pi-fan

Turn on Raspberry Pi 3 fan when CPU temperature reaches a certain level

• R1 can range from 220Ω up to 1kΩ
• The 2N2222 transistor can feed up to 600 mA fan
• If you see a yellow lightning bolt in the top right corner of the screen, that means that you don't have enough power going to the Raspberry Pi, a 5V / 2500 mA will generally do
• The diode role is to "clamp" the voltage spike that occurs whenever the fan is switched off, and so protect the Raspberry Pi
• If you have a small fan like those integrated with some cases (200 mA or less) the diode can be omitted
• Any valid GPIO pin can do
• The program will tun on the fan when CPU temperature reaches fanOnTemperature, the fan will turn off only when the temperature goes below fanOffTemperature
• Values of 60 degrees for fanOnTemperature and 45 for fanOnffTemperature showed during tests good compromize between cooling and between intermittent on/off of the fan, adjust them as per your taste

Allow the script to run at startup

Supposing the script is saved in the /home/pi/progs/ folder:

/etc/rc.local method

Edit the /etc/rc.local script and add the following line:

/home/pi/progs/pi-fan.py &

• It is not necessary to add sudo to the command as the rc.local is run by the root user
• Ensure the last line of the script is exit 0

as a service (preferred method)

Create a service file: sudo nano /etc/systemd/system/pi-fan.service and paste the following:

[Unit]
Description=pi-fan

[Service]
Type=simple
ExecStart=/usr/bin/python3 /home/pi/progs/pi-fan.py
Restart=always
User=pi

[Install]
WantedBy=multi-user.target

Enable the service at startup with sudo systemctl enable pi-fan.service and reboot (or start it manually)