Hello All - Thanks for the replies. Using the RMS to DC converter chip as suggested by bbarney seems like the easiest way to go, but the chip costs $15 US which significantly inpacts the overall cost of my project. SO, at least for now, I am going to investigate some other options. I may come back to this if nothing else works.

I am considering Mister_e's suggestions - the most interesting of which is the modification of the transformerless power supply (Melanie's design):
(http://www.picbasic.co.uk/forum/atta...1&d=1139474240)

Steve: would you care to further elaborate on that approach? Is it possible to get the 120 AC voltage down to the 5V DC range and be able to detect 1V changes in the incoming AC? The transformerless power supply has a Zener in it - if I am not mistaken, that essentially chops off voltages above it's rating (in this case, 12V).

Acetronics: If I gather your response correctly, it sounds like you are addressing frequency measurement. At this time, I am interested in voltage measurement. Please let me know if I misunderstood...

Again, Thanks!