MINI PROJECT REPORT 2008 INFRARED HEADPHONE DONE BY GUIDED BY: RE MY A .M.MENON RE SI I MA. I NX IKRISI I NAN SAJINI SASIKUMAR ABSTRACT ! I | The circuit for INFRARED HEADPHONE is designed to i t | 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. i without disturbing others. It provides minimum transmission loss. It is a low cost project ! o INTRODUCTION c BLOCK DIAGRAM o BLOCK DIAGRAM EXPLANATION o CIRCUIT DIAGRAM
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MINI PROJECT REPORT 2008
INFRARED HEADPHONE
DONE BY GUIDED BY:
RE MY A .M.MENON
RE SI I MA. I NX IKRISI I NAN
SAJINI SASIKUMAR
ABSTRACT
! I | The circuit for INFRARED HEADPHONE is designed to
i
t
| 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.
i
without disturbing others. It provides minimum transmission loss. It is a low cost project
! 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.
i
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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1 IR [
INTERFAC
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AMPLIFIE R DRIVE
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1. TRANSMITTER
IR AUDIO AUDIO HEAD
INTERFA AMPLI —p. INTERF PHONE
CE FIER. ACE
2, RECEIVER
I BLOCK DIAGRAM EXPLANATION
" TRANSMITTER
I
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
I ' 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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IR .CUIT D I A GR , EXPLANATIO
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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)
PCB Artwork on tracing
sheet
Screen
printing (Poly
blue)
HI i
7̂
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