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.


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