I think I broke the GPIO

In my other question, Pi works, GPIO part will not cooperate, I successfully got the LED to light up, but it would only light up if I used certain pins, it wouldn't work with the 3.3V or 5V pins, it was working with only two GPIO pins,

I was searching for other pins that could supply power and then it cold restarted at the touch of one of them.

My LED turned off, and when the RPi turned back on, my LED did not. I thought I had blown something, so I switched out my wires, resistor and LED for new ones -- and still, nothing lit up.

The odd thing is that I am still able to restart the RPi by touching the ground to one pin, so I think my GPIO interface controller isn't broken, but I am not completely sure, what can I do to test if it is broken, short of a multimeter or voltameter?

It turns out that all I needed to do was unplug it and let it rest. I plugged it up today along with a set of buttons and all sorts of novice things. One thing that puzzles me though is this

The cathodes are the long leg?

Yes, my LEDs for some reason, only work when I use the long pin as the cathode. Anyone know why that may be?

1 Answer 1


If a LED works from a gpio the LED will also work from the 3V3 rail and the 5V rail.

Without looking over your shoulder it's hard to know what you are doing wrong.

If you have wiringPi installed I suggest you use its pintest utility. That should be run with nothing connected to the gpios.

Alternatively there is my gpio test which requires my pigpio library. It is slightly more thorough and again nothing should be connected to the gpios.

  • It turns out that I didn't break anything.
    – dockeryZ
    Commented Jan 16, 2015 at 3:49
  • @dockeryZ That's good. I've been extremely fortunate myself because I have abused my Pi's in all sorts of ways but luckily (and it is mainly luck) they are still all working.
    – joan
    Commented Jan 16, 2015 at 8:27
  • Here's what I don't understand about Canakit's GPIO Interface Controller, it only seems to work right if I plugged the ribbon cable in twisted, meaning the pink strip faces the USB ports on the RPi, while it only plugs in one way on the controller. Also, as I mentioned in my question update above, the long pin is the cathode on LEDs, Why?
    – dockeryZ
    Commented Jan 16, 2015 at 16:28
  • also, my LEDs will not get power from the 3.3V side rail, only the 5V rail. I'm learning more slowly each day, soon I'll have built a time machine :D
    – dockeryZ
    Commented Jan 16, 2015 at 16:30
  • @dockeryZ you may have the wrong colour LEDs. The (forward) voltage required to switch them on depends on their colour. Red, green, blue, are normally fine. What colour? LEDs are diodes. They only conduct one way.
    – joan
    Commented Jan 16, 2015 at 16:59

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