to have a SDI-12 interface, and your board got me thinking .
The Mayfly socket has +5V and +3.3V and the board can have the boosted +12V. ( I had done it from the Seeed D6-7).
So thinking of trading off the third 4pin “modbus socket” for a 3pin “SDI-12 socket”. That is 3pins screw connector and “JST PH 3-pin”. The JST PH 3pin 2mm have Adafruit mating cables.
The line interface following https://sdi-12.org/specification
The benefits are one digital interface board, with options for simplicity like 3.3V pass through interface, or plain SDI-12 instrument +5V current limiting.
So just putting it out there for a technical review if you have insights/comments ~ always appreciated before committing to copper. 🙂