Quiz Buzzer

A PROJECT REPORT ON SCHOOL / COLLEGE QUIZ BUZZER SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF BACHELOR OF ENGINEERING IN ELECTRONICS AND COMMUNICATION ENGINEERING

Guided by: -

Submitted by: -

Mr. Nilesh Parihar

Sumit Kumar Dahiya

Lecturer (E.C.E)

Narendra Bagoria Final year (E.C.E.)

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

SOBHASARIA ENGINEERING COLLEGE, SIKAR UNIVERSITY OF RAJASTHAN 2007-08 1

CANDIDATE DECLARATION

This is to certify that work, which is being presented in the project entitled “SCHOOL / COLLEGE QUIZ BUZZER” submitted by undersigned students of final year B.E. in Electronics & Communication Engineering in partial fulfillment for award of degree of bachelor of engineering is a record of our own work carried out by us guidance and supervision of Mr. Nilesh Parihar (Lecturer), Department of Electronics & communication Engineering. This work has not submitted elsewhere for award of any other degree.

Date: 12/ 12/ 2007

(

Place: S.E.C.,Sikar

)

Name: Sumit Kumar Dahiya Enroll. No. 04/13030 (

)

Name: Narendra Bagoria Enroll. No.04/13050

2

CERTIFICATE

THIS IS TO CERTIFY THAT THE WORK, WHICH IS BEING PRESENTED IN THE PROJECT “SCHOOL/COLLEGE QUIZ BUZZER” SUBMITTED BY SUMIT KUMAR DAHIYA AND NARENDRA BAGORIA, STUDENTS OF FINAL YEAR B.E. IN ELECTRONICS & COMMUNICATION ENGNEERING AS A PARTIAL FULFILLMENT

FOR

THE

AWARD

OF

DEGREE

OF

BACHELOR

OF

ENGINEERING IS A RECORD OF STUDENT’S WORK CARRIED OUT BY HIM UNDER MY GUIDANCE AND SUPERVISION. THIS WORK HAS NOT BEEN SUBMITTED ELSEWHERE FOR THE AWARD OF ANY OTHER DEGREE.

DATE: 12/ 12 / 2007

(----------------------)

PLACE: S.E.C., SIKAR

PROJECT GUIDE

(Sh. NILESH PARIHAR)

(Sh.K.B.SINGH)

PROJECT INCHARGE

(H.O.D OF E.C.E. DEPTT.)

3

ACKNOWLEDGEMENT Expressing gratitude is not just a ritual that has to be carried out. Rather it is an opportunity to sincerely thank all those who extended their much-needed help. It gives us immense pleasure in acknowledging the help we have received during our tenure at Sobhasaria Engineering College. We owe our all the obligations and our sincere feelings to our guide Mr. Nilesh Parihar (Lecturer, ECE)

to provide us

valuable guidance and encouragement through out the stages of presentation of our project as well as preparation of report. We regard him for all time he could devote for the project and for helping us grasps the technical wiz-a-wiz of the “SCHOOL / COLLEGE QUIZ BUZZER”. We gladly appreciate the time and patience they could spare their busy schedule. We are highly obliged to Mr. K.B.Singh (H.O.D., ECE) for their appreciation. At last but the most we would like to extend our thanks to all faculty members of Department

of

Electronics

&

Communication

Engineering,

faculty

of

Communication Lab, our friends and colleague for their support and cooperation.

(

)

Sumit Kumar Dahiya (

)

Narendra Bagoria (Final Year ECE)

4

ABSTRACT Manual buzzers used for quiz competitions in schools and colleges create a lot of confusion in identifying the first respondent. Although there are circuits using PCs and discrete ICs, they are either too expensive or limited to only a few numbers of players. The quiz buzzer circuit given here can be used for up to eight players, which is maximum in any quiz com-petition. The circuit uses IC 74LS373 and a few passive components that are readily available in the market. The circuit can be divided into two sections: power supply and quiz buzzer. Fig. 1 shows the power supply section. The regulated 5V power supply for the quiz buzzer section is derived from AC mains. The 230V AC mains is stepped down to 7.5V AC by transformer X1, rectified by bridge rectifier BR1, filtered by C1 and regulated by regulator IC1. Capacitor C2 bypasses ripples in the regulator output.Fig. 2 shows the quiz buzzer section. At the heart of this section is IC 74LS373, an octal latch that is used to transfer the logic state at data input pins D0 through D7 to the corresponding Q0 through Q7 outputs. Data pins D0 through D7 are normally pulled low by resistors R1 through R8, respectively.One terminal of push-to-on switches S1 through S8 is connected to +5V, while the other terminal is connected to the respective data input pins. The switches are to be extended to the players through cord wire. The torch bulbs BL1 through BL8 can be housed in boxes with the front side of the boxes covered with a white paper having the name or number of the contestant written over it for easy identification. Place the boxes above the head level so that these can betseen by the audience also. When the power is switched on using switch S9 (provided terminals ‘A and ‘B’ of both the power supply and quiz buzzer sections are interconnected), the circuit is ready to use. Now all the switches (S1 through S8) are open and Q0 through Q7 outputs of IC 74LS373 are low. As a result, the gates of silicon-controlled rectifiers SCR1 through SCR8 are also low. As soon as a contestant momentarily presses his respective switch,

5

the corresponding output data pin goes high. This triggers the corresponding SCR and the respective bulb glows. At the same time, the piezobuzzer (PZ1) sounds as transistor T1 conducts. Simultaneously, the base of transistor T2 becomes high to make it conduct. Latch-enable (LE) pin 11 of IC2 is tied to ground to latch all the Q0 through Q7 outputs. This restricts further change in the output state due to any change in the state of switches S1 through S8 by any other contestant. Only one of the eight torch bulbs glows until the circuit is reset by on/ off switch S9.

6

INDEX Chapter 1

Chapter 2

Introduction

1

1.1

School / College Quiz Buzzer

1.2

Basic terms

Component description 2.1

Introduction

2.2

7805 IC Voltage Regulator

2-13

2.2.1Definition of 741 pin function 2.3

74LS373 IC 2.3.1 Definition of pin functions 2.3.2 Operating modes 2.3.2.1 Monostable mode 2.3.2.2 Astable mode

2.4

Silicon Controlled Rectifier (SCR)

2.5

Resistor

2.6

Transistor 2.6.1 Types of BJT transistor 2.6.1.1 NPN transistor 2.6.2.2 PNP transistor 2.6.2 Region of operation

Chapter 3

2.7

Capacitor

2.8

Diode

2.9

Light Emitted Diode (LED)

Versatile intercom system 3.1

The circuit

3.2

Construction

Conclusion

14-16

17-18

7

References

19

Chapter: 1 INTRODUCTION 1.1

School / College Quiz Buzzer The attraction of any game show depends on the visual effects. The way in which

they present different rounds makes the game shows effective. The good Quiz show always contains one or more buzzer rounds. The buzzer makes a round of a Quiz show 'fastest finger first '. The active buzzer makes the team to first respond to the question. A common question will be asked for all the teams in these rounds. The team which presses the buzzer first gets first chance to answer. To avoid confusion of the teams to be answered when one or more team presses the buzzer almost simultaneously, buzzer circuits are used. Instead of just showing who pressed the buzzer using some LED or electric bulb, if has some visual effects, audio effects and different options that makes the show entice. So our approach is to make this possible which includes all the features. This project makes the show attractive and easy to operate. This Quiz buzzer is built with the view of making the game show priority less. This project uses PC parallel port to input user's response from the switches placed in the participant's table. Response of the teams can be projected on to a screen. Number of all the teams will be displayed in the screen in order of the response.

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Chapter: 2 COMPONENT DESCRIPTION 2.1 Introduction When a beginner to electronics first looks at a circuit board full of components he/she is often overwhelmed by the diversity of do-dads. An electronic circuit is made up of electronic component. Electronic components are classified as active or passive. Passive component is one that contributes no power gain (amplification) to a circuit or system. It has no control action and does not require any input other than a signal to perform its function. Examples are resistors, capacitors, inductors. Active components are those that are capable of controlling voltages or currents and can create a switching action in the circuit. Examples are transistors, diodes, etc.

