Raspberry Pi 4 PWM Fan Controller Service

This project provides a lightweight and efficient solution for controlling 5V PWM fans (such as the Noctua NF-A4x10) on a Raspberry Pi 4.

Written in C and leveraging the pigpio library, it offers precise fan speed regulation based on CPU temperature, real-time tachometer feedback (RPM monitoring), and configurable hysteresis for smooth operation.

It comes with a systemd service file to ensure the fan controller starts immediately during early boot.

Key Features

• Lightweight & Fast: Written in pure C for minimal resource usage.
• Smart Control: Adjusts fan speed dynamically based on CPU temperature.
• RPM Monitoring: Reads fan speed via the tachometer pin (GPIO17).
• Smooth Operation: Implements hysteresis to prevent rapid speed switching.
• Systemd Integration: Includes a service unit for automatic startup at boot.
• Hardware Support: Optimized for Raspberry Pi 4 and 5V PWM fans.

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1. Requirements

Hardware

• Raspberry Pi 4
• 5V PWM Fan (e.g. Noctua NF-A4x10 5V PWM)
• Connections:
  • 🔵 GPIO18 (Pin 12) (PWM) → blue wire
  • 🟢 GPIO17 (Pin 11) (Tachometer) → green wire
  • 🟡 5V (Pin 4) → yellow wire
  • ⚫ GND (Pin 6) → black wire

Software

• Raspberry Pi OS (Raspbian)
• pigpiod active at boot (pigpio daemon)

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2. Installing development libraries

Open a terminal and run:

sudo apt update
sudo apt install build-essential libpigpiod-if2-1 libpigpiod-if2-dev pigpio

• build-essential → C compiler and make utilities
• libpigpiod-if2-dev → headers and C library to interface with pigpiod
• pigpio → daemon for GPIO/PWM management

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3. Preparing the project directory

sudo mkdir -p /opt/fancontrol
sudo chown $(whoami):$(whoami) /opt/fancontrol

Copy the source files into the folder:

cp fan_control.c /opt/fancontrol/

Enter the folder:

cd /opt/fancontrol

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4. Compiling the program

Compile the C code using the pigpiod_if2 library:

gcc fan_control.c -lpigpiod_if2 -o fan_control

Make it executable:

chmod +x fan_control

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5. Manual start

Start the pigpiod daemon (if it is not already running):

sudo systemctl start pigpiod

Run the program manually for a quick test:

./fan_control

You should see output similar to:

Temp: 51.2°C | Fan: 20% | RPM: 3500
Temp: 53.0°C | Fan: 35% | RPM: 4200
...

To stop manually: Ctrl+C (the program will perform a clean shutdown of the fan before exiting).

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6. Installing the systemd service (early boot)

Create the systemd unit file /etc/systemd/system/fancontrol.service using nano:

sudo nano /etc/systemd/system/fancontrol.service

Paste the following content into the file:

[Unit]
Description=Custom PWM Fan Controller Service for Raspberry Pi
Requires=pigpiod.service
After=pigpiod.service
Before=multi-user.target
DefaultDependencies=no

[Service]
Type=simple
ExecStart=/opt/fancontrol/fan_control
ExecStartPre=/bin/sh -c 'for i in 0 1 2 3 4; do systemctl is-active --quiet pigpiod && exit 0 || sleep 1; done; exit 1'
WorkingDirectory=/opt/fancontrol
User=pi
Group=pi
Restart=always
RestartSec=2
SyslogIdentifier=fancontrol
ProtectHome=true
NoNewPrivileges=true

[Install]
WantedBy=sysinit.target

Save and exit (Ctrl+O, Enter, Ctrl+X).

Note: if you use a user other than pi, modify User= and Group= accordingly.

Enable and start the service:

sudo systemctl daemon-reload
sudo systemctl enable fancontrol
sudo systemctl start fancontrol

Check the status:

systemctl status fancontrol
journalctl -u fancontrol -f

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7. Debug and monitoring

Check that pigpiod is active:

systemctl status pigpiod

Real-time service logs:

journalctl -u fancontrol -f

If the service crashes repeatedly, check journalctl -xe for error messages and the executable's logs.

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8. Stopping and removing the service

To stop temporarily:

sudo systemctl stop fancontrol

To disable at startup:

sudo systemctl disable fancontrol

To remove the unit file:

sudo rm /etc/systemd/system/fancontrol.service
sudo systemctl daemon-reload

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9. Useful customizations

• Code parameters: hysteresis, thresholds, ramp step, and MIN_TIME_AT_LEVEL are defined in the C source as #define — modify fan_control.c and recompile to change behavior.
• Executable path: change it to /opt/fancontrol or wherever you prefer, but update ExecStart in the .service file.
• Logging to file: if you want logs in /var/log/fancontrol.log as well, you can add to the [Service] block:

  StandardOutput=append:/var/log/fancontrol.log
  StandardError=inherit

  and create the file with correct permissions:

  sudo touch /var/log/fancontrol.log
  sudo chown pi:pi /var/log/fancontrol.log

• RPM Test: if the tachometer does not provide pulses, check wiring (pull-up) and that the configured pin is correct.

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10. Example of quick procedures (one-liners)

Compile, copy, and install service (quick example):

# from the folder containing fan_control.c
gcc fan_control.c -lpigpiod_if2 -o fan_control
sudo mkdir -p /opt/fancontrol
sudo cp fan_control /opt/fancontrol/
sudo chown -R pi:pi /opt/fancontrol
sudo chmod +x /opt/fancontrol/fan_control
# copy the service (assuming fancontrol.service already created in cwd)
sudo cp fancontrol.service /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable --now fancontrol

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