From: David VanHorn <microbrix@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 12 Aug 2020 08:50:57 -0700
Subject: Re: [EE] averaging multiple samples to reject AC interference
Thread-Topic: [EE] averaging multiple samples to reject AC interference
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When I implemented the averaging filter it was on a Z8 running at 1 mips.
Didn't notice any performance issues in our application. (MICR reader)

On Tue, Aug 11, 2020 at 7:19 PM Art <ky1k@myfairpoint.net> wrote:

> That's a great idea David, but with averaging, much performance is lost.
> And, even without averaging, there is a finite propagation delay (phase
> error) through the electronics-whether digital or analog.
>
> It occurred to me that I might use a second A/D converter to quantify
> the 60Hz powerline frequency and apply that correction digitally. There
> will still be propagation delay and the amplitude of the 2 data streams
> will never match precisly, but the sampling of the realtime data can be
> delayed and sync'd by some amount by delaying the digital clock time
> sampling of one of the waveforms.
>
> Such a practice probably improves the line frequency interference
> problem, but might require lots of time to figure our whether it is usabl=
e.
>
> I know that a similar technique is used in analog receiver inputs in
> order to reduce line noise arcing, and it does work. MFJ makes the
> hardware, but it takes a very long time to find the correct amount of
> delay/phase/amplitude as the tuned circuit has nearly infinate
> combinations of possible settings. Once the sweet spot is found, it
> works well until the ambient temperature in the shack changes and
> everything needs retweaking::>
>
> The same concept cannot be applied to very low 50 or 60 Hz interference,
> there is no way to make variable inductors and capacitors to make the
> concept work.
> -
> Aloha,
>
> W1ABA
>
>
> On 8/11/20 11:59 AM, David Van Horn wrote:
> > I did a filter some years back where I averaged up enough samples to ge=
t
> a complete cycle of the AC line, inverted it, and added it back to the
> data, which worked pretty well at getting rid of line based interference.
> >
>
>
>
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