Variable power supply with digital control with seven segments display

A
PROJECT STAGE-I REPORT
ON
“Variable Power Supply with Digital Control with
seven segments display”
Submitted in the partial fulfillment of the award of
Bachelor of Technology
(Rajasthan Technical University, Kota)
In
ELECTRICAL ENGINEERING
2013-2014
Guided by: Submitted by:
Mr. Shivraj Sharma PRITAM SOLANKI(EE/10/85)
Assistant Professor PRANSHU TIWARI(EE/10/83)
Department of Electrical Engg. PIYUSH SHARMA (EE/10/82)
PRASHANTJAIN (EE/10/140)
4th year, VIII SEM,EE
DEPARTMENT OF ELECTRICAL ENGINEERING
POORNIMA COLLEGE OF ENGINEERING
ISI-06, RIICO INSTITUTIONAL AREA
SITAPURA, JAIPUR –302 022

DEPARTMENT OF ELECTRICAL ENGINEERING
POORNIMA COLLEGE OF ENGINEERING
This is to certify that project entitled “been carried out by Variable Power Supply with Digital Control with seven segments display
PRITAM SOLANKI, PRANSHU TIWARI, PIYUSH SHARMA, PRASHANT JAIN
in partial fulfilment of the degree of Bachelor of Technology in
Electrical Engineering of Rajasthan Technical University,
Kota, during the academic year 2013-2014
elsewhere for the award of any other degree. The work has been found satisfactory and is approved for submission.
Mr. SHIVRAJ SHARMA Mr. Project Guide JAIPUR -302022
CERTIFICATE
4. To the best of my knowledge and belief this work has not been submitted
r. HARBEER SINGH
Mr. VAIBHAV JAIN
Project Coordinator
HOD, EE Department
i
display” has
under my guidance
. Dr. R.P. RAJORIA
Campus Director (PCE)

ACKNOWLEDGEMENT
We take this opportunity to express our deep sense of gratitude and respect towards our guide,
Mr. Shivraj Sharma Assistant Professor, Department of Electrical Engineering, Poornima
College of Engineering. We are very much indebted to him for the generosity, expertise and
guidance; we have received from him while working on this project and throughout our studies.
Without his support and timely guidance, the completion of our seminar would have seemed a
farfetched dream. In this respect we find ourselves lucky to have him as our guide. He has
guided us not only with the subject matter, but also taught us the proper style and technique of
working and presentation.
We are grateful to our respected Dr. R. P. Rajoria (Campus Director), Dr. Om Prakash
Sharma (Principal,PCE), Mr. Vaibhav Jain (HOD Department Electrical Engineering),
Mr. Harbeer Singh (Seminar Coordinator), for guiding us while working on project.All the
staff members of the Department of Electrical Engineering for their constant encouragement and
all those who helped us directly or indirectly in our endeavor.
PCE/EE/ii
PRITAM SOLANKI
PRANSHU TIWARI
PIYUSH SHARMA
PRASHANT JAIN

PREFACE
Today the world swiftly changing, there are multiple challenges faced by us. Surly it is the
knowledge through technology, which makes us to overcome them. The project stage-I report,
which is an integral part of four years engineering program provides a platform to all the student
to augment their technical study through practical revelation. It is the time, which is effectively
used by students to enhance their interaction with technical atmosphere. The project stage-I is
obligatory as per university course outline. This report is based on work done and theory gained
during analysis of the topic. The report basically introduces working of project in detail.
Variable Power Supply with Digital Control with seven segments display is one of the
applications of electronics to increase the facilities of life. It is facilitates the operation of voltage
regulators around the electronics lab. It provides a system that is simple to understand and also to
operate, a system that would be cheaper and affordable. It adds more comfort to everyday living
by removing the inconvenience of having to move around to operate a fan regulator.
We have been fortunate to get a chance for making the project stage-I under guidance of Mr.
Shivraj Sharma (Assistant Professor, Electrical Engineering Department.) & our project
coordinator Mr. Harbeer Singh.
PCE/EE/iii
PRITAM SOLANKI
PRANSHU TIWARI
PIYUSH SHARMA
PRASHANT JAIN

ABSTRACT
Variable Power Supply with Digital Control with seven segments display is the most
frequently used device in electronic workshops and laboratories is a universal power supply
that provides a variable, fluctuation-free output. Here we present a variable power supply
with digital control that is simple and easy to construct. The circuit is built around an
adjustable 3-terminal positive-voltage regulator IC LM317, CMOS decade counter IC
CD4017, timer IC NE555 and 3-terminal fixed negative-voltage regulator LM7912. The AC
mains supply is stepped down by transformer X1 to deliver a secondary output of 12V-0-12V
AC, 1A. The output of the transformer is rectified by a full-wave rectifier comprising diodes
D1 through D4. Capacitors C1 through C4 are connected in parallel to rectifier diodes to
bypass undesired spikes and provide smooth and fluctuation-free power. Capacitors C5 and
C13 are used as filters to eliminate ripple. Here both negative and positive half cycles are
used to obtain positive as well as negative DC output. LED1, along with current-limiting
resistor R1, is used for mains ‘on’ indication. Timer IC NE555 (IC1) is wired as an astable
multivibrator. It generates clock pulses when switch S2 is pressed. IC CD4017 is a decade
ring counter. Each of its ten outputs goes high one by one when a clock pulse is received. The
outputs of IC CD4017 are connected to the bases of transistors T1 through T10, respectively,
as shown in the figure. LED3 through LED11 are used here to indicate the voltage levels. The
collectors of transistors T2 through T10 are connected to presets VR1 through VR9,
respectively, which are used to set the output voltage. Presets VR1 through VR9 are adjusted
to get the desired output voltage. When switch S2 is pressed, the output of IC1 goes high. As
a result, the outputs of IC2 go high one by one as a ring counter. Since presets VR1 through
VR9 are connected at the collectors of transistors T2 through T10, respectively, different
output resistances appear between the adjustable and ground terminals of IC4, resulting in
different output voltages. By using a properly calibrated digital multimeter you can easily
adjust the presets to obtain 1.5V to 12V. Assemble the circuit on any generalpurpose PCB
and enclose it in a suitable cabinet. Use suitable heat-sinks for regulators IC3 and IC4. Since
pin configurations of the regulators are different, never fix both regulators on the same
heatsink. For S2 and S3, using microswitches will enhance the beauty of the unit. LED2 is
used to indicate the negative 12V DC voltage.
PCE/EE/IX

