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Photoflash firing circuit

Discussion in 'Electronic Basics' started by Gordon Campbell, Mar 4, 2004.

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  1. Evening, all. I apologize if this is the wrong group to make this sort of
    request, but I've run out of ideas.

    I'm looking for a schematic of a circuit that will randomly fire a
    collection of photo flash units.

    I'm working tech for a play next month and we're looking to simulate
    electronic arcing with the flash units. I can find dozens of timers circuits
    to fire the flashes, but every last one uses a set time. I need random or
    something approaching that. I've never seen electrical shorts that arced in
    a set pattern. ;-)
  2. CFoley1064

    CFoley1064 Guest

    Subject: Photoflash firing circuit
    A few questions. How many photoflash units do you have? Are they voltage
    triggering or switch contact triggering? What is the recharge time for the
    photoflash units?

    Assuming you have contact triggering, it might be easiest to just go with 1 ea.
    555 trigger circuit for each strobe. Each 555 would drive a small reed relay,
    which would provide the trigger for each strobe. You could run the whole
    shebang of triggers off one 6V lantern battery, and if you had more than 5
    strobes, it would look semi-random.

    However, I'm guessing your photoflash takes a couple of seconds to recharge, in
    which case your photoflashes will look like a bunch of cameras going off rather
    than an arcs & sparks event.

    One thing you might want to consider, if you've got a bit of a budget and are
    handy with a soldering iron, is getting half a dozen DIY K163 strobe kits (use
    the 0.1 uF cap rather than the 0.47 uF cap for .2 to .4 second cycle), and a
    12VDC power supply, like the ones available at Radio Shack (13.8VDC is OK
    here). The kits are about $15.50 ea. Set all the pots for different times.
    It will give you the randomness you seek, and probably would look more
    realistic than your photoflash (although the photoflash would probably be
    somewhat brighter -- a reflective backing and good sound effects would help
    here). Just turn on the 12VDC to turn your show on, and turn off the power
    supply to turn it off.

    You might be somewhat disappointed with either solution, because a flash
    doesn't have the high UV content of an arc. It will, alas, have the color of a
    flashbulb, no matter what. A light purple wash filter on one of the strobes,
    and light blue wash filter on one more may help here. Stay far away from the
    temptation to use an arc welder here to get your spark light -- safety always
    first backstage.

    Good luck, and break a leg
  3. Bob Masta

    Bob Masta Guest

    Sounds like all you need is a random number generator.
    While there are circuits to do this, you might have better
    luck with a computer. That gives you the ability to
    change things around, including changing them on
    the fly during the performance.

    There are plenty of random number algorithms out there.
    Just set one up to output 8 bits to the printer port, and
    you can drive 8 different stobes. Or you can have
    several single-bit generators running at different rates.

    If you want to test this out, you can download my
    Daqarta software with the LPTX driver. There
    is simple a random generator built into the driver, and
    you can also use the STIM3A signal generator
    to generate much more complex patterns.

    Let me know if you need more info on this. You will
    need a computer that runs real-mode DOS, which
    means an old one, Win9x or earlier. Good use
    for an old junker, even an 8088 PC/XT.

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  4. We're look at 6 or 8 of the flash units and they'll be inside a prop light
    board that is supposed to have had an axe buried into it. :)

    The budget's more or less nil. We're using flashes that I've stripped out of
    disposable cameras. I'll see what I can come up with. Thanks!
  5. Holy cow, I never thought of that Bob. Boy, have I got computers ... Thanks!
  6. Bob Masta

    Bob Masta Guest

    Last night I just recalled an easier way to use Daqarta for this.
    I left an undocumented feature in the DEMO.ADC driver, so
    you don't even need to mess with LPTX. Just open the
    default DQA.CFG file and to the second line add L:1
    DEMO.ADC L:1
    That will allow you to send STIM3A signals out the
    printer port. (L:1 means use LPT1; you can select
    LPT2 with L:2, etc.)

    You control which STIM3A output (DAC0, DAC1, or
    various DigOut bits) will be viewed as the DEMO input
    signal, by changing the input channel on the DEMO
    driver (B-key to toggle the Board active, CTRL-B to
    Control the Board). See Help (CTRL-H) for a list of
    what channel maps to what STIM3A output.

    CTRL-G to bring up the generator. Depending on
    what DEMO channel you set, the 8 bits of the printer
    port output will be the 8 bits of a DAC, or 8 separatrely
    controllable DigOut bits. Select a noise type for the
    DAC and you will have 8 independent random
    outputs. You can slow these down via the CTRL-X
    X-axis sample rate controls, but a better way is to
    use the Timing menu Step option. That will allow
    you to hold each random value for as many samples
    as you want.

    Or, use the DigOut option and set different pulse
    timing cycles on each of the 8 bits. You can make this
    exceedingly complex, so that it will appear quite
    random, yet still have some control over rates of
    individual strobes.


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis

  7. Why not fire them manually with a peg board? Or with a charge discharge
    circuit manually controlled?
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