automatic speed control for fans and coolers
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AUTOMATIC SPEED CONTROLLER FOR FANS AND COOLERS
CHAPTER 1
INTRODUCTION
INTRODUCTION:
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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.
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CHAPTER 2
HARDWARE DESCRIPTION
Block Diagram:
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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:
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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.
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CHAPTER 3
DESCRITION OF COMPONENTS
LIST OF COMPONENTS:
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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:
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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:
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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
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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.
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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°
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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:
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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:
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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
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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:
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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:
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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
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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:
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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.
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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.
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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
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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
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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
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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.
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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.
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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.
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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
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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
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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
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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.
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(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 .
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Fig.3.6.2. Mono stable Mode
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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:
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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.
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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
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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
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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
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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,
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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.
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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
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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:
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Table.6.Pin configuration of IC CD4017
Pin Connection:
Fig. 3.9.Pin diagram of IC 4017
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Ordering Code:
Connection Diagram:
Fig.3.9.1.Connection diagram of IC CD4017B
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Logic Diagram:
Fig.3.9.2.Logic diagram of IC CD4017B
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Table.7.DC&AC Electrical Characteristics
Timing Diagrams:
Fig.3.9.3.Timing diagram of IC CD4017B
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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
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CHAPTER 4
WORKING OF AUTOMATIC SPEED CONTROLLER FOR FANS
AND COOLERS
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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.
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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:
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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
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CHAPTER 5
APPLICATIONS&CONCULSION
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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:
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AUTOMATIC SPEED CONTROLLER FOR FANS AND COOLERS
www.datasheetarchive.com
Electronics for you – Magazine
www.semiconductor.com
www.ecelab.com
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