And Moxie Scores!

[Johan Gustavsson]

...and not only that, but he replies to his own mails :-)

Someone wrote me a very nice mail, telling me that the two switches
were for measuring velocity...Thank you, but I already knew that :-)
However, a few cups of tea later and after bandying the problem around
with some of my more thinking-enabled friends, this kind of solution
presented itself:

   --- Resistor chain
    |
      /
     /
    |
   ---
      |
      | --- Gate bus
      |  |
      |    /
      |   /
      \  |
        --- CV bus

"But", I hear you say, "that wont work. The gate will be floating
around and when pressed down, it'll still have rather silly
values". That's true, so the next generation is:


   --- Resistor 
    |  chain	-12v
      /		|
     /		<	This is an opamp wired as a comparator,
    |		>      /  referenced to, oh, -6v maybe
   ---		<     /
      | pre-gate|  |\
      | ---Bus--+--| ---- Gate 
      |  |	   |/
      |    /
      |   /
      \  |
        --- CV bus

This way, the voltage on the pregate bus would be kept at about v- by
the resistor connected to v-, until a key was depressed. Then, the
voltage would rise to at least 0v (for the lowest key on the
keyboard), which is well above -6v and so the gate output would go
high.

Hmm...Looking at it this way, I suppose the pull-down resistor would
interfere with the CV bus when the key is depressed. could this be
counteracted in an easy way? Perhaps by putting another opamp in as a
voltage follower just *before* the resistor, to act as a buffer? Or
would it be cool enough just to compensate for it with the scale and
range trimmers?

Anyway, would this work? Of course I'd still need the electronics for
S&H and so on, but is it a valid way to get the voltages out of the
keyboard itself?
/Moxie (Quizzical)