What is a Potentiometer

A potentiometer is a manually adjustable electrical resistor that uses three terminals. In many electrical devices, potentiometers are what establish the levels of output. For example, in a loudspeaker, a potentiometer is used to adjust the volume. In a television set, computer monitor or light dimmer, it can be used to control the brightness of the screen or light bulb.

How It Works

Potentiometers, sometimes called pots, are relatively simple devices. One terminal of the potentiometer is connected to a power source, and another is hooked up to a ground — a point with no voltage or resistance and which serves as a neutral reference point. The third terminal slides across a strip of resistive material. This resistive strip generally has a low resistance at one end, and its resistance gradually increases to a maximum resistance at the other end. The third terminal serves as the connection between the power source and ground, and it usually is operated by the user through the use of a knob or lever.

The user can adjust the position of the third terminal along the resistive strip to manually increase or decrease resistance. The amount of resistance determines how much current flows through a circuit. When used to regulate current, the potentiometer is limited by the maximum resistivity of the strip.

Controlling Voltage

Potentiometers also can be used to control the potential difference, or voltage, across circuits. The setup involved in utilizing a potentiometer for this purpose is a little more complicated. It involves two circuits, with the first circuit consisting of a cell and a resistor. At one end, the cell is connected in series to the second circuit, and at the other end, it is connected to a potentiometer in parallel with the second circuit.

The potentiometer in this arrangement drops the voltage by an amount equal to the ratio between the resistance allowed by the position of the third terminal and the highest possible resistivity of the strip. In other words, if the knob controlling the resistance is positioned at the exact halfway point on the resistive strip, then the output voltage will drop by exactly 50 percent, no matter what the input voltage is. Unlike with electrical current regulation, voltage regulation is not limited by the maximum resistivity of the strip.

Rheostats

When only two of the three terminals are used, the potentiometer acts as a type of variable resistor called a rheostat. One end terminal is used, along with the sliding terminal. Rheostats typically are used to handle higher levels of current or higher voltage than potentiometers. For example, rheostats might be used to control motors in industrial machinery.

What Should I Do if I Drop My Cell Phone in Water

If you drop your cell phone in water, it is often possible to salvage it. Time is of the essence, however, so the first thing to do is to get your cell phone out of the water as soon as possible. Leaving a cell phone in water for even a few seconds might damage it beyond repair, but there are a few things that you can try and that sometimes work. The main things are opening the phone as much as possible, taking out the battery and completely drying off all of the components.

Remove the Battery

After retrieving your cell phone from the water, the next thing to do is to remove the battery immediately, without even hesitating to turn off the power. This reduces the risk of a short circuit that would render your phone useless. Dry the battery with a towel, and it set aside to dry thoroughly. The battery itself might not work again, but it can be replaced fairly inexpensively. Even if the battery does work, it is a good idea to get a new one to avoid the risk of having the old one leak battery acid.

Take It Apart

After you have removed the battery, dry off the cell phone with an absorbent towel as best as you can. Use cotton swabs to soak up water in crevices and on any fragile, exposed circuits. If you have dropped your cell phone in water, it also is helpful to disassemble it, if you can, and let all of the parts dry separately. Just be sure that you know how to put it back together. If it is a flip or sliding cell phone, leave it open to allow for maximum evaporation.

Avoid Mineral Damage

If you drop your cell phone in water that isn't pure or another liquid, such as a beverage or in salt water, rinse off the phone with fresh water after you have removed the battery. After you drop your cell phone in water, a quick rinsing is unlikely to do any further damage, but salt, sugar or other materials might. You also could try giving your phone an alcohol bath. The alcohol will displace minerals and microscopic substances and will aid in the evaporation of the fluid. If it is available, you should use an alcohol concentration of 95 percent rather than rubbing alcohol, which usually has a concentration of 70 percent.

Let It Dry

After your phone is clean, leave it in a warm, dry area or near an air conditioner for at least three days before you attempt to replace the battery and turn it on. This is very important, because although you may think that you have thoroughly dried it, the slightest moisture can react with the battery and cause it to short circuit. Putting your cell phone in a container full of dry rice grains also can help dry it out. Make sure that the rice completely covers the phone.

