In-House Summer Training Report On
AUTOMATIC TRAFFIC LIGHT MODEL
Submitted in partial fulfilment of the requirements for the award of degree of
BACHELOR OF TECHNOLOGY In
Instrumentation and Control Engineering
Mentors:
Submitted By:-
Mr. VIVEK JANGHRA
Shashank Pandey (05210403011)
Mrs. AMAN SETIA
Srijan Upadhyay (05410403011)
Mr. VIJAYANAND
Akhilesh Thapliyal (07310403011)
Mrs. VINI TUTEJA
Department of Instrumentation & Control Engineering AMITY SCHOOL OF ENGINEERING & TECHNOLOGY GGS Indraprastha University, New Delhi 1
CERTIFICATE
This is to certify that the project report entitled “Automatic Traffic Lights Model” submitted bySHASHANK PANDEY
05210403011
SRIJAN UPADHYAY
05410403011
AKHILESH THAPLIYAL
07310403011
has been accomplished under my guidance. This report is submitted for partial fulfilment of award of degree of Bachelor of Technology in Instrumentation and Control Engineering at Amity School of Engineering and Technology, affiliated to Guru Gobind Singh Indraprastha University, New Delhi.
Date: 31 July, 2013
Mentors: Mrs. VINI TUTEJA Mr. VIVEK JHANGRA Mrs. AMAN SETIA Mr. VIJAYANAND KUMAR ICE Department Amity School of Engineering & Technology Bijwasan, New Delhi- 61
2
ACKNOWLEDGEMENT
First of all, I would like to thank my project guide Mrs. VINI TUTEJA whose constant guidance and support throughout my entire training helped me in completing this project. I would also like to thank Mrs. PINKY NAYAK, H.O.D, ICE, ASET for her support and encouragement. Sincere thanks to my training coordinator, Mr.VIJAYANAND KUMAR for presenting me, not only with this concept but also giving their valuable guidance which was essential for compilation of this report. Special thanks to our director Dr. REKHA AGGARWAL for providing us the infrastructure such as laboratory and apparatus, equipments which helped in completion of my project. I would also like to thank to Mr. VIVEK JHANGRA for the help he lent me in the form of new ideas, as well as her constructive criticism, which helped us greatly along the way. The Lab assistant in the laboratories of Amity School of Engineering & Technology Mr. KAILASH JOSHI and Mr. SANJEEV also need to be acknowledged for their cooperation and providing us a convenient environment t o work in.
Shashank Pandey (052)
Srijan Upadhyay (054)
Akhilesh Thapliyal (073)
3
ABSTRACT
This automated traffic signal controller can be made by suitably using the 555 Timer and 4017 Counter. This project operates red, amber and green LEDs in the correct sequence for a single traffic light. The time taken for the complete red - green amber sequence can be varied from about 7s to about 1 minute by adjusting the 100K preset. Some amber LEDs emits 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). Each output becomes high in turn as the clock pulses are received. Appropriate outputs are combined with diodes to supply the red, amber and green LEDs. The red LED is connected to the 4 outputs (Q0-Q3) using 4 diodes (D1D4), which makes it light longer than amber and 2 nd green (the right turn) LEDs whereas the 1st green LED is connected to 5 outputs (Q4-Q8) using 5 diodes (D5-D9) which makes it light longest whereas the 2 nd green LED is connected to 3 outputs using 3 diodes (D11- D13) which makes it light longer than amber but less than red and 1st green LED. The amber LED is connected to just 1 output (Q9) only using 1 diode (D10) which makes it light shortest just for (5-6 sec). This project uses a 555 astable circuit to provide the clock pulses for the 4017 counter. Its main features are:-
1. The controller assumes equal traffic densit y on all the roads. 2. In most automated traffic signals the free left-turn condition is provided throughout the entire signal period, which poses difficulties to the pedestrians in crossing the road, especially when the traffic density is high. This controller allows the pedestrians to safely cross the road during certain periods. 3. The controller uses digital logic, which can be easily implemented by using logic gates. 4. The controller is a generalized one and can be used for different roads with slight modifications. 5. The control can also be exercised manually when desired. The time period for which green, yellow and red traffic signals remain ‗on‘ (and then repeat) for the straight moving traffic is divided into eight units of 8 s econds each.
