electronics projects for school students

19 June 2010

- 1 – Email: [email protected]

Electronics projects for School

Students

By

Tamilvanan.A

Email: [email protected]

19 June 2010


Index

Title Page

1. Introduction ……… 3

2. Basic Fundamentals of Electrical circuitry ……… 5

3. Simple LED experiments ……… 10

4. LDR (Light dependent resistor) ……… 13

5. Ohm’s Law and calculating Resistors in combination ……… 14

6. Series, Parallel circuit and short circuiting ……… 16

7. Voltage Divider ……… 19

8. Primary use of PN junction Diode ……… 22

9. Transistor as a switch ……… 24

10. Binary Logic and Logic gates ……… 26

11. Testing the AND, OR and NOT gate IC ……… 29

12. Operating a transistor using a switch ……… 32

13. Transistor AND Gate ……… 34

14. Transistor OR Gate ……… 36

15. Transistor as an inverter (NOT Gate) ……… 38

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16. Basic Theorems in Binary logic and Universal

Logic Gates ……… 40

17. Voltage regulation property of Zener Diode ……… 44

18. Capacitors for timing applications ……… 46

19. Clock/Oscillator using 555 Timer IC ……… 48

20. Flip flops ……… 52

21. Working of J-K flip flop ……… 53

22. Current toggling T flip flop from JK flip flop ……… 56

23. Data transmission using clock and JK flip flop ……… 58

24. Serial lighting using Decade counter IC ……… 60

19 June 2010


Introduction

This compilation of information in Electronics was specially

compiled and edited for school students (6th

grade+) which will help them

to understand the key concepts in Electronics while also explaining the

function of certain components through Do-it-yourself projects which will

later help them to understand and build complex circuitry easily.

Although, However, I must say that this isn’t a complete

reference guide book and many concepts which I really wanted to include

aren’t inside the package as I am considering about publishing a proper

book (a hand book that can even help a beginner understand and make

complex projects) in which I will be sharing almost everything I learnt in this

field until then.

I sincerely would like to thank my supporters who gave me this

opportunity to make a compilation like this one and exhibit my knowledge

in this field. Furthermore, I would also like to notify readers that this

compilation contains some information from the internet (such as IC chips

data sheet information) and I do not claim such information as mine or part

of my work.

For any other doubts, queries or suggestions about this

compilation, feel free to email me in the email address displayed below

each page.

19 June 2010


Lesson 1: Basic Fundamentals of Electrical Circuitry

This Lesson comprises of information on Basic Electrical Circuitry. Since we

won’t be using any professional and cautious equipment like soldering gun,

we will be using the bread board for building our circuits just by plugging in

and plugging out components from it. First, let us acquaint ourselves about

some basic fundamentals of Electric current and Electrical circuits.

For understanding the basic fundamentals of Electricity and current flow let

us consider the following illustrative example of water contained in a water

pipe with a pump which acts similar to the voltage source (battery)

portrayed in the electrical circuit diagram.

In the above illustrative example, the movement of the water

contained inside the pipe constitutes what is known as current while the

pump acts like the voltage source which circulates the water around the

water pipe continuously as long as it is functioning.

In Figure 1(a), the electrical circuit’s wiring is made up of atoms

of the material with which it was fabricated. These so called atoms are

made up of charges, namely, the proton (positive charge) and the electron

(negative charge) whereas, the water pipe consists of something similar i.e.,

“Water”. Hence it can be understood that the movement of the water

inside the pipe or the movement of the charges across the atoms of the

conductor is what that makes up electricity.

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It is said that current flow in a circuit is considered to be along

the direction of flow of positive charges. So assuming the water to be a

medium of positive charges, the current circulates from the positive

terminal of the battery to its negative terminal and keeps looping the same

way until the battery is completely drained whereas, the electrons

(negative charges) are said to be simultaneously circulating in the opposite

direction, i.e., from negative to positive terminal as it is the movement of

electron which induces the movement of positive charges.

So, if electrons stop moving protons also stop moving. In other

words, both move with same speed but in opposite directions hence, it can

be concluded that the force pushing them is equal in magnitude but

opposite in direction.

Now that we have mentioned the two measurable quantities

in electrical circuitry, i.e., voltage and current let’s have a look at a brief

description about it.

Voltage or Electric Potential:

As mentioned earlier, we know that the movement of the

charges of the atoms of the conductor is artificially induced by some sort of

force which acts as the driving force of the electric current. This force which

drives these charges, circulates them and constitutes electric current is

known as Voltage. So, without voltage there won’t be any movement of

charges hence, current cannot be induced without voltage. Unit for voltage

is Volts.

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NOTE: It may also be noted that electricity flows from a high potential point

to a low potential point. i.e., in a circuit consisting of a voltage source and a

resistor, current will move from +ve potential point to –ve potential point

or zero potential point.

Current:

Now that we are familiar with what induces current in a circuit,

lets us understand its relation with voltage. Current is the result of the

movement of the charges of the atoms inside the conductor. Current is a

measurable quantity. It can be defined as the number of charges that

passes by a point in a unit time. Unit for current is Ampere. Example:

1Ampere.

Now it can be understood that increasing voltage, i.e., the

pushing and pulling forces, increases the current as increasing the pushing

and pulling forces across the battery terminals pushes and pulls it with

higher speed and hence more amount of water (charges in electrical circuit)

can pass across within the unit time.

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Symbol Key

In electrical and electronic circuits we won’t be using any diagrammatic

representations of any component as it can be quite huge and cannot be

accommodated within the circuit diagram. Hence, we will be using the

following standard symbols for each component.

Symbol Component Name Description

Voltage source (or)

Battery

The long plate is the

positive terminal while the

short plate is the negative

terminal.

Variable Voltage Source

Voltage Source provided

with a knob to change

output voltage.

Simple toggle switch

A switch that closes the

circuit when the lever is slid

to one side.

Press Switch

Switch that closes the

circuit while pressed and

breaks open when released.

Resistor

Used to limit current or

voltage in a circuit branch.

