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1. INTRODUCTION
1.1 Light Dimmer
Dimmers have the capacity to improve the quality and function of our
environment. They provide cost savings as well as convenience. With improvements
through R & D and a lowering in the cost of manufacture, lighting controls are destined to
become an invaluable part of many of our everyday lives.
A remote device which reduces the light output of a stage lighting fixture by
reducing the total wattage it receives, commonly grouped in banks, panels or packs. Present
technology usually has a dimmer per circuit, as opposed to systems where a limited number
of high-wattage dimmers are patched to a larger quantity of circuits.
In lighting, the electrical device (technically known as a potentiometer) that
regulates the current passing through the bulb filaments and, thereby, the amount of light
emitted from the lighting instruments.
Electronic controls that allow stage lighting to fade up or down slowly, as opposed
to being on or off only.A control that regulates light levels.
Device which provides adjustable voltage to a lighting fixture to control light output.
Can also be a term to refer to a mechanical device, such as a shutter, that controls output.
An instrument used to change the voltage of lights on the set, regulating in this way
thier intensity. NOTE: Not recommended for color cinematography, as the color
temperature of the lights will also change.
Controls the brightness of a particular fixture. A dimmer pack is a device used to
control a fixture from a remote control panel. Dimming may also be a feature within an
intelligent light or a specific control device.
a device in the electrical circuit used for varying the brightness of lamps in a
lighting installation. Dimming controls are ideal for any number of rooms because they
allow you to change design the lighting to suit each mood and activity.
an electronic device designed to regulate light output of incandescent and halogen
lamps; and fluorescent lamps in fixtures equipped with special dimming ballasts. To change
the brightness of the display e.g. during night driving.
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1.2 Light dimmer history
Light dimming is based on adjusting the voltage which gets to the lamp. Light
dimming has been possible for many decades by using adjustable power resistors and
adjustable transformers. Those methods have been used in movie theatres, stages and other
public places. The problem of those light controlling methods have been that they are big,
expensive, have poor efficiency and they are hard to control from remote location. The
power electronics have proceeded quickly since 1960. Between 1960-1970 thyristors and
triacs came to market. Using those components it was quite easy to make small and
inexpensive light dimmers which have good efficiency. Electronics controlling also made
possible to make them easily controllable from remote location. This type of electronic light
dimmers became available after 1970 and are nowadays used in very many locations like
homes, restaurants, conference rooms and in stage lighting.
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2.COMPONENT LIST
There are component which are used in making of the project circuit as given below
Table No 2 Componant Discription
Sr No
Componant Name
Value
Quantity
1
Triac
BT 136
2
2
Diac
--
2
3
Resistor
270 Ώ
2
68K
2
10 K
2
330 pf
2
22 pf
2
4
Capacitor
5
Trimmer
500 K
2
6
Potentiometer
100 K
2
7
PCB
cu Plane
1
Hole Type
1
8
Connecting Wires
1m
1
9
Solder
--
1
10
Soldering Wire
--
1
11
PCB
cu Plane
1
Hole Type
1
100 Watt
1
12
Light
13
Light Holder
--
1
14
AC Line Plug
--
1
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3.DISCRIPTION OF COMPONENTS
3.1 Triacs
TRIAC, from Triode for Alternating Current, is a genericized tradename for an
electronic component that can conduct current in either direction when it is triggered (turned
on), and is formally called a bidirectional triode thyristor or bilateral triode thyristor.
TRIACs belong to the thyristor family and are closely related to Silicon-controlled
rectifiers (SCR). However, unlike SCRs, which are unidirectional devices (i.e. can conduct
current only in one direction), TRIACs are bidirectional and so current can flow through
them in either direction. Another difference from SCRs is that TRIACs can be triggered by
either a positive or a negative current applied to its gate electrode, whereas SCRs can be
triggered only by currents going into the gate. Once triggered, the device continues to
conduct until the current drops below a certain threshold, called the holding current.
The bidirectionality makes TRIACs very convenient switches for AC circuits, also
allowing them to control very large power flows with milliampere-scale gate currents. In
addition, applying a trigger pulse at a controlled phase angle in an AC cycle allows one to
control the percentage of current that flows through the TRIAC to the load (phase control),
which is commonly used, for example, in controlling the speed of low-power induction
motors, in dimming lamps and in controlling AC heating resistors.
