PWM fan on Raspberry Pi 4 build 21.02

I've built my first OpenWrt router with Raspberry Pi 4B and Alfa AWUS036ACM, based on 21.02:

I'm mostly happy, but I can't control the Noctua PWM fan over GPIO 18/pin 12.

I've tried the suggestions in this thread:
And this thread:

Manipulations to controll PWM that I can do with success on the command line in Raspberry Pi OS, seems to be accepted in OpenWrt, but nothing happens. Maybe I am missing something? Or maybe something has changed from earlier versions?

I hope someone can point me in the right direction.

Which noctua fan it is? Personally I use Ice cooler for Raspberry pi4. The old large one and it keeps the rpi4 cool even in extreme summer temperatures without being loud.

I'm using the Noctua 5 volt PWM 40 x 40 x 10 mm. Been using these fans for two other RPi4Bs acting as desktop computers, with a variable speed fan controller I've written in C. Most of the time they are completely silent. That is what I hope to achieve with the OpenWrt router as well.

What are the usual temperatures on your rpi4s?

Mine never crosses 51C

Unecessarily low?

The one I'm sitting at now is typically in the late 50's – right now 58°C. And the one at home, typically somewhat higher. It depends on the surroundings.

BTW: my Pis are old.

To get these into early sixties, I just need to unplug the fan. Ice tower is large enough to keep temperature in early sixties without any noise. :blush: