555 monostable switch

Discussion in 'General Electronics Chat' started by swompy, Mar 27, 2013.

  1. swompy

    Thread Starter New Member

    Mar 27, 2013
    First of all hey new to the forum and needing some advise.

    Will start by explaining what I am trying to achieve:

    Basically I need a light to come on for 3-5 seconds when an ignition switch is turned on, then go off again and stay off until the ignition is turned back on again.

    I bought one of these kit and have assembled it and is working fine in its standard form.

    But I do not want/need the push button start. What is the best way to bypass the switch without causing the light to stay on?

    My first bit of research told me I had to put a 0.1uf capacitor and a 100k resistor from terminal 2 to ground, replacing the trigger switch. which I did (in parallel, was no explanation on how to set this up so guessed this is correct way) but didnt ignite the bulb. Would only work if I bridged the terminal 2 and ground with a wire but it wouldn't trigger the timer.

    So now I am at a lose and needing your advice.

    I hope the above isnt confusing and in short I basically need to bypass the manual switch so that it only triggers the timer on turning the ignition on.

    Thanks in advance
  2. timescope


    Dec 14, 2011
    Connect the resistor and capacitor in series. Resistor to V+ (pin 8), capacitor to ground and the junction of the two to pin 2. Add a 1N4148 diode (with the arrow pointing up to V+) in parallel with the resistor.