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New! Improved! More Zap for your Shekels . . . Build this JACOB’’ S LA This Jacob’s Ladder looks and sounds spectacular and is quite easy to build. As the high voltage sparks climb up the vertical wires they snap and snarl, almost as a warning for you to keep your distance! It even smells bad, as the purplish discharge generates ozone. Never mind the photo, SEE and HEAR how the Jacobs’ Ladder performs by logging on to our website at siliconchip.com.au/videos/ jacobsladder. This short video clip shows how the spark climbs up the wires to the point where it is extinguished and then it starts again at the bottom to repeat the process. It makes quite a lot of noise and does generate ozone. Mind you, while you might expect that it would generate lots of RF interference to radio reception, in practice it does not appear to be a problem, unless you have a radio in very close proximity to the unit when it is operating. 60  S 60   60   S Silicon iliconCChip hip W e described our last Jacob’s Ladder project in the April 2007 and it is still a popular project. But when we recently presented the new High Energy Ignition Module in the November & December 2012 issues, we realised that it would make an ideal Jacob’s Ladder driver and that it should have even more zing and zap than the April 2007 design. And so it has proved to be. By the way, we are aware that there are a number of mains-power Jacob’s Ladder circuits on the internet. These are very dangerous and could easily be lethal. Don’t even consider building one of those. Build ours. That’s not to say you won’t get a helluva belt off ours if you’re silly enough to touch the bitey bits when it’s running. But at least you’ll be able to learn from your mistake – you may not get that chance with a mains-powered type. Ignition module variant In essence, the Jacob’s Ladder presented here is a slight variation on the version which can be used as a self-contained ignition coil tester. Its frequency can be varied up to 75 sparks per second and the “dwell” setting can be used to vary the timing to obtain the best sparks, ie, the noisiest and most nasty! Now we are are not going to reproduce all the information on the High Energy Ignition module – if you want to read that you should refer to the November and December 2012 issues. Instead, we will give all the information which is relevant to this particular variant. So let’s have a look at the circuit of Fig.1. Microcontroller IC1 is the heart of the circuit. It drives the gate of the IGBT (insulated gate bipolar transistor), Q1. These IGBTs are used by the squillion in the ignition system of modern cars. This type of IGBT is a big improvement on the high voltage transistors used in our previous ignition systems and it can be driven directly from the output of the microcontroller via a 1kΩ resistor from pin 9 (RB3). As a result, the circuit is more efficient and very little power is dissipated. In operation, IC1’s RB3 output is alternatively switched high (to +5V) and low to turn Q1 on and off. Each time Q1 is turned on, the current builds up in the primary winding of the coil and this stores energy in the resulting magnetic field. This magnetic field collapses when when Q1 turns off and it induces a very large voltage in the secondary winding, to fire the spark plug, or in our case, to cause a big spark to jump siliconchip.com.au What is a Jacob’s Ladder? By LEO SIMPSON Jacob’s Ladder has its origins in three major religions – Christianity, Judaism and Muslim (we try to please all readers . . .). Jacob, the son of Abraham, dreamed about a “ladder” between earth and heaven with angels climbing up and down. Some references have this ladder made from flames and sparks – hence the electronic version doing the same thing. OK, no flames – but plenty of mean-sounding sparks! Physically, as our photos show, it has two parallel (or near-parallel) metal rods about 300mm long and about 30mm apart, which have such a high voltage between them that sparks jump from one to the other. As the spark is hot, the surrounding air is heated. Hot air rises, so the column of rising air pushes the sparks upward so that they appear to form the “rungs” of a ladder. ADDER across the high voltage terminals of the ignition coil. Incidentally, in the past, most ignition coils have been auto-transformers meaning that the