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Thread: push button switch for clock pulse

  1. #1 push button switch for clock pulse 
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    I am trying to use a push button for a clock pulse, however it seems that the button's contact is not clean enough (even though new) to make a constant signal. The pulse is to drive a 4-bit counter. I want each time i press the button for the counter to count up one. Right now when i push the button, i get any number of random advances of the clock. I tried putting a cap and resistor on the clock input to try and hold the voltage during the button press, but this only helps a little. Maybe a larger capacitor? I tried a 1 uF and 10 uF, 10 seems to be better. Any circuits out there designed for this? Is there a better alternative?

    Another way to approach this would be to create a button that could be high (5V) for say 1 sec. One press activates high for 1 sec, so then all of the jitter is irrelevant.

    Thanks!


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  3. #2 Re: push button switch for clock pulse 
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    Quote Originally Posted by bowser17
    Another way to approach this would be to create a button that could be high (5V) for say 1 sec. One press activates high for 1 sec, so then all of the jitter is irrelevant.

    Thanks!
    This is caused by 'switch bounce', as the contacts meet they bounce and then finally settle in the closed condition. This happens over a period of just a few milliseconds. But the downstream logic counts each and every pulse that this creates.

    To clean this up you can use a monostable which works but is not 'hygenic', or a switch de-bouncer circuit comprised of a couple of gates.

    As yet I can't see any way of attaching a drawing here otherwise I would.

    Steve A.


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  4. #3 Re: push button switch for clock pulse 
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    Quote Originally Posted by bowser17
    I am trying to use a push button for a clock pulse, however it seems that the button's contact is not clean enough (even though new) to make a constant signal.
    this is called "contact bounce". what you need is a "one shot" to "clean up" the output. i can't seem to find very much about them online for some reason. anyway here is a circuit for one: (PDF)
    http://www.imagineeringezine.com/PDF...13oneshots.PDF

    one shots are also known as monostable multivibrators.

    heh, bingo! googling on "contact bounce" yields a plethora of goodies.
    i'm sure you can find something here:
    http://www.google.com/search?hl=en&q...=Google+Search
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