November 2020 - Silicon Chip Online

Outer Front Cover
Contents
Publisher's Letter: Why is electronics male-dominated?
Feature: MEMS (Micro-Electromechanical Systems) by Dr David Maddison
Project: Eight Small LED Christmas Ornaments by Tim Blythman
PartShop
Project: Two Large LED Christmas Stars by Barry Cullen & Tim Blythman
Project: Balanced Input Attenuator for the USB SuperCodec by Phil Prosser
Serviceman's Log: One repair leads to another by Dave Thompson
Vintage Radio: RCA BP-10 "miniature" valve portable radio by Ian Batty
Feature: A Rundown on New 8-pin PIC Microcontrollers by Tim Blythman
Feature: The Vintage Matrox ALT-512 Graphics Card by Hugo Holden
Project: Flexible Digital Lighting Controller, part 2 by Tim Blythman
Feature: Electronic ‘Wearables’ and the Jaycar Sparkle Stitch by Tim Blythman & Nicholas Vinen
Market Centre
Advertising Index
Notes & Errata: USB SuperCodec, August-October 2020; History of the Australian GPO, September 2020; Shirt Pocket Oscillator, September 2020; Frequency Reference Signal Distributor, April 2020; 45V 8A Linear Bench Supply, October-December 2019
Outer Back Cover

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NOVEMBER 2020 ISSN 1030-2662 11 The VERY BEST DIY Projects! 9 771030 266001 $995* NZ $1290 INC GST INC GST LED Christmas Stars Two large LED stars to build Plus Eight More Christmas Ornaments To Make M E M S icro lectro echanical ystems how they work siliconchip.com.au Make your own wearable electronics using Jaycar’s Sparkle Stitch N 2020 1 Kit and Wearable ESP32 Australia’s electronics magazine ovember awesome projects by On sale 24 October 2020 to 23 November 2020 Our very own specialists have developed this fun and challenging Arduino® compatible project to keep you entertained this month with special prices exclusive to Club Members. BUILD YOUR OWN: Star Spangled Beanie Give your Beanie some spark! Using our wearable LEDs and the ESP32 wearable board, we’ve made this Flashing Beanie kit perfect for holiday fun. It is Wi-Fi and Bluetooth® compatible which means you can control it with your Smartphone, and for an extra bit of interest, we’ve patched the wires into the battery compartment on the beanie, so it is all powered by a 3.7V USB-rechargeable lithium battery. SKILL LEVEL: Intermediate TOOLS REQUIRED: Needles, Scissors, Drilling, & Soldering optional WHAT YOU NEED: 1 x Wearable ESP32 Development Board 1 x Black Beanie with Rechargeable LED Head Lamp 1 x Stainless Steel Conductive Thread 2m 1 x Power Pad Slide Switch Pk2 1 x Raft Pad Green Pk10 1 x Raft Pad Red Pk10 1 x JST Crimp Connectors 2-Way RGB, yellow & white LED raft pads also available. See instore or online. XC3810 ST3214 WW4100 KM1058 KM1036 KM1038 PT4452 $39.95 $19.95 $8.95 $7.45 $6.95 $6.95 $4.95 CLUB OFFER BUNDLE DEAL 5995 $ SAVE 35% SEE STEP-BY-STEP INSTRUCTIONS AT: www.jaycar.com.au/star-spangled-beanie See other projects at www.jaycar.com.au/arduino INSULATION TAPE 6 ROLLS Handy Service Aids • One roll each of green, black, yellow, white, blue and red • 5m in length, 19mm wide each colour NM2806 ONLY 3 $ 95 KIT VALUED AT $95.15 WIRE GLUE • Hundreds of hobby, trade and electronics uses • Lead-free • 9ml NM2831 ONLY 9 $ 95 EPOXY BOND GLUE • Bonds in 4mins (approx) • Colorless, permanent bond • Ideal for plastics, metal, glass, concrete etc. • 34ml NA1510 ONLY 9 $ 95 Got a great project or kit idea? If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Shop the catalogue online! Free delivery on online orders over $99* Exclusions apply - see website for full T&Cs. * CONTACT CLEANER LUBRICANT • Used for cleaning & lubricating all types of contacts • Safe on most plastics • 175g spray can NA1012 ONLY 11 $ 50 TEF-GEL ANTI-CORROSION, ANTI-SIEZING, ANTI-GALLING SYRINGE • Will not cold flow or dry out • Resistant to salt water and detergents • 10ml NA1040 ONLY 2495 $ Looking for other projects to do? See our full range of Silicon Chip projects at jaycar.com.au/c/silicon-chip-kits or our kit back catalogue at jaycar.com.au/kitbackcatalogue www.jaycar.com.au 1800 022 888 Contents Vol.33, No.11 November 2020 SILICON CHIP www.siliconchip.com.au Features & Reviews 14 MEMS (Micro-Electromechanical Systems) MEMS combines electronics with miniature machinery, eg the accelerometer in smartphones. We’ve used a few MEMS devices over the years, but haven’t described the how and why of them – by Dr David Maddison 83 A Rundown on New 8-pin PIC Microcontrollers Here’s a quick look at some newer 8-pin micros from Microchip which are superior alternatives to the old PIC12F675 – by Tim Blythman 86 The Vintage Matrox ALT-512 Graphics Card The ALT-512 stands out from its predecessor (ALT-256) due to its ability to display two simultaneous video planes. It was used to make a light pen system with a custom expansion card – by Hugo Holden MEMS combine electronic and mechanical elements into a single tiny package, typically fabricated from silicon, just like ICs – Page 14 104 Electronic ‘Wearables’ and the Jaycar Sparkle Stitch Jaycar’s new Sparkle Stitch is a complete kit to make your own wearable electronics, no extra tools needed! It also serves as an introduction to electronics and maybe a start in fashion design – by Tim Blythman & Nicholas Vinen Constructional Projects 24 Eight Small LED Christmas Ornaments Just in time for Christmas! We’ve got eight colourful Christmas ornaments with designs including a candy cane, Santa on a sleigh and more. They’re simple to build and all of them use the same components – by Tim Blythman 34 Two Large LED Christmas Stars For those who want something with a bit more oomph, here are two big Christmas Stars which use standard LEDs or fancier RGB LEDs. It even works with our LED Christmas Tree from 2018 – by Barry Cullen & Tim Blythman This year we have a large lineup of different Christmas ornaments for you to choose from. While there’s a lot of choice in PCBs, you’ll be pleased to know all the components used are the same – Page 24 44 Balanced Input Attenuator for the USB SuperCodec This stereo balanced input attenuator fits into the same case as the SuperCodec and shares the power supply. It replaces the rear-panel unbalanced RCA inputs but retains the RCA outputs – by Phil Prosser 94 Flexible Digital Lighting Controller – part two In the second part on the Flexible Digital Lighting Controller, we look at how you can control it either via an Arduino, Micromite BackPack V3 or a simple serial adaptor like the CP2102 – by Tim Blythman Your Favourite Columns And if you want something heftier to display, say at the very top of your Christmas tree, then these Stars will be perfect – Page 34 61 Circuit Notebook (1) Automatic hand sanitiser dispenser (2) Wellbeing monitor (3) Boat Computer modified for 4WDs (4) More Boat Computer modifications 64 Serviceman’s Log One repair leads to another – by Dave Thompson 70 Vintage Radio RCA BP-10 “miniature” valve portable radio – by Ian Batty Everything Else 4 6 31 107 Editorial Viewpoint Mailbag – Your Feedback Silicon Chip Online Shop Ask SILICON CHIP 111 Market Centre 112 Notes and Errata 112 Advertising Index And for under the tree, Jaycar’s got a new kit to help introduce you to wearable electronics called the Sparkle Stitch – Page 104 www.facebook.com/siliconchipmagazine NOVEMBER THUR 12TH, FRI 13TH & SAT 14TH NOVEMBER EVERYTHING IS ON SALE ONLINE & INSTORE! • • • • 106 Pieces Precision machined and heat treated Black oxide finished carbon steel Sizes range: M4, M5, M6, M8, M10 Order Code: K72024 Metric Roll Pin Assortment • • • • 120 Pieces Heat treated spring steel construction Black oxide finished Includes assorted sizes: 1.5, 2, 2.5, 3, 4, 5, 5.5, 6, 8, 10mm Order Code: K72204 12 • 50 Pieces • Spring loaded rings to ensure a secure hold when installed • Zinc plated to resist rust and corrosion • Low carbon steel construction • Includes sizes: (5 x 35mm), (6 x 45mm), (8 x 45mm) & (12 x 45mm) Order Code: K74122 12 $ Lynch Pin Assortment SAVE $7.80 $ SAVE $7.80 VGP9 9" Drill Press Locking Clamp • 2" jaw opening • Quick release lever • Swivelling jaw pad Order Code: C103 19 Pin Punch Set - 6 Piece • Ø3, 4, 5, 6, 7, 8mm • 150mm length • Ø6mm hardened steel centre punch • Ergonomically shaped plastic body • Curved end to fit into palm • Automatic single hand operation Order Code: P368 18 20 $ SAVE $6.20 Deburring Tool Pen Style with Pocket Clip • 142mm overall length • Ø11.5 x 104mm long hexagon body • Includes 1 x HSS blades IN MADE N TAIWA Order Code: D040 • Magnetic pick up tool extends 165 - 695mm • 3.6kg fixed & swivel head magnetic pick up tools • 2.3kg fix head magnetic pick up tool Order Code: M0009 16.50 18 $ $ SAVE $5.50 ENDS R EXT MIRRO- 920MM 0 4 2 SAVE $6.20 ALL D N SA THI E AT R MO SALE E H T - CAMERON PDS-2B Bush Driver Set 44 $ SAVE $11 IN MADE N TAIWA • • • • • 2 ONLINE OR INSTORE! Silicon Chip 180mm blade length 360º range Stainless steel Quick lock system Order Code: M970 $ Mirror dimensions 67 x 46mm (LxH) 3 x bright LED lights - rotates 180º Mirror head rotates & swivels 360º Stainless steel telescopic shaft 290-880mm overall length EF-5S - Engineers File Set - Second Cut • 200mm hardened and tempered files • Second cut: Flat, 1/2 Round, Round, Square, Triangular • Includes carry case Order Code: M0008 Order Code: F100 12 $ $ • 10 piece bearing race & seal driver set • 39.5 - 81mm 55 $ 44 SAVE $11 PDS-3BS - Bearing Race & Seal Driver Set Order Code: P031 29 SAVE $9.50 Telescopic Inspection Mirror with 3 x LED Lights PP-10HD - Workshop Hydraulic Bench Type Press • • • • 10 Tonne Bench mount 180mm ram stroke Adjust. ram position Order Code: P141 330 $ SAVE $16.50 UNIQUE PROMO CODE 3DSN20 • • • • SAVE $5.60 • 17 piece bush driver set • 10 - 42mm Order Code: P030 Staff Member Digital Angle Rule SAVE $7.50 4 Piece - Magnetic Pick Up Tool & Inspection Mirror Set 25 SAVE $6.90 ACP-155 Automatic Centre Punch $ SAVE $5.20 $ SAVE $6.90 Order Code: P365 $ • 363 Pieces • M6 machine screws with various lengths, flat washers, lock washers, nylon locknuts and hex key wrenches • Black oxide finish for extra strength Order Code: K74358 25 $ Metric Machine Screw Assortment SAVE $55 Australian Owned Established 1930 “Setting the standard for Quality & Value” machineryhouse.com.au Australia’s electronics magazine siliconchip.com.au Specifications & Prices are subject to change without notification. All prices include GST and valid until 30-11-20 06_SC_291020_SALE Metric Hex Cap Screw Assortment SALE THUR 12TH, FRI 13TH & SAT 14TH NOVEMBER EXTENDED TRADING HOURS OPEN TIL 4PM SAT. 14TH NOVEMBER EVERYTHING IS ON SALE ONLINE & INSTORE! HSS Industrial Centre Drill Set • • • • 5 piece set No. 1, 2, 3, 4, 5 HSS M2 grade Industrial quality HSS Sheet Metal Step Drill Set • • • • • • Order Code: D508 Metric Industrial HSS Reduced Shank Drill Set • HSS M2 grade • 13mm reduced shank • 13, 14, 15, 16, 18, 20, 22 & 25mm Order Code: D1071 39 $ $ SAVE $10.50 Quality alloy steel double ended cutter Quickly remove spot welds Retractable centre point Use with 1/4" variable speed hand drill Hexagonal drive shank, 7mm across the flats Perfect solution for professionals or DIY EDBD-13 Drill Sharpener • • • • Order Code: D1171 69 $ SAVE $19 Spot Weld Drill Bit - Ø10mm • • • • • • 3 piece set For drilling thin material HSS M2 grade 4-12mm x 1mm steps 6-20mm x 2mm steps 6-30mm x 2mm steps Order Code: D070 149 $ SAVE $38 DCE-8 - Digital Caliper • 200mm / 8" • Metric, inch & fraction • Includes battery 79 SAVE $20 Measuring Kit • • • • 3-13mm or 1/8"-1/2" CBN grinding wheel Split point 80W, 240V motor 0 - 25mm micrometer 150mm / 6" rule 150mm / 6" vernier 100 x 70mm square FD-45 Industrial Floor Fan • Ø450mm 3 blade design • Swivels 140º inside frame • 165W, 240V motor IN MADE N TAIWA N 3 X FAS SPEED www.machineryhouse.com.au Order Code: D099 4-WAYING R MEASU Order Code: M739 19 $ $ SAVE $5.20 49 SAVE $17 TiGer 2000S - Wetstone Grinder • • • • German design & technology 200mm stone & 225mm hone wheel 120rpm stone speed Includes straight edge jig, setting gauge & honing paste • 120W, 240V $ Order Code: F026 59 89 $ SAVE $12.50 WHG-6 Digital Height Gauge • • • • • Order Code: M012 0 - 150mm measuring range Ideal for saw blades & routers DRO in mm, inches & fractions 0.01mm resolution Auto on & shut-off No. 4 Cast Iron Bench Vice • 100mm jaw width • 120mm max. opening • Fitted width serrated jaws SAVE $21 RR-5G Manual Section Rolling Machine • 25 x 3mm flat bar cap. • Ø5mm round bar cap. • Hardened & knurled rolls • Weighs 6kg ETIC MAGN E BAS Order Code: W643 Order Code: W859 $ 189 $ 35 X8-PLUS - Industrial Bench Grinder with Linisher & Mitre Table Package Deal 200mm fine & coarse wheels 50 x 915mm linishing attachment Mitre table with angle guide 1hp, 240V motor • 2, 2.5, 3, 4, 5, 6, 8, 10mm • Chrome vanadium steel • Adjustable 3 detent positions on T-bar handle • Free-spinning rotating handle Order Code: H820 $ SAVE $60.50 off RRP 109 $ SAVE $23 Imperial Hex Key Set with T-Bar Handle • 5/64, 3/32, 1/8, 5/32, 3/16, 1/4, 5/16, 3/18" • Chrome vanadium steel • Adjustable 3 detent positions on T-bar handle • Free-spinning rotating handle 79 Torx Key Set with T-Bar Handle • • • • T10, T15, T20, T25, T27, T30, T40, T45, T50 Chrome vanadium steel Adjustable 3 detent positions on T-bar handle Free-spinning rotating handle IN MADE N TAIWA Order Code: H821 $ SAVE $20 RAIN CHECKS TAKEN 65 IN MADE N TAIWA 429 Order Code: S680 SAVE $12 Metric Hex Key Set with T-Bar Handle Order Code: G1590 $ $ SAVE $11.20 SAVE $31 79 IN MADE N TAIWA Order Code: H822 $ SAVE $20 79 SAVE $20 RAIN CHECKS TAKEN DURING THE SALE PERIOD ONLY* *Due to shipping delays, we may experience delays in stock arriving in time for the sale period. Rain checks will be taken ONLY during the sale. SYDNEY (02) 9890 9111 (07) 3715 2200 BRISBANE MELBOURNE 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains 4 Abbotts Rd, Dandenong siliconchip.com.au Australia’s electronics magazine (03) 9212 4422 PERTH November 2020 3 (08) 9373 9999 11 Valentine Street, Kewdale 06_SC_291020_SALE • • • • Order Code: V088 SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke, B.E.(Elec.) Technical Staff Jim Rowe, B.A., B.Sc. Bao Smith, B.Sc. Tim Blythman, B.E., B.Sc. Nicolas Hannekum, Dip. Elec. Tech. Technical Contributor Duraid Madina, B.Sc, M.Sc, PhD Art Director & Production Manager 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 Dave Thompson David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Ian Batty Cartoonist Brendan Akhurst Founding Editor (retired) Leo Simpson, B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (12 issues): $105.00 per year, post paid, in Australia. For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Printing and Distribution: Editorial Viewpoint Why is electronics male-dominated? One of the things that struck me as odd since I started working for Silicon Chip is just how large a percentage of our readers and customers are male. I don’t have an exact figure, but I would guess that it is well over 90%. Why is that? Perhaps my perspective is a bit skewed because my primary mentor when I started dabbling in electronics is a female friend. And in addition to having a decent knowledge of electronics, she is also a capable computer programmer and operator. So I guess I expected to come across more women in the electronics field than I have done while running the magazine. This imbalance in electronics hobbyists is something which Jaycar’s owner, Gary Johnston, is attempting to address with their Sparkle Stitch kit. We have a review of that kit (and some of their related products) starting on page 104 of this issue. It’s a commendable effort, and the fashion aspect of it may well appeal to many girls. But I had to wonder, as I evaluated the kit, why we have to create specific kits for girls. Shouldn’t they be just as interested in ‘standard’ electronics kits? I think that most of our designs and projects should have a broad appeal. I know that there are some very talented high school students, both male and female, building our kits (and related electronics) for HSC projects. But it seems that after high school, women don’t pick up the hobby all that often (or take up electronics, computing and engineering-related careers, for that matter). We also know that girls do very well in high school subjects like mathematics and physics. These subjects require the same sort of logical thought needed to analyse and design circuits. There’s also an artistic aspect to PCB layout which I find very pleasing, quite apart from the engineering of it. And as electronics is something you can do as a hobby, there’s nothing to stop anyone (short of physical disability) from getting into it, regardless of gender. So I guess what I am saying is that it’s a fascinating field, and there ought to be a lot more females who find themselves attracted to it than we see in reality. I don’t have an explanation for that discrepancy. My daughters are too young to understand electronics just yet, but they sure do seem to be fascinated by it. My one-year-old has already started dismantling any device within her reach, and is clearly fascinated by mains cords, plugs, printers, tablets, phones and anything with flashing lights that is within her reach. Will she retain that fascination when she grows older? I don’t know. I can’t see any reason why she should not. I don’t want to push my kids into doing what I do, but I certainly wouldn’t stop them and will provide them with whatever they need to get into it, should they wish to do so. Perhaps this is a generational thing, and the situation might change over time, but I have a feeling that is not the case. It’s entirely possible that no matter how hard we try to get girls and women into “STEM” type subjects, most of them won’t be interested enough to stick with it. I hope that is not the case, though. If any readers have suggestions on how we can get girls interested in electronics and, importantly, stay interested, I would love to hear them. We publish so many different designs and projects that surely, many of them must appeal. Is it just a matter of getting their attention, or do we have to do more? Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 4 Silicon Chip Australia’s electronics magazine siliconchip.com.au MAILBAG your feedback 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”, “Circuit Notebook” and “Serviceman”. Electronic rust prevention doesn’t work on cars issue is no exception, especially the letter from Chris Robertson of Sydney describing a visit to the Army Museum I have noticed a lot of advertising for an electronic rust of Military Engineering. prevention device on TV lately. Could you do an article The vehicle he described seeing is a Ground Elevation on these devices, what’s in them, how they are supposed Meter (GEM), formerly used by Army surveyors to calcuto work and why they don’t work? late spot heights for cartography. Bruce Pierson, RAYMING TECHNOLOGY As an Army telecommunications technician, in 1964 or Dundathu, Qld. so I was tasked to repair the newly-introduced GEM vehiResponse: there are surprisingly many ads on TV for prodPCB Manufacturing and PCB Assembly Services cle operated by the Army survey unit at Enoggera camp, ucts which can’t work. WeFuyong don’t understand why our supBao'an Shenzhen China Brisbane. I had no knowledge of the vehicle nor access to posed ‘watchdogs’ allow consumers to be taken advantage 0086-0755-27348087 technical manuals, but there was an operator available. of. Whether it is exercise equipment which won’t improve Sales<at>raypcb.com The problem, as described, was that the GEM was not your fitness in any measurable way, or electronics which measuring distance accurately or consistently. can’t possibly do what itwww.raypcb.com claims to do, they keep on getThe GEM was a clever instrument for the time. It comting away with it. puted spot height by measuring the distances and angles We have mentioned that electronic rust prevention won’t as it travelled. It used a pendulum apparatus to measure work on cars several times before, including March 2000 the angle and a fifth wheel to measure distance. It had (p107), September 2001 (p100), November 2011 (p101) four-wheel steering, so the chassis (and pendulum base) and February 2013 (p90). remained horizontal when making measurements. For It works well for boats because the water they are imnormal driving, the rear wheels were locked in the conmersed in forms a path for current to flow. A sacrificial ventional mode. anode presents a more attractive route for those electrons; A constant tyre outside diameter was maintained by a hence, it oxidises before the rest of the boat. Hopefully, centralised tyre pressure system which supplied air to all your car is not permanently immersed in a pool of water! tyres from a compressor driven by the engine. Assuming it isn’t, there’s no obvious place to attach a sacWeight distribution was important, so only the driver rificial anode to allow this current to flowing. and operator could travel in the vehicle during measureThis is explained in more detail on the following web ment. Even the comprehensive test equipment and toolpage: https://corrosion-doctors.org/Car/car-electronicboxes were precisely positioned to maintain a horizonrust.htm tal platform. I found the fault to be in the 5th wheel assembly. In Mystery mapping vehicle identified operation, the wheel was lowered to the ground or road When my copy of Silicon Chip arrives each month, I surface. The wheel was connected to a metal disc inside read the Mailbag pages first, as I often find a gem of inforan enclosure, which was machined with over 900 fine mation amongst the contributions. The September 2020 RAYMING TECHNOLOGY Fuyong Bao'an ,Shenzhen, China Tel: 0086-0755-27348087 email: sales<at>raypcb.com web: www.raypcb.com PCB Manufacturing and PCB Assembly Services 6 Silicon Chip Australia’s electronics magazine siliconchip.com.au Helping to put you in Control Ethernet Digital IO, Voltage, Temperature, Humidity Alarm and Control The TCW241 is an Ethernet control unit with 4 digital inputs, 4 relay outputs, 4 analogue inputs and a 1-Wire interface for up to 8 x 1-Wire sensors. SKU: TCC-025 Price: $313.55 ea + GST Modbus RS-485 Red Indicator Easy to mount the SMI2 fits into a standard 22.5 mm borehole for signal lamps. The SMI2 is a universal display unit for monitoring industrial processes. It has an RS485 interface and the Modbus RTU values can be displayed up to four digits. SKU: AKI-030 Price: $149.95 ea + GST Modbus Slave / MQTT - Converter This product allows communication between a Modbus Slave and the MQTT net. 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Silicon Chip Obsolete mobile phone networks As I was part of the team that installed and commissioned the PAMTS (Public Automatic Mobile Telephone Service) switch infrastructure in Sydney, I enjoyed reading Dr Maddison’s article about the history of mobile phone networks (September 2020; siliconchip.com.au/ Article/14572). After spending the following years leading the teams installing the GSM/CDMA networks, I was asked to recover the PAMTS hardware! It was going to be sold to Vietnam (with the possibility of me travelling there to reinstall it), but in the end, they secured a loan from the World Bank and went ahead with an up-to-date network. Chris Newton, Gidginbung, NSW. Feedback on 78xx Switchmode Replacements Current and Temperature Data Logger 8 slots around its periphery. It interrupted a light beam between a lamp and photoelectric cell, generating pulses representing the distance travelled. The fault was simple but expensive. A grub screw holding the lamp had come out and dropped into the rotating disc case, damaging some slots, hence the problem with accuracy and consistency. Intricate work with a feeler gauge cleared the damage sufficiently for the GEM to operate correctly, as a test run to an accurately known height confirmed. I travelled in a separate vehicle; watching the front and rear wheel sets turn in opposite directions was odd. A spare slotted disc was obtained from the USA at enormous cost, in case the problem recurred. Peter Johnston, Merimbula, NSW. I built the 5V and 12V versions of the Switchmode 78xx series regulator replacements (August 2020; siliconchip. com.au/Article/14533) and would like to share some observations that may prove useful to others. Both kits worked straight up driving a 20mA LED load, with the 5V unit delivering 4.99-5.00V and the 12V version showing 11.5V. I was using external 47µF bypass capacitors as recommended. However, when I loaded the 5V unit with a 10W 5W resistor, the output dropped to 4.44V, and to 4.2V with a 4.7W load (~ 1A). Increasing the output bypass with 1000µF improved the droop to about 4.74V. The 12V unit similarly dropped to about 10.8V with a 12W (1A) load. Both ran for about a minute or two before starting to switch on and off at about 0.5Hz. I noticed the inductors had become quite warm. I had been running the input at ~16V (typical for a rectified 12V transformer). When I wound down the supply to 12V (for the 5V unit), suddenly the output improved to 4.9V at full load, and only a small bypass capacitor was needed. With the higher input voltage, a squeal could be heard from the inductor – and this was when the 1000µF improved things. I suspect the is going into pulse-skipping mode at the input higher voltages, and I doubt this is great for inductor life. The 12V unit showed similar characteristics. I clamped a TO-220 heatsink to the inductor, using silicone grease and a chopped-down clothes peg. With this Australia’s electronics magazine siliconchip.com.au modification, and using no more than 12V input, the 5V unit drove a 4.7W resistor at 4.9V for several hours (a little over 1A output). So I think it is difficult to get more than about 0.5A continuously from these devices without a heatsink (probably less with a high ambient temperature), and it is best to have the input voltage around 2-8V higher than the target output voltage. I was surprised to find that the MCP16311 data sheet made no mention of using different value inductors for different input voltages, but only for different output voltages. My experience shows that the recommended inductors will not be suitable up to the maximum 30V input claimed, although moving the bypass capacitors closer to the package might help. Ian Thompson, Duncraig, WA. Response: you are right that it is a bit much to expect a given switchmode regulator configuration (inductor value, compensation component values etc) to work well over a wide range of input and output voltages and currents. We agree that the inductor values recommended in the MCP16311 data sheet are likely only ideal when the input/output voltage differential is modest. It sometimes helps to solder a lowvalue ‘feed forward’ capacitor across feedback resistor R1 (it can be stacked on the same set of pads). This reduces closed-loop gain at higher frequencies and can eliminate the ‘squeal’, probably also improving regulation. Squeal can be a sign of subharmonic isolation, which is generally best avoided. We will go back and analyse our prototypes, and see if we can come up with any recommendations to make these devices less sensitive to the input voltage, and have less voltage sag at higher currents. The need for heatsinking at higher continuous current levels probably cannot be avoided (except perhaps with bulkier and more expensive low-loss inductors). Insulated mains pins are a good idea On reading the article on GPOs (September 2020; siliconchip.com.au/ Article/14573), I was reminded of a couple of incidents from the past, before the introduction of insulation on the Active and Neutral pins. The first occurred while teaching a secondary school class in a computer 10 Silicon Chip Australia’s electronics magazine room. The computers were on desks around the edges of the room, plugged into GPOs on the wall under the desks. A student’s steel ruler got pushed back and fell between the desk and the wall, lodging neatly across the pins of the power plug. The first I knew about it was all the computers going off. The second occurred while working at a residential facility for children with Autism. One of the boys found a 5¢ coin. Thinking it was valuable, he decided to hide it. The place he chose was behind his nightlight. He thought the resulting arc was pretty cool, so he unplugged the night light and repeated the process in a different GPO, which happened to be on a different circuit. Once we worked out why the power had gone out, we were able to reset the circuit breakers and continue preparing dinner. I gave the boy a good 5¢ in exchange and kept the melted one. David Robson, Goughs Bay, Vic. DIY wiring is not a significant hazard The available data does not back up the Nannies who are trying to stop us from building our own electrical devices. “Between 1st July 2000 and 31st October 2011, there were 321 electrocution deaths reported to Australian coroners as identified and closed on the NCIS database. Almost two-thirds (62.0%) of these deaths were unintentional. Additional NCIS database searches indicate that there are at least an additional 39 electrocution deaths still under coronial investigation.” (siliconchip.com.au/link/ab2u) Note that most electrocution data includes lightning strikes, which comprises up to 20% per year. This means that we have a large intentional death rate within electrical deaths, meaning that mental health is a much bigger problem than worrying about a very few DIY electrical projects! siliconchip.com.au Cable Assembly & Box Build Assembly Metal Work Label and Wire Marker CNC Engraving and Machining Functional Test and Logistic Service Electrical box assembly <at>Ampec we specialise in manufacturing of custom design cable assemblies as well as turnkey electronic and electric product assemblies. Fully automatic cut, strip and crimp machines High mix low volume and quick turnaround +61 2 8741 5000 e sales<at>ampec.com.au w www.ampec.com.au The article goes on to say “Despite this, it is likely that most of these deaths are still preventable.” This is an understatement, especially concerning mental health! Looking at the top 20 cause of death from the ABS, electrocutions don’t rate; they are less than 0.1% of all deaths. “Up until 2010, 15 Australians are killed and 300 hospitalised each year because of preventable electrical accidents in the home.” The widespread use of safety switches should have now solved most of these. Preventing people from doing electrical wiring will not change these numbers. Another ridiculous situation is our certification and qualification system in this country. It persists the idea that to keep everyone safe, the wiring rules should be hidden behind a very expensive paywall. Public safety information should be free to all. The Nannies and trade protectionist fail us miserably in not blocking unsafe, poor-quality imported electrical goods. I have tried to report obvious illegal imports, only to encounter obfuscation. Where are the nannies and bureaucrats at the docks stopping this stuff? Hiding behind the piles of ideas about a few DIY ideas are deadly to the majority of the population. There are orders of magnitudes many more deadly devices imported every day than a few DIY projects, generally made by people who care about a good job and care to make it safe! Neil, Footscray, Vic. Comments on AWA radio restoration I would like to comment on Associate Professor Graham Parslow’s Vintage Radio column on the 1940 AWA Radiola 501 in the October 2020 issue (siliconchip.com. au/Article/14613). The comment about resistor R2 being rather blackened (on page 89) points to a problem with C5 being excessively leaky in the past. The longer it was used, the more leakage there would be and the hotter the capacitor and resistor would get. On other sets with similar circuits, 20kW 1W is commonly used for R2. Mounting the speaker transformer on the end of the chassis does get it away from the power transformer. However, it is still a good idea to orientate the speaker transformer laminations at right angles to the power transformer laminations (and often that is adequate, even if they are close together). Some sets are found with transformers mounted at rather odd angles to overcome this problem when the two transformers are near each other. Changing C22 to 47µF is pushing the 5Y3G a bit hard. Several data sources I have seen state that this capacitor should be no more than 10µF. Probably 16µF would be a sensible maximum as electrolytic capacitors these days are very close to the stated value. Early electrolytic capacitors did have quite a wide variation, and finding them to be 50% above the stated values was not uncommon. Rodney Champness, Mooroopna, Vic. Graham Parslow responds: the 47µF capacitor provides good filtering after the surge current has passed. However, I can agree that it is “pushing the 5Y3G a bit hard”. Most 12 Silicon Chip data sheets give a maximum figure of 10µF or 20µF; I did see one that said 32µF maximum. I have a good range of 0.25W and 2W resistors, so naturally, I used a combination of what I had at hand, combining two 10kW 2W resistors to make a replacement for the burnt-out 20kW resistor. When it comes to power ratings, if the components fit, I don’t see the harm in a bit of ‘overkill’. June issue comments I read the Editorial Viewpoint of the June 2020 issue, and I sympathise. It beggars belief that an organisation such as NBN Co could be so poorly organised. I thought that our companies were being run by people who were educated at universities in the best management principles, or maybe that is the problem. They were educated by academics who have never managed a business or a company. It is interesting that some time in the 1940s or 1950s, the PMG (the predecessor to Australia Post and Telstra) requested of the then current government that they be permitted to train technicians etc in house. The result was highly-competent people for the unique jobs of the PMG. Dr Maddison’s article in the June edition about opensourced ventilators is an eye-opener. It seems that a little motivation, of the correct kind, can be very productive. But there was one requirement that was not mentioned. Many component manufacturers restrict the use of their components in life support systems where failure could result in death. If you check the data sheet of just about any integrated circuit, you will find a warning that it is not to be used in life support devices without the prior approval of the manufacturer. On a separate note, I received the first three blocks of the Silicon Chip magazine PDFs on USB and have read many of them already. I am very impressed by the quality of the scans. They would have to be some of the best if not the best scans that I have read. I was reluctant to part with the money for them, but already, I have found quite a few articles of interest. Even the old advertisements are interesting. Finally, I am getting a little annoyed when seeing ads for wire with a particular current rating (7.5A, 10A etc). Technically, for ordinary hookup wire (not mains use), there is no such thing as 7.5A etc wire. The size of a wire needs to be determined by the expected maximum current it will carry, plus the maximum acceptable loss in voltage, plus the maximum acceptable operating temperature. An excellent example of this misleading terminology occurred with one of my neighbours. He has a caravan which has a 12V-powered water pump for the sink. It wasn’t performing well, so he decided to connect a new pair of wires to it directly from the battery which was about 5.5m away, on the tow bar. He bought some dual flex from an autoelectrician mate who told him that the “10 amp” cable would be sufficient. The pump’s running current was 5A. The wire seemed a bit small to me. I calculated the resistance per metre for 1mm2 wire, and the voltage drop at 5A was approximately 1V total (0.5V per wire). It doesn’t seem like much, but it is an 8.3% loss in the available voltage to the motor results in a significant drop in performance. I convinced him to buy 4mm2 wire. This reduced the voltage drop by 75% and provided another 0.75V for the Australia’s electronics magazine siliconchip.com.au pump motor, resulting in a noticeable increase in performance. It would have been better if the pump and battery were closer; then my neighbour would not have needed to pay out $38 for the cable. George Ramsay, Holland Park. Qld. Erlang meter clarification #1 Regarding the letter on p109 of your October issue asking about an Erlang meter, these were a standard part of the Traffic Data Equipment (TDE) installed in PMG (later Telecom and then Telstra) exchanges from the mid-1960s, and probably before. I actually have a portable Erlang meter, which I acquired when all the analog measuring equipment in the lab was retired. The Erlang is a dimensionless unit which represents the “occupancy” (ie, percentage use) of a circuit or group of circuits. The meter pictured would have been used for monitoring up to 200 circuits. Even in the 1960s, these meters were an anachronism. Initially, a technician would have manually recorded the meter reading every three minutes, but the TDE performed this function automatically. The actual meter is nothing special (other than its high quality) – it is simply an ammeter. It measured the current fed from the exchange 50V supply via a 100kW 1% resistor for each occupied circuit. Thus the full scale would be 100mA (50V ÷ 100000W × 200). Ian Binnie, North Ryde, NSW. Erlang meter clarification #2 In response to D. D.’s question about an Erlang Meter, (Ask Silicon Chip, October 2020), these meters were installed in electromechanical telephone exchanges in the 60s and 70s. I first came across a meter like this in a Crossbar Trunk Exchange in the early 1970s. What they really displayed was a concurrent call count, not Erlangs as the Erlang has a time component. Each trunk in a trunk group had a connection that fed 50V DC through a 100kW resistor (0.5mA) when the trunk was busy. These were all connected in parallel and fed to the meter. The meter was on a panel in the exchange control room, and it could be switched between trunk groups or monitor the total call count for the exchange. Dallas Haggar, Caddens, NSW. leaving in 1994. I worked as an OIC for 39 years in SA and the NT. Brian Dunn, Old Noarlunga, SA. Erlang meter clarification #4 In response to the question asked by D. D. of Berowra Hts in the October issue (Ask Silicon Chip), during 30+ years of Telephone Exchange maintenance, I saw and sometimes used Erlang meters. They were installed in Ericsson crossbar exchanges from 1964 until the 1980s to measure route and equipment occupancy. The meter was located in a rack with manual selector knobs to select between many groups of circuits that could be measured, Each device (or trunk) in a group would apply a 100kW resistor between ground and that group’s traffic measurement lead when in use. So if 40 trunks (two-wire voice circuits) in a group were in use, the meter would see 40 x 100kW in parallel (0.5mA per circuit or 20mA total). The resulting meter current would read as 40 Erlangs. The maximum group size was 200 circuits (full-scale on the meter). In the late 1990s, with the demise of the old analog mechanical exchanges, hundreds of these meters will have been recycled. Ian Michie, Blackburn, Vic. How times have changed! I saw this old Philco ad on Facebook. Imagine trying to sell a portable sound system like that today! Dr David Maddison, Toorak, Vic. SC Erlang meter clarification #3 In the days of the PMG after World War 2, Erlang meters were used to measure the use of circuits within the step x step exchanges and to other exchanges. The relay sets involved had a 100kW resistor fitted; the resistors were connected together and were fed into a rotary switch and then to the Erlang meter. When the relay set was in use, a positive (Earth) was put onto this 100kW resistor, and as the Erlang meter had -50V behind it, a reading of one Erlang would be shown. If 15 relay sets were in use, it would read 15 Erlangs. As each exchange had several junctions each to other exchanges, the Erlang meter was able to indicate at a glance what the traffic was in that exchange, both external and internal, and was used to calculate further expansion. I joined the PMG in 1950 as a Technician in Training, siliconchip.com.au Australia’s electronics magazine November 2020 13 MEMS: SILICON CHIP introduced you to tiny MEMS devices in the Digital Spirit Level project back in August 2011, which used a MEMS 3-axis accelerometer. Then in May this year, we described MEMS speakers which measure just 6.7 x 4.7mm. MEMS devices are microscopic and are typically fabricated from silicon, similarly to integrated circuits, combining mechanical and electronic elements in the same tiny package. Their mechanical components are precisely formed at micrometre scales! by Dr David Maddison M EMS devices can provide many different func- clopedia Britannica could be fitted on the head of a pin. tions. These include: accelerometers and gyro- That was achieved in 1985. In the lecture, Feynman also speculated about “swallowscopes as used in smartphones and airbag systems, display projection systems, in-wheel tyre pressure ing the doctor”, the concept of a miniature surgical robot. That goal too has more recently been partly achieved; sensors, biosensors such as blood pressure monitoring devices or ‘labs on a chip’, inkjet printer heads and many see the SILICON CHIP article in August 2018 on ‘pill cams’ and related devices. more that you would likely use in everyday life. The size of the devices formed may be measured in microns (one-thousandth of a millimetre), up to millimetres. Types of MEMS devices MEMS devices are typically sensors or actuators, or MEMS extends techniques used by the semiconductor industry to fabricate mechanical components such as multiple combinations thereof. Examples of MEMS sengears, beams, levers, diaphragms, springs and combs, all at sors are: a much smaller scale than traditional devices. Electronic • mechanical (force, pressure, velocity, position, acceleration etc) components can also be incorporated within the device, • thermal (temperature, heat often on the same piece of silicon. flow etc) MEMS technology was initial• chemical (composition etc) ly developed in the early 1960s, • radiant energy (wavelength, inbut it wasn’t known by that name tensity, polarisation, optical at the time. The term microelecswitching, laser etc) tromechanical systems was first • magnetic (field intensity, flux used in a US DARPA (Defense density, direction etc) Advanced Research Projects • electrical phenomena (electric Agency) report in 1986. field sensor, charge, voltage refOne of the first times that the erence etc) miniaturisation of machines was Other devices include oscillarecognised as a desirable objectors, displays, printers, motors and tive was in 1959, when the faswitches. mous Caltech physicist Richard In this article, we will describe Feynman gave a speech entitled as many of these various types of “There’s Plenty of Room at the MEMS devices as we have space Bottom: An Invitation to Enter a to fit. New Field of Physics”. In this speech, he issued two Uses for MEMS devices Fig.1: Bill McLellan’s 1960 answer to Richard challenges: Some common applications of One was to build a tiny elec- Feynman’s challenge: an electric motor smaller MEMS devices are: tric motor, which was achieved than the head of a pin. It is less than 0.36mm • Automotive and aerospace: senin 1960, but without the break- per side, even smaller than specified. Feynman sors for airbag actuation; fluid through technology that Feyn- had hoped for a breakthrough in technology; however, this was made with conventional level and pressure sensors; navman had hoped for (see Fig.1). techniques very cleverly applied. It still won igation; motion sensors for susThe second was to shrink let- Feynman’s US$1000 prize (about AU$12,000 in pension, active suspension and ters such that the entire Ency- today’s money). Source: Caltech Archives. 14 Silicon Chip Australia’s electronics magazine siliconchip.com.au Micro icroEElectro lectroM Mechanical Systems • • • • • • stability control; brake force sensor for anti-lock brakes; tyre pressure and temperature sensor; various avionics sensors. Chemical: various types of chemical analysis. Communications: mobile phones; fibre optic switches; voltage-controlled oscillators; lasers; optical splitters, couplers, modulators, attenuators and switches; DC-toRF frequency switches; fibre optic components. Computers and electronics: hard disk heads; inkjet printer heads; optical projectors; gaming controllers. Medical: blood pressure sensors; motion sensor to monitor activity such as in heart pacemakers; biological sensor systems; implanted sensors; sensors in prosthetic devices; ‘labs on a chip’. Navigation and Earth science: accelerometers; gyroscopes; seismic motion detectors. Military: munitions guidance; arming systems for munitions; numerous other applications listed under other categories above. Key discoveries and inventions Some key scientific discoveries and technologies that led to the development of MEMS devices are as follows, in date order. • 1745 and 1748: while modern electric motors generally use electromagnetic principles, it is possible to design a motor using electrostatic principles instead. In 1745, Benedictine monk Andrew Gordon described the “electrical whirl” and “electric chimes”, the first electrostatic mechanical devices capable of rotary and linear motion. In 1748, Benjamin Franklin invented the electric wheel, which is regarded as the first true electrostatic motor. Benjamin Franklin is often erroneously credited with the invention of electrostatic electric chimes (“Franklin Bells”), but these were invented by Gordon and used as an annunciator for his experimental lightning rod in 1752. Modern motors are electromagnetic devices as they are significantly more compact and powerful; however, for MEMS devices where it is difficult to fabricate coils to generate magnetic fields, electrostatics is often used instead. For more details, see the following videos: “Electric whirls” – https://youtu.be/6hkIGIAgxFU “Franklin’s Bells (5b1030)” – https://youtu.be/0TvvYa_ Qk6k “Electrostatic Motor” – https://youtu.be/9NkUcJBqVB4 • 1947: the first transistor was invented, paving the way for semiconductor fabrication technologies and electronic technologies that would later be used for MEMS. • 1954: the piezoresistive effect was discovered in silicon and germanium, where it is much greater than in DIY MEMS? Fig.2: Nathanson’s resonant gate transistor. It consists of a gold beam 0.1mm long and 5-10 microns thick which resonates at 5kHz. The inventor describes it as “an electrostatically excited tuning fork employing fieldeffect transistor ‘readout’.” Source: Nathanson et al., 1967, courtesy IEEE. siliconchip.com.au We saw an interesting but rather expensive book on DIY MEMS called “DIY MEMS: Fabricating Microelectromechanical Systems in Open Use Labs” by Deborah Munro from New Zealand. According to the author, MEMS devices could be fabricated in open-use facilities. You can read sample pages or buy the book at Amazon.com There is commercial software for designing MEMS layouts as well as other types of devices called “Layout Editor”. However, it can be used as a free file viewer for various microelectronics designs of any size, or as a free editor for small designs. See https://layouteditor.org/ Australia’s electronics magazine November 2020 15 Fig.3: K.E. Petersen’s electrostatically-driven torsional scanning mirror is etched from a single piece of silicon, with a reflective coating applied to the mirror’s surface. metals. This means that the material changes its resistance in response to a force. So these materials can be used to sense force, an effect now utilised by strain gauges, pressure sensors and certain accelerometers among others. Strain gauges based on this effect were developed in 1958, with Kulite (https://kulite.com/) producing the first commercial strain gauge in 1959. They also invented the silicon pressure sensor in 1961. • 1959: Jack Kilby of Texas Instruments filed the patent for the first integrated circuit (US Patent 3138743; https://patents.google.com/patent/US3138743A/en). He and Robert Noyce (US Patent 2981877; https://patents. google.com/patent/US2981877/en) of Fairchild Semiconductor are considered the co-inventors of the integrated circuit. Fig.4: the different results achieved by bulk micromachining methods with wet and dry etching and isotropic and anisotropic processes. The dark bands represent the etch-resistant masking material. The isotropic methods undercut the mask while the anisotropic methods do not, but must be aligned with the crystal matrix. 16 Silicon Chip This led to small-scale silicon fabrication technologies which are also applicable to MEMS. • 1968: arguably the first MEMS device in terms of the modern understanding of such devices was a 1968 invention (US Patent US3413573; https://patents.google. com/patent/US3413573/en) by Harvey Nathanson. It was a resonant gate transistor comprising a mechanical resonator and a transistor (Fig.2). The purpose of this device was to act as a tuner in miniature radios. The cantilever was about 1mm long. It was created using similar techniques as are used today; a batch fabrication process in which layers of metal and insulators on a silicon substrate are alternatively shaped and undercut by etchants, etchant-resistant masks and sacrificial layers. • 1970: the first silicon accelerometer was produced by Kulite, based on piezoresistivity of silicon where it changes its resistance in response to a mechanical load. • 1977: the first capacitive pressure sensor was developed at Stanford University. • 1979: HP produced the first micromachined inkjet nozzle, “thermal inkjet technology”. • 1980: K.E. Petersen of IBM invented the electrostatically-driven torsional scanning mirror using batch photolithography and thin-film techniques. It consisted of a flat armature-like shape made and etched from a single Fig.5: how surface micromachining uses a sacrificial layer (tan), which is eventually removed, to produce a freestanding structure; in this case, a cantilever beam. Source: memsnet.org Australia’s electronics magazine siliconchip.com.au Fig.6: a MEMS wafer subassembly joined to a CMOS wafer integrated circuit subassembly using eutectic and fusion wafer bonding. A cross-section of the final result is shown at upper right, with a plan view below. This is a gyroscope assembly. Source: Allan Hilton and Dorota S. Temple. piece of silicon, in which the mirror surface had a reflective coating – see Fig.3. The silicon arms (22 and 24) attached to the mirrored surface (30) were arranged as a torsion bar and could twist in response to electrostatic forces as supplied by the electrodes mounted beneath and on either side of the longaxis centreline of the reflector portion (14 & 16). This allowed a light beam to be reflected in one direction or another. This device is now the basis of digital video projector systems (pioneered by Texas Instruments and called digital light processing [DLP]) and optical switches, for example, to switch between several optical fibres, among other applications. See https://patents.google.com/patent/US4317611/en • 1981: IBM invents the scanning tunnelling microscope (STM) that can image individual atoms on a surface using a cantilever and probe. • 1982: a MEMS-based disposable blood pressure sensor is produced by Foxboro/ICT and Honeywell, selling for US$40. • 1982: the LIGA process is invented in Germany (more details below). • 1984: the first polysilicon MEMS device is produced (Howe, Muller). Fig.7: the LIGA process for making high aspect ratio MEMS devices. The first step is at the top, and the process continues clockwise. • 1985: the atomic force microscope (AFM) is invented, based on IBM’s STM. • 1988: the first electrostatic side-drive motors (100 microns across) are made by Richard Muller et al. at UC Berkeley. • 1989: an electrostatic lateral comb drive is fabricated in polysilicon (Tang et al.). Mask F SFx+ Etch Silicon nCFx+ Deposit Polymer Polymer (nCF2) F SFx+ Etch Fig.8: a tall, high aspect ratio gear produced with LIGA technology. siliconchip.com.au Fig.9: in deep reactive ion etching, an area is etched, a polymer coating is deposited and then further etching is performed. The polymer coating is preferentially etched at the bottom and not on the sidewalls due to the dominant flow direction of the plasma etchant. Australia’s electronics magazine November 2020 17 Fig.10(a): a silicon structure formed with deep reactive ion etching (DRIE). Fig.10(b): after the structure in Fig.10(a) is modified by removing the outer pillars and sharpening the central pillar with reactive ion etching (RIE), the result is a needle for interfacing with biological cells. Source: Yael Hanein et al. • 1992: the MEMS deformable grating light modulator (GLM), also known as the grating light valve (GLV), was invented. It has uses in display technology, graphic printing, lithography and optical communications. • 1993: the first surface micromachined accelerometer, the TI ADXL50, went on sale. It was mainly used for airbag deployment systems. More on this later. • 1994: Bosch patents the process for deep reactive ion etching. • 1995: Xenon difluoride, XeF2, was demonstrated as an isotropic etchant for MEMS and used to dissolve sacrificial layers to release moving parts. It is also highly selective, meaning it will not dissolve certain materials but will fully dissolve others giving excellent design flexibility for MEMS devices. • 1999: Lucent’s “LamdaRouter” optical network switches are released, based on MEMS devices. Fabrication techniques Fig.11: a Damasko watch spring made from polycrystalline silicon, which they refer to as “Epi-PolySilicon” (EPS). The silicon is made by vapour deposition followed by deep reactive ion etching (DRIE). It has many advantages over a traditional spring such as being non-magnetic, temperature insensitive, of minimal asymmetry and with highly precise dimensions. 18 Silicon Chip MEMS devices are made using integrated circuit fabrication techniques such as photolithography, etching and deposition etc. But enhancements and modifications of those processes are required, as well as new processes not normally used for IC fabrication. The fabrication processes for MEMS are known generally as microfabrication, and can be broadly divided into two high-level categories. Bulk micromachining, surface micromachining and the related process of wafer bonding are the standard methods. The other category is designed for structures with high aspect ratios and is known as HARMST (high aspect ratio microsystems technology). The main HARMST technologies are LIGA (a German acronym for lithography, galvanoforming moulding); silicon ion etching; and glass and hot embossing. Other, less-common fabrication methods utilise lasers, ion beams and electrical discharge machining. Fig.12: the evolution of MEMS accelerometers, from the 1991 prototype to 2004. Today, such sensors incorporate additional functions such as gyroscopes and are used for airbag inflation, vehicle stability control and vehicle rollover detection among other purposes. Australia’s electronics magazine siliconchip.com.au iPhones disabled by helium gas Fig.13: the functional sections of the ADXL50 accelerometer. Common materials used to manufacture MEMS devices are silicon, polymers, metals and ceramics. Bulk micromachining Bulk micromachining involves taking a substrate and using mechanical or chemical means to remove material. A popular chemical means involves immersing a substrate in an etchant chemical to remove material, a process akin to using ferric chloride for etching patterns on a PCB. This is called wet etching (see Fig.4). With appropriate choices of etchant, etchant temperature and substrate, the rate and preferred direction of etching can be controlled. For example, it is possible to selectively etch along certain crystal planes of a silicon substrate (anisotropic etching) or etch them all evenly at the same time (isotropic). The etching process requires that a suitable masking material, such as silicon dioxide, is used to protect those areas that are to remain. With etching, it is possible to undercut protected areas. It is also possible to dry etch using vapours or plasma instead of liquids. Surface micromachining There are many variations of surface micromachining, but they all involve a multi-stage deposition process in which a combination of both permanent and “sacrificial” layers are laid down (Fig.5). The sacrificial layers are there to support an overlying structure. Once that has been deposited, the sacrificial structure can be removed, for example by etching or dissolving it, leaving a structure such as a cantilever beam. A common sacrificial layer is PSG or phosphosilicate glass. Similar etching and dissolution processes can be applied as with bulk micromachining. Wafer bonding Wafer bonding is a process by which similar materials, such as silicon wafers, can be bonded to each other, or to dissimilar materials such as glass. The technique can be used to produce materials with a variety of desired properties, it can be used for encapsulasiliconchip.com.au This may sound like a myth, but it is true. About two years ago, a new medical MRI facility was being tested, and during testing, about 40 iPhones and Apple watch devices became disabled, but no Android devices were affected. It was thought that the machine must have emitted some type of electromagnetic pulse during testing that destroyed the phones. It was later discovered that there was a helium leak during testing which disabled the devices. iPhones, Apple watches and numerous other devices use MEMS oscillators to generate clock signals instead of traditional quartz crystal oscillators as they are cheaper and smaller. These devices are hermetically sealed in a package which contains either an inert gas or a vacuum. Changes to the gas mix or pressure inside the package can affect the oscillation frequency to such an extent that its output frequency is outside of the bounds at which the CPU or other clock-driven components will function. As helium molecules are small, it is very difficult if not practically impossible to seal the package against an infusion of helium. Therefore, the gas will diffuse through the hermetic seal, changing the atmosphere inside the device and causing its oscillation frequency to shift. This is not usually a problem as such devices are usually only exposed to the very low concentration of helium naturally present in our atmosphere. The devices returned to operation after a few days. The fact that it only affected Apple devices is because most Android devices use quartz oscillators. Apple mentions the susceptibility to helium in its documentation. The MEMS device in question is the SiTime SiT1532 and is said to be the world’s smallest (1.5mm x 0.8mm), lowest power 32.768kHz oscillator, and twice as accurate as a quartz crystal. See the video “MEMS oscillator sensitivity to helium (helium kills iPhones)” at https://youtu.be/vvzWaVvB908 Tests in that video show the device is disabled in a 2% helium environment after 30 minutes. Hydrogen molecules are slightly larger than helium molecules, and did not affect the device in that experiment. The video author also does a very interesting teardown of the MEMS device. tion purposes, or it can be used to create large multi-layered structures – see Fig.6. A variety of bonding techniques can be used such as fusion, anodic, thermocompression, eutectic, glass frit and adhesive bonding. LIGA LIGA is suitable for extremely high aspect ratio parts such as a column several millimetres tall but only 0.03mm thick (see Figs.7 & 8). LIGA works as follows: 1) A thick layer of PMMA (commonly known as Perspex or acrylic) is deposited onto an electrically conducting substrate such as silicon or metal. This PMMA is designed to be sensitive to X-rays or UV light. 2) The PMMA is exposed to X-rays or UV light via a mask and “developed” to remove unwanted material from the exposed areas. 3) Metal is deposited by an electrolytic process akin to electroplating, to fill the cavities where the PMMA was removed. 4) The PMMA is removed, such as by dissolution, leaving a free-standing metal structure. Australia’s electronics magazine November 2020 19 with a plasma as with bulk micromachining, but then the process is stopped, and the hole has an inert Teflon-like polymer layer deposited in it. The etching process then continues, but since the plasma is coming from a vertical direction, the sides of the hole are protected, while the protective layer in the bottom is removed and the substrate to be etched can then also be removed. The process is repeated until the desired hole depth is achieved. Hot embossing Fig.14: an electron micrograph of the ADXL50 single-axis accelerometer sensor. Since the X-ray source has to be a highly collimated beam from a synchrotron, this makes such a method expensive for parts fabrication. A variation of this process takes the part made and then uses it as a tool to create an impression into a polymer layer. The impression formed is then filled with metal. This moulding process can be repeated many times, reducing cost. UV LIGA is a cheaper process and doesn’t need a synchrotron source, but is only suitable for lower aspect ratio parts. Ion etching Deep reactive ion etching (DRIE) is used for making deep, high aspect ratio holes for MEMS devices. But it can also be used to fabricate other devices such as watch springs and deep trenches for capacitors in DRAM chips (see Figs.9-11). The most common process involves standard etching In hot embossing, a high aspect ratio metal part is made by another MEMS process such as LIGA with the inverse pattern of the part that is to be fabricated, and that is used as a mould to make a plastic part. Both the mould and a mouldable plastic are pressed together under vacuum to make the part. Such parts are cheap and are used in microfluidics for medical applications. For more information, see our detailed article on fluidics and microfluidics in the August 2019 issue (siliconchip. com.au/Article/11762). The first popular MEMS device The first MEMS device to obtain large-scale market acceptance was an accelerometer based on CMOS technology. It was fabricated using surface micromachining, as was the device by Nathanson mentioned earlier. The device was made by Analog Devices and called the ADXL50 (see Figs.12-14) and was released to the market once it was fully qualified, in 1993. Its application was to trigger airbags in cars (for more information on airbags, see our November 2016 article at www.siliconchip.com.au/ Article/10424). It incorporated both electronic circuitry along with micromachined structures. How forces change as objects shrink As devices shrink, the relative strength of various natural forces changes. Gravity becomes less important, but the van der Waals force (a short-range force between atoms and molecules) becomes proportionally strong. When the scale of an object changes, its volume changes by the cube of one dimension, and its surface area by the square of that dimension. At smaller scales, friction becomes more significant than inertia; heat dissipation (proportional to surface area) is more significant than heat retention (proportional to volume); and electrostatic forces are more significant than magnetic forces. As devices become smaller, they can be heated or cooled much more quickly, which is important for thermally-activated devices like some inkjet heads. Heat dissipation is not a major problem in most cases. The smaller a cantilever beam is, the lower its spring constant and the more flexible it is. 20 Silicon Chip Electrical resistance is inversely proportional to scale while capacitance changes linearly with scale and electrostatic forces change with the square of scale. Electromagnetic forces scale with the fourth power of conductor length, but for permanent magnets, the amount of strength retained is roughly linear with size (depending on their geometry and the specific application). The fact that electromagnetic forces decrease so dramatically with scale is the reason they are not commonly used in MEMS devices. An electrostatic device is preferred to an electromagnetic device, as the forces involved scale with the square of the dimension, not the fourth-power. In microfluidic devices, a reduction in radius of ten times results in a 10,000 times increase in pressure drop per unit length, due to a fourth power dependence. Consider a mirror on a MEMS device that might be used as part of an optical switch. A 50% reduction in the height, width and thickness of such a device results in the Australia’s electronics magazine torque required to rotate the mirror being reduced by a factor of 32. Beyond MEMS Beyond MEMS is NEMS or nanoelectromechanical systems. These are like MEMS devices but at the nanometre (one-millionth of a millimetre) scale. They are the next step beyond MEMS, and move into the realm of machines that can directly manipulate molecules like DNA, as in nature. As an example of a nanoscale machine from nature, consider the following simulation video by Australia’s Walter and Eliza Hall Institute of Medical Research of various processes involving DNA: www.wehi.edu. au/wehi-tv/molecular-visualisations-dna There are many other similar videos at https://www.wehi.edu.au/wehi-tv Apart from the possible future development of NEMS to manipulate DNA and other biological molecules, experimental NEMS devices are currently being made. There are unique challenges at such scales as intermolecular forces dominate. siliconchip.com.au A look at some MEMS devices There is already a vast variety of MEMS devices available. Here are just some of them – but it is simply not possible to cover all of them in the available space. Some other uses for MEMS not discussed below include blood pressure monitors, pressure monitors for other applications, pill cams, ultrasonic transducers, DNA microarrays, micropumps, flow sensors and microfluidics applications. Texas Instruments digital light processing (DLP) A scanning electron microscope image of the micromirrors on the DLP device. DLP is a MEMS video projection technology using micromirrors to direct a beam to a projected area or away from it and onto a heatsink. Toggling the micromirrors rapidly gives control of brightness from 0% up to 100%. Colours are produced either with one DLP chip and a colour wheel, or with three DLP chips and three differently coloured beams of light. A MEMS micro-mirror device, the core component of a DLP device. Each micromirror drives one pixel. The mirror is mounted on a suspension device with a torsional restoring spring. The mirror is moved by electrostatic forces from the columns at upper left and lower right. Source: Wikimedia user Egmason. MEMS accelerometers MEMS acceleroMotion meters are made of 1.3 Micron Gap many interdigitated 125 2 Micron Microns Overlap fingers, similar to thick the comb drive A single finger of a shown overleaf. typical accelerometer As the device sensor element. It is a differential capacitor experiences a where the rate of force, the capchange of the output is acitance between proportional to the force the fingers changes. experienced. Source: Analog Devices. Rotary MEMS motors Rotary MEMS motors may be driven by electrostatic or by other means. MEMS three-axis gyroscope A MEMS gyroscope is correctly known as a Coriolis vibratory gyroscope. It contains parts that vibrate in all three axes. They will tend to continue to vibrate in the same plane, but if an external rotational force is applied, the Coriolis effect causes a force to be generated between the vibrating structure and its support. This force is measured to determine the rate of rotation. Accelerometers and gyroscopes can be combined in one device, which is then known as an inertial measurement unit (IMU). A MEMS threeaxis gyroscope: (1) outer frame (2) inner frame (3) driving comb electrodes (4) parallel plate sense electrode (5) double folded beams (6) anchors (7) linear beams and (8) self-rotation ring. Source: Minh Ngoc Nguyen et al. Grating light valve (GLV) GLV is a technology that competes with DLP for display projection. Each pixel in a display device is representing by multiple ribbons which are moved electrostatically by a distance a tiny fraction of the wavelength of light. When all the ribbons are aligned, the device acts as a mirror, and all light is directed towards the image. When the ribbons move apart, a diffraction grating is formed. In that case, only some light is directed to the image, while other light goes elsewhere. When the distance between adjacent ribbons is ¼ of the light wavelength, no light is reflected towards the image. By varying the distance between zero and ¼ wavelength, a range of brightnesses is generated. Spectrometer on chip A spectrometer for chemical analysis can be fabricated with MEMS. A MEMS spectrometer on a chip by Si-Ware Systems, on their proprietary Silicon integrated Micro-Optical Systems Technology (SiMOST) platform. MEMS atomic force microscope (AFM) AFMs are based on techniques from scanning tunnelling microscopy (STM). Today, AFM probes or even the principal parts of the device are made with MEMS technology. AFMs are capable of imaging individual molecules and sensing or manipulating individual atoms. The operating principle of an atomic force microscope. PZT refers to a piezoelectric material that can change its dimensions in response to an applied electric field. The tip on the cantilever follows the atomic profile of the surface, with its position being monitored by the deflection of the laser or by other methods. Source: Wikimedia user OverlordQ. An atomic force microscope on a chip developed at Laboratory for Dynamics and Control of Nanosystems at the University of Texas by M. G. Ruppert, A. G. Fowler, M. Maroufi and S. O. R. Moheimani. Strain gauges A MEMS strain gauge relies on the change in capacitance of interdigitated electrodes as it is extended. An electron microscope image of a MEMS electrostatic motor with false colour. The central red object is the bearing, which is surrounded by the rotor. Around the rotor are the stators which are driven with phased voltages. Source: www.mems-exchange.org siliconchip.com.au A grating light valve (GLV) from Silicon Light Machines, Inc. Australia’s electronics electronics magazine magazine Australia’s N November ovember 2020 21 Gears MEMS IR sensor Gears can be fabricated with MEMS, as seen below. Infrared sensors can use photonic sensors such as in CCD or CMOS devices, or they may sense heat such as with thermoelectric infrared sensors. Thermoelectric sensors have the advantage of lower noise and possibly lower cost than photonic sensors. Infrared radiation heats a thermocouple, producing a voltage proportional to the radiation intensity. An actual MEMS strain gauge. As the device is stretched, the capacitance changes in relation to the amount of extension. Source: Michael Suster et al., Case Western University. Optical switches A MEMS optical switch contains several optical fibre inputs and outputs, and any input can be switched to any output via the use of two MEMS tilt mirror arrays. A schematic view of a 3D optical switch. A MEMS demonstration geartrain. Such gears have been driven at 250,000rpm. Source: Sandia National Laboratories. MEMS inkjet printer heads Inkjet printer heads are a common MEMS device in everyday use. A recent development is the move from rapid heating and bulk piezoelectric materials to thin-film piezoelectric materials which are deposited as part of the MEMS fabrication process. This provides more design flexibility and lower cost. Microfluidic technology is also incorporated into inkjet printer heads. Comb drive A MEMS comb drive is a linear actuation mechanism that consists of two interlocking microscopic parts resembling hair combs. As a voltage is applied between them, the parts are drawn together by electrostatAn electron ic forces. Comb microscope image drive actuators of comb drive have been used components. With the application of as the driving elean electric field, the ments for resona- interdigitated fingers tors, electromeare drawn toward each other. When chanical filters, the electric field is optical shutters removed, silicon springs return the and device to its starting microgrippers to position. Source: name just a few Sandia National Labs. applications. Fig.36: a cross-sectional diagram of a MEMS thermoelectric IR sensor. Infrared radiation enters the device and heats the thermocouple. G represents the paths of thermal losses. Source: Dehui Xu, Yuelin Wang, Bin Xiong and Tie Li. MEMS loudspeakers and microphones MEMS loudspeakers are relatively new and were featured in the May 2020 issue of SILICON CHIP (siliconchip.com.au/ Article/14441). MEMS microphones are now commonly found in consumer devices such as smartphones, microphones with earphones, headsets etc. A cross-sectional diagram of a Philips inkjet printer head in which three MEMS wafers are bonded together. The ink is propelled via a thin-film piezoelectric driver which is also deposited during the fabrication process. Source: Philips. Exterior view and a cross-section of a TDK T4064 MEMS microphone, 2.7mm x 1.6mm x 0.89mm. The device has an ASIC (applicationspecific integrated circuit) incorporated into the housing. The diaphragm and the backplate together act as a parallel plate capacitor, and when the diaphragm, moves the capacitance changes and an electrical signal is produced. A comb driver actuator as the driver for a resonator device. Source: Wikimedia user Huseyintet. 22 22 S Silicon Chip Australia’s Australia’s electronics electronics magazine magazine siliconchip.com.au Switches Bio-MEMS MEMS switches offer the ability to switch frequencies between DC and 14GHz (Analog Devices commercial models) and have the advantage of being reliable, small (4mm x 5mm) and having low power consumption. A selection of Bio-MEMS devices follows. Smart contact lens An example of a smart contact lens, the SENSIMED Triggerfish with MEMS technology with continuous ocular monitoring for glaucoma patients. Several companies are developing MEMSbased smart contact lenses. These may have features such as autofocus, data display via Bluetooth, intraocular pressure monitoring for glaucoma etc. An RF relay which uses a comb drive as the actuator. Source: L. Almeida et al., Auburn University. Debiotech NanoPUMP This device is designed for the transdermal infusion of insulin or other substances. It is also the MEMS pump component of the JewelPUMP insulin infusion system and is connected to a reservoir with enough product for a week. It is connected to the patient via a flexible cannula. It also connects to a monitoring and control App on a smartphone. Neural probes MEMS can be used to fabricate silicon neural probes for brain research. Glucose sensor A selection of MEMS neural probes by NeuroNexus. Microneedles MEMS microneedles are fabricated to deliver medication just below the skin. An Analog Devices EVAL-DGM1304SDZ evaluation board featuring a single-pole, four-throw MEMS ADGM1304 switch as well as a calibration transmission line at the bottom. The MEMS chip is at the junction of the five RF lines. MEMS oscillators MEMS oscillators are smaller, cheaper, more temperature stable, more rugged and more power-efficient than quartz crystal oscillators. In some cases, their frequency can be programmed from 1Hz to 725MHz in 1Hz increments. They have found applications in areas such as automotive electronics and smartphones. Also, see the related panel earlier on the effects of helium. A MEMS glucose sensor designed for implanting. Source: Columbia BioMEMS Laboratory. An implantable MEMS sensor for continuous glucose monitoring is being developed (see above). Glucose enters a chamber via a semipermeable membrane and binds with a glucose-sensitive substance attached to a diaphragm. The diaphragm is made to vibrate via an external magnetic field which interacts with a magnetic permalloy attached to it. The vibrational amplitude changes according to glucose concentration. This is measured via the change in capacitance between the moving and the ground electrode. DNA nanoinjector A MEMS DNA nanoinjector invented at Brigham Young University in the USA allows scientists to inject DNA into living cells. A MEMS oscillator. The resonator beam is driven by electrostatic forces between the beam and an electrode beneath it. The dual-output Microchip DSA2311 comes in a 2.5mm x 2.0mm x 0.85mm package and each output can operate between 2.3MHz and 170MHz. Source: Microchip Technology, Inc. siliconchip.com.au A DNA nanoinjector. Australia’s electronics electronics magazine magazine Australia’s The MEMS-fabricated DebioJect intradermal injection microneedle array by Debiotech, for delivery of medications just below the surface of the skin. Virus detection MEMS plays an important role in COVID-19 testing. One test involves the partitioning and multiplication of a small amount of a patient’s viral genetic material into a much larger amount that is easier and more accurate to analyse. This way, a test result can be obtained in minutes rather than hours. Part of the MEMS Microfluidic Array Partitioning chamber of the Combinati Absolute Q platform. This is used for rapid polymerase chain reaction (PCR) analysis, for COVID-19 as well as other tests and analyses. SC N November ovember 2020 23 2020 23 HO HO HO . . . More Yuletide Magic from Tim Blythman Our Tiny LED Christmas Tree from last year was so popular we decided to follow it up in spectacular style with not one, not two, but seven more festive decorations that you can build! They’re small, cheap and easy to put together, so you could easily build all eight for Christmas this year; or even several of each. M any hundreds of our Tiny the same circuit into different shapes so that Santa and his reindeer can be part of the fun, too. LED Christmas Tree from and colours for extra variety. And that’s precisely what we’ve November 2019 (siliconchip. com.au/Article/12086) were built. done. These assorted Christmas orna- The circuit The circuit diagram for our new OrSome people bought ten or more kits! ments are all very tiny, but perfect for We even made some for our own trees decorating your tree. We’ve come up naments, shown in Fig.1, is essentially with unique patterns to suit each Or- the same as last year’s Tree. at home. If you want some more detail about It’s no wonder that they remain so nament, and we’ve also added a twist, the specific design choicpopular, as they are an easy es we made, we recomway to completely deck out mend that you look at the your tree with some great previous article. looking animated decoraIn particular, see the tions. panel about LED CharBut we were struck by lieplexing (on p48 of the a letter from Anthony and November 2019 issue) to Annabel, which we pubfind how we control so lished in our February 2020 many LEDs from an 8-pin Mailbag section. Here we microcontroller. learned that kids as young The circuit is based as nine were successfularound IC1, a PIC12F1572 ly building the Tiny LED 8-bit micro, powered diXmas Tree. Just in case you missed rectly from a 3V CR2032 Now there’s no excuse it, here’s the Tiny button cell. The cell is not to embrace SMD conChristmas Tree project simply wired across the struction! from November 2019 which inspired these micro’s supply pins, pin Not only that, but An1 (VDD or positive supply) thony and Annabel also new designs. Still a perfectly viable and up-to-date project in its own right. it can be used on its own or in conjunction with any and pin 8 (VSS or negative offered up the excellent of the new ornaments. (siliconchip.com.au/Article/12086) supply). idea that we should make 24 Silicon Chip Australia’s electronics magazine siliconchip.com.au Eight LED Christmas DECORATIONS We’re using a PIC12F1572 for reasons explained in the “New PIC” article on page 83 but we’ve created firmware images that suit the PIC12F675 too, so you can use either IC for this project. IC1 comes in a small 8-pin SOIC (small outine integrated circuit) package. It’s compact but easy enough to work with. Four of IC1’s GPIO (general purpose input/output) pins (pins 2, 3, 5 and 6) are connected to 100Ω resistors and in turn to the matrix of 12 LEDs. Between each pair of pins are two LEDs, one facing one direction and the other, the reverse direction. Six combinations of pin pairs multiplied by two LEDs per combinations makes 12 LEDs. We can program the microcontroller to connect the GPIO pins to either the battery positive (“high”) or negative (“low”) or neither (“high-impedance”). Through different combinations, we can light up each one of the LEDs in turn. Note that the LED numbers shown here do not necessarily correspond to the sequence in which they are driven. The numbers in brackets indicate the way they are ordered in the software. We’ve done it this way as we expect that people changing the software pattern will find the software (cyan) numbers more logical than the designators used to lay out the PCBs. These ‘software’ numbers also correspond to the order in which the LEDs were laid out on the original Tree. We’ve tried to keep this order in place for the other Ornaments. The Here’s a selection of the Christmas decorations we’ve made with plenty of time before the big day. Apart from Santa himself (which of course must be red!) the others are available in a variety of colours, courtesy of some clever PCB manufacturers (see parts list). siliconchip.com.au Australia’s electronics magazine November 2020 25 SC TINY led XMAS ORNAMENTS Fig.1: the circuit for our Tiny Christmas Ornaments is essentially the same as that for the Tiny LED Christmas Tree published in November last year, albeit with a newer PIC micro. It is very simple and allows one LED to be lit at a time. The software can light these LEDs in any sequence, and different versions have been created to suit the physical LED layout of each Ornament. upshot of this is that you can use the same software to get different patterns for each design. Software To generate patterns with the LEDs, we program the microcontroller to set its GPIO pins in a particular state, then go to ‘sleep’ for a short while (around 16ms). It then ‘wakes up’, turns the LEDs off and then sleeps again for around 64ms. This cycle repeats, with the program deciding which LEDs are lit so that an interesting pattern is displayed. By keeping the micro in sleep mode most of the time, power consumption is minimised. As the microcontroller is sleeping practically all the time, the power is mostly used to drive the LEDs. And because the LEDs are only on around 20% of the time, the battery lasts for a long time. We stated last year, based on calculations, that a typical battery should last around three months. Our prototype (using 1kΩ LED current-limiting resistors) actually lasted for five months before beginning to dim and fade. As a result, we are recommending that constructors use 100Ω resistors instead, giving around two to three months of life; more than enough to last through Christmas and into the New Year. We’ve created different LED sequence patterns to best suit each Ornament, plus a semi-random pattern which can be used on any of the Ornaments. Since the circuit is effectively the same, you can try the different programs on the various Ornaments to see if they give displays that you like. The Ornaments There are seven new Christmasthemed Ornaments. Five are intended to be used individually, while two can be hung separately or combined to cre- SC Fig.2: as we think the Bauble will be popular, we are offering it in red, yellow, green and blue. That way, you can build a mix and also vary the LED colours. Its pattern (16111196.HEX) cycles the LEDs around the Bauble, or you can use 16111190.HEX to get a random, flickering pattern. 