Shunt

Current sensing is easy to underestimate. An ADC reads voltage, not current. To measure current, the system must first convert current into something measurable.

The first model is: current must be transformed into voltage, magnetic field, or induced current before electronics can measure it.

Shunt resistor: current -> voltage drop
Hall sensor: current -> magnetic field -> Hall voltage
Current transformer: AC current -> magnetic flux -> induced current

These are not three interchangeable implementations of the same idea. They have different physics and tradeoffs.