Lets say I have a 3.3V accelerometer that I have hooked up to the analog inputs. I also have it powered by the Arduino Uno board 3.3V out, and grounded to the Arduino Uno ground pins. Do I need to connect the 3.3V pin to the Aref pin? Or because my power source is the Arduino board, I don't need to use aref at all?
Is there a way to know the voltage fed to AREF inside our sketch?
When we issue the command analogReference(EXTERNAL) what is it that takes place?
But if we have to measure manually the voltage of our rail what's the use of feeding AREF pin?
WarningDon't use anything less than 0V or more than 5V for external reference voltage on the AREF pin! If you're using an external reference on the AREF pin, you must set the analog reference to EXTERNAL before calling analogRead(). Otherwise, you will short together the active reference voltage (internally generated) and the AREF pin, possibly damaging the microcontroller on your Arduino board. Alternatively, you can connect the external reference voltage to the AREF pin through a 5K resistor, allowing you to switch between external and internal reference voltages. Note that the resistor will alter the voltage that gets used as the reference because there is an internal 32K resistor on the AREF pin. The two act as a voltage divider, so, for example, 2.5V applied through the resistor will yield 2.5 * 32 / (32 + 5) = ~2.2V at the AREF pin.
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