Yamaha CS80

Here is blue-sky brainstorm (so forgive possible gross errors):

Patch Memory might done as follows:

1) Use a decent ADC / DAC pair in mapping the pots under the little
front panel to some resolution of memory (ex. 16 bit DACS/ADCS to
16-bit RAM for representing a Patch as an array of such values).
2) Make sure you do two sets for the upper and lower Memories
3) Connect that to a small single board micro-controller (like a small
basic or forth based single chip embeddable board)
4) Write the software (Ha! Nontrivial but quite doable!) to sample the
pots, store that, and then control a variable resistance ladder
(painful to build) or use a DAC (the control signals to the DAC will
set the "resistivity" so that the analog signal in, perhaps suitably
buffered, is output at the right levels, also perhaps suitable
buffered, to the controls that the pots originally controlled (ie.
we're just swapping out the pots).  

Of course, if you trace into the actual voltage levels that the pots
control, then, you can do things like assignable velocity or touch
controls to, for example, patch "crossfading" (switching smoothly from
one patch to another).  Else you would need to program that in
software (and you would need to sample the keyboard with a separate
processor in order to accomplish that seamlessly).

The MIDI part for midi input would need to feed the keyboard sampling
input circuitry because delving into the board structure beyond that
would be a massive job.  The trick in engineering is to always work at
the level of interfaces and change that and not muck with the
underlying spaghetti of boards and wires.

For midi output, the solution exists (Kenton).

However, one would need a master control processor to manage 
1) The patch memory and User Interface
2) The midi output sub-processor (with its associated ADC/DAC circuits)
3) Integrating the Kenton board

This is a non-trivial job.

Any comments on my blue-sky brainstorming is welcome :)

Thanks!

--- In yamahacs80@yahoogroups.com, David Rogoff <david@...> wrote:
>
> Wayne Griffin wrote:
> > --- David Rogoff <david@...> wrote:
> >
> > they can record performances with poly aftertouch. 
> > > A MIDI kits with 
> > > MIDI out for the CS80 would be amazing, but I can't
> > > see anyone taking 
> > > the time and money to design and build them :(
> > > 
> > >  David
> >
> > The man for the job is Tony Karavidas of Encore
> > Electronics. 
> >
> > I'm not certain that an entire new CPU isn't in order-
> > along the lines of what's been done for the Rhodes
> > Chroma or over the last few years.
> The CS80 doesn't have a processor. It has a custom keyboard scanner
chip 
> and matching DAC. Everything else is a ton of standard little CMOS ICs. 
> All the CV routing and "patch" memory voltages are mixed and modulated 
> on lots of separate boards with tons of resistors and Yamaha VCA chips.
> >  We all want patch
> > memory and as much MIDI as possible. I suspect that
> > we'll never get to transmit the pressure data since
> > that seems to imply ADC on every channel, 
> That's actually pretty easy - just a decent speed ADC with an 8-to-1
mux 
> in front.
> > but on a
> > redesigned CPU board... [w]
> >   
> You'd have to start by replacing the KAS board. By the time you're
done, 
> you're basically replacing all the circuit boards under the keyboard!  
> Believe me, I've seriously thought about this, but then I got better...
> 
>  David
>