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Do I need to use a Freq to Voltage converter for a tacho signal from 4 wire fan?


Hi all,

I am using a 4-wire fan supplied by 24V. I was wondering if the tacho output from the fan needs an external timer or a Freq to voltage converter; or can I just use a pull up resistor and connect the tacho signal straight to the input of STM32 using one of its internal Timer.

I appreciate your help!



Cristiana SCARAMEL
ST Employee

Hello @SHamm.2​,

the first suggestion is to check the specifications of the tacho signal on the fan datasheet (output type, pulses per revolution).

If it is a open-drain (open-collector) output a pull-up resistor to supply motor voltage is needed. Then by adding a voltage divider you can get the appropriately shifted signal than can be connected to the STM32 GPIO.

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