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NOVEMBER 2014 ISSN 1030-2662 11 The project we said we would never publish: a D-I-Y VALVE AMPLIFIER! 9 771030 266001 PP255PP3/01272 9 $ 95* INC GST NZ$1290 INC GST The Currawong The 1950s meets the 21st Century! HOW TDR CAN HELP LOCATE CO-AX CABLE FAULTS Free-to-Air Digital TV on your Android Smartphone: Here’s how – NO DOWNLOAD D OWNLOAD CHARGES! CHA RGES! Corning’s amazing GORILLA GLASS: How it’s made siliconchip.com.au November 2014  1 KITS BUILD THEM! Online & in store Power & Automotive Kits High Energy Ignition Kit Ref: Silicon Chip Magazine Nov & Dec 2012 Use this kit to replace a failed ignition module. Suits vehicles with ignition system that use a single coil with points, hall effect/lumenition, reluctor or optical sensors (Crane and Piranha) and ECU. 3V-9V DC-DC Converter Kit Ref: Silicon Chip Magazine March 2004 This great little converter allows you to use regular Ni-CD or Ni-MH 1.2V cells, or alkaline 1.5V cells for 9V applications. Using low cost, high capacity rechargeable cells, the kit will pay for itself in no time! • PCB: 59 x 29mm KC-5391 Kit supplied with PCB, and all electronic components. $ • PCB: 98 x 56mm KC-5513 1595 Ref: Silicon Chip Magazine November 2013 Precisely records where your car or boat has travelled over time, which you can playback on software such as GoogleTM Earth to map your journey. Ref: Silicon Chip Magazine June 2011 Control the speed of 12 or 24VDC motors from zero to full power, up to 20A. Features optional soft start, adjustable pulse frequency to reduce motor noise, and low battery protection. The speed is set using the onboard trimpot, or by using an external potentiometer (available separately, use RP-3510 $2.25). $ Kit supplied with PCB, and all electronic components. • Records onto an SD card (available separately) • Records point-of-interest at the touch of a button • 12VDC powered • PCB: 142 x 74mm $ KC-5525 149 3995 Kit supplied with silk-screened PCB, enclosure with label, pre-programmed PIC, GPS module, and electronic components. The SMD components are already pre-soldered to the PCB to save you the hassle. NEW KITS Potato Clock Kit Mini-D 2 x 10W Class-D Amplifier Kit Ref: Silicon Chip Magazine September 2014 Can deliver more than 10W per channel or 30W mono. Features on-board volume control, lowpower shutdown mode and over-temperature/ current protection. Compact design and highly efficient. Test & Measurement Kits • Powered from 8 - 25VDC • No heatsink required! • PCB: 85 x 46mm KC-5530 Digital Multimeter Kit Learn everything there is to know about component recognition and basic electronics with this comprehensive kit. From test leads to solder, everything you need for the construction of this meter is included. • 9V battery included • Meter size: 123 x 67 x 25mm KG-9250 Kit supplied with double sided, solder-masked and screenprinted PCB, and ALL SMD components pre-soldered to the PCB. $ 2495 Transistor Tester Kit Ref: Electronics Australia September 1983 Have you ever unsoldered a suspect transistor only to find that it checks OK? You can avoid these troubleshooting hassles with the In-Circuit Transistor, SCR and Diode Tester. The kit does just that, test drives WITHOUT the need to unsolder them from the circuit! 27 $ 95 Kit supplied with a Jiffy box, battery and electronic components and panel showing truth table for device checking. 2  Silicon Chip To order call 1800 022 888 You can generate enough electricity to run a digital clock by plugging electrodes into common potatoes! Also works with tomatoes, lemons, apples - even soft drink or beer! • Clock size: 65(W) x 30(H) x 12(D)mm • Recommended for ages 10+ KJ-8937 9 $ 95 Kit supplied with highly accurate digital clock module, metal electrodes with wire, instructions and fluid beakers. Potatoes not included. Fruit/veg not to be consumed after use. 4995 $ Household & Security Kits Kit supplied with DMM case, LCD, solder, battery, test leads, PCB, comprehensive 18 page learning manual and electronic components. • PCB: 70 x 57mm KA-1119 4995 GPS Data Logger/Tracker Kit 12/24VDC 20A Motor Speed Controller Kit • PCB: 106 x 60mm KC-5502 $ Kit supplied with silk-screened PCB, diecast enclosure, pre-programmed PIC and PCB mount components for four trigger/pickup options. Hall-effect and optical pick-ups not included. Infrared Floodlight Kit Temperature Switch Kit Let your CCD camera see in the dark! This infrared light is powered from any 12-14VDC source and uses 32 x infrared LEDs to illuminate an area of up to 5-metres (will vary with light conditions). PCB draws a current of about 300mA. • 12VDC powered, use MP-3147 $17.95 (sold separately) • PCB: 56 x 28mm KG-9140 • Suitable plugpack supply, MP-3282 $14.95 (sold separately) • PCB: 74 x 55mm This kit operates the included relay based on preset temperatures. Ideal as a thermostat, ice alarm, or hydroponics applications, etc. Adjustable temperature range of -30˚ to +150˚C. Kit supplied with PCB, NTC thermocouple and all electronic components. $ Note: Not suitable for colour CMOS cameras. KG-9068 2495 REGISTER ONLINE TODAY! 2995 $ Kit supplied with silkscreened/ gold plated/ solder-masked PCB, 32 x infrared LEDs and all electronic components. SIGN UP NOW & BE REWARDED Earn a point for every dollar spent at any Jaycar Company store* & be rewarded with a $25 Rewards Cash Card once you reach 500 points! *Conditions apply. See website for T&Cs Register online today by visiting www.jaycar.com.au/rewards siliconchip.com.au www.jaycar.com.au Prices valid until 23/11/2014 Contents Vol.27, No.11; November 2014 SILICON CHIP www.siliconchip.com.au Features 16 Gorilla Glass: Unbelievably Tough & Flexible Smart phones and many notebook computers use Gorilla Glass in their screens but few people realise just how tough and flexible it is – by Dr David Maddison 24 Watch TV On Your Android Smartphone, Tablet Or Laptop The Pad TV Tuner is a small USB device. You just plug it in and it works with a free DVB-T tuner Android app on your smartphone or tablet – by Ross Tester 57 Solar Smoothing:What Happens When The Sun Goes Out? Rooftop solar power systems have caused headaches for power distributors Currawong 2 x 10W Stereo Valve Amplifier, Pt.1 – Page 28. 76 How To Find Faults In Coaxial Cables Using TDR TDR or time-domain reflectometry is a technique used to track down faults in cables. Here’s a look at how it works – by Jim Rowe 81 The State Of Play With Electric Vehicles Electric and hybrid vehicle sales are set to soar – by Ross Tester 86 The TV Channel Restack & What It Means To Viewers There’s more disruption to come with TV broadcasting services and it will impact viewers in both Australia and NZ – by Alan Hughes Pro jects To Build 28 Currawong 2 x 10W Stereo Valve Amplifier, Pt.1 It has eight valves and delivers around 10W RMS per channel into 8Ω. Pt.1 describes the features and gives the circuit details – by Nicholas Vinen 48V Dual Phantom Power Supply – Page 40. 40 48V Dual Phantom Power Supply Lots of audio equipment needs phantom power. This unit runs from a 24VAC plugpack and delivers 48V DC via XLR sockets – by John Clarke 66 Programmable Mains Timer With Remote Switching This versatile timer mates with a commercial remote-controlled mains switch and can be programmed to switch the mains socket on and off after a set period or to switch the power on and off at set times – by John Clarke 82 One-Chip 2 x 5W Mini Stereo Amplifier It’s based on a TDA7266D stereo amplifier chip and uses just a handful of other parts – by Nicholas Vinen Programmable Mains Timer With Remote Switching – Page 66. Special Columns 58 Serviceman’s Log Heat can be a real killer in laptops – by Dave Thompson 46 Circuit Notebook (1) Thermocouple-Based Thermostat With Temperature Display & Proportional Phase Control; (2) 20-LED Moving Dot Temperature Display 92 Vintage Radio STC’s Type 500A 5-Valve Radio – by Associate Professor Graham Parslow Departments   4 Publisher’s Letter   6 Mailbag 65 Subscriptions siliconchip.com.au 90 Online Shop 104 Advertising Index 97 98 101 103 Product Showcase Ask Silicon Chip Notes & Errata Market Centre One-Chip 2 x 5W Mini Stereo Amplifier – Page 82. November 2014  1 EVERYTHING IS ON SALE EF-5S Engineers File Set • 200mm hardened and tempered files • Second cut: Flat, 1/2 Round, Round, Square, Triangular • Includes carry case 14 Piece Punch & Cold Chisel Set 31.90 49.50 19.80 $ 22 15 $ $ F100 P364 P365 P367 C Clamps Clamping Force Code Price RPC-C/3 3" 644 Kgf R9710 RPC-C/4 4" 823 Kgf R9711 RPC-C/6 6" 953 Kgf R9712 $5.90 $8.90 $9.90 42.90 $ 36 5/16" Letter 19.80 53.90 $ 16 $ $ P350 P351 $ P350 Carbide Burr Sets CB6-5S - Short Series • Double cut burrs • SD-3, SE-3, SA-3, SC-3, SF-5 • 1/4" x 1-1/2" shank CB6-5L - Long Series • Double cut burrs • SD-3, SD-5, SG-5, SC-5, SF-5 • 1/4" x 6" shank CB6-5S CB6-5L 86.90 $ 69 45 PDS-3BS Bearing Race & Seal Driver Set • 10 Piece • 39.5 - 81mm 41.80 $ 60.50 $ 33 $ $ P030 P031 49 Offset Fabricated Vice 24.20 132.00 $ $ 20 $ $ P354 P355 Standard Drill Press Vices • Fabricated steel design • 152mm jaw width 5/16" Number 109 P351 Universal Deburring Tool Set • 4 x screw on flute countersinks • 1 x deburring tool • 1 x HSS blade • 1 x pocket clip 49.50 B905 V126 92 $ D065 N T IRO CAS 100mm 127mm IECE 64.90 $ 23 P 55 79 B900 V125 • Acme screw thread • Fitted width serrated jaws 99.00 $ V124 Bench Vices $ $ $ $ 39 23 28 $ • Includes: 2 holders, sheet metal holder, 10 pack HSS blades, 20mm countersick blade, 2 x scraper blades, "V" & inverted "V" scraper, 4 telescopic extensions & wrenches D062 103.40 $ 87 V088 V089 V090 • 900 x 450 x 900mm • 2 x shelves • 3-point key lock design • 150kg shalf load cap. • 900 x 450 x 1800mm • 150kg shelf load cap. • 75kg drawer capacity • Made from reinforced metal • 1170 x 580 x 1450mm • 250kg bench capacity • Key lockable drawers • Includes drawer dividers 259 1,023.00 $ 899 $ 715.00 $ 599 $ T774 T762 120 $ WTC-1450 Industrial Tooling Cabinet Workstation $ 141.90 $ $ SC-1800 Industrial Storage Cabinet 297.00 152mm $ BSC-900 Industrial Storage Cabinet $ $ $ Deburring Tool Set $ 33.00 $ 18.70 V067 152mm 27.50 22.00 $ 108.90 $ 127mm 100mm L STEE $ P. T CA EE m SH 1.6m • 17 Piece • 10 - 42mm • Manufactured from high quality carbon steel • Hardened to provide toughness & stable punch life 3/16" Number P020 PDS-2B Bush Driver Set Punch Sets 3/16" Letter 209 $ 15 $ Size 242.00 $ $ $ Model • Includes 22.5, 28.3, 34.6, 43.2, 49.6, & 61.5mm dies 19.80 $ 39 CHP-60 Hydraulic Chassis Punch Set • 2.5, 5.5, 7.0mm • 150mm length • Knurled body for a firm safe grip • Ø3, 4, 5, 6, 7, 8mm • 150mm length • 5 x cold chisels • 4 x pin punches • 4 x tapered punches • 1 x centre punch $ 3 Piece Centre Punch Set 6 piece Pin Punch Set T773 NSW 2  Silicon Chip QLD VIC (02) 9890 9111 (07) 3274 4222 (03) 9212 4422 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains 1 Fowler Rd, Dandenong WA (08) 9373 9999 41-43 Abernethy Rd, siliconchip.com.au Belmont www.machineryhouse.com.au 10_SC_250914 11_UC_#367_301014 Specifications & Prices are subject to change without notification. Sale pricing may exclude some Record Power products. All prices include G.S.T. Valid until 22-11-14 Thursday 20th - Saturday 22nd November FRUSEAGEE Order online or in-store SASIZZLE Professional Series Hole Saw Set Carbide Tipped Tips & Techniques Chapter Chapter Chapter Chapter Chapter Chapter Chapter Chapter Chapter Chapter 01: 02: 03: 04: 05: 06: 07: 08: 09: 10: Setting Up Your Workshop Tools and Techniques Measuring and Marking Fasteners and Workshop Supplies Drilling Grinding, Polishing and Cutting Working with Metal $39.00 Welding ONLY Machining Woodworking Machinery 29 $ Hand Lever Shears HS-6 (S186) • 150mm blade • 4mm flat bar • 9.5mm round 110.00 $ 89 HS-12 (S188) • 300mm blade • 5mm flat bar • 12.7mm round 198.00 $ 165 108.90 $ 89 $ D102 99.00 $ 324 COLOUR PAGES 79 $ S186 S188 $ D108 170 Pieces Jobber Drill Set - HSS L345 185.90 T100 5 Piece Industrial Centre Drill Set 32 $ 220.00 $ 198 • Includes 8 formers • 3/4" & 1" square • 3/8" 1/2", 9/16", 5/8", 3/4", 7/8" round • 1hp, 240V motor • Includes light DB-32 Tube Bender Electric • 5/8", 3/4", 7/8", 1" & 1-1/4" formers • Digital display 0 - 180º angle • 1.2mm mild steel wall thickness • 1.7kW / 2.2hp, 240V D1071 D111 319.00 297 169 T055 $ $ 198.00 $ 660.00 $ $ 561 Drilling Machines 2MT S SBD-25A Bench Drill 352.00 385.00 $ 1,815.00 1,650 $ T070 siliconchip.com.au 429.00 $ 330 $ 349 385 $ $ $ D138 D140 D144 D147 AL-51G Bench Lathe AL-250G Bench Lathe • 230 x 500mm turning capacity • 20mm spindle bore • Quick change gearbox • Speeds 100-1800rpm • 0.55kW, 240V motor • 250 x 500mm turning capacity • 12 spindle speeds • Quick action gearbox • 1hp, 240V motor 1,815.00 $ 1,265.00 $ 1,155 1,595 $ L160 TO: GAIN ACCESS √ √ √ √ √ √ √ √ L149 Shown with optional stand ST-250G Lathe Stand 297.00 $ 220 $ + OS ONLINE PROM RS FE EXCLUSIVE OF DERs OR ur yo K AC TR ECT CLICK & COLL ranty ar Paperless W NEWSLETTERS ASES LATEST RELE NS IO IT ET COMP L150 $7OU0NT VFORUCHEERSE DISC LE PIND S 2MT SPD-25A Pedestal Drill $ $ $ • 20mm drill capacity • 16 spindle speeds • Swivel & tilt table • 1hp, 240V motor • Includes light LE PIND SBD-20B SPD-20B Bench Drill Pedestal Drill $ V503 • 3-13mm or 1/8"-1/2" • Diamond wheels • Split point • Powerful 240V motor $ • 16mm drill capacity • 16 spindle speeds • Swivel & tilt table • 1hp, 240V motor TBRS-25 Manual Tube Bender ON DIAM PP-13C Precision Drill Sharpener HSS Drilling Machines D508 $ D070 59 38.50 • 1000W 240V motor • Portable on wheels • 30L stainless steel tank • Include: brush, crevice tool, wet & dry floor nozzle D126 EEL D WH 79 77.00 $ WDV-30L Industrial Wet & Dry Vacuum Cleaner $ • HSS M2 Bright finish • 4-12 x 1mm • 6-20 x 2mm • 6-30 x 2mm HSS D1282 99.00 $ 3 Piece Sheet Metal Step Drill Set • No. 1, 2, 3, 4, 5 • HSS M2 bright finish • Industrial quality D1272 $ 149 IECE $ • 3-13mm or 1/8"-1/2" • Split point • 80W, 240V motor $ P 130 69 $ EDBD-13 Drill Sharpener • HSS precision ground flutes • Ø1.0 - Ø10mm • 10 drills each size up to 8mm then 5 per size 163.90 139 90.20 $ 69 • M5 x 0.8mm • M6 x 1.0mm • M8 x 1.25mm • M10 x 1.5mm • M10 x 1.75mm $ 88.00 $ $ Metric Thread Repair Kit $ • Precision ground flutes • HSS M2 bright finish 25 Piece Metric (D1272) • Range: 1-13mm • 0.5mm increments 29 Piece Imperial (D1282) • Range: 1/16 - 1/2" • 1 /64" increments • HSS M42 Bi-Metal set • 11 size: 19, 22, 32, 35, 38, 44, 51, 57, 64, 76mm • Ø3/8" & Ø1/2" • Range: 16, 20, 22, 25, 28, 30, 32, 35mm • Ø10mm shank • Heat resistant carbide teeth Step by Step Information and Illustrations Detailed Explanations Range of Activities and More Precision Jobber Drill Sets Hole Saw Set General Set ORE mB 26m .au/SIGNUP house.com2014  3 Nyovember machiner Note: Discount vouchers are valid for online purchases only 11_UC_#367_301014 HANDY WORKSHOP UNTIL 4:00 PM Satu rday 22nd NOVE MBER 2014 SILICON SILIC CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Kevin Poulter Stan Swan Dave Thompson SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Warwick Farm, NSW. Distribution: Network Distribution Company. Subscription rates: $105.00 per year in Australia. For overseas rates, see our website or the subscriptions page in this issue. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. Fax (02) 9939 2648. E-mail: silicon<at>siliconchip.com.au Publisher’s Letter An amplifier to warm the cockles of your heart Doubtless we will have again divided the readers of SILICON CHIP with a controversial article this month. Some will love the Currawong valve amplifier presented in these pages (with more articles to come) and some will inevitably see it as a pointless exercise and so “last century”. Even some of those readers who are keen on valve amplifiers will doubtless find something to criticise, such as the fact that it has negative feedback, or not enough feedback, or not enough power from the tetrodes, or whatever. For our part, we see it is another interesting design exercise, whether it is based on thermionic or solid state devices. Indeed, we have used a mixture, with valves being used for the signal path, to give that all-important “valve sound” and with solid-state devices used in the power supply and infrared remote control. We don’t think too many potential builders will be put off by the fact that it has an infrared remote volume control though; quite the opposite. As with any design exercise, there are compromises on many aspects. If cost was no problem, we could have produced an amplifier with a lot more power and possibly a little less distortion. But we have to be realistic, knowing that a sky-high cost will make the unit unattractive to the vast majority of readers who might like to build a modern valve amplifier. Of course, the over-riding reason why we have designed and presented the Currawong amplifier is that we realise that there is considerable interest in valve amplifiers and “valve sound”, even if we do believe that the best solid-state amplifiers are far superior to any valve design. A quick look at the performance graphs on pages 33, 37 & 38 will show that is the case, on the raw figures. Our Tiny Tim amplifier (SILICON CHIP, October & December 2013, January 2014) is a better performer and much cheaper to build. For valve aficionados though, raw figures are of little interest. Indeed, Allan Linton-Smith, one the proponents of the Currawong, demonstrated an early hard-wired prototype together with our 15W Class-A Stereo Amplifier to an interested group and he reported that most people present preferred the sound of the valve unit. Heresy! Cynically, I just think it can’t have been a very good demo; if I had done it, the preferences would have been entirely the other way! Well, OK, maybe not entirely the other way. Of course, much of the attraction of valve amplifiers relates to the fact that they are inherently simpler technology and for many people they are nostalgic – a throwback to simpler past. Solid-state amplifiers don’t glow in the dark, do they? Much the same can be said of the resurgence in interest in vinyl records and turntables. In many ways, there is more satisfaction in selecting a record to play, reading the sleeve notes, putting the disc on the turntable and then very gently placing the stylus of the cartridge into the lead-in groove – and then it begins to play. By contrast, playing a CD or pressing a button to select a digital sound track is a cold and impersonal process. So there is considerable attraction in old technology and that is why we finally decided to do the work involved in presenting the Currawong. It has not been an easy task to produce it. So even if you regard valve amplifiers as an anachronism and out of place in a magazine called SILICON CHIP, have a read through the article this month and those to come. It is a most interesting exercise and one which makes us realise that those designers from so many decades ago really did achieve very good results with such simple technology. Leo Simpson ISSN 1030-2662 Recommended and maximum price only. 4  Silicon Chip siliconchip.com.au ROHDE & SCHWARZ Enter to WIN 1 of 2 ¸ HMO1002 DIGITAL OSCILLOSCOPES Simply enter the link below and answer 4 questions correctly to be in the running to win! http://www.customer.rohde-schwarz.com/live/rs/internet/campaigns/enter_to_win/ WIN ¸HMO1002 Signal Oscilloscope The competition ends on December 8th 2014, hurry to enter for your chance to win. For further information contact: sales.australia<at>rohde-schwarz.com siliconchip.com.au November 2014  5 MAILBAG Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to “Ask SILICON CHIP” and “Circuit Notebook”. Don’t meddle with the switchboard Earth-Neutral connection The article on the MEN system used in domestic wiring in the August 2014 edition was very good reading. It took me back to when I was an apprentice electrician in the UK. We were on a job when the tradesman sent me to connect an electric drill into the local fuse board (there were no battery drills in the late 1950s). On inspection I found that there was no Neutral, so he told me to connect the Neutral to the Earth. When he checked what I had done, he told me where I had gone wrong. I had twisted the Earth and Neutral wires together and then bolted them to Earth. The way I had done it was very dangerous because if the connection I had made to Earth had come off, using the drill would have been fatal, with the frame of the drill being at 240VAC and looking for a return. What I should have done was connect the Earth and the Neutral via different bolts. That lesson from all those years ago brings me to the MEN GPS car navigation can be illogical I must say I had a laugh at the Publisher’s Letter in the October 2014 issue, on the topic of GPS navigation. I also have a few thoughts on the matter. I finally bought a GPS about five years ago and the only street directory I now have is a 1922 copy which might have some monetary value. One would think picking the quickest route via GPS from Penrith to the airport would be via the M4, the M7 and the M5 but nothing I select will stop it heading off down Mamre Road to Elizabeth Drive and taking the country route. I actually ran the demo of the selected route first time through and was amazed that the airport had apparently been moved to North Shore Crematorium, a place with which I 6  Silicon Chip system and seeing how dangerous it can be. The thought of domestic homes still working apparently as normal without a Neutral would have to be ringing alarm bells in high places. With the homes still working in this way, it goes without saying that the main Earth (homes built before 1973 only having one Earth point) will fail at some stage. When this happens, all appliances with any metal will become live. The only safe appliances would be those that are double-insulated. A simple procedure to check this would be to remove the link between the Neutral and Earth bus-bars. If things stop working you can assume that the Neutral connection has failed. It would be interesting to see how many homes are affected. So in the interest of safety maybe the link should be left off; as an added bonus, how many plumbers would be saved? The MEN system may have benefits for the supplier like the Neutral not being 24VAC above earth (would that kill anyone?) but at what cost? I congratulate you on an excellent am very familiar! Anyhow, a bit of checking of street names quickly confirmed my thoughts that there was a street named after an aviator at both the airport and the crematorium. So now, if I want to go to the airport, I set the GPS, travel down the M4, M7 and M5 and SHMBO awakes along the M5 to announce that I should “stay in the left lane and prepare for a left turn ahead”. That’s fine by me. I now simply drive off in the direction of wherever I may be headed and leave the final destination to the GPS and the lap of the gods. On the other hand, I was up at the Sunshine Coast in early December last year to pick up a secondhand car and was met at the airport by the seller. All well and good. He drove to the nearest registry office article. It certainly made me think about things and it really is a shame that only your readers get to see it. Tom Pawson, Mount Warrigal, NSW. Editor’s note: we must warn against anyone disconnecting the link between Neutral and Earth. That is a task which must only be done by a licensed electrician. Anyone else meddling with it may cause a lethal situation. Wideband RF probe design critique Wide bandwidth scope probes have long been a special interest of mine so I found the Active Differential Probe for Oscilloscopes by Jim Rowe, (SILICON CHIP, September 2014) interesting. I like the idea of the LED at the tip. Also there is a handy application note from Keysight (ex-Agilent) on Eight Hints for Better Scope Probing at http://cp.literature.agilent.com/ litweb/pdf/5989-7894EN.pdf and once we had completed all the documentation and I gave him the remaining $500 in cash, I set the GPS to the address of my uncle whom I hadn’t seen since 1996. All went well until “take the next left and you have reached your destination”. OK, it looked a bit like an RSL retirement village but upon getting out and walking around, things seemed just a bit too quiet. I rang him on my mobile phone and one of my cousins was on the line to ask me for a few landmarks. After exchanging details, she finally told me I should have turned right – sound familiar? I backtracked and was there five minutes later to be met by my cousin waving to me from the front door of the village unit – a happy ending! Alan Greaves, St Clair, NSW. siliconchip.com.au Copper thieves vandalised the MEN system The circuit is not very complex and it is easy to understand but I am puzzled by a few things. There is no obvious attempt to compensate the probe in 10:1 mode, so I’m wondering how you manage to keep the frequency response within +0.2dB/-0.3dB (~2.5% to ~3.5%) to 40MHz. Serendipity? Of course it could well be that the PCB and components provide exactly enough parasitic capacitance that the probe is perfectly compensated on the 10:1 range but what about device variations? I guesstimate that the FET contributes about 1pF of input capacitance (the data sheet is not very explicit). A 10% change in device capacitance (we’re talking about 0.1pF) between devices would cause a wrinkle of about 0.3dB in the frequency response on the 10:1 range and could wreak havoc with the common mode rejection of the probe (depending on circumstances). I suspect that the exact orientation of the FETs on the PCB and even the amount of solder used might have a measurable effect on the frequency response on the 10:1 range, with subsequent impacts on CMR and dynamic range. Similar issues apply to the 3MΩ resistors that provide the low frequency attenuation on the 10:1 range. It is worth noting that the resistors provide the attenuation only for frequencies below 100kHz. In the specification panel “Maximum AC voltage input before overload, both probe tips” is given as 2V In the August 2014 edition of your wonderful periodical I read with great interest the article about the MEN system. I was aware of this system and the potential issues (pun intended) associated with faults and oversights when dealing with the Earth side aspects of this system from my early days of helping an electrician friend. It was great to see it put into a simple and straightforward explanation. peak-peak. The meaning of that is not clear. My initial interpretation was that it meant both inputs have the same overload level but I think what is really meant is that the maximum common mode AC voltage is 2V. In either case, that requires that one or two amplifiers would have to deliver 4V peak-peak before overload. The data sheet for the AD8038 says that the output swing with 5V supply and a 2kΩ load is 0.9V to 4.1V (ie, 3.2V peak-peak). In fact, on page 11 of the data sheet Fig.40 (Output Swing vs Load Resistance) shows output swing is less than 0.5V peak-peak with a 5V supply and 100Ω load (the load on IC3 with the recommended 50-ohm termination). That suggests that the maximum output voltage of the probe would not reach 250mV peak-to-peak or a peak value of little more than 100mV, taking into consideration the attenuation of the 50-ohm termination resistors. Leaving off the 50-ohm termination at the It also reminded me of an event that occurred in my area not so long ago. Some individual or individuals had removed many of the copper earthing wires from the utility poles in the area, presumably for the scrap value of the copper. Upon alerting the local power supplier they immediately sent out crews to rectify the situation. One can only hope that the perpetrator(s) got more than a little tingle for their foolish efforts. Mark Veraart, Perth, WA. oscilloscope would allow much greater output at low frequencies but one metre of 50-ohm coax is likely to restrict the bandwidth to less than 40MHz, which implies that the frequency response would be down 1dB at 20MHz and there would be significant phase shift and time delay associated with it. The data sheet for the AD8038 gives the slew rate as 425V/μs (typical), which gives a maximum output of 4V peak-peak for frequencies below 34MHz before slew rate limiting starts to distort the waveform. So the “Maximum AC voltage input before overload” would apply only for frequencies below 34MHz and should be derated linearly for frequencies above that. The quiescent output voltage of the probe is set by the VGS of the FETs and the data-sheet for the BSS83 gives the threshold value of VGS as between 0.1V and 2V. If by chance the VGS(thresh) of one FET was 1V then the output of the probe is likely to be nearly saturated Desktop 3D Printer Bring your imagination to life. Automatic Bed Levelling High Print Resolution Automatic Material Recognition Up to 300% Faster Faster and More Accurate Setup For Software Selection of Heat Profiles using SmartReel™ Down to 20 Microns Dual Nozzle System See our website for more details www.wiltronics.com.au siliconchip.com.au $1495.00 inc. GST Includes 2 SmartReel™ reels of filament! November 2014  7 Mailbag: continued Cars with keyless entry can lock you out Kyle Cogan, in his letter “Keyless car entry & flat batteries” (page 6, October 2014) raises an important point: modern cars that rely solely on an electronic key for entry are at risk when the vehicle’s battery goes flat. I wish to relate the following story to help readers, should they be caught in this predicament. We had the above situation occur some years ago when my wife’s Mercedes 4WD developed a flat battery, after the lights had been left on. Ordinarily this would not be a problem as the vehicle was designed with a fail-safe mechanical key entry at the driver’s door. In this instance, the lock had previously broken and we had not yet had it fixed under warranty. The lights had been left on and the battery was so flat that the electric locks would not actuate. There was seemingly no way in. My wife called our local motorist’s association and they kindly offered to come and break a window for her! What was needed was access to the battery. There was no way to open the bonnet. Guards under the so the available output swing will be quite small. Adjustment of the FETs’ bias voltages could remedy that although there is no provision for it. Now I am not saying that the probe doesn’t work; it probably does. However, it is curious that the bandwidth specification does not cite an output level for the figures quoted; in fact output levels do not appear in the specifications panel at all. No CMR figure for the probe is given, and the “Maximum AC voltage input before overload” specification seems at odds with the AD8038 data sheet. If the data sheets are to be believed (and generally data sheets are accurate in what they report), then the probe’s performance is remarkable. But I feel that any other probe, built as described, from a random selection of parts, is likely to be struggling to meet the specifications published except in somewhat narrowly defined circumstances not indicated in the specifications. 8  Silicon Chip engine prevented access from below (although one could hardly reach from below anyway). All the wiring was inaccessible other than at one point: the light over the number plate! Disassembling this, I used a jumper lead (fitted with battery clips at one end and alligator clips at the other) to connect a spare 12V lead-acid battery to the light terminals (after using a multimeter to check for polarity). I then pressed the key on the hand-held remote every second or so until the door locks opened. It took about three to four seconds. I figured there was a risk of blowing the light fuse doing this, so as soon the door locks opened, I removed the jumper leads. Note that this technique will only work if the lights have been left on (otherwise the number plate light would not have been connected to the battery). John Goswell, Keinbah, NSW. Comment: it seems as though modern cars need an external charge point to allow the battery to be topped up, to cope with instances like yours. I think some elaboration of the specifications is warranted. Phil Denniss, Darlington, NSW. Jim Rowe comments: you are quite correct in suggesting that with our prototype probes the stray capacitance associated with the range selector switch and the PCB happened to provide just enough compensation on the 10:1 range. We had planned to use a pair of small capacitors wired directly across the switch contacts, if additional compensation proved to be necessary but this did not eventuate. Of course, if constructors do find that additional capacitance is necessary, it can be added in this way – perhaps as a pair of sub-picofarad ‘gimmick’ capacitors. However, note that obtaining exactly the optimum capacitance can be a tedious and repetitive process for such small (sub-picofarad) values. But in fact, we would expect that the variation in FET capacitance would be very tight and that has proved to be the case. Thank you for your analysis of the limitations of the probe with regard to its output level before overload. Presumably, we were also “lucky” with regard to the characteristics of the BSS83 and AD8038 devices used in our prototypes. The main factor limiting the output level is our decision to run the probe from +5V (via a USB port) for user convenience. Using batteries to provide higher supply rails would no doubt improve the performance as far as overload is concerned but that would have required a much bulkier design. In fact, we don’t do our designs from a “random selection of parts”. We had to build a number of prototypes to prove the concept and tried a number of different circuit configurations and component combinations before settling on the final design. The design process for developing such a device can also be very frustrating, as we go through a number of PCBs which have to be rejected for various reasons. By the way, we have found that manufacturers’ data sheets should only be used as an initial guide for component selection, particularly for op amps. Sometimes devices perform better than the data sheets would indicate but often it is the other way, with performance not coming up to expectations. Indeed, manufacturers’ application notes can often lead one up the garden path and we have wondered if some circuits have even been tried! Indeed, from bitter experience, we have come to regard some application notes as marketing material rather than engineering information. To conclude, anyone designing a device solely on the basis of manufacturers’ data sheets and application notes is likely to be quite disillusioned with the result. Nor it is necessarily true that one can define a design’s drawbacks by poring through data sheets. Navigation in the days before Omega When I bought the September 2014 issue, I was intrigued that the cover stated that Omega was “Global Navigation before GPS”. The Astrolabe, Sextant, Greenwich Mean Time and siliconchip.com.au Solar panels for hot water I was interested in the letter from D. S., on page 99 of the September 2014 issue of SILICON CHIP. I previously tried this approach unsuccessfully. I had solar panels in series giving approximately 180V open-circuit and 125V with 5.7A into the 24-ohm, 2400W element, thus heating at about 700W. The voltage, of course, varies with the angle of the Sun (time of day and time of year). Light cloud drops the voltage by half and the power by one quarter but given all day to heat the water, it worked well. The problem was the controller. The electric hot water system has a controller, with a thermostat to disconnect the voltage when the water is up to temperature and a cut-out to prevent the HWS turning into a steam bomb if the thermostat fails. The controller in my HWS was rated to switch 30A at 240VAC. When attempting to break 5A at the Almanac, Norry’s and other sight reduction tables and NAVSAT obviously have been forgotten. The article did say “global real-time radio navigation before GPS.” When I used NAVSAT (TRANSIT), compared to a sextant, I thought I was in real time because the set could be “programmed” to run in “deduced (dead) reckoning (DR)” until the next satellite fix. A sextant fix could be as good as a five nautical mile radius. A NAVSAT fix could be as good as one nautical mile radius; sometimes better if the satellite was 10° above the horizon (60 minutes = 1 degree of latitude; 120V (DC), the thermostat melted into a short circuit blob. After further heating, the cut-out operated, though damaged by arcing to the extent that it could not be reset. I have now given in to conformity and bought an inverter, so the HWS, with its new controller, runs off 240VAC buffered by the grid. With privatised power companies continuing to up their prices and the cost of solar panels falling, a SILICON CHIP “50-400V DC input 50Hz output” inverter project would be popular with readers wanting cheaper hot water. John Burns, Beverley, WA. Comment: a simpler approach may be possible: using the existing HWS thermostat to control a power Mosfet which could easily switch off the DC current and voltages involved. That would still leave the potential issue of corrosion due to DC on the tank element. 1 minute = 1 nautical mile; 1nm x 1.8 = 1 kilometre – approximately). Usually there were six satellites a day. In the early 1980s, I crewed, as the sail-maker, on a yacht that was in the Marina del Rey, California, to Puerto Vallarta, Mexico, Yacht Race. It covered 1000 nautical miles south along the Mexican Baja Coast. The owner of the yacht had bought an Omega set and special charts overprinted with Omega grid lines to use in the race. We weren’t aware that the grid lines were a specific distance apart and anyway, their distance varied depending on one’s distance from the antenna. The AMPLIFIERS FILTERS TRANSFORMERS Available in Australia SOLD INDIVIDUALLY CLARKE & SEVERN ELECTRONICS Ph: 02 9482 1944 BUY ONLINE: www.cseonline.com.au set gave us four numbers that we had to plot for our position. The owner didn’t buy a NAVSAT set because of a reputation of unreliability. I remember the owner running a DR plot, on the chart, while he read the numbers of the Lines of Position from the set. He also did a Noon Sight, with his sextant, to confirm his DR. Interpolation, of the Omega LOPs, was so complicated that the “computer geek” quickly read the manual and helped out. tel: 08 8240 2244 Standard and modified diecast aluminium, metal and plastic enclosures www.hammondmfg.com siliconchip.com.au November 2014  9 Mailbag: continued Nostalgia for valve sound The letter by Brian Collath in the September 2014 issue, perpetuating the “valves are better than transistors” myth, reminded me of two amusing stories. Since about 1970, I’ve had and loved Tannoy loudspeakers but although they are terrific, nothing is perfect and from time to time, I get an urge to buy something better. Although I explore the competition, I usually just end up with another pair of more modern Tannoys. During the 1980s, I visited a local hifi shop asking to audition some loudspeakers. The audition was an enjoyable experience, filling me with a mysterious warm inner glow that I couldn’t explain immediately. When the sales person returned, he asked, “How did you like the amplifier?” “Amplifier? Um . . . I’ve come to audition loudspeakers.” As he explained that he’d used an outrageously expensive valve amplifier, the explanation of the mysterious warm inner glow became obvious. I was enjoying the nostalgia of remembering the distortion of the Although I am not “geeky”, I was enlisted to ponder the meaning of the LOPs on my watch when I was not steering. Our DR plot sort of agreed with the Omega set (definitely more accurate than a sextant). Between the three of us, we were convinced Omega was the “dawn of the new age” if we could only figure out the meaning of the LOPs. When we were about 500 nautical miles into the race, the Omega set became unreliable, giving erroneous LOPs on the other side of the world, and we lost reception of some of the LOPs. We eventually turned the set off. The owner continued the yacht race with his sextant. He relied on my superior night vision when we neared the coast at the end of the race (I could see the surf breaking on the shore!). Later, I made many ocean crossings using my sextant. On one voyage from Hawaii to Tahiti, an owner had a NAVSAT set. After a few days into the 10  Silicon Chip radiograms my parents owned during my childhood. More recently, I and a few friends began taking an elderly friend to jazz concerts because he likes jazz and we hoped to cheer him up. Although he’d thank us politely after each concert, he’d also offend us a bit by complaining that the sound was terrible and the players couldn’t play and . . . He’d also bought a quite good mini hifi system that sounded jolly terrific to me but he complained about that as well. It had tone controls on the front, so I suggested that he might like to use those to make it sound better. Ah. He preferred full bass and treble cut, but still complained. I eventually realised that his “benchmark of perfection” was not modern CD or even old black vinyl but really old 78 RPM black shellac. I made him a special box with IN and OUT connections and a really crummy circuit giving even more bass and treble cut inside. I didn’t bother to create fake noise. He loved it; just like the real thing. He thinks I’m a genius. Keith Anderson, Kingston, Tas. voyage, I put my sextant into its box and relied on the NAVSAT and charts to make landfall. As the 1980s progressed, yacht races began to accept the reliance on NAVSAT and later, GPS. When GPS began, NAVSAT disappeared because it wasn’t all that accurate (especially inaccurate when the chart survey datum did not agree with the NAVSAT datum). I remember one race, north to Mooloolaba from Sydney, where yacht positions were given on the beach. This phenomenon continued until chart datum was upgraded to GPS datum. A major problem with GPS, in the early days, was the threat of unreliability during a military conflict, as was experienced during the Gulf War. Another problem was that one had to buy the military model if one wanted to be very accurate (to the square metre). With the advent of GPS, I’m surprised that Omega lasted so long. Now, with chart plotters, the demand for charts is diminishing. I am in a minority because I have a chart collection, use dividers, run a DR, know how to change magnetic bearings to true bearings on the chart, and do not call charts “maps.” Marshall Miller, Manly, Qld. Alcohol breath analysis is a fraught process I am writing to draw attention to new Victorian legislation making the fact that one over-the-limit drink driving prosecution is enough to cause a loss of licence and resultant job loss in many cases. Also, a $1400 interlock device is then required to be fitted after one indiscretion. See this news item regarding the interlock devices: www.abc.net.au/news/2014-10-01/ vic-drink-drivers-forced-to-installalcohol-interlock-devices/5781552 This is not good enough, with the technology being inadequate to generate legal measurement results. Most speed camera equipment is also not required to pass proper scientific testing, as the testing officer only has to be satisfied as to their accuracy. This is not scientific and should be classed as illegal but the “authorities” are getting away with it. After I won my 67km/h speeding case on similar issues, the same strategy was used to win an appeal on 20th October, 2011 in the Victorian County Court, in the case of Agar v Baker, heard by Judge Allen. It goes to show you don’t need a legal qualification, just determination and the correct facts. While I generally applaud the use of alcohol interlock devices in cars, the problem of accuracy of breath testing machines must be questioned. Some reports (from America, of course) which were never properly questioned, said that these machines were 2.3% accurate while a different scientific finding discovered they had moved the decimal point from 23.0% to 2.3% accuracy. Other tests revealed inaccuracies up to 48%. Findings in a scientific peer-reviewed paper revealed this fact and it was never challenged as untrue. The court finding held. It is for this reason we should understand that many technological devices are being siliconchip.com.au More comment on unsafe products purchased on-line misrepresented as being accurate and are further attacks by those in power on the motoring public. Furthermore, I might mention that now anyone who makes the mistake of over-indulging even slightly can lose their license, job and family due to no income. This is most unjust and this law must be rescinded. Are our politicians completely devoid of knowledge and sympathy? Or is this another attack by those who see CO2 and motor cars as polluting and would rather have bicycles on the road? Reference: http://blog.motorists.org/ its-just-a-decimal-point-the-dirtysecret-behind-breathalyzers/ John Vance, Wangaratta, Vic. Comment: we asked food technologist and designer of the Alscolyser alcohol analyser (S ILICON CHIP, November 2013) Allan Linton-Smith to comment: With over 40 years experience of food and beverage analysis, there is one thing I know for a fact: it is really difficult to analyse alcohol accurately. 4DSC Nov Ad.pdf 1 9/30/2014 5:23:02 PM Some of the methods used for analys- ing ethanol in liquids include density, gas chromatography, IR spectrum analysis and fuel cell detection (such as in the SILICON CHIP Alscolyser). Each has drawbacks, essentially because of interference with other materials and contaminants such as sugars, petroleum spirits, adhesives, solvents etc. “Breathalysers” in general make the assumption that human breath is a fixed fraction of the blood alcohol content (BAC). Typically, they are calibrated on a calculation that BAC is between 2000:1 and 2300:1 – see www.lionlaboratories.com/testingfor-alcohol/the-lion-units-converter/ This conversion factor can vary enormously especially between men and women, small and large people, with levels of hydration and food in the stomach! This allows even bigger errors to creep in! I would go even further to say that breath testing inaccuracies are there for 99% of the time! But remember to drink responsibly at all times – if you want to argue against a driving infringement then get the best law- I read Barrie Davis’ comments in the October 2014 issue regarding potentially unsafe wiring on several imported 10W LED floodlights. I too had purchased a light from overseas and this prompted me to check it out. Earth? What earth? I realised with dismay that the unit only had a two parallel pin plug with no earth whatsoever when used with an adaptor. And the internal design was just as Barrie described and potentially just as dangerous. While I could replace the power cable and earth this device effectively, I am suspicious of the safety of the small LED driver (which was unsealed on my unit). It has certainly made me think again about buying electrical devices from overseas. Thank you Barrie. Brenton Brockhouse, Felixstow, SA. yer you can. But that won’t save any lives! In one state in the USA, everyone Enter C C 4 D S C N ode : OV15 M Y *Conditions apply Selecte d Prod ucts Offer ends 15O%FF 1st December 2014 S AV E 4D Systems designs, develops and manufactures intelligent graphics solutions using the latest OLED and LCD technology available, with custom graphics processors that enable both stand alone and host dependent solutions suitable for a very wide range of applications and projects. CM MY CY CMY K 4D SYSTEMS TURNING TECHNOLOGY INTO ART www.4dsystems.com.au siliconchip.com.au www.facebook.com/4DSystemsAU www.twitter.com/4DSystems November 2014  11 FK675 2W+2W Stereo Kit Here's a compact easy-to-build 2W+2W Stereo Amplifier kit with two 90mm x 50mm 3W Speakers. A great Year 8 or 9 school project. Ask for our BOOMBOX Teacher's Project Notes Maximum Power Output 2W per channel. Frequency Response 20Hz to 20kHz(-3dB). Terra-Terra – an alternative to MEN? Ask about School and Club Discounts Value!! $25.63 inc. GST Plus $7.50 Pack & Post 5 Kit Bonanza for Students Great for Schools Projects Includes:FK109 2 LED Flasher, FK233 Emergency Vehicle Siren with speaker, FK908 Soil Moisture Indicator, FK602 2W Mono Audio Amplifier (Uses the FK233 Siren speaker) FK401 Light-Activated Switch. All 5 kits for $25.50 inc. GST Plus $8.50 Pack & Post Find these and 100s more kits & modules on our website www.kitstop.com.au P.O. Box 5422 Clayton Vic.3168 Tel:0432 502 755 Radio, Television & Hobbies: ONLY 0 the COMPLETE 0 $ 2 6 0 P&P archive on DVD + $1 • Every issue individually archived, by month and year • Complete with index for each year • A must-have for everyone interested in electronics This remarkable collection of PDFs covers every issue of R & H, as it was known from the beginning (April 1939 – price sixpence!) right through to the final edition of R, TV & H in March 1965, before it disappeared forever with the change of name to Electronics Australia. For the first time ever, complete and in one handy DVD, every article and every issue is covered. If you're an old timer (or even young timer!) into vintage radio, it doesn't get much more vintage than this. If you're a student of history, this archive gives an extraordinary insight into the amazing breakthroughs made in radio and electronics technology following the war years. And speaking of the war years, R & H had some of the best propaganda imaginable! Even if you're just an electronics dabbler, there's something here to interest you. NB: Requires a computer with DVD reader to view – will not work on a standard audio/video DVD player Use the from handy order form Order online www.siliconchip.com.au or use the handy in this issue included in order thisform issue 12  Silicon Chip Mailbag: continued That was a very interesting article in your August edition about the potential hazards of the MEN mains system. It was also quite timely in that coincidentally this topic was raised just recently as part of my electrical re-certification training. In fact, there is a proposal here in New Zealand to change from the MEN system to the TT system (Terra-Terra) because of the very reasons outlined in your article, and because many building switchboards now have RCD protection installed which is a fundamental requirement of the TT system. In the TT system, the Neutral is still earthed at the supply transformer but the Earth-Neutral link at the switchboard is removed and RCDs then provide all the protection. So the only thing that the earthed metal framework of every the class 1 appliance is connected to is the stake in the ground. In this configuration, should a fault occur where a live conductor comes into contact with any earthed part of the appliance, instead of a short circuit current tripping an over-current breaker, an earth “fault current” flows with the resulting current imbalance tripping the RCD. So the end result (from the user's perspective) is the same as with the MEN system; the “breaker” trips but without the typical bang, sparks and resultant scorching. I had never heard of the TT system until fairly recently but upon learning about it, I think that the concept of separating the load current circuit from the protective Earth circuit makes a lot of sense. It would certainly solve the issue of water pipes potentially becoming live and posing a danger to plumbers etc. I can’t think of any drawback apart from the extra cost of an RCD protecting every circuit, including the fixed appliances. If a building already has RCD protection installed then it is certainly a very easy conversion. So I personally think that this would be the way to go in the long term. Grant Sexton, Cambridge, NZ. Comment: we hope to feature an article on the TerraTerra system in the near future. was let off the hook because of poor breathalyser calibration technique! Interlock devices fitted to cars typically prevent a driver from starting the engine at 0.025% (to account for inaccuracies), so if you have one of these, just don’t drink anything alcoholic if you plan to drive! Denying science has a penalty I subscribe to an “electronics magazine” to have access to factual, informative and interesting information in the field of electronics. Climate science falls well outside an electronics magazine’s expert area but regrettably SILICON CHIP magazine continues to espouse misleading, nonsiliconchip.com.au factual and non-scientific responses regarding the topic of human induced global warming. To deny science is one of the stupidest things a nonscientist can do. To deny science undermines every aspect of a technical magazine. For a technologist or applied scientist to deny science is tantamount to them declaring their “expert” knowledge has no basis in fact. Based entirely on your ongoing and continuing unscientific responses to the subject of global warming, I shall not be renewing my subscription. The economist Nicholas Stern did warn of the economic consequences of disregarding climate change and that disregard has just cost you $100 per year and an erstwhile loyal reader. Robert Suhr, Mt Crosby, Qld. Comment: we do not deny science; quite the opposite. Scepticism has always been a characteristic of scientists, otherwise new science would never have been developed. More and more information is coming to light which casts a great deal of doubt over the global warming movement. We have covered this topic because it is very relevant to the drive for renewable energy. Solar energy is desirable but the way it has been promoted and subsidised in Australia is a gross misallocation of resources. Wind power is worse because it requires constant and very expensive back-up, with costly gas-fired open-cycle power stations or with the much despised coal-fired base power stations. Australia now has an excess of power generating capacity but expensive solar and wind installations are still being heavily subsidised, to the detriment of consumers, taypayers and overall employment. NEW NBN fibre-to-the node will be less reliable Living in Kingston, Tasmania, my suburb is in the second set of suburbs scheduled for completion of NBN. The adjoining Kingston Beach was in the first set and from what I have heard, people are extremely pleased with the performance of fibre to their home connections although many had frustrations with the final connection to the house, with time-consuming legal/boundary issues caused by rerouting cables. Over the last two years, work has been in fitful progress to my road; it should have been completed in March 2013 but has been delayed by various stoppages over safety and other more obscure problems. Finally, with all the asbestos Telecom pits having been replaced by plastic, in June this year my road was ready for individual connections. During this delay, we have had a change of government. In their infinite technical wisdom, they decided to change the game to fibre-to-the-node, a decision I find non-sensical. In July 2013, I was fortunate to be able attend a lecture by the NBN at the Hobart Amateur Radio Club given by the commercial manager and supported by a senior technical officer. The audience was very impressed with the manager’s technical knowledge and enthusiasm beyond her managerial responsibilities. She was equally impressed and totally surprised with audience’s collective technical knowledge. The technical officer, who was also a New Zealand Radio Amateur, had warned her but she was siliconchip.com.au IP Advanced Radio System ip100h Icom Australia has released a revolutionary new IP Advanced Radio System that works over both wireless LAN and IP networks. The IP Advanced Radio System is easy to set up and use, requiring no license fees or call charges. To find out more about Icom’s IP networking products email – sales<at>icom.net.au ICOM 716 www.icom.net.au, November 2014  13 Mailbag: continued Comments on the MEN system Your article regarding the MEN system (SILICON CHIP, August 2014) has provoked a lot of interest. It really applies to the way most house installations are wired, including my own, but there are some points to be made about modern practice where plastic piping is used rather than copper. Firstly, the main earthing conductor connects to the Earth electrode. This has been a requirement since 1976 although installations older than that may not have earth electrodes unless they had alterations since then and had to be updated. The water piping system also connects to the earth bar on the distribution board as do all exposed metal items, involving electrical equipment, in the installation. AS/NZ 3000 states that the resistance of the main earthing conductor (from the Earth bar to the Earth electrode) shall be 0.5 ohms as a maximum. However, there is no requirement for the Earth electrode to have any minimum resistance at all! In the case of my home, the electrode had a resistance of 25Ω! However, I have a large copper water piping system, much of it buried, and this is the main safety feature rather than the Earth electrode. With an installation current of over 20A, I checked the current going to the Earth electrode and through the still surprised at the level of technical questioning. It all made for a lively, highly constructive evening, much enjoyed by both parties. Modules of the fibreto-home distribution system were available for detailed inspection. For someone whose first job in Australia was at the AWA research labs in North Ryde on mobile communications and experimental fibre optics (yes, Australia could make optical fibre in 1973), this was of a great deal of interest. In 1973, all thoughts for application were for trunk routes and the economical distribution to individual dwellings a problem not fully resolved. 14  Silicon Chip water meter. In both cases, the currents measured were zero on a tong ammeter with a full-scale deflection of 6A (the lowest range available). In a house with non–metallic piping there would be a much more dangerous situation if the Neutral became disconnected as compared to a house with buried metal piping. You will not get much help from an Earth electrode unless it has a very low resistance to ground. Even a load current of 10A would bring all the earthed items up to full mains voltage in the event of a house with no water piping connection, an open Neutral and an earth electrode with a resistance of 25 ohms (in 2007/08 there were 522 shock incidents caused by poor or faulty Neutrals in NSW). There is a good case for having a voltage sensing relay connected between the Neutral link and another remote Earth electrode which would disconnect the mains in the event of an open Neutral, maybe via the smart meter. There is a good article on the above issue titled “Options to Improve the MEN System Into The 21st Century” by Chris Halliday – see powerlogic. com.au Your advice about calling for expert help if you experience even a slight tingle is certainly correct. Alex Brown, Ashburton, Vic. I was therefore intrigued how a delicate elegant principle had evolved into a simple and robust practical individual dwelling distribution system. It was recognised even back in the AWA research labs days that the optical fibre was not going to be the expensive part of a practical installation. The system being used by NBN is a simple light pipe from the substation to home and has no interstage electronics, with “non-precision aligned” plug-in takeoffs requiring minimal skills to install. Intrinsically lightning-proof and rot proof, it is I think the natural system for a future secure communications network. It would seem that two tech- nology advances enabled this simple configuration: first, the advent of high power LEDs (the area of technology I was associated with at AWA); and second, the system of digital coding which seems to be an adaptation of a University of WA’s invention in the late eighties called Q.P.S.X, standing for Queued Packet Switching Exchange. What the current government seems to be trying to save is the costly labour-intensive process of laying the fibre into homes through Telstra pits and sorting out a myriad of historical problems with an outdated and ageing (and in some humid parts of the country, chemically decaying) copper system. Although I suspect there has been some artificial bloating of the workforce for this task, it is probably the most mechanically needed part of the infrastructure upgrade (things don’t last for ever). It is also providing much needed local employment for a reasonable period of time. It’s interesting how governments subsidise short term “job creation” most which fail miserably and are penny pinching for needed work on a project of high future national importance. Apart from the cost of placing an active electronic node at the bottom of the road, the use of the old copper wires is a recipe for short, medium and long term problems. It is the old copper street distribution network which causes the costly maintenance problems! Also, fibre to the home allows for expansion of capacity as technology develops. It is a decision to commit to a hybrid system of the worst kind, a typical short-term decision for immediate financial savings by those who do not understand or want to understand the long-term consequences. Whether I get fibre to node or home, even though promised for all current works, has become mystery and after three or four notices of pending connection in the last eight months, so is the day of actual connection. Meanwhile and perhaps not surprisingly, we have had hints of another new policy: you can have a choice of fibre to node or to the home but guess what, you will have to pay an as yet undetermined amount for fibre-to-the-home. Kelvin Jones. Kingston, Tas. SC siliconchip.com.au siliconchip.com.au November 2014  15 GORILLA GLASS: unbelievably unbelievably tough and flexible Most people know that smart phones and many notebook computers use Gorilla Glass but few would know just how tough or flexible this glass is. Unlike ordinary window glass it can be flexed by extreme amounts and it is very hard. In this article we describe how it is manufactured. By Dr David Maddison T hese days, most people have smart phones or tablet computers but may not be aware of the special material that constitutes the front face of most of these devices. These devices often receive rough treatment as they are accidentally dropped, sat upon or otherwise abused and so have to be extremely rugged overall – but most of all the cover glass. It is designed to be thin, tough, optically clear and extremely smooth and is mostly a glass known by the Corning 16  Silicon Chip trade name of ‘Gorilla Glass’. While glass materials are generally brittle there are a variety of special treatments available to make them extremely hard or tough. Examples include lamination of two or more sheets to make automotive windshields or bullet-resistant glass; thermally or chemically-toughened glass as usually used on the side windows of cars and glass tables or doors in homes; and modern glass bottles, some of which will not even always break if dropped on a concrete surface. In portable electronic devices such as smart phones and tablet computers the marketing emphasis is on how thin a device can be made (even though many would prefer a slightly thicker device with a decent battery life!). Every single component is made as thin as possible, including the cover glass. Since normal glass is not strong enough in its usual form when it is made to the desired thinness, special compositions and treatment of glass is siliconchip.com.au needed that makes it both strong and tough as well as thin. Plastic, an obvious candidate material, generally cannot be produced with the look or feel that is found desirable on the working surfaces of smart devices. Glass composition Glass has been manufactured by mankind since around 3500BC where it was produced in Mesopotamia. Before that, natural glass such as volcanic obsidian was used and extensively traded by stone age societies. Glass, in its most basic form is made from silicon dioxide (silica, SiO2) or (mostly) beach sand. Unfortunately this is not practical to use for large scale production (except for specialised applications requiring strength and heat resistance) as it melts at a very high temperature (between 1600 and 1725°C). So other constituents are added which help lower the melting point and also add certain desirable properties. In most common commercial glasses such as window glass, both limestone (calcium carbonate which is turned into lime, CaO) and sodium carbonate (Na2CO3) are added to the silica base along with some other ingredients. This type of common glass is known as soda-lime-silica glass. It is cheap Samples of Gorilla Glass in various thicknesses. and useful but not especially strong. Other common glasses based on silica include sodium borosilicate glass (Pyrex), lead oxide (crystal) glass and aluminosilicate composition (used in fibreglass, halogen light globes and other applications requiring resistance to high temperatures and thermal shock). Corning uses an aluminosilicate glass for its Gorilla Glass. It is roughly intermediate in properties and cost between a common basic soda-lime-sili- Exterior of Glass Interior of Glass 120 80 40 0 40 80 120 Stress (MPa) Cross section of piece of glass showing both the stress profile at the surface and also at the interior. Overall the forces balance but the surface is in compression, meaning that cracks have difficulty starting. The interior is in tension where cracks could easily propagate should they reach that area but they normally don’t, due to the surface of the glass being in compression. siliconchip.com.au ca glass and the exotic pure silica glass and offers a good mix of properties such as good mechanical properties and workability of the melted glass. A typical composition for aluminosilicate glass (but not the secret one used in Gorilla Glass) is silica (SiO2) 57%, alumina (Al2O3) 16%, lime (CaO) 10%, magnesia (MgCO3) 7%, barium oxide (BaO) 6% and boric oxide (B2O3) 4%. How to strengthen the glass Phone glass has to be tough. One way to turn ordinary brittle glass into a much stronger form is by a special chemical or thermal treatment that puts the surface of the glass in compression compared to the interior of the glass. In other words, the surface is made to expand and would tend to occupy a greater volume than it formerly did but it is constrained from doing so as it is held back by the bulk of the glass comprising the interior. The atoms of the surface glass are thus squeezed closer together. This has the effect that it makes it much harder for cracks to initiate or continue to grow should a crack become initiated as the crack edges are being pushed together. If there is no cracking, there can be no failure of the glass. In addition to making the initiation or propagation of cracks harder by putting the surface in compression, crack initiation can also be made much more difficult by ensuring the glass surface is extremely smooth, with a minimal November 2014  17 The atomic structure of the same material, silicon dioxide, shown in both a highly ordered crystalline form (quartz) and amorphous form (silica glass). The red dots represent silicon atoms while the blue represent oxygen atoms. Elements of the basic crystalline structure can be seen in the glassy form at a short range but there is also great randomness to the structure at a longer range. amorphous atomic structure. After the discovery of glass-ceramic, the Corning company started looking at other ways to strengthen glass. It began work with chemically treated toughened glass in the 1960s and developed a product called “Chemcor” as part of its “Project Muscle” initiative to make a glass product that was strong, light and close to unbreakable. This glass was used in small quantities in some early US “muscle cars” in order to lighten their weight as well as some space craft windows and tableware. Ultimately this glass was considered too strong for most applications and its use waned. A further concern was the way in which, when it did fail, the glass would explode which was number of microscopic defects that CorningWare are a hybrid between a reason that some safety eyeglasses can act as crack initiation centres. traditional glass and ceramic materials that used this product were recalled. The number of surface defects in and possess both types of structure. The glass fell out of favour as glass can be minimised by acid treat- Structurally, glass is said to be amor- a lightweight material in muscle ments, polishing or by the cars because, despite the way the glass is cast. One weight saving, human ADVANTAGES OF GORLLA GLASS example is by forming the head impact forces were • Highly scratch resistant. glass onto a smooth molten found, in experiments, to • Very thin and compatible with touch screen technology. be much greater on the metal surface such as tin, as in the case of float glass. Chemcor glass compared • Very lightweight. Gorilla Glass is made with with laminated glass • Allows thin and lightweight devices without fragility. an extremely smooth surface which had been in use • Available thicknesses 0.4 - 2.0 mm. which not only makes it in cars since the 1930s. • Low distortion of underlying image. extremely transparent but The latter glass had some • Optically clear. makes the image of the un“give” thus reducing derlying display distortion• Extremely smooth. head injuries. free. It also makes the glass Project Muscle was • Recyclable. pleasant to touch and resistshelved in 1971. The ant to staining. phous (a pseudo-random structure) Chemcor class of chemically toughGlass technology has continued while ceramic materials are crystalline ened glass products then became a to improve throughout the ages but (a regular structure). Gorilla Glass is solution in search of a more suitable particularly from the 20th century a pure glass with a pseudo-random, problem to solve. until the present as material behaviour came to be understood at the atomic and molecular level. Glass strength in particular has undergone constant improvement. Thermally toughened glass was first patented in 1900. Laminated glass, which was invented in 1903, was an accidental discovery. Similarly by accident, in 1953 a Corning scientist discovered a remarkable form of material called a glassceramic which they called Pyroceram which found its way into laboratory ware, missile nose cones and microwave oven ware. In 1958, a consumer product was released into the market The 1965 Dodge Coronet A990 muscle car which was specially lightened by place which is familiar to most people a number of modifications, including the removal of some trim and the use today – hard-to-break CorningWare of Corning Chemcor glass windows instead of regular glass. It was an early, dinnerware. “hi-tech” consumer-end use of chemically strengthened glass. There is an Glass-ceramic materials such as unexpected connection between this car and the modern smart phone.... 18  Silicon Chip siliconchip.com.au The fusion draw process. Two streams of molten glass flow down both sides of a v-shaped trough, rejoin at the base of the v and then solidify. It is a continuous and highly automated process. Along comes Apple Then along came Steve Jobs from Apple Inc. In the various published accounts of how Apple requested a new glass product for the iPhone, certain details seem to vary but the following account is supported in the biography of Steve Jobs by Walter Isaacson and also quotes of Jobs and the Corning CEO in 'Wired' magazine. Steve Jobs unveiled the original iPhone to the public on 9th Jan 2007 and it was released on 29th June 2007. For some period before the original unveiling it is said that Steve Jobs had been carrying around an iPhone prototype in his pocket and was upset that the plastic face had become scratched from keys in his pocket. Presumably the prototype screen face was made of plastic. He ordered his staff to find a solution and time was running out before the release date. He wanted a scratch-resistant glass face on the phone. In February 2007 Steve Jobs decided to visit Corning in New York where he met with the CEO Wendell Weeks. He told him that he wanted to have tens of thousands of square metres of very thin, ultra-strong and ultra-scratchresistant glass, a product that did not yet exist and within a seemingly impossible time frame of six months (or less). According to Walter Isaacson, Steve Jobs said to Wendell Weeks “This is what I want, a glass that can do this”. Wendell Weeks said “We once created siliconchip.com.au a type of process that created something called Gorilla Glass”. Steve Jobs said “No, no, no. Here’s how you make really strong glass”. Wendell then said, “Wait a minute, I know how to make glass. Shut up and listen to me”. Wendell Weeks then described the process to make Gorilla Glass. Steve Jobs then said “Fine. In six months I want enough of it to make – whatever it is – a million iPhones”. Wendell then said “We don't have the capacity – none of our plantes make the glass now.” Steve Jobs looked at him and said what he said to Steve Wozniak 20 or 30 years earlier: “Don’t be afraid, you can do it”. Wendell Weeks later told the biographer “I just sat there and looked at the guy. He kept saying, ‘Don’t be afraid. You can do this.’”. While Chemcor glass would be a good starting point this product was not suitable as it was, because it was made much thicker at around 4mm and Apple’s requirement was for glass that was around 1.3mm thin. It was not known if the Chemcor process could be scaled to make much thinner glass and whether the chemical toughening would work with that thinness and the glass still remain ultra-strong. In fact, before Steve Jobs came on the scene with Apple’s requirements, in 2005 Corning had already resurrected internal interest in the Chemcor glass, known in-house as 0317. Motorola had introduced the Razr V3 flip phone which used a glass front screen instead of plastic and Corning wondered if there could be a speciality market for this kind of glass for phones and other small devices like watches. Such a glass would need to be strong like Chemcor but very thin and smooth. Marketers concluded there KNO3 BATH GLASS SURFACE GLASS (CS) COMPRESSIVE STRESS LAYER Composition, depth of layer (DOL) and compressive (CS) are key characteristrics. DOL refers to the depth of the compressive stress layer. (TS) TENSILE STRESS AREA O2 Si Al K:1.33Å Na: 0.97Å Model is for illustration purposes only, illustration is not to scale The aluminosilicate glass is placed in a bath of molten potassium nitrate, KNO³ (common name, saltpetre) and some of the sodium atoms near the surface (grey, 0.97Å in diameter) leave the glass and are replaced by much larger potassium ones (yellow, 1.33Å in diameter). This results in the surface layer being placed in compressive stress and the interior layer in tensile stress. Other elements present in the composition of the glass are oxygen, silicon and aluminium. November 2014  19 Computer model of atomic structure near surface of Gorilla Glass during the ionexchange process, looking from the inside out. Note the larger yellow potassium atoms entering the surface, which are replacing the smaller grey sodium atoms. was a demand for glass of this nature but researchers had not got far by the time in February 2007 when Apple started demanding massive quantities of it. Nevertheless, the project to make glass for this speciality market had the codename “Gorilla Glass”. Fortunately, Corning, while it is a big company, thinks like a small company with a can-do attitude. After the meeting with Steve Jobs, Corning started experimenting with different glass compositions and was coming close to something suitable by the end of March 2007. Inventing a new manufacturing process and equipment for the glass in the short time frame provided was totally out of the question and Corning had to find ways to adapt existing manufacturing processes and equipment to make the glass. And it had to be amenable to producing very large amounts of materials for the millions of iPhones expected to be made. There is only one way to make nearperfect, thin sheets of glass in very large quantities. This is the fusion draw process and it is a proprietary technology that Corning is highly experienced with and a reason for their technological leadership. It is capable of producing exceptionally flat and smooth uniform-thickness sheets of glass with surfaces that are free of contamination (unlike the float 20  Silicon Chip glass process where one surface comes in contact with molten tin). The fusion draw process was first developed in the 1960s for the production of the aforementioned muscle car windshields, shelved and then reinvigorated for Gorilla Glass. The process is also used by Asahi Glass Co, Nippon Electric Glass, and Samsung Corning Precision Glass for making thin, large area glass for flat screen display panels. Fusion draw is a continuous flow process (also known as the overflow down-draw method). Molten glass is continuously loaded into a V-shaped trough and overflows on both sides, runs down the sides and then both flows join together at the bottom of the V to make a continuously moving sheet of glass flowing toward the ground. As the glass progresses it cools and solidifies. Auto- mated machinery cuts off pieces of the glass and stacks them. As with all well-thought-out processes, it sounds simple but just imagine the massive amount of fine tuning that would have been required to make it work perfectly. It was critically important to get the composition of the glass just right as it had to melt at a usable temperature, had to have the right viscosity and it had to produce a glass with reasonable optical and mechanical properties as well as being amenable to the chemical toughening process. This involved juggling the proportions of the six standard ingredients in aluminosilicate glass (see above) as well as a seventh secret ingredient. A Corning YouTube video of the process can be seen at http://youtu. be/q4ZU7zUxdM8 (or search for “The Fusion Process: At the Core of Corning’s Glass Innovations” on YouTube). Once the glass has been cut into sheets and stacked, it is still not Gorilla Glass. It has to be cut and shaped to final size and then surface toughened by an ion-exchange-process. How is Gorilla Glass toughened? After the fusion draw process described above the glass is sent to another factory for cutting to final shape and then it is subjected to an ion-exchange process to place the surface of the glass in compressive stress which is the key to the great strength of this glass. The ion-exchange process involves dipping the glass in a molten bath of potassium nitrate for a period of A 38cm diameter sapphire “boule” from GT Advanced Technologies. To make cover glass for smart devices pieces have to be sliced off with a diamond saw or using a laser process. Sapphire is a potential competitor to Gorilla Glass and is more scratch-resistant but much more expensive and not quite as transparent. siliconchip.com.au time. This causes the small sodium atoms to leave the surface regions of the glass while larger potassium ions enter the glass. Gorilla Glass itself is made in the USA but it is sent to a factory in China for final cutting and toughening. The iPhone 6 – Gorilla Glass or Sapphire Crystal? Apple has never stated what it uses for the cover glass in its various smart products but it is certain that Gorilla Glass was used for the iPhone 1 and it is widely believed that Gorilla Glass is what it uses for all other past and current models of iPhones and iPads. There was recently much speculation as to whether the iPhone 6 would use Gorilla Glass or sapphire crystal as its front glass but it has now been established that the main display glass is not sapphire. Sapphire crystal (aluminium oxide, -Al2O3) is used as the “glass” on high end watches now because of its high hardness and therefore scratch resistance but in that application it is relatively thick and heavy. Sapphire crystal is many times more expensive, 1.6 times heavier and requires 100 times more energy to produce than glass and it is not quite as transparent as Gorilla Glass. Gorilla Glass is strong (but not indestructible). Here a 0.7mm thick sample of Gorilla Glass 2 is subject to a 70mm deflection in a three point bending test. Due to its higher refractive index, sapphire has been claimed to be more reflective than Gorilla Glass. Also, because it is not quite as transparent as Gorilla Glass, the underlying display would need to be brighter and thus more energy-consuming. While it is more scratch-resistant than glass, sapphire does still break. In terms of scratch resistance, sapphire has a hardness of 9 on Mohs scale compared with 10 for diamond and around 7 for Gorilla Glass 3. Nevertheless, Gorilla Glass is not likely to scratch in normal use. The iPhone 5 already uses sapphire for the camera lens cover and the 5S also uses it for the fingerprint scanner. Speculation that Apple may use sapphire for the display in the iPhone 6 arises from its deal with GT Advanced Technologies to supply sapphire materials but these may currently be just for the camera lens and fingerprint scanner (should one be installed) or other products such as the Apple Watch. GT Advanced Technologies certainly has the capability to make very large crystals or “boules” (single crystal synthetic ingots) of sapphire for special applications as shown in the illustration of a piece that is 38cm in diameter. Ultimately, it is thought that Apple did not proceed with sapphire for the main screen on the iPhone 6 because of both supply and cost. GT Technologies was thought not to be capable of ramping up production of flawless large pieces of crystal for an estimated 80 million iPhone 6s. Sapphire will be used on the Apple Watch which will have a much smaller display (38mm or 42mm depending on model) than the phone. Gorilla Glass is not unbreakable Testing Gorilla Glass in the laboratory to measure mechanical properties. siliconchip.com.au Some people have interpreted the great strength of Gorilla Glass to mean that the product is unbreakable. Nothing is unbreakable and it is certainly true that sometimes the Gorilla Glass of smart phones and tablets does break if the devices are dropped onto concrete or other hard surface. There are numerous “tests” people November 2014  21 have done that can be viewed on YouTube in which the outcome is that the glass either does not break under the challenge or it does. What is impressive is the significant amount of abuse that the glass will usually take before it finally breaks. It is interesting that people are prepared to sacrifice their perfectly good phones for these demonstrations. Like any advanced electronic devices phones and tablets have to be treated with respect. As part of their ongoing quality procedures, Corning obtains whatever phones it can with failed Gorilla Glass and examines the failure mode and tries to see how such failure modes can be avoided. Future development Apart from smart phones, tablet and slate computers Gorilla Glass is being increasingly used in notebook computers, as a large cover glass on large scale interactive digital displays, digital signage and marker boards. In interior architecture, designers are exploring the possibilities of making entire walls with Gorilla Glass. Other emerging applications will rely upon glass properties such as it being sleek, cool to the touch and readily cleanable, possessing exceptional damage resistance and being compatible with touch screen technologies. It can also be printed on if necessary. Other anticipated developments include different surface treatments to make the surface antimicrobial (already unveiled), less reflective and less susceptible to fingerprints. MILESTONES IN THE DEVELOPMENT OF GORILLA GLASS • Billions of devices have now been produced that utilise Gorilla Glass. Since the release of Gorilla Glass 1 in 2007 it has been used on 2,400 different models of smart devices, over 33 brands. • Gorilla Glass 2 was released in 2012 and achieved a 20 percent reduction in thickness compared with the previous formulation while keeping its damage resistance, toughness and scratch resistance. The reduction of thickness allowed thinner devices with greater touch sensitivity and brighter images. • Gorilla Glass 3 was released in January 2013 with a feature known as Native Damage Resistance. It is up to 40% more scratch resistant and three times more damage resistant than Gorilla Glass 2. To achieve this the glass was reformulated and extensive atomicscale computer modelling was undertaken. • In July 2013 Corning introduced Gorilla Glass NBT for touch screens on notebook computers. The glass provides improved scratch resistance, reduced scratch visibility and better retained strength when a scratch does develop. According to Corning's marketing materials this glass avoids a common form of damage that happens when a notebook computer screen is closed and there is something on the keyboard such as a pen or USB drive, which causes the screen to break. • Antimicrobial Gorilla Glass has now been developed and unveiled and incorporates ionic silver, which renders the surface of the device anti-microbial for the life of the device. Conclusion At no time in history have materials scientists understood more about the behaviour of materials in terms of their atomic and molecular structures. In addition, never has the ability to do computer modelling of materials been greater than now. This enables scientists and engi- neers to develop materials with properties that were not conceivable even decades ago. Gorilla Glass is but one example of a highly engineered material that improves our technological progress and makes our daily lives so much easier. There will be many more materials SC like it. Companion products Corning has also developed companion materials for Gorilla Glass: Willow glass is a flexible borosilicate glass for display substrates. It will allow the use of flexible, printed displays. Delivered on a roll like newsprint, it is anticipated that the display elements will be printed onto the glass akin to a newspaper printing operation. In roll form the glass can be up to 1.3m wide by 300m long and in sheet form it can be up to 1.1 by 1.2m and 0.1 to 0.2mm thick. Lotus glass is designed as a substrate for OLED and next-generation LCD displays. It is to be used as a display backplane in conjunction with Gorilla Glass for cover material. 22  Silicon Chip Another of the many stringent tests Gorilla Glass is subjected to in the laboratory. siliconchip.com.au ACOUSTIC TREATMENT If you make amplifiers, speakers or just like to listen to audio, treat your listening environment and be amazed at the difference. AURALEX - The best name in acoustic treatment - NOW AVAILABLE. PANELS TRAPS siliconchip.com.au ANALYSIS ISOLATION www.elfa.com.au November 2014  23 Electric Factory Pty Ltd 188 Plenty Road Preston VIC 3072 T: 03 9474 1000 E: sales<at>elfa.com.au Watch Free-to-Air TV on your Smartphone, Tablet or Laptop By ROSS TESTER The photo above is not a wide-screen TV set – though it is showing a wide-screen free-to-air TV image. It’s actually a still image on an Android laptop, showing a televised World Cup match in real time! T he internet is a wonderful, powerful thing. Just think of the things it lets you do every day as a matter or course, which you never would have dreamed of, say ten years ago. But there is another, seldom-thoughtof benefit of the internet: it has in fact spawned the development of a plethora of equipment to use this power – again, equipment which was only the often outlandish musings of science fiction writers of a decade earlier or so. 24  Silicon Chip Take smartphones, for example. These amazingly powerful computers (for that’s what they are) often relegate the ‘phone’ function to a distant second place. It’s all about apps (applications for you Luddites!) which turn your smartphone into, well, anything you want. Now there’s TV on the move Add a tiny USB dongle to your smartphone and you’re able to watch free-to-air digital TV services wherever you are – without using either your phone service or even a broadband connection. We should add that Australian TV services are now all-digital, with analog TV now permanently off the air. And perhaps we should also add that we are talking here about Android phones. Despite all the marketing hype, Android holds about 70% of the smartphone market (and its still growing). Apple users – don’t despair: there are similar services available for siliconchip.com.au you. But they’re not what we are talking about here. Back to the Android smartphone and TV. Recently, Altronics sent us one of their ‘PadTV’ packs to try out. Their Director, Brian Sorensen, waxed lyrical on the ‘phone about how amazing the tiny dongle was. And now we know why! The PAD TV Tuner dongle You almost feel cheated when you look at the dongle. It’s not much bigger than your thumbnail. Yet within this tiny device is all the ‘smarts’ to turn your Android (4.1 or higher) device into a very high performance TV and even a DVR. Think about that for a minute: virtually a complete TV tuner in a package that’s MUCH smaller than the remote control for your home TV! Of course, it doesn’t get anywhere without the computer power of your smartphone or tablet but you carry that in your pocket anyway. Now you can take TV wherever you want it – obviously, assuming there is a TV station to pick up. Whether that’s camping out, on a boat, at a sportsground, in a car (maybe!), at Shown significantly oversize for clarity, the front of the PAD TV tuner has a micro-USB plug to mate with your Android smartphone, phablet or tablet, while the rear has a SSMB connector to take one of the supplied mini antennas. An SSMB-to-TV antenna adaptor is also supplied to connect to an outside antenna. work (sorry, boss – it’s research. . .), you name it – mobile TV at its finest. Now before you take those locations/situations as gospel, we should point out that there are limitations. The most obvious is that there must be a good strength TV signal. That’s not just a function of the dongle and its tiny antenna (though naturally, that does have a major influence), it’s also a function of digital TV with its ‘digital cliff’. You either have a picture, or you don’t – there’s no in-between snowy half-picture like there was with analog. TV reception in a car is also a bit hit- and-miss for much the same reason, added to the fact that the moving car is likely to be in and out of good signal areas, between city buildings, behind hills or mountains, even a large dense tree can interfere with reception. So while it might be tempting to keep the kids amused on a long trip with the PAD TV, it’s probably best to have some DVDs or games available as well! Another limitation is the size of the screen on your device. It might seem pretty cool to watch TV on a 3.5-inch phone but the lack of detail is less than satisfying. Seeing any horse in the Radio, Television & Hobbies: the COMPLETE archive on DVD YES! NA R O M E THA URY T N E QUARTER C NICS O OF ELECTR ! HISTORY This remarkable collection of PDFs covers every issue of R & H, as it was known from the beginning (April 1939 – price sixpence!) right through to the final edition of R, TV & H in March 1965, before it disappeared forever with the change of name to EA. For the first time ever, complete and in one handy DVD, every article and every issue is covered. If you’re an old timer (or even young timer!) into vintage radio, it doesn’t get much more vintage than this. If you’re a student of history, this archive gives an extraordinary insight into the amazing breakthroughs made in radio and electronics technology following the war years. And speaking of the war years, R & H had some of the best propaganda imaginable! Even if you’re just an electronics dabbler, there’s something here to interest you. • Every issue individually archived, by month and year • Complete with index for each year • A must-have for everyone interested in electronics Please note: this archive is in PDF format on DVD for PC. Your computer will need a DVD-ROM or DVD-recorder (not a CD!) and Acrobat Reader 6 or above (free download) to enable you to view this archive. This DVD is NOT playable through a standard A/V-type DVD player. SILICON CHIP Exclusive to ONLY 62 $ 00 +$10.00 P&P HERE’S HOW TO ORDER YOUR COPY: BY INTERNET:^ siliconchip.com.au 24 Hours 7 Days <at> BY EMAIL:# silchip<at>siliconchip.com.au 24 Hours 7 Days BY PHONE:* (02) 9939 3295 9-4 Mon-Fri * Please have your credit card handy! # Don ’t forget to include your name, address, phone no and credit card details. siliconchip.com.au BY FAX:# (02) 9939 2648 24 Hours 7 Days BY MAIL:# PO Box 139, Collaroy NSW 2097 ^ You will be prompted for required information November 2014  25 Melbourne Cup is difficult; identifying it by number or even jockey colours is near impossible! That’s where the larger screens of today’s phones, phablets and tablets really makes a difference. Assuming you don’t have either wrong version Android or wrong port problems, search for the PAD TV app in Google Play, download it and install it. The first one we found was a freebie; there may be others offering more facilities but we didn’t bother to go further. Using it Unfortunately, it’s not simply a matter of plugging in and playing (or viewing in this case). First, you need to download the appropriate app. As an Android device, you would log on to Google Play and search for Pad TV. And here is where you might find the first (and often insurmountable) hurdle. Remember a moment ago we mentioned that you needed to have Android 4.1 or higher. For the latest smartphones and tablets, that shouldn’t be a problem. Check it by going to ‘settings’, thence ‘about phone’ and scroll down to ‘software information’. If it doesn’t say ‘Android version 4.1’ (or higher), you’re out of luck. Yes, some phones can be updated but unless your manufacturer has the appropriate patches, you’re on your own. Your smartphone or tablet must also support USB On-The-Go, or USB OTG. This is a specification and standard that allows USB devices such as digital audio players or mobile phones to act as a host allowing a USB flash drive, mouse, or keyboard to be attached. Most devices now do (especially those with Android 4.1+) but it’s worth checking your specs. Tied up with this is another potential sticking point – the USB port itself. The micro USB male plug on the PAD TV dongle needs to mate with a USB micro female socket (also known as, respectively, type B and type A). Fortunately, these days most smartphones have that micro USB type B port we mentioned earlier. That means the PAD TV dongle will plug straight in. But it’s not always the case. And if you can’t find PAD TV? Once the app is downloaded and installed, setup is straightforward, logical and quick. There are (currently) four types of USB ports: the ‘standard’ type A male and female, the smaller type B male and female, the Mini-A, the Mini-B and finally the Micro-A and MicroB. As their name implies, the micro USB ports are the smallest. There is a combined Micro-A and Micro-B socket which is designed to allow USB OTG, as mentioned earlier. Incidentally, despite countless millions in use, Mini-A and Mini-B USB sockets are now regarded as obsolete. Unfortunately, tablets often have only standard or mini USB ports (or perhaps even a proprietary data connector). You might be able to find an adaptor (did your Tablet come with one?) but if you can’t connect the PAD TV, you’re out of luck . . . again. We found female micro USB adaptors almost impossible to buy. Note that we did say almost! We eventually found one on ebay for the unbelievable price of $2.39 (including postage from China!). Here are the two antennas supplied – the small loop antenna shown plugged into the PADTV Tuner (above) and the small whip antenna on a base, as seen at left. Just be aware that small antennas such as these don’t pick up a whole lot of signal so you need to be in a strong signal area. 26  Silicon Chip We mentioned earlier that the PAD TV dongle requires Android 4.1 or higher to operate. If you cannot find PAD TV when you log onto Google Play and search for it, the chances are your smartphone is not Android 4.1 – Android is clever enough to only show those apps that will operate with the Android iteration on your smartphone. (Go to Google Play from Windows, for example, and you’ll see all that are available). Setting up Once the app is installed, when you plug in the PAD TV dongle, the app will automatically find it and load it. Then you need to set it up. First, you will need to select the appropriate country from the ‘settings’ menu then scan for available channels. This takes a few minutes, particularly if you’re in an area with lots of TV signals. Here’s where you might discover one or more of those wrinkles we mentioned earlier. Our first scan, indoors (wet brick walls), discovered 16 channels but no ABC, 7 or 10. And when we tried to view any of them, they all said ‘No Signal’. Our second scan was outside and this yielded 60 channels, including multiple ABCs, 7s, 9s, 10s, Gems, etc etc. However, not all worked – again, many said ‘No Signal’. But the ones that did work ranged from patchy to excellent. Obviously the PAD TV was picking up translators from here, there and everywhere – but most didn’t have enough power to give us a picture. You can sort the channels into the order you want them by selecting ‘sort channels’ and dragging the three horizontal bars on the right side of the listings and dropping them into position. It would make sense to place the unusable channels at the back of the queue (so far, we haven’t worked out siliconchip.com.au how to delete them but there must be a way!) Antenna adaptor plug If you can’t find any channels, or if you can’t get a picture on any that are found, Altronics include an SSMB-toPAL adaptor which allows you to plug the PAD TV dongle into your home TV antenna. Assuming you have a reliable picture on your home TV, this is a proofof-operation which will allow you to go through the above steps and make sure it’s all working for you. Of course, reverting to the tiny loop or whip antennas might not give you any joy but at least you’ll know that it does work with your smartphone. The phone’s ringing! And speaking of your smartphone, what happens if you are watching TV and someone calls you? No problem – the phone becomes a . . . phone! (It reverts to TV when the call is over). Power While we haven’t measured it, we would imagine that watching TV on your smartphone would be fairly hun- gry on the battery. In fact, the PAD TV dongle itself gets fairly warm with continual use, suggesting that it is dragging a bit of power. So if you need your phone to be always available for phone calls, that’s something to keep in mind. We noticed the battery level symbol had dropped down a couple of notches in the time we were playing researching. Obviously, you can’t plug in a charger while watching TV as they both use the same Micro USB socket. The verdict? Even at significantly higher price, we would rate the PAD TV dongle as a bargain. Of course, there’s plenty of apps around to let you stream live TV to your device (want to watch TV from outer Mongolia?) but all these cost you bandwidth – and significant bandwidth at that. On a limited plan, that’s going to cost you plenty. Not so the PAD TV. Because it receives its signal off-air, there is no bandwidth overhead once you’ve downloaded the PAD TV app (about LINTEK INTO RADIO? How about SiDRADIO? Take a <$20 DTV Dongle and end up with a 100kHz-2GHz SDR! Published October 2013 Don’t pay $$$$ for a commercial receiver: this uses a <$20 USB DTV/DAB+ dongle as the basis for a very high performance SSB, FM, CW, AM etc radio that tunes from DC to daylight! Want to know more? Go to siliconchip.com.au/project/sidradio Want to know more? Go to: siliconchip.com.au/Issue PCBs & Micros available from PartShop /2011/July/Ultra-LD+Mk.3+200W+Amplifier+Module 16MB). So, with the proviso that you must be in a good signal area, you can watch TV on your smartphone wherever you go. We love it! Where from, how much? The PAD TV Digital TV for Android phones package (dongle, loop antenna, tiny whip antenna and PAL-SSMB adaptor) costs just $69.95 and is available from any Altronics store, reseller of via their website (www.altronics. SC com.au). Cat no is D2800. PRINTED CIRCUITS TOMORROWS PRINTED CIRCUITS TODAY Incorporated in 1986, Lintek is a quality Australian manufacturer of Microwave printed circuit boards. Lintek’s patented High Vacuum Deposition process enables the production of extremely accurate microwave circuit features on a wide variety of conventional and exotic substrates including precision milled metal backed carriers. High bond strength to PTFE and minimal side wall undercut are two key features synonymous to Lintek’s process. This innovative process allows Lintek to provide PCB’s for the latest high frequency commercial or military designs as well as the standard FR4 Single sided, DSPTH and Multilayer circuit boards. Unrivalled Accuracy i) Lintek’s process requires significantly less etching to remove a very thin 1-2 micron vacuum deposited copper seed layer instead of the standard 18 microns copper base layer used on Electroless copper processes, thus eliminating undercut and ensuring the repeatability of:a. very fine track and spaces. b. accurate copper features and filters. c. near perfect side wall resolution. d. superb impedance control. Repeatability of Fine track and spaces. e. High bond strength to exotic substrates ii) Plated through holes are stronger and more reliable due to the same amount of copper being deposited in the hole barrel as on the surface. This is particularly important on PTFE materials, which have a large thermal expansion in the Z direction. iii) The elimination of Sodium etching that is normally used on PTFE materials, this saves time, cost and our environment. Testing and Verification Quality System AS/NZS ISO 9001:2008 compliant. Underwriters Laboratories (UL) Approval File Number EI24884. IPC-A-600 Trainer on staff, all Inspectors are IPC-A-600 Certified Specialists. Compliance certification is available on request. Please visit our website to see our latest stock list. www.lintek.com.au Lintek Pty Ltd, 18-20 Bayldon Road, Queanbeyan NSW 2620. Australia Tel: +61 2 6299 1988 Fax: +61 2 6297 6958 sales<at>lintek.com.au siliconchip.com.au Near perfect side wall resolution and minimal undercut. Strong plated through holes, Copper on the surface and through the hole is the same thickness. ISO9001:2008 UL Approval November 2014  27 The Currawo 2 x 10W Stereo Valve Ampl The Currawong amplifier is a tried and tested valve amplifier circuit which has been adapted to components which are readily available in 2014. Each channel uses two 12AX7 twin triodes for the preamp and phase splitter stages and two 6L6 beam power tetrodes in the class-AB ultra-linear output stage. It performs very well, with low distortion and noise. 