I knew I was going to be a Mad Scientist for Halloween this year and I wanted a cool prop for my laboratory (aka garage work bench). As an electrical engineer, I was always fascinated by the electric “Jacob’s Ladder” displays (or, more accurately, high voltage traveling arc). It really is the definitive mad scientist accessory, even though it really serves no (mad) scientific purpose other than demonstrating how high voltage can ionize air and jump large gaps. However, the rapidly rising white hot plasma and its buzzing and crackling sound cannot be beat. I looked into making one but several factors prevented me from doing so:
- High voltage is very dangerous and I have a tendency to shock myself – the combination could be deadly
- Sourcing the parts – I imagine I could get some old HV transformers from a surplus shop or eBay, but I wasn’t sure what I needed
- Exposed spark discharges – I could build it in a transparent box (safer, more $$$), but then the sound would probably be diminished
- Children – this would be on display for Halloween and kids like to look with their hands and not only with their eyes
I really wanted to make one but the above reasons kept steering me away. Then, right about the same time I was giving up on the idea, I stumbled upon this: SparkFun EL Sequencer. Watching the video of those wires flickering and flashing gave me an idea – what if I use electroluminescent wire and that sequencer to simulate the sparks and make a safe(r) “Jacob’s Ladder?” Another timely coincidence occurred after I started thinking up the design of my EL Ladder – I saw this update from the bildr.org Twitter feed: “Have an awesome idea for a project? bildr wants to help fund it and then showcase it on the site.” How could I pass up that offer? Awesome project idea in hand, I contacted bildr with my submission:
My project involves creating an electronic art simulation of a Jacob’s Ladder/High-Voltage Climbing Arc for a Halloween Mad Scientist display. These are the crackling and climbing electrical spark devices that are typically shown in mad scientist labs in movies/TV shows. The actual devices consist of a high-voltage transformer and a diverging set of conductors. The electrical potential is applied across the two conductors and, due to the high voltage present, causes a dielectric breakdown in the air gap between them, resulting in a visual spark discharge. The ionized and heated air rises and carries the current path up the conductors until it reaches the top where they diverge and the discharge is broken. Although the visual and audible properties of these devices provide a dramatic effect, the implementation is actually rather dangerous, especially if the unit is not contained within an enclosure.
My idea is to use electroluminescent wire (like thin, flexible neon) with the appropriate power supply/driver and sequencing circuitry to simulate the effect of the high-voltage climbing arc. Diverging “V” metal rods would be connected to a base (some sort of plastic/metal project box) which would hold the electronics while different lengths of the EL wire would be strung between the rods. The sequencing circuitry would simulate the effect of the climbing arc by sequencing the wires on and off as they go up in the proper order. Also, the circuitry would apply some pulse-width modulation (PWM) on the EL wire drive to make them flicker and dim in/out to increase the realism of the simulation. This project would still create a dramatic visual effect and, combined with a simple audio loop of an actual climbing arc timed to the sequencing (using a cheap single-chip audio recorder, like from a greeting card), would result in a cool Halloween display that would be much safer to operate.
Thanks for the consideration!
Adam with the bildr.org team loved the idea and had me submit the list of components (see below) I would need to build the project. After the budget was approved, Adam graciously sent me the money to cover it via PayPal. Time to get ordering and to building this thing…
My bildr.org submission does a good job laying out the concept for the project, but the way I envisioned it was that the EL wire would simulate the sparks jumping across the gap between the conductive rods, only in my case the rods could be really anything, but I wanted something hollow to run the wires down. A sequencer would turn on/off/fade in/out each wire on the way up to simulate the climbing arc. Since the wire is basically silent and won’t crackle and snap like a real arc, I would have something play back the sound of an actual climbing arc and have the audio synchronized to the light sequence. Wrap it all up in a box with a motion sensor (’cause it’s Halloween and everything needs to have a motion sensor, right?) and you’ve got yourself an Electroluminescent Jacob’s Ladder.