LDR

(Light Dependent

Resistor)

Another variant of resistor

whose resistance varies

depending upon the light

falling on it.

Capacitor

A component similar to a

battery; used to store

charges (current).

PN junction Diode

Allows flow of current only

from Anode to Cathode.

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LED

(Light Emitting Diode)

It’s a component similar to

PN junction diode which

emits light when current

flows through it from

Anode to Cathode.

Transistors

There are two types of

transistors, namely, NPN

and PNP. Each has three

terminals namely, Base (B),

Collector (C) and Emitter

(E).

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Project 2: Simple LED experiments

Aim: To study the working of a LED, to construct series and parallel circuit

using them and to study the effect of resistance in a LED circuit.

Materials Required:

Components Quantity

1. Voltage Source - 1

2. LED’s - (as required)

3. Resistor - 1

4. Switch(Any) - 1

5. Jumper Wires - (as required)

Circuit Diagram:

Working: To test the circuit, simply press the switch and observe the LED

connected. The lamp will glow as the LED conducts current in this

configuration (Forward Bias). Try switching the terminals of the LED and

test it again to see if the lamp glows. This time the LED won’t glow as it

does not conduct current in this configuration (reverse bias).

Conclusion: The LED allows the flow of current only in one direction and

hence was found to be a directional component which restricts the flow of

current in the reverse direction.

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LED in Series and Parallel:

Now let’s try connecting two or more LED’s in series and

parallel to the voltage source using a switch.

Effect of Resistance in a circuit:

Now that you have already tested the circuit described in

figure3 (a), try including a high resistance resistor in your circuit like in

figure 3(d) and observe what happens. You can clearly notice that the LED

will not be as bright as it was before. This is because of the resistance you

included in the circuit.

The resistance imposed limits the current and voltage in the

circuit. Hence, the LED gets a limited range of voltage and current. Thus,

the LED will not glow as bright as before.

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Resistance and Resistors:

Resistance is known as the tendency of a material to

oppose/limit current and Resistor is a device used in a circuit branch to

limit current or voltage (depends upon what branch you connect them).

There are several types of resistors of which we will only be utilizing the

carbon film resistor which are cylindrical in appearance and which has

colored bands around them. These colored bands are used as an alternative

to represent their resistance values since printing contextual content

around such a small component is very difficult.

The convention for finding the value of a resistor is as follows:

Consider the below table for the code of each color to be applied:

Color Code

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

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Project 3: LDR (Light dependant resistor)

Aim: To construct a simple circuit to study the working of LDR (Light

Dependant resistor).

Materials Required:

Name Quantity

1. LDR - 1

2. LED (for testing) - 1


Circuit Diagram:

Principle: LDR is another variant of resistor that varies its resistance

depending upon the amount of light falling on it. When contained in a dark

environment, the resistance of the LDR abruptly increases; Hence, the

amount of current going through it will be low; whereas, when exposed to

bright light, its resistance decreases. Thus, the amount of current going

through it will be high.

Working: In Figure 1(a), Since the LDR is in series to the LED in the circuit,

the amount of current going through the LDR directly influences the LED’s

brightness. When the LDR is kept away from light, the LED’s brightness

decreases as the LDR’s resistance increases. When the LDR is exposed to

light, the LED becomes brighter as the LDR’s resistance decreases.

Applications: Since the LDR is capable of identifying dark lighting from

bright lighting; it can be used for detecting contrast colors (similar to a light

sensor)

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Ohm’s Law and calculating resistance of resistors in combination

Ohm’s Law:

The famous relation which relates Voltage (or) Electrical

potential, Current and Resistance in a branch of a circuit or a circuit as a

whole is given as:

V=IR

Where,

V- Voltage in Volts

I- Current in Amperes

R- Resistance in Ohms

Calculating Resistance in Series and Parallel:

Below is the formula for calculating the total resistance

imposed in a circuit by resistors connected in their respective branches.

This gives you the equivalent resistance of the resistors taken into

calculation.

For resistors connected in series:

The total resistance in the above branch can be found out as:

Total (Equivalent) Resistance= Sum of all the resistances

= R1+R2+R3

=330+220+1000

=1550 Ohms

For resistors connected in Parallel:

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1/Total Resistance=1/R1+1/R2

1/Total Resistance=1/1000+1/1000

=2/1000

Total Resistance =1000/2

Total Resistance =500 Ohms

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Lesson 5: Series, Parallel Circuit and short circuiting

Now that we are well acquainted with basic fundamentals in

Electrical circuitry in the previous chapter, we will be progressing to our

next concept in this chapter, i.e., connecting components in series and

parallel. The very first thing that comes to our mind when we hear the word

“series” is “in a sequence”. The same literary meaning applies even in

electrical circuitry. When referring to a couple of components as in a series,

we mean that they are allocated in a sequence, i.e., one after another in

the same branch.

Whereas, placing components in parallel means to allocate

them in such a way that each component in parallel connection are said to

be in a separate branch which would operate individually even if the other

branch were to be removed or damaged.

Figure 2(a) shows a resistor and LED in series, i.e., two

components which are in the same branch in a sequence. Whereas, in

Figure 2(b) shows the same resistor and LED in parallel branches, i.e., the

resistor can operate individually even if the LED branch is removed or

damaged and vice versa.

NOTE: It is known that in a series circuit, the voltage varies from

component to component i.e., decreases after passing by each component

whereas current remain constant to all components in the same

branch.The contradictory condition applies to Parallel circuitry where,

Voltage is constant in each branch, i.e., the voltage source’s voltage is

maintained constant in the beginning of each branch but current is

distributed from the main branch to the parallel branches depending upon

the resistance in each branch which can be found out by applying Ohm’s

law (Refer “Ohm’s Law and calculating resistance of resistors in

combination” chapter).

