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It is huge... It has colour... It has light... It has movement... It is the ultimate Chrissie Display You’ll have the best looking house in the street WORLD this Christmas! Can you hear it? That faint “Ho Ho Ho” coming from a secret location far, far away but rumoured to be somewhere near the North Pole? Yes, Santa is on his way (hey, Christmas is only a few short weeks away!) and SILICON CHIP is going to help you get right into the Christmas spirit with this amazing, unique, stupendous, magnificent and original Christmas lights display Design by the inspired John Clarke November 2000  13 Words, Music and Artistic Impressions by TestaRossa J ust in case you’re thinking this is one of those tiny little displays published previously, think again. At well over a metre wide and just on a metre high, it’s as big as we could make it and still be reasonably easy to transport. It’s big enough to be seen not just from the footpath, not just from the street, not just from a block or so away but would you believe across a suburb? (Well OK, you do need lineof-sight). And if this is not even big enough for you, it could easily be scaled up to be a real whopper – if you could find a piece of backing board big enough, you could make it metres high and deep. But more on that anon. Chevvy Chase, eat your heart out. Your “National Lampoon Christmas Vacation” house didn’t have one of these. Not even the McCallister home in “Home Alone” could manage one. In fact, you can bet your last dollar that your place will be unique – noone else in the world will build one exactly the same as yours! Apart from the size, this project has a couple of other very snazzy features which we’ll tell you about before we get down to the nitty gritty (which of course you want to do!). First of all, the circuit design borders on genius. As you know, John Clarke comes up with some pretty clever projects in SILICON CHIP but he’s really excelled himself this time. He’s managed to keep the circuit amazingly simple while appearing to be quite complex. For a start, none of the LEDs in this project run from pure DC. As you no doubt know, LEDs need to run from DC – but here they either run from rectified (but unfiltered) low voltage DC or, in many cases, from low voltage AC alone. What this means to you is a significantly lower cost of components and, more importantly, lower heat problems than we might otherwise expect. The whole project runs from a 12V “halogen” transformer which is rated at 5.25A continuous. Current drain of our display was around the 1.7A mark, depending on the number of LEDs lit at the time, so the transformer is operating well within its specs. We tested this all night during Olympic September (our bemused neighbours thought we were a bit early for Christmas or were simply caught up in the Games euphoria…). The transformer runs warm but certainly not as hot as it does running a single 12V halogen lamp. And we’re running more than 600 high brightness LEDs. Yes, you read that right – more than six hundred! This many LEDs takes a lot of wiring – in fact, that part alone is going to take you at least a full day or so to do. But it’s not difficult because we show you how each section is wired and you test as you go, to make sure you haven’t made any mistakes. It’s also simple because all of the control of these LEDs is achieved with just three low-cost ICs. Having said all that, this is probably not the sort of project you would undertake as soon as you’ve learnt to solder. Additionally, it is not a cheap project. 600+ high brightness LEDs alone will set you back about three hundred dollars if bought “off the shelf”. Incidentally, we must thank Jaycar This is what the display looks like in fairly subdued light – the LEDs are starting to become quite dominant. What this photo doesn’t show you is the movement – sled runners, reins and trails chasing, legs moving back and forth and of course, Rudolph’s red nose flashing away merrily. At right is Fig.1, the circuit diagram. It doesn't show all 606 LEDs but shows the drivers for each section of LEDs. All other LED sections are simply duplicates of what is shown. 