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Low Power Wireless for Smart Homes



With the reduction in cost and power supply of wireless systems, smart home automation systems are becoming increasingly popular.

Designers of home automation systems are looking to wireless networks to provide the control and monitoring that they need with low cost and lower power consumption. There are a number of different technologies aiming to provide this capability, from the 802.15.4 ZigBee wireless mesh, through 802.11b/g WiFi to proprietary protocols such as Sigma Designs’ Z-Wave.

Recent developments in process technology have allowed much higher levels of integration, allowing high performance microcontrollers to sit alongside RF transceivers in single chip devices that dramatically simplify the design process. Additionally, low power design techniques have reduced the power consumption of devices to the level where they can be powered by low cost single button cells or even by harvesting energy from the environment. All of this provides designers with a wide variety of options for developing the next generation of smart, connected home automation systems that can be accessed and controlled in many different ways.

ZigBee

ZigBee has been developed with home automation specifically in mind. With over 300 certified products, it aims to provide a global market within the unlicensed 2.4 GHz band so that equipment makers can benefit from economies of scale and low cost, low power architecture. There are eight separate protocols currently being used (see Table 1) with two more being developed to extend the mesh networking approach behind the ZigBee protocol into many different areas.

This mesh approach allows each node to pass information through the network, increasing the range and connectivity at the expense of lower data throughput. This reduces the performance requirements of the RF front end and the memory and processing requirements of the controllers, allowing the nodes to be compact and low cost. This combination of low cost and medium data throughput makes it much more suited to control and automation applications rather than data streaming or large file transfers.

In September 2011, the ZigBee Alliance completed development and ratified the ZigBee Building Automation standard which provides protocols for the secure and reliable monitoring and control of commercial building systems. It is the only wireless mesh network standard for commercial buildings approved by BACnet, an international standard for data communications in building control.

Products using ZigBee Building Automation give building owners and operators control of more building types, previously unreachable rooms or sensitive areas, thanks to its low-power wireless operation. Existing wired BACnet building automation systems can now be expanded with greater ease and reduced operational cost. The standard was developed by numerous Alliance members with major assistance coming from Convergence Wireless, Johnson Controls, Schneider Electric, Siemens, Ingersoll-Rand and Ubilogix.

Protocol

Usage

Certified products

ZigBee Smart Energy

The core standard for monitoring, controlling and automating the delivery and smart use of energy and water.

170 certified products for energy service portals, meters, displays, programmable communicating thermostats and smart plugs.

ZigBee Home Automation

Controlling appliances, lighting, environment, energy management and security.

28 certified products for control of home appliances, lighting, security, heating and cooling systems.

ZigBee Telecom Services

Value-added services using ZigBee nodes including information delivery, mobile gaming, location-based services, secure mobile payments, mobile advertising, zone billing, mobile office access control, payments, and peer-to-peer data-sharing services.

13 Certified products for communication platforms, access points, terminals and location nodes.

ZigBee Remote Control

Removes the line-of-sight restrictions of previous remote control products and adds two-way communication, longer range of use than traditional infrared and extended battery life.

The first product has been certified.

ZigBee Compliant Platform

Used to test every device for ZigBee specification compliance before being sold.

119 platforms are ZigBee Certified.

ZigBee Manufacturer Specific Profile

Manufacturer-specific devices for consumer, commercial and industrial needs not requiring multi-vendor interoperability. Each product is tested for successfully using ZigBee networking.

10 Manufacturer Specific Profile (MSP) products Certified.

ZigBee Input Device

To use ZigBee for mice, keyboards, touchpads, wands and other input devices.

Agreed 2010.

ZigBee Gateway

Connecting ZigBee networks to IP networks and the Internet.

Agreed 2010.

ZigBee 3D Sync

For active 3D glasses.

In development.

ZigBee Retail Services

Monitoring, controlling and automating the purchase and delivery of goods and managing retail supply chain.

In development.

Table 1: The 802.15.4 ZigBee protocols

At the same time, for home automation, the ZigBee alliance has teamed up with an Italian group of white goods makers to blend the strengths of ZigBee Home Automation, ZigBee Smart Energy, ZigBee Telecom Services and ZigBee Gateway to create a platform to control smart appliances, by communicating with broadband networks and Automatic Meter Management systems. The Energy@Home consortium of Electrolux, Enel, Indesit Company and Telecom Italia aims to increase the scope and value of the ZigBee Home Automation protocols and create new value-added services to help reduce power bills.

ByteSnap Design in Birmingham, UK, has developed the industry’s first ZigBee Smart Energy module for smart metering and control in a single, low power platform.

The ZMM-01 uses the ZigBee Smart Energy protocol to control energy equipment within the home or office and also provides a Real Time Clock, accurate up to 2 ppm, which can be used for the equipment.

The module is based on the Ember EM357, a ZigBee radio-on-a-chip which integrates a fully compliant IEEE 802.15.4/ZigBee wireless transceiver with the ARM Cortex-M3 microcontroller, able to run the ZigBee Smart Energy protocol and application code while still consuming just 30 mA to transmit.

It combines this with the Cirrus Logic CS5467 Analogue Front End (AFE) developed specifically for energy measurement applications. The AFE incorporates on-chip functions for measuring voltage and current to calculate active, reactive and apparent power/energy with Energy Linearity: ±0.1% of Reading over 1000:1 Dynamic Range.

