Silicon ChipSeptember 1997 - Silicon Chip Online SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: Make the Internet free of sales tax
  4. Feature: Unravelling Saturn's Secrets by Sammy Isreb
  5. Feature: Hifi On A Budget by Owen Davies & Julian Edgar
  6. Project: Multi-Spark Capacitor Discharge Ignition System by John Clarke
  7. Serviceman's Log: The things I do for money by The TV Serviceman
  8. Order Form
  9. Book Store
  10. Project: Building The 500W Audio Power Amplifier; Pt.2 by Leo Simpson & Bob Flynn
  11. Project: A Video Security System For Your Home by Branco Justic
  12. Back Issues
  13. Feature: Computer Bits by Jason Cole
  14. Vintage Radio: The 5-valve Airking console receiver by John Hill
  15. Product Showcase
  16. Project: PC Card For Controlling Two Stepper Motors by Rick Walters
  17. Notes & Errata: Remote Controlled Gates for Your Home, August 1997
  18. Market Centre
  19. Advertising Index
  20. Outer Back Cover

This is only a preview of the September 1997 issue of Silicon Chip.

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Items relevant to "Multi-Spark Capacitor Discharge Ignition System":
  • Multi-Spark Capacitor Discharge Ignition System PCB pattern (PDF download) [05309971] (Free)
Items relevant to "Building The 500W Audio Power Amplifier; Pt.2":
  • 500W Audio Power Amplifier PCB pattern (PDF download) [01208971] (Free)
  • 500W Audio Power Amplifier panel artwork (PDF download) (Free)
Articles in this series:
  • A 500 Watt Audio Power Amplifier Module (August 1997)
  • Building The 500W Audio Power Amplifier; Pt.2 (September 1997)
  • Building The 500W Audio Power Amplifier; Pt.3 (October 1997)
Articles in this series:
  • Computer Bits (July 1989)
  • Computer Bits (August 1989)
  • Computer Bits (September 1989)
  • Computer Bits (October 1989)
  • Computer Bits (November 1989)
  • Computer Bits (January 1990)
  • Computer Bits (April 1990)
  • Computer Bits (October 1990)
  • Computer Bits (November 1990)
  • Computer Bits (December 1990)
  • Computer Bits (January 1991)
  • Computer Bits (February 1991)
  • Computer Bits (March 1991)
  • Computer Bits (April 1991)
  • Computer Bits (May 1991)
  • Computer Bits (June 1991)
  • Computer Bits (July 1991)
  • Computer Bits (August 1991)
  • Computer Bits (September 1991)
  • Computer Bits (October 1991)
  • Computer Bits (November 1991)
  • Computer Bits (December 1991)
  • Computer Bits (January 1992)
  • Computer Bits (February 1992)
  • Computer Bits (March 1992)
  • Computer Bits (May 1992)
  • Computer Bits (June 1992)
  • Computer Bits (July 1992)
  • Computer Bits (September 1992)
  • Computer Bits (October 1992)
  • Computer Bits (November 1992)
  • Computer Bits (December 1992)
  • Computer Bits (February 1993)
  • Computer Bits (April 1993)
  • Computer Bits (May 1993)
  • Computer Bits (June 1993)
  • Computer Bits (October 1993)
  • Computer Bits (March 1994)
  • Computer Bits (May 1994)
  • Computer Bits (June 1994)
  • Computer Bits (July 1994)
  • Computer Bits (October 1994)
  • Computer Bits (November 1994)
  • Computer Bits (December 1994)
  • Computer Bits (January 1995)
  • Computer Bits (February 1995)
  • Computer Bits (March 1995)
  • Computer Bits (April 1995)
  • CMOS Memory Settings - What To Do When The Battery Goes Flat (May 1995)
  • Computer Bits (July 1995)
  • Computer Bits (September 1995)
  • Computer Bits: Connecting To The Internet With WIndows 95 (October 1995)
  • Computer Bits (December 1995)
  • Computer Bits (January 1996)
  • Computer Bits (February 1996)
  • Computer Bits (March 1996)
  • Computer Bits (May 1996)
  • Computer Bits (June 1996)
  • Computer Bits (July 1996)
  • Computer Bits (August 1996)
  • Computer Bits (January 1997)
  • Computer Bits (April 1997)
  • Windows 95: The Hardware That's Required (May 1997)
  • Turning Up Your Hard Disc Drive (June 1997)
  • Computer Bits (July 1997)
  • Computer Bits: The Ins & Outs Of Sound Cards (August 1997)
  • Computer Bits (September 1997)
  • Computer Bits (October 1997)
  • Computer Bits (November 1997)
  • Computer Bits (April 1998)
  • Computer Bits (June 1998)
  • Computer Bits (July 1998)
  • Computer Bits (November 1998)
  • Computer Bits (December 1998)
  • Control Your World Using Linux (July 2011)
Items relevant to "PC Card For Controlling Two Stepper Motors":
  • PC Stepper Motor Drivers DOS software (Free)
  • PC Card for Controlling Two Stepper Motors PCB pattern (PDF download) [07208971] (Free)
Changing Win95’s Startup Options SILICON CHIP SEPTEMBER 1997 $5.50* NZ $6.50 INCL GST C I M A N Y D 'S A I L AUSTRA E N I Z A G A M S C I ELECTRON SERVICING - VINTAGE RADIO - COMPUTERS - SATELLITE TV - PROJECTS TO BUILD Multi-Spark Capacitor Discharge Ignition ISSN 1030-2662 09 PRINT POST APPROVED - PP255003/01272 9 771030 266001 HIFI ON A BUDGET VIDEO SECURITY SYSTEM BUILDING THE 500W AUDIO AMPLIFIER MAPPING SATURN’S SECRETS September 1997  1 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 Contents Vol.10, No.9; September 1997 FEATURES   4  Unravelling Saturn’s Secrets NASA has a new spacecraft ready to probe Saturn & its moons. Learn about the spacecraft and its mission – by Sammy Isreb 12  Hifi On A Budget Don’t settle for an all in one sound system if have no money. You’ll get much better sound buying genuine hifi gear secondhand – by Julian Edgar PROJECTS TO BUILD Multi-Spark Capacitor Discharge Ignition System – Page 18 18  Multi-Spark Capacitor Discharge Ignition System New design provides a high-energy multi-spark discharge for 2-stroke engines, rotaries and high-performance 4-strokes – by John Clarke 54  Building The 500W Audio Power Amplifier; Pt.2 Add a rugged power supply, a large finned heatsink and fan cooling for really impressive performance – by Leo Simpson & Bob Flynn 62  A Video Security System For Your Home You build a simple controller and add a spare VCR, a miniature CCD camera, a PIR sensor or two and an IR illuminator – by Branco Justic 80  PC Card For Controlling Two Stepper Motors This addressable card plugs into your PC’s parallel port and lets you drive two stepper motors using software control – by Rick Walters Building The 500W Audio Power Amplifier – Page 54 Video Security System For Your Home – Page 62 SPECIAL COLUMNS 38  Serviceman’s Log The things I do for money – by the TV Serviceman 70  Computer Bits Win95, MSDOS.SYS & the Registry – by Jason Cole 74  Vintage Radio The 5-valve Airking console receiver – by John Hill DEPARTMENTS   2  Publisher’s Letter 32  Circuit Notebook 42 Mailbag 44  Order Form 78  Product Showcase 91  Ask Silicon Chip 93  Notes & Errata 94 Market Centre 96  Advertising Index PC Card For Controlling Two Stepper Motors – Page 80 September 1997  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Ross Tester Philip Watson, MIREE, VK2ZPW Bob Young 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: $54 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. ISSN 1030-2662 PUBLISHER'S LETTER Make the Internet free of sales tax Everyone’s talking about the Internet and now the politi­cians and the Australian Tax Office are worried about it. They have realised that all those nasty tax-dodging companies might use it to avoid sales tax and that the budget could suffer bil­lions of dollars because of it. In fact, the Government has just announced an enquiry into that very subject: the Joint Committee of Public Accounts (JCPA). The JCPA will examine the administration of the Australian taxation system and assess the implications for Australia’s tax base. Currently, goods entering Australia are not subject to sales tax if they are below a $50 duty and sales tax free limit and the value of the goods is below $1000 for goods imported by post and below $250 if imported by other means. Apart from the taxation implications, the JCPA is also concerned about consumer protection because Australian laws are of little help to people purchasing faulty or incorrect goods from retailers overseas. Most would agree that this is a most important issue but I don’t think the pollies realise just how big it is. The inquiry was announced on August 7th and the closing date for submissions is Friday, September 19th, 1997! That’s hardly time enough for any person or organisation to make a well-prepared submission. It is typical of the Federal Government’s piecemeal approach to most issues and particularly taxation. Now that the High Court has struck down the States’ various invalid tax schemes and the Government has put together a hasty rescue package which looks pretty shaky, they must see that the whole taxation system is a sinking ship. The Internet is likely to be yet another revenue hole. One way or another, the Govern­ment will have to figure out effective ways of maintaining an adequate tax base. But there just might be a big opportunity here for Austra­lia to do something really adventurous as far as the Internet is concerned. Perhaps we should face the fact that collecting tax on Internet transactions will be an administrative nightmare and that sales tax is a mess anyway: just announce that the whole shebang will be tax free. Or make the tax rate very low. Imagine how commerce could blossom! It could provide a big boost to Australia’s aspirations to be a performer in the technology stakes. Think about it. But you don’t have much time to make submissions since they close on September 19th. For further information, contact Stephen Boyd, the JCPA Inquiry Secretary; phone (06) 277 4615; fax (06) 277 2220. 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 BOSSMAN ELECTRONICS Soon we should be fully set up with this new company which is a subsidiary to OATLEY ELECTRONICS, for the purpose of giving TAX EXEMPT PRICES to entitled organisations. The product range that will be included on this list will increase rapidly. For enquiries call BOSSMAN ELECTRONICS on: 02 9584 3562. PIC IC PROGRAMMER Ready made, coming soon, Email or Fax for more information: $49 SOLID STATE PELTIER EFFECT DEVICES These can be used to make a solid state thermoelectric cooler/ heater. 12V/4.4A 40 x 40 x 4mm. Basic information to suit: $27, 12V DC fan to suit for $8. TO-3 TRANSISTORS IN 1kg BAGS Approx 1kg of semiconductors recovered from working equipment. All devices are in the TO-3 package. Approx 80 devices per kg wide variety of type numbers, some of which are common types of transistors, voltage regulators & Schottky diodes. These devices have been poorly stored & have bent pins, etc. $6. 650nm LASER POINTER SPECIAL Light weight (2XAAA) pen sized pointer with 5mW/650nM laser diode, 140mm long, 18mm diameter: $55. 650nm LASER MODULE Our new module is fitted with a 650nm laser diode! Very small, 35mm long, 10mm diameter, 3 to 4.5V operation: $50. DISCO LASER LIGHT SHOW PACK The above 5mW/650nm kit plus our AUTOMATIC LASER LIGHT SHOW: $99. NEW COMPUTER CONTROLLED STEPPER MOTOR KIT Coming soon. This kit functions similarly to our previous stepper motor kit but has improvements to the driver electronics that can allow larger motors to be driven more efficiently, with much reduced loading on the computers parallel port, together with 2.5kV opto isolation between the stepper driving circuit and the computer. Previous purchasers may contact us for a simple modification to greatly reduce the loading on the computer’s parallel port. PCB and all on board components kit plus software and information: $39, or $49 with two M35 motors included! DIGITAL BAR CODE WANDS New USA made wands fitted with 2.5m long curly cord terminated in a 5-pin 240 degree DIN plug, with optical sensor, visible red LED, a photo IC detector, & precision aspheric optics. Converts barcodes into a digital pulse train as it is manually swept across the barcode. Employs a sapphire tip, pot size is 0.19mm. Output is open collector TTL/CMOS compatible & the wand needs to be powered from 5V. $45. INFRARED TESTER USING CONVERTER TUBES Used high resolution US-made night vision tubes with some blemishes together with a high-voltage generator kit. Have either 25 or 40mm diameter, fibre-optically coupled input and output windows. Use to test infrared remote controls without lensing or as a cheap IR viewer with lensing. Produce a good image in low light, need IR illumination in dark places: $40. MAGNIFIERS/LOUPES Jewellers eyepiece: $3, Twin lens loupes: 50mm $8, 75mm $12, 110mm $15. The set of 4: $30. SUPER BRIGHT BLUE LEDS BY FAR THE BRIGHTEST BLUE EVER OFFERED, super bright at 400mCd: $1.50 each or 10 for $10. 5mm LEDS AT SUPER PRICES 1Cd red: 10 for $4. 300mCd green: $1.10 ea or 10 for $7 (make white light by mixing output of red green & blue). 3Cd red: $1.10 ea or 10 for $7. 3Cd yellow (small torch!) also available in 3mm: 10 for $9. Super bright flashing LEDs: $1.50 ea or 10 for $10. CENTRAL LOCKING This four-door central locking kit is a commercial product that includes 2 master and 2 slave actuators, wiring loom, control unit, necessary hardware and instructions: $60. The UHF REMOTE CONTROL KIT has a switched relay output for operating an alarm etc, an indicator output for driving a buzzer etc, and logic level outputs for operating the CENTRAL LOCKING KIT. Comes with a ready-made transmitter with two pushbuttons (lock, relay on - unlock, relay off), and a receiver PCB and all on-board components. 5 LEDs make for easy tuning and diagnostics: $35. SIREN KIT, includes speaker $12. 12V PANASONIC GEL BATTERY BARGAIN New 12V/2.3Ah Panasonic sealed lead-acid rechargeable video batteries at a fraction of their real value. 180(L) x 60(H) x 22(W)mm, 0.67kg, made in Japan. The contacts (which are easily solderable) are at one end of the battery. $10 each. Now that’s a bargain but what about two of these batteries plus one intelligent GEL/LEAD-ACID BATTERY CHARGER for a total of $25!! 12V/7Ah GEL BATTERY BARGAIN Fresh stock 7Ah battery (150 x 95 x 65mm, 2.7kg) plus one GEL/ LEAD-ACID BATTERY CHARGER for: $33. DC MOTOR SPEED CONTROL– EXPERIMENTERS PACK One 20A motor speed controller kit (similar to SC June 97) $18, plus two small new 12VDC motors (40mm dia. 40mm length) plus one used car windscreen wiper motor (which has internal gear reduction) for: $32. AMPLIFIER - PREAMPLIFIER AND MORE! A professional mostly SM PCB that contains a 5W amplifier based on a TDA1905 IC, and a separate audio preamplifier section. We also provide a prewired high quality unidirectional electret microphone that has a wind filter and a mounting clip. A small speaker and basic hook-up information is also included. Appears to have been designed for a communications system. Great for many applications including a two-way intercom (2 required) that does not require switching! Available at less than the cost of the electret microphone: $15 each, 2 for $24. HELIUM NEON LASER BARGAIN Large 2-3mW HeNe laser head plus a compact potted US made laser power supply. The head plugs into the supply, and two wires are connected to 240V mains. Needs 3-6V/5mA DC to enable. Bargain: $100. LASER ENGINE Brand new complete laser engine as used in laser printers. Includes a Polygon scanner motor with Xtal controlled driver PCB, 5mW/780nm laser diode in collimated housing mirrors/ mirrors lenses etc. Information on how to make the motor and laser operational included. Bargain at $35. SWITCHMODE POWER SUPPLIES Modern design compact (145 x 80 x 50mm), totally enclosed in a perforated metal case, 12VDC/2A & 5VDC/5A out: $17. The same power supply installed within a flat PC type white powder-coated metal box, 380(L) x 365(W) x 55(H)mm, is also available: $20. BARGAIN ARGON LASER HEADS The cheapest way to get a BLUE-GREEN LASER beam! These used Argons have around 30mW output (may require licensing!!) and are guaranteed for 6 months. A power supply for these is based on a transformer with 80V<at>2A and 3V<at>20A secondaries. Ring or email for more information. Head only: $250. MINI TV STATION Make your own mini TV station with this metal-cased, commercial transmitter with telescopic antenna. Dimensions 123 x 70 x 20mm, 12V operation. Includes power switch, indicator LED, RCA audio and video connectors, twin RCA-RCA lead. Our 32mm AUDIO PREAMPLIFIER kit ($8) (comes with an electret microphone), and a CCD camera will complete the station. Transmitter $30 or $20 when purchased with a CCD camera. REGULATED 10.4V-500mA PLUGPACK to power the whole system: $10. AUDIO - VIDEO MONITOR Compact high resolution 5" screen B/W audio and video monitor. Has two-way audio, built in microphone, audio amplifier, speaker and pushbutton “talk” switch. Needs a preamplifier and microphone for remote audio monitoring (our 32mm audio preamplifier is ideal). Has two camera inputs to allow manual or auto switching (adjustable speed) between each camera. Needs 12V DC 1A (our switched mode supply is ideal), size 160 x 190 x 150mm, has audio and video outputs for connecting to a VCR etc. Monitor and 6-way mini input connector only: $125. 650nm VISIBLE LASER POINTER KIT YES, NEW 650nm kit!!!: Very bright! Complete laser pointer that works from 3-4V DC. Includes 650nm/5mW laser diode, new handheld case 125 x 39 x 25mm, adjustable collimator lens, PCB battery holder: $35. learning remote control: $25 for PCB and all on-board components, used PIR to suit: $12. 32mm 10 LED IR ILLUMINATOR New IR (880nm) LEDs have an output about equal to our old 42 LED IR illuminator: $14. 32mm AUDIO PREAMPLIFIER An $8 kit that produces a “line level” signal from an electret microphone, connect the output to our: UHF VIDEO TRANSMITTER ($30) or $20 when bought with the camera for a complete Audio-Video link. 32mm AUDIO AMPLIFIER An LM386 based $9 audio power amplifier which can directly drive a speaker – needs the 32mm preamplifier. WHAT IS 32mm? All boards are 32mm, so you can house these kits in a plastic 32mm joiner: cheap plumbing part. VISIBLE LASER DIODE MODULE KIT – COMING SOON This kit has the same circuit as our “visible laser diode kit” but has a smaller circuit board allowing it to be fitted into a piece of tubing. Dimensions of the board are less than 25mm wide/50mm long. 650nm/5mW laser diode. 3V operation. $29. FAX POLLING Back by popular demand! POLL: 02 95707910 and 02 95794985. PC POCKET SAMPLER KIT Ref EA Aug. 96. Data logger/sampler, connects to PC parallel port, samples over a 0-2V or 0-20V range at intervals of one/hour to one/100µs. Monitor battery charging, make a 5kHz scope, etc! Kit includes on-board components, PCB, plastic box and software (3.5" disk): (K90) $30. WOOFER STOPPER Mk II Works on dogs and most animals, ref SC Feb 96. PCB and all onboard components, transformer, electret mic & horn piezo tweeter: (K77) $43, extra tweeters (drives 4): $7 each. Approved 13.8V/1A DC plugpack (PP6) $10. UHF REMOTE TRIGGER Single channel Rx and Tx: (K77T) $40. MASTHEAD AMPLIFIER KIT Our famous MAR-6 based masthead amplifier. 2-section PCB (so power supply section can be indoors) and components kit (KO3) $15. Suitable plugpack (PP2): $6. Weatherproof box: (HB4) $2.50. Box for power supply: (HB1) $2.50. Rabbit-ears antenna (RF2) $7. (MAR-6 available separately.) USED PIR MOVEMENT DETECTOR Commercial quality 10-15m range, used but tested and guaranteed, have open collector transistor (BD139) output and a tamper switch, 12V operation, circuit provided: $10. 12V - 2.5W SOLAR PANEL KIT US amorphous glass solar panels with backing glass terminating clips, etc – a solar panel kit. On SPECIAL: $20 each or 4 for $60. WIRELESS IR EXTENDER Converts the output of any IR remote control to UHF. Self-contained transmitter attaches to IR remote. Kit includes two PCBs, all components, 2 plastic boxes, Velcro strap: (K89) $39. (9V battery not included). Plugpack for Rx (PP10): $11. CHARACTER DISPLAYS Back in stock late this month! Standard 32 x 4 character displays using Hitachi ICs. ON SPECIAL: $18. NICAD CHARGER & DISCHARGER Professional, fully assembled and tested fast NICAD battery charger and discharger PCB assembly. Switchmode circuit, surfaced mounted on a double-sided PCB. Nominal unregulated input 13.7V DC, 900mA charge current. Appears to use voltage slope detection for charge terminating, also has a timer (4060) to terminate the charge. We supply a thermistor for temperature sensing. For fast-charging 7.2V AA nicads. Basic information provided. Incredible pricing: $9 each or 3 for $21. MOTOR AND PUMP New, compact plastic pump with a 240V AC 50Hz 0.8A 91W 2650 RPM induction motor attached. Probably a washing machine part. Very quiet operation, made in Japan, overall dimensions 160 x 90 x 90mm, weight 1.2kg, inlet 25mm diameter, outlet 20mm dia­meter. Other end of motor has 20mm-long 4mm dia. shaft. Motor can be rewound for lower AC voltage and or reduced power operation without disassembling the unit. We calculated 5.5 turns per volt: $19. CCD IMAGE SENSOR High quality “Thomson” brand, 576 x 550 pixels with antiblooming, with full data but no circuit suggestions available, usable response from 400-1100nm, 30dB S/N at 40 millilux, 2/3" optics compatible format: $35. BEST “VALUE FOR MONEY” CCD CAMERA The best “value for money” CCD camera on the market! Come and see us for a comparison to any cheaper models advertised! Tiny CCD camera, 0.1 lux, IR responsive, high resolution. This camera has a metal lens housing (not plastic) and performs better than many cheaper models. The pinhole lensed version of this camera is also available for the same price: $120. SALES TAX EXEMPT PRICE FOR EITHER OF THE ABOVE IS: $99. If you need different lenses, ring and ask!! COMING: A lower priced high-quality Standard or Pinhole CCD camera Quality product for under $100. Fax/ring or email for more info. SOLAR REGULATOR Ref: EA Nov/Dec 94 (intelligent battery charger). Efficiently charge 12-24V batteries from solar panels but can also be used with simple car battery chargers to prevent overcharging. Extremely high efficiency due to the very efficient MOSFET switch & Schottky isolation diode. We now offer a 7.5A or 15A kit: $26/$29 (K09). NEW SEMICONDUCTOR BARGAINS CA3140 MOSFET input op amp: 5 for $5. TL494 switchmode power supply IC: 5 for $5. NE555 timer IC: 10 for $5. ICL7106 LCD display driver: $5. ICL7107 LED display driver: $5. IRFZ44 MOSFETS: 60V, 0.028 ohm on resistance, 50A: 10 for $30. COLOUR CCD CAMERA - NEW This high-quality CCD camera is built over 3 boards which are joined with a flexible cable that can be folded into a very compact camera. Head board: 42 x 20.5mm, lens height: 24mm. Main board: 42 x 42 x 9mm. Power board 42 x 20.5 x 8.8mm. SPECIAL introductory price: $350 (less with ST exemption). PO Box 89, Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 480 x 128 LCDs Hitachi LM215 dot matrix LCD displays. Clearance: $15 each, 3 for $35. KITS FOR CCD CAMERA SECURITY New INTERFACE KIT FOR TIME LAPSE RECORDING: now has relay contact outputs! Can be directly connected to a VCR or via a OATLEY ELECTRONICS orders by e-mail: oatley<at>world.net WEB SITE: http://www.ozemail.com.au/~oatley major cards with phone and fax orders, P&P typically $6. September 1997  3 By SAMMY ISREB Picture credit: NASA/JPL The Cassini space probe: unravelling Saturn’s secrets Following its spectacularly successful Mars landing, NASA is readying a spacecraft to probe Saturn and its moons. The Cassini probe, as it is known, should provide new insights into the solar system. 4  Silicon Chip Picture credit: NASA/JPL O N OCTOBER 6TH this year, NASA and JPL (Jet Propulsion Laboratories) will launch their latest space probe, the Cassini, using a Titan IV rocket. This launch will herald the start of an almost decade-long mission designed to explore Saturn and its moons. Many aspects of this mission are ground breaking, as we shall see. And as with other space probes, the Deep Space Network site at Tidbinbilla near Canberra will be involved in the mis­sion. Saturn Orbit Insertion: this is a computer-rendered image of Cassini during the Saturn Orbit Insertion (SOI) manoeuvre, just after the main engine has begun firing. The SOI manoeuvre, approximately 90 minutes long, will allow Cassini to be pulled by Saturn’s gravity into a 5-month orbit. Cassini’s close proximity to the planet after the manoeuvre will offer an opportunity to observe Saturn and its rings at high resolution. The launch The Titan IV rocket that will be used to launch the Cassini probe is immense, with a prelaunch weight of 940,000kg, of which 840,000kg is propellant. But despite the power of the Titan IV rocket, its launch energy is not enough to send the almost 5.5-tonne space probe directly on its way. To overcome this, the probe will first be sent towards Venus and will then use the gravitational field of this and other planets to accelerate it towards Saturn. Initially, the Cassini probe and Centaur upper stage of the rocket will be placed in an Earth orbit. This “stack” Cassini Interplanetary Trajectory: this graphic depicts the planned inter­ planetary flight path beginning with the launch from Earth on 6th October 1997, followed by gravity assisted flybys of Venus (21st April 1998 and 20th June 1999) and Jupiter (30th December 2000). The Saturn arrival is scheduled for 1st July 2004, which marks the beginning of a 4-year tour of the Saturn system. September 1997  5 Table1: Cassini Probe Mission Events Mission Event Date Launch on Titan IV launch vehicle 6th October, 1997 Aphelion 1 (furthest distance from the Sun 1st November, 1997 Perihelion 1 (closest approach to Sun) 23rd March, 1998 Venus 1 flyby 21st April, 1998 Deep space manoeuvre to target Venus 2 2nd December, 1998 Aphelion 2 (furthest distance from the Sun 4th December, 1998 Window for using high gain antenna begins 16th December 1998 Window for using high gain antenna ends 10th January, 1999 Venus 2 flyby 20th June, 1999 Perihelion 2 (closest approach to Sun) 27th June, 1999 Earth flyby 16th August, 1999 High gain antenna can be used from now on 29th January, 2000 Jupiter flyby 30th December, 2000 Science observations begin 1st January, 2004 Saturn orbit insertion manoeuvre 1st July, 2004 Manoeuvre to target probe on Titan 12th September, 2004 Huygens probe separates from Cassini to go to Titan 6th November, 2004 Manoeuvre to target for Titan flyby 8th November, 2004 Huygens probe mission at Titan (approx, 4 hours long) 27th November, 2004 First flyby of Titan, Saturn's largest moon 27th November, 2004 Nominal end of mission (after 11 years) 1st July, 2008 End of possible extended mission Unknown will orbit the Earth unpowered for about 15 minutes until it is in line with Venus, at which stage the powerful Centaur stage will be ignited to provide the final push towards Venus and to enable the probe to escape the Earth’s gravitational field. At the end of its 8-minute burn, the Centaur stage will separate from Cassini. However, before this occurs, the various subsystems in the spacecraft will be activated so that it can operate on its own. As well as this, before separation, the Centaur’s computer will point the Cassini’s high gain antenna towards the Sun. This is done so that the antenna shields the instruments and the avionics from the intense heat of the Sun as the spacecraft approaches Venus. Following separation, communication with the spacecraft will be made 6  Silicon Chip through the 34-metre antenna at the Deep Space Network at Tidbinbilla. This will enable ground controllers at the Jet Propulsion Laboratories to monitor the status of the probe and to send commands to prepare it for its long journey to Saturn. Gravity assist As already mentioned, the Cassini probe is not able to make it directly to Saturn. This problem is overcome by using a “gravity assist” technique four times during the flight: at Venus in April 1998 and again in June 1999; at Earth in August 1999; and at Jupiter in December 2000. During a brief period between the Venus encounters and shortly after the Earth flyby, the heat radiation from the Sun will be low enough to allow the antenna to be pointed towards Earth. This will improve communications with the spacecraft and assist in its navigation. As well as using the gravity assists, the Cassini space probe will also use two types of fuels to get to its desti­nation. The first of these fuels is known as “bipropellant” and is used for large course alterations. Bipropellant is made up of two chemicals, mono-methyl-hydrazine and nitrogen tetra­oxide, which ignite when combined in the engine nozzles. These two chemicals are easy to store and, importantly, they do not freeze at the low temperatures that will be experienced on the mission. The second fuel used is hydrazine. This powers the “Reaction Control Thrusters” and will be used for very brief burns to alter the rotational position of the Cassini. The hydra­zine will only be used in small amounts and engineers are confid­ent that about half the original quantity will remain at the end of the planned mission. The main objective of the navigators at JPL is to keep the spacecraft to the planned trajectory for the entire mission. The navigation team provides the project with predictions of the trajectory of the Cassini probe, the various planets, and Sat­urn’s satellites. Based on this information, the team then deter­mines the trajectory correction manoeuvres (TCMs) that are re­ quired to maintain the preplanned trajectory. Without these many small corrections, the spacecraft would miss Saturn by many millions of kilometres. Tracking techniques In order to plan for TCMs, the navigators use a number of different techniques to track the spacecraft’s trajectory and determine its position. The three methods used are: (1) Doppler, (2) ranging, and (3) optical navigation. The Doppler technique is used to measure the speed that the Cassini is approaching or receding from the Earth and is similar to the Doppler technique used in radar speed guns. Basically, the Deep Space Network antenna sends a signal to the spacecraft which is then directly returned. If the spacecraft is approaching or receding from the tracking station, the fre­quency of the return signal will by slightly higher or lower, respectively. This frequency difference allows the spacecraft’s velocity to be determined ABOVE: Huygens Probe Release – artist’s conception of Cassini orbiter with the Huygens probe separating to enter Titan’s atmosphere. After separation, the probe will drift for about three weeks until it reaches its destination. Equipped with a variety of scientific sensors, the ESA Huygens probe will spend 2-2.5 hours descending through Titan’s dense murky atmosphere of nitrogen and carbon-based molecules, beaming its findings to the distant Cassini orbiter as it flies overhead. Picture credit: NASA/JPL Picture credit: NASA/JPL RIGHT: Huygens Probe Exploded View – the probe has a diameter of 2.7 metres and a mass of nearly 350kg. It contains a heat shield, parachute package, engineering equipment including batteries, and several scientific sensors to measure the properties of Titan’s atmosphere and surface. September 1997  7 succes­sive encounters. The first takes place just after the encounter and is designed to correct any errors in the trajectory. The second and third TCMs are essentially course corrections on the way to the next encounter. In addition to these manoeuvres, there is a large deep space manoeuvre between the two Venus encounters. An additional propul­sive correction manoeuvre is also needed before and after the Jupiter encounters. During the Saturn approach, the optical cameras will be calibrated so that images of Saturn’s satellites can be obtained. A flypast of Phoebe, Saturn’s most distant satellite, will occur some 19 days prior to the spacecraft’s arrival at Saturn itself. Communications Picture credit: NASA/JPL Huygens Descent Profile: this picture illustrates the Huygens probe descent profile, beginning with the initial encounter with the Titan atmosphere and subsequent deceleration. As the probe slows, a small parachute is released which deploys the main probe parachute. Once the parachute is fully open, the deceleration shield is jettisoned and the probe drifts towards Titan’s surface. About 40km above the surface the main parachute is jettisoned and a smaller drogue chute carries the probe the remaining distance. and therefore indicates where the probe is headed. Ranging operates on the principle that radio waves travel at the speed of light. Knowing this, navigators can “fire” radio waves at the Cassini probe and measure the time it takes for them to return. The distance of the probe from Earth can then be calculated. When combined with the Doppler method, this allows the spacecraft’s position and speed to be determined very accurately. The optical data consists of pictures of celestial bodies against a star background, as taken with the spacecraft’s 8  Silicon Chip cam­eras. The measurements extracted from these pictures can then be used to determine where the spacecraft is with respect to every­thing else in the field of view. In many cases, however, optical data is used to determine where the celestial body is rather than the position of the spacecraft. This will especially apply to some of the satellites of Saturn that have unknown orbits. During the early part of the cruise to Saturn, the focus of the navigational team will be on successful planetary flybys. The TCMs required typically involve three manoeuvres between The Cassini craft communicates via a 4-metre high gain antenna, along with two wide-beam low-gain antennas. The craft transmits to Earth at a frequency of about 8.4GHz, while the Earth base stations respond at about 7.2GHz. The radio link provides data transmission rates that vary from a low 40 bits per second, right up to 170,000 bits per second. The signals will take around an hour to reach the Earth from Saturn and vice versa! Back on Earth, the three stations that make up the Deep Space Network, will be used to communicate with the spacecraft. This network consists of three sites spaced around the world: (1) Tidbinbilla, Australia; (2) Goldstone, California (USA); and (3) Madrid, Spain. Before any important data is sent from Cassini, it is first placed into one of two solid state recorders carried aboard the craft. These solid state recorders each have a storage capacity of two gigabits. When enough data has been accumulated and the right conditions prevail, an inbuilt processor (called the Com­mand and Data Subsystem) will transmit the information to Earth. Releasing the probe An important part of the Cassini spacecraft is the Huygens probe, which was supplied by the European Space Agency. This probe carries a well-equipped robotic laboratory which will be used to scrutinize the clouds, atmosphere and surface of Saturn’s moon Titan. It will be released by Cassini in November 2004 and will LEFT: The Saturn System – this montage of images of the Saturnian system was prepared from an assemblage of images taken by the Voyager 1 spacecraft during its Saturn encounter in November 1980. This artist’s arrangement shows Dione in the forefront, Saturn rising behind, Tethys and Mimas fading in the distance to the right, Enceladus and Rhea of Saturn’s rings to the left and Titan in its distant orbit at the top. BELOW: Cassini Spacecraft (with Huygens Probe attached) – roughly two storeys tall and weighing more than 5.5 tonnes, Cassini is one of the largest interplanetary spacecraft ever launched. Three separate antennas – one high gain and two low gain – will enable the orbiter to communicate with Earth. Propulsion for large changes to the orbiter’s trajectory is provided by two powerful 445-N engines. Sixteen smaller thrusters will serve to control Cassini’s orientation in space and make small changes to the spacecraft’s flight path. Picture credit: NASA/JPL drop into Titan’s atmosphere several weeks later. After releasing the probe, the Cassini spacecraft will perform a manoeuvre so that it will be above the probe when it arrives at Titan. This will allow the spacecraft to monitor data transmissions from the probe as it approaches Titan’s surface. As before, the received data will be stored in the orbiter’s solid state recorder before being downloaded to one of the Earth sta­tions. As the probe enters Titan’s upper atmosphere it initially uses a heat­ shield to decelerate. Subsequently, at an altitude of about 175km, the probe deploys its main parachute, jettisons the heatshield and begins its experiments. Fifteen minutes later, it jettisons the main chute, deploys a smaller parachute, and de­scends the last 140km or so to the surface, collecting data all the way and transmitting it back to the spacecraft. As the Huygens probe breaks through the clouds of Titan, an onboard camera will capture pictures of the Titan panorama. Other instruments will directly measure the organic chemistry in Titan’s atmosphere and remotely measure the composition of the surface. Once the mission has been completed, the spacecraft will aim its Picture credit: NASA/JPL antenna towards Earth and transmit the recorded probe data. This data will actually be transmitted twice and will be verified on the ground before it is overwritten in the data recorders. After the Huygens probe has completed its mission, the space probe will set about tackling various other scien­tific missions. The spacecraft carries a number of instruments and the main units and their scientific aims are listed in the accompanying panel. The planned mission will finish in 2008, after spending about four years at Saturn and its moons. By then, the Cassini probe will have collected huge amounts of data over its 11-year mission lifetime and will have provided new insights into Saturn and other SC parts of the solar system. September 1997  9 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.dse.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.dse.com.au to t a h W hen do w e got you’v oney no m 12  Silicon Chip Hifi on a Budget Don’t settle for an all-in-one sound system if you have only $600 to spend on hifi gear. You can get much better sound by buying genuine hifi gear secondhand. By OWEN DAVIES & JULIAN EDGAR F OR MANY YEARS now, mainstream budget audio gear has been more show than go. Manufacturers have concentrated on attracting buyers not through good sound quality but by offering more flash­ing lights than an aircraft cockpit. And although they offer a convenient mix of tape, radio and CD facilities, the now popular budget-priced three-inone systems inevitably impose severe compromises in sound quality. For starters, the amplifiers of these systems generally have mediocre output power and distortion figures. The loudspeak­ers will also be quite mediocre. To cut costs, the speaker boxes in budget systems will be manufactured from thin particle board, will house low-cost paper-cone drivers and will lack the proper crossover networks necessary for good hifi sound reproduction. Instead of spending $500-$600 on a new all-in-one system, we suggest that you barter your hard-earned cash for a series of separate secondhand components. The secondhand gear ABOVE: This Philips 260 stereo preamplifier was bought for just $75. It was teamed with the Philips 360 50W RMS/channel power amplifier shown at right (also $75), the two providing an excellent combina­tion. Note that the amplifier features peak power meters on its front panel. It’s obvious that it’s not a budget amplifier as its standard of construction is very high. FACING PAGE: This box is a good prospect for new drivers. Its surface finish is in good condition, so it still looks the part. September 1997  13 A CD player is by far the best budget sound source. This Teac PD-200 player cost just $80. Avoid choosing very old CD players if possible, as many would have worn drive mechanisms. might lack the bells and whistles of the all-in-one stuff (eg, infrared remote control) but if it’s good sound quality that really interests you, the secondhand path is the way to go. Put simply, carefully selected separate components will give better sound quality than a combined unit and will be better built into the bargain. They might lack the integrated look of a combined unit but they can more than compensate for that in how they sound. And isn’t the quality of the sound the reason that you buy a hifi? Separate components also come into their own if one compon­ent needs repairing. The reason for this is that you can continue to use the rest of your gear unless, of course, it’s the amplifi­er that’s at fault. What to buy We recommend that the system be made up of a separate amplifier, CD player, speakers and a tuner if you desire. Avoid cassette decks at all costs unless you have a specific reason for Build It Yourself? Why buy an old amplifier when you can build a new one with better specifications for the same money? While there are plenty of good-quality amplifier kits about, we don’t recommend that you build one unless you’re already an experienced kit builder. A $300 amplifier kit is, after all, just a pile of components and unless you build it 100% correctly, it won’t work. Of course, if you do have previous kit building experience, a kit amplifier is well worth considering. There are also smaller kits like subwoofer adaptors and loudspeaker protectors on the market. The outlay of money for these is comparatively small and they are simpler to make than a kit amplifier. You also end up with a product that’s not readily available, especially on the secondhand market. Incidentally, be very wary of buying an already-constructed kit amplifier. Who made it – a beginner or an experienced elec­tronics technician? You just don’t know, so stay clear unless you have the skills to judge the standard or workmanship or you know the person who built it. 14  Silicon Chip wanting a tape player! Compact discs (CDs) offer far better sound quality than tapes – it’s as simple as that. Cheap, good quality components can be sourced from second­ hand dealers and pawnbrokers, or through private sale. Major chains such as Cash Converters usually have a wide selection of compon­ents at the one site, allowing various units to be compared for price and features. Good deals can be had if you are prepared to bargain with the retailer and you can sometimes get 10% or more off the marked price. But how do you know which components to select? Let’s take a look at what’s available and what to go for. Amplifiers Many amplifiers from the late 1970s and through the 1980s were of unusually high quality. Their front panels and control knobs were made of thick, anodised aluminium, they had ample power outputs and their power supplies were generally more than adequate. Remember, we’re not comparing the very best of today’s amplifiers with the midrange amplifiers of 10 years ago. Instead, we’re looking at what you can now buy new for $200 versus what you can get for that same $200 if you go back a few years. When selecting a secondhand amplifier, brandnames are everything. Sony, Pioneer, Sansui, Onkyo, Philips, Kenwood, Denon, Technics, Rotel and Marantz all produced attractive, good-sounding amplifiers during this era and these are the names worth looking for. When shopping for an amplifier, several physical factors can give clues as to its performance. Check how heavy the unit is – if it appears light for its size, the power supply (mainly the transformer) is probably small and not up to the job of providing the high current demanded by the amplifier modules. Conversely, big transformers and filter capacitors indicate that the power supply can provide a constant high current. A big, heavy amplifier will usually be a powerful amplifier. You should also take a look at the heatsinks. Large, cast aluminium heatsinks indicate high output power and efficient heat dissipation. In fact, high power output is vital. That’s because a 20W RMS amplifier is more likely to distort than one rated at 100W RMS because it can be driven into clipping (overload) more easily. And an amplifier that’s been driven into clipping not only sounds awful but is also likely to damage your loudspeakers if left in this condition. If the amplifier is bought privately, the seller will often have the original owner’s manual. This will usually include a specifications panel which lists power output and distortion levels. In some cases, a sticker on the rear panel will list this information. Amplifiers with power outputs in the range from 40-100W RMS per channel (or more) are the ones to look for. If possible, ask the seller to fire up the amplifier with a signal source and loudspeakers connected. This will allow you to verify that the unit is working correctly. In par­ticular, check that the amplifier is not plagued by excessive hum. You can do this by disconnecting the signal source and winding up the volume control. You should only hear a faint hum and just a little hiss from the loudspeakers when the volume control is fully advanced. While you’re at it, check for scratching noises and pops from the loudspeakers when the volume, balance, bass and treble controls are adjusted. These noises indicate worn or dirty tracks in the control pots. Don’t automatically reject an amplifier if this occurs, though – a spray of electronic contact cleaner will often Portable CD players such as this Sony D-50 can be picked up for about $70. cure the problem. Alternatively, it may be possible to have the pots re­ placed, particularly if you can do the job yourself. Separate units Although harder to find, separate preamplifier and power amplifier units can theoretically provide cleaner sound than an equivalent integrated amplifier. In practice, you’d probably be hard put to tell the difference but if you do come across sepa­rate pre-amplifier and power amplifier units, they’re well worth considering. They can also be used in conjunction with electronic crossovers (available in kit form) to run separate subwoofer and satellite loudspeaker systems. Prices for a good used amplifier generally range from about $80 to $200, depending on the brand and This Kenwood KA-7300 integrated amplifier boasts a power output of 80W RMS per channel and features splittable preamplifier and power amplifier stages. It cost just $150, the price forced downwards by the missing side panel! September 1997  15 can indicate laser tracking problems or excessive wear in the gear drive mechanism. If you or a friend has a CD which is scratched and difficult to play, test it in the unit under consideration and compare the results with a known good machine. A good performance indicates that the error correction circuitry is up to scratch. We can’t stress enough how much better a CD-based system will sound in comparison to magnetic tape. All the problems that plague tape – head wear, hiss, narrow dynamic range and wow and flutter – are nonexistent with the digital technology of compact disc players. And CD players are cheap. Loudspeakers Avoid speaker boxes like this one. Repairing the surface finish – whether it’s plastic, paint or natural wood – is time-consuming and difficult unless you have special skills. As already mentioned, the loudspeaker systems associated with all-in-one units have only mediocre performance. Many of them lack bass response and have a tendency to sound “tinny” and overbright. Some power output. CD players Since its introduction in the early eighties, the compact disc has become a popular and affordable playback medium. It offers fast track access and, most importantly, delivers excellent sound reproduction courtesy of its digital recording format. As such, it’s hard to beat when it comes to buying sound quality. Try to avoid older, first-generation CD players because their mechanisms are likely to be worn and they’re more likely to suffer from mechanical failure. The laser pickup can also fail in older machines. CD players featuring 1-bit D/A (digital-to-anal­ og) serial conversion are generally regarded as sounding better than those with 16bit D/A conversion but it takes a keen ear to pick the difference. Basically, if you find a player in good order and at the right price, you can ignore the conversion technique used. Most of the brands mentioned above apply to CD players as well. These units can be picked up for $80-150. A cheaper alternative can be a portable CD player. Sony and Technics with their Discman and MASH portables, respectively, produce very good miniaturised units. Older models of these units can be purchased for as little as $70 but the sound quality will 16  Silicon Chip This box has easily removed (and replaced) front and rear pan­els. It also uses gussets to strengthen the mitred corner joins. It’s a perfect recipient for new speakers, particularly as its original drivers were nothing to write home about! not be as good as that from a full-sized CD player. Make sure that, in addition to a headphone socket, the unit also has a line level output for connection to an amplifier (a headphone socket may not provide sufficient output to drive an amplifier). Be critical when searching for a CD player. Ensure that all segments of the LCD or LED display light up correctly and be sure to check track access times. Long track access times feature only a single wide-range driver which struggles to cope with the entire frequency range. Others go too far the other way and use three or even four drivers, when just two correctly match­ed drivers would do a better job. Like the equipment that powers them, these speakers are a compromise between performance and price. One inexpensive way around this problem is to source old speaker enclosures and “re-speaker” them. The enclosures must be rigid and constructed from a dense material like chipboard or, ideally, MDF (medium density fibreboard). Secondhand dealers, garage sales and auctions provide the best sources for old, well-made speaker boxes. When tapped, the box shouldn’t vibrate – instead, it should have a low natural resonance so that the resultant sound is not coloured. If the box does resonate unduly, extra internal bracing in the form of timber offcuts (about 30 x 30mm in cross section) can be placed between parallel panels to provide extra stiffness. Make sure that the surface finish of the box is in good condition. If the box is covered in plastic imitation wood­grain, check to ensure that this isn’t peeling anywhere. Repairing the surface finish – whether it’s plastic, paint or natural wood – is time-consuming and difficult unless you have special skills. The best boxes to find are often those where a fascinated young child has deliberately stuck sharp objects through the speaker cones! These boxes can often be picked up for as little as $20 a pair and all you have to do is replace the drivers. The woofers in older enclosures are often useless, as their foam or rubber surrounds perish after about 10 years. A replace­ ment 10-inch “polycone” woofer of reasonable quality can be had for about $70, while an equivalent 8-inch woofer costs about $55. The volume of the box can be determined by measuring the internal dimensions. For example, a box measuring 50 x 25 x 20cm has a volume of 25,000cc (cubic centimetres) or 25 litres. This volume measurement can then be used to select a suitable driver. As a general rule, the larger the enclosure and the woofer, the lower the bass response. Enclosures with vents or ports are known as bass reflex designs. The other type of enclosure is the fully sealed (or infinite baffle) design. A bass reflex design will have better low frequency response but requires a vent (or port) to properly tune the enclosure. This usually consists of a small-dia­meter tube fitted to the baffle. Electronics stores like Jaycar and Dick Smith Electronics list recommended enclosure volumes for each of their woofers. Jaycar also give the recommended cabinet dimensions for Putting The Words Into Practice By now, you’ve probably read the main text and are saying to yourself “Yeah, fine; it all sounds good in theory but I bet these guys have never really gone out and bought stuff at the prices they’re talking about”. Well, read on! Here’s a list of the equipment recently purchased by co-author Owen Davies for a home stereo system and the prices that he paid. Teac PD-200 CD player ...............................................$80 Philips 260 stereo preamplifier.....................................$75 Philips 360 stereo power amplifier ..............................$75 Kenwood KA-7300 integrated amplifier .......................$150 Jaycar active crossover kit ...........................................$70 Satellite speakers: Jaycar 6-inch polycone woofer ....................................$22 x 2 Philips 25mm dome tweeter ........................................$17 x 2 Jaycar crossover .........................................................$15 x 2 Subwoofer ...................................................................$70 TOTAL: $418 Owen built his own speaker boxes and bought stands for the satellite speakers. But even if these cost $100 (they didn’t!), that still adds up to less than $520 for the complete system. both sealed and vented designs and even list the vent details. Old paper cone tweeters can be replaced with more modern dome substitutes that retail for around $25. These feature im­ proved transient response and sound much more realistic. The only modification required will involve increasing the cutout size in the baffle. Crossover networks Installing proper crossover networks can yield vast im­provements in sound quality. A crossover network splits up the signal so that the correct band of frequencies is fed to each driver. This is particularly important for midrange drivers and for tweeters, to ensure that they do not receive bass frequencies which could produce damaging cone excursions. Both 2-way and 3-way crossover networks are available from the major electronics retailers. Lacking from most cheaper and older speaker enclosures is some form of damping material. This material, commonly called “Innerbond”, can be placed inside the box to make it more acous­tically “dead”. It does this by reducing internal reflections which can interfere with the speaker cone and produce unwanted resonances. Even cheaper than Innerbond is quilt wadding, avail­able from most dressmaking supply shops. Using separate satellite and sub­ woofer systems can also produce very good results. These can either be powered actively (ie, by using separate amplifiers for the satellites and sub­woofer) or via a passive type cross–over network. The advantage of this type of setup is that the satellite speakers can be quite small, as their response only needs to go down to about 100Hz, where it will overlap with the upper end of the subwoofer’s response. Conclusion Good hifi sound is available on a budget if you choose good-quality secondhand components and are willing to upgrade old speaker boxes. Although your system mightn’t have the chic ap­pearance that’s apparently all too important these days, it will more than compensate for this in sound quality. And that’s really what it’s all about. SC September 1997  17 Design by JOHN CLARKE A high-energy capacitor discharge ignition system This completely new capacitor discharge ignition system has been designed from the ground up to provide a high energy “multiple spark discharge” to cope with engines which have very high RPM rates. It is intended particularly for use with two stroke engines, high performance four strokes and older vehicles. 18  Silicon Chip Twenty or so years ago, Capacitor Discharge Ignition (CDI) was the acknowledged solution for automotive enthusiasts wanting a high energy ignition circuit. CDI gave a really hot spark which would fire virtually any spark plug no matter how fouled or grotty it was. Tens of thousands of enthusiasts installed them on their cars and hence forward swore by them as the greatest innovation system since Karl Benz thought of the horseless Fig.1: these three circuits show the three types of ignition circuit. Fig.1(a) is the original points-based system. Fig.1(b) shows a typical CDI system which uses a DC-to-DC inverter to charge a capacitor which typically has a value of 1µF. Each time the switch points in the distributor open, it fires an SCR to dump the capacitors’s charge into the coil primary winding. Fig.1(c) shows the arrangement of our new CDI system. It has a DC-to-DC inverter with a regulated 300V DC output which charges up a 1µF capacitor. Instead of using an SCR to dump the capacitor’s charge into the coil, it uses a pair of Mosfets which are depict­ed as S1, a single pole double throw switch. carriage. Well, maybe it wasn’t quite that good but you get the picture. But there was another aspect of CDI which wasn’t good and that was “cross-fire”. Because the CDI spark was so hot and more importantly, because it had such a fast rise-time of only a few microseconds, it often fired the plugs in other cylinders. This problem was most troublesome in V8s, in some sixes and even some four cylinder cars such as the aircooled VW which had the spark leads running close and parallel right across the engine fan housing. Cross-fire is caused by the capacitance between adjacent spark plug leads. The capacitance between the leads causes the fast-rising voltage from the coil to be coupled into the adjacent leads and thereby can deliver unwanted sparks in other cylinders. Cross-fire can cause severe engine damage and sounds simi­lar to pinging. Ultimately, CDI fell into disuse for mainstream cars be­cause of the introduction of lean fuel mixtures in an attempt to meet rising anti-pollution standards. The very fast and very short spark of CDI wasn’t all that good at igniting lean mix­tures. Car manufacturers introduced transistor-assisted ignition with long spark durations to ensure that lean mixtures did burn properly. There was one CDI design which attempted to overcome the lean mixture drawback and that was the so-called “multiple spark discharge” system. However it was a complex design which never really caught on. These days, there is no modern car with an engine manage­ment system which uses CDI, to our knowledge. Whether they are single coil, multi-coil or direct-fire systems, they are all variants of the tried and true transistor assisted ignition (TAI) system. So why design a new CDI? At SILICON CHIP, we have tended to disparage CDI systems for years, knowing that our very popular high-energy TAI system has a wellearned reputation for reliability. But some readers were not about to be put off. They wanted a CDI design and they wanted it for a number of reasons. They wanted them for twostroke and four-stroke motors on motor bikes, out­boards and Go-Karts. And they wanted them for older cars which don’t have lean mixtures and which can be particularly hard, if not impossible, to start when the ignition system gets wet. Old Mini Coopers and 850s are legendary in this regard. Some readers also wanted a CDI for racing applications where multiple spark discharge systems still have a keen follow­ing. With all of these reasons being cited, who were we to say that all these people were wrong? So we went back to the data books and put on our thinking caps. A new CDI design had to be a distinct improvement over the 20-year old designs which did have their fair share of drawbacks. Like what, for example? First, many CDIs had very high voltages applied to the ignition coil, as much as 500V or 600V in some cases. They did this to avoid the inevitable fall-off in spark energy as the engine RPM rose. This very high coil voltage had the drawback of often causing internal breakdown in ignition coils, it made the cross-fire problem significantly worse than it would have been with a lower coil voltage and it put considerably more stress on the ignition leads. So design Main Features  Suitable for 2-stroke, older 4-stroke and perfor­mance engines (racing).  Multiple spark output (see Table 1).  Operates on reluctor, points or Hall effect signals.  Two points inputs for twin coil engines.  Usable to beyond 1000 sparks/second (equals 15,000 rpm for a V8).  Regulated 300V supply for consistent spark energy.  High frequency operation eliminates audible oscillator noise.  Efficient circuitry for minimum heat generation.  