14  Silicon Chip November 2000  15 A leetle dab here, a leetle splash there. . . our resident artist, Ferrari TestaRossa, creating the masterpiece on which our light show is based. Do you like our artist’s pallette – an offcut of PC board, just to keep the electronics theme going! Fig.2 (right): you can create your own work of art, just as good as ours (and probably much better!) using this 4:1 scale artwork as a base. This file is also available on the SILICON CHIP website, www.siliconchip.com.au Electronics for helping us with the parts for this project, not the least being their ability to lay their hands on 600+ high brightness LEDs at very short notice! Good one, Jaycar! The other components, the mounting and backing boards and timber, the paint and various other bits and pieces would probably the best part of a hundred dollars. So to have the best-looking house in the street you’re going to have to invest a bit of the folding stuff. But once done (and protected from the weather) you’ll have a display that your children and grandchildren will look at in awe, Christmas after Christmas after Christmas! And to make it a lot less painful for you, both Jaycar Electronics and Dick Smith Electronics have come to the party with special prices on the complete kit of electronic parts (ie, the PC board, on-board components, LEDs and resistors but not the hardware). It’s significantly less than buying the components even in bulk packs. These kits should be available during early November. By the way, when we gave this project our test run back in September, we were simply amazed at the amount of light it produced. It was easily enough to read a car number plate on the other side of a very dark street – in fact, the whole front yard lit up like – dare we say it – a Christmas Tree! During the day, the LEDs don’t exactly do much (although you could see them flashing even in sunlight). What you do see is a large painting 16  Silicon Chip of Rudolph, complete with red nose, pulling good ol’ Saint Nick in his sleigh full of goodies. And here is where your display gets much of its uniqueness: you get to paint the image. We’re going to give you a head start with a really snazzy poster which you can transfer to the board to use as a base (and we’ll even show you how easy that is). We were going to ask Michaelangelo to paint our image but he was busy slapping a coat of paint on his sister’s chapel or something, so we asked our resident artist, Ferrari TestaRossa, to draw and paint Rudi & Nick ready for the big light job. As you can see, it’s turned out pretty neat. No, neat’s the wrong word. In fact, up close it looks pretty messy (apologies to my 3A art teacher at Cowra Primary – you were right). But move back a couple of metres or so (or even a couple of hundred metres or so) and it looks fantastic! Our point is that you don’t need to be any sort of artist to produce a masterpiece. The real impact is not so much in the image but in the way it lights up at night. At night, the coloured LEDs will animate the display with apparent motion for the reindeer and the sleigh. Even the reins move, Rudolph’s red nose blinks and trails behind the antlers and sleigh give motion as it glides through the sky. We used three different LED colours – red, green and yellow – for the display. Optional white or blue LEDs, which actually twinkle, can be included as separate stars in the night sky backdrop or as a single star. How it works We haven’t tried to show all 600+ LEDs in Fig.1, the circuit diagram – they simply wouldn’t fit even across two pages. But that’s no problem because the circuit can be divided into sections which duplicate again and again. These sections are basically the steady (looking like they’re constantly on) LEDs which outline Santa and his sack, the sleigh body, Rudolph’s body and antlers; the chasing LEDs – the reins, the sleigh runners and the trails; and finally the alternating LEDs – Rudolph’s legs and his red nose. We mentioned before optional white LEDs (not included in the Jaycar or DSE kits) which can be randomly placed to simulate twinkling stars. The steady or continuously driven LEDs (identified on the circuit as LEDs 21-28 – in fact there are 271 of them in our design but you could have up to 800 maximum) are powered directly via the 12VAC supply from the transformer. For one cycle or polarity of the AC waveform, series connected LEDs 2124 are driven via the 180Ω resistor and the reverse connected LEDs 25-28 are off. When the AC waveform swings the opposite way, LEDs 25-28 are driven and LEDs 21-24 will be off . Each lit LED will have a nominal 1.8-2V across it so the current applied to the LEDs will be the supply voltage (nominally 12V) minus the total LED voltage drop (say 8V) all divided by 4 x 6 green chasing 6 yellow chasing 6 yellow chasing 19 green steady (sack) 4-20 white or blue twinkling (stars) no positions shown random placementall optional 4 x 6 yellow chasing November 2000  17 115 yellow chasing 100 red steady (sleigh) 5 red flashing (nose) 2 green steady (eye) 4 x 14 yellow (legs) and 4 x 2 red (hooves) alternate 114 yellow steady (rudolph) 60 green chasing (reigns) 4 yellow steady (beard) 40 red steady (santa) 1 green steady (eye) 2 x 6 yellow chasing 6 red steady (navigation lights) 180Ω, which equals 22mA. Since each LED string is lit for only half of the time, the average current for an individual LED will be around 11mA. The chaser, alternator and twinkle driven LEDs are controlled via the remaining circuitry. Diodes D1-D4 rectify the 12VAC