Turning SPDT Into Clock

Discussion in 'The Projects Forum' started by butler2710@gmail.com, Dec 13, 2006.

  1. butler2710@gmail.com

    Thread Starter New Member

    Nov 20, 2006
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    0
    I need a circuit that will give out a very short clock pulse when a SPDT switch is pressed.

    It needs to give out a pulse whenever the switch position changes, not just when it is in a certain position.

    Thanks!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    It's hard to quantify your requirement. If you can define "very short" it would help. Your switch action is also hard to follow. You seem to describe it at first as a pushbutton switch, and then as something more like a toggle switch.
     
  3. butler2710@gmail.com

    Thread Starter New Member

    Nov 20, 2006
    4
    0
    sorry if I was kinda vague.

    The switch I have is an SPDT switch. It's being used to give out a clock pulse to a PIC whenever it is pressed.

    Unfortunatly I cant just use a push switch because I have to use a footswitch and you can get only get SPDT footswitches.

    The clock pulse needs to be very short as the PIC runs its loop whenever it senses the pulse.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    you will need an R-S latch debouncer on the foot switch to get a clean signal. Look up the spec sheet on a 74LS279 to see how it's done - you can use half of a 74LS00 to debounce the switch. You can apply the signal to a one-shot, like a 74LS121. It might be easier to diddle the progran in the PIC to just run the loop on a change, rather than trying to make the pulse duration shorter than the program loop.
     
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