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

Hal Murray hmurray at megapathdsl.net
Thu Dec 18 18:15:13 EST 2014

csteinmetz at yandex.com said:
> The circuit presented allows one data collection to do both functions  well.
>  It has enough filtering to prevent local interference from  corrupting the
> data, it can locate 60Hz zero crossings to within 1uS  (i.e., frequency
> resolution significantly better than 0.01 Hz,  single-shot, which can be
> filtered/averaged to get whatever  resolution you want in post-processing),
> and it can locate transient  events to within 1uS.  Win-win. 

What sort of interference do you see?  What does an interesting transient 
event look like?

If you are going to post-process the data anyway, why not collect raw data 
and let the post-processing take care of the local interference?  That lets 
you defer decisions about the appropriate filtering.

Is there any database of events that I can check when I see something 
interesting?  Or turn things around and pick an event and see what it looks 
like when it gets here?

I've been collecting frequency data for my local power line.  I grab the PPS 
style time stamps and counts from a modem control pin every 10 seconds.  No 
filtering, just a transformer.  I occasionally get an extra count.  It's 
pretty obvious when you look at the graphs.  They happen ballpark of once a 

A while ago, I was trying to capture the audio too, so I could look at the 
area around the extra counts.  I never got anything clean.  I think that 
setup had grounding problems.  Maybe it's time to try again.

These are my opinions.  I hate spam.

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