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. $GPZDA give the time as:
$--ZDA,hhmmss.ss,xx,xx,xxxx,xx,xx
hhmmss.ss = UTC
xx = Day, 01 to 31
xx = Month, 01 to 12
xxxx = Year
xx = Local zone description, 00 to +/- 13 hours
xx = Local zone minutes description (same sign as hours)

The 1pps output has the advantage of simplicity and easy of
integration with existing digital clock designs.

Say, $15 for the GPS, another $15 for an Arduino, $5 for an LCD, and
whatever crystal you have on hand, stuck in a home-made oven. Maybe
another $20 for all the "glue", and the rest, as they say, is just
software.

The cheapest GPS board or module that I could find is about $40.
http://www.sparkfun.com/categories/4?sort_by=price_asc&per_page=50
Chips seem to run about $8/1000. Using your prices, a commercial
digital alarm clock product would retail about $175-$200. Meanwhile,
WWVB controlled "atomic" alarm clocks are selling for $15.

This one decodes NEMA sentences, and has some compromises due to
running on battery power:
http://www.siliconchip.com.au/cms/A_111192/article.html
To conserve the battery, the GPS module is only used
to synchronise the clock every 44 hours and following
synchronisation, the clock will either skip seconds
or double-step to reach the correct time. After
synchronisation the microcontroller is also able to
calculate the inherent inaccuracy of its crystal oscillator
and will compensate by occasionally skipping or
double-stepping a second. This process can also compensate
for aging of the crystal and will keep the clock accurate
between synchronisations.
http://geoffg.net/GPS_Synchronised_Clock.html
http://www.siliconchip.com.au/cms/gallery/article.html?a=111709


$7.79 Trimble GPS module:

http://www.ebay.com/itm/190626494449

$5.99 GPS antenna with MMCX connector:

http://www.ebay.com/itm/170496886891

$32.00 for a GPS receiver & antenna module:

http://www.ebay.com/itm/180815989220


Be VERY careful if you buy any Rockwell GPS receiver boards on Ebay.
At least one seller is advertising a board with 10 KHz out then ship a
different board, even though they have been sent the information by
people who have tried to use them.

--
You can't have a sense of humor, if you have no sense.