Elenco Fiber Optics Voice and Data Kit User Manual

Page 1

FIBER OPTICS KIT

MODEL FO-30K

Assembly and Instruction Manual

No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

ELENCO

Page 2

INTRODUCTION

The FO-30 kit, an optical voice link, will introduce you to the wonderful world of fiber optics. By building this kit, you will learn how fiber optics works and how it could be applied to the field of communication.

GENERAL OVERVIEW

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Fiber optics is a medium linking two electronic circuits. As shown in the block diagram below, this FO-30 kit consists of three basic elements; they are transmitter, fiber optic cable and receiver. The Transmitter converts an electrical signal into a light signal. The source, either a light-emitting-diode (LED) or laser diode, does the actual conversion. The drive circuit changes the electrical signal fed to the transmitter into a form required by the source.

Fiber-optic cable is the medium for carrying the light. The cable includes the fiber and its protective covering.

The Receiver accepts the light and converts it back into an electrical signal. The two basic parts of the receiver are the detector, which converts it back into an electrical signal, and the output circuit, which amplifies and, if necessary, reshapes the electrical signal.

The other parts which are not included in the diagram consists of connectors which are used to connect the fibers to the source and detector.

TRANSMITTER RECEIVERFIBER OPTIC CABLE

DRIVER

SOURCE

DETECTOR

OUTPUT CIRCUIT

IDENTIFYING RESISTOR VALUES

Use the following information as a guide in properly identifying the value of resistors.

IDENTIFYING CAPACITOR VALUES

Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or μF (microfarads). Most capacitors will have their actual value printed on them. Some capacitors may have their value printed in the following manner.

For the No.01234589

Multiply By 1 10 100 1k 10k 100k .01 0.1

Multiplier

1 2 Multiplier

Tolerance

BANDS

Second Digit

First Digit

Multiplier

Tolerance

103K

100V

Maximum Working Voltage

The value is 10 x 1,000 = 10,000pF or .01μF, ±10%, 100V

The letter M indicates a tolerance of +20% The letter K indicates a tolerance of +10% The letter J indicates a tolerance of +

Note:

The letter “R” may be used at times

to signify a decimal point; as in 3R3 = 3.3

1, 2, 3

The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGE 2)

Electrolytic capacitors have a positive and a negative electrode. The negative lead is indicated on the packaging by a stripe with minus signs and possibly arrowheads.

Warning:

If the capacitor is connected with incorrect polarity, it may heat up and either leak, or cause the capacitor to explode.

Polarity Marking

(+)

(–)

Page 3

Qty. Description Part #

r 1 PC Board 519015A r 2 Switch 541103 r 1 Microphone 568000 r 1 Battery Holder 590096 r 2 Screw 2-56 x 1/4” 641230 r 2 Nut 2-56 644201

Qty. Description Part #

r 1 Lug 661106 r 1 IC Socket 8-Pin 664008 r 2 Test Pins 665008 r 1 Polishing Paper #400 735005 r 3’ Fiber Optic Cable 810020 r 1 Lead-free Solder Tube 9LF99

TRANSMITTER SECTION

PARTS LIST

If you are a student, and any parts are missing or damaged, please see instructor or bookstore. If you purchased this fiber optics kit from a distributor, catalog, etc., please contact ELENCO

(address/phone/e-mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they will not be able to help you.

RESISTORS

Qty. Symbol Value Color Code Part #

r 1 R8 220Ω 5% 1/4W red-red-brown-gold 132200 r 1R7 1kΩ 5% 1/4W brown-black-red-gold 141000 r 2 R1, R3 2.2kΩ 5% 1/4W red-red-red-gold 142200 r 3 R2, R4, R5 10kΩ 5% 1/4W brown-black-orange-gold 151000 r 1 R6 100kΩ 5% 1/4W brown-black-yellow-gold 161000

CAPACITORS

Qty. Symbol Value Description Part #

r 1 C3 100pF (101) Discap 221017 r 1C2 .01μF (103) Discap 241031 r 1 C4 .022μF (223) Mylar 242217 r 1C1 1μF Electrolytic 261047

SEMICONDUCTORS

Qty. Symbol Value Description Part #

r 1 Q1 2N3904 Transistor NPN 323904 r 1 U1 LM741 Integrated Circuit 331741 r 1 D1 LED Red 350002 r 1 D2 LED Transmitter Clear 350005

MISCELLANEOUS

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PARTS IDENTIFICATION

Resistor Capacitors

Electrolytic

Discap

Transistor

Red

Integrated Circuit IC Socket Switch

Lug

LEDs

Microphone

Mylar

Transmitter

Battery Holder Test Pin

Page 4

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SCHEMATIC DIAGRAM

TRANSMITTER

There are 5 main components in the transmitter (see Figure 1A). They are:

a) Power supply (9V battery) b) Microphone (MIC) c) Op-amp LM741, (the driver) d) NPN transistor 2N3904, and e) Transmitter LED

The microphone picks up your voice signal and converts it into a voltage signal. The strength of this voltage signal depends upon the pitch and loudness of your voice. This signal is then ac-coupled through C1 and R2 to the input pin 2 of the LM741 op-amp for amplification.

The gain of the op-amp LM741 depends on the ratio of R6 to R2, which is equal to 100k/10k = 10. Hence, the voice signal coming from the microphone will be amplified 10 times by this op-amp, and the amplified signal will appear at the output of the op-amp.

At 0 Hz (DC) the impedance of C1 is infinite. The amplifier then acts as a voltage follower. A voltage follower is an op-amp in which the output voltage is equal to the input voltage. In our case, the output voltage at pin 6 is equal to the input voltage at pin 3 and pin 2 which is about 4.5V. This 4.5V at the input

pins is due to the effect of resistors R4 and R5 which act as a voltage divider. This constant DC voltage helps keep the NPN transistor (2N3904) on all the time.

The function of the NPN transistor (2N3904) is similar to that of a valve, it controls the flow of the current through the LED. The flow of this current will depend on the base voltage of the transistor. This base voltage in turn depends on the loudness and pitch of your voice. Thus, the light intensity of this LED will vary as you speak into the microphone. This encoded light signal will then be transmitted to the receiver through a fiber optic cable.

The LED (D1) acts as an ON/OFF indicator. It will also indicate the state of the battery. If the LED becomes dim, the battery is weak and should be replaced. C2 filters out any noise that comes through the voltage divider. C3 helps in stabilizing the op-amp. It will also reduce any high frequency noise generated in the transmitter. When S2 is closed (toward the LED D2), C4 is placed into the circuit and the op-amp will oscillate at about 1kHz. As a result, you will hear a shrill noise from the speaker in the receiver.

Figure 1A

Page 5

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CONSTRUCTION

Solder

Soldering Iron

Foil

Solder

Soldering Iron

Foil

Component Lead

Soldering Iron

Circuit Board

Foil

Rosin

Soldering iron positioned incorrectly.

Solder

Gap

Component Lead

Solder

Soldering Iron

Drag

Foil

1. Solder all components from the

copper foil side only. Push the soldering iron tip against both the lead and the circuit board foil.

2. Apply a small amount of solder to

the iron tip. This allows the heat to leave the iron and onto the foil. Immediately apply solder to the opposite side of the connection, away from the iron. Allow the heated component and the circuit foil to melt the solder.

1. Insufficient heat - the solder will not flow onto the lead as shown.

3. Allow the solder to flow around the connection. Then, remove the solder and the iron and let the connection cool. The solder should have flowed smoothly and not lump around the wire lead.

Here is what a good solder connection looks like.

2. Insufficient solder - let the solder flow over the connection until it is covered. Use just enough solder to cover the connection.

3. Excessive solder - could make connections that you did not intend to between adjacent foil areas or terminals.

4. Solder bridges - occur when solder runs between circuit paths and creates a short circuit. This is usually caused by using too much solder. To correct this, simply drag your soldering iron across the solder bridge as shown.

What Good Soldering Looks Like

A good solder connection should be bright, shiny, smooth, and uniformly flowed over all surfaces.

Types of Poor Soldering Connections

Introduction

The most important factor in assembling your FO-30K Fiber Optics Kit is good soldering techniques. Using the proper soldering iron is of prime importance. A small pencil type soldering iron of 25 watts is recommended. The tip of the iron must be kept clean at all times and

well tinned.

Solder

For many years leaded solder was the most common type of solder used by the electronics industry, but it is now being replaced by leadfree solder for health reasons. This kit contains lead-free solder, which contains 99.3% tin, 0.7% copper, and has a rosin-flux core.

Lead-free solder is different from lead solder: It has a higher melting point than lead solder, so you need higher temperature for the solder to flow properly. Recommended tip temperature is approximately 700

F; higher temperatures improve solder flow but accelerate tip decay. An increase in soldering time may be required to achieve good results. Soldering iron tips wear out faster since lead-free solders are more corrosive and the higher soldering temperatures accelerate corrosion, so proper tip care is important. The solder joint finish will look slightly duller with lead-free solders.

Use these procedures to increase the life of your soldering iron tip when using lead-free solder:

• Keep the iron tinned at all times.

• Use the correct tip size for best heat transfer. The conical tip is the most commonly used.

• Turn off iron when not in use or reduce temperature setting when using a soldering station.

•

Tips should be cleaned frequently to remove oxidation before it becomes impossible to remove. Use Dry Tip Cleaner (Elenco

#SH-1025) or Tip Cleaner (Elenco®#TTC1). If you use a sponge to clean your tip, then use distilled water (tap water has impurities that accelerate corrosion).

Safety Procedures

• Always wear safety glasses or safety goggles to protect your eyes when working with tools or soldering iron, and during all phases of testing.

• Be sure there is adequate ventilation when soldering.

•

Locate soldering iron in an area where you do not have to go around it or reach over it. Keep it in a safe area away from the reach of children.

• Do not hold solder in your mouth. Solder is a toxic substance. Wash hands thoroughly after handling solder.

