fan.py

#!/usr/bin/python3
import sys
import time
from gpiozero import LED # doc: https://gpiozero.readthedocs.io/
from systemd import journal

# define the GPIO to control the transistor's B pin
fan = LED(17)

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


# close fan at begining
is_close = True
fan.off()
while True:
    temp = cpu_temp()
    if is_close:
        if temp > 55.0: # upper bound to turn on the fan
            journal.send("{} {} {}".format(time.ctime(), temp, 'Fan ON'))
            fan.on()
            is_close = False
    else:
        if temp < 48.0: # lower bound to turn off the fan
            journal.send("{} {} {}".format(time.ctime(), temp, 'Fan OFF'))
            fan.off()
            is_close = True

    time.sleep(2.0)
    journal.send("{} {}".format(time.ctime(), temp))