28  Silicon Chip siliconchip.com.au I This progress view of the amplifier shows it sitting in its timber plinth but without the protective Perspex covers in place to protect the PCB and protect the user from high voltages. N DESIGNING this amplifier, we wanted to present a unit which is straightforward to build and which has a good appearance. To satisfy the first requirement, most of the circuitry, with the exception of the power transformers, is mounted on a large double-sided PCB. Hence there is no need for point-to-point wiring from valve sockets, tag-strips, tag-boards or any of that stuff from 60 years ago. Using the large PCB also means that we have avoided the need for an expensive metal chassis. Instead, the PCB slides into a timber plinth stained as rosewood (although you can have any timber finish you desire). As a nice finishing touch, most of the PCB will be covered and protected by a Perspex cover. This will prevent little fingers from touching any part of the circuit and remove any risk of electric shock which would otherwise be possible. We hope you will like the appearance. There are two toroidal power transformers used to power the Currawong and these are concealed underneath the PCB, towards the back of the unit. Control panel By Nicholas Vinen ong ifier, Pt.1 • 10W per channel • Low distortion • Good performance • Easy to build siliconchip.com.au At the front of the timber plinth, there is a small control panel suspended below the main PCB. This carries the volume control, the on/off switch, a bi-colour red/green LED, a blue LED and the headphone socket. And while it might seem like a waste to use the Currawong Stereo Valve Amplifier to drive headphones, we know from long experience that readers will definitely want this feature. By the way, the red/green LED comes into play when you first turn the amplifier on. There is an initial delay while the valves heat up and during this time, no HT (high tension or high voltage) is applied to the plates of the valves which could otherwise suffer damage in the long term. So during this delay, the LED is red. Then, when the HT is applied, the LED changes colour to green, indicating that normal operation is possible. The other LED is lit when the headphones are in use. Plugging into the headphone socket enables a relay which disconnects the loudspeakers and connects the headphones via 220Ω resistors. At the rear of the timber plinth is another panel which accommodates the RCA input sockets, the binding post terminals for the loudspeakers and a fused IEC socket for the mains cord. Both the front and rear panels are made from PCB material to provide a high-quality finish. The overall performance is summarised in an accompanying panel and three graphs. It gives very good performance for a valve amplifier. Circuit concept A major difficulty in the design of the Currawong has involved the out­ put transformers. As valve aficionados will be aware, the output transformer is usually the most expensive component in the circuit, apart from the valves themselves. Similarly, these days the power transformer is also very expensive, simply because there is no locally available off-the-shelf unit which can be pressed into service. Yes, you can purchase imported power and output transformers but if we had specified these, the total cost of the amplifier would have been a great deal higher. Instead, we have taken a very unusual approach in selecting the output transformer by employing a standard off-the-shelf 15W line transformer (Altronics M1115) which would normally be employed with a professional solid-state PA amplifier to drive 100V lines. As a line driver, the transformer’s primary winding is driven by a solidstate amplifier and it steps up the voltage in its multi-tapped secondary winding. In the Currawong though, we drive the transformers back to front, with the push-pull valve output stages driving the 100V windings and the primary windings becoming the lowimpedance drive for the loudspeakers. Conveniently, the 100V winding has a centre-tap, which is necessary for push-pull operation. In addition, we use some of the other taps for the “ultra-linear” connection. Make no mistake though; while these are low-cost transformers (being made in large quantities), they have grain-oriented steel cores, a wide frequency response and low harmonic distortion. Better still, the taps on the primary winding enable it to be connected for ultra-linear push-pull operation. On the other hand, selection of this transformer is one of the two limiting factors in the maximum output power of the Currawong, at close to 10 watts per channel. The other factor is the power transformer selection. We would have ideNovember 2014  29 Features & Specifications • • • • • • • • • • • • • • Channels: 2 (stereo) • Dimensions: 294 x 304 x 186mm (W x D x H) including protrusions Valve line-up: 4 x 12AX7 twin triodes, 4 x 6L6 beam power tetrodes HT supply: ~310V, actively filtered Tested load impedances: 4Ω, 6Ω, 8Ω Output power: 2 x 10W (8Ω, 6Ω), 2 x 9W (4Ω) (see Fig.3) Operating mode: Class-A (8Ω), Class-A/AB (6Ω, 4Ω) Input sensitivity: ~1V RMS (8Ω, with feedback enabled) Signal-to-noise ratio: 77dB Channel separation: >60dB, 20Hz-20kHz (4Ω, 6Ω & 8Ω) Harmonic distortion: typically <0.1%, 6Ω & 8Ω (see Figs.3&4) Frequency response: ±0.6dB, 30Hz-20kHz (see Fig.5) Damping factor: >20 (8Ω), >10 (4Ω) Mains power draw: typically 120-130W Other features: ultra-linear outputs, remote volume control option, delayed HT, HT soft-start ally liked to use a transformer with much higher secondary voltages but a specially-designed power transformer would be much larger and more expensive, as already noted. Having said that, there is future potential for this amplifier to be upgraded with better (more expensive) transformers to enable it to deliver substantially more output power. The valves can be replaced without any disassembly. Their sockets are mechanically mounted to the thick (2mm) PCB to prevent the solder joints from breaking loose during valve removal or insertion. The thick PCB also helps to support the relatively high weight of the output transformers, which are mounted on the board for ease of construction. Temperature-sensitive components such as electrolytic capacitors have been kept away from the high-dissipation components, primarily the 6L6 valves and associated 5W cathode resistors. However, due to the compact size we have not been 100% successful; one of the large filter capacitors is near the output valves. Checks of its temperature during extended operation show that direct heat transfer is minimal and should not be a problem. Semiconductors There are some semiconductor components in this circuit but not in the audio signal path. Mostly, these 30  Silicon Chip perform power supply filtering, to get rid of ripple and keep the amplifier quiet. The HT delay and soft-start circuit is also built using solid-state components. We should acknowledge considerable input to the design of this amplifier from Allan Linton-Smith, the designer of the Majestic loudspeaker system featured in the June and September 2014 issues. Allan built the first hard-wired prototype and the concept was then considerably refined and transferred to the final PCB featured in these pages. Allan also suggested using the Altronics line transformers, based on a discovery by Grant Wills that they could be used as cheap and effective ultra-linear valve output transformers – see http://home.alphalink. com.au/~cambie/6AN8amp/Grant _ Wills_6CM5amp.htm Circuit description Fig.1 only shows the circuit for the left channel signal path. The right channel is identical and the corresponding component numbers are provided in blue. The line-level input signal from RCA socket CON1 has a 1MΩ DC bias resistor to ground, in case the signal source is floating. The signal then passes through an RF-rejecting lowpass filter comprising a 120Ω series resistor and 100pF ceramic capacitor. The signal is then AC-coupled to (nominally) 20kΩ logarithmic volumecontrol potentiometer VR1 by a 1.5µF MKT capacitor. This gives a -3dB lowend roll-off at 5Hz. Note that depending on part availability, a motorised potentiometer with a value as low as 5kΩ may be used, in which case the -3dB point rises to 21Hz. The wiper terminal of VR1 is connected to ground via a 1MΩ resistor so that if it briefly goes open circuit during volume changes, the grid of V1a does not float. The signal is fed to this grid via a 22kΩ RF stopper resistor. V1a and V1b form the preamplifier, which is very similar to Jim Rowe’s design from the February 2004 issue of SILICON CHIP (“Using The Valve Preamp In A HiFi System”). Essentially, this consists of two common cathode amplifier stages in series, with negative feedback around both. V1’s plates are fed from a filtered HT rail of around 224V DC, somewhat less than the 308V DC main HT rail due to voltage drops across the two RC filter resistors (6.8kΩ and 47kΩ). These filters reduce coupling between channels, reduce coupling from the output stage to the preamp stages and minimise supply ripple reaching the preamp. The preamp is the most noisesensitive section as the signal level is lowest here. In fact, because hum can be picked up from AC-powered heater filaments, we are running the 12AX7 filaments from regulated 12V DC. Self biasing All valves in the circuit are selfbiased. V1a’s anode runs at around 120V, ie, 224V minus the drop across the 270kΩ resistor. With zero bias, a 12AX7 will conduct around 3mA at this voltage, dropping to near-zero with a grid-cathode bias of around -2.2V. With a 3.3kΩ cathode resistor, V1a’s operating point tends to settle at about 0.3mA and thus the cathode is 1.2V above ground. The output signal from V1a’s anode is coupled to V1b’s grid by a 220nF capacitor and this grid is DC biased using a 1MΩ resistor to ground. V1b runs at a higher power than V1a, with a 680Ω cathode resistor giving an operating current of around 1mA. Therefore, its anode load resistance is lower at 100kΩ. The output at V1b’s plate is coupled back to V1a’s cathode via a pair of parallel 470nF polyester capacitors siliconchip.com.au siliconchip.com.au November 2014  31 Fig.1: the left channel circuit of the Currawong Stereo Valve Amplifier (the right channel is identical). The incoming signal passes through a low-pass RC filter and volume pot VR1 and is then fed into V1 (a 12AX7 twin triode) which provides signal preamplification in two stages. Its output is then fed to V2 (another 12AX7 twin triode) which operates as a phase splitter and gain stage to drive push-pull output pair V3 & V4 (both 6L6 or KT66 tetrodes). Output transformer T3 has tapped connections to the output valve screens for ultra-linear operation. The transformer output is switched to either the speaker terminals (via CON3) or to the headphone socket by relay RLY1. Components with their text in red are late changes to fix a relay switching problem. 32  Silicon Chip siliconchip.com.au E FUSE FUSED IEC MAINS MALE SOCKET N 12V AC 12V AC A 80VA TOROID 230V AC T2 116V AC 1N4007 A LK6 12.2V AC ~ BR1 1A SLOW F1 D2 1N5408 K 10k F3 5A SLOW 3A SLOW F2 A K K – + W04 VEE ~ 400V 470 µF 400V 470 µF +310V K A CURRAWONG STEREO VALVE AMPLIFIER 1 2 3 4 5 CON8 1 2 3 CON7 A D1 1N5408 6 5 K A LEDS 3-6 560Ω MKT 1W 1M 1M E B C λ λ LED1 VEE K LK2 VEE 1k 470Ω 10k 1W 120Ω 16V 1 14 B C E STX0560 OUT ADJ 3 1k C E E C IC1c 10 IN B E B C 13 12 E 1M E +308V 7 IC1d +12V K C ~ + VEE 11 A D4 1N4007 1M B KSC5603DTU Q8 B B Q7 OUT LM1084/LT1084 IC1: 4093B 9 8 C * OR BUJ303A B E Q3 STX0560 C Q5, Q7: BC547 Q6, Q8: BC557 C E E C B A D5 1N4007 100 µF 2 IC1a 150k Q6 B B Q5 E C Q4 STX0560 BC547, BC557 100nF 16V 100 µF +12V 630V 470nF 120Ω (POWER SUPPLY SECTION) K LK1 4 470Ω TAB OUT ADJ IC1b 25V IN 1N5 40 8 A K λ LED6 BLUE BLUE λ LED5 K A A REG1 LM/LT1084-ADJ 2200 µF K BLUE λ LED4 A BLUE λ LED3 1W 47k 1W 47k Q2 STX0560 C Q1 KSC5603DTU* – ~ 1 1 W04 4 3 2 TO REMOTE PCB CON10 2 DC OUT CON9 400V 39 µF +HT Fig.2: the secondaries of toroidal power transformers T1 and T2 are connected in series and rectified using a voltage doubler to produce a 310V HT rail. Most of the ripple is filtered out by a capacitance multiplier comprising high-voltage transistors Q1-Q3 and a 470nF polyester capacitor. T2’s remaining 12VAC secondary drives the 6L6 filaments directly in a series/parallel configuration, while the 12AX7 filaments run from a regulated 12V rail produced by bridge rectifier BR1, a 2200μF filter capacitor and linear regulator REG1. IC1 provides an HT turn-on delay and soft start. SC 20 1 4 WARNING: LETHAL VOLTAGES ARE PRESENT ON THIS CIRCUIT WHILE IT IS OPERATING! S1 15V AC 15V AC 37V AC 37V AC 160VA TOROID 230V AC T1 Phase splitter The phase splitter is another 12AX7 twin triode, V2. The phase splitter provides some gain but its main job is to produce two similar drive signals with opposite phase for the grids of the push-pull output stage valves Signal is coupled to this phase splitter from V1b’s anode via another 220nF polyester capacitor. V2a operates as an inverter, to generate the out-of-phase drive signal. Like V1a and V1b, it is configured as a common-cathode amplifier. It runs from a higher HT rail of around 288V DC which comes from the first HT RC filter stage (6.8kΩ/39µF). Its grid is tied to ground by a 1MΩ resistor, with the voltage across the shared 6.8kΩ cathode resistor providing the required bias potential. This resistor is shared with V2b (and both cathode currents flow through it). V2b’s grid is connected straight to ground so when its cathode voltage increases, the grid-cathode bias voltage decreases. As such, when V2a’s cathode current increases and its anode voltage drops, V2b’s bias increases and thus V2b’s anode/cathode current decreases, causing the voltage at its anode to rise. So the signal at V2b’s anode has the opposite phase to that at V2a’s anode, ie, it is in phase with the signal from the preamp. The 220kΩ anode resistor value has been selected so that the two output signals have a similar swing and so that V2a and V2b both operate with as high an anode voltage as possible, to give maximum drive amplitude for the following stage. These drive signals are applied to the grids of 6L6 output valves V3 & V4 via 220nF polyester capacitors. These grids are again tied to ground by 1MΩ resistors and there are 10kΩ series stopper resistors to prevent parasitic oscillation. Output stage V3 & V4 are self-biased using 330Ω 5W cathode resistors, with around 22V across each. This gives an operating siliconchip.com.au 09/10/14 14:40:21 Currawong THD+N vs Power 10 Filter: 240VAC AP AUX-0025 mains, 1kHz + 20Hz-80kHz signal, 20Hz-20kHz bandpass BW w/AUX-0025, both channels driven 5 Total Harmonic Distortion + Noise (%) (ie, around 1µF) in series with a 9.1kΩ resistor. This sets the closed-loop gain of the preamp section at around 2.75, so that the following phase splitter receives around 3V RMS at maximum volume. Note, however, that there is also a feedback path from the amplifier’s output, which we will cover later. 2 1 0.5 0.2 4Ω 6Ω 0.1 8Ω 0.05 0.02 0.01 0.1 0.2 0.5 1 2 5 10 20 Power ( W atts) Fig.3: distortion versus power for a 1kHz sinewave into 4Ω, 6Ω and 8Ω load impedances. Again, both channels are driven for a realistic test. As you can see, distortion remains low at under 2W and then rises slowly until the onset of clipping at around 8-10W, depending on load impedance. The best power delivery is actually for 8Ω loads, with 6Ω being virtually identical and 4Ω being a little lower, clipping at around 9.5W/channel. This is partly due to output transformer drive impedance mismatch. current of about 65mA. Each output valve is powered from the main HT rail of around 308V, via the primary windings of T3, for a quiescent power of around 20W each. Note that DC and AC currents flow in the two halves of the push-pull winding since both plates of the tetrodes are fed from the transformer centre-tap connection. However, the magnetic fields produced by these direct currents are cancelled, as they flow in opposite directions. This is important because otherwise the transformer would be magnetically saturated. As the current split between V3 & V4 changes in response to the input signal however, an AC magnetic field is induced which is coupled into T3’s secondary. The resultant voltage drives the speakers or headphones. Since the output valve quiescent power of 20W is around twice the amplifier’s power output of 10W per channel into 8Ω, this gives Class-A operation. With lower load impedances (for example, 4Ω), V3 or V4 may be fully cut off during signal peaks, giving Class-AB operation. When the input signal swing is positive, pin 1 of V2a has a negative swing and so the current through V3 drops. At the same time, pin 6 of V2b has a positive swing and thus the current through V4 increases. This causes an increase in current flow from the top (dotted) side of T3’s primary to the other, resulting in a positive swing at the dotted side of the secondary. Thus, the output of the amplifier is in phase with the input. T3 also has taps approximately halfway between each end and the centre (HT) tap. These are connected to the screens of V3 & V4 via 47Ω stopper resistors, providing the ultra-linear connection mentioned earlier. This negative feedback from the transformer to V3 & V4 cancels out some of the transformer distortion. Note that while the feedback signals are high amplitude, the screen gain is much less than for signals applied to the grid, so the feedback doesn’t overpower the drive signals. Because the signal levels in the output stage are much higher and since 6L6 valves require much more filament November 2014  33 Parts List Chassis/power supply 1 timber plinth with base (details to come) 1 top cover cut from 3mm clear acrylic (details to come) 1 small tube acrylic glue 1 front panel, code 01111142, 249 x 30mm 1 rear panel, code 01111143, 248 x 53mm 1 160VA 37+37+15+15V toroidal transformer (Altronics MC5337) 1 80VA 12+12V toroidal transformer (Altronics M5112) 4 screw-on 30mm equipment feet (Jaycar HP0830, Altronics H0890) 4 M4 x 15mm machine screws and nuts (for feet) 1 15mm anodised aluminium knob to suit VR1 1 snap-in fused IEC mains male socket for 1.6mm panels (Altronics P8325) 2 M205 250VAC 1A slow-blow fuses (one spare) 1 red chassis-mount RCA/RCA socket 1 white chassis-mount RCA/RCA socket 2 red RCA line plugs 2 white RCA line plugs 2 red binding posts (Jaycar PT0453, Altronics P9252) 2 black binding posts (Jaycar PT0461, Altronics P9254) 1 SPST ultra-mini rocker switch, 250VAC rated (Altronics S3202, Jaycar SK0975) 1 1m length 2-core mains flex 1 1m length 3-core mains flex 1 200mm length 3mm diameter black heatshrink tubing 1 200mm length 8mm diameter black heatshrink tubing 1 200mm length 20mm diameter black heatshrink tubing 1 1m length heavy duty red hookup wire 1 1m length heavy duty black hookup wire 1 1m length single-core shielded cable 1 1m length medium duty black hook-up wire 1 12-way screw terminal strip (Jaycar HM3194, Altronics P2135A) 6 M3 x 25mm Nylon screws and nuts 1 M4 x 6mm machine screw 2 M4 nuts 2 4mm ID shakeproof washers 1 4mm ID eyelet crimp connector 3 red 6.4mm crimp spade connectors 12 4G x 9mm self-tapping screws 10 small Nylon cable ties current than 12AX7s, we run the filaments of V3 & V4 (and V7/V8) from 6.1V AC, slightly shy of the nominal 6.3V, due to compromises made in power transformer selection. It still works fine; it just takes a little longer for the valves to reach full emission after switch-on. speaker terminals via the normally closed contacts of RLY1 and pluggable terminal block CON3. RLY1 is energised if headphones are plugged into the front panel socket, disconnecting the speaker and re­ directing the signal to headphone socket CON5 via a 220Ω resistor. If LK4 is fitted (and we recommend that it is), feedback is applied from T3’s secondary to V1a’s cathode via a 470nF capacitor and 22kΩ resistor. Since the output is in phase with the input, by applying some of the output signal to V1a’s cathode, we effectively reduce the drive for V1a, giving about 14dB of negative feedback. There is a limit to how much feedback can be applied in this manner due Speaker connections & feedback A 470Ω 1W resistor across T3’s secondary ensures that there is some load even if there is no speaker connected. This is necessary because operating a push-pull transformer-coupled amplifier with no load can lead to very high AC voltages at the valve plates and subsequent flash-over in the valve sockets. T3’s secondary connects to the 34  Silicon Chip Main board 1 double-sided PCB, code 01111141, 272 x 255mm 2 15W 100V line transformers (T1,T2) (Altronics M1115 – do not substitute) 2 5VDC coil 3A contact SPDT micro relays (RLY1,RLY2) (Altronics S4141B) 6 M205 fuse clips (F1-F3) 1 1A M205 slow-blow fuse (F1) 1 3A M205 slow-blow fuse (F2) 1 6A M205 slow-blow fuse (F3) 1 white vertical RCA socket (Altronics P0131) (CON1) 1 red vertical RCA socket (Altronics P0132) (CON2) 2 2-way vertical pluggable terminal blocks (CON3,CON4) (Jaycar HM3112+HM3122, Altronics P2512+P2532) 1 PCB-mount switched 6.35mm stereo jack socket with long pins (CON5) (Jaycar PS0190) 1 3-way vertical pluggable terminal block (CON7) (Jaycar HM3113+HM3123, Altronics P2513+P2533) 1 5-way vertical pluggable terminal block (CON8) (Altronics P2515+P2535) 4 chassis-mount phenolic 9-pin valve sockets with bracket (V1,V2,V5,V6) (Jaycar PS2082) 4 chassis-mount ceramic 8-pin valve sockets with bracket (V3,V4,V7,V8) (Altronics P8501) 6 2-way pin headers, 2.54mm pitch (LK1-LK6) 2 shorting blocks (LK4-LK5) 1 5-50kΩ 16mm dual gang log pot* (VR1) 2 6073B-type mini flag heatsinks 4 M4 x 10mm machine screws 4 M4 shakeproof washers 4 M4 nuts 8 M3 x 15-16mm machine screws 10 M3 x 10mm machine screws 12 M3 shakeproof washers 12 M3 nuts to the phase shift created by the inductance of T3. We have set the feedback to give as much distortion cancellation as possible, while keeping it stable with capacitive loads. The circuit as presented is stable with several microfarads across the load, even when driving it with a square wave. By the way, the 470nF capacitor in the feedback path is important as it damps shifts in valve bias in response to changes in mains voltages and valve temperatures. With feedback enabled, input sensitivity is around 1V RMS. Typical CD/ DVD/Blu-ray players produce around 2V RMS so this should be plenty in most circumstances. With LK4 resiliconchip.com.au 14 M3 Nylon nuts 22 3mm inner diameter Nylon flat washers 8 6.3mm M3 Nylon tapped spacers 2 TO-220 insulating washers and bushes 1 1m length medium duty blue hookup wire (250VAC rated) 1 1m length shielded audio cable 1 200mm length 3mm diameter blue heatshrink tubing 6 small green Nylon cable ties (maximum 2mm wide) 2 small blue Nylon cable ties * ≥ 20kΩ recommended; substitute motorised pot for remote control option (see details in part two next month) Valves 4 12AX7 dual triodes (V1,V2, V5, V6) 4 6L6 beam tetrodes – matched pairs if possible (V3,V4, V7,V8) Semiconductors 1 4093B quad NAND Schmitt trigger IC (IC1) 1 LM/LT1084-ADJ 5A adjustable low-dropout regulator (REG1) 1 KSC5603D 800V 3A high-gain NPN transistor (Q1) 3 STX0560 600V 1A NPN highgain transistors (Q2-Q4) 3 BC547 100mA NPN transistors (Q5,Q7,Q9) 2 BC557 100mA PNP transistors (Q6,Q8) 1 red/green 2-lead bi-colour 3mm LED with diffused lens (LED1) moved, the overall gain is much higher and the input sensitivity is around 350mV RMS for full power. However, distortion rises to around 0.5% at 1kHz and >1% at lower frequencies. Note that the 470nF series capacitors in the feedback network are important. These form high-pass filters in combination with the feedback resistors, with a -3dB point of around 15Hz. If DC feedback is used, the bias time constants in the circuit form a type of relaxation oscillator and the bias voltages never quite settle down, leading to asymmetric clipping and other undesirable behaviour. Power supply The separate power supply circuit siliconchip.com.au 5 blue diffused lens 3mm LEDs (LED2-LED6) 1 W04 1.5A bridge rectifier (BR1) 2 1N5408 3A 1000V diodes (D1,D2) 3 1N4007 1A 1000V diodes (D4-D6) 1 1N4004 diode (D9) SIGNAL HOUND USB-based spectrum analyzers and RF recorders. Capacitors 1 2200µF 25V electrolytic 2 470µF 400V snap-in electrolytic 4 100µF 50V electrolytic 3 100µF 16V electrolytic 5 39µF 400V low-profile snapin electrolytic (Nichicon LGJ2G390MELZ15) (Mouser) 2 1.5µF 63V MKT 5 470nF 630V polyester 2 470nF 63V MKT 8 220nF 630V polyester 1 100nF 63V MKT or 50V multi-layer ceramic 2 100pF ceramic disc SA44B: $1,320 inc GST Resistors (1W, 5%) 9 1MΩ 2 9.1kΩ 2 270kΩ 4 6.8kΩ 2 220kΩ 2 3.3kΩ 2 120kΩ 2 680Ω 2 100kΩ 2 470Ω 6 47kΩ 2 220Ω 2 22kΩ 1 82Ω 5 10kΩ 4 47Ω 4 330Ω (5W, 10%) The BB60C supercedes the BB60A, with new specifications: Resistors (0.25W, 1%) 7 1MΩ 1 560Ω 1 150kΩ 3 470Ω 1 10kΩ 1 330Ω 2 1kΩ 4 120Ω • is shown in Fig.2. All components, except the two power transformers T1 & T2, power switch S1 and the fused IEC mains socket, are on the main board. There are three main power requirements for this circuit: the 310V HT rail, the ~12V DC filament supply for the 12AX7s (at around 1A) and ~6VAC for the 6L6 filaments, at around 4A. We also use the 12V DC rail to power various ancillary circuits, as described below. All of T1’s secondaries are connected in series, along with one of T2’s secondaries, to produce 114VAC. T2’s other secondary provides a little over 12VAC, to run the 6L6 filaments at around 6.1VAC each, in series pairs. The 12VAC is also rectified, filtered • • • • • Up to 4.4GHz Preamp for improved sensitivity and reduced LO leakage. Thermometer for temperature correction and improved accuracy AM/FM/SSB/CW demod USB 2.0 interface SA12B: $2,948 inc GST • • • • • • • Up to 12.4GHz plus all the advanced features of the SA44B AM/FM/SSB/CW demod USB 2.0 interface The BB60C streams 140 MB/sec of digitized RF to your PC utilizing USB 3.0. An instantaneous bandwidth of 27 MHz. Sweep speeds of 24 GHz/sec. The BB60C also adds new functionality in the form of configurable I/Q. Streaming bandwidths which will be retroactively available on the BB60A. Vendor and Third-Party Software Available. Ideal tool for lab and test bench use, engineering students, ham radio enthusiasts and hobbyists. Tracking generators also available. Silvertone Electronics 1/8 Fitzhardinge St Wagga Wagga NSW 2650 Ph: (02) 6931 8252 contact<at>silvertone.com.au November 2014  35 Most of the parts except mainly the power transformers are mounted on a single large PCB to make the assembly easy. The optional remote volume control is built on a separate PCB. and regulated to provide the 12V DC rail (actually about 12.3V DC), for the 12AX7 filaments and DC-powered circuitry. The 114VAC from CON7 is rectified in a half-wave voltage doubler consisting of 1000V 3A diodes D1 & D2 and two 470µF 400V capacitors, giving about 310V across both capacitors with several volts of ripple. Fuse F1 provides some protection against faults. There are two 47kΩ series-connected bleeder resistors to discharge the 470µF capacitors when power is removed. Four blue LEDs are connected in series with the two 47kΩ 1W resistors. The blue LEDs indicate the presence of HT and also illuminate output transformers T3 and T4 (very effective in a room with subdued lighting). The output stage has no HT lowpass filter, unlike the preamplifier and phase splitters. So to prevent HT ripple in the output stage from affecting the signal, we are using an active ripple 36  Silicon Chip filter. This is a capacitance multiplier filter built around high-voltage, highcurrent transistor Q1, configured as an emitter-follower. The traditional HT filter is a large iron-cored choke but these are heavy and expensive, not to mention hard to find these days. Our transistor-based method is more effective and cheaper. Q1 is driven by Q2 and Q3 which are high-voltage high-gain signal transistors, in a “Triplington” configuration; it’s like a Darlington but with an extra stage. The higher the gain in this buffer, the more effective the filter is. Base bias comes from an RC low-pass filter across the incoming HT rail, consisting of a 1MΩ resistor and 470nF polyester capacitor. Q2 and Q3 have a gain of around 70100 each while Q1 has a gain of around 30. So the overall gain is about 70 x 70 x 30 = 147,000 which multiplies the effect of the 470nF capacitor to act as if it is 69,000µF! In practice, it isn’t quite as good as this as the 470nF capacitor discharges slightly through the three base-emitter junctions at the trough of each ripple cycle but despite this, the ripple at Q1’s emitter is just a few hundred millivolts. Q1 has an integral emitter-collector diode so that when the unit is switched off, the output filter capacitors can safely discharge back into the input filter capacitors without doing any damage. D4 protects Q2 while D5 provides similar protection for Q3 but also has a role in the start-up delay, which we’ll explain later. Note that this arrangement also results in HT “soft-start” as it takes a few hundred milliseconds for the 470nF capacitor to charge and the HT rail tracks this voltage. Turn-on delay We have also incorporated a 20-second (or so) turn-on delay, to allow the valve filaments to heat up before HT siliconchip.com.au Low-voltage supplies 5-pin pluggable terminal block CON8 provides separate low-voltage AC connections for the 6L6 filaments (pins 1 & 3) and the regulated supply (pins 4 & 5). Each is fused on the board. siliconchip.com.au The PCB is slid into a slot that runs around the top inside edge of the timber plinth. Perspex covers will be used to protect the PCB and speaker transformers. 09/10/14 14:35:26 Currawong THD+N vs Frequency 10 240VAC mains, output level 1W, 20Hz-80kHz bandwidth, both channels driven 5 Total Harmonic Distortion + Noise (%) is applied. Part of the rationale for this is to prevent “cathode stripping” which can occur with cold cathodes, although the existence of this phenomenon is somewhat controversial. But since the valves aren’t “ready” to operate immediately anyway, it certainly doesn’t hurt to delay the application of HT. IC1 is a quad Schmitt-input NAND gate which runs from the 12V rail and provides the turn-on delay. Note that ground for the 12V rail is labelled VEE and will be close to, but not necessarily at, GND (0V). IC1a is connected as an inverter with a 100µF capacitor from its input to ground. A 150kΩ resistor charges this capacitor from the 12V rail while a 1MΩ resistor discharges it when power is switched off. It takes about 20 seconds for this capacitor to charge to a sufficient voltage for the output of IC1a to go low. During this time, IC1a’s output is high. This is inverted by IC1c and then again by IC1d, so Q4 (another 600V transistor) is switched on initially. This keeps the 470nF capacitor in the HT filter from charging until the delay has ended. Diode D5 in the HT filter prevents the base of Q3 from being pulled below GND when VEE is (slightly) negative. IC1a and IC1c also drive LED1 via two pairs of complementary emitterfollowers (Q5-Q8). LED1 is a bi-colour device and consists of a red LED and green LED on the same die, connected in inverse parallel. Since inverter IC1c is between them, one inverter is always driving one end of LED1 high and the other is driving it low. Thus LED1 is red initially at turn-on and switches to green once the time-out period has expired and the HT rail is powered up. A 1kΩ resistor sets the LED current to about 10mA while another 1kΩ resistor partially isolates the bases of Q5 & Q6 from IC1a’s output. This allows the optional remote control board to independently drive LED1, in order to flash it to acknowledge infrared command reception. The remote control board connects via CON10 and will be described next month. 2 1 0.5 4Ω 0.2 6Ω 8Ω 0.1 0.05 0.02 0.01 20 50 100 200 500 1k 2k 5k 10k 20k Frequency (Hz) Fig.4: distortion versus frequency, with both channels driven at 1W into three different resistive loads. As you can see, the distortion is pretty low for a valve amplifier, especially between 100Hz and 10kHz. Below 100Hz, distortion rises steeply due primarily to the output transformer’s non-linear response. Distortion into lower impedances is only slightly worse than that for 8Ω. Note the 80kHz bandwidth used, to ensure that higher frequency harmonics are included in the measurements. However, we ultimately decided to use one transformer winding to power both, hence they are wired in parallel despite the separate connections. The 12VAC from pins 4 & 5 of CON8 is rectified by 1.5A bridge rectifier BR1 and filtered with a 2200µF capacitor to produce around 15-16V DC with November 2014  37 09/10/14 14:58:07 Currawong Frequency Response +3 Note: parts of this circuit operate at over 300V DC. Do not touch any components or any part of the PCB while the unit is operating or immediately after switch off. The blue LEDs in the circuit indicate when dangerous voltages are present. +2.5 +2 +1.5 Amplitude Variation (dBr) Warning! +1 +0.5 +0.0 4Ω 6Ω -0.5 8Ω -1 -1.5 -2 -2.5 -3 10 20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k Frequency (Hz) Fig.5: the frequency response is pretty flat in the audible range (note: the vertical scale is only ±3dB for the entire diagram). Roll-off at the high frequency end is -3dB at around 50kHz while the low-end -3dB point is below 10Hz. The peak at around 20Hz is partly due to the AC-coupled global feedback and partly due to greatly increased waveform distortion below about 30Hz due to the output transformers. However, the peak amplitude is only around +1.5dB and 20Hz signals are barely audible. about 1V ripple. This is regulated to provide a nice smooth rail by REG1, a low-dropout, high-current equivalent to the LM317. Pins 1 & 3 of CON8 connect straight to the series/parallel-connected 6L6 filaments and as a result, they get about 6.1VAC each. One end of this AC supply is grounded for noise immunity. Now because of this ground connection and the fact that the same transformer secondary is used to feed BR1, the negative end of BR1 actually floats between about +0.7V and -15V. Hence, the need to disconnect VEE from GND. If two separate 12V transformers or windings were used, LK6 could be fitted and thus VEE would be at the same potential as GND. LK6 must not be fitted with the supply arrangement shown here! The circuit will work the same regardless as to whether VEE is connected to GND, as Q4 is the only connection between the two supply “domains”. The DC supply is also used to power relays RLY1 and RLY2 when headphones are plugged in. These are 5V relays, so an 82Ω series resistor drops 38  Silicon Chip the 12V DC to an appropriate voltage. LED2 is also connected across the relay coils, in series with a 330Ω currentlimiting resistor, to indicate when the speakers are disconnected. Unused linking options Note that the supply was also designed to operate with the regulated rail at 6V DC rather than 12V. This would require a different transformer (ie, 6VAC rather than 12VAC) and the option was provided as there are some 12AX7-compatible valves with 6.3V-only filaments (rather than the typical arrangement with a 12.6V centre-tapped filament). However, given the relative rarity of these valves, we aren’t going to go into details as to how to reconfigure the supply except to say that LK1-LK3 are fitted for this purpose. Normally, they are left out. PCB layout We wanted to put as many parts on the PCB as possible to make this amplifier easy to build. Soldering parts to a PCB is certainly a lot easier than point-to-point wiring! It minimises the chances of mistakes and also means that performance will be consistent between amplifiers. The PCB layout was a bit tricky though, due to the voltages involved. We have kept tracks with voltages that may differ by over 60V apart by 2.54mm to prevent arcing, while in other areas low-voltage tracks need to be closer together so they can fit. We also used “star” earthing as much as possible to avoid hum and ripple injection into the preamp stages. Most of the grounds on the board converge on the main power supply filter capacitor negative pin. The board has been designed with plated slots for the valve socket pins so that they fit snugly and neatly. All connectors have been placed along the back of the board, on the underside, to keep the chassis wiring neat. The input signals run from the back of the board to the front (where the volume pot is mounted) through shielded cables that are strapped to the underside of the board, to prevent the low-level input signals from picking up ripple, hum and buzz. We have also used low-profile components where possible, so that a clear perspex shield can be fitted over the top, to prevent prying fingers from getting a shock, as mentioned earlier. The valves, main filter capacitors and output transformers will pass through cut-outs in this shield, with perspex boxes around the transformers. The rest of the components will be safely underneath. Next month That’s all we have room for this month. Over the next couple of months we will present the main PCB layout diagram, describe the assembly procedure, explain how to build the plinth and finish the wiring. We’ll also go through the testing and troubleshooting procedure and describe the optional infrared remote control which SC uses a motorised potentiometer. siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes RIGOL DS-1000E Series NEW RIGOL DS-1000Z Series NEW RIGOL DS-2000 Series 50MHz & 100MHz, 2 Ch 1GS/s Real Time Sampling USB Device, USB Host & PictBridge 70MHz & 100MHz, 4 Ch 1GS/s Real Time Sampling 12Mpts Standard Memory Depth 70MHz, 100MHz & 200MHz, 2 Ch 2GS/s Real Time Sampling 14Mpts Standard Memory Depth FROM $ 339 FROM $ ex GST 654 FROM $ ex GST 934 ex GST Function/Arbitrary Function Generators RIGOL DG-1022 NEW RIGOL DG-1000Z Series RIGOL DG-4000 Series 20MHz Maximum Output Frequency 2 Output Channels USB Device & USB Host 30MHz & 60MHz 2 Output Channels 160 In-Built Waveforms 60MHz, 100MHz & 160MHz 2 Output Channels Large 7 inch Display ONLY $ 439 FROM $ ex GST 688 FROM $ ex GST Power Supply Spectrum Analyser RIGOL DP-832 RIGOL DM-3058E 9kHz to 1.5GHz 100Hz to 1MHz Resolution Bandwidth Optional Tracking Generator Triple Output 30V/3A & 5V/3A Large 3.5 inch TFT Display USB Device, USB Host, LAN & RS232 5 1/2 Digit 9 Functions USB & RS232 1,450 ONLY $ ex GST 460 ex GST Multimeter RIGOL DSA-815 FROM $ 890 ONLY $ ex GST 541 ex GST Buy on-line at www.emona.com.au/rigol Sydney Tel 02 9519 3933 Fax 02 9550 1378 Melbourne Tel 03 9889 0427 Fax 03 9889 0715 email testinst<at>emona.com.au siliconchip.com.au Brisbane Tel 07 3275 2183 Fax 07 3275 2196 Adelaide Tel 08 8363 5733 Fax 08 83635799 Perth Tel 08 9361 4200 Fax 08 9361 4300 EMONA web www.emona.com.au November 2014  39 By JOHN CLARKE 48V Dual Phantom Power Supply for DI boxes & Condenser Microphones Lots of audio equipment needs phantom power. As well as condenser mikes, it’s also required for active DI boxes, preamplifiers and effects units. This phantom power supply runs from a 24VAC plugpack transformer and delivers a regulated 48V DC via XLR sockets. P UBLIC ADDRESS systems in theatres, churches and halls all require microphones, preamplifiers and possibly powered DI (direct injection) boxes and effects pedals for musicians. Many microphones are dynamic types that do not require a power source but the more sensitive condenser microphones require power and the same goes for other items of equipment. While these can often be run from batteries, it is far more convenient to have a “phantom supply”. This avoids the need to check batteries that can go flat at the most inconvenient times, ie, when you need ‘em! So what’s a phantom supply? Well, 40  Silicon Chip it’s a way of providing power to equipment via balanced signal leads. “Phantom” refers to the apparently invisible manner in which power is applied. 48V DC is the favoured phantom supply standard in the commercial sound industry. 24V and 12V are also used but these are not popular. Fig.1 shows how it’s done. The 48V DC supply is applied via 6.8kΩ resistors to the hot (non-inverted) and cold (inverted) signal leads for the device being powered. The output signal leads from the unit are capacitively coupled to the following device, so that the DC voltage is removed from the signal. Phantom supplies should not be confused with the bias voltage applied to electret microphones. A bias supply is applied to an unbalanced lead comprising a shield and signal wire, rather than to a balanced signal line with a shield. Additionally, such a bias supply is typically around 1.5V and has a current of 1mA or less. More information about this can be found at: http://blog.shure.com/shure-notes/ shure-tech-tip-phantom-power-vsbias-voltage/ So what happens if a phantom supply is connected to a dynamic microphone? Will it be damaged by current flow? The answer is “no”. Fig.2A shows this connection. A dynamic microphone employs a coil siliconchip.com.au that’s floating and not connected to the grounded shield. With 48V applied to both sides of the coil, no DC current flows through it. Problems can arise when a dynamic microphone or the connecting lead is wired incorrectly, with one side of the microphone coil connected to ground as shown in Fig.2B. Current would then flow in the coil, leading to magnetisation that may permanently affect the microphone. Problems also occur if a centretapped microphone coil is incorrectly connected to ground at the centre tap (Fig.2C). In this case, a different current may flow in each half of the coil due to slight differences in the values of the 6.8kΩ resistors and imbalances in the coil windings. Getting back to Fig.2A, matching the 6.8kΩ resistors will also improve noise rejection due to more equal impedance matching in the two signal leads. For those unfamiliar with balanced audio leads, the twisted pair wires in the balanced lead carry out-of-phase signals. At the receiving end, the out-of-phase signals are “subtracted” and this has the effect of “adding” the two signals. In addition, because they are twisted, the signal wires each tend to pick up the same level of hum and this is cancelled by the subtraction at the receiving end. A shield wire that’s connected to ground further minimises hum and noise pick-up. Some mixing desks do include a phantom supply for microphones, etc. However, even if you do have such a mixing desk, it may not have sufficient capacity. This new 48V Dual Phantom Power Supply can be used with two phantom-powered devices. As shown in the photos, the 48V Dual Phantom Power Supply is housed in a diecast box, for ruggedness and for shielding. It has two female XLR Fig.1: how phantom power is applied. The 48V DC supply is applied via 6.8kΩ resistors to the balanced signal leads of the device being powered. 2 6.8k 2 POWERED APPLIANCE sockets and two male XLR sockets. The 48V supply is applied to the female XLR sockets, while the male sockets provide the signal output with the DC voltage blocked by 22µF electrolytic capacitors. Circuit details Now take a look at Fig.3 for the full circuit details. As shown, the incoming 24VAC from the plugpack transformer is connected to a half-wave voltage doubler rectifier comprising diodes D1 & D2 and two 470µF 63V electrolytic capacitors. This will result in a nominal DC voltage of about 67V but will typically be much higher at around 75V DC, depending on the incoming mains voltage and the plugpack’s voltage regulation. REG1, an LM317 3-terminal adjustable regulator, is used to derive the 48V DC supply. This device is rated for a maximum differential of 40V between its input and output. With a 75V input and a 48V output, the input to output difference is a comfortable 27V but when power is initially applied, the regulator circuit’s input can be 75V or more while the output can be as low as 1.3V. This is due to REG1’s adjust terminal being initially held at 0V via a 1µF bypass capacitor. Since the LM317 cannot cope with this admittedly brief overload, a pre- SIGNAL OUTPUT 3 regulator comprising Darlington transistor Q1 and 33V zener diode ZD1 is used to protect it from over-voltage. Q1 acts as an emitter follower, while ZD1 has its anode connected to REG1’s output, thereby limiting the voltage across the regulator to about 31.7V (after allowing for the voltage drop across the two base-emitter junctions in Darlington transistor Q1). Following the pre-regulator, the circuit involving REG1 is fairly standard. REG1’s supply input is decoupled using a 100nF MKT capacitor, while the output and adjust terminals are bypassed using 1µF 63V electrolytic capacitors. The minimum load current for REG1 to give its specified performance is 12mA. Since the voltage between the output and adjust terminals could be as low as 1.2V, we would normally connect a 100Ω resistor between these two terminals to provide this minimum current. However, this wouldn’t allow us to use convenient standard resistor values for the adjust-to-ground resistors and so we have used a 150Ω resistor instead. This provides a minimum load of 8mA, with the remaining 4mA required being added by the current through power indicator LED1. In fact, assuming a 48V output and 2V across LED1, the LED current will actually be 4.6mA. +48V DC 6.8k 6.8k DYNAMIC MICROPHONE 6.8k 1 +48V DC 6.8k +48V DC 2 = ‘HOT’ (IN PHASE) 3 = ‘COLD’ (OUT OF PHASE) 1 = GROUND 2 +48V DC 6.8k 6.8k DYNAMIC MICROPHONE 6.8k DYNAMIC MICROPHONE 2 CT 3 3 1 A 3 B C Fig.2: a correctly wired dynamic microphone coil is shown at (A) but problems occur if the microphone is incorrectly wired as shown at (B) and (C) due to current flowing in the coil. siliconchip.com.au November 2014  41 D3 1N4004 SCREW TERMINALS D1 1N4004 A K Q1 TIP122 C K E IN K CON1 24V AC INPUT A D2 1N4004 470 µF B 0.5W ZD1 K OUT K ADJ 100nF 4.7k 63V A REG1 LM317T A A λ K 63V 2.4k SOCKET 63V A POWER LED1 33V 1W 470 µF 1 µF D4 1N4004 150Ω 0.5W 1 µF 63V TP1 10k GND 0.5W 2.7k 0.5W LED * MATCH EACH PAIR OF THESE VR1 1k RESISTORS TO WITHIN 27Ω OUTPUT ADJUST K A +48V 6.8k* 6.8k* 0.5W 6.8k* 0.5W 6.8k* 0.5W 22 µF 63V 0.5W 22 µF 63V 22 µF 63V 3 2 22 µF 63V 3 XLR FEMALE SOCKET1 1 2 1 SHIELD XLR MALE SOCKET1 SHIELD 10Ω 100k 3 2 SHIELD 10Ω 100k 100k 1N4004 20 1 4 48V DUAL PHANTOM POWER SUPPLY XLR MALE SOCKET2 1 SHIELD A SC  2 3 XLR FEMALE SOCKET2 1 B K LM317T TIP122 K ZD1 A 100k C C E OUT ADJ OUT IN Fig.3: the circuit of the 48V Dual Phantom Power Supply. The 24VAC supply input is rectified by voltage doubler D1 & D2 and fed to an LM317T adjustable regulator (REG1) via a pre-regulator consisting of Darlington transistor Q1 & ZD1. The resulting 48V DC output from REG1 is then fed to pins 2 & 3 of the female XLR sockets via 6.8kΩ resistors. Trimpot VR1 (1kΩ) allows the output voltage to be adjusted from 40.8V to 48.8V if the output-to-adjust terminal voltage is at its 1.2V minimum. If the output-to-adjust terminal voltage is at its 1.3V maximum, the current through the adjust resistors is 8.66mA and the output voltage can be adjusted using VR1 from 44.2V to 52.8V. These calculations do not include the current flowing from the adjust terminal itself. This is typically 45µA but can be as high as 100µA. For the adjust terminal to ground resistance used, this can add an extra 0.61V to the output. Note that the output voltage is required to be between 44-52V in order for the phantom supply to comply with the DIN EN 61938 standard. 42  Silicon Chip Diodes D3 & D4 are included as standard protection. D3 allows current flow from the output back to the input if the regulator’s input is shorted. Similarly, D4 allows current to flow from the 1µF bypass capacitor at the adjust terminal if the output is shorted. XLR sockets The 48V DC supply is fed to the XLR sockets via 6.8kΩ resistors. These limit the short-circuit current to a nominal 7mA (6.5-7.7mA range) for each supply pin (pins 2 & 3 on the XLR sockets). Ideally, each 6.8kΩ resistor pair should be matched to within 27Ω to comply with the 0.4% tolerance allowed by the phantom power specifications. That can be easily achieved by using resistors that are from the same manufacturer’s batch. In practice, the resistor values are checked with a digital multimeter before installation. The resistors in each pair do not need to be within 27Ω of 6.8kΩ; just within 27Ω of each other. As mentioned previously, 22µF electrolytic capacitors are used to block the 48V DC on the balanced signal lines from being fed to the XLR male output sockets and these work in company with 100kΩ bias resistors from the outputs to ground. The 22µF capacitors ensure a low-frequency roll-off that’s well below 20Hz for a typical sound mixer or amplifier input impedance of 10kΩ. The 10Ω resistors isolate the ground connections between each pair of female and male XLR sockets to prevent high-level ground loop currents. siliconchip.com.au The 48V Dual Phantom Supply is built on a double-sided plated-through PCB coded 18112141 and measuring 56.5 x 113mm. This is housed in a diecast box measuring 122 x 66.5 x 39mm and a panel label (113 x 56mm) is affixed to the lid. Fig.4 shows the parts layout on the PCB. Begin by installing the resistors, zener diode ZD1 and diodes D1-D4. A digital multimeter should be used to check the resistor values before they are installed. As mentioned above, you will need to select two pairs of 6.8kΩ resistors that are within 27Ω of each other. Make sure the diodes are all installed with the correct polarity. The banded end of each diode must be orientated as shown on the layout diagram. The PC stakes for TP1 and GND can go in next, followed by REG1 and Q1 (don’t get these latter two parts mixed up). As shown, REG1 & Q1 are mounted horizontally, with their leads bent down by 90° so that they go through their respective PCB holes. Be sure to secure the metal tab of each device to the PCB using an M3 x 6mm machine screw and nut before soldering their leads. Trimpot VR1 can now be installed, TP1 22 µF 63V 2.7k 1 µF 63V 6.8k 6.8k 6.8k 10Ω REG1 LM317T 10Ω 22 µF 63V 22 µF 63V A 100nF D4 2.4k 1k 1 µF 63V C 2014 GND VR1 4004 4004 150Ω CON1 Q1 TIP122 ZD1 22 µF 63V 2 3 1 1 3 2 SHIELD 2 XLR MALE SOCKET2 3 SHIELD 100k 1 100k XLR FEAMALE SOCKET2 1 SHIELD 3 XLR MALE SOCKET1 XLR FEMALE SOCKET1 10k 2 SHIELD 100k LED1 D3 100k T NA HP V 8 4 YLPPUS M OSUPPLY 1 4 1 2 1 1 8 148V PHANTOM 4004 4004 33V 470 µF 63V 470 µF 63V 6.8k 24VAC 4.7k + Construction D2 D1 + By contrast, the shield connections of each XLR socket pair are connected together (but not to each other). In other words, the Female Socket1 shield connects to the Male Socket1 shield and the Female Socket2 shield connects to Male Socket2 shield. There is no interconnection between the two sets of shields. In practice, the Socket1 pair shield is also connected to the metal case used to house the circuit. This connection is made via one of the mounting screws that’s used to secure the XLR female socket to the case. Fig.4: follow this diagram to install the parts on the PCB. LED1 should be mounted with the top of its lens 30mm above the board so that it will later protrude through the lid of the case. This view shows the completed PCB assembly. Note that The top of each 470μF capacitor must be covered with insulating tape (12mm-diameter) to ensure that they cannot later short to the case lid. followed by the capacitors. Make sure the electrolytics are installed with the correct polarity. The 2-way screw terminal block (CON1) is next on the list (wire entry holes towards the adjacent edge of the PCB). Alternatively, a DC socket can be fitted instead. A screw terminal block would normally be used, since AC plugpacks are usually supplied with bare leads. Next, install the XLR sockets, making sure that they all sit flush against the PCB before soldering their leads. LED1 can then go in; it must be fitted with the correct polarity and with the top of its lens 30mm above the PCB so that it later just protrudes through the Table 1: Resistor Colour Codes o o o o o o o o o siliconchip.com.au No.   4   1   4   1   1   1   1   2 Value 100kΩ 10kΩ 6.8kΩ 4.7kΩ 2.7kΩ 2.4kΩ 150Ω 10Ω 4-Band Code (1%) brown black yellow brown brown black orange brown blue grey red brown yellow violet red brown red violet red brown red yellow red brown brown green brown brown brown black black brown 5-Band Code (1%) brown black black orange brown brown black black red brown blue grey black brown brown yellow violet black brown brown red violet black brown brown red yellow black brown brown brown green black black brown brown black black gold brown November 2014  43 The PCB is installed in the case by mounting it on two M3 x 6mm tapped spacers (secured with M3 x 12mm countersink screws) at the rear and by fitting six M3 x 12mm screws (one Nylon, the rest metal) into the XLR sockets at the front. + + XLR socket holes: 22mm diameter + + + + + + Before installing the PCB in the case, it’s necessary to drill mounting holes for the XLR sockets and the two rear PCB mounting points. A hole is also required is the lefhand side of the case to accept a cable gland (for the 48VAC supply leads) or a DC plug, while a 3mm hole must be drilled in the lid for the power indicator LED. Fig.5 shows the drilling template for the XLR sockets, while Fig.6 (the front panel artwork) shows the location of the LED (these can also be downloaded in PDF format from the SILICON CHIP website). As shown, the XLR sockets require 22mm-diameter clearance holes, with 3mm-diameter holes for the mounting screws. The 22mm holes can be easily cut using an Irwin Speedbor or similar drill. These are intended for + + + Before going any further, check that all components are orientated correctly and that you haven’t missed any solder joints. That done, apply 24VAC power and check that LED1 lights. If it does, connect your multimeter between TP1 and GND and adjust trimpot VR1 for a reading of 48V. Check that 48V is also present at pins 2 & 3 of the XLR female sockets; ie, by measuring between each pin and GND. Now check pins 2 & 3 of the XLR male sockets. They should each be at a low voltage and this should continue dropping over time as the 22µF capacitors fully charge. In fact, they may take several minutes to drop below 50mV, Preparing the box 13mm Test & adjustment due to capacitor leakage current. If the voltage on one or more pins remains higher than 100mV, change the relevant capacitor. You can use lowleakage 50V capacitors if necessary. + lid of the case. Note that the longer lead is the anode. The PCB assembly can now be completed by covering the top of each 470µF capacitor with a circular piece of insulating tape cut to a diameter of 12mm. This is necessary to ensure that the capacitors cannot later short to the lid of the case. XLR mounting holes: 3mm diameter Fig.5: the drilling and cutout template for the front side of the case. This can also be downloaded in PDF format from the SILICON CHIP website. 