Here are the main components that I finally settled on for the project:
- SparkFun EL Sequencer – uses Triacs to switch individual strands on or off from a single EL driver
- EL Driver – SparkFun recommended this one from Coolight.com so I went with it. Generates >100VAC @ 2kHz from 3-5VDC
- EL Wire – 2.3mm White Electroluminescent wire from Coolight.com, a great EL source run by Burners
- Arduino USB main board – to be used with the WaveShield to produce the audio
- WaveShield – Awesome Arduino shield from Adafruit enables WAV file playback off of an SD card (better than my initial concept of a recordable greeting card)
- 8Ω Speaker for the WaveShield
- PIR Sensor – Simple 5V digital Passive InfraRed sensor from Adafruit to detect motion to turn on the sparks
- PEX Tubing – This served as the “rods” between which the EL strands were strung. The piece I got from the hardware store was already slightly curved, so it worked out well for the divergence after I cut it in half.
- JST connectors to plug into the Sequencer, misc wire (salvaged from an unused 2-pair phone cord, ~26AWG) and heat shrink to keep the fragile solder joints to the EL wire safe.
- Box – after struggling to find the perfect box for this (which would have to be modified with holes for the tubing, etc.) I decided just to make one out of LEGO bricks. There are so many LEGOs in my house it is ridiculous. I was spoiled as a child, what can I say?
Some of the components were ready to go (sequencer, driver, Arduino, PIR) but others had to be built first. I started with the WaveShield since that came as a kit and the build instructions are very well documented. That simple task out of the way, I needed to experiment with the EL wire to figure out just how to wire it up. First, I measured the distance between the rods as I wanted them mounted and cut 8 lengths of EL wire.
Next I needed to attach wires to each strand. As you can see from the second picture, the EL wire has a solid copper core which is coated in a phosphor and two very very fine wires spiral around this core. The core and wires are covered with one transparent sheath while another, thicker transparent tube serves as a light diffuser. To get to the bare wire, you need to first strip back the thicker part then carefully strip back the inner sheath without tearing the thin wires off. Several inches of EL wire were destroyed during this process until I figured out a technique – use your strippers (22AWG I believe) to cut all around the inner sheath but don’t pull it off with the strippers like you may do with other solid wire. Instead, once it is all cut around the circumference, use needle nose pliers to pull the cut sheath off at the end. Using this method I had very little to no further destroyed wires (well, except when I would be too rough with them while soldering). Once the center phosphor-coated wire and the thin, hair-like spiraling wires are exposed, separate the two, carefully twist the thin wires together and scrape off some of the phosphor coating on the center wire. Solder wires to both conductors of the EL wire making sure they don’t overlap and short out when we cover them with shrink wrap. Here is a picture of a strand all wired up with shrink wrap. The adhesive in the shrink wrap does a nice job of oozing out and really securing everything in place. Trust me when I tell you that the thin wires will break with very little force – you must protect that solder joint or it will break. Electrical tape will not do the job. I repeated this process for all 8 strands.
Next up was to modify the tubing. I measured every few inches and alternated poking small and large holes in the tubing. I did this so each tube only had 4 EL strands and the associated wiring inside it. The bigger holes allowed me to insert the shrink-wrapped side in while the other end of each EL wire strand poked into the smaller holes on the opposite rod. A nice coat of silver spray paint and they almost look metallic! All that was left to do with the tubes was to insert each EL strand in, run the wires down, and bring the two rods together. Once the wires were run down the rods, the jumpers with JST connectors were soldered on so all the EL strands could be easily plugged into the EL Sequencer.
