[attachment=2594]


INFRARED HEADPHONE

ABSTRACT

The circuit for INFRARED HEADPHONE is designed to demonstrate the transmission and reception of audio signal through ! infrared radiations. The infrared rays generated by the transmitter circuit are received by the receiver circuit after transmission through air. This communication is much more effective than ordinary communication. It helps to receive audio signals from any audio device like T.V,radio etc.
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without disturbing others. It provides minimum transmission loss. It is a low cost project

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MINI PROJECT REPORT DONE BY
GUIDED BY:
RE MY A .M.MENON
RE SI I MA. I NX IKRISI I NAN
SAJINI SASIKUMAR

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o INTRODUCTION
c BLOCK DIAGRAM
o BLOCK DIAGRAM EXPLANATION
o CIRCUIT DIAGRAM
o CIRCUIT DIAGRAM EXPLANATION
o PCB DESIGNING AND FABRICATION
o PCB LAYOUT
o PCB SCHEMATIC
o COMPONENTS LIST
o CONCLUSION
o REFERENCES
o DATASHEETS
INTRODUCTION
INFRARED HEADPHONES
Using this low-cost project one can reproduce audio from TV without disturbing others. It does not use any wire connection between TV and headphones. In place of a pair of wires, it uses invisible infrared light to transmit audio signals from TV to headphones. Without using any lens, a range of up to 6 metres is possible. Range can be extended by using lenses and reflectors with IR sensors comprising transmitters and receivers.
IR transmitter uses two-stage transistor amplifier to drive two series-connected IR LEDs. An audio output transfonner is used (in reverse) to couple audio output from TV to the IR transmitter. Transistors Tl and T2 amplify the audio signals received from TV through the audio transformer. Low-impedance output windings (lower gauge or thicker wires) are used for connection to TV side while high-impedance windings are connected to IR transmitter. This IR transmitter can be powered from a 9-volt mains adapter or battery. Red LED1 in transmitter circuit functions as a zener diode (0.65V) as well as supply-on indicator.
IR receiver uses 3-stage transistor amplifier. The first
two transistors (T4 and T5) form audio signal amplifier while the third
transistor T6 is used to drive a headphone. Adjust potmeter VR2 for
max. clarity.
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Direct photo-transistor tow aids IR LEDs of transmitter for max. range. A 9-volt battery can be used with receiver for portable operation
INFRARED RADIATIONS
These rays were discovered in 1800 by William Herschel, a British musician and astronomer, when he observed that a thermometer placed just outside the visible spectrum of sunlight shows a greater increase in temperature than one placed in the red region.
The Infrared region of the spectrum lies beyond the red end of the visible range, with wavelengths between 0.01 to 7.5x10 5 cm.
Instruments for detecting infrared radiation include heat-sensitive devices such as thermocouple detectors, bolometers, photovoltaic cells, and photoconductors.
Infrared radiation is absorbed and emitted by the movement (rotations and vibrations) of chemically bonded atoms or groups of atoms of many materials. Some of the materials that absorb infrared radiation are window glass, water and also our atmosphere. Although invisible to the eye, longer infrared radiation can be detected as warmth by the skin. It forms nearly 50% of the Sun's radiant energy, with major portion of the rest being in the visible region.
One of the major uses of infrared rays is Infrared photography. Infrared rays are also reflected off objects, just as visible light. Special films or sensors which have the property to 'see in the dark' are used to observe these rays, which enhance different areas according to their heat emission. For e.g., in an infrared photograph, blue sky and water appear nearly black, whereas unexposed skin shows up brightly.
Infrared photography is used to detect pathological tissue growths' (thermography) and defects in electronic systems and circuits (due to their increased emission of heat). They can also be used to detect heat leaks in houses and forest fires. Shorter infrared rays are used in remote controls.
Physiotherapists use infrared radiation to warm damaged muscles and so speed up healing. Infrared light can also be sent down optical fibres for cable television and phone links.
Atmospheric haze and certain pollutants that scatter visible light are nearly transparent to parts of the infrared spectrum (scattering efficiency increases with the fourth power of the frequency). Infrared photography of distant objects from the air takes advantage of this phenomenon, to observe cosmic objects through large clouds of interstellar dust. However, since water vapour, G3 and C02 in the atmosphere absorb large parts of the infrared spectrum, most infrared astronomical observations are carried out at high altitudes, with the help of balloons, rockets and space-crafts.
The infrared absorption and emission characteristics of materials yield important information about the size, shape, and chemical bonding of molecules, atoms and ions present in them. Infrared spectroscopy is a powerful tool for determining the internal structure of molecules and for identifying the amounts of known species in a given sample. Infrared rays emitted by a given substance indicate the difference of some of the internal energy states, which depend on atomic weight and other atomic properties.
Hence, besides for identification, infrared rays can also be used to determine the amount of a known material in a given substance. Infrared spectroscopy is also used to examine archaeological specimens and for detecting forgeries of art and other objects, which, under visible light, resemble the original.
Infrared radiation plays an important role in heat transfer and is integral to the greenhouse effect.
Powerful infrared radiations can be artificially prepared, by using gases like Carbon dioxide and Carbon mono-oxide, and can be used in light radar systems and to modify chemical reactions.
Virtually every object at the Earth's surface emits electromagnetic radiation primarily in the infrared region of the spectrum. Man-made sources of infrared radiation include, besides hot objects, infrared light-emitting diodes (LEDs) and lasers, which are used in some fibre-optic communication systems and light radar systems respectively.
Other applications of infrared light include its use in remote controls, automatic self-focusing cameras, security alarm systems, and night-vision optical instruments.
AUDIO TRANSFORMERS
There are many ways to package audio transformers. Flat packs are integrated circuit (IC) packages with gull wings or flat leads on two or four sides. Modidar jacks incorporate the RJ-45 form factor and ensure high common mode noise immunity while maintaining signal integrity. Audio transformers improve sound quality by removing interference from audio signals. This interference, or ground noise, is caused by voltages from other devices and produces a humming or buzzing sound. Typically, audio transformers are encased in a magnetic shielding which is filled with an epoxy resin that provides insulation, protects the windings, and prevents vibration of the core material. Some audio transformers do not have a center tap, while other devices have a center tap in only the primary side, only the secondary side, or in both the primary and secondary sides. For audio transformers, the impedance ratio equals the square-of-the-turn ratio.
Audio transformers vary according to output power, operating frequency range, and rated DC current. They also vary in terms of insertion loss, 3-decibel (dB) bandwidth, and direct current resistance. Insertion loss, the measured loss through a device excluding the power division factor, is the ratio of power output to power input. 3-dB bandwidth is the frequency range over which the insertion loss is less than 3 dB for mid-band insertion loss. Direct current resistance (DCR), the resistance of windings as measured in DC current, is often minimized in the design of audio transformers and specified as a maximum Waveguide assemblies, which may contain solid or gaseous dielectric materials, have a hollow metallic conductor and are used in microwave systems. With through-hole technology (TUT), components are mounted on printed circuit boards (PCBs) by inserting component leads through holes in the board and then soldering. In surface mount technology (SMI), components plug into PCBs by soldering component leads or terminals to the top surface of the board. Other ways to package audio transformers include chassis, dish, or disk mounts. H-frame mounting is used in applications with high levels of shock or vibration.
Manufacturers use several methods to pack audio transformers for automatic assembly, shipping, and handling. The tape reel method packs components into a tape system and draws specified lengths or quantities into a reel. The stick magazine method packs components into a tube. Audio transformers that are distributed as individual parts are processed in bulk packs, while components that have leads in four-sides use trays.
Audio transformers are used in car radios and broadcast equipment, and in sound reinforcement applications. In terms of certifications, audio transformers are built and tested according to a variety of standards. For example, both Underwriters Laboratories (UL) and the Canadian Standards Association (CSA) provide marks. The International Electrotechnical Commission (IEC) also publishes applicable standards,
PHOTOTRANSISTOR
Phototransistors also consist of a photodiode with internal gain. A phototransistor is in essence nothing more than a bipolar transistor that is encased in a transparent case so that light can reach the base-collector junction. The electrons that are generated by photons in the base-collector junction are injected into the base, and this current is amplified by the transistor operation. Note that although phototransistors have a higher responsivity for light they are unable to detect low levels of light any better than photodiodes. Phototransistors also have slower response times.
PHOTODIODE
Light-emitting diode, usually called an LED , is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction, as in the common LED circuit. This effect is a form of electroluminescence. An LED is usually a small area light source, often with optics added to the chip to shape its radiation pattern. LEDs are often used as small indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or ultraviolet. LEDs can also be used as a regular household light source. Besides lighting, interesting applications include sterilization of water and disinfection of devices.
