the design and implementation of a four – way traffic light
TRANSCRIPT
THE DESIGN AND IMPLEMENTATION OF A FOUR
– WAY TRAFFIC LIGHT CONTROL CIRCUIT.
BY
IN PARTIAL FULFILMENT FOR THE AWARD OF
HIGHER NATIONAL DIPLOMA IN ENGINEERING
(HND) IN THE DEPARTMENT OF
ELECTRICAL/ELECTRONICS ENGINEERING
SCHOOL OF ENGINEERING
INSTITUTE OF MANAGEMENT AND
TECHNOLOGY (IMT) ENUGU
SEPTEMBER, 2005.
TITLE PAGE
1
THE DESIGN AND IMPLEMENTATION OF A FOUR – WAY
TRAFFIC LIGHT CONTROL CIRCUIT.
BY
IN PARTIAL FULFILMENT FOR THE AWARD OF HIGHER
NATIONAL DIPLOMA IN ENGINEERING (HND) IN THE
DEPARTMENT OF ELECTRICAL/ELECTRONICS
ENGINEERING SCHOOL OF ENGINEERING
INSTITUTE OF MANAGEMENT AND TECHNOLOGY
(IMT) ENUGU
SEPTEMBER, 2005.
APPROVAL PAGE
2
This project has been approved for the Department of electrical electronic
engineering, institute of Management and Technology (IMT) Enugu by
Engr. Uduezue Engr. Ihedioha
Project Coordinator Head of Department
DEDICATION
I dedicate this work to my dear mother for her unrelenting and indispensable
role throughout my scholastic days. I also dedicate this work to those who
channel their efforts to the development of human intellect.
To God be the glory.
3
ACKNOWLEDGEMENT
My appreciation goes to God for his greatness upon my life, also to my project
supervisor Engr. Ihedioha for the immeasurable contributions, useful
suggestions and general supervision and also for giving me such as wonderful
opportunity to undertake a research of this magnitude.
4
I am very grateful to the HOD, the department of Electrical and
Electronic Engineering Engr. Ihedioha for his fatherly relationship, also
acknowledged is our project coordinator, Engr. Uduezue.
I also acknowledge the support given to me by my brothers and sisters
who among them includes Richard, Daniel, Famous and Lawrence.
My unalloyed appreciation goes to friends, prominent among them is
Ugwu Kenneth others includes Oliver, Onome, Greg and others for their love
and support.
I also acknowledge the efforts of my friends and brothers across Nigeria
for their immense contributions and support in making me realize my dream, I
lack words to thank you all but the good Lord whom you have made your best
friend would surely see you through, till you find your TRASURE. To God be
the glory.
5
ABSTRACT
This work has been aimed at efficient means of controlling the traffic
effectively for twenty-four hours. As the world is growing technologically
more and more vehicles jump into the public road adding to the already
existing number. Consequently, more efficient way of controlling the traffics
becomes more desirable as compared to the obsolete way of using the traffic
personnel’s.
6
The design of this traffic light control is grouped basically into three;
digital logic design, the power circuit and the power supply design. The digital
logic design is based on integrated circuits which happens to be the modern
way of designing digital systems, the power circuit design is aimed at lighting
the different LEDS as and when due, while the power supply design strives to
achieve a constant 8V dc supply for powering the circuit.
For this work, the frame with the LEDS mounted on it has been
constructed, the driven circuit was implemented and the entire system enclosed
in the smoothened frame.
The realized work was tested and guaranteed to give a firmly good level
of performance.
TABLE OF CONTENTS
Title page
Approval page
Dedication
7
Acknowledgement
Table of contents
Abstract
CHAPTER ONE
1.0 Introduction
1.1 aims of the project
1.2 Methodology
CHAPTER TWO
2.0 A Review on the Traffic Light Control System
2.1 The Power supply unit
2.2 The transformer
2.3 The rectifier
8
2.4 The filter
2.5 The Voltage Regulator
2.6 The Digital Logic Circuit
2.7 The Oscillator
2.8 The Counter
2.9 The Decoder
2.10 The Logic Gates
2.11 The Power Circuit
2.12 The Booster/Amplifier Stage
2.13 The Lamp/LEDS
CHAPTER THREE
3.0 The Traffic Light Control
9
3.1 The Power Supply Design Specifications
3.2 The Transformers
3.3 Rectifier
3.4 The Filter Capacitor
3.5 The Voltage Regulator
3.6 The Digital Logic Design
3.7 The Oscillator
3.8 The 4017 Decade Counter
3.9 The output Logic Gate Circuit
CHAPTER FOUR
4.0 Problem Encountered
4.1 Construction and Testing
10
4.2 Cost Analysis
4.3 The overall Circuit Diagram of the $-way Traffic Light Control
CHAPTER FIVE
5.1 Conclusion
5.2 Recommendations
REFERENCES.
CHAPTER ONE
1.0 INTRODUCTION
In the ever fast-growing world of business and technology today, there has
become an increasing column of vehicles on every road in different place of
11
the world. Traffic control light has become a very effective tool for sequential
control of the teaming number of vehicles on the road to avert what would have
been a recurrent saga of ghastly accidents at the junctions. There have been
many ways of achieving this, uppermost among these being the employment of
electronic monitoring circuits that which is controlled by presto clock.
In developed countries, the employment of traffic personnels who would
be jumped up and down at the centres of the junction just for the motorists to
acknowledge their rigorous signs has long come of age. In developing
countries where 24 hours traffic flow is involved, many societies are adopting
the usage of the traffic light control. The advantage offered by this method of
traffic control cannot be over emphasized. For one, it offers a more advanced
technology that is less prone to miscalculation and its regrettable occurrence.
They stand out better at night, then offer illumination to the immediate
surroundings which become important for security purpose and in general add
to there entire aesthetic beauty of night life.
The technology behind the design may vary from place to place, but the
fact remains that in all cases an electronic (logic) circuit is made to control a
12
power circuit. The electronic logic circuit is normally composed of the basic
digital components of electronic design which includes oscillators, timers,
counters, decoders, microprocessors, etcetera, while the power circuit includes
the lamps and the drivers circuits. The digital circuit is designed to give an
output commensurate to the design choice. The power supply unit is designed
to generate a steady supply voltage which is used to power the logic circuit.
The output consists of a series of lamps which are expected to light in a
particular sequence depending on the design. By the logic circuit design, the
lamps are made to come up in a particular sequence depending on the design
with each colour meaning different motional status of the vehicles in that
column.
1.1 AIM OF THE PROJECT
Going by the rapid advancement in technology all over the world, the need for
better ways of solving a problem keep coming up every day. Necessity is the
13
mother of invention. It has become imperative for societies, companies,
industries, business ventures, clubs etc to offer 24 hour service, hence thereby
has to be a way of controlling the teaming column of vehicles which convey
both individuals and goods to different destinations of that type. The most
elegant way of directing the motorists is by the use of traffic light control. This
type of control serves a dual purpose. In the day type it directs the vehicles,
whereas it turns out to additionally illuminating the environment in the night,
so that at very far distance, its effect is noticeably felt, conveying its message
to an oncoming vehicle very far from the point.
The project is therefore aimed at building a prototype four-way traffic
light control circuitry.
1.2 METHODOLOGY
Priority was given to the nature of the junction and how far away they are at
different seasons of the year. A lot of design research was carried out on digital
logic design and choice of digital families. Data books were consulted to make
the most suitable choice of components at the most reasonable cost.
14
After the design, a market survey was conducted and some components
used in the design were not obtainable in the market. Hence, alternative
components had to be used and the circuit redesigned. The subsequent stage
involves physically realizing the design work, constructing and packaging the
entire circuitry on the frame. Finally, he work was given a fine finish and
tested.
CHAPTER TWO
A REVIEW ON THE TRAFFIC LIGHT SYSTEM
15
The traffic light system is made up of all the components and circuits used to
realize to lighting effect at the output. Basically it consists of the power supply
units, the digital logic circuit and components, the power circuit and the traffic
light bulbs themselves. Each stage is directly connected to the other such that
the last stage gives the desires output. See fig 2.1
t output
Fig 2.1 block diagram showing the various stages of the four way traffic light
control.
2.1 THE POWER SUPPLY UNIT
Virtually all electronic equipment operates on dc either from a battery or
converter from an energy source such as the ac power line. The importance of
this stage is to provide a predetermined dc voltage say Vs, which is
16
Power supply unit
Digital logic
circuit
Power circuit
Traffic light bulbs
independent of external actors within the limit of the current, I drawn from it
by the load. The power supply unit can be further broken down into the
following stages.
2.1.1 THE TRANSFORMER
This transformer or steps down the voltage from the ac powerline to a lower
operating ac voltage which is within the range of the voltage required by the
logic circuit. The transformer is chosen such that its power rating is higher than
the power required by the system it is powering. It is also important to note that
the bridge rectifier can safely draw only one half of the transformer’s rated
secondary current without exceeding the VA rating of the transformer.
2.1.2 THE RECTIFIER
The rectifier is used to convert the ac from the transformer into a pulsating dc.
There are basically many types of rectifiers but the full-wave bridge rectifier
17
which consists of a 4 diode ring is normally employed. It has the advantage of
delivering an output voltage of twice that of the full wave rectifier with the
transformer secondary centre-tap earthed. Nonetheless the former delivers only
half the current of the latter for a given primary VA rating which is suitable for
our application.
2.1.3 THE FILTER
The essence of the filter is to smoothen the pulsating dc output from the
rectifier into a nearly pure dc required by the electronic circuit. It is basically a
resistor connected in series with a capacitor. The capacitor charges and
discharges between cycles and hence generates a ripple which approximates a
steady dc voltage if the value of the capacitance is high. In practical circuits,
the resistor (which is meant to limit the maximum charging current) is usually
omitted and the capacitor is connected to the rectifier output since the rectifiers
won’t allow the flow back of the currents out of the capacitor to the source.
2.1.4 THE VOLTAGE REGULATOR
18
A voltage regulator is required to maintain a specific output voltage over
various combinations of the input voltage and load. As more load is drawn, the
output voltage of an unregulated supply normally decreases. Regulators are
normally broken down to shunt regulators and series regulators. The former
uses a zener diode as the main regulating device, while the latter employs a
power transistor, some resistors and op-amp as error amplifiers, they are
normally more efficient.
Outputs
19
Step-down transformer
Rectifier Filter Voltage Regulator
Blocks dc
output
Fig. 2.2 Block diagram of a single-phase power supply unit.
2.2 THE DIGITAL LOGIC CIRCUIT
Digital logic design is concerned with the interconnection among digital
components and modules to achieve a particular result/outputs. In modern day
design, the components used to construct most digital systems are
manufactured in integrated circuit form, rather than their discrete forms. All the
devices used in the logic design are in their IC form. The logic circuit design is
composed basically of the oscillator, the counter, decoder and the gates.
2.2.1 THE OSCILLATOR
20
An oscillator can be considered as a circuit that converts a dc input into a time-
varying output. It cannot really be described as a digital logic components, but
within every logic circuit there must be an oscillator or wave from generator of
some sort.
2.2.2 THE COUNTER
A counter is a sequential circuit that goes through a predescribed sequence of
states upon the application of input pulses. The sequence of states in a counter
may follow a binary count or any other sequence of states. The binary count or
any other sequence of states. The binary counter (which is the most popular)
consists of a n flip flops and can count from 0 to 2n-1. common types includes
the binary coded decimal counter (BCD), the 4-bit binary counter, the 8-bit
binary counter etcetera.
2.2.3 THE D ECODER
A decoder is basically a combinational circuit that converts binary information
from n input linear to a maximum of 2n unique output lines. Its favourite thing
in a logic circuit is to cause different things to happen depending ion the state
21
of a counter chip that drives it. In this design, it is used to enable a sequence of
actions in turn, according to an advancing address given by the output of the
binary counter.
2.3 THE LOGIC GATES
A logic gate is an electronic circuit that makes logic decision. It has one output
and one or more inputs. The output signal appears only for certain
combinations of input signals. Logic gates are the building blocks from which
most of the digital systems are built up. They implement the hardware logic
function based on the logical algebra developed by George Boole which is
called Boolean algebra in his honour. In this application the only gate used in
the discrete diode form is the diode OR gate. This is commonly called any-or-
all gate because an output occurs when any or all the inputs are present.
Obviously, the output would be zero if and only if its inputs are zero.
DC desired supply output
2.3.1 THE POWER CIRCUIT
22
Oscillator Counter decoder logic gates
This is the stage that is being controlled by the logic circuit hence, the
output of the logic circuit comes straight to the power circuit the power circuit
consists of transistors booster/amplifier stage and the lightening bulbs.
2.32 The booster/amplifier stage
Each output of the logic gates are required to trigger the base of one of array
of transistors which then boost the current up to the required value for lighting
the bulb/LED that indicates which operation the motorist a particular route
should take. The booster stage can be configured to manifest the output of the
logic gates to take the form of a negative logic.
