Looking at the datasheet for the DS3232, it doesn't appear
that they mean for it to run off of a small coin cell in a
watch. Its battery operating capability is purely to keep
it running when the main power is turned off.
I would suspect that the DS3232's power consumption is due
to its being able to drive sizable loads on its various pins.
There is nothing inherent in temperature correcting a clock
that should take significantly more power than would be used
in a normal watch chip. Measuring the temperature would be
the most power hungry operation, I would suspect... but
fortunately that doesn't have to be done all that often,
perhaps once per minute.
After the temperature is measured, a lookup table can be used
to find a second by second correction value to be added to
the seconds counter.
-Chuck Harris
Dan Rae wrote:
On 12/19/2011 5:34 AM, Chuck Harris wrote:
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, I have recently made a couple of Real Time Clocks for my homebrew radios
using
the Maxim DS3232 IC which has a built in TCXO at 32+ kHz doing what you
describe, the
temperature is checked at intervals and the corrections applied. The
performance is
excellent, once set, getting to what I term "Harrison Level", i.e. less than a
second
a week error. The downside is that the standby battery demand is pretty high
and my
first builds using a Lithium button cell ran for only around a month max, so I
had to
go over to NiMH rechargeables. I suspect using this technology in a watch one
would
have the same problem.
The best crystals for room temperature use are around 4 MHz with temperature
inflections around 20C, and this is what was used in an early Braun alarm clock
I had
which also had this kind of performance. Long gone, alas.
Dan
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