SOFTWARES USED: 1. Cadence OrCAD 9.2 (for Schematic and Simulation of circuit) 2. NOVARM DIPTRACE (for PCB layout)
4
TABLE OF CONTENTS
CHAPTER NO.
TITLE CERTIFICATE
PAGE I
ACKNOWLEDGEMENT
II
ABSTRACT
III
LIST OF FIGURES/TABLES
IV
LIST OF SYMBOLS
V
INTRODUCTION
10
1.1
HISTORY OF TRAFFIC LIGHTS
10
1.2
TECHNOLOGY
11
THE PROJECT
13
2.1
CIRCUIT DIAGRAM
13
2.2
PCB LAYOUT
14
3D LAYOUT
15
1.
2.
2.2.1
LITERATURE REVIEW: 3.
COMPONENTS USED
16
4.
ABOUT THE COMPONENTS
17
4.1.1
RESISTOR
17
4.1.2
DIODE
19
4.1.3
CAPACITOR
21
4.1.4
PRESET
23
5
CHAPTER NO.
TITLE
PAGE
4.1.5
LED
25
4.1.6
IC 555 TIMER
31
4.1.7
IC 4017 DECADE COUNTER
38
4.1.8
POWER SUPPLY
41
4.1.9
PRINTED CIRCUIT BOARD
43
5.
WORKING PRINCIPLE
47
6.
ADVANTAGES OF TRAFFIC LIGHTS
48
7.
DISADVANTAGES OF TRAFFIC LIGHTS
48
8.
APPLICATIONS
49
9.
FUTURE SCOPE
49
10.
REFERENCES
50
11.
APPENDICES
6
51-72
LIST OF FIGURES/ TABLES Figure No.
Name
Page No.
1
Automatic Traffic Light Model
2
PCB Layout
14
3
3D Layout
15
4
Resistor
17
5
Capacitor
21
6
Preset
23
7
LED
25
8
LED‘s Working
26
9
IC 555 TIMER
31
10
PIN configuration of IC 555
34
11
Graph showing counting action of IC 4017
38
12
PIN configuration of IC 4017
39
13
AC source
41
14
Printed circuit Board
43
Table no.
Table Name
Page no.
1.
Resistor Colour codes
18
2.
Colours and materials of LEDs
28
7
9
LIST OF SYMBOLS
S.No
Component
1
Resistance
2.
Diode
3.
Capacitor (Polar)
4
Preset
5
LED
Symbol
8
AUTOMATIC TRAFFIC LIGHT MODEL
Fig.1
9
1. INTRODUCTION
The traffic signals are used to control the flow of vehicles. In recent years the need of transportation has gain immense importance for logistics as well as for common humans. This has given rise to number of vehicles on road. Due to this reason traffic jams and road accidents are a common sight in any busy city. Traffic signals provide an easy, cheap, automated and justified solution to the road points where the vehicles may turn to the other directions. Now a day, due to ever increasing vehicles on the road, it require a efficient control on the four way junction of road. In order to find a solution to this problem the concept of an automatic traffic controller is conceived. Apart from providing efficient control of traffic, it also eliminate chance of human errors since it function automatically. The automatic traffic controller automatically switches on the four way junction for required time in order to control the direction. BASIC IDEA- The project we have chosen is a T- junction 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 and to let the pedestrians cross the road through Zebra crossing, after which the next waiting drivers and pedestrians are given the same treatment. In this way, a cycle has been established which will control the traffic. CONTROL SIGNALS- The control signals are 4 lights. Top light is Red (Stop) – Middle Light is Yellow (Wait) – Bottom Light is Green (Go) – Bottom right Light is also Green (the Go signal for traffic taking right turn). The main circuit components used are astable 555-Timer and a 4017 decade counter. The 555-Timer generates a clock signal for 15 seconds. This signal is used to clock counter circuit. Binary counter is converted to 3 bit – counter to achieve 8 possible cases. The traffic light control is done by using 5 bit output for Red light so that it would light longest, 4 bit output for Green light and 1 bit output for Yellow light.
1.1 HISTORY OF TRAFFIC LIGHTS On 10 December 1868, the first traffic lights were installed outside the British Houses of Parliament in London, by the railway engineer J. P. Knight. They resembled railway signals of the time, with semaphore arms and red and green gas lamps for night use. The gas lantern was turned with a lever at its base so that the appropriate light faced traffic. Unfortunately, it exploded on 2 January1869, injuring the policeman who was operating it. The modern electric traffic light is an American invention. As early as 1912 in Salt Lake City, Utah, policeman Lester Wire invented the first red-green electric traffic 10
lights. On5 August 1914, the American Traffic Signal Company installed a traffic signal system on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio. It had two colours, red and green, and a buzzer, based on the design of James Hoge, to provide a warning for colour changes. The design by James Hoge allowed police and fire stations to control the signals in case of emergency. The first fourway, three-color traffic light was created by police officer William Potts in Detroit, Michigan in 1920. In 1923, Garrett Morgan patented a traffic signal device. It was Morgan's experience while driving along the streets of Cleveland that led to his invention of a traffic signal device. Ashville, Ohio claims to be the location of the oldest working traffic light in the United States, used at an intersection of public roads until 1982 when it was moved to a local museum. The first interconnected traffic signal system was installed in Salt Lake City in 1917, with six connected intersections controlled simultaneously from a manual switch. Automatic control of interconnected traffic lights was introduced March 1922 in Houston, Texas. The first automatic experimental traffic lights in England were deployed in Wolver Hampton in 1927. Ampelmännchen pedestrian traffic signals have come to be seen as a nostalgic sign for the former German Democratic Republic. The color of the traffic lights representing stop and go are likely derived from those used to identify port (red) and starboard (green) in maritime rules governing right of way, where the vessel on the left must stop for the one crossing on the right.
1.2 TECHNOLOGY Optics and Lightings:-
In the mid 1990s, cost-effective traffic light lamps using light-emitting diodes (LEDs) were developed; prior to this date traffic lights were designed using incandescent or halogen light bulbs. Unlike the incandescent-based lamps, which use a single large bulb, the LED-based lamps consist of an array of LED elements, arranged in various patterns. When viewed from a distance, the array appears as a continuous light source. LED-based lamps (or 'lenses') have numerous advantages over incandescent lamps; among them are: • Much greater energy efficiency (can be solar-powered). • Much longer lifetime between replacements, measured in years rather than months. Part of the longer lifetime is due to the fact that some light is still displayed even if some of the LEDs in the array are dead. • Brighter illumination with better contrast against direct sunlight, also called 'phantom light'. • The ability to display multiple colors and patterns from the same lamp. Individual LED elements can be enabled or disabled and different color LEDs can be mixed in the same lamp • Much faster switching.
11
• Instead of sudden burn-out like incandescent-based lights, LEDs start to gradually dim when they wear out, warning transportation maintenance departments well in advance as to when to change the light. Occasionally, particularly in green LED units, segments prone to failure will flicker rapidl y beforehand. The operational expenses of LED-based signals are far lower than equivalent incandescent-based lights. As a result, most new traffic light deployments in the United States, Canada and elsewhere have been implemented using LED-based lamps; in addition many existing deployments of incandescent traffic lights are being replaced. In 2006, Edmonton, Alberta, Canada completed a total refit to LED-based lamps in the cities over 12,000 intersections and all pedestrian crosswalks. Many of the more exotic traffic signals discussed on this page would not be possible to construct without using LED technology. However, colour-changing LEDs are in their infancy and may surpass the multi-colour array technology. In some areas, LED-based signals have been fitted (or retrofitted) with special Fresnel lenses (Programmed Visibility or 'PV' lenses) and/or diffusers to limit the line of sight to a single lane. These signals typically have a "projector"-like visibility; and maintain an intentionally limited range of view. Because the LED lights don't generate a significant amount of heat, heaters may be necessary in areas which receive snow, where snow can accumulate within the lens area and limit the visibility of the indications. Another new LED technology is the use of CLS (Central Light Source) optics. These comprise around 7 high-output LEDs (sometimes 1 watt) at the rear of the lens, with a diffuser to even out and enlarge the light. This gives a uniform appearance, more like traditional halogen or incandescent luminaries. Replacing halogen or incandescent reflector and bulb assemblies behind the lens with an LED array can give the same effect. This also has its benefits: minimal disruption, minimal work, minimal cost and the reduced need to replace the entire signal head (housing).
12
2. PROJECT 2.1 CIRCUIT DIAGRAM
13
2.2 PCB LAYOUT
Fig. 2
14
2.2.1 3D LAYOUT
Fig.
Fig.3
15
3. COMPONENTS USED
S.No.
