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Alliance promotes battery-free wireless sensors

A number of systems— such as Zigbee or other IEEE802.15.4-type radio links—promise in-building wireless sensor connection and control functions. A new alliance has been formed to enable “sustainable” building developments around the product concept EnOcean has created; the new body is called the EnOcean Alliance, and its founding promoters also include Distech, MK Electric (part of Honeywell), Masco, Omnio and Thermokon. Over 70 other member companies currently make or are deploying EnOcean-enabled products. The objective of forming the Alliance is to promote further deployment of the products, and to attract other designers and manufacturers to work with the standard.

The distinguishing features of the technology are that switches and sensors operate entirely from energy-harvested power and require no batteries. Products are fully interoperable, and are already widely deployed, mostly in commercial buildings in central Europe—the history of the technology traces back to developments that Siemens originally carried out. Alliance founder Graham Martin says that building-maintenance managers are very resistant to wireless systems that need batteries, even if the interval between battery changes is long. Energy-harvesting techniques include electromagnetic generation and solarcells. For example, a lighting switch—such as those that MK Electric and others make—has a permanent magnet and a wound armature; the action of clicking the switch slides the magnet in the winding and generates suffi cient power to transmit a short radio message. Other devices—for example, an occupancy sensor that Thermokon makes—uses low-cost amorphous-silicon solar cells to charge a supercapacitor that in turn runs the sensor and radio.

The EnOcean approach is explicitly a low-data-rate-channel, primarily point-to-point link, although by use of repeaters you can construct an elementary network. It does not support mesh networking, which, Martin asserts, has proved problematic in attempts to confi gure large Zigbee networks. EnOcean is “room-level wireless, with gateways into IT backbone networks.” The principal characteristics of the link are that it operates at 315 or 868 MHz, in unlicensed radio bands, as local frequency allocations determine. It uses simple AMSK (amplitude-shift keying) and sends a message lasting under 1 msec that includes a 32-bit unique device identifi er, a manufacturer’s code, and data payload that might be a measured value— such as temperature—or a simple on/off command. One press of a light switch generates enough power to send four to six repetitions of the message frame. Data rate is 125 kbps, and range is up to 300m in free space or 30m in a building—appropriate for in-room use, Martin says. The new Alliance will allocate blocks of device identifiers.

EnOcean holds patents that it believes cover any use of energy-harvesting for wireless signalling. Anyone can use the (published) wireless protocol to build, for example, repeaters and receivers—the protocol is now in the hands of the Alliance. EnOcean—the company—also intends, Martin says, to license the energyharvesting elements of the system but this may not be for “two to four years.”

Most manufacturers today buy complete radio modules from EnOcean; the radio comprises discrete components. Receivers today are, most often, located in stand-alone switch modules, although designers can also incorporate them into, for example, lighting luminaires. A module costs in the region of €20, but the Alliance/company expects this to drop by perhaps 30 to 40% in 2009 once a singlechip implementation—which EnOcean will create and TSMC will fabricate—is available. The chip may also be available as a component; it will add some new features, such as the ability to add simple encryption to the message, and a facility for a simple message-acknowledgement back-channel.

EnOcean Alliance, www.enocean-alliance.org.