#define PIN_PYRO_OUT 7
#define PIN_LED 13
#define CALIBRATION_TIME 5 // 3 seconds
#define DELAY_BETWEEN_EACH_PYRO_READS 25 // milliseconds

#define THRESHOLD 5

int _avg_pyro_value;
int _pyro_value;

void setup() {
  Serial.begin(57600);
  pinMode(PIN_LED, OUTPUT);
  Serial.println("calibrating motion sensor..");
  
  digitalWrite(PIN_LED, HIGH);
  unsigned long endTime = millis() + CALIBRATION_TIME * 1000;
  int count = 0;
  long sum = 0;
  while (millis() < endTime) {
    sum += analogRead(PIN_PYRO_OUT);
    count++;
    delay(DELAY_BETWEEN_EACH_PYRO_READS);  
  }
  
  _avg_pyro_value = sum / count;
  
  digitalWrite(PIN_LED, LOW);
  Serial.println("Calibration ended.");
  Serial.print("Average value: ");
  Serial.println(_avg_pyro_value);
}


void loop() {
  _pyro_value = getPyroValue();

  if (abs(_pyro_value) >= THRESHOLD) {
    digitalWrite(PIN_LED, HIGH);
  } else {
    digitalWrite(PIN_LED, LOW); 
  }
  
  Serial.println(_pyro_value);
  delay(50);
}


int getPyroValue() {  
  int val = analogRead(PIN_PYRO_OUT);
  return val - _avg_pyro_value;  
}