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Measure fan speed?

Fri Apr 16, 2021 7:16 pm

I want to create a rudimentary air flow measurement sensor. Can I take a normal CPU fan, connect the fan speed wire to a GPIO, and then measure the fan speed that way? I don't need high accuracy or even real numbers, I just want to compare air flow between two sources (see which one is more powerful).

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Re: Measure fan speed?

Sat Apr 17, 2021 6:00 am

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Joined: Mon Mar 19, 2018 1:18 pm

Re: Measure fan speed?

Sat Apr 17, 2021 10:00 pm

You can try to use the tacho signal line but I doubt it works without powering the fan. And if it is powered, the fan will spin on its own more than from wind's airflow

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Joined: Fri Apr 09, 2021 6:33 pm

Re: Measure fan speed?

Sat May 01, 2021 5:16 am

You should be able to use the rpm/tach circuit. But it will requiring a pull up resistor on the gpio line to 3V. A 1K resistor will work just fine for that. So the two wires you would have to connect is the Gnd and RPM from that fan.

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