We’ve got all the parts built, now we need a box to enclose the electronics and support the rods with the EL strands. As I mentioned above, I really wasn’t sure what sort of enclosure to get, either something like a metal Bud Box or just a plastic project box from Radio Shack. Then I started thinking – “I have all these LEGOs, why don’t I just build a box?” As you can see from the next several pictures, I did just that, using black bricks. I also used several of the weighted pieces you get with the boat or train sets to give the base extra weight since the rods were so much taller. The EL Sequencer was mounted under the top lid which has two openings for the rods. The diameter of that tubing is perfect for a 2×2 opening in the LEGOs. The rods get pushed down into those white pieces (don’t really know what to call them, but they have cut outs on the sides which I used to pass the wires through from the rods to the EL Sequencer) which keep them from going any further – you can see this in the side view of the top assembly. I made a compartment for the Arduino+WaveShield and included a hole in the back for the power plug. The EL driver sits in the area on the side of that compartment while the speaker is held in place against the front of the box where I used Technic pieces with holes. Finally, the PIR sensor is also mounted in the front and held in place by additional bricks.
With the box built, the next step was to use the wire jumpers with JST connectors to connect the EL Sequencer to the EL strands and the EL Driver (HV white wires to the Output connector on the EL Sequencer and Red/Black power input wires to the Power connector). As you can see in the picture of the Sequencer, I put a jumper in connecting the + BATT terminal to the + Power terminal for the EL Driver. I did this because I wanted to use one supply for the whole system. A 9V AC-to-DC adapter powers the Arduino, which has a nice 5V regulator on it to power its components as well as the WaveShield. I ran 5V and Ground (with another of those JST jumpers) from the WaveShield to the BATT connector on the EL Sequencer to power it and the EL Driver with 5V. The PIR sensor also connects to the EL Sequencer via the “Analog” connection which again feeds the 5V/GND and provides access to I/O pins on the ATmega328. I used one of the analog inputs as a digital input since the PIR has a digital HIGH/LOW output. I check the state of that in software to see when motion has been detected. Finally, another wire connects between the WaveShield and the Analog connection on the EL Sequencer to serve as a trigger to the WaveShield to synchronize the audio output of the climbing arc sound when the PIR triggers the EL light sequence. Here is the EL Ladder Code used for the ATmegas. I used the wavehc library for the Arduino board to work with the WaveShield. The only thing I modified from the daphc example code was to add a trigger input from the EL Sequencer. I based the code for the EL Sequencer on the SparkFun EL Escudo Arduino library. I used the Fade functions to better simulate the motion of the climbing arc as I sequenced each of the EL strands on and off on the way up. I also added the input for the PIR and the trigger output for the WaveShield. Since I needed to adjust the fade and sequence timings from the defaults in the EL Escudo library, I just pulled all the definitions from the library files into a single .pde file. Finally, to program the EL Sequencer, I soldered a 0.1″ header on the board where it says “USB” and used an FTDI Basic Breakout board to program it using the Arduino IDE (Target Board: “Arduino Pro or Pro Mini (3.3V, 8MHz) w/ ATmega328″). These last two pictures show the whole display buttoned up and on my Mad Scientist work bench in our garage. The picture without the flash (slow shutter speed) captured the top three strands illuminated.
Every project needs videos showing it off, so without further delay, here are some short videos showing off the sequencing of the EL wire synchronized with the audio. Note: the first video was recorded with an iPhone, and I forgot to turn it sideways so it looks a little weird. The other three were recorded with a Kodak ZX1. I actually think the iPhone did a better job!
I am really happy with how the project turned out and I think I was able to implement my initial concept fairly well. In the dark the display is quite convincing, especially with the audio. It still doesn’t quite have the same feel or effect as from real electric sparks, but it still looks really cool alongside my other plasma displays. I got lots of “ooohs” and “ahhhs” and “where did you get that from?” on Halloween, which made it all worth while. I searched around and I think this is the first “Jacob’s Ladder” display created using EL wire. Sweet! I learned a lot about using and implementing the EL wire and really had fun putting it all together and seeing it work. I thought the software development portion would be time consuming, but the example code and libraries provided made it really simple. I just had to tweak it until the timing was right. I wanted to give another shout out and thanks to Adam with bildr.org for helping make this project a reality by funding the component purchases. Thanks for checking it out!