Should a 12V PWM fan and Pi use the same ground circuit?

[runeven]

Hi

I'm new to Raspberry Pi and are trying to control a 12V PC fan (Nuctua Redux NF-P14s) via PWM, but are experiencing problems when connecting the fan to an external 12V power supply.

When I connect the fan to the Pi's 5V circuit I can controle the fan speed via the pwm-signal. However, when I connect the fan to an external power supply the fan spins up at 100% speed, but I can't controle it via the pwm-signal.

My question is therefore, should the fan's ground wire be connected to the Pi's circuit? And if so, can I just connect the fan's ground wire to the Pi or should there be a resistor in-between?

Thank in advance

[joan]

Yes, the grounds need to be connected.

No, you don't need a resistor.

[runeven]

Thanks joan - it just works perfect now!