufficient to act as an instruction manual. While I and many other people can build some circuits from a schematic, there is a large potential kitset builder market out there who need step by step instruction. In this day of wordprocessing and cut and paste desktop publishing, there is no reason decent instruction manuals could not be reasonably priced. D. Hire Annandale, NSW Then, each time the interrupt occurs, the microprocessor will complete the current instruction in process for the main program, then jump to a subroutine for the count operation. The simple program below is the subroutine that performs the counting operation. MEMORY LOCATION INSTRUCTION ADDRESS OR DATA 100 101 102 103 104 105 106 LDAA INCA STAA COUNT VALUE RTS Memory location 105 is set aside to store the count value. It is previously cleared to zero in the main program. When the interrupt occurs, that word will be loaded into the accumulator by the LDAA instruction. Next, an INCA instruction is executed. That causes the number in accumulator A to be incremented. Incrementing with this instruction causes 1 to be added to the accumulator value. The next instruction, STAA, causes the number to be restored in memory location 105. Finally, an RTS instruction causes a return from the subroutine. The program counter value which was stored away in the stack when the interrupt occurred is retrieved by the RTS instruction and loaded back into the program counter. Therefore, the main program resumes where it left off. Counting routines can also be used to provide for timing, sequencing and delay operations which are common in digital circuits. For example, the simple subroutine shown below generates a specific time delay when triggered by an interrupt. At the end of the delay time, the program outputs a binary 1 in the least significant bit position of the data bus. MEMORY LOCATION INSTRUCTION ADDRESS OR DATA 52 . LDAA 64 OECA STAA 64 BNE 52 LDAA 65 STAA 100 RTS COUNT VALUE 00000001 OUTPUT PORT 53 54 55 56 57 58 59 60 61 62 63 64 65 100 START Memory location 53 is assigned a count value. Next, that count number which is proportional to the length of the delay is loaded into the accumulator by the LDAA instruction. For short delays, a low value number will be used. For long delays, a high value will be used. The decrement instruction (DECA) subtracts one from it. It is then restored by the STAA. Next, the BNE or branch if not equal to zero instruction is executed. That cheoks to see if the count value has been decremented to zero. If it hasn't, the program loops back to location 52 for additional decrementing. The process repeats as the counter is decremented once each pass through the loop. When the count value reaches zero, the BNE instruction NO STOP Fig.8: this is the flow chart for the time delay program shown on this page (the one that starts at memory address 52). Starting at the top, we find that the program loads a count value, which is then decremented by 1 and eventually tested against zero. If the decrement doesn't result in zero, it is repeated until it does equal zero. When the count equals zero, a binary 1 is loaded in the accumulator and then output to port 100. detects it. It then executes the LDAA instruction in location 59. That loads the number 00000001 into the accumulator. Then, the STAA instruction outputs this value (00000001) to the address designated (100). In this program, the length of the delay is determined by the time it takes for the various instructions to be executed. Most of the time involved is that time required to load, decrement and store the count value. Since most microprocessors are controlled by a crystal clock oscillator, the clock cycle time is precisely known. With that information then, the time it takes to execute various instructions can also be determined. By knowing the amount of time it takes for each instruction to be executed, the delay count .value can be determined to create a delay of a specific duration. This program ends with the RTS, which was triggered by an interrupt. ~ SEPTEMBER 1988 73 TV ANTENNAS & ACCESSORIES ~ ~ ~ ALARM EQUIPMENT OFF Il (Q)CIDh) • Panels • PIR's • Keypads • Stickers • Sirens • Antennas • Amplifiers • Wall sockets • Splitters • Baluns , , . ;,1 ILLUMINATED ROCKER SWITCH • Great for amps• SPOT, 8A, 240V • Illuminated actuator• As used In Pi master 60/60 • Size 21 x 15mm • Panel cutout 13 x 19.5mm Cat. SK-0965 Original price $7.50 ea 9 eARGAi~ ~ ~<at>% OFF CROSSOVERS Take 25% off all the following crossovers. Cat X'over Freq CX-2611 2 way 2kHz CX-2612 2 way 3.5kHz CX-2614 2 way 3.5kHz CX-2615 3 way 800, 5kHz CX-2616 3way 800,5kHz CX-2621 3 way 800, 3.5kHz CX-2619 3 way 600, 3.5kHz Power 65Wrms 50W rms 40Wrms 40Wrms 65Wrms 200Wrms 80Wrms Normal 18.95 13.95 9.95 15.50 28.95 69.50 32.95 Sale (ea) 14.21 10.46 7.46 11.62 21.71 52.12 24.71 PRICE~" FOR ~~I I~ SEPT ~N ~ $1.95 each ~ _u_ TWEETY PIE This incredible little piezo screamer measures 87(L) x 38(H)mm emits a ;h~6dJr:a~~·~ea~::r~n~;_As used in Cat. LA-5255 NORMALLY $17.95 SAVE$3 ONLY $14.95 DUMMY CAMERA BARGAIN - 25% OFF We all know that shoplifting and vanallsm cost a small fortune very year. It has been demonstrated that tel9Vision survelllance cameras in the right environment can discourage this activity. This is where you come in. We have made a great purchase of realisticlooking Dummy TV Cameras. They are Australian made, are supplied with adjustable swivel mounting bracket, fixing screws, flashing LED circuit board and 2 flashing LEDs. Also supplied is the 2 x D cell nylon battery holder to power the flasher circuit. A lake cable wallplate Is also supplied as well as a very conspicuous 210(W) x 160(H) sett adhesive sign which says "THESE PREMISES ARE PROTECTED BY TIME-LAPSE ANTI-THEFT CAMERAS" The text of the sign Is in orange-red fluorescent ink against a black background. BUT HURRY I We have around 300 only. Cat. LC-5310 1 • 4 pea WAS $49.95 4 ohm 1o watt Cat. CE-2322 NORMALLY SALE $5. SAVE $3 $37.46 5 - 9 pea $32.21 WAS $42.95 10 - 19 pea WAS $39.95 $29.96 $28.46 ea 8 ohm 1o watt Cat. CE-2325 NORMALLY $1 SALE $9.95 CLOCK MOVEMENT WITH BUILT-IN PENDULUM DRIVER This module measures 87rrm long x 55 wide x 35mm deep and uses 1 x AA battery. Clock movement Is supplied with 3 sets of hands, and pendulum is a suspended arm within the module which swings back and forth. A suitable pendulum can be attached to the bottom of the arm. Fit your own custom clock face. Great for novel applications. Cat. XC-0103 WAS $22.95 NOW $16.95 SAVE $6.00 UHF TV TUNER Sanyo Model T1087RA Yet another fabulous scoop purchase. A oompact high quality tuner that operates from 526-814MHz (corresponding to channels 28 thru 63). This tuner Is designed for Australian standard reception (AS1053 1973), and Is offered at a very low price. You can grab one now for the silly price of $29.951 This price Includes circuit diagrams and connec1ion drawing. You can have a photocopy of the complete manual for $4 but a lot of the info Is In Japanese! This is a ve,y cheap way to convert a VHF only TV to UHF! (Some skill may be required). Spees: Power+ 12V DC noninal<at> 14mA. Case neg. Bandwidth 526-814MHz (28-63 eh). AFT +6.5V. Dimensions 150 x 65x 28mm Tuning multirotation ol 1/4" shaft. Knob not supplied. Cat. DM-1000 NORMALLY $29.95 NOW $14.95 SAVE~<at>% ON BUG BOXES Bug boxes are a range of plastic antistatic enclosures basically for IC's. The system is completely modular. You can purchase a single tray or establish a full blown storage and retrieval system from the modules. Refer to our 1988 catalogue for full details. Computer Leads Lower Everyday Prices • 250 plug - Centronics lead • 25D plug - 25D skt lead • 25D plug - 25D plug lead WAS 28.95 32.95 30.95 NOW 18.95 19.95 19.95 BUG BOX PUSHBUTTON SWITCH A flat tray with clear locking lid. Will hold 60 x 8 pin or 30 x 14. 16, 18 or 20 pin IC's. Slides into cage described below. Quallty Japanese made DPDT push on/push off switch rated at 125V 3 amp. Complete with black round knob. These are commonly used as on/off power switches for mains products, and normally cost about $4 - $5. Jaycar has a quantity available for only $1.95. Cat. SP-0730 NORMALLY $5.95NOW $4.15 Cat. HB-6350 LSI BUG BOX Same as Bug Box, but with larger oompartments. .NOR MALLV $7.95NOW $5.55 $1.95 ea 10+ $1.75 ea Knobs available separately: Cat. HK-7791 50t ea ©IXHMJ ©©~~ u1<at> ~ □ !Rl ®IP~©~[Q) FOR THE PRICE OF ECONOMY COAX Yes, for a short time only, you can purchase HIGH QUALITY air spaced 75 ohm ooax for the same price as our eoonomy 75 ohm cable. Normally Its $1.20 per metre, but you can buy It for only 800: per metre. Or, Hyou buy 50 metres or more, It's only 60e metre. That's hatt price! Cat. WB-2006 80t metre 50m or more 60t metre Moulded cabinet, will accept LP to 6 bug boxes. NORMALLV $9.95NOW $6.95 Cat. HB-6366 BUG CAGE COVER A clear acrylic door which clips on bug cage and holds boxes in. NOR MALL V $6.95NOW $4.85 - .. . ' ....,..,::::.----• ::.....- LSI BUG BOX PLUG & SOCKET TERMINAL STRIP Brand new product. It's like a standard type 12 way barrier strip or terminal strip but its 2 strips of 12 which can be unplugged from each other. So if you have any number of semi permanent wires from 1 to 12 that you have to unplug, this is the Ideal way. Cat. HM-3202 $4.95-Ei€3 'U'!Rl□ <at><at> ~ IR1 ®W□'U' © IHl rn1~[Rl<at>~□ [N) $2.00 Ca!.SP-0760 ~[N]© !Ml~IL~ ir© d[N]P !Ml~IL~ ~[Q)~!Pir©!Rl This Is a DPST 240V 1.5A switch mechanism that is actuated by a 1rlggef similar to the trigger In a modern electric drlH. We haven, a clue what you could use them for - you work that out! But this COfll)Onent worklng-for-an-pRlcation Is cheap at least. Made In the UK quality. Worth over S1o but this month only $2.001 High quality UK made 'Greenpar' brand. Converts BNC male to the type 'N' fitting used in satellite receivers and other microwave gear. 'N' connector has male centre pin. The outer oonnector is a male threaded fitting. (Not constant Impedance). A rare component and worth collecting al this price. Thermal/Magnetic 0.5 Amp Circuit Breakers Quallty made E-T-A German make. Single pole plunger type, 240V AC or 65V DC. Will interrupt when current exc88ds 0.5 arrp. Has thermal overload (slow current increase) and magnetic overload (fast current increase) for double circuit protection. Has 2 aux oontacts (NO & NC) to trigger remote alarms Hn 8 C.8 S . r y Cat. SC-2280 Normally $4.50 SALE PRICE $2 SAVE$2.50 - , _ 0Ni.Ys3.oo ZENER DIODE BARGAINS BARGAIN No.1 12 volt 1 watt Pkt 25 Cat. ZR-1370 $2.95 SAVE $5.80 BARGAIN No.2 6 volt 500mW Pkt 50 Incorporates a 5mm LED In a plastic bezel for PC mounting. 4 colours RED Cat. ZD-1780 GREEN Cat. ZD-1781 YELLOW Cat. ZD-1782 ORANGE Cat. ZD-1783 I 5mm, 3-5 volt operation. Pulse rate 2Hz, 1.2 Its. ailable in 3 colours D Cat. ZD-1730 EEN Cat. ZD-1731 .. LLOW Cat. ZD-1732 1.50 ea 10+ $1.35 ea 48,t each without the cable grommet. NORMALLY $3.95 Limited q uantlty Cat. PP-1400 10+ 42,t each ONLY $1.95 ea DIRECT IMPORT light duty HOOK-UP WIRE ON 25 metre ROLLS 10 up $1.75 each ELEPHONE DOUBLE DAPTOR SENSA Now all hobbyists can afford to have a roll of each colour hook-up wire by their workbench. Quality 1310.12 tinned hook-up wire on plastic spools. Cat. WH-3004 Red Cat. WH-3000 Yellow Black Cat. WH-3001 Green Cat. WH-3005 Cat. WH-3008 Cat. WH-3002 Blue Cat. WH-3007 Cat. WH-3003 White AS $7.95 AVE 47% $3.95 per reel ii 6 WAY POWER OUTLET WITH MAINS FILTER Not only is It a 6 way power board, it incorporates a voltage surge and spike protector and noise rejection filter network. Supplied with two metre cord and mains plug, safety shutters on each outlet, illuminated master on/off switch and even a safety circuit breaker. Cat. MS-4030 $59.95 NOTE : If you require absolute mains suppression don1 forget our Australian made SqueekY Clean Mains Filters. ~~~\\ ~ :/,' ·-.,,,,_ c:I /\ D /~ '1' /~ HIGH VOLTAGE CAPACITOR PACK FUELCUTOUT SOLENOID 4~1.-;;, ~ :.:..:~- ~ __ ~ ~• » i~ -~ ~ z,i? Who needs a noisy car alarm, after you have installed one of these in your vehicle. It's operated from a hidden switch. Simply turn It on when you leave your car, and nyour car is stolen, It won1 go very far without any petrol. Supplied with instructions, pre-wired switched, hardware and even two alarm stickers. Quality M&D Alarm brand. Add to this our deluxe red light flasher kit • KJ-7000 $19.95, and who needs an alarm? Cat. XC-2050 - $69.95 DON'T MISS OUT!! LIMITED QUANTITY!! WON'T LAST OVER 175 CAPS FOR $10.00 ~ - r-, Cat. R ~i ~ I I TV COLOUR BAR PATTERN GENERATOR Ref: EA October 1987 Will provide 8 different patterns and colour bars. Power Pack to suit Cat. MP-3020 $ 14.95 Cat. KA-1691 This is rare. Attention servicemen. We can offer you a bag of over 175 pcs of both high quality Polycarbonates and ceramic capacitors. Many of these are from current colour TV manufacturers surplus. Limited quantity, and probab~• will never be repeated. (We rarely see high quality high voltage caps anymore). Here's what you get: Polycarbonate We have many different values In small quantities so most bags will be different. Higher quantities include: 0.0056, 0.047, 0.068, 0.056, 0.1, 0.18, 0.22, 0.27, 0.33, 0.56, in voltages 200V, 400V, 630V, 1.5kV, 1.6kV, 2kV Ceramic: Include a good range of values. 1OOpF , 220, 270, 330, 470,500,680, 1000, 2200, 4700pF in voltages 400V, 500V, 1kV, 2kV and 3kV. $149 - ~~q~I~RFCHOKEPACK Over 50 pieces supplied I A pack of 30 brand new RF chokes with at least 14 different values I Popular values include: 1.5, 4.7, 12, 15, 18, 22, 68, 100 & 1OOOuH. Each choke is resin dipped and colour cod ed (they look like bead tantalums). A colour coding chart is supplied so that you can decipher the value. BONUS I Not only do you get 30 useful chokes we will give you at no extra charge at least another 30 more RF chokes! These are genuine chokes but are commonly called 'peaking coils'! They look like a 1/2 watt resistor. (Read the choke value in uH as you would a resistor value). Cat. RC-5600 WAS $10.00 NOW $5 Sensation - Below 1/2 Price At this price one would believe that these Micron Amber 12" monitors fell off the back of a truck! They didn't, but grab one anyway while they last - because at this price they won't be around for long. These are brand new, nonglare Serles Iii 18MHz band width , 900 resolution line quality amber monitors. See our 1988 catalogue for full details. Cat. XM-4500 CATALOGUE PRICE $229.50 NOW ONLY $109.50 SAVE AN ___ ._...--·--,. .,. ._.__ AMAZING $120 :( \. -~-.:.- ,:::'··; GORE HILL OPEN 'TIL 4 pm SATURDAY ADCOLA SOLDERING STATION - Station only $159.50 40W iron to suit $49.95 BOW iron to suit $55.00 Purchas a station and one iron together and receive a FREE 200g roll of solder and a roll of desolderwick - worth $9.45 volts DC 300mA ORMALLY $14.95 OW ONLY $7.50_.:_..••~ ;·-•.-. '• t. MP-3008 ' • C ADCOLA 240V IRONS ···•r ·;:•.·•, ... "!':- Now you can enjoy SINE WAVE power at AROUND 85% EFFICIENCY for much the same cost as inferior square wave - and this unit gives a genuine 300VA, not less. The Jaycar Sine Wave Inverter has tremendous surge capability. It will, for example, start a small refrigerator. We are very proud al this Australian made and designed product. The price, however, may have to rise soon, so hurry! Cat. Ml-5020 399 NEW'88 S30 12 watt $36.95 Cat. TS-1492 S50 16 watt $39.95 Cat. TS-1494 Purchase either of these irons and receive a FREE roll of desolderwick - worth $2.50 TRANSFORMER BARGAIN This 1OOVA unit measuring 100(H) x 90(W) x 75(D)mm features a mounting bracket that enables you to mount It vertical or on its side. Primary winding is tapped from 200-240 volts. Secondaries are 1 x 16V, 1 x 12V. Both would be minimum 2 amps. SQUEAKY CLEAN MAINS FIL TE Fully approved 4OUTLET The MS-4020 will supply up to 4 appliances. Each 240V socket is independently filtered. The filter will suppress Interference from RF sources, spikes, transients and lighting, and supply up to 4 outlets with a total load al 4 amps. Cat. MS-4020 $'14"" - =======''-:-~~r _. . ·.: ·:··.,'.....:';-. ., . =======-::' -\,=, ·=· NORMALLY $269 SAVE$40 SEPT ONLY BARGAIN Electros We are hopelessly overstocked and need to move some electros. Brand new, 1st grade quality RT style. Cat. RE-5905 470uF 50V RT Normally $1 .90 ea $229 SPECIAL 10 for $2 20UTLET ~ The two outlet will handle up to 7.5 •mi-The two aocketa are not lndependenUy filtered althoughCat. MS-4025 __.,,, 1·' • j 1 , , _...--J ---- NORMALLY $99 SAVE $20 NOW $79 100uF 25V RT Normally 55~ ea SPECIAL 10 for 60t SOOMW <at> 6V Audio Amplifier A six transistor 1/2 watt amp for the cost of 2 hamburgers. It has 2 transistor tape preamp which is NAB equalised and a4 transistor power amp. It has facilities to take 2 line level inputs. The board measures roughly 110(L) x 48(W)mm. Each amp comes with schematic/connection diag. (2 required for stereo. Cat. AA-0290 ONL y $3.95 ea 10+ $3.50 each ~'~~' = • 1 - HEAD OFFICE MAIL ORDERS 115 Parramatta Road Concord 2137 P.O. Box 185 Concord 2137 HOTLINE (02) 7471888 Telephone (02) 747 2022 Telex 72293 FACSIMILE (02) 744 0767 FOR ORDERS ONLY TOLLFREE (008) 022 888 ;LI ~ ,I MAIL ORDER VIA YOUR 1:r ROAD FREIGHT ANYWHERE VISA POST & PACKING $5 $9.99 $ 2.00 $10 $25 $24.99 $ 3.75 $49.99 $ 4.50 $99.99 $ 6.50 OVER $100 $10.00 $50 IN AUSTRALIA $13.50 SYDNEY· CITY 117YorkSt. (02)2671614- GORE HILL 188 Pacific Hwy cnr Bellevue Ave (02) 439 4799. Mon-Fri 9 - 5.30 Sat 9 • 4pm CARLING FORD Cnr. Carlingford & Pennant Hills Rd (02) 872 4444. BURANDAQLD 144 LOQan Rd (07) 393 0777 · Mon-Fn 9- 5.30 Thurs 8.30 • Sat 9- 12 , CONCORD RSTVILLE Mon-Fri 8.30 • 5.30 Thurs 8.30 pm• Sat 9 • 12 Mon-Fri 9 -5.30 Thurs 8.30 pm - Sat 9 - 2pm 115 Parramatta Rd (02) 745 3077 . Mon-Fri 8.30. 5.30 • Sat 8.30-12 MELBOURNE-CITY Shop 2, 45 A'Beckett St City (03) 663 2030 Mon-Fri 9 • 5.30 Fri 8.30 • Sat 9 • 12 SPRINGVALE VIC AMATEUR RADIO By GARRY CHATT, VK2YBX DC-to-DC battery charger for 12V gel batteries Want to recharge a 12V gel cell from your car battery? This simple circuit will do the job. Based on an LM3524 switching regulator and a BUZ71 Fet power transistor, it provides a 14.4V output at currents up to two amps. A significant problem encountered by amateur operators in the field is that of battery life. If equipment is operated from sealed lead acid cells, there's usually no way to recharge a flat battery without access to a 240 volt generator and a suitable charger. Attempting to charge a spent 12 volt gel battery by connecting it directly to a 12 volt car battery is not a good idea. If the car battery is fully charged, it may deliver very high currents to the gel battery and if it is not fully charged, it will be a futile exercise. But there is a way of charging a 12V gel battery from a source of lower potential. It can be done by using a step-up switching regulator. The circuit described here is capable of supplying 14.4V DC at 2 amps, which is quite ample for charging sealed gel cells. It is capable of operating at around 80% efficiency from input voltages as low as lOV. How it works Basically, the circuit comprises a pulse width modulator (PWM) which drives inductor Ll via switching transistor Ql, as in Fig.1. In this circuit, Ql is used to switch Vin across inductor L1 at a pulse rate determined by the PWM generator. For the duration of each pulse, Ql is turned on and energy is drawn from the supply and stored in Ll. Diode D1 is reverse biased, and output current is supplied by the charge stored in capacitor Cout• When Qt turns off, Vl will rise to the point where D1 turns on. The Vout -JONr Lfl --1 OFF 1-- + PWM Cout+ -= RL i lout .,. Fig.1: basic scheme for the switchmode charger. It uses a pulse width modulator (PWM) to drive inductor L1 via switching transistor Qt. When Ql is on, current is supplied to the load by Cout; when Ql is off, the current is supplied via L1 and D1. 78 SILICON CHIP output current is then supplied through L1 and D1 to the load and any charge lost from Cout during the previous cycle is replenished. The complete circuit is shown in Fig.2 and uses an LM3524 Pulse Width Modulator chip which is available from several manufacturers. An RC network connected from pins 6 and 7 of the LM3524 sets the frequency of operation to about 50kHz. Resistors Rl and R2 set the voltage on pin 2 to 2.5V by dividing down the internallygenerated 5V reference (VREF) at pin 16. R3 and R7 form a second voltage divider. Under no load conditions, this also sets the voltage at pin 1 of the chip to 2.5V. This divider acts as a voltage sensing circuit connected to the output of the regulator. As the output of the circuit is loaded, the output voltage drops, as does the voltage at pin 1 of the chip. When this happens, ICl automatically increases its output pulse width, thus allowing higher output current to be supplied at the preset output voltage. In our circuit the output voltage is set by R3 and R7 to about 14.4 volts, which is sufficient to safely charge a typical sealed gel battery. If you wish, you can increase the output voltage to about 15.2V by increasing R7 to 1 lkO. The pulsed output from IC1 appears at pin 12 and drives NPN transistor Ql via diode D1. Qt, in turn, drives Q2 which is a BUZ71 Fet power transistor. Each time pin 12 ofICl goes high, Ql and Q2 turn 87 10k +v~o------+-------....------.....- - + - - - - - - t - - - - - - - - , ea + 4.7 16VWJ 89 1k 15 1&ao 16VW + - C2 IC1 LM3524 .Ol C6 .01 R10 1k 16 81 4.7k VR1 83 2.2k 86 120k C3 .0022 10k C4 470pF ).. LED1 CHARGE ... ~ ~ B EQc SWITCHMODE CHARGER VIEWED FROM BELOW GOS K A Fig.2: the PWM output from the LM3524 IC appears on pin 12 and drives Fet power transistor Q2 via D1 and Qt. R7 and R3 set the output voltage to about 14.4V but this can be increased by increasing R7 to 11kn. PARTS LIST 1 PCB, code SC 141-0988-1 , 88 x 52mm 1 small heatsink, DSE Cat. H-3490 4 alligator clips to suit (for battery connections) 1 panel-mount fuseholder 1 3A fuse 1 T0-220 mica washer and insulating bush A small heatsink must be fitted to the BUZ71 power Fet to aid cooling. Isolate the Fet from the heatsink using a mica washer and insulating bush. (Note: the PCB was modified slightly after this photo was taken). off and current is supplied to the load and to C5 via 11 and D2. When pin 12 is low, Ql and Q2 are on and the output current is supplied by C5. D1, R4, R5, RB and Ql ensure that the Fet is turned on hard, thus ensuring clean switching and minimising power dissipation in the Fet. The main advantage of the Fet over bipolar transistors is its small dynamic resistance, typically less than rn. This allows the device to switch relatively high currents without the need for substantial heatsinking. Diode D2 is a high speed fast recovery diode capable of handling 7 amps, which is more than enough for this application. R6 presents a light load to the circuit when no external load is connected, thus ensuring good regulation from no-load to full load conditions. Semiconductors 1 LM3524 voltage regulator IC (Geoff Wood Electronics) 1 BUZ71 power FET transistor (Geoff Wood Electronics) 1 BC54 7 NPN transistor 1 BY229 or MUR1550 fast recovery diode 1 1N914 silicon diode 1 3mm red LED Capacitors 2 2 2 1 1 1OOOµF 16VW electrolytic 4. 7.µF 16VW electrolytic .01µF ceramic .0022µF greencap 470pF ceramic ~ Resistors (0.25W, 5%) 1 x 120k0, 1 x 1OkO, 3 x 4 .7k0, 1 X 2.2k0, 2 X 1k0, 1 X 2700, 1 x 4 70, 1 x 1OkO 5mm trimpot (horizontal mount) SEPTEMBER 1988 79 Fig.3: install the parts on the PCB as shown here. The spare pad adjacent to pin 14 of ICl can be used to terminate the anode lead for the optional charge indicator LED. Charge indication is provided by LED 1 which is wired between pin 14 of IC1 and ground. Note that the LM3524 has two output devices (see Fig.4). In this circuit, we are using one to drive Qt and the Fet, and the other to drive the charge indicator LED. As the pulse width narrows, as Fig.4: you can use this pattern to etch your own printed circuit board or you can buy a ready-etched board from the usual suppliers (see address panel, page 104). occurs when the circuit is lightly loaded, the brilliance of the LED drops. Under high load conditions, the pulse width will be longer and so the LED will be driven harder. Construction A small printed circuit board (PCB) has been designed to simplify Further notes on the RF sniffer probe & preamplifier FERRITE 1~!1 ,on .Di OUTPUT l--:-0 The circuit diagram for the RF sniffer probe published in the June issue was for an initial prototype, rather than tor the final version which was shown in the coded photograph. The above diagram shows the correct version, the main differences being the connections for the 4 7 on base bias resistors on transistor stages Q 1 , 02 and Q3. 80 SILICON CHIP The supply feedpoint was also shown incorrectly - it should go to the midpoint of the two 1on resistors as shown above. The coded photograph published on page 7 3 of the June issue is correct as are other constructional details. Our thanks to those readers who took the trouble to point out the above discrepancies. construction. Fig.3 shows where all the parts go. You can install the parts in any order but watch the polarity of the IC, transistors and electrolytic capacitors. Inductor 11 is made from 20 turns of 1mm enamelled copper wire wound on a 30mm length of ferrite rod (available from retailers as "antenna rod"). A small heatsink must be fitted to the power Fet. The type recommended is from Dick Smith Electronics (Cat. H-3490) and comes with two small pegs which allow it to be soldered directly to the PCB. Use an insulating bush and mica washer to isolate the metal tab of the Fet from the heatsink. The PCB can be housed in any suitable enclosure, either plastic or metal, as the RFI (radio frequency interference) generated by the regulator is minimal. The unit should include fuse protection to guard against output shorts, and this can easily be implemented using a chassis mount fuse holder on the enclosure. A 3A fuse should do the job. Before using the switching regulator, VR1 should be adjusted to give optimum efficiency. To do this, connect a 12V 18-watt (or thereabouts) lamp across the output and adjust VR1 for minimum current drain from the battery. Finally, don't charge a battery that is still connected to other equipment. The circuit has no high voltage, spike or current limiting protection, so damage could result if you try. ~ NEW RZ-1 WIDEBAND RECEIVER "THE SCANNERS DELIGHT" COVERS SOO KHz TO 905MHz RANGE The new KENWOOD Wideband Receiver is a multipurpose receiver that covers the 500KHz-905MHz range. Its advanced features are made possible through the use of advanced microprocessor technology. Features Wideband Frequency Coverage (SOOK Hz - 905MHz), including FM Stereo Broadcast and Multi-Channel Television Sound. 100 Easy-To-Operate Multi-Function Memory Channels with Message Capability. 