44  Silicon Chip use in timber but they also work well on aluminium. Drill just down to a depth where the internal ribs of the box begin; any further and the drill will begin to wobble. The inside piece can then be forced sideways in several directions by inserting a screwdriver in the centre hole and applying leverage. Do this until the inside piece eventually gives way and falls out, then clean up the hole with a round file. If you don’t have a Speedbor drill, drill a series of small holes around the inside perimeter of the hole, then knock out the centre piece and file the job to a smooth finish. Each XLR female socket also requires a cut-out between the top of its 22mm hole and the top edge of the box (see Fig.5). This cut-out is necessary to allow the ‘push to release’ lever on each XLR female socket to be inserted. It’s just a matter of making these cutouts using a hacksaw after the 22mm holes have been drilled. The two mounting holes for the rear of the PCB are marked out after the XLR cut-outs have been made. It’s just a matter of temporarily fitting the PCB assembly into the case, marking out the two holes, the removing the PCB and drilling them to 3mm. Deburr the holes using an oversize drill, then countersink them from the outside to suit countersink-head M3 screws. Next, drill the hole in the side of the case for the power cable (either to accept a cable gland or a DC power plug). This hole should be positioned siliconchip.com.au XLR Female Socket2 (see photos). This is necessary to prevent the screw from making a connection between this socket’s shield and the case, thereby creating an earth loop (and causing hum). That’s because the lower mounting hole of each female socket connects the shield to the case when a metal screw is used. By the way, you will have to cut a thread in the plastic of XLR Female Socket2 with one of the M3 metal screws before replacing this with the Nylon screw. Do all the screws up so that there is a gap of about 2.5-3mm between the socket and the case, so that the lip on the inside of the lid will fit between them. Front panel label NYLON SCREW towards the rear of the case must be directly in-line with the DC socket (if used). Final assembly Once all the holes have been drilled, the PCB assembly can be mounted in the case. The first step is to install two M3 x 6mm tapped spacers to support the rear edge of the PCB. Secure these using M3 x 12mm countersink head screws inserted up through the base of the case, then drop the PCB into position and fit nuts to hold the assembly in place. The PCB assembly is secured to the front of case by fitting M3 x 12mm mounting screws to the XLR sockets. Seven of these screws are metal but a Nylon screw must be used for the lower (righthand) mounting hole of The front-panel label can be produced by printing it onto photo paper. This is then affixed to the case lid using a suitable glue or neutral-cure silicone and the hole cut out for the LED. For a more rugged label, print a mirror image onto clear overhead projector film, so the print side will be on the back of the film when the label is affixed to the lid (eg, using silicone sealant). Alternatively, you can print onto an A4 sized synthetic ‘Dataflex’ self-adhesive label if you have an inkjet printer or onto a ‘Datapol’ self-adhesive label if you have a laser printer. Further information on where to buy these labels is in the panel in the Mains Switch Timer article published elsewhere in this issue. Once the label is in place, it’s then just a matter of attaching the lid using the four countersunk M3 screws provided and the 48V Dual Phantom SC Power Supply is ready for use. 24VAC SILICON CHIP 48V Dual Phantom Power Supply + Power Input 1 Output 1 Input 2 Output 2 Fig.6: the front-panel artwork is also available on the SILICON CHIP website. You will need to drill a hole in the case lid for the power LED. siliconchip.com.au Parts List 1 PCB, code 18112141, 113 x 56.5mm 1 panel label, 113 x 56mm 1 diecast box 122 x 66.5 x 39mm (Altronics H 0453) 1 24VAC plugpack (50mA minimum rating) 2 XLR female 3-pin connectors (compact, PCB mount, 90°) (Altronics P 0875) (Female Socket1, Female Socket2) 2 XLR male 3-pin connectors (PCB-mount, 90°) (Altronics P 0874) (Male Socket1, Socket2) 1 2-way PCB-mount screw terminal block with 5.08mm spacings (CON1) 1 cable gland (3-6.5mm dia. cable) 1 PCB-mount DC socket, 2.1mm or 2.5mm (Jaycar PS-0520, Altronics P0620, P0621A – optional) 2 M3 x 6mm spacers 2 M3 x 10mm machine screws (to secure REG1 and Q1) 7 M3 x 12mm machine screws (for XLR socket mounting) 1 M3 x 12mm Nylon or polycarb­ onate screw (lower right female XLR socket mounting) 2 M3 x 12mm countersink-head screws (rear PCB mounting) 4 M3 nuts 2 PC stakes 1 25mm length of insulation tape 1 1kΩ mini horizontal trimpot (VR1) Semiconductors 1 LM317T adjustable regulator (REG1) 1 TIP122 NPN Darlington transistor (Q1) 4 1N4004 1A diodes (D1-D4) 1 33V 1W zener diode (ZD1) 1 green 5mm LED (LED1) Capacitors 2 470µF 63V PC electrolytic (26.5mm height maximum) 4 22µF 63V PC electrolytic 2 1µF 63V PC electrolytic 1 100nF MKT polyester Resistors (0.25W, 1%) 4 100kΩ 1 2.7kΩ 0.5W 1 10kΩ 0.5W 1 2.4kΩ 0.5W 4 6.8kΩ 0.5W* 1 150Ω 1 4.7kΩ 0.5W 2 10Ω * Select each pair to be within 27Ω of each other November 2014  45 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. REG1 78L05 +5V 100nF 11 THERMOCOUPLE 14 –IN V+ IC 1 IC1 OUT 10 µF AD595 AD595 +12V IN GND 16V TANT 4.7k ALUMEL G 10k 10mV/°C 1 100k 1 CHROMEL +IN + VOUT +A 3 9 FBK SET TEMP VR1 470Ω 8 G 1k ICE POINT COMP COM 7 2 2V = 200°C 10k 6 IC2 3 5 4 1.7V = 170°C 2.7k V– 4 TEMPERATURE DISPLAY LED VOLTMETER 2 100k 7 10mV/°C IC2, IC3: TLC271 3 2 100k 1W 7 6 IC3 4 B 5 C K Q1 BC548 10k E A BR1 ZD1 24V + 1W LED1 LIGHT PIPE λ λ LDR1 K E B2 100nF ZD1 A K K A G WARNING: ALL PARTS AND WIRING IN THIS AREA OPERATE AT MAINS POTENTIAL 2N2646 E 46  Silicon Chip provides cold junction compensation so that the output is relative to absolute temperature, not ambient temperature. Its output is fed to a LED voltmeter which originally displayed a range of 0-99.9V but was modified to turn off the decimal point and change the resolution to 10mV. This was done by bypassing the input resistor of its onboard potential divider (labelled R15, 1104 = 1.1MΩ) and connecting the incoming N A GND B B1 SC R1 78L05 BC548 E B2 AC MAINS K Thermocouple-based thermostat with temperature display & proportional phase control A cheap thermocouple, a compensation IC, LED voltmeter and a few other parts can be used to build a very useful thermostat which controls a mains-powered heater proportionally over a wide temperature range. Most of these parts are available on eBay. With a 5V DC supply, an Alumel/ Chromel (Type K) thermocouple can be used to sense temperatures over the range of 0-300°C. An AD595 (IC1) ~ 47Ω LED1 A – B1 560Ω ~ SCR1 BT151-800 A UJT1 2N2646 300W BAND HEATER LOAD 470Ω A WHITE 4A/500V K C IN OUT A G wire directly to its onboard calibration trimpot. This pot was then readjusted so that when fed a 3V signal, the display read 30.0. Pin 3 of the LED display was then cut to disable all the decimal points. The voltmeter was purchased on eBay: www.ebay.com.au/itm/DC-DigitalDisplay-Voltmeter-Voltage-GreenLED-Panel-Meter-0-99V-3-WireCarGauge-/350817907651 To provide the thermostat function, the target temperature is adjusted using VR1. The difference between the voltage at its wiper and the siliconchip.com.au 20-LED moving dot temperature display This circuit provides a 20-segment temperature display, indicating from 0-30°C in 1.5°C steps. It also has an under-temperature LED which turns on when the temperature is below 1.3°C and an over-temperature LED for when it’s above 31°C. The temperature is measured using an LM35 precision temperature sensor, IC2, which provides a linear DC output voltage that’s proportional to the temperature in °C. Its output is connected to two cascaded LM3914 dot/bar drivers, IC3 & IC4, to provide a 20-segment display (in measured temperature is multiplied by a factor of 10 by IC2, a TLC271 low-drift rail-to-rail op amp. IC2 is configured as a differential amplifier. The lower the measured temperature is compared to the set temperature, the higher IC2’s output voltage. IC3, another TLC271, operates as a voltage-to-current converter. It maintains the voltage across the 560Ω resistor to match the pin 6 output of IC2, so with IC2’s output at 1V (ie, monitored temperature 10°C below the set-point), there will be 1V across the 560Ω resistor, meaning that LED1 is driven at 1V ÷ 560Ω = 1.8mA. The harder LED1 is driven, the lower LDR1’s resistance will be. LED1’s output is coupled to LDR1 using a light-pipe which can be a TOSLINK cable, length of clear PVC or an acrylic rod (with suitable light shielding, eg, opaque heatshrink). As LDR1’s resistance drops, the time constant of the low-pass filter comprising the LDR itself, the 10kΩ dot mode). A separate LM393 dual comparator provides the under and over-temperature indication. Each LM3914 contains 10 individual comparators referenced to a precision ladder divider. Both ends of the divider are available at pins 4 & 6 so the upper and lower reference voltages can be set. The LM35’s output voltage is nominally 10mV/°C but in this circuit, negative feedback has been applied which increases that to 100mV/°C so that for example at 25°C, the output is 2.5V. A resistive divider is placed between the OUT terminal and ground, with the GND terminal of IC2 connected to the midresistor and the 100nF capacitor decreases. As a result, SCR1 is turned on sooner during each mains half-cycle, once the 100nF capacitor charges to a high enough voltage to cause unijunction transistor UJT1 to conduct. When it does, the capacitor charge is dumped into SCR1’s gate and the rectified 230VAC is connected across the heater. So, as the sensed temperature drops (or the set temperature increases), the heater is turned on for more of the time, bringing the temperature back up. Similarly, if the sensed temperature is too hot, power to the heater is reduced. This method of control gives tighter temperature control than the more typical hysteretic (on/off) control. The 4.7kΩ and 2.7kΩ resistors either side of VR1 give a range of 1.72V at VR1’s wiper, allowing the target temperature to be set in the range of 170-200°C. For a different range, change these fixed resistor values, point. The upper part of the divider is a fixed 200Ω while the lower part is adjustable between 1kΩ and 3kΩ using VR2. Ignoring IC2’s operating current, when the divider ratio is 10:1, ie, 1.8kΩ in the lower “leg”, the voltage at the OUT terminal is multiplied by a factor of 10. That’s because for every volt the OUT terminal increas­ es, the GND terminal increases by 0.9V, so with the differential voltage between OUT and GND at 100mV (for 10°C), the voltage between GND and the circuit ground will be 900mV. IC2’s operating current increases continued on page 48 Connect input here 3 2 1 This photo shows how the LED voltmeter is modified. or use a higher value pot for a wider spread of minimum and maximum temperatures. The minimum practical setting is around 70°C while the upper limit is about 300°C as set by the wattage of heater used and the 5V supply. Finally, note that the circuitry in the red shaded area operates at mains potential (ie, 230VAC). John Russull, Tottenham, UK. ($50) co n tr ib u ti on MAY THE BEST MAN WIN! As you can see, we pay $$$ for contributions to Circuit Notebook. Each month the BEST contribution (at the sole discretion of the editor) receives a $150 gift voucher from Hare&Forbes Machineryhouse. That’s yours to spend at Hare&Forbes Machineryhouse as you see fit - buy some tools you’ve always wanted, or put it towards that big purchase you’ve never been able to afford! 100% Australian owned Established 1930 “Setting the standard in quality & value” www.machineryhouse.com.au siliconchip.com.au 150 $ GIFT VOUCHER Contribute NOW and WIN! Email your contribution now to: editor<at>siliconchip.com.au or post to PO Box 139, Collaroy NSW November 2014  47 Cut track to pin 3 λ K A VR4 1k DOT/ 9 BAR 1k 4 7 5 IC1b IC1: LM393 +3.0V REF ADJ 8 7 VREF RHI 6 +3.1V RLO 4 VR3 10k 1k 5 IN IC4 LM3914 6 10 11 O9 12 O8 13 O7 14 O6 15 O5 16 O4 17 O3 1k V+ Vout VR2 2k 1k 200Ω +9V 4 2 1k RLO V– 1 µF IC2 OUT LM35 V+ 2 8 3 IC1a VR1 1k +130mV 33k GND 1 +9V K D1 1N4148 REF ADJ 8 VREF 7 RHI 6 5 IN IC3 LM3914 V+ 3 K λ A LED1 UNDER RANGE OUT 10k DOT/ 9 BAR 10 O10 11 O9 12 O8 13 O7 14 O6 15 O5 16 O4 18 O2 O1 1 17 O3 K K K K K K K K K K GND LM35 DZ V+ 3 1 K O1 V– 2 18 O2 K K K K K K K K K O10 K LEDS D1 A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A λ A LEDS 2 – 11 1k 1k 100 µF 0V +9V 48  Silicon Chip A OVER RANGE LED22 1k LEDS 12 – 21 Moving dot temperature display – ctd from page 47 K A 1k Circuit Notebook – Continued the voltage across the lower divider leg but this small current of around 50µA is swamped by the 200µA/°C across the 200Ω resistor. The output of IC2 is fed to the IN terminals (pin 5) of IC3 & IC4 and also to pins 2 & 5 of IC1. With pin 4 (Rlo) of IC3 at 0V and pin 6 (Rhi) at 1.5V, the internal window comparators have thresholds of 0.15V, 0.3V, 0.45V, etc, corresponding to 1.5°C, 3.0°C, 4.5°C and so on. So LED2 at output O1 (pin 1) turns on when the temperature is below 1.5°C, O2 for 1.5-3.0°C and so on, ending with O10 which turns on when the temperature is between 13.5°C and 15°C. Above 15°C, IC4 takes over as its Rlo input is at 1.5V and Rhi is at 3.0V. The upper voltage tap on this resistor ladder is set to 3.0V by adjusting VR4 which forms part of a voltage divider between the Vref pin (pin 7) and REFadj pin (pin 8) of IC3. REFadj is maintained at 1.25V so a reference voltage of 3.0V is achieved with VR4 set to around 400Ω, forming a 1kΩ:1.4kΩ divider. In this case, the voltage at the REFadj pin is 3.0V x 1kΩ ÷ (1kΩ + 1.4kΩ) = 1.25V. The current pulled from the REFadj pin also sets the output LED current. In this case, it is 1.25V ÷ 1.4kΩ x 10 = 9mA each. For under-range LED1, IC1a pulls its cathode low when its pin 2 inverting input, driven by IC2, is below the reference voltage on its pin 3 noninverting input which is set to 0.13V by adjusting VR1. IC1b works in the opposite manner, with its output going low when the voltage from IC2 is above 3.1V, driving LED22. When LED22 is on, drive for LED21 is cut off since D1 is forward biased, so only one of LED21 and LED22 is on at a time. Note that while set in “dot” mode, the small amount of noise on the signal can cause two adjacent LEDs to be partially switched on simultaneously. If you would prefer “bar” mode, where multiple LEDs are lit (ie, the same LED that would be lit in dot mode plus all the lower-numbered ones down to LED2), connect each pin 9 of IC3 and IC4 to the 9V supply rail. Mahmood Alimohammadi, Tehran, Iran. ($50) siliconchip.com.au Birthday BONANZA! NOVEMBER ‘14 LOTS OF SPECIALS AND DEALS TO CELEBRATE OUR BIRTHDAY WITH US! LED Strip Lighting Encased in an attractive aluminium alloy, this pre-assembled LED strip features a generous beam angle with evenly distributed light. Available in 2 colour temperatures, fixed or linkable models. Mounting screws included. 12VDC powered. FROM 1995 $ 280 Lumens 4000-4500K Natural White Fixed ST-3930 $19.95 Linkable ST-3934 $24.95 ONLINE OR IN-STORE LED Rechargeable Floodlights Bring plenty of light anywhere without the need for mains power or generator. Rechargeable battery. 3-hour burn time. Ultra-long life 50,000 hour cool white LED. IP65 weatherproof enclosure. Mains charger included. 10W 500 Lumens SL-2887 $49.95 520 Lumens 5600-7000K Cool White Fixed ST-3932 $34.95 Linkable ST-3936 $39.95 30W 1500 Lumens SL-2889 $99.95 Suitable 12/24VDC Dimmer ST-3938 $14.95 FROM 4995 $ s Efergy Wireless Power Monitor NEW SCIENCE KIT! Potato Clock Monitor your power usage and reduce your power bills with one of these Efergy power monitors. All monitors work with single or 3-phase installations (extra sensor pack required - MS-6201 sold separately). Each kit includes a weatherproof wireless transmitter with CT sensor and indoor LCD display (except MS-6204). Transmitter and LCD display each powered by 3xAA batteries (sold separately). Efergy Elite Power Monitor MS-6200 The large, easy to read LCD display gives you clear live power consumption, live running costs, stores your usage by day/week/month, and calculates your average daily, weekly and monthly power and running costs. Add the MS-6205 Engage Online Monitoring Hub (sold separately) to start monitoring your home energy usage online and in real-time using the free Smartphone/Tablet App available for both Android and iOS. 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Great tools for technicians, researchers or for general hobby work that involves soldering, connecting wires between small parts, and other fiddly jobs. 1295 $ WAS $14.95 NOW $12.95 SAVE $2 WAS $14.95 NOW $12.95 SAVE $2 WAS $22.95 NOW $14.95 SAVE $8 WAS $22.95 NOW $14.95 SAVE $8 WAS $29.95 NOW $19.95 SAVE $10 WAS $29.95 NOW $19.95 SAVE $10 To order call 1800 022 888 LDS ONA MCD LED Magnifying Lamp FROM NEW LOWER PRICE Also available in warm and cool white. D LED Light Globes T MS GHA EFFIN IN R Ph: (03) 6272 9955 MA Visit our NEW premises E D AV FIEL ING SPR D RK R T PA WEN VEY HAR MAN R NO Lot 1, 187/205 Main Rd, Moonah TAS 7009 Accessories available: 2 x Sensors to Suit MS-6200/2/4 (for 3-Phase Systems) MS-6201 $39.95 Efergy Engage Hub to Suit MS-6202 MS-6205 $89.95 DER • 127mm lens diameter • 5 dioptre lens • Mains powered QM-3548 99 $ SL-2232 Suitable Rolling Floor Base QM-3549 $89.00 www.jaycar.com.au November 2014  49 TEST EQUIPment bonanza DOUBLE REWARDS POINTS! 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Drop $ proof up to 2 metres. 109 • Cat III 600V, 4000 count • AC/DC voltages up to 600V • AC/DC current up to 10A • Temperature, resistance, capacitance, frequency and more • True RMS for accurate readings • Autoranging, continuity, diode check • Size: 138(L) x 68(W) x 37(D)mm QM-1551 • Cat IV 600V, DOUBLE POINTS 4000 count • AC/DC voltages up to 1000V • AC/DC current up to 10A • Resistance, frequency, continuity, diode, temperature and more • True RMS for accurate readings • Size: 180(L) x 82(W) x 57(D)mm QM-1574 Cat IV True RMS DMM with Smartphone App CAT III 400A Autoranging AC/DC Clampmeter • CAT IV 600V, 40000 count • AC/DC voltages up to 1000V • AC/DC current up to 10A • Bluetooth® and PC connectivity • Data hold/storage, triple LCD display • Size: 182(L) x 82(W) x 55(D)mm QM-1576 WAS $219.00 • Cat III 600V, 4000 count • AC/DC voltages up to 600V • AC/DC current up to 400A • Resistance, capacitance, frequency, temperature and more • Data hold, non-contact voltage, relative measurement • Size: 198(H) x 66(W) x 36(D)mm $ QM-1563 Quality clampmeter with current ranges up to 400A AC/DC and 30mm jaw size to accommodate conductors up to 350MCM. Perfect for the working installer or tradesman. View live measurements, trend graphs, data log, and email your results or upload them to the Cloud all from your Smartphone! Non-Contact Thermometer with Dual Laser Targeting $ 189 SAVE $30 $ 119 Temp/Humidity USB Datalogger 99 Log temperature and humidity readings and store them in internal memory for later download to a PC. Mounting bracket and software included. Measure the temperature of any surface from a safe distance with this compact sized non-contact thermometer. With a wide temperature range and laser targeting, this portable instrument is easy to use for quick and accurate temperature checking of any surface. • Windows 2000/XP/Vista compatible • Temp range: -40 to 70˚C (±1˚C) • Humidity range: 0 to 100% (±3˚C) • 32,000 memory samples $ QP-6013 Also available: USB/LCD Model QP-6014 $149.00 (Shown) 119 • Temp range: -50˚C to +650˚C (±1%) • Size: 146(L) x 104(W) x 43(D)mm QM-7221 Professional Laser Distance Meter with Smartphone App Compact Digital Sound Level Meter Measure distance, area, and volume. Store the last 20 measurements for easy comparison and referral. Pair with a Smartphone to email measurements with a picture or upload to the Cloud. Measure sound levels between 30 to 130dB and can be set for fast or slow responses. Data hold, min/max functions. Backlit LCD. Supplied with carry case, wind $ sock and battery. 99 • Range: 0.05 to 70m (±1.5mm) • Requires 2 x AA batteries • Size: 134(L) x 52(W) x 30(H)mm QM-1624 • 3.5 digit display • A and C selectable weighting • Size: 210(L) x 55(W) x 32(D)mm QM-1589 Free Digitech LDM app available from the App StoreSM and Google PlayTM Digital Storage Oscilloscopes Ideal DSO for the advanced hobby user or technician. Full data storage capabilities and USB interface. Portable, easy to use. • Sampling rate: 500MSa/s (QC-1932) / 1GSa/s (QC-1934) • Memory depth: 32k (QC-1932) / 2M (QC-1934) $ 209 $ FROM 499 100:1 OSCILLOSCOPE PROBE KIT Basic and professional models available: 25MHz Dual Channel with 5.7" Screen QC-1932 $499.00 100MHz Dual Channel with 7" Screen QC-1934 $899.00 FREE*! VALUED AT $59.95 (QC-1903) * Valid with purchase of QC-1932 or QC-1934 siliconchip.com.au www.jaycar.com.au Savings off original RRP. Limited stock on sale items TOOLS BONANZA 1000V 7-Piece Screwdriver Set 1000V 6-Piece Electronic Screwdriver Set High quality, bright red drivers that are insulated right to the tip. Storage case included. TD-2022 Set of six slotted and phillips screwdrivers with ergonomic and insulated handles. Excellent non-slip grips. Storage case included. TD-2026 See website for full contents. FREE*! $ KEYRING SCREWDRIVER VALUED AT $2.50 (TD-2086) 1995 * Valid with purchase of TD-2026 A must have for your workbench! This soldering package includes essential items you need to do an awesome soldering job. See website for full specifications. Will cut any shape out of aluminium, plastic, copper and other unhardened metals up to 18 gauge. Designed to fit in the palm of your hand for easy use, simply drill a 1/4" hole to start. TH-1768 14 $ 95 3-in-1 Heat Blower and Soldering Iron Kit includes: 60W Lead-Free Digital Soldering Station Metal Desoldering Tool 1mm Lead-Free Solder 200g Goot Soldering Iron Tip Cleaner PCB Holder with Movable Arm TS-1390 TH-1862 NS-3094 TS-1510 TH-1980 • Piezo ignition • Child resistant latch • Up to 500˚C • Size: 148(L) x 35(W) x 23(D)mm TH-1604 SOLDERING BUNDLE DEAL DEAL INCLUDES SAVE $52.80 169 $ SAVE OVER $50 $169 TS-1390,TH-1862, NS-3094, TS-1510, & TH-1980 ELECTRICAL SERVICE BUNDLE PACK 2995 $ Also available: 1mm Conical Tip TH-1603 $3.95 Useful service aids for electrical jobs. See website for full specifications. Kit includes: Isopropyl Alcohol 99.8% Spray Circuit Board Lacquer Circuit Board Cleaner J-B Weld Epoxy Pack Black Liquid Electrical Tape Anti-Static Field Service Foldable Mat Ideal for anyone who manufactures, repairs or services sensitive electronic equipment. 250ml 175g 175g 25ml 118ml NA-1066 NA-1002 NA-1008 NA-1518 NM-2832 Total valued at over $70! • 3mm thick, hard wearing face • Includes a ground lead, wrist strap and 2 pouches • Mat folds out to approx. 600 x 600mm TH-1776 $149 $16.95 $17.95 $17.95 $19.95 Great Bundle Price Total valued at over $220! A handy unit with flame/flameless heat blower and soldering iron function. Great for general heating, drying, melting, soldering, heat shrinking, etc. SERVICE AID BUNDLE DEAL DEAL INCLUDES 4995 $ SAVE $22 Precision 1kg electronic scale with 0.01g resolution. Weighs in grams, ounces, pounds, grains, carats and troy ounces. Indicates proximity when you are near a stud via its large LCD and shows a target graphic when you're spot on. Also has built-in laser level and voltage detection. Battery included. • Automatic calibration • Tare and counting function • Powered by mains or batteries (not included) • Size: 175(W) x 75(H) x 260(D)mm QM-7264 • Continuous live wire detection • Thumb dial adjustable feet for levelling the laser • Size: 180(H) x 67(W) $ x 38(D)mm QP-2288 4995 LED Headband Magnifier This magnifying headset leaves both hands free and can be worn over prescription or safety glasses. Ideal for jewellery, radio electronics & camera repair, etc. 2995 $ $49.85 NA-1066, NA-1002, NA-1008, NA-1518 & NM-2832 Digital Bench Scale 3-in-1 Stud Detector with Laser Level siliconchip.com.au 2495 SOLDERING BUNDLE PACK Nibbling Tool • Adjustable head strap • Built-in LED work light • 1.5X, 3X, 8.5X or 10X magnification • Requires 2 x AAA batteries QM-3511 $ See website for full contents. $ 149 $8.95 $11.50 $11.50 $14.95 $24.95 Great Bundle Under $50 $ 4985 SAVE OVER $20 Inspection Camera with 3.5" Detachable Wireless LCD View and record video and pictures in confined and dark locations. The head and flexible boom are IP67rated for use in harsh environments. • 1m flexible boom • 2.4GHz wireless transmission • Hook, mirror, magnet and 2GB microSD card included QC-8712 $ 249 Also available: Extension Shaft 2m QC-8702 $79.00 150mm Precision Digital Vernier Calipers Features a 5 digit LCD display that will show readings in metric and imperial. The caliper can be zeroed at any point along the scale making comparative measurements easy. Battery included. • Auto power off • Thumbscrew slide damper • Resolution: 0.01mm / 0.0005" TD-2082 To order call 1800 022 888 $ 2995 Pocket Moisture Meter An intelligent meter suitable for measuring water content in building materials and wooden fibre articles. Features 8mm electrode and backlit digital LCD screen. Carry case and batteries included. • Range: 6 to 44% (wood) / 0.2 to 2.0% (material) • Size: 96(H) x 40(W) x 20(D)mm • Lightweight, only 83g QP-2310 $ 2995 November 2014  51 www.jaycar.com.au 3 AUTO BONANZA "Condura" Style DC Rocker Switches Superb looking rocker switches that you see in 70-100ft luxury motor cruisers. Basic switch comes with double-LED illumination, a standard rocker cover and a standard range of decals to customise the switch toyour application. For more professional finish, special laser-etched covers are available to match the basic switches. • Rated 20A <at>12V, 10A <at>24V Typical decals include: windscreen wipers, horn, heater & many more. BASIC SWITCHES White SK-0910 $12.95 Red SK-0912 $12.95 Blue SK-0914 $12.95 Amber SK-0916 $12.95 LASER-ETCHED COVERS 12V Power SK-0920 Fridge SK-0921 Aux Battery SK-0922 Interior Light SK-0923 Spot Lights SK-0924 12/24VDC HIGH POWER LED $2.95 $2.95 $2.95 $2.95 $2.95 $ 1295ea Horn Rear View Camera Inverter Driving Lights Thermofan DEAL! $2.95 $2.95 $2.95 $2.95 $2.95 BUY SWITCH & COVER FOR $13.90 SAVE $2! SWITCH INCLUDES ONE UNIT OF SK-0910, SK-0912, SK-0914 OR SK-0916 COVER INCLUDES ONE UNIT OF SK-0920, SK-0921, SK-0922, SK-0923, SK-0924, SK-0925, SK-0926, SK-0927, SK-0928 OR SK-0929 LIGHT BARS Spot/Flood Combo LED Light Bars 5,400 Lumen LED Light Bars This high power single row LED light bar uses six 10W Cree XM-L LEDs to produce a whopping 5,400 lumens - equivalent to a 400W halogen. Virtually unbreakable IP68 waterproof and aluminium construction, stainless steel mounting brackets. Shock and vibration resistant. ® • Input voltage: 9-36VDC • High quality PWM thermal management electronics • Beam distance: 474m (SL-3970) / 316m (SL-3971) $ 249 ea Spot or flood beam available: 12" long, Spotlight SL-3970 $249 12" long, Floodlight SL-3971 $249 This high power dual row LED light bar features high quality Osram LEDs with extremely optically efficient lenses. Virtually unbreakable IP68 waterproof and aluminium construction, stainless steel mounting brackets. Shock and vibration resistant. FROM • Input voltage: 9-30VDC $ • High quality PWM thermal management electronics • Beam distance: 755m (SL-3982) / 1163m (SL-3984) 499 Available in 2 sizes: 20" Long, 8,400 Lumens SL-3982 $499 40" Long, 16,800 Lumens SL-3984 $899 500 Lumens Mini LED Driving Lights 3500 Lumens 5" LED Driving Lights • 12/24VDC • Input voltage: 9-60VDC • Beam distance: 145m (SL-3916) / 50m (SL-3915) • Compact 70(H) x 40(W) x 55(D)mm • Sold individually • 12/24VDC • Input voltage: 9-36VDC • Beam distance: 378m (SL-3919) / 183m (SL-3918) • Sold individually Amazingly bright, an all-round solution for many different applications. Equivalent to a 35W halogen. Virtually unbreakable IP68 waterproof and aluminium construction, stainless steel mounting brackets. Shock and vibration resistant. Spot or flood beam available: Spotlight SL-3916 $49.95 Floodlight SL-3915 $49.95 $ DEAL! Extremely bright vehicle driving lights that only draws 34W of power. Equivalent to a 300W halogen. Virtually unbreakable IP68 waterproof and aluminium construction, stainless steel mounting brackets. Shock and vibration resistant. $ 129 ea 4995 ea BUY 2 FOR $79 SAVE $20.90 Extremely bright drop-in replacement LED headlights for your car. Each kit contains 2 x 25W per LED bulbs, 2 x controller assemblies, and all the wiring is pre-terminated to appropriate connectors to make installation as quick and easy as possible. Spot or flood beam available: Spotlight SL-3919 $129 Floodlight SL-3918 $129 $ 139 ea SAVE $30 • Cree® XLamp CXA1512 LED • Ballast size: 65(L) x 50(W) x 16(H)mm H7 Cree® Module • 1800 Lumens per LED bulb SL-3499 WAS $169 NOW $139 SAVE $30 Warning: State road and traffic authorities do not allow retrofitting of these products to cars with ordinary headlights - even if it’s really simple to do so. ER SOCKET SPLITTERS 12/24VDC CIGARETTE LIGHT • LED power indicator light PP-2005 WAS $9.95 Note: Please ensure your lights are angled correctly. These lights are not ADR approved. 7 To order call 1800 022 888 $ 1695 SAVE $3 SL-3490 SL-3492 SL-3494 SL-3495 SL-3496 $49.95 $49.95 $49.95 $79.95 $49.95 FROM $ 4995 Limited stock. Not available online. • Plug can be rotated 180˚ • Power on/off switch function • USB output: 5VDC 2A (max) PP-2128 WAS $19.95 SAVE $2 52  Silicon Chip • 12V 6000K colour temp • 300% more light than halogen 2-Way Splitter with 2 x USB Ports $ 95 BUY 2 FOR $198 SAVE $60 HID provides far greater light output than standard automotive lights. This series of kits all feature a slim ballast design for ease of installation in engine bays and tight spaces. H1 Slim Ballast HID Kit H3 Slim Ballast HID Kit H4 Slim Ballast HID Kit H4 Slim Ballast HID High + Low Kit H7 Slim Ballast HID Kit H4 (High / Low Beam) Cree® Module • 1600/1800 Lumens per LED bulb SL-3498 WAS $169 NOW $139 SAVE $30 2-Way Splitter DEAL! Slim Ballast HID Light Kits 12VDC Mounting LED Headlamp Modules 4 SK-0925 SK-0926 SK-0927 SK-0928 SK-0929 UP TO 20% O 4-Way Splitter with 1 x USB Port FF • Dash or console mounted • Mounting hardware included • USB output: 5VDC 1A (max) • 1.2m long lead • 10A max $ 95 PS-2019 WAS $19.95 17 Limited stock SAVE $2 siliconchip.com.au www.jaycar.com.au Savings off original RRP. Limited stock on sale items POWER BONANZA Energy Saving Powerboard Save power and money by automatically switching off appliances when not in use. 6 power sockets: 1 x control, 1 x always-on and 4 x auto-off sockets. Vertical Power Tower A versatile 8-outlet power board with 2 x 1A built-in USB ports to charge any USB product. Surge and overload protected. • 10A, 2400W rated • Surge protection: 3150 joules • Size: 225(H) x 170(W) x 170(D)mm MS-4023 WAS $69.95 • 10A, 2400W rated • Surge protection: 700 joules • Size: 340(L) x 120(W) x 35(D)mm MS-4081 WAS $39.95 NOW $29.95 SAVE $10 Also available: Energy Saving Powerboard with IR Sensor for AV MS-4080 WAS $69.95 NOW $49.95 SAVE $20 (shown) $ FROM $ 2995 9 $ 95 Europe, Middle East, Asia PP-4023 $9.95 UK, HK, Singapore, Malaysia PP-4024 $9.95 USA, Japan,Thailand,Taiwan PP-4025 $9.95 5495 DEAL! Features worldwide voltage input, perfect mobile device charging solution for home and travel needs. • Input voltage: 100-240VAC, 50/60Hz ea Recharge Li-ion battery packs, AAA/AA and 9V Ni-MH and Ni-Cd rechargeable batteries Batteries not included $ 39 CHARGER + BATTERY BUNDLE DEAL 1 MB-3639 + SB-1739 FOR $40.90 SAVE $10 DEAL 2 MB-3639 + SB-1738 FOR $41.90 SAVE $15 95 1995ea BUY 2 FOR $29.95 SAVE $9.95 Portable 4000mAh Power Bank with Solar Charger Charged via the included 12V in-car cigarette USB charger or from the built-in solar panel. It has two USB ports that output up to 2.1A. Supplied with 6 interchangeable connectors to suit many devices, and a carabineer so you can attach it to a bag. $ 5995 SAVE $10 0-260VAC Variable Laboratory Autotransformer (Variac) DEAL! • Includes USB charging port (500mA) • Size: 120(L) x 62(W) x 35(H)mm MB-3639 $ • Size: 76(L) x 33(W) x 29(D)mm MB-3615 WAS $69.95 4 Ports (2 x 2.1A) + (2 x 1.0A) MP-3454 $29.95 (Shown) Universal Battery Charger Rechargeable Ni-MH batteries: AAA, Pack of 4 SB-1739 $10.95 AA, Pack of 4 SB-1738 $16.95 FROM 2495 $ 2 Ports (2 x 2.1A) MP-3459 $24.95 Note: These do not convert voltages. Shows how much an appliance is costing to run and tracks the total power being used. Shows instantaneous voltage or current being drawn and peak levels. • 10A max rated MS-6115 USB Mains Power Adaptor These travel adaptors will allow you to use your AU/NZ appliances while travelling overseas. Mains Power Meter SAVE $15 SAVE UP TO $20 Travel Adaptors TRACK YOUR POWER & SAVE $$ Controls AC voltage and of voltage-dependent parameters such as current, power, temperature, light intensity, motor speed etc. It enables the AC input to a mains powered appliance to be easily varied from 0 to full line voltage (or greater). Encased in heavy-duty steel housing. • Rated power handling: 500VA (fused) • Input voltage: 240VAC <at>50Hz • Output Voltage: 0~260VAC <at>50Hz • Size: 165(D) x 120(W) x 160(H)mm MP-3080 WAS $229 189 $ SAVE $40 FORMERS 10% OFF STEPDOWN TRANS Dielectrically Isolated Transformers Non-Dielectrically Isolated Transformer Includes overheat protection. Two-pin US 110 - 115V socket and cord plug for 240V power. • 50W rated • 240VAC to 115VAC MF-1091 WAS $49.95 $ Quality fully-enclosed stepdown transformer with fold up metal carry handles, approved 3-wire power cord & two-pin US 110 - 115V socket. Suitable for use with precision electric and electronic appliances. • 240VAC to 115VAC isolated • Includes a resettable circuit breaker See website for specifications. 120W 250W 500W 1000W 4495 SAVE $5 DC to DC Converter Modules DC voltage converter modules that will output user selectable voltages (excluding AA-0238). These could be used to power 12VDC devices from a 6VDC motorbike battery or to run 12VDC devices from a 24VDC source such as those found in trucks. • Protection against short-circuits, overload and overheating • Compact size and features mounting holes 1.5A AA-0236 $24.95 • 6-28VDC Input, 3-15VDC Output 2.0A AA-0237 $29.95 • 6-14VDC Input, 11-26VDC Output $ FROM 2495 1.1A AA-0238 $24.95 • 24VDC Input, 12VDC Output siliconchip.com.au To order call 1800 022 888 MF-1080 MF-1082 MF-1084 MF-1086 WAS $99 WAS $129 WAS $229 WAS $369 FROM $ 89 MF-1086 SAVE UP TO $37 NOW $89 NOW $116 NOW $206 NOW $332 SAVE $10 SAVE $13 SAVE $23 SAVE $37 RE CABLES TINNED COPPER SINGLE CO FROM 7.5A & 15A Tinned Cables Flexible heavy duty tinned copper cables suitable for $795 general purpose, automotive and marine applications. Supplied on easy to use 10m handy pack reel and available in 3 colours. 7.5A 18/19 AWG Red WH-3045 $7.95 Black WH-3046 $7.95 Green WH-3047 $7.95 15A 16 AWG Red WH-3054 $12.95 Black WH-3055 $12.95 Green WH-3056 $12.95 November 2014  53 www.jaycar.com.au 5 PART Y BONANZA TY LIGHTS SAVE UP TO 30% ON THESE PAR This portable LED flashing strobe light, has a magnetic base which can be placed on any iron/steel surface. This compact 14-channel DMX moving spotlight features a user selectable 540˚ pan and 270˚ tilt and 9 gobos plus open and wheel spin effect. Built-in movement macros via master/slave or DMX. 9 $ 95 • Powered by 3 x AAA batteries or 4.5V power supply (not included) SAVE $5 Available in 3 colours Red SL-3325 WAS $14.95 NOW $9.95 SAVE $5 Blue SL-3327 WAS $14.95 NOW $9.95 SAVE $5 Amber SL-3329 WAS $14.95 NOW $9.95 SAVE $5 Note: Limited stock. Not available online. $ • Mains powered • Channels: brightness, strobe • Size: 240(W) x 200(H) x 310(D)mm SL-3466 WAS $119 89 SAVE $10 24 • Mains or battery powered (2 x C batteries, sold separately) • 280mm long AB-1220 WAS $34.95 FREE*! 79 $ SAVE $20 FREE*! * Valid with purchase of AB-1220 Produces clouds of white fog on demand. Fantastic for use with laser light shows, mirror balls and other party lighting. • Mains powered with 3m wired remote controller • 800ml fog juice capacity • Size: 330(L) x 160(W) x 140(H)mm AF-1214 WAS $99.95 8995 $ SAVE $10 Spare Snow Juice 1L AF-1217 $9.95 BUBBLE LIQUID 946ML VALUED AT $6.95 (AB-1222) SAVE $14 Fog Machine • 240VAC operation • Size: 337(L) x 210(W) x 170(H)mm AF-1216 WAS $99 Spare Bubble Liquid 946ml AB-1222 $6.95 105 $ NOTE: Snow machine liquid may cause eye or skin irritation and can be slightly slippery on smooth surfaces. Handling and safety directions available online. balls which float majestically to the ground like real snow. The resulting blanket of snow dissolves slowly leaving minimal residue. SAVE $10 SAVE $30 This compact 2-channel DMX Par 64 spotlight offers 3 operating modes: sound-active, automatic and DMX control. It features 177 UV emitting LEDs, brightness control, strobe effect and a built-in microphone. L EFFECTS SPECIAL DEALS FOR SPECIA Snow Machine Bubble Machine Produces a jet of small foam $ 95 Create instant, continuous bubbles with this affordable portable bubble machine! $ Note: Limited stock. Not available online. This 5-channel DMX Par 64 spotlight offers complete control over stage, party or DJ lighting setup. Designed for easy installation, safe, energy efficient and long life operation. Individually addressable via DIP switch and include a mounting bracket. • Mains powered • Channels: red, green, blue, brightness, strobe • Size: 245(L) x 195(Dia)mm SL-3424 WAS $99 269 • Mains powered • Variable electronic strobe/dimmer • Size: 249(H) x 173(W) x 173(D)mm SL-3440 WAS $299 SNOW JUICE 1 LITRE VALUED AT $9.95 (AF-1217) * Valid with purchase of AF-1216 Spare Fog Juice 1L AF-1212 $17.95 FREE*! FOG JUICE 1 LITRE VALUED AT $17.95 (AF-1212) * Valid with purchase of AF-1214 MENT SAVE OVER 10% ON DJ EQUIP XLR LED Light with Gooseneck No DJ or engineer should be without one of these. Four bright LEDs provides enough light to see what you're doing without disturbing the audience. • Powered by phantom power • 400mm long AM-4124 WAS $24.95 $ 21 95 SAVE $3 Note: Limited stock. Not available online. Mixing console not included. XLR Unidirectional Microphone Dynamic, unidirectional microphone with an anti-pop grille, built-in on/off switch and XLR termination. Supplied with a 3m XLR to 6.5mm plug cable. • Frequency response range: 50Hz to 13kHz • Sensitivity: -50dB • Output Impedance: 600 ohm $ 95 AM-4192 14 Multifunction Megaphone A battery operated megaphone with built-in message record feature for repeat announcement replay. Lightweight and portable with shoulder strap. • Power output: 10WRMS • Built-in alarm, whistle and LED torch • Requires 8 x AA batteries (not included) • Size: 270 (L) x 162(W) x 235(H)mm $ 95 AM-4055 SAVE $7 WAS $69.95 62 Desktop Mic Stand Excellent build quality with diecast aluminium legs, steel column and padded feet. • Adjustable up to a height of 200mm and folds up to 240mm long • Includes mic holder with 5/8" adapter AM-4111 1795 $ 54  Silicon Chip 6 To order call 1800 022 888 DJ Mixer Two channels each with RCA inputs for CD or other line level source and a set of dedicated phono inputs. The BPM counter is capable of accurately measuring the beats per minute automatically. • Level meters on each channel • 2 band EQ on each channel • Phono and line level inputs • Mic and headphone outputs • Line level preamp outputs • Selectable CF curve • Size: 330(W) x 22(H) x 102(D)mm AM-4206 WAS $149 129 $ SAVE $20 USB MIDI Interface Connect any MIDI device to your computer: keyboards, controllers, instruments, sound cards, samplers, drum machines etc. 1995 $ SAVE $10 • Plug and play, no software or drivers required • MIDI in and MIDI out connectors • 2m long cable XC-4934 WAS $29.95 Limited Stock. Not Available Online siliconchip.com.au www.jaycar.com.au Savings off original RRP. Limited stock on sale items BUILD IT BONANZA IONAL KITS SAVE UP TO 20% ON EDUCAT Electric Current Experiment Kit Snap-on Electronic Project Kits Learn the common principles of electric current and magnetism. SAVE UP TO $4 PC Programmable Line Tracer Kit Heavy Duty Robot Chassis Virtually unbreakable glass reinforced ABS plastic vehicle chassis. Comes assembled with 2 x 6V motors with gear trains and includes gear grease and allen key (electronics not included). Learn about robotics and programming. Run it in line tracer mode by drawing a thick dark line on paper for the robot to follow. $ • Overall size: 172(L) x 130(W) x 60(H)mm • Recommended for ages 12+ KR-3130 $ 95 2995 • Assembly time: 10min • Requires 2 x AA batteries • Base size: 120(L) x 99(W) x 23(H)mm • Recommended for ages 8+ KJ-8919 WAS $24.95 Asuro Programmable Robot Kit Autonomous multi-sensor robot ideal for hobbyists and school projects. RISC processor robot "brain" featuring two odometers and several display elements. • Some soldering required • Recommended for ages 14+ KR-3120 69 7995 $ TIBLE PRODUCTS POPULAR ARDUINO COMPA EtherTen Eleven Talk to the world with all the features from Eleven and the Ethernet Shield combined in a single, integrated board. Includes onboard Ethernet, a USB-serial converter, a microSD card slot for storing gigabytes of web server content or data, and even Power-Over-Ethernet support. "Eleven" is based on the Arduino Uno but with improvements. Top spec ATmega328P Microcontroller, independent prototyping area, visible LEDs, and firmly mounted micro-USB connector to power your Eleven from most cellphone chargers! Includes USB cable and guide sheet. XC-4210 $ • ATmega328P MCU running at 16MHz • 10/100base-T Ethernet built-in $ XC-4216 3995 6995 128x128 Pixel OLED Display Module High resolution, full colour 128x128 pixel OLED module perfect for your display needs including graphics, gauges, graphs and interactive displays. • 16,384 full colour RGB pixels • 28.8 x 26.8mm active display area • Size: 44(W) x 36(H) $ 95 x 5(D)mm XC-4270 DOUBLE POINTS 49 Large Dot Matrix Display Panel This large, bright 512 LED matrix panel has onboard controller circuitry designed to make it easy to use straight from your board. • 32 x 16 high brightness blue LEDs on a 10mm pitch • Viewable over 12 metres away 39 $ DOUBLE POINTS Switchmode Power Regulator This is a high tech switchmode supply with a selectable 5V or 7VDC output. The input voltage range of 6 to 28VDC is very flexible and it will not overheat at higher input voltages like the 7805 and other linear regulators may. • Up to 1A output current • Suits EtherTen or EtherMega POE $ XC-4258 1995 Ramp not included siliconchip.com.au 95 Red LED Display Blue LED Display To order call 1800 022 888 SAVE $4 Learn practical electronic principles such as static electricity, electric motors, solar power and more. 80 Experiments KJ-8970 WAS $19.95 NOW $16.95 SAVE $3 (Shown) 50 Experiments KJ-8972 WAS $24.95 NOW $20.95 SAVE $4 7 2095 $ 12-In-1 Electrical Experiment Kit Simple snap together electronic project kits, no tools or soldering required. Both kits are great educational tools with fun bright coloured pieces. See website for full details of the projects. Recommended for ages 6+. • Assembly time: 30min • Requires 2 x D batteries, scissors, and tape (not included) • Size: 99(L) x 70(W) x 45(H)mm $ 95 • Recommended for ages 8+ SAVE $2 KJ-8901 WAS $9.95 • Requires 2 x AA batteries • Size: 120(L) x 64(W) x 55(H)mm • Recommended for ages 12+ KJ-8906 FROM 1695 $ XC-4250 $39.95 (shown) XC-4251 $89.95 StepDuino A self-contained board with onboard stepper motor drivers, servo interface, microSD card slot, and 20x4 character LCD. Perfect for building robots or other mechatronics projects: just connect the stepper motors and go! 149 $ • 2 x 4-wire stepper motor controllers • 1 x servo interface • Serial communications header • Compatible with the Arduino IDE • Size: 113(W) x 74(H) x 25(D)mm XC-4249 3.2" LCD Touchscreen Display Kit Add an interactive touchscreen display to your existing Arduino projects. Draw lines, shapes, text, display images, play sound and log data to microSD card. Includes LCD display, 4D Arduino Adaptor Shield, 5way interface cable and USB programming adaptor with pre-loaded software. • Operating voltage: 4.5 - 5.5VDC • Screen display area: 64.8 x 48.6mm • Screen resolution: 240 x 320 pixels • 65K True to life colours XC-4280 $ 119 DOUBLE POINTS 3-Axis Accelerometer Module IR Temperature Sensor Module • Independent X, Y, and Z axis outputs • Can run from either 5V or 3.3V • Zero-G free-fall detection XC-4226 • -33 to +220˚C measurement range XC-4260 This module can operate in either +/-1.5g or +/-6g ranges, giving your project the ability to tell which way is up. Perfect for Arduino projects, robotics projects, tilt sensors, vehicle dataloggers, and whatever else you can dream up. $ 1995 Connect this to your board and point it at a surface or heat source to remotely measure its temperature. Includes onboard power supply, communication support and a software library and examples. 3495 $ November 2014  55 www.jaycar.com.au 7 securit y bonanza Outdoor Security Camera with PIR 2.4GHz Wireless DVR Kit with Solar Powered Camera Motion activated video recording in HD 720p to microSD card (32GB microSD card $47.95 XC-4992 sold separately). Features infrared LEDs for day/night use, LCD display, schedule function, and playback on PC/TV. No wiring needed! This DVR kit has a solar powered digital wireless camera with PIR sensor and 2 x 5W LED lights. • Kit includes DVR receiver with mains adaptor, remote control, camera sensor light with rechargeable Li-ion battery, solar panel and USB and AV cables • Solar charged camera DEAL! • Supports up to 4 cameras WIRELESS DVR • DVR size: 207(L) x 92(W) BUNDLE DEAL x 77(D)mm QC-3644 + QC-3646 QC-3644 FOR $389 SAVE $109 159 • IR range up to 9m $ • 5MP colour CMOS sensor • Weatherproof IP66 camera • Powered by batteries or 6VDC power supply (not included) • Size: 140(H) x 75(Dia)mm QC-8027 Spare camera QC-3646 $199.00 High Volume Wireless Doorbell Rings with loud sound and strobe light. Ideal for use in a factory or for the hearing impaired. $ 2.4GHz Digital Wireless Video Doorphone 49 95 Not your average video doorphone. This unit incorporates PIR motion detection on the camera face and will record any visitor within range. It will also take crystal clear images of your visitor pressing the doorbell. • Portable, up to 30m range • 7 selectable melodies • Requires 4 x C cells (not included) • 210mm long LA-5002 269 • 3.5" LCD wireless monitor $ • Up to 80m range • IP55 weatherproof camera • Power supplies and mounting hardware included • Camera size: 74(W) x 134(H) x 31(D)mm QC-3400 Motion Activated Tracking Spotlight A unique way to protect your home against intruders. Motion is detected via the two front facing PIR sensors. Once activated, the light will pan left or right to follow a person. $ The 4 x 3W LEDs combine to produce a remarkable 500 lumens of light. DOUBLE POINTS 119 • Rotational range of light: 240˚ • Detection up to 13m away depending on vertical angle • PIR sensor and LED built into base • Built-in dummy camera with blinking LED • Size: 215(L) x 77(Dia)mm SL-2705 REGISTER ONLINE TODAY! 299 $ Spare 3.5" LCD Wireless Monitor QC-3402 $159.00 Solar Rechargeable LED Floodlight The 3W solar panel comes with a bracket allowing you to bolt it onto a surface to catch as much sunlight as possible. LED light automatically turns on when darkness falls, and activates when the PIR detects motion. $ 3m cable included. • 10W cool white LED • Light size: 175(H) x 145(W) x 53(D)mm SL-2808 WE ARE MOVING 195 Victoria St Mackay QLD 4740 SIGN UP NOW & BE REWARDED Earn a point for every dollar spent at any Jaycar Company store* & be rewarded with a $25 Rewards Cash Card once you reach 500 points! *Conditions apply. See website for T&Cs 159 DOUBLE POINTS Visit our NEW premises Register online today by visiting www.jaycar.com.au/rewards Ph: (07) 4953 0611 YOUR LOCAL JAYCAR STORE - Free Call Orders: 1800 022 888 AUSTRALIAN CAPITAL TERRITORY Belconnen Fyshwick Ph (02) 6253 5700 Ph (02) 6239 1801 NEW SOUTH WALES Penrith Port Macquarie Rydalmere Smithfield Sydney City Taren Point Tuggerah Tweed Heads Wagga Wagga Warners Bay Wollongong NEW Ph (02) 4721 8337 Ph (02) 6581 4476 Ph (02) 8832 3120 Ph (02) 9604 7411 Ph (02) 9267 1614 Ph (02) 9531 7033 Ph (02) 4353 5016 Ph (07) 5524 6566 Ph (02) 6931 9333 Ph (02) 4954 8100 Ph (02) 4226 7089 WE ARE Mackay MOVING! 