Mini Project Report

“ELECTRONIC CANDLES”

Submitted in partial fulfillment of the requirements

For the award of degree of

Bachelor of Technology

In

Electronics and Communication

Guide Submitted by

Prof. Piyush Chanana Suraj Singh (1051152807)

Priya Mittal (0981152807)

Sumit Dalal (0031152807)

Sunny Yadav(0071152807)

BHARTIYA VIDHYAPEETH’S COLLEGE OF ENGINEERING

A-4, PASCHIM VIHAR, ROHTAK ROAD, NEW DELHI- 110063

AFFILIATED TO

GURU GOBIND SINGH INDRAPRASTHA UNIVERSITY, DELHI-1100006

CERTIFICATE

This is to certify that the dissertation/project report (course code- 28 ) entitled ‘ELECTRONIC

CANDLES’ done by Mr. Suraj Singh(1051152807) , Ms. Priya Mittal (0981157308), Mr. Sumit

Dalal (0031152807), Mr. Sunny Yadav (0071157308) an authentic work carried out by them at

BVCOE under my guidance. The matter embodied in this project work has not been submitted

earlier for the award of any degree or diploma to the best of my knowledge and belief.

DATE: 18th March 2010 Signature of the guide

Name of the guide : Mr. Piyush Chanana

Desigination : Professor, BVCOE

ACKNOWLEDGEMENT

We take this opportunity to thank Mrs. Anuradha Basu, HOD of ECE Department for having permitted us to carry out this project work.

We wish to express our deep sense of gratitude to our project guide Mr. Piyush Chanana for providing us his valuable guidance and kind support towards the fulfillment of the project.

Finally, yet importantly, we would like to express our heartfelt thanks to our beloved parents for their blessings, our friends/classmates for their help and wishes for the successful completion of this project.

ABSTRACT

In this project our main aim was to study the complete working of “Circuit Maker” and then how to design a PCB (Printed Circuit Board).Here we have designed a PCB for “Electronic candles”. For this first we understood the various integral parts of the circuit i.e. 555 Timer IC, SCR1(c106),serial in/parallel out shift register and power supply. After studying all these parts our objective was to obtain a circuit which will produce a randomly flickering light effect in an electric bulb. During this we also studied the various characteristics of SCR1(c106) and 555 timer.

Contents

S.No. Page no.

1. Introduction 1-3

2. Hardware Description

2.1) Regulated DC Power Supply 4-5

2.2) 555-Timer IC 5-10

2.3) Serial IN Parallel Out Shift Register 11-12

2.4) Logic Gates 13-14

2.5) Silicon Controlled Rectifier 14-17

2.6) Electric Bulb 17

3. Design and Implementation 18-20

4. Component Requirements 21

5. Conclusion 22

6. Future Scope 23

7. Bibliography 24

List of Figure

S no. Name of the diagram Page no.

1. Block diagram of design 2

2. Circuit diagram of Regulated DC power supply 4

3. Pin diagram of 555-timer 5

4. Schematic of a 555 timer in monostable mode 7

5. 555 Astable circuit 8

6. 555 timer configuration in astable mode 9

7. Connection diagram of 74LS164IC 11

8. Logic diagram of 74LS164IC 11

9. Schematic diagram of NAND gate 13

10. Schematic diagram of Ex-NOR gate 14

11. Figures of SCR 14

12. SCR connection diagram 15

13. Volt-Ampere characteristics curve of an SCR 16

14. Circuit diagram of electric candle 18

INTRODUCTION

This project work is an attempt to design electronic candle that can produce the effect of

candle light in a normal electric bulb. A candle light as we all know , resembles a

randomly flickering light. These aren't the only electric candles, but they are easily

among the best - behaving incredibly like a real candle. The LED bulbs flicker more

realistically than most other flameless candles, just like a real flame. One of the biggest

advantages of these lights is the quality of the flicker. Generally, flickering LED candles

have a randomized flickering program me "cycle", that repeats itself. Lengthen this cycle

(which requires more memory in the electronics), and the candle can be made to be more

realistic. So the objective of this project activity is to produce a randomly flickering light

effect in an electric bulb.