2.32 THE LAMP/LEDS
This is the final stage of the power circuit. The main terminals of the bank of
transistors are connected to the bulbs/LEDs, which generates the desired
lighting effect in accordance with the logic design. The bulbs are made of
different colours to indicate different operations of the motorist. The red colour
indicates no movement, the yellow colour indicates ready to stop whereas the
green light light indicates "move"
CHAPTER THREE
23
3.0 THE TRAFFIC LIGHT CONTROL
DESIGN AND CONSTRUCTION
The main objective of this design is to achieve a circuit capable of controlling
the lighting of some bulbs/LEDs which are indicative of the next operation a
motorist should take at a four way junction. The lighting come on in sequence,
reflecting different colours. They are to stay on for a period of time determined
by the clock set before going off. The design of the entire circuiting has done in
different modules. This to make for easy analysis, better arrangement and for
purpose of troubleshooting. The various modules in which the design has been
done are as shown in fig 2.1.
3.1 THE POWER SUPPLY DESIGN SPECIFICATIONS
The aim of the power supply design is to obtain a circuit capable of producing
a regulated voltage of 9Vdc and a current of about 0.30Amps from a 220ac
mains supply. The block diagram of the power supply is already shown in fig
2.2.
3.1.1 THE TRANSFORMER
24
On determining the voltage drops across the various components, the minimum
regulator input voltage and the desired regulated voltage, the values can be
used to calculate the required secondary output voltage of the transformer.
Vsec >VR + VRmin +Vrect
Where,
Vsec is the transformer secondary voltage
VR is the desired regulated voltage = 8V
VRmin is the minimum voltage by which the regulator
Input must exceedd the output. VRmin = ZV.
Vrect is the voltage drop across the diode bridge Vrect = 1.4
Vsec> 8+2+1.4 = 11.4V
In practice, there is no commercially available transformer with such a voltage
rating at the secondary winding, therefore a 220/IC, V, 500Ma transformer was
chosen in its place.
25
3.1.2 RECTIFIER
For the bridge rectifier, we require a full bridge rectifier consisting of four
diodes. However instead of acquiring four diodes and connecting them up
together to form a bridge, a composite rectifier which is smaller and more
reliable was chosen in the alternative.
3.1.3 THE FILTER CAPACITOR
The maximum voltage level Vmax at the transformer secondary output is 12V
x 2 = 16.97
This voltage is reduced to a maximum value of 16.97 – 1.4V = 15.6V after
passing through the bridge rectifier. Since the ac to dc converter is a two pulse
type with full voltage, the average dc voltage, Vdc becomes 2 Vmax = 9.9V =
Vdc
If we allow for 10% of ripple at the filter capacitor output, it implies that
Vripple = 10% of Vdc = 0.99V.
The value of the capacitor is given from the expression.
26
C = Ic x Idc
Vripple
Where Ic = charging time for the capacitor
Vripple = allowable ripple volktage
I = continous output current
Since Tc = 1 = 1
Fc 2f
Where fc = the ripple frequency
F = the ac power supply frequency = 50Hz
Tc = 1 = 1 = 0.01 or 10x10-3
2x50 100
Tc = 10ms
Also Vripple = 0.99V
27
And I = 0.3A
Therefore, C = 0.3A x 10X10-3 = 3.03 x 10-3F or 3030UF
Hence a commercially available capacitor of value 3300µF was chosen to
satisfy this requirement.
3.1.4 THE VOLTAGE REGULATOR
The importance of the voltage regulator has already been discussed in sec
2.1.4. The voltage regulator chosen is the lin7808, a three-terminal non-
adjustable regulator. This come from the simplest family that is commercially
available. It is chosen because of its elegance in usage, once the power supply
filter is very near to the regulator, the 7808 requires no other preceding filter
capacitor. It requires no variable resistor or any capacitor for setting of the
output voltage. It contains an intrinsic.
3.2 THE DIGITAL LOGIC DESIGN
In modern day technology, the components used in the design of all digital
systems come in integrated circuit form. IC’s have been chosen in this design
28
because they are cheap, easy to use and implement, small in size, thereby
occupying less space, have higher reliability. Give reduced component count
and are easier in fault diagnosis.