Components rated to operate up to 100°C. September 1997  19 Fig.2: the circuit of the Multi-Spark CDI can be split into two separate sections, each using an IR2155 self-oscillating half bridge Mosfet driver. IC1 and Mosfets Q1 & Q2 comprise the 12V DC to 300V DC inverter. IC2 and Mosfets Q6 & Q7 charge and discharge the dump capacitor via the ignition coil primary and provide the multiple spark feature. WARNING! This circuit produces 300V DC which can give you a nasty shock. Do not touch any part of the circuit while it is operating. aim number one was to set the coil voltage to a much more moderate level of about 300V. Second, because the DC-DC inverters of the time used rela­tively slow bipolar transistors (eg, 2N3055s), the inverter frequency was typically only 2kHz. This typically sets an upper limit on the maximum spark rate of about 300 to 400 sparks per second, as the inverter needs a couple of cycles 20  Silicon Chip of operation after each discharge in order to recharge the dump capacitor. The 2kHz inverter operation was quite audible too and could often be heard through car radios. So the new design would use Mosfets in the inverter and would operate at above 20kHz to make it inaudible. Third, CDIs used an SCR (silicon controlled rectifier) to discharge the dump capacitor and these are typical- ly rated for an AC supply frequency of 400Hz maximum. While the SCRs will operate at higher frequencies, it is an unspecified condition and it ultimately also sets a limit on the maximum spark rate. That effectively rules out using an SCR in the new design. Fourth, and a rather serious drawback this one, some CDI systems would not operate when the battery was low. This meant that while the battery might be able to slowly crank the engine, the CDI’s inverter would not start and hence there would be no spark. In other words, just when you most wanted the CDI to work, it would not be on the job. Another factor which limited the inverter operating fre­quency was the speed of the rectifier diodes. High speed fast recovery diodes were expensive and so, even if the inverter could have run much faster, the standard rectifier diodes could not have handled the high frequency output. Applications While we have addressed all the above disadvantages, the drawback of potential cross-fire remains even though we have reduced the high voltage to 300V. Therefore, we do not recommend using the system on six cylinder and V8 engines unless you can improve the lead dress of the spark plug leads so that each lead is more widely separated from its neighbour. Nor do we recommend using this CDI on any car with an engine management computer. We take the attitude that the factory designed ignition system will always be optimum for the particu­lar car. On the other hand, if you have an older car with factory electronic ignition there is no reason why this CDI system should not be a satisfactory substitute, particularly if the original module has failed and is expensive to replace. The new CDI system can be connected to distributors with conventional points, Hall effect or reluctor pickups. It is capable of operation to very high engine speeds, much higher than even racing engines. For example, it can run as high as 30,000 RPM in a 4-cylinder engine. This figure is so high that it’s academic but it does indicate that full spark energy is main­tained over the entire RPM range of any practical engine. All the other features of the new design are summarised in the features and specifications panels elsewhere in this article. However, we do need to explain one of the key features and that is “multi­ple spark discharge”. Multiple spark discharge Whereas the original CDI designs produced just one spark each time the Fig.3: this is the primary coil voltage when producing four sparks (top waveform). Note the 284V negative excursion for the first and third sparks and the 292V positive excursion for the second spark. The lower trace is the tachometer output signal which was used to trigger the oscilloscope. Fig.4: the CDI produces very high spark rates. The top trace shows the voltage measured at the source of Q6 when driving the ignition coil, while the lower trace is the tachometer output which indicates that the rate is 1000 sparks/ second. Note that capacitor C2 charges up to the full 300V (308V shown) before firing into the coil on the negative edge of the lower trace. This means that the circuit can deliver the full spark energy even at this excessively high engine speed. points opened, the multi-spark discharge (MSD) CDI was able to produce several sparks in quick succession each time the points opened. Our new design incorporates this feature and produces up to 10 sparks each time a spark plug is to be fired, depending on the engine speed. This feature can be disabled so that the CDI produces just two sparks for each cylinder firing, September 1997  21 Fig.5: the circuit caters for distributors with (a) points; (b) Hall Effect sensors; or (c) reluctor pickups. regardless of engine speed. Now let us have a look at some of the details of the new design. Fig.1(a) shows the schematic diagram of the conventional Kettering ignition system which has been used on cars for over 60 years. It comprises an ignition coil which has its primary wind­ing connected to the battery supply with a switch at the negative side. The switch can be a conventional set of points or a switch­ing transistor, as used in most modern ignition systems. When the switch is closed, current builds up in the primary winding with the ultimate value limited by the internal resistance of the coil and a ballast resistor, if used. This current 22  Silicon Chip is usually around 3 to 5 amps. When the switch opens, the resulting collapse of the coil’s magnetic field causes the secondary winding to produce a high voltage to fire the spark plug. As the engine speed rises, the current has less time to build up in the coil primary and so inevitably the spark energy is reduced. Modern transistor assist­ed ignition systems get around this problem by using dwell exten­ sion, lower inductance coils or more than one ignition coil. Fig.1(b) shows a typical CDI system which uses a DC-to-DC inverter to charge a capacitor which typically has a value of 1µF. Each time the switch points in the distributor open, it fires an SCR to dump the capacitor’s charge into the coil prim­ary winding. The poor old coil gets such a belt that it produces a much higher voltage in the secondary and fires the spark plug. Fig.1(c) shows the arrangement of our new CDI system. It has a DC-toDC inverter with a regulated 300V DC output which charges up a 1µF capacitor. Instead of using an SCR to dump the capacitor’s charge into the coil, it uses a pair of Mosfets which are depicted as S1, a single pole double throw switch. The ca­pacitor charges up via the coil to 300V when S1 is in position A and discharges through the coil when the switch is in position B. Thus each time a spark plug is to be fired, two sparks are produced, one with positive polarity and one with negative polar­ity. With a simple change to the timing circuitry controlling the two Mosfets, the CDI can be made to produce more than two sparks by repetitively charging and discharging the dump capacitor during each spark plug firing period. The oscilloscope waveforms in Fig.3 show the primary coil voltage when producing four sparks (top waveform). Note the 284V negative excursion for the first and third sparks and the 292V positive excursion for the second spark. The lower trace is the tacho­meter output signal which was used to trigger the oscillo­scope. Table 1 shows the multi-spark information for four, six and eight cylinder engines. Here we show the RPM versus the number of sparks produced. As you can see, the number of sparks ranges from as many as six sparks per firing at 600 RPM in a 4-cylinder engine down to two sparks per firing at 15,000 RPM, again in a 4-cylinder engine. Circuit description Fig.2 shows the circuit diagram of the Multi-Spark CDI. It can be split into two separate sections, each using an IR2155 self-oscillating half bridge Mosfet driver. IC1 and Mosfets Q1 & Q2 comprise the 12V DC to 300V DC inverter. IC2 and Mosfets Q6 & Q7 charge and discharge the dump capacitor via the ignition coil primary and provide the multiple spark feature. IC1 oscillates at about 22kHz as set by the 33kΩ resistor between pins 2 and 3 and the .001µF capacitor from pin 3 to ground. Two complementa- Table 1: RPM vs. Spark No. & Duration No. of Sparks RPM Spark Duration (Crankshaft Degrees 4-Cylinder 4-Stroke Engines 600 6 8 900 6 13 1200 6 16 1500 6 20 2250 4 19 3000 4 25 4500 4 37 9000 2 21 2 36 15,000 6-Cylinder 4-Stroke Engines Fig.6: these waveforms show the reluctor output (lower trace) and the resulting source voltage of Q8 with no coil connected. Note that the coil fires on the negative edge of the reluctor wave­form. ry outputs at pins 5 & 7 alternately switch Mosfets Q1 & Q2 to drive the centre-tapped primary winding of transformer T1. With Q1 on, the full 12VDC is applied to the top half of the transformer primary winding. Because of the transformer coupling to the second primary winding, the lower half of the transformer primary winding also has 12V across it. Similarly, when Q2 turns on the 12V is also impressed across the top primary winding. The resulting waveform on the primary is stepped up by the secondary winding. Q1 & Q2 have internal avalanche protection. Should the switch off transient across them reach 60V, the internal zener diode will safely quench the spike voltage. The 10Ω resis­tors in series with the gates of the Mosfets are included to slow their switching speed and thus reduce the interference which would otherwise be induced into the vehicle’s electrical system. Two 10µF MKT capacitors are used to decouple the DC supply to transformer T1. They effectively bypass the supply lead induc­tance so that the full 12V supply is delivered to the transformer at the high switching rate. Inductor L1 is connected in series with the supply to prevent 22kHz switching currents from appear­ing on the vehicle’s electrical supply. The .01µF capacitor on the 12V input is there for the same reason. The stepped up secondary voltage of T1 is full-wave recti­fied by high speed diodes D2-D5 and the resulting 300V DC is filtered with a 1µF 275VAC capacitor. Voltage feedback trickery As described so far, the circuit does not have any means of maintaining a constant 300V DC output and so variations in the battery voltage and spark rate would inevitably cause the high voltage DC output to vary over a fairly wide range which would be undesirable. However, the IR2155 Mosfet driver has no inbuilt means of providing voltage regulation. Therefore, we have to trick the circuit into maintaining a more or less constant vol­tage. The voltage feedback comprises four 75V zener diodes ZD1-ZD4 which are connected in series so that they begin to conduct at 300V. When current flows through the zeners they switch on transistor Q3 via a 10kΩ base resistor. When transistor Q3 turns on, it pulls pin 1 of IC1 from close to +12V down to around +6V and this tricks the IC into activating its internal under­volt­age cutout circuit (threshold +8.4V) which switches both pins 7 and 5 low. This stops the Mosfets 400 8 8 600 8 12 800 6 11 1000 6 14 1500 6 21 2000 4 16 3000 4 24 6000 2 14 10,000 2 22 8-Cylinder 4-Stroke Engines 300 14 11 450 12 13 600 10 15 750 10 18 1125 8 21 1500 8 20 2250 6 29 4500 4 32 7500 2 15 from driv­ i ng transformer T1 and this situation is maintained until the zeners stop conducting; ie, when the high voltage supply drops back below 300V. Transistor Q3 then switches off and IC1 resumes normal operation. Thus, the output voltage is stabilised at 300V while Q3 turns the oscillator on and off at a rate dependent on the load current drawn from the 300V supply and the actual DC supply voltage. Circuit feeds itself Three 33kΩ resistors in series feed current from the 300V output back to the supply pins of IC1 and an internal zener limits the resulting voltage to September 1997  23 Here the new Multi-Spark CDI is shown mounted in the engine compartment of a Mitsubishi Sigma. Note the long parallel run of the spark plug leads. We suggest that the spacing between these leads should be increased to reduce any possibility of cross-fire. 15V. With +15V present at pins 1 & 8 of IC1, diode D1 is reverse biased and therefore the IC no longer draws current from the +12V battery line. The idea behind this to make sure that the circuit will run even with a very flat battery. Hence the circuit will start with as little as 9V from the battery and then will continue to run even if the battery drops down to 5V. This could make all the difference when you have a sick battery which can barely crank the engine over or if you have to push start the car. The 300V supply also feeds IC2, the second IR2155. Note that IC2 is connected to operate in a different fashion to IC1. In this case, the drain (D) of Q6 is connected to the 300V supply which is at a much higher potential than the +15V at pin 1 of IC2. For Q6 to fully turn on, its gate (G) must be raised above the drain by several volts. This is achieved using 24  Silicon Chip diode D6 and capacitor C1. Initially, IC2 starts with a 15V supply derived from the 300V rail, as mentioned above. Q7 is the first to be switched on and it pulls one side of capacitor C1 low. C1 then charges to the +15V supply via D6 and Q7. When Q7 turns off and Q6 turns on, Q6 pulls pin 6 of IC2 up to the 300V rail and so pin 8 is jacked up above +300V by the 15V across C1. C1 maintains the voltage between pins 7 and 8 until next recharged via D6 and Q7. (Note that pins 6, 7 & 8 of the IR2155 are float­ing outputs which can be shifted to 600V above the pin 4 ground). C1 needs to be relatively large at 100µF since it can be called upon to keep its charge for up to 100ms during slow crank­ing of the motor. The totem-pole output of Mosfets Q6 and Q7 drives the ignition coil primary via the 1µF 275VAC capacitor C2. Diode D7 is included to prevent pin 6 from going much below the pin 4 ground while D7 itself is current limited by the series 22Ω resistor. The 22kΩ resistor between pin 7 and the source of Q6 ensures that this Mosfet is held off when there is initially no supply between pins 8 and 7. The 22Ω gate resistors slow the turn on and turn off times for Q6 and Q7 to limit transients when switching the 1µF 275VAC capacitor. Multi-sparking Pins 2 and 3 of IC2 are connected to an assortment of resistors, diodes and capacitors and these are instrumental in providing the multi-spark operation. These components comprise a timer and an astable (oscillator) connection. The astable oscil­lator is formed by the 180kΩ resistor at pin 2 and the .0047µF capacitor at pin 3. The 10kΩ resistor between pin 3 and the .0047µF capacitor is there to prevent excess current into this pin when driven by the mono­stable part of the circuit. The only other differ- ence to the normal astable mode is the addition of diode D11 and the 180kΩ resistor in series. This ensures a longer discharge time for the .0047µF capacitor via one 180kΩ resistor and a shorter charge time via both 180kΩ resistors when D11 is forward biased. Note that the .0047µF capacitor is only tied to ground when transistor Q4 is switched on via the trigger circuit from either points, Hall effect or reluctor signals. Capacitor C3 is also connected to the collector of Q4. Initially, when Q4 is off, C3 is discharged and held at the pin 1 supply voltage (+15V) via the 13kΩ resistor at Q4’s collector and the 33kΩ resistor at D10’s anode. This last resistor pulls pin 3 well above the upper threshold (2/3rds the pin 1 supply) via D10. Pin 2 goes low but the .0047µF capacitor cannot be discharged and so IC2 does not oscillate; so Q7 is off and Q6 is on (if there is supply voltage across C1). When Q4 switches on, the anode of D10 is pulled low via C3. Thus, the 33kΩ resistor is effectively out of the oscillation circuit and so the .0047µF capacitor is charged and discharged via the components at pin 2 as previously discussed. Q6 and Q7 now switch on and off alternately, so the coil is fired repeti­tively via C2. C3 charges via the 33kΩ resistor and when this voltage reaches the upper threshold of pin 3’s input, D10 conducts and stops IC2 from oscillating again. The circuit thus remains with Q6 on and Q7 off until triggered again. Note that, at high RPM, Q4 is off for less time than it takes C3 to recharge via the 33kΩ resistor and switch off IC2’s oscillation. The instant this transistor switches off, IC2 stops oscillating since C3 is imme­diately pull­ed high. This is a fail-safe condition to prevent sparks designated for one cylinder from accidentally firing the next cylin­der in sequence. The trigger circuit also drives transistor Q5 to provide a low voltage (+12V) tacho­ meter output. This is necessary since a tacho connected to the coil would otherwise give false readings. Fig.4 shows some more waveforms which demonstrate the cir­cuit performance. The top trace shows the voltage measured at the source of Q6 when driving the ignition coil while the lower trace is the tachometer output which indicates that the input Parts List For Multiple Spark CDI 1 PC board, code 05309971, 112 x 144mm 1 diecast case, 171 x 121 x 55mm 1 ETD29 ferrite transformer (T1) assembly (Philips 2 x 4312 020 3750 2 3C85 cores, 1 x 4322 021 3438 1 former, 2 x 4322 021 3437 1 clips.) 1 Neosid iron powdered core 17-732-22 (L1) 2 cord grip grommets 1 solder lug 6 3mm x 15mm screws, nuts & star washers 5 TO-220 style insulating bushes 6 TO-220 insulating washers 1 2m length of red and black automotive wire 1 1.5m length of 0.63mm enamelled copper wire 1 22m length of 0.25mm enamelled copper wire 1 140mm length of 0.8mm tinned copper wire 1 400mm length of 1mm enamelled copper wire 6 PC stakes Semiconductors 2 IR2155 self-oscillating half bridge drivers (IC1,IC2) 2 MTP3055E TO-220 14A 60V N-channel Mosfets (Q1,Q2) 2 IRF822 TO-220 2A 500V N-channel Mosfets or equivalent (Q6,Q7) 3 BC337 NPN transistors (Q3-Q5) 5 1N914 signal diodes (D1,D8-D11) 6 1N4936 fast recovery 500V 1.5A diodes (D2-D5,D6,D7) 4 75V 1W zener diodes (ZD1-ZD4) 1 S14K 275VAC MOV (MOV1) Capacitors 2 100µF 16VW electrolytic (-40°C to 105°C rated; Hitano EHR series or equivalent) 2 10µF 63V or 100V MKT (Philips 373 21106 or equivalent) 2 1µF 275VAC MKP X2 (Philips 336 20105 or equivalent) spark rate is at 1kHz (60,000 rpm). Note that capacitor C2 charges up to the full 300V (308V shown) before 1 0.47µF 63V MKT polyester (C3); or 1 x 0.15µF MKT polyester (C3); or 1 x 0.12µF MKT polyester (C3) 1 0.1µF 63V MKT polyester 1 .01µF MKT polyester 1 .0047µF 63V MKT polyester 1 .001µF 63V MKT polyester Resistors (0.25W 1%) 2 680kΩ 1 13kΩ 2 180kΩ 4 10kΩ 2 56kΩ 1 2.2kΩ 6 33kΩ 1W 5% 2 220Ω 2 33kΩ 3 22Ω 1 22kΩ 2 10Ω Miscellaneous Automotive connectors, eyelets for coil connection, cable ties, solder, etc. Reluctor trigger circuit 1 5.1V 400mW zener diode (ZD5) 1 1N914 signal diode (D12) 1 .0022µF 63V MKT polyester capacitor 1 470pF 63V MKT polyester capacitor (or 100°C rated ceramic) 2 47kΩ 0.25W 1% resistor 2 10kΩ 0.25W 1% resistor 1 390Ω 1W 5% resistor 2 PC stakes Points trigger circuit 1 1N914 signal diode (D12) 1 1N914 signal diode (D13) (optional; see text) 1 .01µF MKT polyester capacitor 1 47Ω 5W resistor 1 47Ω 5W resistor (optional; see text) 2 PC stakes Hall effect trigger circuit 1 Bosch rotating vane assembly to suit distributor 1 Siemens HKZ101 Hall sensor (Jaycar Electronics) 1 1N914 signal diode (D12) 1 820Ω 0.25W 5% resistor 1 100Ω 0.25W 1% resistor 3 PC stakes firing into the coil on the negative edge of the lower trace. This means that the circuit can deliver the full September 1997  25 Reluctor Pickup Fig.7: this component overlay for the PC board includes the trigger input circuitry for a reluctor distributor. spark energy, even at this excessively high rpm. Disabling multi-spark operation If you wish, the multi-spark feature can be easily disa­bled by (1) removing C3, D10, D11, the two 180kΩ resistors and the 33kΩ and 13kΩ resistors; and (2) installing a 180kΩ resistor in place of the 33kΩ resistor and a link in place of D10. This causes IC2 to produce a single 0.5ms pulse to switch on Q7. This fires the coil in one direction when Q7 switches on and in the other direction when Q6 switches on. A Metal Oxide Varistor (MOV1) is connected across the coil to quench the high voltage transient which will occur if the coil is left open circuit on the secondary. Leaving the coil output open circuit can cause it to break down internally and this quickly leads to failure. In addition, there is provision on the PC board to use two 1µF capacitors to drive the coil. Two 26  Silicon Chip 680kΩ resistors are connected in series across C2 to discharge it should the coil become disconnected from the circuit. This im­ proves safety since a 1µF capacitor charged to 300V can produce a nasty shock. Trigger circuits Fig.5 shows the alternative circuits provided for points, Hall effect and reluctor triggering. These are all included on the PC board. The points circuit is easy enough and we have provided for distributors which have one or two sets of points. Both pairs of points have a 47Ω 5W resistor to provide a “wetting current”. This current keeps the points clean and thereby provides more reliable operation. Diode D12 or D13 feeds the respective points signal into transistor Q4. The two-points facility provides for twin-cylinder engines with two coils or for rotary engines which have two plugs per chamber. The Hall effect circuit has power supplied via a 100Ω resistor. The 820Ω resistor is the pullup for the internal open collector transistor. Diode D12 supplies the high-going signal to Q4. The reluctor circuit comprises a 10kΩ load across the pickup coil together with a 470pF noise suppression capacitor. Transistor Q8 is biased on using a 5.1V zener diode. The circuit is designed to trigger after the reluctor signal goes negative. The .0022µF capacitor is used to speed up the switch off action of Q8 while the 10kΩ pullup resistor on Q8’s collector provides the signal to Q4 via diode D12. Fig.6 shows the reluctor output (lower trace) and the resulting source voltage of Q8 with no coil con­nected. Note that the coil fires on the negative edge of the reluctor waveform. Construction The Multi-Spark Capacitor Discharge Ignition is constructed on a PC Table 2: Capacitor Codes ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 1µF 1u0   105 0.47µF 470nF   474 0.15µF 129nF   154 0.12µF 120nF   124 0.1µF 100nF   104 0.01µF 10nF   103 0.0047µF 4n7   472 .0022µF 2n2   222 .001µF 1n0   102 470pF 470p   471 board which is coded 05309971 and measures 112 x 144mm. It is housed in a diecast case measuring 171 x 121 x 55mm. Begin assembly by checking the PC board against the pub­lished pattern. There should not be any shorts or breaks between tracks. Make any repairs as necessary. Note that the PC board requires two semicircular cutouts on the sides to fit into the recommended case. The corners should also be rounded off and small notches are need to give clearance for the vertical chan­nels in the diecast case. Make sure the PC board fits into the case before starting assembly. Other types of diecast cases with multiple integral ribs on the sides cannot be used since the Mosfets need to be Hall Effect Pickup Fig.8: this diagram shows the trigger components for a Hall effect distributor. Conventional Points Pickup Fig.9: the trigger components for a conven­tional points distributor. Table 3: Resistor Colour Codes ❏ No. Value 4-Band Code (1%) 5-Band Code (1%) ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ 2 2 2 2 6 2 1 1 6 1 1 1 2 1 3 2 680kΩ 180kΩ 56kΩ 47kΩ 33kΩ 33kΩ 22kΩ 13kΩ 10kΩ 2.2kΩ 820Ω 390Ω 220Ω 100Ω 22Ω 10Ω blue grey yellow brown brown grey yellow brown green blue orange brown yellow violet orange brown orange orange orange brown orange orange orange brown red red orange brown brown orange orange brown brown black orange brown red red red brown grey red brown brown orange white brown brown red red brown brown brown black brown brown red red black brown brown black black brown blue grey black orange brown brown grey black orange brown green blue black red brown yellow violet black red brown orange orange black red brown orange orange black red brown red red black red brown brown orange black red brown brown black black red brown red red black brown brown grey red black black brown orange white black black brown red red black black brown brown black black black brown red red black gold brown brown black black gold brown September 1997  27 Winding the coil & mounting the power transistors Fig.10: here are the winding details for the bobbin of trans­former T1. Note that the primary wind­ings are bifilar; ie, they are wound together. bolted to a flat surface. Fig.7 shows the component overlay for the PC board with trigger input circuitry for a reluctor distributor. Fig.8 shows the different trigger components for a Hall effect distributor while Fig.9 shows the trigger components for a conventional points distributor. You can start the board assembly by inserting the PC stakes at the external wiring connection points and then installing the wire links. Note that there are two links that run beneath the inverter transformer (T1). This done, install the resistors and use the colour code table and your multi­meter to check each value. When inserting the diodes and zeners, take care with their orientation and be sure to place each type in the correct posi­tion. Install the ICs and transistors, taking care to orient them as shown. The Mosfets are oriented with their metal flanges towards the edge of the PC board and are seated as far down on the board as they will go. Be sure to install the correct type in each location. The capacitors can be installed next. The accompanying table shows the value codes which will be printed on each component. The electrolytic capacitors must be oriented with the correct polarity. Once the capacitors are in, install the varistor (MOV1). The battery input filter toroid core (L1) is wound with 12 turns of 1mm enamelled copper wire. Ensure that the wire ends are stripped of insulation before soldering it into place. The 28  Silicon Chip Fig.11: the four Mosfets are mounted on the side of the case, using an insulating washer and an insulating bush. toroid is affixed to the PC board using a screw and nut with an insulating bush to locate the screw and protect the winding. Winding the transformer Transformer T1 is wound as shown in the diagram of Fig.10. Start by terminating the 0.25mm enamelled Fig.12: this is how the Siemens Hall sensor should be installed to provide reliable triggering. The vane needs to penetrate the sensor by between 8mm and 11.5mm. The triggering point is between 0.1mm and 1.8mm from the centre line of the unit. copper wire on pin 7 as shown. Neatly wind on 360 turns and insulate between each winding layer with insulation tape. Terminate the winding on pin 8. The primary windings are wound together (bifilar) side-by-side. Termi­ nate the 0.63mm enamelled copper wires at pins 2 and 4 as shown, then wind on 13 turns and terminate on pins 11 and 9 respective­ly. Check that pin 2 connects to pin 11 and pin 4 connects to pin 9, using a multimeter on the “Ohms” range. Finish the windings with a layer of insulation tape. The ferrite cores are inserted into the bobbin and secured with the clips or a cable tie. Insert and solder the transformer into the PC board with the orientation shown in Fig.7. Next, insert the PC board into the case and mark the positions for the Mosfet mounting holes on the side panel. Remove the PC board and drill out these holes and two holes at each end for the cord grip grommets. Also drill a hole for the earth lug screw. The holes for the Mosfet mounting must be deburred with a larger drill to prevent punch-through of the insulating washer. Attach the PC board to the case with the supplied screws and secure each Mosfet to the case with a screw, nut, insulating washer and insulating bush. Fig.11 shows the details. If you use a mica washer apply a smear of heatsink compound to the mating surfaces before assembly. Silicone rubber washers do not require heatsink com- Installation If you are using the existing points or a reluctor distribu­tor, the CDI unit can be installed into the vehicle. Be sure to locate the CDI case in a position where air flows over it and make sure it is away from the exhaust side of the engine. It can be secured to the engine bay with self-tapping screws into the two diagonally opposite exter­ nal securing points on the case. Alternatively, you could use brackets. Wire up the positive connection to the positive 12V ignition, the negative wire to the chassis and the trigger input to the points or reluctor. The ignition coil requires a connection to both sides of the primary. Disconnect any other wires that are part of the original ignition system. Note that the reluctor coil requires the correct polarity connection in order to give the correct spark timing. This is best determined by testing the engine. If it does not fire, reverse the reluctor leads and try again. You may find that with the CDI installed, the spark timing is little advanced, due to its fast rise time. If so, you may need to retard the static timing slightly to prevent pinging or a slightly rough idle. When starting an engine fitted with this CDI, it is a good idea to turn on the ignition for one or two seconds before crank­ing the engine. This will give the circuit time to generate the 300VDC and fully charge the 100µF supply capacitor for IC1. If you are going to install the CDI on an engine with two coils and two sets of points, you can use the trigger circuit with the two points facility. The CDI can then drive both coils in SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. OR D ER FOR M PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏  3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________  Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ pound. Use two washers each for Q6 