1. PROJECT
on
WIRELESS AUDIO TRANSMITTER FOR TV
Submitted by
Mr. Abhishek Sharma 1120503
Mr. Danish Khan 1120528
Mr. Pawan Gupta 1120520
in
Electronics & Telecommunication Engineering
Under the Guidance of
Prof Zafar Khan
Anjuman-i-Islam's
M.H.SabooSiddikCollegeofEngineering
8, M.H. Saboo Siddik Polytechnic Road, Byculla-400008
University of Mumbai
2014-15
2. CERTIFICATE
This is to certify that
Mr. Abhishek Sharma
Mr. Danish Khan
Mr.Pawan Gupta
are bonafide students of M.H.Saboo Siddik College of Engineering, Mumbai, they
have successfully carried out the project titled “Wireless Audio Transmitter For
Tv” in the partial fulfillment of requirement of mini project II in electronics and
telecommunication engineering from Mumbai University during the academic year
2014-2015.
______________
(Er. Zafar Khan)
Project Guide
___________________ ____________________
Internal Examiner External Examiner
___________________ __________________
Head Of Department Principal
3. ACKNOWLEDGEMENT
We give our sincere thanks to our guide Prof Zafar Khan for his guidance and
constant support, whenever we needed it. We also extend thanks to our teaching staff
whom we approached for academic help for our project. We also thank the project
co ordinators and non teaching staff as well for arranging necessary facilities. We are
highly grateful to the Head of Department(EXTC), the Principal and the Director for
providing facilities, conductive environment and encouragement.
Mr. Abhishek Sharma ____________
Mr. Danish Khan ____________
Mr. Pawan Gupta ____________
4. ABSTRACT
This project allows you to watch your favourite TV programmes late at night without disturbing
other family members. The project uses a FM transmission principle. Most modern TVs are
nowadays equipped with audio-in/out and video-in/out RCA sockets. Using an RCA-to-RCA cord,
connect the audio output of your TV to the transmitter’s input. Adjust the gain of the audio
preamplifier for clear reception in a portable FM receiver equipped with an earphone socket.
6. 5.1: Countinuity Test 29
5.2: Power On Test 29
Chapter 6: Future Scope 30
Chapter 7: Conclusion 31
References 32
7. List of Figures
Fig 1.3 Block Diagram
Fig 2.1 BC547 Transistor Pinouts
Fig 2.1.1 BC 547 Transistor
Fig 2.2 Battery
Fig 2.3 Berg Connector
Fig 2.4 Antenna
Fig 2.5 White Led Spectrum
Fig 2.5.1 Different Types Of Led’s
Fig 2.6(a) 1N4007 Diode
Fig 2.6(b) PN Junction Diode
Fig 2.7 Resistors
Fig 2.7.2 Trimpot(PRESET)
Fig 2.8 Capacitor
Fig 2.8.1 Trimmer Capacitor
Fig 3 Schematic Diagram
Fig 4 Layout Diagram
8. 8
CHAPTER 1: Introduction
If u want to watch TV during night times it will be a disturbance for other family members. This
circuit is useful in order to get out of this problem by using headphones instead of speakers.
Wireless communication means the transfer of information without the use of enhanced electrical
conductors. The purpose of this circuit can be achieved by using both radio frequency or infrared
waves generated from a transmitter place near the sound source. But it is efficient to choose the
radio frequencies because they will give you much more flexibility to change how and where
you listen. In these days people willing to spend lots of money on their home theatre systems and
speakers. But speakers has high cost. So, the cheaper option will be wireless TV headphones.
They can be used effectively upto 20 feet.
1.1. Motivation:
Everyone require something or other kind of motivation, if we consider today’s world most of
the systems used robotics as well as the communication became wireless. The use of hardware
has reduced to the least by using vlsi techniques. This project is basically motivated by the
people of society who are busy with there work and don’t get time to be refreshed without any
disturbance. We have seen old age is most problem facing age, as in old age peoples hearing
capability is reduced, So by this project they can also enjoy their programs without disturbing
any other. Also,if we combine wireless transmission with other technology then it can be
program to perform multiple task by minimum usage of physical structure. It can produce a
system with maximum efficiency and minimum efforts.
1.2. Objective:
The essential aims to built a WIRELESS TV HEADPHONE CIRCUIT are
To design one main transmitter circuit unit that takes analog input to the receiver of
output.
9. 9
To replace the cable/wire with wireless system.
To design and implement a system that transmits the stereo audio sound, then seperates it
into wireless speaker units using two different frequencies
Fig 1.3 Block Diagram
10. 10
CHAPTER 2: Hardware Requirements
2.1. Transistor
BC547
The BC547 transistor is an NPN Epitaxial Silicon Transistor. The BC547 transistor is a general-
purpose transistor in small plastic packages. It is used in general-purpose switching and
amplification BC847/BC547 series 45 V, 100 mA NPN general-purpose transistors.
