The ADNS-2620 is a small form factor optical mouse sensor. It is used to implement a non-mechanical tracking engine for computer mice. Now you can make your own optical mouse or input device. Project description, more information and ordering can be found at https://www.sparkfun.com/products/10026 Datasheet: http://www.sparkfun.com/datasheets/BreakoutBoards/ADNS2620.pdf Datasheet: http://www.sparkfun.com/datasheets/Widgets/AV02-1278EN.pdf Datasheet: http://www.sparkfun.com/datasheets/Widgets/AV02-0998EN.pdf ADNS2620 Arduino Library: http://www.sparkfun.com/datasheets/Widgets/ADNS2620.zip HID Code: http://www.sparkfun.com/datasheets/Widgets/hid-mouse.zip Additional Design Files: http://www.sparkfun.com/datasheets/Widgets/Copper+IGES.zip Example Project: http://web.media.mit.edu/~mellis/mouse/