[sdiy] Aftertouch via Pressure

[Glen]

At 09:53 AM 7/9/03 , jhaible at debitel.net wrote:

>I expect it would be hard to get such a stucture _sensitive_.
>The weight of the whole keyboard action must not cause an
>Aftertouch output, but the additional pressure from the fingers
>has to ...

I think it's mostly a matter of choosing springs with the proper amount of
tension. With springs to regulate both the upward and downward travel, you
could essentially "float" the weight of the keyboard above the sensor tubing.

Then you tweak things further by choosing different diameters of tubing,
and tubing with different degrees of stiffness in its walls. 

Finally, you can move the whole tubing assembly either toward the front of
the keyboard, or somewhat more toward the center or rear of the keyboard.
Moving away from the very front edge of the keyboard will apply more
pressure to the tubing, but will offer a shorter range of travel. Adjusting
this, will also be at least somewhat dependent on the diameter of tubing
you have selected.

If you wanted, you could replace the tubing with a magnet and hall effect
sensor (not the switching type, of course). I'm sure there are other types
of sensors that would be appropriate as well.

It's certainly a mechanical engineering project, but it shouldn't be *too*
difficult to arrange something appropriate. Once someone on the list
actually builds one, others will find it much easier.   ;)


later,
Glen Berry