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Open switch:

So, everyone knows what an open switch in circuit is. But, do

you know whether an open switch conducts or does not conduct or

partially conducts? The answer in the case of mechanically driven switches

(common press, push and slide switches) is that it does not conduct and the

truth behind the concept is that the battery does not even induce the

current in the circuit (if there aren’t any other branches to conduct

through). The reason is simple because, current requires a positive

potential point and a negative potential point to conduct. When the

junction between any two points in the circuit breaks (opening the switch)

the two potential points are not interconnected. Hence, the battery does

not even induce current in the circuit. Consider the following diagram for

an open switch circuit:

Short Circuit:

As we know that a closed switch conducts, we might

misunderstand the problems that are yet to be faced in it. The problem

referred here is known as “short circuit”. Unlike its literary meaning, a short

circuit does not mean that it is short in length. It means that it is an “easy to

travel” path for current to flow without any sort of effort thereby draining

the battery’s power rapidly. So it is often necessary to emphasize on

balancing the resistance in each parallel branches of the circuit. This does

not mean that you are not only to ensure that there aren’t any branches

without any resistance, but, also to ensure that you do not over load any

parallel branch with very high resistance misleading the current to divert to

any other branch.

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As described in the above diagram, the branch encircled in red

is a short circuit, meaning that it forms an effortless path for current to

progress (without any resistance) hence all the current from the voltage

source gets diverted through the last branch, leaving no current on any of

the other branches. The diversion of current through a short circuit does

not depend on its position in the circuit. As long as current has access to

“too low resistance” or “no resistance” path, it deviates through that path

no matter how far it is away from the battery and drains the battery

rapidly.

NOTE: Considering the case of two or more possible short circuit branches

in a closed circuit switch, the current diverts through the branch closest to

it as it is mentioned earlier that current chooses an effortless path to flow

which does not only mean that it chooses the very low resistance path but

also chooses the shortest among such branches.

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Voltage Divider

Voltage divider is a network formed using certain components

such as capacitor or resistor to split a high input voltage to obtain a desired

voltage level for our application. It can be formed by coupling the two

components in series and paralleling out an additional branch from

between them to obtain the desired voltage amount. Right here in this

chapter you will be exhibited a detailed description on Resistive dividers

(Voltage dividers formed by resistors), how to calculate voltage across

voltage dividers and also on how to select proper resistance for obtaining

your desired voltage from a high voltage input.

In the above circuit the two resistors in the same branch are in

series and the output line is a separate parallel line. Hence, it can be

understood now that the current across the two resistors is same as

current is constant across all components connected in series, whereas,

voltage across each component varies in series (which is why voltage is split

after the first resistor).

To calculate the voltage obtained across the output line, first it

is necessary to calculate the current in the series branch across the two

resistors and the voltage drop caused by the first resistor.

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To calculate the current in the series connection first it is

necessary to calculate the total resistance in the series branch and then

calculate the current using Ohm’s Law formula as shown below:

Total resistance = R1+ R2 (Ohms)

Current in the series branch = Input voltage/Total Resistance (Amperes)

Now that we know the current in the series branch, the

voltage drop caused by the resistor(s) (the voltage negation caused by the

resistor(s)) before the parallel output line has to be calculated. For this, we

simply have to apply Ohm’s Law for the resistor(s) before the output line

like shown below:

Voltage Drop = Current in the series branch x Total resistance before the

output line

Output Voltage = Input Voltage – Voltage drop caused before output line

NOTE: If the resistance of the two resistors in the voltage divider network is

same, i.e., if both resistors have same resistance, then the input voltage

gets split by half, i.e., the output voltage = Input Voltage/2.

Choosing resistors for voltage divider network:

For constructing a voltage divider network we require at least

two resistors (we won’t be considering complex voltage dividers). Assuming

you have chosen one of the resistors for forming the voltage divider

network, the resistance of the second resistor to be included for getting the

desired voltage from the input voltage can be calculated as follows:

The formula for finding the resistor value for splitting the voltage can be

given as:

Output voltage = Input voltage x Total resistance after the output line

Total resistance in the series line

For Example consider the following problem:

For obtaining 5V output from a 9V input voltage supply where the second

resistor, R2=500Ohms, what resistor (R1) should be coupled in series with

resistor R2 in the voltage divider network?

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5 (Output Voltage) = 9 (Input voltage) x 500 (Total resistance after output line)

(500+R1) (Total resistance in series line)

5 = 9 x 500

(500+R1)

1 = 1

900 (500+R1)

500+R1 = 900

R1 = 900-500

R1 = 400 Ohms.

19 June 2010


Project 7: Primary use of PN junction Diode

Aim: To construct a circuit using a PN junction diode and study its primary

use.

Materials Required:

Name Quantity


7. Bulb - 1

8. Resistor (Optional) - 1

9. PN junction Diode/Rectifier - 1

10. Switch(Any) - 1


Circuit Diagram:

Principle: The above circuit is an illustrative example of the primary use of a

diode in a circuit. The PN junction Diode which restricts the flow of current

in one direction allows the flow of current only when the anode (A) and

cathode (C) of the diode are connected to the positive and negative

terminal of the voltage source respectively. This configuration of

connecting the diode is known as forward bias while connecting the

opposite way is known as Reverse Bias.

Working: To test the circuit, simply press the switch and observe the Lamp

connected. The lamp will glow as the diode conducts current in this

configuration (Forward Bias). Try switching the terminals of the diode and

test it again to see if the lamp glows. This time the lamp doesn’t glow as the

diode does not conduct current in this configuration (reverse bias).

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Conclusion: The PN junction diode allows the flow of current only in one

direction and hence was found to be a directional component which

restricts the flow of current in the reverse bias mode (when anode and

cathode of the diode are connected to the negative and positive terminal of

the voltage source respectively). This component can also be used to

restrict the flow of AC (Alternating Current) and allow the flow of DC

current.

19 June 2010


Project 8: Transistor as a switch

Aim: To construct a circuit which utilizes transistor as an electrical switch in

common emitter mode.

Materials Required:

Name Quantity


2. Resistor (Optional) - 1

3. NPN Transistor - 1


5. Switch (any) - 1


Circuit Diagram:

Principle: The NPN transistor is a component which when connected in

common emitter mode acts as an electrical switch and switches on circuit

loop B when the control circuit loop A is switched ON.

Working: Consider two circuit loops A and B connected together in a

junction using the NPN transistor. The circuit loop A acts as a control circuit

for the main circuit loop B. When circuit loop A is switched ON, it activates

the transistor in Base(B) junction and starts conducting from Collector(C) to

Emitter(E) junction thereby switching on circuit loop B and turns on the

LED. When the switch connected to Base (B) junction is turned off, the

transistor stops conducting from Collector (C) to Emitter (E) junction and

hence circuit loop B turns off.

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Conclusion: The transistor in common emitter mode acts as an electrical

switch which can be controlled by another control circuit. This property of

NPN transistor can be used for autonomous switching of circuit branches in

electronic circuitry.

Applications: Can be used to turn ON and OFF any component in the circuit

depending upon the input from any sensors like the LDR (Light dependent

resistor) when connected in the Base-Emitter junction circuit.

Note: This book contains information only on NPN transistors and not on

PNP transistors as PNP transistors won’t be necessary in any of the circuits.

However, the following context will provide you information on how the

PNP transistor is different from the NPN transistor.

The PNP transistor is simply a contradictory version of the NPN type

transistor. Its junction polarities are just opposite i.e., it allows the flow of

current from Emitter to Collector junction only if the Base junction is

grounded to the negative terminal of the battery.

19 June 2010


Lesson 9: Binary Logic and Logic Gates

Below is a small description about IC chips after which you will be taken

through Basic Logic Gate IC’s which deals with Electronic Logic using binary

numbers, i.e., 1 (+5V in digital circuits) and 0 (0V).

What are IC CHIPS?

IC chip or Integrated circuit chip are chips holding miniaturized

circuits in micro scale (10-6

) embedded inside them. IC’s are made for a

specific purpose and hence it can only be used for its purposes and similar

ones and cannot be utilized for any other as you cannot make any changes

to the circuits inside them. So People usually purchase specific purpose

oriented IC chips which suits their desire for building circuits.

IC’s generally look like a Black rectangular enclosure which are

embedded with serial numbers which defines its purpose. They also host

series of metal pins around its edges (usually over the two opposite sides

along the length of the rectangle). The pins are internally connected to the

circuits and serves specific purpose depending upon to which circuit they

are connected.

Since an IC’s internal circuitry cannot be seen through naked

eye (as they are in micro scale). Every IC has documentation sheets known

as datasheets describing the specific purpose of each pin around its

corners. So, when a user wants to use an IC to its utmost, he/she has to

refer to its datasheets which is available online free of cost.

Binary LOGIC:

Binary logic is a method of encoding what humans understand

into something what machines can understand. Like mentioned earlier, it is

constituted by two alphabets (0’s and 1’s) unlike ours which is from A-Z.

Similar to how humans work with numbers, machines encode

them into their own language, i.e., into a series of 1’s and 0’s and perform

calculations with them like us and give us our anticipated output. These so

called binary numbers (1 and 0) are nothing but electrical signals. In other

words, 1 refers to existence of current whereas, 0 refers to absence of

current.

For example, if an LED where to be connected to a voltage

source through a switch, opening the switch will switch off the LED which is

interpreted by machines as 0 and closing the switch will turn it ON which is

interpreted as 1.

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Embedded Systems:

These are nothing but electronic computer systems which are used to

perform a single or a few dedicated functions (These devices are smaller

units of big electronic systems which are built

solely for some specific purposes). They are

usually a part/module of a Huge Electronic

system. Basically they can be described as

units from which the whole system is built

with. For example, the clock/timer circuit in

any of your electronic components and any

complete and individually represent able

circuitry of an electronic device. Embedded

systems usually consist of one or more

components of which some can be programmed. An example of embedded

systems is the microcontroller.

Microcontrollers:

A Microcontroller is a small chip (similar to IC chip) which can be

programmed to operate in a user

defined manner. It consists of a basic

CPU capable of performing simple

binary operations, storage unit where

programs can be stored, a small RAM

unit where Data’s that is to be

processed or manipulated are stored

temporarily. In general it is a smaller

version or replica of a computer

which can perform only binary

operations. It can be part of a whole

electronic system in order to simplify

the flow of instructions (nothing but electrical signals) in a complex circuit.

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Basic Logic Gates

In this section you will be shown how computer processors perform

calculations using some basic circuitry known as LOGIC gates. Below are

some examples of LOGIC gates and you will be taught on how to implement

them on an IC chip containing these LOGIC GATES.

AND (Multiplication) Gate:

OR (Addition) Gate:

NOT (Inverter) Gate:

For testing these gates using IC we will be connecting an LED in the OUTPUT

junction to verify the output for each combination of input in the truth

table.

19 June 2010


Lesson 10: Testing the AND, OR and NOT GATE IC

The IC gates described over here house about four of each logic gate inside

them of which we will be only using only one. First we start by powering

the IC chip by connecting its +Vcc terminal and GND terminal to + and –

terminal of the voltage source. But however as described in the figure

below the +Vcc (power supply +) is directly connected to each input port.

So leaving the pin connected to the Input port idle will constantly provide it

with logic 1 which is provided from +Vcc pin.

Considering only the circuit in the left bottom corner, to

provide logic 0 in any one of its input’s we simple short circuit the pin

externally to the GND pin due to which the power supply will not go the

input of the gate and all will flow directly to the GND pin instead, making

that input 0. Similarly, try out all the combinations given in the truth table

by leaving the connection idle for providing binary ‘1’ and grounding each

input to provide binary ‘0’ and verify whether the LED is glowing or not.

OR Gate IC also hosts a similar connection inside it hence; try

out the same connections for OR Gate IC and verify the outputs for

different input combinations with the truth table for OR GATE.

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Likewise try out the connection for NOT Gate IC for which datasheet

diagram is given below:

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Applications: AND Gate can be used in cases where you want to turn ON a

component only when there is an input from two sensor systems

connected to the input ports. In advanced security systems, where there

are two levers on the two sides of a door to open it, the two levers have to

be activated at the same time to open the door. A simpler example of AND

gate would include the working of a microwave oven. The oven’s heater

will not function unless the door is closed and the button is pressed.