Fig 2.1 BC 547 Transistor Pinouts
The BC547 transistor is an NPN bipolar transistor, in which the letters "N" and "P" refer to the
majority charge carriers inside the different regions of the transistor. Most bipolar transistors
used today are NPN, because electron mobility is higher than hole mobility in semiconductors,
allowing greater currents and faster operation. NPN transistors consist of a layer of P-doped
semiconductor (the "base") between two N-doped layers. A small current entering the base in
common-emitter mode is amplified in the collector output. In other terms, an NPN transistor is
"on" when its base is pulled high relative to the emitter. The arrow in the NPN transistor symbol
is on the emitter leg and points in the direction of the conventional current flow when the device
is in forward active mode. One mnemonic device for identifying the symbol for the NPN
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transistor is "not pointing in." An NPN transistor can be considered as two diodes with a shared
anode region. In typical operation, the emitter base junction is forward biased and the base
collector junction is reverse biased. In an NPN transistor, for example, when a positive voltage is
applied to the base emitter junction, the equilibrium between thermally generated carriers and the
repelling electric field of the depletion region becomes unbalanced, allowing thermally excited
electrons to inject into the base region. These electrons wander (or "diffuse") through the base
from the region of high concentration near the emitter towards the region of low concentration
near the collector. The electrons in the base are called minority carriers because the base is doped
p-type which would make holes the majority carrier in the base.
Fig 2.1.1 BC 547 Transistor
Whenever base is high, then current starts flowing through base and emitter and after that only
current will pass from collector to emitter. So that the LED which is connected to collector will
glow to indicate that transistor is ON.
2.2. Battery
An electrical battery is a combination of one or more electrochemical cells, used to convert
stored chemical energy into electrical energy. The battery has become a common power source
for many household and industrial applications.
12. 12
Batteries may be used once and discarded, or recharged for years as in standby power
applications. Miniature cells are used to power devices such as hearing aids and wristwatches;
larger batteries provide standby power for telephone exchanges or computer data centers.
2.2.1 WORKING OF BATTERY:
A battery is a device that converts chemical energy directly to electrical energy. It consists of a
number of voltaic cells; each voltaic cell consists of two half cells connected in series by a
conductive electrolyte containing anions and cat ions. One half-cell includes electrolyte and the
electrode to which anions (negatively-charged ions) migrate, i.e. the anode or negative electrode;
the other half-cell includes electrolyte and the electrode to which cat ions (positively-charged
ions) migrate, i.e. the cathode or positive electrode. In the red ox reaction that powers the battery,
reduction (addition of electrons) occurs to cat ions at the cathode, while oxidation (removal of
electrons) occurs to anions at the anode. The electrodes do not touch each other but are
electrically connected by the electrolyte. Many cells use two half-cells with different electrolytes.
In that case each half-cell is enclosed in a container, and a separator that is porous to ions but not
the bulk of the electrolytes prevents mixing.
Each half cell has an electromotive force (or emf), determined by its ability to drive electric
current from the interior to the exterior of the cell. The net emf of the cell is the difference
between the emfs of its half-cells. Therefore, if the electrodes have emfs and, in other words, the
net emf is the difference between the reduction potentials of the half-reactions.
The electrical driving force or across the terminals of a cell is known as the terminal voltage
(difference) and is measured in volts. The terminal voltage of a cell that is neither charging nor
discharging is called the open-circuit voltage and equals the emf of the cell. Because of internal
resistance, the terminal voltage of a cell that is discharging is smaller in magnitude than the
open-circuit voltage and the terminal voltage of a cell that is charging exceeds the open-circuit
voltage. An ideal cell has negligible internal resistance, so it would maintain a constant terminal
voltage of until exhausted, then dropping to zero. If such a cell maintained 1.5 volts and stored a
13. 13
charge of one Coulomb then on complete discharge it would perform 1.5 Joule of work. In actual
cells, the internal resistance increases under discharge, and the open circuit voltage also
decreases under discharge. If the voltage and resistance are plotted against time, the resulting
graphs typically are a curve; the shape of the curve varies according to the chemistry and internal
arrangement employed.
An electrical battery is one or more electrochemical cells that convert stored chemical energy
into electrical energy. Since the invention of the first battery (or "voltaic pile") in 1800 by
Alessandro Volta, batteries have become a common power source for many household and
industrial applications. According to a 2005 estimate, the worldwide battery industry generates
US$48 billion in sales each year, with 6% annual growth. There are two types of batteries:
primary batteries (disposable batteries), which are designed to be used once and discarded, and
secondary batteries (rechargeable batteries), which are designed to be recharged and used
multiple times. Miniature cells are used to power devices such as hearing aids and wristwatches;
larger batteries provide standby power for telephone exchanges or computer data centers.
2.2.2 Principle of operation
A battery is a device that converts chemical energy directly to electrical energy. It consists of a
number of voltaic cells; each voltaic cell consists of two half cells connected in series by a
conductive electrolyte containing anions and cations. One half-cell includes electrolyte and the
electrode to which anions (negatively charged ions) migrate, i.e., the anode or negative electrode;
the other half-cell includes electrolyte and the electrode to which cations (positively charged
ions) migrate, i.e., the cathode or positive electrode. In the redox reaction that powers the battery,
cations are reduced (electrons are added) at the cathode, while anions are oxidized (electrons are
removed) at the anode. The electrodes do not touch each other but are electrically connected by
the electrolyte. Some cells use two half-cells with different electrolytes. A separator between half
cells allows ions to flow, but prevents mixing of the electrolytes.
Each half cell has an electromotive force (or emf), determined by its ability to drive electric
current from the interior to the exterior of the cell. The net emf of the cell is the difference
14. 14
between the emfs of its half-cells, as first recognized by Volta. Therefore, if the electrodes have
emfs and , then the net emf is ; in other words, the net emf is the difference
between the reduction potentials of the half-reactions. The electrical driving force or
across the terminals of a cell is known as the terminal voltage (difference) and is measured in
volts. The terminal voltage of a cell that is neither charging nor discharging is called the open-
circuit voltage and equals the emf of the cell. Because of internal resistance, the terminal voltage
of a cell that is discharging is smaller in magnitude than the open-circuit voltage and the terminal
voltage of a cell that is charging exceeds the open-circuit voltage. An ideal cell has negligible
internal resistance, so it would maintain a constant terminal voltage of until exhausted, then
dropping to zero. If such a cell maintained 1.5 volts and stored a charge of one coulomb then on
complete discharge it would perform 1.5 joule of work. In actual cells, the internal resistance
increases under discharge, and the open circuit voltage also decreases under discharge. If the
voltage and resistance are plotted against time, the resulting graphs typically are a curve; the
shape of the curve varies according to the chemistry and internal arrangement employed.
As stated above, the voltage developed across a cell's terminals depends on the energy release of
the chemical reactions of its electrodes and electrolyte. Alkaline and carbon-zinc cells have
different chemistries but approximately the same emf of 1.5 volts; likewise NiCd and NiMH
cells have different chemistries, but approximately the same emf of 1.2 volts. On the other hand
the high electrochemical potential changes in the reactions of lithium compounds give lithium
cells emfs of 3 volts or more.
15. 15
Fig 2.2 Battery
2.3. Berg Connector
A Berg connector is a brand of electrical connector used in computer hardware. Berg connectors
are manufactured by Berg Electronics Corporation of St. Louis, Missouri, a division of
Framatome Connectors International.
Berg connectors have a 2.54 mm (=.100 inch) pitch, pins are square (0.64 mm x 0.64 mm =
approx. 0.025 x 0.025 inch), and usually come as single or double row connectors.
Many types of Berg connectors exist. Some of the more familiar ones used in IBM PC
compatibles are:
Fig 2.3 Berg Connector
the 4-pin polarized Berg connectors used to connect 3.5-inch floppy disk drive units to
the power supply unit, usually referred to as simply a "floppy power connector", but often
also referred to as SP4.
the 2-pin Berg connectors used to connect the front panel lights, turbo switch, and reset
button to the motherboard, and
the 2-pin Berg connectors used as jumpers for motherboard configuration.
2.4. Antenna
A Yagi-Uda antenna, commonly known simply as a Yagi antenna or Yagi, invented in 1926
by Shintaro Uda and Hidetsugu Yagi, of Tohoku Imperial University, Japan, is a directional
16. 16
antenna system consisting of an array of a dipole and additional closely coupled parasitic
elements (usually a reflector and one or more directors). The dipole in the array is driven, and
another element, typically 5% longer, effectively operates as a reflector. Other parasitic elements
shorter than the dipole may be added in front of the dipole and are referred to as directors. This
arrangement increases antenna directionality and gain in the preferred direction over a single
dipole. Directional antennas such as the Yagi-Uda are commonly referred to as beam antennas or
high-gain antennas (particularly for transmitting). Yagi antennas with added corner reflectors
and/or UHF elements are commonly used for reception of television broadcasts. Yagi-Uda
antennas are also widely used by amateur radio operators for communication on frequencies
from short wave, through VHF/UHF, and into microwave bands. Amateur radio operators
(hams) often homebrew this type of antenna, and have published many technical papers and
software.
Description:
Yagi-Uda antennas are directional along the axis perpendicular to the dipole in the plane of the
elements, from the reflector through the driven element and out via the director(s). Typically all
elements are spaced about a quarter-wavelength apart. (See also log-periodic antenna.) All
elements usually lie in the same plane, supported on a single boom or crossbar; however, they do
not have to assume this coplanar arrangement: for example, some commercially available Yagi-
Uda antennas for television reception have several reflectors arranged to form a corner reflector
behind the dipole. The bandwidth of a Yagi-Uda antenna, which is usually defined as the
frequency range for which the antenna provides a good match to the transmission line to which it
is attached, is determined by the length, diameter and spacing of the elements. For most designs
bandwidth is typically only a few percent of the design frequency. Yagi-Uda antennas can be
designed to operate on multiple bands. Such designs are more complicated, using pairs of
resonant parallel coil and capacitor combinations (called a "trap" or LC) in the elements. The
trap serves to isolate the outer portion of an element from the inner portion at the trap design
frequency. In practice the higher frequency traps are located closest to the boom of the antenna.
