Using a modern USB joystick on a vintage computer (Atari compatible)

[Mark Wickens]

I've seen plenty of examples of adapters to use a vintage joystick with 
a modern computer.

I'd like the opposite - to use a USB controller with a vintage computer 
(Atari compatible - for example ZX Spectrum, Commodore 64). Does anyone 
know of an adapter or a homebrew project?

Thanks, Mark.