OR Gate can be used in situations where the functioning of a

component/device requires input from any one of the sensors connected to

the input pins. A more illustrative example of an OR gate would be a single

alarm system that inspects two doors where the alarm will go off even

when either one of the doors are opened or if both are opened.

NOT Gate can be utilized in inspection systems to inspect

proper working of any device. Consider a case where a device is inspected

for proper functioning. If the device’s power line where to be shared to the

input of a NOT Gate, it would be easy to notify whether the device is

shutdown or damaged by fixing an alarm system in the output pin.

19 June 2010


Project 11: Operating a transistor using a switch

Aim: To construct a transistor switch circuit using a single press switch

powered by a single voltage source.

Materials Required:

Name Quantity

1. Voltage Source(s) - 1

2. Resistor (300 Ohm) - 1

3. Resistor (10K Ohm) - 1



6. Switch (any) - 1


Circuit Diagram:

Principle: Unlike what we constructed using two voltage sources in a class

earlier using the NPN type transistor, we will be constructing a much

simpler way as used in many complex circuits which use a single voltage

source.

19 June 2010


Working: The circuit consists of two parallel loops which are isolated by the

transistors. Hence, although they are parallel branches from a single

voltage source, their operation can be better understood considering them

as two individual circuits. The circuit loop from the Base-Emitter junction of

the transistor is the control branch while the circuit in the Collector-Emitter

junction is the main circuit which is controlled.

The circuit branches meet at a common point after the emitter

junction. Hence, they both have a common path in the last junction

connected to the negative terminal of the battery. The main branch

consisting of the LED will only conduct only if the Base-Emitter junction is

supplied with current, i.e., the LED will light up only when the switch

connected in the Base-Emitter branch is closed.

19 June 2010


Project 12: Transistor AND Gate

Aim: To construct a circuit that utilizes the transistor as an AND Gate.

Materials Required:

Name Quantity






12. Switch (any) - 2


Circuit Diagram:

Principle: As you are already well aware about the application of the

transistor as an electrical switch, you wouldn’t find it hard to notice that all

you did in the circuit above was place those two electrical switch in series

such that the current in that branch would only conduct only if both the

switches are in conducting mode (turned ON) which very well suits the

truth table of AND logic GATE (Refer truth table of AND logic gate).

19 June 2010


Working: The two NPN type transistors are kept in series such that current

in that branch connected to the first transistor’s collector junction will not

pass through unless both transistors are saturated (making them

conductive by applying sufficient voltage in the Base junction). When the

two switches connected to the Base junction of the transistor are open, the

transistors would be in OFF mode due to which the branch in which the

transistors are connected will not have any current. As soon as the two

switches in the Base junctions of the two transistors are closed, the

transistors turn ON and start conducting from Collector to Emitter junction.

Hence, as a result, the LED turns ON only when the two switches are closed.

This explains the similarity of the two switches acting as the two inputs (A &

B) in the logic gate and the LED being the output (C).

19 June 2010


Project 13: Transistor OR Gate

Aim: To construct a circuit that utilizes the transistor as an OR Gate.

Materials Required:

Name Quantity


15. Resistor (5K Ohms) - 2

16. Resistor (100 Ohms) - 1





Circuit Diagram:

Principle: Similar to how we connected the transistors in series for the

construction of AND Gate, we will be using the two transistors in parallel

for the OR Gate’s construction. Unlike the And Gate, the OR Gate turns ON

the LED even when either one of the parallel branches starts conducting

current. This principle makes use of what you had already learned in your

first class where you studied the working of two switches in series and in

parallel connections.

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Working: Since the two NPN type transistors are in two parallel branches,

current can pass by and turn ON the LED even when either one of them

start conducting. In other words, the LED should light up when either one

of the two switches are closed or when both of them are closed. The only

case when the LED will not light up is when both the two switches are open.

Consider the truth table of OR Gate for verification.

19 June 2010


Project 14: Transistor as an inverter (NOT Gate)

Aim: To construct a circuit using a transistor which will utilize it like an

inverter.

Materials Required: Name Quantity


22. Resistor (100Ohm) - 1






Circuit Diagram:

Principle: As explained in the previous project, the NPN transistor is

connected in the same common emitter mode in this project also giving the

same results in the first two circuit loops. The third circuit loop consisting of

the LED is the loop in which current is going to be inverted with

correspondence to the current in the base junction of the transistor.

Working: When the switch connected to the base of transistor is open, the

third circuit loop consisting of the LED which is not linked to the transistor

works normally by lighting up the LED. When the switch connected to Base

junction of transistor is closed and conducts current to base, the transistor

gets activated and redirects the flow of current from the voltage source

powering the LED, through itself and into the emitter thereby, diverting the

current from going through the LED signifying that the flow of current

(binary 1) in base inverts the result by turning off the LED (binary 0) and

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switching off current in base junction (binary 0) turns on the LED (binary 1).

The base resistor is 3K ohms while the collector resistor is 100 Ohms.

Conclusion: The transistor can also be used as an inverter in common

emitter mode. This experiment also explains that Binary 0 does not only

refer to switching off current in a branch but also signifies that binary 0 can

also be achieved by diverting the current from the specified branch to

another branch.

19 June 2010


Lesson 15: Theorems in Binary logic and Universal Logic Gates

This Chapter will provide an overview of a few theorems in

Binary logic which might be quite useful for simplifying complex Binary logic

equations thereby also exhibiting the working of what are known as

Universal Logic Gates which are nothing but Logic Gates from which all

other logic gates can be derived from.

Universal Gates:

The so called Universal Logic Gates mentioned earlier are

NAND and NOR which are a combination of NOT-AND and NOT-OR

respectively. As the name says, NAND can be obtained by simply inverting

(adding NOT) the output of AND GATE while NOR can be obtained the same

way by inverting the output of OR gate.

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Basic Theorems in Binary Logic:

There are several theorems in Binary logic of which we will be

looking into those which will help us to verify the output for Universal logic

Gates and hence prove that they can be used to obtain any type of gate in

Binary logic.

