Motion tracking is used in many areas. Cars, robots – practically everything that moves and needs control has some kind of tracking. There are many ways of doing this, but Paul suggests pretty original solution. He decided to try optical mouse method. With proper optics he was able to track movement when sensor is faced to ground from moving vehicle.
He used an ADNS-3080 single chip optical mouse sensor. They are widely used in optical mice. They are cheap to buy or you can scavenge from damaged mouse. This isn’t the one part used. From sensor data goes to PIC18F2221 microcontroller which is responsible for further actions depending on motion detected. Device has a custom housing and optics that probably is most expensive part in this project.