Intro

Raspberry Pi fan-control service to adjust PWM fan speed automatically based on CPU temperature. It will help in reducing fan noise and power consumption. It is written in C. Main objective is to keep it fast and use minimum CPU and memory resources.

If you just want PWM fan On/Off based on CPU temperature. Connect fan's PWM, ground and +5V wires directly to the GPIO pins. Enable fan either from raspi-config or UI. Set the PWM pin and CPU temperature in the setup. Lowest temperature limit of 60°C can be bypassed by editing /boot/firmware/config.txt manually. Find dtoverlay=gpio-fan entry and change the temp=60000 to the desired temperature. Fan will start at the specified CPU temperature and it will stop 10°C below that. The downside is fan will run at full speed and bit noisy, specially if you are using an open RP4 case.

This service is specifically written for Noctua 5V PWM fan and Raspberry Pi 4. It may work for other PWM fans and RP models. You should know the intended fan's specifications, like max / min RPM and target frequency. Adjust these values in code/config and rebuild the binary (if needed).

I connected Noctua fan wires directly to the RP4 GPIO pins. It's been almost 3 years without any issue, your mileage may vary. If your fan does not support PWM or you want to safeguard hardware either build your own circuit or buy a pre-built PCB with transistor and diode like EZ RP Fan Controller.

⚠️ WARNING: I accept no responsibility if you damage your Raspberry Pi or fan.

Specs:

Noctua Fan	HW	OS	WiringPi	pigpio
NF-A4x10 5V PWM Fan	Raspberry Pi 4 Model B	raspios-bookworm-arm64-lite	3.1	79

Hardware Prep

• The default noctua fan connector will not connect directly to GPIO header. You need to do some modifications. There are multiple options:

  1 - Dupont Jumper Wires Male to Female:
  Noctua's existing wire is pretty long. Get short jumper wires somewhere between 2-4" long. Male part of jumper wire will connect to Noctua connector and Female part will connect to GPIO. I used it for few months.

  2 - Dupont Female Pin Connectors 2.54mm Pitch:
  It is the cleanest option, as shown in the preview. You need dupont Female pin connectors, crimping tool, wire cutter & stripper, heat-shrink-tube & heat-gun or dupont connector housing.
  Better options for dupont connectors are Molex Crimp Terminals Series: 70058 Part No: 16020098 or Harwin Series: M20 Part No: 1180042. I used Molex connectors and IWISS IWS-2820 crimping tool. Cover these connectors with either heat shrink tube (3.00mm diameter tube) or dupont connector housing.

  3 - Use Wires from Old Fan:
  If you have some old unused fan laying around that has dupont connector wires. Cut the wires from that fan, cut the Noctua connector and do some wire joining. Noctua fan's OmniJoin adaptors can be used for joining wires.

• Complete specification of Noctua fan is available at Noctua Whitepaper. Details of Raspberry Pi GPIO pin layout is available at GPIO Pinout. Screenshots attached for quick reference.

  Fan Wires	GPIO Layout

• Fan wires connection to RP4 pins:

  Fan Wires	RP4 Pins
  Yellow +5V	Physical Pin 4
  Black Ground	Physical Pin 6
  Blue PWM Signal	Physical Pin 12
  Green RPM Signal	Physical Pin 16

  Fan's PWM signal wire is connected to the RP4 Physical pin 12 - GPIO pin 18. This fan-control code uses GPIO 18 as default. There are 4 pins on RP4 that support hardware PWM GPIO 12/13/18/19. If you are going to use a different GPIO pin make sure you change the PWM_PIN in params.conf with the one you use.
  The green tachometer wire on Noctua fan is used to calculate RPM. Connect the fan's RPM signal wire to the RP4 Physical pin 16 - GPIO pin 23. By default, tacho output is disabled in params.conf. (refer to Points to Note)

Steps

❯ Install C Library

• Install either WiringPi or pigpio C library.

  • WiringPi
    Download and install WiringPi C library.

    Install:
    sudo dpkg -i wiringpi_3.1_arm64.deb

    ℹ️ Note:
    WiringPi has been revived. Latest release supports RasberryPi OS Bookworm. Check the github repo for updates.

  • Pigpio
    Download and install pigpio C library.

