555 monostable self triggering

Discussion in 'The Projects Forum' started by willip7, Jan 10, 2012.

  1. willip7

    Thread Starter New Member

    Jan 10, 2012
    2
    0
    Hi all, I've searched the forums and the web for this info without any definitive answer. I am constructing a basic 555 monostable circuit that when powered gives an output to a relay for 2 seconds, then go off and stay off until power is removed and then re-applied. I want the circuit to trigger automatically (ie when power is applied) and as such I don't want to have to physically push a switch to trigger the circuit. Is there a simple way of doing this ? I realise that a pullup resistor is to be used on Pin 2, and to trigger it Pin 2 must briefly go low. Can a simple capacitor between Pin 2 and ground be used ? If so can anyone attach a simple schematic to assist me. Many thanks in advance, Paul
     
    Last edited: Jan 10, 2012
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Here you go. Change R1 to 18k for 1.98 seconds (give or take for component tolerances.)
     
    Last edited: Jan 10, 2012
    nishadkharade and willip7 like this.
  3. willip7

    Thread Starter New Member

    Jan 10, 2012
    2
    0
    Many thanks. Perfect response, and it works a treat !!!:)
     
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