26 Silicon Chip Australia’s electronics magazine Fig.3: our prototype Cane (overleaf) is green only because there were delays getting red PCBs due to COVID-19. But this overlay diagram shows the PCB in red! The Candy Cane is designed to be hung with the ‘hook’ at the top via a small hole. The firmware (16111199.HEX) scans the LEDs from one end to the other. siliconchip.com.au SC ate a centrepiece for your (full-sized) tree. Of course, you can also still build the Tiny Trees published last year, for a total of eight different Ornaments. The five new individual Ornaments are a Stocking, Christmas Cap, Candy Cane, Star and Bauble. Since we figure that any tree looks great covered in baubles, we’re making that design available in four different solder mask colours. You could get an assortment of coloured baubles and deck out your tree in spectacular fashion! Like last year’s Tree, the Stocking PCB also comes in different colours. The two special Ornaments are the Reindeer and Santa’s Sleigh. These can be hung individually, but we’ve also added extra pads to these PCBs so that they can be wired up together, with the wires acting as the harness (whoa there, Rudolph!). With these, you can even rig up a larger battery pack, so that you can harness up a full complement of a dozen Reindeer, just like Santa does, but not worry about running out of power on Christmas Eve. Just like last year’s Tiny Tree, the choice of LEDs is entirely up to you as well. We built our prototypes with a random mix of red, green and white LEDs, but you could also add yellow, amber, pink, cyan or blue to the mix. Our kits come with the ‘standard’ colours, but you can also order extra sets With a 1.27mm pin spacing, it’s easy enough to solder individual pins on the PIC12F1572’s SOIC-8 package. If you do make a solder bridge between the pins, flux paste and solder braid can be used to fix it. The blobs of solder shown here are much larger than is needed, but it works; a bit too much solder is better than not enough! of LEDs in those other colours via our Online Shop at the same time (see the parts list for details). For example, you might like to build a blue Bauble and deck it out with blue LEDs. But as long as Rudolph has a red nose, it doesn’t matter! Construction We know you’re excited, so we’ll jump right into the construction. For the most part, all seven of the new Ornaments are very similar. Refer to the PCB overlay diagrams, Figs.2-8, which show where the components go on both sides of each Ornament. The instructions here apply to all the Ornaments, but if you’re building the Reindeer or Santa Sleigh, we’ll follow up with extra information about SC how these can be wrangled together. As each Ornament has a unique pattern, if building multiple types, you should avoid getting the pre-programmed micros mixed up. If you have pre-programmed PIC microcontrollers, then you won’t need to fit CON1, the programming header. In that case, you should remove the small snap-off tab for CON1, as it will be easier to do this now than later. The exceptions are the Bauble, the Reindeer and the Santa Sleigh. The Bauble has a removable tab, but that is also the best way to hang it, so it should be left on. The Reindeer and Santa Sleigh don’t have removable tabs as these are used for wiring in the ‘harness’. Depending on what your plans are, C siliconchip.com.au Fig.4: the Star Ornament with a white PCB silkscreen is one of the more striking variants and will look great against a green Christmas tree. It is also one of the more compact PCBs. This means that some traces are close to where the CON1 section snaps off. Its pattern (16111198.HEX) has the LEDs radiating out from the centre of the PCB to each tip in turn. Australia’s electronics magazine November 2020 27 Fig.5 (above): although some of the LEDs on the Cap are at slightly different angles, the cathodes are still towards the left-hand side. The tab for CON1 is very close to some LEDs at lower right, so remove this tab with care. The 16111193.HEX pattern cycles up from each LED in the bottom row in turn, similar to the original Tree Ornament. Fig.6 (right): don’t expect to get any big presents in these Stockings; they’re very small! You can still hang them from the fireplace if you don’t have room on your tree. The green PCBs will look striking, while red is more traditional. The pattern (16111194.HEX) involves the LEDs cycling down each side in turn, similar to that used for the Candy Cane. you may not need to fit the cell holder to the Reindeer or Santa Sleigh, as the harness can be used to power these Ornaments. For the other Ornaments (the Star, the Stocking, the Cap and Candy Cane), if you do not need to program the micros in-circuit, carefully score along the line of small holes with a hobby knife. This ensures that the copper traces don’t tear off the PCB. Then carefully flex the tab; flat-nosed pliers are suitable for this. It should snap fairly cleanly, but you can tidy this up with a file. Do all of this outside while wearing a mask if possible, as the PCB dust can be an irritant. Soldering This is probably the most critical part. For soldering small surfaceThe LEDs on the front of the PCB are 3216 (1206 imperial) sized and at 3.2 x 1.6mm, are easy enough to manage with most standard soldering iron tips. Note the small green triangle at the upper left of each LED, aligned with the little white cathode mark seen underneath the part. 28 Silicon Chip Australia’s electronics magazine mounted parts, we recommend having a fine-pointed soldering iron, tweezers, flux paste, solder braid (solder wick) and a magnifier. A ball of adhesive putty like Blu-tack can be used to hold the PCB during soldering. The solder flux creates smoke when heated, so a solder fume extractor is handy to have too, or alternatively, work next to an open window. It’s best to have a clean work area with plenty of space and light. The small SMD parts have been known to jump out of the tweezers’ grip. If your work area isn’t tidy, you will have no hope of finding a dropped part! A good technique for working with the SMD parts is to solder one lead to roughly place (tack) the part. If necessary, remelt this join and adjust the part with tweezers until the component is flat against the PCB and all pins are square within their pads. Then carefully apply solder to the remaining pads, then go back and refresh the first pad by applying a bit more fresh solder. It’s also a good idea to apply flux paste to the pads and pins before solsiliconchip.com.au Fig.7: unfortunately, most manufacturers don’t offer brown PCBs! The spots along the Reindeer’s back are holes in the top solder mask, which allows the natural PCB colour to show through. The LED on the nose should be red for the first Reindeer in the harness (Rudolph), and a different colour for the rest. The pattern (16111195.HEX) makes the LEDs course down from the antlers along the Reindeer’s body in two passes, giving the impression of great speed! CAUTION – watch those button cells with small children about! As with any project that uses button cells, care should be taken to ensure there is no chance that it can get into the hands of a small child. Many will immediately put it in their mouth and if swallowed, it can do serious harm. If you have small children (under about five years), either cover the Ornaments in clear heatshrink tubing or glue the battery in place (eg, using neutral-cure clear silicone sealant) so that it cannot be easily removed. dering them. This helps to draw the solder from the iron onto the pads and pins. Use a magnifier to inspect the solder joints. There should be a good fillet between the pad and pin, but not so much solder that it bridges to a nearby pin. See our photo for a closeup view of a good solder joint. The solder should look smooth and glossy. You should also pay close attention to the overlay diagrams to check your progress as you assemble each Ornament. If you’re building multiple ornaments (and why wouldn’t you?) you can either make them one at a time, or do them all in parallel – it’s up to you. Just make sure that if you do them in parallel, you don’t get parts for different Ornaments mixed up. Before going any further, figure out which colour LEDs you want to place where on each Ornament. Because the LEDs can look identical when out of the pack, it’s best to either fit all of each LED colour in one go, or else only take out the number that you need at any given time. If you do lose track of the LED colsiliconchip.com.au ours, most DMMs set on diode test mode will illuminate an SMD LED if you touch the probes to either end; but be careful not to press too hard, or you might flick the part away! If it doesn’t light up, try swapping the probes. Usually, it will light with the black probe to the pad marked with a green dot (the cathode). The remainder of the instructions describe how to assemble any single Ornament. Start by fitting IC1 on the back of the PCB. Check the IC’s orientation by looking for a small dot in one corner and a bevel along one edge. These two features must line up with the line marked on the silkscreen and shown in the associated PCB overlay diagram. The dot should also be closest to the notch shown in the IC outline. Also, the PCB pad for pin 1 is rectangular, while the others are rounded. Use the technique mentioned above to tack the IC in place by a single pin. Don’t be concerned if you make a solder bridge; focus on ensuring the IC is correctly located, with all eight leads Australia’s electronics magazine aligned within their respective pads. Remelt the solder and adjust if necessary, then solder the remaining pins. If you have a solder bridge between two or more pins, apply flux paste and rest some solder braid on the bridge. Press the soldering iron onto the braid and once the solder has melted, carefully draw the braid away. If there is a lot of solder, you may need to repeat this process. The rest of the components have a much coarser pin pitch and are easier to solder, as well as much less likely to bridge. Place the 10kΩ resistor next. It will be marked ‘103’ or perhaps ‘1002’ (although you may need a magnifier to read it). It and the other resistors are not polarised, so they can be installed either way around. Refer to the PCB overlay diagram and board silkscreen to see where it goes. With that in place, fit the four 100Ω resistors. They are marked ‘101’ or perhaps ‘1000’, and fit on the pads marked 100. Now flip the PCB over to install the November 2020 29 SC Fig.8: as for the Reindeer, a mahogany PCB solder mask would have been great for Santa’s Sleigh, but red it is. The LEDs (using 16111197.HEX) follow a similar pattern to the Reindeer, strobing along the length of the Sleigh in multiple passes. While sticklers would use green LEDs along the Sleigh’s starboard side and red for the port side, any combination of colours is sure to light up the sky. LEDs. These are polarised and need to have their cathode fitted closest to the pad marked with a line. Typically the LED cathode is marked with a green dot or arrow, but we have seen some that have their anode marked this way. So it’s best to check with a DMM (as described above). When it lights up, the black probe is on the cathode side. We’ve orientated the LEDs all the same way on each board as much as possible. The cathodes should all point to the left and/or down with the boards orientated as shown in Figs.2-8. The cathode side of the LEDs is indicated on the PCB overlay diagrams with a box around that LED pad. But note that on the actual PCBs, some of the decorative silkscreen patterns are printed over the component footprints, so they are not always visible. As long as you remember the left/ down rule and make sure the boards are orientated as we show them, all the LEDs should work. Use the same technique as before; solder one lead, ensure it is square and flat, then solder then second lead and refresh the first. This is doubly important for the LEDs, as this is the side of the PCB that will be seen. With this done, clean up the flux 30 Silicon Chip residue on the smaller components using a solvent like isopropyl alcohol, methylated spirits or acetone. While not necessary with most fluxes, it helps to make the front of the PCB look neater for when it is placed on your Christmas tree (or wherever you plan to display it). For most Ornaments, the last step is to mount the coin cell holder. Check the notes for the Reindeer and Santa Sleigh combination below if you plan to wire up a harness. In that case, you don’t need the cell holder (although you could still fit it). Its orientation is important to ensure that you can get the cell in and out. Both pads connect to the positive side of the battery, with the negative terminal being the large circular pad on the PCB. For the Candy Cane, Cap and Stocking, you can fit it either way around. For the others, check that the little tabs on the battery holder are facing towards the middle of the PCB. This way, the holder’s opening will face towards the nearest edge of the board. As the cell holder is larger than the other components, and made entirely of metal, you should turn up the temperature on your soldering iron before soldering it (if possible). As for the other components, sol- Simply resting a five-way pin header into CON1 makes enough contact to program the PIC. Apply gentle force to ensure that the pins bite in slightly during the programming process. We’re using a PICkit 4, but a PICkit 3 will also work. Australia’s electronics magazine siliconchip.com.au der one lead and adjust it so that the other lead lines up with its pad. Then solder the second lead and go back to refresh the first. If you have a programmed PIC, then all you need to do is fit the cell (positive side up, as per the marking on the battery holder) and the Ornament should flash away. If it doesn’t flash at all, remove the battery and check for short circuits on the battery holder or PIC. If only some of the LEDs work, check the LED orientation, and the LED, resistor and PIC soldering. If you have fitted a blank PIC, it won’t do anything until you program it. In-circuit programming While CON1 is designed for a row of pin headers, you do not need to fit it, even if you need to program the PIC on the board. Unless you plan to program the PIC multiple times, merely holding the header in place to make contact with the pads is usually sufficient and gives a neater final result. Our diagreams and photos show a right-angled header attached, as it allowed us to lay the programmer and PCB flat to prototype our software, although a vertical pin header would work too. You might like to use a rightangle header if you are looking to program your own patterns. Another reason to fit CON1 is that pins 2 & 3 on CON1 can be used to supply power to the board, in place of the onboard cell. If you prefer to use a USB power supply, the Ornaments will happily run from 5V (and will be much brighter). Feed 5V into pin 2 of the connector and connect the ground to pin 3. That’s how we powered our Santa with Reindeer, although it works for the other ornaments too. To fit CON1, rest the header pins in the pads, with the exposed ends facing back, so that the pins are less visible from the front. Solder one pin and check the connector is straight, then solder the remaining pins. You could snap the CON1 section off the PCB once programming is complete. It’s a bit more awkward to do once CON1 has been fitted, but it can be done with care. You’ll need a PICkit 3 or PICkit 4 (or another programmer than can work with PIC12F1572s). We use the MPLAB X IPE software siliconchip.com.au Parts list – Tiny LED Xmas Ornaments 1 surface-mount coin cell holder [Digi-key BAT-HLD-001-ND, Mouser 712-BAT-HLD-001 or similar] 1 10kW 3216/1206 size SMD resistor [eg, Altronics R8188] 4 100W 3216/1206 size SMD resistors [eg, Altronics R8044] 12 3216/1206 size SMD LEDs, any combination of colours [eg, Altronics Y1041, Y1056, Y1073, Y1079, Y1085] 1 CR2032 lithium coin cell (CR2025 is also suitable but with reduced lifespan) 1 5-way right-angle or vertical header strip (CON1) (optional; for programming IC1) Plus one of the following: * Tree: green, red or white PCB coded 16111191, 54 x 41mm, plus PIC12F1572-I/SN programmed with 16111191.HEX * Cap: red PCB coded 16111193, 54 x 56mm, plus PIC12F1572-I/SN programmed with 16111193.HEX 16111191R 16111191W 16111191G 16111193 16111194G * Stocking: red or green PCB coded 16111194, 41 x 81mm, plus PIC12F1572-I/SN programmed with 16111194.HEX 16111194R * Reindeer: red PCB coded 16111195, 91 x 97mm, plus PIC12F1572-I/SN programmed with 16111195.HEX 16111195 16111196R * Bauble: red, yellow, green or blue PCB coded 16111196, 53 x 46mm, plus PIC12F1572-I/SN programmed with 16111196.HEX 16111196G 16111196Y * Santa’s Sleigh: red PCB coded 16111197, 79 x 91mm, plus PIC12F1572-I/SN programmed with 16111197.HEX 16111196B 16111197 * Tiny Star: white PCB coded 16111198, 56 x 54mm, plus PIC12F1572-I/SN programmed with 16111198.HEX 16111198 * Candy Cane: red PCB coded 16111199, 84 x 60mm, plus PIC12F1572-I/SN programmed with 16111199.HEX 16111199 Extra parts for Reindeer harness (one set for each Reindeer) [not included in kits] 1 2-pin 2.54mm-pitch socket header AND 2 male-female jumper wires OR 2 lengths of 0.63mm diameter enamelled copper wire Extra parts to power Reindeer Harness from AA cells [not included in kits] 1 2-pin 2.54mm-pitch socket header 1 2xAA or 3xAA battery holder, ideally with switch (eg, Jaycar PH9280) Kits Each kit comes with all the parts required to build one Ornament (except the coin cell) and includes 12 red, 12 green and 12 white LEDs so you can mix and match them as you see fit. Other LED colours are available; they are listed below. All kits are $14 each (10% discount for active subscribers) plus postage, which is $10 per order within Australia. (If you order 50 kits, the postage is still $10). All kits have the same catalog code (SC5579) with options for the Ornament type and PCB colour (for those Ornaments available in more than one colour). For example: for a red bauble kit, you would order SC5579/bauble/R. For the sleigh, order SC5579/sleigh (because there is only one colour) You can still order the original Tiny LED Xmas Tree kit via the earlier catalog code, SC5180. Extra LEDs * 10 amber amber: Cat SC3394, $0.70 * 10 yellow yellow: Cat SC3405, $0.70 * one pink pink: Cat SC3406, $0.20 * 10 blue blue: Cat SC3396, $0.70 * 10 cyan cyan: Cat SC5199, $1.00 Australia’s electronics magazine November 2020 31 Fig.9: we powered Santa’s Sleigh and two Reindeer from a pair of AAs in a Jaycar PH9280 switched battery enclosure. The red wires are for +3V and the grey wires 0V; you could use different colours, just don’t cross them over! With each Ornament drawing less than 1mA, many more could be powered this way. IC1 operates from 2V to 5.5V, so it is well-suited to running from two or three AA cells or USB power. As shown in the photo on page 24, we rigged it up with plugs and sockets for flexibility. But you could solder wires straight to the pads. Ideally, each Ornament should be tested separately before wiring them together. (integrated programming environment), which can be downloaded for free as part of the MPLAB X IDE (integrated development environment). There are downloads for Windows, Mac and Linux at www.microchip. com/mplab/mplab-x-ide The latest version (5.40) only works with 64-bit processors, so you may need an older version if you have a 32-bit processor; older versions can be found at www.microchip.com/development-tools/pic-and-dspic-downloads-archive When installing this software, ensure that you enable support for 8-bit processors (which includes the PIC12F1572). Before connecting a programmer, make sure there is no cell fitted to the Ornament. The PICkit programmers can supply 5V, and it is not a good idea to apply 5V to a 3V cell (the programmer is probably smart enough to avoid doing this, but better safe than sorry…). The following process assumes you are using a PICkit and the MPLAB X IPE, although other programmers will work similarly. Start by browsing to open the HEX file (found in the software zip download from the SILICON CHIP website). There is a HEX file for each PCB design; find the number which matches the PCB you are programming. Alternatively, 16111190.HEX is simply a 32 Silicon Chip semi-random pattern which will work with any of the Ornaments. Connect the programmer to the computer and then connect the programmer to the Ornament. The pin marked with an arrow on the PICkit programmers is pin 1, and this connects to pin 1 of CON1. If you have not soldered CON1, then place a row of pin headers into the PICkit header and rest this in the pads on the PCB instead of plugging it into the header. Apply a gentle force to ensure contact is made. Set your programmer to provide power to the target. The MPLAB X IPE has buttons for ‘Apply’ and ‘Connect’. You’ll need to click these before clicking ‘Program’. If all is well, the LEDs should start flickering when programming is complete. Since one of the LED pins is also used for programming, some LEDs may light out of sequence. Detach the programmer and fit the cell to check its full operation. There’s not much more to it than that. Mounting The Ornaments have several mounting options. Most of them have a plated-through hole at the top to which a loop of tinned or enamelled copper wire can be soldered, so that the Ornament can be hung on a tree branch. The Bauble lacks these pads, but it can be hung from a wire soldered to the Australia’s electronics magazine pads of CON1 (the centre pad is best). The Tiny LED Xmas Tree can be made to stand up on a flat surface by soldering two or more tinned copper wires to the pads for CON1 (eg, pins 1 & 5) and bending them to contact the surface. You can twist the wire onto the branches of your tree to secure it, although, with a traditional pine tree (real or fake), the needles typically do a good job of keeping the Ornament on the tree. Most ornaments also have a larger pad on the rear of the PCB. This can be used to solder a safety pin or similar to the Ornament, so that it can be worn on clothing or otherwise secured to a tree. Fig.9 and the photo on page 24 shows how you can wire up the Reindeer and Santa Sleigh PCBs and use this to create a stunning centrepiece to your decorations. You don’t need to stop at two Reindeer; add as many as you like (eight is the traditional number, but that leaves out poor Rudolph with his glowing red nose!). We used jumper wires, but you could use enamelled copper wire with a diameter of around 0.63mm, and that will hold the whole assembly together as a single semi-rigid unit. Once they’re powered up, they should run for months on their coin cells, providing plenty of blinkenlights for your Christmas tree! SC siliconchip.com.au SILICON CHIP .com.au/shop ONLINESHOP PCBs, CASE PIECES AND PANELS THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 21109181 21109182 01106193/5/6 01104201 01104202 CSE200103 06102201 05105201 04104201 04104202 01005201 01005202 07107201 SC5500 19104201 SC5448 15005201 15005202 Subscribers get a 10% discount on all orders for parts $5.00 $5.00 $12.50 $7.50 $7.50 $7.50 $10.00 $5.00 $7.50 $7.50 $2.50 $5.00 $10.00 $10.00 $5.00 $7.50 $5.00 $5.00 USB SUPERCODEC SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) AUG20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 01106201 18105201 04106201 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 $12.50 $2.50 $5.00 $7.50 $5.00 $5.00 $2.50 $1.50 $5.00 $20.00 $20.00 LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) SUPERCODEC BALANCED ATTENUATOR DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR NOV20 NOV20 NOV20 NOV20 NOV20 NOV20 SEE P31 16109201 16109202 01106202 16110201 16110204 $3.00ea $12.50 $12.50 $7.50 $5.00 $2.50 NEW PCBs PRE-PROGRAMMED MICROS As a service to readers, Silicon Chip Online Shop 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. $10 MICROS ATmega328P-PU ATmega328P-AUR ATtiny85V-10PU PIC10F202-E/OT PIC12F1572-I/SN PIC12F617-I/P PIC12F675-I/SN PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1705-I/P PIC16F88-I/P $15 MICROS RF Signal Generator (Jun19) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) LED Christmas Ornaments (Nov20; specify variant) Door Alarm (Aug18), Steam Whistle (Sept18), White Noise (Sept18) Trailing Edge Dimmer (Feb19), Steering Wheel to IR Adaptor (Jun19) Car Radio Dimmer Adaptor (Aug19) Tiny LED Xmas Tree (Nov19) Microbridge (May17), USB Flexitimer (June18), Digital Interface Module (Nov18), GPS Finesaver (Jun19) Ol’ Timer II (Jul20) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) Ultrasonic Cleaner (Sep20) Flexible Digital Lighting Controller Slave (Oct20) UHF Repeater (May19), Six Input Audio Selector (Sept19) Universal Battery Charge Controller (Dec19) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) PIC16F877A-I/P 6-Digit GPS Clock (May09), 16-bit Digital Pot (Jul10), Semtest (Feb12) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sept19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sept16) $30 MICROS PIC32MX695F512L-80I/PF PIC32MZ2048EFH064-I/PT Colour MaxiMite (Sept12) DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20) KITS & SPECIALISED COMPONENTS LED CHRISTMAS ORNAMENTS (CAT SC5579) (NOV 20) Complete kit including programmed micro but no coin cell (specify PCB shape & colour) $14.00 SWITCHMODE 78XX KIT (CAT SC5553) (AUG 20) RGB STACKABLE LED CHRISTMAS STAR (CAT SC5525) (NOV 20) DCC BASE STATION HARD-TO-GET PARTS (CAT SC5260) (JAN 20) FLEXIBLE DIGITAL LIGHTING CONTROLLER (CAT SC5636) (OCT 20) MICROMITE EXPLORE-28 (CAT SC5121) (SEP 19) Complete kit including PCB, programmed micro, diffused RGB LEDs and other parts 4 x Si8751AB ICs, 8 x S1HB15N60E-GE3 Mosfets, switchmode converter module, 6N137 opto, high-voltage resistors and capacitors plus SMD LEDs. $100.00 D1 MINI LCD WIFI BACKPACK (OCT 20) SHIRT POCKET AUDIO OSCILLATOR (SEP 20) ULTRASONIC CLEANER (SEP 20) COLOUR MAXIMITE 2 (JUL 20) Complete kit including 3.5-inch touchscreen, PCB and ESP8266-based module Kit: including 3D-printed case, and everything else except the battery and wiring - 64x32 pixel white OLED (0.49-inch/12.5mm diagonal) - Pulse-type rotary encoder with integral pushbutton 40kHz 50W ultrasonic transducer (Cat SC5629) ETD29 transformer components + three Mosfets (Q1-2,Q6) (Cat SC5632) Short form kit: includes everything except the case, CPU module, power supply, optional parts and cables (SC5478) Short Form kit (with CPU module): includes the programmed Waveshare CPU modue and everything included in the short form kit above (SC5508) $38.50 $70.00 $40.00 $10.00 $3.00 $54.90 $35.00 $80.00 $140.00 Includes PCB and all onboard parts (choice of 3.3V, 5V, 8V, 9V, 12V & 15V versions) Two BTN8962TA motor driver ICs & one 6N137 opto-isolator Complete kit – includes PCB plus programmed micros and all onboard parts Programmed micros – PIC32MX170F256B-50I/SO + PIC16F1455-I/SL VARIOUS MODULES & PARTS - 16x2 I2C LCD (Digital RF Power Meter, Aug20) - DS3231 real-time clock SMD IC (Ol’ Timer II, Jul20) - WS2812 8x8 RGB LED matrix module (Ol’ Timer II, Jul20) - MAX038 function generator IC (H-Field Transanalyser, May20) - MC1496P double-balanced mixer (H-Field Transanalyser, May20) - AD8495 thermocouple interface (DIY Reflow Oven Controller, Apr20) - Si8751AB 2.5kV isolated Mosfet driver IC (Charge Controller, Dec19) - I/O expander modules (Nov19): PCA9685 – $6.00 ¦ PCF8574 – $3.00 ¦ MCP23017 – $3.00 - SMD 1206 LEDs, packets of 10 unless stated otherwise (Tiny LED Xmas Tree, Nov19): yellow – $0.70 ¦ amber – $0.70 ¦ blue – $0.70 ¦ cyan – $1.00 ¦ pink (1 only) – $0.20 - ISD1820-based voice recorder / playback module (Junk Mail, Aug19) - 23LCV1024-I/P SRAM & MCP73831T (UHF Repeater, May19) - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) - LM4865MX amplifier & LF50CV regulator (Tinnitus/Insomnia Killer, Nov18) - 2.8-inch touchscreen LCD module with SD card socket (Tide Clock, Jul18) $12.50 $30.00 $30.00 $20.00 $7.50 $3.00 $15.00 $25.00 $2.50 $10.00 $5.00 $4.00 $11.50 $1.50 $10.00 $22.50 $10 flat rate for postage within Australia. Overseas? Place an order via our website for a quote. All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars and included GST where applicable. To Place Your Order: INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00, Mon-Fri) siliconchip.com.au/Shop Use your PayPal account silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au Your order to PO Box 139 Collaroy NSW 2097 Call (02) 9939 3295 with with order & credit card details You can also order and pay by cheque/money order (Orders by mail only). Make cheques payable to Silicon Chip Publications. 11/20 More bling for your festivities! Two LE T Two LED L ED Christmas Stars Either of of these these two Either two Christmas Stars Christmas Stars will willlook spectacular atop atop look spectacular tree –– or or anywhere anywhere aatree else.They They certainly certainly else. provide aa better better display provide display than an angel on than an angel on aa stick! They They can also stick! also sit atop our Stackable sit atop our Stackable LEDChristmas Christmas Tree LED Tree from late 2018 and from late and will integrate with will integrate with thatTree. Tree. But they that they work perfectly work perfectly wellstandalone standalone well too,requiring requiring too, onlyUSB USB only power for for power operation. operation. That means means That youcan can you alsouse use also them them outdoors! outdoors! 34 Silicon Chip Design by Barry Cullen Words & software by Tim Blythman See page 43 for details of the special SILICON CHIP LED Christmas Star kit offer Australia’s electronics magazine siliconchip.com.au The two versions of our Christmas Star: on the left (black PCB) is the more complicated RGB LED Star (here shown not powered) while on the right (green PCB) is the basic LED Star with a time exposure allowing most LEDs to light up. These images are about half life size. Yep, they’re big, bold and beautiful! T he reason that we’re presenting two different Christmas Stars is to give you a choice. One is slightly simpler to build, the other is a bit more time-consuming and expensive to put together, but it also gives a much fancier display. So you can choose one or the other depending on how much time and money you want to invest in the project. The Basic Star features 30 single-colour LEDs arranged in any colour pattern you like, while the RGB Star has 30 RGB LEDs which can each display one of seven colours. So with the RGB Star, you can have various different colourshifting patterns; we have programmed several different patterns like that into its onboard microcontroller. Both Stars use relatively simple circuitry, with each LED being driven from the output of a simple shift register IC via a current-limiting resistor. The shift registers are daisychained so that a stream of serial data can be used to update the pattern in the Star. It’s the same scheme used in our November 2018 Stackable LED Christmas Tree (siliconchip. com.au/Series/329). The main difference is that in that project, each little tree board had eight LEDs driven from a single shift register, and you connected multiple boards to add more LEDs. The Star has almost four times as many LEDs on board; hence, they are driven from multiple shift registers. Because it uses the same daisy-chaining scheme, one (or more!) Stars can be placed at the end of each of the LED tree ‘branches’. We’d wager that a large Stackable Tree with multiple Stars on it would make for a spectacular sight! As mentioned earlier, the RGB LED Star has an onboard micro to provide patterns so that it can be used in a standalone manner; for example, atop a regular Christmas tree (real, plastic or other). This is the simpler of the two LED Stars but it gives a great display with singlecolour LEDs. With high-brightness LEDs the display is really good indoors during daylight . . . but it’s at night when the flashing LEDs really come into their own! Because it’s operated on low voltage DC (5V; ie USB) it can be used outdoors as well. Incidentally, the camera sees the white LEDs as much brighter but they’re really quite well matched in real life. siliconchip.com.au Australia’s electronics magazine November 2020 35 SC 30 LED STACKABLE STAR Fig.1: this version of the LED Star uses single-colour LEDs – your choice of which LED goes where to achieve the patterns you want. It’s slightly simpler and a little cheaper to build. The random number generation circuitry is in the lower left-hand corner of the circuit, and below that are the four links which configured it to operate either standalone or atop the Stackable LED Tree. 36 Silicon Chip Australia’s electronics magazine siliconchip.com.au The more basic LED Star can also be operated in this manner, but rather than using a micro to generate patterns, it has an onboard discrete random number generator to make its LEDs twinkle nicely. ment, it can produce much more complicated and dazzling patterns. We have programmed it to cycle through ten different amazing patterns automatically over time. You could modify the software to add even more. Circuit description Basic Star details The circuits of both versions of the Stackable LED Star (shown in Figs.1 & 3) are quite similar to the Stackable LED Christmas Tree. The main difference is that the Tree used a single shift register to drive eight single-colour LEDs, while the Stars use four shift registers to drive 30 singlecolour LEDs or twelve shift registers to drive 30 RGB LEDs. In each case, the shift registers are daisy-chained, similarly to how the individual chips in the Stackable Tree could be daisy-chained by plugging the Tree PCBs together. In this case, though, the chained connections are made via tracks on a single PCB. The other major difference in Fig.1 is that the clock and latch lines feeding from input connector CON1 to the shift registers are joined together on this board and routed as a single track, while they were routed separately on the Tree boards. This is a trade-off which simplifies the PCB routing, while slightly complicating how data is routed to the shift registers. Also, while the Stackable Tree used a separate driving arrangement to create control data for the LEDs, either based on a random number genera tor or software running on a PC or an Arduino, both stars have the option to use onboard circuitry to drive the LEDs. This allows them to be used as self-contained ornaments, needing only a source of 5V DC (eg, from a USB charger) to operate. Fig.1 is the circuit of the basic Star, with 30 single-colour LEDs labelled LED1-LED30. You can choose whichever colours take your fancy, although we suggest that if you decide to use any white LEDs, you should probably use all high-brightness types. Otherwise, the white LEDs are liable to out-shine the others! The LEDs are driven from the outputs of daisy-chained serial-to-parallel shift registers IC1-IC4, with 1k currentlimiting resistors meaning that each LED receives about 1.5-3.5mA, depending on its forward voltage. That can be as low as about 1.5V for a high-brightness red LED, or over 3V for a blue or white LED. As the four 8-bit registers have a total of 32 outputs, two are unused (outputs Q0 of IC2 & IC3). Each shift register has a high-value bulk bypass capacitor plus a lower value high-frequency bypass capacitor. There is also an electrolytic capacitor near input connector CON1 to provide bulk bypassing for the whole board. With links LK1-LK4 in one position, power and data for the shift registers are routed from pin header CON1, which can be plugged into a Stackable Tree or any of the driving circuits we published for it. In this case, the output of the last shift register is also routed back to CON1, so that it can finish making its way through a Stacka- In the case of the simpler Star with single-colour LEDs, this circuitry is virtually identical to the Discrete LFSR Random Number Generator from our August 2019 issue (siliconchip.com.au/ Article/11775). That project was mainly designed to drive the Stackable Tree, producing an LED twinkling pat tern, and it does the same job with the Star. However, the Star which uses RGB LEDs has an onboard ATmega328P (ie, the same micro used in the Ardui no Uno). That means Fig.2: full-size PCB layout for the simpler that, when used as LED star, as seen in Fig.1 opposite. This version uses a standalone orna- single-colour LEDs – your choice as to which goes where. siliconchip.com.au Australia’s electronics magazine ble Tree, should one be attached. In the alternative link positions, power instead comes from micro USB connector CON2 and data to control the LED states comes from the random number generator comprising shift registers IC5 and IC6, XOR gates IC8a-IC8d and diodes D1-D16. This is clocked by an RC oscillator circuit based on schmitt trigger inverters IC7a & IC7b. For a full explanation of how this part of the circuit operates, see the August 2019 article. Essentially, November 2020 37 l l l l l l l l l l l l l l l l l l l l l l l l SC Ó RGB LED STACKABLE STAR Fig.3: this version of the LED Star uses RGB LEDs, with the pattern determined either by data shifted in via pin header CON1, or by the variety of patterns produced by microcontroller IC13. These patterns have been specially designed to suit the layout of the LEDs on the star, including taking into account the way they have been wired to the twelve shift registers. 38 Silicon Chip Australia’s electronics magazine siliconchip.com.au ‘random’ bits appear at the output of buffer IC7d at a rate of one bit for each pulse from the oscillator. The oscillator frequency is set to around 5Hz due to the time constant of the 100µF timing capacitor and 1k charge/discharge resistor. One slight change in how this circuit works compared to the August 2019 version is that a 2N7002 small-signal Mosfet (Q1) has been used in place of NPN transistor Q1 in the original design. But they do the same job, which is to ensure that the circuit does not get stuck in the ‘all zeros’ state, which would result in no more random data being produced. RGB LED Star details The circuit of the RGB version is shown in Fig.3. The LED-driving portion of the circuit is identical to the other version, except that there are three times as many serial-to-parallel shift registers. This is because they must drive the three individual elements in each RGB LED (ie, red, green & blue) separately. Similarly to the more basic version, with links LK1-LK5 in the positions shown, data is fed to the shift registers from input connector CON1, and this can come from a Stackable Tree or any of the suitable drivers for it. However, this time, the clock and latch lines are not wired in parallel. Instead, they are routed to the twelve shift registers separately, making it a bit easier to drive (and more readily compatible with an existing Stackable Tree arrangement). That’s why there are five jumper links on this board, rather than four as before. The other difference is in the onboard driving circuitry. With LK1-LK5 in the alternative positions, the serial data and clocks come from microcontroller IC13, an Atmel ATmega328P. It can be clocked either using an internal 8MHz RC oscillator, or external 8MHz ceramic resonator X1. In the latter case, capacitors internal to the resonator provide the required load capacitance. Our software configures the internal RC oscillator, so X1 is not required unless you plan to reprogram it using the standard Arduino bootloader, which expects an external crystal or resonator to be present. IC13 also has the required bypass casiliconchip.com.au Australia’s electronics magazine pacitors for its power supply pins, plus an RC reset circuit on its pin 29 (not required, but it doesn’t hurt). There’s an antenna connected to the analog input on pin 25, to act as a source of random noise. The micro can be programmed using a standard six-pin AVR programming header, although we can supply the chip pre-programmed to save you the effort. To create a pattern, the software in IC13 simply has to produce 96 bits of serial data in SPI fashion from pins 9 and 10 (digital output PD5 for data and PD6 for the serial clock) and then pulse pin 12 (PB0) high and then low again, to update the colours of the 30 RGB LEDs. As each LED is effectively driven with a three-bit signal, that means there are eight possible states: off, red, green, blue, yellow (red+green), magenta (red+blue), cyan (green+blue) or white (red+green+blue). These are then changed for each LED at set intervals to create pleasing patterns of light on the Star. Programming link JP1 can be removed to disconnect IC13 from the 5V power supply during programming, although you could also just unplug the power supply from CON1 or CON2 for the same effect. Construction Despite the circuit differences, the procedure for building the two Stars is quite similar. Both use mostly SMD parts except for the connectors and LEDs. It’s best to fit all the SMDs first. Refer to the relevant PCB overlay diagram, Fig.2 or Fig.4, depending on which version of the Star you’re building. All of the SMDs are relatively easy to solder, but you still need to use the right procedure to get the best results. Essentially, once you have located the right part and orientated it correctly, you tack one pin to a pad and check its alignment. If it’s correct, then you solder the opposite pin and then all the rest; otherwise, you re-melt the first joint and gently nudge the part to get it into the correct position. Once all the pins have been soldered, you refresh the original, tacked joint with some extra flux and/or solder, then clean up any accidental bridges between pins with flux paste and solder wick. November 2020 39 There are a couple of different approaches to tacking that first pin. You can add a little flux to the pad, locate the part on it and then touch it with the tip of a soldering iron pre-loaded with a bit of solder. Or, you can add a little solder to the pad and heat it while sliding the part into place. Both methods work; the former perhaps gives a neater result while the latter is a bit quicker. SMD parts Start by fitting the 74HC595 ICs, which come in 16-pin SOIC packages. Pin 1 is marked either with a dot on the top face in one corner, or a bevelled edge along the pin 1 side. Make sure you have correctly located the LEDs at a different current level than specified). On the single-colour board, there is one 10k resistor and all the rest are 1k. Next, mount the SMD ceramic capacitors. There is a 100nF bypass capacitor for each IC on both boards, except IC13 on the RGB board, which has three (two for bypassing and one for reset). So there are eight on the basic board and 16 on the RGB board. Now fit the micro USB socket. This is also a surface-mounting device, although it also has pins that go through the board to hold it in place. Apply flux to its pads. Make sure it’s flat on the board and its signal pins are correctly located over their pads, then solder one of the mounting pins. Recheck the signal pin alignment before soldering the pin 1 and other mounting orientated pins. it as shown in The next step is to the corresponding load a little solder on the overlay diagram before tip of your iron and touch it soldering each IC in place. to the two signal pins at either There are either four or 12 end, so that some solder flows of these, depending on which onto each pin and pad with the version you’re building. aid of the flux paste applied For the RGB Star, the only earlier. remaining IC is microconYou don’t need to solder troller IC13 which has 32 the three middle pins, but pins, eight per side. Use you can if you want to. the same basic technique Regardless, check for to solder it, again makbridges with a magnifier ing sure its pin 1 dot is and if you find any, clean in the location shown. them up with more flux But be extra careful paste and some solder to check that the pins wick. on all four sides are Next, fit the surfacecorrectly aligned Fig.4: this PCB layout matches the circuit on page 38, mounting electrolytic after you’ve tackthe RGB LED Star. While it’s slightly more complicated to capacitors. There are soldered that first build, it can give much more exciting displays. eight for the basic pin. version or five for Ironically, the the RGB version. Seven (or five) of these can be substitutsituation is a bit more complicated with the single-colour ed with 22µF SMD ceramics. These cost about the same, LED version as there are four more 14-pin ICs to solder: and while they have less capacitance, they are significanttwo 74HC164s, one 74HC14 and one 74HC86. ly smaller, have much lower ESR and ESL and better long Don’t get these mixed up and make sure they are orienreliability. It will work either way, so the choice is yours. tated correctly, then solder the single SOT-23 package tranThe final SMD component is the ceramic resonator, sistor (Q1), followed by diodes D1-D16. Make sure their which is only on the RGB board. This part is a bit tricky cathode stripes all face to the right, as shown. to solder because it has no leads, only pads on the underAlso, don’t sneeze while handling these diodes or you side. That means you need either a hot air reflow system might lose half a dozen! If dropped on the floor, they’re or reflow oven to solder it. almost impossible to find (unless your floor is white viThe good news is that, as described above, it’s entirely nyl perhaps). optional; we expect most constructors will simply leave The next job for both boards is to fit all the SMD resisits pads empty. tors. For the RGB version, fit the 1M and 10k resistors That just leaves the LEDs and the headers. For the RGB near IC13 where shown, then the remaining 90 resistors, version, the LEDs are all the same, so the only thing you which are all 1k (or a different value if you want to drive 40 Silicon Chip Australia’s electronics magazine siliconchip.com.au Parts list – basic Stackable LED Star Parts list – RGB Stackable LED Star 1 double-sided PCB coded 16109201, 194 x 185mm 1 6-pin right-angle header (CON1) 1 SMD USB socket with through-hole mounting pins (CON2) 4 3-pin headers with jumper shunts (LK1-LK4) 1 double-sided PCB coded 16209202, 194 x 185mm 1 6-pin right-angle header (CON1) 1 SMD USB socket with through-hole mounting pins (CON2) 5 3-pin headers with jumper shunts (LK1-LK5) 1 2-pin header with jumper shunt (JP1) 1 3x2-pin header (optional; for programming IC13) 1 8MHz ceramic resonator, 3.2x1.3mm SMD package (X1) Semiconductors 4 74HC595 8-bit serial-to-parallel shift registers, SOIC-16 (IC1-IC4) 2 74HC164 8-bit shift registers, SOIC-14 (IC5,IC6) 1 74HC14 hex schmitt trigger inverter, SOIC-14 (IC7) 1 74HC86 quad 2-input XOR gates, SOIC-14 (IC8) 1 2N7002 small-signal N-channel Mosfet, SOT-23 (Q1) 30 5mm LEDs (LED1-LED30; any mix of colours) 16 1N4148WS small signal diodes, SOD-323 (D1-D16) Capacitors 1 100µF 10V SMD electrolytic, 5x5mm 7 100µF 10V SMD electrolytic, 5x5mm OR 7 22µF 10V X7R SMD ceramic, 3216/1206 size 8 100nF 50V X7R SMD ceramic, 2012/0805 size Resistors (all SMD 2012/0805 size) 1 10kW 30 1kW (or value[s] to suit LEDs) Abracon AWSCR-8.00CELA-C10-T3; optional – see text Semiconductors 12 74HC595 8-bit serial-to-parallel shift registers, SOIC-16 (IC1-IC12) 1 ATmega328P-AUR 8-bit microcontroller programmed with 1620920A.hex, TQFP-32 (IC13) 30 5mm RGB LEDs (4-pin common cathode type) Capacitors 5 100µF 10V SMD electrolytic, 5x5mm OR 5 22µF 10V X7R SMD ceramic, 3216/1206 size 16 100nF 50V X7R SMD ceramic, 2012/0805 size 3 1kW need to be careful of is to make sure that they are all orientated correctly. The PCB overlay diagram and PCB silkscreen shows which way the flat side (cathode end) of each one goes. Note that the LEDs are installed proud of the board by around 10mm. This is because the leads have a small section that’s slightly thicker around 10mm from the base of the lens, so you can’t push them all the way down onto the PCB. We reckon that this doesn’t matter too much, and in fact might make the LEDs a bit more visible at an angle. The basic procedure is the same for the non-RGB board, except that you will probably want to mix up the colours. You can use the same pattern that we did, or come up with your own one entirely. You could even just install different colours randomly if all you’re after is a ‘twinkle’ type effect. Once the LEDs are in place, fit the vertical headers for the links. If you’re going to put the Star on top of the stackable Tree, also fit the right-angle header at the bottom (CON1). You can mount this on either the front or the back of the board, depending on which is best for plugging into your existing Tree. Now is also a good time to fit the 3x2 pin programming header on the RGB Star, if you intend to reprogram IC13. If you’re using a pre-programmed chip and don’t want to Resistors (all SMD 2012/0805 size) 1 1MW 1 10kW 90 1kW (or value[s] to suit LEDs) change its coding, then there’s no need to fit this header. You can always solder it in later if necessary. Finally, plug in the jumper shunts onto the appropriate headers. Use the configurations shown in our PCB overlay diagrams if you want the Star to be self-contained and powered from the USB socket. Alternatively, place all the 3-pin shunts in the opposite positions (LK1-LK4 or LK5) if the Star will sit atop a Stackable LED Tree, or be driven via external circuitry at CON1. Programming the RGB LED Star If you’re building the RGB LED Christmas Star, you’ve most likely used a pre-programmed ATmega328 chip, so it will happily be flashing away with its default patterns as soon as power is applied. But if your ATmega328 is not programmed, or you are interested in changing the default patterns, read the following text which explains how to program the chip. If you have a blank microcontroller, you just need to download the HEX file from our website and use the following procedure to upload this into the flash memory of the micro. Or you can use the free Arduino IDE (integrated development environment) software to create your own patterns. In this case, you can use our source code as a starting point. Fig.5: if you don’t have an Atmel AVR programmer, you can use an Arduino Uno or similar to program the chip on this board. To do that, you need to make up a cable with 6-pin sockets at each end, wired as shown here. SC siliconchip.com.au Australia’s electronics magazine November 2020 41 The rear of the RGB LED Star leaves you in no doubt as to which version it is! But more importantly, it has instructions for running the star in various modes. We’ll assume that you’re comfortable using the Arduino IDE, which you can download from siliconchip.com.au /l/aatq The programmer You’ll need an Atmel AVR programmer. Unlike an Arduino board, the RGB LED Christmas Star does not have a serial upload capability; it lacks the serial/USB converter and the bootloader firmware which are needed for the Arduino IDE to program it directly. Instead, we use an I(C)SP programmer. ISP here simply stands for “in-circuit serial programmer”. You might already have one of these, like Jaycar Cat XC4627. You’ll need one with a six-pin header. If your programmer has a 10-pin header, then adaptors like Jaycar’s XC4613 are available. But you don’t need a dedicated programmer if you have a spare Uno board lying around. It’s pretty easy to make a cable that turns the Uno into an AVR programmer. In any case, the process is much the same. Just make sure you choose the programmer type (instead of ‘Arduino ISP’) as instructed by your programmer manual. We used a pair of 6-pin (2x3) header sockets. These plug directly into the ISP header on Arduino boards; the RGB LED Star also has a matching header. Alternatively, you could make do with a set of six jumper wires temporarily rigged up to match our wiring. The ISP wiring harness is worth having as it isn’t difficult to make and it can be used to rescue some ‘bricked’ Arduino boards; our article about Fixing Busted Unos from March (siliconchip.com.au/Article/12582) has some more background to this. The first thing to do is to make up the harness, as shown in Fig.5. Five wires go between the corresponding pins on the six-pin header, while the sixth pin on one header goes to a flying lead which plugs into I/O pin D10 on the programmer board. We soldered a single pin header to the end of that wire. Before connecting the harness, configure the ‘spare’ Uno as a programmer by uploading the “ArduinoISP” sketch to it. This can be found under the Files -> Examples -> 11.ArduinoISP menu. Other boards can be used. We’ve had success using a Mega, but had trouble with a Leonardo. We suspect that this is due to the way the bootloaders work on the different boards. R3 clones of these boards (which have the ISP header) should also work. Now connect the five-wire end of the harness to the programmer Uno. The sixth wire should be plugged into digital pin 10. This is what allows the ‘master’ micro to control and program the slave. Note that pin 1 (as shown in Fig.5) should go to pin 1 on the Uno; it will typically have a dot or other marking nearby. There is one more step to complete our programmer. Run a male-male jumper wire between the 5V and RST pins on the Uno’s header. This pulls the RST pin high, preventing the host from programming the programmer instead of its attached target. Making a board profile The RGB LED Christmas Star is obviously not an Arduino, so we need to make a special board profile to program it from the Arduino IDE. This isn’t too complicated, just some text to tell the IDE how to work with something similar to (but not the same as) the Uno. The ATmega328P on the RGB LED Christmas Star is the same processor as used in the Uno, after all. But it lacks the serial interface and bootloader, and it also runs on an internal 8MHz oscillator instead of an external 16MHz crystal. Close the Arduino IDE and find the “boards.txt” file in our software download for this project (as shown in Screen1). This contains the profile which needs to be imported. We have Screen1: once you’ve added our custom board profile to your IDE, you can select it as shown here to program the micro on the RGB Star. 42 Silicon Chip Australia’s electronics magazine siliconchip.com.au found a few similar profiles around, but all required some changes to work correctly; our version has been tested with the Arduino IDE version 1.8.5. The contents of this file need to be added to your existing “boards.txt” file. On our Windows PC, this was found at “C:\Program Files (x86)\Arduino\ hardware\arduino\avr”; it may be different if you have installed the IDE to a different location. If you have trouble with this file, you can also type in the additions manually. Once you have done that, restart the IDE. Manual changes require a restart of the IDE to be loaded. If you look in the Tools menu, you should see a new board, as shown in Screen1. Select this as the board and select the serial port of the programmer. Now click on “Burn Bootloader” from the Screen2: the above text should be added to your Arduino IDE ‘boards.txt’ file. Sketch menu. If you don’t feel like typing it out by hand, it can be found in our software This doesn’t actually burn a bootdownload for this project. loader, but it does set the configuration fuses which allows the 8MHz internal oscillator to work. So unless you’ve fitted a crystal and are confident it will You might get an error message that the bootloader file work, you should simply use the internal oscillator option. cannot be found; that is fine, as there is no bootloader file If you have used a 16MHz crystal or resonator, the Uno required. board type can be used. While it is not the same as the Uno, Now open the “RGB_Christmas_Star” sketch. Instead of it is the closest match. For an 8MHz crystal or resonator, using the “Upload” command, we need to use the “Upload use the board “Lilypad Arduino”. using Programmer” command. The keyboard shortcut for Once you’ve programmed the RGB LED Christmas Star this is Ctrl-Shift-U. The upload process here is a bit slower, to your satisfaction, detach the programming lead and rebut should still complete in under 10 seconds, after which turn the jumpers to their original positions (if changed) the Star will start to cycle through its patterns. by reinstating the jumper next to the ISP header. Plug in a micro-USB lead to power the unit, and it should light up The sketch with the programmed patterns. The sketch we have written is made of subroutines which By connecting the DO connection from one Star to the rely on other, simpler subroutines. While this might seem DI connection on another Star (and also connecting the complicated, it makes the code quite modular. other four wires on the headers in parallel), the main Star The clockSequence() routine, which is the first to run, can also drive those Stars, as long as their jumpers are set calls the clockCycle() subroutine in each of the seven colto the appropriate positions. SC ours (red, yellow, green, cyan, blue, magenta and white). This, in turn, calls the setSnake() routine with differing parameters, which generates several different patterns. The setSnake() routine works by putting red, green and blue values (corresponding to the LEDs) into an array. M Chri erry ! The clockCycle() routine also calls the mapBits() subroustma o H o Mila oel! s! tine, which translates an array of colour values (the LEDS Ho H Joyeux N dM ajid array) into a bitmap which can be written directly into the shift registers (dataBits). This is followed by the sendBits() routine, which shifts and latches this data onto the LEDs. Bon While it appears a complicated way of doing things, you God Nata le Jul! can make simple customisations by changing what is present in the loop() function. Or you can make more elaboFeliz Shen Dan rate patterns by modifying the other functions. Navidad! Ku CHRISTMAS STAR KITS RGB VERSION ai Le Conclusion If you have fitted an external oscillator or crystal to the RGB LED Christmas Star, then there are equivalent board options, although there is little reason to do so when the 8MHz internal oscillator works just fine. There’s also the complication that once the fuses are set to use a crystal, they can’t be set back without a crystal. siliconchip.com.au COMPLETE KIT: just $3850 INC GST PLUS P&P* Comes with all parts including the black PCB, programmed micro and LEDs with diffused lenses for better visibility at wider angles. We have plenty of stock (at press time) ready for you to build for this Christmas Season. But don’t delay or you may miss out! See www.siliconchip.com.au/shop/20/5525 Australia’s electronics magazine *P&P $10 – Flat rate for any size order (in Aust) November 2020 43 Balanced Input & Attenuator for the USB Part 1 – by Phil Prosser This compact balanced input attenuator is designed to fit into the same instrument case as the USB SuperCodec. It provides four attenuation settings of 0dB, -10dB, -20dB and -40dB and has performance to match the superlative SuperCodec. Together, they form a potent recording and/or measurement system. T he SuperCodec USB Sound Card described over the ent devices (the measurement system and the device under test or DUT). last three issues has excellent recording and playback Another thing that the Audio Precision devices have but performance. So it can form the core of a high-perforthe SuperCodec lacks is input attenuators. The AP systems mance audio measurement system. One thing that it lacks compared to our Audio Precision can measure a wide range of signals from line level (well systems is a balanced input. Our AP System One and Sys- below 1V RMS) up to the output of multi-hundred-watt amplifiers (50V+ RMS). tem Two devices both have balanced and unbalanced inputs, As we mentioned previously, you can build our 2-Chanand you can select between them. There are times where you need those balanced inputs; nel Balanced Input Attenuator for Audio Analysers (May sometimes, you want to measure the performance of a bal- 2015) and hook it up to the SuperCodec inputs. That would solve anced audio device. both problems and But even with give you a test instruunbalanced devicment with flexibility es, it is common to approaching that of get better results usthe AP System Two ing balanced meas(and in some senses, urements. That’s exceeding it). because it helps to Fig.1: one channel of the Balanced Input Attenuator. There is an RF However, then you eliminate the com- filtering and DC-blocking stage before the relay-switched resistor-based would have two boxmon-mode noise attenuator. After the attenuators are the over-voltage protection stages, inherent in con- buffers and differential-to-single-ended converters before the signals are fed es or three boxes, two different power supnecting two differ- to the ADC inputs on the SuperCodec board. 44 Silicon Chip Australia’s electronics magazine siliconchip.com.au Features & specifications • Adds stereo balanced inputs (6.35mm TRS sockets) to the front panel of the USB SuperCodec • Balanced inputs replace the rear-panel unbalanced RCA inputs of the original design • Unbalanced outputs (RCA) remain on rear panel • Retains the 192kHz/24-bit recording & playback capabilities of the original SuperCodec • Fits into the SuperCodec case and uses the same power supply • 0dB, 10dB, 20dB and 40dB attenuation settings selected via front panel switch • CMRR: >60dB <at> 50-100Hz; >70dB <at> 1kHz; >50dB <at> 10kHz • SNR: 114dB <at> 0dB, 113dB <at> -10dB, 114dB <at> -20dB & -40dB • THD: 0.00010% (-120dB) <at> 0dB; 0.00014% (-117dB) <at> -10dB; 0.00028% (-111dB) <at> -20dB • Signal handling: 1V RMS <at> 0dB; 3.6V RMS <at> -10dB; 10V RMS <at> -20dB; 50V RMS <at> -40dB plies, cabling connecting them etc. That’s less convenient than having a single ‘all-in-one’ do-everything device. Also, the May 2015 project only has three attenuator settings (0dB, 20dB and 40dB) and we think that it doesn’t quite have the performance to match the SuperCodec, for reasons we’ll explain shortly. Hence, we came up with this project. It does a similar job to the May 2015 attenuator but with the addition of a -10dB attenuator setting and lower impedances for less noise. Importantly, it has been designed to integrate with the USB SuperCodec and fit in the same case, by keeping the PCB assembly compact and designing it to run off the same power supply rails. So with the addition of this balanced input board and some free or low-cost software, you can build an audio testing Here is the finished add-on board, with low-profile components to fit under the SuperCodec PCB. The inputs, RF filtering and AC-coupling components are at right, with the divider resistors in the middle. To their left are the attenuation selection relays, with the buffer op amps next to them, then the balanced-to-single-ended conversion circuitry at far left. siliconchip.com.au Australia’s electronics magazine November 2020 45 0 SuperCodec Balanced Input CMRR left channel, 0dB left channel, -10dB left channel, -20dB left channel, -40dB right channel, 0dB right channel, -10dB right channel, -20dB right channel, -40dB 10 Common Mode Rejection Ratio (dB) 23/07/20 10:59:20 20 30 40 Recording professional audio 50 60 70 80 90 100 20 50 100 200 500 1k Frequency (Hz) system that only a few years ago would have cost many thousands of dollars. 5k 10k 20k Fig.2: we tested the common-mode rejection ratio (CMRR) for both channels on our prototype, at four different frequencies and all four possible attenuation settings. The resulting plot is a bit messy but gives you an idea of the CMRR spread. A higher CMRR is better since it rejects proportionally more of the hum, buzz and EMI that may be picked up in cables etc. Another reason you might want to build the balanced input attenuator is to interface the USB SuperCodec with professional audio equipment. It gives you much greater recording flexibility, allowing you to use either balanced or unbalanced signals. And with the attenuator, it can handle much ‘hotter’ signals than the 1V RMS of the original Sound Card design. The 10dB attenuation setting puts professional +4dBu signals right in the sweet spot of the analog-to-digital converter (ADC), with good headroom. In this configuration, it can handle up to 3.6V RMS without clipping, or you can switch to the -20dB setting to handle signals up to 10V RMS, with relatively little degradation in performance at ‘normal’ signal levels. The design provides very well balanced inputs, with common mode rejection typically better than 60dB. The attenuation ranges of 0dB, -10dB, -20dB and -40dB allow full-scale inputs of 1V, 3.6V, 10V and 50V RMS which correspond to 1.4V, 5V, 14V and 71V peak or 2.8V, 10V, 28V and 142V peak-to-peak. This allows low-level signals, preamplifier outputs and power amplifier outputs to be used as signal sources (among other devices). Operating principles Fig.3: the noise floor of the combined Balanced Input Attenuator & SuperCodec ADC with the attenuator set to 0dB and the inputs shorted out. This shows that the new board adds minimal noise to the overall system. Fig.4: the same plot as Fig.3 but this type the attenuator has been switched to -10dB. As explained in the text, this is the setting where the Johnson (thermal) noise contribution of the attenuator resistors is highest. Despite this, the noise floor has only increased by around 1dB compared to Fig.3. 46 Silicon Chip Refer now to the block diagram, Fig.1. If you have a copy of the May 2015 issue, (or a download from siliconchip. com.au/Article/8560) you might also like to read back over the earlier Balanced Input Attenuator design, as this design has many similarities. The balanced input is via a 1/4-inch (6.35mm) standard tip-ring-sleeve (TRS) type connector (also often referred to as a “jack socket”). This was chosen over an XLR connector to save space, so that it will fit in the SuperCodec case. 6.35mm TRS is bog-standard, and often used for balanced signals, which makes this a versatile choice. We’re sticking with the standard TRS pinout of tip = “Hot” or positive, ring A view inside the "new" SuperCodec with the added PCB at bottom. It is designed to slot into the edge guides in the recommended Hammond 1455N2201BK aluminium case. Australia’s electronics magazine siliconchip.com.au = “Cold” or negative and sleeve for signal ground/screen. The balanced signals pass through an RF filter and DCblocking capacitors, then into the resistor and relay-based switched attenuator. After that, they pass through a clipping stage to provide over-voltage protection before going onto a set of buffer op amps. The buffered signals are then converted from balanced to single-ended signals, which are then fed to the inputs of the USB Sound Card already described. Performance We thoroughly tested the performance of the Balanced Input Attenuator to make sure it was up to SuperCodec standards. Fig.2 shows the measured common-mode rejection ratio (CMRR) value for both channels of the prototype, at all four attenuation settings and measured at four different frequencies. As you can see, the CMRR is between 71dB and 89dB at 1kHz for both inputs, and at all attenuation settings. Those are pretty good figures, and 1kHz is a typical test frequency. CMRR is slightly worse at lower and higher frequencies, but is better than 63dB at all tested frequencies below 1kHz, and better than 53dB at 10kHz. CMRR will be almost entirely a function of matching of the attenuator and balanced receiver resistors. So if you pay more attention when selecting those resistors, you could beat our prototype figures. With the 0.1% resistors specified, the attenuation error is less than ±0.1dB across all tested frequencies. Fig.5: we measured the total harmonic distortion (THD) with a -7.66dBV sinewave fed into the balanced inputs and a 0dB attenuator setting. The result shows very little difference from the same test without the Balanced Input Attenuator add-on. So it appears that the added circuitry is not introducing any extra distortion to the signals. Fig.6: the same test as Fig.5 but with the attenuator set to -10dB. Other than the signal level falling by the expected amount, there isn’t much difference. The increase in THD reading is mainly due to the change in signal level; increasing the input signal level by 10dB would likely give the same result as in Fig.5. And here's a view from the opposite end, with the lid removed, showing how the new PCB fits "upside down" above the existing SuperCodec board. siliconchip.com.au Fig.7: and the same test again with an attenuator setting of -20dB. The same comments as for Fig.6 apply. Note how the signal level drops by very close to 10dB and 20dB in these two tests, showing off the excellent attenuation accuracy. Australia’s electronics magazine November 2020 47 Benefits of balanced signals Professional audio equipment uses balanced signals carried on three conductors: the positive “Hot”, negative “Cold” and a screen. Electromagnetic interference picked up in the cable (usually heard as hum or buzz) affects both the Hot and Cold signals similarly. The balanced receiver subtracts the Cold signal from the Hot, resulting in twice the signal with severely attenuated noise. In other words, if the Hot signal is signal x 1 + noise and the Cold signal is signal x -1 + noise, Hot – Cold gives you (signal x 1 + noise) - (signal x -1 + noise) = signal x 2 + noise x 0 This is a great way to reject noise and hum from things like ground loops, especially on long cable runs. Besides added complexity in the circuitry, the main disadvantage of this approach is that converting a balanced signal into an unbalanced signal generally introduces a bit of white noise; so while hum and buzz are rejected, the signal-to-noise ratio (SNR) can suffer a bit. When testing audio equipment, we often need to analyse the signal between two particular points in the device under test (DUT). We certainly want to avoid measuring any voltages within the ground system of the DUT or our test equipment itself. By using a balanced input in this situation, we can connect the Cold conductor to an appropriate ground reference point in the DUT. The Hot connection is then used to measure the signal of interest. Any noise between the USB Sound Card ground and the DUT ground is subtracted out of this measurement. When measuring low voltages and exceptionally low distortion levels on signals at moderate voltages, this is extremely important, as sometimes we are looking for microvolt or even nanovolt level distortion signals. As good as balanced interfaces are, Earthing remains essential. To achieve good results below -100dB, you will need to work on the test Earthing and layout. You might be surprised how much things like the orientation of the equipment being tested and its proximity to computer equipment and even the operator can affect the results! 48 Silicon Chip The noise and distortion performance is not significantly worse than the straight USB Sound Card with a 10kΩ input impedance (the input impedance options are described below). There is a small increase in THD on the -10dB range for the 100kΩ input impedance version. Fig.3 shows the output spectrum with the attenuator on the 0dB setting and the inputs shorted to ground. If you compare it to Fig.5 on page 27 of the August 2020 issue, showing the same measurement for the SuperCodec alone, you will see that there isn’t all that much extra noise being introduced by the Balanced Attenuator. Fig.4 shows the same measurement but with the attenuator on the -10dB setting, which is the worst case (as explained below). Overall, the noise has only crept up by about 1dB compared to the 0dB attenuator setting, so that’s a good result. Fig.5 shows the THD+N measurement for a test signal of around 300mV RMS being fed into the Balanced Input Attenuator with the attenuation setting at 0dB. This is virtually unchanged from the measurements we made previously without the Balanced Input Attenuator board. You can compare this to Fig.4 on page 27 of the August 2020 issue, but note that the test signal level is slightly different. Fig.6 shows that the distortion performance on the -10dB setting, with the same signal applied as for the 0dB setting, is barely any worse. So the attenuator does not appear to be introducing any signal distortion. Similarly, Fig.7 shows the result with the attenuator on the -20dB setting. The THD measurement has risen to 0.0003% / -111dB. However, note that if the applied signal amplitude were increased to a level that you would need the 20dB of attenuation to measure, the THD level would probably drop quite close to the 0.0001% / -120dB shown in Fig.5. Circuit details Refer now to the full circuit diagram, Fig.8, and compare it to the block diagram, Fig.1. Let’s consider the left channel signal path, starting at CON1; the right channel is the same. The input signal goes via a ferrite bead with a 22pF bypass capacitor to filter off the worst of any RF signals on the input. The USB Sound Card is Australia’s electronics magazine AC-coupled, so a DC blocking capacitor is included between the input RF filter and the attenuator. We want a lower cutoff frequency (-3dB point) an order of magnitude below 20Hz, so we have chosen 1.5Hz. This means that any non-linearities in the DC-blocking capacitors will not introduce any distortion, so long as they are not gross non-linearities (as is found in high-K ceramic capacitors, for example). For a 100kΩ input impedance, as used in the May 2015 Attenuator design, this demands the DC blocking capacitor be 1µF. But the Johnson noise in a 100kΩ resistance is enough to affect the performance of the USB SuperCodec, so we really need a lower input impedance, say 10kΩ. This demands a 10µF DC-blocking capacitor for the same 1.5Hz -3dB point. The current through these capacitors is extremely low, and pretty much any film capacitor will work well. You could use an electrolytic, but many people don’t like the idea of electrolytics in the signal path (even though they work OK for signal coupling). Also, they tend not to last as long as film capacitors. And as mentioned above, ceramic is a poor choice, so plastic film it is. The switched attenuator The input attenuator reduces the input signal level by 0, 10, 20 or 40dB. That means division ratios of 3.16:1, 10:1 and 100:1. We chose these values as 0dB (ie, straight through) gives the best sensitivity and a useful 1V RMS input level. -10dB is well suited to professional audio signal levels. It is also low enough to be useable with consumer equipment like CD, DVD and Blu-ray players which tend to produce an output signal of around 2.2V RMS. The -20dB and -40dB settings are handy for power amplifier testing. The attenuator is a simple resistive divider. The total series resistance sets the input impedance of the balanced interface, and as mentioned above, this has an impact on the noise performance and the size of the DC blocking capacitor required. Thermal noise The noise impact will depend on the attenuation setting. At 0dB, the divider is effectively bypassed and so the insiliconchip.com.au put impedance has no real effect on the performance. At the other three settings, the input impedance ‘seen’ by the SuperCodec is the upper and lower halves of the divider, bisected by the selected tap, in parallel. The worst case is the -10dB setting, at 21.6% of the overall input resistance (ie, 21.6kΩ for the 100kΩ option and 2.16kΩ for the 10kΩ option). For the -20dB setting, it is 9% of the input resistance and for the -40dB setting, it is 1% of the input resistance. Thermal noise in a resistance is calculated as √(4 x K x T x B x R) where K = 1.38 x 10-23, T is the temperature in Kelvin, B is the bandwidth in Hz and R is the resistance in ohms. At room temperature (around 300K), for a bandwidth of 20kHz and a resistance of 21.6kΩ, this works out to 2.67µV RMS, which is -111.5dBV. That is a higher level than the inherent noise in the SuperCodec ADC, so it would definitely degrade performance. A source impedance of 21.6kΩ to the buffer op amps would also increase their distortion contribution slightly. For 1/10th the resistance, that noise level drops by a factor of √10 = 3.16, to 845nV RMS or -121.5dBV. This is usefully below the noise floor of the SuperCodec, so it will have little impact on performance at -10dB, and even less on the -20dB and -40dB settings. In fact, the biggest impact on performance is likely to be EMI pickup due to the higher input impedance in this case. Consider errors caused by loading the DUT with 10kΩ. A preamp might have a 100Ω resistor in series with its output. If we measure this preamp with a 10kΩ input impedance balanced line test set, we will introduce a 1% scaling error. That probably does not matter in most cases, but it does need to be considered. We certainly would not want errors greater than this. So 10kΩ is the lower practical limit, especially when you consider that film capacitors with values above 10µF are expensive and bulky, and would not fit in the space available. We also need to consider power dissipation in the divider. With 50V RMS fed into the divider, the power dissipation is 0.25W for a 10kΩ divider. This is spread out through several resistors, siliconchip.com.au Parts list – Balanced Input & Attenuator 1 assembled USB SuperCodec without 2x12-pin headers attached or front/rear panels drilled but with loose MCHStreamer module (described in Aug – Oct 2020 issues) 1 assembled Balanced Input Attenuator board (see below) 1 set of Test Leads (optional; see below) 2 6x2-pin header sockets, 2mm pitch with pigtails (supplied with MiniDSP MCHStreamer) 1 180mm length of heavy-duty figure-8 shielded audio cable [Altronics W2995, Jaycar WB1502] 1 1m length of red medium-duty hookup wire 1 1m length of black medium-duty hookup wire 1 1m length of green medium-duty hookup wire 1 30cm length of 5mm diameter black or clear heatshrink tubing 1 30cm length of 2.4-2.5mm diameter black or clear heatshrink tubing Balanced Input Attenuator board 1 double-sided PCB coded 01106202, 99.5 x 141.5mm 2 6.35mm DPDT switched stereo jack sockets (CON1,CON2) [Altronics P0076, Jaycar PS0180, element14 1267402] 1 right-angle 3-pin polarised header (CON3) [Altronics P5513, Jaycar HM3423] 1 right-angle 4-pin polarised header (CON4) [Altronics P5514, Jaycar HM3424] 4 4-5mm ferrite suppression beads (FB1-FB4) [Altronics L5250A, Jaycar LF1250] 8 2A DPDT 5V DC coil telecom relays (RLY1-RLY8) [Altronics S4128B/S4128C, Mouser 551-EA2-5NU] 1 DP4T right-angle PCB-mount switch (S1) [Altonics S3008] Semiconductors 6 NE5532AP or NE5532P dual low-noise op amps, DIP-8 (IC1-IC6) 2 12V 1W zener diodes (ZD1,ZD2) 2 3.9V 1W zener diodes (ZD3,ZD4) 8 1N4148 small signal diodes (D1-D8) Capacitors 1 100µF 16V electrolytic 4 10µF 100V polyester film*, 15mm lead pitch [Mouser 871-B32562J1106K] 6 10µF 35V electrolytic 6 100nF 63V MKT 8 100pF 50V C0G/NP0 ceramic 4 22pF 250V C0G/NP0 ceramic Resistors (all 0.25W ±1% metal film unless otherwise specified) 4 1MW 2 3.3kW 1 82W 4 68W 4 39W* 4 33W 6 10W 4 6.81kW* ±0.1% [Mouser 71-CMF556K8100BEEK] 4 2.15kW* ±0.1% [Mouser 71-RN55C-B-2.15K] 16 1kW ±0.1% [Mouser 71-PTF561K0000BXR6] 4 900W* ±0.1% [Mouser 71-CMF55900R00BHEB] 4 100W* ±0.1% [Mouser 71-CMF55100R00BEEB] * for 100k input impedance, substitute these instead: 4 1µF 250V polypropylene film, 7.5mm lead pitch [Mouser 667-ECW-F2105HAB] 4 68.1kW ±0.1% [Mouser 279-H868K1BYA] 4 21.5kW ±0.1% [Mouser 279-YR1B21K5CC] 4 9kW ±0.1% [Mouser 71-PTF569K0000BYEK] 4 1kW ±0.1% [Mouser 71-PTF561K0000BXR6] 4 390W ±1% Test Lead parts 2 90° 6.35mm TRS line plugs [Altronics P0048 or P0049] 2 1.2m lengths of microphone cable (or length to suit) [Altronics W3024/W3029, Jaycar WB1534] 2 small red alligator clips [Altronics P0110, Jaycar HM3020] 2 small black alligator clips [Altronics P0111, Jaycar HM3020] 2 small green alligator clips [Altronics P0102] 1 30cm length of 6mm diameter black or clear heatshrink tubing 1 30cm length of 3mm diameter black or clear heatshrink tubing 1 30cm length of 2.4-2.5mm diameter black or clear heatshrink tubing Australia’s electronics magazine November 2020 49 50 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.8: the circuit of the Balanced Input Attenuator add-on board. CON1 and CON2 are the new 6.35mm TRS jack socket inputs connectors, while CON3 and CON4 connect to the ±9V supplies and CON4 input header on the USB SuperCodec Sound Card board respectively. The attenuator resistor taps are selected via relays RLY1-RLY8, and the signals then pass to op amp buffers IC1-IC4 and the differential-to-single-ended converter stages based on dual op amps IC5 & IC6 before going to the ADC. siliconchip.com.au Australia’s electronics magazine November 2020 51 but heating in those resistors could lead to some inaccuracies. The ratings of the divider resistors would allow up to 80V RMS to be fed in, but besides this being possibly unsafe, we prefer not to run them at their limits. So there is no perfect answer. Hence, we are providing resistor values for the input attenuator that give either a 10kΩ or 100kΩ input impedance. Remember to choose the right value capacitor to go with them. Our inclination is to go with 10kΩ, but we fully understand why others might choose 100kΩ. We have used relays to switch between the four possible attenuation settings. This is a little bit expensive, as these are a few dollars each, but it makes the design nice and clean in terms of layout and avoids the possibility of noisy, unreliable wafer switches failing. The relays give a satisfying “clunk” as you switch across ranges, suiting such a high-performance device. Buffers The voltage divider output impedance varies depending on the range selected. This does not suit the balanced-tosingle-ended converter, so buffers are needed. We use two paralleled op amps to do this, driving two balanced-to-singleended converters. These are combined at the output to get a 3dB improvement in signal-to-noise ratio compared to using fewer op amps. The differential-to-single-ended converters subtract the Cold input signal from the Hot input signal. The matching of resistors in these is important, at least within each arm of each converter. So we have specified 0.1% tolerance 1kΩ resistors here. This tolerance is required to deliver the specified performance. We have chosen 1kΩ resistors as they have a low enough resistance to add negligible thermal noise to the convertor without loading the op amp outputs too much. And as many constructors will likely have plenty of 1kΩ 1% resistors, they could select well-matched pairs using just about any DMM and avoid the cost of 0.1% types. The output of the differential-tosingle-ended convertors is combined through 10Ω resistors (necessary to allow for the op amps having different offset voltages), which then feed into the USB Sound Card. We have included input protection comprising diodes clipping to a 3.9V rail. We have tested that this does not impact distortion performance. Note though that if you connect this to a high-voltage source on the 0dB range, you will damage this part of the circuit! There is additional protection on the power supply rails provided by 12V zeners, which again should only operate under extreme fault modes. Next month Unfortunately, we don’t have room for the construction details this month. That will have to wait for the next issue. As well as describing the construction, and what you have to do to get the Balanced Input Attenuator to fit into the same case as the USB SuperCodec, the second and final article in this series will also cover the testing procedure, and how to make some handy balanced SC test leads. Subscribe to SILICON CHIP and you’ll not only $AVE $AV AVE MONEY AV but we GUARANTEE you’ll get your copy! When you subscribe to SILICON CHIP (printed edition) in Australia we GUARANTEE you’ll never miss an issue! Subscription copies are despatched well before the on-sale date (the magazine is due on sale around the end of the previous month). It is unusual for copies to go astray in the post – but when we’re mailing out many thousands of copies, it does happen occasionally. So we make this promise to you: if you haven’t received your SILICON CHIP anywhere in Australia by the end of the month of issue, contact us and we'll give you online access to that issue and also post you a replacement copy in our next mailing. You can contact us via e-mail at silicon<at>siliconchip,com.au Remember: it’s cheaper to subscribe anyway - do the maths and see the savings! Remember: we pick up the postage charges – so you $ave even more! Remember: your newsagent may have sold out when you get there - and you’d miss out! Remember: you don’t have to remember to go out and buy your copy - it’s delivered right to your letter box! Remember: you can also subscribe to the online version, or get a discounted, combined print+online subscription Convinced? We hope so! And we make it particularly easy to take out a subscription – for a 6 month trial, a standard 12 month or a giant 24-month with even bigger savings! To subscribe, simply go to our website – www.siliconchip.com.au – click on the “subscriptions” tab and follow the prompts. We accept payment by Paypal, Visa, Mastercard, EFT/Direct Deposit or Cheque/Money Order (sorry, no Amex or Diners). We’re waiting to welcome you to the SILICON CHIP family! 52 Silicon Chip Australia’s electronics magazine siliconchip.com.au Workbench & Projects: Must haves for beginners and pros! 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Fully sealed and waterproof. 12VDC operation. • Blue, red and amber available • 70(Dia) x 45(H)mm LA5326-LA5328 • Reed switch and magnet • Normally CLOSED (NC) per pair • Self adhesive or screw mount LA5072 JUST 525 $ PIEZO SIREN Emits a 120dB output. Supplied with mounting bracket and connecting cable. • 12VDC 300mA LA5258 21 $ $ EA JUST 3995 $ AC/DC - DC CONVERTER Solve your power cabling problem quickly and easily by sending 24VAC down the long run, then converting it to 12VDC. Connection is by screw terminals. 1A max. MP3350 JUST 2695 95 JUST 6495 $ GIGABIT POE INJECTOR Adds inline power to a single network cable up to 100m. Supports up to gigabit for ultra-fast connectivity. YN8040 ON SALE 24.10.2020 - 23.11.2020 think. possible. Your destination for... network & digital storage Leads, Adaptors & Converters Wire Your Own Network ACTIVE USB 3.0 EXTENSION LEADS 24-PORT PATCH PANELS - CAT6 NOW FROM 169 $ 19" RACK MOUNT ENCLOSURES SAVE UP TO $50 6U to 12U in Swing or Fixed frame. Ideal for IT or phone system installations, PA systems, etc. Solid steel powder coated to provide high strength and rigidity. 6U Flat Packed HB5170 WAS $189 NOW $169 SAVE $20 6U Assembled HB5171 WAS $219 NOW $199 SAVE $20 12U Flat Packed HB5174 WAS $249 NOW $229 SAVE $20 6U Swing Frame HB5180 WAS $279 NOW $249 SAVE $30 12U Swing Frame HB5182 WAS $349 NOW $299 SAVE $50 KEYSTONE RJ45 SOCKET JACKS Cat5E YN8028 Cat6 YN8029 $3.95ea. RJ45 MODULAR PLUGS Packet of 10. For stranded and solid CAT6 cable. PP1447 $14.95 24 port patch panel with a hard metal exterior. Numbered ports and a labeling area for each port. YN8048 WAS $79.95 NOW JUST 7495 $ SAVE $5 6-WAY PDU WITH SURGE & OVERLOAD PROTECTION NOW JUST Power up to six components in your rack setup. 6 x 240V outlets and fits any standard 19" rack. • 10A output, 1.6m long MS4094 WAS $74.95 69 $ 95 SAVE $5 FROM NETWORK CABLE 1 $ 30 Designed for reliable high-speed networks installations. Cat5E WB2020 $1.30/m Cat6 WB2030 $1.45/m /m Hard Drive Data Recovery FROM 4 $ HARD DRIVE POWER CABLES 95 A range of SATA and eSATA data/ power cables for use with computers and external serial ATA devices. HDD Power to 2 x HDD Sockets PL0750 $4.95 SATA to SATA PL0978 $5.95 SATA RA to SATA PL0981 $7.95 HDD Power to SATA PL0758 $5.95 HDD Power to 2 x SATA PL0759 $7.95 FROM 9995 $ HARD DISK DRIVES Ideal storage solution or simply for backing up your files. 2.5" 1TB Ideal for laptops. XC5680 $99.95 3.5" 2TB Desgined for surveillance systems. XC5682 $159 Allows you to store files on two hard drives. Tool less & driverless. Supports 2.5" and 3.5" HDD. • RAID Level: RAID 0, RAID 1, JBOD, Spanning • Max. Tansfer Rate: 5Gbps • Capacity: 8TB Per Bay XC4688 USB 3.0 SATA HDD DOCKING STATION Strip wire up to 5-6mm, and doubles as a punch-down tool for 110/88-type ONLY terminals with blade. TH1738 NOW FROM 39 $ 95 SAVE $10 8 $ • Will crimp the following lugs: 6P2C, 6P4C - RJ11, 6P6C RJ12, 8P - RJ45 • Also cuts and strips cable TH1935 ONLY 22 95 $ More ways to pay: REDUNDANT ARRAY OF INDEPENDENT DISKS (RAID): RAID is a way of storing the same data in different places on multiple hard disks to protect data in the case of a drive failure. 95 NOW JUST 49 $ FROM 3695 $ RS-232 DB9M TO USB CONVERTERS Connect a variety of RS-232 devices to your modern computer with these adaptors. To USB Adaptor XC4927 $27.95 (Shown) To USB 1.5m Lead XC4834 $29.95 FROM 2795 $ USB RJ45 EXTENSION ADAPTOR Connect any USB device to your computer from up to 50m away via a standard Cat 5 network cable (sold separately). • PC and MAC® compatible • Transmitter and receiver included XC4884 ONLY 3295 $ Need a PC Lead? We stock a huge range of computer leads. Listed BELOW are just some of the most popular ones. See website or instore for full range. USB 3.0 3.5" SATA HDD ENCLOSURE Connect 2.5" or 3.5" SATA hard drives to Backup your data up to ten your computer. Plug and play technology. times faster than a USB 2.0 connection. USB 3.0 for fast data transfer. • Suits 3.5" SATA HDD up to 8TB • Transfer Rate: 430Mbps • Supports SATA I/II/III • HDD capacity: up to 8TB XC4667 WAS $59.95 Single XC4687 WAS $49.95 NOW $39.95 Dual XC4689 WAS $64.95 NOW $54.95 6P/8P MODULAR CRIMPING TOOL CAT-5 PUNCH-DOWN TOOL & STRIPPER JUST 99 $ USB 3.0 2 BAY RAID HDD ENCLOSURE Feature a built-in extender to run your USB devices over long distances. 5m XC4126 $36.95 10m XC4128 $74.95 95 SAVE $10 4P/6P/8P MODULAR CRIMP TOOL WITH NETWORK/POE TESTER Combination crimper tool and a cable tester in one unit. • Tests both UTP and STP cable • Single and multi-wired cable crimping • Detachable cable tester NOW TH1939 WAS $74.95 6495 $ SAVE $10 D9 MALE TO D9 MALE EXTENSION CABLE All pins wired straight through. 1.8m long. WC7535 ONLY 1095 $ VGA MONITOR CONNECTING CABLE D15HD Male to D15HD Male. 1.8m long. WC7582 ONLY 1295 $ MINI DISPLAYPORT TO VGA CONVERTER Supports up to 1080 resolution. 1.8m long. WQ7440 ONLY 2995 $ 57 think. possible. Your destination for the best rewards & perks. love jaycar? you're going to love our rewards! SHOP In store & online EARN POINTS For dollars spent 1 point = $1 CLUB OFFER 54 95 99 $ 95 SAVE $30 4-DOOR REMOTE CONTROLLED CENTRAL LOCKING KIT CAR AMPLIFIER WIRING KIT A complete 8G wiring kit for installing an amplifier into your vehicle. AA0442 RRP $69.95 account profile and more... CLUB OFFER SAVE $15 SAVE $15 + PERKS offers, event invitations, 200 points = $10 eCoupon 79 $ CLUB OFFER $ GET REWARDS eCoupons for future shops in store • Lock and unlock your car doors from a distance. • Kill switch LR8842 RRP $94.95 12/24VDC LED STROBE LIGHT WITH MAGNETIC/PERMANENT BASE Amber LED vehicle warning lights for alerting other drivers or pedestrians. 12/24VDC. ST3278 RRP $129 CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE 25M GAFFER TAPE 200 PIECE SPRING ASSORTMENT 5MM LED CLIPS - PK100 USB TO PARALLEL BI-DIRECTIONAL CABLE 20% Adhesive and strong. 