Here's the gist. A sensor from a bike computer is used to detect the rotation of a bike tire. The output of this sensor and the turning angle (controlled by the thumb joystick) is read by an Arduino and relayed to a computer over a usb cable. The computer reads the number of rotations and angle of the joystick and uses these values to control a virtual bike within google earth!
Stuff you will need:
Indoor bike stand (or suitable stationary bike)
Bike cadence sensor (or reed switch and magnet)
- Small thumb joystick or harvest this from a PS2 controller
Computer with windows or osx (sorry linux :( blame google for not releasing the google earth browser plugin for linux)