Assemble Components

In all of the following assembly steps, the components must be installed on the top side of the PC board unless otherwise indicated. The top legend shows where each component goes. The leads pass through the corresponding holes in the board and are soldered on the foil side.

Use only rosin core solder.

DO NOT USE ACID CORE SOLDER!

Page 6

Figure D

Electrolytics have a polarity marking indicating the (–) lead. The PC board is marked to show the lead position.

Warning: If the capacitor is connected with incorrect polarity, it may heat up and either leak or cause the capacitor to explode.

Figure E

You have received one of four different types of microphones. If you have type A or B, mount it with the leads in the correct holes on the PC board. If you have type C or D, then bend the leads as shown.

ASSEMBLY INSTRUCTIONS FOR TRANSMITTER

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Figure A

Mount the lug as shown.

Figure B

Bend the leads as shown. Mount the LED transmitter with the flat side in the direction shown below.

Figure C

Mount the LED with the flat side in the same direction as marked on the top legend.

Figure F

Mount the transistor in the correct direction as marked on the top legend.

Figure G

Insert the IC socket into the PC board with the notch in the direction shown on the top legend. Solder the IC socket into place. Insert the IC into the socket with the notch in the same direction as the notch on the socket.

Mount flush

with PC board

Flat

Lug

PC Board

Flat

(–) (+)

Polarity

Mark

Socket

PC Board

Notch

Marking

Lug (see Figure A)

D2 - LED Transmitter Clear

(see Figure B)

S2 - Switch

R7 - 1kΩ 5% 1/4W Resistor

(brown-black-red-gold)

8-Pin IC Socket U1 - 741CN

(see Figure G)

D1 - LED Red (see Figure C)

S1 - Switch

R2 - 10kΩ 5% 1/4W Resistor

(brown-black-orange-gold)

C1 - 1μF Electrolytic Capacitor

(see Figure D)

Q1 - 2N3904 NPN Transistor

(see Figure F)

C4 - .022μF (223) Capacitor

R5 - 10kΩ 5% 1/4W Resistor

(brown-black-orange-gold)

C3 - 100pF (101) Capacitor

R6 - 100kΩ 5% 1/4W Resistor

(brown-black-yellow-gold)

R8 - 220Ω 5% 1/4W Resistor

(red-red-brown-gold)

R4 - 10kΩ 5% 1/4W Resistor

(brown-black-orange-gold)

C2 - .01μF (103) Capacitor

MIC - Microphone

(see Figure E)

R1 - 2.2kΩ 5% 1/4W Resistor R3 - 2.2kΩ 5% 1/4W Resistor

(red-red-red-gold)

Page 7

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TESTING PROCEDURE

QUIZ 1

Answers: 1. transmitter, fiber optic cable, receiver; 2. electrical, light; 3. light;

4. light, electrical; 5. voice, electrical; 6. IO; 7. 4.5; 8. current; 9. battery; 10. noise

1. Connect a 9 volt battery to the battery holder.

2. Switch S2 to the 1kHz position (toward LED D2) and S1 on (toward LED D1). Observe that LED D1 and D2 are on.

3. If you have a voltmeter, measure the DC voltage on pins 2, 3, and 6 of the IC. All of these voltages should be 1/2 the battery voltage.

4. If you have an oscilloscope, connect it to test point TP. Switch S2 in the 1kHz position (toward

LED D2) to place C4 in the circuit. You should see a 6V peak-to-peak square wave of about 1kHz on the scope.

5. Switch S2 to the mic position (toward the battery), speak into the microphone and observe your voice waveform on the scope.

If you experience any problems, see the Troubleshooting Guide on page 20.

1. The FO-30 Kit consists of three basic elements that are found in every fiber optic link. They are _____________, _____________, and _____________.

2. The function of the transmitter is to convert an _____________ signal into a _____________ signal.

3. The function of the fiber optic cable is to transmit a _____________ signal from the transmitter to the receiver.

4. The receiver accepts a _____________ signal and converts it back to an _____________ signal.

5. The microphone picks up a _____________ signal and converts it to an _____________ signal.

6. The gain of the LM-741 is equal to _____________.

7. The DC output to the op-amp is _____________ volts.

8. The NPN transistor (3904) controls the _____________ through the LED.

9. The LED (D1) indicated the state of the _____________.

10. C2 filters out any _____________ that comes

through the voltage divider.

Screws and Nuts

Mount the two screws in the position as shown in the pictorial diagram. Place the nuts on the screws and tighten them from the back side of the PC board.

9V Battery Holder

Solder the 9V battery holder to pad J1 and J2 in the correct position as shown in the pictorial diagram.

To point marked TP on PC board

GND & TP - Test Point

To point marked GND on PC board

Page 8

FIBER OPTICS

FIBER OPTICS AND ITS ADVANTAGES

SECTION A

-7-

The obvious questions concerning fiber optics are these: Why go through all the trouble of converting the signal to light and back? Why not just use wire? The answers lie in the following advantages of fiber optics.

a) Wide bandwidth b) Low loss c) Electromagnetic immunity d) Light weight e) Small size

f) Safety

g) Security

Of all the above mentioned advantages, wide bandwidth, low loss and electromagnetic immunity are probably the most important features.

Bandwidth is an effective indication of the rate at which information can be sent. Potential information-carrying capacity increases with the bandwidth of the transmission medium. From the earliest days of radio, useful transmission frequencies have pushed upward five orders of magnitude, from about 100kHz (100 x 10

Hz) to about 10GHz (10 x 109Hz). Optical fibers have a potential useful range to about 1THz (1 x 1012Hz). The information-carrying possibilities of fiber optics have only begun to be exploited, whereas the same potentials of copper cable are pushing their limits. To give perspective to the incredible capacity that fibers are moving toward, a 10GHz (10 x 10

) signal has

ability to transmit any of the following per second.

a) 1,000 books b) 130,000 voice channels

Loss indicates how far the information can be sent. As a signal travels along a transmission path, be it copper or fiber, the signal loses strength. The loss of strength is called attenuation. In a copper cable, attenuation increases with frequency. The higher the frequency of the information signal, the greater the loss. In an optical fiber, attenuation is flat. Loss is the same at any signaling frequency up until a very high frequency. The combination of high bandwidth and low loss has made the telephone industry probably the heaviest user of fiber optics.

Unlike copper cables, optical fibers do not radiate or pick-up electromagnetic radiation. Any copper conductor acts like an antenna, either transmitting or receiving energy. One piece of electronic equipment can emit electromagnetic interference (EMI) that disrupts other equipment. Among reported problems resulting from EMI are the following:

• An electronic cash register interfered with aeronautical transmissions at 113MHz.

• Coin-operated video games interfered with police radio transmissions in the 42MHz band.

• Some personal computers tested by the Federal Communications Commission (FCC) in 1979 emitted enough radiation to disrupt television reception several hundred feet away.

Since fibers do not radiate or receive electromagnetic energy, they make an ideal transmission medium when EMI is a concern. Furthermore, signals do not become distorted by EMI in fiber. As a result, fiber offers very high standards in error-free transmission.

The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGES 24-29)

Page 9

PRINCIPLES OF LIGHT

WAVELENGTH

SECTION B

Plastic Optical Cable

Core

Cladding

Jacket

-8-

FIBER MATERIAL

There are many materials that can be used to transmit light. The two most popular optical fibers are glass, which has the best optical characteristics, and plastic. Plastic is less expensive and does not break easily. This kit uses a plastic optical cable similar to the one shown.

Light occupies only a small portion of the electromagnetic spectrum shown in Figure 2A. The equation λ = c/f is used to convert frequency to wavelength, where λ = wavelength, c = speed of light, and F = Frequency of the light wave.

Note that in Figure 2A, the visible range of light is approximately 380 x 10-9meters (violet) to 750 x 10

-9

meters (red). When using plastic as the fiber optic cable medium, the best results occur around 660 x 10

-9

(orange-red).

Light also can be thought of as little bundles of energy being rapidly transmitted. These discrete groups of energy are called photons, and the amount of energy present in each photon is dependent on the frequency at which they are transmitted. Higher frequencies produce more energy than lower frequencies of light. The equation for the amount of energy in each photon is E = hƒ. Where E = energy in joules, h is Planck’s constant (6.63 x 10

-34

joules-seconds), and ƒ is the frequency

in hertz.

It is important to remember that light can be explained on a wave or a photon energy packet when investigating the properties of fiber optics.

Sonic

Sound

AM Radio

Shortwave Radio

Television & FM Radio

Radar

Infrared Light

Ultraviolet Ray

X-Ray

Gamma Ray

Cosmic Ray

Frequency

(Hz)

Visible Light

Wavelength

(nm)

Ultraviolet

Violet

Blue

Green

Orange

Red

Infrared

400

455

490

550

620

750

800

Figure 2A

Page 10

REFRACTION

-9-

Figure 2B

Refraction

Red

Orange

Yellow

Green

Blue

Violet

Refraction

White Light

The speed of light can be defined as the velocity of electromagnetic energy in a vacuum such as space. The speed of light will vary as it travels from one material to another, which, because of wave motion, results in light changing its direction. This change of direction of light is called refraction. In addition, different wavelengths of light travel at different speeds in the same material.

The best example of refraction if the prism of Figure 2B.

White light entering the prism contains all colors. The prism refracts the light and changes speed as it enters the prism. Because each color or frequency changes speed differently, each is refracted differently. Red light deviates the least and travels the fastest, while violet light deviates the most and travels the slowest. The white light then emerges from the prism divided into the colors of the rainbow.

REFRACTIVE INDEX

One of the important measures that you often come across in light is refractive index. The refractive index can be defined as the ratio of the speed of light in a vacuum to the speed of light in a material.

n = c(vacuum) / c(material)

where: n is the refractive index c is the speed of light

Since the speed of light in a vacuum is always faster that the speed of light in any material, the refractive index is always greater than one. The amount that a ray of light is refracted depends on the refractive index of the two materials.

The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGES 36, 37)

Page 11

REFLECTION

Before trying to explain reflection, we must first define some important terms shown in Figure 2C.

-10-

Figure 2C

Reflected Ray

Refracted Ray

Angle of Refraction

Angle of Incidence

Incident Ray

Normal

Interface

n1is less than n

• The normal is an imaginary line perpendicular to the interface of the two materials.

• The angle of incidence ( θ

) is the angle between

the incident ray and the normal.

• The angle of refraction ( θ

) is the angle between

the refracted ray and the normal.

Light passing from a lower refractive index to a higher one is bent toward the normal, as shown in Figure 2C. Light going from a higher index to a lower

will refract away from the normal, as shown in Figure 2D-1. As the angle of incidence increases, the angle of refraction approaches 90

to the normal. The angle of incidence that yields an angle of refraction of 90Oto the normal is the critical angle as shown in Figure 2D-2. If the angle of incidence increases past the critical angle, the light is totally reflected back to the first material so that it does not enter the second material as shown in Figure 2D-3. The angles of incidence and reflection are equal.

The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGE 39)

Page 12

SNELL’S LAW

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Figure 2D

Figure 2D-1 Figure 2D-2 Figure 2D-3

Critical Angle

Light is bent away from normal

Light does not enter

second material

Angle of

Refraction

Angle of Incidence

Angle of

reflection

Angle of

incidence

When the angle of reflection is more than the critical angle, light is reflected.

n1is greater than n

The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGE 40)

Snell’s Law states the relationship between the incident and refracted rays.

sin θ1= n2sin θ

where: n1and n2are refractive indexes

θ1and θ2are angle of incidence and angle of

refraction respectively.

The law shows that the angles depend on the refracted indices on the two materials. Knowing any three of the values, of course, allows us to calculate the fourth through simple rearrangement of the equation.

The critical angle of incidence θc, where θ

90O, is

θc = arcsin (n

2/n1

)

At an angle greater than θc, the light is reflected. Because reflected light means that n

and n2are

equal (since they are in the same material), θ

and

θ2are also equal. The angle of incidence and

reflection are equal. These simple principles of refraction and reflection form the basis of light propagation through an optical fiber.

Page 13

OPTICAL FIBER CONSTRUCTION

-12-

The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGES 40, 44)

The optical fiber has two concentric layers called the core and the cladding. The inner core is the lightcarrying part. The surrounding cladding provides the difference in the refractive index that allows total internal reflection of light through the core. The fiber usually has an additional coating around the

cladding. The coating, which is usually one or more layers of polymer, protects the core and cladding from shock that might affect their optical or physical properties. Figure 2E shows the cross-section of an optical cable

Core

Cladding

Jacket

Figure 2E

Page 14

HOW LIGHT TRAVELS THROUGH AN OPTICAL CABLE

SECTION C

-13-

Figure 2F

Light is propagated by total internal reflection

Cladding

Core

Angle of RefractionAngle of Incidence

The above paragraphs are reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGES 40, 44, and 45)

To best understand how light propagates through an optical fiber, let us look at an example. Assume that the core has a refractive index (n

) of 1.48 and the

cladding has a refractive index (n

) of 1.46 (these values are typical for optical fibers). By applying Snell’s Law, we can calculate the critical angle:

θc = arcsin (n

2/n1

)

θc = arcsin (1.46/1.48) = 80.6

or approximately

Figure 2F shows that as light rays are injected into the fiber, they strike the core-to-cladding interface at an angle greater than that of the critical angle (80.6

). As a result, the light will reflect back to the core. Since the angles of incidence and reflection are equal, the reflected light will again be reflected. The light will continue zig-zagging down the length of the fiber. Any light that strikes the interface at less than the critical angle will be absorbed by the cladding. This total internal reflection forms the basis of light propagation through a simple optical fiber.

Page 15

AN IMPORTANT UNIT IN FIBER OPTICS (THE DECIBEL)

-14-

The “DECIBEL” Section is reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E

The decibel is an important unit that you will use continually in fiber optics as well as in electronics. It is used to express gain or loss in a system or component. A transistor, for example, can amplify a signal, making it stronger by increasing its voltage, current or power. This is called gain. Similarly, loss is a decrease in voltage, current, or power. The basic equations for the decibel are:

dB = 20 log

10(V1/V2

) dB = 20 log10(I1/I2) dB = 10 log

10(P1/P2

)

Where V is voltage, I is current, and P is power. The decibel then is the ratio of two voltages, currents, or powers. Notice that voltage and current are 20 times the logarithmic ratio, and power is 10 times the ratio.

The basic use of the decibel is to compare the power entering the system, circuit, or component to the power leaving it. In fiber optics, we deal mostly with loss and optical power. The source emits optical power. As light travels through the fiber to the receiver, it loses power. This power loss is expressed in decibels. For example, if the source emits 1,000 microwatts (μW) of power and the detector receives 20μW, the loss through the system is about 17dB.

