I try to port my GPIO project from quick2wire to WiringPi. My aim is to read the state of a photocell connected to pin 24 of my raspberry pi (model B, revision 2).

My code (python 3) looks like this:

import wiringpi2 as wiringpi
import time

# wiringpi.wiringPiSetupGpio() # it would work with this instead of wiringPiSetupSys()

counter = 0
status = "unknown"
while True:
    counter += 1
    light = wiringpi.digitalRead(24)
    if not light:
        status = "ON"
        status = "OFF"
    print('(' + str(counter) + ') ' + status)

When I wiringpi.wiringPiSetupGpio() instead of wiringpi.wiringPiSetupSys() the code works as expected. Using wiringpi.wiringPiSetupSys() however the output doesn't change - it would stay ON or OFF no matter how the state of the photo cell changes.

I also made sure that the pin is exported

$ gpio exports
GPIO Pins exported:
   5: in   0  none 

As I checked the state of the photocell with gpio gpio -g read 24 in the shell, I can exclude the possibility of a hardware issue.

As I want to use the code in a web application, I would strongly prefer to use wiringPiSetupSys() as a non-root user.

Can you help me solve or analyze the cause of this issue?

  • Did you ever get it to work in your code? I can't get my python script to output the status of the pin.
    – Ryan
    Apr 11 '17 at 16:44
  • I decided to do the whole GPIO thing without a library like wiring pi. They all didn't work as expected and I didn't want some update to break the whole system. Also, using GPIO with plain python is not that hard. Find my code for reading a pin here (notice that I used an interrupt instead of looping the request, which should be advantageous in most cases): github.com/speendo/photocell/blob/…
    – speendo
    Apr 13 '17 at 10:55

Found the solution myself.

The gpio documentation clearly states

This exports the given pin (BCM-GPIO pin number) as an input or output and makes it available for a user program running as the same user to use.

So to make it work, I had to do the following:

gpio unexport 5
gpio export 24 in
$ gpio exports
GPIO Pins exported:
  24: in   1  none  

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