and Q7. Check that the metal tabs of the Mosfets are indeed isolated from the case by measuring the resistance with a multimeter. Finally, attach the wires for the supply, trigger input and coil output and secure them with the cordgrip grommet. The earth connection goes to a solder lug which is secured to the case. You can test that the inverter operates by connecting the circuit to a 12V 3A power supply. The voltage between the tab of Q6 and the case should be about 300V. Take care, however, since this voltage can cause a severe electric shock. September 1997  29 Fig.13: use this circuit to provide a tacho signal if your car has an impulse tachometer. Fig.14: this is the full-size etching pattern for the PC board. parallel. Both coils will then fire simultaneously when each set of points open. This is more or less standard practice with racing rotaries. If you do want to fire two coils simultaneously, you will probably need to add an extra 1µF 275VAC capacitor (C2). There is provision for this on 30  Silicon Chip the PC board. Hall effect trigger While many readers will wish to use their original points/distributor setup in their initial installation, a Hall effect distributor is a much better proposition. A Hall effect pickup does not suffer from any wear and tear and is unaffected by dirt. The Hall sensor recommended is the Siemens HKZ101 available from Jaycar Electronics. You must also obtain a rotating vane assembly to suit your distributor. These are available from automotive aftermarket retailers selling Bosch ignition systems. Make sure that you have one of these before purchasing the Hall sensor. Fig.12 shows how the Siemens Hall sensor should be in­stalled to provide reliable triggering. The vane needs to pene­trate the sensor by between 8mm and 11.5mm. The triggering point is between 0.1mm and 1.8mm from the centre line of the unit. To install the sensor, first remove the distributor from the vehicle. To do this, rotate the engine until cylinder number 1 is at the firing point; this is indicated when the rotor button is aligned with the number 1 spark plug lead. With the distributor out of the engine, find the position where the points just open for the number 1 cylinder and mark the position on the distribu­tor where the centre of the rotor is now positioned. This is the point where the Hall effect sensor’s output should go high. Next, remove the rotor, points and capacitor plus ancillary com­ponents. The Hall sensor should be mounted near where the points were located so that there is sufficient lead length to exit from the distributor. The exact location for the Hall sensor is deter­ mined as follows. Fit the vane assembly to the distributor and align the rotor with the marked firing point. The Hall sensor should now be positioned so that the leading edge of one of the metal vanes is about halfway through the slot. You will have to know the dis­tributor rotation direction. Mark the position for the sensor, taking care to ensure that the vane will pass through the gap without fouling. Note that Fig.12 shows the configuration for a clockwise rotating distributor. Anticlockwise rotating distributors are timed as the vane enters the Hall sensor from the other side. A suitable mounting plate can now be made to fit the Hall sensor onto the distributor advance plate. The mounting plate must be elevated so that the vane penetrates the Hall sensor by 8-11.5mm. The Hall sensor is riveted The Multi-Spark Capacitor Discharge Ignition system is housed in a diecast box which provides adequate heatsinking for the four Mosfets. to the adaptor plate through 3.5mm holes which are countersunk beneath the plate. The adaptor plate can then be secured to the advance plate using machine screws, nuts and washers. Try to take advantage of existing holes left where the points were mounted. The leads from the Hall sensor should pass through the existing points lead grommet. Check that the vanes pass through the gap in the sensor without fouling and that the lead dress allows for full movement of the distributor advance plate. Specifications Spark energy ��������������������������������������� 45mJ Number of sparks per firing ����������������� Minimum of 2, (see Table 1) Spark separation ��������������������������������� 0.5ms for the first 2 sparks then 0.66ms, 0.34ms, 0.66ms, etc Spark duration ������������������������������������� About 200µs per spark Multiple spark duration ������������������������ 2 sparks 500µs; 4 sparks 1.3ms; 6 sparks 2.2ms; 8 sparks 3.1ms; 10 (add 200µs for last spark) sparks 4.1ms; 12 sparks 5ms; 14 sparks 6ms Reluctor circuit sensitivity �������������������� 400mV RMS Inverter operating frequency ��������������� 22kHz Operating voltage �������������������������������� Down to 5V (requires a minimum of 9V to start circuit) Now reinstall the distributor in the engine, with the rotor pointing towards the number 1 cylinder firing point. Do a static timing check, with the engine set to fire when the vane is cen­tral to the Hall sensor. Connect the Hall sensor leads to the CDI unit using suit­able automotive connectors. Start the engine and use a timing light to set the spark timing. Tachometer connection The tachometer output signal is a 12V square wave which should be sufficient to trigger most electronic tachometers. For example, the tacho­ meter featured in the August 1991 issue can be directly triggered without modification. If the signal does not work with your tacho, it may be an impulse type which requires a high voltage. The circuit shown in Fig.13 should solve this problem. As shown, this uses the primary of a 2851 240VAC to 12VAC mains transformer to produce a high voltage pulse when switched via transistors Q1 & Q2. The coil voltage is limited by the .033µF capacitor connected between collector and SC emitter of Q2. September 1997  31 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. Thermatic fan monitor A few years back I installed therm­atic fans in my 1981 Holden Statesman. Not keen on the suggested method of wiring (I wanted to keep the high current carrying wires as short as possible) I came up with an alternative plan. The fans were mounted on a frame and this bolted to the radiator supports. This allowed for easy removal when working on the engine or radiator. A few months back, I forgot to reconnect the fans after working on the engine. Luckily I’m a “gauge watcher” and correct­ed the fault on the roadside before any damage was done. Mindful of the fact that I am not the only one in the family that drives the car, I designed a circuit that would alert the occupants that all is not well with the fans. Referring to the overall diagram, resistors R1 and R2 were installed into a small jiffy box close to the bat32  Silicon Chip tery and relays. Shielded cable was used to connect the monitor points to the circuit. On the monitor circuit, op amp IC1a is configured as a comparator with R3 and VR1 setting a reference for the inverting input. VR1 is adjusted so that IC1a’s output is +12V when the fan is running and 0V when it is not. LED1 indicates that the fan is running. Another input to the circuit is from the thermostatic switch. When the fans should be on, +12V is present, while 0V indicates when the fans are off. These two inputs are applied to the exclusive OR gate IC2d. When the therm­ostatic switch is active and if the fan is not running (ie, a fault), pin 11 of IC2d will go high. Alternatively, if the thermostatic switch is not active and the fan is running (another fault), pin 11 is also high. The components around IC1b and IC2c operate in the same manner for the second fan. Diodes D1 and D2 form a wired OR gate for the outputs of IC2c & IC2d. If a fault occurs with either fan, the oscillator formed by IC1d and its associated components is enabled and it oscillates at about 2Hz. This gates IC1c via switch S1 and diode D4 to drive the piezo buzzer at 4.5kHz. LED3 provides a flashing visual indication of the fault. Switch S1 allows the audible alarm to be muted but in a special way. Assume a fault is present. Therefore +12V will be present at the cathodes of D1 & D2, enabling the oscillators and therefore the audible alarm. If S1 is now switched, the low output at pin 3 of IC2a will disable IC1c, silencing the buzzer. Note that LED3 will continue to flash. Once the fault is cleared, the cathodes of D1 & D2 go low, disabling IC1d and IC2a’s output now goes high. With S1 still in the “disabled” position, IC1c is enabled giving a continuous output from the buzzer. The vehicle occupants are forced to toggle the switch to silence it. This arrangement means you cannot forget to “enable” the audible alarm after a fault is cleared. Power for the circuit is derived from the vehicle’s igni­tion switch via diode D4 and is filtered by C3. Each time the ignition is turned on, the buzzer gives a short beep. I. Bennet, Yallambie, Vic. ($35) Addressing the 16s message recorder 1kΩ resistors and this causes pin 13 of IC1 to go high. Pin 2 of monostable timer IC2 is held high until one of the sense lines is pulled high. This causes pin 13 of IC1 to go low to trigger IC2 for a duration depending on VR1. This should be set to match the length of the stored message. If you have multiple messages it is best to have them the same duration. For example, you could have eight 2-second messages: “Your Lights Are On”; “A Door Is Open”; “Your Engine Is Overheating”, etc. When IC2 is triggered, pin 3 will go high to drive a relay which has switch contacts directly across the playback pins of the ISD1016. This will then play the selected message. C. Milborn, Bundoora, Vic. ($35) This circuit is designed to work with the 16-second Message Recorder published in the July 1993 issue of SILICON CHIP. It is used to select several prerecorded messages stored in the ISD1016 recorder chip. It is ideal if you want to add some life to your car. For example, you could set up sensors or switches in the car and when something is activated your Message Recorder could tell you, “Your lights are on” or “Your door is open” or the temperature has exceeded a certain limit. You can hook up sensors or switches to pull down different address locations with a message to suit the situation. For example, at address AO I used an LDR in position S1 and when enough light fell on the LDR it pulled AO high thus announc­ing the message that was stored at that address. The circuit is based on a 4078 8-input NOR gate with each input going to an address line on the ISD1016 recorder. Each input is held low via Intercom uses touch phones Just three 9V batteries, a 6-way phone cable and two touch phones make up this elegant intercom. To make a call, lift a handset and push the buzzer switch until the called party an­swers. The same procedure applies to calls in the opposite direc­tion. Nicholas d’Apice, Greenwich, NSW. ($15) September 1997  33 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.dse.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.dse.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.dse.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.dse.com.au SERVICEMAN'S LOG The things I do for money In my never ending quest to earn money, I never cease to be amazed at what I am asked to repair. Recently, I ended up repairing a video games machine on the footpath but first I faced up to a couple of TV sets. I must admit that I feel more comfortable working on TV sets and VCRs but you cannot be too fussy these days if you expect to earn a living. Computers, computer monitors, microwave ovens, video cameras and even the odd video games machine are now all part of the job as far as I am concerned, although many organisations prefer to specialise in just a few areas. But I still like working on TV sets (mostly) and so the first two jobs I tackled when I arrived at the shop this morning were a couple of Philips TV sets that had come in late the previ­ ous day. The first was a 34cm Philips GR1-AX chassis (model number 14GR1224/75R) which apart from making a buzzing noise was otherwise quite dead. This popular model is now well known with few surprises left. But to those not familiar with it, it can be a little daunting the first time it is encoun­tered. If the main fuse is intact like this one was, there are really four main conditions possible for the main B+ rail which normally sits at 95V. First, if it measures only 1.5V across C2660, the crowbar circuit is probably faulty and you have to check SCR 6641, zener diodes 6638-6640 and diode 6642. Second, if it measures only 5V, the procedure is to check the standby circuitry from the remote control, the microprocessor and from transistor 7631. Third, if it measures 10V, FET 7610 is probably open cir­cuit and D6610, D6613, R3616 and R3680 also have to be checked. Finally, if it correctly measures 95V but the set is still dead, inductor L5524 is a likely culprit (it can go open circuit) but it could also be the flyback transformer (5530) that’s at fault. In this case, it was the latter and a new one quickly cured the problem. Fig.1: the 11V rail in the Philips 21MK2460 is derived from pin 16 of the transformer winding via a 1Ω safety resistor and diode 6180. 38  Silicon Chip I also reworked a few suspect solder joints on the deflection yoke plug and socket connections and also on some of the inductors, transformers, transistors and even IC7020-B. By the way, the 9V and 12V rails are critical on this model and so I always replace C2523 (6.8µF) with a 10µF 63VW 105°C type (and also occasionally C2542). Finally, a few words ought to be mentioned about the “Hotel Mode”. Once again, for those unfamiliar with this model or who never read the instruction book, it is fitted with a childproof lock which prevents the tuning from working and limits the maxi­mum volume level. To unlock this, all you have to do is select program site No.38 and press STORE and CONTROL+ simultaneously. Another Philips The second Philips set was a late-model 21MK2460 using an Mk.2 chassis. The customer’s complaint was that there was no picture or sound and, as far as he was concerned, it was dead. However, turning up the screen control soon revealed a blank raster but that’s about all there was. This was my first time with this model although I did have a circuit for it on my files. My first thought on the problem was that perhaps it was stuck in the AV (audio-video) mode but con­ necting an external video source made no difference. The problem seemed to be situated in the small signal circuits and as it was affecting both sound and picture, I checked the low tension 12V rail supplying them. This measured OK and so I next turned my attention the logic circuits and the 5V supply rail to them. This time, there was a clue – the 5V rail was down to just 3V which meant that I now had something to go on. By tracing this rail back towards its source, I quickly discovered that it is derived from an 11V rail via transistors 7182 and 7184. And this 11V rail revealed as a very faint hairline fracture in the copper track immediately adjacent to the pin. This was defi­nitely an 11 out of 10 on the “dj” (dry joint) scale. The rest was an anticlimax – soldering this microscopic crack fixed the problem once and for all. But what caused it in the first place? My guess is that the transformer pin was slight­ ly crooked and the fracture occurred when it was forced into its mounting hole during assembly. A job for the Terminator was also low, measuring just 7V from diode D6180. I then measured all the other rails from transformer 5161 and found them all to be correct bar this one. The circuit here is quite simple (see Fig.1). The top of the transformer winding terminates on pin 16 and goes to diode 6180 via a 1Ω safety resistor. The rectified output is then filtered using a 680µF electrolytic capacitor (C2180) to produce the +11V rail. The 1Ω resistor checked out OK and it made no difference when I substituted C2180 – the rail was still too low. However, when I disconnected the 5V rail, the 11V rail came good. In fact, disconnecting anything from this rail caused it to rise but I could not determine whether it was an excessive load problem or an insufficient supply problem. I disconnected pin 42 of the microprocessor (IC7200) and all the other components one by one but they all restored the 11V rail. They couldn’t all be faulty, could they? Surely not. My next thought was that perhaps diode D6180 was intermit­tent, so I tacked another one in parallel with it to the copper side of the PC board. This made no difference, so I decided to short out R3180 by connecting the new diode’s anode directly to pin 16 of transformer T5161 via a short length of hookup wire. When I did this, the 11V rail immediately came good again and the set burst into life. What’s more, the 5V rail was also now correct so what was happening? I removed and replaced R3180 but it still wouldn’t work properly without the wire link between R3180 and pin 16 of the transformer. By now, it was obvious that the connection between pin 16 and R3180 was not kosher, despite the fact that it looked per­fect. However, when I checked this path with an ohmmeter it meas­ured no resistance. Of course, that only meant that the fault was not showing up under no-load conditions. There was a lot of white paint surrounding pin 16 and so I decided to scrape this away with a utility knife. And there at last was the fault, I was about half-way through the second Philips set when the local video store rang and asked me to fix their Mortal Combat. “Mortal who?” I responded. “You know, the one-arm bandit”. This sounded dangerous. “You mean you want me to fix a one arm mortal combat bandit? Are you sure you got the right number?” “No, No, I mean the video game machine”. Ah ha! A cyborg repair – a job for the Terminator. Eventually the story unravelled as follows. The video store, which is a pretty small shop, was supplementing its meagre income with a video games slot machine. This was located near the entrance and the kids had been fairly pounding it recently be­cause first the picture gave lines and then it went dead. Because it was a fine day, I decided to abandon my stuffy workshop as soon as I had finished the Philips set and have a go at fixing this. Normally, I would be quite reticent at taking on such unfamiliar equipment but I was feeling unusually optimistic. It couldn’t be anything too complicated, could it? I didn’t realise that I would be fixing the thing on the pavement but, as it turned out, that was the only way I could find sufficient space to gain access to the machine. The game consisted of a sturdy wooden case on wheels with a 20-inch CRT on top and the controls on the front. The case was reinforced with steel and multiple locks and chained to the front of the shop. Good neighbourhood, this, I thought. Anyway, I eventually removed the front and rear panels and found that the parts were generally quite accessible. What’s more, the unit appeared to be very well-made. On the base of the cabinet was an expensive looking September 1997  39 Serviceman’s Log – continued of things that needed doing. First, both the protective glass and the tube surface were covered with dust and dirt. However, the glass is easily removed by unclipping two suitcase-type latches inside the cabinet and hinging back the control panel. Once this has been done, the rest is easy and the picture looked a lot better after I had finished cleaning the glass surfaces with detergent and a damp cloth. On the downside, my cleaning efforts revealed a further problem in the form of visible retrace lines. These were elimi­nated by reducing the screen control setting and setting up the sub-brightness. All that remained to do was to relock it all up and extract my fee from the proprietors. This had turned out to be a rela­tively straightforward job and for once my optimism had paid off. The crook microwave power supply and this was neatly terminated, with all the voltages clearly marked. The actual games circuitry consisted of a large PC board that looked just like a computer mother­ board and, finally, there was the TV moni­ tor board. These boards were connected by a large wiring loom to the various controls and to the money collector. Power supply checks The whole machine looked quite dead so I decided to start by checking all the different rails in the power supply. I was surprised to find them all correct and so took the next step of looking at the monitor board. The CRT heaters were on but because of the street noise, I couldn’t determine whether the line output stage was working. However, the B+ voltage on the line output transistor was correct, as were the screen voltage on the CRT 40  Silicon Chip socket and the voltages on the RGB output transistors. It all looked pretty good so far, so I turned my attention to the computer board. This was clamped to the side of the cabi­net and was awkward to get at. Anyway, while I was loosening the clamps, the large edge connector fell off with an ease that was all too apparent. I reconnected it and pushed it home as far as it would go. It could travel quite some distance and I noticed that the wiring loom connected to it was heavy and quite tight. It didn’t take a genius to figure out that the connector could easily come loose if someone was giving the case a good thumping. And that’s just what young kids are inclined to do when the game isn’t going too well. I repowered the machine and it immediately came to life with sound and picture. But although the picture was reasonable, there were a couple My next job in this day’s potpourri was a Sanyo Micro-Convection microwave oven, model EM-5710. This particular unit is now approximately 20 years old and features a stainless steel oven, a heating element in the roof and a fan. The problem that it had first became evident seven years ago but, on that occa­sion, the owner had decided not to opt for a full repair and instead went for a temporary one. I first saw the oven back in 1990, when it was brought in dead. The 8-amp power fuse was open circuit and the 25W SES globe had failed. I also noticed at the time that the convection fan in the roof was loose due to worn bearings. However, the customer was adamant that he didn’t want to spend money on getting this “minor problem” fixed up. This time, seven years later, it was sparking badly in the roof from two different locations. First, there is a ceiling partition between the element, fan and the main oven and this material had, over the years, been caked with variety of differ­ent foods that had gradually become carbonised. Once it reaches this state, the microwaves regard it as unwanted metal and the area absorbs a lot of energy. As a result, it gets hot and generates sparks which creates even more carbon. The second source of the sparks was the fan itself. This was lurching around in its now totally worn out bearing case and was striking the stainless steel roof, all the time giving a shower of sparks. It is quite possible that minute molten metal particles were spraying the partition below and were responsible for starting the fire there in the first place. Fairly obviously, the first job was to clean up the mess and I spent some time removing the dirt, rust and carbon deposits around where the fan was hitting the roof. The carbon on the partition was removed by cutting it out, just as a surgeon would cut away a cancer. Despite the oven’s age, the fan bearing was still available from Sanyo, as indeed was the belt. After reinstalling it, the acid test came when the power was connected and all the sequences tested. A mug of water was used to ensure that the magnetron had a load to absorb its energy, while a small fluoro tube (with its metal ends removed) from a discarded portable torch was placed in the water to check for the presence of microwaves. When the oven came on, the fluoro tube glowed brighter than it ever did in the torch. More importantly, the sparks had stopped and the rest of the oven was neutral, even when the water boiled. Purple patch My next story concerns a Compaq Presario 14SV monitor, vintage 1995, with the complaint that “first it had purple lines, now it has no picture”. This super VGA monitor is made by Samsung for Compaq and, as is my policy, I first connected it to a com­ puter to confirm the symptoms. This was just as well as the symptoms I observed were completely different to those described by the customer. I did get a picture of sorts but there was no horizontal control and I also noticed that the green LED power indicator wasn’t working. I prepared for surgery and dived in. Removing the back is quite easy provided that you know about the two concealed catches at the top. Once inside, you realise that the bottom PC board is inaccessible unless you remove all the metalwork and then the motherboard. My gut feeling was that there was a dry joint somewhere and the clue would have to be the LED. So once I got the chassis out, I checked the LED and the connections all the way back to the power supply where, to my relief, I found that there was indeed a dry joint on 3-terminal regulator IC202. On the dry-joint scale of 1 to 10, this was about a 6. I resoldered the regulator and then carefully inspected the rest of the chassis for similar faults. This revealed no further prob­lems, so I reassembled the motherboard into its metalwork and reconnected all the plugs and sockets. When I switched it on, the monitor’s picture locked perfectly and the power indicator LED shone green and so it was put aside to soak test before being finally pronounced cured. The old Sanyo My final story this month comes from K. Sims of Black For­rest, SA). I’ll let him tell the story in his own words. I’ve been in the lighting and sound business for around eight years now. TV’s certainly aren’t my cup of tea but, on this occasion, I decided to tackle a project that would be a bit more of a challenge. The set in question was a Sanyo CTP 5604 that was found in the “equipment graveyard” room at a night club that I have been working for. Apparently, it had been there for about two years but no-one knew where it originally came from. As the manager was junking all the rubbish from the offices, I decided to take a look at the set to see if it could be rescued. Plugging it in for a quick inspection revealed a squashed image no more than about 8cm high across the centre of the screen and there was no sound. This seemed to be two rather unrelated faults but as the picture is the most important of the two I decided to start there. Because the set had its back towards me, I decided to remove the rear cover and have a quick look inside for any obvi­ ous signs of trouble. As I was about to switch the set off, I noticed that the picture had “grown” to the extent that it now almost filled the screen. This indicated that the fault was heat sensitive and that a search of the deflection board for dry capacitors would be a good place to start. After shifting the set to my home and making a list of the capacitors that needed replacement I also noticed that 0.5W resistor R452 had been overheating, to the extent that its outer insulation (and colour coding) had burnt off the resistor’s inner core. PCB POWER TRANSFORMERS 1VA to 25VA Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 After a few calls, I was informed that Sanyo had a techni­ cal information line that you can call for information on assort­ed topics regarding repair. They kindly faxed out a schematic for the deflection board and informed me that R452 was actually a 33Ω resistor. It still tested OK but I replaced it for good measure. After replacing half the listed electrolytics, I realised that the worst one (C444, 4.7µF) was actually a non-polarised type. Eventually, I ended up replacing this capacitor and the remaining high-value electrolytics with low-leakage types ob­tained from a TV repair centre. On powering the set up again, I was rewarded with . . . absolutely nothing! I could still hear the whistle from the scanning coils and the tube heater was a lovely shade of orange but there was no picture at all. On closer examination, I then noticed that a 3W resistor adjacent to R452 had come adrift, probably due to a dry joint. A little resoldering fixed that problem and that did it – the set came good. It seems that replacing all those suspect capacitors cured the fault and the set now delivers a top class picture and sound. I also spent around an hour looking for the vertical cen­tring control only to finally find that it wasn’t a pot but a jumper lead that goes to one of three connecting posts on the deflection board. The UHF tuner was also removed and the tuning mechanism relubricated, as it had frozen SC solid from lack of use. September 1997  41 MAILBAG Howard’s way & valve amplifiers Well, the August 1997 issue is full of interest. I approve of your editorial about John Howard’s stance on green­ house gas emissions. I also noted your answer in the same issue to a query about tube amplifiers and their sound differences to solid state pro­ducts. I feel there are a couple of issues that need mentioning. A major part of the reason why many people prefer tube products is due to the limitations inherent in our present digital playback systems. There are several areas where these systems are vastly inferior (and some where they are superior) to analog systems. They include rise time (just look at a square wave of about 5kHz from a DAT machine), spatial capabilities and distortion products which tend to be non-harmonically related to music and several other problems. Tube products do tend to mask these problems. Of course, when the new DVD system is finalised, many of these problems may disappear. The other reason why people may prefer tube products is related to the low levels of negative feedback utilised by these amplifiers. The fact is that most loudspeakers exhibit serious back-EMF effects when driven by step functions. This back-EMF signal is presented to the driving output stage. Some of the signal will travel back down the NFB line, thus causing musically unrelated information to be amplified by the output stage. Be­cause this information is not harmonically related to the input signal, the sound can be very unpleasant to the ear. Eliminate the NFB line and you eliminate the problem. Be­cause it is difficult to achieve this with solid state products, most take the easy way out and use loop NFB lines. One of the few solid state amplifiers available today which uses no loop NFB around the output stage is the Australian designed and manufactured ME. Tube amplifiers tend to have quite large power supplies relative to power output. This fact allows them better overload characteristics than equiv42  Silicon Chip alent solid state products. Just check out the energy storage capacity of a typical, good quality tube amplifier. In short, I would caution readers in characterising ampli­fiers as having a solid “transistor sound” or “tube sound”. I have heard many good and bad examples of both types of technolo­gy. Tubes are not the panacea that many regard them to be. They represent a “knee-jerk” reaction to problems, which (hopefully) will not be with us much longer. On the other hand, typical solid state amplifiers have many design deficiencies, which need to be addressed. High levels of NFB are not the answer many consider it to be. T. Wilson, Hurstville, NSW. Comment: while we agree with some of your comments about valve (tube) amplifier sound, we do not agree with your comments about loudspeaker back-EMF. Yes, loudspeakers do generate back-EMF and that is one reason why it is important for an amplifier to have a very low output impedance which leads to good damping factor. Any extraneous signals generated by the speaker tend to be “damped” and so the loudspeaker is forced to more faithfully follow the audio signal. As far as power supply storage is concerned, it is irrele­vant to the overload characteristic of an amplifier. When an ampli­ fier overloads, it is overloaded, regardless of the actual vol­tage on the supply rails! The truth about audio cards I read SILICON CHIP on a regular basis and I commend you for what is a very interesting and informative publication. However, the article in your August 1997 issue entitled, “The Ins and Outs of Sound Cards” contained some inaccura­cies which I would like to point out. (1). The acronym “MIDI” stands for “Musical Instrument Digital Interface” and not “Direct Input”, as stated. MIDI inter­faces are used equally for transmitting and receiving data. (2). Many small amplified speakers are designed to work properly when connected to the speaker output on the sound card. These units, when their internal amplifiers are switched off, connect the input signal directly to the speakers, enabling them to use the sound card’s power amplifier. Their amplifier inputs are preceded by a resistive divider, in a similar manner to some automotive equaliser/boosters. (3). A fair percentage of PC owners also own some form of MIDI compatible device, usually a small keyboard, and probably don’t realise the potential to connect it to their PC. You state that MIDI interfaces are rarely used in the home, which I totally disagree with. Nearly every home computer user that I know uses their MIDI interface and will tell you that it adds greatly to their computing experience. (4). To call a software configurable sound card a “Plug‘n’Play wannabe” is an insult to it. Software configured cards make no claims whatsoever to being even related to Plug‘n’Play. Plu­g‘n’Play technology, with all its big promises, has been slow to deliver, requiring as it does, bug-free interaction between the devices, the system BIOS and the operating system. DOS games, of which many people including myself still use, do not understand Plug‘n’Play and nothing is more frustrating than a sound card deciding to change its port address or IRQ, often for no apparent reason, at boot time. Thank goodness for the “Use automatic settings” check box. Un­check­ing this will usually force a card’s settings to lock. Jason Cole’s comments about conflicts with other cards are testimony to the infancy of Plug‘n’Play. (5). 