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Build a LED torch This is an idea whose time has come. No longer will conventional torches with incandescent bulbs be good enough. Now you can build a solid-state torch with a white LED. You get high brightness with cool white light, low battery drain and you will NEVER ever have to replace a torch bulb again. M OST TORCHES chew through batteries as if they own shares in Eveready (with apologies to Mr Mallory and co). This one won’t. In fact, with intermittent use, you could get a life approaching the “shelf life” of the battery. You’ll certainly get at least six times the battery life of a normal twoAA-cell torch . Our LED torch runs much, much cooler than any torch you've ever experienced. You’ve probably seen the warnings on those superbright bulbs that have the capacity to melt normal torches. We’re not claiming that this is anything near as bright but, by the same token, this one runs cold to the touch. Our LED torch uses just one “AA” battery. That’s right, one only. And what’s more, it will continue to shine brightly for the whole of the battery life – however long that is. Ordinary torches start to dim (actually the light gets more and more 14  Silicon ilicon C Chip hip 14  S Design by JOHN CLARKE yellow and loses intensity) as soon as the battery voltage starts to drop off and really “lose their bundle” at about 1.2V per cell. Ours works with virtually full brightness down to below 1V (at which time you could regard the battery as dead). Impressed? You sure would be if you could see this little beauty “in the flesh”. It has a brilliantly white light (not the yellow you’re used to from most torch bulbs). LED light is a completely different type of light. It’s softer, more diffuse – without the hot spots and shadows you get with normal globes. The torch uses just one of the high intensity white LEDs which have recently come onto the market. When we say “one of” that’s deliberate, because there’s a choice. You can get high intensity or much higher intensity, depending on how This looks just like a standard torch – mainly because we used a standard torch (or two) to house the project(s). The main photo shows a heavy-duty and high quality aluminium torch which turns the lamp on by screwing the lens assembly out (Dick Smith Electronics Cat Y-1103). The inset shows a much cheaper lightweight torch which has a rotary switch to turn it on and off (the blue knob on the end). We can fit the LED assembly into virtually any 2xAA-cell torch, albeit with minor “surgery”. much you want to pay for the LED. More on those choices shortly – and if you want to know more about these devices, see the separate panel “On White LEDs and White Light etc”. The other aspect which makes this project so interesting is the electronics side. Now you’re probably thinking that we mean the usual series resistor which “ordinary” LEDs use to limit current to safe levels. Not so! White LEDs have a minor dilem­ ma – they require a forward voltage of around 3V to 3.5V. Not even two brand new 1.5V batteries in series can deliver enough voltage to light a white LED – and our design uses just one “AA” cell (ergo, 1.5V). The solution? A tiny inverter cir­ cuit inside the torch which steps the 1.5V up to drive the LED at maximum efficiency. This inverter is built on a PC board which is very close to the size of a standard “AA” battery and in fact is designed to take the place of one of the AA cells in a 2-cell torch. Clever, what? We receive a lot of emails (and even some letters too!) here at SILICON CHIP asking for simple, easy-to-build pro-jects which are relatively cheap and above all useful . . . something suitable for everyone from beginners wanting to build their first real project to old-timers (the word used in the most affectionate way!) wishing to keep their irons hot! That’s usually a near impossible wish list. But what we have here is a project which is right up to date, is quite inexpensive and simple to build, unique (we haven’t seen a similar pro­ ject anywhere else) and is very useful. Could you ask for more? The circuit As we said before, driving a white LED is not quite as simple as it would seem, especially from a low voltage. That’s why we have included an inverter to step up the 1.5V from the AA battery to more than 3.5V to drive the LED. The circuit consists of