Non-linearity on analog inputs (UNO R3)

Projects General Guidance
1

Config : UNO R3 + a 10k potentiometer connected to UN0 pins (+5V, GND), and cursor to pin A03.
Program is the one we find in all tutorials (analog read).

The problem is the following :

  • cursor set in the middle of its range. If not connected I have 2.5V, this is ok
  • if I connect cursor to A03, then I have only 0.1V or less, whereas I should have 2.5V and a value around 500.
  • if I connect curost to min, I get a value 0. If I connect cursor to max I get a value of 1023. This is ok.
  • the problem is I can not get values above 500, the value drops immediately from 1000 to 120, typically.
  • it's the same situation with a 100k potentiometer.

Is it a problem with the impedance of A03 input ? what is its value ? (I've not found it in documentation)

2

The voltages are measured with a multimeter?

The Arduino inputs are very-high impedance so the voltage on the potentiometer's wiper shouldn't change when connected to an Arduino input. (Assuming the Arduino is powered-up.)

If everything is wired correctly and the voltage changes when connected, your Arduino may be damaged.

Have you tried a different analog input?

3

What is a cursor in this context?

Normally a cursor is a mark on a display where writing is about to appear, but this is a point, not something you can attach to a pin.

4

ooops, you're right: I changed from A03 to A04 input and now it works :when the cursor is in the middle position I can read a value of ~500 and voltmeter shows ~2.5V (I do the measures with a voltmeter)
Are analog inputs so fragile ? whaouh ...
Pfff .. I should not say that I'm an engineer ... ok ,we learn every day ...
Thank you guys !

5

what I call cursor is the middle position of the potentiometer (sorry, I'm french ...)

6

Thanks for the translation.

This implies that the A3 input pin is damaged, or somehow set to be an output with a logic zero on it.

Have you tried another pin for this extra input?

7

It could be damaged by over-voltage or static discharge (which is also excess voltage). But in most cases when a chip gets damaged the whole chip gets killed.

8

In my experience a pin can easily become damaged leaving the rest of the chip still working.

9

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