Monostable to Astable 555

Discussion in 'The Projects Forum' started by DC_Kid, Jun 29, 2009.

  1. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    i am looking for a simple way to have a 555 start up in a high output state and then transistion to astable oscillator after a period of time.

    any suggestions?
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    If the delay is not to long you can use a simple RC time constant on the Reset pin. Cap from Reset to GND and Rx to Vcc. When the power is applied the Reset pin is held low until it charges.
     
  3. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    i'll give it a wurl. thanks.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    If you allow a few parts & a comparator, it will work. Connect 555 as astable, connecting timing resistor to output of comparator. Output of 555 charges a cap. via diode & resistor, forming your initial delay. Cap. + fed to + in to comp., -in to V divider. When comp goes hi, normal timing restored to 555. Holding reset down keeps output lo. When power is applied , timing cap. holds pin 2 lo, output hi.
     
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