Build Your Own Arduino Voltmeter Circuit and Voltage Divider Which Can Measure Voltages From 0V to 30V, Including 12V. Visit To learn More.

This project goes a little beyond simple Arduino programming though. A 12V to 5V power supply drives the device, which is laid out on a blank PCB.

Options to power the Arduino Nano include USB, VIN, and 5 volt pin, meaning you have power options for almost any situation.