Programmable Duty Cycle Generation

Discussion in 'The Projects Forum' started by winzo, Feb 16, 2009.

  1. winzo

    Thread Starter New Member

    Feb 16, 2009
    Hi All,

    I'm looking for a programmable (serial or parallel) chip that can generate a duty cycle 0-100%, sourced by a 3 or 5 V supply. The tricky part is I need a low freq range: 1-30Hz. This output will be strobing the FSELECT pin of an AD9832 for FSK.

    I looked at the MC8640 but it seemed way too advanced. Any suggestions?
  2. kahafeez

    Active Member

    Dec 2, 2008
    Why don't you use a microcontroller....

    PWM..... pulse width modulation
    Last edited by a moderator: Feb 21, 2009
  3. winzo

    Thread Starter New Member

    Feb 16, 2009
    I looked into using a PIC microcontroller, but from what I could figure, none could generate PWM signals at that low a frequency (1-30Hz).

    But a microcontroller solution just seems like overkill. Is there anything that I can load a few words into from a serial connection, and it will generate a waveform at a certain % duty cycle, at a certain frequency? If it needs to be externally clocked, that is doable as well...
  4. jpanhalt


    Jan 18, 2008
    The 12-series PICs in 8-pin packages run with almost no peripheral components. You generate the PWM in software, not the CCP/PWM packages they may come with. Make high, delay1, make low, delay2, and so forth. It's hardly overkill today. One might even argue that by comparison, PWM using a discrete component, like an NE555 is overkill in that application. If you need more accuracy, you can always and easily use a crystal or resonator.

  5. italo

    New Member

    Nov 20, 2005
    there is no such a thing as 0% duty cycle or 100% duty cycle. So unless you change your question to something that is possible then I may help you.
  6. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    How do one call a steady 5V or 0V then?

    Better get one's fact straight in an international forum.:mad:
  7. mik3

    Senior Member

    Feb 4, 2008
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Interesting! What's your reasoning there? I can make an 8-pin PICAXE 08M microcontroller PWM from full OFF (0% duty cycle) to full ON (100% duty cycle) or anywhere in between. I can easily do a slow 1 to 30HZ PWM. Two pots for two ADC inputs..FREQ and DUTY. One logic level PWM output. Programming in BASIC. Component wise it doesn't get much simpler.

  9. winzo

    Thread Starter New Member

    Feb 16, 2009
    I used a 555 in prototyping, but I needed something programmable because I can't swap R/C in my final version.

    So I'm going with the PIC12F683. Thanks for the help everyone!