Typically, a triband beam will have two pairs of traps per element.
17. 17
Fig 2.4 Antenna
2.4.1. Theory of Operation:
In order to understand the operation of a Yagi-Uda, a simple antenna consisting of a reflector,
driven element and a single director as discussed in the previous section will be studied. The
driven element is typically a λ/2 dipole and is the only member of the structure that is directly
excited.
All the other elements are considered parasitic. That is, they reradiate power which they receive
from the driven element (they also interact with each other).One way of thinking about it is to
consider a parasitic element to be a normal dipole element with a gap at its centre, the feed point.
Now instead of attaching the antenna to a load (such as a receiver) we connect it to a short
circuit. As is well known in transmission line theory, a short circuit reflects all of the incident
power 180 degrees out of phase. So one could as well model the operation of the parasitic
element as the superposition of a dipole element receiving power and sending it down a
transmission line to a matched load, and a transmitter sending the same amount of power down
the transmission line back toward the antenna element.
If the wave from the transmitter were 180 degrees out of phase with the received wave at that
point, it would be equivalent to just shorting out that dipole at the feed point (making it a solid
element).The fact that the parasitic element involved isn't exactly resonant but is somewhat
shorter (or longer) than λ/2 modifies the phase of the element's current with respect to its
18. 18
excitation from the driven element. The so-called reflector element, being longer than λ/2, has an
inductive reactance which means the phase of the its current lags the phase of the open-circuit
voltage that would be induced by the received field.
The director element, on the other hand, being shorter than λ/2 has a capacitive reactance with
the voltage phase lagging that of the current. If the parasitic elements were broken in the centre
and driven with the same voltage applied to the centre element, then such a phase difference in
the currents would be equivalent to a phased array, enhancing the radiation in one direction and
decreasing it in the opposite direction. Thus one can appreciate the mechanism by which
parasitic elements of unequal length can lead to a unidirectional radiation pattern.
2.5. Led
Light Emitting Diodes (LED) have recently become available that are white and bright, so bright
that they seriously compete with incandescent lamps in lighting applications. They are still pretty
expensive as compared to a GOW lamp but draw much less current and project a fairly well
focused beam.
The diode in the photo came with a neat little reflector that tends to sharpen the beam a little but
doesn't seem to add much to the overall intensity.
When run within their ratings, they are more reliable than lamps as well. Red LEDs are now
being used in automotive and truck tail lights and in red traffic signal lights. You will be able to
detect them because they look like an array of point sources and they go on and off instantly as
compared to conventional incandescent lamps.
19. 19
LEDs are monochromatic (one color) devices. The color is determined by the band gap of the
semiconductor used to make them. Red, green, yellow and blue LEDs are fairly common. White
light contains all colors and cannot be directly created by a single LED. The most common form
of "white" LED really isn't white. It is a Gallium Nitride blue LED coated with a phosphor that,
when excited by the blue LED light, emits a broad range spectrum that in addition to the blue
emission, makes a fairly white light.
There is a claim that these white LED's have a limited life. After 1000 hours or so of operation,
they tend to yellow and dim to some extent. Running the LEDs at more than their rated current
will certainly accelerate this process.
There are two primary ways of producing high intensity white-light using LED’S. One is to use
individual LED’S that emit three primary colours—red, green, and blue—and then mix all the
colours to form white light. The other is to use a phosphor material to convert monochromatic
light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent
light bulb works. Due to metamerism, it is possible to have quite different spectra that appear
white.
Fig 2.5 Whits Led Spectrum
20. 20
LEDs are semiconductor devices. Like transistors, and other diodes, LEDs are made out of
silicon. What makes an LED give off light are the small amounts of chemical impurities that are
added to the silicon, such as gallium, arsenide, indium, and nitride.
When current passes through the LED, it emits photons as a byproduct. Normal light bulbs
produce light by heating a metal filament until it is white hot. LEDs produce photons directly
and not via heat, they are far more efficient than incandescent bulbs.
Fig : circuit symbol
Not long ago LEDs were only bright enough to be used as indicators on dashboards or electronic
equipment. But recent advances have made LEDs bright enough to rival traditional lighting
technologies. Modern LEDs can replace incandescent bulbs in almost any application.
2.5.1. Types of LED’S
LEDs are produced in an array of shapes and sizes. The 5 mm cylindrical package is the most
common, estimated at 80% of world production. The color of the plastic lens is often the same as the
actual color of light emitted, but not always. For instance, purple plastic is often used for infrared
LEDs, and most blue devices have clear housings. There are also LEDs in extremely tiny packages,
such as those found on blinkers and on cell phone keypads. The main types of LEDs are miniature,
high power devices and custom designs such as alphanumeric or multi-color.
