#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 9, 4, 5, 6, 7); // the pins used on the LCD panel

/************************Hardware Related Macros************************************/
#define         MG_PIN                       A1     //CO2 sensor Analog output to Arduino Analog Input 0
#define         DC_GAIN                      8.5   //define the DC gain of amplifier
#define         SensorPin A0            //pH meter Analog output to Arduino Analog Input 0


/***********************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

#define         samplingInterval         20
#define         printInterval           60000  //print every 60000ms
#define         ArrayLenth               40    //times of collection


/**********************Application Related Macros**********************************/
//These two values differ from sensor to sensor. user should derermine this value.
#define         V400        (705)                 //measure the CO2 in the atmosphere(approximate 400ppm)
#define         V40000   (260)                  //measure 100% CO2

#define Offset 0.07           //pH meter deviation compensate

/*****************************Globals***********************************************/
float slope=(V40000-V400)/(4.602-2.602);  //calculate the correction line
           //log40000=4.602
           //log400=2.602

int pHArray[ArrayLenth];   //Store the average value of the sensor feedback
int pHArrayIndex=0;

void setup()
{
    Serial.begin(9600);
    lcd.begin(16, 2);              // start the library
    lcd.setCursor(0,0);            //set the cursor in the LCD to (0,0)
}


void loop()
{
    int percentage;
    float analogValue;
    float volts;

    static unsigned long samplingTime = millis();
    static unsigned long printTime = millis();
    static float pHValue,voltage;
    if(millis()-samplingTime > samplingInterval)
    {
      pHArray[pHArrayIndex++]=analogRead(SensorPin);
      if(pHArrayIndex==ArrayLenth)pHArrayIndex=0;
      voltage = avergearray(pHArray, ArrayLenth)*5.0/1024;
      pHValue = 3.5*voltage+Offset;
      samplingTime=millis();
    }
    analogValue = MGRead(MG_PIN);
    volts=analogValue*5/1024;
    percentage = MGGetPercentage(analogValue);
    if ((millis() - printTime > printInterval)){

    /******print CO2 value in serial******/
      Serial.print(analogValue);
      Serial.print( "\t" );
      Serial.print(volts);
      Serial.print( "V" );
      Serial.print( "\t" );
      Serial.print("CO2:");
      Serial.print(percentage);
      Serial.print( "ppm" );
      Serial.print( "\t" );

    /******print CO2 value in LCD******/
      lcd.setCursor(0,0);
      lcd.print("CO2:");
      lcd.print(percentage);
      lcd.setCursor(10,0);
      lcd.print( "ppm" );

    /*****print pH value on serial******/
      Serial.print( "Time point:" );
      Serial.print(millis());
      Serial.print( "\t" );
      Serial.print("  pH value: ");
      Serial.println(pHValue,4);
      Serial.print("\n");

    /*****print pH value on lcd******/
      lcd.setCursor(0,1);
      lcd.print("pH value: ");
      lcd.println(pHValue,4);

      printTime=millis();
  }
}

double avergearray(int* arr, int number){
  int i;
  int max,min;
  double avg;
  long amount=0;
  if(number<=0){
    Serial.println("Error number for the array to avraging!/n");
    return 0;
  }
  if(number<5){   //less than 5, calculated directly statistics
    for(i=0;i<number;i++){
      amount+=arr[i];
    }
    avg = amount/number;
    return avg;
  }else{
    if(arr[0]<arr[1]){
      min = arr[0];max=arr[1];
    }
    else{
      min=arr[1];max=arr[0];
    }
    for(i=2;i<number;i++){
      if(arr[i]<min){
        amount+=min;        //arr<min
        min=arr[i];
      }else {
        if(arr[i]>max){
          amount+=max;    //arr>max
          max=arr[i];
        }else{
          amount+=arr[i]; //min<=arr<=max
        }
      }//if
    }//for
    avg = (double)amount/(number-2);
  }//if
  return avg;
  delay(1000);
}

/*****************************  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 ;
    return v;
}

/*****************************  MQGetPercentage **********************************
the function which turns the analog value to the CO2 concentration
************************************************************************************/
int  MGGetPercentage(float analogValue)
{
     float logConc=2.602 +(analogValue-V400)/slope; //calculate the log of CO2 concentration
     return pow(10,logConc);
}