On 24/02/2011 5:32 AM, Bo Berglund wrote:
On Wed, 23 Feb 2011 10:20:19 +0100, Sven Barth
<[email protected]> wrote:
<snip>
Yeah, but my efforts are not successful in using a USB connected GPS
sensor and trying to get accuracy from the telegrams sent by it. I
think much of the time wobble I see is caused by USB latency in the
track from the GPS sensor to the USB hub to the next USB hub and then
into the laptop.
Add to this the way the device driover (Prolific USB2Serial) might
buffer up the data before it reaches the Windows serial system and
there are lots of places time can be lost.
As I posted just a minute ago I found the perfect solution in a Garmin
device with microsecond accurate pulse output.
Have just ordered one for testing.
In any case, most GPS engines have a certain latency in even sending out
the serial time signals, and, as I understand it, don't consider the
time as important as the position in the internal program, in terms of
what they output. The internal time, is of course, critical. So if you
are interested in anything like millisecond timing, the 1 PPS signal
(as in other post) is definitely the way to go. This is used regularly
by amateur (and quite possibly professional) astronomers for timing
stuff, eg to get exact times of a video stream on a frame by frame
basis. If you can't find enough information from your existing
sources, try a search on "occultation timing".
cheers,
John Sunderland
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