#define ECHO_PIN 2
#define TRIG_PIN 3
#define RELAY_PIN 5

byte motorStatus = 1;

float readDistanceCM() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  int duration = pulseIn(ECHO_PIN, HIGH);
  return duration * 0.034 / 2;
}

void setup() {
  
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(RELAY_PIN, OUTPUT);
  
  delay(1000);
}

void loop() {
  float distance = readDistanceCM();

  if(distance > 50) {
    if(motorStatus == 0){
      motorStatus = 1;
      digitalWrite(RELAY_PIN, HIGH);
      delay(10);
    }
  }
  else
  {
    if(motorStatus == 1){
      motorStatus = 0;
      digitalWrite(RELAY_PIN, LOW);
      delay(10);
    }
  }

}