10-Band Programmable Capability. Keyboard Frequency Selection. Auto-Mode and Auto-Step Operations. Multi-Scan Function. Easy-To-Read Large LCD Display. Compact and Lightweight. Auto-Selectable Dual Antenna Terminals. Built-in speaker. Front-mounting phones jack. Easy -to-operate, illuminated keys. Accessory terminals are Line Out/Video Out/External Speaker Terminal. Squelch circuit for FM (narrow) mode. UP / DOWN Keys for VFO and memory channel. Specifications Frequency Range: 500KHz - 905MHz Mode: A3[A3E] (AM), F3[F3E] (FM) Circuitry: AM , FM(N) =Triple conversion system FM(W) =Double conversion system Sensitivity: AM (S+N / N =10dB) = Less than 5 uV (BC band 10uV) . FM (N) = 12dB SINAD less than 6uV (500KHz - 60MHz) less than 3uV (60 - 905MHz). Operating Temperature: -10° - +60°C. Audio Output Power: 2W (at 8 ohms load 10% distortion). Current Drain: Less than 1A (audio power output 1W). Antenna Impedance: 50- 300 ohms. Power Requirement: 13.8VDC ± 15%. Dimensions: 180(W) x 50(H) x 158(0) mm. Weight: 1.5kg. KENW D ELECTR 4E WOODCOCK PLACE, LANE COVE, SYDNEY, N.S.W. 2066. Ph. (02) 428 1455. YOUR DEALER BELOW Wil l GUARANTEE SATISFACTION vie.: ~: ::~i::H SUPPLIESPTY. UD. - 614 SOUTH ROAD, MOORABBIN (0 3>5534566 Further, beware of dealers not listed in !his advertisement who are selling Kenwood communications equipment. All Kenwood products offered by them are not supplied by Kenwood Electronics Australia Ply. Ltd . and have no guarantee applicable. N.S.W.: TAS.: EMTRONICS - 94 WEN1WORTH AVENUE, SYDNEY (02) 2110988 REG STOCKMAN COMMUNICAIIONS-CNR BANOCKBURN ROAD & SHIRI.EY ~ . INVEREll (067) 221303 QLD.: R08ERTSON ELECIRONICS - 62 DESMOND ST~. CESSNOCK (049) 90 7908 MACEl£C PIY. UD. - 99 KENNY ~ . WOll.ONGONG (042) 291455 S.A. & N.T.: Al£)( JOHNSON - 19 BANKSIA ~ . O'CONNOR, Ac.I. (062) 47 9125 DX ENGINEERING - 158 GRANITE~. PORT MACQUARIE(065) 849922 W.A.: FRANK BOUNDY - USMORE (066) 86 2145 CAPTAIN COMMUNICATIONS PIY. un - 28 PARKS ~ . PARRAMATTA (02) 633 4333 EMTRONICS - SHOP s 10 7, 288-294 QUEEN ST~ . MELSOURNE (03) 670 0 330 BRIAN STARES_ 11 MALMS8URY STREET, BAUARAT (0 53) 39 2808 SUMNER ELECIRONICS _ 78 KING ~ . liNDIGO (054) 43 1977 WAISONS WIRELESS - 72 BRISBANE~. HOBART (002) 344303 MARINE & COMMUNICATION - 19 CHARU:S ST~. LAUNCESTON (003) 31 2711 V.K. ELECIRONICS - 214 MOUNTSTREET, BURNIE (004) 317733 MITCHELL RADIO CO. - 59 AlBION ROAD, ALBION (07) 357 6830 EMTRONICS - 416 LOGAN ROAD, STONES CORNER, BRISBANE (07) 394 2555 INTERNAIIONAl COMMUNICATIONS SYSTEMS PTY. UD. - 8 NU STREET, PORT ADELAIDE (08) 47 3688 WIWS ELECIRONICS - 165 ALBANY HIGHWAY, VlCTORIA PARK (09) 470 1118 BAY RADIO - 22 GRACE STREET, FERNDALE (09) 4513561 FORD ELECIRONICS - UNIT 19, 70 ROBERTS ST~ , OSBORNEPARK (09) 2421766 SEPTEMBER 1988 81 Pt.4: Feedback versus distortion AT IS NEGA11VE Negative feedback can reduce distortion caused by non-linearities in amplifier circuits. The reduction depends on the ratio of open loop gain to closed loop gain at the frequency of the distortion component. We look at frequency components, harmonics and class B power output stages. By BRYAN MAHER Let's talk about distortion and audio amplifiers, especially power amplifiers, together with the AC signal voltages [and their waveforms) which we put in and get out. We start with a sinewave, as shown in Fig, 1. Sinewaves are widely used as test signals in electronic engineering but pure sinewaves rarely occur in speech or music. Speech or music signals have very complex waveforms but they can all be described in terms of one or more definite frequencies and repeating predictable waveforms. Furthermore, all can (if you wish) be described by equations and could all be generated by suitable linear circuits, or simulated on a digital computer. Non-linearity distortion Before discussing non-linearity distortion, we need to know more about sinewaves and the concepts of "frequency components" and "harmonics". The sinewave [including the cosine) is usually regarded as the fundamental "building block" of all cyclic waveforms. All periodic waveforms can be considered as being the sum of many sinewaves of different but related frequencies. Need convincing? Let's do a little experiment. We could take any number of sinewave generators, each giving output at a different frequency and combine those signals together in a linear operational adding circuit such as that depicted in Fig.2. For an example let's take four sine generators, each generating different frequencies as follows: (1). A lkHz sinewave at some reference amplitude; (2). A 3kHz sinewave, at 37.5% of the reference amplitude and inverted; ie, reversed in phase; (3). A 5kHz sinewave, at 8.125% of the reference amplitude and inphase with 1; (4). A 7kHz sinewave, at 3.125% of the reference amplitude and inverted. s Fig.1: a pure sinewave signal. Sinewave signals are widely used when testing audio amplifiers and loudspeakers, but pure sinewaves rarely occur in speech or music. Instead, the latter have quite complex waveforms. 82 SILICON CHIP "'SJNEWAVE GENERATORS Fig.2: this simple adder circuit can be used to combine four different sinewave signals (see text). Using the adder circuit of Fig.2, let's add those four signals together. If we had a 5-beam oscilloscope (CRO), we could view all four separate sine waveforms and their sum. Since a 5-beam oscilloscope is an extremely rare beast, we can simulate what will happen by drawing carefully on graph paper each of the four aforementioned sine waveforms. We take care to draw them to scale, all starting at the same point, and reversing the sign of those so indicated above. Fig.3 is the finished product. Listening test If we were to conduct the electronic experiment using four real synchronised sinewave generators and the adder of Fig.2, we really would see on the 5-beam oscilloscope all the separate sine waves (one on each beam) and on the fifth beam the sum waveform predicted in Fig.3. Using headphones you could listen to each sinewave separately and confirm that each had a different pitch [frequency). But the sum waveform voltage would have a quite different sound, though it would have the basic pitch of the lowest frequency sinewave. Musicians would say that the sum waveform sounds as if it contains ''harmonics''. Harmonics We call a 3kHz sinewave signal the "third harmonic" of a lkHz sinewave simply because it is three times the frequency. The expression came from the world of music, where the "second harmonic" of any note means " one octave higher" , the fourth two octaves higher, etc. Odd harmonics such as the third must then mean "one and a half" octaves higher. So how do harmonics relate to distortion in amplifiers? The relationship is simple. When an amplifier distorts a signal, due to its inherent non-linearities, it adds harmonics which weren't there before. Let's see why? FEEDBACK? i,..----- ONE CYCLE - - - - - - , - . i / Audio amplifiers 1kHz FUNDAMENTAL SINE WAVE TIME While every active device (ie, every transistor, FET etc) does contribute a share of distortion, the output stage usually contributes the largest share. In most audio amplifiers, the output stage usually operates in class-B mode or a variation, class AB, which is somewhere between class A and class B. We'll explain these modes before going further. An amplifier stage employing two transistors as in Fig.4 may be operated in either class A or class AB or class B, depending on the bias and drive used. (1). Class A: a transistor amplifier stage is operating in class A if that transistor is conducting current throughout the whole 360 degrees of the signal cycle (ie, all the time). All single transistor linear stages must operate in class A. +v INPUT BIAS PLUS DRIVE OUTPUT TIME 7kHz SEVENTH~- HARMONIC ,.-... ,.-... ,,-... ,,-... ,,-... ~~C>~~ I'"":) ,....._ ,.-... ,....._ ~<.::> . TIME Fig.3: the complex waveform reproduced in colour is the output from our adder circuit (Fig.2). The resultant waveform consists of a 1kHz fundamental combined with its third, fifth and seventh harmonics as shown. -v Fig.4: depending on the bias and drive used, a transistor amplifier can operate in class A, class B or class AB. SEPTEMBER 1988 83 distortion, but the lowest power efficiency; class B gives the most distortion and the highest efficiency; and class AB is a compromise. Output power stage + cuRiiNT 0 ~ - - - - r - - + - - - i . - - + - - ~ - - - - - - - - .. . - - - - - ~ (b) + OUTPUT CURRENT TIME (c) o· go• 1ao· 210· 350• Fig.5: when an amplifier is operated in class B, Qt conducts on the positive half of the sinewave signal (a) while Q2 conducts on the negative half (b). The resulting output current waveform is shown at (c). +3DV +3DV 01 INPUT 01 OUTPUT -30V RL Fig.6(a): in this circuit both Qt and Q2 are non-conducting for input signals between ± 0.6V. Fig.6(b): here, Dt, D2, R2 and R3 provide forward bias to Qt and Q2 to minimise crossover distortion. .,. -3DV A very basic class B complementary power output stage is shown in Fig.6(a). When the input drive signal is positive, Ql drives output current from the + 30V rail to the output, through the load R1 to ground. During that time Q2 is cutoff; ie, just loafing along doing nothing. A half cycle later when the input drive signal is negative , Ql becomes cut off and Q2 takes over the conduction process, allowing current to flow from ground, through the load R1 , to the negative rail. Fig.5 illustrates the current conduction of each transistor in turn when a test sinewave is used as signal. At (a) is the current waveform for Ql, at (b) the waveform for Q2, while at (c) is shown the output current which is simply the sum of current waveforms in the two output transistors; ie the sum of (a) and (b). A little thought convinces us that what Fig.5 demands is output transistors capable of switching instantaneously from cut-off state to conducting state and vice versa. That's a difficult demand to make of transistors, because their base region must contain more current carriers when in the conducting mode and less when in the cut-off mode. However, they try. Base-emitter voltage (2). Class B: when two transistors are operated in class B each transistor conducts in turn, meaning that, in Fig.4, Ql conducts only during the positive half cycle of a sinewave signal, with Q2 conducting only on the negative half. Fig.5 illustrates how each transistor delivers half the signal; there is no overlap, one transistor must cut off just as the other begins to conduct. As there are 360 degrees in one complete cycle we say that in class B operation, each transistor conducts for 180 degrees out of each cycle. (3). Class AB: an amplifier is 84 SILICON CHIP operating in class AB if the output transistors conduct for more than 180 degrees but less than 360 degrees of each cycle. So in class AB there is some overlap in transistor conduction times; ie, near the middle of the cycle there is some time during which both transistors are conducting. The class of operation for a circuit is decided by the value of bias voltage applied to the transistors (or FETs, valves etc) and how hard they are driven. Designers choose one of the three classes for an amplifier design, considering that: class A gives the least In any NPN junction transistor the base must be about 0.6 volts more positive than the emitter (and in PNPs 0.6 volts more negative) before the transistor can conduct. Therefore, in the simple circuit Fig.6(a), Ql would go out of conduction when the input signal voltage falls below + 0.6 volts but Q2 would wait until the input voltage falls down through zero and down to - 0.6 volts before taking over conduction. We would have a time when neither transistor is conducting, so the output current would be interrupted each side of the crossover COMPONENTS GALORE! _ ,_ ECONOMY TRANSFOR~f RS I ULTRASONIC lf~~J~Vr~rm ~~t 40kHz (L 19990) and receive at 40kHz (L 19991) with up to 20V I/P on the transmitter. These units can·t be heard and so are ideal for TV remote controls , water level detectors, burgatar alarms, motion detectors and information carriers as they can be either pulsed or used in the conlinuous wave mode. Full specifications below ror design purposes. KEY S'f!TCHES + 10 2155 240V 6· 15V 1A Cal. Ml 2155 $9.95 $8.95 2156 240V 6· 15V 2A Ca1. M12156 $14.95 $13.95 2840 240V 9V CT Cat.M 12840 $5.95 $4.95 2851 240V 12-GV CT 150mA Ca1.IA12851 $5.95 SS.SO 2860 240V 1SV CT 250mA Cat. M12860 $5.95 $4.95 6672 240V 15-30V 1A tapped Cat. M16672 $14.95 $13 .95 Maxim um Input Voltage: 20V rms Centre Frequency (kHz): 40 + - 1.0 Sound Pressure Level 10V RMS : 11 0dB min . Sensitivity (dB/v/ubar) min. : - 65 min. Ba ndwidth (kHz): ELECTRET MIC INSERTS With pins for easy bOard insertion . Cat. C10170 1-9 10 I 100 I $1.20 $1.00 $0.90 THIS MONTH ONLY! PANEL METERS Q,~ ~a9l\~iea! range of panel meters at great prices! Cat.No. Description Price 0 10500 MU45 0- tmA 12.50 01 0502 MU45 50-0/SOuA 12.50 0 10504 MU4 50- tOOuA 12.50 0 105 10 MU45 0-5A 12.50 0 105 18 MU45 0- 1A 12.50 0 10520 MU45 0-1 A 12.50 01 0525 MU45 0· 20V 12.50 0 10530 MU52E 0· 1A 14.50 01 0533 MU 52 E 0-SA 14.50 010535 MU45 VU PMetre 14.95 01 0538 MU65 0·50uA 16.95 01 0540 MUGS 0- l mA 16.95 0 10550 MUGS 0-1 00uA 16.95 0 10560 MU65 0·20V 16.95 ~!