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Digital Multimeter

multimeter is a combination of a multirange DC voltmeter, multirange AC voltmeter,

multirange ammeter, and multirange ohmmeter. An un-amplified analog multimeter

combines a meter movement, range resistors and switches.

For an analog meter movement, DC voltage is measured with a series resistor connected

between the meter movement and the circuit under test. A set of switches allows greater

resistance to be inserted for higher voltage ranges. The product of the basic full-scale

deflection current of the movement, and the sum of the series resistance and the movement's

own resistance, gives the full-scale voltage of the range. As an example, a meter movement

that required 1 milliampere for full scale deflection, with an internal resistance of 500 ohms,

would, on a 10-volt range of the multimeter, have 9,500 ohms of series resistance.

[3]

For analog current ranges, low-resistance shunts are connected in parallel with the meter

movement to divert most of the current around the coil. Again for the case of a hypothetical 1

mA, 500 ohm movement on a 1 Ampere range, the shunt resistance would be just over 0.5

ohms.

Moving coil instruments respond only to the average value of the current through them. To

measure alternating current, arectifierdiode is inserted in the circuit so that the average value

of current is non-zero. Since the average value and the root-mean-square value of a waveform

need not be the same, simple rectifier-type circuits may only be accurate for sinusoidal

waveforms. Other wave shapes require a different calibration factor to relate RMS andaverage value. Since practical rectifiers have non-zero voltage drop, accuracy and sensitivity

is poor at low values.

To measure resistance, a small battery within the instrument passes a current through the

device under test and the meter coil. Since the current available depends on the state of

charge of the battery, a multimeter usually has an adjustment for the ohms scale to zero it. In

the usual circuit found in analog multimeters, the meter deflection is inversely proportional to

the resistance; so full-scale is 0 ohms, and high resistance corresponds to smaller deflections.

The ohms scale is compressed, so resolution is better at lower resistance values.

Amplified instruments simplify the design of the series and shunt resistor networks. Theinternal resistance of the coil is decoupled from the selection of the series and shunt range
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resistors; the series network becomes avoltage divider. Where AC measurements are

required, the rectifier can be placed after the amplifier stage, improving precision at low

range.

Digital instruments, which necessarily incorporate amplifiers, use the same principles as

analog instruments for range resistors. For resistance measurements, usually a small constantcurrent is passed through the device under test and the digital multimeter reads the resultant

voltage drop; this eliminates the scale compression found in analog meters, but requires a

source of significant current. An autoranging digital multimeter can automatically adjust the

scaling network so that the measurement uses the full precision of the A/D converter.

In all types of multimeters, the quality of the switching elements is critical to stable and

accurate measurements. Stability of the resistors is a limiting factor in the long-term accuracy

and precision of the instrument.

Quantities measuredContemporary multimeters can measure many quantities. The common ones are:

Voltage,alternatinganddirect, involts. Current, alternating and direct, inamperes.

Thefrequencyrange for which AC measurements are accurate must be specified.

Resistanceinohms.Additionally, some multimeters measure:

Capacitanceinfarads. Conductanceinsiemens. Decibels. Duty cycleas apercentage. Frequencyinhertz. Inductanceinhenrys. Temperaturein degreesCelsiusorFahrenheit, with an appropriate temperaturetest

probe, often athermocouple.

Digital multimeters may also include circuits for:

Continuity tester; sounds when a circuit conducts Diodes(measuring forward drop of diode junctions), andtransistors(measuring

current gainand otherparameters)

Battery checking for simple 1.5 volt and 9 volt batteries. This is a current loadedvoltage scale which simulates in-use voltage measurement.

Varioussensorscan be attached to multimeters to take measurements such as:

Light level Acidity/Alkalinity(pH) Wind speed Relative humidity
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Analog

Display face of an analog multimeter

Resolution of analog multimeters is limited by the width of thescale pointer, parallax,

vibration of the pointer, the accuracy of printing of scales, zero calibration, number of ranges,and errors due to non-horizontal use of the mechanical display. Accuracy of readings

obtained is also often compromised by miscounting division markings, errors in mental

arithmetic,parallaxobservation errors, and less than perfect eyesight. Mirrored scales and

larger meter movements are used to improve resolution; two and a half to three digits

equivalent resolution is usual (and is usually adequate for the limited precision needed for

most measurements).

