[time-nuts] Small time server for mobile use.

[Pete Stephenson]

On Tue, May 12, 2015 at 7:11 PM, Mark Spencer <mark at alignedsolutions.com> wrote:
> Hi sorry for a possibly OT post.
> Has anyone had practical experience with small commercially available time servers / ntp servers suitable for mobile  use in a vehicle.

I don't know about any commercially-available products, but it sounds
like it'd be pretty straightforward to do with a Raspberry Pi or
something similar if you don't mind a little bit of DIY.

What constraints do you have on budget, size, power requirements, and cooling?

>  The use case is I am in need of an accurate (ie.  within 100 ms) time source for several pc's in moving vehicle.    Being able to run directly off a 13.8 or 28 VDC  source would be a major plus but AC power is also available.

The Pi runs on 5V DC. DC-DC buck converters that can convert 7-35V to
5V DC are cheap, efficient, and widely available. Shouldn't be a
problem.

> Hold over if there are gaps in GPS coverage is also a major plus.

How long would you need holdover? Seconds or minutes (e.g. driving
through a tunnel)? Hours? Days? Would the computers in the vehicle be
subject to large temperature shifts?

A Pi should be able to handle +/- 100ms of holdover in the
minutes-to-hours range using NTP.

> We already have a GPS with a 1 pps output, but an integrated box with it's own GPS would be best.

A tiny integrated module like the Adafruit Ultimate GPS breakout[1] is
cheap, handy, and emits a 1PPS signal. It's also extremely small and
can be purchased in "hat" form[2] that mounts directly to the Pi.

Cheers!
-Pete

[1] https://www.adafruit.com/products/746
[2] https://www.adafruit.com/products/2324

-- 
Pete Stephenson

On Tue, May 12, 2015 at 7:11 PM, Mark Spencer <mark at alignedsolutions.com> wrote:
> Hi sorry for a possibly OT post.
> Has anyone had practical experience with small commercially available time servers / ntp servers suitable for mobile  use in a vehicle.
>
>  The use case is I am in need of an accurate (ie.  within 100 ms) time source for several pc's in moving vehicle.    Being able to run directly off a 13.8 or 28 VDC  source would be a major plus but AC power is also available.
>
> Hold over if there are gaps in GPS coverage is also a major plus.
>
> We already have a GPS with a 1 pps output, but an integrated box with it's own GPS would be best.
>
> Yes I am aware I could feed a 1 pps signal into a laptop and use that as a time server and I may end up going that route.
>
> There is a small Ethernet LAN in the vehicle.  The pc's currently get their time via a wireless connection to various NTP servers.   I need to be able to ensure accurate time on the PC's if there is no wireless coverage.
>
>
> This is for a one off project so piecing together various parts is an option but a single box COTS solution would be nice.  I've found a few candidates via web searches but would welcome any feed back.
>
> Thanks in advance
>
> Mark Spencer
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-- 
Pete Stephenson