[time-nuts] Casio Watches 13 Year Drift in Seattle
Tom Van Baak
tvb at LeapSecond.com
Sun Jun 28 10:33:38 UTC 2015
> I think there may be a new Time-Nut in the Seattle area, , ,
>
> https://www.youtube.com/watch?v=hwOMUhS8gV0
>
> John, KM6QX
John,
Thanks for posting that. I will have to look this person up.
Given typical tempco plots for 32 kHz crystals I would assume the lost time is due to temperature: wall or room temperature is lower than wrist temperature. Someone on the list with that model watch should do a quick test to confirm. Also a measure of voltco would be interesting.
Note the days of quartz being adjusted with a trimmer capacitor are long gone. It's done digitally now. See, for example, paragraph 8.3 of http://www.nxp.com/documents/data_sheet/PCA2003.pdf
It's much more convenient to periodically delete pulses than have to add them so that's why wristwatch oscillators are designed to run fast rather than slow.
/tvb
More info:
32 kHz watch circuit with programmable output period and pulse width
http://www.nxp.com/documents/data_sheet/PCA2002.pdf
The Principle of Digital Trimming
http://www.emmicroelectronic.com/sites/default/files/public/products/datasheets/v3022_ds_0.pdf
Digital trimming for frequency adjustment
http://www.google.com/patents/US5530407
Method for digital frequency trimming an oscillator in an electronic timepiece
http://www.google.com/patents/US4282595
AVR4100: Selecting and testing 32kHz crystal oscillators for Atmel AVR microcontrollers
http://www.atmel.com/images/doc8333.pdf
Quartz Crystal Theory
http://www.jauchusa.com/ablage/med_00000818_1327049076_Quartz%20Crystal%20Theory%202007.pdf
Crystal Theory
http://www.euroquartz.co.uk/portals/0/pdf/tech-notes.pdf
MSP430 32-kHz Crystal Oscillators
http://www.ti.com/lit/an/slaa322b/slaa322b.pdf
Introduction to the quartz tuning fork
http://www.d.umn.edu/~jmaps/phys5061/labs/projects/qtf/ajp_qtf.pdf
The Accuracy and Stability of Quartz Watches
http://tf.nist.gov/general/pdf/2276.pdf
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