MINI EMERGENCY LIGHTINTEGRATED PROJECT REPORT
SUBMITTED BY:-Name of students:- University Roll No:-Sumedha
Sharma 1411981236Suryaveer Sen 1411981240Sushmita Sharma
1411981241Tanvi Thakur 1411981244SUPERVISED BY:-Tajinder Pal
SinghAsst. ProfessorECE DEPARTMENTAPRIL(2015)
CHITKARA UNIVERSITY , HIMACHAL PRADESH
CERTIFICATEI hereby certify that the work which is being
presented here in the Project Report entitledMINI EMERGENCY LIGHT ,
is an authentic record of my own work carried out during a period
from January 2015 to April 2015 (2nd semester) under the
supervision of Mr. Tajender Singh, Asst. Professor, ECE
Department.
Signature of Student(s)Name Of Students:- Signature:-
Sumedha Sharma (1411981236)
Suryaveer Sen (1411981240)
Sushmita Sharma (1411981241)
Tanvi Thakur (1411981241)
Date: 1st MAY, 2015 Place:- CHITKARA UNIV.
This is to certify that the above statement made by the
student(s) is correct to the best of myknowledge.
Signature of Supervisor
Mr. Tajender Singh , Asst professor, ECE Department.
INTRODUCTIONAn emergency light is a battery-backed lighting
device that comes on automatically when a building experiences a
power outage.Emergency Lights are standard in new commmercial and
high residential building, such as college dormitories.Most
buildingg codes require that they can be installed in older
buildings as well.
Modern emergency lighting is installed in virtually every
commercial and high occupancy residential building.The light
consists of one or more incadescents bulb or one or more high
intensity Light Emitting Diodes(LED).The emergency lighting heads
are usually either PAR 36 sealed beams or wedge base lamps.All
units have a some sort of reflector to focus and intensify the
light they produce. They can either be in the form of a plastic
cover over the fixture,or a reflector placed behind the light
source. Most individual light sources can be rotated and aimed for
where light is needed most in emergency, such as towards fire exit.
Modern fixtures usually have a text button of some sort which
temporarily overrides the unit and causes it to switch on the
lights and operate on the battery power even if the main power is
ON. Modern systems are operated usually in low voltage, 6-12
volts.This both reduces the size of the batteries required and
reduces the load on the circuit to which the emergency light is
wired.Modern fixtures include a small transformer in the base of
the fixture which steps down the voltage from main current to the
low voltage required by the lights. Batteries are commonly made of
lead- calcium, and can last for 10 years or more on continuous
charge.US fire safety codes require a minimum of 90 minutes on
battery power during the power outage alonng the path of
progress.
Emergency lighting is often referred to as egress lighting.
Emergency lights are used in commercial buildings as a safety
precaution to power outages, so that people will be able to find
out their way out of the building. Exit signs are often used in
conjunction with the emergency lighting.
In recent years , emergency lighting has started to move away
from the traditional two-head -unit with manufacturers stretching
the concept of emergency lighting to accommodate and integrate the
emergency lighting into the Architecture.
An Emergency lighting installation source may be either a
central stand by source such as a bank of lead acid batteries and
control gear/chargers supplying slave fittings throughout the
building, or may be constructed using self contained emergency
fittings which incorporate the lamp, battery , charger and control
equipment.
This is an LDR based emergency light that turns on a high watt
White LED when there is darkness in the room. It can be used as a
simple emergency lamp in the childs room to avoid the panic
situation in the event a sudden power failure.
It gives ample light in the room.
The circuit is too simple so that it can be enclosed in a small
box. A 12 volt miniature battery is used to power the circuit. Two
transistors T1 and T2 are used as electronic switches to turn on /
off the white LED. When there is sufficient light in the room, LDR
conducts so that the base of the PNP transistor T1becomes high and
it remains off. T2 also remains off since its base is grounded. In
this state, White LED remains off. When the light falling on the
LDR decreases, it cease to conduct and T1 forward bias providing
base current to T2. It then turns on and White LED switches on.
Schematic of Mini Emergency Light Circuit
White LED used in the circuit is 1 watt High bright Luxeon LED.
Since 1 watt White LED consumes around 300 milli ampere current, it
is better to switch off the lamp after few minutes to conserve
battery power.Emergency lighting systems for specific purposes do
tend to get less common as the applications become more and more
precise. This DIY details with an interesting low power consuming
emergency lighting system. It charges from the main power supply
and gets activated as soon as the mains supply is turned off.
