Dimming an EL panel is harder than it looks

Assembly

We’re almost out of this guys, stick with me.

Circuit board and enclosure

There isn’t much to be said about my circuit board and enclosure.  The case I used was the Hammond 1593LBK.  It’s probably a little larger than I needed, but with such a large transformer, I didn’t have too many options.

You can see where I added an LED and button.  These were intended to aid in debugging, and to give the user a way to swap between modes of operation.  Unfortunately, the shaft of my button isn’t long enough to penetrate the top of the enclosure.  I’m only planning one user mode for the final product, so I really don’t need the button.  I figured I’d just leave this like it is and change modes for demonstration purposes by just reprogramming firmware.

The battery holder is similar to the one I used in the DJ jacket, but it holds two cells instead of three.

Shirt

The EL panel is meant to be worn under the user’s clothing so that it can shine through.  I did this by Velcroing it to an undershirt.  The Velcro on the undershirt was the iron-on variety while the velcro on the panel was the adhesive backed type.

I was hoping the panel would be more flexible as the edges are pretty easy to make out under a shirt.  If I slouch my shoulders right though, it isn’t obvious, and in a dark room, you can’t tell at all.

My original plan was to cut the EL panel out into my desired shape, but I realized that that was fairly difficult because of the way the panel was assembled and sealed to be one piece.  Cutting it could have caused damage and made the whole piece a lot less durable.  Instead, I simply printed out the desired design on overhead transparency paper and taped it to my panel to block the light appropriately.  This also gave me the ability to change my design after the fact.

28 thoughts on “Dimming an EL panel is harder than it looks

  1. yea there is a MUCH MUCH easier way to do this..
    you take the standard inverter and the el panel and put a CDS photocell in series then take a standatd lm328 amplifier and hook the output to a bicolor LED and shine that on the photocell
    DONE! i can give you schematics and stuff if you want

    • So you’re just talking about putting an adjustable resistance in series with the EL panel? I suppose that would work, but it’s not the most efficient way to do it.

      Also, looking at a few datasheets, the maximum power dissipation though a CdS cell is around 100mW. If I were to use one on a panel, it might need to dissipate upwards of 7-800mW. It couldn’t take the heat. I suppose you could put a few in series, but that’s going to get pretty messy.

      This solution might work in smaller loads like short EL wires though. Thanks for the tip!

    • When I first read your comment above I thought you were using the photocell to read the light from the EL panel and then reverse the voltage polarity when it detected maximum brightness, which should generate AC that would self-regulate to the right frequency to sustain that brightness level. But then when you mentioned LEDs you lost me! But would a feedback control mechanism like what I thought you meant actually work?

      • Matthew was recommending using a optoisolator as a variable resistance. The idea is that you could control current from a low-voltage circuit and not have to worry about the 120V blowing anything up.

        You present an interesting idea, but I think it would end up being more trouble than it’s worth. The EL panel is a fairly “slow” material. It takes a few milliseconds for it to react to changes in current, so using its brightness in some kind of feedback system would prove difficult. To say nothing of the wiring/mechanical complications this would create.

  2. >> I chose the 1N4148 which has a gate capacitance of just 4pF.

    Not gate. Junction.

    Since you were ordering from Digi-Key anyway, you could have purchased some BAT-41 Schottky diodes (19,000 in stock) . The BAT-41’s capacitance is 2pF, half of the 1N4148’s capacitance, and its forward voltage at 20mA forward current is 0.30 volts per diode, significantly less than the 1N4148’s 0.95 forward volts per diode.

    • Whoops, typo. Thanks.

      I figured out my diode problem after I already made my order, so I had to use what I had on hand. Next time I’ll be sure to choose more wisely. Thanks for the tip!

  3. while pouring over various patents on zinc sulfide phosphors i discovered reference to the color shift in el wire, my 555 based driver was a quick and dirty means of observing it myself and as an excuse to learn something about driving el wire… more of a first attempt using spare parts before devoting more time to designing a proper circuit rather than basing it off some simple dc to ac inverter circuit i found in the internet

    along with the brightness being a function of frequency i found voltage had a similar effect but would cause the el wire to age faster than driving at a higher frequency would, and yes driving at higher voltages also caused my salvaged transformers to overheat and leak paraffin wax everywhere

    • Oh by all means, I think it’s great what you did, and it really helped me in my initial research! I was just making a point that in general, there aren’t too many resources available on EL wire and driving it properly.

      • there really arent, i had to resort to reading dozens of white papers and patents to figure everything out, my result was a working driver that was extremely inefficient, occasionally overheated and administered ~130 volt shocks when i wasn’t paying attention

        ive also been working out some ideas on mixed frequency driving el wire to increase lifespan while making it brighter by rapidly switching between low and high frequencies at a rate where it would be brighter while impacting lifespan al little as possible

  4. I also noticed the frequency shift.
    Wonder if this effect can be used to make a variable spectrum microscope light?
    For certain applications this would be handy indeed as if the wavelength shift is linear then you could image a sample at a range of multispectral frequencies rather than green or blue.

    I like the Supertex HV852 for this as it draws under 5mA with small wires allowing a PIC to directly drive it and adjust frequency with a single drive lead and a capacitor.
    So one 12F683 can run six separate EL wires, with Charlieplexing even more.

    • as far as i have observed there is only a single color shift at ~2000 hertz and i have not found any information to indicate there any more

      it is far from linear and im not sure the amount of light would be sufficient for a microscope anyways

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