int trig = 18;
int echo = 19;
int led1 = 23;
void setup() {
Serial.begin(9600);
pinMode(trig, OUTPUT);
pinMode(echo, INPUT);
pinMode(led1, OUTPUT);

}

void loop() {
digitalWrite(trig, LOW);
delayMicroseconds(2);
digitalWrite(trig, HIGH);
delayMicroseconds(10);
digitalWrite(trig, LOW);
long duracao = pulseIn(echo, HIGH);
int distancia = duracao * 0.0343 / 2;
Serial.print("distancia: ");
Serial.print(distancia);
Serial.println("cm");
delay(1000);
if(distancia < 20 ){
  digitalWrite(led1, HIGH);
};
else{
  digitalWrite(led1, LOW);
}
}