To achieve this, the entire circuit can be divided into three parts. The first part comprises

IC1 (555), IC2 (74LS164), IC3 (74LS86), IC4 (74LS00) and the associated components.

These generate a randomly changing pulse.

The second part of the circuit consists of SCR1 (C106), an electric bulb connected

between anode of SCR1 and mains live wire and gate trigger circuit components.

It is basically half-wave AC power being supplied to the bulb.

The third part is power supply to generate regulated 5V DC from 230V AC for random

signal generator. It comprises a step down transformer(X1), full-wave rectifier (diodes

D3 and D4), filter capacitor (C9), followed by a regulator (IC5).

The figure below shows the block diagram of the design.

Block diagram of design

Figure 1

It consists of following blocks:

Power supply: It is a reference to a source of electrical power. A device or system that

supplies electrical or other types of energy to an output load or group of loads. It may

include a power distribution system as well as primary or secondary sources of energy

Clock generator : It is a circuit that produces a timing signal known as a clock signal

and for use in synchronizing a circuit's operation. The signal can range from a simple

symmetrical square wave to more complex arrangements. The basic parts that all clock

generators share are a resonant circuit and an amplifier

Serial to Parallel Converter: It is a 8 – bit Serial in / Parallel out shift register which has gated serial inputs and an asynchronous clear. It operates on frequency 36MHz clock frequency typically.

Pattern generator: It generates the different patterns to trigger the circuit.

Interface : It act as an interface between pattern generator and device.

Device: A device may be a computer device or electronic equipment. It can be computer hardware, peripheral or electronic equipment, integrated circuit

POWER SUPPLY

CLOCK GENERATOR

SERIAL TO PARALLEL

CONVERTER

PATTERN GENERATOR

INTERFACEDEVICEOUTPUT

Output: Output can refer to output can refer to or an observable output such as amplification of an analog signal.

.

HARDWARE DESCRIPTION

To design electronic candle the following components have been used:

1. Regulated DC Power supply

2. 555-Timer IC

3. Serial in/ parallel out shift register

4. Gates

5. Silicon Controlled Rectifier(SCR1(C106))

6. Electric Bulb

This section gives brief description of each of the components.

Component 1: Regulated DC Power supply

It comprises a step down transformer, full wave rectifier, filter capacitor, followed by a

regulator

Circuit Diagram of Regulated DC power supply

Figure 2

The regulated DC output is very smooth with no ripple. It is suitable for all electronic

circuits

Transformer: Transformers convert AC electricity from one voltage to another with

little loss of power. Transformers work only with AC and this is one of the reasons why

mains electricity is AC.

Rectifier: There are several ways of connecting diodes to make a rectifier to convert AC

to DC. The bridge rectifier is the most important and it produces full-wave varying DC.

A full-wave rectifier can also be made from just two diodes if a centre-tap transformer is

used, but this method is rarely used now that diodes are cheaper.

Smoothing : Smoothing is performed by a large value electrolytic capacitor connected

across the DC supply to act as a reservoir, supplying current to the output when the

varying DC voltage from the rectifier is falling.

Regulator: Voltage regulator ICs are available with fixed (typically 5, 12 and 15V) or

variable output voltages. They are also rated by the maximum current they can pass.

Negative voltage regulators are available, mainly for use in dual supplies. Most

regulators include some automatic protection from excessive current

Component 2: 555-Timer IC

The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and

multivibrator applications. Depending on the manufacturer, the standard 555 package includes

over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-

line package (DIP-8).