1. A = A

2. A+A = A

3. A.A = A

De Morgan’s Theorem:

A mathematician named De Morgan developed a pair of

important rules regarding group complementation in Boolean algebra.

These rules or theorems were statements which related two Binary Logic

Gate’s operation (AND and OR) in a single equation. The mathematical

expressions for the two statements were given as follows:

1. A.B = A + B

2. A+B = A . B

Deriving Basic Logic Gates from Universal Logic Gates:

Verify the output obtained from the circuit provided above with the truth

table of OR Gate.

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Verify the output obtained from the circuit provided above with the truth

table of AND Gate.

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IC pin diagram KEY

NAND IC

NOR IC

NOT IC

AND IC

OR IC

19 June 2010


Project 16: Voltage regulation property of Zener Diode

Aim:

To study the voltage regulation property of a Zener diode and hence

to use it for regulated power supply for from a high voltage power source.

Materials Required:

Name Quantity

1. Zener diode - 1


3. Resistor 100 Ohm - 1

4. Resistor (2k Ohm) - 1

5. Jumper Wires - (As required)

6. LED (optional) - 1

Circuit Diagram:

Principle: Zener Diodes are a special variant of diodes which come printed

with a voltage value printed on them known as “breakdown voltage”. It is

said that the Zener Diode, when connected in reverse bias mode in parallel

to the power source, will not allow the elevation of the voltage beyond its

breakdown voltage (with a few decimal errors) in its parallel branch

irrespective of the increase in input voltage. Hence, it regulates the

maximum voltage that can enter a circuit branch.

19 June 2010


Working: The Zener Diode has a special characteristic in reverse bias mode

which allows current to flow through it abundantly when the voltage

supplied to it is greater than its breakdown voltage and allows feeble

current when the voltage supplied to it is below its breakdown voltage. Its

property is as if it would suddenly turn into a pure conductor when input

voltage increases beyond a specific value. Hence, when the voltage

increases beyond the breakdown voltage, the diode allows more than

enough current through it to maintain its breakdown voltage in the nearby

parallel branch.

If the breakdown voltage of the Zener diode is assumed to be

5.6V then the maximum voltage through the resistor in parallel will not

exceed 5.6V (with minute errors). However, when the Zener diode

experiences an input voltage greater than its breakdown voltage, it

conducts enormously that it could damage itself due to heavy current

hence it is always necessary to include a resistor before including the Zener

diode in the circuit which is why there is another resistor in series after the

Variable Power supply.

Conclusion: The Zener Diode is a component which can be used for

maintaining a maximum voltage through a branch and hence, can be used

for powering components such as IC chips which are sensitive to high

voltage power.

Applications: Zener Diodes can prevent high voltage from entering the

circuits and thus can prevent the damage caused by short circuits. Zener

diodes are mainly used in protective circuits such as stabilizer circuits

through which common household devices are powered. Hence, Zener

diodes can be used across power lines to power electronic and electrical

devices as a protective measure.

19 June 2010


Project 17: Capacitors for Timing Application

Aim: To build a circuit using a capacitor to understand the working of

Capacitor in series and to use it for timing applications.

Materials Required:

Name Quantity


2. Resistor (any) - 1

3. Capacitor (50 uf) - 1

4. LED - 1


Circuit Diagram:

Principle: Capacitor is a component that is similar to a battery, i.e., it can be

used for storing current temporarily; hence, it can be used for a variety of

purpose. One such purpose which is very prominent is using it for timing

applications. Capacitor is a device which acts like a dam door in a circuit

loop. It allows the inflow of current only until the dam tank gets full (until

battery is 100% charged) after which it closes due to which it stops the

inflow of further current through it, until it completely empties itself. So, it

can be considered to be a device that allows flows of current in the branch

in which it is included, only until it gets full.

Working: When the voltage source is connected and turned on, the

capacitor starts to allow flow of current until it can store enough. Hence,

the LED can only be expected to be turned on for a fraction of a second as

in real time we use capacitors which are of small values (capacitance of a

capacitor is measured in farads). Once the capacitor gets full, it stops the

inrush of current from the voltage source thus turning off the LED.

19 June 2010


The time period for which the capacitor allows current

depends upon the capacitance of the capacitor (in farads) and the

resistance of the resistor included. For increasing the time period for flow

of current, one can either increase the capacity of the capacitor by

choosing a higher capacitance capacitor so that more current has to flow to

fill it thereby increasing the time period or by increasing the resistance of

the resistor due to which the capacitor fills up little by little, taking more

time to fill it as the amount of current that flows through a high resistance

resistor is very less.

Conclusion: The capacitor can be used for triggering a device for a certain

period of time in this manner.

Applications: Can be used for timing the lighting of the LCD screen for a

particular period of time in a mobile phone. When you press any button on

your mobile phone, the LCD screen of your mobile, lights up for a few

seconds which is set by the capacitor connected in series between the

battery and the LCD screen pin.

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555 Timer IC chip

This section of the chapter will explain the pin diagram of 555 Timer IC

chips which is broadly used for timing applications in several circuits.

Hence, this can be considered as an abridged version of the datasheet for

555 Timer IC. For more information on the 555 Timer IC, consider the

datasheet of the IC which is available online for free.

1) Ground- The negative power supply of the IC.

2) Trigger- A short low pulse (current pulse) on the trigger starts the

timer. We simply have to provide a starting current pulse to start the

timer inside it.

3) Output- During a particular timing interval (depends upon what

capacitor you use), the output pin voltage will be equal to the voltage

provided in +Vcc pin.

4) Reset- Forces output pin 3 to OFF mode (binary 0) if connected to

ground.

5) Control- Is used to adjust the minimum trigger voltage. Not used in our

applications. Connect to ground with a .01uF cap to eliminate supply

noise from Vcc.

6) Threshold- When threshold crosses above 2/3 of the voltage in +Vcc

pin, timing interval ends.

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7) Discharge- automatically connects to ground pin automatically when

output goes low, i.e., binary ‘0’ (Controls timing).

8) +Vcc- positive Power supply. Typical range: 4.5v to 16v.

