#include <LiquidCrystal.h>
int trig_pin = A0;
int echo_pin = A1;
long echotime;
float distance;
LiquidCrystal lcd(0x27, 16, 2);
int buzzer = 13;

void setup() {
  Serial.begin(9600);
  pinMode(trig_pin, OUTPUT);
  pinMode(echo_pin, INPUT);
  digitalWrite(trig_pin, LOW);
  lcd.begin(16,2);
  pinMode(buzzer, OUTPUT);

}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(trig_pin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trig_pin, LOW);
  echotime = pulseIn(echo_pin, HIGH);
  distance = 0.0001*((float)echotime*340.0)/2.0;
  lcd.setCursor(0,0);
  lcd.print(distance);
  lcd.println(" cm");
  delay(1000);
  if (distance < 31) {
    tone (buzzer, 1000);
    delay (2000);
    noTone (buzzer);
    delay (500);
    tone (buzzer, 1000);
    delay (2000);
    noTone (buzzer);
    delay (500);}
}