ACKNOWLEDGMENT

I rejoice in expressing my prodigious gratification to Mr. Diwakar

Agrawal, Department of Electronics & Communication Engineering

Department, G.L.A. Institute of Technology & Management, Mathura for his

indispensable guidance, generous help, perpetual encouragement, constant

attention offered throughout in preparing the mini project.

LIST OF CONTENTS

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Abstract………………………………………………...4

Introduction…………………………………………....4

Component List………………………………………..5

Component Description……………………………....6

Circuit Diagram……………………………………....18

Working Principle…………………………………....18

Observation & Simulation Results………………….19

Conclusion………………………………………….....19

Bibliography………………………………………….19

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Abstract

Here is the circuit for a portable electric LED flasher. It uses nine LEDs. When the

IC555 output is high all the LEDs remain 'off, 'and when the IC 555 output is low LEDs

remains 'off.'

The circuit is built around timer IC 555 (IC1), which is wired as an astable multi vibrator

generating square wave. The output of IC1 drives transistor Q1.

Introduction

FLASHERS FOR DIWALI

The circuit is a LED Flasher whose flashing speed depends on the output square wave

frequency of the IC 555.When the output of the IC 555 is high ,the transistor Q1 is on and

the LEDS are OFF and when the output of IC555 is Low then transistor Q1 is OFF and the

LEDS are ON.

About Multisim

NI Multisim

NI Multisim (formerly MultiSIM) is an electronic schematic capture and simulation

program which is part of a suite of circuit design programs, along with NI Ultiboard.

Multisim is one of the few circuit design programs to employ the original Berkeley SPICE

based software simulation. Multisim was originally created by a company named Electronics

Workbench, which is now a division of National Instruments. Multisim includes

microcontroller simulation (formerly known as MultiMCU), as well as integrated import and

export features to the Printed Circuit Board layout software in the suite, NI Ultiboard.

Multisim is widely used in academia and industry for circuits education, electronic

schematic design and SPICE simulation.

HISTORY

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Multisim was originally called Electronics Workbench and created by a company

called Interactive Image Technologies. At the time it was mainly used as an educational tool

to teach electronics technician and electronics engineering programs in colleges and

universities. National Instruments has maintained this educational legacy, with a specific

version of Multisim with features developed for teaching electronics.

In 1999, Multisim was integrated with Ultiboard after the original company merged

with Ultimate Technology, a PCB layout software company.

In 2005, Interactive Image Technologies was acquired by National Instruments

Electronics Workbench Group and Multisim was renamed to NI Multisim.

What Is NI Multisim?

Multisim equips educators, students, and professionals with the tools to analyze

circuit behavior. The intuitive and easy-to-use software platform combines schematic

capture and industry-standard SPICE simulation into a single integrated environment.

Multisim abstracts the complexities and difficulties of traditional syntax-based simulation,

so we no longer need to be an expert in SPICE to simulate and analyze circuits. Multisim is

available in two distinct versions to meet the teaching needs of educators or the design needs

of professionals.

Multisim makes it easier to engage students and reinforce theory. Educators

worldwide are using the academic features of the Multisim education edition to foster

learning and guide student exploration of circuit concepts. Using “what-if” experiments and

simulation-driven instruments to visualize circuit behavior, students gain intuition and a

deeper understanding of circuit concepts.

Engineers, researchers, and domain experts use the Multisim environment for

schematic capture, SPICE simulation, and circuit design. Without needing any expertise in

SPICE, engineers can use simulation to reduce prototype iterations earlier in the design

flow. Multisim can be used to identify errors, validate design behavior, and prototype faster.

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Schematics can then be transferred to NI Ultiboard layout to prototype completed printed

circuit boards (PCBs).

Component List

1. Resistance.a) 2 resistances of 1.6 K b) 1 resistances of 1K.c) 1 resistance of 100 ohm.

2. BJT Transistora) NPN BJT transistor BC547BP.

3. Capacitora) 2 capacitors of 100nF.

4. IC 555.

5. 12 V DC Power Supply.

