[time-nuts] 1PPS to 32.768 khz

Chris Albertson albertson.chris at gmail.com
Wed Oct 19 14:20:09 EDT 2016

Even if the micro controller had to directly control the LEDs on the clock
your suggestion would be not only simpler bot several orders of magnitude
more accurate.    I'd guess that a first attempt to build a 32KHz GPSDO
would not be perfect but the PPS signal is effectively dead-in perfect in
this use case.

The disadvantage of using there GPS directly to increment the clock is you
loose hold over.  The clock stops when GPS goes away.

A GPSDO has a "flywheel effect" and can continue to run on it's own if the
GPS is interrupted.  When the GPS signal returns it can slowly recover.
But do you care?

One other unleaded idea, can you control the frequency of a 32K crystal by
controlling its temperature?   If you can then that might be easier then
using a diode tuner.   It is easy t build a heater, epoxy a resistor to the

On Wed, Oct 19, 2016 at 6:15 AM, Dave Martindale <dave.martindale at gmail.com>

> If the "big digital clock" doesn't display the time with fractional-second
> precision, then it only needs to be updated at 1 Hz, which can be done with
> the 1 PPS directly.  Consider replacing the 32 kHz crystal, divider chain,
> and microprocessor with a new microcontroller that takes 1 Hz input and
> drives the display in the same way.
> For an extra bonus, use a microcontroller with a serial port, and connect
> the GPS receiver serial output to the serial port on the micro.  Then you
> can decode the serial data stream from the GPS, and automatically set the
> clock to the correct time after a power failure - something the original
> clock could not do.  As a double bonus, make the clock display leap seconds
> correctly when they happen.

Chris Albertson
Redondo Beach, California

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