/raspberry-pi-pwm-fan-2

Raspberry Pi PWM Fan control in C and Python

Primary LanguageC

Raspberry Pi PWM Fan Control in C and Python

  • CPU-efficient - Does not rely on Python to run - is a C binary with 0% CPU utilization in top. Python 3 implementation only included as a POC.
  • Non-stepwise - Avoids constant on/off cycling of fan by using different on/off temps, off grace periods, and easing if within min/max configured temps.
  • Configurable - Uses environment variables for overriding default configuration.
  • systemd Service - Setup as a persistent system service so that it runs on boot.
  • Raspberry Pi 3/4 Support - 0% CPU utilization, tested on both Raspberry Pi 3 and 4 models.

Wiring

  • Default configuration is for a 5V Noctua PWM fan, but other PWM fans should support the same wiring
  • "Pin #" are the board pin numbers; as-in "pin 1 starts at J8" numbers
  • "GPIO #" are the BCM GPIO numbers used for software configuration via environment variables
  • "Duty cycle signal" must be on a PWM capable GPIO pin:
    • Raspberry Pi 3/4 (channels share setting)
      • GPIO12 - PWM0
      • GPIO18 - PWM0
      • GPIO13 - PWM1
      • GPIO19 - PWM1
    • You may have to disable audio since it requires PWM to work via dtparam=audio=off in /boot/config.txt
Pin # GPIO # Name Color Notes
4 5V Yellow
6 Ground Black
12 18 Duty cycle signal Blue PWM channel #0
18 24 Tachometer signal Green (optional) Any GPIO pin should work
17 Tachometer pull-up Orange (optional) bridge to "tachometer signal" with a 1k Ω resistor; not a wire from fan

Raspberry Pi PWM fan wiring diagram

For a more detailed explaination of the wiring visit DriftKingTW's blog post "Using Raspberry Pi to Control a PWM Fan and Monitor its Speed." These scripts are based on their fantastic work.

Scripted install.sh Install

IMPORTANT!: The service does not start by default because it expects you to configure the GPIO pin and PWM fan duty cycle hertz to your fan's specification.

See: Environment Variables Config »

# From the Raspberry Pi (builds for installed OS variant)
sudo install.sh

# Running with defaults:
# - IMPORTANT! Only for Noctua 5V PWM fans!
sudo ./pwm_fan_control2

# Display help and exit:
#   sudo ./pwm_fan_control2 --help

# For testing other fans configurations override environment variables by CLI with sudo:
#   export PWM_FAN_SLEEP_S=5 && \
#   export PWM_FAN_MIN_DUTY_CYCLE=40 && \
#   sudo -E bash -c './pwm_fan_control2'

# Configure the service (PWM_FAN_PWM_FREQ_HZ, etc. - see readme.md):
# - Not required for Noctua 5V PWM fans
sudo nano /etc/systemd/system/pwm_fan_control2.service
sudo systemctl daemon-reload

# Start the service:
sudo service pwm_fan_control2 start

# Enable service at boot:
sudo systemctl enable pwm_fan_control2.service

# Misc control:
#   sudo service pwm_fan_control2 status
#   sudo service pwm_fan_control2 stop
#   sudo service pwm_fan_control2 restart

# Uninstall - stops and removes installed system service + binary:
#   sudo make uninstall

Manual Build and Install

Requirements:

# Install build tooling
sudo apt install git build-essential

# Obtain and install up-to-date fork of WiringPi
mkdir ~/install && cd ~/install
git clone https://github.com/WiringPi/WiringPi.git
cd WiringPi
sudo ./build

# Get this project
git clone https://github.com/folkhack/raspberry-pi-pwm-fan-2.git
cd raspberry-pi-pwm-fan

Building:

  • Building/installing are done through a simple makefile
  • compile-debug mode has CLI output with current CPU temp, mode of operation, fan duty cycle, and fan RPMs (if configured) for testing new fan configurations
# From the Raspberry Pi (builds for installed OS variant)
make compile

# Compile with CLI debugging enabled - NOT FOR PRODUCTION USE!!
#   make compile-debug

Running:

Must be ran with root permissions!

sudo ./pwm_fan_control2

# Display help and exit:
#   sudo ./pwm_fan_control2 --help

# Override environment variables by CLI with sudo:
#   export PWM_FAN_SLEEP_S=5 && \
#   export PWM_FAN_MIN_DUTY_CYCLE=40 && \
#   sudo -E bash -c './pwm_fan_control2'

# Use a .env configuration as sudo (sample .env included .env.sample):
#   source .env && sudo -E bash -c './pwm_fan_control2'

# Unset previously set environment variables:
#   unset PWM_FAN_SLEEP_S
#   unset PWM_FAN_MIN_DUTY_CYCLE

Installing as system service:

IMPORTANT!: The service does not start by default because it expects you to configure the GPIO pin and PWM fan duty cycle hertz to your fan's specification.

