Here is what the current interface is; I have installed the prototype cards into an ATR.poly slave. It has 2 RJ45 for the RS-485 which is almost wired pin for pin. I use T-586B for my RJ45 (yellow RS-485) links downstream and upstream, as well as 2 DB-25 Wire-Wrap tails installed along one of the long sides. I have also mounted an RS-485 to Android Converter which has been installed into two small female headers (these will be standard on the PCB).  The photo on the right below was my functional prototype. If you look at the left side of the photo you will see the DB-25 as well. The Molex connector in the foreground is a hard drive male connector and it will be soldered on to the PCB as well, I need to have 5volts for the Arduino, Ground, 24vdc for lights and its own ground. 

As you can see from the photos this was my first attempt at an ATR.poly MASTER as the Master is the interface with an Ethernet connection. Also, you will notice the three groups of wire two at the top the other below:

   One group is for data.

   The second Group is for Status lamps

   The third group I can't remember as my functional unit is packed as well as my Documentation.

When the PCB comes in then mess goes away. Instead, nothing is plugged into Arduino directly, like all of the RS-485 wires will just simply be soldered to the baseboard, into which the Arduino will just plug into. Around the Arduino, there will be male Wire-Wrap headers to take care of jumpers ie. between RS-485 module and Arduino itself. And life is good. BTW Wire-Wrap is not twisting two wires together. This technique provides a  gas-tight joint, just as reliable as a soldered joint. If you are interested in this method please refer to MIL-STD 1130C. Here is a picture of the tool.