Resistance measurements, in particular, are of low precision due to the typical resistance

measurement circuit which compresses the scale heavily at the higher resistance values.

Inexpensive analog meters may have only a single resistance scale, seriously restricting the

range of precise measurements. Typically an analog meter will have a panel adjustment to set

the zero-ohms calibration of the meter, to compensate for the varying voltage of the meter

battery.
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Resistor

From Wikipedia, the free encyclopedia

Jump to:navigation,search

Resistor

A typical axial-lead resistor

Axial-lead resistors on tape. The tape is removed during assembly before the leads are formed and

the part is inserted into the board. In automated assembly the leads are cut and formed.

A resistor is apassivetwo-terminalelectrical componentthat implementselectrical

resistanceas a circuit element.

Thecurrentthrough a resistor is indirect proportionto thevoltageacross the resistor'sterminals. This relationship is represented byOhm's law:

whereIis the current through theconductorin units ofamperes,Vis the potential differencemeasured across the conductor in units ofvolts, andR is the resistance of the conductor in

units ofohms.
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The ratio of the voltage applied across a resistor's terminals to the intensity of current in the

circuit is called its resistance, and this can be assumed to be a constant (independent of the

voltage) for ordinary resistors working within their ratings.

Resistors are common elements ofelectrical networksandelectronic circuitsand are

ubiquitous in electronic equipment. Practical resistors can be made of various compounds andfilms, as well asresistance wire(wire made of a high-resistivity alloy, such as nickel-

chrome). Resistors are also implemented withinintegrated circuits, particularly analog

devices, and can also be integrated intohybridandprinted circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial

resistors are manufactured over a range of more than nineorders of magnitude. When

specifying that resistance in an electronic design, the required precision of the resistance may

require attention to themanufacturing toleranceof the chosen resistor, according to its

specific application. Thetemperature coefficientof the resistance may also be of concern in

some precision applications. Practical resistors are also specified as having a maximum

powerrating which must exceed the anticipated power dissipation of that resistor in aparticular circuit: this is mainly of concern in power electronics applications. Resistors with

higher power ratings are physically larger and may requireheat sinks. In a high-voltage

circuit, attention must sometimes be paid to the rated maximum working voltage of the

resistor.

Practical resistors have a seriesinductanceand a small parallelcapacitance; these

specifications can be important in high-frequency applications. In alow-noise amplifieror

pre-amp, thenoisecharacteristics of a resistor may be an issue. The unwanted inductance,

excess noise, and temperature coefficient are mainly dependent on the technology used in

manufacturing the resistor. They are not normally specified individually for a particular

family of resistors manufactured using a particular technology.[1]A family of discrete

resistors is also characterized according to its form factor, that is, the size of the device and

the position of its leads (or terminals) which is relevant in the practical manufacturing of

circuits using them.
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Oscilloscope

From Wikipedia, the free encyclopedia


This article is about current oscilloscopes, providing general information. For history of oscilloscopes,seeOscilloscope history. For detailed information about various types of oscilloscopes, see

Oscilloscope types. For the film distributor, seeOscilloscope Laboratories.

Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. Numbers in the

picture indicate: 1. Deflection voltage electrode; 2. Electron gun; 3. Electron beam; 4. Focusing coil;

5. Phosphor-coated inner side of the screen

ATektronixmodel 475A portable analog oscilloscope, a very typical instrument of the late 1970s

An oscilloscope, previously called an oscillograph,[1][2]

and informally known as a scope,

CRO (for cathode-ray oscilloscope), or DSO (for the more modern digital storageoscilloscope), is a type ofelectronic test instrumentthat allows observation of constantly

varying signalvoltages, usually as a two-dimensional graph of one or more electrical

potential differencesusing the vertical ory-axis, plotted as a function of time (horizontal or

x-axis). Many signals can be converted to voltages and displayed this way. Signals are often

periodic and repeat constantly, so that multiple samples of a signal which is actually varying

with time are displayed as a steady picture. Many oscilloscopes (storage oscilloscopes) can

also capture non-repeating waveforms for a specified time, and show a steady display of the

captured segment.

