Cool set-up :) Where are all of these clocks in the ntpq picture though? I'm surprised that stratum 1 devices have such large offsets from each other... A solid PPS set-up should easily give sub 1ms accuracy, but it looks like these all disagree by a few, if not dozens of, ms. I assume this is due to asymmetric network paths in NTP? Even so, I would've expected the offsets to be lower. And what's up with the 80ms offset from time-c-wwv?
On Tue, Dec 7, 2021 at 8:59 AM John Sloan <[email protected]> wrote: > I have four home-built clocks, each using a Raspberry Pi, all with > slightly different designs, all running gpsd and ntpd (so all are NTP > servers on my home network). Three are GPS disciplined; one is WWVB > disciplined. Two of the GPS clocks use the modem-control lines on a serial > port for the 1PPS signal, one uses the simulated modem-control signals on a > USB-connected GPS dongle. One of the GPS clocks has a cesium chip-scale > atomic clock - specifically, a Jackson Labs Technologies dev board with a > Microsemi CSAC - for holdover (there’s no kill like overkill). > > All four clocks use an Adafruit “Pi Plate” LCD board with a two-line > display to display the date and time. > > https://www.adafruit.com/product/1115 > > The display format could have been anything I chose, but I implemented one > that looks like this (using a 24-hour time so no AM/PM). > > Tue 2021-Dec-07 > 06:33:49 MST > > They all run the same trivial Python script that I wrote to read the > system clock (which is disciplined to NTP, and hence to GPS or WWVB time) > and drive the display. The script runs five times a second. Efficiency is > not really an issue since this is running on a quad-core processor. An > entire core could be dedicated to just updating the display. I leave that > to the Linux scheduler. This approach combines the accuracy of > GPS-disciplined time with support for time zones and Daylight Saving Time > adjustments in the system clock. > > The time on the LCD is as accurate as I need it to be, since it’s just a > human-read display. The NTP time provided by each clock is at least > competitive with getting the time from NTP servers across the internet. I > have another Raspberry Pi that uses ntpq to query all of my clocks, along > with two commercial NTP servers on my network, plus two external servers, > and compares them. Based on its own measurements, it typically chooses the > atomic clock as the best reference. > > There is undoubtedly a lot of room for improvement in all of this, > especially in my WWVB clock. > > Here is a link of all of my blog articles on clock- and time-related stuff. > > https://coverclock.blogspot.com/search/label/Horology > > Some of those articles will include links to my GitHub repositories for > those projects. > > Here is an album of photographs of all of my NTP servers, both home-brew > and commercial. > > https://flic.kr/s/aHsmgrizkL > > :John > > -- > J. L. Sloan Digital Aggregates Corporation > +1.303.489.5178 3440 Youngfield Street > mailto:[email protected] #209 > http://www.diag.com Wheat Ridge CO 80033 USA > > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
