Hi all,

Could someone point me somewhere or give some advice on monitoring 240VAC
50Hz mains voltage using PIC A/D.

The reason I wish to do this is to display the output of a variac on an LCD
panel.

Immediate methods that come to mind are:
a) Step down the mains with a step down transformer, rectify the output,
filter, and resistive voltage divider.
b) Leave the step down transformer out of the equation, and use higher
voltage rated filter caps, and a bigger resistor divider.

Both the above methods could empoy a level of PIC protection by using an
op-amp configured as a voltage follower with no gain to clip the output to
the AD 5V rail limit.  I figure both methods should give a reasonably enough
linear output.

I can see problems with both of these methods however, particularly in
regards to ground rail impedance caused by the high voltage divider, esp. in
option(b), and causing major headaches for the low voltage ground reference
side for the digital electronics.  Can anyone suggest a better way ?

Hmmm.  Maybe I should have just stuck with the simple moving iron meters ;)

Regards,
Ian

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