Hi, I posted a thread as a noob a few months back about this project, and was given great advice that a Nano would do the job required. And it has. I've a small 5 axis mill/engraver at home, so have cut the casings and PCB'c (should be called MCB's (machined not printed lol))
Above are two devices (left) the BME280 housing (below left) and then the main PCB/MCB's. The Nano goes on the larger board after the resistors, jumpers (GND & SDA) and RGB LED and OLED headers are soldered. Then solder the Nano and place on the top board with the three buttons and 20mm speaker
Medical grade Nylon is uncoloured, and LED's look great in it, the red is from the Nano's power light!!! I did put black enamel on one to take it out. But my boy likes the I'Robot look lol. The green is from the RGB LED on it's lowest PWM power setting, as the BMP goes up from 0 to target it glows brighter, then turns blue at correct pressure. Red for over pressure. The lump of plastic the parts are sat on is billet cast Nylon.
Pins used are...
3,6,9 PWM to the LED A1 speaker 2,7,11 buttons A4,A5 I2C to OLED and BME280 5v to buttons 3.3v to BME280 both GNDs are used and connected via the top board.
The sketch does two types of lung physio (button/menu selected), and allows setting changes stored on the EEPROM to all settings. I know the EEPROM is 'Lifed' so I'm staying away from Writes and using Put and Update instead. However I'm also only using 15 EEPROM addresses (I think the Nano has 1024 but dont know for sure???) so could include an EEPROM register to shift user settings up the addresses if one fails? Do EEPROMs fail in the same way? do they go High to Heaven or Low to Hell? can you tell? I spose a bit of code with Write/Read, did what was written return would tell!
Anyway, many thanks for the advice to date, I'm off to buy a Mega for the next project :o