[time-nuts] Simple AC mains zero-cross detector

[nuts]

On Sat, 20 Dec 2014 18:31:29 -0500
"Mike Garvey" <r3m1g4 at verizon.net> wrote:

> From a Time-Nut perspective, isn't phase/frequency of the (nominal)
> 60 Hz all we'd be interested in?  Phase is best measured at a zero
> crossing as this is the (only) phase measurement point which is
> independent of amplitude.
> Mike

One overkill AFSK demod is to sample the signal and compute the arcsin,
essentially producing a straight line of phase versus time. We had made
a AFSK demod using linear regression on this line to determine
frequency. This isn't overkill when you have a DSP chip there anyway. 

Now I don't see a reason why similar analysis couldn't be done with
power line monitoring. Over some moving window of time, you could even
produce the difference signal between the sine wave due to the
regression fitting from the raw signal and thus display the noise on
the line.