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Why the pull-up resistor is used with debounce buttons?

Discussion in 'General Electronics Discussion' started by Dani, Mar 5, 2013.

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  1. Dani

    Dani

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    Mar 5, 2013
    Why the pull-up resistor is used with debounce buttons?
     
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    A pull up or down resistor is used to force the logic to return to the 'negative' (not pressed) state between button presses...
     
  3. Dani

    Dani

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    Mar 5, 2013
    My understanding is that a pull-up resistor prevent excessive amount of pulse, So using it with de-bounce buttons on trainer is only to force these pulse to slow down?
     
  4. BobK

    BobK

    7,673
    1,684
    Jan 5, 2010
    You cannot simply connect a button to a digital input, because, when the button is not pressed there would be no signal on the input. This is called a floating input. In CMOS logic, a floating input can give undefined results, it may read as either high or low. the pull-up resistor guarantees that it reads high when the button is not pressed. It has nothing to do with de-bouncing.

    Bob
     
  5. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    I'm sorry to say it, but you need to reeducate your understanding. As said, a pull up or down resistor only predefines the idle level of a digital input, and return the input to this level after activation.
    You define the lenght of the active level pulse by pressing the push button. When you release the button the pulse ends and the signal return to the inactive state.

    If the resulting pulse is shorter, or longer, than the time you press the button, there is some form of electronic processing circuit between the button input and the pulse output.
     
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