The ZMM-01 simplifies working with ZigBee Smart Energy by implementing a complete ZigBee SE smart meter that needs only a shunt resistor and current transformer (CT) to form a meter that meets IEC EN62053-21 class 1 or 62053-23 class 2.

While a module makes it easier for a system developer to add wireless capabilities to an existing design, most smart home equipment is being developed from scratch to provide the lowest bill of materials. The CC2420 from Texas Instruments is a low cost, true single chip RF transceiver for ZigBee and smart home wireless networks. It includes a digital direct sequence spread spectrum baseband modem providing a spreading gain of 9 dB and an effective data rate of 250 kbps.

NXP’s acquisition of UK chip designer Jennic brings technologies for both ZigBee and Jennic’s own JenNet protocols. The JN5148-001 is an ultra-low-power (under 18 mA) transceiver and microcontroller. A large memory footprint of 128 Kbytes of RAM allows it to run both a network stack for ZigBee and an embedded application or in a coprocessor mode. The low operating current allows it to be driven directly from a coin cell battery.

It also has a range of enhanced peripherals such as low power pulse counters running in sleep mode designed for pulse counting in AMR applications and a unique Time of Flight ranging engine. This allows accurate location services to be implemented on wireless sensor networks. To minimize the complexity of developing such systems, NXP provides a series of software libraries and interfaces that control the transceiver and peripherals of the device. These remove the need for the developer to understand wireless protocols and greatly simplify the programming complexities of power modes, interrupts and hardware functionality.

Z-Wave

As the Jennic parts show, ZigBee is not the only wireless protocol being used for smart homes. With over 500 products on the market, the Z-Wave Alliance claims to be the world’s largest ecosystem of interoperable wireless control solutions. Products using Z-Wave have been installed in more than a million homes in the US in the last year alone.

Products using the technology include innovative remote controls for Z-Wave certified door locks, in-wall dimmers, plug-in modules for lights and small appliances, wall outlets and scene controllers. Jasco also makes the advanced GE Z-Wave Energy Monitoring Module that captures the power used by devices like computers and TVs, and interprets the voltage, frequency, kilowatts and kilowatt-hours data as well as power factor.

ISM Band

The Industrial, Scientific and Medical (ISM) band is also being used for home automation. With well-established, unlicensed frequency bands around the world, new low power design technology and volume production to bring down the cost of equipment, it is used for applications such as home security and alarms, remote keyless entry and automatic meter reading. The Si4420 Universal ISM Band FSK Transceiver from Silicon Labs is a single chip, low power, multi-channel FSK transceiver designed for use in applications requiring FCC or ETSI conformance for unlicensed use in the 315, 433, 868 and 915 MHz bands. It is part of the EZRadio system that produces a flexible, low cost, and highly integrated solution that does not require production alignments.

The Si4420 is a complete analog RF and baseband Zero-IF transceiver including a multi-band PLL synthesizer with PA, LNA, I/Q down converter mixers, baseband filters and amplifiers, and an I/Q demodulator so that only an external crystal and bypass filtering are needed. It has an integrated PLL for easy RF design, and its rapid settling time allows for fast frequency-hopping. This bypasses problems from multipath fading and interference to provide the robust, reliable wireless links needed for the home.

The transceiver also reduces the load on the microcontroller with the integrated digital data processing features: data filtering, clock recovery, data pattern recognition, integrated FIFO and TX data register. To minimize the system cost, the Si4420 can provide a clock signal for the microcontroller, avoiding the need for two crystals.

WiFi

WiFi is another key technology that is increasingly becoming adopted for home automation as a result of its popularity for home networking. Microchip has combined its RF and low power, low cost microcontrollers in modules to add to equipment to provide a quick and easy way of linking them to the Internet. The MRF24WB0MA and MRF24WB0MB are low-power 2.4 GHz 802.11-compliant surface mount modules with all the required RF components such as the crystal oscillator, bypass and bias passives. They integrate the MAC, baseband, RF and power amplifier and include hardware support for AES, and TKIP (WEP, WPA, WPA2 security), all of which are used to make WiFi networks more secure. The integrated module design frees the designer from RF and antenna design tasks, but more importantly ensures that the equipment designs will pass regulatory compliance testing, providing significantly quicker time to market.

The modules are designed to be used with Microchip’s TCP/IP software stack running on PIC18, PIC24, dsPIC33, or PIC32 microcontrollers. The stack has an integrated driver that implements the API that is used in the modules for command and control, and for management and data packet traffic though a four-wire serial slave SPI interface that provides the interrupt, hibernate, reset, power and ground signals.

This combination of the module and a PIC running the TCP/IP stack allows a wireless web server to be implemented quickly and easily, linking directly to an existing WiFi network in the home and providing a hub for home automation control and access to equipment from any Web browser.

Conclusion

While ZigBee is becoming increasingly popular as a protocol for wireless home automation, there are several other options. With many new protocols emerging, designers have a wide choice of technologies for implementing wireless networks and adding intelligence to all kinds of equipment in the home. This is helping to reduce power consumption and energy bills and increase the usability of everyday devices. With Web access via gateways or added directly as a low cost server, equipment can be controlled by Web browser technology from anywhere in the world and from any type of device – from the desktop PC to smartphones and tablet PCs. A wide range of implementation options is available, from the dedicated RF transceivers to integrated devices that include microcontroller cores to fully compliant modules.
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