Automatic Speed Control for Fans and Coolers

AUTOMATIC SPEED CONTROLLER FOR FANS AND COOLERS

CHAPTER 1

INTRODUCTION

INTRODUCTION:

SSCET EEE DEPARTMENT Page 1


This is a device to control the speed of fan and coolers automatically. During

summer nights the temperature is quality high but as time passes temperature starts dropping. So it

is required to reduce the speed of a fan or cooler after particular periods.

The circuit consist of IC1 (555 Timer IC) which is used as an astable multi vibrator

used to generate clock pulses. These are fed to decade dividers or counters formed by IC2 and IC3

(IC CD4017B). These ICs act as divide by 10 and divide by 9 counters respectively. The values of

capacitor C1 and resister R1 and R2 are adjusted so that the final output of IC3 goes high after 8

Hours.

The device presented here makes the fan run at a full speed for pre- determined

time. This speed is decreased to medium after some time and to slow then onwards after a period

of 8 hours, the fan or cooler is switched off. By using this device these reducing can be done

automatically. This also makes the reduced conception of power.



CHAPTER 2

HARDWARE DESCRIPTION

Block Diagram:



Fig.2.1. Block diagram

Block Diagram Description:

The block diagram is shown above the important parts consist of a 555 Timer IC

and 1 divide by 9 and divide by 10 counter and relays. Each block in the block diagram is

explained in detail in below.

Astable Multivibrator:

In this block diagram Astable multivibrator which is used as a pulse generator

circuit it’s high and low state are both unstable. It provides clock pulses for the working of the

decade counter1. The output of the multivibrator toggles with the low and high continuously,

infect generating a train of pulses.

Decade counter1:



It accepts the output from the astable multivibrator as clock pulse. And the counter

starts counting when there is an output at the astable output.

Decade Counter2:

It accept the output from the decade counter1 and counter start counting till there is

an output from the decade counter1 and it act as a divide by 9 counter.

Relay:

This device simply acts as an electronic switch. When the output from the decade

counter 2 reaches the relay terminal it will control the speed of the fan or cooler by switching of

relays.



CHAPTER 3

DESCRITION OF COMPONENTS

LIST OF COMPONENTS:



S.NO

COMPONENTS RATING/TYPE QUANTITY

1. Resistors22K1M10K

214

2. Capacitor 220µ,16V0.01µ

11

3. Transformer 230/(9-0-9)V, 50HZ,500mA 1

4. Transistor BC 548 5

5. Relays SPDT6V,100Ω

4

6. Diodes 1N4001 13

7. IC 555 Astable Multivibrator 1

8. IC 4017B Decade Counter 2

3.1. POWER SUPPLY:



The input to the circuit is applied from the regulated power supply. The a.c. input

i.e., 230V from the mains supply is step down by the transformer to 12V and is fed to a rectifier.

The output obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c

voltage, the output voltage from the rectifier is fed to a filter to remove any a.c components present

even after rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant

dc voltage.

Fig.3.1. Power supply

3.2. TRANSFORMER:



3.2.1 History:

The phenomenon of electromagnetic induction was discovered independently

by Michael Faraday and Joseph Henry in 1831. However, Faraday was the first to publish the

results of his experiments and thus receive credit for the discovery. The relationship

between electromotive force (EMF) or "voltage" and magnetic flux was formalized in

an equation now referred to as "Faraday's law of induction":

.

Where the magnitude of the EMF in volts and ΦB is the magnetic flux through

the circuit (in Webers).

Faraday performed the first experiments on induction between coils of wire,

including winding a pair of coils around an iron ring, thus creating the first toroidal closed-core

transformer.

Fig.3.2.1 Faraday’s experiment with induction between coils of wires

3.2.2 Basic principles:

The transformer is based on two principles: first, that an electric current can

produce a magnetic field (electromagnetism), and, second that a changing magnetic field within a

coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the



current in the primary coil changes the magnetic flux that is developed. The changing magnetic

flux induces a voltage in the secondary coil.

Fig.3.2.2. an ideal transformer

An ideal transformer is shown in the adjacent figure. Current passing through the

primary coil creates a magnetic field. The primary and secondary coils are wrapped around

a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes

through both the primary and secondary coils.

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-up transformers increase voltage, step-down transformers reduce voltage. A step down

power transformer is used to step down the AC voltage from the line voltage of 110 VAC or 220

VAC i.e.; it converts higher voltage at the input side to a lower voltage at the output.


http://www.electronics-project-design.com/PowerSupplies.html

http://www.electronics-project-design.com/PowerSupplies.html

http://en.wikipedia.org/wiki/File:Transformer3d_col3.svg


Usually, DC voltages are required to operate various electronic equipment and these

voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c input

available at the mains supply i.e., 230V is to be brought down to the required voltage level. This is

done by a transformer. Thus, a step down transformer is employed to decrease the voltage to a

required level.

3.2.3 Equivalent circuit:

The physical limitations of the practical transformer may be brought together as an

equivalent circuit model (shown below) built around an ideal lossless transformer. Power loss in

the windings is current-dependent and is represented as in-series resistances Rp and Rs. Flux

leakage results in a fraction of the applied voltage dropped without contributing to the mutual

coupling, and thus can be modeled as reactance of each leakage inductance Xp and Xs in series with

the perfectly coupled region.

Iron losses are caused mostly by hysteresis and eddy current effects in the core, and

are proportional to the square of the core flux for operation at a given frequency. Since the core

Flux is proportional to the applied voltage; the iron loss can be represented by a resistance RC in

parallel with the ideal transformer.

A core with finite permeability requires a magnetizing current Im to maintain the

mutual flux in the core. The magnetizing current is in phase with the flux; saturation effects cause

the relationship between the two to be non-linear, but for simplicity this effect tends to be ignored

in most circuit equivalents. With a sinusoidal supply, the core flux lags the induced EMF by 90°



and this effect can be modeled as a magnetizing reactance (reactance of an effective inductance)

Xm in parallel with the core loss component. Rc and Xm are sometimes together termed the

magnetizing branch of the model. If the secondary winding is made open-circuit, the current I0

taken by the magnetizing branch represents the transformer's no-load current.

The secondary impedance Rs and Xs is frequently moved (or "referred") to the

primary side after multiplying the components by the impedance scaling factor (Np/Ns) 2.

Fig.3.2.3. Transformer equivalent circuit

3.2.4 Step down transformer:


http://en.wikipedia.org/wiki/File:Transformer_equivalent_circuit.svg


Fig.3.2.4. Step down Transformer

Step down transformers can step down incoming voltage, which enables you to

have the correct voltage input for your electrical needs. For example, if your equipment has been

specified for input voltage of 110 volts, and the main power supply is 220 volts, you will need

a step down transformer, which decreases the incoming electrical voltage to be compatible with

your 110 volt equipment.

A transformer is a electrical device with one winding of wire placed close to one or

more other windings, used to couple two or more alternating-current circuits together by

employing the induction between the windings. A transformer in which the secondary voltage is

higher than the primary is call a step-up transformer, if the secondary voltage is less than the

primary, then its a step-down transformer. The product of current times voltage is constant in each

set of windings, so that in a step-up transformer, the voltage increase in the secondary is

accompanied by a corresponding decrease in the current.

3.3. RESISTOR:



Resistors (R) are the most fundamental and commonly used of all the electronic

components, to the point where they are almost taken for granted. There are many different Types

of Resistors available to the electronics constructor, from very small surface mount chip resistors

up to large wire wound power resistors. The principal job of a resistor within an electrical or

electronic circuit is to "resist" (hence the name resistor) or to impede the flow of electrons through

them by using the type of material that they are composed from. Resistors can also act as voltage

droppers or voltage dividers within a circuit.

Fig.3.3.1. A Typical Resistor

Resistors are "Passive Devices", that is they contain no source of power or

amplification but only attenuate or reduce the voltage signal passing through them. This

attenuation results in electrical energy being lost in the form of heat as the resistor resists the flow

of electrons through it.

Then a potential difference is required between the two terminals of a resistor for

current to flow. This potential difference balances out the energy lost. When used in DC circuits

the potential difference, also known as a resistors voltage drop, is measured across the terminals as

the circuit current flows through the resistor.

Most resistors are linear devices that produce a voltage drop across themselves

when an electrical current flow through them because they obey Ohm's Law and different values

of resistance produces different values of current or voltage. This can be very useful in Electronic

circuits by controlling or reducing either the current flow or voltage produced across them.

There are many thousands of different Types of Resistors and are produced in a

variety of forms because their particular characteristics and accuracy suit certain areas of



application, such as High Stability, High Voltage, High Current etc, or are used as general purpose

resistors where their characteristics are less of a problem. Some of the common characteristics

associated with the humble resistor are; Temperature Coefficient, Voltage Coefficient, Noise,

Frequency Response, Power as well as Temperature Rating, Physical Size and Reliability.

. In all Electrical and Electronic circuit diagrams and schematics, the most commonly

used symbol for a fixed value resistor is that of a "zig-zag" type line with the value of its resistance

given in Ohms, Ω. Resistors have fixed resistance values from less than one ohm, ( <1Ω ) to well

over tens of millions of ohms, ( >10MΩ ) in value. Fixed resistors have only one single value of

resistance, for example 100Ω'sbut variable resistors (potentiometers) can provide an infinite

number of resistance values between zero and their maximum value.

3.3.1. Standard Resistor Symbols:

The symbol used in schematic and electrical drawings for a Resistor can either be a

"zigzag" type line or a rectangular box.

There are a large variety of fixed and variable resistor types with different

construction styles available for each group, with each one having its own particular

characteristics, advantages and disadvantages compared to the others. To include all types would

make this section very large so I shall limit it to the most commonly used, and readily available

general purpose types of resistors.

3.3.2. Color coding:



Color Digits [1-3] Multiplier [4] Tolerance [5] TC [6]

Black 0 1

Brown 1 10 1% 100ppm

Red 2 100 2% 50ppm

Orange 3 1k 15ppm

Yellow 4 10k 25ppm

Green 5 100k 0.5%

Blue 6 1M 0.25%

Violet 7 10M

Gray 8

White 9

Gold 5%

Silver 10%

Table.1.Resistance color coding

3.3.3. Resistance color coding:



Fig.3.3.2. Resistance color coding

3.4. CAPACITOR:

Just like the Resistor, the Capacitor, sometimes referred to as a Condenser, is a

passive device, and one which stores its energy in the form of an electrostatic field producing a



potential difference (Static Voltage) across its plates. In its basic form a capacitor consists of two

or more parallel conductive (metal) plates that do not touch or are connected but are electrically

separated either by air or by some form of insulating material such as paper, mica or ceramic

called the Dielectric. The conductive plates of a capacitor can be either square, circular or

rectangular, or be of a cylindrical or spherical shape with the shape and construction of a parallel

plate capacitor depending on its application and voltage rating.

When used in a direct-current or DC circuit, a capacitor blocks the flow of current

through it, but when it is connected to an alternating-current or AC circuit, the current appears to

pass straight through it with little or no resistance. If a DC voltage is applied to the capacitors

conductive plates, a current flows charging up the plates with electrons giving one plate a positive

charge and the other plate an equal and opposite negative charge.

This flow of electrons to the plates is known as the Charging Current and continues

to flow until the voltage across both plates (and hence the capacitor) is equal to the applied

voltage Vc.

At this point the capacitor is said to be fully charged with electrons with the

strength of this charging current at its maximum when the plates are fully discharged and slowly

reduces in value to zero as the plates charge up to a potential difference equal to the applied supply

voltage and this is illustrated below.

3.4.1. Capacitor Construction:



Fig.3.4.1. Capacitor construction

The parallel plate capacitor is the simplest form of capacitor and its capacitance

value is fixed by the surface area of the conductive plates and the distance or separation between

them. Altering any two of these values alters the value of its capacitance and this forms the basis

of operation of the variable capacitors. Also, because capacitors store the energy of the electrons in

the form of an electrical charge on the plates the larger the plates and/or smaller their separation.

the greater will be the charge that the capacitor holds for any given voltage across its plates. In

other words, larger plates, smaller distance, more capacitance.

By applying a voltage to a capacitor and measuring the charge on the plates, the ratio

of the charge Q to the voltage V will give the capacitance value of the capacitor and is therefore

given as: C = Q/V this equation can also be re-arranged to give the more familiar formula for the

quantity of charge on the plates as: Q = C x V.

The property of a capacitor to store charge on its plates in the form of an

electrostatic field is called the Capacitance of the capacitor. Not only that, but capacitance is also

the property of a capacitor which resists the change of voltage across it.



3.4.2. Voltage Rating of a Capacitor:

All capacitors have a maximum voltage rating and when selecting a capacitor

consideration must be given to the amount of voltage to be applied across the capacitor. The

maximum amount of voltage that can be applied to the capacitor without damage to its dielectric

material is generally given in the data sheets as: WV, (working voltage) or as WV DC, (DC

working voltage). If the voltage applied across the capacitor becomes too great, the dielectric will

break down (known as electrical breakdown) and arcing will occur between the capacitor plates

resulting in a short-circuit. The working voltage of the capacitor depends on the type of dielectric

material being used and its thickness.

Another factor which affects the operation of a capacitor is Dielectric Leakage.

Dielectric leakage occurs in a capacitor as the result of an unwanted leakage current which flows

through the dielectric material. Generally, it is assumed that the resistance of the dielectric is

extremely high and a good insulator blocking the flow of DC current through the capacitor (as in a

perfect capacitor) from one plate to the other.



3.5. TRANSISTOR (BC548):

BC548 is general purpose silicon, NPN, bipolar junction transistor. It is used for

amplification and switching purposes. The current gain may vary between 110 and 800. The

maximum DC current gain is 800.

Fig.3.5.1 BC 548 Fig.3.5.2.Pin description of BC 548

3.5.1. Thermal Characteristics of BC 548:

Characteristic Symbol Max Unit

Thermal Resistance, Junction to Ambient

R_JA 200 °C/W

Thermal Resistance, Junction to Case

R_JC 83.3 °C/W

Table.2. Thermal characteristics of BC 548



3.5.2. Maximum ratings:

RATING SYMBOL BC546 UNIT

Collector –Emitter Voltage

VCEO 65 VDC

Collector-Base voltage

VCBO 80 VDC

Emitter-Base voltage

VEBO 6.0 VDC

Total Device Dissipation @ T

A = 25°CDerate above 25°C

PD

6255.0

mWmW/°C

Total Device Dissipation @ T

C= 25°CDerate above 25°C

PD

1.5 12

WattmW/°C

Operating and Storage Junction

Temperature RangeTJ

, Tstg –55 to +150°C

Table.3. Maximum ratings of BC 548



3.5.3. Electrical Characteristics (TA = 25°C unless otherwise noted):

Off Characteristics:

Collector –Emitter Breakdown Voltage (IC = 1.0 mA, IB = 0)

V(BR)CEO 65 - - V

Collector –Base Breakdown Voltage (IC = 100 µA dc)

V(BR)CBO 80 - - V

Emitter –Base Breakdown Voltage (IE = 10 A, IC = 0)

V(BR)EBO 6.0 - - V

Collector Cutoff Current(VCE = 70 V, VBE = 0) VCE= 50 V, VBE = 0) (VCE = 35 V, VBE=0)(VCE= 30 V, TA= 125°C)

ICES - 0.2 15 Ma

Table.4. Electrical characteristics of BC 548



3.5.4. Small signal characteristics:

Current–Gain — Bandwidth Product(IC = 10 mA, VCE = 5.0 V, f = 100 MHz) BC 548

fT 150 300 - Mhz

Output Capacitance(VCB = 10 V, I C= 0, f = 1.0 MHz)

Cobo — 1.7 4.5 pF

Input Capacitance(VEB = 0.5 V, IC = 0, f = 1.0 MHz) Cibo - 10 - pF

Table.5. Small signal characteristics BC 548

The BC548 is a general purpose silicon NPN BJT transistor found commonly in

European electronic equipment; the part number is assigned by Proelectron, which allows many

manufacturers to offer electrically and physically interchangeable parts under one identification.

The BC548 is commonly available in European Union and Commonwealth Countries and is often

the first type of bipolar transistor young hobbyist’s encounter. The BC548 is often featured in

circuit diagrams and designs published in Electronics Magazines such as "Silicon Chip" and

"Elektor".

As a representative of the large family of bipolar transistors the BC548 provides a

"stepping off point" to the use of more esoteric, higher voltage, current or frequency devices for

beginners.



The "BC" part of the number designates a low power silicon NPN transistor. The

BC548 is one of many such. Other part numbers have different characteristics and ratings. Its

complementary, PNP transistor with similar characteristics is the BC558.

A family of older "BC" transistors predates the TO-92 BC54x series, the BC107,

BC108 and BC109, (with complements BC177, BC178 and BC179). These are generally housed

in the TO-18 metal package, the same as what the North American 2N2222 uses. These older

transistors have similar characteristics as the TO-92 BC5xx devices and are generally electrically

interchangeable. The older devices possess a lower Vcebo voltage but similar collector current and

frequency characteristics.



3.6. IC 555 TIMER:

The 555 timer IC was first introduced around 1971 by the Signe tics Corporation as the

SE555/NE555 and was called "The IC Time Machine" and was also the very first and only

commercial timer is available. It provided circuit designers and hobby tinkerers with a relatively

cheap, stable and user-friendly integrated circuit for both monostable and astable applications. The

555 come in two packages, either the round metal-can called the 'T' package or the more familiar

8-pin DIP 'V' package. About 20-years ago the metal-can type was pretty much the standard

(SE/NE types). The 556 timer is a dual 555 version and comes in a 14-pin DIP package, the 558 is a

quad version with four 555's also in a 14 pin DIP case .Inside the 555 timer, are the equivalent of over

20 transistors, 15 resistors, and 2 diodes, depending of the manufacturer. The equivalent circuit, in

block diagram, providing the functions of control, triggering, level sensing or comparison,

discharge, and power output. Some of the more attractive features of the 555 timer are: Supply

voltage between 4.5 and 18 volt, supply current 3 to 6 m A, and a Rise/Fall time of 100 n Sec. It

can also withstand quite a bit of abuse. The Threshold current determine the maximum value of Ra +

Rb. For 15 volt operation the maximum total resistance for R (Ra + Rb) is 20 Mega-ohm. The

supply current, when the output is 'high', is typically 1 milli -amp (m A) or less.

3.6.1. General Description:

The LM555 is a highly stable device for generating accurate time delays or oscillation.

Additional terminals are provided for triggering or resetting if desired. In the time delay mode of

operation, the time is precisely controlled by one external resistor and capacitor. For astable

operation as an oscillator, the free running frequency and duty cycle are accurately controlled with

two external resistors and one capacitor. The circuit may be triggered and reset on falling

waveforms, and the output circuit can source or sink up to 200mA or drive TTL circuits.



Features:

Direct replacement for SE555/NE555

Timing from microseconds through hours

Operates in both astable and monostable modes

Adjustable duty cycle

Output can source or sink 200 m A

Output and supply TTL compatible

Temperature stability better than 0.005% per °C

Normally on and normally off output

Available in 8-pin MSOP package

Pin diagram:

Fig.3.6.1.Pin diagram of 555 Timer



Pin 1 (Ground):The ground (or common) pin is the most-negative supply potential of the device,

which is normally connected to circuit common (ground) when operated from positive supply

voltages.

Pin 2 (Trigger): This pin is the input to the lower comparator and is used to set the latch, which in

turn causes the output to go high. This is the beginning of the timing sequence in mono stable

operation. Triggering is accomplished by taking the pin from above to below a voltage level of

1/3V+ (or, in general, one-half the voltage appearing at pin 5).

Pin 3 (Output): The output of the 555 comes from a high-current totem-pole stage made up of

transistors Q20 - Q24. Transistors Q21 and Q22 provide drive for source-type loads, and their

Darlington connection provides a high-state output voltage about 1.7 volts less than the V+

supply level used.

The state of the output pin will always reflect the inverse of the logic state of the

latch, and this fact may be seen by examining.

Since the latch itself is not directly accessible, this relationship may be best explained

in terms of latch-input trigger conditions.

Pin 4 (Reset): This pin is also used to reset the latch and return the output to a low state. The reset

voltage threshold level is 0.7 volt, and a sink current of 0.1mA from this pin is required to reset the

device. These levels are relatively independent of operating V+ level; thus the reset input is TTL

compatible for any supply voltage. The reset input is an overriding function; that is, it will force the

output to a low state regardless of the state of either of the other inputs.

It may thus be used to terminate an output pulse prematurely, to gate oscillations

from "on" to "off", etc. Delay time from reset to output is typically on the order of 0.5 µS.

The minimum reset pulse width is 0.5 µS.

Pin 5 (Control Voltage): This pin allows direct access to the 2/3 V+ voltage-divider point, the

reference level for the upper comparator.

Use of this terminal is the option of the user, but it does allow extreme flexibility

by permitting modification of the timing period, resetting of the comparator, etc. When the 555

timer is used in a voltage-controlled mode, its voltage-controlled operation ranges from about 1



Volt less than V+ down to within 2 volts of ground (although this is not guaranteed). Voltages

can be safely applied outside these limits, but they should be confined within the limits of V+

and ground for reliability. By applying a voltage to this pin, it is possible to vary the timing of the

device independently of the RC network. The control voltage may be varied from 45 to 90% of the

Vcc in the monostable mode, making it possible to control the width of the output pulse

independently of RC.

Pin 6 (Threshold):Pin 6 is one input to the upper comparator (the other being pin 5) and is used to

reset the latch, which causes the output to go low.

Resetting via this terminal is accomplished by taking the terminal from below to above

a voltage level of 2/3 V+ (the normal voltage on pin 5). The action of the threshold pin is level

sensitive, allowing slow rate-of-change waveforms. The voltage range that can safely be applied to

the threshold pin is between V+ and ground. A dc current, termed the threshold current, must also

flow into this terminal from the external circuit. This current is typically 0.1µA, and will define the

upper limit of total resistance allowable from pin 6 to V+. For either timing configuration

operating at V+ = 5 volts, this resistance is 16 Mega- ohm. For 15 volt operation, the maximum

value of resistance is 20 Mega Ohms.

Pin 7 (Discharge): This pin is connected to the open collector of an NPN transistor (Q14), the

emitter of which goes to ground, so that when the transistor is turned "on", pin 7 is effectively

shorted to ground. Usually the timing capacitor is connected

between pin 7 and ground and is discharged when the transistor turns "on". The conduction state of

this transistor is identical in timing to that of the output stage. It is "on" (low resistance to

ground) when the output is low and "off" (high resistance to ground) when the Output is high. In

both the monostable and astable time modes, this transistor switch is used to clamp the appropriate

nodes of the timing network to ground. Saturation voltage is typically below 100mV (milli -Volt).

Pin 8 (V +): The V+ pin (also referred to as Vcc) is the positive supply voltage terminal of the

555 timer IC. Supply-voltage operating range for the 555 is +4.5 volts (minimum) to +16 volts

(maximum), and it is specified for operation between +5 volts and +15 volts. The device will

operate essentially the same over this range of voltages without change in timing period.

Actually, the most significant operational difference is the output drive capability, which increases

for both current and voltage range as the supply voltage is increased. Sensitivity of time interval



to supply voltage change is low, typically 0.1% per volt. There are special and military devices

available that operate at voltages as high as 18 volts.

3.6.2. Monostable Multivibrator Circuit details:

Pin 1 is grounded. Trigger input is applied to pin 2. In quiescent condition of output

this input is kept at + VCC. To obtain transition of output from stable state to quasi-stable state, a

negative-going pulse of narrow width (a width smaller than expected pulse width of output

waveform) and amplitude of greater than + 2/3 VCC is applied to pin 2. Output is taken from

pin3.Pin4is usually connected to + VCC to avoid accidental reset. Pin 5 is grounded through a

0.01uF capacitor to avoid noise problem. Pin 6 (threshold) is shorted to pin 7. A resistor RA is

connected between pins 6 and 8. At pins 7 a discharge capacitor is connected while pin8 is

connected to supply VCC.

3.6.3. 555 monostable multivibrator operations:

(a) The operation of the circuit is explained below:

Initially, when the output at pin 3 is low i.e. the circuit is in a stable state, the transistor

is on and capacitor- C is shorted to ground. When a negative pulse is applied to pin 2, the trigger

input falls below +1/3 VCC, the output of comparator goes high which resets the flip-flop and

consequently the transistor turns off and the output at pin 3 goes high. This is the transition of the

output from stable to quasi-stable state, as shown in figure. As the discharge transistor is cutoff, the

capacitor C begins charging toward +VCC through resistance RA with a time constant equal to RAC.

When the increasing capacitor voltage becomes slightly greater than+2/3VCC, the output of

comparator 1 goes high, which sets the flip-flop. The transistor goes to saturation, thereby

discharging the capacitor C and the output of the timer goes low.

Thus the output returns back to stable state from quasi-stable state. The output of

the Monostable Multivibrator remains low until a trigger pulse is again applied. Then the cycle

repeats. Trigger input, output voltage and capacitor voltage waveforms are shown in figure.



(b) Mono stable Multi vibrator Design Using 555 timer IC:

The capacitor C has to charge through resistance RA. The larger the time constant

RAC, the longer it takes for the capacitor voltage to reach +2/3VCC. In other words, the RC time

constant controls the width of the output pulse. The time during which the timer output remains

high is given as,

tp =1.0986RAC

Where RA is in ohms and C is in farads. The above relation is derived as below.

Voltage across the capacitor at any instant during charging period is given as,

Vc = VCC (1- e-t/RAC)

Substituting Vc = 2/3 VCC in above equation we get the time taken by the capacitor to

charge from 0 to +2/3VCC.

So +2/3VCC. = VCC. (1 - e-t/RAC) or t - RAC loge 3 = 1.0986 RAC So pulse width, tP =

1.0986 RAC s 1.1 RAC .



Fig.3.6.2. Mono stable Mode



Fig.3.6.3. Waveforms generated monostable mode

3.7. RELAYS:

“A relay is an electrically controllable switch widely used in industrial controls,

automobiles and appliances.”

The relay allows the isolation of two separate sections of a system with two

different voltage sources i.e., a small amount of voltage/current on one side can handle a large

amount of voltage/current on the other side but there is no chance that these two voltages mix up.

Fig.3.7.1. Circuit symbol of a relay

3.7.1 Operation:



When current flows through the coil, a magnetic field are created around the coil

i.e., the coil is energized. This causes the armature to be attracted to the coil. The armature’s

contact acts like a switch and closes or opens the circuit. When the coil is not energized, a spring

pulls the armature to its normal state of open or closed. There are all types of relays for all kinds of

applications.

Fig.3.7.2. Relay Operation and use of protection diodes

Transistors and ICs must be protected from the brief high voltage 'spike' produced

when the relay coil is switched off. The above diagram shows how a signal diode (eg 1N4148) is

connected across the relay coil to provide this protection. The diode is connected 'backwards' so

that it will normally not conduct. Conduction occurs only when the relay coil is switched off, at

this moment the current tries to flow continuously through the coil and it is safely diverted through

the diode. Without the diode no current could flow and the coil would produce a damaging high

voltage 'spike' in its attempt to keep the current flowing.

3.7.2. In choosing a relay, the following characteristics need to be considered:

The contacts can be normally open (NO) or normally closed (NC). In the NC type, the

contacts are closed when the coil is not energized. In the NO type, the contacts are closed

when the coil is energized.

There can be one or more contacts. i.e., different types like SPST (single pole single

throw), SPDT (single pole double throw) and DPDT (double pole double throw) relay.



The voltage and current required to energize the coil. The voltage can vary from a few volts

to 50 volts, while the current can be from a few milliamps to 20milliamps. The relay has a

minimum voltage, below which the coil will not be energized. This minimum voltage is

called the “pull-in” voltage.

The minimum DC/AC voltage and current that can be handled by the contacts. This is in

the range of a few volts to hundreds of volts, while the current can be from a few amps to

40A or more, depending on the relay.

3.7.3. Advantages & Applications:

Advantages:

Automated Load Sharing by transformers

No manual errors

Fit and forget system

Highly sensitive

Low cost and reliable circuit

Applications:

Process Industries

Power Distribution Stations

Agriculture Transformers



3.8. DIODE:

In electronics, a diode is a type of two-terminal electronic component with a

nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a

crystalline piece of semiconductor material connected to two electrical terminals. A vacuum tube

diode (now rarely used except in some high-power technologies) is a vacuum tube with two

electrodes: a plate and a cathode.

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

direction (called the diode's forward direction), while blocking current in the opposite direction

(the reverse direction). Thus, the diode can be thought of as an electronic version of a check valve.

This unidirectional behavior is called rectification, and is used to convert alternating current to

direct current, and to extract modulation from radio signals in radio receivers.

However, diodes can have more complicated behavior than this simple on–off

action. Semiconductor diodes do not begin conducting electricity until a certain threshold voltage

is present in the forward direction (a state in which the diode is said to be forward biased). The



voltage drop across a forward biased diode varies only a little with the current, and is a function of

temperature; this effect can be used as a temperature sensor or voltage reference.

Semiconductor diodes have non-linear electrical characteristics, which can be

tailored by varying the construction of their P–N junction. These are exploited in special purpose

diodes that perform many different functions. For example, diodes are used to regulate voltage

(Zener diodes), to protect circuits from high voltage surges (Avalanche diodes), to electronically

tune radio and TV receivers (varactor diodes), to generate radio frequency oscillations (tunnel

diodes, Gunn diodes, IMPATRT diodes), and to produce light (light emitting diodes). Tunnel

diodes exhibit negative resistance, which makes them useful in some types of circuits.

Diodes were the first semiconductor electronic devices. The discovery of crystals'

rectifying abilities 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 as

germanium are sometimes used.

3.8.1. Semiconductor diodes:

Fig.3.8.1. Typical diode packages in same alignment as diode symbol.

A modern semiconductor diode is made of a crystal of semiconductor like silicon

that has impurities added to it to create a region on one side that contains negative charge carriers

(electrons), called n-type semiconductor, and a region on the other side that contains positive

charge carriers (holes), called p-type semiconductor. The diode's terminals are attached to each of

these regions. The boundary within the crystal between these two regions, called a PN junction, is

where the action of the diode takes place. The crystal conducts a current of electrons in a direction


http://en.wikipedia.org/wiki/File:Diode_pinout_en_fr.svg


from the N-type side (called the cathode) to the P-type side (called the anode), but not in the

opposite direction. However, conventional current flows from anode to cathode in the direction of

the arrow (opposite to the electron flow, since electrons have negative charge).

Another type of semiconductor diode, the Schottky diode, is formed from the

contact between a metal and a semiconductor rather than by a p–n junction.

3.8.2. Current–voltage characteristic:

A semiconductor diode’s behavior in a circuit is given by its current–voltage

characteristic, or I–V graph (see graph below). The shape of the curve is determined by the

transport of charge carriers through the so-called depletion layer or depletion region that exists at

the p–n junction between differing semiconductors. When a p–n junction is first created,

conduction-band (mobile) electrons from the N-doped region diffuse into the P-doped region

where there is a large population of holes (vacant places for electrons) with which the electrons

"recombine". When a mobile electron recombines with a hole, both hole and electron vanish,

leaving behind an immobile positively charged donor (dopant) on the N side and negatively

charged acceptor (dopant) on the P side. The region around the p–n junction becomes depleted of

charge carriers and thus behaves as an insulator.

However, the width of the depletion region (called the depletion width) cannot grow

without limit. For each electron–hole pair that recombines, a positively charged dopant ion is left

behind in the N-doped region, and a negatively charged dopant ion is left behind in the P-doped

region. As recombination proceeds more ions are created, an increasing electric field develops

through the depletion zone which acts to slow and then finally stop recombination. At this point,

there is a "built-in" potential across the depletion zone.

If an external voltage is placed across the diode with the same polarity as the built-

in potential, the depletion zone continues to act as an insulator, preventing any significant electric

current flow (unless electron/hole pairs are actively being created in the junction by, for instance,

light. see photodiode). This is the reverse bias phenomenon. However, if the polarity of the

external voltage opposes the built-in potential, recombination can once again proceed, resulting in

substantial electric current through the p–n junction (i.e. substantial numbers of electrons and holes

recombine at the junction). For silicon diodes, the built-in potential is approximately 0.7 V (0.3 V

for Germanium and 0.2 V for Schottky). Thus, if an external current is passed through the diode,



about 0.7 V will be developed across the diode such that the P-doped region is positive with

respect to the N-doped region and the diode is said to be "turned on" as it has a forward bias.

A diode’s 'I–V characteristic' can be approximated by four regions of operation.

Fig.3.8.2. I–V characteristics of a P–N junction diode

3.8.3. Types of semiconductor diode:

There are several types of junction diodes, which either emphasize a different

physical aspect of a diode often by geometric scaling, doping level, choosing the right electrodes,

are just an application of a diode in a special circuit, or are really different devices like the Gunn

and laser diode and the MOSFET:

Normal (p-n) diodes, which operate as described above, are usually made of doped

silicon or, more rarely, germanium. Before the development of modern silicon power rectifier

diodes, cuprous oxide and later selenium was used; its low efficiency gave it a much higher

forward voltage drop (typically 1.4 to 1.7 V per "cell", with multiple cells stacked to increase the

peak inverse voltage rating in high voltage rectifiers), and required a large heat sink (often an

extension of the diode’s metal substrate), much larger than a silicon diode of the same current

ratings would require. The vast majority of all diodes are the p-n diodes found in CMOS integrated

circuits, which include two diodes per pin and many other internal diodes.


http://en.wikipedia.org/wiki/File:Diode-IV-Curve.svg


DiodeZenerdiode

Schottkydiode

Tunneldiode

Light-emittingdiode

Photodiode VaricapSilicon controlled

rectifier

Fig.3.8.3. some diode symbols.

Applications:

Radio demodulation

Power conversion

Over-voltage protection

Logic gates

Ionizing radiation detectors


http://en.wikipedia.org/wiki/File:Diode_symbol.svg

http://en.wikipedia.org/wiki/File:Zener_diode_symbol.svg

http://en.wikipedia.org/wiki/File:Schottky_diode_symbol.svg

http://en.wikipedia.org/wiki/File:Tunnel_diode_symbol.svg

http://en.wikipedia.org/wiki/File:LED_symbol.svg

http://en.wikipedia.org/wiki/File:Photodiode_symbol.svg

http://en.wikipedia.org/wiki/File:Varicap_symbol.svg

http://en.wikipedia.org/wiki/File:SCR_symbol.svg


3.9. IC 4017 DECADE COUNTER:

The M74HC 4017 is a high speed CMOS decade counter divider fabricated with

silicon gate C2 MOS Technology. The M74HC 4017 is a five stage Johnson counter with 10

decoded outputs. Each of the decoded outputs is normally low and sequentially goes high on the

low to high transition of the clocked input. Each output stays high for 1 clock period of the low to

high after output 10 goes slow, and can be used in conjunction with the clock enable (CKEN) to

cascade several stages. The clock enabled input disables counting when in the high stage. A clear

(CLR) input is also provide which when taken high sets all the decoded outputs low. All inputs are

equipped with protection circuit against static discharge and transient excess voltage.

Pin Number & Purpose:



Table.6.Pin configuration of IC CD4017

Pin Connection:

Fig. 3.9.Pin diagram of IC 4017



Ordering Code:

Connection Diagram:

Fig.3.9.1.Connection diagram of IC CD4017B



Logic Diagram:

Fig.3.9.2.Logic diagram of IC CD4017B







Table.7.DC&AC Electrical Characteristics

Timing Diagrams:

Fig.3.9.3.Timing diagram of IC CD4017B



Features:

Wide supply voltage range: 3V to 15V

High noise immunity: 0.45V

Medium speed operation: 5 MHz

Low power: 10Micro W

Fully static operation

Applications:

Automotive

Instrumentation

Medical electronics

Alarm systems

Industrial electronics

Remote metering



CHAPTER 4

WORKING OF AUTOMATIC SPEED CONTROLLER FOR FANS

AND COOLERS



Working:

The circuit for the automatic speed controller for fans and coolers is shown in the figure.

The supply voltage of 230V, 50Hz is given to the step down transformer and it is converted

to 9V.

The bridge rectifier converts AC to pulsating DC supply and is filtered with smoothing

capacitor.

In the circuit diagram IC1 (555 timer IC) act as an astable multivibrator. It is used to

generate clock pulses. The pulses are fed to a decade divider counter, which is formed by

IC2 and IC3.

These ICs act as divide by 10 counters and divide by 9 counters respectively. The values

of capacitors C1, resister R2 and R2 are so adjusted that the final output of IC3 goes high

about 8hours.

The first two outputs of IC3 (Q0 and Q1) are connected through diode D1 and D2 to the

base of the transistor T1. Initially output Q0 is high and there for relay RL1 is energized. It

remains energized when Q1 becomes high. The method of connecting the gadget of the fan

or cooler is given in the figure.

Initially the fan shall get A/C supply directly so it shall be run at high speed. When the

output Q2 becomes high and Q1 becomes low, relay RL1 is turned off and relay RL2 is

turned on.

The fan gets A/C through a resistance and its speed drops to medium. This continues until

output Q4 is high. When Q4 goes low and Q5 goes high, relay RL2 is activated thus the fan

run at low speed.

Throughout the process, pin 11 of the IC is low, so T4 is cut off, thus keeping T5 in

saturation and relay RL4 is on. At the end of the cycle, when pin 11(Q9) becomes high T4

get saturated and T5 is cut off. Relay RL4 is switched off, thus switching of the fan or

cooler.



Using the given circuit the fan shall run at high speed for a comparatively lesser time when

either of Q0 or Q1 output is high. At medium speed it will run for a moderate time period

when any of three outputs(Q2 to Q4) is high, while at low speed it will run for a much

longer time period when any of the four outputs(Q5 to Q8) is high.

It is possible to make the fan run at the three speeds for an equal amount of time by

connecting three terminal decoded outputs of IC3 to each of the transistors T1 to T3. One

can also get more than three speeds by using an additional relay transistor and associated

components and connecting one or more outputs of IC3 to it.

It has been designed to reduce the amount of electric power.

Circuit Diagram:



Fig. Existing arrangement for fan speed control

Fig. Modified arrangement for speed control

Fig. Speed control arrangement for cooler with different windings for various speeds



CHAPTER 5

APPLICATIONS&CONCULSION



Applications:

Used to control the speed of fans and coolers automatically.

This device can be used in bed rooms during night hours.

This device can be used as a power saving system for hotels and houses.

Advantages:

No manual support is needed, it is fully automatic.

Electrical energy can be saved to a greater extent.

Only less power is needed for the operation.

Lifetime of fan or coolers can be increased.

.

CONCLUSION:

The automatic speed controller for fans or coolers is used to control the speed

automatically. We can also assign different time periods for each speed by designing the circuit to

the need. By using this circuit the electric power can be saved to a greater extent and increase

lifespan of fans and coolers.

BIBLIOGRAPHY:



www.datasheetarchive.com

Electronics for you – Magazine

www.semiconductor.com

www.ecelab.com


Documents

Automatic Speed Control for Fans and Coolers