Software design and embedded system tools. » zigbee

How to choose Xbee module

admin — Sun, 24 Oct 2010 15:57:23 +0000

How to choose Xbee module.

Two steps you should consider when you want to buy Xbee module.

1. Range of send/receive signal of Xbee module.

Xbee module can be separated obviously into two series in term of “The range of send and receive signal”.
The word “PRO” was used to indicate the difference between each series. Xbee series without word “PRO”
is designed for short-range wireless communication (around 100 metre when use outdoor) with power output between 1 – 2 mW.
Example of Xbee module in this series is XBee 802.15.4 .
Xbee series with word “PRO” is more powerful. It’s designed for long-range communication (up to 1600 metre when use outdoor) and
have power output between 50-60 mW. Example of Xbee module in this series is XBee-PRO 802.15.4 .

However, the practical range that Xbee can operate may depend on many factors such as the environment of system , type of antenna , type of obstacles , etc.
Xbee use frequency band at 2.4 Ghz that is the same as Bluetooth or Wireless Lan so when you use Xbee in the environment that Bluetooth or Wireless Lan exists,
signal of Xbee may be disturbed by these devices and cause the data loss during communication.

The 2.4 Ghz frequency band is arranged into the Microwave band (S Band). One important characteristic of Microwave is
“The power of transmission is highest when placement of sender and receiver device is in line-of-sight (no obstacles between them)”. Therefore , the Xbee “PRO” series that
have the range of communication up to 1.6 Km is only in case that you place the devices in line-of-sight with the best quality of antenna and no interference signal, other
conditions will reduce the signal strength and make the range that Xbee can communicate to be less than 1.6 Km.

2. Series of Xbee

Xbee has two series , Series1 and Series2. The difference between Series1 and Series2 can be concluded as following
2.1 Series2 is designed to use in mesh network while Series1 cannot be used in mesh network (Series1 is suitable for point-to-point or point-to-multipoint task).
2.2 They use different chipset , different firmware and different protocols so you can’t use Xbee Series1 together with Series2 in the same time.
2.3 Zigbee protocol is only supported on Series2 and no longer supported on Series1.
2.4 Series2 can be separated into 2 sub-series , Znet2.5 and ZB. The difference between Series2 Znet2.5 and Series2 ZB is
“Series2 (ZB) can upgrade firmware over-the-air while Series2 (Znet2.5) and Series1 can upgrade firmware with X-CTU via serial communication only”

Please see the article on ladyada or faludi website for more information about upgrading Xbee module.

So before you buy Xbee module , you should consider about the application and environment of your system first.
For example, in agriculture , suppose you have 10 Acre strawberry garden and you want to apply wireless sensor network (WSN) technology in order to measure the tempurature
in each cultivated area , in this case you should select the Xbee “PRO” series because your area is wider than the range that normal Xbee series can operate.
Otherwise if you want to build the WSN network that consist of many sensor nodes (Xbee node) and data communication in your network is very complicate,
you should select to use Mesh Network instead of Star Network (I will talk about Xbee Topology in the next article) .

The next article will be about Xbee Topology , comparison of each antenna type that affect to the range of signal transmission , interference signal and
Xbee applications.

Thank you,
Jitkasem

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More on Xbee part one.

admin — Sun, 10 Oct 2010 16:22:55 +0000

Xbee is the device that integrate Microcontroller and RF IC into one piece (one module).
It work as transceiver equipment (the equipment that can both send and receive signal).
Xbee is half-duplex and it operate at 2.4 GHz frequency band. It consume low electric power and easy to use because
the interface used for sending and receiving data with Xbee is UART (TTL), so we can connect the UART communication pin of Xbee to
the UART of microcontroller directly.

Common features summary of Xbee
1. Operating Frequency ISM Band 2.4 GHz
(ISM Band is the frequency band that reserved for use in scientific , medical and industrial purpose. To know more
about ISM Band , please visit this wikipedia page)
2. Supply Voltage between 2.8 – 3.4 Volt
3. Can use together with various types of antenna such as Chip Antenna , Whip Antenna and connector like
U.FL connector , RP-SMA connector (but you have to find the 2.4 GHz antenna in order to use with these connectors).
4. Power Down Current < 10 uA
5. RF data rate of Xbee is about 250 Kbps (this is the data rate of signal that sent via the air)
6. Serial interface data rate is between 1200 - 115200 Bps (this is the data rate of communication between Xbee module
and microcontroller)

Xbee has 20 pin (you can see pin-arrangement in the above picture).The function of each pin is described in page 7 of this datasheet.
Xbee also has Digital I/O line and 10 bits Analog to Digital converter module.

The distance between adjacent pin of Xbee is 2.0 mm so it cannot attach to the protoboard directly because
in general , standard distance between each pin of IC (Pitch) is 2.54 mm or 1 mil. However there’re many
tools used for convert the 2mm-10pin of Xbee into standard pitch (2.54mm) such as “2mm 10pin XBee Socket” or
“Breakout Board for XBee Module”.You should try to search for them at Sparkfun.com.

