The Raspberry Pi 4 tends to run rather hot, and active cooling is a more important option. PiCFan provides a PWM Cooling Fan Controller written in C, which is installed as a Systemd service.
This software is very much in alpha state, and is probably riddled with bugs. It also lacks decent documentation. I am however making this repo visible while I work on it.
Quite a bit of work is still required to tidy this little daemon and its documentation up.
In order to operate, picfan expects a fan which has a PWM input attached to GPIO18 (pin 12 on the Raspberry Pi GPIO header).
I have tested mainly on a Raspberry Pi 4. The code compiles and installs on a 3b+ although I have not installed a fan yet. The code also seems to work on a Pi Zero (which doesn't need a fan).
I intend to supply a circuit diagram for a PWM controller in the future.
##Installation I haven't got around to familiarising myself with Autotools, so I have only written a rudimentary Makefile. This software depends on the bcms2835 library by Mike McCauley. The bcm2835 library can be found at http://www.airspayce.com/mikem/bcm2835/index.html
Installation currently requires the following steps, best performed as root, as it will try to install bcm2835.a in /usr/local/lib:
make
make install
This will install picfan in /usr/local/bin, as well as installing a Systemd service called picfan.service.