CO2 Monitor

CO2 monitor and log based on MQ-135 with temperature and relative humidity correction.

Jan 20, 2020

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10 respects

environmental sensing

Components and supplies

Resistor 221 ohm

Resistor 10k ohm

Temperature sensor with thermistor VMA-320

Alphanumeric LCD, 16 x 2

SD card logging shield VMA-304

Resistor 1k ohm

MQ-135

General Purpose Quad Op-Amp

Arduino UNO

Project description

Code

Time.cpp

c_cpp

Time and date utility

1#include "Arduino.h"
2#include "Time.h"
3
4Time::Time (byte  hr, byte mnt, byte sec, byte d, byte m, byte y) { 
5  _timeStart = (hr*60UL+mnt)*60UL+  sec; //initialize _timeStart 
6  _lastMillis = millis();               //last  time millis() was called
7  _curTime = _lastMillis/1000UL;        //time since  start of program in seconds (rollover after 49000 days, rollover is prevented by  updDate() after 1 day)
8
9  //initialize _Time[]
10  _Time[0]      = hr;
11  _Time[1]      = mnt;
12  _Time[2]      = sec; 
13
14  //initialize _Date[]
15  _Date[0]      = d;
16  _Date[1]      = m;
17  _Date[2]      = y;
18
19  _dayRollover  = false; 
20}
21
22
23void Time::updTime() {
24  unsigned long curMillis  = millis();
25  _curTime   += curMillis/1000UL - _lastMillis/1000UL;  //update  _curTime
26  _lastMillis = curMillis;                              //record _lastMilles  for use during next call of updTime()
27
28  unsigned long curTime = _curTime  + _timeStart;
29  if               (curTime/(24UL*60UL*60UL) > 0) _dayRollover  = true;  //if time goes beyond 23:23:59 dayrollover occurs and time returs toe
30  //update _Time[]
31  curTime      =    curTime%(24UL*60UL*60UL);
32  _Time[0]     =    curTime/(60UL*60UL);
33  curTime      =    curTime%(60UL*60UL);
34  _Time[1]     =    curTime/60UL;
35  curTime      =    curTime%60UL;
36  _Time[2]     =    curTime;
37
38  //if needed, update _Date
39  if (_dayRollover) updDate();  //if dayrollover, then adjust date
40}
41
42
43void Time::updDate() {
44  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
45  const byte day   = 0; //makes code more  easy to read
46  const byte month = 1;
47  const byte year  = 2;
48  
49  _Date[day]++;
50  if (_Date[day] > maxDays[_Date[month]]) {  //if monthrollover then adjust month
51    _Date[day]     = 1;
52    _Date[month]++;
53    if (_Date[month] > 12) {                 //if  yearrollover then adjust year
54      _Date[month] = 1;
55      _Date[year]++;
56    }
57  }
58  _curTime = _curTime - (24UL*60UL*60UL);    //update _curTime (subtract  one day)
59  _dayRollover = false;
60}
61
62
63unsigned long Time::lastMillis()  {
64  return _lastMillis;
65}
66
67
68String Time::timeToString(String sign)  {
69  return toString(_Time, sign);
70}
71
72
73String Time::dateToString(String  sign) {
74  return toString(_Date, sign);
75}
76
77
78String Time::toString(byte*  tostring, String sign) {
79  String string = "";
80  string += leadingZeros(tostring[0]);
81  for (byte i=1; i<3; i++) {
82     string+= sign;
83     string+= leadingZeros(tostring[i]);
84  }
85  return string;
86}
87
88
89String Time::leadingZeros(byte value) {
90  String string = "";
91  if (value < 10) {
92    string += "0";
93  }
94  string += String(value);   
95  return string;
96}
97

#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;
}

Calculations.h

c_cpp

Header to Calculations.ccp

1#include "Arduino.h"
2
3//this library holds all physiscs calculations
4
5//Calculate   Temperature from analog input value
6double calcTemp(int Value);
7
8//Calculate   vapour pressure from temperature
9double calcPw(double Temp);
10
11//Calculate   relative humidity from wet and dry bulb temperature and vapour pressures at respective   temperatures
12double calcRH(double Td, double Tw, double Pwd, double Pww);
13
14//Calculate   sensitivity factor (Rs/R0) as function of relative humidity and temperature
15double   calcfRHT (double RH, double T); 
16
17//Calculate sensor resistance (Rs) from   analog input, after signal amplification with OpAmp
18double calcRs(int sensorReading);
19
20//Calculate   CO2 concentration from measured sensor resistance (Rs) and relative humidity and   temperature correction factor
21double calcCO2(double Rs,double fRHT);
22

#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);

Calculations.cpp

c_cpp

Calculation of temperature, relative humidity, sensor resistance based on values read from A0, A1 and A2. From these date it calculates water vapour pressures and sensor correction factor are derived. Finally the CO2 concentration is measured

1#include "Arduino.h"
2#include "Calculations.h"
3
4
5double  calcTemp(int Value) {  //https://playground.arduino.cc/ComponentLib/Thermistor2/
6  double Temp;
7  Temp = log(10000.0/(1024.0/Value-1)); // for pull-up configuration
8  Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp )) * Temp  );
9  Temp = Temp - 273.15;                // Convert Kelvin to Celcius
10  
11  return Temp;//degrees C
12}
13
14
15double calcPw(double Temp) {  //R.C. Rodgers  and G.E. Hill, Brittish Journal of Anaesthesia (1978),50, 415
16  const double  A = 7.16728;
17  const double B = 1716.984;
18  const double C = 232.538;
19  double exponent = A - B/(Temp+C); 
20  double Pw = pow(10,exponent);
21  
22  return Pw;//kPa
23}
24
25
26double calcRH(double Td, double Tw, double pWd,  double pWw) {  //https://www.1728.org/relhum.htm
27  double RH;
28  if(Tw >= Td)  { //to prevent RH>1 due to measurement errors where Tw >= Td
29    RH = 1.0;
30  }
31  else {
32    double pav = 101.55; //atmospheric pressure in kPa http://www.klimaatatlas.nl/klimaatatlas.php
33    double N = 0.0006687451584; //kPa/K
34    RH  = (pWw - N*pav*(1+0.00115*Tw)*(Td-Tw))/pWd;
35  }
36  
37  return RH; //dimensionless
38}  
39
40
41double 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
42  const double Intercept = 1.782663144;
43  const double RC_RH     = -0.748177946;
44  const double RC_T      = -0.015924756;
45  const double RC_RHT    =  0.006677957;
46  double calcfRHT = Intercept + RC_RH*RH + RC_T*T + RC_RHT*RH*T;
47  
48  return  calcfRHT; //Rs/R0 dimensionless
49}
50
51
52double calcRs(int sensorReading)  {   //Calculates Rs from amplified analog signal
53  const double gain = 1.0 +  10000.0/1000.0; //amplification of opamp as function of resistances in opamp circuit
54  const double Rref = 10.0; //Reference resistance (in kOhm) built in MQ-135 board  
55  double sensorOrigReading = sensorReading/gain;
56/*formula derivation:
57  *sensorOrigReading = 1024*Rref/(Rref+Rsensor)
58 *sensorOrigReading = 1024*1/(1+Rsensor/Rref)
59  *(1+Rsensor/Rref)  = 1024/sensorOrigReading
60 *Rsensor = (1024/sensorOrigReading-1)*Rref
61  */
62  double Rsensor = (1024.0/sensorOrigReading-1.0)*Rref; 
63  
64  return  Rsensor; //kOhm
65}
66
67
68double calcCO2(double Rs, double fRHT) {
69  const  double R410    = 270.0; //Measured resistance (in kOhm) after one night with open  window
70  const double fRHT410 = 1.08;  //calcutated correction factor after one  night with open window
71  const double a  =  410.0;
72  const double b  = -2.769034857;  //slope from Mad Frog
73  
74  double CO2 = a*pow((Rs/fRHT)/(R410/fRHT410),b);  //CO2atm = 410 ppm
75  
76  return CO2;//ppm
77}
78

#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
}

CO2v2.ino

c_cpp

Main program

1#include <SPI.h>
2#include <SD.h>
3#include <LiquidCrystal.h>
4#include  "Time.h"
5#include "Calculations.h"
6
7const int rs = 8, en = 7, d4 =  6, d5 = 5, d6 = 4, d7 = 3;
8LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
9
10//  set up variables using the SD utility library functions:
11Sd2Card card;
12SdVolume  volume;
13SdFile root;
14//pin connected to CS of SD card shield
15const int  chipSelect = 2;
16
17#define _dd_   20
18#define _mm_    1
19#define _yy_   20
20
21#define  _hr_   17
22#define _min_   54
23#define _sec_   0
24
25char fileName[13];
26
27//Set  start time and date
28Time myTime(_hr_,_min_,_sec_,_dd_,_mm_,_yy_); //hr,min,sec,d,m,y
29
30//used  connections to Arduino
31const byte Td_sensor  = A0;
32const byte Tw_sensor  =  A1;
33const byte CO2_sensor = A2;
34const byte checkLight =  9;
35
36
37//Data  are stored in data array (double data[]) to ease printing and writing to SD card  and LCD screen. Here the positions of the data in the array are given. 
38const  byte Td   = 0; //deg Celcius
39const byte Tw   = 1;  
40const byte RH   = 2; //relative  humidity
41const byte CO2  = 3; //ppm
42const byte pWd  = 4; //kPa
43const byte  pWw  = 5; 
44const byte fRHT = 6; //-
45const byte Rs   = 7; //kohm
46const byte  numData = 8; //number of data in data []
47
48
49const String degC = String ("\\xC2\\xB0")  + String("C");
50const String labels[numData] = {"Td" ,"Tw" ,"RH","CO2","pWd","pWw","fRHT","Rs"  };
51const String units [numData] = {degC ,degC ,"-" ,"ppm","Pa" ,"Pa"  ,"-"   ,"kohm"};
52
53
54void setup() {
55  pinMode(Td_sensor ,INPUT);
56  pinMode(Tw_sensor ,INPUT);
57  pinMode(CO2_sensor,INPUT);
58  pinMode(checkLight,OUTPUT);
59
60  lcd.begin(16, 2);
61  lcd.print("hello, world!");
62  
63  Serial.begin(9600);
64  String fileNameConst = String("WK") + myTime.dateToString("") + String(".txt");
65  strcpy(fileName,fileNameConst.c_str());
66
67  Serial.print("Initializing SD  card...");
68
69  // see if the card is present and can be initialized:
70  if  (!SD.begin(chipSelect)) {
71    Serial.println("Card failed, or not present");
72    // don't do anything more:
73    while (1);
74  }
75  Serial.println("card  initialized.");
76  delay(200);
77  
78  // if the file is available, write  to it:
79  // prepare datastring with current time and datalabels as column headers
80  myTime.updTime();
81  String dataString = myTime.dateToString();
82  dataString+=  ",";
83  dataString+= myTime.timeToString();
84  for (int i = 0; i<numData;  i++) {
85    dataString+= ",";   
86    dataString+= labels[i];
87  }
88
89  File dataFile = SD.open(fileName,FILE_WRITE);
90  if (dataFile) {
91    dataFile.println();
92    dataFile.println(dataString);
93    dataFile.close();
94  }
95  // if the  file isn't open, pop up an error:
96  else {
97    Serial.println("error opening  datalog.txt");
98  } 
99}
100
101
102void loop() {
103  myTime.updTime();
104  digitalWrite(checkLight,LOW);   //put here to see if the system is working. now  not needed anymore as LCD was installed
105
106  Serial.println(myTime.timeToString()  + " " + myTime.dateToString());
107
108  //fill data array with fresh measurement  results
109  double data [numData];
110  data[Td]   = calcTemp(readSensor(Td_sensor));  //degrees C
111  data[Tw]   = calcTemp(readSensor(Tw_sensor));  
112  data[pWd]  = calcPw(data[Td]);                 //kPa
113  data[pWw]  = calcPw(data[Tw]);
114  data[RH]   = calcRH(data[Td],data[Tw],data[pWd],data[pWw]); //dimensionless
115  data[fRHT] = calcfRHT(data[RH],data[Td]);      //humidity and temperature correction  factor, dimensionless
116  data[Rs]   = calcRs(readSensor(CO2_sensor));   //kohm
117  data[CO2]  = calcCO2(data[Rs],data[fRHT]);     //ppm
118
119  dataToScreen(labels,data,units);
120
121  dataToLCD(labels,data);
122  
123  // make a string for assembling the data to  log:
124  String dataString = "";
125
126  dataString += myTime.dateToString();  //start with current time and date
127  dataString += ",";
128  dataString +=  myTime.timeToString();  
129
130  for (int i=0; i<numData; i++) {          //add  all data to dataString
131    dataString += ",";    
132    dataString += String(data[i]);
133  }
134
135  // open the file. note that only one file can be open at a time,
136  // so you have to close this one before opening another.
137  File dataFile =  SD.open(fileName, FILE_WRITE);
138
139  // if the file is available, write to it:
140  if (dataFile) {
141    dataFile.println(dataString);
142    dataFile.close();
143  }
144  // if the file isn't open, pop up an error:
145  else {
146    Serial.println("error  opening datalog.txt");
147  }
148  
149  //halfway time: show time, date, Rs and  CO2
150  lcd.clear();
151  lcd.print(myTime.timeToString());
152  lcd.print("   ");
153  lcd.print(myTime.dateToString());
154  lcd.setCursor(0,1);  
155  lcd.print("Rs=");
156  lcd.print(data[Rs],0);
157  lcd.print("  CO2=");
158  lcd.print(data[CO2],0);  
159  
160  digitalWrite(checkLight,HIGH);
161  const unsigned long loopDuration  = 30000;
162  while (millis() - myTime.lastMillis() < loopDuration) { //wait until  loopDuration 
163    ;
164  }
165}
166  
167
168//return sensor value
169int readSensor(const  byte address) {
170  int value = 0;
171  byte numMeas = 32; //should not be larger  than 2^6=64 (int value may roll over)
172  for (int i=0; i<numMeas; i++) {
173    value  +=  analogRead(address);
174    delay(100);  //this makes the sketch slow (32 times  100 times 3 = 9600 millisec (almost 10 sec)
175  }
176  value /= numMeas;
177  return  value;
178}
179
180
181//write data to screen
182void dataToScreen(const String  label[],const double data[],const String unit[]) {  //all arguments declared constant  as this procedure is not supposed to change any data
183  for (int i=0; i<numData;  i++) {
184    if (i==RH) { //RH is printed as % instead of fraction
185      Serial.print(label[i]),  Serial.print(":\	"), Serial.print(data[i]*100,2),  Serial.print("\	"), Serial.println("%");
186    }
187    else {
188      Serial.print(label[i]), Serial.print(":\	"), Serial.print(data[i],2),      Serial.print("\	"), Serial.println(unit[i]);  
189    }
190  }
191  Serial.println();
192}
193
194
195//write  data to LCD
196void dataToLCD(const String label[],const double data[]) {
197  lcd.clear();  
198  for (int i = Td; i<=CO2; i++) {
199       lcd.print(label[i]);
200       lcd.print("=");
201       int decimals = 1;
202       if (i==CO2) decimals = 0;
203       if (i== RH)  decimals = 2;
204       lcd.print(data[i],decimals);  
205       lcd.print(" ");  
206       if (i== Td) lcd.print(" ");
207       if (i== Tw) lcd.setCursor(0,1);  
208  }
209}
210

#include <SPI.h>
#include <SD.h>
#include <LiquidCrystal.h>
#include  "Time.h"
#include "Calculations.h"

const int rs = 8, en = 7, d4 =  6, d5 = 5, d6 = 4, d7 = 3;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

//  set up variables using the SD utility library functions:
Sd2Card card;
SdVolume  volume;
SdFile root;
//pin connected to CS of SD card shield
const int  chipSelect = 2;

#define _dd_   20
#define _mm_    1
#define _yy_   20

#define  _hr_   17
#define _min_   54
#define _sec_   0

char fileName[13];

//Set  start time and date
Time myTime(_hr_,_min_,_sec_,_dd_,_mm_,_yy_); //hr,min,sec,d,m,y

//used  connections to Arduino
const byte Td_sensor  = A0;
const byte Tw_sensor  =  A1;
const byte CO2_sensor = A2;
const byte checkLight =  9;


//Data  are stored in data array (double data[]) to ease printing and writing to SD card  and LCD screen. Here the positions of the data in the array are given. 
const  byte Td   = 0; //deg Celcius
const byte Tw   = 1;  
const byte RH   = 2; //relative  humidity
const byte CO2  = 3; //ppm
const byte pWd  = 4; //kPa
const byte  pWw  = 5; 
const byte fRHT = 6; //-
const byte Rs   = 7; //kohm
const byte  numData = 8; //number of data in data []


const String degC = String ("\\xC2\\xB0")  + String("C");
const String labels[numData] = {"Td" ,"Tw" ,"RH","CO2","pWd","pWw","fRHT","Rs"  };
const String units [numData] = {degC ,degC ,"-" ,"ppm","Pa" ,"Pa"  ,"-"   ,"kohm"};


void setup() {
  pinMode(Td_sensor ,INPUT);
  pinMode(Tw_sensor ,INPUT);
  pinMode(CO2_sensor,INPUT);
  pinMode(checkLight,OUTPUT);

  lcd.begin(16, 2);
  lcd.print("hello, world!");
  
  Serial.begin(9600);
  String fileNameConst = String("WK") + myTime.dateToString("") + String(".txt");
  strcpy(fileName,fileNameConst.c_str());

  Serial.print("Initializing SD  card...");

  // see if the card is present and can be initialized:
  if  (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    // don't do anything more:
    while (1);
  }
  Serial.println("card  initialized.");
  delay(200);
  
  // if the file is available, write  to it:
  // prepare datastring with current time and datalabels as column headers
  myTime.updTime();
  String dataString = myTime.dateToString();
  dataString+=  ",";
  dataString+= myTime.timeToString();
  for (int i = 0; i<numData;  i++) {
    dataString+= ",";   
    dataString+= labels[i];
  }

  File dataFile = SD.open(fileName,FILE_WRITE);
  if (dataFile) {
    dataFile.println();
    dataFile.println(dataString);
    dataFile.close();
  }
  // if the  file isn't open, pop up an error:
  else {
    Serial.println("error opening  datalog.txt");
  } 
}


void loop() {
  myTime.updTime();
  digitalWrite(checkLight,LOW);   //put here to see if the system is working. now  not needed anymore as LCD was installed

  Serial.println(myTime.timeToString()  + " " + myTime.dateToString());

