How to DIY an Indoor Carbon Dioxide Detector

Tutorial by Phoebe

It's 12:50, right after lunch. The gloomy winter has arrived months ago, and you had just settled your brain for a short winter's nap in the warm office. Some people may think that ventilation is the same thing as air conditioning, but does it really make sense of keeping a closed, dense space air-conditioned all day long? The high temperature and poor heat dissipation makes the room similar to a "greenhouse", and Carbon Dioxide is the largest contributor to the greenhouse effect. Thus I decided to DIY an simple indoor carbon dioxide detector with Arduino.

Hardware Used
1) DFRduino UNO R3
2) LCD12864 Shield for Arduino
3) Arduino Compatible CO2 Sensor
4) 7.4 V, 2200 ma lipo battery (with charge and discharge protection circuit)
Please remember installing the U8g library into Arduino IDE library before uploading the following code.

/*
 # This Sample code is for display the CO2 sensor output on LCD12864.

 # Editor : Phoebe
 # Date   : 2014.1.15
 # Ver    : 0.1
 # Product: LCD12864 Shield for Arduino
 # SKU    : DFR0287

 # Hardwares:
 1. Arduino UNO
 2. LCD12864 Shield for Arduino  
 3. CO2 Sensor

 #Steps:
 1.Connect the CO2 Sensor to the Analog pin 0
 2.Power the UNO board with 7~12V 

*/

#include "U8glib.h"

U8GLIB_NHD_C12864 u8g(13, 11, 10, 9, 8);   // SPI Com: SCK = 13, MOSI = 11, CS = 10, A0 = 9, RST = 8

#define         MG_PIN                       (1)     //define which analog input channel you are going to use
#define         BOOL_PIN                     (2)
#define         DC_GAIN                      (8.5)   //define the DC gain of amplifier

#define         READ_SAMPLE_INTERVAL         (50)    //define how many samples you are going to take in normal operation
#define         READ_SAMPLE_TIMES            (5)     //define the time interval(in milisecond) between each samples in 

#define         ZERO_POINT_VOLTAGE           (0.324) //define the output of the sensor in volts when the concentration of CO2 is 400PPM
#define         REACTION_VOLTGAE             (0.020) //define the voltage drop of the sensor when move the sensor from air into 1000ppm CO2

float           CO2Curve[3]  =  {
  2.602,ZERO_POINT_VOLTAGE,(REACTION_VOLTGAE/(2.602-3))};  

int percentage;
float volts;

/*****************************  LCD12864 display ***********************************
Display the voltage & ppm data on the LCD12864
************************************************************************************/ 
void draw() {
  u8g.setFont(u8g_font_unifont);   
  u8g.drawStr( 0,11,"Voltage:");
  u8g.setPrintPos(70,11);
  u8g.print(volts); 
  u8g.drawStr( 110, 11,"V" );
  u8g.drawStr(0,30,"CO2:");
  if (percentage == -1) {
    u8g.drawStr( 40,30,"<400" );
  } 
  else {
    u8g.setPrintPos(40,30);
    u8g.print(percentage,DEC);
  }
  u8g.drawStr( 80,30,"ppm" );  
  u8g.drawStr( 3, 63,"www.DFRobot.com" );
}

/*****************************  MGRead *********************************************
Input:   mg_pin - analog channel
Output:  output of CO2 Sensor
Remarks: This function reads the output of CO2 Sensor
************************************************************************************/ 
float MGRead(int mg_pin)
{
  int i;
  float v=0;

  for (i=0;i=ZERO_POINT_VOLTAGE) {
    return -1;
  } 
  else { 
    return pow(10, ((volts/DC_GAIN)-pcurve[1])/pcurve[2]+pcurve[0]);
  }
}

void setup() {
  u8g.setRot180();// rotate screen, if required
}

void loop() { 

  volts = MGRead(MG_PIN);
  percentage = MGGetPercentage(volts,CO2Curve);
  u8g.firstPage();
  do  {
    draw();
  } 
  while( u8g.nextPage() );
  delay(200);
}

As seen on the screen, the indoor co2 concentration is < 400 PPM which is suitable for survival:)