eli5: when a 5V signal is attached/applied directly to an input pin on an arduino, does that input pin act as ground?

Question

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

Answer 1

Analog inputs are voltage meters and they measure voltage, not current. You don’t need any current to be flowing into/out of the pin, so you don’t need a “complete circuit” with power and ground.

By analagy, imagine a garden hose. It’s turned on at the tap, but ends in a pressure sensor that blocks the end and measures the water pressure. No water is moving, but the sensor can still measure the pressure.

Voltage is electric pressure. Tap, turned on, is 5v source. Sensor is input pin.