[sdiy] VCO autotune for poly analog modular

[Magnus Danielson]

From: Amos <controlvoltage at gmail.com>
Subject: Re: [sdiy] VCO autotune for poly analog modular
Date: Tue, 3 Apr 2007 18:28:22 -0400
Message-ID: <908a4c120704031528p51bfd1f6tc4e9fe6816f1a1de at mail.gmail.com>

> Yes you can do this.
> 
> Possible disadvantages/challenges:  You'll either need (A) a processor
> burly enough to interpolate a curve between your sampled note values +
> stored offsets, or (B) a LUT containing offset values for every note
> at every octave setting of each oscillator in your system.  The former
> demands more CPU horsepower than you might otherwise need, and the
> latter means a heinously-long calibration routine.

A small AVR or PIC is able to do this. They will be twiddeling their little
thumbs while doing it. They are cheap too.

> Also, you may need to experiment to find a waveform that is "easy to
> count" from the processor's POV.  Not doing this may cause your
> routine to time out or hang.

Saw or Squarewave is what you want, toss in a gain-stage (say x100 or so) to
gain the through zero and then a series of CMOS not-gates for final gain
prior to hitting the counter input.

Cheers,
Magnus