What Is a USB Dongle

The Universal Serial Bus (USB) port is a small connector that allows a data cable to be attached so that, for example, pictures can be passed from a digital camera to a computer. On desktops, laptops, printers and other hardware, the USB port also allows for expanded functionality. Many hardware devices smaller than a pack of gum are made with one end designed to slip into the USB port. These devices are called USB dongles and can add features to the computer or machine that were not built in by the manufacturer.

A storage or memory USB dongle, also called a memory stick, provides a convenient means to pass files between computers or devices. The memory stick contains a rewritable solid-state memory chip that does not require power to retain its contents. As capacities have grown and price has dropped, these portable, plug-and-play storage drives have replaced floppy disks and even compact disks for exchanging files and archiving data.

Another type of USB dongle can add WiFi® functionality to a computer to provide wireless Internet connectivity. Most desktop computers can accommodate internal WiFi cards, but laptops and notebooks rely on external gadgets to increase features. The USB WiFi dongle comes in many models with the most basic model working with operating system software to locate nearby wireless networks in order to share access, commonly within the home or office.

A WiFi finder or scanner also comes in the form of a USB dongle, allowing a person to scan for free public hotspots while mobile. This type of USB dongle features LEDs that light without having to boot the laptop, indicating a wireless network has been detected. A series of LEDs can indicate signal strength, allowing one to glance at the dongle to see instantly if accessibility is increasing or decreasing. Different colored LEDs might also specify encrypted or unencrypted networks.

If you require Bluetooth® a personal area network (PAN) used to wirelessly connect your digital devices to each other — consider a USB Bluetooth® dongle. Bluetooth® has become increasingly useful for passing data between cell phones and computers, for syncing personal digital assistants (PDAs) to laptops, and for sharing files between laptops and desktops, to name just a few benefits of the technology. The advantage of Bluetooth® over other types of networking is that it is easy to activate and use with virtually no networking experience required, and it eliminates the need to haul various cables around. 

If you spend a lot of time on a laptop, you might want to make your printer and laptop Bluetooth®-enabled. By doing so you can wirelessly link the two machines in a few seconds to send print jobs to the printer without having to move the laptop to the printer and attach a cable. Newer printers feature a USB port that can be used with a Bluetooth® USB dongle, but other types of Bluetooth® adapters are also available if a USB port is not present.

Company employees might be familiar with the proprietary USB dongle that acts as a security token to authenticate software in order to protect it from use by unauthorized persons. This type of dongle might also verify credentials or supply a password to a Virtual Private Network (VPN) for field personnel, for example, operating on a secured system. Without the USB security dongle and proper credentials, a person cannot log into the network or access the software under its protection.

What are SDHC Cards

SDHC (Secure Digital High-Capacity) cards are flash memory cards with a minimum capacity of 4GB (gigabytes). SDHC cards provide removable memory for compatible digital devices including cameras, camcorders, PDAs, MP3 players and more. Secure Digital refers to a specific format within the flash card market. SDHC cards are designed for devices that are compatible with the SDHC 2.00 specification. Products designed exclusively to support previous SD specifications 1.0 and 1.1 will not be able to utilize SDHC cards.

The growing demand for high-capacity flash memory springs partially from the increasing use of high-definition video and high-resolution digital photography. SDHC cards meet the challenge of these demanding products not only by providing ample storage but also by introducing a new feature: classifications of data transfer speed (DTS). Consumers can get the best performance value out of their digital products by using flash memory cards that support the device's highest standards for data transfer speed. The SDHC specification 2.00 calls for cards to be classified according to the minimal sustained DTS as follows:

1. Class 2: minimum sustained DTS of 2MB/sec
2. Class 4: minimum sustained DTS of 4MB/sec
3. Class 6: minimum sustained DTS of 6MB/sec

SDHC cards are classified to guarantee a specific sustained DTS. This potentially saves consumers money, as flash cards are priced not only according to capacity, but also to speed. For example, if a product's maximum DTS is 2MB/sec, dishing out extra cash for Class 4 or Class 6 SDHC cards would be a waste of money. Conversely, devices that can utilize the 4MB/sec or 6MB/sec DTR will perform significantly better with Class 4 or Class 6 SDHC cards, respectively.

Secure Digital was forced to create a new specification for SDHC cards when the previous specification topped out at a capacity of 2GB. This occurred previously when SD cards hit the 512MB wall. The new 2.00 specification should last a bit longer, as it allows SDHC cards to reach a maximum capacity of 32GB. Secure Digital is so-named because of its ability to protect copyright content through digital rights management or DRM. Because of this, it is a favored flash memory format in the audiovisual industry. 

SDHC cards are about the size of a postage stamp. Insiders expect them to be available through several different manufacturers by summer 2006, and prices will vary. Before purchasing, be sure your device is compatible. There are several card formats available on the market, and devices are proprietary. If a device manual does not list SDHC cards, or state it is "SD specification 2.00 compatible," the device cannot utilize these cards.

What is a Wireless TV Router

A wireless TV router is a device that allows a television signal to be broadcast to other areas of the home without cables. This will allow viewing in a number of different ways, depending on the type of home equipment. For example, the wireless TV router could send a signal to a computer or a video projector for use on a large screen.

The technology behind wireless TV routers is still in the process of being fully developed. However, Apple has announced its intentions to manufacture a product known as iTV. This is essentially a wireless TV router that will allow users to download movies from a system, such as iTunes™ and then play those movies on a standard or high-definition television set. While this can be done now, it requires connecting a computer by wires to the TV set.

Another technology in development is known as WHDI, or wireless home digital interface. A number of companies are responsible for developing this technology. They include: Sony, AMIMON, Hitachi, Motorola, Samsung and Sharp. Together, these companies are setting a standard for a new type of wireless TV router that will cater specifically to high-definition applications.

The demand for a fully functional wireless TV router is growing. With TVs becoming flatter and lighter, the locations where they can be placed continues to expand. However, unsightly wires make some locations impractical, or unattractive, without a great deal of additional work, such as running wires behind walls.

Further, with more TVs in more rooms of the home, it may take a lot of extra cable to fully outfit each set. With a wireless TV router, the hardware setup would become as simple as plugging the router in and making sure each television was connected. However, before this happens, there are still some obstacles to overcome.

As with any new technology, standardization will be a big key in order to get such products on the market in an affordable and acceptable form. For those waiting for such technology, it should be encouraging that WHDI has so many industry leaders working on a product together. This helps with standardization.

Another obstacle will be existing televisions, which are not outfitted to receive wireless signals such as the kind that will be utilized by a wireless TV router. In order to take advantage of such technology, users will either have to replace television sets with sets that can receive those signals, or buy an adapter for existing televisions. So even after buying the wireless TV router, there is likely to be some additional expense.

What Is the Difference Between Mbps and MBps

MBps is an abbreviation for Megabytes per second, whereas Mbps is an abbreviation for megabits per second. Eight megabits equal one Megabyte. These abbreviations are commonly used to specify how much data can be transferred per second between two points. In some cases, mbps is used as an abbreviation for megabits per second; however, the lowercase m technically means "milli" not "mega," so it doesn't really mean the same thing.

To put megabits and Megabytes in perspective, let's back up for just a moment. One bit of data is a single "on" or "off" digit, a one or zero. It takes eight bits to represent a single character, or one byte of data.

1. 8 bits = 1 byte
2. 1000 bytes = 8 kilobits (kb) = 1 Kilobyte (KB)
3. 1000 Kilobytes (KB) = 8 megabits (Mb) = 1 Megabyte (MB)

As a point of possible confusion it should be mentioned that there are two different systems for calculating multiples of data: the decimal system as noted above, and the binary system. 

According to the binary system, used in relation to computer storage and memory, it takes not 1000 bytes to equal a KB, but 1024 bytes. This is because the binary system is base 2, and 2¹⁰ = 1024. Technically, the designations in this case are Kibibyte (KiB) and Mebibyte (MiB), but these haven't caught on in the public sector, leading many uses of "MB" to mean 1024 kilobytes, and others to mean 1000 kilobytes. When considering MBps, however, the decimal system applies, as the reference is to data transfer rates and not data storage.

Data transfer rates are quite handy for gauging performance levels of various hardware devices. Everything from USB and Firewire® ports to memory card readers and mobile devices are associated with corresponding transfer rates, often measured in megabits or Megabytes per second. 

We must also translate speed to value when considering Internet service plans, advertised by download and upload speeds expressed in kilobits per second (kbps) or megabits per second. For example, a typical Digital Subscriber Line (DSL) plan might have an upper transfer limit of 1,500 kbps, which can also be expressed as 1.5 Mbps. A cable plan might be advertised with speeds up to 5,000 kbps or 5 Mbps; and fiber optic Internet can reach speeds of 50 Mbps or more. 

The wireless G network (802.11g) has a maximum transfer rate of 54 Mbps, making it much faster than all but the fastest fiber optic Internet plans. Thankfully, going wireless won’t slow your surfing. The more current wireless N standard (802.11n) can’t speed up your Internet connection, but will allow faster data transfer rates between local networked computers of up to 100 Mbps, or about twice the data transfer rate of G networks.

As if the abbreviations aren't close enough to cause confusion, it doesn’t help that they are often expressed in the wrong case. When in doubt look for translations such as the kilobit or Kilobyte equivalent, or simply ask someone if the specification is indeed megabits per second or Megabytes per second.

What Are Omnidirectional Microphones

Omnidirectional microphones can pick up sound from virtually any direction. This design can be useful when a device needs to pick up ambient sound or is used in an environment where sound sources are moving and it is not practical to move the microphone along with them. It does have some drawbacks, however, including muddy sound quality in some cases.

Microphone Design

The distinctive rounded end is a well-known characteristic of an omnidirectional microphone. The look is created by the bulging mesh installed over the electronic pick-up, which protects the internal electronics and can limit interference like breath noises and pops. Some omnidirectional microphones take this mesh covering one step further, with a cover made from foam used as a protective sleeve over the head of the device. The foam does not prevent sound from entering the mic, and also acts as a shield against wind and explosive breath sounds. The extreme sensitivity of omnidirectional microphones requires meticulous design to keep sound as crisp and clear as possible.

Wireless omnidirectional microphones that transmit signals without the use of a cable are also available. Small wireless mics called lavaliers are usually clipped to the speaker's lapel or blouse and fed to either a concealed wireless transmitter or a channel on an audio mixing board. Omnidirectional lavalier microphones also have the distinctive round shape of their larger counterparts.

Uses

The most common uses of an omnidirectional microphone involve groups of singers or instrumentalists. A microphone can be suspended from the ceiling above a choral group or positioned between a vocalist and an accompanying piano or guitar. Solo performers can hold an omnidirectional microphone in various positions and still be amplified.

This equipment can also be useful for meetings and events where there may be multiple speakers but a single microphone, or where it is important to capture sound from several angles. As different speakers add to the conversation or change position, the microphone will still be able to pick up their voices. The alternative is tracking individual speakers with unidirectional mics, which can be time-consuming and expensive, especially for small organizations that don’t have a large budget for sound equipment.

Potential Advantages

Omnidirectional microphones can be very easy to set up and use, even by inexperienced people who may not have used one before. As a result, someone with little or no experience can usually manage the set up, helping to reduce expenses for an event. This can be helpful at events where attendees may need to use a microphone to speak, like town hall meetings and wedding parties.

The broad pickup abilities of an omnidirectional microphone also make it very usable in environments where wide coverage is needed or where the precise origins of sounds may not yet be known. For example, someone recording wildlife might use an omnidirectional microphone to pick up general sounds and background noises because he or she cannot predict how the subjects might move.

