[sdiy] polysix keyboard interface help

[ChristianH]

There is no ground involved in the keyboard circuit. Those 16 lines are
divided into 8 outputs (going into the keyboard) and 8 inputs (reading
from the keyboard), with the key contacts indeed sitting at 61 of the 64
matrix positions. Usually, there are diodes in series to each contact,
in order to prevent unwanted effects if multiple keys are pressed at the
same time (some people tend to do so when playing on a polyphonic
keyboard... ;-)
The microcontroller sequencially activates one of the outputs and reads
the 8 inputs, repeating that for all 8 outputs. Using this, it can query
any key contact.
I have no idea how the keys are ordered within the matrix, but usually the
keys are simply assigned from bottom to top in groups of 8 to matrix
rows or columns.

So, it's not a matter of connecting certain lines to ground, but instead
connecting an output to an input of the matrix, just like a keyboard
contact does. 
This could be done using lots of CMOS switches, but it should be
possible to use 8 octal buffers, gated by the 8 microcontroller outputs,
each buffer providing data for the 8 inputs. 
If the source is using a microcontroller too, it might be feasable to
read the Polysix's 8 output lines by the interface processor, and then
matchingly outputting 8 bits from the interface into the 8 Polysix input
lines. I have no idea about speed requirements, but I'd guess that
today's processors should be fast enough to satisfy that ancient Polysix
contoller in time.

Chris



On Thu, 16 Feb 2006 10:27:33 +0100 jure zitnik <kokoon at gmail.com> wrote:

> i recently got an non-midified korg polysix. i've already built a
> midibox (from ucapps.de) so i know a bit about it and it could
> probably be easily programmed as midi-in for the polysix.
> what i have in mind is to put a midibox core + dout (digital-out)
> modules between the polysix keyboard and the polysix voice assigner
> (that's what the keyboard is connected to)
> there's 16 wires going from the keyboard and i assume it's some sort
> of matrix-encoded signal.
> 
> the question is - how would i start finding out what's what - pressing
> keys and measuring voltage on separate wires on the connection? which
> one is ground? the schematic of the board that the keyboard connects
> to is here: http://www.oldcrows.net/~oldcrow/synth/korg/polysix/manuals/service/p6smm6.pdf
> 
> thanks guys,
> jure