electronics for a diy ribbon controller

[Stopp,Gene]

The story of my home-built ribbon controller is in the DIY archives (I
think...). I used a long strip of material from an anti-static bag. You
must use the black rubbery type of anti-static bag (carbon impregnated
rubber? something like that probably). For the metal strip I used a thin
piece of spring steel about 1/4" wide (used for de-soldering
surface-mount chips). For the Gate output I used a pushbutton mounted
near the end of the controller. (The original Moog ribbon controller
uses a finger-capacitance gap that runs the length of the ribbon, right
next to it, for the S-trig.)

It works pretty good. One problem is that the resistance of the material
is kind of high, like in the megohms for the whole thing. There is a
buffer and a cap for the sample and hold (1/4 TL084) and the cap must be
small to avoid portamento when moving the ribbon contact spot. The small
cap makes the whole thing very sensitive to finger contact and drift and
such. But the thing only got used for wild effects during jam partys, so
no big deal. I wouldn't want to use it for "fretless" playing, however.
The same spot never has the same voltage twice.

Another possibility is the material that is used for FCC-compliance
chassis gaskets in card-cage rackmount equipment. This stuff is like a
small black rubber rope, about 1/8" in diameter, cut to length and
stuffed into a slot in a metal panel so that it seals the gap between
other panels in the unit. It's resistive, and it's a low resistance -
something like 10 ohms per foot. I haven't tried this for ribbon
controller experiments, but it looks promising. One problem with the low
resistance is that it will be a pretty good drain on the power supply,
pretty much ruling out using batteries. Probably the best idea would be
to use a series current regulator as a constant current source ( maybe a
78xx regulator?). You would need to somehow limit the current if you
were to touch the ribbon at the top and bottom at the same time, thereby
shorting out the strip.

 - Gene

 ----------
From: Puentstein at aol.com
To: synth-diy at mailhost.bpa.nl
Subject: electronics for a diy ribbon controller
Date: Wednesday, February 25, 1998 12:13AM

Greetings,
After fumbling around with a 2 foot long piece of metal, a bit of vhs
tape,
and a 9 volt battery, (for now), this hookup 'seems' to work right
(measuring
variable voltage off the tape):

                          + --------------------meter------------------
_
                tape:    ____________________________  _
                            ___________________________    >-----voltage
source
         metal bar :   I___________________________I  +

 ...The tape voltage appears to change "exponentially" as in the higher
up the
tape you move your finger the quicker the voltage increases.  Is this
the
correct way to wire one of these things??   Also, how can I get an
"s-trig"
(zero resistance) whenever the tape connects with the metal?    Sorry
I'm all
questions but my objective is to learn something/build a stand alone
controller without frying the innards of an old Moog.
Thanks for any info, Randy