LED cube resistors

Hi everyone :slight_smile:
I'm about to order parts for my first LED cube, a 4x4x4.
My question is, on all the tutorials that I've seen, people have attached a resistor to each of the 16 anodes coming out the bottom, but surely it would be more economical to attach one to each cathode, as only 4 resistors would be used.
Any reason why?
Many thanks.

Power dissipation in the resistor?

Also, wouldn't that reverse bias the neighboring LED and effectively switch it off? You'd have to have a diode for each LED to prevent the reverse biasing, and then you're back to one component per LED - plus the resistors.

but surely it would be more economical to attach one to each cathode, as only 4 resistors would be used.
Any reason why?

Yes because you should only have the current from one or a fixed number of LEDs going through the resistor. If not then the brightness of the LED will change according to how many are on at once.

Grumpy_Mike:
If not then the brightness of the LED will change according to how many are on at once.

Thanks.
Surely there will only be one led on per layer as the cubes work on pov?

If you want a really slow refresh rate, you can get by with just 1 LED on.
If you want a flicker-free refresh rate, like 24Hz or 30Hz for the whole cube, then you will turn on whole layers at a time. The cube will also seem brighter as each LED can be for (1/# of layers)/time element vs (1/# of LEDs)/time element.

4x4x4 = 64. You can have each LED on for 1/64 the time, or 1/4 the time. I'd go for 1/4.

Thanks very much, 16 resistors it is then :slight_smile:
Thanks again.