pH.ino

#define VOLTAGE 5.00    //system voltage
#define OFFSET 12       //orp zero drift voltage
#define LED 13          //operating instructions

#define SensorPin A0            //pH meter Analog output to Arduino Analog Input 0
#define orpPin A5               //orp meter output,connect to Arduino controller ADC pin
#define Offset 0.00             //deviation compensate
#define LED 13
#define samplingInterval 20

#define printInterval 30000
#define ArrayLenth  40    //times of collection
int pHArray[ArrayLenth];   //Store the average value of the sensor feedback
int pHArrayIndex=0;    
int orpArray[ArrayLenth];
int orpArrayIndex = 0;

double orpValue;

unsigned long time_cnt = 0;

void setup(void)
{
  pinMode(LED,OUTPUT);  
  Serial.begin(9600);
  Serial.println("Time, pH, ORP");
}
void loop(void)
{
  static unsigned long samplingTime = millis();
  static unsigned long orpTimer = millis(); //analog sampling interval
  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;

      orpArray[orpArrayIndex++] = analogRead(orpPin);  //read an analog value every 20ms
      if (orpArrayIndex == ArrayLenth) orpArrayIndex = 0;
      orpValue = ((30 * (double)VOLTAGE * 1000) - (75 * avergearray(orpArray, ArrayLenth) * VOLTAGE * 1000 / 1024)) / 75 - OFFSET; //convert the analog value to orp according the circuit

      samplingTime=millis();
  }
  
  if(millis() - printTime > printInterval)
  {
        Serial.print(time_cnt++);
        Serial.print(", ");
        Serial.print(pHValue,2);
        Serial.print(", ");
        Serial.println(orpValue,2);
        digitalWrite(LED,digitalRead(LED)^1);
        printTime=millis();
  }
}
double avergearray(int* arr, int number){
  int i;
  int max,min;
  double avg=0;
  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;
}