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EETE OCT 2015

Sponsored Contributed Article LED lighting in home automation: ready, aim, … By Josh Israelsohn, Mouser Electronics Examples of commercial home automation equipment date back to at least 1975 with the launch of Pico Electronics’ X10 project in Scotland. Although engineers of the day could not have imagined many of today’s implementation technologies, the architectures and use models that they did imagine inform system designs to this day. Among the first applications for early home-automation systems were lighting and appliance controls, both of which homeautomation providers implemented as simple on-off mainspower switches. Conveniently for installation, the network physical media was the power line as well, operating with highspeed bursts during the AC zero crossings and communicating one bit per crossing. Accounting for communication overhead and message duplication built into the protocol, early systems realized a communication rate of about 20 baud. With 12-bit control messages (8-bit address and 4-bit command), latencies for simple commands in the 600 to 750 ms range could be said to have pushed the limits of good taste… or market tolerance. Beyond that, the challenges to power-line communication are legend and the reliability of home-automation systems fell short of market expectations for many years. …Then technology caught up Today, home-automation systems are enjoying resurgence and, for the first time in their four-decade history, appear poised for broad-market adoption. As many have seen in other segments, this turn derives from a confluence of several technology advances, none necessarily driven by home-automation applications per se, but which combine to serve such uses far better than any set of technologies previously available for the purpose. For residential lighting in the context of home automation, three specific areas of technological innovation have contributed to making systems more attractive to the broad residential market: Communication, control, and the lighting devices themselves. At the heart of many home-automation implementations is a wireless network, which solves many of the problems suffered by power-line communication schemes including difficulty communicating across phases of split 240/120-V systems, adjacent-dwelling interference, and glacial data rates. Currently, wireless devices conforming to IEEE 802.15.4 are most common, particularly those conforming to ZigBee Alliance specifications popular in IoT applications. ZigBee provides 250 kpbs data rates in the 2.4 GHz ISM band; lower rates to 20 kbps in geo-specific sub-GHz spectrum. Unlike WiFi, which forms star networks extendible only by adding dedicated hardware repeaters, ZigBee nodes form mesh networks, which extend automatically with each additional node. Dedicated home-automation control hardware has given way to software applications that run on the universal wireless HMI device—the mobile phone. Gateway hardware solves the connectivity problem created by mobiles’ lack of compatible radios and serves as the bidirectional interface between the 802.15.4 Zigbee wireless home-automation network and nearly ubiquitous 802.11x WiFi data communication LANs, as shown in figure 1. Because the HMI and system-control functions are not always present, timing, sequencing, and grouping functions must reside within the individual client devices. Moving these functions to the client devices also provides for multiple HMI interfaces to coexist on the same network through a single gateway. Basic setups such as lighting groupings and scenes reside within the light controls. Commercial leads the way Fluorescent fixtures have long dominated commercial lighting where their diffuse light output, high colour temperature, and efficiency have provided benefits in office spaces where lighting installations can cover floor space seemingly by the acre. Historically, simple switches controlled fluorescent lighting troffers. Lighting for large cubical-farms might switch troffers in clusters or wire multi-tube devices with each tube position ganged to a separate circuit, allowing stepwise dimming by switching off one or more tubes in each troffer. Overall, however, traditional fluorescent lighting devices did not invite control by dimmers and systems rarely included occupancy detection. Meanwhile, LED lighting and new lighting-controls are allowing companies to realize cost reductions in excess of those that simple lumen-per-watt comparisons suggest. In residential lighting, incandescent bulbs compatible with standard threaded Edison sockets, such as A, BR, and PAR series bulbs, dominate. Dimming, enlightened Automated or not, a traditional dimmer blanks its output during the leading portion of each half power cycle and, once activated, remains on until a power-line zero crossing. Incandescent light bulbs—roughly 98% efficient as heaters, are in effect thermal low-pass filters with long time constants relative to the line-power period. An LED, by contrast, is essentially an electrons-in-photons-out DC current-driven device. LEDs are not natively compatible with AC voltage sources and traditional dimmers that chop up the AC voltage Figure 1: Modern home-automation systems replace central control hardware with application software that runs on a smart phone. A gateway bridges the WiFi connected phone to the automation system’s 802.15.4 mesh network. 8 Electronic Engineering Times Europe October 2015 www.electronics-eetimes.com


EETE OCT 2015
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