Where can I know voltage between GND(ground) and each port of UNO R3?
5[V] is ideal EMF(electromotive force) of arduino UNO R3.
Since I stated &quot;ideal&quot; ,the actual EMF be slightly lower than 5[V].
In this instance , EMF can be assumed as voltage between GND and port of UNO R3 as ports are connected only by a wire.