A ten minute look at the INA219 current sensor, hooked up to an Arduino Uno, measuring the current flow from a battery to a bulb. Part of my 18650 current monitoring project.
http://www.ti.com/lit/ds/symlink/ina219.pdf
https://cdn-learn.adafruit.com/downloads/pdf/adafruit-ina219-current-sensor-breakout.pdf