[time-nuts] Re: PRS-10 sawtooth correction with microcontroller

[Greg Maxwell]

Has anyone tried talking to SRS?  If TO doesn't do the right thing
already then it should only require a modest bit of firmware to do so,
and then a $1 microcontroller and gps unit (perhaps a nice new dual
frequency one) would turn the FS725 into a great GPSDO.

Anyone know if the FS740 rubidium version contains a PRS10? I would
assume-- might be interesting to spy on its serial communication.

On Sun, Dec 25, 2022 at 1:16 PM Matthias Welwarsky via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> On Donnerstag, 22. Dezember 2022 00:22:37 CET James Wilson via time-nuts
> wrote:
> > After running in many of the familiar problems of connecting a GPS timing
> > module 1PPS signal to a PRS-10, I want try building a software sawtooth
> > correction board. I’ve seen previous discussion of some of the commands to
> > use for adjusting the PLL and PPS control on the PRS-10 and getting the
> > sawtooth error from ublox GNSS modules, but not a start-to-finish
> > description of how to put everything together.
>
> > My idea to use a microcontroller with multiple UART ports; one connected to
> > the ublox module and the other connected to the PRS-10, with level shifters
> > as needed. The microcontroller sits between the two devices, and gets the
> > PPS sawtooth correction info from the ublox (specifically via the
> > UBX-TIM-TP message and its qErr field), and then adjusts the PRS-10’s PPS
> > time offset by this value to null out the sawtooth for the next pulse.
>
> I suggest you try correcting the 1PPS pulse of the timing module itself, using
> a variable delay line. I don't have a particular part in mind, Maxim might
> have something.
>
> There was a very elaborate GPSDO project discussed last year on this list that
> used this technique.
>
> BR,
> Matthias
>
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