const float VOLTAGE = 5.00;    //system voltage
#define OFFSET 0       //zero drift voltage
#define LED 13         //operating instructions

double orpValue;

#define ArrayLenth  40    //times of collection
#define orpPin 1          //orp meter output,connect to Arduino controller ADC pin

int orpArray[ArrayLenth];
int orpArrayIndex=0;

double avergearray(int* arr, int number){
  int i;
  int max,min;
  double avg;
  long amount=0;
  if(number<=0){
    printf("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;
}

#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 20, 4);

float U;  // tension mesurée à l'entrée analogique
float ORP; // sortie potentiel Redox
int counter; int N = 10; // création compteur et nombre d'itération du compteur

void setup() {
  Serial.begin(250000);
  pinMode(LED,OUTPUT);
  lcd.init(); lcd.backlight();
}

void loop() {
  static unsigned long orpTimer=millis();   //analog sampling interval
  static unsigned long printTime=millis();
  if(millis() >= orpTimer)
  {
    orpTimer=millis()+20;
    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*1000/1023))/75-OFFSET;

    //convert the analog value to orp according the circuit
  }
  if(millis() >= printTime)   //Every 800 milliseconds, print a numerical, convert the state of the LED indicator
  {
    printTime=millis()+800;
    Serial.print("ORP: ");
    Serial.print((int)orpValue);
        Serial.println("mV");
        digitalWrite(LED,1-digitalRead(LED));
  }
  U = 0; ORP = 0;
  for (counter = 0; counter < N; ++counter) {
  U += analogRead(A1)*5.0/1023; // 0 si 0V et 1023 si 5V - lecture de la broche A15
  ORP += 1e3*(2-analogRead(A1)*5.0/1023)-OFFSET; 
  }
  lcd.clear();
  lcd.setCursor(0, 1); lcd.print("U = ") ; lcd.print(U/N,5); lcd.print(" V");
  lcd.setCursor(0, 2); lcd.print("ORP = ") ; lcd.print(int(ORP/N)); lcd.print(" mV");
  lcd.setCursor(0, 3); lcd.print(millis()%100);
  delay(1e3);

}