Pin Diagram of 555-Timer

Figure 3

The connection of the pins are as follows:

Nr. Name Purpose

1 GND Ground, low level (0 V)

2 TRIG A short pulse high-to-low on the trigger starts the timer

3 OUT During a timing interval, the output stays at + V CC

4 RESETA timing interval can be interrupted by applying a reset pulse to low (0 V)

5 CTRLControl voltage allows access to the internal voltage divider (2/3 VCC)

6 THRThe threshold at which the interval ends (it ends if the voltage at THR is at least 2/3 VCC)

7 DISConnected to a capacitor whose discharge time will influence the timing interval

8 V+,VCC The positive supply voltage which must be between 3 and 15 V

Table 1

The 555 has three operating modes:

Monostable mode: In the monostable mode, the 555 timer acts as a “one-shot” pulse

generator. The pulse begins when the 555 timer receives a trigger signal. The width of

the pulse is determined by the time constant of an RC network, which consists of

a capacitor(C) and a resistor(R). The pulse ends when the charge on the C equals 2/3 of

the supply voltage. The pulse width can be lengthened or shortened to the need of the

specific application by adjusting the values of R and C.

Schematic of a 555 in monostable mode

Figure 4

The pulse width of time t, which is the time it takes to charge C to 2/3 of the supply

voltage, is given by

where t is in seconds, R is in ohms and C is in farads.

Applications include timers, missing pulse detection, bounce free switches, touch

switches, frequency divider, capacitance measurement, pulse-width modulation (PWM)

etc

Astable mode - In this mode , the '555 timer ' puts out a continuous stream of

rectangular pulses having a specified frequency. Resistor R1 is connected between

VCC and the discharge pin (pin 7) and another resistor (R2) is connected between the

discharge pin (pin 7), and the trigger (pin 2) and threshold (pin 6) pins that share a

common node. Hence the capacitor is charged through R1 and R2, and discharged only

through R2, since pin 7 has low impedance to ground during output low intervals of the

cycle, therefore discharging the capacitor.

555 Astable Circuit

Figure 5

In the astable mode, the frequency of the pulse stream depends on the values of R1,

R2 and C:

The high time from each pulse is given by

and the low time from each pulse is given by

where R1 and R2 are the values of the resistors in ohms and C is the value of the

capacitor in farads.

Applications include LED and lamp flashers, pulse generation, logic clocks, tone

generation, security alarms, pulse position modulation ,etc.

Bistable mode or Schmitt trigger : The Bistable Circuit toggles between the states.

Triggering one input sets the output to the low state, while triggering another input sets

the output to the high state. The name "bistable" means "two stable states".It can

operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses

include bounce free latched switches, etc.

In designing of electronic candle, the clock signal is generated by using the 555 timer in

Astable mode. The detailed description of it is given below:

This is the free running mode and the trigger is tied to the threshold pin. It is a timing circuit whose 'low' and 'high' states are both unstable. As such, the output of an Astable multivibrator toggles between 'low' and 'high' continuously, in effect generating a train of pulses. This circuit is therefore also known as a 'pulse generator' circuit.

555 timer configuration in astable modeFigure 6

In this circuit, capacitor C1 charges through R1 and R2, eventually building up enough voltage to trigger an internal comparator to toggle the output flip-flop. Once toggled, the flip-flop discharges C1 through R2 into pin 7, which is the discharge pin. When C1's voltage becomes low enough, another internal comparator is triggered to toggle the output flip-flop. This once again allows C1 to charge up through R1 and R2 and the cycle starts all over again.

C1's charge-up time t1 is given by: t1 = 0.693(R1+R2)C1. C1's discharge time t2 is given by: t2 = 0.693(R2)C1. Thus, the total period of one cycle is t1+t2 = 0.693 C1(R1+2R2).

The frequency f of the output wave is the reciprocal of this period, and is therefore given by:

The HIGH and LOW times of each pulse can be calculated from:

HIGH Time = 0.69 (R1 + R2) × C

LOW Time = 0.69 (R2 × C)

The duty cycle of the waveform, usually expressed as a percentage, is given by:

where f is in Hz if R1 and R2 are in mega ohms and C1 is in microfarads.

