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SALVAGE ENGINEERING “The whole may be less valuable than the sum of the parts” I f any single item has come to represent the cost-effective “state of the art” in modern consumer electronic devices, it surely must be the ubiquitous solar garden lamp. Selling for around $50 when first introduced in the mid 90s, the early models earnt bad press due to their inefficient and short lived filament lamp. Their panel placement (flat on top) was also a design flaw for non- tropical latitudes, where the sun is at a lower angle even in summer. Slanted panels will better pick up such valuable sunlight and allow dirt, leaves and even snow to slide off as well. LED replacement using the colours of the era (red, amber and green) of course gave unrealistic night lighting. Although red is well known for preserving one’s night vision, that colour rather implies leading the wayward rather too encouragingly up (or down?) the garden path as well... It wasn’t until the early 2000 ultrabright white LED breakthrough that normal white lighting became possible – but at a price! Those first white LEDs were around $10 each and although now much cheaper, they still fetch a premium over other colours. They also demand 3.6V rather than the 1.82V of normal LEDs, meaning mutiple cell batteries (typically 3 x 1.2V NiCd/ NiMH ) would be needed. Since each solar cell photovoltaic (PV) wafer typically produces 0.5V this implies a more costly 8-segment (4V) PV as well. by Stan Swan* 80  Silicon Chip Those solar garden lights can often be bought for next to nothing but reveal a treasure-trove of electronic goodies just waiting for the experimenter . . . siliconchip.com.au X Here’s one of the older-style “ordinary” component controllers from a bargain store solar lamp. How can they possibly make these for the price? So because they’re now efficient and reliable and allow easy DIY lighting but have more costly components, one would expect 2006 solar powered garden lamps to be still around the original $50 mark; not on your life! Old hands don’t know whether to laugh or cry, as hardware, chain and bargain stores worldwide now have shelves stashed to the rafters with bargain solar garden lamps at prices well under $5. Even that may be laughable, since bulk buying can land you a 10-pack for as little as $2 each here in NZ. You could hardly fold up and ship their cardboard box for that sum and most Chinese students here consider them At the bottom is one of the newer SMD controllers. If you want continuous operation (ie, not turning off at dawn) cut the PC board track where shown with the red “X”. grossly under-priced – “Even in China they’d cost more than that”! Sadly such throwaway prices imply electronic junk, only serving to persuade many youngsters that electronic careers have no money in them. Well – you can hardly blame them. With many sparkies often now earning executive incomes and boring mains electrical hardware costing an arm and a leg, “bright sparks” may feel they’d be better off working with copper instead of silicon. Rather than such gloomy navel gazing however, let’s turn the approach around and think positively. Interestingly, the present lamp models being sold add value externally rather than with the light itself. Instead of UV-prone plastic, pricier models increasingly offer sturdy stainless steel poles and mount brackets and classier designs that better integrate into gardens. Hands up all those who want a A$100 solar powered cane toad-style light at their front gate! Forgoing such whims and focusing on the internals reveals most of the models examined here had very similar hand-assembled electronic internals, although a more recent trend towards “pick and place” surface mount devices (SMD) seems apparent. Aha – a cheap source of SMD parts for you to practice on? Many full descriptions of the simple Solar Lamp salvaged parts with approx value if purchased new * Rugged business card sized, epoxy embedded, 4-segment 2V at ~30mA solar panel. Usually hot melt secured but easily detaches with a heat gun. Can be carefully drilled for more convenient mounting Say $5 – perhaps vertically for valuable low-angle winter sun. * 1.2V, 600mAh rechargeable Nicad cell. Although these are now inferior to much higher capacity (and $1 less harmful) NiMH versions, they are still considered ideal for powerful work and multiple charges. 50c * Single AA battery holder – easily separates with snips from plastic mount. * Schottky diode (typically a 1N5819) – valuable for its lower voltage drop (~200mV) than ordinary silicon 50c diodes and just the sort of item you never have on hand when needed. $1 * Ultra-bright white LED – may be only a “cooking version” but usually 5000mCd. $1 * Switch – suitable for school project DC work. $1 * Precision inductors – typically 470mH (microhenry) range, handy for AC theory, RF and calibration work. ~ 50c * BC547 style transistors – with tiny “hard to buy” SMD types now showing up. 20c * Assorted resistors, capacitors and screws. 10c * Assorted short lengths of coloured wire. Priceless! * Clear plastic dome – to keep snails from your garden seedlings etc. * Assorted sectioned plastic support tubes – donate to your local kindy perhaps? * Clear plastic Total Internal Reflection (TIR) optical guides – handy for physics? * Cardboard box – corner reflector 2.4GHz antenna when foil covered (a ZigBee antenna article follows soon!). siliconchip.com.au March 2006  81 Just how efficient are they? Removing the white LED and replacing it with a 1N4148 type diode fed to a ~470mF electrolytic capacitor will make a convenient low current, voltage boosted half-wave rectifier DC supply. Test loading gave the following values (in all cases just from a single AA Nicad power source): Vin I in ~Pin Vout I Out ~P out ~efficiency V mA mW V mA mW % 1.2 17 20 2 5.5 11 55% 1.2 12 14 3 3.1 9 64% 1.2 6 7 4 1.2 5 71% 1.2 4 5 5 0.4 2 40% 1.2 3 4 6 0.2 1.2 30% 1.2 3 4 7 0.15 1.0 25% 1.2 3 4 8 0.1 0.8 20% 1.2 3 3 9 0.06 0.5 16% 1.2 3 3 10 0.01 0.1 3% 1.2 3 3 11 0 To run the inverter continuously (when it takes ~3mA at idle), or at least run it as needed to top up a supply capacitor, you remove the PV sensing point from the pc board. Just lift the PV red wire and Schottky diode off the board and solder them directly together. This now gives a full-time solar top-up/powered circuit, with a typical charge rate of ~12mA into the Nicad cell in mid day overcast. Although the supply output may be rough to our Picaxe, an extended run with both an 08M and 433MHz transmitter powered across the 470mF capacitor was faultless. but sophisticated circuitry are on line, with Australian Colin Mitchell’s site at www.talkingelectronics.com.au/ Projects/SolarLight/SolarLight.html particularly lucid. Typically, the single 1.2V AA Nicad inside is trickle charged from the 2V solar panel. In full sunlight the panel output is about 30mA – about twice the night time current demand of ~12-15mA. This nicely means five sunshine hours will give some 10 hours of night-time illumination – enough for most needs unless you regularly stagger home from a club at 4AM in winter and drop your house key in the long grass. Only a single 1.2V AA cell? How can that power any LED, let alone a 3.6V white one? The secret is to convert, via a high frequency (~100kHz) transistor oscillator, this low-voltage DC into pulses that’ll briefly flash the LED. Human “persistence of vision” visually smoothes any flashes over say 20Hz, so these spikes give a seemingly steady light output. This is aided by the white LED phosphor “after glow”. The Latest From SILICON CHIP The oscillator is a simple coil and capacitor (LC) type – those fat “resistors” shown in the picture are in fact inductors. The return of daylight stops the oscillation when even a small voltage is again PV generated. Just in time for that elusive house key to glint in the morning sunshine. . . What? You live in the mountains, never go outside at night, have no need for a garden light, or don’t even want to know how they work – but instead just want to – gulp – gut them for parts! It seems a telling statement about today’s electronics but these garden lamps are such a parts goldmine that they’re indeed worth purchasing just to scrap. Additionally, schools’ electronics classes, long taunted with the agony of defeat when circuits fail to work, should perhaps seriously consider them for their motivational benefits. Imagine the kids’ enthusiasm when you start the class with a working device, which is then progressively dismantled into individual parts by the period end, all set for a fresh project next time. A brand new working item, tool use, fiddly parts handling, identification and storage, with more to follow? Yay – this seems very educational indeed and sure beats frog dissection in biology – you can’t re-use frog internals! So there you go – even if you paid $3 each, you’ve more than tripled your initial investment, with over $10 worth of electronic goodies all set for some serious circuitry next month – try doing that with an Ipod. Who said there’s no money in electronics! SC * stan.swan<at>gmail.com 160 PAGES 23 CHAPTE RS Completely NEW projects – the result of two years research & development • Learn how engine management systems work • Build projects to control nitrous, fuel injection and turbo boost systems • Switch devices on and off on the basis of signal frequency, temperature and voltage • Build test instruments to check fuel injector duty cycle, fuel mixtures and brake & temperature Mail order prices: Aust. $A22.50 (incl. GST & P&P); Overseas $A26.00 via airmail. Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 82  Silicon Chip From the publishers of Intelligent turbo timer I SBN 095852294 - 4 9 780958 522946 $19.80 (inc GST) NZ $22.00 (inc GST) TURBO BOOST & nitrous fuel controllers How engine management works siliconchip.com.au