[time-nuts] Designing an embedded precision GPS time

[Hal Murray]

tnuts at joshreply.com said:
> I am trying to build the most accurate fee running, low power time base I can.

> I am trying to beat existing products like the Dallas DS3231 and Micro
> Crystal RV-8803-C7-32.768kHz-3PPM-TA-QC, which use (I think) a similar
> strategy. I’m hoping I can beat them by using more accurate temp tensing,
> longer and more exhaustive calibration effort, and anything else possible!  

That should be easy.
  http://users.megapathdsl.net/~hmurray/time-nuts/Temp-tcxo32khz-a.png

Do you need an accurate output frequency, or just know what the actual 
frequency is so you can compensate when counting cycles to keep track of 
elapsed time?

I would start by bolting your setup to a large thermal mass and putting it 
inside an insulated box.  Not too well insulated or it will cook itself.  You 
want the thermal time constant to be long enough to give your control loop 
plenty of time to react.  You also want the thermal sensor at the same 
temperature as the crystal.



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