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From: "John Jardine"
Subject: Re: 100Hz from 25.6kHz crystal.
Date: Tue, 3 Dec 2002 16:05:03 -0000
References: <5Q1H9.32847$zX3.firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 3 Dec 2002 15:52:57 GMT
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John Fields wrote in message
> On Tue, 3 Dec 2002 14:46:52 -0000, "John Jardine"
> >That is one weird crystal frequency!. Crystals that work at such low
> >frequencies are not much good at keeping time
> Like the 32768Hz. ones in most of the watches in the world?
> John Fields
> Professional circuit designer
Yes ... The watch crystals keep 'customer acceptable' good time.
Xtal wise, the watch manufacturers are limited in what they can choose to
use and this is set by the power required by the xtal oscillator circuit and
the following binary divider chains needed to get down to 1HZ. This results
in the 32768Hz compromise.
Compare this 32768Hz timekeeping, against that of the clock in your auto,
where the designers didn't have to worry about power consumption.
The vehicle clock will invariably be fitted with a higher frequency 4Mhz
xtal. This xtal is naturally much more stable over time and temperature and
results in about 10X better timekeeping!.
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