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Project of the Month: Our very own specialists are developing fun and challenging Arduino®-compatible projects for you to build every month, with special prices exclusive to Nerd Perks Club Members. Sure, you can buy off the shelves but where's the FUN in that! IoT Smart Wireless Switch STEP-BY-STEP INSTRUCTIONS AT: jaycar.com.au/iot-wireless-switch Take your first step into DIY home automation. You will be able to view and control your appliances from the convenience of your phone or tablet over your home Wi-Fi network. Turn appliances on or off, or even modify the provided source code to create your own home Internet of Things (IoT) automation innovations. WHAT YOU NEED: WI-FI MINI ESP8266 MAIN BOARD PROTOTYPING SHIELD FOR WIFI MINI 433MHZ WIRELESS TRANSMITTER MODULE REMOTE CONTROLLED MAINS OUTLET CONTROLLER XC-3802 XC-3850 ZW-3100 MS-6148 $24.95 $4.95 $13.95 $19.95 Phone not included. VALUED AT $63.80 NERD PERKS CLUB OFFER BUNDLE DEAL $ 3995 SAVE 35% SEE OTHER PROJECTS AT: www.jaycar.com.au/arduino More Switch? Upgrade To Multiple Switches: 9 $ 95 $ SPARE OUTLET MS-6149 Suitable for MS-6148 above to control more power. 39 95 Add Portable Power: 4 $ 95 Add A Controller: $ 49 95 3 MAINS OUTLET WITH REMOTE CONTROL MS-6147 BATTERY BANK 4 X AA USB A SKT WITH SWITCH BLACK MP-3083 2 CHANNEL REMOTE CONTROL RELAY BOARD LR-8855 Upgrade the above project by using 3 mains outlet. 30m range. Remote control up to 4 outlets. Makes a superb back-up charger for any USB powered device such as an MP3 player or PDA. Slide on/off switch. Add remote control functions to a new project or existing installation. Momentary or latching mode. 40m max transmission range. 12VDC. NERD PERKS CLUB MEMBERS RECEIVE: 15% OFF 3D PRINTER FILAMENT* *Excludes 3D printer parts & accessories Catalogue Sale 24 April - 23 May, 2018 EARN A POINT FOR EVERY DOLLAR SPENT AT ANY JAYCAR COMPANY STORE* & BE REWARDED WITH A $25 JAYCOINS GIFT CARD ONCE YOU REACH 500 POINTS! Conditions apply. See website for T&Cs * REGISTER ONLINE TODAY BY VISITING: www.jaycar.com.au/nerdperks To order: phone 1800 022 888 or visit www.jaycar.com.au Contents Vol.31, No.5; May 2018 SILICON CHIP www.siliconchip.com.au Features & Reviews 14 Drone Air Taxis – Autonomous, Pilotless and Soon! Already trialling in several countries, you’ll soon be able to call up a pilotless drone taxi from your smartphone. Fares are projected to be not much more than street taxis but there will be no traffic hang-ups! – by David Maddison 24 Tiny capsule measures, radios your gut gas data Medical specialists need to know what gases are in your gut – but they are loathe to operate. Now researchers in Australia have come up with a capsule that measures gases and radios the info in real time – by Ross Tester 43 LTspice Simulation: Analysing/Optimising Audio Circuits Continuing our occasional tutorial series to help you understand the very versatile LTspice simulation software. It’s still available (free!) from new owners, Analog Devices – by Nicholas Vinen 82 El Cheapo Modules 16: 35-4400MHz frequency generator Based on the ADF4351 PLL, this <$30 module can produce a signal from 35MHz to 4.4GHz with crystal accuracy. It can even be used as a sweep generator – by Jim Rowe Constructional Projects 28 800W (+) Uninterruptible Power Supply (UPS) One of our most exciting projects ever: a build-it-yourself UPS which we believe isn’t as good as commercial models . . . it’s much better! And if you need even more grunt, this design allows it – by Duraid Madina and Tim Blythman 36 Multi-use Frequency Switch Some Drone “Taxis” are still figments of their proponents’ imagination – but some are already in testing phase – Page 14 Tiny capsules pass through the gut, reading and sending gas data as they go – Page 24 Suffer from blackouts in your office or home? You need a UPS to ensure you don’t lose valuable data. It’s also the answer to maintaining power after a disaster – Page 28 If you need something controlled when it exceeds a certain frequency – up or down – this superb circuit will do it. Anything that produces a frequency (or can have a sensor fitted) can be switched – by John Clarke 57 USB Port Protector – just in case! We thought we’d fried a laptop when something managed to drop onto the exposed USB port components. We were lucky – but made up this low cost, mini PCB to guard against “oopses” in the future! – by Nicholas Vinen 70 12V Battery Balancer 12V batteries in series need careful attention to charging if you’re expecting a long life. This little balancer does it automatically for you and you can even use them in parallel for extra power handling – by Nicholas Vinen Your Favourite Columns 63 Serviceman’s Log I reckon servicemen are cursed – by Dave Thompson 76 Circuit Notebook (1) 20V, 2.5A adjustable power supply with current limiting (2) A personal “speedometer” for joggers (3) Sunset switch to discourage possums and other night visitors! (4) Adjustable audio low-pass filter 90 Vintage Radio Zenith Royal 500 “Owl Eye” AM Radio – by Dr Hugo Holden Everything Else! 2 Editorial Viewpoint Feedback 88 Product Showcase 94 SILICON CHIP Online Shop 4 Mailbag – Your siliconchip.com.au   96    103    104    104 Ask SILICON CHIP Market Centre Advertising Index Notes and Errata Switch just about any device if its output frequency goes above or below limits which you set – Page 36. USB ports can be fried if you’re not careful (we know!!!). Be safe with this low-cost USB Port Protector – Page 57 You can’t simply charge 12V batteries in series as you would a single battery – you need a battery balancer to ensure they don’t get out of balance – Page 70 www.facebook.com/siliconchipmagazine SILICON SILIC CHIP www.siliconchip.com.au Publisher Leo Simpson, B.Bus., FAICD 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 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 Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates: $105.00 per year in Australia. For overseas rates, see our website or the subscriptions page in this issue. Editorial office: Unit 1 (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 Printing and Distribution: Derby Street, Silverwater, NSW 2148. ISSN 1030-2662 Recommended & maximum price only. 2 Silicon Chip Editorial Viewpoint Trusting our lives to computers In the January editorial, I raised concerns about the digital security of autonomous vehicles. While two fatal accidents relating to (semi-)autonomous vehicles have been in the news lately, both appear to be due to failures in the sensors or software. One resulted in Uber suspending North American autonomous vehicle testing for an indeterminate period. Consider that in the last 12 months, around 1250 people were killed in road accidents in Australia. Let’s imagine that by making every vehicle on our roads autonomous, we could halve that, to 625 deaths per year (without any negative effects). This seems like it would be a good thing. But will the general public accept software errors killing two people every day in Australia alone? Most of these people will not have done anything wrong and there may be nobody to “blame” in most of these incidents. Based on the reaction to the aforementioned deaths, I don’t think it would go down well at all. And then consider the future posed by the article on flying passenger drones in this issue. This brings us the possibility of fatal crashes involving not just drone passengers but also (from time to time) some hapless people on the ground, too. They could be minding their own business when, with no warning, a drone falls on them. Yes, flying is very safe these days but commercial aviation is heavily regulated and the aircraft are well-maintained. They still crash occasionally. And while there are a huge number of planes in the air at any given time, there would have to be many more small drones to have a significant impact on transportation. They’d have to come crashing down to earth from time to time. So the question is this: will the general public get used to the idea of computer errors or hardware failures being responsible for so many deaths? A different approach to project construction On another topic, we have the first part of a very practical major project in this issue, namely, the lithium-battery-based Uninterruptible Power Supply. This is an unusual project for us because while it’s quite a large and complex design, there’s little soldering involved. It’s mostly built from off-the-shelf building blocks that are wired together. It does have a custom control PCB, the details of which will be presented next month but even this is based on pre-built Arduino and relay driver modules. When you look at the UPS box, mostly what you see are the large batteries and the impressive sinewave inverter. The fascinating aspect of this project is that you could take essentially the same design and scale it down to a tiny backup supply for a few LED lights. Or you could scale it up to a huge device that would keep a household running for days without mains power. The design principles used would be basically the same. So we had some “spirited” discussions about just how best to present it in the magazine. Is it just a UPS or is it something much more than that? We wound up mentioning some of the many other possibilities in the article. But there are lots of aspects of this design to be explored. We’ll finish describing this UPS design – which has quite a few different uses – over the next couple of issues. But we intend to revisit the concept in the future, to flesh it out. For example, we may add solar panels to keep the batteries charged when the grid fails. And we might increase the size of the battery bank and inverter power. This would greatly expand its possible uses. In the meantime, some readers may see what we’ve done and decide to expand the design on their own. There’s certainly nothing to stop you from doing that. Nicholas Vinen Celebrating 30 Years siliconchip.com.au siliconchip.com.au Celebrating 30 Years May 2018  3 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”. Information from ACMA about LED interference It was with some interest I read a letter during the night on TV channel interference by D. McC. in the April 2018 issue of Silicon Chip. Your response was a bit surprising. ACMA recognises LED lights as a cause of interference (siliconchip. com.au/link/aajp). This information was provided to me by an employee of ACMA who was investigating TV interference at my premises and adjoining addresses. Our problems developed a few years ago and have increased over that time. There seems to be a number of factors involved including solar panel inverters and radiation from power lines (which is worsening). We need someone with the right equipment to visit our area after hours (ACMA have difficulty with staff beyond business hours!) to make observations when interference actually occurs. We also have a radio reception problem on the AM band at 873kHz, causing increased background noise. Geoff Lloyd, Hornsby Heights, NSW. Response: it definitely is plausible that poorly designed LED switchmode drivers could cause significant interference but we're unsure why it would affect just one TV channel frequency. Perhaps the affected stations are at an odd harmonic of the switching frequency. Grid-feed inverters and power-line based networking certainly are contributing to a much higher level of RF background noise and can swamp AM reception in some areas. Game Boy mystery solved In the Ask Silicon Chip section of the February 2018 issue, B. M. of Kiama Downs asked about a watering system project based on a Game Boy. The article appeared in Electronics Australia, June 2000, on page 41. John Heffernan, via email. 4 Silicon Chip More range for the nRF24L01+ Digital Radio Modules I read Jim Rowe’s interesting article in the January 2018 edition regarding working with the nRF24L01+ digital radio modules. I purchased a couple from the Silicon Chip Online Shop and yesterday, updated the firmware on a couple of LCD BackPacks I previously built for other uses and programmed them with your “checkout” program. It worked straight out of the box but I found a few ways to tweak the hardware and software to achieve better range and performance. Firstly, I think the recommended 10µF bypass capacitor should be considered mandatory! Without these, I was getting a range of not much more than 1.5m and even then, it was a little erratic in one direction. After fitting 10µF MLCC capacitors, range went up to about 7-8m but no more, without lots of time-outs (1 in 4). Also, it was still a little asymmetric. I downloaded the Nordic IC product specifications and also went back to the September 2016 Circuit Notebook article and noticed they both used a lower data rate and a higher power setting. I tried your code with RegData(5) set to &H2626 (for 250kb/s, and 0dBm) LED interference can affect some TV channels I also had the same problem D. McC. had (Ask Silicon Chip, April 2018, page 89). The family living across the street from us had a tree in their front yard all decked out in LED lights. When the lights were turned on, channel 10 would disappear and channel 7 would pixellate. The family concerned are a rather prickly bunch and weren't going to have a bar of it. I managed to talk the husband into coming over for a demonstration while his wife at home turned the lights off and on. Sure enough, the reception fault Celebrating 30 Years and RegData(3) set to &H2453 (to set ARD to 1500µs, to suit the slower speed). I must admit that I haven’t a clue what the first bytes in each RegData value relate to – I was concerned they might involve the CRC – maybe you can shed some light on this. Anyway, this worked, and the range was at least doubled – to 16m+ going from a room downstairs, through a couple of doorways, upstairs, and around a corner – so not really “lineof-sight”. With the increased power setting (0dBm) and lower data rate (250kb/s) and the devices fitted with 10µF MLCC bypass capacitors, I got reliable communications at 200m with line-of-sight (I had one unit set up on a bin near the road). It’s possible that this set-up is capable of more range but I ran out of road and was starting to get amongst trees in our local park. Finally, I don’t understand why you’re reversing the byte order of the payload before transmission and then reversing them again on reception, before output. I deleted both the byte reversal process when assembling the followed the light operation. The light installer wouldn't believe it! A week later, the installation crew arrived with boxes of lamps sourced from China. They changed all the lamps and we had no more problems. I could not get any information from the installers on the lamps and the prickly neighbour was not all that forthcoming with information either. Looking from the side fence, I could see that they had a glass outer envelope, were supposedly LEDs and glowed with a slight orange tint. I hope that helps. Fred Thorpe, Narrabeen, NSW. siliconchip.com.au Helping to put you in Control Ethernet Modbus TCP 8 isolated The A-1855 Remote Modbus module provides 8 Isolated Digital Inputs and 8 transistor Digital Outputs (sink). Ethernet supports a Modbus TCP protocol. SKU: YTD-555 Price: $164.00 ea + GST Modbus RTU/ASCII 8AI Provides 8 Analog Inputs (0~10v), 4 transistor digital outputs and 2 analog outputs (0~10v). RS-485 interface supports a simple ASCII protocol and Modbus RTU. SKU: YTD-410 Price: $149.00 ea + GST Digital Pressure Sensor Our new budget priced pressure sensor. An IP65 pressure transmitter with two-wire, 4 to 20 mA output, LED display and ¼” G ( parallel BSP) process connection. ±0.5% F.S. accuracy. 0 to 10 Bar. SKU: FSS-1584 Price: $159.00 ea + GST Isolated Serial Converter The Yotta Control A-1521 is an isolated RS232 to RS232/422/485 serial converter. Features baudrate to 115.2kbps, 3000VDC isolation and 1030VDC powered. SKU: YTC-201 Price: $119.00 ea + GST Small Cooling Thermostat Small DIN-rail mount cooling thermostat with built in bimetallic sensor for keeping things cool. SKU: HEC-005 Price: $19.95 ea + GST Starter Kit Programmable Logic Relay TECO SG2-12HR-D Starter Kit. Kit includes all the components required for your SG2, with a 15% Saving on the regular price. SKU: TEC-080 Price: $359.00 ea + GST Large Temperature Display Large Temperature Indicator with range -19.9 to 99.0degC. SKU: HNI-080 Price: $269.00 ea + GST For Wholesale prices Contact Ocean Controls Ph: (03) 9782 5882 oceancontrols.com.au Prices are subjected to change without notice. 6 Silicon Chip data to transmit (PrepmsTime), and removed the “RestByteOrder” subroutine. This didn’t make any difference to the operation of the units. Ian Thompson, Duncraig, WA. Jim Rowe replies: it sounds like the changes to the RegData values are worthwhile. Note that 0dBm is only 1mW, so this higher power setting is still perfectly legal. I implemented the data byte reversal because the nRF24L01 datasheet implied that it was required but you have apparently found that it isn’t. How to reach audiophile nirvana I read your response to the query regarding directionality in audio cables on page 91 of the April 2018 issue. You left out some important details. It's a little-known fact that the "break-in period" can be reduced significantly by hanging the cables up by one end. Furthermore, directionality can be improved by stroking the cables by hand while they hang. Firmly stroking each cable, from bottom to top, for about an hour each day over a month, will virtually eliminate any need for further "break-in". Phil Denniss, Darlinghurst, NSW. Computer security seems like a joke Your remark in the February 2018 Editorial Viewpoint that “Unless you become a hermit and live in a cave in the mountains, I’m not sure that you can ever be completely safe from these flaws” seems to be on the money. In just the last few months, the following has occurred: 1. WPA2 WiFi encryption has been shown to be flawed and vulnerable. 2. Equifax (a credit rating agency) in the USA has been hacked and the personal details (social security numbers, accounts etc) of 150 million US citizens have been stolen. I recently found out that Equifax operates in Australia too. 3. Spectre & Meltdown were discovered (the topic of your editorial). These are reputedly launched through JavaScript on web pages. These apparently also put “the cloud” in jeopardy. 4. Recently, it was reported that all that is needed now for ID theft is someone’s Driver’s License number. Enough other personal details are available (eg, through Social Celebrating 30 Years Media) to then enable the theft. Recently, telcos and electricity suppliers have been asking for License numbers. 5. The Russian government allegedly had a backdoor into Kaspersky anti-virus software which they used to get their hands on secret information from the NSA. This is scary as anti-virus software requires privileges and access to core parts of the computer. In the past, there were strong rumours of Microsoft providing backdoors for the NSA etc. 6. It was revealed that the Australian Electoral Commission is using archaic systems and software. DOS was mentioned as still being in use. Regarding your recommendation of “patching”, this concept is in itself not secure and creates vulnerabilities. The business models of Apple and Microsoft exacerbate this. Remember you don’t own the OS, you are a renter and the landlord has another key. A recent example is Apple purposely and surreptitiously interfering with (ie, reducing) the iPhone’s speed. Now I wouldn’t suggest one becomes a hermit but because hardware is now so cheap, I suggest that you should have two systems, one airgapped (the one holding private information) and one connected to the ‘net for browsing. Regularly wipe and re-install the OS on the internet-connected computer. This is much easier with Linux. The “Data Breach Mandatory Notification” legislation came into effect on the 22nd of February. Though it is (at the moment) limited to companies with $3 million turnover and above, it should be a wake-up call to everyone. J. Williams, Elanora, Qld. Comment: while it’s true that patching your operating system can introduce bugs, including security vulnerabilities and backdoors, unpatched systems are even more vulnerable. A computer connected to the internet that hasn’t been updated in a year or more and that isn’t behind a comprehensive firewall is almost certainly to have been already compromised. Image on monochrome TV is not a moiré pattern On page 81 of the March 2018 issue, in the article on the Analog TV A/V Modulator, I noticed the caption for the right-hand image of the test pattern on siliconchip.com.au a B&W set says that the screen features "moiré pattern[s]" due to the interaction of the screen and camera. But you can see that this patterning only occurs in the parts of the picture which have colour (ie, in the colour bars). This is due to the 4.433MHz PAL colour modulation sidebands modulating the CRT beam on the TV set. There is no (or little) patterning in the black, white or grey areas of the picture. This could be eliminated by adding an LC trap circuit in series with the video signal line, tuned to 4.433MHz. A switch could be added to switch it out for use with colour sets. It could be added to the pin 11 input of IC6. Alternatively, it's possible to fine-tune the TV slightly so it is less noticeable. As usual, it was an excellent magazine; I would not miss it. You have some very clever and innovative designers. Rod Humphris (ex RMIT), Ferntree Gully, Vic. Faulty premises Earth connections are still a menace The Publisher's Letter in the August 2014 issue of Silicon Chip warned of the dangers of faulty Earth connections and the possibility of electrocution during the removal and replacement of water meters. I was sufficiently concerned that I bought a clamp meter to check the current in the incoming water pipe of our house. I was relieved to find that any current was below the threshold of measurement. In The Australian, 7th March, 2018, there is an account of a child who is in a critical condition in hospital after receiving a severe shock from a garden tap. It seems likely that a faulty Neutral/Earth connection was responsible. It would seem prudent to have house Earth connections checked every few years since they can be degraded by corrosion, with fatal consequences. James Goding, Princes Hill, Vic. Leo Simpson responds: This issue raises its head again, in the most tragic circumstances! I agree entirely that Neutral and Earth connections to all properties should be checked a matter of routine by the supply authorities and if anomalies are found, they should be fully investigated and rectified, no matter how many properties may be affected in any one instance. siliconchip.com.au In fact, it probably should be a requirement that any property being sold or leased should have a test certificate to state that the wiring is safe, just as most states have a requirement that a home swimming pool must be fully compliant with fencing and other regulations I was certainly not happy that the anomaly I discovered at my home (as detailed in the August 2014 issue) was not fully investigated and remedied. Changing the colour of Earth wires is not permitted The comments by Thomas Siegmeth on page 6 of the March 2018 issue regarding the misuse of green or green/ yellow wire for non-Earth wiring in a mains-powered device are correct. However, the comment about sleeving the green/yellow conductor to solve this is not correct. The last paragraph of AS/NZS 3000 clause 3.8.2 prohibits the use of sleeving to use a green/yellow wire as an Active or Neutral conductor. Geoff Coppa, Alstonville, NSW. Response: we agree that this is not acceptable since it would be possible for the sleeving to fall off, or someone might cut it off and then forget. Some ideas for future seismographs I received my April edition of SiliChip yesterday and was particularly interested to read your 3-Axis Arduino Seismograph article. I have a particular interest in seismology and appreciate your point when you say that there are few standard seismic data formats that support multi-channel recording. One that does is the PSN format developed by a polymath electronicssoftware Californian gentleman named Larry Cochrane. Larry and his clever equipment have been the backbone of serious amateur seismology for the last couple of decades but sadly Larry is soon retiring and many amateurs worldwide are now scratching their heads and pondering life post-Larry. Larry and his hardware and software are available at his website: http://psn.quake.net Using Larry's equipment I operate a little seismic observatory at Coonabarabran, NSW, data from which is posted at: www.map.id.au/seismic Any earthquake big enough to make the news is likely to show up here. You con Celebrating 30 Years May 2018  7 may be interested to note that I have recorded the last three North Korean nuclear tests, including the latest one which wasn't far from being a Chinacabinet rattler. The details are at: www. map.id.au/seismic/epso_events_nk_ nuclear_tests.html On my property, I operate a threeelement seismic array, where the sensors are at the vertices of an equilateral triangle measuring 200 metres per side. This gives me the ability to unilaterally compute the bearing to a particular earthquake/blast/event. I wish to make a similar array but with the triangle measuring around 4km per side. My small seismic array is hardwired with buried cables but a large array will require RF links of some sort and I have been pondering my options. Reading your article, another possibility occurred to me. If the Arduino logger could incorporate precision GPS timing as well, one could potentially create a powerful tool for seismic monitoring (eg, for mining and engineering structures) and the creation of large seismic arrays. Generally speaking, professional seismograph equipment costs a fortune, so making a seismic array by deploying many autonomous precision-timed loggers is not an option. But if your Arduino could timestamp data to an absolute precision of say 10 milliseconds or better, then that would be potentially really useful to me. It also means you don't have to fiddle with setting RTCs and dealing with their time drift. So would you consider a future design improvement/upgrade to incorporate GPS timing as well? I'm not sure if this is really possible, but if so it would be most interesting. Incidentally, I think your use of WAV for this application is clever. WAV data will be generally a lot more compact than standard seismic formats, and it is then also trivial to "listen" to earthquakes. Listening to spedup seismograph data was quite a hobby at one time, and I own a 33rpm vinyl record made in the 1960s which contains exactly that. Anyway, it was a great article and clever to think of using WAV to solve the compact-multi-channel problem. Michael Andre Phillips, Coonabarabran, NSW. Nicholas responds: Thanks for your feedback. It certainly would be possible 8 Silicon Chip to use a GPS module for timing; we considered it but thought it unnecessary. If you want to synchronise multiple geographically-distributed seismographs then it makes a lot of sense and we will certainly incorporate such a feature in any future seismograph. We did find and consider the PSN file format when designing our seismograph but it has a major problem in that it does not store the data for multiple orientations or sensors in an interleaved fashion like the WAV file format. Rather, multi-sensor files are simply multiple single-sensor files "glued" together. That makes it almost impossible to generate them on-the-fly. You have to record to multiple individual files and then combine them when they are complete. Whereas with a .wav file with multiple channels, we can simply append new data on the end and then update the header periodically and no post-processing is needed. How accurate are GPS speed readings on an incline? I was intrigued by Leo Simpson's assessment of the Navman Driveduo in the February issue of Silicon Chip. I use a GPS in my 1969 vehicle which has its speedometer hidden in a black hole in the dashboard and of course it measures in miles per hour. So I use a GPS unit as a speedometer, to give me some peace of mind on speed-related matters. It reads my speed to within 1km/h. Or does it? As an engineer, I am always interested in how and why things work and I have some questions about GPS. For instance, it would appear to me that it measures speed in the horizontal plane only, my reason for this summation is that the location is based on the intersection of the signals from satellites in orbit at my location on the Earth’s surface; this can be shown as a vertical line emanating from the centre of the Earth. The different locations over a set time will give the speed of travel between these two points on the Earth’s surface. One assumes here that one is travelling on a level surface. But what happens when one is travelling on a steep gradient? Does the GPS speed reading drop as it only takes into account movement in a plane that's tangential to a spheroid representing the Earth? I believe there are some models of GPS which include an altimeter. It is Celebrating 30 Years possible that these models may well give an accurate speed reading on steep inclines but without this function, how does the two-dimensional GPS operate on slopes? I know that there is some variation on gradients as my speedometer tells me so. John Hardisty, Burnie, Tas. Response: as far as we know, all GPS receivers track altitude as well as latitude and longitude, regardless of whether the altitude is displayed. So it should be possible for a GPS unit to give an accurate speed reading even on a steep incline. This does require the correct calculation to be used, which takes into account changes in altitude; we assume most units will do this but who knows. GPS speed readings are likely to be most accurate when travelling "on the flat" but they are always behind the eight-ball in adjusting to changes in speed. This is due to the averaging required to hide slight inaccuracies in GPS position readings. As you might expect, GPS accuracy is also poorer in hilly country or in "canyon-like" city streets with lots of high-rise buildings. The OBD setup is generally quicker to respond and is probably more accurate but tyre wear (and long-term changes in wheel diameter) would also affect accuracy; not that OBD is any good to you in a 1969 vehicle! The only truly accurate speed measurement system would involve a RADAR or LIDAR setup. Updated GPS-based Frequency Reference wanted Regarding your September 2011 update of the popular GPS-based Frequency Reference project, I note that like most GPS-based frequency references, it has a fixed output frequency of 10MHz. While this is a common frequency used by test equipment, I have seen some devices which use a reference frequency which cannot easily be derived from 10MHz. For example, the Philips PM5193 function generator needs a reference frequency of 8.589934592MHz so I would like to see a GPS-based Frequency Reference design which provides reference frequencies other than 10MHz. One possible way to achieve this is to use a DDS IC such as the AD9956 with a 48-bit (or longer) frequency siliconchip.com.au word (with a frequency multiplier IC for the reference oscillator) to generate frequencies with the smallest possible error. This error should be calculated and displayed by the unit. Bryce Cherry, Rockhampton, Qld. Response: we are working on a new GPS-based Frequency Reference design and have taken your suggestion into account. It will have a fixed 10/20/40MHz (selectable) output and multiple configurable outputs which are derived from the main reference clock using programmable PLLs. These low-jitter outputs should be programmable from 0.1-167MHz in steps of around 10kHz. Another faulty motor run capacitor The letter from Ian Thompson on page 8 of the March 2018 issue was very helpful. I live in a rural area without reticulated water and so water to the house is supplied from underground tanks via a pump. Given that the area is rural and reasonably heavily wooded, we get our fair share of blackouts. To cope with this, we have a 2.4kVA inverter-generator which I plug into an appropriate socket at the main switchboard. This has worked successfully for eight years. Recently, during a blackout, the pump tripped the overload protection on the generator. That had never happened before. So like Leo Simpson, I assumed that it was bearings in the pump or motor. I dismantled the pump and found no problems with the pump or motor bearings. I checked the pump controller and found no problem there either. The points in the controller had some small amount of carbon on them but not more than I would expect from eight years of use. The power was back on so I reassembled the pump and it worked normally. During the next blackout, the pump was able to run off the generator but it seemed to be loading it more than usual. Having read the aforementioned letter in the March 2018 issue, I realised that I had not checked the run capacitor. I thought that if the capacitor failed, the motor would simply not run. Two days later we had a blackout and the pump tripped the generator again. So I removed the capacitor and measured its capacitance. It was marked as 20μF but measured 11.6μF. 10 Silicon Chip I purchased a 20μF motor capacitor from Jaycar which measured 19.9μF. I fitted it and re-connected the pump. The blackout was still in effect so I switched it on under generator power and it ran perfectly. It now runs more quietly with the new capacitor but I don’t understand why. Thanks for the tip. Peter Chalmers, Clear Mountain, Qld. Navman and DTV antenna Your article on the Navman GPS satnav is very much welcome. I am an enthusiast for this “Real Time” Traffic Information System, yet I am often criticised for using one. For example, “you don’t know your way home”... and then I say, “why does it take you so long to get home, were you stuck in a traffic jam?” Anyway, I was most impressed with the article but I use the TomTom 520 with voice commands, where the RTT (Real Time Traffic) information is received via Bluetooth from my phone and is displayed down a panel on the right-hand side of the TomTom screen. I get an icon on my phone and the TomTom showing a “Two Car” symbol which indicates that I am sharing traffic information with fellow users. This, in turn, helps TomTom developers improve mapping quality and provide regular map updates, eg, for speed cameras and road changes. But regardless of the brand of the unit, the article was wonderful reading. The whole magazine is great. I also liked Leo’s Digital TV antenna project. Peter Casey, West Pennant Hills, NSW. Response: Google Maps also shares traffic data with other users, which is a great feature and a good reason to prefer using a phone for navigation – but you do need a reasonable amount of data on your plan. Smartphone app makes project hard to justify Most days I drive a section of road, taking my kids to school, which has 100km/h point-to-point average speed cameras. I have been imagining about a device on the dashboard with two buttons, one marked 100km/h and the other 110km/h, these being the only two speeds I have encountered average speed cameras at. Pressing the appropriate button at the start of the policed zone would Celebrating 30 Years cause the device to (via GPS) start to track your average speed and would warn you via an LED or alarm sound if this exceeded the maximum you had chosen. Pressing the button again at the end of the policed zone would turn off the monitoring. Additionally, it could learn the location of the speed zone and will automatically monitor the area in the future. The March 2018 editorial prompted me to submit this as there probably is a bad app for this already! Love your magazine; keep up the good work. Alan Williams, Adelaide, SA. Comment: as you have implied, there are already a number of smartphone apps for average speed cameras and while we aren’t sure if they do exactly what you have suggested, it does seem like they would be useful to ensure you don’t run afoul of an average speed camera. On that basis, we probably can’t justify a custom-designed device for this purpose. Another option would be to fit cruise control to your car (or use it if you already have it). In many cases, except when you’re travelling down a steep hill, it will hold your vehicle very close to the set speed. This is especially true if you have an automatic transmission which is able to change down for engine braking (or you could do it yourself with a manual transmission). An easier method for assembling RTL-SDR kit Jim Rowe was absolutely right when he said, in the November 2017 issue, that assembling those RTL-SDR kits was difficult. I bought one of those kits and assembled all but the connection from the toroid T1 to the RTL2832U chip. It then sat for months while I pondered how to do it. I ended up soldering two dressmaker's brass pins to a piece of Veroboard as pictured to the upper right, then bent the pins so that when the Veroboard was on top of the RTL2832U IC, the pins would apply pressure to pins 4 and 5 and make an electrical connection. I have been using the kit now for several months without any problems. I don't see why this should be any less reliable than, say, a socketed IC. I used 22 SWG tinned copper wires soldered to the Veroboard and to the main PCB for support in two places siliconchip.com.au Shown at right are two brass pins soldered to a piece of veroboard. Below it is the board attached to the Banggood SDR kit in a way that the brass pins from the board apply pressure to pins 4 & 5 of the RTL2832U IC, so that it makes electrical contact. with a third wire soldered to the frame and bent so that the pins were aligned with and able to apply sufficient pressure to the pins of the RTL2832U chip. The very thin wires from toroid T1 were soldered to the Veroboard tracks to complete the circuit. Regarding the software, you can in- stall Airspy's SDR# for Windows as described in Jim's November review. However, the Windows software for SDR are something of an ordeal to install, so instead, I installed a recent version of gqrx (version 2.11, from http://gqrx.dk) on Linux Mint (version 18.3) to get this SDR-RTL kit fully operational very quickly. Note that for HF reception, gqrx needs to use the parameters as shown in the adjacent screen grab. I am very pleased with the result, although a wideband HF preamp is worth adding for receiving marginal signals. R. Matthews, Adelaide, SA. Confusion over slowing of GPS clock pulses Thank you for published the Analog Clock-based 1pps signal source in the Circuit Notebook section of the May 2017 issue, as I requested. I finally got around to assembling it. Initially, everything worked as expected. The startup LED did its thing and a 40ms pulse got fed into my digitally-controlled analog clock, which ran as expected. I let it run on the bench for some siliconchip.com.au Celebrating 30 Years hours but when I next checked the time on it, my clock was very slow; losing one hour in six. So something was quite wrong. Stopping the board and restarting it caused it to perform as expected. I then attached a CRO probe to monitor the 1pps output. It timed at exactly 1Hz, so I let it run like that. Checking after one hour and a bit, I noticed the clock started losing time again and the CRO pulse was now 0.5Hz, exactly half the expected rate. I have no idea what is going on in that PIC chip. However, I observed there is a 1pps pulse available at the white GPS connector wire for a short time when the GPS had locked onto its satellites. So I decided to use that instead. I simply removed Q2 and shorted the collector-emitter pins to turn on the GPS permanently. There now was a nice 1pps pulse available but at only 3.3V peak-to-peak. A 4050 buffer (all 6 gates in parallel) boosted that to a 5V pulse and with that my clocks keep running right on time. There was perhaps a misunderstanding at my initial request as low power consumption is not an issue May 2018  11 with my two clocks, both using 1970s technology. A 5V/2A plug pack easily provides the almost 5W of power requirement. So the extra drain of the permanently on GPS is no problem. If you think running the GPS powered like I do might do long-term damage to the PIC chip please let me know but I doubt it. Klaus Sussenbach, Doubleview, WA. Response: this is because the GPS Analog Clock board drives the clock mechanism with one pulse per second, but the pulses alternate in polarity between positive and negative, as required by the clock motor. We realise now that the software would need to be modified to produce a positive pulse each time. The reason it starts out at 1Hz is that this is the unit “quick stepping” the hands around to the correct time (it assumes they start out set at 12 o’clock). A modified version of the firmware is available for download on our website under May 2017. This produces positive pulses only at 1Hz with no quick stepping, to suit clocks like yours. Praise for Super Clock and feedback on Altimeter I built the Micromite Super Clock about a year ago and I must say it’s been one of the best projects I’ve ever made. I have been a keen clock collector for many years and I greatly appreciate the accuracy of the clock. I used the DS3231 RTC as the timebase with a view to changing to the GPS if the lack of accuracy warranted it. During the past eight months, the clock has lost less than 1.5 seconds after I adjusted the basic accuracy with the Micromite software. I used www.timeanddate.com/ worldclock/timezone/utc as my time reference and it’s interesting to notice the occasional difference with phone and TV time. As a result of the incredible performance, I’ve given up on the GPS timebase because it would no doubt be a problem supplying the GPS module with a good signal at all times inside the house. I recently constructed the Micromite Altimeter which works satisfactorily except for the Humidity sensor which reads quite low against two weather stations. At the moment, the Micromite reads 23% against 37%. The sensor responds to my finger or breath and 12 Silicon Chip rises to 100% very quickly and returns in similar time. I think a sensor change may be in order. The temperature reading looks good but I can’t determine whether you take this reading off the BMP180 barometer sensor or the DHT22 humidity/ temp sensor. I don’t fly and I built the altimeter to use for bushwalking, car trips etc where it’s interesting to follow the terrain. This is not the first altimeter I’ve built. About 10 years ago I built a PICbased unit from an article in EPE magazine. This suited my purpose better than the Micromite because you could set the altitude directly into it from contour maps or start from home with the known altitude set. The Micromite is more suited to aviators in its present configuration and I wonder whether you could modify the software along the lines of the “QNH” mod you recently included so that a base altitude can be entered in. I feel such a modification would greatly increase the appeal of the unit for us non-aviators. Finally, I would like to suggest that you dispense with the large “TOUCH TO CHANGE” area on the screen and use a touch screen function similar to the Super Clock. The area of the present screen is somewhat wasted by the TOUCH button especially as it’s so bright and detracts from the overall readability of the screen. I have modified my unit to use just one case rather than the two as presented. The sensors are fitted into a cut-down smaller plastic box on the back of the main case. The little box is ventilated with a number of holes and the lid screws for the small box now retain the sensor housing to the main case. The heating problem is no longer an issue and in addition when walking as the unit is only on for short periods. Bob Temple, Churchill, Vic. Response: note that your local microclimate can vary considerably from that of nearby weather stations (Bureau of Meteorology or your own). Just as your local temperature can vary by several degrees compared to other nearby sites, humidity can vary considerably too and depends on your proximity to bodies of water, vegetation, being in a valley and so on. Faulty LCD screen for BackPack Firstly, congratulations on achieving Celebrating 30 Years 30 years. Thirty years of producing a truly quality product reflects passion and commitment. You have, I believe, contributed, in a big way, to the education of many of today’s electronics engineers; by firstly kindling their interest in the subject and then by showing them where a career in the industry might lead. I believe you have contributed, both directly and indirectly, to the advancement of humanity. Also many have become materially better off through your endeavours. For me, I am still being thoroughly entertained each month. I am not a whiz so I get a big thrill from making things from recycled parts and getting them going with PICAXE and now Micromite. On that topic, I built the Micromite Plus LCD BackPack V2 in May 2017 but ran into problems running the GUI CALIBRATE command. The following is an example of what happens when I try to calibrate the touchscreen: > gui calibrate Warning: Inaccurate calibration > gui calibrate Warning: Inaccurate calibration (calibration could complete twice) > gui calibrate Error: Touch hardware failure > gui calibrate Done. No errors (calibration successful) > gui test touch (however test touch failed three times) > gui calibrate (tried to re-calibrate) Error: Touch hardware failure ...and so on. After installing the replacement programmed Micromite chip you so kindly sent me, I became very despondent as the touchscreen still didn’t respond correctly. It still had intermittent failures so I put the project aside. I was then greatly heartened to find others with very similar problems, as per “BackPack problems may be due to bad LCD connections” in Mailbag, December 2017, so I dusted off my BackPack and started “hiking” again. I checked my construction again and finding no faults, reconnected the LCD, fired it up and guess what, it works. I was so excited I went and hugged my darling wife! Problem is, I don’t know exactly what fixed it. The only difference is that when I reassembled the LCD to the BackPack, I left out the four small Nysiliconchip.com.au lon washers. This would have brought the two boards closer by about 0.5mm and also allowed the male and female headers to further engage, maybe creating a better connection. Now the “calibration” and “gui test lcdpanel” commands execute OK. However, there are missing pixels on my screen. If I colour in the entire screen there appears a grid of vertical and horizontal lines where the pixels do not respond to touch. Has anyone else reported this fault? Are we dealing with a dud batch of LCD boards? Stephen Somogyi, Barrington, NSW. Response: it does sound like your original problem was due to intermittent bad connections on the LCD header. Yours is the first report we’ve had of missing pixels/rows/columns on the LCD screen. We have had a few people complain that the touch controller doesn’t work and we replaced the screens in those instances, and a couple of other screens that were totally dead. A few were also replaced because they were damaged in transit (cracked). Overall they do not appear to be too unreliable but the defect rate is still higher than we would like. We will send you a replacement screen as yours seems to be faulty. Using relays to switch 3-phase mains I found the Lath-E-Boy Controller project in the January issue (siliconchip.com.au/Article/10933) interesting. But I have a comment regarding the text in the breakout box on page 43, titled “Using it with a 3-phase motor”. It says that RLY3 will need to be a four-pole type to allow it to switch all three phases. That's fair enough but it will need to be a relay specifically designed for switching threephase mains. That's because there's nominally 400V DC between phases (415V DC for 240VAC). The relay will need sufficient internal dielectric strength and physical separation between contacts to handle this. I built a relay box some years ago using 250VAC-rated Omron relays and switching three-phase mains, it generated a loud bang and welded all contacts together upon first operation! I'd be inclined to err on the safe side and use a 250VAC-rated relay (eg, the Jaycar model suggested for singlephase use) to drive a 415V four-pole contactor. A contactor with a 12V coil would remove the requirement for an extra relay. Cheers and keep up the good work. Kit Scally, Canberra, ACT. WRESAT article enjoyed Thank you for continuing the great tradition of in-depth science-technology articles. Catching up on my wet weather reading with the covers on in Adelaide, and after the recent publicity of the WRESAT launch anniversary and interviews on the ABC, I greatly enjoyed reading the WRESAT article in the October 2017 issue. It took me back to my visit to the Woomera museum in winter 2008 and staying in the Redstone block at the ELDO. I found the other resources page very useful. I started reading electronics magazines (and constructing projects) at the age of 13 while the last moon landings were being made. The only launch I have ever attended was the Woomera weather balloon. Keep up the good work and congratulations on the 30th anniversary. Roger Curtain, Williamstown, Vic. SC Radio, Television & Hobbies: the COMPLETE archive on DVD YES! NA MORE THA URY T N E QUARTER C NICS O OF ELECTR ! HISTORY This remarkable collection of PDFs covers every issue of R & H, as it was known from the beginning (April 1939 – price sixpence!) right through to the final edition of R, TV & H in March 1965, before it disappeared forever with the change of name to EA. For the first time ever, complete and in one handy DVD, every article and every issue is covered. If you’re an old timer (or even young timer!) into vintage radio, it doesn’t get much more vintage than this. If you’re a student of history, this archive gives an extraordinary insight into the amazing breakthroughs made in radio and electronics technology following the war years. And speaking of the war years, R & H had some of the best propaganda imaginable! Even if you’re just an electronics dabbler, there’s something here to interest you. • Every issue individually archived, by month and year • Complete with index for each year • A must-have for everyone interested in electronics siliconchip.com.au 62 $ 00 +$10.00 P&P Exclusive to: SILICON CHIP ONLY Order now from www.siliconchip.com.au/Shop/3 or call (02) 