#define PHpin A0


// pH promenne
float Healthy1_mv=1.96;
float average=0;
float mvReading=0;
float PHValue=0;
float mvReading_7=3.50; // hodnota vrácena sondou při kalibraci v roztoku pH7
float mvReading_4=4.26; // hodnota vrácena sondou při kalibraci v roztoku pH4
float Slope=0;
float Vs=5;
float offset=0;

// Kelman filter
float varVolt=1.12184278324081E-05;
float varProcess=1e-9;
float Pc=0.0;
float G=0.0;
float P=1.0;
float Xp=0.0;
float Zp=0.0;
float Xe=0.0;


void setup() {
  Serial.begin(115200);


  }

void loop() {


    mereni_ph();
   delay(1000);


}



void mereni_ph()
{
  Slope_calc();

  int i=0;
  unsigned long sum=0;
  long reading=0;
  average=0;
  while(i<=50){
  reading=analogRead(PHpin);
  sum=sum+reading;
    delay(2);
    i++;
  }
  average=sum/i;
  Pc=P + varProcess;
  G=Pc/(Pc + varVolt);
  P=(1-G)*Pc;
  Xp=Xe;
  Zp=Xp;
  Xe=G*(average-Zp)+Xp;


mvReading=Xe*Vs/1024;     //Converting to mV reading and then to pH
Serial.println("");
Serial.print("mvReading : ");
Serial.println(mvReading);

PHValue=(7-((mvReading_7-mvReading)*Slope));
Serial.println("");
Serial.print("PHValue : ");
Serial.println(PHValue,1);
Serial.println("------------------");

}

void Slope_calc()
{
  offset=Healthy1_mv-mvReading_7;
  Slope=3/(Healthy1_mv-mvReading_4-offset);
}