void setup() {
  pinMode(12, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(10, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  float distancia = sonar(7, 8);
  Serial.println(distancia);
  digitalWrite(10, HIGH); // verde
  if (distancia <= 15 && distancia >= 3) {
    digitalWrite(10, LOW); // verde
    // amarelo
    digitalWrite(11, HIGH); delay(500);
    digitalWrite(11, LOW); // amarelo
    // vermelho
    digitalWrite(12, HIGH); delay(3000);
    digitalWrite(12, LOW); // vermelho
  }
delay(200);
}

float sonar(int pino_TRIG, int pino_ECO) {
  float tempo, distancia;
  pinMode(pino_TRIG, OUTPUT) ;
  pinMode(pino_TRIG, INPUT) ;
  digitalWrite(pino_TRIG, LOW) ;
  delayMicroseconds(2);
  digitalWrite(pino_TRIG, HIGH) ;
  delayMicroseconds(10);
  digitalWrite(pino_TRIG, LOW) ;
  tempo = pulseIn(pino_ECO, HIGH);
  distancia = (tempo * 0.0343) / 2;
  return distancia;
}