// https://forum.arduino.cc/t/ultrasonic-sensor-only-gives-0cm/1247438/1

const int echoPin = 2;
const int triggerPin = 3;
int pulseValue;
float centimetersDistance;
const int ledGreen = 4;
const int ledRed = 5;

void setup() {
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(triggerPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(5);
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW); 

  pulseValue = pulseIn(echoPin, HIGH);
  centimetersDistance = pulseValue * 0.034/2;

  Serial.print("Distance: ");
  Serial.print(centimetersDistance);
  Serial.println(" cm ");
  delay(500);

  if(centimetersDistance >=10) {

    digitalWrite(4, HIGH);
    digitalWrite(5, LOW);
}   else  {
    digitalWrite(4, LOW);
    digitalWrite(5, HIGH);
}
}