Traffic Lights Logic Controller
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The project we have chosen is an 8-lane traffic controller. The basic idea behind the design is to avoid the collision of vehicles by providing appropriate signals to different directions for a limited time slot, after which the next waiting drivers will be given same treatment. In This way a cycle will be established which will control the traffic.
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Traffic Lights Logic Controller
1. INTRODUCTION
Traffic signals are used to control the flow of vehicles.In the recent years, the need
of transportation has gain immense importance for logistics as well as for common
human. This has given rise to the number of vehicles on the road. Due to this
reason, traffic jams and road accidents are a common sight in any busy city.
Traffic Signals provide an easy, cheap, automatic and justified solution to the road
points where the vehicles may turn to other directions e.g. roundabouts, culverts,
busy walk throughs etc.
BASIC IDEA
The project we have chosen is an 8-lane traffic controller. The basic
idea behind the design is to avoid the collision of vehicles by providing
appropriate signals to different directions for a limited time slot, after which the
next waiting drivers will be given same treatment. In This way a cycle will be
established which will control the traffic.
CONTROL SIGNALS
The control signals are 3-lights.
Top light is Red(Stop),
Middle light is Yellow(Wait)
Bottom light is Green(Go).
STATES OF TRAFFIC FLOW
There are 8-lanes and at most two ways can be safely open. In this way a
minimum of 4-states are possible for which different vehicles will pass through.
These four states according to direction are :
1. North-South South-North
2. South-East North-West
3. East-West West-East
4. East-North West-South
STATE DIAGRAM
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2. These states are shown graphically below:
State --- 1
State
State
---2
State ---3
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3. GENERAL FLOW OF CIRCUIT
1.
Timer
2.
Counter
3.
Decoder
4.
Output Logic
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4. TIMER
In our project we used 555 Timer IC as the Timer or Pulse Generator.
555 IC
INTRODUCTION
The 555 timer IC is an amazingly simple yet versatile device. It has been around
now for many years and has been reworked into a number of different
technologies. The two primary versions today are the original bipolar design and
the more recent CMOS equivalent. These differences primarily affect the amount
of power they require and their maximum frequency of operation.
The 555 Timer is a TTL digital logic circuit that is used in the controller circuit to
produce a periodic square wave signal. The period and duty cycle of the square
wave signal are determined by the resistors and capacitors connected to the timer.
APPLICATIONS
Precision timing
Pulse generation
Sequential timing
Time delay generation
Pulse width modulation
Pulse position modulation
Linear ramp generator
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5. FUNCTIONAL BLOCK DIAGRAM
The figure to the right shows the functional block diagram of the 555 timer
IC. The IC is available in either an 8-pin round TO3-style can or an 8-pin
mini-DIP package. In either case, the pin connections are as follows:
1. Ground.
2. Trigger input.
3. Output.
4. Reset input.
5. Control voltage.
6. Threshhold input.
7. Discharge.
8. +VCC. +5 to +15 volts in normal use.
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6. PIN CONNECTIONS
OPERATION
The operation of the 555 timer revolves around the three resistors that form a
voltage divider across the power supply, and the two comparators connected to
this voltage divider. The IC is quiescent so long as the trigger input (pin 2)
remains at +VCC and the threshhold input (pin 6) is at ground. Assume the reset
input (pin 4) is also at +VCC and therefore inactive, and that the control voltage
input (pin 5) is unconnected. Under these conditions, the output (pin 3) is at
ground and the discharge transistor (pin 7) is turned on, thus grounding whatever
is connected to this pin.
WORKING FORMULAE
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7. The frequency, or repetition rate, of the output pulses is determined by the
values of two resistors, R1 and R2 and by the timing capacitor, C.
The HIGH and LOW times of each pulse can be calculated from:
Before calculating a frequency, one should know that it is usual to make R1=1 kW
because this helps to give the output pulses a duty cycle close to 50%, that is, the
HIGH and LOW times of the pulses are approximately equal.
