OLEDLOFASZ

// Internal Temperature Sensor
// Example sketch for ATmega328 types.
//
// https://playground.arduino.cc/Main/InternalTemperatureSensor/
//
// April 2012, Arduino 1.0

#include <U8g2lib.h>
U8G2_SSD1306_128X32_UNIVISION_F_SW_I2C u8g2(U8G2_R0, /* clock=*/ SCL, /* data=*/ SDA, /* reset=*/ U8X8_PIN_NONE);

void setup()
{
  Serial.begin(9600);

  Serial.println(F("Internal Temperature Sensor"));
  u8g2.begin();
  u8g2.clearBuffer();
  u8g2.setDrawColor(1);
  u8g2.setFontPosTop();
  u8g2.setFontDirection(2);
  u8g2.setFont(u8g2_font_timB12_tr);
  u8g2.drawStr(127,32, "NAGYLOFASZ");
  u8g2.sendBuffer();
  delay(2000);
}

void loop()
{
  // Show the temperature in degrees Celsius.
  Serial.println(GetTemp(),1);
  u8g2.clearBuffer();
  u8g2.setDrawColor(1);
  u8g2.setFontPosTop();
  u8g2.setFontDirection(2);
  u8g2.setFont(u8g2_font_timB12_tr);
  u8g2.setCursor (127,32);
  u8g2.print(GetTemp(),1);
   u8g2.sendBuffer();
  delay(1000);
}

double GetTemp(void)
{
  unsigned int wADC;
  double t;

  // The internal temperature has to be used
  // with the internal reference of 1.1V.
  // Channel 8 can not be selected with
  // the analogRead function yet.

  // Set the internal reference and mux.
  ADMUX = (_BV(REFS1) | _BV(REFS0) | _BV(MUX3));
  ADCSRA |= _BV(ADEN);  // enable the ADC

  delay(20);            // wait for voltages to become stable.

  ADCSRA |= _BV(ADSC);  // Start the ADC

  // Detect end-of-conversion
  while (bit_is_set(ADCSRA,ADSC));

  // Reading register "ADCW" takes care of how to read ADCL and ADCH.
  wADC = ADCW;

  // The offset of 324.31 could be wrong. It is just an indication.
  t = (wADC - 324.31 ) / 1.22;

  // The returned temperature is in degrees Celsius.
  return (t);
}