AW: Ribbon controllers

[WeAreAs1 at aol.com]

Hello list,

I have the JP8000 service manual.  The physical assembly of the ribbon sensor
itself is not explained, but the circuit that it connects to is clearly
shown.  The sensor outputs two voltages, one for pressure and one for
position.  The voltage range is roughly 0 to 5 volts.  The Position voltage
gets slightly filtered (just a couple of .01uf caps to ground to kill big
spikes) and then goes directly into one of the analog mux inputs.  The
Pressure voltage goes into the base of a small-signal NPN transistor,
configured as a basic transistor switch.  This transistor's output switches
between 0 and 5 volts, and is also read by the same mux.  

I don't have a JP8000, but as far as I remember, its ribbon is not actually
"pressure sensitive", per se.  The ribbon's "Pressure" sensor is probably
there so the CPU can detect when you have placed your finger on it, and when
you have released it.  It can then start reading the Position voltage, using
the voltage of your first Position as the "zero" point.  (It does work this
way, doesn't it?)

I'm not sure, but it is quite possible that the ribbon outputs a Pressure
voltage that is continuously variable (just like the Position voltage),
although Roland is obviously not using it in that way.

I don't know how much the ribbon sensor would cost from Roland, but if
there's any interest, I could find out (I do Roland authorized service).
 Most of the JP8000 parts are available now.

Micahel B.