Dario Greggio wrote:
> Take 20 samples/sine
> for each sample
> take previous sum
> divide by 20
> subtract this (sum/20) from previous sum
> add new sample to sum

That makes no sense for any reasonable interpretation of "measure mains
voltage".  Remember this is a AC signal.  This description above is not
totally clear, but it looks like you're box filtering the signal, sortof, I
guess.  Box filtering a AC signal with a aperture width a multiple of the
period will always yield 0.  In other words, the sum of any consecutive 20
samples (one whole period) will be 0.

Again, it's too early to jump into the implementation since there isn't yet
a clear definition of what exactly you want.  On top of that this
implementation appears broken, at first glance at the level of detail of
what I think the above description is saying anyway.


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