Controlling a fan on a relay with python

Question

I have a Raspberry pi Model B revision 2 and I've set up a mini 5v fan on a relay switch which i want to control with python now. I will be running a crontab every hour to check the temperature of the pi and if the temperature is above 50C i will be running the fan for like 10 min. This is my current setup:

The relay is connected like this diagram here:

I've setup the relay this way, because it has a light on top of it (a red light) which i want it to be on when the fan is working...and off when its not.

Here is my script:

#!/usr/bin/python3
import time
import os
import sys
import RPi.GPIO as GPIO

# Identify which pin controls the relay
FAN_PIN = 3
# Temperature check. Start fan after 50C, Shut down under 50C
FAN_START = 50

def GPIOsetup():
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(FAN_PIN, GPIO.OUT)
    GPIO.setwarnings(False)

def getCPUtemperature():
    res = os.popen('vcgencmd measure_temp').readline()
    return(res.replace("temp=","").replace("'C\n",""))

def fanON():
    GPIO.output(FAN_PIN, 0)
    print "fan on"
    return()

def fanOFF():
    GPIO.output(FAN_PIN, 1)
    print "fan off"
    return()

def getTEMP():
    CPU_temp = float(getCPUtemperature())
    if CPU_temp>FAN_START:
        fanON()
    else:
        fanOFF()
    return()

def main():
    GPIOsetup()
    getTEMP()

try:
    main()
finally:
    print ("Finish")
    #GPIO.cleanup()

Now the problem is that i am getting some warnings which i just cant get rid off:

root@raspberrypi:/home/pi# python fan.py
fan.py:14: RuntimeWarning: This channel is already in use, continuing anyway.  Use GPIO.setwarnings(False) to disable warnings.
  GPIO.setup(FAN_PIN, GPIO.OUT)
fan.py:14: RuntimeWarning: A physical pull up resistor is fitted on this channel!
  GPIO.setup(FAN_PIN, GPIO.OUT)
fan off
Finish

The line in question as you can see is this:

GPIO.setup(FAN_PIN, GPIO.OUT)

Why am I getting this error ? i have GPIO.setwarnings(False) in my code. And also should i be using that pin for controlling the relay ? Is there optional pin i should be using ? Thanks.

Answer 1

Final code:

#! /usr/bin/env python3
import os
import RPi.GPIO as GPIO
import time
import datetime
import sys

# 5 * * * * sudo python /home/pi/fan.py
# A crontab will run every hour and check the temp. If the temp is > 49 the script will start the fan
# until the temperature goes down to 28. When it does, the script will end, shutting down the fan as well.
# If the script executes again while a previous script is running, the latter will exit
# ... meaning the pi is in hell, and will never get bellow FAN_END value :P

# Identify which pin controls the relay
FAN_PIN = 18 # the yellow box ex: GPIO18
# Temperature check. Start fan if temp > 49C
FAN_START = 49
# Temperature check. Shut down under 28C
FAN_END = 28

# Get what action. If you manually turning on/off the fan
action = sys.argv.pop()


def GPIOsetup():
    GPIO.setwarnings(False) 
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(FAN_PIN, GPIO.OUT)

def fanON():
    GPIOsetup()
    GPIO.output(FAN_PIN, 0) #fan on
    return()
def fanOFF():
    GPIOsetup()
    GPIO.output(FAN_PIN, 1) #fan off
    return()

def get_temp_from_system():
    res = os.popen('vcgencmd measure_temp').readline()
    return(res.replace("temp=","").replace("'C\n",""))

def check_fan(pin):
    GPIOsetup()
    return GPIO.input(pin)

def run(pin):
    current_date = datetime.datetime.now()
    temp = get_temp_from_system()
    if float(temp) >= FAN_START:
        print(temp+' @ '+str(current_date))
        if check_fan(pin) == 1:
            print('Fan is Off...Starting Fan')
            fanON()
        else:
            time.sleep(5) # Remove, if you want real-time checking
            print('Fan is ON')
    elif float(temp) <= FAN_END:
        print(temp+' @ '+str(current_date))
        if check_fan(pin) == 0:
            print('Fan is on...Shuting it Down')
            fanOFF()
            GPIO.cleanup()
            return 1 # exit script. The pi has cooled down
        else:
            time.sleep(5) # Remove, if you want real-time checking
            print('Fan is OFF')
    else:
            pass # while the script is passing through here, there will be no output on screen


if action == "on" :
   print "Turning fan on"
   fanON()
elif action == "off" :
   print "Turning fan off"
   fanOFF()

# first check if script is already running
if check_fan(FAN_PIN) == 0:
    print('Fan is on, script must be running from another instance...')
else:
    temp = get_temp_from_system()
    if float(temp) < FAN_START:
        print('Pi is operating under normal temperatures.')
    else:
        try:
            while(True):
                tmp = run(FAN_PIN)
                if tmp == 1: # value returned from line 60
                    break
        except KeyboardInterrupt:
            fanOFF()
            GPIO.cleanup()
        finally:
            fanOFF()
            GPIO.cleanup()

Answer 2

In addition to moving off the I2C pin, you'll want to un-comment (remove #) the last line so your GPIO will cleanup. This will reset the GPIO and remove your warnings and errors the next time your script runs.