How to check for keyboard input, while waiting for switch input?

Question

I'm a beginner at programming so bare with me. I'm having some problems with implementing a way to stop my script manually. CTRL+C works perfectly fine in the terminal, but it seems it doesn't always work. I found that out the hard way. See, I set up a script for controlling a LED with a switch, then I set up that script to run on boot which worked fine. The problem is the script is in an infinite loop. It constantly checks if the button has been pressed. Nothing I tried could stop the script and I couldn't even log in to my Pi anymore. I had to format the SD card and reinstall Raspbian. I want to prevent that, so how would I do that?

Here's the code I'm using:

#import of libraries
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)

#pin 8 input, pin 10 output
GPIO.setup(8, GPIO.IN)
GPIO.setup(10, GPIO.OUT)

while True:
    value = GPIO.input(8)

    #if the value on pin 10 equals False light up the LED
    if value == False:
        GPIO.output(10, GPIO.HIGH)
        print("Button pressed")

        #constantly check for changes on pin 10
        while value == False:
            value = GPIO.input(8)

    #else turn it off
    else:
        GPIO.output(10, GPIO.LOW)

I tried implementing this:

while True:
    input = raw_input("")
    if input == "stop": 
        sys.exit(0)
    else:
        MAIN

But now both inputs (button and keyboard) are getting mixed up, and the main script doesn't work correctly anymore.

How would I implement a way for the script to check if there has been any keyboard input, while the script is actually waiting for a switch press? Is that even possible? What are other alternatives?

Answer 1

You could import time at the start of your script and, and use something like

time.sleep(1)

to sleep for 1 second every time the loop is executed. This doesn't have to be a whole second - you could use 0.1 for example.

Alternatively, instead of polling the input, you could use interrupt driven IO. Create a function to do something when the button has been pressed, and use GPIO.add_event_detect to register that function as a callback:

# callback function to be executed when GPIO interrupt is triggered
def callbackfunction():
    # handle the input...

GPIO.add_event_detect(8, GPIO.RISING, callback=callbackfunction)

There's good information on interrupt driven GPIO here: https://code.google.com/p/raspberry-gpio-python/wiki/Inputs

There's a tutorial on interrupt driven IO here: http://raspberrywebserver.com/gpio/using-interrupt-driven-gpio.html

Answer 2

Not sure how you set it up to run at boot, but if you replaced the login process with it, you really have no shell to return to, so ^C is not going to do anything.

You could set it to run once you login (.profile and/or .bashrc come to mind here) and you have a shell to exit to, but I don't have enough info to answer this question.