>
> PMFJI, I have not seen Appl. Note 521, but a transformer is considered to be a
> separately derived voltage source by the National Electrical Code(N.E.C.)
> and the voltage
> across the secondary windings is of course ungrounded unless you connect one
 of
> the windings to ground.

App Note 521 specifically talks about wiring the 115V directly to the PIC
without the use of an isolation transformer. After reading here I've decided
that it's a bad idea and I plan to use a transformer.

> I hope this helps.

It really does. I'll go ahead and step the voltage down to 9VAC and detect the
zero crossings from there.

BAJ