LED Cube Questions

[_V1qY]

Hi, I want to build a 4^3 LED Cube but I have a few questions, I hope you can help me with.

What exactly is the need for the transistors? From what I understand, they only allow the circuit to be completed if one of the pins sends out '1'. But this is kind of backwards thinking. Why is this necessary? Surely just sending '1' directly to the pin instead of going through a transistor would have the same effect?

 

[Armadillo]

We talking about this

http://www.instructables.com/id/LED-Cube-4x4x4/step7/The-controller/

Looking at the circuit, I would say the transistors are there to switch gnd on and off to the cathodes on the leds. You can't just wire directly to the controller as them pins are not gnd, so transistors are on them instead. Output from the the pin, transistor gets switched on, and connects the leds to gnd. No output from controller, transistor is off, no gnd for led, so no light.