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

They're 12v so the arduino powers one lead at 5v for the signal, the ground is shared between the 5v and 12v, and finally the LED's are driven by a 12v source separate from the arduino (12v x 2a ...

The LTM8065 is a power module step-down regulator with up to 40V input voltage, which can safely operate from unregulated or fluctuating 12V to 36V input supplies in noisy environments.