/*
 * UltrasonicRead.ino
 * XIAO ESP32-C3 on HelloWorld board (Week 8)
 *
 * HC-SR04 ultrasonic distance sensor:
 *   Trig -> D1, Echo -> D2
 *   VCC -> 5V, GND -> GND
 *
 * Sends a 10 µs trigger pulse, measures echo pulse width,
 * and prints distance in cm over USB serial.
 */

const int trigPin = D1;
const int echoPin = D2;

const unsigned long PULSE_TIMEOUT_US = 30000;  // ~5 m max range
const int SAMPLES = 5;

float readDistanceCm() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  unsigned long duration = pulseIn(echoPin, HIGH, PULSE_TIMEOUT_US);
  if (duration == 0) {
    return -1.0;
  }
  return duration * 0.034 / 2.0;  // round-trip time -> one-way distance (cm)
}

void setup() {
  Serial.begin(115200);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  float sum = 0;
  int valid = 0;

  for (int i = 0; i < SAMPLES; i++) {
    float d = readDistanceCm();
    if (d > 0) {
      sum += d;
      valid++;
    }
    delay(10);
  }

  if (valid == 0) {
    Serial.println("Out of range");
  } else {
    float avg = sum / valid;
    Serial.print("Distance: ");
    Serial.print(avg, 1);
    Serial.println(" cm");
  }

  delay(200);
}