one shot help

Discussion in 'The Projects Forum' started by kuxz2008, Jan 13, 2010.

  1. kuxz2008

    Thread Starter Member

    Nov 16, 2009
    i would like to know how do i connect the output of the one shot to a relay as i wanted to activate the relay for about 5sec when the one shot is triggered.

    the one shot circuit is attached with this message.
  2. SgtWookie


    Jul 17, 2007
    The formula for the time delay in that circuit is Ts=1.1RC, or Time_in_Seconds=1.1 x Resistance x Capacitance.
    Since your cap is 1uF and your resistor is 1 MEG, your time delay will be 1.1 seconds.
    If you want closer to 5 seconds, then you will need to use a 4.55 MEG resistor.
    Or, you could change to a 4.7uF cap - a little too long - and the cap would be larger and more expensive to change than the resistor.

    To trigger the relay, connect a 100 Ohm resistor from pin 3 of the 555 to the base of a 2N2222 resistor.
    Connect the emitter of the transistor to ground.
    Connect the collector of the transistor to the ground side of the relay coil.
    Connect the other side of the relay coil to +V.
    Note that you will also need a diode connected across the relay coil; cathode towards +V.
  3. Wendy


    Mar 24, 2008

    And no reading required.