PIR detection library for Arduino

main.ino

#include "pir.h"

Pir pir;

void setup() {}

void loop() {
  pir.update();

  if (pir.movementOn) {
    Serial.println("Movement detected!");
  }

  if (pir.movementOff) {
    Serial.println("Movement stopped.");
  }
}

pir.cpp

#include "pir.h"

Pir::Pir() {
  pinMode(PIR_PIN, INPUT);

  _resetInterval();

  // give the sensor a couple seconds to wake up
  _intervalStart = millis() + 5000;
}

void Pir::update() {
  _resetMovementVariables();
  _makeReading();

  if (millis() > _intervalStart + READING_INTERVAL) {
    _analyzeInterval();
    _resetInterval();
  }
}

void Pir::_resetMovementVariables() {
  movementOn = false;
  movementOff = false;
}

void Pir::_makeReading() {
  int pirReading = analogRead(PIR_PIN);

  if (pirReading < _pirLow)  _pirLow = pirReading;
  if (pirReading > _pirHigh) _pirHigh = pirReading;
}

void Pir::_analyzeInterval() {
  int difference = _pirHigh - _pirLow;

  if (!_seesMovement) {
    if (difference > MOVEMENT_THRESHOLD) {
      movementOn = true;
      _seesMovement = true;
      _lastSustainingMeasurement = millis();
    }
  } else {
    if (difference > SUSTAIN_THRESHOLD) {
      _lastSustainingMeasurement = millis();
    } else {
      if (millis() > _lastSustainingMeasurement + SUSTAIN_BUFFER) {
        movementOff = true;
        _seesMovement = false;
      }
    }
  }
}


void Pir::_resetInterval() {
  _pirLow  = 4096;
  _pirHigh = 0;

  _intervalStart = millis();
}

pir.h

#ifndef Pir_h
#define Pir_h

#include "application.h"

#define PIR_PIN A0

#define READING_INTERVAL   250
#define SUSTAIN_BUFFER     750
#define MOVEMENT_THRESHOLD 2500
#define SUSTAIN_THRESHOLD  1000

class Pir {
public:
  Pir();

  void update();

  bool movementOn  = false;
  bool movementOff = false;

private:
  void _resetMovementVariables();
  void _makeReading();
  void _analyzeInterval();
  void _resetInterval();

  long _intervalStart;
  long _lastSustainingMeasurement;

  int _pirLow;
  int _pirHigh;

  bool _seesMovement = false;
};

#endif