6. LEDa) 3 RED LIGHT LED.b) 3 GREEN LIGHT LED.c) 3 SKY BLUE LIGHT LED.

Component Description

Resistance

Resistors "resist" the flow of electrical current. The higher the value of

resistance (measured in ohms) the lower the current will be.

Resistors are color coded. To read the color code of a common 4 band 1K

ohm resistor with a 5% tolerance, start at the opposite side of the GOLD tolerance band and

read from left to right. Write down the corresponding number from the color chart below

for the 1st color band (BROWN). To the right of that number, write the corresponding

number for the 2nd band (BLACK) . Now multiply that number (you should have 10) by

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the corresponding multiplier number of the 3rd band (RED)(100). Your answer will be

1000 or 1K. It's that easy.

* If a resistor has 5 color bands, write the corresponding number of the 3rd band to the

right of the 2nd before you multiply by the corresponding number of the multiplier band. If

you only have 4 color bands that include a tolerance band, ignore this column and go

straight to the multiplier.

The tolerance band is usually gold or silver, but some may have none. Because

resistors are not the exact value as indicated by the color bands, manufactures have included

a tolorance color band to indicate the accuracy of the resistor. Gold band indicates the

resistor is within 5% of what is indicated.

Silver = 10% and None = 20%. Others are

shown in the chart below. The 1K ohm

resistor in the example (left), may have an

actual measurement any where from 950 ohms

to 1050 ohms.

If a resistor does not have a tolerance band, start from the band closest to a lead.

This will be the 1st band. If you are unable to read the color bands, then you'll have to use

your multimeter. Be sure to zero it out first!

 

Resistor Color Codes

Band Color 1st Band # 2nd Band # *3rd Band # Multiplier x  Tolerances  ± %

Black 0 0 0 1  

Brown 1 1 1 10     ± 1%

Red 2 2 2 100     ± 2 %

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Orange 3 3 3 1000  

Yellow 4 4 4 10,000  

Green 5 5 5 100,000     ± 0.5 %

Blue 6 6 6 1,000,000     ± 0.25 %

Violet 7 7 7 10,000,000     ± 0.10 %

Grey 8 8 8 100,000,000     ± 0.05 %

White 9 9 9 1,000,000,000  

Gold 0.1     ± 5 %

Silver 0.01     ± 10 %

None     ± 20 %

BJT Transistor

Working

Fig.NPN BJT with forward-biased E–B junction and reverse-biased B–C junction

An NPN transistor can be considered as two diodes with a shared anode. In typical

operation, the base-emitter junction is forward biased and the base–collector junction is

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reverse biased. In an NPN transistor, for example, when a positive voltage is applied to the

base–emitter junction, the equilibrium between thermally generated carriers and the

repelling electric field of the depletion region becomes unbalanced, allowing thermally

excited electrons to inject into the base region. These electrons wander (or "diffuse")

through the base from the region of high concentration near the emitter towards the region of

low concentration near the collector. The electrons in the base are called minority carriers

because the base is doped p-type which would make holes the majority carrier in the base.

To minimize the percentage of carriers that recombine before reaching the collector–

base junction, the transistor's base region must be thin enough that carriers can diffuse across

it in much less time than the semiconductor's minority carrier lifetime. In particular, the

thickness of the base must be much less than the diffusion length of the electrons. The

collector–base junction is reverse-biased, and so little electron injection occurs from the

collector to the base, but electrons that diffuse through the base towards the collector are

swept into the collector by the electric field in the depletion region of the collector–base

junction. The thin shared base and asymmetric collector–emitter doping is what

differentiates a bipolar transistor from two separate and oppositely biased diodes connected

in series.

Voltage, current, and charge control

The collector–emitter current can be viewed as being controlled by the base–emitter

current (current control), or by the base–emitter voltage (voltage control). These views are

related by the current–voltage relation of the base–emitter junction, which is just the usual

exponential current–voltage curve of a p-n junction (diode).

The physical explanation for collector current is the amount of minority-carrier

charge in the base region. Detailed models of transistor action, such as the Gummel–Poon

model, account for the distribution of this charge explicitly to explain transistor behavior

more exactly. The charge-control view easily handles phototransistors, where minority

carriers in the base region are created by the absorption of photons, and handles the

dynamics of turn-off, or recovery time, which depends on charge in the base region

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recombining. However, because base charge is not a signal that is visible at the terminals,

the current- and voltage-control views are generally used in circuit design and analysis.

In analog circuit design, the current-control view is sometimes used because it is

approximately linear. That is, the collector current is approximately βF times the base

current. Some basic circuits can be designed by assuming that the emitter–base voltage is

approximately constant, and that collector current is beta times the base current. However, to

accurately and reliably design production BJT circuits, the voltage-control (for example,

Ebers–Moll) model is required.[1] The voltage-control model requires an exponential

function to be taken into account, but when it is linearized such that the transistor can be

modelled as a transconductance, as in the Ebers–Moll model, design for circuits such as

differential amplifiers again becomes a mostly linear problem, so the voltage-control view is

often preferred. For translinear circuits, in which the exponential I–V curve is key to the

operation, the transistors are usually modelled as voltage controlled with transconductance

proportional to collector current. In general, transistor level circuit design is performed using

SPICE or a comparable analog circuit simulator, so model complexity is usually not of much

concern to the designer.

Turn-on, turn-off, and storage delay

The Bipolar transistor exhibits a few delay characteristics when turning on and off.

Most transistors, and especially power transistors, exhibit long base-storage times that limit

maximum frequency of operation in switching applications. One method for reducing this

storage time is by using a Baker clamp.

Transistor 'alpha' and 'beta'

The proportion of electrons able to cross the base and reach the collector is a

measure of the BJT efficiency. The heavy doping of the emitter region and light doping of

the base region causes many more electrons to be injected from the emitter into the base than

holes to be injected from the base into the emitter. The common-emitter current gain is

represented by βF or hFE; it is approximately the ratio of the DC collector current to the DC

base current in forward-active region. It is typically greater than 100 for small-signal

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transistors but can be smaller in transistors designed for high-power applications. Another

important parameter is the common-base current gain, αF. The common-base current gain is

approximately the gain of current from emitter to collector in the forward-active region. This

ratio usually has a value close to unity; between 0.98 and 0.998. Alpha and beta are more

precisely related by the following identities (NPN transistor):

Function

Transistors amplify current, for example they can be used to amplify the small

output current from a logic IC so that it can operate a lamp, relay or other high current

device. In many circuits a resistor is used to convert the changing current to a changing

voltage, so the transistor is being used to amplify voltage.

A transistor may be used as a switch (either fully on with maximum current, or fully

off with no current) and as an amplifier (always partly on).

The amount of current amplification is called the current gain,

Coding

Codes beginning with B (or A), for example BC108, BC478

The first letter B is for silicon, A is for germanium (rarely used now). The second

letter indicates the type; for example C means low power audio frequency; D means high

power audio frequency; F means low power high frequency. The rest of the code identifies

the particular transistor. There is no obvious logic to the numbering system. Sometimes a

letter is added to the end (eg BC108C) to identify a special version of the main type, for

example a higher current gain or a different case style. If a project specifies a higher gain

version (BC108C) it must be used, but if the general code is given (BC108) any transistor

with that code is suitable.

Capacitor

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This is a measure of a capacitor's ability to store charge. A large capacitance means that

more charge can be stored. Capacitance is measured in farads, symbol F

There are many types of capacitor but they can be split into two groups, polarised and

unpolarised. Each group has its own circuit symbol.

Polarised capacitors (large values, 1µF +)

Examples:       

Circuit symbol:   

Electrolytic Capacitors

Electrolytic capacitors are polarised and they must be connected the correct way

round, at least one of their leads will be marked + or -. They are not damaged by heat when

soldering.

