Python

#!/usr/bin/python
# -*- coding: utf-8 -*-

import RPi.GPIO as GPIO
import time
import sys

# Configuration
FAN_PIN = 14            # BCM pin used to drive transistor's base
WAIT_TIME = 1           # [s] Time to wait between each refresh
FAN_MIN = 20            # [%] Fan minimum speed.
PWM_FREQ = 25           # [Hz] Change this value if fan has strange behavior
INITIALIZING_TIME = 5   # [s] Time Pi is initializing (max fan speed)

# Configurable temperature and fan speed steps
tempSteps = [50, 60, 70]    # [°C]
speedSteps = [60, 70, 100]
# [%]

# Fan speed will change only of the difference of temperature is higher than hysteresis
hyst = 5

# Setup GPIO pin
GPIO.setmode(GPIO.BCM)
GPIO.setup(FAN_PIN, GPIO.OUT, initial=GPIO.LOW)
fan=GPIO.PWM(FAN_PIN,PWM_FREQ)
fan.start(0);


i = 0
cpuTempOld=0
fanSpeedOld=0
initializing_cnt=0



# We must set a speed value for each temperature step
if(len(speedSteps) != len(tempSteps)):
    print("Numbers of temp steps and speed steps are different")
    exit(0)

try:
    while (1):
        # Read CPU temperature
        cpuTempFile=open("/sys/class/thermal/thermal_zone0/temp","r")
        cpuTemp=float(cpuTempFile.read())/1000
        cpuTempFile.close()

        # Calculate desired fan speed
        if initializing_cnt <= INITIALIZING_TIME:
            initializing_cnt += WAIT_TIME
            fanSpeed = 100
        else:
            if(abs(cpuTemp-cpuTempOld > hyst)):

                # Below first value, fan will run at min speed.
                if(cpuTemp < tempSteps[0]):
                   fanSpeed = speedSteps[0]

               # Above last value, fan will run at max speed
                elif(cpuTemp >= tempSteps[len(tempSteps)-1]):
                   fanSpeed = speedSteps[len(tempSteps)-1]

                # If temperature is between 2 steps, fan speed is calculated by linear interpolation
                else:
                    for i in range(0,len(tempSteps)-1):
                        if((cpuTemp >= tempSteps[i]) and (cpuTemp < tempSteps[i+1])):
                            fanSpeed = round((speedSteps[i+1]-speedSteps[i])\
                                       /(tempSteps[i+1]-tempSteps[i])\
                                       *(cpuTemp-tempSteps[i])\
                                       +speedSteps[i],1)

        if((fanSpeed != fanSpeedOld) ):
            if((fanSpeed != fanSpeedOld)\
                and ((fanSpeed >= FAN_MIN) or (fanSpeed == 0))):
                fan.ChangeDutyCycle(fanSpeed)
                fanSpeedOld = fanSpeed

        # Wait until next refresh
        time.sleep(WAIT_TIME)


# If a keyboard interrupt occurs (ctrl + c), the GPIO is set to 0 and the program exits.
except(KeyboardInterrupt):
    print("Fan ctrl interrupted by keyboard")
    GPIO.cleanup()
    sys.exit()