Ready for prime time

May 5, 2005
The first wave of innovative sensors and controls based on Zigbee wireless standards is set to debut in the coming months.

Leland Teschler
Executive Editor

Your next wireless mouse or remote control for your TV could well be running a new wireless standard called Zigbee. The recently finalized protocol promises to both make existing wireless applications more capable and usher in new kinds of consumer electronics, building controls, healthcare devices, and even industrialautomation equipment.

Zigbee promoters outline a future where Zigbee-enabled controls help shrink the energy use in your home to a bare minimum; Zigbee-based monitors keep an eye on elderly residents living alone and warn medics about changes in habits that are potentially serious; Zigbee-powered irrigators keep plants green with just-enough water usage.

It looks as though the future is now for such devices. Well-known manufacturers such as Eaton Corp. and Invensys have Zigbee products scheduled for commercial release later this year. New companies such as Control4 and Lusora have devised clever uses for the technology that promise to improve the quality of life for many consumers.

The attraction of Zigbee centers on cost and scale. It is the first scheme, say its followers, inexpensive enough to be practical for use in isolated controls with sensors that must work reliably while consuming little power. Zigbee manages both feats by sending data at a superlow rate and by using a special networking scheme called meshing. The low rate, about 250 kbps, is too low for beaming audio, real-time video, or complicated Web pages. It is fine, however, for keeping tabs on temperature sensors, proximity switches, and similar uses characterized by relatively slow changes.

The mesh-networking feature avoids communication problems caused by obstacles that could otherwise block RF signals. The idea is to use any available wireless device in the network as a means of forwarding messages, if need be. That eliminates the requirement for a clear RF path between any two points in the network. Moreover, mesh networks are designed to reconfigure themselves on the fly as RF paths disappear or come free. This quality is particularly important in warehouses and industrial plants dotted with RF-unfriendly towmotor trucks and metal shelving.

Zigbee nodes can be relatively inexpensive. Today, for example, it takes just two chips — a controller and a transceiver — plus a few passive components to define any Zigbee device. Circuitry for the two chips will be combined onto one IC later this year.

Another facet of Zigbee that holds down costs is its economical handling of network traffic. Other kinds of wireless networks employ special trafficking gear such as hubs and routers. But Zigbee I/O points themselves can take on these functions. Thus there is no such thing as a stand-alone router in an ordinary Zigbee setup. Switches, sensors, or I/O controllers on the network could be set up to handle routing duties in the course of their normal operation.

Protocols for Zigbee are optimized for applications that are time critical. It takes about 30 msec for a Zigbee device to join a network, and about 15 msec for a device to access other network nodes. It can be problematic for other wireless protocols to establish connections fast enough.

"There can't be a two-second delay between the instant a homeowner hits a light switch and when the light comes on," points out Venkat Bahl, vice chair of the Zigbee Alliance and marketing vice president at Ember Corp. "The homeowner will think the switch isn't working and may flip it several times. But that scenario is a possibility with wireless protocols other than Zigbee."

The Zigbee Alliance is an association of companies that are promoting the technology. Advocates there say the standard's protocols make more sense for remote sensing and control than the Bluetooth standard which is associated with PDAs and PCs.

Besides transitioning more quickly from sleep mode to active transmitting, Zigbee devices consume less power than Bluetooth nodes. This comes partly from the use of a much smaller protocol stack (28 kbytes compared to 250 kbytes). So the controller running a Zigbee device needs correspondingly less memory and consumes less power. In addition, Zigbee networking supports potentially thousands of devices per network compared to Bluetooth's eight. Finally, Zigbee vendors say 30 m is a typical range for a Zigbee device, compared to about 10 m for Bluetooth.

Applications Arrive
With the first Zigbee specification now final, Zigbee Alliance members are focused on interoperability testing and fielding products. The Alliance is also promoting the technology by devising sets of application profiles, software that lets programmers use application-specific commands when setting up Zigbee controllers for tasks in a few broad categories. These application profiles are analogous to the software that lets programmable logic controllers obey commands entered in ladder logic.

