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CEBus Network Architecture and Topology


Smart House System

Other Autmation Systems


The X-10 system uses a standardized protocol and command set to handle a variety of home automation tasks. It relies on a power line carrier (PLC) communication system that superimposes a higher-frequency (120KHz) amplitude shift keyed (ASK) carrier on top of the 60Hz (or 50Hz) power line carrier.

X-10 controllers can be plugged in at any point in the house wiring system. Commands from a controller are transmitted through the entire house-wiring network, and are not limited to any particular branch of the circuit (a phase coupler allows the signal to bridge the gap between the two 110V. circuits that typically feed a house). A special blocking device can be installed at the breaker panel to prevent the X-10 signals from exiting the home system and being broadcast into other homes or apartments that may share the same power system.

All X-10 receivers, or "modules" will receive any command sent by any X-10 controller in the home wiring system, in that system. Some newer modules can send as well as receive. For the purposes of this document, an X-10 module can be classified as an I/O interface device.

When a module receives a command, it checks the "address" attached to the command to see if it is the intended recipient. If the command was meant for a different module, the command is ignored. When the intended module gets the command, it acts upon it accordingly, switching something on or off, dimming a light, sending a different command to some other device, etc.

X-10 commands are limited to a set of 16 commands, called the standard function set. However, most modules recognize only a basic function set of seven commands.

An extended code packet has also been developed to increase the number of possible transmitted functions, which is useful for home automation systems that control several types of subsystems, such as HVAC, security, audio, etc. However, due to the nature of the X-10 technology, this slows down the data transmission rate due to the increased number of AC cycles required to carry the additional information.

Addresses in the code are described by a four-bit "house" code (letters A-P) and a four-bit "unit" code (numbers 1-16), thus A-1, A-7, C-14, G-9, etc.

To instruct one or more modules to carry out a function, house/unit code message packets are transmitted to all of the modules for which the command is intended. This "arms" the modules. Then, another message packet is sent, with the desired function code. The armed modules carry out this function. A module is "disarmed" by the first house/unit code message packet received that does not match its house/unit code after a function code is received, or by the reception of an "all off" function.

The two most common X-10 module types are lighting modules and appliance modules. Lighting modules usually control resistive loads, such as incandescent lights, and can switch the lights on or off or dim them down or up. Appliance modules use a relay to switch the attached devices on or off.

X-10 controllers can be stand-alone plug-in devices, or can be hard wired into a system. Some are simple, with only a few basic controls, while others may have built-in timers, clocks, and telephone access capabilities. The controllers generally have built-in buttons, dials, etc. to provide the user interface to the system.

Other devices have been added to compliment the X-10 system, such as radio frequency (RF) or infrared (IR) controllers and modules. These are used to help cover situations not suited to power line carrier technology. For example, a security system may use RF wireless door/window sensors. A "base station" controller receives the RF command from the sensor, translates it to an X-10 command, and then transmits it on the power line network. Naturally, to extend the X-10 system's utility in this way adds cost and complexity to the system, without any improvement in reliability, since it still relies on the X-1 0 power line communications technology for network communications.

Repeaters may be required in larger systems where signal attenuation is a problem.

An X-10 system is low cost and usually easy to install, since most X-10 components use existing house wiring as the communication medium. However, there are some drawbacks:

New enhancements to the X-10 technology are improving the reliability of the system, but it is still subject to problems. The performance of this technology is more difficult to improve; it would require a substantial increase in cost and complexity, which would defeat the purpose of the X-10 system: a low-cost system that performs adequately well for many basic home automation needs.

New X-10 "modules" are being developed all the time to handle a variety of tasks. As mentioned, a module can be a transmitter, a receiver, or include both transmitter and receiver. It can be designed to control specific types of equipment. So, just what can a module do? Here is a partial list:

Some major X-10 manufacturers include Honeywell, Leviton, Advanced Control Technologies, IBM, and X-10 USA.

