[time-nuts] GPS for ntp

Joseph Gray jgray at zianet.com
Fri Oct 24 16:33:50 EDT 2014


Tom,

Thanks for the information and your comments as to the suitability of these
units. First hand knowledge is always appreciated. I had already figured
out that there were four models :-)

I was reading the documentation from ublox and the time stamping interrupt
caught my eye. However, it is listed as only being available on the R
model. I can't find anyone selling that model.

Timestamping a message to the nearest 100 ns is what I am after. If I can't
do it directly with the ublox, I'll have to look at the PRU on the
Beaglebone. It has a 200 Mhz clock and single cycle instructions.

Joe Gray
W5JG
 On Oct 24, 2014 1:39 PM, "Tom Van Baak" <tvb at leapsecond.com> wrote:

> Joe, et al.
>
> I put some info at: http://leapsecond.com/pages/reyax/
>
> Here's what you need to know about those Reyax GPS boards:
>
> 1) These are simple, well-made, low-cost, tiny GPS boards. Four models are
> available, based on three u-blox chips. The prices are $14 $16 $20 $27.
>
> 2) The 3 chips are u-blox MAX-7C, NEO-7N, NEO-M8N. See
> http://www.u-blox.com for chip info. Board documentation:
> http://www.reyax.com/Module/GPS/RYN25AI/RYN25AI.pdf
> http://www.reyax.com/Module/GPS/RY725AI/RY725AI.pdf
> http://www.reyax.com/Module/GPS/RY825AI/RY825AI.pdf
>
> 3) The 4 boards available:
> http://www.ebay.com/itm/171493874434
> http://www.ebay.com/itm/181553452840
> http://www.ebay.com/itm/181562403752
> http://www.ebay.com/itm/181566850426
>
> 4) The only difference between the $14 RYN25AI and $16 RYN25DI is that
> RYN25DI adds a ±10 V RS232 transceiver. The other 3 boards have a typical
> "inverted" logic-level (3.3V) serial interface, suitable for uP or SBC or
> UART/USB interface chip.
>
> I have no affiliation with seller "reyax" but their boards seem a step
> above some of the other GPS stuff on eBay. In general I gravitate to
> low-cost GPS receiver breakout boards with serial I/O and clean 1PPS
> output. It's amazing how well these integrated antenna boards work: a truly
> "3-pin" timing solution: power, ground, 1PPS.
>
> Note these are not "timing receivers" in the sense of RINEX output or
> external clock input or position-hold with sawtooth correction. But for
> less demanding work, the ±20 ns level that many of these receivers offer
> more than enough.
>
> 5) You can also find similar boards from US sellers such as
> http://parallax.com/ , http://adafruit.com/ , http://sparkfun.com/
>
> 6) All of this is grossly overkill for NTP (at the 1 ms or even 1 us
> level). But if some of you are pushing NTP to sub-microsecond limits, cheap
> GPS/1PPS receivers like this are of interest.
>
> For more details, including almost medical-grade photos of a GPS patch
> antenna, see:
> http://leapsecond.com/pages/reyax/
>
> /tvb
>
> ----- Original Message -----
> From: "Joseph Gray" <jgray at zianet.com>
> To: <Brian.Inglis at systematicsw.ab.ca>; "Discussion of precise time and
> frequency measurement" <time-nuts at febo.com>
> Sent: Thursday, October 23, 2014 9:18 PM
> Subject: Re: [time-nuts] GPS for ntp
>
>
> > OK, I see source of the confusion. There is a difference of "one"
> character
> > in the two part numbers. The RYN25 has the older Ublox chipset. The RY725
> > has the Neo-7N chipset. There is only a $6 difference in price. I think
> > I'll get a few to play with.
> >
> > Joe Gray
> > W5JG
>
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