Loss = 10 log

(Pr/Ptr)

= 10 log

(20/1,000)

= –16.989 dB

Where P

is the power transmitted from the source and Pris power received by the receiver. A 10dB loss represents a loss of 90% of the power; only

10% remains. A useful figure to remember is 3dB, which represents a loss of one half of the power.

Fiber optic links easily tolerate losses of 30dB, meaning that 99.9% of the power from the source is lost before it reaches the detector. If the source emits 1,000μW of power, only 1μW reaches the detector. In fiber optics, it is common to omit the negative sign.

Page 16

-15-

Both ends of the optical cable are terminated in the same way. Please follow the steps below.

1) Use a razor blade (a very sharp knife will do) to cut the cable at a right angle to the length of the cable. Make the cut as close to 90

as possible.

2) Place the polishing paper on a work bench or other flat surface, and apply a few drops of water or oil to it. Hold the cable at a right angle to the polishing paper and polish the end that was just cut. The cable should not flex while polishing. To avoid flexing, clamp the cable between the two PC boards with only a small length of the cable extending beyond the edge of the PC board.

3) Repeat steps 1 and 2 for the other end.

4) Mount the two ends of the cable to the two connectors on the transmitter and receiver PC board as shown in the figure.

ASSEMBLY INSTRUCTIONS

HOW TO TERMINATE AN OPTICAL FIBER

Answers: (1) wide bandwidth, low loss, electromagnetic immunity (2) rate (3) attenuation (4) glass, plastic

(5) radiation (6) loss, gain (7) light, light (8) reflect (9) cladding, core (10) reflection

QUIZ 2

1. The three most important features of fiber optics are _________, _________ and __________.

2. Bandwidth is an indication of the _________ at which information can be sent.

3. The loss of signal strength is called ________.

4. The two most popular optical fibers are ________ and _________.

5. Unlike copper cables, optical fibers do not radiate or pick up _________.

6. The Decibel is a unit used to express _________ or _________ in a system or component.

7. Refractive index is the ratio of the speed of _________ in vacuum to the speed of _________ in any material.

8. If the angle of incidence is greater than the

critical angle, light will completely _______ back.

9. The optical fiber has two concentric layers called

the _________ and __________.

10. The total internal _________ forms the basis of

light propagation through a simple optical fiber.

Page 17

PARTS IDENTIFICATION

-16-

PARTS LIST

If you are a student, and any parts are missing or damaged, please see instructor or bookstore. If you purchased this fiber optics kit from a distributor, catalog, etc., please contact ELENCO

(address/phone/e-mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they will not be able to help you.

RESISTORS

Qty. Symbol Value Color Code Part #

1R3 10Ω 5% 1/4W brown-black-black-gold 121000

r 1R2 2.2kΩ 5% 1/4W red-red-red-gold 142200 r 1 R1 200Ω Pot 191322

CAPACITORS

Qty. Symbol Value Description Part #

3 C1, C3, C5 .047μF (473) Mylar 244717

r 1C6 10μF Electrolytic 271045 r 1C2 47μF Electrolytic 274744 r 1 C4 220μF Electrolytic 282244

SEMICONDUCTORS

Qty. Symbol Value Description Part #

r 1 Q1 LPT80A Phototransistor 32T80A r 1 U1 LM-386 Audio Op-amp Integrated Circuit 330386 r 1 D1 LED Red 350002

MISCELLANEOUS

Qty. Description Part #

r 1 PC Board 519015B r 1 Switch 541103 r 1 Battery Holder 590096 r 1 Speaker 590102 r 2 Screws 2-56 x 1/4” 641230

Qty. Description Part #

r 2 Nuts 2-56 644201 r 1 Lug 661106 r 1 IC Socket 8-pin 664008 r 6” Wire 22ga. Black 814120 r 6” Wire 22ga. Red 814220

RECEIVER SECTION

Resistor Capacitors

Electrolytic

Mylar

Transistor

Red

Integrated Circuit IC Socket

SwitchLED

Phototransistor

Potentiometer

Battery

Holder

Lug

Speaker

Page 18

RECEIVER

Figure 3A

-17-

There are 4 main components in the receiver (refer to Figure 3). They are:

a) Power Supply (9V battery) b) Phototransistor LPT80A (the detector) c) Audio op-amp LM-386 d) Speaker

The phototransistor Q1 (LPT80A) used in a common-collector configuration has high current gain. This transistor acts as a valve which controls the flow of current to the potentiometer R1. The flow of current is directly proportional to the intensity of light striking the base. The more intense the light, the more current will flow through transistor Q1. The current will then be coupled to the audio amplifier (LM386) through capacitor C1 for amplification.

The gain of the audio amplifier (LM386) is internally set to 20. Hence, the voltage signal that is coupled through C1 to input pin 2 will be amplified 20 times, and will appear on the output of the op-amp (pin 5).

The above amplified voltage will then be coupled through C4 to the speaker. The speaker then converts this voltage into sound.

The LED (D1) acts as an ON/OFF indicator. It will also indicate the state of the battery. If this LED becomes dim, the battery is weak and should be replaced. C2 filters out any noise at the power supply (9V battery).

