Lego Turing Machine: The building blocks of computing in play

The Lego machine is based on the theoretical device set out by Turing in his paper.

Turing described the hypothetical machine as being able to move backwards or forwards over a strip of infinite tape, which is divided into cells. The machine could read, write or erase symbols inside each cell.

The machine would be controlled by a series of rules that tell it whether to move the tape, how to manipulate a cell's contents and which rule to jump to next.

In the Lego Turing Machine each cell on the building-block tape, seen above, is made of a black switch, which can be switched on to represent a symbol or turned off to represent a blank cell.

Photo: Centrum Wiskunde & Informatica

As the Lego machine moves along the tape, it checks the contents of each cell using a light sensor. The sensor detects the light reflected from each cell to check whether it contains a black switch, representing a symbol, or a white Lego block, representing a blank cell. The Lego tape is made up of 32 cells.

Photo: Centrum Wiskunde & Informatica

A rotating beam with two orange arms mounted above the Lego tape can flip the black switches in both directions - either inscribing a symbol on the tape or erasing it.

Photo: Centrum Wiskunde & Informatica

The machine reads from the Lego tape.

Photo: Centrum Wiskunde & Informatica

Here you can see the machine representing the computation of 2 + 2.

Photo: Centrum Wiskunde & Informatica

And here the machine is representing the result of the 2+2, which is of course 4.

Photo: Centrum Wiskunde & Informatica

The movement of the Lego tape and the operation of scanner are controlled by a series of corkscrews and rotors.

Photo: Centrum Wiskunde & Informatica

A side view of the machine.

Photo: Centrum Wiskunde & Informatica

Another close-up of the machine.

Photo: Centrum Wiskunde & Informatica