3.2 Diac
The DIAC, or "diode for alternating current", is a diode that conducts current only
after its breakover voltag
When this occurs, the diode enters the region of negative dynamic resistance, leading
to a decrease in the voltage drop across the diode and, usually, a sharp increase in current
through the diode. The diode remains "in conduction" until the current through it drops
below a value characteristic for the device, called the holding current, IH. Below this value,
the diode switches back to its high-resistance (non-conducting) state. This behavior is
bidirectional, meaning typically the same for both directions of current.
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Most DIACs have a three-layer structure with breakover voltage around 30 V. In
this way, their behavior is somewhat similar to (but much more precisely controlled and
taking place at lower voltages than) a neon lamp
DIACs have no gate electrode, unlike some other thyristors that they are commonly
used to trigger, such as TRIACs. Some TRIACs, like Quadrac, contain a built-in DIAC in
series with the TRIAC's "gate" terminal for this purpose.
DIACs are also called symmetrical trigger diodes due to the symmetry of their
characteristic curve
3.3 Trimmer
A trimmer or preset is a miniature adjustable electrical component. It is meant to be set
correctly when installed in some device, and never seen or adjusted by the device's user.
Trimmers can be variable resistors (potentiometers), variable capacitors, trimmable
inductors. They are common in precision circuitry like A/V components, and may need to
be adjusted when the equipment is serviced. Trimpots are often used to initially calibrate
equipment after manufacturing. Unlike many other variable controls, trimmers are mounted
directly on circuit boards, turned with a small screwdriver and rated for many fewer
adjustments over their lifetime. Trimmers like trimmable inductors and trimmable
capacitors are usually found in superhet radio and television receivers, in the Intermediate
frequency, oscillator and RF circuits. They are adjusted into the right position during the
alignment procedure of the receiver.
Trimmers come in a variety of sizes and levels of precision. For example, multi-turn
trim potentiometers exist, in which it takes several turns of the adjustment screw to reach
the end value. This allows for very high degrees of accuracy
3.4 Potentiometer
A potentiometer informally a pot, is a three-terminal resistor with a sliding contact
that forms an adjustable voltage divider.If only two terminals are used, one end and the
wiper, it acts as a variable resistor or rheostat.
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A potentiometer measuring instrument is essentially a voltage divider used for
measuring electric potential (voltage); the component is an implementation of the same
principle, hence its name.
Potentiometers are commonly used to control electrical devices such as volume
controls on audio equipment. Potentiometers operated by a mechanism can be used as
position transducers, for example, in a joystick. Potentiometers are rarely used to directly
control significant power (more than a watt), since the power dissipated in the potentiometer
would be comparable to the power in the controlled load.
3.5 RESISTORS –
A Resistor is a heat-dissipating element and in the electronic circuits it is mostly
used for either controlling the current in the circuit or developing a voltage drop across it,
which could be utilized for many applications. There are various types of resistors, which
can be classified according to a number of factors depending upon:
(I)
Material used for fabrication
(II)
Wattage and physical size
(III)
Intended application
(IV)
Ambient temperature rating
(V)
Cost
Basically the resistor can be split in to the following four parts from the construction
viewpoint.
(1) Base
(2) Resistance element
(3) Terminals
(4) Protective means.
The following characteristics are inherent in all resistors and may be controlled by
design considerations and choice of material i.e. Temperature co–efficient of resistance,
Voltage co–efficient of resistance, high frequency characteristics, power rating, tolerance &
voltage rating of resistors. Resistors may be classified as
(1) Fixed
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(2) Semi variable
(3) Variable resistor.
In our project carbon resistors are being used.
3.6 CAPACITORS:
The fundamental relation for the capacitance between two flat plates separated by a
dielectric material is given by:-
C=0.08854KA/D
Where: -
C= capacitance in pf.
K= dielectric constant
A=Area per plate in square cm.
D=Distance between two plates in cm
Design of capacitor depends on the proper dielectric material with particular type of
application. The dielectric material used for capacitors may be grouped in various classes
like Mica, Glass, air, ceramic, paper, Aluminum, electrolyte etc. The value of capacitance
never remains constant. It changes with temperature, frequency and aging. The capacitance
value marked on the capacitor strictly applies only at specified temperature and at low
frequencies.
