#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
// the pH meter Analog output is connected with the Arduino’s A0
int phval = 0;
// Store the average value of the sensor feedback
unsigned long int avgval;
int buffer_arr[10], temp;

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.begin(16, 2);
  lcd.backlight();
  lcd.setCursor(0, 0);
  delay(2000);
  lcd.clear();
}

void loop() {
  // Get 10 sample value from the sensor for smooth the value
  for (int i = 0; i < 10; i++) {
    buffer_arr[i] = analogRead(A0);
    delay(30);
  }
  // sort the analog from small to large
  for (int i = 0; i < 9; i++) {
    for (int j = i + 1; j < 10; j++) {
      if (buffer_arr[i] > buffer_arr[j]) {
        temp = buffer_arr[i];
        buffer_arr[i] = buffer_arr[j];
        buffer_arr[j] = temp;
      }
    }
  }
  avgval = 0;
  // take the average value of 6 center sample
  for (int i = 2; i < 8; i++)
    avgval += buffer_arr[i];
  // convert the analog into millivolt
  float volt = (float)avgval * 5.0 / 1024 / 6;
  // convert the millivolt into pH value
  float ph_act = 3.5 * volt;
  lcd.setCursor(0, 0);
  lcd.print("pH Val:");
  lcd.setCursor(8, 0);
  lcd.print(ph_act);
  delay(1000);
}