2.2

IC 7805 Voltage Regulator It is very easy to get stabilized voltage for ICs by using a three terminal voltage

regulator.The power supply voltage for a car is +12V - +14V. At this voltage, some ICs can not operate directly except for the car component ICs. In this case, a three terminal voltage regulator is necessary to get the required voltage. The three terminal voltage regulator outputs stabilized voltage at a lower level than the higher input voltage. A voltage regulator cannot put out higher voltage than the input voltage. They are similar in appearance to a transistor. On the left in the photograph is a 78L05. The size and form is similar to a 2SC1815 transistor. The output voltage is +5V, and the maximum output current is about 100mA. The maximum input voltage is +35V. (Differs by manufacturer.)

9

Fig. 2.2.1 IC 7805 Voltage Regulator

On the right is a 7805. The output voltage is +5V, and maximum output current is 500mA to 1A. (It depends on the heat sink used) The maximum input voltage is also +35V. There

are

many

types

with

different

output

voltages.

5V, 6V, 7V, 8V, 9V, 10V, 12V, 15V, 18V. Component Lead of Three Terminal Voltage Regulator Example of 78L05 Part number is printed on the flat face of the regulator, and indicates the front. Rightside:Input Center : Ground

10

Leftside:Output

2.3

IC 74LS373 The SN54 / 74LS373 consists of eight latches with 3-state outputs for bus

organized system applications. The flip-flops appear transparent to the data (data changes asynchronously) when Latch Enable (LE) is HIGH. When LE is LOW, the data that meets the setup times is latched. Data appears on the bus when the Output Enable (OE) is LOW. When OE is HIGH the bus output is in the high impedance state. The SN54 / 74LS374 is a high-speed, low-power Octal D-type Flip-Flop featuring separate D-type inputs for each flip-flop and 3-state outputs for bus ori- ented applications. A buffered Clock (CP) and Output Enable (OE) is common to all flip-flops. The SN54 / 74LS374 is manufactured using advanced Low Power Schottky technology and is compatible with all Motorola TTL families.  Eight Latches in a Single Package  3-State Outputs for Bus Interfacing  Hysteresis on Latch Enable

11



Edge-Triggered D-Type Inputs

LOGIC DIAGRAMS SN54LS / 74LS373

2.4

Silicon Controlled Rectifier (SCR): The TYN 204-1004 family of Silicon Controlled Rectifier uses a high

performance glass passivated technology.

12

This general purpose family of silicon controlled rectifier is designed for power supplies up to 400 Hz on resistive or inductive load.

Fig. 2.4.1 Silicon Controlled Rectifier

2.5

Resistors: A resistor is a two-terminal electrical or electronic component that resists

an electric current by producing a voltage drop between its terminals in accordance with Ohm's law: The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. Resistors are used as part of electrical networks and electronic circuits. The resistance of a resistor is given by the formula

where: •

ρ is the resistivity of the material that the resistor is made from

•

l is the length of the resistive material, between the end contacts

•

A is the (presumed uniform) cross sectional area of the resistive material

13

Fig 2.5 symbolic representation of resistor

2.6

Transistor A transistor is a semiconductor device, commonly used as an amplifier or an

electrically controlled switch. The transistor is the fundamental building block of the circuitry in computers, cellular phones, and all other modern electronic devices. Transistors are the basic devices providing control of this kind. Modern transistors are divided into two main categories: bipolar junction transistors (BJTs) and field effect transistors (FETs). Application of current in BJTs and voltage in FETs between the input and common terminals increases the conductivity between the common and output terminals, thereby controlling current flow between them A bipolar junction transistor (BJT) is a three-terminal device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons and holes. A BJT consists of three differently doped semiconductor regions, the emitter region, the base region and the collector region. These regions are, respectively, p type, n type and p type in a PNP, and n type, p type and n type in a NPN transistor. Each semiconductor region is connected to a terminal, appropriately labeled: emitter (E), base (B) and collector (C). The base is physically located between the emitter and the collector and is made from lightly doped, high resistivity material. The collector surrounds the emitter region, making it almost impossible for the electrons injected into the base region to escape being collected, thus making the resulting value of α very close to unity, and so, giving the transistor a large β. A cross section view of a BJT indicates that the collector–base junction has a much larger area than the emitter–base junction.

14

The bipolar junction transistor, unlike other transistors, is usually not a symmetrical device. This means that interchanging the collector and the emitter makes the transistor leave the forward active mode and start to operate in reverse mode. Because the transistor's internal structure is usually optimized to forward-mode operation, interchanging the collector and the emitter makes the values of α and β in reverse operation much smaller than those found in forward operation; often the α of the reverse mode is lower than 0.5. The lack of symmetry is primarily due to the doping ratios of the emitter and the collector. The emitter is heavily doped, while the collector is lightly doped, allowing a large reverse bias voltage to be applied before the collector–base junction breaks down. The collector–base junction is reverse biased in normal operation. The reason the emitter is heavily doped is to increase the emitter injection efficiency: the ratio of carriers injected by the emitter to those injected by the base. For high current gain, most of the carriers injected into the emitter–base junction must come from the emitter. 2.6.1Types of BJT BJT is basically of two types: NPN and PNP. 2.6.1.1 NPN transistor NPN is the bipolar transistor, in which the letters "N" and "P" refer to the majority charge carriers inside the different regions of the transistor. Most bipolar transistors used today are NPN, because electron mobility is higher than hole mobility in semiconductors, allowing greater currents and faster operation.

Fig 2.6.1.1 NPN transistor symbol

15

NPN transistors consist of a layer of P-doped semiconductor (the "base") between two N-doped layers. A small current entering the base in common-emitter mode is amplified in the collector output. The arrow in the NPN transistor symbol is on the emitter leg and points in the direction of the conventional current flow when the device is in forward active mode. 2.6.1.2 PNP transistor The other type of BJT is the PNP with the letters "P" and "N" referring to the majority charge carriers inside the different regions of the transistor. Few transistors used today are PNP, since the NPN type gives better performance in most circumstances.

Fig 2.6.1.2 PNP transistor symbol PNP transistors consist of a layer of N-doped semiconductor between two layers of P-doped material. PNP transistors are commonly operated with the collector at ground and the emitter connected to a positive voltage through an electric load. A small current flowing from the base allows a much greater current to flow from the emitter to the collector. The arrow in the PNP transistor symbol is on the emitter leg and points in the direction of the conventional current flow when the device is in forward active mode. 2.6.2 Regions of operation Bipolar transistors have five distinct regions of operation, defined mostly by applied bias:

16

•

Forward-active (or simply, active): The emitter-base junction is forward biased and the base-collector junction is reverse biased. Most bipolar transistors are designed to afford the greatest common-emitter current gain, βf in forward-active mode. If this is the case, the collector-emitter current is approximately proportional to the base current, but many times larger, for small base current variations.

•

Reverse-active (or inverse-active or inverted): By reversing the biasing conditions of the forward-active region, a bipolar transistor goes into reverse-active mode. In this mode, the emitter and collector regions switch roles. Since most BJTs are designed to maximise current gain in forward-active mode, the βf in inverted mode is several (2 - 3 for the ordinary germanium transistor) times smaller. This transistor mode is seldom used, usually being considered only for failsafe conditions and some types of bipolar logic. The reverse bias breakdown voltage to the base may be an order of magnitude lower in this region.

•

Saturation: With both junctions forward-biased, a BJT is in saturation mode and facilitates high current conduction from the emitter to the collector. This mode corresponds to a logical "on", or a closed switch.

•

Cutoff: In cutoff, biasing conditions opposite of saturation (both junctions reverse biased) are present. There is very little current flow, which corresponds to a logical "off", or an open switch.