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4.OPERATIONAL PRINCIPLE
The operation of the dimmer is based on the fact that, during a full cycle of an
AC waveform, a thyristor will only allow a part of the waveform to be delivered to the load
(lamp). Take a look at the following waveforms:
Figure 4.1 Circuit Waveform at diiff. modes
Both waveforms above comes from the same dimmer. The only difference is that
the waveform on the left will bright the lamp higher than the waveform on the right. That is
because, on the left waveform, the triac will be conductive earlier than the triac shown in
the right waveform.
The time that the triac becomes conductive is symbolized with the Greek letter α
(ALPHA) and is measured in angles from the zero point of the waveform. This zero point is
the point that the voltage is 0 volts, and this happens 2 times every one full period of the
wave form. When the α becomes smaller, then the dimmer becomes conductive sooner and
the lamp is brighter. When the α becomes bigger, then the triac delays more to become
conductive and thus the lamb is dimmer.
A full wavelength period is 360 degrees (2π). Due to the fact that during a full
wave length the zero cross occurs twice, α can take values from 0° to 180 degrees (0 - π).
When α = 0°, the full power is delivered to the load and when α = π, no power is delivered
to the load.
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1. CIRCUIT DESIGN
5.1 CIRCUIT DIAGRAM OF 555 IC TESTER
Fig .5.1 CIRCUIT DIAGRAM OF Light Dimmer
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5.2 PCB LAYOUT :
Fig .5.2 PCB LAYOUT DIAGRAM OF Light Dimmer
.
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6.WORKING
6.1 Working Of The Circuit
A light dimmer works by essentially chopping parts out of the AC voltage. This
allows only parts of the waveform to pass to the lamp. The brightness of the lamp is
determined by the power transferred to it, so the more the waveform is chopped, the more it
dims.
Mains power is comprised of an alternating current that flows in one direction and then
in the other, along the cable, at the rate of 50 or 60 cycles per second (known as Hertz). The
value 50 or 60Hz is dependent on the countries power system. The current alternates back
and forth changing direction at the zero point. If we were to look at this waveform it would
appear as a stretched S shape on its side ~. Draw a line through the middle and this is what
is called the zero crossing point. At this instant in time no current is flowing in either
direction. This is the point at which a dimmer is electronically synchronized to turn the
power ON or OFF. By chopping the waveform at the zero-crossing point, smooth dimming
can be achieved without the lamp flickering. This turning on and off of the power device
occurs every time the mains crossing point is reached (half phase), 100 or 120 times per
second.
Typically light dimmers are manufactured using a Triac or Thyristor as the power
control device. These electronic parts are semiconductors not dissimilar to transistors. A
Thyristor is a Uni.-directional device and hence, because AC power flows in both
directions, two are needed. A triac is a bidirectional device and therefore only one is
needed. An electronic circuit determines the point in time at which they turn ON (conduct).
The ON state continues until the next zero-crossing point, at which point the device turns
itself OFF. The electronic circuit then provides a delay, which equates to the dimness of the
lamp, before turning the control device back on. The slight capacitance of the load, filters
the
chopped
waveform
resulting
in
a
smooth
light
output.
Some controllers use a microprocessor control with the above timing function
being handled by an analogue circuit. More sophisticated systems, called digital dimmers,
operate the switching direct from microprocessor. This has the advantage of greater
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reliability,
quieter
operation,
lower
cost
and
smaller
controls.
Below is a typical picture of the mains sine wave, and a phase-controlled waveform
6.2 Circuit Waveform
Figure 6.2 a) Main Power Sine Wave
Figure 6.2 b) AC Chopped Wave
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7.P.C.B. MANUFACTURING PROCESS
7.1 P.C.B.
It is an important process in the fabrication of electronic equipment. The design of
PCBs (Printed Circuit Boards) depends on circuit requirements like noise immunity,
working frequency and voltage levels etc. High power PCBs requires a special design
strategy.
The fabrication process to the printed circuit board will determine to a large extent
the price and reliability of the equipment. A common target aimed is the fabrication of small
series of highly reliable professional quality PCBs with low investment. The target becomes
especially important for customer tailored equipments in the area of industrial electronics.