Low-cost options with relatively high quality are also available. This can be useful for organizations concerned about budget, or people starting to learn about sound systems who are not able to invest in expensive specialized equipment. An omnidirectional microphone can be used in a variety of applications, while a more focused unidirectional device is less flexible.

Potential Disadvantages

Ideally, an omnidirectional mic would pick up sound in a perfect circle around its center. The laws of physics make this somewhat challenging, however, and in real-world use, this type of microphone cannot pick up sound perfectly from every direction. It can also cut out some high and low frequencies, and sound coming from an extreme angle may not be reliably detected.

The inability to discriminate between wanted and unwanted sounds means that ambient noise can be picked up and amplified. Some performers may want the sounds of an enthusiastic audience to be included in the session, for instance, but others may want these noises blocked out. A unidirectional microphone may be better at keeping background noise out of the recording and amplifying equation.

Another risk with omnidirectional microphones involves the triangle between the microphone, the performer, and the speakers. If an omnidirectional microphone is placed too close to the speakers, it will pick up extraneous noise. This noise is then fed back into the system through the microphone and amplified again. The result is a very unpleasant phenomenon called a feedback loop. Great care must be taken to avoid putting an omnidirectional microphone directly in front of the speakers.

Unidirectional Microphones

The design of an omnidirectional microphone contrasts with unidirectional microphones, which only pick up sound from a more targeted source. There are several different types of unidirectional mics, each classified by its polar pattern or directionality — the shape created when the sound pickup is mapped on a flat plane. Some options can include a shotgun microphone, which is a highly directional device intended for pointing at a specific point source of sound; and a cardioid, which is named for the heart-like shape of its polar pattern. While multiple unidirectional microphones can offer better sound quality in some cases by capturing specific sources with less background noise, they can be expensive and more difficult to set up correctly.

What is a Multiplexer

A multiplexer, sometimes referred to as a multiplexor or simply a mux, is an electronic device that selects from several input signals and transmits one or more output signals. In its simplest form, a multiplexer will have two signal inputs, one control input and one output. One example of an analog multiplexer is the source control on a home stereo unit that allows the user to choose between the audio from a compact disc (CD) player, digital versatile disc (DVD) player and cable television line, for example.

Multiplexers also are used in building digital semiconductors such as central processing units (CPUs) and graphics controllers. In these applications, the number of inputs is generally a multiple of two, the number of outputs is either one or relatively small multiple of two, and the number of control signals is related to the combined number of inputs and outputs. For example, a two-input, one-output multiplexer requires only one control signal to select the input, and a 16-input, four-output multiplexer requires four control signals to select the input and two to select the output.

Types of multiplexers also are used in communications. A telephone network is an example of a very large virtual multiplexer that is built from many smaller, discrete ones. Instead of having a direct connection from every telephone to every other telephone — which would be physically impossible — the network muxes individual telephone lines onto a small number of wires as calls are placed. At the receiving end, a demultiplexer, or demux, chooses the correct destination from the many possible destinations by applying the same principle in reverse.

There are more complex forms of multiplexers. Time-division multiplexers, for example, have the same input/output characteristics as other multiplexers, but instead of having control signals, they alternate between all possible inputs at precise time intervals. By taking turns in this manner, many inputs can share one output. This technique is commonly used on long-distance phone lines, allowing many individual phone calls to be spliced together without affecting the speed or quality of any individual call. Time-division multiplexers generally are built as semiconductor devices, or chips, but they also can be built as optical devices for fiber optic applications.

Even more complex are code-division multiplexers. Using mathematical techniques developed during World War II for cryptographic purposes, they have since found application in modern code division multiple access (CDMA) cellular networks. These semiconductor devices work by assigning each input a unique complex mathematical code. Each input applies its code to the signal that it receives, and all signals are simultaneously sent to the output. At the receiving end, a demux performs the inverse mathematical operation to extract the original signals.

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.