rpi-pwmfan.py

#!/usr/bin/python3

import time
import pigpio

# Pin configuration
PWM_PIN = 12  # Pin to drive PWM fan - HW PWM works on GPIO 12, 13, 18 and 19 on RPi4B
TACH_PIN = 6  # Fan's tachometer output pin

# Temperature thresholds
MAX_TEMP = 70  # [°C] Above this temperature, the fan is at max speed
MIN_TEMP = 45  # [°C] Above this temperature, the fan starts
OFF_TEMP = 40  # [°C] Below this temperature, the fan is off

# Fan settings
PWM_FREQ = 25000  # [kHZ] Noctua Specs: Target_Frequency=25kHz
PULSE = 2  # Noctua Specs: Noctua fans put out two pulses per revolution

# Fan speed settings
RPM_MAX = 5000  # Noctua Specs: Max=5000
RPM_MIN = 1500  # Noctua Specs: Min=1000
RPM_OFF = 0

# Timing
WAIT = 2  # [s] Interval before adjusting RPM

# Initialize pigpio
pi = pigpio.pi()

# Remember pin modes
orig_pwm_pin_mode = -1
orig_tach_pin_mode = -1

# Global variables
t = time.time()
rpm_pulse = 0
tach_pin_callback = None


def getCpuTemperature():
    with open('/sys/class/thermal/thermal_zone0/temp') as f:
        return float(f.read()) / 1000


def handleTachometerPulse(gpio, level, tick):
    """Handle the interrupt generated by the falling edge of the tachometer pulse."""
    global rpm_pulse
    rpm_pulse += 1  # Increment pulse count when a pulse is detected


def getFanRPM():
    global t, rpm_pulse
    
    dt = time.time() - t
    if dt < 0.002:
        return  # Reject spuriously short pulses
    
    frequency = rpm_pulse / dt
    rpm = (frequency / PULSE) * 60
    
    # Reset pulse counter and timestamp
    rpm_pulse = 0
    t = time.time()
    
    return rpm


def setFanRPM(rpm):
    duty_cycle = int((rpm / RPM_MAX) * 1000000)
    pi.hardware_PWM(PWM_PIN, PWM_FREQ, duty_cycle)


def setup():
    global orig_pwm_pin_mode, orig_tach_pin_mode, tach_pin_callback
    
    print("Setting up...")
    
    orig_pwm_pin_mode = pi.get_mode(PWM_PIN)
    orig_tach_pin_mode = pi.get_mode(TACH_PIN)
    
    # Set pin modes
    pi.set_mode(PWM_PIN, pigpio.ALT5)  # ALT5 mode for hardware PWM
    pi.set_mode(TACH_PIN, pigpio.INPUT)
    
    # Add event to detect tachometer pulse
    tach_pin_callback = pi.callback(TACH_PIN, pigpio.FALLING_EDGE, handleTachometerPulse)
    
    setFanRPM(RPM_OFF)  # Set fan speed to off initially
    
    return


def cleanup():
    # Turn off the fan
    setFanRPM(RPM_OFF)
    
    # Pin mode cleanup
    if orig_pwm_pin_mode != -1:
        pi.set_mode(PWM_PIN, orig_pwm_pin_mode)
    
    if orig_tach_pin_mode != -1:
        pi.set_mode(TACH_PIN, orig_tach_pin_mode)
    
    if tach_pin_callback is not None:
        tach_pin_callback.cancel() # Remove the callback associated with the tachometer pin
    
    pi.stop()
    return


def main():
    print("PWM FAN control starting...")
    setup()
    
    while True:
        try:
            temp = getCpuTemperature()
            print(f"CPU Temperature: {temp:.1f}")
            
            if temp >= MAX_TEMP:
                setFanRPM(RPM_MAX)
            elif temp >= MIN_TEMP:
                delta = temp - MIN_TEMP
                rpm = min(RPM_MAX, max(RPM_MIN, int(RPM_MIN + delta)))
                setFanRPM(rpm)
            elif temp < OFF_TEMP:
                setFanRPM(RPM_OFF)
            
            rpm = getFanRPM()
            print(f"Fan RPM: {rpm:.2f}")
            time.sleep(WAIT)
        
        except KeyboardInterrupt:
            cleanup()
            break
        except Exception as e:
            print("Something went wrong")
            print(e)
            cleanup()


if __name__ == "__main__":
    main()