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Gore Hill Ph (02) 9439 4799 Cairns Ph (07) 4041 6747 Launceston Ph (03) 6334 2777 Hornsby Ph (02) 9476 6221 Caloundra Ph (07) 5491 1000 VICTORIA Liverpool Ph (02) 9821 3100 Capalaba Ph (07) 3245 2014 Cheltenham Ph (03) 9585 5011 Maitland Ph (02) 4934 4911 Ipswich Ph (07) 3282 5800 Newcastle Ph (02) 4968 4722 Labrador Ph (07) 5537 4295 Coburg Ph (03) 9384 1811 Arrival dates of new products in this flyer were confirmed at the ONLINE ORDERS OFFICE HEAD time of print but delays sometimes occur. Please ring your local Website: www.jaycar.com.au 320 Victoria Road, Rydalmere NSW 2116 store to check stock details. Savings off Original RRP. Prices valid from 24th October 2014 to 23rd November 2014. Ph: (02) 8832 3100 Fax: (02) 8832 3169 Ferntree Gully Frankston Geelong Hallam Kew East Melbourne City Mornington Ringwood Roxburgh Park Shepparton Springvale Sunshine Thomastown Werribee Ph (03) 9758 5500 Ph (03) 9781 4100 Ph (03) 5221 5800 Ph (03) 9796 4577 Ph (03) 9859 6188 Ph (03) 9663 2030 Ph (03) 5976 1311 Ph (03) 9870 9053 Ph (03) 8339 2042 Ph (03) 5822 4037 Ph (03) 9547 1022 Ph (03) 9310 8066 Ph (03) 9465 3333 Ph (03) 9741 8951 WESTERN AUSTRALIA Joondalup Maddington Mandurah Midland Northbridge Osborne Park Rockingham NEW Ph (08) 9301 0916 Ph (08) 9493 4300 Ph (08) 9586 3827 Ph (08) 9250 8200 Ph (08) 9328 8252 Ph (08) 9444 9250 Ph (08) 9592 8000 Email: techstore<at>jaycar.com.au Occasionally there are C discontinued items advertised on a special / lower price in this promotional flyer that has limited to nil stock in 56  Silicon hip certain stores, including Jaycar Authorised Stockist. These stores may not have stock of these items and can not order or transfer stock. siliconchip.com.au Solar Smoothing: what happens when the sun goes out? While past governments have been actively encouraging the installation of solar power systems (with generous buy-back schemes) on the rooftops of Australia, that’s caused no end of headaches for power distributors. by Ross Tester T he electricity generating and distribution system has major difficulties in coping with the quality and quantity of power injected back into the grid from the huge numbers of private solar power generation systems. This has forced some electricity generators and distributors to impose limits on the amount of solar injection they will accept. On a bright, sunny day when all of the photovoltaic systems are generating peak power, it amounts to an over-supply, beThe 50kVA ‘Solar Smoother’ recently installed by Magellan Power at the cause it’s not possible to instantly adjust new Carnarvon (WA) Police and Justice Centre. the system to cope. And while feed-in systems theoretically provide “clean” power back to the grid, it’s not always so. the peaks and troughs of a typical solar panel installation. Of course, the photovoltaic panels do not supply constant It’s no shrinking violet, either: the Magellan Solar power – output rises gradually from zero around dawn to Smoother supplied to the WA government is rated at 50kVA a peak at midday, falling once again to zero at night. While and occupies a cabinet some 2400 x 800 x 2000mm (other this can be taken into account by thermal or even hydro models are available in ratings from 5kVA to 100kVA). This generators, it still requires careful management. Overcontains modular MPPT battery chargers, 3-phase bidirecvoltage, even by a relatively small amount, is responsible tional IGBT-based inverters and lithium-iron-phosphate for significant equipment failure. (LiFePO4) batteries. Because it contains both chargers and The opposite side of the equation is perhaps even more inverters, there is no need for an external inverter. of a problem. If it’s a cloudy day, or worse, a large cloud Systems are available to suit PV installations of 200-470V temporarily covers a town or suburb’s solar panels, the solar DC, with a voltage window of 190-265VAC. Frequency winpower injection level will suddenly drop and generators will dow is 46.5Hz-53Hz, with energy efficiency between 90 and have to work doubly hard to maintain the power authority’s 95%. Single and 3-phase models are available and they will guarantees of quality. Then the sun comes out again and . . . detect over-voltage, under-voltage, over-frequency, underThe peaks and troughs need to be “filled in” to achieve frequency and islanding (lack of grid supply). Similarly, a constant supply for industry, commerce and domestic battery over-temperature, under-voltage and over-voltage customers. are all monitored. Transient response is just one second. In July 2012, the WA regional utility Horizon Power 44 days of logged data are held in non-volatile memory introduced a new specification called ‘Generation Manage- (at 15 minute sampling intervals), or a year of data logged ment for Solar Installers’ to ensure a smoothing device was at two hour intervals. Data is accessible via RS232/RS485 installed on every new solar power system to help with and USB ports. power fluctuations. Magellan Power has more than twenty years experience This provides backup power to the grid while the genera- in the power electronics industry, designing and manutors ramp up and down, reducing long term wear and tear facturing AC and DC power systems for both backup and of the equipment. grid-connect applications. The company also offers a range Another WA company, Perth-based Magellan Power, has of other power control systems, for domestic and industrial recently delivered its first ‘Solar Smoother’ to the new $52.2 applications. million Carnarvon Police and Justice Complex. Contact MagellanPower on (08) 9434 6621 or via their This does exactly what its name suggests – it smooths out website: www.magellanpower.com.au SC siliconchip.com.au November 2014  57 SERVICEMAN'S LOG Heat can be a real killer in laptops The computer servicing business is changing and I’m now seeing increasing numbers of tablets and laptops, as opposed to the more-traditional desktop machines. A big problem with laptops is overheating due to dust build-up inside them and improper user attempts to remove this dust. As I may have mentioned before, the computer servicing business is changing and events at my workshop over the past few months have illustrated just how much. Most readers will be aware that Microsoft has killed off support for its once favourite son (Windows XP) and is pushing people instead onto Windows 8. The result is a lot of confused and sometimes irate customers who end up buying an Apple Mac instead. Aside from the natural reluctance we all have to change, you also have to factor in the collateral financial damage due to existing hardware not wanting to run later versions of Windows. 58  Silicon Chip In addition, other (often-expensive) software might not be compatible with later Windows versions and so upgrading suddenly takes a darker turn. When clients ask me why they have to change, I give them the usual spiel about technology, progress, security and compatibility. However, with XP a familiar and still functional operating system and their hardware happy to keep on running it, it can be a tough sell to convince some to upgrade. For others, its all the motivation they need to defect to Apple. The demise of XP isn’t the only event making an impact on the computer repair landscape, though. When Dave Thompson* taken in context with the surge in popularity of the likes of smartphones and tablets, many customers are electing to not repair or upgrade their old desktop when it inevitably fails. Instead, they are choosing to use a laptop, smartphone or tablet to do the job, whether it is checking the latest racing results, bidding on an online auction, replying to emails or surfing the net. You can perform all these tasks on an internet-connected smartphone or tablet, though admittedly some find it a bit fiddly until they get used to virtual keyboards and such. But when faced with a large bill to replace an old desktop machine, a lot of people are looking seriously at these alternatives. In the past week alone, I’ve had three customers who decided to forgo repairing their broken desktop PCs. One guy had a laptop he’d purchased a while back but hadn’t used much because he didn’t like the fact that it had a smaller screen and keyboard than his desktop machine. However, he soon figured out that he could plug a keyboard, mouse and the otherwise redundant desktop monitor into it, to create a very usable substitute when his desktop PC failed. The other two customers went down what is becoming a well-worn path among my clients. At some stage in the past, they had both either purchased or been given iPads or iPhones and like many people, had been seduced by their form and function. When I gave them the bad news that their respective Windows-based desktop machines had failed and needed replacing, they both went out and bought an iMac instead, their reasons being that they liked the way iOS worked, the devices all “talked” to each other and it just made sense to keep things the same across devices. In real terms, this all means that I’m now getting more tech-support calls for laptops and tablets (and, to a lesser extent, smart-phones) than desktops. All of these devices have their own unique problems and while it seems an obvious step to just recalibrate siliconchip.com.au Items Covered This Month • • • • Heat is a killer for laptops Sony KDL52Z5500 TV set Zapped QED A270 amplifier Remote spotlight repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz the business to include the repair of these devices, this isn’t as easy or as practical as it first appears. That’s mainly because most of these gadgets are now so cheap to buy that they are not economical to repair, even if you can find the parts for them. When people hear how much it is likely to cost to fix their tablet or smartphone, most elect to junk it and buy another one. In fact, I would say that as many as eight out of 10 of my customers choose not to proceed with such repairs. This leaves me in the unenviable position of either (1) charging an assessment fee, which will likely result in the person getting miffed and not returning (because, in their eyes, I’ve made them pay for doing nothing), or (2) not charging for the assessment work, leaving me working for nothing and quietly going broke. Sticking my neck out I’ll go on record and state that tablets will soon have had their day and that the sale and use of desktop and laptop computers will rise again, though likely not to the same levels they were before. This is because users will discover that while tablets are very handy for taking on holiday or checking the odd racing result or composing the odd email, you can’t easily write a 500-word report on one, let alone an article for a magazine or something like a novel. Their fiddly virtual keyboards and small screens simply make those jobs too difficult. I know I’m sticking my neck out but I think that once the novelty wears off, normal service will likely resume. Fortunately, laptops are a different animal from smartphones and tablets and servicing and repairing them may well keep companies like mine alive. There are a host of things that can go wrong with a laptop that don’t affect smartphones and tablets the same way, leaving more opportunities for repairs to be made economically. What’s more, for some reason, people are more reluctant to throw out a laptop even though, in many cases, a laptop is cheaper than a tablet or smartphone. This factor also gives me some hope for the future of the repair industry. In fact, I’ve found that some users want their laptop repaired even when faced with a major problem like a dead motherboard or a cracked screen. However, these are two repair scenarios that often result in the machine being scrapped due to the non-availability and cost of spare parts. If I get a laptop in that has suffered a broken screen and it’s less than a few years old, I usually advise the owner to make an insurance claim because the machine is too good to scrap and replacing the screen (assuming it’s available) usually isn’t cheap. In such cases, it’s worth spending the money in order to keep the machine going and besides, that’s what insurance is for. Of course, it can all hinge on such things as the insurance excess and whether or not the part is available. As an example, as part of an insurance claim, I recently called the local agents of a certain well-known brand, asking for a quote and the expected delivery time for a replacement screen for a 6-year-old laptop. The insurance company subsequently agreed to my final quoted price and so I duly ordered the screen. Now screens from this company usually take 3-5 days to arrive and when this one didn’t show up after almost two weeks I called them and asked what was happening. I was somewhat surprised at their answer; they told me that while they did have a dwindling supply of spare screens for this model sitting in their warehouse, they wouldn’t sell me one as they wanted to save their remaining stock for future warranty claims. I don’t know when they were planning on informing me of this aboutturn but I thought it exceedingly poor service from one of the more respected brands around – especially considering there wouldn’t be many laptops of that model and age still under any type of warranty. I’m guessing that this practice will become more prevalent as ualiEco Circuits Pty Ltd. siliconchip.com.au November 2014  59 Serr v ice Se ceman’s man’s Log – continued The fault condition exhibited dark shading, a reddish hue, picture smearing and ghosting. This view shows the set stripped down to reveal the metal frame that runs around the outside of the LCD panel. Sony KDL52Z5500 TV Set Repair G. S. of Baulkham Hills, NSW recently ran into problems with a Sony KDL52Z5500 LCD TV. The set had an annoying fault when switched on from cold but would come good after about 30 minutes. Here’s his story . . . My Sony KDL52Z5500 132cm LCD TV set was purchased in 2009 and is a top-of-the-line 200Hz model that has given excellent performance. It cost around $3500 back then so you can imagine my dismay when it suddenly developed an intermittent heat-sensitive fault. The problem started about a year ago and initially took the form of a narrow vertical flickering band on the lefthand side of the screen when the set was first switched on. This band was only a few centimetres wide and it always completely disappeared a few minutes after switch-on as the set warmed up. This situation persisted for several months and then the problem took a turn for the worse. At switch-on, the entire lefthand side of the screen now took on a reddish hue with very dark shading, picture smearing and vertical ghosting. This problem also partially spilled over into righthand half of the screen (see photo). As if that wasn’t bad enough, the picture now took about 30 minutes (or more) to come good. What’s more, during those 30 minutes, the picture was virtually unwatchable and that meant a frustrating wait in order to watch a program. In the end though, it always came good until one day it didn’t! During the middle of winter, the dark shading remained unchanged on several occasions, even after the set had been on for several hours. After a year of putting up with this annoying problem, it was time to see if something could be done to fix it. I’d already spent some time researching the problem on-line and this indicated that the fault probably lay in the ‘tabs’ that connect the LCD to the driver circuits (typically on two long, narrow PCBs) that run along the top edge of the panel assembly. As shown in one of the photos, these tabs are thin flexible strips, typically 40mm wide, and there are 16 of them in the Sony KDL52Z5500. They have multiple conductive tracks and are electrically bonded to edge pads that run along the front of the driver PCBs. The tabs then bend down through 90° to make the connections to transparent electrodes at the top of the LCD. With repeated thermal cycling or if the screen is flexed (due to mishandling), the bonding contacts between the tabs and the PCB or to the LCD panel itself can sometimes become faulty. It’s this that causes the dark shading and other problems such as ghosting and banding when the set is switched on from cold. This type of fault often clears as the panel warms up, with the display suddenly coming good. In severe cases though, the fault remains no matter how long the set is left on. Another possibility apparently is manufacturers save money by stocking less spare parts and as devices become more throwaway. themselves because they can feel the overly-hot air being expelled or can hear the fan roaring away when it used to be quiet. Some models have a temperature monitor or fan-speed sensor that alerts users when things aren’t right with the cooling system. This can also sometimes result in the machine being either shut down or prevented from booting until the problem is resolved. As a result, users often hit the web to find out how to fix the problem and, acting on on-line advice, often use a vacuum cleaner or air-compressor to suck or blow through any vents or apertures in the machine to clear away any lint or fluff. While this sometimes clears the problem, it can actually make things Laptop overheating The more laptops I see the more I learn about their flaws and peculiarities. I’ve discovered that many share a common problem – overheating. Users often diagnose overheating problems 60  Silicon Chip siliconchip.com.au that the very fine tracks in the tabs can sometimes develop microscopic cracks, resulting in the tracks going high resistance or even open circuit. So what can be done about it? Well, I found a video on YouTube at http://youtu.be/B-mJX9TvAbc which describes an interesting cure. This involved removing the plastic dress frame at the front of the set and then the metal frame that goes right around the outside of the LCD to reveal the tabs. A strip of felt was then slid under the inside front edge of the metal frame in line with the offending tab and the frame replaced. When this was done, the felt strip applied pressure to the flexible tab and this fixed the problem (temporarily at least). It was worth a try. After all, I had nothing to lose; if the KDL52Z5500 couldn’t be fixed, it would have to be scrapped. In order to remove the plastic dress frame, I first had to remove the back panel. That’s best done with the set lying face down on a soft foam mattress or similar. A gazillion screws secure the rear panel in place and once they had all been removed, it was just a matter of lifting it free. The next step involved undoing several screws to free the dress frame. Some of these screws are hidden behind the speaker pods and the stand, so these parts had to be removed as well. I then unplugged a couple of leads that run to small PCBs on the bottom section of the dress frame, unclipped the side control panel and re-attached the stand. Next, I enlisted a family member to help to lift the set clear of the frame and stand it back upright again. That gave access to the metal frame that runs around the outside of the LCD. This frame was then removed by undoing nine small screws, unclipping it at the sides and carefully lifting it clear to reveal the tabs. It was now time to fire the set up and see if I could locate the offending tab (or tabs). To do this, I jury-rigged the side control panel (which has the mains power switch attached to it), reconnected the speakers and applied power. The fault was present so I tried pushing against the eight lefthand tabs using the flat face of a wooden ruler whereupon the set suddenly came good. It had only been on for a few minutes, so applying pressure to the tabs seemed to ‘fix’ the problem. What’s more, I could make the problem come and go at will. The far lefthand tab seemed to be the one that was causing the trouble – release the ruler and the fault would appear; reapply pressure to this tab and it was gone. That suggested a fix similar to that shown in the YouTube video. I didn’t have any felt strips but I did have a roll of draught excluder, as used around windows and door frames. This is simply a 12mm-wide soft rubber strip with an adhesive backing and it appeared to be ideal for the job. I cut an 800mm length, peeled away the backing and carefully affixed it to the inside front edge at the top of the metal frame, so that it would press against the tabs on the lefthand side. I was very careful not to cover any screw holes during this process – forcing a screw through the rubber could cause small fragments to come adrift and these could then find their way down between the LCD panel and its backlight panel. If that happened, there would be little chance of successfully retrieving them and the LCD would then display black fragment-shaped “blobs” at various locations. While I was at it, I decided to also fit another 800mm length of draught excluder to the other side of the metal frame. That done, the power was switched off and the metal frame reinstalled around the LCD. Applying power now brought up a perfect picture from cold. I subsequently tested the set for several days before reinstalling the dress frame and the rear panel and putting it back into service. It’s worked perfectly for several months now but who knows how long that will last. With constant thermal recycling, it may only be a matter of time before the problem rears its ugly head again. The draught excluder “cure’ may last two more days, another month, six months, two years or for the life of the set. I’m not overly optimistic about it lasting but even if it’s just a few more years, the work will have been well worthwhile. worse by forcing lint build-up into the fan assembly, stalling it completely. On the other hand, these measures might clear some dust and allow the fan to work again but without a proper clean out, the fan won’t run at full speed and the system will soon choke up again. Of course the environment the machine is used in will make a big difference. Users in Christchurch have to deal with a very nasty form of dust caused by dried-out liquefaction. For those who don’t know, liquefaction is a by-product of the more serious quakes we’ve had here. When the ground shakes, it can turn into liquid mud due to rising water (there are various demonstrations of this phenomenon on YouTube for those interested) and this liquid then rises to the surface, creating a thick, sometimes stinking mess that eventually dries out and turns into a particularly nasty, gritty dust. When our hot and blustery northest winds blow through town, the air is choked with this stuff and it gets absolutely everywhere, including inside electronic gear. Laptops and desktop computers usually have several cooling fans and Removing the metal frame reveals the tabs (arrowed) which connect the driver boards to the top of the LCD. Two strips of draught excluder were attached to the inside front edge at the top of the metal frame. These press against the flexible tabs at the top of the panel when the frame is replaced. siliconchip.com.au November 2014  61 Serr v ice Se ceman’s man’s Log – continued Can a burst of RF energy from a microwave communications dish fry a stereo amplifier? G. M. of Pukekohe, NZ believes he has come across one such case . . . During my 40-plus years in this profession, I have seen lots of strange electronic faults in audio and video appliances. In most cases, there is a logical explanation for the fault or failing that, a half-believable theory for the cause. The job I am going to tell you about definitely fits the latter category, as there is no way to prove my theory as to what caused the fault. And since I wasn’t present when it happened, I can only rely on the owner’s version of events and add a couple of theories of my own to come to any conclusion. The appliance in the hot-seat was a fairly old QED A270 integrated stereo amplifier, a minimalistic English design from about 20 years ago. The only controls on the front panel are a mains on-off switch, a volume control and two rotary switches to select the input source and a tape output. QED are better known these days for their cables and interconnects but there was a period in their history when they manufactured some goodquality, well-respected hifi gear. Their design philosophy was to use discrete components rather than integrated circuits throughout the signal path and to keep the overall component count to a minimum in order to keep the signal as clean as possible. In this particular case, the owner had been more than happy with the sound from the amplifier. It’s teamed with a NAD CD player, Infinity bookshelf speakers and an old NAD tape deck and it had performed reliably over the years. In fact, it had been on my workbench just once since new for a fairly minor fault but now it was completely dead. I called in to the lady’s home to check the amplifier and confirm the symptoms. Sure enough, it was dead but I wasn’t going to service it in the house, so I unplugged everything and removed it from the cabinet. As I did this, the owner recounted the events just before the amplifier stopped working. I listened intently, if rather sceptically, to her explanation as to the cause of the amplifier’s current state and nodded agreeably as you do to maintain good customer relations. What’s more, I held my tongue, a skill that comes with maturity and stark memories of having put my foot in it on many prior occasions! While I was there, I checked both speakers with an impedance meter to confirm their integrity. When an amplifier fails, it’s often the hardworking output stage which succumbs and the speakers can be unwitting victims. If you are lucky, the fuse blows, sacrificing its worthless little self to save the life of the much more expensive speakers. Sometimes, however, the fuse does not blow quickly enough or some wellintentioned do-it-your-selfer has replaced the original fuse with a higherrated fuse to keep the party going. In this case though, my customer lived alone and her lifestyle and choice of music were hardly likely to lead to that scenario. As luck would have it, the speakers were OK and I said I would phone her as soon as I had diagnosed the problem and could estimate the repair cost. A couple of days later, I set the amplifier up on my workbench and popped the hood. The mains fuse had blown and a quick check with a multimeter confirmed the cause – three of the four output transistors had shorted! Considering the age of the unit and the fairly obvious extent of the damage, I really didn’t want to spend too much time on this job. I had to be as efficient as possible and avoid going too much beyond my minimum charge, otherwise there was a good chance the owner would reject my estimate and choose to replace the amplifier instead. I didn’t have a service manual so I searched on-line to see what I could find. I wanted to check how far the damage may have gone into the driver stages and a circuit diagram would help in this regard. Unfortunately, the search proved to be pretty fruitless – the best I could find was a couple of hand-drawn, almost illegible circuit diagrams, one of the front end and the other of the power amplifier stages. Further research suggested that the original output devices were going to be hard to find. I wasn’t keen on shoehorning substitute transistors into such an old amplifier and although other components may test OK right now, they may have been weakened by the output stage fault and fail sometime in the near future. In short, it was going to be expensive to fix and could create a potential warranty issue. And that meant that the these suck in air from the outside world. If this air is full of dust, the dust has to go somewhere and it usually ends up building up on the insides of the machine, collecting on anything in the way and especially components that tend to generate static electricity, which attracts the dust even more. This is a recipe for disaster and possibly the reason I now see so many computers with overheating problems. Very few machines have any kind of air-filtering system and even those that boast such a feature usually only have a thin piece of foam rubber to act as a filter and this is about as effective as a colander at keeping dust out. However, it’s not a good to open up a desktop and vacuum it out or blow it out with compressed air. Of course this is what the DIY’ers often do but I always cringe inside when people tell me they’ve done this. That’s because a vacuum cleaner often generates static electricity and this can easily destroy computer electronics. I’ve handled more than a few cases where the machine has simply stopped working after the owner has attacked it with a vacuum cleaner. Blowing a PC out with compressed air can also cause problems, not just through static electricity (which can be generated by some compressor/air hose arrangements) but because there is often moisture in the compressed air and water and electronics don’t mix. No doubt some people will claim they’ve cleaned things out this way for years without problems and while that may be true, the next time might be different. If you are contemplating attacking your machine with compressed air or a vacuum cleaner, my advice is simple: don’t do it. If you really must, then be aware of the dangers of static electricity and be careful. In particular, try Did RF Zap This QED A270 Amplifier? 62  Silicon Chip siliconchip.com.au amplifier really wasn’t worth fixing. So what did the owner tell me happened in those final moments before the amplifier failed? Well, her house overlooks the local rugby stadium which is about two hundred metres away as the crow flies. Apparently, the stadium was being readied for an international match to take place that afternoon and she was idly gazing through her window at the proceedings as she listened to her stereo. Because the stadium is only rarely used for an event that’s televised live, most of the camera equipment is set up on the day and microwave linked to the city studio. She was watching a small team of technicians setting up the mobile microwave antenna. As they did so, they swung the dish in her direction and at that very instant, her amplifier “shrieked” and died. That was enough proof – she was convinced that they were to blame. Her description of the “shriek” was my first clue as to what caused the fault. The second clue was that both output stages would not normally fail at the same time. And the third clue was the coincidental timing of events. Being a minimalistic design, the QED A270 amplifier had little in the form of RF protection in the signal path and the rough schematic I had obtained was enough to confirm this. While it had the usual RC filters to roll off the upper end of the audio spectrum to keep the amplifiers stable, these weren’t enough to protect the unit when it was targeted with the narrowly-focussed beam of RF energy destined for a studio some 30km away. I suspect that the output transistors took the brunt of the energy that was picked up by the speaker leads, which were acting as antennas. Either that or they were fed the rogue signal courtesy of some poorly-screened input cables. Of course, it’s possible that no amount of RF protection could have saved it and any other amplifier would have suffered the same fate. There’s an old adage that says that the customer is always right and in this case, it was probably true. In the end, the owner wisely decided not to have the QED repaired and she is now enjoying her music courtesy of a very tidy secondhand Yamaha receiver that I had stored away for just such an occasion. to keep the hose in contact with the computer’s case to discharge any static and avoid contact with any internal hardware – static electricity can cause sparks that can leap considerable distances. Note too that water condenses inside air-compressor tanks and it can either be purged from the system using a valve that’s usually found on the bottom of the tank or removed using an in-line filter. Preferably, both methods should be used. The only real way to deal with overheating laptops is to strip them down and clean them properly. Most laptops have carefully designed air channels and ducts to maximise airflow and any dust build-up in the airways or on the fan itself can cause the fan to slow down, in turn causing overheating and keeping the fan running. This also affects battery life; fans use power and having fans running more than necessary is something laptop designers want to avoid. In most cases, to access the heatsink and fan assembly, the machine must be stripped down. You’d think there might be some consideration for cooling system maintenance but most manufacturers don’t provide a handy access panel. This means that everything must be taken apart to get to the heatsink and fan. This makes for an expensive fix labour-wise, which is probably why people try to resolve it themselves. Once access has been gained to the heatsink and fan assembly, it can be removed from the motherboard by undoing several screws and then unplugged. There are usually three or four tiny screws holding a thin metal ducting onto the plastic fan housing and this has to be removed as well. In addition, some strong fibre tape usually seals this ducting to the fins of the heatsink and this must be carefully removed if it is to be reused, though I usually replace it with aluminium “100-mile-an-hour” tape which is ideal for the purpose. Once the ducting is clear, I then have total access to the fan itself and it is usually here that I find a block of lint similar in consistency to the doughnut-shaped one that builds up in the lint filter of a laundry hot-air dryer. It is this blob of lint that often gets pulled or forced back into the fan by vacuuming or blowing with an air-compressor. I use a soft artist’s brush to clean each vane of the fan, taking care as age and heat can cause them to become brittle and replacement usually means buying the whole fan and heatsink assembly. I also generally lubricate the fan using light machine oil before reassembling everything. If you have access to a power supply, it is good practice to power the fan up to check how it performs but extreme care should be taken to keep the voltage and current below the fan’s electrical rating as they can burn out very easily. Replace heatsink compound siliconchip.com.au Another important step is to replace the heatsink compound with suitable material. Many people simply reuse the heat transfer tape that’s commonly fitted but this is a big “no-no” as it’s usually damaged during removal or has become thinner with age. Heatsink compound can be purchased at any electronics store and as you only need a smidgen, it lasts for ages so there is no excuse for re-using old worn-out stuff. After reinstalling the fan/heatsink assembly, I give the inside of the case a good brush down and a blow-out with dry, filtered compressed air before putting everything back together. Done November 2014  63 Serr v ice Se ceman’s man’s Log – continued properly, this gives the laptop a new lease of life and the fan should keep things cool for years to come, until the dust builds up again. Remote spotlight repair A remote control system that won’t control something can be very frustrating. This one would turn a light on but wouldn’t turn it off again until G. B. of Essendon, Victoria tracked the fault down, Here’s what happened . . . A few years ago, my wife and I built a new house and in the course of events, I neglected to consider lighting for the back yard. The ideal position for a couple of floodlights was high on the garage wall, with another unit positioned behind the garage where the rubbish bins are located. That way, they would light up the way to the bins and the clothes line. Unfortunately, there were no spare conduits between the garage and the house to run some cables. Then one day, while walking around Bunnings pondering this problem, I spied some remotely-operated power points (manufactured by Kambrook) and a remotely-operated spotlight from Arlec. I purchased these and duly installed them. The remote power point (installed inside the garage) was used to switch a double 200W spotlight that lights the backyard, while the Arlec single-spotlight unit was connected directly to an outdoors-type power point located in the rubbish bin area. Because they are remote controlled, these lights can all be switched on and off from within the house. However, the supplied remotes were ditched in favour of my own home-grown controller consisting of a PIC16F684 chip, a Jaycar 434MHz module and four buttons fitted into a GPO face plate. The Arlec unit uses a PT2262 remote control encoder, while the Kambrook unit uses a different chip (the number had been ground off). This meant that I had to ‘reverse engineer’ the Kambrook unit to figure out the protocol. Anyway, I got it all to work and all was OK for about three years until, one day, the Arlec unit would turn on OK but would require several switch presses to get it to turn off. Eventually, it failed to turn off altogether and required a manual switch off and on again to reset it. This went on for about six months and into the middle of winter. In the end, the trips back from the bins in the dark (and sometimes the rain) were starting to get a bit tricky, so I decided I’d better do something about the problem. The Arlec unit has a weatherproof enclosure attached to the light to house the PCB and I needed to take a look at this. First, I unplugged the unit from the outdoor power point, then gave the rusted hinge a few squirts of WD40 so that I could spin it around to get access to the PCB enclosure. Four screws and a rubber gasket hold the enclosure’s cover on and these were easily removed. I fully expected that the problem would be corrosion caused by a leak around the gasket but the back of the PCB showed no signs of any such problems. Nor was there any sign of water ingress into the enclosure. That meant that the PCB would now have to be removed so I took a photo of the connections and drew a sketch as well, just for good measure. The single-sided PCB is freed from the enclosure by undoing two screws. Removing it reveals the 230VAC connector, which also carries the connection from the relay (mounted on the PCB) for the spotlight. The circuit itself derives its power directly from the 230VAC mains via a 1µF 250V mains-rated capacitor connected to the Active, so the whole circuit is potentially lethal. There is a 220kΩ resistor in parallel with the 1µF 250VAC capacitor and a 4.7kΩ resistor in series with the capacitor. There is also a 4.7kΩ resistor in the Neutral line. Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column? If so, why not send those stories in to us? We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 64  Silicon Chip Both these 4.7kΩ resistors feed a bridge rectifier and across this rectifier is a 470µF 16V electrolytic and two back-to-back 12V zener diodes for over-voltage protection. The rest of the circuit consists of the PT2262 decoder, a relay driver transistor and a few other bits and pieces. Once the PCB had been removed from the unit, I set it up on the workbench. I connected 12V directly across the AC input part of the bridge rectifier rather than wire it up to the 230VAC. As mentioned, the circuit is normally directly powered from the mains and cannot be worked on safely when connected in this manner. Anyway, on the bench it seemed to work fine. I used the original remote fob that was supplied with the unit and it would switch on and off every time. I then checked the PCB more closely with a magnifying glass but couldn’t detect anything irregular so I removed the electrolytic capacitors and tested them. They all checked out fine so I reinstalled them and tested all the diodes. These also checked out OK, so I then decided that the best thing to do would be to reconnect it to the enclosure and give it another test. Perhaps all my messing around had somehow fixed it (eg, by resoldering a bad solder joint). Once it was reconnected, I used the supplied remote fob to test it in-situ, just to clear my home-grown unit. The fault was still there; it would switch on fine but it wouldn’t switch off, no matter which remote fob/switch was used. I removed the PCB again, set it up on the workbench again and turned my attention to the 1µF 250VAC mains capacitor. When I’d previously tested it, it measured 0.22µF instead of 1µF, about a quarter of its original value. It all fell into place then: the Vcc supply line to the PT2262 must be dropping below its minimum level when the relay operates, even though the latter only draws 30mA. This would be caused by the increased impedance of the 1µF capacitor not supplying enough power for the circuit when the relay is on. Conversely, with the relay off, there is only minimal current draw and so the Vcc rail is maintained at the proper level, allowing the unit to switch on. Fitting a new capacitor fixed the problem. So I really should have been much more suspicious of its low value when SC I first tested the capacitor. siliconchip.com.au The Perfect Christmas Gift! Especially for yourself . . . If you regularly purchase SILICON CHIP over the counter from your newsagent, why not drop a subtle hint (or maybe not so subtle!) to your spouse, children, etc, that you would like a SILICON CHIP subscription for Christmas. Why? It costs less to subscribe – instead of paying $9.95 per issue, it costs just $8.75 per issue (12 month subscription) – and we pay the postage! So there’s more than a 10% saving and it’s delivered every month direct to your mailbox. How can we do this? It’s all about economics. Printing enough copies to send out to newsagents, in the hope that they’ll sell, is wasteful (and costly!). When readers take out subscriptions, we know exactly how many copies we need to print to satisfy that demand. That saves us money – so we pass the savings onto our subscribers. It really is that simple! You REAP THE BENEFIT! But there’s more! Subscribers also automatically qualify for a 10% discount on any purchases made from the SILICON CHIP online shop: books, printed circuit boards, specialised components, binders – anything except subscriptions! And you get exclusive FREE downloads (PCB patterns, software, panels, etc) from the SILICON CHIP online shop. So why not take out a subscription (or even better, get someone else to do it for you!)? They can choose from 6 months, 12 months or 24 months – and the longer the sub, the bigger the savings. Choose the print edition, the online edition or both! Most people still prefer a magazine they can hold in their hands. That’s a fact. But in this digital age, many people like to be able to read SILICON CHIP online from wherever they are – anywhere in the world. That’s also a fact. NOW YOU CAN – have either or both. The on-line edition is exactly the same as the printed edition – even the adverts are normally included. So you don’t miss out on anything with the on-line edition (flyers and catalogs excepted). they OK, so how do you go about getting you the Christmas Present you REALLY want? It’s simple: order a subscription online, 24 hours a day (siliconchip.com.au/shop and follow the prompts); email us with the subscription request and credit card details (silicon<at>siliconchip.com.au); fax us the same information (02) 9939 2648 (international 612 9939 2648) or phone us, Monday-Friday, 9am-4.30pm, on (02) 9939 3295 (international 612 9939 3295). Leave this page where it can be ‘accidentally’ spotted! siliconchip.com.au November 2014  65 Programmable mains timer with remote switching Remote-controlled mains switches are very convenient but what if you could add a versatile easy-to-program timer to one of these units? Well, now you can. This Remote Switch Timer can be programmed to switch the power on and off after a set period or to switch the power on and off at set times. By JOHN CLARKE M AINS TIMERS are ideal for switching appliances on or off at predetermined times. Their complexity ranges from simple mechanical timers with a synchronous motor and switch actuator cams through to complex menu-driven fully-electronic timers which tend to have fiddly buttons and can be difficult to program. However, none have the advantage of remote control, whereby the timer is remote from the actual mains-switched power socket. To give an example, say you have an appliance in your garage that you want to control with a mains timer. Wouldn’t it be nice if you could pro66  Silicon Chip gram and control the timer without having to be in the garage? This idea can be extended to a lot of applications. To meet this need, we’ve devised this “Remote Switch Timer”. It’s designed to work with just about any commercially-available remote control mains socket (provided the hand-held remote is powered by a 12V battery). Basically, it interfaces with the remote’s PCB and provides the extra timing functions. The remote then automatically switches the mains socket on and off, as required. As shown in the photos, the Remote Switch Timer is housed in a plastic box, along with the PCB from the remote. It has 10 pushbutton switches and a 2-line LCD which has a dimmable backlight for night-time use. The front-panel buttons are used to program and control the unit. Remote control mains sockets For those unfamiliar with these devices, a remote control mains socket consists of a mains plug and piggyback socket, together with a relay and UHF receiver inside the plastic housing. It is controlled using a UHF hand-held remote control which is used to switch the mains socket on and off. Both 3-channel and 8-channel siliconchip.com.au The Jaycar remote controlled mains switch comes with a 3-channel hand-held remote. The MS-6142 comes with a three mains sockets, while the MS-6145 has one socket. remotes are typically available and these come either with a single socket or with a number of sockets. Alternatively, the additional sockets have to be purchased separately. The remote controls each socket individually and it’s just a matter of either using a learning procedure to set the socket’s channel number of setting a channel switch on the rear of the socket. The Altronics A0340, Jaycar MS6145 and Jaycar MS-6142 are typical of the units currently available. How does it work? The SILICON CHIP Remote Switch Timer is designed to activate any pair of on/off switches on the remote control. It does this by controlling two small relays which have their contacts wired across the desired on and off switches on the remote’s PCB. Basically, it’s just a matter of removing the remote’s PCB from its case and housing it together with the Remote Switch Timer inside a plastic utility case. The two are then wired together and powered from an external 12V DC plugpack and an optional internal 9V back-up battery. As well as using the new automatic timing functions, you can still manually control the mains socket using separate On and Off pushbuttons on the Remote Switch Timer. Alternatively, another hand-held remote can be used. In preset-time mode, the Remote Switch Timer is used to send an on or siliconchip.com.au The Altronics A0340 has an 8-channel remote control and is supplied with a single mains socket. Additional mains sockets can be purchased separately. off signal to the remote mains socket after a set period of time. You simply program when you want the socket to switch on or off and then press the Set/ Start button. The timer then automatically switches after the preset time, which can range from a minimum of one minute to a maximum of 255 hours and 59 minutes (that’s more than 10 days!). During the time-out period, the displayed time decreases by one every minute until the timer reaches zero. The relay for that timer function then closes and the UHF signal from the remote is sent to the mains socket. To set the time-out period, you first select either the On or Off timer using the Next pushbutton. The separate Up and Down hours and minutes pushbuttons are then used to set the required timing period. If you want more complexity, the Remote Switch Timer can use both its timers. One timer can be set to turn the mains socket on after a preset time, while the other can be set to then turn it off (or vice versa). In addition, the On and Off pushbuttons can be used to set the initial status of the remote control mains socket; ie, you can start with the mains power on or off. Default timing cycle The default timing cycle for the unit is for it to run once only. This is where the timers are set to their required values and decrease over time until they reach zero. Once a timer has counted down to zero, there is no more control from that timer unless it’s set to a new value. Note that the timer will just show dashes when the time-out is zero. The default setting can be changed from “once only” to “repeat”. This is where the timers are returned to their original settings after both timers have timed out. As an example, let’s say that you’ve set the On timer to two minutes and the Off timer to three minutes. This means that after two minutes, the On timer will have counted down to zero and sent an “on” signal to the mains socket to turn on the power. The Off timer now continues to count down and when it too reaches zero (ie, after one minute more), an “off” signal will be sent to the mains socket. Both timers will then be reset to their original 2-minute and 3-minute settings and so the cycle repeats every three minutes. The on and off timers for this countdown style of timing are called the “ON IN” and “OFF IN” timers (ie, on in a certain period and off in a certain period). The once only and repeat timer options are predictably named “ONCE ONLY” and “REPEAT”. This style of timer is quite useful (and simple to use) for many timer applications. However, for even more flexibility, a “real-time” timer mode is also included. This is similar to setting an alarm clock and allows you to set the time of day for the on/off switching to occur. November 2014  67 Parts List 1 double-sided, plated-through PCB, code 19112141, 104 x 76mm 1 front panel PCB, code 19112142, 157 x 94mm* OR 1 front panel label, 144 x 84mm* 1 UB1 plastic utility case, 158 x 95 x 53mm* 6 M3 x 9mm tapped spacers* 1 LCD module with backlighting (Altronics Z-7013, Jaycar QP5512) 1 UHF remote-controlled mains switch with 12V powered remote controls (eg, Altronics A0340, Jaycar MS-6145, MS6142) 2 SPST DIP 5V reed relays (Altronics S4100A, Jaycar SY4030) (RLY1,RLY2) 1 4MHz low-profile crystal (HC49US case) (X1) 10 click-action pushbutton PCB switches (white) (Jaycar SP0723, Altronics S1099) 1 12V DC plugpack (100mA or greater) 1 16-way SIL pin header with 2.54mm pin spacing 1 panel-mount DC socket (2.1 or 2.5mm to suit plugpack) 4 2-way polarised headers (2.54mm pin spacing) 4 2-way polarised header plugs (2.54mm pin spacing) (CON1CON4) 12 M3 x 5mm machine screws (2 preferably countersunk for the rear of the box) 1 100mm cable tie 1 400mm length of medium-duty black hook-up wire 1 200mm length of medium-duty red hook-up wire Semiconductors 1 PIC16F88-I/P microcontroller programmed with 1911214A. hex (IC1) 1 LP2950ACZ-5.0 low-dropout 5V regulator (REG1) 1 BC337 NPN transistor (Q1) 6 1N4148 diodes (D1,D2,D4-D7) 2 1N4004 1A diodes (D3,D8) Capacitors 2 10µF 16V PC electrolytic 1 100nF MKT polyester 2 33pF C0G (NP0) ceramic Resistors (0.25W, 1%) 1 100kΩ 1 330Ω 0.5W 1 10kΩ 2 100Ω 1 2.2kΩ 1 10kΩ miniature horizontal trimpot (VR1) *Alternative enclosure parts 1 sealed polycarbonate case with clear lid 115 x 90 x 55mm (Jaycar HB-6246 or similar) 1 front panel label, 103 x 78mm 4 M3 x 12mm tapped spacers Optional parts for battery back-up 1 9V battery snap with lead (Jaycar PH-9232, Altronics P 0455) 1 9V battery (522/6LR61) 1 9V U-clamp battery holder (Jaycar PH-9237, Altronics S 5050) 1 2-way polarised header & plug (2.54mm pin spacing) (CON5) 1 M3 x 6mm machine screw 1 M3 nut selection as to whether you want a timer to be operational or not. There are two possible settings for real-time switching: (1) where the sequence occurs once only; and (2) where the on and off cycle is repeated each day. As before, these options are called “ONCE ONLY” and “REPEAT”. For the once only selection, the timer will revert to zero (with the LCD showing dashes) once that timer has matched the clock. For the repeat selection, the timer will remain at its time setting so that it can repeat the switching sequence each day. Clock accuracy The long-term timing accuracy depends on the accuracy of the crystal timebase used in the Remote Switch Timer. This in turn is dependent of the crystal tolerance and on temperature variations throughout the year. For a standard ±50ppm crystal, the clock could be fast or slow by up to 130s (ie, two minutes & 10 seconds) over a period of 30 days. However, the timing accuracy can be easily adjusted by changing a value in the software that runs in the PIC microcontroller used in the Remote Switch Timer. Basically, the can be adjusted to run faster or slower in 1ppm steps, up to a maximum of ±99ppm. A 1ppm change represents about 2.6s in 30 days, while the 99ppm maximum adjustment corresponds to 256s in 30 days. Adjusting the clock accuracy may be necessary if you want the “ON AT” and “OFF AT” timers to switch the unit at certain times of the day. However, it will not usually be necessary for the “ON IN” and “OFF IN” timers which are used to switch the unit in a certain time period. Battery back-up In order to do this, a real time clock is required and the one used here is in 24-hour format. Real-time switching For this mode, we call the real-time timers “ON AT” and “OFF AT” (ie, on at a certain time and off at a certain time). You can set either one timer or both. The timers are also in 24-hour format and are compared against the time on the clock. When the clock and timers match, an on or off signal is sent to the mains socket. Note that in this mode, the timer values do not change during the time68  Silicon Chip out period. Instead, they are simply compared with the clock for a timeout match. Note that a 00h:00m setting for either timer will show as dashes on the LCD and there is no on or off switching for this setting. 