// --- Bio-Avatar: Automation & Homeostasis ---
// Project: Mission to Mars - Technology Class

const int trigPin = 5;    // Pin for Trigger
const int echoPin = 18;   // Pin for Echo
const int ledPin = 2;     // Built-in LED for status

void setup() {
  Serial.begin(115200);   // Communication at 115200 baud
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin, OUTPUT);
  Serial.println("--- System Online: Awaiting Data ---");
}

void loop() {
  // 1. Generate the ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // 2. Capture the Raw Data (Time in microseconds)
  long rawData = pulseIn(echoPin, HIGH);

  // 3. THE CALIBRATION LINE (The Magic Formula)
  // This translates the "Raw Data" into "Real Distance"
  float distanceCM = 0.0172 * rawData; 

  // 4. Automation Logic (Homeostasis)
  Serial.print("Distance: ");
  Serial.print(distanceCM);
  Serial.println(" cm");

  // Efficiency Rule: Save energy if no obstacle is close
  if (distanceCM < 20) {
    digitalWrite(ledPin, HIGH); // Alert active
    Serial.println("STATUS: Object nearby - System Alert!");
  } else {
    digitalWrite(ledPin, LOW);  // Power Saving Mode
    Serial.println("STATUS: Safe - Conserving Resources.");
  }

  delay(500); // 0.5 second interval for continuous monitoring
}