9939 3295 and quote your credit card number. Celebrating 30 Years May 2018  13 Fancy a quick aerial taxi ride to the airport . . . or perhaps to a fancy restaurant? That dream may become a reality sooner than you think. Some very large companies, including Airbus, Bell Helicopter, Boeing, Daimler, Intel, Toyota and Uber, as well as many smaller ones, are involved in the development of aerial drone taxis. And some are planning to have that taxi service available as early as 2020! Kitty Hawk’s “CORA” – now flying in trials in New Zealand (see panel page 23). Courtesy www.kittyhawk.com A By Dr David Maddison lmost two years ago (August 2016) we looked at Personal Flight Vehicles and their future (www. siliconchip.com.au/Article/10035). In that time, some have disappeared completely, some are still in planning and some are actually in production. But most of those featured were not intended for commuter use, nor did many have the option of operating autonomously. So we thought it opportune to look at the subject again, with particular emphasis on aircraft intended for public passenger use. Based on quadcopters These vehicle are primarily based on the familiar quadcopter or other multi-rotor formats used for hobbyist and professional photographic “drones” or more correctly, unmanned aerial vehicles. Quadcopters (four rotors) or other multi-rotor aircraft such as hexacopters (six) or octocopters (eight) are an attractive and potentially cheaper option than helicopters for commuter use, for a couple of reasons. They are mechanically much simpler, as their blades 14 Silicon Chip are usually fixed pitch (rather than variable pitch) and they have a potentially smaller landing footprint than helicopters of the same passenger capacity. They also usually use electric motors for propulsion, which are easier to maintain than internal combustion motors. Some of the first attempts at vertical flight in the early years used multi-rotor craft similar to quadcopters but they were mechanically complex and very difficult, if not impossible, to effectively control. The advent of high speed computers, three-axis accelerometers and solid state gyroscopes now enable these aircraft to be controlled with simple commands, eg, speed, yaw, pitch and roll that are One major problem yet to be fully solved with electric aircraft translated into complex comand passenger drones in particular is the length of time required mands to control the aircraft. to recharge their batteries. Most passenger drones will be used In this article we will surlike taxis and therefore will have a large number of relatively short vey some of the large number trips with battery recharging required after each trip. of passenger drones now unAs an example, a trip of ten minutes might require a few hours der development. to recharge the batteries. This will adversely affect the economNote that while many comics of operation and one solution may be a hybrid system with panies have passenger drones a liquid-fuelled generator to recharge the batteries in flight or a in development, relatively replaceable battery pack system. few have flown prototypes Uber has partnered with ChargePoint (www.chargepoint. and many will inevitably fail com), a company that makes electric vehicle infrastructure, such to survive. as charging stations, to develop a standardised rapid charging Some of the illustrations connector that will fit any electric VTOL vehicle that uses its shown are artist’s impresUber Elevate Vertiports (see below). The system is planned to sions; very few actually show be ready by 2020. the aircraft in flight. Battery Charging Celebrating 30 Years siliconchip.com.au Uber vision for the future showing various flight paths of Uber Air vehicles around a city. Airbus CityAirbus Airbus Pop.Up The CityAirbus by Airbus (www.airbus.com) is designed for an air taxi role and will carry up to four passengers. Initially there will be a pilot but the aircraft will operate autonomously once regulations permit. Eight propellers and motors are used and in each ducted fan nacelle there are two motors and two fixed pitch propellers. The motors are Siemens SP200Ds with an output of 100kW each. There are four battery packs with a combined capacity of 110kWh, with a total power delivery of up to 560kW. The aircraft can cruise at 120km/h with an endurance of 15 minutes. So it has a range of up to 30km. Unmanned flights are expected to start at the end of this year. This is a demonstration concept only and not intended to be built. It is a joint exercise between Airbus engineers and automotive engineers at the Italian design company Italdesign. The concept has either an automotive “undercarriage” or a quadcopter “over-carriage” attached to a common passenger module. The module can also be carried by other modes of transport such as rail. A video “Pop.Up” may be viewed at siliconchip.com. au/link/aajf siliconchip.com.au Celebrating 30 Years May 2018  15 Airbus Vahana AirSpaceX AirSpaceX (http://airspacex.com) [not related to Elon Musk’s SpaceX] is developing the MOBi 2025 which carries a range of modules for different purposes such as passengers or freight. It will have a range of 115km and a cruise speed of 241kph. It will operate either autonomously or with a pilot. A TEDx talk about eVTOL flight by Jon Rimanelli, founder of AirSpaceX: “Traffic is taking over our lives. The solution is to look up. | Jon Rimanelli | TEDxDetroit” siliconchip. com.au/link/aajh Airbus Vahana prototype first test flight which occurred on January 31, 2018 in Oregon, USA. Another flight occurred the next day. A3 by Airbus (www.airbus-sv.com) is the advanced projects and partnerships division of Airbus in Silicon Valley, California. The single-seat Vahana has eight motors and propellers on two tiltable wings. The wings rotate for vertical take-off and rotate again for forward flight. It is 6.2m wide, 5.7m long, 2.8m high and has a maximum take-off weight of 745kg. Its cruise speed is 175km/h and each motor is rated at 45kW. The Vahana is equipped with a ballistic parachute as a safety measure. Video: “Airbus Vahana Flying Taxi” siliconchip.com.au/link/aajg Artists impression of the Vahana when fully developed. AirSpaceX MOBi 2025. It has a range of modules for different purposes such as passengers or cargo or specialised modules for other purposes such as military surveillance. Another concept by AirSpaceX is the MOBi One. This electric passenger drone will have a range of 104km, cruise at 240km/h with a maximum speed of 400km/h, a passenger capacity of 2-4 and be capable of piloted or autonomous operation. It will be 10m long, 12m wide and 3m tall. Production is expected to start in 2020. See video: “Mobi-One: AirSpaceX’s autonomous, electric air taxi lands in Detroit” siliconchip.com.au/link/aaji AirSpaceX MOBi One concept. Multi-rotor flight mechanics In a conventional winged aircraft, variations in roll, pitch and yaw are made with aerodynamic control surfaces but in a multi-rotor aircraft (which usually lack control surfaces), these variations are effected by altering the rotational speed of one or more propellers. In a quadcopter, one pair of propellers rotate in one direction and the other pair in the opposite direction. This is to counteract the tendency of the aircraft to rotate in the opposite direction to the propellers, as would be the case if they all rotated in one direction. In helicopters, this tendency is counteracted by the tail rotor, or more rarely by a contra-rotating pair of main blades. When the speed of all propellers is increased, the vehicle goes up; conversely when the propeller speed is decreased the vehicle descends. 16 Silicon Chip To make a quadcopter in an “x configuration” roll or pitch pairs of propellers corresponding to the desired direction are sped up. For example, to pitch forward, the speed of the two rear propellers is increased or to roll to the right the two left side propellers are sped up. Pairs of propellers are matched in speed to prevent the quadcopter rotating due to torque reaction. If the quadcopter is to be deliberately rotated about its yaw axis, opposite pairs of propellers are slowed or sped up (compared to the other pair) which removes the balance against the torque reaction and the quadcopter will rotate about its yaw axis. In multi-copters with more than four sets of propellers such as hexacopters and octocopters control of the vehicle is similar but with more groups of propellers being controlled. Celebrating 30 Years siliconchip.com.au Aurora eVTOL Safety and Regulations Concept of Aurora eVTOL in production form. Aurora Flight Sciences (www.aurora.aero/evtol), owned by Boeing, is developing the eVTOL passenger drone. It is an electric design with eight propellers for vertical lift plus a wing with a pusher propeller for horizontal cruise. It will carry two passengers including pilot or cargo. Operational testing is anticipated to start in 2020 in Dallas-Fort Worth, USA and Dubai, UAE. Uber has partnered with Aurora to be the manufacturer of one of the drones it intends to use for its Uber Air service. Video: “Aurora Flight Sciences’ Electric VTOL Aircraft” siliconchip.com.au/link/aajj Subscale demonstrator of Aurora eVTOL aircraft in a test flight. During the this test flight there was a successful transition from vertical to forward flight. Image credit: Karen Dillon, Aurora Flight Sciences. Bartini Flying Car The Russian Bartini. The electric Bartini Flying Car by Bartini in Skolkovo, Russia (https://bartini.aero) will be offered either as a two or four-seat model and uses ducted fans for vertical take-off, after which the fan pods are rotated for horizontal flight. It uses variable pitch propellers. siliconchip.com.au In contrast to helicopters, multi-rotor aircraft cannot auto-rotate to enable a relatively safe landing in the event of an engine failure – providing there is somewhere safe to land! And unlike almost any other aircraft, most proposed “passenger” drone designs are unable to glide any distance (if at all) in the event of loss of power. So additional levels of redundancy for critical aircraft systems such as twin motors coupled to twin propellers, partitioned power sources (ie, all batteries normally contribute to flight but if one bank fails remaining ones can supply power to all motors), redundant flight control systems and even a ballistic parachute may be needed. A ballistic parachute can be ejected from, then open and save the aircraft at a relatively low altitude; they are becoming more common on light aircraft now. Regulations As there are (as yet) few or no regulations allowing for the flight of autonomous passenger drones in most jurisdictions, one way these drones may be introduced is to fly them with pilots first, until regulations can be established for autonomous operations. This assumes that the vehicles can gain appropriate airworthiness certification, given their radical differences compared to existing certified aircraft types. In April 2017, A3 by Airbus (a division of Airbus Industries) in partnership with the Association for Unmanned Vehicle Systems International (AUVSI) [www.auvsi.org] called for industry co-operation in developing standards for “urban air mobility”. At a workshop held at the Airbus Experience Center in Washington, DC, which included participants from the US Federal Aviation Administration (FAA), the two key regulatory areas considered were certification of autonomous passenger aircraft and air traffic management of such aircraft. Currently there is no clear pathway to certification of autonomous passenger aircraft, including airworthiness standards for Vertical Take-off and Landing (VTOL), electric propulsion, fly-bywire systems, software and sense-and-avoid systems. Such a pathway for certification needs to be developed. In terms of air traffic management, such aircraft need to be managed in point-to-point autonomous operations in an environment that also includes manned aircraft. Rules would also be required that allow for Beyond Visual Line of Sight (BVLOS) operations and operation over people. A ballistic parachute (such as that seen here on a small unmanned drone) could save an aircraft that has run out of battery charge or has a motor or control failure. Such parachutes are already used on many manned light aircraft. Image courtesy Mars Parachutes. Celebrating 30 Years May 2018  17 It is designed to be able to use hydrogen fuel cells when suitable models are available which will dramatically extend its range. The cost is expected to be a relatively low: US$100,000 to $120,000. The company plans to demonstrate flight of a two-seat model later this year (2018) and a possible four-seat model in 2020. Tests will be conducted in Dubai, Singapore or Sydney. Funding for this project is via the Blockchain.aero consortium. This aircraft has unusually detailed specifications published for it, such as: width 4.5m, length 5.2m, height 1.7m, range 150km or up to 550km with hydrogen fuel cells, payload 400kg, take-off weight 1100kg, lift to drag ratio 4 to 5, propeller loading 146kg/square metre, battery weight 320kg, battery density 200Wh/kg with the possibility of up to 700Wh/kg with hydrogen fuel cells. Battery capacity is 64kWh with the possibility of up to 224kWh with hydrogen fuel cells, power output 30kW, eight thrusters each rated at 40kW, maximum altitude 3000ft, cruising speed 300km/h, energy used for flight 51kWh, energy used for one minute of hover 5.3kWh, energy used for 30 minutes of cruise 45.9kWh, energy reserve 13kWh, energy used per 1km of flight at cruise 0.30kWh, energy used per minute of cruise 1.5kWh. A video (computer generated) of this vehicle can be seen at “Bartini Vision 2020 - Bartini Aerotaxi Is Man’s Wheels In the Air for Blockchain community” siliconchip.com. au/link/aajk Bell Air Taxi Carter CarterCopter Electric Air Taxi Carter Aviation Technologies in Texas, USA (www.cartercopters.com) are developing an electric helicopter based around their highly efficient “slowed rotor” technology. They are also working in collaboration with Uber to develop a four-passenger drone that can cruise at 280km/h. It has a rear-mounted rotor that provides an anti-torque force for the main rotor up to a speed of 160km/h. Then the main rotor is disengaged from the engine and the antitorque rotor turns to become a thruster and thus the aircraft operates like an autogyro. The main rotor is 10.4m in diameter and the rear rotor is 3.0m. The maximum payload is 363kg. The empty weight of the vehicle is 1451kg. The range of the vehicle is from about 180km to 256km depending on payload and speed. For detailed technical analysis of the design decisions made for this aircraft, see: siliconchip.com.au/link/aajm Cormorant and CityHawk Bell Air Taxi concept. Bell Helicopter company (www.bellhelicopter.com) is also working with Uber to develop an air taxi but is a concept only at this stage. See: siliconchip.com.au/link/aajl Taxi, sir? Rendition of the CityHawk on the streets of Manhattan Passenger space in the Bell Air Taxi concept. 18 Silicon Chip The Cormorant is being developed by Israeli firm Urban Aeronautics (www.urbanaero.com as part of their “Fancraft” series of VTOL vehicles, without external propellers and with internal ducted fans powered by a single gas turbine engine. The autonomous military aircraft is designed to take a 500kg payload of cargo or battlefield casualties. This payload limit imposed by the international Missile Celebrating 30 Years siliconchip.com.au DeLorean Aerospace DR-7 Artist’s conception of CityHawk flying over an urban area. Note the large internal counter-rotating ducted fans and associated vanes which are steerable. Technology Control Regime which also applies to military drones. See the video at: “Cormorant UAV (formerly AirMule) Pattern Flight Over Terrain (short)” siliconchip. com.au/link/aajn In April 2017 it was decided to design a vehicle based on the Cormorant for civilian use as an air taxi for four people as well as for emergency medical transport use. This vehicle is called the CityHawk. It will use a gas turbine engine at first but will later may be converted to compressed hydrogen at 10,000psi, or battery power. As of November 2017 the Cormorant was fitted with a Safran Arriel 2S2 735kW gas turbine engine. The plan with the CityHawk is to relocate the engine from the centre to the side to enable a passenger compartment to be installed there and to add an additional engine on the other side for redundancy in the event of one engine failure. A ballistic parachute will be fitted. Some specifications for the CityHawk are as follows: empty weight 1170kg, maximum take-off weight 1930kg, maximum speed 270km/h, range with four people 150km plus 20 minute reserve, range with pilot only 360km with 20 minute reserve. Video: “CityHawk: the flying car you’ve been waiting for” https://youtu.be/A1TPviF8YqU DeLorean Aerospace (www.deloreanaerospace.com) is developing the patented DR-7 which has two tiltable ducted fans which are horizontal for take-off and are rotated for forward flight, with lift being generated by wings. Ehang 184 Ehang, based in China, is developing the single-passenger Ehang 184 drone. It is reported to be very close to market, assuming regulatory permission is granted. It is a four arm, eight motor, eight propeller aircraft that weighs 260kg, has a cruise speed of 100km/h, a flight duration of 25 minutes and can carry a payload of 100kg. Recharging takes one hour. There have now been numerous manned flights of this drone (see below). Note that in the company’s own promotional video there is an eight arm, sixteen propeller two passenger model that is also designated an Ehang 184 but there is no mention of this on the company website at www.ehang.com See the video at: “EHANG 184 AAV Manned Flight Tests” https://youtu.be/Mr1V-r2YxME This has been widely broadcast in recent news bulletins. Flexcraft Flexcraft Consortium (http://flexcraft.pt/en) of Portugal is designing a nine-person plus pilot hybrid electric aircraft. It has two fans in its wings for vertical take-off and a separate motor for forward flight. Quoted range is 926km, with a fuel capacity of 532 litres. Different passenger and cargo modules can be attached. Look mum, no hands! One of the few drones already flying: the two-seat model of the Ehang 184 in a manned flight test. siliconchip.com.au Celebrating 30 Years May 2018  19 US$59,000) but their latest project is to make a patented five seat “flying taxi” passenger drone “Formula” which they say they’ll place into commercial service sometime this year. It uses a linear crank-less “free-piston” petrol engine to drive a turbine to produce electric power for propulsion. It has 48 vertical thrusters at four corners plus four horizontal thrusters and foldable wings that can be deployed for forward flight. The company quotes a remarkably affordable US$97,000 for this aircraft. Its range is quoted as 450km with a speed of 320km/h. Video: “Formula Project by Hoversurf” https://youtu.be/sxoG3eT6WJ8 The Portugese “Flexcraft” hybrid electric VTOL. I.F.O. Jetcapsule HopFlyt I.F.O. above a city street. Landing gear folds down to form legs. The capsule is lowered for entry and exit. HopFlyt’s eight-engine, four-person “Venturi”. Founded in December 2016, HopFlyt of Maryland, USA (https://hopflyt.com) are developing the four-person Venturi. It has its propellers mounted in venturi channels within tiltable canard wings to give improved efficiency and longer range. It has eight wing channels containing the motors and contra-rotating propellers. Some specifications: weight 815kg, wingspan 8m, length 7m. Video of test of 1/7th scale model: “HopFlyt Hover Test” https://youtu.be/oc_hUL0v-3s HoverSurf Formula HoverSurf (www.hoversurf.com), a Russian company with offices in Virginia, USA, are currently making or about to make a quadcopter format “hoverbike” (priced from HoverSurf’s Taxi R-1 20 Silicon Chip The I.F.O. or Identified Flying Object is a proposed design by Pierpaolo Lazzarini (www.lazzarinidesign.net) for Italian company Jet Capsule. To be powered by eight electric motors, it has an estimated speed of 200km/h with a claimed duration of around an hour. Video: “I.F.O. The Identified Flying Object” https://youtu.be/3ysmPDwVZFI Jetpack Aviation Jetpack Aviation (www.jetpackaviation.com) of California, USA was first mentioned in the August 2016 SILICON CHIP article on Personal Flight Vehicles for their personal Jetpack. Their unnamed multi-rotor aircraft is in very early stages of development but is expected to have 12 motors and propellers mounted on six arms. It will carry one person. Jetpack Aviation’s concept for a passenger drone. Celebrating 30 Years siliconchip.com.au Jetpack are looking at extending flight times beyond the 20 minutes it would have with batteries by the use of a small generator, possibly based on a small gas turbine engine. Two arms will fold so that it can fit in a domestic garage. There will be a number of safety features such as a ballistic parachute and an energy absorbing structure. See video at “Jetpack company developing new electric VTOL flying car” https://youtu.be/Bfo_iOjsbvc For an interview with one of the inventors, Australian David Mayman, see https://newatlas.com/david-maymanvtol-flying-car-jpa-interview/47700/ Joby Aviation It is envisaged that a passenger will request a Lilium Jet directly from their smartphone. The 36 electric jets work much like turbofan motors in a conventional jet aircraft but the compressor fan at the front is turned by an electric motor rather than a gas turbine. The wing assemblies are rotated for vertical take-off. There is a ballistic parachute for safety and multiple redundancy in the engines and other flight systems. Video: “The Lilium Jet – The world’s first all-electric VTOL jet” https://youtu.be/ ohig71bwRUE Passenger Drone California-based Joby Aviation (www.jobyaviation.com) is developing an electric S2 two-passenger aircraft which has 16 propellers – 12 for vertical lift, which fold back for forward flight and four mounted on the rear of the wings for forward propulsion. This company has received US$100 million in backing from Toyota and Intel. The aircraft is powered by lithium nickel cobalt manganese oxide batteries and will be capable of flying at 320km/h. The cost of the aircraft is expected to be US$200,000. Video: “30-sec TECH: the amazing Joby S2 tilting VTOL multi-rotor” https://youtu.be/AYhs4OFEgDw Lilium The German Lilium Jet drone (https://lilium.com) is a unique five-seat electric jet with a large 300km range and a 300km/h top speed. The first manned flight is envisaged to be in 2019 and it is expected consumer flights will start in 2025. The price for a typical airport to city centre flight such as from JFK Airport to Manhattan is anticipated to be less than a typical road taxi. siliconchip.com.au Passenger Drone operating autonomously – without pilot or passenger. Passenger Drone (http://passengerdrone.com) is a California-based company developing a two seat autonomous passenger drone, about the size of a small car. It can also be flown manually if desired and has eight motor positions with sixteen motors and sixteen propellers. When operated in autonomous mode the aircraft is monitored and guided via the company’s “Ground Control and Monitoring Center” using the 4G mobile telephone network. Some specifications of this vehicle are as follows: empty weight including batteries 240kg; maximum take-off weight 360kg, maximum payload 120kg; maximum thrust 560kg; maximum speed 60-70km/h; flight time 20-25 minutes (without range extender); dimensions 4.2m x 2.3m x 1.8m. No details on the range extender option have been released but it is assumed to be a small petrol or jet fuelpowered generator to recharge the batteries. A corporate promotional video can be seen at “Passenger Drone - The most advanced Manned Autonomous VTOL in the World !!!” https://youtu.be/IStmyk3R3Hc Also see “Passenger Drone First Manned Flight” https:// youtu.be/V3pi4HfQ0Gc Videos of the avionics system display can be seen at “PassengerDrone Avionics Demo Video 1” https://youtu.be/L43JZ3_CgAI; “PassengerDrone Avionics Demo Video 2” https://youtu.be/o4sZIWZFYKc and “PassengerDrone Avionics Demo Video 3” https://youtu. be/OvHhK-8LkQA Celebrating 30 Years May 2018  21 Sky-Hopper Terrafugia TF-X Sky-Hopper proof of flight concept. Sky-Hopper (http://tinagebel.wixsite.com/sky-hopper) is a Dutch company in an early start-up phase and currently only have a proof-of-flight concept. Their stated goal is to “develop an eco-friendly electric aircraft that is as safe, reliable, affordable and easy to use as a mainstream car”. The skeletal prototype has 16 motors and several flight controllers and it will be developed as autonomous vehicle. Video: “Sky-Hopper, first manned flight of electric multicopter” https://youtu.be/Omv_WdryGRc Volocopter SureFly The Workhorse Surefly (http://workhorse.com), based in Ohio, USA, is a drone under development that will offer both an autonomous mode and piloted mode. It has a petrol-powered generator based upon an automotive engine as well as batteries that drive eight motors at four locations with eight propellors. It seats two including the pilot and has a kerb weight of 500kg and a maximum takeoff weight of 682kg. The 4-cylinder 2-litre engine drives two 100kW generators, which also keep the batteries charged. They comprise a twin pack each of 7.5kWh which will enable a 5-minute flight time in the event of an engine or generator failure; otherwise the engine and generator will power the eight 3-phase AC motors. The top speed is about 113km/h with a service ceiling of 4000ft and an estimated range of 113km (70 miles). It has a ballistic parachute as well as redundancy in other critical systems. Videos: Static ground test, “Workhorse Surefly CES 2018 Test” https://youtu.be/8gIBujk7cAE; “SureFly Octocopter Behold The Future” https://youtu.be/hr8vksAI3jI The Workhorse Surefly. For storage, the rotor arms can be folded down to the side of the vehicle for storage. 22 Silicon Chip Terrafugia (www.terrafugia.com) is designing an autonomous mass market four-seat flying car. It will have folding wings with wingtip mounted propellers used for vertical flight which later fold back to allow The TF-X in driving mode. . . forward propulsion via a and flying mode. The wing-tip rear mounted ducted fan. propellers (used for vertical One megawatt (1341hp) take-off) are folded back during of power is available at forward flight and thrust comes launch via a gasoline hy- from a rear-mounted ducted fan. brid electric drive. Range is 800km, cruise speed is 320km/h and pricing will be in the range of high end luxury cars. Video: “The Terrafugia TF-X” https://youtu. be/wHJTZ7k0BXU Rendition of the Volocopter 2X in operation. The fully electric Volocopter 2X (www.volocopter.com/ en) is an 18-propeller 2-seat autonomous drone and has the backing of German car company Daimler. Each of the 18 motors delivers a power output of 3.9kW and it has a cruise speed of 100km/h. One of the advantages of this design is that it is relatively quiet. It is currently certified in Germany as a light sport multicopter and also as an ultralight. Its maximum take-off weight is 450kg (including a payload of 160kg) and its range is 27km at the optimal cruise speed of 70km/h. It has a ballistic parachute and redundancy in motors and propellers as well as other safety systems. Its nine separate battery packs can be fast-charged in under 40 minutes, or slow-charged in under two hours and the packs can also be quickly swapped if necessary. Videos: “Volocopter’s flying taxi takes off at CES” https:// youtu.be/tODIvUmH6cs and “Making of Dubai Public Demonstration Flight” https://youtu.be/ROJ76foyihs Celebrating 30 Years siliconchip.com.au XTI Aircraft TriFan 600 The Y6S in forward flight. The XTI TriFan 600. Once the plane reaches cruise speed, a door closes over the fuselage-mounted fan. XTI Aircraft Company, based in Colorado, USA (www. xtiaircraft.com) is designing the hybrid fuel and electric power TriFan 600, primarily aimed at the business market. As the name suggests this aircraft has three combined lifting and forward propulsion fans. The company claims this aircraft can be flown under current aviation regulations. The maximum cruise speed will be 556km/h and the range will be 2222km. Cruise altitude will be 29,000ft. There is space for a pilot and five passengers. Video: “XTI Aircraft Video 2017 with Slides.mp4” https://youtu. be/AOapUy1ee64 Y6S The 2-seat Y6S is being developed by Autonomous Flight Ltd (www.autonomousflight.com) in the UK. It is a tri-fan design with a tiltable pair of front rotors and wings for forward flight. It will have a maximum speed of 113km/h, 1500ft cruising altitude and a range of 130km. Manned test flights will start later this year. A remarkably inexpensive price of US$27,500 has been stated. Video: “‘Y6S’ drone will be the first in the world to carry passengers and could revolutionise city commutes” https://youtu.be/CtMPe24-WtA Uber flight demonstrations in 2020 As stated earlier, Uber are not building any aircraft of their own but are working in conjunction with other manufacturers. By 2020, Uber will need aircraft such as those mentioned in this article which are in advanced stages of development for its demonstrator flights; vertiport infrastructure to be built; permission to fly in the airspace of the flight corridors between vertiports and appropriate regulations to allow operation of the aircraft and certification of aircraft types. Initially aircraft will be piloted but they will eventually become autonomous. By the same year, Uber plan to have overcome three factors: (1) efficient flights, meaning the passenger drones can fit into existing airspace use; (2) acceptance of noise made by the vehicles and (3) acceptance by passengers that the vehicles are safe. Stop Press: Kitty Hawk’s “Cora” trialling across the pond . . . As this issue went to press, inforIt appears to be supported at mation came through that Google Cohigh level in the NZ government, Founder Larry Page’s company, Kitty with Prime Minister Jacinta Ardern Hawk, had received certification to helping to launch the Cora trial. trial their “Cora” self-flying taxi in The company’s aim is to have a New Zealand, under approval from the commercial flying taxi service in New Zealand Government Department operation before 2022. While it can of Civil Aviation. land and take off from a normal It had previously been certified as an runway, Cora doesn’t need to do so. experimental aircraft by the US FAA. Kitty Hawk’s “Cora” in flight And with a noise level far beThe fully-electric, two-seat Cora has low that of a helicopter, it will not an 11m wingspan, with twelve wing-mounted rotors to cause great disruption when it does pop down in builtenable vertical take-off and landing (VTOL) plus a sin- up areas – in places like building rooftops and car parks. gle larger pusher-prop to enable it to fly like a normal It is somewhat ironic that Kitty Hawk chose New Zeaaircraft once airborne. (see also photo page 14). land for this next phase of aviation: Kitty Hawk is of Capable of completely autonomous flight, Cora is said course the site celebrated as the first manned flight by to have a range of 100km and a top speed of 150km/h. the Wright Brothers on December 13 1903 – but many in New Zealand was chosen as a test site because of its New Zealand claim that local farmer Richard Pearse flew more relaxed regulations for such projects than, say, (and landed) a heavier-than-air machine on 31 March Australia. 1903, nine months earlier than the Wright Brothers. SC siliconchip.com.au Celebrating 30 Years May 2018  23 Swallow a Tiny Capsule to Check Your Gut! by ROSS TESTER Researchers at two Melbourne universities have come up with a new way to analyse the gases in your gut, which could provide answers to many medical mysteries. And that information can be transmitted instantly to a smartphone app via Bluetooth. W e’re all used to swallowing capsules containing medicine. They’re designed to stay “sealed” until they reach a part of the body where the medicine needs to go, then the capsule dissolves. For example, depending on the capsule skin composition and/or thickness, it might stay intact until it reaches the stomach, or the intestine, etc. More recently, medical specialists have been using another type of “capsule”, one definitely not designed to break down because it contains an ultra-miniature camera, along with a light source and a memory card. They’re intended to take photos every so often as they pass right through the system. After a period of up to few days, they’re recovered (use your own imag- ination!) and the photos are analysed (perhaps a poor choice of word, there) to find evidence of, say, ulcers, blockages, cancers and other nasties. After suitable treatment, the camera can be used over and over – they’re still too expensive to be throw-away items, though that is changing. Another type of capsule can be used to measure and analyse body temperature, respiration, blood and waste chemistry and so on. But until now, they’ve all suffered the same disadvantage – clinicians had to wait until the capsule emerged before the data could be read. Gas-sniffing capsule A group of researchers from Melbourne, led by Kourosh KalantarZadeh of RMIT University and Peter Gibson of Monash University has recently published a paper in “Nature Electronics” detailing a tiny ingestible electronic capsule which reports, via radio, the concentration of various gases in the human gut. When paired with a pocket-sized receiver and a mobile phone app, the pill reports conditions in real-time as it passes from the stomach to the colon. Such data could clarify the conditions of each section of the gut, what microbes are up to and which foods may cause problems in the system. Until now, collecting such data has been a challenge. Methods to bottle it involved cumbersome and invasive tubing and inconvenient whole-body calorimetry. Early human trials of the gas-smiffing capsule have already hinted that The electronics are packed into a capsule measuring just 26 x 9.8mm. It uses a receiver connected to a smartphone app. 24 Silicon Chip Celebrating 30 Years siliconchip.com.au At 26 x 9.8mm, it’s larger than typical medicine capsules – but still well within the “comfort zone” of most people. the pill can provide new information about intestinal wind patterns and gaseous turbulence from different foods. The capsule is made according to the “000” standard: 26mm in length, with a 9.8mm external diameter. It includes sensors for CO2, H2 and O2 gases that occur in various aerobic and anaerobic conditions, a temperature sensor, a microcontroller and a 433MHz transmission system plus the button cells which power it. One end of the capsule contains a gas-permeable membrane that allows for fast diffusion of gut gases. A non-transparent, polyethylene shell houses the internal electronic components. The polymer shell is machined in two pieces, sealed together using a bio-compatible adhesive. Interestingly, the capsule was made non-transparent, as volunteers showed hesitation in swallowing capsules with transparent covers, where they could see the electronic circuits inside. A combination of thermal conductivity and semiconducting sensors, with an extraction algorithm, generate the gas profiles and determine the gas concentration in both aerobic and anaerobic segments of the gut. siliconchip.com.au The gas-sensing capsule uses a separate receiver which can be linked by Bluetooth to a smartphone or computer. It is not yet in commercial production. Celebrating 30 Years May 2018  25 Inside the gut gas measuring capsule prototype. It is made from non-transparent material because volunteers showed a reluctance to swallow anything where they could see electronics inside! Capsule accuracy for measuring H2 and O2 was found to be better than 0.2%, and for CO2 it was 1%. The key technological differences between human gas sensing capsules and those used for animal trials on pigs is the implementation of an advanced gas detection algorithm. This uses heat modulation to distinguish between H2 and CO2 with much higher accuracy. An oxygen sensor is included to locate the capsule in different gut segments, along with a temperature sensor to measure the core body temperature and sense the excretion of the capsule out of the body of volunteers (when the temperature drops below 35°C). The capsules also incorporate membranes with embedded nanomaterials that allow for the fast diffusion of dissolved gases, while efficiently blocking liquid. Following trials on pigs, the researchers tested the capsule in six healthy people. For the first, researchers monitored the pill’s intestinal trek using ultrasound and linked locations with gas profiles. Overall, it took 20 hours to get from one end to the other, spending 4.5 hours in the stomach, 2.5 hours in the small intestine, and 13 hours cruising through the colon. In that time, the pill took continuous gas measurements, revealing potentially useful information in addition to gut position. For instance, CO2 and H2 levels peaked in the early hours of its time in the colon while O2 levels crashed throughout this stretch of the trip. That correlates with how anaerobic bacteria (those that live without oxygen) inhabit the colon and ferment undigested food into short-chain fatty acids that play significant roles in our health and metabolism. In the next human trial, the researchers had one person swallow the pill twice. The first time, he ate a very highfibre diet (50 grams per day) for two days prior to swallowing the pill. Two weeks later, he swallowed another pill after eating a low-fibre diet (15 grams per day) for two days. In the high-fibre test, the man passed the pill in about 23 26 Silicon Chip One end of the capsule has a semi-permeable membrane to allow gases to enter and be analysed; however liquids are prevented from entering hours. But he was not happy about it. The super dose of fibre caused abdominal pain. In its four hours in the colon, the pill recorded elevated levels of O2, which could mess up anaerobes. Indeed, an analysis of fecal bacteria during this phase showed a shift toward species associated with poor gut health. There were also problems in the low-fibre scenario. The pill took a little more than three days to work its way out. It spent 13 hours in the stomach, 5.5 hours in the small intestines, and a huge 54 hours in the colon. In fact, about 36 hours after taking the pill, the man was given a high dose of fibre to try to move things along. Prior to that fibre intervention, H2 gas levels in the colon had plummeted, suggesting a drop off in fermentation. It picked back up 12 hours after the fibre treatment. Last, the researchers recruited four more healthy patients to pass the pill. Two ate a high-fibre diet (though not quite as high as the first trial), while the remaining two ate a low fibre diet. This showed similar patterns seen in the earlier trials. In an accompanying editorial, mechanical engineer Benjamin Terry of the University of Nebraska-Lincoln concluded that the capsules “have remarkable potential to help us understand the functional aspects of the gut microbiome, its response to dietary changes, and its impact on health.” “It might not be too long before a routine healthcare visit involves a check of your vital signs and a request to swallow a tiny electronic monitoring device,” he added. SC Acknowledgement: Information based on Nature Electronics, Vol 1, January 2018 Celebrating 30 Years siliconchip.com.au Introducing: Part 1: by Duraid Madina and Tim Blythman Our all-new 800W Uninterruptible Power Supply (+) We’ll say it right up front: this will not be a cheap project to build. But if you do build it, we believe you will end up with a UPS that is a better performer than anything else on the market at even two or three times the price. And even then (unlike most commercial units), the design is quite flexible if you wish to expand its already exceptional capabilities. So if you’re in the market for a UPS (and who isn’t, with the quality [?!] of mains power these days?) you will go a long way to find better value than this. 28 Silicon Chip Celebrating 30 Years siliconchip.com.au We searched high and low for a high quality, low-cost case to house the UPS but proved the two terms are mutually exclusive! However, this case is ideal for the job, being pre-drilled and slotted for excellent ventilation. I f you aren’t familiar with the concept of an Uninterruptible Power Supply (UPS), it provides a back-up for the mains supply to an important piece of equipment (such as a corporate server or other mission-critical system), so that it won’t shut down during blackouts. The typical use for a UPS is to give plenty of time – a few minutes to perhaps an hour or so – to save work before it’s lost – or in large organisations, long enough for a mains generator to be fired up and take over. Some UPSes are designed to give hours, and occasionally days or even more, of power to enable an enterprise to keep working as if the blackout didn’t exist. But these are VERY expensive systems, relying on a large (and even more expensive!) battery bank to keep them supplied. A UPS is now standard equipment for computer systems in commerce or industry but they are becoming more popular for home or small business. Laptop computers don’t need a UPS as their internal battery does the same job. But the printer or large monitor connected to a laptop will obviously cease working during a blackout. Powered via a UPS, work can continue. Disaster power A UPS like the one we are describing could be used in a lot more situations. ifications Features & spnsec plug For example, perhaps with a few modifications, it could power all your computers, your modem and all your entertainment equipment in the event that you experience a blackout for many hours. It could keep some or most lights working, allowing an orderly (and safe) exit from deep within otherwise-dark office blocks (sorry, you’ll have to use the stairs as the lifts won’t be working!). Or if you have a much longer blackout, it could perhaps run your refrigerator for several days during a long power outage which could occur after a bush fire, a big storm or a flood. That would mean you would not lose any food due to spoilage. And of course, it means that you can keep your mobile phones and notebooks and tablets fully charged so you can stay in contact with the outside world. Just how long you could run a refrigerator would depend on the power rating of its compressor and the temperature setting. Or perhaps it could allow you to also run a gas heater or oven which requires 230VAC at low power to run the igniter and the control electronics. So a UPS is an important accessory for a variety of reasons in both business and in the home. But why would you want to build this one instead of buying a commercial unit? Wouldn’t that be cheaper? Not in this case. • Power input: 10A mai s • Output socket: four switched GPO 800W er: pow ut • Continuous outp • Peak output power: 1200W • Battery capacity: 588Wh • Inverter type: pure sinewave , 4h <at> 135W, 5h <at> 110W , 1h <at> 500W, 2h <at> 260W, 3h <at> 175W • Approximate runtime: 35m <at> 800W <40ms (two mains cycles) • Response time after mains failure: cycle) g back to mains: ~20ms (one mains • Power interruption when switchin ustable) • Brownout threshold: 200VAC (adj AC (adjustable) 260V d: shol thre out cut• Over-voltage y 5 hours from flat • Battery charging time: approximatel • Quiescent current: 19W battery ing off inverter, battery charging, low • Status indicators: mains good, runn UPS software) rce ng interface (compatible with open-sou • PC interface: USB serial monitori s are nearly flat erie batt n kout; continuous tone sounded whe • Audible alert: beeps during a blac e harg battery cut-out with zero battery disc • Protection: 10A mains fuse, lowe) harg disc es (full • Battery longevity: at least 1500 cycl siliconchip.com.au Celebrating 30 Years LiFePO4 batteries This UPS has high capacity, very safe LiFePO4 batteries which can be deep discharged without damage – something that can easily occur in a long blackout. Plus it uses an Arduino to monitor and control it. And while this UPS is conservatively rated at 800W, it actually employs a 24V DC to 240VAC true sinewave inverter which is rated to deliver 1200W or up to 2400W surge (useful to start motors or run a microwave oven for a short period). May 2018  29 To a large degree, our 800W UPS is based on existing modules which we connect together in an appropriate manner. The photos above show two of the main components: at left is the pair of Drypower 12V, 23Ah batteries which we connected in series for 24V DC, while at right is the Giandel pure sinewave inverter, which is used to power equipment from the batteries when mains power goes down. The conservative limitation to 800W is determined by the batteries but you could possibly run at the full 1200W continuous output of the inverter for short periods without any problems. So let’s talk about the batteries. Most commercial UPSes come with sealed lead-acid (SLA) batteries. The problem with SLA batteries, apart from being very heavy and bulky, is that they are easily damaged or even destroyed if you allow them to discharge below 11V – and that can easily occur in a typical UPS. We speak from experience – and we’ve heard that our experience is not uncommon. We used to have a UPS on the SILICON CHIP office server, because blackouts are fairly common in the northern beaches of Sydney (we’ve had quite a few in the last decade). But the one we were using failed because its lead-acid battery was deeply discharged by a long blackout over a weekend. We replaced it but only a few months later, it went bad again after yet another extended blackout so we just gave up and removed it. As it uses Lithium iron-phosphate batteries our new UPS design is a lot more robust than that commercial unit so it won’t fail in the same manner. They will survive hundreds, if not thousands of blackouts (perish the thought!). Why did we use lithium iron-phosphate batteries instead of lithium-ion or lithium-polymer? In a word: safety! They are much less likely to catch fire! While a fire is unlikely with a Lithium-ion or Lithiumpolymer battery, it isn’t unheard of – and the sudden failure of a battery of this size could be very dramatic. And since this is a DIY project, we can’t rule out mistakes being made during construction. So we wanted the safest possible option. While some UPSes are able to guarantee no loss of power at all during a blackout, most operate by feeding the incoming mains directly to the load, as long as the mains voltage is OK, but then switching over to inverter operation if the mains waveform goes bad or disappears entirely. Normally this switching is done with a relay or relays and so there is a very brief switch-over period where the load gets no power. But most devices will not be affected by this. For example, 30 Silicon Chip all desktop and server computers these days run from a switchmode power supply, which rectifies the mains to charge a large capacitor or capacitors to around 350V, which then power the switching circuitry. It takes some time for the filter capacitor bank to discharge to the point where the output voltages are affected. So as long as the switch-over time is short, the supply and thus computer will operate uninterrupted. Similarly, a motor-driven appliance such as a refrigerator will have some inertia and the loss of mains for a fraction of a second will likely not affect its normal operation. And most low-cost UPSes do not have a sinewave output when running off the battery. They usually have a “modified square wave” or even a square wave output, since it’s easier to produce and the switchmode supply in a computer will run just fine off a square wave (or even high-voltage DC, for that matter). Our design uses a “proper” sinewave inverter so is usable with a much wider range of devices. Want more grunt? Now before we go on to discuss the design philosophy behind this project, we should point out that many aspects can be modified or greatly expanded to suit your particular application. Want higher power output or much longer run for more extended blackouts? No problem, just substitute a bigger inverter and a bigger (much bigger) battery bank. Want to operate from solar panels to use it for off-grid power? Again, no problem (we will discuss these various possibilities in a later article). 