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REMOTE CONTROLLER FOR GARAGE DOORS $4.50 DECEMBER 1993 NZ $5.95 INCL GST PRINT POST APPROVED – PP255003/01272 SERVICING – VINTAGE RADIO – COMPUTERS – AMATEUR RADIO – PROJECTS TO BUILD SOUND BLASTER LED STROBOSCOPE WITH DIGITAL READ-OUT ELECTRONIC ENGINE MANAGEMENT: CHANGING THE SOFTWARE BUILD A MELODY GENERATOR 16-BIT CD-QUALITY STEREO SOUND FOR YOUR PC BUILD THIS: 25-WATT AUDIO AMPLIFIER MODULE Vol.6, No.12; December 1993 FEATURES FEATURES FIT YOUR GARAGE door with remote control by building this up-to-date circuit. It features a UHF keyring transmitter & a receiver that’s built around a pre-aligned front-end module. Turn to page 16.   4 Sound Blaster Grows Up by Darren Yates 16-bit CD-quality stereo sound card reviewed   8 Electronic Engine Management, Pt.3 by Julian Edgar Changing the engine management software 40 The LM1875 Audio Amplifier IC by Darren Yates Features in-built thermal & short circuit protection 53 Programming The 68HC705C8 Microcontroller by Barry Rozema Lesson 3: answers to exercises & the direct addressing mode 90 Index To Volume 6, Jan–Dec. 1993 All the year’s features & projects PROJECTS PROJECTS TO TO BUILD BUILD WANT TO MEASURE the speed of rotating machinery. This stroboscope uses high-intensity LEDs as its light source & gives a digital readout of the speed in RPM – see page 22. 16 Remote Controller For Garage Doors by Branco Justic It’s easy to build & there are no alignment hassles 22 Build A Low-Voltage LED Stroboscope by Darren Yates A digital readout shows the speed in RPM 32 A Low-Cost 25W Amplifier Module by Darren Yates Compact module is based on a single IC 62 Peripherals For The Southern Cross Computer by Peter Crowcroft An 8x8 LED matrix display & an EPROM emulator 80 Build A 1-Chip Melody Generator by Bernie Gilchrist Choose from six different melodies or a medley of tunes SPECIAL SPECIAL COLUMNS COLUMNS 42 Remote Control by Bob Young Servicing your R/C transmitter BASED ON A SINGLE IC, this compact audio amplifier module can deliver 25W RMS into an 8Ω load & can be powered from single or dual supply rails. Construction starts on page 32. 56 Serviceman’s Log by the TV Serviceman Whingeing Willie & the bouncing TV set 70 Vintage Radio by John Hill My no-hassles radio museum 84 Amateur Radio by Garry Cratt, VK2YBX A look at selective tone calling DEPARTMENTS DEPARTMENTS   2 36 82 86 Publisher’s Letter Circuit Notebook Back Issues Order Form 87 92 95 96 Product Showcase Ask Silicon Chip Market Centre Advertising Index ONE OF THE BEST ways of modifying an electronic engine management system is to change the software. This month, we take a look at the practicalities of chip re-writing – see page 8. December 1993  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Marketing Manager Sharon Lightner Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 1a/77-79 Bassett Street, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER The future of private motor vehicles As I write this editorial, it is only a few days to the running of the 1993 World Solar Challenge race from Darwin to Adelaide. It remains to be seen whether the race sets records for speeds and race duration but is sure to be another step in the development of solar and electric vehicle technology. Ultimately though, the major spur for all this present research and develop­ment is the mandating of “zero emissions” vehicles for California in the very near future. If it wasn’t for the urgency created by the Californian legislators, no doubt there would be little development in this field at all. As it is, if a major car developer wins the Darwin to Adelaide race, they will be seen as the leaders in electric vehicle technology and will be poised to take the spoils in the Californian market. This might lead you to think that if it wasn’t for the artificial situation created in California there would be no reason to develop cars with lower or zero emissions. That would be a short-sighted view because air pollution continues to be a problem in large cities and our supplies of fossil fuels will continue to be depleted. So there needs to be a strong incentive for electric vehicles to be developed. On the hand, I do not believe that some time in next cen­tury we will suddenly “run out of energy sources”. It is true that fossil fuels will continue to be used up but I have enormous faith in the ability of man to solve any energy shortages. In fact, there is a word we use to describe that ability – “re­sourceful”. Part of man’s resourcefulness is his ability to extrapolate into the future and foresee problems before they become insurmountable. So whatever happens, it is highly likely that we will still be driving our private motor vehicles well into the next century although they may not be petrol powered; they will probably be electric and they may well draw most of their energy directly from the sun. After all, solar powered planes have already flown, so why can’t solar powered cars be a reality at some time in the future? Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. 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. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip LED BRAKE LIGHT INDICATOR This “brilliant” brake light indicator employs 60 high intensity LEDs (550-1000mCd) to produce a display that is highly visible, even in bright sunlight. The intensity produced is equal to or better than the LED brake indicators which are now included in some late model “upmarket” vehicles. The LED displays used in most of these cars simply make all the LEDs turn on every time the brakes are applied. The circuit used in this unit can perform in this manner and, for non-automotive applications, it can be customised to produce a number of sweeps (110) starting at the centre of the display and with a variable sweep rate. It not only looks spectacular but also attracts more attention. All the necessary “electronics” is assempled on two identical PCBs and the resulting overall length of the twin bargraph dis­play is 460mm. It’s simple to install into a car since only two connections are required: Earth and the brake­ LASER SCANNER ASSEMBLIES These are complete laser scanners as used in laser printers. Include IR laser diode optics and a very useful polygon scanner ( motor-mirror). Produces a “fan” of light (approx. 30 deg) in one plane from any laser beam. We provide information on polygon scanner only. Clearance: $60 400 x 128 LCD DISPLAY MODULE – HITACHI These are silver grey Hitachi LM215XB dot matrix displays. They are installed in an attractive housing and a connector is provided. Data for the display is provided. BRAND NEW units at a low: $40 LASER OPTICS The collimating lens set is used to improve the beam (focus) divergence. The 1/4-wave plate and the beam splitter are used in holography and experimentation. All are priced at a fraction of their real value: 1/4 wave plate (633nM) ..............................$20 Collimating lens sets ..................................$45 Polarizing cube beam splitters ....................$65 GREEN LASER TUBES We have a limited supply of some 0.5mW GREEN ( 560nm) HeNe laser tubes. Because of the relative response of the human eye, these appear as bright as about a 2mW red tube: Very bright. We will supply this tube and a suitable 12V laser power supply kit for a low: $299 CCD ELEMENT BRAND NEW high sensitivity monolythic single line 2048 element image sensors as used in fax machines, optical charachter recognition and other high resolution imaging applications: Fairchild CCD122. Have usable response in the visible and IR spectrum. Supplied with 21 pages of data and a typical application circuit. $30 INFRARED TUBE AND SUPPLY These are the key components needed for making an INFRARED NIGHT VIEWER. The tubes will convert infrared light into visible light on the phosphor screen. These are prefocussed tubes similar to type 6929. They do not require a focus voltage. Very small: 34mm diameter, 68mm long. All that is needed to make the tube light connecting wire. The case for the prototype unit which would be suitable for mounting on the rear parcel shelf, was mainly made from two aluminium “L” brackets that were screwed together to make a “U” section. A metal rod and its matching holders (commonly available from hardware shops) are used for the supporting leg. $60 for both the PCBs, all the onboard components & instruc­tions: the 60 LEDs are included! We also have available a similar kit that does not have the sweeping feature. It produces similar results to the commercial units installed in cars: all the LEDs light up when power is applied. $40 for both the PCBs and all the onboard components. This kit is also supplied with the 60 LEDs and it uses different PCBs, that have identical dimensions to the ones supplied in the above­ mentioned kit. operational is a low current EHT power supply, which we provide ready made or in kit form: powered by a 9V battery and typically draws 20mA. INCREDIBLE PRICING: $90 For the image converter tube and an EHT power supply kit! All that is needed to make a complete IR night viewer is a lens an eyeiece and a case: See EA May and Sept. 1990. ALUMINIUM TORCHES – INFRARED LIGHTS These are high quality heavy-duty black anodised aluminium torches that are powered by four “D” cells. Their focussing is adjustable from a spot to a flood. They are water resistant and shock proof. Powered by a krypton bulb – spare bulb included in cap. $42 Note that we have available a very high quality INFRARED FILTER and a RUBBER lens cover that would convert this torch to a good source of IR: $15 extra for the pair. PASSIVE NIGHT VIEWER BARGAIN This kit is based on an BRAND NEW passive night vision scope, which is completely assembled and has an EHT coaxial cable connected. This assembly employs a high gain passive tube which is made in Russia. It has a very high luminous gain and the resultant viewer will produce useful pictures in sub-moonlight illumination. The viewer can also be assisted with infrared illumination in more difficult situations. It needs an EHT power supply to make it functional and we supply a suitable supply and its casing in kit form. This would probably represent the best value passive night viewer that we ever offered! BECAUSE OF A SPECIAL PURCHASE OF THE RUSSIAN-MADE SCOPES, WE HAVE REDUCED THE PRICE OF THIS PREVIOUSLY ADVERTISED ITEM FROM $550 TO A RIDICULOUS: $399 This combination will be soon published as a project in EA. NOTE THE REDUCED PRICE: LIMITED SUPPLY. Previous purchasers of the above kit please contact us. 24VDC TO MAINS VOLTAGE INVERTERS In the form of UNINTERRUPTABLE POWER SUPPLIES (UPS’s).These units contain a 300W, 24V DC to 240V 50Hz mains inverter. Can be used in solar power systems etc. or for their original intended purpose as UPS’s. THESE ARE VERY COMPACT, HIGH QUALITY UPS’s. They feature a 300W - 450W (50Hz) SINEWAVE INVERTER. The inverter is powered by two series 12V 6.5Ahr (24V). batteries that are built into the unit. There is only one catch: because these NEW units have been in storage for a while, we can not guarantee the two batteries for any period of time but we will guarantee that the batteries will perform in the UPS’s when these are supplied. We will provide a 3-month warranty on the UPS’s but not the batteries. A circuit will also be provided. PRICED AT A FRACTION OF THEIR REAL VALUE: BE QUICK! LIMITED STOCK! $239 ATTENTION ALL MOTOROLA MICROPROCESSOR PROGRAMMERS We have advanced information about two new STATE OF THE ART microprocessors to be released by Motorola: 68C705K1 and 68HC705J1. The chips are fully functional micros containing EPROM/OTPROM and RAM. Some of the features of these new LOW COST chips include: *16 pin DIL for the 68HC705K1 chip * 20 pin DIL for the 68HC705J1 chip * 10 fully programmable bi-directional I/O lines * EPROM and RAM on chip * Fully static operation with over 4MHz operating speed. These two chips should become very popular. We have put together a SPECIAL PACKAGE that includes a number of components that enable “playing” with the abovementioned new chips, and also some of the older chips. IN THIS PACKAGE YOU WILL GET: * One very large (330 x 220mm) PCB for the Computer/Trainer published in EA Sept. 93; one 16x2 LCD character display to suit; and one adaptor PCB to suit the 68HC705C8. * One small adaptor PCB that mates the programmer in EA Mar. 93 to the “J” chip, plus circuit. * One standalone programmer PCB for programming the “K” chip plus the circuit and a special transformer to suit. THE ABOVE PACKAGE IS ON SPECIAL AT A RIDICULOUS PRICE OF: $99 Note that the four PCBs supplied are all silk screened and solder masked, and have plated through holes. Their value alone would be in excess of $200! A demonstration disc for the COMPUTER/TRAINER is available for $10. No additional software is currently available. Previous purchasers of the COMPUTER/ TRAINER PCB can get a special credit towards the purchase of the rest of the above package. PLASMA BALL KIT This kit will produce a fascinating colourful changing high voltage discharge in a standard domestic light bulb. The EHT circuit is powered from a 12V supply and draws a low 0.7A. We provide a solder masked and screened PCB, all the onboard components (flyback transformer included), and the instructions at a SPECIAL introductory price of: $ 25 We do not supply the standard light bulb or any casing. The prototype supply was housed in a large coffee jar, with the lamp mounted on the lid – a very attractive low-cost housing! Diagrams included. LASER DIODE KIT – 5mW/670nm Our best visible laser diode kit ever! This one is supplied with a 5mW 670nm diode and the lens, already mounted in a small brass assembly, which has the three connecting wires attached. The lens used is the most efficient we have seen and its focus can be adjusted. We also provide a PCB and all on-board components for a driver kit that features Automatic Power Control (APC). Head has a diameter of 11mm and is 22mm long, APC driver PCB is 20 X 23mm, 4.5-12V operation at approx 80mA. $85 PRECISION STEPPER MOTORS This precision 4-wire Japanese stepper motor has 1.8 degree steps – that is 200 steps per revolution! 56mm diameter, 40mm high, drive shaft has a diameter of 6mm and is 20mm long, 7.2V 0.6A DC. We have a good but LIMITED supply of these brand new motors: $20 HIGH INTENSITY LEDs Narrow angle 5mm red LED’s in a clear housing. Have a luminous power output of 550-1000mCd <at> 20mA. That’s about 1000 times brighter than normal red LED’s. Similar in brightness SPECIAL REDUCED PRICE: 50c Ea or 10 for $4, or 100 for $30. IR VIEWER “TANK SET” ON SPECIAL is a set of components that can be used to make a complete first generation infrared night viewer. These matching lenses, tubes and eyepieces were removed from working tank viewers, and we also supply a suitable EHT power supply for the particular tube supplied. The power supply may be ready made or in kit form: basic instructions provided. The resultant viewer requires IR illumination. $180 We can also supply the complete monocular “Tank Viewer” for the same price, or a binocular viewer for $280: Ring. MINI EL-CHEAPO LASER A very small kit inverter that employs a switchmode power supply: Very efficient! Will power a 1mW tube from a 12V battery whilst consuming about 600 mA! Excellent for high-brightness laser sights, laser pointers, etc. Comes with a compact 1mW laser tube with a maximum dimension of 25mm diameter and an overall length of 150mm. The power supply will have overall dimensions of 40 x 40 x 140mm, making for a very compact combination. $59 For a used 1mW tube plus the kit inverter. OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 MAJOR CARDS ACCEPTED WITH PHONE & FAX ORDERS P & P FOR MOST MIXED ORDERS AUSTRALIA: $6; NZ (Air Mail): $10 December 1993  3 Sound Blaster Grows Up! The days of Sound Blaster cards being synonymous with games cards are numbered. The new Sound Blaster 16 ASP is a CD-quality 16-bit stereo sound card for use with audio sampling as well as multi-media presentations. By DARREN YATES 4  Silicon Chip This screen graphic shows Creative WaveStudio displaying the amplitude envelope of the Windows sound file CHIMES.WAV. When the PLAY icon is selected, the sound file is played through with a marker indicating the current position. I F YOU’VE BEEN around kids of late who have grown up with the PC rather than those silly little games machines, they’ll tell you that a game isn’t a game unless you have a Sound Blaster card. And they’re right too! Unless you have some pretty fancy software, the PC speaker doesn’t lend itself to realistic sound reproduction and you can be surprised how much a sound card can add to the enjoyment of a game. (Not that we do that here, boss!) However, the idea of sampling or recording audio input onto the PC is one which is likely to arouse the interest of many readers. The problem with the original Sound Blaster card was that it was only an 8-bit system. The quality of sound produced digitally is proportional to the number of bits used – in fact, the usual rule is 6dB of dynamic range for each bit. Thus, an 8-bit card would give you a range of 48dB, which is on a par with an standard cassette deck; ie, pretty poor. Now that digital signal processing has become a viable reality, the people at Creative Labs Inc in the USA have finally come up with a 16-bit CD-quality sound card nicely wrapped with bundled software in a packag priced at only $399. We recently obtained a copy of this latest addition to the Sound Blaster audio range from Dick Smith Electronics, who carry a wide range of the Sound Blaster products. Opening the box After clawing our way through the packaging, we were almost overcome with cards and books and discs and even a nicely-built microphone popped out. Seriously though, the 16-bit ASP system is jammed-packed with features which we’ll outline in a moment. The first thing we did was to install the card into one of our 386DX 40MHz machines and load in the first of the five discs that come with the package. Having looked through the directory of the disc, we found INSTALL.EXE and confidently marched forth. All of the input & mixing levels are controlled by software through the Mixer control window. Individual controls for inputs include microphone, MIDI, CD & line levels. The bass & treble levels for each channel can be changed either together or separately using the mouse. December 1993  5 When recording a track using SoundO’le, this is the screen you will see. The level display indicates the current signal level & the timer displays the current recording time as well as the total time of the recorded file. The JukeBox program allows you select any number of stored MIDI files & play them through the SoundBlaster voice generator chip. You can pause at any time, as well as skip any selection. The installation program was simple to use and is automatic, just asking for the drive where the Sound Blaster files are to be stored (only because we were running two hard drives) and for the location of Windows. Now before those of you who dislike Windows dismiss the 16-ASP as a waste of time, the software also gives you the option of running either from the DOS prompt or Windows – pretty good, huh? It also automatically checks and selects the I/O addresses for the internal card. User manuals Note that we haven’t mentioned anything about user manuals at this stage. It’s not because there aren’t any – there are! It’s just that whenever you get a new toy to play with, who reads the manuals beforehand? But having push­­ed our luck getting this far, common sense suggested that we were heading for a fall if we went any This is the main setup window for the Talking Scheduler program. This is a multimedia program which allows you to incor­porate text-tospeech and voice annotation to your appointments. The speech & pitch controls allow you to change the tone of the artificially generated voice. 6  Silicon Chip further without consulting the manual. Because of the mountains of software included, there are six manuals that explain it but amongst it all was a nice, lit­tle, thin one entitled, in big letters, “Getting Started”. It was only about 30-odd pages – you little beauty! As it turned out, we had already sailed through the first eight pages and we were moving along comfortably. The software in­stallation is set up so that if you have an ordinary system with just a serial card, video card and printer card, there’s nothing you have to do to the 16-ASP card before you install it. If you have other cards in your machine, you may have to change some of the jumper settings on the ASP-16 card but the manual explains all of this so there’s little chance of striking problems. Sound Blaster Software To explain all the features, it’s easiest to go through the ASP-16 in terms of the software. The main Sound Blaster software comes on the first two discs, with the other three for the textto-speech, PC Animate and Inter­Active multimedia software. As already noted, Sound Blaster comes with DOS and Windows versions. The Windows version is the easiest to run (but is slower to get going), so we will go through this first (Windows 3.1 preferred). When you boot up Windows, you’ll find that it has created its own menu group and each program has its own icon. Now if you want to use it just to play games (what a waste!), we can tell you that there’s nothing left to do. You can just load in your game and the installed driver which is automatically loaded when you boot up will take care of the rest – there’s no need to get into Windows or type anything else! Having booted up in Windows, the first thing you’ll prob­ably want to do is try out the audio recording and see how good it is – and we can tell you it is excellent. The card employs a 16bit 90dB CODEC (coder-decoder) chip which is used in DAT recorders and allows sampling of CD-quality 16-bit sound at up to 44.1kHz. It also has two built-in audio amplifiers which can be set to either power external speakers or headphones. The Windows Sound Blaster Icon group includes six sections which are; WaveStudio, SoundO’le, JukeBox, Scheduler, SB16 Mixer and Mosaic. Both WaveStudio and SoundO’le allow you to record audio signals but it is SoundO’le which gives you the most options. Double-clicking on the SoundO’le icon brings up the recording session mode but before you hit the record button, there are two things to check: the recording options and the mixer options. There are a wide number of choices available for recording parameters. These include mono or stereo input, 8 or 16-bit sampling size and sampling rates of 11, 22 or 44.1kHz. You can also include echoes and reverb, as well as change the amplitude and speed of the recording. However, its biggest advantage over a number of other software packages, including Microsoft’s Sound for Windows which we reviewed several months ago, is that you can continu- ously record and dump the sound file straight to your hard disc. For example, say you have an empty 120Mb hard drive. This allows you 12 minutes of continuous stereo audio sampled at 44.1kHz/16-bits. program, you can then use the simple read command and get the computer to actually say what ever is entered as an ASCII text file, or is typed in inside inverted commas. Curiosity definitely got the better of me with this novel piece of software. I started off by just typing a few well chosen words and within a second or so, back they came! Next, I tried a text file – in fact, this very article – and again back it came. Although it is artificially generated speech using selected “mouth sounds” or phonemes, it was fairly easy to hear and under­stand. In some cases though, words were spelt out rather than spoken and this probably occurs when a word is not part of a given vocabulary or SB­TALKER doesn’t know how to pronounce it. However, this is an area of computing which will take off in years to come when more efficient and faster algorithms can be written to make speech sound more lifelike than at present. One thing worth noting is that this software has been patented which shows you that it’s an idea that isn’t quite as old as you may think. Overall, the ASP-16 is the most advanced sound card I’ve seen so far for such a reasonable price and with 16-bit CD-quality sound, you can look forward to seeing and hearing some of the best games available. The SoundBlaster ASP-16 sound system is available from Dick Smith Electronics and also from Rod Irving SC Electronics. Multimedia applications This ability to record direct to the hard disc makes it extremely useful in multimedia applications. Multimedia is the process whereby both sound and vision are used in a presentation for greater impact. Included with the bundled software is a copy of HSC Interactive, a Windows-based program which allows you to link sound files with bitmap images as well as animated vision. The 113-page manual is a little long to go through here but nevertheless, it allows you to take control of your PC and create a presentation from the ground up. The program allows you to control when sound is played and allows for interactive usage via either keyboard or mouse. Animation is created through a program called PC Animate Plus which allows you to draw and paint individual frames, then cut and paste these frames together. You can view these frames as you go and generate special effects such as smooth fades. And, of course, you can add in sound. Test to speech translation Finally, one of the more unusual programs which utilises the Sound­ Blaster card is the SBTALKER text-tospeech translator. Once you install the Silicon Supply and Manufacturing 74HC11 $0.45 74HC27 .40 74HC30 .40 74HC76 .55 74HC86 .45 74HC138 .85 74HC139 .50 74HC154 3.15 74HC165 .85 74HC174 .65 74HC373 1.05 74F00 74F02 74F08 74F10 74F11 74F20 74F21 74F27 74F30 74F32 74F36 .40 .40 .40 .40 .40 .40 .40 .40 .40 .40 .85 74F38 74F151 74F163 74F169 74F175 74F241 74F244 74F257 74F258 74F353 74LS00 .65 .55 .70 1.92 .65 .95 .90 .60 1.80 1.45 .50 74LS01 74LS02 74LS03 74LS05 74LS11 74LS12 74LS13 74LS14 74LS20 74LS21 74LS27 MAIL ORDER SPECIALIST .50 .50 .45 .45 .50 .50 .85 .55 .55 .40 .40 74LS30 74LS33 74LS49 74LS73 74LS74 74LS83 74LS85 74LS90 74LS92 74LS109 74LS126 .40 .50 2.35 1.10 .45 .75 .60 .90 1.20 .90 .50 PO Box 92 Bexley North NSW Australia 2207 74LS138 74LS139 74LS147 74LS148 74LS151 74LS155 74LS158 74LS160 74LS164 74LS175 74LS191 Credit Cards welcome -Visa, Mastercard, Bankcard. Plus Sales Tax, packing and postage .60 .60 2.35 1.05 .50 .50 .70 .75 .75 .80 .80 74LS193 74LS196 74LS240 74LS241 74LS245 74LS257 74LS273 74LS366 74LS368 74LS373 74LS374 .80 1.35 .90 .95 .80 .60 .80 .55 .60 .80 .85 Ph.: (02) 554 3114 Fax: (02) 554 9374 After hours only bulletin board on (02) 554 3114 (Ringback). Let the modem ring twice, hang-up, redial the BBS number, modem answers on second call. December 1993  7 Electronic Engine Management Pt.3: Chip Re-Writing – by Julian Edgar One of the best ways of modifying an electronic engine management system is to change the software. If different fuel and ignition maps are programmed into the main memory chip, then different output data will be selected by the ECM in response to the various sensor inputs. The beauty of modifying the ECM in this manner is that there are no physical changes made to the system. The original wiring harness, input sensors, injectors, ignition system and so on can be left unchanged. Also, the outputs from the ECM not directly related to engine performance – like transmission, air-conditioning and cooling fan control – can be left untouched. One of the difficulties in chip rewriting is that the knowledge required to get into the software and make any changes is held by a select few. Secondly, major engine modifications may Intended for a BMW, this Bosch Motronic electronic control module (ECM) features a reprogrammed main memory chip from Fueltronics. 