Wireless Lighting Control in Multi-Medium Smart-Building Infrastructure

The smart building revolution is happening now, bringing enhanced comfort and convenience to residential homes and lower operating costs as well as greater employee productivity in the commercial sector. The world market could be worth almost $78 billion by 2022.

Wireless control of lighting is a key element of this revolution, allowing versatile operating modes and helping avoid wasting energy without the upheaval and cost of a large rewiring project. Installing wireless controls is reckoned to save up to 70% of the cost of rewiring existing premises, or 15% of the wiring cost in a new-build project.

While some new homes, such as premium properties, may be designed to be smart from the outset, existing houses are likely to be upgraded in stages. An owner may prioritize the heating or lighting system as an easy first step into smart technologies, and then may expand the system with other smart features such as appliance controllers, window blinds or door locks. There appears to be a bright future for smart building devices of all types, from simple light switches, wall plugs or radiator caps to sophisticated central controllers. This brings opportunities for new brands to win market share by delivering products that may be technically advanced or simply more stylish than those offered by more established competitors.

Interoperability and coexistence will be key concerns for developers looking to succeed in a marketplace where customers tend to introduce smart features to their buildings on a gradual basis.

Candidate Connectivity Standards

A number of connectivity standards for controlling devices such as lights, radiator valves, window openers and appliances in smart buildings have been proposed. Popular standards, with certified products currently in the market, include EnOcean, KNX, ZigBee^® and Z-Wave^®.

EnOcean and Z-Wave operate in sub-GHz radio frequency bands. In Europe this is 868 MHz. Z-Wave is based on mesh network topology, which supports up to 232 nodes. The protocol makes provision for interoperability at the application level, and a number of Z-Wave System-on-Chip devices are available, such as the Sigma Designs ZM5202. The Z-Wave stack resides on the chip, and is accessed through the API also provided, which allows the developer simply to load the application into the device’s integrated program memory, as Figure 1 shows. The SoCs enable a one-chip solution with all hardware features such as a sensor ADC, 128-bit security encryption and a controller for a triac dimmer integrated in the device.

Figure 1: The Z-Wave protocol is accessed via the API provided.

The EnOcean technology is based on an extremely lightweight radio protocol that enables batteryless modules operating from a solar cell or other energy-harvesting system such as a kinetic converter or Peltier element to transmit short telegrams containing sensor data. This is a powerful proposition for items such as light switches, which can be positioned anywhere in a room to communicate with a line-powered lighting actuator (Figure 2) built using a system module such as the EnOcean TCM300U. EnOcean switches can also be easily incorporated in a larger home-automation network. The German KNX developer Weinzierl (www.weinzierl.de), for example, has built an EnOcean-KNX gateway, which receives the EnOcean wireless telegram and generates the appropriate signal on the KNX bus.

Figure 2: Wireless sensors communicate with line-powered actuators.

KNX claims to be the only standard that is approved worldwide according to norms such as ISO/IEC14543-3, EN-50090 (CENELEC), EN13321-1/2 (CEN), the Chinese home automation standard GB/T20965, and US ANSI/ASHRAE 135. Unlike the wireless-based EnOcean, ZigBee and Z-Wave standards, the KNX bus can operate on various media, including twisted pair cables (KNX TP), AC power lines (KNX PL) and Ethernet/Wi-Fi (KNXnet/IP), as well as wireless (KNX RF) operating in the 868 MHz frequency band. The KNX Association also provides manufacturer-independent tools for device developers and system installers.

ZigBee Home Automation is a special profile of the well-known ZigBee standard based on 2.4 GHz radio. It is optimized for controlling home devices, and uses the ZigBee PRO mesh networking stack. ZigBee Pro can be implemented on a wide variety of microcontrollers. Silicon Labs has a number of ZigBee modules, such as the ETRX357, which incorporate a single-chip ZigBee transceiver combined with the ZigBee PRO compliant EmberZNet meshing stack. These modules allow developers without RF experience to add wireless networking capability to their products.

Working with the Chosen Standard

Each standard is backed by its own alliance or association that manages the technical specification as well as legal aspects such as licenses and product certification. The certification process ensures interoperability between products from different manufacturers. OEMs looking to penetrate markets currently using any of these standards must offer their new product designs for certification.

Typically, the path towards developing a certified, interoperable device, such as a light fitting, switch, or dimmer begins by acquiring a developer kit such as the RBK-ZW500DEV-CON Z-Wave kit by Sigma Designs. Sigma also has a number of lower-cost regional kits that serve the different allocations of sub-GHz frequency bands in territories such as Europe, North America and Japan. In the case of Z-Wave, purchasing the developer kit also gives access to Sigma's software development kit SDK for Z-Wave. The SDK allows access to resources such as protocol libraries, application examples and documentation online. Using the available tools, the developer can make necessary decisions such as hardware selection, protocol choice and the class of device and commands. Upon completion of hardware and software development, the product can then be submitted for certification by the Z-Wave Alliance.

Centralizing Control

In a smart building, lighting may need to be activated in several ways, not limited to conventional manual switching or dimming via a wall-mounted control. A central controller may be programmed to turn lights on or off at certain times, or in response to occupancy sensors that also form part of the home security system, or to signals from ambient light sensors that can be used to adjust dimming for optimum illumination and energy efficiency.

In addition, given growing consumer adoption of networked mobile devices, smart building users are attracted to colorful apps that allow them to control aspects of the smart building, such as lighting, heating, appliances and security settings from a tablet or smartphone. A gateway device linking the smart building network with an Internet router provides the key to this functionality, as shown in Figure 3. Any smart building technology needs such a gateway to the IP-based domain, whether to communicate with a tablet connected to the building's Wi-Fi network, or with a mobile device connected to the Internet via cellular or Wi-Fi hotspot anywhere in the world. Gateways are available from a number of manufacturers, which are suitable for connecting a smart home network such as an EnOcean, KNX, ZigBee or Z-Wave environment to the building's Internet router.

Figure 3: Connecting the smart home network to the IP domain allows settings to be controlled using a variety of devices.

App developers can take advantage of features supported by the chosen technology to provide convenient functions for the end user. These include configuring groups of devices to allow control with a single click, or creating custom "scenes" to apply desired settings for lighting, heating and other appliances automatically. The user could create a "home cinema" scene, which simultaneously dims lights, closes blinds, adjusts the temperature and turns on the flat-panel TV, or a "go to sleep" scene to lock doors, close windows, turn down heating and turn off all lights except in the bedroom.

Conclusion

The standards that define connections between devices within smart buildings each provide a structure that product developers need to be able to address quantifiable markets and ensure interoperability with other products already in the marketplace. The associations promote their own standards vigorously, but developers must choose based on the resources they have available and accurate assessment of the opportunities and competition.