  //fill data array with fresh measurement  results
  double data [numData];
  data[Td]   = calcTemp(readSensor(Td_sensor));  //degrees C
  data[Tw]   = calcTemp(readSensor(Tw_sensor));  
  data[pWd]  = calcPw(data[Td]);                 //kPa
  data[pWw]  = calcPw(data[Tw]);
  data[RH]   = calcRH(data[Td],data[Tw],data[pWd],data[pWw]); //dimensionless
  data[fRHT] = calcfRHT(data[RH],data[Td]);      //humidity and temperature correction  factor, dimensionless
  data[Rs]   = calcRs(readSensor(CO2_sensor));   //kohm
  data[CO2]  = calcCO2(data[Rs],data[fRHT]);     //ppm

  dataToScreen(labels,data,units);

  dataToLCD(labels,data);
  
  // make a string for assembling the data to  log:
  String dataString = "";

  dataString += myTime.dateToString();  //start with current time and date
  dataString += ",";
  dataString +=  myTime.timeToString();  

  for (int i=0; i<numData; i++) {          //add  all data to dataString
    dataString += ",";    
    dataString += String(data[i]);
  }

  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  File dataFile =  SD.open(fileName, FILE_WRITE);

  // if the file is available, write to it:
  if (dataFile) {
    dataFile.println(dataString);
    dataFile.close();
  }
  // if the file isn't open, pop up an error:
  else {
    Serial.println("error  opening datalog.txt");
  }
  
  //halfway time: show time, date, Rs and  CO2
  lcd.clear();
  lcd.print(myTime.timeToString());
  lcd.print("   ");
  lcd.print(myTime.dateToString());
  lcd.setCursor(0,1);  
  lcd.print("Rs=");
  lcd.print(data[Rs],0);
  lcd.print("  CO2=");
  lcd.print(data[CO2],0);  
  
  digitalWrite(checkLight,HIGH);
  const unsigned long loopDuration  = 30000;
  while (millis() - myTime.lastMillis() < loopDuration) { //wait until  loopDuration 
    ;
  }
}
  

//return sensor value
int readSensor(const  byte address) {
  int value = 0;
  byte numMeas = 32; //should not be larger  than 2^6=64 (int value may roll over)
  for (int i=0; i<numMeas; i++) {
    value  +=  analogRead(address);
    delay(100);  //this makes the sketch slow (32 times  100 times 3 = 9600 millisec (almost 10 sec)
  }
  value /= numMeas;
  return  value;
}


//write data to screen
void dataToScreen(const String  label[],const double data[],const String unit[]) {  //all arguments declared constant  as this procedure is not supposed to change any data
  for (int i=0; i<numData;  i++) {
    if (i==RH) { //RH is printed as % instead of fraction
      Serial.print(label[i]),  Serial.print(":\	"), Serial.print(data[i]*100,2),  Serial.print("\	"), Serial.println("%");
    }
    else {
      Serial.print(label[i]), Serial.print(":\	"), Serial.print(data[i],2),      Serial.print("\	"), Serial.println(unit[i]);  
    }
  }
  Serial.println();
}


//write  data to LCD
void dataToLCD(const String label[],const double data[]) {
  lcd.clear();  
  for (int i = Td; i<=CO2; i++) {
       lcd.print(label[i]);
       lcd.print("=");
       int decimals = 1;
       if (i==CO2) decimals = 0;
       if (i== RH)  decimals = 2;
       lcd.print(data[i],decimals);  
       lcd.print(" ");  
       if (i== Td) lcd.print(" ");
       if (i== Tw) lcd.setCursor(0,1);  
  }
}

Time.h

c_cpp

Header for Time.ccp

1/*
2 *Time.h - Time library
3 *Records starting time and date of project   (as given in source code by programmer)
4 *Can return String with current Time   (hh:mm:ss) 
5 *Can return String with current date (dd-mm-yy)
6 *Can return   millis since start Time
7 *Created by Koen Meesters, december 2019
8 *Last edited   Februari 2020
9 */
10#ifndef Time_h
11#define Time_h
12
13#include "Arduino.h"
14
15class   Time {
16  public:
17    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
18    
19     String timeToString(String sign = ":"); //returns time in a String, default   sign for time is :
20    String dateToString(String sign = "-"); //returns date   in a String, default sign for date is -
21
22    unsigned long lastMillis(); 
23     void updTime();                         //update the time in _Time[3]
24    
25   private:
26    byte _Time[3];                          //stores time in 3 bytes   hr min sec
27    byte _Date[3];                          //stores date in 3 bytes   day month year
28    bool _dayRollover;                      //flag set if time   goes beyond 23:59:59   
29
30    unsigned long _timeStart;               //start   time in seconds
31    unsigned long _curTime;                 //current time in   seconds
32    unsigned long _lastMillis;              //millis() last time updTime()   was run 
33
34
35    void updDate();                         //update the date   in _Date[3] (should be run at least every day, otherwise it misses 1 dayrollover)
36     
37    String toString(byte*, String sign);    //makes a string from _Time[3]   or _Date[3]
38    String leadingZeros(byte value);        //adds leading zeros   if number is smaller than 10 ( 3 --> "03") 
39};
40
41#endif
42

/*
 *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

Calculations.h

c_cpp

Header to Calculations.ccp

1#include "Arduino.h"
2
3//this library holds all physiscs calculations
4
5//Calculate  Temperature from analog input value
6double calcTemp(int Value);
7
8//Calculate  vapour pressure from temperature
9double calcPw(double Temp);
10
11//Calculate  relative humidity from wet and dry bulb temperature and vapour pressures at respective  temperatures
12double calcRH(double Td, double Tw, double Pwd, double Pww);
13
14//Calculate  sensitivity factor (Rs/R0) as function of relative humidity and temperature
15double  calcfRHT (double RH, double T); 
16
17//Calculate sensor resistance (Rs) from  analog input, after signal amplification with OpAmp
18double calcRs(int sensorReading);
19
20//Calculate  CO2 concentration from measured sensor resistance (Rs) and relative humidity and  temperature correction factor
21double calcCO2(double Rs,double fRHT);
22

#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);

Calculations.cpp

c_cpp

1#include "Arduino.h"
2#include "Calculations.h"
3
4
5double
6  calcTemp(int Value) {  //https://playground.arduino.cc/ComponentLib/Thermistor2/
7
8  double Temp;
9  Temp = log(10000.0/(1024.0/Value-1)); // for pull-up configuration
10
11  Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp )) * Temp
12  );
13  Temp = Temp - 273.15;                // Convert Kelvin to Celcius
14  
15
16  return Temp;//degrees C
17}
18
19
20double calcPw(double Temp) {  //R.C. Rodgers
21  and G.E. Hill, Brittish Journal of Anaesthesia (1978),50, 415
22  const double
23  A = 7.16728;
24  const double B = 1716.984;
25  const double C = 232.538;
26
27  double exponent = A - B/(Temp+C); 
28  double Pw = pow(10,exponent);
29  
30
31  return Pw;//kPa
32}
33
34
35double calcRH(double Td, double Tw, double pWd,
36  double pWw) {  //https://www.1728.org/relhum.htm
37  double RH;
38  if(Tw >= Td)
39  { //to prevent RH>1 due to measurement errors where Tw >= Td
40    RH = 1.0;
41
42  }
43  else {
44    double pav = 101.55; //atmospheric pressure in kPa http://www.klimaatatlas.nl/klimaatatlas.php
45
46    double N = 0.0006687451584; //kPa/K
47    RH  = (pWw - N*pav*(1+0.00115*Tw)*(Td-Tw))/pWd;
48
49  }
50  
51  return RH; //dimensionless
52}  
53
54
55double calcfRHT (double
56  RH, double T) {   //Own fit from MQ-135 datasheet. It is presumed that CO2 readings
57  are equally influenced by temperature and RH as ammonia readings in given graphs
58
59  const double Intercept = 1.782663144;
60  const double RC_RH     = -0.748177946;
61
62  const double RC_T      = -0.015924756;
63  const double RC_RHT    =  0.006677957;
64
65  double calcfRHT = Intercept + RC_RH*RH + RC_T*T + RC_RHT*RH*T;
66  
67  return
68  calcfRHT; //Rs/R0 dimensionless
69}
70
71
72double calcRs(int sensorReading)
73  {   //Calculates Rs from amplified analog signal
74  const double gain = 1.0 +
75  10000.0/1000.0; //amplification of opamp as function of resistances in opamp circuit
76
77  const double Rref = 10.0; //Reference resistance (in kOhm) built in MQ-135 board
78  
79  double sensorOrigReading = sensorReading/gain;
80/*formula derivation:
81
82  *sensorOrigReading = 1024*Rref/(Rref+Rsensor)
83 *sensorOrigReading = 1024*1/(1+Rsensor/Rref)
84
85  *(1+Rsensor/Rref)  = 1024/sensorOrigReading
86 *Rsensor = (1024/sensorOrigReading-1)*Rref
87
88  */
89  double Rsensor = (1024.0/sensorOrigReading-1.0)*Rref; 
90  
91  return
92  Rsensor; //kOhm
93}
94
95
96double calcCO2(double Rs, double fRHT) {
97  const
98  double R410    = 270.0; //Measured resistance (in kOhm) after one night with open
99  window
100  const double fRHT410 = 1.08;  //calcutated correction factor after one
101  night with open window
102  const double a  =  410.0;
103  const double b  = -2.769034857;
104  //slope from Mad Frog
105  
106  double CO2 = a*pow((Rs/fRHT)/(R410/fRHT410),b);
107  //CO2atm = 410 ppm
108  
109  return CO2;//ppm
110}
111