8  Silicon Chip not be easily met by software changes alone. Changing the chip Chip rewriting is currently big business, with basically two different approaches being taken. The first approach is to sell chips on the basis that a change of chip alone will yield useful performance gains. This implies that the original program was not fully optimised in the first place, otherwise how could useful gains be made in a chip produced in the aftermarket scene? In naturally aspirated (non-turbo) cars, a chip-change alone will yield only a marginal power improvement – in the region of 5-10%. As a guide, a performance increase on the road from a chip-change might knock 0.2 seconds from a 0-100km/h time, dropping this time from perhaps 9.8 to 9.6 seconds. This perfor­mance gain generally comes from running a more aggressive (ad­ vanced) timing map, with steeper ramp angles. Extra fuel is injected to match the new timing (a factor that could lead to an increase in fuel consumption). In turbocharged cars, the situation is a little different. With many cars running ECM-controlled turbo boost pressures, the chip-change might also include a lift in boost pressure. The greater gas flows which result from this will give a more sub­stantial power gain – often as much as 20% in round figures. The ignition and fuel maps are also changed to give the correct ignition timing and fuel mixtures to go with the increase in boost pressure. In both naturally inducted and turbo cars, a lift in the rev limiter can also be included in the new software. The rev limiter built into the engine management systems of cars is designed to prevent over-revving, which is potentially very damag­ing to the engine. With the pistons having to be accelerated to full speed, stopped, and then accelerated again in the opposite direction every time the crankshaft turns, the strain on engine parts such as the con-rods is very great. Increasing the engine revs dramatically increases the loads placed on engine components, bringing them closer to the point of failure. Too high an RPM will cause breakage, with perhaps the piston exiting the side of the block or trying to come through the head! However, an engine which is still developing usable torque high in the rev range will yield more power if the engine can rev higher. This is because of the equation: Power (kW) = Torque (Nm) x RPM/9550. In some engines, the manufacturer has been conservative in the rev limit imposed, mostly to improve engine longevity. If a potentially shorter working life is tolerable, then the rev limit can be raised with a power improve- When mechanical limitations, such as fuel injector size, prevent effective software changes, higher capacity components need to be fitted to the engine. The results can be worthwhile, as illustrated in Fig.3. ment. Increasing the rev limit is an engine-to-engine proposition, though. Other engine modifications Much greater power (and potentially economy) gains can be gained if major engine modifications are performed and the ECM software then changed to suit. In other words – as has always been the case – airflow into and out of the engine can be im­­­­­-proved, thus giving potentially more power when mixed with the appropriate amounts of fuel. All of the traditional “hotting-up” methods can be used: free-flow exhausts and mufflers, better air filters, bigger valves, porting the head, different camshafts and so on. Once these mechanical changes have been made, the car can then be “driven” on a chassis dynamometer, with exhaust gas analysis being used to constantly monitor the mixture under different loads. The areas then requiring modification can be ascertained and the ECM software appropriately rewritten. The Power at wheels (kW) SUZUKI SWIFT GTi 1300 RPM Fig.1: this chassis dynamometer graph shows the effect of replacing the ECM chip in a Suzuki Swift GTi 1300 fitted with a DOHC 16-valve engine. No other engine modifications were made. December 1993  9 Power at wheels (kW) NISSAN PULSAR GTI RPM Fig.2: the effect of chip replacement in a Nissan Pulsar GTi 1800 (DOHC 16-valve engine), fitted with a free-flow exhaust system. Power at wheels (bhp) DAIHATSU CHARADE 1.3CRi Road Speed (mph) Fig.3: the effect of chip replacement in a 1992 Daihatsu Charade CRi 1300, fitted with larger fuel injectors. car should then be rechecked in its final form. If done with appropriate expertise, the car should also remain quite legal in terms of its emissions. Sometimes, however, a hardware change will be needed in addition to the software modifications. This could come about, for example, when the engine power has been greatly increased. The original fuel injectors may simply not be able to pass enough fuel, even if held open for long duty cycles. In this case, the original injectors 10  Silicon Chip would then be replaced with larger units and the software reprogrammed to provide short­er pulse widths at all but the highest load situations. With an all-out race engine, the standard ECM may not be adequate and would then be replaced with a fully programmable computer. Chip switches Another approach is to use more than one new software pro­ g ram, with the change over between different programs being ef­fected by a dash-mounted switch. For example, in a turbocharged car, one switch position could give a high boost and rich top-end mixture for maximum power, while another switch position could be for the standard software program. Yet another position could be for lowboost, lean-mixture economy running, while the final switch position could have a blank program. The blank program would be in place as a security measure, to make it more diffi­cult to steal the car! Other alternative switch position Power & torque outputs should be measured on a chassis dynamometer to assess the results of any software or hardware changes. Changing the ECM chip alone will lead to only a marginal improvement in a naturally aspirated car. programs can include a “valet” (or son and daughter) mode, where the rev limiter is reduced to perhaps 4000RPM. Some manufacturers (notably in the United States) have fitted valet switches as standard to their powerful V8-engined sports cars. Rewriting original-equipment car ECM memory chips requires appropriate computer programming expertise, good mechanical understanding, and access to sophisticated equipment such as exhaust gas analysers and chassis dynamometers. The car manufacturers also make it very difficult to gain entry to their software, with encryp­tion codes and other security measures employed. “Breaking in” can take months. There are a few companies in Australia that are modifying car ECM software for specific applications, and a much greater number selling general “hot-up” chips. Many of these chips origi­nate overseas and are being sold by retail outlets with little understanding as to what has actually been done to the program. Chips that aren’t so hot There have also been some interesting tales circulated of “hot” chips which actually retard timing and fuel compared to the standard chip, until the last few hundred RPM where they revert to the original manufacturer’s specifications. The cars drive poorly until the end of the rev range, at which point they appear to go like hell! If you choose to swap the ECM chip alone, then carry out performance and/or chassis dynamometer tests before and after chip fitment – and try to get a money-back SC guarantee. Acknowledgement: thanks to Fuel­tronics (16 Payne­ ham Rd, Stepney, SA 5069 – phone 08 363 2199) for provid­ing some of the information used in this article. December 1993  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Remote controller for garage doors The circuit presented here has all the required elec­tronics for a garage door opener or other motorised device. It features a 304MHz UHF remote control transmitter, the receiver & decoding circuitry, door logic & motor switching relays. Design by BRANCO JUSTIC We last featured a remote controller for garage doors in the March and April 1991 issues of SILICON CHIP. This new project updates that design with completely new circuitry and the main PC board has fewer components on it too. The main features of the circuit are provision for upper and lower limit door travel switches and over-current sensing for UP and DOWN modes of 16  Silicon Chip operation. This latter feature can be used to detect obstructions and immediately stop door operation to prevent damage to the motor, drive mech­anism or possibly even your car. The unit is based on a pre-built (and pre-aligned) UHF receiver module and features a small keyring transmitter that has more than half a million possi­ble codes – 531,441 to be precise. You press the button on the transmitter and the door goes up; press it again and the door goes down – no more getting out of the car to open the garage door! The circuit has provision for a manual switch which can be mounted somewhere on the wall inside the garage. This works in a similar way to the button on the transmitter: press it once for the door to go up and press it again to make the door go down. If you press the button before the door reaches the end of its travel, it will stop. You then have to press the button again to make the door go in the opposite direction. This applies also to operation via the transmitter. Rather than re-invent the wheel, both the transmitter and the pre-built receiver front-end are the same as used in the UHF Remote Switch project that was featured in the December 1992 issue of SILICON CHIP. The front-end D1 1N4148 18 S1 HIGH LOW A LED1 λ K 12V R4 82 Ω 1 2 3 4 5 6 7 8 10 11 12 13 L1 ETCHED ON BOARD C1 .001 A1 A2 R2 6.8k 17 C B E R3 1k A3 C2 .001 A4 C4 6.8pF C3 2-7pF 304MHz SAW FILTER C5 4.7pF Q1 2SC3355 R5 150 Ω A5 A6 IC1 AX5026 A7 A A8 K A9 15 A10 C E B VIEWED FROM BELOW 16 R1 1M A11 A12 UHF REMOTE CONTROL TRANSMITTER 9 14 Fig.1: the transmitter is based on trinary encoder IC1. When S1 is pressed, IC1 generates a series of pulses at its pin 17 output to switch transistor Q1 on & off. This transistor is wired as an oscillator & operates at 304MHz due to its tuned collector load & the SAW filter in the feedback path. module of the receiver comes prealigned (to 304MHz) and uses surface mount components to give an assembly that measures just 35 x 25mm. It is fitted with a pin connector along one edge and plugs into the receiver PC board just like any other component. This eliminates alignment hassles and means that you don’t have to wind any tricky coils. How it works – transmitter The transmitter is based on an AX5026 trinary encoder IC – see Fig.1. When pushbutton switch S1 is press­ ed, this IC gener­ ates a sequence of pulses at its output (pin 17). The rate at which these pulses are generated is set by the 1MΩ timing resis­tor between pins 15 and 16 (R1), while the code sequence is set by the connections to the address lines (A1-A12). Each of these address lines can be tied high, tied low or left open circuit (O/C), giving 531,441 possible codes. The pulse coded output from IC1 drives RF transistor Q1. This transistor is connected as an oscillator and operates at 304MHz, as set by a tank circuit consisting of L1 (etched on the PC board), C3, C4 and C5. In addition, a SAW (surface acoustic wave) resonator is used to provide a narrow-band feedback path. Its lowest impedance is at its resonant frequency of 304MHz and thus the tuned collector load must be set to this frequency in order for Q1 to oscillate. The SAW resonator ensures frequency stability and makes the transmitter easy to align. It ensures that the oscillator will only start and pulse LED 1 when the tuned circuit is virtually dead on frequency. C3 is used to adjust the centre frequency of the tuned circuit. This point corresponds to maximum current consumption and is found by adjusting C3 to obtain peak brightness from the indicator LED (LED 1). Power for the transmitter is derived from a miniature 12V battery (GP23 or equivalent) and this is connected in series with the pushbutton switch (S1). When S1 is pressed, the current drawn by the circuit is only a few milliamps, the exact figure depend­ing on the code word selected at address lines A1-A12. How it works – receiver Fig.2 shows the circuit details of the receiver. Its job is to pick-up the coded RF pulses from the transmitter and decode these pulses to generate an output. As already mentioned, the receiver is based on a complete “front-end” module. This processes the received signal via a bandpass filter, an RF preamplifier, a regenerative detector, an amplifier and a Schmitt trigger. Its input is connected to a short antenna, while its output delivers a digital pulse train to the input (pin 14) of IC1. IC1 is an AX-528 Tristate decoder and is used to decode the 12-bit pulse signal that’s generated by the transmitter. As with the AX-5026 encoder, this device has 12 address lines (A1-A12) and these are connected to match the transmitter code. If the code sequence on pin 14 of IC1 matches its address lines, and the code sequence rate matches its timing (as set by R1), the valid transmission output at pin 17 switches high. This output connects via diode D1 to the December 1993  17 18  Silicon Chip +12V 0.1 2 7 RLA1 5 CODING LINES M 0. 22 5W RLB2 DOOR MOTOR 0. 22  5W RLB1 1,3,6,8,10, 11,12 RECEIVER MODULE RLA2 ANTENNA 0.1 3 14 13 12 11 10 8 7 6 5 4 10 100k 100k 10 100k 100k +12V 1 2 100k VR2 220k 180k 100k VR1 220k 180k 9 IC1 AX528 18 6 5 2 3 1M IC4b IC4a LM358 15 16 17 4 8 D1 1N914 MANUAL S1 7 10k 1 10k +8V .01 0.1 D13 1N914 +8V D12 1N914 1M LIMITS S2,S3 3.3M 10M IC3b 6 5 AC INPUT +8V D10 1N914 100k 100  5W D11 1N914 D16 D17 220k D3 1N914 13 14 10 15 D15 D14 Q3 Q1 2 1 1000 100k IC3a 8 IC2 4017 4x1N5402 10 3 ENA CLK Q4 RST 16 GARAGE DOOR CONTROLLER 4 D2 1N914 0.1 7 2 B1 12V 100k 0.1 0.1 13 1000 D18 1N4004 IC3d 100k D4 1N914 4.7k B 12 D6 1N4004 D5 1N914 +8V E 11 OUT GND 10 IC5 78L08 D8 1N914 D9 1N914 D7 1N4004 4.7k GND C IN VIEWED FROM BELOW IN B 10M Q1 BC337 10 E C RLA OUT +8V +12V 9 IC3c 4093 8 Q2 BC337 B 7 14 E C D 10 +8V GDS RLB 10  +12V LAMP G Q3 MTP3055 S D +12V PARTS LIST Transmitter 1 transmitter case 1 PC board, 30 x 37mm 1 miniature PC-mount pushbutton switch 1 12V battery, GP23 or equivalent 1 304MHz SAW resonator Semiconductors 1 AX-5026 trinary encoder (IC1) 1 2SC3355 NPN transistor (Q1) 1 1N4148 silicon diode (D1) 1 3mm red LED (LED1) Capacitors 2 .001µF ceramic 1 6.8pF ceramic 1 4.7pF ceramic 1 2-7pF miniature trimmer Resistors (0.25W, 5%) 1 1MΩ 1 150Ω 1 6.8kΩ 1 82Ω 1 1kΩ Receiver 1 PC board, 144 x 87mm ▲ clock input (pin 14) of IC2, a 4017 decade counter. This counter can also be clocked by manual switch S1 and by limit switch­ es S2 and S3. The length of the clock pulses produced by the operation of S2 and S3 is limited by the time constant of the associated 0.1µF capacitor and 3.3MΩ resistor. The .01µF capacitor filters out any noise picked up by the wires used to connect S1, S2 and S3, while the 10MΩ resistor discharges the 0.1µF capacitor after S2 or S3 has been operated. Fig.2 (left): the heart of this circuit is IC1 & IC2. IC1’s output at pin 17 goes high when a valid code is detected. Pin 17 then clocks IC2 which controls the switching of relays RLA & RLB via transistors Q1 & Q2. IC4a & IC4b provide over-current monitoring & they can clock IC2 into a STOP mode whereby the relays are not energised. IC3d, IC3c & Q3 light the lamp for about two minutes after the transmitter button is pressed. 1 front-end module (aligned to 304MHz) 2 12V DPDT relays 1 momentary contract pushbutton switch (S1) 2 microswitches (S2,S3) 1 12V SLA battery 1 12V lamp 4 2-way insulated terminal blocks 1 3-way insulated terminal block 2 100kΩ trimpots (VR1,VR2) Semiconductors 1 AX-528 tristate decoder (IC1) 1 4017 decade counter (IC2) 1 4093 quad Schmitt NAND gate (IC3) 1 LM358 dual op amp (IC4) 1 78L08 3-terminal regulator 2 BC337 NPN transistors (Q1, Q2) 1 MTP3055 Mosfet (Q3) 4 1N5404 rectifier diodes (D14-D17) 11 1N914, 1N4148 signal diodes (D1-D5,D8-D13) 3 1N4004 rectifier diodes (D6,D7,D18) Note that when the power is first applied, IC2 is reset by a short pulse on the reset line, by virtue of the 0.1µF capacitor connected to the +8V supply line. The counter is also reset when its Q4 output goes high; a pulse is applied to the reset input via diode D3. This means that IC4 can only have four exclusive output states: Q0 high, Q1 high, Q2 high or Q3 high. Outputs Q0 and Q2 do not drive anything so they correspond to “Stop” modes while outputs Q1 and Q3 switch the “Up” and “Down” relays (via transistors Q1 & Q2). Thus, a succession of clock pulses from decoder IC1 correspond to the following modes: Stop, Up, Stop, Down, Stop, Up, etc. Two separate over-current detectors, comprising op amp com­parators IC4a and IC4b, detect higher than normal motor currents that would result when the door reaches its Up or Down stop positions or if the door is obstructed. The outputs of these over-current detectors then apply a pulse to the clock input of IC2, which causes it to go into the Stop mode. Capacitors 2 1000µF 16VW PC mount electrolytic 5 10µF 16VW PC mount electrolytic 6 0.1µF monolithic 1 .01µF monolithic Resistors (0.25W, 5%) 2 10MΩ 2 10kΩ 1 3.3MΩ 2 4.7kΩ 2 1MΩ 1 100Ω 5W 3 220kΩ 1 10Ω 2 180kΩ 2 0.22Ω 5W 8 100kΩ Where to buy the parts A kit of parts for this garage door controller is avail­ able from Oatley Electronics, PO Box 89, Oatley, NSW 2223, Aus­tralia. Phone (02) 579 4985. The prices are as follows: (1) Receiver kit (PC board and all on-board com­ ponents) $79; (2) Transmitter kit (including case & battery) $19; (3) 17V AC plug­pack $18. Add $2.50 for postage & packing. The counter can be disabled from clocking by its ENA-bar input being held at “0”. The output of the mono­ stable comprising Schmitt NAND gates IC3a & IC3b is normally high, thus enabling the counter to clock. However, this monostable is triggered via isolating diodes D4 & D5 each time Q1 (up) or Q3 (down)of IC2 first go high. This monostable therefore prevents the counter from stepping for approximately two seconds after the Up or Down modes are first activated. This two-second disabling of the counter prevents it being triggered by the over-current detectors, which would otherwise happen since a motor draws relatively high cur­rents when it first starts up. Courtesy lamp driver A second monostable made up of gates IC3c & IC3d is used to switch a lamp via Mosfet Q3. This monostable is also operated via diodes D4 and D5 each time Q1 (up) or Q3 (down) of IC2 goes high. The time constant of the monostable causes the lamp to light for just under two minutes. December 1993  19 A .001 S1 D1 K 6.8k C3 6.8pF LED1 K 82  A 1k 1M Q1 4.7pF SAW 150  .001 IC1 AX5026 1 12V BATTERY Fig.3: keep all leads as short as possible when installing the parts on the transmitter PC board & take care with the orientation of the encoder IC. A combination of a 12V battery and a 17V 1A AC plugpack are used to power the controller. The 100Ω 5W resistor in series with the bridge rectifier limits the charging current to the battery. Note that the two 1000µF capacitors in the power supply are rated at 16VW but if the 12V battery is not present that voltage rating will be exceeded. A 7808 3-terminal regulator provides a +8V supply for the receiver, decoder and op amps, while the relays and motor are driven directly from the 12V battery. Note that each relay has two pairs of contacts to connect the motor across the 12V supply in one direction or the other. The system is fail-safe since only one relay can be energised at a time and when the circuit is in Stop mode, both relays are de-energised and the motor is isolated from the 12V battery. Construction Let’s discuss the transmitter first. The component layout for the PC board is shown in Fig.3. All the parts, including the battery terminals and the switch (S1), are mounted on a small PC board which fits inside a plastic transmitter case. Before mounting any of the parts, you must first file the edges of the PC board so that it will fit in the case. The receiver is based on this pre-built front-end module which comes ready aligned & tuned to 304MHz. It is soldered into place on the PC board just like any other component. 20  Silicon Chip This also removes two shorting strips. One of these strips runs along the bottom of the board, while the other runs down the righthand edge (as viewed from the copper side). Make sure that these two short­ing strips are completely filed away; if they are not, the bat­tery terminals will be shorted and the positive battery terminal will be shorted to C3. The most important thing to remember with the transmitter assembly is that all component leads should be kept as short as possible. Apart from that, it’s simply a matter of installing the parts as shown in Fig.3. Be sure to orient IC1 correctly and note that the flat side of the trimmer capacitor (C3) is adjacent to one end of the board. The SAW resonator and switch should both be mounted flat against the board, while the transistor should only stand about 1mm proud of the board. Take care when mounting the switch – it must be correctly oriented, otherwise it will appear as a short and the transmitter will be on all the time (the switch will only fit comfortably in one direction). The LED should be mounted with its top about 7mm proud of the board, so that it later protrudes about halfway through a matching hole in the lid. Be careful with the orientation of the LED – its anode lead is the longer of the two. Check the board carefully when the TO MOTOR 0.1 3.3M 100k 0.1 IC2 4017 100  5W D3 10uF 10  VR1 100k A 1 10uF 10uF 0. 22  5W IC5 10uF D7 1000uF D13 100k 180k 220k 10k 10M D8 D6 100k 180k D12 10k IC4 LM358 100k 100k 100k 4.7k 4.7k 0.1 D9 RELAY B Q2 LAMP LIMIT SWITCH Q3 S DG Q1 220k D11 IC3 4093 220k D10 0.1 1 100k A 10M 10uF 0.1 D5 0. 22  5W RELAY A D4 TP TO S1 1 .01 0.1 ANTENNA D2 1M 1M D1 IC1 AX528 RECEIVER 1 BOARD 0.1 AC POWER BATTERY D18 1000uF VR2 D14-D17 Fig.4: the front-end module is installed on the receiver PC board with its component side facing the adjacent 0.1µF capacitor. Don’t forget to install the two insulated wire links (shown dotted) on the copper side of the PC board. assembly is completed – it only takes one wrong component value to upset the circuit operation. This done, slip the board into the bottom half of the case, install the battery and test the circuit by pressing the switch button. Don’t worry if the LED doesn’t flash at this stage – that probably won’t occur because Q1 will not be oscillating. To adjust the oscillator stage, press the switch and tune C3 using a plastic tool until the LED does start to flash. When this hap­pens, the oscillator is working and you can tweak C3 for maximum transmitter output (ie, max­imum LED brightness). The lid of the case can now be snapped into position and secured using the small screw supplied. Receiver assembly Fig.4 shows the parts layout on the receiver board. Install the parts exactly as shown, leaving the receiver module till last. This module must be installed with its component side away from the AX528 decoder (IC1). Do not forget to install the link underneath IC1 or the insulated link which runs from the anode of D18 to the common­ed connection to the two relays (+12V). A second insulated link runs from the cathode of D13 to point A below the front-end module. The antenna consists of a length of insulated hook-up wire and can be either 250mm or 500mm long. The latter will give slightly greater range. When the receiver assembly is complete, check all your work carefully to see that it agrees with the wiring diagram of Fig.4. This done, apply power and use your DMM to check that pin 17 of the AX528 switches high when the transmitter button is pressed. Coding Initially, all the A1-A12 address lines will be open cir­ cuit but you can tie selected address pins high or low by con­necting them to adjacent copper tracks. In both cases, a +5V rail runs adjacent to the inside edge of the address pins, while a ground track runs around the outside edge of the address pins. For example, you might decide to tie A1 and A8 high, tie A3 and A6 low, and leave the rest open circuit. Short wire links can be used to make the connections but note that you will have to scrape away the solder mask from the supply rail at each con­nection point so that the track can be soldered. Make sure that the transmitter code matches the receiver code otherwise the remote control won’t work. Note that the over-current setting trimpots (VR1 & VR2) are set during installation of the door mechanism. Full instruc­tions on installation and typical mechanisms were featured in SC the April 1991 issue. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 2 1 3 3 2 8 2 1 2 1 1 1 1 1 2 Value 10MΩ 3.3MΩ 1MΩ 220kΩ 180kΩ 100kΩ 10kΩ 6.8kΩ 4.7kΩ 1kΩ 150Ω 100Ω 5W 82Ω 10Ω 0.22Ω 5W 4-Band Code (1%) brown black blue brown orange orange green brown brown black green brown red red yellow brown brown grey yellow brown brown black yellow brown brown black orange brown blue grey red brown yellow violet red brown brown black red brown brown green brown brown not applicable grey red black brown brown black black brown not applicable 5-Band Code (1%) brown black black green brown orange orange black yellow brown brown black black yellow brown red red black orange brown brown grey black orange brown brown black black orange brown brown black black red brown blue grey black brown brown yellow violet black brown brown brown black black brown brown brown green black black brown not applicable grey red black gold brown brown black black gold brown not applicable December 1993  21 Build this low-voltage LED stroboscope If you need to measure the speed of rotating machinery in revs per minute, try this new lowvoltage LED stroboscope. It uses pulsed highintensity LEDs as the light source to stop motion & gives a readout of the RPM on a 3-digit LED display. By DARREN YATES Have you ever had to measure the speed of rotating machin­ery? Unless your head is mounted on a 360 degree swivel axis and has an inbuilt rev counter, it’s quite a difficult job – without a stroboscope, that is! There are all sorts of situations where a stroboscope is a useful tool. Typical applications include calibrating and check­ing motor speed controllers in industry, measuring engine idle speed in model aircraft, and checking the speed of lathes and other rotating machinery. 22  Silicon Chip A stroboscope is also useful as a diagnostic tool because it can effectively slow down motion. Many machines operate at a pace that’s faster than the eye can see, so when a malfunction occurs it can be difficult to locate the source of the problem. However, by using a stroboscope that runs slightly out of sync with the machine being monitored, it’s possible to slow the motion down so that the eye can actually follow what is happen­ing. For example, newspapers coming off a printing press are automatically folded by a machine that works at high speed. Because of this, it can be very difficult to locate the exact cause of any problems, such as paper tearing. By using a strobo­scope, it’s possible for the operator to visually “slow” the machine down, locate the problem and make the necessary adjust­ments to correct the problem. The concept behind a stroboscope is easy enough to under­stand. It’s basically a device that emits a high-intensity flash of light at a set interval. The frequency of these flashes is usually adjustable by means of a potent­iometer. In this unit, the flash frequency can be set anywhere from 1Hz to 317Hz – a range that effectively covers from 6019,000 RPM. In order to measure RPM, the strobe light is pointed at a white dot or line painted on the axis of the machine. The flash frequency is then adjusted until the white dot appears to be stationary (equivalent to one flash per rev) and the speed of the machine read off the digital display directly in RPM. There’s just one point to watch out for here – the dot (or line) will also appear to be stationary if the strobe flash­es at some exact multiple or fraction of the rev rate (eg, twice per rev or once every two revs). For this reason, it’s always necessary to use the flash setting at which the line is brightest when it ap­pears stationary. Slow motion effects are made possible by adjusting the flash frequency so that it is slightly out of sync with the machine being monitored. This has the effect of making the ma­chine appear to be in slightly adjacent positions for each suc­cessive flash, even though it may have gone through several cycles between flashes. As a result, the machine appears to run in slow motion. Adjusting the stroboscope to give slow motion effects is not as difficult as it sounds. You simply aim it at the machine and rotate the pot for the desired effect. In most stroboscopes, the active flashing element is an xenon tube. But although this is capable of producing a bright light, it does require a high voltage to drive it – typically around 350V or so. This high voltage is usually derived by charg­ing up a capacitor which is then discharged via the xenon tube when it is triggered by a pulse transformer. The main drawback of this technique is that the high vol­tage required to fire the tube is dangerous. Certainly, the voltage that appears across the main discharge capacitor is potentially fatal, so due care must be exercised in the design and construction of such devices. High-brightness LEDs By contrast, this design is completely safe because there are no high voltages involved. This has been achieved by elimi­ nating the xenon tube and substituting an array of high-bright­ ness LEDs instead. The whole circuit runs off a 12V DC plugpack supply, so high-voltage mains wiring is also eliminated. The LEDs specified are 5mm red high-intensity types which are available from Altronics (Cat. Z 0149) for 50 cents each in quantities of 10 or more. They have a brightness of about 1000mCd and are arranged in a circular pattern inside a torch body. By the way, all stroboscopes work best in subdued light conditions. They can’t work in bright light because you cannot see the flashes. How it works Fig.1 shows the circuit details of the LED Stroboscope. It’s virtually identical to the Digital Voltmeter for PARTS LIST 1 PC board, code 04112931, 100 x 55mm 1 PC board, code 04112932, 100 x 55mm 1 PC board, code 04112933, 53mm diameter 1 plastic zippy case, 130 x 67 x 42mm 1 front panel label 1 torch case (see text) 1 12VDC 500mA plugpack 1 2.1mm DC socket 1 5-pin DIN plug 1 5-pin DIN socket 1 1-metre length of 3-pair telephone cable 4 10mm x 3mm tapped spacers 4 5mm untapped spacers 1 100mm length of 0.1-inch spaced ribbon cable 1 10kΩ log potentiometer (VR1) 1 1MΩ 5mm horiz. trimpot (VR2) Semiconductors 1 LM358 dual op amp (IC1) 1 4049B hex inverter (IC2) 1 MC14553 3-digit counter (IC3) 1 4511 7-segment display driver (IC4) 1 BC548 NPN transistor (Q1) 3 BC557 PNP transistors (Q2,Q4,Q6) 3 BC337 NPN transistors (Q3,Q5,Q7) 1 BD679 NPN Darlington transistor (Q8) 1 1N4004 diode (D1) 1 7809 3-terminal regulator 3 HDSP-5303 7-segment common-cathode displays 31 high-brightness LEDs (LEDs1-31) (Altronics Cat. Z-0149 or equivalent) Capacitors 1 2200µF 16VW electrolytic 2 0.1µF 63VW MKT polyester 1 .033µF 63VW MKT polyester 2 .01µF 63VW MKT polyester 2 .0033µF 63VW MKT polyester Resistors (0.25W, 1%) 1 2.7MΩ 1 3.3kΩ 2 470kΩ 3 1kΩ 4 100kΩ 1 390Ω 2 47kΩ 7 270Ω 7 10kΩ 8 47Ω 1 4.7kΩ This view shows the control module of the LED Stroboscope. It consists of two PC boards which are stacked back-to-back on 5mm spacers & secured to the lid of the case. The three LED displays are viewed through a Perspex window. Miscellaneous Solder, screws, nuts & washers December 1993  23 24  Silicon Chip 47  VR1 10k 3 IC2a 4049B +9V 2 C E VIEWED FROM BELOW B 2.7M 0.1 VR2 1M 47k 47k 100k 0V +12V 500mA PLUG-PACK 4 10k 470k .0033 IC1a LM358 I GO B Q1 BC548 IC2b E C 3 2 7809 GND .033 IN 7 10k 1 6 10k 10k E CB IC2c 0.1 OUT LED STROBOSCOPE 5 4.7k 2200 16VW D1 1N4004 A 470k .0033 100k 100k +9V +V K 8 +9V 8 10 4 IC1b IC2d 9 1 5 6 7 +9V IC2e 11 12 10 4 3 A LE 9 7 7 1 B 6 2 C IC4 4511 4 3.3k 15 D2 D1 D0 5 6 D 15 E Q8 BD679 C B 2 1 10k K A 47  15 E    47         47  10k 1k 3 47       31xRED LED 10k E c b 47  C Q4 BC557 E B d DISP1 HDSP-5303   C a g Q3 BC337 C B e f  B 10 9 1 2 10 9 6 4 7 11 Q2 BC557 7x270  12 13 f g 14 e d c b a 16 MR 13 8 IC3 MC14553 IC2f CLK LE 14 11 12 16 +9V 100k .01 .01 +9V 8 5 3      1k Q5 BC337 47  B 5 DP      E C 3 47  B Q6 BC557 DISP2 HDSP-5303 390     C E +9V 1k +V B Q7 BC337 +9V E C 3 DISP3 HDSP-5303 The VCO board (left) & the counter board (right) are joined together via a 10mm-length of 5-way rainbow cable. This allows the two boards to be “folded” together so that they can be stacked on 5mm spacers. Note how the 2200µF capacitor on the VCO board is mounted (bottom left). Cars pub­lished in the June 1993 issue, despite the fact that the two projects perform totally different functions. VCO operation ▲ Op amps IC1a and IC1b (LM358) are connected to form a vol­tage controlled oscillator (VCO). IC1a is wired as an integrator while IC1b acts as an inverting Schmitt trigger. In operation, IC1a’s output (pin 1) ramps up and down due to the presence of Schmitt trigger IC1b and transistor Q1 in its negative feedback loop. When power is first applied, IC1a’s