12V or 24V operation? Our initial design brief for this project was to have a rated output of at least 500W. So what would be the right battery voltage? To deliver 500W, a 12V inverter would require an input current of over 40A, which would be harsh on the battery and inverter and require very thick cables. So we started looking for inverters and batteries in the range of 24-48V. It quickly became apparent that 24V batteries and in- Celebrating 30 Years siliconchip.com.au These three photos show some of the other modules we used – while not so fundamental as those shown opposite, they’re important nevertheless! At left is the Victron Battery Balancer, required because we used (for economy reasons) two 12V DC batteries instead of a single 24V DC. Even when adding in the cost of the balancer, two batteries are a much better proposition. Centre is the 12V switchmode power supply used to power the Arduino, while at right is the 24V, 5A mains charger for the batteries. verters were less common and more expensive than 12V types, and 36V/48V batteries and inverters even more so. Two 12V batteries (24V) seemed like the best compromise. We decided to use two Drypower 23Ah 12.8V LiFePO4 batteries in series, which were supplied by Master Instruments (Cat No IFM12-230E2). We considered using a 25.6V LiFePO4 battery but a similar capacity model cost significantly more than twice as much as the two 12V batteries. Using two batteries meant that we would need a charge balancer, to ensure that the two battery voltages are kept similar – but even when we include the cost of the balancer, the two 12V batteries are still significantly cheaper. This battery bank then drives a Giandel 24V/1.2kW pure sinewave inverter which we bought from the Giandel Australia website for $138 plus postage (Cat No PS1200DAR/24). This is excellent value. It comes with a pair of battery cables with eyelet lugs and also a remote control that attaches to the unit using telephone-style flat cabling. We hooked this up to an Arduino, which is then able to monitor the inverter status and switch it on and off. This inverter has a typical efficiency figure of around 90% and it includes a cooling fan and substantial heatsinks so it can deal with the approximately 100W of dissipation at full power. As already noted, the inverter is rated at 1.2kW (2.4kW peak) but the specified batteries can’t supply sufficient current to allow such a high power delivery. They are rated at 35A continuous which works out to around 800W at the output when you take inverter losses into account. That’s still handily above the target we had set ourselves for this project. The 588Wh nominal capacity of the battery bank is specified at a 5-hour discharge rate, which is what our specification of five hours battery life for a 110W load is based on. Curves are not provided to show how capacity diminishes at higher discharge rates but lithium-chemistry batteries normally have a low internal impedance so we believe our moderate de-rating of capacity with increasing load should be approximately right. We also considered designing a “line interactive” or “onsiliconchip.com.au line” UPS, where the load is always powered by the inverter and the charger provides the DC current to operate it when mains is available. This avoids the need to switch the load between mains and the inverter and also, poor mains power quality (ie, distorted waveform) is not transferred through to the load. However, that approach would require a charger capable of around 30A which would be large and quite expensive and it would also be less efficient due to the constant conversion from 230VAC to low-voltage, high-current DC and back to 230VAC. Hence, we decided to design a “standby UPS” instead, as presented here. By the way, the inverter output is specified as 240VAC; somewhat higher than 230VAC. So when the UPS switches the load to the inverter, the supply voltage will typically increase slightly. But this is still well within the Australian mains specification of 230VAC+10%,-6% so it should not present any problems. In many parts of Australia, the mains supply is typically above 240VAC anyway. Charging and mains switching Having decided on the two most important components of our UPS system, ie, the batteries and inverter, there were still other important details to be determined. These included how the batteries are charged once mains returns after the inverter has been operating (and indeed, are kept charged long-term), how we determine when to switch the output sockets from mains to the inverter output and how that switching is performed. Charging is quite simple; we purchased a 5A mains charger designed for LiFePO4 batteries and it’s permanently wired to the incoming mains socket so that whenever mains is present, it’s charging the batteries. Like other Lithiumbased rechargeable batteries, LiFePO4 use a constant-current/constant-voltage (CC/CV) charging scheme. So the charger will deliver 5A to the batteries until the voltage across them reaches 29.2V (14.6V per battery or 3.65V per cell). It will then hold the terminal voltage at 29.2V as the charge current decreases until it reaches a low level, at which point the batteries are considered charged. Celebrating 30 Years May 2018  31 Fig.1: block diagram of the SILICON CHIP 800W UPS. Much of the “magic” is in the Arduino software and shield which will be described in detail next month, along with full circuit and construction details. However, the inverter needs to be kept on constantly so that it’s always ready to take over, should the mains supply cut out. Therefore, it draws several watts from the batteries constantly and the battery voltage will never quite reach 29.2V (it sits at around 29.15V). This should not pose a problem; they are effectively float charged. Enter the Arduino controller We’re using an Arduino Uno to monitor the mains voltage, via a small mains transformer. The primary of this transformer is connected across the incoming mains supply and the voltage from the secondary is divided down and fed to one of the Arduino’s analog inputs via a biasing network which keeps the analog pin voltage in the 0-5V range. The Arduino is constantly sampling the mains waveform and if it detects an under-voltage or over-voltage condition, or a significant deviation from a sinewave, it immediately switches the output over to the inverter. It only switches the output back to mains when it determines that the mains waveform and voltage are stable and have been for a few seconds. The switching is accomplished by using three DPDT relays which are controlled via a relay driver shield and the Arduino. Both the Active and Neutral wires are switched. Relay logic for safe switching Now refer to Fig.1 which is the block diagram for our high power UPS. It shows how the three relays are arranged. RLY2 is the mains changeover relay and it is arranged so that there is no possible way that the output of the inverter could be connected to the mains. RLY1 is used to connect mains to RLY2 (and on to the output) while RLY3 is used to connect the inverter to RLY2 (and on to the output). Why do we need three relays when it might seem that only one or two relays might be able to switch the load between incoming mains or the output from the inverter? 32 Silicon Chip The reason for using three relays in this manner is that there is no way to precisely lock the phase of the inverter output waveform to the incoming mains waveform. While both are nominally at 50Hz, they could be in phase, 180° out of phase or anywhere in between. The phase difference between them is likely to slowly drift over time, due to slight differences in the two frequencies. So it’s entirely possible that the momentary mains voltage could be +350V while the momentary inverter output voltage could be -350V. A single 250VAC-rated relay is not designed to handle 700V DC between two terminals on the same pole. There could be an insulation breakdown and/ or major contact arcing and this could destroy the inverter. By having an extra relay between each AC source and ensuring that both RLY1 and RLY3 are off at the time when RLY2 is switching, we avoid applying any more than the normal mains peak voltage across a single relay. When the unit is powered off, all the relays are off and so the output sockets are not connected to anything, except for the Earth pins, which are connected to mains Earth and also the unit’s chassis. When the unit powers on, it checks the mains voltage and waveform and assuming they are good, it switches RLY1 on. This connects mains to the output sockets and load(s). If mains goes bad or disappears altogether, the unit immediately switches RLY1 off. Then, after a short delay, it switches RLY2 and RLY3 on. So the load is briefly disconnected from mains altogether (for around 10ms), then connected to the output of the inverter, which is already running. When mains power comes good again, RLY3 is switched off and after a brief delay, RLY2 is switched off and RLY1 switched on. Again, there is a brief period where the outputs are not connected to either mains or the inverter. This ensures a safe change-over. The unit is also designed to perform a sequenced change- Celebrating 30 Years siliconchip.com.au over in this manner should its own power supply fail or when it is purposefully switched off, using a switch mounted on the rear panel. This allows you to, for example, disconnect the UPS from mains so you can move it to a different location without it discharging its batteries. Indicator LEDs We’ve fitted three indicator LEDs on the front panel, so you can tell what is happening. The green LED at far left is on continuously while the output is connected to mains and flashes if mains is not present or not clean. The yellow LED in the middle lights continuously when the output is being fed from the inverter. While the output is running off mains (and the green LED is solidly lit), the yellow LED will also flash to indicate that if there is a problem with the inverter, such as if the Arduino detects it is not running when it should be. The red LED at right starts flashing when the battery voltage drops. The flashes become faster as the batteries discharge until it is on continuously when the remaining charge is around 10%. The unit is also fitted with a piezo buzzer which beeps intermittently while the output is running off the inverter and it changes to a continuous tone when the batteries are nearly flat. If the battery voltage drops below about 21V, the Arduino switches the inverter and relays off. It also shuts itself down. The drain on the battery becomes almost zero. While these batteries do incorporate their own over-discharge protection, we feel it’s still good practice to minimise the load at low voltages. The unit is able to “bootstrap” itself and power back up when mains returns and this procedure is described below. It can also be manually switched off and powered back on later if necessary. Powering itself We need a source of 12V DC to run the three relays and Parts list – 800W Uninterruptible Power Supply (UPS) 1 vented 3U rack-mount case, 559mm deep [Bud Industries RM-14222+TBC-14253+TBC-14263] [Digi-Key 377-1392-ND; 377-1396-ND; 377-1397-ND] 2 Drypower IFM12-230E2 12.8V 23Ah Lithium Iron Phosphate batteries [Master Instruments] 1 Victron Energy 2x12V Battery Balancer [Master Instruments – www.master-instruments.com.au] 1 Giandel PS-1200DAR/24V Pure Sinewave Inverter with cables [www.giandel.com.au] 1 5-7A LiFePO4 charger [Master Instruments, AliExpress] 1 DETA 6224B Silver Four Outlet Power Point or similar [Bunnings 4430423] 3 12V DC coil, 10A 240VAC cradle relays [Jaycar SY4065] 3 DPDT chassis-mount relay cradles [Jaycar SY4064] 1 12V 1.3A enclosed switchmode power supply [Jaycar MP3296] 1 12.6V CT 7VA transformer [Jaycar MM2013] 4 screw-on equipment feet [Jaycar HP0832] 1 3AG safety fuseholder [Jaycar SZ2025] 1 3AG 10A 250VAC fuse 1 connector to suit battery charger (see text) 1 Arduino Uno or compatible 1 Freetronics 8-Channel Relay Driver Shield [Core Electronics Cat CE04549] 1 Arduino control shield (details next month) 1 green chassis-mount LED with chrome bezel [Altronics Z0265, Jaycar SL2645] 1 yellow chassis-mount LED with chrome bezel [Altronics Z0224] with 1kW series resistor 1 red chassis-mount LED with chrome bezel [Altronics Z0264, Jaycar SL2644] 3 1kΩ 0.25W resistors 1 NO momentary pushbutton switch Fasteners 8 M5 x 90-100mm bolts or machine screws 12 M5 x 10mm machine screws 28 M5 nuts 6 M4 x 10mm machine screws 6 M4 nuts 6 M4 shakeproof washers siliconchip.com.au 4 M3 x 32mm machine screws 6 M3 x 15mm machine screws 28 M3 x 10mm machine screws 1 M3 x 6mm machine screw 34 M3 flat washers 34 M3 nuts 4 25mm-long 3mm ID untapped spacers 8 15mm-long 3mm tapped Nylon spacers 4 M3 x 25mm Nylon machine screws Cables, wires and insulation 1 2-wire mains cable with figure-8 plug* 2 3-wire mains cables with moulded 10A plugs* 1 100mm length of 40A+ rated wire 1 2m length red medium duty hookup wire 1 2m length black medium duty hookup wire 1 2m length yellow medium duty hookup wire 1 1m length white light duty hookup wire 1 1m length yellow light duty hookup wire 1 1m length red light duty hookup wire 1 1m length black light duty hookup wire 1 cable gland to suit 3-wire mains cable [eg, Jaycar HP0732] 1 150mm length 6mm diameter heatshrink tubing 1 50mm length 10mm diameter heatshrink tubing 1 50mm length 16mm diameter heatshrink tubing 1 50mm length 20mm diameter heatshrink tubing * Can be cut from spare power cables, extension cords or similar Other hardware 2 Carinya MABF2101 Make-a-Bracket flat plates, 100 x 200 x 1mm [Bunnings 3975858] 6 Carinya MA0003 25 x 25 x 40 x 1mm angle brackets [Bunnings 3975955] 5 adhesive wire clamps 6 small P-clamps 10 4mm crimp eyelets 2 red 6.3mm insulated crimp spade lugs (for the power switch) 30 small black cable ties Celebrating 30 Years May 2018  33 5V DC for the Arduino. While we could simply run both off one of the batteries, this would not be ideal as it would present an unbalanced load to the overall battery pack. It would also place a load on the batteries when they are nearly flat. To avoid this problem, we have fitted a small mains switchmode power supply inside the case and wired this in parallel with the output sockets. So when mains power is present, this powers the Arduino and relays and when running off the inverter, the inverter powers this switchmode converter instead. When the output is switched off, this totally disconnects the Arduino and relay power supply. So during a short blackout, the Arduino will be powered by the inverter and will simply switch back to mains power once it’s restored. But if there’s a long blackout and it powers down, when mains power comes back, the output is disconnected. So how does it start back up and switch on the inverter (in case it’s needed later) and RLY1? The answer is that we’ve added a small relay on the Arduino shield which normally connects the secondary of the mains-sensing transformer to a diode. Current flows through that diode and into the 12V supply bypass capacitors, providing an initial source of power for the module. (Note that this fourth relay is not shown in the diagram of Fig.1 but it is on the control shield). Once RLY1 is on, that relay is also energised, disconnecting the transformer from the diode. This means that the transformer is not being loaded, so its output is once again a good proxy for the mains voltage. In fact, this relay is briefly energised before RLY1, giving the Arduino the chance to verify that the mains waveform is clean before the load is connected. The inverter can not necessarily be used at this stage because the batteries are probably flat. But they will start charging as soon as mains returns and will soon be ready for use. Switching it on without a mains source We have considered that this unit may also be useful as a source of emergency power. For example, you could use it to back up the power to your fridge so that the contents don’t go off during a blackout but you might later decide to unplug your fridge and move it to power some other equipment such as lights, a TV and so on. In this case, during an extended blackout, you may need to switch the UPS off and then later switch it back on but unless you have a generator, you won’t have a source of 230VAC to “bootstrap” it. So we have added a momentary pushbutton switch to the front panel which briefly connects the nominally 24V battery bank to the input of a 12V regulator which then feeds the Arduino and relays. Holding this button for a few seconds gives the unit enough time to switch the inverter on and power the load from the inverter. You can then release the button and the unit will continue to run until it is switched off or the battery goes flat. We’ve also fitted a rocker switch on the rear panel which allows you to shut down the internal switchmode supply that powers the Arduino and relays. This means you can unplug the UPS from the mains, flick the switch and it will gracefully shut down. The batteries will remain charged and it can be powered back on later by flicking the switch again and plugging it 34 Silicon Chip back into mains, or alternatively, using the pushbutton method described above. Inverter control The inverter has a “soft start” feature which ramps its output voltage up over a few seconds when it’s switched on. This would be handy in many situations but is unwanted in a UPS because you need to be able to switch over to inverter power in a very short time. But there’s also a delay of around 0.5-1 second between pressing the on/off button and the inverter powering up, so clearly we have no choice but to run it constantly, ready to switch over. We do need to ensure it’s shut down when the batteries go flat. While it has an internal under-voltage lockout that’s actually very close to the minimum specified voltage for these batteries (20V total, 10V per battery), it isn’t that accurate. We should ideally switch the inverter off before the battery voltage drops that low. And we also need to ensure it’s switched on when the unit is starting up. The inverter we’ve specified is supplied with a small “remote control” box that has a single LED and a pushbutton switch. It’s attached to the inverter via a 4-wire telephone style flat cable. The same controls (LED and button) are provided on the inverter itself. The LED and button share one common connection, with the LED wired between the common terminal and a second wire. A small current flows through this loop when the inverter is powered. The button briefly connects this common wire to a third wire. If the button is held down for around half a second, the inverter starts up or shuts down. We’ve interfaced the inverter with the Arduino using two optocouplers. The Arduino drives one to simulate a button press, shorting the two wires to switch power. The second optocoupler LED is connected in place of the LED on the remote control box and pulls an Arduino pin low when the inverter is operating. A software routine on the Arduino compares the inverter status to the desired status and “presses” the button when necessary to turn it on or off. This isolation allows the Arduino ground to be connected to the battery negative terminal and it can then monitor the battery voltage using a simple resistive divider (100Ω/10kΩ) to one of its analog pins, allowing it to determine the charge state, both for display purposes and to decide when to shut the inverter down. Choosing a case Commercial UPSes of this size are often housed in rackmounting cases. This is convenient since they can then mounted in a server rack, along with the servers they are protecting. But rack-mount cases can also be fitted with feet and used in a standalone manner. We spent some time trying to find a low-cost metal box to build the UPS into but in the end, couldn’t find a good solution. It was also difficult to find a rack-mount case which would fit all the required hardware (due to the required depth of at least 450mm) but we eventually located one at a reasonable price. It’s three rack units tall (3RU = 133.5mm), the standard 19-inch width and made from aluminium by a US company called Bud Industries. It is supplied as a kit which includes the front, back, sides and hardware while the top, bottom, rack rails and handles are available separately. Celebrating 30 Years siliconchip.com.au The completed UPS (sans lid!) showing the internal layout. The two batteries are clamped under the punched metal plates at the right while the pure sinewave inverter is on the left. We’ll show the layout and construction detail next month. While you might think the silver Deta four-outlet power point on the rear panel seems like gilding the lily somewhat, they’re only a couple of dollars dearer than a boring old white one . . . and it really looks the part, matching the aluminium case! We haven’t bothered fitting the rack rails or handles to our prototype but they aren’t expensive or difficult to obtain. Luckily, availability is good; the case is available from US electronics retailers Digi-Key and Mouser and they both offer free express international delivery if you order the required items together (see parts list). We also fitted it with instrument feet from Jaycar as there are quite a few exposed screw heads on the underside. We’ve opted for a solid base and vented lid as the inverter and batteries can get quite warm during operation. The side panels have many drilled holes which provides decent ventilation and also makes fitting cable clamps quite easy. One of the good aspects of using a natural aluminium case such as this one is that it’s quite easy to Earth the entire chassis. This is critical for safety; if a mains wire comes loose inside and contacts the case, it will cause the fuse to blow. Otherwise, the case could become live which would be very dangerous. We have Earthed the rear and bottom panels separately, with the other panels electrically connected via common screws and also direct panel contact. Sourcing a battery charger Master Instruments can supply two suitable battery chargers, the Fuyuan FY2902000 (2A) or FY2907000 (7A). The 2A version has a standard 2.1mm inner diameter DC plug so you just need a matching socket while the 7A version uses an XLR plug; suitable sockets are readily available (eg, from Jaycar). Other chargers are available but they may come with a different plug and so you will need to find a matching socket. Or alternatively, cut the plug off and crimp some eyelet terminals onto the bare wires for direct connection to the battery terminals. Regardless of which charger you use, it must be designed specifically for LiFePO4 batteries and have a charge termination voltage of 29.2V. While these batteries are quite robust, they may not last very long if regularly charged to the wrong voltage. Control algorithm The most critical part of the Arduino software is the “mains-good” detection algorithm. The transformer secondary voltage, which is a proxy for the mains voltage, is siliconchip.com.au sampled 1000 times per second, ie, 20 times per cycle for a 50Hz supply. These samples go into a 32-sample buffer, so there is just over one full cycle worth in the buffer at all times. To convert this into a meaningful number, we calculate both a root-mean-squared (RMS) average and measure the peak-to-peak voltage. For a sinusoidal signal, the RMS value is exactly equal to the peak-to-peak value divided by 2 x √2, or approximately 2.8284. The peak-to-peak calculation is usually quicker to pick up excessively high mains voltage while the RMS calculation is faster at detecting a brownout or blackout, the latter often being detected within a quarter of a cycle (5ms). The RMS calculation starts by taking the average of the ADC readings to establish a ‘mean’ that we can reference the values to. We then add the squares of the differences between our values and the mean. Then we divide the sum by the number of samples – this is our mean of squares, and its square root is the RMS value, after which the scaling factor is applied to get our actual RMS value in volts. As soon as the mains voltage reading is found to be outof-bounds, the relay switching sequence begins, to transfer the load(s) over to the inverter. The unit will not switch the load back to mains operation unless the mains voltage stays within a tighter set of bounds for several seconds. This increase in the strictness acts as a kind of hysteresis, preventing the unit from switching back and forth if the mains voltage is on the cusp of being too high or too low. The unit will simply switch to the inverter in this case and won’t switch back until the mains voltage goes back to a more normal value. The transformer introduces quite a bit of error into the voltage measurements made by the Arduino (and to a lesser extent, resistor and regulator tolerances). We will provide a calibration process to allow you to set the thresholds more accurately in a later article. Construction There will be detailed construction and wiring details in the second article in this series, to be published in the June issue. That article will also have details on the control shield circuitry, including assembly instructions required to build the driver shield. SC Celebrating 30 Years May 2018  35 Turn things on or off if they’re too fast ... or too slow... etc! Deluxe Frequency Switch by John Clarke Switch devices on or off according to the frequency of just about any sensor signal up to 10kHz. So you can switch something on or off if a sensor signal frequency goes above or drops below a figure which you can easily set. Features • Energises a relay when a signal goes above a preset frequency and keeps it on until the signal drops below a second preset frequency • Adjustable hysteresis can be used instead of setting upper and lower frequencies • Switching frequency can be from 1Hz up to 10kHz. • Adjustable switching delay • Two sets of 5A changeover relay contacts • Easy pushbutton set-up • Can be set up on the bench or in situ • Threshold can be set using a signal generator or frequency meter (eg, DMM) • On-board signal frequency range indicators • Power, threshold and relay-on LED indicators T feathering blades on suitably and much more. here are many applications for equipped turbines. It is also much easier to set up a device of this type. Just some Of course, there are countless oth- than our previous Frequency Switch of the things we thought of “off er uses – you’re probably thinking of in June 2007 (siliconchip.com.au/ the top of our heads” include: • Cutting power (or fuel) to a motor others that suit your particular appli- Article/2261) and the main reason for cation. that is that it is based on a PIC16F88 if it exceeds a certain speed As long as it has, or can be fitted rather than the LM2917 frequency to • Switching a fan on at low vehicle speeds to provide improved cool- with a sensor, to provide a frequency voltage converter. (That first Frequenwhich varies with speed, temperature, cy Switch was quite tricky to set up!) ing. • Giving a warning to change gears flow etc, you can use our new Deluxe when the engine RPM is approach- Frequency Switch. It can do all of this Setting the two frequencies You need to set up two ing the tacho red line. frequencies, not one as you • Switching from long might have thought. to short intake run- Specifications Why do you need two ners at a particular en- Supply voltage: 10-16V frequencies? We need to set gine RPM to optimise Supply current: 20mA with relay off; 60mA with relay on two frequencies because if power delivery. Signal frequency range: 1Hz to 10kHz the signal from your cho• Switching off a pump sen sensor varies by even if a flow meter records Signal amplitude: >1.4V peak-to-peak a small amount at close to the water flow is out- Threshold setting resolution: 20Hz at 10kHz; 1Hz at 2.27kHz; 0.2Hz at the switching threshold, side a specific range. 1kHz; 0.002Hz at 100Hz. the relay would be con• Switching on an alarm Hysteresis: 0-50% stantly chattering on and if wind speed exceeds Switching delay: signal period plus 0-500ms off – not good at all. So a certain threshold. Signal frequency bands: <10Hz, 10-100Hz, 100Hz-1kHz, 1-10kHz we set an upper frequency • Applying a brake or 36 Silicon Chip Celebrating 30 Years siliconchip.com.au threshold above which the sensor signal must rise before the relay switches on. And then we set a lower frequency threshold below which the sensor signal must drop before the relay is switched off. You can set the two frequencies close together or far apart. Setting the frequencies is dead-easy and there are several methods for doing it. The first method is to feed in your wanted set frequency, say 500Hz, from an oscillator or other source to the sensor input and then press switch S2. Then feed in the wanted lower frequency, say 400Hz, and then press S1. The second method is arguably even easier. You just set one frequency, say 500Hz, and then use an on-board trimpot (VR1) to set the hysteresis. This will effectively set the lower frequency (down to a minimum of 250Hz in this example) and you can tweak it at the time of installation. If you don’t have an oscillator you could use the real signal that you intend controlling the unit with, so long as you can hold steady it at the required frequency/frequencies for long enough to press the switch(es). Alternatively, if that’s too difficult, you actually can get the microcontroller to generate the wanted frequencies. This second method is more involved than the first and we will describe the procedure later in this article. Detection time and delay You can also configure the unit with a switching delay which is adjusted with trimpot VR2 and can be set between zero and 500ms (ie, half a second). This ensures that if the signal frequency only momentarily crosses one of the thresholds, it will not cause the relay to switch. The input signal frequency must remain at or beyond the threshold for the entire delay time before any relay switching will occur. Each time the frequency crosses the threshold, the delay time starts again. Fig.1: This block diagram describes how the microcontroller measures frequency. If you prefer switching to happen immediately then set the response time to zero (ie, VR2 fully anticlockwise). LED indicators To help in the set-up and installation procedures, we have included indicator LEDs to show when an input signal is present and its frequency range: • LED2 lights for frequencies between 0.5Hz and 10Hz; • LED3 lights between 10Hz and 100Hz; • LED4 between 100Hz and 1kHz; • LED5 for frequencies between 1kHz and 10kHz and all four LEDs light if the frequency is above 10kHz. Other LEDs show when the set threshold frequency is reached and whether the relay is on or off. Relay options The relay is a double-pole changeover (double throw) type (ie, DPDT) which can switch one or two loads, each up to 5A/48V (8A if you use the specified relay from Altronics). You have the option to get the relay to switch on if the sensor signal rises above the threshold frequency (set by Here’s the complete frequency switch, ready to mount inside its case (it suits a UB3 jiffy box but could also be mounted inside the equipment it is controlling if there is room). siliconchip.com.au Celebrating 30 Years S2) and switch off if the sensor signal drops below the threshold set by S1. The alternative is to get the relay to switch on if the sensor drops below the lower threshold frequency (set by switch S1) and switch off if the sensor signal rises above the threshold frequency (set by switch S2). The second mode is activated by installing a link at JP1 on the PCB. Block diagram Fig.1 (above) shows how the Deluxe Frequency Switch monitors the signal frequency. The PIC16F88 micro’s internal clock is derived from a 20MHz crystal which is driven by an internal oscillator amplifier. The resulting 20MHz clock signal is divided by four to produce a 5MHz signal which drives an internal 16-bit timer, TIMER1. This comprises two 8-bit cascaded timers, TIMER1H and TIMER1L. We have implemented an 8-bit overflow counter (OVER) in the unit’s firmware. That extends TIMER1 out to 24 bits, so it rolls over every 3.355 seconds [or 224÷5,000,000]. This equates to an input frequency close to 0.3Hz. Hence, the unit is designed to handle signals from 1Hz and up. The input signal is fed to pin 6, which is also the Capture/Compare/ PWM (CCP) pin. The Capture module hardware in the micro is configured so that on each positive signal transition at this pin (ie, low-to-high), the values of TIMER1H and TIMER1L are copied into the CAPTURE1H and CAPTURE1L registers and an interrupt flag is set. This then trigMay 2018  37 Fig.2: the circuit is based around a PIC16F88-I/P, which measures the incoming frequency and energises the relay if the frequency is above or below certain values and whether JP1 is present or not. It also has pre-settable response times and hysteresis to prevent “chattering”. LEDs give you visual indication of the operation as well. gers an interrupt handler routine which copies the contents of the OVER register into the CAPTURE OVER variable. The timers and overflow counters are then reset to zero, ready to count until the next input positive going edge. The captured count represents the number of pulses from the 5MHz clock signal over the period between the two positive input signal edges. So for example, a 1Hz input signal will have a one-second period between each positive edge. The count value stored will therefore be 5,000,000 (5M). At 1kHz, the period between positive edges is 1ms and the captured value will be 5000. To calculate the frequency, all we need to do is to perform the calculation F(Hz) = 5,000,000 ÷ value. Or we can calculate the period as P(s) = value ÷ 5,000,000. But in reality, the micro just has to convert the upper and lower threshold settings to these same count units and then compare the counter values 38 Silicon Chip to those stored values, to determine whether either threshold has been crossed. On-board frequency generation Where the microcontroller produces an output frequency for you to measure during adjustment as per setup method on page 41), pin 6 (CCP1) is configured differently. Rather than being in Capture Mode, with pin 6 as an input, it is used in Compare Mode and pin 6 is an output. TIMER1 is still driven with the same 5MHz signal but the TIMER1L, TIMER1H and OVER registers are preloaded with values calculated from the frequency to be produced. Each time OVER register overflows, the pin 6 output toggles and new values are loaded into the TIMER1L, TIMER1H and OVER registers. Because pin 6 toggles each time the counters overflow, the output frequency would be half what you might expect based on the period value for Celebrating 30 Years the required frequency. So we need to divide the period by two to give two separate half periods. This means there will be an error whenever an odd period value is used, since dividing it by two will yield a remainder of one. To solve this, and avoid the inaccuracy, two different pre-load values are used. They are used alternately to load into the TIMER1L and TIMER1H registers. So the duty cycle will not quite be 50% but the frequency produced TP1 voltage Hysteresis (adjusted with VR1) when setting upper threshold 5V 3.75V 2.5V 1.25V 625mV 312.5mV 50% 43% 33% 20% 12% 6% Table 1: Hysteresis setting versus voltage at TP1. siliconchip.com.au will be accurate. The values from each of the separate period values are loaded into the TIMER1L, TIMER1H and OVER counters alternately. At the same time, the output at pin 6 is changed in level. For those interested, the values to pre-load into TIMER1L, TIMER1H and the OVER variable are calculated as 224 - (5,000,000 ÷ f (Hz)) ÷ 2, with the alternative value being one higher in cases where 5,000,000 ÷ f Hz is odd. Circuit description The full circuit shown in Fig.2 is based on microcontroller IC1, a PIC16F88. This monitors the input frequency, jumper state (JP1 and JP2), switch state (S1 and S2) and trimpot settings (VR1 and VR2). It also drives the frequency LEDs (LED2-LED5), threshold LED (LED6) and the relay coil (RLY1) and its associated LED (LED7) via NPN transistor Q2. Power is fed in via CON1 and the supply is nominally 12V DC. Diode D1 provides reverse polarity protection and its cathode connects directly to the positive terminal of the relay coil, applying a nominal 11.4V to it as well as to the 5V regulator, REG1 and it powers the rest of the circuit. A 10F electrolytic capacitor is used to filter the supply voltage and transients are clamped using a 16V zener diode (ZD1), with the peak current limited by the series 47Ω resistor. The supply is further filtered by another 10F capacitor and then REG1 reduces the 11.4V supply to 5V for IC1 and input conditioning transistor Q1. The power LED, LED1, is connected across the 5V supply with a 3.3kΩ series current-limiting resistor. The input signal is fed into CON2 and it’s AC-coupled via a 10F capacitor and 10kΩ resistor to the base of Q1. The 470pF capacitor filters any transients while diode D2 clamps the base voltage at -0.7V for negative excursions. Q1 inverts and amplifies the signal, suitable for the capture compare input (CCP1) at pin 6 of IC1. Frequency measurement modes When the micro is configured to generate frequencies for setting the upper and lower thresholds, the output signal appears at pin 6 and TP3. For this to work, there must be no input signal at CON2 and this means that Q1 is biased off and it will not load the siliconchip.com.au Fig.3: component layout for the Deluxe Frequency Switch with a matching photo below. We suggest using an IC socket for IC1 – and make sure when you place the connectors, their wiring access holes all point to the outside of the PCB. output signal from pin 6. 20MHz crystal oscillator X1 is connected to IC1, between its CLKO and CLKI pins, to allow for accurate and wide-ranging frequency measurements. The MCLR-bar reset input is tied to the 5V supply via a 10kΩ resistor to provide a power-on reset for the microcontroller. Internal pullup currents within IC1 hold the RB1 and RB2 inputs high when switches S1 and S2 are not pressed and similarly, are enabled for the RB5 and RB6 inputs which are connected to jumpers JP1 and JP2. These inputs are pulled low if a switch is pressed or jumper plug inserted and this can be sensed by IC1. Output pins RA0 (17), RB4 (10), RB7 (13) and RA1 (18) drive signal indicators LED2-LED5 via 3.3kΩ currentlimiting resistors at around 1mA each. Similarly, output RA4 (pin 3) drives the threshold LED, LED6. The RB3 output (pin 9) switches transistor Q2 on when it goes high. This transistor in turn switches on the relay. Diode D3 quenches back-EMF from the coil as Q2 is switched off. Celebrating 30 Years LED7 is also switched on when the relay is powered. It’s wired across the relay coil and uses a 10kΩ series resistor due to the higher voltage (11.4V). It provides the same current to LED7 as for the other LEDs. Trimpots VR1 and VR2 set the default hysteresis and delay time and both are connected across the 5V supply, with their wipers connected to analog inputs AN2 (pin 1) and AN3 (pin 2) respectively. The voltages at these pins are converted to digital values using IC1’s inbuilt 10-bit analogto-digital converter (ADC). The 100nF capacitors between each of these two pins and ground provide a low-impedance source for the ADC during conversions. Construction The Deluxe Frequency Switch is built on a double-sided PCB coded 05104181 and measuring 102 x 58.5mm. It will fit in a plastic utility box measuring 129 x 68 x 43mm. Follow the overlay diagram, Fig.3, when installing the parts. Fit the resistors first. The colour codes are shown May 2018  39 overleaf but we recommend that you use a digital multimeter (DMM) to check the values before soldering them. Diodes D1, D2, D3 and ZD1 are next and these need to be inserted with the correct polarity, with the striped end (cathode, k) oriented as shown in the overlay diagram. Diode D2 is the 1N4148 type while D1 and D3 are 1N4004. Parts list – Deluxe Frequency Switch 1 double-sided PCB coded 05104181, 102 x 58.5mm 1 DPDT 12V DC coil relay (RLY1) [Jaycar SY-4052 {5A}, Altronics S 4270A {8A}] 2 2-way screw terminals with 5.08mm pin spacing(CON1,CON2) 2 3-way screw terminals with 5.08mm pin spacing (CON3) 2 2-way pin headers with shorting blocks (JP1,JP2) 1 18-pin DIL IC socket (for IC1) 1 20MHz crystal (X1) 2 SPST PCB-mount tactile pushbutton switches (S1,S2) [Jaycar SP0600, Altronics S 1120] 2 PC stakes (TP GND,TP3) Semiconductors 1 PIC16F88-I/P microcontroller programmed with 0510418A.HEX (IC1) 1 LP2950ACZ-5.0 low dropout regulator (REG1) 1 BC547 100mA NPN transistor (Q1) 1 BC337 500mA NPN transistor (Q2) 1 16V 1W zener diode (1N4745) (ZD1) 2 1N4004 1A diodes (D1,D3) 1 1N4148 signal diode (D2) 7 3mm LEDs (LED1-LED7) Capacitors 1 100µF 25V PC electrolytic 2 10µF 16V PC electrolytic 1 10µF non-polarised (NP) PC electrolytic 4 100nF 63V/100V MKT polyester 1 1nF 63V/100V MKT polyester 1 470pF ceramic 2 27pF NP0/C0G ceramic Resistors & Potentiometers (all 1%, 0.25W) 1 1MΩ 1 100kΩ 4 10kΩ 6 3.3kΩ 1 1kΩ 1 47Ω 1 10kΩ vertical multi-turn trimpot, 3296W style (VR1) 1 10kΩ mini horizontal trimpot, 3386F style (VR2) 40 Silicon Chip We recommend using an IC socket for IC1. Take care with orientation when installing the socket and when inserting the IC. For the test points, we used two PC stakes, one for TP GND and the other for TP3. We left the remaining test points as bare pads so a multimeter probe can be inserted. Install the two 2-way pin headers for JP1 and JP2 and then follow with the capacitors. The electrolytic types must be fitted with the polarity shown (long lead to pad marked plus; the stripe indicates the negative side) and note that the 10F NP capacitor is non polarised and so can be installed either way around. Next, mount transistors Q1 and Q2 and also REG1. Take care not to mix them up as they come in identical packages. Trimpots VR1 and VR2 are next to be fitted. They may be marked as 103 instead of 10kΩ. Orient VR1 with the adjusting screw as shown. CON1 to CON3 can now be installed. CON1 and CON2 are 2-way types and CON3 comprises two 3-way screw connectors dovetailed together. Fit all connectors with the wire entry to the edge of the PCB. Finally, the LEDs and relay RLY1 can be installed. We placed the LEDs close to the PCB, but they can be mounted higher or mounted off the PCB if you wish, connected with flying leads. Although presented as a bare PCB, the unit fits in a UB3 Jiffy box. In this case, attach the PCB to the base of the box using spacers. First, mark out and drill 3mm holes for each of the corner mounting holes. You will also need to drill holes at each end of the box for cable glands. A gland at one end is used for the power and signal wires while a gland at the other end allows the relay contacts to be wired up as required. Set up You have several options for setting the unit up. You can set it up before installation using or an oscillator or the actual signal source (if it can be held steady enough) when you install it. 1) Oscillator method: Power the unit up with a 12V power supply wired to CON1. Connect the oscillator to CON2. Set the signal amplitude to 2V peakto-peak or 0.7V RMS. Set the oscillator to your desired upCelebrating 30 Years Using a tacho signal Say you are using the engine tacho signal to switch the relay if a certain engine RPM is exceeded – say 6000 RPM. If you have a 4-cylinder, 4-stroke engine, 6000 RPM = 100 revolutions per second. Since this type of engine fires two cylinders per crankshaft rotation, then the threshold should be set to 200Hz [100 x 2]. per threshold frequency (eg, 500Hz) and press S2. Then reduce the oscillator to set the lower threshold (eg, 400Hz) then press S1. That’s all there is to it. If you want to set a single threshold frequency (ie, the upper threshold) and use the hysteresis setting, fit a link to JP2. Then adjust trimpot VR1 for the required hysteresis (percentage) while you monitor the voltage at TP1. Then set the oscillator for the desired frequency and press S2. Alternatively, if you want to set a single threshold frequency at the lower threshold and use the hysteresis setting for the upper threshold, fit a link to JP2. Then adjust trimpot VR1 for the required hysteresis while you monitor the voltage at TP1. Then set the oscillator for the lower threshold frequency and press S1. Table 1 shows some the relationship between the voltage at TP1 and the percentage hysteresis. For example, if you set VR1 to give 1.25V at TP1, the hysteresis will be 20% and the resulting lower threshold frequency will be 20% lower than the frequency you set with switch S2. Note that you can also set the unit with only one threshold frequency and that will mean the relay will latch on when the signal goes above the threshold and will stay on until the power is turned off. To set just a single threshold frequency, set the oscillator to the desired frequency and then press S2. Then disconnect the signal from CON2 and wait until the signal LEDs all are off. Then press S1 to set the lower frequency to zero. No link is required at JP1 if you want the relay to switch on as the frequency rises above the threshold set by S2 (and turns off when the frequency drops below that set by S1). Alternatively, install JP1 if you want the relay to switch on as the frequency falls below the threshold set by S1 (and turn off when the frequency rises siliconchip.com.au above the threshold set by S2). lier) you need to adjust trimpot VR2. You can set the delay anywhere between zero and half a second. If you don’t want a delay set VR2 fully anti-clockwise. 2) Frequency meter method: The advantage of this approach is that you don’t need an oscillator but you will need a frequency meter or oscilloscope to measInstallation ure the frequency appearing at TP3. Connect the 10-16V To get into this DC power source between the mode, connect your +12V and GND inputs at CON1. frequency meter or For automotive installations, DMM between TP3 automotive-rated wire should and GND. be used and the +12V termiSwitch off power, nal needs to connect to the hold down both S1 switched side of the ignition. The PCB is designed to fit into a UB3 Jiffy box, as shown here – and S2 and then That way, the unit only opbut it could also be “built in” to equipment it is controlling. You switch on the powerates when the ignition is may also be able to source the 10-16V DC from that equipment – er. The micro then switched on and the vehicle as long as it isn’t turned off by the frequency switch! produces a 100Hz battery won’t go flat after long signal at TP3. Then remove JP1, use S1 & S2 to ob- periods of being parked. To adjust this default frequency to tain the lower threshold frequency, inThe easiest way to connect the GND obtain your desired upper threshold, sert JP1 again and press S1. terminal in a vehicle is to wire it to the press S1 and S2 until it reaches your Alternatively, if you just want to set chassis using a crimped eyelet secured target. S2 increases frequency, while the upper threshold frequency with S2 to a convenient screw terminal. S1 decreases frequency. and have the hysteresis setting made You may need to drill a separate hole Short presses of the switches will for the lower threshold as set by trim- in the chassis for this connection, or alter the frequency at a slow rate. For pot (VR2), then you must have a link utilise an existing earth connection. faster changes, hold the switch down fitted to JP2 before you start the proceWire CON2 to a suitable sensor. This and the rate will change to a faster rate dure. Similarly, you can set the lower can be the speedometer sensor, an ECU after two seconds. Continue to depress threshold with S1 and have the upper tachometer output, an injector or camthe switch for another two seconds and threshold set by the hysteresis percent- shaft position sensor and so on. If you the frequency will change at an even age value as set by VR2. haven’t already set the unit up, do so faster rate. Now turning off the power takes the as described above above. This allows you to run through the micro out of the mode whereby it proThe relay contacts are labelled Norentire frequency range in less than one duces an output frequency at TP3. It mally Open (NO), Normally Closed minute but still be able to do finer adthen reverts to normal operation, mon- (NC) and Common (COM). justments with brief switch presses. itoring the input frequency instead. To switch power to a load, wire one Having reached your target frequenThen fit a link to JP1 if you want the of its supply lines in series between cy, insert JP1. Then press S2 to set the relay to switch on as the frequency falls either the COM and NO terminals (so upper threshold frequency. Then rebelow the threshold set by S1 (and turns that it’s only powered when the relay move JP1. Then press S1 to reduce off when the frequency rises above that is energised) or COM and NC terminals the frequency to the lower threshold. set by S2). (so it’s switched off when the relay is Then re-insert JP1 and press S1 to set No link is required at JP1 if you want energised). the lower frequency threshold. the relay to switch on as the frequency Note that the relay contact current Note the two-step process to set each rises above the threshold set by S2 (and rating is 5A for the Jaycar relay and 8A frequency. In other words,with JP1 out, turns off when the frequency drops be- for the Altronics relay (see parts list). use S2 and S1 to adjust the frequency to low that set by S1). If a higher current is required, you the wanted value, insert JP1 and press If you want to configure the unit with can switch 12V DC to the coil of a largS2 to set the upper threshold. a switching delay (as described ear- er relay using RLY1. SC Resistor Colour Codes o o o o o o Qty. Value 1 1MΩ 1 100kΩ 4 10kΩ 6 3.3kΩ 1 1kΩ 1 47Ω siliconchip.com.au 4-Band Code (1%) brown black green brown brown black yellow brown brown black orange brown orange orange red brown brown black red brown yellow violet black brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown brown black black red brown orange orange black brown brown brown black black brown brown yellow violet black gold brown Celebrating 30 Years Small Capacitor Codes Qty. Value o o o o 4 1 1 1 F Code 100nF 0.1F 1nF 0.001F 470pF 27pF - EIA Code IEC Code 104 102 470 27 100n 1n 470p 27p May 2018  41 SAD HAPPY To discover that the elusive bit that you want is stocked in the Silicon Chip ONLINE SHOP! There's a great range of semis, other active and passive components, BIG LEDs, PCBs, SMDs, cases, panels, programmed micros AND MUCH MORE that you may find hard to get elsewhere! Because you can't find that difficult-to-get special project part at your normal parts supplier. . . Or perhaps they've discontinued the kit you really want to build. . . If it's been published in a recent Silicon Chip project and your normal supplier doesn't stock it, chances are the SILICON CHIP ONLINE SHOP does! HERE ARE JUST SOME EXAMPLES (oodles more on our website!) WeMos R1 D2 WiFi Board A WeMos R1 D2 Arduino-compatible WiFi board which includes a connector for an external antenna. This is a clone board used in the WiFi Water Tank Level Meter (Feb 2018).................$15.00 Micromite LCD BackPack V2 complete kit Includes PCB (green), 2.8-inch TFT touchscreen, programmed micro, SMD Mosfets for PWM backlight control, lid and all other onboard parts (May 2017).............$70.00 5m Water Level Sensor (4-20mA) Pressure-based water level sensor with a 5-6m lead as used in the WiFi Water Tank Level Meter (Feb 2018)..........$95.00 Microbridge complete kit Includes PCB, programmed micro & IC socket, 3.3V LDO, all capacitors, USB socket, pin headers and 1kW resistor (May 2017)........................$20.00 ea Micromite Plus LCD BackPack kit Includes PCB, 2.8-inch TFT touchscreen, programmed micro, 20MHz crystal, laser-cut case lid and other onboard parts (Nov 2016) ………………… $70.00 ea Micromite Plus Explore 100 kit Includes PCB, programmed 100-pin SMD micro, and all other non-optional onboard parts except the LCD panel (Sept-Oct 2016) ……………… $69.90 ea Micromite Plus Explore 64 kit Includes PCB, programmed 64-pin SMD micro, crystal, connectors and all other onboard parts (Aug 2016) ………… $30.00 ea GPS MODULE Onboard antenna, 1pps output, operation to 10Hz, cable included VK2828U7G5LF GPS/ GLONASS …………………………$25.00 5V 0.8W 160mA Solar Panel Monocrystalline silicon, 99 x 69mm, ~6V open circuit, ~5V full load, two solder pads on the underside of the panel…$4.00 Logic-level Mosfets Pair of CSD18534KCS N-channel …… $5.00 Or complementary pair of N & P-channel Mosfets (as used in Burp Charger) … $7.50 IPP80P03P4L04 P-channel Mosfet SC200 Amplifier hard-to-get parts Includes all power transistors, diodes D2-4, 150pF 250V C0G capacitor, 4 x 0.1W and a 6.8W 3W SMD resistors (no PCB) (Jan 17).........................