使用Raspberry GPIO的Python和PHP

Question

With a little Python script I'm able to detect a button state that is connected in my Raspberry board. This is the script:

#!/usr/bin/env python

import os
import RPi.GPIO as GPIO
import time

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BOARD)

GPIO.setup(12, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

try:
    while True:
        if(GPIO.input(12) == 1):
            print 'Btn on'
            os.system('date')
            time.sleep(5)
        else:
            os.system('clear')
            print 'Waiting'
    time.sleep(2)

except KeyboardInterrupt:
    GPIO.cleanup()  

In this way, using PuTTY, or directly in the Raspberry terminal, I can easily detect the state of this button.

Now I would create the same thing but in PHP. I need to create a PHP web page that will be in the var/www/html directory of my Raspberry, and should just show me the same thing. When I press the button, I will get a simple echo "Btn on" with the timestamp, and if not pressed just another echo with "Waiting".. Is it possible? I tried directly exec the Python script, in PHP, in this way:

$command = escapeshellcmd('sudo -u www-data python btn.py');
$output = shell_exec($command);
echo $output;

but it's not working. Any idea?

Answer 1

It does not work because shell_exec waits for the python script to finish before it returns. However, the python script obviously does not reach the end because of the infinite loop. The simplest fix would be to poll the button status once with the python script and do any looping in php. Alternatively the python can write to a fifo file, from which the php script can read - but then be careful, because if you leave the python script running, it will fill the memory of the raspberry.