output ramps down line­arly until it reaches the lower threshold of IC1b (about 3V). At this point, pin 7 of IC1b goes high and turns on Q1. This pulls pin 2 of IC1a low via a 4.7kΩ resistor and so the voltage on pin 1 rises as the .033µF capacitor charges in the opposite direc­tion. When it reaches the upper threshold of the Schmitt trigger (about 6V), pin 7 of IC1b switches low again and Q1 turns off. Pin 1 of IC1a Fig.1 (left): the complete circuit of the LED Stroboscope. IC1a & IC1b form a VCO, with VR1 setting the output frequency. The pulse output appears at pin 7 of IC1b & drives an array of high-brightness LEDs via Darlington transistor Q8. It also clocks pin 11 of IC3, a 3-digit counter. IC4 decodes the counter outputs &, together with IC3, drives three 7-segment LED displays to show the speed of the rotating object in RPM. now ramps down again and so the cycle continues indefinitely. As a result, a sawtooth waveform appears on pin 1 of IC1a, while a corresponding pulse waveform appears at pin 7 of IC1b. This pulse waveform has a duty cycle of about 5%, as set by the ratio of the 4.7kΩ and 100kΩ resistors on pin 2 of IC1a. Its repetition rate is directly proportional to the input voltage set by VR1 – the higher the voltage on VR1’s wiper, the higher the output frequen­cy. The output from the VCO is used to switch Dar­ lington transistor Q8 (BD-679) and this in turn drives the LED array. Thus, each time pin 7 of IC1b goes high, Q8 turns on and lights the LEDs. The LED array consists of 31 high-brightness LEDs, arranged in five lines of five series LEDs plus two lines of three series LEDs. A 47Ω current limiting resistor is fitted in series with each line of LEDs to limit the pulse current through them to a safe value. This current is quite high but is still within the LED ratings due to the short duty cycle. Counter circuit As well as driving the LED array, the VCO also directly drives a counter circuit with a 3-digit LED readout. This counter measures the VCO frequency and is calibrated to read directly in RPM. In greater detail, the pulse waveform at pin 7 of IC1b clocks pin 11 of IC3, a CMOS 4553 3-digit counter. This IC con­tains three separate dec- ade counters, as well as the necessary output latches and multiplexing circuitry for three 7-segment LED displays. The .01µF capacitor between pins 3 & 4 sets the frequen­cy of an internal oscillator and this in turn sets the speed at which the outputs are multiplexed. The BCD outputs appear at pins 5, 6, 7 & 9 and are decoded using IC4, a CMOS 4511 7-segment display driver. This IC converts the 4-bit BCD code from IC3 into 7-segment outputs which then directly drive the LED displays via 270Ω current limiting resis­ tors. Each display is switched on at the correct time by the D0-D2 digit driver outputs from IC3. These outputs switch the dis­plays via PNP/ NPN transistor pairs Q2-Q7. IC2 provides the required latch enable (LE) and memory reset (MR) timing signals for IC3. IC2a and IC2b are used to form a standard squarewave oscillator. Its output fre­quency can be adjusted using VR2, which provides calibration. Each time pin 4 of IC2b switches high, pin 6 of monostable stage IC2c switches low and this provides the LE pulse for IC3. Each time a pulse is received, the current count in IC3 is latched into the output registers and the display is updated. After latching, the counters inside IC3 must be reset so that a new count can begin. This task is performed by the MR pulse and this is obtained by feeding the output from IC2c through a delay circuit consisting of stages IC2d-IC2f. Normally, pin 12 of IC2e is low but when pin 6 goes high at the end of the LE pulse, pin 12 also goes high for a brief peri­od. When pin 12 goes December 1993  25 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au This close-up view shows the completed VCO board, after it has been stacked with the counter board. The trimpot (VR2) allows the counter circuit to be calibrated, so that it shows the correct speed of the rotating object in RPM. low again, pin 15 of IC2f goes high and resets IC3 to 000. IC3 then begins counting the pulses applied to its clock input from the VCO as soon as the MR signal goes low again. Power for the circuit is derived from a 12V DC plugpack supply. This drives a 7809 3-terminal regulator to derive a 9V supply rail, while a 2200µF capacitor provides supply line decou­pling. Diode D1 protects the circuit against damage if the supply is connected with reverse polarity. Because the high-brightness LEDs and the LED displays draw a fair amount of current, the plugpack should be rated at 500mA. A 300mA plugpack will work but LED brightness will be reduced. Construction The LED Stroboscope is built on three PC boards: a VCO board (code We mounted the LED array & the speed control pot (VR1) inside an old torch case but a suitable piece of conduit could also be used. The various connections to the control module are run via a 5-way cable fitted with a DIN plug. 04112931), a counter board (code 04112932) and a LED array board (code 04112933). The first two boards measure 100 x 55mm and are mounted back-to-back on 5mm spacers inside a plastic case. The LED array board is circular in shape and is mounted separately, along with the speed control pot, inside the torch body or in some other suitable tube (eg, plastic conduit). It is connect­ ed back to the control Brief Specifications Range .................0-19,000 RPM Light Source .......High-brightness LEDs Power Supply .....12V DC <at> 500mA Readout...............3-digit LED display Resolution...........100 RPM Accuracy..............1% ± 100 RPM circuitry via a 1-metre cable fitted a 5-pin DIN plug. Fig.2 shows how the parts are installed on the boards. The parts can be mounted in any order, although it’s always best to mount the smaller parts first. Don’t forget the small wire link immediately beneath DISP 3 and make sure that all polarised parts are correctly oriented. These include the tran­sistors, diodes, ICs and electrolytic capacitors. The six transistors on the counter board all face in the same direction but be sure to use the correct type at each loca­tion. Q2, Q4 & Q6 are all BC557 PNP types, while Q3, Q5 & Q7 are BC337 NPN types. It’s easy to get these transistors mixed up so take care when installing them on the board. Note that each transistor should be pushed down onto the board as far as it will comfortably go before RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 2 4 2 7 1 1 3 1 7 8 Value 2.7MΩ 470kΩ 100kΩ 47kΩ 10kΩ 4.7kΩ 3.3kΩ 1kΩ 390Ω 270Ω 47Ω 4-Band Code (1%) red violet green brown yellow violet yellow brown brown black yellow brown yellow violet orange brown brown black orange brown yellow violet red brown orange orange red brown brown black red brown orange white brown brown red violet brown brown yellow violet black brown 5-Band Code (1%) red violet black yellow brown yellow violet black orange brown brown black black orange brown yellow violet black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown brown black black brown brown orange white black black brown red violet black black brown yellow violet black gold brown December 1993  29 Q2 Q4 Q3 10k 1k DISP3 Q5 270  270  270  Fig.2: install the parts on the three PC boards exactly as shown in this wiring diagram. Take care with the orientation of the three LED displays & note that the 2200µF capacitor is mounted with its body flat against the VCO board, as shown in one of the photographs. 10k 1k 1 2 3 4 5 Q6 Q7 DISP1 10k 1k DISP2 270  270  IC4 4511 IC3 4553 270  270  1 390  .01 1 8 2 9 100k 100k 2200uF 0.1 0.1 47k 47k 100k D1 IN GND OUT 4.7k 1 .033 Q1 IC2 4049B 1 0.1 2.7M VR2 7809 3 5-PIN DIN SOCKET .0033 .01 IC1 LM358 5 7 470k 47W 10k Q8 6 100k 470k 10k 7 10 9 6 8 0.1 10k 10k SUPPLY SOCKET 3.3k E C B 1 4 10 1 2 3 4 5 .0033 7x 47  soldering, so that it doesn’t later foul the front panel. Don’t force them down too far though, otherwise you could fracture the leads inside the transistor bodies. Take care also when installing the 7-segment LED displays. They must be oriented with the decimal point of each display at bottom right. The 7809 regulator is mounted flat against the VCO board by bending its leads at right angles so that they mate with the mounting holes. It is then secured to the board using a screw and nut. The LED array board is easy to assemble. Just make sure that the LEDs 1 4 5-PIN DIN PLUG 2 3 31xLED are all correctly oriented. If any LED does go in the wrong way, then all the LEDs in that row will fail to light because that LED will be reversed biased. Once all the parts are in, the VCO STROBOSCOPE X 1000 RPM + 12VDC 500mA 30  Silicon Chip VR1 5 and counter boards can be placed end-to-end and their 1-5 terminals connected together via a short length of 5-way rainbow cable. The 5-pin DIN socket and the power supply socket are now mounted at either end of the case Fig.3: this full-size artwork can be used as a drilling template for the front panel. The cutout for the LED displays can be made by drilling a series of small holes around the inside perimeter, then knocking out the centre piece & filing the job to size. comes from the 9V regulator, while the LED array is supplied from the 12V plugpack via D1. Test & calibration Fig.4: check your PC boards against these full-size etching patterns before installing any of the parts. In particular, check that there are no broken tracks or shorts between tracks due to incorrect etching. and the remaining wiring installed – see Fig.2. Note that these two sockets must be positioned towards the bottom of the case, to provide sufficient clearance for the PC boards. At this stage, it is a good idea to go back over the board assemblies and check for wiring errors. When you are satisfied that everything is correct, the two boards can be stacked togeth­er using 5mm spacers and 10mm-long screws inserted from the VCO board side. The assembly is then secured by fitting a 10mm tapped spacer to each mounting screw – see photos. Connecting the LED array A 1-metre length of 5-way cable is used to connect the LED array board and pot VR1 to the control circuit (we actually used 3-pair telephone cable, with one wire left unused). This cable is fitted with a 5-pin DIN plug at one end, while the other end passes through a hole drilled in one end of the torch before connecting to VR1 and the LED array. The pot is mounted by drilling a hole through the side of the torch case, while the LED array board can be secured using silicone sealant. Be sure to remove the switch contacts from inside the torch to prevent it from shorting against any of the circuitry. The 10kΩ pot we used was a 16mm type which was easily fitted in the torch case. If you have a bigger housing than the one we used, you could use a standard size pot. Note that differ­ent supply voltages are used for the pot and the LED array. The pot supply To test the unit, apply power and check that the three 7-segment displays light up. At this stage, the readout won’t be calibrated but you should see recognisable numbers appear and the readout should vary as you vary the control pot (VR1). The high-brightness LEDs should also begin flashing as soon as power is applied, depending on the setting of VR1. Check that the flash rate can be varied with VR1 (note: for higher settings of VR1, the flash rate is so fast that the LEDs appear to be continuously lit). A word of warning here. If you suffer from migraine head­ aches or epilepsy, then stay well away from this project. The bright flashes of light produced by the strobe can quickly trig­ger an attack. Assuming everything works correctly, the unit can now be calibrated. You will need a digital frequency meter for this job. The first step is to set VR1 so that the VCO frequency at pin 7 of IC1b is 200Hz (as measured on the DFM). This done, VR2 is adjusted until the stroboscope display reads 12.0 (corresponding to 12,000 RPM). Alternatively, you can calibrate the unit against a machine that rotates at a known speed. To do this, set VR1 to the lowest setting at which the reference line appears stationary and adjust trimpot VR2 for the correct reading on the display. Final assembly All that remains now is to install the control module inside the plastic case. The first step is to attach the front-panel label to the lid and use it as a drilling template for the board mount­ing screws. This done, drill a series of small holes around the inside perimeter of the display cutout area. The centre piece can then be knocked out and the job filed to a smooth finish so that the red Perspex® window is a tight fit. It’s now simply a matter of securing the control module to the lid using four 5mm-long machine screws. If necessary, the Perspex window can be glued into position using epoxy resin but don’t use too much as this would spoil the appearance of the unit. SC December 1993  31 Looking for a lowcost audio power module that’s easy to assemble? This compact module will deliver 25W RMS into an 8-ohm load & can be powered from single or dual supply rails. By DARREN YATES A Low-Cost 25W Amplifier Module A S POWER amplifier modules go, this unit may not rank at the top for raw power but you’ll be hardpressed to find a sim­ pler or more versatile circuit. It’s based on a single IC, the LM1875T 20W audio amplifier from National Semiconductor. This IC comes in a TO-220 package and, combined with a handful of other parts and a suitable power supply, delivers 25W RMS into 8 ohms and 20W RMS into 4 ohms. What’s more, the specifications are quite impressive for such a barebones circuit. With a signal-to-noise (S/N) ratio of 110dB and a distortion figure of just 0.025% for 1kHz at 20W, it could well be used as the basis for a hifi stereo amplifier. The frequency response extends from 14Hz to 32  Silicon Chip beyond 100kHz when meas­ured at 1W RMS. The module is also easy to construct and no setting-up adjustments are necessary. And, as mentioned in the introduction, it can be powered from either single or dual supply rails (you can build either version on the same board). The supply voltage can range from 20V to 50V for a single supply rail, or from ±10V to ±25V for dual supply rails. Depending on the supply voltage, the output power ranges from 4W into 8 ohms (20V supply) to 25W into 8 ohms (50V supply). To guard against device failure, the LM1875 includes inter­nal short circuit protection. This protects the device if the output is shorted to ground via either an AC or a DC path. It also has current limiting to 4A to prevent damage when driving reactive loads, which makes it a highly robust module that can handle more than its share of knocks. Because so much power has to be dissipated by such as small package, the LM1875 also has in-built thermal protection. This shuts the device down if there is excess heat build-up in the chip itself (in excess of about 175°C). Other specifications of the device include a supply rejec­tion figure of -94dB, an open loop gain of typically 90dB and a power bandwidth of 70kHz. If you’d like more information on the LM1875 audio amplifier, refer to the data article elsewhere in this issue. Because there are two possible power supply arrangements, we’re presenting two circuit diagrams – see Figs.1 & 2. Both circuits have low component counts and differ only in a few minor details. 10 35VW Dual supply version The dual supply version (see Fig.2) uses the same feedback and Zobel network components as the single supply version. Apart from the power supply itself, the main difference between the two circuits is the input DC biasing arrangement. Pin 1 of IC1 is connected to the 0V rail via a single 22kΩ resistor. In addition, the 2200µF output coupling capacitor is omitted, since pin 4 of IC1 normally sits within ±50mV of 0V, with no signal present. The power supply uses a mains transformer with a centre-tapped 35V secondary. The resulting outputs from bridge rectifier BR1 are filtered using two 2200µF capacitors to give nominal ±25V supply rails and these go to pins 5 and 3 of IC1 via 2A fuses. 1 1k INPUT 1 1M 2 2200 63VW 5 4 IC1 LM1875 +25V 3 1 180k 0.22 4- 8  10k 22 63VW S1 A F1 1A BR1 PW04 .01 250VAC 17.5V +50V 240VAC 2200 63VW 17.5V N E CASE 25W AUDIO POWER MODULE SINGLE SUPPLY Fig.1: the single supply version of the 25W Amplifier Module. IC1 drives the loudspeaker via a 2200µF capacitor. +25V 220 35VW 0.1 1 1k INPUT 1M 1 22k 2 5 4 IC1 LM1875 1 3 180k 4- 8  0.22 10k -25V 22 63VW S1 A .01 250VAC 0.1 220 35VW F1 1A F3 2A F2 2A BR1 PW04 17.5V +25V 240VAC Construction Construction of the amplifier is quite straightforward – see Figs.3 & 4. All you have to do is follow the diagram for the version you require. In either case, start by checking the PC board carefully for any defects by comparing it with the published pattern. This done, begin the board assembly by soldering in the wire links and by installing PC stakes at the external wiring points. The resistors and capacitors can now be installed, 220 63VW 0.1 22k +50V 22k Single supply version Fig.1 shows the circuit for the single supply version. As shown, the input signal is coupled via a 1kΩ stopper resistor and a 1µF capacitor to the non-inverting input of IC1 at pin 1. This input is biased to ½Vcc (ie, half the supply rail) via the three 22kΩ resistors and the associated 10µF capacitor. The closed loop gain of the amplifier is set to 19 by the 180kΩ and 10kΩ feedback resistors on pin 2 and follows the stan­dard non-inverting amplifier feedback rules (ie, G = 180/10 + 1 = 19). The 2.2µF capacitor and the 10kΩ resistor set the lower 3dB frequency point to 7Hz. The output from the amplifier appears at pin 4 of IC1 and drives the loudspeaker via a 2200µF coupling capacitor (to prev­ent DC from flowing in the speaker coil). Also connected to the output is a series 1Ω resistor and a 0.22µF capacitor. These components form a Zobel network and this provides high-frequency stability when driving capacitive loads. Power for this circuit is derived from a mains transformer with a 35V secondary winding (either a single 35V winding or two 17.5V windings connected in series). The resulting AC voltage drives bridge rectifier BR1 (PW04), the output of which is then filtered with a 2200µF capacitor to give a nominal +50V DC rail. Further on-board supply decoupling is provided by a 220µF 63VW capacitor, while a 2A fuse protects against any external shorts to ground. Finally, a .01µF capacitor is connected across the power on/off switch (S1) to minimise the switch-off “thump”. F2 2A 22k +25V 17.5V 2200 35VW N E CASE 2200 35VW -25V 25W AUDIO POWER MODULE DUAL SUPPLY Fig.2: the dual supply version of the 25W Amplifier Module. December 1993  33 IC1 LM1875 22k 180k 1uF 10k 180k 2200uF 1uF 22uF 10uF 1M 1 1M 10k 22k 0.22 0.22 GND 220uF IN 1k F2 0.1 1k 220uF F2 0.1 IN 0.1 GND 1 22k 22k 10uF IC1 LM1875 220uF F3 GND V+ POWER SUPPLY GND V- SPEAKER Fig.3: parts layout for the single supply version. GND POWER SUPPLY V+ GND SPEAKER Fig.4: parts layout for the dual supply version. Fig.5 (above): this diagram shows how the LM1875 audio amplifier IC is insulated from the heatsink using a mica washer & insulating bush. Smear all mating surfaces with heatsink compound before bolting the assembly together, then use your DMM to confirm that the device is correctly isolated. Fig.6 at right shows the full-size PC artwork. This is the dual supply version of the 25W Amplifier Module. Check the supply rail voltages, the quiescent current & the DC offset voltage across the output terminals before connecting a loudspeaker – see text. 34  Silicon Chip followed by the fuse clips. Make sure that the electrolytic capacitors are correctly oriented, otherwise they may be destroyed when power is applied. The fuse clips must also be correctly oriented, with the retaining tabs towards the outside. Once these parts are in, install the LM1875 and then fit 15mm spacers to the corner mounting positions of the board. The board and the heatsink can then be placed on a flat surface and the mounting hole marked out for the IC. Drill this hole to 3mm and carefully remove any metal swarf using an oversize drill to ensure a perfectly smooth surface. The IC is now bolted to the heatsink using a TO-220 insu­ lating kit (ie, a mica washer and insulating bush). Fig.5 shows the assembly details. Smear all mating surfaces with heatsink compound before bolting the assembly together, then use your multimeter to confirm that the metal tab of the IC is indeed electrically isolated from the heatsink. Note that no provision has been made for the power supply components on the PC board. This has been done deliberately to avoid potential hum problems due to circulating earth currents when using two modules in a stereo amplifier. If you wish to run two modules, you should use a common power supply and ideally the transformer should have a rating of about 80VA, although for most applications a 60VA unit will suffice. The transformer used to test the prototype was a 60VA unit with two 17.5V secondary windings from Dick Smith Electronics (Cat. M-6676). A 30V 60VA power transformer could also be used, although this will result in reduced power output. Do not use a 30V 1A transformer as its rating will be insufficient. Testing Before applying power, check that all parts are correctly located and oriented. This done, install the fuse(s) and connect the power supply leads with your multimeter (switched to Amps) in series with the positive rail. Do not connect the loudspeaker or an audio input signal at this stage. Now switch on and check that the current settles down to 50-70mA following a brief surge to charge the main filter capaci­tor(s). Note that you must have the heatsink fitted, otherwise the thermal overload protection circuit may cut in and switch the device off. Check the supply rail voltages – they should be within 10% of the values shown on the circuit. If the quiescent current is correct, check the DC offset voltage across the loudspeaker terminals. It should be less than ±50mV. If this checks out, the loudspeaker can be connected (switch off first) and an audio input SC signal applied for final testing. PARTS LIST Single Supply Version 1 PC board, code 01112931, 87 x 64mm 6 PC stakes 4 15mm x 3mm tapped spacers 1 TO-220 heatsink mounting kit (ie, mica washer & insulating bush) 4 15mm x 3mm machine screws 2 2AG fuse clips 1 1 amp 2AG fuse 1 heatsink (Altronics Cat.H-0580 or equivalent). Semiconductors 1 LM1875T 20W audio amplifier (IC1) Capacitors 1 2200µF 35VW electrolytic 1 220µF 63VW electrolytic 1 22µF 63VW electrolytic 1 10µF 35VW electrolytic 1 1µF 63VW electrolytic 1 0.22µF 63VW MKT polyester 1 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 1MΩ 1 10kΩ 1 180kΩ 1 1kΩ 3 22kΩ 1 1Ω PARTS LIST Dual Supply Version 1 PC board, code 01112931, 87 x 64mm 7 PC stakes 4 15mm x 3mm tapped spacers 1 TO-220 heatsink mounting kit (ie, mica washer & insulating bush) 4 15mm x 3mm machine screws 4 2AG fuse clips 2 1 amp 2AG fuse 1 heatsink (Altronics Cat.H-0580 or equivalent). Semiconductors 1 LM1875T 20W audio amplifier (IC1) Capacitors 2 220µF 63VW electrolytic 1 22µF 63VW electrolytic 1 1µF 63VW bipolar electrolytic 1 0.22µF 63VW MKT polyester 2 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 1MΩ 1 10kΩ 1 180kΩ 1 1kΩ 1 22kΩ 1 1Ω Power supply parts 1 35V 60VA power transformer (DSE Cat. M6676 or equivalent - see text) 1 PW04 bridge rectifier (BR1) 1 mains switch (S1) 1 2200µF 63VW electrolytic capacitor 1 .01µF 250VAC polyester capacitor Power supply parts 1 35V centre-tapped 60VA power transformer (DSE Cat. M6676 or equivalent - see text) 1 PW04 bridge rectifier (BR1) 1 mains switch (S1) 2 2200µF 63VW electrolytic capacitors 1 .01µF 250VAC polyester capacitor Miscellaneous Tinned copper wire, solder, screws, nuts & washers. Miscellaneous Tinned copper wire, solder, screws, nuts & washers. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 3 1 1 1 Value 1MΩ 180kΩ 22kΩ 10kΩ 1kΩ 1Ω 4-Band Code (1%) brown black green brown brown grey yellow brown red red orange brown brown black orange brown brown black red brown brown black gold gold 5-Band Code (1%) brown black black yellow brown brown grey black orange brown red red black red brown brown black black red brown brown black black brown brown brown black black silver brown December 1993  35 CIRCUIT NOTEBOOK 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. Single chip touch switch This touch switch circuit provides on/off operation from a single touch pad and draws negligible current while in standby. The circuit uses a single 4011 quad NAND gate package with IC1c & IC1d connected as an RS flipflop. The other two gates are connected with a time-constant at pin 6, arranged so that each time the touch plate is touched to pull pin 1 high, the RS flipflop changes state. Pin 10 drives transistor Q1 which can be used to control an external circuit. A word of warning: don’t leave your 240V motor speed control This circuit was developed to control a universal (brush-type) motor for a home-made coil winding machine. In this partic­ular application, there were two prime requirements: (1) motor speed control over a wide range of speeds and loads; and (2) a capability of counting shaft revolutions (ie, coil turns). These and other requirements are met by the circuit shown. Among the features of this circuit are: (1) A constant speed characteristic from very low speeds to the maximum speed of the motor over the full load torque range of the motor. (2) Symmetrical full-wave phase control to maintain maximum load performance of the motor while at the same time minimising motor brush wear (compared to half-wave speed controllers). It also ensures zero DC in the mains leads which otherwise might upset electricity authorities and lead to excessive corrosion in earth­ing conductors. (3) Optical speed sensing plus an opto-coupled Triac output stage for maximum electrical isolation between the speed control cir­cuit and the motor. 36  Silicon Chip +3-15V TOUCH PLATES 1M 1 4011B IC1a 2 3 8 Q1 BC557 14 IC1c 10 4.7k 9 OUTPUT 1M 5 .001 IC1b 6 12 4 IC1d 13 10M 11 7 0.1 0V fingers on the touch plates for more than a second, otherwise the circuit will oscillate at a high frequency and the result will be indeterminate. Matthew Inman, Beacon Hill, NSW. ($15) (4) Soft-start/stop characteristics to prevent jerky motor starts and sudden stops. Speed sensing is accomplished by using a segmented disc and an optical sensor to detect the rotation of the disc. The disc was made by drawing a circle with 32 alternate black and white sectors on paper with the aid of a CAD program. The circle was cut out and glued to a plastic disc which, in turn, was mounted on a shaft driven by the motor. The sensor consists of an infrared transmitting diode (D1) and a complementary receiving diode (D2). The diodes are mounted in holes drilled in an opaque plastic block in such a way as to prevent the direct passage of infrared radiation between them. The block was mounted adjacent to the rotating disc so that radiation from the transmitting diode was reflected from the disc to the receiving diode. As the disc rotates, it modulates the reflected radiation at the rate of 16 pulses per disc revolution. Diode D2 converts the reflected radiation to electrical pulses which are amplified and buffered by bootstrapped emitter follower stage Q1. These pulses are applied to the clock input of IC1, a 4060 CMOS counter. Normally, the input stage of this de- vice is used as a self-oscillating clock generator but in this case, it is used to further amplify the signal from D2 and im­prove noise immunity. IC1 divides the input pulse rate to produce one output pulse at pin 7 for every 16 input pulses (ie, one pulse per shaft revolution). The resulting output pulses are then fed to an external counter/display (not shown) for counting shaft revolu­tions. The output from pin 9 of IC1 is a squared-up version of the input pulses and is applied to the “trigger” input of IC4. This IC produces an output pulse of constant width (adjustable by VR1) for each input pulse. The output pulses (from pin 3) are then in­tegrated by an RC network to produce a DC voltage proportional to the shaft speed. The input pulse rate of 16 per shaft revolution is fast enough to permit a relatively short time constant in the integrator components without too much ripple in the integrated output voltage. This results in a reasonably fast response for stable speed control at practical shaft speeds. IC3b compares the integrated DC voltage with an adjustable DC voltage from speed control VR2. At low shaft speeds, the vol­tage at pin 8 of IC3b will be less than the voltage at pin 9. This will cause the output of IC3b to go MOTOR 0.18 250VAC Q2 BC148 4 560  2W 560  G DISC FRONT VIEW MT1 L1 4.7mH TRIAC1 SC143D MT2 OPT1 MOC3021 IRD1 .033 470k 100k 0.33 18k 10 100k 100k 1 5 0.1 3 330  2 .01 100k SET MAX SPEED VR1 470k 12 TO COUNTER (NOT SHOWN) 7 8 Q4 CIN IC1 4060 16 100k 0.47  IRD2 BPW50  470k 12V Q1 BC558 100k 470pF 0.1 820k 560k .001 1000 10 11 COUT R 13 Q0 9 100k .01 11 3 10 IC3a LM339 7 6 13 4 IC4 555 STOP 8 SPEED VR2 10k RUN 22k 1 1k 6.8k 220k 47k 8 9 IC3b 100 IRD2 14 4.7k BLOCK DISK 120  SHAFT 2  6 1 4.7k OUT IC2 7805 GND IN D5 1N4002 D1-D4 4x1N4002 T1 E N 240VAC 120  IRD1 CQY89A S1 F1 1.5A A high, thus turning on Q2. The resulting current through the LED section of opto-coupler OPT1 will turn on the Triac-driver section of OPT1, which thus turns on Triac 1 to power to the motor (M). As the shaft speed rises, the voltage level at pin 8 of IC3b will rise. If this voltage tries to rise above the voltage level at pin 9, the output of IC3b will go low, turning off Q2, OPT1 and Triac 1. As a result, the circuit will try to maintain a constant shaft speed at which the input voltages at pins 8 and 9 of IC3b are equal. This is not the whole story, however. The input voltage at pin 9 of IC3b is modulated by a 100Hz saw­ tooth waveform generated by IC3a. This waveform is synchronised to the mains positive and negative half cycles. As the shaft speed approaches the value set by VR2, the voltage level at pin 8 of IC3b intersects the saw­tooth waveform applied to pin 9. This results in a pulsed output from IC3b. The phase of this pulsed output (relative to the mains waveform) varies with the voltage at pin 8 relative to the vol­tage at pin 9. If the motor tries to slow down, the output of IC3b will go high earlier in each half cycle, thus causing Triac 1 to conduct for a greater proportion of each half-cycle and thereby driving the motor harder. Conversely, if the motor should try to speed up, the reverse will apply and Triac 1 will apply less power to the motor. Inductor L1, its parallel 560Ω resistor and the 0.18µF capacitor across the motor form a filter to minimise RFI (radio frequency interference) and reduce the voltage spikes generated by the motor. The inductor was wound with as many turns of 0.3mm enamelled wire as would fit on a 25mm iron dust toroid. The inductance was measured as approximately 4.7mH. This filter proved effective in reducing motor-induced voltage spikes that otherwise might harm Triac 1. Note that the filter values chosen might need to be altered for different motor sizes, although they do not appear to be critical. Finally, note that some parts of this circuit (ie, around the filter, Triac, opto­­ coupler and motor) operate at potentially lethal mains voltages, so exercise extreme care when working on it. H. Nacinovich, Gulgong, NSW. ($50) The circuit of the motor speed controller. Speed sensing is accomplished by using a segmented disc & an optical sensor to detect the rotation of the disc. December 1993  37 Manufacturer’s data on the LM1875 20W audio power amplifier IC As used in the amplifier module elsewhere in this issue, the LM1875 IC requires only a few external components to deliver 25W into 8 ohms. It has quite impressive specifications for its size, as well as in-built thermal & short circuit protection. By DARREN YATES The LM1875 Audio Amplifier IC from National Semiconductor is now a few years old but it is still one of the most cost-effective devices available when it comes to simplicity and output power. The LM1875 comes in a 5-lead TO-220 package. The heatsink tab is connected to the negative supply rail of the amplifier (ie, to pin 3). However, it must be isolated from the heatsink via a TO-220 insulating kit otherwise earth loops are likely to be a problem. Fig.: this diagram shows the pinout details for the LM1875. The device must be isolated from its heatsink using a TO-220 mounting kit. Fig.3: THD vs power output. 