MAX485, ok with 2 nodes, when 3rd node powered up voltage drop below 2V (SOLVED)


I made a MAX485 module with the schematics below…

Everything was working OK when 2 nodes were connected, can Rx or Tx between the master/slave nodes on the Arduino Nano.

  • I have tried using 20K pull-up/down at A,B or even no pull-up/down on A,B, same results.

  • I tried with 120R termination or 1K R termination, same results.

  • Was running at the lowest speed of 9600, same results.

I’m using just very short Cat 5E twisted pair cables during the tests…

I can visually see it is not working as the Rx,Tx LED becomes very dim or not litted at all…

Any idea why does it drop the voltages when 3 or 4th nodes was connected ??

Thank you for reading this…


When running on 2 nodes, everything was ok.


When connected n power up the 3rd node, voltages dropped below 2V


Here is a picture of my setup with the newly made PCB…


Someone in another forum helped me solve it by removing the 10K pullup from the DE/RE pins and allow the Arduino Nano to control the HIGH/LOW state..