This Lego Logic Blocks project appears to only be theoretical, however the idea behind it is pretty neat. The goal is to make a set of logic gates that use light as inputs and outputs. The project only talks about building a NAND gate, however it should be pretty easy to build any of the other gates as well. While they probably wouldn’t be practical to use for anything except the simplest circuits, they would be fun toys to play with. I could also see these as being useful for teaching how logic circuits work- you could actually see the state of all of the inputs and outputs. The other cool thing about them is that they could be directly interfaced to things such as optical encoders or switches.

Has anyone attempted to make something like this? Think it would work?