We can save energy by deep-sleeping the ESP32. During this time, the chips do not consume a lot of energy but also are not responsive. This is why Espressif included a mysterious Ultra Low Power core (ULP) which is active when the main processor sleeps. People say it has to be programmed in Assembler, and nearly nobody was able to program it in the Arduino environment.
Until now.

Links:
Arduino IDE ULP repository: https://github.com/duff2013/arduino_ulp
Sketch: https://github.com/SensorsIot/ESP32-U...
ULP commands: https://docs.espressif.com/projects/e...
Technical Reference: https://www.espressif.com/sites/defau...
Otii power Supply: https://www.qoitech.com

Supporting Material and Blog Page: http://www.sensorsiot.org
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