supply from the transformer to give a pulsating DC voltage to drive the chaser, alternate and twinkle LEDs. This voltage is isolated by diode D5 and smoothed by the 470µF capacitor. REG1, a 7812 regulator, provides the fixed 12V output required by IC1-IC3. Three oscillators provide the timing pulses required for (a) the chasers, (b) the alternate switching (legs) and flashing (nose) LEDs and (c) the optional “twinkling” LEDs (stars). All are based on IC1, a hex (or six-way) Schmitt trigger inverter. The inverters can be made to oscillate by connecting a capacitor between input and ground and a resistor between the Schmitt output and the input. Each operates in a similar manner, the main difference being their speed. We’ll describe the chaser oscillator, based on IC1a. The chaser circuits The photograph of the PC board above is reproduced same size as the original, as is the component overlay (Fig.2, below). Between these two you should have all the information you need to successfully complete the PC board. Initially, the 4.7µF capacitor is discharged so the input (pin 1) is low and the output (pin 2) is high. The capacitor charges via the 5.6kΩ resistor and VR1 until the capacitor voltage reaches the upper threshold of the Schmitt trigger input. The output then goes low and the capacitor discharges via the resistors. The output of IC1a goes high again when the lower threshold of the Schmitt trigger input is reached. Thus oscillation continues. VR1 sets the operating frequency. In the case of the chaser, pulses from IC1a trigger the input of the decade counter IC2. This has ten separate outputs which go high in succession at each positive clock. In our case, though, we don’t allow it to count all the way to ten. First one ouput goes high, then the next output goes high with the first output going low. The next output then goes high and then the final output which resets the counter immediately so that the first output is again set high and so on. 4017 ICs are often used to drive a couple of LEDs direct. But not 260 LEDs! To drive the LEDs, we use IC3, a ULN2003A. This contains seven Darlington transistors. Each of these is capable of driving up to 30 strings (each of 4) of LEDs. So the three chase outputs are connected to three Darlington drivers in IC3a. The pattern in which the LEDs are arranged makes them light one after another – the lights “chase” each other and simulate movement. The reins, the trails and the runners are all driven from the chaser outputs. When pin 4 of IC2 is high, pin 16 of IC3 is pulled low to turn on the “A” output LEDs (LEDs 1, 4, 7, 10 etc). These are powered from the unfiltered 12V DC supply via a 390Ω resistor. Then when pin 2 of IC2 goes high, pin 15 of IC3 is pulled low to turn on the “B” output involving LEDs 2, 5, 8, 11 etc. Finally, when pin 3 goes high, pin 14 of IC3 turns on the “C” output, (involving LEDs 3, 6, 9, 12 etc). This process continues but your eyes do not flick back to the start – they follow the movement along the strings. The alternating circuits The alternating circuits switch the LEDs on and off on alternate legs, again simulating movement, while at the same time flashing the red LEDs on Rudolph’s red nose on and off. 18  Silicon Chip Operation of the alternating circuits is somewhat similar to the chasers, except that there are only two states. We could use another 4017 and count to two but we had spare gates available in the 40106 so these were used instead. Output from IC1b is fed to the input of two Schmitt inverter gates, IC1c and IC1e. One of these (IC1e) drives one of the ULN2003A’s inputs direct – when its output is high, the ULN2003 pin5/12 Darlington turns on. This switches one of the alternating LED banks. IC1c also switches high and low in unison with IC1e but its output is connected to yet another inverter, IC1d. Therefore when IC1e’s output is high, IC1d’s output is low and vice versa. IC1d switches the ULN2003 pin4/13 Darlington so the other alternating LED banks light. Twinkle twinkle little star(s) The twinkle circuit itself is included because it requires only four additional low-cost components – the IC gates would otherwise be wasted. The circuit is even simpler – the oscillator, which runs quite a lot faster than the other two, drives a ULN2003A Darlington direct while the output from that Darlington drives Fig.3: the simple test jig which you can lash together to make sure your PC board is working properly. It’s a lot easier to troubleshoot the main display LEDs if you know the electronics are working! the input to the last Darlington. Thus the two strings of LEDs also light alternately but due to the speed of operation, appear to twinkle rather than flash. The reason this circuit is regarded as optional is the price of white (or blue) LEDs. These are quite a lot more expensive than coloured LEDs – ten times as much – so to keep the cost of the kit as low as possible, are not included. Provision is made for those who want them. PC board construction With the exception of the LEDs and their current-limiting resistors, all components mount on a PC board coded 16111001 and measuring 89 x 60mm. The LEDs and resistors mount directly onto the hardboard display and are wired together and connect to the appropriate PC board terminals. Begin construction by checking the PC board for shorts between tracks and breaks in the copper circuit. Also check that the hole sizes are correct. You will need a 3mm hole for the regulator tab to be bolted down on the PC board. Insert all the diodes, links and resistors first – use the accompanying resistor colour code table as a guide to the resistor values. Alternatively you can use a digital multimeter to select the resistor value required for each position. When installing the ICs, ensure each is placed in the correct position Parts list 2 1220 x 915 sheets of Masonite WhiteCote or similar hardboard 1 4.2m length of 50 x 25mm pine 1 PC board coded 16111001, 89 x 60mm 1 12V 5.25A (63VA) or similar enclosed halogen lamp transformer (eg Jaycar MP-3050) 1 3m length of red medium duty hookup wire 1 3m length of black medium duty hookup wire 1 3m length of green medium duty hookup wire 1 3m length of blue medium duty hookup wire 1 20m length of 0.8mm tinned copper wire 1 length (to suit location) 10A figure-8 cable 1 M3 x 6mm screw and nut 2 2-way terminal blocks 10 PC stakes Semiconductors 1 74C14, 40106 hex Schmitt trigger (IC1) 1 4017 decade counter (IC2) 1 ULN2003 Darlington driver (IC3) 1 7812 1A 12V 3-terminal regulator (REG1) 5 1N4004 1A diodes (D1-D5) 343 yellow 5mm high brightness LEDs 157 red 5mm high brightness LEDs 106 green 5mm high brightness LEDs 8 white or blue 5mm LEDs (optional) 7 5mm standard LEDs, any colour (for test jig) Capacitors 1 470µF 25VW PC electrolytic 2 10µF 16VW PC electrolytic 2 4.7µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 1 0.1µF MKT polyester (coded 104 or 100n) Resistors (0.25W 1%) 1 10kΩ (brown-black-black-red-brown) 9 5.6kΩ (green-blue-black-brown-brown) 1 1kΩ (brown-black-black-brown-brown) 3 2.2kΩ (for test jig) (red-red-black-brown-brown) 37 390Ω (orange-white-brown-black-brown) 35 180Ω (brown-grey-brown-black-brown) 3 220kΩ or 250kΩ horizontal mount trim pots (VR1-VR3) (coded 224 or 254) Miscellaneous Wood screws, PVA glue, neutral cure silicone sealant, acrylic paint, wide-point marker pens, carbon paper (if required) November 2000  19 Here’s how we transferred the artwork onto our Masonite board. First, we printed the poster out on a laser printer in “tile” mode and then sticky-taped the whole lot together. Then we stuck this on the Masonite and traced the whole thing with carbon paper. There are other ways to do this – eg, it’s real simple if you have access to an overhead projector! and is oriented correctly; likewise the electrolytic capacitors. PC stakes can now be inserted as well as the trimpots. REG1 is mounted by bending the leads to fit into the holes provided, soldering them in and bolting the metal tab to the PC board. Testing To ensure everything works correctly, we use a special test jig as shown in Fig.3. Wire up seven LEDs as shown and apply power. Check that the chaser LEDs (three to the left) move from right to left and that the alternating LEDs (next two) flash alternately. The twinkle LEDs to the right should also alternate but the speed may be too fast to tell. Adjust the chaser and alternating trimpots VR1 and VR2 so that the chaser is slightly faster than the alternator and at a rate The LED wiring on the rear of the display may look like a dog’s breakfast but is actually quite logical. All LEDs are soldered leg to leg where possible, then joined with either tinned copper wire or insulated wire. The wiring diagram overleaf shows this more clearly. The wood blocks are pine offcuts which keep the back sheet of Masonite away from the wiring. 20  Silicon Chip of about two steps per second. The twinkle trimpot should be adjusted so that the LEDs are flickering at a fast rate. If the circuit does not operate check for shorts on the PC board and power to IC1 and IC2. There should be 12V between pins 14 and 7 of IC1 and between pins 16 and 8 of IC2. Your masterpiece Here’s where the real fun part starts. Even if you’re not a “real” artist, you can produce a more-than-acceptable result. In fact, there are several ways to do it, depending on your ability, the equipment you have access to and the depth of your pockets. You could, of course, design and paint your original artwork directly onto the “whitecote” Masonite. But if you’re a mere mortal, you may need to use someone else’s creative genius. Reproduced herewith is our masterpiece. The JPEG file is also available for downloading on www.siliconchip. com.au What can you do with it? Our original plan was to get a local computer graphics house to print it out full size (A0 – 1188 x 840mm). Then we found that a poster this size isn’t exactly cheap – we were quoted about $165 at our local Kinco’s Steady LED Bank Fig.4: the “steady” bank of LEDs (the ones which are apparently on the whole time) are driven from the two halves of the AC waveform. Wire them as shown. This layout is repeated many, many times! and scrape it with a straight edge to remove all the timber swarf. We also used a very much larger drill, twisted in the fingers, to remove any swarf from the front of the board. With 20/20 hindsight, we don’t think this step is all that important because the paint you’re about to apply hides any rough edges. Painting store. Chief bean counter and he who must be obeyed (CBC & HWMBO) hasn’t really recovered yet from that quote. Scratch that idea. One tried-and-trusted method of transferring artwork is the “grid” method. You will note a fine blue grid printed over the artwork – this grid is scaled up (4:1) to the 1220 x 915 sheet and used to draw the image on. Another way, if you have the facilities, is to print out a copy of the artwork on overhead projector transparency and project the image onto the Masonite. You then simply trace over it with a pencil. The method we finally used was a bit more creative. We simply printed the image out as “tiles” on a laser printer, stuck them all together, then traced the artwork onto the Masonite using carbon paper. Mind you, finding carbon paper at your local newsagents or stationers these days is not quite the simple task you might expect (kids everywhere are asking “what’s carbon paper?). We were fortunate in having an A3 printer – that only needed 12 sheets. If you have to print it out A4, be prepared to use double that number. It’s a lot of sticking together but it works. for drilling our holes – through both paper and Masonite. You need 5mm holes for the LEDs – this allows them to poke right through and sit on their collars. A few tips: (a) secure the paper artwork to the board properly so that it doesn’t move around, allowing your holes to drift (b) support the board adequately so that the drill doesn’t flex it when you apply pressure. (c) use a drill with a trigger lock. I didn’t – and that makes it even more tiring on the hand. (d) In some ways it’s easier just to start all the holes with the paper in place then remove the paper to drill them out fully. (e) If you do manage to get a hole out of position by a few mm or so, don’t worry. It’ll look alright on the night (adjust your paintwork to suit. Whatever you do, don’t try to correct mistakes – that only makes things worse!). When you have drilled all the holes right out, turn the board over Having transferred the basic image to the Masonite and drilled the holes, it’s time to start painting. We purchased some $2.75 tubes of Acrylic paint at a local art supplies store – you’ll need a red, blue, green, yellow, black, white and brown. Of course you can mix intermediate colours from the primaries if you wish to save a couple of bob. As far as colours are concerned, we probably don’t need to remind you that the jolly fat gent is basically red and Rudolph is either fawn with grey or grey with fawn (no, not that sort of fawn – Rudolph is not that kind of reindeer. Until he got to pull the sleigh all the other reindeers used to laugh and call him names, remember?). Apart from that, it’s up to you – just remember the colours of the LEDs you’re going to get in your kit. Acrylic paint dries pretty quickly, even when applied thick. We used some el-cheapo brushes (in deference to CBC & HWMBO) so our artwork didn’t turn out all that smooth. But as we said before, it matters not one Fig.5: to make the LEDs chase, you simply arrange them in a particular flashing pattern. This shows how to do it: 1 to 4, 7 & 10; 2 to 5, 8 & 11; 3 to 6, 9 & 12, and so on. The chasers are driven from rectified but unsmoothed DC. Drilling the ’oles Got a spare hour or ten? You’re gonna need it! Drilling 600+ holes may not seem like such a tough task but believe me, my hand ached something fierce after the first hundred or two. I was really glad that the cordless drill battery was just as run down as I was and needed a couple of recharges – just for the breaks it gave me. We simply used the paper layout, still stuck in position from tracing, as the template Fig.7: the optional “twinkling” LEDs are for stars and these can be spread around the board as desired. Fig.8: the alternating LEDs (the reindeer legs) are also driven from pulsating DC. String “D” is in one leg, string “E” is in the opposite leg. November 2000  21 Fig.8: this diagram shows the complete project wired, viewed from the BACK of the the Masonite (ie, the side you poke the LEDs through and the side on which all the wiring is done). Compare this with the photo one page back. We have split the project into two sections and turned them on their sides for clarity – otherwise we would have had LEDs going across the “gutter” between the pages which might make the drawing difficult to follow. 