#include <Servo.h>
#define trig 8
#define echo 7
long pul_echo;
float dis;
int flag = 1;
int sw = 5;
Servo servo1;
unsigned int val;
void setup()
{
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);
  servo1.attach(9, 500, 2500); 
  pinMode(sw, INPUT_PULLUP);
  Serial.begin(9600);
}
void loop(){
  if(digitalRead(sw)==0&&flag== 1){
    while(digitalRead(sw)==0);
    flag = 0;

  }
  if(digitalRead(sw)==0&&flag == 3){
    while(digitalRead(sw)==0);
    flag = 1;
  }
 
  if(flag==0){
    servo1.write(45);
    delay(2000);
    servo1.write(0);
    delay(500);
    flag=3;
    }
   Serial.println(flag);
  if(flag==1){
    digitalWrite(trig,0);
  delay(10);
  digitalWrite(trig,1);
  delayMicroseconds(10);
  digitalWrite(trig,0);
  pul_echo = pulseIn(echo,1);
  dis = (pul_echo/2.0)/29.0;
  if(dis<50){
      servo1.write(45);
    }
    else if(dis>50){
      servo1.write(0);
  }
  }
  
}