The layout of a PCB has to incorporate all the information of the board before one can go
on the artwork preparation. This means that a concept which clearly defines all the details of
the circuit and partly defines the final equipment, is prerequisite before the actual lay out
can start. The detailed circuit diagram is very important for the layout designer but he must
also be familiar with the design concept and with the philosophy behind the equipment.
7.2BOARD TYPES:
7.2.1 Single Sided Boards
The single sided PCBs are mostly used in entertainment electronics where
manufacturing costs have to be kept at a minimum. However in industrial electronics cost
factors cannot be neglected and single sided boards should be used wherever a particular
circuit can be accommodated on such boards.
7.2.2 Double Sided Boards
Double-sided PCBs can be made with or without plated through holes. The
production of boards with plated through holes is fairly expensive. Therefore plated through
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hole boards are only chosen where the circuit complexities and density of components does
not leave any other choice.
7.3 CHRONOLOGY
The following steps have been followed in carrying out the project.
1.
Study the books on the relevant topic.
2.
Understand the working of the circuit.
3.
Prepare the circuit diagram.
4.
Prepare the list of components along with their specification.
5.
Estimate the cost and procure them after carrying out market survey.
6.
Plan and prepare PCB for mounting all the components.
7.
Fix the components on the PCB and solder them.
8.
Test the circuit for the desired performance.
9.
Trace and rectify faults if any.
10.
Give good finish to the unit.
11.
Prepare the project report
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7.4DESIGN SPECIFICATION
7.4.1 PCB DESIGNING
The main purpose of printed circuit is in the routing of electric currents and signal
through a thin copper layer that is bounded firmly to an insulating base material sometimes
called the substrate. This base is manufactured with an integrally bounded layers of thin
copper foil which has to be partly etched or removed to arrive at a pre-designed pattern to
suit the circuit connections or other applications as required.
The term printed circuit board is derived from the original method where a printed
pattern is used as the mask over wanted areas of copper. The PCB provides an ideal
baseboard upon which to assemble and hold firmly most of the small components.
From the constructor’s point of view, the main attraction of using PCB is its role
as the mechanical support for small components. There is less need for complicated and
time consuming metal work of chassis contraception except perhaps in providing the final
enclosure. Most straight forward circuit designs can be easily converted in to printed wiring
layer the thought required to carry out the inversion cab footed high light an possible error
that would otherwise be missed in conventional point to point wiring .The finished project
is usually neater and truly a work of art.
Actual size PCB layout for the circuit shown is drawn on the copper board. The
board is then immersed in FeCl3 solution for 12 hours. In this process only the exposed
copper portion is etched out by the solution.
Now the petrol washes out the paint and the copper layout on PCB is rubbed
with a smooth sand paper slowly and lightly such that only the oxide layers over the Cu are
removed. Now the holes are drilled at the respective places according to component layout
as shown in figure.
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7.4.2 LAYOUT DESIGN
When designing the layout one should observe the minimum size (component body
length and weight). Before starting to design the layout we need all the required components
in hand so that an accurate assessment of space can be made. Other space considerations
might also be included from case to case of mounted components over the printed circuit
board or to access path of present components.
It might be necessary to turn some components around to a different angular
position so that terminals are closer to the connections of the components. The scale can be
checked by positioning the components on the squared paper. If any connection crosses,
then one can reroute to avoid such condition.
All common or earth lines should ideally be connected to a common line routed
around the perimeter of the layout. This will act as the ground plane. If possible try to route
the outer supply line to the ground plane. If possible try to route the other supply lines
around the opposite edge of the layout through the center. The first set is tearing the circuit
to eliminate the crossover without altering the circuit detail in any way.
Plan the layout looking at the topside to this board. First this should be translated inversely,
later for the etching pattern large areas are recommended to maintain good copper adhesion.
It is important to bear in mind always that copper track width must be according to the
recommended minimum dimensions and allowance must be made for increased width
where termination holes are needed. From this aspect, it can become little tricky to negotiate
the route to connect small transistors.
There are basically two ways of copper interconnection patterns under side the
board. The first is the removal of only the amount of copper necessary to isolate the
junctions of the components to oneanother. The second is to make the interconnection
pattern looking more like conventional point wiring by routing uniform width of copper
from component to component.