Page 19

Q1 - Phototransistor

(see Figure D)

L1 - Lug (see Figure E)

C3 - .047

F Mylar Cap. (473)

R1 - 200Ω Pot (see Figure F)

R3 - 10Ω 5% 1/4W Resistor

(brown-black-black-gold)

S1 - Switch

C2 - 47μF Electrolytic Capacitor

(see Figure B)

C6 - 10μF Electrolytic Capacitor

(see Figure B)

D1 - LED (see Figure A)

C1 - .047

F Mylar Cap. (473)

R2 - 2.2kΩ 5% 1/4W Resistor

(red-red-red-gold)

8-Pin IC Socket U1 - LM386N Integrated Circuit

(see Figure C)

6” Black Wire - Strip 1/8” of insulation off of both ends of the wire.

6” Red Wire - Strip 1/8” of insulation off of both ends of the wire.

C4 - 220μF Electrolytic Capacitor

(see Figure B)

C5 - .047μF Mylar Cap. (473)

Figure D

Insert the phototransistor into the PC board in the direction shown.

Figure C

Figure A

Mount the LED with the flat side in the same direction as marked on the top legend.

Figure B

Electrolytics have a polarity marking indicating the (–) lead. The PC board is marked to show the lead position.

Warning: If the capacitor is connected with incorrect polarity, it may heat up and either leak or cause the capacitor to explode.

Figure F

ASSEMBLY INSTRUCTIONS FOR RECEIVER

-18-

Mount flush

with PC board

(–) (+)

Polarity

Mark

PC Board

Notch

Marking

Flat

Notch

Socket

Speaker and 2 Wires

Solder the wires to the correct position as shown.

– +

9V Battery Holder

Solder the 9V battery holder to pad J1 and J2 in the correct position as shown.

Screws and Nuts

Mount the two screws in the position as shown. Place the nuts on the screws and tighten them from the back side of the PC board.

Figure E

Mount the lug as shown. Make sure that the phototransistor lens lines up with the lug hole.

Page 20

-19-

INSERT THE CABLE

TESTING PROCEDURE

Answers: (1) power supply, phototransistor, audio op-amp, speaker (2) light, electrical (3) intensity

(4) 20 (5) C4 (6) electrical, sound (7) On-Off (8) noise (9) volume (10) audio

Slide the cable through the lug and butt the cable up against the phototransistor.

1. Plug a fresh 9 volt battery into the battery holder.

2. Turn S1 on (toward the pot), observe that LED

D1 is on.

3. If you have a voltmeter, measure the DC voltage

at pin 5, it should be about 4V.

4. Connect one end of the fiber to the source

connector to the transmitter, and the other end to

the detector connector of the receiver. Make sure switch S2 of the transmitter is in the off position (toward the battery). Now, speak into the microphone. You should hear your voice from the speaker of the receiver. Now, place C4 into the circuit by sliding switch S2 toward the infrared LED. You should hear a shrill noise from the speaker.

1. The receiver consists of 4 main components.

They are _________, _________, _________ and ________.

2. The phototransistor Q1 converts a __________

signal into an __________ signal.

3. The flow of the current through Q1 is directly

proportional to the ________ of light that strikes its base.

4. The gain of the audio amplifier (LM386) is

internally set to _________.

5. The amplifier signal is coupled to the speaker through __________.

6. The speaker converts an _________ signal into a _________ signal.

7. The LED D1 acts as an _________ indicator.

8. C2 filters out any __________ at the power supply.

9. The pot R1 is a __________ control device.

10. The LM386 chip is an __________ amplifier.

QUIZ 3

Page 21

Foil Side of Receiver PC Board

Foil Side of Transmitter PC Board

-20-

TROUBLESHOOTING GUIDE

PROBLEM POSSIBLE CAUSE

IF LED D1 DOES NOT LIGHT Check battery connection.

Check orientation of D1. Check soldering around S1.

THERE IS NO DIM RED GLOW FROM THE Check the value of R1, R4, R5 and orientation of TRANSMITTER LED D2 transistor Q1 and U1.

Check soldering around Q1 and U1.

THERE IS NO WAVEFORM ON THE Check soldering around S2. OSCILLOSCOPE WHEN S2 IS ON Check the value of C4.

Check soldering around U1.

THERE IS NO VOICE SIGNAL ON TEST Check resistors R2, R4, R5, and R6. POINT TP Check microphone orientation.

Check capacitors C1 and C3. Check U1.

TRANSMITTER

PROBLEM POSSIBLE CAUSE

IF LED D1 DOES NOT LIGHT Check battery connection.

Check orientation of D1 or battery life. Check soldering around S1.

NO SOUND FROM THE SPEAKER Check speaker and C4 orientation.

Check U1 orientation and soldering. Check fiber optic cable connection.

THE OUTPUT VOLTAGE IS NOT EQUAL Check orientation of U1. TO 4V Check soldering around S1, R1, U1, C5 and C4.

RECEIVER

Contact ELENCO®if any parts are missing or damaged. DO NOT contact your place of purchase as they will not be able to help you.

