.. Original article at http://text.maze.io/2010/01/28/arduino-1-wire-temperature-sensor-hacking
   
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    |    _   _   \   _   |   ____\   _    /      |   |/  _  \
    |    /   /   /   /   |  |     |  /___/   _   |   |   /  /
    |___/___/   /___/____|________|___   |  |_|  |___|_____/
            \__/                     |___|
    
  
   (c) 2010 Wijnand 'maze' Modderman - http://maze.io/


Arduino 1-Wire Temperature Sensor Hacking
=========================================
  
.. image:: http://i.maze.io/6acbb1fb.jpg
   :align: left
   :alt: Arduino Duemilanove
   :class: figure

So, I have an Arduino_ Duemilanove_ (wtf is wrong with those Arduino_ people and their board names?) and 
I decided it was time to get some progress with hacking the Dallas Semiconductor temperature monitors 
I got from `Maxim IC <http://www.maxim-ic.com/>`_.

.. image:: http://i.maze.io/288acf7e.jpg
   :align: right
   :alt: DS18S20
   :class: figure

The sensors are DS18S20_ sensors, 1-Wire temperature monitors. Using them in the Arduino was made 
easy by `Robin James' OneWire library <http://www.pjrc.com/teensy/td_libs_OneWire.html>`_.

The pinout on the Arduino_ uses 1 digital pin, ground and +5.5V with a 4.7kΩ pullup resistor. 

The schematics are as follows::

        .-------------------.
        o d0             a5 o
        o d1    A D      a4 o
        o d2    R U      a3 o
        o d3    D E      a2 o
        o d4    U M      a1 o
        o d5    I I      a0 o
        o d6    N L         |
        o d7    O A     vin o
        o d8      N     GND o    R1
        o d9      O     GND o    ___ 
        o d10     V     +5V o---|___|---o
        o d11     E    +3V3 o           |
        o d12         RESET o           |
 +------o d13               |           |
 |   +--o GND               |           |
 |   |  o AREF              |           |
 |   |  |                   |           |
 |   |  '-------------------'           |
 |   +---------------------------+      |
 +-------------------------------)------+
                                 |      |    ____
                                 +------^---|    | IC1
                                 |      +---|    |
                                 |      |  -|____|
                                 |      |    ____
                                 +------^---|    | IC2
                                 |      +---|    |
                                 |      |  -|____|
                                 |      |    ____
                                 +------^---|    | IC3
                                 |      +---|    |
                                 |      |  -|____|
                                 |      |    ____
                                 +------^---|    | IC4
                                        +---|    |
                                           -|____|
                                        

As you can see I can stack multiple sensors on the same 1-Wire bus. You can practically stack endless amounts of 1-Wire devices on this bus, as long as the bus can deliver sufficient power.

Some example code::
  
  #include <OneWire.h>
  ...
  
  void getTemperature(byte *addr) {
    byte present = 0;
    byte data[12];
    int i, hByte, lByte, tRead, tSign, cTemp;
 
    ds.reset();
    ds.select(addr);
    ds.write(0x44, 1); // start conversion, enable parasite power
    delay(1000);       // now we wait!
    present = ds.reset();
    ds.select(addr);
    ds.write(0xEE);    // read scratchpad
    for ( i = 0; i < 9; i++) {           // we need 9 bytes
      data[i] = ds.read();
    }
 
    lByte = data[0];
    hByte = data[1];
    tRead = (hByte << 8) + lByte;
    tSign = (tRead & 0x800);
    if (tSign) { // test MSB
      tRead = (tRead ^ 0xffff) + 1; // 2's comp
    }
    cTemp = (5000 * tRead);
    if (tSign) {
      Serial.print("-");
    }
    Serial.print(cTemp);
    Serial.print("\n");
  }

.. _Arduino: http://www.arduino.cc/
.. _Duemilanove: http://www.arduino.cc/en/Main/ArduinoBoardDuemilanove
.. _DS18S20:  http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2815