"most led cube projects use multiplexing to control the LED." True
"No two Led's are ON at the same time." False.
I believe many (most?) cubes multpiplex whole layers.
So a 5x5 might have 4 shift registers sinking current thru the cathodes of LEDs 1-25 on layer 1, with a P-channel MOSFET, or PNP, as he Anode driver providing the current for that layer.
Then the cathdes are updated, and the next Anode driver turned on.
Can have very fast refresh that way.
I was thinking of making a 9x9 cube with my 96-bit shift register driver board.
81 bits to sink cathodes,
9 bits to pull 9 P-channel gates low layer by layer.
Array with 12 bytes/layer to hold the layers info and the cathode info for that layer.
OE/ is wired up, so it'd be
void loop(){
if (time for array layer change){
OE/ off,
increase layer count, reset to 0 if reach 9 (layers 0-8)
shift out 12 bytes via SPI.transfer for:next loop
OE/on
}
update array for any pattern, etc
} // end loop