40  Silicon Chip Incidentally, even if this IC is not driving a load, it must be bolted to a heatsink as the quiescent current of 70mA is enough to cause the thermal protection circuitry to switch in (more on that later). Main features The main features and specifications of the LM1875 are as follows: • Up to 30W power output into 8 ohms; • Typical harmonic distortion of 0.015% <at> 1kHz, 20W output; • Short circuit protection; • Supply voltage range of 20-60V; • 94dB supply rejection ratio; • In-built thermal protection; • Low noise (S/N ratio in excess of 100dB); • Open loop gain typically 90dB; Fig.4: THD vs frequency for 4Ω & 8Ω loads at 10W. • 70mA (typical) quiescent current. The LM1875 can drive either 4Ω or 8Ω loads but it delivers slightly more power into 8Ω loads. With 4Ω loads, the maximum output power is 20W. Although the data sheets indicate that the device can deliver a maximum output power of 30W into 8Ω, this is at its absolute maximum supply voltage of 60V. With practical power supplies, some allowance must be made for variations in mains voltage and therefore 25W is a more realistic rating. Single or dual rails The LM1875 can be operated from dual or single supply rails and the amplifier module project featured in this issue shows both supply arrangements. The pinout diagram can be seen in Fig.1. Fig.2 shows the internal circuit diagram of the IC. Two NPN devices, Q35 and Q39, are the output transistors. If you look closely, the emitter resistor for Q35 is split in half and this split feeds another NPN device, Q36, which monitors the output current on positive half cycles of the output signal. In fact, Q36 and Q37 form part of a “load-line” protection system which shuts down drive to the Fig.5: power output vs supply voltage (8Ω load). Fig.6: PSRR vs frequency (positive & negative rails). Fig.2: the internal circuit diagram of the LM1875. Q35 & Q39 are the output transistors, while Q36 & Q37 form part of a “load-line” protection system which shuts down drive to the output stage if the loading conditions are excessive. output stage if the loading conditions are excessive. Fig.3 shows the distortion vs output power for both 4Ω and 8Ω loads while Fig.4 depicts distortion as a function of frequen­cy. As you might expect, the device has increased distortion at both ends of the audio spectrum. Power output Fig.5 shows the expected power output at 1% total harmonic distortion for supply rails of between ±10V to ±30V (RL = 8Ω). Power supply rejection characteristics vs frequency are shown in Fig.6. Note the difference between the positive and negative rails, with the negative rail being some 30dB or Fig.7: power dissipation vs power output (RL = 4Ω). so worse at 20kHz. The maximum figure of 94dB is relative to a 0Ω signal source resistance, a 4Ω load and at a frequency of 1kHz. The in-built thermal protection activates when the die temperature reaches 175°C and shuts down the device, which remains off until the die cools down to 145°C. In the case of a continuous load or over-drive problem, if the die rises to 150°C the device will again shut down. The beauty of this is that if the fault is a one-off event, the thermal circuitry will allow the die to heat up further than if it is a continuous fault. Figs.7 & 8 show details on the power output vs power dissi­pation Fig.8: power dissipation vs power output (RL = 8Ω). for 4Ω and 8Ω loads. Notice how the device dissipation is much higher for 4Ω loads. In fact, even with a 1°C/W heatsink, the LM1875’s internal thermal shutdown circuitry switches on once the power output reaches 20W. By this stage, the power dissipation has reached about 32W and the die temperature has surpassed the 175°C mark. With an 8Ω load, the LM1875 will happily deliver 25W con­ tinuously without running the risk of thermal shutdown. Stability Most power amplifiers don’t drive capacitive loads all that well and the LM1875 doesn’t either. Long speaker leads can pro­duce enough capacitance to drive some amplifiers into VHF oscilla­tion. In this case, the manufacturer’s data sheets recommend that you add a Zobel network consisting of a 0.22µF capacitor and a 1Ω resistor to the output. This has been included in the amplifier module in this month’s issue. As with most designs, PC board layout is important in minimising the noise and distortion components. Keeping the input signal away from the supply rails will help keep the SC distortion low. December 1993  41 REMOTE CONTROL BY BOB YOUNG Servicing your R/C receiver This month, we will look at the technical aspects of servicing the modern R/C receiver. Apart from using your eyes, the equipment required is a toothbrush, a can of CRC-226, a voltmeter, an oscillo­scope & a signal generator. To begin, one must keep in mind at all times that the receiver has lived out its entire operational life in an extreme­ly harsh environment; usually subjected to high levels of vibra­tion, high “G” forces, crash damage, plus possible water and dust ingress. As if this were not enough, receivers which fail in flight due to a simple component failure then have to undergo the trauma of a crash, before the wretched thing can be lobbed up on the bench of some poor serviceman, usually waiting with baited breath for the next horror story. Servicing model equipment adds backed into the propeller of the model behind me. Its prop chewed the leads off my servos and receiver and sliced the battery pack in half. In the crash which followed, the engine bearer smashed through the receiver case and broke some components. Do you think it will cost much to repair?” Or “I had my hydro howling and it hit a submerged log. It did a triple somersault and sank in 50 metres of salt water. It was only under the water for about two days before I could get it out. Do you think it is repairable? PS: you will notice the Rx case is a funny copper colour and another thing, I “I had my hydro howling & it hit a submerged log. It did a triple somersault & sank in 50 metres of salt water. It was only under the water for two days before I could get it out”. a new dimension to “Mondayi­ tis”. Every Saturday and Sunday, the weekend warriors are out there doing their thing, flying and crashing, racing and sinking, lead-footing and rolling. Every Monday the phones run hot with their horror stories. “I was flying along, minding my own business, when this tree jumped in front of my model...” Or “I was in this pylon race and I accidentally 42  Silicon Chip cannot seem to see any tracks on the PC board. I am sure they were there the last time I drained the water out of the receiver, after I collided with me mate’s Deep V.” Don’t laugh, I have had all of the above and more happen to me personally. In one horrific period, I lost six models in six consecutive flights. It was the closest I ever came to giving up flying completely. Oddly enough, they were mostly due to pro­pellers breaking in flight. The models quite literally explode in mid air when a prop sheds one blade. At the time, I was reworking big motors for my speed runs and using nylon props. In the end, I tried virtually every brand of nylon prop on the market and was finally forced to use wooden props. These break easily on rough fields and the cost is very high. However, the cost of a lost model is even higher so I had to grit my teeth and persevere with wooden props. Nylon props have improved a lot since then but always make sure they are correctly balanced. Crash hazards The last crash in the series was the most galling, however. At the time I was training for the World Aerobatics Championships in Pennsylvania, USA (1971) and used to get up at 5am and drive to “Bedrock” for a session before work. I did this every day for three months. Now “Bedrock” (Heath­cote Road, Sydney) was a dirt strip which used to grow a new crop of rocks overnight. I used to take a broom and sweep the strip every morning and every morning there would be a new crop of rocks. This particular morning as usual, I stood at the side of the runway, midway along the strip, and taxied to the end of the runway to take off. I opened the throttle and began the take-off and as the model drew level with me, I spotted a new rock right in front of my prop. Too late – the prop shattered, the nose of the model disintegrated and the whole mess fell in a heap at my feet. It never even left the ground! I was hopping mad and one model short with six weeks to go to the championships. CAP FLEXIBLE TUBE 300mm LONG Fig.1 (above): the end of the antenna is often glued to an aluminium chassis in a zig-zag pattern, as shown here. This is undesirable, as it allows noise pickup & cancel­lation in the folded sections, resulting in detuning of the front-end. Fig.2 at right shows the correct way to deal with the antenna. Such is the pressure on the dedicated contest flyer. You never knew when the next blow would be struck. Somehow you always made it to the contest but the amount of midnight oil used in the effort leaves one exhausted. However, the real point of this story is that the explosive vibration levels experienced by models throwing a prop blade can be transmitted to the receiver and servos. Also, the electronics must survive the fall to earth. This must be kept in mind at all times when servicing model equipment. With this background, we can now move on to the servicing of receivers. If the receiver is your own then you know its exact history and the probable cause of the problem. If the receiver belongs to a friend or customer, then suspect everything! If the receiver comes from a model aircraft, then suspect everything, including the aircraft. Non-electronic faults To clarify this last point, another story is in order. By far the worst receiver repair I ever had to deal with belonged to a friend of mine and was one of my first Mark VII production receivers. Because of this, I had to be particularly careful about establishing the cause of the problem. Despite all the care lavished on prototypes and early production units, faults can easily slip through. Anyway, the complaint took the form of a loss of control at the top of a loop. My friend swore blind that the fault had only begun to manifest itself in the last few weeks. Prior to that, the receiver had worked flawlessly. To compound the problem for me, in the earlier receivers we had an antenna phasing problem which caused a TO RECEIVER similar result. I was sure the Mark VII receiver was free of this fault but one could never be sure. After exhaustive testing, I began to suspect detuning due to engine vibration or simple component degradation and I went through that receiver with a fine tooth comb. I could not find a fault of any kind. Week after week this went on until finally, in exasperation, I went flying with him to see the problem for myself. Now this business of going with a customer is a real pain for it usually entails a 100km round trip in heavy traffic and blows away at least half a day. But sometimes it is unavoidable. To cut a long story short, The model was a very fast swept wing semi-scale F-86 Sabre. As soon as I saw the model I knew what came next. Sure enough the loop was performed and the model did a perfect flick roll off the top of the loop. It wasn’t loss of control in the true sense but a genuine flick-roll. As it turned out, Bill had moved the centre of gravity (CG) back the week before the problem began. The whole thing was an aerodynamic problem. Moving the CG forward cured the problem and I heard no more complaints about that particular receiver. I have spent a considerable amount of time on the foregoing because these sorts of problems caused me endless trouble until I had gained sufficient experience to recognise this sort of fault. Filling out the complaint sheet correctly is a vital part of servicing in model work and the serviceman must stay alert to any external factors causing what appears to be a purely electronic problem. Antenna installation Antenna installation is a classic 25mm problem often encountered in model work. Most model receivers come with one metre of hookup wire for an antenna. The problem is that this is too long for many models, particularly model cars. Most cars come with a flexible tube about 30cm long into which the last 30cm of the Rx antenna is slid. What do you do with the excess 70cm? You dare not cut the antenna short, for it will detune the receiver front-end badly. Now the ingenuity used by some modellers in devising the worst possible use for this excess antenna often leaves me speechless. Usually it is wound up in a ball and left lying under the servos or some such electrically noisy device. Often it is glued to the aluminium chassis in a zig-zag pattern, as shown in Fig.1. This is undesirable, as it allows noise pickup and cancel­lation of the folded sections, resulting in detuning of the Rx front-end. The correct way is to make a small bobbin and drill two holes in each end about 25mm apart. Thread the end of the antenna through one hole and wind the excess into a coil on the bobbin. Thread the 30cm to be inserted into the flexible tube through the other hole and Bob’s your uncle. It makes a neat little antenna (Fig.2) which should be mounted well clear of servos, battery packs and inter­wiring. In electric models, keep it well clear of the speed controller and motor batteries as well. All of these devices generate electrical noise and will interfere with the receiver. I cannot stress too strongly that the best reception is achieved with the maximum length of antenna, in the clearest location possible. On aircraft, a 90 degree change in direction is December 1993  43 REMOTE CONTROL – CTD permissible (from cockpit to fin and down to the tip of the tailplane) but do not fold the antenna back upon itself more than about 5cm. The maximum which can be cut off most receiver anten­ nas without serious receiver detuning is about 10cm. This often occurs during a crash and is a commonly asked question. Grilling the modeller Therefore, from my point of view, the first step in receiv­er servicing is to grill the customer on the symptoms and estab­lish the nature of the fault. Be sure to ask if there have been any changes to the model prior to the fault appearing. Changes in antenna location, CG of the model or new servos can all introduce problems. Battery problems Always be alert to battery problems as they are very high on the list of probable causes, although not as high as in the transmitter. Crash damage and engine vibration radically alters the statistical analysis of fault probabilities. Make sure you get the battery pack used during the flight when the A fault occurring at the end of eight 15 minute flights often indicates that a battery has gone flat. Check the capacity of the battery with a cycling charger or a graph. I routinely graph all batteries sent in for servicing. Do not forget to ask if the battery charged correctly and fully the night before. Batteries charged and left to stand for a week will self-dis­charge and this will influence flight duration. A slope soarer (with two servos) flown gently will last about 3.5 hours on a 500mAh battery pack. A 4-servo pattern ship flown vigorously will last about two hours and a helicopter with four servos about 45 minutes. The corollary to this is that the servos in each of these models will be subject to different rates of wear. In addition, helicopters are subject to a lot of vibra­tion. Be sure to find out what type of model your customer is flying. If the model comes in as well, I look at the antenna and advise the customer on the correctness of the installation. In this regard, I always routinely replace the receiver antenna on the grounds that it gets severely stressed “Always be alert to battery problems as they are very high on the list of probable causes. And make sure you get the battery pack used during the flight when the fault oc­curred”. fault oc­curred. Often, the model battery pack is difficult to remove and the modeller will send in a spare pack. If the fault is in the battery, you can spend a lot of time on a wild goose chase. I will not give a warranty on a repair unless I can examine the actual batteries to be used. Always be aware that the indus­try standard for average battery consumption for a flight battery is 270mA, as against approximately 120-150mA for the Tx. This means that the receiver battery is the shortest duration member in the Tx/Rx battery pair. Also be aware that this will vary depending upon the number of servos and the style of flying of the operator. 44  Silicon Chip in a crash; I often find the conductor broken inside the insulation. Receiver checks Finally, it is time to move onto an examination of the receiver. Regardless of the nature of the complaint lodged by the customer, begin with a very close physical examination of the receiver case, its PC board and components. Often, old crash damage has been missed or has just become obvious. Look for impact marks on the case. Plastic cases often return to shape after an impact, leaving almost no trace of the object which distorted the case. Aluminium cases were better in this regard, as they were stronger. They also protected against electrical noise and left marks if a sharp object impacted with the case. The real danger here is that delicate components which are unsupported inside their housings, such as crystals and IF coils, can be cracked internally and it is difficult to check on this. A vibration table is a great help and will often show up this type of fault, while freezer cans can be of help too. Next, move to the servo leads or pins and give them a visual inspection and a good scrub with a toothbrush and CRC-226. Remove any dust or dirt and inspect the PC board for corrosion. Often, receivers are purchased secondhand and whilst the current owner may be using it in an aircraft, the previous owner could have had it in a submarine, with no waterproofing! Be suspicious of everything is my motto. Somebody bringing back a model and radio that you have just serviced – in a bucket – is no joke. I once had an alcoholic customer who did just that. Some modellers really take their modelling seriously and faults in the radios or servicing are never forgiven. Next, cut open the receiver battery pack and examine the cells individually for signs of corrosion or physical damage. If there are signs of damage, discard the pack. Damaged cells will often let go in flight under engine vibration with disastrous results. Short circuited cells are a common problem in airborne battery packs. Do not replace a single cell as this will often result in unequal stress on that cell and premature failure of the pack. Pull back the insulation on the battery leads and examine them for “black wire” corrosion. Examine the battery connector for signs of damage or corrosion. Water on the connectors will result in electrolysis and damage to the pins. Always be on the alert for this type of problem. Finally, charge the pack and check each cell voltage. They should be within 0.07V of each other. Any cell showing a greater deviation than this is suspect. The actual terminal voltage will depend upon the internal chemical composition of the cell. This will vary from brand to brand but most will come off the charger at about 1.35-1.4V per cell. That’s about it for this month. Be sure to keep those nicads cycled. SC SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Lesson 3 Programming the Motorola 68HC705C8 microcontroller In Lesson 2, we covered the following topics: (1) Mne­monics; (2) Addressing Modes; and (3) the 6805 Instruction Set. This month, we look further at addressing modes. By BARRY ROZEMA Table 1 Opcode Mnemonic A. Mode No. Bytes No. Cycles A6 LDA IMM 2 2 C6 LDA EXT 3 4 86 SWI INH 1 10 C7 STA EXT 3 5 CC JMP EXT 3 3 43 COMA INH 1 3 A3 CPX IMN 2 2 42 MUL INH 1 11 Before moving into new territory, let’s first take a look at the answers to the exercises in Lesson 2. Exercise 1: fill in the blank spaces in Table 2 (Lesson 2). A look at the instruction set in Lesson 2 and/or the op code map on page 30 of the Motorola MC68HC705C8 technical summary (BR594/D) should have given you the information to get the re­sults shown in Table 1. You should also have modified your programs in last months lesson to get the following results. Each exercise is a modifica­tion of the previous program. You add the same instructions on to the program with a change to the data. The flow charts have the new or modified processes shown with an asterisk (*). Exercise 2: rewrite the flow chart and the program to make the LEDs give a smooth inward pattern; ie, to make the LEDs close in one bit at a time instead of two. To do this, you will need to examine the bit pattern to get the hex values. Table 2 shows the bit map. Notice that the bits come “on” one bit at a time in an inward direction. The asterisks show the data that’s added to give a smoother display pattern. Table 3 shows the modified program. To do this, you need to change the immediate byte that sets the time delay. Remember, the time delay uses a subroutine that is in the MAL-4 monitor ROM. There are seven time delay subrou­tines and each one is set by loading the accumulator before jumping to the subroutine. You may have found that experimenting with various delay values by changing the immediate byte in the LDA #$?? instruction quickly became rather tedious. A better way is to make the delay time adjustable while the program is running. To do this, you load the accumulator with the value of the input port instead of a fixed value; ie, you use extended addressing instead of imme­diate. The PORT A input port address is $0000. The instruction looks like this: LDA $$0000. The modified process is shown with an asterisk in the flow chart of Fig.2 and Table 4 shows the modified program. Note: remember to enable PORT A by turning switch 7 of DIP SW2 (Bit 6) on. Kitt scanner Exercise 4: rewrite the flow chart and the program to make an 8-bit “Kitt” scanner; ie, one LED on at a time switching from left to right and back again. Better visual effect This program will need to produce a display with a pattern like the one in Exercise 3: experiment with the time the bit map of Table 5. If you make the delay to give a better visual effect. time delay adjustable as in exercise 3, Table 2 the program will repeat the following instructions. B7 B6 B5 B4 B3 B2 B1 B0 HEX A6 xx LDA #$xx 0 0 0 0 0 0 0 0 $00 C7 00 01 STA $$0001 1 0 0 0 0 0 0 1 $81 * C6 00 00 LDA $$0000 CD 14 D9 JSR $$14D9 1 1 0 0 0 0 1 1 $C3 The xx will contain the pattern data. 1 1 1 0 0 1 1 1 $E7 * There are 14 patterns to be displayed 1 1 1 1 1 1 1 1 $FF before the program starts again. The December 1993  53 Table 3 ADDRESS CODE LABEL MNEMONIC OPERAND COMMENT 0030 A600 START LDA #$00 0032 C70001 STA $$0001 Clear accumulator & store at output 0035 A632 LDA #$32 0037 CD14D9 JSR $$14D9 003A A681 LDA #$81 003C C70001 STA $$0001 003F A632 LDA #$32 0041 CD14D9 JSR $$14D9 0044 A6C3 LDA #$C3 0046 C70001 STA $$0001 0049 A632 LDA #$32 004B CD14D9 JSR $$14D9 004E A6E7 LDA #$E7 0050 C70001 STA $$0001 0053 A632 LDA #$32 0055 CD14D9 JSR $$14D9 0058 A6FF LDA #$FF 005A C70001 STA $$0001 005D A632 LDA #$32 005F CD14D9 JSR $$14D9 Set time delay 50 ($32) x ACC = 0.5 seconds 0062 CC0030 JMP $$0030 Jump to start ADDRESS CODE LABEL MNEMONIC OPERAND COMMENT 0030 A600 START LDA #$00 0032 C70001 STA $$0001 Clear accumulator & store at output 0035 C60000 LDA $$0000 0038 CD14D9 JSR $$14D9 003B A681 LDA #$81 003D C70001 STA $$0001 Set time delay 50 ($32) x ACC = 0.5 seconds Load accumulator & store at output Set time delay 50 ($32) x ACC = 0.5 seconds Load accumulator & store at output Set time delay 50 ($32) x ACC = 0.5 seconds Load accumulator & store at output Set time delay 50 ($32) x ACC = 0.5 seconds Load accumulator & store at output Table 4 Fig.1: the flow chart for Exercise 2. The program first turns on the two outside LEDs at the output port, then turns the remaining LEDs on to give a smooth inward pattern; ie, the LEDs close in one bit at a time. Set time delay input port A times ACC Load accumulator & store at output 0040 C60000 LDA $$0000 0043 CD14D9 JSR $$14D9 0046 A6C3 LDA #$C3 0048 C70001 STA $$0001 004B C60000 LDA $$0000 004E CD14D9 JSR $$14D9 0051 A6E7 LDA #$E7 0053 C70001 STA $$0001 0056 C60000 LDA $$0000 0059 CD14D9 JSR $$14D9 Addressing modes 005C A6FF LDA #$FF In Lesson 2, we covered the following three addressing modes: Inherent, Immediate and Extended. This lesson, we will introduce another 005E C70001 STA $$0001 0061 C60000 LDA $$0000 0064 CD14D9 JSR $$14D9 Set time delay input port A times ACC 0067 CC0030 JMP $$0030 Jump to start program will take 14 x 11 bytes = 154 bytes plus two jumps (one jump to go back to the start and one to jump to the RAM at location $0100). The last jump is needed because the MAL-4 only has 144 bytes of user RAM at page zero ($0030 - $00BF) – see the memory map in the November 1993 issue of SILICON CHIP. 54  Silicon Chip Set time delay input port A times ACC Load accumulator & store at output Set time delay input port A times ACC Load accumulator & store at output Set time delay input port A times ACC Load accumulator & store at output Table 2 B7 B6 B5 B4 B3 B2 B1 B0 HEX 0 0 0 0 0 0 0 1 $01 0 0 0 0 0 0 1 0 $02 0 0 0 0 0 1 0 0 $04 0 0 0 0 1 0 0 0 $08 0 0 0 1 0 0 0 0 $10 0 0 1 0 0 0 0 0 $20 0 1 0 0 0 0 0 0 $40 1 0 0 0 0 0 0 0 $80 0 1 0 0 0 0 0 0 $40 0 0 1 0 0 0 0 0 $20 0 0 0 1 0 0 0 0 $10 0 0 0 0 1 0 0 0 $08 0 0 0 0 0 1 0 0 $04 0 0 0 0 0 0 1 0 $02 addressing mode called “Direct” or “Zero Page”. Direct Addressing Mode Symbol for Direct add­r ess­ ing: $ or Z or none. The CPU requires two bytes of data to process this instruc­tion. The first byte is the op-code, while the second byte is the Low address of the operand in memory. This is like the ex­tended addressing mode except that you can only address zero page. The CPU sets the High address to $00 and so you can only address data from $0000 to $00FF. The CPU requires the operand (byte) which is “directly” at zero page in memory. The memory location for this byte is known at the time the program is writ­ten. The opcode for direct addressing is found in Lesson 2, Table 1, column 5. In these lessons, we will use the “Z” symbol to indicate Direct addressing (Z for Zero page). The mnemonics will have a “Z” tacked on the end of them, eg: ADDZ, ANDZ, ORAZ, EORZ, LDAZ, STAZ and LDXZ. The MAL-4 can make good use of zero page (Direct) address­ing. Most of the user RAM is located at zero page, as are all of the input/output, timer, watchdog and other control registers. Thus, it is possible to write programs that use more direct (zero page) addressing than extended. This saves one byte of program each time you use direct instead of extended addressing. The program in Table 6 is the same as in Table 3 from Lesson 2 except that direct addressing was used instead of ex­tended addressing, were possible. The four asterisks (*) in Table 6 indicate instructions with direct (zero page) addressing. The first three (STAZ $01) are used because the output port (PORT B) is at address $0001 which is in zero page of memory. The last in­ struction (JMPZ $30) is used because our program is written in zero page RAM, from $0030. Running the program Load the program into the MAL-4 and run it from location $0030. The output port LEDs should flash in the pattern described in Lesson 2. If not, go back and check that the program Table 6 ADDRESS CODE LABEL MNEMONIC OPERAND COMMENT 0030 A600 0032 B701 START LDA #$00 * STAZ $01 Clear accumulator & store at output 0034 A632 LDA #$32 0036 CD14D9 JSR $$14D9 0039 A6C3 LDA #$C3 003B B700 STAZ $00 003D A632 LDA #$32 003F CD14D9 JSR $$14D9 0042 A6FF LDA #$FF 0044 B700 STAZ $01 0046 A632 LDA #$32 0048 CD14D9 JSR $$14D9 Set time delay 50 ($32) x ACC = 0.5 seconds 004B BC30 JMPZ $30 Jump to start * * * Set time delay 50 ($32) x ACC = 0.5 seconds Load accumulator & store at output Set time delay 50 ($32) x ACC = 0.5 seconds Load accumulator & store at output Fig.2: this modified flow chart will provide a better visual effect than the flow chart shown in Fig.1. In this case, the time delays have been set by loading the accumulator with the value of the input port instead of a fixed value. has been entered correctly. If there are problems, Mode 2 (the disassemble mode) may help you find your mistake. Things to do In Lesson 4, we will continue with addressing modes and we will explain relative addressing. Make sure that you read up on 8-bit 2’s complement negative numbers. Finally, rewrite all your programs in Exercises 2-4 to use direct addressing were possible. Note SC the saving on memory. December 1993  55 SERVICEMAN'S LOG Whingeing Willie & the bouncing TV What does one do when a set bounces? Much depends on why it has bounced but there is also the customer’s reaction to consider. Most customers are understanding & reasonable – even apologetic. But every so often ... Yes, every so often one strikes a stinker and this is about one such customer. But first, why do sets bounce? Broadly, there are two categories. The one we all dread is the one which, strictly speaking, is our own fault. The scenario is typical: an intermittent fault with erratic behaviour, resulting in a long and involved process of trial and error to track it down. Usually, this involves re-making suspect joints, running the set through hot and cold cycles, and replacing the most likely components, based on previous experience, measurements and a certain amount of gut feeling. Nothing works at first but, eventually, one particular effort seems to be the answer; the set runs for days, or even weeks, without so much as a hint of trouble. So back it goes to the customer. A week later – or even sooner – it is back in the shop, with the customer complaining that it is just as bad as ever. The customer’s approach will vary. If they have been warned as to such a possibility – and I make it a point to do this – they will usually accept the situation philosophically, or even apologeti­cally. A few will be more upset, but mostly at the device rather than the serviceman. In any case, one can only start over again, and write off the extra time to experience – the only good point being that many suspect components have already been eliminated. And, with persistence, the real culprit will eventually be found. The other bounce The other kind of bounce is quite different and typically involves a dead set with a routine fault that’s easily recog­ nised. The faulty component is replaced, any minor adjustments attended to, and the set goes back to the customer – another job completed. Except that, a week later or so, it’s back in the workshop – dead again. It’s a completely different fault, of course, and it is not the serviceman’s fault, but one can hardly blame the customer for not always appreciating this point. But again, most customers will accept a truthful explana­tion, if it is carefully presented. And I normally waive any further labour charge in the interest of goodwill. But, as I said at the beginning, once in a while one strikes a stinker. 