When working with and troubleshooting electronics, you normally poke around with a voltmeter, measuring electrical potential from one point to another. You also may want to know current, which when multiplied by the voltage will give you the power that your system draws. This value is a bit more difficult to measure, but this device by Electronoobs not only measures current and voltage, but calculates the power and displays all three simultaneously.
The way this works is that by using a small resistor — .01 ohms— in series with the circuit’s load, it measures the voltage drop across it. In order to transform this tiny voltage drop into a value large enough for the Arduino Nano used here to properly sense, two operational amplifiers are used in series for an amplification factor of 121. Voltage is also obtained, and since it’s designed to work with values of up to 15V, a voltage divider is used to output a value within the proper range.
With these two values known — and a bit of calibration—the device multiplies voltage times current to obtain power in watts. As set up here, the Nano sends all three values to an I2C OLED in order to display everything without any human math involved!