~ ~lNK~ ; Do not look directly into UV Tubes. Cal. H28600 ................. $29.95' "If ordering by mail please include an extra $2 for .. special" packinq. • Cat. No. Col. 1-9 Z 10 150 Red $0.08 Z1 0 151 Gm $0.15 Z 10152Ylw $0.15 cw 3 2 100 + $0.10 $0.12 $0.12 $0.12 I R14700 A 14710 R1 4720 A 14730 A1 4740 R14750 A1 4760 R14770 R14780 A1 4790 R1 4800 A 148 10 R14820 .R14830 10A ......... $3.50 20A ......... $3.50 SOR ......... $3.50 100A ....... $3.50 200A ....... S3.50 SOOR ....... $3.50 1K .......... $3.50 2K ........... $3.50 SK . ...... $3.50 10K ......... $3.50 20K .... .. $3.50 SOK .. ....... $3.50 100K .... .. . $3.50 200K ....... $3.50 $3.20 $3.20 $3.20 $3.20 $3.20 $3.20 $3.20 $3.20 $3.20 $3.20 S3.20 $3.20 $3.20 $3.20 ~~g~ ::~ ~ • 19 1 $2.95 $2.50 P10962 3 PIN CHASIS MALE + $3.00 ..... ... .............. $2.50 $4.50 ... .. . ······ ···· ······ $3.90 10 + 100 00 Save a fort~~f~'l~J ensive throw away batteries with these quality Nlcads and Rechargers! Size Desc. 1-9 10 + 100+ AA 450 mA. H. S2.95 S2.75 $2.50 C 1.2 A.H. $9.95 S9.50 $8.95 $9.95 S9.50 $8.95 D 1.2 A.H. • ~{ " " '" S14060 $1.50 $1.10 ~;~ T 5 ~'.~~-- ____ _;;,. ,~ $4.95 - - - RCA GOLD PLATED F ~,'ih~?.~~~RJi~S,~J.T.~n connection . Essential tor laser disc players to get that fantastic sound quality Plug Cal. P1 0151 $2.95 Sockel Cal. P101 50 $2.25 TYPE 1-9 10 + 100 , gp $0.60 $0.60 $0.50 $0.65 $0.65 $0.60 $0.60 $0.65 $0.60 $0.50 $0.50 $0.40 $0. 60 $0.60 $0.50 $0.50 $0.60 $0.50 9S 9C 15P 15S 15C 25P 25S 25C $0. 70 $0.70 $0.60 $0.70 $0.70 $0.70 $0.70 $0. 75 $0.70 $1 .30 3 Type 1-9 Female S2 .95 Male ... S2.95 L.!. Une~M!-1.,M\~J~J/gtP.ys plus two utilily keys. Light grey ,n colour . OUTPUT ARRANGEMENT , Output Pin N°· Symbol 1 .................... NA 2 ........... ........ Shield plate 3 ..................... Column2 4 ........ . .... Row4 5 ................... Column3 6 .Rawl 7 .................... .Column 1 8 .. ....... Row2 9 ..................... Aow 3 10 .................. N A Cat. C19030 10+ $2.50 S2 .50 100 ; S1.95 S1 .95 : 0<at>] ~ RECHARGEABLE12V LJ,i p, ~1.i ~g~~rv~ c~JJi~e~ es ideal for security syslems, emergency lighting or as a computer backup power supply. etc. Cat. S15029 ..... Normally S19.95 1.9 10 + $13.95 $12.95 CHROME LED BEZELS 9mm hole. available 3 colours Cat.No. Description $ 14030 Red S 14032 Green LOW PROFILE IC SOCKETS Save a small lortune on 1hese "D1rec1 Import" low profile IC sockets 1 PCB mounting solder tail. Dual wipe. All tin plated phosphor bronze or berryllium and dual wipe for reliability. Cat.No. Description 1-9 10 1 P10550 8 p1n ... ...... $0.20 $0.15 P10560 14 ptn . . $0.25 $0. 20 P10565 16 pin .... S0.35 S0.20 P 10567 18 pin .. $0.40 S0 .30 P10568 20 pin $0.40 $0.30 P10 569 22 p,n $0.40 S0.30 P10570 24 pin . S0.40 $0.30 P1 0572 28 pin $0.50 S0.40 P10575 40 pin $0.50 S0.40 Aco$ ~•~~,s •·• · \ GOLD INSERT LOW PROFILE IC SOCKETS $3.75 Dimensions: O verall : 63mm across. 5mm high LEDs· 10 x 5mm x 1mm Cat .No. 1-9 10 • Zt0t80 $2.95 $2.75 • • • • Gold machined pins Extremely high quahty Anti-wicking Ideal for professional use or where field service of components is required. Cat. No. Description 1·9 10 + P10620 8 pin $1.20 $1.10 P1 0624 14 pin S1 .60 $1.50 P10626 16 pin $1 .90 $1.80 P10628 18 pin S2 .00 S1.80 P1 0630 20 pin S2.20 S2.00 P10632 22 ptn S2.40 $2.20 P1 0634 24 p,n S2.60 S2.40 P10640 28 ptn S2.90 S2 .60 P10644 40 pm $3.00 S2.70 • TAG TANTALUM t~P~ C1Ifi?ft~p~g~C1"'1;~J R1 6124 R161 25 R1 6126 R161 28 R16216 R16220 R16222 R 16224 R 16228 R16300 R16302 R16304 R16306 R16308 R16310 R1631 1 R1631 2 R16314 R16316 R16318 R1 6320 R16322 R16324 R16326 R16328 16V 4.7u F .... 16V 10uF .. . 16V 15uF . 16V 22uF .. ... 25V 2.2uF . 25V 4.7uF .. 25V 6.8uF . 25V 10uF . 25V 22uF .... 35V 0.1uF .. 35V 0.15uF .. 35V 0.22uF.. 35V 0.33uF .. 35V 0.47uF . 35V 0. 68uF.. 35V 0.82uF .. 35V 1.0uF .. 35V 1.5uF . 35V 2.2uF .. 35V 3.3uF . 35V 4.7uF .. 35V 6. 8uF . 35V 10uF 35V 15uF .. . 35V 22uF . 0. 48 0 .52 0.75 0.85 0.40 0.70 0.70 0.60 2.40 0.30 0.30 0.30 0.30 0.30 0.35 0.35 0.30 0.50 0.50 0.35 0.70 0.80 0.80 1.40 3.50 1 Cat.R1 4405 .... ..... $45 .95 SPECIAL, $35.95 Numb,t,;'li)lil,~nV 1t 1- 11 Minor Scale Divi sion : 1150 turn Shatt Bore: 6.35mm ( 1/4 .. ) Finish : Clear Anodize Body Size : 22.2mm diameter (.875.. ) Depth : 22.2mm (.875" ) Weight : 19.8g (0.7oz.J Cat.R14400 ..... $26.95 SPECIAL, $21.50 Num,,,t,;'9'il.~n'.2,k 1-11 Minor Scale Division: 11100 turn Shatt Bore : 6.35mm ( 1/4") Finish: Satin Chrome Body Size : 46.04mm diameter (1.81 2") Depth : 25 .4mm (1 ") Weight : 85.g (3o z.J Cat.R14410 ... .... .. $46.95 SPECIAL, $37.50 ,I' • • • Rod Irving Electronics MELBOURNE : 48 A 'Beckett St. Phone (03) 663 6151 NORTHCOTE : 425 High St. Phone (03) 489 8866 CLAYTON : 56 Ren ver Rd . Phone (03) 543 7877 SOUTH AUSTRALI A; Electronic Di scounters PIL, 305 Morohett St, ADELAIDE 1 ~g~r:e,i ?! J..2! ~~ ?t!u> H•r •,',II•• 1,., 1, '1e,gh!COSl!>I MAIL ORDER : Local Orders: (03) 543 7877 Interstate Orders: (008) 33 5757 AU Inqu iries : (03) 543 7877 CORRESPONDENCE : P.O. Box 620. CLAYTON 3168 Telex: AA 151938 Fax : (03) 543 2648 - - MAIL ORDER HOTLINE 008 335757 SPECTROL MULTIDIALS Numbe"'/'li)lil,~nV 1i · l · 1 Minor Scale Division : 1/500 turn Shatt Bore: 6.35mm ( 1/4 .. ) Finish : Satin Chrome Body Size: 25.4 x 44 .45mm (1 X 13/4 ") Depth : 25.4mm (1.. ) Weight : 45.4g (1 602.) $0.18 :r·· ·:1•·:e·_··._ • ,4'.~~ 1 S.P.0 .T. 12VCoil 10A240VS 1411 4 $3.95 $0.20 DB 25 CRIMP SPECIALS! [!]0<at>] (z] ~ ~ (B[£]<at>) P10964 3 PIN LINE FEMALE P10966 3 PIN CHASIS FEMALE ,oo . s. P.D.T. 3A conneclors.. $1.95 DB25 CONNECTOR SPECIALS! $9.50 NEW TRANSISTORS Rod Irving Electronics have two new transistors which will replace a multitude ol common hard to gel devices. The PN 100is a NPN general purpose medium power amp and switch with continuous collector current up to SOOmA The PN200 is a PNP general purpose amp at collector currents to 1 Amp. Both are T0-82 plastic package PN100 REPLACES: PN2221 . PN 2222. PN2222A. PN3585. PN356S, PN3569. PN3643. PN5133, 2N2219A, 2N2222A. 2N3414 . 2N341 5, 2N3416 , 2N34 17. 2N3700 , 2N370 4, 2N3904 , 2N4 123. 2N4 124. 2N4401 . 2N5088. 2N52 10 PN200 REPLACES : PN2907. PN2907A, PN3638. PN3638A. PN3640, PN3644, PN4121 , PN4143, PN4248 , PN4249. PN4250. PN4355. PN491 6. PN4917. PN:5910, 2N2905A. 2N 3467. 2N3702. 2N3906, 2N4 125. 2N4 126. 2N4291 . 2N4402. 2N4403. 2N5086. 2N5087, 2N5447 PNIOO Cat. T90001 PN200 Cat. T90002 10, 1-9 10 + $0.07 $0.06 $0.12 $0.10 $0.12 $0.10 HIGH INTENSITY RED LED BAR GRAPH $9.95 CANNON TYPE CONNECTORS 1-9 P10960 3 PINUNEMALE . $4.95 ........... ........... $3.95 . 10 TURN WIRE WOUND POTENTIOMETER Spectrol Model 534 ¼ " shaft. l..!..J 10+ $0.12 S0.15 $0.15 $0.15 $3.90 .. .................... $3.50 .......,___ . .., Equiv (Bourns 3540S . Beckman 7256) Dials to suit 16-1-1 1, 18- 1-11 , 21·1·11 . R14100 SK R14050 SOR A 14055 100A R14 110 10K R14060 200A A 14120 20K A14070 500R R14130 SOK A1 4 140 100K A14080 1K A 14090 2K 10 1·9 •ii;§t, i r: QUA~: = : : " Cat. No. Col. 1-9 2 10 140 Red $0.15 z 101 •1 Gm $0.20 Z10143 Ylw $0.20 Z 10 t45 0 ,a $0.20 QUALITY 5mm LEDS CENTRONICS SOLDER _ PLUGS ~ ~ECIALS; . ~ ii~ iit! M~~~d 15W llouro holder. Suitable for Scotchcal, Eprom erasing etc. As used in ETI Eprom . $4.95ea $4.25ea $3.95ea fs~;;;;;;, SPECTROL 64Y ~/:IJ/IJ,~ p':', J f;l_!f.1P0,J!> Transmit: 4.0 (at 100dB) Receiver: 5.0 {al - 73d8 ) Impedance: Transmit : 500 Receiver: 5000 Cat. l 19990 (Transmitter) $6.95 Cat. L19991 (Receiver) .... $6.95 10 1 Cat. S1 2500 ......... Normally $7 .95 1·9 10 + 25 + =- ::_---...-.. WIRE WRAP IC SOCKETS These quality 3 level wire wrap sockets are tin-plated phosphor bronze. Cat.No. Description 1-9 1O.,. 8 p,n S1 .50 S1 .40 P10579 P10580 14 p,n $1.85 $1.70 P10585 16 pin S1.95 S1.80 P10587 18 pin S1.95 S1 .80 P10590 20 pin $2.95 $2.70 P10592 22 ptn $2.95 $2.70 P1 0594 24 pin $3.95 S3.50 P10596 28 pin $3.95 $3 .50 P 10598 40 p,n $4.95 S4.50 1s rn1tW~rfi::M~bNLYJ LOCAL ORDERS &INQUIRIES (03) 543 7877 POSTAGE RATES : S1 S9.99 S10 S24.99 S2 5 S49 .99 S50 S99.99 $100 S199 S200 S499 S500 pl us The above postage ra tes are for basic postage only . Road Freight . bulk y and fragile item s will be c harged al differen t ral es . Alt sa les ta x exempt order s and wholesale inqu iries to : RITRONICS WHOLESALE . 56 Renver Rd, Clayton . Ph . (03) 543 2166 (3 1ines) Errors and omissions excepted Pnces and spec1hcations sub1ect 10 change !~;~~:a~~ . x1;;11~~;,,,f~~.'.~~~~~.. M arh1ne~ · Apple ,1; a reqistered 11ac1cm.1, ~ ·oenolc!> rcg, s terrd ·radmar ~<. pt 1ht'" re!,pec1 1ve o w ner!> Fig.9: distortion can be measured using a harmonic wave analyser such as this H-P "Dynamic Signal Analyser". It displays relative amplitudes of the fundamental and each of the harmonics. Fig.7: input and output waveforms for the circuit shown in Fig.6(a). The output waveform shows severe crossover distortion because Ql and Q2 are non• conducting for signals between - 0.6V and + 0.6V. In Fig.8, the output from the circuit Fig.6(b), we notice the striking resemblance to the sum waveform "A" in Fig.3. Having previously demonstrated that the resultant waveform in Fig.3 is in fact the sum of a number of harmonic sine waves, we know that the voltage waveform photographed in Fig.8 is likewise. That is the justification for the use of the harmonic wave · analyser as a distortion measurement method. Enter negative feedback. Fig.8: the circuit shown in Fig.6(b) greatly reduces distortion. Even better results can be obtained by matching the diodes and transistors and trimming resistor values, but we need negative feedback for a really good amplifier. point as in the oscilloscope photo Fig. 7 where we are still using the test sinewave as an input signal. Clearly this produces a horribly distorted output current, especially on small signals (low volume). Distortion from this cause is, not surprisingly, called "crossover distortion". Many and wonderful are the circuits proposed and used to reduce this crossover distortion, one of the simplest being shown in Fig.6(b). The resultant output waveform is shown in Fig.8, an improvement on Fig. 7 but crossover distortion is still clearly evident. Without feedback, such improvements can reduce 86 SILICON CHIP crossover distortion, but cannot eliminate it. The distortion demonstrated in Fig.7 and Fig.8 could be measured using a harmonic wave analyser such as the Hewlett Packard "Dynamic Signal Analyser" model 3561A shown in Fig.9. Such an instrument displays on its screen the relative amplitudes of the fundamental frequency and each of the harmonics, as in Fig.10. We observe that crossover distortion creates an output signal rich in odd harmonics. Fig.10 shows the large fundamental (going well off screen) and also all measurable harmonics up to the 19th. Fig.11 is a block diagram of a complete amplifier, shown divided (for convenience of explanation) into two sections, the differential stage and the rest of the amplifier. We now proceed to enclose all that within one overall negative feedback loop. As before, the feedback signal is subtracted from the input voltage to give the error signal "E" which is the signal actually amplified (as explained in Pt.3 of this series, in the July 1988 issue). We call V(in) the test sinewave input to the power amplifier, and V(out) the output. Suppose we have chosen Rl = 4k0 and R2 = 1kn. This gives a voltage divider ratio of R2/(Rl + R2) = 0.2. The output from the amplifier will be an amplified version of the test sinewave V(in) plus the distortion harmonics introduced at the output stage. From our experience with Fig.3 and the harmonic analyser (Figs.8, 9 & 10), we expect the distortion generated in the output stage to consist of many sinewaves, all at odd multiples of ,.,.. l 008 Hz CAl.!JRAT!ON DISABLED RAHGE: ·S dB!/ F'REE RUN Off 98 a\lrH BAHll IMllltC SID£JAND ' aVras .,. ,.,.. /J)JY e Vns: I e Hz •1t1 Si!\RTI llt r,' r, ' ' J.1 : ll. Dtrntt NU" HARi! r;, BUI 190,97 Hz YI IH,I .Vru ... STOP: 20 809 Hz- THII 33,t l Fig.10: the output of the harmonic wave analyser here shows 33% THD (total harmonic distortion), mostly due to third and fifth harmonics in the output. the frequency of V(in), decreasing in strength as we go to higher orders. Let's label the the 3rd harmonic signal voltage VH3; the 5th, VH5; the 7th, VH7; the 9th, VH 9 ; the 11 th, Vm1; and the 13th, VH13· There will be more harmonics of still higher orders but the above is enough to make the operation of the system clear. Also we call "G" the open loop gain of the amplifier (ie, gain from E to the output). From Fig.11 we observe that: V(out) = G.E + VH3 + VH5 + VH7 + VHg + Vm1 + Vm3 E = (V(in) - FB) FB = 0.2V(out) FEEDBACK SIGNAL Thus V(out) = GV(in) - 0.2V(out) + VH3 + VH5 + VH7 + VHg + Vm1 + Vm3 (V(out))(l + 0.2G) = GV(in) + VH3 + VH5 + VH7 + VHg + Vm1 + VH13 If the open loop gain of our amplifier is 15,000 at low frequencies, we can write: V(out)(l + 0.2 x 15,000) = 15,000V(in) + VH3 + VH5 + VH7 + VHg + Vm 1 + Vm3 3001V(out) = 15,000V(in) + VH3 + VH5 + VH7 + VHg + Vm1 + Vm3 Thus V(out) = 4.998V(in) + VH3/3001 + VH5/3001 + VH7/3001 + VHg/3001 + Vmi/3001 + Vm3/3001. .,. Fig.11: by introducing negative feedback, harmonic distortion can be greatly reduced. If the open loop gain (G) is 15,000, harmonics generated by non-linearities in the output stage will be attenuated by a factor of 3001 (see text). We conclude from the above foray into a little algebra that at low frequencies the gain for the wanted input signal V(in) is 4.998 or approximately 5 but for the harmonics generated by the nonlinearities of the output stage, the gain is 1/3001; ie a severe attenuation. If you like you can regard it as a case of small distortion harmonics being fed back from the output to the inverting input, then amplified to the output stage where they (being inverted) almost cancel the distortion harmonics as they are produced by the output stage. Equilibrium is reached when the small fraction 1/3001 of each produced harmonic is heard in the output. Observe that the low frequency open loop gain of this amplifier is 15,000 but the feedback reduces