How to test RPi.GPIO setup?

Question

After several maddening errors it occurs to me that there is a problem in my GPIO setup, to wit, RPi.GPIO is failing silently.

To test this theory I got my multimeter, set it to volts, put one probe in ground and another probe in the GPIO port (GPIO 17 in this case) and get 0 volts coming through.

Ordinarily I would think there is a loose conection, or a problem with the board (I am using the Adafruit T-Cobbler http://www.adafruit.com/products/1105 ) but I am able to move a servo with this command (using servoblaster) (which does not use the RPi.GPIO library)

echo p1-22=50 > /dev/servoblaster

My question is - am I testing the GPIO correctly? Is there a better way to test if I am getting any current through the GPIO setup?

The code I am using (Python) is as follows

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

dirPin = 4
stepPin = 17


GPIO.setup(dirPin, GPIO.OUT)
GPIO.setup(stepPin, GPIO.OUT)

for i in range(0, 3):
   GPIO.output(dirPin, 1)
   GPIO.output(stepPin, 1)
   time.sleep(15000)
   GPIO.output(dirPin, 1)
   GPIO.output(stepPin, 0)   
   time.sleep(10)

Answer 1

One method of testing this would be to connect an LED to the pin and see if you can flash it. I use an LED bar graph like this one from adafruit.

I mounted this and the corresponding resistors to a piece of stipboard, and added a set of male and female headers to each end (by using both male and female headers on both ends, I can hook it up easily no matter what type of pins the Pi or microcontroller I am testing has). You could do this with plain LEDs as well, but I would suggest at least 8. This allows testing a full port (microntrollers group pins into ports) at once.

One thing I did notice in your code is the long sleep 15000 time:

time.sleep(15000)

Was this so you could test the voltage? Because currently you are sleeping for more than 4hrs.