CONTENTS
Certificate …i
Acknowledgement ...ii
Preface …iii
Contents …iv
Figure index …vi
Table index …viii
Abstract …ix
CHAPTER PAGE NO.
1. Introduction 1-1
1.1. Introduction 1
2. Circuit Description 2-4
2.1. Block diagram 2
2.2. Circuit diagram 3
2.3. Working of the circuit 4
3. Component Description 5-25
3.1. Component requirement 5
3.2. Component description 6
3.2.1 Monostable multivibrator (NE 555) 6
3.2.2 Decade counter (CD 4017) 8
3.3.3 LM 79LXX 11
3.3.4 LM 317 15
3.3.5 Regulator section (IC-7809) 18
3.3.6 Transformer 20
3.3.7 Power supply 20
3.3.8 Resistor 20
3.3.9 LED 22
3.3.10 Capacitor 22
3.3.11 Diode 23
3.3.12 Transistor 24
4. Seven segment display 26-28
4.1 Introduction 26
4.2 History 26
PCE/EE/IV

4.3 Concept and visual structure 27
4.4 Implementation 27
4.5 Displaying letters 28
5. PCB Designing 29-30
5.1 Printed circuit board 29
6. Soldering of component 31-33
6.1 Introduction 31
6.2 Soldering tools 32
7. Reault and application 34-34
7.1 Result analysis 34
7.2 Specification of the motor 34
7.3 Application 34
7.4 Advantage 34
8. Conclusion 35
Reference 36
PCE/EE/V

FIGURE INDEX
figure no. Figure name Page no.
2.1 Block Diagram of variable power supply with digital
PCE/EE/VI
control
2
2.2 Circuit Diagram of variable power supply with digital
control
3
3.1 Monostable Multivibrator (NE 555) 6
3.2 Decade counter (CD 4017) 8
3.3 Typical application & connection diagram of LM79LXX 12
3.4 Typical performance characteristics of LM79LXX 14
3.5 Typical applications of LM317 16
3.6 Regulator IC-7809 18
3.7 Step down transformer 20
3.8 Power supply 20
3.9(a) Variable Resistor 21
3.9(b) Fixed Resistor 21
3.10 LED 22
3.11 Electrolytic capacitor 23
3.12 Diode 24
3.13 Transistor 25
4.1 A typical 7-segment LED display component, with
decimal point
26
5.1 Copper PCB 29

5.2 PCB for variable power supply with digital control
PCE/EE/VII
30
6.1 Soldering Iron 32

TABLE INDEX
Table no. Name Page
3.1 Data sheet of IC-555 07
3.2 Data sheet of DC characteristics of CD 4017 09
3.3 Data sheet of AC characteristics of CD 4017
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10
3.4 Data sheet of characteristics of LM79LXX 13
3.5 Data sheet of characteristics of LM317 17
3.6 Data Sheet of IC-7809 19
4.1 Hexadecimal encoding for displaying the digits 0 to F 28
7.1 Results for variable resistors 34

CHAPTER-1
INTRODUCTION
1.1.INTRODUCTION :
Variable Power Supply with Digital Control with seven segments display is the most
frequently used device in electronic workshops and laboratories is a universal power supply
that provides a variable, fluctuation-free output. Here we present a variable power supply
with digital control that is simple and easy to construct. The circuit is built around an
adjustable 3-terminal positive-voltage regulator IC LM317, CMOS decade counter IC
CD4017, timer IC NE555 and 3-terminal fixed negative-voltage regulator LM7912. The AC
mains supply is stepped down by transformer X1 to deliver a secondary output of 12V-0-12V
AC, 1A. The output of the transformer is rectified by a full-wave rectifier comprising diodes
D1 through D4. Capacitors C1 through C4 are connected in parallel to rectifier diodes to
bypass undesired spikes and provide smooth and fluctuation-free power. Capacitors C5 and
C13 are used as filters to eliminate ripple. Here both negative and positive half cycles are
used to obtain positive as well as negative DC output. LED1, along with current-limiting
resistor R1, is used for mains ‘on’ indication. Timer IC NE555 (IC1) is wired as an astable
multivibrator. It generates clock pulses when switch S2 is pressed. IC CD4017 is a decade
ring counter. Each of its ten outputs goes high one by one when a clock pulse is received. The
outputs of IC CD4017 are connected to the bases of transistors T1 through T10, respectively,
as shown in the figure. LED3 through LED11 are used here to indicate the voltage levels. The
collectors of transistors T2 through T10 are connected to presets VR1 through VR9,
respectively, which are used to set the output voltage. Presets VR1 through VR9 are adjusted
to get the desired output voltage. When switch S2 is pressed, the output of IC1 goes high. As
a result, the outputs of IC2 go high one by one as a ring counter. Since presets VR1 through
VR9 are connected at the collectors of transistors T2 through T10, respectively, different
output resistances appear between the adjustable and ground terminals of IC4, resulting in
different output voltages. By using a properly calibrated digital multimeter you can easily
adjust the presets to obtain 1.5V to 12V. Assemble the circuit on any generalpurpose PCB
PCE/EE/01