Valuable features:

Free running modes, 50% duty cycle

Good astable frequency stability 2% @100kHz,0.5%

Component 3: Serial in Parallel out shift register (74LS164)

Connection Diagram of 74LS164 IC

Figure 7

Logic Diagram of 74LS164 IC

Figure 8

This 8-bit parallel-out serial shift register features AND -gated serial (A and B) inputs and an asynchronous clear (CLR) input. The gated serial inputs permit control over

incoming data because a low at either input inhibits entry of the new data and resets the first flip-flop to the low level at the next clock pulse. A high-level input enables the other input, which determines the state of the first flip-flop. Data at the serial inputs can be changed while the clock is high or low,provided that the minimum setup-time requirements are met. Clocking occurs on the low-to-high-level transition of the clock (CLK) input. All inputs are diode clamped to minimize transmission-line effects.The SN74ALS164A is characterized for operation from 0°C to 70°C.

FUNCTION TABLE

INPUTS OUTPUTS

CLR’ CLK A B QA QB QH

L X X X L L LH L X X QAD QB0 QH0

H Up H H H QAn QGn

H Up L X L QAn QGn

H Up X L L QAn QGn

Table 2

QA0, QB0, QH0 = the level of QA, QB, or QH, respectively,before the indicated steady-state input conditions wereestablished.H = high level (steady state), L = low level (steady state)X = irrelevant (any input, including transitions)Up = transition from low to high levelQAn, QGn= the level of QA or QG before the most recent↑ transition of the clock; indicates a 1-bit shift.

FEATURES

Typical shift frequency of 35MHz

Asynchronous master reset

Gated serial data input

Fully synchronous data transfer

Component 4: Logic Gates

The hardware implementation of the electronic candle uses the following gates:

1. NAND Gate : The NAND gate is a digital logic gate that behaves in a manner

that corresponds to the truth table given below

Truth Table Schematic

Diagram of NAND GATE

Table 3 Figure 9

A LOW output results only if both the inputs to the gate are HIGH. If one or both inputs

are LOW, a HIGH output results. The NAND gate is a universal gate in the sense that

any Boolean function can be implemented by NAND gates.

Exclusive-NOR GATE : The XNOR gate is a digital logic gate whose function is the

inverse of the exclusive OR (XOR) gate. The two-input version implements logical

equality,behaving according to the truth table to next page

INPUTA B

OUTPUTA NAND B

0 0 1

0 1 1

1 0 1

1 1 0

Truth Table Schematic Diagram of Ex-NOR GATE

Table 4 Figure 10

A HIGH output (1) results if both of the inputs to the gate are the same. If one but not

both inputs are HIGH (1), a LOW output (0) results.

Component 5: SILICON CONTROLLED RECTIFIER (C106)

Shockley diodes are curious devices, but rather limited in application. Their usefulness may be expanded, however, by equipping them with another means of latching. In doing so, each becomes true amplifying devices (if only in an on/off mode), and we refer to these as silicon-controlled rectifiers, or SCRs.The progression from Shockley diode to SCR is achieved with one small addition, actually nothing more than a third wire connection to the existing PNPN structure: (Figure below)

INPUTA B

OUTPUTA XNOR B

0 0 1

0 1 0

1 0 0

1 1 1

Figure 11

The SCR has become the workhorse of the industrial control industry. Its evolution over the years has yielded a device that is less expensive, more reliable, and smaller in size than ever before. Typical applications include : DC motor control, generator field regulation,Variable Frequency Drive (VFD) DC Bus voltage control, Solid State Relaysand lighting system control.

SCR Connection DiagramFigure 12

The SCR is a three-lead device with an anode and a cathode (as with a standard diode) plus a third control lead or gate. As the name implies, it is a rectifier which can be controlled - or more correctly - one that can be triggered to the “ON” state by applying a small positive voltage ( VTM ) to the gate lead. Once gated ON, the trigger signal may be removed and the SCR will remain conducting as long as current flows through the device.

