GPIO inputs on Raspberry Pi

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Now that I have GPIO outputs working nicely for Home Assistant using either a Raspberry Pi or an Orange Pi, I want to get GPIO inputs working as well. Naively, that’s pretty easy to do in python on the Raspberry Pi:

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(17, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

while True:
    print('Reading...')
    if GPIO.input(17) == GPIO.HIGH:
        print('Pressed')
    else:
        print('Released')
    time.sleep(1)

That code is of course horrid. Its horrid because its polling the state of the button, and its quite likely that I can sneak a button press in during one of those sleeps and it will never be noticed. Instead we can use edge detection callbacks to be informed of button presses as they happen:

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
GPIO.setup(17, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

def event_callback(channel):
    print('Event detected: %s' % GPIO.input(17))
    
GPIO.add_event_detect(17, GPIO.BOTH, callback=event_callback, bouncetime=50)

while True:
    time.sleep(1)

This second program provides helpful output like this:

pi@raspberrypi:~ $ python gpio_button_edge_detect.py 
Event detected: 1
Event detected: 0

Which is me pressing the button once (it go high when pressed, and then low again when released). This is of course with a button wired to GPIO17 with a current limiting resistor between the button and the 3.3v rail.

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