Wireless RS-232C to Bluetooth Adapters
I put together one, maybe three years ago, for BT'ing serial NMEA0183 data from a chartplotter to Carlson SurvCE so that we could add depth soundings to RTK observations. The BT was something like this:
But without the aerial, so I think it was a lower class (shorter range). It needed a null modem and a power supply (in this case I used 2 or 3 1.5V AA rechargeable batteries). I'm away for 3 days, but when I get back I'll post some images of the setup. It works well, and it's a great feeling when you get things up and running.
As I explained on the phone the solution is a Sena SD-1000 Serial to Bluetooth. But you explained that you(or the county) has no budget to make any purchase for the survey dept, even this lost cost $160 option.
Sorry to say this but you can't help those that won't help themselves.
Licensed Surveyor in NY
sUAS Remote Pilot
Here's the one I put together. I originally put it together as a BT for a Sokkia Set 3B so that it could wirelessly talk with a iPAQ DC, but then I pulled it and wired it up for the depth sounder - to RTK SurvCE.
The BT module in it is the one on the left below:
The black case strapped to the back is the DC battery pack, lasts forever as the BT power demand is low. I've also wired in a digital voltage display.
You need to be able to serial connect to a computer to run the BT module setup to configure baud etc.
I see in my notes that I also played around with cheaper TLL-RS232 converters and "open" BT modules and set one up for the Sokkia.
However the "premade" BT link is simpler. All up I think the components were say $50. Research/setup/stress time probably came to $5,000.