[sdiy] Aftertouch via Pressure

[The Peasant]

Looking good, Tom,

My only concern with this design is that you must ensure 
that each rubber hose piece has exactly the same volume of 
air to be squished out by the key. Otherwise the effect 
will be slightly inconsistent from key to key.

Take care,
Doug
______________________
The Electronic Peasant

www.electronicpeasant.com


Quoting Tom Arnold <xyzzy at sysabend.org>:

> 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...
> 
> -- 
> 
> ----------------------------------------------------------
--------------
>  - Tom Arnold -       When I was small, I was in love,   
>               - 
>  - Sysabend   -       In love with everything.           
>               -
>  - CareTaker  -       And now there's only you...        
>               - 
>  --------------         -- Thomas Dolby, "Cloudburst At
> Shingle Street" -
> 
>