8-bit sound cards generally had a maximum sampling rate of 22kHz but neither the maximum sampling rate, nor the resolution (8-bit), determined whether the card could produce stereo sound. The Sound Blaster Pro is an 8-bit stereo card, contradicting Jason’s comment that 8-bit cards were mono only. The available bandwidth across an 8MHz, 8-bit ISA slot is orders of magnitude higher than that needed for stereo CD-quality digital audio data transfer. SILICON CHIP’s yougest reader This is a photo of my 21/2 year old son Kylan perusing a recent issue of SILICON CHIP. I thought you might like to know that your reader base is somewhat wider than you may have imag­ined! B. Low, Gwynneville, NSW. SMART ® FASTCHARGERS Brings you advanced technology at affordable prices As featured in ‘Silicon Chip’ Jan. ’96 This REFLEX® charger charges single cells or battery packs from 1.2V to 13.2V and 110mAh to 7Ah. VERY FAST CHARGING. Standard batteries in maximum 1 hour, fast charge batteries in max. 15 minutes AVOID THE WELL KNOWN MEMORY EFFECT. (6). The Sound Blaster 32, AWE32 and AWE64 are all 16-bit cards. There are no, and probably never will be, sound cards with a D-A and A-D resolution of more than 16 bits (not interpolated). CD quality sound is 16bit, which is capable of exceeding the dyna­mic range of our ears, thus there is no necessity for higher resolution. The 32 and 64 represent the polyphony of the wavet­able synths packaged with these cards; ie, the number of instru­ment sounds they can produce simultaneously. Incidentally, the AWE64 uses the same 32-voice synth as the AWE32 but combines a software wavetable synth and the associated mixing hardware to give an effective 64-note polyphony. Some manufacturers are now producing PCI sound cards which could be called 64-bit but I believe that the PCI bus is necessary for communication with the Dolby Pro-Logic, Dolby Digital (AC3) and other advanced signal processors that they contain. Ultimately, the conversion resolution is still 16 bit. (7). Your article quotes $150-$200 for a Vibra 16 and around $500 for a Sound Blaster AWE32. The same issue of SILICON CHIP has a Rod Irving Electronics advertisement, with these cards at $89 for the Vibra 16, $159 for the Sound Blaster 32 (which is a slightly downspec’d AWE32) and $179 for an AWE64! (8). The Sound Blaster range of sound cards is excellent in most re- spects, particularly software updates, as Jason has said. However, all Sound Blasters, even the top line AWE64 Gold, are lagging behind even some of the cheapest cards in one important area, full duplex support. The Sound Blaster provides for only one 16-bit DMA channel and one 8-bit, meaning that when playing and recording simultaneously, one of these operations must occur in 8-bit. This severely limits the creation of sound effects and voice overs for multimedia presentations, etc, where the multi­tracking abilities of full duplex are utilised. Sound cards using ESS Technology and Crystal Semiconductor chip sets are available for as little as $30, with two 16-bit DMA channels, excellent software support, Plug’n’Play functionality and Sound Blaster compatibility. Further, they have a Wave Blaster upgrade connector, allowing Creative’s own wavetable synth to be fitted. My point is that even though Creative’s range of sound cards have managed to stamp a de-facto standard into the sound card industry, there are many alternatives, some of which are often more suitable for particular applications. On a lighter note, I am looking forward to the full con­structional details for your “Big Bruiser” amplifier module. I might even build a pair to hook up to my AWE64. C. Burchall, Ashwood, Vic. NO NEED TO DISCHARGE. Just top up. This saves time and also extends the life of the batteries. SAVE MONEY. Restore most Nicads with memory effect to remaining capacity and rejuvenate many 0V worn-out Nicads EXTEND THE LIFE OF YOUR BATTERIES Recharge them up to 3000 times. DESIGNED AND MADE IN AUSTRALIA 12V-24V Converters, P. supplies and dedicated, fully automatic chargers for industrial applications are also available. For a FREE detailed technical description please Ph: (03) 6492 1368 or Fax: (03) 6492 1329 2567 Wilmot Rd, Devenport, TAS 7310 SILICON CHIP This advertisment is out of date and has been removed to prevent confusion. September 1997  43 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. 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Please have your credit card details ready 44  Silicon Chip OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia 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. 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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 Bookshop Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1997 (4th edition). 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. 383 pages, in hard cover at $55.00. Guide to TV & Video Technology By Eugene Trundle. First pub­lished 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $75.00. 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 $55.00. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. 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. 305 pages, in paperback at $69.00. 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 & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Radio Frequency Transistors Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $95.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First published 1989. 6th edition. This just has to be the best refer­ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semi­-custom electronics & data communications. 63 chapters, soft cover at $125.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order  ❏ Bankcard  ❏ Visa Card  ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $55.00. Understanding Telephone Electronics By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. This is a very useful text for anyone wanting to become familiar with the basics of telephone technology. The 10 chapters explore telephone fundamentals, speech signal processing, telephone line interfacing, tone and pulse generation, ringers, digital transmission techniques (modems & fax machines) and much more. Ideal for students. 367 pages, in soft cover at $49.95. Video Scrambling & Descrambling For Satellite & Cable TV By Rudolf F. Graf & William Sheets. First pub­lished 1987. This is an easy-to-understand book for those who want to scramble and unscramble video signals for their own use or just want to learn about the techniques involved. It begins with the basic techniques, then details the theory of video encryption and decryption. It also provides schematics and details for several encoder and decoder projects, has a chapter of relevant semiconductor data sheets, covers three relevant US patents on the subject of scrambling and concludes with a chapter of technical data. 246 pages, in soft cover at $50.00. ✓ Title o o o o o o o o o o Price Guide to Satellite TV $55.00 Servicing Personal Computers $90.00 Video Scrambling & Descrambling $50.00 The Ar t Of Linear Electronics $70.00 Digital Audio & Compact Disc Technology $90.00 Radio Frequency Transistors $95.00 Guide to TV & Video Technology $55.00 Electronic Engineer's Reference Book $160.00 Audio Electronics $75.00 Understanding Telephone Electronics $55.00 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ add $10.00 per book; elsewhere add $15 per book. TOTAL $A September 1997  53 Building the 500W Audio Power Amplifier Last month, we presented the circuit details of this new 500W amplifier and in this issue we present it in its final form, in a large chassis with its brute force power supply, loudspeaker protector module and fan-forced cooling. Pt.2: By LEO SIMPSON & BOB FLYNN I T IS ONE THING to see a large PC module with 14 power transistors on the heatsink and quite another to see that module assembled into a chassis with the necessary power supply, cooling fan and all the other hardware. Whichever way you look at it, this amplifier’s a brute. It is brutishly heavy, it has a brute force power supply and pity help the loudspeakers that can’t handle its brute output. The amplifier chassis is a 3-unit high rack-mounting case which is 406mm deep, not including the handles and the loudspeak­er terminals. The front panel is bare except for the handles and the large illuminated power switch. On the rear panel is the 120mm cooling fan, XLR input socket, loudspeaker terminals, mains fuse and 3-pin IEC power socket. Inside the chassis, the large toroidal 54  Silicon Chip transformer is mounted at the front with the bank of filter capacitors running down the lefthand side. The amplifier module is mounted on the righthand side but the single side finned heatsink is enclosed totally within the chassis. Fan cooling To ensure effective fan cooling, the heatsink is raised off the floor of the chassis by 5mm. The diagram of Fig.1 shows how this is done – the heatsink is shown in end elevation. This allows the fan to force air under the amplifier module and heat­sink base and then up through the fins to the ventilation slots in the lid of the case. The result is an effective cooling system with no ugly fins outside the case. This is big advantage when the amplifier has to be moved frequently, as it will be if September 1997  55 it is used for band and disco work. Now let’s move on to the assembly details for the amplifier module. Fan-Cooling Airflow Fig.1: to ensure effective fan cooling, the heatsink is raised off the floor of the chassis by 5mm. This allows the fan to force air under the amplifier module and heatsink base and then up through the fins to the ventilation slots in the lid of the case. Fig.2 (below): the component overlay for the PC board. Note that the U-shaped heatsinks for Q6 & Q8 should be left off until the output transistors are mounted on the heatsink. 56  Silicon Chip PC board assembly Because there are so many power transistors and because they need a practical spacing between each one, the PC board is quite long at 362mm and is 99mm wide. It is coded 01208971. All the power transistors mount along one edge and are fixed to a large single-sided heatsink which is made in two parts, each 200mm long and 118mm high. These are tied together with a small fishplate at the top to make one long heatsink assembly. Fig.2 shows the component overlay for the PC board. The suggested procedure for assembling the PC board involves mounting all the small components first and then the power transistors, although there are a few wrinkles along the way. The first step is to check the PC pattern for any defects such as broken tracks or undrilled holes. Fix any defects before proceeding and then install all the wire links. Then install the diodes and zener, making sure that they are installed with cor­rect polarity and don’t confuse the 1N914s with 1N4936s or the zener diode. Next, insert the small resistors (not the wirewounds) and the capacitors. Make sure that the electrolytics are all installed the right way around on the PC board. Note that the 100pF ceramic capac- itor between the collector of Q8 and the base of Q9 has a rating of 500V. In practice, it does not have to be that high but it does need to be more than 200VW. The rating of 275VAC for the 0.15µF capacitor in the output filter might seem excessive but anything less than 250VAC would be very risky. A lower rated capacitor could be blown when the amplifier is delivering high power at high frequencies. The 6Ω 3W resistor in the output filter is made up of three 18Ω 1W resistors in parallel. Choke L1 is wound with 21.5 turns of 1mm enamelled copper wire on a 13.7mm plastic former (see parts list). When installing the fuse clips, note that they each have a little lug at one end which stops the fuse from moving. If you insert the fuse clips the wrong way around, you will not be able to fit the fuses. A 390Ω 5W resistor is installed in parallel with each of the power supply fuses. These resistors serve no purpose when the amplifier is working normally but they are used when the quies­cent current is initially adjusted (without the fuses fitted). Next, mount all the small transistors; ie 2N5401s, BC5XX series and MJE340/350s. Don’t install Q9 at this stage as it will be mounted on the heatsink. Both Q6 and Q8 will be fitted with U-shaped heatsinks but these should not be fitted until all the output transistors are mounted on the main heatsink; otherwise the U-shaped heatsinks will just get in the way. Note that the transistor pairs Q1/ Q2 and Q4/Q5 are thermal­ly bonded; the pairs are mounted on the board so that their flat surfaces are touching. The thermal bonding is assisted with a smear of heatsink compound. Solder in one of the pair so that it is angled very slight­ly towards where its mate will be and then smear a little heat­sink compound over its flat surface. Then solder in the collector and emitter of its mate and push the two together before solder­ ing the base lead, to lock the two transistors together. Repeat this process for the other pair of transistors. Incidentally, note that the pinouts of the 2N5401s are reversed from those of the BC546s; don’t insert the wrong tran­ sistors in the wrong positions, otherwise they’ll blow as soon as the amplifier is turned on. Mounting the power transistors Before the power transistors can be mounted on the main heatsink, it must be fully drilled and tapped where necessary. Each transistor is secured to the heatsink with an M3 machine screw. Fig.3 gives the full details of the heatsink dimensions, the hole sizes and so on. As previously stated, this heatsink comprises two parts measuring 200mm long by 118mm high. The two parts are attached at the top by a small aluminium fishplate. Fig.3 also shows the drilling detail for the righthand end of the heatsink assembly. Two holes (B on diagram) are drilled to clear the heads of the handle on the front panel. The way to mount the 14 power transistors is as follows. First, attach each power transistor to the heatsink using an M3 (3mm) screw, washer and silicone heatsink pad. The details are shown in Fig.4. Make sure that each transistor is straight and parallel to its neighbour. All the transistor leads should be straight and parallel as well. This done, sit the heatsink on a flat surface and “introduce” the PC board to the power transistor leads. The PC board should be at rightangles to the heatsink. Make sure that each trio of transistor leads pass through their respective holes in the PC board. Push the board onto the leads so that the bottom surface of the board is 10mm from the lower edge of the heatsink. Make sure that the PC board is paral­lel to the heatsink and then solder one lead of one transistor at each end of the board. This done, recheck that the board is oriented exactly as you want it and then tighten all the transistor mount­ing screws. Finally, solder all the remaining transistor leads and cut the excess pigtails off. Q9, the MJE340 Vbe multiplier transistor, is mounted on the heatsink instead of on the PC board as pictured in last month’s article. The reason we have mounted it on the heatsink is that it gives slightly better thermal compensation of the quies­ cent current. Accordingly, Q9 is mount­ed on the heatsink with the same details as in Fig.4 and connected to the PC board with three flying leads. Note that each lead should be sleeved to prevent any possibility of shorts. The other visible difference between the amplifier module pictured last month and the way it is finally shown in the chas­ sis involves the wiring of the temperature sensor on the heat­sink. This is not wired to the amplifier PC module but connects to the loudspeaker protector board. We’ll talk about this later. Next, fit the U-shaped heatsinks to transistors Q6 & Q8 and the amplifier module is essentially finished apart from mounting it in the chassis. Chassis assembly Quite a lot of work has to be done to the chassis before any componentry September 1997  57 possibility of shorts and to make connections easy; it can be quite awkward trying to make speaker connections with heavy wires when the terminals are close together. The general layout of the components in the chassis is shown in Fig.5 and this shows all the wiring as well. Most of the work in the chassis involves the power supply and its heavy duty wiring. The circuit of the power supply is shown in the diagram of Fig.6. The chassis mount mains fuse is a 5-amp slow blow type. This is most important because a standard quick blow fuse will fail at the first switchon because of the high inrush currents into the 800VA toroidal power transformer. This is compounded by the fact that the 80,000µF filter capacitor bank will also have a very high inrush current at switch-on. In fact, it is normal to see the 240VAC lights on the same circuit momentarily dim when the power supply is switched on. Instead of using a 3-core power flex anchored with a cordgrip grommet and so on, we have used an IEC power socket. The Active wire from the power socket goes to the fuse and then the Active and Neutral are twisted together and run to the DPDT rocker switch on the front panel. It is important to wire this switch the right way around otherwise the neon illumination will be on, regardless of whether the amplifier is on or off. The mains wires from the power switch run to an insulated 3-way terminal block which also accommodates the .01µF 275VAC suppression capacitor which is wired directly across the trans­former primary. The 240VAC wires to the fan also connect to this terminal block but should not be connected at this stage. Before you mount the terminal block, place a piece of Presspahn (or Elephantide) measuring about 30 x 40mm between it and the chassis. This will prevent any possibility of flash­overs to chassis. Fig.3: these are the drilling details for the heatsink assembly. It two parts measuring 200mm long by 118mm high and these are attached at the top by a small aluminium fishplate. can be installed. All the holes need to be drilled for all the hardware, the circular cutout made for the fan and various cutouts made for the power 58  Silicon Chip switch, the XLR and IEC sockets and the mains fuse. Note that the heavy duty speaker terminals are mounted 40mm apart. We did this to reduce the Transformer mounting Mounting the toroidal transformer in the chassis does pres­ent a problem because of the large securing bolt. Because we have used a rack-mounting chassis and because it must be assumed that at least some users will want to mount the amplifier in a rack, the bolt head cannot protrude from the This chassis view clearly shows the revised mounting details for Q9, the MJE340 Vbe multiplier transistor. The transistor must be mounted as shown in Fig.4 and is connected to the PC board via three flying leads. base panel of the chassis. To solve this problem, we mounted the transformer on a separate panel within the chassis but raised on suitable pillars to clear the bolt. By the way, because of the weight of the transformer, the base panel should be made of steel at least 1.6mm thick. When mounting the bridge rectifier, smear a little heatsink compound on the mating surface and the chassis, to improve heat transfer. All the wiring to and from the filter capacitors should be run in heavy duty hookup wire while the busbars connecting all the filter capacitors together should be made with two strands of 16 gauge tinned copper wire. Note that the whole amplifier has single-point earthing so it is important to follow the wiring details of Fig.5 quite closely. Note also that the transformer wiring runs down the side of the transformer, behind the power switch. This is important because these heavy wires can otherwise radiate rectifier buzz into the amplifier module. Incidentally, toroidal transformers do have a significant hum leakage field and it is important to orient them for minimum hum pickup by the circuit. The orientation shown in the photos is close to optimum for this circuit. Both sides of the filter capacitor bank have two 15kΩ 1W bleed resistors connected across them. As well, a red LED is connected across each side of the capacitor bank in series with a 15kΩ resistor. The LEDs indicate when voltage is present across the capacitors, and as you will find, even with the bleed resis­tors connected, it takes quite a while for the capacitors to discharge after the amplifier is turned off. Safety precaution After the power supply wiring is complete and before you apply power, we suggest that you mount a clear Perspex sheet over the bank of capacitors. Fig.4: attach each power transistor to the heatsink using an M3 (3mm) screw, washer and silicone heatsink pad. September 1997  59 Fig.5: this diagram shows the general layout of the components in the chassis and all the interconnecting wiring. Take care with the mains wiring and note that the 160V DC developed across the filter capacitor bank and the amplifier supply rails is potentially lethal – see text and warning panel. 60  Silicon Chip Fig.6: this is the circuit of the power supply. The 5-amp fuse must be a slow blow type to cope with the switch-on surge currents. This will prevent accidental contact with the 160V DC supply. Note that the full DC supply is potentially lethal! The Perspex shield will also provide a degree of safety if one of the capacitors suddenly overheats and vents to the atmosphere! At this stage, the power supply wiring is complete but the amplifier module and the loudspeaker protection module is not installed. Now apply power and check that the supply voltage is close to ±80V. Both LEDs should light. Then switch off and allow the capacitors to completely discharge. This will take about 10 minutes. adjust the locknuts so that the top of the heatsink is level with the top of the case sides. When the lid is finally installed on the case, the heatsink is prevented from moving by the countersunk screws which secure it to the lid. Connect the XLR input socket to the amplifier module via shielded cable Mounting the amplifier module The 160V DC supply across the filter capacitor bank and the amplifier supply rails is potentially lethal! After the power supply wiring is complete and before you apply power, mount a clear Pers­pex sheet over the cap­acitor bank to protect against inadvertent contact – now or in the future! Note that the capacitors take some time to discharge after the power is switched off. As noted above, Fig.2 shows the scheme for mounting the amplifier module. You will need the four M3 countersunk heatsink support screws in place and the two pillars which support the front of the PC board. The heatsink should have four clearance holes drilled in the lower edge (see Fig.3) to mate with the support screws. What happens is that locknuts are fitted to each of the four support screws and then the heatsink merely sits on top of the nuts. You need to Fig.7: follow this diagram when wiring the XLR input socket. Note that shielded microphone cable is used to make the connections to the amplifier module. as shown in Fig.7. Do not make any connections to the amplifier output at this stage and do not install the loud­speaker protection module. Make the positive and negative 80V supply connections to the amplifier module. Switching on You are now ready to power up the amplifier module and make voltage checks. First, double check all your wiring against the circuits and diagrams in this article. This done, remove fuses F1 and F2 on the amplifier module. The 390Ω 5W resistors across the fuses should be in place and trimpot VR2 should be rotated fully anticlockwise. Apply power and measure the voltages shown on the circuit featured last month (Fig.1, page 26). There should be less than ±20mV DC at the output. Now connect your multi­meter across the 390Ω 5W resistor (across fuse F1) and adjust trimpot VR2 to obtain 30 volts. This provides a total quiescent current of 77mA or about 13mA per output transistor. Now measure the voltage across the other 390Ω 5W resistor (across fuse F2). It should be within 10% of the value across F1. You now need to leave the amplifier running for at least an hour. This will allow it to gradually warm up. Measure the voltage across the 390Ω resistors again and adjust VR2 to again give 30V. Next month, we will provide details of the loudspeaker protection module (based on the article in the April 1997 issue of SILICON CHIP) and will include the artwork for the main PC board. We also intend to describe a temperature operated switch for the fan so that it will only operate when needed. SC September 1997  61 Worried about break-ins? You can get peace of mind by building your own video security system. You’ll need a spare VCR, a low-cost CCD video camera, one or two PIR sensors, an IR illuminator and this VCR Security Controller to operate the VCR. Design by BRANCO JUSTIC A Video Security System For Your Home W ITH PEOPLE’S RISING con- cern about break-ins and vandalism, video security systems are becoming very widespread. Now they are just starting to appear in upmarket homes although they are quite expensive and can cost thousands of dollars. However, there is no need to lay out lots of dollars if you want your own video security system. CCD video camera modules are becoming very small and quite cheap at around $150 or less so they can be the basis of an effective home video security system. The CCD camera featured in this article is quite tiny. Its PC board measures just 33mm square so it can be 62  Silicon Chip Fig.1: the VCR Security Controller is triggered into the recording mode when one of the PIR sensors detects motion. Note that the camera and the VCR are always on but the monitor does not have to be present. Fig.2: the circuit uses a 4093 to control two relays which are connected in parallel with the Record and Stop buttons on the VCR or its remote control. easily concealed. Nor is there any need for ugly spotlights in order for the camera to work. They can function