[time-nuts] 1PPS to 32.768 khz

Chris Albertson albertson.chris at gmail.com
Wed Oct 19 02:26:30 EDT 2016

What you want is a GPSDO.  Most people here build these to run at 10MHz.
But you need one that runs at 32768 kHz.

Try this:  Divide the crystal oscillator's output by 32768.  This will give
you one Hz.   Compare the phase of this with the phase of your PPS from the
GPS.  Push and pull the crystal oscillator so that the phase is locked.

The first and most critical step is to build a good 32768 Hz oscillator
that can be fine tuned by a controlling voltage.   Usually a reverse biased
diode is used because the capacitance of the diode depends on the voltage
across it.     You'll need a very good quality 32768 Hz voltage controlled
oscillator (VCO).

In short, go the other way around, don't try and scale up the 1PPS, scale
the 32K down to 1Hz

That said, y you really don't have to divide the 32K signal.   Measure the
time from the zero crossing of the PPS to the nest zero crossing of the 32K
signal and control the VCO to keep this time constant.   What you are
building isa phase locked loop

Now my questions.
> 1. Does anyone know of a device that will take a 1PPS GPS timing signal
> and generate a 32.768 kHz sine wave output ?
> I have big digital clock that uses an 8 bit micro processor and an
> external 32.768 crystal. Obviously the external crystal is
> awful for accuracy.
> I have searched every where using as many search terms as I can think of
> and can’t believe there is not a device that performs
> this function.
> I have found a couple of Epson RTC chips that might come close that 1pps
> but I don’t think that corrects the 32khz just the clock time.
> 2. 10 Mhz Freq Standard
> I am not in the same league as the majority of the list members and just
> starting to dabble in GPSDO stuff.
> I have tried to find a thunderbolt as a starting device but it appears
> those are either dried up or people want too much money.
> I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO ?
> For the money it appears to offer a beginner a lot of features.
> Thanks and reading the daily digest of what you guys are working on.
> I have a feeling if I am not careful you guys could cost me a lot of
> money. hehe
> Lee
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Chris Albertson
Redondo Beach, California

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