I am working on a Raspberry Pi (3B plus) project that - at times -needs to operate on battery power, and on external power whenever available. The RPI needs to operate only when a dedicated sensor detects a preset signal level.
To save power, I want to keep the RPi powered off, only to be powered up when a (power savvy) Adafruit Trinket M0 senses the signal-level of interest. The Trinket then activates a relay that connects the RPi to the supply power (be it battery, or external power supply).
When the signal level drops below the level of interest, the Trinket will not power down the RPi, until it receives a 'Safe-to-power-down' from the RPi.
I came up with a wiring diagram, (see picture), but, not being an electrical engineer, I would really appreciate some input. Would it work like this? How can I improve, or change it? By the way, both switches should be physically coupled, and labeled (BATT - EXT+COMM)