Oscilloscopes are commonly used to observe the exactwave shapeof an electrical signal.

Oscilloscopes are usually calibrated so that voltage and time can be read as well as possibleby the eye. This allows the measurement of peak-to-peak voltage of a waveform, the
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frequency of periodic signals, the time between pulses, the time taken for a signal to rise to

full amplitude (rise time), and relative timing of several related signals.[3]

Oscilloscopes are used in the sciences, medicine, engineering, and telecommunications

industry. General-purpose instruments are used for maintenance of electronic equipment and

laboratory work. Special-purpose oscilloscopes may be used for such purposes as analyzingan automotive ignition system, or to display the waveform of the heartbeat as an

electrocardiogram. Some computer sound software allows the sound being listened to be

displayed on the screen as by an oscilloscope.

Before the advent ofdigital electronicsoscilloscopes usedcathode ray tubesas their display

element (hence were commonly referred to as CROs) and linear amplifiers for signal

processing. More advanced storage oscilloscopes used special storage CRTs to maintain a

steady display of a single brief signal. CROs were later largely superseded by digital storage

oscilloscopes (DSOs) withthin panel displays, fastanalog-to-digital convertersanddigital

signal processors. DSOs without integrated displays (sometimes known as digitisers) are

available at lower cost, and use a general-purposedigital computerto process and displaywaveforms.
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Features and uses

Basic oscilloscope

[edit] Description

[edit]Display and general external appearance

The basic oscilloscope, as shown in the illustration, is typically divided into four sections: the

display, vertical controls, horizontal controls and trigger controls. The display is usually a

CRT or LCD panel which is laid out with both horizontal and vertical reference lines referred

to as the graticule. In addition to the screen, most display sections are equipped with three

basic controls, a focus knob, an intensity knob and a beam finder button.

The vertical section controls the amplitude of the displayed signal. This section carries a

Volts-per-Division (Volts/Div) selector knob, an AC/DC/Ground selector switch and the

vertical (primary) input for the instrument. Additionally, this section is typically equipped

with the vertical beam position knob.

The horizontal section controls the time base or sweep of the instrument. The primary

control is the Seconds-per-Division (Sec/Div) selector switch. Also included is a horizontal

input for plotting dual X-Y axis signals. The horizontal beam position knob is generally

located in this section.

The trigger section controls the start event of the sweep. The trigger can be set to

automatically restart after each sweep or it can be configured to respond to an internal or

external event. The principal controls of this section will be the source and coupling selector

switches. An external trigger input (EXT Input) and level adjustment will also be included.

In addition to the basic instrument, most oscilloscopes are supplied with a probe as shown.

The probe will connect to any input on the instrument and typically has a resistor of ten times

the oscilloscope's input impedance. This results in a .1 (-10X) attenuation factor, but helps to

isolate the capacitive load presented by the probe cable from the signal being measured.

Some probes have a switch allowing the operator to bypass the resistor when appropriate.[3]
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[edit]Size and portability

Most modern oscilloscopes are lightweight, portable instruments that are compact enough to

be easily carried by a single person. In addition to the portable units, the market offers a

number of miniature battery-powered instruments for field service applications. Laboratory

grade oscilloscopes, especially older units which usevacuum tubes, are generally bench-topdevices or may be mounted into dedicated carts. Special-purpose oscilloscopes may berack-

mountedor permanently mounted into a custom instrument housing.

