# How does an LED matrix work?

I've wired up a 3x3 matrix as in the attached image. My understanding is that if I apply 3.3 volts to row C and connect column 1 to ground, the electricity should flow through the bottom-left LED (as in the top-right of the image), turning it on. What seems to be happening, though, is that the electricity bypasses the LED and flows directly to the ground, meaning no LEDs light up (as in the bottom part of the image). This makes sense to me since electricity usually follows the path of least resistance. But everything I am reading online seems to indicate that what I am trying should light up the LED. What am I missing here?

I should also note that I have a 100 ohm resistor at the beginning of each row.

• How do you know electricity flows? Is there voltage across your series resistor, or did you connect an ammeter in series? Check your work carefully: continuity of connections, directions of diodes, etc.
– Kaz
Commented Nov 15, 2012 at 4:14
• I don't think the grid is wired the way you think it is. The lower image... where you have the red "L"-shape... those wires don't connect - they simply cross. For fun, google "diode rom". Commented Nov 15, 2012 at 4:18
• I just know that my LED won't turn on and if I disconnect column 1 just before the cathode it does turn on. Putting my own specific circuit aside though, I guess I'm just struggling to understand how a matrix works in the first place. In a working LED matrix, why is it that the current flows through the LED and doesn't bypass it and go straight to ground? Commented Nov 15, 2012 at 4:26
• It can't bypass it. The LED is the only path. The lines in the grid overlap, but don't connect. As far as your problem is concerned... if you've connected the intersections, you're doomed. If you have not, then I'd suspect your LED is installed backwards. Commented Nov 15, 2012 at 4:39
• And @TonyEnnis is absolutely right. I tried it again with the wires crossed but not connected and it works (and it makes a lot more sense to me too!). I feel a little silly for not realizing this. I guess I just saw lots of pictures of LED Matrices where it looked like they were connected, although they must not have been. Commented Nov 15, 2012 at 4:40