The first Zigbee profile handles lighting. Recently completed, it will be soon joined by profiles for HVAC, industrial process control, and building automation. In addition, "Some Alliance members are writing their own application profiles for more specialized areas," explains Zigbee Alliance chairman Bob Heile. "We expect the open source community to write profiles as well. Alliance members writing profiles will first make them available to other Alliance members, later to the technical community at large."

The Alliance also has a group constructing ways of bridging between Zigbee and other kinds of networks. Such connections are possible today, but only through proprietary schemes. The idea behind the Alliance efforts is to simplify the task of third parties trying to develop devices with more versatility. One quest, says Heile, is to concoct a gateway which lets two different Zigbee networks behave as though they are one in the same.

A recent meeting of the Alliance featured an open house where companies pursuing the technology displayed their efforts. We've described here some of the more notable products that target home healthcare, building controls, and remote sensing.

Home to homeowner: "The toilet is leaking."

The Home Heartbeat system from Eaton Corp. gives homeowners an awareness of what's going on inside their house, even if they happen to be thousands of miles away.

Two key components of the system are a base station and a Home Key. Eaton envisions the Key going into your pocket or onto a key chain. When the Key leaves the range of the base station, it carries with it the last status of items such as doors, windows, and lights, as read by sensors on the Zigbee network. Homeowners wondering whether they left the garage door open could conceivably tell by looking at the LCD in their Home Key. (However, the system stops short of asking a sympathetic neighbor to come over and rectify the problem.)

The base station is smart enough to notice if one of the sensors changes state when the Home Key is out of range. In this case it can send the homeowner's cell phone a text message detailing what's wrong.

Eaton has devised a variety of sensors for the system. In addition to proximity switches for doors and windows, there are devices designed to detect leaking pipes, ac loads, and even remind homeowners about periodic maintenance items such as low batteries in smoke detectors or the need for seasonal gutter cleaning.

One noteworthy piece of the system is a water shut-off valve. It can be controlled and activated by sensors in the network.

Home Heartbeat is set to debut this summer in the form of a do-it-yourself kit that includes a base station, Home Key, and one sensor.

No more meter readers

NURI Telecom in Korea expects to bring an automatic meter-reading system-to the U.S. this year. The idea is that Zigbee-enabled meters in a neighborhood will form their own mesh network. A single controller in the area monitors gas use in real time and sends the data to a center station.

But the system is expected to handle more than just utility metering. NURI thinks the basic technology will let utilities offer services for home monitoring, fire alarms, and control of home appliances. The heart of the meter is a Zigbee communication module which NURI devised working with chip and protocol developer Ember Corp. The module will be an OEM component available for use by other companies fielding Zigbee products. The system is already working in scores of Korean homes as a governmentsponsored pilot project.

A new twist on, "I've fallen and I can't get up"

The Lusora Intelligent Sensory Architecture (Lisa) from Lusora Inc. is basically a home-monitoring system for senior citizens. Zigbeebased Lisa gear includes a light switch with a tiny digital camera (left); a pendant (center) worn around the neck; and movement tags (right), which can let the system generate an alert based either on detected movement or the lack of any movement.

Zigbee doesn't have the bandwidth to handle video. So lightswitch/camera combos deliver still images to a controller. An alert from the pendant or from one of the tags activates the camera.

The pendant includes accelerometers that detect the forces of a person falling. It also contains a panic button.

Lisa can send a warning either to a monitoring company or family member if something is up. It can be programmed to generate an alert, for example, if a bedroom or refrigerator door hasn't opened by noon.

San Francisco-based Lusora expects to offer the first Lisa devices this fall.

Not the Jetsons, but close

Control4 aims to take home automation out of the exclusive realm of the rich. Based in Salt Lake City, the company has devised an array of audio and video controls, displays, and intelligent light switches that employ Zigbee schemes. The full list of Control4 gear includes audio servers, protocol bridges, AV controls, thermostats, media management, and lighting controls.

