Arduino Due: connect AREF pin to 5V allowed?

hello,
I'm not sure about that because the description about Arduino pins is ambiguous about that:
Is it allowed to connect the Arduino Due AREF pin to 5V ,
in order to get a 5V reference voltage level on all ADC pins A0...A11 ?

Don't do that, you will damage SAM3X chip!

From Due spec:

The Due’s analog inputs pins measure from ground to a maximum value of 3.3V. Applying more than 3.3V on the Due’s pins will damage the SAM3X chip.

3.3V is maximal value you can measure on analog inputs.

Using voltage deviders you can measure much higher voltages, here I measure up to 16.8V with Uno 5V analog input pins:

Hermann,

thank you, I feared that, but in the documentation of analogReference is written:
https://www.arduino.cc/en/Reference/AnalogReference

analogReference()
Description

Configures the reference voltage used for analog input (i.e. the value used as the top of the input range). The options are:

DEFAULT: the default analog reference of 5 volts (on 5V Arduino boards) or 3.3 volts (on 3.3V Arduino boards)
INTERNAL: an built-in reference, equal to 1.1 volts on the ATmega168 or ATmega328 and 2.56 volts on the ATmega8 (not available on the Arduino Mega)
INTERNAL1V1: a built-in 1.1V reference (Arduino Mega only)
INTERNAL2V56: a built-in 2.56V reference (Arduino Mega only)
EXTERNAL: the voltage applied to the AREF pin (0 to 5V only) is used as the reference.

note, that for EXTERNAL there is no restriction mentioned regarding Due or Zero boards!

(BTW, JFYI, I already have 1:5 voltage deviders (ready soldered on small backpanes) for my Mega board, measuring board supply voltages 0 ... 25V, but using them on my Dues would cause a upper limit drop to 16.5V which I wanted to circumvent by a 5V external analog reference on the Due board, dispensing with additional voltage deviders.

You are on very dangerous ground, the Reference documentation is for all Arduino models, perhaps its a doc bug not to mention the Arduino moduls that are not 5V there.

Anyway, even if you would connect 5V to Due AREF (which would kill that pin or not), you can never do what you want (measure from 0-5V) because of this sentence from Due spec (in bold) pointed to above:

Warning: Unlike most Arduino boards, the Arduino Due board runs at 3.3V. The maximum voltage that the I/O pins can tolerate is 3.3V. Applying voltages higher than 3.3V to any I/O pin could damage the board.

Hermann.

yes, thank you, I already understood your warning, I just wanted to explain why this 5V AREF thing is so incredibly abiguous, weird and confusing in the Arduino documentation - once they mention 3.3V boards (e.g., for

DEFAULT: the default analog reference of 5 volts (on 5V Arduino boards) or 3.3 volts (on 3.3V Arduino boards)

and other time they don't (as for EXTERNAL, see above)

and now I even read that AREF wouldn't work at all for the DUE unless one destroyed an on-board resistor before ...

hell, what a mess!

Yeah, I share your frustration, it seems "Arduino Due" is the unloved child of the Arduino family.

I have posted several times that I cannot understand that and comparing it with other Arduinos it is still by far the best Arduino model:

Frequency and RAM size only comparable microcontroller is an ESP8266 (and that is even a bit quicker in integer performance comparison of 2nd link).

But as long as Arduno Due can be bought for just 12$ and the Due forum here on arduino.cc remains active the world is in order though :wink:

Hermann.