[time-nuts] 1PPS to 32.768 khz

Jim Harman j99harman at gmail.com
Fri Oct 21 13:42:26 EDT 2016

On Thu, Oct 20, 2016 at 7:08 AM, Bob Camp <kb8tq at n1k.org> wrote:

> One problem with a PLL and a 1 Hz input are the values of components
> you get in the loop.
> The other issue is the cost of the VCXO that will get
> you to 32,768 KHz.

As I mentioned earlier, the DS3231 chip (about $6.50 qty 1 or $17.50 on a
breakout board) might be a reasonable approach for this. It is a
self-contained 32.768 KHz TCXO that lets you vary the frequency in steps of
0.1 ppm using its I2C interface. Left to its own devices, it measures the
ambient temperature and switches its on-chip capacitors in and out to
control its frequency.

It has both 1 PPS and 32,768 Hz outputs. Connected to an Arduino-class
processor, you could measure the time delay between its PPS and the PPS
from a GPS and tweak the oscillator accordingly, making a complete 32.768
KHz GPSDO including the GPS with just 3 chips.

And you get RTC functionality and battery backup circuitry thrown in for


--Jim Harman

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