See: Environment Variables Config »

# Install:
sudo make install

# Uninstall - stops and removes installed system service + binary:
#   sudo make uninstall

# Configure the service (PWM_FAN_PWM_FREQ_HZ, etc. - see readme.md):
sudo nano /etc/systemd/system/pwm_fan_control2.service
sudo systemctl daemon-reload

# Start the service:
sudo service pwm_fan_control2 start

# Enable service at boot:
sudo systemctl enable pwm_fan_control2.service

Environment Variables

After installation you can edit the service file:

# Edit system service:
sudo nano /etc/systemd/system/pwm_fan_control2.service

# Reload systemd and restart service:
sudo systemctl daemon-reload
sudo service pwm_fan_control2 restart

systemd configuration environment variables in service:

Useful for setting a few configuration values.

[Unit]
Description=PWM fan speed control
After=network.target

[Service]
Environment=PWM_FAN_SLEEP_S=5
Environment=PWM_FAN_MIN_DUTY_CYCLE=40
ExecStart=/usr/sbin/pwm_fan_control2
Type=simple
User=root
Group=root
Restart=always

[Install]
WantedBy=multi-user.target

systemd configuration using a config file:

  • Useful for large amounts of configuration values
  • Sample configuration/template provided with .env.sample
  • Following example uses .env.sample file at /home/pi/install/raspberry-pi-pwm-fan-2/.env.sample
  • Recommended to move this to /etc and rename it for your own needs
[Unit]
Description=PWM fan speed control
After=network.target

[Service]
EnvironmentFile=/home/pi/install/raspberry-pi-pwm-fan-2/.env.sample
ExecStart=/usr/sbin/pwm_fan_control2
Type=simple
User=root
Group=root
Restart=always

[Install]
WantedBy=multi-user.target

Environment Varibale Reference:

NOTE: These environment variables are fully supported by both the Python 3 POC and the formal C implementation!

Variable Default Type Notes
PWM_FAN_BCM_GPIO_PIN_PWM 18 unsigned short BCM GPIO pin for PWM duty cycle signal
PWM_FAN_BCM_GPIO_PIN_TACH 24 unsigned short (optional) - BCM GPIO pin for PWM tachometer signal; 0 to disable tachometer support
PWM_FAN_PWM_FREQ_HZ 2500 unsigned short PWM duty cycle target freqency Hz - from Noctua Spec at 25kHz
PWM_FAN_MIN_DUTY_CYCLE 20 unsigned short Minimum PWM duty cycle - from Noctua spec at 20%
PWM_FAN_MAX_DUTY_CYCLE 100 unsigned short Maximum PWM duty cycle
PWM_FAN_MIN_OFF_TEMP_C 38 float Turn fan off if is on and CPU temp falls below this value
PWM_FAN_MIN_ON_TEMP_C 40 float Turn fan on if is off and CPU temp rises above this value
PWM_FAN_MAX_TEMP_C 46 float Set fan duty cycle to PWM_FAN_MAX_DUTY_CYCLE if CPU temp rises above this value
PWM_FAN_FAN_OFF_GRACE_S 60 unsigned short Turn fan off if CPU temp stays below MIN_OFF_TEMP_C this for time period
PWM_FAN_SLEEP_S 1 unsigned short Main loop check CPU and set PWM duty cycle delay
PWM_FAN_TACH_PULSE_PER_REV 2 unsigned short from Noctua spec at 2 pulses per revolution
PWM_FAN_TACH_MIN_TIME_DELTA_S 0.005 float Tachometer event time delta cutoff to avoid spuriously short pulses

Python POC - ./pwm_fan_control_poc.py

Included is a Python 3 implementation that supports colored stdout output and writes CPU temp, PWM duty cycle, and tachometer values to a CSV file.

Python POC Quickstart:

Setup:

# For colored terminal output:
sudo apt install python3-termcolor

Running:

  • Must be ran with root permissions
  • Will write a CSV file ex: test_1667157372.3389149.csv with CPU temp, fan duty cycle, and fan speed
sudo python3 ./pwm_fan_control_poc.py

# Override environment variables by CLI with sudo
#   export PWM_FAN_SLEEP_S=5 && \
#   export PWM_FAN_MIN_DUTY_CYCLE=40 && \
#   sudo -E bash -c 'python3 pwm_fan_control_poc.py'

# Use a .env configuration as sudo (sample .env included .env.sample)
#   source .env && sudo -E bash -c 'python3 pwm_fan_control_poc.py'

Notes/Misc

Why C over Python:

When running the Python POC at full 25khz PWM frequency (Noctua Spec) CPU consumption can be upwards of 5-10%. With C and WiringPi it's at 0% on a Raspberry 4.

WiringPi instead of pigpio:

I did try to port this over to the better-supported pigpio library. Unfortunately it resulted in consistent 5-10% CPU use on a Raspberry Pi 4 which was unacceptable.

Easing Function:

A quartic bezier easing function was used to smooth fan speed at the upper/lower boundries of the configured temps PWM_FAN_MIN_OFF_TEMP_C and PWM_FAN_MAX_TEMP_C. At temps closer to the lower boundry, the fan speed is kept close to the PWM_FAN_MIN_DUTY_CYCLE, and at the higher boundry fan speed will stay closer to PWM_FAN_MAX_DUTY_CYCLE.

Links: