[time-nuts] NMEA time off

Pete Lancashire pete at petelancashire.com
Thu Mar 3 18:20:44 UTC 2011


I've got three of them one was $1 at a g'sale.

-pete "got to stop buying this crap" .. never

On Thu, Mar 3, 2011 at 1:06 AM, Joseph Gray <jgray at zianet.com> wrote:
> Months ago a bought an old Delorme Tripmate for $5 (for that price,
> why not?). Tonight I finally got around to fooling with it. After
> finding out that it was designed to talk only to Delorme software
> without some finagling, I got it to spit out NMEA data to Teraterm and
> other programs.
>
> I discovered two things about the Tripmate. First, the sensitivity
> sucks indoors. It is currently showing 13 satellites visible, but only
> tracking three. Second, the time data from the GPRMC sentence is about
> two seconds behind UTC (using my calibrated eyeball for measuring).
>
> Is the time delay simply due to a firmware error, a low priority
> processing and outputting the NMEA data, or something else?
>
> I was going to attach the Tripmate to a modified Linksys WRT54G WiFi
> router and make it an el-cheapo NTP server. No reason, other than just
> for fun. Even without the two second delay, I know that the WRT54G
> will not be a very accurate NTP server. I was assuming that I'd be
> able to at least get better than one second accuracy, though. I guess
> I can just put in a large fudge factor for ntpd to compensate.
>
> Unrelated to the above, I also have a Timex Ironman runner's watch
> with mating GPS unit (another $5 purchase). The GPS is worn on the arm
> and transmits data to the watch for displaying distance, speed, etc. I
> need to get a battery for the watch, but I believe everything works.
> Taking the GPS unit apart, I find that it is a Garmin. I see some
> interesting test points on the circuit board, so I'm going to see if I
> can get some serial data directly from the GPS, without using the
> watch.
>
> Joe Gray
> W5JG
>
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