I2C
https://github.com/adafruit/Adafruit_INA219
http://henrysbench.capnfatz.com/henrys-bench/arduino-current-measurements/ina219-arduino-current-sensor-voltmeter-tutorial-quick-start/
https://learn.adafruit.com/adafruit-ina219-current-sensor-breakout
2 €
Aliexpress