Acknowledgement

**********

“As it is said a single flower doesn’t make a garland”.

This thought hold true for this project. I would like to thank my teachers who have always

supported me throughout, and have given me the extra motivation to succeed during difficult

times. I would like to thank the members of the Traffic light team. I have thoroughly enjoyed

working with my team as it has given me the opportunity to gain valuable work experience

and gain some practical skills which complement my college studies.

I would like to specially thank our supervisor, Mr Taher and Mr Abubacker for all his time,

invaluable advice and encouragement throughout the project.

**************

09003 Faisal Chowdhury

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENT

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION

CHAPTER 2 DISCUSSION

CHAPTER 3 RESULT AND CONCLUSION

CHAPTER 4 RECOMMENDATION

CHAPTER 5 REFRENCES

09003 Faisal Chowdhury

1. Introduction

Traffic Light

Traffic lights, which may also be known as stoplights, traffic lamps, traffic signals,

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. They assign the right of way to road users by the use of

lights in standard colors (Red - Amber - Green), using a universal color code (and a

precise sequence, for those who are color blind). Traditionally, incandescent and halogen

bulbs were used. Because of the low efficiency of light output and a single point of failure

(filament burnout) municipalities are increasing retrofitting traffic signals with LED arrays

that consume less power, have increased light output, last significantly longer, and in the

event of an individual LED failure, still operates albeit with a reduced light output. With the

use of optics, the light pattern of an LED array can be comparable with the pattern of an

incandescent or halogon bulb.

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Typically traffic lights consist of a set of three colored lights: red, amber and green. In a

typical cycle,

Illumination of the green light allows traffic to proceed in the direction denoted,

Illumination of the amber light denoting if safe to, prepare to stop short of the

intersection, and

Illumination of the red signal prohibits any traffic from proceeding.

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09003 Faisal Chowdhury

Discussion

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 7s to about 2½ minutes by adjusting the 1M preset. Yellow LED is used

instead of amber. The 555 astable circuit provides clock pulses for the 4017 counter which

has ten outputs (Q0 to Q9). Each output becomes high in turn as the clock pulses are

received. Appropriate outputs are combined with diodes to supply the amber and green

LEDs. The red LED is connected to the ÷10 output which is high for the first 5 counts (Q0-

Q4 high), this saves using 5 diodes for red and simplifies the circuit.

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Parts Used

• resistors: 470 × 3, 22k, 100k • 555 timer IC, such as NE555

• capacitors: 0.1μF, 1μF 16V radial, 10μF 16V radial • 4017 counter IC

• diodes: 1N4148 × 6 • DIL sockets: 8-pin, 16-pin

• LEDs: red, amber (or yellow), green • on/off switch

• 1M preset, horizontal • battery clip for 9V PP3

• stripboard: 20 rows × 21 holes

Circuit diagram

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Stripboard Layout and LED connections

Soldering precaution taken

Components PicturesReminders and

Warnings

1IC Holders(DIL sockets)

Connect the correct way round by making sure the notch is at the correct end. Do NOT put the ICs (chips) in yet.

2 Resistors No special precautions are needed with resistors.

3

Small value capacitors(usually less than 1µF)

may be connected either way round.

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4

Electrolytic capacitors(1µF and greater)

Connect the correct way round. They will be marked with a + or - near one lead.

5 Diodes Connected the correct way round.

6 LEDs

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.

7

Wire Links between points on the circuit board.

single core wire

Use single core wire, this is one solid wire which is plastic-coated. If there is no danger of touching other parts you can use tinned copper wire, this has no plastic coating and looks just like solder but it is

stiffer.

8

Battery clips, buzzers and other parts with their own wires

  Connected the correct way round.

10 ICs (chips)

Connected the correct way round. Many ICs are static sensitive.

Carefully inserted ICs in their holders: make sure all the pins are lined up with the socket then push down firmly with your thumb.

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Details of the components used -:

Light Emitting Diodes (LEDs)

Function -LEDs emit light when an electric current passes

through them. LEDs have a + for anode and k or - for

cathode .The cathode is the short lead and there may be a slight flat on the

body of round LEDs. Inside the LED the cathode is the larger electrode. LEDs

can be damaged by heat when soldering, but the risk is small unless you are very slow.

Special precautions are needed for soldering most LEDs.