primary and secondary windings are connected together at one end. However, many modern ignition coils are true transformers, with completely separate primary and secondary windings. The particular ignition coil we are using for the Jacob’s Ladder is from a VS series Holden Commodore. These can usually be purchased from a wrecker or via ebay (which is where we got ours). We paid $27.50 including postage. Apart from being a readily available high energy ignition coil, the Commodore unit has a further advantage in that it has two high voltage terminals and these normally drive two spark plugs in series when used in the Commodore V6 engine. In our case, the two high-voltage terminals make it very suitable for a Jacob’s Ladder. Just connect a stiff wire to each terminal and it’s done. Now back to the circuit description. In operation, IC1 monitors two separate voltages, at pin 1 & 18. REG1 LM2940CT-5 +5V OUT 100F 100nF 100nF 2 14 Vdd 3 AN2/RA2 RB7/AN6 RA3 RA0 RA4 RB1 18 AN1/RA1 RB4 100nF X1 4.0MHz 13 17 F1 10A FAST BLOW 7 22pF RB3 RB6 6 RB0 RB2 9 12 EHT COIL C OSC1 22pF 12V BATTERY 10 IC1 PIC16F88 15 11 RB5 OSC2 -E/P 16 NOTE: SEPARATE LEAD FROM COIL PRIMARY TO BATTERY POSITIVE 13.6V TVS DWELL VR1 10k +12V 1000F 25V GND 4 1 10 +12V IN 1k MCLR FREQUENCY VR2 10k The dwell period and spark rate are set by trimpots VR1 and VR2, each connected across the 5V supply. VR1 (dwell) is monitored by input AN1 (pin 18), while VR2 (frequency) is monitored by input AN2 (pin 1). The dwell is adjustable from 129µs to 26ms and is set by monitoring the voltage at TP1. However, this is not necessary. In practice, you simply tweak VR1 to give the “hottest” (ie, best looking!) spark discharge. We are using the coil/spark test mode of the software for the High Energy Ignition module. In the original circuit (November 2012) this was selected 1k G Q1 ISL9V5036P3 (IGBT) SPARK GAP: CAUTION: THIS WILL BITE! COMMODORE IGNITION COIL E 8 Vss GND 5 LM2940CT-5 ISL9V5036P3 SC 2013 JACOB'S LADDEr Fig.1: the circuit incorporates additional components to protect the regulator against peak voltages which are superimposed on the positive supply line from the battery. siliconchip.com.au C G C GND IN E GND OUT February 2013  61 This scope grab shows the Jacob’s Ladder circuit running at 76 sparks/second and a sweep speed of 5ms/div. The yellow trace shows the high voltages (around 400V peak) at the collector of the IGBT, while the green trace shows the fluctuation on the positive battery rail. The blue trace is the voltage across the transient voltage suppressor (TVS), showing that it is doing its job of protecting the regulator. 62  Silicon Chip REG1 LM2940 +5V 100F TVS VR1 10k DWELL project and will not only give a long operation time, it can be disconnected and recharged for the next zap! For longest life you could run this from a 12V car battery but they are rather heavy and difficult to lug around. And they can be messy. Building it The Jacob’s Ladder module is built on the same PCB as the ignition system, coded 05110121 and measuring 89 x 53mm. This is housed in a 111 x 60 x 30mm diecast aluminium case to give a rugged assembly. A cable gland at one of the case provides the cable entry points for the positive and negative leads from the 12V battery and the lead from the IGBT’s collector to one of the primary connections on the Commodore ignition coil. There are significantly less components required for the Jacob’s Ladder; WIRE LINK +12V 10 4MHz TO 12V BATTERY + X1 IC1 GND PIC16F88 COIL 100nF WIRE LINKS Q1 ISL9V5036P3 (UNDER) 1k TO 12V BATTERY – TO COIL PRIMARY – (COIL PRIMARY + CONNECTS DIRECTLY TO BATTERY + VIA A 10A FAST-BLOW FUSE) 1k IGNITION 12 05110121 101150 C 2012 22pF 1000F 22pF Fig.2: the Jacob’s Ladder circuit uses the electronic ignition PCB (from November 2012) but as you can see, significantly fewer components are required (hence the empty holes). Note the wiring connection for the + side of the coil primary; it connects directly to the CASE/ battery + terminal via CHASSIS a fuse. Don’t be tempted to run the PCB wiring from this fuse. Keep the wiring separate. suppressor (TVS). It clamps transient voltages to around 23V, a safe level for the regulator. As well, we have included a 1000µF 25V capacitor to provide further filtering for the input to the regulator. Even so, it is most important that the +12V line to the module must be a separate wire to the