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Chapter 1 Introduction 1.1 Traffic light Traffic lights, also known as traffic signals, stop lights, stoplight, traffic lamps, stop-and-go lights, robots or semaphore, are signaling devices positioned at road intersections, pedestrian crossings, and other locations to control competing flows of traffic. Traffic lights have been installed in most cities around the world to control the flow of traffic. They assign the right of way to road users by the use of lights in standard colours (Red - Amber (Officially Yellow in the United States) - Green), using a universal colour code (and a precise sequence, for those who are colour blind). They are used at busy intersections to more evenly apportion delay to the various users. The most common traffic lights consist of a set of three lights: red, amber, and green. When illuminated, the red light indicates for vehicles facing the light to stop; the amber indicates caution, either because lights are about to turn green or because lights are about to turn red; and the green light to proceed, if it is safe to do so. There are many variations in the use and legislation of traffic lights, depending on the customs of a country and the special needs of a particular intersection. There may, for example, be special lights for 1

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Chapter 1

Introduction

1.1 Traffic light

Traffic lights, also known as traffic signals, stop lights, stoplight, traffic lamps, stop-and-

go lights, robots or semaphore, are signaling devices positioned at road intersections,

pedestrian crossings, and other locations to control competing flows of traffic. Traffic

lights have been installed in most cities around the world to control the flow of traffic.

They assign the right of way to road users by the use of lights in standard colours (Red -

Amber (Officially Yellow in the United States) - Green), using a universal colour code

(and a precise sequence, for those who are colour blind). They are used at busy

intersections to more evenly apportion delay to the various users. The most common

traffic lights consist of a set of three lights: red, amber, and green. When illuminated, the

red light indicates for vehicles facing the light to stop; the amber indicates caution, either

because lights are about to turn green or because lights are about to turn red; and the

green light to proceed, if it is safe to do so. There are many variations in the use and

legislation of traffic lights, depending on the customs of a country and the special needs

of a particular intersection. There may, for example, be special lights for

pedestrians, bicycles, buses, trams, etc; light sequences may differ; and there may be

special rules, or sets of lights, for traffic turning in a particular direction. Complex

intersections may use any combination of these.

Traffic light technology is constantly evolving with the aims of improving reliability,

visibility, and efficiency of traffic flow.

1.2 Aim of the project

This project operates red,amber and green LEDs in the correct sequence for a single

sequence for a single traffic light.

1.3 Organization of the report

Chapter 2 describes the very building blocks and working of timer IC555, decade counter

IC4017 and LEDs that we have selected for our project. Chapter 3 gives the detailed

working of the circuit while Chapter 5 discusses the future scope of the project and gives

the conclusion.

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Chapter 2

Literature Survey

2.1 IC 555

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; they are pin-compatible and functionally

interchangeable.

This page contains only a description of the 555 timer IC itself. Functional circuits and a

few of the very wide range of its possible applications will be covered in additional pages

in this category.

Figure 2.1 Internal sections of IC 555

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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. Threshold input. 

7. Discharge. 

8. +Vcc +5 to +15 volts in normal use. 

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

threshold 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.

The three resistors in the voltage divider all have the same value (5K in the bipolar

version of this IC), so the comparator reference voltages are 1/3 and 2/3 of the supply

voltage, whatever that may be. The control voltage input at pin 5 can directly affect this

relationship, although most of the time this pin is unused.

The internal flip-flop changes state when the trigger input at pin 2 is pulled down below

+Vcc/3. When this occurs, the output (pin 3) changes state to +VCC and the discharge

transistor (pin 7) is turned off. The trigger input can now return to +VCC; it will not affect

the state of the IC.

However, if the threshold input (pin 6) is now raised above (2/3)+VCC, the output will

return to ground and the discharge transistor will be turned on again. When the threshold

input returns to ground, the IC will remain in this state, which was the original state when

we started this analysis.

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The easiest way to allow the threshold voltage (pin 6) to gradually rise to (2/3)+VCC is to

connect it to a capacitor being allowed to charge through a resistor. In this way we can

adjust the R and C values for almost any time interval we might want.

The 555 can operate in either monostable or astable mode, depending on the connections

to and the arrangement of the external components. Thus, it can either produce a single

pulse when triggered, or it can produce a continuous pulse train as long as it remains

powered.

Astable multivibrator:

Fig 2.2 Astable Multivibrator

If we rearrange the circuit slightly so that both the trigger and threshold inputs are

controlled by the capacitor voltage, we can cause the 555 to trigger itself repeatedly. In

this case, we need two resistors in the capacitor charging path so that one of them can

also be in the capacitor discharge path. This gives us the circuit shown to the left.

In this mode, the initial pulse when power is first applied is a bit longer than the others,

having a duration of 1.1(Ra + Rb)C. However, from then on, the capacitor alternately

charges and discharges between the two comparator threshold voltages. When charging,

C starts at (1/3)VCC and charges towards VCC. However, it is interrupted exactly halfway

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there, at (2/3)VCC. Therefore, the charging time, t1, is -ln(1/2)(Ra + Rb)C = 0.693(Ra + 

Rb)C.