CHAPTER-2
CIRCUIT DESCRIPTION
PCE/EE/02
2.1. BLOCK DIAGRAM:
The following shows block diagram of how Variable Power Supply with Digital
Control with seven segments display work.
Fig.2.1.Block Diagram of variable power supply with digital control

2.2. CIRCUIT DIAGRAM:
The following shows circuit diagram of wireless speed control of single phase
induction motor.
Fig.2.2.Circuit
Diagram of variable power supply with digital control
PCE/EE/03

PCE/EE/04
2.3. WORKING OF THE CIRCUIT:
The most frequently used device in electronic workshops and laboratories is a
universal power supply provides a variable, fluctuation-free output. Here we present a
variable power supply with digital control that is simple and easy to construct. The circuit is
built around an adjustable 3-terminal positive-voltage regulator IC LM317, CMOS decade
counter IC CD4017, timer IC NE555 and 3-terminal fixed negative-voltage regulator
LM7912. The AC mains supply is stepped down by transformer X1 to deliver a secondary
output of 12V-0-12V AC, 1A. The output of the transformer is rectified by a full-wave
rectifier comprising diodes D1 through D4. Capacitors C1 through C4 are connected in
parallel to rectifier diodes to bypass undesired spikes and provide smooth and fluctuation-free
power. Capacitors C5 and C13 are used as filters to eliminate ripple. Here both negative and
positive half cycles are used to obtain positive as well as negative DC output. LED1, along
with current-limiting resistor R1, is used for mains ‘on’ indication. Timer IC NE555 (IC1) is
wired as an astable multivibrator. It generates clock pulses when switch S2 is pressed. The
output of IC1 is connected, via an RC network, to the clock input of counter IC CD4017
(IC2). IC CD4017 is a decade ring counter. Each of its ten outputs goes high one by one
when a clock pulse is received. The outputs of IC CD4017 are connected to the bases of
transistors T1 through T10, respectively, as shown in the figure. LED3 through LED11 are
used here to indicate the voltage levels. The collectors of transistors T2 through T10 are
connected to presets VR1 through VR9, respectively, which are used to set the output
voltage. Adjustable voltage regulator IC LM317 (IC4) develops 1.25V nominal reference
voltage (VREF) between its output and the adjustable terminal. The reference voltage appears
across resistor R16. When the voltage is constant, a constant current flows through one of the
output-setting variable resistors (VRset, VR1 through VR9), giving an output voltage at pin 2
of IC4 as follows:
VOUT=1.25(1+VRset/R16).
Presets VR1 through VR9 are adjusted to get the desired output voltage. The collector of
transistor T1 is directly connected to ADJ terminal (pin 1) of IC4, so the output voltage of
IC4 will be the voltage across fixed resistor R16, which is equal to 1.25V. When switch S3 is
pressed, pin 3 of IC2 goes high and the output voltage becomes 1.2V. When switch S2 is
pressed, the output of IC1 goes high. As a result, the outputs of IC2 go high one by one as a
ring counter. Since presets VR1 through VR9 are connected at the collectors of transistors T2
through T10, respectively, different output resistances appear between the adjustable and
ground terminals of IC4, resulting in different output voltages. By using a properly calibrated
digital multimeter you can easily adjust the presets to obtain 1.5V to 12V. A fixed, negative
12V DC can be obtained by using fixed, negative-voltage regulator IC LM7912 (IC3). Thus
the power supply unit can be used for circuits requiring both negative and positive DC
voltages. When CD4017 is reset by pressing switch S3, the output voltage becomes 1.2V and
all the voltage-indication LEDs turn off. Assemble the circuit on any generalpurpose PCB

CHAPTER-3
COMPONENTS DESCRIPTION
3.1 COMPONENTS REQUIREMENTS:
1. IC NE555 1
2. CD4017 1
3. LM79LXX 1
4. LM317 1
5. LM7809 1
6. IC Base 8 Pin 2
7. IC Base 16 Pin 1
8. IC Base 6 Pin 2
9. Transistor BC-548 1
10. Diode IN4007 6
11. LED 5 mm , Green 3
12. 5 mm , Red 3
13. 5 mm , Yellow 4
14. Capacitor 1000 mfd / 25 V 1
15. 10 mfd / 50 V 1
16. 4.7 mfd / 50 V 1
17. 1 mfd / 63 V 1
18. 0.1 mfd Ceramic 1
19. 0.01 mfd Ceramic 2
20. Variable Resistance 200K 9
21. Resistance 47 Ohms 2
22. 330 Ohms 1
23. 47K 1
24. Transformer 0-12 Volts, 500 ma 1
PCE/EE/05

3.2 COMPONENTS DESCRIPTIONS:
3.2.1 MONOSTABLE MULTIVIBRATOR (NE 555) :
A multivibrator is an electronic circuit used to implement a variety of simple twostate
systems such as oscillators, timers and flip-flops. A monostable multivibrator, as its name
indicates, has a stable state and a quasi-stable state. An external trigger must be applied to
change from the stable state to the quasi-stable state.
Fig 3.1 Monostable Multivibrator (NE 555)
Here, two NE 555 ICs are wired as monostable multivibrators. The trigger to the first
multivibrator is the signals from the infrared receiver module. This multivibrator is used to
delay the clock pulse of the decade counter. The second multivibrator is triggered by the opto
coupler. The LM555/NE555/SA555 is a highly stable controller capable of producing
accurate timing pulses. With monostable operation, the time delay is controlled by one
external resistor and one capacitor. With astable operation, the frequency and duty cycle are
accurately controlled with two external resistors and one capacitor. When the low signal input
is applied to the reset terminal, the timer output remains low regardless of the threshold
voltage or the trigger voltage. Only when the high signal is applied to the reset terminal,
timer's output changes according to threshold voltage and trigger voltage. When the threshold
voltage exceeds 2/3 of the supply voltage while the timer output is high, the timer's internal
discharge Tr. turns on, lowering the threshold voltage to below 1/3 of the supply voltage.
During this time, the timer output is maintained low. Later, if a low signal is applied to the
trigger voltage so that it becomes 1/3 of the supply voltage, the timer's internal discharge Tr.
turns off, increasing the threshold voltage and driving the timer output again at high.
PCE/EE/06

Table 3.1 Data sheet of IC-555
PCE/EE/07

3.2.2 DECADE COUNTER (CD 4017) :
In digital logic and computing, a counter is a device which stores (and sometimes displays)
the number of times a particular event or process has occurred, often in relationship to a clock
signal. Decade counter is a counter that counts through 10 states. It is also known as a mod-
10 counter.
Fig 3.2 Decade counter (CD 4017)
Here, CD 4017 is used as decade counter. Here actually ten outputs are there from which five
are used (Q0 to Q4), Q5 is not used and Q6 is used to reset. The output of monostable
multivibrator (IC1) is used to delay the clock pulse of the decade counter. The CD4017BC is
a 5-stage divide-by-10 Johnson counter with 10 decoded outputs and a carry out bit. The
CD4022BC is a 4-stage divide-by-8 Johnson counter with 8 decoded outputs and a carry-out
bit. These counters are cleared to their zero count by a logical “1” on their reset line. These
counters are advanced on the positive edge of the clock signal when the clock enable signal is
in the logical “0” state. The configuration of the CD4017BC and CD4022BC permits medium
speed operation and assures a hazard free counting sequence. The 10/8 decoded outputs are
normally in the logical “0” state and go to the logical “1” state only at their respective time
slot. Each decoded output remains high for 1 full clock cycle. The carry-out signal completes
a full cycle for every 10/8 clock input cycles and is used as a ripple carry signal to any
succeeding stages.
PCE/EE/08

Table 3.2 Data sheet of DC characteristics of CD 4017
PCE/EE/09

Table 3.3 Data sheet of AC characteristics of CD 4017
PCE/EE/010

3.2.3 LM 79LXX :
The LM320L/LM79LXXAC series of 3-terminal negative voltage regulators features fixed
output voltages of b5V, b12V, and b15V with output current capabilities in excess of 100
mA. These devices were designed using the latest computer techniques for optimizing the
packaged IC thermal/ electrical performance. The LM79LXXAC series, even when combined
with a minimum output compensation capacitor of 0.1 mF, exhibits an excellent transient
response, a maximum line regulation of 0.07% VO/V, and a maximum load regulation of
0.01% VO/mA. The LM320L/LM79LXXAC series also includes, as self-protection circuitry:
safe operating area circuitry for output transistor power dissipation limiting, a temperature
independent short circuit current limit for peak output current limiting, and a thermal
shutdown circuit to prevent excessive junction temperature. Although designed primarily as
fixed voltage regulators, these devices may be combined with simple external circuitry for
boosted and/or adjustable voltages and currents. The LM79LXXAC series is available in the
3-lead TO-92 package, and SO-8; 8 lead package. The LM320L series is available in the 3-
lead TO-92 package. For output voltage other than b5V, b12V and b15V the LM137L series
provides an output voltage range from 1.2V to 47V.
Features:
· Preset output voltage error is less than g5% overload,
PCE/EE/011
line and temperature
· Specified at an output current of 100 mA
· Easily compensated with a small 0.1 mF output
capacitor
· Internal short-circuit, thermal and safe operating area
protection
· Easily adjustable to higher output voltages
· Maximum line regulation less than 0.07% VOUT/V
· Maximum load regulation less than 0.01% VOUT/mA

Fig 3.3 Typical application & connection diagram of LM79LXX
PCE/EE/012

Table 3.4
Data sheet of characteristics of LM79LXX
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Fig 3.4 Typical performance characteristics of LM79LXX
PCE/EE/014

3.2.4 LM 317:
The LM317 series of adjustable 3-terminal positive voltage regulators is capable of supplying
in excess of 1.5A over a 1.2V to 37V output range. They are exceptionally easy to use and
require only two external resistors to set the output voltage. Further, both line and load
regulation are better than standard fixed regulators. Also, the LM317 is packaged in standard
transistor packages which are easily mounted and handled. In addition to higher performance
than fixed regulators, the LM317 series offers full overload protection available only in IC’s.
Included on the chip are current limit, thermal overload protection and safe area protection.
All overload protection circuitry remains fully functional even if the adjustment terminal is
disconnected.
Normally, no capacitors are needed unless the device is situated more than 6 inches from the
input filter capacitors in which case an input bypass is needed. An optional output capacitor
can be added to improve transient response. The adjustment terminal can be bypassed to
achieve very high ripple rejection ratios which are difficult to achieve with standard 3-
terminal regulators. Besides replacing fixed regulators, the LM317 is useful in a wide variety
of other applications. Since the regulator is “floating” and sees only the input-to-output
differential voltage, supplies of several hundred volts can be regulated as long as the
maximum input to output differential is not exceeded, i.e., avoid short-circuiting the output.
Also, it makes an especially simple adjustable switching regulator, a programmable output
regulator, or by connecting a fixed resistor between the adjustment pin and output, the
LM317 can be used as a precision current regulator. Supplies with electronic shutdown can
be achieved by clamping the adjustment terminal to ground which programs the output to
1.2V where most loads draw little current. For applications requiring greater output current,
see LM150 series (3A) and LM138 series (5A) data sheets. For the negative complement, see
LM137 series data sheet.
Features:
· Guaranteed 1% output voltage tolerance (LM317A)
· Guaranteed max. 0.01%/V line regulation (LM317A)
· Guaranteed 1.5A output current
· Adjustable output down to 1.2V
· P(+) Product Enhancement tested
· 80 dB ripple rejection
· Output is short-circuit protected
PCE/EE/015

