Um monitor de temperatura triplo baseado em NTC, LM35 e o termômetro interno do Arduino.

InternalTemp.c

double readInternalTemp() {
  ADMUX = _BV(REFS1) | _BV(REFS0) | _BV(MUX3);
  delay(2);
  
  double result;
  byte mean = 0;
  for(;mean < MEAN_TEMP_INTERNAL; mean++){
    ADCSRA |= _BV(ADSC);
    while (bit_is_set(ADCSRA, ADSC));
    result += ((ADCH << 8) | ADCL);
  }
  result /= mean;
  
  result = (result - TEMP_INTERNAL_TOS) / TEMP_INTERNAL_K;
  return result;
}

parameters.h

#ifndef PARAMETERS_H
#define PARAMETERS_H 1

#include "Arduino.h"
#include "limits.h"
#include "debug.h" 


#if DEBUG > 0
#define SYNAP_SYS_BOARD "Arduino DEBUG" 
const byte LASERS[]    = { 2,  3,  4,  5,  6};
const byte SERVOS[]    = {12, 11, 10,  9,  8};
#elif defined(__AVR_ATmega2560__)  || defined(__AVR_ATmega1280__)  // Arduino Mega e Variantes
//#elif defined(ARDUINO_ARCH_AVR) && defined(ARDUINO_AVR_MEGA2560)
#define SYNAP_SYS_BOARD "Arduino MEGA"
const byte LASERS[]    = { 2,  3,  4,  5,  6};
const byte SERVOS[]    = {12, 11, 10,  9,  8};
#elif defined(__AVR_ATmega328P__) // Arduino UNO
//#elif defined(ARDUINO_ARCH_AVR) && defined(ARDUINO_AVR_UNO)
#define  SYNAP_SYS_BOARD "Arduino UNO"
const byte LASERS[]    = { 2,  3,  4,  5,  6};
const byte SERVOS[]    = {12, 11, 10,  9,  8};
#else
#error "Este codigo ainda nao esta pronto para outras plataformas"
#endif



#define TEMP_INTERNAL_TOS  19
#define TEMP_INTERNAL_K    10

#define MEAN_TEMP_ROOM      10
#define MEAN_TEMP_INTERNAL  10
#define MEAN_TEMP_HEAT_SINK  10


#define PIN_TEMP_HEAT_SINK A0
#define PIN_TEMP_ROOM      A1


const byte NUM_LASERS  = sizeof(LASERS) / sizeof(*LASERS);
const byte NUM_SERVOS  = sizeof(SERVOS) / sizeof(*SERVOS);

#define MAX_SERVO_ANGLE 179
#define MIDLE_SERVO_ANGLE (MAX_SERVO_ANGLE/2)
#define MIN_SERVO_ANGLE 0
#define SERVO_DELAY_TEST 250

#define DELAY_TEMP_ROOM       (1000)
#define DELAY_TEMP_HEAT_SINK  (1000)
#define DELAY_TEMP_INTERNAL   (1000)

// user apenas DEFAULT ou INTERNAL
#define TEMP_AREF  (INTERNAL) // cuidado ao fazer esta mudanca vc pode danificar o arduino
#endif

readInternalTemp.c

double readInternalTemp() {
  ADMUX = _BV(REFS1) | _BV(REFS0) | _BV(MUX3);
  delay(2);

  double result;
  byte mean = 0;
  for (; mean < MEAN_TEMP_INTERNAL; mean++) {
    ADCSRA |= _BV(ADSC);
    while (bit_is_set(ADCSRA, ADSC));
    result += ((ADCH << 8) | ADCL);
  }
  result /= mean;

  result = (result - TEMP_INTERNAL_TOS) / TEMP_INTERNAL_K;
  return result;
}

readRoomTemp.c

double readRoomTemp() {
  double temp;
  byte mean = 0;
  for (; mean < MEAN_TEMP_ROOM; mean++)
    temp += analogRead(PIN_TEMP_ROOM);
  temp /= mean;
#if (TEMP_AREF == (DEFAULT))  // para leitura com 5V de referencia
  const double fator = .48828125;
#elif (TEMP_AREF == (INTERNAL))  // para leitura com 1.1V de referencia
  const double fator  = .107421875;
#else
  const double fator = 0;
#endif
  temp  *= fator;
  return temp;
}

resultado.txt

/temp/heatsink/23.74/
/temp/room/6.03/
/temp/internal/20.74
/temp/heatsink/21.30/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.31/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.29/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.32/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.34/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.34/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.32/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.34/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.32/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.33/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.34/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.33/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.34/
/temp/room/6.05/
/temp/internal/20.71
/temp/heatsink/21.34/

temperatura_loop.ino

void loop() {
  long time = millis();
  if ((time - lastTimeTempHeatSink) > DELAY_TEMP_HEAT_SINK) {
    analogReference(DEFAULT);
    delay(10);
    double temp = readHeatSingkTemp();
    Serial.print("/temp/heatsink/");
    Serial.print(temp);
    Serial.println("/");
    lastTimeTempHeatSink = time;
  }
  if ((time - lastTimeTempRoom) > DELAY_TEMP_ROOM) {
    analogReference(TEMP_AREF);
    analogRead(PIN_TEMP_ROOM);

    Serial.print("/temp/room/");

    double temp = readRoomTemp();
    Serial.print(temp);
    Serial.println("/");

    analogReference(DEFAULT);
    lastTimeTempRoom = time;
  }

  if ((time - lastTimeTempInternal) > DELAY_TEMP_INTERNAL) {
    Serial.print("/temp/internal/");
    Serial.println(readInternalTemp());
    lastTimeTempInternal = time;
  }

  delay(500);
}