Correspondence Lesson 10: Home Controls

So far in this course, we've limited our coverage to technologies for the commercial, industrial, and institutional sectors. In this lesson, however, we will take a look at a variety of residential control technologies. While these technologies were the province of electronic enthusiasts for many years, electrical contractors, home designers, and homebuilders are now showing a healthy interest in

So far in this course, we've limited our coverage to technologies for the commercial, industrial, and institutional sectors. In this lesson, however, we will take a look at a variety of residential control technologies. While these technologies were the province of electronic enthusiasts for many years, electrical contractors, home designers, and homebuilders are now showing a healthy interest in this market.

We use residential automation technologies to control three main systems: security, entertainment, and energy management. You can also combine them with a variety of sensors and inputs to create an infinite number of control schemes that can:

1. Monitor a certain area of the home (nursery, backyard) via audio, video, or both.

2. Turn air conditioning or heating on and off (according to schedule or via telephone).

3. Control any electrical device with a handheld controller.

4. Provide a more complex security system than old-style burglar alarms.

5. Set the controller to call a parent at work if the children don't come home at a preset time.

6. Make repetitive phone calls.

7. Send the same fax to multiple numbers automatically.

8. Gently raise the light levels in the room as well as volume levels of a stereo in the morning to replace a screaming alarm clock.

Controllers. The brain of the home automation system, a controller coordinates the sensors and equipment on the system, performs various logic functions, and ensures the desired events take place at the right time.

A simple central controller can control up to 256 separate devices; turning them on/off, or dimming lights, according to a schedule programmed into the unit via the computer. The user issues controller commands, based on the time desired for each operation. Mid-range systems offer the same type of control as the simpler ones; plus they have the ability to react to other pieces of equipment instead of reacting only to a clock. The advanced systems incorporate all these features, plus security, climate control, entertainment, telephone (voice mail and automatic calling), and other built-in abilities.

There are two primary types of home automation control devices: those using centralized intelligence and those using distributed intelligence. The original, and still most popular, home controller is the central intelligence type, which bundles a processor, timer, and various inputs together into one package. Connecting to other pieces of equipment in a star pattern, a typical installation has one controller regulating all of the devices in the home.

Distributed intelligence systems use many controllers rather than one. In effect, each device you want to control has its own controller attached or built in. Therefore, each sends control signals, receives control signals, and responds only in predetermined circumstances.

The controllers used in distributed intelligence systems are special microcomputers, usually contained on a single chip. These chips perform the same functions as the much larger central controllers, but on a smaller scale. They perform only the controlling functions pertaining to the device with which they are associated.

The most basic function of any controller is to listen and speak. Listening refers to the controller's ability to receive and interpret signals from sensors and control devices. Speaking refers to the controller's ability to send signals to the various items connected to it. All residential controllers perform the basic speak and listen functions, and almost all have a built-in timer.

Beyond the basic capabilities of controllers is their ability to perform logical functions. By far the most important of these is the if/then function. This type of logic allows the controller to make decisions based on certain conditions. For example, you could program this type of controller to follow commands, such as:

If the bedroom light turns on, and
if it is a weekday, and
if it's between 6:30 a.m. and 7:00 a.m.,
then turn on the coffee maker.

This capability allows controllers to perform more complex tasks than simply turning things on and off at preset times. This also requires the controller to do a much better job of listening, because it must know what devices are in use at all times.

While controllers have great capabilities, you must program them in advance to ensure proper execution of functions. They must also have a database containing designations of the devices you want to control (these are generally called addresses), communication information for sensors, and one or more interfaces with means of communications such as copper wire, radio signals, or others.

You generally program a controller using a PC. The simple controllers connect to the computer only when being programmed, and run independently thereafter. Others require connection to the computer at all times. You must program distributed intelligence control chips with a portable, handheld programming tool.

This process is not very difficult, although it can be a bit tedious, as the programmer must define a large number of addresses, inputs, outputs, and logical functions. Once complete, however, extensive programming should never again be necessary.

Communicating. Components of home automation systems communicate in five ways:

Electronic signals over electronic cables. Used in almost any configuration and frequency, these signals allow for almost any type of signal; even data transmission.

