Protoshield's pushbutton usage

[EDevil]

Hello.

I'm new at this arduino business so please bear with me. I built the protoshield but for the life of me can't seem to figure out how to use the S1 button included in the protoshield.

In this image the S1 button is connected to an digital input/output of the arduino. According to the schematics S1 is connected to the ground. So when the button is pressed I read GND, when it's not the value is seems to vary.

I'm trying to use the button to light up a led but the normal circuits I find in the net are not like this. Can anybody shed some light on this?

Thanks.

[adafruit]

you need a pullup resistor
http://www.ladyada.net/learn/arduino/

[EDevil]

I've read the tutorial, but none of the examples use the builtin button in the protoshield. I understand those circuits with 5V and resistors but the image show a direct wire from the button to an arduino input.

I don't undetstand what we're supposed to read from that, GND or undefined if the button in not pressed...

[unwiredben]

You need to take a 10K resistor and connect it from the digital input pin to +5V. You also connect that input pin to the button. This causes the input voltage to be pulled to 5V when the button isn't pressed, but the resistance is high enough so the ground can assert itself nicely when the button is pressed.

You can also use the internal pull up resistors built into the AVR chip -- see the explanation at http://www.arduino.cc/en/Tutorial/DigitalPins. This is easier and doesn't require extra components.

[EDevil]

Thanks a lot!

The idea of sticking two wires on the same arduino input didn't seem "right" but now it makes sense.

Thanks for the software resistors tip as well.