Suggestion for PWM fan control of Raspberry Pi Zero 2W

[jkwedar]

The commonly shared PWM fan control examples weren’t quite right for my use case on the Raspberry Pi Zero 2W. Most are designed with the Pi 4 or 5 in mind, but the MeshAdv-Mini setup with a Zero 2W has different requirements. I needed a solution that was lightweight, headless, and tailored to the specific behavior of the fan.

Setup: Raspberry Pi Zero 2W (SSH access only, no desktop environment) Raspbian GNU/Linux 12 (Bookworm) Waveshare UPS HAT (C) (optional) MeshAdv-Mini enclosure with PWM-controlled fan PWM fan (typically 3-wire: red, black, blue) connected to the MeshAdv-Mini PWM fan header

Raspberry Pi Zero 2W: Automatic Fan Control with PWM + systemd This sets up automatic fan control using a Waveshare UPS HAT and GPIO-based PWM on a Pi Zero 2W. The fan spins only when needed and stops when idle.

Step 1: Calibrate Your Fan (Optional, Recommended)

sudo nano /root/fan_calibrate.py

Paste this:

#!/usr/bin/env python3

import RPi.GPIO as GPIO
import time

FAN_PIN = 18

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(FAN_PIN, GPIO.OUT)

pwm = GPIO.PWM(FAN_PIN, 25)
pwm.start(0)

print("Enter fan speed (0-100). Type 'exit' or press Ctrl+C to quit.")

try:
    while True:
        val = input("Set fan speed: ").strip()
        if val.lower() == 'exit':
            break
        try:
            dc = int(val)
            if 0 <= dc <= 100:
                pwm.ChangeDutyCycle(dc)
            else:
                print("Enter a value from 0 to 100.")
        except:
            print("Invalid input.")
except KeyboardInterrupt:
    pass
finally:
    pwm.ChangeDutyCycle(0)
    pwm.stop()
    GPIO.cleanup()
    print("Fan off. GPIO cleaned up.")

Then make it executable and run:

sudo chmod +x /root/fan_calibrate.py
sudo /root/fan_calibrate.py

Find the lowest duty cycle where the fan reliably starts (e.g., 25%) and remember that value.

Step 2: Create the Fan Control Script

sudo nano /usr/local/bin/fan_control.py

Paste this:

#!/usr/bin/env python3

import time
import RPi.GPIO as GPIO

FAN_PIN = 18
FAN_MIN = 25  # Minimum duty cycle for reliable spin

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(FAN_PIN, GPIO.OUT)
pwm = GPIO.PWM(FAN_PIN, 25)
pwm.start(0)

def get_cpu_temp():
    try:
        with open("/sys/class/thermal/thermal_zone0/temp", "r") as f:
            return float(f.read()) / 1000.0
    except:
        return 0.0

try:
    while True:
        temp = get_cpu_temp()

        if temp < 45:
            fan_speed = 0
        elif temp > 70:
            fan_speed = 100
        else:
            fan_speed = (temp - 45) * 4

        if 0 < fan_speed < FAN_MIN:
            fan_speed = FAN_MIN

        pwm.ChangeDutyCycle(fan_speed)
        print(f"CPU Temp: {temp:.1f}°C | Fan: {int(fan_speed)}%")
        time.sleep(15)

except KeyboardInterrupt:
    pass

finally:
    pwm.ChangeDutyCycle(0)
    pwm.stop()
    GPIO.cleanup()

Then: sudo chmod +x /usr/local/bin/fan_control.py

Step 3: Create the systemd Service

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

Paste this:

[Unit]
Description=MeshAdv Mini Fan Control Script
After=network.target

[Service]
ExecStart=/usr/bin/python3 /usr/local/bin/fan_control.py
Restart=on-failure
User=root

[Install]
WantedBy=multi-user.target

Then enable and start the service:

sudo systemctl daemon-reload
sudo systemctl enable fan_control.service
sudo systemctl start fan_control.service

Verifying It Works

Watch live output: sudo journalctl -u fan_control.service -f

Check CPU temp:

cat /sys/class/thermal/thermal_zone0/temp
(straight °C = divide by 1000)

Stress test (optional):

yes > /dev/null &
yes > /dev/null &

Let temp rise above 45°C — the fan should start. Then: killall yes

**Note: This solution was developed and tested in my specific environment with the help of ChatGPT. It works reliably on a Raspberry Pi Zero 2W running Raspbian Bookworm with the MeshAdv-Mini and a PWM-controlled fan. Your setup may require minor adjustments, especially if your Python environment or GPIO configuration differs. Always test and calibrate based on your specific hardware.