[time-nuts] Serial or other simple protocols for exchanging time

[Ralph Aichinger]

Am Do., 8. Aug. 2019 um 05:09 Uhr schrieb Gary Chatters <
gcarlistaa at garychatters.com>:

> I would expect that making your Arduino device look like a GPS receiver
> outputting NMEA messages and a PPS signal would be about the simplest
> approach you could take.  It has the advantage that there is existing
> software to deal with the messages, including NTP drivers.
>

Yes, this is exactly my thinking. I am looking for a simple way to monitor
this
rubidium device (and the Arduino clock linked to it), and having an NTP
server
tracking its performance is probably the easiest way to do this (graphing
drift,
catching systematic errors in the Arduino programming etc.).

- How is your Arduino going to get time?
>

>From a GPS receiver with PPS output, via serial NMEA.

I plan to do three things when the Arduino based clock is set (by plugging
in a cable and pressing a button or something, so not continuously):

1. the GPS signal will be sanity checked (enough sats, is there a fix)
2. the PPS divider (either on the Arduino itself or one of  Tom's PicDivs)
    of the rubidium will be reset to zero when the next PPS from the GPS
    arrives.
3. The NMEA time from the GPS is parsed and used to set time and date
    above seconds level on the Arduino based clock.


> - What is the computer going to do with it?
>

For now mainly monitor it: Is the rubidium off from GPS time, did the
dividers/counters count right, etc., both to check hardware and my
poor attempts at programming ;)

/ralph -- thanks!



>
>
>
> Gary
> WA9ZZZ
>
> On 8/7/19 8:13 AM, Ralph Aichinger wrote:
> > Hi everybody!
> >
> >
> > I am a newbie and am wondering what options there are for exchanging time
> >
> > on a more basic level than NTP or PTP (that is for situations when a
> >
> > full network stack is too complex).
> >
> >
> > For now I have found:
> >
> >
> > NMEA (probably ZDA only)
> >
> > IRIG timecode (this is rather complex, I would rather have a
> >
> >                full network stack than IRIG?)
> >
> > SMPTE timecode (this too?)
> >
> >
> > Are there any other obvious candidates I missed? How did e.g.
> >
> > HP atomic clocks tell their time to connected devices before
> >
> > there was the NTP protocol? Did they output NMEA or something
> >
> > else? Did they emit IRIG directly?
> >
> >
> > I want to create an Arduino based clock that tells time to a computer
> >
> > it is linked too. For exact seconds alignment I want to use a PPS signal,
> >
> > but I need a means to tell the computer about second numbers, hours etc.
> >
> > too.
> >
> >
> > Of course I could invent a serial protocol, but I suppose if I invented a
> >
> > text based serial protocol, it would probably end up looking very
> >
> > similar in structure to NMEA ZDA sentences.
> >
> >
> > *Is* NMEA the most practical time protocol at the 1 second level
> >
> > (that is when a PPS pulse takes care of second alignment?) or should
> >
> > I use something else if I am free to design stuff clean slate?
> >
> >
> > TIA
> >
> > /ralph
> >
>
>
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