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Topic: 4 wire pc fan question (Read 746 times) previous topic - next topic

kurama

Hello guys,
   Does anybody know what the facnspecs :
http://www.formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf
mean by 2 pulses per revolution, tach output. Is there one Hall or 2?

johnwasser

Could be one Hall and two magnets or one magnet and two Halls.  Does it matter?
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kurama

Hey John, nice to hear from you.
    The problem is that i want to know exactly how many times per revolution an output signal is send from the tach. I think that there is one hall and one magnet, and the first pulse is the start and the second the end, so 2 pulses/rev. Using this info i can get a math model of the fan, which in turn i will use to make a pid controller.
    If you have any ideas on my Hall problem, please let me know :)


    Mircea.
PS: sorry for my English, not my first language 

johnwasser

The spec doesn't say how long each pulse is but I believe they mean two full pulses per revolution LOW HIGH LOW HIGH.  Make sure you use a pull-up resistor because it's an open-collector output (only drags the line down to 0v, won't supply +v).
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