AUDIO DEVICE AUDIO AUDIO \
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IR AUDIO AUDIO HEAD
INTERFA AMPLI ”p. INTERF PHONE
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I BLOCK DIAGRAM EXPLANATION
" TRANSMITTER
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Infrared headphone has a transmitter connected to audio output
¦ from anv audio source like TV, radio etc. The transmitter has 5
| parts
1) Audio Device
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1 2) Audio Interface
| 3) Audio Amplifier
4) IR Driver
5) IR LED
Audio device is as explained before. The audio output is given to an audio interface circuit which is a transformer connected in stepupmode.The output is given to an audio amplifier mainly RC coupled amplifier where it is amplified to drive the IR driver. The IR driver has a Iiigh current transistor which is used to drive IR LED connected to emitter. The IR LED generate the infrared radiation corresponding to audio Input.
RECEIVER
The receiver section is what the user carries with him. The receiver section has 4 points.
1) IR Interface
2) Audio Amplifier
3) Audio Interface
4) Headphone
The IR interface is photo diode or transistor. Then receives the IR radiations and produce corresponding electrical signals. This is given to audio amplifier where it is amplified and given to audio interface circuit. It give the input to the headphone where the transmitted audio signal is received.
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CIRCUIT' DIAGRAM
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IR.CUIT DIAGR,
EXPLANATION
An IR headphone has two parts.
One is the transmitter and the other is the receiver
TRANSMITTER
The transmitter has an audio input from tv, radio etc., an audio transformer, an amplifier and IR driver AND IR LED's. The transformer is connected in inverse so as to amplify signals and offer impedence matching. The signal is then given to an audio amplifier. When base voltage increases the transistor is ON and the collector voltage decreases simultaneously.The red LED connected to its collector glows when collector voltage decreases. The voltage is given to the base of transistor BD 140. It is a high current transistor with collector current of up to I amphers. The low voltage makes the BD 140 transistor off and its collector voltage increases and the LED emits radiations.A 9v battery or adapter provides voltage supply.
RECEIVER
The transmitted IR rays are received by a photo transmitter and converted to corresponding electrical signals. This is amplified by audio amplifier comprising of T4 and T5. When base voltage of T4 increases making it ON and thus collector voltage decreases. Tliis is given to base of IS and it becomes OFF and its collector voltage increases. This amplified signal is given to audio interface where it is given to head set and the audio signal is received
PCB FABRICATION
PCB Artwork (Dip Trace)
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PCB Artwork on tracing sheet
Screen printing (Poly blue)
PCB Artwork on Cu plate using paint
Etching (FerricChloride)
Removal of paint from Copper plate by scrubbing
T
Drying
Drilling (0.9mm Bit) and Cleaning
Printed Circuit Board (PCB) is a piece of art. The performance of an electronic circuit depends on the layout and desien of PCB. A PCB mechanically supports and connects components by conductive pathways, etched from copper sheets laminated on to insulated substrate. PCB's are used to route electrical currents and signals tlirough copper tracks which are firmly bonded to an insulating base.
PCB Fabrication involves the following steps: -
1. Drawing the layout of the PCB in a paper. The track layout of the electronic circuit should be made in such a manner that the paths are in easy routes. It is then transferred to a Mylar sheet. The sheet is then touched with black ink.
2. The solder side of the Mylar sheet is placed on the shiny side of the five-
star sheet and is placed in a frame. Then it is exposed to sunlight with Mylar sheet facing the sunlight.
3. The exposed five-star sheet is put in Hydrogen Peroxide solution. Then it
is put in hot water and shook till unexposed region becomes transparent.
4. This is put in cold water and then the rough side is stuck on to the silk
screen. This is then pressed and dried well.
5. The plastic sheet of the five-star sheet is removed leaving the pattern on the screen.
6. A Copper clad sheet is cut to the size and cleaned. This is placed under the screen.
7. Acid resistant ink is spread on the screen so that a pattern of tracks and a pad is obtained on the Copper clad sheet. It is then dried.
8. The dried sheet is then etched using Ferric chloride solution(32Baume)
till all the unwanted copper is etched away. Swish the board to keep the etch fluid moving. Lift up the PCB and check, whether all the unwanted copper is removed. Etching is done by immersing the marked Copper clad in Ferric Chloride solution. After that the etched sheet is dried.
