trouble writing PIR library (C++)

Hello I am trying to convert the playground code for detecting presence using PIRs Arduino Playground - PIRsense into a library so I can connect several PIRs together.

I am new to C++ but have followed a few examples. The code compiles but doesn't seem to work as expected. I get readings from two PiRs the first few times but then I only get readings from one of them (the second object initialised). I have the suspicion that objects don't work as I think in C++ and one object is overwriting variables for all, I have declared variables protected but not much luck.

all comments, suggestions much appreciated.

#ifndef PIR_H
#define PIR_H

#include "WProgram.h"
#include "inttypes.h"

class PIR
    PIR(int nodeId, int pinId, long pause);
    void initialise();
    void checkStatus();
    int _nodeId;
    int _pinId;
    unsigned long lowIn;         
    unsigned long start;
    unsigned long end;
    int _pause;

    bool _ready;
    bool lockLow;
    bool takeLowTime;


#include "PIR.h"

 * The Parallax PIR Sensor is an easy to use digital infrared motion sensor module. 
 * (
 * The sensor?s output pin goes to HIGH if motion is present.
 * However, even if motion is present it goes to LOW from time to time, 
 * which might give the impression no motion is present. 
 * This program deals with this issue by ignoring LOW-phases shorter than a given time, 
 * assuming continuous motion is present during these phases.

bool lockLow = true;

PIR::PIR(int nodeId, int pinId, long pause){
_nodeId = nodeId;
_pinId = pinId;
_pause = pause;

void PIR::initialise(){

    pinMode(_pinId, INPUT);
    digitalWrite(_pinId, LOW);

    //give the sensor some time to calibrate
    for(int i = 0; i < 30; i++){
    Serial.println("SENSOR ACTIVE");
    _ready = true;

void PIR::checkStatus(){
    if (_ready == true) {
        if(digitalRead(_pinId) == HIGH){
              //makes sure we wait for a transition to LOW before any further output is made:
              lockLow = false;            
              start = millis()/1000;
            takeLowTime = true;
        if(digitalRead(_pinId) == LOW){
                 lowIn = millis();          //save the time of the transition from high to LOW
                 takeLowTime = false;       //make sure this is only done at the start of a LOW phase
               //if the sensor is low for more than the given pause, 
               //we assume that no more motion is going to happen
               if(!lockLow && millis() - lowIn > _pause){  
                 //makes sure this block of code is only executed again after 
                 //a new motion sequence has been detected
                 lockLow = true;                       
                 end = (millis() - _pause)/1000;
                 Serial.print( _nodeId );
                 Serial.print( " " );
                 Serial.print( _pinId );
                 Serial.print( " " );
                 Serial.print( end - start );


don't use the global variable lockLow, make it a class member instead, othwise this variable is not unique to each sensor!


Thanks Mike, I tried that but the problem seems to persist. One sensor works more than one doesn't.