I was following LED Light bar project in Arduino Project handbook and I noticed some odd behavior in the Arduino.
I accidentally didn't ground the back half of the breadboard (because I didn't realise there was a break see in the circuit below). I figured that out but noticed it seemed to make the digital pin 2 behave as ground and not light the LED when the ground wasn't connected to the back of the bread board. I tried Googling this but can't find any explanation. can anyone explain why this happens?
UPDATE To make it a bit clearer I thought it was acting as ground because before I connect the ground between the right and left of the board (the connection I originally forgot to add, see the image) I would of expected only the front 4 LED's to light but what appears to happen is all BUT the LED connected to pin 2 lights up. When I bridge the gap in the ground rail all LEDs including the one connected to Pin 2 Lights hence why it appeared to me to be acting as ground, as the LED clearly works.
Update 2 Here is a video of the result: http://youtu.be/5dg0PHDOorA