the closed loop gain down to approximately 5. Therefore we say that we have applied 15,000/5 as a feedback "quantity". This is usually expressed in decibels; ie, approximately 70dB of feedback. The high frequency problem The above calculation holds good for all frequencies for which G = 15,000, and this will probably be true for frequencies up to about 3kHz, in a typical power amplifier. That presents a problem because harmonics at higher frequencies will have less feedback available to reduce them to low levels. Suppose the amplifier's open loop gain falls from 15,000 at low frequencies to 200 at 32kHz. This means that harmonics at 32kHz or thereabouts will no longer be reduced by a factor of 3000 but by the smaller factor of 41. You may argue "So what that's way above audibility". Ahah yes, but those less-reduced distortion harmonics will beat with every other music component present in the amplifier, producing sum-anddifference products which we call intermodulation. So even if you can't hear high distortion products, they can still make the sound unpleasant. Now we see the reason for making amplifiers with an open-loop frequency bandwidth extending as high as possible. ~ SEPTEMBER 1988 87 PT.11: THE QUEENSLAND 25kV 50Hz AC SUBURBAN SYSTEM THE EVOLUfION OF ELECTRIC RAILWAYS While Sydney and Melbourne had electrified suburban rail systems in the 1920s, Brisbane held off until the 1970s. The city then leap-frogged the rest of Australia by installing high voltage electrification. By BRYAN MAHER Up until the 1950s, all locomotive power in Queensland was traditional steam, even for Brisbane's suburban services. Then the State government undertook a bold venture to provide long distance air conditioned diesel-electric mainline trains. First to run was the Brisbane to Cairns " Sunlander". Electrification of the Brisbane suburban rail system, first mooted as far back as 1915, had a shortlived start during 1947. At the time, electric trams had been running in Brisbane city since 1887. In 1952 the tramway system reached peak performance in terms of the number of tramcars, with nearly OVERHEAD WIRE 25kV 50Hz SINGLE PIIASE TRANSFORMER SILICON CONTROLLED RECTIFIERS FIELDS RAILS Fig.1: the 25kV AC overhead wire feeds the primary winding of an onboard power transformer, with the return circuit via the wheels and rails. The two secondary windings feed thyristor bridges which control DC traction motors. 88 SILICON CHIP 200km of track. The total service then had 325 tramcars, including drop-centre and corridor types. Against this background the electrification of the city and suburban rail system seemed natural. Planning for a 1500V DC railway proceeded and civil engineering works were completed in 1947-1957. Elections then brought a change of government and a reduction in loan funds. The new government overruled the electrification program, opting instead for a gradual introduction of diesel-electric locos for the suburban service. Later, the Brisbane tramway system suffered a major setback. In September 1962, 68 trams stored for the night in the Paddington depot were caught in a disastrous fire. As the inferno raged the few night shift maintenance men managed to drive three cars out before the depot roof partially collapsed. This short-circuited the 600V DC on the trolley wires and tripped the circuit breakers at the substation. Without traction power, the workers could only stand (powerless!) and watch as 20% of the tramcar fleet was destroyed. Though a handful of new .trams were built, by the mid 1960s diesel buses gradually took over the city and inner suburban service. The end to Brisbane's electric trams and electric trolley buses came in April 1969. Twenty-two trams were acquired by the Brisbane Tramway Museum Society and can be seen operating today at Ferny Grove. Electric suburban railway Back on the suburban railway scene, the same State Government revived the idea of electrifying the whole suburban railway system in These are the new 3-car sets which are used in Brisbane and its suburbs. They are powered from 25kV AC via the overhead line and each 3-car set has eight 135kW DC traction motors, giving a total power of 1.08MW. the late 1970s. The big day came in November 1979 when electric trains were inaugurated. The electric system ran from Darra, via Roma Street and Central stations, to Ferny Grove, a distance of 34km, serving a total of 26 stations. Progressively extended, electrification has now reached Beenleigh, using the new Merrivale Bridge across the Brisbane River. It presently reaches east to Moreton Bay suburbs, west to Ipswich and north to Caboolture. The suburban electric cars, made by Walkers/ ASEA Ltd in their Maryborough workshops, are constructed of stainless steel and fully air-conditioned. They are 23 metres lorig, 2.72 metres wide and 3.87 metres high. They are normally run as 3-car sets which can be coupled up to form six or 12-car trains. The three-car sets are semipermanently coupled to form one unit, 72.42 metres long and weighing 150.2 tonnes fully loaded. Three-car sets are used for off-peak periods and 6-car trains run during peak hours, with specials of 12 cars used regularly. A 6-car train seats 496 passengers, and can carry a maximum of 1000 passengers. Designed for a maximum speed of 100km/h, a fully loaded train can be brought from full speed to standstill in a distance of 425 metres. 25kV AC 50Hz supply The Brisbane railway electrification scheme was the first in Australia to use high voltage 50Hz AC. The overhead catenary wire runs at 25kVAC 50Hz. As Fig.1 shows, the high voltage overhead wire feeds via a lightweight pantograph and main circuit breaker to the primary winding of the onboard transformer, with th'e return circuit via the wheels and rails. The on-board transformer is mounted under the floor of the middle car of each 3-car group. Two 690V secondary windings on the transformer feed thyristor bridges, phase-controlled by timing trigger circuits as indicated in Fig.2. This provides up to 1100V DC for the armatures of the four traction motors of this car. A third secondary winding on the transformer supplies 136V AC (via an intermediate transformer) to another controlled thyristor bridge supplying the field windings of the traction motors. All secondary circuits also pass to the leading car where a further two controlled thyristor bridge rectifiers supply armature current to the four DC traction motors of this car. Yet another thyristor bridge rectifier supplies the separately excited motor field windings. The trailing car has no traction motors but is equipped with a driver's cabin and controls (so the 3-car set can be driven in either direction), An auxiliary converter mounted under the trailing car provides a 415VAC 3-phase · 50Hz 135kVA supply to all auxiliaries including oil pump motors, air conditioning, fluorescent interior lighting and headlights. A separate single phase rectifier bridge supplies the DC motor driven main air compressor for door operation and air brakes. A 110V DC battery provides for marker and emergency lighting, emergency ventilation, emergency air compressor and also the 50V DC SEPTEMBER 1988 89 OVERHEAD WIRE 25kV 50Hz I I I I I I I c56RAIL I -!- I I I FOUR MOTORS I I I I I I I I I I I I I I I I I I I I I I '----"~-¾------~1 \ I FLEX CABLES I JOIN CARS I I I I I I I I I I I I II I TO AUXILIARIES I I I ..___ _ _ _ _ _ __,, I ------- OM-CAR _______ L __________ J M-CAR _____________ I J (a) Fig.2(a): This diagram shows the electrical system of Brisbane's 3-car set in more detail. Note the 1.290 resistors which are switched across each pair of traction motors during regenerative braking. Each of these resistors dissipates several hundred kilowatts during braking. circuits for the driver's control systems and all car door operation. A large iron-cored reactor helps in smoothing the rectified DC supply for the traction motor armatures. Even though the motor field windings are separately supplied by DC, the motor field yoke is made of laminated steel to minimise eddy currents caused by 100Hz ripple current. The main transformer is rated at 1.635MVA, of which 1.34MVA is for traction power. With careful distribution of the heavy loads such as the main transformer, reactor and air compressors over all three cars, the loading is kept to a low 15.25 tonnes per axle. Traction motors This 3-car set makes quite a complex electrical unit, driven by eight ASEA 480V 310-amp DC traction motors, each rated continuously at 135kW. These are connected in series pairs across the controlled 90 SILICON CHIP 1100V DC supply, giving a total power of 1.0BMW for the 3-car unit. On level track and with a full passenger load, the train can briskly accelerate to 48km/h within 60 seconds. Top speed is lO0km/h. Motor bogies Each bogie of the leading and middle cars is equipped with two traction motors, each motor driving one axle. The drive is through a 5. 7: 1 traction gear mounted on the axle. The motor top speed is 3 780 RPM at a train speed of lO0km/ hour. The motors are hung on roller bearing suspension tubes on each axle. Such a mounting allows the motor drive pinion to remain in mesh with the driving axle gear as the wheels rise and fall with track variations. All motor armatures and train axles run in roller bearings. The primary suspension takes the form of rubber bonded Chevron spring elements, suspending each axle box horizontally and vertically. Air bag secondary suspension units transmit body weight to the bogie frames. The air bags have a control system designed to keep the body at a nominated height above the bogie, even with changing passenger loads. At the same time, the air pressure within the suspension bags is continually sensed by an electropneumatic transducer. The electrical signal so produced is used to modify motor current during acceleration (to prevent wheel slip) and braking effort (to prevent wheel skid when stopping). Thus, if a car is lightly loaded, it will have less braking effort applied than a more heavily laden car in the same 3-car set. Traction rods, torsion bars, and vertical and horizontal hydraulic shock absorbers combine to provide smooth riding conditions under ac- celeration, braking or negotiation of curves. Brakes The brake system uses electrical dynamic braking blended with electrically controlled air brakes. A back-up compressed air brake is in readiness at all times, to fully control the train should the electrical brake be insufficient. The changeover is automatic and smooth in action. The dynamic brake acts by varying the current to the field windings of the traction motors while a heavy duty 1.29 ohm braking resistor is connected across the armatures. The motors then act as DC generators, with the current generated being dissipated in the braking resistor. This electrical load on the motors (now acting as generators) smoothly slows the train. Because this regeneration process depends on motor armature speed, the braking control system must continually sense train speed and automatically apply more field current to the motors as the train slows down. The resulting system is sufficiently accurate, as Fig.3 shows, to provide constant deceleration of one m/sec2 when slowing from 90km/hour to 40km/hour. Below 40km/hour, this deceleration rate cannot be provided by dynamic braking alone as this would demand too much field current. Below 40km/h, the air brakes steadily take over to bring the train to a complete stop. There are four brake cylinders on each bogie, actuating composition brake blocks for each wheel. The braking action is in three modes, all controlled automatically without the driver having to be concerned about which mode is operating at any one moment. In mode 1, the electropneumatic brake system is automatically modified for passenger load and graduated application/release. This is automatically blended with mode 2, the dynamic brake effort. As the driver applies brakes, the electropneumatic system applies air to the brake cylinders until the brake shoes touch the running wheels. At This photograph shows the lightweight catenary for the single-phase 25kV supply. Note the negative return wires on the mast. the same time the traction motors controls, emergency lighting, conare switched to dynamic regen- trol circuits for the air conditioning, erative mode which provides most emergency fresh-air ventilation systems and the control of the elecof the braking effort. If the rate of decrease in speed is tropneuma tic brakes. less than that demanded by the Because thei r ope ra tion is driver, the system automatically in- critical, the traction controls are creases the air pressure in the powered by 50V DC obtained from brake cylinders to increase the rate. a 1.2kW voltage regulator mounted of retardation. Thus the change- .on each car and powered by the over from dynamic to air braking is ll0V DC battery. These voltage smooth, automatic and unnoticed stabilisers also provide a regulated AC supply of ± 50V peak at 200Hz by the passengers. for control of the traction thyristor Train controls rectifier bridges. All control and emergency functions are powered by a 48-cell 110V Driver's controls DC lead-acid battery slung under Control signals for the accelerathe leading car of each 3-car set, tion and braking are transmitted giving adequate control in the event throughout the train from the driver's end via a 3-wire PWM of loss of the 25kV supply. The 1 lOV DC systems include the (pulse-width modula ted) signal train communication radio and the derived