Connecting fan directly to Arduino

I have a 120mm 12vdc fan out of an old server. It has a 4 pin connector. I do not currently have it hooked up to my Arduino. I am wondering which pin directly on the Arduino to hook it to so the fan will trigger? Detected devices in the device list are Arduino pin 2(Act3) and pin A5(Act4). My Arduino is powered by external power adapter.

The Vin pin on the Arduino is connected to your Adapter directly and perhaps your adapter is powerful enough to power your fan too. In that case, just connect Vin and GND to power your fan.

One pin of the fan is a speed feedback signal, you can leave that unconnected.

Finally, one of the pins of the fan is a PWM input. The fan has an internal transistor to switch the 12V power when given a 0-5V input. That is the pin you want to connect to the actuator pin.

If you set up a fan actuator in the device manager, the fan will turn on when heating or cooling.

So in the image below, pin 4 is your actuator pin. Pin 1 and 2 power the fan (Vin and GND).

Hi Elco,

Does the BrewPi need to be powered through the 12V power port to do this or should it work being powered by USB? I’m trying to figure out why my fan isn’t kicking on.


You can also power it from USB. Are you providing external power to the fan? How is it connected to BrewPi?