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CHAPTER 1

INTRODUCTION

1.1 AUTOMATIC CONTROL

In the fast-paced world, there is little time for every processes and greater need

for automatically operating systems. The idea for an Automatic temperature controlled

fan stems from this need.

Automatic temperature controlled fan allow you to experience total freedom by

eliminating manual operations for cooling a system during a process. The temperature

of all types of machines used in an industry will increase due to its continues working.

It is necessary to cool the machines for their long life and better working.

Automatic temperature controlled fan will cool the surroundings according to

the surrounding temperature.

1.2 WHAT IS AUTOMATIC TEMPERATURE CONTROLLED FAN?

Automatic temperature controlled fan is a device, that can be used for cooling the

surroundings of a machine or room automatically with the changes in the temperature of

the surroundings.

It uses a thermister for sensing the temperature and a fan for providing cooling. When the

temperature is raised above a fixed point the device automatically switch on the fan and

there by reduces the temperature.

It is an efficient device that can be used for cooling purposes of the machines in an

industry. It can also be used with ceiling fans in a house for cooling a room automatically

according to the temperature.

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1.2.2 ADVANTAGES OF AUTOMATIC TEMPERATURE CONTROLLED FAN

1. Simple and easy to construct.

2. Low cost.

3. Fully automatic.

4. Can be used for a number of applications.

5. Besides, since an optocoupler is used, the control circuit is fully isolated from

power circuit, thus providing added safety.

6. For any given temperature the speed of fan can be adjusted to a desired value.

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CHAPTER 2

BLOCK DIAGRAM

Temperature

sensor

Current to

Voltage

converter

amplification

comparator

Load

2.1. Block diagram description

2.1.1 Temperature sensor

Here we use a NTC (negative temperature coefficient) thermistor. The resistance of the

thermistor decreases with rise in temperature and resistance increases with fall of

temperature. The value of thermistor resistance at 25°C is about 1 kilo-ohm.

2.1.2 Current to voltage converter

There is a current to voltage converter for converting temperature variations into voltage.

Here an op amp is connected as I to v converter. It converts temperature variations into

voltage.

2.1.3 Amplification

To amplify the change in voltage due to change in temperature, instrumentation amplifier

Formed by op-amps A2, A3 and A4 are used. Resistor R2 and zener diode D1

combination is used for generating reference voltage as we want to amplify only change

in voltage due to the change in temperature.

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2.1.4 Comparator

Op-amp μA741 (IC2) works as a comparator. One input to the comparator is the output

from the instrumentation amplifier while the other input is the stepped down, rectified

and suitably attenuated sample of AC voltage. This is a negative going pulsating DC

voltage. Comparator compares the two inputs to give output.

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2.1.5Load

The output from the comparator is coupled to an optocoupler, which in turn controls the

AC power delivered to fan (load).

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CHAPTER 3

AUTOMATIC TEMPERATURE CONTROLLED FAN

3.1 POWER SUPPLY

3.1.1 TRANSFORMER

In brief a transformer is device that

Transfers electric power from one circuit to another

Does so without any change of frequency

Accomplishes this by electromagnetic induction

Contains to electric circuits which are linked by mutual induction

The power supply for this project requires a step-down transformer with 250 V and

output with +12 V&-12V.

3.1.2 RECTIFIER

The rectifier circuit is the heart of a power supply. We use full wave bridge rectifier. The

description is as follows

Full wave bridge rectifier

Fig 3.1 Rectifier

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During the positive half cycles of the secondary voltage diodes D2 and D4 are

conducting and diodes D1 and D3 not conducting. Therefore, current flows through the

secondary winding, diode D2, load resister RL and D4. During the negative half cycles

D1 and D3 are conducting and diodes D2 and D4 are not conducting. Therefore, current

flows through the secondary winding, diode D1, load resistor RL and diode D3.In both

cases, the current passes through the load resistor in the same direction. The rectifier used

in this project is bridge rectifier.

3.1.3 FILTER

The rectifier used in this problem is shunt capacitor filter. A filter circuit is a device

which removes the ac component of rectifiers output but allows the dc component to

reach the load.

The filter circuit should be installed between the rectifier and the load. A filter

circuit is generally a combination of inductor (L) and capacitor (C). The filtering action

of inductor and capacitor depends upon the basic electrical principles. A capacitor passes

ac readily but does not pass dc at all. On the other hand the inductor opposes ac but

allows dc to pass through it. It then becomes clear that suitable network of inductor and

capacitor can effectively remove the ac component to reach the load.

3.1.4 VOLTAGE REGULATORS

A voltage stabilizer is an electronic circuit that supplies a constant voltage regardless

of changes in load current, temperature, and AC line voltage. Although voltage regulators

can be designed using op-amps, it is quicker and easier to use IC Voltage regulators.

In this project a 12V supply is needed. For this first a step down transformer with

rating 230/12-0,500mA is used. The stepped down voltage is rectified using a bridge

rectifier making use of four 1N4007 diodes. The output of the rectifier is filtered using a

capacitive filter. Then the output is given to a voltage regulator IC 7812 to produce a 12V

output.

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Regulator IC (LM 7812)

The LM7812 monolithic 3-terminal positive voltage regulators. They are intended as

fixed voltage regulators in a wide range of applications. In addition to use as fixed

voltage regulators, these devices can be used with external components to obtain

adjustable output voltages and currents. Considerable effort was expended to make the

entire series of regulators easy to use and minimize the number of external components.

Fig 3.2 LM 7812

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3.2 CIRCUIT DIAGRAM OF AUTOMATIC TEMPERATURE

CONTROLLED FAN &IT’S EXPLANATION

Fig 3.3 CIRCUIT DIAGRAM

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In this circuit, the temperature sensor used is an NTC thermistor, i.e. one having a

negative temperature coefficient. The value of thermistor resistance at 25°C is about 1

kilo-ohm. Op-amp A1 essentially works as I to V (current-to-voltage) converter and

converts temperature variations into voltage variations. To amplify the change in voltage

due to change in temperature, instrumentation amplifier formed by op-amps A2, A3 and

A4 Misused. Resistor R2 and zener diode D1 combination is used for generating

reference voltage as we want to amplify only change in voltage due to the

change in temperature.

Op-amp μA741 (IC2) works as a comparator. One input to the comparator is the output

from the instrumentation amplifier while the other input is the stepped down, rectified

and suitably attenuated sample of AC voltage. This is a negative going pulsating DC

voltage. It will be observed that with increase in temperature, pin 2 of IC2 goes more and

more negative and hence the width of the positive going output pulses (at pin 6) increases

linearly with the temperature. Thus IC2 functions as a pulse width modulator in this

circuit. The output from the comparator is coupled to an optocoupler, which in turn

controls the AC power delivered to fan (load).The circuit has a high sensitivity and

The output RMS voltage (across load) can be varied from 120V to 230V (for a

temp.range of 22°C to 36°C), and hence wide variations in speed are available. Also note

that speed varies linearly and not in steps. Besides, since an optocoupler is used, the

control circuit is fully isolated from power circuit, thus providing added safety. Note that

for any given temperature the speed of fan (i.e. voltage across load) can be adjusted to a

desired value by adjusting potentiometer.

3.3 COMPONENTS

3.3.1 RESISTOR

A resistor is a two-terminal passive electronic component which implements

electrical resistance as a circuit element. When a voltage V is applied across the terminals

of a resistor, a current I will flow through the resistor in direct proportion to that voltage.

The reciprocal of the constant of proportionality is known as the resistance R, since, with

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a given voltage V, a larger value of R further "resists" the flow of current I as given by

Ohm's law

I = V/R

The ohm (symbol: Ω) is the SI unit of electrical resistance, named after George

Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and

manufactured over a very large range of values, the derived units of milliohm (1 mΩ =

10−3

Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 10

6 Ω) are also in common usage.

3.3.2 CAPACITORS

A capacitor (formerly known as condenser) is a device for storing electric

charge. The forms of practical capacitors vary widely, but all contain at least two

conductors separated by a non-conductor. Capacitors used as parts of electrical systems,

for example, consist of metal foils separated by a layer of insulating film.

Capacitors are widely used in electronic circuits for blocking direct current while

allowing alternating current to pass, in filter networks, for smoothing the output of power

supplies, in the resonant circuits that tune radios to particular frequencies and for many

other purposes.

A capacitor is a passive electronic component consisting of a pair of conductors

separated by a dielectric (insulator). When there is a potential difference (voltage) across

the conductors, a static electric field develops in the dielectric that stores energy and

produces a mechanical force between the conductors. An ideal capacitor is characterized

by a single constant value, capacitance, measured in farads. This is the ratio of the

electric charge on each conductor to the potential difference between them.

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3.3.3VARIABLE RESISTOR (PRESET)

This type of variable resistor (a preset) is operated with a small

screwdriver or similar tool. It is designed to be set when the circuit is

made and then left without further adjustment. Presets are cheaper than

normal variable resistors so they are often used in projects to reduce

the cost.

Fig 3.6 Variable Resistor

3.3.5optocoupler

In electronics, an opto-isolator, also called an optocoupler, photocoupler, or optical

isolator, is "an electronic device designed to transfer electrical signals by utilizing light

waves to provide coupling with electrical isolation between its input and output". The

main purpose of an opto-isolator is "to preventhigh voltages or rapidly changing voltages

on one side of the circuit from damaging components or distorting transmissions on the

other side." Commercially available opto-isolators withstand input-to-output voltages up

to 10 kV[3]

and voltage transients with speeds up to 10 kV/μs.

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An opto-isolator contains a source (emitter) of light, almost always a near infrared light-

emitting diode (LED), that converts electrical input signal into light, a closed optical

channel (also called dielectrical channel), and a photosensor, which detects incoming

light and either generates electric energy directly, ormodulates electric current flowing

from an external power supply. The sensor can be a photoresistor, a photodiode,

a phototransistor, a silicon-controlled rectifier (SCR) or a triac. Because LEDs can sense

light in addition to emitting it, construction of symmetrical, bidirectional opto-isolators is

possible. An optocoupled solid state relay contains a photodiode opto-isolator which

drives a power switch, usually a complementary pair of MOSFET transistors. Aslotted

optical switch contains a source of light and a sensor, but its optical channel is open,

allowing modulation of light by external objects obstructing the path of light or reflecting

light into the sensor.

3.3.6Triac BT136

TRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic

component which can conduct current in either direction when it is triggered (turned on),

and is formally called a bidirectional triode thyristor or bilateral triode thyristor.

A TRIAC is approximately equivalent to two complementary unilateral thyristors (one is

anode triggered and another is cathode triggered SCR) joined inantiparallel (paralleled

but with the polarity reversed) and with their gates connected together. It can be triggered

by either a positive or a negative voltage being applied to its gate electrode (with respect

to A1, otherwise known as MT1). Once triggered, the device continues to conduct until

the current through it drops below a certain threshold value, the holding current, such as

at the end of a half-cycle of alternating current (AC) mains power. This makes the

TRIAC a very convenient switch for AC circuits, allowing the control of very large

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power flows with mill ampere-scale control currents. In addition, applying a trigger pulse

at a controllable point in an AC cycle allows one to control the percentage of current that

flows through the TRIAC to the load (phase control).

3.3.4Operational amplifiers

An op amp is a DC-coupled high-gain electronic voltage amplifier with a differential

input and, usually, a single-ended output. An op-amp produces an output voltage that is

typically hundreds of thousands times larger than the voltage difference between its input

terminals.

Operational amplifiers are important building blocks for a wide range of electronic

circuits. They had their origins in analog computers where they were used in many

linear, non-linear and frequency-dependent circuits. Their popularity in circuit design

largely stems from the fact that characteristics of the final op-amp circuits with negative

feedback (such as their gain) are set by external components with little dependence on

temperature changes and manufacturing variations in the op-amp itself.

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. Op-amps may be packaged as components, or used as elements of more

complex integrated circuits. The op-amp is one type of differential amplifier.

The circuit symbol for an op-amp is shown where:

: non-inverting input

: inverting input

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: output

: positive power supply

: negative power supply

Operation

The amplifier's differential inputs consist of a input and a input, and ideally the op-

amp amplifies only the difference in voltage between the two, which is called the differential

input voltage. The output voltage of the op-amp is given by the equation,

where is the voltage at the non-inverting terminal, is the voltage at the inverting

terminal and AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the

absence of a feedback loop from the output to the input).

The magnitude of AOL is typically very large—10,000 or more for integrated circuit op-

amps—and therefore even a quite small difference between and drives the amplifier

output nearly to the supply voltage. This is called saturation of the amplifier.

Without negative feedback, and perhaps with positive feedback for regeneration, an op-amp

acts as a comparator. If the inverting input is held at ground (0 V) directly or by a resistor,

and the input voltage Vin applied to the non-inverting input is positive, the output will be

maximum positive; if Vin is negative, the output will be maximum negative. Since there is

no feedback from the output to either input, this is an open loop circuit acting as

a comparator.

An op-amp with negative feedback (a non-inverting amplifier)

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If predictable operation is desired, negative feedback is used, by applying a portion of the

output voltage to the inverting input. The closed loop feedback greatly reduces the gain of

the amplifier. If negative feedback is used, the circuit's overall gain and other parameters

become determined more by the feedback network than by the op-amp itself. If the feedback

network is made of components with relatively constant, stable values, the unpredictability

and inconstancy of the op-amp's parameters do not seriously affect the circuit's

performance. Typically the op-amp's very large gain is controlled by negative feedback,

which largely determines the magnitude of its output ("closed-loop") voltage gain in

amplifier applications, or the transfer function required (in analog computers). High

input impedance at the input terminals and low output impedance at the output terminal(s)

are important typical characteristics.

For example, in a non-inverting amplifier (see the figure on the right) adding a negative

feedback via the voltage divider Rf,Rg reduces the gain. Equilibrium will be established

when Vout is just sufficient to reach around and "pull" the inverting input to the same voltage

as Vin. The voltage gain of the entire circuit is determined by 1 + Rf/Rg. As a simple

example, if Vin = 1 V and Rf = Rg, Vout will be 2 V, the amount required to keep V– at 1 V.

Because of the feedback provided by Rf,Rg this is a closed loop circuit. Its overall gain

Vout / Vin is called the closed-loop gain ACL. Because the feedback is negative, in this

case ACL is less than the AOL of the op-amp.

Op-amp characteristics

Ideal op-amps

An equivalent circuit of an operational amplifier that models some resistive non-ideal

parameters.

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An ideal op-amp is usually considered to have the following properties, and they are

considered to hold for all input voltages:

Infinite open-loop gain (when doing theoretical analysis, a limit may be taken as open

loop gain AOL goes to infinity).

Infinite voltage range available at the output (vout) (in practice the voltages available from

the output are limited by the supply voltages and ). The power supply sources

are called rails.

Infinite bandwidth (i.e., the frequency magnitude response is considered to be flat

everywhere with zero phase shift).

Infinite input impedance (so, in the diagram, , and zero current flows

from to ).

Zero input offset voltage (i.e., when the input terminals are shorted so that , the

output is a virtual ground or vout = 0).

Infinite slew rate (i.e., the rate of change of the output voltage is unbounded) and power

bandwidth (full output voltage and current available at all frequencies).

Zero output impedance (i.e., Rout = 0, so that output voltage does not vary with output

current).

Infinite Common-mode rejection ratio (CMRR).

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Op amp as instrumentation amplifier

Although the instrumentation amplifier is usually shown schematically identical to a

standard op-amp, the electronic instrumentation amp is almost always internally

composed of 3 op-amps. These are arranged so that there is one op-amp to buffer each

input (+,−), and one to produce the desired output with adequate impedance matching for

the function.

The most commonly used instrumentation amplifier circuit is shown in the figure. The

gain of the circuit is

The rightmost amplifier, along with the resistors labeled R2 and R3 is just the

standard differential amplifier circuit, with gain =R3 / R2 and differential input

resistance = 2·R2. The two amplifiers on the left are the buffers. With Rgain removed

(open circuited), they are simple unity gain buffers; the circuit will work in that

state, with gain simply equal to R3 / R2 and high input impedance because of the

buffers. The buffer gain could be increased by putting resistors between the buffer

inverting inputs and ground to shunt away some of the negative feedback; however,

the single resistor Rgain between the two inverting inputs is a much more elegant

method: it increases the differential-mode gain of the buffer pair while leaving the

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common-mode gain equal to 1. This increases the common-mode rejection ratio

(CMRR) of the circuit and also enables the buffers to handle much larger common-

mode signals without clipping than would be the case if they were separate and had

the same gain. Another benefit of the method is that it boosts the gain using a single

resistor rather than a pair, thus avoiding a resistor-matching problem (although the

twoR1s need to be matched), and very conveniently allowing the gain of the circuit

to be changed by changing the value of a single resistor. A set of switch-selectable

resistors or even a potentiometer can be used for Rgain, providing easy changes to the

gain of the circuit, without the complexity of having to switch matched pairs of

resistors.

The ideal common-mode gain of an instrumentation amplifier is zero. In the circuit

shown, common-mode gain is caused by mismatches in the values of the equally-

numbered resistors and by the mis-match in common mode gains of the two input

op-amps. Obtaining very closely matched resistors is a significant difficulty in

fabricating these circuits, as is optimizing the common mode performance of the

input op-amps.

An instrumentation amp can also be built with 2 op-amps to save on cost and

increase CMRR, but the gain must be higher than 2 (+6 dB).

Current to voltage converter

A current-to-voltage converter (or transimpedance amplifier) is an electrical device that

takes an electric current as an input signal and produces a corresponding voltage as an

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output signal. Three kinds of devices are used in electronics: generators (having only

outputs), converters (having inputs and outputs) and loads (having only inputs). Most

frequently, electronic devices use voltage as input/output quantity, as it generally requires

less power consumption than using current.

In some cases, there is a need for converters having current as the input and voltage as the

output. A typical situation is the measuring of current using instruments having voltage

inputs. A current-to-voltage converter is a circuit that

performs current to voltage transformation. In electronic circuitry operating at signal

voltages, it usually changes the electric attribute carrying information from current to

voltage. The converter acts as a linear circuit with transfer ratio k = VOUT/IIN, called the

transimpedance, which has dimensions of [V/A] (also known as resistance). That is why

the active version of the circuit is also referred to as a transresistance or transimpedance

amplifier.

Typical applications of current-to-voltage converter are measuring currents by using

instruments having voltage inputs, creating current-controlled voltage sources, building

various passive and active voltage-to-voltage converters, etc. In some cases, the

simple passive current-to-voltage converter works well; in other cases, there is a need of

using active current-to-voltage converters. There is a close interrelation between the two

versions - the active version has come from the passive one.

Ideal current-to-voltage converters have zero input resistance (impedance), so that they

actually short the input source. Therefore, in this case, the input source has to have some

resistance; ideally, it has to behave as a constant current source. Otherwise, the input

source and the current-to-voltage converter can saturate.

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CHAPTER 4

PCB DESIGN

4.1 INTRODUCTION TO PCB DESIGN

The PCB design starts right from the selection of the laminates .The two main

types of base laminate are epoxy glass and phenolic paper laminates are generally used

for simple circuits. Though it is very cheap and can easily be drilled, phenol paper has

poor electrical characteristics and it absorbs more moisture than epoxy glass. Epoxy glass

has higher mechanical strength.

The important properties that have to be considered for selecting the PCB

substrate are the dielectric strength, insulation resistance, water absorption property,

coeff. of thermal expansion, shear strength, hardness, dimensional stability etc.

4.1.1 MANUFACTURING PROCESS

The steps involved in manufacture are

a. Artwork preparation.

b. Resist preparation.

c. Resist application fixing.

d. Acid etches.

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e. Cleaning and inspection.

f. Resist removal.

4.1.2 PCB FABRICATION

The fabrication of a PCB basically of four steps.

a. Preparing the PCB pattern.

b. Transferring the pattern onto the PCB.

c. Developing the PCB.

d. Finishing ie) drilling, cutting, smoothing, turning etc.

a. Preparing the PCB pattern.

Pattern designing is the primary step in fabricating a PCB in this step, all

interconnection between the components in the given circuit are converted into PCB

tracks several factors such as positioning, the diameter of holes, the area that each

component would occupy, the type of end terminal should be considered.

b. Transferring the PCB Pattern

The copper side of the PCB should be thoroughly cleaned with the help of alcoholic

spirit or petrol must be completely free from dust and other contaminants.

The mirror image of the pattern must be carbon copied and to the laminate the

complete pattern may now be made each resistant with the screen printing technology.

c. Developing the PCB

In this developing all excessive copper is removed from the board and only the

printed pattern is left behind. About 100ml of tape water should be heated to 75 ° C and

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30.5 grams of FeCl3 added to it, the mixture should be thoroughly stirred and a few drops

of HCl may be added to speed up the process.

The board with its copper side facing upward should be placed in a flat bottomed

plastic tray and the aqueous solution of FeCl2 poured in the etching process would take

40 to 60 min to complete.

After etching the board it should be washed under running water and then held

against light .the printed pattern should be cleanly visible. The paint should be removed

with the help of thinner.

d. Finishing Touches

After the etching is completed, hole of suitable diameter should be drilled, then the

PCB may be tin plated using an ordinary 35 Watts soldering rod along with the solder

core, the copper side may be given a coat of varnish to prevent oxidation.

Drilling

Drills for PCB use usually come with either a set of collects of various sizes or a

3-Jaw chuck. For accuracy however 3-jaw chunks aren’t brilliant and small drill below 1

mm from grooves in the jaws preventing good grips.

Soldering

Begin the construction by soldering the resistors followed by the capacitors and

the LEDs diodes and IC sockets. Don’t try soldering an IC directly unless you trust your

skill in soldering. All components should be soldered as shown in the figure. Now

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connect the switch and then solder/screw if on the PCB using multiple washers or spaces.

Soldering it directly will only reduce its height above other components and hamper in its

easy fixation in the cabinet. Now connect the battery lead.

Assembling

The circuit can be enclosed in any kind of cabinet. Before fitting the PCB

suitable holes must be drilled in the cabinet for the switch, LED and buzzer. Note that a

rotary switch can be used instead of a slide type.

Switch on the circuit to be desired range. It will automatically start its timing

cycles. To be sure that it is working properly watch the LED flash. The components are

selected to trigger the alarm a few minutes before the set limit.

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4.2 PCB LAYOUT

4.3 COMPONENTS LAYOUT

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CHAPTER 5

CONCLUSION

Technology makes life simpler and easier. Our aim was to control the temperature of

a machine or room automatically according to the temperature changes. Our mini project

”AUTOMATIC TEMPERATURE CONTROLLED FAN” was an interesting subject for

us. This provided us the opportunity for familiarizing and learning various fields of

electronics. As a team, each of us has dedicated our time and effort for the success of this

project. We are extremely satisfied with the result o this project and we would like to

develop this mini project into higher levels in future. Through this project various fields

of electronics is understood, thus electronics is imbibed through this project.

This circuit allows us to control the temperature automatically. since all the

components used in our project are low cost and readily available our product costs very

low

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BIBILIOGRAPHY

1. www.microchip.com

2. www.nationalsemiconductors.com

3. http://datasheetreference.com

4. www.electronicsforu.com

5. www.wikipedia.org