Here is my 3x3x3 LED Cube project. It runs using a PIC16F690. Along with the brief explanation of how to make it, I have also included the .asm file for the PIC and a piece of software written in VB.NET that you can create your own LED patterns. These can be exported as .asm files and put into the main .asm code.
Step 1: Building
Each layer of 9 LEDS are connected with all of the cathodes together. The cube is multiplexed, meaning that only one layer is on at any one time. It happens so quickly that the whole cube looks like it is illuminated. RB5, RB6 and RB7 controll which layer is being illuminated.
From the picture you can see the connections to the top layer. I have only connected RC2 to show you how the connection should be made, the rest of the LEDs are connected the same way.
The easiest way to connect the LEDs together is to drill 9 holes into a piece of wood (picture 2), then place the LEDs into the holes, bend the legs and solder the cathodes together. After 3 of these are created, simple stack them and solder the anodes together. You should end up with 9 anodes and 3 common cathodes to connect to you circuit.
All you need to build this cube is:
1 x 5v regulator
1 x switch
1 x PIC16F690
3 x NPN tansistors
3 x 330 ohm resistros
9 x 220 ohm resistors
1 x 220uF capacitor
27 x LEDs
oh, and MPLab PIC programming software. (Other software may work, but my .asm file may have to be changed a little)
Step 2: The software
Now that you have an idea of how to build the cube, here is the software that you can use to generate the LED cube patterns.
Along with the software is the .asm file, in this file, there are already some patterns loaded in and it is pretty straight forward to see how to insert your own patterns.
The second picture shows you how the software saves the binary info for the patterns.
Layer 1, Layer 2, Layer 3 and Layer 4 are 4 registers used in the PIC. Obviously Layers 1,2 and 3 represent the top, middle and bottom layers, but they are only 8 bits, so another register is used Layer 4, which holds the 9th LEDs data for the 3 layers and the brightness and time the LEDs need to be on.
Hope this is a good enough explanation of the project. It's not too hard to build, just takes a bit of time to arrange the LEDs.
I have also added a zip file with the source VB code as someone asked for it!