Controlling LEDs with an Arduino

This post will cover the process of controlling multiple LED's using an Arduino. With this hack we'll make the Arduino, send a distress signal using a LED, a second LED is used to indicate the end of SOS cycle.

Both LED's are connected the same way except to different pins (Digital 10 and 9). +5V is connected to the resistor which is connected to the + (long leg) of the LED, - (short leg) of the LED is connected to the ground.

Any resistor that is bigger than 330 ohms can be used, but keep in mind that the smaller the resistance the bigger the glow.

First some definitions,

int redLEDPin = 10;
int yellowLEDPin = 9;

I choose to use pin 10 for the red LED, pin 9 for yellow LED.

int shortPulse = 250;
int longPulse = 125;
int letterDelay = 1000;

Morse code uses a short element and a long element to represent letters and numbers. We will use 250 ms for long element 125 ms for short element, after each letter we'll have 1 second delay.

//letters 0 for short pulse 1 for long
int letterS[] = {0, 0, 0};
int letterO[] = {1, 1, 1};

void setup(){
  pinMode(redLEDPin, OUTPUT);
  pinMode(yellowLEDPin, OUTPUT);

blinkLetter takes an array as it's argument, it will iterate over the array blink the red LED accordingly.

void redLed(int time){
    digitalWrite(redLEDPin, HIGH);
    digitalWrite(redLEDPin, LOW);

redLed function takes a time variable as its input it will keep the LED on for the given time.

void yellowLed(){
    digitalWrite(yellowLEDPin, HIGH);
    digitalWrite(yellowLEDPin, LOW);

To represent the letters, I used an array, 1 to represent a long element, 0 to represent a short element.

void blinkLetter(int* letter){
  for(int i=0; i<3; i++){
    int val = letter[i];

    if(val == 0)

yellowLed uses a fixed time to signal us that the SOS cycle is complete, we are starting over.

void loop() { 


Main loop just cycles through the letters and blink the yellow LED to signal us that the cycle is complete. When the circuit is hooked-up and code uploaded, it should look like this.