I am attempting to make an alarm on AC main failure based on Arduino Mini Pro.
The idea is that when AC main failure happens the Arduino Mini Pro shall wake up and periodically "beep" between "sleeps."
I want to use 3.3V/8MHz version of Arduino primarily sourced by AC adapter and to use its hardware interrupt to detect the AC failure.
When AC fails it should be powered by coin cell battery until AC main returns. Primary goal here is to work on battery as long as possible.
While reading various posts, threads, articles, I understood that this should be done with op-amp and MOSFET but struggling to figure out how.
Because of coin cell battery's low voltage to power 3.3V Arduino, I understood that solution based on Schottky diodes are not the right option, especially due to reverse current it may blow up my battery over a time.
Appreciate experts' help!