GPIO Inputs - LED Control via a Button and Interrupt
The previous example of using a button to light an LED, everything worked fine, but our processor was at 100%, this needs fixing, so in this example instead of constantly polling and setting GPIO pins, we are using a interrupt where by we do nothing until a button is actually pressed.
Create a new file in the normal way ( you can download the python file here to save time)
<sxh [py][; options for SyntaxHighlighter]>
sudo nano LED-Button-i.py
#import modules import RPi.GPIO as GPIO # This imports the GPIO library that allows the use of the GPIO pins, import time # This imports the time library (for delays among other things) # These libraries are built in to Raspbian. GPIO.setmode (GPIO.BOARD) # This sets the GPIO pin numbering. Our LED is connected to Pin 12, # so we can reference it by using BOARD as pin 12. However there is # another option (BCM) where we can reference a pin by it's name, pin # 12 is called GPIO18 (a reference to its place on the chip). GPIO.setup(11, GPIO.IN, pull_up_down=GPIO.PUD_DOWN) # setup GPIO Pin 11 as an input, and set # the resistor to Pull Down (PUD_DOWN) # this is the pin the button is connected to # button is connected from pin 11 to the # +3.3v pin on the GPIO # this def buttonPressed needs to be defined before it can be reference in the GPIO.add_event_detect def buttonPressed(channel): # this is where our code will look when button is pressed print "Button is Pressed" # print something to the screen GPIO.output(12,1) # set GPIO pin 12 to high (3.3v) so LED will come on # this is where we setup the GPIO input to use the event buttonPressed that was # defined previously. bouncetime is a simple switch debouncer in mS. GPIO.add_event_detect(11, GPIO.RISING, callback=buttonPressed, bouncetime=500) GPIO.setup(12, GPIO.OUT) # Sets the GPIO pin as output. This is connected to the LED, then # from the LED to 0v via a 330 Ohm resistor. GPIO.output(12, 0) # sets the GPIO Pin 12 to low (so 0v) try: while True: # start a loop time.sleep(1) # 1 second delay (or LED wont stay illuminated GPIO.output(12,0) # Set PIN 12 to 0v so LED is off except KeyboardInterrupt: # if Ctrl-C is pressed, exit loop GPIO.cleanup() # reset GPIO pins to default state #End
Once you have your file saved, you can run it by using:
sudo python LED-Button-i.py
Here you can see the code running.
The main advantage using the interrupt is that my processor occupancy on the Pi Zero is now around 10% normal, and 14% when I press the button. That's much better than the previous constant 100%.