detecting a switch

Using Arduino General Electronics
1

i have connected a magstrip reader to my mega2650 i can get it to read most of the time
one of the inputs it use is card detected.
in my test proram i have led 13 lighting up when the input (using pin 4) detects the card in

when a card in inserted into reader it grounds that pin

the problem is if i move my hand close to the reader it will trigger that pin 4 input.

what can i do to the connection at pin 4 to keep the interference out and ensure it only detects when the switch is pushed

thanks in advance

2

Turn on the pin4 internal pullup resistor.

pinMode (pin4, INPUT_PULLUP); // IDE 1.0.1

pinMode (pin4, INPUT);
digitalWrite (pin4, HIGH); // earlier IDEs

3

just tried that and still same issue even just touching my finger on the plastic of the connecter triggers it

4

Do you have a ground connection between the reader and the Arduino?

5

yes there is a ground going from the arduino (next to 5v pin) that goes to card reader, at the card reader that ground feeds 2 switched and a chip,

do i need a separate ground to the metal frame of the card reader as well??

6

If the metal frame isn't already connected to the card reader ground inside the card reader (which you can check with a multimeter), then try grounding the metal frame.