[time-nuts] New precision watch

Chuck Harris cfharris at erols.com
Mon Dec 19 08:34:12 EST 2011


With the CMOS logic used in watches, the big power hog
is due to charging and discharging the gate capacitance
of the various logic gates.  The faster you charge and
discharge the gate's, the more power you loose due to
I2R losses, and E-M radiation.

Thankfully, the high capacity lithium cells available today
provide lots more uA-hours than the older silver-oxide cells
of yor, so it is possible for the energy budget on a
premium electronic watch to be higher than was previously
acceptable.  I would think that most watch manufacturers would
take that extra power budget, and use it to extend the time
between cell changes, and to spin more fancy dial motors.

It is not clear to me that a 32KHz xtal is any less stable
than a 262KHz xtal, though.  I would think there would be a lot
more to be gained by using a microprocessor/thermistor to
measure the temperature within the watch, and provide an
adjustment to compensate for the xtal's natural temperature
sensitivity.

-Chuck Harris

Perry Sandeen wrote:
> List,
>
> I saw an ad today for a Bulova Champlain Precisionist watch.  It is supposed to be
> accurate to + 10 seconds a year.  What stood out in the as is that they are using
> a 262,144 KHz crystal eight times the frequency commonly used.
>
> I don’t know if it is more accurate than the Seiko (?) discussed on the list about
> a year ago, but it seems to be about USD $2,100 cheaper.   Around USD $600 or less
> depending on the model.  Is a 10 MHz or so crystal on the horizon?
>
> Regards,
>
> Perrier




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