Components
Specifications
1
Resistor
470 Ω, 10 K Ω
3+1
2
Diode
1N4148
9
3
Capacitor
100 μf
1
4
Preset
100 K Ω
1
5
LED
Red, Amber, Green
1+1+2
6
I.C
555 Timer, 4017 Counter
1+1
7
Power Supply
9V-12V A.C
1
8
PCB
Copper coated
1
Table- 1
16
Quantity
4. ABOUT THE COMPONENTS 4.1 RESISTORS: A resistor is a piece of materials that obeys Ohm’s Law. The name comes from its main property. It resists the flow of charge through itself, hence allowing us to control the current. Resistors can be made of various kinds of material, but whatever the choice it must conduct some electricity otherwise it wouldn‘t be of any use. Two wires are connected to opposite ends of the resistor. When we apply a potential difference between the wires we set up a current from one wire to another wire through the resistor. The size of the current is proportional to the difference in voltage between the wires. The resistance (in units of Ohms) is defined as the ratio of the applied voltage ( in Volts ) , divided by the current, I (in Ampere ) , produced by the applied voltage. Resistors come in wide variety of sizes and shapes , but the most common type is a cylinder with wires at the ends.
Fig. 4
Symbol- 1
Resistors, like diode and relays , are another of the electronic parts that should have a section in the installer‘s parts bin . They have become a necessity for the mobile electronics installer ,whether it to be door locks, parking lights, timing circuits ,remote starts, LED‘S , or just to discharge a stiffening capacitor. The tolerance band is usually gold or silver, but some may have none. Because resistors are not the exact value as indicated by the colour bands, manufactures have included a tolerance colour band to indicate the accuracy of the resistor. Gold band indicates the resistors is within 5% of the what is indicated. Silver is equal to 10% and None is equal to 20%. Others are shown in the chart below. For example 1 K ohm resistor may have an actual measurement anywhere from 950 ohms to 1050 ohms. If a resistor does not have tolerance band, start from the band closest to lead. This will be the 1st band. If you enable to read the colour bands , then you‘ll have to use your multimeter. Be sure to zero it out first.
17
4.1.1 Resistor Colour Codes:
Color
Significant Multiplier figures 0
–
1
±1%
2
±2%
3
–
Black
0
×10
Brown
1
×10
Red
2
×10
Orange
3
×10
Yellow
4
×10
Green
5
×10
Blue
6
×10
Violet
7
×10
Gray
8
×10
White
9
×10
Gold
–
×10
Silver
–
None
–
Temp. Coefficient (ppm/K)
Tolerance
250
U
F
100
S
G
50
R
15
P
4
(±5%)
–
25
Q
5
±0.5%
D
20
Z
6
±0.25%
C
10
Z
7
±0.1%
B
5
M
8
±0.05% (±10%)
A
1
K
9
–
-1
±5%
J
–
×10
-2
±10%
K
–
–
±20%
M
–
Table- 1
18
–
4.2 DIODES
In electronics, a diode is a two-terminal electronic component with asymmetric conductance, it has low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p – n junction connected to two electrical terminals A vacuum tube diode has two electrodes, a plate (anode) and a heated cathode. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be viewed as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, including extraction of modulation from radio signals in radio receivers — these diodes are forms of rectifiers. However, diodes can have more complicated behavior than this simple on – off action. Semiconductor diodes begin conducting electricity only if a certain threshold voltage or cut-in voltage is present in the forward direction (a state in which the diode is said to be forward-biased. The voltage drop across a forward-biased diode varies only a little with the current, and is a function of temperature; this effect can be used as a temperature sensor or voltage reference. Semiconductor diodes' nonlinear current – voltage characteristic can be tailored by varying the semiconductor materials and doping, introducing impurities into the materials. These are exploited in special-purpose diodes that perform many different functions. For example, diodes are used to regulate voltage (Zener diodes), to protect circuits from high voltage surges (avalanche diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to produce light (light emitting diodes). Tunnel diodes exhibit negative resistance, which makes them useful in some types of circuits. 4.2.1 About 1N4148 Diode:
The 1N4148 is a standard silicon switching diode. It is one of the most popular and long-lived switching diodes because of its dependable specifications and low cost. The 1N4148 is useful in switching applications up to about 100 MHz with a reverserecovery time of no more than 4 ns.
