4x4x4 Led Cube Transistor Debate Please post

hello!

this first post , first time trying understand arduino uno.
my big question cant seem understand this:
what purpose of using 4 npn transistors 4 levels of 4x4x4 led cube?

i understand used switch entire level on , off when connected gnd, why?
could not connect 4 layers arduino directly?

ive heard talk allow incorporation of external power source power leds. if so, power source connected 1 one legs on transistor.

thanks million,

the arduino outputs cannot drive enough current leds. means few on in layer bright , many on dim. transistor allows external source switched.

Arduino Forum > Using Arduino > LEDs and Multiplexing > 4x4x4 Led Cube Transistor Debate Please post

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