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CEBus Network Architecture and Topology

The CEBus standard allows the use of a variety of network media, including:

CEBus communications hardware, language, and protocol are available on a chip made by Intellon Corporation in Ocala, Florida. Intellon sells the chip to manufacturers for incorporation in their products. lntellon can also manufacture private label/OEM CEBus products. Developer kits are available through lntellon.

CEBus home automation systems can be installed in existing dwellings, using the original 110V. or 220V. household wiring for data exchange. While this is not the optimum situation for rapid data throughput, such as for video signals, it does provide additional flexibility where rewiring is inconvenient or prohibitively expensive. IR or RF would typically be used for remote control purposes. CEBus technology may be encapsulated within individual appliances that connect to the power outlets, or within remote control devices that plug into the outlets.

The CEBus standard includes such technologies as power-line spread spectrum modulation. Spread spectrum starts modulation at one frequency and changes the frequency during its cycle. It begins each burst at 100 KHz, linearly increasing the frequency to 400 kHz over a 100-microsecond period. The burst ("superior" state) and the absence of burst ("inferior" state) create similar digits, so a pause interval is not required.

A digital 1 is created by an interior (or superior) state that lasts 100 microseconds. A digital 0 is created by an inferior or superior state that lasts 200 microseconds. This means that the transmission rate will vary, depending upon the number of 1s vs. 0s.

No matter what media is used, the CEBus control channel data is transmitted at roughly 8,000 bits per second. Media can also carry data channels. Data throughput will depend on the capabilities of the medium. CEBus control messages are always of the same format, no matter what medium is used. A message contains the address of the recipient, but does not include any routing information, thus the recipient can be anywhere on the network, on any medium.

The CEBus control channels carry commands and status messages. These messages consist of strings or packets of data bytes that can vary in length, depending upon how much data is in the message. Packets can be hundreds of bits long. Minimum packet size is 64 bits, and each packet takes an average of about 1/117 second to be transmitted and received.

There are commands for allocating data channels, but the majority of the CEBus standard concerns the control channel specifications. Data channel encoding is not specified in the CEBus standard.

Device addresses are set in hardware at the factory, and allow 4 billion possibilities. CEBus also offers a defined language of object-oriented controls, including commands such as volume up, fast forward, rewind, pause, skip, temperature up or down 1 degree, etc.

Messages may be addressed to (sent to) a specific device, or a special address may be used to reach all devices on a network or just a specified group of devices. Addresses may be either individual or group addresses. Devices may belong to more than one group. Note: Not all CEBus-compatible devices support group addressing, and the number of groups a device may support can vary. This varies by manufacturer and model.

CEBus topology allows devices to be placed anywhere on the network, independent of the medium, as long as the device has the correct CEBus interface for that medium. Messages being sent from one media type to another are sent via a router circuit. The router may be a separate device, or it may be integrated within an appliance.

Control messages are distributed among the CEBus devices and routers. A centralized controller is not used for delivery management. No specific topology is specified in the CEBus standard. All controlled device connection points on a medium are treated logically as though they were on the same bus. This means that all controlled devices on a particular medium sense the arrival of a data packet simultaneously. All devices read the destination address in the message, but only those with a matching address read the rest of the contents of the message and react to them.

Audio-video requirements are available, but the Electronics Industry Association (EIA) has not yet released specifications. It should describe a cluster-controller bus, consisting of a thin cable with eight twisted-pair wires. It is designed for interconnection of a cluster of home entertainment products within a small area, typically one room. Maximum cable length is 30 feet. The cable carries three audio channels, four video channels, plus the CEBus control channel. A single connector is used to connect the cable to a controlled device. In terms of fiber optics, the CEBus technical requirements have been released, but specifications are still under development by the EIA.

In terms of coaxial cables, CEBus specifies a dual-cable system. One cable connects to in-home video sources (VCRs, cameras, etc.). The other cable is used for distribution to any receivers in the system. At the head end, any external video signals are combined with the signals from in-home sources.

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The Echelon system is based upon the existence of intelligent control devices (nodes). In an Echelon system, also referred to as a "LonWorks" network, communication between devices may be either peer-to-peer (distributed control) or master-slave (centralized control). A common protocol is used for all communications.

