Reading PC fan tachometer - Raspberry Pi Forums

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what want control 3pin fan using pwm
need understanding use resistor , npn transistor control speed
4pin fan connect pwm output fans pwm input wire (not sure if safe fan @12v)

reading fan bit confused
did reading found can use cheap 74hc4040 chip count interruptions tachometer , read it
breadboard friendly chip count interruptions tachometer , let device read value
hoping use easy 1 wire chip (like ds1820b works)

end goal working software managed fan controller can add in linux desktop (motherboard don't let control fans based on gpu temp via bios , never have enough fan plugs)

don't need software side, part easy me
don't want buy wrong part , have , pay shipping again or worse , fry something

i thought fan output signal open collector , pulsed twice per revolution. i'm sure i've checked several times pc fans.

in other words should able connect wire pi gpio, set gpio's internal pull-up 3v3 , read pulses. gpio read 1 read 0 twice revolution.

google pc fan open collector output.


raspberrypi



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