Testing an LED

LED cannot be directly connected to a battery or power supply

it will be destroyed because too much current will pass through and burn

it out. LEDs must have a resistor in series to limit the current to a safe

value, for quick testing purposes a 1k resistor is suitable for most LEDs

if your supply voltage is 12V or less.

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Presets

These are miniature versions of the standard variable resistor. They are designed to be

mounted directly onto the circuit board and adjusted only when the circuit

is built. For example to set the frequency of an alarm tone or the sensitivity of

a light-sensitive circuit. A small screwdriver or similar tool is required to

adjust presets. Presets are much cheaper than standard variable resistors so

they are sometimes used in projects where a standard variable resistor would

normally be used. Multiturn presets are used where very precise adjustments

must be made. The screw must be turned many times (10+) to move the slider

from one end of the track to the other, giving very fine control.

Preset

(open style)

Presets

(closed style)Multiturn preset

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Preset Symbol

 

555/556 Astable

An astable circuit produces a 'square wave’;

this is a digital waveform with sharp transitions

between low (0V) and high (+Vs). The

durations of the low and high states may be

different. The circuit is called an astable

because it is not stable in any state: the output is

continually changing between 'low' and 'high'.

The time   period (T) of the square wave is the

time for one complete cycle, but it is usually better to consider frequency (f) which is the

number of cycles per second.

4017 decade counter (1-of-10)

The count advances as the clock input becomes high (on the rising-edge). Each output Q0-Q9

goes high in turn as counting advances. Some

functions (such as flash sequences) outputs may be

combined using   diodes . The reset input should be low

(0V) for normal operation (counting 0-9). When high

it resets the count to zero (Q0 high). It can be done

manually with a switch between reset and +Vs and a

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555 astable output, a square wave

(Tm and Ts may be different)

 

555 astable circuit

 

10k resistor between reset and 0V. Counting to less than 9 is achieved by connecting the

relevant output (Q0-Q9) to reset, for example to count 0,1,2,3

connect Q4 to reset. The disable input should be low (0V) for normal operation. When high it

disables counting so that clock pulses are ignored and the count is kept constant. The ÷10

output is high for counts 0-4 and low for 5-9, so it provides an output at 1/10 of the clock

frequency. It is used to drive the clock input of another 4017 (to count the tens).

Diodes

       Circuit symbol:   

Function-Diodes allow electricity to flow in only

one direction. The arrow of the circuit symbol

shows the direction in which the current can flow.

Diodes are the electrical version of a valve and

early diodes were called valves.

Forward Voltage Drop- Electricity uses up a little

energy pushing its way through the diode, rather

like a person pushing through a door with a spring. This means that there is a small voltage

across a conducting diode, it is called the forward voltage drop and is about 0.7V for all

normal diodes which are made from silicon. The forward voltage drop of a diode is almost

constant whatever the current passing through the diode so they have a very steep

characteristic

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Rectifier diodes (large current)

Rectifier diodes are used in power supplies to convert alternating current (AC) to direct

current (DC), a process called rectification. They are also used elsewhere in circuits where a

large current must pass through the diode.

All rectifier diodes are made from silicon and therefore have a forward voltage drop of 0.7V.

The table shows maximum current and maximum reverse voltage for some popular rectifier

diodes. The 1N4001 is suitable for most low voltage circuits with a current of less than 1A.

Reverse Voltage

When a reverse voltage is applied a perfect diode does not conduct, but all real diodes leak a

very tiny current of a few µA or less. This can be ignored in most circuits because it will be

very much smaller than the current flowing in the forward direction. However, all diodes

have a maximum reverse voltage (usually 50V or more) and if this is exceeded the diode will

fail and pass a large current in the reverse direction, this is called breakdown.

Ordinary diodes can be split into two types: Signal diodes which pass small currents of

100mA or less and Rectifier diodes which can pass large currents. In addition there are LEDs

(which have their own page) and Zener diodes (at the bottom of this page).

Protection diodes for relays-Signal diodes are also used to protect transistors and ICs from

the brief high voltage produced when a relay coil is

switched off. The diagram shows how a protection

diode is connected 'backwards' across the relay coil.

Current flowing through a relay coil creates a

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magnetic field which collapses suddenly when the current is switched off. The sudden

collapse of the magnetic field induces a brief high voltage across the relay coil which is very

likely to damage transistors and ICs. The protection diode allows the induced voltage to drive

a brief current through the coil (and diode) so the magnetic field dies away quickly rather

than instantly. This prevents the induced voltage becoming high enough to cause damage to

transistors and ICs.

