Hardware Reference
In-Depth Information
Chapter 5
XBees
Radio communication is a fundamental method of communicating over varying distances without having an
encumbrance of wires. Arduino developers take advantage of radio communication in robotics, home automation,
and remote-sensing applications. To avoid the headaches of developing radio communications systems from scratch,
a lot of developers use XBee radio modules to add wireless functionality to projects. The XBee is a full-featured radio
transceiver module made by Digi International ( www.digi.com ) and is compliant with FCC regulations as long as you
use the module without modification and adhere to a few other restrictions.
The restrictions that apply to the use of the XBee by the FCC and by other countries are listed in the data sheet
provided by Digi. Most XBee modules are also compliant with the ZigBee communication protocol , a standard based
on the IEEE 802.15.4 standard. XBees have the ability to communicate with other ZigBee-compliant devices.
The minimum hardware to get started exploring the world of XBees is a USB adapter, a serial adapter, an
Arduino-compatible board, and two XBee modules. You can use the USB XBee adapter sold by Adafruit Industries
( www.adafruit.com/products/247 ) or the one sold by SparkFun Electronics ( www.sparkfun.com/products/8687 ).
The USB adapter is needed to interface with the computer for initialization and setup, and can provide a connection
from the computer to other XBee modules.
The XBee has a small pin pitch that's not breadboard compatible, and it's a 3.3V device, so to use the XBee with
an Arduino, you need a serial adapter to make the connections more easily and to convert the voltage levels. There
are a few different styles of serial adapters that can be used for connecting the Arduino to the XBee: the two most
notable are shields and breakout boards. They come with and without voltage conversion. Shields provide a method
of simplified packaging—excellent for semipermanent setups. Shields limit the number of devices that can be easily
used and are usually restricted to boards with the standard Arduino pin out. For greater development flexibility, it is
recommended to use breakout boards instead of shields. XBee breakout boards, such as the adapter available from
Adafruit ( www.adafruit.com/products/126 ) or SparkFun ( www.sparkfun.com/products/9132 ), will work for the
examples in this chapter and Chapter 6.
The examples in this chapter are built using one ATmega328 Arduino-compatible board, two series 2 XBee
modules, one USB adapter, and a serial breakout board. The focus of this chapter is on the series 2 XBee modules,
but they are not the only modules available from Digi. The first section describes the various models of the XBee
modules and the differences in functionality.
Buying XBees
It can be a bit difficult to discern the differences between XBee modules and match them to your project
requirements. There are currently nine different series, with multiple variations on antennas, functionality, and
transmission power. The series number is not an indication of version revisions, but of functionality and features.
Modules with the same series number are always compatible with one another. When deciding what XBee set to
purchase, you need to take constraints and the type of project into consideration. For example, for remote-control
robots, an XBee that uses a point-to-point communication protocol with an extended transmitting range would be
sufficient, even though the data rate may not be as fast as other modules. XBees for large sensor networks, on the
 
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