Some time ago I finished a keyboard based (again) on the mbed NXP LPC1768.
It was used to emulate a keypad which was mounted inside my car. With the rotary switch it was possible to scroll through a long list, like POI’s (Point Of Interests). One click of the rotary switch resulted in one keypress. Attach it to a USB port and you have a working keyboard.
One of the problems I encountered was that not all key emulation commands were documented. The ultimate goal is to interface with my onboard systems in the car and to be able to blindly navigate trough menu’s without thouching the screen. I will connect this to my iPod interface for my Seat Alana sound system.