Monday, February 21, 2011

555 Timer Contest Entry: EL Inverter

This project actually started before the contest was announced, its purpose is to provide a simple tunable circuit to drive EL components. Most drivers you can fins will only provide enough power to light a few feet of EL wire and drive at a static frequency. I wanted to observe the color shift that occurs when driving at higher frequencies.

The circuit is a simple 555 timer in astable mode with a 10k potentiometer to adjust the working frequency from around 150 to 3000 hertz. The output is used to switch a tip122 power transistor which sinks a transformer that produce close to 100 volts ac. Please note that many audio transformers are potted with a low melting point wax and can get warm enough to leak and fill the holes of your breadboard!

The only difference between the circuit i designed and what i built is a 10 ohm power resistor between the emitter pin of the power transistor and ground to prevent it from sinking too much current and overheating.
The transformer im using is an old 5v wall wart transformer being run backwards.

The circuit works perfectly as expected, although since the duty cycle is not constant the voltage does increase a fair bit as the operating frequency increases.

A nice color shift from aquamarine to blue is observed when adjusting the frequency above 2000 hertz.


  1. Umm is the color shift caused by over voltaging that EL wire there?

  2. no, driving el wire at higher voltages just increases the brightness

    the color shift is documented although i haven't quite found a reason why it occurs, only information on how to take advantage of it using variable frequency driving

  3. I'm attempting to build this circuit but its failing miserably, which is even worse considering how simple it is. I think i'm having transformer troubles, think you can shoot me an e-mail and maybe help me out there is a time constraint when i need to build this, so it would be very much appreciated

  4. sorry about the late response, i have been busy moving to a new city for university

    so long as you build the circuit as described the only issue should be the transformer or supplied voltage, i originally used a 6 volt ac transformer backwards to bring 5 volts up to around 90 to 100 volts

    i have had decent success using audio transformers, although i did have a few transformers potted with paraffin wax overheat and leak into my breadboard at one point

  5. i like you post its very informative. keep sahring more.
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