There are two designs of electrolytic capacitors; axial where the leads are attached to

each end (220µF in picture) and radial where both leads are at the same end (10µF in

picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit

board.

It is easy to find the value of electrolytic capacitors because they are clearly printed

with their capacitance and voltage rating. The voltage rating can be quite low (6V for

example) and it should always be checked when selecting an electrolytic capacitor. If the

project parts list does not specify a voltage, choose a capacitor with a rating which is greater

than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.

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Tantalum Bead Capacitors

Tantalum bead capacitors are polarised and have low voltage ratings like electrolytic

capacitors. They are expensive but very small, so they are used where a large capacitance is

needed in a small size.

Modern tantalum bead capacitors are printed with their capacitance, voltage and

polarity in full. However older ones use a colour-code system which has two stripes (for the

two digits) and a spot of colour for the number of zeros to give the value in µF. The standard

colour code is used, but for the spot, grey is used to mean × 0.01 and white means × 0.1 so

that values of less than 10µF can be shown. A third colour stripe near the leads shows the

voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V).

The positive (+) lead is to the right when the spot is facing you: 'when the spot is in sight,

the positive is to the right'.

For example:   blue, grey, black spot   means 68µF

For example:   blue, grey, white spot   means 6.8µF

For example:   blue, grey, grey spot   means 0.68µF

Unpolarised capacitors (small values, up to 1µF)

Examples:      

Circuit symbol:   

Small value capacitors are unpolarised and may be connected either way round. They

are not damaged by heat when soldering, except for one unusual type (polystyrene). They

have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the

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values of these small capacitors because there are many types of them and several different

labelling systems!

Many small value capacitors have their value printed but without a

multiplier, so you need to use experience to work out what the multiplier

should be!

For example 0.1 means 0.1µF = 100nF.

Sometimes the multiplier is used in place of the decimal point:

For example:   4n7 means 4.7nF.

Capacitor Number Code

A number code is often used on small capacitors where printing is difficult:

the 1st number is the 1st digit,

the 2nd number is the 2nd digit,

the 3rd number is the number of zeros to give the capacitance in pF.

Ignore any letters - they just indicate tolerance and voltage rating.

For example:   102   means 1000pF = 1nF   (not 102pF!)

For example:   472J means 4700pF = 4.7nF (J means 5% tolerance).

IC 555

IC555 as Astable Multivibrator

The astable multivibrator generates a square wave, the periodof which is determined

by the circuit external to IC 555. The astable multivibrator does not require any external

trigger to change the state of theoutput. Hence the name free running oscillator. The time

during which the output is either high or low is determined by the two resistors and

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a capacitor which are externally connected to the 555 timer.The above figure shows the 555

timer connected as an astable multivibrator.

Initially when the output is high capacitor C starts charging towards Vcc through RA and RB.

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However as soon as the voltage across the capacitor equals 2/3 Vcc , comparator1

triggers the flip-flop and the output switches to low state.Now capacitor C discharges

through RB and the transistor Q1. When voltage across C equals 1/3 Vcc, comparator 2’s

output triggers the flip- flop and the output goes high. Then the cycle repeats.

The capacitor is periodically charged and discharged between 2/3 Vcc and 1/3 Vcc

respectively. The time during which the capacitor charges from 1/3 Vcc to 2/3 Vcc is equal to

the time the output remains high and is given by

where RA and RB are in ohms and C is in Farads. Similarly the time during which the

capacitor discharges from 2/3 Vcc to 1/3 Vcc is equal to thetime the output is low and is given

by

Thus the total time period of the output waveform is

Therefore the frequency of oscillation

The output frequency, f is independent of the supply voltage Vcc.

The output waveform may be observed in the waveform viewer.

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12 Volt DC power supply.