Fig 2.5.1: Different types of LED’S
21. 21
2.5.2. Advantages of using LEDs
Efficiency:
LEDs produce more light per watt than incandescent bulbs; this is useful in
battery powered or energy-saving devices.
Size:
LEDs can be very small (smaller than 2 mm2
) and are easily populated onto
printed circuit boards.
On/Off time:
LEDs light up very quickly. A typical red indicator LED will achieve full
brightness in microseconds. LEDs used in communications devices can have even
faster response times.
Cycling:
LEDs are ideal for use in applications that are subject to frequent on-off cycling,
unlike fluorescent lamps that burn out more quickly when cycled frequently, or
HID lamps that require a long time before restarting.
Cool light:
In contrast to most light sources, LEDs radiate very little heat in the form of IR
that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed
as heat through the base of the LED.
Lifetime:
LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000
hours of useful life, though time to complete failure may be longer.
No Toxicity:
LEDs do not contain mercury, unlike fluorescent lamps.
22. 22
2.5.3. Disadvantages of using LED’s
High price:
LEDs are currently more expensive, price per lumen, on an initial capital cost
basis, than most conventional lighting technologies.
Temperature dependence:
LED performance largely depends on the ambient temperature of the operating
environment. Over-driving the LED in high ambient temperatures may result in
overheating of the LED package, eventually leading to device failure.
Voltage sensitivity:
LEDs must be supplied with the voltage above the threshold and a current below
the rating. This can involve series resistors or current-regulated power supplies.
Area light source:
LEDs do not approximate a “point source” of light, but rather a lambertian
distribution. So LEDs are difficult to use in applications requiring a spherical light
field. LEDs are not capable of providing divergence below a few degrees. This is
contrasted with lasers, which can produce beams with divergences of 0.2 degrees
or less.
Blue Hazard:
There is increasing concern that blue LEDs and cool-white LEDs are now capable
of exceeding safe limits of the so-called blue-light hazard as defined in eye safety.
2.6. Diode 1N4007
Diodes are used to convert AC into DC these are used as half wave rectifier or full wave
rectifier. Three points must he kept in mind while using any type of diode.
1.Maximum forward current capacity
2.Maximum reverse voltage capacity
3.Maximum forward voltage capacity
23. 23
Fig 2.6(a): 1N4007 diodes
The number and voltage capacity of some of the important diodes available in the market
are as follows:
Diodes of number IN4001, IN4002, IN4003, IN4004, IN4005, IN4006 and IN4007 have
maximum reverse bias voltage capacity of 50V and maximum forward current capacity of 1
Amp.
Diode of same capacities can be used in place of one another. Besides this diode of more
capacity can be used in place of diode of low capacity but diode of low capacity cannot be used
in place of diode of high capacity. For example, in place of IN4002; IN4001 or IN4007 can be
used but IN4001 or IN4002 cannot be used in place of IN4007.The diode BY125made by
company BEL is equivalent of diode from IN4001 to IN4003. BY 126 is equivalent to diodes
IN4004 to 4006 and BY 127 is equivalent to diode IN4007.
Fig 2.6(b):PN Junction diode
24. 24
2.6.1. PN JUNCTION OPERATION
Now that you are familiar with P- and N-type materials, how these materials are joined together
to form a diode, and the function of the diode, let us continue our discussion with the operation
of the PN junction. But before we can understand how the PN junction works, we must first
consider current flow in the materials that make up the junction and what happens initially within
the junction when these two materials are joined together.
2.6.2. Current Flow in the N-Type Material
Conduction in the N-type semiconductor, or crystal, is similar to conduction in a copper wire.
That is, with voltage applied across the material, electrons will move through the crystal just as
current would flow in a copper wire. This is shown in figure 1-15. The positive potential of the
battery will attract the free electrons in the crystal. These electrons will leave the crystal and flow
into the positive terminal of the battery. As an electron leaves the crystal, an electron from the
negative terminal of the battery will enter the crystal, thus completing the current path. Therefore, the
majority current carriers in the N-type material (electrons) are repelled by the negative side of the
battery and move through the crystal toward the positive side of the battery.
2.6.3. Current Flow in the P-Type Material
Current flow through the P-type material is illustrated. Conduction in the P material is by
positive holes, instead of negative electrons. A hole moves from the positive terminal of the P
material to the negative terminal. Electrons from the external circuit enter the negative terminal
of the material and fill holes in the vicinity of this terminal. At the positive terminal, electrons
are removed from the covalent bonds, thus creating new holes. This process continues as the
steady stream of holes (hole current) moves toward the negative terminal.
2.7. Resistors
25. 25
A resistor is a two-terminal electronic component designed to oppose an electric current by
producing a voltage drop between its terminals in proportion to the current, that is, in accordance
with Ohm's law:
V = IR
Fig 2.7 Resistors
The primary characteristics of resistors are their resistance and the power they can
dissipate. Other characteristics include temperature coefficient, noise, and inductance. Less well-
known is critical resistance, the value below which power dissipation limits the maximum
permitted current flow, and above which the limit is applied voltage. Critical resistance depends
upon the materials constituting the resistor as well as its physical dimensions; it's determined by
design.
Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits.
Size, and position of leads (or terminals) are relevant to equipment designers; resistors must be
physically large enough not to overheat when dissipating their power.
A resistor is a two-terminal passive electronic component which implements electrical resistance
as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I
will flow through the resistor in direct proportion to that voltage. The reciprocal of the constant
of proportionality is known as the resistance R, since, with a given voltage V, a larger value of R
further "resists" the flow of current I as given by Ohm's law:
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous
in most electronic equipment. Practical resistors can be made of various compounds and films, as
well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors
26. 26
are also implemented within integrated circuits, particularly analog devices, and can also be
integrated into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance: common commercial
resistors are manufactured over a range of more than 9 orders of magnitude. When specifying
that resistance in an electronic design, the required precision of the resistance may require
attention to the manufacturing tolerance of the chosen resistor, according to its specific
application. The temperature coefficient of the resistance may also be of concern in some
precision applications. Practical resistors are also specified as having a maximum power rating
which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is
mainly of concern in power electronics applications. Resistors with higher power ratings are
physically larger and may require heat sinking. In a high voltage circuit, attention must
sometimes be paid to the rated maximum working voltage of the resistor.
The series inductance of a practical resistor causes its behaviour to depart from ohms law; this
specification can be important in some high-frequency applications for smaller values of
resistance. In a low-noise amplifier or pre-amp the noise characteristics 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 position of its leads (or terminals) which is relevant in the practical manufacturing
of circuits using them.
This formulation of Ohm's law states that, when a voltage (V) is present across a resistance (R), a
current (I) will flow through the resistance. This is directly used in practical computations. For
example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a current
of 12 / 300 = 0.04 amperes (or 40 mill amperes) will flow through that resistor.
2.7.1. What is a trimpot?
A trimpot or trimmer potentiometer is a small potentiometer which is used for adjustment, tuning
and calibration in circuits. When they are used as a variable resistance (wired as a rheostat) they
are called preset resistors. Trimpots or presets are normally mounted on printed circuit boards
and adjusted by using a screwdriver. The material they use as a resistive track is varying, but the
most common is either carbon composition or cermet. Trimpots are designed for occasional
adjustment and can often achieve a high resolution when using multi-turn setting screws. When
trimmer potentiometers are used as a replacement for normal potentiometers, care should be
taken as their designed lifespan is often only 200 cycles.
Trimpot definition
27. 27
Trimmer potentiometers and preset resistors are small variable resistors which are used in
circuits for tuning and (re)calibration.
2.7.2. Types of trimpots
Several different versions of trimpots are available, using different mounting methods (through
hole, smd) and adjusting orientations (top, side) as well as single and multi-turn variations.
2.7.2(a) Single turn:
Single turn trimmers/presets are very common and used where a resolution of one turn is
sufficient. They are the most cost effective variable resistors available.
Fig 2.7.2 Trimpot
2.7.2(b) Multi turn:
For higher adjustment resolutions, multi-turn trimpots are used. The amount of turns varies
between roughly 5-25, but 5, 12 or 25 turns are quite common. They are often constructed using
a worm-gear (rotary track) or leadscrew (linear track) mechanism to achieve the high resolution.
Because of their more complex construction and manufacturing, they are more costly than single
turn preset resistors. The lead screw packages can have a higher power rating because of their
increased surface area.
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2.8. Capacitor
A capacitor or condenser is a passive electronic component consisting of a pair of conductors
separated by a dielectric. When a voltage potential difference exists between the conductors, an
electric field is present in the dielectric. This field stores energy and produces a mechanical force
between the plates. The effect is greatest between wide, flat, parallel, narrowly separated
conductors.
Fig 2.8 Capacitor
An ideal capacitor is characterized by a single constant value, capacitance, which is measured in
farads. This is the ratio of the electric charge on each conductor to the potential difference
between them. In practice, the dielectric between the plates passes a small amount of leakage
current. The conductors and leads introduce an equivalent series resistance and the dielectric has
an electric field strength limit resulting in a breakdown voltage.
The properties of capacitors in a circuit may determine the resonant frequency and quality factor
of a resonant circuit, power dissipation and operating frequency in a digital logic circuit, energy
capacity in a high-power system, and many other important aspects.
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A capacitor is a passive electronic component consisting of a pair of conductors separated by a
dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static
electric field develops in the dielectric that stores energy and produces a mechanical force
between the conductors. An ideal capacitor is characterized by a single constant value,
capacitance, measured in farads. This is the ratio of the electric charge on 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 called "plates", referring to an early means of construction.
In practice the dielectric between the plates passes a small amount of leakage current and also
has an electric field strength limit, resulting in a breakdown voltage, while the conductors and
leads introduce an undesired inductance and resistance.
Fig: Battery of four Leyden jars in Museum Boerhaave, Leiden, the Netherlands.
