Charlie Thompson's
Quartz Watch Timebase

Here's way to monitor the 32.768 KHz crystal in your quartz (plastic) watch.

This circuit relies on capacitive coupling of the watches' oscillator to
the outside world.  Hence this only works with "plastic" digital watches.

You'll need a frequency counter capable of resolving 32.768000 KHz
since a deviation of only 1ppm results in a 3 second/month accumulated error.

The circuit is basically a very high gain (not so linear but who cares) amplifier
followed by a 32768 Hz crystal filter. US Patent #4044597 serves as the
original inspiration for this project.
The only "special" component in the circuit diagram is a 32768 Hz crystal.
You can usually find one on an old IBM-PC motherboard.
The crystal looks like a small metallic tube about 1/16" in diameter.

Click here to see a photo of the breadboarded circuit.
Note the square "plate" on the left-hand side.  This is the
capacitive coupling plate for the wristwatch oscillator coupling.

The wristwatch is placed on the "plate" as shown here.
You can monitor the output of the crystal filter and should see
a waveform similar to this.

If you do...just move your scope BNC end over to your frequency
counter and you should see something like this on your counter.
Be sure to keep offending stuff like video displays, TV's, computers turned off
while performing the frequency measurement.

Remember that 1 ppm frequency error is about 3 seconds/month.

Most quartz wristwatches include a trimmer cap to allow tuning the 32768 Hz oscillator.

Good luck!

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Rev 1.1 5/26/2002