an astable multivibrator (Q1 & Q2) which os­ cillates at around 11kHz, driving a transistor buffer (Q3). This then drives a switchmode boost converter (Q4) which drives the LED. When power is first applied, one of the two transistors in the multivibrator will turn on first. It matters little which one is first but let’s assume Q1 turns on, biased via its 82kΩ base resistor. Q2 will be turned off because as Q1’s collector goes low, the 330pF capacitor will pull Q2’s base low. However, that capacitor now charg­ es (via the 82kΩ resistor) until the point is reached where Q2 receives enough base bias voltage to turn on. Its collector then goes low, pulling Q1’s base low via the .001µF capacitor and therefore turning Q1 off. The .001µF capacitor now starts to charge – and so the process keeps re­ peating for as long as power is applied. The smaller capacitor in Q2’s base (330pF vs .001µF in Q1’s base) means that Q1 will be on for a shorter time than Q2. The result is a continuous series of pulses turning the buffer transistor, Q3, on and off at 11.64kHz, with a duty cycle (or on time to off time) of about 30%. When Q3 is off, Q4 is forward-biased and the inductor in its collector cir­ cuit (L1) is energised. When Q3 turns on, Q4 turns off and the collapsing magnetic field of L1 supplies a pulse of current to the white LED via diode D1, lighting it. This also charges the 4.7µF elec­ trolytic capacitor which effectively smoothes the current “bursts”. With­ out this capacitor, the LED would appear much brighter since the pulse current would be higher. But the LED would also be at risk of destruction as the current peak would be significantly higher than it could withstand. December 2000  15 Fig.1: the circuit diagram of the “works” which drives the ultra-bright white LED from a single AA cell. The three parts of the circuit, labelled here and described in the text, are the multivibrator (based on Q1 & Q2), a buffer (based on Q3) and a switch-mode boost converter (based on Q4). Q4 is turned off for just enough time to discharge the energy in L1 after which it is turned on again. The energy delivered to the LED can be calculated from the formula: Power = L x I PK 2 x f/2      where L is the inductance in Henrys, IPK is the peak inductor current and f is the operating frequency. The peak current is limited by the resistance of L1 (about 3Ω) and the 1Ω resistor in series with Q4’s emitter. As the current rises through the 1Ω resis­ tor the emitter voltage rises, reducing the base drive to Q4. This limits the peak inductor cur­ rent to about 220mA. The first oscilloscope trace (Fig.2 below), shows the base drive to Q4 at the top and the voltage across the 1Ω resistor at the bottom. Note how the current builds up to about 224mA when the base of Q4 is high. You will recall the operating fre­ quency, set by the multivibrator, is about 11kHz while the inductance of L1 is about 220µH. The power delivered to the LED (from the above formula) is about 64mW. Average LED current can be worked out from the formula: I=P/V, where V is the voltage drop across the LED itself (3.4V) plus diode D1 (0.6V), or 4V. Therefore the average LED current is about 64mW/4V, or 16mA. The LED is designed for a maximum average current of 20mA. The second oscilloscope waveform (Fig.3) also shows Q4’s base voltage at top but has the collector voltage at the bottom. This shows that the voltages reaches close to 5V as Q4 is turned off, releasing the charge in the inductor through D1 and LED1. Power for the circuit is delivered by a single 1.5V cell. The circuit will operate to below 1V. It is also protected against the bat­ tery being connected back-to-front, as no current can flow “backwards” Fig.2: the top trace shows the base drive to Q4 while the bottom waveform is the voltage across the 1Ω resistor. The peak current is 224mV/1Ω or 224mA. 16  Silicon Chip through LED1, D1 or any of the transis­ tors because the supply is well below the reverse breakdown voltage of any of these devices. In fact, we deliberately connected the battery back-to-front and measured the current. It was zero – 0.0µA! Incidentally, we mentioned before that the capacitor across the LED was there to protect it. But this capacitor could also be re­ sponsible for damaging or destroying the LED if the circuit was powered up with the LED disconnected, then connected. Without