[edit]Inputs

The signal to be measured is fed to one of the input connectors, which is usually a coaxial

connector such as aBNCorUHF type.Binding postsorbanana plugsmay be used for lower

frequencies. If the signal source has its own coaxial connector, then a simplecoaxial cableis

used; otherwise, a specialised cable called a "scope probe", supplied with the oscilloscope, is

used. In general, for routine use, an open wire test lead for connecting to the point being

observed is not satisfactory, and a probe is generally necessary. General-purpose

oscilloscopes usually present an input impedance of 1megohmin parallel with a small but

known capacitance such as 20 picofarads.[4]

This allows the use of standard oscilloscope

probes.[5]

Scopes for use with very high frequencies may have 50-ohm inputs, which must be

either connected directly to a 50-ohm signal source or used with Z0 or active probes.

Less-frequently-used inputs include one (or two) for triggering the sweep, horizontal

deflection for X-Y mode displays, and trace brightening/darkening, sometimes calledz'-axis

inputs.

The green line is the waveform, the red vertical partial line represents the location of thetrigger, and the yellow line represents the trigger level. If the scope was simply set to trigger

on every rising edge, this waveform would cause three triggers for each cycle:

Assuming the signal is fairly highfrequency, your scope would probably look something like

this:
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Except that on the scope, each trigger would be the same channel, and so would be the same

color.

Examples of use

Lissajous figureson an oscilloscope, with 90 degrees phase difference betweenxand yinputs.

One of the most frequent uses of scopes istroubleshootingmalfunctioning electronicequipment. One of the advantages of a scope is that it can graphically show signals: where a

voltmetermay show a totally unexpected voltage, a scope may reveal that the circuit is

oscillating. In other cases the precise shape or timing of a pulse is important.

In a piece of electronic equipment, for example, the connections between stages (e.g.

electronic mixers,electronic oscillators,amplifiers) may be 'probed' for the expected signal,

using the scope as a simple signal tracer. If the expected signal is absent or incorrect, some

preceding stage of the electronics is not operating correctly. Since most failures occurbecause of a single faulty component, each measurement can prove that half of the stages of a

complex piece of equipment either work, or probably did not cause the fault.

Once the faulty stage is found, further probing can usually tell a skilled technician exactly

which component has failed. Once the component is replaced, the unit can be restored to

service, or at least the next fault can be isolated. This sort of troubleshooting is typical of

radio and TV receivers, as well as audio amplifiers, but can apply to quite-different devices

such as electronic motor drives.

Another use is to check newly designed circuitry. Very often a newly designed circuit will

misbehave because of design errors, bad voltage levels, electrical noise etc. Digitalelectronics usually operate from a clock, so a dual-trace scope which shows both the clock
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signal and a test signal dependent upon the clock is useful. Storage scopes are helpful for

"capturing" rare electronic events that cause defective operation.

Pictures of use

Heterodyne

AC hum on sound.

Sum of a low-frequency and a high-frequency signal.

Bad filter on sine.

Dual trace, showing different time bases on each trace.

[edit] Selection
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Types and models

Main article:Oscilloscope types

The following section is a brief summary of various types and models available. For adetailed discussion, refer to the other article.

[edit] Cathode-ray oscilloscope (CRO)

Example of an analog oscilloscope Lissajous figure, showing a harmonic relationship of 1 horizontal

oscillation cycle to 3 vertical oscillation cycles.

Foranalog television, an analog oscilloscope can be used as avectorscopeto analyze complex signal

properties, such as this display ofSMPTE color bars.

The earliest and simplest type of oscilloscope consisted of acathode ray tube, a verticalamplifier, a timebase, a horizontal amplifier and apower supply. These are now called

"analog" scopes to distinguish them from the "digital" scopes that became common in the

1990s and 2000s.

Analog scopes do not necessarily include a calibrated reference grid for size measurement of

waves, and they may not display waves in the traditional sense of a line segment sweeping

from left to right. Instead, they could be used for signal analysis by feeding a reference signal

into one axis and the signal to measure into the other axis. For an oscillating reference and

measurement signal, this results in a complex looping pattern referred to as aLissajous curve.