19 June 2010


Project 18: Clock/Oscillator

Aim: To construct a clock/oscillator circuit using the 555 Timer IC which is

used for timing applications in data transmission circuits.

Materials Required:

Name Quantity


29. Resistor (10K Ohms) - 2

30. Resistor (250 Ohms) - 1

31. 555 Timer IC - 1




35. Capacitor (500nF) - 1

Circuit Diagram:

Principle: The clock/Oscillator (not the clock used for displaying time)

circuit is a part of every complex circuit that is used to transmits/receive

data. In other words, it would be apt to say that there is no circuit in the

device of computer which does not have an oscillator. This circuit is what

that helps to synchronize the transmission and reception of data between

19 June 2010


two systems when exchanging. However, complex circuits in computer

require high speed oscillators which are built using individual components.

This circuit is just an example oscillator circuit which will help you to

understand its working.

Working: As mentioned in the datasheet section of the 555 Timer IC, the

described pins when connected as shown in Figure 1(a), would give a

clocked (fluctuating) output through the output pin which is connected to a

LED through a resistor. The clock simply produces pulses for a specific

interval of time, i.e., the output “fluctuates”; meaning, turns ON (binary ‘1’)

and goes OFF (binary ‘0’) for a particular interval of time which is set by the

capacitor.

The Voltage divider network consisting of the two 10K resistors

is used to ensure that only half of the voltage provided in +Vcc pin is sent to

the Discharge pin of the IC (Remember that in a voltage divider network,

the output will be half of input voltage if both the resistors are of same

resistance).

The capacitor in the circuit is kept in the main parallel branch

which does not have any resistor (resistance) after the voltage divider

network. Hence, the current in the main branch connecting several other

pins will short circuit only for a while (due to the capacitor in series). This

property of short circuiting for a while and then providing current into the

pins connected in parallel during discharge period causes the “Clocked”

Output.

The so obtained output keeps fluctuating in given interval

which is configured by the capacitor connected in the circuit. The number

of fluctuations in voltage per second is called as “Frequency”. Thus, it is

now understood that the frequency of the clocked output can be modified

by changing the capacitor in the circuit. The Unit of frequency is Hertz.

During the Clocked output, the output will rise from a lower

voltage to a higher voltage when fluctuating from ‘0’ to ’1’. This point

where the voltage rises is called the rising edge of the clock. Similarly the

falling edge occurs when the output falls from a higher voltage to a lower

voltage (when fluctuating from binary ‘1’ to binary ‘0’).

Applications: Used almost everywhere in communication systems and in

computer. Ex: RAM, Processor, Network Card, etc.

19 June 2010


Project 19: Flip Flops

Flip Flops:

Flip flops, are circuits built using Logic Gates (Universal Logic

gates in most cases) which are used as memory cells (circuits used for

storing binary data) primarily in some memory devices. There are several

types of flip flops of which a few are mentioned below:

1. S-R Flip flop (Set- Reset)

2. J-K Flip flop

3. D Flip flop

4. T Flip flop (Used for toggling current i.e., turning ON/OFF devices)

Basic S-R Flip flop:

The Basic S-R (Set-Reset) Flip flops constructed using Universal

Logic Gates, NAND and NOR is described below:

R-S Flip flop using NAND Gates

R-S Flip flop using NOR Gates

Try out the above connections using the NAND and NOR IC chips and verify.

R S Q

1 1 Q

1 0 0

0 1 1

0 0 ?

R S Q

1 1 ?

1 0 0

0 1 1

0 0 Q

19 June 2010


Project 20: Working of J-K flip flop

J-K Flip Flop:

In previous chapter it would have been clear that both R-S flip-

flops constructed using NAND and NOR Gates have unpredictable

conditions. The J-K flip-flop is nothing but an advanced version of the S-R

flip-flop which overcame this disadvantage. Besides, the J-K flip-flop also

has overriding pins in it (pins which force a specific output despite the input

given in J and K ports). Hence, the J-K flip-flop is believed to be an

integrated form of the R-S type.

Below is the circuit of J-K flip constructed using Logic Gates

But, however, we won’t be constructing the circuit using logic gates as we

will only be testing the J-K flip flop to see its working including all of its

features.

JK flip flop circuit constructed using NAND Gates

The above circuit constructed using NAND gates shows that

the JK flip flop uses four inputs along with a clock input whose values are

computed and displayed at one end through two output pins, Q and Q .

The two primary inputs, J and K are the two inputs whose mode of

operation gives four different combinations with each combination’s

output given out through the output pins. The Clock input is used to refresh

the system each time a single clock pulse is completed. Hence, it is used for

keeping record of the time for which the previous output will hold on.

Of the two output pins, Q is considered the primary

output. The JK flip flop is mainly used for storing bits and can be quite

useful as a memory cell for storing data. It is said to be in “Set” state when

it is said to store binary ‘1’ (when Q is ‘1’) and said to be in “cleared” state

19 June 2010


when it stores binary ‘0’ (when Q is ‘0’). The preset and clear inputs are

overriding inputs which when configured to “preset” state (when preset is

binary ‘1’ and clear is binary ‘0’) will force it store binary ‘1’ irrespective of

the inputs J and K. Whereas, when configured to “clear” state (when preset

is binary ‘0’ and clear is binary ‘1’), the primary output will be stored as

binary ‘0’ irrespective of the inputs in J and K. No matter what the value of

Q is, the output Q will always store the complement of what is stored in

Q, i.e., if Q is ‘1’ then Q will be ‘0’ and if Q is ‘0’ then Q will be ‘1’.

Verify the output of the IC given to you with the following truth table.

Preset Clear J K Clock Q Q

x x 0 0 Falling

edge

No change

x x 0 1 Falling

edge

0 1

x x 1 0 Falling

edge

1 0

x x 1 1 Falling

edge

Toggles

previous

output

1 0 any any Falling

edge

1 0

0 1 any any Falling

edge

0 1

Each time it can be remembered that the circuit stores the output during

the falling edge of the clock. So, when changing the inputs you will have to

wait till the falling edge after which it will display the respective output for

the current input state.

