hardware_pwm_fan

#!/usr/bin/python3

import getopt
import sys
import time
import sdnotify
from subprocess import check_output
from rpi_hardware_pwm import HardwarePWM

# Defaults
HARD_PWM_CHAN = 0
SLEEP_TIME = 5
OFF_TEMP = 35
MAX_TEMP = 80
FAN_LOW_PCT = 20
VERBOSE = False
NOTIFY = False


def usage():
    """Print usage information"""
    print(f'Usage: {sys.argv[0]} [-hvn] --hard_pwm_channel=[0 | 1] [-off-temp=<temp>] ')
    print('  [-high-temp=<temp>] [-fan-low-pct=<pct>] [-sleep=<sec>]')
    print('')
    print('  -h, --help                Print this help')
    print('  -v, --verbose             Verbose output')
    print('  --off-temp=<temp>         Temperature at which the fan is turned off')
    print('  --high-temp=<temp>        Temperature at which the fan is at full speed')
    print('  --fan-low-pct=<pct>       How slow the fan is at the lowest speed')
    print('  --hard-pwm-channel=<chan> GPIO channel to use for the hardware PWM fan')
    print('  --sleep=<sec>             Time to sleep between temperature checks')
    print('  -n, --notify              Enables systemd notify support')
    print('')
    print('Note: You must specify a hardware PWM channel for this to work, and')
    print('  have loaded the pwm or pwm-2chan dtoverlay for the Raspberry Pi.')
    print('  See /boot/overlays/README and /boot/config.txt for more info.')
    print('')

def gettemp():
    """Get the current temperature"""
    return float(check_output(['cat', '/sys/class/thermal/thermal_zone0/temp']).decode()) / 1000.0


def fan_speed(temp: float):
    """Calculate the fan 'curve' (not really a curve)"""
    max_speed = 100
    min_speed = max_speed * FAN_LOW_PCT / 100
    if temp < OFF_TEMP:
        return 0
    elif temp > MAX_TEMP:
        return max_speed
    else:
        # linear interpolation
        return int(
            min_speed + ((temp - OFF_TEMP) / (MAX_TEMP - OFF_TEMP)) * (max_speed - min_speed))

def main():
    """Main function"""
    global HARD_PWM_CHAN, SLEEP_TIME, OFF_TEMP, MAX_TEMP, FAN_LOW_PCT, VERBOSE, NOTIFY
    try:
        opts, _ = getopt.getopt(sys.argv[1:], 'hv', ['off-temp=', 'high-temp=', 'fan-low-pct=',
                                                     'hard-pwm-channel=', 'sleep=', 'verbose', 'notify'])
    except getopt.GetoptError as err:
        print(err)
        print('')
        usage()
        sys.exit(2)
    for opt, arg in opts:
        if opt in ('-h', '--help'):
            usage()
            sys.exit()
        elif opt in ('-v', '--verbose'):
            VERBOSE = True
        elif opt in ('--off-temp'):
            OFF_TEMP = int(arg)
        elif opt in ('--high-temp'):
            MAX_TEMP = int(arg)
        elif opt in ('--fan-low-pct'):
            FAN_LOW_PCT = int(arg)
        elif opt in ('--hard-pwm-channel'):
            HARD_PWM_CHAN = int(arg)
        elif opt in ('--sleep'):
            SLEEP_TIME = int(arg)
        elif opt in ('-n', '--notify'):
            NOTIFY = True

    print('')
    print(f'HARD_PWM_CHAN: {HARD_PWM_CHAN}')
    print(f'SLEEP_TIME: {SLEEP_TIME}')
    print(f'OFF_TEMP: {OFF_TEMP}')
    print(f'MAX_TEMP: {MAX_TEMP}')
    print(f'FAN_LOW_PCT: {FAN_LOW_PCT}')
    print(f'VERBOSE: {VERBOSE}')
    print(f'NOTIFY: {NOTIFY}')
    print('')

    pwm = HardwarePWM(HARD_PWM_CHAN, hz=25000)
    pwm.start(100)

    if NOTIFY:
        systemd = sdnotify.SystemdNotifier()
        systemd.notify('READY=1')

    try:
        while True:
            temp = gettemp()
            speed = fan_speed(temp)
            pwm.change_duty_cycle(speed)
            if VERBOSE:
                print(f'Temp: {temp:.1f}C, Speed: {speed}%')
            if NOTIFY:
                systemd.notify('WATCHDOG=1')
            time.sleep(SLEEP_TIME)
    except KeyboardInterrupt:
        pwm.stop()
        print('')
        print('Exiting on KeyboardInterrupt')
        sys.exit()

if __name__ == '__main__':
    main()