With the Nintendo Wii there is support for the old NES, SNES and N64 games.
To play these games you can buy a "classic" controller for about $20. But what if you already have an old NES/SNES or N64 controller? Why can't you just use those? Well Raphaël Assénat has done just that. He created an adapter that took those older controllers and adapted them to a Gamecube-type adapter (the gamecube controllers are compatible with the Wii machine.)
Here's an Nintendo 64 Controller guts before being installed
He did this with a little more technical knowledge then I have so I'll leave in his words:
Because of the complexity of the Gamecube's controller protocol, it's not
possible to build a simple conversion circuit without using programmable
components. For this project, I used an atmel Atmega8 microcontroller. Maybe
it's a little overkill, but using this chip allowed me to use my Multiuse tiny 1
PCB. Given the small size of this circuit, it's possible to fit it inside an
Here's a video of the N64 Controller to Wii Mod in action
He has a full how-to with loads of pictures, the programming firmware and sourcecode all on his site so go check it out.