in low ambient light and are sensitive to infrared which is invisible to human eyes. Therefore, you only need a relatively low power infrared LED illuminator for the system to work even in pitch darkness. The problem is that just having a camera outside your house and a video monitor inside is not much good if you’re not at home. If someone does something naughty on your property you need to be able to record it with a VCR. This is the sort of system which is routinely installed in shops and service stations. But the VCRs used in shops usually run 4-hour tapes at half speed so they can record an 8-hour stretch. One or two tapes can record a whole day’s trading. However, a system with a VCR running continuously is not practical for the homeowner. You have to remember to change tapes and that is not possible when you are away. So the system pre­sented here uses one or two passive infrared (PIR) sensors to monitor the camera’s field of view and then switch the VCR on for a fixed period if any motion is detected. Fig.1 shows the con­cept. The heart of the system is the VCR Security Controller board. This is hooked up to one or two PIR sensors and it con­trols two relays. The camera, IR illuminator, VCR controller and PIR sensors are continuously powered from a 12V DC plugpack and the VCR itself is switched on; ie, not on standby. The camera is connected to the video input on the VCR which can be connected to a standard TV or video monitor. Note that the video monitor does not need to be turned on at all, unless you want to check what has been recorded on the tape. The VCR controller has two relays and these are used to operate the Record and Stop functions on the VCR. The relays can either be used to operate the VCR directly, via connections across the Record and Stop buttons in the machine, or they can operate via connections across the Record & Stop buttons of the infrared remote control. Better still, if you have an old VCR with a wired remote control, it would be a simple matter to make connections via the remote control plug on the rear of the machine. Alternatively, if you don’t fancy modifying your existing remote control you could purchase a “learning remote control” and modify that instead. To be realistic though, you would probably want to dedicate one VCR to this security September 1997  63 Parts List 1 PC board, 103 x 52mm 2 relays with SPDT contacts 1 12V DC plugpack Fig.3: PIR sensors can have normally open or closed contacts or have a pull-down output involving a TTL stage or an open-collector transistor. Semiconductors 1 4093 quad NAND gate (IC1) 1 BC548 NPN transistor (Q1) 3 C8050 NPN transistors (Q2, Q3, Q5) 1 BC558 PNP transistor (Q4) 1 5.6V 400mW zener diode (ZD1) 5 1N4148 silicon diodes (D1, D2, D3, D4, D5) 2 G1G silicon diodes (D6, D7) 3 red light emitting diodes (LED1, LED2, LED4) 2 green light emitting diodes (LED3, LED5) Capacitors 3 22µF 25VW electrolytic 3 0.1µF monolithic 2 .015µF monolithic Fig.4: this is the component overlay for the PC board. Be aware that the C8050 transistors may be supplied in a different pinout from the EBC sequence that the board is designed for. application so it would not matter if it was internally modified or its remote control was modified. Each time one of the PIR sensors detects motion in the camera’s field of view it causes the “Record” relay in the VCR Security Controller to operate momentarily. This sets the VCR into record mode and it stays that way until the “Stop” relay on the VCR Security Controller operates momentarily. The time bet­ ween the record and stop signals will depend on how long the PIR sensors continue to detect motion and a delay period of about 60 seconds after motion. VCR controller circuit Fig.2 shows the circuit of the VCR Security Controller. It uses just one 4093 quad Schmitt NAND gate IC, five transistors, two relays and not much else. Transistor Q1 is turned on when one or both of the PIRs connected at the input senses motion. The input from Resistors (0.25W, 5%) 2 10MΩ 1 6.8kΩ 1 2.2MΩ 5 4.7kΩ 1 220kΩ 3 2.7kΩ 1 100kΩ 2 1.5kΩ 3 47kΩ 1 1kΩ the PIRs is coupled via diodes D1 & D2 and there are a number of options for connecting the PIRs to cope with devices that have normally open or normally closed outputs or TTL outputs. Fig.3 shows these options. When Q1 turns on it pulls pins 1 & 2 of IC1 low, causing pin 3 to go high. This quickly charges capacitor C3 via Resistor Colour Codes ❏ No. ❏  2 ❏  1 ❏  1 ❏  1 ❏  3 ❏  1 ❏  5 ❏  3 ❏  2 ❏  1 64  Silicon Chip Value 10MΩ 2.2MΩ 220kΩ 100kΩ 47kΩ 6.8kΩ 4.7kΩ 2.7kΩ 1.5kΩ 1kΩ 4-Band Code (1%) brown black blue brown red red green brown red red yellow brown brown black yellow brown yellow violet orange brown blue grey red brown yellow violet red brown red violet red brown brown green red brown brown black red brown 5-Band Code (1%) brown black black green brown red red black yellow brown red red black orange brown brown black black orange brown yellow violet black red brown blue grey black brown brown yellow violet black brown brown red violet black brown brown brown green black brown brown brown black black brown brown This picture shows the assembled VCR Security Controller board, together with the miniature CCD camera and an infrared illuminator board. The CCD camera measures just 33mm square and only need low-power IR illumination to work, even in pitch darkness. diode D3 and so pin 4 of IC1b goes low. This low signal is coupled via 0.1µF ca­pacitor C4 to pins 12 & 13 of gate IC1d and so pin 11 goes high for about a second to turn on NPN transistor Q3 and relay RLY1, the Record relay. Thus the VCR starts recording. When Q1 turns off, pin 3 goes low again but C3 can not discharge quickly via the now reverse-biased D3. C3 takes about a minute to discharge via resistors R6 & R7 and that causes pin 4 to go high again. This high signal is coupled via 0.1µF capacitor C5 to pins 8 & 9 of IC1c and so pin 10 goes briefly low to turn on PNP transistor Q4, NPN transistor Q5 and relay RLY2, the Stop relay. So the VCR stops recording. Five LEDs indicate the status of the VCR Security Con­troller board. LED1 turns on whenever the output of IC1a is high and so indicates when one of the PIRs is detecting motion. LED2 is on whenever relay RLY1 is actuated and indicates when the Record function is being selected. Similarly, LED3 is on when relay RLY2 is actuated and indicates when the Stop function is being selected. Both LED2 and LED3 will only turn on briefly. LED4 turns on while ever the output of IC1b is low and indicates that the VCR is in the recording mode. Finally, LED5 will always be on while the +5V rail is present. Transistor Q2 and zener diode ZD1 function as a 5V regula­tor, used in place of a conventional 3-terminal regulator as it takes less quiescent current. The quiescent current taken by the whole circuit is not much more than a milliamp since transis­tors Q1Q4 are normally off and IC1 is a CMOS IC which draws only a few mi­croamps. Assembling the PC board The components for the interface fit on a PC board measur­ing 103 x 52mm. An IR illuminator is necessary to complete the security system and two versions are shown here. The small one has 10 IR LEDs and will be quite suitable for close-up applications, while the larger 30-LED unit is necessary for covering larger open areas. September 1997  65 real trap for young players. The board is designed for transistors with the conventional EBC pinouts but check the transistors you have been supplied because they could have the ECB pinout se­quence. If so, you will have to bend the leads to make a correct installation. If you don’t fancy modifying your existing remote control you can purchase a “learning remote control” and modify that instead. Test procedure The assembly is quite straightforward – just follow the component layout of Fig.4. Fit the resistors first, followed by the capacitors, diodes and LEDs. Once this has been done, fit the transistors and the relays, followed by the IC. One point to watch when installing the transistors is to check the pinouts of Q2, Q3 & Q5. These are specified as C8050 gener­al purpose NPN transistors and their pinouts can vary – a Where To Buy A Kit Of Parts The PC board and other parts for this project are avail­able from Oatley Electronics, who own the design copyright. Their address is PO Box 89, Oatley, NSW 2223. Phone (02) 9584 3563; fax (02) 9584 3561. The prices are as follows: Video Controller board with all parts .....................................................$25 Used PIR sensors to suit .......................................................................$10 Small IR illuminator kit (with 10 880nm IR diodes) ................................$14 Large IR illuminator kit (with 30 880nm IR diodes) ...............................$30 CCD camera module ...........................................................................$120 12V DC plugpack to suit ........................................................................$10 Please add $5 to for postage and packing. 66  Silicon Chip Do not hook the PC board up to your VCR before you have done a bench test. To do this, connect the PC board to a 12V DC power supply. If you have PIR sensor, connect it to one of the inputs, using the correct hookup, as shown in Fig.3. Otherwise, simulate a trigger pulse by momentarily connecting either input to the free end of resistor R19 or R20. You should see LED1 light with each trigger pulse. LED4 should come on with the first trigger pulse and stay on for at least one minute after the last trigger pulse. LED2 will light momentarily when the PIR is initially triggered (activating the Record relay), while LED3 will light momentarily when the timing period has ended (activating the Stop relay). To avoid waiting a minute or more for the timer to complete its cycle, temporarily solder a link across R7 as shown in the circuit diagram. This reduces the timing cycle to a few seconds and makes testing easier. Troubleshooting should be easy, as the circuit is not com­plicated. If it doesn’t work as described, first check that you haven’t accidentally swapped any of the transistors or put them in the wrong way around – it is easy to do. Also, make sure all the diodes and electrolytic capacitors have been fitted with the right polarity. Connecting the remote control As already noted, the VCR Controller board can be connected across the Record and Stop buttons in your VCR. If you don’t mind accessing the internals of your VCR, that way is probably the most effective. Alternatively, you can connect the relays across the buttons in the remote control handpiece, or you can adapt a programmable IR remote control transmitter. If you intend to modify your remote control handpiece you will need to open the case and remove the batteries as a first step. Most IR remote controls are made in a similar way with PC tracks forming the switch contacts WARNING! THESE PREMISES ARE UNDER CONSTANT VIDEO SURVEILLANCE Fig.5: as a further deterrent to criminals and villains, make a copy of this notice and put it in your window. underneath each key in the keypad. All you need do is locate the tracks for the Record and Stops keys and connect the relay contact in parallel with the keys. When soldering wires across the tracks do NOT solder di­ rectly on the pads where the buttons make contact. If you do, you will probably render the Record and Stop buttons inoperative. This would be a tragedy, particularly if you were using a “learn­ing” as these buttons still have to be used to program the con­ trol. Better still, program the remote before you solder any wires to the back of the copper side of the board. Connecting the PIR sensors When connecting the PIR detector you need to identify the supply and output connections. You may need to unclip the case of the PIR to access the connections on its PC board. You may also need to operate the PIR on its own to identify whether its con­ tacts are normally open or normally closed or a “pull-down” output (ie, open-collector or TTL). That done, use the diagram of Fig.3 to make the PIR connections to the VCR Controller board. Now try the whole system running. When the PIR detects movement, LEDS 1, 4 & 2 should operate and recording should begin. LED4 will stay on for the duration of the timing period. When movement has ceased, LED3 will operate and recording should be stopped. Installing the system Because of the noise filtering in the input circuit of the VCR Controller, you can connect the PIR detectors with up to 30 metres of telephone cable. For best results the CCD camera should be connected with 75Ω coaxial cable. The cable length is not critical and can again be up to 30 metres or so, depending on the camera module. The IR light source is placed behind or alongside the camera so it lights the viewed area. The camera and the light source can be powered by the same 12V DC supply. Another facility you may want to add is a ‘time stamp’ on the VCR tape when recording. Some VCRs can be programmed to add the time and date when making a recording but most don’t have this feature. A simple way to achieve time stamping is with a talking alarm clock recorded onto the audio track of the VCR. Simply disconnect the speaker of the clock and connect the clock’s audio output to the VCR’s audio input socket. You might need a 100Ω load resistor in place of the speaker, to avoid latching up the amplifier output stage. The VCR should be well concealed and well away from the camera. Ideally, the camera should also be concealed but you might want to make a copy of the notice in Fig.5 and stick it to a window where potential thieves and vandals will see it. After all, it is better to discourage someone from committing a crime in the first place rather than getting evidence after the SC fact. September 1997  67 Silicon Chip Back Issues September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV. July 1991: 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; The Snowy Mountains Hydro Scheme. September 1991: Digital Altimeter For Gliders & Ultralights; Ultrasonic Switch For Mains Appliances; The Basics Of A/D & D/A Conversion; Plotting The Course Of Thunderstorms. 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. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music System; The Care & Feeding Of Battery Packs; How To Make Dynamark Labels. October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2; A Look At Australian Monorails. November 1990: How To Connect Two TV Sets To One VCR; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Build A Simple 6-Metre Amateur Band Transmitter. November 1989: Radfax Decoder For Your PC (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. December 1990: The CD Green Pen Controversy; 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Operating an R/C Transmitter; Index to Vol. 2. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages. February 1990: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC; The Australian VFT Project. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Low-Cost Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing Your Microwave Oven. 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. June 1990: Multi-Sector Home Burglar Alarm; Build A Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car; Fitting A Fax Card To A Computer. 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. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. November 1991: Build A Colour TV Pattern Generator, Pt.1; A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Build a Turnstile Antenna For Weather Satellite Reception. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; Guide Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; 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; IR Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. August 1992: An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI Explained. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. January 1993: 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 Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. ORDER FORM Please send me the following back issues: _____________________________________________________________________ _____________________________________________________________________________________________________________ _____________________________________________________________________________________________________________ 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 ___________ 68  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) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503.  Card No. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; A Windows-Based Logic Analyser. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-based Logic Analyser, Pt.2; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80Based Computer; A Look At Satellites & Their Orbits. 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 Cockroach. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. February 1994: Build A 90-Second Message Recorder; 12240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags - How They Work. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Engine Management, Pt.6. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Pre­ amplifier;The Latest Trends In Car Sound; Pt.1. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. September 1996: VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­grammable Ignition (see March 1996); Cathode Ray Oscilloscopes, Pt.5. March 1995: 50 Watt Per Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. April 1995: FM Radio Trainer, Pt.1; Photographic Timer For Dark­ rooms; Balanced Microphone Preamp. & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. May 1995: What To Do When the Battery On Your PC’s Mother­board Goes Flat; Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; A 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Door Minder; Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. November 1995: Mixture Display For Fuel Injected Cars; CB Trans­verter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; Index To Volume 8. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; Use your PC As A Reaction Timer. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Nicad Zapper; Engine Management, Pt.11. March 1996: Programmable Electronic Ignition System; Zener Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Engine Management, Pt.12. October 1994: Dolby Surround Sound – How It Works; Dual Rail Variable Power Supply; Build A Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Build A Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. May 1996: Upgrading The CPU In Your PC; Build A High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. December 1996: CD Recorders ­– The Next Add-On For Your PC; Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source (for Sound Level Meter calibration); Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. February 1997: Computer Problems: Sorting Out What’s At Fault; Cathode Ray Oscilloscopes, Pt.6; PC-Controlled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Alert-A-Phone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Madel Railways; Build A Jumbo LED Clock; Audible Continuity Tester; Cathode Ray Oscilloscopes, Pt.7. April 1997: Avoiding Windows 95 Hassles With Motherboard Upgrades; A Low-Tech Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Model Train Controller; Installing A PC-Compatible Floppy Drive In An Amiga 500; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. May 1997: Windows 95 – The Hardware Required; Teletext Decoder For PCs; Build An NTSC-PAL Converter; Neon Tube Modulator For Light Systems; Traffic Lights For A Model Intersection; The Spacewriter – It Writes Messages In Thin Air; A Look At Signal Tracing; Pt.2; Cathode Ray Oscilloscopes, Pt.9. June 1997: Tuning Up Your Hard Disc Drive; PC-Controlled Thermometer/Thermostat; Colour TV Pattern Generator, Pt.1; Build An Audio/RF Signal Tracer; High-Current Speed Controller For 12V/24V Motors; Manual Control Circuit For A Stepper Motor; Fail-Safe Module For The Throttle Servo; Cathode Ray Oscilloscopes, Pt.10. July 1997: Infrared Remote Volume Control; A Flexible Interface Card For PCs; Points Controller For Model Railways; Simple Square/Triangle Waveform Generator; Colour TV Pattern Generator, Pt.2; An In-Line Mixer For Radio Control Receivers; How Holden’s Electronic Control Unit works, Pt.1. August 1997: The Bass Barrel Subwoofer; 500 Watt Audio Power Amplifier Module; Build A TENs Unit For Pain Relief; Addressable PC Card For Stepper Motor Control; Remote Controlled Gates For Your Home; How Holden’s Electronic Control Unit works, Pt.2. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, August 1991, February 1992, July 1992, September 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear sheets) at $7.00 per article (includes p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. A complete index to all articles published to date is available on floppy disc at $10 including packing & postage. September 1997  69 COMPUTER BITS BY JASON COLE Win95, MSDOS.SYS & the Registry Do you want to stop the Windows 95 boot logo from ap­pearing each time you start Windows 95? Or do you just want to stop the computer from re-booting into safe mode if you haven’t previously shut down Windows 95 correctly? You can do all this and much more by editing the msdos.sys file. Fig.1: Typical MSDOS.SYS File [Paths] WinDir=C:\WINDOWS WinBootDir=C:\WINDOWS HostWinBootDrv=C [Options] BootDelay=1 BootMulti=1 BootGUI=1 Network=1 BootWarn=0 Logo=1 ; ;The following lines are required for compatibility with other programs. ;Do not remove them (MSDOS.SYS needs to be >1024 bytes). ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxa ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxb ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxc ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxd ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxe ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxf ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxg ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxh ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxi ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxj ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxk ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxl ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxm ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxn ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxo ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxp ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxq ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxr ;xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxs 70  Silicon Chip Turning off your computer without first correctly shutting down Windows 95 is generally not a good idea. Doing so can cause unallocated file errors on the HDD (hard disk drive) and this can cause all sorts of problems. These file errors are caused by programs that have not been allowed to terminate normally. As a result, socalled temporary files (ie, .tmp files) are left in the temp directory on your hard disc. In greater detail, temporary files are files that are created as a program works. If the program is not terminated correctly, these temporary files remain on the hard disc when you shut the computer down, which means that the FAT (file allocation table) is not correctly updated. But inevitably, there may be times when turning off the computer while Windows is still open is required (or it can just happen if there is a power failure) If so, you don’t really want it rebooting into safe mode or asking you any ques­tions. You may also not want the Windows 95 splash screen (or boot logo) to appear because you want to check for errors in config. sys and auto­exec.bat when booting Windows 95. Alternatively, you might want the boot menu options to always appear, or you might need to prolong the boot delay. Programmers and hardware designers occasionally require these options so that they can test new ideas. The answer is to edit the msdos. sys file. Editing msdos.sys Msdos.sys for Windows 95 has changed since the version that came with MSDOS 6.22 in that it is now quite readable when opened in a text editor. This means that you can easily modify it your­self to give the startup options that you require. The msdos.sys file lives in the root directory of the HDD and has hidden, read-only, system attributes. If you want to play around with this file then go for it but first, make a backup of the file and make sure that you have a working boot disk, just in case things go wrong. That way you can easily copy the original back later if something goes wrong. Once you’ve made the backup, undo the attributes (type attrib -r -h -s msdos.sys at the command prompt) and open the file with a text editor. The resulting file will look similar to that shown in Fig.1. From the [Options] section in Fig.1, you can see that this machine operates as follows: (1) it has a boot delay of one second (Bootdelay=1); (2) it can boot into the previous version of DOS, giving it dual boot capabilities (BootMulti=1); (3) it boots the machine straight into Windows (BootGUI=1); (4) the network will be active (Network=1); (5) there will be no warning if Windows has previously been shut down by just turning off the computer (BootWarn=0); and (6) the splash screen will be displayed (Logo=1). However, these are just some of the possible options and you can easily add in other options yourself and alter the exist­ing options to suit. Note that if the option isn’t listed in the msdos. sys file, the system takes the default action. Fig.2 shows a list of some other (but not all) options for the msdos.sys file. Note that most settings require a value of 1 (ON) or 0 (OFF). The other entries in Fig.1 are in the [Paths] section, as follows: (1) WinDir=C:\WINDOWS – this line is a path statement that de­fines the location of the Windows 95 parent directory. (2) WinBootDir=C:\WINDOWS – this line shows the path for the Windows 95 startup files. (3) HostWinBootDrv=C – this line defines the location of the boot drive root directory. These options are there for multiple HDD systems. MSDOS.SYS is fairly powerful so be careful as a wrong set­ting can cause your machine to hang. That’s why it’s Fig.2: Options For MSDOS.SYS Option Default What It Does BootDelay =2 Initial startup delay (seconds) BootGUI =1 Automatic Windows 95 startup. Set this value to 0 to boot to the command prompt. BootKeys =1 Enables startup keys F4, F5, F6, F8. Changing this value to 0 overrides the BootDelay setting. BootMenu =0 Hides startup menu (press F8 to display). Change to 1 to automatically see the menu without having to press F8. BootMenuDefault =1 Sets the default (highlighted) item on the startup menu (see Note 1). BootMenuDelay =30 Delay (seconds) that the startup menu remains visible before running the default menu item (only if Boot­Menu=1). The value can be from 1-99 but a value of 4-7 seconds is usually suitable. BootMulti =0 Setting this value to 1 enables dual-boot capabili­ties. Press F4 to launch the previous version of MS-DOS or F8 to access the startup menu (see Note 3). BootWarn =1 Displays the safe mode startup warning & menu. BootWin =1 This line enables Windows 95 as the default operating system. Setting this value to 0 enables the previous operating system (eg, MS-DOS 6.x). Logo =1 Displays the animated logo as Windows 95 boots. Note 1: Menu option 3 is highlighted if a previous Windows 95 load failed. Note 2: The delay gives the user time to press the function key. The default is 0 if BootKeys=0. Note 3: If BootKeys=0, then setting BootMenu=1 and BootMulti=1 has no affect on the default action. Note 4: Network=1 must be present or Safe Mode with network sup­port doesn’t appear as option 4 on Startup Menu. important to make a backup before you start experimenting. Don’t forget to restore the attributes of the msdos.sys file after you have fin­ished (type attrib +r +h +s msdos. sys at the command prompt). The Registry Strictly speaking, Windows 95 does not need autoexec.bat, nor does it need config.sys. About the only time you require these two files is for some DOS-based programs. Windows 95 does, however, need the msdos.sys file discussed above so don’t delete it. The reason why you don’t normally require autoexec.bat or config.sys is because Windows 95 make extensive use of the Regis­try. The Registry has been around since Windows 3.x but, prior to Windows 95, was not used that much. The Registry is basically a unified database where Windows 95 keeps all its configuration information. And although it’s laid out in a logical fashion, September 1997  71 Fig.3: the Configuration Backup Utility comes on the Windows 95 CD ROM and is useful for making Registry backups. it can be rather difficult to understand its workings. Basically, the Registry is split up into six different areas called “Keys”. You can find the necessary information on these in the Windows 95 Resource Kit. This kit comes as a 1348-page book which also includes a CD-ROM. However, in you already own a copy of Windows 95 on CD, you already have an on-line version of the Resource Kit in the D:\Admin\ Reskit directory (assuming that D: is your CD-ROM drive). Fig.4: when the backup process is complete, the main dialog box lists the latest backup and any previous backups. The older backups can be deleted if you wish. Once you’ve learnt a little about the Registry you will want to delve deep into its bowels and see what you can find. But first, you’ll want to make a backup in case things go wrong. To do this, you can use Microsoft’s own Configuration Backup utility. This can be found on the Windows 95 CD at D:\ Other\Misc\Cfgback and the relevant executable is Cfgback.exe. There is no shortcut to this program in the Start menu but there’s nothing to stop you from copying the program to your hard disc and creating the Fig.5: this is the opening window that appears when you run the Registry Editor. Note that the Registry is divided into six different sections called “Keys”. 