Motivation

Imagine a situation where the Flash floods swept through your hometown, and your house was surrounded by the water, What to do?

What might be a easy way to send a helping message? ==> S.O.S

But, next question is how you want to send it?

• Write a message in your house? –> What about the hylicoptor flighting at night?
• Using flashlight as indicator? –> Cool, but are you gonna standing at your house and doing this whole day?

Now, let me show you a good idea to achieve this with an Arduino board, a couple of LED lights, some resistors, and some wires. After finish this lab, you will be able to implement this on your own less than an hour!

Idea:

Encode the S.O.S message as Morse code, and repeatefly flash the LED at specific frequency!

Specifically, Here is the Morse code translation:

• S –> “…” –> 2 milisecond flash
• O –> “- - -“ –> 5 milisecond flash

In this example, I used 2 milisecond flash to represent “.”, and 5 milisecond flash to represent “-“. Then, you just throw this into a loop, Power up the kits, Open a favorite TV channel, and Waiting for the help!

Lab Setup:

Supplies:

• Switch
• 3 LED light
• 3 220-ohm Resistors

• 1 10-kilohm Resistor

  DESIGN THE CIRCUIT:

Circuit Diagrams and Schematic Diagrams:

The actually setup:

THE CODE:

pinMode(pin, state);

You use function pinMode() whenever you have a wire connected to the Arduino board, and you want to specify whether you want to use it as input or output. For example: pinMode(3, OUTPUT) says “set pin3 as output”.

digitalRead(pin);

digitalWrite(pin, state);

Telling Arduino which pin you want to turn on/off? Ex. digitalWrite(3, HIGH), says “turn on the the LED connected at pin3”.

Here are the entire code that I used:

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/**
 * Project Name: Arduino Projects Book - Project 02: SOS -- Morse Code Emergence Distress Singal
 * File Name: Project2_SOS_LED_version.ino
 * Description: 
 * Author: Zhengqi Dong
 * Created:
 * Updated:
 */
 #define ledPin 4

int duration[] = {200, 200, 200, 500, 500, 500, 200, 200, 200};
int swtichState = 0;
void setup() {
  pinMode(2, INPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
}

/* Function: blink the red LED when button is pressed. */
void loop() {
  swtichState = digitalRead(2);
  if(swtichState == LOW){
    digitalWrite(3, HIGH);  //green LED
    digitalWrite(4, LOW);   //red LED
    digitalWrite(5, LOW);   //red LED
  }else{ //button is pressed
    digitalWrite(3, LOW);
    int i;
    for(i =0; i<9; i++){
      flash(duration[i]);
    }
    delay(1000);
    digitalWrite(4, HIGH);
    digitalWrite(5, LOW);
    delay(250);   //pause for 2.5 ms
    digitalWrite(4, LOW);
    digitalWrite(5, HIGH);
    delay(250);
  }
}

void flash(int delayPeriod){
  digitalWrite(ledPin, HIGH);
  delay(delayPeriod);
  digitalWrite(ledPin, LOW);
  delay(delayPeriod);
}

Video Showcase

Bonus: Resistor color code cheetsheet

Reference:

Fitzgerald, S., & Shiloh, M. Arduino Projects Book. Arduino AG, 2017