[time-nuts] How to get 32.768KHz from 10MHz.

Jim Lux James.P.Lux at jpl.nasa.gov
Wed Jul 23 11:55:00 EDT 2008

At 07:09 AM 7/23/2008, Max Skop wrote:
>How does one get a 32.768KHz signal from our 10MHz reference.
>There does not appear to be a nice divide ratio to do this.
>With a locked 32.768KHz signal one could lock the oscillator of  any 
>of the cheap (low cost) LCD clocks that are available with nice big 
>digits, temperature sensors and calendars, etc.
>Any suggestions on how to do it??
>ps. I got sucked in good. Six months ago all I had was an HP 10811 
>and now I have another crystal oscillator, two rubidiums and a 
>Trimble GPS.

There's two approaches to your high level problem (driving a 
clock)... one is to make 32.768 kHz, the other is to directly drive 
the 1pps.  Obviously, dividing down 10M to get to 1Hz is easy.

But, for the other, you don't need to have a perfect symmetrical sine 
wave.  All you need to do is make sure that there are 32,768 
transitions in a second, so any sort of rough and ready divider 
scheme will work.

Now.. in the lab what I did is use a HP3325B to make clocks run on Mars time



Since the 3325 was locked to the lab's maser, it's probably the most 
accurate Mars clock around (bearing in mind that Mars's rotation 
isn't nearly as stable as the maser, so it's superfluous accuracy)

You can do other nifty things, by the way... you can make a clock 
that displays solar elevation ("sundial time") because the rate can 
be changed systematically.

I never did get around to programming a PIC to do some of this stuff, 
but it would be quite straightforward.

Jim Lux

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