The shape of the curve can be interpreted to identify properties of the measurement signal in

relation to the reference signal, and is useful across a wide range of oscillation frequencies.
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[edit] Dual-beam oscilloscope

The dual-beam analog oscilloscope can display two signals simultaneously. A special dual-

beamCRTgenerates and deflects two separate beams. Although multi-trace analog

oscilloscopes can simulate a dual-beam display with chop and alternate sweeps, those

features do not provide simultaneous displays. (Real time digital oscilloscopes offer the samebenefits of a dual-beam oscilloscope, but they do not require a dual-beam display.)

[edit] Analog storage oscilloscope

Trace storage is an extra feature available on some analog scopes; they used direct-view

storage CRTs. Storage allows the trace pattern that normally decays in a fraction of a second

to remain on the screen for several minutes or longer. An electrical circuit can then be

deliberately activated to store and erase the trace on the screen.

[edit] Digital oscilloscopes

Main article:Digital storage oscilloscope

A Rigol DS2000 Series Oscilloscope. A modern low cost DSO.

While analog devices make use of continually varying voltages, digital devices employ

binary numbers which correspond to samples of the voltage. In the case of digital

oscilloscopes, an analog-to-digital converter (ADC) is used to change the measured voltages

into digital information.

The digital storage oscilloscope, or DSO for short, is now the preferred type for most

industrial applications, although simple analog CROs are still used by hobbyists. It replaces

the unreliable storage method used in analog storage scopes with digitalmemory, which can

store data as long as required without degradation. It also allows complex processing of the

signal by high-speeddigital signal processingcircuits.[3]

A standard DSO is limited to capturing signals with a bandwidth of less than half the

sampling rate of the ADC (called theNyquist limit). There is a variation of the DSO called

the digital sampling oscilloscope that can exceed this limit for certain types of signal, such as

high-speed communications signals, where the waveform consists of repeating pulses. This

type of DSO deliberately samples at a much lower frequency than the Nyquist limit and then

uses signal processing to reconstruct a composite view of a typical pulse. A similar technique,

with analog rather than digital samples, was used before the digital era in analog sampling

oscilloscopes.[16][17]
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A digital phosphor oscilloscope (DPO) uses color information to convey information about a

signal. It may, for example, display infrequent signal data in blue to make it stand out. In a

conventional analog scope, such a rare trace may not be visible.

[edit] Mixed-signal oscilloscopes

File:Mixed Signal Oscilloscope (Agilent Technologies MSOX-4154A).png

A Mixed Signal Oscilloscope displaying both analog and digital characteristics of inputs. (Agilent

MSOX 4154A)

A mixed-signal oscilloscope (or MSO) has two kinds of inputs, a small number of analogchannels (typically two or four), and a larger number of digital channels(typically sixteen). It

provides the ability to accurately time-correlate analog and digital channels, thus offering a

distinct advantage over a separate oscilloscope and logic analyser. Typically, digital channels

may be grouped and displayed as a bus with each bus value displayed at the bottom of the

display in hex or binary. On most MSOs, the trigger can be set across both analog and digital

channels.

[edit] Mixed-domain oscilloscopes

A Tektronix MDO4000 Mixed Domain Oscilloscope

A mixed-domain oscilloscope (or MDO) has three kinds of inputs, a small number (typically

two or four) analog channels, a larger number (typically sixteen) digital channels, and one RF

channel. It provides the ability to accurately time-correlate analog, digital, and RF signals

with each other, and allows the user to see how the RF spectrum changes over time.

Tektronix invented the MDO, and are currently the only company to offer a mixed-domain

oscilloscope.

[edit] Handheld oscilloscopes

Handheld oscilloscopes are useful for many test and field service applications. Today, a handheld oscilloscope is usually adigital sampling oscilloscope, using aliquid crystaldisplay.

[edit] PC-based oscilloscopes

A new type of oscilloscope is emerging that consists of a specialized signal acquisition board

(which can be an externalUSBorparallel portdevice, or an internal add-onPCIorISA

card). The user interface and signal processing software runs on the user's computer, ratherthan on an embedded computer as in the case of a conventional DSO.
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CapacitorFrom Wikipedia, the free encyclopedia


This article is about the electronic component. For the physical phenomenon, seecapacitance. For anoverview of various kinds of capacitors, seetypes of capacitor.

