const int trigPin = 7;
const int echoPin = 4;
int buzz = 10;
long duration;
int distance;
void setup() {
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(13, OUTPUT);
pinMode(2, OUTPUT);
Serial.begin(9600);
}
 void loop()
{
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distance= duration*0.034/2;
if(distance <= 50 && distance >= 20)
{
digitalWrite(13, HIGH);
}
 else
{
digitalWrite(13, LOW);
}
 if(distance <= 20)
{
digitalWrite(2, HIGH);
tone(buzz, 2000);
delay(100);
noTone(buzz);
delay(100);
tone(buzz, 2000);
delay(100);
noTone(buzz);
delay(100);
tone(buzz, 2000);
delay(100);
noTone(buzz);
tone(buzz, 2000);
delay(100);
noTone(buzz);
delay(100);
}
 else
{
 digitalWrite(2, LOW);
}
}