ThisMini Emergency Lampturns on when power fails to give
coolwhite lightin the room. It uses 1 wattWhite LEDto provide
sufficient light in the room. It is an ideal emergency lamp in the
Childs study room to avoid the panic situation of sudden power
failure. The circuit and the battery pack can be enclosed in a
plug-in type adapter box.230 volt AC is reduced to low volt AC by
the step down transformer X1 and rectified by the full wave diode
bridge comprising D1 through D4. Capacitor C1 is the smoothing
capacitor to remove ripples from the rectified DC. When the mains
power is available, battery charges through R1 and D5.At the same
time, base of T1 will be high through R1 and the PNP transistor T1
remains off. When the power fails, T1 gets forward bias and
conducts. White LED connected to the collector of T1 turns on by
using the battery power. The lamp remains on till the mains power
resumes.
1 Watt White LED requires 3 volts and around 100-300 mA current
for sufficient brightness. The 4.5 volt rechargeable battery pack
used in cordless phone can be used. It is rated 4.5 V 1.5 Amps.
Brightness of the LED can be controlled using R3. If a 100 ohms
preset is used in series with R3, the brightness of LED can be
controlled as per the requirements. R3 should be 10 ohms 1 watt
resistor.
Components
ResistorsR1 100 Ohms, R2 470 Ohms, R3 10 Ohms 1 watt
CapacitorsC1 470 uF25 V
DiodesD1 D5 IN4007
TransistorT1 BD140 PNP1Watt White LED, Toggle switch, 4.5 volt
battery pack
Components Description
1.) RESISTOR :- A resistor is a passive two terminal electrical
component that implements electrical resistance as a circuit
element. Resistors act to reduce current flow, and, at the same
time, act to lower voltage levels within circuits. In electronic
circuits resistors are used to limit current flow, to adjust signal
levels bias active elements, terminate transmission lines among
other uses. High-power resistors that can dissipate many watts of
electrical power as heat may be used as part of motor controls, in
power distribution systems, or as test loads for generators. Fixed
resistors have resistances that only change slightly with
temperature, time or operating voltage. Variable resistors can be
used to adjust circuit elements (such as a volume control or a lamp
dimmer), or as sensing devices for heat, light, humidity, force, or
chemical activity.Resistors are common elements of electrical
networks and electronic circuits and are ubiquitous inelectronic
equipment. Practical resistors as discrete components can be
composed of various compounds and forms. Resistors are also
implemented within integrated circuits.The electrical function of a
resistor is specified by its resistance: common commercial
resistors are manufactured over a range of more than nineorders of
magnitude. The nominal value of the resistance will fall within a
manufacturing tolerance.
2. ) CAPACITOR :- A capacitor is originally known as a
condenser) is a passive used to store energy in an electric field.
The forms of practical capacitors vary widely, but all contain at
least two (electrical conductors plates) separated by adielectric
(i.e.insulator). The conductors can be thin films, foils or
sintered beads of metal or conductive electrolyte, etc. The
nonconducting dielectric acts to increase the capacitor's charge
capacity. A dielectric can be glass, ceramic, plastic film, air,
vacuum, paper, mica, oxide layer etc. Capacitors are widely used as
parts of electrical circuits in many common electrical devices.
Unlike aresistor, an ideal capacitor does not dissipate energy.
Instead, a capacitor stores energy in the form of an electrostatic
field between its plates.When there is a potential difference
across the conductors (e.g., when a capacitor is attached across a
battery), an electric fielddevelops across the dielectric, causing
positive charge +Q to collect on one plate and negative charge Q to
collect on the other plate. If a battery has been attached to a
capacitor for a sufficient amount of time, no current can flow
through the capacitor. However, if a time-varying voltage is
applied across the leads of the capacitor, displacement current can
flow.
3.) DIODE :- In electronics, a diode is a two-terminal
electronic component with asymmetric conductance; it has low
(ideally zero) resistance to current in one direction, and high
(ideally infinite) resistance in the other. A semiconductor diode,
the most common type today, is a crystalline piece of semiconductor
material with a pn junction connected to two electrical terminals.A
vacuum tube diode has two electrodes, a plate(anode) and a heated
cathode. Semiconductor diodes were the first semiconductor
electronic devices. The discovery of crystals' rectifyingabilities
was made by German physicist Ferdinand Braun in 1874. The first
semiconductor diodes, called cat's whisker diodes, developed around
1906, were made of mineral crystals such as galena. Today, most
diodes are made of silicon, but other semiconductors such
asselenium or germanium are sometimes used.
4.) TRANSISTOR :- A transistor is a semiconductor device which
is used to amplify and switch electronic signals and electrical
power. It is composed of semiconductor material with at least three
terminals for connection to an external circuit. A voltage or
current applied to one pair of the transistor's terminals changes
the current through another pair of terminals. Because the
controlled (output)powercan be higher than the controlling (input)
power, a transistor can amplify a signal. Today, some transistors
are packaged individually, but many more are found embedded in
integrated circuits.The transistor is the fundamental building
block of modern electronic devices, and is ubiquitous in modern
electronic systems. Following its development in 1947 by American
physicists John Bardeen, Walter Brattain, and William Shockley, the
transistor revolutionized the field of electronics, and paved the
way for smaller and cheaper radios, calculators, and computers,
among other things.
