In article ,
Jeff Liebermann wrote:

On Sun, 20 May 2012 00:41:44 -0700, isw wrote:

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.

Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA
"sentences" in ASCII that tell you the precise time. Just use those.

The NEMA sentences are not synchronized to GPS time and add delays in
the decoding process. The time might be off a fraction of a secod.
However, using the NEMA sentence is probably adequate for a consumer
alarm clock.

Much better, in the long run -- the time they report has a bit of
sample-to-sample jitter, true, but the long-term drift is close enough
to zero to not matter.

You don't correct your local oscillator on the basis of its time
difference compared to a particular sample -- you correct it to force
the long-term drift to zero. The longer it runs, the more accurate it
becomes.

The notion of using irregular or not-continuous data samples to create
accurate clocks even over jittery channels has been around for a while.
Both MPEG 2 and Cable Modems use versions of it.

Isaac