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--- gpio_inputs_-_button_led_control_using_an_interrupt [2016/08/09 22:56] – created walkeradmin
+++ gpio_inputs_-_button_led_control_using_an_interrupt [2016/12/13 21:28] – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ====== GPIO Inputs - Button LED Control using an Interrupt ======
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+\\
+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 {{ :led-button-i.zip |here}} to save time)
+\\
+    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
+\\
+===== Example Output =====
+\\
+Here you can see the code running {{ :led-button-i.mp4 |(video)}}
+\\
+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%.
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