This arrangement uses dedicated copper wires run between the various pieces of equipment. This is usually in the form of an 8-wire telephone type cable. While having excellent transmission characteristics, the use of copper conductors (also called hard wiring) is more expensive and difficult to install than other methods. This is especially true in existing home installations. In such cases, running new cables through existing walls is cost prohibitive.

Electronic signals sent through power lines. A powerline carrier system performs communications functions less expensively than hard wiring, but not as effectively. This term implies a building's existing power lines carry the communications signals; providing the signal at all places on the power wiring system.

By sending control signals over the existing wires in a building, no new control wiring is necessary. This saves a great deal on material and labor costs. Instead of running multiple control wires from a special controller to all various controlled items, you just tie the controller and control devices into the power-wiring network. However, most of these systems are limited. They can send the proper signals to turn something on/off, or dim lights; nothing more. While this is good enough for most types of control installations, it's not enough for complex systems requiring data transmission.

These send a variety of 121 kHz signals into the power system. The controller assigns a code for each of the devices in the home to be controlled. Once the devices are set to this code, they will sense the 121 kHz signal, and respond when they recognize a signal for their code. Since the 121 kHz signal is only about 4V, no other equipment should have any reaction to it.

Radio waves. Rather than communicating over copper wires, some systems are set up with radio waves. These are typically termed RF systems. RF simply means radio frequency, which are electromagnetic waves generated at radio frequencies; operating at different frequencies, and usually at lower power levels than commercial radio.

Security systems commonly use wireless systems. These units generate frequencies and coding of radio signals and send instructions, which are decoded and acted upon only by encoded devices. Annual battery replacement and higher initial cost are drawbacks.

One practical advantage of RF signals is they can pass through walls and most other structures.

Infrared light. Some types of systems can communicate with coded pulses of infrared light. We commonly call these IR systems. IR stands for infrared. Like RF systems, these systems require devices that can transmit and receive the special signals. Unlike RF signals, however, infrared signals cannot pass through walls.

All television, videocassette recorders, and stereo remotes use IR light pulses to communicate with the appliances they control. The power levels of all these remotes are fairly low. The only significant difference between IR and RF systems is the frequency of the light pulses they emit.

Optical fiber. Optical fiber signal transmission is the finest communications medium available. Optical fiber is necessary when you must transmit large amounts of video.

Interfaces. When combining two or more communication methods, some method of cross-communications is necessary. We commonly call such devices interfaces. The simplest types of controllers communicate only via powerline carrier signals; thus, combining them with devices using other communication means requires a separate interface device operating as a go-between. The more advanced controllers frequently have one or more interfaces built in.

Some widely used interfaces are:

Burglar alarm interface. This device receives input from a security system and sends out a prearranged series of signals upon activation.

Universal modules. This device is a power relay that's turned on or off by a control signal. It operates as a maintained or momentary contact relay, and ties home control systems to many types of electrical and electronic devices.

Telephone responders. A telephone responder is an interface between the telephone system and home automation system. It receives phone calls, gives access to the automation system if a special code is entered, and can control between 12 and 256 different devices, depending on the brand.

Transceivers. The most common of these devices receive RF signals, decode and interpret them, and send the appropriate powerline carrier signals through the home's power lines. They plug directly into a wall outlet.

IR/RF links. These devices connect home automation systems with TVs, stereo devices, and VCRs. You can also use them to control such equipment from remote locations. For instance, even though a stereo system may be in the home's living room, this link allows you to control it from the bedroom. In this instance, an interface in the bedroom receives the IR signal from the remote, translates it into RF, and transmits the RF signal throughout the home. Another interface in the living room receives the RF signal, translates it back into IR, and transmits the IR signal to the stereo.

Sensors and actuators. If the controller is the brain of a home automation system, then the sensors and actuators are its eyes and muscles. Sensors pick up a stimuli, interpret or measure them, and relay the information to the controller. The many types of sensors include thermostats, electrical sensors, light sensors, humidity sensors, proximity sensors, magnetic sensors, and so on.

Actuators are devices that cause action. These are the parts of the system that make something happen. These include motors, valves, solenoids, or anything else that causes an action.

With few standards in the home automation industry, don't take compatibility for granted. Verify voltages, current levels, and signal protocols before connecting devices to controllers.

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