72  Silicon Chip relevant shortcut in your Start menu using the Explorer. In fact, this is a good idea because it’s handy to be able to make a quick backup on a regular basis, even if you’re not into Registry hacking. When you start this program, you basically follow the bouncing ball. The backup menu screen is shown in Fig.3. All you have to do is enter some information in the Selected Backup Name panel (eg, a name, the date or the current general setup of the computer) and then click the Backup button. You will be asked if you really want to back up the Regis­ try and then another dialog box will appear, informing you that the process may take a few minutes. When the backup is complete, the main dialog box will show the latest backup, along with any previous backups (Fig.4). You can select any of these older backups and delete them if you wish but don’t delete the latest backup. Now that the Registry has been backed up, you are ready to take a look at its contents. You do that by running the Registry Editor (ie, Reg­edit.exe) and you will find that this program is already on your HDD. To load the Registry Editor, click the Start button, then click the Run option and type C:\Windows\Regedit on the Open line. The Registry Editor will now open when you click OK (see Fig.5) and you’re ready to start exploring its contents. I don’t want to delve too deeply into Fig.6: the data in the Registry depends on the hardware and software in the computer. The data appears in the righthand pane and is accessed by clicking down through the folders in the lefthand pane. the Registry because it differs from one computer to another, depending on its hardware and software setup. However, the basic layout is always the same – your Registry will appear to look just like anybody else’s but the actual data shown in the righthand pane will be different (see Fig.6). Note that the Registry Editor can both export and import data which is handy when you’re fiddling with the unknown. This lets you export that part of the Registry you are play­ing with and, when you want it back the way it was, you can import it again. If you know what you are doing, you can also add new keys and data to the Registry. But be warned – the Registry Editor is a powerful tool, which means you can easily corrupt the Registry so that important settings are lost. If you do that, you will have to reinstall Windows 95 unless, of course, you have backed-up the Registry beforehand and can fully restore it. SC Making Registry Backups If you’re going to explore the Registry, it’s imperative that you make backups first. By itself, Windows 95 makes a reasonable job of backing up the two files that form the Registry –System.dat and User.dat. Each time Windows 95 successfully starts, it backs up the Regis­ try by copying System.dat and User. dat to Sys­ tem.da0 and User.da0 respectively. If Windows 95 refuses to restart after you have hacked the Registry, copying the two .da0 files over the current .dat files should fix the problem. Note that these are all read only, hidden, system files, so you will have to undo their attributes first before copying the .da0 files over the .dat files. That said, you still must make backups to protect you from Registry hacking disasters and two very worthwhile utilities for doing this are provided on the Windows 95 CD ROM. The first, Configuration Back­up (Cfgback.exe), was covered in the main article. The second is known as the Emergency Recovery utility (ERU.exe) and you’ll find it in the Other\Misc\ERU folder. As well as User.dat and System. dat, the Emergency Recovery Utility also backs up and restores other critical system files. As with Cfgback.exe, the ERU lets you back up to floppy discs so that you can restore things to working order again even if you can no longer start Windows. Tip: How To Rename The Recycle Bin You can rename anything that appears on your Desktop by right clicking the icon and then clicking Rename. This applies to everything except -– you guessed it – the Recycle Bin. If you've always wanted to change the name of the Recycle Bin, you have to hack the Registry. Launch the Registry Editor (click Start, click Run, type C:\Windows\Regedit and click OK). Now burrow down to HKEY_CLASSES_ROOT,CLSID, {645FF040-5081-101B-9F0800AA002F954E} and change the Default value from "Recycle Bin" to the name of your choice. Another (easier) way to change the name of the Recycle Bin is to use the Microsoft Power Toys. These can be downloaded from the Micro­ soft Web site and they are often also made available on the CD ROMs that are included with some popular computer magazines. We'll have more to say about the Microsoft Power Toys in next month's column. September 1997  73 VINTAGE RADIO By JOHN HILL The 5-valve Airking console receiver A guy came to see me the other day with a vintage radio repair. It was a 5-valve Airking, a console receiver from 1937 with an 8-inch (200mm) Jensen electrodynamic speaker. The radio had been in his family for several generations and it was my job to restore it to working order. The Australian Official Service Manual for 1937 lists no Airkings in its index. Obviously, the receiver was one of those made by one manufacturer but sold under another name. Just who made the chassis is anyone’s guess but the rubber-stamped “Air k­ing” name on the dial indicates a badge-engineered job without a decent badge to go with it. My initial inspection of the chassis gave me a few misgivings about the repair. There were several problems that I could see immediately: (1) some of the loudspeaker connections had come adrift from the plug and the cone had several rips in it; (2) the dial pointer was missing, which meant that another pointer would have to be substituted or made; and (3) the set used European (Philips) 8-pin, side-contact valves. That last problem could have proved a major stumbling block. Although the European valves work just as well as any other type, they The rubber stamped “Airking” name on the dial indicates a badge-engineered job without a decent badge to go with it. It would appear as though the Airking was produced for the lower end of the price range. 74  Silicon Chip are now hard to find and expensive to buy. In fact, this problem had already been encountered at some time in the past as one of the sockets had been replaced with an octal socket and valve. Fortunately the owner wasn’t at all fussed about originali­ty. He just want­ed the set to work and didn’t care what had to be done to achieve that goal. I like customers like that! On closer examination, it was discovered that the Airking was fitted with two power rectifier valves: (1) an EZ2; and (2) its octal equivalent, a 6X5, in the odd octal socket. But while the EZ2 was clearly occupying the rectifier socket, it appeared that the octal socket was actually intended as a detector stage. Just why it was now fitted with the 6X5 was a mystery. I suggested to the owner that this was probably the result of someone filling an empty socket, simply to make the set look complete. I have seen many radios fitted with all sorts of inap­propriate valves and believed this to be the case with the Airk­ing. However, the owner had known the set for a very long time and was inclined to reject this theory. Unfortunately, the cardboard valve placement diagram had been torn and the missing portion that would have shown the original valve type was missing. It did, however, indicate that the original power supply rectifier was an EZ3. This is similar to the EZ2 that was fitted but has higher ratings. It was all rather confusing. It was time to investigate the octal socket, to determine what sort of valve it may have had in it. Checking the wiring revealed only four connections to the socket and, to my surprise, these tied in with the 6X5 rectifier. These connections were heaters (2), cathode (1) and the joined plates (1). The mystery was solved when the missing part of the valve layout diagram was found in the box in which chassis was packed. Much to my surprise, the original valve in this position was also an EZ3 and it really did function as the detector stage. This is the first radio receiver I have seen that used a power rectifier as a signal diode for detection purposes. Although the Airking appears to be a 5-valve receiver, the re­ceiving part of the set amounts to only three valves. No doubt it was sold as a 5-valve radio but really, it’s not! Why the manufacturer didn’t use a duo diode triode (as was common in the mid-1930s) I’ll never know? To employ a separate socket which only uses a diode doesn’t make much sense. The use of a duo diode triode would not have increased the cost of the receiver by very much and the extra audio stage would have given a considerable boost to the set’s performance. Perhaps the more up-market Airkings were given an extra audio stage? The old Airking cleaned up rather well, as this front view of the chassis shows. The three controls are for tuning, volume and frequency range. Checking it out But let’s not speculate on the whys and wherefores of the marketing approach for a 1937 radio receiver. Instead, let’s get back to the repair itself. As with any vintage radio repair, the set was thoroughly checked before any repairs were attempted. First, the primary and secondary windings of the power transformer were checked with an ohmmeter and were found to be intact. A high voltage leakage test was then conducted using a 500V megohmmeter and this showed that the insulation was also OK. Similarly, continuity checks on the aerial, oscillator and shortwave coils indicated that they were all in working order, as were the 465kHz IF transformers. So far, things were looking good! The next item to be inspected was the loudspeaker. The torn paper cone wasn’t too bad and continuity checks confirmed that the field coil and the output transformer were both intact. According to the owner, the set had always been stored in the house and this has certainly contributed to its excellent condition. A receiver that has spent 20-30 years in a damp shed deteriorates badly and items such as field coils and output transformers A Jensen electrodynamic loudspeaker with a 3kΩ field coil is used in the Airking. Fortunately, both the field coil and the output transformer were in working order. suffer accordingly. New capacitors The set was still fitted with all its original “Channex” paper capacitors. As with any restoration of mine, they were discarded without a second thought and replaced with modern polyester types. Subsequent checks using a high-voltage megohmmet­er revealed that many of the old capacitors were very leaky. The original electrolytics had already been “replaced” but not in the true sense of the word. Instead, some- one had simply connected the new capacitors in parallel with the old electrolyt­ics, a practice that should definitely be avoided. My checks on the original capacitors showed that although they were defunct as far as capacitance was concerned, they were by no means open circuit. As a result, leaving them in circuit leads to unnecessary high tension leakage which, in turn, can overload other components. My approach was to completely remove the old electrolytics from the chassis. As a precaution, I also September 1997  75 The EL3 output valve (centre) is flanked by a power rectifier on each side. The 6X5 (left) is actually used as a diode detector – a most unusual set up! removed the replacement capacitors and installed two new 4.7µF 450V units. Ever since I added the megohm­ meter to my range of test instruments, I make a point of disconnecting any mica capacitors (which usually don’t cause much trouble) and subjecting them to a 1000V leakage test. If they pass the test, they go straight back into service. If they fail, they are replaced from my stock of spares. In this case, they all tested OK. It didn’t take long to sort out the speaker leads at the plug, as not all of the connections had come adrift. The speaker cone was repaired with Silastic® and while these cone patchups are not particularly neat looking, the result is quite an effec­tive repair. Several previously repaired speaker cones have now seen up to 10 years service and the silicone rubber compound is still flexible and is still adhering to the paper. With the speaker repairs completed, a suitable dial pointer was scrounged from my junk box and while it may be slightly short, it certainly looks better than none at all. Another prob­lem with the dial was that one of the dial lamps had burnt a hole through the celluloid dial face. This can be particularly annoy­ ing because the light shines through the hole and attracts atten­tion to it. Not having a spare Airking dial on hand I opted for the easy way out and blackened the dial lamp with a black Texta® pen. In addition, 150mA re- This close-up view clearly shows the side contact valve base. Once inserted into the socket, the valve can only be removed by pulling on the glass envelope and this often loosens the base. 76  Silicon Chip Repairs to the EF5 IF amplifier valve included re-attaching the top cap and reconnecting the metal spray shield to the cathode pin of the valve base. placement lamps were substituted for the 300mA originals, as they operate at much lower temperatures. Valves checks Neither of my valve testers can accommodate side contact valves so there was no way the valves could be tested other than by trying them in circuit. As luck would have it, all but one (an EK2) worked OK. Fortunately, a replacement valve was available from amongst my spares which saved having to do a socket changeo­ver. The EF5 IF amplifier valve required a few repairs, however. It had a loose The octal base with its keyed spigot is shown here. Octal valves give little trouble with socket connections but their big advantage is that they are more readily available than side contact types. EVATCO CHECK OUT OUR BOOKS Valve Amplifiers Theory & practice of valve amplifier design 374pgs Mullard Circuits for Audio Amplifiers Circuits and plans for audio amplifiers 136pgs $59.95 P&P $6 $26.95 P&P $6 Principles of Power $69.95 P&P $8 Guide to valve power amplifier design 368pgs History of the British Radio Valve $39.95 P&P $7 Covers 1904-1940 with data & equivalents 210pgs Principles of Electron Tubes $49.95 P&P $7 Learn the basics of how valves work 398pgs The missing section of the valve socket diagram solved the mystery of the unknown valve type. The receiver originally used an EZ3 power rectifier as a diode detector. TUBES Matching included EL34 Svetlana $24.00 6L6GC Svetlana $30.00 EL34G+ Sovtek $20.00 6L6GC Sovtek $14.00 E34L Tesia $24.00 6550C Svetlana $48.00 12AX7 Sovtek $8.00 5881 Sovtek $19.00 SSAE for CATALOGUE ELECTRONIC VALVE AND TUBE COMPANY PO Box 381 Chadstone Centre Vic 3148 Tel/Fax: (03) 9571 1160 Mobile: 0411 856 171 Email: evatco<at>werple.net.au Silicon Chip Binders REAL VALUE AT $11.95 PLUS P &P The Airking’s two shortwave coils are wound on a common former. Because of the valve line-up, the shortwave reception is poor. top cap and the wire that connects to the metal-spray shield had detached itself. The valve was repaired by re­solder­ing the top cap and gluing it firmly to the glass (using Super Glue®). The shield was reconnected by binding the base of the metal-spray with fine fuse wire and soldering it to the cathode wire that protrudes from the top of the valve base. As a matter of interest, the original valve types were as follows: EK2 frequency changer, EF5 IF amplifier, EZ3 detector, EL3 audio output and EZ3 power rectifier. Note that the detector provides no automatic gain control function and that the volume control (a 3kΩ wirewound pot) is placed in the cathode circuit of the two radio frequency valves. So it was all a relatively straight­ forward repair. The 5-valve cum 3-valve Airking works reasonably well on the broadcast band but shortwave reception is only mediocre. Considering the valve line-up, that’s not surprising! The logical thing to do would be to replace that 6X5 with a duo diode triode but as the repair had already gone over budget, the set was left as SC it was originally designed. ★  Heavy board covers with 2-tone green vinyl covering ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A11.95 plus $3 p&p each (NZ $6 p&p). Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. September 1997  77 PRODUCT SHOWCASE Butane powered 120W soldering iron Butane powered soldering irons have been available for quite a few years now and they are very handy for all sorts of jobs where a mains-powered soldering iron cannot be used. As good as they are, butane-powered irons have not been a proposition where high power is required, that is, until now. Altronics Distributors now have the Iroda Pro-120 butane iron which is claimed to be equivalent to a 120-watt iron. This has all the convenience features of a normal butane iron, such as quick heating, no power cords, light weight and best of all, it comes with a blow torch tip. This enables it to do all sorts of jobs that just aren’t possible SOUND EASY V2,BOXCAD V2 BY BODZIO SOFTWARE Comprehensive s/design software available distributed by WAR AUDIO Windows interface.SVGA. Box modelling , 7 type enclosures, 10 alignments for box optimizer, Box time response, Room placement, Import Clio, Lms, Imp, Mlissa etc, Crossover modelling , Optimizing , D’APPOLITO modelling and much more. BOX CAD includes complex impedence and electrical modelling and more. $350.00 upgrades from $60.00. Clio Professional electro-acoustic measurement system $1650.00 Frequency Response • Electrical & Acoustical Phase • FFT Analysis • THD • Anechoic Transfer Function • MLS Analysis • Impulse Response • ETC • Waterfall • Impedance THD+Noise 0.015% • T/S Parameters • 1/3 Octave RTA • Signal Generator / Level Meter • Oscilloscope • SPL • dBV • Volt Amplitude • LC Meter • 16-Bit D/A • Freq. Range 1Hz22kHz ±1dB • Freq. Accuracy > 0.01% • WAR AUDIO U203/396 Scarb Bch Rd Osborne Park W.A. 6017 Ph 09-2425538 F 09-4452579 ACUTTON, AXON, FOCAL, RAVEN LUMINOUS, NEW, CABASSE, 78  Silicon Chip with a normal 120W iron. The unit is a good size, being 240mm long and about 25mm in diameter. It weighs just 200g with the tank full. Some of these irons are a little tricky to light as they come with a lid mounted flint strike so lighting is a two-handed job. The Iroda iron is much easier; the handle has a built-in piezoelectric thumb starter for easy ignition. You just push it forward with your thumb and the iron is ready within 15 seconds. Pull the starter backwards and the iron is off. The heat control is just below the starter so you have one-hand control for igni­tion and temperature. The iron comes with a 2mm chisel tip which is a bit small for some work but it can be changed for a larger tip, depending on the job to be done. The gas tank gives up to four hours opera­tion and can be refilled using a standard butane refill canister. Normally retailing for $129, the Iroda Pro-120 (Altronics Cat. T-2600) 1GHz 8-digit frequency counter Frequency counters have certainly become cheaper over the years, to the point where it is no longer worthwhile building one from a kit. This nicely made instrument has an 8-digit 7-segment display and is housed in a steel case finished in grey enamel. It is rated for operation up to 1GHz and features high sensitivity. On the front panel it has two BNC sockets, one to cover the range up to 100MHz and the other, involving a prescaler, covering 80MHz to 1GHz. Ten pushbutton switches provide the is available at an introductory price of $99.00 for the month of September and this includes a roll of solder and a butane refill. Spare chisel and torch tips are available for $15.95 each. The iron comes with a 12-month warranty, not includ­ing the tips. The Iroda Pro-120 is available from Altronics, 174 Roe St, Perth, WA 6000. Phone 1 800 999 007. controls. Apart from the power switch and input attenuator switch, there are three buttons for range selection and four for the gating time. Interestingly, there is also a hold control which is not a usual feature on a frequency counter. It apparently interrupts the display update circuit so that you can read a frequency, hit the hold button and then disconnect. You can then take note of the reading at your leisure. This could be very convenient in some measurement situations. Other features include LEDs for overrange and kHz or MHz indication. Frequency resolution depends on the range and gating time. For example, with the 1GHz range and 10-second gating, the resolution is 100Hz. On the 10MHz range, with 10-second gating, the resolution is 0.1Hz, dropping to 1Hz resolution if one-second gating is selected. We found it an easy instrument to use and we do like the hold feature. It is available from all Jaycar Electronics stores (Cat QT-2330) and is priced at $299.50. Handheld Gauss/Tesla meter uses Hall effect probe F. W. Bell’s model 5080 Gauss/Tesla will measure up to 30kG (kilogauss) with a basic accuracy of 1%. Key features include auto zero, peak hold, max/min hold, auto range and relative mode. Gauss or Tesla readings can be selected. The 5080 is the top of three models and it also can give readings in ampere/metres and features an analog output (±3V) and an RS-232 port for down­loading data to a PC. Built-in software makes calibration simple with user prompts on the liquid crystal display. The bottom-of-therange model 5060 is a DC measurement unit (ie, not AC fields). It has a basic accuracy of 4% and two ranges of 2kG and 20kG. The models 5070 and 5080 are better, at 2% and 1%, respectively. Frequency band­width of the 5070 is DC to 10kHz while the 5080 is DC to 20kHz. The 5070 has ranges of 200G, 2kG and 20kG, while the 5080 has 300G, 3kG and 30kG. Priced from under $1000, all three models come equipped with a detachable transverse probe, zero gauss chamber, instruc­tion manual, hard carrying case and two 9V batteries. Axial and other style probes are options, as well as extension cables and AC mains adaptors. For further information, contact Independent Distribution SC Network on (02) 9524 0684 or fax (02) 9524 0679. SILICON CHIP This advertisment is out of date and has been removed to prevent confusion. Please feel free to visit the advertiser's website at: www.telstra.com.au September 1997  79 Addressable card for controlling two stepper motors Based closely on the design published last month, this new interface card allows you to control two stepper motors via your PC. It plugs into the PC’s parallel port and you can connect up to eight units in daisy-chain fashion. By RICK WALTERS We envisage that this new design will be suitable for those who wish two drive two stepper motors to achieve 2-axis control. The new card is capable of independently driving each stepper motor in either forward or reverse direction, or it can drive just one stepper motor at a time. When a motor is not stepping, its driver transistors can be turned off to prevent the motor from overheating. 80  Silicon Chip As with last month’s design, the card is set with a unique address from 1-8 so that it can be individually selected and two or more cards can be coded with the same address in a master-slave setup. In operation, an address from 0-7 is placed on three pins of the PC port connector then the strobe line is toggled. This latches the address in a decoder. If this is the address selected by a jumper on the card, the logic level present on the port’s normal data lines is latched (stored) and fed to the motor driv­ers. Circuit details Refer now to Fig.1 for the circuit details. The decoding and latching circuitry is identical to that published last month but, for those who missed that article, we’ll recap the details. IC1, a 74HC137 one-of-eight active low decoder, is used as the address latch. This IC looks at the BCD address Fig.1 (right): when the correct address is fed into IC1, the data on the Port A lines is latched into IC2 and appears at its Q outputs. These outputs then drive transistors Q1-Q24 to control the stepper motors. September 1997  81 8 & 9 of IC3c are pulled high via a 10MΩ resistor and so pin 10 is low and LED1 is off. When a valid address is received, pins 8 & 9 of IC3c are pulled low via D1 (since the decoded output from IC1 goes low). As a result, pin 10 of IC3c switches high and LED1 lights to show that the card has been selected. The 0.1µF capacitor connected from pins 8 & 9 of IC3c to ground ensures that the LED remains on for at least one second. Motor drivers Transistors Q1-Q24 make up four H-bridge circuits which drive the stepper motor coils. These circuits are identical, so we will only describe the circuit based on tran­sistors Q1-Q6. This top circuit is driven from the Q0 & Q1 outputs of IC2. Let’s first consider the situation when Q0 is high and Q1 is low. In that case, transistor Q5 will turn on and this will also turn on transistors Q1 and Q4. As a result, current now flows from the positive supply rail and through transistor Q1, coil M1A and transistor Q4 to ground. Conversely, when output Q1 is high and Q0 is low, transis­tors Q6, Q2 and Q3 turn on and the current flows through coil M1A in the opposite direction. If both the Q0 and Q1 outputs are low, all transistors are off and no current flows. Therefore, depending on the logic levels on the Q0-Q7 out­puts, we can control the direction of the current pulses through the coils and thus the stepping direction of each motor. To actually step a motor, it is necessary to switch the current through its coils in a logical sequence. Table 3 lists the different driving modes and shows the binary code required at IC2’s output. This code is, of course, identical to that required at D0-D7 (Port A) of CON1. The decimal value is also shown in Table 3 and this can be used in a Basic program to apply Fig.2: exercise care when installing the power transistors on the PC board. You must use the correct type at each location and it must be correctly oriented. data on its A, B & C inputs and pulls the corresponding decimal output (Y0-Y7) low. However, this can only happen when the strobe line from inverter stage IC3b goes high and momentarily pulls the latch enable (LE) input of IC1 high via the series .001µF capacitor. As a result, the card will be addressed if the decoded output is selected by the address link. In that case, the decoded low will be fed to pin 2 of IC3a and to the cathode of D1. At the same time, the high strobe signal is inverted by IC3d and so pin 1 of IC3a goes high and momentarily pulls the LE input (pin 11) of IC2 high via a second .001µF capacitor. IC2 is a 74HC573 8-bit data latch. When its LE input is taken high, it latches the data present on its D0D7 inputs as fed in via Port A of the parallel port. This data is transferred through to IC2’s Q outputs and is used to control the stepper motors via transistor H-bridge driver circuits. The LE signal then goes low 47ms later (as set by the 47kΩ pull-down resistor), so that the data remains latched until the arrival of the next strobe signal. D1, IC3c and LED1 form the card selected indicator. Normally, pins Table 1: Resistor Colour Codes ❏ No. ❏  1 ❏  1 ❏  9 ❏  8 ❏  1 82  Silicon Chip Value 10MΩ 47kΩ 10kΩ 2.2kΩ 470Ω 4-Band Code (1%) brown black blue brown yellow violet orange brown brown black orange brown red red red brown yellow violet brown brown 5-Band Code (1%) brown black black green brown yellow violet black red brown brown black black red brown red red black brown brown yellow violet black black brown Parts List 1 PC board, code 07208971, 120 x 112mm 1 D25 PC-mount male rightangle connector 2 stepper motors, Oatley Electronics M35 or equivalent 1 8-way x 2-pin header strip (2.54mm pitch) 1 jumper for header strip 1 3 way terminal block (5.08mm pitch) 8 PC stakes This view clearly shows how the power transistors are fitted to the heatsink. Note that each transistor must be isolated from the heatsink using a TO-220 insulating washer. Semiconductors 1 74HC137 decoder (IC1) 1 74HC573 8-bit latch (IC2) 1 74HC02 quad NOR gate (IC3) 8 BD682 PNP Darlington transistors (Q1,Q2,Q11Q14,Q23,Q24) 8 BD679, BD681 NPN Darlington transistors (Q3,Q4, Q9,Q10,Q15,Q16,Q21,Q22) 8 BC548 NPN transistors (Q5,Q6,Q7,Q8,Q17-Q20) 1 5mm red LED (LED1) 1 1N914 small signal diode (D1) Capacitors 2 100µF 25WV PC electrolytic 2 0.1µF monolithic ceramic 1 0.1µF MKT 2 .001µF MKT Resistors (0.25W, 1%) 1 10MΩ 8 2.2kΩ 1 47kΩ 1 470Ω 9 10kΩ Heatsink parts (optional) 1 aluminium bar, 110 x 6 x 3mm 16 TO-220 insulating washers 8 3mm x 15mm bolts 8 3mm nuts 16 3mm flat washers Fig.3: this diagram shows the drilling details for the aluminium heatsink. the correct bit pattern to the parallel port. Almost all motors can be powered from the 12V supply, including centre-tapped 5V motors (as we don’t use the CT). If you want more torque and a faster stepping speed, you can run the motors from a higher voltage but you should add a resistor in series with each coil to keep the motor current within specifica­tion. PC board assembly Fig.2 shows the parts layout on the PC board (code 07208971). As usual, check your etched PC board against the full-size pattern shown in Fig.4 before installing any of the parts. Once this has been done, begin the assembly be installing PC stakes at the eight external wiring pints, then install the wire links (11), the resistors and the diode (D1). The ICs (or IC sockets if you use them) can go in next, followed by the capacitors, address jumper, the LED and the D connector. Take care with the LED polarity – its anode lead will Miscellaneous Tinned copper wire for links be the longer of the two. In addition, the cathode lead is adjacent to a flat section on the bevel at the bottom of the plastic body. The eight BC548 transistors can now be installed, followed by the 16 power transistors. Note that it is advisable to bolt the power transistors to a common heatsink if you intend driving high-current stepper motors for long periods. The heatsink September 1997  83 Listing 1 10 REM Step both motors clockwise 20 PORTA = &H378 ‘This is for LPT1 Use &H278 for LPT2 30 PORTC = PORTA + 2 ‘and card 1 selected 40 DATA 85, 102, 170, 153, 170, 102, 85, 153 50 FOR A = 1 TO 4: READ ROTCW(A): NEXT ‘Read data for clockwise steps 60 FOR A = 1 TO 4: READ ROTCCW(A): NEXT ‘Read data for anticlock steps 70 OUT PORTA,85: OUT PORTC,11 ‘Set motor to known position 80 FOR A = 1 TO 12 ‘Go forward 12 steps of 30 degrees 90 FOR B = 1 TO 4: OUT PORTA,ROTCW(B) ‘Four steps of 7.5 degrees 100 OUT PORTC,11: OUT PORTC,10 ‘Select card one, then take strobe low 110 FOR C = 1 TO 350: NEXT ‘Delay to allow motor to step 120 NEXT B: NEXT A 130 OUT PORTA,0: OUT PORTC,11: OUT PORTC,10 ‘De-energise motor coils 140 FOR A = 1 TO 20000: NEXT ‘Pause for a while 150 REM Now step motor anticlockwise 160 FOR A = 1 TO 12 ‘Go backwards 12 steps of 30 degrees 170 FOR B = 1 TO 4: OUT PORTA,ROTCCW(B) ‘Four steps of 7.5 de­grees 180 OUT PORTC,11: OUT PORTC,10 ‘Select card one, then take strobe low 190 FOR C = 1 TO 350: NEXT ‘Delay to allow motor to step 200 NEXT B: NEXT A 210 OUT PORTA,0: OUT PORTC,11: OUT PORTC,10 ‘De-energise motor coils fitted to the prototype was cut from square-section (6 x 12mm) aluminium rod and is 110mm long. Fig.3 shows the drilling details for the heatsink. The best procedure is to first loosely attach the transistors to the heatsink and then mount the entire assembly on the PC board. Be sure to use insulating washers to isolate the metal faces of the transistors from the heatsink. The BD682 PNP transistors are all mounted on one side of the heatsink, while the BD679 NPN types are all mounted on the opposite side. Once the assembly is in position, solder one lead at either end, then tighten all the mounting bolts. The assembly can then be adjusted so that it sits parallel to the PC board and the remaining leads soldered. Finally, complete the assembly by fitting the 8-way pin header, the DB25 connector and the 3-way terminal block. Testing the board To test the board, first connect it to the computer via a standard printer cable. You will also need a power supply capable of supplying 5V at a few milliamps plus a 12V supply capable of powering the two stepper motors (probably around 2A capacity). If necessary, you can obtain the 5V supply from the games port on the computer (provided it has one). Pin 5 on the 9-pin “D” connector is the +5V rail, while pins 4, 5 & 12 are ground. If you only have one card, the address jumper should be fitted to the C1 position. That way, you won’t have to alter the program shown in Listing 1 in order to address the card. Now load Basic and enter the program shown in Listing 1. The line numbers can be omitted if you are using Qbasic. You can also omit the remarks (after the ‘), as they are only Table 2 Fig.4: here is the full-size etching pattern for the PC board. 