the LED load, the voltage across the capacitor would be very much higher than the LED could handle. If the LED was then connected with the capacitor charged . . . phht – one dead LED. While this is a remote possibility, it could happen if the torch is switched on with the LED disconnected and we have taken steps to prevent this Fig.3: the same trace at top but the lower trace is Q4’s collector voltage. This peaks out at almost 5V – enough to cook the LED without a capacitor across it. happening by hardwiring the LED in position. Construction The white LED torch is actually built inside a . . . torch! We’ll describe the mechanical side a little later but basically, any torch that takes two AA cells will be satisfactory. One of the cells is replaced with a small PC board measuring 49 x 14mm. The components for the inverter need to be assembled on this board so they occupy a space no larger than an AA cell. That means soldering compo­ nents to both sides of the board. Begin, as usual, by ensuring your PC board is correctly etched and agrees with the printed PC board pattern. Normally we insert semiconductors last but in this case, transistors Q1, Q2 and Q3 can be installed first. They are arranged so that they lean towards the centre of the board, at about a 45° angle. The collector leads insert fully into the holes, the base and emitter leads don’t. Solder all leads in and cut the excess off. Now insert the 330pF and .001µF capacitors, as far down as possible onto the PC board. Make sure the tops of these capacitors aren’t any higher than the tops of the transistors. While inserting capacitors, place the 0.1µF and 4.7µF capacitors at the other end of the PC board, again as far down on the board as you can. Note that the 4.7µF tantalum capacitor is polarised. The two 82kΩ and one 10kΩ re­ sistors are mounted next. These are mounted “end on” and laid over at about a 45° angle so they too are lower than the tops of the transistors. Diode D1 can be soldered in next – watch its polarity! Apart from the inductor, which we will look at short­ ly, the only other “component” on the top side of the PC board is a wire link. Because of the proximity of other parts, we suggest that this be a short length of insulated hookup wire. You could use a length of resistor pigtail but we would still be inclined to in­ sulate it – just in case. Fig.4: most of the components are soldered through the PC board in the normal way but there are five soldered on the bottom side, as shown in the lower view at right. Compare these to the photos of the boards below. At the bottom is the same-size PC board artwork. wound a new coil on it, about the right inductance. Of course, this means taking off the old windings; the outer insulation is removed, the primary (outside) layer is unwound, then the fine secondary winding is removed by slicing through the wire with a sharp knife and peeling it off (that’s a lot quicker than unwind­ ing several hundred turns!). The inductor winding consists of 150 turns of 0.16mm enamelled copper wire. Tin one end and solder it to one of the former’s connection points (on the end), then wind on the 150 turns in several layers. The windings don’t need to be side-by-side but try to keep them evenly distributed over the full width of the former. When all the turns are on, cut the wire to a suitable length, tin the end and solder it to the other end of the former. The winding should be pro­ tected by a layer of insulation tape. To help the inductor sit as low as possible on the PC board, we cut a flat section on each of the former’s ends, just clear of the tape covering the winding. Mount the former onto the middle of the PC board and solder the two ends to the board with short lengths of resistor pigtail. You’ll need to take one around the end of the 0.1µF capacitor – make sure it doesn’t short to it. The other side of the board The remaining components, four resistors and transistor Q4, all mount on the copper side of the PC board. You’ll need a soldering iron with a fine point to solder the components to the copper pads. The resistors mount as flat as possi­ ble, with one lead snaking back over the board to connect to the appropri­ The inductor We looked everywhere for a suitable ferrite core and former (ie, small!) for the 220µH inductor (L1) but couldn’t find what we wanted. Eventually, we raided the junk