[sdiy] PLL module

[David G. Dixon]

> Ah, well, an octave _divider_ is also useful as it drops a VCO output by
> an octave.  I've
> also used the divide by 3 circuit to do - uh, divide by 3 which produces a
> perfect fifth
> below the input frequency (actually I think it's an octave and a fifth
> below).

Yeah, I got that!  That's why it's more useful than a simple octave divider!
Of course, I suppose one could extend this idea to the whole harmonic series
by dividing by every integer up to 12.  Slap on a mixer for all the division
outputs (perhaps suitably lowpass filtered to recover sine waves from the
squares) and you've got a low-budget analog additive synthesis module!  (...
or am I smoking crack (again)?)

> My circuit can work with input signals other than a VCO to some degree or
> other.  It
> prefers a signal like a sawtooth VCO where the signal swing goes rail to
> rail from the
> perspective of the 4046 IC.  It also works best with one zero crossing per
> cycle.

Well, it's dead easy to convert any zero-crossing to a rising edge with a
comparator, so I guess you could fire this thing with any wave.  However, as
you say, it should be a clean wave and not, for instance, a resonant filter
output with all those little siney wiggles -- that would surely confuse the
hell out of it!