Hello,
I want very good accuracy for my ADC measurements.
I have been wondering about the best way to configure the
ADC on my Arduino uno. I could provide a voltage regulator
calibrated to 5.0 volts so that the Aref would be accurate.
Then I thought it was too bad that I couldn't use 1.024
volts as the external Aref voltage because I read that 1.1
volts was the lower limit for that. So, I thought I might
provide a calibrated 2.048 Aref divided down from the 3.3
volt regulator. It seems that the 2 mv resolution may be
better than the 4.8+ mv the other way. What do you think?
Herb
Depends on what you're measuring.
Absolute Aref voltage is irrelevant if you're measuring a ratiometric source like a pot, or an analogue pressure sensor, or an ACS712 or other hall sensor. As long Aref comes from the same source as supply voltage of the sensor (Aduino default).
A stable/known Aref voltage is only important for "voltage output" sensors.
And then it might be better to use an external A/D with buildin reference, like the ADS1115.
Because we are in the hobby world (no mass production), absolute voltage of a reference source is irrelevant.
You can always calibrate the errors out in code.
3.3volt of an Uno/Mega (not Nano or other small boards) is stable enough to be used as reference for a 10-bit A/D.
Same for the 1.1volt Aref or 2.56volt Aref (Mega).
A lower Aref voltage will give you ofcourse finer voltage steps, but also a lower voltage range.
Leo..