Arduino UNO R4, AnalogRead returns strange values

Hardware UNO R4 UNO R4 Minima
1

When I tested the following code on my Arduino Uno R4 Minima,
I cannot get 0 and 1023.
Arduino Uno R4 WiFi also showed the same thing.
When I ran the code on my Arduino Uno R3, I can get 0 and 1023,
that means no problem with my variable registor and wires.

Did I miss something?

int pin_vr = A1;

void setup() {
  pinMode(pin_vr, INPUT);
	Serial.begin(9600);
  while (!Serial) ;
}

void loop() {
	int value = analogRead(pin_vr);

	Serial.println(String(value));

	delay(100);
}

This is the resulting plot.
Minimum value is about 20, and maximum value is about 900.

Snap85
Snap851180×740 73.8 KB

2

What values do you get on the R4s if you take pin A1 directly to GND or 5V ?

3

Thank you for your comment.

When I take pin A1 directly to GND, I got 0
and directly to VCC, I got 1023.

As I said, I did exactly the same thing with Arduino Uno R3.
Same variable resistor, same wires, same breadboard, same sketch
and I got 0 and 1023.

I am trying to figure out what is the difference.
Does anyone have similar experience or can give some hints about this?

4

Try adding a 0.1uF capacitor from A1 to ground and see if that clears your readings up.

5

Thank you for your valuable comment.
I added 0.1uF capacitor from A1 to ground and I can get 0 and 1023.
Still there is a little bit fluctuation but much better than before.

When I tested some other Arduino boards with SAMD21 microcontroller
there was no problem like this.

This is the difference between SAMD21 and RA4M1 ?

I will dig out RA4M1 datasheet.
Any clues regarding the analog input characteristics of the RA4M1 would be welcome.

This is the resulting plot when I put 0.1uF capacitor.

Snap85
Snap851180×740 68.9 KB

Thank you again for you all and especially van_der_decken :slight_smile: