#include <SR04.h>

#define TRIG_PIN 12

#define ECHO_PIN 11

SR04 sr04 = SR04(ECHO_PIN, TRIG_PIN);

int a;

void setup() {

    Serial.begin(9600);

    delay(1000);

    pinMode(8, OUTPUT);

}

void loop() {

    a = sr04.Distance();

    if (a < 12) //Checks if object is less than 12cm

    {

        for(int i = 0; i<3; i++) 

        {

            digitalWrite(8, HIGH); //Turns buzzer on

            digitalWrite(4, HIGH); //Turns red light on

            delay(100);

            digitalWrite(8, LOW); //Turns buzzer on

            digitalWrite(4, LOW); //Turns red light off

            delay(100);

        }

    }

    if (a > 12 && a < 24) //Checks if object is between 12cm and 24cm

    {

        digitalWrite(4, LOW); //Turns red light off

        digitalWrite(7, LOW); //Turns green light off

        digitalWrite(9, HIGH); //Turns yellow light on

    }

    if (a > 24)  //Checks if object is greater than 24cm

    {

        digitalWrite(4, LOW); //Turns red light off

        digitalWrite(7, LOW); //Turns yellow light off

        digitalWrite(9, HIGH); //Turns green light on

    }

    delay(250);

}