#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
}

CO2v2.ino

c_cpp

Main program

1#include <SPI.h>
2#include <SD.h>
3#include <LiquidCrystal.h>
4#include
5  "Time.h"
6#include "Calculations.h"
7
8const int rs = 8, en = 7, d4 =
9  6, d5 = 5, d6 = 4, d7 = 3;
10LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
11
12//
13  set up variables using the SD utility library functions:
14Sd2Card card;
15SdVolume
16  volume;
17SdFile root;
18//pin connected to CS of SD card shield
19const int
20  chipSelect = 2;
21
22#define _dd_   20
23#define _mm_    1
24#define _yy_   20
25
26#define
27  _hr_   17
28#define _min_   54
29#define _sec_   0
30
31char fileName[13];
32
33//Set
34  start time and date
35Time myTime(_hr_,_min_,_sec_,_dd_,_mm_,_yy_); //hr,min,sec,d,m,y
36
37//used
38  connections to Arduino
39const byte Td_sensor  = A0;
40const byte Tw_sensor  =
41  A1;
42const byte CO2_sensor = A2;
43const byte checkLight =  9;
44
45
46//Data
47  are stored in data array (double data[]) to ease printing and writing to SD card
48  and LCD screen. Here the positions of the data in the array are given. 
49const
50  byte Td   = 0; //deg Celcius
51const byte Tw   = 1;  
52const byte RH   = 2; //relative
53  humidity
54const byte CO2  = 3; //ppm
55const byte pWd  = 4; //kPa
56const byte
57  pWw  = 5; 
58const byte fRHT = 6; //-
59const byte Rs   = 7; //kohm
60const byte
61  numData = 8; //number of data in data []
62
63
64const String degC = String ("\\xC2\\xB0")
65  + String("C");
66const String labels[numData] = {"Td" ,"Tw" ,"RH","CO2","pWd","pWw","fRHT","Rs"
67  };
68const String units [numData] = {degC ,degC ,"-" ,"ppm","Pa" ,"Pa"
69  ,"-"   ,"kohm"};
70
71
72void setup() {
73  pinMode(Td_sensor ,INPUT);
74
75  pinMode(Tw_sensor ,INPUT);
76  pinMode(CO2_sensor,INPUT);
77  pinMode(checkLight,OUTPUT);
78
79
80  lcd.begin(16, 2);
81  lcd.print("hello, world!");
82  
83  Serial.begin(9600);
84
85  String fileNameConst = String("WK") + myTime.dateToString("") + String(".txt");
86
87  strcpy(fileName,fileNameConst.c_str());
88
89  Serial.print("Initializing SD
90  card...");
91
92  // see if the card is present and can be initialized:
93  if
94  (!SD.begin(chipSelect)) {
95    Serial.println("Card failed, or not present");
96
97    // don't do anything more:
98    while (1);
99  }
100  Serial.println("card
101  initialized.");
102  delay(200);
103  
104  // if the file is available, write
105  to it:
106  // prepare datastring with current time and datalabels as column headers
107
108  myTime.updTime();
109  String dataString = myTime.dateToString();
110  dataString+=
111  ",";
112  dataString+= myTime.timeToString();
113  for (int i = 0; i<numData;
114  i++) {
115    dataString+= ",";   
116    dataString+= labels[i];
117  }
118
119
120  File dataFile = SD.open(fileName,FILE_WRITE);
121  if (dataFile) {
122    dataFile.println();
123
124    dataFile.println(dataString);
125    dataFile.close();
126  }
127  // if the
128  file isn't open, pop up an error:
129  else {
130    Serial.println("error opening
131  datalog.txt");
132  } 
133}
134
135
136void loop() {
137  myTime.updTime();
138
139  digitalWrite(checkLight,LOW);   //put here to see if the system is working. now
140  not needed anymore as LCD was installed
141
142  Serial.println(myTime.timeToString()
143  + " " + myTime.dateToString());
144
145  //fill data array with fresh measurement
146  results
147  double data [numData];
148  data[Td]   = calcTemp(readSensor(Td_sensor));
149  //degrees C
150  data[Tw]   = calcTemp(readSensor(Tw_sensor));  
151  data[pWd]
152  = calcPw(data[Td]);                 //kPa
153  data[pWw]  = calcPw(data[Tw]);
154
155  data[RH]   = calcRH(data[Td],data[Tw],data[pWd],data[pWw]); //dimensionless
156
157  data[fRHT] = calcfRHT(data[RH],data[Td]);      //humidity and temperature correction
158  factor, dimensionless
159  data[Rs]   = calcRs(readSensor(CO2_sensor));   //kohm
160
161  data[CO2]  = calcCO2(data[Rs],data[fRHT]);     //ppm
162
163  dataToScreen(labels,data,units);
164
165
166  dataToLCD(labels,data);
167  
168  // make a string for assembling the data to
169  log:
170  String dataString = "";
171
172  dataString += myTime.dateToString();
173  //start with current time and date
174  dataString += ",";
175  dataString +=
176  myTime.timeToString();  
177
178  for (int i=0; i<numData; i++) {          //add
179  all data to dataString
180    dataString += ",";    
181    dataString += String(data[i]);
182
183  }
184
185  // open the file. note that only one file can be open at a time,
186
187  // so you have to close this one before opening another.
188  File dataFile =
189  SD.open(fileName, FILE_WRITE);
190
191  // if the file is available, write to it:
192
193  if (dataFile) {
194    dataFile.println(dataString);
195    dataFile.close();
196
197  }
198  // if the file isn't open, pop up an error:
199  else {
200    Serial.println("error
201  opening datalog.txt");
202  }
203  
204  //halfway time: show time, date, Rs and
205  CO2
206  lcd.clear();
207  lcd.print(myTime.timeToString());
208  lcd.print("   ");
209
210  lcd.print(myTime.dateToString());
211  lcd.setCursor(0,1);  
212  lcd.print("Rs=");
213
214  lcd.print(data[Rs],0);
215  lcd.print("  CO2=");
216  lcd.print(data[CO2],0);
217  
218  
219  digitalWrite(checkLight,HIGH);
220  const unsigned long loopDuration
221  = 30000;
222  while (millis() - myTime.lastMillis() < loopDuration) { //wait until
223  loopDuration 
224    ;
225  }
226}
227  
228
229//return sensor value
230int readSensor(const
231  byte address) {
232  int value = 0;
233  byte numMeas = 32; //should not be larger
234  than 2^6=64 (int value may roll over)
235  for (int i=0; i<numMeas; i++) {
236    value
237  +=  analogRead(address);
238    delay(100);  //this makes the sketch slow (32 times
239  100 times 3 = 9600 millisec (almost 10 sec)
240  }
241  value /= numMeas;
242  return
243  value;
244}
245
246
247//write data to screen
248void dataToScreen(const String
249  label[],const double data[],const String unit[]) {  //all arguments declared constant
250  as this procedure is not supposed to change any data
251  for (int i=0; i<numData;
252  i++) {
253    if (i==RH) { //RH is printed as % instead of fraction
254      Serial.print(label[i]),
255  Serial.print(":\	"), Serial.print(data[i]*100,2),  Serial.print("\	"), Serial.println("%");
256
257    }
258    else {
259      Serial.print(label[i]), Serial.print(":\	"), Serial.print(data[i],2),
260      Serial.print("\	"), Serial.println(unit[i]);  
261    }
262  }
263  Serial.println();
264}
265
266
267//write
268  data to LCD
269void dataToLCD(const String label[],const double data[]) {
270  lcd.clear();
271  
272  for (int i = Td; i<=CO2; i++) {
273       lcd.print(label[i]);
274       lcd.print("=");
275
276       int decimals = 1;
277       if (i==CO2) decimals = 0;
278       if (i== RH)
279  decimals = 2;
280       lcd.print(data[i],decimals);  
281       lcd.print(" ");
282  
283       if (i== Td) lcd.print(" ");
284       if (i== Tw) lcd.setCursor(0,1);
285  
286  }
287}
288

#include <SPI.h>
#include <SD.h>
#include <LiquidCrystal.h>
#include
  "Time.h"
#include "Calculations.h"

const int rs = 8, en = 7, d4 =
  6, d5 = 5, d6 = 4, d7 = 3;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

//
  set up variables using the SD utility library functions:
Sd2Card card;
SdVolume
  volume;
SdFile root;
//pin connected to CS of SD card shield
const int
  chipSelect = 2;

#define _dd_   20
#define _mm_    1
#define _yy_   20

#define
  _hr_   17
#define _min_   54
#define _sec_   0

char fileName[13];

//Set
  start time and date
Time myTime(_hr_,_min_,_sec_,_dd_,_mm_,_yy_); //hr,min,sec,d,m,y

//used
  connections to Arduino
const byte Td_sensor  = A0;
const byte Tw_sensor  =
  A1;
const byte CO2_sensor = A2;
const byte checkLight =  9;


//Data
  are stored in data array (double data[]) to ease printing and writing to SD card
  and LCD screen. Here the positions of the data in the array are given. 
const
  byte Td   = 0; //deg Celcius
const byte Tw   = 1;  
const byte RH   = 2; //relative
  humidity
const byte CO2  = 3; //ppm
const byte pWd  = 4; //kPa
const byte
  pWw  = 5; 
const byte fRHT = 6; //-
const byte Rs   = 7; //kohm
const byte
  numData = 8; //number of data in data []


const String degC = String ("\\xC2\\xB0")
  + String("C");
const String labels[numData] = {"Td" ,"Tw" ,"RH","CO2","pWd","pWw","fRHT","Rs"
  };
const String units [numData] = {degC ,degC ,"-" ,"ppm","Pa" ,"Pa"
  ,"-"   ,"kohm"};


void setup() {
  pinMode(Td_sensor ,INPUT);

  pinMode(Tw_sensor ,INPUT);
  pinMode(CO2_sensor,INPUT);
  pinMode(checkLight,OUTPUT);


  lcd.begin(16, 2);
  lcd.print("hello, world!");
  
  Serial.begin(9600);

  String fileNameConst = String("WK") + myTime.dateToString("") + String(".txt");

  strcpy(fileName,fileNameConst.c_str());

  Serial.print("Initializing SD
  card...");

  // see if the card is present and can be initialized:
  if
  (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");

    // don't do anything more:
    while (1);
  }
  Serial.println("card
  initialized.");
  delay(200);
  
  // if the file is available, write
  to it:
  // prepare datastring with current time and datalabels as column headers

  myTime.updTime();
  String dataString = myTime.dateToString();
  dataString+=
  ",";
  dataString+= myTime.timeToString();
  for (int i = 0; i<numData;
  i++) {
    dataString+= ",";   
    dataString+= labels[i];
  }


  File dataFile = SD.open(fileName,FILE_WRITE);
  if (dataFile) {
    dataFile.println();

    dataFile.println(dataString);
    dataFile.close();
  }
  // if the
  file isn't open, pop up an error:
  else {
    Serial.println("error opening
  datalog.txt");
  } 
}


void loop() {
  myTime.updTime();

  digitalWrite(checkLight,LOW);   //put here to see if the system is working. now
  not needed anymore as LCD was installed

  Serial.println(myTime.timeToString()
  + " " + myTime.dateToString());

  //fill data array with fresh measurement
  results
  double data [numData];
  data[Td]   = calcTemp(readSensor(Td_sensor));
  //degrees C
  data[Tw]   = calcTemp(readSensor(Tw_sensor));  
  data[pWd]
  = calcPw(data[Td]);                 //kPa
  data[pWw]  = calcPw(data[Tw]);

  data[RH]   = calcRH(data[Td],data[Tw],data[pWd],data[pWw]); //dimensionless

  data[fRHT] = calcfRHT(data[RH],data[Td]);      //humidity and temperature correction
  factor, dimensionless
  data[Rs]   = calcRs(readSensor(CO2_sensor));   //kohm

  data[CO2]  = calcCO2(data[Rs],data[fRHT]);     //ppm

  dataToScreen(labels,data,units);


  dataToLCD(labels,data);
  
  // make a string for assembling the data to
  log:
  String dataString = "";

  dataString += myTime.dateToString();
  //start with current time and date
  dataString += ",";
  dataString +=
  myTime.timeToString();  

  for (int i=0; i<numData; i++) {          //add
  all data to dataString
    dataString += ",";    
    dataString += String(data[i]);

  }

  // open the file. note that only one file can be open at a time,

  // so you have to close this one before opening another.
  File dataFile =
  SD.open(fileName, FILE_WRITE);

  // if the file is available, write to it:

  if (dataFile) {
    dataFile.println(dataString);
    dataFile.close();

  }
  // if the file isn't open, pop up an error:
  else {
    Serial.println("error
  opening datalog.txt");
  }
  
  //halfway time: show time, date, Rs and
  CO2
  lcd.clear();
  lcd.print(myTime.timeToString());
  lcd.print("   ");

  lcd.print(myTime.dateToString());
  lcd.setCursor(0,1);  
  lcd.print("Rs=");

  lcd.print(data[Rs],0);
  lcd.print("  CO2=");
  lcd.print(data[CO2],0);
  
  
  digitalWrite(checkLight,HIGH);
  const unsigned long loopDuration
  = 30000;
  while (millis() - myTime.lastMillis() < loopDuration) { //wait until
  loopDuration 
    ;
  }
}
  

//return sensor value
int readSensor(const
  byte address) {
  int value = 0;
  byte numMeas = 32; //should not be larger
  than 2^6=64 (int value may roll over)
  for (int i=0; i<numMeas; i++) {
    value
  +=  analogRead(address);
    delay(100);  //this makes the sketch slow (32 times
  100 times 3 = 9600 millisec (almost 10 sec)
  }
  value /= numMeas;
  return
  value;
}


//write data to screen
void dataToScreen(const String
  label[],const double data[],const String unit[]) {  //all arguments declared constant
  as this procedure is not supposed to change any data
  for (int i=0; i<numData;
  i++) {
    if (i==RH) { //RH is printed as % instead of fraction
      Serial.print(label[i]),
  Serial.print(":\	"), Serial.print(data[i]*100,2),  Serial.print("\	"), Serial.println("%");

    }
    else {
      Serial.print(label[i]), Serial.print(":\	"), Serial.print(data[i],2),
      Serial.print("\	"), Serial.println(unit[i]);  
    }
  }
  Serial.println();
}


//write
  data to LCD
void dataToLCD(const String label[],const double data[]) {
  lcd.clear();
  
  for (int i = Td; i<=CO2; i++) {
       lcd.print(label[i]);
       lcd.print("=");

       int decimals = 1;
       if (i==CO2) decimals = 0;
       if (i== RH)
  decimals = 2;
       lcd.print(data[i],decimals);  
       lcd.print(" ");
  
       if (i== Td) lcd.print(" ");
       if (i== Tw) lcd.setCursor(0,1);
  