56  Silicon Chip This story started with a phone call from a stranger. He opened the conversation by asking whether I provided warranty service for Samsung sets. I said “yes” and asked what was the nature of the problem. It was quite simple as he described it; the picture had crept down from the top and up from the bottom ever so slightly, revealing “...a little black line”. So I said, “OK, bring it in and we’ll have a look at it”. And so it duly turned up at the shop, along with the various sales dockets which I had asked him to bring along, to substan­ tiate the warranty claim. The set turned out to be a model CB-3325J, fitted with a P/58SC chassis. I turned it on while he was there and, yes, his description was quite accurate; a very mar­ginal degree of vertical underscan. I told him it looked as though it needed nothing more than a small adjustment and suggested that he leave it with me for an hour or so. I would have to remove the back of the set and I wanted time to confirm that the fault was a simple as it looked. As it transpired, he had other things to do, so he suggested that he leave it with me and call back in a couple of days. Well, that was fine by me; it would mean that I could fit it in with other jobs more conveniently and also allow me to soak test it for a couple of days. So everyone was happy. I also took advantage of the extra time to run the set for several hours before I touched it. And it simply performed as it had when first switch­ed on; there was no change of any kind. Subsequently, I pulled the back off, reset the height con­trol and looked for anything else that was obviously wrong, but found nothing. I then replaced the back and ran the set daily until the customer returned. It ran perfectly during all that time. When he returned, I filled out the necessary warranty claim, demonstrated the set to him, and sent him on his way. And, as usual, one tends to mentally write off such jobs almost imme­diately; there are other jobs to do. The balloon goes up But a couple of weeks later the balloon went up. The cus­tomer was on the phone in a most belligerent manner. His com­plaint now was that the picture had shrunk drastically; it was now only about 10cm high in the centre of the screen. But more to the point, he was accusing me of not having fixed the set in the first place. I pointed out that there was no “fixing” involved in the first call; it was a simple adjustment. His reply was that I should have seen that this was going to happen, to which I testi­ly replied that my crystal ball had been a mite cloudy that day. At a more practical level, I advised him to bring the set back in. It was still under warranty and it would cost him nothing to have it fixed. And so the set landed back on the bench and the owner went on his way muttering all kinds of nasty things about Samsung, yours truly, and the industry in general. I let him rave; I had the more important job ahead of finding the fault. I wasn’t expecting it to be a particularly difficult job but, as I have mentioned in these notes before, Samsung circuits and manuals are disturbingly short on voltages and waveforms. In some cases, the only voltages given are the rail voltages and this is something which can cause a lot of wasted time. One important point I noted about the fault was that there was no suggestion of non-linearity; it was a simple loss of amplitude only. Such a clue could be valuable in nominating the most likely fault areas, or in interpreting CRO patterns. I began by making a preliminary check around IC301 (KA2131), a 9-pin vertical output IC – see Fig.1. My first check was at pin 4, the supply rail pin. This connects to the 25V rail via diode D302 and it checked OK. From here, I went to the height control, VR301 (1kΩ) and simply tried varying it. I wasn’t really surprised when it had only a marginal effect. Jungle chip My next stop was IC101, a 28-pin jungle chip which, among other things, contains the vertical oscillator, horizontal oscil­lator and the sync separator. I spent some time here with the CRO, particularly around pins 3 and 4. Pin 3 carries the vertical drive signals for IC301, entering that IC on pin 6. Pin 4 takes feedback signals from the output circuitry of IC301. Well, there were waveforms at all these points and most of them seemed to have reasonable shape but, without any reference, I was flying blind in regard to amplitude. However, I was some­what suspicious of the oscillator amplitude (or vertical drive voltage) on pin 3. It did seem a bit light on. This thought lead me to pin 2, which is the supply rail for what is labelled the “Ramp Gen” but is really the vertical oscil­lator. This pin is connected to the 12V rail via a 470kΩ ¼W resistor (R302). And this was the culprit; it had gone high. December 1993  57 SERVICEMAN'S LOG – CTD Fig.1: this diagram shows the jungle IC (IC101) & the vertical output IC (IC301 at top right) in the Samsung CB-3325J colour TV set. It was routine from there on. I fitted a new resistor, reset the height control, checked everything over once again, and gave it a soak test for several days. I also took the opportunity to make a complete voltage check around these two ICs, and other important points, and filed them with the manual. I then called the customer and told him it was ready. He called in the next day, signed the warranty claim, and went on his way grumbling and mumbling, mainly along the lines that the set was “no so-and-so good” etc, etc. I didn’t bite; I was only too happy to see the back of him and I hoped that it would be for good. Alas, it was not to be. Would you believe that he was back on the phone again barely a week later? His complaint was legiti­mate enough – the set was now completely dead. Privately, I wondered what I had done to deserve such bad luck. Of all the customers they could have picked, the gods had to pick Whingeing Willie. OK, so he did have a gripe. But what really annoyed me was that he was now quite abusive at a personal level – as if the failure was my fault. And customer or not, I made this point quite strongly. The failure was not my fault; odd components can fail at any time and it was just unfortunate that there had been two such failures in 58  Silicon Chip quick succession. Such a coincidence was rare but it was not the first time it had happened. And I went on to state the situation as I had before; the set was still under warranty, he could bring it in at any time, I would give it priority, and it would cost him nothing. So he duly turned up with the set and continued his tirade of abuse. But I wasn’t prepared to take it lying down and took the opportunity to have my say. I repeated the point that the failure was not my fault, emphasising that it is virtually impossible to predict when a particular component is going to fail. Fig.2: the horizontal output stage in the Samsung CB-3325J. It failed when IC101 shut-down due to some other fault. On a percentage basis, component failure rates are remark­ably low – and have improved amazingly in recent years – but the day of zero failure is a still long way off. That is one of the reasons why manufacturers provide war­ ranty cover. And in this case the warranty service had been close at hand, he had not had to resort to a commercial carrier, and the job had been done in the shortest possible time. In view of this, I told him that he didn’t really have much to complain about. I doubt that I really convinced him but it quietened him down somewhat. Anyway, he went off, still in something of a high dudgeon but with a silencer now fitted. And so I turned to the more practical problem of finding this new fault. It wasn’t very hard really, although there was a side effect. It soon became apparent that IC101 was again in­volved, since it now appeared to be completely inoperative. This lead me to the supply pin (pin 7) which is supposed to be at +12V. Only there wasn’t any voltage on it. The culprit was resis­ tor R121, a 1.5Ω resistor, apparently part of a decoupling net­ work. It was open circuit. A new resistor soon had the set up and running again but it was still not quite right. It was now suffering from significant horizontal underscan. I was glad I had caught that before Whinging Willie had had a chance to see it; he’d have had a seizure on the spot. Again, it didn’t take long to find the culprit. It was another resistor, this time R411 (68Ω). This resistor supplies current from the 16V rail to the collector of the horizontal driver transistor (Q401) via the primary of the horizontal drive transformer (T401) –see Fig.2. It had gone high by just enough to affect the drive. But it wasn’t really the resistor’s fault. Deprived of drive from IC101, Q401 would have been drawing excessive current and R411 would have been well on the way to complete failure. Anyway, it was easily fixed. I went over the set again, made sure all adjustments were optimised, tried to visualise what else might go wrong, and finally pronounced the job finished. I made out the warranty claim and rang the customer. He wasn’t any happier when he called this time. He con­ tinued his abuse of both Samsung in general and myself in partic­ ular. Among other things, he declared his temptation to “...go and wrap the set around Mr Samsung’s ears”. I told him I didn’t think that would do him any good and I think this made him realise just how ridiculous the suggestion was. And I had the last word – I reminded him again that he had been given first class service, with no argument, at no cost, and a minimum of waiting time. What more did he expect? At that he went on his way and that, thankfully, was the last I saw of him. It all happened many months ago and I am hopeful that this happy state will continue. I don’t want his custom again. Customer ignorance But the incident did make me think. Although this was an extreme case, customer dissatisfaction along these lines is nothing new; it has been cropping up from time to time for as long as I can remember. So why does it happen? Basically, it is due to customer ignorance, although the industry itself may be at least partly responsible. More exactly, this ignorance is in the form of two funda­mental misconceptions. The first is that the serviceman, by some magical process, is able to test – or even look at – any compon­ent and predict it’s end-of-life point. The second misconception arises December 1993  59 out of the first. It as­sumes that because such predictions are possible, a competent serviceman will check all components in the device being serviced and replace all those which are about to “wear out”. And this “wear” concept is another part of the misconception; the idea that all parts will eventually wear out. I won’t dwell on the impracticality of testing every component in a set; suffice it to say that the mind boggles! So the message we have to try to put across is that very few modern components have a predictable life. Valves did and picture tubes still do but most others have a theoretically infinite life. When they fail, it is usually a catastrophic failure which can happen at any time. And, of course, it is quite impractical to test all the components in a set. Does the customer have any idea how many there are? In most cases, the part would have to be removed for testing and then replaced. Quite apart from anything else, this could easily create more faults than it would prevent and it would really amount to a virtual rebuilding of the set. Would the customer be prepared 60  Silicon Chip to pay for such an exercise? Of course not. Having written all that, I am forced to concede how seem­ingly impossible the task would be. Nevertheless, I think we should keep these misconceptions in mind and, whenever the oppor­tunity is favourable, do our best to gently nudge the customer’s thinking in the right direction. Who knows; we might score once in a while. J. L.’s routine faults But enough of the philosophising; its time to get back to the bench – J. L.’s bench, that is, where we left him last month running through some typical routine faults. More precisely, he had just solved an acute case of the warbles in a Sharp audio cassette deck. He goes on. The next job on the bench was another audio cassette tape deck, this time an Hitachi model. A note taped to the top of the cabinet said that the machine had been “wowing” for some time but had now stopped altogether. I soon had the cover off and began a close inspection of the works. There was nothing wrong with the power supply or the electronics. It seemed to me that this had to be another mechani­cal problem. In fact, when I turned the power on, I noticed that the capstan flywheel made a short movement in the direction of normal rotation but then sprang back to its original position. It was obviously being jammed by some very elastic medium. I examined the cassette well, half believing that it was another pinch roller, like the last job. It wasn’t but it was another perished rubber part. This time it was the main drive belt. This is a flat belt, about 5mm wide. It had softened and stuck to the motor pulley. When the motor started, it stretch­ed the belt and wound several layers around the pulley. The belt was a write off, so I had to remove the motor and its mounting plate, fit a new belt, then reassemble the motor and test the unit. It wasn’t quite as easy as it sounds, since the remains of the old belt were very difficult to remove from the motor pulley. I had to use copious quantities of spirit to soften the deposit, then scrape and wipe until it was all gone. Following these two audio jobs, it was back to colour tele­vision for another brief exercise. This was a 50cm Philips set fitted with a KT2A-2 chassis. The owner reported that the on/off switch must be broken because the set would not switch on. I don’t know why customers always blame the power switch when a set won’t start. There are a hundred other things that could be blamed but it’s the power switch that cops all the stick! (It’s obvious J. L.; when they press the switch nothing happens – so the switch must be at fault!) On this occasion, I was soon able to absolve the switch simply by putting my ohmmeter across the active and neutral pins on the power plug. The meter showed infinity when the switch was off and a hundred or so ohms with the switch closed. Next, I went to the power supply section on the horizontal output board. The supply configuration in this set is most unu­sual. It’s effectively two separate DC supplies, connected in series by a Triac that’s triggered by a variable pulse derived from one of the bridge rectifiers. It’s a funny arrangement and one that is not at all easy to service if any part of it breaks down. In this case, I was lucky; I found the cause of the trouble after only 10 minutes’ work. I established that there were correct voltages being sup­plied from the bridges but very little at the output. So it seemed reasonable to assume that the regulator was at fault and my usual practice is to test transistors and diodes first. I was only a few minutes into the testing when I noticed a dry joint at one of the regulator transistors attached to a large heatsink. It didn’t look bad enough to be totally open circuit but it was and a touch with the iron soon restored the set to working order. So much for a “faulty” power switch! The last job for the day was a General Electric portable colour TV set, said to have an intermittent colour problem. The problem was intermittent but not in the usual sense of the word. When first switched on, the set would come up with a good black and white picture. Then, after anywhere from 30 seconds to five minutes later, the colour would snap on and stay that way as long as the set was left untouched. Switching off or changing channels would lead to a repeat of the black and white process. The fault was easy to diagnose. It was caused by maladjustment of the sub-carrier oscillator. The oscillator was tending to run off-frequency and the AFC circuit was having difficulty pulling it back. The service manual gives details of the adjustments required and it took only a minute or two to effect a complete cure. The adjustment calls for the AFC circuit to be disabled so that the colour can be “floated” by tuning the oscillator. As the adjustment is made, the colours run first one way then the other. The correct setting is between the two runs, where the colour just stands still. When the AFC is re-enabled, the picture should be in colour and should stay that way. In this case, it did and the set went home to a happy customer. After that, it was time for me to go home. Not every day is as straightforward as this one. But then, if I didn’t get an occasional day free from the bad SC jobs, I’d go stark raving mad. VIDEO & TV SERVICE PERSONNEL TV & VIDEO FAULT LIBRARIES AVAILABLE AS PRINTED MANUALS $90 EACH + $10 DELIVERY BOTH MANUALS VIDEO & TV $155 + $15 DELIVERY OR AS A PROGRAM FOR IBM COMPATIBLES $155 + $10 DELIVERY FOR MORE INFORMATION CONTACT TECHNICAL APPLICATIONS FAX / PHONE (07) 378 1064 PO BOX 137 KENMORE 4069 AUSTRALIAN MADE TV TEST EQUIPMENT 12 Months Warranty on Parts & Labour HIGH VOLTAGE PROBE Built-in meter reads positive or negative 0-50kV. For checking EHT & focus as well as many other high tension voltages. $120.00 + $5.00 p&p DEGAUSSING WAND Great for comput er mon­­­i t­o rs. Strong magnetic field. Double insulated, momentary switch operation. Demagnetises colour picture tubes, colour computer monitors, poker machines video and audio tapes. 240V AC 2.2 amps, 7700AT. $85.00 + $10.00 p&p TV, VCR TUNER REPAIRS From $22. Repair or exchange plus p&p. Cheque, Money Order, Visa, Bankcard or Mastercard Phone for free product list 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone (02) 774 1154 Fax (02) 774 1154 D & K WILSON ELECTRONICS Have you found those components yet? We know that it can be difficult, frustrating and a waste of your valuable time. So why haven’t you contacted us? We specialise in hunting down and locating components – old, obsolete, leading edge, normally available but now scarce due to allocation by overseas manufacturers. Integrated circuits, resistors, capacitors, transistors, diodes, valves, varistors, etc. Any brands Let us save your valuable time Contact us now on 833 1342 We are also distributors for Electrolube lubricants and chemi­cals Hakko - desoldering & soldering irons; SMD tools; replacement parts NTE - replacements semiconductors 2/87a Queen St, St Marys, NSW 2760. Phone (02) 833 1342 Fax (02) 673 4212 December 1993  61 This photo shows the Southern Cross computer hooked up to the 8x8 LED display & to the simple RS232 interface of Fig.2 which has been built up on a small piece of Veroboard. Peripherals for the Southern Cross Z80 computer This month, we present a number of peripherals for the Southern Cross Z80 computer which was featured in the August 1993 issue of SILICON CHIP. We look at ways to connect the Southern Cross to a person­al computer to make it easy to write programs, introduce an 8x8 LED Matrix display board which can produce interesting visual messages & describe an EPROM emulator. By PETER CROWCROFT & CRAIG JONES 62  Silicon Chip While it is desirable to learn how to enter machine code using the hex keypad of the Southern Cross computer, it is much easier to write these programs on a personal computer and then download them for testing. The fast way to write such programs is to use a text editor on a PC and then use a Z80 assembler to produce a file suitable for downloading to the Southern Cross. A public domain Z80 assem­bler, Z8T, is supplied with the Southern Cross kit and produc­es what is called an Intel hex output file. This is an ASCII file with a checksum every 16 data bytes and other information to help ensure that the transmission can be checked by software at the receiving system. +5V +5V 4.7 RTS V+ 1 C1+ DSR PC SERIAL PORT DB25 TXD RXD 16 TXD 2 VCC 4 C2+ 1 13 14 Q2 BC547 4.7k B 6.8k 1 3 47k D1 1N4148 10 2 CTS PC SERIAL PORT DB25 IC1 C1- MAX232 C2- R1IN R1OUT T1OUT V- T1IN GND 6 SOUTHERN CROSS BIT PORT CN4 5 12 11 RTS 4 SOUTHERN CROSS BIT PORT CN4 E 2.2k DOUT RXD 3 4.7 GND B +5V DSR 6 15 SG E D2 1N4148 CTS 5 DIN 1 DIN 1 C SG 7 C Q1 BC547 C VIEWED FROM BELOW 4.7k DOUT E GND Fig.1 at left is the ideal circuit for an RS-232 serial interface as the MAX232 IC is designed for this job. However, most RS-232 applications for an RS-232 interface for the Southern Cross will be satisfied by the transistor circuit of Fig.2 (right). There are basically two ways to connect the Southern Cross to a PC. First, you can connect it to the serial or parallel port of a PC and download the assembled program from the PC into the RAM space (2000H to 3FFFH). Second, you can use an EPROM emula­tor. In this case, the assembled program is moved to the emulated ROM space (2000H to 3FFFH.) The Monitor uses almost 4K of ROM so there is 4K free for you to use for your own programs. Serial downloading Assuming that you have written a program on your PC and have created an Intel hex file using the Z80 assembler, you will then want to download the hex file to the start of RAM (2000H) on the Southern Cross. By the way, making the jump from a raw novice to being able to write such programs will probably take several weeks at least, assuming that you can devote plenty of time to your Southern Cross, once you have it up and running. We certain­ly do not make light of this achievement but we feel sure that most people who purchase the Southern Cross will do it. The serial port on the Southern Cross is on connector CN4. Unfortunately, this cannot be connected directly to the PC serial port, since it operates on 12V while the Southern Cross operates at 5V. An interface board is required and two such inter- face circuits are shown in Figs. 1 & 2 – see above. For reliable serial communications, the guaranteed way is shown in Fig.1, using a MAX232 IC. A much simpler circuit is shown in Fig.2. This should be adequate in most cases but cannot be guaranteed for all situations. It can be assembled onto a small piece of Veroboard. Three wires are required between the PC and the interface board, while four wires extend from the interface to the Southern Cross. To download the file we must do two things: prepare the Southern Cross to receive the file and then get the PC to send the file. On the Southern Cross go to the address you want to put the file and press Function 1. The Southern Cross is now in ‘ready to receive Intel Hex file’ mode. To send the file from the PC you should first make sure that its serial port is not already being used by a mouse or other hardware item. Next you must set up the port with the DOS command: MODE COM1: 4800,N,8,1 This sets the PC’s port to 4800 baud to match that for the Southern Cross which is set to 4800 baud in the Monitor. Then enter the DOS command COPY filename.hex com1: This starts the file transfer. Alternatively, you could use a communications program, if you have one. When the Intel hex file is fed to the Southern Cross, the Monitor checks that it has been received correctly and converts it into machine code in the correct memory locations. If the transfer was successful a ‘C’ is displayed. Press any key to return to the Monitor. The downloaded file should be in RAM at the address (usually 2000H) it was sent to. If an error has occurred an ‘E’ will be displayed. If it did not come down at all, then nothing will be displayed. The baud rate for file transfer may be changed in software as outlined in the user manual supplied with the Southern Cross. 8 x 8 LED display This add-on board allows you make your own moving message displays. One or two display boards may be Parts List for the 8x8 LED Display 1 PC board, 108 x 60mm 1 CMD-58813 8x8 LED display 2 74HC273 octal D flipflops (IC1, IC2) 1 UDN2981 cathode driver (IC3) 1 ULN2803A anode driver (IC4) 1 DPDT slide switch (S1) 1 10µF electrolytic capacitor 2 18-pin IC sockets 2 20-pin IC sockets 1 16-pin box header connector 1 16-pin IDC socket connector 1 500mm length of 16-strand flat cable December 1993  63 1 10 VCC D7 D6 D5 D4 D3 D2 ROW LATCH I/O SELECT D1 D0 83H S1a 1 3 14 5 12 6 11 7 10 8 9 2 15 16 4 13 VCC 20 CLR O8 18 D8 17 D7 O7 9 19 1 16 4 14 D6 ROW O6 15 13 D5 LATCH 12 8 D4 IC1 O5 74HC273 9 7 D3 O4 4 D2 6 O3 3 D1 5 O2 11 82H O1 CLK 82H 2 5 8 7 6 3 2 O1 I1 I4 I5 O4 I7 O5 I3 O8 83H O7                                                               11 IC4 UDN2981A 10  14 ANODE DRIVER I2  15 I8 I6 LD1 CMD-5881F 18 12 D4 D3 D5 O6 D2 13 D6 D1 O3 16 D7 D8 80H O2 81H RESET 17 18 GND VCC GND 20 SOUTHERN CROSS I/O PORT D7 D6 D5 D4 COLUMN LATCH I/O SELECT 81H S1b 80H D3 D2 D1 D0 18 O8 19 16 O7 15 14 D6 O6 13 12 D5 O5 9 8 D4 COLUMN O4 LATCH 6 7 D3 O3 5 4 D2 O2 IC2 74HC273 3 2 D1 O1 11 CLK 17 1 D8 D7 1 I1 4 5 O1 18 15 O4 O5 14 I4 I5 CATHODE 11 DRIVER O8 I7 O7 12 6 13 IC3 I6 06 ULN2803A 3 03 16 I3 2 17 O2 I2 8 7 I8 9 CLR 10 8x8 DOT LED MATRIX Fig.3: the 8x8 LED matrix display is driven from the parallel port of the Southern Cross computer via two Tri-state latch ICs (IC1 & IC2) & two buffer ICs (IC3 & IC4). Switch S1 switches the latches between two sets of port addresses, thus allowing two LED matrix displays to be used together. used and they are connected to connector CN1 of the Southern Cross. Each board is designed so that the display section may be cut away from the circuit section and connected by flat ribbon cable. The circuit of the 8x8 LED Matrix display is shown in Fig.3. It is connected to the parallel I/O port of the Southern Cross via connector CN1. Data lines D1-D8 are used to drive two 74HC273 octal D-flipflops, each used as 8-bit latches (IC1, IC2). The eight outputs of the two latches are buffered by the UDN2981A anode driver (IC4) and ULN2803A cathode driver (IC3), 64  Silicon Chip respectively. These drive the rows and columns of the 8x8 LED matrix display. Latch IC1 is also connected to the system Reset to ensure that the LEDs are not lit when the circuit is first powered up. Slide switch S1 switches the latches between two sets of port addresses. In this way, two LED Matrix displays can be used together, one operating from port addresses 80h and 82h and the other operating from port address­es 81h and 83h. The LED Matrix display is multi­ plexed and relies on per­sistence of vision to produce its complex patterns so that moving messages (for example) can be displayed. In the kaleidoscope program, each LED may seem to be on all the time but it is not. Each LED is turned on for only 15 microseconds every half a millisecond. This is a duty cycle of 3%. Peak current through the LEDs is 70mA but the average current is only 2mA. Constructing the LED display Assembly of the LED display board does not involve many components and should not take long at all. The component layout diagram is shown in Fig.4. First, fit the 11 wire links to the board. Some of these may be hard to spot. Don’t forget the two short links, near the slide switch. Fit the LED display so that its out- LD1 CMD-5881F D7 1 D6 D5 IC3 ULN2803A D4 D2 10uF 1 IC2 74HC273 1 The 8x8 LED display is, as its name suggests, a matrix of 64 LEDs which are driven in multiplex fashion from the parallel port of the Southern Cross computer. Note the slide switch to change the address of the display, so that two can be used in conjunction with each other. line matches the screen printed outline on top of the board. This is most important because if you do it the other way around the display will be upside down and won’t work. Sockets are supplied for the four ICs and these can be soldered in next. This done, fit the 10µF capacitor, the slide switch and the rightangle flat cable connector. You will have to make up the 16 way cable which uses IDCs (insulation displacement connectors. These are squeezed together with a vise to apply even pressure to the connector halves. When you finish each connector, inspect the pins closely to be sure that each pin is connected to the cable strand that it is supposed to go to. It is rather easy when doing hand construction of these cables to find one pin has gone in skewed and is shorting between two adjacent V-pins. Make sure that pin 1 at one end of the cable goes to pin 1 at the other end, and not pin 16. To check that the board is