19 June 2010


Aim: To study the working of J-K flip flop IC chip.

Materials Required:

Name Quantity

1. IC 7476 - 1

2. LED - 2


4. Jumper Wires -(As required)

Circuit Diagram:

Working: Similar to how you tested the basic logic gates and universal logic

gate ICs, Verify the output of the JK flip flop IC by trying out all the

combinations. To provide binary ‘1’ to any input, simply couple it to the

positive power supply. To provide binary ‘0’, simply ground it (connect it to

negative supply).

19 June 2010


Project 21: Current toggling T flip flop from JK flip flop

Aim: To construct a power toggling circuit that toggles current in the circuit

i.e., turns on/off the current with the push of a push switch

Materials Required:

Name Quantity

12. JK flip flop IC - 1

13. Clock(Any)(Electronic Oscillator) - 1


15. Resistor (optional) - 1



Circuit Diagram:

Principle: T flip-flop also known as the Toggle Flip flop is a flip flop that

toggles the states of its two outputs, Q and ~Q (Q NOT) when the input T is

HIGH during the falling edge of the clock cycle and remembers the state

until changed using the same method. It is just a one input variant of JK flip

flop and can be obtained from the JK flip flop just by coupling the two

primary input pins, J and K together.

Working: To turn on the LED, simply press and hold the press switch till the

falling edge of the clock and wait for the LED to turn ON. Once the IC

toggles the states of Q and ~Q to HIGH and LOW respectively, it turns on

the LED. Release the switch now to hold the current states. To turn it off,

repeat the process i.e., press and hold the switch till the two outputs

change states and turns off the LED and then release the switch.

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Applications: Since the T flip flop is capable of changing and remembering

the states of its two outputs depending upon the input provided, this type

of circuitry can also be used as an alternative for a computer’s memory cell

in the main memory for storing and rewriting a bit (either 1 or 0). Main use

of this type of circuitry is turning ON and Turning OFF a device as it does

not require you to press and hold the input for remembering the output.

19 June 2010


Project 22: Data transmission using clocks and J-K flip flop

Aim: To construct a circuit using J-K flip flop IC chips and a clock to observe

how a circuit transmits binary data (‘1’ and ‘0’) between each other

Materials Required:

Name Quantity

1. IC 7476 (JK flip flop) - 1

2. LED bulbs - (As required)



Circuit Diagram:

Note: Please remember to power every IC used in the circuit. They can be

powered individually or powered using a single voltage source by

connecting all the ground pins to the negative terminal of the voltage

source.

Principle: The circuit in the above diagram is an example of how binary data

is transmitted between JK flip flop IC chips which are used as memory cells

as mentioned earlier. The 555 Timer IC clock pulse is shared among the IC

chips in a series which helps to synchronize the data transmission between

them. The LED’s connected in the output pins helps us to visualize the

transmission. Wherever the LED is turned OFF, the data transferred is

binary ‘1’ and wherever it is turned OFF the data transferred is binary ‘0’.

19 June 2010


Working: The JK flip flop is said to transmit binary ‘1’ when J and K are set

to ‘1’ and ‘0’ respectively, i.e., Q transmits ‘1’ and Q transmits ‘0’.

Whereas, it transmits the opposite signals (Q=’0’ and Q =’1’) when J and K

are set to ‘0’ and ‘1’ respectively. Leaving the first flip flop’s J=1 and K=0 for

one clock cycle, i.e., transmitting ‘1’ from the first flip flop, will trigger it to

send ‘1’ continuously until transmission of ‘0’ starts. The continuous

transmission applies even when transmitting ‘0’ by setting J=0 and K=1.

Try transmitting a pattern of ‘1’s and ‘0’s by altering the inputs to see how

data is transmitted.

NOTE: The data ‘1’ and ‘0’ can be sent through the first flip flop’s pins using

the same technique which we employed in Basic Logic gates IC chips (either

leaving it idle which will send binary ‘1’ or short circuiting it to the ground

pin which will transmit binary ‘0’) as these IC’s also house the same

architecture which was used in those IC chips.

Applications: This circuit is what is known as a shift register in computers

which transports the data from memory cells located in one end to the

memory cells in the other end.

19 June 2010


IC 4017 Decade Counter

The 4017 is a counter IC which is used to count clock pulses.

• There are 10 outputs labeled Q0 - Q9

• Each output will go High (emit binary ‘1’) in a series while all others

remain low (emit binary ‘0’).

• Each time the Clock input rises the next output goes high

• The outputs have current limiting circuits and so LED bulbs can be

used without series resistors when a 5v - 9v power supply is used. For

supply voltages greater than 9v series resistors may still be needed.

• The reset pin (15) is usually low. When it is momentarily taken high

(binary ‘1’), the counter starts from first.

• The Clock input is pin 14. The output changes on the rising edge of

the Clock

• CI is the Clock Inhibit. This is usually held low. When CI is made high,

the outputs do not change even if the Clock continues to change. The

CI input effectively stops the counter.

• Carry is an output that can be used to join multiple counter IC chips.

Carry is High (binary ‘1’) for Q0 to Q4 and Carry is low (binary ‘0’) for

Q5 to Q9. This means that the Carry goes high (rising edge of clock)

when the counter output goes from 9 to 0 so connecting the Carry to

the Clock of the next counter will cause the next counter to progress

by 1 count for every 10 counts of the first counter.

19 June 2010


Project 23: Serial lighting using Decade counter IC

Aim: To construct a circuit using the Decade counter IC using LED bulbs for

serial lighting effect.

Materials Required:

Name Quantity

1. Decade counter IC - 1

2. LED bulbs - (As required)



Principle: The Decade counter IC is an IC that provides sequential output

through its output pins from Q0-Q9 one after another lighting each LED one

at a time connected to them which appears to look like serial lighting. This

type of lighting can also be used for count down timing sequence for games

too.

Applications: Can be used for lighting LED bulbs in a specific pattern, can be

used for serial lighting, can be used as counting device for electronic

instruments and can be used as countdown timer.

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electronics projects for school students

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