I have a project on the way that has a voltage range of 0-75 milli-volts. I understand there is an INTERNAL settings for 1.1 volts however I am curious if the EXTERNAL AREF can be used with a voltage of less then 1 volt? If so, what is the minimum voltage required?
Thank you.
You can use it at less than 1V but it will not be much use because the accuracy is limited by the noise and at lower reference voltages the size of a step is much smaller than the noise.
I forget the 'datasheet' answer (but it's in there) but it can't be lower then around the band-gap value of +1.1vdc or so. There are external ADC modules that have programmable gain stages that can be very useful for measuring low voltages without requiring external voltage references or signal amplifiers. The ADS1115 is one I've been working with recently, it uses a simple I2C interface to the arduino.
Lefty
Edit: Looked it up:
VREF Reference Voltage min = 1.0 max = AVCC units = V
Thank you.