If an SCR's gate is left floating (disconnected), it behaves exactly as a Shockley diode. It may be latched by break over voltage or by exceeding the critical rate of voltage rise between anode and cathode, just as with the Shockley diode. Dropout is accomplished by reducing current until one or both internal transistors fall into cutoff mode, also like the Shockley diode. However, because the gate terminal connects directly to the base of the lower transistor, it may be used as an alternative means to latch the SCR. By applying a small voltage between gate and cathode, the lower transistor will be forced on by the resulting base current, which will cause the upper transistor to conduct, which then supplies the lower transistor's base with current so that it no longer needs to be activated by a gate voltage. The necessary gate current to initiate latch-up, of course,

will be much lower than the current through the SCR from cathode to anode, so the SCR does achieve a measure of amplification.

This method of securing SCR conduction is called triggering, and it is by far the most common way that SCRs are latched in actual practice. In fact, SCRs are usually chosen so that their breakover voltage is far beyond the greatest voltage expected to be experienced from the power source, so that it can be turned on only by an intentional voltage pulse applied to the gate.

It should be mentioned that SCRs may sometimes be turned off by directly shorting their gate and cathode terminals together, or by "reverse-triggering" the gate with a negative voltage (in reference to the cathode), so that the lower transistor is forced into cutoff. I say this is "sometimes" possible because it involves shunting all of the upper transistor's collector current past the lower transistor's base. This current may be substantial, making triggered shut-off of an SCR difficult at best. A variation of the SCR, called a Gate-Turn-Off thyristor, or GTO, makes this task easier. But even with a GTO, the gate current required to turn it off may be as much as 20% of the anode (load) current!

Volt-Ampere Characteristics

Figure One below illustrates the volt-ampere characteristics curve of an SCR.

Volt-ampere characteristics curve of an SCR.Figure13

The vertical axis + I represents the device current, and the horizontal axis +V is the voltage applied across the device anode to cathode. The parameter

It defines the RMS forward current that the SCR can carry in the ON state, while VR defines the amount of voltage the unit can block in the OFF state.

Biasing

The application of an external voltage to a semiconductor is referred to as a bias.

Forward Bias OperationA forward bias, shown below as +V, will result when a positive potential is applied to the anode and negative to the cathode .Even after the application of a forward bias, the device remains non-conducting until the positive gate trigger voltage is applied.After the device is triggered ON it reverts to a low impedance state and current flows through the unit. The unit will remain conducting after the gate voltage has been removed. In the ON state (represented by +I), the current must be limited by the load, or damage to the SCR will result.

Reverse Bias Operation The reverse bias condition is represented by -V. A reverse bias exists when the potential applied across the SCR results in the cathode being more positive than the anode. In this condition the SCR is non-conducting and the application of a trigger voltage will have no effect on the device. In the reverse bias mode, the knee of the curve is known as the Peak Inverse Voltage PIV (or Peak Reverse Voltage - PRV) and this value cannot be exceeded or the device will break-down and be destroyed. A good Rule-of -Thumb is to select a device with a PIV of at least three times the RMS value of the applied voltage.

Component 6: Electric Bulb

The electric bulb, is a source of electric light that works by connecting the circuit part to it and produce a randomly flickering light effect in it.

DESIGN AND IMPLEMENTATION

The given figure shows the circuit diagram of Electronic Candle

Circuit diagram of electronic candle

Figure 14

The above given circuit diagram is a simple circuit that can produce the effect of candle

light in a normal electric bulb .To achieve this , the entire circuit diagram is divide into

three parts:

The first part is the power supply to generate regulated 5V DC from 230V AC for

random signal generator. It comprises a step down transformer(X1), full-wave rectifier

(diodes D3 and D4), filter capacitor (C9), followed by a regulator (IC5).

The second part comprises of IC1(555), IC2 (74LS164), IC3 (74LS86), IC4 (74LS00)

and the associated components. These generate a randomly changing pulse.