    Install:
    unzip -o pigpio-master.zip
make
sudo make install

    ℹ️ Note:
    Uninstall Pigpio:
    If pigpio was installed using the previous step, manually remove all files under /usr/local/* mentioned here. To remove the distro provided pigpio package run cmd sudo apt --purge autoremove pigpio

❯ Install FanControl

• Download the latest fan-control release for the library that was installed in the previous step. Create folder /opt/gpio/fan. Copy fan-control and params.conf from the latest release under build folder to this newly created folder /opt/gpio/fan. Make sure both files are under the ownership of root and fan-control is executable. Fan-control will work with default values without params.conf.

  Create folder:
  sudo mkdir -p /opt/gpio/fan/

  Make binary executable [If needed]:
  sudo chmod +x /opt/gpio/fan/fan-control

  Change ownership [If needed]:
  sudo chown root:root /opt/gpio/fan/fan-control
sudo chown root:root /opt/gpio/fan/params.conf

• Create service to automatically run the fan-control at startup. Copy fan-control.service from the latest release under service folder to /etc/systemd/system/. Make sure file is under the ownership of root. Enable the service.

  Change ownership [If needed]:
  sudo chown root:root /etc/systemd/system/fan-control.service

  Enable Service:
  sudo systemctl enable fan-control

  Start Service [If needed]:
  System reboot will automatically start the service. To start without reboot.
  sudo systemctl start fan-control

  Check Service Status:
  sudo systemctl status fan-control

  Check Journal Logs:
  sudo journalctl -u fan-control

Points to Note

• Noctua's green RPM signal wire (aka tacho) connectivity is optional. It generates tacho output signal. It does not add any value in controlling fan speed. That is why it is disabled by default in params.conf. To retrieve RPM periodically through tacho output signal in the logs, connect the wire as mentioned under Hardware Prep and enable it in params.conf. Change TACHO_ENABLED to 1.

• Fan runs at full speed when RP4 is booted. When fan-control service starts during boot process fan will either switch off or adjust its speed, depending on CPU temperature. Fan-control service runs the fan within the temperature range from 40–55°C and above. Temperature range is configurable through params.conf. Noctua fan's recommeded minimum RPM is 1000. I kept the minimum RPM at 1500 in this service. Table below explains the fan's operation:

  Temp	RPM
  <= 40°C	0
  > 40°C	1500
  Temp++	RPM++
  >= 55°C	5000

• params.conf can be used to configure values of adjustable parameters. Fan-control service will work with default values without params.conf. Restart fan-control service after any change in params.conf. Table below gives an overview of all adjustable parameters.
  _{* Do not change values if you do not know what you are doing}

  Parameters	Default	Info
  PWM_PIN	18	HW PWM GPIO pins on RPi4B: 12, 13, 18, 19
  TACHO_PIN	23	Tacho pin, enable through TACHO_ENABLED
  RPM_MAX	5000	Fan's max speed. Noctua Specs: Max=5000
  RPM_MIN	1500	Fan's min speed. Noctua Specs: Min=1000
  RPM_OFF	0	Fan off
  TEMP_MAX	55	Max temperature in °C to run fan at max RPM
  TEMP_LOW	40	Min temperature in °C to start fan at min RPM
  WAIT	5000	Wait interval between adjusting RPM
  TACHO_ENABLED	0	Enable tacho, 0=Disable 1=Enable
  THERMAL_FILE	/sys/class/thermal/thermal_zone0/temp	Path to RP4 thermal file

• The 5V pins on RP4 i.e., physical pin 2 and 4 are not GPIO. They are connected to the 5V power supply and are always on. Those cannot be turned off without some form of circuit using mosfet or transistor. The point is if you run shutdown command from a shell or UI the fan will keep on running at full speed unless you unplug the RP4.

• Fan-control logs to the journal at startup and exit. It also logs periodically when fan is on. You can change log level to MaxLevelStore=info in journald.conf to reduce logging.

Build

• Install libsystemd-dev. It is required for compiling fan-control source code.

  sudo apt install libsystemd-dev

• Binary is available in the release. If for any reason you want to recompile.

  WiringPi:
  sudo gcc -Wall -O2 fan-control-wiringpi.c -o fan-control -lwiringPi -lsystemd
  Pigpio:
  sudo gcc -Wall -O2 fan-control-pigpio.c -o fan-control -lpigpio -lsystemd