Execute command only once inside of infinite loop

Question

I have a raspberry pi wich i'm using to monitor an input from the GPIO ports, to do this i need to run an infinite loop.

When i receive a LOW in my input i want to execute a system command usint subprocess.call. The problem is that it executes this command for as long as the input is receiving LOW i have tried this to make it execute only once but i can't make it work.

while 1:
    if (GPIO.input(11) != GPIO.HIGH ):
         puerta_abierta = 1
         if(puerta_abierta == 1 ):
              call(["mpg123", "file.mp3"])
              puerta_abierta = 0
    else:
        puerta_abierta = 0

Blender · Accepted Answer · 2013-04-17 02:52:37Z

2

You could do something like this:

called = False

while True:
    if GPIO.input(11) != GPIO.HIGH:
        if not called:
            call(["mpg123", "file.mp3"])
            called = True

You could also break out of the loop, but that might not be what you intend to happen:

while True:
    if GPIO.input(11) != GPIO.HIGH:
        call(["mpg123", "file.mp3"])
        break

answered Apr 17, 2013 at 2:52

Blender

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1 Comment

Isaac Gonzalez Over a year ago

Thanks your fist option does work, i guess i didn't explained myself good enough. I want that after it has played it doesn't activate untill my input is LOW again

Sheng · Accepted Answer · 2013-04-17 02:52:59Z

1

Like this:

puerta_abierta = 0
while 1:
    if (GPIO.input(11) != GPIO.HIGH ):
        puerta_abierta += 1
        if(puerta_abierta == 1 ):
            call(["mpg123", "file.mp3"])
    else:
        puerta_abierta = 0

answered Apr 17, 2013 at 2:52

Sheng

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4 Comments

tdelaney Over a year ago

This solution will call mpg123 every time the input goes HIGH and then LOW again because it resets puerta_abierta. Not sure if this is good or bad because its how the original code works, but violates the posters request that mpg123 only be called once.

Sheng Over a year ago

Yes, it is. When I wrote the code, I knew it. And I think it is what the asker wants.

tdelaney Over a year ago

I like (and upvoted) your answer but wanted to toss in a caveat for the original poster in case it wasn't obvious.

Sheng Over a year ago

@tdelaney Thank you! I should write this in case of need.

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