On Sun, 09 Feb 2014 17:46:10 -0800 Hal Murray <[email protected]> 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?) _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
