[time-nuts] GPS for Nixie Clock

[Chris Albertson]

What kind of micro processor are you using to run the Nixie tube clock?  If
that processor could run NTP you would not need GPS.   But of course you
could always do both.   GPS requires a view of the sky and maybe that is
not available in a multi story building unless near a window.  NTP would be
available any place there is WiFi.     Even without network connection, NTP
is a good way to interface the GPS as it knows how to talk to most GPSes
made. can handle GPS outages (like when the clock is moved away from a
window)

That said, you are likely not using a uP big enough to run NTP as a setup
like that is about $40 vs. using a bare AVR chip for about $3.  But even
with the smaller uP you might think about having the chip keep it's own
internal time and using GPS to discipline that internal time, much like the
way NTP works.   Basically the uP has a flywheel and GPS regulates it's
speed.  Let's you handle holdover gracefully.

If using NMEA sentences from GPS, remember that the NMEA standard allows
those senates to come out at any time during the second to which they
apply.  In other words the sentence itself can be up to almost a second
"off".

If you are looking for a GPS for use indoors I think you don't care about
anything other then receiver sensitivity.  Without that you have nothing,
no signal.  It is more important than a few less nanoseconds of uncertainty
in the time solution.   So those ublox receivers look good.   I'm looking
to buy some for another application, mobile robots, I'll use GPS for gross
level navigation and it would be nice if it still worked indoors

On Sun, Jul 10, 2016 at 10:24 PM, Mark Sims <holrum at hotmail.com> wrote:

> The Jupiter receiver defaults to Motorola output, but can be switched to
> Zodiac.  It talks at 9600:8:N:1
> Frankly, it is the wrong receiver to use, particularly with an indoor
> antenna.  I would go with a modern GPS receiver with standard NMEA output
> and a 1PPS signal.   They are MUCH more sensitive and usually work indoors
> and can be had for dirt cheap.   Most have an on-board ceramic patch
> antenna.  Ublox receivers seem to work well indoors.
>
> NAVSPARK makes a tiny little GPS board with 1PPS output.  6 for $36 or one
> free for $10 shipping (no antenna supplied, has a U.FL connector).  It
> speaks NMEA at 115,200:8:N:1  or can be setup for 9600 baud.
>
> The delay between message and 1PPS is receiver dependent.  Usually it is
> small enough to not be noticeable.  Some receivers send the message before
> the 1PPS, others after it.   You can compensate for the differences/delays
> in software.
>
>
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-- 

Chris Albertson
Redondo Beach, California