working the Southern Cross monitor has a kaleidoscope built into it. Put the switch in the up position. This will connect the two latches on the board to ports 80H and 82H. Press Function E. (To remind you – press the Reset key, then the Fn key then the ‘E’ key.) A pattern of ran­ d omly generated D1 D0 IC4 UDN2981 IC1 74HC273 1 S1 symmetric images should appear on the display. This will continue until Reset is pressed. Programming the 8x8 Multiplexing the 8x8 can be done in several ways. One of them is to use the subroutine already written in the Monitor. In this subroutine, SKATE, one row of 8 LEDs is scanned at a time. The LEDs to be turned on in that row are given by the bit pattern of the 8 positions. A bit pattern of 10000001 (or 81h) will turn on the outer two LEDs. A pattern of 11111111 (FFh) will turn them all on. To program this, the byte representing the top row is stored in the register pair HL. HL+1 stores the byte for the second row from the top, HL+2 the byte for row 3 etc. We can conveniently use system call 16 to scan the 8x8 display rather than re-invent the wheel and write our own code. An example will show this more clearly. Using a piece of paper, form the letter A of your choice using the 8x8 SOUTHERN CROSS I/O PORT Fig.4: the component layout of the 8x8 LED matrix display. Do not omit the very short links on either side of the slide switch. matrix. We decided on codes 18, 24, 42, 42, 42, 7E, 7E & 42 as follows: 00011000 = 18h 00100100 = 24h 01000010 = 42h 01000010 = 42h 01000010 = 42h 01111110 = 7Eh 01111110 = 7Eh 01000010 = 42h Do you see the capital A outlined by the 1‘s in the code above and how to derive the hex byte representing the 0 & 1 pat­tern? Hand enter these bytes into locations 2000h to 2007h of the Southern Cross. Next, enter the code shown in Table 1 at 2100h, then do Fn 0. You should have the letter “A” displayed on the LED matrix. Table 1 2100 2103 2105 2106 21 00 20 0E 16 F7 C3 00 21 LD HL,2000H LD C,16H RST 30H JP 2100h ;point HL to buffer ;system call SKATE ;call it ;repeat the loop December 1993  65 33pF RESET S1 33pF X1 6MHz 1 330  TO PC STROBE 6 ERROR 7 BUSY 8 D3 5 D2 4 D1 3 D0 2 GND 1  3 2 4 7 30 29 28 27 34 33 1 P14 A K DIPSW 31 IC1 8748 2 1 B C 330 LED2 READY 10k 10 37 A14 36 A13 35 A12 24 A11 23 A10 22 A9 21 A8 11 19 DB7 18 DB6 17 DB5 16 DB4 15 DB3  47k B Q1 BC547 5D 6D 7D 8D 20 VCC 5O 6O 7O 8O 16 A4 15 A3 14 A2 13 A1 12 A0 E C VCC 11 4 10 1 OC TARGET RESET D1 1N4148 C 4D IC2 4O 74HCT573 17 A5 3D 3O 3 18 A6 2D 2O 2 19 A7 1D 1O 5 6 7 8 13 DB1 14 DB2 9 12 DB0 VIEWED FROM BELOW 3 4 32 39 WR P26 P25 P24 P23 P22 P21 P20 ALE DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 5 P15 T1 SS EPROM EMULATOR 38 XTAL2 P27 XTAL1 RESET EA P13 P12 P11 P10 P17 P16 TB 26 VDD 6 INT 27 1 26 2 23 21 24 25 3 4 5 6 7 8 9 10 WE A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 28 20 CE IC3 62256 VCC 14 D7 D6 D5 D4 D3 D2 D1 D0 18 D7 17 D6 16 D5 15 D4 14 D3 13 D2 12 D1 11 D0 A14 17 A12 16 A13 15 A8 14 A9 13 A11 12 A10 11 A0 18 A1 17 A2 16 A3 15 A4 14 A5 13 A6 12 A7 11 D4 D3 D2 D1 20 VCC O4 O3 O2 O1 14 15 16 17 18 7 10 20 E1 E2 1 19 B1 B2 B3 B4 B5 B6 B7 A7 A0 VCC 20 10 E 19 10 A1 A2 A3 A4 IC6 A6 74HCT245 A5 DIR 1 19 D7 D6 D5 D4 D3 D2 D1 D0 A0 A1 A2 A3 A7 A6 A5 A4 VCC 3 A14 4 A12 5 A13 6 A8 7 A9 8 A11 9 A10 2 VCC 9 A7 8 B6 A6 7 B5 A5 6 IC5 A4 B4 74HCT245 5 B3 A3 4 A2 B2 3 B1 A1 2 A0 B0 E 1 DIR B7 D5 IC4 O5 74HCT541 13 D6 O6 9 11 O8 D8 12 8 O7 D7 6 5 4 3 2 D5 D4 D3 D2 D1 D0 28 VCC A5 A4 A3 A2 A1 A0 47k NETWORK D6 4 3 1 2 14 5 VCC A14 A13 A12 A11 A10 A9 A8 A7 A6 5 A5 6 A4 7 A3 8 A2 9 A1 10 A0 VCC 4 A6 28-PIN 3 D7 EPROM A7 SOCKET 25 22 OE A8 24 20 A9 CE 21 A10 23 A11 2 A12 26 A13 27 A14 19 18 17 16 15 13 12 11 A12 10k A14 LED1 DATA A11 A13 66  Silicon Chip The EPROM emulator can be used with the Southern Cross or any other 8-bit computer for that matter. It can emulate 8K, 16K or 32K EPROMs. EPROM emulator ▲ This replaces the EPROM in a computer system with RAM. It has a 28-way cable and 28-pin header plug which takes the place of the EPROM in the target computer. In our case, the target computer is the Southern Cross but it could be any computer system which uses an 8K, 16K or 32K EPROM. The RAM imitates or emulates the EPROM. The target system reads the RAM and thinks it is reading an EPROM. Essentially, it is an independent block of RAM which can be access­ ed from two sides: (1) from the target Fig.5 (left): the EPROM emulator uses an 8748 microcontroller (IC1). This takes data from the host computer a nibble (four bits) at a time & stores it as 8-bit data in a 62256 static RAM (IC3). The target computer then “sees” the RAM as a normal EPROM. X1 2x33pF 1 10k 1 1 IC4 74HCT245 1 10k 1 IC2 74HCT573 This example demonstrates how using the subroutines in the Monitor simplifies code development and reduces time. Just four lines of code have put the contents of the 8-word buffer on the display. Add some bit shift instructions, delays and a bigger message buffer and you can move a message across the screen. Or you can develop a maze game. Examples of each of these types of programs, a maze game and a scrolling message program, have been supplied on the floppy disc which accompanies the 8x8 kit. Now let us look at the last peripheral to be described this month, the EPROM Emulator. 1uF TO PC 1 IC3 8748 IC6 74HCT541 0.1 1 DIPSW 47k Q1 330  S1 OUTPUT TO EPROM IC5 74HCT245 IC3 62256 330  0.1 4x47k D1 LED2 LED1 Fig.6: the component layout for the EPROM emulator. Note that all the ICs are mounted in sockets & must be oriented exactly as shown. The device is connected to the Southern Cross computer via a 28-way flat cable fitted with 28-pin DIP headers. system which can read from it; and (2) from the host PC which can write to it. Hardware and software make sure that simultaneous access from both sides is not possible. The advantage of this system is that program development time can be a matter of seconds rather than tens of minutes or even hours under the old blow-and-erase cycle. The RAM can be written to by the external computer, so the target system imme­diately sees a ‘new’ EPROM. In addition, the emulator gives the capability to download and test other programs in its unused RAM. The emulator described here is an ‘intelligent’ design with an 8748 (or 8749) microcontroller and, as already noted, it can emulate 8K, 16K or 32K EPROMs. A floppy disc with a public domain Z80 assembler is provided as well as a Monitor for the Southern Cross and program examples. The principle of operation is that the program to be tested on the Southern Cross is prepared and assembled in your PC. It is then downloaded to the emulator. While it is being down­ loaded, the Southern Cross system is held in RESET state. When the trans­ fer is successfully completed, a message appears on the PC screen, the Southern Cross system is released from the RESET state and then it is in control. The circuit diagram of the emulator is shown in the diagram of Fig.5. Only four of the eight available data lines from the parallel port are used to transfer data from the PC to the emula­ tor. This results in a saving of two ICs and the elimination of a DB25 port connector on the emulator PC board. The speed cost is about a 10% reduction in data transfer rate compared to that possible if all eight lines were used with DOS commands to do the transfer. This was judged to be an acceptable trade-off in this instance. December 1993  67 Table 2 IDC Pin Name Male Sub-D Pin # Cable Strand # 1 Ground 18-25 1 2 Data line 0 2 3 3 Data line 1 3 5 4 Data line 2 4 7 5 Data line 3 5 9 6 Strobe 1 10 7 Error 15 8 8 Busy 11 9 & 10 Not Connected 6 4 & 2 resp. Prices & availability Since the first article on the Southern Cross in August 1993, the prices for the kits have needed to be adjusted to compensate for currency movements. The prices are as follows: Southern Cross Computer ..................................................................$194 Dallas 1213B SmartSocket ...................................................................$63 Dallas 1216B SmartSocket ...................................................................$84 8x8 LED Display ....................................................................................$73 EPROM Emulator ................................................................................$129 Technical manual of IC data sheets ......................................................$12 The kits containing all the components may be ordered in Austra­lia from Alpine Technology, PO Box 934, Mt Waverley, Vic 3148. Phone or fax (03) 751 1989. You may pay by Bankcard, Mastercard, cheque or money order. Buyers outside Australia should contact DIY Electronics in Hong Kong. Phone/fax (852) 725 0610. The emulator board, emulator software and the software which you are already using in your PC must combine together to operate the EPROM emulator. Power for the emulator comes from the Southern Cross via the 28-pin socket. The 2-way DIP switch selects the size of EPROM to be emulated. The simple RS-232 interface of Fig.2 can be built up on a small piece of Veroboard as shown here. 68  Silicon Chip To emulate the Southern Cross (8K EPROM), both DIP switches will be in the OFF position. The 8748 microcontroller receives the program from the PC a nibble (4 data bits) at a time. It assembles them into bytes (8 data bits) and generates the address and all the timing signals to write the byte into the 62256 static RAM. It also controls the target (ie, the Southern Cross) system via the RESET line, reads the DIP switches, and communicates back to the PC. IC2 is a 74HCT573 Tri-state octal D-type latch which is controlled by the 8748 to switch data from the four input data lines into the addresses of the static RAM (IC3). IC4, IC5 and IC6 are also Tri-state chips which are controlled by the target computer (via the 8748) in accessing data stored in the RAM when the circuit is emulating EPROM. Construction All the components are mounted Parts List for the EPROM Emulator 1 PC board, 114 x 58mm 1 6MHz crystal 1 2-way DIP switch 1 miniature momentary contact switch (S1) 1 200mm-long 28-strand ribbon cable 1 150mm-long 10-strand ribbon cable 2 28-pin DIP headers 1 10-pin IDC connector 1 10-pin box header connector 1 25-pin male sub-D connector 1 25-pin sub-D case 1 40-pin IC socket 1 28-pin IC socket 4 20-pin IC sockets Semiconductors 1 8748 microcontroller (IC1) 1 74HCT573 octal Tri-state D flipflop (IC2) 2 74HCT245 octal Tri-state transceivers (IC5, IC6) 1 74HCT541 octal Tri-state buffer (IC4) 1 62256 static RAM (IC3) 1 BC547 NPN transistor (Q1) 1 1N4148 signal diode (D1) 1 3mm yellow LED (LED 1) 1 3mm green LED (LED2) Capacitors 1 1µF electrolytic 1 0.1µF monolithic 2 33pF ceramic Resistors 1 47kΩ SIL resistor network 1 47kΩ ¼W 1 10kΩ ¼W 1 330Ω ¼W on a double-sided PC board which is screen printed on top to show the layout – see Fig.6. Sockets are used for all the ICs and these can be placed and soldered after all the small components are inserted. Make sure that the transistor, the two LEDs, the diode and the electrolytic capacitor are inserted with correct polarity. A single wire connects the “TO TARGET RESET” pads of the emula­tor to RESET on the target system. Two cables with IDC connectors need to be made up. One cable Continued on page 88 Silicon Chip Book Shop Dedicated To Bringing You Books On State Of The Art Technology These books are written by acknowledged specialists in their fields and will fill a longfelt requirement for reference texts. Each book is up to date, well written and most important­ly, available now. Linear Electronic Design The Art of Linear Electronics, by John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured - a must for anyone inter­ested in audio design. 336 pages, in paperback at $45.95. Digital Audio Satellite TV Newnes Guide to Satellite TV; Installation, Recept­ion & Repair. By Derek J. Stephenson. 2nd edition, published 1991, reprinted 1992. This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 284 pages, in hard covers at $45.95. Digital Audio and Compact Disc Technology. Produced by the Sony Service Centre (Europe). 2nd edition, published 1992. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 247 pages, in paperback at $59.95. Optoelectronics Optoelectronics: An Introduction, by J. C. A. Chaimowicz. First published 1989, reprinted 1992. This field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Power Electronics Power Electronics Handbook, Components, Circuits & Applica­tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors and Triacs in single and three phase circuits. 417 pages, in hard cover form at $59.95. TV & Video Newnes Guide to TV & Video Technology, by Eugene Trundle. First published 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95. To order any of these books, fill out the coupon below & send it with your remittance to SILICON CHIP Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ ______________________________________Postcode_____________ Daytime Phone No._____________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card Card No. Signature__________________________ Card expiry date_____/______ Books Required (please tick) ❏ ❏ ❏ ❏ ❏ ❏ Newnes Guide to Satellite TV ($45.95) Optoelectronics: An Introduction ($55.95) Linear Electronic Design ($45.95) Digital Audio & Compact Disc Technology ($59.95) Power Electronics Handbook ($59.95) Newnes Guide to TV & Video Technology ($39.95) Mail coupon to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details; or fax the details to (02) 979 6503. December 1993  69 VINTAGE RADIO By JOHN HILL My no-hassles radio museum Most of my collection now sits on show in a new museum in Maryborough. It didn’t cost me a cent & I only have to spend as much time there as I choose. Here’s how it all came about. Way back in the October 1991 issue of SILICON CHIP, I did a story on two Victorian radio museums – the “Cats­ wisker” museum in Chiltern and the “Orpheus” museum in Ballarat. In that particular article, I expressed the desire to have my own radio museum but dismissed the idea at the time due to the many problems associat­ed with such a project. Some of these problems are: finding a suitable building in an appropriate place, the overall expense of such a venture and the time spent in managing the museum itself. It doesn’t take long to realise that a private museum could be a bad financial proposition. In many instances, the expense of setting up may never be recouped because of poor returns and ongoing costs. Not all museums are successful ventures! It is interesting to note that, at the time of writing, the “Catswisker” collection has been for sale for quite some time and the “Orpheus” collection has been relocated to one of Ballarat’s other tourist attractions. The small number of people visiting the original Orpheus museum did not justify the amount of space it occupied. Richard Wil­son’s growing electronics business needed room to expand and the museum space had to be utilised. Personally, that was a bit of a blow because it meant the end of my Sunday job. Well, we are in tough times, so I The radio museum has been tastefully arranged, with the exhibits being wellspaced & uncluttered. Most of the receivers are in working order. 70  Silicon Chip guess that part time museum curators are ex­pendable. Bob Adkins of the Catswisker found the museum a tie and it prevented him from doing all the things retired people like to do. Because of his museum commitments, he was unable to go away for a month or so and enjoy a holiday. Someone had to be there in case tourists wanted to see the museum. Richard Wilson was in a similar situation and he employed me on Sundays because it was the only way he could have a day off. My museum All of the forgoing put me in a good position to realise that having your own radio museum is not all fun and admission dollars. I was indeed fortunate to have this first-hand informa­tion as it prevented me from putting myself in a similar situa­tion. However, things happen in mysterious ways and it seems as though I was destined to have a radio museum. What’s more, it is now a reality. The good part about “my” museum is that it hasn’t cost me a cent and it will require no more of my time than I care to put into it. Yes, I know that it all sounds too good to be true, so allow me to explain some of the details. In the small rural city in which I live (Maryborough, Vic­toria), there is a group of people who call themselves “Gold­en Era Steam and Rail, Mary­ borough”. Basically, they are interested in steam power and railways but they also have some affiliation with the local “Creative Arts” group. In fact, many members belong to both groups. Together, they decided that Mary­­ borough needed an addi­tional tourist attraction and reckoned that a top class museum would be a great asset for the This corner of the museum houses a collection of test instru­ments. Shown are valve testers signal generators, oscilloscopes & other items of test equipment from the past. The radio museum has five console style receivers on display, all of which are in working order. This one is a mid-1930s model Commodore, a 5-valve autodyne superhet. city. Accordingly they sent let­ters to several local collectors (myself included), inviting them to attend a meeting to discuss plans for a museum and to have “meaningful talks”. Those invited to that first meeting were Bill Harper, Bill Holland, Warren Tattersall and myself, plus delegates from the Maryborough City Council and a few other interested people. Bill Harper is a retired radio technician who spent about 40 years with radio station 3CV Central Victoria, which transmits from Maryborough. He has worked in many different aspects of radio, including being an announcer. In early broadcasting, people had to be versatile. Bill Holland is in his 70s and is a radio/TV repairman from way back. He is also a collector of old radios and associated equipment which he has acquired during his lifetime. Warren Tattersall runs a camera shop in town and is a keen collector of cameras and photographic equipment. What the Golden Era Steam and Rail people had in mind was to utilise the three collections as the basis for a museum dis­play, adding to it as time progressed. Bill Harper’s task was an advisory The radio receivers are displayed on shelves or pedestals of various heights. At this stage, there is plenty of room to accom­modate additional exhibits. one. It was hoped to build a replica of 3CV’s original broadcasting studio and as Bill is one of the few people still around who remembers what it looked like, his input was invaluable. It was also planned that the studio would be connected to a street loudspeaker system, enabling music and announcements to be “broadcast” to shoppers and city visitors in High Street, the main shopping area. The studio was to use the call sign 3HHH, the “triple H” standing for Harper, Hill and Holland. It was a bold plan and its main instigator was Jim Tanner. Jim had a vision in his mind’s eye about every detail of the museum and without his efforts the museum complex may never have been completed – or even started for that matter! A building was available in High Street, its position being a great advantage because of its central location. This building has since been extensively altered to accommodate an arts and crafts shop at the front, the museum complex in the middle and an art studio at the rear. The building is quite large and it runs from the main street through to the street behind where there is ample room for parking (including tour buses). The City Council provided a loan to help get things started. Such an enterprise cannot succeed without a sizable injection of funds. As the Creative Arts group comes under coun­cil control, December 1993  71 Bill Holland’s 1920s corner – a display of early loudspeakers & regenerative receivers. Bill also has a glass cabinet full of early radio equipment & other interesting items. After much searching, 3CV’s old studio console has returned to Maryborough. It was retrieved from a collector in Deniliquin. that makes the museum, in effect, affiliated with the council which is a definite advantage for an undertaking of this magnitude. Another good aspect of the museum project is the fact that a large proportion of the work was done by volunteers and approximately 30 people toiled relentlessly in order to outfit the museum and renovate the building. These people have helped considerably in containing costs to a reasonable level. Naturally, there had to be proper steps taken to protect and insure the exhibits, because the collections involved are worth many thousands of dollars. Establishing a museum costs 72  Silicon Chip money – big money – and I was glad that my personal finances were not involved. An agreement has been signed by all parties concerned to the effect that the collections are on loan for a minimum 5-year period, after which a new agreement will be negotiated. Part of the agreement also states that if the items on loan are subjected to unreasonable damage due to poor supervision or careless han­ d ling, the collections can be withdrawn by their owners. Dust problems I noticed during my time at the Orpheus museum that dust can be a problem as far as valuable old radios are concerned. Admittedly, I’m a fanatic when it comes to dust but a dusty display area will eventually reduce a well-restored radio to something of lesser value. Over a period of time, dust and its constant removal can do considerable damage to polished surfaces such as those on timber and bakelite radio cabinets. My collection of radios has always been kept under wraps and in a darkened room. The reason for the darkened room is that continual exposure to sunlight will fade timbers and speaker cloths and eventually destroy the delicate paintwork on dial glasses. Some plastics also react unfavourably to regular daily doses of sunshine. If the Golden Era Steam and Rail people wanted to display my radio collection they would have to look after it in a similar manner. And so a dust-free environment was another aspect of the agreement. Dust control has been achieved by relatively simple means. The display area for the radios is basically a very large carpet­ed room with three archways for entrances. Filtered air is pumped into this room to create a slight pressure build-up. The air thus continually flows out of the room and this prevents dust from coming in. The dust-free room may not be 100% dust proof but it is very close to it. As entry to the museum is through the arts and crafts shop, that area acts as a buffer zone for the museum. The filtered air method of dust control is a far better arrangement than doing nothing at all about it. Running the museum on a daily basis is made possible by a team of helpers who give what time they can. Once again, costs are kept to a minimum because of volunteers. The next stage The completion of the radio museum sees the end of stage one of the proposed development. The camera display is next on the list and will be followed by another area which will include antiques, collectables and memorabillia. These items will be supplied by interested local supporters. Already in place is a huge twin-cylinder, double-acting steam engine and alternator. The old steam engine originally powered the Maryborough Knitting Mill and lit up the streets of the city back in the days before Ma- RESURRECTION RADIO Vintage Wireless Specialists Repairs – Restoration – Sales These three Stromberg-Carlson receivers are all on display at the Museum of Creative Arts & Sciences. They are all post-war models. Our skilled technicians offer QUALITY repairs and restoration. We also have a large stock of bakelite and timber radios fully restored and for SALE. Parts are available for the enthusiast, including over 900 valve types, high voltage cap­a citors, transformers, dial glasses, knobs, grille cloth etc. Circuit diagrams for most Australian makes and models. Send SAE for our catalog. WANTED: Valves, Radios, etc. Purchased for CASH Call in to our showroom at: 51 Chapel Street (PO Box 1116), Windsor, Vic 3181. Phone: (03) 529 5639; Fax (03) 510 4486 Many smaller items, including some early transistor radios, are on show in this glass cabinet. Perhaps the most interesting exhibit here is the well constructed home-made crystal set (centre front). ryborough was connected to the SEC power grid. A display of early lighting is planned to complement this part of the museum. The Central Victorian Car Club has also offered to display the odd vintage car for short periods from time to time if space permits. It appears as though the Museum of Creative Arts and Sciences will be well supported by various groups and individu­als. Now some readers may be surprised to read that I have let my collection of old radios go out of my control, so to speak, for a period of five years or more, as the case may be. Well, to be perfectly honest, I was glad to see them go because they had taken up so much space at home and storage was becoming a real hassle. Marital problems were imminent if something wasn’t done! For the first time in many years I now have room to move and work in my den and it’s great feeling! If you are in a simi­lar situation with more radios than you have storage space for, then just give them away for five years – it solves the problem instantly! A few toys Of course I wasn’t generous enough to give everything away and I’ve kept some of my real treasures. A bloke my age needs a few toys to play with when the mood demands it. So there it is! “My” museum is a reality, it cost me noth­ing to set up, I don’t have to look after it and I have access to it at any time. What’s more, the radios are well insured and I can take them back if they are not looked after. That’s a very good arrangement as far as I’m concerned! Really, it’s great to have my collection on permanent dis­play. It should be available for people to see instead of being locked up in a dark room where no one can appreciate those fine old receivers from yesteryear. I might add that those fine old receivers have taken me nearly 10 years to find and restore, so the radio museum display represents most of my spare time for the past decade. If you’re ever driving through Maryborough, be sure to call in and take a look. The museum hours are 10am-4pm Monday to Saturday and 1pm-4pm on Sundays. Footnote: since writing the above, John Hill advises that the replica 3CV studio may soon become a genuine radio studio. The museum committee has applied for a broadcast licence and hopes to start a community radio station, using a 10W transmitter on SC the AM band. December 1993  73 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd This simple project produces a 64-note melody using just a 3-pin IC in a TO-92 plastic package, plus a few external parts. Six different ICs are available to give six different melodies, whilst a seventh chip produces a medley of tunes. By BERNIE GILCHRIST : s i h t d l i Bu T ABLE 1 shows the range of melody and medley ICs that are available for this project. A separate kit can be constructed for each melody required or the melody can be changed simply by swapping the IC. It should also be possible to change ICs using a 2-pole 2-position switch. Power for the circuit is derived from a single 1.5V cell but there is provision for an external 3-12V supply as well. The sound level produced by the small loudspeaker specified is quite impressive and can be reduced if necessary, as described later. At the heart of this project is a UM66TxxL low-power CMOS IC, part of a series designed for use in door bells, telephones and toys. This IC is an LSI (large scale integration) device which includes a ROM (read only memory) that is programmed with the note scales and rhythm codes. The oscillator and control circuitry is also built into the chip. The output from IC1 is a modulated rectangular waveform which is almost equal to the supply voltage in amplitude; ie, slightly less than 1.5V peak-to-peak. The required sound is achiev­ed by varying the frequency and width of the pulses. The output from IC1 appears at pin 1 and drives transistors Q1 and Q2 which operate as a Darlington output stage to drive an 8Ω loudspeaker. Resistor R2 is used for supply voltages greater than 3V and protects both Q2 and the loudspeaker from excess current (see Table 2). The 1µF electrolytic capacitor connected between Vdd (pin 2) and Vss (pin 3) is used to decouple the supply to IC1. This prevents the relatively high switching current in the output stage from interfering with the operation of the IC. D1, R1, R2 and LED 1 are used only if the supply voltage is 3V or more. These parts can be omitted if the circuit is to be powered from a 1.5V battery and R1 and R2 replaced by wire links. D1 protects the circuit if the external supply voltage is acci­ dentally reversed, while R1 and LED 1 together form a 2.3V regulator to limit the supply voltage to the IC (3.3V max). Table 2 shows the suggested values for R1 and R2 for exter­ nal supply voltages of 3-12V. Note that the 1.5V battery must be removed if you intend using an external supply. Assembly Fig.2 shows the parts layout on the PC board (code ZA-1324). You can install the parts in any order 1-Chip Melody Generator 80  Silicon Chip D1 1N4007 EXTERNAL BATTERY OFF S1 ON PARTS LIST R1 SEE TEXT 1k Q1 BC549 1.5V 2 A LED1 GREEN  1 50VW IC1 UM66T 3 1 B 1 PC board, code ZA-1324, 78 x 33mm 1 8-ohm 0.2W loudspeaker 1 AA single cell battery holder 1 SPDT slide switch 1 countersunk screw & nut (to secure battery holder) R2 SEE TEXT 8W SPEAKER C E Q2 BC337 B C Semiconductors 1 UM66TxxL melody generator IC (IC1) - see Table 1. 