$35.00 2.4GHz WiFi Antennas Supplied with a matching chassis-mount SMA socket and attached U.FL/IPX connector cable. 2dBi omnidirectional (28mm)….$10.00 5dBi (175mm)………….….......$12.50 AD9833 DDS module A Direct Digital Synthesis module using the AD9833 IC and a 25MHz crystal oscillator. (April 2017) with programmable attenuator (green) ….… $25.00 without attenuator (blue) …………………... $15.00 Elecrow 1A/500mA Li-Ion/LiPo charger board with USB power-pass through Provides a regulated 5V output at 500mA from the cell, plus a 1A charger and automatic input-to-output passthrough. Supplied with three 2-wire JST 2.0 cables.…............. $15.00 ea Isolated High-Voltage Probe Pack of hard-to-get parts including HCNR201-050E linear optocoupler, op amps and HV capacitors & resistors (Jan 2015) ……………………… $35.00 SiDRADIO parts 125MHz crystal oscillator, mixer, dual gate Mosfet, 5V relay and more ……… $20.00 RF Coil Former pack (Oct 2013) …… $5.00 Currawong stereo valve amplifier Hard-to-get parts including 5 x 39µF 400V capacitors, HV transistors, regulator and blue LEDs (Nov 2014) ………… $50.00 A high-current P-channel Mosfet with low onresistance in a TO-220 package. Used in the Water Tank Level Meter (Feb 2018) and AM Radio Transmitter (Mar 2018).….....… $4.00 Ultra Low Voltage Bright LED Flasher kit Includes PCB, LDR, high-brightness blue LED, all SMD parts, an extra capacitor plus extra resistors to change flash frequency and duty cycle (Feb 2017) …….… $12.50 CP2102-based USB/TTL serial converter Includes a micro-USB socket and 6-pin right-angle header (top) …………. $5.00 Includes a USB Type-A socket and 5-pin header with a 5-way female Dupont cable (bottom) …………………. $5.00 MCP1700 3.3V Low-dropout Regulator 3.3V LDO regulator in a convenient TO-92 package, as used in many projects; up to 6V input and 250mA output ……………………………………… $1.50 DS3231-based RTCC module Real-time clock & calendar module w/ 4KB EEPROM, I2C interface & mounting hardware with LIR2032 cell ………...… $7.50 no cell ……………………….. $5.00 Don't forget: Silicon Chip Subscribers qualify for a 10% discount on all these items! YES! We also stock most Silicon Chip project PCBs from 2010 and even earlier! Log on now: www.siliconchip.com.au/shop 42 Silicon Chip Celebrating 30 Years siliconchip.com.au Y Using Analysing and optimising audio circuits by Simulation Part IV by Nicholas Vinen We concluded our last tutorial (September 2017) saying that our next LTSpice tutorial would cover simulating op amps and audio circuits. It has been a while coming . . . but here it is! S imulating audio circuits can be useful for a number of reasons, including: • optimising filter component values for the desired roll-off point and minimal passband ripple • characterising complex and/or cascaded filter responses – corner frequency, roll-off rates, out-of-band attenuation, bandwidth limitations, etc • optimising amplifier circuits for stability, bandwidth, etc • measuring frequency response and headroom • checking expected circuit operation • verify DC operating conditions • checking that component voltages, currents, dissipation and heating are within safe operating limits This article will cover most of the above tasks and the circuits and techniques presented here can be applied to the remainder (and others we haven’t mentioned). Filter optimisation There are dozens of different kinds of filters that you might use in an audio circuit, including low-pass, high-pass, band-pass and notch types from simple passive (RC, LC) filters to complex multi-pole active filters or resonant passive filters. The characteristics of the most simple RC filters can be calculated quite easily, using well-known formulas such as f (-3dB) = √(2π x R x C) to determine the corner frequency for an RC high-pass or low-pass filter. But as soon as you start working with multi-pole filters or multiple cascaded RC filters, the calculations become much more difficult. Luckily, simulating such circuits is simple and will quickly give you gain and phase plots. For example, let’s say that we have two cascaded RC low-pass filters with a buffer stage between them. And say they use identical components, so they have the same -3dB corner frequencies and 6dB/octave roll-off. We can use 1kΩ resistors and 1nF capacitors to keep it simple. So we expect the resulting combination to have a 12dB/octave roll-off but the -3dB frequency of a single filter (159kHz) is now the -6dB point of Fig.1: a simple secondorder RC low-pass filter drawn up in LTspice, using ideal buffer E1 to isolate the stages. We can then compare its performance to more typical second-order filter circuits to see their pros and cons. siliconchip.com.au Celebrating 30 Years the combined filter. So what is the new -3dB point? Simulating it Rather than using an op amp model as the buffer stage between the two filters, we’ll use a unity-gain voltagecontrolled voltage source. This has the benefit of being simpler to use (no need to wire up supply rails etc), infinite bandwidth, no distortion and no noise. To set up this simulation, we create a new schematic sheet in LTspice and add and wire up the components as shown in Fig.1. Refer to the earlier articles in this series for details on how to do this. See www.siliconchip.com. au/Article/10677 We already introduced the voltagecontrolled voltage source, in this case, component E1. You need to right-click on it and set the “Value” field to 1 so that it operates at unity gain. For the voltage source, right-click on it and click on the “Advanced” button to show all the fields, then set the “AC Amplitude” field to 1V (under “Small signal AC analysis”). We label the input and output nets using the “Label Net” button in the toolbar, for easier analysis later. Finally, select the Simulate -> Run menu option and then switch to the AC Analysis tab and set the type of sweep to Octave, the number of points per octave to 10, start frequency to 10Hz and stop frequency to 10MegHz (other options would be valid but let’s stick with these for now). Do not set the stop frequency to May 2018  43 Fig.2: Bode plots showing the frequency and phase response for the intermediate and output notes of the Fig.1 circuit. We can then use cursors to determine their -3dB points and calculate the roll-off rates. 10MHz, since this will be interpreted as 10mHz! Having run the simulation, click on the output node and a plot similar to that shown in Fig.2 should appear (we’ve also clicked on the junction of C1 and R1 to compare the response of a single stage). The output response is shown in green and the green dotted line is the output phase. The intermediate response is shown in blue. As you would expect, the combined response has a steeper roll-off. Now, to determine the -3dB point, click on the “V(output)” label at top and cursors appear, along with the box shown at lower right, which contains additional information. Drag the horizontal cursor to the right until the Mag: reading in the box is very close to -3dB and then you will see the corner frequency at left, which is just above 100kHz. Phase and group delay readings are also shown. Comparing other multi-pole filter arrangements The problem with cascading two RC filters with a buffer in between to produce a two-pole filter, is that the resulting output impedance pf the cascaded filter is relatively high. But it is possible to build a two-pole filter around a single buffer/gain stage and obtain a very low output impedance. Two common approaches to this are Sallen-Key and Multiple-Feedback filters. An excellent website for designing such a filter is at: siliconchip.com.au/ link/aajq One of the biggest problems with designing this type of filter to achieve a specific response is that you inevitably need components with unrealistic values, such as 4.39kΩ or 1.42nF. With some tweaking, you may arrive 44 Silicon Chip at component values which are close to what’s actually available. But that leaves us with two questions: how much does the deviation from ideal values affect the filter response, and which of the two filters topologies is best? LTspice can help us answer both these questions. For this exercise, let’s aim to build a realistic filter with the same -3dB point and roll-off as we determined above with our naive attempt, ie, 102.375kHz and 12dB/octave respectively. At the website above, we set the filter order to 2, cutoff frequency to 102.38kHz and experimented with the “Desired Rx” value until we got realistic looking values below. This was with a “Desired Rx” value of 2.4kΩ. We then drew up both resulting filter circuits in LTspice, as shown in Fig.3. There are several important points to note about this circuit we’ve drawn up. Firstly, we have chosen to use LT1464 op amps as these have 1MHz bandwidth and this will provide a good demonstration of how op amp bandwidth effects filter behaviour. Also, we have used the Net Label tool to label the supply rails of each op amp V+ and V- and we then added two extra stacked voltage sources, V2 and V3, both set to 5V DC with the junction connected to ground. By labelling the top and bottom V+ and Vas well, we’re providing ±5V supply rails for each op amp without cluttering up the schematic. The output of the “naive” filter has been re-labelled out1 so that we can label the two new filter outputs out2 and out3, for easy comparison. (In case you can’t immediately see out2 and out3, they are just above U2 and U3). U2 is used for the Sallen-Key second-order filter which uses two resistors and two capacitors, all with different values, while the MultipleFeedback second-order filter is based around U3 and it uses three equal-value resistors plus two capacitors. The Multiple-Feedback filter is an inverting type while the Sallen-Key is non-inverting; this may be imortant in some applications. While we were able to use equal-value resistors in the Multiple-Feedback filter, that isn’t guaranteed to always be the case. Note that the output of the two new filters is taken from the output pin of an op amp, so the impedance is low and can be fed into another filter network. You would need an extra op amp buffer for the naive filter to achieve the same result. Now since these are all second-order low-pass filters with the same corner Fig.3: here we’re simulating three low-pass filter circuits drawn using op amp models, all with a -3dB point of 100kHz. Celebrating 30 Years siliconchip.com.au if we needed to). So it ends up attenuating the signal even further. Another couple of things to note: both of the new filters give less attenuation of the signal below the -3dB point, ie, they roll-off more quickly which is good if you’re going for a “brick wall” type response. And the use of a real op amp has actually pushed the naive filter -3dB point slightly higher, to around 110kHz, which is why the curves don’t all meet at one point. Higher bandwidth op amps Fig.4: the resulting frequency response plots of the three filter circuits shown in Fig.3 (green=out1, blue=out2, red=out3). While the graphed lines may seem light here, they are quite visible on-screen. frequency, you would expect the results to be very similar but you might be surprised. Comparing filter responses We now run the same AC analysis as before but this time, after clicking on the out1, out2 and out3 nets to plot the response, we right-click on the phase axis at right and click the “Don’t plot phase” button to de-clutter the resulting Bode plot. We’ve expanded the plot to fill the window for increased clarity and the result is shown in Fig.4. The naive filter response is shown in green, Sallen-Key in blue and Multiple-Feedback in red. The most surprising aspect to this plot is that while both the additional filters have a much faster roll-off above the ~100kHz -3dB point, above 1MHz (the -3dB bandwidth of the op amps), the naive filter actually provides superior attenuation. And as shown the Sallen-Key filter does a particularly poor job at higher frequencies, with a peak at around -15dB attenuation at 1.8MHz and it’s not much better at higher frequencies either. This is because capacitor C4 couples some of the signal from the input straight to the op amp’s output and its limited bandwidth means that it isn’t able to prevent that coupled signal from feeding through. (To explain, there is no extra open-loop gain at higher frequencies and that means that negative feedback cannot act to provide a low output impedance). The Multiple-Feedback filter does a better job because capacitor C5 is siliconchip.com.au a smaller value and there are two resistors, R5 and R7, in series before it, plus C6 will shunt much of the feedthrough signal to ground. Even so, you can see that the slope of the red trace changes slightly around 1MHz to be more flat, allowing the blue trace of the naive filter to “catch up” to it at 1MHz. That’s because the naive filter starts with a completely passive RC filter which rejects at least some portion of the signal regardless of the op amp bandwidth. And the op amp’s limited bandwidth actually helps us here, since there’s no path for the signal to “feed through” it (ignoring parasitic PCB capacitance, which we aren’t simulating here although we could add it So how does this change if we use a higher bandwidth op amp? That’s easy to test; simply delete U1-U3 and replace them with LT1357s which have a gain-bandwidth product of 25MHz. Then re-run the simulation. The result is shown in Fig.5. All three curves now meet at the design -3dB point of 102.375kHz and it’s clear that the Multiple-Feedback filter now gives the best performance, with much less effect on frequencies below 100kHz than the naive filter, a much quicker roll-off above this point and very little change in its rate of attenuation up to 10MHz; just a slight change in the rate of attenuation, which reaches -75dB at 10MHz. By comparison, the Sallen-Key filter gives virtually identical performance up to 1.4MHz but it reaches a maximum attenuation of -50dB at 2.2MHz, above which is attenuation factor actually falls, giving -40dB at 10MHz. Its Fig.5: the same frequency response plots as shown in Fig.4 but this time, with 25MHz op amps, giving better results. You can see that the Sallen-Key filter is still less than ideal but its rebound has been pushed to a higher frequency. Fig.6: a similar plot to Fig.5 but this time up to 100MHz, so we can see how the filters behave between 10MHz and 100MHz. Celebrating 30 Years May 2018  45 Fig.7: a simplified hifi audio amplifier circuit simulated using components available in the libraries supplied with LTspice. curve crosses the naive filter for a second time at 2.73MHz, with the naive filter continuing to provide attenuation, reaching -72dB at 10MHz. If we go back to the schematic, right-click on the simulation command (which starts with “.ac”) and change the finish frequency to 100MHz (“100MegHz”), we get the plot shown in Fig.6. This shows that the Sallen-Key bode plot has a peak of -31dB at 35MHz, above which it again begins to slowly roll off. By comparison, the MultipleFeedback filter does continue to increase its attenuation at higher frequencies although at a reduced rate. The naive filter overtakes it at 15MHz, where both reach -78.5dB. The Multiple-Feedback filter reaches -100dB at 100MHz while the Naive filter is at -132dB by 100MHz. Simulating an amplifier with discrete components Our article on Amplifier Stability and Compensation in the July 2011 issue gave fairly detailed information on using SPICE to simulate an amplifier and test it for stability under difficult conditions, for example, when it is driven into clipping. Rather than go back over that, we will instead build a simple amplifier circuit in the simulator to analyse the amplifier efficiency, determine the dissipation in the major components and examine how power flows from the transformer through to the loudspeaker load. We’ve drawn up a minimalistic hifi Fig.8: the voltage across load resistor RL is shown in mauve while the dissipation in that resistor (ie, load power) is in green. 46 Silicon Chip power amplifier circuit in LTspice and this is shown in Fig.7. We’ve used only components from the built-in libraries. The test input signal, a 2.1V peak sinewave is from V1. This is fed into the base of PNP transistor Q1, which forms a differential input pair with Q2. Q2 is connected to the output via a 12kΩ/510Ω divider, setting the amplifier gain to 24.5 times. NPN transistors Q3 and Q4 are the current mirror load for the input pair while PNP transistor Q5 is the constant current source for their emitters. The differential stage output current flows from the collector of Q1 to the base of Q8, the VAS (voltage amplification stage) transistor which has a 100pF compensation capacitor, to stabilise the amplifier. Fig.9: this shows how the amplifier output voltage plus the AC and DC supply voltages behave when power is first applied. Celebrating 30 Years siliconchip.com.au Fig.10: this demonstrates how current is drawn in brief bursts from the simulated transformer secondaries at their voltage peaks. Q10 and its two base resistors form the Vbe multiplier that sets the bias voltage for the output stage and thus the quiescent current. The bias resistor values were determined experimentally and set the output stage quiescent current to 120mA per transistor pair. PNP transistor Q9 is the constant current source for the VAS while Q6 controls the base bias for both Q5 and Q9. The output stage consists of driver transistors Q11 and Q14 and power transistors Q12, Q13, Q15 and Q16 (in Darlington emitter follower configuration). These have 0.1Ω emitter resistors and there is an RLC filter at the output to isolate the load (at high frequencies) and ensure stability. The test load is an 8-ohm resistance, RL. The power supply consists of sinewave voltage sources V2 and V3 which represent the two halves of a centretapped transformer secondary (45-045VAC). This is rectified by bridge rectifier DP1-DP4 and the supply is filtered by a pair of 10,000F capacitors. Examining power supply behaviour Fig.8 shows the output voltage in mauve. This is a zoomed-in portion of the simulation output since the waveform is clipped initially as the power supply filter capacitors charge up. But if we’re interested in looking at the output power, that muddies the water. As expected, the output is a sinewave. The 2.1V peak input has been amplified by the 24.5 times gain to yield peak voltages of just over ±50V. The green plot is the instantaneous dissipation in the load resistor. This is plotted by holding down the ALT key in Windows and then clicking on the load resistor, RL. Control-clicking the green text at the top (“V(output)*I(RL)”) then yields the integral box shown at lower right. This reveals that the amplifier is delivering siliconchip.com.au around 165W average to the load in this condition. The instantaneous dissipation in RL is 0W when the applied voltage passes through 0V and rises to a peak of around 330W at both the positive and negative sinewave maxima. Note that this is a sine-squared waveform which is why there is a 2:1 ratio between peak and RMS power, not the sqrt(2) ratio you would expect for a normal sinewave. Fig.9 shows a “zoomed out” version of the simulation plot where you can see the V+ (green) and V- (blue) power rails initially charging up. This is unrealistically fast as we have simulated a transformer with a zero ohm output impedance; you could add a small series resistance and/or inductance if you wanted a more realistic simulation of amplifier switch-on. The mauve waveform once again shows the amplifier output and you can see that it is initially clipped by the low supply rail voltages, especially on negative excursions due to R25 and C11, which form an RC low-pass filter for the negative rail at the front end of the amplifier. These components are important to prevent supply rail ripple due to the load current from affecting the input pair and VAS but they do slow down the amplifier’s start-up somewhat. And as shown, they also make the waveform initially clip asymmetrically. Normally, this would not be a problem as there would typically be a relay between the amplifier and the output terminals with a delayed switch-on to prevent a thump from the speakers at power-up. The red and cyan traces in Fig.9 are the simulated transformer secondary waveforms and they show how the supply rails are pumped up when the transformer secondary voltages peak and the rails slowly decay, as the load current is drawn during the subsequent mains half-cycles. You can also see how the two halves of the centretapped secondary alternately charge up the supply rails. This is shown in more detail in Fig.10. This time the supply rails are plotted in blue (V+) and cyan (V-) while the simulated secondary voltages are in red and green. Current from voltage sources V2 and V3, representing the transformer secondaries, is shown in grey and mauve. Ignoring the initial very high current on the first mains half-cycle, the remaining current pulses are semirealistic and you may be surprised to see that zero current is drawn from the transformer most of the time, with brief peaks to nearly 40A being drawn over a ~1ms period every 10ms. Calculating amplifier efficiency If we zoom into the plot so that we remove the initial surge current and then CTRL-click the I(V2) text at the top of the window, this gives us an RMS current of 8.3A. If we assume a Class-AB amplifier efficiency of 70%, for 165W output we need an input power of 235W and with two 60VAC secondaries, you would expect 2A [235W ÷ 60V ÷ 2] = drawn from each supply rail. Fig.11: averaging the power drawn from the transformer to calculate the amplifier input power, so we can calculate its efficiency. The circuit is shown larger in Fig.7. Celebrating 30 Years May 2018  47 Fig.12: the instantaneous dissipation in the output and driver transistors. These can be averaged to estimate how hot they will get. The reason for the discrepancy is the fact that current is only drawn for such a short period during the secondary voltage peaks. This means that I^2R losses in the transformer, wiring, rectifier etc will all be a lot higher than you would get with a resistive load on the transformer. If you think about it, though, it’s very rare for a transformer to have a resistive load. Transformers are mostly used to drive rectifiers in similar configurations to this. Hence, transformer ratings tend to be quite conservative as they have to deal with supplying such high peak currents with a low duty cycle. So does this mean that a huge amount of power is being wasted in the transformer? Not really. It just means the power factor is poor. We can determine the real power drawn from the “transformer” by labelling the output (top) of V2 as V2V and the bottom of V3 as V3V, then re-running the simulation, and plotting the product of current and voltage. To do this, we right-click on the resulting plot and selecting “Delete Traces”, then right-click again and select “Add Trace” and type in the formula: “I(V2)*V(V2V)”. Add another trace with the formula “I(V3)*V(V3V)”. We can then zoom into a single mains cycle and controlclick the formula at the top of the window to get an average reading. The result is shown in Fig.11. You need to be careful when zooming that you get exactly 20ms (or a multiple thereof) on the horizontal axis or the averaged values will not be correct. We get a figure of very close to 123W for both V2 and V3. Thus the total power draw of the circuit is 246W. That means the actual amplifier efficiency is 67% [165W ÷ 246W], pretty close to the 70% that we estimated earlier. 48 Silicon Chip Determining device dissipation We can measure the dissipation in the output transistors, driver transistors and rectifier diodes by alt-clicking them and then control-clicking the formula that appears at the top of the window. Fig.12 shows the dissipation of one pair of output transistors in green and blue and one of the drivers in red. As you can see, we get a reading of around 17.5W for each of the four main output devices. Repeating the same exercise gives a dissipation figure of 2W total for the two drivers plus 2W in each of the rectifier diodes, for a total (including the load) of 245W [165W + 17.5W x 4 + 2W x 5], leaving just one watt unaccounted for, most of which turns out to be due to the 0.1Ω emitter resistors. So this shows how the simulation can help you determine efficiency, calculate device dissipation and so on. It’s a good idea to check dissipation for the smaller transistors too. Depending on the current through each stage, they could potentially be buys close to their specified limit as they would normally be in much smaller packages than the output transistors. You could also easily measure the peak and average current in the output devices to check that they are within with each device’s capabilities. Conclusion While this article has covered a lot of ground, there are still many other audio circuits that we have not discussed and which can benefit from a SPICE simulation but we don’t have the space to cover them all. However, the above should give you an idea of how to “probe” and measure the simulated circuits. It’s especially helpful for tweaking component types and values to achieve an optimal result. For example, you could increase the amplitude of the input sinewave to the amplifier and investigate what happens when the amplifier is driven into clipping. You could build a simulated loudspeaker load based on resistors and inductors and possibly even include a crossover network, to better explore how the load’s reactance affects amplifier operation, stability and efficiency. All the circuits shown in this article are available for download from the SILICON CHIP website (in a ZIP package) so feel free to experiment, probe, tweak and find out for yourself just how they work and what effect your changes will have. After all, you can’t blow anything up! In fact, why not over-drive things to destruction just to see what happens? It’s a simulation: you won’t have to buy any new components! SC Linear Technology More than a year ago, Analog Devices completed the acquisition of Linear Technology (the owners of LTspice). LTspice is still available as a free download but you can now access it via siliconchip. com.au/link/aajo You may find that if you have an older installation of LTspice, the automatic update feature no longer works because the URL it fetches is no longer valid. We suggest you download and install the latest version from the above link, which should then be able to keep itself up-to-date. One major advantage of the new version is that there are now many Analog Devices (ADxxxx) parts available to simulate, along with the existing set of Linear Technology (LTxxxx) parts. However! We have found the latest version of LTspice (version XVII) to be considerably less stable than the older version that we used (version IV). Hence, you may wish to keep your old version of the software in case these bugs have not yet been fixed. You may notice that some of our screen captures are from the earlier version, for this reason. 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LARGE 59 ROWS/862 HOLES HP-9572 $9.95 SMALL 25 ROWS/400 HOLES HP-9570 $4.95 Due early May. 4 $ 95 1 ea $ 75 METAL OXIDE VARISTORS (MOV) Snap to centre positive 2.1mm DC connector. Works great for Arduinos, development boards, electronic projects and more! • 0.3m long Ideal protection against voltage spikes and transients. Helps prevent damage to sensitive equipment such as microprocessors and digital electronics. • Range from 10-460VAC, 100-6500 5 3 PIN PLUG PACK CASE HB-5900 Make your own plug in power supplies with our vented case. Complete with earth pin. HM-3208 Build a stackable shield, or make your current shield stackable. Alternatively, shorten the pins to make female headers just like the Duinotech main boards. INCLUDES: 1 × 10-pin, 2 × 8-pin, 1 x 6-pin & 1 x 2x3-pin (for ICSP). RASPBERRY PI STARTER KIT XC-9010 149 $ Just about everything you need to get started with a Raspberry Pi. Includes: Raspberry Pi 3B, acrylic case, power supply and USB cable, book (Programming the Raspberry Pi: Getting Started with Python), microSD card loaded with NOOBS software and getting started guide. FROM RN-3411 9V BATTERY SNAP DC LEAD BATTERY PH-9251 $ 95 ARDUINO® STACKABLE HEADER 4 ea $ 95 2.1MM DC CONNECTORS • 3.0A rated. PLUG PA-3711 SOCKET PA-3713 To order: phone 1800 022 888 or visit www.jaycar.com.au 55 ¢/m 14 95 HEAVY DUTY POWER CABLES Suitable for 250V wiring. PVC insulation. 7.5A 24 X 0.2mm. WH-3040-WH3042 $0.55/m or $42/100m roll 10A 32 X 0.2MM. WH-3050-WH3052 $0.80/m or $72/100m roll $ OFFICIAL RASPBERRY PI CASE XC-9006 Snap-together case with numerous removable panels. Stylish red and white design. Four rubber feet included. 3 7 $ 95 $ 95 2.1MM PCB MOUNT DC SOCKET PS-0531 COPPER HEATSINK FOR RASPBERRY PI HH-8584 Snap-in, PCB mounted 2.1mm DC power socket with SPST black rocker switch. • Electrical rating: 5A <at> 15VDC Helps dissipate extraneous heat. Self-adhesive pads for peel and stick use. Pack of 2. See terms & conditions on page 8. 51 Power Control & Monitoring 240VAC: 12VDC: $ 200A DC WATT METER POWER ANALYSER WITH LCD DISPLAY $ 59 $ 95 TPLINK SMART WI-FI PLUG YN-8446 Easily manage your household electronic devices anytime, anywhere! Turn on/off. Just connect to your Wi-Fi network and control using the free App. 9 29 95 Due mid May MAINS POWER METER WITH EXTENDABLE LCD DISPLAY MS-6108 Smart design with LCD screen connected to main unit with a 1.5m cable allowing you to take readings from hard to reach places. Displays watts, cost, volts, amps, and CO2 emission. All-in-one power meter, voltmeter, amp-hour meter, ammeter and energy meter. Slots between various links of a power system. Check charge going to a battery from battery charger or alternator, solar panel output, charge controller output, health and performance of batteries, evaluate charging efficiency or measure power and energy consumption of any load device with a battery. • 75A continuous / 200A Max • Up to 60VDC compatibility BARE LEADS MS-6190 $49.95 WITH ANDERSON CONNECTORS MS-6192 $59.95 19 95 $ 95 19 95 $ 24 HOUR MECHANICAL TIMER SWITCH MS-6113 Simple and effective for automatically switching your appliances on and off at particular times. Set-up takes mere seconds, then set and forget. • Override switch • 10A <at> 240V (2400W) max load 19 95 $ REMOTE CONTROLLED MAINS OUTLET CONTROLLER MS-6148 $ DUAL USB SMART CAR CHARGER CAR BATTERY DISCHARGE WITH LCD VOLTAGE DISPLAY MP-3692 PROTECTOR MB-3676 With two USB outlets capable of a combined 4.8A, you can charge your devices in minimal time. • Battery voltage or USB charging current display • Output: 2.4A x 2 (max) • Input power: 12-24V Turn any standard mains outlet on and off via remote. Good for switching off hard-to-reach power points. • Up to 30m range $ $ NOW 149 $ 48 95 DIGITAL DC POWER METER MS-6170 140A DUAL BATTERY ISOLATOR KIT WITH WIRING MB-3686 WAS $159 An ideal addition to any low voltage DC system. Features real time display of the voltage, current draw and power consumption. Includes internal shunt. • 0-20A Allows two batteries to be charged from your engine alternator at the same time. See website for contents. • Emergency override feature • LED status indicator • 67(L) x 67(W) x 53(H)mm 9 ea 9 $ 95 HC-4030 UNIVERSAL BRASS BATTERY TERMINALS Heavy duty, solderless, marine grade brass. Perfect for isolating your battery to prevent battery drain when not in use. Sold in pairs. SADDLE HC-4030 LUG BOLT STYLE HC-4034 ISOLATING (NEGATIVE POST) HC-4038 $ INOX BATTERY CONDITIONER 19 95 FROM 3.7V 18650 2600MAH LI-ION PROTECTED BATTERY SB-2299 3.2V LIFEPO4 RECHARGEABLE BATTERIES Fully protected against overcharge, over-discharge, short-circuit, and overcurrent to keep the battery in good shape and devices safe. • Rechargeable Lithium iron phosphate (LiFePO4) is more chemically stable type of lithium rechargeable cell. Very popular due to increased safety and longer cycle life. • 600mAh, 1600mAh & 3000mAh available 52 Capable of taking an 8-16VDC input voltage, and giving a stable, regulated 13.8V/14.4V 4-stage charger output to give your auxiliary battery a full 100% charge. • Input voltage: 8 - 16VDC • Output current: 40A max $ FROM 39 95 SF-2249 BATTERY ISOLATOR SWITCHES WITH AFD* QP-2263 Versatile battery tester for vehicle or vessel batteries. • LCD panel of voltage as well as LED indication for under/overcharge • Suitable for 12V and 24V batteries 1195 $ 4 STAGE 40A DC TO DC BOOST CHARGER MB-3690 WAS $349 24 95 SB-2305 $ NOW 299 12/24V BATTERY TESTER NA-1420 Removes or reduces sulphation. 92ml pack sufficient for most automotive batteries. Due mid May Warns you when battery power is running low & disconnects power through the unit when power gets too low. Plug and play operation, no tools required! • Max Power Output: 8A • Connection: Cigarette Lighter • 95(L) x 35(W) x 155(H)mm SAVE $50 SAVE $10 $ 95 FROM 49 95 Durable and rated for massive output. Protects alternator when switching batteries in and out of the circuit. 2 POSITION SF-2249 $39.95 4 POSITION SF-2250 $49.95 *AFD - Alternator Field Disconnect SB-1723 FROM $ 2 $ 95 NI-MH RECHARGEABLE BATTERIES Nickel Metal Hydride (Ni-MH) batteries offer superior features to Nickel Cadmium (Ni-Cd) rechargeable batteries. AA,AAA, C, D & 9V. Nipple or solder tabs. • Higher current capacities • High drain performances Follow us at facebook.com/jaycarelectronics 39 95 DUAL CHANNEL LI-ION AND NI-MH BATTERY CHARGER MB-3635 Supports charging of LiFePo4, Li-ion, Ni-MH, and Ni-Cd batteries. Individual charging lanes. LCD feedback. • Charging Current: 500mA / 1000mA • 67(W) x 129(H) x 38(D)mm Catalogue Sale 24 April - 23 May, 2018 TECH TALK: Multi State Charging States Smart Chargers have a pre-set charging cycle such as 3, 4 or 9 stages. The charging voltage and current is optimised in each stage to suit the type of battery being charged, this ensure maximum operating efficiency and battery life. Below are some common charging states: READ THE FULL ARTICLE: jaycar.com.au/charging-states DESULPHATION: Pulsing current and voltage, removes sulphate from the lead plates in sulphate batteries. RECONDITION MODE: This mode charges at higher voltage to recondition the sulphate and increase battery life. SOFT START: Charging starts with reduced current until battery voltage reaches a normal condition for charge. ANALYSIS: Tests the condition of the battery. If is unable to hold charge it needs to be replaced. BULK MODE: During this stage the battery is charged to up to 80% capacity, which is the majority of its charge. FLOAT: When battery is fully charged, this state maintains a trickle, minimal charge current, to ensure the battery remains fully charged. PULSE MODE: Maintaining the battery at 95-100% capacity. The charger monitors the battery voltage and injects a pulse to maintain the battery charge. ABSORPTION MODE: Completes the charge up to (or close to) 100% at a slower charge rate in order to protect the batteries working life. Multi-State Battery Chargers: High tech SLA battery chargers for automotive, marine, motorcycle, workshop or industrial use. Capable of recharging the battery and maintaining the charge state indefinitely. Safe to leave connected for months. $ 49 95 $ 89 95 169 $ 6/12VDC 1.5A 3 STATE CHARGER MB-3609 6/12VDC 4A 4 STATE CHARGER MB-3611 Suits all SLA batteries: Wet cell, gell cell and AGM • Output voltage: 6/12VDC • Max output current: 1.5A • Capacity: 6-20Ah • 110(L) x 58(W) x 46(D)mm Uses a microprocessor to diagnose the battery's state of charge. Suits all SLA batteries: wet cell, gell cell and AGM. • Output voltage: 6/12VDC • Max output current: 1A/4A • Capacity: 7-80Ah • IP65 rated • 200(L) x 70(W) x 50(D)mm 12V-7.2A/24V-3.6A 9 STATE CHARGER MB-3613 Fully automatic 9 state charger for 12 or 24V sealed lead acid (SLA) batteries- wet cell, gel cell and AGM. • Output voltage: 12/24VDC • Max output current: 7.2A/3.6A • Capacity: 14-160Ah • IP65 rated • 210(L) x 90(W) x 60(D)mm $ $ NOW 299 SAVE $50 12V-15A/24V-7.5A 9-STATE CHARGER MB-3607 WAS $349 Fully automatic 15A high current charger with maintenance charging of all types of SLA batteries as well as leadcalcium batteries from 50 - 250Ah, and either 12V or 24V. • Output voltage: 12/24VDC • Max output current: 15A/7.5A • Capacity: 50-250Ah • IP65 rated • 260(L) x 135(W) x 70(H)mm $ Advanced electronic and fully automatic. Charge multiple batteries such as cranking and house batteries simultaneously once connected to shore power. • 5 multi-stage charging • Initialize, fast charging, optimizing, maintaining, smart storage modes • Suits flooded, standard AGM & GEL batteries • IP68 waterproof rated • LED system & status indicators 12A 12/24V DUAL MB-3616 WAS $299 20A 12/24/36V TRIPLE MB-3617 WAS $399 79 95 12VDC LEAD ACID BATTERY TESTER QP-2261 Tests most automotive cranking lead acid batteries, including an ordinary lead acid battery, AGM flat plate, AGM spiral, and GEL batteries. • 6-30VDC voltage range • 125(L) x 70(W) x 25(H)mm MB-3616 ON-BOARD MARINE BATTERY CHARGERS FROM 34 95 BATTERY BOXES Protect your batteries with these sturdy boxes. Perfect for mounting in your boat, trailer or caravan. FITS 40AH SLA BATTERY HB-8100 $34.95 FITS 100AH SLA BATTERY HB-8102 $39.95 Battery not included To order: phone 1800 022 888 or visit www.jaycar.com.au SAVE $50 $ NOW 349 SAVE $50 MB-3617 SB-1698 $ NOW 249 FROM 129 $ 12VDC SLA DEEP CYCLE GEL BATTERIES Leakproof and completely sealed, ideal for solar power, 4WD, camping etc. 26AH SB-1698 $129 40AH SB-1699 $199 100AH SB-1695 $379 See terms & conditions on page 8. SB-1680 $ FROM 279 12VD DEEP CYCLE AGM BATTERIES Designed to store large amounts of energy, they give superior deep cycling performance for many different recreational and industrial applications such as camping, boats, motorhomes etc. 75AH SB-1680 $279 100AH SB-1682 $329 53 Workbench Essentials: There has been an obvious resurgence in people getting back to the workbench and reviving skills involving manual dexterity. As you will see across the following pages, Jaycar has all the DIY tools you'll need to equip your workbench so you can create projects from the power of your brain and your hands. $ NOW 249 SAVE $50 3 5 4 179 $ $ NOW 59 95 SAVE $10 1 $ 39 95 6 $ 59 95 $ 2 NOW 69 95 1. ANTI STATIC MAT TH-1776 • Ideal for field service people • Mat folds out to work area of 600 x 600mm (approx) • 2 pouches at one end • Ground lead and and wrist strap included 2. 8 PIECE SCREWDRIVER AND TOOL SET TD-2031 • Quality rubber-moulded insulation for in-hand comfort • VDE approved to 1000V • Insulated right to the tip 3. 65W ESD CONTROLLED SOLDERING STATION WITH DIGITAL DISPLAY TS-1440 WAS $299 • Excellent temperature stability and anti-static characteristics • 230-240VAC supply voltage • 200 - 480°C temperature range • 65W capacity heater • 0.5mmt tip supplied • 146(L) x 115(W) x 98(H)mm 4. SOLDER FUME EXTRACTOR TS-1580 WAS $69.95 • Removes dangerous solder fumes • Ball bearing high volume fan • ESD safe • Spare filters, pack of 5 - sold separately (TS-1581 $9.95) • 260(H) x 200(W) x170(D)mm 5. 0 TO 30VDC 5A REGULATED LAB POWER SUPPLY MP-3840 • Digital control, large LED display • Built-in over-current & short circuit protection • Output current: 0-5A • 270(L) x 120(W) x 185(H)mm 6. MINI TRUE RMS AUTORANGING DMM QM-1570 WAS $89.95 • Compact, IP65 rated • Drop tested from 2m height • Cat III 600V Safety Rating • AC/DC voltages up to 600V • AC/DC current up to 10A • Temperature -20°C to 750°C • Includes test leads and carry case SAVE $20 CAT III Clamp Meters Our range of CAT III Clamp Meters makes the best general troubleshooting tool for commercial and residential electricians and includes features found on more expensive units such as autoranging, data hold, non-contact voltage, relative measurement and auto power-off. Multi function with Resistance, Capacitance, Frequency and Temperature, all Clamp Meters are supplied with quality temperature probe and carry case. MP-3242 NEW LOW PRICE! ORRP $239 199 $ $ SAVE $40 VARIABLE LABORATORY AUTOTRANSFOMER (VARIAC) MP-3080 Encased in heavy-duty steel housing, this unit enables the AC input to a mains powered appliance to be easily varied between 0 to full line voltage (or greater). • 500 VA (fused) rated power handling • 0-260 VAC <at> 50Hz output voltage $ 22 95 WAS $129 WAS $159 SAVE $10 SAVE $30 SAVE $10 $ 59 95 $ 99 149 $ 400A AC QM-1561 400A AC/DC QM-1563 • Cat III 600V, 4000 count • AC/DC voltage < 600V • AC current < 400A • Jaw opening 30mm • Cat III 600V, 4000 count • AC/DC voltage < 600V • AC/DC current < 400A • Jaw opening 30mm 54 • Cat III 600V, 4000 count • AC/DC voltage < 600V • AC/DC current < 1000A • True RMS, min-max, bargraph and more • Jaw opening 40mm Follow us at facebook.com/jaycarelectronics Versatile switchmode power supplies in a range of different configurations. 12VDC 5A MP-3242 $59.95 19VDC 3.4A MP-3246 $59.95 24VDC 2.7A MP-3248 $59.95 12VDC 5A (5 PLUGS) MP-3243 $64.95 8 5 WAY CRIMPING TOOL Consists of all the standard 1/4" (6.35mm) QC tabs and receptacles and also odd QC sizes ie: 3.3mm and 4.8mm sizes. 160 pieces. 1000A TRUE RMS AC/DC QM-1566 60W DESKTOP STYLE AC ADAPTOR $ 95 QUICK CONNECT PACK PT-4530 WAS $69.95 FROM 59 95 $ TH-1828 Cuts and strips wire. Can also cut bolts with diameter M2.6, M3.0, M3.5, M4.0 & M5.0. 34 95 42 PIECE ASSORTED SOLDER SPLICE HEATSHRINK PACK WH-5668 Quickly create sealed soldered joint in one go. Each splice has just the right amount of solder to create a secure and well-insulated connection. Includes assorted colours and sizes to suit various cable size. See website for full contents. Catalogue Sale 24 April - 23 May, 2018 EXCLUSIVE CLUB OFFERS: FOR NERD PERKS CLUB MEMBERS WE HAVE SPECIAL OFFERS EVERY MONTH. LOOK OUT FOR THESE TICKETS IN-STORE! 15% OFF 15% OFF F 3D PRINTER F O 15%FILAMENT* 3D PRINTER FILAMENT* PRINTER 3DEXCLUSIVE ENT* MOFFER CLUB FILA *EXCLUDES 3D PRINTER PARTS & ACCESSORIES NOT A MEMBER? Visit www.jaycar.com.au/nerdperks NERD PERKS CLUB OFFER *EXCLUDES 3D *EXCLUDES 3D PRINTER PARTS PRINTER PARTS & ACCESSORIES & ACCESSORIES CLUS E CLUB OFIV FER NERD PERKS CLUB OFFER NOT A MEMBER? NERD PERKS CLUB OFFER EX Sign up NOW! It’s free to join. Valid 24/7/17 to 23/8/17 NOT A MEM BER? E Sign up NOW! It’s free to join. EXCLUSIV CLUB OFFE 2RFOR JUST $6 $49.90 BER? NOT A MEM! It’s free to join. Valid 24/7/17 to 10% OFF 23/8/17 Sign up NOW Valid 24/7/17 to 23/8/17 PORTABLE POWER SUPPLY BUNDLE PURE SINE WAVE INVERTERS 600W - 1500W 9V ALKALINE BATTERY SB-2423 $3.95 2.1MM DC PLUG WITH SCREW TERMINALS PA-3711 $4.95 9V BATTERY SNAP PH-9232 95¢ VALUED AT $9.85 MAINS WI-FI CONTROLLER MODULE WITH APP SAVE 35% MS-6126 REG $29.95 SAVE 15% 12V 600W 20A MI-5720 12V 1000W 30A MI-5722 12V 1500W 30A MI-5724 NERD PERKS NERD PERKS NERD PERKS NERD PERKS SAVE SAVE SAVE SAVE 20% 20% SOLDERING IRON TIP CLEANER TS-1512 REG $12.95 CLUB $9.95 Cleans and rejuvenates soldering iron tips. 15g. ABS IP66 ENCLOSURE HB-6404 REG $34.95 CLUB $27.95 Large 200(L) x 200(W) x 130(D)mm. 35% 20% THERMAL TRANSFER TAPE NM-2790 REG $12.95 CLUB $7.95 100x100x0.5mm. Pack of 2. 12V 45W DIN RAIL POWER SUPPLY MP-3190 REG $49.95 CLUB $39.95 Single output. Built-in EMI filter. NERD PERKS NERD PERKS NERD PERKS NERD PERKS SAVE SAVE HALF PRICE! 25% 15% 20% NON-CONTACT IR THERMOMETER QM-7218 REG $34.95 CLUB $27.95 Ultra compact. IP67 rated. 30 DRAWER CABINET HB-6323 REG $29.95 CLUB $24.95 280(W) x 210(H) x 130(D)mm. ANTI STATIC WRIST STRAP TH-1781 REG $17.95 CLUB $8.95 Expanded lead length approx. 1.8 m NERD PERKS NERD PERKS NERD PERKS SAVE HALF PRICE! SAVE 15% DIGITAL AUDIO CONVERTER & REPEATER AC-1592 REG $54.95 CLUB $44.95 Signal output to TOSLINK and Coaxial ports simultaneously. GREENCAP CAPACITOR PACK - 60 PIECES RG-5199 REG $11.95 CLUB $5.95 From 0.001uF to 0.22uF. 100V. NERD PERKS CLUB MEMBERS RECEIVE: 15% OFF 3D PRINTER FILAMENT* SAVE USB 3.0 SDXC/MICRO SD CARD READER XC-4782 REG $16.95 CLUB 11.95 Supports up to 32GB SDHC and 2TB SDXC. NERD PERKS SAVE 25% 25% 250G DUST REMOVER SPRAY CAN NA-1018 REG $19.95 CLUB $14.95 Non-CFC, non-flammable gas. BLADE FUSE HOLDER SZ-2013 REG $34.95 CLUB $24.95 32VDC. 30A. YOUR CLUB, YOUR PERKS: REMEMBER TO GET YOUR CARD SCANNED AT THE COUNTER TO GET POINTS*. $1 = 1 POINT, 500 POINTS = $25 JAYCOINS GIFT CARD Conditions apply. See website for T&Cs * *Excludes 3D printer parts & accessories To order: phone 1800 022 888 or visit www.jaycar.com.au See terms & conditions on page 8. 55 What's New: We've hand picked just some of our latest new products. Enjoy! $ 59 CAR BOOM BOX 95 WITH AMPLIFER QM-3410 6” woofer and powerful tweeter, for great overall sound. Play your favourite music from multiple sources using various inputs: RCA, USB, microSD card slot or stream live via Bluetooth. • USB & microSD card input • 1200W PMPO output • FM Radio • Power: 12VDC, 2A /240VAC • 400(W) x 220(H) x 195(D)mm 169 $ $ TPLINK AC1200 VDSL/ADSL MODEM ROUTER YN-8440 69 95 Takes your standard microphone level and boosts it for compatibility with line-level 6.5mm inputs. Stereo RCA output. • Volume control • Mains powered 9 $ 95 9 Build a project with heaps of 7-segment displays without using up a lot of IO pins! • SPI interface • 15mm panel height with red 9mm digits • MAX7219 features dimming and digit decoding $ Due early May. 39 95 12V BATTERY LOW VOLTAGE PROTECTOR MB-3677 NBN/UFB REPLACEMENT POWER SUPPLY 12V 2.5A MP-3538 Automatically shuts off power to the connected device if voltage drops below 11.6V. • Power status indicator • No installation required Plug-in replacement power supply for direct connection into your NBN or UFB connection box. No wiring required. Suitable for use with FTTP optical fibre boxes as used in Australian NBN and New Zealand UFB networks. Compliant with Australian and New Zealand Safety Standards. • Input: 100 - 240VAC 50/60Hz • Output: 12VDC 2.5A 69 95 19 95 $ LED PROJECTION LIGHT SL-3403 RGB 8X8 LED MATRIX ZD-1810 Light up your home or garden. Mains powered, IP65 weatherproof housing. Includes a garden stake, stand, and wall-mounting kit. • 125(D) x 155(H) x 100(W)mm Full RGB 8x8 Matrix controlled through 32 pins. Flush edges for creating extended displays. • 192 LEDs in 64 pixels 12 95 $ 95 8 DIGIT 7 SEGMENT DISPLAY MODULE XC-3714 19 95 $ $ 2 CHANNEL MICROPHONE MIXER WITH PREAMPLIFIER AM-4201 Unlock the full potential of your internet connection. Combined dual band Wi-Fi speeds of up to 1.2Gbps, eliminating lag and buffering from your online experience. Due early May. $ 9 $ 95 IR REMOTE CONTROL FOR ARDUINO® XC-3718 LED TRAFFIC LIGHT MODULE FOR ARDUINO® XC-3720 LED PUSHBUTTON MODULE FOR ARDUINO® XC-3722 Add IR remote control to your next Arduino® project. Compact design with 21 buttons including numbers and channel controls. Set up a basic status display for your next project. Universal colour codes: RED, YELLOW, GREEN. Stop, Caution, Go. • 10mm red, yellow, green LEDs A simple pushbutton module with a green LED, ideal for adding an input to a breadboard design or other project. • 5V and 3.3V compatible TERMS AND CONDITIONS: REWARDS / NERD PERKS CARD HOLDERS FREE GIFT, % SAVING DEALS, DOUBLE POINTS & MEMBERS OFFERS requires ACTIVE Jaycar Rewards / Nerd Perks Card membership at time of purchase. Refer to website for Rewards/Nerd Perks Card T&Cs. PAGE 3: Nerd Perks Card holders receive special price of $34.95 for Power Usage Monitor Project (1 x XC-3802 + 1 x XC-4610 + 1 x XC-3850 + 1 x WH-3025 + 1 x HM-3230) when purchased as bundle. PAGE 7: Nerd Perks Card holders receive special price of $6.00 for Portable Power Supply Deal (1 x SB-2423 + 1 x PA-3711 + 1 x PH-9232) when purchased as bundle. Nerd Perks Card Holders gets 10% OFF Regular Price for Pure Sinewave Inverters with Solar Regulators 600W-1500W applies to MI-5720, MI-5722 & MI-5724. 15% OFF 3D Printer Filament (excludes 3D printer parts & accessories). STUA RT H WY GA ON RA W YA R A LV I CA NA ON COLES EXPRESS Head Office 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ES CR AW RR YA 1800 022 888 www.jaycar.com.au GI RD OR GA GE E AV N ST A NE TO YS RO S OO Y E W WA R N TE ENT GA E C AR B M O HO UT RD Y RE WA NT TE CE S GA ING TH OR PP O H LW FOR YOUR NEAREST STORE & OPENING HOURS: NEW STORE: PALMERSTON Gateway Shopping Centre, Cnr Stuart Hwy, Roystonea Ave & Yarrawonga Rd NT 0830 PH: (08) 8900 0025 97 STORES & OVER 140 STOCKISTS NATIONWIDE 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 Stockist. 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 April - 23 May, 2018. Don’t let one small “oops” fry your computer – and cost you $$$$! USB PORT PROTECTOR by Nicholas Vinen Using your PC or laptop to power a 5V project that you’re working on is very convenient – but it’s so easy to make a small slip while plugging something into a breadboard and oops! That’s exactly what happened to one of our staff members. For a while after the incident, it looked like his (own!) laptop was toast. But fortunately he was able to safely reset it and it came back to life. But he was SO lucky! Next time he’ll definitely be using this simple, economic device . . . W e won’t name the hapless person who thought he’d cooked his laptop. To avoid embarrassment, we’ll simply refer to him as A.P. (ie, Accident Prone). This is one of those projects we know will be useful because A.P. kept asking “is it finished yet” as he obviously needed it! That incident obviously spooked him and why wouldn’t it? He could have lost a lot of work and spent quite a bit of money and time on buying a new computer and then setting it up, which could have taken several days. We do a lot of development work, increasingly with Arduinos and similar microcontroller modules. We also do quite a bit of bread-boarding, often in combination with the Arduinos. When you’re doing this kind of work and you have external power supplies or voltage sources connected to your siliconchip.com.au circuit, that’s just asking for trouble. You may not realise it but when an Arduino board (or similar) is plugged into your computer’s USB port, you’re just one slip away from potential disaster. For example, say you’re running the Arduino from a 12V plugpack, because it’s driving some 12V relays or a motor or whatever. So there’s a source of 12V right near a bunch of other connections on the Arduino board, just looking for an excuse to find its way onto the USB 5V rail and into your computer. One slip, and oops! It could blow up the Arduino, your shield(s), and even your computer. Not only will this USB port protector vastly improve the chances of your computer surviving such an event, it may also prevent damage to the Arduino board and whatever Celebrating 30 Years May 2018  57 Fig.1: the circuit diagram of the USB Port Protector. Diode D3, zener TVS1 and transistor Q1 are all connected between VCC and GND and shunt current when an excessive voltage is applied, while polyswitch PTC1 and fuse F1 prevent large currents from flowing if the fault is serious. Diodes D1 & D2 and zener TVS2 protect the D+ and D- data lines. shields or other circuitry are plugged into the USB port. We can’t promise it will be 100% safe but it’s certainly a lot safer than if you aren’t using any protection... You might expect USB ports to have some kind of builtin protection against external voltages being fed in. After all, all kinds of devices can be plugged into these ports, including external hard disks and amplifiers and other gear which has its own, separate power supply. In fact, many USB ports do have some protection, such as series PTC thermistors (“polyswitches”) to limit fault currents, transient voltage suppressors and so on. But this protection varies between computers and is often absent in laptops and notebook computers. Let’s face it, there’s a lot less space inside portable computers – and manufacturers also want to keep the computer as light as possible and save money where they can. That means leaving out anything that isn’t absolutely necessary. Regardless of what sort of protection your USB port may have, this USB Port Protector is small and cheap, so why not add in an extra layer of defence? If you ever manage to activate its protection, it will have paid for its cost many times over! Circuit description The circuit of the USB Port Protector is shown in Fig.1. USB plug CON1, which plugs into your computer, is shown on the left side while the USB socket, CON2, goes to the connected device (Arduino, etc) is on the right. Just to be clear – the potential danger of overload from excessive voltages or currents comes via CON2. The ground connection and the two differential data lines, D+ and D-, are wired straight through between plug and socket (ie, CON1 and CON2) while 5V flows through fuse F1 and positive temperature coefficient thermistor PTC1. 