battery positive terminal, as shown on the circuit. We have added these components after twice blowing the regulator and the microcontroller while having fun (um, doing important research) with our prototype Jacob’s Ladder. REG1 also has a 100µF filter capacitor at its output, required for stable operation. By the way, note that word “battery”. Don’t even think about running this from a mains supply. A 12V SLA (sealed lead-acid) battery, as shown in the first photograph, is perfect for this 100nF with LK2 (connected to pin 12 of IC1). Since we don’t need link options, the Jacob’s Ladder version of the circuit merely has pin 12 connected to 0V, to achieve the same outcome. Trimpot VR2 is used to set the spark rate, with a range of 15-75Hz (clockwise for increased frequency). IC1 is powered from a regulated 5V supply derived using REG1, an LM2940CT-5 low-dropout regulator designed specifically for automotive use. It features both transient overvoltage and input polarity protection. H o w e v e r, e v e n t h o u g h t h e LM2940CT-5 is a rugged regulator, it needs protection from the very high transient voltages which can be superimposed on the +12V line from the battery. Hence, we have incorporated extra protection with the 10Ω series resistor and the 13.6V transient voltage This shows the same waveforms as Scope1 but with the sweep speed slowed to 50ms/div. This capatures more of the spike voltages on the supply lines. Without the input protection components, these spike voltages would be a great deal higher and would damage the regulator. Note that the spike voltages differ because each spark discharge takes a different path across the gap. VR2 10k FREQUENCY siliconchip.com.au Again, same waveforms as before but with sweep speed upped to 200µs/div. Here see the ringing of the coil primary after the main spike. The voltage is clipped to 413V by the protection limiting inside the IGBT. hence large areas of the PCB are unpopulated. The first step is to check the PCB for any defects and in the unlikely case that there are any defects, fix them. Then install the components shown in the diagram of Fig.2. If you are using a PCB supplied by SILICON CHIP, Altronics or Jaycar you will find that some of the components to be installed are Same conditions as the grab at left but with sweep speed upped again to 20µs/div. Here we see that the spike voltages across the supply lines are very fast and both are actually clipped by the scope. not as indicated on the silk-screened component layout on the top of the PCB itself. For example, the red wire from the positive terminal of the battery does not connect to the +12V pin at the top right-hand corner of the PCB. Instead it connects to the PC pin marked “Tacho” which is not being used for its original function in this Jacob’s Ladder version of the circuit. We will detail the other component variations as we go through the assembly procedure. Begin the assembly by installing the four PC stakes at the external wiring points, ie, Tacho, GND, COIL, and TP GND. Then install three short wire links. One goes in the position labelled LK2 at one end of the microcontroller, another is wired in the position for the For the Jacob’s Ladder, there are several differences in component placement to those for the electronic ignition. Follow the component overlay diagram at left and this photo rather than the (white) silk-screen component overlay printed on the PCB. siliconchip.com.au February 2013  63 M3 x 5mm SCREWS INSULATING BUSH PCB M3 NUT M3 x 6.3mm TAPPED NYLON SPACERS Q1 2 x TO-220 SILICONE INSULATING WASHERS M3 x 10mm SCREW M3 x 5mm SCREWS The completed Jacob’s Ladder in daylight, showing which bits connect to where! All the circuitry is inside the metal box, with the Holden Commodore twin ignition coil mounted on top, spaced above the box by about 15mm with the aid of a pair of precision (Coke bottle cap) spacers. These are needed to allow the wires from the circuit to connect via spade lugs under the coil. Using crocodile clips on the coil terminals allows a great deal of flexibility when positioning the vertical (spark) wires, for best visual effect. 