very accurate clock

[doanerock]

I am looking to create a esp32 clock, but I want to add a ±1ppm VCTCXO Oscillator so that I can have it so that my esp32 clock can go a year and still be very accurate because of the external VCTCXO Oscillator. Has anyone tried this before? Is this possible?

[ESP_Sprite]

Sure, I see no reason this wouldn't work... but since the ESP32 is a WiFi-enabled chip, you may also want to think about using NTP to sync it to a reliable time source.

[doanerock]

It is my plan to use NTP or GPS to set the clock. I want to be able to keep very reliable time if NTP/GPS is not available for long periods of time. Which is why I am looking for clarification/advice on how to ensure time is kept accurate. I know that there are reliable real time clocks, but I do not want to use one.

[ESP_Sprite]

A VCXO would work fine then. Do note that the RTC internal to the ESP32 has no battery backup option, though; if the ESP32 loses power, it also loses it's understanding of the time. If you need this, it's probably better to go the external RTC route.

[doanerock]

For the "RTC internal to the ESP32 has no battery backup option" I plan on having a rechargeable 18650 for any times that wall power is lost. So I am aware that if the esp32 looses power it looses time.

So this is great news so far, Are you saying it is possible to attache an external VCXO oscillator to the esp32 Module or the Soc. I am hoping to use the module, because I am hoping to avoid making my own module.
Do you have any guides on how to properly attach a VCXO oscillator, like which pins to be used, which frequency to use, do multiple frequencies work, do some frequencies work better than others? How to recompile the code to use the external VCXO oscillator. IF you could guide me toward the documentation necessary to accomplish my goal that would be appreciated.

[ESP_Sprite]

You would use the VCXO instead of an external 32KHz oscillator; it should be 32KHz. You can enable the 32KHz RTC option in menuconfig. Sorry, I don't quite know the hardware docs well enough to be able to say how you should connect it.

[doanerock]

I want to confirm that this would work with the module and not just the SoC. I can add my own VCTCXO Oscillator to the module via IO32 or IO33. I can only use a Oscillator with 32KHz? I thought I saw references where the Oscillator could be 40Khz.
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