Rs485 Network with 2 nodes has stopped responding

I've built an rs-485 network in my shop, so control various outlets, fans, and heaters. The network has been running wonderfully for a few months now, but for some reason node #2 has slowly started to miss messages, and when I try to add a 3rd node, the entire network shuts down.

Each node in the network is an Arduino Nano Every with a Max485 chip soldered onto a custom made circuit board. I know pins are correct, as this network has been functioning perfectly for a few months. The master node is connected to a RasPi, which sends my data to a website.

The network has a terminating resistor of 120 ohm at the master node and the last node. The master node also has bias resistors of 560 ohm from 5v to A and GND to B. I sized all these resistors based of this calculator.

The only thing that I can think may be a problem, is that I switch from 22 AWG twisted wire to 18 AWG solid wire halfway through the network. The master & first node is on the 22 AWG, the rest of the nodes are after the switch. I did this mainly because I ran out of the first wire, and had some other wire left around. I don't really understand why this would be the problem, as again it has been functioning for a few months now.

I guess my biggest question, is where can i start troubleshooting? How would I even narrow down the problem?

Start by removing the 560 Ohm resistors, that is probably messing up the network impedance. Is your network wired with twisted pair? Is there a common ground to each node (I include it with the network cable). Try this link, it is an app note for your drivers. RS-485 Cable Specification Guide | Maxim Integrated
See sketch below:

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.