not quite pwm needs to be proportional to input signal

Discussion in 'The Projects Forum' started by waveplant, Apr 23, 2009.

  1. waveplant

    Thread Starter New Member

    Apr 23, 2009
    Hi ,
    I need a circuit that will take a fairly low frequency square wave and shorten the pulse width IN PROPORTION to the input signal. for example if I wish to shorten the width by 50% if my input pulse width was 30% the output should be 15%. if input was 60% output needs to be 30% the input and output signals need to be related just divided(hmm divider may have answered my own question) I believe that the standard 555 circuits wont do this. Thanks very much for any help
  2. -SK-


    Apr 14, 2009
    A simple microcontroller circuit would do well here; use one pin for edge-triggered counting to get your pulse width, another for your input signal, and then make a new PWM output on a 3rd pin.
  3. hgmjr

    Retired Moderator

    Jan 28, 2005
    One thing to consider is that you will only be able to correctly determine the width the input pulse after it has terminated. That means that the shortened pulse would need to be delayed by the width of the input pulse on which the shortened output pulse's width is dependent.

    If that limitation is compatible with your requirements then I would agree with the recommendation that you employ a microcontroller to accomplish this project.

  4. waveplant

    Thread Starter New Member

    Apr 23, 2009
    Thanks for that, the delay would probaly not be critical in this application, I would rather not use a microcontroller so if there is an alternative I would be most interested , thanks again