INTRODUCTION TO LEDLEDs form an inevitable part in the modern
electronics as simple indicators to optical communication devices.
Light Emitting Diodes exploit the property of the p-n junction to
emit photons when it is forward biased. LEDs are specially made
diodes to emit light when a potential is applied to its anode and
cathode.The history of LED date backs to 1907 when Captain Henry
Joseph observed the property of electro-luminescence in Silicon
Carbide. The first LED was designed in 1962. It was developed by
Holonyak worked at General Electric (GE). It was a GaAsP device.
The first commercial version of LED came in
What makes LED ideal?
LEDs are extensively used in electronic circuits because of its
advantages over bulbs. Some important features that make LED ideal
in electronic circuits are:LEDs are encapsulated in plastic or
resin cases so that they can withstand mechanical shocks.
Unlike bulbs, LEDs do not generate heat and power loss through
heating is practically nil.
LEDs require very low current and voltage typically 20
milliampere current and 1.8 volts. So these are ideal in battery
operated circuits.
What is inside an LED?
Inside the casing of an LED, there are two terminal posts
connected by asmall chipmade of Gallium compound. This material
exhibits the property of photon emission when the p-n junction is
forward biased. Different colours are produced by dopping the base
material with other substances.
LED technology follow some physicsBrightness is an important
aspect of LED. Human eye has maximum sensitivity to light near 550
nm region of yellow green part of the visible spectrum. That is why
a Green LED appears brighter than a Red LED even though both use
same current. The important parameters of LED responsible for its
performance are:Luminous flux
Indicates the light energy radiating from the LED. It is measured
in terms of Lumen (lm) or Milli lumen (mlm)
Luminous intensity
The luminous flux covering a large area is the luminous intensity.
It is measured as Candela (cd) or milli candela (mcd) Brightness of
LED is directly related to its luminous intensity.
Luminous efficacy
It is the emitted light energy relative to the input power. It is
measured in terms of lumen per watt (lm w).
Forward current, forward voltage, Viewing angle and Speed of
response are the factors affecting the brightness and performance
of LEDs. Forward current ( IF ) is the current flowing through the
LED when it is forward biased and it should be restricted to 10 to
30 milli amperes other wise LED will be destroyed.Viewing angle is
the off axis angle at which the luminous intensity fall to half its
axial value. This is why LED shows more brightness in full on
condition. High bright LEDs have narrow viewing angle so that light
is focused into a beam. Forward voltage (Vf) is the voltage drop
across the LED when it conducts. The forward voltage drop range
from 1.8 V to 2.6 Volts in ordinary LEDs but in Blue and White it
will go up to 5 volts. Speed of response represents how fast an LED
is switched on and off. This is an important factor if LEDs are
used in communication systems.Light Emitting Diode Types
Is LED requires a Ballast resistor?LED is always connected to
the power supply through a series resistor. This resistor is called
as Ballast resistor which protects LED from damage due to excess
current. It regulates the forward current to the LED to a safer
limit and protects it from burning.Value of the resistor determines
the forward current and hence the brightness of LED. The simple
equationVs Vf / Ifis used to select the resistor value. Vs
represent input voltage of the circuit, Vf the forward voltage drop
of LED and If, the allowable current through the LED. The resulting
value will be in Ohms. It is better to restrict the current to a
safer limit of 20 mA.The table given below shows the forward
voltage drop of common LEDs.
RedOrangeYellowGreenBlueWhite
1.8 V2 V2.1 V2.2 V3.6 V3.6 V
A typical LED can pass 30 40 mA safe current through it. Normal
current to give sufficient brightness to a standard Red LED is 20
mA. But this may be 40 mA for Blue and White LEDs. Current limiting
ballast resistor protects LED from excess current that is flowing
through it. The value of the ballast resistor should be carefully
selected to prevent damage to LED and also to get sufficient
brightness at 20 mA current. The following equation explains how a
ballast resistor is selected.R = V / IWhere R is the value of
resistor in ohms, V is the input voltage to the circuit and I is
the allowable current through LED in Amps. For a typical Red LED,
the forward voltage drop is 1.8 volts. So if the supply voltage is
12 V (Vs), voltage drop across the LED is 1.8 V ( Vf ) and the
allowable current is 20 mA ( If ) then the value of the ballast
resistor will beVs Vf / If = 12 1.8 / 20 mA = 10.2 / 0.02 A = 510
Ohms.But 510 ohms resistor is not usually available. Therefore 470
ohms resistor can be used even though the current through the LED
slightly increases. But is advisable to use 1 K resistor to
increase the life of the LED even though there will be a slight
reduction in the brightness.Following is a ready reckoner for
selecting limiting resistor for various versions of LEDs at
different voltages.VoltageRedOrangeYellowGreenBlueWhite
12 V470 470 470 470 390 390
9 V330 330 330 330 270 270
6 V180 180 180 180 120 120
5 V180 150 150 150 68 68
3 V56 47 47 33 --
Added coloursAn LED that can give different colours is useful in
some applications. For example, an LED could indicate all systems
OK when it becomes Green and faulty if it becomes Red. LEDs that
can produce two colours are called Bicolour LEDs.A bicolour LED
encloses two LEDs(usually Red and Green) in a common package. The
two chips are mounted on two terminal posts so that the anode of
one LED forms the cathode of the other. Bicolour LED gives Red
colour if current passes in one direction and turns Green when the
direction of current is reversed.Tricolour and multicolour LEDsare
also available which have two or more chips enclosed in a common
package. The Tricolour LED has two anodes for red and green chips
and a common cathode. So it emits red and green colours depending
on the anode that carries current. If both the anodes are connected
to positive, both the LEDs lights and yellow colour is produced.
Common anode and separate cathode type LEDs are also
available.Bicolour LED glows in different coloursranging from green
through yellow orange and red based on the current flowing through
their anodes by selecting suitable series resistor to restrict
anode current. Multicolor LED contains more than two chips-usually
red, green and blue chips- within a single package. Flashing type
multicolor LEDs are now available with two leads. This gives a
rainbow colour display which is highly attractive.Colourful Light
Emitting Diodes
Infra Red diode The Source of Invisible lightIR diodes are
widely used in remote control applications. Infrared is actually a
normal light with a particular colour which is not sensitive to
human eye because its wave length is 950 nm, below the visible
spectrum. Many sources like sun, bulbs, even the human body emit
infra red rays. So it is necessary to modulate the emission from IR
diode to use it in electronic application to prevent false
triggering. Modulation makes the signal from IR LED stand out above
the noise. Infra red diodes have a package that is opaque to
visible light but transparent to infra red. IR LEDs are extensively
used in remote control systems.Photodiode It can see lightThe
Photodiode generates current when its p-n junction receives photons
from visible or infrared light. The basic operation of a photo
diode relies on the absorption of photons in a semiconductor
material. The photo-generated carriers are separated by an applied
electric field, and the resulting photocurrent is proportional to
the incident light. The velocity at which the carriers move in the
depletion region is related to the strength of the electric field
across the region and the mobility of carriers.
A photon that is absorbed by the semiconductor in the depletion
region will cause the formation of an electron- hole. The hole and
electron will be transported by the electric field to the edges of
the depletion region. Once the carriers leave the depletion region
they travel to the terminals of the photo diode to form a photo
current flowing in the external circuitry. In most circuits the
photo diode is reverse biased, so that charge is carried by
extrinsic charge carriers. The response time of a photo diode is
typically 250 nano seconds.LASER Diode Pointing a beam
A laser diode is similar to an ordinary transparent LED but
produces Laserwith high intensity. In the laser beam a number of
atoms vibrate in such a fashion that all the emitted radiation of a
single wave length is in phase with each other. Laser light is
monochromatic and passes in the form of a narrow pencil beam. The
beam of typical laser diode is 4 mm x 0.6 mm which widens only to
120 mm at a distance of 15 m.Laser diode can be switched on and off
at higher frequencies even as high as 1 GHz. So it is highly useful
in telecommunication systems. Since the laser generates heat on
hitting the body tissues, it is used in surgery to heal lesions in
highly sensitive parts like retina, brain etc. Laser diodes form
important components in CD players to retrieve datas recorded in
compact discs.
How does the LDR (photoresistor) works
The resistance is very high in darkness, almost high as 1M but
when there is light that falls on the LDR, the resistance is
falling down to a few K (10-20k @ 10 lux, 2-4kOmega; @ 100 lux)
depending on the model.Light dependent resistors come in different
shapes and colors.LDRs are very useful in many electronic circuits,
especially in alarms, switching devices, clocks, street lights and
more. There are some audio application uses such as audio limiters
or compressors. It is used to turn ON or OFF a device according to
the ambient light.
This mini emergency lighting are used to automatically give
lighting when ac line power go out.
Which they consist of one lamps, a battery, and a low voltage
sensor.
This projects design take advantaged of simple circuit techniques
and cheap.Special feature:
1. Small-sized : output with 2.4V 5W lamp and 3V battery.
2. No transformer so Lightweight and easy to build.
3. No relay so be Silent and small.
4. etc.
How it works.
To begin with we use 4-5V dc power supply that without
transformer. Next, the AC 220V input to passed trough R1 to cut
current down and D1 to rectifier AC to DC in half wave type. Then,
the dc pulse or fluctuating signal is smoothed with C1-capacitor.
Which has voltage dropped across of 4.5VdcAnd then SW1 is used to
turn on-off the next circuit as sensor,control,battery charger and
lamp circuit. First of all, in normally power the lamp go out not
light since current pass to R4 to base of Q1 cause it is bias so
high current flow through D2-diode,R5-resistor to collector-emitter
of Q1. Thus not has current bias to base of Q2,Q3 ( Darlington
transistor) cause they not conduct current, so not has current pass
Lamp, it so not light.
And later the power AC line go out, So not has current through
S1, and then current from 3V battery not current through D2 be due
to diode not allow current as , is a one-way street. It will not
work if you put it in backward. And making Q1 does not work.But
this battery current will flow to R5 through base Q2,Q3 they so is
bias current is result of high current flow to Lamp glow light up
at once.Friends can use Nicad Battery or NiMH battery the size is
1.2V x 2 give the light has just enough. This circuit can charge
automatically batterys.
COMPONENTS Q1,Q2,Q3______C9014,C9013___1A 50V__NPN
transistor
D1____________1N4148 75V 150mA Diodes
D2_______________1N4004 400V 1A Diodes
L1_______________2.4V 5W Lamp
L2_______________Neon Lamp
S1______________Slider Switch
C1______________ 47F 50V Electrolytic Capacitors
R1______________220K___1/2W resistors
R2______________33K___1W resistors
R3______________10K___1/2W resistors
R4______________1K____1/2W resistors
R5______________15K___1/2W resistors
B1______________3V battery (AA 1.2V)
Automatic LED Emergency Light Circuit
This is the simple and cost effective automatic emergency light
circuit with light sensing. This system charges from main supply
and gets activated when main supply is turned OFF. This emergency
lamp will work for more than 8 hours.When power supply is turned
OFF, the circuit senses the day light and according to the light it
turns on the LEDs. If the light is present even though power fails
the circuit turns OFF the LEDs. Here LDR (Light Dependent Resistor)
is used to sense the light.Automatic Emergency Light Circuit
Principle:When power supply is available, battery charges through
the diode D2. At the same time white LEDs will glow based on the
light conditions. When power fails, the white LEDs which are
connected MOSFET will glow based on the light condition till the
battery shuts down.When LDR (Light Dependent Resistor) is in light,
the resistance of LDR is very low. As a result base of the
transistor Q1 becomes high. As a result white LEDs which are
connected to MOSFET turns OFF.When the circuit is in dark, the
resistance of LDR is in order of mega ohms. Now the base of the
transistor becomes low, as a result transistor Q1 switches the
white LEDs to ON state.Automatic Emergency Light Circuit
Diagram:
Automatic Emergency LED Lights Circuit Diagram
Circuit Components:9V step down transformer
Diode bridge 1A
7808 voltage regulator
Light dependent resistor 2M ohm
IRF540 MOSFET transistor
BC548 PNP transistor
DC battery 6V, 4.5Ah
Pot 10k
4 high bright LED, s 3v@15mA
red led
1n4007 diodes 1
electrolytic capacitor 470uF
ceramic capacitor 0.1uF
1k resistors 210 ohm resistors
Automatic Emergency Light Circuit Design:Here step down
transformer is used to reduce input AC voltage to low AC voltage.
Diode Bridge is used to convert input AC voltage to pulsating DC.
Here capacitor C1 is used to remove the ripples from the rectified
DC. LED D1 indicates the main supply and resistor R1 is used to
protect the LED D1 from high voltage.In this circuit transistor Q1
switches states white LEDs based on the supply as well as light
conditions. The output of LDR is connected to the base of
transistor Q1 to switch the transistor based on the light
conditions. The collector terminal of the transistor Q1 is
connected is connected to the gate of MOSFET to switch white LEDs
according to the conditions.In this circuit voltage regulator 7808
is used to regulate voltage and current. This IC has built in
current limiting circuit. The output of this voltage regulator is
positive 8V.2 white LEDs are connected in series, so two white LEDs
glow with the current that is required for a single LED. As a
result energy is saved. For a white LED we need a minimum of 3.6V
and maximum of 20mA current.How to Operate Automatic Emergency
Light Circuit?Give the connections according to the circuit
diagram.
While giving the connections, take care in such a way that there
is no common connection between AC and DC supplies.
Apply the main supply to the circuit, now you can observe that
LEDs will not glow and battery will charge.
Remove the AC supply and place circuit in dark, now LEDs will
glow.
If you place the circuit in light, then LEDs turns OFF.
PHOTORESISTOR OR LDRA photoresistor or light-dependent resistor
(LDR) or photocell is a light-controlled variable resistor. The
resistance of a photoresistor decreases with increasing incident
light intensity; in other words, it exhibits photoconductivity. A
photoresistor can be applied in light-sensitive detector circuits,
and light- and dark-activated switching circuits.A photoresistor is
made of a high resistance semiconductor. In the dark, a
photoresistor can have a resistance as high as a few megohms (M),
while in the light, a photoresistor can have a resistance as low as
a few hundred ohms. If incident light on a photoresistor exceeds a
certain frequency, photons absorbed by the semiconductor give bound
electrons enough energy to jump into the conduction band. The
resulting free electrons (and their hole partners) conduct
electricity, thereby lowering resistance. The resistance range and
sensitivity of a photoresistor can substantially differ among
dissimilar devices. Moreover, unique photoresistors may react
substantially differently to photons within certain wavelength
bands.
A photoelectric device can be either intrinsic or extrinsic. An
intrinsic semiconductor has its own charge carriers and is not an
efficient semiconductor, for example, silicon. In intrinsic devices
the only available electrons are in the valence band, and hence the
photon must have enough energy to excite the electron across the
entire bandgap. Extrinsic devices have impurities, also called
dopants, added whose ground state energy is closer to the
conduction band; since the electrons do not have as far to jump,
lower energy photons (that is, longer wavelengths and lower
frequencies) are sufficient to trigger the device. If a sample of
silicon has some of its atoms replaced by phosphorus atoms
(impurities), there will be extra electrons available for
conduction. This is an example of an extrinsic semiconductor.
DESIGN CONSIDERATION OF LDRPhotoresistors are less
light-sensitive devices than photodiodes or phototransistors: the
two latter components are true semiconductor devices, while a
photoresistor is a passive component and does not have a
PN-junction. The photoresistivity of any photoresistor may vary
widely depending on ambient temperature, making them unsuitable for
applications requiring precise measurement of or sensitivity to
light.
Photoresistors also exhibit a certain degree of latency between
exposure to light and the subsequent decrease in resistance,
usually around 10 milliseconds. The lag time when going from lit to
dark environments is even greater, often as long as one second.
This property makes them unsuitable for sensing rapidly flashing
lights, but is sometimes used to smooth the response of audio
signal compression.
APPLICATIONS OF LDRPhotoresistors come in many types.
Inexpensive cadmium sulphide cells can be found in many consumer
items such as camera light meters, street lights, clock radios,
alarm devices, night lights, outdoor clocks, solar street lamps and
solar road studs, etc.They are also used in some dynamic
compressors together with a small incandescent or neon lamp, or
light-emitting diode to control gain reduction. A common usage of
this application can be found in many guitar amplifiers that
incorporate an onboard tremolo effect, as the oscillating light
patterns control the level of signal running through the amp
circuit.The use of CdS and CdSe photoresistors is severely
restricted in Europe due to the RoHS ban on cadmium.Lead sulphide
(PbS) and indium antimonid (InSb) LDRs (light-dependent resistors)
are used for the mid-infrared spectral region.Ge:Cuphotoconductors
are among the best far-infrared detectors available, and are used
for infrared astronomy and infrared spectroscopy.
READING A PHOTORESISTOR USING REFLEX
OVERVIEW
Photoresistors are used in many applications because they either
increase or decrease in resistance depending on the amount of
light. A common application for photoresistors is the triggering of
an event when the light passes a certain point.This example
demonstrates the use of a Photoresistor to toggle the User
LED.BrainStem application examples require the BrainStem Support
package.
THE SETUP
There are several hardware components needed for this
example:40-Pin EtherStem 1.0 Module
40-Pin Breakout Board
Ethernet Cable
Photoresistor
Resistor
PHOTORESISTOR
A photoresistor is a sensor whose resistance varies with light
intensity Most photoresistors decrease in resistance as the light
intensity increases. Typically, the resistance must be converted to
a voltage so that an A2D converter can measure it.A voltage divider
circuit is the easiest way to convert a resistance to a voltage.A
voltage divider is just two resistors in series connected between a
voltage supply and ground. If R1 is connected to the voltage supply
and R2 is connected to ground then the voltage at the junction
between the two resistors is:
If R1 is the photoresistor, the voltage will increase with
increasing light intensity.If R2 is the photoresistor, the voltage
will decrease with increasing light intensity.
CONFIGURATION
Connect the BrainStem to the development board with a power
supply connected and the Ethernet cable connecting the Stem to the
host computer. Connect the Photoresistor to the 3.3V output and to
the A2D pin [A2D0 for this example]. Connect a resistor in series
between the Photoresistor and ground.
APPLICATION OF LDR IN STREET LIGHT There have been lot of
problems in street lights. Major problem in some places is every
evening a person has to come and switch ON the street light and it
should be again switched off in morning. Yes, this may not be the
situation in everywhere but exists in many places.So this problem
can be overcome by using a simple circuit. Below shown circuit will
be automatically switched ON and OFF during night and morning times
respectively.
Automatic light schematic
In above circuit R1 can be used to adjust the sensitivity. And
the working of the circuit is very simple. The LDR will have very
low resistance during day time so the transistor Q1 will be in OFF
condition. And during night time the resistance will be very high
so automatically the transistor Q1 will be ON.The Q1 is PNP
transistor and the emitter of Q1 is given to base of Q2. So the Q2
transistor will be ON only if the transistor Q1 is ON. The TRIAC is
used in the circuit to make is circuit complete. As the TRIAC will
allow voltage to pass from either directions only when there is a
certain threshold voltage in gate terminal. And the gate of TRIAC
is controlled by transistor Q2.So totally the lamp will be ON
during night time and will be again switched off during day light.
To change the sensitivity of the circuit to light adjust R2.If you
have any doubts, do not hesitate to comment below. We will come to
you with an appropriate solution.
LIGHT ALARM CIRCUIT WITH LDR
This musical light alarm circuit is very simple, uses only 7
components, a LDR and a 3.6 V battery or 3 x 1.2 volts rechargeable
batteries. The well-known UM66 is used as the sound generator and
will give a pleasent wake up alarm.As you probably know the LDR is
a light dependent resistor. Normally the resistance of an LDR is
very high, sometimes as high as 1M, but when they are illuminated
with light resistance drops dramatically. In the circuit adjust the
220K preset to the desired sensitivity, meaning adjusting the
threshold point where the alarm start singing.When there is light
on the light dependent resistor the T1 transistor will start
conducting and powers the UM66 musical integrated circuit. The
produced musical note will be amplified by transistor T2 and fed
into the 8 speaker.On the UM66 IC are different numbers, each
number giving a different musical note (in this example we use
UM66T). You may use 2 x 1.5V batteries but 3 x 1.2V NiCad or NiMH
are better because you can recharge them.Light alarm electronic
circuit schematic
Working Principle of LDRA light dependent resistor works on the
principle of photo conductivity. Photo conductivity is an optical
phenomenon in which the materials conductivity (Hence resistivity)
reduces when light is absorbed by the material.When light falls
i.e. when the photons fall on the device, the electrons in the
valence band of thesemiconductor material are excited to the
conduction band. These photons in the incident light should have
energy greater than the band gap of the semiconductormaterial to
make the electrons jump from the valence band to the conduction
band. Hence when light having enough energy is incident on the
device more & more electrons are excited to the conduction band
which results in large number of charge carriers. The result of
this process is more and more current starts flowing and hence it
is said that theresistance of the device has decreased.This is the
most common working principle of LDRCharacteristics of LDRLDRs are
light dependent devices whose resistance decreases when light falls
on them and increases in the dark. When a light dependent resistor
is kept in dark, its resistance is very high. This resistance is
called as dark resistance. It can be as high as 1012 . And if the
device is allowed to absorb light its resistance will decrease
drastically. If a constant voltage is applied to it and intensity
of light is increased the current starts increasing. Figure below
shows resistancevs. illumination curve for a particular
LDR.Photocells or LDRs are non linear devices. There sensitivity
varies with the wavelength of light incident on them. Some
photocells might not at all response to a certain range of
wavelengths. Based on the material used different cells have
different spectral response curves.When light is incident on a
photocell it usually takes about 8 to 12ms for the change in
resistance to take place, while it takes seconds for the resistance
to rise back again to its initial value after removal of light.
This phenomenon is called as resistance recovery rate. This
property is used in audio compressors.
Also LDRs are less sensitive than photo diodes and photo
transistor. (A photo diode and a photocell (LDR) are not the same,
a photo-diode is a p-n junction semiconductor device that converts
light to electricity, whereas a photocell is a passive device,
there is no p-n junction in this nor it converts light to
electricity).Types of Light Dependent Resistors:Based on the
materials used they are classified as:-
i) Intrinsic photo resistors (Undoped semiconductor): These are
pure semiconductormaterials such as silicon or germanium. Electrons
get excited from valance band to conduction band when photons of
enough energy falls on it and number charge carriers increases.ii)
Extrinsic photo resistors: These are semiconductor materials doped
with impurities which are called as dopants. Theses dopants create
new energy bands above the valence band which are filled with
electrons. Hence this reduces the band gap and less energy is
required in exciting them. Extrinsic photo resistors are generally
used for long wavelengths.Construction of a PhotocellThe structure
of a light dependent resistor consists of a light sensitive
material which is deposited on an insulating substrate such as
ceramic. The material is deposited in zigzag pattern in order to
obtain the desiredresistance& power rating. This zigzag area
separates the metal deposited areas into two regions. Then the
ohmic contacts are made on the either sides of the area.
Theresistances of these contacts should be as less as possible to
make sure that theresistancemainly changes due to the effect of
light only. Materials normally used are cadmium sulphide, cadmium
selenide, indium antimonide and cadmium sulphonide. The use of lead
and cadmium is avoided as they are harmful to the environment.
IMAGES FOR MINI EMERGENCY LIGHT
VOLTAGE REGULATORA voltage regulator is designed to
automatically maintain a constant voltage level. A voltage
regulator may be a simple "feed-forward" design or may include
negative feedback control loops. It may use an electromechanical
mechanism, or electronic components. Depending on the design, it
may be used to regulate one or more AC or DC voltages.Electronic
voltage regulators are found in devices such as computer power
supplies where they stabilize the DC voltages used by the processor
and other elements. In automobile alternators and central power
station generator plants, voltage regulators control the output of
the plant. In an electric power distribution system, voltage
regulators may be installed at a substation or along distribution
lines so that all customers receive steady voltage independent of
how much power is drawn from the line.
Automatic voltage regulator
Voltage regulator for generators.To control the output of
generators (as seen in ships and power stations, or on oil rigs,
greenhouses and emergency power systems) automatic voltage
regulators are used. This is an active system. While the basic
principle is the same, the system itself is more complex. An
automatic voltage regulator (or AVR for short) consist of several
components such as diodes, capacitors, resistors and potentiometers
or even microcontrollers, all placed on a circuit board. This is
then mounted near the generator and connected with several wires to
measure and adjust the generator.How an AVR works: In the first
place the AVR monitors the output voltage and controls the input
voltage for the exciter of the generator. By increasing or
decreasing the generator control voltage, the output voltage of the
generator increases or decreases accordingly. The AVR calculates
how much voltage has to be sent to the exciter numerous times a
second, therefore stabilizing the output voltage to a predetermined
setpoint. When two or more generators are powering the same system
(parallel operation) the AVR receives information from more
generators to match all output.ADVANTAGES OF AUTOMATIC EMERGENCY
LIGHT OVER CONVENTIONAL EMERGENCY LIGHT
The simple automatic emergency light has the following
advantages over the conventional emergency light :-
1.) The charging circuit stops automatically when the battery is
fully charged. So U can leave the emergency light connected to AC
mains overnight without any fear.
2.) Emergency Light automatically turns ON when MAINS fail. So u
do not need a torch to locate it.
3.) When MAINS power is available,emergency light is
automatically turns Off.
CONCLUSION AND FUTURE SCOPE
CONCLUSION:
Today, in industries and as well as in household applications an
emergency light is employed where there is frequent non uniform
voltage distribution occurs. Many types of emergency lights from
rechargeable torches to systems like generators are available in
market. All of them require a switch to operate them when frequent
power failure occurs. The present one deals with a model which
senses the mains as well as daylight to switch on the emergency
light. This emergency light holds requirements of domestic purposes
also. There is no need to search the switch in the dark as it
switches on /off automatically.
There are some special features in this project which are as
follows:When mains power is available, it senses and switches off
the lamp instantly. This may be a common feature in any of the
emergency power systems.
It incorporates an opto-eye which senses the ambient light and when
the ambient light reaches a present low level when there is no
power, it switches on the emergency light automatically. The
switching is instantaneous.
In most of the emergency lights there is a drawback. The discharge
level of the battery is not being controlled to a safe level. The
batteries get discharged completely and lose their life rapidly.
This is a very serious complaint from the users. In this one,
cut-off is provided at predefined manufacturers minimum discharge
level which gives the specified life of the battery.
FUTURE SCOPE
MINI EMERGENCY LIGHTINTEGRATED PROJECT REPORT
SUBMITTED BY:-Name of students:- University Roll No:-Sumedha
Sharma 1411981236Suryaveer Sen 1411981240Sushmita Sharma
1411981241Tanvi Thakur 1411981244SUPERVISED BY:-Tajender SinghAsst.
ProfessorECE DEPARTMENTAPRIL(2015)
CHITKARA UNIVERSITY , HIMACHAL PRADESH
CERTIFICATEI hereby certify that the work which is being
presented here in the Project Report entitledMINI EMERGENCY LIGHT ,
is an authentic record of my own work carried out during a period
from January 2015 to April 2015 (2nd semester) under the
supervision of Mr. Tajender Singh, Asst. Professor, ECE
Department.
Signature of Student(s)Name Of Students:- Signature:-
Sumedha Sharma (1411981236)
Suryaveer Sen (1411981240)
Sushmita Sharma (1411981241)
Tanvi Thakur (1411981241)
Date: 1st MAY, 2015 Place:- CHITKARA UNIV.
This is to certify that the above statement made by the
student(s) is correct to the best of myknowledge.
Signature of Supervisor
Mr. Tajender Singh , Asst professor, ECE Department.
REFERENCES:
Websites:
www.google.com www.wikipedia.org www.datasheetcatalog.com
Text books:
Linear and Digital circuit IC applications by Roy Choudary
Electronic devices and circuits by Jocab Milliman .
