In many threads I’ve read warnings about resistors, the AREF pin input resistance, and the possibility that the reference voltage may be affected.
I’ve found a mention of the reference input resistance in the ATmega328 datasheet:
And here is a diagram of the ADC:
Now my question is : where do I picture that 32kOhm resistor? Hard to mitigate it if I don’t know that.
And the next question: how accurate is that value?
Good question.
I would assume to ground, but the analog input resistance is NOT referenced to anything in particular...
What happens when you leave it floating? If the reference goes to zero, it's being pulled down, etc.
Typically, you'd use a regulated/controlled voltage source capable of a few milliamps or more and it wouldn't be an issue.
And, you can always measure the actual in-circuit voltage and use that in your software.
The 32kΩ is between AREF and GND. I have measured it in the past and I think it was pretty accurate. It can be used to create a voltage divider when a voltage with a resistor is applied to AREF.
You have to tune the code for the circuit anyway. Even if you use 1% external resistors, then some tuning is needed, especially when averaging/oversampling is used.
Clear and to-the-point.
Thank you.
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