•

2.7

Avalanche breakdown region

Capacitor: A capacitor is a passive electronic component that stores energy in the form of an

electrostatic field. In its simplest form, a capacitor consists of two conducting plates separated by an insulating material called the dielectric. Capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the plates' separation. Capacitance also depends on the dielectric constant of the dielectric material separating the plates. The capacitor's capacitance (C) is a measure of the amount of charge (Q) stored on each plate for a given potential difference or voltage (V) which appears between the plates: 17

The standard units of Capacitance, farad: F microfarad: µF (1 µF = 10-6 F) nanofarad: nF (1 nF = 10-9 F) picofarad: pF (1 pF = 10-12 F)

2.8 Diode: In electronics, the word diode describes 2 classes of device: • •

a device that passes current in one direction much more readily than in the other Some other devices with structures related to silicon diodes (eg Diac). Most diodes have 2 terminals, and most are used for their unidirectional current

property, but neither of these applies to all diodes. The directionality of current flow most diodes possess is sometimes generically called the rectifying property). The most common function of a diode is to allow an electric current to flow in one direction (called the forward biased condition) but to block it in the opposite direction (the reverse biased condition). Most modern diodes are based on semiconductor p-n junctions. In a p-n diode, conventional current can flow from the p-type side (the anode) to the n-type side (the cathode), but cannot flow in the opposite direction

A semiconductor diode’s current–voltage, or I–V, characteristic curve is related to the transport of 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 Pdoped region where there is a large population of holes (places for electrons in which no

18

electron is present) 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 on the N-side and negatively charged acceptor on the P-side. The region around the p-n junction becomes depleted of charge carriers and thus behaves as an insulator. However, 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 and 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 a significant electric current. 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. For silicon diodes, the built-in potential is approximately 0.6 V. Thus, if an external current is passed through the diode, about 0.6 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.

2.9

Light Emitted Diode (LED): An LED is a special semiconductor which emits light when current is passed

through it. There are many different physical styles. The emitted color spectrum is usually very narrow. It can generally be specified as a specific wavelength in the electromagnetic spectrum. The emitted color selection is somewhat limited. The most commonly available colors are red, green, amber, yellow, blue and white. The red, green, yellow and amber have a working voltage of approximately 1.8 volts. You can refer to

19

the data sheet for each LED to find the exact value. The actual working voltage is determined by the breakdown voltage of the particular semiconductor material.

Fig 2.9.1 Schematic Symbol

Fig 2.9.2 Description

2.7.1 I–V characteristics of a P-N junction diode

20

Chapter: 3 SCHOOL / COLLEGE QUIZ BUZZER Manual buzzers used for quiz competitions in schools and colleges create a lot of confusion in identifying the first respondent. Although there are circuits using PCs and discrete ICs, they are either too expensive or limited to only a few number of players. The quiz buzzer circuit given here can be used for up to eight players, which is maximum in any quiz com-petition. The circuit uses IC 74LS373 and a few passive components that are readily available in the market. The circuit can be divided into two sections: power supply and quiz buzzer. Fig. 1 shows the power supply section. The regulated 5V power supply for the quiz buzzer section is derived from AC mains. The 230V AC mains is stepped down to 7.5V AC by transformer X1, rectified by bridge rectifier BR1, filtered by C1 and regulated by regulator IC1. Capacitor C2 bypasses ripples in the regulator output.Fig. 2 shows the quiz buzzer section. At the heart of this section is IC 74LS373, an octal latch that is used to transfer the logic state at data input pins D0 through D7 to the corresponding Q0 through Q7 outputs. Data pins D0 through D7 are normally pulled low by resistors R1 through R8, respectively.One terminal of push-to-on switches S1 through S8 is connected to +5V, while the other terminal is connected to the respective data input pins.

