You've become familiar with the XBee modules included in the kit, but Digi makes a great variety of XBees with different features and for different functions. So, which module is best suited for your applications? Why are there different types of antennas? Should you use a "PRO" version, or is the regular XBee enough? In this guide, we will look over the different XBee options to help you answer these questions.
Note that the XBee you select will affect the parameters of your application:
- The location of your application affects the operating frequency of the XBees.
- To get greater range, you may select an external antenna, a different operating frequency, or even an XBee-PRO.
- Power consumption is an important factor to consider.
- The required network topology also impacts the type of module you need.
This comparison table may help you select an XBee based on your requirements:
- Through-hole technology (THT) XBees include the 20-pin socket and require holes for mounting the component on the printed circuit board (PCB), although it is common for the carrier board to contain a female socket.
- Surface-mount technology (SMT) XBees include 37 pads. They are placed directly on the PCB, which means they do not require holes or sockets for mounting the component.
Through-hole technology is used in prototyping and production. SMT is recommended for high-volume applications, as the component can be placed automatically by a pick-and-place machine and you save the cost of a socket on each board.
Not all XBees are available in both form factors; some modules do not include the SMT footprint.
Antennas are devices that focus energy in a particular direction. The attributes of a given antenna affect not only the range of a module but also its price. The following antenna options are available on XBee radios:
A PCB antenna is formed directly on the module with conductive traces. A PCB antenna performs about the same as a wire antenna and within 5% of the whip antenna.
An integrated wire antenna consists of a small wire (about 80 mm) sticking up perpendicular to the PCB. It utilizes a 1/4-wave wire soldered directly to the PCB of the OEM module.
A whip antenna is a solid but flexible wire antenna that protrudes about 25 mm above the surface of the XBee PCB. It can be moved around to maximize signal strength, or to stick out of an enclosure. Because it can be moved, it can also be broken off if care is not taken or if the solder connection becomes stressed. It has a range advantage over the chip antenna but only when used outdoors.
A U.FL antenna is a tiny connector for your own external antenna. Typical connection is either a dipole antenna with U.FL connection, or a U.FL to RP-SMA adapter cable. This is a good option if your object is in a box and you want your antenna outside the box.
A RP-SMA antenna (reverse-polarity SMA) is a bigger connector for your external antenna. XBee radios are equipped with an RP-SMA female plug, and the antenna is an RP-SMA male jack. This is another good option if your object is in a box and you want your antenna outside the box.
XBee vs. XBee-PRO
Both XBee and XBee-PRO modules are small, high-performance, low-cost, wireless data radios. They are pin-compatible with one another and you can mix and match them on the same network. However, there are a few differences between them:
- XBee-PRO modules are slightly longer than regular XBees and use more power.
- The XBee-PRO is capable of receiving weaker signals than is the XBee, which means the XBee-PRO has better receiver sensitivity.
- Because the XBee-PRO is both more sensitive and transmits more power, it can send and receive data over longer distances than the XBee.
- The XBee-PRO has a higher MSRP.
XBee modules are available in a wide variety of RF frequencies used around the world. XBee frequency affects range, and it also affects the location where you can deploy your application due to regulation differences between countries. Modules with different frequencies can NOT be mixed on the same network. Developers can support frequencies including:
- 2.4 GHz
- 902 - 928 MHz
- 865 - 868 MHz
To determine the frequency that is best for your application, you need to answer two questions:
Where is your application going to be deployed?
Since some frequencies are not allowed for unlicensed use in certain countries, it is important to consider the location of your application when you select the frequency of your XBees:
- 900 MHz radio frequency band is for unlicensed use only in North America and Australia.
- 868 MHz radio frequency band is for unlicensed use only in Europe.
- 865 MHz radio frequency band is for unlicensed use only in India.
- 2.4 GHz is an unlicensed radio frequency band used worldwide.
- What is the maximum range your application needs to communicate?
900 MHz, 868 MHz, and 865 MHz XBees offer much greater range than 2.4 GHz XBees.
Radio communication protocols
XBee modules support multiple wireless protocols which are suitable for many different network topologies. Open standards include ZigBee, 802.15.4, and Wi-Fi. Digi has also developed proprietary protocols such as Multipoint and DigiMesh. The following list includes the supported protocols:
Not all XBee devices can run all communication protocols. The combination of XBee hardware and radio firmware determines the protocol that an XBee device can execute. Refer to the XBee RF Family Comparison Matrix above for more information about the available XBee RF modules and the protocols they support.
IEEE 802.15.4 is a standard which specifies the physical layer and media access control for low-rate wireless personal area networks. It is the basis for the ZigBee, ISA100.11a, WirelessHART, and MiWi specifications, each of which further extends the standard by developing the upper layers which are not defined in IEEE 802.15.4. The modules included in this kit are IEEE 802.15.4. The standard is designed specifically for energy efficient communications in a point-to-point or a point-to-multipoint configuration and includes sleeping and security.
- Single point communications.
- Fast connections between two devices.
- Non-expandible networks that need low power or intermittent functioning.
ZigBee / ZigBee SE (Smart Energy)
ZigBee is a specification for a suite of high-level communication protocols. Its main purpose is to create a meshed network topology (hierarchy) to allow a number of devices to communicate among them.
- Large systems that need to expand without a loss of function.
- Systems that need extended communications.
- Systems using non-directional communications patterns.
- Systems with intermittent function of the individual modules due to power loss or cyclical functioning.
- Large-scale networks with low power functioning on end devices.
- Linked embedded devices or devices that move.
- Systems that require interoperability between devices made by different vendors.
DigiMesh (Digi proprietary)
DigiMesh is a proprietary peer-to-peer wireless networking protocol developed by Digi International Inc. DigiMesh forms a meshed network. The protocol allows for time-synchronized sleeping nodes/routers and low-power battery powered operation. The protocol is currently supported by several 900 MHz, 868 MHz, 865 MHz, and 2.4 GHz Digi radio modules.
- Systems that require the ability to sleep on all nodes.
- Systems that require simplified network setup and expansion.
- More robust mesh networks (no parent/child dependencies).
- Systems that require longer range options for each hop.
- Systems with larger frame payloads.
- Environments where increased reliability is important due to routers that come and go due to interference or damage.
Multipoint (Digi proprietary)
XBee multipoint RF modules are ideal for applications requiring low latency and predictable communication timing. They provide quick, robust communication in point-to-point, peer-to-peer, and multipoint/star configurations. Multipoint modules can be deployed as a pure cable replacement for simple serial communication or as part of a more complex hub-and-spoke network of sensors.
- Multipoint networks with longer range options.
- Systems that do not require fast communication.
IEEE 802.11 (Wi-Fi)
XBee Wi-Fi RF modules provide wireless connectivity to end-point devices in 802.11 bgn networks. Using the 802.11 feature set, these modules are interoperable with other 802.11 bgn devices, including devices from other vendors.
- Cloud-connected Wi-Fi products.
- Ideal for industrial applications that require fast time to market.
- Easily connect to a smartphone or tablet for configuration or data transfer.