64  Silicon Chip Fig.3: here’s how the IGBT is mounted underneath the PCB. 6.3mm Nylon spacers hold the PCB at the right height and also insulate it from the case. Two silicone insulating washers are used to insulate the IGBT from the case. 1nF capacitor adjacent to the pins 5, 6 & 7 (of the microcontroller) while the third replaces the 10µF capacitor near the original “TACHO” PC stake. These can followed by the three resistors. Follow with the IC socket, making sure it is orientated correctly but don’t install the PIC micro yet. The capacitors can go in next. Orientate the two electrolytics as shown) then install crystal X1 and trimpots VR1 & VR2. The TVS can be installed either way around as it is not a polarised device. Regulator REG1 can then go in. Be sure to fasten REG1’s tab to the PCB using an M3 x 10mm machine screw and nut before soldering its leads. IGBT mounting details Fig.3 shows the mounting details for IGBT transistor Q1. It’s secured to the base of the case, with its leads bent at right angles and passing up through the underside of the PCB. For the time being, simply bend Q1’s leads upwards through 90° and test fit it to the PCB but don’t solder its leads yet. Its tab mounting hole must be clear of the edge of the PCB, as shown in the diagrams. Then fit the PCB assembly inside the case and slide it to the left as far it will go, to leave room for Q1. The mounting hole positions for the PCB and Q1’s tab can then be marked inside the case, after which the PCB can be removed and the holes drilled to 3mm (hint: use a small pilot drill first). Deburr these holes using an oversize drill. In particular, Q1’s mounting hole must be slightly countersunk inside the case to completely remove any sharp edges. The transistor’s mounting area on the case should also be carefully smoothed using fine emery paper. These measures are necessary to prevent the insulating washers which go between Q1’s metal tab and the case from being punctured by metal swarf or by a high-voltage arc during operation. Having drilled the base, the next step is to mark out and drill the hole in the case for the cable gland. This hole is centrally located the end of the case at which the IGBT is mounted. It should be carefully reamed to size so that the cable gland is a close fit. You will also have to drill a 3mm hole for the earth connection in the other end of the case – see photos. Installing the PCB Once the case has been drilled, fit 6.3mm tapped Nylon stand-offs to the PCB’s corner mounting holes using M3 x 5mm machine screws. That done, the next step is to fasten Q1 in place. As shown in Fig.3, its metal tab is insulated from the case using two TO-220 silicone washers and an insulating bush and it’s secured using an M3 x 10mm screw and nut. Do this screw up finger-tight, then install the PCB in the case with Q1’s leads passing up through their respective mounting holes. The PCB can now be secured in place using four more M3 x 5mm machine screws, after which you can firmly tighten Q1’s mounting screw (make sure the tab remains centred on the insulating washers). Finally, use your multimeter to confirm that Q1’s tab is indeed isolated from the metal case (you must get an open-circuit reading), then solder its leads to the pads on top of the PCB. External wiring All that remains now is to run the external wiring. You will need to run three leads through the cable gland siliconchip.com.au and solder them to the relevant PC stakes for the power, coil and input trigger connections. Don’t be tempted to use mains cable for the three leads – brown, blue and green/yellow should never be used for anything but mains. The earth connection from the PCB goes to an solder lug that’s secured to the case using an M3 x 10mm screw, nut and star washer. Initial checks & adjustments Now for an initial smoke test – apply power to the unit (between +12V and GND) and use your DMM to check the voltage between the +5V PC stake and GND. It should measure between 4.85V and 5.25V. If so, switch off and insert the programmed PIC (IC1) into its socket, making sure it goes in the right way around. You can now do some more tests by connecting the car’s ignition coil between the +12V battery terminal via a 10A in-line fuse. The unit should be powered from a 12V car or motorcycle battery or a sealed lead acid battery, NOT from a mains power supply. The negative coil wire (shown in blue on the diagram) connects to the “coil” terminal on the PCB. Before connecting the +12V power, set the dwell trimpot (VR1) fully anticlockwise. Then apply power and slowly adjust VR1 clockwise. The sparks should start and gradually increase in