raspberry-pi-hardware-pwm-fan

A simple python script to control a PWM fan attached to your Raspberry Pi with one of the Pi's hardware PWM timers. These PWM timers are implemented in hardware so they don't take resources from the CPU, and their timing is far more predictable.

There are some caveats to using the hardware PWMs on a Pi. There are only two channels available and both are in use for audio normally. See /boot/overlays/README for more information. You must enable the pwm or the pwm-2chan overlay for this to work.

Installation

Note: adjust these for your installation.

Clone this repository
pip install -r requirements.txt
cp hardware_pwm_fan /home/pi/scripts && chmod +x /home/pi/scripts/hardware_pwm_fan
Edit hardware-pwm-fan.service to set your fan's set points
Copy and enable the systemd unit

sudo cp hardware-pwm-fan.service /etc/systemd/system
sudo systemctl daemon-reload
sudo systemctl enable hardware-pwm-fan.service --now

Hardware considerations

By default, GPIO 18 is used for PWM0 and 19 is used for PWM1, but these pins share functions with PCM. GPIO 12 and 13 are better choices for PWM. Use dtoverlay=pwm,pin=12,func=4 or dtoverlay=pwm,pin=13,func=4 if you want to use those pins; otherwise you can just use dtoverlay=pwm. The -2chan variant is if you want to configure both PWM channels for some reason.

This confuses me every time I try and set this. https://github.com/raspberrypi/firmware/blob/3a232374735c2bc5b7188ba2dfc0cbba8fa30d97/boot/overlays/README#L3250 has all of the info you need.

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