Thank you, CrossRoads It may not seem like it, but there's a lot of work in that dual layer design That's why I would happily share it with anybody who wants to use it. Of course, it would be nice if I could first prove that it's correct by building a board myself. I'm afraid that's going to take months, because soldering the 8x8x8 cube together is a tedious task. But it will be done one day and I'll be back here to inform you about it!
In the meantime, I've finished putting together the circuit today for the 4x4x4 test cube. I've done it on 3 solderless prototyping boards, without any soldering. I hope it will work. It also includes variable resistors to the LED cathode columns, so we'll know exactly just how much current we'll need for the big cube.
The 4x4x4 test cube is also soldered together and ready to go. It will take a few more days to write some basic software for it. I'm hoping that in about one week from now I will be able to show you some nice video about the 4x4x4 cube working. Perhaps I'm too optimistic, it will be a miracle if everything will work on the first go. Actually, I'm hoping that at least it will do something, even if not exactly what is expected and I'll be able to debug it. If no LED will light at all, that won't be funny... let's hope it does not happen.