DS18B20 Device Discovery
########################

:title: DS18B20 Device Discovery
:date: 2014-08-19 10:57
:category: Projects
:tags: arduino, electronics
:slug: ds18b20-device-discovery
:related_posts: soil-temperature-monitoring-part-two,soil-temperature-monitoring-part-one
:author: Chris Ramsay
:status: published
:language: en
:show_source: True

.. contents::

.. PELICAN_BEGIN_SUMMARY

A little bit of work stemming from from the soil temperature monitoring project;
this is an aside on DS18B20 temperature sensing device address discovery with
the Arduino. Being that I am going to have a handful of sensors in the ground
and therefore not easily accessible for identification I need to find a way of
easily finding out all the device addresses in one fell swoop.

.. PELICAN_END_SUMMARY

Arduino - Device Address Discovery
----------------------------------

As already discussed in `Soil Temperature Monitoring - Part One`_ connecting the DS18B20
to an Arduino is trivial; ground, positive and data are all that is
required, with data to the Arduino digital pin 3. Pull up is achieved
with a 4K7.

.. image:: https://farm8.staticflickr.com/7616/16819964307_e39b7bddd4_c.jpg
   :width: 800
   :height: 563
   :scale: 100
   :alt: DS18B20 Basic Circuit

*Simple circuit employed for address discovery*

Below is a sample of the code I used to discover the sensor addresses.

.. code-block:: c
   :linenos: table

    #include <OneWire.h>
    #define ONE_WIRE_BUS 3

    OneWire  oneWire(ONE_WIRE_BUS);

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

    void loop() {}

    void discover(void) {
      byte i;
      byte data[12];
      byte addr[8];

      Serial.print("Starting...\n\r");
      while(oneWire.search(addr)) {
        Serial.print("\n\r\n\rDevice has address:\n\r");
        for( i = 0; i < 8; i++) {
          Serial.print("0x");
          if (addr[i] < 16) {
            Serial.print('0');
          }
          Serial.print(addr[i], HEX);
          if (i < 7) {
            Serial.print(", ");
          }
        }
        if ( OneWire::crc8( addr, 7) != addr[7]) {
          Serial.print("CRC is not valid!\n\r");
          return;
        }
      }
      Serial.println();
      Serial.print("Done");
      oneWire.reset_search();
      return;
    }

This is what it looked like with five sensors attached:

.. code-block:: bash

    Starting...

    Device has address: 0x28, 0xC8, 0xCC, 0xBF, 0x04, 0x00, 0x00, 0xB6
    Device has address: 0x28, 0xBA, 0x17, 0xD0, 0x04, 0x00, 0x00, 0x64
    Device has address: 0x28, 0xF5, 0xE4, 0x83, 0x05, 0x00, 0x00, 0x26
    Device has address: 0x28, 0xE3, 0x67, 0xCE, 0x04, 0x00, 0x00, 0x9C
    Device has address: 0x28, 0xE7, 0x17, 0x11, 0x05, 0x00, 0x00, 0x1D

    Done

Now it will just be a process of elimination to find out which sensor matches
which address.

.. _cloud detection: {filename}/projects/2014-03-04_cloud-detection-part-one.rst
.. _Soil Temperature Monitoring - Part One: {filename}/projects/2014-04-10_soil-temperature-monitoring-part-one.rst