#include <U8g2lib.h>
#include <Wire.h>

volatile float Threshold;
volatile float item;
U8G2_SSD1306_128X64_NONAME_1_HW_I2C u8g2(U8G2_R0, U8X8_PIN_NONE);

void page1() {
  u8g2.setFont(u8g2_font_timR12_tf);
  u8g2.setFontPosTop();
  u8g2.setCursor(0,20);
  u8g2.print(String("CO value:") + String(String(item)) + String(" % "));
}

void setup(){
  Threshold = 50;
  item = 0;
  u8g2.setI2CAddress(0x3C*2);
  u8g2.begin();
  u8g2.enableUTF8Print();

  pinMode(A0, INPUT);
  pinMode(13, OUTPUT);
}

void loop(){
  item = (map(analogRead(A0), 1, 1024, 1, 100));
  u8g2.firstPage();
  do
  {
    page1();
  }while(u8g2.nextPage());
  if (item >= Threshold) {
    digitalWrite(13,HIGH);

  } else {
    digitalWrite(13,LOW);

  }

}