LED

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as

indicator lamps in many devices and are increasingly used for other lighting. Introduced as a

practical electronic component in 1962, early LEDs emitted low-intensity red light, but

modern versions are available across the visible, ultraviolet and infrared wavelengths, with

very high brightness.

When a light-emitting diode is forward biased (switched on), electrons are able to

recombine with electron holes within the device, releasing energy in the form of photons.

This effect is called electroluminescence and the color of the light (corresponding to the

energy of the photon) is determined by the energy gap of the semiconductor. LEDs are often

small in area (less than 1 mm2), and integrated optical components may be used to shape its

radiation pattern.[4] LEDs present many advantages over incandescent light sources including

lower energy consumption, longer lifetime, improved robustness, smaller size, and faster

switching. LEDs powerful enough for room lighting are relatively expensive and require

more precise current and heat management than compact fluorescent lamp sources of

comparable output.

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Light-emitting diodes are used in applications as diverse as replacements for aviation

lighting, automotive lighting (particularly brake lamps, turn signals and indicators) as well

as in traffic signals. LEDs have allowed new text, video displays, and sensors to be

developed, while their high switching rates are also useful in advanced communications

technology. Infrared LEDs are also used in the remote control units of many commercial

products including televisions, DVD players, and other domestic appliances.

Parts of an LED. Although not directly labeled, the flat bottom surfaces of the anvil

and post embedded inside the epoxy act as anchors, to prevent the conductors from being

forcefully pulled out from mechanical strain or vibration.

Working Of LED

The LED consists of a chip of semiconducting material doped with impurities to

create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to

the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes

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—flow into the junction from electrodes with different voltages. When an electron meets a

hole, it falls into a lower energy level, and releases energy in the form of a photon.

The wavelength of the light emitted, and thus its color depends on the band gap

energy of the materials forming the p-n junction. In silicon or germanium diodes, the

electrons and holes recombine by a non-radiative transition which produces no optical

emission, because these are indirect band gap materials. The materials used for the LED

have a direct band gap with energies corresponding to near-infrared, visible or near-

ultraviolet light.

Fig.The inner workings of an LED

Fig.I-V diagram for a diode.

An LED will begin to emit light when the on-voltage is exceeded. Typical on

voltages are 2–3 volts LED development began with infrared and red devices made with

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gallium arsenide. Advances in materials science have enabled making devices with ever-

shorter wavelengths, emitting light in a variety of colors.

LEDs are usually built on an n-type substrate, with an electrode attached to the p-

type layer deposited on its surface. P-type substrates, while less common, occur as well.

Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.

Most materials used for LED production have very high refractive indices. This means

that much light will be reflected back into the material at the material/air surface interface.

Thus, light extraction in LEDs is an important aspect of LED production, subject to much

research and development.

Circuit Diagram

Working Principle

Working of the circuit is simple. When output pin 3 of IC555 goes high, transistor

Q1 conducts and LEDs are OFF.

When output pin 3 of IC555 goes low.The collector of transistor Q1 is connected to

anodes of all the LEDs (LED1 through LED9). So when Q1 is cut-off the LEDs

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glow, and when Q1 conducts the LEDs go off. Current-limiting resistor R4 protects

the LEDs from higher currents.

In brief, the LEDs flash alternately depending on the frequency of IC555.

A 12V DC power supply is used to power the circuit.

Observation & Simulation Results

Conclusion

The LEDs flash according to the output frequency of the IC555.

Bibliography

1. http://www.electronicsforu.com/electronicsforu/lab/ad.asp?

url=www.electronicsforu.com/electronicsforu/circuitarchives/view_article.asp?

sno=99&title

2. http://www.the12volt.com/resistors/resistors.asp#calc

3. http://www.kpsec.freeuk.com/components/capac.htm

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4. http://en.wikipedia.org/wiki/Bipolar_junction_transistor

5. http://www.ni.com/multisim/whatis.htm

6. http://en.wikipedia.org/wiki/NI_Multisim

7. http://en.wikipedia.org/wiki/Light-emitting_diode

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