The DS3231 trim register sensitivity is speced at 0.1 ppm per count typ at 25 C. The trim range is +/- 127 counts so the fastest you can slew the pps pulse is about 12.7 ppm or about +/- 1.1 sec per day if my calculations are correct.
The chip reads the temperature sensor and adjusts the oscillator frequency in the same size steps so it is effectively a digital TCXO. The resolution of the temperature sensor readout is 0.25 C so stabilizing the chip temperature using that sensor would probably help the overall stability, especially at extreme ambient temperatures. I have thought about making a GPSDO using a DS3231 as a digitally controlled oscillator, with the control based on the time difference between the GPS and DS3231 pps times, but that is still on the "to-do" list. On Mon, Dec 30, 2019 at 6:09 AM MLewis <[email protected]> wrote: > I was watching the PPS LED on my M8T board vs. the LED I put on the RTC > DS3231's SQW output enabled for 1 Hz for a PPS. As expected they're not > aligned, and the drift of that misalignment shows they're obviously not > at the same frequency. > > It got me wondering. Between the DS3231's Aging Trim, insulating and > perhaps a heater for some temperature control, does anyone know if the > DS3231's PPS could be synced and stabilized into a reasonable PPS source > through an opto-isolator? > > Might a fibre-optic line be useful as a transmission cable, gapping two > LEDs functioning as an opto-isolator, thereby providing both isolation > and high-speed coupling for the PPS to the device that wants to read the > PPS? > > I don't know if the onboard temperature sensor is precise/stable enough > to be useful for maintaining a stable temperature with a heater. It's > accuracy is listed as +/- 3 C, but that doesn't speak to the stability > of the temperature it reports. > > The SQW output can be set to 1 Hz, 1.025 kHz, 4.096 kHz or 8.192 kHz. > > It also has a 32 kHz output pin. I don't know if that's actually 32 kHz > or 2^15 = 32,768 Hz. > Ah, there it is. "outputs a 32.768kHz square-wave signal". > > Has anyone done this, or does it seem like it may be worthwhile? > > Thanks, > > Michael > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > -- --Jim Harman _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
