Adam of Xbox-Scene added an accelerometer to his Xbox 360 controller, enabling players to control one of the analog sticks with a simple tilting motion. Video after the jump.
The accelerometer works by outputting varying voltages for varying accelerations. I will use a 3-axis accelerometer so it will output 3 varying voltages. I will use an analog-to-digital converter to get the signals into a micro controller. The micro controller will do the processing that determines how the controller is tilted. It will then be output as an analog voltage to the controller in place of the on board potentiometers that are controlled by the analog stick