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Thread: DC Fan PWM sensing

  1. DC Fan PWM sensing

    I have a project where I have interfaced a Duratrax Electronic Speed Control to a Phidgets servo control, to operate a 12V DC brushless fan. That works fine, but my question rests on sensing the Fan speed. The fan I am using (4715KL-04W-B56) I believe, transmits a PWM signal via one of the extra leads that relates to speed (RPM). Any ideas how to read this with my 8/8/8 interface kit?

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    Re: DC Fan PWM sensing

    Hey elcray!

    Do you happen to have a link to the speed controller product page and any docs/datasheets?

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

  3. Re: DC Fan PWM sensing

    Quote Originally Posted by Alex View Post
    Hey elcray!

    Do you happen to have a link to the speed controller product page and any docs/datasheets?
    The speed controller is a cheap Duratrax instellisense, but the item I have in question is the signal from the fan. Unfortunately, I can't find a spec from the mfg of the fan that shows anything about the leads; other than red and black +/- dc power; which, I think I could have figured out myself ;->

  4. Re: DC Fan PWM sensing

    Chances are kind of slim that you'll be able to read that PWM with the 8/8/8, because of its slow sample rate. The 8/8/8's digital inputs only sample at 125 Hz, and your PWM frequency would have to be far lower than that to get an accurate reading.

    You may be able to get a rough measurement by low-pass filtering the PWM signal and feeding the result into an analog input.

  5. #5

    Re: DC Fan PWM sensing

    Maybe if you change what you want to sense...
    If sensing fan speed seems un-do-able, maybe measuring analog voltage would give you an approximation you could work with.
    Sometimes a 'quick 'n dirty' solution is the only solution.

  6. Re: DC Fan PWM sensing

    Quote Originally Posted by Dave View Post
    Chances are kind of slim that you'll be able to read that PWM with the 8/8/8, because of its slow sample rate. The 8/8/8's digital inputs only sample at 125 Hz, and your PWM frequency would have to be far lower than that to get an accurate reading.

    You may be able to get a rough measurement by low-pass filtering the PWM signal and feeding the result into an analog input.
    Thanks. That's kind of what I expected, but just wanted to be sure.

    Quote Originally Posted by kdwyer View Post
    Maybe if you change what you want to sense...
    If sensing fan speed seems un-do-able, maybe measuring analog voltage would give you an approximation you could work with.
    Sometimes a 'quick 'n dirty' solution is the only solution.
    That might be possible. All I'm really trying to accomplish is to make sure that something isn't blocking the fan from turning. I might hit that from a different direction.

    Thanks all for the feedback.

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