domestic appliances controlled by light source

8/9/2019 Domestic Appliances Controlled by Light Source

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06621A0466 LIGHT OPERATED DOMESTIC06621A0496 APPLIANCES

ABSTRACT

AIM: To operate domestic appliances using light source.

A 230volts single phase AC supply is given to a light controller circuit, where

it is converted into 6volts dc through a regulator (A 7806 IC) and an op-amp is

used as comparator. The circuit is based on a voltage comparator circuit wired

around IC 1. The non inverting input of IC1 is given with a reference voltage of

6V using resistors . The photo resistor and comparator are connected such that

when the light beam falls on the photo resistor .The non-inverting terminal voltage

of the comparator will be greater than the inverting terminal voltage, and the out put of the

comparator goes high (~12 V).This makes transistor Q1 on and it drives the relay. As a

result we get a relay switching according to the intensity of the light falling on the LDR. If

there is any abrupt interruption of the light beam at any point the load operation is stopped.

Any kind of light beam can be used to operate the load which is one of the advantages.

B.TECH III/IV YEAR AURORAS ENGINEERING COLLEGE

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1. INTRODUCTION

1.0 LIGHT CONTROLLER CIRCUIT:

In this circuit an optical link (or) Opto coupler is placed between the light controller

circuit and isolation circuit for the isolation purpose. This isolation circuit has an inbuilt

LED and Photo transistor used for enhancement of the output. This happens when the LED

works, then the photo transistor senses the light which results in enhancement of the

output.

1.1 RELAY CIRCUIT:

An electromagnetic relay switch of 6 volts is used here to isolate AC and DC parts. One

end of the switch is connected to AC and the other end is connected to DC. This circuit

protects from over voltage, by isolating both the circuits. For continuous operation load a

timer can be used (Optional). So when the light sensing device `senses the light (from any

source) load appliances connected to the one end of the electromagnetic relay switch is

operated.


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2. BLOCK DIAGRAM

2.0 Block Diagram

Fig 2.0: Block Diagram

2.1 BLOCK DIAGRAM DESCRIPTION:

The entire circuit for the domestic appliances controlled by light source is divided into

four main parts.

They are as follows

2.1.1 Rectifying Circuit

2.1.2 Regulating Circuit

2.1.3 Comparator Circuit

2.1.4 Isolation Circuit.

These circuits are clearly explained below.

2.1.1 Rectifying Circuit:

This part of the circuit consists of a 230v primary to 12 v secondary transformer and a

rectifier. The 230 v ac supply is given to the transformer which is step down to 12 ac


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supply . this 12v ac supply is given to the rectifier. The rectifier rectifies the 12 v ac supply

to 12 v dc supply.

2.1.2 Regulating Circuit:

The regulator circuit consists of a regulator 7806. The 12 v dc supply is given to the

regulator 7806 where it is further brought down to 6v dc supply with the help of the

regulator. This is the regulation part.

2.1.3 Comparator Circuit:

The comparator circuit consists of a comparator ICLM311 and a LDR. The output from

the regulator is given to the comparator. When the LDR senses light the comparator

compares the inverting and non-inverting terminals. when the non inverting terminal

voltage is greater than the inverting terminal voltage the required maximum output voltage

is obtained.

2.1.4 Isolation Circuit:

The isolation circuit consists of an opto coupler and an electromagnetic relay switch.

When the maximum required output is received from the comparator the opto coupler

which acts as isolation between the comparator and the switch sends a signal to the switch

and the switch operates. When the switch operates the domestic appliance starts working.


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3. LIGHT OPERATED DOMESTIC APPLIANCES

3.0 CIRCUIT DIAGRAM

fig3.0: light operated domestic appliances

3.1 WORKING PRINCIPLE:

Adjust POT R1 to set the desired light intensity for switching the relay. For this

illuminate the LDR with the desired light intensity. The relay will be either ON or OFF.

Adjust POT R1 slowly so that the state of the relay changes. Thats it. Now the circuit is

set for the given intensity of light. Assemble the circuit on a good quality PCB or common

board. You can use either a 12 V battery or a well regulated & filtered 12V DC mainsoperated power supply. The pin 5&6 (Balance & Balance/Strobe) of IC LM311 are shorted

to minimize the chance of oscillations. The pin out of LM311 is also given together with

the circuit diagram. The whenever the LDR or the photo resistor senses the light

beam the IC gives the required maximum output voltage to the optical link (opto

coupler) where the electrical signal is converted to a light beam, transferred, then

converted back to an electrical signal, makes the electromagnetic relay switch

operates and the domestic appliance starts working.


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4. DESCRIPTION OF THE COMPONENTS

The detailed description of the components used in the control of domestic

appliances using a light source is clearly explained below.

4.1 230 V AC primary to 12 V AC Secondary Transformer

Transformer is static piece of apparatus by means of which electric power in

one circuit is transformed to electric power of same frequency in another circuit.

Its based upon MUTUAL INDUCTION. The mutual induction between two circuits

linked by a common flux.

Fig 4.1: Transformer

Transformers convert AC electricity from one voltage to another with little loss

of power. Transformers work only with AC and this is one of the reasons why

mains electricity is AC. Step-down transformers reduce voltage. Most power supplies

use a step-down transformer to reduce the dangerously high mains voltage to a

safer low voltage.

The input coil is called the primary and the output coil is called the secondary.

There is no electrical connection between the two coils , instead they are linked by

an alternating magnetic field created in the soft-iron core of the transformer. The

two lines in the middle of the circuit symbol represents the core.


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Fig4.1.1: Basic model of a Transformer with output waveform.

Fig4.1.2: Transformer showing the windings.

The colorful picture of a transformer is as shown above. Transformers waste

very little power so the power out is (almost) equal to the power in. Note that as

voltage is stepped down current is stepped up.

The ratio of the number of turns on each coil, called the turns ratio, determines

the ratio of the voltages. A step-down transformer has a large number of turns on

its primary (input) coil which is connected to the high voltage mains supply, and

a small number of turns on its secondary (output) coil to give a low output

voltage. In most situations, power that travels over power lines is at a higher

voltage due to the fact that there are power losses in route to their destinations.


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When the power reaches its destination, the power level can be stepped down.

Thus, if power voltage comes through power lines at a higher voltage current than

needed, step down transformers will decrease the voltage input allowing equipment

to run with a power source that is the same voltage.

4.2 DIODES

In electronics a diode is a two-terminal device .Diodes have two active

electrodes between which the signal of interest may flow, and most are used

for their unidirectional electric current property.

Fig 4.2: Diodes

The most common function of a diode is to allow an electric current to pass

in one direction (called the forward biased c ondition) and to block the current

in the opposite direction (the reverse biased condition). Today the most

common diodes are made from semiconductor materials such as silicon or

Germanium.

Fig 4.2.1: diodes shown along with symbols.


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4.3 Zener Diode

Fig 4.3: Zener diode schematic symbol.

Current-voltage characteristic of a Zener diode with a breakdown voltage of 17 volt.

A Zener diode is a type of diode that permits current in the forward directionlike a normal diode, but also in the reverse direction if the voltage is larger

than the breakdown voltage known as "Zener knee voltage" or "Zener voltage".

Fig 4.3.1: Zener diode

A conventional solid-state diode will not allow significant current if it is

Reverse-biased below its reverse breakdown voltage. When the reverse bias

breakdown voltage is exceeded, a conventional diode is subject to high current

due to avalanche breakdown. Unless this current is limited by external

circuitry, the diode will be permanently damaged. In case of large forward bias

the diode exhibits a voltage drop due to its junction built-in voltage and

internal resistance. The amount of the voltage drop depends on the

semiconductor material and the doping concentrations.

A Zener diode exhibits almost the same properties, except the device is

specially designed so as to have a greatly reduced breakdown voltage, the so-

called Zener voltage. A Zener diode contains a heavily doped p-n junction


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allowing electrons to tunnel from the valence band of the p-type material to

the conduction band of the n-type material. In the atomic scale, this tunneling

corresponds to the transport of valence band electrons into the empty

conduction band states; as a result of the reduced barrier between these bands

and high electric fields that are induced due to the relatively high levels of

doping on both sides. A reverse-biased Zener diode will exhibit a controlled

breakdown and allow the current to keep the voltage across the Zener diode at

the Zener voltage. For example, a diode with a Zener breakdown voltage of 3.2

V will exhibit a voltage drop of 3.2 V if reverse bias voltage applied across it

is more than its Zener voltage. However, the current is not unlimited, so the

Zener diode is typically used to generate a reference voltage for an amplifier

stage, or as a voltage stabilizer for low-current applications.

The breakdown voltage can be controlled quite accurately in the doping

process. While tolerances within 0.05% are available, the most widely used

tolerances are 5% and 10%.

Another mechanism that produces a similar effect is the avalanche effect as

in the avalanche diode. The two types of diode are in fact constructed the

same way and both effects are present in diodes of this type. In silicon diodes

up to about 5.6 volts, the Zener effect is the predominant effect and shows a

marked negative temperature coefficient. Above 5.6 volts , the avalanche effect

becomes predominant and exhibits a positive temperature coefficient.

In a 5.6 V diode, the two effects occur together and their temperature

coefficients neatly cancel each other out, thus the 5.6 V diode is the component

of choice in temperature-critical applications.

Modern manufacturing techniques have produced devices with voltages lower

than 5.6 V with negligible temperature coefficients, but as higher voltage

devices are encountered, the temperature coefficient rises dramatically. A 75 V

diode has 10 times the coefficient of a 12 V diode. All such diodes, regardless

of breakdown voltage, are usually marketed under the umbrella term of "Zener

diode".

4.3.1 Uses:


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Zener diodes are widely used to regulate the voltage across a circuit. When

connected in parallel with a variable voltage source so that it is reverse biased,

a Zener diode conducts when the voltage reaches the diode's reverse

breakdown voltage. From that point it keeps the voltage at that value.

4.4 REGULATOR

A voltage regulator is an electrical regulator designed to automatically

maintain a constant voltage level.

It may use an electromechanical mechanism, or passive or active electronic

components. Depending on the design, it may be used to regulate one or more

AC or DC voltages.

Fig 4.4: Electronic symbol for Voltage Regulator.

All modern electronic voltage regulators operate by comparing the actual

output voltage to some internal fixed reference voltage. Any difference is

amplified and used to control the regulation element in such a way as to

reduce the voltage error.

This forms a negative feedback servo control loop ; increasing the open-loop

gain tends to increase regulation accuracy but reduce stability (avoidance of

oscillation, or ringing during step changes). There will also be a trade-off

between stability and the speed of the response to changes. If the output

voltage is too low (perhaps due to input voltage reducing or load current

increasing), the regulation element is commanded, up to a point , to produce a

higher output voltage - by dropping less of the input voltage (for linear series

regulators and switching regulators), or to draw input current for longer


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periods (boost-type switching regulators); if the output voltage is too high, the

regulation element will normally be commanded to produce a lower voltage.

However, many regulators have over-current protection, So entirely stop

sourcing current (or limit the current in some way) if the output current is too

high, and some regulators may also shut down if the input voltage is outside a

given range.

(7806): There are quite a few solid-state voltage regulators on the market that can

be applied to automotive use. One of the simplest is the 7806, a 6 volt, 1 amp

regulator .

Fig 4.4.1: 7806 Regulator

4.5 CAPACITORS:

A capacitor or condenser is a passive electronic component consisting of a

pair of conductors separated by a dielectric. When a voltage potentialdifference exists between the conductors, an electric field is present in the

dielectric. This field stores energy and produces a mechanical force between

the plates. The effect is greatest between wide, flat, parallel, narrowly

separated conductors.


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Fig 4.5: Capacitor

An ideal capacitor is characterized by a single constant value, capacitance,

which is measured in farads. This is the ratio of the electric charge on each

conductor to the potential difference between them. In practice, the dielectric

between the plates passes a small amount of leakage current. The conductors

and leads introduce an equivalent series resistance and the dielectric has an

electric field strength limit resulting in a breakdown voltage.

The properties of capacitors in a circuit may determine the resonant

frequency and quality factor of a resonant circuit, power dissipation and

operating frequency in a digital logic circuit, energy capacity in a high-power

system, and many other important system characteristics Function

Capacitors store electric charge. They are used to smooth varying DC supplies

by acting as a reservoir of charge. They are also used in filter circuits because

capacitors easily pass AC (changing) signals but they block DC (constant) signals.

Capacitance

This is a measure of a capacitor's ability to store charge. A large capacitance

means that more charge can be stored. Capacitance is measured in farads, symbol

F. However 1F is very large, so prefixes are used to show the smaller values.

Three prefixes (multipliers) are used, (micro), n (nano) and p (pico):

means 10 -6 (millionth), so 1000000F = 1F

n means 10 -9 (thousand-millionth), so 1000nF = 1F


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P means 10 -12 (million-millionth), so 1000pF = 1nF

Capacitor values can be very difficult to find because there are many types

of capacitor with different labeling systems !

There are many types of capacitor but they can be split into two groups,

polarized and un polarized. Each group has its own circuit symbol.

4.5.1 Electrolytic capacitors:

Fig 4.5.1: Electronic Capacitors

Electrolytic capacitors are polarized and they must be connected the correct way

round, at least one of their leads will be marked + or -. They are not damaged by

heat when soldering.

There are two designs of electrolytic capacitors; axial where the leads are

attached to each end (220F in picture) and radial where both leads are at the

same end (10F in picture). Radial capacitors tend to be a little smaller and

they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are clearly

printed with their capacitance and voltage rating. The voltage rating can be

quite low ( 6V for example) and it should always be checked when selecting an

electrolytic capacitor. If the project parts list does not specify a voltage, choose


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a capacitor with a rating which is greater than the project's power supply

voltage. 25V is a sensible minimum most battery circuits.

4.6 RESISTORS

A Resistor is a two-terminal electronic component designed to oppose an

electric current by producing a voltage drop between its terminals in

proportion to the current, that is, in accordance with Ohms law:

V = IR

Resistors are used as part of electrical networks and electronic circuits. They

are extremely commonplace in most electronic equipment. Practical resistors can

be made of various compounds and films, as well as resistance wire (wire

made of a high-resistivity alloy, such as nickel/chrome).

The primary characteristics of resistors are their resistance and the power

they can dissipate. Other characteristics include temperature coefficient, noise ,

and inductance . Less well-known is critical resistance , the value below which

power dissipation limits the maximum permitted current flow, and above which

the limit is applied voltage. Critical resistance depends upon the materials

constituting the resistor as well as its physical dimensions; it's determined by

design.

Resistors can be integrated into hybrid and printed circuits , as well as

Integrated circuits . Size, and position of leads (or terminals) are relevant to

equipment designers; resistors must be physically large enough not to overheat

when dissipating their power.

Resistor


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Three resistors

Type Passive

Electronic symbol

(Europe)

(US)

Fixed and Variable Resistors

There are two kinds of resistors, FIXED and VARIABLE. The fixed resistor

will have one value and will never change . The tapped resistor has several

fixed taps and makes more than one resistance value available. The sliding

contact resistor shown in C has an adjustable collar that can be moved to tap

off any resistance within the ohmic value range of the resistor.

There are two types of variable resistors, one called a POTENTIOMETER and the other a RHEOSTAT . An example of the potentiometer is the volume

control on your radio, and an example of the rheostat is the dimmer control

for the dash lights in an automobile. There is a slight difference between

them. Rheostats usually have two connections, one fixed and the other

moveable. Any variable resistor can properly be called a rheostat. The

potentiometer always has three connections, two fixed and one moveable.

Generally, the rheostat has a limited range of values and a high current-

handling capability. The potentiometer has a wide range of values, but it

usually has a limited current-handling capability. Potentiometers are always

connected as voltage dividers.

These are miniature versions of the standard variable resistor. They are designed

to be mounted directly onto the circuit board and adjusted only when the circuit is

built. For example to set the frequency of an alarm tone or the sensitivity of a


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light-sensitive circuit. A small screwdriver or similar tool is required to adjust

presets.

Presets are much cheaper than standard variable resistors so they are

sometimes used in projects where a standard variable resistor would normally

be used. Multi turn presets are used where very precise adjustments

must be made. The screw must be turned many times (10+) to move the slider

from one end of the track to the other, giving very fine control.

Preset

(open style)

Presets

(closed style)Multi turn preset

Fig 4.6: showing various kinds of presets

4.7 Light Dependent Resistor

A Light Dependent Resistor ( LDR, photoconductor, or photocell) is a device

which has a resistance which varies according to the amount of light falling on its

surface.

A typical light dependent resistor is picture is shown. Different LDR's havedifferent specifications, however the LDR's we sell in the REUK Shop are fairly

standard and have a resistance in total darkness of 1 M Ohm, and a resistance of a

couple of k Ohm in bright light

Uses for Light Dependent Resistors


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Light dependent resistors are a vital component in any electric circuit which is

to be turned on and off automatically according to the level of ambient light - for

example, solar powered garden lights, and night security lighting.

An LDR can even be used in a simple remote control circuit using the backlight

of a mobile phone to turn on a device - call the mobile from anywhere in the

world, it lights up the LDR, and lighting (or a garden sprinkler ) can be turned on

remotely!

Light Dependent Resistor Circuits:

There are two basic circuits using light dependent resistors - the first is

activated by darkness, the second is activated by light. The two circuits are very

similar and just require an LDR, some standard resistors , a variable resistor and

any small signal transistor

Fig 4.7 : Light Dependent Resistor.

In the circuit diagram above, the LED lights up whenever the LDR is in

darkness. The 10K variable resistor is used to fine-tune the level of darkness

required before the LED lights up. The 10K standard resistor can be changed as

required to achieve the desired effect, although any replacement must be at least


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1K to protect the transistor from being damaged by excessive current.

By swapping the LDR over with the 10K and 10K variable resistors , the circuit

will be activated instead by light. Whenever sufficient light falls on the LDR the

LED will light up.

Using an LDR in the Real World:

The real world circuit, the LED (and resistor) between the positive voltage input

(Vin) and the collector (C) of the transistor would be replaced with the device to

be powered.

Typically a relay is used - particularly when the low voltage light detecting

circuit is used to switch on (or off) a 240V mains powered device. A diagram of

that part of the circuit is shown above. When darkness falls (if the LDR circuit is

configured that way around), the relay is triggered and the 240V device.

4.8 ICLM311:

An operational amplifier , which is often called an op-amp , is a DC - coupled

high - gain electronic voltage amplifier with differential inputs and, usually , a

single output. Typically the output of the op-amp is controlled either by

negative feedback , which largely determines the magnitude of its output

voltage gain, or by positive feedback , which facilitates regenerative gain and

oscillation. High input impedance at the input terminals and low output

impedance is important typical characteristics.

Op-amps are among the most widely used electronic devices today, being

used in a vast array of consumer, industrial, and scientific devices. Many

standard IC op-amps cost only a few cents in moderate production volume;

however some integrated or hybrid operational amplifiers with special

performance specifications may cost over $100 US In small quantities.


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Modern designs are electronically more rugged than earlier implementations

and some can sustain direct short circuits on their outputs without damage.

The op-amp is one type of differential amplifier. Other types of differential

amplifier include the fully differential amplifier (similar to the op-amp, but

with 2 outputs), the instrumentation amplifier (usually built from 3 op-amps),

the isolation amplifier (similar to the instrumentation amplifier, but which

works fine with common-mode voltages that would destroy an ordinary op-

amp), and negative feedback amplifier (usually built from 1 or more op-amps

and a resistive feedback network).

Fig 4.8: Amplifier

The LM311 is a voltage comparator that has input currents nearly a thousandtimes lower than devices like the LM106 or LM710. It is also designed to operate

over a wider range of supply voltages from standard 15V op amp supplies down

to the single 5V supply used for IC logic. The output is compatible with RTL,

DTL and TTL as well as MOS circuits. Further, the LM311 can drive lamps or

relays, switching voltages up to 50V at currents as high as 50 m A.

Both the inputs and the outputs of the LM311 can be isolated from system

ground, and the output can drive loads referred to ground, the positive supply or the negative supply. Offset balancing and strobe capability are provided and outputs

can be wire OR'ed. Although slower than the LM106 and LM710 (200 ns response

time vs. 40 ns) the LM311 is also much less prone to spurious oscillations.

The LM311 has a temperature range of 0C to +70C.


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Features

Operates from single 5V supply

Input current: 150 n A max. over temperature

Offset current: 20 n A max. over temperature

Differential input voltage range: 30V

Power consumption: 135 m W at 15V

Pin Configuration:

Fig 4.8.1: Pin Configuration of LM311

4.9 OPTO COUPLER:

An opto coupler integrated circuit. In electronics , an opto coupler is a

device that uses a short optical transmission path to transfer an electronic

signal between elements of a circuit , typically a transmitter and a receiver,

while keeping them electrically isolatedsince the electrical signal is converted

to a light beam, transferred, then converted back to an electrical signal, there

is no need for electrical connection between the source and destination circuits .

Isolation between input and output is rated at 7,500V peak for 1 second. The

opto-isolator is simply a package that contains both an infrared light-emitting


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diode LED and a photo detector such as a photosensitive silicon diode ,

transistor Darlington pair , or SCR. The wave-length responses of the two

devices are tailored to be as identical as possible to permit the highest measure

of coupling possible. Other circuitryfor example an output amplifier may be

integrated into the package. An opto-isolator is usually thought of as a single

integrated package, but opto-isolation can also be achieved by using separate

devices.

Digital opto-isolators change the state of their output when the input state

changes; analog isolators produce an analog signal which reproduces the input.

Configurations

Schematic diagram of a very simple opto coupler with an LED and

phototransistor. The dashed line represents the isolation barrier, over which there is

no electrical contact.

A common implementation is a LED and a phototransistor in a l light- tight

housing to exclude ambient light and without common electrical connection,

positioned so that light from the LED will impinge on the photo detector.When an electrical signal is applied to the input of the opto isolator , its LED

lights and illuminates the photo detector, producing a corresponding electrical

signal in the output circuit. Unlike a transformer the opto-isolator allows DC

coupling and can provide any desired degree of electrical isolation and

protection from serious over voltage conditions in one circuit affecting the

other. A higher transmission ratio can be obtained by using a Darlington


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instead of a simple phototransistor, at the cost of reduced noise immunity and

higher delay. With a photodiode as the detector, the

output current is proportional to the intensity of incident light supplied by the

emitter. The diode can be used in a photovoltaic mode or a photoconductive

mode. In photovoltaic mode, the diode acts as a current source in parallel with

a forward-biased diode. The output current and voltage are dependent on t he

load impedance and light intensity. In photoconductive mode, the diode is

connected to a supply voltage, and the magnitude of the current conducted is

directly proportional to the intensity of light. This opto coupler type is

significantly faster than photo transistor type, but the transmission ratio is very

low; it is common to integrate an output

amplifier circuit into the same package.

The optical path may be air or a dielectric waveguide . W hen high noise

immunity is required an optical conductive shield can be integrated into the

optical path. The transmitting and receiving elements of an optical isolator may

be contained within a single compact module, for mounting, for example, on a

circuit board; in this case, the module is often called an opto isolator or opto-isolator . The photo sensor may be a photocell , phototransistor , or an optically

triggered SCR or TRIAC. This device may in turn operate a power relay or

contractor.

Analog opto isolators often have two independent, closely matched output

phototransistors, one of which is used to linearize the response using negative

feedback.

Switched-mode power supplies use opto couplers for mains isolation. As

they work in an environment with much electrical noise and with signals

which are not small, opto couplers with low transmission ratio are

preferred.

Where electrical safety is paramount, opto couplers can totally isolate

circuitry which may be touched by humans from mains electricity.

Medical equipment often uses opto couplers.


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Opto couplers are used to isolate low-current control or signal circuitry from

transients generated or transmitted by power supply and high-current control

circuits. The latter are used within motor and machine control function blocks.

4.10 Light-emitting diode LED

Blue, green, and red LEDs; these can be combined to produce most perceptible

colors, including white. Infrared and ultraviolet (UVA) LEDs are also available.

Fig: Schematic figure of an LED

A light-emitting-diode (LED) is a semiconductor diode that emits light when an

electric current is applied in the forward direction of the device, as in the simpleLED circuit . The effect is a form of electroluminescence where incoherent and

narrow- spectrum light is emitted from the p-n junction in a solid state material.

Fig 4.10: Figure showing LED

LEDs are widely used as indicator lights on electronic devices and

increasingly in higher power applications such as flashlights and area lighting.

An LED is usually a small area (less than 1 mm 2) light source, often with optics


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added directly on top of the chip to shape its radiation pattern and assist in

reflection. The colour of the emitted light depends on the composition and

condition of the semi conducting material used, and can be infrared , visible ,

or ultraviolet. Besides lighting, interesting applications include using UV-LEDs

for sterilization of water and disinfection of devices, and as a grow light to

enhance photosynthesis in plants.

4.11. TRANSISTOR SL100:

Function

Transistors amplify current, for example they can be used to amplify the small

output current from a logic IC so that it can operate a lamp, relay or other high

current device. In many circuits a resistor is used to convert the changing current to

a changing voltage, so the transistor is being used to amplify voltage.

Fig 4.11: Transistors

A transistor may be used as a switch (either fully on with maximum current, or

fully off with no current) and as an amplifier (always partly on). The amount of

current amplification is called the current gain, symbol h FE.

Types of transistor

There are two types of standard transistors, NPN and PNP, with different circuit

symbols. The letters refer to the layers of semiconductor material used to make the

Transistor. Most transistors used today are NPN because this is the easiest type to make


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from silicon. If you are new to electronics it is best to start by learning how to use NPN

transistors

Fig 4.11.1: npn and pnp transistor symbols.

The leads are labeled base (B), collector (C) and emitter (E).These terms refer to the

internal operation of a transistor but they are not much help in understanding how a

transistor is used, so just treat them as labels!

NPN

Fig 4.11.2: The symbol of an NPN Bipolar Junction Transistor.

NPN is one of the two types of bipolar transistors, in which the letters "N" and

"P" refer to the majority charge carriers inside the different regions of the transistor.

Most bipolar transistors used today are NPN, because electron mobility is higher

than hole mobility in semiconductors, allowing greater currents and faster operation.

Fig 4.11.3: NPN Transistor

NPN transistors consist of a layer of P- doped semiconductor (the "base") between

two N-doped layers. A small current entering the base in common-emitter mode is


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amplified in the collector output. In other terms, an NPN transistor is "on" when its

base is pulled high relative to the emitter.

The arrow in the NPN transistor symbol is on the emitter leg and points in the

direction of the conventional current flow when the device is in forward active mode.

One mnemonic device for identifying the symbol for the NPN transistor is "not

pointing in or `never points in".

PNP

The other type of BJT is the PNP with the letters "P" and "N" referring to themajority charge carriers inside the different regions of the transistor.

Fig 4.11.4: The symbol of a PNP Bipolar Junction Transistor.

PNP transistors consist of a layer of N- doped semiconductor between two layers of

P-doped material. A small current leaving the base in common-emitter mode is

amplified in the collector output. In other terms, a PNP transistor is "on" when its

base is pulled low relative to the emitter.

Fig 4.11.5: PNP Transistor


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The arrow in the PNP transistor symbol is on the emitter leg and points in the

direction of the conventional current flow when the device is in forward active mode.

Fig 4.11.6: PNP Transistor Symbol

One mnemonic device for identifying the symbol for the PNP transistor is "points in proudly or points in permanently".

Darlington Pair

A Darlington pair is two transistors connected together to give a very high current

gain. In addition to standard (bipolar junction) transistors, there are field-effect transistors

which are usually referred to as FETs. They have different circuit symbols and properties

and they are not (yet) covered by this page.

Transistors have three leads which must be connected the correct way round. Please

take care with this because a wrongly connected transistor may be damaged instantly when

you switch on.

If you are lucky the orientation of the transistor will be clear from the PCB or strip

board layout diagram, otherwise you will need to refer to a supplier's catalogue to identify

the leads. The drawings on the right show the leads for some of the most common case

styles.


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Please note that transistor lead diagrams show the view from below with the leads

towards you. This is the opposite of IC (chip) pin diagrams which show the view from

above.

Testing a transistor

Transistors can be damaged by heat when soldering or by misuse in a circuit. If you

suspect that a transistor may be damaged there are two easy ways to test it:

Testing with a multimeter

Use a multimeter or a simple tester (battery, resistor and LED) to check each pair of

leads for conduction. Set a digital multimeter to diode test and an analogue multimeter to a

low resistance range.

4.12 ELECTROMAGNETIC RELAY SWITCH:

An electromagnetic relay is a type of electrical switch controlled by an electromagnet .

He electromagnetic relay is used in a variety of applications, including alarms and sensors,

signal switching, and the detection and control of faults on electrical distribution lines. The

electromagnetic relay was invented in 1835, and its straightforward function has not

changed much since. Consumers interact with the electromagnetic relay in a variety of

forms daily, from timed office lights to test buttons and other quality control devices.

The core of the electromagnetic relay, naturally, is an electromagnet, formed by

winding a coil around an iron core. When the coil is energized by passing current through

it, the core in turn becomes magnetized, attracting a pivoting iron armature. As the

armature pivots, it operates one or more sets of contacts, thus affecting the circuit. When

the magnetic charge is lost, the armature and contacts are released. Demagnetization can

cause a leap of voltage across the coil, damaging other components of the device when

turned off. Therefore, the electromagnetic relay usually makes use of a diode to restrict the

flow of the charge, with the cathode connected at the most positive end of the coil


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Fig 4.12: Electromagnetic relay switch

Contacts on an electromagnetic relay can take three forms. Normally opened contacts

connect the circuit when the device is activated and disconnect it when the device is not

active, like a light switch. Normally closed contacts disconnect the circuit when the relay is

magnetized, and a change-over incorporates one of each type of contact. The configuration

of the contacts is dependant upon the intended application of the device.

The electro magnetic relay is capable of controlling an output of higher power than the

input, and it is often used as a buffer to isolate circuits of varying energy potentials as a

result. When a low current is applied to the electromagnet, throwing the switch, the device

is capable of allowing a higher current to flow through it. This is advantageous in some

applications, such as tripping alarms and other safety devices, because a safer low current

can be used to activate an application requiring more energy.

Fig 4.12.1: Aautomotive style miniature relay, dust cover removed

4.13 BULBS:

The incandescent light bulb , incandescent lamp or incandescent light globe is a source

of electric light that works by incandescence (a general term for heat-driven light

emissions which includes the simple case of black body radiation). An electric current

passes through a thin filament , heating it until it produces light. The enclosing glass

bulb prevents the oxygen in air from reaching the hot filament, which otherwise


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would be destroyed rapidly by oxidation . Incandescent bulbs are also sometimes

called electric lamps , a term also applied to the original arc lamps .

Incandescent bulbs are made in a wide range of sizes and voltages , from 1.5 volts

to about 300 volts. They require no external regulating equipment and have a low

manufacturing cost, and work well on either alternating current or direct current

(producing negligible flicker on either.) As a result the incandescent lamp is widely

used in household and commercial lighting, for portable lighting, such as table lamps,

some car headlamps and electric flashlights , and for decorative and advertising

lighting.

Fig 4.13: Incandescent bulb.

Some applications of the incandescent bulb make use of the heat generated, such

as incubators , brooding boxes for poultry , heat lights for reptile tanks , infrared

heating for industrial heating and drying processes, and the Easy-Bake Oven toy. In

cold weather the heat shed by incandescent lamps contributes to building heating, but

in hot climates lamp losses increase the energy used by air conditioning systems.

Incandescent light bulbs are gradually being replaced in many applications by

other types of electric light such as ( compact ) fluorescent lamps , high-intensity

discharge lamps , light-emitting diodes (LEDs), and other devices. These newer

technologies give more visible light for the same amount of electrical energy input,

and often generate much less heat. Some jurisdictions, such as the European Union

are in the process of phasing-out the use of incandescent light bulbs in favor of more

energy-efficient lighting.


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5. SOLDERING

5.0 CLASSIFICATION OF FLUXES

1. INORGANIX FLUX

2. ORGANIC FLUX

3. ROSIN BASED FLUX

4. NO CLEAN FLUX

1. INORGANIC FLUX

Consist of mixture of salts/acids such as HCL, H3PO4, Zncl 2, Nh 4Cl, Na 2Bo, having

picking action through generated HCI acid in contact with moisture or added water. These

fluxes are very corrosive in nature and generally not used in electronic assemblies.

2. NON ROSIN BASED FLUXES

These fluxes do not contain Rosin but contain only activators based on GLIMTIC,LACTIC ACIDS/HYDROCHLORIDES, water soluble and meditatively corrosive hence

must be cleaned after soldering process thoroughly.

3. ROSIN BASED FLUXES

Rosin which is naturally available from pine a tree by tapping is made into crystalline

structure with pale yellow to Dark brown colour is used as base.

Rosin is a mixture of several organic compounds like ABETIC ACID, PIMARIC ACID,

etc., pure Rosin is a weak pickling agent. For heavier passivation layer, surface activatorslike Bromides/ chlorides are added. The acid contents for various R type of fluxes are given

below.

R ROSIN NON ACTIVATED. ACID CONTENT: < 0.2%

RAM ROSIN MILDLY ACTIVATED. ACID CONTENT: 0.2% TO 0.4%

RA ROSIN ACTIVATED. ACID CONTENT: 0.4% to 4%

RSA ROSIN SUPER ACTIVATED. ACID CONTENT: > 4%

4. NO CLEAN FLUX


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Does not contain natural Rosin but obtained by synthetic resins solvents, foaming

agents and activators. Generally does not leave any residues.

5.1 SOLDER ALLOY

1. Tin is not appreciably affected by air or water.

2. The corrosion resistance of tin is an important factor for using as a coating on

Copper wire to protect against corrosion.

3. Tin reacts and alloys with metal easily.

4. Lead is soft and dense, but surface gets quickly corroded.

5. Lead reduces the melting temperature and brittleness thus adding to the overall strength

of alloy.

5.2 METALLURGY OF SOLDER JOINTS

When two metals A and B are soldered with a filler material S. The following

regions occur in the final joint structure.

1. PURE A

2. ALLOY OF A AND S

3. PURE S

4. ALLOY OF S AND B

5. PURE B

The alloy region consists of irreversible compounds created out of the metals and the

filler. The filler, the thickness of this alloy being 0.1 to 1.0 microns. This zone is usually

called as intermetallic layer in case of Cu-Solder (sn-pb) combination. They are typically

cu3sn, cu6sn5. This intermetallic layer is mainly responsible for the strength of the joint.

This layer thickness increases with time and temperature of the soldering. This

intermetallic layer is brittle in nature. Hence the thickness of this layer has to be controlled.

CHEMICAL COMPOSITION OF Sn63, Sn60

Sn63 Sn60

TIN : 62.5-62.5% 59.5% - 61.5%


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Composition

Solid Melting : 183 Deg.C 183 Deg.C

Range

Liquid : 183 Deg.C 188 Deg. C

Melting range

Plastic : Nil Slight

Region

5.3 What is solder?

Solder is an alloy (mixture) of tin and lead, typically 60% tin

and 40% lead. It melts at a temperature of about 200C. Coating

a surface with solder is called 'tinning' because of the tin content

of solder. Lead is poisonous and you should always wash your

hands after using solder.

Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex.

The flux is corrosive, like an acid, and it cleans the metal surfaces as

the solder melts. This is why you must melt the solder actually on the

joint, not on the iron tip. Without flux most joints would fail because metals quickly

oxidise and the solder itself will not flow properly onto a dirty, oxidised, metal surface.

The best size of solder for electronics is 22swg (SWG= standard wire gauge).

5.4 Desoldering

At some stage you will probably need to desolder a joint to remove or re-position a wire or

component. There are two ways to remove the solder:


Reels of solder

Figure 5.3(i)

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1. With a desoldering pump (solder

sucker)

Set the pump by pushing the spring-loaded

plunger down until it locks.

Apply both the pump nozzle and the tip of your soldering iron to the joint.

Wait a second or two for the solder to melt.

Then press the button on the pump to release the

plunger and suck the molten solder into the tool.

Repeat if necessary to remove as much solder as possible. The pump will need emptying occasionally by unscrewing the nozzle.

2. With solder remover wick

(copper braid)

Apply both the end of the wick and the tip of your soldering iron to the joint.

As the solder melts most of it will flow onto the wick, away from the joint .

Remove the wick first, then the soldering iron.

Cut off and discard the end of the wick coated with solder.

After removing most of the solder from the joint(s) you may be able to remove the wire

or component lead straight away (allow a few seconds for it to cool). If the joint will not

come apart easily apply your soldering iron to melt the remaining traces of solder at the

same time as pulling the joint apart, taking care to avoid burning yourself.

5.5 Soldering iron


Figure 5.4(i)

Solder remover wic

Figure 5.4(ii)

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For electronics work the best type is one powered by mains electricity (230V in the

UK), it should have a heatproof cable for safety. The iron's power rating should be 15 to

25W and it should be fitted with a small bit of 2 to 3mm diameter.

5.6 Other types of soldering iron

Low voltage soldering irons are available, but their extra safety is undermined if you

have a mains lead to their power supply! Temperature controlled irons are excellent for

frequent use, but not worth the extra expense if you are a beginner. Gas-powered irons are

designed for use where no mains supply is available and are not suitable for everyday use.

Pistol shaped solder guns are far too powerful and cumbersome for normal electronics use.

5.7 Soldering iron stand

You must have a safe place to put the iron when you are

not holding it. The stand should include a sponge which

can be dampened for cleaning the tip of the iron.

Figure5.7 (i)

5.8 Desoldering pump (solder sucker)

A tool for removing solder when desoldering a joint to correct a mistake or replace a

component.

Figure 5.8(i)Figure 5.8(i)

5.9 Solder remover wick (copper braid)

This is an alternative to the desoldering pump shown above.

Figure 5.9(i)

5.10 Reel of solder


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The best size for electronics is 22swg

(SWG standard wire gauge).


5.11 Side cutters

For trimming component leads close to the circuit board.

5.12 Wire strippers

Most designs include a cutter as suitable for trimming component leads.


5.13 Small pliers

Usually called 'snipe nose' pliers, these are for bending component leads etc. If you put a

strong rubber band across the handles the pliers make a convenient holder for parts such as

switches while you solder the contacts .


5.14 Small flat-blade screwdriver

For scraping away excess flux and dirt between tracks, as well as driving screws!


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Figure 5.14(i)Figure 5.14(i) Figure 5.14(ii)Figure 5.14(ii)

5.15 Heat sink

You can buy a special tool, but a standard crocodile clip works just as well and is

cheaper.


The following tool is only required if you are using strip board:

5.16 Track cutter

A 3mm drill bit can be used instead; in fact the tool is usually just a 3mm drill bit with a

proper handle fitted.

PCB rubber

This is an abrasive rubber for cleaning PCBs. It can also be used to clean strip

Figure 5.16(i)

WORKING


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The working of a domestic appliances controlled by a light source is as follows. The

primary of the transformer is given a 230v AC supply. As the transformer is a step down

transformer the output is 12 V ac supply. The rectifier connected to the secondary of the

transformer converts the 12V dc supply. The 12V dc supply is further reduced to 6 V dc

supply using a regulator 7806. Regulator operates by comparing actual output to some

fixed internal reference voltage. As we are using regulator 7806 the required internal

reference voltage is 6v. And hence the 12v dc supply is reduced to 6v dc supply.

When the light is incident on the Light dependent resistor (LDR), where the resistance

is dependent on the intensity of the light, the non inverting and the inverting terminals of

the op-amp IC311 are compared. If the non inverting terminal voltage is greater than the

inverting terminal voltage then the signal is passed to the opto coupler or the optical link.

The opto coupler or the opto isolator provides isolation between the comparator circuit and

the relay switch, hence this is known as isolating circuit as it provides isolation. The opto

coupler is optical transmission path to transfer an electronic signal between elements of

a circuit , typically a transmitter and a receiver, while keeping them electrically isolated

since the electrical signal is converted to a light beam, transferred, then converted back to

an electrical signal, there is no need for electrical connection between the source and

destination circuits.

When the non inverting terminal is greater than the inverting terminal the electronic

signal is passed to the opto coupler, the opto coupler consists of a led which glows when

the electronic signal is passed. The LED glows and the electric signal is converted to light

signal. When the led glows the receiver in the opto coupler coverts the light signal received

to electronic signal again. This electronic signal is sent to the electromagnetic relay switch

where the switch operates and the bulbs or the domestic appliance connected to the other

end of the electromagnetic relay switch can be operated. The voltage on the other end of

the electromagnetic relay switch is obtained in ac again. thence in the working of the

domestic appliances controlled by the light source the ac voltage supply is converted to dc

voltage after the rectifying process and is again converted to ac supply after the operation

of the electromagnetic rely switch.

CONCLUSION: Hence the light operated domestic appliances controller can be

operated using any light source.


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BIBLIOGRAPHY

1. http://www.circuitstoday.com/


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2. http://en.wikipedia.org/wiki/Opto-isolator

3. http://www.alldatasheet.com/datasheet-pdf/pdf/17875/PHILIPS/LM311N.html

4. http://www.circuitstoday.com/photo-switch-circuit

5. http://www.electronics-lab.com/projects/sensors/001/index.html

6. http://www.rikenresearch.riken.jp/eng/research/5720

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http://en.wikipedia.org/wiki/Opto-isolatorhttp://www.alldatasheet.com/datasheet-pdf/pdf/17875/PHILIPS/LM311N.htmlhttp://www.circuitstoday.com/photo-switch-circuithttp://www.electronics-lab.com/projects/sensors/001/index.htmlhttp://www.rikenresearch.riken.jp/eng/research/5720http://en.wikipedia.org/wiki/Opto-isolatorhttp://www.alldatasheet.com/datasheet-pdf/pdf/17875/PHILIPS/LM311N.htmlhttp://www.circuitstoday.com/photo-switch-circuithttp://www.electronics-lab.com/projects/sensors/001/index.htmlhttp://www.rikenresearch.riken.jp/eng/research/5720

domestic appliances controlled by light source

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