84  Silicon Chip Card No. Address Card 1 11 Card 2   9 Card 3 15 Card 4 13 Card 5   3 Card 6   1 Card 7   7 Card 8   5 Table 3: Stepper Motor Sequences Full Step - One Winding Energised Step No. Polarity Q0 Q1 Polarity Q2 Q3 Polarity Q4 Q5 Polarity Q6 Q7 Step 1 M1A+ 1 0 M1B0 0 0 M2A+ 1 0 M2B0 0 0 Decimal 17 Step 2 M1A0 0 0 M1B+ 1 0 M2A0 0 0 M2B+ 1 0 68 Step 3 M1A- 0 1 M1B0 0 0 M2A- 0 1 M2B0 0 0 34 Step 4 M1A0 0 0 M1B- 0 1 M2A0 0 0 M2B- 0 1 136 Q0 Q1 Polarity Decimal Full Step - Both Windings Energised Step No. Polarity Q2 Q3 Polarity Q4 Q5 Polarity Q6 Q7 Step 1 M1A+ 1 0 M1B+ 1 0 M2A+ 1 0 M2B+ 1 0 85 Step 2 M1A- 0 1 M1B+ 1 0 M2A- 0 1 M2B+ 1 0 102 Step 3 M1A- 0 1 M1B- 0 1 M2A- 0 1 M2B- 0 1 170 Step 4 M1A+ 1 0 M1B- 0 1 M2A+ 1 0 M2B- 0 1 153 Q0 1 Q1 0 Polarity M1B0 Q2 0 Q3 0 Polarity M2A+ Q4 1 Q5 0 Polarity M2B0 Q6 0 Q7 0 Decimal 17 1 0 M1B+ 1 0 M2A+ 1 0 M2B+ 1 0 85 Half Step - Windings Turned On & Off Step No. Polarity Step 1 M1A+ Step 2 M1A+ Step 3 M1A0 0 0 M1B+ 1 0 M2A0 0 0 M2B+ 1 0 68 Step 4 M1A- 0 1 M1B+ 1 0 M2A- 0 1 M2B+ 1 0 102 Step 5 M1A- 0 1 M1B0 0 0 M2A- 0 1 M2B0 0 0 34 Step 6 M1A- 0 1 M1B- 0 1 M2A- 0 1 M2B- 0 1 170 Step 7 M1A0 0 0 M1B- 0 1 M2A0 0 0 M2B- 0 1 136 Step 8 M1A+ 1 0 M1B- 0 1 M2A+ 1 0 M2B- 0 1 153 there to give you an idea of what the software is doing and play no part in the program operation. When you run this program, the motors should both rotate clockwise one revolution, stop briefly and then step anticlockwise to their original positions. In addition, the “selected” LED should light to confirm that the card has been addressed. Note that the values shown in Listing 1 are for a single full step with both stepper windings energised. As an experiment, try loading the “one winding energised” values into the program and check the torque difference. If you use LPT2 as the parallel port (instead of LPT1), you will have to change line 20 (ie, change &H378 to &H278). The address value for each card from 1-8 is given in Table 2. The illogical sequence of the numbers is due to the fact that both C1 and C3 on PortC are inverted logic; ie, if they are programmed high in Basic (or any other language), they will actually go low. If the stepper motors you use are different to those speci­fied in the parts list, your results may not be the same as ours. If the motor runs in the wrong direction, just swap one pair of motor leads on the PC stakes. The stepper motors we used have 7.5° steps and if yours are different (eg, if they have 1.8° steps), you will have to change the number 12 in lines 80 and 160 to get a complete revolution. For example, if the motor has 1.8° steps, you would have to change the number 12 to 50. Fault finding The stepper motors used with the prototype card were M35s from Oatley Electronics. If you strike problems, first check that the address jumper is set for card 1 (C1). If so, check that LED1 lights when you run the program. If the LED doesn’t light, connects pins 4 & 16 of IC1 together and rerun the program. If the LED now lights, check IC3b and the components between IC3b and pin 4 of IC1. The same technique can be used to test the circuitry that drives the LE input of IC2 (ie, connect pin SC 11 to pin 20). September 1997  85 SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. 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. Pink noise source is weak I recently built the Sound Level Meter featured in the December 1996 issue and the Pink Noise Source in the January 1997 issue of SILICON CHIP. When I measured the output of the Pink Noise Source it was changing between 120-150mV on the 0dB set­ting. I have also endeavoured to measure the -60dB setting but have been unable to find a meter or scope sensitive enough. I’ve checked all the components and they all seem to be alright out of circuit. I tried to calibrate the Sound Level Meter but was unsuc­cessful due to the fact that when I went to adjust VR1 (after adjusting VR2 to give an output of 1V) after switching the Pink Noise Source to the -60dB setting, it was 200mV over (600mV) and no adjustment of VR1 would bring my multi­meter to read 400mV. I tried to calibrate the meter more than once without success. The Pink Noise Source has an output when plugged into an amplifier. Please help. (G. C., Warworth, NZ). •  The output level from your Pink Noise Source is clearly too high. It Can a VGA monitor display PAL video? At long last I have got around to doing something which has been on my mind for a long time, that is to thank you most profu­sely for an informative and entertaining magazine. I most enjoy the “Serviceman’s Log” segment and the various projects even if I never build most of them. In the past I only bought those issues in which there was something of particular interest and some issues would be missed altogether because of the way I move around the country. I should be about 60mV, whereas your unit gives 120-150mV. First, check all your components for correct placement and value. If all are correct, you may have a particularly noisy transistor (Q1) which could be replaced to reduce the noise level. As a final resort, the level can be reduced by changing the value of the feedback resistor between pins 6 and 7 of IC1b from 100kΩ to 47kΩ. The -60dB level can be assumed to be correct due to the divider action of the 100kΩ and 100Ω resistors. Since the -60dB level is equivalent to only 60µV you would need a very sensitive AC millivoltmeter to measure it. Most audio THD (total harmonic distortion) test sets could measure it, as could the AC milli­voltmeter featured in the August & September 1988 issues of SILICON CHIP. This instrument has a noise floor of less than one microvolt. Proximity detector burns out resistor I have built the ultrasonic proximity detector featured in your publication “Electronic Projects for Cars”. My problem is that the project is not working and the 10Ω resistor gets hot to the have now taken out a subscription so I won’t miss any of it. I also have a question: is it possible to use a computer monitor, EGA or VGA, as a dedicated monitor for a VCR? If so, what additions or modifications are needed? (G. M., Clare, SA). •  EGA and VGA monitors are not suitable for normal video use since their horizontal timebase frequencies are so much higher than for PAL video. It is possible to obtain a video card for your PC so that you can display PAL video on a VGA monitor but that is an extra level of complication. point of smoking. This project was build from purchased components as per instruction. I then purchased a complete kit and I had the same problem. Can you help? (P. T., Glen Wav­erley, Vic). •  The fact that the 10Ω resistor is becoming overheated sug­ gests that either there is a short circuit across the supply or one of the semiconductors or electrolytic capacitors is connected around the wrong way. We suggest that the most likely offender is D3, the 16V zener diode. You do need a multimeter to check the voltages on the PC board. In this way you should be able to locate where the fault lies. Dolby Surround decoder I have a number of problems with the Dolby Pro-Logic Decod­ e r described in the December 1995 and January 1996 issues. The first problem is that the effects pot (in the effects mode) does work but the surround (L-R) signal is very much attenuated and exhibits some degree of distortion. I also note that the volume level in the L and R channels is also significantly reduced compared to normal line level and when the main amplifier volume is increased to balance the centre channel, much hiss and some hum can be heard from the main L and R channels. With the unit set to Pro-Logic mode, the surround channel level is greater than in the effects mode but exhibits a heavy breathing-like effect. I should not have heard anything from the surround channel at this stage as I was not using a Pro-Logic source. I also noticed that the L & R channels were greatly attenuated and lacking frequency reproduction from approximately 800Hz and up. The second problem involves the use of the noise sequencer. In the effects mode, when the noise button is pressed, the noise signal is sent to the September 1997  91 Fan speed control I recently discovered that I had two burnt out resistors in the air conditioning fan speed control of my Corona wagon. As they are situated within the air conditioning system and not readily accessible, and are very expensive to replace, I decided to investigate the possibility of replacing them with an electronic control system. Whilst obtaining some transistor data I came across your June 1997 issue with the DC motor speed control circuit and it appears to be ideal for the situation. However, I would prefer to retain the existing control switch rather than use a potentiometer. The existing fan heater shows a relay and rotary switch tapping the speed control resis­tor. With the switch on Hi, the fan is at maximum speed, a condi­ tion which left channel, then the centre, then the right, and finally the surround before repeating itself. No problem there. However, when this noise signal is sent to the L and R channels, it can also be heard in the centre and surround channels at the same time. When the unit is set to the Pro Logic mode, the noise sent to the L channel is heard in the L and R channels; the noise sent to the centre is heard is heard in the L, R and cen­tre; the noise sent to the R channel is heard in the L and R; and the noise sent to the surround is heard only in the surround channel. In either mode, it appears that the volume of the noise in the L and R channels is significantly lower than in the centre only and surround only channels. Your comments please? (C. C., Leeming, WA). •  Firstly, the surround channel will give an output regardless of whether the signal source is encoded with Dolby Pro-Logic or not. It will not, however, give a true surround sound unless recorded with the Pro-Logic encoding. The noise sequencer will give a signal in the surround and centre channels when only left and right 92  Silicon Chip cannot be obtained through the Mosfets. I have endeavoured to design a circuit to enable this to be done using your speed control. I have used the car switch to progressively parallel resistors to reduce the voltage to IC1. To use this it would be necessary to invert the input voltage to motor voltage relationship in ICI. I have assumed that exchanging the inputs to error amp 1 would achieve this. If this is not feasible would you please assist me in suggesting an alternative circuit? The maximum fan current is 10 amps. (L. H., Birmingham Gardens, NSW). •  Without knowing the exact mechanism of your fan switch, it should be possible to use it to control the Speed Controller by using it to switch resistors in parallel with the 4.7kΩ resistor to ground, ie, the resistor at the junction of the 18kΩ and 47kΩ resistor. noise channels are selected. This is because the left and right channels now include the surround and centre signals. This selection is supposed to be used for a 2-channel (left and right) loudspeaker setup. If the left and right channels do not produce signals above about 800Hz, then this would be the cause of the low output level. Check the values of the resistors and capacitors across IC4a and IC4c. The effects output may be distorted and low in volume be­cause of an incorrect component in the signal path from the S’ output of IC1 to the low pass input at pin 47 of IC1. This signal path includes the delay (IC2) and associated components. Finally, the switch wiring to S2 may be wrong, thus causing incorrect signal selection. Substituting the TL064 I particularly want to build the Audio Mixer for Camcorders described in the March 1993 issue of SILICON CHIP. Unfortunately, the kit is no longer available in this state and worse still, neither is the TL064 quad op amp. Could you please advise a suitable substitute for this IC? (J. M., Aldinga Beach, SA). •  We do not believe this chip is obsolete. For example, it is listed in the current Altronics catalog; Cat. Z-2864 <at> $2.50. As an alternative, you can use the TL074 which is a direct equival­ ent although it will result in a slightly higher overall current drain. Using the Discolight on low voltage I am a secondary school teacher and one of my students wishes to build a version of the Discolight (July & August 1988) as a project. The catch is that students are not allowed to build projects which involve 240VAC mains wiring. Is it possible to modify the project so that we could use 12V quartz iodide lamps running from 12V DC? (D. C., Men­tone, Vic). •  It is not possible to use the Discolight to control lamps running from pure DC but it should present no problems running your 12V lamps from 12VAC. However, you will need a big power transformer if you are to maximise the number of lamps to be controlled. Each Triac could control up to 10 amps so the four channels in total could control up to 40 amps or 480 watts. If you were to use 12V 20W halogen lamps, you could control up to 6 lamps per channel. Heavy power cables will be required to mini­mise voltage losses. As we have noted in these pages previously, if you vary the filament voltage of 12V halogen lamps you will markedly reduce their life although that may not be important in this applica­tion. Video distribution amplifier wanted I am interested in the stereo preamplifier with selectable gain, as described in the April 1994 issue of SILICON CHIP and also featured in the Circuit Notebook pages of the June 1996 issue. I would like to use this for a video distribution amplifi­er with one input and four outputs. At the moment I am trying to put two PC boards together to make one mono input and four mono outputs for audio distribution. Can you help me with alterations to this board for audio and possibly video? (P. M., Auckland, NZ). •  We cannot recommend the LM833 Speed control for fish tank pump I have a friend living on a property with a home electrici­ty supply. He has had the system in operation for about 17 years. It was built before commercial systems were available and is decidedly home-made. Amongst other voltages available in his system, he has a 32V DC supply from 16 lead-acid accumulators and from this he runs an electric air pump to supply air to his tropical fish. Due to the number of fish and the number of tanks he has he could not find a commercial pump to suit, so he has a home-made pump run by an aircraft electric motor which he runs from half the 32V bat­tery supply; ie, at 16V. He then alternates for video signals because its bandwidth is inadequate for this application. Instead, you will need a wideband op amp or discrete amplifier which can handle a bandwidth of at least 5MHz. The LM833 will easily handle the audio side of things and just one circuit will be able to drive four outputs, each with its own 100Ω series resistor and 0.33µF coupling capacitor. Fixing hum from DC plugpacks Have you any articles from previous editions of SILICON CHIP on how to deal with the problem of hum from DC plugpacks? So far, I have tried shielding (the earth) and connecting a 10µF capacitor across the output. No luck. (T. F., Malanda, Qld). •  Hum in DC plugpacks can be a very difficult problem to solve, depending on the application. The most effective approach is to use a 3-terminal regulator circuit to follow the plug­pack and this will certainly bring the ripple down to a very low value. We published a suitable circuit and a small PC board in an article entitled “The Eliminator” in the May 1992 issue of SILI­CON CHIP. The PC board can be installed in a small plastic utili­ty case which can then be glued to the back of your DC plugpack. the half bank manual­ly until both halves need charging, as near as he can estimate. This pump runs 24 hours a day and 365 days each year and has done for a few years now. It only stops when the rubber diaphragm tears and he switches to an identical standby pump until repairs are made. Now the point of this letter is would the motor speed con­ trol described in the June 1997 issue work on the 32V supply (probably 38V when charging) and be able to supply 15V to the motor? It should be well able to supply the current because he thinks it only draws a few amperes but the higher voltage is the concern. I suppose it would require the voltage divider supplying A1+ and the voltage divider supplying A1- to be altered. I see that In some situations though, the hum problem may be caused by a lack of earthing in the circuit being powered. This is impossi­ble to solve unless the DC plugpack concerned has an Earth pin on the plug section and a corresponding earth output connection. Such plugpacks are very rare. NTSC to PAL video conversion I have a faint recollection of seeing a project which will convert NTSC signals to PAL signals. I have a VHS PAL hifi stereo VCR. I would like to play VHS-NTSC format tapes in it and the BUK456-60 can stand 60V from drain to source but does this simplistic view cover all the difficulties? (R. B., Seymour, Vic). •  We can see no real problems with your application. The only thing that could worry the Mosfets is noise spikes from the charger. These are hardly likely to exceed 60V but if you are concerned, an iron cored choke and an electrolytic capacitor on the input to the speed control would remove the threat. There is no need to alter any other components, although you should check the temperature of the voltage regulator tab (REG1), as it may possibly need a small heatsink at this higher voltage. If the motor only draws a couple of amperes then you will only need one Mosfet. watch on my PAL TV. Do you have a project that will do this? If so, which edition of your magazine was it in and what was the esti­mated cost? (D. H., Melbourne, Vic). •  We described an NTSC-to-PAL converter in the April 1997 issue of SILICON CHIP. However it is of no use with your VHS VCR. If you want to play NTSC tapes, the only way to do it is with an NTSC VCR. You could then use our NTSC-to-PAL converter to watch the resulting video signal on a PAL TV. A better ap­proach would be to purchase a dual-standard VCR which could play both sorts of tapes SC and feed them to a PAL TV. Notes & Errata Remote Controlled Gates For Your Home, August 1997: the relay wiring to both motors M1 and M2 on the circuit diagram (page 69, August 1997) is incorrect. The diagram at right shows the corrected relay wiring for motor M2. Motor M1, which is driven by relays RLY1 and RLY2, should be wired in exactly the same fashion as shown here. The parts layout diagram shown on page 70 of the August 1997 issue is correct. September 1997  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE 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): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. C COMPILERS: Ever ything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140.00 for the set. Debug monitors: $70 for 6 CPUs. All compilers inc ‘HC12, XASMs and monitors: $480. 8051/52 or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75. Try the new C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo disk: FREE. All prices + $5 p&p. GRAN­ TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Internet: http://www. mpx.com.au/~lgrant To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 9979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________  Bankcard    Visa Card    Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my Signature­­­­­­­­­­­­__________________________  Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip I/O CARD FOR APPLE II/e: (8 Digital and 1 Analogue I/O). Instruc­tions and applications $40. Magazine Binders (15) 4 Blue and 11 Brown, in good condition $75. 014 075819 or (02) 9896 0838 AH. MICROCRAFT IS NOW ON THE WEB: Dunfield (DDS) products are now available ex-stock at a new low price; please ask for our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent registered mail • Call Bob for more de­ t ails. MICRO­CRAFT, PO Box 514, Concord NSW 2137. Phone (02) 9744 5440 or fax (02) 9744 9280. http://www.micro.com.au email sales<at>micro.com.au 9TH BIRTHDAY SPECIALS !!!!!!!!! PCB VIDEO CAMERA MODULES $69 with Board or Pinhole Japanese Optical Glass (no plastic) Lenses. HOME CCTV INTERFACE PACKAGE See & Listen on all TVs & Record on all VCRs connected to TV antenna system, Commercial 400 Line C Mount Camera with In-built Microphone/Pre Amp, Lens, Mounting Bracket, 20m Plug In Cable and Modulator Mixer Module (see p74 EA July) LIMITED QUANTITY! Only! $199. 12-15 VDC Monitor with Reg DC O/P, PCB module & 100' Cable Only! $199. Tiny Cameras in Lightweight Cases Only! $137. 12VDC Video Monitors Only! $99. WIRELESS Tx or Rx Modules Only! $29. PCB Audio Modules from $20. INFRARED ILLUMINATORS PCB, HOUSING & 50 LED Kit Only! $29. 10cm x 10cm PCB & 180 LED Kit $119. Complete 240vac Lamp $149. A REAL DUMMY CAMERA! Real Case, Lens & Bracket, may be converted to a REAL CAMERA Only! $69. 3200 millicandela Super Bright Red LEDs from 50 cents. Flashing Red, Green, Yellow, Orange LEDs $1. PCB Camera Modules 420/460 Line 0.05 lux $144/$177. DIGITAL SIGNAL PROCESSING 470 TVL COLOUR CAMERAS from $499 28 x 28mm PCB Modules THE TINIEST! HIGH RESOLUTION 570 TVL External Hor & Vert Sync CAMERAS Only! $299. Dome Ceiling Cameras $197. Colour Modules & Cameras $449. Quad Screen Processors from $410. Colour Quads 512 x 512 Only! $999. 74mW Infra Red LEDs from 48 cents! BEFORE YOU BUY! Ask for our Detailed, Illustrated Price List & Application Notes. Also available CCTV Technical, Design, & Reference Manual. Prices include tax. Discounts available! Allthings Sales & Services 08 9349 9413 fax 08 9344 5905. MicroZed have 8-pin 6 I/O 12C508 at $3.66 ea. 1 off price quartz window version $24.40. HOMEMADE GENERATORS: how to instructions. Eight pages free text and colour photos on the Internet at: http://www.onekw.co.nz/ A SIMPLE PIC84 PROGRAMMER: LED model 6 lights $70, LCD model 16 x 1 char. $80, pp $5. Others available. EST Electronics (02) 9789 3616. Fax (02) 9718 4762. MicroZed Computers BASIC STAMPS & PIC Tools With third party supporting products, all in stock. Easy to learn, easy to use sophisticated CPU based controllers. PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 72 2777 – may time out to Mobile 014 036775 Fax (067) 72 8987 http://www.microzed.com.au/~microzed Credit cards OK. Send two 45c stamps for info WEBSITE WITH FREE CIRCUITS http://www.airborn.com.au Also: Programmers for 89C2051 and 89C51: $188 Eval. Kit: $233 Romem: Free! (02) 9925 0325 ELECTRONICS AirBorn MicroZed new Web page address: http://www.microzed.com.au/~microzed DATAMAN EPROM PROGRAMMERS: Dataman S4 world’s leading handheld programmer/ROM emulator, onscreen editor, over 1500 device types including EPROMS/EEPROM/Flash up to 8Mbits. Dataman-48 up to 4-pin DIL. Adapters for PLCC, etc. DOS/Win software, free updates. Call or email for details. DIGITAL GRAPHICS P/L. Phone (02) 9888 3105 dgriffo<at>ozemail.com.au http://www.ozemail.com.au/~dgriffo SATELLITE EQUIPMENT: mesh antenna, 2.3 metre (7 foot 6 inch) in carton by Superior Antenna in USA, $600 LNBF 25K, $100 and Echostar low threshold LT-830 receiver $300 several sets or split. Phone 9484 3847 (Business Hours). COMPONENT STORAGE RACKS: accommodate components such as ICs, trimpots, TO-220s, etc., whilst still in their anti-static tubes. Features: compact size, anti-static protection until ready to use, stackable side to side or top to bottom, capacity of 2880 40-pin ICs to 18,000 8-pin ICs, solid construction, index­ i ng matrix provided, anti-static tubes supplied if required. V.E.E. SYS. Ph/Fax (03) 5342 0510. PCBs MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Electronics, Ph/Fax (02) 9554 9760. sesame<at>nettrade.com.au 68HC11 & 68HC05 DEVELOPMENT SYSTEMS: Oztechnics, PO Box 38, Illawong, NSW 2234. Phone (02) 9541 0310, fax (02) 9541 0734. http://www.oztechnics.com.au/ H.P. 3455A MULTIMETER: 61/2-digit $400 ONO. (063) 51 4368. Lithgow NSW. MicroZed have 5V UPS. Uses 2 x AA nickel cadmium cells. Silicon Chip Binders ★  Heavy board covers with 2-tone green vinyl covering REAL VALUE AT $11.95 PLUS P &P ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A11.95 plus $3 p&p each (NZ $8 p&p). Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. September 1997  95 14 Model Railway Projects Shop soiled but HALF PRICE! Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop soiled or have minor cover blemishes. Otherwise, they're undamaged and in good condition. SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) This book will not be reprinted Yes! 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Enclosed is my cheque/money order for $­A__________ or please debit my Advertising Index Airborn Electronics......................95 Daycom.......................................77 Dick Smith Elecronics.. 10,11,34-37 Electronic Valve & Tube Co..........77 Harbuch Electronics....................41 Instant PCBs................................95 Jaycar ............................IFC, 45-52 Kits-R-US.....................................96 MicroZed Computers...................95 Model Railways Book..................96 Oatley Electronics..........................3 Rod Irving Electronics .......... 86-90 ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Scan Audio..................................43 Card No. Silicon Chip Back Issues....... 68-69 Signature­­­­­­­­­­­­___________________________  Card expiry date______/______ Silicon Chip Bookshop.................53 Name Street ______________________________________________________ PLEASE PRINT ______________________________________________________ Suburb/town_________________________________ Postcode_________ Silicon Chip Binders................OBC Silicon Chip Software..................29 Silicon Chip Wallchart..............OBC Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). Smart Fastchargers.....................43 Telstra..........................................79 WAR Audio..................................78 Microprocessor For Digital Effects Unit This is the 68HC705-C8P pro­ gramm­ed micro­pro­cessor IC for the Digital Effects Unit (see Feb­. 1995). Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­ lica­ tions, PO Box 139 Collaroy 2097. Phone (02) 9979 5644; Fax (02) 9979 6503. 96  Silicon Chip Circuit Ideas Wanted Do you have a good circuit idea. If so, why not sketch it out, write a brief description of its operation & send it to us. Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. We pay up to $60 for a good circuit but don’t make it too big please. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, 2097. Zoom Magazine.........................IBC _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: •  RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 9587 3491. •  Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. -Y D-I PACT R! M OFE O C WO B SU AUG/SEPT 19 $5 50* 97 ® BLOWN XR-8 IAL: WRX , GSR, GT -R, VR4, PP255003 ISSN 1326-1 726 08 9 77 13 26 17 20 09 GT4 & 30 00GT ST APPR OVED - BO SPEC A us tr al ia T w o D IY ’s fa st es t dr ag bi ke Co m m od F ue l pu or e tu rb m p fa ct os ch P ic ki ng th e ri gh ar t t co m p ra ti o PRINT PO 4WD TUR /02111 AWESOM 550 bhp E! PLUS: 11 sec O Skyline OO O SPRINT! September 1997  97