[sdiy] Clarification on Breath Controller Q

[The Old Crow]

On Tue, 31 Jul 2001 gmuir at sympatico.ca wrote:

> I did want to clarify my original question a bit. I realize that you
> can simply feed a BC-1 or BC-2 signal through a DX and run that MIDI
> CC through a MIDI to CV converter, but what I am looking to do is keep
> the signal from the BC in the ANALOG domain (a la CS-01) to avoid
> unnecessary quantization of the control voltage during the conversion
> process(as many have described in their experiments).
>
> My guess is that one of the pins on the BC plug takes a voltage from
> one of the rails, which powers the internal circuitry, and that
> another pin feeds the synthesizer with a steady CV (which in the case
> of a DX gets sampled into the digital domain and integrated with the
> outgoing MIDI data).

> Does anyone have any ideas?

  I think the BC-1 is a passive device: a (resistive) pressure sensor and
a trimpot.  IIRC the tip-center-ring of the mini phone plug goes like
this, but I'll have to look at the schematic at home later to be sure:

  Tip: CV out, goes from +V to ground.

  Center: +V input to the top end of the sensor.  I think the trimpot is
in series with +V, but it has been years since I looked inside a BC-1.  I
think the DX7 used +V = +5V.

  Ring: Common/ground.

  A DX7 would just feed the CV to one channel of an A/D chip and digitize
it at regular intervals.  For analog use, just need a simple circuit of 1
or 2 op-amps to span and zero the CV to whatever range you want.

Crow

/**/