Olin Lathrop ha scritto:
> But how do you want to handle harmonics and spikes?  Are you trying to
> detect the spikes or want to filter them out?  If you want more of a
> smoothed RMS, what kind of response time?  You can't start thinking about
> the right filter until you know what you want it to accomplish.

No, I need the Basic 220V, indeed filtered "somehow" - but my response 
time is in the range of 1-5 seconds i.e. less than an average multimeter.
Basically, let's avoid spikes such as pumps starting etc.


> If that's all you want, a simple peak detector followed by two low pass
> filter will work nicely.  You don't need to store 20 recent samples, only 1
> and a flag.  As the samples come in, look for local minima and maxima.  Each
> go into separate low pass filters.  You adjust the time constant and number
> of poles of these filters to get the random noise reduction and reponse time
> you want.  Keep in mind that each filter will only be fed at the line
> frequency of 50Hz.  Every time you update the filters, the final filtered
> maxima minus the final filtered minima times a fixed constant is the line
> voltage.

ok... I guess I get this too.
Something like the "simple" (you showed it many times)

new_value = (ADC_value+(old_value) ) / 2

done for both max and min.



>> I also have to say that, after the IIR, overall sum of 20 samples does
>> no longer yeld 0... !
> 
> Actually it should yield 20x whatever the representation of 0 line voltage
> is in your system.  If your input signal is offset by half Vdd and that is
> not subtracted out then you will get 20x that offset.  However, the AC
> information you are looking for will be gone and only this "effective zero"
> will be left.


makes sense, and this is indeed a different application. Useful to know 
for the future :)
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