LaserComm

LaserComm is a communication device that uses Huffman encoding to transmit a message of 0s and 1s over a laser.

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Step 1: Step 1: Coding Your Message

First of all, you need to choose and code a message to send over the laser. Watch this video on Huffman coding to learn how to condense your message into 0s and 1s.(https://www.youtube.com/watch?v=ZdooBTdW5bM)The advantage of Huffman coding is that the most commonly used characters use less bits(1s and 0s). Just remember to include spaces! The receiving end will get 1s and 0s, they will have to be decoded by hand with a key. The key will look something like E5R3G2H1K1_1, this gives the character and the number of times said character appears in the message. If you create a tree based on this type of key, there is only one way to decode the messgae of 1s and 0s.

Step 2: Step 2: Gather Supplies and Tools

To make this project you will need these supplies:

  • 2 Arduino Uno micro controller boards
  • 2 breadboards
  • 2 tripods (one should swivel)
  • 1 laser
  • 1 ping-pong ball
  • 1 photo resistor(light sensor)
  • 1 10KΩ resistor
  • 1 330Ω resistor
  • 1 transistor
  • Wires (plenty of them)
  • Pieces of ribbon cable
  • USB cable for Arduino

Now for the tools:

  • Hot glue gun
  • Soldering iron and wire
  • Wire snips

Step 3: Build Transmitting End

Solder some ribbon cable to the positive and negative terminals of the laser. Then hot glue the laser to the swiveling tripod. Attach the laser to your breadboard along with everything else in this diagram that I made. You should try it first without the transistor so you don't burn out your laser.(By the way, the resistor is a 330Ω)

Step 4: Step 4: Build Receiving End

Solder the photoresistor to some ribbon cable. This will make it easier to organize your wires. Use the diagram shown to organize the pin out of your circuit. I hot glued a ping pong ball to the photoresistor in order to disperse the light enough for the sensor to read and to make the target for the laser bigger. Glue the ping pong ball to the tripod, and you are set up. This end will be the end that attaches to a computer to gather readings from the serial ports on the Arduino.

Step 5: Step 5: Upload Code on Arduino IDE

If you do not already have the Arduino software go to http://arduino.cc to download it.

Code for transmitter:

// LaserComm
// Laser Communication Device // Corbin Newhard

int laserPin = 13;

String message = "HELLO WORLD";

byte l[] = {0, 0};

byte o[] = {0, 1, 0};

byte h[] = {0, 1, 1, 0};

byte e[] = {0, 1, 1, 1};

byte w[] = {1, 0, 0};

byte r[] = {1, 0, 1};

byte d[] = {1, 1, 0};

byte space[] = {1, 1, 1};

void setup(){

Serial.begin(9600);

pinMode(laserPin, OUTPUT); }

void loop(){

for (int i = 0; i < message.length(); i++){

Serial.print(message[i]);

sendCode(message[i]);

Serial.println(); }

delay(5000); }

void sendCode(char x){

switch(x){

case 'L' : for (int i = 0; i < sizeof(l); i++){ if (l[i] == 0){dot();} else{dash();} } break;

case 'O' : for (int i = 0; i < sizeof(o); i++){ if (o[i] == 0){dot();} else{dash();} } break;

case 'H' : for (int i = 0; i < sizeof(h); i++){ if (h[i] == 0){dot();} else{dash();} } break;

case 'E' : for (int i = 0; i < sizeof(e); i++){ if (e[i] == 0){dot();} else{dash();} } break;

case 'W' : for (int i = 0; i < sizeof(w); i++){ if (w[i] == 0){dot();} else{dash();} } break;

case 'R' : for (int i = 0; i < sizeof(r); i++){ if (r[i] == 0){dot();} else{dash();} } break;

case 'D' : for (int i = 0; i < sizeof(d); i++){ if (d[i] == 0){dot();} else{dash();} } break;

case ' ' : for (int i = 0; i < sizeof(space); i++){ if (space[i] == 0){dot();} else{dash();} } break; }

}

void dash()

{ Serial.print("-"); digitalWrite(laserPin, HIGH); delay(600);

digitalWrite(laserPin, LOW);

delay(100);

}

void dot()

{ Serial.print("."); digitalWrite(laserPin, HIGH); delay(200);

digitalWrite(laserPin, LOW);

delay(100);

}

(Replace and add your own letters and message)

Code for receiver:

const int sensorpin = 0;
boolean isStarted = false;

long lastTime = 0;

long duration = 0;

long darkTime = 0;

long darkDuration;

int threshold = 600;

long highPulse = 75;

long lowPulse = 10;

void setup() {

Serial.begin(9600);

}

void loop() {

float light;

light = analogRead (sensorpin);

//Serial.println(light);

if (light < threshold && !isStarted) {

isStarted = true;

lastTime = millis();

darkDuration = millis() - darkTime;

if (darkDuration > 600) {

Serial.println ();

}

}

if (light >= threshold && isStarted) {

isStarted = false;

duration = millis() - lastTime;

darkTime = millis();

if (duration > highPulse) {

Serial.print ("1");

}

if (duration > lowPulse && duration <= highPulse) {

Serial.print ("0");

}

} }

Step 6: Testing

Set your two stations a few hundred yards from each other. Position the laser so that it visibly lights up the ping pong ball. once you see this, check the computer on the receiving end to see the ones and zeroes being displayed in the serial monitor. from there you can decode and read your message. Good luck and happy hacking!!!

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