1 BC549 NPN transistor (Q1) 1 BC337 NPN transistor (Q2) 1 1N4007 silicon diode (D1) 1 5mm green LED (LED 1) E K B K A E 3 2 1 C VIEWED FROM BELOW MELODY GENERATOR Fig.1: the melody is generated by IC1 & this drives Darlington output pair Q1 & Q2 which in turn drive the loudspeaker. Capacitors 1 1µF 50VW PC electrolytic Resistors (0.25W, 5%) 1 1kΩ 1 R1 - see Table 2 1 R2 - see Table 2 TABLE 1 IC Type Melody Catalog Number UM66T01L Jingle Bells + Santa Claus Is Coming To Town + We Wish You A Merry Christmas K-5502 UM66T05L Home Sweet Home K-5504 UM66T09L Wedding March (Memdelssohn) K-5506 UM66T19L For Elise K-5508 UM66T32L Waltz K-5510 UM66T33L Mary Had A Little Lamb K-5512 but be sure to use the correct part at each location. Use wire links for R1 and R2 if you are going to power the circuit from a 1.5V battery, other­wise refer to Table 2 for the values of these components. Note that using a link for R2 will give the maximum output from the speaker but the battery life will be quite short. Alternatively, you can increase the battery life at the expense of output level by installing a low value resistor for R2 (eg, 10Ω). Take care when mounting the transistors. Do not push them too far down into the board because the leads spread and this may damage the connections inside them. Check that all polarised parts have been oriented correctly before applying power. These include the diode, transistors, IC, LED and the electrolytic capacitor. The LED leads are easy to identify – the cathode (K) lead is the shorter of the two. Although LED 1 is not intended to operate as a power indi­cator, it could also be used for this purpose if you are using an external (3V or greater) supply. All you have to do is reduce the value of R1 so that the LED current is about 5-10mA. The values shown for R1 in Table 2 give a current of about 1mA (ie, not enough to light the LED), so just divide the value shown for a given voltage to obtain the current Where to buy the kit This project was designed by Dick Smith Electronics who own the copyright on the PC board. Com­plete kits are available from all Dick Smith Electronics Stores or by mail order from PO Box 321, North Ryde, NSW 2113. The price is $9.95 plus $3 p&p. Please quote the relevant catalog number when ordering – see Table 1. required. Do not use a red LED for LED 1, as its forward voltage drop will be only about 1.8V (as opposed to 2.3V for a green LED). Once all the parts are in, install the battery and switch on. If everything is correct, the circuit will immediately start playing back the tune programmed into IC1. If it doesn’t, switch off immediately and check for SC wiring errors. S1 1.5V AA CELL TABLE 1 Supply R1 R2 1.5V link link 3V 560W link 6V 3.3kW 10W 1W 9V 6.8kW 22W 1W 12V 8.2kW 27W 5W D1 R2 R1 A EXT BATT 1uF LED1 K IC1 1 2 3 1k Q1 Q2 SPEAKER Fig.2: this wiring diagram shows all parts in position but note that some parts can be left out if power comes from a 1.5V battery. December 1993  81 Silicon Chip (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone; How To Quieten The Fan In Your Computer. December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor For Shortwave Receivers; Why Diesel Electrics Killed Off Steam; Index to Volume 1. February 1989: Transistor Beta Tester, Cutec Z-2000 Stereo Power Amplifier, Using Comparators To Detect & Measure, Minstrel 2-30 Loudspeaker System, VHF FM Monitor Receiver, LED Flasher For Model Railways, Jump Start Your New Car March 1989: LED Message Board, Pt.1; 32-Band Graphic Equaliser, Pt.1; Stereo Compressor For CD Players; Amateur VHF FM Monitor, Pt.2; Signetics NE572 Compandor IC Data; Map Reader For Trip Calculations; Electronics For Everyone – Resistors. April 1989: Auxiliary Brake Light Flasher; Electronics For Everyone: What You Need to Know About Capacitors; Telephone Bell Monitor/ Trans- December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. mitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Electronic Pools/Lotto Selector; Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2; PC Program Calculates Great Circle Bearings. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. October 1989: Introducing Remote Control; FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. November 1989: Radfax Decoder For Your PC August 1990: High Stability UHF Remote Trans- Please send me a back issue for: ❏ February 1989 ❏ March 1989 ❏ July 1989 ❏ September 1989 ❏ January 1990 ❏ February 1990 ❏ July 1990 ❏ August 1990 ❏ December 1990 ❏ January 1991 ❏ May 1991 ❏ June 1991 ❏ October 1991 ❏ November 1991 ❏ March 1992 ❏ April 1992 ❏ August 1992 ❏ September 1992 ❏ January 1993 ❏ February 1993 ❏ June 1993 ❏ July 1993 ❏ November 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 March 1993 August 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ November 1988 May 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 June 1992 November 1992 April 1993 September 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ➦ Use this handy form to order your back issues December 1988 June 1989 December 1989 June 1990 November 1990 April 1991 September 1991 February 1992 July 1992 December 1992 May 1993 October 1993 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 82  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. mitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Windows 3 & The Dreaded Un­ recov­erable Application Error; Index To Volume 4. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; Laser Power Supply; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; LowCost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1; Setting Screen Colours On Your PC. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Electric Vehicle Transmission Options; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; PEP Monitor For Amateur Transceivers. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Installing Windows On Your PC; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; Build A Fax/Modem For Your Computer; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic February 1992: Compact Digital Voice Recorder; 50-Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ ories; Valve Substitution In Vintage Radios. April 1992: Infrared Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; LowCost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; What’s New In Oscilloscopes?; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Off-Hook Timer For Tele­phones; Multi-Station Headset Intercom, Pt.2. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. November 1992: MAL-4 Microcontroller Board, Pt.1; Simple FM Radio Receiver; Infrared Night Viewer; Speed Controller For Electric Models, Pt.1; 2kW 24VDC to 240VAC Sinewave Inverter, Pt.2; Automatic Nicad Battery Discharger. December 1992: Diesel Sound Simulator For Model Railroads; Easy-To-Build UHF Remote Switch; MAL-4 Microcontroller Board, Pt.2; Speed Controller For Electric Models, Pt.2; 2kW 24VDC to 240VAC Sinewave Inverter, Pt.3; Index to Volume 5. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up; A Look At The Digital Compact Cassette. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2; Double Your Disc Space With DOS 6. July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; Build An AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Low-Cost Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits; Unmanned Aircraft – Israel Leads The Way; Ghost Busting For TV Sets. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Electronic Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; FM Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Mini Disc Is Here; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier, Pt.3; Build A Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card; Preventing Damage To R/C Transmitters & Receivers. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock, although stocks are low for some older issues. For readers wanting articles from sold-out issues, we can supply photostat copies (or tearsheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. December 1993  83 AMATEUR RADIO BY GARRY CRATT, VK2YBX Selective tone calling in commercial & amateur radio Signalling systems designed & used in commercial communications are now finding their way into amateur communica­tions. This article sets out to explain the difference between the various commonly used systems & why different systems exist. The use of a signalling system can greatly improve the effi­ ciency of a communications system, by allowing many users to operate on the same communications frequency without causing interference. A signalling system thus allows greater utilisation of the RF spec­trum. A multitude of signalling systems already exist around the world, ranging from very simple single tone or sub-audible tone systems to sophisticated computer-controlled proprietary sys­tems. However, most commonly encountered systems in use in Aus­tralia fall into the following categories. CTCSS signalling The Continuous Tone Controlled Squelch System, or CTCSS as it is commonly known, is a system where­ by an RF carrier is modulated with a continuous audio tone, in addition to speech. Originally known as Tone Squelch, modern systems now utilise tones in the low frequency range, from 67Hz to 250.3Hz (see Table 1). When the modulated carrier signal is received, a decoder detects the particular tone in use and uses it to unmute the receiver. In this way, transmissions using a different tone, or no tone, are ignored by a CTCSS equipped receiving station. The CTCSS tone is 84  Silicon Chip filtered out in the receiver, prior to the audio stage. This system is widely used in simplex commercial radio systems, where it may be necessary to selectively call base stations, other mobiles, or operate various remote receiver functions. As the system is operating on a shared frequency basis, it is important to ensure that the channel is free before transmitting, in order to minimise interference caused by simul­taneous transmissions from a number of mobile stations. One of the disadvantages of CTCSS is that, due to the very nature of the tones used, repeater operation in CTCSS mode is often unreliable or impossible. This is because most transceivers are designed to deliberately Table 1: CTCSS Codes 67.0 94.8 131.8 171.3 203.5 69.4 97.4 136.5 173.8 206.5 71.9 100.0 141.3 177.3 210.7 74.4 103.5 146.2 179.9 218.1 77.0 107.2 151.4 183.5 225.7 79.7 110.9 156.7 186.2 229.1 82.5 114.8 159.8 189.9 233.6 85.4 118.8 162.2 192.8 241.8 88.5 123.0 165.5 196.6 250.3 91.5 127.3 167.9 199.5 roll off the audio response outside the speech range, particularly below 300Hz. Modern commercial repeaters specifically designed for CTCSS operations employ special decoding circuitry for this purpose. In addition, CTCSS tones are not compatible with the DTMF tones used in phone patch operations. Nevertheless, some form of signalling through repeaters is necessary, and a signalling system known as SELCALL is often used. This system comprises a range of discrete audio frequen­ cies, each corresponding to a digit from 0-9, plus two extra tones for “repeat”, where adjacent tones are identical, and “group” signalling, where a number of mobiles are to be called simultaneously. 5-tone sequential tone sets The 5-tone principle has been accepted internationally by a number of leading standard associations such as CCIR, EIA, ZVEI, NATEL and EEA. As can been seen from Table 2, while the broad principle has been adopted, there are a number of sequential tone sets in use around the world, as dictated by the appropriate standard association. Selective calling also facilitates ANI and Group calling through repeaters. Automatic number identification (ANI) is used to indicate that a call has been received at an unattended mobile radio. As the transceiver initiating the call is equipped with a unique 5-tone code, it is a relatively simple matter to store and display the code, revealing the identity of the sender and time of transmission at the unattended end of the radio link. In addition, the signalling system can be used to activate an Table 2: Tone Sequential Standard Table 3: DTMF Signalling Frequencies Tone CCIR EEA EIA ZVE-1 ZVEI-2 ZVEI-3 0 1981 1981 600 2400 2400 2200 1 1124 1124 741 1060 1060 970 2 1197 1197 882 1160 1160 1060 3 1275 1275 1023 1270 1270 1160 4 1358 1358 1164 1400 1400 1270 5 1446 1446 1305 1530 1530 1400 6 1540 1540 1446 1670 1670 1530 7 1640 1640 1587 1830 1830 1670 8 1747 1747 1728 2000 2000 1830 9 1860 1860 1869 2200 2200 2000 R* 2110 2110 459 2600 970 2400 G 2400 2400 2151 2800 885 2600 ITPS* 100ms 40ms 33ms 70ms 70ms 70ms High Group Frequencies (Hz) Low Group Frequencies (Hz) Note: R = Repeat tone; G = Group tone; ITPS = International Tone Period Standard audio alarm, indicating “call received” status. Group calling allows a base operator to call a group of mobiles, without disturbing other mobiles on the same frequency, and preserves some degree of security. DTMF signalling DTMF or “touch tone” signalling is commonly used in amateur circles to gain or restrict access to repeaters. In addition, the use of the standard DTMF (dual tone multi frequency) tones, as shown in Table 3, allows easy interconnection to the PSTN tele­phone network, a great advantage for those utilising phone patch interconnect equipment. In fact, commercial trunked radio tran­sceivers use DTMF signalling so that the very basis for their existence (interconnection to the PSTN as a competitor to the AMPS cellular network) is easily achieved. However, there are particular disadvantages in using DTMF signalling in the mobile radio environment. Table 3 shows the combinations of two tones required to produce a DTMF “digit”. The difference in level between the two tones must be held to specif­ic limits to ensure accurate signalling. The maximum allowable “twist” of these tones is 4dB (AUSTEL standard TS-002) in Austra­lia and 3dB in New Zealand. In an RF environment, this twist level can normally only be guaranteed to within 6dB, making the system unreliable. Also, the minimum achievable signal to noise ratio in a DTMF system can be mathematically calculated to be at least 6dB worse than that achieved by a 5-tone sequential system, because in a DTMF system, the deviation per tone is only half that used in a 5-tone system. There are a number of other disadvantages with DTMF radio signalling in areas such as speed, timing, dynamic range and intermodulation products. Digital coded squelch A further development in signalling technology is the DCS or “digital coded squelch” system, where each of a group of codes corresponds to a digital TTL data stream sent typically as an 8-bit word, either in bursts or contin- Table 4: DCS Codes 023 131 251 371 532 025 132 252 411 546 026 134 255 412 565 031 143 261 413 606 032 145 263 423 612 036 152 265 431 624 043 155 266 432 627 047 156 271 445 631 051 162 274 446 632 053 165 306 452 654 054 172 311 454 662 065 174 315 455 664 071 205 325 462 703 072 212 331 464 712 073 223 332 465 723 074 225 343 466 731 114 226 346 503 732 115 243 351 506 734 116 244 356 516 743 122 245 364 523 754 125 246 365 526 1209 1336 1477 1633 697 1 2 3 A 770 4 5 6 B 852 7 8 9 C 941 * 0 # D uously. Unlike analog tone systems, the advantage of a digital system is the enormous number of mobiles that can be operated on the one frequency. Some com­mercial users are currently operating 250 DCS mobile transceivers on the one frequency! Table 4 shows a list of the commonly used 104 DCS codes. Each code corresponds to a specific data stream. Pocket pagers Although not a signalling system used in 2-way communica­tions, the POCSAG code system used in pocket pagers is certainly worth mentioning as an advanced one-way signalling system. In 1975, the British Post Office established the Post Office Code Standardisation Advisory Group to study and design a digital radiopaging message format. Two years later, that group recom­ mended what is today called POCSAG. Understanding this system requires a good working knowledge of Boolean algebra and is beyond the scope of this article. Suffice to say, POCSAG is the predominant paging signalling system in use in the world today. One interesting piece of test equipment we discovered whilst working on this article is the “CD-1 Communications Decod­er Unit”, a stand-alone tone decoder capable of displaying CTCSS, DCS and DTMF signalling tones received by radio. Designed as an accessory for a service monitor, this unit can easily be wired to any receiver and used to display signalling codes in use. The unit is available from Raedale Pty Ltd in Queensland. Telephone (075) 76 3000. The most obvious use is the monitoring of unauthorised users of commercial repeaters. No doubt there is a similar appli­cation to which the unit could be put in amateur radio. Signalling Technology Pty Ltd of Melbourne (phone 03 786 0077) also stock a useful range of encoding and SC decoding products. December 1993  85 ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. Please have your credit card details ready 86  Silicon Chip ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia PRODUCT SHOWCASE Power amplifier modules from A-One A-One Electronics has specialised in ready-built audio modules for some time and these two are from the top of their Acoustic Fidelity range. First up is a 250W power amplifier module featuring Hitachi 2SJ50 and 2SK135 complementary Mosfets. The input has a trimpot for minimising the DC offset at the output and a heavy duty relay is used to switch the loudspeaker load. This is a high performance amplifier, with a frequency response flat to within ±0.8dB from 3Hz to 20kHz and a rated harmonic distortion of less than 0.03%. Depending on the power transformer used, power output is a maximum of 150 watts RMS into 8W or 250 watts into 4W. The AF-2 module (Cat S-0342) is well priced at $228.00. For those wanting higher power again, module, look no further than the AF-3 module which is rated at 300 watts. It is essentially the same entirely Solid-state pressure sensors SenSym has introduced a new DIP package that will accommodate any of its various pressure sensor die. This small package will allow for assembly onto a PC board via automatic insertion equipment. The package will also conserve board space, since it measures only 0.47 by 0.55 inch with the spacing between the rows of mounting pins only 600 mils. One configuration will allow for 1/2 inch board spacing. The package will support pressure ranges from 4" H2O full scale to to 100 psi full scale and is available in absolute, gauge or differential configurations. These packages were specifically designed for electronic equipment that requires the measurement and control of pressure. Many such applications exist in the medical field such as, ventilators, spirometers and respirators, as well as in pneumatic controls, HVAC and others. Pricing will depend upon the type of sensor die and pressure range but will be competitive with other low cost SenSym sensors. For more information, contact NSD Australia, 205 Middleborough Road, Box Hill, Vic 3128. Phone (03) 890 0970. complementary circuit as in the AF-2 module but with higher supply rails and four each of the Hitachi 2SK135 and 2SJ50 Mosfets. The specifications are the same as before except that the power is upped to 200 watts into 8W and 300 watts into 4W. Price of the AF-3 (Cat S-0343) AUDIOPHILES! Now high audiophile quality components & kits are available in Australia. Buy direct & save. *Kimber, Wonder, Solen & MIT Capacitors *Alps Pots *Holco resistors *High Volt. Cap. *Gold Terminals & RCA *WBT Connectors *Kimber Cables * Interconnect Cables *Output Transformers (standard or customised) *Power Transformers *Semiconductors *Audio Valves & Sockets *Wonder Solder *Welborne Labs Accessories Valve & Solid State Pre-Power Amplifier Kits *Contan Stereo 80 Valve Power Amp. (As per Elect. Aust. Sept. & Oct. ’92) *Welborne Labs Hybrid Preamp. & Solid State Power Amplifier Send $1.00 for Product Catalog PHONE & FAX: (03) 807 1263 CONTAN AUDIO 37 WADHAM PARADE MT. WAVERLEY, VICTORIA 3149. December 1993  87 formed per second. Input impedance is 1 Gohms and inputs are protected against over voltages to 200V. There is also a 4-bit isolated output port provided. The LLAD 140 is a 2/3-length card and comes supplied complete with user manual and utility disc. Interfacing is via a DB-15 connector located on the end of the board. For more information, contact Boston Technology Pty Ltd, PO Box 1750, North Sydney, NSW 2059. Phone (02) 955 4765. Australasian satellite TV book Written by Mark Long and Jeffrey Keating, "The World of Satellite TV" gives a comprehensive description of the technology involved in the delivery of satellite TV. It also explains why some installations need big dishes and gives with actual footprints and transponder loadings for satellites in our region. This second edition of "The World of Satellite TV" has been accepted by many as the best satellite book available. It can be purchased from Dick Smith Electronics, Jaycar Electronics or Peter C. Lacey for $29.90 plus $5 pack and postage. The Australian distributor is Peter C. Lacey Sermodule is $299.00. Both modules are rugged circuits with the well-proven Hitachi Mosfets. Get into them while they last. They're available at A-One Elec troncis Pty Ltd, 432-434 Kent Street, Sydney NSW 2000. Phone (02) 267 4819. Low cost 15-bit 4-channel A/D card Boston Technology Pty Ltd has announced the Australian release of the Low cost PC board prototypes vices Pty Ltd, 80 Dandenong Road, Frankston, Vic 3199. Phone (03) 783 2388. LLAD 140 15-bit 4-channel A/D card for PC/XT/AT/386/486 and compatible computers. The LLAD 140 analog interface has four differential analog input channels, each with 0.25mV resolution over an input range of ±5 volts, with excellent stability and noise immunity. Standard linearity is 0.005%. Reproducibility is ±1 count or better. Readings are accurate to within .025% of full scale at normal operating temperatures, and 7.5 conversions are per- Southern Cross Z80 Computer – ctd from p.68 connects the 10-pin IDC socket with the 25-pin Centronics sub-D male connector using 10-strand flat cable. The other cable connects the 28-pin EPROM socket on the target system to the 28-pin EPROM socket on the emulator board. Two identical 28-pin DIP plug connectors have to be con­nected to either end of the 28-strand flat ribbon cable. You need to decide on the cable length which should ideally be no more than 200mm long. The method of making these cables is described above. The parallel port cable has eight connections as listed in Table 2. Make the 10-pin IDC socket connector first. To do this, match cable strand 1 (usually hatched red colour) to the triangle pin 1 moulded in the IDC socket. Press the socket together, then 88  Silicon Chip lay out the cable and the 25-pin male sub-D connector in front of you. Find pin 1 of the IDC connector and solder the other end of the wire to pin 18 of the sub-D connector. Work through pins 2-8 of the 10-pin IDC connector and solder in all eight connections to the sub-D connector as outlined in Table 2 above. Remember that pin 2 of the IDC header is strand three of the ribbon cable, pin 3 is strand five, pin 4 is strand seven, etc. Finally, fit the sub-D cover onto the 25-pin connector to relieve the strain on the solder connections. Does it work? Connect the EPROM emulator to the Southern Cross computer and to your PC and power both systems up. A new PC board manufacturing service has been set up to meet the demand for small volumes of quality double sided, through hole plated boards. By adopting the latest disposable photo tooling techniques, Don Alan has managed to almost eliminate tooling costs. The resulting prices will challenge bread boarding techniques for prototypes and one off manufacturing. Don claims that prices will range from a quarter of the usual price of other PC board manufacturers. All PC boards are 1.6mm fibreglass, double sided, through hole plated, 35µm copper (1 oz), solder resist and component overlayed. Non rectangular and internal profiles and cut outs Type ‘em scmv1_2.hex’ on the PC keyboard. The Data LED should light up on the emulator for about second, then the Ready LED should turn on, the buzzer should sound and ‘2000’ should appear in the Address displays on the Southern Cross (you may have to press the Reset button). If this is OK, enter ‘em 3digit.hex’. Go to Address 1800 and press Function 0. A 3-digit count should be displayed on the right three displays. It should be possible to increase or decrease the readout with the “+” and “-” keys respectively. All the procedures and software for the emulator are sup­plied on a floppy disc which comes with the kit. The designers suggest that the emulator software be used in conjunction with a program such as Norton Commander for most efficient creation of code for SC the Southern Cross. are available. All artwork must be a Protel Easytrax or Autotrax file. A free design kit is available that includes a hole size guide, Protel Easytrax (Freeware) PC board layout software for the PC, a program that checks and quotes your PC board file, design data and a tutorial for those who are using a computer to lay out PC boards for the first time. Files may be delivered by 1200 or 2400 Baud modem, 24 hours a day. Modem number (08) 373 5489. For further information, contact Donald Kay, Don Alan Electronics, PO BOX 404, Brooklyn Park, SA 5032. phone (08) 43 3957. New Scope desoldering tool This new solder sucker from Scope Laboratories uses a tough seethrough plastic which helps you see when to clean out excess solder. It will be available shortly from your normal Scope stockists. For further information, contact Scope Laboratories, PO Box 63, Niddrie, Vic 3042. Phone (03) 338 1566. 100MHz digital storage oscilloscope Featuring sampling speeds of 100Ms/sec on two channels in single shot mode, or 10Gs/sec on all four channel in repetitive mode, the DL1300A offers up to double the sampling speed of Yokogawa's DL1200A model by increasing the acquisition memory to 64K per channel. A fast screen update rate allows the DL1300A to display incoming waveforms in real time, while simultaneously displaying up to a 1000 times expanded segment of the same waveform, also in real time. The display is a high resolution amber raster scan CRT. Several levels of brightness allow adjustable contrast between waveforms, measurements and the screen grid. The standard DL1300A is provided with a GPIB interface, external trigger, and clock interface which allows synchronisation of the timebase to an external signal such as a data clock or shaft encoder. Options include a thermal printer, an RS232C communications port, and a memory card interface which can store and recall front panel setup and waveform data. A video option is also available, allowing a standard video monitor to display the DL1300A screen. Automatic measurement facilities are provided including RMS voltage, peak to peak voltage, frequency and rise/fall times. Two channels may also be tested by a GO/NOGO function, with the result causing waveform capture or an automatic hard copy printout. For further information, contact Tony Richardson, Yokogawa Australia Pty Ltd, Centrecourt D3, 25-27 Paul St North, North Ryde, NSW 2113. Phone (02) 805 0699. December 1993  89 Index to Volume 6: January-December 1993 Features 01/93 1 Silicon Chip 5th Birthday Sweepstakes 01/93 79 Panasonic’s Super-Quiet Dot Matrix Printer 02/93 1 Silicon Chip 5th Birthday Sweepstakes 02/93 6 Microwave Disinfection of Medical Waste 02/93 14 Sony’s New 8mm Video Camera 03/93 4 Sanyo’s Big Screen Video Projector 03/93 16 Sony’s New VGP-G700 Colour Video Printer 04/93 6 The Digital Compact Cassette 04/93 21 Silicon Chip 5th Birthday Sweepstakes 05/93 4 Hifi Review: Dynaudio Image 4 Loudspeakers 05/93 16 The Microsoft Windows Sound System 06/93 6 Dick Smith’s Trans-Australia Balloon Attempt 07/93 4 The Keck Optical Telescope, Pt.1 07/93 18 Tektronix TDS 320 100MHz Digital Scope 07/93 22 Programming the Motorola 68HC705C8, Lesson 1 07/93 26 Data: The ISD1016 Voice Recorder IC 08/93 4 Ghost-Busting for TV Sets Now Feasible 08/93 6 The Keck Optical Telescope, Pt.2 09/93 4 Swiss Railways’ Fast New Locomotives 09/93 53 Test Equipment Review: The Handyscope 10/93 4 Darwin to Adelaide on Solar Power 10/93 16 Mini Disc Is Here! 10/93 28 Review: Magnet LS-621 2-Way Loudspeakers 10/93 80 Programming The Motorola 68HC705C8, Lesson 2 11/93 8 Review: Tektronix TDS 544A Colour Oscilloscope 11/93 53 The World Solar Challenge 11/93 72 Review: Epson’s Stylus 800 Inkjet Printer 11/93 80 Review: The Autoplex Unimeter 12/93 4 Sound Blaster Grows Up! 12/93 40 Data On The LM1875 20W Audio Amplifier IC 12/93 53 Programming The Motorola 6HC705C8, Lesson 3 12/93 92 Index to Volume 6 90  Silicon Chip Electrical Energy 01/93 82 Pt.22: The Balmain & Ultimo Power Stations 04/93 08 Pt.23(a): Winning The White Metal – The Story Of Aluminium 05/93 86 Pt.23(b): Winning The White Metal – The Story Of Aluminium 06/93 88 Pt.24: How Aluminium Is Refined Engine Management 10/93 08 Pt.1: The Advantages Of Electronic Control 11/93 04 Pt.2: Airflow Measurement 12/93 08 Pt.3: Changing The ECM Software – Chip Re-Writing Vintage Radio 01/93 32 Restoring A 1920s Kit Radio 02/93 96 The Awakening Of The Dragon 03/93 84 Paper Capacitors Cause Lots Of Trouble 04/93 88 Restoring An Old Radio Chassis 05/93 56 A Few Old Receivers From The 1920s 06/93 56 A Look At High Tension Filtering 07/93 86 In The Good Ol’ Days Of My Childhood 08/93 62 How To Deal With Block Capacitors 09/93 86 Restoring An Old Valve Tester 10/93 94 Those Never-Ending Repair Problems 11/93 82 The Vexed Question Of Originality 12/93 70 My No-Hassles Vintage Radio Museum Serviceman’s Log 01/93 44 Samsung CB15F; Acer MM211 Computer Monitor; Samsung VB711 VCR 02/93 64 Thorn 9007; Acer MM211 Computer Monitor; Panasonic NV-G22A VCR (G Mechanism) 03/93 42 Samsung CB349Z; Teac MV307 VCR; Hitachi VT-640E VCR 04/93 32 National TC-1809; HMV B4803/ Rank Arena D1 Chassis 05/93 40 National Panasonic TC-2690/ M14 Chassis 06/93 30 Grundig ST-70/460; Cintel IMD 07/93 30 Samsung CB-5012Z; Samsung CB-518F 08/93 40 Panasonic 2970V; High Energy Ignition System 09/93 40 Akai CTK-107; Teac MV-400 VCR 10/93 58 Panasonic TC-48P10; Sanyo/79P Chassis 11/93 34 Hanimex CTV-10; AWA AV47 VCR; Sharp VC-8300 VCR; Sharp Cassette Deck 12/93 56 Samsung CB-3325J; Hitachi Cassette Deck; Philips KT2A2 Chassis; General Electric Portable Colour TV Remote Control 01/93 66 Installing & Adjusting The LowCost Speed Controller, Pt.3 04/93 53 Practical Applications For The Low-Cost Speed Controller 05/93 53 Unmanned Aircraft – The Ultimate In Remote Control 06/93 80 Unmanned Aircraft – The Early Developments 07/93 80 Unmanned Aircraft – Current Models In Service 08/93 53 Unmanned Aircraft – Israel Leads The Way 09/93 82 Servicing Your R/C Transmitter –The Basics, Pt.1 10/93 86 Servicing Your R/C Transmitter, Pt.2 11/93 42 Preventing Damage To R/C Transmitters & Receivers 12/93 42 Servicing Your R/C Receiver – The Basics Computer Bits 02/93 42 File Backups Plus A Useful Utility For LHA & PKZIP 04/93 64 Upgrading To A 386 – Now I Know What A “Kludge” Is 05/93 64 Upgrading To A 386 – More On Kludging A Computer 06/93 71 Double Your Disc Space With DOS 6 10/93 34 Using DOS 6.0’s DoubleSpace 11/93 70 More Experiments For Your Games Card Amateur Radio 01/93 88 Remote Monitoring Of Radio Transmissions 03/93 81 A General-Coverage Shortwave Receiver From England Projects to Build 01/93 16 Peerless PSK60/2 2-Way Hifi Loudspeakers 01/93 26 Build A Flea-Power AM Radio Transmitter 01/93 40 High-Intensity LED Flasher For Bicycles 01/93 58 A 2kW 24VDC to 240VAC Sinewave Inverter, Pt.4 02/93 16 Build The Electronic Cockroach 02/93 26 Three Simple Projects For Model Railroads 02/93 38 A Low Fuel Indicator For Your Car 02/93 46 The MAL-4 Microcontroller Board, Pt.3 02/93 56 Audio Level/VU Meter With LED Readout 02/93 80 A 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5 03/93 20 Build A Solar Charger For 12V Batteries 03/93 32 An Alarm-Triggered Security Camera 03/93 50 Low-Cost Audio Mixer For Camcorders 03/93 57 Test Yourself On The Reaction Trainer 03/93 74 A 24-Hour Sidereal Clock For Astronomers 04/93 14 A Solar-Powered Electric Fence 04/93 22 Build An Audio Power Meter 05/93 82 Kenwood’s Mighty Little TH-28A & TH-78A Transceivers 06/93 53 The Smith Chart – What It Is & How To Use It 07/93 84 Antenna Tuners: Why They Are Useful 08/93 72 A Look At Satellites & Their Orbits 09/93 60 Emtron’s ENB-2 Noise Bridge 10/93 68 Judging Receiver Performance 12/93 84 Selective Tone Calling In Commercial & Amateur Radio Circuit Notebook 01/93 01/93 01/93 01/93 8 LED VU Scanner Display 9 Parking Lights Reminder 9 Cable Tester With LED Indicators 9 Simple Tester For IR Remote Controls 02/93 24 Horn Blower For Mobile Tele­ phones 02/93 24 Square Wave Frequency Doubler 02/93 25 Simple Way To Make PC Boards 02/93 25 Robotics Interface For PCs 03/93 24 A 20-Metre Direct Conversion Receiver 03/93 24 Blown Fuse Indicator 03/93 25 Simple 2-Input Logic Gate Identifier 04/93 72 Breakerless Pick-Up For Car Ignition 04/93 72 Dynamic Noise Reduction Circuit 04/93 37 Three-Function Home Weather Station 04/93 56 12VDC to 70VDC Step-Up Voltage Converter 04/93 80 A Digital Clock With Battery Back-Up 05/93 20 A Nicad Cell Discharger 05/93 26 Build The Woofer Stopper 05/93 32 Remote Volume Control For Hifi Systems 05/93 64 Alphanumeric LCD Demonstration Board 05/93 70 A Low-Cost Mini Gas Laser 06/93 12 Build An AM Radio Trainer 06/93 18 Remote Control For The Woofer Stopper 06/93 24 A Digital Voltmeter For Your Car 06/93 36 Windows-Based Digital Logic Analyser 06/93 64 Remote Volume Control For Hifi Systems, Pt.2 07/93 32 Build A Single Chip Message Recorder 07/93 38 Light Beam Relay Extender 07/93 53 Build An AM Radio Trainer, Pt.2 07/93 60 Windows-Based Digital Logic Analyser, Pt.2 07/93 70 A Low-Cost Quiz Game Adjudicator 08/93 18 Low-Cost Colour Video Fader 08/93 30 A Microprocessor-Based Sidereal Clock 08/93 56 Build A 60-LED Brake Light Array 08/93 82 The Southern Cross Computer 09/93 16 Automatic Nicad Battery Charger 09/93 24 Stereo Preamplifier With IR Remote Control 09/93 34 Build a +5V to ±12V DC Converter 09/93 56 An In-Circuit Transistor Tester 09/93 72 Remote-Controlled Electronic Cockroach 10/93 30 Courtesy Light Switch-Off Timer For Cars 10/93 40 Stereo Preamplifier With IR Remote Control, Pt.2 10/93 57 A Solid State Message Recorder 10/93 66 FM Wireless Microphone For Musicians 10/93 70 Build A Binary Clock 11/93 16 Build A Jumbo Digital Clock 11/93 26 High Efficiency Inverter For Fluorescent Tubes 11/93 56 Stereo Preamplifier With Remote Control, Pt.3 11/93 64 Build A Siren Sound Generator 12/93 16 Remote Controller For Garage Doors 12/93 22 Build This Low-Voltage LED Stroboscope 12/93 32 A Low-Cost 25W Amplifier Module 12/93 62 Peripherals For The Southern Cross Z80 Computer 12/93 80 Build This 1-Chip Melody Generator 04/93 73 VFO Controlled Transmitter For 80 Metres 05/93 8 Interface For The LCD Panel Meter 05/93 8 Seven Day Hose Controller 06/93 10 Add-On Circuit For A Sidereal Clock 06/93 10 Battery Monitor For Solar Chargers 06/93 10 Refinement For The Interphone Exchange 06/93 11 Repeater Time-Out Indicator 06/93 11 Discrete Step-Down Voltage Converter 07/93 16 Battery Charge Status Monitor 07/93 16 Single-Chip Combination Lock 07/93 17 Pulser Probe For TTL & CMOS 07/93 17 Low-Cost Piezo Screamer Siren 08/93 28 Low-Cost Isolation Amplifier 08/93 28 Low Distortion Oscillator 08/93 29 Phase Adapter For Digital Multimeters 09/93 10 Wide Range Phase Control 09/93 10 Regulator For Solar Panels 09/93 11 Microcontroller Timer 10/93 24 RF-Linked IR Remote Control Extender 10/93 25 Electronic Mousetrap Catches ‘Em Alive 10/93 25 Electronic Starter For Fluorescent Lights 11/93 40 Low-Cost Controller For Model Trains 11/93 40 6/12V Gel Cell Charger 11/93 41 Flash Meter 11/93 41 Power Supply Pre-Regulator Circuit 12/93 36 Single Chip Touch Switch 12/93 36 240V Motor Speed Control Notes & Errata 01/93 100 Automatic Nicad Battery Discharger, November 1992 01/93 100 Low-Cost Speed Controller, November 1992 01/93 100 High-Current 0-20V Power Supply, December 1992 01/93 100 Stereo AM Tuner, Feb-April 1991 02/93 101 Studio Twin 50 Amplifier, MarchApril 1992 03/93 92 LED Flasher for Bicycles, January 1993 04/93 93 High Energy Ignition System, May, June 1988, May 1990 04/93 93 Audio Mixer For Camcorders, March 1993 05/93 92 Traffic Light Simulator, February 1993 06/93 94 Woofer Stopper, May 1993 07/93 94 Nicad Cell Discharger, May 1993 09/93 94 Colour Video Fader, August 1993 09/93 94 Studio Twin 50 Stereo Amplifier, April-May 1992 09/93 94 Amateur Radio, August 1993 December 1993  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. IF generator is nifty Your design for the IF signal generator on page 58 of the July 1993 issue of SILICON CHIP will be a major asset for my service bench. I wish to make mine on a piece of stripboard, just like most of the other small bits of test equipment I have made. All of these work OK and I hope this one does too. However, I have discovered an anomaly with your published PC board layout, in respect to the position of the 1.5kΩ resistor feeding ICIc and ICId. Can you please clarify this. I think that this “radio trainer” is a great idea. I am reminded of the crystal sets I used to make and it seems to me a pity that the children of this day will not know of these things. I guess a good follow-up would be an FM trainer? Your Vintage Radio column is excellent! I still work with these “monsters” and love every minute of it. However, I wonder if anyone has considered a course in “antique” musical equipment, with particular reference to guitar amplification? I have re­stored about 10 of these so far (almost exclusively “Fender” amplifiers), much to the delight of their owners, who always seem to say “I’ve never heard it sound so good”. There must be hundreds of these Modifications to SLA battery charger I’m building the SLA charger as featured in the July 1992 issue of SILICON CHIP and was wondering if you could scrawl a “quick-n-dirty” diagram showing where two LEDs could be placed to indicate “on charge” and “full” or “trickle” – maybe even a dual-colour LED. Also I intend to have a switch to change the output to give 6.9V. Is this output OK to charge a 6V 92  Silicon Chip around and there are many still in use today, much treasured by the fact that only they can supply “that” sound. I recently witnessed a sad case of neglect with mains wir­ing, not attended to by a previous technician. Most of these amplifiers have a “voltage select” switch on the rear panel, as well as switches, fuse holder, etc. This amplifier had vaporised most of the valve filaments as a result of (I can only gather) “knob twiddling” when the thing didn’t work. It didn’t work because the wire feeding the mains fuse had come adrift, to arc on the adjacent switch contact. I hate to think of the conse­quences had the system not been properly earthed. In every one of these I get, I arm myself with the wire cutters, new cable and heatshrink tubing. I completely isolate the con­nections to the switch, including the transformer taps, and just connect up to the 240V tap. I then tuck away any unused wiring after insulating the ends with the heatshrink, before checking all other wiring with particular reference to the earth connec­tion. The old insulation on these switches is very much suspect and I do not trust them one little bit (same goes for old radios with voltage select functions). I also appreciate your editorial in the July 1993 issue – it says so much and I agree all the way. I recently SLA battery? (P. N., West Wya­long, NSW). • Since this circuit is essentially a constant voltage regula­tor, it is not possible to have LEDs which show charge and trick­le modes. All you can do is connect a LED across the output of the charger in series with a 4.7kΩ resistor which will indicate that the unit is on. If you want to charge 6V batteries, you will need to delete the 2.2kΩ resistor at pin 5 and use a parallel combination of 5.1kΩ and 100kΩ instead. purchased the old “Miniwatt” valve manual for $15.00. I won’t part with it. I have a laugh when I think I could have had one for 25 shillings, but I used to borrow or ask someone for the loan of theirs, back in those wonderful days. When do you think the old “transistor” radios will become collector’s items? I have a few of these and some of them seem worthy of restoration, especially for their shortwave capabili­ ties. (L. T., Eaglehawk. Vic). • While there is a difference between the published PC board layout and the circuit for the IF calibration oscillator, it will work either way since the 1.5kΩ resistor only has the effect of slightly reducing the drive to the crystal. Wants woof level for Woofer Stopper I have completed the “Woofer Stopper” project in the May 1993 issue of SILICON CHIP. Would you kindly let me know what voltage I can expect at the speaker terminals? At the moment it is 7V AC. Thank you for a first class magazine. (A. B., Young, NSW). • The voltage across the speaker terminals will be around 9V or 10V AC. However, that will depend largely on the frequency response of your multimeter. Most multimeters do not have a good response to 20kHz and so you can expect a reduced reading. In other words, 7V AC is probably about right for your multimeter. Higher input voltage for 2kW inverter I have been interested in wind powered alternators and associated power systems for some time. After some consideration, one must conclude that the currently available solutions leave a lot to be desired since the general usage is to run the system with an inverter to give 240VAC. It also makes a lot of sense to have the DC side of the system at the highest voltage practical. It’s hard to estimate what this would be but I would guess 72112V. This greatly reduces the input current and the problems associated with it. The cost of batteries is also reduced as one can use 12V heavy duty automotive types. I have studied your articles on the 2kW sinewave inverter. It would appear that the input section could be redesigned to allow for a higher input voltage. I don’t have the design skill to do this as I am a mechanical engineer. The only problem I see is the higher voltages involved, this being handled by IGBTs. (B. B., Warrnam­ bool, Vic). • Before we started designing the 2kW inverter, the question of what voltage should be used to supply the inverter caused much discussion. Obviously, a high initial voltage to work from would solve many problems and provide higher efficiency. However, it was concluded that any voltage above 24V would render the invert­er impractical for many users who would want to run it from their vehicle batteries. For the alternative power user who can connect any number of batteries in series, an inverter which runs from a higher voltage is a practical proposition. In fact if the DC voltage was 360V, then no step-up inverter would be required. You could simply just use the sinewave portion of the 2kW inverter. This high voltage is rather dangerous though and the extra precautions required to protect people from electric shock from the batteries would add to the cost. A more practical input voltage for the DC-DC inverter would be around 120V. The current drawn from the inverter would be reduced by a factor of five to only 20A compared to our original design operating from 24V. The changes necessary for the higher voltage involve changing the transformer windings, changing Mosfets Q5-Q16 for higher voltage types, and changing the zener diode voltage for ZD2 and ZD4. The 8 x 10µF 63VW capacitors at the DC input to transformer T1 will also need changing to higher voltage types. In fact, these changes require some careful redes­ign. To change the transformer, the primary windings will need 1 turn each for every 24V increase in supply. If 120V is used, the primary will have 10 turns. The secondary will need a Better crossover for a cheap loudspeaker Over several years (due to very limited income) I have established a fairly reasonable hifi system. I feel the main flaw in the system is the speakers and wish to upgrade. Currently I am using a pair of cheap “Masuda” 3-way speakers rated at 60W. I have also recently obtained a pair of Teac surround speakers rated at 30-60W. Driving these speakers is a Kenwood 100W re­ceiv­er. The sound reproduction is satisfactory, however I feel that the system is capable of a much improved performance. An investigation into the components of my speakers indi­cated a fairly rudimentary setup. The drivers appear to be rea­ sonable, however the crossover network is hardly satisfactory. The network simply consists of a capacitor in line with the tweeter and midrange (2.2µF and 8µF respectively) and an inductor in line with the woofer, thus producing a simple 6dB/ octave filter. What I would like to know is how to maximise the perfor­mance of these components. Is it worth upgrading to a 12dB/octave crossover, or should I just replace the entire system with a driver kit? As for the surround speakers, is there a surround sound decoder available (even in kit form) which would suit this system? As a modification or alternative, would the addition of a subwoofer be justified with 10-inch drivers already incorporated in the main system? I mainly use this system in an enclosed space but it is also often used in an open, party situation where an intensity of up to 100dB is often achieved. Not far after this, I am presented with ugly distortion. 100dB is achieved at approximate- reduction in turns for 360V output. Make sure that the gauge of winding wire has no more that 5A per square mm in both primary and sec­ondary windings. If a 120V supply is to be used, the recommended replacement for Q5-Q16 is the Philips BUK437-400A ly half volume and distortion sets in at about three-quarter volume. Is such distortion expected from 60W speakers driven by a 50W per channel amplifier? I hope you can supply me with some suggestions in order to enhance my system. (J. D., Blackburn South, Vic). • We do not think you will gain much improvement by changing the crossover to a 12dB/octave network, since the quality of your drivers may not justify having a better network. If you can afford it, the best solution is to upgrade to a better loudspeaker system. In general, choose the best 2-way system you can afford, rather than a bigger 3-way system which will generally have lesser quality drivers for the same money. The symptoms of distortion which you obtain above the “half volume” setting are most likely due to overload in your speakers or amplifier. Either way, you should not exceed this setting because you run the risk of burning out your tweeters, at the very least. This situation is very common and many people damage their speakers in this way. The fact is that a speaker rated at 60 watts may be easily overloaded by an amplifier which is capable of only 50 watts. This is because speaker power ratings are nominal and often inflated in the case of cheaper loudspeaker systems. Secondly, any amplifier which is driven well into clipping (ie, overload) will deliver far more than its ratings suggest, although the sound quality will be horribly distorted. It is this excess power which blows speakers, especially tweeters. So if your speakers make horrible sounds above a certain volume setting, you are being warned of impending damage. which has a 400V 14A rating. ZD2 and ZD4 should be rated at 300V at 3W. However, the above information really only gives the “broad brush” changes which would be needed. In fact, you are looking at a complete redesign and this could take several hundred man-hours. December 1993  93 Wrong connection for low fuel indicator I recently purchased a Low Fuel Indicator Kit as published in the February 1993 issue of SILICON CHIP and I installed it according to the instructions, checking everything out with a multimeter, etc. I have a Holden Barina (1991 Model) which has the fuel gauge constant. It does not work through the ignition, so I installed the kit direct from the battery with a switch to turn it off when the red light comes on. Now what is happening is that when I switch on, the red light comes on continuously even when you turn the ‘pot’ around. It is definitely connected to the correct sensor wire in the car. Any clues? (R. C., Reservour, Vic). • We assume that when you say your Barina has the fuel gauge “con­stant”, you mean that the fuel gauge continues to indicate the Microprocessors temporarily unavailable I’m currently building the Remote Volume Control for Hifi Systems presented in the May and June issues of SILICON CHIP magazine. I have had difficulties hunting for IC7 (AD7112­ CN) in this particu­lar circuit. Could you tell me where I can get this IC and how much will it cost. I would also want to know if the microproces­sor ICI (MC­68HC705C8P) is still available for purchase. (T. L., No address). • The AD7112CN is available from NSD Australia. In NSW, phone (02) 646 5255: in SA, phone (08) 211 849; Qld, (07)854 1911; and in Victoria, (03) 890 0970. We currently have no stocks of the MC68HC705C8P and with the world-wide shortage of semiconduc­ tors, we are not expecting further stocks for several months. When we have them back in stock, we will advertise them. Manual wanted for Tektronix scope I have purchased SILICON CHIP for several years now and find it most enjoyable and informative. As an 94  Silicon Chip fuel level in the tank even after the ignition is turned off. This is a common feature of Japanese late model sedans but the fuel gauge is still connected via the ignition switch. What happens is that there is a gel damping system inside the meter which maintains the reading when power is removed – the fuel gauge will continue to show its last reading even if the battery is disconnected. If you want proof of this, go to your local petrol station and fill the car’s tank. Then look at the fuel gauge before you restart the engine – the gauge will still show the fuel level before you filled the tank. Once you start the car, the pointer will move up to the full tank mark. What this means is that you should connect the low fuel indicator via the ignition switch, as specified in the article. Once you do that, it should work properly. invalid hobbyist, I have purchased kit test equipment where possible. I did lash out and buy an old Tektronix 545B scope with a CA type plug-in unit which is a 2-channel 24MHz unit. My hope is that one of your readers may have an operator’s handbook or service book for this 545B oscilloscope that they no longer need or would be prepared to copy. I would gladly pay for copying and postage of same. I would also be prepared to pay a reasonable sum for an original manual. Although physically very large, the scope is very good for my needs when working properly. (D. Gardner, 8 Harris St, Castle­maine, Vic 3450). Offset voltage query for equaliser I am writing to you regarding a problem I am having con­ structing one of your project designs – the Studio Series 20-Band Stereo Equaliser described in the August 1989 issue of SILICON CHIP. The outputs of ICs 3-7 all have DC offsets very close to zero. However, the outputs of ICs 1 & 2 (pins 1 & 7) all have DC offsets of between 37mV and 41mV (with supply voltages of -14.99V and +15.03V and no input signal). Replacing the supplied ICs with Motorola LM833s gave the same offsets. After disconnecting the inputs and outputs of IC1 from the circuit, I obtained the following: roughly 3.4V at the non inverting inputs and 14V at the inverting inputs and outputs. The only explanation I can think of is that these values are a result of the proximity of the ICs to other components. Any help that you could give me in solving this problem would be much appreciated. (N. T., Turramurra, NSW). • According to our calculations, the output offset voltage for the LM833s in this circuit should typically be +50mV due to the input bias current via the 100kΩ resistor at pin 5 (or pin 3). In fact, prompted by your letter, we measured the offset voltage of the LM833 in our prototype 32-band equal­iser which uses a very similar circuit. The offset voltage was +48mV. With this in mind, it appears that the DC offsets in your equaliser are a little better than typical. Such offsets will not cause any problems. We trust that you are only concerned because our voltage checking procedure in the September 1989 issue makes the remark that the “voltage in each case should be within a few millivolts of 0V”. We should have said “within 100mV of 0V in the case of the LM833s”. We apologise for the confusion this may have caused you. Multi-turn pot for power supply Can you tell me the correct value for the multi-turn pot (VR4) used in the dual tracking power supply published in the April 1990 issue. The schematic indicates 10kΩ but the parts list indicates 5kΩ. Which value is correct? What effects would flow from an incorrect value? In some circumstances, I will want to recalibrate the upper limit to 30V to avoid accidental damage to prototype circuits. Will the design values allow this? If not, what adjustments to component values would be needed? (P. L., Osborne Park, WA). • VR4 should be 5kΩ. To set the maximum output to 30V, change the 15kΩ resistor in series with VR2 to 3.3kΩ and adjust VR2 to get a 30V output, SC as set out in the article. MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. ANTIQUE RADIO ANTIQUE RADIO RESTORATIONS: specialist restoration service provided for vintage radios, test equipment & sales. Service includes chassis rewiring, recon­ densering, valve testing & mechanical re­­furbishment. Rejuvenation of wooden, bakelite & metal cabinets. Plenty of parts – require details for mail order. About 1200 radios within 16,000 square feet. Two-year warranty on full restoration. Open on Saturday 10am-4.30pm; Sunday 12.30-4.30pm. 109 Cann St, Bass Hill, NSW 2197 Phone (02) 645 3173 BH or (02) 726 1613 AH. FOR SALE WEATHER FAX programs for IBM XT/ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & RTTY receiving program. Suitable for CGA, EGA, VGA and Hercules cards (state which). Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. NE602 $3.50, BF981 $1.50, BC549c $0.18, BC547/557 $0.15 ea, BC327/337 $0.22 ea. Send name and address and I will put you on my mailing list. Goodwin Electronics, PO Box 31081, Chris­tchurch, New Zealand. Visa, Mastercard, Bank­card accepted. Post­ age $5 Australia/Pacific, $4 NZ. 68705 MICRO EMULATOR!!!: Yes! A fair dinkum 68705 hardware ICE for $285 (B&T $330). Run programs in RAM, builtin disassembler, single step, break points, the works! It even emulates 2716, 2732 and 2764 EPROMs. Can be used with a CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $20 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & send both with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy Beach, NSW 2097. Or fax the details to (02) 979 6503. PC, MAC etc. Optional 687053/U/R ($115) and C4/C8 ($95) programmers for direct connec­tion to 68705 emulator. Kits and further info from Graham Blowes, Mantis Micro Products, 38 Garnet St, Niddrie 3042. Phone (03) 337 1917(ah), (03) 575 3349(bh), fax (03) 575 3369. CUSTOMERS REQUIRED. No previous experience necessary. 100% Aus­tralian 8K-4Mb DIP or SIMM Printer Buffer Short Form Kit. In­cludes Z80 Source and ROM files. $38. With EPROM $52. Don McKen­ zie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. FOR SALE: Inter Venture Logic Bridge Model 136 (see SC Feb. 1993). Won as prize. Never used. Value $690. Sell $400 or n/o. Contact Barry Flanigan, 2 Daly Ct, Churchill 3842. Phone (051) 22 1321. SATELLITE RECEIVER: Winersat WR920 PLL, 66 channels, infrared remote, video/audio. IFs are adjustable. Includes position steer­ ing facilities (in excellent condition.) $400.00. Phone Rod (08) 387 0372. SATELLITE RECEIVER: NEC 4GHz commercial unit. Intelsat/Palapa use. $180.00 o.n.o. Phone Rod (08) 387 0372. THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 December 1993  95 SECONTRONICS COMPONENTS, COMPUTERS, ELECTRON TUBES S/H TEST EQUIPMENT, COMPUTER REPAIRS WESTERN DIGITAL HD 170Mb 13ms $395 I/O + IDE/FDD $35 RESISTORS AT I/O CARDS $22 MOST VALUES AVAIL. 2SD1169 $2.00 1/3W CARBON $2/100 2N3440 $0.80 1/2W CARBON $4/100 2N3439 $0.80 1W CARBON $5/100 2SC3157 $4.00 2W CARBON $8/100 27C41 $0.80 5W WIREWOUND $0.30 7406 $0.20 10W RESISTORS $0.60 8250 $5     8251 $2      8259 $2     6809 $8 KB 327OPC KEYBOARDS, 3 ONLY, $110.00 ea VALVES: QQV07/50 $25 ECF80 $6 12AU7 $6 12AU7A $7 12AU7WA $9 1S2 $3 1T4 $6 CV553 $3 2C39A $30 2C40A $40 3A4 $8 5651 $6 5651A $6 4-400A $80 6J6WA $7 QB3/300 (10 ONLY) $145 ea SPECIAL: SURFACE MOUNT COMPONENT PACK – 180 RESISTORS, 40 ZENERS, 30 TRANSISTORS AND 2 ICs. $6.50 INC. PACK & POST PHONE OR MAIL ORDERS, CREDIT CARDS ACCEPTED FOR ORDERS $20 & OVER, DISCOUNTS FOR QUANTITY ORDERS. NOW AT SHOP 5, 79 RICKSTON ST, MANLEY WEST, QLD. 4179. OPEN TUES - FRID 9.30AM - 5PM, SAT. 9AM - 2PM. MAIL ORDERS TO PO BOX 34 CANNON HILL QLD. 4170. PHONE (07) 396 1859, FAX (07) 855 1014. TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS Reply Paid No.2, PO Box 438, Singleton, NSW 2330. Ph: (065) 76 1291. Fax: (065) 76 1003. MEMORY & DRIVES PRICES AT NOVEMBER 1ST, 1993 SIMM 1Mb x 3 70ns 1Mb x 9 70ns 4Mb (72-pin) 4Mb x 9 70ns 4Mb x 8 80ns $70 $82 $320 $250 $230 DRAM DIP 1 x 1Mb 70ns 256 x 4 70ns 1Mb x 4 Z DRIVES SEAG 42Mb SEAG 107Mb SEAG 130Mb SEAG 214Mb SEAG 528Mb 28ms 15ms 16ms 16ms 12ms $10 $8 $35 $190 $285 $290 $355 $985 Zeus 2000SCH: $150 Parts Database: $30 Zeus 2000PCB: $200 Micro PCB: $80 Payment by cheque/mo. Add $5 postage. G. A. GEORGOPOULOS 34 Scouller St, Marrickville, NSW 2204. All Electronic Components..........89 IBM PS.2 50/55/70 70/35 90/95 2Mb 4Mb 4Mb $160 $320 $320 TOSHIBA T3200SX T44/6400 T5200 4Mb 4Mb 8Mb $360 $340 $680 A-One Electronics.................. 38-39 $130 $330 David Reid Electronics ..............59 Altronics ................................ 26-28 Antique Radio Restorations.........95 MAC 2Mb SI & LC 4Mb P’Book CO-PROCESSORS 387SX to 25 $105 387DX to 33 $105 Laser PTR HP with 2Mb $203 Sales tax 21%. Overnight delivery. Credit cards welcome. Contan Audio...............................87 Dick Smith Electronics........... 12-15 D & K Wilson Electronics.............61 Emona.........................................11 Ring for Latest Prices Harbuch Electronics....................59 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Jaycar ................................... 45-52 Tel: (02) 980 6988 Fax: (02) 980 6991 PELHAM ICL 286 Board Kits All in one board with two serial, printer, IBM keyboard, high density floppy & IDE mono video interface. Up to 4Mb RAM, 80286-16cpu, MS-DOS compatible, 130 page manual, small size 170mm x 255mm. Max I/O kit for PCs, 7 relays, ADC, DAC, stepper driver, TTL inputs, with software $169 PC I/O card with 8255 chip 24 I/O lines programmable as inputs or outputs $69 1.5 watt AM broadcast transmitter XTAL locked $49 2.5 watt FM broadcast transmitter 88-108MHz. $49 Digi-125 audio power amp (over 19,000 sold since 1987) 50 watt/8 $14 125 watt/4 $19 New 200 watt/2 version $29 Infrared relay kit $9 Remote control tester $4 $299 Ampo little PC ELECTRONIC CAD FOR DOS Advertising Index All in one NEC V40 CPU board, MS-DOS compatible, high density floppy. SCSI hard disk, 2 serial, printer, solid state hard disk, IBM keyboard interface, (4W), CMOS single +5V rail, up to 768Kb RAM, 384Kb ROM, 145mm x 250mm, 98page manual. $299 P.C. Computers 36 Regent St, Kensington, SA. Phone (08) 332 6513. JV Tuners.....................................61 Oatley Electronics..........................3 PC Computers.............................96 Pelham........................................96 Peter C. Lacey Services..............56 Philips Test & Measurement....OBC RCS Radio ..................................95 Resurrection Radio......................73 Rod Irving Electronics .......... 74-79 Secontronics................................96 Silicon Chip Back Issues....... 82-83 Silicon Chip Book Club................69 Silicon Supply & Manufacturing.....7 SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 I/O pins, board space includes prototyping area. Program it on a PC (only 33 instructions) with development kit which includes one “BASIC STAMP” ($249 plus S/T & post), extra modules ($66 plus S/T & post). Send 45c stamp for more information. Parallax distributor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­dale, NSW 2350. Facsimile (067) 72 8987. MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. NICAD BATTERY Charger Conditioner Analyser. As featured in SILICON CHIP. September 1993. Complete kit $135.00. 96  Silicon Chip Built and tested $185. P&P $10. C.I.E., 524 Abernethy St, Kitchener, NSW 2165. Phone (049) 91 1389. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. PAT TV & SATELLITE Scrambling News Monthly, with the latest on de­scrambling techniques & addresses, where to buy the latest descramblers. Send stamp for info. John Papp, Box 37885 Winnellie, NT 0821. SPRINKLER CONTROLLER KITS: standard and enhanced versions avail­ able. Very reliable and versatile designs control 8 stations and have 32 programmable START and RUN times. These kits use latest technology I2C chips (refer Technical Applications.................61 Transformer Rewinds...................96 Yokogawa..................................IFC SILICON CHIP July 1992). All settings stored in EEPROM. Kits come complete with LCD and case. Standard version $135 incl. p&p. Enhanced version uses 68705U3 and has built-in calendar, allowing day of fortnight watering, (ie SA, SU, MO, etc), externally triggerable cycles and rain switch software. $175 incl. p&p. Requires 24V AC. Relays extra at $3.75 each (require 9 for full kit). Kits and further info from Graham Blowes, Mantis Micro Products, 38 Garnet St, Niddrie 3042. Phone (03) 337 1917 (AH), (03) 575 3349 (BH). Fax (03) 575 3369. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590.