The arcade shield is an arduino shield specially developed for the Prosjekt:Arcade Machine. It's put on top of an arduino that has a reprogrammed firmware (not programmable using the normal arduino IDE anymore) and connects to a double category-5 female connector. A set of Joystick and controls (8-axis joystick with one fire-button and 4 additional color buttons) can be connected to the cat5 connector. The arduino then polls the buttons, and the reprogrammed 8u2 transmits button presses using a USB HID Keyboard ClassDriver implementation.
NOTE: AS OF 10.7.2012, THE ARCADE SHIELD IS DEPRECATED AND WAS REPLACED BY A CUSTOM ATMEGA32U4-BASED SOLUTION.