Connect voltage supply

I want my Arduino UNO to detect the voltage and print out its value. Where should i connect the ends of the wire (belonging to a simple electric circuit) to supply a test voltage to the Arduino board?

Hi, you should connect one of the wire's 2 conductors to one of the Arduino's analog inputs, like A0, and the other to ground (GND). But you must ensure that the voltage will not exceed 5V, otherwise the Arduino will be damaged.

What is this simple circuit?

Do you have a multimeter? Start by using that to see what voltage is present. Use a high range setting to begin.


If you are using a computer attached to your Arduino you must have the ground of the external voltage at the same level as the ground on your external circuit or your external circuit must be floating with respect to the computer's ground.

Thanks! That helped.