energy with increased dwell. Stop adjusting VR1 when the spark energy reaches its maximum. You can also set the spark frequency using VR2 but we found the best result was with it set to maximum, ie, clockwise. Mounting the Commodore ignition coil We mounted the Commodore ignition coil onto the lid of the case using two M3 bolts and nuts. Since the two primary connection are recessed underneath the coil, we had to space it off the lid of the case and we used two PET soft drink bottle lids for this. Brand is unimportant – just make sure you don’t use metal caps! We made the connections to the coil primary with red crimped male spade connectors (Jaycar PT-4518). Finally, we fitted a pair of crocodile clips with screws (Jaycar HM-3025) with stiff wire, about 250mm long. You can dispense with the plastic siliconchip.com.au finger grips since the sparks jump between the crocodile clips and then climb the wires. Note how the clips fasten to the coil terminals in our photos – if you mount them the other way (ie, with the bodies closer together) you’ll probably find that the sparks jump across the crocodile clips but don’t climb up the wires. In fact, you’ll probably have to experiment somewhat with the wire positions to get the climbing action reliable. We found that very close to parallel was right. We also bent the top 10mm or so of the wires away from the ladder, as you can also clearly see in the pic. Want to use taller wires? Give it a go – but if they are too tall it becomes unwieldy. Fitting a “chimney” We also experimented with a clear plastic (acrylic?) tube over the whole ladder. This has the added advantage of creating a vertical airflow as the air inside the tube heats up. This adds to the rising spark effect. The biggest problem was finding a clear tube (a) big enough – it needs to be about 150mm inside diameter and (b) cheap enough to warrant its use. In the end, being somewhat tight in both the wallet and time departments, we gave the idea away! However, if you can find such a tube it will add to the spectacle and should also assist the spark if there is any form of breeze. We found wind impedes the climbing effect. The tube needs to be open-ended top and bottom to create the draught. An acrylic tube will also assist somewhat in keeping the zaps contained – but don’t rely on it! A thick acrylic tube should have hundreds of kilovolts of insulation but you can never be sure. The moral of the story is, keep your fingers (and anyone else’s!) away from the vertical wires. Before making any adjustments – moving the wires for a better display, for example – disconnect the battery and make sure gravity or any other force cannot accidentally make a connection when you don’t want it to! As we said earlier, accidentally touching the wires while in operation (why would anyone touch them deliberately?!!) will certainly give you some energy you didn’t know you had – and may even (perish the thought!) cause you to issue forth with naughty words! Parts list – Jacob’s Ladder 1 VS Commodore ignition coil (source from a wrecker or ebay) 1 PCB, code 05110121, 89 x 53mm 1 diecast aluminium case, 111 x 60 x 30mm (Jaycar HB5062) 1 cable gland to suit 3-6mm cable 1 transistor insulating bush 2 TO-220 3kV silicone insulating washers (Jaycar, Altronics) 1 4MHz HC-49 crystal (X1) 1 18-pin DIL IC socket 1 in-line 3AG fuse holder and 10A 3AG fuse (fast-blow) 1 solder lug 2 crocodile clips with screws (Jaycar HM-3205) 2 250mm lengths approx. 1.5mm diameter steel wire 2 red crimp spade lugs (Jaycar PT4518) 4 6.3mm tapped Nylon standoffs 8 M3 x 5mm screws 3 M3 x 10mm screws and nuts 2 M3 x 30mm screws and nuts 1 M3 star washer 4 PC stakes 1 500mm length of red automotive wire 1 200mm length of black automotive wire 1 200mm length of blue automotive wire Semiconductors 1 PIC16F88-E/P microcontroller programmed with 0511012A.hex (IC1) 1 ISL9V5036P3 ignition IGBT (Q1) (X-On; x-on.com.au) 1 LM2940CT-5 low drop out 5V regulator (REG1) (Altronics Z0592, Jaycar ZV1560) 1 13.6V transient voltage suppressor (TVS) (Jaycar ZR-1175) Capacitors 1 1000µF 25V PC electrolytic 1 100µF 16V PC electrolytic 3 100nF MKT (code: 104) 2 22pF ceramic (code: 22) Resistors (0.25W 1%) 2 1kΩ (code: brown black black brown or brown black red brown) 1 10Ω (code: brown black black gold brown or brown black black brown) 2 10kΩ mini horizontal trimpots (VR1,VR2) SC February 2013  65