/*
 * ============================================================
 *  HC-SR04 Ultrasonic Distance Sensor — Sample Sketch
 *  Tishvi Electronics | guide.tishvi.com
 * ============================================================
 *  Wiring:
 *    HC-SR04 VCC  → Arduino 5V
 *    HC-SR04 GND  → Arduino GND
 *    HC-SR04 TRIG → Arduino Pin 9
 *    HC-SR04 ECHO → Arduino Pin 10
 *
 *  What this sketch does:
 *    1. Sends a 10µs ultrasonic pulse every 200 ms
 *    2. Measures how long the echo takes to return
 *    3. Converts the time to distance in centimetres
 *    4. Prints the distance to the Serial Monitor
 *    5. Prints a simple proximity alert if object < 10 cm
 *
 *  No external libraries needed — uses built-in pulseIn()
 * ============================================================
 */

// ── Pin Definitions ──────────────────────────────────────────
const int TRIG_PIN = 9;   // Trigger: Arduino → Sensor
const int ECHO_PIN = 10;  // Echo:    Sensor  → Arduino

// ── Settings ────────────────────────────────────────────────
const int   ALERT_CM    = 10;    // Distance threshold for "close" alert
const float SPEED_SOUND = 0.0343; // Speed of sound at ~20°C (cm/µs)

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.begin(9600);
  Serial.println("HC-SR04 Distance Sensor — Tishvi Sample Sketch");
  Serial.println("-------------------------------------------");
  Serial.println("Open Serial Monitor at 9600 baud to see readings.");
}

void loop() {
  // ── 1. Fire the ultrasonic pulse ───────────────────────────
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);          // 10µs HIGH pulse
  digitalWrite(TRIG_PIN, LOW);

  // ── 2. Measure the echo return time ────────────────────────
  // pulseIn() waits for the ECHO pin to go HIGH, measures how long it stays HIGH
  // Timeout = 25000µs → max measurable distance ≈ 430 cm
  long durationUs = pulseIn(ECHO_PIN, HIGH, 25000);

  // ── 3. Convert to centimetres ──────────────────────────────
  // Sound travels to object AND back, so divide by 2
  float distanceCm = (durationUs * SPEED_SOUND) / 2.0;

  // ── 4. Print result ────────────────────────────────────────
  if (durationUs == 0) {
    // Timeout: nothing detected within range
    Serial.println("Distance: OUT OF RANGE  (> 430 cm or no echo)");
  } else {
    Serial.print("Distance: ");
    Serial.print(distanceCm, 1);  // 1 decimal place
    Serial.print(" cm");

    // ── 5. Proximity alert ─────────────────────────────────
    if (distanceCm < ALERT_CM) {
      Serial.print("  ⚠ CLOSE!");
    }
    Serial.println();
  }

  delay(200);   // Wait 200 ms before next measurement
}