[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


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.


More info:

32 kHz watch circuit with programmable output period and pulse width

The Principle of Digital Trimming

Digital trimming for frequency adjustment 

Method for digital frequency trimming an oscillator in an electronic timepiece 

AVR4100: Selecting and testing 32kHz crystal oscillators for Atmel AVR microcontrollers

Quartz Crystal Theory

Crystal Theory

MSP430 32-kHz Crystal Oscillators

Introduction to the quartz tuning fork

The Accuracy and Stability of Quartz Watches

More information about the time-nuts mailing list