5

I have really bad eyesight, so whenever I plug in the power wire and the GND wire I always double check if I'm actually plugging in to the power port not one of the two GND ports.

Why does an Arduino UNO have two GND ports, and for what application would one use both of them?

  • 2
    There is actually a third one next to pin 13 on my Uno. It's just convenience to have multiple ground headers. That way you even do without a breadboard for very simple projects. – Gerben Aug 31 '14 at 12:00
8

In electronics circuits, a major point in connecting two circuits and make them "talk" together is to ensure, at the minimum, that they have a common reference of voltage (typically called GND and defined as 0V voltage).

On Arduino, GND pins can be used in 2 situations:

  1. to directly power the Arduino with an external supply which cannot be plugged to USB or power jack. In this case, the positive voltage of that external power source shall also be supplied to Vin pin.
  2. to connect Arduino GND to your circuits.

Having 2 distinct GND pins is, I think, just a matter of convenience when you want to build prototypes but don't necessarily have a breadboard (if you use a breadboard, you will just need to connect its power rail to Arduino GND pin and use this power rail directly).

1

If you are not using a shield and are directly adding components to the arduino it is nice to have 2 ground so you can attach several components without having to add a bread board.

To be precise, you have 3 ground, since the third is sitting on the left hand side of the board (looking in to the USB port)

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