The components of a home automation system can be broken down into several categories. Click on the menu on the left side of this page to see them.
Controlled devices include the tremendous range of equipment that a home
automation system is capable of controlling. They include household appliances,
door openers, power door locks, sprinkling systems, lighting systems, HVAC
systems, audio/video systems, home theater equipment, power drapes, security
systems, telephone systems, intercoms, messaging systems, information systems,
and many other types of equipment. There are far too many types of devices
to list here.
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Sensing devices can report values, such as temperature, humidity, light
levels, sound levels, etc., or states (such as on, off, open, closed, etc.).
The signals sent by sensors are converted into data that can be displayed
to the user or used by a controller program to make informed decisions
based on certain conditions. The signals can be converted at the sensor
itself, if it has the appropriate circuitry, by an intermediate protocol
converter (translater) or by the system controller. This data is a form of feedback.
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I/0 Interface Devices
I/O (input/output) interface devices provide the logical communication
link between the controller(s) and the controlled devices in a system.
They are the means of making various devices compatible with the physical
and logical structure of the system. I/O interface devices may be separate
equipment items, or they may be built in to a controlled device, in which
case it would just be considered a feature of the controlled device rather
than a separate equipment item.
Many equipment items that are typically part of home automation systems
come with some kind of built-in industry-standard control interface. For
example, VCRs, TVs, home theater, and audio equipment may have either infrared
or serial interfaces, or both. Most use standardized protocols that allow
remote controls from many manufacturers to interact with them.
Some controlled devices require optional or third party I/O interface
devices that allow those devices to be integrated into the home automation
system. Lighting equipment can be controlled with a variety of proprietary
or third party dimmers or switches that have built-in I/O capabilities.
Other equipment items that are less commonly used in home automation systems
may require the use of "generic" I/O interface devices. As an example,
to control a coffee maker, you would need some kind of generic on/off switch
with its own I/O interface. To control a reversible irrigation pump, you
might need a two-relay device with its own I/O interface.
Most I/O interface devices provide one-way communications from the controller(s)
to the controlled devices, although there are some types, such as RS-232
interfaces, which allow two-way communications. An example would be a smart
thermostat with a built-in RS-232 interface.
An I/O interface device can serve several communications functions,
Converting analog signals to digital signals that can be used by the
controller. This would, for example, convert the analog voltage from a
thermocouple (temperature sensor) to a digital signal that could be used
by the controller. Converting signals from the controller to a physical
and logical form that can be received and understood by the controlled
devices. Converting commands from the controller into a different set of
commands that a controlled device understands. System interface devices
have varying amount of built-in intelligence. For example, you might have
a specialized I/O interface device that receives standardized commands
from a central controller, translates those commands into a new set of
commands that is understood by the device it is designed to control, and
transmits those commands in the correct form and syntax to the device.
This kind of "smart" device may sound like a combination of a controlled
device and a controller, but it is more appropriate to call it an I/O interface
device. Still another type of system interface device would be a dimmer.
The dimmer would interpret the commands from the system and raise or lower
lighting levels accordingly.
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Controllers provide the intelligent control functions in a home automation
system. They can range from a simple lamp timer unit to a smart keypad
to a powerful computer. Controllers include any intelligent device capable
of sending commands that are understood by the controlled devices.
The control functions may be contained in a single central controller,
or there may be other controllers besides the central controller that have
a limited subset of control functions.
All controllers must have sufficient data in order to control the controlled
devices. Data can come from user input, sensor input, a timer, a control
program, or some combination of these. To obtain user input, the system
must have one or more user interfaces.
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User interfaces allow the user to interact with the system by sending information
to the controller or by presenting information to the user about the system.
The form and capabilities vary widely. Depending on the system and the
type of user interface, you could do any or all of the following:
Issue direct commands to the system (such as "turn on the kitchen lights").
Obtain feedback from the system (such as the temperature of the bedroom,
via a thermostat). Program the controller to carry out certain functions
automatically, based on time, sequence, or conditions. Some controllers
may have an integral user interface (like the keyboard on a computer),
or there may be remotely located user interfaces with varying degrees of
built-in intelligence (such as wall-mounted or hand-held keypads or touch panels). A dumb
keypad is only used as a remote user input for a controller. A smart
keypad might function as a remote user interface for a controller, but
also could have enough on-board intelligence to issue its own commands
to certain controlled devices; hence it could function as both user interface
Similarly, a user interface device does not have to be entirely devoted
to user input and/or feedback. For example, a keypad might incorporate
a temperature sensor or a light dimmer and a microphone for use with an intercom
system within the same physical enclosure.
A user interface may accept a variety of user input types. Keystrokes
or button presses are the most common modes of entering data, but some
systems may accept voice input or other forms of communication.
Not all controllers have a "user" interface. Some specialized controllers
may simply use input from sensors (or other equipment), and
programming to make intelligent decisions based on that input.
Typical user interface devices include:
- Push-button panels, with or without visual displays.
- Touch-panel displays, with fixed or programmable screen layouts.
- Computer keyboards and monitors.
- Hand-held remote controls.
- Telephone interfaces to allow long-distance remote control.
- Television controllers with on-screen menus.
Most high-level home automation systems are hybrid systems, using a variety
of user interface devices, each suited to certain tasks. For example, some
systems might allow you to carry out all control, programming, and feedback
functions from a personal computer, but might limit the number of functions
available from a hand-held remote control unit or a wall-mounted push-button
Don't confuse user interfaces with sensors. Even though there can be
some overlap in function (both can accept "input" from a user), for the
purposes of this discussion, a user interface is designed to provide a means
of conscious, intentional interaction with the system. For example, a home
automation system might use an infrared motion sensor to determine when
you enter a room and automatically send the equivalent of a button press
to turn on the room lights or to trigger a whole sequence of events, but
it is something that happens automatically, without any conscious choice
on the part of the user.
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The system network includes all of the controllers, sensors, wires, cables,
RF (radio frequency) links, IR (infrared) links, adapters, connectors,
junction boxes, dimmers, ballasts, power supplies, etc. that connect the
various system components. This might sound like the simplest part of the
system, but it can actually get quite complex. In many systems, this is
the area that requires the most planning and can be the most labor-intensive
part of a total system installation.
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Some system controllers allow the user to program the system with the system's
own user interface(s). Other systems require the use of a separate computer
(typically a PC) to program the system controller. Still others may allow
certain functions to be programmed with the system's own user interface(s),
but require a separate computer to program the more advanced functions
or change certain basic operating parameters.
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