21

The switches are to be extended to the players through cord wire. The torch bulbs BL1 through BL8 can be housed in boxes with the front side of the boxes covered with a white paper having the name or number of the contestant written over it for easy identification. Place the boxes above the head level so that these can betseen by the audience also. When the power is switched on using switch S9 (provided terminals ‘A and ‘B’ of both the power supply and quiz buzzer sections are interconnected), the circuit is ready to use. Now all the switches (S1 through S8) are open and Q0 through Q7 outputs of IC 74LS373 are low. As a result, the gates of silicon-controlled rectifiers SCR1 through SCR8 are also low. As soon as a contestant momentarily presses his respective switch, the corresponding output data pin goes high. This triggers the corresponding SCR and the respective bulb glows. At the same time, the piezobuzzer (PZ1) sounds as transistor T1 conducts. Simultaneously, the base of transistor T2 becomes high to make it conduct. Latch-enable (LE) pin 11 of IC2 is tied to ground to latch all the Q0 through Q7 outputs. This restricts further change in the output state due to any change in the state of switches S1 through S8 by any other contestant. Only one of the eight torch bulbs glows until the circuit is reset by on/ off switch S9.

3.2 Construction: Suggested PCB layout is shown in Fig. 3.2 and the corresponding components layout in Fig. 5. Care should be taken when wiring DPDT switch S1. Suggested cabinet layout is shown in Fig.6. Note that the transformer is mounted in a separate enclosure and placed at a minimum distance of 20 cm from the main enclosure containing the condenser mic, PCB etc. If transformer and diode are mounted inside the same enclosure it will result in howling because of air pressure variation which is very difficult to control. Using a 2-core shielded cable is recommended with the shield connected to the ground as it will also avoid electrical noises. A regulated power supply will give good

22

audio reproduction. The circuit diagram of suggested power supply is shown in Fig3.2.1There must be separate power supplies for each station.

Fig. 3.2.1 Supply

23

Fig. 3.2.2 Circuit

24

CONCLUSION

Manual buzzers used for quiz competitions in schools and colleges create a lot of confusion in identifying the first respondent. Although there are circuits using PCs and discrete ICs, they are either too expensive or limited to only a few number of players. The quiz buzzer circuit given here can be used for up to eight players, which is maximum in any quiz com-petition. The circuit uses IC 74LS373 and a few passive components that are readily available in the market. The circuit can be divided into two sections: power supply and quiz buzzer. Fig. 1 shows the power supply section. The regulated 5V power supply for the quiz buzzer section is derived from AC mains. The 230V AC mains is stepped down to 7.5V AC by transformer X1, rectified by bridge rectifier BR1, filtered by C1 and regulated by regulator IC1. Capacitor C2 bypasses ripples in the regulator output.Fig. 2 shows the quiz buzzer section. At the heart of this section is IC 74LS373, an octal latch that is used to transfer the logic state at data input pins D0 through D7 to the corresponding Q0 through Q7 outputs. Data pins D0 through D7 are normally pulled low by resistors R1 through R8, respectively.One terminal of push-to-on switches S1 through S8 is connected to +5V, while the other terminal is connected to the respective data input pins. The switches are to be extended to the players through cord wire. The torch bulbs BL1 through BL8 can be housed in boxes with the front side of the boxes covered with a white paper having the name or number of the contestant written over it for easy identification. Place the boxes above the head level so that these can betseen by the audience also. When the power is switched on using switch S9 (provided terminals ‘A and ‘B’ of both the power supply and quiz buzzer sections are interconnected), the circuit is ready to use. Now all the switches (S1 through S8) are open and Q0 through Q7 outputs of IC 74LS373 are low. As a result, the gates of silicon-controlled rectifiers SCR1 through SCR8 are also low. As soon as a contestant momentarily presses his respective switch, 25

the corresponding output data pin goes high. This triggers the corresponding SCR and the respective bulb glows. At the same time, the piezobuzzer (PZ1) sounds as transistor T1 conducts. Simultaneously, the base of transistor T2 becomes high to make it conduct. Latch-enable (LE) pin 11 of IC2 is tied to ground to latch all the Q0 through Q7 outputs. This restricts further change in the output state due to any change in the state of switches S1 through S8 by any other contestant. Only one of the eight torch bulbs glows until the circuit is reset by on/ off switch S9.

REFERENCE Books: 1.

Electronics for you

2.

Integrated circuits:- Ramakant A Gaykward

3.

Principle of Electronics:- V.K. Mehta

Sites: 1.

www.datasheetarchive.com

2.

www.electronicsforu.com

3.

www.centralsemi.com

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