Warranty Likely Voided

Unless you have insurance for your cell phone and it covers water damage, there probably is no point in sending it to the manufacturer with the hope that the warranty will cover the cost of a replacement. If you drop your cell phone in water, the warranty probably will be voided. The manufacturer's technicians will be able to tell immediately that it has been dropped in water because of the moisture-sensitive stickers that are placed inside almost all cell phones. The best thing to do is to dry it out yourself and hope that it still works.

Do Batteries Really Last Longer if They Are Stored in the Refrigerator

Some household batteries may last slightly longer if stored in the refrigerator or freezer. Even when not being used, the internal components slowly corrode over time; cool temperatures can slow down this process. The type of battery and how it is stored will greatly affect whether refrigeration is an efficient means of extending its shelf life, however. Rechargeable varieties get more benefit from the cooler temperatures than alkalines do. All types of batteries must be protected from moisture in the refrigerator, so they should be kept in a sealed container.

Refrigerating Alkaline Models

Since most manufacturers recommend storing batteries in a cool, dry location to last as long as possible, it may seem logical to keep alkaline models in the refrigerator. Most refrigerators maintain an average temperature of 40° Fahrenheit (approximately 10° Celsius) or lower, and the atmosphere inside is very low in humidity. This seems like an ideal storage environment, as the lower temperature reduces the power drain on the electrolyte fluid inside the battery, which acts as a medium for the flow of the electrical current. According to the results of several tests, storage at very cold temperatures will increase the shelf life, but only by a small amount. Alkaline models stored in a refrigerator can retain 93% of their power after five years, compared to 90% for non-refrigerated models stored in other cool, dry areas.

The downsides of refrigeration for alkaline varieties may outweigh the minor extension in their shelf life. Although a refrigerator has low humidity, batteries that are not sealed in an air-tight container may be subject to contact with moisture from other items in the refrigerator, which can destroy the electrical circuit. Extremely cold temperatures can also corrode the contact points on either end of the battery, rendering them unusable. One of the biggest downsides is that the batteries must be returned to room temperature before they can be used, so they cannot simply be taken out of cold storage and put immediately into electronics.

Refrigerating Rechargeable Models

Rechargeable varieties, such as nickel-metal hydride (NiMh), can benefit greatly from cold storage when cared for properly. While rechargeable models offer many advantages over alkaline varieties, they suffer from a fairly short charge life, and may need to be charged every few days when stored at room temperature. Carefully stored in the refrigerator, a rechargeable battery can hold at a 90% charge for months at a time.

For best results, rechargeable batteries need to be kept in a sealed freezer bag inside an airtight container to reduce the risk of moisture damage or condensation. Any moisture can cause corrosion inside of the battery, making it unusable. Like alkaline models, rechargeables will need to be thawed before they can be used.

Other Ways to Extend Shelf Life

People who are concerned about getting the most use out of their batteries should consider investing in rechargeable models, which can be used dozens of times without replacing. This not only cuts down on the cost of supplies over time, but is also more environmentally friendly. Recharging the batteries before they are completely depleted can also extend their lifespan, as draining a battery fully usually causes it to wear down more quickly.

It is also best to use the right type of battery for specific electronics. Some devices, such as digital cameras, use up a lot of power quickly, and eat up regular alkaline varieties in just a few hours. Some batteries are built to withstand the increased power needs of high-drain electronics, so they should be used to reduce costs.

Batteries should be removed from electronic devices when they are not in use to extend their life. Most electronics draw small amounts of power even when they are turned off, sometimes called "vampire power" or "phantom load." These electronics will drain batteries over time. For rarely used devices, removing the batteries can cut down on energy costs.

Rather than worrying too much about refrigeration, most users get more benefit from finding a cool location with low humidity to store their batteries. While cold storage may extend the shelf life slightly, exposure to heat and humidity will cause a much more rapid decline. Some experts recommend avoiding storing batteries in the kitchen, since using the stove can cause frequent and rapid temperature jumps. Cool closets that do not receive much light are often excellent storage locations.

What Is HDMI®

HDMI® (High-Definition Multimedia Interface) is an interface standard used for audiovisual equipment such as high-definition television and home theater systems. With 19 wires wrapped in a single cable that resembles a USB wire, HDMI® is able to carry a bandwidth of 5 Gbps (gigabits per second). This is more than twice the bandwidth needed to transmit multi-channel audio and video, future-proofing HDMI® for some time to come. This and several other factors make HDMI® much more desirable than its predecessors, component video, S-Video and composite video. 

HDMI® is an uncompressed, all-digital signal, while the aforementioned interfaces are all analog. With an analog interface, a clean digital source is translated into less precise analog, sent to the television, then converted back to a digital signal to display on screen. At each translation, the digital signal loses integrity, resulting in some distortion of picture quality. HDMI® preserves the source signal, eliminating analog conversion to deliver the sharpest, richest picture possible. 

Previous video interfaces required separate audio cables, with the vast majority of people using standard RCA L/R analog audio jacks. HDMI®, with its abundant bandwidth and speed, carries not only video but also up to eight digital audio channels for uncompromised surround-sound. It replaces the tangle of wires behind the system with a single cable, greatly simplifying the entire setup process of the home theater system while delivering top tier performance. 

Though standard HDMI® or "Type A" has 19 wires, "Type B" will have 29 wires. The latter is targeted for the motion picture industry and other professional applications. Both varieties are "Intelligent HDMI®," referring to the built-in capability for HDMI®-enabled components to talk to each other via the interface. Auxiliary information can provide all-in-one remote functionality and other interoperable features not possible in previous interface technologies.

HDMI® supports standard video formats, enhanced video and high-definition. It is also backwards compatible with DVI (Digital Video Interface). High-end graphics cards featuring a DVI port can connect to a HDMI® interface via a DVI/HDMI® cable. This is simply a cable with a DVI connector on one end and a HDMI® connector on the other. As a rule, HDMI® cables should not run longer than 15 feet (5 meters), or degradation of the signal could occur.

As of 2005, many high-end television sets were sold with at least one HDMI® interface. Some experts advise that two HDMI® interfaces will provide more flexibility, and for those who want to connect a game console, three might serve better. Multiple interfaces will become common on digital TVs as the industry incorporates HDMI® interfaces into more peripheral components.

What Are Transducers

Transducers are electric or electronic devices that transform energy from one manifestation into another. Most people, when they think of transducers, think specifically of devices that perform this transformation to gather or transfer information. In reality, however, anything that converts energy can be considered a transducer.

Found Throughout Everyday Life

Common transducers that detect or transmit information include microphones, Geiger meters, pressure sensors, thermometers and antennae. A microphone, for example, converts sound waves that strike its diaphragm into an analogous electrical signal that can be transmitted over wires. A pressure sensor turns the physical force being exerted on the sensing apparatus into an analog reading that can be easily represented. Many people think of a transducer as being some sort of technical device, but they can be found in many places throughout everyday life.

Most transducers have an inverse that allows for the energy to be returned to its original form. Audio cassettes, for example, are created by using a transducer to turn the electrical signal from the microphone pick-up — which went through a transducer to convert the sound waves into an electrical signal — into magnetic fluctuations on the tape head. These magnetic fluctuations are then read and converted by another transducer — in this case, the stereo system — to be turned back into an electrical signal. This signal is then fed by wire to speakers that act as yet another transducer to turn the electrical signal back into audio waves. 

Other transducers turn one type of energy into another form, not to measure something in the external environment or to communicate information, but rather to make use of that energy in a more productive manner. A light bulb, for example, converts electrical energy into visible light. Electric motors are another common form of electromechanical transducer, converting electrical energy into kinetic energy to perform a mechanical task. The inverse of an electric motor — a generator — also is a transducer, turning kinetic energy into electrical energy that can then be used by other devices.

Efficiency

As in all energy conversions, some energy is lost when transducers operate. The efficiency of a transducer is found by comparing the total energy put into it to the total energy coming out of the system. Some transducers are very efficient, and others are extraordinarily inefficient. 

A radio antenna is one example of an efficient transducer. The antenna acts as a transducer to turn radio frequency power into an electromagnetic field. When the antenna is operating well, this process can be more than 80 percent efficient. Most electrical motors, by contrast, are less than 50 percent efficient. A common light bulb, because of the amount of energy that is lost as heat, is less than 10 percent efficient.

What is a DVD-ROM

A Digital Versatile Disc — Read Only Memory, or DVD-ROM, is a media storage disk that closely resembles a CD or compact disk. The major difference is that the DVD-ROM is formatted to hold far more data. A CD commonly has a capacity of 650 megabytes, while the smallest capacity DVD can store about seven times more data, or 4.38 gigabytes (GB). 

