Sunday, October 27, 2013

EL Wire Animation

EL Wire Animation

Here is a video of an animation I did using electro-luminescent (EL) wire. For those of you who aren't familiar with EL technology, it uses a coating that phosphoresces, when excited by a high voltage, low amperage alternating current. It can be used like "neon" tubing, but is flexible, and does not get hot. It comes in an assortment of colors, and is relatively easy to work with.

The video shows the animation just after it is turned on. It starts out "asleep" with the eyes closed. After a few seconds it "wakes up". The eyes open, tentatively at first, and blink occasionally, at random intervals. The device has a proximity sensor that can tell if someone is close to it. After a few minutes, if no one is standing close, it "goes to sleep", with the eyelids becoming progressively heavier, and finally closing. If someone approaches it again "wakes up". If, after it has gone to sleep, no one approaches for several minutes, it turns the electronics off completely. Thank you Ayako for being the model for these eyes.


EL material is actually readily available in three form factors, wire, ribbon, and sheet. You may have seen the sheet material built into night lights. These have a panel, a couple of inches square, that glows, usually blue or green, when plugged into an outlet. As I said above, in order to make it glow, the material must be energized with alternating current, usually in the range of 100-150V and a frequency of a couple of thousand hertz. Producing this is a little more complicated than just slapping a 9V battery into a circuit like one might do in a conventional microcontroller project. Luckily, inverters that handle the conversion from battery or mains power are are readily and inexpensively available.

An animation like this requires an additional piece, however. This is commonly referred to as an EL Sequencer.  (see photo below)

 I used one I bought from Sparkfun.This one has an arduino compatible microcontroller that can control eight independent pieces of EL wire, seven of which I used for this device. The circuit for switching the EL wire could certainly be home-built, but since it involves switching high voltage AC current, the design is somewhat more complicated than the typical circuits that I build. I bought the wire from Light 'N Wire Productions.

Potential Improvements

I had originally planned to use a sound sensor (piezo microphone) rather than a proximity sensor so the animation would wake up when it heard something rather than when it "saw" something. I couldn't get it to work dependably though. The problem was that the frequency of the inverter is 1000-2000hz, and this is in the human audible range, the same range I wanted to sense with the microphone. At the time I built this project I knew next to nothing about filters and couldn't make one that would filter out the hum from the inverter but still leave the microphone sensitive enough to work. I still don't know much about filters but I might take another swipe at converting it to audio sensibility. It just seems that it fits with the metaphor better.

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