00h:00m also corresponds to midnight, so it is not possible to have the timer switch at precisely midnight. However, switching times one minute before (23h 59m) and one minute after midnight (0h 1m) are possible. This rather minor shortcoming allows for simplified timer operation because it doesn’t require an extra An option is to include a battery back-up for the Remote Switch Timer. That way, all settings will be retained and timing will continue in the event of a black-out or if mains power is removed from the unit. Of course, the mains socket will not be powered in the event of a blackout and so it will not respond to any on or off signals from the unit. However, when power is restored, the last on or off signal is sent again after a short delay. That way, the mains socket will switch to the required setting for the present time. Note that the backlighting for the siliconchip.com.au siliconchip.com.au K A 1N4004 7,8 2 RLY 2 100Ω C K A 1N4148 33pF OSC1 16 15 OSC2 RB1 Vss 5 RB5 RB4 11 RB2 8 S10 S9 A S5 D7 REMOTE SWITCH TIMER S8 S3 S4 K A S7 D6 S2 K A S6 D5 K A D4 S1 SC S1: S2: S3: S4: S5: 4 14 13 12 11 6 7–10 5 1 4x 1N4148 K 20 1 4 HOUR UP HOUR DOWN MINUTES UP MINUTES DOWN SET/START S6: NEXT S7: CYCLE S8: ON S9: OFF S10: BACKLIGHT 10 RB0 6 RA2 RA3 1 RA4 2 3 18 RA1 IC1 PIC16F88 PIC1 6F8 8 RB6 RA0 7 12 17 RB3/PWM Vdd RA5/MCLR RB7 13 LED 16 CATHODE D7 D6 D5 D4 EN RS GND R/W D0–D3 3 CONTRAST 16 x 2 LCD MODULE Vdd 2 LED 15 ANODE LCD CONTRAST 10k VR1 10k 330 Ω 1W 4 14 9 100nF 2.2k B X1 4.0MHz E 33pF Q1 BC337 C 100Ω E B BC 33 7 D2 1N4148 K A 6 2 A D1 1N4148 (POWER DETECT) 10V 10 µF +5V Fig.1: the circuit is based on PIC16F88-I/P microcontroller IC1 and an LCD module. IC1 monitors switches S1-S10, drives the LCD, controls the timing and drives miniature relays RLY1 & RLY2. The relays have their contacts wired across the On and Off buttons of a UHF remote control module. OUT IN GND LP2950 UHF REMOTE OFF SWITCH 1,14 7,8 1,14 RLY 1 K 100k GND IN OUT REG1 LP2950ACZ–5.0 16V 10 µF 6 Circuit details Take a look now at Fig.1 for the circuit details of the Remote Switch Timer. It’s quite simple and is based on a PIC16F88-I/P microcontroller (IC1), an LCD module, a couple of miniature relays, 10 pushbutton switches and a few other parts. Most of the complexity is hidden inside the software that’s programmed into IC1. This allows the micro to monitor the switch inputs and drive the LCD module and relays according to the actions required by the switches and internal timers. IC1’s RA2, RA3, RA4 & RB0 data lines send character data to the LCD module. In addition, the RA1 & RB7 lines drive the Enable (EN) and Register Select (RS) inputs. The LCD is set to run using four bits of data to save on outputs from IC1. The necessary data bits are sent to the LCD as two separate transfers, to make up the eight bits necessary to fully drive the display. The RA2, RA3, RA4 & RB0 lines also drive a matrix based on pushbutton switches S1-S10 and diodes D4-D7. To check if a switch is closed, the RA2, RA3, RA4 & RB0 lines are driven low and the RB2, RB4 & RB5 inputs monitored. These latter inputs are normally pulled high (to +5V) via internal pullups but one of these inputs will go low (ie, close to 0V) if a switch is closed. When a low is detected, the RA2, RA3, RA4 & RB0 lines are taken high again and then taken low one at a time while IC1 continues monitoring RB2, RB4 & RB5. This allows the micro to determine which switch button is being pressed. For example, if S3 is closed, this will be detected when RA4 goes low and in turn pulls RB4 low. Diodes D4-D7 are there to prevent shorts between the RA2, RA3, RA4 & RB0 lines if two switches are pressed at the same time. Shorts between these lines would not only affect switch detection but would also affect the drive CON2 CON1 + – CON4 CON5 A K D8 1N4004 UHF REMOTE ON SWITCH UHF REMOTE SUPPLY (OPTIONAL) + – TO 9V BATTERY SNAP 12V DC TO SOCKET + – CON3 A K D3 1N4004 LCD module is switched off to conserve the battery when the unit is running from battery power alone. Without battery back-up, the Remote Switch Timer will reset with all timers set to zero when a black-out ends. In addition, the mains socket will be reset with the power off. In summary, it’s an incredibly versatile unit that’s easy to program. It should cover a very wide range of timing applications. November 2014  69 ON 14121191 H CLCD TI WMODULE S S NIA M F HZ-7013 U R OF R(B/L) E MI T 16X2 ALTRONICS RLY1 SY4030 D1 OFF 4148 4004 4148 D6 4148 D7 UP HOURS S1 BACKLIGHT VR1 10k 100nF IC1 PIC16F88–I/P 10k DOWN 100Ω UP S2 S3 Q1 S7 S8 CYCLE ON S6 S9 NEXT DOWN MINUTES S4 S5 OFF SET/START TIMER FOR UHF MAINS SWITCHES FRONT VIEW TO REMOTE’S ON SWITCH CON1 19112141 TIMER FOR UHF MAINS SWITCH (LCD MODULE UNDER) CON2 TO REMOTE’S OFF SWITCH DC INPUT SOCKET UHF – + SUPPLY POWER FOR UHF REMOTE GND CON4 CON3 (IC1 UNDER) +12V D5 S10 100Ω D2 4148 SUPPLY + – 330Ω 19112141 C 2014 D4 4148 UHF 2.2k 33pF 10 µF 33pF 4148 4004 + – Backup CONTRAST 100k D8 4MHz BC337 D3 X1 GND LP2950 ACZ-5.0 +12V REG1 10 µF RLY2 SY4030 14 13 12 11 10 9 8 7 6 5 4 3 2 1 16 15 CON5 – STRESS RELIEF HOLES FOR BATTERY SNAP LEADS + FOR 9V BATTERY SNAP LEAD (OPTIONAL) REAR VIEW Fig.2: install the parts on PCB as shown here. Be sure to use a socket for IC1 and make sure that all polarised parts are correctly orientated. The 2-way header sockets (CON1-CON5) are the only parts that mount on the rear of the board. signals to the LCD and cause corrupted characters to be displayed. Ports RB1 & RB6 drive relays RLY1 & RLY2 via 100Ω resistors. The NO (normally open) contacts of the relays go to CON1 & CON2 and these in turn are wired in parallel with the ON and OFF switches respectively on the UHF remote’s PCB. Diodes D1 & D2 are there to prevent damage to RB1 & RB6 by clamping the back-EMF generated by the coils when the relays switch off. The 100Ω resistors in series with the relay coils also help protect IC1’s RB1 & RB6 outputs. They are not needed 70  Silicon Chip in normal operation but will limit the back-EMF current from a relay coil if its associated diode fails or develops a dry joint connection. Timing A 4MHz crystal (X1) between pins 15 & 16 of IC1 is used to provide an accurate reference for the timing oscillator. It’s loaded with fixed 33pF capacitors to ensure it starts correctly. Normally, the crystal would be trimmed to a precise 4MHz using a trimmer capacitor in place of one of the fixed values. However, without suitable calibrated test equipment, it’s not possible to accurately adjust the trimmer without a great deal of trial and error. As a result, as previously stated, we chose to use a software adjustment procedure instead. If the 4MHz crystal is precisely on frequency, the program runs at exactly 1MHz. The software uses a counter (Timer1) that overflows after a count of 40,000 or after 1/25th of a second if the clock frequency is precisely 1MHz (ie, 25 of these 40,000 counts will take 1s). If the crystal runs too fast or too slow, it’s just a matter of altering the 40,000 number used in the counter to provide the correct 1s period. For example, for a 1ppm adjustment, the number for Timer1’s overflow counter must either be 40,001 (ie, one more) if the crystal is too fast or 39,999 (ie, one less) if the crystal is too slow. Note that this change is only done for one of the 25 overflow counts that make up one second for Timer1. The remaining 24 counts still use 40,000 as the count. As stated, the overall adjustment range is from -99ppm to +99ppm. In operation, the software then adds or subtracts the ppm correction value from 40,000 in order to compensate for the crystal frequency. The overflow ppm adjustment is done via the front-panel switches as described later, with the setting shown on the LCD. The correction required is determined by comparing the time of the Remote Switch Timer against a known accurate clock over a set period. Each 2.592 seconds in 30 days that it is off is equivalent to 1ppm. Note that the clock on the Remote Switch Timer shows the seconds, so that the clock’s accuracy can be checked. The timing functions, however, are only to the nearest minute. Backlighting Backlighting is provided for the LCD so that the timer can be used in the dark. This can be adjusted in 16 steps from fully off through to full brightness by pressing the Backlight pushbutton (S10). This brings up the backlighting value which is shown as a number ranging from 0-15, with 15 being full brightness. A bargraph is also used to show the brightness setting. For brightness levels between 1-14, the backlight LEDs are driven using PWM (pulse width modulation). Pin 9 (PWM) of IC1 provides the PWM siliconchip.com.au to power up and for the companion mains socket to power up if there has been a blackout. Construction All the parts (except for the UHF remote) are installed on a PCB coded 19112141 and measuring 104 x 76mm. Fig.2 shows the parts layout on the PCB. Begin by installing the resistors and diodes. Table 1 shows the resistor colour codes but we recommend that you also check each one using a DMM before installing it. Be sure to install the diodes with the correct polarity. REG1 and Q1 are next on the list. These two devices look the same, so be careful not to get them mixed up. Once they’re in, install an 18-pin socket for IC1, with the notched end towards D5. Follow with the capacitors. The two 10µF electrolytics must be installed with the polarity shown and bent over so that they lie flat against the PCB, so that they later sit below the top edge of the LCD module (see photo). The ceramic and MKT capacitors can be mounted either way around. Crystal X1 and trimpot VR1 can now go in, followed by the two relays. Note that each relay must be installed with its notched end towards the LCD. Now for the LCD module. This is mounted using a 16-way SIL pin header at the bottom lefthand edge. Begin by fitting the header in place with its short pins going into the PCB. Solder these pins, then fit the LCD module over the longer pins and push it all the way down before soldering these pins as well. The 10 pushbutton switches can now be installed. These go in with The completed timer PCB. Note how the two 10μF electrolytic capacitors are bent over so that they don’t later foul the lid of the case. waveform and this drives the cathodes of the backlight LEDs via transistor Q1 and a 330Ω current-limiting resistor. For level 0, there is no drive to the LED cathodes (Q1 permanently off) and for level 15, the LEDs are continuously driven (Q1 permanently on). At other levels, the duty cycle of the PWM pulse determines the LED brightness. At half brightness, for example, the LEDs are switched on and off via Q1 using a 50% duty cycle. The PWM frequency is 66.66kHz, so the on and off switching of the LEDs will not be noticeable. The contrast of the LCD module is adjusted using VR1. It’s just a matter of tweaking VR1 to suit. Power supply The Remote Switch Timer is normally powered from a 12V DC plugpack supply connected to CON3. Diode D3 provides reverse polarity protection and the nominal 11.4V supply rail is then filtered using a 10µF capacitor and used to power the backlight LEDs in the LCD module. The 11.4V rail is also fed to lowdropout regulator REG1. This produces a regulated 5V rail to power microcontroller IC1, the LCD module and the remaining circuitry. The optional 9V back-up battery is connected to CON5. Diode D8 provides reverse polarity protection and both it and D3 isolate the two supplies. IC1’s RA0 input (pin 17) monitors the 12V supply line from CON3. If this goes to 0V but IC1 is still powered via the back-up battery, the software detects this loss of 12V power and switches off the backlight. When the 12V is subsequently restored, this is detected by RA0 and the last ON or OFF signal is resent to the remote PCB by turning on the appropriate relay. In practice, the ON or OFF relay is activated about 3s after power is restored and remains on for around 900ms. This 3s delay gives enough time for the remote control circuit Table 2: Capacitor Codes Value µF Value IEC Code EIA Code 100nF   0.1µF 100n 104 33pF   NA   33p   33 Table 1: Resistor Colour Codes o o o o o o siliconchip.com.au No.   1   1   1   1   2 Value 100kΩ 10kΩ 2.2kΩ 330Ω 100Ω 4-Band Code (1%) brown black yellow brown brown black orange brown red red red brown orange orange brown brown brown black brown brown 5-Band Code (1%) brown black black orange brown brown black black red brown red red black brown brown orange orange black black brown brown black black black brown November 2014  71 0V TO CON4 +12V TO CON4 OFF TO CON2 ON TO CON1 Fig.3: here’s how to make the connections to the Altronics UHF remote PCB. The red and black leads shown are all part of the original wiring. The timer PCB is mounted on spacers on the rear of the front panel and is secured using eight M3 x 6mm machine screws. +12V TO CON4 ON CONTACTS: TO CON1 OFF CONTACTS: TO CON2 0V TO CON4 is almost certainly fully functional and it can be installed in a case, along with the remote’s PCB module. If it doesn’t work, go back over the PCB and check carefully for incorrect component values, incorrectly orientated parts and missed solder joints. Case installation Fig.4: the wiring connections to the Jaycar UHF remote. You will need to scrape away the solder masking from some of the tracks before soldering the leads. their flat sides orientated as shown and must be pushed all the way down before soldering their pins. The PCB assembly can now be completed by installing CON1-CON5. These polarised 2-way headers are installed on the rear of the PCB with their plastic tabs orientated as shown in the bottom diagram of Fig.2. Wiring the header sockets The header sockets are wired by crimping the wires into the crimp lugs and then pushing them into the socket shell. These wires can all initially be about 100mm long and you will need to use red and black leads for CON3CON5 as shown. The leads for CON1 & CON2 run to the ON & OFF switches on the remote PCB, so their polarity is unimportant. Test & adjustment Before applying power, make sure that IC1 is out of its socket and that 72  Silicon Chip all polarised parts are correctly orientated. That done, apply 12V DC to CON3 and use a DMM to check the supply between pins 14 & 5 of IC1’s socket. This should be somewhere between 4.75V and 5.25V. If this is correct, switch off, install IC1 (notch towards D5) and reapply power. The LCD should now show characters. Adjust VR1 for best contrast, then switch the backlighting on by pressing the backlight button (S10). Check that brightness can be adjusted by holding S10 down (the adjustment direction changes each time you press S10). Now press the On button (S8). A click from the ON relay should immediately be heard and the top line of the LCD should display “ON”. Similarly, pressing the Off button should briefly turn the OFF relay on and cause “OFF” to be displayed on the bottom line of the LCD. If the unit passes these tests, then it The PCB can be installed either in a UB1 plastic utility case (158 x 95 x 53mm) or in a sealed polycarbonate case with a clear lid (115 x 90 x 55mm). A front panel PCB coded 19112142 and measuring 157 x 94mm can be used with the UB1 box. This PCB replaces the plastic lid and comes with all holes drilled and screen-printed lettering. It’s available from the SILICON CHIP PartShop, as is the main PCB. Alternatively, a label measuring 144 x 84mm can be used with the existing lid on the UB1 box. A front panel label measuring 103 x 78mm is also available for the polycarbonate box. These labels can be downloaded in PDF format from the SILICON CHIP website and printed out. You will need to print out two copies – one onto plain paper for use as a drilling template and another onto photo paper to use as the front-panel label. The labels show the screwmounting locations for the PCB on the lid, along with the switch locations. A rectangular cut-out for the LCD surround will also be required for the siliconchip.com.au Dataflex & Datapol Labels (1) For Dataflex labels, go to: www.blanklabels.com.au/index. php?main_page=product_ info&cPath=49_60&products_ id=335 (2) For Datapol labels go to: www. blanklabels.com.au/index. php?main_page=product_ info&cPath=49_55&products_ id=326 UB1 box but this isn’t necessary for the polycarbonate case with the clear lid. The PCB mounting holes should be drilled to 3mm, while the switch holes should be started using a pilot drill and then carefully enlarged to 10mm using a tapered reamer. The rectangular display cut-out can be made in the UB1 box lid by first drilling a series of holes around the inside perimeter, then knocking out the centre piece and filing to a smooth finish. Once the holes have been drilled, the front-panel label can be affixed to the lid using a suitable glue or neutralcure silicone. Alternatively, you can print onto an A4-size synthetic “Dataflex” sticky label if you have an inkjet printer or onto a “Datapol” sticky label if you have a laser printer. This can then be trimmed to size and affixed to the base of the case using the label’s self-adhesive backing. Dataflex and Datapol labels are siliconchip.com.au Above: these two views show the inside of the unit with all wiring completed (Jaycar remote PCB used, no back-up battery fitted). Use neutral-cure silicone or hot melt glue to hold the wiring to the remote PCB in place. Features & Specifications • • • • • • • • Power: 12V DC at 30mA Current: 30mA with full backlighting; 3mA with backlighting off Battery backup current: typically 3mA On & Off IN: adjustable from 0h 0m to 99h 59m in 1-minute steps On & Off AT: adjustable from 0h 0m to 23h 59m (0h 0m shown as --:-– and timer is off) Real Time Clock: 24-hour format with hh:mm:ss Crystal tolerance compensation: ±99ppm Dimming: off to full brightness in 16 steps; 66.66kHz PWM (pulse width modulation). November 2014  73 Instructions For Using The Remote Switch Timer The very first time the Remote Switch Timer is powered up, the backlighting will be off and the timer will be in the ON IN and OFF IN Once Only mode (Fig.5). Two lines will be displayed on the LCD, with the top line showing ON IN“---:--” and the lower line OFF IN ---:--   The inverted commas in the first line show that the ON IN time can be changed using the Hours and Minutes Up/Down buttons. The dashes mean that the timer is off. Note that three dashes are allocated for the hours position and two for the minutes. This represents three digits for the hours and two for the minutes. The settings can be up to 255h 59m. Note that if you want an hour value above 127, it’s quicker to reach this by pressing the down button to count back from zero hours. Pressing the Next button (S6) moves the inverted commas to the second line. The LCD then shows OFF IN “---:--” and the hours and minutes for this setting can again be adjusted using the up and down buttons. Depending on the above setting, you also need to select whether the mains switch is initially on or off. That’s done by pressing the ON or OFF button (Fig.7). Pressing the Set/Start pushbutton (S5) then starts the timing, with the colon between the hours and minutes digits flashing and the inverted commas off. Pressing the Set/Start button again stops the timing or you can do this to change the ON IN or OFF IN values. Note that timing will not begin unless the colon is flashing. Changing the cycle To check which cycle you are running or to change the cycle, press the Cycle button (S7). The current cycle will be displayed and this will initially be ON/OFF IN Once Only. Other selections are ON/OFF IN Repeat, ON/OFF AT Repeat and ON/ OFF AT Once Only (Figs.8-10). You can just view the setting, by pressing the Cycle button for up to 10s. Pressing it for longer than 10s lets you move to the alternative settings. After 10s, the cycle indicator will be shown and the unit will count down from 10 to 0. When zero is reached, the cycle changes to the next selection. It’s just a matter of holding the Cycle button down until the required cycle is reached. The hours & minutes settings for the ON/OFF AT cycle are achieved in exactly the same manner as for the ON/OFF IN cycle, with the Next pushbutton again used to select the OFF AT timer. Adjust ppm correction Pressing the Next button after OFF AT has been selected brings up the “Adjust ppm” correction value on the top line and the real time clock on the bottom line (Fig.11). A right arrow shows which line can be changed using the Hours and Minutes buttons. As before, pressing the Next button cycles through the selections. The ppm setting is initially zero but can be changed using either the Hours or Minute buttons to ±99 maximum. A positive value speeds up the clock, while a negative value slows it down. A 1ppm change represents about 2.6s in 30 days or about 1s every 11.5 days. The 99ppm maximum adjustment corresponds to 256s in 30 days or about 8.53s per day. The real-time clock runs continuously and its time can only be changed in Set mode. The seconds are reset to zero each time the hours or minutes are changed, allowing the clock to be easily synchronised with another clock. Note that only the clock is shown in run mode, not the ppm crystal correction value. In practice, it’s all very straightforward and is far less complicated than it sounds. A few minutes spent playing with the buttons will familiarise you with the way it works. What’s remembered? If you don’t use the battery back-up, then the Remote Switch Timer will power off in a blackout or when you disconnect power. When power is restored, the timers will be at zero (showing dashes) and the clock will initially begin from zero (midnight). However, the cycle setting, backlight dimming level and crystal ppm correction value will all be restored to their values before power went off. By contrast, with battery back-up, the clock and timers will continue to run and their settings will not change. In addition, the last ON or OFF setting required for the remote mains socket will be remembered and re-sent after a 3s delay when power is restored. available from www.blanklabels.com. au and sample sheets are available on request to test in your printer – see panel. Once the label is in position, the Remote Switch Timer PCB can be attached to the rear of the lid using tapped spacers and M3 x 5mm ma74  Silicon Chip chine screws. M3 x 9mm spacers are used for the UB1 box, while M3 x 12mm spacers are used for the polycarbonate case so the LCD module sits inside the clear lid (this eliminates the need for a display cutout). Alternatively, if you are using a PCB front-panel with the UB1 box, it’s simply a matter of mounting the PCB on M3 x 9mm spacers. DC socket & battery holder An 8mm-diameter hole has to be drilled in the lefthand end of the case for the panel-mount DC socket. This can then be fitted in position siliconchip.com.au Fig.5: when first powered up, the unit is in ON IN and OFF IN Once Only mode. The inverted commas indicate that the ON IN time can be set using the Hours and Minutes buttons. Fig.6: the unit has been programmed here to turn on in 7.5 hours and off after 15 hours. Pressing the Set/Start button starts the timers. Fig.7: pressing the On or Off button sets the initial on/off state of the remote mains socket. Fig.8: different settings (or modes) are selected by pressing and holding down the Cycle button. ON/OFF-IN Repeat mode has been selected here. Fig.9: the ON/OFF-AT mode. Both Once Only and Repeat settings are available. Fig.10: the unit has been programmed here to turn on and off at set times. Fig.11: pressing the next button after OFF AT has been selected lets you adjust the clock and set the time. and the wiring leads connected (the other ends of these wires terminate in 2-way header socket CON3). Be sure to connect these leads to the correct terminals on the DC socket (check with a DMM if necessary). As stated, the back-up battery is optional. If you wish to use it, it’s just siliconchip.com.au a matter of connecting a 9V battery snap to CON5 and installing a 9V battery holder. Before soldering the battery snap leads, loop them through the adjacent strain relief holes. The holder can be secured to the base or to one side of the case using an M3 x 6mm machine screw and nut. Remote control PCB Before removing the remote’s PCB module, the remote control mains socket (either from Jaycar or Altronics; see parts list) should be set to operate as described in the instructions. This will familiarise you with the way the units works and allow you to set the channel number and test its operation. Once you’ve done that, the handheld remote can be disassembled. The Jaycar remote has one screw located beneath the battery cover and when removed, the two halves of the remote case can be cracked open along the sides with a screwdriver. By contrast, the Altronics remote has two screws under the battery compartment lid and removing these allows you to split the case. It’s then just a matter of removing the remote PCB and connecting the leads from CON1, CON2 and CON4. CON1 is wired across the ON contacts for the selected channel, CON2 across the OFF contacts and CON4 to the UHF remote’s supply rails. Figs.3 & 4 show the details. On the Jaycar remote, it will be necessary to scrape away the solder masking from the rear of the PCB before soldering the connections. Once all the wires are in place, fit a cable tie around the four switch wires to prevent them from pulling away from the PCB. It’s also a good idea to use neutral-cure silicone or hot melt glue to hold the wires in place. The remote PCB can now be mount­ ed on the base of the case. Both the Jaycar and Altronics remotes have two holes that can be used as mounting points, although the Jaycar unit’s holes will need to be enlarged to 3mm. In each case, the unit can be mounted (copper side up) on 9mm tapped spacers and secured using M3 x 5mm machine screws. Once it’s in place, plug the various leads into the sockets on the back of the timer PCB and fasten the lid down. That’s it – the unit is ready for use. The full instructions on driving it are SC in the accompanying panel. Helping to put you in Control LogBox RHT 32K Readings IP65 dual channel data logger with built-in temperature & humidity sensor. 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SKU: KTA-290 Price:$79 +GST Power Multiplexer Carrier The Texas Instruments TPS2113A autoswitching power multiplexer allows you to switch seamlessly between two power sources of 2.8 V to 5.5 V, while blocking reverse current into either source & and the board also breaks out a USB Micro-B connector that can be used to supply one of the rails. It has an adjustable current up to 2 A. SKU: POL-2596 Price:$9.95 +GST Bluetooth 4.0 BLE Shield Bluetooth Low Energy (BLE) shield for Arduino based on the Nordic Semiconductor nRF8001. This shield lets your Arduino talk to your smartphone or other Bluetooth 4.0 equipped devices. 3.3 V or 5 V powered. SKU: SDA-001 Price:$34.95 +GST New MeanWell Slim Line Series MeanWell has recently announced the released of their highly anticipated new slim line series: EDR-120, NDR-120 & EDR-150. Only EDR-120 & NDR-120 offers standard output such as 12 VDC, 24 VDC and 48 VDC. EDR-150 is currently only available with 24 VDC output, but can be adjusted up to 156 W. These series will be available in late October. Contact us via phone, fax or e-mail to place your preorder. Price starting from $35 ea + GST. For OEM/Wholesale prices Contact Ocean Controls Ph: (03) 9782 5882 oceancontrols.com.au November 2014  75 How to find faults in coaxial cables using TDR TDR or time-domain reflectometry is a technique used to track down faults in cables – mainly coaxial cables but other types as well. But do you know how TDR actually works? This article is a primer on TDR. It’s a lot easier to understand than you may think and we also explain what the terms “velocity factor” and “characteristic impedance” mean. By JIM ROWE D ON’T BE PUT OFF by that complex sounding term “time-domain reflectometry” or its cryptic acronym “TDR”. They’re just techno jargon for a fault-finding technique that’s simpler than it sounds – at least in principle. First off, we need to explain that the main use for TDR is for finding faults and discontinuities in cables – primarily coaxial cables. These are the cables used to carry RF signals between antennas, receivers and transmitters and also to carry RF, video and high-speed digital signals between professional and domestic equipment. In essence, coaxial cables behave as transmission lines, in that when electrical energy is fed into one end of the cable, it takes a finite time for that energy to travel along the cable to HIGH SPEED OSCILLOSCOPE the other end. That’s because the distributed inductance and capacitance inside the cable force the energy to propagate along it in the form of an electromagnetic wave (a combination of electric and magnetic energy). This is very similar to light energy travelling along a fibre-optic cable – which is not surprising, because light is simply electromagnetic (EM) energy of a much higher frequency. When any kind of EM energy is propagating through empty space (ie, a vacuum), it does so at the speed of light, equal to 299,724,580 metres per second, or near enough to 300,000km/s. By the way, this equates to 300 metres per microsecond (300m/μs) and also to 300 millimetres per nano­ second (300mm/ns). Both of these figures are worth remembering. When EM energy is propagating through a more substantial medium like a coaxial cable (or a fibre-optic cable in the case of light), it moves at a slower speed; still very fast but not quite as fast as light in a vacuum. Velocity factor In the case of EM energy propagating along a coaxial cable or similar transmission line, its speed or velocity (Vp) is related to the speed of light in a vacuum by a factor known as the “velocity factor” (Vf) of the cable. In other words: Vp = Vf.c . . . (1) where c is the speed of light in a vacuum. Fig.1: the basic circuit for a Step TDR. It uses a step generator with a source resistance of Rsource, while the load at the end of the coaxial cable has a resistance of Rterm. A high-speed oscilloscope is used to monitor the voltage at the input end of the cable. INPUT Rsource STEP GENERATOR 76  Silicon Chip TRANSMISSION LINE (COAXIAL CABLE OR SIMILAR) CHARACTERISTIC IMPEDANCE = Zo LOAD (Rterm) siliconchip.com.au As you might expect, the value of Vf is closely related to the dielectric constant Er of the dielectric material used in the cable itself – between the centre conductor and the outer screen conductor. In fact: Vf = 1/√ √Er . . . (2) Most commonly available coaxial cables use a polyethylene (PE) dielectric in either solid or cellular foam form – or as small discs of solid PE spaced apart (“air-spaced” PE). A small number of cables for specialised applications use dielectric materials like fluorinated ethylene propylene (FEP), poly tetrafluoroethylene (PTFE) or polyvinyl chloride (PVC). Table 1 shows the dielectric constant Er, the velocity factor Vf and the propagation velocity Vp of some common types of coaxial cable dielectric, along with the figures for air or a vacuum for comparison. This information comes in handy when you’re using a TDR adaptor with a scope to locate the position of faults or discontinuities in cables. Characteristic impedance Now let’s consider another important aspect of coaxial cables and other transmission lines: their characteristic impedance. Just as the distributed capacitance and inductance of a cable forces EM energy to propagate along it at a specific velocity, they also force the energy to adopt a specific voltageto-current ratio. This V/I ratio is called the cable’s characteristic impedance, and is usually represented as “Zo”. The value of Zo for any particular cable depends mainly on the ratio of the outer conductor’s inside diameter (D) to the inner conductor’s outside diameter (d), together with the dielectric constant of the insulating material between them (Er). In fact, if you neglect the series resistance of the inner and outer conductors per unit length, Table 1: Common Coaxial Cable Dielectrics DIELECTRIC MATERIAL (DIELECTRIC Er CONSTANT) AIR (OR VACUUM) 1.00 1.00 300mm/ns SOLID PE 2.3 0.66 198mm/ns CELLULAR FOAM PE 1.4 – 2.1 ~0.87 261mm/ns Vf (VELOCITY FACTOR) Vp (VELOCITY OF PROPAGATION) AIR SPACED PE ~1.1 0.95 285mm/ns SOLID PTFE 2.1 0.69 207mm/ns CELLULAR FOAM PTFE 1.4 0.84 252mm/ns SOLID FEP 2.1 0.69 207mm/ns CELLULAR FOAM FEP 1.5 0.82 246mm/ns -9 Note: velocities shown in millimetres per nanosecond (10 s) the Zo of a coaxial cable can be found from this simple formula: Zo = (138Ω/√ √Er) x log(D/d)        . . . (3) which can be simplified to: Zo = 138Ω x Vf x log(D/d) . . . (4) Although you can calculate the Zo of any particular cable with this formula, it’s generally not necessary because cable manufacturers usually provide this information. Table 2 shows the relevant details for some common coaxial cables. All of them have a Zo of either 50Ω or 75Ω. Knowing the Zo of a cable is important because when the cable is used to transfer electrical energy from a source or “generator” to a load, you only get maximum power transfer when the generator’s source resistance/ impedance and the load’s resistance/ impedance are both matched to the Zo of the cable. If the load resistance is not matched to the cable impedance (Zo), some of the energy reaching the load end of the cable is reflected back along the cable to the generator (with a polarity which may be the opposite of the ‘incident’ energy). If the source resistance of the generator is not matched to the cable Zo either, some of this returned energy is reflected back towards the load again. The net result is that some of the energy bounces back and forth along the cable and is wasted as heat. So a cable’s Zo or characteristic impedance is most important in that it allows you to match the resistance of the load and generator to it, in order to achieve the most efficient transfer of energy/power (and preserve signal integrity). TDR basics Having explained coaxial cable operation and the significance of Vp (velocity of propagation) and Zo (characteristic impedance), we are primed to understand the basics of TDR. First, there are actually three versions of TDR, known as “Step TDR”, “Pulse TDR” and “Spread-Spectrum TDR”. We’re going to be dealing mainly with Step TDR because it’s the version most commonly used nowadays and it’s the easiest to understand. Now take a look at the simple circuit in Fig.1. It shows a length of coaxial cable connected between a voltage step generator and a load resistor. The step generator has a source resist- Table 2: Typical Characteristics Of Some Common Coaxial Cables (VELOCITY OF PROPAGATION) D/d (mm/mm) Zo (CHIMAPREADCATNERCISET) IC Loss (dB/m <at> F) COMMON USES 4.7/1.0 75W 0.2 <at> 1GHz CABLE TV & SATELLITE ANTENNA INSTALLATIONS 198mm/ns 2.9/0.81 50W 1.056 <at> 2.4GHz THIN ETHERNET, RF & INSTRUMENTATION SOLID PE 198mm/ns 3.7/0.64 75W 0.39 <at> 1GHz BASEBAND VIDEO, DOMESTIC TV ANTENNAS RG-174/U SOLID PE 198mm/ns 1.5/(7 x 0.16) 50W 2.46 <at> 2.4GHz WI-FI PIGTAILS, GPS & INSTRUMENTATION RG-213/U SOLID PE 198mm/ns 7.2/(7 x 0.75) 50W 0.27 <at> 1GHz LOW LOSS UHF ANTENNA CABLES Vp CABLE TYPE DIELECTRIC RG-6/U CELLULAR FOAM PE 261mm/ns RG-58/U SOLID PE RG-59/U Note: RG-XX/U type numbers are a carr y-over from US militar y specs during WW2. They are nowadays used mainly to identify matching connectors. siliconchip.com.au November 2014  77 Table 3: Scope Displays With Step Generator CONDITIONS RESULT Zo = Rsource Rterm = Zo (CORRECT MATCHING) ALL ENERGY IS CARRIED TO THE LOAD, WITH NO REFLECTED ENERGY Ei Zo = Rsource Rterm = ZERO (SHORT CIRCUIT AT LOAD END) ALL ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH REVERSED POLARITY (Tr = 2 x cable transit time) Ei Zo = Rsource Rterm = INFINITY (OPEN CIRCUIT AT LOAD END) ALL ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH THE SAME POLARITY (Tr = 2 x cable transit time) OSCILLOSCOPE DISPLAY Er (= –Ei) Tr Er (= +Ei) Ei Tr Zo = Rsource Rterm = 2 x Zo (TWICE Zo & Rsource) ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH THE SAME POLARITY (Tr = 2 x cable transit time) Ttransit = L/Vp Ei Er (= +Ei/3) Tr Zo = Rsource Rterm = Zo/2 (HALF Zo & Rsource) ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH REVERSED POLARITY (Tr = 2 x cable transit time) Er (= –Ei/3) Ei Tr ance of Rsource, while the load has a resistance of Rterm (shortened from Rterminating). The only other item in the circuit is a high-speed oscilloscope with its input being used to monitor the voltage at the input end of the cable. To begin, consider the situation where both Rterm and Rsource are correctly matched to the Zo of the cable. What would you expect to see on the scope? In this case, you would see a single voltage step as shown in the top trace of Table 3. The step would have an amplitude of Ei volts and would continue at that level indefinitely – or at least until the generator output falls again. Note that the value of Ei will be equal to half of the generator’s open-circuit output voltage, because the effective input resistance of the cable will be equal to Rsource and together they will constitute a 2:1 voltage divider. Shorting the cable Now consider what the scope would show if the load resistor Rterm were replaced with a short circuit – in effect, a resistor of zero ohms. This would be an extreme mismatch at the load end of the cable and as a result all of the voltage step energy would be reflected Scheduled for publication in the December issue, this do-it-yourself adaptor lets you use any reasonably “fast” scope to perform step TDR on your own cables. 78  Silicon Chip back towards the generator as another voltage step Er – with the same amplitude as Ei but of opposite polarity. So the scope display would look like the second trace in Table 3, with the voltage at the cable input dropping to zero as soon as the reflected energy arrived back. Note the significance of Tr. It is the time between the start of the voltage step and its sudden end. It represents the time taken for the incident step to travel to the end of the cable, plus the time taken for the reflected step to travel back to the start. In other words, it will be equal to twice the cable transit time. And we can work out the transit time. It’s equal to: . . . (5) where Vp is the velocity of propagation in the cable (as before, measured in mm/ns), while L is the cable length in millimetres. So Tr will equal twice this value and if we measure Tr using the scope we can calculate the effective length of the cable using this rearranged equation: L = (Tr x Vp)/2                    . . . (6) where L is the cable length in millimetres, Tr is the step “length” in nanoseconds and Vp is the velocity of propagation in mm/ns. So by measuring Tr, we can quite easily work out the cable length – or more precisely the distance to the short circuit. Disconnecting the cable Next consider what would happen if we removed the short circuit from the load end of the cable and left it without any termination at all – an open-circuit. This will again represent an extreme mismatch but of the opposite kind to a short circuit. All of the voltage step energy will again be reflected back to the generator as a voltage step Er, but this time with the same polarity as Ei. When the reflected step reaches the start of the cable, the scope will show the voltage suddenly rising to twice its initial value, as shown in the third trace of Table 3. The Tr time will still have the same significance as before, in this case allowing us to work out the cable length to the open circuit. Get the idea? Now let’s consider what would happen if we don’t connect a short circuit or an open circuit to the end of the cable but instead connect a load siliconchip.com.au Voltage reflection coefficient Perhaps you’re wondering why the value of Er is only equal to a third of Ei, when the load resistance is twice the value of Zo? That’s because Er and Ei are related by a factor called the voltage reflection coefficient (Rho), which has a value given by this expression: Er/Ei = Rho = (Zload - Zo)/(Zload + Zo) ...(7) where Zload is the load impedance, which in this case is equal to 2Zo. Rearranging this and substituting for Zload, we find that the value of Er becomes: Er = Ei(2Zo - Zo)/(2Zo + Zo)    = Ei.Zo/3Zo = Ei/3          2.00 1 .00 0.80 0.60 0.40 0.30 RG-174/U 0.20 RG-213/U 0.10 0.08 0.06 RG-58/U 0.05 0.04 0.03 0.02 0.01     . . . (8) Next consider what will happen if we again connect a load resistor to the end of the cable but this time with a value which is HALF the value of Zo and Rsource. Again this is a mismatch, so some of the voltage step energy will be reflected back towards the generator as before. This time though, the reflected voltage Er will be reversed in polarity compared with Ei, because the load resistance is lower than Zo. You can see the resulting downward step in the fifth (lowest) trace in Table 3. You’ll also see that the value of Er is again equal to one third of Ei, which is confirmed thus: Er = Ei(Zo/2 - Zo)/(Zo/2 + Zo)    = Ei(-Zo/2)/(3Zo/2) = -Ei/3          . . . (9) From these five examples you’ll be starting to see how TDR works and how it allows us to calculate some important details about the operation of a cable and transmission line: (1) Whether the cable is correctly terminated in a matched load, which means no reflected energy. This is shown by the voltage step extending indefinitely. (2) If there is a further step in the scope display, indicating some kind of mismatch, then the Tr time between the siliconchip.com.au 3.00 CABLE LOSS IN DECIBELS PER METRE (dB/m) resistor with a value Rterm which is TWICE the value of Zo and Rsource. This is again a mismatch, although not as severe as a short or open circuit. Some of the voltage step energy will be reflected back towards the generator but not as much as before – and with the same polarity as Ei. So the scope will show an upward step after time Tr, with a step height Er in this case equal to Ei/3 as shown in the fourth trace of Table 3. 