mg811test.ino

/************************Hardware Related Macros************************************/
#define         MG_PIN                       A0     //define which analog input channel you are going to use
#define         BOOL_PIN                     2
#define         DC_GAIN                      7.5   //define the DC gain of amplifier
 
/***********************Software Related Macros************************************/
#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 
                                                     //normal operation
 
/**********************Application Related Macros**********************************/
//These two values differ from sensor to sensor. user should derermine this value.
#define         ZERO_POINT_VOLTAGE          0.76 //define the output of the sensor in volts when the concentration of CO2 is 400PPM
#define         REACTION_VOLTGAE             0.31 //define the voltage drop of the sensor when move the sensor from air into 1000ppm CO2
 
/*****************************Globals***********************************************/
float CO2Curve[3]  =  {2.602,ZERO_POINT_VOLTAGE,(REACTION_VOLTGAE/(2.602-3))};   
                                                     //two points are taken from the curve. 
                                                     //with these two points, a line is formed which is
                                                     //"approximately equivalent" to the original curve.
                                                     //data format:{ x, y, slope}; point1: (lg400, 0.324), point2: (lg4000, 0.280) 
                                                     //slope = ( reaction voltage ) / (log400 –log1000) 
 
void setup()
{
    Serial.begin(9600);                              //UART setup, baudrate = 9600bps
    pinMode(BOOL_PIN, INPUT);                        //set pin to input
    digitalWrite(BOOL_PIN, HIGH);                    //turn on pullup resistors

  // Serial.print("MG-811 Demostration\n");                
}
 
void loop()
{
    int percentage;
    float volts;
// Serial.print( analogRead(MG_PIN));
    volts = MGRead(MG_PIN);
//    Serial.print( "SEN-00007:" );
   // Serial.print(volts); 
//    Serial.print( "V           " );
 
    percentage = MGGetPercentage(volts,CO2Curve);
    //Serial.print("CO2:");
    if (percentage == -1) {
        Serial.print( "<400" );
    } else {
        Serial.print(percentage);
    }
 
    //Serial.print( "ppm" );  
    //Serial.print("\n");
 
//    if (digitalRead(BOOL_PIN) ){
//        Serial.print( "=====BOOL is HIGH======" );
//    } else {
//        Serial.print( "=====BOOL is LOW======" );
//    }
 
    Serial.print("\n");
 
   //c delay(200);
}
 
/*****************************  MGRead *********************************************
Input:   mg_pin - analog channel
Output:  output of SEN-000007
Remarks: This function reads the output of SEN-000007
************************************************************************************/ 
float MGRead(int mg_pin)
{
    int i;
    float v=0;
 
    for (i=0;i<READ_SAMPLE_TIMES;i++) {
        v += analogRead(mg_pin);
        delay(READ_SAMPLE_INTERVAL);
    }
    v = (v/READ_SAMPLE_TIMES) *30/1024 ;     //change the factor for proper range
    return v;  
}
 
/*****************************  MQGetPercentage **********************************
Input:   volts   - SEN-000007 output measured in volts
         pcurve  - pointer to the curve of the target gas
Output:  ppm of the target gas
Remarks: By using the slope and a point of the line. The x(logarithmic value of ppm) 
         of the line could be derived if y(MG-811 output) is provided. As it is a 
         logarithmic coordinate, power of 10 is used to convert the result to non-logarithmic 
         value.
************************************************************************************/ 
int  MGGetPercentage(float volts, float *pcurve)
{
   if ((volts/DC_GAIN )>=ZERO_POINT_VOLTAGE) {
      return -1;
   } else { 
      return pow(10, ((volts/DC_GAIN)-pcurve[1])/pcurve[2]+pcurve[0]);
   }
}