Raspberry Pi- GPIO Events in Python

Question

I am using the GPIO pins on my Raspberry Pi with a PIR sensor to detect motion. When the sensor detects motion I want to then move the software onto other functions.

At the moment, to detect motion I have my program constantly running in a loop while it is waiting for motion to be detected. While this works at the moment, for use in the future this will be incredibly inefficient and am hoping to improve on this by assigning it to an event.

Is there any way to bind my GPIO input to an event that is detected by the program without manually running a loop.

Here is my current loop for detection motion:

var = 1
counter = 0
while var == 1:
    if GPIO.input(7):
        counter += 1
        time.sleep(0.5)
    else:
        counter = 0
        time.sleep(1)

    if counter >= 3:
        print "Movement!"
        captureImage()
        time.sleep(20)

The counter and detecting motion multiple times is used to reduce the number of false positives that the sensor picks up.

Answer 1

The RPi.GPIO Python library now supports Events, which are explained in the Interrupts and Edge detection paragraph.

So after updating your Raspberry Pi with sudo rpi-update to get the latest version of the library, you can change your code to:

from time import sleep
import RPi.GPIO as GPIO

var=1
counter = 0

GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

def my_callback(channel):
    if var == 1:
        sleep(1.5)  # confirm the movement by waiting 1.5 sec 
        if GPIO.input(7): # and check again the input
            print("Movement!")
            captureImage()

            # stop detection for 20 sec
            GPIO.remove_event_detect(7)
            sleep(20)
            GPIO.add_event_detect(7, GPIO.RISING, callback=my_callback, bouncetime=300)

GPIO.add_event_detect(7, GPIO.RISING, callback=my_callback, bouncetime=300)

# you can continue doing other stuff here
while True:
    pass

I chose the Threaded callbacks method because I suppose that your program does some other things in parallel to change the value of var.