0.006 1 2 4 6 8 10 20 40 60 100 200 400 600 1GHz 2 3 FREQUENCY IN MEGAHERTZ & GIGAHERTZ Fig.2: these curves show the losses in three common types of 50Ω coaxial cable as a function of frequency. RG-174/U cable ranges from 0.06dB/m at 1MHz up to almost 2.5dB/m at 2.4GHz, while RG-213/U cable ranges from just 0.006dB/m at 1MHz up to 0.49dB/m at 2.4GHz. RG-58/U cable is midway between these two. initial step and the “reflection” step can be used to work out the length of cable L between the generator end and the mismatch. (3) The amplitude and polarity of the reflected voltage step Er can be used to work out the effective resistance of the mismatched load. Cable losses There’s one complication we need to consider before moving on: the effect of cable losses. In the discussion so far, we’ve made the assumption that the cables being tested are “perfect”, in the sense that when the generator and load resistances are properly matched to the cable’s Zo, all of the energy fed into the cable at one end emerges from the other end and passes into the load. In other words, we’ve assumed that the cables are lossless. But in the real world, nothing is perfect. As shown in column six in Table 2, all cables have a loss which is usually listed in terms of decibels per metre (dB/m), or decibels per 100 feet (dB/100ft) in countries like the USA which still use the Imperial system. Because cable losses rise with increasing frequency, the loss figure is usually qualified with a frequency figure, as shown. To put things into perspective, look at the curves in Fig.2. These show the losses in three common types of 50Ω coaxial cable, all plotted against frequency. As you can see, the small diameter RG-174/U cable has a loss figure ranging from 0.06dB/m at 1MHz up to almost 2.5dB/m at 2.4GHz, while RG-213/U cable with its much larger diameter has a loss figure ranging from only 0.006dB/m at 1MHz up to 0.49dB/m at 2.4GHz. The common RG-58/U cable is midway between the other two in terms of its loss factor – ranging from November 2014  79 Fig.3: a Pulse TDR is almost idential to a Step TDR, the difference being that the stimulus generator delivers a narrow voltage pulse rather than a DC voltage step. HIGH SPEED OSCILLOSCOPE INPUT TRANSMISSION LINE (COAXIAL CABLE OR SIMILAR) Rsource NARROW PULSE GENERATOR CHARACTERISTIC IMPEDANCE = Zo 0.013dB/m at 1MHz up to just over 1.00dB/m at 2.4GHz. So real cables do lose some of the input EM energy (as heat), even when the generator and load are correctly matched to their Zo. But what effect does this have when you are checking a cable using Step TDR? This depends on things like the cable loss factor and the cable’s length. These are not likely to have much effect on a fairly short cable but when you’re checking a fairly long run of a relatively lossy cable, the cable loss will tend to attenuate the indicated level of reflected step Er. So any mismatch will appear to be less serious than it should. Pulse TDR Remember that the version of TDR we’ve been discussing so far is Step TDR – the name referring to the way it uses a voltage step waveform as the incident “stimulus” being fed into the cable to be tested. But we’re now going to look briefly at the other basic version: Pulse TDR, where a short voltage pulse is used as the stimulus rather than a step. Fig.3 shows the basic circuit for a Pulse TDR. It’s almost identical to the Step TDR circuit of Fig.1, the only difference being that the stimulus generator is now labelled ‘Narrow Pulse Generator’; it generates a narrow voltage pulse rather than a step. In effect, Pulse TDR works in much the same way as Step TDR. If you compare the traces shown in Table 4 with those for Step TDR in Table 3, you’ll see that the only differences are that Table 4: Scope Displays With Pulse Generator CONDITIONS RESULT Zo = Rsource Rterm = Zo (CORRECT MATCHING) ALL ENERGY IS CARRIED TO THE LOAD, WITH NO REFLECTED ENERGY Zo = Rsource Rterm = ZERO (SHORT CIRCUIT AT LOAD END) ALL ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH REVERSED POLARITY (Tr = 2 x cable transit time) OSCILLOSCOPE DISPLAY Ei Ei Er (= –Ei) Tr Zo = Rsource Rterm = INFINITY (OPEN CIRCUIT AT LOAD END) ALL ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH THE SAME POLARITY (Tr = 2 x cable transit time) Ei Er (= +Ei) ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH THE SAME POLARITY (Tr = 2 x cable transit time) Er (= +Ei/3) Ei Tr Zo = Rsource Rterm = Zo/2 (HALF Zo & Rsource) ENERGY REFLECTED BACK TO THE GENERATOR, BUT WITH REVERSED POLARITY (Tr = 2 x cable transit time) Ei Tr 80  Silicon Chip each voltage step of Table 3 is now replaced with a voltage pulse. The basic behaviour is unchanged, because we’re still looking at the effects caused by the interaction between cable parameters Vp and Zo and changes in load resistance. Step TDR is more popular But if there’s so little difference between the two, why is Step TDR more popular than Pulse TDR? For a couple of reasons, one being that during the stimulus pulse in Pulse TDR, the scope can’t be allowed to monitor the cable input voltage Ei because it would be overloaded. So with this approach, the stimulus pulse creates a ‘dead zone’, during which the scope can’t look for reflections. But when the pulse width is made very narrow to reduce the dead zone, this also reduces the TDR’s range. So Pulse TDRs generally need to provide a number of different pulse widths, to achieve different trade-offs between dead zone and range. Another allied problem with Pulse TDRs is that because a pulse stimulus carries much less energy than the step stimulus, the technique is not capable of delivering the same signal to noise ratio. So with real-world (read “lossy”) cables, Pulse TDR can’t reveal cable faults or discontinuities as clearly as Step TDR. Summarising Tr Zo = Rsource Rterm = 2 x Zo (TWICE Zo & Rsource) LOAD (Rterm) Er (= –Ei/3) You should now have a reasonable understanding of what TDR is, how it works and how it’s used for checking coaxial cables in particular. Think of it as “echo location for cable faults” if you like. And as you may have guessed, this article is a prelude for a planned lowcost adaptor which lets you use any reasonably “fast” scope to perform Step TDR on your own cables. Look SC for it in the December issue. siliconchip.com.au What’s the State-Of-Play with by Ross Tester Electric Vehicles Despite a relatively slow uptake by the market, a recent report suggests that’s all about to change. The 197-page, $US4000 ‘Electric Vehicle Forecasts, Trends and Opportunities 2015-2025’ report by UK research group IDTechEx claims that world-wide pure electrics and hybrids sales are expected to exceed half a trillion dollars by 2025. T he electric vehicle market here in Australia has been patchy, to say the least. The Toyota Prius (hybrid) has been far and away the most popular but other entrants into the hybrid market, such as the Holden Volt, have found it a much tougher market to crack. Pure electrics, such as the Mitsubishi iMiEV (see SILICON CHIP February 2011) and Nissan LEAF (SILICON CHIP, August 2012) have had an even more difficult history. Mitsubishi was reported to have ceased importing the iMiEV back in 2013 (though that’s not certain!), while Nissan has still been selling discounted 2012-build LEAFs this year in Australia, despite the 2014 model being released overseas. Indeed, the latest figures we’ve seen said that of the 266,370 vehicles sold in Australia last year, only 42 were electrics. Perhaps they will be given a ‘jump start’ with the impending release of two heavyweights here in Australia . . . Tesla Tesla Motors, with their (very) up-market – and up-price – range of pure electrics, are preparing to open showrooms in Sydney and Melbourne ‘before the end of the year’. We’re not sure where they will be getting their stock from, however: Tesla has closed its order books in the USA for the time being as they simply cannot keep up with demand. Tesla has earned an enviable reputation for developing outstanding vehicles. Its luxury Model S also achieves a perfect 5.0 NHTSA safety rating but at an expected price of about Tesla Model S siliconchip.com.au $AU100,000 it won’t be the car for everyone! prices) and hire a car when you get there. BMW Hybrids BMW’s $64,000 all-electric i3, announced earlier this year, was reported as being available ‘around the end of the year’ (ie, about now! So far, we haven’t seen any ramp-up in advertising, which we would have expected for an imminent release. BMW are promoting this as a ‘premium vehicle’ to fit in with their ‘premium brand’; hence the ‘premium price’. The main problem with pure electric vehicles (and even hybrids to some extent) is price. The iMiEV was the cheapest of the lot and it sold for more than $30,000 – for a vehicle which compared with several other sub-compacts in the $15-$20,000 range. The LEAF didn’t fare much better – even with a $39,990 price tag (much better than the original $54,000+) it too has not proved a marketing show-stopper. Perhaps marketing is the key – with limited range all-electrics (the LEAF is supposed to be good for 170km but experience suggests 130-150 is closer to the mark) they cannot be marketed as a family car. However, they are the perfect “second” car; none better for commuting to work, running down to the shops, taking the kids to sport on weekends and so on. With dramatically lower ongoing costs (both ‘fuel’ and maintenance) they make the normal family car seem incredibly hungry. But if you want to go away for holidays etc, you need to either take that normal car or as many people do now, fly (at heavily discounted We mentioned hybrids earlier and the IDTechEx report states that sales for these are rapidly growing worldwide, at the expense of conventional cars. Mitsubishi’s PHEV Outlander is but one example released here recently – again, though, it is at a significant premium to the ICE-only varieties. New models Over the years, there have been literally dozens of announcements from car companies, both large and unknown, that they are planning on introducing an electric car ‘shortly’. With few exceptions (Tesla and BMW included!) these cars either disappear or are still a twinkle in a developer’s eye. Once again, though, that could be changing. The IDTechEx report states that Foxconn (a company which makes Apple equipment) has recently partnered with another Chinese manufacturer, BAIC Motor Corp, to produce a sub-$15,000 pure electric car. It also reports that General Motors is well down the path of releasing a $30,000 pure electric and also achieving one of the ‘holy grails’ of electric vehicles, a model with 200 mile (320km) range per charge. Tesla, too, is putting a lot of effort into new battery technology (a significant proportion of electric vehicle cost), aiming to produce a battery for $100 per kWh within the decade. That could translate to even higher range. (See www.idtechex.com/ev). SC BMW i3 November 2014  81 One-Chip Mini 2 x 5W Stereo Amplifier It doesn’t get much simpler than this. With one IC and not much else, you get a stereo 5W amplifier that can operate over a wide range of voltages, from 3.5V to 15V. That means it can run off a single or multiple Li-Po cells, USB power or a lead-acid battery. It’s a small and inexpensive module that can do a range of audio amplification jobs. By NICHOLAS VINEN O UR VARIOUS “chip amplifier” or “champ” projects have been very popular because they’re easy to build and in many cases, are all you need to drive a small (or possibly even large) speaker. The Champion (SILICON CHIP, January 2013) was no exception. Unfortunately, the AN7511 IC we used in that project has been discontinued by Panasonic and has become difficult to obtain. The TDA7266D used in this little module is one of the most common small Class-B audio amplifier ICs available today and is made by ST Microelectronics. While there is a through-hole version, the SMD package variant is easier to get and smaller too. It has large pins so it isn’t too difficult to solder; the only tricky part is the large thermal pad as this can suck away quite a bit of heat while soldering. That does mean it’s fairly effective at taking away heat during operation though, so for most applications, the PCB makes a quite adequate heatsink. This single package provides a ster­ eo bridge-tied load (BTL) amplifier, which is ideal for getting maximum Class-B power into a pair of speakers. For example, it will deliver nearly 1W per channel into 8Ω speakers with a supply of just 4V, as is typically avail82  Silicon Chip able from a single Li-Ion or Li-Po cell. Its performance is pretty respectable too, as you can see from the specs and performance graphs. This IC also has over-temperature protection, output short circuit protection and shut-down/mute functions. We’ve added RCA socket inputs, a volume control and supply reverse polarity protection to complete the package. In comparison to the Mini-D switching amplifier from the September 2014 issue, this amplifier is smaller, simpler and costs less to build. It can also run off lower supply voltages. Of course, the Mini-D does offer substantially more power with higher efficiency and can run off higher voltage supplies. It’s basically a case of “horses for courses”; build the one that best suits your requirements. Circuit description The full circuit is shown in Fig.1. The input signal for each channel, from RCA sockets CON1 & CON2, passes through low-pass filters comprising 100Ω series resistors and 1nF ceramic capacitors to ground. These filters reduce audible hash and noise which may be picked up by the input leads. 10Ω resistors in series with each input ground improve channel isolation. The audio signals are then ACcoupled to the 10kΩ volume control potentiometer(s) with 4.7µF ceramic capacitors, giving a -3dB bass roll-off point around 7Hz. You can either use two trimpots (VR2/VR3) for preset volume or a dual log pot (VR1) for adjustable volume. The bottom end of each pot is AC-coupled to ground to prevent DC current passing through the pots, which would cause audible crackling during volume adjustment. The signals then go straight into IC1’s input pins, pin 7 for the left channel and pin 14 for the right channel. An internal half-supply bias voltage provides the correct DC levels. The internal negative feedback sets the gain to 26dB (20 times). The output signals go straight to terminal blocks CON4 and CON5. The outputs are bridge-tied so neither speaker has a ground connection. In other words, both ends of each speaker is actively driven with anti-phase signals, for maximum power delivery. The components connected to pin 8 (mute) and pin 9 (standby) prevent clicks and pops at power-up. When power is applied, both pins are held low so the outputs are off. Over time, the 10µF capacitor charges and IC1 first comes out of standby mode and siliconchip.com.au CON3 + 3.5-14.4V 4.7 µF 1 470 µF 4.7 µF X7R 16V L/ESR X7R 100Ω 4.7 µF X7R 6 Vcc VR1a/VR2 LED1 Q1 IRFML8244 15 7 IN1 2 CON7 K 10k LOG/10k 1nF COG 1 λ K G S Vcc − POWER A 100k D LEFT INPUT CON1 2 ZD1 15V OUT1+ 2 10k A 4.7 µF 10Ω X7R LEFT SPKR CON4 22k 1 RIGHT INPUT CON2 100Ω OUT1– 5 4.7 µF X7R VR1b/VR3 IC1 IC 1 10k LOG/10k 1nF COG OUT2+ 19 1 2 4.7 µF 88 MUTE X7R 9 9 STBY STANDBY CON6 OUT2– 16 1 2 RIGHT SPKR CON5 TDA7266D TDA7 266D 14 IN2 10Ω 2 Vref Vref 1k 10 µF 16V 47k SIG GND PAD 13 0 PWR PWR PWR PWR GND GND GND GND 1 10 11 20 TDA7266D SC 20 1 4 ZD1 LED1 ONE-CHIP MINI STEREO AMPLIFIER A K D K A 11 IRFML8244 G 10 20 S 1 Fig.1: the circuit of the One-Chip Mini Stereo Amplifier. It’s based on TDA7266D amplifier chip and can deliver in excess of 5W per channel. VR1 is the volume control, while Mosfet Q1 provides supply reverse polarity protection. into active mode, and then once other voltages have stabilised, the outputs are un-muted. If the two pins of CON6 are shorted, eg, by a switch, or if pin 1 is pulled low, the 10µF capacitor will discharge and the unit will mute its outputs and then go into standby mode. In standby mode, the quiescent current drops to a low level. If this short is then removed, the unit powers back up and operates as normal. So CON6 can thus be used to save power when the amplifier isn’t being used and it may be under control of a microcontroller. If you don’t need this feature, you can leave the connector off and the amplifier will simply operate whenever power is available. Each power supply pin of IC1 (pins 6 & 15) has an adjacent 4.7µF ceramic bypass capacitor plus there is a 470µF electrolytic reservoir capacitor. LED1 siliconchip.com.au Features & Specifications • • • • • • • • • • • • • Supply voltage: 3.5-15V • Standby muting: 110dB Quiescent current: 40-60mA Standby current: ~0.25mA Load impedance: 4Ω or higher (see Table 1) Output power: in excess of 5W per channel, thermally limited Gain: adjustable, up to 26dB (20x) Signal-to-noise ratio: ~96dB Channel separation: ~66dB Input impedance: 10kΩ Power supply rejection ratio: ~56dB THD+N, 2 x 1W: typically 0.03% <at> 1kHz, <0.1% 100Hz-5kHz (see Figs.2 & 5) Frequency response: 20Hz-20kHz, ±1dB, typically ±0.1dB (see FIg.3) Other features: power indicator LED, standby, short circuit protection, overtemperature shut-down November 2014  83 Parts List 1 double-sided through-plated PCB, code 01109141, 39 x 63.5mm 2 switched right-angle PCB-mount RCA sockets, white & red (CON1,CON2) OR 2 2-way pin headers or polarised headers, 2.54mm pitch (CON1,CON2) 3 2-way mini terminal blocks, 5.08mm pitch (CON3-CON5) 1 10kΩ 9mm dual gang PCB-mount log pot (VR1) OR 2 10kΩ mini horizontal trimpots (VR2,VR3) 1 2-pin polarised header (optional, for standby function) 6 M3 x 6mm machine screws (for mounting) 3 M3 tapped Nylon spacers (for mounting) Semiconductors 1 TDA7266D 2x5W amplifier IC, PowerSO-20 (IC1) 1 IRFML8244 N-channel Mosfet or equivalent, SOT-23 (Q1) (element14 1857298) 1 15V 500mW zener diode, SOT23 (ZD1) (eg, BZX84-C15; element14 1826097) 1 high-brightness SMD LED, size 3216/1206* (eg, element14 2290350) OR 1 2-way pin header, 2.54mm pitch plus off-board high-brightness LED Capacitors (SMD 3216/1206* ceramic unless stated) 1 470µF 16V low-ESR electrolytic 1 10µF 16V electrolytic 6 4.7µF 25V X7R (element14 1828835) 2 1nF 50V X7R or C0G/NP0 (element14 1414658) Resistors (SMD 3216/1206*, 1/8W, 1%) 1 100kΩ (element14 9241060) 1 47kΩ (element14 9336583) 1 22kΩ (element14 9241027) 1 10kΩ (element14 513222) 1 1kΩ (element14 9240942) 2 100Ω (element14 1632521) 2 10Ω (element14 9335790) * 2012/0805 size also suitable (or an external LED connected to CON7) lights to indicate when power is applied. Mosfet Q1 provides reverse polar84  Silicon Chip Fig.2: distortion versus power with both channels driven, at four different supply voltages. This is valid for brief bursts; at higher supply voltages, the maximum power available will drop due to thermal limiting. Note that a useful amount of power is available even with a supply below 5V DC. Fig.3: the frequency response is very flat above 100Hz. Below that, there is a small amount of bass cut or boost depending on the position of the volume pot(s). This is due to their varying source impedance interacting with IC1’s somewhat reactive input impedance. The effect is not very noticeable. ity protection. The supply voltage is fed in via CON3 and if the polarity is correct, Q1’s gate is pulled up via the 100kΩ resistor, switching it on and making the connection between IC1’s ground and pin 1 of CON3. 15V zener diode ZD1 protects Q1’s gate from high-voltage supply spikes. If the supply is connected the wrong way around though, Q1’s gate is pulled below its source and thus Q1 is off and no supply current can flow. Again, ZD1 protects Q1’s gate from going too far negative. Speaker load & power The Mini Stereo Amplifier can drive speakers of 4-16Ω. However, power is limited at higher supply voltages with lower speaker impedances due to the lower efficiency under these conditions. Table 1 shows the maximum voltage for each typical speaker impedance before there is a risk of thermal shutdown at higher power levels. Maximum contiuous power is available at the upper voltage specified, ie, best power into 8Ω is available at around 9.5V. Under these conditions, it will deliver 2 x 5W at 10% THD+N or 2 x 4W at 1% THD+N. Note that there is nothing stopping you from running the unit from a higher voltage than shown in Table 1 but if you drive it hard, it could oversiliconchip.com.au LEFT IN 10 µF 4.7 µF 1k CON6 22k + A 4.7 µF 100k k LED1 4.7 µF CON3 POWER CON2 (VR3) 4.7 µF Q1 470 µF + RIGHT IN RIGHT SPKR + 10Ω LEFT SPKR IC1 TDA7266D – 1nF (VR2) 4.7 µF10k 100Ω STANDBY CON4 + – 10Ω 100Ω 1nF 1 VR1 + 47k 4.7 µF CON1 CON5 ZD1 15V Fig.4: install the parts on the PCB as shown here. Most of the parts are SMDs and the procedure for installing them is described in the text. Be sure to fit IC1 and the two electrolytic capacitors with the correct polarity. Table 1 Load Impedance 4Ω 6Ω 8Ω 16Ω Supply Voltage 3.6-6.5V 3.6-8.5V 4-9.5V 6-14V heat and shut down briefly. Normal operation will resume once the chip has cooled. The IC can typically dissipate 5W total before its die reaches 150°C and it shuts down. Construction The amplifier is built on a doublesided PCB coded 01109141 (39 x 63.5mm). Most of the components are SMDs but there are a few through-hole parts involved too. Fig.4 shows the assembly details. Start by fitting IC1, the amplifier chip. Because it’s relatively large and the board is its heatsink, you will need a relatively powerful (and/or hot) iron to do this. The simplest technique involves little more than a typical soldering iron and some flux paste. First, tin the large mounting pad on the PCB with a thin layer of solder. Spreading a little flux paste on this pad before adding solder will help spread it out. Keep the solder thin and even; if you add too much, remove the excess using some solder wick (again, flux paste helps). Once you’re happy with that, tin the underside of the IC in the same manner. You may need to hold it in some sort of clamp or vice while doing so. Then spread a little flux paste on the tinned PCB pad and place the IC on top, ensuring that its orientation is correct, ie, the notched corner (pin 1) is in the upper-right corner, near the siliconchip.com.au Fig.5: distortion versus frequency at 1W with both channels driven into 8-ohm loads. This is similar to the curve shown in the TDA7266D data sheet. The distortion is mostly due to crossover artefacts. dot on the PCB overlay. Push it down to make sure it’s in intimate contact with the board. Line the IC up with its pads, place a dab of flux paste on one of the pins, then put a little solder on the tip of your soldering iron and touch the pin gently, without disturbing the IC. The flux paste should help “suck” the solder onto that pin and pad. Check the IC alignment and if necessary, reheat the joint and gently nudge it into place. Once the alignment is good, use the same technique to solder the diagonally opposite pin. It’s then simply a matter of heating the main tab under the IC until the two layers of solder melt and solidify into a single mass. Make sure the board is on a heat-resistant surface, then place the soldering iron tip on one of the exposed pads at either end of the IC and melt some solder wire in, to “wet” the joint and help transfer heat. Hold the iron in place until you see a puff of vapour from the liquefying flux under the IC and the solder at the opposite end of the thermal pad re-flows. Note that this procedure could take continued on page 101 November 2014  85 As most Australian and New Zealand readers know, there has been a huge shift in the television landscape with the move to digital and the subsequent closure of the analog service. You may think that the disruption is over . . . but think again! There is more to come – and it has the potential to severely impact TV viewers around Australia and New Zealand. W ith the closure of the analog TV service in Australia and the “digital restack” most of the TV channels numbered 52 to 69 (695-820MHz) have become unoccupied. And as we saw in September 2014 SILICON CHIP, there are many thousands of low-power audio devices, mainly wireless microphones, which also currently use this band and will have to vacate by January 1 2015. As a result of the restack, the Commonwealth Government agency ACMA was able to sell this spectrum (plus 140MHz in the 2.5GHz band) for almost $2 billion, which represented a significant windfall to the government. In fact, the Government refers to this as the “digital dividend”. The intended use for this spectrum is mobile broadband using 4G/LTE technology in the new 700MHz band. This should not be confused with the existing 4G service in the 2.5GHz band. Australia is not alone in reaping benefits from the move to digital – the New Zealand Government sold a similar spectrum for $NZ270 million to TelecomNZ, Vodaphone and 2degrees. The restack Mobile broadband and TV services cannot easily share the same portion of a spectrum as the risk of mutual interference is too high. Fig.1: this is the Australian 4G/LTE frequency allocation – it shows where your old television frequencies have been reallocated to. The winners here are the growing mobile data services. 86  Silicon Chip siliconchip.com.au BLOCK A Band 3 (VHF high) BLOCK B Band 4 (UHF) BLOCK C Band 4 (UHF) BLOCK D Band 5 (UHF) Channel 6 Channel 28 Channel 34 Channel 40 Channel 7 Channel 29 Channel 35 Channel 41 Channel 8 Channel 30 Channel 36 Channel 42 Channel 10 Channel 31 Channel 37 Channel 43 Channel 11 Channel 32 Channel 38 Channel 44 Channel 12 Channel 33 Channel 39 Channel 45 Frequency range(s) used on a specific transmitter site 174-195MHz* & 209-230MHz* 526-568MHz 568-610MHz 610-652MHz BLOCK E Band 5 (UHF) Channel 46 Channel 47 Channel 48 Channel 49 Channel 50 Channel 51 652-694MHz *195-209MHz (“Channel 9 & 9A”) reserved for DAB+ Digital Radio [capital cities at present] Fig.2: in the restack, Australian RF channels are regrouped into similar frequencies sharing the one tower. In addition all transmitting antennas on an individual site will have the same polarisation, either horizontal or vertical. As a consequence the Commonwealth Government committed $170 million (including advertising) to restack 1500 transmitters in 440 sites, with the restack scheduled for completion by the end of this year. When the analog TV spectrum was laid out many years ago provision was made for a vacant analog channel to be placed either side of a transmitter channel in any one viewing area to prevent mutual interference. Fortunately this is not required for digital TV, which is one of the reasons why digital is more efficient in its use of the spectrum. The restack has allocated all transmissions for a given coverage area to a sequential block of channels. The advantages of this are simpler receiving antenna design, with improved performance. On any one site, the transmitter for each of the five networks is allocated an RF channel from one of the blocks listed in Fig.2 and a 6th channel (a spare) is left unallocated. Note that there are some exceptions – eg, NSW Central Coast & Queensland Gold Coast. They are exceptions because they have nine channel allocations and eight active transmitters on each site, because of overlapping licence areas. The other exception is community TV. However, the Minister for Communications recently announced (on September 10) that Community Television, currently located in mainland state capitals using Block B, would cease transmission as free-to-air services on December 31, 2015 and become solely internet-based. At the time of writing, the various community TV stations were lobbying heavily to have this decision siliconchip.com.au overturned so they could remain on air, using the spare channel which the Minister maintains is necessary for “testing”. Radio frequency channels vs logical channel numbers In the above discussion the channels referred to are radio frequency transmission channels, not the “TV channels” or “logical channel number” which are what the user selects. When a digital TV or set-top-box is being set up it will search through the radio frequency transmission channels starting from RF channel 6. When a signal is received, the logical channel numbers (or “TV channel numbers”) will be stored as labels associated with the radio frequency channel on which they were found. These logical channel numbers (LCN) are transmitted along with the electronic program guide and the actual program material. It is the LCN that the viewer selects to view a program. This means that the viewer selects programs by a network number and not the frequency used by the TV tuner. As an example, in Perth the ABC transmits the same four programs on RF channels 12, 29, 41, 47 and 49. However all viewers select programs based on logical channel numbers of 2, 21, 22, 23, etc regardless of the RF channel being used. New Zealand uses European RF channel numbers, so be careful when comparing them to Australian channel numbers. A similar restack has been used in Europe with blocks of eight RF channels, of which two cannot be used because of potential interference. As part of their restack Europe is selling European channels 57 – 64. In New Zealand most free to air transmitters are on either European channels 32, 34, 36 or 33, 35, 37 with all antennas on any one site using the same polarisation. 4G/LTE – and what it means to you Earlier we mentioned that the broadband mobile service will use the newly-vacated TV channels (and 2.5GHz bands) for providing 4G or LTE (Long-Term Evolution) mobile broadband services to devices like tablets and mobile phones. These are marketing names being used by the wireless broadband companies. Fig.3: frequencies used by USA, Australia, New Zealand and Europe for TV and mobile broadband. The Americas and parts of East Asia use the same 700MHz 4G/LTE band as Australia. November 2014  87 With rare exceptions, not only are combined VHF/UHF antenna not required any more, they are actually likely to cause interference to digital TV reception. If you’re in a capital city (VHF TV only), the UHF section could pick up 4G/LTE signals; if you’re in a country area (mostly UHF TV) the VHF section could pick up a range of unwanted RF. Use the chart opposite to select the right antenna. The amount of interference that may be generated between 4G/LTE transmitters and normal TV receivers is determined by the design of the equipment including the TV antenna, cabling and the receiver. Another factor is the width of the guard band provided by ACMA. This band, at 698.5MHz, separates TV services using frequencies below 694MHz from 4G/LTE using frequencies above 703MHz (inclusive). New Zealand has a similar cut-off frequency. Many TV antennas currently on the Australian market are designed to receive RF channels 52-69 along with other channels. This includes old VHF/ UHF antennas and some new band three/UHF “digital” antennas as well as some UHF-only antennas. As a result they will be sensitive to the 4G/LTE transmissions and could therefore make the interference created by this service even worse. Tests have been done to assess the interference to 4G/LTE service by TV transmitters. However no known tests have been done to assess the interference to TV by 4G/LTE! Interference can happen if the TV antenna is close to the device using 4G/LTE or if a mobile phone tower is between the TV antenna and the TV transmitter. The effect is that whenever the tablet or the mobile phone transmits, the TV reception can break up or freeze – and/or the sound can be disrupted. VHF/UHF transmissions to cease nationally Once Community TV stations in 88  Silicon Chip mainland capitals cease transmission on UHF, only a handful of areas may need a VHF/UHF antenna – a few areas where both bands will continue to be used. Therefore, a much cheaper Band-3-only (VHF) design will suffice and should suffer no (or minimal) interference from 4G/LTE. Caveat Emptor – let the buyer beware The first issue for consumers is that imported antennas are often designed for Europe and even the newer designs labelled “LTE” provide no protection from Australian or New Zealand wireless broadband. Also, these antennas often contain a 790MHz low pass filter, which is not much use in Australia/NZ. A second issue is that most of the antennas available from Australian manufacturers are designed to receive up to channel 69 which makes them sensitive to 4G/LTE transmissions. The final issue is that masthead and wideband distribution amplifiers are particularly susceptible to interference from 4G/LTE signals, so they need to contain a 698MHz low-pass filter to remove these signals. For example, the Kingray Edge series and Johansson 4GP series of masthead amplifiers contain the necessary filters. Reducing interference So, what can you do? For a start the TV antenna that you are using should be designed to receive only the channels of the transmitter site for your viewing area. This will maximise the TV signal and minimise interference. This particularly applies to weak signal areas using RF channel 51 such as Newcastle, Illawarra, SW Slopes/E. Riverina NSW, Southern Downs Qld, Murray Valley, Nhill, Geelong Vic, NE Tasmania. Low-powered translators using channel 51 in 154 towns and suburbs around Australia are also susceptible. To determine the RF channels used in your area you should go to http:// myswitch.digitalready.gov.au/ and enter your street address. Click on ‘Channels for…’ and scroll down to ‘Technical information for…’ The RF transmission channels that your antenna will be required to receive will be shown there. The panel opposite titled “Suitable TV Antenna Designs” will then provide you with details of the antenna suited to your location. If a masthead amplifier is required it should not amplify signals outside the range of band 3 (174-230MHz) and UHF (526-694MHz). For New Zealande readers the range is the European channels 26-47 (510686MHz). Existing installations which are suffering from interference and do not contain an amplifier can be improved by inserting a filter at the input to the receiver as illustrated below. This low pass filter will reduce the 4G/LTE signal to just 1/316 of its original power (-25 dB). FROM A NONAMPLIFIED TV ANTENNA TO TV RECEIVER This technique will not work for antennas which contain an amplifier (ie, an antenna that uses a power pack) such as those used on caravans, boats, flat outside and indoor antennas. This is because the filter must precede any amplification. As a further issue the locations used by these antennas often have mobile broadband devices close to the antenna. People who receive their signal via a Master Antenna Television system (usually large apartment blocks, hotels etc) will require a qualified antenna installer to locate and rectify any issues. Finally, a corroded antenna is a potent source of trouble, so any old antenna should be replaced as a matter of course. Antenna installers You need to be careful when accepting the advice of an antenna installer. siliconchip.com.au They may not have kept up with recent changes and you could end up with an inappropriate antenna based on what they have used in the past. For example, there are still people installing the large and expensive antennas required for analog channel 2 – despite the fact that the last channel 2 signal was switched off in December 2013! Antenna installers are not required to have any training in antenna selection and unfortunately the endorsement scheme used in Australia has been dismantled by the Department of Communications. There is a new version of the Australian Standard AS1417-2014 Receiving Antennas for Radio and Television in the VHF and UHF band due to be published soon but there is no compulsion for the industry to use it. As a consequence you are on your own when selecting a qualified installer. SUITABLE TV ANTENNA DESIGNS These diagrams will help you identify the various types of TV antenna discussed in the article. The difference between the antennas for a particular polarisation is the element length and spacing which in turn is determined by the frequency or channel number STRONG SIGNAL AREA: AREA: Dark Green on http://myswitch.digitalready.gov.au/ Antenna suppliers Antenna manufacturers and importers also have an important role to play. They need to supply the industry with antennas designed for the unique technical characteristics of the Australian and New Zealand market. This will reduce the chance of an installer using an inappropriate antenna. This means that suppliers should: • Not sell antennas designed to receive any channel lower than channel 6 or higher than channel 51 (European channel 48). • Discontinue VHF/UHF combination antennas or cross polarised antennas (by the end of this year all transmitters on a site will have the same polarisation). • Not sell UHF log periodic antennas. Most of these are not required because of their wide frequency range and lack of sensitivity. As a minimum, any antenna designed for block E should contain a 698MHz low pass filter in the balun box. Marine and caravan antennas as well as amplified indoor antennas need to have 174-230 and 526-694MHz filters installed internally between the antenna and the amplifier. Existing broadband antennas typically quoted as being able to receiving channels 0- 69 will produce unreliable reception and could cost much more than the right antenna for your area. siliconchip.com.au   Total Dipole length (mm) Gain (dbi) Horizontal Polarisation Vertical Polarisation Block A 740 Block B 273 Block C 254 Block D 237 Block E 222 7 Yagi 10 Yagi 10 Yagi 11 Yagi 11 Yagi Phased Array Phased Array Phased Array Phased Array Phased Array MEDIUM SIGNAL AREA: Light Green on http://myswitch.digitalready.gov.au/ Block A Block B Block C Block D Block E Total Dipole length (mm) Gain (dbi) Horizontal Polarisation Vertical Polarisation 740 273 254 237 222 8 Yagi 11 Yagi 11 Yagi 12 Yagi 12 Yagi Phased Array Phased Array Phased Array Phased Array Phased Array FRINGE AREA: Orange on http://myswitch.digitalready.gov.au/ Block A Block B Block C Block D Total Dipole length (mm) Gain (dBi) Horizontal Polarisation Vertical Polarisation 740 273 254 237 Block E 222 >10 Phased Array Yagi >13 Phased Array Yagi >13 Phased Array Yagi >14 Phased Array Yagi >14 Phased Array Yagi Exceptions to above table: • Gosford NSW and Gold Coast Qld requires blocks D and E to be horizontally polarised. • Bouddi and Wyong NSW require blocks D and E to be vertically polarised. • Currumbin and Gold Coast Southern Hinterland Qld require a unique antenna for channels 34, 35, 36, 37, 38, 39, 49, 50 with vertical polarisation. • Remote area towns (excluding WA) receiving Imparja and Southern Cross Television from a local transmitter generally require a Block A antenna for the ABC transmitter out of town and another antenna pointed in town in a different channel block. A UHF/ VHF diplexer can connect the antenna cables together to feed the receiver. SC November 2014  89 SILICON CHIP .com.au/shop ONLINESHOP Looking for a specialised component to build that latest and greatest SILICON CHIP project? Maybe it’s the PCB you’re after. Or a pre-programmed micro. Or some other hard-to-get “bit”. The chances are they are available direct from the SILICON CHIP ONLINESHOP. As a service to readers, SILICON CHIP has established the ONLINESHOP. No, we’re not going into opposition with your normal suppliers – this is a direct response to requests from readers who have found difficulty in obtaining specialised parts such as PCBs & micros. • • • • • PCBs are normally IN STOCK and ready for despatch when that month’s magazine goes on sale (you don’t have to wait for them to be made!). Even if stock runs out (eg, for high demand), in most cases there will be no longer than a two-week wait. One low p&p charge: $10 per order, regardless of how many boards or micros you order! (Australia only; overseas clients – email us for a postage quote). Our PCBs are beautifully made, very high quality fibreglass boards with pre-tinned tracks, silk screen overlays and where applicable, solder masks. Best of all, those boards with fancy cut-outs or edges are already cut out to the SILICON CHIP specifications – no messy blade work required! HERE’S HOW TO ORDER: 4 Via the INTERNET (24 hours, 7 days) Log on to our secure website: siliconchip.com.au, click on “SHOP” and follow the links. 4 Via EMAIL (24 hours, 7 days) email silicon<at>siliconchip.com.au – Clearly tell us what you want and include your contact and credit card details 4 Via FAX (24 hours, 7 days) (02) 9939 2648 (INT: 612 9939 2648). Clearly tell us what you want and include your contact and credit card details 4 Via MAIL (24 hours, 7 days) PO Box 139, Collaroy NSW 2097. Clearly tell us what you want and include your contact and credit card details 4 Via PHONE (9am-5pm, Mon-Fri) Call (02) 9939 3295 (INT 612 9939 3295) – have your order ready, including contact and credit card details! YES! You can also order or renew your PRE-PROGRAMMED MICROS SILICON CHIP subscription via any of these methods as well! Price for any of these micros is just $15.00 each + $10 p&p per order# As a service to readers, SILICON CHIP ONLINESHOP stocks microcontrollers and microprocessors used in new projects (from 2012 on) and some selected older projects – pre-programmed and ready to fly! Some micros from copyrighted and/or contributed projects may not be available. PIC12F675-I/P PIC16F1507-I/P PIC16F88-E/P PIC16F88-I/P PIC16LF88-I/P PIC16LF88-I/SO PIC16F877A-I/P PIC18F2550-I/SP PIC18F45K80 PIC18F4550-I/P PIC18F14K50 UHF Remote Switch (Jan09), Ultrasonic Cleaner (Aug10), Ultrasonic Anti-fouling (Sep10), Cricket/Frog (Jun12) Do Not Disturb (May13) IR-to-UHF Converter (Jul13), UHF-to-IR Converter (Jul13) PC Birdies *2 chips – $15 pair* (Aug13) Wideband Oxygen Sensor (Jun-Jul12) Hi Energy Ignition (Nov/Dec12), Speedo Corrector (Sept13), Auto Headlight Controller (Oct13) 10A 230V Motor Speed Controller (Feb14) Projector Speed (Apr11), Vox (Jun11), Ultrasonic Water Tank Level (Sep11), Quizzical (Oct11) Ultra LD Preamp (Nov11), 10-Channel Remote Control Receiver (Jun13), Revised 10-Channel Remote Control Receiver (Jul13), Nicad/NiMH Burp Charger (Mar14) (NEW): Remote Mains Timer (Nov14) Garbage Reminder (Jan13), Bellbird (Dec13) LED Ladybird (Apr13) 6-Digit GPS Clock (May-Jun09), Lab Digital Pot (Jul10) Semtest (Feb-May12) Batt Capacity Meter (Jun09), Intelligent Fan Controller (Jul10) USB Power Monitor (Dec12) GPS Car Computer (Jan10), GPS Boat Computer (Oct10) USB MIDIMate (Oct11) USB Data Logger (Dec10-Feb11) Digital Spirit Level (Aug11), G-Force Meter (Nov11) Intelligent Dimmer (Apr09) Maximite (Mar11), miniMaximite (Nov11), Colour Maximite (Sept/Oct12), Touchscreen Audio Recorder (Jun/Jul 14) PIC32MX150F128D-501P/T 44-pin Micromite (Aug14) (NEW!) PIC32MX250F128B-50I/SP Micromite (May14) – also includes FREE 47F tantalum capacitor PIC32MX250F128B-I/SP GPS Tracker (Nov13) Micromite ASCII Video Terminal (Jul14) PIC32MX470F512H-I/PT Stereo Audio Delay/DSP (Nov13), Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) dsPIC33FJ128GP802-I/SP Digital Audio Signal Generator (Mar-May10), Digital Lighting Controller (Oct-Dec10), SportSync (May11), Digital Audio Delay (Dec11) Level (Sep11) Quizzical (Oct11), Ultra-LD Preamp (Nov11), LED Musicolor (Nov12) dsPIC33FJ64MC802-E/P Induction Motor Speed Controller (revised) (Aug13) dsPIC33FJ128GP306-I/PT CLASSiC DAC (Feb-May 13) ATTiny861 VVA Thermometer/Thermostat (Mar10), Rudder Position Indicator (Jul11) ATTiny2313 Remote-Controlled Timer (Aug10) ATMega48-20AU Stereo DAC (Sep-Nov09), RGB LED Strip Driver [-20AU chip] (May14) PIC18F27J53-I/SP PIC18LF14K22 PIC18F1320-I/SO PIC32MX795F512H-80I/PT When ordering, be sure to nominate BOTH the micro required AND the project for which it must be programmed. SPECIALISED COMPONENTS, SHORT-FORM KITS, ETC NEW: ONE-CHIP AMPLIFIER - SMD parts (Nov 14) DIGITAL EFFECTS UNIT WM8371 DAC IC & SMD Capacitors [Same components also suit Stereo Echo & Reverb, Feb14 & Dual Channel Audio Delay Nov 14] (Oct14) AD8038ARZ Video Amplifier ICs (SMD) For Active Differential Probe (Pack of 3) $15.00 $25.00 (Sept 2014) $12.50 (Aug14) $35.00 (May14) $5.00 does not include micro (see above) nor parts listed as “optional” (May14) $20.00 HYBRID BENCH SUPPLY- all SMD parts, 3 x BCM856DS & L2/L3 (May 14) $45.00 USB/RS232C ADAPTOR MCP2200 USB/Serial converter IC NICAD/NIMH BURP CHARGER (Apr14) $7.50 (Mar14) 1 SPD15P10 P-channel logic Mosfet & 1 IPP230N06L3 N-channel logic Mosfet $7.50 10A 230V AC MOTOR SPEED CONTROLLER (Feb14) $45.00 GPS Tracker MCP16301 SMD regulator IC and 15H inductor SiDRADIO - SMD parts RF Probe All SMD parts (Nov13) $5.00 (Oct13) $20.00 (Aug13) Same as LF-UF Upconverter parts but includes 5V relay and BF998 dual-gate Mosfet. $5.00 44-PIN MICROMITE Complete kit inc PCB, micro etc MAINS FAN SPEED CONTROLLER - AOT11N60L 600V Mosfet RGB LED STRIP DRIVER - all SMD parts and BSO150N03 Mosfets, 40A IGBT, 30A Fast Recovery Diode, IR2125 Driver and NTC Thermistor P&P: FLAT RATE $10.00 PER ORDER# PCBs, COMPONENTS ETC MAY BE COMBINED (in one order) FOR $10-PER-ORDER P&P RATE LF-HF Up-converter Omron G5V-1 5V SPDT 5V relay (Jun13) $2.00 “LUMP IN COAX” MINI MIXER SMD parts kit: (Jun13) $20.00 Includes: 2 x OPA4348AID, 1 x BQ2057CSN, 2 x DMP2215L, 1 x BAT54S, 1 x 0.22Ω shunt LF-HF UP-CONVERTER SMD parts kit: (Jun13) $15.00 Includes: FXO-HC536R-125 and SA602AD and all SMD passive components CLASSiC DAC Semi kit – Includes three hard-to-get SMD ICs: (Feb-May13) $45.00 CS8416-CZZ, CS4398-CZZ and PLL1708DBQ plus an accurate 27MHz crystal and ten 3mm blue LEDs with diffused lenses ISL9V5036P3 IGBT Used in high energy ignition and Jacob’s Ladder(Nov/Dec12, Feb13) $10.00 2.5GHz Frequency Counter (Dec12/Jan13) LED Kit: 3 x 4-digit blue LED displays $15.00 MMC & Choke Kit: ERA-2SM+ Wideband MMC and ADCH-80+ Wideband Choke $15.00 ZXCT1009 Current Shunt Monitor IC As used in DCC Reverse Loop Controller/Block Switch (Pack of 2) (Oct12) $5.00 G-FORCE METER/ACCELEROMETER OR DIGITAL SPIRIT LEVEL Short form kit          (Aug11/Nov11) $44.50 $40.00 (contains PCB (04108111), programmed PIC micro, MMA8451Q accelerometer chip and 4 Mosfets) IPP230N06L3 N-Channel logic level Mosfets As used in a variety of SILICON CHIP Projects (Pack of 2) $7.50 JST CONNECTOR LEAD            (Jan12)   2-WAY $3.45 3-WAY $4.50 *All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars and included GST where applicable. # P&P prices are within Australia. O’seas? Please email for a quote LOOKING FOR TECHNICAL BOOKS? YOU’LL FIND THE COMPLETE LISTING OF ALL BOOKS AVAILABLE IN THE SILICON CHIP ONLINE BOOKSTORE – ON THE “BOOKS & DVDs” PAGES OF OUR WEBSITE 11/14 PRINTED CIRCUIT BOARDS PRINTED CIRCUIT BOARD TO SUIT PROJECT: PUBLISHED: NOTE: These listings are for the PCB only – not a full kit. If you want a kit, contact the kit suppliers advertising in this issue. PCB CODE: Price: 12V SPEED CONTROLLER/DIMMER (Use Hot Wire Cutter PCB from Dec 2010 [18112101]) USB-SENSING MAINS POWER SWITCH JAN 2009 10101091 $45.00 DIGITAL AUDIO MILLIVOLTMETER MAR 2009 04103091 $35.00 INTELLIGENT REMOTE-CONTROLLED DIMMER APR 2009 10104091 $10.00 INPUT ATTENUATOR FOR DIG. AUDIO M’VOLTMETER MAY 2009 04205091 $10.00 6-DIGIT GPS CLOCK MAY 2009 04105091 $30.00 6-DIGIT GPS CLOCK DRIVER JUNE 2009 07106091 $20.00 UHF ROLLING CODE TX AUG 2009 15008091 $10.00 UHF ROLLING CODE RECEIVER AUG 2009 15008092 $45.00 6-DIGIT GPS CLOCK AUTODIM ADD-ON SEPT 2009 04208091 $5.00 STEREO DAC BALANCED OUTPUT BOARD JAN 2010 01101101 $25.00 DIGITAL INSULATION METER JUN 2010 04106101 $25.00 ELECTROLYTIC CAPACITOR REFORMER AUG 2010 04108101 $40.00 ULTRASONIC ANTI-FOULING FOR BOATS SEP 2010 04109101 $25.00 HEARING LOOP RECEIVER SEP 2010 01209101 $25.00 S/PDIF/COAX TO TOSLINK CONVERTER OCT 2010 01210101 $10.00 TOSLINK TO S/PDIF/COAX CONVERTER OCT 2010 01210102 $10.00 DIGITAL LIGHTING CONTROLLER MASTER UNIT OCT 2010 16110101 $10.00 DIGITAL LIGHTING CONTROLLER SLAVE UNIT OCT 2010 16110102 $25.00 HEARING LOOP TESTER/LEVEL METER NOV 2010 01111101 $25.00 UNIVERSAL USB DATA LOGGER DEC 2010 04112101 $25.00 HOT WIRE CUTTER CONTROLLER DEC 2010 18112101 $10.00 433MHZ SNIFFER JAN 2011 06101111 $10.00 CRANIAL ELECTRICAL STIMULATION JAN 2011 99101111 $25.00 HEARING LOOP SIGNAL CONDITIONER JAN 2011 01101111 $25.00 LED DAZZLER FEB 2011 16102111 $15.00 12/24V 3-STAGE MPPT SOLAR CHARGER FEB 2011 14102111 $15.00 SIMPLE CHEAP 433MHZ LOCATOR FEB 2011 06102111 $5.00 THE MAXIMITE MAR 2011 06103111 $15.00 UNIVERSAL VOLTAGE REGULATOR MAR 2011 18103111 $10.00 12V 20-120W SOLAR PANEL SIMULATOR MAR 2011 04103111 $10.00 MICROPHONE NECK LOOP COUPLER MAR 2011 01209101 $25.00 PORTABLE STEREO HEADPHONE AMP APRIL 2011 01104111 $10.00 CHEAP 100V SPEAKER/LINE CHECKER APRIL 2011 04104111 $10.00 PROJECTOR SPEED CONTROLLER APRIL 2011 13104111 $10.00 SPORTSYNC AUDIO DELAY MAY 2011 01105111 $30.00 100W DC-DC CONVERTER MAY 2011 11105111 $15.00 PHONE LINE POLARITY CHECKER MAY 2011 12105111 $10.00 20A 12/24V DC MOTOR SPEED CONTROLLER MK2 JUNE 2011 11106111 $15.00 USB STEREO RECORD/PLAYBACK JUNE 2011 07106111 $20.00 VERSATIMER/SWITCH JUNE 2011 19106111 $25.00 USB BREAKOUT BOX JUNE 2011 04106111 $10.00 ULTRA-LD MK3 200W AMP MODULE JULY 2011 01107111 $25.00 PORTABLE LIGHTNING DETECTOR JULY 2011 04107111 $15.00 RUDDER INDICATOR FOR POWER BOATS (4 PCBs) JULY 2011 20107111-4 $80 per set VOX JULY 2011 01207111 $20.00 ELECTRONIC STETHOSCOPE AUG 2011 01108111 $10.00 DIGITAL SPIRIT LEVEL/INCLINOMETER AUG 2011 04108111 $10.00 ULTRASONIC WATER TANK METER SEP 2011 04109111 $15.00 ULTRA-LD MK2 AMPLIFIER UPGRADE SEP 2011 01209111 $5.00 ULTRA-LD MK3 AMPLIFIER POWER SUPPLY SEP 2011 01109111 $25.00 HIFI STEREO HEADPHONE AMPLIFIER SEP 2011 01309111 $20.00 GPS FREQUENCY REFERENCE (IMPROVED) SEP 2011 04103073 $15.00 GPS FREQUENCY REFERENCE DISPLAY (B) SEP 2011 04103072 $15.00 HEARING LOOP RECEIVER/NECK COUPLER SEP 2011 01209101 $10.00 DIGITAL LIGHTING CONTROLLER LED SLAVE OCT 2011 16110111 $30.00 USB MIDIMATE OCT 2011 23110111 $25.00 QUIZZICAL QUIZ GAME OCT 2011 08110111 $25.00 ULTRA-LD MK3 PREAMP & REMOTE VOL CONTROL NOV 2011 01111111 $30.00 ULTRA-LD MK3 INPUT SWITCHING MODULE NOV 2011 01111112 $20.00 ULTRA-LD MK3 SWITCH MODULE NOV 2011 01111113 $10.00 ZENER DIODE TESTER NOV 2011 04111111 $20.00 MINIMAXIMITE NOV 2011 07111111 $10.00 ADJUSTABLE REGULATED POWER SUPPLY DEC 2011 18112111 $5.00 DIGITAL AUDIO DELAY DEC 2011 01212111 $25.00 DIGITAL AUDIO DELAY Front & Rear Panels DEC 2011 01212112/3 $20 per set AM RADIO JAN 2012 06101121 $10.00 STEREO AUDIO COMPRESSOR JAN 2012 01201121 $30.00 STEREO AUDIO COMPRESSOR FRONT & REAR PANELS JAN 2012 0120112P1/2 $20.00 3-INPUT AUDIO SELECTOR (SET OF 2 BOARDS) JAN 2012 01101121/2 $30 per set CRYSTAL DAC FEB 2012 01102121 $20.00 SWITCHING REGULATOR FEB 2012 18102121 $5.00 SEMTEST LOWER BOARD MAR 2012 04103121 $40.00 SEMTEST FRONT PANEL MAR 2012 04103123 $75.00 INTERPLANETARY VOICE MAR 2012 08102121 $10.00 12/24V 3-STAGE MPPT SOLAR CHARGER REV.A MAR 2012 14102112 $20.00 SOFT START SUPPRESSOR APR 2012 10104121 $10.00 RESISTANCE DECADE BOX APR 2012 04104121 $20.00 RESISTANCE DECADE BOX PANEL/LID APR 2012 04104122 $20.00 1.5kW INDUCTION MOTOR SPEED CONT. (New V2 PCB) APR (DEC) 2012 10105122 $35.00 HIGH TEMPERATURE THERMOMETER MAIN PCB MAY 2012 21105121 $30.00 HIGH TEMPERATURE THERMOMETER Front & Rear Panels MAY 2012 21105122/3 $20 per set MIX-IT! 4 CHANNEL MIXER JUNE 2012 01106121 $20.00 PIC/AVR PROGRAMMING ADAPTOR BOARD JUNE 2012 24105121 $30.00 CRAZY CRICKET/FREAKY FROG JUNE 2012 08109121 $10.00 CAPACITANCE DECADE BOX JULY 2012 04106121 $20.00 CAPACITANCE DECADE BOX PANEL/LID JULY 2012 04106122 $20.00 WIDEBAND OXYGEN CONTROLLER MK2 JULY 2012 05106121 $20.00 PRINTED CIRCUIT BOARD TO SUIT PROJECT: PUBLISHED: PCB CODE: Price: WIDEBAND OXYGEN CONTROLLER MK2 DISPLAY BOARD JULY 2012 05106122 $10.00 SOFT STARTER FOR POWER TOOLS JULY 2012 10107121 $10.00 DRIVEWAY SENTRY MK2 AUG 2012 03107121 $15.00 MAINS TIMER AUG 2012 10108121 $10.00 CURRENT ADAPTOR FOR SCOPES AND DMMS AUG 2012 04108121 $20.00 USB VIRTUAL INSTRUMENT INTERFACE SEPT 2012 24109121 $25.00 USB VIRTUAL INSTRUMENT INT. FRONT PANEL SEPT 2012 24109122 $25.00 BARKING DOG BLASTER SEPT 2012 25108121 $20.00 COLOUR MAXIMITE SEPT 2012 07109121 $20.00 SOUND EFFECTS GENERATOR SEPT 2012 09109121 $10.00 NICK-OFF PROXIMITY ALARM OCT 2012 03110121 $5.00 DCC REVERSE LOOP CONTROLLER OCT 2012 09110121 $10.00 LED MUSICOLOUR NOV 2012 16110121 $25.00 LED MUSICOLOUR Front & Rear Panels NOV 2012 16110121 $20.00/set CLASSIC-D CLASS D AMPLIFIER MODULE NOV 2012 01108121 $30.00 CLASSIC-D 2 CHANNEL SPEAKER PROTECTOR NOV 2012 01108122 $10.00 HIGH ENERGY ELECTRONIC IGNITION SYSTEM DEC 2012 05110121 $10.00 USB POWER MONITOR DEC 2012 04109121 $10.00 1.5kW INDUCTION MOTOR SPEED CONTROLLER (NEW V2 PCB)DEC 2012 10105122 $35.00 THE CHAMPION PREAMP and 7W AUDIO AMP (one PCB) JAN 2013 01109121/2 $10.00 GARBAGE/RECYCLING BIN REMINDER JAN 2013 19111121 $10.00 2.5GHz DIGITAL FREQUENCY METER – MAIN BOARD JAN 2013 04111121 $35.00 2.5GHz DIGITAL FREQUENCY METER – DISPLAY BOARD JAN 2013 04111122 $15.00 2.5GHz DIGITAL FREQUENCY METER – FRONT PANEL JAN 2013 04111123 $45.00 SEISMOGRAPH MK2 FEB 2013 21102131 $20.00 MOBILE PHONE RING EXTENDER FEB 2013 12110121 $10.00 GPS 1PPS TIMEBASE FEB 2013 04103131 $10.00 LED TORCH DRIVER MAR 2013 16102131 $5.00 CLASSiC DAC MAIN PCB APR 2013 01102131 $30.00 CLASSiC DAC FRONT & REAR PANEL PCBs APR 2013 01102132/3 $25.00 GPS USB TIMEBASE APR 2013 04104131 $15.00 LED LADYBIRD APR 2013 08103131 $5.00 CLASSiC-D 12V to ±35V DC/DC CONVERTER MAY 2013 11104131 $15.00 DO NOT DISTURB MAY 2013 12104131 $10.00 LF/HF UP-CONVERTER JUN 2013 07106131 $10.00 10-CHANNEL REMOTE CONTROL RECEIVER JUN 2013 15106131 $15.00 IR-TO-455MHZ UHF TRANSCEIVER JUN 2013 15106132 $7.50 “LUMP IN COAX” PORTABLE MIXER JUN 2013 01106131 $15.00 L’IL PULSER MKII TRAIN CONTROLLER JULY 2013 09107131 $15.00 L’IL PULSER MKII FRONT & REAR PANELS JULY 2013 09107132/3 $20.00/set REVISED 10 CHANNEL REMOTE CONTROL RECEIVER JULY 2013 15106133 $15.00 INFRARED TO UHF CONVERTER JULY 2013 15107131 $5.00 UHF TO INFRARED CONVERTER JULY 2013 15107132 $10.00 IPOD CHARGER AUG 2013 14108131 $5.00 PC BIRDIES AUG 2013 08104131 $10.00 RF DETECTOR PROBE FOR DMMs AUG 2013 04107131 $10.00 BATTERY LIFESAVER SEPT 2013 11108131 $4.00 SPEEDO CORRECTOR SEPT 2013 05109131 $10.00 SiDRADIO (INTEGRATED SDR) Main PCB OCT 2013 06109131 $30.00 SiDRADIO (INTEGRATED SDR) Front & Rear Panels OCT 2013 06109132/3 $25.00/pr TINY TIM AMPLIFIER (same PCB as Headphone Amp [Sept11]) OCT 2013 01309111 $20.00 AUTO CAR HEADLIGHT CONTROLLER OCT 2013 03111131 $10.00 GPS TRACKER NOV 2013 05112131 $15.00 STEREO AUDIO DELAY/DSP NOV 2013 01110131 $15.00 BELLBIRD DEC 2013 08112131 $10.00 PORTAPAL-D MAIN BOARDS DEC 2013 01111131-3 $35.00/set (for CLASSiC-D Amp board and CLASSiC-D DC/DC Converter board refer above [Nov 2012/May 2013]) LED PARTY STROBE (also for Hot Wire Cutter [Dec 2010]) JAN 2014 16101141 $7.50 BASS EXTENDER Mk2 LI’L PULSER Mk2 Revised 10A 230VAC MOTOR SPEED CONTROLLER NICAD/NIMH BURP CHARGER RUBIDIUM FREQ. STANDARD BREAKOUT BOARD USB/RS232C ADAPTOR MAINS FAN SPEED CONTROLLER RGB LED STRIP DRIVER HYBRID BENCH SUPPLY 2-WAY PASSIVE LOUDSPEAKER CROSSOVER TOUCHSCREEN AUDIO RECORDER THRESHOLD VOLTAGE SWITCH MICROMITE ASCII VIDEO TERMINAL FREQUENCY COUNTER ADD-ON VALVE SOUND SIMULATOR PCB VALVE SOUND SIMULATOR FRONT PANEL (BLUE) TEMPMASTER MK3 44-PIN MICROMITE OPTO-THEREMIN MAIN BOARD OPTO-THEREMIN PROXIMITY SENSOR BOARD ACTIVE DIFFERENTIAL PROBE BOARDS MINI-D AMPLIFIER COURTESY LIGHT DELAY DIRECT INJECTION (D-I) BOX DIGITAL EFFECTS UNIT NEW THIS MONTH: DUAL PHANTOM POWER SUPPLY REMOTE MAINS TIMER REMOTE MAINS TIMER PANEL/LID (BLUE) ONE-CHIP AMPLIFIER JAN 2014 01112131 $15.00 JAN 2014 09107134 $15.00 FEB 2014 10102141 $12.50 MAR 2014 14103141 $15.00 APR 2014 04105141 $10.00 APR 2014 07103141 $5.00 MAY 2014 10104141 $10.00 MAY 2014 16105141 $10.00 MAY 2014 18104141 $20.00 JUN 2014 01205141 $20.00 JULY 2014 01105141 $12.50 JULY 2014 99106141 $10.00 JULY 2014 24107141 $7.50 JULY 2014 04105141a/b $15.00 AUG 2014 01106141 $15.00 AUG 2014 01106142 $10.00 AUG 2014 21108141 $15.00 AUG 2014 24108141 $5.00 SEP 2014 23108141 $15.00 SEP 2014 23108142 $5.00 SEP 2014 04107141/2     $10/set SEP 2014 01110141 $5.00 OCT 2014 05109141 $7.50 OCT 2014 23109141 $5.00 OCT 2014 01110131 $15.00 NOV 2014 NOV 2014 NOV 2014 NOV 2014 18112141 19112141 19112142 01109141 $10.00 $10.00 $15.00 $5.00 Vintage Radio By Associate Professor Graham Parslow STC’s Type 500A 5-Valve Mantel Radio STC’s 1938 Type 500A is a well-made 5-valve mantel radio which was housed in a handsome timber cabinet. The unit featured here was obtained in quite good condition and required relatively little work to restore it to full operation. T This STC 1938 500B tombstone model still has it original speaker grille and knobs. Exactly the same grill and knobs would have been installed on the model 500A pictured above but these parts have been changed at some stage during the set’s life. 92  Silicon Chip HE 1938 STC Type 500A mantel radio is among the author’s favourite radios. The attraction started with a visit to the palatial Como House (now a National Trust building) in Melbourne. One member of the wealthy family that previously lived in Como House was an avid radio listener and an STC Type 500A radio is displayed (in working condition) in her bedroom. It made a lasting impression on me at the time, well before radio collecting became a passion. Some years later, the Type 500A radio featured here was offered on eBay and I duly purchased it (in 2006) for $300. Since then, it has occupied a prominent place in my home and has always been appreciated for its outstanding craftsmanship. STC’s pro­ motional material at the time stated that the “two-tone cabinet” was made from “specially selected highly-figured walnut veneers, hand rubbed” and with a “full piano finish”. I’m certainly not the only person to appreciate its qualities because my Type 500A radio came with an inter- esting story. It turned out that it had spent a long life of active service on a farm in the Illawarra region of NSW. When the farmer died, the radio was passed on to his son who kept it as a treasured memento before reluctantly deciding to sell it because he was moving to the US. We exchanged a number of pleasant emails during the transaction and when the radio arrived, I felt that I had inherited an obligation to get it going again and to look after it. Prior modifications In deference to its history, the radio hasn’t been fully restored though. To keep the radio functional and “updated”, the previous owner had had the knobs, speaker and speaker grille replaced at some stage, probably during the 1960s. The speaker is mounted on a baffle-board which is angled at 30° to the front face at one end of the cabinet. Its relatively easy to remove this to gain access to the grille material. The speaker itself was originally an electrodynamic type and was plugged into a 5-pin socket on the rear of the siliconchip.com.au chassis. Two wires ran to the remotelymounted output transformer, two were for the electromagnet and the fifth wire was an earth lead. The speaker grille fabric had probably been replaced when the permanentmagnet loudspeaker was installed. This ‘new’ speaker was a Rola 6-inch (150mm) type H of 1950s vintage. It had been installed professionally, presumably by a local serviceman, and the work included adding a 2kΩ 20W resistor to replace the electromagnet in the HT filter circuit. The HT filter electrolytics (C10 & C11, both 8µF) were also replaced at the time. The grille fabric and knobs originally used on the 500A were also used on the 1938 STC tombstone model 500B. This set is shown in one of the accompanying photos and is another of the author’s prized radios. It’s displayed next to the 500A and clearly demonstrates what the 500A’s original grille fabric and knobs look like. I’ve left my 500A just the way it came to me though, as I consider the replacements to be a genuine part of the radio’s history. The chassis of the old Type 500A was in good order but required cleaning. The back-lit dial uses two 6.3V globes that shine through a green transparent sheet and a second opaque sheet with transparent station call-signs. STC aimed high STC stands for Standard Telephones and Cables and the company began life in London as International Western Electric in 1883. It became STC in 1925 when it was taken over by ITT of the USA. Two important high-points for the company involved supplying the radio systems for the Queen Mary and Queen Elizabeth ocean liners (1936-39) and patenting pulse code modulation (PCM) in 1938. STC’s Australian operations date from 1923 when Western Electric set up a manufacturing subsidiary in Sydney. Local manufacturing expanded significantly in 1936 following the construction of a new factory at 252274 Botany Road, Alexandria, Sydney. This new factory employed some 700 people and was involved in building domestic radio receivers (such as the Type 500A), commercial transmitters and military equipment. The sales motto for STC was “for tone it stands alone”. All pre-war radios were high-specification models and this included both the cabinet work and the electronic circuitry. As a result, these radios were aimed at the higher end of the market and were relatively expensive. This changed after the war when the “Bantam” range siliconchip.com.au Most of the original components had survived in this radio, the exceptions being the loudspeaker, the output transformer, the celluloid dial cover, two 8µF HT filtering capacitors and two other coupling capacitors. of domestic radios was introduced to compete on price. Circuit details Fig.1 shows the circuit details of the STC Model 500A. The ‘A’ suffix describes the case type. On the other hand, the chassis is labelled 500-I and the ‘I’ defines the circuit used and its features. For this particular circuit, the 1938 STC sales manual lists the features as including automatic volume control, tone control, a clearly marked tuning dial, a chromium dial escutcheon, an electromagnetic moving-coil loudNovember 2014  93 Fig.1: a 5-valve super­heterodyne circuit with a 450kHz IF stage is used in the Type 500A. Valve V1 is a 6A7 frequency converter stage, V2 is a 6D6 IF amplifier, V3 a 6B7 diode-pentode detector/amplifier stage, V4 a type 42 output pentode and V5 a type 80 rectifier. speaker and a “threshold sensitivity” control. The circuit itself is a 5-valve super­ heterodyne type using a 450kHz IF stage. It includes a 6A7 frequency converter (V1), a 6D6 IF amplifier stage (V2), a 6B7 diode-pentode detector/amplifier stage (V3) and a type 42 pentode (V4) for the audio output. The 450kHz IF stage employs two metal dust core transformers and STC state that resistance coupling is used between the detector/amplifier (V3) and output stage (V4). The last claim is a bit odd though, because C3 provides conventional capacitive coupling to the type 42 output pentode. Potentiometer AS11-R (50kΩ) acts as a top-cut tone control in conjunc- tion with C2. The volume control pot (500kΩ) is labelled AS11-G and this alters the gain of the 6B7. The top of the volume pot also accepts signals from a gramophone pick-up, with the signal fed in via terminals on the rear of the chassis (see photo). The threshold sensitivity is adjusted by a trimpot marked as SP5130 on the circuit diagram and located at the lefthand rear of the chassis. This trimpot alters the RF gain of the 6A7 converter valve. The final valve in the line-up is a type 80 rectifier. This provides fullwave rectification of the high-voltage secondary output of a conventional mains transformer to provide the HT line. This HT line is filtered by capacitors C10 & C11 (both 8µF) and the The original twin-flex mains cord ran to a plug to the right of the speaker socket and this plug was used to select between a line voltage of 200VAC or 240VAC (see Fig.1). This warning label on the rear panel advises the user to check that the plug position correctly corresponds with the supply voltage . 