[Marcus Gritsch] wanted to do his retro gaming using retro hardware… or at least using some retro hardware. Although he was playing his Commodore 64 games in an emulator, he figured that using an original controller would boost the nostalgia quite a bit. This is a vintage Competition Pro joystick that has buttons and a joystick of a similar quality to arcade hardware and a DE-9 connector. He managed to connect new to old by building his own USB to C64 joystick adapter.
His project started out by breadboarding a circuit based on a PIC 24FJ64GB002 microcontroller. This does all of the work, having native USB support, and no problem reading and translating the signals from the old hardware which are simply conductors for each internal switch that pull to ground when actuated. Once working, he soldered everything to some protoboard; a connector at each end, the chip itself, a voltage regulator, and some passive components. It’s a, robust build that should give him years of emulated fun.

http://hackaday.com/2011/10/18/c64-joystick-adapter/