Hi Dale, maybe a variation on the TV sync-separator
circuit, using one transistor? This will detect only
the very peak of each wave, and is self adjusting.
With the simple low pass RC filter this should give
good triggering on your wave as the harmonics are
much lower in amplitude. I don't think that zero-cross
or any half voltage conversion to digital will work
as well. :o)
-Roman


Dale Botkin wrote:

> I am interested.  I did some searching & reading and came up with this:
>
> ----/\/\/\/\------|-----
>      3.3K         |
>                   = .47uF
>                   |
>                  GND
>
> If I read the stuff I found on passive LPF design right, that should give
> me a 102Hz cutoff, correct?  But I'm not sure what effect the bias
> resistor(s) for the transistor will have.  I will gladly take advice and
> suggestions on this matter.

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