[sdiy] Keyboard Encoder Experiments...

[Steve Ridley]

> I have always wanted to have a keyboard where you could actually sense
> the true position of each key...I don't actually know how useful this
> might end up being...

Bob Moog did a lot of work on this sort of thing during his "wilderness 
years" in the 1980s.

http://emfinstitute.emf.org/exhibits/moogkeyboard.html

There was an article about it in Computer Music Journal, vol 14 no.2.

http://links.jstor.org/sici?sici=0148-9267(199022)14%3A2%3C52%3AEOTKIT%3E2.0.CO%3B2-8

Each key's top surface had a layer of conductive material with a
thin insulating layer over it.  An AC signal was applied to each 
corner of the conductive layer, and finger capacitance to ground
caused a current to flow.  My comparing the currents at each
corner, finger position on each key could be detected.  Normal
key movement was detected by capacitive means and there was some
sort of force sensing resistor arrangement for aftertouch.

Moog did a capacitive pitch bender device for Synton - used in the 
Syrinx and the 3000 keyboard.  Schematics here:

http://www.synthdiy.com/show/?id=906

might give a clue the capacitive sensing in the multiply
touch sensing keyboard (or might not).

There is mention of an earlier version in the Proceedings Of
The 1982 Internationa Computer Music Conference, San Fransisco
CMA, 601-605, but goodness knows where you'll find a copy.


There's also some reference to front to back force sensing here:

http://www.bikexprt.com/music/refine.htm

and an early side-to-side motion system in US Patent 1,914,831.


Steve