>>> Trying to detect the peak value and scale that is IMO a
>>> bad idea because a single brief spike could throw the
>>> reading way off.
>
> True, but you can filter first and then detect the peaks.
> Each peak is then the result of a bunch of input samples,
> and therefore random noise is attenuated.

Random noise probably would be attenuated indeed, but what if, for
instance, some power SCR/TRIAC-regulated load were present on the
line? Tops of the sine would be heavily suppressed, the filter won't
restore the shape.


> True RMS requires much more computation.

Looks like the statement is not true. RMS approach being a "statistic"
approach does not require that many measurements per sine period as
the peak-detect polling does to achieve the same precision.
Considering the fact that PIC24FJxxx got high-speed 17-bit x 17-bit
hardware multiplier, we may conclude that the total of required
operations per second would be much less.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist