PWM fan control

Description

This script is dedicated to control a PWM fan on my Raspberry PI 4B 8 Go. To use correctly this script, please install the fan following the information bellow :

Be sure to plug the cable accordingly !

Script overview

pwm_fan_control.py

import RPi.GPIO as GPIO # type: ignore
import time
import subprocess

# Configuration constants
GPIO_PIN = 14
TEMP_THRESHOLD = 50.0
PWM_FREQUENCY = 100

# GPIO pin setup
GPIO.setmode(GPIO.BCM)
# Set to false, other processes occupying the pin will be ignored
GPIO.setwarnings(False)
GPIO.setup(GPIO_PIN, GPIO.OUT)
pwm = GPIO.PWM(GPIO_PIN,PWM_FREQUENCY)

# Initialize PWM
dc = 0
pwm.start(dc)

def get_cpu_temperature():
    """Retrieves the CPU temperature using vcgencmd."""
    try:
        temp_str = subprocess.getoutput("vcgencmd measure_temp | sed 's/[^0-9.]//g'")
        return float(temp_str)
    except Exception as e:
        print(f"Error retrieving temperature: {e}")
        return 0.0

try:
    while True:
        temp = get_cpu_temperature()
        time.sleep(1)

        # Adjust duty cycle based on temperature
        if temp >= TEMP_THRESHOLD:
            new_dc = 100
        else:
            new_dc = 0

        # Update duty cycle if necessary
        if new_dc != dc:
            dc = new_dc
            pwm.ChangeDutyCycle(dc)

except KeyboardInterrupt:
    print("Stopping the script.")
finally:
    pwm.stop()
    GPIO.cleanup()

Setup

1. Ensuring the GPIO lib is isntalled : pip freeze | grep RPi.GPIO
2. Creating a systemd service file : sudo nano /etc/systemd/system/pwm_fan_control.service
3. Add :
   pwm_fan_control.service

   [Unit]
   Description=My Python Script Service
   After=network.target
   
   [Service]
   User=palpi
   ExecStart=/usr/bin/python /home/palpi/palpi/scripts/pwm_fan_control.py
   WorkingDirectory=/home/palpi/palpi/scripts
   StandardOutput=null
   StandardError=null
   
   [Install]
   WantedBy=multi-user.target
   

4. Reloading systemctl : sudo systemctl daemon-reload
5. Enabling our service : sudo systemctl enable pwm_fan_control.service
6. Starting our service : sudo systemctl start pwm_fan_control.service
7. Checking our service : sudo systemctl status pwm_fan_control.service

How to test the script

• Stress the CPU to increase the temp : fulload() { dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null & }; fulload; read; killall dd
  The more | dd if=/dev/zero of=/dev/null the higher it will reach
• You can check the temp with vcgencmd measure_temp|sed 's/[^0-9.]//g'