gunrunnerjohn posted:crood58 posted:JohnGaltLine posted:On the RS485, every example I've seen and all the documentation I've seen shows some common ground. Most just use a third wire while many industrial applications use earth ground. In any case it doesn't matter to me as it will only be two wires between devices and track common will be connected to them anyway.
I disagree. I have this working perfectly fine for weeks without a common ground shared. I don't know why tutorials show this, but it maybe just a safety factor. Why would track common be connected to RS485? I don't recommend that at all. I would keep track power & ground separated from 5V DC power. Hence the Optamp.
The reason for the ground is the common mode voltage capability of the RS-485 drivers. The ground is typically necessary when going between widely separated points that could have different power systems and different grounding. Of course, if the two devices have no issue of having excessively different ground levels, you probably don't need the ground.
If the RS-485 is using optical isolation, then keeping the ground reference should no longer be necessary. B+B SmarkWorx has optically isolated RS-485 that apparently solve this issue, I'd assume they're not the only ones.
Here's a good description of the ground: Why does RS485 (and RS422) require to connect the logic Ground?
I can see this industrial applications, but I would assume that 99% of the time a Arduino or Raspberry Pi would be fed off of the same power source and would not require this common ground for the RS485 bus. Making only two wires required. Technically speaking my Arduino and Raspberry Pi are sharing earth ground.