Fig 3.5 Typical applications of LM317
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Table 3.5
Data sheet of characteristics of LM317
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3.2.5 REGULATOR SECTION (7809):
Fig 3.6 Regulator IC-7809
A voltage regulator is an electrical regulator designed to automatically maintain a constant
voltage level. IC 7809 is used here. It is a 9V regulator. It regulates the rectified 12V to 9V.
This 9V is supplied to the whole circuit. These voltage regulators are monolithic integrated
circuits designed as fixed–voltage regulators for a wide variety of applications including
local, on–card regulation. These regulators employ internal current limiting, thermal
shutdown, and safe–area compensation. With adequate heatsinking they can deliver output
currents in excess of 1.0 A. Although designed primarily as a fixed voltage regulator, these
devices can be used with external components to obtain adjustable voltages and currents.
Features:
· Output current up to 1.5 A
· Fixed output voltage of 5V, 6V, 8V, 9V, 10V, 12V,
PCE/EE/018
15V, 18V and 24V available
· Thermal overload shutdown protection
· Short circuit current limiting
· Output transistor SOA protection

Table 3.6 Data Sheet of IC-7809
PCE/EE/019

3.2.6 TRANSFORMER (230/(12-0-12))V:
A transformer is a device that transfers electrical energy from one circuit to another through
inductively coupled conductors — the transformer's coils or "windings". Transformer is used
here to step down the supply voltage to a level suitable for the low voltage components.
The transformer used here is a 230/(12V-0-12V) step down transformer.
Fig 3.7 Step down transformer
3.2.7 POWER SUPPLY:
The power supply supplies the required energy for both the microcontroller and the
associated circuits. It is the most essential part of the circuit because to run its constituent
IC’s circuit has to be provided with power. These IC’s can run on DC power. Hence the
required D.C supply has to be generated.
Fig 3.8 Power supply
PCE/EE/020
3.2.8 RESISTOR:
A resistor is a two-terminal electronic component designed to oppose an electric
current by producing a voltage drop between its terminals in proportion to the current, that is,
in accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across
the resistor divided by the current I through the resistor. A resistor is a passive two-terminal
electrical component that implements electrical resistance as a circuit element. The current
through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus,

the ratio of the voltage applied across a resistor's terminals to the intensity of current through
the circuit is called resistance. The electrical functionality of a resistor is specified by its
resistance: common commercial resistors are manufactured over a range of more than nine
orders of magnitude. When specifying that resistance in an electronic design, the required
precision of the resistance may require attention to the manufacturing tolerance of the chosen
resistor, according to its specific application. The temperature coefficient of the resistance
may also be of concern in some precision applications. Practical resistors are also specified as
having a maximum power rating which must exceed the anticipated power dissipation of that
resistor in a particular circuit: this is mainly of concern in power electronics applications.
Resistors with higher power ratings are physically larger and may require heat sinks. In a
high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage
of the resistor.
Practical resistors have a series inductance and a small parallel capacitance; these
specifications can be important in high-frequency applications. In a low-noise amplifier or
pre-amp, the noise characteristics of a resistor may be an issue. The unwanted inductance,
excess noise, and temperature coefficient are mainly dependent on the technology used in
manufacturing the resistor. They are not normally specified individually for a particular
family of resistors manufactured using a particular technology. A family of discrete resistors
is also characterized according to its form factor, that is, the size of the device and the
position of its leads (or terminals) which is relevant in the practical manufacturing of circuits
using them.
Fig.3.9 (a) Variable Resistor Fig 3.9 (b)Fixed Resistor
PCE/EE/021

3.2.9 LED (Light Emitting Diode):
A light-emitting-diode (LED) is a semiconductor diode that emits light when an electric
current is applied in the forward direction of the device, as in the simple LED circuit. The
effect is a form of electroluminescence where incoherent and narrow-spectrum light is
emitted from the p-n junction.
Fig. 3.10 LED
PCE/EE/022
3.2.10 CAPACITOR
A capacitor (originally known as condenser) is a passive two-terminal electrical
component used to store energy in an electric field. The forms of practical capacitors vary
widely, but all contain at least two electrical conductors separated by a dielectric (insulator);
for example, one common construction consists of metal foils separated by a thin layer of
insulating film. Capacitors are widely used as parts of electrical circuits in many common
electrical devices.
When there is a potential difference (voltage) across the conductors, a static electric
field develops across the dielectric, causing positive charge to collect on one plate and
negative charge on the other plate. Energy is stored in the electrostatic field. An ideal
capacitor is characterized by a single constant value, capacitance, measured in farads. This is
the ratio of the electric charge on each conductor to the potential difference between them.

Fig 3.11 Electrolytic capacitor
The capacitance is greatest when there is a narrow separation between large areas of
conductor; hence capacitor conductors are often called "plates," referring to an early means of
construction. In practice, the dielectric between the plates passes a small amount of leakage
current and also has an electric field strength limit, resulting in a breakdown voltage, while
the conductors and leads introduce an undesired inductance and resistance.
Capacitors are widely used in electronic circuits for blocking direct current while
allowing alternating current to pass, in filter networks, for smoothing the output of power
supplies, in the resonant circuits that tune radios to particular frequencies, in electric power
transmission systems for stabilizing voltage and power flow, and for many other purposes.
PCE/EE/023
3.2.11 DIODE:
A diode is a two-terminal electronic component with asymmetric transfer
characteristic, with low (ideally zero) resistance to current flow in one direction, and high
(ideally infinite) resistance in the other. A semiconductor diode, the most common type
today, is a crystalline piece of semiconductor material with a p-n junction connected to two
electrical terminals. A vacuum tube diode, now rarely used except in some high-power
technologies and by enthusiasts, is a vacuum tube with two electrodes, a plate (anode) and
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, including extraction of modulation from radio signals in

radio receivers—these diodes are forms of
rectifiers. However, diodes can have more
complicated behavior than this simple on
conducting electricity until a c
state in which the diode is said to be
biased diode varies only a little with the current, and is a function of temperature; this effect
can be used as a temperature sensor
on–off action. Semiconductor diodes do not begin
certain threshold voltage is present in the forward direction (a
forward-biased). The voltage drop across a forward
ertain Semiconductor diodes' nonlinear current
). forward-ased
varying the semiconductor materials
These are exploited in special purpose diodes that perform many
example, diodes are used to regulate voltage (
voltage surges (avalanche diodes
diodes), to generate radio frequency
diodes), and to produce light (
resistance, which makes them useful in some types of circuits.
Diodes were the first semiconductor electronic devices
abilities was made by German physicist
diodes, called cat's whisker diodes
such as galena. Today most diodes are made of
germanium are sometimes used.
3.3.12 TRANSISTOR:
), varactor
, A transistor is a semiconductor device
doping) the materials.
), diodes, IMPATT
). negative
. crystals' rectifying
such as
electronic signals
and power. It is composed of a
connection to an external circuit. A voltage or current applied to one pair of the transistor's
terminals changes the current flowing through another pair of termi
PCE/EE/024
ased or voltage reference.
Fig 3.12 Diode
current–voltage characteristic can be tailored by
and introducing impurities into (doping
different functions. For
Zener diodes), to protect circuits from high
diodes), to electronically tune radio and TV receivers (
oscillations (tunnel diodes, Gunn diodes
), light emitting diodes). Tunnel diodes exhibit
, devices. The discovery of
Ferdinand Braun in 1874. The first semiconductor
diodes, developed around 1906, were made of mineral crystals
. silicon, but other semiconductors
used to amplify and switch
semiconductor material with at least three terminals for
terminals. Because the

controlled (output) power can be higher than the controlling (input) power, a transistor can
amplify a signal.
Fig 3.13 Transistor
Today, some transistors are packaged individually, but many more are found
embedded in integrated circuits. The transistor is the fundamental building block of modern
electronic devices, and is ubiquitous in modern electronic systems. Following its
development in the early 1950s the transistor revolutionized the field of electronics, and
paved the way for smaller and cheaper radios, calculators, and computers, among other
things.
PCE/EE/025

CHAPTER-4
Seven segment display
4.1 INTRODUCTION:
A seven-segment display (SSD), or seven
device for displaying decimal numerals that is an alternative to the more complex dot matrix
displays.
Seven-segment displays are widely used in digital clocks, electronic meters, and other
electronic devices for displaying numerical information.
Fig 4.1 A typical 7
seven-segment indicator, is a form of electronic display
7-segment LED display component, with decimal point
4.2 HISTORY:
Seven-segment displays can be found in patents as early as 1908 (in U.S. Patent 974,943, F
W Wood invented an 8-segment display, which
In 1910, a seven-segment display illuminated by incandescent bulbs was used on a power
plant boiler room signal panel.[5] They did not achieve widespread use until the advent of
LEDs in the 1970s.
They are sometimes used in posters or tags, where the user either applies colo
printed segments, or applies color through a seven
figures such as product prices or telephone numbers.
For many applications, dot-matrix LCDs ha
in LCDs 7-segment displays are very common. Unlike LEDs, the shapes of elements in an
LCD panel are arbitrary since they are formed on the display by a kind of printing process. In
contrast, the shapes of LED
they have to be physically moulded to shape, which makes it difficult to form more complex
shapes than the segments of 7
factor of 7-segment displays, and the comparatively high visual contrast obtained by such
displayed the number 4 using a diagonal bar).
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etimes seven-segment digit template, to compose
have largely superseded LED displays, though even
segments tend to be simple rectangles, reflecting the fact that
7-segment displays. However, the high common recognition
ment power-plant
colour to pre-segment
ve

displays relative to dot-matrix digits, makes seven-segment multiple-digit LCD screens very
common on basic calculators.
4.3 CONCEPT AND VISUAL STRUCTURE:
The seven elements of the display can be lit in different combinations to represent the arabic
numerals. Often the seven segments are arranged in an oblique (slanted) arrangement, which
aids readability. In most applications, the seven segments are of nearly uniform shape and
size (usually elongated hexagons, though trapezoids and rectangles can also be used), though
in the case of adding machines, the vertical segments are longer and more oddly shaped at the
ends in an effort to further enhance readability.
The numerals 6, 7 and 9 may be represented by two or more different glyphs on seven-segment
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displays, with or without a 'tail'.
The seven segments are arranged as a rectangle of two vertical segments on each side with
one horizontal segment on the top, middle, and bottom. Additionally, the seventh segment
bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment
displays (for full alphanumerics); however, these have mostly been replaced by dot
matrix displays.
The segments of a 7-segment display are referred to by the letters A to G, where the optional
DP decimal point (an "eighth segment") is used for the display of non-integer numbers.
4.4 IMPLEMENTATION:
Seven-segment displays may use a liquid crystal display (LCD), a light-emitting diode (LED)
for each segment, or other light-generating or controlling techniques such as cold cathode gas
discharge, vacuum fluorescent, incandescent filaments, and others. For gasoline price totems
and other large signs, vane displays made up of electromagnetically flipped light-reflecting
segments (or "vanes") are still commonly used. An alternative to the 7-segment display in the
1950s through the 1970s was the cold-cathode, neon-lamp-like nixie tube. Starting in 1970,
RCA sold a display device known as the Numitron that used incandescent filaments arranged
into a seven-segment display.
In a simple LED package, typically all of the cathodes (negative terminals) or all of the
anodes (positive terminals) of the segment LEDs are connected and brought out to a common
pin; this is referred to as a "common cathode" or "common anode" device. Hence a 7 segment
plus decimal point package will only require nine pins (though commercial products typically
contain more pins, and/or spaces where pins would go, in order to match standard IC sockets.
Integrated displays also exist, with single or multiple digits. Some of these integrated displays
incorporate their own internal decoder, though most do not: each individual LED is brought
out to a connecting pin as described. A multiplexed 4-digit, seven-segment clock display with
only 12 pins Multiple-digit LED displays as used in pocket calculators and similar devices
used multiplexed displays to reduce the number of I/O pins required to control the display.
For example, all the anodes of the A segments of each digit position would be connected
together and to a driver circuit pin, while the cathodes of all segments for each digit would be
connected. To operate any particular segment of any digit, the controlling integrated circuit
would turn on the cathode driver for the selected digit, and the anode drivers for the desired

segments; then after a short blanking interval the next digit would be selected and new
segments lit, in a sequential fashion. In this manner an eight digit d
segments and a decimal point would require only 8 cathode drivers and 8 anode drivers,
instead of sixty-four drivers and IC pins.[4] Often in pocket calculators the digit drive lines
would be used to scan the keyboard as well, providing f
multiple keys at once would produce odd results on the multiplexed display.
can encode the full state of a 7
and abcdefg, where each letter represen
representation, a byte value of 0x06 would (in a common
and 'b', which would display a '1'.
4.5 DISPLAYING LETTERS:
Hexadecimal digits can be displayed on
uppercase and lowercase letters are used for A
unambiguous shape for each letter (otherwise, a capital D would look identical to an 0 and a
capital B would look identical to an 8). Also the digit 6 must be displayed with the top bar lit
to avoid ambiguity with the letter b
Table 4.1 Hexadecimal encoding for displaying the digits 0 to F
PCE/EE/028
further savings; however, pressing
7-segment-display. The most popular bit encodings are gfedcba
represents a particular segment in the display. In the gfedcba
common-anode circuit) turn on segments 'c'
ISPLAYING seven-segment displays. A particular combination of
A–F; this is done to obtain a unique,
al b.
display with seven
urther A single byte
ts

CHAPTER 5
PCB DESINGING
5.1. PRINTED CIRCUIT BOARD
A printed circuit board, or PCB, is used to mechanically support and electrically connect
electronic components using conductive pathways, tracks, or traces, etched from copper
sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board
(PWB) or etched wiring board. A PCB populated with electronic components is a printed
circuit assembly (PCA), also known as a printed circuit board assembly (PCBA).
Fig 5.1 Copper PCB
PCBs are inexpensive, and can be highly reliable. They require much more layout effort and
higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are
much cheaper and faster for high-volume production. Much of the electronics industry's PCB
design, assembly, and quality control needs are set by standards that are published by the IPC
organization. Conducting layers are typically made of thin copper foil. Insulating layers
dielectric is typically laminated together with epoxy resin prepregnated . The board is
typically coated with a solder mask that is green in color. Other colors that are normally
available are blue and red. There are quite a few different dielectrics that can be chosen to
provide different insulating values depending on the requirements of the circuit. Some of
these dielectrics are poly tetra fluoroethylene (Teflon), FR-4, FR-1, CEM-1 or CEM-3. Well
known prepregnated materials used in the PCB industry are FR-2 (Phenolic cotton paper),
FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass and
PCE/EE/029

epoxy), FR-6 (Matte glass and
polyester), G-10 (Woven glass and epoxy), CEM
paper and epoxy), CEM-2 (Cotton paper and epoxy), CEM
CEM-4 (Woven glass and epoxy), CEM
is an important consideration espe
fiber offers the best dimensional stability. In some PCB the lamination are also uses so the
possibility of error is minimize.
`For the PCB layout we required dip trace software. In the dip trace softwa
component are available, so according to requirement we use the component are form the
desire circuit with the help of these components.
After the formation of desire circuit we used the run command and now all the components
are place at appropriate place and connection are shown in given accurate place. After
designing of PCB layout on the software we required take printout of it as shown in figure.
Now this circuit is superimposed on the PCB so that this circuit is completely drawn on PCB.
Now PCB is placed in the solution of the KOH so that all the unwanted copper is removed.
After 35min the PCB is take out from the solution and now PCB designing is completed.
Fig 5.2. PCB
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CEM-3 (Woven glass and epoxy),
CEM-5 (Woven glass and polyester). Thermal expansion
especially with BGA and naked die technologies, and glass
riate for variable power supply with digital control
CEM-1 (Cotton
cially software all the

CHAPTER 6
SOLDERING OF COMPONENT
6.1 INTRODUCTION
Soldering is the process of a making a sound electrical and mechanical joint between certain
metals by joining them with a soft solder. This is a low temperature melting point alloy of
lead and tin. The joint is heated to the correct temperature by soldering iron. For most
electronic work miniature mains powered soldering irons are used. These consist of a handle
onto which is mounted the heating element. On the end of the heating element is what is
known as the "bit", so called because it is the bit that heats the joint up. Solder melts at
around 190 degrees Centigrade, and the bit reaches a temperature of over 250 degrees
Centigrade. This temperature is plenty hot enough to inflict a nasty burn, consequently care
should be taken.
It is also easy to burn through the PVC insulation on the soldering iron lead if you were to lay
the hot bit on it. It is prudent, therefore, to use a specially designed soldering iron stand.
These usually incorporate a sponge for keeping the bit clean. Soldering irons come with
various ratings from 15W to over 100W. The advantage of a high wattage iron is that heat
can flow quickly into a joint, so it can be rapidly made. This is important when soldering
connectors as often there is a quite a large volume of metal to be heated. A smaller iron
would take a longer time to heat the joint up to the correct temperature, during which time
there is a danger of the insulation becoming damaged. A small iron is used to make joints
with small electronic components which are easily damaged by excess heat.
Always use a good quality multi core solder. A standard 60% tin, 40% lead alloy solder with
cores of non-corrosive flux will be found easiest to use. The flux contained in the longitudinal
cores of multi core solder is a chemical designed to clean the surfaces to be joined of
deposited oxides, and to exclude air during the soldering process, which would otherwise
prevent these metals coming together. Consequently, don't expect to be able to complete a
joint by using the application of the tip of the iron loaded with molten solder alone, as this
usually will not work. There is a process called tinning where conductors are first coated in
fresh, new solder prior to joining by a hot iron. Solder comes in gauges like wire. The two
commonest are 18 SWG, used for general work, and the thinner 22 SWG, used for fine work
on printed circuit boards.
PCE/EE/031

6.2 SOLDERING TOOLS
Different soldering jobs will need different tools and different temperatures too. For circuit
board work you will need a finer tip, a lower temperature and finer grade solder. You may
also want to use a magnifying glass. Audio connectors such as XLR's will require a larger tip,
higher temperature and thicker solder. Clamps and holders are also handy when soldering
audio cables.
6.2.1 SOLDERING IRON
There are several things to consider when choosing a soldering iron.
PCE/EE/032
1. Wattage
2. adjustable or fixed temperature
3. power source (electric or gas)
4. portable or bench use
Fig. 6.1 Soldering Iron
6.2.2 SOLDER WIRE
The most commonly used type of solder is rosin core. The rosin is flux, which cleans as you
solder. The other type of solder is acid core and unless you are experienced at soldering, you
should stick to rosin core solder. Acid core solder can be tricky and better avoided for the
beginner. Rosin core solder comes in three main types - 50/50, 60/40 and 63/37. These
numbers represent the amount of tin and lead are present in the solder, as shown below.
Table 6.1: Types Of Solder Wire

Solder Type % Tin % Lead Melting Temp (°F)
50/50 50 50 425
60/40 60 40 371
63/37 63 37 361
6.2.3 FLUX
In metallurgy, a flux is a chemical cleaning agent which facilitates soldering, brazing, and
welding by removing oxidation from the metals to be joined. Common fluxes are: ammonium
chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering
galvanized iron (and other zinc surfaces); and borax for brazing or braze-welding ferrous
metals. Different fluxes, mostly based on sodium chloride, potassium chloride, and a fluoride
such as sodium fluoride, are used in foundries for removing impurities from molten
nonferrous metals such as aluminium, or for adding desirable trace elements such as titanium.
PCE/EE/033

CHAPTER 7
RESULT AND APPLICATION
7.1 RESULT: The voltage varied by different values of variable resistors are tabulated as
shown below:
Resistance Value
O/P Voltage
(in Ohm)
(in volts)
200K 1.0
200K 1.5
200K 2.0
200K 3.0
200K 5.0
200K 7.0
200K 9.0
200K 10.0
200K 12.0
Table 7.1: Results for variable resistors
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7.3 APPLICATION:
1. Variable power supply through variable resistors is more reliable.
2. Variable power supply with digital control with seven segments output delivers great user
friendly also.
3. The same circuit finds its application to control the level of the voltages.
4. This circuit also finds its application for RF power amplifier.
7.4 ADVANTAGES
This circuit is simple to use and efficient.
It can be assembled with ease.
It is cost effective and hence very economical.
It is compact in size.
It is efficient enough for displaying the voltage values.

CONCLUSION
Variable Power Supply with Digital Control with seven segments display is one of the
applications of electronics to increase the facilities of life. And it is the most frequently used
device in electronic workshops and laboratories is a universal power supply that provides a
variable, fluctuation-free output.
With the knowledge of new techniques in ‘Electronics’ we are able to make our life more
comfortable. One such application of electronics is used in “RF power amplifier”.RF power
amplifiers can save much energy if they are supplied with a variable voltage as described in
the state of the art. The design of the power supply of these amplifiers is challenging since
many requirements have to be accomplished: very low output voltage ripple; wide output
voltage variation at kHz frequencies; fast load current steps; etc. A typical solution is the use
of a multiphase dc-dc converter based on the buck topology. In this paper, we propose the use
of digital control for these power supplies. The main advantage is that current loops are
removed. The design of this control circuit and main trade-offs are discussed. The results
obtained from a 240 W prototype show the advantages and the limitations of this proposal.
PCE/EE/035

REFERENCE
1. http://en.wikipedia.org/wiki/sevensegmentsdisplay
2. http://en.wikipedia.org/wiki/trasister
3. http://www.datasheetarchive.com/wireless%20speed%20control%20of%
20single%20phase%20induction-datasheet.html
4. http://en.wikipedia.org/wiki/LM7809
5. http://en.wikipedia.org/wiki/LM317
6. http://en.wikipedia.org/wiki/CD4017
7. http://en.wikipedia.org/wiki/NE555
8. http://en.wikipedia.org/wiki/LM79LXX
1. Electronic Devices and Circuits – J. B.Gupta
2. Linear Integrated circuits – Gayakwad
3. Power electronics – Md.Rashid
PCE/EE/036

Variable power supply with digital control with seven segments display

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