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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
  #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)
          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

Once you have your file saved, you can run it by using:

  sudo python

Example Output

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%.

gpio_inputs_-_led_control_via_a_button_and_interrupt.txt · Last modified: 2023/03/09 22:35 by