48mm wide. NM2810 RRP $16.95 CLUB $12.95 25% 20% 25% 20 types from 10mm to 70mm long. HP0638 RRP $19.95 CLUB $14.95 Black plastic panel mounting clips for 5mm LEDs. HP1103 RRP $12.95 CLUB $9.95 CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE ABS INSTRUMENT CASE 55F 2.5VDC SUPER CAPACITOR GAS LEAKAGE DETECTOR RG59 75 OHM COAX CABLE 20% 95(W) x 158(D) x 47(H)mm. High impact ABS plastic UL-94-HB. HB5922 RRP $13.95 CLUB $10.95 25% 20% USB 1.1 Compliant A type male connector. XC4847 RRP $39.95 CLUB $29.95 10% High density. Over 500,000 cycles. RE6704 RRP $22.95 CLUB $16.95 Detects butane, propane, acetylene, and methane (natural gas) gases. QP2299 RRP $49.95 CLUB $39.95 CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE SOLDER STAND WITH SOLDER DISPENSER 14-PCE HOBBY KNIFE SET PIEZO HORN TWEETER LED POWER SUPPLIES 20% 16mm diameter shaft. Metal base. TS1504 RRP $24.95 CLUB $19.95 25% Blades, tweezers, screwdriver etc. TH1916 RRP $19.95 CLUB $14.95 20% 100WRMS. 8.0Ω. 93dB<at>1W. CT1930 RRP $12.95 CLUB $9.95 15% OFF EXCLUSIVE CLUB OFFER TRAILER CONNECTORS* *Includes plugs, sockets and adaptors. See T&Cs for details. 58 click & collect Buy online & collect in store 30m roll of standard RG59 coax cable. Black or white. WB2001 or WB2005 RRP $22.95ea. CLUB $19.95ea. 20% Dimmable. 75W, metal case, IP67 rated. 12V 5A MP3378, 24V 3.15A MP3379 RRP $99.95ea. CLUB $79.95ea. YOUR CLUB, YOUR PERKS KEEP UP TO DATE WITH THE LATEST OFFERS & WHAT'S ON! Visit www.jaycar.com.au/member-access ON SALE 24.10.2020 - 23.11.2020 think. possible. Your destination for... workbench essentials 1. HEATSHRINK ASSORTMENT TRADE PACK 4. 7-PCE HEX NUT DRIVER SET • 160 piece • 1.5, 2.5, 3, 5, 6 and 10mm diameters • Black, red, and clear • Storage case WH5524 • M3, M3.5, M4, M4.5, M5, M 5.5, and M6 • Plastic storage case NOW TD2339 WAS $34.95 2995 5 $ ONLY 2495 $ 2 2. LED HEADBAND MAGNIFIER • Fits over prescription or safety glasses • Adjustable head strap • 1.5x, 3x, 8.5x or 10x magnification • Requires 2 x AAA batteries ONLY QM3511 2995 SAVE $5 5. 2-IN-1 NETWORK CABLE TESTER AND DMM • Measure AC & DC voltages up to 600V • LAN tester checks faults & miss wired conductors • CAT III, 2000 count • AC/DC voltage up to 600V NOW XC5078 WAS $89.95 • Made from sturdy ABS with solid clasps • Removable compartment trays • 335(L) x 420(W) x 60(D)mm HB6305 ONLY 1895 $ 7995 SAVE $10 6. RECHARGEABLE LITHIUMION SOLDERING IRON SET • Comes with 12W (500°C) / 30W (600°C) tips, hot knife, solder & sponge • Built-in rechargeable Li-ion battery • Up to 50 minutes operation at full charge • LED light for illumination NOW • Charge via USB TS1545 WAS $99.95 4 7995 $ 6 SAVE $20 20MHZ USB OSCILLOSCOPE • Takes up very little NOW JUST 24 $ bench space • Highly accurate USB interface plug & play • Automatic setup • Waveforms can be exported as Excel/Word files • Spectrum analyser (FFT) • Includes 2 probes QC1929 $ SAVE $5 DIGITAL STEM THERMOMETER ULTRA PORTABLE 199 $ • Temp: -50°C - 200°C / -58°F - 392°F • Fast response, min/max memory and data hold • Stainless steel probe, splashproof body • 205mm long QM7216 WAS $29.95 JUST JUST 19 $ 95 3-30VDC TESTER WITH VOLTAGE/POLARITY READOUT 395 $ LOW VOLTAGE CIRCUIT TESTER • Tests wiring systems on cars, trucks, boats etc. • Works on 6/12/24V systems TD2049 • Works on 6/12/24V systems • Stainless steel testing probe • LED Indicators: Green (-), Red (+) QP2216 NOW 4995 $ NON-CONTACT AC VOLTAGE DETECTOR JUST 24 $ • Detects AC voltages from 200 to 1000V • LED flashlight function • 2 x AAA batteries included QP2268 95 SAVE $10 2-IN-1 LASER MEASURING TAPE Measure up to 30m using the laser or up to 5m with the retractable tape. Metric and imperial. • USB rechargeable • Auto power off • Non-slip grip QM1627 WAS $59.95 NOW JUST 1495 95 SAVE $5 JUST More ways to pay: 1 $ $ 3. 19 COMPARTMENT STORAGE 3 0-15V ANALOGUE BENCH VOLTMETER • Choose either 3V and 15V scales via separate banana plugs • Zero offset adjustment • Quick and easy to read display of volts QP5040 WAS $19.95 STAINLESS STEEL WIRE STRIPPER, CUTTER, PLIERS 110MM PRECISION LONG NOSE PLIERS JUST JUST Strips wire up to 2.6mm and cut steel wires up to 3.0mm. • Soft rubber handle TH1841 19 $ 95 • Made from carbon steel • Insulated soft-grip handle TH2334 2995 $ HEX RATCHET CRIMPING TOOL 150MM PRECISION SIDE CUTTERS JUST JUST Crimp F, N, BNC, TNC, UHF, ST, SC & SMA connectors onto RG6 or RG58 coax cable. TH1833 39 $ 95 • Made from carbon steel • Designed for sharp cutting in precision wiring • Insulated soft-grip handle TH1891 4495 $ 59 High-end equipment: PRO! beginner to PRO! THREE FILAMENT 3D PRINTER Whether you are just starting out, a keen hobbyist or a professional we have a range of printers, soldering stations, and digital multimeters to suit your needs and budget. Come in store or visit the website to see the full range. ENTRY MID COLOUR MIXING TECHNOLOGY JAYCAR EXCLUSIVE: FIRST IN AU & NZ RETAIL MARKET! JUST JUST 1499 $ JUST 549 1349 $ $ FINDER LITE 3D PRINTER MOOZ-3Z TRIPLE FILAMENT 3D PRINTER 3D PRINTER/CNC/LASER ETCHER • Fully assembled • Low noise operation of 50dB or even less • Featured with a 3.5" touch panel, slide-in build plate, assisted levelling, SD card slot and more • Prints up to 140(L) x 140(W) x 140(H)mm TL4222 See website for details. • 3D print, engrave and laser cut with a single machine • Featured with 3.5" colour touch screen, heated build plate, easy swap & interchangeable modules and more • Includes easy to use software • Prints up to: 125(L) x 125(W) x 125(H)mm TL4400 See website for details. • Equipped with a three-color print head for colour mixing • Easy-to-use controller and mobile app • Featured with 3.5" LCD touch pad, Wi-Fi USB connectivity, magnetic heat bed and more • Supplied with a roll each of cyan, magenta and yellow filament to get you started. • Prints up to: 100(H) x 100(Dia.)mm TL4412 See website for details. 50W ESD SAFE SOLDERING STATION ENTRY 10W 240VAC SOLDERING STATION MID • Compact and lightweight • Suitable for lead-based and lead-free solder • 100-450°C temperature range JUST • 240VAC powered • 100(L) x 65(W) x 63(D)mm TS1610 34 $ ECONOMY TRUE RMS AUTORANGE MULTIMETER 95 JUST 39 $ • Adjustable temperature (160-450°C) • Digital display • High temperature stability • 240VAC powered • 160(L) x 104(W) x 124(D)mm TS1640 WAS $159 • Cat III 600V, 4000 count • AC/DC voltages up to 600V • AC/DC current up to 10A • Continuity, diode check and more QM1551 95 ALL METERS INCLUDES TEST LEADS NOW JUST 149 $ SAVE $10 TRUE RMS DIGITAL MULTIMETER WITH NON-CONTACT VOLTAGE DETECTION ENTRY • Cat III 1000V, 4000 count • Voltages: up to 750VAC, up to 1000VDC • AC/DC current up to 10A • Min/max hold, capacitance and more QM1321 60W ESD SAFE SOLDERING STATION MID JUST 69 $ 95 • Outstanding, fast, accurate soldering station from Thermaltronics • Uses the proven Curie Point technology • Works with leaded and unleaded solder • 350°C to 398°C Temp range • 0.5mm chisel tip included • 240VAC powered TS1584 WAS $379 ALSO AVAILABLE: Spare Tips With Heating Element FROM $29.95 PRO! NOW JUST 349 $ SAVE $30 MULTIFUNCTION ENVIRONMENT METER • Sound level meter, light meter, humidity meter and temperature meter in one unit • Cat IV 600V, 4000 count • AC/DC voltages up to 250V • AC/DC current up to 10A • LUX, SPL, humidity and more QM1594 WAS $139 PRO! NON-CONTACT VOLTAGE NOW JUST 119 $ SAVE $20 TERMS AND CONDITIONS: REWARDS / CLUB MEMBERS FREE GIFT, % SAVING DEALS, & MEMBERS OFFERS requires ACTIVE Jaycar Rewards / membership at time of purchase. Refer to website for Rewards / membership T&Cs. IN-STORE ONLY refers to company owned stores and not available to Resellers. Page 2: Club Offer: Gesture Controlled Powerpoint project includes 1 x each of XC4410, XC3742, ZW3100, MS6149, PH9251 & SB2423 for $59.95. Page 3: LoRa Data Communications Bundle includes 2 x XC4410 + 2 x XC4392 + 1 x XC4394 for $199. Page 4: Multibuys: 3 x LA5046 for $99. Page 6: Club Offer: 15% OFF Trailer Connectors includes plugs, sockets and adaptors. For your nearest store & opening hours: BUNN INGS To Parr amatt tta a PU B PA P ARK Rydalmere 320 Victoria Rd Rydalmere, NSW 2116 (02) 8832 3120 OAD VIC TToOParra am matta RrrIA RO PAA RKD PARK R EUS T ON S T Parking Parking Available 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer were confirmed at the time of print but delays sometimes occur. Please ring your local store to check stock details. Occasionally there are discontinued items advertised on a special / lower price in this promotional flyer that has limited to nil stock in certain stores, including Jaycar Authorised Resellers. These stores may not have stock of these items and can not order or transfer stock. Savings off Original RRP. Prices and special offers are valid from catalogue sale 24.10.2020 - 23.11.2020. 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. Automatic hand sanitiser dispenser We wanted an automatic sanitiser dispenser as it is not ideal to press down on the dispenser with possibly contaminated hands. While we were able to source some sanitiser (with difficulty!), we could not find an automatic dispenser, so I decided to make one. The basic parts were mostly salvaged from empty hand wash bottles – pipes, spray nozzles and a big plastic bottle. To make it automatic, we used a small DC-powered submersible liquid pump. After making a small hole in the cover of the bottle, we inserted the spray nozzle which we salvaged from a liquid hand wash dispenser. Next, we attached the pump and rolled up the rubber pipe up to the shoulder of the nozzle. The pump is submerged into the liquid sanitising agent. The nozzle mouth is connected to the pump discharge. The nozzle mouth may be plugged slightly with small objects to reduce the rate at which the liquid is dispensed. The goal is to run the pump for a short period when somebody brings their hands within 15cm of the nozzle. We choose the HC-SR04 based siliconchip.com.au ultrasonic distance-measuring sensor because I had quite a few of them on hand. Instead of using a full Arduino board, I deployed just the ATmega328 chip. This has a 16MHz crystal and load caps connected so it can be programmed directly with the code from an Arduino board. It’s powered from a 5V supply derived from a 12V battery. The Arduino code constantly triggers the ultrasonic sensor; if it detects an object nearby, it brings its digital outputs at pins 18 and 19 high until the object moves away. When pin 18 goes high, it forwardbiases the base-emitter junction of NPN transistor Q1 via a 150W current-limiting resistor. This sinks current from the negative terminal of the motor, which also runs from the 5V supply. Diode D1 absorbs the motor’s back-EMF spikes. If you use a pump that needs more voltage, you can use the same arrangement but just connect its positive terminal straight to the 12V battery (or use a 9V battery, if you have a 9V pump). The BD139 can supply at least 1A in the configuration shown here, so should be adequate to drive any small pump. Australia’s electronics magazine The proximity limit of 15cm can be adjusted in the sketch code, which can be downloaded from siliconchip. com.au/Shop/6/5679, along with the required Arduino libraries. You can program the chip on an Arduino Uno board and then transfer it over to a socket on the project circuit board. Bera Somnath, Vindhyanagar, India. ($100) November 2020 61 Wellbeing monitor I needed a device that could monitor the welfare of a senior family member living alone to supplement regular phone calls. The circuit I came up with reports hourly movement activity. A smartphone notification message is sent if movement is below a threshold for defined active hours. Movement events are recorded hourly to an SD card and can be reviewed to establish normal activity patterns, and thus identify any significant changes. It comprises a passive infrared sensor (Jaycar Cat XC4444), an ESP8266 WiFi module (Jaycar XC3802 or WeMos D1 mini), a micro SD card shield (Jaycar XC3852) and a few other components. The wiring is elementary, as the SD shield plugs into the ESP8266 module. The unit connects to an available WiFi network and uses the Blynk IoT application that will work on most smart devices wherever an internet connection is available. When the PIR senses movement, its output pulls digital input pin D1 of the ESP8266 high. The number of these events are counted each hour, and if the number is less than a preset value between certain hours, a notification is sent to a family member. Thus alerted, the family can contact the senior by phone, or visit, or inform a neighbour. The total movement events per hour are also logged to an SD card file that can be reviewed online and graphed for the current or any previous day. The LED flashes briefly when movement is detected, and when the PIR resets after the timeout delay. The PIR timeout pot should be set to about 10 62 Silicon Chip several keywords such as “H” to show the help, “S” for settings, “L” for the hourly event log, “ST” for statistics of the previous 35 days and more. Notifications can be temporarily turned off for a number of hours using preset buttons, or for longer times in the modify settings option. There is also an hourly blackout option to cease notifications for individual hours. Configuration seconds, and the sensitivity pot to about midrange. While the PIR module operates from 5V it outputs at 3.3V, for compatibility with the I/O pins of the ESP8266. The remote device runs the Blynk IoT platform with a basic software interface comprising the main Terminal screen with RTC and Notification Widgets, two Value Displays, two Tabs and five Buttons to disable and re-enable notifications. The second screen has a chart that plots total and daily movement events against time. If the available internet service has limited monthly data allowance, then a limited data option can be set. This activates the WiFi only for a 90 second period if an alarm message is required, and also once a day when a status message is sent that confirms the system is functional, allowing the user to remotely interrogate the hourly movement events for the day. The terminal screen understands Australia’s electronics magazine A web page-based configuration is provided on first power up after loading the software sketch. It permits selection of an existing WiFi network, the network password, the Blynk Authorisation Token and the text for two notification messages (the monitored person’s name and a ‘not OK’ message.) This means that the WiFi and Blynk connection parameters do not have to be hardcoded into the sketch. The settings are then saved to EEPROM and are loaded on bootup. Other settings are changed using the modify settings option in the terminal screen. See the user manual for more details of installing, setting up and using the Wellbeing Monitor (available for download from siliconchip.com. au/Shop/6/5680). A QR Code download is also provided to quickly recreate a copy of the Blynk Project. If you have Blynk already on your smart device, open the app, log in, create a new project then tap on the QR Code icon next to the info icon at the top right of the project page. Then scan the QR Code for this project using the device camera. Phillip Webb, Hope Valley, SA. ($100) siliconchip.com.au Boat Computer modified for 4WDs I was interested to see the Boat Computer modification (April 2016; siliconchip.com.au/Article/9887) for fitting in a four-wheel drive with an altitude display in the August 2020 issue (Circuit Notebook). Some time ago, I installed the Boat Computer in my four-wheel drive and also modified the software to suit. My software strips out the navigation capability and has three screen displays. At switch on, it shows a digital speedo (useful because car speedos are almost always inaccurate) and a compass. The compass display has been redesigned to work like a marine steering compass, which I find more intuitive. Unlike the original software, the compass does not blank when the vehicle stops because a car does not swing at anchor. The second screen shows time, date and day of the week. Serious grey nomads can easily lose track of the latter, which can result in problems when arriving in town and finding the shops and attractions are shut. This information assumes Eastern Standard Time (10 hours in front of GMT). For other time zones, the variable timezone should be adjusted to the difference from GMT in seconds. The third screen shows latitude, longitude, altitude and number of satellites. The latter is to give some indication of precision. The modified software is available for download from the Silicon Chip website (siliconchip.com.au/ Shop/6/5681). Greg Hoyes, Upper Kedron, Qld. ($50) More modified Boat Computer software I saw the article about getting the altitude information to appear on the Boat Computer by Tim Blythman (Circuit Notebook, August 2020; siliconchip.com.au/Article/14539) and have added it to my program. I have made a few other modifications to it. I use mine as my primary speedometer. I have been running this for a long time now, and have it on the top of my dash. It appears just above my steering wheel and just under my normal line of vision. I have also fitted a shroud to get rid of sunlight on the screen. I am an NBN “Fixed Wireless” installer and sometimes need to know in what direction I am driving to be able to determine which direction the siliconchip.com.au tower is I need to point to (the bearing is given on the work order). My daughter also has one in her car and is often asked by friends what it does. The other changes I made are as follows: 1) I locked the baud rate for the GPS module to 9600 baud as I have found it to be the usual rate. 2) I have added a 24-hour clock on the heading screen, as my satnav loses the clock when I go into navigate mode. 3) I have included automatic backlight control. I am using a Jaycar LDR (RD3480) in series with a 56kW resistor. The LDR looks out through a hole on the back of the case, which gives Australia’s electronics magazine good light control and requires no access to car wiring. 4) I have modified the km/h reading to give the reading in 1/10th km/h resolution (the decimal place is in a smaller font). When I loaded it with the altitude changes, I initially loaded it using the V4 fonts library. But when I loaded the V6 fonts into the library, the program crashed after loading the main program. I then “crunched” the fonts file and it all loaded okay. Both these files are available for download from the Silicon Chip website (siliconchip.com.au/ Shop/6/5681). Ray Saegenschnitter, Huntly, Vic. ($50) November 2020 63 SERVICEMAN'S LOG One repair leads to another Dave Thompson There are people out there who obviously love their older radios and stereos. Since word got around that I can repair these devices, quite a few have come through the workshop. While most repairs are simple, there have been some that required a good bit of thinking. Most of these type of repairs don’t warrant much attention due to being relatively simple fixes; replace the odd component here, or reflow dry joints there, and away we go for another 40 years. But there were a couple of recent fixes of which I have been quite proud. While they didn’t require me to do enough research to earn a doctorate, I did have to do some searching and thinking to come up with a solution. The first was an amplifier which is no stranger to my workshop. This is one of those jobs that proves the old engineering maxim: as soon as you mess 64 Silicon Chip with something that has been working well for years, it will develop a heap of problems (perhaps a corollary to “if it ain’t broke, don’t fix it”?) There’s probably a rational explanation for this phenomenon. It often happens that you take the case off an old amplifier just to check it over and huff the cobwebs out, then a month later the caps fail, and the transistors or valves need replacing. Perhaps I disturbed something with my low-pressure air, or the journey to Australia’s electronics magazine the workshop shook up those old solder joints. Or maybe I just displeased the audio gods by intruding on sacred ground! Mechanics often claim that a car engine is never the same once the head has been off, and I’m convinced there are many parallels in electronics. Whatever the cause, there is always the sneaking suspicion that I’ve done something to cause a rift in the space-time continuum, and now I’m paying the price. siliconchip.com.au Welcome back, old friend This lump of a stereo amplifier is one of those old 70s jobs that appear to be milled out of a solid billet of brushed steel, with a couple of polished wooden caps slapped on each end of the case. The power transformer alone is heavier than most modern audio systems, including their speakers! Everything inside is heavy-duty, and the connections are wire-wrapped, a construction method peculiar to that era. While wrapping is an excellent way of connecting individual circuit boards together, and the cabling has obviously stood the test of time, it is a royal pain in the woofer to work on. This is especially true if I need to uninstall and reinstall the board several times for testing purposes – re-wrapping it each time is highly impractical. While I still possess a wire-wrapping tool and a few spools of wrapping wire, purchased circa 1975, I haven’t used them for many years. In cases like this, unless the custom- siliconchip.com.au er specifically wants to retain the vintage authenticity of the device, I replace wrapped joints with soldered connections. While I know my way around this Pioneer SX-series amp, having repaired it before, I think I was the first person to take the covers off. Initially, the problem was that the speaker protection relay was not kicking in at switch-on, and if it did, it would randomly drop out. I documented that repair in the February 2020 issue (siliconchip.com.au/Article/12339). Now I’m wondering if by opening it up I somehow jinxed it, because here it is again less than a year later with a different fault. I knew I shouldn’t have disturbed the gremlins slumbering within its circuitry... The customer reported that, while using it, it made some loud static and clicking and popping noises, then the amp fell silent. The panel lights still glow, but there is no action from the speaker-protection circuit and no other signs of life. At first, I thought my previous repair might have failed, but I removed the protection board and relay and inspected and tested them; all appeared Australia’s electronics magazine Items Covered This Month • • • It’s never as easy as it seems The water-logged electric toothbrush Fixing substandard industrial machinery *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz OK. This is where the now-soldered interconnecting wiring came in handy – if I had re-wrapped the boards back in, it would have made removing them again that much more work. And though there was some slack left in the factory wiring, wrapping uses up a couple more centimetres of wire length each time, so I would have had to replace all the wires. Instead, I could just desolder it, then reconnect everything when I was done. The power supply seemed to be the next place to check. Fortunately, the circuit diagram is freely available online, and I had already downloaded it. November 2020 65 This made things a whole lot easier. The annotation on the schematic is also excellent, with test points and current and voltage values clearly marked. With my trusty (and still working!) analog multimeter – after last month’s shenanigans – I rang out the various outputs on the power supply board and found three of the nine listed were well out of spec. As mentioned earlier, the power supply is a heavy-duty unit and delivers a range of voltages from 5.4V to ±51.5V DC, as well as 7.5V AC. I measured around ±14V on the nominally ±51.5V lines, and zero on two other points, which both should have been +13.5V. I knew I wouldn’t get any joy without these voltages present and fully accounted for. In the last repair, I replaced all the electrolytic capacitors on this board, and a couple of the power transistors. However, there were still about a dozen smaller transistors I hadn’t tested. Looking through the circuit diagram, it was apparent that I was going to at least have to remove some of those in the part of the circuit responsible for these sub-par readings. Pulling them out is as easy as using a solder-sucker and a hot soldering iron. Unhealthy though it might be, I love the smell of that old solder burning – it reminds me of watching my dad working in his workshop. I found several open-circuit transistors, or more accurately, my Peak Semiconductor Analyser found them. I know that I could have used my multimeter to discover them, but I have an analyser, so I use it. Amplifiers of this era often used proprietary components, or possibly transistors and diodes that were manufactured at the time in relatively small batches and ended up not being used in much else. In this case, the part numbers weren’t familiar, so I hit the web and discovered an abundance of forum posts regarding the same problem. After some research, I discovered that these transistors aren’t overly specialised, and audio purists derided several as being too noisy for use in amplifier circuits anyway. Editor’s note: that probably doesn’t matter if they’re in the power supply, unless the audio circuitry is particularly poorly designed. Luckily, there were recommendations for substitute transistors that 66 Silicon Chip Australia’s electronics magazine would offer significantly quieter performance. Many of these types are still widely available and inexpensive. While I had some on hand, my supply of new old stock (NOS) components is dwindling. So I decided just to buy what I needed new from element14 and Digi-key. After receiving the parts, I replaced all the transistors in that section of the supply. After re-soldering the board in, but without hooking up the outputs yet, I powered it on and measured the output voltages. The numbers were better, but still way off, so something else was clearly wrong. It wasn’t that easy Referring to the circuit diagram, I measured as many of the resistors and caps as I could in-situ, in case one had failed. While not an ideal method, the figures on my LCR meter were within tolerance. That left the diodes. This board has 12, and most are straightforward silicon varieties, with the only difference being their currenthandling characteristics. Two of the diodes are zeners, one rated at 13V and one at 14V, 500mW. I couldn’t measure them properly in-circuit, so I removed them and tested them with my analyser. Both were open-circuit. I replaced them with suitable parts from my own stocks and powered the amp up again; this time, I had voltage outputs that, while a little high, were within 10% of stated values. After connecting the power supply board outputs, I switched the amp on, and after a few seconds the speakerprotection relay kicked in – an excellent sign! I ran the amp on my workbench at half-volume for 24 hours and periodically checked the voltages and component temperatures on the supply board. All remained normal, though as expected, a couple of fibre-sleeved load resistors got warm. I then cycled the power on and off around 20 times within an hour, and the relay kicked in every time. I reassembled everything, re-soldering any connections that were a bit temporary and buttoned it all back up. The customer picked it up and hopefully that’s the last I see of this behemoth for a while! The radio repair The second repair came by way of an enquiry from a reader; he had an siliconchip.com.au older General Electric Superadio 3 radio that had started drifting off-station. The radio was usually used in a setting that once the station was selected, it didn’t change, but lately, he’d turn it on and after a few minutes, the radio de-tuned and was thus unusable. For people of a certain age, modern radios often don’t cut the mustard. While they might have much more sophisticated circuitry, and accurate and stable digital tuner sections, the sound output is often not as good when compared to older models. I’ve found many newer sets sound ‘tinny’, which could be due to smaller speakers and flimsier construction. While perhaps not as portable (in the modern sense), many of us prefer our older radios. So that is why we try to keep them going as long as we can. The Superadio duly arrived at the workshop, and I fired it up to test it. It did sound good, which was likely down to the substantial dual speaker system, consisting of a 165mm woofer and a 50mm tweeter. However, after a short period, the station slowly drifted off, and the audio sounded like any other radio does when slightly off-tune; awful! Fortunately, this model was popular in its day, so it didn’t take me long to find a lot of information about it online. It turns out that the station drift is a known problem, and is usually down to the tuning potentiometer wearing out. The job was made slightly more difficult due to there being two different circuits (and circuit boards) employed in this model, so determining which one I had was the first hurdle. Luckily, the online ‘fan pages’ I found enabled me to quickly determine that it was an earlier board. This information also documented several other inherent ‘flaws’ with the original design, and offered fixes for these issues. Older radios are typically tuned using a variable capacitor, a so-called “tuning gang”. I have a drawer full of these sometimes-substantial components, salvaged from radios over the years, and they are a marvel of engineering. Essentially, they are just a set of rotating metal plates that intertwine. The degree they overlay determines the overall capacitance. One of the marvels of modernisation (and circuit design) was to shrink the size of these variable capacitors down to a small mostly-plastic version which siliconchip.com.au was used in the majority of ‘pocket’ transistor radios. These ‘miniature’ tuning gangs are still being manufactured, and are available from the usual suppliers. In this radio, though, varactor-diode tuning was employed. While this is usually a robust system, it relies on the integrity of the potentiometer used to tune the radio. When the carbon track inside the pot inevitably wears out, tuning becomes increasingly erratic. And to make matters worse, the value of that potentiometer is 300kW, a rather oddball figure and (for me) very difficult to source. It is also an unusual size, 16.5mm in diameter, and I couldn’t find any new versions to replace it with, regardless of electrical value. While I could squeeze a modern pot in there with modifications, it would be preferable to use a similar-sized replacement. Back when this radio was designed, there was no doubt a good supply of different potentiometer values and physical sizes; but over time, manufacturers pared down their product lines to supply only standard sizes and values. So replacing pots in older equipment is increasingly problematic. I went through my pots bins and trawled the usual supplier suspects, but nobody had a 300kW pot of any size. Needing to compromise Fortunately, one of the websites included a ‘mod’ where a 500kW pot could be used instead. However, even if I could find one to fit on the board, Australia’s electronics magazine this would have the effect of shifting stations down the scale and making tuning in the upper regions of the band very finicky. I went back to the customer and asked if this would matter; his original communication stated he tuned the radio to one station and left it there. Assured this wouldn’t be an issue, I proceeded to disassemble the unit. Like most of these jobs, it was merely a matter of removing the external knobs, taking out some standard screws, desoldering a couple of flying leads and removing the back half of the case. If only modern manufacturers would use these methods, instead of those pesky security fasteners and breakaway clips; life would be so much easier for us servicemen! Once exposed, I removed the old tuning pot by the usual methods and replaced it with a similarly-sized 500kW model sourced from an online supplier. I didn’t bother with matters like choosing a logarithmic or linear taper; I found a 500kW pot the right size, so it would have to do! After all, tuning wasn’t going to be the same after the fix anyway, and the customer would simply ‘set and forget’. I considered making the suggested mods for the first-revision board that aimed to improve performance. While they might not be pertinent to the owner, I figured that as the thing was already dissected on my workbench, I might as well do them. The antenna circuit Q can be increased by changing one resistor on the November 2020 67 board. The original is 100kW; changing it to around 50kW apparently helps, so I just soldered another 100kW resistor across the original. There is another similar mod that significantly lowers the AM noise floor. The fix is again to parallel a 100kW resistor across an existing 100kW on the board, halving the resistance. The radio can apparently also benefit from a narrower ceramic filter, and as I already had a suitable replacement in my parts boxes, I removed the original 280kHz component and replaced it with a 120kHz version. Later revisions of the radio had these mods already implemented at the factory. Another mod is to improve bass response by increasing the size of certain off-board capacitors. However, as the customer already liked the sound, and the case would require modification to cram in bigger capacitors, I didn’t bother. Once reassembled, I ran the radio for three days on the bench, and it didn’t drift at all. So that was my jobs done, and thank goodness for resources like the internet and decent documentation. Perhaps I should also thank the electronic spirits inside these devices, lest I incur their wrath once again! 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. way through before slowing to a crawl as the formed product exited the machine, with the motor protesting, and finally the variable speed drive shutting down to protect itself. The machine was supposed to roll a 96mm top hat from up to 1.2mm steel, yet plainly did not have the torque to run smaller gauge. The motor was rated at 5.5kW; we replaced it with an 11kW unit with a chunky gearbox, along with a very much larger VSD. Suddenly, these machines didn’t look so cheap. We fired it up again and found the current drain was precisely the rated current of the new motor, which was sort of good but it needed to roll thicker steel, so it would probably need more torque. Furthermore, the section emerging from the machine was quite warm to the touch, which indicated it was being rolled up too abruptly as the machine was too short, and the roller stations were too close together. This was resulting in the product being forced into shape instead of being guided. So, hoping for the best, we loaded the thicker material and off it went for a few metres, until the drive chain shattered. An examination revealed that the strain was so great the links had stretched until one gave up. A good quality chain was fitted and tried again; the motor was protesting, and disturbing noises were coming from the front roller set, but the piece was emerging from the machine. After the machine had measured and cut off the section, one of the workers picked it up and promptly dropped it with a yelp, saying something along the lines of “it was rather hot’. He was right! It was dangerously hot, with zinc flaking off the steel, so a tremendous amount of friction was being generated in the last roller set. Checking the gap between the roller pairs that sandwich the steel, we measured 0.8mm but it should have been 1.5mm, to allow for the full range of steel used. So the machine had become a roller mill trying to compress the steel thinner. Goodness knows how the bearings coped! The rollers now needed to be turned down slightly in a lathe, as there was no gap adjustment. This is not an easy thing as they usually are extremely hard steel. Fortunately(?) the manufacturer hadn’t bothered with that Australia’s electronics magazine siliconchip.com.au Fixing substandard industrial machinery G. S. of Montrose, Tasmania, has sent in the following saga both as a servicing story and also to remind our readers that if the price seems too good to be true, it probably is. That includes industrial equipment! In previous submissions to Serviceman’s Log, I reported on work I do for a long-term client that manufactures steel building products. He has made a habit of purchasing old, worn-out machines, and as he is blessed by having a very skilled fitter in his employ, we have been largely successful in bringing them back to life. Recently, he strayed from this policy and elected to purchase two new “top hat” roll formers from a manufacturer in Asia. He paid around 30% of what locally built machines cost, which should have rung alarm bells, but he saw it as a great deal. Roll formers are essentially a long heavy steel frame with ‘stations’ spaced along its length that are fitted with rollers. They are progressively shaped to slowly form the required product profile from a steel strip. There are generally top and bottom rollers that sandwich the material between them and either the top or bottom row are driven by heavy chains and sprockets, in turn, driven by an electric or hydraulic motor. There are plenty of examples of such machines on YouTube if you are interested. I received a call saying the machines had shown up, but the electrician refused to connect them, stating they were substandard and wasn’t risking his license to do so. As I was eyeing retirement, we were trying to get a new electrician up to speed, and he was on a steep learning curve. His background was commercial, so he had a bit of a hard road ahead learning to be an industrial electrician. I went to the factory and found two nicely painted machines, which looked very short for the task at about eight metres (more about this later). Looking them over, I discovered all the problems we get with a lot of Asian machines: no Earthing on the motors, green Active conductors, no emergency stop system, no guards, no motor overload protection on the hydraulic pump and so on. So refusing to connect them as they stood was valid. I got the electrician onto replacing the switchgear and rewiring it while I sorted out the safety circuitry. This required the installation of a safety relay and the addition of three emergency stop buttons, low voltage control circuity and circuit breakers. Meanwhile, the fitter fabricated guards for the roller stations and guillotine, finally resulting in something you could use with a reasonable chance of survival. So all should be well, but of course, it wasn’t. We loaded a strip of 1mm steel and set it going. It got most of the Servicing Stories Wanted 68 Silicon Chip and had made them from mild steel, so it was easy to run them down to the proper size. Just to be sure, we added an oil feed so that lubricant was sprayed on the strip. This resulted in a motor current about 20% less than the rating, so finally, all was well. Well, almost; the bearings also needed replacing, as they just weren’t up to the job. So several thousand dollars later, we got to a machine that would do what it was supposed to do, without the operator risking life and limb. The final cost was perilously close to what a locally-built machine would have cost (which presumably would have worked off the bat). The second machine purchased has an even deeper profile, and the feeling is we will need to change its sprockets to slow it down and get enough torque to do the job. We haven’t started on that one yet, as the client still needs to get over the shock of the first unit. There are some very good Asian machines on the market, but it is an expensive process to discover which ones they are, so caveat emptor! The water-logged electric toothbrush G. C. of Nelson Bay, NSW, was getting ready to use his electric toothbrush when, as he lifted it off the charger, it started all by itself. Unfortunately, the toothbrush then decided to switch off after 30 seconds and then wouldn’t start again, so he decided to see if it was repairable... My toothbrush cost less than $30, so it was uneconomical to repair on a commercial basis, but that’s irrelevant in this case as it was my own toothbrush and it’s never useful to charge yourself. Upon inspection, it appeared that the inner bottom (charging) end was removable, so I used the tiny knife from my Swiss Army Card to pry this bottom base part out of the handle (this blade is great for opening iPhone screens too). When the bottom popped out, unfortunately, so did some gungy looking water, so the reason for the toothbrush malfunctioning was obvious. I kept going and eventually found that the complete motor, battery and charger electronics assembly could be pushed out by pressing (very) firmly on the brush end. I always found it a challenge the first time I have to open something, as I have to figure out how siliconchip.com.au hard each part can be pushed before it either opens or breaks. The PCB has a wireless charging coil at the bottom end, diodes to rectify it and quite a few SMD components, presumably to make the regulated charger for the NiMH 2.4V/500mAH battery. The 8-pin SMD IC has to be a microcontroller of some sort as it would have to control the charging, monitor the tiny pushbutton and control the transistor that switches the DC motor on and off. The final part is, of course, the little DC motor that moves the brush. Everything was slipped into, clipped or soldered to a cunningly designed moulded plastic part which holds it all in place. The electronics was wet and had some slight corrosion; toothpaste and water is not a recommended environment for electronics, so I unsoldered the PCB and followed my usual routine for wet electronics. I got out my trusty Jaycar ultrasonic cleaner, waited 90 seconds and voilà – no more visible contamination. After a quick rinse in clean water, out came the hot air gun until everything was dry. I decided to set up a simple test jig before trusting the NiMH battery. I just soldered wires to the + and - battery pads on the PCB and reconnected the motor leads, then set the voltage to 2.4V with a low current limit on my bench supply. Switching it on, nothing happened and the motor stayed off when the tiny pushbutton was depressed, but at least no smoke escaped. After years of experience, I’ve found that mechanical parts fail much more often than solid-state parts, so next, I checked the miniature switch. Press- Australia’s electronics magazine ing it produced quite inconsistent resistance readings, varying between 1W and 10W. I’ve found this frequently happens with these little switches, especially when they have been wet, so the switch had to go. I had ordered 100 of these switches when I had to repair several car remote controls (all love jobs too, and all had been wet) and I still had a great many of them left, so it was just a matter of out with the old switch and in with the new. I also decided, as the solder joints didn’t look quite ‘right’ to me, to apply flux and redo every solder joint, which only took a few minutes for this little PCB. This time, when I applied power, the toothbrush worked correctly, with the motor turning on and off as usual. It was then just a matter of resoldering the connections to the PCB. I did make two changes – I replaced the very thin motor wires with some stripped out of Cat6 cable, and also added some 1mm Teflon insulation to one lead of the charging coil where it came very close to other components. I even remembered to finally check that the wireless charging light turned on when the toothbrush was very close to the charger base station. All that remained was to reassemble it, but as I wasn’t impressed with the original sealing method, I made new seals at the motor end and to the bottom base part with neutral-cure silicone sealant. Over many years I’ve found that silicone seals 100%, but can usually be removed, even if requiring a bit more force than the original sealing method. At least it will never leak and kill the insides again, so it shouldn’t need to be disassembled again! SC November 2020 69 Vintage Radio 1940 1940 RCA RCA BP-10 BP-10 Personal Personal Radio Radio By Ian Batty The incredible shrinking portable radio: RCA’s next-generation all-B7G set, the BP-10. I bought this radio some time ago for reasons that I can’t quite recall. But after picking it out and doing a bit of research, I was glad that I had. The RCA BP-10 is pretty much the first outing for the all-glass, B7G “miniature” valve lineup that, with its B9A cousins, was to dominate valve production until transistors took over. While Compactron tubes by GE and subminiature designs further refined valve technology, the only true innovations that came later were metal-ceramic Nuvistors by RCA, and all-ceramic VHF/UHF types. RCA, established in 1919, had become a major market force by 1935. Their successful development and release of metal valves that year confirmed RCA as a serious research and development player. Successful, reliable and robust as they were, metal valves were similar in size to their conventional precursors. The fact that pin 1 was reserved for earthing the metal case prohibited the development of twin triodes and other multi-unit types. It’s strange to think that an “octal” valve should actually be a 7-pin device with a factorysupplied shield. Metal valves had mounted the element assembly onto pins in a glass base disc with some support from a metal base rim, pointing to the possibility of all-glass construction. All-glass construction was pioneered in the specialised Acorn series, designed for the VHF range. Their small size (just 18mm in diameter) and use of peripheral connections allowed the 954 pentode’s application “for wavelengths as short as 0.7 meters” – that’s around 430MHz. 70 Silicon Chip Ongoing development yielded triodes capable of oscillating past 1GHz. But the connection ring’s size, plus the limited number of possible connections, restricted Acorns to applications where no other design could be used. B7G valves Consumer-applicable construction materialised in the B7G series, first released in mid-November 1939. A full description of the lineup appears in RCA’s Radio Review of April 1940. B7G construction economised and improved valve construction, reliability and performance, equalling and bettering their mainstream octal predecessors. First, the element structure was designed to fit inside a T5½ (11/16th of an inch; around 17.5mm, with a maximum diameter of ~19mm) light bulb, which is just a little wider than an Acorn valve (eg, 955 acorn triode, 14mm envelope diameter). Designers were able, for example, to reproduce the gain of the octal 1N5 pentode in the B7G 1T4, and improve slightly on the 1A7’s conversion gain with the 1R5. Using an all-welded construction, where the valve assembly was welded directly on to the base pins, unreliable solder joints were eliminated, as was the octal valve’s infamous loosening of the envelope’s attachment to the base. Curiously, there seemed to be some confusion over the exhaust tip. Although I’ve never seen an example, provision was made for a base exhaust Australia’s electronics magazine that would have protruded down between the pins. Some advice exists that the central shield on the B7G base should never be filled with solder, as this would have prevented the insertion of base-exhausted B7Gs. The electrical path from any B7G electrode, via its base pin to the equipment’s circuit, is very short. This meant that B7G and their larger B9A cousins would operate at up to 860MHz in UHF TV tuners. Indeed, three early B7G releases were simply re-packaged Acorns. So we have improved reliability, compact size, and improved highfrequency operation. Need a batterypowered transmitter delivering over a watt at 100MHz? Look up the data for the 3B4. The BP-10 It’s curious that one of RCA’s competitors, Sonora, just beat RCA to market given that the four B7G valves were all invented by RCA. It appears that RCA had supplied samples to other manufacturers, realising that industrywide uptake would be a real commercial advantage. The BP-10’s first date of issue was early March 1940. For one of the most thorough descriptions of any set I’ve come across, see TinkerTom’s excelsiliconchip.com.au The RCA BP-10 is shown above slightly smaller than actual size (230mm wide, 1.9kg), and was one of the first commercial radios to use B7G-type valves. The set’s power is controlled via the opening of its flip-top lid. This version is one of the later models which have an arm (upper left) to limit the angle of the lid. lent writing on Blogspot (http://bp-10. blogspot.com). The BP-10 was a runaway success, with some 210,000 produced between 1940 and 1942. Production ceased with the United States’ entry into WWII. It has been variously described as a “music box” (open the lid, and it plays), the first truly Art Deco radio, and a “camera construction” radio. The latter tag would capitalise on the ubiquity, usefulness and total portability of film cameras of the day. Part of RCA’s delay in the BP-10’s release was caused by the creation of a substantial marketing campaign. The BP-10 was seen in movies, photographed with movie stars of the day, mentioned by famous columnist and broadcaster Walter Winchell and advertised in pride of place by major department stores. And you could “personalise” your set. A spares list contains a set of engraved metal letters that buyers could attach to their prized possessions: mine belonged to “OM” – one wonders whether the family might one day read this article. The review set’s tuning capacitor code of 91742 hints at a construction date of September 17th, 1942. It uses valves with date code RE6 (NovemberDecember 1940) and the decorative RCA Victor brand. It’s a conventional valve set, using sockets mounted onto a pressed-andpunched steel chassis. Most wiring is point-to-point. B7G valves, at under 25% of the volume of even the most compact octals, would challenge designers to apply miniaturisation techniques elsewhere. The largest single components, the A and B batteries, were targeted. The 1.5V filament supply could come from a single 950 (“D” size) cell. B7G valves work just fine with high tensions of 60V+, so the logical choice was 67.5V – one-half of the old 135V HT battery. RCA’s original instructions quote some 3~5 hours of life for the LT cell against some 25~40 hours for the HT battery. Purchasers were advised of the discrepancy, and warned to always try replacing the LT cell before replacing the HT battery. Battery life is certainly a compromise compared to STC’s octalequipped 418, which had a battery life ten times longer (or more). The most unusual result of shrinking this set is the loudspeaker: it is oval-shaped with a permanent magnet that seems to be cut in half! The vacated space allows relaxed mounting for the two audio valves, although RCA service notes describe possible problems with the speaker’s magnetic field upsetting the output valve’s internal electron flow. Hmmm... Since you’d only glance at the internals when changing batteries, most might not notice the quality of construction. It’s good, and even though the RF/IF section is built within a metal trough, most components can be accessed for testing or replacement. Left: To showcase the small size of the B7G-type valves, here are how pentagrid converters changed over time. From left to right: 2A7, 6SA7, 1R5 (B7G) and 1E8. Right: the ‘strange’ 3-inch, 3W loudspeaker, which looks to use a permanent magnet that has been cut in half. siliconchip.com.au Australia’s electronics magazine November 2020 71 V4 Output V3 1st Audio 2nd IF V2 1st IF 1st IF V1 Converter Antenna Gang Oscillator Gang 1.5V “A” Battery 67.5 “B” Battery Oscillator Coil The rear view of the BP-10 chassis showcasing the miniature B7G-type valves. A bit of a ‘spy radio’ Louis Muelstee, in his superb four-volume series “Wireless For the Warrior”, features the BP-10 in his supplement to Volume 4. Muelstee states: “BP-10 receivers were issued to the French Resistance pending the mass production of MCR-1 ‘biscuit tin’ receiver. In 1943, 150 units were delivered in France during a clandestine landing (operation ‘Orion’), to Commander Paul Riviere alias ‘Marquis’. A BP-10 receiver which belonged to him can be seen in the ‘Museum of the Order of the Liberation’ in Paris.” Circuit description Four-valve portable designs were well refined by the late 1930s, and the BP-10 yields few surprises. The signal from the loop antenna connects directly to the 1R5 converter’s signal grid, and the loop is tuned by one half of the gang. AGC is applied in series with the loop’s winding. The converter’s local oscillator (LO) uses the screen grids (internally-connected grids 2 and 4) as the oscillator anode. This differs from other designs that ‘collect’ the two screens and the main anode to function as the anode in the oscillator circuit. Padder V1 1st IFT V2 The tuning gang, unusually, uses non-symmetrical sections and a padder. The antenna section’s range is 10~325pF while the oscillator section is only 10~225pF. Such asymmetry would usually eliminate the need for a padder, but the BP-10’s oscillator section obviously had too high a maximum capacitance, as 270pF capacitor C4 was added in series with the oscillator gang. The 1R5 screens connect, via oscillator coil L3’s primary, to the screen of the 1T4 IF amplifier for supply. Since the IF amplifier is part of the AGC circuit, I’d expect the 1T4’s screen current to fall on strong signals, allowing its screen voltage to rise. This would also allow the 1R5’s screens to rise, thus increasing the supply voltage to the LO section – usually a recipe for frequency instability. That aside, the LO circuit is what you’d expect: an untuned primary with a tuned secondary and a high-value oscillator grid resistor. The RCA circuit lists oscillator grid voltages at both ends of the tuning range, but don’t be surprised if you’re unable to get the correct measurements. It’s common for such low-power circuits to stop working when a test probe is placed on the grid due to meter loading. The 1R5 converter’s anode feeds the signal to the first IF transformer, which has a tuned, untapped primary and 2nd IFT V3 Volume Control Antenna Gang Oscillator Gang The underside view of the BP-10 chassis. 72 Silicon Chip V4 Australia’s electronics magazine siliconchip.com.au secondary. Its output signal feeds the 1T4 IF amplifier. As noted above, this shares its screen supply with the LO circuit, provided via 15kW resistor R2 and bypassed by 20nF capacitor C10. The IF amplifier also receives AGC, supplied in series with the first IF primary. The AGC line is bypassed to ground for RF and IF by 50nF capacitor C7. Amplified IF is applied, via the second IF transformer, to the diode within the demodulator/audio preamp 1S5 valve. It’s a sharp-cutoff pentode with a diode designed for this application, offering an audio gain up to 66 times. Demodulated audio, filtered by 100pF capacitor C13, passes via 47kW resistor R5 to the 1MW volume control potentiometer, R6. Audio from R6’s wiper goes via 1nF coupling capacitor C14 to the control grid of the 1S5. This stage gets contact potential bias via high-value 10MW grid resistor R4. This allows the grid to drift weakly negative due to the space charge “cloud” of electrons surrounding the valve’s heated filament (see June 2020, p39 for details). The signal’s DC component is fed back, as AGC, via 3.3MW resistor R3 to the IF and converter stages. The 1S5 uses high-value screen and anode resistors: 4.7MW (R8) for the screen and 1MW (R7) for the anode, with the screen bypassed for audio by 50nF capacitor C15. R7 and R8 only permit low electrode currents (reducing the valve’s mutual conductance), but the potential loss of gain is made up by their high resistance values. Expect a gain of some 35+ times. The output from the 1S5 goes, via 1nF capacitor C19, to the signal grid of the 1S4 output pentode. This original valve, with its 100mA filament drain, could not economically be put in series with the other three valves to allow 6V operation, as their filaments only demanded 50mA. The 1S4 was quickly superseded by the near-identical 3S4 that possessed a tapped filament. This could be powered from 1.4V, drawing 100mA, or 2.8V, drawing the more common value of 50mA. The 1S4/3S4 amplifier requires a -7V bias for Class-A operation. This is supplied by 820W resistor R9, in series with the battery’s negative terminal to ground, so passing the set’s entire HT current. It’s a simple solution, but it does “steal” some 7V from the HT. The output valve’s 3.3MW grid resistor, R10, connects from the grid to the negative terminal of the HT battery, supplying the required -7V bias. Cleaning it up The front cover was in excellent condition inside and out, and the set was mercifully free from battery corrosion. The case, though, had lost much of its leatherette covering and the rear cover was corroded. After a clean-up and application of new vinyl, it looks a treat. Only three valves, all original RCA-branded, remained. Regrettably, two (the 1T4 IF amplifier and the 1S5 demodulator/audio preamplifier) tested low on gain, and so needed replacement. Electrically, the set offered several challenges. The LT battery current draw ranged anywhere from about 100mA to 200mA. This turned out to be due to corroded or dirty valve sockets; an application of spray cleaner fixed this. The HT current measured above 15mA. Leaky audio coupling capacitor C19 was putting a positive voltage on the 1S4 grid. Having replaced it, I expected the set to come good. siliconchip.com.au Australia’s electronics magazine November 2020 73 But no; the 1S5 screen voltage was low, and removing the valve only let it rise a bit, so screen bypass capacitor C15 was also leaky. Having replaced that too, I tested the set’s audio stage. I found the gain was low from the top of the volume control pot, but normal at the 1S5 grid. C14 was pretty much open-circuit. Replacing it resulted in screeching oscillation! So I decided (in a move I possibly should have made earlier) to replace all the 70+ year-old paper capacitors, along with 10µF electrolytic capacitor C17. I could now get some reception, but the tuning capacitor was hopelessly scratchy. The plates looked to be aligned OK. Luckily, a spray of contact cleaner on the ball bearings and the pressure/grounding spring at the other end restored it to correct operation. How good is it? The first of anything can be a bit ho-hum. Maybe it’s the problem of any first, but I found the BP-10 to be workable without being remarkable. For 50mW output, it needs around 1.5mV/m at 600kHz and 1mV/m at 1400kHz for signal-to-noise ratios exceeding 20dB. Its RF bandwidth is around ±3kHz at -3dB; at -60dB, it’s ±26kHz. The frequency response from the antenna to the speaker is 120~2700Hz. Trying to get maximum possible output resulted in a virtual square wave at only 70mW. At the more usual 50mW, total harmonic distortion (THD) was around 14%, and 5% at 10mW. The output is low compared to manufacturer’s figures, which have the 1S4 giving 180mW with around 60V HT. However, everything tested OK, and the set is loud enough for its intended use. It does benefit from correct loop orientation; the ability to reorientate it is useful for picking out distant stations while nulling strong city transmitters. And that converter screen changing with the AGC voltage, potentially compromising frequency stability? It shifts by less than 500Hz from no signal to a strong signal. Hats off to the designers on that point. Notes The original RCA circuit shows 67V at the 1S4 screen. Given the loss of some 7V across back-bias resistor R9, and the fact that the converter and IF amp anodes both show 60V means that 60V is the correct figure for the 1S4 screen when measured to chassis. The 67V readings would be taken to battery negative, but the notes do not make this clear. The RCA circuit usefully shows voltage gains for each stage. Be aware that the RF/IF gains are for modulated RF/IF signals and the audio gains are for audio. The “loss” shown for the second IF is at the intermediate frequency, and does not account for the additional loss in demodulating a 30%-modulated test signal. Consult the measurements in my circuit diagram for more details. Is it worth buying? Like all “firsts”, it’s well worth having. With some 200,000+ made, you’ll still find good examples online, some with original leather cases. Thank you to Graham Parslow of the HRSA for the loan of his STC 418 for the size comparison. Further reading ● For a thoroughly engaging and comprehensive description, visit http://bp-10.blogspot.com ● For Louis Muelstee’s description, see: siliconchip.com.au/link/ab3j and think about his entire “Wireless For The Warrior” series, my top reference for British and other military radios. ● RCA’s description of B7G technology: siliconchip.com.au/link/ab3k ● Techies, see: siliconchip.com.au/ SC link/ab3l The STC Melody 418 (left), at nearly 75cm tall, shown next to the RCA BP-10. 74 Silicon Chip Australia’s electronics magazine siliconchip.com.au Build It Yourself Electronics Centres® End Of Year Super Savers Power your camping fridge without risk of draining your battery! 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Western Australia Build It Yourself Electronics Centres Sale Ends November 30th 2020 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2020. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. B 0092 Find a local reseller at: altronics.com.au/storelocations/dealers/ New 8-pin PIC microcontrollers by Tim Blythman Like many microcontroller manufacturers, Microchip frequently releases new devices. It’s easy to continue using the same micros you always have, but if you do, you’ll miss out. The newer micros are often cheaper than the ones they replace and also run faster, have more memory and more features! Here’s a report on the latest low-cost, 8-pin, 8-bit micros from Microchip. W e have been using the lowcost, 8-bit PIC12F675 microcontroller for more than ten years now. It was first mentioned in the Product Showcase section of our July 2003 issue. It then went on to feature in four Circuit Notebook entries (August 2006 and September, October & December 2008) before finally appearing in a project: the 433MHz UHF Remote Switch in the January 2009 issue (www.siliconchip.com. au/Article/1284). In early 2018, we noticed that prices on the PIC12F675 were starting to creep up, so much so that the PIC12F617 was actually cheaper, despite having twice as much flash memory, twice the RAM, twice the internal oscillator speed plus two hardware PWM (pulse width modulation) channels. It is also more power-efficient. So we started using this chip from the June 2018 Temperature Switch project (www.siliconchip.com.au/ Article/11101) onwards. We do still use the PIC12F675 occasionally; for example, we used it in last year’s Tiny LED Xmas Tree (www. siliconchip.com.au/Article/12086). However. . . Just recently, it has become clear that the PIC12F675 is moving towards mature status. Microchip’s resellers are no longer offering any discounts for purchasing larger quantities. In fact, the Microchip Technology web page for the PIC12F675 (www. microchip.com/wwwproduct/en/ PIC12F675) states that a newer alternative is available, although Microsiliconchip.com.au chip assures us that the 12F675 will never be discontinued, like any of their parts. We therefore decided to investigate the other 8-pin Microchip parts, to see whether any offered benefits over the PIC12F617. New PICs There are several newer 8-bit PIC models shown on Microchip’s part selector, and all of them are superior to the 12F675, both in features and price. This can be found at www.microchip. com/ParamChartSearch/chart.aspx? branchID=1005 We’ve also produced a summary of the most important parameters, shown in Table 1. Currently, the cheapest 8-pin PIC is the PIC12F1571, followed by its bigger sibling, the PIC12F1572. The main difference between these two parts is that the PIC12F1571 has 1kwords of flash memory and 128 bytes of RAM while the PIC12F1572 has 2kwords of flash memory and 256 bytes of RAM. Australia’s electronics magazine We’re using the units of kilo-words here because these parts use a 14-bit instruction word, so this count corresponds to the number of flash memory instructions that each can store. Note that when storing data in flash, unless you do something fancy, it is common to store one byte per word, wasting the other six bits. When storing text, it is often possible to pack two 7-bit characters into each flash word, but it requires extra processing to extract this data. So while a 2kword part has 3.5kbytes of flash, that doesn’t necessarily translate into 3.5kbytes of data storage. Peripherals The only other difference between those two parts is that the PIC12F1572 features the EUSART (enhanced universal synchronous/asynchronous receiver/transmitter) peripheral. Other features on the PIC12F1572 not seen on the PIC12F675 include a 5-bit DAC, which can be internally connected to other analog peripherals like the ADC or comparator. The PIC12F1572 also has six timer peripherals compared with the older parts’ two. It can produce three PWM waveforms without software intervention. The PIC12F675 does have 128 bytes of EEPROM which the newer part lacks, although the PIC12F1572 does have the ability to write to its own flash memory, of which 128 bytes is designated as high-endurance (same for the 1571 and 1612). These 128 bytes of flash are intended to be used in the same fashion November 2020 83 PIC 12F675 12F617 12F1571 12F1572 Released 2003 2010 2013 2013 Cost (1xDIP) $1.66 $1.33 $0.94 $1.01 Flash words 1k 2k 1k 2k RAM 64b 128b 128b 256b EEPROM 128b None None None Max int. oscillator 4MHz 8MHz 32MHz 32MHz PWM channels 0 2 3 3 Timers 2 3 6 6 DAC No No 5-bit 5-bit Supply range 2.0-5.5V 2.0-5.5V # # Standby current 1nA 50nA 20nA 20nA µA/MHz 100 65 30 30 #1.8-3.6V (LF variants) or 2.3-5.5V (F variants) 12F1612 2014 $1.28 2k 256b None 32MHz 2 5 8-bit # 50nA 32 Table 1 – 8-pin PIC comparison as EEPROM, so combined with the generally larger amount of flash memory available, it is not a significant downgrade. May 2019 issue at siliconchip.com. au/Article/11628) can be used to program these parts. Other parts Like many new 8-bit PICs, the PIC12F1572 has a 32MHz internal oscillator which can be set in software to run from 31kHz to 32MHz in powers of two. So instructions can be processed at up to 8MHz, or eight times faster than the PIC12F675 and four times faster than the PIC12F617. Many newer PICs (including parts like the PIC16F1455 which forms the Microbridge interface on Micromite BackPack PCBs) also feature a larger instruction set compared to the earlier parts. The new instruction set includes opcodes which allow access to larger memories and suit indirect addressing modes. Indeed, there is a swathe of new peripherals which can be found in varying combinations on the other 8-pin PICs. Peripheral Pin Select, a common feature on PIC32 devices, now provides the option of swapping most digital peripherals to alternative pins. This can be done while the device is running, so many of these can be changed at will. Some chips have a numerically controlled oscillator, which can be used to generate a square wave with a 50% duty cycle and precise frequency. A voltage reference (FVR) peripheral also provides several reference voltages; typically 1.024V, 2.048V and 4.096V. Depending on the device capabilities, these may be directed internally to the ADC, DAC or comparator peripherals. Of course, it is the varying combinations of these peripherals which provide the great diversity in part numbers. These peripherals also have the benefit of doing in hardware what might have previously been done in software, freeing up processor resources for other functions. Another hardware change is that low-voltage programming (also seen on PIC32 devices) is also common. This means that the VPP high voltage (typically 9-13V) is not needed. So economical programmers such as the Snap (see our review in the 84 Silicon Chip Processor speed use more power. Quite the opposite; they generally use less energy at the same speed compared to the older chips. There are even more low-power modes which can be used to reduce power consumption by shutting down parts of the micro which are not currently used (including the processor, in “sleep” mode). Many parts also have ‘LF’ variants which offer even lower power consumption and low-voltage operation, at the cost of a reduced maximum operating voltage. The key factor here is the removal of an internal voltage regulator which powers the core. For example, the PIC12F1572 can operate from 2.3V to 5.5V, while the PIC12LF1572 works in the lower 1.8V to 3.6V range. The so-called ‘enhanced’ parts can be identified by the part number, usually of the form ‘PIC1XF1XXX’, although five-digit part numbers are also used. More information can be found in the migration guide http:// ww1.microchip.com/downloads/en/ DeviceDoc/41375A.pdf Pin compatibility Fortunately, the newer 8-pin parts are generally pin-compatible with the older parts. In particular, the power and programming pins (including MCLR) are all in the same locations. The older parts use the “GP” designation for their (single) GPIO port, but the newer parts designate these as belonging to the “RA” port. Some of the eight-pin parts even have 14-pin and 20-pin siblings which are also pin-compatible on the ‘top’ eight pins. This makes it easier to move from smaller to larger parts, or make code work on a range of parts. For example, the eight-pin PIC12F1612 belongs to a large family which includes the 14-pin PIC16F1615 and the 20-pin PIC16F1619, with broadly similar features within the family. These parts all boast an 8-bit DAC. Migration Some of the new instructions are designed to allow C language features to be compiled more efficiently and effectively, meaning less need for writing code in assembly language. Although these processors can run faster, that doesn’t necessarily mean that they will Australia’s electronics magazine As an example, we got hold of some PIC12F1572 chips and used them instead of PIC12F675 chips on some of our Christmas decoration prototypes, to see if it would be possible to ‘migrate’ our design to the newer PICs. The software for the decorations is very simple. The pins are driven directly as GPIO (general purpose input/ siliconchip.com.au output) pins. The only peripheral that gets any real use is the watchdog timer, which is used to wake the processor up after it sleeps to conserve power. Note that the PIC12F1572 has a slightly narrower supply voltage range, working from 2.3V to 5.5V, compared to the PIC12F675 working from 2.0V to 5.5V. But since lithium cells usually don’t drop below 2.3V until they are pretty much exhausted, this won’t have much effect on cell life. For both the GPIO and watchdog timer, we had to make code changes. For the GPIO ports, this was simply a matter of changing the names which we used to refer to the I/O ports. We ‘cheated’ by adding three #define directives at the top of the source file to create aliases, allowing us to continue using the older register names: #define ANSEL ANSELA #define TRISIO TRISA #define GPIO LATA The watchdog timer has changed because it now has more features, and those extra features didn’t fit within the same set of control registers. An instruction to allocate a prescaler from the T0 peripheral to the watchdog timer is no longer needed as the watchdog timer now has its own prescaler. The register which sets the prescaler value has also changed. Thus, the command which sets the different prescaler values to get different watchdog timeouts had to change as well. This is necessary to achieve the specific LED flash rate and intervals. Interestingly, because the watchdog timeout intervals are not continuous, we could not get precisely the same 18ms/72ms periods as we had with the PIC12F675. The closest equivalents for the PIC12F1572 are 16ms/64ms, meaning that decorations with the newer PIC flash slightly faster. The chip configuration directives are different. We only had to make two changes from the defaults. The first one was to disable brown-out resetting, as this allows the decorations to continue flashing even when the cell voltage gets quite low. Since it is hardly a critical device, glitchy operation at low voltages is better than shutting down prematurely. We also enable the internal oscillator as the main clock source, instead of an external crystal. By default, the PIC12F1572 starts up at 500kHz. We could change this, but since it spends so much time in sleep mode and does very little actual processing, that doesn’t make any real difference. Conclusion Progress marches on, and older devices are slowly being replaced by newer designs. For the most part, the extra features make it a worthwhile change, with better resources, peripherals and processor speeds. It pays to keep track of newer parts being released by manufacturers, so you can migrate your code to them before the old parts are prohibitively expensive or hard-to-get. The 12F1572 isn’t even the newest 8-pin PIC; Microchip has recently released the PIC16F15213. To future proof ourselves, we’re going to distribute our new Ornament kits with programmed PIC12F1572 microcontrollers instead of the PIC12F675. Except for the slightly faster flashing rate, constructors won’t notice any differences. The construction process SC is the same. Build the world’s most popular D-I-Y computer! 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SILICON CHIP Subscribers: Subscriber’s price just $126 plus $10 p&p $AVE Order now (or more information) at www.siliconchip.com.au/shop/20/5508 siliconchip.com.au Australia’s electronics magazine November 2020 85 THE MATROX ALT-512 testing the world's second(?) graphics card Last month, Dr Hugo Holden described how the groundbreaking ALT256 worked. Now it’s time for him to look at Matrox’s next product, with twice as much memory and some new capabilities. S ince the ALT-256 was one of the world’s first computer graphics cards, the ALT-512 might have been the second. However, around that time in the 1970s, other companies such as Vector Graphics were producing S-100 graphics cards too. The ALT-512 was unique at the time in that it had enough video RAM on the one board to have two planes, both 256 x 240 pixels, and the two planes can be viewed simultaneously, with the A plane having twice the intensity of the B plane. This allowed for an image with four shades of grey. Repairing and testing the ALT-512 The card I bought on eBay appeared to be unused, but it was dead. The video sync circuitry was not operating. Investigation showed that the video sync generator circuits were being reset before the second counter in the chain, IC A2, had reached its terminal count. A 74LS00 quad dual-input NAND gate in the gating circuits around the counter had failed in a very unusual 86 Silicon Chip manner (I have not seen a 74 series IC with this fault before). Even though one of the gate’s inputs was low, the output of the gate (with a normal output swing) was responding to the other input. In other words, it was as though the input pin which was held low externally, leading to the logic circuitry inside the gate, had gone open-circuit inside the IC and assumed a logic high state. Once this IC was replaced, the card sprang to life. I then set about creating a display. I found that a checkerboard pattern was straightforward to plot in BASIC, but very slow to load, taking 15 minutes or more. The ALT-512 has two video planes and a total of eight display modes. These modes select which plane is plotted or viewed and how the two planes are displayed, singly or mixed together. With different weighting on planes A & B, four shades of grey are possible (see Fig.5). I wrote an 8080 assembly language program (GRPH3.COM) to plot any size of checkerboard to either video plane. As assembly language code runs much faster than BASIC, this takes just a few seconds to plot the checkerboard. I was then able to select, via the keyboard, the various output modes to combine the images. I found that this made all sorts of interesting patterns possible, depending on the relative size of the checkerboards on each plane. Screens 5 & 6 show two of the checkerboard pat- Fig.5: by mixing the signals from the two video planes with differing intensities, it is possible to generate a display with four shades of grey, as shown here. Australia’s electronics magazine siliconchip.com.au Screens 5 & 6: two of the generated checkerboard patterns. All of these screens are displayed on an amber monitor. Screen 7: here is an example pattern formed when combining the two video layers. Screens 8-10: like Screen 7 above, these are some of the different patterns that can be generated by combining both video layers. You can output the four shades of ‘grey’ above as shown in Fig.5. terns I generated, photographed on an Amber VDU (video display unit, ie, monitor). Screens 7-10 show some of the patterns it’s possible to generate by combining two such patterns in various display modes. Four shades of grey are available in two of the modes, because plane A has twice the weighting (video amplitude) of plane B and they are logically ORed and each pixel displayed on top of the other. The four possible video amplitude levels for each visible pixel in the 256 x 240 pixel array are off (black), dark grey, light grey and white, assuming a white (P4) phosphor monochrome VDU. Displaying an image This initial result with the checkerboards got me wondering what sort of “photographic image” the ALT-512 could produce. It would require the two planes be plotted separately and displayed simultaneously. I would have to be frugal with memory, as I have just 48KB of RAM in my SOL-20 (three PT 16KRA RAM cards) and that has to run CP/M as well as my test program. For each pixel plane, one byte can hold eight consecutive pixel values, so 32 bytes per video line (256 ÷ 8) and siliconchip.com.au 240 lines tall. So in theory, 7680 bytes could hold the data to plot one plane. Therefore, the image file would use up 15,360 bytes or 15kB of memory when loaded into the SOL. That would consume the storage capacity of one of the three 16KRA memory cards in my SOL pretty much entirely. I looked around to see what a fourlevel greyscale image might look like and found one in an old video game, reproduced in Screen 11. This made me realise that a four-grey level image in a 256 x 240 pixel array could look ‘respectable’. The next question became how to create the 15kB file from a video image, in the correct format, and get it into the SOL’s memory for loading into the two planes of the ALT-512 graphics card. Screen 11: a four-level greyscale image from a video game. Australia’s electronics magazine It could come across in the usual way as a .ENT file on the serial link, or perhaps transferred to the SOL with the Xmodem protocol using PCGET. Once it was in the SOL’s RAM, I could write an 8080 assembly program to use that data array to program the ALT-512 card. I won’t detail the process here, but what I was able to do was scale down a graphics image to the required 256 x 240 pixel resolution, convert it to a four-level greyscale image, then split out the two components into two separate 7680-byte files, named APLANE and BPLANE. Once I had loaded the APLANE & BPLANE files in SOL-20 RAM at known addresses, I could then read them and load them into the ALT-512 video planes with an 8080 program. This decoded the bytes and displayed the picture. I loaded the BPLANE.BIN file to address 4000H and the APLANE.BIN file to address 5E00H. Then I wrote the final 8080 program (PLOT.COM) to write the values into the ALT-512’s RAM. The result is shown in Screens 12 & 13, using two of the possible eight video display modes (again, on an Amber VDU). The ALT-512 allows each plane to be displayed independently, or November 2020 87 Screens 12 & 13: an example image shown in two different video configurations. The lefthand image is mode three (of eight), and the righthand image is interleaved (mode seven) – the interleaved mode appears more pixelated. The mode is set via sending 0-7 (decimal) to a control port. together, with pixels directly on top of each other or interleaved. This is described in the manual. The interleaved configuration makes the individual pixels readily visible, as can be seen in Screen 13. Summary I think Matrox’s first two video cards are impressive, especially given that they were implemented with nothing more than 74-series TTL ICs and some low-capacity memory. It is easy to take modern high-resolution colour graphics for granted, as they are now everywhere: in phones, tablets, computers and on TV sets (and that’s just for starters). However, it is always worth looking back and seeing how a technology started and appreciating where it came from. Also, it is fun and a technical challenge to repair and restore vintage computers and the cards for them. It’s also challenging to write the software to make them work. Designing a light pen For a bit of fun, I designed a light pen project using the ALT-512. This gives you an idea of one of the possible uses of the ALT-512 at the time it was released. It took me quite a while to become familiar with the ALT-512, specifically the card’s registers. Unlike Matrox’s first card, the ALT-256, the 512 could extract the data from the card’s graphics RAM. That, and the fact that the ALT-512 has two video planes, come in very handy in designing a high-speed light pen system. The first step was to come up with a way to extract the image from the ALT-512’s graphics RAM and then write it to a named disk file. I had to master 8080 assembly language to do that, before I started on the light pen project, or I would not be able to store and re-display any light pen artwork that I created. There are several ways a light pen can be implemented, either mostly in software or in hardware. I decided to go down the about 80% hardware 20% software route in the interests of speed and performance. Design concept The light pen is basically a phototransistor which picks up the light of the scanning CRT beam and, based on the time that it picks up this light, it can figure out which part of the screen it is over, allowing you to ‘draw’ on the screen. But the light pen can’t pick up the CRT beam unless the pixels it’s over are illuminated. Various tricks have Screens 14 & 15: a screenshot with one separate layer dedicated to illumination (left), and that layer then turned off (right) showing just the image. 