void setup() {
  // put your setup code here, to run once:
Serial.begin(115200);
pinMode(2, OUTPUT);//LED green light
pinMode(3, OUTPUT);//LED yellow light
pinMode(4, OUTPUT);//LED red light
pinMode(5, OUTPUT);//trigger
pinMode(6, INPUT);//echo
}

void loop() {
  // put your main code here, to run repeatedly:
digitalWrite(4, HIGH);//activate red light