@james-dareboprc-govt-nz, those power issues you came across on GitHub (regarding getting the brush to spin and wondering about setting the spin rate) were quite old (2017?) when we first started using YosemiTech sensors and early in my knowledge of DIY electronics. The short-story is that once we figured out that we needed to add a capacitor (i.e. powering a device wasn’t just about voltage), then we had no problems.
I strongly urge you to get the Y511 turbidity sensor with the auto-brush/wiper. Otherwise you will be seeing sensor drift within a week or so (depending on the season) and will need to manually clean your sensor. The extra US$150 is definitely worth it. More details here: https://www.envirodiy.org/topic/problems-with-obs3/#post-15556
I like your solution for testing the RS-485 adapter boards from China before soldering them onto a Mayfly-Modbus-Wing.
By the way, when I have found a RS-485 adapter board that doesn’t work, I have solved the issue 14 out of 15 times by soldering on a 120 ohm resistor (1/4 W) directly to the A+ and B- terminals on the RS-485 adapter, as I showed and described here: https://github.com/EnviroDIY/SensorModbusMaster/issues/14#issuecomment-678554101