![]() ![]() Simply, it’s good for exact measurements of external voltages. But the internal 1.1V reference is more stable and hardly depends on the supply voltage or temperature (thus absolute measurements can be made). The default reference voltage AVcc is only useful when measuring voltages that are directly dependent on the supply voltage. ![]() Now note that since the measurements of the input voltages are made relative to the reference voltage, fluctuations of the reference voltage will influence the result! External AREF ![]() The analog reference voltage can be set with the function “ analogReference()“. The voltages are always measured relative to the ground (GND). The Arduino has three reference voltage options: AVcc (default reference voltage) which is connected to the digital 5V rail, the internal 1.1V and the option to use an external voltage reference. In the ATMEGA328 at the core of the Arduino Uno, this reference voltage is also the maximum voltage that can be measured. To measure an analog signal there has to be a voltage level to compare it with. John Errington’s page has lots more very useful information. When it comes to converting a measurement from a number to a voltage, we need to multiply the reading by the size of step. Using default settings, a return value of 0 would represent approximately 0V, and a return value of 1023 would represent approximately 5V. This results in a number in the range 0-1023. The basic usage is very simple → int value = analogRead (A0) // Read A0 Usually, the selection of the analog input is done by “ analogPin = n ” where n is the analog pin number. As you already might have noticed, the Arduino Uno has six analog input (ANALOG IN) pins. An Arduino has a number of analog inputs, which enables us to measure analog parameters like a voltage, current, resistance, temperature, light and so on. ![]()
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