88 Silicon Chip Australia’s electronics magazine siliconchip.com.au been used to get this to work, such as strobing raster locations with bright rectangles or just increasing the CRT’s brightness. The pen itself is not complex. Several pens were made for Commodore computers which plug into their games port and use the support electronics and software there. I elected to use a dual-button pen which focuses on a pixel without the pen needing to touch the face of the CRT screen, the Inkwell 184C. I decided that since the ALT-512 can produce two simultaneously displayed graphics planes (256 x 240 pixels), I could have one plane as the “illumination plane” and the other as the plane to write to (Screen 14). Then, after the image was plotted, I could simply turn off the illumination plane (Screen 15). This way, I would not have to scan the CRT’s face with progressive illuminated pixels, slowing the proceedings, or have to alter the video monitor’s brightness or contrast controls to get the pen working. I could not find any schematics of light pen processing circuits at all, except a basic block diagram. This showed a horizontal counter, to keep track of the pixel count along one scanning line (the X-counter) and a line counter, to keep track of the scanning lines (Y-counter). The idea is that those counters are reset during the vertical refresh interval, and when the light pen detects light, those counters are stopped. Then, the X and Y counts provide address coordinates to the computer indicating the pixel under the pen, to be illuminated. Technical challenges While the principles of operation seemed simple enough, there were some interesting challenges in implementing it. Firstly, the actual video data which reaches the video monitor is not precisely synchronised with the counters in the graphics card. This is because the video card’s RAM data is clocked out of the graphics card via a shift register, so there is a 12-clock delay before it exits the card via the composite video signal. Rather than pre-loading the X coordinate counters on my circuit card with initial values to get around this (which would be possible), I decided to create a digital delay with a sepasiliconchip.com.au I decided to use a pre-built light pen with two buttons, the Inkwell 184C. The buttons are used to enable draw and erase modes, and it plugs into the interface card using its standard DB-9 plug. rate counter (74LS93 and some logic gates) instead. As well as stopping the counters when light is detected, their resets must also be inhibited. The counter outputs themselves act as the data latches to save more ICs being needed on the card. Also, with the type of synchronous counters I used (74LS161), the clock input must be high when the count is disabled. This required the signal from the light pen to be synchronised with the high phase of the clock. Once the light pen data was acquired, the data search, or re-acquisition of new light pen data, should be inhibited until the software has finished acquiring the X and Y coordinates and has loaded these to the ALT-512 and activated the specified pixel. This allowed for the fact that my software (not written yet) would have some unknown amount of delay introduced by its execution time and delays in the ALT-512. Also, after light pen activation, the process was synchronised with the vertical reset, so that any data acquisition could only occur after this time, regardless of the initially unknown software or processing delays. This was to ensure a ‘fresh start’ for the next light pen detection process. Implementing these functions required some additional gates and flip-flops. On top of this; as the light pen has two buttons, pressing one would need Australia’s electronics magazine to signal the software to switch pixels on (ie, drawing) and the other would enable the pixels to be switched off again (erasing). Interfacing the light pen circuitry to the SOL-20’s S-100 bus required port decoders for the input and output ports and circuitry to support that. In the interests of expediency, I decided to use John Monahan’s buffered S-100 prototype card upon which to build the light pen circuitry. Finally, once the hardware was decided on, there was the software driver to design. Port decoders In the circuit diagram, Fig.6, the port decoder section is based around the four large ICs at left. IC101 and IC104IC110 were designed into the prototype card. The additional 74LS04, 74LS27 and 74LS10 gates (IC100, IC102, IC103 & IC109) allowed me to create three input ports at addresses 08H (8), 09H (9) and 0AH (10) and one output port at address 08H, shown in green. Input port 0AH (10) can be used to read two flags assigned to bit 0 and bit 1 of the data bus. FLAG1 indicates the state of the light pen flip-flop which is latched when the light pen “sees” a pixel. FLAG2 is used to monitor which of the two light pen buttons is being pressed. Input port 08H reads the value of the X-position dot or pixel counter, indicating the position of the pixel on the scanning line. Similarly, input port November 2020 89 Fig.6: the light pen interface circuit. IC101-IC110 are the chips which interface with the S-100 bus (six bus drivers plus an 8-bit digital comparator), and these were already designed into Monahan’s buffered S-100 Prototype card PCB. Some of the added ICs connect to the ALT-512 via a ribbon cable and keep track of the current CRT beam X and Y pixel coordinates. When the light pen senses the light from the display, those coordinates are frozen until the computer reads the data out and resets the flag. siliconchip.com.au Australia’s electronics magazine November 2020 91 09H reads the value of the Y-counter (line counter). To allow the 74LS682 (IC110) to detect more than one port address, I disabled the detection of address lines A0 and A1 by connecting the P0-Q0 and P1-Q1 inputs together. I’m not sure if this is a standard approach or not, but it works because the input pairs ultimately are inputs to XOR gates, so it disables any response from the gate. Address bits A1 and A0 are instead decoded by the additional gates, along with the output data at pin 19 of the 74LS682, which goes low when A3 is high and A4-A7 are low. This creates possible address ports of 08H, 09H, 0AH and 0BH. On this prototype board, the address lines A0 to A7 are reversed from the P0-P7 pin labels on the 74LS682 IC. I’m not sure why it was wired this way on the PCB, but it reverses the order of the jumpers connected on Q0 to Q7 for an address comparison, so it’s a possible trap to watch out for when setting the jumpers. The 74LS10 chip (IC109) is set up so that a write to the 08H port brings its output pin 6 high. As we shall see later, when asserted during the vertical retrace interface, this resets FLAG1 so that a new light pen pixel location can be sensed during the next screen refresh. The PWR-bar signal from the S100 bus is used to ensure that FLAG1 is also reset at power-up. FLAG1 is continuously checked by a software loop to see if a light pen signal has been detected. Light pen circuitry The remainder of the circuitry is for interfacing with the ALT-512 and light pen, and this is shown on the righthand side of Fig.6. The ALT-512 has some useful signals available on a 16-pin DIL connector. I made a ribbon cable with a plug at each end to interface with the prototype light pen card. The DCLK or dot clock from the Matrox card is the master clock rate for 512-pixel mode, so this is presented to the clock input (pin 3) of 74LS74 flipflop IC118a. This generates a signal at pin 5, which gives one pulse for each of the 256 pixels per line on the monitor. Because pixels appear on the monitor 12 counts late compared to the timing of the sync pulse counters within the Matrox card, 74LS93 counter IC116 (and the gating around it) delays the start of counting by 12 pulses. So the CLK pulse to the X-coordinate counters (IC114 & IC115) starts counting 12 pulses late at the start of each scanning line. After counting to 12, IC116 stops. CLK pulses then emerge from pin 11 of IC122d. IC116 is reset before the start of each line by the horizontal reset pulse, so the process repeats for each row of pixels. IC112 and IC113 are the line counter ICs, which generate the Y-coordinate data. They are clocked by the H-sync pulse (SH) from the Matrox card and reset via the vertical reset pulse (RV). When the control software activates the light pen, it sends a low pulse to pin 4 of IC109b and if either light pen button is active, pin 3 of IC121a goes low. This is the LPEN ACTIVE signal, and it releases the set input on IC118b, thereby allowing it to accept data from the light pen on its pin 12. When the light pen ‘sees’ a pixel, its output falls low. This becomes the data signal for this flip-flop. Most of the time there is no signal, so a high level is clocked to the Q output (pin 9). But just after the rising edge of the CLK pulse, if there is a pixel detected, a low level is clocked to pin 9. This is important because, as mentioned earlier, the 74LS161 counters require that the clock pulse is high when the enable TE input changes state. A master control flip-flop was created with two 74LS00 gates, IC120c/d. When the pixel is detected, several things happen. Pin 11 of IC120d goes low and the red ACQUIRE LED lights up. The 74LS161 counters are disabled via their TE inputs and stop on their current count value, corresponding to the detected pixel. Their reset inputs (CLR) are also inhibited by the outputs of 74LS00 gates IC122a/b, so the 74LS161 counters ef- The top of the completed interface board in the top slot of my SOL-20 computer. The stickers which label the ICs and the test points were made on a Brother label machine. 92 Silicon Chip Australia’s electronics magazine siliconchip.com.au When making a prototype, it is essential to avoid an out of control “Bird’s Nest” of wires. I used lengths of solid, uninsulated wire down the middle of the ICs for power and Kynar (wire wrap wire) soldered point-to-point style for signal connections. These wires were routed to avoid covering any IC pins and bundled up to keep everything neat. fectively latch the pixel coordinates when a pixel is detected. At the same time, output pin 8 of IC120c (FLAG1) goes high. This is the signal which alerts the software that the 74LS161 counters are latched in a stable state and holding the X and Y pixel coordinate data. This signal also enables the reset signal for the latch during subsequent vertical retrace events, allowing the computer to reset FLAG1 once it has read the X and Y coordinate registers. The FLAG2 signal is defined by IC119c/d, wired as a flip-flop, at output pin 11. This flag indicates which button is being pressed on the pen, alerting the software to either illuminate or rub out a pixel. The state of this flipflop indicates the last button pressed on the light pen. This is implemented in hardware in the interests of speed. Building the interface As I mentioned earlier, I built the light pen interface on an S-100 bus prototyping card that already had provision for the bus interface ICs. You can see the resulting layout in my photos. I arranged the logic ICs on a grid in the prototyping area. I then wired it up using PTFE wire wrap wire (Kynar), except I didn’t actually wrap the wires. Each wire is individually soldered. I arranged the route of each wire so that for the most part, the wires do not cross the soldered IC pins (except locally when one IC pin connects to another on the same IC). This is important because as the number of wires increases, it becomes siliconchip.com.au difficult to get at the IC pins for soldering. I found it best to wire the power supply pins up first along with the monolithic ceramic bypass capacitors for each IC. I then checked that was all good before proceeding to the signal wiring. The power rails run down the middle of the ICs using uninsulated goldplated solid wire which I bought in Akihabara, Japan. This makes it easy to wire the usual pin 14 (or 16) and pin 7 (or 8) to the supply rail and common. Watch out for the non-standard power supply pins on the 74LS93! I used small loops of insulated wire to hold down the bundles of wire to the PCB’s surface, keeping it all tidy. For the signal runs, I used multi-coloured PTFE wire with 0.32mm diameter conductors, as this makes it easier to trace the wires. Since it was a prototype, I fitted and labelled many test points. I made these by soldering gold-plated loops to spare ‘doughnuts’, suitable for attaching a scope probe, and coloured glass stand-offs. The DB9 connector for the light pen was screwed to two 2mm metric hex posts mounted to the board with two extra 4-40 UNC threads cut through their walls. Testing and software First, I checked the port decoders and made sure everything there was working perfectly before proceeding. Although the final software was written in Intel 8080, BASIC was an invaluable tool to quickly test ports with INP and OUT instructions. I Australia’s electronics magazine also wrote a software driver in BASIC (MBASIC on my SOL), but it’s just a little too slow for my liking. Still, it is much quicker for debugging and testing than the assembly language program, at least with my programming skills. The software is simple and interactive to a degree, with some on-screen messages that appear on the SOL-20’s text video monitor. The graphics monitor/VDU is a separate video monitor for the graphics display, driven by the ALT-512 card’s video output. Upon starting the program, the A plane is illuminated (all pixels on) and a one-pixel border is created in the B plane. Both planes are initially visible. The light pen becomes active if one of its buttons is continually pushed, say the pixel-on button. If the pixel off button is pushed instead, you can rub out previously illuminated pixels. So an image can be drawn while the program is running. It’s terminated by pressing E on the keyboard. After the image is drawn, if you press M, the program escapes to “Mode Control”. This is the graphics mode that controls the display register of the ALT-512 graphics card. For example, in this mode, the “Illumination Plane” plane A can be turned off, just leaving the B plane alone, with the image that has been drawn with the light pen. Also, in the Mode condition, if the R key is pressed, it returns to the light pen loop to keep adding to the image if you wish. For those who are interested, the 8080 code can be downloaded from the Silicon Chip website. SC November 2020 93 Flexible D i g i ta l Lighting Controller Part two – Controlling it – by Tim Blythman Our new Digital Lighting Controller is a great way to control Christmas lighting displays, among many other applications. We described the fourchannel slave unit last month, which does the actual light dimming. Now we will explain a few different ways to control one or more of them. T he first article in this series described a follow-up to our hugely successful Digital Lighting Controller from 2010. There are several significant advantages to the new unit. It can control twice as many lights (64 compared to 32) as well as RGB LED strips. It also gives you more options for controlling the light show, including using an Arduino, a Micromite or a PC. The new slave unit also uses a Mosfet-based trailing edge dimming technique, making it compatible with new94 Silicon Chip er LED lamps. It receives serial data via an optoisolator, making the interface simple and safe. That means that you can control the lights directly from a computer, using not much more than a tiny USB-serial adaptor, such as the common CP2102based types. As such, we’ve designed a small adaptor board with a USB socket at one end and a Cat5 socket at the other, making this dead easy. We have also written PC software that can be used to run the Digital LightAustralia’s electronics magazine ing Controller using this Adaptor, written in the cross-platform programming language, “Processing”. We’re providing a few sample programs to demonstrate different possibilities. As well, we have designed a PCB for a Micromite-based master controller. While this is based on the Micromite V3 BackPack hardware, we are programming it in C (and not Micromite’s native BASIC) for improved performance and some extra features needed in this role. We’ll also describe an Arduinobased master unit. siliconchip.com.au Communications protocol The serial protocol we are using to communicate between the slave unit and master unit of the Digital Lighting Controller is inspired by DMX512, which uses serial data at 250,000 baud over an RS-485 differential physical layer. Our system, on the other hand, operates at 38,400 baud with a logic-level single-ended signal, making it compatible with virtually any microcontroller or computer. The 8-bit raw serial data gives 256 brightness levels for each light. At a binary level, the data is practically indistinguishable from that used in DMX512 (see https://en.wikipedia.org/wiki/ DMX512). It’s only the electrical part of the protocol that differs. One simple trick The DMX-512 protocol (and by extension, ours) relies on devices receiving a serial ‘break’ to synchronise with the master controller. This happens when the serial signal sits at a logic zero level for an entire data byte (eight bits) plus the stop bit. As the receiver does not see the stop bit, it assumes a framing error has occurred (the transmitter has not sent correctly framed data) – see Fig.9. To guarantee that a break is received correctly, most transmitters will send around 13 bit-times of zero. DMX-512 requires 23 bit-times at the zero level, followed by at least three bit-times at the one level (called a “mark after break”). Since a break is not normal data, we also need a special way of sending it. We’ll explain three different options. Hardware break Some hardware, especially devices like USB-serial converters, can send a break automatically. This requires a Fig.9: the serial break signal is necessary to synchronise data between the master and slave units. It’s not as simple to send as normal serial data, but there is generally a way to do it. special command, and the controlling software must be able to issue it. During our testing, we found that TeraTerm (a popular Windows serial terminal program) can send a break by using the Alt-B key combination. Paired with a CP2102 USB-Serial converter, we were able to successfully send commands to slave units by pressing Alt-B (to send a break), then Alt-<at> (to send a 0x00 byte) followed by the data. While handy to know about, this technique is not available on all hardware or through the software interface of the Processing programming language, so we investigated other options. Baud rate A well-known trick for sending a break on serial hardware with variable baud rates is to send carefully crafted data at a slower baud rate. An example can be seen at the bottom of Fig.9. Here, a zero byte at a slower (by half) baud rate appears to be a break condition to the receiver, which is operating at a higher baud rate. This is what we have done for the Processing program we have created. We switch from 38,400 baud to 9600 baud and transmit a 0xC0 byte. At 38,400 baud, this is equivalent to 28 bit times (one start bit and six data bits times four) at the zero level followed by 12 bit times (two data bits plus one stop bit times four) at the one level, which satisfies the DMX-512 break and makeafter-break criteria. Bit-banging The final technique (which we use in our Arduino and Micromite code) is to take control of the serial output pin and manually hold it low for an appropriate time. The isn’t an option under the Processing language, as we don’t have direct hardware control. Still, it is quite easy with many microcontrollers, where direct control of the I/O pins is possible. Our Micromite master unit uses a variant of this. Since 38,400Hz is close to many audio sample rates, we control both the audio and serial data via an interrupt which is triggered 38,400 times per second. The interrupt directly drives the output pin for the serial data, producing the break condition by counting out (Left): the Micromite Master consists of a Micromite V3 Backpack and 3.5in touch panel paired with this add-on board. (Below): a simpler option allowing Slave units to be controlled from a PC is shown below. A small PCB connects to a CP2102 USB-Serial adapter. siliconchip.com.au Australia’s electronics magazine November 2020 95 enough zero and one bits, followed with the serial data. So it is effectively a software serial solution that also incorporates the break. Master hardware Our most basic controller design is the CP2102 Adaptor PCB, which connects a low-cost CP2102 USB/Serial adaptor to a Cat5 cable. Last month, we said that you could simply use a Cat5 test cable with an Arduino Uno or similar for testing. But if you are trying to operate multiple slaves, the 6N137 fast optoisolator on the slave units requires a reasonable amount of current to work correctly – at least 5mA. The 220Ω resistor on each slave ensures that it will work even with a 3.3V signal. But under more typical conditions and with a 5V supply, the slave unit can consume up to 16mA. Many microcontrollers can only supply 20mA per pin, so you’ll probably only be able to drive two or maybe three slave units directly. Even then, the microcontroller pin will be working quite hard. Our CP2102 Adaptor includes a driver circuit capable of delivering around 200mA so that it can drive more slave units; up to 16, in fact. Conveniently, it also has an RJ45 socket, so pre-made Cat5 leads plug right in. Its circuit is shown in Fig.10. CON1 is a six-way header which corresponds to the most common type of CP2102 module. The CP2102 can either be soldered onto this board or plugged in via a header socket. This circuit is designed to work with the 3.3V versions of the CP2102 module, but should work with 5V versions too SC Ó (we haven’t tested it, though). The serial signal from the computer is fed to the base of PNP transistor Q1 via a 10kΩ resistor. When TX is high, which is the idle state, no base current flows and the second 10kΩ resistor pulls Q1’s collector low. When TX is low, Q1 conducts and Q1’s collector voltage goes to +3.3V. So the output signal is inverted. N-Channel Mosfet Q2 forms a second inverter. In the idle state, it is off as its gate is held low by the 10kΩ resistor. When TX goes low, Q2 switches on, pulling its drain low and allowing current to flow through DATA+/DATAlines from the 5V rail. The 27Ω 1W protects Q2 from a short circuit across the DATA+ and DATA- pins while still ensuring that all slave units receive enough current, even if a full complement of 16 are attached. We haven’t added any capacitors as such a device will usually be attached to a computer’s USB port, and the USB specifications say that a maximum of 10µF should be present on the bus. Since the CP2102 module already has a 10µF capacitor on board, we can’t add more. But the 10µF that is present will help to stabilise the 5V rail on our module. You could also use this converter board with other serial sources. They must be logic-level (not RS-232 or RS485), but they can use either 5V or 3.3V signalling. If using 5V signalling, pin 1 of CON1 should be connected to a source of 5V rather than 3.3V. Thus, you can use this hardware with an Arduino board to drive multiple slave units. See Fig.13 for an example of how to do this. A 3.3V Micromite can drive it too, using wiring DLC CP2102 INTERFACE Fig.10: the CP2102 interface is simple, but allows a computer to control the full complement of up to 16 slave units (controlling 64 sets of lights!). Mosfet Q2 can supply up to 200mA to drive the 16 optos in such a setup. 96 Silicon Chip Australia’s electronics magazine similar to that for the CP2102 USBSerial adaptor. CP2102 Adaptor construction Referring to the PCB overlay diagram (Fig.11), start by fitting the two 10kΩ resistors and follow with the larger 1W resistor. Place Q2 next. Check that it is the 2N7000 part and orientate it to match the silkscreen on the PCB. Crank its leads out, if necessary. Do the same for Q1 and trim the leads for both transistors. Slot the RJ45 socket (CON2) in place and ensure it is flat against the PCB. The tabs should help to hold it in place. Solder two end pins and confirm the part is still flat and square before soldering the remainder. As discussed, you may wish to solder the CP2102 Adaptor PCB directly to your CP2102 USB-Serial Adaptor. In this case, we recommend soldering a pin header for CON1, then solder the CP2102 USB-Serial Adaptor to the top of these pins. Alternatively, since most CP2102 USB-Serial adaptors are fitted (or at least supplied) with headers, you can fit the CP2102 Adaptor board with a female header socket. This is soldered to the top of the PCB (as seen in the photo), then bent over to align with the CP2102 USB-Serial adaptor header. Some heatshrink tubing applied to the whole assembly will provide protection and insulation. But leave the heatshrink off until you’ve tested it and confirmed that it works. Once the whole unit is assembled, connect its USB plug to a computer and run a CAT5 cable from the CP2102 adaptor to your first Digital Lighting Controller slave unit. The COM light on the slave unit should not light up Fig.11: the USB Adaptor board is easy to make, thanks to the prebuilt USB-Serial module. Just fit the few parts as shown here and you’re ready to connect your PC to the lighting controller slave units. siliconchip.com.au Screen1: Processing is easy to learn and is similar to the Arduino IDE. Creating your own sequence software is as simple as writing values to an array which is then automatically sent to the slaves. yet; if it does, there may be a problem with your construction. You don’t need to connect any lamps yet as the front panel LEDs will provide feedback, but you can if you want to. Testing Most up-to-date operating systems have built-in support for these devices and it will be automatically recognised on being plugged in. If this doesn’t happen, you can download drivers from siliconchip.com.au/link/ab59 If you have a terminal program like TeraTerm, you can use this to communicate with the Digital Lighting Controller slave unit. Open a connection to the correct serial port (eg, COM port on Windows) and set the baud rate to 38,400. Then send a break with Alt-B, then a 0x00 byte with Ctrl-2 (the same as Ctrl<at>, but there’s no need to press shift). Any non-zero data bytes following this should cause the CH0-CH3 LEDs to light on a connected slave (depending on what address is set). You can press the tilde key (~) as it has a relatively high ASCII value of 126. Other terminal programs may work similarly, but we haven’t tested these. PC control software We’ve written some sample programs in the Processing language to interface with the CP2102 Adaptor. We’ve used Processing for a few reasons: it’s freely available, open-source and available on Windows, Mac and Linux and there is even an Android variant. Thus it’s a siliconchip.com.au Screen2: the Digital Lighting Controller Processing sample program allows lamps to be controlled using sliders. You can use our sample code to create your own sequence and control software. great choice for making software that can be used on many computers. It is based on Java. As we have mentioned previously, the Arduino IDE is based on Processing. So if you’ve had experience with Arduino, then you should be at home with Processing. We’re using Processing version 3.5.3 on Windows 10, although we did test our programs on a Raspberry Pi running Processing 3.4 too. You can download Processing from https://processing.org/download/ Once installed, you can also export a standalone app for your platform (you will also need to have Java installed to run the standalone app). Once Processing is installed, open the sketch program in our download package (“Simple_DLC_Master”) using the File -> Open menu option. You should see the first few lines of the code, as shown in Screen1. Then run it using Ctrl-R or by pressing the green play arrow. This simple program provides basic control of up to 16 lamp channels – see Screen2. The serial port (COM port under Windows) is selected by pressing “+” or “-” and then press “s” to start a connection. The COM port name will light up green, and the COM light on the slave unit should start flickering in time with the “TX” icon on the application. If it doesn’t light up green, then the serial port may not be available or may be in use by another program. Clicking on the sliders changes the output levels and thus the brightness Australia’s electronics magazine of any connected lamps. You can press the “OFF” button to set all the lights to the off state immediately. If all this is working well, your Digital Lighting Controller System is complete and functional. You may wish to use this program as the basis for your own custom controller, but we still have a few more options to show you. Lights and sound We’ve also written a Processing program which emulates the basic features of the master unit used with the 2010 Digital Lighting Controller. So you can use the existing sequencing software to generate sequences (accompanied by music) to run on the newer Digital Lighting Controller hardware. That software is included in the download package for this project. The older software was limited (by the file format it generates) to controlling 32 channels, so this program is also. But you could use our software as the basis of a system which synchronises sound and lights for more than 32 channels with some modifications. The sketch is called “Digital_Lighting_Controller”, and it uses an external library to provide some features; in this case, the audio playback. The library can be added in the Processing IDE by clicking Sketch -> Import Library… -> Add Library… (see Screen3); Then type the word ‘minim’ in the search window; this is the name of the library. The correct library is shown in Screen4. Click this item and then click install. Open the sketch and run it. A window November 2020 97 Screen3: we are using the ‘minim’ Processing library for audio playback so that we can synchronise the light display with sound. The library system works similarly to Arduino libraries, although the interface is a bit different. should appear, as shown in Screen5. This has some control buttons at the top, the status of the first 32 output channels below, and details on the file currently being played at the bottom of the screen. We have included some demonstration sequences but could not include music due to copyright – see the text file accompanying the demo sequences for details. The original music files are still available online but need to be converted to a PCM (uncompressed) WAV format, for example, using software like Audacity (a free download). For more information on using the original Christmas Light Controller software, refer to the December 2010 issue, starting on page 66 (siliconchip. com.au/Article/391). There are seven pages in that issue explaining how the sequencing software works, so it’s well worth a read if you plan to use it. It can create two file types. Those with the LSN file extension are simply lighting sequences and will play on their own. Those with an LSQ file extension are similar but must be accompanied by a WAV file of the same name, which will be played at the same time. In our Processing software, use the “Open” button to select a file of either LSN or LSQ type. Then click the “Up” or “Down” buttons to scroll through the available serial ports to find the CP2102 Adaptor. Finally, click on the COM port name to connect to it. At this point, the COM light on the slave units should start flashing. Now click the “Play” button to start the sequence playback. The mimic lights on 98 Silicon Chip Screen4: search for ‘minim’ in the Contribution Manager screen; the correct item is highlighted here. This is the only extra software that is needed to work with our example code. the window should flash in time to those connected to the slave units, and music will play from your computer. The “Pause” and “Stop” buttons work as you would expect. Micromite master We have also put together some test software for both the Micromite and Arduino platforms. These programs are simple, but are a good start for those wishing to design their own controller, especially to control more than 32 lighting channels. If you would prefer a standalone master unit, we’ve also designed a Micromite based unit that can do the same job as the PC software described above, without tying up your computer. Like the older dsPIC-based design, it reads data from an SD card and produces a stereo audio output plus serial data to control the lamps. Now, while we say it’s based on a Micromite, due to the amount of computing power involved, it wasn’t possible to make this work in the BASIC language (ie, using MMBasic). Fortunately, it is easy to program the Micromite hardware with ‘C’ code compiled using Microchip’s MPLAB X software. You’ll need the Micromite V3 BackPack hardware to build our Micromite master. There are two reasons for this. The first is that the V3 BackPack is the only one that has the SD card socket wired back to the microcontroller. The second is that the V3 BackPack supports the larger 3.5in ILI9488 LCD module. This has 480 x 320 pixels, and we use this to display more information Australia’s electronics magazine than would be possible on the smaller 2.8in displays. For information on building the V3 BackPack, see our August 2019 issue (siliconchip.com.au/Article/11764). But construction is pretty self-explanatory, and we sell a complete kit for this module (siliconchip.com.au/ Shop/20/5082). So you shouldn’t have trouble building it even if you don’t have that magazine; there’s no need to add any of the optional components. Since the SD card uses pin 4, make sure you don’t fit a memory chip, as it would interfere with SD card operation. You will also need to make a small add-on board; its circuit is shown in Fig.12. This provides extra hardware interfaces, including the lighting slave driver. That part of the circuit is identical to the circuit of the CP2102 Adaptor shown in Fig.10. The serial output is also available at pin header CON3 for testing purposes. The board also includes a stereo audio output via a 3.5mm headphone socket. The Micromite produces the audio signals as a PWM signal on pins 5 (left) and 24 (right) of I/O header CON1. A pair of 10kΩ resistors provide a 2.5V midpoint on the 5V rail to re-bias these signals, which is bypassed by a 220µF capacitor. We’ll follow the left channel from here as the right is identical in operation. The PWM signal is low-pass filtered by a 3kΩ series resistor and 100nF capacitor to the 2.5V rail to remove the PWM signal and harmonics. It is then AC-coupled and biased to 2.5V, then fed to non-inverting input pin 3 of op amp IC1. Our prototype uses an LMsiliconchip.com.au Screen6: the PIC32PROG GUI is the simplest way to program the PIC microcontroller for this project. It can also be used to reinstate the MMBasic interpreter, in case you ever need to do that. Screen5: our demo software plays sequence files generated by the original Digital Lighting Controller software from 2010. It has lamp mimics so you can easily check that everything is working as expected. C6482AIN, but we also successfully tested the lower-voltage MCP6272. IC1 is configured for unity gain by direct feedback from output pin 1 to inverting input pin 2 through a 3kΩ resistor. Since we are using a 3.3V Micromite, the output swing is at most 3.3V and should not stray too close to SC Ó the op-amp’s 0V and 5V rails. Still, a rail-to-rail op-amp is preferred due to the low headroom. The output from the op-amp is again AC-coupled by a 1µF capacitor and biased to circuit ground by a 22kΩ resistor. A 100Ω series resistor isolates the output from the external wiring. DIGITAL LIGHTING CONTROLLER MASTER siliconchip.com.au The buffered stereo signals are fed to stereo 3.5mm socket CON4, and can be used as a line-level signal to feed to an amplifier, or for driving headphones. PIC32 software As we mentioned, BASIC is too slow to handle both the audio and control Fig.12: the Micromite master board includes the same driver circuit as the CP2102 Adaptor, plus an op-amp circuit to feed audio from the PIC32 to a 3.5mm stereo jack socket. Australia’s electronics magazine November 2020 99 data. But our solution (written in C) should still look familiar to those who use the graphical capabilities of the Micromite BackPack. At power-up, it shows a splash screen while it scans the SD card. It looks for sequence files (with LSN or LSQ file extensions) and displays a count of those found. If there is an error (for example, no card is inserted), an error code and message is shown. The “Reset” button can then be used to perform a soft reset of the microcontroller, which might clear the error. The control signal (on the RJ45 socket CON2) is sent the whole time the unit is running, so you should see the COM light of the attached slaves light up. When the scan is complete, two options are shown. The first is “Test mode”. Pressing this goes to a screen showing 16 sliders and three buttons. The “Toggle” button at left cycles between the four groups of 16 sliders, to allow the control of any of the 64 lamp outputs. Touching the slider above will adjust the brightness of that lamp. The “Tone” button toggles a 600Hz sine wave output at the audio socket CON4. The sound continues for a short while after being turned off due to buffering (the RAM buffers for audio and control data total 28kB). “Exit” returns to the main page. If all is well, the second button labelled “Continue” leads to a page with playback controls. The playback screen shows information about the currently selected sequence, including its duration and information about any associated WAV file. Fig.14: this Micromite add-on board can be attached to the main Micromite V3 BackPack via female header 220mF strips, as shown here, or you can solder pin headers to this board and sockets to the BackPack. The rest of the construction is straightforward; lay the electrolytic capacitor over and ensure its orientation is correct. Also check the orientation of IC1 and don’t mix up Q1 and Q2. Pressing “Play” starts playback of the sequence. It can be paused with the “Pause” button, which will light up when it is active. Play can also be used to resume from a pause. The “Loop” button cycles between “Loop off”, “Loop one” and “Loop all”. The “Next” and “Previous” move between sequences manually. If a track is playing, Previous returns to the start of the current track, while it moves to the previous track if playback is stopped or paused. In summary, this Micromite master code provides similar features to the original Digital Lighting Controller master, but is more intuitive to drive and has the extra test mode features. Software operation The software starts by initialising the LCD, SD card and other I/O peripherals and starts a timer interrupt. The 38,400Hz timer interrupt manages quite a few things. The main tasks are to shift out the serial data to control attached slaves, and to play back the audio data. A state machine cycles through producing a break condition, a make condition and then the 65 data bytes that are sent. At the end of each cycle (which Fig.13: this shows how to connect an Arduino board (in this case, an Uno) to lighting slaves using the CP2102 interface. You can use our example code as a starting point for your own lighting control software. 100 Silicon Chip Australia’s electronics magazine lasts around 17ms), the software also checks if the sequence data requires any of the lamp brightness values to change. Another part of the interrupt routine processes data from 56 x 512-byte audio buffers, which are effectively raw WAV data. Compensation is made for the difference between the playback rate (38,400Hz) and the audio sample rate, and whether the sample format is 8-bit or 16-bit, stereo or mono. As each buffer empties, it is marked as empty, and the next is processed. The main loop re-loads empty buffers from the SD card. This is so that the SPI peripheral is not interrupted by the interrupt routine, which would cause data corruption if it was not managed very carefully. The 28kB buffer allows audio to play for about 1/6 second at CD quality. When all the buffers empty, playback stops. The sequence data is managed similarly, although its size is not proportional to its playback length. The test tone is 600Hz because the 512-byte buffers are filled with eight 64-cycle samples of sinewave data. Using whole sinewave cycles means that the software doesn’t have to keep track of what part of the wave it is producing; it merely fills each block with the same data each time. Projects with a graphical interface always devote a lot of resources to this, and much of the code is for displaying data on the LCD. This is kept to a minimum during playback, to reduce demand on the processor when it is working hardest. Construction We’ll assume that you’ve already built the Micromite V3 BackPack and have the mounting parts for the 3.5in LCD. Note that if you order the Microsiliconchip.com.au This PCB turns a Micromite V3 Backpack into a controller capable of playing WAV audio and driving the Slave units of our Digital Lighting Controller. mite V3 BackPack kit from the SILICON CHIP ONLINE SHOP (Cat SC5082), you have the option to have the chip preprogrammed for this project. The add-on PCB is quite simple, so building it will probably take less time than the BackPack. Refer to its overlay diagram, Fig.14, during construction. Start by fitting the smaller resistors where shown. Use a multimeter to check the values if you aren’t sure about the colour bands. Follow with the larger 1W resistor near CON2. Fit the 1µF ceramic capacitors next, as they are small and have a low profile. These are not polarised, so can be fitted either way. Follow with the 100nF MKT capacitors. The single electrolytic capacitor needs to be laid on its side to fit into the PCB stack. Bend its leads, observing their polarity (longer lead = positive) and solder it to the PCB. Install the transistors next, being sure not to mix them up. The BC557 (PNP) is near the top of the PCB with the Nchannel Mosfet underneath it. Be sure to align them with their footprints; you may need to crank the leads to fit their pads. Parts list – CP2102 Adaptor module 1 PCB coded 16110204, 45 x 20.5mm 1 CP2102 USB-Serial converter [SILICON CHIP ONLINE SHOP SC3543] 1 6-way female header socket (CON1) OR 1 6-pin header (CON1) – see text 1 RJ45 PCB-mount socket (CON2) [Altronics P1448] 1 BC557 PNP transistor, TO-92 (Q1) 1 2N7000 N-Channel Mosfet, TO-92 (Q2) 2 10kW 1/4W or 1/2W resistors 1 27W 1W resistor 1 10cm length of 25mm diameter heatshrink tubing (optional; clear is ideal) IRM-02-5 module availability Since last month, many vendors have sold out of the Meanwell IRM-02-05 module. Digi-key was expecting more stock around late October but this may sell quickly too. If you can’t get the IRM-02-05, use the IRM-01-5. It is a drop-in replacement; the only difference is its 1W rating instead of 2W. The board draws less than 1W – the only reason we didn’t specify the IRM-01-5 initially is that the difference in price is very small. siliconchip.com.au The usual arrangement for the Micromite 18-way header is to fit the male header to the Micromite BackPack PCB and the female header to the PCB below this, although the reverse will work perfectly well. This might be necessary if you have previously fitted the female header to the Micromite BackPack, as we did with our Micromite RCL Box (June & July 2020; siliconchip.com.au/ Series/345). Fit the headers, ensuring both are square. You might like to temporarily secure the boards together using the 12mm tapped spacers and machine screws. We fitted the four-way header to our boards too, but it is not strictly necessary as the master unit PCB does not have a corresponding socket. Solder IC1 in place, observing the pin 1 notch orientation. We used a socket so we could try different op amps, but you will get more reliable results by soldering this chip directly to the PCB. Finally, add CON2 and CON4. CON3 (the serial data header) is entirely optional. Push each connector down firmly onto the PCB. In particular, the RJ45 socket does not have much clearance above it, so it must be flat against the PCB. Solder one pin in place and check Parts list – Micromite master module 1 Micromite V3 BackPack with 3.5in LCD (kit Cat SC5082, programmed with 1611020B.HEX) 1 USB Type-A to Mini-B cable 1 double-sided PCB coded 16110201, 86 x 55mm 1 UB3 Jiffy box [Jaycar HB6013, Altronics H0203] 2 M3 x 12mm tapped spacers 2 M3 x 25mm machine screws 1 18-pin header (CON1) 1 18-way female header socket (CON1) 1 RJ45 PCB-mount socket (CON2) [Altronics P1448] 1 2-pin header (CON3; optional) 1 PCB-mount stereo 3.5mm socket (CON4) [Altronics P0094] Semiconductors 1 LMC6482AIN or MCP6272 dual rail-to-rail op-amp, DIP-8 (IC1) 1 BC557 PNP transistor, TO-92 (Q1) 1 2N7000 N-channel Mosfet, TO-92 (Q2) Capacitors 1 220µF 16V electrolytic 4 1µF ceramic 3 100nF MKT Resistors (all ¼W 1% metal film, except where noted) 4 22kW 4 10kW 4 3kW 2 100W 1 27W 1W 5% Australia’s electronics magazine November 2020 101 each connector is still flat before soldering the remaining pins. Plug the PCB into the back of the Micromite BackPack for testing and programming. Most modern operating systems will already have drivers for the Microbridge USB interface, but if not, instructions can be found in the original Micromite BackPack article. Programming the PIC Unless you have purchased a preprogrammed microcontroller or kit, the PIC32 on the BackPack needs to be programmed with a HEX file. Since we are not using BASIC, we can’t use the regular MMBasic upload method, but you can use the onboard Microbridge IC over USB, which is the simplest method. Alternatively, if you have a PIC programmer such as a PICkit 3, PICkit 4 or Snap, you can program the chip using that. We fitted a right-angled header to the ICSP header on the BackPack so that it wouldn’t foul the boards above or below. But it did protrude far enough to hit the enclosure. We simply shortened our pins slightly (by about 1mm) with a pair of sidecutters to solve that. Microbridge programming We previously described how to use the Microbridge to program a HEX file to the PIC32 on the Micromite BackPack using the command line. But there is also a Windows GUI program available called “P32P GUI” (see Screen6). It can be downloaded from the Back Shed Forum at www.thebackshed.com/docregister/ ViewDoc.asp?DocID=21 Extract the program from the ZIP file and run it. Select the HEX file (16110201.HEX, available from our website) using the “select file” button, then press the pushbutton on the Micromite BackPack PCB; the LED on the BackPack should light up, indicating that it is ready to be programmed. Then push the “flash PIC32” button to start the process. Once complete, the LCD should show the main screen. also connect speakers or headphones to the 3.5mm socket. Check that you get a test tone and that the slave responds to commands. There is also some debugging data output at 38,400 baud on the USB-serial adaptor (Microbridge), which you can view using a serial terminal program such as TeraTerm. You can copy the sample LSQ files from our software bundle to an SD card; even without WAV files, you will be able to initiate playback of the lamp sequences. Use the Digital Lighting Sequencer software (originally written for the 2010 Lighting Controller) to generate custom sequences. PICkit programming Finishing the master unit While the PICkit 3 and PICkit 4 (but not Snap) can supply power when programming the chip, it is best to power it from the USB socket if the LCD is attached, as its backlight requires substantial current. In the Microchip IPE, select “PIC32MX170F256B” as the part, click “Apply”, then “Connect”. Browse for the HEX file, then click “Program”. The LCD should light up with the splash screen. To complete the board stack, remove the two spacers closest to the main (14-way) LCD header. Thread 25mm machine screws through the acrylic front panel, washers and LCD PCB, and secure with the existing 12mm spacers. The Micromite BackPack PCB is then secured with two more 12mm spacers on the 25mm screws and the existing machine screws at the other end. Finally, secure the new master unit PCB onto the new spacers using short machine screws. Operation With no SD card inserted, only the “Test” screen will be operational. Connect an RJ45 cable to a slave unit and Case cutting Fig.15 shows the holes required in Fig.15: holes must be cut in the Jiffy box for the SD card, USB socket, audio output socket and RJ45 slave connector. Download and print this diagram for use as a template. To make rectangular cutouts, drill a series of small holes just inside the perimeter, then use a file or side cutters to knock out the centre section, and flat or triangular files to smooth the edges. 