There isn't much, really. First, solder the microcontroller's socket to the perfboard, then the socket of the driver. I didn't use a socket for the driver initially, which I regretted later...
Here is a schematic.
If you do this in a clever way, there will not be too much effort in connecting the driver to the controller. Port B controls the common cathodes, so all port B pins connect to the driver inputs (green). PB0 is on the wrong side of the controller, but that is no problem. PB6 and PB7 are somewhat out of place. I simply used two wires to connect them. That won't win me a beauty contest, but the electronics will vanish under the cube anyway. Make sure that PB6 and PB7 are connected in the right order: It changes between the controller and the driver.
OK, start by positioning the two ICs/sockets. Note that there is an offset of two holes on the board.
Now, connect port B to the driver. Start with the conveniently placed ports 1 to 5. I didn't even use wires, but it might be easier to do so.
Now turn the board over and connect the two ground pins of both ICs.
Next, connect port 6 and port 7 using wires. Note that the yellow and white wires are changing order.
On the bottom side, connect port 0 to the driver (here marked in yellow) and connect analog and digital ground on the ATMega8 (black wire, white outlines).
Also connect digital and analog Vcc pins (red wire, pins VCC and AVCC) and GND pins.
Finally, add a red and a black wire to the ATMega's Vcc/Gnd pins do connect your battery. Done!
Now we have to connect cube and electronics. For this we need another sixteen wires. Let's start with the common cathodes, i.e. the LED groups. So far that vertical wires from each group just end on the board. Now we need to connect wires to each of them.
And we connect them to the driver output. Start with the top right group, then connect the top left group. Continue with the second level. Keep alternating between right and left.
Do exactly the same thing with the bottom layers (layer 3 and 4). Alternate between right and left as shown.
Now connect the columns of the cube. Here is how. This time there is no driver; the columns of the cube are directly connected to the microcontroller. Here is a bottom view of the cube. Every column is shown with their respective controller pin.
Again, begin by soldering wires to the "feet" of the columns, i.e. the anodes of the LEDs.
Connect the LEDs in the right order. Start in the corner and connect all four LEDs of one row.
Then connect the LED anodes of the second row. Here, two columns are connected.
And the last two anodes are done.
If your wires aren't too long, you can flip the electronics over and hide the wiring.
I fixed the two parts of perfboard to each other with a few pieces of wire. I soldered them to one board, inserted threaded them through the other board and just bend them at 90°. See the picture below.
And that is the hardware completed. In the picture below, there is a pigtail connected to the ISP pins of the controller. I used that to program the controller while I kept adding new patterns. Depending on your means of programming, you might or might not need this.
So, all that is left is the software. A brief description and the final part of this project will be posted in part 4.