There are various kinds of DVDs, but the DVD-ROM refers to a read-only disc, or a disc that cannot be written over. If you purchase a DVD movie from the local video store, you have a good example of a DVD-ROM. Blank DVDs with designations like "DVD-R" and "DVD+R" are formatted, recordable DVDs. The —R and +R refer to competing format standards, but both will record movies, audio or other data.

A DVD-ROM encodes data in the form of a spiraling trail of pits and lands separated by mere nanometers. The trail starts at the center of the DVD-ROM and winds around countless times until it reaches the outer edge. In the case of a double layer disk, the trail continues on a second layer of material. If the disc is also double-sided, the trail of pits and lands extends to side two. 

A laser beam in the DVD player tracks the beam as the disc spins, while a special device reads the intensity of the reflection as it bounces off the pits and lands. The reflective variance gets translated to bits of data which form bytes. Hence, DVDs, including the DVD-ROM, can vary in capacity as follows:

1. Single-sided single-layer disc — 4.38 GB
2. Single-sided double-layer disc — 7.95 GB
3. Double-sided single-layer disc — 8.75 GB
4. Double-sided double-layer disc — 15.9 GB

The DVD-ROM has replaced the videocassette, being far more efficient and superior in all respects. For one, a DVD-ROM stores data in digital form, while the videocassette uses less precise analog technology. A DVD-ROM, under normal conditions, remains error free and consistent, regardless of the amount of times it is viewed, while a video cassette stretches with wear and eventually needs replacement. The DVD-ROM can also hold more information in a higher format, and one can skip to specific scenes without the need for fast-forwarding or rewinding. Finally, the DVD-ROM is much more compact and easier to store, and DVD players can double as CD players.

If purchasing a DVD player, be sure to get one that can play all DVD-ROM formats, including double-sided, double-layered discs. For home theater systems look for models equipped with a 192 kilohertz (kHz), 24-bit digital/analog converter (DAC) for true Dolby theater quality. By comparison, standard DVD players use 96 kHz, 24-bit DACs. This is still a big improvement over CDs, however, which use 44.1 kHz, 16-bit sampling to produce audio. For this reason, people are moving towards DVDs to store music. An audio DVD can hold just over an hour of multi-channel music at 192 kHz, the highest bit rate; about two hours at 96 kHz; and close to seven hours at the standard CD sampling rate of 44.1 kHz. 

While cassettes, videocassettes and laser diskc have become legacy technologies, the DVD-ROM appears to be here to stay. Recordable DVDs are available wherever music and movies are sold, including department stores, office supply chains and discount marts.

What Is CDMA

CDMA stands for Code Division Multiple Access. It is a technique used for digital communication, and wireless technology in particular, that involves multiplexing. Whereas conventional communication systems use constant frequencies, CDMA uses multiple access, or multiplexing. Accomplished through the specific type known as spread spectrum in this case, multiplexing uses varied frequencies to transmit audio signals. This, coupled with code division, which requires a certain code to send and receive the frequency, further protects CDMA communications from interference.

Radio systems, one of the earliest forms of telecommunication, required users to communicate on distinct frequencies. Frequency Division Multiple Access (FDMA), one form of early wireless communication, only allowed users to operate on a single frequency. When tuning in to a radio to get sound, for instance, the listener must select one frequency or another, and must tune the frequency to filter out noise in the spectrum. Another form of early radio communication was Time Division Multiple Access (TDMA). In this case, users could not share a frequency, and each user had to coordinate his or her turn on that frequency in order to communicate.

Both FDMA and TDMA posed restrictions for early users, particularly the military. As early as World War II, militaries recognized the high value in using wireless technology to communicate across vast distances. Military communication units did not always have the time to wait their turn to transmit sound, or to find the right frequency. 

Some telecommunication systems allowed military communication units to transmit sound into the same spectrum their adversaries used. Military signals needed a unique identification through a distinct code to avoid interference from enemy communication. The receiver of that message on the other end could then retrieve the message based on its unique code in the spectrum. 

Just as the radio moved from military use to commercial use, so too was the case with the wireless technology. CDMA became the early choice for personal communication because it could allow multiple users to communicate within the spectrum, avoiding interference or blocking among users. In 1999, CDMA became the standard technology for the telecommunications industry for its growing wireless systems. Since there are large numbers of users in the system communicating at the same time, code division ensures that each user’s signal remains separate in the spectrum.