Archive of the former Yahoo!Groups mailing list: Yamaha CS80

> On Fri, 1 Oct 2004, David Rogoff wrote:
>
> > What is in the CS-80's sensors? I know it's a rubber cushion and,
> > according to the schematics, electronically it acts like a
> > potentiometer, outputing a voltage proportional to the pressure, but I
> > don't know what's going on inside it. Are there (widely, cheaply)
> > available force sensors that could be used to add pressure sensing to
> > an existing keyboard (if you could figure out where to mount them)?

--- In yamahacs80@yahoogroups.com, The Old Crow <oldcrow@o...> wrote:
>
> They are "force-sensing resistors" which are sold in a variety of
> configurations these days. I'll have to find out if any are
suitable as
> aftertouch sensors.

Scott,

Thanks for the info. I looked up some of these on google. They all
have various voltage vs. pressure responses which made me wonder how
the CS-80's sensors responded. So, I decided to do a little
experiment. After trying various ideas involved postage scales and
bath scales, I thought of using a 2-liter coke bottle (actually diet
root beer) as a weight. I soldered a wire to the pressure sensor
output of a key (see pic cs80_pressure.jpg in Files page). I placed
the bottle, upside-down, at the front edge of a white key. I kept
adding more water and recording the voltage.

The results are in the files pressure_vs_voltage.xls and
aftertouch_response.jpg in the Files page. It's a kind of log
response, toping out with a little under 7 volts for any force over 70
oz (about 2Kg). The response is a little weird: it would stay the
same for several ounces and then jump. I'm not sure why it did this.
Maybe it's stiffness in the rubber piece over the sensor.

I also ran the output to an oscilloscope and looked at the curve as a
I pressed down on the key (sorry - no picture). It definitely looked
smooth and continuous, without the steps I had recorded. Any ideas?

Anyway, this is way more than most people want to know, but it could
be useful if someone was trying to build a new keyboard, or looking to
replace broken sensors on a CS-80.

David