[time-nuts] 60Hz zero-crossing
wb6bnq at cox.net
Sun Jul 3 22:12:13 UTC 2011
The part that I am confused on is how the DCD pin is being accessed and time
stamped. Where would I find software for that purpose ?
Perhaps some of the others can straighten me out ? Especially if there is
software that will run on an old Win 98 laptop.
Tom Van Baak wrote:
> > OK, I wasn't paying attention as the info passed by. 'Xactly how is this
> > huge signal introduced to the PC? I remember something about a voltage
> > divider off the hot side of the line, put on an input pin of the PC's
> > com port and then somehow timestamped and put on a data file. Howsat
> > done again? Sorry to be so lame, but I really wasn't paying attention.
> > Don
> Hi Don,
> What I did in the quick PC experiment was feed the output of a
> 5 VAC wall-wart transformer through 1k to DCD (pin1) of the
> PC's serial port. Probably not wise to voltage divide raw mains
> power and send it to a serial port. If using a high-z input of a
> microcontroller, the doc2508.pdf app note that you found shows
> both sides of mains going through 1M resistors.
> There was concern that noise would cause false triggering. There
> are a variety of hardware-only or software-only solutions to this
> concern. Bill found a robust ZCD circuit if you need a hardware
> solution. Time-stamping samples is the basis of software solutions.
> Note looking for a sample 990 to 1010 milliseconds from the last
> sample is a nice way get 1PPS from 60 Hz. This is more immune
> to noise than traditional division-by-60 techniques.
> As it turns out, I've gotten clean 1PPS data with no h/w or s/w
> filtering so maybe this whole noise concern is overblown.
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