Byron A. Jeff wrote:

> Another thing is that the same issue I raised is still present. Presuming
> I use a transformer and I tie one leg of the secondary to the PIC input pin,
> where does the other leg go? GND? All the transformer does is change the
> voltage, it does not address the issue of how to integrate the return...

Well, it does. With a transformer you can safely tie one side of the
secondary to ground. With mains input directly, you need to tie
the neutral to the PIC "ground", but you must not connect this to a real
ground, since not only can't you be sure the active and neutral are not
reversed, even if the neutral really is neutral, connecting it to
ground will trip earth-leakage detectors due to ground-loop currents.

The transformer primary is easily protected from fingers; the entire
PIC circuit is not. If you do want to float the PIC at mains potential,
then use an isolation transformer during testing, and even then
you still have to be careful of the transformer secondary, since it
can kill you too. A low-voltage transformer is much safer.

Mind you, you Yanks only have to be careful of 115V - 240V will
kill you twice as fast!

--
Clyde Smith-Stubbs       | HI-TECH Software,       | Voice: +61 7 3354 2411
clyde@hitech.com.au      | P.O. Box 103, Alderley, | Fax:   +61 7 3354 2422
http://www.hitech.com.au | QLD, 4051, AUSTRALIA.   |
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