#define sdReverse 5
#define trigger 2
#define echo 15
#define led 4
#define buzzer 18

bool reverseOn;

void setup() {
  Serial.begin(115200);
  pinMode(sdReverse, INPUT);
  pinMode(led, OUTPUT);
  pinMode(buzzer, OUTPUT);
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
}

void loop() {
  delay(10);

  reverseOn = digitalRead(sdReverse);

  if(reverseOn == HIGH) {
    distanceSensor();
    digitalWrite(led, HIGH);
  } else {
    digitalWrite(led, LOW);
    noTone(buzzer);
  }
}

void distanceSensor() {
  digitalWrite(trigger, HIGH);
  delay(10);
  digitalWrite(trigger, LOW);

  int duration = pulseIn(echo, HIGH);
  float cmMsec = duration / 58;
  buzzerTone(cmMsec);
}

void buzzerTone(float distance) {
  if(distance < 30 && distance > 20) {
    tone(buzzer,200);
  } else if (distance < 20 && distance > 15) {
    tone(buzzer,400);
  } else if (distance < 15 && distance > 10) {
    tone(buzzer,600);
  } else if (distance < 10 && distance > 5) {
    tone(buzzer,800);
  } else if (distance < 5) {
    tone(buzzer,1000);
  } else {
    noTone(buzzer);
  }
}