Raspberry PI fan control with hardware PWM

fancontrol.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

from rpi_hardware_pwm import HardwarePWM
import time
import sys
import syslog
import os
import signal

# Configuration
PWM_CHANNEL = 0 # Hardware PWM channel
PWM_FREQ = 25 # [Hz] Change this value if fan has strange behavior
WAIT_TIME = 1 # [s] Time to wait between each refresh

# Configurable temperature and fan speed steps
tempSteps = [60, 70, 80]  # [°C]
speedSteps = [40, 60, 100]  # [%]

# Fan speed will change only of the difference of temperature is higher than hysteresis
hyst = 1

# Will keep fan running until temperature drops below lowest of tempSteps minus this value
shutdown_hyst = 10  # [°C] 

# Setup hardware PWM
pwm = HardwarePWM(pwm_channel=PWM_CHANNEL, hz=PWM_FREQ)
pwm.start(0)

i = 0
fanSpeed = 0
cpuTempOld = 0
fanSpeedOld = 0

systemdRun = bool(os.environ.get('INVOCATION_ID'))

if systemdRun:
    syslog.openlog("fancontrol", logoption=syslog.LOG_PID)

def logger(message):
    if systemdRun:
        syslog.syslog(message)
    else:
        print(message)

def error(error):
    pwm.stop()
    if systemdRun:
        syslog.syslog(syslog.LOG_ERR, error)
        sys.exit(-1)
    else:
        sys.exit(error)

def get_temp():
    cpuTempFile = open("/sys/class/thermal/thermal_zone0/temp", "r")
    cpuTemp = float(cpuTempFile.read()) / 1000
    cpuTempFile.close()
    return cpuTemp

def stop():
    pwm.stop()
    sys.exit()

def handle_sigterm(sig, frame):
    logger("Interrupted by SIGTERM")
    stop()

signal.signal(signal.SIGTERM, handle_sigterm)

# We must set a speed value for each temperature step
if len(speedSteps) != len(tempSteps):
    error("Error: Numbers of temp steps and speed steps are different")

logger("Starting, CPU temp %.1f'C" % get_temp())

try:
    while 1:
        # Read CPU temperature
        cpuTemp = get_temp()

        # Calculate desired fan speed
        if abs(cpuTemp - cpuTempOld) > hyst:
            # Below first value, fan will run at min speed.
            if cpuTemp < tempSteps[0]:
                if (cpuTemp < tempSteps[0] - shutdown_hyst or fanSpeed == 0):
                    fanSpeed = 0
                else:
                    fanSpeed = speedSteps[0]
            # Above last value, fan will run at max speed
            elif cpuTemp >= tempSteps[len(tempSteps) - 1]:
                fanSpeed = speedSteps[len(tempSteps) - 1]
            # If temperature is between 2 steps, fan speed is calculated by linear interpolation
            else:
                for i in range(0, len(tempSteps) - 1):
                    if (cpuTemp >= tempSteps[i]) and (cpuTemp < tempSteps[i + 1]):
                        fanSpeed = round((speedSteps[i + 1] - speedSteps[i])
                                         / (tempSteps[i + 1] - tempSteps[i])
                                         * (cpuTemp - tempSteps[i])
                                         + speedSteps[i], 1)

            if (fanSpeed != fanSpeedOld):
                logger("CPU temp %.1f'C, set fan speed to %.1f%%" % (cpuTemp, fanSpeed))
                pwm.change_duty_cycle(fanSpeed)
                fanSpeedOld = fanSpeed

            cpuTempOld = cpuTemp

        # Wait until next refresh
        time.sleep(WAIT_TIME)


# If a keyboard interrupt occurs (ctrl + c), the PwM enable is set to 0 and the program exits.
except KeyboardInterrupt:
    logger("Interrupted by keyboard")
    stop()

fancontrol.service

[Unit]
Description=FanControl Service
After=multi-user.target

[Service]
Restart=always
ExecStart=/usr/bin/python3 /opt/FanControl/fancontrol.py

[Install]
WantedBy=default.target

manual.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

from rpi_hardware_pwm import HardwarePWM
import sys

# Configuration
PWM_CHANNEL = 0 # Hardware PWM channel
PWM_FREQ = 25 # [Hz] Change this value if fan has strange behavior

# Setup hardware PWM
pwm = HardwarePWM(pwm_channel=PWM_CHANNEL, hz=PWM_FREQ)
pwm.start(0)

try:
    while 1:
        fanSpeed=float(input("Fan Speed: "))
        pwm.change_duty_cycle(fanSpeed)


except(KeyboardInterrupt):
    print("Fan ctrl interrupted by keyboard")
    pwm.stop()
    sys.exit()

To enable hardware PWM control you will need:

1. add one of this to /boot/config.txt:

• dtoverlay=pwm-2chan to use GPIO_18 as the pin for PWM0 and GPIO_19 as the pin for PWM1
• dtoverlay=pwm-2chan,pin=12,func=4,pin2=13,func2=4 to use GPIO_12 as the pin for PWM0 and GPIO_13 as the pin for PWM1

2. reboot
3. install library sudo pip3 install rpi-hardware-pwm