I’ve done this, it’s straight forward enough if you give the SDI-12 device time to get going rather than expect a sub-millisecond response as soon as you wake the MCU.
How did you exactly go about giving the SDI-12 device LoRaWAN capabilities. I’m unfamiliar with SDI-12 devices in general, I’ve just noticed that many sensors are of that type. Is there any special device and/or configuration needed?
To add LoRaWAN to SDI-12 you need a relatively generic simple LoRaWAN based module that you can program, add in some code and perhaps a way to power down the devices whilst not in use, et voila! SDI-12 is a serial protocol over a single wire and you can have as many devices on that bus as you like.
So once you have SDI-12 running, adding new devices is a case of sending the appropriate commands and picking the data out of the return message. You can ask what is on the line, so you can poll for new devices and if you know what the capabilities are of a device, make use of it - that is to say, you can’t put a device on the bus and have it automagically know what to do with it.