// Parking Sensor — Arduino UNO + HC-SR04 + 3 LEDs + passive buzzer
// Robot Maker Toolkit starter project. Wiring matches the app's audited
// HC-SR04 table: TRIG->D9, ECHO->D10, VCC->5V, GND->GND.

const int trigPin   = 9;
const int echoPin   = 10;
const int greenLed  = 4;   // clear (> 100 cm)
const int yellowLed = 5;   // getting close (30-100 cm)
const int redLed    = 6;   // close (< 30 cm)
const int buzzer    = 3;   // passive buzzer via tone()

const int ZONE_SAFE = 100; // cm
const int ZONE_NEAR = 30;  // cm
const int ZONE_STOP = 10;  // cm - continuous tone below this

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

float readDistanceCm() {
  digitalWrite(trigPin, LOW);  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH); delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  long duration = pulseIn(echoPin, HIGH, 30000); // 30 ms timeout (~5 m)
  if (duration == 0) return -1.0;                // no echo = out of range
  return duration * 0.0343f / 2.0f;
}

void loop() {
  float d = readDistanceCm();
  bool valid = d > 0;

  Serial.print("Distance: ");
  if (valid) { Serial.print(d); Serial.println(" cm"); }
  else       { Serial.println("out of range"); }

  digitalWrite(greenLed,  valid && d > ZONE_SAFE  ? HIGH : LOW);
  digitalWrite(yellowLed, valid && d <= ZONE_SAFE && d > ZONE_NEAR ? HIGH : LOW);
  digitalWrite(redLed,    valid && d <= ZONE_NEAR ? HIGH : LOW);

  if (!valid || d > ZONE_SAFE) {
    noTone(buzzer);                 // clear: silence
    delay(150);
  } else if (d > ZONE_STOP) {
    tone(buzzer, 2000, 60);         // beep, faster as you close in
    int gap = map((int)d, ZONE_STOP, ZONE_SAFE, 60, 400);
    delay(constrain(gap, 60, 400));
  } else {
    tone(buzzer, 2000);             // STOP: continuous tone
    delay(60);
  }
}