CO2 Monitor

#include "Arduino.h"
#include "Calculations.h"


double calcTemp(int Value) {  //https://playground.arduino.cc/ComponentLib/Thermistor2/
  double Temp;
  Temp = log(10000.0/(1024.0/Value-1)); // for pull-up configuration
  Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp )) * Temp );
  Temp = Temp - 273.15;                // Convert Kelvin to Celcius
  
  return Temp;//degrees C
}


double calcPw(double Temp) {  //R.C. Rodgers and G.E. Hill, Brittish Journal of Anaesthesia (1978),50, 415
  const double A = 7.16728;
  const double B = 1716.984;
  const double C = 232.538;
  double exponent = A - B/(Temp+C); 
  double Pw = pow(10,exponent);
  
  return Pw;//kPa
}


double calcRH(double Td, double Tw, double pWd, double pWw) {  //https://www.1728.org/relhum.htm
  double RH;
  if(Tw >= Td) { //to prevent RH>1 due to measurement errors where Tw >= Td
    RH = 1.0;
  }
  else {
    double pav = 101.55; //atmospheric pressure in kPa http://www.klimaatatlas.nl/klimaatatlas.php
    double N = 0.0006687451584; //kPa/K
    RH  = (pWw - N*pav*(1+0.00115*Tw)*(Td-Tw))/pWd;
  }
  
  return RH; //dimensionless
}  


double calcfRHT (double RH, double T) {   //Own fit from MQ-135 datasheet. It is presumed that CO2 readings are equally influenced by temperature and RH as ammonia readings in given graphs
  const double Intercept = 1.782663144;
  const double RC_RH     = -0.748177946;
  const double RC_T      = -0.015924756;
  const double RC_RHT    =  0.006677957;
  double calcfRHT = Intercept + RC_RH*RH + RC_T*T + RC_RHT*RH*T;
  
  return calcfRHT; //Rs/R0 dimensionless
}


double calcRs(int sensorReading) {   //Calculates Rs from amplified analog signal
  const double gain = 1.0 + 10000.0/1000.0; //amplification of opamp as function of resistances in opamp circuit
  const double Rref = 10.0; //Reference resistance (in kOhm) built in MQ-135 board 
  double sensorOrigReading = sensorReading/gain;
/*formula derivation:
 *sensorOrigReading = 1024*Rref/(Rref+Rsensor)
 *sensorOrigReading = 1024*1/(1+Rsensor/Rref)
 *(1+Rsensor/Rref)  = 1024/sensorOrigReading
 *Rsensor = (1024/sensorOrigReading-1)*Rref
 */
  double Rsensor = (1024.0/sensorOrigReading-1.0)*Rref; 
  
  return Rsensor; //kOhm
}


double calcCO2(double Rs, double fRHT) {
  const double R410    = 270.0; //Measured resistance (in kOhm) after one night with open window
  const double fRHT410 = 1.08;  //calcutated correction factor after one night with open window
  const double a  =  410.0;
  const double b  = -2.769034857; //slope from Mad Frog
  
  double CO2 = a*pow((Rs/fRHT)/(R410/fRHT410),b); //CO2atm = 410 ppm
  
  return CO2;//ppm
}

#include "Arduino.h"

//this library holds all physiscs calculations

//Calculate Temperature from analog input value
double calcTemp(int Value);

//Calculate vapour pressure from temperature
double calcPw(double Temp);

//Calculate relative humidity from wet and dry bulb temperature and vapour pressures at respective temperatures
double calcRH(double Td, double Tw, double Pwd, double Pww);

//Calculate sensitivity factor (Rs/R0) as function of relative humidity and temperature
double calcfRHT (double RH, double T); 

//Calculate sensor resistance (Rs) from analog input, after signal amplification with OpAmp
double calcRs(int sensorReading);

//Calculate CO2 concentration from measured sensor resistance (Rs) and relative humidity and temperature correction factor
double calcCO2(double Rs,double fRHT);

#include "Arduino.h"
#include "Time.h"

Time::Time (byte hr, byte mnt, byte sec, byte d, byte m, byte y) { 
  _timeStart = (hr*60UL+mnt)*60UL+ sec; //initialize _timeStart 
  _lastMillis = millis();               //last time millis() was called
  _curTime = _lastMillis/1000UL;        //time since start of program in seconds (rollover after 49000 days, rollover is prevented by updDate() after 1 day)

  //initialize _Time[]
  _Time[0]      = hr;
  _Time[1]      = mnt;
  _Time[2]      = sec; 

  //initialize _Date[]
  _Date[0]      = d;
  _Date[1]      = m;
  _Date[2]      = y;

  _dayRollover  = false; 
}


void Time::updTime() {
  unsigned long curMillis = millis();
  _curTime   += curMillis/1000UL - _lastMillis/1000UL;  //update _curTime
  _lastMillis = curMillis;                              //record _lastMilles for use during next call of updTime()

  unsigned long curTime = _curTime + _timeStart;
  if               (curTime/(24UL*60UL*60UL) > 0) _dayRollover = true;  //if time goes beyond 23:23:59 dayrollover occurs and time returs toe
  //update _Time[]
  curTime      =    curTime%(24UL*60UL*60UL);
  _Time[0]     =    curTime/(60UL*60UL);
  curTime      =    curTime%(60UL*60UL);
  _Time[1]     =    curTime/60UL;
  curTime      =    curTime%60UL;
  _Time[2]     =    curTime;

  //if needed, update _Date
  if (_dayRollover) updDate(); //if dayrollover, then adjust date
}


void Time::updDate() {
  const byte maxDays[13] = {0,31,29,31,30,31,30,31,31,30,31,30,31}; //2020 is leap year, next year change num days of February
  const byte day   = 0; //makes code more easy to read
  const byte month = 1;
  const byte year  = 2;
  
  _Date[day]++;
  if (_Date[day] > maxDays[_Date[month]]) {  //if monthrollover then adjust month
    _Date[day]     = 1;
    _Date[month]++;
    if (_Date[month] > 12) {                 //if yearrollover then adjust year
      _Date[month] = 1;
      _Date[year]++;
    }
  }
  _curTime = _curTime - (24UL*60UL*60UL);    //update _curTime (subtract one day)
  _dayRollover = false;
}


unsigned long Time::lastMillis() {
  return _lastMillis;
}


String Time::timeToString(String sign) {
  return toString(_Time, sign);
}


String Time::dateToString(String sign) {
  return toString(_Date, sign);
}


String Time::toString(byte* tostring, String sign) {
  String string = "";
  string += leadingZeros(tostring[0]);
  for (byte i=1; i<3; i++) {
     string+= sign;
     string+= leadingZeros(tostring[i]);
  }
  return string;
}


String Time::leadingZeros(byte value) {
  String string = "";
  if (value < 10) {
    string += "0";
  }
  string += String(value);   
  return string;
}

/*
 *Time.h - Time library
 *Records starting time and date of project (as given in source code by programmer)
 *Can return String with current Time (hh:mm:ss) 
 *Can return String with current date (dd-mm-yy)
 *Can return millis since start Time
 *Created by Koen Meesters, december 2019
 *Last edited Februari 2020
 */
#ifndef Time_h
#define Time_h

#include "Arduino.h"

class Time {
  public:
    Time(byte hr = 0, byte mnt = 0, byte sec = 0, byte d = 1, byte m = 1, byte y = 20); // date by default initialized to 1-1-2020
    
    String timeToString(String sign = ":"); //returns time in a String, default sign for time is :
    String dateToString(String sign = "-"); //returns date in a String, default sign for date is -

    unsigned long lastMillis(); 
    void updTime();                         //update the time in _Time[3]
    
  private:
    byte _Time[3];                          //stores time in 3 bytes hr min sec
    byte _Date[3];                          //stores date in 3 bytes day month year
    bool _dayRollover;                      //flag set if time goes beyond 23:59:59   

    unsigned long _timeStart;               //start time in seconds
    unsigned long _curTime;                 //current time in seconds
    unsigned long _lastMillis;              //millis() last time updTime() was run 


    void updDate();                         //update the date in _Date[3] (should be run at least every day, otherwise it misses 1 dayrollover)
    
    String toString(byte*, String sign);    //makes a string from _Time[3] or _Date[3]
    String leadingZeros(byte value);        //adds leading zeros if number is smaller than 10 ( 3 --> "03") 
};

#endif