fancontrol

#!/usr/bin/env python3

import logging

import sys
import subprocess
import time

from gpiozero import OutputDevice
from signal import signal, SIGABRT, SIGILL, SIGINT, SIGSEGV, SIGTERM

logger = logging.getLogger()
logger.setLevel(logging.INFO)

handler = logging.StreamHandler(sys.stdout)
formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s')
handler.setFormatter(formatter)
logger.addHandler(handler)


ON_THRESHOLD = 65  # (degrees Celsius) Fan kicks on at this temperature.
OFF_THRESHOLD = 55  # (degress Celsius) Fan shuts off at this temperature.
SLEEP_INTERVAL = 5  # (seconds) How often we check the core temperature.
GPIO_PIN = 17  # Which GPIO pin you're using to control the fan.


def get_temp():
    """Get the core temperature.

    Run a shell script to get the core temp and parse the output.

    Raises:
        RuntimeError: if response cannot be parsed.

    Returns:
        float: The core temperature in degrees Celsius.
    """
    output = subprocess.run(['vcgencmd', 'measure_temp'], capture_output=True)
    temp_str = output.stdout.decode()
    try:
        return float(temp_str.split('=')[1].split('\'')[0])
    except (IndexError, ValueError):
        raise RuntimeError('Could not parse temperature output.')


def main_loop(fan):
    logging.info("Starting Fan Controller...")
    # Validate the on and off thresholds
    if OFF_THRESHOLD >= ON_THRESHOLD:
        raise RuntimeError('OFF_THRESHOLD must be less than ON_THRESHOLD')

    while True:
        temp = get_temp()
        logger.debug("Temperature: {}".format(temp))

        # Start the fan if the temperature has reached the limit and the fan
        # isn't already running.
        # NOTE: `fan.value` returns 1 for "on" and 0 for "off"
        if temp > ON_THRESHOLD and not fan.value:
            logger.info("Temperature above threshold, setting fan on: {} > {}".format(temp, ON_THRESHOLD))
            fan.on()

        # Stop the fan if the fan is running and the temperature has dropped
        # below the limit.
        elif fan.value and temp < OFF_THRESHOLD:
            logger.info("Temperature below threshold, setting fan off: {} > {}".format(temp, OFF_THRESHOLD))
            fan.off()

        time.sleep(SLEEP_INTERVAL)

if __name__ == '__main__':
    fan = OutputDevice(GPIO_PIN)

    def exit_handler(*args):
        logging.info("Exiting: Setting fan off.")
        fan.off()
        sys.exit(0)

    for sig in (SIGABRT, SIGILL, SIGINT, SIGSEGV, SIGTERM):
        signal(sig, exit_handler)

    main_loop(fan)