58 Silicon Chip We’ve used both a fuse and PTC because the fuse reacts faster to very high currents, protecting the rest of the circuitry on the board if there’s a serious fault, but the PTC does not need to be replaced if it “trips” and helps the circuit to handle moderate overloads without damage. PTC1 normally has a low resistance – around 100mΩ below 1A – but if the current through it increases, its resistance rises, limiting it at around 2A (given enough time for it to heat up). This would normally only occur if the 5V line rises above 5.5V and the Port Protector is shunting current in order to prevent it rising further. In fact, the Port Protector does very little as long as the USB supply voltage is in the normal range of 0-5.25V and the D- and D+ lines are in the normal range of 0-3.3V. Green LED1 lights up to indicate power is present but that’s about it. The unit draws around 3mA in this condition. If the 5V rail is pulled negative, ie, below 0V (eg, you’ve accidentally shorted it to the output of a transformer or some other supply rail) then schottky diode D3 will conduct. This prevents VCC from going below about -0.5V. D3 is a high-current diode, capable of handling 15A continuously and 275A for around 5ms, so it makes a very effective clamp. It limits the voltage on VCC to -0.55V at 15A, so your PC is safe from damage from negative voltages on the supply line. Should the overload condition persist, either PTC1 will limit the overload current to a safe level or F1 will blow, disconnecting the compromised circuitry from your computer. Clamping positive voltages It’s even more likely that you might accidentally short the 5V rail to a higher voltage, eg, 12V from a car battery. Just think of the heavy currents which will fry anything connected to it! The Port Protector has active and passive Celebrating 30 Years siliconchip.com.au Fig.3: the fuse blow time for F1 (black) and “trip” time for PTC1 (blue) at various current levels. The relevant portion of Q1’s SOA curve from Fig.2 is plotted in red and you can see that F1 will protect Q1 for fault currents above 2A. Fig.2: safe operating area (curves) for the ECH8102 PNP transistor, used in this device as a protective shunt. The vertical red line corresponds to a shunt voltage of 5.5V and its intersection with the SOA curves shows how long the transistor is guaranteed to survive at various collector current levels. systems to handle this situation. The active system is the first line of defence. It comprises high-current PNP transistor Q1 and shunt voltage reference REF1. The 1.2kΩ/1kΩ resistive divider across the 5V supply feeds 45.45% of the supply voltage to the adjust terminal of REF1. It’s designed to sink current into its cathode terminal as soon as this adjust terminal exceeds +2.5V. So given the voltage divider, that means that it will sink current when the supply exceeds 5.5V (2.5V ÷ 45.45%). This will cause a voltage to develop across the 470Ω resistor and once that voltage exceeds around 0.7V (Q1’s baseemitter voltage), Q1 will switch on and shunt the 5V supply rail, pulling it down. In this manner, REF1 and Q1 act to limit the 5V supply rail to just over 5.5V. Q1 is capable of handling more than 10A but since there will be 5.5V between its collector and emitter, it can only do that for a very short time before it overheats. But at the same time PTC1 will rapidly heat up and increase its resistance, to limit that current. And in any case, if the current exceeds 3A, for example, the fuse will very quickly blow before Q1 is damaged. So REF1/Q1 act together as a very precise and very fast clamp. When REF1 is sinking current from Q1’s base, Q2 will also normally switch on as its base is also pulled around 0.7V below its emitter, via the 10kΩ resistor. This will light up red LED2, indicating that the clamp is operating and that you have a problem. LED2’s current is limited by its low base current and relatively fixed gain (hFE). REF1 can sink up to at least 100mA and Q1 has a current gain (hFE) in the hundreds, so Q1 is more than capable of passing its full peak current rating of 24A in this circuit. Note that LED2 may go out if there is a persistent overload, since when Q1 heats up, its base-emitter voltage will drop and it may drop low enough below Q2’s base-emitter switch-on voltage that it will no longer switch on. But chances are that PTC1 and/or F1 will have acted to limit the fault current by that stage anyway. siliconchip.com.au The only problem with the clamp provided by Q1 and REF1 is the reaction time. It takes a short time for REF1 to react to an increase in the feedback voltage and it also takes time for Q1 to switch on – around a microsecond. Passive clamping This is why we also have a transient voltage suppressor, TVS1 connected across the 5V supply rail. It’s a passive device which will react more-or-less instantly to excessive voltage. But like most zener-type devices, the difference between the voltage at which it will start to conduct current and the voltage across it when a large current is flowing is quite large. We’ve selected the most suitable device possible but it’s still not ideal. The “working voltage” for TVS1 is defined as 5V but it’s designed to pass only 1mA or so at 6.0V. The clamping voltages are specified as 9.8V at 1A and 13.5V at 42A. So clearly, we can’t rely on this device to protect the PC since it would allow quite a high voltage to be fed back in before taking effect. Hence our dual-action strategy, with TVS1 there to limit very brief, high-voltage excursions (eg, a static discharge) and also to “fill in the gaps” for the short period until Q1/REF1 are able to switch on and shunt the fault current. Protection for the signal lines We’ve also included 3V transient voltage suppressor TVS2 (take care of the metal tab on the underside of its body, as it could short out the connection when soldered) and dual schottky diodes D1 and D2 to protect against damaging voltages being fed in via the D+ and D- signal wires. This is unlikely, since these lines normally go straight to some sort of USB/serial adaptor or micro on a development board and so there aren’t many exposed components to accidentally short. But it’s still possible that a high voltage fed into your Celebrating 30 Years May 2018  59 +5V rail (or +3.3V rail, or some other supply point) could damage the USB/serial adaptor or microcontroller and allow current to flow through into the D+ and/or D- lines. So we decided that we should provide at least some protection for these lines, as well. The half of dual diodes D1/D2 that connects between ground and the signal line prevents them from being pulled too far below ground. We’re using smaller diodes here since a large diode would have too much capacitance and would interfere with USB signalling. But these diodes are still rated at 300mA continuous and 1.25A for 10ms, with a forward voltage below 1V up to several hundred milliamps. So they should provide decent protection. TVS2 has a breakdown voltage of around 3.6V at 1mA and a clamping voltage of 6.5V at 25A. So the combination of D1/D2 and TVS2 should conduct significant current away from the D+/D- lines well before their voltages reach 5V. Most USB ports would not be damaged by these voltages. We can’t put a voltage suppressor like TVS2 directly between the D+ and D- lines and ground because it would have far too much capacitance. But the series diodes between D+/D- and TVS2 have a much lower capacitance that’s effectively in series with that of TVS2, so they have virtually no effect on signalling. We tested our prototype with a “hi-speed” USB card reader and it functioned normally. Is it bulletproof? In a word, no, but if it does fail, the Port Protector is likely to fail in such a way that it still protects your computer. Parts list – USB Port Protector 1 double-sided PCB, coded 07105181, 32.5 x 19mm 1 PCB-mount USB Type A horizontal plug (CON1) 1 PCB-mount USB Type A horizontal socket (CON2) [eg, Altronics P1300] 1 SMD fuse, 3216/1206 package, 1A super fast blow [Vishay MFU1206FF01000P100] 1 SMD 1.1A PTC thermistor, 3216/1206 package [Bourns MF-NSMF110-2] 1 30mm length of 20mm diameter clear heatshrink tubing Semiconductors 1 AN431AN shunt reference IC, SOT-23 (REF1) 1 ECH8102 12A PNP transistor, ECH8 (Q1) 1 BC856 100mA PNP transistor, SOT-23 (Q2) 1 high-brightness green LED, 3216/1206 package (LED1) 1 high-brightness red LED, 3216/1206 package (LED2) 1 CDSOD323-T05S transient voltage suppressor, SOD-323 (TVS1) 1 SM2T3V3A transient voltage suppressor, DO-216AA (TVS2) 2 BAT54SFILM dual 300mA schottky diodes, SOT-23 (D1,D2) 1 15A 30V schottky diode, DO-214AB (D3; MCC SK153) Capacitors 1 100nF SMD X7R ceramic, 3216/1206 package Resistors (all SMD 3216/1206 package, 1%) 1 47kΩ (coded 4702 or 473) 1 10kΩ (coded 1002 or 103) 1 1.2kΩ (coded 122) 1 1kΩ (coded 102) 1 470Ω (coded 471) 60 Silicon Chip While our testing shows that it’s robust and can handle significant overloads without damage, if you apply just the right (worst possible) combination of voltage and current, it may be possible to blow Q1 or TVS1 before fuse F1 blows. Still, our testing suggests that the most likely outcome of a serious overload is for F1 to blow and at least it’s cheap and (relatively) easy to replace. The difficulty in designing a circuit like this to be able to withstand anything you can throw at it is that in order to effectively protect against a high current source being connected to the VCC line, it needs to absorb quite a lot of power in a brief period. And while the PTC and/or fuse should ideally cut the power to protect the other components, they may not be fast enough. Fig.2 shows the “safe operating area” (SOA) curves for transistor Q1, taken from the ECH8102 data sheet. We’ve added a vertical red line to show the typical voltage of about 5.5V across Q1 while it is conducting. While this is a high-current transistor, it is quite tiny so if a high current is applied, it will quickly overheat and might fail. As shown in Fig.2, it’s guaranteed to survive 24A at 5.5V (132W!) for somewhere between 500µs and 1ms. For longer periods, the maximum allowable current is lower; around 3A (16.5W) for 10ms, 1.5A (8.25W) for 100ms and 300mA (1.65W) continuously. Beyond this, it may survive but that isn’t guaranteed. Our testing has shown that for a single pulse, these ratings are very conservative. But it’s good practice to design a circuit to stay within these ratings. The “trip” times for PTC1 (blue) and F1 (black) are shown in Fig.3. We’ve also plotted the relevant portion of the SOA curve for Q1 in red so that you can compare them. As you can see, F1 responds considerably faster than PTC1 and in fact is very likely to blow before Q1’s SOA is exceeded for currents above 2A. For fault currents between 300mA and 2A, it’s possible that Q1 will overheat and fail before either F1 blows or PTC1 acts to limit the current. And in fact, PTC1 is not guaranteed to do anything for fault currents below 1A. You will need to notice red LED2 lighting and resolve the fault yourself. Still, as we said above, the ratings for Q1 seem to be pretty conservative and as long as the overload is limited to no more than a second or two, we would expect it to survive. Looking at Fig.2, you may wonder why we’ve bothered with the PTC at all, given that its “trip” current is higher than the fuse blow current over most of the graph. But keep in mind that PTC1 is considered to be “tripped” when it has reached a high enough resistance value to keep the fault current below 2.2A. It will still have some effect in reducing the fault current even at lower current levels and shorter time spans, because its resistance will start to increase well before it has fully tripped. And you also have the option of replacing F1 with a zeroohm resistor (or just soldering across the pads) and relying on PTC1 to limit fault currents. This does increase the risk of blowing Q1 in a serious fault (although, as we said, it’s pretty robust) but doing so would also increase the chance that the unit will survive a moderate overload unscathed and you won’t have a blown fuse to replace. Note that while replacing Q1 is a bit of a pain, it’s actually quite cheap (under $1) so if Q1 does “throw itself on the grenade” and fail while protecting your computer from damage, at least it isn’t an expensive failure. Celebrating 30 Years siliconchip.com.au Figs.4&5: top and bottom overlay diagrams for the USB Port Protector. Use these as a guide during construction. Be careful with the polarity for TVS1, TVS2, Q1 and LEDs1&2. It’s easiest to start by fitting Q1 and TVS1, then the remainder of topside SMD components, then the bottom-side components and finally, CON1 and CON2. The matching photographs above are reproduced close to twice actual size, for clarity. Sourcing the parts Most of the parts are surface-mount devices (SMDs) and they are all available from Digi-Key or Mouser in the USA. Most are also available from element14 in Australia. While both Digi-Key and Mouser offer free express international delivery for orders over $AU60, the parts for this project will cost you much less than that. So we are also making the parts available a kit, to make it easier to build the USB Port Protector. The complete kit, including PCB and the USB input and output sockets will sell for $15.00 (Cat SC-4574). Construction The USB Port Protector is built on a double-sided PCB that measures 32.5 x 19mm and is coded 07105181. All but four of the components are mounted on the top side of the board, as shown in the overlay diagrams, Figs.4 & 5 and matching photos. The only through-hole components are the USB plug and socket. By the way, you may notice a minor difference between the overlay diagrams and the PCB photos: we’ve changed TVS2 to a more suitable part since building the prototype. Most of the parts are fairly easy to solder, although some of them are quite close together, to keep the unit compact. It’s easiest to do in the following order. Start with transistor Q1. This is in a fairly small ECH8 package, with four short leads on each side. The good news is that most of the adjacent leads are connected together so it doesn’t matter if you bridge the pins when soldering (in fact, it’s pretty much unavoidable). Pin 4 is the base connection and you need to make sure it doesn’t short to pin 3, the emitter. Start by identifying pin 1. There is a dot printed in the corner on the top of the package but you will need a magnifier and good light to see it. Orientate the part so that it matches the pin 1 markings on the PCB and smear a thin layer of flux paste on all eight of its pads. Apply a tiny amount of solder to the pad for pin 4, then heat this solder while sliding the part into place. Check that the other seven pins are correctly located above their pads using a magnifier. If not, re-heat the solder joint and carefully nudge the part. Repeat as necessary until it’s lined siliconchip.com.au up, then solder the four pins on the opposite side of the package. These are all joined together so you can do it as one big solder joint. Now apply solder to the three remaining pins and add a bit of fresh solder to pin 4 as well. To tidy up the solder joints, apply a little more flux paste on top of the solder and then use some solder wick to remove the excess. Clean up the flux residue with some methylated spirits, isopropyl alcohol or other flux cleaner and then inspect it visually to ensure all the solder joints are good. That’s the trickiest part out of the way. Next, solder TVS1 in place, next to Q1. It’s fairly small and its cathode stripe will not be terribly obvious so again, use magnification to identify the cathode and orientate it correctly before tacking it place and soldering the opposite pin. Now solder the SMD passive components in place; this includes five resistors, one capacitor and the PTC thermistor. None are polarised; just be careful to fit each in the location shown in Fig.4. The resistors will be printed with a small code indicating their value (eg, 1.2kΩ code is 122; or 12Ω x 102) but the capacitor will not be marked. The resistor codes are also shown in the parts list opposite. The next components to mount are reference REF1 and transistor Q2. These are in identical SOT-23 packages so don’t get them mixed up after taking them out of their packaging. They are polarised but have three pins each so the orientation is obvious – see the pinouts in Fig.1. Next are the two LEDs. Usually, the cathode is marked with a green dot but sometimes the anode is marked instead. The easiest way to check is with a DMM set on diode test mode. The LED will light up with the red probe connected to the anode and black to the cathode. You can confirm the colour at the same time. Note that some DMMs (eg, those powered by two AA cells) may not apply sufficient voltage to light up a green LED. Solder these where shown on the overlay diagram; LED1 is green while LED2 is red and the cathodes are orientated towards the USB plug, as shown by the “K” markings on the PCB. Now solder schottky diode D3 in place. Add a little flux paste to the pads first as it’s quite large but the procedure Celebrating 30 Years May 2018  61 is much the same as for the other two-pin devices. Just make sure you apply the iron for long enough to form good solder fillets between the PCB and terminals of the device. Then flip the board over and fit the four remaining SMDs on the bottom side, as shown in Fig.5. D1, D2 and ZD1 are polarised; also pay particular attention to the location of the cathode stripe on ZD1. The fuse is not polarised. Finally, fit the USB plug and socket as shown. Both need to be pushed down firmly onto the PCB before soldering. The plug has a notch on the underside which the edge of the PCB fits into. Note that the USB plug pins may be quite short and may not protrude very far through the bottom of the PCB, so it’s a good idea to solder them on both sides. Just make sure you don’t accidentally bridge the pins. Testing Inspect the board to verify that all the solder joints are good and that you have no unwanted bridges, then plug it into a USB port on your PC. If you have a USB charger, you could use that instead. Check that the green LED lights up but the red LED should not. You can then carefully measure the voltage across D3. You should get a reading in the range of 4.5-5.25V (usually quite close to 5V), with the red probe to its cathode (striped) end. Now plug a small device like a USB card reader or flash drive into the socket and verify that it powers up correctly. Try reading the contents of the card/flash drive on your PC and verify that it works normally without any unexpected disconnection events. If you want to verify that the Port Protector will definitely protect your computer, you will need a ~6V supply and a resistor with a value between 2.2Ω and 10Ω. Unplug the Port Protector and anything that’s plugged into it and use a clip lead to connect the USB socket shell to the ground terminal of your 6V supply. Connect one end 62 Silicon Chip of the test resistor to the positive output of the 6V supply (battery pack, plugpack, etc) and then touch the other end of the resistor to the USB socket pin that’s immediately adjacent to fuse F1, on the underWe finished side of the board. our Port Protector If you can do this with clear heatshrink tube . . . while looking at the just in case A.P. managed to drop something into the Protector PCB! top of the board, you should see both LED1 and LED2 light up. LED2 indicates that the protection is operating. If you have a helper, they could measure the voltage across D3. It should be close to 5.5V. This confirms that the device is working. Using it To avoid accidentally shorting the 5V supply or either of the signal lines during use, we suggest you encapsulate the entire device in a short piece of heatshrink tubing, as shown above. Clear tubing is convenient since you can still see the components – but any colour will work. Cut the tubing so that it covers the entire USB socket, up to the lip that’s around the open end, and the very base of the USB plug, up to where it projects from the PCB. Then it’s just a matter of applying a little heat, eg, from a hot air gun, hair drier or lighter (with the flame some distance below the tubing). Rotate the assembly until the tubing has shrunk into place and try to avoid burning yourself in the process. If it gets too hot to hold, put it down and let it cool before shrinking the remainder of the tubing. If you manage to blow the fuse, you will simply have to cut the tubing off, desolder the fuse, clean the old solder off using flux paste and some solder wick, solder a new fuse in place and apply a fresh length of heatshrink tubing. Or if you’re really clever, you may be able to cut a flap in the tubing around the fuse, replace it and then glue the flap back in place. SC Celebrating 30 Years siliconchip.com.au SERVICEMAN'S LOG The Serviceman's Curse I reckon servicemen are cursed. I don’t mean that people swear at us a lot (though they might!), I mean that we bear the Curse of the Serviceman. This means that when anything breaks down, we always consider the repair option first. It doesn’t really matter what has broken or whether we usually repair or service these things in our day jobs, it’s just that we simply can’t help ourselves from wanting to fix something that’s broken. This is mostly fine if we just have ourselves and our own household to think about, but for some, it also means that when any of our friends, acquaintances or colleagues break something, we are often expected to fix their stuff as well, just because we are servicemen! As if being our own go-to repair siliconchip.com.au guy isn’t enough. This is what I mean by a Serviceman’s Curse. While the more prosperous servicemen among us may have learned to suppress the curse and are able to chuck away the broken device and go out and buy a replacement instead, for me and many others, that is a difficult Celebrating 30 Years Dave Thompson* Items Covered This Month • • • • Car battery charger CIG Transmig 200 welder Compaq CQ61 laptop R&R MR16 LED downlight repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz decision to make and we would have to force ourselves to even consider it. When something in my household breaks, my first instinct is to weigh up all possible options to repair it myself, with the very last option being to buy another one. Perhaps if I won big on the lottery, or inherited a few gazillion May 2018  63 bucks, this attitude might change – I’d sure like to test that theory! But in the meantime, I always consider repair before replacement. I know plenty of people who think the other way. They replace anything that breaks with the latest and greatest new version, regardless of whether it was repairable or not, but not many of these people are servicemen. I can’t really blame them; after all, they don’t bear the curse! Of course, there are exceptions; if a repair isn’t feasible or economically sensible, such as a dropped dinner plate or wine glass then the curse doesn’t really apply. Having said that, I have been known to glue people’s favourite plates or porcelain figurines back together. But if the broken article is even remotely within my skillsphere, then the curse awakens. My neighbour invokes the curse A recent example involves a neighbour who tried to start his car the other day while he still had a battery charger connected. He subsequently discovered that the charger no longer worked. I’ve done this myself in the past and perhaps due to dumb luck, I’ve had no problems, though it stands to reason that one probably shouldn’t leave anything connected when cranking the engine unless it’s designed to handle it. This is especially true if the car battery is dead flat to begin with and we are essentially relying on the output of the charger alone to supply enough grunt to fire up the motor. In such situations, the current draw through the leads and internal components of the charger can be considerable, and when the car starts there is even more current introduced into the circuit by the alternator’s output. Many car battery chargers are simply not designed to withstand this kind of punishment. Ordinarily, a guy would just think the charger was dead, chuck it in the bin and go out and buy another one – especially given the current (hah!) prices of chargers these days. In this case, the sticky wicket was that my neighbour had borrowed the charger from a friend, and while it was by no means new, it looked to him to be a reasonably flash model as far as car battery chargers go. He didn’t relish the thought of having to cough up to replace it. He brought it over to my workshop in a bit of a panic and asked if I could have a look at it, at least to see whether it was repairable. If not, he’d be chowing down on a large crow sandwich and splashing out for a new charger. I promised to see what I could do, mindful of the fact that this would probably end up being one of those “pro bono” jobs all servicemen get saddled with and would more than likely take up time I could ill afford to spare. That said, I couldn’t refuse a neighbour in need, especially as it was highly likely that I could fix the charger. The Serviceman’s Curse strikes again! The charger was about as simple as any electronic device can get. A mains cable enters the plastic case through a cheap-but-effective clamping arrangement and connects via a fuse to the primary of a reasonably heavy-duty transformer. The secondary is wired to a small PCB with a glass thermal cut-off switch, a couple of carelesslyplaced diodes and three LEDs. Attached to that board are a couple of cables which then exit the case through a rubberised grommet with comically-large alligator clips on each end; one red and one black. He might have thought it flash but I disagreed; it was a bog-standard battery charger. The battery connector cables looked to me to be a little on the light side, considering the size of the transformer and the cables that make up your average set of jumper leads. But I suppose these modern-style, piddly-thin wires would have the advantage of being self-limiting and besides, they’d ordinarily only have to cope with a few amps at the most for relatively short periods anyway. Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column? If so, why not send those stories in to us? We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 64 Silicon Chip Celebrating 30 Years The LED indicators were mounted inside the case but shone to the outside world by way of clear plastic light tubes. I’ve seen this method used before, especially in devices like amplifiers, radios and laptops and it tends to work fine for them. But the inside of this charger gets hot then cools down, over and over, and this, when combined with the natural ageing process, causes the plastic to go opaque. Because of this, the amount of light reaching the user would likely be pretty low. I’d wager these indicators would be barely visible during the day, especially in bright sunlight. I’d confirm that theory once I’d fixed the thing… Testing the charger I plugged the charger into my lightbulb based load box and flicked the box’s socket switch to on. I’ve gotten into the habit of using this load box, largely because it is set up on my workbench permanently and this makes it the handiest power socket for any mains-powered devices that cross my desk. It can’t hurt, regardless of whether I really need it or not. The neighbour told me he’d plugged the charger in and got no indication of power, and with no specific mention of fuses blowing or circuit-breakers popping, it was unlikely that a shortcircuit was present. However, the test rig socket is right there, so I used it. The load box consists of two 250W incandescent bulbs (remember them?) mounted in a couple of lamp sockets screwed to the top of a suitably-sized, plastic hobby box. The lamps are wired in series with the Active wire and all three mains wires are then terminated into a standard dual, switched mains socket on the front of the box. The box is powered from a wall socket. I generally power any mains-powered equipment under test into the protected socket on the load box. If there is an internal short or other, similarlynasty electrical fault present, the lights glow to let me know while they limit the voltage applied to the load, giving me time to switch everything off safely without the drama of blowing fuses or the guts of the device under test flying across the workbench. I also have an adjustable auto-transformer (generally known as a Variac, but mine isn’t Variac-branded) and I siliconchip.com.au use that for similar jobs, especially those where it is more prudent to slowly bring up the voltage than apply it all at once. I mostly use the lightbulb load box for mains-powered stuff though, especially valve amps and similar devices. Both methods save replacing fuses and reduce the risk of damaging other equipment on the same circuit, and both are invaluable to the serviceman who needs to work with mains-powered devices and they are well worth the effort of building or purchasing. As expected, the battery charger did nothing on switch-on. No bright lights on the load box and nothing on the front panel of the charger. For all intents and purposes, it was as if I hadn’t plugged it in. Delving into its innards My first thought was a blown fuse. There must be one, and while some chargers have a fuse socket accessible from the outside, this model didn’t, so it had to be inside. Getting in was easy enough, with only four long, PKstyle screws holding the case together at each corner. It is refreshing to be able to open up something without having to resort to cruder methods of removing those ridiculous and unnecessary “security” fasteners that seem to be all the rage these days. It’s also getting increasingly rare to find the screws out in the open and easily accessible to normal tools, instead of being buried inside deep channels or concealed under rubber feet, plastic bungs or warranty seals. Once the screws were out, the case split apart easily and the various components were laid bare. There indeed was a fuse, in line with the Active lead and right next to the cable clamp. The fuse was obviously intact as I could see it clearly, but I popped it from its holder and checked it with my meter anyway. If it was dead, it wouldn’t be the first time a fuse appeared undamaged but was, in fact, open-circuit; a classic beginner’s trap. In this case, though, the fuse rang out OK. On to the next component in the troubleshooting queue: the transformer. This also looked OK but then again, something would have had to fail catastrophically for it to appear otherwise. I measured the secondary windings and got around 0.5W on my analog siliconchip.com.au multimeter; probably not that accurate a reading but at least it had continuity. When I measured the primary though, it appeared to be open circuit. A current surge might have burned out the windings but I could see no darkening of the yellow tape they typically use to bind transformer coils with and there wasn’t even the faintest whiff of that distinctive burnt-enamel smell that almost always goes handin-hand with high-current component failures. I’d have to dig further. After making a note of what went where, I desoldered the transformer’s wires and removed the four screws going down through the laminations and holding it to the bottom of the case. I do like these simple-to-disassemble devices. With the tranny out and sitting on the bench, I re-measured the windings with another meter just to be thorough but got the same result; the primary side was definitely open-circuit. Ordinarily, this is where most servicemen/repairmen would start looking for a replacement transformer but as I’ve already made clear, I hate throwing things away (that curse again). Anyway, without having any part numbers or any other information written on the component, I’d have to either take an educated guess as to its specifications or assess other, similar chargers to determine or approximate the voltages and ratings of their transformers. Either method would likely lead me to a replacement component that would be close enough for rock and roll – it’s a car battery charger after all – but that’s a bit too wishy-washy for my liking. Besides, I wasn’t finished with this dead transformer yet. Fixing it the hard way I started by removing as much of the yellow tape that bound the windings as possible, a task made difficult by the way the E-I core kept getting in the way. I got out one of my craft knives and slid the edge of the blade between two of the hundreds of tightlylaminated shaped metal shims that make up the core. It went in relatively easily, meaning the laminations weren’t potted or bonded together with varnish, as some are. I removed the transformer’s folded heavy-metal outer cover by bending four metal locking tabs on the base out of the way and lifting it clear. Celebrating 30 Years With the core now totally exposed, I used a sharpened flat screwdriver to carefully pry free a couple of the E and I-shaped laminations from one side. Now loosened, I could ease out the rest of the laminations one by one until there was a large pile of them lying on the bench. What remained was a hard, white plastic bobbin that held the primary and secondary windings, and it was a simple matter to strip the remaining yellow tape away from the primary side. Once gone, I could see nestled at the very top of the now-exposed windings a black, rectangular, twolegged component that I assumed to be a thermal fuse, wired in series with the primary winding. I already knew it would be open circuit, as the clean state of the windings showed nothing had burned out but I measured it anyway. It was dead as John Cleese’s parrot. I unsoldered it and measured the windings beyond it. My meter made it around 50W and whether that was about right or not I’ll leave to the mathematicians; all I needed to know was that it seemed about right to me. I located another thermal fuse in my parts store, which according to the data sheets I downloaded from the web was a suitable substitute for the original. Once soldered in, I re-bound the primary windings with similar tape and set about re-assembling the core, a grubby job as each one is coated in an anti-corrosion substance that if not May 2018  65 actually oil, has very much the consistency and feel of it. However, after I’d stuffed as many of the laminations back into the bobbin as I could, I still had about a dozen “E”s and “I”s left over. No biggie, or so I thought. After a quick megger check to make sure my insulation was good, I temporarily rigged up a mains cable to the primary and used my auto-transformer to power it up slowly. My multimeter showed the secondary voltage rising as expected as I wound up the power, but then it happened; the transformer started to buzz. Above about 150VAC, the transformer was buzzing very loudly; I guess I was going to need those extra laminations after all! By using some wood-workers’ clamps and a lot of very colourful language, I managed to shoe-horn all the remaining laminations back into the core. It was then thankfully buzz-free. That just left the simple matter of reassembling everything, giving it another insulation test and trying it out. It worked as well as it did before and while those LEDs were barely visible, my neighbour was hugely relieved and grateful. He offered to pay, but I declined; it was the neighbourly thing to do. Darn this Serviceman’s Curse! CIG Transmig 200 welder repair Sometimes it doesn't take a large fault to stop equipment worth thousands of dollars from working. G. S., of Castle Hill, NSW, recently saved a heavy-duty welder from the boneyard and here is how... My ex-neighbour Paul is into old Ford Falcons from the 1960s. He restored a '64 ute some three years ago and has two 1964 2-door coupes awaiting restoration. He also recently acquired a '63 Falcon station-wagon that he's working on at the moment. Sitting in his garage among that lot is a real gem – a 1967 Ford Mustang coupe that's currently a body shell and a pile of parts. So why is he mucking around with the Falcon station-wagon and not putting all his effort into the Mustang restoration? I dunno but he'll come up with all sorts of excuses if pressed on the matter! Vehicle restoration projects invariably require rust repairs and so, about eight years ago, Paul acquired a second-hand CIG Transmig 200 welder. This is a large 3-phase machine and 66 Silicon Chip The faulty contactor shown inside the welder. is mounted on a sturdy metal trolley that can be trundled around in his garage. It probably cost around $3000 new but had been acquired for a pittance by one of Paul's mates when a business shut up shop. Having no real use for it, the mate eventually passed it on to Paul for an even lesser pittance and he subsequently used it while restoring the ute. It then sat unloved at the back of Paul's garage for three years until he got his station wagon restoration underway. It wasn't long before the welder was needed for this project and so the machine was duly trundled out and hooked up to the garage's 3-phase power outlet. Paul then pressed the trigger on the wire-feed nozzle to check its operation but no wire fed through. Instead, the 3-phase circuit breaker in the household fuse-box tripped out. Puzzled by this, Paul reset the breaker and pressed the wire-feed trigger a second time. The circuit breaker immediately tripped out again and it did so a third time after he had reset it. At that stage, Paul decided to ask my brother, who is a licensed electrician, to take a look at the machine for him. I went along for the ride and when we got there, we found that Paul had already removed the side panels from the machine. It took my brother just a few minutes to diagnose a faulty contactor. This normally pulls in and powers up a large transformer and various other parts in the machine when the wireCelebrating 30 Years feed trigger is pressed. Our snap diagnosis was that the contactor was probably full of gunk and this conclusion was reinforced when my brother demonstrated that the machine could be powered up by manually assisting the contactor to “pull in” by pressing on it with an insulated probe. Even then, the wire-feed mechanism still wasn't working, so it looked like this welder had two separate faults: (1) a faulty contactor and (2) a fault in the wire feed mechanism or in the circuitry that controls the wire feed motor (or perhaps even a faulty motor). There was no point trying to diagnose the wire-feed problem until the contactor problem had been resolved, so it was up to Paul, an electrical fitter by trade, to take things from there. He's not a man to let the grass grow under his feet and so, the very next day, he carefully labelled all the relevant connections, then pulled the contactor out and cleaned it to within a millimetre of its life. It did indeed prove to have a lot of gunk inside and when it was refitted, he was gratified to find that it now pulled in when the wire-feed trigger was pressed without tripping the circuit breaker. So that solved problem number one. Now for problem number two. With no access to a manual, circuit diagrams or spare parts, Paul figured that his next best step was to seek professional help to get the wire feed mechanism working. siliconchip.com.au The faulty tantalum capacitor on the control board was replaced with a similar electrolytic capacitor, with the adjacent 7812 regulator circled in red. As a result, he loaded the machine onto a trailer and carted it off to a specialist welder repair shop. They duly called back a week later to say that both the wire-feed mechanism and motor were OK and that they had diagnosed a faulty control board. Unfortunately, given the age of the machine (it's probably late 1980s or early 1990s vintage), replacement control boards were no longer available. And as far as they were concerned, without a replacement control board, the machine wasn't repairable. Never one to give up, Paul now figured that he would try to get the control board fixed. And that's when he flicked the problem my way. I suggested that the best approach would be to remove the board from the machine and drop it around to me. That way, I could inspect the board for dodgy solder joints and test the various semiconductors, electrolytic capacitors and other parts at my leisure. Having made the suggestion, I thought he might drop the board off in a week or two but as I said, he's not a man to let the grass grow under his feet. He turned up at my house within the hour, clutching his faulty control board with the external wiring leads all carefully labelled. I took a look at it the next day. Despite its age, it was still in good condition with no signs of corrosion. Its main parts included a couple of 555 timer ICs, an LM3900 quad amplifier IC, several transistors, a relay, two stud-mount SCRs and a stud-mount siliconchip.com.au diode. The external leads ran off to a couple of pots and some spade clips. So had one of the semiconductors failed? Or was it a faulty relay, a dodgy capacitor or a dry solder joint? If it wasn't the latter, the easiest approach might be to simply blanket-replace the ICs and transistors and check out the SCRs, the diode and the relay. It didn't come to that though, because I quickly spotted what was almost certainly the cause of the problem. There were five 10µF 16V tantalum capacitors on the PCB, two of them in the timing circuits of the 555 timers. Four of these tantalums were dark blue but the fifth had turned a pale blue colour with a greenish band across it. Surely it wasn't going to be this ridiculously easy? I stuck a multimeter across the capacitor and it registered a dead short! I then traced the PCB tracks from the capacitor and found that it was across the output of an adjacent LM340T-12 12V regulator. This device is mounted on a small heatsink in one corner of the board and provides a regulated 12V rail to the 555 timers and the quad amplifier (and possibly also the relay). I removed the capacitor and the short across the regulator's output disappeared. I then replaced it with a 10µF 16V electrolytic that I had on hand. Two other 10µF bypass tantalums on the PCB were also replaced with electrolytics, while those in the timing circuits of the 555 timers were left in place. In theory, the LM340T-12 should have survived since these devices are short-circuit proof. However, I replaced it with an equivalent 7812 regulator as a precaution, along with an adjacent electrolytic capacitor for good measure. At that stage, it was tempting to apply power to the circuit and check the operation of the 555 timers. However, not having a circuit diagram (no luck with Google), I was afraid that this might risk damaging something, especially if two of those external leads shorted together. The best bet would be to test the control board in the welder itself. I called Paul and told him what I had found. He was on my doorstep some 25 minutes later, collected the part and shot back home to refit it. I was cautiously hopeful that it would now work and I didn't have Celebrating 30 Years to wait long to find out. An ecstatic Paul was back on the phone an hour later and he was floating somewhere between his Mustang chassis and seventh heaven. “You're a genius”, he exclaimed. “The welder is working perfectly!” There's nothing like a bit of flattery to massage the ego but at the end of the day, this was really a joint effort. My brother diagnosed the faulty contactor, Paul fixed the contactor, the service centre correctly diagnosed a faulty control board and yours truly fixed the control board. So a part costing less than a dollar was all that prevented this valuable welder from working. It's since been used to weld some fresh sheet metal into that old Falcon station wagon but it's the Mustang restoration that I reckon he should be getting stuck into. Editor’s note: older Tantalum capacitors seem to go short circuit more often than you might expect so it’s well worth taking a good look at any such capacitors first when repairing something made before the year 2000 or so. Compaq CQ61 laptop repair and refurbishment B. P., of Dundathu, Qld, spent quite some time refurbishing and repairing an old laptop for his wife to use. In the process, he discovered and fixed some classic laptop hardware problems and also ran into some time-consuming software pitfalls... Our daughter has just started university. After five years of intensive use, her old laptop was well and truly the worse for wear, so she bought herself a new laptop and she gave us her old one when she came home during her mid-year break. When I assessed the old laptop, it was in a rather dilapidated condition. The keyboard had one key cap missing on the numeric keypad and most of the top row of keys (numbers and symbols) no longer worked. The top silver layer of the touchpad was also worn off in places, revealing the black base colour, the keyboard surround had a lot of the black paint worn off it and the lid hinges were loose. Although the laptop still worked, it was certainly beat up. I started the repair by removing the old keyboard, by undoing the securing screws on the bottom of the laptop. I ordered a new keyboard and while waiting for it to arrive, decided to conMay 2018  67 tinue working on it by plugging in a USB keyboard. This allowed me to do a factory reset so that we could start with a fresh copy of Windows 7. After that was done, I uninstalled all the trial software and I installed some additional programs that were needed. Then I partitioned the 500GB hard drive into two separate partitions so that data could be stored on the D:\ drive, separate from the operating system on C:\. I noticed some issues with the Compaq factory version of Windows 7 that I wasn't happy with, so I decided to do a fresh install of Windows 7 from an OEM disc (ie, one purchased from Microsoft) instead. This all went well, but then I noticed that the webcam driver was not installed in Device Manager; it was showing up as an unknown device. I tried to locate the correct driver for the webcam on the internet, however, this proved difficult. I did eventually find the driver and installed it but when I went to test it with Skype, Skype said that it was already in use by another program. It wasn’t, though. I thought I would try uninstalling the webcam driver in Device Manager and then scanning for new hardware. This did not work, as the webcam then showed up as an unknown device again. I decided to do another factory reset to try to get the webcam working correctly but because I'd altered the hard drive partitioning, the restore partition was no longer present. I still had the set of three restore discs that we'd made when the laptop was new, so I decided I would just use those. I set about restoring the laptop from those discs, but when I got to disc three, it had a read error, so the factory reset failed. This left me with a blank hard drive. That meant using the OEM disc to reinstall Windows 7 again. So I was back to square one, with the webcam still showing up as an unknown device. I then realised that we had a related Compaq laptop model, a CQ42, that uses the same HP-101 webcam. I checked what driver the webcam used and it was a standard Windows driver. I'd recently installed Windows 7 on the CQ42 without any issues and Windows had found and installed the webcam, so I wondered why I was having so many problems with the CQ61's webcam. 