[time-nuts] Casio Watches 13 Year Drift in Seattle

Tom Van Baak tvb at LeapSecond.com
Sun Jun 28 06:33:38 EDT 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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