box and found a trig­ ger transformer for a Xenon flashtube. It was about the right size and if we Top and bottom views of the completed PC board, here shown with the LED already solderd in. This board is for the cheaper torch style (ie, one with a separate switch) but the other type is similar – the main difference is that the thumbtack (left end) is connected to the – supply line in the alternate version. December 2000  17 Fig.5: these drawings show how both types of torch are assembled. On the left is the cheaper, switchedtype torch, along with its LED soldered into the bulb base. On the right is the screw-out torch version. On some models of torch the hole in the reflector will be too small to allow the LED to poke through – this will have to be carefully filed out to about 5.5mm. ate place. These leads must be protected against shorting with short lengths of insulation. If you could manage to get hold of some of those really tiny 1/8W resistors, they could almost solder point-topoint on the board. Before you solder in R1, you need to determine how “hard” you want to run the white LED – and therefore how much current you are going to put through it. R1 can be either a 1Ω resistor or a link (ie, 0Ω). The latter will result in a brighter light but at the expense of battery life. Table 1 shows the difference in current: it’s not much but it could be significant with a flattening battery. If you elect to use a link, make sure it (like the resistor lead) is covered with insulation. Finally, solder in Q4, the only transistor which is NOT a BC548. It is mounted so that it bends over at 90° and actually lies flat on the insulation covering R1. Again, a fine-pointed iron will be a necessity to avoid any solder bridges. Choosing the LED There are currently three “brightnesses” of ultra-bright white LEDs available: 1500-2000mcd, 5600-6000mcd and 8000mcd. The more you pay, theoretically, the brighter the LED. But we’ll “led” you in on a little secret: we connected 5600mcd and 8000mcd LEDs to the circuit and measured the output on a very sensitive Minolta lightmeter – and got absolutely identical results (down to 0.1 “f” stops.) So to be honest, we’d stick to 5600mcd LEDs and save a few bob! Connections to the board Remember we said that this PC board replaces one of the AA cells; the board actually takes the place of the cell and it needs connections at each end simular to an AA cell. How do we do this? With a small washer for the + end and a drawing pin (minus the point) for the – end, that’s how! To hold these items in place we use PC stakes. On the positive (washer) end push the two stakes “upside down” through the board (ie, the longer end goes through the board from above) and solder them in position underneath. Cut each stake with sidecutters so that there is 3mm above and below the PC board surfaces and then carefully bend them inwards (towards each other) so they somewhat follow the curve of the 3mm washer. 18  Silicon Chip The washer is placed at the end of the PC board so that it is proud of the edge (see the illustration). It is then sol­ dered to both PC stakes, above and below the PC board. You should have no problems soldering the washer to the stakes as long as it is clean and bright. If it is at all dull (ie, oxidised) it will pay you to polish it first with a piece of fine wet’n’dry paper. The opposite end of the board is similar, except Parts List 1 2 x AA-cell torch (DSE Y1127, Y1103, Jaycar ST3000 or similar) 1 PC board, code 11112001, 49 x 14mm 1 M3 tin plated washer 1 12mm OD plated steel thumb tack 4 PC stakes or 2 PC stakes and 1 20mm length of 1mm tinned copper wire 1 40mm length of 2mm OD insulating sleeving 1 5mm LED bezel 1 100mm length of light duty hookup wire (blue or black) 1 60mm length of light duty hookup wire (yellow) 1 Xenon tube trigger transformer (8mm diameter x 11mm long bobbin) (DSE M-0104 or sim) 1 2.5m length of 0.16mm enamelled copper wire 1 50mm length of 8mm wide insulation tape Semiconductors 1 5mm white LED (LED1) – 1500-2000mCd (DSE Z 3980, Jaycar ZD 1786), or 5600-6000mCd (DSE Z3981, Jaycar Z 1780), or 8000mCd (DSE Z 3982) 3 BC548 NPN transistors (Q1Q3) 1 BC338 NPN transistor (Q4) 1 1N914, 1N4148 switching diode (D1) Capacitors 1 4.7µF low voltage tantalum 1 0.1µF monolithic ceramic 1 .001µF ceramic (5mm OD max) 1 330pF ceramic (5mm OD max) Resistors (0.25W, 1%) 2 82kΩ 1 10kΩ 2 1kΩ 1 220Ω 1 1Ω 5% (or link – see text) Here’s how the LED mounts in the bulb base, the glass bulb having first been (carefully!) removed. The anode (longer) LED lead solders to the contact on the bottom of the lamp base while the cathode bends up and over the lip of the base to be soldered to the edge. On the right is the LED and holder inserted into the torch lamp assembly. that we use a brass (or tin) plated thumbtack, with the convex surface pointing outwards, instead of the washer. First of all, hold the thumb-tack in a pair of pliers and break the pin off with another pair of pliers. Then proceed as before, except that in this case you won’t need to shorten the PC stakes at all – just bend them over towards each other. That completes the assembly of the electronics – but make sure the PC board slides into the torch body you are going to use and, if the torch is metal, that there are no exposed component leads, etc which could short to the case. Fitting to the torch There are two different types of torch and you need to determine which type yours is, because fitting is slightly different. One type has a switch on it, usually switching the negative battery connec­ tion (because the globe end normally contacts the + end of the top battery). The other type has no “switch” as such; the torch is turned on by screw­ ing the globe/lens assembly out. This removes the pressure holding open the battery off the torch end, allowing them to touch and thus turning the torch on. You may know of this torch as a “Mag” brand but there are others with similar switching arrangements. Ours was in fact an “Arlec” brand courtesy of Dick Smith Electronics. We’ll look at the switched-type first. Wiring a switched-type torch We need to break the globe so that the white LED can be mounted inside the metal globe base. Wear safety gog­ gles and break the glass with pliers wrapped in a small piece of cloth. Carefully clean any glass or glue res­ idue from the globe base and remove the excess solder from the bottom so you can see right through the base. Slide a 5mm LED bezel over the LED from the lead end (collar at front) so that the base of the LED sits on the collar. Bend the cathode (shorter lead) 90° so that it emerges from one of the slits in the bezel. Pass the anode lead through the hole in the globe base and push the LED and bezel in so virtually all of the bezel is inside the base. Solder the anode to the bottom of the base and clip off the excess lead. Now bend the cathode lead back down 90°, over the outside edge of the metal base. Centre the LED within the base if necessary then cut the cathode lead off so there is just the tiniest bit over the metal edge – just enough to Capacitor CAPACITOR Codes CODES Resistor Colour Codes         No. 2 1 2 1 1 Value 82kΩ 10kΩ 1kΩ 220Ω 1Ω 4-Band Code (1%) grey red orange brown brown black orange brown brown black red brown red red brown brown brown black gold gold (5%) 5-Band Code (1%) grey red black red brown brown black black red brown brown black black brown brown red red black black brown Value EIA Code IEC Code  4.7µF   4.7µ 475  0.1µF   100n 104  .001µF   1n0 102  330pF   330p 331 December 2000  19 to the LED anode. Solder these two wires respectively to the LED cathode and anode (- and +) positions on the PC board. You can now assemble the torch and give it the “Smoke” test – if it doesn't smoke and the white LED comes on when you turn it on, well done! Wiring a twist-type torch On the left is the standard bulb “as it comes” in the heavy duty torch, without reflector of course. On the right is the LED version – we’ve disassembled the torch to take this photo (for clarity) but you don’t need to do this. That’s fortunate because some torches are very difficult to pull apart! be able to solder the cathode in place. You now have a white LED assembly which is virtually equivalent in size to the original bulb – and one which will fit into the variety of bulb holders used in torches. Hard-wiring the LED Remember we mentioned before that the LED could be damaged if connected across the charged capac­ itor? For this reason, we’ve decided to permanently wire the LED in place – just in case. Place the LED bulb assembly in its torch holder and solder a short (2cm) length of black wire to the LED cath­ ode and a similar length of red wire This type of torch, with