Button: Normally Open vs. Normally Closed

The button I had purchased has two wiring options: Normally Open and Normally Closed (NO and NC). The following video demonstrates the results of each wiring scenario.

With NO, the circuit is open by default. When the button is fully depressed and held, the circuit is closed and the light will come on. With NC, the opposite is true. The light is always on, and only turns off when the button is fully depressed.

The code from this sketch is a sample code that came bundled with the Arduino IDE. You can find the code at the end of this post.

Circuit Design:

An LED is connected to the digital 13 pin  and ground. The button is connected to the digital 2 pin and ground via a 10k amp resistor.

Here is a picture:

Here is the code:

/*

Button

Turns on and off a light emitting diode(LED) connected to digital

pin 13, when pressing a pushbutton attached to pin 7.

The circuit:

* LED attached from pin 13 to ground

* pushbutton attached to pin 2 from +5V

* 10K resistor attached to pin 2 from ground

* Note: on most Arduinos there is already an LED on the board

attached to pin 13.

created 2005

by DojoDave <http://www.0j0.org>

modified 17 Jun 2009

by Tom Igoe

http://www.arduino.cc/en/Tutorial/Button

*/

// constants won't change. They're used here to

// set pin numbers:

const int buttonPin = 2;     // the number of the pushbutton pin

const int ledPin =  13;      // the number of the LED pin

// variables will change:

int buttonState = 0;         // variable for reading the pushbutton status

void setup() {

// initialize the LED pin as an output:

pinMode(ledPin, OUTPUT);

// initialize the pushbutton pin as an input:

pinMode(buttonPin, INPUT);

}

void loop(){

// read the state of the pushbutton value:

buttonState = digitalRead(buttonPin);

// check if the pushbutton is pressed.

// if it is, the buttonState is HIGH:

if (buttonState == HIGH) {

// turn LED on:

digitalWrite(ledPin, HIGH);

}

else {

// turn LED off:

digitalWrite(ledPin, LOW);

}

}

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