I understand RS-485 needs a common ground (that the differential is related to)
Connecting a multidrop 485 network. The EIA RS-485 Specification labels the data wires "A" and "B", but many manufacturers label their wires "+" and "-". In our experience, the "-" wire should be connected to the "A" line, and the "+" wire to the "B" line. Reversing the polarity will not damage a 485 device, but it will not communicate. This said, the rest is easy: always connect A to A and B to B.Signal ground, don't forget it. While a differential signal does not require a signal ground to communicate, the ground wire serves an important purpose. Over a distance of hundreds or thousands of feet there can be very significant differences in the voltage level of "ground." RS-485 networks can typically maintain correct data with a difference of -7 to +12 Volts. If the grounds differ more than that amount, data will be lost and often the port itself will be damaged. The function of the signal ground wire is to tie the signal ground of each of the nodes to one common ground. However, if the differences in signal grounds is too great, further attention is necessary. Optical isolation is the cure for this problem. Contact B&B Technical Support for more details.
Is this really true?
The ground is just in case we use a long link right?
does the wiring have to include 1 or more ground conductors?
Anyone running other protocols on top of RS485??
Anyone using CAT5 for this?
But I want to get a simple multi-Arduino RS-485 system running sooner..