68 Silicon Chip I then tried to tell Windows to use the driver that it should be using, but this idea didn't work out and I was still in the position of not having the webcam working. At this point, I decided to give the laptop a rest and do something else. I went to my shed to look for something and when I opened a box to check inside it, I discovered another Compaq CQ61 that I'd been given some time ago that I'd forgotten about. This CQ61 was a cheaper variant with much lower specifications than the one I was working on, so I would use it for parts. I started dismantling it with the intention of using the top case half to replace the well-worn top case half on the one I was fixing. The touchpad still had its original silver colour and the keyboard surround was still in asnew condition. These new parts would make a huge difference to the original one. Unfortunately, the keyboard on this laptop was also faulty and unusable. After unscrewing a multitude of screws, I had the donor laptop fully dismantled and I retrieved the parts that I wanted to use for the refurbishment. Then I turned my attention to the laptop I was working on and I dismantled it. I was now ready to reassemble it, using the better parts from both laptops. Before proceeding further, I decided to give the interior a good clean because there was a considerable amount of dust inside it from the many years of heavy use. I used a small paintbrush with natural bristles in order not to generate static electricity while brushing the dust off the motherboard components. When I got to the heatsink, I removed the fan for cleaning and I noticed that there was a thick layer of dust on the inside of the heatsink's fins, where the fan had been blowing air through it. This dust was removed and the fan was then thoroughly cleaned, before being refitted. This is a very common problem with older laptops and often causes them to overheat and either lose performance or become unstable. It was fortunate that I had stumbled across the other laptop and as a result, decided to take apart the one I was Celebrating 30 Years working on because if I hadn’t done so and cleaned it out, chances are I would have run into some of these problems later. At this point, I decided to also transfer the lid assembly from the donor laptop (including the display and webcam) because it was in slightly better condition than the original lid. By this time, I was also suspecting that the original webcam may be faulty, so this was the perfect opportunity to test this theory. With the laptop partly assembled, I propped the lid against a box, so that I could connect it up and test the screen and the webcam. Once booted, I checked Device Manager and the webcam was now installed. I loaded Skype and tested it and it now worked, indicating that the original webcam had been faulty all along. I then noticed that there was a problem with the replacement screen, as it had several dead pixels in the lower right-hand section of the screen. This blemish was not that bad and it would not make a huge difference to the laptop, but seeing that the original screen was in better order, I would swap them over. I dismantled the lid and fitted the original screen to it and then I reassembled it and continued with reassembling the laptop. It's very important to take particular note of which screws go where when reassembling a laptop. There are around five different length screws in some laptops and each screw must be used in the correct location to prevent damage (when putting a long screw in where a short one should go). siliconchip.com.au After a bit more work, the laptop was reassembled and back in working order again, except for the keyboard. I was still waiting for the replacement. In the meantime, my wife could just use the laptop with the USB keyboard. Eventually, the replacement keyboard arrived and I fitted it; the laptop was then fully refurbished and it has a new lease on life. This laptop is now around seven years old and it would be classified as being quite outdated. But it's still quite suitable for light duty work, such as web browsing, emailing, letter writing and other general duties. For a bit of work and less than $20 for the replacement keyboard, it's as good as new. That’s a lot cheaper than buying a new laptop, even a basic one, and it’s still perfectly adequate for most jobs and uses less electricity than a desktop computer. Having the donor laptop on hand certainly saved me quite a bit on replacement parts and resulted in a more cosmetically appealing end result with the new top case shell to replacing the well-worn old one. This was my first major laptop repair and I was surprised that it was nowhere near a difficult as I had imagined it would be. It's simply a matter of proceeding with caution and paying close attention to details. There are also plenty of videos on YouTube which go into considerable detail about laptop repairs but I managed to do the refurbishment without referring to any. MR16 LED downlight repair D. M., of Toorak, Vic, had a 12V MR16 LED downlight fail far short of its claimed 20,000+ hour lifespan. It would have been cheaper to just buy a new one but he wanted to know what had gone wrong so set to taking it apart… I wanted to know what had failed inside the MR16 LED lamp as I find the claims for LED downlight life expectancy, typically of 20,000 to 50,000 hours, quite unlikely. At eight hours per day, that would amount to a service life of 7-17 years. Although LED downlights have not been available for 17 years, in my experience, most such lamps don’t even last seven years. My particular light was a Muller-Licht (house brand) Reflektor rated at 320 lumens and 5W. I carefully examined siliconchip.com.au the light to determine how it might be disassembled without damage. I found I could gently pry the top retaining ring off the body with a knife which also caused the release of the light diffuser, revealing the LEDs and their heatsink. Two Phillips-head screws could then be removed from the heatsink, allowing the separation of the top and base portions of the light assembly (see photos at right). LED lights typically contain a driver which delivers a constant current to the LEDs. I quickly determined that it was the driver that had failed as when power was applied directly to the LEDs, they lit up. I decided to obtain and install a suitable replacement driver. I found one online that was rated at the same current as the LEDs, 650mA and only cost about $2.50. This driver has pins attached with the correct size and spacing to plug into an MR16 socket. So these could be used to replace the existing pins on the lamp body, or alternatively, they could be desoldered from the driver if necessary for other applications. The driver utilises a PT4115 chip. The website where I bought it has details of the circuit; see siliconchip. com.au/link/aajr I removed the old driver from the LED body and then the old MR16 pins. Be careful removing the old pins as it is easy to break the plastic body. In this lamp, the pins were hollow. You may be able to cut them and then drill through to remove them (with a very small diameter drill). I tried twisting them with pliers which ended up cracking the body of the case. Alternatively, it might be easier to leave the pins in place and desolder the old driver, then solder them to the new driver board. The driver is housed in the otherwise empty “well” in the base of the lamp, just above the pins. Having soldered the new driver in place, I glued the ends to ensure the pins would not move. Make sure any conductive parts that might contact each other to cause a short circuit are appropriately insulated. The lamp worked fine after that and so I put it back into service. This particular lamp replaced an existing halogen downlight and is driven by an old-style iron core transformer Celebrating 30 Years Prying off the cover revealed the retaining ring, diffuser, LEDs and their heatsinks. After removing two screws the LED enclosure could be separated showing two leads attached to a driver PCB. The LED driver shown above is the replacement one and is mounted differently to the old driver. Left: the replacement MR16 driver. Right: the failed MR16 driver. supplying 12VAC. These transformers are not as efficient as more modern electronic ones but they do work with LED replacement lamps. Some modern electronic “transformers” designed for use with halogen lamps will not work with LED replacements as they do not draw enough current (or perhaps it’s because they’re a non-resistive load). There are many different designs of LED downlight. Some such as the one described here might be relatively easy to disassemble, others might be more difficult or impossible. Note that type of repair is not very economical, especially if you include your time in the calculation but I found the job to be both fun and educational. SC May 2018  69 Look after your Lithiums! By Nicholas Vinen 2x 12V Battery Balancer Two 12V batteries are often significantly cheaper than one equivalent 24V battery but you need to be careful connecting batteries in series as their voltages and state-of-charge may not be identical. The difference in voltage can increase over time, leading to battery damage from overcharging and/or under-charging. This compact, low-cost device keeps them balanced so that they last a long time. O cause they tolerate overcharging much less than a similar n page 28 of this issue, we describe a high-perforlead-acid battery would. mance Uninterruptible Power Supply (UPS) you This design incorporates a low-voltage cut-out which can build yourself, that uses two 12V LiFePO4 batprevents the batteries being discharged too far if it is unteries wired in series to form a 24V battery. able to keep them balanced and its very low quiescent This was a much cheaper solution than buying a 24V batcurrent of under 0.02mA means it will have virtually no tery with equivalent performance, even taking into account effect on battery life. the $100 or so we paid for a commercial battery balancer. It also incorporates a LED to show when it is monitoring You can build this balancer for a lot less than that and the battery voltages and two more LEDs to show when one it will do a similar job. or the other is being discharged or shunted. Our version can’t handle quite as much By default, the low-voltage cut-out is set up so that the current, because it lacks the large batteries are only balanced when they are being charged, heatsink. however, there are definitely situations where you might But you can want the batteries to be balanced during discharge, too. easily parallel In that case, you just need to several of our change a resistor or two in balancers if you order to adjust the cut-out need a higher curthreshold so it is near the rent capacity and minimum battery voltthe cost would still age. In this case, the cutbe quite reasonable. out will still act to proIt can be used with prettect the batteries but will ty much any battery chemallow balancing during istry, as long as the battery charging and discharge, voltages will stay within the right down to that lower range of 5-16V. threshold. Balancing is most critical Shown rather significantly oversize for clarity (the PCB It’s a compact unit at with lithium-based rechargemeasures only 31.5 x 34.5mm) – see the $2 coin for reference – just 31.5 x 34.5 x 13mm, able batteries, though, beall components mount on this single board. 70 Silicon Chip Celebrating 30 Years siliconchip.com.au Fig.1: the circuit for the Battery Balancer, shows the balancing section at top and low-voltage cut-out at bottom, based around dual micropower op amps IC1 and IC2 respectively. IC1 drives dual Mosfets Q1 & Q2 to perform balancing while necessary; IC2 drives the indicator LEDs and disables IC1 using Mosfet Q3 when the battery voltage is low. so you can tuck it away inside just about any device. And if the 300mA balancing current is not sufficient for your purposes, all you need to do is wire two or more units in parallel and they will operate in concert to keep the batteries balanced. Balancing operation There are two sections to the circuit; the balancer and the low-battery cut-out. The entire circuit is shown in Fig.1, with the balancing circuitry in the top half and the lowvoltage cut-out below. Starting with the balancing section, schottky diodes D1 and D2 are connected in series with the two batteries so that no damage should occur if they are wired up incorrectly. These diodes are then connected to Mosfets Q1a and Q2b at the right-hand side of the circuit diagram, via a pair of 27Ω 3W resistors. These Mosfets are normally switched off and no current can flow through them. If the voltage across one battery rises by more than 100mV above the other, the Mosfet across that battery is switched on. siliconchip.com.au If the battery is being charged, this has the effect of shunting some of the charge current around that battery so that it receives a lower charging current than the other, decreasing the voltage differential over time, as the battery with the lower voltage is then receiving more charging current. If the unit is operating while the battery is not being charged, the effect is to slightly discharge the battery with the higher voltage until they are closer in voltage. It’s a linear circuit so the shunt current is proportional to the difference in voltage. As the imbalance rises, so does the shunt current until the limit of around 300mA is reached. This is to prevent the Mosfet and resistor from overheating. Detecting a voltage difference A resistive divider comprising two 10MΩ resistors and 200kΩ trimpot VR1 is connected across the battery, before diodes D1 and D2 so that their forward voltage does not affect the calculation of the difference in voltages. VR1 is adjusted so that the voltage at its wiper is exactly half that of the total battery. This half-battery voltage is buffered by voltage follower op amp IC1a. Celebrating 30 Years May 2018  71 ing current, all the dissipation would be in this resistor and none in the Mosfet, meaning the maximum current • Minimum battery voltage: 5V would be 200mA [14V ÷ 68Ω]. • Nominal battery voltage: 12-13V We realised we could increase this • Maximum battery voltage (fully charged): 16V by 50% by splitting the dissipation be• Battery voltage difference for balancing to start: approximately 100mV tween the Mosfet and its series resis• Battery voltage difference for maximum balancing current: approximately 130mV tor. The resistor has a 3W rating while • Maximum balancing current: approximately 300mA (multiple units can be paralleled) the Mosfet has a 2W rating, giving the • Maximum balancing power: approximately 4.5W (multiple units can be paralleled) possibility of a total of just under 5W. • Maximum recommended charging current: 10A per unit With a battery voltage of 29V and a • Quiescent current: < 20A balancing current of 300mA, dissipa• Low-voltage cut-out threshold: 27V (can be changed) tion is around 2.7W in the resistor and • Low-voltage cut-out hysteresis: 0.25V 1.7W in the Mosfet. We achieve this dissipation sharing This op amp has a very high input resistance of around by preventing the Mosfet from turning on fully and using 40GΩ, resulting in a low input bias current of approxi- a lower value limiting resistor. This is the purpose of Q1b mately 250pA, so the high values of these resistors (cho- and the three resistors between TP2 and TP3. These resistors bias the gate of Q1b at a voltage that’s sen to minimise the quiescent current) will not result in a initially about halfway between the negative and positive large error voltage. The other half of the dual op amp, IC1b, compares the terminals of the upper battery (ie, at a voltage between that voltage at the junction of the two batteries (from pin 2 of of pins 1 & 2 of CON1). However, as the balancing current CON1) to the output voltage from IC1a. If the upper bat- for the upper battery increases, the voltage at the junction tery has a higher voltage than the lower battery then the of the 27Ω resistor and Q1a drops and therefore so does half-battery voltage will be higher than the voltage at pin 2 Q1b’s gate voltage. Q1b is a P-channel Mosfet and so it switches on when of CON1. That means that the voltage at non-inverting input pin 5 will be higher than at the inverting input, pin 6. its gate is a few volts below its source terminal. The source As a result, IC1b’s output will swing positive. The ra- terminal is connected to the gate of Q1a, which is about 2V tio of the 390kΩ feedback resistor to the 10kΩ resistor that above pin 2 of CON1 when Q1a is in conduction. So as the current through Q1a builds and Q1b’s gate voltgoes to the battery junction (ie, 39:1) means that the output will increase by 40mV for each 1mV difference in bat- age drops, eventually Q1b begins to conduct, pulling the gate of Q1a negative and cutting it off. This forms a negatery voltages. Once the voltage at output pin 7 has risen by a couple tive feedback path and due to the gate capacitances, the of volts, N-channel Mosfet Q1a will switch on as its gate circuit stabilises at a particular current level. With 300mA through the 27Ω resistor, the voltage across is being driven above its source, which connects to pin 2 it will be 8.1V [0.3A x 27Ω] and this translates to a gateof CON1 via a low-value shunt resistor (47mΩ). So current will flow from the positive terminal of the up- source voltage for Q1b of around -2V, ie, just enough for it per battery, through diode D1, the 27Ω 3W resistor, Mosfet to conduct current. The 4.7kΩ resistor between output pin Q1a and then the 47mΩ resistor to the negative terminal 7 of IC1b and the gate of Q1a prevents Q1b from “fighting” the output of the op amp too much. of the upper battery. Note that 8.1V is slightly more than half the typical voltOnce this current starts to flow, it will also develop a voltage across the 47mΩ resistor which will increase the age of one 12V battery and this is why the resistor dissipates voltage at pin 6 of IC1b, providing negative feedback. This slightly more than the Mosfet, in line with their ratings. feedback is around 1mV/20mA, due to the shunt value. This prevents Q1a from switching fully on. Rather, its Balancing the other battery The other half of the balancing is a mirror-image; for balgate voltage will increase until the current through the 47mΩ resistor cancels out the difference in the two voltages. ancing the lower battery, Mosfet Q2b is a P-channel type and Hence, the maximum shunt current of 300mA will thus switches on when its gate is driven below its source. be achieved with an imbalance around 130mV (100mV + As with Q1a, its source is connected to the junction of the two batteries via the 47mΩ resistor. 300mA x 0.047Ω ÷ 2). When the lower battery voltage is higher than the upThe 10MΩ resistor between pin 3 of IC1a and pin 2 of CON1 serves mainly to prevent the balancer from operating per battery, output pin 7 of IC1b goes negative, switching should the junction of the batteries become disconnected Q2b on. And the same current-limiting circuitry is present but from CON1. It also makes setting the unit up and adjusting VR1 easier. It has a negligible effect on the voltage at this time, Q2a is an N-channel Mosfet, so that as current pin 3 since there’s normally such a small voltage across it. builds through the lower 27Ω resistor and the voltage at the junction of it and Q2b rises, Q2a switches on and limCurrent limiting its the current to a similar 300mA value, with roughly the Had we specified 68Ω resistors in series with Q1a and same dissipation split between the two components. A 10nF capacitor across IC1b’s 390kΩ feedback resistor Q2b (rather than 27Ω), there would be no need for additional current limiting circuitry since the resistors would naturally slows down its action so that it doesn’t react to any noise limit the balancing current within their dissipation ratings. or EMI which may be present at the battery terminals (eg, However, this would mean that at the maximum balanc- due to a switchmode load). Features & specifications 72 Silicon Chip Celebrating 30 Years siliconchip.com.au Fig.2: use the PCB overlay diagram at left and matching photo at right as a guide to assembling the PCB. Only one SMD component (a 10MΩ resistor)is soldered to the bottom, the rest go on the top as shown. The main aspects to pay attention to during constructon are that the semiconductors are correctly orientated and that you fit the resistors and capacitors in the correct locations. It also prevents the circuit from oscillating due to the negative feedback and the action of the current limiters. Under-voltage cut-out Commercial battery balancers tend to only operate when the battery voltage is near maximum, as this is when they are being charged. That avoids the possibility of the balancer discharging the batteries when they are under load. However, we’re not convinced this is a good idea. It’s possible to have a sufficient initial imbalance that one battery could be over-charged before the balancer even activates. And full-time balancing also has the advantage that it can start re-balancing the cells as soon as an imbalance occurs, which also avoids over-discharge and gives it more time for re-balancing. There is one other advantage to having a higher undervoltage lockout threshold and that is that it will prevent the balancer being triggered due to differing internal resistance of the batteries when under heavy load. This could create a voltage difference between the batteries even when they are at an equal state of charge. If you want the balancer to be active even when the bat- teries are not being charged, you still need the under-voltage lockout circuitry to prevent the balancer from over-discharging either battery. But in that case, you would change its threshold to be close to the fully-discharged voltage of your combined battery. For a pair of lithium-based 12V rechargeable batteries, this would normally be around 20V total. That’s to protect against the case where one battery has a failure (eg, shorted cell) which causes its voltage to drop dramatically. The under-voltage detection circuitry will then prevent the balancer from over-discharging the other battery in response, and potentially destroying it. See the section below on how to change the cut-out threshold if you want to take this approach. The increased battery drain of the low-voltage cut-out section is only about 10µA. As a bonus, it drives the three LEDs to indicate when the balancer is operating and which battery is being shunted. This is implemented using IC2a, another LT1495 op amp. Its positive supply is the same as for IC1a but its negative supply is connected directly to the negative terminal of the bottom battery, allowing it to sense the total battery voltage Many years ago, long before the days of smartphones and computers, even before the days of television, it was considered a “right of passage” for dads to sit down with the sons (or daughters) and help them as they built their own radio receiver. FM? Not on your life no such thing! DAB+? Hadn’t been invented yet! No, it was all good, old reliable AM Radio. And they could listen to stations hundreds, perhaps thousands of miles away! The beauty of it all was that they were building something that actually worked, something they’d be proud to show their friends, to their school teachers, to their grandparents! Enjoy those days once again as they build the SILICON CHIP Super-7 AM Radio See the articles in November & December 2017 SILICON CHIP (www.siliconchip.com.au /series/321) SUPERB SCHOOL PROJEC T! • • • • • • • Covers the entire AM radio broadcast band. Has on-board speaker ... or use with headphones. SAFE! –power from on-board battery or mains plug-pack Everything is built on a single, glossy black PCB. All components readily available from normal parts suppliers Full instructions in the articles including alignment. See-through case available to really finish it off! IT LOOKS SO GOOD THEIR FRIENDS WON’T BELIEVE THEY BUILT IT! siliconchip.com.au Celebrating 30 Years May 2018  73 (ie, between pins 1 and 3 of CON1) more easily. This is done using a string of three resistors (390kΩ, 6.8MΩ and 1MΩ) connected across the batteries. These form a divider with a ratio of 8.19 [(390kΩ + 6.8MΩ) ÷ 1MΩ + 1]. The divided voltage from the battery is applied to inverting input pin 2 of IC2a. A 3.3V reference voltage is applied to the non-inverting input at pin 3. This is provided by micropower shunt reference REF1, which is supplied with around 2A via a 10MΩ resistor. The voltage at pin 2 of IC2a is therefore above the voltage at pin 3 when the battery voltage is above 27V [3.3V x 8.19]. When this is the case, output pin 1 of IC2a is driven low, pulling the gate of N-channel Mosfet Q3 to the same voltage as the negative terminal of the bottom battery. As the source of Q3 is connected to the junction of the two batteries, Q3 is off and so does not interfere with the operation of the balancer. However, should the total battery voltage drop below 27V, the output of IC2a goes high, switching on Q3 and effectively shorting input pin 3 of IC1a to the junction of the two batteries. This means that the voltages at pins 5 and 6 of IC1b will be equal (with no current flow through the 47mΩ resistor, as will quickly be the case), therefore preventing any balancing from occurring. When the output of IC2a goes high, this also causes a slight increase in the voltage at its pin 3 input, due to the 10MΩ feedback resistor. This provides around 1% or 250mV hysteresis, preventing the unit from toggling on and off rapidly. In other words, the battery voltage must increase to 27.25V to switch the balancer back on. When the output of IC2a is low and the balancer is active, IC2a also sinks around 0.25mA through LED1 and its 100kΩ series resistor, lighting it up and indicating the balancer is operating. And when one or the other battery is being shunted, IC2b amplifies the voltage across the 47mΩ shunt by a factor of 2200 times. So if there is at least 20mA being shunted, that results in around 1mV across the 47mΩ resistor which translates to 2.2V at output pin 7 of IC2b, enough to light up either LED2 or LED3. LED2 is lit if it’s the upper battery being shunted and LED3 if it’s the lower battery. dissipate up to around 4.5W. If you’re using a 3A charger, that means it can handle a ~10% imbalance in charge between batteries (which would be unusually high). However, with a 10A charger, it will only handle a ~3% imbalance, with a 20A charger ~1.5% etc. A greater imbalance could potentially lead to over-charging as the balancer can’t “keep up”. So if your charger can deliver more than 5A, you may want to consider paralleling multiple balancers and we would strongly recommend it for a charger capable of 10A or more. When properly adjusted, the balancers will share the load. Realistically, one of them will start balancing first but if it’s unable to keep the imbalance voltage low, the others will quickly kick in and shunt additional current. Since the only external connections are via 3-way pin header CON1, you could simply stack the boards by running thick (1mm) tinned copper wire through these pads and soldering them to each board in turn. You can then solder the battery wires to these wires. Changing the cut-out voltage Construction To change the cut-out voltage, simply change the values of the 6.8MΩ and 390kΩ resistors using the following procedure. First, take the desired cut-out voltage and divide by 3.3V. Say you want to make it 24V. 24V ÷ 3.3V = 7.27. Then subtract one. This is the desired total value, in megohms. So in this case, 6.27MΩ. This can be approximated a number of ways using standard values. For example, 3.3MΩ + 3.0MΩ = 6.3MΩ which is very close. So use these values in place of the 6.8MΩ and 390kΩ resistors. Keep in mind there will still be around 1% hysteresis, so the switch-on voltage will be about 24.24V. Two more examples would be a 22V cut-out, which would require 5.67MΩ total; you could use 5.6MΩ + 68kΩ. Or for a 20V cut-out, you would need 5.06MΩ which could be formed using 4.7MΩ + 360kΩ. The 12V Battery Balancer is built on a small doublesided PCB measuring 31.5 x 34.5mm and uses mostly surface-mounted parts. These are all relatively large and easy to solder. Refer to the overlay diagram, Fig.2, to see where each component goes on the board. Some of them (the ICs, Mosfets, diodes and trimpot) are polarised so be sure to fit them with the orientation shown. There are two small SOT-23 package devices, Mosfet Q3 and voltage reference REF1. Fit these first. They look almost identical so don’t get them mixed up; only the tiny coded markings on the top of each set them apart. Tack solder the central pin to the pad in each case then check that the other two pins are centred on their pads and that all pins are in contact with the PCB surface. If not, reheat the initial solder joint and nudge the part into place. Then solder the two remaining pins and add a little extra solder to the first pin (or a bit of flux paste and heat it) to ensure the fillet is good. Next, solder IC1, IC2, Q1 and Q2. They are all in eight- Paralleling multiple boards As stated, one board can handle around 300mA and will 74 Silicon Chip Sourcing the parts The PCB is available from the SILICON CHIP Online Shop – simply search for the board code 14106181. All the other parts are available from Digi-Key. While they are based overseas (in the USA), you can pay using Australian dollars and they offer free courier delivery for orders of $60 or more. You can find the semiconductors on their website by searching for their part number and then narrowing down the list (eg, ignoring listings which are out of stock or only sold in large quantities). For the other, more generic parts like SMD resistors, you can find them by searching for (for example) “SMD resistor 1206 4.7k 1%” and then sorting the result by price. The cheapest part which matches the specifications should do the job just fine. But be careful because sometimes the search results include parts with different properties than you are expecting. You will need to skip over those. Mouser, another large electronics retailer based in North America, will almost certainly have all the required parts too. And if you don’t want to order from overseas, chances are that you can get most of them from element14 (formerly Farnell; http://au.element14.com). Celebrating 30 Years siliconchip.com.au pin packages and must be orientated correctly. Identifying pin 1 can be a bit tricky. For IC1 and IC2, you have to find the chamfered edge which is quite subtle. Pin 1 is on that side. Q1 and Q2 have pin 1 marked by a much more clear divot in the corner of the package. But you can also orientate IC1 and IC2 by matching the position of the markings up to our photo. In each case, make sure the device is positioned correctly and tack solder one pin, then as before, check the locations of the other pads are correct and solder them before refreshing the first joint. If you accidentally bridge two pins with solder, use a little flux paste and some solder wick to clean it up. The only remaining SMD parts which are polarised are diodes D1 and D2. Fit these now, ensuring the striped end goes towards the top edge of the PCB, as shown in Fig.2 and marked with “K” on the PCB. Then solder the two 3W resistors in place. Follow with the remaining SMD ceramic capacitors and chip resistors as shown in the overlay diagram. For the two-pin devices, make sure that you apply the soldering iron long enough so that the solder adheres to the PCB and the component. Adding a little flux paste to the PCB pads before positioning the part will make this easier. There is a single component on the underside of the board, a 10MΩ resistor positioned between CON1 and VR1. Solder it in place but use a minimal amount of solder, so that you don’t plug the through-holes underneath. You can add more solder later after CON1 and VR1 are in place. All that’s left then is to solder trimpot VR1 with the adjustment screw orientated as shown, and a pin header for CON1. We used a normal pin header but a polarised header would be a good idea if you’re going to use a plug to make connection to the batteries so that it can’t be accidentally reversed. If it is reversed, D1 & D2 should prevent damage but the balancer won’t work! Or you can solder the battery wires directly to these three pads. They only need to be rated to handle 300mA per board; medium duty hookup wire should be more than sufficient, even if paralleling multiple boards. Testing & set-up Connect your batteries in series, then connect the negative-most terminal directly to the negative terminal on CON1. Do not connect the junction of the two batteries to the Balancer just yet. Ensure that the total battery voltage is well above the threshold and that they are reasonably close to being balanced. You can ensure they are balanced by charging both independently and then connecting them in parallel via a low-value, high-power resistor (eg, 1Ω 5W) and leaving them for a few hours. The voltage across the resistor should drop to a very low level once their voltages equalise. Now connect the most positive terminal to the positive pin of CON1 via a 1kΩ resistor and check that LED1 lights up. LEDs 2 & 3 should remain off. Measure the voltage across the 1kΩ resistor. It should be under 20mV. If it’s under 5mV or over 20mV, disconnect the battery and check for errors in your PCB assembly or battery wiring. Assuming the voltage is within the specified range, remove or short out the 1kΩ test resistor and then connect the junction of the two batteries to pin 2 of CON1. LED2 and LED3 may light up. If so, rotate the adjustment screw siliconchip.com.au Parts list – 2 x 12V Battery Balancer 1 double-sided PCB, coded 14106181, 31.5 x 34.5mm 3 3-way right-angle or vertical pin header (CON1) Semiconductors 2 LT1495CS8 dual micropower op amps, SOIC-8 (IC1,IC2) 1 ZXRE330ASA-7 micropower 3.3V reference, SOT-23 (REF1) 2 DMC3021LSDQ dual N-channel/P-channel power Mosfets, SOIC-8 (Q1,Q2) 1 2N7000 N-channel signal Mosfet, SOT-23 (Q3) 1 green LED, SMD 3216/1206 (LED1) 1 red LED, SMD 3216/1206 (LED2) 1 blue LED, SMD 3216/1206 (LED3) 2 S1G 1A schottky diodes or similar, DO-214AC (D1,D2) Capacitors (all SMD 3216/1206 X7R ceramic) 2 100nF 50V (measure value before installing!) 1 10nF 50V (measure value before installing!) Resistors (all SMD 3216/1206 1%) For tips and tricks 6 10MΩ (Code 1005) on soldering SMD 1 6.8MΩ (Code 6804) components, refer to the 2 5.6MΩ (Code 5604) SILICON CHIP articles “How to Solder 1 2.2MΩ (Code 2204) Surface Mount Devices” 1 1MΩ (Code 1004) in March 2008 2 390kΩ (Code 3903) www.siliconchip.com.au/ 2 100kΩ (Code 1003) Article/1767 2 10kΩ (Code 1002) and 2 4.7kΩ (Code 4701) October 2009 1 1kΩ (Code 1001) www.siliconchip.com.au/ 2 27Ω 3W (SMD 6331/2512) Article/1590 [eg, TE Connectivity 352227RFT] 1 47mΩ [eg, Panasonic ERJ-L08KF47MV] 1 200kΩ 25-turn vertical trimpot (VR1) in VR1 until they are both off. Now check that there is no balance current flowing by measuring the voltage between TP1 and TP2, and between TP3 and TP4. In each case, the reading should be zero. If you get a non-zero reading between TP1 and TP2, current is flowing through Q1a. And if there’s a voltage between TP3 and TP4, current is flowing through Q2b. Since you started out with balanced voltages, this should not be the case, so adjust VR1 further until you get a zero reading across both pairs of test points. Ideally, VR1 should be adjusted to halfway between the point where the voltage starts to rise between one pair of test points, and the point at which the voltage rises across the other pair of test points. This ensures the balancing will be, for lack of a better word, balanced! The maximum reading you should get between one pair of test points should be 8.8V. Any more than that and you risk the resistor dissipation rating being exceeded. In this case, disconnect the batteries and change the 10MΩ resistor right next to VR1 on the top side of the board with a slightly lower value (eg, 9.1MΩ or 8.2MΩ) to reduce the current limit. If that doesn’t fix it then it’s likely that the current limiting circuitry is not working so you should check for soldering problems or faulty components. SC Celebrating 30 Years May 2018  75 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. 20V, 2.5A Adjustable Power Supply with current limiting This adjustable power supply is based on the venerable LM723C regulator IC and a handful of low-cost components. It provides an adjustable output voltage of 0-20V and adjustable current limit of 0-2.5A. When the current limit is reached, the output voltage drops to keep the current constant and LED2 lights to indicate that it is in current limiting mode. It also provides voltage and current metering (using analog meters) and multiple supplies can be built and connected in series or parallel, to obtain higher voltages or currents. Normally, an LM723-based regulator cannot have an output voltage lower than 2V but because this design uses the LM723C to drive a separate NPN pass transistor and due to the clever feedback arrangement, the output voltage can be adjusted all the way down to 0V. It will also drop to 0V if short-circuited, due to the builtin adjustable current limiter. Mains power is switched by DPST switch S1 and passes through fuse F1 to be applied to the primary of 230V to 24V transformer T1 (60VA). Bridge rectifier BR1 and the 3300µF capacitor provide a ~30V DC unregulated supply rail. A 10nF capacitor across T1's secondary reduces switching interference when the diodes in BR1 go into and out of conduction. The main regulating transistor is Q4, a 2N3055 configured as an emitterfollower. Current flows from the main filter capacitor to its collector via a 1W 7W resistor and 1N5401 3A diode D1, which are used to provide the current limiting feature, as described below. The current from Q4's emitter flows through two parallel 0.1W 2W resistors to the output. These resistors effectively form a 0.05W 4W resistor which is used as a shunt to measure the current flow. The voltage across these resistors is 50mV/A and this is translated into a current by trimpot VR3 and fed to the ammeter movement. Say VR3 is adjusted for a resistance of 125W. This will feed 1mA (2.5 × 50mV ÷ 125W) to the meter at 2.5A, giving a full-scale reading on a 1mA meter. If the meter used reads 0-5A, then you would adjust VR3 for 250W instead, so that it would reach half-scale at 2.5A. Similarly, the voltmeter is connected across the output via trimpot VR4. For a 0-20V 1mA meter, you need to feed it 1mA at 20V output, so you would adjust VR4 for 20kW. Higher resistance settings are needed for meters with a higher voltage range, for example, 30kW for a 0-30V type. The output voltage is controlled by IC1, using its pin 5 (non-inverting) and pin 4 (inverting) inputs and pin 11, which is the collector of its internal output transistor. The emitter of that transistor is internally connected to the cathode of a 6.2V zener diode, which is supplied with current via the 220kW resistor to pin 10 and its anode is connected to ground via pin 9. When the voltage at pin 5 is higher than the voltage at pin 6, the IC sinks current from the base of Q3 via the 4.7kW resistor, into pin 11. This causes Q3 to conduct, delivering current to the base of Q4, thus raising the output voltage. When Q3 switches off, the 47W resistor between Q4's base and emitter causes it to switch off as well, lowering the output voltage. A fraction of the output voltage is fed back to the inverting input at pin 4, via a fixed resistive divider comprising 62kW and 22kW resistors. The bottom end of this divider goes to the wiper of potentiometer VR2 rather than ground. Pin 6 of IC1 provides a nominal 7.15V reference. This is used to bias both the inverting and non-inverting input pins. The non-inverting pin bias is fixed at around 5.28V due to another 62kW/22kW divider, from the reference output to pin 5 and then to ground. The voltage at the wiper of VR2 can be varied from the 7.15V reference, down to 0V. Consider the case when the wiper of VR2 is at the 7.15V end, ie, fully anticlockwise. We know that the non-inverting input is held at 5.28V. To get the same 5.28V at the inverting input (pin 4), the output would need to be 0V. As VR2 is rotated clockwise and its wiper voltage decreases, the output voltage must increase in order to keep the two input voltages equal. Hence, VR2 can be used to vary the output voltage all the way down to 0V and up to 20.16V (5.28V × [62kW + 22kW] ÷ 22kW). The 470pF capacitor between pins 4 and 13 reduces the bandwidth of the feedback loop, by feeding back fast changes in the output voltage directly to the inverting input pin. Since pin 13 is internally connected to the base drive for the output stage, 8.2V zener diode ZD1 limits the drive to that output stage, preventing saturation and keeping the IC operating in linear mode. Stability is also im- Issues Getting Dog-Eared? Keep your copies safe with these handy binders REAL VALUE AT $16.95 * PLUS P & P Order now from www.siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *See website for overseas prices. 76 Silicon Chip Celebrating 30 Years siliconchip.com.au proved by the 1.8kW resistor across the output terminals, which provides a minimum load. The current limit is set using potentiometer VR1 and controlled by PNP transistor Q2. With no current drawn from the output, the voltage across VR1 and its 220W and 100W padder resistors will be around 0.7V, ie, the forward voltage of diode D1. This voltage increases at around 1V/A, due to the 1W resistor in series with D2. VR1 controls what fraction of this voltage is applied to the base of Q2. When this fraction exceeds around 0.6V, Q2 switches on and supplies current to pin 11 of IC1, the same pin that is driving output transistors Q3 and Q4. Since pin 11 can only sink around 2mA, due to the 4.7kW series resistor, this has the effect of forcing the output transistors to switch off, reducing the output voltage. This, in turn, lowers the output current, which reduces the base drive to Q3 and thus the output voltage should stabilise at a level where the output current flow is at a value as determined by the rotation of VR1. The padder resistors are chosen to give a near-zero output current when VR1 is fully anti-clockwise and the full 2.5A that the supply is capable of siliconchip.com.au when it is fully clockwise. The same voltage which drives the base of Q2 is also applied to the base of PNP transistor Q1 via a 47W resistor. Thus, Q1 will switch on when Q2 does, indicating that current limiting is in effect by lighting LED2. Construction I have produced a single-sided PCB design for this power supply; a PDF pattern can be downloaded from the Silicon Chip website. The following components are mounted off-board: T1, VR1, VR2, LED1, LED2, Q4 and the voltmeter and ammeter. A wiring diagram is supplied with the PCB pattern, to show how these are connected. Q4, the main transistor, is in a TO-3 package and should be mounted on a substantial heatsink as it can dissipate up to 75W or so. Q3, its driver transistor, should have a small flag heatsink fitted. While this circuit is based on an old design, the parts are still available and the LM723C and 2N3055 are still in production. The other parts are either generic or have been replaced with more modern versions. Gianni Pallotti, North Rocks, NSW. ($75) Celebrating 30 Years Most of the components on the prototype PCB have been mounted vertically to keep it compact. Note the heatsink on Q3. May 2018  77 Personal Speedometer for jogging I built this device to keep track of how far and how fast I go when jogging. I know there are plenty of smartphone apps to track this type of activity but since jogging is a bit of an “escape” for me, I don’t like to carry my phone while I’m doing it. Also, even if I did bring my phone, I wouldn't be able to choose between the dozens of available apps. Most of these apps seem to also require an internet connection while you’re jogging, making it a bit prohibitive to use. This unit also costs a lot less to build than buying a typical smartphone, so I don't have to worry about breaking or losing it. It uses a GPS receiver to track your jogging and has an OLED display to show the results. I purchased the major parts from AliExpress for around $20. Because your route might have areas where you backtrack, run laps or repeat sections, I have included some buttons to give the unit waypoints. Basically, after you run each straight section and are about to make a turn, you press the “P” button to indicate to the unit that you have just completed a section. This way, it will correctly track the distance you jog even if you loop back around. This also serves as a kind of “lap” button, ie, it will show the distance 78 Silicon Chip that you’ve travelled since you last pressed the P button, as well as the total distance travelled in this session so far. You can press the “Q” button when you’ve finished jogging and it will show you the total distance you’ve travelled, how long it took and your average speed in km/h. You can do this at any time after you have finished jogging since the data is stored in EEPROM and only cleared when you press the P button to start the next session. As shown in the circuit diagram, there isn’t much hardware required; you can build it using an Arduino Uno, a Nano or a bare ATmega328P IC. If using the bare IC, you will need to load it with the minimal Arduino bootloader which can operate without a crystal. Details on how to do this are shown at: www.arduino.cc/en/Tutorial/ ArduinoToBreadboard The OLED display is controlled via an I2C serial bus so it’s wired up to the SDA and SCL control lines at pins 27 and 28 of IC1 respectively. NMEA serial data from the GPS receiver is fed to pin 15 of IC1 (digital input PB1). The battery voltage is reduced by a 330kW/390kW resistive divider and fed to analog input ADC0 at pin 23 so Celebrating 30 Years that the micro can monitor the battery voltage. The GPS receiver, micro and OLED are all powered from a 3.3V rail produced by an HT7333-1 250mA lowdropout (LDO) regulator with power from a single lithium-ion or lithiumpolymer cell. These have a nominal voltage of around 3.7V but typically vary from 4.1-4.2V fully charged, down to around 3.0-3.3V when fully discharged. There is no cell reverse polarity protection so ensure it is wired correctly! I built the unit on a small piece of double-sided prototyping matrix board, with the Arduino Nano, OLED display and buttons mounted on one side and the battery and other components soldered to the opposite side. The GPS receiver was connected by flying leads (see photograph to the right). Make the connections using point-to-point wiring, as shown in the circuit diagram. Having built the unit, take it outdoors (so it has a clear path to the GPS satellites) and power it up. The 1pps LED on the GPS receiver should start to flash and then you will get a display on the OLED screen indicating your current latitude, longitude, the number of satellites in view, current time in UTC and your current speed. Press the P button and a new line will appear below the others, indicating the distance that you’ve travelled siliconchip.com.au in km, for the current segment and in total (initially both zero), the number of segments you have traversed (also initially zero) and the number of seconds elapsed. Press the Q switch and check that the summary appears. You can then press the P button to start a new session and take the unit out for a test jog! The software (including header file) will be available from the Silicon Chip website and is labelled "ARDUINO_ GPS_OLED_speedo_meter.ino". Bera Somnath, Vindhyanagar, India. ($70) Sunset Switch to discourage possums We had trouble with possums in a tree outside our back door. Every morning, the ground was covered in droppings, leaves etc. We accidentally left on our outdoor spotlights one night and noticed that there was a significant reduction in possum-related mess. Whilst it is not difficult to turn on the spotlights as it turns dark and turn them off again in the morning, I needed a “sunset” switch so I wouldn't forget. The circuit I devised is based on a light-dependent resistor (LDR). When it's light, the LDR's resistance is low, so the voltage at pin 2 of comparator IC1 (actually an LM358 op amp) is low. The non-inverting input, pin 3, is supplied with a reference voltage that's derived from the 9V supply and siliconchip.com.au adjusted using trimpot VR1. As darkness falls, the LDR resistance increases and the voltage at pin 2 rises. Eventually, it rises above that of pin 3 and so output pin 1 goes low, switching off transistor Q1 and allowing current to flow from the 9V supply through the two 1kW resistors to the base of Q2, which then switches on. This energises the coil of relay RLY1, closing the contacts and applying 230VAC to the spotlight(s) plugged into the 3-pin mains socket. The 11kW resistor between pins 1 and 3 of IC1 provides hysteresis, which prevents the relay from chattering (switching on and off rapidly) at dawn and dusk, when a cloud passes overhead, etc. Celebrating 30 Years If using a different type of relay for RLY1, ensure that its "must operate" voltage is below 9V or it may not work reliably. Most 12V DC coil relays will switch on at 9V but a relay with a 9V DC coil would certainly work if you can find one with appropriate contact ratings. Power for the circuit is derived from the same mains supply that is fed through to the spotlights, using a small 9V centre-tapped transformer with a bridge rectifier (BR1) at its output that feeds a 470µF filter capacitor and 7809 linear regulator (REG1). Diode D1 quenches the relay coil back-EMF at switch-off while a neon and series resistor across the switched mains supply indicate that power is present. I fitted a 2A fuse in the Active line to protect the circuit and this provides more than enough current to operate a few 10W LED floodlights but you would need a higher-current fuse if you want to power halogen lamps or similar. I aimed one spotlight directly at the tree trunk and another into the foliage. You may need to experiment to get the best result. This circuit could be used for many other purposes that need to sense light levels and switch on or off in dark or light conditions. Jon Kirkwood, Castlecrag, NSW. ($40) May 2018  79 Adjustable low-pass filter An adjustable active low-pass filter can be useful in a number of audio applications. For example, it can be used to clean up and reduce the distortion of a sinewave from a direct digital synthesiser (DDS). Or it can be used to limit the bandwidth of a noise source. This one can be adjusted to have a -3dB point between about 600Hz and 100kHz. RC (resistor-capacitor) filters are first-order filters and so have the slowest roll-off (6dB/octave). They also have desirable characteristics, like a lack of ripple in the passband without tuning, and very low noise and distortion when the right components are used. Hence, this filter is based on passive RC filters but does offer some active buffering and amplification if required. The input signal is AC-coupled with a 10µF non-polarised capacitor, or DC coupled if S1 is closed, shorting out that capacitor. It is then fed to potentiometer VR1 which acts as a level control, with diodes D1 and D2 clipping Frequency Switch 1.5kHz 9/17 4.5kHz 8/16 12kHz 7/15 30kHz 6/14 83kHz 5/13 200kHz 4/12 660kHz 3/11 1MHz 2/10 the signal so it does not exceed the supply rails and the 200W resistor limits the current through those diodes. The level-adjusted signal is then fed to low-noise buffer op amp IC1a. It operates with unity gain if switch S18 is open or two times