its integral reflector, is more efficient than the cheaper “bulb only” torch types. The downside is that it is a bit more tricky to work with. You could disassemble the whole thing but that’s not easy so we took an simpler route. This torch normally uses a globe which has two stiff wire legs which you push into a base (after you screw off the reflector head assembly!). The two contacts in the base normally connect to the torch case (– battery connection) and to the top of the bat­ teries (+ battery connection). We simply short both the base con­ tacts together so they form the “–” connection from the case back to the thumbtack on the PC board, then we solder the cathode (K) lead of the LED to this common point. On white LEDs and white light and colours and Kelvins… The idea of using LEDs for torch lighting is not new – we published a LED torch in February 1994 using a high brightness amber LED. The LED was simply driven via 2-AA cells with suitable current limiting. Even though red, green, yellow and even blue LEDs have been around for a while, white LEDs took a lot longer to become a comm ercial reality. For a long time they tried to make them work by combining the outputs of red, green and blue LEDs to produce white (similar to making white in a TV picture tube). The results were anything but satisfactory. We’re not sure if white LEDs happened exactly this way but hey, why spoil a good story for the facts . . . One day, the white-coated brigade who had been tearing what was left of their hair out over white LEDs looked towards the heavens for inspiration. Instead he/she/they saw the fluorescent tubes in the laboratory ceiling and like Archimedes, shouted “Eureka!” “Why not coat a blue LED with a phosphor, just like in a fluorescent tube,” they thought. Why not indeed? Now just in case you don’t know what happens inside a fluorescent tube, the ultraviolet electrical discharge in the tube makes the phosphors (the white powder inside the tube which goes everywhere when you smash one!) fluoresce, or glow. The result is light – and depending on the type(s) of phosphor, the light can be virtually any colour. If the phosphor produces light over a broad spectrum, the result is white light, more or less. 20  Silicon Chip White light has a “colour temperature”, measured in Kelvins. Low colour temperatures, say from 1500K to 2800K, are reddish to yellowish, such as from candlelight and most incandescent bulbs. The yellowish-white light of a halogen bulb would be about 3000K-3500K while at the top end of the spectrum (5000K and above) it is the bluish-white light of a “daylight” fluorescent tube. Average sunlight (as distinct from daylight) is regarded as having a colour temperature of 4100K.­ “Pure white” light in television is considered to be 6500K; the photographic industry uses 5500K; the printing industry uses 5000K. Part of the reason for different colour temperatures being used as standard is the mechanism by which each of the media produce colours. The overriding aim of all of them is to get skin tones looking as natural as possible because these are the most quickly judged as being “right” or “wrong” to the eye. In the white LED, the phosphor converts the blue light into a wide spectrum white light. Now where have we heard that before? As a bonus, white LEDs produce what is a virtually an ideal light source, because the colours of objects will appear close to what you would see in daylight. White LEDs, by the way, are made from an InGaN (Indium Gallium Nitride) chip (blue LED) which is coated with a YAG (yttrium aluminum garnet), an inorganic phosphor. So now you have a great piece of trivia to drop when the conversation at your next dinner party starts to wane… The anode lead of the LED will be connected via a short length of hookup wire to the appropriate point on the PC board. First of all, proceed with the assem­ bly of the PC board as for the other torch, with one difference: instead of connecting a length of hookup wire to the cathode connection point on the PCB, use a short length of tinned copper wire and solder that to the thumbtack. The anode connection is the same – a short length (say 25mm) of hookup wire. Push the completed PC board as­ sembly through the torch until that short length of hookup wire emerges from the front. You might have to jiggle it around slightly to get it