Wow! This is some phenomenal engineering!
> Another area that stumped me is how to shut the power off 100% on the device, so that it can remain “off” for weeks or months.
This is actually a pretty solvable problem...
https://circuitcellar.com/resources/quickbits/soft-latching-...
Then the microcontroller can choose at any time to completely shut off the entire circuit (including itself), and extremely little power will be consumed until something (like a button) completes the power-on circuit again.
For ease of prototyping, there are off-the-shelf units you can play with: https://www.sparkfun.com/sparkfun-soft-power-switch-jst-2mm....
Some more advanced soft power switch circuits (like the SparkFun switch) also include the ability to forcibly power down a misbehaving device by holding down the button.
The design used in the SparkFun switch also allows your microcontroller to know if the button is pushed while the device is running, so you could imagine repurposing your existing button to also restore power to the device if the device is off, and still retain the existing functionality for cycling through watch faces. Then, either the device could automatically shut itself off after a period of inactivity or when the battery gets too low, or the user could click and hold the button for some number of seconds to turn the device off completely that way.
> Another area that stumped me is how to shut the power off 100% on the device, so that it can remain “off” for weeks or months.
This is actually a pretty solvable problem...
https://circuitcellar.com/resources/quickbits/soft-latching-...
Then the microcontroller can choose at any time to completely shut off the entire circuit (including itself), and extremely little power will be consumed until something (like a button) completes the power-on circuit again.
For ease of prototyping, there are off-the-shelf units you can play with: https://www.sparkfun.com/sparkfun-soft-power-switch-jst-2mm....
Some more advanced soft power switch circuits (like the SparkFun switch) also include the ability to forcibly power down a misbehaving device by holding down the button.
The design used in the SparkFun switch also allows your microcontroller to know if the button is pushed while the device is running, so you could imagine repurposing your existing button to also restore power to the device if the device is off, and still retain the existing functionality for cycling through watch faces. Then, either the device could automatically shut itself off after a period of inactivity or when the battery gets too low, or the user could click and hold the button for some number of seconds to turn the device off completely that way.