94  Silicon Chip HT coil in the electrodynamic loudspeaker. As previously mentioned, in this particular set, the latter had been replaced by a 2kΩ 20W resistor. Restoration Despite the set’s age, the cabinet was in good condition. It was polished with O-Cedar wood polish but was otherwise left unchanged. However, the celluloid dial window was nearly opaque due to oxidation. The original celluloid was blowmoulded to clear the rather-stylish dial pointer which stands out from the back of the metal escutcheon. This means that a flat replacement window mounted behind the escutcheon would have fouled the pointer, so an alternative method had to be found. Unfortunately, when I first acquired this radio I didn’t have the skill to duplicate a blow-moulded window profile (although this is a technique that has subsequently been learnt). As a result, for this radio, a clear-plastic section was carefully cut from acetate sheet to fit the profile of the outer rim of the escutcheon. It was then carefully glued in using a few small dabs of super glue. The result was agreeably satisfactory and allows the green back-lit dial to continue to impress more that 70 years after it was manufactured. The siliconchip.com.au KEEP YOUR COPIES OF SILICON CHIP AS GOOD AS THE DAY THEY WERE BORN! The STC Type 500A radio has pick-up terminals to accept the output from a record player. The pick-ups used in 1938 were either large magnetic types or piezo-electric crystals as shown in this advertisement from Levenson’s Radio. dial back-lighting is achieved using incandescent dial globes which shine through a layer of green backing positioned behind an opaque dial-plate with transparent call-signs. the 1930s but each room had a light, so double-adapting from the light fixture was fairly common. Users who wanted a switch had to install their own. Mains cord replacement Although it appeared to be in reasonable (but dusty) condition, the radio was ‘dead on arrival’ (DOA) with no audio output. This was due to an open-circuit primary on the output transformer and this was quickly es- The original 2-core mains lead installed in the 1960s is now illegal in this type of equipment. In addition, this cord was terminated in a loose socket that made poor contact and this socket had to be orientated to match the mains voltage. This meant that the 200VAC tap on the power transformer could be incorrectly selected. As a result, the 2-core mains lead was replaced with a modern 3-core lead which was directly connected to the 240VAC tap on the power transformer. This cord will be substituted with a cloth-covered cord in the near future, so that it is more in keeping with the set’s age. It is interesting to note that 2-core mains leads were common in 1938 and most radios, including this one, had no mains switch. This was because if a switch was installed, it was obligatory to switch the Active lead. However, many users spliced the power cord into a light bayonet socket using a 2-pin B-22 plug, so there was a random chance as to which lead would be the Active. A DPDT switch would have overcome this problem but that would have added to the cost and users generally didn’t demand this feature. Wall sockets were only sparsely installed during siliconchip.com.au Dead on arrival Magazines are sneaky things: left to themselves, they’ll hide, they’ll get crushed, folded, spindled, dogeared, pages will disappear . . . not good when you want to refer to an article in the future. ONLY 14 95 $ INC GST PLUS p&p A SILICON CHIP binder will keep your copies in pristine condition – and you’ll always be able to find them! * Each binder holds up to 14 issues * Made from heavy duty vinyl * Easy-fit wire inserts ORDER NOW AT www.siliconchip.com.au/shop Where do you get those HARD-TO-GET PARTS? Many of the components used in SILICON CHIP projects are cutting-edge technology and not worth your normal parts suppliers either sourcing or stocking in relatively low quantities. Where we can, the SILICON CHIP PartShop stocks those hard-to-get parts, along with PC boards, programmed micros, panels and all the other bits and pieces to enable you to complete your SILICON CHIP project. The same punched chassis was used by STC for a range of radios and this explains the rather unusual use of a 3-gang tuning capacitor frame with one section missing. A 3-gang tuner would have been necessary in models with an additional tuned RF stage. SILICON CHIP PARTSHOP www.siliconchip.com.au/shop November 2014  95 This view shows the Type 500A after restoration. The new 3-core mains cord bypasses the voltage selection plug (to the right of the loudspeaker socket) and is wired directly to the transformer. It also allowed the chassis to be safely earthed. tablished because there was no plate voltage on the type 42 output pentode. In addition, the cathode heater of this valve was glowing red but the valve itself remained cool. The usual cause of a blown output transformer is excessive current through the output pentode (and thus the output transformer). This can be caused by changed resistor values in The pick-up terminals are on the rear of the chassis, directly above the antenna terminal. There’s no provision to switch out the RF section when using the record player; instead, the user has to tune to a quiet spot on the dial, to avoid interference. 96  Silicon Chip the grid bias circuit or failure of the audio coupling capacitor (C3 in this circuit), leading to a more positive grid than is healthy and increased power dissipation. It’s also common to encounter both faulty resistors and a faulty capacitor together. A replacement transformer was installed and the radio then performed perfectly. There is a quick way to check power dissipation in the output pentode and that is to simply remove it. With the 42 pentode in circuit, the power consumption is 51W and this drops to 38.5W after it’s removed. A dissipation of 12.5W for the components associated with this stage is acceptable, so the stage appeared to be running normally. Importantly, the replacement output transformer wasn’t running warm – they can get quite hot when excess current flows. Nevertheless, true peace of mind required direct checking and the results were all good. First, the wirewound 400Ω cathode resistor was checked and its value found to be spot on. This resistor sets the grid bias voltage on the output pentode (the grid itself is tied to earth via R11, which holds the grid negative relative to the positive cathode). The cathode measured +11.7V with +223V on the anode plate. Coupling capacitor C3 (0.01µF) was also checked. This was a Ducon replacement of 1960s manufacture and it measured OK. The fact that it was a replacement meant either that the original had failed or the repairman who had worked on the set had substituted it as a precaution. The final check involved measuring the DC voltage across the output transformer’s primary. This measured 15V DC while the DC resistance measured 600Ω, giving a calculated power dissipation of just 0.38W. Pick-up terminals The 500A’s back panel features two screw terminals to accept the output from an external turntable pick-up (see the advertisement from Levenson’s Radio). These two terminals connect to the volume control (AS11-G) in the first audio stage but note that there’s no switch to switch the RF front-end out of circuit. Instead, the radio was tuned to a quiet part of the dial when the record player was being used. In operation, the pick-up may have produced as much as 1V, so sensitivity wasn’t a problem. It’s worth noting that many valve radios included provision for a pick-up during the 1950s and even into the 1960s before portable transistor radios took over. Finally, despite its age, this the radio still looks good and it still sounds good. It may not be completely original but it’s still well worthwhile having in SC a collection. siliconchip.com.au PRODUCT SHOWCASE Turning metal into components We all know the frustration that can occur in waiting for a component to be machined by someone else so you can move forward in assembling and finishing your project. And when the part arrives you find it does not fit as you had intended and will need more machining! How many times have you said to yourself ‘if only I had the machine’! Well, the if only now can be a reality. If you go to Hare & Forbes Machineryhouse they have on show and in stock, a wide range of metal turning lathes to suit everyone’s application. For instance, this compact AL-51G bench lathe has many convenient facilities ideal for the enthusiast model engineer wanting to make small components. It has a turning capacity of 230 x 500mm, can screw-cut metric New R&S Tracking Power Supplies The HMC804x power supplies developed by Rohde & Schwarz subsidiary HAMEG Instruments are equipped with one (R&S HMC8041), two (R&S HMC8042) or three (R&S HMC8043) channels. All models from this series deliver up to 100W of power and are adjustable between 0V and 32V in steps of 1mV. Tracking is available in the two multichannel models and enables combined parallel or serial operation. It is still possible to provide power to several circuits independently. Changes to current and voltage values are carried out synchronously in combined channels. & imperial threads that works in conjunction with gears and the Norton gearbox and is supplied with three and four-jaw chucks, faceplate, fixed and travelling steadies – all this for only $1,265.00 including GST! Simply call into your nearest Hare & Forbes Machineryhouse store or jump online, sign up to become a Machin- Ocean Controls new range of Slip Rings Ocean Controls is now carrying a range of slip rings. These allow the transfer of power or data signals through a continuously rotating junction. Commonly, you’d find slip rings in wind turbines, weather sensors, radar antennae, industrial applications and robotics. They prevent cables from twisting and allow rotating equipment to spin continuously without needing to be unwound. Three models are available, with 3, 6 or 12 conductors. Each is capable of carrying 240VAC. The 6 and 12-wire models can carry 2A per conductor, and the 3-wire model is rated to a massive 10A per conductor. eryhouse mate to place your order and have it shipped direct to you. Contact: Hare & Forbes Machineryhouse 1/ 2 Windsor Rd Northmead NSW 2152 Tel: (02) 9890 9111 Website: www.machineryhouse.com.au Antenna, filter and power amplifier analysis Copper Mountain Technologies Planar TR1300/1 Compact VNA is an excellent low cost solution for magnitude and phase measurements over the frequency range of 300kHz to 1.3GHz. This 2-port, one-path vector network analyser weighs just 1kg and provides the user with high accuracy measurements and a variety of analysis capabilities in frequency and time domains. Dynamic range of transmission measurement is 130 dB, output power adjustment -55 dBm to +3 dBm, including TDR (Time Domain Reflectometry). Copper Mountain Technologies VNAs are flexible, easy to maintain and are a fraction of the cost of traditional analysers. The Software is easy to use and completey free. The Planar TR1300/1 is priced at $3250 + GST. Contact: Contact: Contact: Unit 2, 75 Epping Rd, North Ryde NSW 2113 Tel: (02) 8874 5103 Fax: (02) 8874 5199 Website: www.rohde-schwarz.com.au 3/24 Wise Ave, Seaford, Vic 3198 Tel: (03) 9782 5882 Website: www.oceancontrols.com.au 4/8A Kookaburra Rd, Hornsby NSW 2077 Tel: (02) 9482 1944 Fax: (02) 9482 1309 Website: www.clarke.com.au Rohde & Schwarz Australia Pty Ltd siliconchip.com.au Ocean Controls Clarke & Severn Electronics November 2014  97 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. Send your email to silicon<at>siliconchip.com.au Running two video cameras for a car I fitted a reversing camera that displays on my head unit and it always worked perfectly. I have recently added a front camera and that required the addition of a DPDT toggle on-offon switch and two SPDT relays to allow me to view either camera on my head unit. Sometimes the pictures from one or both cameras come on as monochrome and show tearing. Therefore, I am thinking that some sort of “glitches” are happening in the introduced circuitry that the head unit does not like. Both cameras are identical. The video cable shielding seems to be effective as I see no evidence of interference when the picture is OK. Can you suggest a solution please? Please reply as if speaking to a 7-year old. Although I have successfully built several kit projects from your magazine, I don’t really know how most of them work. (W. H., via email). • We think you have incorrectly wired the power switch or relay connections. Make sure that power to each camera is fully disconnected when the other camera is powered. Either that or there is an intermittent short between the wires or connections that has both cameras on at the same time. This would cause the picture tearing and a black and white picture. We are not sure if the cameras are wireless or simply wired to the display unit. If wired to the display using video leads, then these may have a poor shield connection. Remote GSM monitoring I am looking at building the GSM Remote Monitoring project (SILICON CHIP, March 2014) but I just had a thought and can’t find an answer. Is the Arduino shield A-tick approved? I could not see any reference in your article or notice an A-Tick on the shield. If it’s not approved, wouldn’t that make anyone who made this project liable to legal action by ACMA? If not a legal project, shouldn’t you have a disclaimer or warning about that in the article? • The module used in the GSM Shield, SIM900 is GCF certified – see www.simcom.ee/modules/gsm-gprs/ sim900/ Optus, Telstra and Vodafone Pacific are all members of GCC – see www.globalcertificationforum.org/ members/operators/operator-members-list.html So in theory at least, the SIM900 module should be OK to use on most Australian mobile networks. We are not sure whether the complete module requires separate certification. It’s possible but almost all the mobile functions are provided by the SIM900 – the Arduino board basically just connects the antenna, I/O pins and power supply. We think it’s unlikely to cause serious interference. The only real variable is the power supply arrangement but given the radical difference in frequency between GSM (900MHz+) and the frequencies at which switchmode regulators operate (typically <2MHz) it is doubtful that this will have much of an effect. If you have some programming experience and won’t be using the device in a major city, you may want to consider using a 3G module rather than the Speed Control For A 1-Horsepower Motor I would like to build the Speed Controller for Universal Motors (SILICON CHIP, February 2014) but I am in the USA and we have 60Hz mains. Will the firmware still work correctly at this higher frequency? If not, is there a fix that would make it function properly at 60Hz? Also, I am going to use the controller on a 1 HP, 180V DC, 5.3A permanent magnet motor with a 220VAC supply. Do you think it is possible to demagnetise the permanent magnets with the 23A current limit and/or the 10A average limit if the motor gets stalled? If so, what modifications would you recommend to the current limits? (S. G., via email). • You do not need to change anything for 60Hz if you can use 98  Silicon Chip a 220VAC supply. The current in the 15V zener diode ZD1 will be a little higher but that is well within its limits. However, if you did run it at 110V 60Hz, then the two 220nF 250VAC X2 capacitors would need to be increased to 330nF or 470nF to allow sufficient current flow for the 15V zener diode. In addition, the 10A rating will restrict its use to 1.1kW loads with a 110V supply. Whether the magnets become demagnetised under stalled conditions depends on the design of the motor. Presumably, a properly designed motor would not lose magnetism when stalled (for a short period). In fact, the stall current could well be higher than 23A peak and 10A average when used directly from the mains rather than via the controller. So if the motor is not damaged when stalled and powered directly via the mains, it will not be damaged when using the controller. The current levels driving a load in the controller are measured across a 0.01Ω 3W resistor. You could use a higher value such as 0.015Ω resistor to lower the current limit. The firmware is not dependent on the mains frequency as the IGBT is switched on and off at 980Hz without synchronising to the mains frequency and so does not require changing for 60Hz mains. Finally, the outlet GPO would need to be changed to suit plugs for American power tools. siliconchip.com.au GSM one we specified but chances are the software would require changes. Apparently, 3G coverage outside cities is much better than 2G (GSM). Do not attempt this though unless you are confident that you can successfully modify the software and debug it. Headlight reminder for an Austin Healey I want to build the Headlight Reminder from the August 2001 issue. Are the RR1500 wire links directional? Also I am fitting this to an Austin Healey which does not have door switches. I just want it to work on the headlights, so will I be able to leave some parts out? (I. W., via email). • The door switch input does not need to be used but omitting that feature does not save on parts as the associated IC2b gate is within the IC2 4030 quad NOR gate package. Use the Door Switch Unused linking shown for LK3, LK4 & LK5. The wire links (or 0Ω resistors) can be inserted in any direction; they are not polarised. The same comment applies to the resistors and these can go in with either orientation. The diodes, ICs and the electrolytic capacitors must be oriented correctly. Burp charger hiccup I have been trying to build the Burp Charger (SILICON CHIP, March 2014) and I seem to have got into all sorts of trouble. As best I can work out, if I shut things down by any means (kill the power source, turn the switch off, yank the thermistor plug), the Burp FET goes into thermal meltdown unless I first disconnect it from the battery. The very first time I was sure it was working fine, I left it charging and when I returned hours later the Burp FET, its 0.1Ω resistor and the adjacent circuit board had all become engaged in a race to see who could produce the most smoke. I had thought I had built the (Jaycar) kit correctly. I replaced IC3 and FET Q2 (with a IRF9540) and it seems to be working except for the shut-down thing and I obviously can’t leave it like that. Plus why did it turn into smoke in the first place? I built a second one thinking that this would help me diagnose exactly what’s gone wrong with the siliconchip.com.au Valiant Has A Reluctant Reluctor I have a Valiant slant six with an earlier version of your electronic ignition. It has a reluctor distributor and I have to admit always having had trouble starting the thing. In recent times, the problem became much worse, to the point where the car just won’t start. After three days (off and on) working on it, I am a defeated man. I found there was no spark rather than a fuel issue and after checking the distributor pick up coil (280Ω) I decided it must be the old ignition module. And rather than look into it more deeply I decided it was time to buy your latest ignition project and dispense with the effort of finding the faulty part. Alas, the new kit behaved the same so here I am with two units and no real progress but ever so much wiser. It turns out that nothing was actually wrong. It seems I am operating just on the triggering threshold of the pick-up coil pulse sensing circuitry. What I found was that at cranking speed, the reluctor/pick-up coil only produces a pulse of around 0.3V and my testing seems to show that the ignition module needs more like 0.6V (minimum) to trigger a spark. first one (I have a couple of crappy old chargers that could stand being replaced). Unfortunately, I seem to have ended up in the same place, except that I have cooked the PIC as well! Any ideas? Is the specified SPP15P10 so different from the IRF9540 that it’s never going to work properly? I remain impressed with your magazine and with “el burpo”. (P. M., via email). • You have discovered a flaw in our design – see the errata on page 101 of this issue. The two modifications listed there (adding a resistor and changing the power switch arrangement) should fix it. Q2 is an SPP15P10 as its on resistance is lower than the IRF9540, although this isn’t critical and the IRF9540 will work as well. ADSL modem reset box wanted A really useful project would be an ADSL modem reset box. It would ping a couple of servers every 15 minutes. So rather than spend $375 on a reconditioned distributor or $175 on a replacement Bosch pick-up coil that may or may not be any better I thought I’d see if you could help. I’m hoping that there’s a way to tweak the pick-up coil sensing circuitry and solve my problem once and for all. (R. L., Robina, NSW). • The reluctor in your Valiant would seem to be faulty as it should provide several volts of signal rather than 0.3V, even at cranking speed. The reluctor trigger in the SILICON CHIP ignition system requires at least 0.6V to trigger. A lower threshold setting would tend to produce erratic firing. Check the gap between the reluctor and its magnets on the distributor and adjust it so that you have the smallest possible gap but not so small that you run the risk of contact. The gap would need to allow for the temperature range of operation from a cold through to hot engine. The reluctor may have a shorted turn but unfortunately, a resistance measurement will not necessarily reveal this as it will only reduce the resistance by a small amount (in a multi-turn coil). If there is no response, it cuts the power to the modem and re-tests after 10 minutes or so (some modems takes ages to boot). So many weekends and night times I have been called in to restart a modem. There are a lot of people and readers with web applications nowadays. (B. H., via email). • We suppose it would be useful if you have a flaky ADSL modem. A properly operating modem shouldn’t need resetting as it should reconnect if there is a line failure. In our own case, such a device wouldn’t be very useful with our modem since usually we reset it because the connection has become slow rather than failed completely. It would be possible to include a speed test and reset it if the link is slow but that could give false triggers when the link is being heavily utilised and would also be annoying if it decided to reset the modem while you are in the middle of doing something. November 2014  99 USB Problem With The Micromite I recently I purchased and put together your 44-pin Micromite kit (SILICON CHIP, August 2014). It all went together fine; even the soldering was simple enough to do as I have done SMD kits before. If I remember correctly the micro was still sealed in its carrier tape and I did wonder at the time as to just how it was programmed. Anyhow, I had put it all together, checked all the soldered joints and powered it up via the laptop USB connection. The green power LED came on and I measured the voltages (3.3V and 5V appear correct). However, the laptop says “unknown USB device”. I went to Device Manager, found the Unknown Device, right clicked it and selected update driver. After some time, it came back and told me that it has the latest drivers installed. If that is so, why does it not recognise it? I am at a loss to know what to do next. I don’t know if it the Micromite at fault or the computer set-up so where to from here? Can I confirm if it is the Micromite and has it been programmed? Or is it my laptop set-up? I do recall I did also have a set up It probably depends on how many ADSL modems in use have this kind of failure mode; perhaps there are a significant number out there. It’s a simple enough project so could be worthwhile. This could be done with a low-cost pre-built embedded module with Ethernet plus a mains-rated relay interface with suitable GPO sockets etc. Siren for model radio-controlled boats I would like to make a small electronic siren to install into a model police boat which I made and sometimes sail on a lake. I would also like to add a red and a blue flashing LED “police light”. Do you have any suitable articles for making this? (B. D., via email). • Perhaps the best solution is to use a couple of the projects sold by Jaycar in Short Circuits 2. One is a Hee-Haw siren (Jaycar Cat. KJ-8204 and instructions KJ-8205). This has a single flash100  Silicon Chip problem with the Freetronics USBto-Serial interface module recently not recognising the USB device; it said the same thing (Unknown Device etc). I emailed them with my dilemma and they sent me a zip file with their driver and installation instructions and all is well; the laptop now recognises it. So where to next? (G. W., via email). • The microcontrollers are programmed using a surface-mount IC socket on a programming adaptor board. The Micromite chip isn’t responsible for the USB interface; the FT232RL chip (IC2) does that. It’s possible that you lack drivers for this chip but that seems unlikely. However, try loading the drivers found here and see if that helps: www.ftdichip.com/Drivers/VCP.htm If not, perhaps the USB chip isn’t operating correctly. Carefully check the soldering of IC2 and CON3 with a magnifying glass in a good light. Also check that IC2’s pin 1 dot is in the right place and that the 100nF capacitor above IC2 (C7) has good solder fillets between the ends of the capacitor and the PCB pads. Those are all the critical components for the USB function. ing LED light. For two alternating LEDs that flash, use the KJ-8200 red/green flasher and KJ-8201 instructions and change the green LED to blue – see www.jaycar.com.au Maximite USB driver problem I am trying to install the USB driver for the Maximite but am getting an error message, to the effect that “Windows has found driver software for your device but encountered an error while attempting to install it”. I have tried copies downloaded from your site and CircuitGizmo but both give the above error. Any thoughts? (R. W., via email). • It does work and thousands of people have it running on Windows, Mac and Linux. For Windows, you must install the device driver and exactly follow each step in the notes provided with the driver. Most problems are caused by skipping or modifying a step. For Mac users, there are notes in the download section of the main Maximite web page. If you are using Windows 8 you must instruct it to install “uncertified” drivers. The procedure is documented in this thread on the Back Shed forum: www.thebackshed.com/forum/ forum_posts.asp?TID=5313&PN=1 Repairing Holden V8 ignition modules I am having issues finding components to repair the ignition modules used by Holden on older V8 engines. These modules are becoming very rare and reconditioned units are also very expensive. I have done extensive research online but I am still unable to discover which TO-3 transistor is used to switch the coil. Very few of these transistors have any markings at all, which makes them difficult to identify. The transistor is a TO-3 type with three legs and is mounted in an alloy case which serves as a heatsink. The transistor is also fully insulated from the case. The bias or drive resistor looks like a 1W wirewound unit but its resistance is a mystery. I can only surmise that its value would be quite low as it does generate a fair amount of heat and I suspect that this is in part the reason for failure. The PCB under this resistor is also usually heatdamaged and discoloured. Every failed unit I have seen has this resistor burnt out. The only unit I have seen with markings on the transistor has three sets of numbers: 21020, 507331 and 0304. I have been unable to find any kind of cross-reference which identifies the transistor from these numbers. Any help or advice would be greatly appreciated. (D. S., via email). • The transistors are probably specifically made for the ignition which is probably a Bosch system. The transistors are probably no longer easy to obtain. The third lead of the transistor would be the collector, with the case isolated. The MJ10012 is a TO-3 power transistor for ignition systems and could be used as a replacement. Its case needs to be isolated from the heatsink with an insulating washer and insulating bushes and the collector connection made via an eyelet, to the transistor case. This is a Darlington so the base siliconchip.com.au drive need only be 100mA to switch the transistor on. Alternatively, we recommend our High Energy Ignition that uses an IGBT as the switching transistor, as published in November and December 2012 issues. This IGBT could also be used as a replacement transistor and the gate drive need only be via a 1kΩ resistor (that has little dissipation). The IGBT is an ISL9V5036P3-F085. The MJ10012 is available from Jaycar Electronics (Cat ZT-2222) although the H version may suit your 3-leg requirements better. The IGBT is available from SILICON CHIP – see www.siliconchip.com.au/Shop/7 and search for the High Energy Ignition. Circuit confusion with switching regulator I recently purchased a Jaycar kit for the simple 1.5A Switching Regulator, but have yet to construct it (SILICON CHIP, February 2012). On checking the circuit diagram, I was confused by the orientation of the IRF9333 Mosfet (Q1) used to switch the regulator on. I recently received the EPE article Notes & Errata Burp Charger for Nicad and NiMH Batteries, March 2014: disconnecting power using switch S1 allows current flow from the supply into IC3 and Mosfet Q2 via the 0.1Ω and 1kΩ resistors. This causes Q2 to switch on and so battery current flows through the 0.1Ω resistor. This problem can be solved by removing S1 and bridging the two switch contact points on the PCB. Power is then switched either via the DC plug or at the input power source. It is also recommended to connect a 100kΩ resistor between pins 6 & 7 of IC3b. This prevents a possible partial conduction of Q2 in an especially low switch-on threshold Mosfet. This resistor can be placed photocopy, which is identical to the SILICON CHIP article. My question is that being a P-channel Mosfet, the supply voltage at the drain connection should be negative with respect to the source connec- Mini 2 x 5W Stereo Amplifier . . . from p85 a while (up to about 30 seconds), simply because of the mass which needs to be heated. If it takes longer than 30 seconds then your iron may not have enough power. By the way, don’t touch the IC or board during this procedure or immediately afterwards as it will be stinking hot! It’s then just a matter of soldering the remaining IC pins and cleaning up any bridges using solder wick. Refresh the joints on the first two pins you soldered, too. Adding flux paste is recommended for both procedures; when soldering the pins, it reduces the chance of bad joints. Clean off any excess flux using an appropriate solvent (metho will do in a pinch) and check the joints under magnification to ensure that solder has flowed properly onto every pin and pad. Remaining SMDs You can now proceed to fit all the smaller SMDs. Start with the two 3-pin SOT-23 packages. It’s simply a matter of flowing a little solder onto one of the pads, heating that solder while sliding the device into place (using siliconchip.com.au tweezers, for example), soldering the two remaining pads and then refreshing the solder on that first pad. Don’t get the two devices mixed up. If using the on-board power indicator LED, fit it now. First, you will need to check its orientation. Unfortunately, markings for SMD LEDs are not consistent. Some DMMs will light a LED in diode test mode, with the red lead indicating the anode but if your DMM won’t light it in either direction, you may need to connect the LED to a 9V battery via a 1-10kΩ series resistor. Orientate the LED so that the anode (positive) terminal goes to the pad marked “A” and then use a similar method as above to solder it in place. Try not to overheat it but do make sure that the solder has flowed properly onto the ends of the LED and the pads. Once again, flux paste is your friend. Now proceed to fit all the surfacemount resistors and capacitors. Use the same method as described above. The resistors will have their values printed on top although you may need a magnifying glass to see them. The capacitors are unmarked, however the under the PCB across the terminals of the 100nF capacitor that also connects between pins 6 & 7 of IC3b. Bistro Paging System, Circuit Notebook, October 2014: the column connections to the keypad are reversed, ie, the “star” key should be column 1 and pin 3 while the “hash” key should be column 3 and pin 5. The part number above the keypad is for the piezo buzzer not the keypad; the correct keypad number is Jaycar SP0770. The part number (Jaycar AB3452) for the 400Hz buzzer was also omitted; this specifies the correct electromechanical or solid state style buzzer compatible with a micro output. tion, should it not? In this circuit, it is positive, ie, it is illustrated the wrong way round. The correct orientation is shown in the May 2012 Solar Panel Lighting Controller circuit diagram, where an IRF9540 P-channel power 10nF capacitors will be much slimmer than the 4.7µF types. Through-hole parts Dovetail two of the terminal blocks and fit these for CON4/CON5, with the wire entry holes facing the righthand edge of the board. Also fit terminal block CON3 with the wire entry at the bottom. If using the dual-gang log pot, it can go in now, otherwise solder the two mini horizontal trimpots in place. You can now complete the assembly by fitting the two electrolytic cap­ acitors (longer leads towards the “+” symbols at right), the RCA sockets and the pin header(s), if you require them. Testing & use There isn’t much to testing the board. First, hook up an appropriate power supply with current metering (or connect a DMM in amps mode in series with one of the supply leads). Check that the quiescent current is less than 75mA and that LED1 lights. It’s then just a matter of turning down the volume control, hooking up a signal source and speakers and checking that the audio from both channels is clear and undistorted. SC November 2014  101 DIY Cruise Control Kit Wanted Are you planning to release a automotive cruise control kit or circuit? I don’t recall ever seeing one in your magazine and have surfed your website but could not see anything there. I know that many cars now have cruise control integrated in the engine management computer but there are vast numbers of cars that either don’t have cruise control fitted or this was only available as an added cost option. Commercial add-on units are available but even the cheapest of these are $300 or more and frankly, this seems grossly overpriced given the relative simplicity of the circuitry. It doesn’t have to be adaptive, just a basic system to maintain road speed (although with the cheap proximity sensors available now it probably wouldn’t add too much to the complexity or cost). The inputs are already there for most cars built in the last 20 years: vehicle speed sensor signal, engine speed sensor and throttle position sensor. And with drive by wire, you don’t even need mechanical actuators. Simplistically, you just compare the road speed with the set speed and output a voltage to the throttle potentiometer or a mechanical actuator like a vacuum or stepper motor. Mosfet is used in the Q1 position. In the switching regulator circuit, for the Simple Switcher, the Mosfet’s internal reverse protection diode will conduct on switch-on, negating the purpose of the FET. (I. N., via email). • The Mosfet is shown correctly. There’s no requirement for the voltage at the drain of a P-channel Mosfet to be negative relative to its source (same applies with N-channel in reverse). This was explained in our Circuit Notebook pages in April 2012 and a similar (brief) explanation follows. Mosfets are intrinsically a symmetrical device, ie, the drain and source are interchangeable and current can flow in either direction, controlled by the gate voltage. But they typically have an internal “parasitic” “body” diode. In an N-channel Mosfet, this has the anode at the source and cathode at the drain, whereas with a P-channel it’s the opposite. As long as the Mosfet 102  Silicon Chip Of course, there would be a few added safeguards like brake cut-out, clutch-cut out, over-rev cut-out etc. This is beyond my limited know­ ledge of electronics but should be a doddle for experts and probably most students. (E. F., via email). • Cruise controls have been published in the distant past (in Electronics Australia) and that was when most cars had a similar throttle arrangement with a throttle cable actuating a carburettor valve. As you are aware, most cars now have fuel injection and many are “drive by wire”. The main problem with designing a cruise control is not with the electronics but with an effective and safe mechanical or electrical method of controlling the throttle that would be compatible for all vehicles. Every installation would be different, depending on brand and model of car. With these factors in mind, this is not a DIY project that could be successfully adapted to a wide range of cars. Note that VDO in Australia do have cruise control kits but they differ between each make and model of vehicle and include the operating controls that match the existing steering stalk switches and all parts required to control the throttle. is arranged so that this body diode is reverse-biased, such that it prevents current from flowing when the Mosfet is off, then it will work. In the case of the Simple Switcher, we want to stop current flowing if the supply polarity is incorrect. In this case, Q1’s drain will be negative relative to its gate and source, so the body diode is reverse biased. So as long as the Mosfet channel is switched off (ie, gate voltage is not negative relative to source) then no current will flow. With the correct supply polarity, the body diode is forward biased but it is “shorted out” by the channel, which is switched on (gate below source), avoiding the voltage loss (and power dissipation) due to the diode’s forward voltage. In the case of the Solar Panel Lighting Controller, the Mosfet is being used to block current from flowing from diode D1 to L1 when it is off and hence the body diode connection is reversed compared to the Simple Switcher. In other words, we’re using it to prevent current from flowing (or allowing it to flow) in the opposite direction and hence the diode must be orientated differently. Incidentally, while most discrete Mosfets have three pins, a Mosfet is actually a 4-terminal device. The fourth pin is labelled “bulk” or “substrate”. The control voltage is the gatesubstrate voltage, the drain and source are interchangeable and there are two parasitic diodes, drain/substrate and source/substrate. You can actually buy Mosfets like this (eg, BSS83) and they’re typically used for analog switching. However, most of the time it’s more convenient to have a 3-terminal device and so a typical Mosfet has the source connected to the substrate internally and thus it is no longer completely symmetrical. This also prevents the possibility of destruction through SCR latch-up. How to tweak the Flexitimer I recently built one of your Flexi/ Interval Timers from the April 2010 issue of your magazine. The unit works great but I’m after some advice on how I can speed up the discharge of the circuit when the power is disconnected. I apply power to the circuit and it switches the relay as required. When the unit times out and switches the relay back on (one-shot operation) I then have to turn it off and wait 45 seconds for the unit to discharge before I can run it again (it’s operating my garage door remotely so I’m unable to use the restart circuit). I’m after some advice on how I can discharge the unit quicker so that when the power is re-applied (within the 45-second period) it switches the relay and starts the count-down timer. The unit is powered by a 12V DC 1.5A plugpack. I have also changed resistor R3 from 100kΩ to 330kΩ. (D. B., via email). • The 470µF supply bypass capacitor would be the culprit, holding up power to the circuit for 45 seconds. When using a 12V DC plugpack it is probably not necessary to have such a large bypass capacitor and a 10µF 16V capacitor should be suitable, to allow the supply to drop much faster. continued page 104 siliconchip.com.au MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP WORLDWIDE ELECTRONIC COMPONENTS FOR SALE PCB MANUFACTURE: single to multi­ layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. 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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 Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au November 2014  103 Positions Vacant Retail Store Manager (Full Time) We presently seek a retail sales manager to lead our team in our new Virginia, Qld store. Do you have a passion for electronics and experience in retailing and managing teams? Do you wish to take your retail career to the next level? The successful candidate will have: Retail sales experience. A sound understanding of electronic components. Leadership ability. Excellent customer service skills. Strong communication. A high level of self-motivation. We offer a fun, challenging and dynamic work environment. You will be rewarded with a base salary with bonus incentives based on sales performance. If you meet the above criteria and wish to apply for this opportunity please send your application and attach your resume in confidence to: Daniel.neuss<at>altronics.com.au • • • • • • Advertising Index 4D Systems Pty Ltd...................... 11 Altronics.........................loose insert Clarke & Severn Electronics.......... 9 Electric Factory Pty Ltd................ 23 Emona Instruments...................... 39 Hammond Manufacturing............... 9 Hare & Forbes............................. 2-3 Icom Australia.............................. 13 Jaycar .............................. IFC,49-56 Keith Rippon .............................. 103 KitStop.......................................... 12 Retail Sales – Full Time and Casual (2) LD Electronics............................ 103 We presently seek retail sales people to join the team in our new Virginia, Qld store. Do you have a passion for electronics and experience in retail? Are you a people person with a love of technology? The successful candidates will have: Retail sales experience. An understanding of electronics. Excellent customer service skills. We offer a fun, challenging and dynamic work environment. You will be rewarded with a base salary with bonus incentives based on sales performance. If you meet the above criteria and wish to apply for this opportunity please send your application and attach your resume in confidence to: Daniel.neuss<at>altronics.com.au LEDsales.................................... 103 • • • Lintek Pty Ltd............................... 27 Master Instruments................. OBC‑ Microchip Technology................... 15 Mikroelektronika......................... IBC Ocean Controls............................ 75 QualiEco Circuits Pty Ltd............. 59 Internal Wholesale Sales Representative – Loganholme Quest Electronics....................... 103 We require the services of a bright and enthusiastic and outgoing team player to join our friendly wholesale sales team. Duties include: Phone sales. External sales rep support. Customer service enquiries. Counter sales. The ability to multi-task and work unsupervised is essential. We seek a person preferably with industry experience and an interest in electronic theory and audio visual systems. We offer a fun, challenging and dynamic work environment. You will be rewarded with a base salary with bonus incentives based on sales performance. If you meet the above criteria and wish to apply for this opportunity please send your application and attach your resume in confidence to: Daniel.neuss<at>altronics.com.au Radio, TV & Hobbies DVD....... 12,25 • • • • Rohde & Schwarz.......................... 5 Sesame Electronics................... 103 Silicon Chip Binders................... 103 Silicon Chip Online Shop........ 90-91 Silicon Chip PCBs...................... 103 Silicon Chip Subscriptions........... 65 Silvertone Electronics.................. 35 Tronixlabs................................... 103 Ask SILICON CHIP . . . continued from page 102 You could also speed up discharge of the supply capacitor by connecting a 1kΩ resistor across the supply on the cathode (K) side of diode D3 to 0V (GND), or directly across the capacitor. Threshold voltage switch for fridge I built the Threshold Voltage Switch (SILICON CHIP, July 2014) and enjoyed building it. I have a solar panel on my van’s roof, running an Engel fridge 104  Silicon Chip inside with an Allrounder 120Ah battery. The voltage varies quite a lot between day and night as it is hooked up to run permanently. The fuse to run this fridge on DC is gold-plated as they want A$50 to replace it. I wonder if it would be possible to use your design without a lot of modifications to switch the power to the fridge off when a preset voltage of say 11.7V DC occurs? This would save me replacing the fuse as the fridge cost is $A1000 in the first place. (P. M, Rochedale South, Qld). • The Threshold Voltage Switch can Wiltronics........................................ 7 Worldwide Elect. Components... 103 be set to switch the relay at 11.7V. For a refrigerator, you would need a relay that can switch the necessary motor current. It seems some Engel fridges draw up to 4.2A but the peak current could be a lot higher. The 30A relays mentioned on page 32 of the July 2014 article should be suitable. Whether the Threshold Voltage switch switches the relay on or off is dependent on LK3’s position. VR3 adjusts the switching threshold. SC siliconchip.com.au siliconchip.com.au November 2014  105