The Control4 vision is to handle most aspects of climate control, lighting, and audio/video media through wireless controllers. Of course, audio and video signals get beamed throughout the house via Wi-Fi or other high-bandwidth protocols. Wireless control signals, however, follow Zigbee standards. The full system can pull off fairly sophisticated effects such as automatically dimming lights when a receiver turns on.

Even "kid control" is not beyond the system's capability: The press of button could conceivably power down room lights and kill any nocturnal Xbox use. The system can sense ac loads through Zigbee-enabled outlets. This lets parents tell the system to switch off an outlet after a prescribed period of video gaming.

Light dimmer switches, automated blind mechanisms, sprinkler controls, door sensors, and similar devices are scheduled for release this year. Because the components all communicate wirelessly, installation takes place without the involvement of contractors or routing of wire bundles. And an Internet connection lets homeowners keep an eye on their house or change settings from anywhere in the world.

The bugs this system catches aren't in software

System operation

One of the more offbeat applications for Zigbee networks is in catching termites. Developersat Software Technologies Group Inc., Westchester, Ill., worked with a researcher at the University of Florida to devise wireless bait stations that are each a Zigbee node.

In operation, the bait stations go into the ground at numerous spots surrounding a house. Each bait station has a special sensor that triggers when termites eat at the wood it contains. The station then signals this activity to a receiver, which sends an e-mail to exterminators.

The wireless approach beats the technique now used on several levels, say developers at STG. Existing methods force exterminators to physically check each station for activity. Termites could cause severe damage long before evidence of them could turn up during a periodic inspection. In contrast, the Zigbee bait stations monitor pest activity 24/7. And exterminators need not make long trips just to examine bait stations.

Zigbee may help you make that flight

One projected use for Zigbee is as a mechanism for more rapid processing of returned rental cars. Developer Software Technologies Group Inc. demonstrated the concept on a scale-model Mini Cooper at a recent-technology expo. But the firm thinks there is a bigger market among companies renting real cars as opposed to toys.

STG suggests making each rental car a Zigbee node. Cars pulling into the return bay would automatically upload data about odometer readings and fuel levels, as well as any service-me-now warnings from the on-board vehicle computer. STG says the Zigbee module could also carry accelerometers that would report any fender-benders during the rental period.

The firm hasn't yet signed up a customer but is shopping the idea around.

How to make a Zigbee node

A Zigbee node today can consist of as few as two ICs plus a power source and a few passive components, as depicted in this view created by Zigbee chip and protocol house Ember Corp. The two ICs, basically a microcontroller configured for the Zigbee protocol and a transceiver, will become one device later this year.

Some Zigbee nodes can double as routers, hubs, and other kinds of network hardware. But these extra duties generally don't incur extra electronics. A Zigbee controller equipped with a sufficiently large flash memory can carry out such tasks in the course of its normal operation. Nevertheless, a few applications may add another processor for computational horsepower.

There can be differences in how various vendors of Zigbee electronics approach implementation. Ember, for example, says not all transceiver makers handle security functions and encryption the same way. Approaches where software carries out encryption could potentially be less efficient than those employing special-purpose hardware.

Regardless of the functions designed into the Zigbee node, firms developing equipment for the standard have special obstacles associated with the low bandwidth of Zigbee signals. The software work for developing specific applications can be tricky. The relatively low information capacity of Zigbee makes it impractical to repeatedly download tweaks to application programs as the application evolves. So special development kits help speed things up by creating temporary connections to Zigbee controllers over higher-bandwidth channels such as Ethernet.


Atmel Corp., Zigbee-compatible microcontrollers
(408) 441-0311
Control4, Zigbee-based home-automation systems
(801) 523-3100
Eaton Corp.,
Zigbee-based homemonitoring systems
(216) 523-5000
Ember Corp., Zigbee transceiver chips, development kits
(617) 951-0200
Lusora Inc.,
Zigbee-based home-monitoring equipment
(415) 561.6724
Software Technologies Group Inc.,
Zigbee system software and development
(708) 547-0110
Zigbee Alliance, Zigbee vendor organization

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