60Hz AC will likely be more long-term accurate, while the
32KHz crystal will probably be more precise. The 32KHz
crystal will probably also have a somewhat more predictable
error function and you can likely calibrate your device
to adjust for some major portion of the error. If you can
monitor both signals, you could probably arrive at a quite
good time base, especially after a few days of calibration.

If you can interface to a SW receiver, of course you
can use WWV; NIST suggests that the recieved accuracy
is about 0.1 ppm for frequency and 1 ms for timing.

--Bob

On Tue, Jun 08, 1999 at 11:22:58AM -0400, Wagner Lipnharski wrote:
> Does anyone already did any research about what is more accurate to get
> 1Hz division; the 60Hz power line frequency or a cheap 32768Hz crystal?
> The fast answer could lead to the crystal, but it could not be the
> truth.  I have an "old red led display table clock" that steals clock
> from the 60Hz power, I never needed to adjust its timming error (it was
> never noticed) except for day-light-savings adjustments.  Dallas RTC
> DS-1644 has almost one minute/month error with an internal crystal.
>
> --------------------------------------------------------
> Wagner Lipnharski - UST Research Inc. - Orlando, Florida
> Forum and microcontroller web site:  http://www.ustr.net
> Microcontrollers Survey:  http://www.ustr.net/tellme.htm

--
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Bob Drzyzgula                             It's not a problem
bob@drzyzgula.org                until something bad happens
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