• Blink two LEDs simultaneously - Test your skills: Now try to figure out how to blink two LEDs alternately.

Connect a jumper from digital GROUND to your breadboard. 

/*

 * Blink

 *

 * The basic Arduino example.  Turns on an LED on for one second,

 * then off for one second, and so on...  We use pin 13 because,

 * depending on your Arduino board, it has either a built-in LED

 * or a built-in resistor so that you need only an LED.

 *

 * http://www.arduino.cc/en/Tutorial/Blink

 */

int ledPinB = 12;                // LED connected to digital pin 12

int ledPin = 13;                // LED connected to digital pin 13

void setup()                    // run once, when the sketch starts

{

  pinMode(ledPin, OUTPUT);      // sets the digital pin as output

  pinMode(ledPinB, OUTPUT);      // sets the digital pin as output

}

void loop()                     // run over and over again

{

  digitalWrite(ledPin, HIGH);   // sets the LED on

  digitalWrite(ledPinB, HIGH);   // sets the LED on

  delay(1000);                  // waits for a second

  digitalWrite(ledPin, LOW);    // sets the LED off

  digitalWrite(ledPinB, LOW);    // sets the LED off

  delay(1000);                  // waits for a second

} 

Blink an LED without delay

Delay causes everything in the program to pause. If you have a program in which several operations are being performed you should avoid using delay, unless you want this effect. This program also makes use of the serial port feature of the Arduino programming environment. Once the program is running, try clicking on the SERIAL MONITOR icon (next to the UPLOAD button). If the program is running correctly, you will see the word "blink" printed at the bottom of your sketch each time the LED blinks.

int ledPin = 13; // choose the pin for the LED

int inPot = 2;   // choose the input pin (for a pushbutton)

int potval = 0;     // variable for reading the pin status

unsigned long ledCounter = 0; // a special int variable for really big numbers

int toggle = 0; // this will be either 1 or 0 and contolls the light turning on or off

void setup() {

  pinMode(ledPin, OUTPUT);  // declare LED as output

  Serial.begin(9600);

}

void loop(){

  /*

   inPot = analogRead(inPot);  // read input value

   Serial.println(inPot);

   */

  ledCounter ++; // adds 1 to our variable

  if (ledCounter == 300000) { // if it equals 300000

    ledCounter = 0; // reset counter

    Serial.println("blink"); //prints the word bilnk in the Serial monitor

    if (toggle == 0){ // check out light switch variable

      digitalWrite(ledPin, HIGH); // turns light on

      toggle = 1; // changes the switch for next time through

    }

    else if (toggle == 1){ // if toggle is 1 and not 0 then ...

      digitalWrite(ledPin, LOW); // turns light on

      toggle = 0; // changes the switch for next time through

    }

  }

}