[LAU] hardware - buttons and knobs?

[Josh Lawrence]

Something mentioned in the hardware synths thread prompted me to ask
this question...

So how does one go about adding buttons/knobs/switches that do
specific things to a standard computer?  My best example of this is
the Muse Receptor - it is a standard computer, yet it has knobs that
do various tasks.  I realize there is a hardware and software answer
to this question, but I'm more interested in the hardware part.

In other words:

1)Where can I buy a knob?
2)Where do I plug it in?

Finally, I also realize you can buy MIDI knob boxes; that's not what
I'm talking about here.

-- 
Josh Lawrence
http://www.hardbop200.com