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

David McGaw david at endor.com
Wed Jul 23 13:27:29 EDT 2008

Divide 10 MHz by 250 to get 40 kHz, to be within range of the clock's 
logic, then use a presettable counter loaded by the 1 PPS to count 
off 32768 clocks per second.

David McGaw

At 11:30 AM 7/23/2008, you wrote:
>    I was faced with this problem a few years ago, too.
>    I essentially followed John's solution, but used the 1pps GPS pulse as
>    the PLL reference.
>    I then used the 32.768K vco output to injection-lock the 32.768K
>    crystal on the LCD clock.
>    Much to my surprise, it worked quite well. And, as pointed out already,
>    jitter isn't an issue for this application.
>Bill Ezell
>They said 'Windows or better'
>so I used Linux.
>    John Franke wrote:
>The only thing that comes to mind is to divide the 10 MHz by 2500000
>(5x5x100000) and then use a phase locked loop to multiply by 8192.  Of
>course the PLL would best control a varactor with a clock crystal vice
>controlling an RC oscillator.  Other divisor multiplier pairs are:
>1250000/4096, 625000/2048, 312500/1024, 156250/512, and 78125/256.
>John  WA4WDL
>----- Original Message -----
>From: "Max Skop" [1]<mskop at bigpond.net.au>
>To: [2]<time-nuts at febo.com>
>Sent: Wednesday, July 23, 2008 10:09 AM
>Subject: [time-nuts] How to get 32.768KHz from 10MHz.
>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.
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