gain if the switch is closed. Its output is then fed to the first passive low-pass filter stage, which uses a fixed 1.6kW resistor and a combination of eight capacitors from 100pF to 68nF, selected by DIP switch bank S2-S9. This gives a selectable -3dB point of between 616Hz (all eight switches closed) and 1MHz (only S2 closed). The -3dB point can be calculated by adding up the capacitors which are switched into the circuit by S2-S8 and then feeding this into the following formula: f(Hz) = 1 ÷ (2π × 1600W × C) where C is the sum of the capacitor values in farads. The values with one switch closed at a time are 1.5kHz, 4.5kHz, 12kHz, 30kHz, 83kHz, 200kHz, 660kHz and 1MHz. The capacitor values were cho- sen to give a good range of intermediate frequencies between these values and below 1.5kHz, when more than one switch is closed. Having passed through the first RC filter, the signal is then buffered by another low-noise op amp, IC1b, again with the option of two times gain, using switch S19. The signal is then fed to another identical filtering and buffering/amplification arrangement, this time using DIP switch bank S10-S17 and op amp IC2a. DIP switches S10-S17 can be left open if a single-order filter is desired; in this case, IC1b will simply act as a gain stage/buffer (depending on the setting of S19). If the two DIP switch banks are configured identically, the -3dB point will be reduced by 36% compared to a single filter. For example, if S2-S8 are open and S9 is closed, the first stage will have a -3dB point of 1463Hz (1 ÷ [2π × 1.6kW × 68nF]). If S10-S16 are also open and S17 also closed, the overall -3dB Values with one switch closed 80 Silicon Chip Celebrating 30 Years siliconchip.com.au Circuit Ideas Wanted Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP on-line shop, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au point of the circuit will then be 936Hz (1463Hz × 64%). The roll-off above the -3dB point is 6dB/octave for a single stage (first-order) filter and 12dB/octave for a second-order filter. It would be possible to configure the two DIP switch banks differently and this would give you a dual-slope response, with around -6dB/octave between the two corner frequencies and then -12dB/octave above the higher of the two. The output from both filter banks is fed to CON2 via a 100W resistor (OUT1), to isolate any output capacitance from op amp IC2a and prevent oscillation. Op amp IC2b inverts the siliconchip.com.au signal from IC2a and this is fed to a separate, complementary output (OUT2), again via a 100W resistor. Depending on the positions of switches S18-S20, the maximum possible gain is eight times. The output level can be fine-tuned using VR1. For the best performance, set VR1 at the highest level possible and enable the minimum number of gain stages to obtain the required output amplitude. The circuit requires split rails to function and these are provided from a 15VAC plugpack by a half-wave voltage doubling rectifier, two filter capacitors and 7815/7915 linear regulators. Petre Petrov, Sofia, Bulgaria. ($50) Celebrating 30 Years May 2018  81 Using Cheap Asian Electronic Modules Part 16: by Jim Rowe 35MHz-4.4GHz digitally controlled oscillator This programmable frequency module is based on the ADF4351 PLL (Phase-Locked Loop) IC and it can produce a sinewave from 35MHz to 4.4GHz, with crystal accuracy. It can even be used as a sweep generator and costs less than $30. T hat’s an impressive range of frequencies that can be produced by this surprisingly compact (48 x 36.5 x 10mm) module. It is available from various Chinese websites including Banggood (siliconchip.com.au/link/ aajb) and AliExpress, as well as eBay, for around $30. It’s essentially a smaller, lower-cost version of the ADF4351 development board sold by Analog Devices. It runs from 5V and has two RF outputs, one 180° out of phase with the other, allowing it to produce either single-ended or differential signals. It’s controlled using a serial bus that’s connected via a 10-pin header, which also makes connection to the 3.3V supply rail. The ADF4351 chip at the heart of the module is an advanced phaselocked loop (PLL) device. Before we delve into how the ADF4351 works, it’s a good idea to briefly cover the operation of PLLs. Fig.1 shows the block diagram of a basic PLL. It incorporates a negative feedback loop, similar to the one used to improve the performance of audio amplifiers. But in this case, rather than having a voltage divider providing the feedback signal, we have a frequency divider in the loop. The PLL’s output signal (Fout) is produced by the voltage-controlled 82 Silicon Chip oscillator (VCO) at upper right. The frequency divider divides this output frequency by a factor of N. The resulting signal (Ffb) is then fed to the negative input of phase detector PD, which compares its frequency and phase with Fref, the signal from a low-frequency reference oscillator, fed to its positive input. The PD output “error” pulses are fed to charge pump CP, which uses them to develop a fluctuating DC voltage with a polarity and amplitude proportional to the frequency/phase differences between Fref and Ffb. This voltage is then low-pass filtered and used to control the VCO’s frequency. This feedback action causes the VCO frequency (Fout) to stabilise at very close to N times the reference frequency, Fref. The PLL is then described as being “in lock”, since the feedback action keeps Ffb locked to Fref in both frequency and phase. So even if Fref is fixed, by changing the division ratio N, we can control the frequency of Fout. Basic PLLs like this have been in use for many decades but more elaborate versions have also been developed, to overcome some of the limitations of a basic PLL. One of these limitations is that the minimum change in Fout is equal to Fref, so you need quite a low reference frequency to have fine control over the output frequency. But it’s easier to produce accurate and stable reference oscillators at higher frequencies, so one of the first enhancements to PLLs was to add a reference frequency divider between the Fref input and the phase detector PD. Also, if the output frequency needs to be up in the GHz (Gigahertz) range, it’s not easy to provide a programmable divider working at these frequencies. So another early PLL improvement was to add a fixed “prescaler” to the feedback loop, between the VCO output and the input of the main (programmable) feedback divider. Fig.1: block diagram of a basic phase-locked loop. They’re typically used to generate a stable high-frequency signal from a fixed lowfrequency signal. Celebrating 30 Years siliconchip.com.au Fig.2: block diagram of the ADF4351 wideband synthesiser IC. The integrated voltage-controlled oscillator has an output frequency range of 2.2 to 4.4GHz, which, when combined with the RF divider, provides the ~35MHz to 4.4GHz range. The fractional-N PLL controls the frequency from its three registers via the equation: Fout = Ffb × (INT + FRAC ÷ MOD). Unfortunately, this reduces the output frequency adjustment resolution. However, this can be overcome by adopting what’s referred to as a “dual modulus prescaler”. This is essentially a prescaler with a division ratio that can be switched from one value (say P) to another (like P+1) by an external control signal. We don’t have space here to fully explain the operation of modern (and quite elaborate) PLLs but the prior description should be enough to understand how the ADF4351 works. Inside the ADF4351 The block diagram of the ADF4351 IC (Fig.2) is somewhat more complex than the basic PLL shown in Fig.1. The VCO part of the device is labelled “VCO CORE” and shaded pink. There are actually four VCOs inside the core, each used to generate a different frequency range. They are all tuned by the dual varicap diode shown to its right, using a tuning voltage fed in via the Vtune pin. Above the VCO core, you can see the phase comparator and charge pump, both blue. The charge pump output goes to the CPout pin, so that an external low-pass filter can be used to smooth the pulsating output of the charge pump before it is fed back into siliconchip.com.au the ADF4351 via the Vtune pin. The differential outputs from the bottom of the VCO core go to three different destinations. One of these is to the yellow “RF DIVIDER” block to its right. This programmable frequency divider can divide the VCO output frequency by 1 (ie, no division), 2, 4, 8, 16, 32 or 64. This lets the chip generate low output frequencies while the VCO core is operating at much higher frequencies (2.2-4.4GHz). The outputs from the RF divider are fed directly to the chip’s main RF output stage, which drives the A+ out and A- out pins. The RF divider outputs also go to the inputs of two different multiplexers (digital selector switches), shown in mauve. The auxiliary multiplexer on the right switches between the direct output lines from the VCO core and the outputs from the RF divider and so determines which is fed to the auxiliary RF output stage and then to the B+ and B- output pins. The PDBRF pin allows both RF output stages to be disabled when they are not needed, to save power. The feedback (F/B) multiplexer at left determines which of the same two signal pairs go to the feedback divider, in the yellow box. It’s also rather more Celebrating 30 Years complex than the simple feedback divider shown in Fig.1. That’s because the ADF4351 offers the ability to implement either an integer-N or a fractional-N PLL, as required. So the feedback divider needs three registers which hold the integer division value, the fractional division value and the modulus value, plus control circuitry labelled “third-order fractional interpolator”. This circuitry effectively allows the feedback frequency to be divided by a rational number (fraction). The output of this divider is then fed, via a buffer, to the phase comparator. The circuitry shown in the upperleft corner of Fig.2 takes the input from the external reference oscillator (fed into the REFin pin) and processes it before feeding it to the other phase comparator input. As mentioned earlier, one of the refinements to earlier PLLs was to add a reference signal frequency divider, so that high-frequency reference oscillators could be used; hence the 10-bit R counter. But the ADF4351 also provides a frequency doubler and an additional divide-by-two stage for the reference input, both of which can be switched in or out under software control. This gives the chip a great deal of flexibility. May 2018  83 Fig.3: complete circuit diagram for the ADF4351 frequency synthesiser module. The whole chip is controlled by means of a simple 3-wire serial peripheral interface (SPI), shown at centre left of Fig.2. Serial data from the PC or microcontroller is fed in via the DATA pin, clocked into the serial data register and function latch via clock pulses fed to the CLK pin, and then latched into the various control registers by feeding in a pulse via the LE (latch enable) pin. All functions of the ADF4351 chip are configured using six 32-bit control words, sent over this serial bus. Multiplexer C and the other blocks at the upper right of Fig.2 allow external monitoring of the ADF4351’s status. The “LOCK DETECT” block monitors the phase comparator and provides a high logic output on the LD pin when the PLL is locked. Multiplexer C allows either of the two phase comparator inputs or this lock status to be fed to MUXout pin. 84 Silicon Chip The fast lock switch provides a signal which can be fed into the external low pass filter (between the CPout and Vtune pins) when in “fast lock” mode. So that covers the operation of the IC itself. The synthesiser module The full circuit of the module is shown in Fig.3 and most of the real work is done by IC1. All of the programming and status monitoring signals to and from the module are available at CON1. This includes the DATA, CLK and LE lines (ie, the serial bus) and also the CE (chip enable), LD (lock detect), MUXout and PDBRF (power down RF buffer) lines. The reference signal is provided by a 25MHz crystal oscillator (XO), shown at upper left, with its output fed to the REFin pin of IC1 via a loading/coupling circuit comprising two 1nF capacitors and a 51W resistor. Celebrating 30 Years Note that there is also provision for feeding in a different reference signal, via the SMA socket labelled MCLK. In order to do this, you’d need to remove the 0W resistor connected to pin 3 of the onboard XO. If you are using the onboard XO, the MCLK socket can be used to monitor its output via a scope or frequency counter. The resistors and capacitors connecting the CPout and SW pins of IC1 (pins 7 and 5) to the Vtune pin (pin 20) form the low-pass loop feedback filter. The RF output signals from the RFOA+ and RFOA- pins (12 and 13) are taken to the RFout+ and RFoutSMA sockets via matching/filtering circuits using L2, L3, L5 and L6, plus two 1nF capacitors. Notice that the output pins are fed with the +3.3V supply voltage via L2 and L3. In this module, the auxiliary RF outputs RFob+ and RFob- (pins 14 and 15) are not wired up. siliconchip.com.au Fig.4: when connecting the ADF4351 synthesiser module to an Arduino-based device, a few extra resistors are needed. These resistors form a voltage divider, as the module can only handle 3.3V signals, while the Arduino’s outputs have a swing of 5V. Note the changes needed if using a V2 module at the end of this article. The whole module operates from a 3.3V supply, derived from the 5V input at CON2 via REG1, an ASM1117 low-dropout regulator. This AVdd rail powers all of the analog/RF circuitry directly. The digital supply rail, DVdd, is derived from AVdd using LC filters comprising inductors L4 and L1 and a number of bypass capacitors. There are two indicator LEDs. LED1 is connected between the DVdd line and ground and indicates when the module has power while LED2 is connected to the LD (lock detect) pin of IC1 (pin 25) and indicates when the PLL is in lock. All the remaining components are for bypassing and stability, apart from fuse F1 and diode D1, which prevent damage in the event that the 5V power source is connected with reversed polarity. Controlling it with an Arduino I initially hooked the module up to an Arduino Uno using the simple circuit shown in Fig.4. The three main control lines MOSI, SCK and LE are not taken directly to the DAT, CLK and LE pins of the module but instead via 1.5kW/3kW voltage dividers. This is because the inputs of the ADF4351 can only cope with 3.3V signals, whereas the Arduino outputs have a 5V output swing. The LD signal fed back from the module to the Arduino’s D2 pin does not need a divider because it’s going the other way and the Arduino inputs function well with a signal having a swing of 3.3V. siliconchip.com.au Note also that Fig.4 indicates that the 5V supply for the module can come from either a plugpack or from the 5V output of the Arduino. I adapted an Arduino sketch I found on the internet, written by French radio amateur Alain Fort F1CJN (siliconchip.com. au/link/aaje). Mr Fort’s sketch was written for an Arduino with an LCD button shield but I decided to adapt it so that it would work with the simple configuration shown in Fig.4, relying on the Arduino IDE’s Serial Monitor to send commands to the ADF4351 and to indicate the PLL’s output frequency and whether it was locked or not. I also connected one of the PLL module’s RF outputs to my frequency counter, via a prescaler, so I could monitor it. The results were quite impressive. I could type in any frequency between 35MHz and 4.4GHz, with a resolution of 0.01MHz (10kHz) and the module’s output would lock to that frequency in the blink of an eye. I also monitored the current drawn by the module and found that it varied between 110mA and 145mA, depending on the output frequency. I also checked the accuracy of the module’s 25MHz on-board reference XO and found it to be 25.0000734MHz or only 73.4Hz high. Since this equates to an error of just +2.936ppm, it seems quite accurate. So that’s one easy way to get the ADF4351 module going with an Arduino. The sketch (“ADF4351_and_ Arduino_SC_version.ino”) is available for download from the Silicon Chip website. Driving it from a Micromite I also hooked the module up to a Micromite LCD BackPack combination and wrote some code so that it could be controlled via the LCD touchscreen. The circuit is shown in Fig.5 and it’s about as simple as you can get. In this The bottom view of this module is shown at approximately twice actual size. The bottom of the board is populated by five 10kW 10kW pulldown resistors for the breakout pin connections. Celebrating 30 Years May 2018  85 Fig.5: when connecting the ADF4351 module to a Micromite no extra components are needed, unlike with an Arduino. However, the newer version of the module requires a 10kW resistor between CE and +3.3V. case, no resistive dividers are needed on the SCK, MOSI and LE lines because the Micromite’s logic pins have a swing of 3.3V. I used a “software” SPI port rather than the hardware one used by the Micromite to communicate with the LCD and touchscreen, to prevent possible interaction. The embedded C code (CFUNCTION) needed to provide this added port is included in the MMBasic program I wrote for this approach. Software SPI port performance is limited but that isn’t a problem as the amount of data to transfer is small. A USB charger was used to supply 5V to the ADF4351 module because its current drain is a little too high for the BackPack to provide. The software uses just two screens, as shown below. The initial screen (at left) displays the current frequency and gives you the option of touching the button at the bottom if you want to change it. You will then get the second screen, which allows you to key in a new frequency, displayed below the current frequency. When you’re happy with the new figure, simply touch the OK button and the module jumps to the new frequency. The program returns to the main screen, displaying the new frequency. So for those who would like to team up the module with a Micromite, this program (“Simple ADF4351 driver program.bas”) should get you off to a good start. Like the Arduino sketch, it’s available from the Silicon Chip website. Performance I checked the module’s RF output performance at quite a few different frequencies, using my Signal Hound USB-SA44B spectrum analyser controlled by Signal Hound’s “Spike” software. The results were quite impressive, as you can see from the two spectrum plots. One plot shows the output at 275MHz, with the only significant spurs visible being at ±50MHz with an amplitude of -57dBm. The other plot shows the output at 4.200GHz, with two spurs again visible but this time both on the low side: one at 4.150GHz (far left) with an amplitude of about -53dBm and the oth- The sample program running on a Micromite LCD BackPack. These are the only two screens the software uses, one to enter a specific frequency for the module to output and another to display the current frequency. 86 Silicon Chip Celebrating 30 Years siliconchip.com.au Spectrum analysis of the ADF4351 module’s output performance at 275MHz (left) and 4.2GHz (right). The RF output performance over the full range was good, with only a few visible spurs outside the programmed frequency. These normally correspond to beat frequencies or integer-multiples of the reference and oscillator frequency. er at 4.175GHz with an amplitude of -61dBm. In both cases, the amplitude of the main output carrier is very close to 0dBm. This turned out to be the case over most of the range, in fact. The only region where the carrier level did drop (to around -20dBm) was in the vicinity of 2.45GHz – perhaps by design, to minimise interference with WiFi and Bluetooth systems. Overall, the ADF4351 frequency synthesiser module is very impressive, especially when you consider its frequency range and price. It could even be used to make your own VHF/UHF signal and sweep generator, teamed up with a Micromite and a 4GHz digital attenuator module that we will describe in next month’s issue. These changes will be critical to successfully connect the module to a micro, so here are the main details listed below: 1. Many of the connections to the 10-way pin header (CON1) have changed, as shown in Fig.6. 2. There is now no on-board pullup resistor connecting IC1’s CE pin to the +3.3V (DVdd) line, nor are there pulldown resistors connected between the CLK, DATA and LE pins and ground. To ensure normal operation of the module with either an Arduino or a Micromite, an external 10kW resistor must be connected between the CE and +3.3V pins of CON1. To ensure maximum stability, it’s a good idea to also connect an external 10kW resistors between the LE pin and ground. Once the above changes are made, version 2 of the module performs just as well as the earlier version. Useful links The module from AliExpress: www. aliexpress.com/item//32848807357. html The module from eBay: www.ebay. com.au/itm/142521016834 ADF4351 data sheet: siliconchip. com.au/link/aajc Fundamentals of PLLs: siliconchip. SC com.au/link/aajd Fig.6: CON1 has been changed completely on the newer version of the ADF4351 module. Every signal, except for CLK, is connected to a different pin location. A new version of the ADF4351 synthesiser module Just recently we received a second ADF4351 Synthesiser module and discovered that it was a “V2” module which had been changed in a number of ways compared with the first version. Are Your S ILICON C HIP Issues Getting Dog-Eared? REAL VALUE AT $16.95 * PLUS P & P Keep them safe, secure & always available with these handy binders Order now from www.siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *See website for overseas prices. siliconchip.com.au Celebrating 30 Years May 2018  87 PRODUCT SHOWCASE COMING THIS MONTH: Entry-level R&S Spectrum Analyser with advanced-level features 18, 19 & 20TH MAY SEA WORLD GOLD COAST QUEENSLAND The 2018 WIA RADIO & ELECTRONICS CONVENTION – “BEYOND 2O2O” The latest Rohde & Schwarz spectrum analyser is the first analyser on the market to integrate the three most-commonly-used instruments on an RF engineer’s workbench, in one budget-friendly instrument. It combines a 5kHz to 1GHz Spectrum Analyser (with instant option up to 3GHz), a Network Analyser and an inbuilt Signal Generator. The R&S FPC1500 is the world’s first spectrum analyser to include a one-port vector network analyser with internal VSWR bridge, an independent CW signal generator and a tracking generator. It is ideal for education, for applications in service and repair shops and for advanced hobbyists. Despite its budget-friendly concept, the R&S FPC1500 is designed to the same quality standards as high-end Rohde & Schwarz instruments, providing solid RF performance and a comprehensive, future-ready feature set. Spectrum analyser For applications requiring a high sensitivity to characterise extremely weak signals, the R&S FPC1500 offers a low noise floor level of –150dBm (typ.), which can be further extended to –165dBm (typ.) through an optional, keycode-activated preamplifier. Its high maximum input power allows users to measure RF signals up to +30dBm (1W). This combination of high sensitivity and high input power level gives the R&S FPC1500 an exceptionally wide measurement dynamic range. Network analyser Thanks to the internal VSWR bridge, the R&S FPC1500 can perform reflection measurements. This allows users to measure impedance on antennas or RF circuits with the Smith chart display or use distanceto-fault measurements to detect faulty locations on a long RF cable. Signal generator The tracking generator integrated into the R&S FPC1500 enables scalar transmission measurements on passive and active RF components that do Contact: not produce their own Rohde & Schwarz (Aust) Pty Ltd RF signal, eg, amplifiUnit 2, 75 Epping Rd, Lane Cove NSW 2113 ers, filters and even RF Tel: (02) 8874 5188 cables. Web: www.rohde-schwarz.com/au/ 88 Silicon Chip The WIA Annual General Meeting (AGM) and Technical Forum will be held over the weekend of 18th, 19th and 20th May 2018 at SeaWorld on the Gold Coast (Queensland). This year’s event is being organised by the Gold Coast Amateur Radio Club (GCARC) with most of the weekend’s activities taking place at the Sea World Resort. As has become the tradition, there will be a Friday night dinner which will lead into a full day convention on Saturday, with a field day on the Sunday plus many unique tours. Registration and detailed information is available at www.wia.org.au/convention or by emailing wiaagm<at>wia.org.au. CeBIT IN MAY, TOO Immediately prior to the WIA Convention, CeBIT Australia, the largest and longest running business technology conference in the Asia Pacific, will take place from 15-17 May 2018, at the International Convention Centre, Darling Harbour, Sydney. This year’s CeBIT is themed “The Future of Business Technology” and the FutureTech Stage will feature a host of the world’s most renowned industry experts on matters relating to the Internet of Things (IoT), FinTech, Artifi- Contact: cial Intelligence (AI) CeBIT and Machine Learning. Registrations: www.cebit.com.au Jaycar has Wireless Qi Charging Got an iPhone®8, 8 Plus, iPhone X, Samsung Galaxy Note 8 / S8 / S8 Plus, S7 / S7 Edge or other Qi-enabled device? Jaycar stores now have available the new MB-3667 Wireless Charger – it supports fast (10W) and standard (5W) wireless charging. Retail price is $39.95 Contact: Jaycar Electronics (all stores) Head Office: 320 Victoria Rd, Rydalmere 2116 Tel: (02) 8832 3100 Web: www.jaycar.com.au Celebrating 30 Years siliconchip.com.au HO SE U ON SE W E CH IT TO IP IN JA N 20 16 ) .au THIS CHART m o pi .c h SIL IC c on t a (or ic sil • Huge A2 size (594 x 420mm) • Printed on 200gsm photo paper • Draw on with whiteboard markers (remove with damp cloth) • Available flat or folded will become as indispensable as your multimeter! How good are you at remembering formulas? If you don’t use them every day, you’re going to forget them! In fact, it’s so useful we decided our readers would love to get one, so we printed a small quantity – just for you! Things like inductive and capacitive reactance? Series and parallel L/C frequencies? High and low-pass filter frequencies? And here it is: printed a whopping A2 size (that’s 420mm wide and 594mm deep) on beautifully white photographic paper, ready to hang in your laboratory or workshop. This incredibly useful reactance, inductance, capacitance and frequency ready reckoner chart means you don’t have to remember those formulas – simply project along the appropriate line until you come to the value required, then read off the answer on the next axis! Here at SILICON CHIP, we find this the most incredibly useful chart ever – we use it all the time when designing or checking circuits. If you don’t find it as useful as we do, we’ll be amazed! In fact, we’ll even give you a money-back guarantee if you don’t!# Order yours today – while stocks last. Your choice of: Supplied fold-free (mailed in a protective mailing tube); or folded to A4 size and sent in the normal post. But hurry – you won’t believe you have done without it! #Must be returned post paid in original (ie, unmarked) condition. Read the feature in January 2016 Silicon Chip (or view online) to see just how useful this chart will be in your workshop or lab! NOW AVAILABLE, DIRECT FROM www.siliconchip.com.au/shop: Flat – (rolled) and posted in a secure mailing tube $2000ea inc GST & P&P* Folded – and posted in a heavy A4 envelope $1000ea inc GST & P&P* *READERS OUTSIDE AUSTRALIA: Email us for a price mailed to your country (specify flat or folded). ORDER YOURS TODAY – LIMITED QUANTITY AVAILABLE siliconchip.com.au Celebrating 30 Years May 2018  89 Vintage Radio By Dr Hugo Holden The Royal 500 “Owl Eye” AM Radio The Zenith Royal 500 radio appeared in 1955, one year after the Regency TR-1 which was the first commercial transistor radio in 1954. Unlike the Regency TR-1 though, by the time that the Zenith Royal 500 was released, the technology had rapidly progressed into the conventional circuitry we know today as the typical “7 transistor AM radio”. The Regency TR-1 was powered by a 22.5V battery to help overcome the effects of the large base-collector junction capacitances of the very early transistor types and it had a low intermediate frequency (IF) of 262.5kHz to help overcome transistor bandwidth limitations. It also had a single ClassA output stage. However, the Zenith Royal 500 had more advanced transistors, the conventional 455kHz IF and was powered by 6V from four AA cells. It also had a conventional transformer-coupled Class-B push-pull audio output stage. The styling of the Royal 500 could be said to be distinctive, with the metallic surrounds for the black tuning and volume controls and the metallic speaker grille, so much so that in later years it became known as the “Owl Eye” radio. Also of interest was that its case was labelled on the back as “Unbreakable Nylon”. That might seem to have been asking for trouble but my sample does appear to have lasted well, with no 90 Silicon Chip cracks in the case. Also on the back and shown in the photo below, the radio is described as “TUBELESS - 7 TRANSISTORS”. Circuit details The transistors used in the Royal 500are germanium NPN types, as was the case in other very early AM radios, such as the Regency TR-1 (www. siliconchip.com.au/Article/3761, April 2014) and the Sony TR-72 (www. siliconchip.com.au/Article/6938, March 2014). However, by the early 1960s most manufacturers had changed to germa- Celebrating 30 Years nium PNP types and by the early 1970s there was a general shift to silicon transistors in most new equipment. As shown in the circuit diagram of Fig.1, while the design of the Royal 500 now looks to be conventional, it represented a very rapid development in solid-state radio technology. It became the “world standard” for an AM radio, with three IF transformers, a detector diode and a 3-transistor two-transformer audio system with a Class-A driver stage and as already noted, a push-pull output stage. In one aspect, the circuit was not world standard, in that it has separate oscillator and mixer transistors. Most later radios had a single mixeroscillator transistor (often referred to as a converter) and saved a transistor by this approach. Then again, quite a few designs added an audio preamp transistor, so the total transistor count remained the same at seven. Interestingly, the circuit has an error, because the detector diode X1 siliconchip.com.au Fig.1: it’s important to note that the circuit diagram has an error where the detector diode X1 (centre) is drawn reversed. Earlier versions of this circuit had 2200W & 18kW resistors between C15 & C16; these were changed to the current values of 4700W & 47kW respectively, to stabilise the collector current of the 2N35 driver transistor and increase gain. (1N295) is drawn reversed (it is hard to see and is at the secondary output of the third IF transformer, T3). It is not wired this way in the real radio though, where the diode cathode is returned to ground (negative). Subsequently there were a number of circuit variations in the Zenith Royal 500, dictated by parts supply, with changes to the AGC design and some versions using PNP transistors too. The negative-going AGC voltage is developed across C22, a 16µF 3V electrolytic capacitor. With low signal levels this electrolytic capacitor is subject to a small voltage of the correct polarity from the bias network of the 2N216 and first IF amplifier (the 100kW and 4700W resistors connected to C22’s positive electrode). This also forward-biases the detector diode X1 a little, which helps with detecting low level signals. However, with most reasonable signal levels from local stations, the AGC voltage on the positive terminal of C22 goes negative with respect to the radio’s ground and then C22 is subject to reversed polarity; not good for an electrolytic capacitor. This is actually a “classic mistake” in the design of AGC circuits in many, but not all, transistor radios. In fact, this problem appears to have gone unnoticed for over half a century siliconchip.com.au for many transistor radio designs. The practical remedy today is to fit a bipolar electrolytic AGC filter capacitor instead. Perhaps not surprisingly, this AGC filter capacitor often does go open-circuit in early transistor radios and C22 was open-circuit in my Zenith radio. The unbypassed feedback causes oscillation of the IF stages. That turned out to be the case when I first switched on my Zenith radio and it was clear from the heterodyne sounds on tuning stations that the IF was oscillating. It would only weakly receive stations and there was a lot of random noise and static too. Investigation revealed that the mixer transistor had partially failed and the first IF transistor was noisy. The faulty components are indicated in red on the circuit. All the other electrolytic capacitors, aside from C22, were normal on test for capacitance, ESR and leakage which surprised me, considering their age. Editor’s note: modern electrolytic capacitors will tolerate a small negative bias voltage (<1.5V) long-term without failure. would cause oscillations in the IF amplifier stages unless neutralisation was employed. On this circuit, this is effected by the 11pF and 3900W feedback components around the two 2N216 IF transistors. Many European-made PNP transistors for IF work such as the OC45 also required neutralisation when used in 455kHz IF stages in typical AM radio circuits. When it comes to replacing the 2N916 transistors, you need an NPN germanium type with the same feedback capacitance properties or the IF stage will become unstable and oscillate. The alternative would be to adjust the feedback components to compensate. I couldn’t find any 2N194 or 2N216 transistors, however I found some 2N94s which made suitable replacements. In radios of the mid to late 1960s, germanium transistors with very low feedback capacitances became available, making the need for IF neutralisation unnecessary. These included PNP transistors such as the AF117 or AF127. Neutralisation Construction Vintage transistors such as the 2N916 have fairly high base to collector feedback capacitance and this Two photos in this article show the interior of the Zenith radio. Note that all the transistors are in sockets and Celebrating 30 Years May 2018  91 this feature helped with the faultfinding. While the tuning dial only lists frequencies up to 1400kHz, the radio can still tune above that frequency (to about 1600kHz). The electrolytic capacitors are housed in white ceramic tubes with their ends sealed with hard resin. There was no evidence of any physical leakage of electrolyte from any of them and as noted, only one was faulty. One thing to bear in mind when repairing and testing vintage transistor radios is that they have phenolic PCBs, and the adhesion of the copper tracks to the board is nowhere near as good as with modern fibreglass PCBs. So it pays to avoid soldering if possible and when forced to, use a good temperature-controlled iron with the minimal required heat. Also, in radios where the transistors are soldered on, they should, if possible, have heat-extracting clips placed on their leads while soldering. Vintage germanium transistors are far more sensitive to heat damage than modern silicon devices. So the advantage of sockets for transistors is that they do not get exposed to heat from soldering but the disadvantage is that the socket connections can become intermittent. In any case it is better to do exhaustive tests before concluding that any component in the radio needs removal or desoldering. Fortunately, electrolytic capacitors can be checked in circuit with an ESR (Equivalent Series Resistance) meter. The first step in fault-finding is to ensure the DC operating conditions and voltages are correct on all the transistors. After that, AC tests with a signal generator and the oscilloscope can be helpful, if available. The manufacturer’s general alignment instructions should be followed. However, if the IF transformers have not been touched and the original transistors are present and working OK, it would be better in most cases not to try adjusting the IF transformers. In particular, it can be very easy to break the slugs as they can be frozen in after 60 years without being touched. So if the slugs can’t be easily adjusted, leave them as they are. If transistors have been replaced in the IF circuits, then the transformer slugs should be re-adjusted. Or if the IF transformers have been tampered with 92 Silicon Chip by another party they will most likely require checking and adjustment. Any test signal generator should be as loosely coupled in as possible or the generator itself can disturb the tuning conditions of the circuit that it is connected to. The best way is to simply use one or two turns of wire around the ferrite rod (some early transistor radio alignment instructions did specify a magnetic loop to do it and this was a very wise idea). Editor's note: the AM Transmitter featured in the March 2018 issue can be modified to tune between 440kHz and 600kHz by replacing a single capacitor. It can then be used as an alignment source at 450 or 455kHz. The details are in the article at: www.siliconchip. com.au/Article/11004 Aligning the IF stages One useful method to adjust the IF transformers is to temporarily deactivate the local oscillator. In this particular radio it just involved unplugging the oscillator transistor and coupling the signal generator in with a 1-turn loop on the ferrite rod, set for a 1kHz modulated 455KHz carrier. The detected audio can be seen at the volume control with an oscilloscope, heard in the speaker or measured with an AC millivoltmeter. Coupling a 455kHz signal to the ferrite rod still works without deactivating the local oscillator, but a higher signal level will be required to break through the mixer. In many cases it is of little help sweeping the IF and plotting the response curve, because the IF coils are all tuned to a maximum peak at the same frequency (typically 455kHz). The point being that the IF amplifier band-pass characteristic is largely Operation Input signal frequency Connect inner conductor from oscillator to 1 455kHz 2 1620kHz 3 1260kHz 4 535kHz 5 Repeat steps 2, 3 and 4 One turn loosely coupled to wavemagnet While obscured in the photos, the Royal 500 does have a separate mono earphone jack (J1 on Fig.1). Source: www.transistor-repairs.com/ schematics.html set by the design of the IF transformers themselves, not by the technician adjusting or “stagger tuning” the IF stages. Therefore, in my view, an IF sweep generator or “wobbulator” for tuning the IF stages in AM transistor radios has little utility for repairs and adjustments. The opposite is true in correctly adjusting analog television video IF amplifiers though. Also, generally, it is best to set the IF transformers, or the radio’s other adjustments, with a low level modulated RF signal, with the modulation tone just slightly more audible than noise, so that the radio’s AGC is just below threshold. This is because small changes in the observed demodulated audio output voltage amplitude at the detector are suppressed by AGC action which occurs with stronger signals. Connect outer shield conductor from oscillator to Set dial at Trimmers Purpose Chassis 600kHz Adjust T1-T3 for maximum output For IF alignment Gang wide open C1C Set oscillator to dial scale 1260kHz C1A Align loop antenna Gang closed Adjust slug in T6 Set oscillator to dial scale All alignment steps for the Royal 500. Check www.transistor-repairs.com/ schematics.html for a great listing of schematic diagrams on Zenith radios. Celebrating 30 Years siliconchip.com.au One of the selling points of the Zenith Royal 500 was that it worked using just four inexpensive AA 1.5V cells. The Royal 500 shown in this article is a model B. It was released in 1956 and used the PCB shown above, instead of being hand-wired. The transistors are all mounted in plug-in sockets, which makes it easy to remove and replace them. While this version of the Royal 500 used NPN transistors, later models made the switch to PNP transistors as they became more common. Setting the local oscillator The oscillator coil slug is set to calibrate the pointer with the dial (or set the lowest tuning frequency with the variable capacitor fully meshed) at the low end of the band. The oscillator trimmer capacitor is then set at the high end of the dial to make sure the tuning range and dial pointer are correct. The general rule is that the inductances set the low end of the band and the trimmer capacitors on the tuning gang set the high end. The exception to this rule is when there is an adjustable padder capacitor in series with the oscillator section of the tuning gang. This sets the low end of the band. Ideally the frequencies that the local oscillator tunes over should be set according to the manufacturer’s instructions to ensure the dial scale calibration is as good as possible. This also requires that the IF centre frequency is correctly set. The antenna circuit is tuned (near the high end of the band) for maximum signal, by adjusting the trimmer capacitor on the relevant section of the tuning gang. In the case of the Zenith Royal, the manufacturer’s instructions specified a test frequency of 1260kHz. siliconchip.com.au If a radio station sits near to this frequency, and in the absence of good test generators, it is better used as the signal source for this adjustment as there are no generator loading issues to consider. In Sydney, station 2SM at 1269kHz would be ideal. Often the ferrite rod antenna tuning cannot be easily set for a peak at the low end of the band, because it requires sliding the antenna coil on the ferrite rod to adjust the inductance. But often the coil is held in place with wax and it is better to leave it alone. Mechanical considerations On the mechanical side of things, a small amount of lubricant can be added to the moving metal surfaces such as the variable capacitor shaft and bearings. In this radio there is a ball bearing epicyclic reduction system where the centre tuning knob rotates at a greater rate than the dial pointer shell surrounding it; this aids fine tuning. Cleaning and lubrication of the onoff switch and volume control is often required. In this radio, there was corrosion and a white oxide on the transistor bodies. This was carefully removed without affecting the labels or logos and the transistors bodies wiped with Celebrating 30 Years a small amount of WD40 to help protect them. A coat of clear varnish can be added after that, if required. Performance After repairs my sample Zenith 500 radio performed well with good sensitivity and a reasonable tone, despite the small sized speaker. It is as good as any transistor radio made a decade or more later, possibly better, because of the quality of the case and components used. For example the variable capacitor frame in the radio is solid 1/8-inch thick brass and the speaker has a goodsized magnet although it is compact overall. For all vintage transistor radios I recommend using carbon zinc cells as their current-sourcing ability is much lower than alkaline cells for short circuit conditions. And if the carbon zinc cells leak fluid, it is much less destructive than that from alkaline cells. Conclusion I think the Zenith Royal 500 transistor radio makes a very worthy member of a vintage transistor radio collection. It indicates how quickly transistor radio technology accelerated just two years after the introduction of the Regency TR-1. SC May 2018  93 SILICON CHIP .com.au/shop ONLINESHOP Looking for a specialised component to build that latest and greatest Silicon Chip project? Maybe it’s the PCB you’re after? Or a pre-programmed micro? Or some other hard-to-get “bit”? The chances are they are available direct from the Silicon Chip Online Shop. • • • • • PCBs are normally IN STOCK and ready for despatch when that month’s magazine goes on sale (you don’t have to wait for them to be made!). Even if stock runs out (eg, for high demand), in most cases there will be no longer than a two-week wait. One low p&p charge: $10 per order, irregardless of how many items you order! (AUS only; overseas clients – check the website for a postage quote). Our PCBs are beautifully made, very high quality fibreglass boards with pre-tinned tracks, silk screen overlays and where applicable, solder masks. 