@neilh, thanks for all of these tips. I’m just now diving back into all this, and actually need to make a lot of progress in the next 10 days.
I decided to still go with the Acculevel, because I needed the extra depth range.
Do you have any working Arduino code for the Acculevel? or even the nanolever. It would be a great place to start. My goal is to build a KellerModbus library, that builds on our EnviroDIY/SensorModbusMaster library.
For powering, we just developed a shield for the Mayfly and will be posting those plans & Eagle files and soldering instructions to the EnviroDIY/SensorModbusMaster library.