In October 1745, Ewald Georg von Kleist of Pomerania in Germany found that charge could be
stored by connecting a high voltage electrostatic generator by a wire to a volume of water in a
hand-held glass jar. Von Kleist's hand and the water acted as conductors and the jar as a
dielectric (although details of the mechanism were incorrectly identified at the time). Von Kleist
found, after removing the generator, that touching the wire resulted in a painful spark. In a letter
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describing the experiment, he said "I would not take a second shock for the kingdom of France."
The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor,
which was named the Leyden jar, after the University of Leiden where he worked.
2.8.1. What are trimmer capacitors?
Trimmer capacitors are variable capacitors which serve the purpose of initial calibration of
equipment during manufacturing or servicing. They are not intended for end-user interaction.
Trimmer capacitors are almost always mounted directly on the PCB (Printed Circuit Board), so
the user does not have access to them, and set during manufacturing using a small screwdriver.
Due to their nature, trimmer capacitors are cheaper than full sized variable capacitors and rated
for many fewer adjustments.
Fig 2.8.1 Trimmer Capacitor
Trimmer capacitors are used to initially set oscillator frequency values, latencies, rise and fall
times and other variables in a circuit. Should the values drift over time, these trimmer capacitors
allow repairmen to re-calibrate equipment when needed. There are two types of trimmer
capacitors: air trimmer capacitor and ceramic trimmer capacitor.
Trimmer capacitor definition
A trimmer capacitor is a variable capacitor used for initial calibration and recalibration of
equipment. It is commonly mounted directly on a PCB and accessed only by professional
repairmen, not the end-user.
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2.8.2. Characteristics
1. Voltage rating, capacitance range, polarity
Trimmer capacitors can be rated for voltages up to 300 volts, although voltage ratings of up to
100 volts are much more common. Since trim caps are variable capacitors, they come in a
capacitance range rather than a single capacitance value. The minimum capacitance is usually
between 0.5 pF and 10 pF, while the maximum capacitance is usually between 1 pF and 120 pF.
The actual capacitance value can be varied between the minimum and maximum capacitance
values for a given trimmer capacitor, but it can never be set to zero. It is worth noting that
trimmer capacitors are not polarized.
2. Tolerances and accuracy
Trimmer capacitors do not boast a good capacitance value tolerance. Sometimes, the tolerances
can be as high as -0 to +100%. This means that a trimmer capacitor can have a maximum
capacitance two times larger than nominal. However, bad tolerances do not pose a great problem
to engineers because trimmer capacitors are variable. Even if the maximum value is different
between individual capacitors, they can still be set by turning the screwdriver a certain angle.
Accuracy depends mostly on the operator, as he can choose to spend more time in order to set
the capacitor to a desired value. Often, trimmer capacitors are set by robots instead of human
operators, and they can achieve much better precision. In order to achieve a better accuracy, it is
advised to use a non-metallic tool, since metal screwdrivers will introduce a source of
capacitance that will vary the capacitance value when the tool is moved away from the capacitor.
3. Construction and properties of trimmer capacitors
There are two types of trimmer capacitors: air trimmer capacitor and ceramic trimmer capacitor.
These two types use different materials as the dielectric. Both types use rotating action to change
the capacitance value. The construction of trimmer capacitors is similar to the construction of
their larger variant, the variable capacitor. Trimmer capacitors can be made of semi-circular
metal plates. One is fixed, while the other can be rotated using a screwdriver. The user changes
the capacitance by rotating the shaft and increasing or reducing the amount of overlap between
the two plates. Another way to make a trimmer capacitor is to place a metallic screw in a non-
conductive threaded cylinder. The screw represents one electrode, while the other is located at
the base of the cylinder. By rotating the screw, the distance between the two plates is varied
which results in a change of capacitance. This construction is used in RF and microwave
applications.
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2.8.3. Applications for trimmer capacitors
The potential applications for trimmer capacitors are numerous. They are used whenever there is
a capacitance value that needs to be matched to a certain circuit during the manufacturing
process. The reason for their use (instead of using precise fixed-value capacitors) is that other
elements in the circuit have their own tolerances and their values could differ by as much as 20%
from what the engineer expected to see in a circuit. In order to adapt to those tolerances, trimmer
capacitors are used. They are commonly used in various RF circuits, VHF through microwave.
Special non-magnetic types are used in medical devices such as MRI and NMR scanners, which
produce very high magnetic fields that would otherwise destroy capacitors containing
ferromagnetic materials such as steel. Other common applications include oscillators, tuners,
crystal oscillators and filters. Trimmer capacitors can be found in communication equipment
such as mobile radios and aerospace transmitters and receivers, signal splitters and CATV
amplifiers.
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3.1 DESCRIPTION
3.1.1 OPERATION EXPLANATION
There are three components that work together to create and transmit a signal to where it can be
recorded or amplified. The first part is the actual microphone. The second part is the wireless
microphone is the transmitter. The final component, the antenna broadcasts that signal to a short
distance.
