Lego boe bot

Crazyrabbit

Lately I have developed an interest in LEGO robots. I really like their motors. They are so quiet. You can sneak up on someone and they don't hear a thing. It is easy to modify the cables for the motors ans switches, but the encoders and light sensors are another story. How do they work on only 2 wires. The encoder even counts up and down with the LEGO brick micro-controller. Must be some hidden circuitry in the brick. I even tried a scope and only saw a +6V line. Any ideas would be appreciated. Here is a short video using a BS2 programmed with the whiskers escape code straight from the book.

https://www.youtube.com/watch?v=33PUn6qZJxk&feature=youtu.be