[sdiy] TZ triangle core

[Ian Fritz]

Hi --

I got this working today.  All that was necessary was to add a second 
polarity switcher and to flip its polarity based on the sign of the Lin CV.

So the circuit is now :

Lin CV --> polarity switch 1 --> polarity switch 2 --> integrator --> 
Schmidt triggger
Lin CV --> comparator --> polarity switch 2 control
Schmidt trigger  --> polarity switch 1 control

It adds up to 6 op amps and an OTA. Really, a simple circuit for what it 
does. For the old Electronotes unit, I'm counting 9 op amps an OTA and a 
couple of logic chips.

I built this as a simple ancillary VCO to work with my new Traveling-Wave 
Chaos circuit, so I'm not looking for high performance at this point.  But 
it might be worth setting it up with good parts (like real comparators) to 
see what it is capable of.

Ian