Whatever approach is used (centralized vs. distributed), each node has a potentially high level of built-in intelligence. The nodes computational capabilities allow processing functions to be distributed throughout the system. For example, an Echelon-based temperature sensor can be intelligent, performing programmed analysis of local temperature readings and filtering the results so that only significant changes are reported to a central controller or to other nodes. Control functions can also be distributed throughout the system, providing better performance and reliability.

Nodes communicate with each other on a peer-to-peer basis using a common protocol. Each node contains embedded intelligence that handles the protocol and carries out processing and control functions. Each node also includes an I/O interface that connects the node's micro-controller with the communications network. On each node, most of these capabilities are provided by a single chip, called the Neuron chip, which is available in several versions from Motorola and Toshiba. The Echelon Lonworks technology is an open, but proprietary, technology.

The Echelon approach does not use existing house wiring for communications. While this requires additional wiring during installation, it eliminates the problems and limitations associated with power line carrier (PCL) systems like X-10. Transmission is much faster and more reliable, and is not subject to power line interference, static, or changing line load conditions. In addition, Echelon is not limited to any particular communications network wiring/connection type. A variety of transceivers and connectivity products are available. Gateways are available for Ethernet, Tl, X.25, Bitbus, Profibus, CAN, Modnet, SINEC, Grayhill, Opto22 (digital), OptoMux, Modbus, ISA bus, STD32 bus, PC/104 bus, VME bus, and EXM bus.

The built-in capabilities of the Neuron chip allow a tremendous range of computation and intelligent functions to be carried out at the local (node) level, but the Echelon LonWorks technology is not limited to node-level processing; it also provides compatibility with host-based applications. Host based applications are those that run on a processor other than one of the processors in the Neuron chip. This could be a component microprocessor that uses a Neuron chip as a communication coprocessor, or a Windows-based PC that communicates with the system using a serial port or PC adapter board. These applications allow the addition of servers, consoles, or monitors to the system, and can provide centralized control for non-distributed automation systems. They are also appropriate for migrating existing applications, creating complex network management utilities, or building gateways to other systems.

A typical node in an Echelon system performs a simple task. Devices such as proximity sensors, switches, dimmers, motion detectors, relays, motor controllers, stepper motors, etc., may all be nodes on the network. The interconnected set of communicating nodes performs the super-set of complex control functions required for automating a home.

Smart House System

Appliance control signals, status information, and message data are carried on the same channel and use the same protocol. The exceptions are video signals and telephone data.

The basic topology consists of a star with branches that correspond to the electrical branch circuits. At the star's hub is a System Controller, which is typically placed in close proximity to the circuit breakers for the home's electrical system. The System Controller includes an uninterruptible power supply, surge suppressors, the telephone gateway, and the head end for the coax cables. The System Controller handles the following tasks:

The System Controller handles all message routing. Smart House has specified a formal language for appliance control and status messages.

The Smart House system is based on three cable groups or types:

Smart House wiring is best for new construction, since retrofitting would involve substantial rewiring. Wall switches are not wired directly to outlets. Rather, wall switches are connected to applications cables that include a communications channel. When a switch is opened or closed, a signal is sent to the System Controller, which acts according to a programmed table to control various lights or outlets. This approach allows for relocation of appliances, as well as switch reassignment, in which the same switch might perform different functions, depending on the time of day or other factors.

Smart House specifies a dual coaxial cable system. A downstream cable carries video signals from sources such as cable TV, satellite dishes, antennas, etc. An upstream cable carries video signals from internal sources, such as CCTV, VCRs, computer terminals, etc. The head end in the Smart House Service Center combines these upstream and downstream signals for distribution on the downstream coaxial cable. This approach is similar to the one used in the CEBus system.

The telephone gateway provides an intercom function and access to the Smart House system for remote control operation. Specific ring patterns indicate intercom calls from specific telephones in the home. The telephone gateway includes a modem for remote control purposes. The touch-tone signals from an external telephone can activate programmed data messages for operating appliances or services in the home. A security code is required for access. Synthesized voice instructions are available for remote control assistance.

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