Is there a limit to the voltage I can supply to AREF? It looks like the two builtin values I can use are 5V and 1.1V, but it's unclear to me whether that means "you can use any value between 1.1V and 5V" or "you can use any reasonable value, just don't try to run 120VAC into AREF". I'm trying to connect a scanner CCD and the datasheet says it outputs up to 12V.
Maximum is the voltage supplied to the processor, 5v effectively.
I’ve same question of what is maximum voltage applied to ADC0, ADC1,… Of course, going beyond Vref will saturate the 12bit word but my question is about far we can saturate & not destroy any ADC electronics
That's effectively what I was asking. 5.1V probably won't hurt anything but 12V is a bad idea. I suppose I'll start making some voltage dividers...
Of course, going beyond Vref will saturate the 12bit word
sp. “10 bit”
Again: I've same question of what is maximum voltage applied to ADC0, ADC1,... Of course, going beyond Vref will saturate the 10bit word but my question is about far we can saturate & not destroy any ADC electronics. I ask this question to see if i need design an isolated-amplifier in order to measure voltage that can sometimes have peak beyond Vref !
It's my understanding that 5vdc is the max voltage that can be safely applied to any pin on the Arduino - that includes the Aref pin or any of the other ADC pins.
My understanding is use of Aref pin allows 3 vdc, or 2 vdc to use the full 1023 bits rather than having to range them over the 5 vdc reference.
5vdc max anyway is a good rule. You might get away with 5.1vdc, 5vdc is a good round number.
Also, be sure to realize that you can at NO TIME source over 40 mA of current to any of the pins. Based on this, Ohm's law tells us that you must have at least 125 Ohms of resistance between an output and Ground or another pin.
That being said, it's important to remember that 40mA is the threshold at which damage will start being done, so it's best to keep it at about 25mA or below.