form a solid state chopper public address system, car door circuit in the driver's cabin. One ":~ <lC\C\[\L\[\ TIME TIME Fig.2(b) & (c): these waveforms show the thyristor bridge rectifier output at full power (b) and at two-thirds power (c). SEPTEMBER1 988 91 switched across the braking resistors, DC current is applied to the separately excited fields as demanded by the PWM signal. Simultaneously, the dynamic brake voltage generated by the rotating armatures returns a signal indicating the extent of electric braking actually achieved. These two demand and response signals are compared in an analog difference circuit to determine the air pressure applied to the braking cylinders. In this way, dynamic and air braking is automatically blended. Automatic warning system Close-up view of the thyristor control gear mounted under the trailing car of the 3-car set. Thyristors are far more efficient than the resistive controllers used in older electric train sets. wire is active when acceleration is called for, another wire becoming active when braking effort is demanded by the driver. The degree of acceleration or braking demanded is determined by the signal pulse width; 100% pulse width corresponding to either maximum traction power or maximum braking. Minimum pulse width would mean a train coasting under momentum or downgrade with no traction force nor brake applied. A pulse width of 50% would demand medium acceleration or medium braking, depending on the third wire selected. The PWM coded signal is fed to a decoder circuit mounted in each car. The analog signal so derived is modified separately in each car by the weight of passengers in that car, as indicated by the air pressure transducer in each bogie air-bag suspension. In this way, if a train carries unevenly distributed passenger loading, a packed motor car would have more traction current applied to its traction motors than a lightly loaded motor car on the same train. The same applies to braking, as noted above. The automatic blending of electric dynamic brake with the pneumatic brake is achieved by a differential measurement. For electric dynamic braking, with the traction motor armatures 100~-----------+----------"'"'"'/ The Westinghouse automatic warning system consists of magnetic transmitters mounted on track sleepers between the rails ahead of electric colour-light signals, and magnetic receivers mounted under the train. The signal circuit state (green or otherwise) is conveyed to the stationary sleeper-mounted electromagnet, changing its magnetic polarity which is sensed by the train-mounted magnetic receiver. Thus, the state of each signal being approached, as well as being visible to the driver, is indicated audibly by a bell in the driver 's cabin in the case of a clear signal, or in the case of a red or amber signal by an air horn. Automatic brake application follows the air horn if the driver does not respond within three seconds. Results Compared to the diesel-hauled suburban trains which they replaced, these "state-of-the-art" electric trains have resulted in a 25 % faster trip as well as a much more enjoyable ride. This has successfully attracted many more travellers to the suburban service, significantly reducing the peak-hour traffic crush on suburban main roads. Next month we will further investigate high voltage "industrial frequency" electric railways. Acknowledgements TIME REQUIRED TO STOP TRAIN Fig.3: relative stopping times for air braking and dynamic braking. In practice, the two systems are automatically blended by on-board sensors. 92 SILICON CHIP Grateful thanks to Queensland Railways and Walkers/ASEA for technical data and photographs. ~ THE ELECTRONICS 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 11 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 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 The Serviceman's Log Projects For * Amateur * Constructional The Enthusiast Radio, by Garry * Cratt, VKZYBX HiFi Review * Digital Electronics Course The Way I See It, by Neville * Circuit Notebook * Willams * ·* Vintage Radio * Book Reviews Junk Mail 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 POSTAGE FREE SUBSCRIPTION COUPON OVERLEAF ► SEPTEMBER 1988 93 FREEPOST SUBSCRIPTION COUPON To: Freepost 25, Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097, Australia. BACK ISSUES NO POSTAGE STAMP REQUIRED IN AUSTRALIA PLEASE START my subscription in ............................ .............................. . NAME (Mr/Mrs/Ms) ...... ........................... .. ....... ......................................... . STREET ......................... ......... ......... ................... ........ ..................... ........... . SUBURB/TOWN ................................................. .........POSTCODE ............ . 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Subscription cost: 1 year (12 issues) 2 yea rs (24 issues) Air mail □ $A130 □ $A65 Enclosed is my cheque or money order for $ .. ......... or please debit my □ Bankcard □ Visa Card Card No. I I I I I Signature ............... ................. .................. Ca rd expiry date .... .. ./ ...... ./ ..... .. Note: photocopy this coupon if you don't wish to cut the magazine, or include the relevant details in a letter. 94 SILICON CHIP Issue Highlights May 1988: Optical Tachometer for Aeromodellers ; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm; Restoring Vintage Radio Receivers. June 1988: Stereo Control Preamplifier; Breakerless Ignition For Cars; Automatic Light Controller; Mega-Fast Nicad Battery Charger. July 1988: Fitting a Fuel Cut-Off Solenoid; Booster for TV & FM Signals; The Discolight Light Show; Tone Burst Source for Amplifier Testing. August 1988: Build a Plasma Display; Remote Chime/Doorbell; High-Performance AC Millivoltmeter; Getting the Most Out of Nicad Batteries. Price: $5.00 each (incl. p&p). Fill out the coupon on page 1 0 2 (or a photostat copy or letter) and send it to: Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097. L™ITED NUMBERS OF BACK ISSUES ARE AVAILABLE SO DON'T DELAY I PRODUCT SHOWCASE I The antenna can be rotated in either direction with this hand-held controller. Weatherproof UHF/VHF antenna has inbuilt rotator Based on the "Mini-State" design originally produced by RCA, this fully enclosed antenna incorporates a 5-element Yagi for the UHF bands and a circular travelling wave antenna for the VHF bands. Both antennas are fed to an amplifier before being fed down the cable to a wall-mounted socket plate. This is powered by 12V DC which may be supplied by a mains plugpack or from a cigarette lighter socket plug (which is supplied). Since the antennas are fully enclosed, there is no way of knowing which way they are pointed, hence the rotator. This consists of a handheld wire controller and a motor system to rotate the antenna system inside the housing; the housing itself does not rotate. Using the rotator is a matter pressing the rocker switch on the controller to ffigh output piezoelectric siren alarm This piezo alarm is ideal for security applications or in industry to indicate dangerous conditions in machinery. It is a self-oscillating siren sweeping a frequency range of 1500 to 3500Hz. Minimum sound output is 110dB at 1 metre with a supply voltage of 12V DC although it may be operated at voltages down to 6V DC. Operating temperature range is - 20°C to + 70°c. For further information, con- rotate the array in one direction or the other, while watching the picture quality. The unit is intended mainly for use in reasonably strong signal areas and with that proviso, would be ideal for use on boats and caravans and for commercial offair monitoring for television OB (outside broadcast) vans. Its dimensions are 533mm in diameter and 178mm high. It is available from all Jaycar stores at $399.00. Capacitors for memory backup tact IRH Components, 32 Parramatta Road, Lidcombe, NSW 2141. Phone (02) 648 5455. Where it is necessary to power random accessory memory (RAM) while a computer is powered down, the designer essentially has two choices: a lithium or other expensive long life battery which will eventually need replacement or a high value double layer capacitor. For the latter approach, Murata have the AC 200 series of 5.5V ceramic double-layer capacitors (compatible with most microprocessor and TTL ligic), with values ranging from 18,000µF to 100,000µF (or 0.918 to 0.1 Farad). To give an idea of their size, the SEPTEMBER1988 95 AC 200 series 0.1F measures only 12.5mm in diameter and 7mm in height. Other values are smaller, at 11 x 6.5mm, with 5mm pin spacings. For further information, contact the Australian distributor for Murata products, IRH Components, 32 Parramatta Road, Lidcombe, NSW 2141. Phone (02) 648 5455. Hands-free telephone adaptor needs no connections For those who fancy a hands-free phone similar to that featured elsewhere in this issue but don't wish to build it, this unit could be the answer. It consists of a cradle for the handset and a separate headset so you can have fully hands-free but private conversations. The cradle has an electret microphone to pick up sound from the earpice of the phone handset and a small loudspeaker to drive the mouthpiece. It can be powered from three AA cells or a 4.5V DC plugpack. It also has a mute switch from the headset microphone and a jack socket to connect a tape recorder. The separate headset is light and comfortable and the flexible microphone boom can be bent to obtain a comfortable position. To use the system, you just dial the number on your regular phone in the normal way and then place the handset in the cradle. We tried it and it works well. Recommended retail price is $134.95 from Arista outlets. A handy tapered reamer for your workshop The DIC SC-5000 solder cleaner, unlike conventional desoldering stations, is so easy to handle because it has a vacuum pump built in and requires no connecting tubes or separate compressor. Just one power cord and that's all. The integration of the suction nozzle and vacuum pump results in greater suction power. Due to it's powerful 60 watt ceramic heater, it heats rapidly and recovers immediately during use. Exact temperature control is accomplished by a zero-crossing feedback circuit, eliminating RF interface and preRU1JIE.·\\>,, venting damage to integrated circuits, multi-layer boards and through -hole-plated PC boards. With the flick of a switch the DIC becomes a hot blow gun. And at the recommended retail price of $495 the DIC SC-5000 won't burn a hole in your pocket. Available now in Australia exclusively through Tecnico Electronics and appointed Distributors. SYDNEY 439 2200 MELBOURNE 235 3686 11 Waltham Street, Artarmon, NSW. 2064. • !~~!~~2m~~~~!~2~,~~~ the UN 1526 96 SILICON CHIP Drilling holes in sheet metal and plastic boxes is an easy job to botch. Unless you know what you are doing it is inevitable that you will end up with three-sided holes or worse - jagged, torn holes in distorted panels. Drilling plastic can also be a problem if the drill speed is to high, as the plastic tends to melt. The solution to these problems is to always drill a small pilot hole, say 5mm, and then ream out the hole to the correct diameter. That's where this tapered reamer from David Reid Electronics comes into its own. It tapers from 22mm to 4mm so it can cope with just about any hole requirement. It is priced at just $15.95. Shorted turns tester for line output transformers SPECTACULAR ELEASE • .IIJi. v11c=I NEWSA-100 SPEAKER KIT Television repair technicians will find this economical shorted turns tester a boon when confronted with suspect line output transformers. The unit will also test the scan coils of picture tube yokes and even automotive ignition coils. Made in Australia, the tester is economically priced at $65 plus sales tax where applicable. Contact J.V. Tuners, 216 Canterbury Road, Revesby, NSW 2212. Phone (02) 774 1154. Custom polystyrene capacitors made in Australia Since the introduction of VIFA speaker kits in Australia in 1985, thousands of speakers have been built with superb results. VIFA is now proud to release four new speaker kits ranging from a mere $399 to $1199 per pair including cabinets. Never before have speaker kits been so popular in Australia than after the heavy devaluation of the dollar. Similar fully imported quality loudspeakers are today typically 2-2½ times more expensive. And these speakers may very well be using Danish VIFA drivers anyway, as VIFA supply more than 50 of the world's most respected loudspeaker manufacturers with drivers. But why the big savings? Because fully imported speakers suffer from 25% import duty, 20-30% freight, 30% sales tax and 28% handling charges (typically). So if you would rather put your money into better quality than in other people's pockets, VIFA speaker kits are the only way to go. Are they difficult to build? No, the kits are supplied with all parts needed including fully built crossovers and pre-cut flatpack cabinets ready to assemble. No soldering or carpentry skills are needed, just a Phillips head screwdriver, some simple hand tools and a few hours of your leisure time. Are they as good as people say? Read the reviews, !isten and compare with any other speakers twice the price or more. Need we say anymore? VIFA for the quality conscious audiophile. For full details please contact Sole Australian Distributor: SCAN AUDIO Pty. Ltd. P.O. Box 242, Hawthorn 3122. Fax (03)4299309 Phone: !0314292199 (Melbourne) 02 5225697 (Sydney) 07 3577433 (Brisbane) 09 3224409 (Perth) Stocked by leading stores throughout Australia • Polystyrene capacitors YES Made here in Australia? YES Made Special to Type? YES Where From? Allied Capacitors Australia Allied Capacitors Australia specialises in custom made good quality, high stability polystyrene capacitors. Why design circuitry which requires additional components to achieve a specific capacitance; we can wind exactly the capacitance you need to match your design criteria within the ranges of 10pF to 1µ.F and up to 10,000VDC. If you're looking for special values or close tolerance capacitors you can have them made in Australia. You might want them for high quality audio amplifiers, crossover networks or any other application where low power factor, extremely high insulation resistance, long-term stability or Capacitors are manufactured to 0 .25%, 0 .5%, 1.0%, 2.0%, 2.5% , 5%, 10% and 20% and are priced according to tolerance. A11 capacitors are tested to 2 .5 times the rated voltage. ~----------- 1 Yes, I am interested in your capacitors. Interested? Please post me details of the following values: Call us now on: (02) 938 4690 II ... /. VDC I I Name (Please print) · OR Cut out and post this coupon to Post Office Box 7 40 . VDC ... / ... VDC . .. / . . . VDC Address L· ~~~~~- ~~~~~~J ~-&_o_~_v_a_1e_,_N_~_.w_._21_o_o___ SEPTEMBER 1988 97 close tolerance is paramount. Where these qualities are desirable, polystyrene capacitors are the answer. Allied Capacitors of Brookvale manufacture polystyrene capacitors in virtually any value over a wide range of voltage ratings. Minimum order quantity is 25, to make it worthwhile to set the machines up. For further information, contact Allied Capacitors, PO Box 740, Brookvale, NSW 2100. Phone (02) 938 4690. Vacuum power solder sucker At one time or another all of us have come up against the problem of having to desolder and remove components from a printed board. Most of us manage with a variety of solder suckers or solder wick. For servicing or manufacturing operations which involve a lot of IC replacements, these methods are not practical. A soldering iron with a hollow tip and a separate vacuum INTERESTED IN ELECTRONICS? Right now we have quite a number of vacancies for staff throughout Australia. We need: • • • Sales staff - ambitious self-motivated people who are interested in a retail career. Junior Technicians - we will train you in the audio, digital. communications, security and video fields. Senior Technicians - experienced in the RF and digital fields. (Technical vacancies particularly in Sydney and Melbourne and from time to time in other capitals.) We offer: _ _ _ _ _ Security (our compan.,,_ is 20 years old) Job satisfaction (over "5000 interesting i:1roducts) Opportunity for advancement An attractive salary package Generous staff discounts Give us a calll Sydney: R Johnson (02) 888 3200 Perth: P Evans (09) 227 8243 Melbourne/Adelaide: A McEwin (03) 592 2366. Brisbane: N Wickson (07) 391 6490 98 SILICON CHIP pump is the usual set up but this is quite expensive. Now there is the SC-5000 desoldering tool. It is a 240VAC 60 watt handheld tool with its own built-in vacuum pump. It is easy to use. Just touch the iron tip to the joint to melt the solder and then press the button to suck it off. We found it very quick and effective and there was no problem with lifting off tracks or IC pads. It is a touch noisy as the vacuum pump motor is actuated but that is not a real problem. A tubular reservoir holds the accumulated solder and this is easily removed and emptied. A cleaning rod for the iron tip is stored in the pistol grip handle where it is always readily available. There is also a temperature control, in the base of the pistol grip, adjacent to the power cord entry. As a final bonus, the unit can be converted to a miniature hot air blower which could be handy when testing small components for their temperature sensitivity. When not in use, the unit stores in a neat vinyl carrying case. Available from Geoff Wood Electronics, the SC-5000 desoldering tool sells for $399 plus sales tax where applicable. For further information, phone (02) 427 1676 or call in at 229 Burns Bay Rd, Lane Cove. Vader Voice - ctd from page 63 voltage at pin 14 of IC1 and pins 1, 2, 4, 5, 15 and 16 of IC2. Second, check that about + 4.5V is present at pins 1, 2, 3, 8, 9 and 10 of ICl and pins 3, 13 and 14 of IC2. When S2 is closed, pin 7 of IC1 b should be high (ie, close to + 9V), pin 6 should be low and pin 5 should be about + 6V. If these checks aren't positive, check around the associated circuit closely for faulty soldering, reversed electrolytic capacitors or wrong components . Remember that the circuit should work as a normal mini public address system when S2 is closed, for Normal operation. Operation of the oscillator, ICl b, can be checked by increasing the .0022µF capacitor to 4.7µF. This will cause it to operate at below 201-iz. When an analog multimeter (switched to a 10VDC range) is used to measure the output at pin, the meter's pointer should jitter rapidly. ~ ------------ 1--1TM --------------, THE NEW STANDARD SPEED, PERFORMANCE, RELIABILITY \ •.:i!,7:"~ 386 80386 - 20MHz Cache Memory Up to 8MB on board 8 expansion slots Floppy drive options 360/1 .2/720/1.44 ~:.~A:t t ..•.. , • ~ ~ ~ 80286-12 6/8/1 0/1 2MHz Up to 1 MB on board 8 expansion slots Floppy drive options 360/1.2/720/1 .44 80286 - 16 6/8/10/12/16MHz Up to 8MB on board Floppy drive options 360/1 .2/720/1 .44 \ ~ ii:y--~✓ t;'' + , '·: ., . f I f i f~ 1-l . ~i.,.:.· ~'''/4m:.r )~ : .:.r• : .11 \ \ \ \J .,i-l, :.\ ~d c::x,•,·.;••.··.:,·,• ·.,· .. ·.,- .. · ..~;;_·1u. ·-,LL,· , ' .. -~ ' a) l f I i '1 l :.± t H , I I 8086 - 10 4. 77 /8/10MHz 8 expansion slots 8086 - 10 4. 77 /8/10/MHz Multi 1/0 and video card on motherboard • EXTENSIVE DEALER NETWORK THROUGHOUT AUSTRALASIA FOR YOUR LOCAL DEALER PHONE (02) 660 5767 AUSTRALASIAN DISTRIBUTORS: ~ 233 BULWARA RD, ULTIMO, NSW 2007. f!,g~ ,9'?_& PHONE (02) 5521855. FAX: (02) 552 1801. 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. Poor reception with bow-tie antenna I recently built the UHF Bow-Tie Antenna described in the January 1988 edition of SILICON CHIP but am disappointed with the results. The set in question is a portable 8-year old Pye (able to receive SBS) - though I didn't expect to receive this channel with the inbuilt antenna. My location in WA is on the city fringe and is not considered a poor reception area. I have only tried the antenna at about one metre above the set at this stage. The question is: "what have I done wrong!" Reception on all channels is poorer than received on the simple V-antenna supplied with the set. (J. J., Kingsley, WA). • What you have done wrong is to use the antenna inside your home instead of installing it outside. Indoor reception of UHF signals is always unpredictable. To expect a high-gain UHF antenna to work properly indoors is like expecting a Brock Commodore to handle well with flat tyres. Put it outside, as high as possible and you'll get a brilliant picture. If you're already getting something Success with Studio 200 power amp I have just finished assembling your Studio 200 se.ries power amplifier and I congratulate you on a very well designed piece of equipment. There are a few things that I would like to enquire about, as follows. First. is there any reason why a fuse is not installed on the primary side of the transformer, so as to protect the rest of the house in case of a short? Second, the Raychem polyswitch that was included is rated to trip with 100W driving through an an load. From the 100 SILICON CHIP which is vaguely watchable with the rabbit-ears on your TV set, you'll get a much better picture when your bow-tie array is properly installed. We promise. Wants preamp for power amplifier Congratulations on a very fine electronics magazine. It certainly appeals to an everyday down-toearth enthusiast like me. As I soon intend to construct the 100W amplifier module (December 198 7) to use for both guitar and PA purposes, the question of a preamplifier comes to mind. I have a separate mixer/preamp but would prefer to incorporate a simple unit inside the amplifier case. Do you intend to publish one as a project? I would only require one low and one high impedance input (lkQ and 50kf2) for microphone and guitar. If more were required, I could plug in the mixer. Also, in you March 1988 issue, "Ask Silicon Chip" contained a letter entitled "Transistor replacement for amplifier". In this, you commented on PA use for this amplifier not being recommended if enclosed data sheet, I can't figure out how the value of 100W into an was derived. If you have a different data sheet on the polyswitches, showing more detail of their transfer functions (eg, current-resistance graphs), could you send a copy of it to me? Finally, is there a dealer in Australia that carries the full range of polyswitches? I am after one to protect a 200 loudspeaker from greater than 1OOW and one to protect a 150 loudspeaker from greater than 30W. (M. H., Bundamba, Qld). • Fitting fuses to the primary windings of large transformers is always something of a problem. driven into a transformer. What if the amplifier were driven at low volume, say 10-20 watts? Would protection diodes then be necessary and, if so, where should they be connected? Finally, in relation to the masthead amplifier in the July 1988 issue, I notice that you feed DC up to the masthead unit. Would this not produce corrosion due to electrolysis in the connections (although they are internal)? Many of the commercial units feed AC up the mast which is then rectified and filtered "upstairs". Keep up the good work. (J. W ., The Gap, Qld). • We do have a guitar version of the 1OOW amplifier module in mind but it is sometime off yet. We would not recommend using the 100 watt amp module to drive a line transformer without protection diodes, regardless of the power level. When distant line-powered speakers are switched up or down in level via their own switched attenuators, they can reflect nasty spikes back down the line to the amplifier. Without the protection diodes in place, the transistors could be "popped" while delivering Large toroidal transformers can be a particular problem because of their tendency to draw very high surge currents at switch-on. The result is that primary fuses can be prone to "blow" when no fault occurs. Polyswitches are good devices but as far as we are concerned the only sure-fire way to select them is to pick the device from the spec sheets and then test them out in the circuit to see if they trip at the desired current levels. That is what we did. We don't have comprehensive specs on the devices and nor can we refer you to a dealer with a bigger range of the devices. only a relatively low power level. Similarly, disconnecting a loudspeaker or the line itself can cause the transformer itself to produce large back voltages which could destroy the output transistors if protection diodes are not in place. In short, transformers are tricky and dangerous loads to connect to any amplifier. As far as the masthead amplifier is concerned, it is fairly standard practice to send DC up the cable although some designs do use AC power. DC possibly does accelerate any corrosion processes but if the unit is well-sealed against the elements, this should not be a problem. Wants to build a radar detector I have a project suggestion for you: a radar detector to cover the new units the police have, as well as the old X and K bands. I realise the difficulties due to the frequencies involved but it would be a popular project and is something that hasn't appeared in any of the magazines to my knowledge. A 4-track cassette recorder for home recording, possibly using a pre-assembled mechanism, would also be interesting. (J. W., The Gap, Qld). • We're not keen on the idea of a radar detector project. They are now illegal in several Australian states and for us to publish a design would possibly raise legal problems. In any case, what's wrong with sticking to the speed limits? We'll have a look at the concept of a 4-track cassette recorder although we'll make no promises at this stage. Studio 200 amplifier could be improved In the December 1987 issue you published a 100W circuit using the readily available 2N3055/2N2955 output devices. While these are quite serviceable, you should have used the MJ15003/4 with the 2N3055/2955 suggested as cheaper alternatives with poorer performance. The following comments are applicable to this design. Adjusting the Speedi-Watt for minimum brilliance I purchased and built the Speedi-Watt described in the December 1988 issue of SILICON CHIP and it works perfectly with my electric drill. However, the real reason for building it was to dim the table-lamp in my son's bedroom. It uses a 25 watt lamp and even at the minimum setting of the Speedi-Watt it is hardly dimmed at all. What do I do now? (P. B., Emu Plains, NSW). • Didn't read the article, did you? The very last paragraph of the article mentions adjusting VR2 for minimum brilliance of the lamp. You will have to pull the circuit board out of the case to do the adjustment. Disconnect the unit from the mains before doing the adjustment. To reduce the minimum brilliance level, which you plainWhile the Studio 200 does use the MJ15003/15004 devices, the circuit can be improved by attention to details which can be easily implemented at little additional cost. Wherever possible, metal film resistors should be used instead of the carbon film resistors