9. The unwanted resist ink is removed using Sodium Hydroxide solution. Holes are then drilled.
PCB PARAMETERS
Copper thickness - 72m.il (1mm ^ 39.37 mils)
Track width - 60m.il
Clearance - 60niil
Pad width - 86mil
Pad height - 86mil
Pad shape - Oval
Pad hole size - 25mil
On board - Through
Hole size - 0.9mm (36mil)
Base - Paper phenolic, hylam
PCB quality - FRC4
SOLDERING
Soldering is the process of joining metals by using lower melting point to weld or alloy with joining surfaces.
SOLDER
Solder is the joining material that melts below 427 degree connections between components. The popularly used solders are alloys of tin (Sn) and lead (Pb) that melts below the melting point of tin.
Types:
1. Rosin core: - 60/40 Sn/Pb and 63/67 Sn/'Pb solders are the most common types used for electronics assembly. These solders are available in various diameters and are most appropriate for small electronics work (0.02"-0.05" dia. is recommended)
2. Lead free: - Lead free solders are used as more environmental friendly substitutes for leaded solder, but they are typically not as easy to use mainly because of their higher melting point and poorer wetting properties.
3. Silver: - Silver solders are typically used for low resistance connections but they have a higher melting point and are more expensive than Sn/Pb solders.
4. Acid-Core: - Acid-core solders should not be used for electronics. They are intended for plumbing or non-electronics assembly work. The acid-core flux will cause corrosion of circuitry and can damage components.
5. Other special solders: -
¢ Various melting point eutetics: These special solders are typically used for non-electronics assembly of difficult to construct mechanical items that mist be assembled in a particular sequence.
¢ Paste solders: These solders are used in field applications or in
specialized manufacturing applications.
Flux
In order to make the surface accept the solder readily, the components terminals should be free oxides and other obstructing films. The lead should be cleaned chemically or by abrasion using blades or knives.
Small amount of lead coating can be done on the portion of the leads using soldering iron. This process is called tinning. Zinc chloride or Ammonium chloride separately or in combination is mostly used as fluxes. These are available in petroleum jelly as paste flux.
Flux is a medium used to remove the degree of wetting. The desirable properties of flux are:-
¢ It should provide a liquid cover over the materials and exclude air gap up to the soldering temperature.
¢ It should dissolve any oxide on the metal surface.
¢ It should be easily displaced from the metal by the molten soldering operation.
¢ Residues should be removable after completing soldering operation.
The most common flux used in hand soldering of electronic components is rosin, a combination of mild organic acids extracted from pine trees.
Soldering Iron
It is Hie tool used to melt the solder and apply it at the joint in the circuit. It operates in 230V supply. The iron bit at the tip gets heated while few minutes. The 50W and 25W soldering irons are commonly used for soldering of electronic circuits.
Soldering Steps
1. Make the layout of the components in the circuit. Plug in the chord of the soldering iron into the mains to get heated.
2. Straighten and clean the components leads using a blade or a knife. Apply a little flux on the leads. Care must be taken to avoid the components getting heated up.
3. Mount the components on the PCB by bending the leads of the . components. Use nose pliers..
4. Apply flux on the joints and solder the joints. Soldering must be done in minimum time to avoid dry soldering and heating up of the components.
5. Wash the residue using water and brush.
6. Solder joints should be inspected when completed to determine if they have been properly made.
o Qualities of a good solder joint:
A) Shim surface.
B) Good, smooth fillet.
o Qualities of a poor solder joint:
1. Dull or crystallized surfaces: - This is an indicator of a cold solder joint. Cold solder joints result from moving the components after the
soldering has been removed but before the solder has hardened. Cold solder joints may work at first but will eventually fail.
2. Air pockets: - Air pockets (voids) result from incomplete wetting of
surfaces, allowing air to be in contact with the connecting metals. This will cause oxidation of the joint and eventual failure. Blowholes can occur due to vaporization of the moisture on the surface of the board and exiting through the molten solder. Boards should be clean and dry prior to soldering. Ethanol (100%) can be used as a moisture chaser if boards are wet prior to soldering.
3. Dimples: - Dimples in the surface do not always indicate a serious
problem, but they should be avoided since they are precursors to voids.
4. Floaters: - Black spots "floating" in the soldering fillet should be
avoided because they indicate contamination and a potential for failure as in the case of voids. These black spots usually result from overheated (burnt) Rosin or other contaminants such as burnt wire insulation. Maintaining a clean tip will help to avoid these problems.
5. Balls: - A solder ball, instead of a fillet can occur if the trace was heated but the lead was not (vice-versa). This prevents proper wetting of both surfaces and results in solder being attached to only one surface (Component or trace).
