These xtals often need tuning by tweaking the capacitance.=20
remember also that they are designed to run over a fairly narrow temp
range (i.e. strapped to people) and accuracy will fall off outside
that range.
All the watch modules I've ever taken apart have had a trimmer.
Obviously you can't trim by measuring the xtal freq as the  measuring
probe will change the capacitance - you need to generate a signal from
the PIC to measure, but remember that you will get jitter from the
PIC's main clock sampling the 32K xtal, so you need to measure over a
reasonably long period - probably several seconds at least..=20

On Tue, 17 Dec 2002 08:17:47 -0500, you wrote:

>Any idea what sort of accuracy I should get from a cheap watch xtal in a
>PIC oscillator?
>
>I'm using one as the T1 osc on a '877. I let the timer free-run (I don't
>preset it - it rolls over in 2 seconds), and have an interrupt routine =
that
>keeps track of time-of-day. When I compare the time of day from this =
with
>the actual time, the PIC has lost about 6 seconds in 8 hours. Not very =
good.
>
>Larry
>
>Larry Bradley
>Orleans (Ottawa), Ontario, CANADA

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