specified. They offer lower noise and higher stability. Similarly, all ceramic capacitors should be replaced with equivalent polystyrene capacitors. The next improvement is the use of "star" earthing which I had expected you to have used. This is achieved by making all ground/ earth connections (including the speaker return) to a common point. This results in lower noise levels and reduced distortion. The power supply can be upgraded by fitting a 500VA transformer, or alternatively by using two 300V A units , giving improved power output into lower impedance loads. Channel separation can be improved by providing a se_parate bridge rectifier and filter capacitors for each channel. I have two other criticisms. The first concerns the use of a stabilising network at the output of the ly need to do, take a thin-bladed screwdriver and rotate VR2 anticlockwise. This effectively sets it to the highest resistance condition, with 2Mf! in parallel with the dimmer control VR1. You may have to repeat the adjustment, with the trimmer at a higher setting, after trying the circuit with the lamp in question. On the other hand, in the unlikely event of the extreme anti-clockwise setting of VR2 not giving sufficient dimness, you can remove the trimpot entirely from circuit. This may result in no light at all for the minimum dimmer setting and you may now have a "dead-spot" at the minimum setting of the pot, VR1. This can be alleviated by soldering a 4.7Mf! resistor [or a similar value) in place of the trimpot, between the pads for the wiper [ie, the centre terminal of the trimpot) and the connection common to the 2.2kf! resistor. amplifier. In compensating for the capacitance on output leads, to provide a stable amplifier, the price paid is less control of the speaker at high frequencies; ie, the damping factor reduces at high frequencies. Second, the bolt on the front of the amplifier makes it look cheap and homemade. Are there any distributors who handle boxes with a sub-assembly panel? I would gladly pay the additional expense if I could obtain such a box. Before I finish, have you considered investigating the analog circuits as fitted to CD players. I subscribe to the AUDIO AMATEUR in the USA and this is an area currently being examined in detail. It may well explain some of the differences and anomalies in this "perfect" medium. (R. C. , Ringwood, NSW). • We have had to abbreviate your letter a little but the main points are there. No measureable improvement will be gained in this circuit by using metal film resistors. We recently measured the signal to noise ratio of the amplifier with improved test equipment. The measurement was SEPTEMBER1988 101 Silicon Chip Back Issues Issue Highlights November 1987: Car Stereo in Your Home; 1GHz Frequency Meter; Capacitance Adapter for DMMs. Alarm ; End of File Indicator for Modems ; Simple Door Minder; Low Ohms Adapter for Multimeters . December 1987: 1 00W Power Amplifier Module; Passive lnfrared Sensor for Burglar Alarms; Universal Speed Control and Lamp Dimmer; 24V to 12V DC Converter. March 1988: Remote Switch for Car Alarms; Telephone Line Grabber; Low Cost Function Generator; Endless Loop Tape Player. wtie UHF wer Supp; Subcarrier April 1988: Walkaround Throttle tor Model Railroads ; pH Meter for Swimming Pools; Slave Flash Trigger; Headphone Amplifier for CD Players. February 1988: 200 Watt Stereo Power Amplifier; Deluxe Car Burglar May 1988: Optical Tachometer for Aeromodellers; High Energy Ignition for Cars; Ultrasonic Car Burglar January 1 Antenna; D ly; Gusto Adapter fo uners. Alarm; Restoring Vintage Radio Receivers . June 1988: Stereo Control Preamplifier; Breakerless Ignition For Cars; Automatic Light Controller; Mega-Fast Nicad Battery Charger. July 1988: Fitting a Fuel Cut-Ott Solenoid ; Booster tor TV & FM Signals; The Discolight Light Show; Tone Burst Source tor Amplifier Testing. August 1988: Build a Plasma Display; Remote Chime/Doorbell; High Performance AC Millivoltmeter; Getting the Most Out of Nicad Batteries. BACK ISSUES ORDER FORM Please send me a back issue tor: □ March 1988 □ August 1 988 □ April 1988 □ November 1987 □ May 1 988 □ December 1987 □ June 1988 Enclosed is my cheque or money order tor $ _ _ _ _ _ or please debit my Card No IL__L__.L..-.L..-_L.__L..__L.._- ' - -- ' - - - ' - ---'---'--'--'-___,__- - ' -__, Signature _ _ _ _ _ _ _ _ _ _ Card expiry date__J__J_ _ Please print Name_______________________ Stree~-------------------Suburb/town _ _ _ _ _ _ _ _ _ _ _ _ _ Postcode____ □ February 1988 □ July 1988 □ Bankcard □ Visa Card Price : $A5.00 each (includes postage) . Overseas orders add $A1 .00 per issue for postage. NZ & PNG orders are sent by air mail. Detach and mail to: SILICON CHIP PUBLICATIONS PO BOX 139 COLLAROY BEACH NSW 2097 L - - - - - - - - - - - - - - - - - - - - - - - ~ - ---- -- - ------_j 102 SILICON CHIP better than - 115dB unweighted with respect to full power and -119dB A-weighted. We know of few amplifiers which can better this. In fact, for most power amplifier circuits, metal film resistors offer no advantage. (Note: in the mat. ching stereo control unit published in June and July 1988, we have specified metal film resistors in critical positions). Nor can any improvement be expected by changing the small ceramic capacitors to styros since the signal voltages across them are very small. If you have a look at the printed wiring pattern and the wiring layout you will see that we have used a "star" earth wiring arrangement. Sure, you could also make slight improvements to the overall performance by substantially upgrading the power supply as you suggest but the audible benefit, if any, would not be worth the greatly increased cost. On the other hand, going to separate bridge rectifiers and filter capacitors for each channel can lead to great problems with high circulating currents. It also makes "star" earthing difficult if not impossible. As far as the output stabilising network is concerned, it is true that it does lead to a higher output impedance at high frequencies (around 0.40 at 10kHz). However, damping factor is really only important over the "piston" range of a woofer; ie, up to no more than about 200 to 300Hz. Above these frequencies the crossover network inevitably has far more effect over the driver performance than the amplifier's output impedance. Indeed, many tweeters and midrange drivers have fixed or variable attenuators which make a nonsense of any worries about damping factor . We note your objection to the bolt on the front panel but what about the four large roundhead screws which attach the front panel to the rest of the chassis? In the metal (flesh?) the bolt in question is practically invisible. We don't see it as being a great drawback. Again, it would be costly to eliminate it. We don't know of a supplier of rack continued on page 104 Notes on the UHF Remote Switch & UHF Remote Chime/Doorbell Some readers have reported difficulties with these projects. Here how to solve the problems: First, readers should note the errata published in the June and July 1988 issues for the UHF Remote Switch receiver (March 1988). These changes were all incorporated into the UHF Remote Chime/Doorbell (August 1988). The kits we inspected failed to work because of incorrect component types and values. The following comments apply to both projects: Transmitter: low-voltage miniature ceramic capacitors must be used where specified. Keep their leads short by pushing them all the way down onto the PCB. Do not use the larger lkV ceramic capacitors. Their stray capacitance will upset the tuned frequency and can result in a transmitter that continues oscillating after the power switch has been released. Result - a flat battery. Similarly, the 0.lµF capacitor must be a miniature polyester type (do not use a metallised polyester type). The trimmer capacitor must be a 2-6pF type as specified - you will not be able to correctly set the transmitter frequency with other values. Receiver: the four .001µF capacitors used in the front end must all be ceramic types as specified. Do not use metallised polyester (greencap) types they don't operate well at 304MHz. 13 was also found to be incorrect. It must be a 3.3µH inductor (a 3.3mH inductor will seriously degrade the sensitivity of the receiver). Finally, the PCB patterns were inadvertently omitted from the wiring diagrams for the Remote Chime/Doorbell (p.59, August 1988). The diagrams are reprinted below. '70~F r= B <at>) c. 12V l~ ~~_J 6pf Fig.3: parts layout for transmitter. Fig.4: 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. ANTENNA 12VDC PLUG-PACK I 80 SPEAKER Fig.5: mount the parts on the transmitter PCB as shown here. SEPTEMBER1988 103 Cash in your surplus 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($7.00) Name ... ............ .......... .... ...... .. ... ...... ............... ........ ........ ..... •···· ··· ·· ······ ······· ··· ····· ·· Address .. ..... .. ..... ... .. .... ........... ........ .. ... ..... .... .. ..... ... ...... ..·..... .. . Suburb/Town ...... .. .... .... ...... .. .... ..... ...... .... ... ....... .... ... ...... ... Postcode ... . Enclosed is my cheque or money order for$ ...... .... ... .. . Bankcard D Visa Card D .... .. or please debit my Card No '-I--'---'-- '---'--- ' --'-·---'-~ - ' - -~ -'-~~~-~ Signature ...... ... ....... .. ... ..... .. ... . McKenzie, 29 Ellesmere Crescent, Tullamarine 3043 . FOR SALE NEW 64K-256K PRINTER BUFFER design release. VER 4 .0 and REV G boards now available. Double-sided PCB, EPROM and instructions : $39.00. Optional additions include 2 by 7 -segment LED front panel display of percentage full , 1 to 99 copies select, 3 polled computer inputs, printer switches, computer switches , and serial converter boards. For a free catalog sent a 37c stamp to : Don Ask Silicon Chip - SILICON CHIP RADIO/TV RESTORERS - We have a large stock of new valves. Send SAE for list or phone Shellharbour TV Service , 268 Mary St, Shellharbour, 2529. (042) 95 1175. ctd from page 103 boxes of this size with a subassembly panel. We assure you we are aware of all the points you have raised. But if we don't keep costs to realistic levels, the kitset suppliers just won't even look at stocking the kits - they know what most people will spend. We have seen some of the articles in the AUDIO AMATEUR and agree that the systems of filtering, oversampling and output circuitry may cause some of the small discernible differences in CD players. 104 Having trouble getting your EA/ETI/SC kit to work? Phone (03) 7 49 3480 for estimate or send kit to K. Hunter, 5 Yatama Crescent, Werribee 3030. PROJECT REPAIRS - What they don't explain is why some people claim that they don't get any real satisfaction from CDs. Got any ideas? (Editor's note: before these pages went to publication, this reader pointed out that although the printed boards did use star earthing, the Studio 200 did not, in that the speaker earth returns did not go back to the power supply earth. We have since been able to check whether a modification along these lines made measureable difference. It didn't). ~ Advertisers Index Allied Capacitors ... ...... .... ..... 97 Altronics .. .... .. .... ........ .. .. 54-5 7 Anabelle Bits ...... ... ...... ........ 99 Arista Electronics .. .. .. .... ...... . 36 Avtek .... .. .... ... .... .. .. .. .......... 37 Dauner Electronics .. .. .. .. ..... . 43 David Reid Electronics .... .... .. 45 Dick Smith Electronics .. .. . 12, 13 64,65 ,98 Elmeasco .. .. .... .. .. .... .. ........ IFC Geoff Wood Electronics ... ... .. 21 Jaycar Electronics .... .. .. .. 26-29 74-77 J.V. Tuners .. .............. ......... 43 Kenwood Australia .. .... ... .. .. .. 81 Philips Components .... .. ..... . IBC RCS Radio .... ..... ...... .. .. ....... 81 Rod Irving Electronics .. .. .. ..... 85 Scan Audio .. .. ...... ...... .. .. ..... 97 Tecnico Electronics .. .... ..... .. 96 Temple Smith Aust. .. .... .. ... OBC PC Boards 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, Welshpool, WA 6106. Phone (09) 350 5555 . • Marday Services, 2139 Great North Rd , Avondale , Auckland , NZ. Phone 88 5730 . Notice to Subscribers Are you about to change your address? Please advise us by the middle of the month to ensure that your next issue arrives at your new address. It helps us if you can send your old address label too. If you have any query about your subscription call us or write to us at: SILICON CHIP' PO Box 139 , Collaroy Beach , NSW 2097 . Yes Yes Yes Yes Yes Yes Yes Yes 'Y( Yes !s Yes Yes Yes Yes Ve'" In today's competitive p roduction w o rld, engineers need to have supply at their finger tips . The " just in time management " philosophy is proving to be a commercial reality. Philips are prep ared. When you call your component supplier you need some p ositive answers. Philips Components promises to deliver more yes's to yo ur questions because they are leaders in: • Quality • Product Range and Stock availability Not just platitudes but a strong commercial reality as a result of massive research investment , modern systems for efficient productio n and stock control and that absolutely vital element. .. top calibre, friendl y people. Apart from being the largest supplier of electronic components in the world , Philips aim to be the friendliest. If you h ave a problem right now call the Philips "Componentline " and hean hat magic phrase ... "Yes,we can do it " . Sydney 43 9 3322 Melbo urne 2 35 36 77 Adelaide 243 0155 Perth 277 4 199 Brisbane 844 01 9 1. United Notions 817 PHILIPS