Capacitors

Examples:        Circuit symbol:   

Function - Capacitors store electric charge. They are used with resistors in timing circuits

because it takes time for a capacitor to fill with charge. They are used to smooth varying DC

supplies by acting as a reservoir of charge. They are also used in filter circuits because

capacitors easily pass AC (changing) signals but they block DC (constant) signals.

Capacitance

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. However 1F is very large,

so prefixes are used to show the smaller values.

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Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

µ means 10-6 (millionth), so 1000000µF = 1F

n means 10-9 (thousand-millionth), so 1000nF = 1µF

p means 10-12 (million-millionth), so 1000pF = 1nF

Resistors

Function

Resistors restrict the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED.

Connecting and soldering

Resistors may be connected either way round. They are not damaged by heat when soldering.

Resistor values - the resistor color code

Resistance is measured in ohms, the symbol for ohm is an omega . 1 is quite small so resistor values are often given in k and M . 1 k = 1000     1 M = 1000000 .

Resistor values are normally shown using coloured bands. Each colour represents a number as shown in the table.

Most resistors have 4 bands:

The first band gives the first digit. The second band gives the second digit.

The third band indicates the number of zeros.

The fourth band is used to shows the tolerance (precision) of the resistor.

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The ResistorColour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

IC

Integrated Circuits are usually called ICs or chips. They are complex circuits which have

been etched onto tiny chips of semiconductor (silicon). The chip is packaged in a plastic

holder with pins spaced on a 0.1" (2.54mm) grid which will fit the holes on stripboard and

breadboards. Very fine wires inside the package link the chip to the pins.

Pin numbers

The pins are numbered anti-clockwise around the IC

(chip) starting near the notch or dot. The diagram shows

the numbering for 8-pin and 14-pin ICs, but the principle is the same for all sizes.

IC holders (DIL sockets)

ICs (chips) are easily damaged by heat when soldering and their short pins cannot

be protected with a heat sink. Instead we use an IC holder, strictly called a DIL

socket (DIL = Dual In-Line), which can be safely soldered onto the circuit board. The IC is

pushed into the holder when all soldering is complete.

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IC holders are only needed when soldering so they are not used on breadboards.

Commercially produced circuit boards often have ICs soldered directly to the board without

an IC holder, usually this is done by a machine which is able to work very quickly. Please

don't attempt to do this yourself because you are likely to destroy the IC and it will be

difficult to remove without damage by de-soldering.

Removing an IC from its holder

If you need to remove an IC it can be gently prised out of the holder with a small flat-blade

screwdriver. Carefully lever up each end by inserting the screwdriver blade between the IC

and its holder and gently twisting the screwdriver. Take care to start lifting at both ends

before you attempt to remove the IC, otherwise you will bend and possibly break the pins.

Using diodes to combine outputs

The outputs of ICs must never be directly connected together.

However, diodes can be used to combine two or more digital

(high/low) outputs from an IC such as a counter. This can be a

useful way of producing simple logic functions without using

logic gates!

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The diagram shows two ways of combining outputs using diodes. The diodes must be capable

of passing the output current. 1N4148 signal diodes are suitable for low current devices such

as LEDs.

For example the outputs Q0 - Q9 of a 4017 1-of-10 counter go high in turn. Using diodes to

combine the 2nd (Q1) and 4th (Q3) outputs as shown in the bottom diagram will make the

LED flash twice followed by a longer gap. The diodes are performing the function of an

OR gate.

Building of the body of traffic signal

Two juice boxes were taken and cut accordingly

Reinforced with tape

Place was made for the circuit to fit in

A4 paper was used for covering the box

3 holes were made for the LEDs to be seen

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Conclusion and results and recommendation

The circuit for a typical traffic light was constructed in a circuit board. The working of

the related components was studied in detail.

All Traffic signals in future possibly will harness the solar energy since it LEDs

need less power.

09003 Faisal Chowdhury

Refrences-

"The man who gave us traffic lights". BBC. 2009-07-16.

http://www.bbc.co.uk/nottingham/content/articles/2009/07/16/john_peake_knight

_traffic_lights_feature.shtml

http://www.freewebs.com/trafficlightsignals2/euroheads.htm

"Traffic Signals". Institute of Transportation Engineers. September 2007

09003 Faisal Chowdhury