Page 22

-21-

GLOSSARY

ABSORPTION Loss of power in an optical fiber,

resulting from conversion of optical power into heat and caused principally by impurities, such as transition metals and hydroxyl ions, and also exposure to nuclear radiation.

ANGLE OF INCIDENCE Angle between the incident ray

and the normal.

ANGLE OF REFRACTION Angle between the refracted ray

and the normal.

ATTENUATION A general term indicating a

decrease in power from one point to another. In optical fibers, it is measured in decibels per kilometer at a specified wavelength.

BANDWIDTH A range of frequencies.

CABLE A fiber covered by a protective

jacket.

CAPACITOR A capacitor stores electrical

energy when charged by a DC source. It can pass alternating current (AC) but blocks direct current (DC) except for a very short charging current, called transient current.

CLADDING The outer concentric layer that

surrounds the core and has a lower index of refraction.

CONNECTOR A connector is a device which is

used to connect both ends of the fiber to the source and detector.

CORE The central, light-carrying part

of an optical fiber; it has an index of refraction higher than the surrounding cladding.

dB Decibel.

DECIBEL A standard logarithmic unit for

the ratio of two powers, voltages or currents. In fiber optics, the ratio is power. dB = 10 log

(P1/P2)

ELECTROMAGNETIC Any electrical or electro- INTERFERENCE magnetic energy that causes

undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.

EMI Electromagnetic interference.

FIBER A light-carrying conductor made

up of glass or plastic.

INDEX OF REFRACTION The ratio of the velocity of light

in free space to the velocity of light in a given material. Symbolized by n.

INTERFACE Surface that separates two

materials.

LED Light-emitting diode.

LIGHT Electromagnetic radiation which

is visible to the human eye.

LIGHT EMITTING DIODE A semiconductor diode that

spontaneously emits light from the PN junction when forward current is applied.

NORMAL An imaginary line perpendicular

to the interface of two materials.

OP AMP A semiconductor device which

is used to amplify current, voltage, or power.

PHOTON A photon of electromagnetic

energy. A “particle” of light.

PHOTO-TRANSISTOR A transistor that detects light.

PLASTIC FIBER An optical fiber having a plastic

core and plastic coating.

PC BOARD Its full name is printed circuit

board. It is a conductive pattern glued to one or both sides of an insulating material. Holes are punched or drilled through the conductor and board to allow the interconnection of electronic parts.

PRISM A device which splits white light

into a rainbow of colors.

SOURCE The light emitter, either an LED

or a laser diode in a fiber optic link.

WAVELENGTH The distance between the same

two points on adjacent waves.

The “GLOSSARY” Section is reproduced by permission TECHNICIAN’S GUIDE TO FIBER OPTICS 2E (PAGES 256-264)

Page 23

-22-

The course includes a 61 page manual and all of the material necessary to conduct nine stimulating experiments related to fiber optic communications. The experiments will give you a better understanding of fiber optics techniques and real fiber optics hardware.

Fiber Optic Lab Kit

with training course Model FO-40K

Fiber Optic Splice Kit

Model TK-25

For mending or extending 1,000μm plastic fiber. It contains fiber sleeves and retention clips to complete ten splices. No special tools, polishing or adhesive required. Instructions included.

Understanding Fiber Optics

Model VT-501

Learn tomorrow’s technology today! Fiber optics is changing the way we live, think and communicate. You will learn about fiber optic cables, connectors, couplers, splicers, transmitters and receivers.

58 minutes viewing time.

Fiber Continuity Tester

Model ST-90

Powerful Krypton light source provides long range over multimode fiber.

Requires two “AA” batteries. Included with kit.

Fiber Optic Viewing Scope Kit

Model ST-92

This fiber optic viewing scope kit makes it simple to view ST/SC/FC - supplied with dual face plates.

Zoom lens: 160X, 180X, and 200X.

Requires two

“AA” batteries.

Included with kit.

Carbide Fiber Scribe

Model ST-91

Wide inclined

carbide tip for easy

cleaving. Lightweight, pen-

size body clips to shirt pocket.

Fiber Optical Stripper

Model ST-88

Strips 125 micron

fiber with 250 micron

buffer coating without

scratching or nicking fiber.

Fiber Optic Tool Kit

Model TK-5000

HIGH QUALITY FIBER OPTIC TOOLS PROVIDE CUTTING, CRIMPING

POLISHING AND INSPECTION OF FIBER OPTIC TERMINATIONS

C-200 Case

ST-92 Viewing microscope

C-10 Parts case

ST-90 Fiber continuity tester

ST-88 Fiber optical stripper

ST-91 Carbide fiber scribe

ST-340 Kevlar scissors

ST-950 Hex-type crimping tool

ST-86 Polishing pad SC (37.8mm)

ST-87 Polishing pad ST (32.8mm)

ST-89 Foam swab cleaning kit

Includes:

Page 24

ELENCO

150 Carpenter Avenue

Wheeling, IL 60090

(847) 541-3800

Website: www.elenco.com

e-mail: elenco@elenco.com