just some short hints, I am in a haste...
1)Where can I buy a knob?
every electronic DIY
shop
2)Where do I plug it in?
microcontroller. They
do the job to translate it to computer, for
instance over serial or USB.
Google for Arduino for a readymade open source project with which you
easily should build your own box.
Finally, I also realize you can buy MIDI knob boxes; that's not what
I'm talking about here.
The DIY approach has the advantage of more resolution and better timing
as good old Midi, especially when you use softsynths which speak OSC.
Cheers,
Malte
--
Malte Steiner
media art + development
-www.block4.com-