For example, when a push button is pressed. The 5V supply connects to the signal cable, which is attached to Pin 2, for example.
But where does the current ‘sink’ into? Doesn’t it need an explicit ground pin? If it goes right into Pin 2, is that the ground pin in disguise?
Or is the signal pin (pin 2) the one applying the current through the push button..?
In: 0
For the Arduino to properly sense the voltage on the incoming pin and respond to it, the Arduino and the device sending the signal need to have a common ground reference.
The usual way to do this is to have the Arduino and the device connected in such a way that their grounds are tied together, or to link the Arduino’s ground pin to the external device’s ground. Depending on your circuit design and the power limitations, this may or may not be a workable system, but for a push button sending a signal, it should work.
This thread from the Arduino forums may help shed some more light on the issue:
https://forum.arduino.cc/t/connecting-grounds-together-why/64678
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