The logic family chosen for this design is the CMOS family. This has to
do with its excellent features of a high fan-out, low power dissipation and an
excellent noise immunity when compared with other logic families. CMOS
chips operate from a minimum supply voltage of 3V to a maximum supply
voltage of about 18V. the normal operating voltage is between 5 – 15V. CMOS
chips also possess zero quiescent current and rail-to-rail output swings.
SPECIFICATIONS
The digital logic design is aimed at obtaining a continuous series of ten (10)
HIGH level logic signals which come up one after the other and are all group
into four families which are logically operated to light: a green LED, a yellow
LED and a red LED consecutively after which then red LED remains on till the
next cycle. This sequence is suppose to repeat itself for as long as the supply is
present.
29
Short circuit protection that makes it to shut down once senses excessive
current drain.
Some features of the MA 7808 were illustrated in the table below from the fair child
data book.
Dev
ice
No
Func
tion
Inpu
t vo
ltage
ra
nge
(V)
Out
put
volta
ge
rang
e (V
)
Out
put
curr
ent (
A)
max
Out
put
curr
ent p
eak
(A)
Line
re
gula
tion
(%)
Load
re
gula
tion
(%)
Qui
esce
nt
curr
ent
(MA
)
Rip
ple
reje
ctio
n db
m
in
Dro
p ou
t vo
ltage
(V)
Out
put
volta
ge d
rift
MA
7808
3-term
Pos.VR
7.7-
8.3
1.0 2.2 2.0 2.0 4.3 56 2.0 -0.8
3.2.1 THE OSCILLATOR
The only integrated circuit IC used for the generation of clock pulses is the 555
timer chip. This is an IC that is commonly known as the universal timer. The
features and made of the IC is illustrated below.
Functions of the leads
30
When using the 555 timer as an astable multivibrator or the most
important leads are the trigger input, output, threshold, and discharge
leads. The functions of the leads is demonstrated below.
Ground 1 8 +Vcc
Trigger 2 7 Discharge
Output 3 6 Threshold
Reset 4 5 Control voltage
However, the reset and control voltage terminals can be used to provide
extra features for some other applications.
(ii) The 555 timer Astable multivibrator circuit
31
555
outDSCH
THRSH CONTN
C2
R1 R3
R2
VC
TRIG Gnd
32
VO
In this circuit, the timing of the output wave form is set by resistors R1 and R2
and capacitor C1 on the other hand, resistor R3 is used to improve the shape of
the output waveform. The value of this device is mostly about 1Kп. The
second capacitor is added to eliminate noise pickup at the unused control
voltage lead.
Looking at the circuit, we see that the capacitor C1 is connected from the
threshold lead to ground. During the first period of time, the discharge lead acts
like an open circuit, and the capacitor charges through resistors R1 and R2 to
the trigger voltage level.
The trigger lead is directly wired to the threshold lead. When the capacitor
voltage is below the threshold, the output lead is at the logic level 1. However,
as Vc reaches the trigger level of the output switches to 0 state. Concurrently,
the internal circuitry of the 555 IC switches the discharge lead to logic ) or
ground. Now C1 begins to discharge through R2. As Vc reaches a low-level
threshold, the output returns to the 1 level.
33
This switch in the output logic stage makes the discharge lead again act
like an open-circuit. In this way, C1 begins to recharge and the timing cycle
repeats.
The output of the 555 timer astable multivibrator is an asymmetrical square
wave. The pulse width T and a pulse interval T2 are given by the equations
T1 = (R1+R2)C1Inz
T2 = R2C1Inz
Using these values, the period and frequency of the output square wave implies
Period = T = T1+T2
Frequency = 1 = 1
T T1+T2
In the present design,
C1 = 47Uf
R1 = 3.3Kп
Let F = 0.25Hz (ie one clock count in 4 seconds)
34
F = 1 = 1 = 1
T T1+T2 (R1+2R2)C1Inz
0.25 = 1
(3.3 + 2R2) x 103 x 47 x 10-6 x Inz
3.3+2R2 = 1Kп
0.25 x 103 x47 x10-6 x Inz
2R2 = (122.7 – 3.3)Kп
2R2 = 119.5
R2 = 119.5/2
= 59.7k
The commercially available, 56K standard resistor is used instead.