19
Symbol- 2
4.2.2 Specifications:
VRRM = 100 V (maximum repetitive reverse voltage) IO = 200 mA (average rectified forward current) IF = 300 mA (maximum direct forward current) VF = 1.0 V at 10 mA. IFSM = 1.0 A (pulse width = 1 s), 4.0 A (pulse width = 1 µs) (non-repetitive peak forward surge current) PD = 500 mW (power dissipation) TRR < 4 ns (reverse-recovery time)
4.2.3 Applications:
High speed switching
20
4.3 CAPACITORS
There exist two types of capacitors: (i)
Polar Capacitor
(ii)
Non- Polar Capacitors
Since, in our project we have used polar type of capacitor, so here, we will discuss about polar capacitors, only. Aluminium electrolytic capacitors are constructed from two conducting aluminium foils, one of which is coated with an insulating oxide layer, and a paper spacer soaked in electrolyte. The foil insulated by the oxide layer is the anode while the liquid electrolyte and the second foil acts as the cathode. This stack is then rolled up, fitted with pin connectors and placed in a cylindrical aluminium casing. The two most popular geometries are axial leads coming from the centre of each circular face of the cylinder, or two radial leads or lugs on one of the circular faces.
Fig. 5
In aluminium electrolytic capacitors, the layer of insulating aluminium oxide on the surface of the aluminium plate acts as the dielectric, and it is the thinness of this layer that allows for a relatively high capacitance in a small volume. This oxide has a dielectric constant of 10, which is several times higher than most common polymer insulators. It can withstand electric field strength of the order of 25 megavolts per meter which is an acceptable fraction of that of common polymers. This combination of high capacitance and reasonably high voltage result in high energy density. Most electrolytic capacitors are polarized and require one of the electrodes to be positive relative to the other; they may catastrophically fail if voltage is reversed. This is because a reverse-bias voltage above 1 to 1.5 V will destroy the centre layer of dielectric material via electrochemical reduction. Following the loss of the 21
dielectric material, the capacitor will short circuit, and with sufficient short circuit current, the electrolyte will rapidly heat up and either leak or cause the capacitor to burst, often in a spectacularly dramatic fashion. To minimize the likelihood of a polarized electrolytic being incorrectly inserted into a circuit, polarity is very clearly indicated on the case. A bar across the side of the capacitor is usually used to indicate the negative terminal. Also, the negative terminal lead of a radial electrolytic is shorter than the positive lead and may be otherwise distinguishable. On a printed circuit board it is customary to indicate the correct orientation by using a square through-hole pad for the positive lead and a round pad for the negative. Special bipolar capacitors designed for AC operation are available, usually referred to as "non-polarized" or "NP" types. In these, full-thickness oxide layers are formed on both the aluminium foil strips prior to assembly. On the alternate halves of the AC cycles, one of the foil strips acts as a blocking diode, preventing reverse current from damaging the electrolyte of the other one. Modern capacitors have a safety valve which is typically either a scored section of the can or a specially designed end seal to vent the hot gas/liquid, but ruptures can still be dramatic. An electrolytic can withstand a reverse bias for a short period, but will conduct significant current and not act as a very good capacitor. Most will survive with no reverse DC bias or with only AC voltage, but circuits should be designed so that there is not a constant reverse bias for any significant amount of time. The electrolyte is usually boric acid or sodium borate in aqueous solution, together with various sugars or ethylene glycol which are added to retard evaporation. Getting a suitable balance between chemical stability and low internal electrical resistance is not a simple matter; in fact, the exact compositions of high-performance electrolytes are closely guarded trade secrets. It took many years of research before reliable devices were developed. The electrolytic solvent has to have high dielectric constant, high dielectric strength, and low resistivity; a solute of ionic conductivity facilitators is mixed within. Electrolytes may be toxic or corrosive. Working with the electrolyte requires safe working practice and appropriate protective equipment such as gloves and safety glasses. Some very old tantalum electrolytes, often called "Wet-slug", contain corrosive sulphuric acid; however, most of these are no longer in service due to corrosion.
