Analog Pin A0 on my Nano produces non-linear readings almost exponential ones

Hi, I have got a problem with my Arduino Nano v3. Since round about two weeks the A0 pin doesn’t produce linear readings anymore. The other pins seems to work normal.

Please have a look at the screenshot. This is the normal ReadAnalogVoltage example ( arduino.cc/en/Tutorial/ReadAnalogVoltage) with a 50K potentiometer. A1 (red line) raise and falls linear when turning the knob. But the A0 line (blue) does not.

So I counterchecked the voltage with a multimeter. When the knob is positioned round about to the middle I got a 2.35V reading at A1 pin. That’s fine. But if I plug in the cable on the breadboard into to A0 row, the voltage falls down to 0.15V. :confused: There is nothing else plugged in here. Just the pure Arduino Tutorial Example.

It is not related to this specific setup. But a general problem of my Arduino Nano. I made a pcb board which utilize A0 with a sound sensor for clap detection. It didn’t work anymore, that was how I stumbled upon this problem.

The Arduino itself looks quite normal. Do you have an idea what happened to it and how to fix it back to the normal behavior?

Thanks

ArduinoAnalogVoltageBoard.jpg

Hi,
You probably have damaged the internal circuit, maybe to much drain current.
Test the blink sketch on pin A0 and see if it can blink the LED.

But if I plug in the cable on the breadboard into to A0 row, the voltage falls down to 0.15V.

That's a clue there is a low impedance on the pin, double check it with a multimeter.The pin should be high impedance.
Post the result

a) The Blink example works fine on both pins.

b) I measured the voltage again with a multimeter. As you can see, the knob has not been moved. A1 = 0.8V vs. A0 = 0,04V.