Loss of Serial Communication When Connecting Common Ground

Development Tools IDE 1.x
1

Hi All,

Running it a frustrating problem. When connecting common ground between Arduino and power supply serial communication is lost. TX(4) pin goes to >4V while RX(3) goes to <0.5V. FYI I am using software serial on a Arduino Nano.

The circuit contains the following components.

  1. 14V 30A DC Switching Power Supply (PYRAMID PSV-300)
  2. ECUMASTER EMU (Communication is based on RS232 at 19200. Output levels are <5V)
  3. DC-DC Buck Convertor 12V to 5V. (POLOLU D36V6F5, Also tested with POLOLU D24V22F5)
  4. Arduino Nano
  5. CANBUS Module (Not Shown, Issue is still present with this completely removed)

I have posted some hand drawn schematics to illustrate what wiring worked and what wiring didn't work.

IMG-8988
IMG-89884032×3024 3.17 MB

IMG-8989
IMG-89894032×3024 3.11 MB

IMG-8990
IMG-89904032×3024 3.14 MB

Troubleshooting that has been completed so far.

  1. If the Arduino Nano is powered via Laptop/Wall wart serial communication works as intended.
  2. The moment I bridge the GND from Arduino to Power Supply serial communication stops working.
  3. Having the Arduino Nano powered via +5V port using a 5V regulator serial communication does not working.
  4. Having the Arduino Nano powered via USB port using a 5V regulator Serial communication does not work.

This circuit is to be installed within a vehicle where the grounds are common hence would like to figure out why serial communication stops working when grounds are common.

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