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JK Flip Flop and Schmitt Trigger

Discussion in 'General Electronics Discussion' started by Blumpkinson, Oct 17, 2013.

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  1. Blumpkinson

    Blumpkinson

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    Jul 29, 2013
    I am trying to uses a JK flip flop to convert a momentary button to a latched button and am running into some issues. I have been using CD74HC107E and have been unable to get it to function reliably.

    [​IMG]

    Is there something i'm missing with the above schematic? I want the J and K to be high so that the clock input will switch Q with each falling edge. The data sheet for the flip flop is below. It claims to have buffered inputs to help debounce, would a low pass filter/schmitt trigger be nessecary for this application

    Thanks


    http://www.mouser.com/ds/2/405/schs139d-127059.pdf
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Have a look at this thread. I think it's the same issue here.
     
  3. Blumpkinson

    Blumpkinson

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    Jul 29, 2013
    That was the problem, thank you.

    Ran into another problem, the FF is supposed to have a schmitt trigger input, however i'm still running into bounce problems. I've tried setting up an external RC filter like the one from the other thread, however the FF no longer switches. Would I be better off starting with a different type of FF?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It might be worth posting the circuit you're using now.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    That would be very helpful indeed.
    Plus: a Schmitt trigger doe not relief you from the bounce problem. It helps only if the slew of your input signal is very slow. Your RC filter may slow down the signal edge too much so the level never reaches the threshold of the input if you press the button only momentarily. What happens if you press the button for a little longer?
    Can you observe the signal using an oscilloscope?
     
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