1

so that there a 2 wires rather than 3 to connect between the two for purposes of serial communication. And the same question for 3 arduino megas on a common rail and using serial connections?

3

All voltages are ground referenced, hence the ground is the only (supply) connection required. Remote modules can be self-powered and signals will still be discriminated as long as ground is connected.

  • thank you for your prompt reply , the 9v and negative rail are connected for purposes of powering the arduino boards anyway. I should have asked Do I need an additional connection between the grounds to that provided by the power connection. – wobbler Mar 24 '15 at 15:35
  • If they're using a common ground then their grounds should be already connected. – Ignacio Vazquez-Abrams Mar 24 '15 at 15:36

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