through. Next, discard the globe by pulling it out. Make a small “U” shape from a 10mm length of resistor lead off-cut (or tinned copper wire), just wide enough to push into the two contacts in the base which you just pulled the lamp from (the legs of the “U” about 1.5mm wide). Put that aside for a moment. The LED has a flange moulded on its base which makes it too thick to fit through the hole in the torch reflector, IRECT OMPONENTS COMPONENT 1-9 PRICE 10+ PRICE AXIAL ELECTROLYTIC CAPACITORS 10uF <at> 450 volt $2.60 $2.00 22uF <at> 450 volt $3.35 $2.80 47uF <at> 450 volt $7.44 $6.30 22uF <at> 50 volt $0.55 $0.50 AXIAL POLYESTER CAPACITORS (630V) 1-9 PRICE 10+ PRICE 0.001uF $0.60 $0.50 0.0022uF $0.65 $0.55 0.0047uF $0.65 $0.55 0.01uF $0.70 $0.60 0.022uF $0.85 $0.75 0.033uF $1.40 $1.25 0.047uF $1.55 $1.35 0.1uF $1.70 $1.45 0.22uF $1.85 $1.60 0.47uF $2.50 $2.20 RADIAL POLYESTER CAPACITORS (630V) 1-9 PRICE 10+ PRICE 0.001uF $0.35 $0.32 0.0022uF $0.35 $0.32 0.0047uF $0.35 $0.32 0.01uF $0.38 $0.32 Table 1: Performance Cell Voltage R1=1Ω: 1.5V 1.2V 1.0V R1=0Ω: 1.5V 1.2V 1.0V LED Current 18mA 10mA 5.6mA 21mA 12.5mA 7.3mA Cell Current 120mA 83mA 54mA 130mA 92mA 55mA so this needs to be carefully filed off. Don’t damage the top surface of the LED as you do this. Now remove the U-shaped wire from the base and solder it to the cathode (ie, shorter) lead of the LED, right up close to the body of the LED. The “U” should be centred on the body but en­ sure that it’s not too close to the anode lead, risking a short. Cut off most of the LED anode lead (leave just a couple of mm) and solder the hookup wire emerging from the front of the torch to the anode. Ensure that you haven’t shorted out anode and cathode in the process. Push the U-shaped wire and white LED all the way into the holes in the lamp base. Obviously, the anode connecting wire goes back down into the torch 0.022uF $0.42 $0.38 0.033uF $0.65 $0.55 0.047uF $0.65 $0.55 0.1uF $0.90 $0.80 0.22uF $1.00 $0.90 0.47uF $1.25 $1.10 RADIAL ELECTROLYTIC CAPACITORS (16V) 1-9 PRICE 10+ PRICE 1uF $0.26 $0.22 2.2uF $0.26 $0.22 3.3uF $0.26 $0.22 4.7uF $0.28 $0.24 10uF $0.30 $0.26 22uF $0.32 $0.28 33uF $0.35 $0.28 47uF $0.38 $0.30 100uF $0.38 $0.30 220uF $0.40 $0.32 330uF $0.50 $0.45 470uF $0.55 $0.50 1000uF $0.70 $0.55 2200uF $0.90 $0.70 3300uF $1.35 $1.10 4700uF $1.50 $1.20 RADIAL ELECTROLYTIC CAPACITORS (25V) 1-9 PRICE 10+ PRICE 4.7uF $0.22 $0.18 10uF $0.22 $0.18 22uF $0.22 $0.18 33uF $0.33 $0.26 47uF $0.38 $0.30 100uF $0.42 $0.32 220uF $0.55 $0.45 330uF $0.60 $0.50 body – but check that it doesn’t foul anything as it goes and check once again that nothing shorts! Before final assembly, test the torch by putting in an AA cell and screwing on the back. With the connection now made between the LED cathode and the torch body, the LED should light. If it doesn’t, remove the PC board and check your wiring and compo­ nent placement. If it is necessary to work on the PC board out of the case, temporarily solder any standard LED across the anode and cathode points on the PC board, rather than trying to make contact with your white LED. Assuming all is well, fix the white LED in place with a dollop of neutral cure silicone sealant, hot melt glue, or other adhesive. Then carefully screw the reflector assembly back on, ensuring the LED comes through the hole in the middle. You may need to remove the assembly and reposition the LED slightly if the alignment isn't spot on. You can adjust the focus (wide or spot) by the position of the reflector with respect to the LED. Screwing the reflector all the way in should turn the torch off. SC 470uF $0.65 $0.52 1000uF $0.90 $0.70 2200uF $1.30 $1.00 3300uF $1.85 $1.45 4700uF $2.60 $2.00 RADIAL ELECTROLYTIC CAPACITORS (50V) 1-9 PRICE 10+ PRICE 10uF $0.22 $0.18 22uF $0.22 $0.18 33uF $0.38 $0.30 47uF $0.38 $0.30 100uF $0.60 $0.50 220uF $0.75 $0.60 330uF $0.80 $0.70 470uF $1.20 $1.00 1000uF $1.50 $1.20 2200uF $2.80 $2.00 4700uF $4.30 $3.75 MAINS CABLE – BROWN COTTON COVERED Per mtr 1-9 PRICE 10+ PRICE $2.80 $2.20 DIAL CORD – 0.6mm Per mtr 1-9 PRICE 10+ PRICE $0.75 $0.50 24-hour online ordering: www.direct-components.com Fax: (08) 9479 4417 Email: capacitor<at>bigpond.com Snail mail: PO Box 437, Welshpool, WA 6986 Aust. Post – $0-50 = $5.00; $51-100 = $7.50; $101-500 = $9.50 Air Express: <3kg = $11.00; 3-5kg = $16 ABN: 70-032-497-512 December 2000  21