Python: Multiple infinite Loops on RaspberryPi

Question

I wrote a function to let a LED blink with variable parameters. The code looks like this:

#!/usr/bin/python
import RPi.GPIO as GPIO
import time
from threading import Thread


GPIO.setmode(GPIO.BOARD)

def blink(port, hz):
    """ Funktion zum Blinken von LEDs auf unterschiedlichen GPIO Ports und unterschiedlicher Hz angabe"""
    GPIO.setup(port, GPIO.OUT)
    while True:
        GPIO.output(port, GPIO.HIGH)
        time.sleep(0.5/hz)
        GPIO.output(port, GPIO.LOW)
        time.sleep(0.5/hz)

blink(16, 5)

As far the code works well. Now I want to call the blink() function a second time with different parameters:

...
blink(16, 5)
blink(15, 10)

But with the first function calls a infinite Loop , the second call of blink() does not work. Is there a way to start a second infinite loop?

Fix your variable names

Mad Physicist
– Mad Physicist

2018-03-15 08:46:46 +00:00
Commented Mar 15, 2018 at 8:46 — Mad Physicist
– Mad Physicist, Commented Mar 15, 2018 at 8:46
hz versus hertz ?

Raptor
– Raptor

2018-03-15 08:47:46 +00:00
Commented Mar 15, 2018 at 8:47 — Raptor
– Raptor, Commented Mar 15, 2018 at 8:47
Looks like someone discovered a use case for multithreading

Mad Physicist
– Mad Physicist

2018-03-15 08:47:56 +00:00
Commented Mar 15, 2018 at 8:47 — Mad Physicist
– Mad Physicist, Commented Mar 15, 2018 at 8:47
sorry, edited..

Kai
– Kai

2018-03-15 08:49:36 +00:00
Commented Mar 15, 2018 at 8:49 — Kai
– Kai, Commented Mar 15, 2018 at 8:49

Kai · Accepted Answer · 2018-03-15 09:17:10Z

2

I see you've imported Thread, so something like this might do the trick(with a grain of salt here, I don't have my rpi around so I can't test it):

#!/usr/bin/python
import RPi.GPIO as GPIO
import time
from threading import Thread


GPIO.setmode(GPIO.BOARD)

def blink(port, hz):
    """ Function to let LEDs blink with different parameters"""
    GPIO.setup(port, GPIO.OUT)
    while True:
        GPIO.output(port, GPIO.HIGH)
        time.sleep(0.5/hz)
        GPIO.output(port, GPIO.LOW)
        time.sleep(0.5/hz)

Thread(target=blink, args=(16, 5)).start()
Thread(target=blink, args=(15, 10)).start()

edited Mar 15, 2018 at 9:17

Kai

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answered Mar 15, 2018 at 8:52

Alexander Ejbekov

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2 Comments

Kai Over a year ago

but now I have the problem that I can´t stop it with Ctrl-C

Alexander Ejbekov Over a year ago

@Kai ah, that's a different story. Keyboard interrupts are a bit more complicated when you introduce threads. You will need to make a queue for that. This is a good guide on where to start.

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