Raspberry Pi Forums

Hi everybody,

I'm rather new to my Raspberry Pi and I've been trying to set up the GPIO pins to light up a simple LED. Using a Pi Cobbler Breakout Kit, I've attached it to a breadboard and wired up one LED with a 220 ohm resistor. However, every attempt to light the LED has been a failure. For some reason it won't light up no matter what I try to do. I've wired it up to pin #17 and then connecting it to ground as well. I also know to run the code through root. I've been using this code:
{
import RPi.GPIO as GPIO
from time import sleep

GPIO.setmode(GPIO.BCM)

GPIO.setup(17, GPIO.OUT)

while True;
GPIO.output(17, True)
sleep(2)
GPIO.output(17, False)
sleep(2)
}

I would greatly appreciate if you had any tips to solve this. I just can't seem to get any output whatsoever from the GPIO pins on this raspberry pi.
Thanks,
Kian

Are you sure the ribbon cable on the cobbler (or RPi) is on correct way? Seems to be a common error where the cable is wrong way around.
Post a picture.

Have you got the LED round the right way? Cathode (short leg), flat on the packaging to GND, anode to the GPIO pin (with the resistor in series with the LED).

The first test (to check you are doing things right) is to run the LED from a 3v3 pin to Gnd (through a resistor).

This tests LED polarity and your u derstanding of the GPIO pin layout.

I have the LED the right way and I believe the ribbon cable is the right way as well. The gray cable is towards the SD and it only goes in one way in the cobbler. I also tried the 3.3V and nothing happened. I've attached a couple pictures.

Note: Before finding the right configuration, I realized I had the ribbon cable on the wrong way on the pi and tried running code through that. However, I've long since corrected that. Maybe I could've damaged something?

Thank you all for the quick responses.

If the Pi boots there will be 3V3 available on the 3V3 pins on the expansion header (pins 1 and 17).

What colour LED? Some have a higher forward voltage requirement. Try a 5V rail pin (e.g. pins 2 or 4).

I can't be sure from the picture, but I think the wiring needs a slight change. The yellow wire and resistor are ok, but it looks like the led and the other wire are all on the same strip of the breadboard, effectively bypassing the led. I'd try moving the wire one row along (it looks like it's in row 29, move it to 28 or 30) and move the end of the led nearest it to the same row. Leave the leg of the led nearest the resistor where it is.

P_Monty: You are correct! I can't believe I could have overlooked that, I've been using breadboards for about a month now. I feel silly.
Thank you so much!

No problem - things like that are easily done...

Perhaps an illustration of "Linus's Law'': "Given enough eyeballs, all bugs are shallow.''

From The Cathedral and the Bazaar: Eric Raymond

(But kudos to @P_Monty for eyeballing it!)