Olin,

> 1  -  This does not apply to analog inputs.  I have noticed small Vdd
> protection diode current cause significant errors on the remaining
> analog
> channels.  I'm guessing this is because the internal reference voltage
> gets messed up.

No. Only digital I/O necessary to detect zero cross.
>
> 2  -  I would keep the protection diode current well under the
> specified
> maximum.

Yes. As the writer says - 50uA - just 10% of the MAX.
>
> 3  -  This topology should never be used if any part of the PIC circuit
> goes anywhere near where humans can touch.  It would never get
> regulatory
> approval,

I do not agree. What's the difference if 240VAC is on the resistor when
the triac on the same board is at the same potential? Provided the
circuit is enclosed, what is the difference?

> and is safety hazard in any case (imagine a little dirt or
> moisture on the resistor).

You fry the PIC?

> It is fine if this circuits in encapsulated
> inside a grounded metal box

A lot of our stuff is encapsulated, but this project will probably not
be. But we never encapsulate in grounded metal boxes - always in
plastic.

> 4  -  Unless this is a very high volume product where every cent
> matters,
> I would spend a few extra resistors and diodes to make it just a little
> more failsafe.

Well yes, it is high volume, and every cent does matter, but what would
you suggest? An opto is over-kill and is not necessary when the entire
circuit can be assumed to be at mains potential, and is therefore
always out of human contact - either double insulated or encapsulated.

Regards,

Sean

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