[sdiy] TZ triangle core

[David G. Dixon]

> Turns out it doesn't. The reason is that it only will work with one input
> polarity.  The opposite polarity puts the integrator/ST out of phase, so
> the system runs immediately to the rail.  <headslap>

I haven't wrapped my head completely around what you're trying to do, but
I'll tell you how I solved the problem with my own TZFM.  I simply fed the
triangle through an optional inverter (an opamp with either +1 or -1 gain
depending on the status of a n-channel JFET which shorts the + input when
turned on) and drive the comparator/schmitt trigger with the output.  The
polarity of the FM signal drives a comparator which determines the state of
the JFET.  The nice thing about this circuit is that it doesn't require edge
detection or anything like that, so it's actually failsafe (i.e., it will
always go in the right direction).

I don't know if you'd be able to use this technique or not.  I'm using 2164
as the current source of the tricore, so my currents go around in a loop
(which I think you said yours does as well).