3.2.2 THE 4017 DECADE COUNTER.
The 4017 is probably the most popular and useful of all CMOS decade
counter/divider ICs. It comes in a 16 pins Dual in line package (DIP) form. It is
actually a 5-stage Johnson counter that has ten fully decoded outputs that
sequentially switched high on the arrival of each new clock pulse, only one
output being high at any moment. Each output can provide several milliamps
35
of drive current to an external load. The diagram below shows the various pins
of the IC and the functions associated with each pin. There are the clock, reset
(RS) and inhibit input terminal and ten decoded output and one carry (CO)
output terminals.
V+
16
C
15
3 2 4 7 10 1 5 6 9 11
FIG 3
The 4017 counter connected in the normal mode
In normal use, the 4017 is connected in the basic decade divider mode as
shown above, with its RESET and INH terminal grounded. In this mode, the
ICS Johnson counter stages advance one step on the arrival of each new clock
36
CLK
4017INH
GND 0 1 2 3 4 5 6 7 8 9
13
8
1412
pulse rising edge, and simultaneously set one of the ten decoded \output high
while the other nine outputs remain low; the outputs go high sequentially in
phase with the clock signal, with the selected output remaining high for one
full clock cycle an additional carry out (CO) signal completes one cycle for
every ten clock input cycles, and can be used to ripple clock additional 4017 in
multi-decade counters. Note that this IC has buffer-style inputs that are not of
the wave shape. The clock pulses must switch fully between normal logic
levels, rise and fall times must be less than 400ns, and clock pulse-widths must
be grater than 15ns.
The pin -15 is the ICs RESET control; normally this control is tied to
logic 0, but when it is taken to logic1, it resets all the ICs counters and sets all
decoded outputs except output "0" to the logic – 0 stage. The pin 13 is the
clock Inhibit (INH) terminal. Normally this terminal is tied to logic 0, but when
it is taken to logic – 1, it fully inhibits the ICs clocking and counting actions.
One of the 4017’s most important features is its provision of teen fully decoded
outputs, making the IC ideal for use in a whole range of "sequencing"
operations in which the outputs are used to drive LED displays, relays,
37
transistors, input to other ICs inputs that drive other logic gates as is the case in
this design.
The 4017 operates very simply, for each pulse on the clock input pin
turns the currently high outputs low and makes the next output high. When the
10th output is high and a pulse is received, the 10th output goes low and the 1st
output goes high and the sequence begins again. The 4017 also has two other
inputs. The first is the reset input on a rising edge, this resets 4017 to the first
output. The last input is a disable pin, labeled a s an enable pin with a circle on
the input (bubble means not). When this pin is high, the 4017 will not advance
to the next output but the reset pin is still active.
The 4017 has 11 outputs. There are the regular 10 outputs and a carry out that
outputs a pulse on the clock pin is received.
If one’s application requires counting to a less than 10, one can feed the
first unused output into the reset pin (ie if counting to 4, feed the 5th (N) output
into the reset pin).
38
The diagram below shows the implementation of the count to N and hold
operation.
V+
16
15
Fig. 3.1 Implementation of a count to N and halt operation.
Below is the data description of 4017 from fair child data book.
Table of Data of the 4017 Decade Counter
Device Function Module Parallel Clock Max Clock to q output delay Quiescent
39
CLK CO
INH
GND 0 1 2 3 4 5 6 7 8 9
2
No load transistor clock rate MAZ (typ) VDD= 10V
ns (typ)
VDD= 10Vpower dissipation mw VDD= 10V
4017 5-bit Johnson Counter
1 of 100 Johnson counter
NAL H
H L13.8 104 1.4
3.3 THE OUTPUT LOGIC GATE CIRCUIT AND THE POWER
CIRCUIT
The basic logic gate circuit used at the output stage is the OR gate and NOR
gate of the diode- transistor family. The figure below illustrates this idea.
VCC
output to load
Fig (a) The nPn OR gate
40
A
B
C
R
VCC
Output to Load
Fig (b) The pnp NOR gate
In the figure a above, the output of c is at the logic level of 1 when either A or
B or both are at logic 1. This is a good feature of the OR gate as shown in the
truth table below.
A B c
0 0 0
0 1 1
1 0 1
41
A
B
C
R
1 1 1
However in the case of this design the output transistor dictates whether the
output logic gate will be an OR gate or a NOR gate depending on the desired
result.
