#define TRIGGER_PIN 13
#define ECHO_PIN 12
int LED1 = 2;
int LED2 = 3;
int LED3 = 4;
int LED4 = 5;


void setup() {
    Serial.begin(9600);
    pinMode(TRIGGER_PIN, OUTPUT);
    pinMode(ECHO_PIN, INPUT);
    pinMode(LED1, OUTPUT);
}

void loop() {
 digitalWrite(TRIGGER_PIN, LOW);
 delayMicroseconds(2);
 digitalWrite(TRIGGER_PIN, HIGH);
 delayMicroseconds(10);
 digitalWrite(TRIGGER_PIN, LOW);
 long duration = pulseIn(ECHO_PIN, HIGH);
  float distance = (duration * 0.0343) / 2;
  if (distance < 40){
    digitalWrite(LED1, HIGH);
    } else {
    digitalWrite(LED1, LOW);
  }
  delay(500);
  }