On Sun, 20 May 2012 00:13:49 -0700, isw wrote:

ALmost certainly a crystal; ceramic resonators have way too much drift
with temperature. 32 KHz crystals are very difficult to trim because
they don't like to have any extraneous capacitance hung on them.

32.768KHz crystals are somewhat of a special case when it comes to
trimming. The problem is that the crystals are tuning forks, not bulk
quartz devices like higher frequency devices. What's inside:
http://en.wikipedia.org/wiki/File:Inside_QuartzCrystal-Tuningfork.jpg
Typical specs are something like 7-12pF shunt capacitance. It is
possible to trim the frequency with a variable capacitor that is
centered around this capacitance. It's done all the time in
electronic wrist watches.


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