22  Silicon Chip November 2000  23 jot nor tittle how good or bad your artwork is, as long as from a distance it looks the part. It’s a good idea to concentrate on one main colour and leave that to dry before painting adjacent colours. A broad-nibbed marker pen is used to roughly highlight and outline various sections. It can also be used to smooth out any rough spots on things like the runners and reins. In fact (another 20/20 hindsight) the reins could be completely done with the marker pen and look even better. For the movement trails, we haven’t shown any artwork – all you need to do is apply a light “swish” of appropriately coloured paint (grey with a bit of yellow in it or overprinting it works well), heaviest at the start and trailing off towards the end. The photo gives a good idea of what we mean. You might also like to look at painting the white Masonite a different colour, especially if you are using white LEDs as stars. And if you think your artwork is THAT good, don’t forget to sign it. Who knows, it could be worth $$$$ in years to come! Strengthening the board As you probably know, 3mm Masonite is not exactly the most rigid stuff ever invented. It warps badly if not supported properly. To prevent warping, we glued a frame of 50 x 25mm dressed pine right around the back edge of the frame. As we planned to place another sheet of protective Masonite on the back when the project was complete, we glued some offcuts of 50 x 25mm pine in various spots, well clear of any LED mounting holes. Wiring up This wiring job is going to take some time to do (it took us nearly two days) so it is recommended that you position the board in a place where it can be safely worked on without needing to move it (eg, to get the car in and out of the garage!). Support the board around the edges so that the LEDs can be inserted easily without resistance from underneath. We also recommend testing each block as it is wired so that the whole circuit will work when completed and to ensure that if you have made a mistake this will not be repeated throughout the whole wiring. Also the wiring must be kept low enough so that the rear sheet of hardboard can be placed on the back without disturbing any connections. Our artwork shows the suggested colour guide for LEDs. Of course the choices are up to you: for example, I originally had all yellow LEDs on the antlers but John said the tips of the antlers needed red “navigation” LEDs. He was right – they look fantastic! Another tip: keep each of the trail chasers the same colours. Having a multi-coloured chaser doesn’t work well because the eye notices the colour change rather than the chase. Of course, you could change any of the 6-LED sets to another LED colour if you wish. While the PC board is intended to be sandwiched inside the two pieces of Masonite with the LEDs and resistors, there will be constructors who wish to place it in an external case, as shown here. 24  Silicon Chip The LEDs are all wired up as banks or blocks. For example the steady LEDs are connected as a bank of 8 and one resistor. The circuit is simply duplicated as many times as required to obtain the necessary number of connected LEDs. Use tinned copper wire to interconnect LEDs where the spacing is beyond the length of the LED leads. This will be necessary when a particular outline is finished and the LEDs need to be wired to another outline on the drawing. Additionally, for the last block where there are less LEDs needed than required by a block, you can increase the resistors to keep a more-or-less equal current flowing through the LEDs (and therefore much the same brightness). A normal block of eight LEDs (where there are two lots of four LEDs in series) can be truncated to two or three LEDs in series. Use two series connected 390Ω resistors for these to obtain a similar LED brightness. The steady LEDs can be wired in banks of eight as shown in Fig.4. Wire the LEDs in series as shown by bending the leads and soldering in a daisy chain. Most LEDs legs will be long enough to solder direct to their neighbours but where the leads will not reach to the adjacent LED, use tinned copper wire. Connect the anode of LED21 to the cathode of LED28 with tinned copper wire. The free end of the 180Ω resistor connects back to the 12VAC(1) terminal. The cathode of LED24 and anode The PC board is designed to mount inside this commonly available waterproof case. When completed, the holes under the terminal strip should be sealed with silicone sealant to protect the components inside. of LED25 connect to the 12VAC(2) terminal (again refer to Fig 4). The