  }
}

Time.cpp

c_cpp

Time and date utility

1#include "Arduino.h"
2#include "Time.h"
3
4Time::Time (byte
5  hr, byte mnt, byte sec, byte d, byte m, byte y) { 
6  _timeStart = (hr*60UL+mnt)*60UL+
7  sec; //initialize _timeStart 
8  _lastMillis = millis();               //last
9  time millis() was called
10  _curTime = _lastMillis/1000UL;        //time since
11  start of program in seconds (rollover after 49000 days, rollover is prevented by
12  updDate() after 1 day)
13
14  //initialize _Time[]
15  _Time[0]      = hr;
16
17  _Time[1]      = mnt;
18  _Time[2]      = sec; 
19
20  //initialize _Date[]
21
22  _Date[0]      = d;
23  _Date[1]      = m;
24  _Date[2]      = y;
25
26  _dayRollover
27  = false; 
28}
29
30
31void Time::updTime() {
32  unsigned long curMillis
33  = millis();
34  _curTime   += curMillis/1000UL - _lastMillis/1000UL;  //update
35  _curTime
36  _lastMillis = curMillis;                              //record _lastMilles
37  for use during next call of updTime()
38
39  unsigned long curTime = _curTime
40  + _timeStart;
41  if               (curTime/(24UL*60UL*60UL) > 0) _dayRollover
42  = true;  //if time goes beyond 23:23:59 dayrollover occurs and time returs toe
43
44  //update _Time[]
45  curTime      =    curTime%(24UL*60UL*60UL);
46  _Time[0]
47     =    curTime/(60UL*60UL);
48  curTime      =    curTime%(60UL*60UL);
49  _Time[1]
50     =    curTime/60UL;
51  curTime      =    curTime%60UL;
52  _Time[2]     =
53    curTime;
54
55  //if needed, update _Date
56  if (_dayRollover) updDate();
57  //if dayrollover, then adjust date
58}
59
60
61void Time::updDate() {
62  const
63  byte maxDays[13] = {0,31,29,31,30,31,30,31,31,30,31,30,31}; //2020 is leap year,
64  next year change num days of February
65  const byte day   = 0; //makes code more
66  easy to read
67  const byte month = 1;
68  const byte year  = 2;
69  
70  _Date[day]++;
71
72  if (_Date[day] > maxDays[_Date[month]]) {  //if monthrollover then adjust month
73
74    _Date[day]     = 1;
75    _Date[month]++;
76    if (_Date[month] > 12) {                 //if
77  yearrollover then adjust year
78      _Date[month] = 1;
79      _Date[year]++;
80
81    }
82  }
83  _curTime = _curTime - (24UL*60UL*60UL);    //update _curTime (subtract
84  one day)
85  _dayRollover = false;
86}
87
88
89unsigned long Time::lastMillis()
90  {
91  return _lastMillis;
92}
93
94
95String Time::timeToString(String sign)
96  {
97  return toString(_Time, sign);
98}
99
100
101String Time::dateToString(String
102  sign) {
103  return toString(_Date, sign);
104}
105
106
107String Time::toString(byte*
108  tostring, String sign) {
109  String string = "";
110  string += leadingZeros(tostring[0]);
111
112  for (byte i=1; i<3; i++) {
113     string+= sign;
114     string+= leadingZeros(tostring[i]);
115
116  }
117  return string;
118}
119
120
121String Time::leadingZeros(byte value) {
122
123  String string = "";
124  if (value < 10) {
125    string += "0";
126  }
127
128  string += String(value);   
129  return string;
130}
131

#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

c_cpp

Header for Time.ccp

1/*
2 *Time.h - Time library
3 *Records starting time and date of project  (as given in source code by programmer)
4 *Can return String with current Time  (hh:mm:ss) 
5 *Can return String with current date (dd-mm-yy)
6 *Can return  millis since start Time
7 *Created by Koen Meesters, december 2019
8 *Last edited  Februari 2020
9 */
10#ifndef Time_h
11#define Time_h
12
13#include "Arduino.h"
14
15class  Time {
16  public:
17    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
18    
19    String timeToString(String sign = ":"); //returns time in a String, default  sign for time is :
20    String dateToString(String sign = "-"); //returns date  in a String, default sign for date is -
21
22    unsigned long lastMillis(); 
23    void updTime();                         //update the time in _Time[3]
24    
25  private:
26    byte _Time[3];                          //stores time in 3 bytes  hr min sec
27    byte _Date[3];                          //stores date in 3 bytes  day month year
28    bool _dayRollover;                      //flag set if time  goes beyond 23:59:59   
29
30    unsigned long _timeStart;               //start  time in seconds
31    unsigned long _curTime;                 //current time in  seconds
32    unsigned long _lastMillis;              //millis() last time updTime()  was run 
33
34
35    void updDate();                         //update the date  in _Date[3] (should be run at least every day, otherwise it misses 1 dayrollover)
36    
37    String toString(byte*, String sign);    //makes a string from _Time[3]  or _Date[3]
38    String leadingZeros(byte value);        //adds leading zeros  if number is smaller than 10 ( 3 --> "03") 
39};
40
41#endif
42

/*
 *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

Downloadable files

Wiring CO2 measurement and logging project

Measures CO2 concentration. Correction for temperature and relative humidity. Writes results to SD card and LCD display

Wiring CO2 measurement and logging project

Comments

Only logged in users can leave comments

Anonymous user

2 years ago

Cool project. It looks like you are deriving the CO2 concentration based on other metrics using a formula. So how precise are those CO2 concentrations ? How satisfied are you of the MQ-135 sensor ?

ArduinoKoen

2 years ago

Dear Jan, I have derived my formulas from datasheets on mq135. The measurement is corrected for water content in the air and temperature. Since I used the monitor inside, RH and T did not really vary much. The meter readings however were highly fluctuating. One would expect that during the night the value gradually will come back to the background CO2 concentration. This value however is different every day. It seems that some pollutants adsorb on the element that do not come off easily. Good about MQ 135 is that it senses human presence quite well. As soon as someone enters the room, the readings go up. Especially when all windows and doors are closed. From the time needed to reach a new steady state I have derived that our house needs better ventilation. I also found datasheets stating that mq135 is sensitive to many more gasses than only CO2. So, MQ135 shows large measuring drift, is not selective and can still give an impression on ventilation in your house and air quality (good/reasonable/bad). Sensitivity should be set via calibration, not with data from the datasheet as it varies from sensor to sensor and from time to time. For me it was a fun project and I had in mind to do an update of my project with my experiences... Good luck. Groet, Koen. Outlook voor Android downloaden (https://aka.ms/ghei36) ------------------------------- Van: Hackster.io <help@hackster.io> Verstuurd: maandag 26 oktober 2020 11:29 Aan: koenmeesters@hotmail.com Onderwerp: New comment for CO2 Monitor

Anonymous user

2 years ago

Hi Koen, On AliExpress I find a whole range of MQ-135's. Which one did you use? Thnx Jaap

Anonymous user

4 years ago

Cool project. It looks like you are deriving the CO2 concentration based on other metrics using a formula. So how precise are those CO2 concentrations ? How satisfied are you of the MQ-135 sensor ?

ArduinoKoen

2 years ago

Anonymous user

4 years ago

Hi Koen, On AliExpress I find a whole range of MQ-135's. Which one did you use? Thnx Jaap

Anugrah_123

5 years ago

how to add calculations.h directory .pls uplode a zip file of thes directory

IoT_hobbyist

2 years ago

It is similar to how to add pitches.h, see: https://arduinogetstarted.com/tutorials/arduino-potentiometer-triggers-piezo-buzzer#content_arduino_code_-_melody_-_voltage_threshold

ArduinoKoen

2 Followers

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Downloadable files