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Timing Current Lapses

Discussion in 'Electronic Design' started by Bill Wayne, May 29, 2007.

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  1. Bill Wayne

    Bill Wayne Guest

    First of all, I apologize if this is the wrong group or if this
    question has been addressed in the FAQ.

    I've been interested in circuitry for a while, and am now trying to
    design them. One thing in particular I want to do is create a setup
    where, after a given time, the circuit *breaks*. This is to trigger
    capacitors, which are connected to solenoids. I think you can guess
    (or is it guass?) where I'm trying to go with this.

    The 555 timer seems to be popular, but from what I understand it
    rapidly flips between a low and high current. What would be a good way
    to do what I intend?

    Thanks in advance,
  2. MooseFET

    MooseFET Guest

    No, I can't guess right now what you want to do. I am sitting here
    with a glass of wine, thinking out the wonders of the applications of
    the LM555. Life is truely amazing there must be a million ways you
    can wire up a 555 to do a million different things. Among them are
    various circuits that oscillate and make single pulses. Some of these
    puses are high and can be used to tuen on a MOSFET for a brief time
    others are low.

    I predict that if you can be more specific, many people will give you
    many suggestions. Among them will be some that will work, perhaps
    after you decide to put a bypass capacitor on pin 5.

    There will also be some folks suggesting that your application would
    be better served by a PIC. Although these people are well meaning,
    you should ignore them for that way leads to maddess. The only
    microprocessor anyone should ever consider using is the 8051.
  3. Rich Grise

    Rich Grise Guest

    Guessing is useless, so most won't even bother.

    What are you actually trying to accomplish?

  4. Bill Wayne

    Bill Wayne Guest

    Gauss gun. I thought the pun made it clear.
  5. Bill Wayne

    Bill Wayne Guest

    First of all, I'd like to say that I'm planning on building a coilgun.
    It seems the pun wasn't as obvious as I had hoped.

    In any case, it seems that what I planned won't exactly work out. A
    better option instead seems to be using 555 circuits so that after
    time N, the output switched from low to high and completes the
    capacitor circuit that runs through the solenoid. Would this work?
    Assuming it does, what would be an efficient way to recharge the
    capacitor after it discharges?

  6. Rich Grise

    Rich Grise Guest

    Probably not. I wouldn't put a 555 withihn 10 feet of a coilgun. You
    use a pushbutton to fire the first coil, then optical interruptors and
    SCRs to time the ensuing pulses based on the position of the slug.

    I'd also physically space out the coils to account for acceleration
    along the barrel, that simplifies your timing requirements.
    A power supply? Use enough series resistance so that your power supply
    doesn't blow a fuse, and charge them as fast as you need to to be ready
    for your next shot. But whichever way you do it, over the long run you'll
    be expending pretty much the same amount of watt-hours.

    Good Luck!
  7. Bill Wayne

    Bill Wayne Guest

    I think I understand how that would work. I was already planning on
    spacing the coils to optimize the end velocity, but I can see how that
    would help with timing.

    I'm trying to imagine how this would look in practice, though. As I
    see it, some distance before each capacitor is an photodiode connected
    to an SCR gate. When the sensor detects the projectile has passed over
    it (probably either by detecting sparks caused by friction or by
    modifying the projectile), it supplies electricity to gate and allows
    the capacitor to conduct through the SCR. That seems much less
    complicated than either other setup, at least in theory.
    So the supply would be connected to each capacitor. I had imagined
    that could cause the gun to fire preemptively, but it seems your
    recommended capacitor setup solves that problem, too.
  8. Rich Grise

    Rich Grise Guest

    No, it's by interrupting the light beam from your emitter to your
    I need to make a disclaimer here - I've never actually done anything like
    this, it's just sort of a seat-of-the-pants "that's the way I'd do it"
    kind of stuff.

    But if I've helped you build a coil gun, that'd be a feather in my cap! :)

  9. Bill Wayne

    Bill Wayne Guest

    Yes, I see how that would make much more sense.
    Same. Most of the calculations I've been making have been for
    optimization, and all the circuit designs I've been designing are more
    intuition based.
    I'll be sure to properly attribute it. :)
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