Digital input pin gives 5v in output

Other Hardware General Electronics
1

Hello, I am just playng with my board and I found something I just can't understand.
I have this piece of code:

void setup() {
...
pinMode(10,INPUT);
...
}
void loop(){
...
buttonStateA = digitalRead(10);
...
}

If I measure the voltage on disconnected pin 10, it is 4.85 v.
If I connect pin 10 to a pulldown resistor (100k connected to ground), the voltage on the resistor is 3.53 (not 0 v).

If I comment the digitalRead in loop() things changes:

If I measure the voltage on disconnected pin 10, it is 0 v.
If I connect pin 10 to a pulldown resistor, the voltage on the resistor is 0 v.

With pin 5 instead of pin 10, voltage on the pin is 0, either when floating pin or with pulldown resistor, even if I read its value in loop().

Can I conclude that pin 10 is not working?

Thanks!

2

Can I conclude that pin 10 is not working?

No.
Post ALL your code.
Read the rules about posting code:-
How to use this forum

Then read this:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

If I connect pin 10 to a pulldown resistor (100k connected to ground), the voltage on the resistor is 3.53 (not 0 v).

Try that again with 10K.

If I measure the voltage on disconnected pin 10, it is 0 v.

Why? Measuring the voltage on an input pin means little.

either when floating pin

Never have a floating pin it tells you nothing.

3

Thanks for your help, I have already red some articles about inputs and floating pins, but I am still confused.
I need to spend more time on this subject.

4

A multimeter on a floating pin is going to act as a pull-down resistor as they generally have
10M input impedance. If the pin is undamaged that is plenty and an input pin should read
0V, since the pin's impedance is in the 10^10 ohm range.

The pin in question is either fried or connected to some other trace on the board.

5

Instead of the hassle with external resistors you can just use the build in pull up resistors. You enable them with

pinMode(pin, INPUT_PULLUP);