Particle Photon 2 internal RTC

Hello everyone,

I recently acquired a Particle Photon 2 dev board and I'm currently working on a project where I need to log data offline using external memory. One of the challenges I'm facing is how to power the built-in RTC (Real-Time Clock) in the Photon 2 to maintain accurate time even after restarts.

In Photon 1, we could power the RTC by connecting a coin cell to the VBAT pin. However, I'm wondering if there's a similar solution for the Photon 2 that doesn't involve using a Li-ion battery.
I'd appreciate any advice or suggestions on how to power the RTC in the Photon 2 for maintaining accurate time offline.

The RTC on the P2, Photon 2, M-SoM (RTL872x) is similar to the Boron, B-SoM, Tracker, Argon (nRF52840) in that it's just a counter in the MCU that's incremented off the CPU clock. This is different than the Photon 1, P1, E-Series, Electron (STM32F205) that have a separate logic block in the MCU for the RTC that can be powered separately.

In order to maintain time across resets, you'll need to use an external RTC, probably connected by I2C or SPI. One option is the AB1805 which is what is used on the Tracker. The link contains a design that can power the AB1805 RTC for 20 days using a small, inexpensive supercapacitor.

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