The third part of the circuit consists of SCR1 (C106), an electric bulb connected between

anode of SCR1 and mains live wire and gate trigger circuit components. It is basically

half-wave AC power being supplied to the bulb

The functioning of the system is as follows:

The first part of the circuit will provide a regulated voltage to the external circuit which may also I am required in any part of the external circuit or the whole external circuit .The best part is that you can also use it to convert AC voltage to DC and then regulate it ,simply You need a transformer to make the AC main drop down to a safe value i.e. 12-15 volts and then us a rectifier to convert AC into DC.

This circuit can give +5V output at about 150mA current, but it can be increased to 1 A when good cooling is added to 7805 regulator chip. The circuit has over overload and terminal protection. The capacitors must have enough high voltage rating to safely handle the input voltage feed to circuit.

If you need other voltages than +5V, you can modify the circuit by replacing the 7805 chips with another regulator with different output voltage from regulator 78xx chip family. The last numbers in the chip code tells the output voltage.

In the second part ,The random signal generator of the circuit is built around an 8-Bit serial in/parallel out shift register (IC2). Different outputs of the shift register IC pass through a set of logic gates(N1 through N5) and final output appearing at pin 6 of gate N5 is fed back to the inputs of pins 1and 2 of IC2. The clock signal appears at pin 8 of IC2, which is clocked by an astable multivibrator configured around timer(IC1). The clock frequency can be set using preset VR1 and VR2. it can be set around 100Hz to provide better flickering effect in the bulb.

The random signal generated from the above triggers the gate of SCR1. The electric bulb

gets AC power only for the period which SCR1 is fired.

SCR1 is fired only during the positive half cycles. Conduction of SCR1 depends upon

the gate triggering pin3 of IC2, which is random. Thus, we see a flickering effect in the

light output.

Assemble the circuit on a general purpose PCB and enclose it in a suitable case. Fix bulb

and neon bulb on the front side of the cabinet. Also, connect a power cable for giving

AC mains supply to the circuit for operation. The circuit is ready to use. Since the circuit

uses 230V AC, care must be taken to avoid electric shock.

Components Requirements

555 timer IC

Serial in /parallel out shift register IC- 74LS164

NAND Gate IC- 74LS00

XNOR Gate IC- 74LS86

Variable Resistors (100KΩ)

Capacitors(100µF,10µF,1000µF,0.1µF)

Resistors ( 10kΩ,100kΩ,180Ω)

Step down transformer(230v AC primary to7.5v-0-7.5v, 250mA secondary

transformer)

Regulator IC-7805

SCR1(C106) thyristor

Diodes(1N4148,1N4001,1N4007)

Bulb(60W,230v)

Neon Bulb

Connecting Wires

Power Supply

CONCLUSION

The system has been designed on PCB that uses various components in its designation.

It has been designed and studied in detail by implementing it. The hardware of this

project is designed to the stage of random signal generation successfully and rest of the

portion can not design due to unavailability of components. We have also studied the

CIRCUIT MAKER software during this project. Circuit maker is a schematic design,

simulation and PCB design tool and the major portion of the project has been simulated

on it. In future the same will be ported onto a small size PCB.

FUTURE SCOPE

Standard wax candles used for decoration and mood lighting produce an open flame and high temperatures. This is unsuitable for many applications where accidents are likely, especially around children and pets.In many situations use of candles and other open flames may be prohibited by local fire and building regulations. It is possible to realistically simulate these lighting effects electrically. In these situations Electronic candles can be very useful.

BIBLIOGRAPHY

1. Kennedy George, “ Digital Electronics ”, 4th edition, Tata Mc-Graw Hill Publication Company

2.Wolfgang wieske, “Application of Thyristor”, Bpb publication

3.Taub Herbert, Schilling Donald, “Digital integrated Electronics” , International

edition-1974, Tata Mc-Graw Hill Publication Company

4.www.ieee.org

5.www.electronicsforu.com