Started ad-libbing a circuitry. Solar powered, with a battery.

Ultra-low power. So many choices. Components galore.

My vague idea is to create a circuit based on a massive dragnet of ideas from other circuits, features, and available online. End goal is to be manufacturable end to end with no in-house work but out of box, all components in stock. Cost is irrelevant.

After a massive search I stopped at

MCU: STM32U575 — ultra-low power

BLE: Nordic

E-Paper: Waveshare

Battery: SEIKO Manganese Lithium

Antenna: Self-made built-in

TIMER: Go with the internal.

Took me a week to search for the components.

Must eventually go with external timer. Currently found a seiko/epson crystal 20ppm accuracy, way too low but fine for development.

Need something better than 5ppm, or even better 1ppm at 32k, which is like what, 5 sec/month error? Now it's a second per day error depending on temperature. There are temperature controlled/corrected oscillators or external timers. Seiko / epson seem the way to go but later for a future iteration.