As of the time of writing I am currently using a:

• Dfrobot Firebeetle esp32 board
• Adafruit 320x240 TFT LCD w/ ILI9341 driver
• Sparkfun MS5803-14BA breakout

These were the initial items I purchased but I am reviewing where they should be changed.

MCU

I am currently using the esp32 which has 512kb of RAM along with WIFI and BLE 4.0 to allow for communication while still enclosed and watertight.

As alternatives I am considering:

• STM32L4R9XXX

This seems to be a very powerful chip and even has MIPI DSI inbuilt. However, I have not been able to find any small boards using this so it would require a fully custom PCB which would take a long time to develop the skills for. Additionally, the STM32 does not have any wireless capabilities built-in, requiring a separate chip to handle that.

• nrf52840

There are a lot of boards developed around this, and it appears to have been used in smartwatches, proving its capability. It looks to support pow power modes, which are very important for long-term battery operation, and BLE 4.0 which is likely the more useful protocol out of BLE and wifi.

• RP2040

This is a very new chip and so I don't know much about it yet but it seems capable of some very impressive things such as outputting 480p @ 60hz over DVI. The main concern is that it does not natively support wireless, and I am yet to see any long term low power tests as current low power modes do not seem suitable for long term sleep.

As a final option, I will be keeping my eye on the esp32-3 to see how that develops and when boards start to become available.

MCU Board

I am currently using the firebeetle ESP32 with 512kb of RAM, onboard LIPO charging circuitry, a deep sleep current of 80 uA, and measures 58x29mm.

As an alternative, I am looking at the TinyPico (Nano) as they are smaller boards and look to support a lower deep sleep current, vital for times when there are long periods between dives. The advantage of the TinyPico is that the pins for a standard header making it easy to prototype / solder to as a standalone unit, although it does have fewer pins broken out than the fire beetle board.  In contrast, the TinyPico nano is even smaller and has more pins broken out than even the fire beetle board. The problem with it is that the pins are not in a breadboard format making soldering and prototyping that bit more difficult.

Display

I am currently using an Adafruit 320x240 TFT LCD w/ ILI9341 driver.

I am looking at the alternative of using a Waveshare 2.4inch 320x240 IPS LCD with an ST7899 diver. This has the advantage of both having a better viewing angle due to being IPS rather than TFT, along with having a driver capable of faster speeds.