[sdiy] Aftertouch via Pressure

[Tom Arnold]

On Wed, Jul 09, 2003 at 07:44:09AM -0600, Ian Fritz wrote:
> >But the mechanical part is difficult. You must find a way to insert
> >the tube (hose?) beneath the keys, such that it's equally actuated from
> >blacks's and white's. And, worst of all, you have to find a way to
> >get enough key travel even with the additional thickness of the
> >tube. But then again, the SH-2000's keyboard also has reduced
> >key travel, and it plays nicely ...
> 
> Agreed.  This sounds pretty challenging.  You also have to have a perfect 
> pressure seal.  And you may have to think some about atmospheric pressure 
> variations if you use air for the pressure fluid.

Got some pressure sensors from Jameco namely because they were cheap ( $8 ).
They are low pressure ( 1psi ) Motorola sensors.

My idea for the pickup assembly will look something like this :
( warning : bad ASCII art ahead )

  I  I  I  I  I  I  I  I  I  I  I  I  I
*=======================================-[]

Where :
* is a sealed stopper.
= is a piece of small copper pipe with fittings at every key.
I is a short piece of soft rubber hose, heat sealed at the end and slipped on
  the fittings.
-[] is the pressure sensor.

The pipe will run along the bottom front edge of the keyboard assembly, in 
my case a Pratt/Reed Syntauri assembly I have earmarked for abuse.  The soft
rubber hoses will run under the keys to be squished.  Possibly cutting notches
for the hoses in the existing felt pad.

I cant see how to run a single hose on this mechanism so I've come up with this
overly complex plumbers nightmare. If I can fit in a single hose I will.
Output of the transducer will feed into an amp and then a microcontroller.
The reason for this is to have a very quick way to calibrate the unit. Just a 
couple pushbuttons to set sensitivity.  Aftertouch "off" will be automatically
set if the microcontroller sees no gate off the keyboard for a period of time
so variations in ambient air pressure can be accounted for.

Hey, its a fun project and at the very least I'll have a modern art sculpture
when I'm done...

-- 
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 - Tom Arnold -       When I was small, I was in love,                  - 
 - Sysabend   -       In love with everything.                          -
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