Great to hear you are doing a power shield with capability to deliver to the EnviroDIY water quality data portal.
There hasn’t been a hw solution yet that I liked, that so I haven’t done anything with the Arduino libs. Maybe that will change.:)
I’m planning on doing a poster at http://calsalmon.org/conferences/36th-annual-salmonid-restoration-conference on different types of pressure sensors for “measuring low water levels accurately across a 10C diurnal change in temperature.”
If you have a solution (or a plan) to have a switchable +12V from a low cost solar powered storage source I’d be happy to reference it.
My objective is switchable +12V powered sensors, with low cost power storage, charging from ~15W solar panel, with a comms solution that can deliver the reading to an internet location and be accessed over the internet.
The assumption is that sensor depth readings are taken every 15minutes, and cellular data is pushed ~ 1-4Hrs.
The system shuts down inbetween activity and takes less than 0.5mA.
The power storage design assumes little sunlight for storms that are two weeks at a time in parts of the year.
Dynamic power issues are of course Cellphones(2G/3G) can take ~0.7A for about a 1Minute to connect and deliver to an internet location.
I did a software prototype on Nuttx(PX4)/Olimex H407, but gave up when I scoped the amount of work still needed to support some of the basic Nuttx subsystems.
It has been running for over a year on the H407 board with external +12V, reading a Keller Nanolevel over RS485 and pushing to Thingspeak/ParticileWiFi
I haven’t attempted to standardize on the modbus lib – so its probably not very useful.
The results are visible through http://azonde.info/pm2/WaterDepthTempNanoLevel.htm that pulls from thingspeak.