Digital ports sensing high with proximity of finger?

Other Hardware General Electronics
1

Hello, I very recently got the Starter kit, and was playing around with it.
However today when I took it out something odd is going on.

I wanted to build a simple modification of the hold button on pin 2 Turn on LED on pin 13.
But I noticed it would sense the button pressed without even touching the button, basically hovering the finger in close proximity to pin 2 will make the pin go high.
I tried other pins and they are all the same, so if I say use pin 7 as a button, then moving a finger close to this pin will make it go high, I don't even have to touch anything. It's like it has become capacitive.
This happens even if I disconnect everything, and use the on-borad led for pin 13, then hovering a finger close to the pin configured will make the led come on. Even getting close to the pin's on the Atmega will make it sense the pin high.

So did something happen to the board, or what is going on?

2

However today when I took it out something odd is going on.

Uh-oh...

So did something happen to the board, or what is going on?

You've got a floating input.
Perfectly normal.

3

Doh, ok thanks. Thought I had broken something. :wink:

4

Turn on the internal pullup, problem goes away.

5

CMOS inputs are extremely sensitive as they need only a fraction of a pA (pico-amp,
a millionth of a micro-amp) to respond (at room temperature). They pick up nearby
signals and static electricity if left unconnected.

6

Yes, pretty small. I think '328P datasheet says 1uA.

7

And this is precisely why - and how - you can use them as proximity sensors, with sketches for this very purpose.

CrossRoads:
Yes, pretty small. I think '328P datasheet says 1uA.

Maximum.