Olin,

> I think we agree anyway.  By "near where humans can touch" I meant
> things
> like user buttons, etc.  These things should be isolated from mains by
> some sort of dialectric to several thousand volts as required by
> various
> regulations.  If your PIC is part of the circuit on the "hot" side,
> then
> there is no problem as long as it is isolated from where a human could
> touch.

OK. Thanks for clarifying. I took it as it would never get regulatory
approval simply because the high voltage was on the PIC and/or the
resistor. Yes, we most certainly agree. I have had a lot of experience
with UL and other approvals, and we always design to the most stringent
rule - whether we need to get approval or not.

One interesting point in all these circuits (that I have seen) is that
they always seem to drive from the neutral. In Australia, we use a MENS
system - where the neutral or "cold" of the AC line is actually tied to
Ground at the point of supply entry into a building.

Theoretically, the neutral is as good as ground and you can grab onto
it - although have sufficient lack of faith in Australian electricians
that I do not make a habit of this without testing first! :-) However,
my point being that since these circuits have there power supplies
configured to provide 5 volts above neutral - then there is no way we
are ever going to see the 339.5 volts on this line.

I know in "my world" - the circuit contained inside the confines of my
little plastic box - I can not assume that we are on an equivalent of
an MENS system and also can not assume that it will be wired correctly
(see previous note), but assuming that it is correctly connected to the
neutral, would this not rule out any transients etc. raised by Roman
and others? And is this perhaps the reason they have chosen the
neutral? The books are published in the UK, and I am not sure if the
neutral is tied to ground, but I assume that it is.

Cheers,

Sean

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