This is a very early thought-dump for a dual-AA battery powered indoor sensor with E-Paper display.

Specifications:

- Preferably AA battery powered - Why no lithium?  Kids... and their propensity to play with things that they probably shouldn't.

- Low power - Keep the uC in sleep for as long as possible.  Thinking about grabbing sensor values and updating the display every 10-15 minutes or so.

- E-Paper Display - Good power efficiency when compared to LCD's and OLED's.  Just not sure what the best way is to attach the panel to the PCB?  Double sided tape?  Nails through the display?

Components:

- STM32L431CBT6

- TPS610994YFFR (Low Iq 3.3v Boost)

- SGP41-D-R4 (Gas)

- SHT45-AD1B-R3 (Temp/Humidity)

- BME280 (Pressure)

- Good Display E-Paper Panel GDEY0213B74

Briefly checking around for STM32, CubeMX code examples, found some Arduino code fromSensirion AG for their sensors.  Should be easy enough to port over with the official datasheets:

Sites - Code Examples

• Sensirion Gas Index Algorithm
• Sensirion Core
• Sensirion I2C SGP41
• Sensirion I2C SHT
  

Good Display / Buy-LCD E-Paper Display GDEY0213B74 -- from their datasheet, a reference circuit for driving the display.  Seems simple enough:

Another example schematic that may prove useful:
https://www.crystalfontz.com/products/document/3991/CFA-10084AdapterBoardDatasheet.pdf


Panel dimensions are approximately 60 mm x 30 mm (2.4" x 1.2"), so a PCB a bit larger to accommodate mounting holes on each corner should fit all of the electronics without any issue... and slapping the E-Paper panel on the back of the PCB seems like it would work nicely.


Headers
- SWD Header (5 pin - 3.3v, SWCLK, SWDIO, NRST, GND)
- UART Header(3 pin - TX, RX, GND)