One channel relay control

Question

I'm trying to connect a small one line relay to my Raspberry Pi but the relay doesn't react. The red light on the relay is on the whole time.

#!/usr/bin/python
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

# init list with pin number

pinList = [27]

# loop through pin and set mode and state to 'high'

for i in pinList: 
    GPIO.setup(i, GPIO.OUT) 
    GPIO.output(i, GPIO.HIGH)

# time to sleep between operations in the main loop

SleepTimeL = 2

# main loop

try:

  GPIO.output(27, GPIO.LOW)
  print "FOUR"
  time.sleep(SleepTimeL);
  GPIO.cleanup()
  print "Good bye!"

# End program cleanly with keyboard
except KeyboardInterrupt:
  print "  Quit"

  # Reset GPIO settings
  GPIO.cleanup()

Answer 1

My 8 relay module is set up to control the heating and air conditioning in a remote building. I run 5v to all the relay coils - that is the high side. I run GPIO pins to the low side. The GPIO pins are normally high - 3.3v. When a GPIO pin is made to go down it looks like ground to the relay to which it is attached and the relay operates/closes.

#      GPIO09 -  Turn on or off a specified relay so
#                it stays on or off after the program ends 
#                at power on all pins are in input state ready to sense hi or lo
#    

import RPi.GPIO as GPIO                      ## Import GPIO library
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BOARD)                     ## Use board pin numbering

pinarr=[3,5,7,11,13,15,19,21]
dirarr=["on","off"]
devarr=["Air Conditioning","Heater","Unused","Unused","Unused","Unused","Unused","Unused"]

##  Use a dictionary as a lookup table to give a name to the GPIO_function return code
pin_use = {0:"GPIO.OUT",1:"GPIO.IN",40:"GPIO.SERIAL",41:"GPIO.SPI",
42:"GPIO.I2C",43:"GPIO.HARD_PWM",-1:"GPIO.UNKNOWN"}

                   
for i in range(0,8):                         ##  set pins to be outputs and at 3.3 volts  
    GPIO.setup(pinarr[i], GPIO.OUT)

for i in range(0,8):
    print "\n"
                     
print("GPIO09 Starting")

##for i in range(0,8):                         ##  Print current relay usage   
##  fno = GPIO.gpio_function(pinarr[i])      ##  get function number
##  print "Relay " + str(i+1) + " pin " + str(pinarr[i]) + " usage is " +  pin_use[fno]
    
while 1 == 1:
    
    for i in range(0,8):                         ##  get and display pin on/off status  
        func = GPIO.input(pinarr[i])
        print "Relay " + str(i+1) + " " + devarr[i] + " pin " + str(pinarr[i]) + " is " + dirarr[func]

    print " "

## Ask user for relay #
    relno = raw_input("Enter number of relay to change: ")
    if not relno:
        print "exiting"
        raise SystemExit

    if(int(relno) < 1):
        print "Bad choice - exiting"
        raise SystemExit
                
    if(int(relno) > 8):
        print "Bad Choice - exiting"        
        raise SystemExit

    relno = int(relno)
    
    ans = raw_input("ON or OFF ?  1 or 0: ")

    if (ans == "1"):
        print "Turning on relay " + str(relno) + " Pin " + str(pinarr[relno -1])
        GPIO.output(pinarr[relno - 1],False)         ## Switch off pin = conduct
        for i in range(0,2):
            print "\n"

    if (ans == "0"):
        print "Turning off relay " + str(relno) + " Pin " + str(pinarr[relno -1])
        GPIO.output(pinarr[relno - 1],True)          ## Switch on  pin = non-conduct
        for i in range(0,2):
            print "\n"