When the capacitor voltage reaches (2/3)VCC, the discharge transistor is enabled (pin 7),

and this point in the circuit becomes grounded. Capacitor C now discharges through Rb

alone. Starting at (2/3)VCC, it discharges towards ground, but again is interrupted halfway

there, at (1/3)VCC. The discharge time, t2, then, is -ln(1/2)(Rb)C = 0.693(Rb)C.

The total period of the pulse train is t1 + t2, or 0.693(Ra + 2Rb)C. The output frequency

of this circuit is the inverse of the period, or 1.44/(Ra + 2Rb)C.

Note that the duty cycle of the 555 timer circuit in astable mode cannot reach 50%. On

time must always be longer than off time, because Ra must have a resistance value

greater than zero to prevent the discharge transistor from directly shorting VCC to ground.

Such an action would immediately destroy the 555 IC.

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Table 2.1 Data sheet of IC555

2.2 4017 Decade counter

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The 4017 decade counter has ten outputs which go HIGH in sequence when a source of

pulses is connected to the CLOCK input and when suitable logic levels are applied to the

RESET and ENABLE inputs.

The counting action of the 4017 can be understood from the graph below:

Fig 2.3 Counting action of 4017

Just one of the individual outputs is HIGH at a time. This is quite different from the

behaviour of a BCD counter like the 4510 in which it is the combination of 0's and 1's

which represents the count. As you can see, the ÷10 output is HIGH for counts 0-4 and

LOW for counts 5-9. The 4017 is an extremely useful device for project work and is used

in the Games Timer and in various DOCTRONICS construction kits including the Light

Chaser and the Matrix Die. When you are familiar with the 4017, you will be able to

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think of lots of useful applications. Internally, the 4017 contains five bistable subunits.

These are interconnected in a pattern known as aJohnson counter. The outputs of the

bistables are decoded to give the ten individvual outputs.

Johnson counter

A Johnson counter is one type of walking ring counter using a shift register circuit in

which the NOT-Q, or inverse output of the final stage is connected to the serial input of

the first stage.

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Fig 2.4 decade counter

Tabel 2.2 Absolute maximum ratings

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Tabel 2.3 DC specifications

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Tabel 2.4 Dynamic Electrical properties

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2.3 Light Emitting Diodes (LEDs)

Circuit symbol:

Function

LEDs emit light when an electric current passes through them.

Connecting and soldering

LEDs must be connected the correct way round, the diagram may be labelled a or + for

anode and k or - for cathode (yes, it really is k, not c, for cathode!). The cathode is the

short lead and there may be a slight flat on the body of round LEDs. If you can see inside

the LED the cathode is the larger electrode (but this is not an official identification

method).LEDs can be damaged by heat when soldering, but the risk is small unless you

are very slow. No special precautions areneeded for soldering most LEDs.

Colours of LEDs

LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white

LEDs are much more expensive than the other colours. The colour of an LED is

determined by the semiconductor material, not by the colouring of the 'package' (the

plastic body). LEDs of all colours are available in uncoloured packages which may be

diffused (milky) or clear (often described as 'water clear'). The coloured packages are

also available as diffused (the standard type) or transparent.

Tri-colour LEDs

The most popular type of tri-colour LED has a red and a green LED combined in one

package with three leads. They are called tri-colour because mixed red and green light

appears to be yellow and this is produced when both the red and green LEDs are on.

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The diagram shows the construction of a tri-colour LED. Note the different lengths of the

three leads. The centre lead (k) is the common cathode for both LEDs, the outer leads (a1

and a2) are the anodes to the LEDs allowing each one to be lit separately, or both

together to give the third colour.

Bi-colour LEDs

A bi-colour LED has two LEDs wired in 'inverse parallel' (one forwards, one backwards)

combined in one package with two leads. Only one of the LEDs can be lit at one time and

they are less useful than the tri-colour LEDs described above.

Reading a table of technical data for LEDs

Suppliers' catalogues usually include tables of technical data for components such as

LEDs. These tables contain a good deal of useful information in a compact form but they

can be difficult to understand if you are not familiar with the

abbreviations used. The table below shows typical technical data for some 5mm diameter

round LEDs with diffused packages (plastic bodies). Only three columns are important

and these are shown in bold. Please see below for explanations of the quantities.

Tabel 2.5 Technical data for LEDs

IF max. Maximum forward current, forward just means with the LED connected

correctly.

VF typ. Typical forward voltage, VL in the LED resistor calculation.

This is about 2V, except for blue and white LEDs for which it is about 4V.

VF max. Maximum forward voltage.

VR max. Maximum reverse voltage. You can ignore this for LEDs connected the correct

way round.

Luminous intensity Brightness of the LED at the given current, mcd = millicandela.

