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help with simple circuit

Discussion in 'Electronic Design' started by Eric, Jul 14, 2004.

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  1. Eric

    Eric Guest

    I'm very new to electronics so this is probably a pretty basic circuit
    that I need to build. Here's what I'm trying to do. I currently have
    a manual switch that is control by a moving object. When the object
    hits the switch, the switch is turn on and the circuit is completed.
    The problem is that sometimes the object hits the switch multiple
    times in a single pass. I'm looking for a way to basically add a
    timer or delay so that after the switch is completed once it will take
    x time until it can be completed again. From my basic knowledge I was
    thinking that a capacitor with a variable pot could do what I want. I
    would like to here some thoughs on this simple problem.


  2. Tim Wescott

    Tim Wescott Guest

    Find a datasheet for a 555 timer that has a debounce circuit.
  3. CFoley1064

    CFoley1064 Guest

    Subject: help with simple circuit
    Hi, Eric. First, you might want to try looking at your switch. Microswitches
    are made with built-in mechanical hysteresis to prevent what you're talking
    about. They are made to snap on with a certain amount of detent on the switch,
    and then the switch arm will have to move back significantly before the switch
    snaps off. A microswitch is the right switch for this job.

    Having said that, you still have to look at the issue of contact bounce, which
    occurs even in microswitches. Contact bounce usually occurs too quickly too
    have multiple turn-on/turn-off cycles on a relay or other physical load
    (although some slower switches can cause multiple hits on fast reed relays).
    Contact bounce usually occurs over several milliseconds, which can be a problem
    when interfacing a switch with control logic operating in the ns/us range.

    Another post suggested a 555 debounce circuit, which might work well for slow
    make/slow break switches as well as contact bounce. There are other solutions,
    too. How about giving some information on your circuit, like what kind of
    switch you have, what power source is being switched, what's the switch load,
    and the other details. If you've got a circuit where 120VAC is being switched
    to drive a relay or lamp load, a 555 might not be the appropriate solution.

    You might get a more enthusiastic response to a basic newbie question on

    Good luck
  4. Eric,

    You did not provide enough information to obtain a reasonable answer.

    What does the switch look like? Current, voltage i.e. what does it have to
    switch? On or off? What kind of power is available? How long will it take to
    be sure the next hit is a wanted one? Or reverse, what is the maximum time
    in which a false hit can be expected?

    That's not to say there is no answer. It sounds: Take a 555. Use it as a
    non-retriggerable monostable. Trigger it with you switch and make it drive a
    relay that drives the load. But if you understand this, you would not have
    put your question.

    BTW. That's why this question should have been placed in

    petrus bitbyter
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