CIRC
07

What We're Doing

Up to this point we have focused entirely on outputs, time to get our Arduino to listen, watch and feel. We'll start with a simple pushbutton. Wiring up the pushbutton is simple. There is one component, the pull up resistor, that might seem out of place. This is included because an Arduino doesn't sense the same way we do (ie button pressed, button unpressed). Instead it looks at the voltage on the pin and decides whether it is HIGH or LOW. The button is set up to pull the Arduino's pin LOW when it is pressed, however, when the button is unpressed the voltage of the pin will float (causing occasional errors). To get the Arduino to reliably read the pin as HIGH when the button is unpressed, we add the pull up resistor.

(note: the first example program uses only one of the two buttons)

The Circuit

The Parts

	CIRC-07 Breadboard Sheet x1		2 Pin Header x4		Pushbutton x2		Wire
	10k Ohm Resistor Brown-Black-Black-Red x2		560 Ohm Resistor Green-Blue-Black-Black x1		Red LED x1

Code (no need to type everything in just)

File > Examples > 2.Digital > Button

(example from the great arduino.cc site, check it out for other ideas)

/*
  Button

 Turns on and off a light emitting diode(LED) connected to digital
 pin 13, when pressing a pushbutton attached to pin 2.


 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 30 Aug 2011
 by Tom Igoe

 This example code is in the public domain.

 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);
  }
}

Not Working? (3 things to try)

Making it Better?

On button off button:

The initial example may be a little underwhelming (ie. I don't really need an Arduino to do this), lets make it a little more complicated. One button will turn the LED on the other will turn the LED off. Change the code to.

int ledPin = 13; // choose the pin for the LED
int inputPin1 = 3; // button 1
int inputPin2 = 2; // button 2

void setup() {
  pinMode(ledPin, OUTPUT); // declare LED as output
  pinMode(inputPin1, INPUT); // make button 1 an input
  pinMode(inputPin2, INPUT); // make button 2 an input
}

void loop(){
  if (digitalRead(inputPin1) == LOW) {
    digitalWrite(ledPin, LOW); // turn LED OFF
  } else if (digitalRead(inputPin2) == LOW) {
    digitalWrite(ledPin, HIGH); // turn LED ON
  }
}

Upload the program to your board, and start toggling the LED on and off.

Fading up and down:

Lets use the buttons to control an analog signal. To do this you will need to change the wire connecting the LED from pin 13 to pin 9, also change this in code.
int ledPin = 13; ----> int ledPin = 9;
Next change the loop() code to read.

int value = 0;
void loop(){
  if (digitalRead(inputPin1) == LOW) { value--; }
  else if (digitalRead(inputPin2) == LOW) { value++; }
  value = constrain(value, 0, 255);
  analogWrite(ledPin, value);
  delay(10);
}

Changing Fade Speed:

If you would like the LED to fade faster or slower, there is only one line of code that needs changing;
delay(10); ----> delay(new #);
To fade faster make the number smaller, slower requires a larger number.