#include <Servo.h>

float duration_us,distance_cm ;

const int SERVO_PIN = 9;
Servo servo; 

const int TRIG_PIN  = 6;  //ultrasonic
const int ECHO_PIN  = 7;  

void setup() {
  Serial.begin (9600);       
  pinMode(TRIG_PIN, OUTPUT); 
  pinMode(ECHO_PIN, INPUT); 
  servo.attach(SERVO_PIN);   
  servo.write(0);

}

void loop() {
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  duration_us = pulseIn(ECHO_PIN, HIGH);
  distance_cm = 0.017 * duration_us;

 if(distance_cm <= 100 && distance_cm >= 80 ){
  servo.write(90);
 
}
 else{
  servo.write(0);
 }

delay(250);
  

}