Transistor Q1 acts as an audio preamplifier. Transistor Q2 works as an FM oscillator and
modulator in conjunction with other passive components. Trimmer capacitor VC1 connected
across inductor L1 can be varied to achieve the desired frequency. Inductor L1 comprises 4 to 6
turns of closely wound 25SWG enameled copper wire on 4mm dia. air core. A 20-30cm long
wire serves as an antenna.
Most modern TV’s are nowadays equipped with audio-in/out and video in/out sockets. Using an
appropriate cord, connect the audio output of your TV to the transmitter’s input. Adjust the gain
of the audio preamplifier with the help of preset VR1 for clear reception in a portable FM
receiver equipped with an earphone socket. This transmitter draws only a few milliampere of
current and doesn’t require on/off switch.
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CHAPTER 5: HARDWARE TESTING
5.1 CONTINUITY TEST:
In electronics, a continuity test is the checking of an electric circuit to see if current flows (that it
is in fact a complete circuit). A continuity test is performed by placing a small voltage (wired in
series with an LED or noise-producing component such as a piezoelectric speaker) across the
chosen path. If electron flow is inhibited by broken conductors, damaged components, or
excessive resistance, the circuit is "open".
This test is the performed just after the hardware soldering and configuration has been
completed. This test aims at finding any electrical open paths in the circuit after the soldering.
Many a times, the electrical continuity in the circuit is lost due to improper soldering, wrong and
rough handling of the PCB, improper usage of the soldering iron, component failures and
presence of bugs in the circuit diagram. We use a multi meter to perform this test. We keep the
multi meter in buzzer mode and connect the ground terminal of the multi meter to the ground.
We connect both the terminals across the path that needs to be checked. If there is continuation
then you will hear the beep sound.
5.2 POWER ON TEST:
This test is performed to check whether the voltage at different terminals is according to the
requirement or not. We take a multi meter and put it in voltage mode, and measure voltage at
different points in circuit to make sure we are getting required voltage at those particular points.
First we apply less voltage and check whether the capacitors are getting charged, it is indicated
by the lamp which is connected in series with supply and circuit. Initially lamp should glow fully
because initially when capacitors are not charged they act as short circuit and due to the flow of
short circuit current the series lamp glows, and when capacitors get gradually charged they act as
open circuit, in this condition the series lamp stops glowing. If it happens then we can conclude
that the circuit is working prope.
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CHAPTER 6: Future Scope
‘Wireless Audio Transmitter From Tv’ is still a young technology, so many consumers are
unaware of the advantages this type of interaction can bring to everyday life. In this chapter we
mention few future systems based on ‘Wireless Audio Transmitter From Tv’ which resembles
the fluency of this technique over others.
Primary goal of this project is to receive a audio signal from tv and listen to it from a certain
distance.Now a days everybody wants home theatre which is a theater built in a home,
designed to mimic (or exceed) commercial theater performance and feeling, more commonly
known as a home cinema.Also,this sound system or home theatre are very much costly,But this
project can really help you to experience the performance of theatre at no cost.Due to wireless
transmission cost is reduced upto a great extent.
Most important thing is that this can be used not only in TV applications,but also in
Computers,Laptops,Mobile and portable music system.This is very much effective where noise
volume has to be reduced.Also,it can be used as an alternative to Bluetooth technology, as this
consumes lesser power.
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CHAPTER 7
CONCLUSION
This is an excellent way of reducing the disturbances caused to others while watching our
favorite TV programs, so this must be encouraged among the people. Wireless audio
transmission is an area of communication that is always moving with technological
advancements. As the new digital radios become more available, dramatic improvements will be
heard by listeners. Careful design of the new transmissions systems will pay off with reduced
costs and improved performance and reliability. HD Radio FM is both robust and efficient in the
difficult mobile environment, SDR provides flexibility and Cognitive Radio will definitely
define a whole new level of wireless audio transmission from tv.
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References
[1] Russell Mohn, “A Three Transistor Discrete FM Transmitter,” ELEN 4314
Communications Circuits - Design Project, pp. 1, April 2007.
[2] “FM broadcasting in the United States”
[3] “The Future of Radio”. The Swedish Radio and TV Authority, 2008.
[4] T.U.M Swarna kumara et al., “A Mini Project on Simple FM-Transmitter”.
[5] E. F. Louis, Principles of Electronic Communication Systems. McGraw-Hill, 2008
[6] “Phase-Locked Loop Tutorial, PLL”
[7] C. Renee, “An Industrial White Paper: HD Radio”
[8] C. W. Kelly, “Digital HD Radio AM/FM Implementation Issues”, USA.
[9] C. W. Kelly, “HD-Radio: Real World Results in Asia”, USA.
[10] B. Groome, “HD Radio (I.B.O.C).”
[11] D. Ferrara, “Advantages and Disadvantages of HD Radio”
[12] D. Correy, “HD Radio: What it is and What it is not”
[13] www.beyondlogic.org
[14] www.wikipedia.org
[15] www.howstuffworks.com
[16] www.alldatasheets.com
