int  rojo=3,ama=4, verde=5;
int trigger =6, echo=7;
long pulso=0, distancia=0;

void setup(){
  pinMode(rojo, OUTPUT);
  pinMode(ama, OUTPUT);
  pinMode(verde, OUTPUT);
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
  Serial.begin(9600);
}
void loop(){
  digitalWrite(trigger,0);
  delayMicroseconds(2);
  digitalWrite(trigger,1);
  delayMicroseconds(10);
  digitalWrite(trigger,0);
  pulso=pulseIn(echo,HIGH);
  distancia=(pulso/58); //[cm]
  Serial.println(distancia);
  if(distancia<=20){
    digitalWrite(rojo, HIGH);
    delay(1000);
    digitalWrite(rojo, LOW);
    digitalWrite(ama, HIGH);
    delay(700);
    digitalWrite(ama, LOW);
    digitalWrite(verde, HIGH);
    delay(1000);
    digitalWrite(verde, LOW);
    digitalWrite(ama, HIGH);
    delay(700);
    digitalWrite(ama, LOW);
  }
  else{
    digitalWrite(rojo, LOW);
    digitalWrite(ama, LOW);
    digitalWrite(verde, LOW);
  }

}