#define PIN_LED 2
#define PIN_ECHO 13
#define PIN_ALARM 10
#define PIN_TRIGGER 12
#define FREQUENCY 988

unsigned long duration = 0;
double distance = 0.0;

void setup() {
  // put your setup code here, to run once:
  pinMode(PIN_LED, OUTPUT);
  pinMode(PIN_ECHO, INPUT);
  pinMode(PIN_TRIGGER, OUTPUT);
  pinMode(PIN_ALARM, OUTPUT);
}


void loop() {
  // put your main code here, to run repeatedly:

  digitalWrite(PIN_TRIGGER, LOW);
  delayMicroseconds(2);
  digitalWrite(PIN_TRIGGER, HIGH);
  delayMicroseconds(10);
  digitalWrite(PIN_TRIGGER, LOW);
  delayMicroseconds(2);

  duration = pulseIn(PIN_ECHO, HIGH);
  distance = ( duration / 2 ) * 0.0343;


  if (distance < 200) {
    digitalWrite(PIN_LED, HIGH);
    tone(PIN_ALARM, FREQUENCY);
    delay(100);
    digitalWrite(PIN_LED, LOW);
    noTone(PIN_ALARM);
    delay(100);
  } else {
    digitalWrite(PIN_LED, LOW);
    noTone(PIN_ALARM);
  }
}