[sdiy] Odd keyboard on Ensoniq

[Rainer Buchty]

> What I really want to know is how the aftertouch is supposed to work
> and if there is a way to get my EPS fully functional again.

Check this out:

http://wwwbode.cs.tum.edu/~buchty/ensoniq/schematics/sq80/sq80-kbd-lower.jpg
http://wwwbode.cs.tum.edu/~buchty/ensoniq/schematics/sq80/sq80-kbd-upper.jpg
http://wwwbode.cs.tum.edu/~buchty/ensoniq/schematics/sq80/sq80-kpc.jpg

The EPS presumably uses the same keyboard as the SQ80; at least they use
the same basic technology (Ensoniq was quite proud of their patented
polypressure-capable keyboard).

For DIYers (not sure about the patent situation concerning commercial
exploitation...) this seems to be an interesting way to equip any vanilla
keyboard with pressure sensitivity. The custom chip used in the control
circuitry (KPC) is presumably only a bunch of counters and could be easily
emulated with a CPLD or FPGA.

Concerning your problem I wonder if the problem is related with the clock
signal fed into pin 8 of the KPC chip. It seems to work otherwise, cause
if not the keyboard processor would report an error code to the main
processor (e.g.  keyboard calibration failed).

Let me know off-list if you need the Ensoniq keyboard protocol (EKP) so
that you could e.g. build a MIDI-to-EKP conversion unit in case your
keyboard circuitry can't be reanimated.

Rainer