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Re: [gpsd-dev] PPS over USB

From: Ed W
Subject: Re: [gpsd-dev] PPS over USB
Date: Fri, 04 May 2012 20:39:20 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:12.0) Gecko/20120428 Thunderbird/12.0.1

On 01/05/2012 23:14, Gary E. Miller wrote:
Yo All!

As some of you may know, esr has been helping the bufferbloat project
with some gpsd issues.  Their goal is to get good time from a USB
connected GPS.

Esr negotiated with Navisys to special build three units of a ublox 6
and a pl2303 with PPS conencted to USB.  They call them a GR-601 and I
just received the samples.  The preliminary results are pretty good if a
clock stable to about 1 milliSec is your goal.

Just curious but is the goal: accuracy, cheapness, off-the-shelf or something else?

I admit I haven't tried it, but I sell loads of PL2303 adaptors that just happen to dismantle very easily. I don't see any theoretical reason why you couldn't easily modify one to either put 5V power on a serial pin, or just drill a hole in the case and poke wires directly inside. This would allow you to grab say an old Garmin 18 off ebay and use that?

I got part way through the implementation of using the GPIO inputs as PPS on the PC Engines Alix boards. The goal was to enable a fairly cheap machine that could connect pretty much directly to something like a Garmin 18 (or the rather nice looking Skytraq modules, some of which seem to offer seriously accurate PPS options) and give you an inexpensive Stratum 1 box. (PC Engines boards are circa $110 for basically an entire 500Mhz i586 including ram, processor, USB, mini-PCI and up to 3 network ports)

So, just trying to understand if the goal is to be more off the shelf than a DIY prolific bodge? Or if you want an entire Stratum 1 box with microsecond accuracy, then perhaps the Alix route gets you the finished product with 2W consumption for decently low money?


Ed W

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