6. Excess solder: - Excess solder usage can cover up other potential
problems and should be avoided. It can also lead to solder bridges. In addition, spherical solder joints can result from the application of too much solder.
PCB SCHEMATIC
TRANSMITTER
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This project INFRARED HEADPHONE was designed to reproduce audio from TV without disturbing others . It does not use any wire connection between TV and headphone. In place of a pair of wires it uses invisible IR radiations . Range of upto 5 mtrs is possible. Range can be extended using lenses and reflectors.
COMPONENTS LIST
S.NO COMPONENTS QTY
1 AUDIO TRANSFORMER 1
2 TRANSISTOR
BC548 3
BEL 187 1
BD140 1
3 IR PHOTO TRANSISTOR 1
4 LED 1
5 IR LED 2
6 RESISTER
4.7K 3
22K 1
2.2K 2
470K 1
12 OHM 1
100 OHM 1
10 K 1
7 POTENTIOMETER
100K 1
8 CAPACITOR
.01 UF 2
.1 UF 2
100 UF 1
47 P 1
9 BATTERY 9 V 2
10 HEAD PHONE 1
ESTIMATE
COST OF COMPONENTS =Rs.244
PCB FABRICATION = Rs.700
TOTAL COST =Rs.944
REFERENCE
Basic Radio & Television by SP S harm a Electronics maker
Audio and Video System s,by RG Guptha Electronics Zone
MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Order this document by BC54G/D
Amplifier Transistors
BASE
NPN Silicon
EMITTER
MAXIMUM RATINGS
Rating Symbol BC 546 BC 547 BC 548 Unit
Collector-Emitter Voltage vCEO 65 45 30 Vdc
Collector-Base Voltage VCBO 80 50 30 Vdc
Emitter-Base Voltage vEBO 6.0 Vdc
Collector Current ” Continuous <C 100 mAdc
Total Device Dissipation @ T/\ = 25°C Derate above 25°C PD 625 5.0 mW rnWrC
Total Device Dissipation @ 1q = 250C Derate above 25°C Pd 1.5 12 Watt mW/"C
Operating and Storage Junction Temperature Range TJ.Tstg -55 to+150 °C
THERMAL CHARACTERISTICS
Characteristic Symbol Max Unit
Thermal Resistance, Junction to Ambient R0JA 200 °C/W
°c/w
Thermal Resistance, Junction to Case R0JC 83.3
BC546, B
BC547, A, B, C
BC548, A, B, C
CASE 29-04, STYLE 17 TO-92 (TO-226AA)
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© Motorola, Inc 1996
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0.2 0.5 1.0 2.0 5.0 10 20 50 100 200 lrj, COLLECTOR CURRENT (mA)
Figure 8. "On" Voltage
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0.2 0.5 1.0 2.0 5.0 10 20 50 100 200 lc, COLLECTOR CURRENT (mA)
Figure 9. Collector Saturation Region
Figure 10. Base-Emitter Temperature Coefficient
BC546
Figure 2. "Saturation" and "On" Voltages
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Figure 4. Base-Emitter Temperature Coefficient
BC547/BC548
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Figure 5. Capacitances
Figure 6. Current-Gain - Bandwidth Product
PACKAGE DIMENSIONS
SECTION X-X
MOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. CONTOUR OF PACKAGE BEYOND DIMENSION R IS UNCONTROLLED.
4. DIMENSION F APPLIES BETWEEN P AND L. DIMENSION D AND J APPLY BETWEEN L AND K MINIMUM. LEAD DIMENSION IS UNCONTROLLED IN P AND BEYOND DIMENSION K MINIMUM
DIM INCHES MILLIMETERS
MIN MAX MIN MAX
A 0.175 0.205 4.45 5.20
B 0.170 0210 4.32 5.33
C 0.125 0.165 3.18 4.19
D 0.016 0.022 0.41 0.55
F. 0.0)6 0.019 0.41 0.48
G 0.045 0.055 1.15 1.39
H 0.095 0.105 2.42 2.66
J 0.015 0.020 0.39 0,50
K 0.500 ” 12.70 ”
L 0.250 ” 6.35 ”
N 0.060 0.105 2.04 2.66
P ” 0.100 ” 2.54
R 0.115 ” 2.93 ”
V 0.135 ” 3.43 ”
CASE 029-04 (TO-226AA) ISSUE AD
STYLE 17:
PIN 1. COLLECTOR 2. BASE 3 EMITTER