That reference is by default the supply voltage line for the chip. This should be 5V but will only be as accurate as the regulator supplying it.

The analog sensor on the Arduino board senses the voltage on the analog pin and converts it into a digital format that can be processed by the microcontroller. Here, we are feeding the input voltage ...

Little Bird Electronics posted an article about using an analog voltage reference with Arduino. This is a tool available when using an analog-to-digital converter. By setting up either an internal … ...