Wasn't able to find following values needed to properly add Nano Matter to an analog circuit using analog Read&Write:
Internal Reference voltage. Is it stable ?
Maximum AREF pin voltage
Input Impedance of AREF pin (someone suggested 32k)
Maximum Analog Input Voltage
Analog Input Impedance
Maximum Digital Input Voltage
PWM Output Voltage. 3.3?, 5.0? Is it stable ?
PWM Output Impedance
These values really should be included in the Product Specification. 5V mentioned in various posts, but I am not confident that 5V applies to Nano Matter with a 3.3V microprocessor. Would love to use external AREF = 4.096 and don't want to load up with unneeded voltage follower OpAmps.
Internal Reference voltage. Is it stable ? - How stable do you want it to be?
Maximum AREF pin voltage 3.3V
Maximum Analog Input Voltage 3.3V
Analog Input Impedance in the order of 10MΩ but that is not important because you never use it in this mode, It is recommended to use a 10 to100 MΩ Maximum Digital Input impedance.
PWM Output Voltage. 3.3?, 5.0? Is it stable ? it is 3.3V yes it is stable
PWM Output Impedance - What do you mean by that?
Is the internal reference voltage 3.3 ?
To rephrase my question: Is internal reference V stable enough to make 12 bit precision ADC meaningful ? Or is 10 bits precision (or lower) more realistic ? My alternative is to connect a precision voltage source, for example, LM4040CIZ-2.5, to AREF. Might that be an improvement over the internal reference source ?
If I supply AREF = 2.50 and analog input goes to 3.1, will the Nano be damaged ? (I will have a 3.00V +/-2% Zener protecting the input.)
Somewhere I read that analog input impedance temporarily drops when taking an analog reading. If true, how low would it go ?
My concern regading PWM output impedance is whether-or-not I should add a Voltage Follower between Nano PWM and an active filter which turns PWM into DC voltage.
Again, all this information should be included in Product Specifications, because answers specific to one Arduino product cannot safely be applied to others. Just a half-page Table of Absolute and Recommended Maximum Values as in Product Specifications for every analog IC. I did look where you directed me with no success. Remarkably, not even the microprocessor manufacturer's reference manual specifies maximum permissible voltages or impedances.
No. The default reference is 3.3V which is derived from the regulated 5V supplied from the USB connection. It is as stable, and accurate as the regulator from 5V to 3.3V (or as we call it 3V3).
Note this is the data sheet of the processor used in the Arduino product not the Arduino itself. From that data sheet I can't see any mention of internal reference sources, so In have to conclude it doesn't have any. However, you can feed in a lower stabilised AREF, and then it will use that. Providing your code switches to use an external reference voltage before you use it. If you don't do that then you will damage your Nano. This applies to any Arduino not just this one.
Also the data sheet for the processor says it is good enough as a 12bit A/D.
I hope that includes a resistor as well to drop the excess voltage across and not just the diode.
That is an odd way of putting it, but I suppose you could consider it somewhat true, because when you take a reading the input is connected to the internal sample and hold circuit. This lasts as long as it takes to charge up the sample and hold capacitor. Which in turn depends on the impedance which you present to the analogue input. I am not at all convinced that this is a problem, or any sort of concern. Suppose you want to measure the value of a pot, with the outer connections to ground and power and the wiper to the analogue input. You would use something like a 10 to 30KΩ pot, so that is the impedance you are presenting to the A/D input. You can't do things like measure a 1MΩ resistor with any internal A/D on a processor, there would be too much noise.
With a 50mA absolute maximum you could use a passive filter if you want. It all depends on what speed you have set the PWM and how smooth you want the resulting DC voltage.
Note that good practice dictates never run things at the absolute maximum, I would not connect this to a circuit drawing anything over 30mA.
