Here’s a great LEGO based Turing machine, Denis writes –
I chose to implement in Lego a slightly different version of the original Turing machine. Instead of having a bi directional tape, it uses a stack. When the symbol beneath the stack is read (and removed), the machine changes “states” and can add zero, one or two symbols on top of the stack.
This variation is maybe very different yet it is possible to show that this simple machine has the same capabilities than a Turing machine. Among other things, it can emulate a Turing machine placed on the stack.
I programmed a small interface (through an Access database so Microsoft Access must be installed on your computer) to enter an test simple Automaton With Append (AWA or AAA in French). Follow this link to download the demo: AAA.zip.
One reason to build the automaton with append instead of the original Turing machine was that I avoided building a bi directional (near) infinite tape.