102 Silicon Chip Australia’s electronics magazine siliconchip.com.au The PCB mounts below the Micromite PCB and sits to one side, allowing its RJ45 socket and headphone jack to protrude from the case. the master unit Jiffy box. Note that the BackPack PCB sits reversed compared to our other projects, so that the SD card slot is at the top. Thus, the RJ45 and 3.5mm sockets are at the left, and the USB socket is at the right. Check this carefully before you begin cutting. It can be fiddly to get the board into the case. Try putting the left-hand side of the acrylic front panel in place, then pivot the right-hand end down to get the sockets into their corresponding holes. If they are snug, you might need to enlarge the holes slightly. Then you just need to attach the acrylic panel into the UB3 Jiffy box with the supplied screws to complete assembly (or slightly longer self-tappers, if you find they’re a bit short). Any USB power supply should be capable of powering the unit. Conclusion The many options that we’ve presented here demonstrate just how flexible the new Digital Lighting Controller can be. We think many people will want to take advantage of being able to control mains-powered lamps through such a simple interface and incorporate our design into existing lighting displays along with addressable LED strips, especially when using an Arduino. We’ll have more information about combining our mains slave units with LED strips in a short follow-up article next month, which will cover both Arduino and Micromite-based approaches. In the meantime, we expect that many people will use our slave units with their own custom controllers. We look forward to seeing what you can create, using the new Flexible Digital Lighting Controller as a starting point! SC Some people are justIMPOSSI BLE to buy Christmas gifts for! You know how hard it is: you want to give a Christmas Gift that will really be appreciated . . . but what to give this Christmas? Problem solved! Give them the Christmas Gift that KEEPS ON GIVING – month after month after month: a SILICON CHIP gift subscription For the technical person in your life, from beginner and student through to the advanced hobbyist, technician, engineer and even PhD, they will really appreciate getting their own copy of SILICON CHIP every month in the mail. They’re happy because they don’t have to queue at the newsagent each month. You’re happy because it actually costs less to subscribe than buying it each month CHOOSE FROM 6, 12 OR 24 month subscriptions Start whenever you like (Jan-Dec is very popular!) And we even pay for the postage! Don’t forget to let us know wh o the gift sub is for! Ordering your gift subscription is easy! eMAIL (24/7) To MAIL PAYPAL (24/7) PHONE (9-4, Mon-Fri) ONLINE (24/7) Place OR OR OR OR Log onto silicon<at>siliconchip.com.au Use PayPal to pay All order details – including Your Call (02) 9939 3295 with your order with order & credit card details silicon<at>siliconchip.com.au (including credit card details) – credit card details & contact no Order: http://siliconchip.com.au/giftsub and follow the prompts! include your contact info! Don’t forget to include all details! and tell us who the gift is for! to PO Box 139, Collaroy NSW 2097 CHRISTMAS IS ONLY 7 WEEKS AWAY! siliconchip.com.au Australia’s electronics magazine November 2020 103 Wearable ESP32 and the Sparkle Stitch Kit Electronic “wearables” have been around for a while, but we haven’t gotten into them until now. Not only can these particular electronic products be attached to clothing (or even made part of it!), but they can also connect to WiFi networks. So you could even design clothing that lights up and adapts to your location, or is controlled by your smartphone! W earable electronics is a growing field, mainly due to the popularity of the Arduino system, which was one of the early adopters of wearable electronics. People whose main interest is clothes and accessories might not have a strong electronics background. As Arduino is aimed at ‘creative’ people rather than ‘technical’ people, it’s a good match. One of the earlier variants of Arduino wearables was dubbed the Lilypad. The distinguishing feature of many of these boards is a round shape and several large pads around the edges for making connections (hence the name Lilypad). In fact, in addition to the items we’re reviewing in this article, Jaycar also stocks the Duinotech Lilypad Plus (Cat XC3920). This is a variant on the original Lilypad design that uses the ATmega32u4 microcontroller (making it like the Leonardo). The large pads allow wires to be easily attached via alligator clips or even by tying conductive thread through the holes. A complement of small add-on boards in the vein of Arduino modules is also available. Review by Tim Blythman & Nicholas Vinen 104 Silicon Chip Australia’s electronics magazine siliconchip.com.au The Duinotech Wearable ESP32 Development Board from Jaycar (XC3810) is a compact but powerful processor ideal for creating wearable electronics. We recently had the opportunity to try out Jaycar’s new Duinotech Wearable ESP32 Development Board (Cat XC3810). It’s a disc-shaped PCB 56mm across with eight large Lilypad-style pads as well as two rows of nine standard 2.54mm header pads. The eight larger pads break out connections to the battery positive, USB positive, 3.3V rail and ground as well as GPIOs 12, 14, 27 and 33. A modest number of components cover the thin (0.6mm) board. The largest part is the ESP32-WROOM-32 module, which contains a 4MB flash memory IC as well as the microcontroller and WiFi chipset. A CH340G USB-Serial converter IC provides a serial programming and debugging interface via a micro-USB socket, while a low-dropout (LDO) AP2114 regulator in a SOT-223 package provides a 3.3V rail. This is necessary as the ESP32 is a 3.3V microcontroller. There’s also a battery connector; an LDO regulator is needed for running from a Li-ion battery which can discharge close to 3.3V. A battery charging IC, an MCP73811T-420 in an SOT-23-5 SMD package complete the line-up. One LED near the ESP32 module’s antenna is connected to GPIO pin number 13. The module is 7mm thick due to the battery connector; if that were removed, it would be about half as thick. The battery connector is a locking type, but will also accept a standard 0.1-inch pitch female header. This board is very suitable for portable and wearable applications. Battery operation is seamless, with the option of charging during operation, while the micro-USB socket makes connection simple. The ESP32 microcontroller is from Espressif Systems and is a cousin of the ESP8266 microcontroller that we have used in various forms. Both of these can be easily programmed in the Arduino IDE through board add-ons via the Boards Manager. As well as offering WiFi, the ESP32 microcontroller can also communicate via Bluetooth. Software Most people will program the Duinotech Wearable ESP32 Development Board with the Arduino IDE. We used version 1.8.5 for our tests, but we suspect versions as old as 1.6.4 should work. Enable the ESP32 add-on by adding https://dl.espressif. com/dl/package_esp32_index.json to the Additional Boards Manager URL (in Preferences), then install the “ESP32 by Espressif Systems” option via the Tools -> Board -> Boards Manager menu. We used the latest version at the time, version 1.0.4. When installation is complete, there should be many new board options available. We couldn’t see a close match for the Duinotech Wearable ESP32 Development Board, but it appears many ESP32-based boards use the ESP32siliconchip.com.au The ESP32 Boards add-on for the Arduino IDE adds a multitude of options. We used the “DOIT ESP32 DEVKIT” board profile with the Duinotech Wearable ESP32 Development Board. WROOM-32 module; we chose the “DOIT ESP32 DEVKIT” and were able to get the onboard LED flashing. WiFi and Bluetooth Using the example sketch “SerialToSerialBT”, we were able to quickly and easily set up a virtual serial communication link to a mobile phone. This is an easy way to send commands wirelessly; it’s certainly easier than trying to toggle switches on a board that may be sewn into a garment. WiFi works as expected, with code similar to that for the ESP8266. The “WiFiScan” sketch was able to quickly give a listing of nearby WiFi access points. Accessories While there’s an incredible number of things that can be done with a bare wireless-capable board, many people will want to connect something to illuminate their wearable. With 17 GPIO pins available, there’s no shortage of potential for connecting peripherals. But the availability of addressable RGB LEDs means that even a single GPIO pin can control practically any number of LEDs. Jaycar also stocks many accessories to fill this gap. There is the WW4100 conductive thread, which can be easily connected to the development board by tying it into the large Lilypad-style pads. Flexible insulated silicone wire is also available (see Cat WH3034 and WH3036). These can all be sewn into the fabric, making it a part of the wearable. There are also a number of a directly-controllable LED “raft pads” in various colours as well as addressable RGB LED raft pads. These come in packs of five or ten. Jaycar also stocks the Sparkle Stitch Kit (shown opposite), Australia’s electronics magazine Stainless steel conductive wire (2m, Cat WW4100) can be used to easily make connections by simply tying it into connecting pads. November 2020 105 This mask is one of the many projects that can be built using the Sparkle Stitch Kit. A selection of LED “raft pads” from Jaycar. These are available in various combinations and various colour LEDs. which includes fabric, thread, electronic parts and sewing accessories. It is a great wearables starter kit, but it lacks a controller, and the Duinotech Wearable ESP32 Development Board would be an ideal choice to complement it. Sparkle Stitch Jaycar sent us a kit to evaluate. The kit contains: • 25 LED raft pads in various colours • two wearable cell holders with matching lithium cells • a wearable slide switch • conductive thread • one pair of red/black alligator clip jumper leads • elasticised thread (aka elastic band) • coloured lightweight felt cloth • Dacron filler • a hot glue gun and glue sticks • a multimeter with test leads • ten assorted needles, a threading aid, fusible tape and a plastic thimble • a thread cutter • a 62-page instruction booklet • a storage case The idea with this kit is that it contains everything you need to create wearable electronics (eg, clothes with LEDs that light up) even if you have no tools and relatively little knowledge of electronics. It would be ideal for teenagers of either gender, although we suspect that it will appeal more to girls. Having said that, which kid doesn’t want a light-up superhero costume? The instruction book is impressively comprehensive, covering not just how to wire the components together but also a great deal of information on sewing and basic electronics. A bright child (or young adult) with decent reading comprehension and the ability to follow instructions should have no trouble getting the electronics working based on the information within. One of the reasons that it is easy to follow is that it contains many clear illustrations and photos showing exactly what you need to do to achieve the desired result. The main ‘project’ in the book is a wearable LED mask (see above), and several different templates are included to produce differently shaped masks. Different colours of felt are also provided, so you can customise the shape and colours, and also the LED patterns. It also shows you how you can stick paste gems, stickers or other doodads on the mask to jazz it up. Our sample kit included large felt rectangles in tennis ball yellow, regular yellow, dark blue and red. As well as the conductive thread, it also has cotton thread in black, white, red, green, blue and yellow. The supplied multimeter is naturally a very basic one, 106 Silicon Chip but more than good enough for the sort of checks that you would need to perform when putting wearables together. The hot melt glue gun is a small, nicely decorated mainspowered type. Basically, if you want to get into wearables but are not sure what you need, or have a teenager who wants to jazz up their clothes, combining the Sparkle Stitch with the ESP32 Development Board would be a great starting point. You could then add some more accessories like extra raft pads to expand your possibilities. We think the Cat KM1040 RGB addressable raft pads would be an excellent ‘add-on’ to the Sparkle Stitch kit, for those who want to do something a bit fancier, and they don’t cost too much. Advanced users As mentioned earlier, the ESP32 Development Board also has standard header pads (and includes matching pins). There are enough pins on these to connect many peripherals. We envisage that some people will create their own ‘shields’ to stack onto the Board and give it extra features. This would be the perfect place to mount an LCD or OLED screen, or to connect an amplifier or sound module to add audio effects to a wearable project. We demonstrated Arduino code for the 3.5in LCD modules in our May 2019 issue (siliconchip.com.au/ Article/11629) and also for our D1 Mini LCD Backpack project in October this year (siliconchip.com.au/ Article/14599). That code should work with this Board although we haven’t tested it. Verdict The Duinotech Wearable ESP32 Development Board has a powerful processor, WiFi and Bluetooth. It will make an excellent basis for both simple and advanced wearable projects. The provision of battery interface circuitry also lends it well to all manner of portable projects, and not just wearables. It is available now from Jaycar stores (these are Australian prices; check the Jaycar catalog, ads or website for NZ): • Duinotech Wearable ESP32 Development Board ........................................................ (XC3810): $39.95 • Sparkle Stitch Kit .............................(KM1080): $79.00 • 2m stainless steel conductive wire .. (WW4100): $8.95 • 5 x RGB addressable raft pads ..........(KM1040): $6.95 • 10 x red LED raft pads .......................(KM1038): $6.95 • 10 x yellow LED raft pads ..................(KM1034): $6.95 • 10 x green LED raft pads ...................(KM1036): $6.95 • 5 x white LED raft pads ......................(KM1032): $4.95 SC Australia’s electronics magazine siliconchip.com.au 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 On Gerber files, FPGAs and PID coefficients I have just received my copy of the October issue in the mail to find that you plan a couple of things of particular interest to me. I like the idea of using a laser engraver to make a PCB, so I am looking forward to that article. Currently, I am looking at the Creality CP-01 from Altronics. But so far, I have not found a unit that accepts Gerber files, and thus the Gerber file has to be converted to JPEG, and then using a photo application to invert positive to negative. You have noted that you have not published many articles on FPGAs, and I think that is likely due to the difficulty in soldering these devices onto PCBs. Also, programming these devices requires some expensive tools. I would like to mention a possible improvement to the thermocouple wiring on DIY Solder Reflow Oven Controller (April-May 2020; siliconchip. com.au/Series/343). As you say, thermocouples are not that accurate, but it depends on the class. For class 1 it is ±0.5°C, and for classes 2 and 3, it is ±1°C. My suggestion is to obtain a type-K plug and panel-mount socket and use a short length of T/C cable cut off the thermocouple to go between the socket and T/C module. This eliminates the multiple cold junction points, which will not be at the same temperature due to the layout of the components. It also makes it just a bit more professional. Be aware that there may be a lacquer coating on the wire which needs to be cleaned off, and that the fibreglass insulation may make your hands itch. One thing on this unit is that the PID coefficients don’t seem to match what I know of standard PID settings, as the D value is so high. Is there a units change? Lastly, I’d like to comment on the Serviceman’s Log by Dave Thompson. I am glad he managed to fix his analog meter. It is lucky because the jewels in meters are usually spring-loaded and siliconchip.com.au so all that happened was one jewel was pushed down, enabling the other pivot to pop out. Simple to fix. What he could have had was one of the hairsprings having been bent so the coils touch each other, causing calibration problems or worse, a bent pointer. Both are fixable with great patience and care, but I won’t go into details on that. Please ask him if he has experience with taut band suspension meters such as the spot galvo. I’m not sure if the AVO was that or had standard pivot and jewels. (W. D. K., Bayswater, Vic) • You are right that you probably have to convert Gerber files to an image format for use with the laser engraver software. We cover all the steps in that article, which is planned for the December issue. Many FPGAs are available on development boards these days, removing soldering from the equation (many also come in quad flat packs which are not all that hard to solder with some practice). Software is becoming less of a problem too; many types now have free software available. We have covered these aspects in a couple of articles to date, and no doubt will have more to say in future. As for the thermocouple interface for the Solder Reflow Oven, we agree that adding proper thermocouple adapters is definitely nicer. But the cheaper and easier method described in those articles is adequate for the soldering task. There are substantial temperature differences around the oven, and a degree or two here and there in measurement is less than this variation. As for the PID parameters, the units used are not conventional; they are references to counts of the interrupt service routine (ISR). The PID loop parameters were tuned using an empirical approach. They are a compromise that gives good-but-not-ideal performance in the reflow oven application. Phil initially identified an appropriate value for P, which in a steady state gave reasonable behaviour. With I and Australia’s electronics magazine D at zero, there is a latency in settling that runs to many minutes. So he increased the I value to reduce the settling time. While this did not result in temperature oscillations, overshoot was observable, so the I value has been chosen to achieve a reasonable settling time with manageable overshoot. The D value was finally tweaked to reduce the overshoot. On considering your question, it might be that a reduction in I and a reduction in D would be better. Some lights do not meet electrical standards I have an oyster light fitting that can be clipped to a ceiling fan or be mounted as a ceiling light. There is no Earth connection at all to the metal base, and I am wondering whether this legal. I have been a subscriber of you magazine for years and are still enjoying it. (M. W., Murray Bridge, SA) • Such luminaires are not legal as the metal enclosure is not Earthed and there is no Earthing of the fitting if it has a metal connection for the lamp, such as a bayonet or Edison screw. According to the AS/NZ3000 wiring rules, “A protective earthing conductor, connected to a terminal or suitably insulated and enclosed, shall be provided at every lighting point. The exposed conductive parts of luminaires shall be earthed.” (section 5.4.3 Lighting points). Capacitors – more than meets the eye Have you published an article on capacitors? It seems there is more to these devices than meets the eye, and I am curious about why certain types are chosen for a specific application. This was initially triggered by the observation of the use of ceramics and green caps, then the rise and fall of tantalum caps. However, a couple of recent incidents have rekindled and broadened my curiosity. Recently, the circulation pump on November 2020 107 our solar hot water service became intermittent. The motor run capacitor was only a fraction of its rated capacitance when measured with a multimeter. Being out of town, I looked for a temporary replacement from my parts at hand. An old power supply had a couple of X2 capacitor rated at 250V and when connected in series, gave a little more than the required 0.8µF with the benefit of a theoretically increased voltage rating. This combination was bigger than the original but just fitted in the motor, and brought back reliable operation for three weeks until a proper motor run capacitor could be obtained. So what is the difference between the X2 caps and the motor run cap? The web page at siliconchip.com.au/ link/ab5k gave me confidence that X2s are suitable for mains use, while siliconchip.com.au/link/ab5l has a broader background which raises more questions. For example, how does one tell a polyester film and a polypropylene capacitor apart, given that they look similar? Finally, my son and I are trying to build an indicator light for the electric fence. We had the idea that a neon lamp in parallel with a capacitor that was charged via an 8kV, 500mA diode (UX-C2B) salvaged from a microwave power supply and a 51kW resistor might work as a “relaxation oscillator”. Testing it, it flashes every 3-4 electric fence pulses, and it does not load the fence energiser. However, I am now curious about the best capacitor to use. The trial used a 1µF polyester (or is it polypropylene?) rated at 250V from the same microwave switchmode power supply that donated the diode. (D. G., Koyuga, Vic) • Capacitors are indeed a topic with more depth than most people realise. Unfortunately, we haven’t published an in-depth article on capacitors, with the possible exception of our August 2002 article on tantalum capacitors (siliconchip.com.au/Article/6744). Your problem is prevalent – many motor failures are actually motor capacitor failures. These capacitors must have quite high capacitance and voltage ratings, especially motor start capacitors. Hence, start capacitors are usually some type of electrolytic, and they don’t tolerate long-term hightemperature operation well. According to Wikipedia (https://w. wiki/fJj), motor run capacitors are gen108 Silicon Chip erally polypropylene types as they must handle current continuously. Many X2 capacitors are also polypropylene, so provided they have a sufficient ripple current rating, they should be suitable. Some X2 capacitors are polyester, and those should be OK too, again as long as they can handle the current. There is no apparent difference in the appearance; you have to look up the part code to see if it is polyester or polypropylene. X2 capacitors are definitely suitable for mains use. The X part of the designation indicates that they are suitable for being connected between mains phases (eg, Active and Neutral). Y-class capacitors are suitable for connection between Active and Earth (they are required to fail opencircuit rather than short-circuit for safety) but can also safely be used between phases. X/Y-class capacitors can lose capacitance if abused (eg, exposed to high voltage spikes or passing more current than they are designed for). X/Y-class capacitors which are designed to handle significant currents, at least in the short-term, are sometimes referred to as “pulse” capacitors. We pulled up a data sheet for a randomly selected 2.2µF 275VAC X2 capacitor (Kemet R46KN422000P0M) to check its ratings. It is rated to handle just 250mA continuously at 50Hz, so it would only really be useful for a motor of about 60W. They make a 10µF version which is rated for more than 1A at 50Hz. So it appears that the main difference between a motor run capacitor and an X2 capacitor is that X2 capacitors are not designed to handle significant currents at mains frequencies, while motor run capacitors are. X2-class capacitors probably also have slightly different construction to meet their safety requirements. For your electric fence indicator, you want a low-leakage capacitor so ceramic, polyester or polypropylene should all be fine as long as they have a sufficiently high voltage rating. Presumably, that is limited by the neon as it will conduct at around 80V. For a proper discussion on capacitors, we would have to explain the many different ceramic dielectrics (NP0/C0G, X5R, X7R, Y5V etc), along with the many different plastic films used (polyester, polystyrene, PET, Australia’s electronics magazine polypropylene), varying plastic film construction methods, mica capacitors, electrolytic capacitors (aluminium, organic, solid, tantalum etc) and much more! Help fixing an Iamm Multimedia Player Years ago, I purchased an “Iamm HD Multimedia Player Cinema & Opera Juke Box” (model NTD36HD). This unit has never operated correctly. I tried to get it running after purchase, then put it aside and forgot about it. I found it again recently and thought what a waste it could not be used. I wondered if any of your staff or readers could be of any assistance, as I have had no success finding anything useful on the web. The hard drive is accessible via the USB socket and a computer. But when the unit is hooked up to a TV and audio system and powered up, it shows its start-up screen and plays its startup ‘music’, then very briefly goes to the screen displaying choices (movies, photos and music). The screen quickly goes blank, and the unit is effectively dead, save for the whirr of the harddrive still spinning. I have tried without success to find where I can get the ‘firmware’ to reload it. Does anyone out there have any experience with these multimedia players? (D. R., Goughs Bay, Vic) • We do not have any experience with that brand. Perhaps a reader can help. Linear Bench Supply voltage variations I am building the 45V 8A Linear Bench Supply from the October & November 2019 issues (siliconchip.com. au/Series/339). I have gotten to the point of the initial tests and calibrations before installing the main heatsink components, but some readings seem a bit off. The supply rails seem OK. The A5 pin of CON6 reads around 2.9V, which is under the 3-4V range suggested in the magazine, but the temperature reading when I plugged in the display matched close enough to a nearby thermometer. I did the initial calibrations so that TP5 measured exactly 15.6V and TP6 measured exactly 6V. TP1 and TP3 were both very close to 0V each. TP2 measures -115.7mV which is siliconchip.com.au below 0V as the article suggested, but TP4 is 12.1mV which is close to zero. I did have a little trouble fitting IC4 as I haven’t done any SMD soldering before, but after blasting it with hot air and clearing the bridges, I tested it in-situ and it seemed to be working. Is the 12.1mV reading anything to worry about? I have a little pocket oscilloscope which I used to test the oscillators. Pin 3 of IC3 was close to the 60kHz but about 51% duty cycle. The -5V rail was correct though. The Fan PWMs have me a bit worried. Pin 1 of IC2 measures 260Hz instead of the mentioned 280Hz, although it has an exact 50% duty cycle. However, pin 7 was showing a voltage. The displayed temperature was 30°C, so I carefully used an ice cube to drop the temperature back down to 25°C, and I still saw around 3V on pin 7. If it’s already on, does it need to drop lower than 25°C to switch off? (S. B., Banyo, Qld) • None of these readings concern us. The 12.1mV at TP4 corresponds to 16mA at the output, which is not precisely zero, but doesn’t sound excessive. It’s below the threshold of the meter readings. The PWM frequency isn’t critical; 260Hz is fine. We suspect that variation in the thermistor resistances and zener voltages mean your supply has a different temperature response. Compare the waveform on pin 5 of IC5 to the voltage on pin 6 (see the scope grabs on p28-29 in the October issue). If you see the duty cycle on pin 7 increase as the temperature increases, it is working correctly. You could try replacing the thermistor with a potentiometer (say 20kW, or at least above 10kW) and try sweeping it up and down to check the response. Using a Micromite as an audio scope Do you have software or do you intend to write a program for the Micromite Backpack to be an X-Y vector scope? I need to display the Lissajous pattern of a stereo audio signal without tying up my CRO. (P. S., Mount Pleasant, SA) • Peter Mather has posted a twochannel timebase scope CFUNCTION on the Back Shed Forum at www. thebackshed.com/forum/ViewTopic. php?TID=8077 siliconchip.com.au It has a ~1MHz sample rate. He has also posted the source code. A quick glance through it suggests that the code which draws the pixels as X/T and Y/T could be combined to draw X/Y. How RMS power is determined Thank you for your wonderful magazine, which I have been purchasing and reading since 1987. Concerning the Ultra-LD Mk4 amplifier project (August-October 2015; siliconchip.com.au/Series/289), the rated power is listed at 135W RMS into 8W with ±57V DC supply rails. The term RMS is generally used to refer to voltage or current and not power. Power (in the audio industry) is simply the product of RMS volts and RMS amps where the signal is a sinusoidal wave. With supply voltages of ±57V DC, my calculations show that the maximum RMS voltage is 40.3V RMS (57 ÷ √2). Hence the power would be 203W RMS (V2 ÷ R) into a resistive load of 8W. Even with a Vce(sat) max of 3V for the output transistors used, it is difficult for me to see how the 135V RMS is derived. Are you able to shed alight as to why the power rating is 135V RMS for this superb amplifier? (J. D. S., Endeavour Hills, Vic) • You are right that the term “RMS power” is confusing, but it is common. As described in Wikipedia at the following link, “RMS power” is the power measured or calculated with a continuous sinusoidal signal (ie, it’s calculated based on the RMS sinewave voltage): siliconchip.com. au/link/ab4o We measure it by increasing the signal level until the point where distortion starts to rise, then measuring the continuous power delivered at that setting. Your calculation ignores several important factors such as the fact that the output voltage cannot swing railto-rail (due to several factors, including the driver and output transistor base-emitter voltages). Plus the supply voltage will not remain at ±57V DC at full load, and there will be significant ripple on the supply rails, which will lead to earlier clipping. There are also losses in the output transistors (as you point out), losses Australia’s electronics magazine in the output filter, losses in the wiring and tracks etc. In short, you have to measure the real-world power delivery (or a very accurate simulation). The music power is stated as being somewhat higher than 135W as this is a short-term measurement and so the supply voltage will not sag as badly. You could probably get 150W RMS from this amplifier module, or perhaps a little bit more, with a larger transformer and larger supply filter capacitors which would both help to reduce supply voltage sag and ripple under load. How much do precision voltage references drift? On many occasions, I have appreciated the value of the Simplified 10V Precision Voltage Reference by Jim Rowe (August 2014; siliconchip.com. au/Article/7976). The IC is now six years old, and my version still runs happily on its original 9V batteries. My question is: how significant is the age-related degradation that has taken place? Also, what would be the best and/ or most economical method to recalibrate it if necessary? Is there a better or more accurate standard easily achievable? Thanks for the great magazine, keep up the good work. (C. O. D., Adelaide, SA) • Jim Rowe responds: It’s good to hear that you have found the Precision Voltage Reference of use. Analog Devices quote the ageing rate of the AD587 device as ±15ppm per 1000 hours, but this figure of 1000 hours probably refers to hours of operation rather than merely the passage of time. So unless you have been using your Voltage Reference continuously over the last six years, I would expect that it would still be very close to its original calibration. As my original prototype has only been used about two or three times a year in the last six years, I thought I would test it this morning with three different reference instruments. The readings I obtained were 10.001V, 9.999V and 9.9976V – with the last figure from a Yokogawa 7562 bench DMM which has itself not been recalibrated since 2010. The testing was done at 16.3°C, about 9°C cooler than the original testing temperature in 2014. This suggests that your Reference is probably still November 2020 109 quite accurate too, which is good news, since it isn’t all that easy to recalibrate. Adjusting Mosfet dead time with a scope Is there any way to set the dead time on the Class-D amplifier module (November & December 2012; siliconchip. com.au/Series/17) using an oscilloscope? (B. C., Albion, Vic) • It would be possible to use a scope to observe the Mosfets switching on and off to help guide you in setting the dead time to the optimal value. But doing so is quite tricky as the upper Mosfet in each pair is ‘floating’, so measuring their gate-source voltages would require an isolated probe, or a scope with individually isolated channels. An easier approach would be to insert a shunt in the ground connection of each pair of Mosfets and monitor the voltage across it. The dead time setting is optimal when it is set as short as possible without a large spike in current draw during the transition period, when one Mosfet switches off and the other switches on. You would need to break the track and solder in a shunt, and given that its value would need to be low, you’d need a pretty sensitive scope or amplifier. But it could be done. And this would have the distinct advantage that it would take into account the switch-on and switch-off delays of each Mosfet, which cannot be determined by merely observing their gate drive waveforms. Output from photoelectric smoke alarms Around 20 years ago, I built your Smoke Alarm Control Panel project (January & February 1997; siliconchip. com.au/Series/149). The installation has been running since then without any hiccups, bar the replacement of a couple of ICs and the power supply. I check it annually. A while back, I decided to replace the aging Kambrook smoke detectors with newer Quell detectors, namely the Q946 ionisation-type detectors. These appear to use an A5364CA CMOS IC. The replacement was a fairly straightforward exercise, and the new detectors work as intended. The problem I now have is that Quell made available a different smoke 110 Silicon Chip detector for the kitchen location, which is a photoelectric type (Q301H). I cannot figure out how to interconnect the alarm output from this device to the Control Panel. I would be grateful if you can provide me with advice and help with this issue, as I do not want to have the kitchen area unprotected. (H. B., Mt Kuring-Gai, NSW) • The alarm output from the photoelectric smoke detector (Q301H) should be available at pin 10 of the A5364CA IC. For the alarm test input, use the additional circuit of the Control Panel for Smoke Alarms comprising Q4, except using a 200kW resistor (instead of the 1MW resistor) at Q4’s collector. Connect the opposite end of the 200kW resistor directly to the “push to test” button. Stopping nuisance smoke alarms Do you know of a clever way I can turn off the smoke detector while cooking? Also, have you designed an aspect ratio converter? I need to convert VHS footage from 4x3 to 16x9 without using a computer. (J. H., via email) • We published a smoke detector kill switch in February 1996 to prevent an alarm when cooking: siliconchip.com. au/Article/5038 We have not published an aspect ratio converter. There are commercially available units such as the Miranda ARC371P; we suggest you try one of those: siliconchip.com.au/link/ab5j Building a sinewave inverter I am wondering if you have a design for a pure sinewave inverter (230V AC). (A. R., Eltham, Vic) • We published a 2kW 24V DC to 230V AC pure sinewave inverter in the October 1992 to February 1993 issues (siliconchip.com.au/Series/173). That design is outdated, but we have not updated it, since commercial versions are far cheaper now. There is no way we could design an inverter for the cost that you could buy one these days. Combining AND gates for a clock I want to build a clock with local time, UTC and sidereal time on six 7-segment displays. I would like the Australia’s electronics magazine same crystal to run all the clocks. I have found a circuit to generate the 1.002738Hz for the sidereal clock, and it also generates a 50Hz for the local time. But it requires a 1MHz crystal and a 4068B IC (8-input AND gate). I found out that the 4060B IC can do frequency division and could be capable of dividing 2MHz to 1MHz. The 4068B IC is now hard to find (Mouser has it, but the delivery cost is prohibitive). Can I use seven 2-input AND gates instead? And how can I divide the 50Hz signal down to 1Hz for the local clock? (R. M., Melville, WA) • Yes, you can make up an 8-input AND gate from seven cascaded 2-input AND gates. A 50Hz to 1Hz divider circuit is shown at siliconchip.com. au/link/ab5i It uses two 4017B ICs fed with the 50Hz signal from the secondary of a mains transformer, but you could feed in the 50Hz output from your digital divider instead. Looking for historical documents I worked at Fairchild Australia in Melbourne from 1965 to 1974 as an Applications Engineer and Manufacturing Manager. Recently, I was asked to contribute to a history of the manufacture of semiconductors in Australia. I remember Jamieson Rowe visited the Fairchild factory at Kilsyth and then wrote an article about our factory. I think Electronics Australia also published articles on other manufacturing facilities over the years. I would be very grateful if someone could point me in the direction of any such articles that I could use. Do you have a listing of all articles that I could scan? I am interested in the period from the 1950s to the 1980s. (B. O. S., Blackburn, Vic) • Jim Rowe responds: after a bit of searching back through old EA indices, I believe I have found that article to which you are referring. It was in the February 1973 issue, and titled “Fairchild now making TO-92 transistors here”. The only other articles on Australia’s short-lived semiconductor industry I came across were these: May 1972: “Local Semiconductor Breakthrough” June 1972: “Centre Industries Making GE Diodes” March 1973: “Philips’ Hendon facility in SA” SC siliconchip.com.au MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP KIT ASSEMBLY & REPAIR FOR SALE VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com GREAT VALUE PARTS and more are found in the Tronixlabs ebay store via tronixlabs.com.au – for enquiries or support please email support<at> tronixlabs.com DAVE THOMPSON (the Serviceman from S ILICON C HIP) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. 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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 Australia’s electronics magazine November 2020 111 Coming up in Silicon Chip Automotive Electronics Advertising Index Altronics...............................75-82 In this two-part series, Dr David Maddison describes the many types of electronic modules found in modern cars, trucks, vans and buses and also how they communicate with each other. You might be surprised to learn just how many electronic modules are in your car, and how advanced they are. Ampec Technologies................. 11 Dave Thompson...................... 111 Digi-Key Electronics.................... 5 Digital Lighting Controller, part three This follow-up article contains details of an alternative ‘slave’ unit which can drive up to 64 sets of addressable RGB LEDs. You can mix and match this LED slave with the mains-light controlling slave already described. We’ll also demonstrate how to attach RGB LEDs directly to an Arduino or Maximite ‘master’, allowing more than 64 lighting channels to be driven. Heart Beat Simulator Emona Instruments................. IBC Hare & Forbes..........................2-3 Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 Make a soft toy for your kid or pet to cuddle up with that has a life-like heartbeat. This small device produces a soft noise and vibration that simulates a beating heart, powered by an internal battery. Power saving techniques mean that it should last a long time. Making PCBs with a laser engraver Andrew Woodfield describes how you can use a low-cost laser engraver to transfer a PCB pattern onto a blank fibreglass/copper laminate. This avoids the need to purchase pre-sensitised PCBs or sensitising film, and once you have the procedure down, it allows for easy and relatively painless etching. Leach PCB Assembly.................. 9 LEDsales................................. 111 METCASE Enclosures.............. 63 Microchip Technology......... 7,OBC Ocean Controls........................... 8 RayMing PCB & Assembly.......... 6 SC Christmas Decorations........ 43 The Bass Block This easy-to-build subwoofer is relatively compact but will really add oomph to a small speaker system. It is based on principles described in our “Bass Barrel” project from August 1997, but using more modern drivers that you can still purchase. SC Colour Maximite 2............... 85 Note: these features are planned or are in preparation and should appear within the next few issues of Silicon Chip. The Loudspeaker Kit.com......... 66 The December 2020 issue is due on sale in newsagents by Thursday, November 26th. Expect postal delivery of subscription copies in Australia between November 24th and December 11th. Silicon Chip Subscriptions....... 52 Silicon Chip Online Shop......... 33 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 10 Notes & Errata USB SuperCodec, August-October 2020: on page 74 of the October 2020 issue, in the testing procedure, the text states that the ±9V rails should each measure between ±8.5V and ±10.5V. However, the resistor values specified for the final design could result in readings as low as ±8V (typically around ±8.2V). This is normal, and the circuit will operate as designed. Also note that the L1 and L3 part numbers given for Digi-key in the parts spreadsheet are a bit larger than the ones used in the prototype; it is better to use the parts from Altronics or Jaycar if possible (which were the ones tested). History of the Australian GPO, September 2020: on page 40, the article states that the Australian mains voltage standard was changed in 2000 to 230V AC +6%,-10%. It was in fact changed to 230V AC +10%,-6%. Shirt Pocket Oscillator, September 2020: the inductors specified for L1 are both too big to fit easily in the space available. The Murata 17156C is a good fit, with the slightly cheaper and slightly larger Murata 22R156C also being a reasonable choice. Frequency Reference Signal Distributor, April 2020: the MAX4450s are specified in the parts list as being the SOT-23-5 version (MAX4450EUK+T), but the PCB is designed for the SC-70-5 version (MAX4450EXK+T). Make sure to use the latter type. 45V 8A Linear Bench Supply, October-December 2019: in the parts list on page 74 of the November 2019 issue, the correct part code for transistors Q4-Q7 is FJA4313, not FJA4314. 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