Um, since we're all talking about the same uP's here (PIC's), and PICS can only see a POSITIVE signals on their ADC's (from what I understood from the datasheets), I assumed that everyone understood that the signal would already be "rectified" prior to even dropping the voltage to usable ADC levels (although I think I did mention that it was on my 2nd post). Looking at a non-rectified signal doesn't make sense to me, as you'd go from using 1024 steps on a 10 bit converter, to using only 512 steps (9 bits). Since a PIC's ADC can only really see positive values, you'd have to first subtract 512 from each sample to get those "negative values" in the first place (yet more processing time). Am I missing something here?!? Yes the signal can be symmetrical (nominally it will be), but it may not be if the line voltage fluctuates and/or I'm adjusting the triac turn on time to match user settings. I'm basing calculations on 1/2 of each line cycle, as the incoming AC voltage is assumed to be symmetrical to begin with (so the next one "should" be the same any ways), and it cuts the amount of response lag in half. >The average of a symetrical AC waveform is zero! The squaring in an RMS >measurement effectively transforms all the negative cycles to positive >cycles, so you get a non zero result. > >Mike <> -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body