No, it was an undocumented one-off using a random cheap devboard from Aliexpress (i.e. not some specifically optimized circuit!), built (IIRC) using the Arduino IDE - aside from spending the time to find and configure the low power mode properly, this was done in the dumbest, most naive way possible, and still worked.
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Do you have an example of such a setup handy?
No, it was an undocumented one-off using a random cheap devboard from Aliexpress (i.e. not some specifically optimized circuit!), built (IIRC) using the Arduino IDE - aside from spending the time to find and configure the low power mode properly, this was done in the dumbest, most naive way possible, and still worked.