Help me understand a 3x3x3 LED Cube design

3x3x3 led cube

Okay, so I saw the cube recently posted on hackaday.com. I decided I would build one, but saw the (lack of) instructions. Basically I've built the 3x3x3 cube of LEDS and I've got a common cathode for each layer (of 9) then a common anode for each column of 3. Making a total of 3 CC's and 9CA's. I also have 5v voltage regulators, tons of resistors (of all different kinds, I will match them for the LED's) and a good selection of capacitors. Now I want to connect them to a PIC16F628A (has more than 12 I/O pins so I should be good)

**broken link removed**

Could someone please help me figure out this circuit though? I need to modify it (don't have the cap he used) and more importantly I'd like to know how it works.

If I understand correctly:
of course LED's are multiplexed, I get that part. The resistors are to limit current to the LED's, the transistors are to switch on/off, the PIC controls which lights are on.

My questions:
Why only 3 transistors? Don't you need one per column?
Are the 2 different value resistors because of the # of LEDs in the series?
Can I substitute the cap for a different value IE would a 100uF or a 470uF do anything different?
What purpose does the cap actually serve here?

cube leds 3x3x3

Okay, so studying up I have found this:

The capacitor is just a filter capacitor, it doesn't need to be 220uF, in fact it could be just about anything over 10uF.
The set of 220Ohm resistors are current limiting to the diodes (already assumed that).
The PIC is driving the columns, while the transistors are driving the rows (this is because the rows have 9 LEDs and columns only have 1 or 3 depending on how you look at it-- its really only driving 1 at a time per column)
The 330Ohm resistors are for the transistors, to draw current.
The voltage regulator has a very obvious use.

And lastly, the PIC can be substituted for the one I'm using.


Just in case anyone read this and had the same questions as me.

Re: 3x3x3 LED Cube

Try this instead, i made the pcb with Eagle. If you want to know more then check this out - https://www.electro-tech-online.com...-led-cube-can-i-use16f628-instead-16f690.html

Re: 3x3x3 LED Cube

Hello, Firstly I apologize I do not speak English, I am French.
I just wanted to know if anyone has built this cube with a PIC16F628a, the HEX file does not work for me.
I think I noticed errors on the file Eagle, I believe that the transistors are mounted upside down, and GND PIC is not connected, are there other errors?.
Could you please help me, thank you all. I have no LED lights, just the power LED.
Thank you for reading and sorry for the rough translation.
Best Regards. JeanMichel63