# Fan bang-bang control with pwm
import os
import time
import RPi.GPIO as GPIO

# Settings
M_TIME = 5     # Measure time interval
ON_TEMP = 70   # upper temp value -> Fan turned on
OFF_TEMP = 60  # lower temp value -> Fan turned off
FAN_PIN = 14   # Transistor for the cooling fan is connected to pin 14
PWM_F = 1000   # PWM frequency in kHz. Change only when fan makes fancy noises
DC = 50        # PWM duty cycle for the FAN (0 ... 100, where 100 is the maximum)

# setup GPIO
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(FAN_PIN, GPIO.OUT)

# Activate PWM on the FAN_PIN
p = GPIO.PWM(FAN_PIN, PWM_F)

# funtion for reading the cpu temperatur and return it as float
def getCPUtemp():
    res = os.popen('vcgencmd measure_temp').readline()
    return (res.replace("temp=", "").replace("'C\n", ""))

# main loop for the bang-bang control
while True:
    # get temperature
    temp_float = float(getCPUtemp())

    try:
        # if actual temp axceeded the upper value, turn fan on
        if (temp_float > ON_TEMP):
            p.start(DC)
        # if actual temp drop below the lower value, turn fan off
        elif (temp_float < OFF_TEMP):
            p.stop()

    except:
        # for debugging
        print "ERROR"

    # cycle time of the control. for temperature it dont have to be fast
    time.sleep(M_TIME)