[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?)





More information about the time-nuts mailing list