RP4 PWM Fan Controller

           

Preview

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Intro

Service to adjust RP4 PWM (Pulse Width Modulation) 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 you can specify from setup is 60°C. This limit can be bypassed by editing /boot/config.txt manually. Search for dtoverlay=gpio-fan entry and change the temp=60000 value to your 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). Raspberry Pi crystal oscillator clock frequency on RPi4B is 54MHz and on all earlier models it is 19.2MHz. WiringPi function pwmSetClock requires a divisor of clock frequency to set the target frequency of fan. The process is well documented in the fan-control service code.

I connected Noctua fan's 3 wires directly to the RP4 GPIO pins. It's been almost 2 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 C Lib Ver
NF-A4x10 5V PWM Fan	Raspberry Pi 4 Model B	raspios-bullseye-arm64-lite	2.70

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. Buy short jumper wires somewhere between 2-4" long. You need atleast 3 of them. Male part of jumper wire will connect to Noctua connector and Female part will connect to GPIO. This is what I used in the beginning for few months.

  2 - Dupont Female Pin Connectors 2.54mm Pitch:
  This is the one I am using now, as shown in the preview. It is the cleanest option. It could be the most expensive option if you do not have all the tools. You need dupont Female pin connectors, crimping tool, wire cutter/stripper, heat shrink tube/heat gun or dupont connector housing.
  You can either buy connectors and housing kit or buy dupont connectors separately. 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. For crimping I used IWISS IWS-2820 crimping tool. Cover these connectors with either heat shrink tube (I used 3.00mm diameter tube) or dupont connector housing.
  If you go with this route. You have to cut the noctua fan wire to the required length. Make sure you calculate required wire length properly before cutting. If you cut it too short you will end up inserting wire joints. Strip wires (Practice stripping on the other end first). Attach dupont connectors to the stripped wires, crimp them with crimpping tool. Add heat shrink tubes to the connectors and shrink them with heatgun or attach connector housing.

  3 - Use Wires from Old Fan:
  If you have some old fan laying around that has dupont connector wires and you have no plan of using it. Cut the wires from that fan (You need 3 wires), cut the Noctua connector and do some wire joining (Google around how to join electrical wires). Noctua fan comes with 4 OmniJoin adaptors, you can use that as well 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

  Fan's PWM signal wire is connected to the RP4 Physical/Board pin 12 - GPIO/BCM pin 18. This fan-control code is targeted at GPIO pin 18. There are 4 pins on RP4 that supports hardware PWM GPIO 12/13/18/19 You can use any one of those for this fan-control code. Make sure you replace the pin number in code with the one you use.
  The Green tachometer wire on Noctua fan is used to calculate RPM. I wrote the code for calculating RPM during development. It is fully functional code and uses Physical/Board pin 16 - GPIO/BCM pin 23. If you noticed that green wire is not connected in the preview. I do not use this tachometer wire after final deployment. Final code and binary in this repo have those function calls commented out. If you are interested in retrieving RPM, connect the Green Noctua fan wire to GPIO pin 23, uncomment setupTacho and getFanRpm function calls and rebuild binary.

Steps

⮞ Install Packages

• Install WiringPi C library. You can download it from WiringPi. Installation instructions are available at Install.

  Quick Reference:
  Unzip sudo unzip -o WiringPi-master.zip -d WiringPi
  Build and Install sudo ./build

• Install libsystemd-dev package. This is needed for logging to systemd journal. This program logs to the journal at startup and exit. It will also log when fan is on (at 5 seconds interval) if MaxLevelStore=debug in journald.conf. You can change log level to MaxLevelStore=info in journald.conf to reduce logging. If you do not want journal logging at all from this fan-control service you can skip libsystemd-dev package installation and remove journal logging from code, explained in the Build section below.

  Install Package:
  sudo apt install libsystemd-dev

  Check Journal Logs:
  sudo journalctl -u fan-control

⮞ Install FanControl

• Create a folder /opt/gpio/fan for fan-control binary (You can use your preferred location). Copy/Paste fan-control binary from this repo folder build to this newly created folder /opt/gpio/fan Make sure file is under the user:group of root and it is executable. Copy params.conf config file from this repo folder build to this newly created folder /opt/gpio/fan. Make sure file is under the user:group of root. params.conf is optional, fan-control service will work with default values without params.conf.

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

  Make file executable:
  chmod +x /opt/gpio/fan/fan-control

  Change files 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/Paste fan-control.service from this repo folder service to /etc/systemd/system/. Make sure file is under the user:group of root. Enable this service. This service starts fan-control as early as possible during startup without any warnings in the log.

  Change ownership of file [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 this service. If you want to start it instantly without rebooting.
  sudo systemctl start fan-control

  Check Service Status:
  sudo systemctl status fan-control

Points to Note

• Fan will run at full speed when RP4 is booted. After few seconds when fan-control will be loaded either it will switch off or adjusts its speed, depending on CPU temperature.

• Fan-control service runs the fan within the temperature range from 40–55°C and above. Feel free to change the range according to your desired value through params.conf and restart the service. 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 without rebuilding binary. It is optional file, fan-control service will work with default values without it. Most useful parameters could be TEMP_MAX and TEMP_LOW. Change values in params.conf and restart fan-control service. 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 functionality is disabled in code
  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
  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. I run my RP4 24x7, do a reboot from shell once in a while and unplug it if a shutdown is really needed for any reason.

Build

• Binary is available under repo folder build. Latest binary is built on raspios-bullseye-arm64-lite OS with Wiring Pi ver 2.70. If for any reason you want to rebuild.

  Build command:
  sudo gcc -Wall -O2 fan-control.c -o fan-control -lwiringPi -lsystemd

• Test binary after build.

  Run binary:
  sudo ./fan-control
  Ctrl+C to exit

• If you are not interested in journal logging. Comment out the include header sd-journal.h and journal logging lines starting with sd_journal_print

  Build command without journal logging:
  sudo gcc -Wall -O2 fan-control.c -o fan-control -lwiringPi