> Hi Robert,
>
> I didn't think my watch would have a trimmer but perhaps it does.
> That is impressive that you were able to get it down that much in
> error, although 4 min/month is huge (that's 8 seconds per day or
> about 88 ppm)

Sean, a trimmer in a clock is a very good idea. I've just serviced
a few of those "bank" clocks, you know, the white ones that flip
black cards over. That make/model (Twemco BQ17) uses two
D cells and either an ICM7213 time-base IC or a 16C54 with a
32kHz crystal. Almost all of those I looked at were reported to be
either slightly slow or fast (and people in the workplace notice
these things !!). Measurement of the crystals shows from 32767.6Hz
to 32768.5Hz. None are tempco so the best you can do is use the
cap trimmer to get it back to 32768.0Hz. The difference might
not seem like much but after a few months the clock shows an
obviously wrong time

Whenever possible the clock is modified to use 50Hz as the primary
time-base and the battery option as back-up. The thread the other
day about deliberately picking up hum from surrounding cables is
food for thought as a possibility for making stationary battery clocks
more reliable

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads