Mini emergency-light
ERPunitJain
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Dec 13, 2015
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About This Presentation
MINI EMERGENY LIGHT
Slide Content
MINI EMERGENCY LIGHT
INTEGRATED PROJECT REPORT
SUBMITTED BY:-
Name of students:- University Roll No:-
Sumedha Sharma 1411981236
Suryaveer Sen 1411981240
Sushmita Sharma 1411981241
Tanvi Thakur 1411981244
SUPERVISED BY:-
Tajinder Pal Singh
Asst. Professor
ECE DEPARTMENT
APRIL(2015)
CHITKARA UNIVERSITY , HIMACHAL PRADESH
1
INTEGRATED PROJECT REPORT
SUBMITTED BY:-
Name of students:- University Roll No:-
Sumedha Sharma 1411981236
Suryaveer Sen 1411981240
Sushmita Sharma 1411981241
Tanvi Thakur 1411981244
SUPERVISED BY:-
Tajinder Pal Singh
Asst. Professor
ECE DEPARTMENT
APRIL(2015)
CHITKARA UNIVERSITY , HIMACHAL PRADESH
1
CERTIFICATE
I hereby certify that the work which is being presented here in the Project Report entitled
MINI 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: 1
st
MAY, 2015 Place:- CHITKARA UNIV.
This is to certify that the above statement made by the student(s) is correct to the best of my
knowledge.
Signature of Supervisor
Mr. Tajender Singh , Asst professor, ECE Department.
2
I hereby certify that the work which is being presented here in the Project Report entitled
MINI 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: 1
st
MAY, 2015 Place:- CHITKARA UNIV.
This is to certify that the above statement made by the student(s) is correct to the best of my
knowledge.
Signature of Supervisor
Mr. Tajender Singh , Asst professor, ECE Department.
2
3
INTRODUCTION
An 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
4
An 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
4
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 child’s room to avoid the panic situation in
the event a sudden power failure.
It gives ample light in the room.
5
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 child’s room to avoid the panic situation in
the event a sudden power failure.
It gives ample light in the room.
5
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.
This Mini Emergency Lamp turns on when power fails to give cool white light in the room. It uses 1
watt White LED to provide sufficient light in the room. It is an ideal emergency lamp in the Child’s
study room to avoid the panic situation of sudden power failure. The circuit and the battery pack can be
6
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.
This Mini Emergency Lamp turns on when power fails to give cool white light in the room. It uses 1
watt White LED to provide sufficient light in the room. It is an ideal emergency lamp in the Child’s
study room to avoid the panic situation of sudden power failure. The circuit and the battery pack can be
6
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
Resistors
R1 100 Ohms, R2 470 Ohms, R3 10 Ohms 1 watt
Capacitors
C1 470 uF25 V
Diodes
D1 – D5 IN4007
Transistor
T1 BD140 PNP
1Watt 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
7
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
Resistors
R1 100 Ohms, R2 470 Ohms, R3 10 Ohms 1 watt
Capacitors
C1 470 uF25 V
Diodes
D1 – D5 IN4007
Transistor
T1 BD140 PNP
1Watt 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
7
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 circuit s and are ubiquitous
in electronic 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 nine orders 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.insu lator ). 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.
8
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 circuit s and are ubiquitous
in electronic 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 nine orders 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.insu lator ). 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.
8
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 conduct ance ; 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 p–n 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
9
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 conduct ance ; 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 p–n 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
9
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) power can 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
10
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) power can 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
10
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 LED
LEDs 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.
11
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 LED
LEDs 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.
11
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 a small 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 physics
Brightness 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
12
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 a small 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 physics
Brightness 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
12
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
equation Vs – Vf / If is 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.
13
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
equation Vs – Vf / If is 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.
13
Red Orange
1.8 V 2 V 2.1 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 / I
Where 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 be
Vs – 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.
Voltage Red
12 V 470 Ω 470 Ω
9 V 330 Ω 330 Ω
6 V 180 Ω 180 Ω
5 V 180 Ω 150 Ω
3 V 56 Ω 47 Ω
Added colours
An 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 LEDs are 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 colours ranging 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
14
1.8 V 2 V 2.1 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 / I
Where 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 be
Vs – 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.
Voltage Red
12 V 470 Ω 470 Ω
9 V 330 Ω 330 Ω
6 V 180 Ω 180 Ω
5 V 180 Ω 150 Ω
3 V 56 Ω 47 Ω
Added colours
An 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 LEDs are 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 colours ranging 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
14
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 light
IR 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
15
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 light
IR 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
15
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 light
The 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 1MΩ but when there is light that falls on the
LDR, the resistance is falling down to a few KΩ (10-20kΩ @ 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.
16
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 light
The 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 1MΩ but when there is light that falls on the
LDR, the resistance is falling down to a few KΩ (10-20kΩ @ 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.
16
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 4.5Vdc
And 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.
17
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 4.5Vdc
And 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.
17
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
18
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
18
L1_______________2.4V 5W Lamp
L2_______________Neon Lamp
S1______________Slider Switch
C1______________ 47µF 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 LED’s. 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 LED’s
will glow based on the light conditions. When power fails, the white LED’s 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 LED’s 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 LED’s to ON state.
Automatic Emergency Light Circuit Diagram:
19
L2_______________Neon Lamp
S1______________Slider Switch
C1______________ 47µF 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 LED’s. 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 LED’s
will glow based on the light conditions. When power fails, the white LED’s 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 LED’s 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 LED’s to ON state.
Automatic Emergency Light Circuit Diagram:
19
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 LED’s based on the supply as well as light conditions.
20
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 LED’s based on the supply as well as light conditions.
20
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 LED’s 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 LED’s are connected in series, so two white LED’s 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?
1.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.
2.Apply the main supply to the circuit, now you can observe that LED’s will not glow and
battery will charge.
3.Remove the AC supply and place circuit in dark, now LED’s will glow.
4.If you place the circuit in light, then LED’s turns OFF.
PHOTORESISTOR OR LDR
A 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 (MΩ), 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
21
conditions. The collector terminal of the transistor Q1 is connected is connected to the gate of
MOSFET to switch white LED’s 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 LED’s are connected in series, so two white LED’s 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?
1.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.
2.Apply the main supply to the circuit, now you can observe that LED’s will not glow and
battery will charge.
3.Remove the AC supply and place circuit in dark, now LED’s will glow.
4.If you place the circuit in light, then LED’s turns OFF.
PHOTORESISTOR OR LDR
A 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 (MΩ), 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
21
wavelength bands.
A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own
charge carrier s 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 LDR
Photoresistors are less light-sensitive devices than photodiod es 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 LDR
Photoresistors 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.
22
A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own
charge carrier s 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 LDR
Photoresistors are less light-sensitive devices than photodiod es 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 LDR
Photoresistors 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.
22
READING A PHOTORESISTOR USING REFLEX
OVERVIEW
23
OVERVIEW
23
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.
24
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.
24
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
25
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
25
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 1MΩ, but when they are illuminated with light resistance drops
dramatically. In the circuit adjust the 220KΩ 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
26
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 1MΩ, but when they are illuminated with light resistance drops
dramatically. In the circuit adjust the 220KΩ 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
26
fed into the 8Ω 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 LDR
A 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
the semiconductor 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
27
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 LDR
A 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
the semiconductor 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
27
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 LDR
Characteristics of LDR
LDR’s 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 Ω. 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 LDR’s 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 LDR’s 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
28
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 LDR
Characteristics of LDR
LDR’s 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 Ω. 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 LDR’s 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 LDR’s 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
28
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 Photocell
The 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
desired resistance & 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. The resistances of these
contacts should be as less as possible to make sure that the resistance mainly 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
29
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 Photocell
The 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
desired resistance & 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. The resistances of these
contacts should be as less as possible to make sure that the resistance mainly 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
29
VOLTAGE REGULATOR
A 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
30
A 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
30
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.
31
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.
31
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.
32
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.
32
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
33
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
33
MINI EMERGENCY LIGHT
INTEGRATED PROJECT REPORT
SUBMITTED BY:-
Name of students:- University Roll No:-
Sumedha Sharma 1411981236
Suryaveer Sen 1411981240
Sushmita Sharma 1411981241
Tanvi Thakur 1411981244
SUPERVISED BY:-
34
INTEGRATED PROJECT REPORT
SUBMITTED BY:-
Name of students:- University Roll No:-
Sumedha Sharma 1411981236
Suryaveer Sen 1411981240
Sushmita Sharma 1411981241
Tanvi Thakur 1411981244
SUPERVISED BY:-
34
Tajender Singh
Asst. Professor
ECE DEPARTMENT
APRIL(2015)
CHITKARA UNIVERSITY , HIMACHAL PRADESH
CERTIFICATE
I hereby certify that the work which is being presented here in the Project Report entitled
MINI 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: 1
st
MAY, 2015 Place:- CHITKARA UNIV.
This is to certify that the above statement made by the student(s) is correct to the best of my
knowledge.
Signature of Supervisor
Mr. Tajender Singh , Asst professor, ECE Department.
35
Asst. Professor
ECE DEPARTMENT
APRIL(2015)
CHITKARA UNIVERSITY , HIMACHAL PRADESH
CERTIFICATE
I hereby certify that the work which is being presented here in the Project Report entitled
MINI 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: 1
st
MAY, 2015 Place:- CHITKARA UNIV.
This is to certify that the above statement made by the student(s) is correct to the best of my
knowledge.
Signature of Supervisor
Mr. Tajender Singh , Asst professor, ECE Department.
35
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 .
36
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 .
36
37
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