#define TRIG_PIN 5
#define ECHO_PIN 4
#define DISTANCE_THRESHOLD 30
#define RELAY_CONTROL_PIN 6
#define POTENT_PIN 9

volatile bool fired = false;
volatile bool inter = false;
volatile int duration = 0;
volatile bool newDistance = false;
volatile bool relayOn = true;
volatile int threshold = 0;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(RELAY_CONTROL_PIN, OUTPUT);
  pinMode(POTENT_PIN, INPUT);
  attachInterrupt(digitalPinToInterrupt(ECHO_PIN), distanceInterrupt, CHANGE);
  threshold = analogRead(POTENT_PIN) / 40;
  Serial.println("Threshold: ");
  Serial.println(threshold);
  enableRelay();
}

void loop() {
  // Start a new measurement:
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  delay(250);
}

void distanceInterrupt() {
  if (digitalRead(ECHO_PIN) == HIGH) {
    duration = micros();
  }
  else {
    duration = micros() - duration;
    newDistance = true;
  }
  if (newDistance == true) {
    int distance = duration/58;
    Serial.println("\n\n Distance in interrupt: ");
    Serial.println(distance);
    newDistance = false;
    if (distance < threshold && relayOn == true) {
      disableRelay();
      relayOn = false;
    }
    else if (distance > threshold && relayOn == false) {
      enableRelay();
      relayOn = true;
    }
  }
}

void enableRelay() {
  digitalWrite(RELAY_CONTROL_PIN, HIGH);
  Serial.println("Relay Enabled");
}
void disableRelay() {
  digitalWrite(RELAY_CONTROL_PIN, LOW);
  Serial.println("Relay Disabled");
}