Kind of antenna that able to connect to Xbee module (I explain only four antenna kinds).

Chip antenna.

This kind of antenna is suitable for use in small project that restrict in size or dimension because its antenna is small single chip.
You can pack it in the box but only plastic box (don’t enclose it with steel box because the signal cannot spread through the steel).

Wire antenna.

With this kind of antenna, the range of the signal and stability is conformable with specification. However, the antenna that extrude from the Xbee module
may look untidy and you cannot pack it into the box too. If you want to use Xbee module in general task and don’t have limitaion in space or size of the workpiece
, I recommend this kind of antenna.

UFL antenna.

This kind of antenna is suitable for the task that designed to place the Xbee module inside the box but allow the antenna to emerge from the box. With UFL antenna ,
you need to connect the UFL to SMA wire from the Xbee module to antenna. At this point , it may reduce the signal strength , however , at the antenna,
the signal can be amplified again so you should consider the expansion radio (Gain) at the antenna too.

SMA antenna.

With this kind of antenna , the range of the signal and stability is in line with Xbee specification and is the best when compare to other types.
The signal can be amplified again at the antenna too.
The only disadvantage of SMA antenna is “it’s so difficult to adapt this kind of antenna to use inside the box”.

The next article will be about “how to choose the Xbee module to befit your embedded project”.

Reference : www.thaieasyelec.com , www.thaieasyelec.net

Thank you,
Jitkasem

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Wireless sensor network (WSN)

admin — Fri, 13 Aug 2010 14:58:52 +0000

Wireless sensor network (WSN)

What is WSN?

The wireless sensor network was primarily developed as a military application to survey a battlefield. However, now a WSN is commonly used in many other industrial and commercial applications to monitor environmental conditions, health care applications and traffic controls. There are many different kinds of wireless sensor networks however; they all normally come equipped with a radio transceiver or a wireless communication device or a power source.

There are many applications to this technology and typically involve monitoring, tracking or controlling. Area monitoring comes as one very commonly used to be able to track any kind of movement whether it is heat, pressure, sound, light or vibrations in an specific area.

This technology is now being utilized by almost every industry and this includes the environmentally related industry as this is a technology which allows the reading of many different kinds of changes in the atmosphere and how they can guide those in the industry to determine simple factors like water levels or more complex aspects of the environment like the possibility of an earthquake in an specific area.

Vehicle tracking and movement can also be tracked through this technology and therefore, it is also being used by the security industry. Medical science also depends on the wireless sensor network to be able to track the changes on some of the health monitors which will immediately notify the medical staff of a change in the monitoring device.

Zigbee is a technology developed as a global standard to comply with the needs of low cost and low power wireless networks. It has been designed with the facility to be able to provide an easy to use wireless solution which creates a secure and reliable network. Some of the features of Zigbee include the ability to support multiple network functions like the point to point or multipoint to point and also the mesh networks as well. Since it functions on a low duty cycle it is also considered to be very good on battery life. And it has the direct sequence spread spectrum as well. It also has the ability to run for years without any kind of maintenance and with an automatic meter reading.

TinyOS has been designed for wireless sensor networks. It works in component based software that supports high degree of data in a very small space and which has been designed to minimize power consumption, while being able to use all its sophisticated protocols. The wireless sensor network has been created taking into consideration a variety of applications, incorporating various components and being capable of deployment of new environments. However, it also requires greater processing compared to the wired networks. It is a complex mechanism which needs to be properly processed. There are many different kinds of WSN platforms and they vary in size and capacity depending on which components are active.

SOS is an operating system for wireless sensor network which is normally utilized for message passing services, dynamic memory allocations and module loading. The components of the SOS are comparable in functionality to Tiny components. SOS project is now no logner continue to develop. However, the source code is still available to download up until now.

Another specific Operating system for the WSN is the EPOS or Embedded Parallel Operating System which is based on runtime support for the environment. This framework allows programmers to develop their own applications and tools through their system in accordance with the requirements of these particular applications.

The right Operating system for the Wireless sensor network will allow applications to express when certain software components are not being used, allowing the system to work on the levels that it needs to and thus implement less power as well.

Thanks.

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Xbee

admin — Wed, 18 Nov 2009 15:15:58 +0000

Xbee is one of popular wireless module in the world. It support two-ways communication (one Xbee
module can send or receive the data to/from other modules).The different between Zigbee
and Xbee is Zigbee is name of industry standard while Xbee is name of Zigbee standard
module produced by Digi.Xbee can communicate via UART (TX,RX signal) and sending the signal (data) within the short range is very accurate.Xbee module have an internal IC that help
in encoding the data.The main advantage of this module is it consume low watt (low
electric power),small size and cheap.Although it is restricted to send data within short
distance, it can send data from one node to another node and this feature make it
appropriate for making wireless sensor network.

The below image is the picture of xbee module

Picture of Xbee module

Below is useful links for doing Xbee on Arduino

Programming Arduino Wirelessly

Arduino Xbee Interface Circuit (AXIC)

XBee radios

Arduino+XBee+LCD Info Device

Thank you.