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PIC12F675-I/P PIC12F675-I/P PIC16F1455-I/P PIC16F1507-I/P PIC16F88-E/P PIC16F88-I/P PIC16LF88-I/P PIC16LF88-I/SO PIC16LF1709-I/SO UHF Remote Switch (Jan09), Ultrasonic Cleaner (Aug10) PIC16F877A-I/P 6-Digit GPS Clock (May-Jun09), Lab Digital Pot (Jul10), Semtest (Feb-May12) Ultrasonic Anti-fouling (Sep10), Cricket/Frog (Jun12), Do Not Disturb (May13) PIC16F2550-I/SP Batt Capacity Meter (Jun09), Intelligent Fan Controller (Jul10) IR-to-UHF Converter (Jul13), UHF-to-IR Converter (Jul13) PIC18F4550-I/P GPS Car Computer (Jan10), GPS Boat Computer (Oct10) PC Birdies *2 chips – $15 pair* (Aug13), Driveway Monitor Receiver (July15) PIC18LF14K22 Digital Spirit Level (Aug11), G-Force Meter (Nov11) Hotel Safe Alarm (Jun16), 50A Battery Charger Controller (Nov16) PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite (Sept/Oct12) Kelvin the Cricket (Oct17), Triac-based Mains Motor Speed Controller (Mar18) Touchscreen Audio Recorder (Jun/Jul 14) Heater Controller (Apr18) PIC32MX170F256B-50I/SP Micromite Mk2 (Jan15) – also includes FREE 47F tantalum capacitor Courtesy LED Light Delay for Cars (Oct14), Fan Speed Controller (Jan18) Micromite LCD BackPack [either version] (Feb16), GPS Boat Computer (Apr16) Microbridge (May17) Micromite Super Clock (Jul16), Touchscreen Voltage/Current Ref (Oct-Dec16) Wideband Oxygen Sensor (Jun-Jul12) Micromite LCD BackPack V2 (May17), Deluxe eFuse (Aug17) Hi Energy Ignition (Nov/Dec12), Speedo Corrector (Sept13) Micromite DDS for IF Alignment (Sept17) Auto Headlight Controller (Oct13), 10A 230V Motor Speed Controller (Feb14) PIC32MX170F256B-I/SP Low Frequency Distortion Analyser (Apr15) Automotive Sensor Modifier (Dec16) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 Projector Speed (Apr11), Vox (Jun11), Ultrasonic Water Tank Level (Sep11) PIC32MX250F128B-I/SP GPS Tracker (Nov13), Micromite ASCII Video Terminal (Jul14) Quizzical (Oct11), Ultra LD Preamp (Nov11), 10-Channel Remote Control PIC32MX470F512H-I/PT Stereo Audio Delay/DSP (Nov13), Stereo Echo/Reverb (Feb 14) Receiver (Jun13), Revised 10-Channel Remote Control Receiver (Jul13) Digital Effects Unit (Oct14) Nicad/NiMH Burp Charger (Mar14), Remote Mains Timer (Nov14) Driveway Monitor Transmitter (July15), Fingerprint Scanner (Nov15) PIC32MX470F512H-120/PT Micromite PLUS Explore 64 (Aug 16), Micromite Plus LCD BackPack (Nov16) MPPT Lighting Charge Controller (Feb16), 50/60Hz Turntable Driver (May16) PIC32MX470F512L-120/PT Micromite PLUS Explore 100 (Sep-Oct16) Cyclic Pump Timer (Sep16), 60V 40A DC Motor Speed Controller (Jan17) dsPIC33FJ128GP802-I/SP Digital Audio Signal Generator (Mar-May10), Digital Lighting Controller Pool Lap Counter (Mar17), Rapidbrake (Jul17), Deluxe Frequency Switch (May18) (Oct-Dec10), SportSync (May11), Digital Audio Delay (Dec11) Garbage Reminder (Jan13), Bellbird (Dec13), GPS Analog Clock Driver (Feb17) Quizzical (Oct11), Ultra-LD Preamp (Nov11), LED Musicolor (Nov12) LED Ladybird (Apr13) dsPIC33FJ64MC802-E/P Induction Motor Speed Controller (revised) (Aug13) Battery Cell Balancer (Mar16) dsPIC33FJ128GP306-I/PT CLASSiC DAC (Feb-May 13) When ordering, be sure to select BOTH the micro required AND the project for which it must be programmed. SPECIALISED COMPONENTS, HARD-TO-GET BITS, ETC USB PORT PROTECTOR COMPLETE KIT (MAY 18) AM RADIO TRANSMITTER (MAR 18) All parts including the PCB and a length of clear heatshrink tubing MC1496P double-balanced mixer IC (DIP-14) VINTAGE TV A/V MODULATOR MC1374P A/V modulator IC (DIP-14) SBK-71K coil former pack (two required) (MAR 18) ALTIMETER/WEATHER STATION (DEC 17) Micromite 2.8-inch LCD BackPack kit programmed for the Altimeter project GY-68 barometric pressure and temperature sensor module (with BMP180, Cat SC4343) DHT22 temperature and humidity sensor module (Cat SC4150) Elecrow 1A/500mA Li-ion/LiPo charger board (optional, Cat SC4308) PARTS FOR THE 6GHz+ TOUCHSCREEN FREQUENCY COUNTER (OCT 17) DELUXE EFUSE PARTS (AUG 17) Explore 100 kit (Cat SC3834; no LCD included) one ERA-2SM+ & one ADCH-80A+ (Cat SC1167; two packs required) IPP80P03P4L04 P-channel mosfets (Cat SC4318) BUK7909-75AIE 75V 120A N-channel SenseFet (Cat SC4317) LT1490ACN8 dual op amp (Cat SC4319) $15.00 $2.50 $5.00 $5.00 ea. $65.00 $5.00 $7.50 $15.00 $69.90 $15.00/pk. $4.00 ea. $7.50 ea. $7.50 ea. MICROBRIDGE COMPLETE KIT (CAT SC4264) (MAY 17) PCB plus all on-board parts including programmed microcontroller (SMD ceramics for 10µF) $20.00 MICROMITE LCD BACKPACK V2 – COMPLETE KIT (CAT SC4237) (MAY 17) includes PCB, programmed micro, touchscreen LCD, laser-cut UB3 lid, mounting hardware, SMD Mosfets for PWM backlight control and all other on-board parts $70.00 POOL LAP COUNTER (MAR 17)   two 70mm 7-segment high brightness blue displays + logic-level Mosfet (Cat SC4189) $17.50 laser-cut blue tinted UB1 lid, 152 x 90 x 3mm (Cat SC4196) $7.50 P&P – $10 Per order# STATIONMASTER (CAT SC4187) (MAR 17) Hard to get parts: DRV8871 IC, SMD 1µF capacitor and 100kW potentiometer with detent $12.50 ULTRA LOW VOLTAGE LED FLASHER (CAT SC4125) (FEB 17) SC200 AMPLIFIER MODULE (CAT SC4140) (JAN 17) kit including PCB and all SMD parts, LDR and blue LED hard-to-get parts: Q8-Q16, D2-D4, 150pF/250V capacitor and five SMD resistors $12.50 $35.00 VARIOUS MODULES & PARTS ESP-01 WiFi Module (El Cheapo Modules, Part 15, APR18) $5.00 WiFi Antennas with U.FL/IPX connectors (Water Tank Level Meter with WiFi, FEB18): 5dBi – $12.50 ~ 2dBi (omnidirectional) – $10.00 NRF24L01+PA+NA transceiver with SNA connector and antenna (El Cheapo 12, JAN18) $5.00 WeMos D1 Arduino-compatible boards with WiFi (SEPT17, FEB18): ThingSpeak data logger – $10.00 ~ WiFi Tank Level Meter (ext. antenna socket) – $15.00 Geeetech Arduino MP3 shield (Arduino Music Player/Recorder, VS1053, JUL17) $20.00 1nF 1% MKP (5mm lead spacing) or ceramic capacitor (Arduino LC Meter, JUN17) $2.50 MAX7219 LED controller boards (El Cheapo Modules, Part 7, JUN17): 8x8 red SMD/DIP matrix display – $5.00 ~ red 8-digit 7-segment display – $7.50 AD9833 DDS module (with gain control) (for Micromite DDS, APR17) $25.00 AD9833 DDS module (no gain control) (El Cheapo Modules, Part 6, APR17) $15.00 CP2102 USB-UART bridge $5.00 microSD card adaptor (El Cheapo Modules, Part 3, JAN17) $2.50 DS3231 real-time clock with mounting spacers and screws (El Cheapo, Part 1, OCT16) $5.00 MICROMITE PLUS EXPLORE 100 COMPLETE KIT (no LCD panel) (SEP 16) (includes PCB, programmed micro and the hard-to-get bits including female headers, USB and microSD sockets, crystal, etc but does not include the LCD panel) (Cat SC3834) $69.90 MICROMITE LCD BACKPACK V1 COMPLETE KIT (CAT SC3321) includes PCB, micro, 2.8-inch touchscreen and includes UB3 lid (clear, matte black or translucent blue). Also specify what project the micro should be programmed for (FEB 16) $65.00 THESE ARE ONLY THE MOST RECENT MICROS AND SPECIALISED COMPONENTS. FOR THE FULL LIST, SEE www.siliconchip.com.au/shop *All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. O’seas? Please email for a quote 05/18 PRINTED CIRCUIT BOARDS NOTE: The listings below are for the PCB ONLY. If you want a kit, check our store or contact the kit suppliers advertising in this issue. For unusual projects where kits are not available, some have specialised components available – see the list opposite. NOTE: Not all PCBs are shown here due to space limits but the Silicon Chip Online Shop has boards going back to 2001 and beyond. For a complete list of available PCBs etc, go to siliconchip.com.au/shop/8 Prices are PCBs only, NOT COMPLETE KITS! PRINTED CIRCUIT BOARD TO SUIT PROJECT: PUBLISHED: PCB CODE: Price: CLASSiC DAC MAIN PCB APR 2013 01102131 $40.00 CLASSiC DAC FRONT & REAR PANEL PCBs APR 2013 01102132/3 $30.00 CLASSiC-D 12V to ±35V DC/DC CONVERTER MAY 2013 11104131 $15.00 LF/HF UP-CONVERTER JUN 2013 07106131 $10.00 10-CHANNEL REMOTE CONTROL RECEIVER JUN 2013 15106131 $15.00 IR-TO-455MHz UHF TRANSCEIVER JUN 2013 15106132 $7.50 “LUMP IN COAX” PORTABLE MIXER JUN 2013 01106131 $15.00 L’IL PULSER MKII TRAIN CONTROLLER JULY 2013 09107131 $15.00 L’IL PULSER MKII FRONT & REAR PANELS JULY 2013 09107132/3 $20.00/set REVISED 10 CHANNEL REMOTE CONTROL RECEIVER JULY 2013 15106133 $15.00 INFRARED TO UHF CONVERTER JULY 2013 15107131 $5.00 UHF TO INFRARED CONVERTER JULY 2013 15107132 $10.00 IPOD CHARGER AUG 2013 14108131 $5.00 PC BIRDIES AUG 2013 08104131 $10.00 RF DETECTOR PROBE FOR DMMs AUG 2013 04107131 $10.00 BATTERY LIFESAVER SEPT 2013 11108131 $5.00 SPEEDO CORRECTOR SEPT 2013 05109131 $10.00 SiDRADIO (INTEGRATED SDR) Main PCB OCT 2013 06109131 $35.00 SiDRADIO (INTEGRATED SDR) Front & Rear Panels OCT 2013 06109132/3 $25.00/pr TINY TIM AMPLIFIER (identical Headphone Amp [Sept11]) OCT 2013 01309111 $20.00 AUTO CAR HEADLIGHT CONTROLLER OCT 2013 03111131 $10.00 GPS TRACKER NOV 2013 05112131 $15.00 STEREO AUDIO DELAY/DSP NOV 2013 01110131 $15.00 BELLBIRD DEC 2013 08112131 $10.00 PORTAPAL-D MAIN BOARDS DEC 2013 01111131-3 $35.00/set (for CLASSiC-D Amp board and CLASSiC-D DC/DC Converter board refer above [Nov 2012/May 2013]) LED Party Strobe (also suits Hot Wire Cutter [Dec 2010]) JAN 2014 16101141 $7.50 Bass Extender Mk2 JAN 2014 01112131 $15.00 Li’l Pulser Mk2 Revised JAN 2014 09107134 $15.00 10A 230VAC MOTOR SPEED CONTROLLER FEB 2014 10102141 $12.50 NICAD/NIMH BURP CHARGER MAR 2014 14103141 $15.00 RUBIDIUM FREQ. STANDARD BREAKOUT BOARD APR 2014 04105141 $10.00 USB/RS232C ADAPTOR APR 2014 07103141 $5.00 MAINS FAN SPEED CONTROLLER MAY 2014 10104141 $10.00 RGB LED STRIP DRIVER MAY 2014 16105141 $10.00 HYBRID BENCH SUPPLY MAY 2014 18104141 $20.00 2-WAY PASSIVE LOUDSPEAKER CROSSOVER JUN 2014 01205141 $20.00 TOUCHSCREEN AUDIO RECORDER JUL 2014 01105141 $12.50 THRESHOLD VOLTAGE SWITCH JUL 2014 99106141 $10.00 MICROMITE ASCII VIDEO TERMINAL JUL 2014 24107141 $7.50 FREQUENCY COUNTER ADD-ON JUL 2014 04105141a/b $15.00 TEMPMASTER MK3 AUG 2014 21108141 $15.00 44-PIN MICROMITE AUG 2014 24108141 $5.00 OPTO-THEREMIN MAIN BOARD SEP 2014 23108141 $15.00 OPTO-THEREMIN PROXIMITY SENSOR BOARD SEP 2014 23108142 $5.00 ACTIVE DIFFERENTIAL PROBE BOARDS SEP 2014 04107141/2 $10.00/set MINI-D AMPLIFIER SEP 2014 01110141 $5.00 COURTESY LIGHT DELAY OCT 2014 05109141 $7.50 DIRECT INJECTION (D-I) BOX OCT 2014 23109141 $5.00 DIGITAL EFFECTS UNIT OCT 2014 01110131 $15.00 DUAL PHANTOM POWER SUPPLY NOV 2014 18112141 $10.00 REMOTE MAINS TIMER NOV 2014 19112141 $10.00 REMOTE MAINS TIMER PANEL/LID (BLUE) NOV 2014 19112142 $15.00 ONE-CHIP AMPLIFIER NOV 2014 01109141 $5.00 TDR DONGLE DEC 2014 04112141 $5.00 MULTISPARK CDI FOR PERFORMANCE VEHICLES DEC 2014 05112141 $10.00 CURRAWONG STEREO VALVE AMPLIFIER MAIN BOARD DEC 2014 01111141 $50.00 CURRAWONG REMOTE CONTROL BOARD DEC 2014 01111144 $5.00 CURRAWONG FRONT & REAR PANELS DEC 2014 01111142/3 $30.00/set CURRAWONG CLEAR ACRYLIC COVER JAN 2015 SC2892 $25.00 ISOLATED HIGH VOLTAGE PROBE JAN 2015 04108141 $10.00 SPARK ENERGY METER MAIN BOARD FEB/MAR 2015 05101151 $10.00 SPARK ENERGY ZENER BOARD FEB/MAR 2015 05101152 $10.00 SPARK ENERGY METER CALIBRATOR BOARD FEB/MAR 2015 05101153 $5.00 APPLIANCE INSULATION TESTER APR 2015 04103151 $10.00 APPLIANCE INSULATION TESTER FRONT PANEL APR 2015 04103152 $10.00 LOW-FREQUENCY DISTORTION ANALYSER APR 2015 04104151 $5.00 APPLIANCE EARTH LEAKAGE TESTER PCBs (2) MAY 2015 04203151/2 $15.00 APPLIANCE EARTH LEAKAGE TESTER LID/PANEL MAY 2015 04203153 $15.00 BALANCED INPUT ATTENUATOR MAIN PCB MAY 2015 04105151 $15.00 BALANCED INPUT ATTENUATOR FRONT & REAR PANELS MAY 2015 04105152/3 $20.00 4-OUTPUT UNIVERSAL ADJUSTABLE REGULATOR MAY 2015 18105151 $5.00 SIGNAL INJECTOR & TRACER JUNE 2015 04106151 $7.50 PASSIVE RF PROBE JUNE 2015 04106152 $2.50 SIGNAL INJECTOR & TRACER SHIELD JUNE 2015 04106153 $5.00 BAD VIBES INFRASOUND SNOOPER JUNE 2015 04104151 $5.00 CHAMPION + PRE-CHAMPION JUNE 2015 01109121/2 $7.50 DRIVEWAY MONITOR TRANSMITTER PCB JULY 2015 15105151 $10.00 DRIVEWAY MONITOR RECEIVER PCB JULY 2015 15105152 $5.00 MINI USB SWITCHMODE REGULATOR JULY 2015 18107151 $2.50 VOLTAGE/RESISTANCE/CURRENT REFERENCE AUG 2015 04108151 $2.50 LED PARTY STROBE MK2 AUG 2015 16101141 $7.50 PRINTED CIRCUIT BOARD TO SUIT PROJECT: PUBLISHED: ULTRA-LD MK4 200W AMPLIFIER MODULE SEP 2015 9-CHANNEL REMOTE CONTROL RECEIVER SEP 2015 MINI USB SWITCHMODE REGULATOR MK2 SEP 2015 2-WAY PASSIVE LOUDSPEAKER CROSSOVER OCT 2015 ULTRA LD AMPLIFIER POWER SUPPLY OCT 2015 ARDUINO USB ELECTROCARDIOGRAPH OCT 2015 FINGERPRINT SCANNER – SET OF TWO PCBS NOV 2015 LOUDSPEAKER PROTECTOR NOV 2015 LED CLOCK DEC 2015 SPEECH TIMER DEC 2015 TURNTABLE STROBE DEC 2015 CALIBRATED TURNTABLE STROBOSCOPE ETCHED DISC DEC 2015 VALVE STEREO PREAMPLIFIER – PCB JAN 2016 VALVE STEREO PREAMPLIFIER – CASE PARTS JAN 2016 QUICKBRAKE BRAKE LIGHT SPEEDUP JAN 2016 SOLAR MPPT CHARGER & LIGHTING CONTROLLER FEB/MAR 2016 MICROMITE LCD BACKPACK, 2.4-INCH VERSION FEB/MAR 2016 MICROMITE LCD BACKPACK, 2.8-INCH VERSION FEB/MAR 2016 BATTERY CELL BALANCER MAR 2016 DELTA THROTTLE TIMER MAR 2016 MICROWAVE LEAKAGE DETECTOR APR 2016 FRIDGE/FREEZER ALARM APR 2016 ARDUINO MULTIFUNCTION MEASUREMENT APR 2016 PRECISION 50/60Hz TURNTABLE DRIVER MAY 2016 RASPBERRY PI TEMP SENSOR EXPANSION MAY 2016 100DB STEREO AUDIO LEVEL/VU METER JUN 2016 HOTEL SAFE ALARM JUN 2016 UNIVERSAL TEMPERATURE ALARM JULY 2016 BROWNOUT PROTECTOR MK2 JULY 2016 8-DIGIT FREQUENCY METER AUG 2016 APPLIANCE ENERGY METER AUG 2016 MICROMITE PLUS EXPLORE 64 AUG 2016 CYCLIC PUMP/MAINS TIMER SEPT 2016 MICROMITE PLUS EXPLORE 100 (4 layer) SEPT 2016 AUTOMOTIVE FAULT DETECTOR SEPT 2016 MOSQUITO LURE OCT 2016 MICROPOWER LED FLASHER OCT 2016 MINI MICROPOWER LED FLASHER OCT 2016 50A BATTERY CHARGER CONTROLLER NOV 2016 PASSIVE LINE TO PHONO INPUT CONVERTER NOV 2016 MICROMITE PLUS LCD BACKPACK NOV 2016 AUTOMOTIVE SENSOR MODIFIER DEC 2016 TOUCHSCREEN VOLTAGE/CURRENT REFERENCE DEC 2016 SC200 AMPLIFIER MODULE JAN 2017 60V 40A DC MOTOR SPEED CON. CONTROL BOARD JAN 2017 60V 40A DC MOTOR SPEED CON. MOSFET BOARD JAN 2017 GPS SYNCHRONISED ANALOG CLOCK FEB 2017 ULTRA LOW VOLTAGE LED FLASHER FEB 2017 POOL LAP COUNTER MAR 2017 STATIONMASTER TRAIN CONTROLLER MAR 2017 EFUSE APR 2017 SPRING REVERB APR 2017 6GHz+ 1000:1 PRESCALER MAY 2017 MICROBRIDGE MAY 2017 MICROMITE LCD BACKPACK V2 MAY 2017 10-OCTAVE STEREO GRAPHIC EQUALISER PCB JUN 2017 10-OCTAVE STEREO GRAPHIC EQUALISER FRONT PANEL JUN 2017 10-OCTAVE STEREO GRAPHIC EQUALISER CASE PIECES JUN 2017 RAPIDBRAKE JUL 2017 DELUXE EFUSE AUG 2017 DELUXE EFUSE UB1 LID AUG 2017 MAINS SUPPLY FOR BATTERY VALVES (INC. PANELS) AUG 2017 3-WAY ADJUSTABLE ACTIVE CROSSOVER SEPT 2017 3-WAY ADJUSTABLE ACTIVE CROSSOVER PANELS SEPT 2017 3-WAY ADJUSTABLE ACTIVE CROSSOVER CASE PIECES SEPT 2017 6GHz+ TOUCHSCREEN FREQUENCY COUNTER OCT 2017 KELVIN THE CRICKET OCT 2017 6GHz+ FREQUENCY COUNTER CASE PIECES (SET) DEC 2017 SUPER-7 SUPERHET AM RADIO PCB DEC 2017 SUPER-7 SUPERHET AM RADIO CASE PIECES DEC 2017 THEREMIN JAN 2018 PROPORTIONAL FAN SPEED CONTROLLER JAN 2018 WATER TANK LEVEL METER (INCLUDING HEADERS) FEB 2018 10-LED BARAGRAPH FEB 2018 10-LED BARAGRAPH SIGNAL PROCESSING FEB 2018 TRIAC-BASED MAINS MOTOR SPEED CONTROLLER MAR 2018 VINTAGE TV A/V MODULATOR MAR 2018 AM RADIO TRANSMITTER MAR 2018 HEATER CONTROLLER APR 2018 DELUXE FREQUENCY SWITCH MAY 2018 USB PORT PROTECTOR MAY 2018 2 x 12V BATTERY BALANCER MAY 2018 PCB CODE: 01107151 1510815 18107152 01205141 01109111 07108151 03109151/2 01110151 19110151 19111151 04101161 04101162 01101161 01101162 05102161 16101161 07102121 07102122 11111151 05102161 04103161 03104161 04116011/2 04104161 24104161 01104161 03106161 03105161 10107161 04105161 04116061 07108161 10108161/2 07109161 05109161 25110161 16109161 16109162 11111161 01111161 07110161 05111161 04110161 01108161 11112161 11112162 04202171 16110161 19102171 09103171/2 04102171 01104171 04112162 24104171 07104171 01105171 01105172 SC4281 05105171 18106171 SC4316 18108171-4 01108171 01108172/3 SC4403 04110171 08109171 SC4444 06111171 SC4464 23112171 05111171 21110171 04101181 04101182 10102181 02104181 06101181 10104181 05104181 07105181 14106181 Price: $15.00 $15.00 $2.50 $20.00 $15.00 $7.50 $15.00 $10.00 $15.00 $15.00 $5.00 $10.00 $15.00 $20.00 $15.00 $15.00 $7.50 $7.50 $6.00 $15.00 $5.00 $5.00 $15.00 $15.00 $5.00 $15.00 $5.00 $5.00 $10.00 $10.00 $15.00 $5.00 $10.00/pair $20.00 $10.00 $5.00 $5.00 $2.50 $10.00 $5.00 $7.50 $10.00 $12.50 $10.00 $10.00 $12.50 $10.00 $2.50 $15.00 $15.00/set $7.50 $12.50 $7.50 $2.50 $7.50 $12.50 $15.00 $15.00 $10.00 $15.00 $5.00 $25.00 $20.00 $20.00/pair $10.00 $10.00 $10.00 $15.00 $25.00 $25.00 $12.50 $2.50 $7.50 $7.50 $5.00 $10.00 $7.50 $7.50 $10.00 $7.50 $2.50 $2.50 LOOKING FOR TECHNICAL BOOKS? YOU’LL FIND THE COMPLETE LISTING OF ALL BOOKS AVAILABLE IN THE BOOKS & DVDs” PAGES AT SILICONCHIP.COM.AU/SHOP 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 Programmable Ignition System with a V12 I have a collection of interesting cars, bikes and engines and have a habit of putting what I consider to be better engines into some of my cars. My Audi-engine Porsche 924 was not very brisk so some years ago I replaced it with a two-litre, six-cylinder supercharged Toyota motor. Although I converted it to LPG and distributor ignition, it is very smooth and lively and the 924 didn't have computers to complicate things. Three years ago, I bought a 1986 Porsche 928 in reasonable order for $6000. It has a 5-litre V8 that is jammed into the engine bay and has subsequently started leaking oil and is very difficult to service. So I replaced its engine with a V12 from a Toyota Century. It is very clean and compact and fitted in easily once I simplified the bulky intake manifolds. Like the 924, I now have the V12 running mechanically with a Jaguar V12 distributor from the exhaust camshaft and an LPG fuel system. But none of the 928's complicated wiring, instruments or computer operate properly, making it undrivable. Because the 928 injectors are batch fired, I hope to be able to extend the wiring to four more, put its cog sensor ring on the V12 flywheel, use its other sensors and air flow meter through the existing computer to do the basic management on the V12 and just design a separate ignition computer. The Century V12 uses coil-on-plug wasted spark ignition, with three coils on the front of both banks (60° apart), so a six-cylinder coil-on-plug driver system, as used in the Ford Falcon, might work. I have a Jaycar kit (KC5442) based on the 2007 Programmable Ignition System by John Clarke (siliconchip.com. au/Series/56) that I was going to use on the 924. Could I add a low-tension, timed feed to the six wasted spark coils and add an appropriate advance to the existing ignition kit? 96 Silicon Chip Both banks have the usual 1-5-3-6-24 firing order. The 928 computer may need to be tricked into thinking that it is firing eight cylinders. I have not altered any of the existing wiring or mechanical systems in the 928 in case I have to put the V8 back at some stage, hence my attempt to adapt the new engine to the existing systems. (I. I., via email) • The Programmable Ignition System would work with the V12 in a wasted spark system that is essentially a 6-cylinder firing sequence as far as the ignition system is concerned. It would fire two spark plugs simultaneously, one of which is on a cylinder to be fired and the other on a cylinder that has opposite phase, ie, between the exhaust and intake stroke. You would need a trigger (Reluctor, Hall Effect or similar) that runs from the distributor and presumably this is already in place. I am not sure if the Porsche 928 computer would co-operate with this system. Presumably, since you are planning on using the original V8 cog sensor from the 928, it should be none the wiser that you are running a V12. WiFi Water Tank Level Meter for remote tanks Can you estimate how much data the WiFi Water Tank Level Meter (February 2018; siliconchip.com.au/Article/ 10963) would use when transmitting the data via WiFi, at the default timing settings? Many farms will not have access to WiFi due to the distances. The only solution would be a cheap prepaid 3G/4G modem/WiFi-Router. $10/ month will buy 1.5GB. In my case, the tank is 600 metres away and would be line-of-sight but for a heavily wooded area. In the past, I have tried external directional antennas and high powered WiFi repeaters but the signal at the tank is always unusable. The same kit but using 433MHz or one of the CB data channels would Celebrating 30 Years be a winner for farmers. However, I do not have the technical expertise to modify the kit and would lose the data in the cloud facility. (N. McM., Yass River, NSW) • The data transmitted for a single update should be under 1KB. One update every 10 minutes means 144 updates per day or around 4,500 per month. So around 4.5MB per month. Clearly, 1.5GB is more than enough. We may look at doing a 4G version of the project at some point in the future but as you have suggested, it’s probably easier to power a "personal hotspot" from the same 5V supply as the main unit. They don't draw a lot of current as they often have an internal, rechargeable lithium-ion battery which lasts for many hours of use and they automatically go into a low-power mode when there is no traffic. Cost and output power of AM Transmitter I am interested in building the AM Radio Transmitter project from the March 2018 issue (siliconchip.com. au/Article/11004). Can you please tell me the approximate cost of the parts and the output power I can expect. (S. C., via email) • Assuming you purchase the PCB and main IC from us and the remainder of the parts from Jaycar, the total will cost around $45 without the optional USB output. While there is 700mV RMS across L1, it is so inefficient and the wire antenna is so much shorter than ¼ of a wavelength (which would be 75m) that the radiated power is only a few microwatts. Running Water Tank Level Meter from mains I am interested in building the WiFi Water Tank Level Meter project which was published in the February 2018 issue (siliconchip.com.au/Article/ 10963). As we have mains power at our siliconchip.com.au How does the Full-Wave Motor Speed Controller's mains supply work? I can't make sense of the 5V power supply circuit in the FullWave 10A Motor Speed Controller (March 2018; siliconchip.com.au/ Article/10998). There seems to be no return path for that portion of mains energy being dumped through D1 on one cycle and then through D2 on the reverse mains polarity. Are the two GNDs connected or should the 5V ground be connected to Active or am I missing something? (D. McI., Eastwood, NSW) • The 5.1V rail is connected to mains Active via the 47W resistor and the wire passing through the centre of T1. So the 5.1V rail "floats" at mains Active potential with GND being 5.1V below this. Supply current is coupled from the Neutral conductor, through the 470nF X2 capacitor and series 1kW tanks, is it possible to power it from a 5V power supply and do away with the charger/solar cells/power saving circuitry or would this involve changing the software? (B. S., Dunedin, New Zealand) • Yes, you certainly can run it from a USB charger fed into the micro USB socket on the ESP8266 board. This is mentioned in passing as a possibility in the article. We set up the prototype in the same manner, without the Elecrow charger board, and it worked fine. We ended up putting the mains USB charger in a separate IP65 enclosure and used silicone to seal the holes in the box for the mains input cable and USB output cable. Resistor burned out due to short circuit In December 2015, EPE Magazine re-published the High-Energy MultiSpark Capacitor Discharge Ignition design by John Clarke (originally published in Silicon Chip in December 2014 and January 2015; siliconchip. com.au/Series/279). I have just finished building it. I powered it up using a 12V DC bench supply but as soon as I did so, the 10W ¼W resistor in series with 16V 1W zener diode ZD1 burned out. siliconchip.com.au resistor and then through either D1 or D2 into the 5V supply. We covered the operation of this type of supply in detail in an article about SPICE simulations in the June 2017 issue, starting on page 38 (siliconchip.com.au/Article/10677). In brief, we can consider what happens when the Neutral voltage is above the Active voltage and is rising, which will be the case during roughly one-quarter of the mains 50Hz cycle. In this case, current will flow from Neutral into the 470nF capacitor, charging it up but also coupling some current through the 1kW series resistor, diode D1 and the 47W resistor, back to Active. During this time, assuming the 470µF supply filter capacitor was charged up to 12V initially, it will be discharging as there is no source of current to replenish it I looked at the schematic again. When the rail voltage isn't near 16V DC, that zener will remain off. Won't this result in the 10W resistor frying? Obviously, the resistor and zener values are wrong. (J. J., South Africa) • When the supply voltage is below 16V and ZD1 does not conduct, this should not damage the 10W resistor as very little current will be flowing through it. We had no such problems on our prototype. If this resistor burns out with a 12V DC supply, that strongly suggests that either ZD1 has been fitted backwards or there is a short circuit across either IC1, IC2 or one of their bypass capacitors. Check for correctly oriented components and that you have no accidental solder bridges. You may have to isolate sections of the circuit to find where the short circuit is located. Question about zero ohm resistors I am interested in the Earthquake Early Warning Alarm project featured in the March 2018 issue (siliconchip. com.au/Article/10994). However, I live on a reasonably busy road with speed humps not far from the house and heavy trucks can make Celebrating 30 Years But when the Neutral voltage starts to fall (still being above active, but reducing), the 470nF capacitor will discharge via the 1kW series resistor and diode D2 into circuit ground. In doing so, it charges the 470µF supply filter capacitor back up to 12V, with current flowing via the 47W resistor back to Active. This "returns" much of the energy drawn earlier back to the mains, leaving just the desired 12V across ZD1. This same current flow will continue as Neutral becomes negative compared to Active, except now the 470nF X2 capacitor is charging up in the opposite direction. In the final mains quadrant, the 470nF capacitor discharges again while the 470µF filter capacitor also discharges, albeit more slowly. Then the process repeats. quite a rattle when they bounce over them (particularly if they are speeding, which unfortunately often happens). However, I assume that I should be able to circumvent this by adjusting VR1, as suggested at the end of the article. There is one thing that puzzles me, though: what's the story with the zero ohm resistors? Until I read the article, I was not aware that such a component even existed! Why did you use these in the prototype when two bits of wire would do, as you suggest? One final query, surely that photo on the cover and at the start of the article is a still from a movie? Surely that is not genuine?! Scary, if it is! (G. G., Figtree, NSW) • Zero ohm resistors are (or at least were) commonly used where wire links are required since they can easily be bent to standard lengths, can be inserted by automated equipment designed for handling resistors and provide some insulation. For example, this allows you to have wire links passing under the zero ohm resistors without them shorting. There are also surface-mount zero ohm resistors and these can be handy to allow signals to jump over tracks on a two-layer board when there are already tracks in the way on the other layer. May 2018  97 Also, purchased in sufficient quantities, zero ohm resistors work out cheaper than tinned copper wire. We've seen them supplied in kits where wire links are required. In this case, we needed links about the same length as a resistor so using zero ohm resistors was the simplest approach. Stationmasters not working properly I had two Stationmaster train controllers built for me by someone who advertises in your magazine. Both are exhibiting the same strange symptoms. With a 15V DC supply, I measured a triangular waveform at pin 7 of IC1 but it was only about 880Hz, not 8kHz as stated in the article. The amplitude was about 840mV. I also measured a square wave at pin 1 of IC1 of about 900Hz, with an amplitude just under 3V. The voltage at the Vcc test point was 5V and 2.5V at the Vcc ÷ 2 test point. I am able to adjust VR1 to get the LEDs to switch off and on (as per the instructions). I can also measure a triangle wave on pins 9 and 11 of IC1 but nothing on pins 10 and 13, as shown in the dia- gram on page 37 of the article. The output waveforms on the TRACK terminals look like PWM but only at about 5V peak-to-peak. Strangely, as I rotate the speed control clockwise, while the output pulse width increases, the whole waveform shifts down the Y-axis. At maximum speed (forward or reverse), the waveform disappears completely. I contacted the person who assembled the two kits for me and his response was to contact you! Can you help me? (P. S., Banyo, Qld) • The frequency may be incorrect if the resistors connecting to IC1a and IC1b are incorrect or the 10nF capacitor is actually 100nF. Check the resistors, especially the 1kW resistor between pins 7 and 3 and the 10kW resistor between pins 1 and 6. The waveforms at pins 10 and 13 of IC1c/IC1d should not be triangular but rather a DC level, as shown in blue in Fig.4. The caption of Fig.4 is incorrect. It should be referring to the yellow and red traces as the IC1 pin 9 and pin 12 signals. If you don't have the full voltage swing at the track, IC3 may not be receiving the required voltage at pin 5. That voltage will depend on the supply applied to CON1. Check also Fitting a modern mains cord to a vintage radio I am currently restoring a vintage Kreisler 1954 Duplex radio. It’s an 11-51 5-valve console radiogram. I’ve hit a snag regarding the mains power cable. By today’s electrical standards it’s highly illegal and potentially dangerous. I’d like to replace the cable with a legal, safer one but I have no way to do it safely. The Active wire is soldered to two tags on the on/off pot and the Neutral soldered to another tag. There is no Earth connection. How can I get around this? (R. B., Nowra, NSW) • Without a view of the chassis, it is not possible to make a specific suggestion. However, in most cases, it is possible to fit a 3-core flex with a 3-pin plug. You can always find a point to attach a solder or crimp lug for the chassis to Earth and while it would be better to have an insulated termi98 Silicon Chip nal block for the Active and Neutral connections, if they are sleeved, that will improve safety. The 2-core flex or cotton-covered 3-core cord in all old sets should be replaced as a matter of course. They are usually perished, frayed or both. And throw out the old mains plug – it is usually hazardous. There are several ways to securely anchor the cord inside the chassis. You could have it enter via a hole (fitted with a rubber grommet) in the rear of chassis and then fit a separate cord clamp. Alternatively, you could take the modern approach and fit a cord-grip gland that's super glued tight as we do in many of our mains operated projects these days. We know that most restorers don't bother but you never know when a poorly anchored power cord may create a serious hazard to you or someone in your family. Celebrating 30 Years that pins 7 and 1 are connected to ground. Also, make sure your oscilloscope is DC coupled and correctly grounded. Where to get acoustic filling for speakers Can you tell me where you got the acoustic BAF filling for the Majestic speakers? It's hard to find any kind of acoustic filling, but especially the bonded acetate fibre kind. (P. T., Casula, NSW) • This wadding is known by several names: innerbond, acoustic filling, BAF (bonded acetate fibre) etc. Jaycar have it, their catalog code is AX3694. Using a three-terminal coil for Jacob's Ladder I have a three-terminal ignition coil (rather than the VS Commodore one specified, which has two terminals). Can this be used for the project (February 2013; siliconchip.com.au/Article/ 2369) and if so, how do I wire it up? (P. M., Alfredton, Vic) • As far as we are aware, three-terminal ignition coils include an IGBT to switch current to the primary winding. So there is a +12V terminal for the coil primary and the other end of the coil is switched to ground via the IGBT. The second terminal is the ground/chassis terminal and the third terminal is the IGBT gate connection. For the Jacob's Ladder project, you could bypass the IGBT driver that's in the coil assembly and connect directly to the coil. Alternatively, remove the driver IGBT from the Jacob's Ladder PCB and connect the gate drive to the IGBT gate connection of the coil. Induction Motor Speed Controller at 60Hz I wonder if it is possible to change the 1.5kW Induction Motor Speed Controller from the April and May 2012 issues (siliconchip.com.au/ Series/25) to operate from 0 to 60Hz. (B. F. S., Sao Paolo, Brazil) • If you set the over-speed (O/S) DIP switch on, the range is 0-75Hz. You could limit it to 0-60Hz by inserting a resistor between the +3.3V rail and the speed pot. For a 10kW pot, use 2.4kW. Or use a second potentiometer wired as a rheostat (variable resistor) and adjust siliconchip.com.au Subscribe to SILICON CHIP and you’ll not only save money . . . but we GUARANTEE you’ll get your copy! When you subscribe to SILICON CHIP (printed edition) in Australia, we GUARANTEE that you will never miss an issue. 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We’re waiting to welcome you into the SILICON CHIP subscriber family! Double precision floating point maths for the Micromite Is there any thought to have a version of MMBasic that supports 64bit floating point maths, ie, double precision? This would allow the Micromite Plus to be more easily used for astronomical projects. (G. L., Wynn Vale, NSW) • Geoff Graham replies: As it happens, I have been experimenting with double precision floating it until you get 60Hz output with the speed pot at maximum. Dual transducer AntiFouling fuse blown We purchased your excellent kits for anti-fouling our NOELEX 30 yacht using two transducers (New Marine Ultrasonic Anti-Fouling Unit, May-June 2017; siliconchip.com.au/Series/312). They were assembled and installed, then switched on December 3rd, 2017. They have operated continuously, except for the odd time when they were inadvertently switched off by mistake, usually for only a few minutes each time. The performance was good and fully up to the standard expected in your articles in the Silicon Chip magazine sent with the electronic kits. We are very pleased with the unit and with your whole professional sales process. However, yesterday we discovered the 3A fuse had blown. I replaced this fuse but now I find it does not power up as usually expected. Now, when switched on, the power light comes on as before, but then goes off and the only light working is the fault light which blinks roughly every two seconds. I tried switching off, disconnecting the two transducers then switching on again, but we found this made no difference. What else could be at fault? What faults activate the fault light? Your help will be appreciated. (C. B., Christchurch, NZ) • A blown fuse probably means a shorted Mosfet or shorted turn in a transformer or a short in the ultrasonic transducer wiring. For each Mosfet, check for a dead short between the drain and source of Q1, Q2, Q3 or Q4. Depending on your 100 Silicon Chip point on the Micromite Plus and if you would like to try it out you can download it from: http://geoffg.net/ Downloads/Micromite/Micromite_ V5.04.09_Beta.zip This beta also includes other changes introduced in previous betas. For example, it includes the fix for image corruption of 5-inch displays, the ability to use display drivmultimeter, you may need to desolder each Mosfet to get a sensible reading. A Mosfet will read high ohms (megohms) if it is OK or near to zero ohms if shorted. In each case, before making the measurement, short the gate to the source to ensure the Mosfet is not switched on. It’s also best to swap the multimeter leads and check each Mosfet in both polarities to ensure that the body diode is not affecting the reading. If the Mosfet is shorted, the resistance reading will be low with both polarities. The resistance of the wiring to the transducer (when disconnected from the Anti-Fouling unit) should be very high after its capacitance charges via the multimeter. If the Mosfets and transducer wiring are OK, the transformer is the remaining suspect. Questions on safe mains wiring I have a few questions related to mains wiring for projects. I notice that the Currawong amplifier wiring shown on pages 93 & 94 of the December 2014 issue (and page 47 of the October 2016 issue) has a piece of heatshrink on both ends of the active wire from the IEC socket fuse to the power switch and is referred to as "heatshrink-covered wire to Active". Other Silicon Chip amplifier and mains-powered projects I have looked at do not appear to have that exact requirement. Can you please tell me the purpose of the heatshrink tubing? Can I solder the mains Earth to an uninsulated ring lug rather than crimping to an insulated ring lug? I'm using an IEC power connector from Jaycar with mains connection, fuse and a double pole switch. In view of my initial question about Celebrating 30 Years ers written in BASIC, static variables, etc. My plan for future beta versions is to keep adding small improvements (incrementing the beta number) and keep the beta open for some months until it has accumulated enough changes and is stable enough to warrant a full release. If you find any bugs in this new version of the firmware, please let me know. heatshrink, does the short active wire required from the fuse terminal to the switch need the heatshrink on each end and is soldering acceptable rather than crimp terminals? All connections will be insulated with heatshrink, cable-tied to minimise movement and covered with a heatshrink hood as detailed in the Currawong project. (M. N., North Rocks, NSW) • The reason behind covering the IEC connector with large diameter heatshrink is to prevent any accidental contact of wires from the right speaker terminals to mains connections, should they come adrift. The Active and Neutral wires and the metal strip connecting the fuse to Active on the back of the IEC connector are covered. You could also use a moulded rubber cover (Jaycar PM-4016) instead of the heatshrink tubing. We don't always use this full enclosure method of protection as it depends on whether low voltage wiring is close by. The rear of an IEC fused connector does have exposed metal where the fuse connects to the Active terminal (and we recommend covering this with silicone sealant) and insulated crimp connectors still have a small amount of bare metal exposed on the IEC connector terminals between where the insulation on the crimp connector ends before meeting the IEC housing. While fingers might not make easy contact with the very small gap of exposed bare metal, a loose wire can. Yes, you can use uninsulated lugs for the mains Earth connections and you can solder rather than crimp them. This is because accidental contact with Earth is safe. Any Neutral or Active wire terminal connection that is exposed should be covered with insulation such as heatsiliconchip.com.au shrink tubing to prevent direct accidental contact with mains voltages. That includes wiring on the mains switch and the spare terminal(s) of a double throw switch. Soldering is acceptable rather than crimping so long as the wires are cable tied together (which is required anyway). It is important when soldering to the IEC connector to check that the terminals are correctly soldered with sufficient heat and flux to ensure the joints fully adhere to the terminals and do not form dry joints. Programming Arduino projects with a Mac I’m very interested in the WiFi Water Tank Level Meter in the February 2018 issue (siliconchip.com.au/Article/ 10963). Being dependent on a large concrete tank for our farm household water I need such a device. Currently, I bribe grandchildren to do this but as they become older, the idea of climbing up on a 3.6m high concrete tank appeals less despite generous bribes. During the course of the article, many mentions are made of using a PC to program and upload data to the Arduino-based unit. My question is, will an Apple MacBook do this task? The article seems to read as though it’s a Windows-based program. My confusion is that often PC is used to denote a Windows-based personal computer or laptop. (D. C., Cambooya, Qld) • The Arduino IDE is available for Windows, Mac OS X 10.7 or newer and Linux. See: www.arduino.cc/en/ Main/Software So if your MacBook runs Mac OS X 10.7 or newer (or it can be upgraded) then you should be able to follow the procedures set out in the magazine. Older versions of the Arduino IDE (10.6) will work on older versions of Mac OS X (eg, 10.6.8 and before). Note though that we are not sure whether the sensors used are safe to place in drinking water tanks. Control DC motor speed with AC motor current I have made an automatic saw which is mounted on slides and driven by a speed adjustable geared DC motor. The speed is altered by a variable voltage supply so the saw motor is not overloaded by the forward travel into the siliconchip.com.au work. The saw motor is a universal type. I want to know how to link the forward travel speed to the load being encountered by the saw motor for a new saw. The load will vary during the cut operation. I am planning to control the DC motor speed using either Jaycar kit KC5502 (20A 12/24V DC Motor Speed Controller Mk.2, June 2011; siliconchip.com.au/Article/1035) or KC5225 (High-Current Speed Controller For 12V/24V Motors, June 1997; siliconchip.com.au/Article/4868). But both of these motor speed controllers are manually controlled. The first stage will be the fast approach of the saw to the work, a second stage is a very slow approach as the moving blade contacts the work and then the automatic stage where the current draw of the saw motor varies the forward travel speed. It will have to be reversible but I can do that with a toggle switch. The new saw motor I am planning to use draws 9A at full load. I would like to be able to set the automatic load speed to maintain around 8-8.5A to get the best forward cut speed without erratic loading of the cut motor. Thank you for any help you can give. (G. T., Londonderry, NSW) • Take a look at the circuit of our Full Wave, 230VAC Universal Motor Speed Controller in the March 2018 issue. In particular, observe the use of the current transformer, rectifier and filtering to measure the motor current of the mains-powered motor. You could copy that part of the circuit to measure your saw motor current. The current transformer provides mains isolation as the insulated mains wire only passes through the centre core of the transformer and the secondary winding of the transformer is isolated. The voltage obtained can be used to provide the speed control for the Jaycar kit KC5502 motor speed controller, where the speed potentiometer can be replaced with a DC control voltage applied to where the wiper would connect. Note that you will need to provide amplification, voltage inversion and level shifting using an op amp to get the required speed control against saw motor current. The voltage inversion is important since you want the DC motor speed to reduce as the saw moCelebrating 30 Years tor's current draw increases when it is heavily loaded. Motor Speed Controller thermistor woes I have purchased and built three K6036 kits for the 10A/230V Universal Motor Speed Controller design published in the February and March 2014 issues (siliconchip.com.au/ Series/195). I had no problems with assembly and all three ran fine for a short time. I connected a 1600W vacuum cleaner to test. I can vary the speed easily all the way down to stop. But after running for about three minutes at say 75% load, the speed pot (VR1) no longer allows me to get full power. If I run with the top off the box and use a vacuum cleaner (with plastic piping for safety) close to the NTC thermistor, after about 15 seconds, the speed increases to full speed or near full speed. I can repeat this on all the kits I have emailed Altronics and they were helpful and suggested contacting you and one of your technical gurus who designed this circuit. What do you recommend? Should the thermistor be removed? It is hot to touch but technically the resistance should drop. Am I misunderstanding something? I shorted out the NTC thermistor but used a heat gun with heating turned off to reduce the current demand. Once running, I turned up the heat and increased load but the motor speed becomes erratic and it will not run at full speed. So perhaps the thermistor was just clouding the issue. My plan is to control these kits from a PC via an opto-isolation circuit, to control 2000W vacuum cleaners. It is to control boundary layers in my 10% scale wind tunnel. (J. B., Surrey Hills, Vic) • The heat gun is probably producing interference that is making the controller run erratically. We still suspect the NTC thermistors are at fault as they should drop in resistance with more heat and not restrict the maximum speed. Your tests suggest that the thermistors are working the other way and this may indicate that they are a Positive Temperature Coefficient (PTC) type and not the NTC type specified. We suggest you check for any markMay 2018  101 ings on the thermistors and check the kit notes to see if a part code is supplied, in an attempt to determine whether they are PTC or NTC. Failing that, connect a DMM set to measure resistance across one thermistor and heat it with a heat gun or similar. If the resistance increases as it gets hotter, you have been supplied the wrong part. Relay problem with Arduino LC Meter I have built the Arduino LC Meter project (June 2017; siliconchip.com. au/Article/10676) and have encountered two problems. Firstly, the relay appears to have incorrect pin connections. The impulse to the relay coil should go to pin 13, not pin 2 as in the circuit diagram. Wired up as per the article, the relay coil does not receive the calibration pulse required as the coil is not energised. Pin 2 not being connected to anything in the relay. Secondly, the Arduino sketch, in the comments, mentions that the serial interface with the new chip should have the serial address revised in the code, but the actual revised address is not provided. My inexperience may be the problem, but changing the address to 38 did not work. (W. S., Lake Cathie, NSW) • According to the data sheet of the relay we specified in the parts list, pins 2 and 13 are internally joined. So the circuit and wiring seem to be correct as presented. Are you sure you have the correct relay? It should be labelled PRMA1A12 or TRR1A05D00. Which serial interface address to use was explained on pages 82 and 83 of the March 2017 issue, in the article on the serial LCD module (siliconchip. com.au/Article/10584). If your module has the PCF8574AT chip, it will probably be set up for an address of 3F hex. ers are a bit of a worry. I figure they’re bound to end up getting pranged before too long. I was thinking of fitting a grille to each woofer, Altronics Cat C3715. I was wondering if this would compromise the sound quality. Would you recommend fitting something like that or should I use a conventional speaker grille made from grille cloth on a frame? (B. D., Ashburton, Vic) • If you have pets or young children in your home, protective grilles are prudent insurance. They will have no effect on the sound quality. Grille cloth may look better but it offers less protection and may rattle or buzz at high bass levels. Nicholas Vinen attached grilles to his Majestics (see the photo below). He bought them from eBay rather than using the Altronics grilles, only because the photo on the Altronics website makes them look rather "chunky" and he preferred a finer mesh. He attached them using the clips supplied with the grilles but had to add small springs and rubber pads (from Bunnings) to space them off from the face of the speaker, as the speaker surround sits about 10mm proud of the front panel. The supplied screws were long enough to pass through and compress the springs to hold the clips in place. Fitting a grille to the Majestic speakers I am building a pair of Majestic speakers and looking forward to getting them working soon. I noticed there was an error with the specification of the screws to attach the Celestion horn. They should be M6 size, not 6BA. Also, the exposed cones of the woof102 Silicon Chip Celebrating 30 Years You could also mount the clips at 45° angles rather than 90° as some constructors may prefer the resulting appearance. Is lower amplifier distortion noticeable? I have an Electronics Australia Mosfet-based amp I built sometime around 1990. There is a Silicon Chip amplifier design (March - May 2012; siliconchip. com.au/Series/27) which appears to have about 10 times less distortion. I was wondering whether the reduction in distortion provided by the newer design was actually audible. Given the best speakers create distortion of about 0.5% THD, does the elimination of a tiny fraction of a percent distortion from the power amplifier actually matter? Or are there other factors involved apart from sinewave distortion such as response to transients? I would be interested to understand more about this. I think other readers would also be interested in this. By the way, thanks for a great magazine. (B. D., via email) • The Ultra-LD Mk3 (described in 2012; siliconchip.com.au/Series/27) and the Ultra-LD Mk4 (described in 2015; siliconchip.com.au/Series/289) are superior to anything we described in S ilicon C hip ten years before and orders of magnitude better than anything ever described in Electronics Australia or in any other magazine, for that matter. Also as Douglas Self points out, Mosfet-based amplifiers are not capable of achieving the low levels of distortion of a good bipolar transistor based design. Unless you have cloth ears, you will certainly notice a big improvement in sound quality when listening to CDs. Do not bother making comparisons with MP3 recordings unless they have the highest possible bit-rate and even then they are not as good as the best CDs. While it might seem that the higher distortion from loudspeakers would mask the much lower distortion of amplifiers, that is not the case. The quality of distortion from loudspeakers tends to be quite different to that from amplifiers. With that said, your system will sound even better if you have low distortion loudspeakers. SC siliconchip.com.au MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP FOR SALE KIT ASSEMBLY & REPAIR tronixlabs.com.au – Australia's best value for supported hobbyist electronics from Adafruit, SparkFun, Arduino, Freetronics, Raspberry Pi – along with kits, components and much more – with same-day shipping. PCB MANUFACTURE: single to multi­ layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au PCBs MADE, ONE OR MANY. Any format, hobbyists welcome. Sesame Electronics Phone 0434 781 191. nev-sesame<at>outlook.com www.sesame.com.au LEDs, BRAND NAME and generic LEDs. Heatsinks, fans, LED drivers, power supplies, LED ribbon, kits, components, hardware, EL wire. www.ledsales.com.au Where do you get those HARD-TO-GET PARTS? Where possible, the SILICON CHIP On-Line Shop stocks hard-to-get project parts, along with PCBs, programmed micros, panels and all the other bits and pieces to enable you to complete your SILICON CHIP project. SILICON CHIP On-Line SHOP www.siliconchip.com.au/shop DAVE THOMPSON (the Serviceman from SILICON CHIP) 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 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 KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith 0409 662 794. keith.rippon<at>gmail.com ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Celebrating 30 Years May 2018  103 Coming up in Silicon Chip Altium Designer 2018 review We have been using Altium Designer to draw up circuits and design PCBs for many years now. In that time, quite a few improvements have been made to the software. We'll describe the new features and also point out some of the pre-existing features that have been improved or are particularly useful. Advertising Index Altronics................................ FLYER Dave Thompson......................... 103 Digi-Key Electronics....................... 3 Emona........................................ IBC El Cheapo Modules – RF attenuators Hare & Forbes.......................... OBC Jim Rowe describes a programmable, 63-step, 4GHz RF digital step attenuator module with a range of applications. Jaycar............................... IFC,49-56 Introduction to programming the Cyprus CY8CKIT LD Electronics............................ 103 This low-cost module incorporates a 32-bit microcontroller and a set of reprogrammable analog circuitry which can be used for a wide range of tasks. Touchscreen GPS Frequency Reference This new design is much more compact with many new features including multiple programmable-frequency outputs, ultra low-drift operation, improved status display and 5V operation. The Latest Agricultural Technology The rapid advancement of technology is having a huge effect on agriculture and Australia is at the forefront. We take a look at some of the latest robots and monitoring devices aimed at increasing crop yields and food quality and reducing the environmental impact of farming. LiFePO4-based Uninterruptable Power Supply The second article in this series will have details of the control circuit and shield PCB, and describe how to build the case and wire up the components. Note: these features are planned or are in preparation and should appear within the next few issues of Silicon Chip. The June 2018 issue is due on sale in newsagents by Thursday, May 24th. Expect postal delivery of subscription copies in Australia between May 23rd and June 8th. Keith Rippon Kit Assembly......... 103 LEACH Co Ltd.............................. 27 LEDsales.................................... 103 Master Instruments.................... 103 Microchip Technology..................... 5 Ocean Controls.............................. 6 PCBcart........................................ 9 Sesame Electronics................... 103 Silicon Chip Shop............. 42,94-95 Silicon Chip Subscriptions.......... 99 Silicon Chip Wallchart................. 89 SC Radio, TV & Hobbies DVD...... 13 The Loudspeaker Kit.com............ 81 Tronixlabs................................... 103 Vintage Radio Repairs............... 103 Wagner Electronics........................ 7 WIA Radio & Electronics Conv..... 11 Notes & Errata Majestic Speakers, June & September 2014: In the September issue, the two screws used to attach the tweeter to the horn are listed as 6BA x 20mm when they should be M6 x 20mm. These same two screws are not mentioned in the parts list in the June issue. Battery-Pack Cell Balancer, March 2016: there is a risk of damage to IC1 and IC2 when batteries with many cells are initially plugged in. Two small (¼W) 10kW through-hole resistors can be added to solve this. Solder them between pin 2 and pin 15 of both IC1 and IC2. These pins are adjacent but on opposite sides of the IC packages. The resistor bodies will need to be kept close to the ICs to avoid interfering with the battery header (CON1). Alternatively, they can be soldered from pin 15 of IC3 to ground (pin 20), and the other from pin 16 of IC3 to ground. WiFi Water Tank Level Meter, February 2018: the WeMos D1 R2 board we used in this project was actually a clone made by Robotdyn; the original D1 R2 does not have a connection for an external antenna. The boards in our shop (Cat SC4414) are the same as the board shown in the article. 6-Element VHF TV Yagi Antenna, February 2018: a photo caption on page 40 says that the dipole ends are made using 39mm lengths of aluminium tubing but they are closer to 30mm; refer to Fig.1 on page 39 which correctly shows the distance between the semicircular cut-outs at each end as 27mm. AM Radio Transmitter, March 2018: the circuit diagram on page 67 (Fig.2) shows the 10nF antenna coupling capacitor connected to the wrong end of antenna coil L1. Also, Mosfet Q3 has the wrong part number in the parts list. It should be IPP80P03P4L04, as in the circuit and overlay diagrams. The Clayton’s “GPS” Time Signal Generator, April 2018: the parts list gave an incorrect Jaycar part number for the D1 Mini ESP8266 module. It should be XC3802. 104 Silicon Chip Celebrating 30 Years siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes FREE OPTIONS Bundle! New Lower Prices! 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