PARAMETERS CALCULATION
In this project we want to design a circuit to produce a frequency of approximately
0.25 Hz( 4 sec ) for generating clock pulse. What values of R1, R2 and C should
we use?
R1 should be 1kΩ, as already explained. This leaves you with the task of selecting
values for R2 and C. The best thing to do is to rearrange the design formula so that
the R values are on the right hand side:
Here we choose the value of C as 1µF and R1 is selected as 1kΩ.
Therefore the value of R2 is found as:
1 + 2R2 = ( 1.44 ) / ( f * C )
1 + 2R2 = ( 1.44 ) / ( 0.25 * 1µ)
R2 = 2.8 MΩ
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8. Hence the circuit parameters for timer are:
Vcc = 5 V
R1 = 1 kΩ .
R2 = 2.8 MΩ .
C = 1µF
TIMER WIRING DIAGRAM
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9. COUNTER
INTRODUCTION
In this project we need a 5-bit synchronous binary up-counter. Since such a 5-bit
counter is not available in packaged form so we have to design it using basic gates
and flip flops.
SYNCHRONOUS COUNTERS
A synchronous counter is one whose output bits change state simultaneously, with
no ripple. The only way we can build such a counter circuit from J-K flip-flops is
to connect all the clock inputs together, so that each and every flip-flop receives
the exact same clock pulse at the exact same time. We know that we still have to
maintain the same divide-by-two frequency pattern in order to count in a binary
sequence, and that this pattern is best achieved utilizing the "toggle" mode of the
flip-flop, so the fact that the J and K inputs must both be (at times) "high" is clear.
A general structure of a counter is shown below:
The red question marks are indicating that there some other connections will be
made in order to complete the whole counter.
To determine the gates required at each flip-flop input, let's draw up a truth table
for all states of the counter.
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14. S TAT E D E C O D E R
INTRODUCTION:
Here we use a demultiplexer as a state decoder to detect the counts of the 5-bit
counter.For the decoding of 5-bit counter we have to use the 5 to 32 line decoder.
This decoder is not available in the packaged form so we have to cascade two 4
to 16 line decoders.
In this case we use the I.C 74154 which is a 24-pin package.
DECODER WIRING DIAGRAM
The interconnections for the decoder is shown below:
:
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15. OUTPUT LIGHTING LOGIC
INTRODUCTION
The output lights will turn On and Off according to the logic designed for the
flow of traffic for a particular time slot.
There are a total of 24- Lights needed for 8-ways, and there are a maximum of 4-
states( each having 3-lights i.e. red,yellow and green ) of flow.In this way we need
to control only 12-lights and the other 12 are the raplica of the previous,so they
can be connected in parallel.
PRACTICAL TRAFFIC LIGHT TIMINGS
In order to determine that for how long the red, yellow and green lights are ON
and for how much time they are OFF, we carried out a survey of traffic signals
installed at different locations including Hassan Square, Water Pump Roundabout,
Nipa and Gulshan-e-Iqbal Roundabout.As a conclusion we found the following
timings:
LIGHTS
RED YELLOW GREEN
ON OFF ON OFF ON OFF
1 minute and 2 minutes 1 minute and
30 second 2 second 30 second
45 second 15 seconds 45 second
The timings above are for one complete cycle of counts. We have tried our level
best to design our circuit according to these timings.
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21. B O M ( B I L L O F M AT E R I A L S )
Item Quantity Reference Part
1 1 C1 1µ
2 1 C2 0.01µ
3 1 RA 1k
4 1 RB 2.82M
5 1 SW1 SW MAG-SPDT
6 1 U LM555
7 2 U1,U2 74154
8 7 U1,U2,U14,U16,U17,U18,U19 7432
9 3 U4,U5,U15 7404
10 5 U6,U7,U10,U11,U12 7476
11 1 U13 7408
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