4x4x4 Led Cube Transistor Debate Please post

Using Arduino LEDs and Multiplexing
1

Hello!

This is my first post and first time trying to understand the Arduino Uno.
My big question that I cant seem to understand is this:
What is the purpose of using 4 npn transistors for the 4 levels of a 4x4x4 led cube?

I understand that they are used to switch the entire level on and off when connected to GND, but why?
Could you not simply just connect the 4 layers to the arduino directly?

Ive heard talk that they allow the incorporation of an external power source to power the leds. If so, is the power source connected to one one the legs on the transistor.

Thanks a million,

2

The arduino outputs cannot drive enough current for all the LEDs. This means that a few on in a layer are extra bright and many on are dim. The transistor allows an external source to be switched.