Oh! Wow! I thought of something like this some time ago. But different. Like in a LED-cube of at least 16 to a side, and multicolored. Aand soldering in some sort of mesh, to have some fpga-like functionality.

OP here

That's very cool! Never heard of LED-Transistor logic, and after reading the article I know why :).

I'd like to implement MCPU on an FPGA next weekend, so hope to have two implementations soon.