Python Forum

Hi All,

I am using a python script to control some GPIO pins on a raspberry pi.
Is as follows:

from gpiozero import PWMLED
import time
import os
from decimal import Decimal

led = PWMLED("GPIO12") 				#set the GPIO pin number you are using here. It uses the GPIO method of numbering.
						#details on pin numbering can be found here: https://gpiozero.readthedocs.io/en/stable/recipes.html
setZero=open("/var/www/html/alpha.txt", "w")
setZero.write("0")
file.close()

while True:					#a loop that never stops running
	try:					#prevents an bug with the code that would cause it to terminate when writing to alpha.txt file
		initial=open("/var/www/html/alpha.txt", "r") 	#open the alpha.txt file as read only. Declare it as "initial"
		brightness=(initial.read())	#declare the variable brightness by reading the variable "initial". Convert the string into a number
		x = Decimal(brightness)		#convert the number into a decimal. Store it as the variable X
		int_brightness = round(x,2)	#round the variable x to 2 decimal places. PHP should handle this, but just in-case. Store the rounded variable as int_brightness
		led.value = int_brightness	#set the brightness of the LED to the value of int_brightnesss
	except:
		()				#return nothing if code fails
	finally:
		()				#return nothing if code fails

The trouble is with the following lines:

setZero=open("/var/www/html/alpha.txt", "w")
setZero.write("0")
file.close()

If I run the script without these 3 lines, the code works fine. As soon as I add it, the LED stops illuminating (I assume the while true loop is not executing). I have confirmed that on startup the script successfully writes a 0 to the file though.

Any ideas on what might be causing this to fail? There is no returned output in the console

You start with brightness 0, which is equal to off. Why would anything happen?

Brightness starts with off. This changes from a slider in php which writes to the alpha.txt file. The code in the while True loop looks for a change in the value and writes it to the GPIO pin. The reason brightness is set to 0 at the start is so that when the Pi boots up the light starts off.

I would put a print statement in the while loop. Probably a conditional one if the brightness changes, otherwise you'll get a flood of output. You'll have a variable to track the previous value for the conditional. Set that up with a dummy value to make sure it prints the first time through the loop, to confirm that the loop is executing.

My guess is the initial value is messing up the PHP somehow, but I really have no clue. That's why I suggest print statements.