voltage reference cal.

Projects Programming
3

Two ways to solve that problem.

  1. Change Aref from default to one of the internal reference voltages (1.1volt or 2.56volt).
    And drop the "voltage to measure" with a voltage divider to that range.
    This is the easiest way, and only needs one line of code in setup().

  2. Measure VCC internally, and use that value in your code.
    Google "Arduino secret voltmeter" for instructions.

Note that only voltages, or sensors with a voltage output need the above.
Many sensors are ratiometric (pot, thermistor, ACS712 etc.), and give worse results with a stable reference.
Leo..