The OR gate was used to light the GREEN LED which symbolizes that the
traffic should move whereas the NOR gate is used for the RED LED which
signifies that the traffic should halt. In former case, the emitter (npn) follower
is used as a buffer that powers the LED whereas in the latter case, the pnp
transistor arrangement is used as a bubbled gate that NOTS the point C
instructions.
The resistor R is a pull down resistor which ensures that C maintains a definite
state each time. When either A or B is at logic state of 1, they drive a
corresponding current down the resistor R. the equivalent voltage drop across
R sets the point C high and the transistorized stage responds consequently to
this change in state. When on the other hand neither A nor B is in logic state of
42
1, the resistor R pulls the point C down to the logic state 0 (ground) and the
transistorized stage also responds to this change.
CHAPTER FOUR
THE IMPLEMETATION OF THE WORK
4.1 PROBLEM ENCOUNTERED
In the course of this work, there were quite a few hitches but only the major
ones are hereby highlighted. The biggest problem encountered was being able
to get a workable design that meets with the components available in the
market. The circuits were re-designed a couple of times before a final design
was obtained. Another problem encountered was in choosing and acquiring the
materials for constructing the frame. A choice has to be made between wood
and metal. Finally, wood was chosen as compared to metal because it is
cheaper and easier to handle.
43
4.2 CONSTRUCTION AND TESTING
Having identified the respective terminals of the component that was used in
this design with the aid of a digital multimeter, it was first implemented on a
project board to ascertain its workability before it was transferred permanently
to the Vero board. However, each of the blocks was simulated in a computer
with the help of the software (Electronics workbench) to confirm that the
output is comparable to the design expectation. The input of the digital logic
was fed with a clock and tested first, since it remains the brain that monitors
the rest of the circuit.
4.4 COST ANALYSIS
In the course of the implementation of this project the underlisted cost was
incurred for the respective constituent components that make the project as a
single entity or that aided in testing of the work.
S/N Materials Cost (N)
1 A wooder frame 2000
2 A bread board 700
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3 A vero board 100
4 Conectors 100
5 Soldering leads 80
6 LEDs 120
7 Capacitors 100
8 The 555 timer IC 50
9 The 4017 IC 100
10 A transformer 150
11 A voltage regulator 60
12 A full bridge rectifier 30
13 12 transistors 360
14 Resistors 200
15 Diodes 180
The total cost of implementing this circuit is N4330, therefore the circuit is
complex and yet cost effective.
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CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
5.2 In conclusion, it is pertinent to state that despite all the hitches arising
from the unavailability of components and materials and technological
drawbacks, the design and construction of this four way traffic light control
was successfully realized. And as a matter of fact, since we are in a
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technological advancing world, I strongly believe that it takes nothing less than
pure determination and the ability to respond to such changes to survive in the
present rapidly improving standards of the world system. So being aware of all
these challenges, I made special effort to examine the technological problems
encountered and also made additional modification in order to enhance the
services of this design.
5.3 Based on the ease of manufacture, cost, user-friendly, reliability, safety,
durability etcetera, for the design of such public used product, this exquisite
project has been made as simple as possible. This project also has been made
as complete as required considering mostly the economic factor, and cost of
materials for private and public uses which determine the response of the user
towards the acquisition of such product.
5.3.1 During the course of this design some unforeseen problems were
encountered, but were meticulously rectified. Hence, locating of faults were
easy during the testing.
Finally, it is essential to say that the experience we gathered in the design and
construction of this project has been rewarding.
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5.2 RECOMMENDATION
In view of the theoretically and practical constraints encountered in the course
of this project, we make the following general recommendations;
It is important that much research should be done on the work in other to make
it synchronize with the present day advancement in technology.
A much more improved and detailed circuit should be used in the future to
enable the system perform more functions.
The government should encourage the research into this field by promoting it
through the installation of such system in government established offices and
quarters.
REFERENCES
P. Horowitz and H. Winfield "the Art of Electronics" Cambridge University
press, 2nd edition 1989
B.W. Williams "Power Electronics; Devices, Drivers, Applications and
Passive Components" Macmilliam London, 2nd edition.
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M.M. Mano "Digital Logic and Computer Design", Prentice-Hall of India
private limited New Delhi, original US edition 1984.
G.D. Fink and A.A. Mckenzie "Electronics Engineers Handbook", McGraw-
Hill Book Company, 1st edition, 1975.
A. Rrennd "Poer Supply System, NTT Review, vol 2, No.6, Nov. 1990.
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