Re: [gpsd-dev] PPS over USB

[Ed W]

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?

Cheers

Ed W