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7.4.3 ETCHING PROCESS
Etching process requires the use of chemicals. acid resistant dishes and running
water supply. Ferric chloride is mostly used solution but other etching materials such as
ammonium per sulphate can be used. Nitric acid can be used but in general it is not used due
to poisonous fumes.
The pattern prepared is glued to the copper surface of the board using a latex type of
adhesive that can be cubed after use. The pattern is laid firmly on the copper using a very
sharp knife to cut round the pattern carefully to remove the paper corresponding to the
required copper pattern areas. Then apply the resistant solution, which can be a kind of ink
solution for the purpose of maintaining smooth clean outlines as far as possible. While the
board is drying, test all the components.
Before going to next stage, check the whole pattern and cross check with the circuit
diagram. Check for any free metal on the copper. The etching bath should be in a glass or
enamel disc. If using crystal of ferric- chloride these should be thoroughly dissolved in
water to the proportion suggested. There should be 0.5 lt. of water for 125 gm of crystal.
To prevent particles of copper hindering further etching, agitate the solutions carefully by
gently twisting or rocking the tray.
The board should not be left in the bath a moment longer than is needed to remove
just the right amount of copper. Inspite of there being a resistive coating there is no
protection against etching away through exposed copper edges. This leads to over etching.
Have running water ready so that etched board can be removed properly and rinsed. This
will halt etching immediately.
Drilling is one of those operations that calls for great care. For most purposes a
0.5mm drill is used. Drill all holes with this size first those that need to be larger can be
easily drilled again with the appropriate larger size.
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7.4.4 COMPONENT ASSEMBLY
From the greatest variety of electronic components available, which runs into
thousands of different types it is often a perplexing task to know which is right for a given
job.
There could be damage such as hairline crack on PCB. If there are, then they can be
repaired by soldering a short link of bare copper wire over the affected part.
The most popular method of holding all the items is to bring the wires far apart after
they have been inserted in the appropriate holes. This will hold the component in position
ready for soldering.
Some components will be considerably larger .So it is best to start mounting the
smallest first and progressing through to the largest. Before starting, be certain that no
further drilling is likely to be necessary because access may be impossible later.
Next will probably be the resistor, small signal diodes or other similar size
components. Some capacitors are also very small but it would be best to fit these afterwards.
When fitting each group of components mark off each one on the circuit as it is fitted so that
if we have to leave the job we know where to recommence.
Although transistors and integrated circuits are small items there are good reasons
for leaving the soldering of these until the last step. The main point is that these components
are very sensitive to heat and if subjected to prolonged application of the soldering iron,
they could be internally damaged.
All the components before mounting are rubbed with sand paper so that oxide
layer is removed from the tips. Now they are mounted according to the component layout.
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7.4.5 SOLDERING: This is the operation of joining the components with PCB after this operation the
circuit will be ready to use to avoid any damage or fault during this operation following care
must be taken.
1. A longer duration contact between soldering iron bit & components lead can exceed the
temperature rating of device & cause partial or total damage of the device. Hence before
soldering we must carefully read the maximum soldering temperature & soldering time for
device.
2. The wattage of soldering iron should be selected as minimum as permissible for that
soldering place.
3 .To protect the devices by leakage current of iron its bit should be earthed properly.
4. We should select the soldering wire with proper ratio of Pb & Tn to provide the suitable
melting temperature.
5. Proper amount of good quality flux must be applied on the soldering point to avoid dry
soldering.
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8.ADVANTAGES OF CIRCUIT
We have dealt with simple knob operated in wall dimmers but the more sophisticated
types are programmable. These dimmers often known as scene dimmers have many
advantages over manual ones, including convenience, increased design flexibility, energy
savings, repeatability, reduced lamp replacement costs and security.
Convenience & Ambience
Intelligent lighting forms part of home automation where the circuit levels are preprogrammed according to use and according to other factors such as time of day. Light
fittings can be controlled individually or grouped together in circuits. Each circuit or fitting
can be set to be at a different level of brightness. These levels are then stored as a "scene"
which can best be though of as being a complete look of a room. Some systems have 10 or
more programmable scenes.
