float duration_us, distance_cm;
void setup() {
  Serial.begin (9600);       
  pinMode(7, OUTPUT); // set trig pin to output mode
  pinMode(8, INPUT);  // set echo pin to input mode
  pinMode(2, OUTPUT); // LED
  pinMode(3, OUTPUT); // BUZZER
}
void loop() {
  digitalWrite(7, LOW);
  delayMicroseconds(10);
  digitalWrite(7, HIGH);
  delayMicroseconds(10);
  digitalWrite(7, LOW);
  duration_us = pulseIn(8, HIGH);
 distance_cm
		= duration_us * 0.0344 / 2;
  Serial.print("distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");
  delay(500);

  if(distance_cm<10){
    digitalWrite(2, HIGH);
    delay(1000);
    digitalWrite(2, LOW);
    delay(1000);
    analogWrite(3, 200);
  }

  else{
    digitalWrite(3, LOW);
    digitalWrite(2, LOW);
  }
} 
// sound speed in air =0.0344

//ULTRASONIC SENSOR - DETECTS DISTANCE OF ANY OBJECT
//VCC - EITHER 5V OR 3.3V
//GND - GROUND PIN (ANY)
//TRIG - ANY DIGITAL PINS (OUTPUT TYPE PINMODE)
//ECHO - ANY DIGITAL PINS (INPUT TYPE PINMODE)