// Include library found here: 
// http://milesburton.com/index.php?title=Dallas_Temperature_Control_Library
#include <OneWire.h>

// DS18S20 Temperature chip i/o
OneWire ds(8);  // on pin 8

int ledPin =  13;    // LED connected to digital pin 13

  // Do configuration
  
  // The buffer window size determines how many single temperature data samples
  // are collected and held at the same time. The program takes the average of 
  // all these samples. With the standard values for windowSize (6) and
  // fetchInterval (10000) there are six samples collected in a minute. A read-
  // out thus gives the average over a minute.
  //
  // Standard: 6
  int const windowSize = 6;

	// Time between temperature fetches
	// 
	// Standard: 10 seconds
  unsigned long fetchInterval = 10000;
  
  // Frequency of status blinker
  // Has nothing to do with the temperature stuff, but indicates that the 
  // arduino is doing something
  //
  // Standard: 1 second
  unsigned long blinkInterval = 1000;
  
  
  // Initialize variables
  int toggle = 1;
  double currentTemp, temperature;
  unsigned long lastBlinkTime;
  unsigned long lastFetchTime;
  double tempArray[windowSize];
  int first;

void setup(void) {

  // Initialize inputs/outputs
  // Start serial port
  Serial.begin(38400);
  delay(2000);
  
  // Initialize the digital pin as an output:
  pinMode(ledPin, OUTPUT);     
  
  // At startup, fill array with current temperature
  currentTemp = fetchTemp();
  for(int i = 0; i < windowSize; i++) {
        shift_in(currentTemp, tempArray, windowSize);
  }
  
  temperature = currentTemp;
}

// Main loop
void loop(void) {

  // If there has been passed a certain time
  if (millis() - lastFetchTime > fetchInterval) {
  
    // save the last time
    lastFetchTime = millis();   

    // Fetch current temp
    currentTemp = fetchTemp();

    // Shift in current temperature into temperature array
    shift_in(currentTemp, tempArray, windowSize);
    
    // Determine averaged temperature
    temperature = mean(tempArray, windowSize);
  }
  
    // Do some blinking every time
    if (millis() - lastBlinkTime > blinkInterval) {
      // save the last time
      lastBlinkTime = millis();   
  
      if(toggle == 1) {
        digitalWrite(ledPin, LOW);
        toggle = 0;
      }
      else {
        digitalWrite(ledPin, HIGH);
        toggle = 1;
      }
    }
  
  // Send data only when you receive data:
  if (Serial.available() > 0) {

        while(Serial.available()) {
          Serial.flush();
        }

	// Say what you got to say:
	Serial.println(temperature);
	}
}

// Calculates the mean of all items in the array
double mean(double *a, double length) {
  double sum = 0;
  for(int i = 0; i < length; i++) {
    sum += a[i];
  }
  return (sum/length);
}

// Assigns the new item as first element of an array and shifts every other
// items one position to the end. The last item is discarded
void shift_in(double newItem, double *a, double length) {
  for(int i = 0; i < length-1; i++) {
    a[i+1] = a[i];
  }
  a[0] = newItem;
}

// The self-contained fetch temp function.
// Most of the code was taken from the example code of this page:
// http://www.arduino.cc/playground/Learning/OneWire
double fetchTemp(void) {
  
  byte i;
  byte present = 0;
  byte data[12];
  byte addr[8];

	// Some test routines
  if ( !ds.search(addr)) {
       ds.reset_search();
  }

  if ( OneWire::crc8( addr, 7) != addr[7]) {
      Serial.print("CRC is not valid!\n");
  }

  if ( addr[0] != 0x28) {
      Serial.print("Device is not a DS18B20 family device.\n");
  }

  ds.reset();
  ds.select(addr);
  ds.write(0x44,1);         // start conversion, with parasite power on at the end

  delay(1000);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.

  present = ds.reset();
  ds.select(addr);    
  ds.write(0xBE);         // Read Scratchpad
  
  for ( i = 0; i < 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
    
    // Debug output:
   	//Serial.print(data[i], HEX);
    //Serial.print(" ");
  }
  
  int HighByte, LowByte, TReading, SignBit, Tc_100, Whole, Fract;
  double result;
  
  LowByte = data[0];
  HighByte = data[1];
  TReading = (HighByte << 8) + LowByte;
  SignBit = TReading & 0x8000;  // test most sig bit
  if (SignBit) // negative
  {
    TReading = (TReading ^ 0xffff) + 1; // 2's comp
  }
  Tc_100 = (6 * TReading) + TReading / 4;    // multiply by (100 * 0.0625) or 6.25

  Whole = Tc_100 / 100;  // separate off the whole and fractional portions
  Fract = Tc_100 % 100;

  result = Whole;
  result += ((double)Fract/100);
  if(SignBit) {
    result *= -1;
  }
  
  return result;
}