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  1. #1
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    Holding button for 2s to trigger 555 timer

    I would like to implement a circuit so that after a person holding a tact-switch for 2s, a signal will be sent to trigger a 555 timer to start timing.

    Firstly, I think of a simple RC circuit to delay the signal. However, there is a problem that it needs time for the capacitor to discharge if the person holding the switch less than 2s. Then if the person press again the switch, it will take much shorter time to trigger the timer. Or if the person press the switch repeatedly, the 555 timer will be triggered in the end.

    The circuit does not have a microcontroller. The power is 5V.

    Could you suggest a circuit to implement this function?

    Thank you very much!

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  2. #2
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    Re: Holding button for 2s to trigger 555 timer

    Instead of the standard resistor/button arrangement on the 555 input used on the monostable configuration (resistor on the top, button NO on bottom), try replacing it by a voltage divider with 2 resistors (biasing below Vcc/3), and a capacitor to the ground and a button NC to the 5V. The time needed to switch the voltage between the 2 resistors from 5v to >1,6V (>Vcc/3) will be defined approximatelly by the capacitor multiplied with the parallel equivalent of both resistors. Further adjustements needed from your side in order to choose suited values.
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  3. #3
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    Re: Holding button for 2s to trigger 555 timer

    Hi,

    On button press: the capacitor gets slowly discharged by a high ohmic resistor
    On button released: the capacitor fastly gets discharged via a diode

    Klaus
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