The powerTimer is a small PCB designed to add ultra-low-power sleep capability to microcontrollers that lack adequate sleep modes. It uses an RV3028-C7 real-time clock (drawing only 45 nA) and an SR latch to control power delivery to a secondary microcontroller. The secondary MCU can signal 'DONE' to cut its own power until the next timer or alarm interrupt. The project was motivated by the ESP32's insufficient deep-sleep power draw for long battery life in a camera application.
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