free running pulse

Discussion in 'General Electronics Chat' started by assassinelec, Mar 22, 2011.

  1. assassinelec

    Thread Starter New Member

    Mar 22, 2011
    hi all ,

    the circuit below should work as free running pulse generator, the question is what is the different between the free running pulse generator and the square wave generator ? i am trying to find an answer but still confused..any help would be appreciated

  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    In difference. A "square wave" usually means that the signal has an almost an instantaneous transition between two fixed voltage levels. And also usually means that the high and low intervals are equal in length. A "pulse generator" usually means that the signal is like a square wave, but with unequal high and low periods. The terms are very general an open to interpretation.

  3. gerty

    AAC Fanatic!

    Aug 30, 2007
    The "free running" part comes from the fact it needs no signal to start it.
    Ken covered the rest of it..
  4. SgtWookie


    Jul 17, 2007
    If you take a look at datasheets for 555 timers, you'll find the circuit configuration you've shown listed as an "astable multivibrator", which essentially means that it's a self-oscillating free-running circuit that will put out rectangular aka "square" waves continuously.

    As shown, the duty cycle will always be greater than 50%, as R1 and R2 are in the C1 charge path, but only R2 is in the C1 discharge path to pin 7.