[time-nuts] Line Frequency

nuts nuts at lazygranch.com
Mon Feb 10 03:36:41 EST 2014

On Sun, 09 Feb 2014 17:46:10 -0800
Hal Murray <hmurray at megapathdsl.net> wrote:

> > Maybe a couple of back to back diodes (zeners?) across the
> > capacitor to make sure the voltage stays in the input range of the
> > op amp/comparator. 
> The standard approach in the digital world is Schottky diodes.  They
> come with a pair in a tiny 3 pin package.
> Most digital logic has built-in protection diodes.  Look at the fine
> print in the data sheets.  There is usually a max current and/or max
> voltage/time/area spec.  It may be off in the general info sheet for
> the logic family.  It's common to take advantage of those diodes by
> using a current limiting resistor.
> > I like the LT1122 for speed. It is not too pricey. But there is
> > always the ubiquitous LM111 family. 
> I'm missing the big picture.  Why are you adding another chip?  What
> are you going to connect this signal to?
> As tvb has shown, you can connect the AC line directly to a PIC input
> pin with a big enough current limiting resistor.  I'm using an AC
> wall wart and a pair of resistors to get within range of the modem
> control signals.  I've had no noise events in the past 50 days.
> I did have noise problems with boxes running off an isolated power
> brick.  I never tracked it down.  I assume it was a missing green
> wire ground so the chassis ground jumped around when interesting
> stuff came in over the power line.
> ----------
> You can feed the signal into the audio input and capture the raw data
> and look for glitches.

You should really have isolation from the mains. The transformer scheme
is fine. I don't like the high value resistor approach.  

Any chance you had your measurement scheme running when they blew up
that Metcalf PGE yard last (April 16 at 1AM?)

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