chaser wiring is perhaps most difficult since the LEDs do not connect in series to adjacent LEDs but connect in series to the third LED along (ie, LED 1, 4, 7, 10, etc connect, LED 2, 5, 8, 11, etc connect; and LEDs 3, 6, 9, 12, etc connect). The cathode (K) leads for LEDs 10, 11 & 12 connect to the A, B & C PC board terminals respectively. Follow this wiring carefully since it is important to obtain the correct direction effect around the sleigh rails and for the reins and trails. If some of the chasers are running backwards this is easily changed by swapping the connections to the A, B & C terminals on the PC board. Twinkle LEDs, if fitted, are simply wired as shown in Fig.5. Make sure the 390Ω resistor goes to the 12VDC on the PC board, not the 12VAC. The K leads on LED30 and LED32 go to the F and G outputs on the PC board. If you use white (or blue) LEDs anywhere else on the design, remember they have a higher voltage drop and resistor values will need to be adjusted accordingly. When wiring is complete and the entire circuit is working, you will need to secure the wiring to the board using masking tape and some Silicone sealant. Some LEDs may be a little sloppy in their holes: make sure that any loose LEDs are secured with sealant and that potential problems with wires shorting are held apart with the sealant and/or insulation tape. The PC board is also secured with sealant and is wired to the 2-way terminal strip for the 12VAC wiring. Drill a hole for the wiring to exit from the rear of the pine strips or through the rear of the hardboard backing sheet. Secure the terminal strip with a wood screw and attach another 2-way strip to the rear of the hardboard once secured with wood screws. Give it another check to make sure it works and if all is well, screw the back on with at least eight small woodscrews across each edge. The backing will help prevent warping so it is essential it is supported well itself. Location Ideally, the display should be used Fig.9: full-size artwork for the PC board. You can use this to check for defects in commercial boards or if you want to make your own board. (PC board patterns can also be downloaded from the SILICON CHIP website.) inside – say in a large window or the fixed panels of sliding doors. If you must use it outside, we would apply several coats of clear spray or even two-part clear polyurethane over the whole thing – front, back and sides – to protect it, and the electronics inside, from the elements. If you do use it outside, protect it as much as possible (eg, under an eave) and make sure the transformer is run inside with a long figure-8 cable connecting it to the display. Remember it draws the best part of 2A (depending on the number of LEDs lit at any one time) so heavy duty cable is essential if you are not to suffer unacceptable voltage drops over long cable lengths. And that’s just about it. But before we conclude, we mentioned before the possibility of making the display even larger. Realistically, you’re limited by the size of a mounting board you can get. 2400 x 1200mm is pretty much the limit from most hardware stores. Of course, you could always make a frame which held more than one sheet! On the circuit, we’ve indicated the number of LEDs the various circuit elements will handle – just keep your design within these limits. And you could also use giant (10mm) LEDs on a larger display. They’re not as easy to get in superbright and you’ll be paying the best part of $1000 for 700 of these. But if, for instance, you had a corporate budget to play with and really wanted to impress . . . SC WOW! The sky’s the limit. Wheredyageddit ? At time of going to press, two kit suppliers had indicated that they planned to release “shortform” kits (ie, the PC board and electronics but not the hardware (timber, paint etc) for the Christmas Light Display. In both cases (and, we should add, completely independently) Dick Smith Electronics and Jaycar Electronics have come up with kit prices which we believe are exceptional value – especially when compared to retail component prices (see text). Details/availability are as follows: Dick Smith Electronics: Kit sells for $148.00 (Cat K3003) Note: this kit is not available in all Dick Smith Electronics stores. It should be released 2nd week November (or soon after), only at Dick Smith PowerHouse stores or through DSE Direct Link mail/fax/email/internet order service (Phone 1800 355 544; fax 02 9395 1155, email directlink<at>dse.com.au Jaycar Electronics: Kit sells for $169.00 (Cat KC5302) This kit INCLUDES the specified transformer and 10m figure-8 cable, worth about $30. It should be available around the end 1st week November (or soon after) from all Jaycar stores and through Jaycar TechStore mail/fax/ online order service (Phone 1800 022 888; fax 02 9743 2061, email techstore<at>jaycar.com.au November 2000  25