A tiny rust application for Raspberry Pi 4 to control a 5v fan's speed based on the CPU temperature.
The service will log the temperature and duty cycle 15 seconds after first startup, then it will log it again every 15 minutes. The fan speed is adjusted every 5 seconds
To get access to the PWM functionality you need to enable it in
the /boot/firmware/config.txt file.
Simply add the following line to the end of config.txt
dtoverlay=pwm,pin=12,func=4
The Rpi4 cannot drive the fan directly, you will need additional components to achieve this.
In my case I used a KSP06 (MPSA06) NPN transistor, 1N4148 diode, and a 1.5k ohm resistor. For the transistor any general purpose NPN transistor will do, most people use a 2N2222
Here is the circuit diagram.
If soldering this simple circuit onto some vero board or perf board is too far out-side of your comfort zone, you can get an off the shelf solution like: https://thepihut.com/products/fan-controller-for-raspberry-pi
Honestly, I haven't got a good answer, other than I wanted a small memory footprint. And the rust app did the trick.
While I am confessing, ChatGPT wrote most of the app.
I actually started with a C++ app then it hit me like a ton of bricks, I haven't used C++ in 15 years and I recall nothing. Then I thought Rust... and it is way different so ChatGPT and I got going on this little app.
cargo build --releasesudo cp target/release/pi-fan-speed /usr/local/bincd scriptsEdit the file pi-fan-speed.service and update the line
containing User=<your user> and set the user, you want the
fan service to run as. I just used my username on the pi
Then install the systemd service.
./install.shUse journalctl to view the log for the service and after 15 seconds you should see the first log message.
journalctl -u pi-fan-speed -f
Nov 02 16:51:57 storage systemd[1]: Started pi-fan-speed.service - Fan Speed Control Service (duty cycle based on CPU temp).
Nov 02 16:52:03 storage pi-fan-speed[132437]: CPU Temperature: 42.35°C, Fan Duty Cycle: 30%