#define SensorPin A0          // the pH meter Analog output is connected with the Arduino’s Analog

unsigned long int avgValue;  //Store the average value of the sensor feedback

float b;

int buf[10],temp;

void setup()

{

  pinMode(13,OUTPUT);  

  Serial.begin(9600);  

  Serial.println("Ready");    //Test the serial monitor

}

void loop()

{

  for(int i=0;i<10;i++)       //Get 10 sample value from the sensor for smooth the value

  { 

    buf[i]=analogRead(SensorPin);

    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(buf[i]>buf[j])

      {

        temp=buf[i];

        buf[i]=buf[j];

        buf[j]=temp;

      }

    }

  }

  avgValue=0;

  for(int i=2;i<8;i++)                      //take the average value of 6 center sample

    avgValue+=buf[i];

  float phValue=(float)avgValue*5.0/1024/6; //convert the analog into millivolt

  phValue=3.5*phValue;                      //convert the millivolt into pH value

  Serial.print("    pH:");  

  Serial.print(phValue,2);

  Serial.println(" ");

  digitalWrite(13, HIGH);       

  delay(800);

  digitalWrite(13, LOW); 

}

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