Re: SBC hardware for stratum 0

[David Taylor]

On 22/03/2024 11:33, Jaap Winius via wrote:
> Hi folks,
>
> Years ago I wrote a page that describes how to use ntp together with
> gpsd and a Garmin GPS 18 LVC to create a statum 0 NTP server. I always
> had it attached directly to the serial port on my server machine, but
> hardware specs change and my new AMD motherboard no longer has one.
> Now my only choice is to use an RS-232 PCIe card instead, but sadly
> that's not possible as my design maxed out all of the available PCIe
> lanes.
>
> To continue using my old Garmin, an ideal solution would be to find a
> low-power, single-board computer that also has a UART 16550A (or
> better), an RS-232 interface and a male DE-09 serial port connector.
>
> Does anyone here know if anything like this actually exists and works
> reasonably well? Perhaps as a hat for a Raspberry Pi? Or, maybe if
> there's a better place to ask this question.
>
> Thanks,
>
> Jaap Winius

Jaap,

You may be able to use your new PC.  Look carefully at the board and its
documentation and you may find there's a 10-pin header ready for a COM port.

If not, the Raspberry Pi is an excellent low-cost solution.  NTP supports the
two RX/TX pins on the 40-pin header for the serial data, and the GPIO-18 pin
for the PPS signal.  These are all at 3.3V level, not 5V and certainly not +/-
12V!  Even the old Raspberry Pi 1B has enough power to service many NTP
clients, so I'd go for the lowest cost you can find (e.g. Raspberry Pi 3B+).

If you take that approach, may I suggest using a more modern GPS which includes
support for more satellites such as Galileo and the Russian and Chinese
constellations?  There's a Raspberry Pi HAT with a u-blox module just requiring
an SMA antenna feed:

  https://store.uputronics.com/index.php?route=product/category&path=60_64

in particular:


https://store.uputronics.com/index.php?route=product/product&path=60_64&product_id=81

I have used these units on many Raspberry Pi cards and they've been 100% 
reliable.

Cheers,
David
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