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Viewing angle Standard LEDs have a viewing angle of 60°, others emit a narrower beam

of about 30°.

Chapter 3

Implementation

TRAFFIC LIGHT PROJECT

3.1 Parts required

1. Resistor:470x3,22k,100k

2. Capacitors:0.1uF,1uF 16v radial,10uF 16v radial

3. Diodes: 1N4148x6

4. LEDs: red, amber(or yellow),green

5. 1M preset, horizontal

6. 555 timer IC, such as NE555

7. 4017 counter IC

8. DIL sockets for ICs:8-pin,16-pin

9. Battery clip for 9v PP3

3.2 Circuit Diagram

Fig 3.1 Circuit diagram

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3.3 Description

This project operates red,amber and green LEDs in the correct sequence for a single

traffic light.The time taken for the complete red-red& amber-green-amber sequence can

be varied from about 2-1/2 minutes by adjusting the 1M preset.Some amber LEDs emit

light that is almost red so you may prefer to use a yellow LED.

The 555 astable circuit provides clock pulses for the 4017 counter which has ten

outputs(Q0 to Q9). The 4017 decade counter has ten outputs which go HIGH in sequence

when a source of pulses is connected to the CLOCK input and when suitable logic levels

are applied to the RESET and ENABLE inputs.

Each output becomes high in turn as the clock pulses are received.Appropriate outputs

are combined with diode to supply the amber and green LEDs.The red LED is connected

to the \10 output which is high for the first 5counts(Q0-Q4 high),this saves using 5 diodes

for red and simplies the circuit.

3.4 Software used

1. Eagle software

2. Proteus 7 proffessional

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Chapter 4

Procedure

4.1 Draw schematic

1. Place the components required on the schematic page of eagle software selecting

the appropriate packages.

2. Connect the components with wires and connecters as per requirements.

3. Place nodes wherever required.

4. Run the program and check for errors.

5. If errors are encountered then rectify them.

6. Hence final schematic is ready.

4.2 Make layout

1. Click on board then board window will open.

2. Now group the components and move it inside the square present on the screen.

3. Resize the square to fit the circuit.

4. Click on autorouter,then adjust settings then click on ok.

5. Hence the layout is ready.

4.3 Transferring circuit on PCB

1. Redraw the circuit diagram on butter paper by placing butter paper on graph paper

using marker pen.

2. Before the ink dries, press the butter paper against copper containing side of PCB.

3. Hence mirror image of the circuit schematic id transferred on the Copper containing

side of PCB(glass epoxy).

4. Darken the connection lines on the PCB using a marker pen. Make sure two lines

don’t short.

4.4 Etching Process

1. Take a solution of Ferric Chloride and add to it some hydrogen peroxide(to quicken

the etching process). Keep the PCB in it for 45 minutes.

2. Remove the PCB when all the Copper surrounding the connection lines made by

marker pen is lost.

3. Dry the PCB.

4. Cover the PCB with flux and then tin the tracks.

4.5 Continuity

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1. Remove a little part of marker pen using a blade.

2. Using multimeter check for continuity at each point.

4.6 Drilling

1. Make holes for the component leads on the PCB.

2. Use a hand drill.

4.7 Soldering

1. Solder the components at respective places.

2. Check for continuity between the various connected pins.

3. For IC’s first solder the IC holder in the drilled holes and then place IC in it,for

precaution.

4.8 Output

1. Give power supply (+9V and Ground) to the circuit.

2. See the output on three LED’s. If they are glowing in binary sequence from 0 to 9

such that ‘1’ denotes ‘on’ LED and ‘0’ denotes ‘off’ LED.

3. Hence Traffic light is implemented.

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Chapter 5

Results

5. 1 Proteus simulation result

Fig 5.1 Simulation result

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Fig5.2 Schematic Diagram

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Fig 5.3 Waveforms

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Applications and conclusions

5.1 Application

Traffic lights for public transport often use signals that are distinct from those for private

traffic. They can be letters, arrows or bars of white or coloured light.

Some pedestrian and roadway traffic signals are fitted with readouts showing a

countdown until the next signal change.

Some traffic-light controlled junctions have a light sequence that stops all vehicular

traffic at the junction at the same time, and gives pedestrians exclusive access to the

intersection so that they can cross in any direction (including diagonally). This is known

as a pedestrian scramble in some places.

Traffic lights have been installed in most cities around the world to control the flow of

traffic. They assign the right of way to road users by the use of lights in standard colours

(Red - Amber (Officially Yellow in the United States) - Green), using a universal colour

code (and a precise sequence, for those who are colour blind). They are used at busy

intersections to more evenly apportion delay to the various users.

5.2 Conclusion

Thus we have successfully build and executed the traffic light project.

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References

Wikipedia

www.electronicsforyou.com

www.electronics-lab.com

www.redcircuits.com

www.electro-tech-online.com

http://demonstrations.wolfram.com/TrafficLights/

http://projects.kittelson.com/pplt/displays2.htm

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