int A, distance;

void setup() {

pinMode(2, OUTPUT); //trigger
pinMode(3, INPUT); //echo
pinMode(7, OUTPUT); //buzzer
pinMode(8, OUTPUT); //LED
Serial.begin(9600);
}

void loop() {
digitalWrite(2, HIGH);
delayMicroseconds(10); 
digitalWrite(2, LOW);
A=pulseIn(3, HIGH);
distance=A*0.034/2;

Serial.println(distance);

if (distance<20){
tone(7,500,500);
digitalWrite(8, HIGH);}

else {
digitalWrite(8, LOW);
digitalWrite(7, LOW);
}
}