How to connect to common ground when using the TB6612FNG

Question

Instructions for the SparkFun TB6612FNG indicate that the ground connections for the voltage driving the motors and the logic voltage must be connected together. For motor voltage, I am using a model TE-5305 bench power supply as shown, with a green middle post for GND:

I am assuming that I would make the ground connection for the power supply at that post. What I am confused about is the ground connection for the Arduino board. Connecting the grounds of a device like the power supply and the tiny Arduino board seem "disproportionate" in some way. Am I OK?

Also, should I connect the black negative post of the power supply to its own ground post, as suggested by some sources online? If I don't connect them together, where would I connect the negative post in the circuit?

PS: I did read about ground loops in this answer here: https://electronics.stackexchange.com/a/56130/27163
However, I am still lost with the specifics for the case at hand.

Answer 1

In that sort of power supply, the power supply output is not connected to Ground. The green terminal does provide a connection to the AC Safety Ground which you may use if desired.

The Arduino "Ground" is really the negative terminal of the Arduino circuit, and has not relation to the AC Safety Ground. The Arduino "Ground" should be connected to the negative terminal of the power supply.

I probably would not make any connection to the power supply's Green Safety Ground terminal.

In electronics, the term "Ground" is used with several different conflicting meanings. Most often the "Ground" in a circuit (like the Arduino) just means the negative terminal of the power supply, and does not imply any actual connection to the Earth or to the AC Safety Ground.

Answer 2

You should connect the arduino to the black and red binding posts (Gnd, Vin respectively) and leave the earth (green) binding post unconnected. This will let the Arduino GND float relative to earth ground which is generally bad for ESD protection but good for preventing oscilloscope probing problems for those new to electronics.

If you connect Gnd to Earth and then try to connect an oscilloscope ground on a probe to anything except Gnd on the Arduino you will create a short through the ground on the instruments and possibly damage the Arduino or oscilloscope depending on the power supply configuration.