Once set up scenes can be easily recalled manually from touch screen, switch panels,
infra-red or wireless remote controls. They can be recalled automatically by time clock, or
according to occupancy. Once a new scene is selected the lighting will fade to the new set
of levels at a pre-determined fade rate.
Energy Saving
When dimming a lamp the energy saved is as high as 98% of the proportion of
unused energy. Because the human eye perceives light non-linearly, it is possible to reduce
light levels by over 10% before the reduction in brightness is noticed. This would lead to a
near 10% saving in energy consumption. A 50% reduction in dimming levels would save
around 40% of the energy.
Intelligent dimmers ramp or fade a lamp to a preset level. This is particularly
important when the lamp is first turned on. Incandescent lamps tend to fail at this point due
to thermal shock of the cold lamp filament. By fading the lamp to the set level, also know as
"soft start", a lamps life is extended considerably. At 10% dimming, a lamp will last twice
as long and at 50% dimming it will last 20 times as long. Voltage stabilisation, available on
more expensive systems, protects lamps against spikes and peaks in mains voltage.
Not all lamps are dimmable, some like compact fluorescent lamps, can only be
switched on or off. However, energy can still be saved even if they are turned off
automatically when not required. For example, during a bright day the lamps near a window
can be turned off where normally they would be left on. A sensor that measures daylight
provides an input value to the controller that will measure the value over time and use that
information to switch or dim circuits to per-determined levels.
Energy savings can be derived through occupancy detection. Sensors are mounted in
rooms, which detect if there is movement within the room or area. They feed that
information back to the controller, which counts a period of time that no movement has
been detected for. Each time movement is detected the count will be reset. Once movement
has not been detected for a preset period of time the lighting in that room or area can be
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either switched off or turned down to a low energy saving level. After a further period of no
movement they can be turned off altogether. In warm climates and in the summer months
when air-conditioning is used, lowering the thermal load of the lighting can also save
energy.
Security
Lighting can play an important part in security, deterring intruders whether the
property is occupied or not. Low levels of illumination can be programmed to operate at
night in certain rooms or hallways. When the house is vacated lighting levels can be
selected that copy normal usage. This can be by time clock or by selecting a vacation mode.
Dimmed or selectively switched levels of illumination will save energy and is more
effective than leaving lighting on or using simple plug in timers.
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9.DISADVANTAGES OF CIRCUIT
- A lamp consists of fine coils of wire held in place by a series of supports. When the
current flow abruptly changes the magnetism change can be stronger than when supplied
with a simple sine wave. If the dimmer has inadequate suppression the filaments will vibrate
against the support posts (this is called lamp singing). A good quality dimmer will filter the
abrupt current changing waveform that cause buzzing. This is known as EMI reduction.
Changing the lamp brand to a higher quality one may also help to reduce lamp sing.
- The normal light dimmer you buy in your local hardware center is a simple analog
based one. However, these dimmers tend to have poor suppression and accuracy. As
component values vary over time, the zero-crossing becomes inaccurate resulting in
increased electrical and audible noise. If you find that your lamps blow more often than they
should, it might be time to change your dimmer! Good quality dimmers are operated
digitally using sophisticated designs, these units generate less noise, are more reliable and
can control different lamps (low voltage, halogen etc) makes like "FUTRONIX" work like
this and are amongst the best available.
Dangerous to use because 230 v directly connected to the circuit so many
precautions can be handaled
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10.APPLICATION OF CIRCUIT
-This light dimmer circuit used for light brightness controlling purpose in the house and
other places also
-Also this circuit used for saving electricity purpose in the house and other places
-We can also control other load like fan speed , motor speed and other equipment which is
run on ac supply
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11.PRECAUTIONS
1. The soldering iron being used for soldering of semiconductors should be of low
voltage.
2. While soldering semiconductors heat sinks should be used.
3. While soldering solder should not spread over the entire circuit and solder tip should
be sharp and smooth.
4. While mounting components their values should be visible.
5. Semiconductors and other polarized components should be mounted with correct
polarity.
6. Time should be carefully observed while etching process takes place on the PCB.
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12..REFERENCES
Referances List
 www.electrokit.com
 www.red-circuit-kit.com
 http://www.talkingelectronics.com
 Two-stage reverse phase control with dimming function, Atmel
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