CODEWITHSUNDEEP
pythonraspberry-pigpio
Son of 8-Bits
Son of 8-Bits

Reputation: 63

Start and stop application within python using the RPi GPIO?

I'm using this python script:

import RPi.GPIO as GPIO
import subprocess
from time import sleep

GPIO.setmode(GPIO.BCM)
GPIO.setup(4, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(25, GPIO.OUT, initial=GPIO.LOW)

try:  
    while True:
        if GPIO.input(4):
            GPIO.output(25, 1)
            subprocess.call("/script/start.sh", shell=True)
        else:
            GPIO.output(25, 0)
            subprocess.call("/script/stop.sh", shell=True)
        sleep(0.2)

finally:
    GPIO.cleanup()

(Without subprocess) when I press the button (GPIO 4) an LED goes on, press it again and it's off. Works great. I'm currently using 2 scripts to start and stop an application. Those work fine when used outside of Python. When I try to implement the subprocess stuff things start to go wonky.

The scripts are:

#!/bin/bash
FILENAME=$(date +"%Y%m%d_%H%M")
rec -c 2 -b 24 -r 48000 -C 320.99 /mnt/usb/${FILENAME}.mp3
exit

and

#!/bin/bash
reco=`pidof -s rec`
kill $reco
exit

The process will be started, and it'll keep running, but the python script won't shut it down unless I hit ctrl+c, defeating the point of using the GPIO switch.

What I want to achieve is:

switch = high -> application starts
switch = low -> application stops

Wait/loop so I can start recording again if I press the switch.

How can I get this working properly?

Upvotes: 0

Views: 4051

Answers (1)

jayant
jayant

Reputation: 2389

Since you're trying to kill the process you start in start.sh. This is what I recommend:

import RPi.GPIO as GPIO
import signal
import subprocess
import os
from time import sleep

GPIO.setmode(GPIO.BCM)
GPIO.setup(4, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(25, GPIO.OUT, initial=GPIO.LOW)

rec_proc = None
try:  
    while True:
        if GPIO.input(4):
            GPIO.output(25, 1)
            if rec_proc is None:
                rec_proc = subprocess.Popen("/script/start.sh",
                           shell=True, preexec_fn=os.setsid)
        else:
            GPIO.output(25, 0)
            if rec_proc is not None:
                os.killpg(rec_proc.pid, signal.SIGTERM)
                rec_proc = None
        sleep(0.2)

finally:
    GPIO.cleanup()

Upvotes: 1

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