// Source : https://how2electronics.com/ph-meter-using-ph-sensor-arduino-oled/#:~:text=For%20testing%20the%20Ph%20meter%20designed%20above

#define pHSensorPin1 A0 // the pH sensor 1 Analog output
#define pHSensorPin2 A1 // the pH sensor 2 Analog output
unsigned long int avgValue1;  //Store the average value of the sensor 1 feedback
unsigned long int avgValue2;  //Store the average value of the sensor 2 feedback
int buf1[10],temp1;
int buf2[10],temp2;

void setup()
{ 
  Serial.begin(9600);  
}

void loop()
{

// Ph sensor 1
for(int i=0;i<10;i++)       //Get 10 sample value from the sensor for smooth the value
  { 
    buf1[i]=analogRead(pHSensorPin1);
    delay(10);
  }
  for(int i=0;i<9;i++)        //sort the analog from small to large
  {
    for(int j=i+1;j<10;j++)
    {
      if(buf1[i]>buf1[j])
      {
        temp1=buf1[i];
        buf1[i]=buf1[j];
        buf1[j]=temp1;
      }
    }
  }
  avgValue1=0;
  for(int i=2;i<8;i++)                      //take the average value of 6 center sample
    avgValue1+=buf1[i];
  float phValue1=(float)avgValue1*5.0/1024/6; //convert the analog into millivolt
  phValue1=3.5*phValue1;                      //convert the millivolt into pH value
  Serial.print("pH_1:");  
  Serial.print(phValue1,2);
  Serial.println(" ");
 
//Ph sensor 2
for(int i=0;i<10;i++)       //Get 10 sample value from the sensor for smooth the value
  { 
    buf2[i]=analogRead(pHSensorPin2);
    delay(10);
  }
  for(int i=0;i<9;i++)        //sort the analog from small to large
  {
    for(int j=i+1;j<10;j++)
    {
      if(buf2[i]>buf2[j])
      {
        temp2=buf2[i];
        buf2[i]=buf2[j];
        buf2[j]=temp2;
      }
    }
  }
  avgValue2=0;
  for(int i=2;i<8;i++)                      //take the average value of 6 center sample
    avgValue2+=buf2[i];
  float phValue2=(float)avgValue2*5.0/1024/6; //convert the analog into millivolt
  phValue2=3.5*phValue2;                      //convert the millivolt into pH value
  Serial.print("pH_2:");  
  Serial.print(phValue2,2);
  Serial.println(" "); 
}