Miniature low-voltage capacitors, by a cm ruler

A typicalelectrolytic capacitor

A capacitor (originally known as condenser) is apassivetwo-terminalelectrical component

used to storeenergyin anelectric field. The forms of practical capacitors vary widely, but all

contain at least twoelectrical conductorsseparated by adielectric(insulator); for example,one common construction consists of metal foils separated by a thin layer of insulating film.

Capacitors are widely used as parts ofelectrical circuitsin many common electrical devices.

When there is apotential difference(voltage) across the conductors, a staticelectric field

develops across the dielectric, causing positive charge to collect on one plate and negative

charge on the other plate.Energyis stored in the electrostatic field. An ideal capacitor is

characterized by a single constant value,capacitance, measured infarads. This is the ratio of

theelectric chargeon each conductor to the potential difference between them.

The capacitance is greatest when there is a narrow separation between large areas of

conductor, hence capacitor conductors are often calledplates, referring to an early means ofconstruction. In practice, the dielectric between the plates passes a small amount ofleakage
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currentand also has an electric field strength limit, resulting in abreakdown voltage, while

the conductors andleadsintroduce an undesiredinductanceandresistance.

Capacitors are widely used in electronic circuits for blockingdirect currentwhile allowing

alternating currentto pass, in filter networks, for smoothing the output ofpower supplies, in

theresonant circuitsthat tune radios to particularfrequencies, in electric power transmissionsystems for stabilizing voltage and power flow, and for many other purposes.

[1]
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Light-emitting diodeFrom Wikipedia, the free encyclopedia


"LED" redirects here. For other uses, seeLED (disambiguation).

Light-emitting diode

Red, pure green and blue LEDs of the 5mm diffused type

Type Passive,optoelectronic

Working principle Electroluminescence

Invented Oleg Losev(1927)[1]

Nick Holonyak Jr.(1962)[2]

First production 1968[3]

Electronic symbol

Pin configuration anodeandcathode
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Parts of an LED. Although not directly labeled, the flat bottom surfaces of the anvil and post

embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled

out from mechanical strain or vibration.

A modern LED retrofit "bulb" with aluminiumheatsink, a lightdiffusingdome andE27 screwbase,

using a built-in power supply working onmains voltage

A light-emitting diode (LED) is asemiconductorlight source.[4]

LEDs are used as indicator

lamps in many devices and are increasingly used for otherlighting. Appearing as practical

electronic components in 1962,[5]

early LEDs emitted low-intensity red light, but modern

versions are available across thevisible,ultraviolet, andinfraredwavelengths, with very highbrightness.

When a light-emittingdiodeis forward-biased(switched on),electronsare able torecombine

withelectron holeswithin the device, releasing energy in the form ofphotons. This effect is

calledelectroluminescenceand thecolorof the light (corresponding to the energy of the

photon) is determined by theenergy gapof the semiconductor. A LED is often small in area

(less than 1 mm2), and integrated optical components may be used to shape its radiation

pattern.[6]

LEDs present manyadvantagesover incandescent light sources includinglower

energy consumption, longerlifetime, improved physical robustness, smaller size, and faster

switching. LEDs powerful enough for room lighting are relatively expensive and require

more precise current andheat managementthan compactfluorescent lampsources ofcomparable output.
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Light-emitting diodes are used in applications as diverse asaviation lighting,automotive

lighting, advertising, general lighting, andtraffic signals. LEDs have allowed new text, video

displays, and sensors to be developed, while their high switching rates are also useful in

advanced communications technology. Infrared LEDs are also used in theremote control

units of many commercial products including televisions, DVD players and other domestic

appliances.

Colors and materials

Conventional LEDs are made from a variety of inorganicsemiconductor materials. The

following table shows the available colors with wavelength range, voltage drop and material:

ColorWavelength

[nm]

Voltage drop

[V]Semiconductor material

Infrared

> 760 V< 1.63

Gallium arsenide(GaAs)

Aluminium gallium arsenide(AlGaAs)

Red 610 < < 7601.63 < V

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