LiFi
Communication
System

#define LED_PIN 13
#define LDR_PIN A0

int threshold = 400;

// Average 3 LDR readings for stable bit detection
int readStableBit() {
  int sum = 0;
  for (int i = 0; i < 3; i++) {
    sum += analogRead(LDR_PIN);
    delay(5);
  }
  int avg = sum / 3;
  return (avg < threshold) ? 1 : 0;
}

void setup() {
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("LiFi System Ready");
}

void loop() {
  if (Serial.available()) {
    String input = Serial.readString();
    input.trim();
    String received = "";

    for (int i = 0; i < input.length(); i++) {
      char ch = input[i];
      char out = 0;

      // Transmit + receive each bit (LSB first)
      for (int b = 0; b < 8; b++) {
        int bit = (ch >> b) & 1;
        digitalWrite(LED_PIN, bit);
        delay(120);
        int r = readStableBit();
        out |= (r << b);
        delay(200);
      }
      received += out;
    }

    Serial.print("Output: ");
    Serial.println(received);
  }
}