#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) 

    {

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

        {

            digitalWrite(8, HIGH);

            delay(100);

            digitalWrite(8, LOW);

            delay(100);

        }

    }

    else

    {

        digitalWrite(8, LOW);

    }

    delay(250);

}