Symbol- 3
22
4.4 PRESET
A trimmer or preset is a miniature adjustable electrical component. It is meant to be set correctly when installed in some device, and never seen or adjusted by the device's user. Trimmers can be variable resistors, potentiometers, variable capacitors, or trimmable inductors. They are common in precision circuitry like A/V components, and may need to be adjusted when the equipment is serviced. Trim pots are often used to initially calibrate equipment after manufacturing. Unlike many other variable controls, trimmers are mounted directly on circuit boards, turned with a small screwdriver and rated for many fewer adjustments over their lifetime. Trimmers like trimmable inductors and trimmable capacitors are usually found in superhet radio and television receivers, in the Intermediate frequency, oscillator and RF circuits. They are adjusted into the right position during the alignment procedure of the receiver.Trimmers come in a variety of sizes and levels of precision. For example, multi-turn trim potentiometers exist, in which it takes several turns of the adjustment screw to reach the end value. This allows for very high degrees of accuracy. Often they make use of a worm-gear (rotary track) or a leadscrew (linear track). There are 3 pins/terminals on a preset. The maximum resistance that a preset can provide is written on it. If 100K is written on preset, p reset, it means that we can vary its resistance from 0 Ohm to 100K. A movable metal is rotated in clockwise or anticlockwise direction that changes changes the resistance of preset. Now, we name the three thre e terminals termi nals as A, B, C.
Fig. 6
23
Symbol- 4
If we take terminal A and terminal B, and rotate the movable metal met al in clockwise direction, the resistance of preset increases from 0 to maximum. As we move the metal in anticlockwise direction, the resistance decreases.
If we take terminal A and terminal C, and rotate the movable metal met al in anticlockwise direction, the resistance of preset increases from 0 to maximum. As we move the metal in clockwise direction, the resistance decreases.
24
4.5 LEDs:
A Light Emitting Diode, usually called a LED is a semiconductor diode that emits incoherent narrow spectrum light when electrically biased in the forward direction of the p-n junction, as in the common LED circuit. This effect is a form of electroluminescence
Fig. 7 The LED consists of the chip of the semiconducting materials doped with the impurities to create a p-n junction diode. As in other diode, the current flow easily from the p-side or anode to the n-side or cathode, but not in the reverse direction. Charge carriers like electrons and holes are flow into the junction from electrodes with different voltages. When an electron meets a hole it falls into the lower energy level, and releases the energy in the form of photon. The wavelength of the light emitted and thus it color depend on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes the electrons and holes are recombine by a non-radiative transition, which produces a no optical emission, because these are the indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near – infrared ,visible or near – near – ultraviolet ultraviolet light. LED development began with the infrared and red devices made with Gallium Arsenide. Advances in material science have enable making devices with ever shorter wavelengths emitting the light in a variety of colors. LEDs are usually built on n-type substrate with an electrode attached to the p- type layer deposited on its surface. P-type substrates, while less common, occur as well. Most materials used for LED production have very high refractive indices. This means that much light will reflected back into the material / air surface interface.
25
Fig. 8
A LED is usually a small area light source, often with optics added to the chip to shape its radiation pattern and assists in reflection. LEDs are often used as a small indicator lights on electronic devices and increasingly in higher power applications such as flashlight and area lighting. The color of the emitted light depends on the composition and condition of the semiconducting materials used, and can be infrared, visible, or ultraviolet. LEDs can also be used as a regular household light source. Besides lighting, interesting applications include sterilization of water and disinfection of devices.
Symbol- 5
26
4.5.1 Colours and Materials:
Conventional LEDs are made from a variety of inorganic semiconductor materials. The following table shows the available colors with wavelength range, voltage drop and material:
Color
Infrared
Wavelength [nm]
λ
> 760
Voltage
Semiconductor material
drop [ΔV]
ΔV <
Gallium arsenide (GaAs)
1.63
Aluminium gallium arsenide (AlGaAs)
Aluminium gallium arsenide (AlGaAs) Red
610 < λ < 760
Gallium arsenide phosphide (GaAsP)
1.63 < ΔV <
Aluminium gallium indium
2.03
phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Gallium arsenide phosphide (GaAsP) Orange
590 < λ < 610
2.03 < ΔV <
Aluminium gallium indium
2.10
phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Gallium arsenide phosphide (GaAsP) Yellow
570 < λ < 590
2.10 < ΔV <
Aluminium gallium indium
2.18
phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Traditional green: Gallium(III) phosphide (GaP) Aluminium gallium indium phosphide (AlGaInP) Green
500 < λ < 570
1.9 < ΔV < 4.0
Aluminium gallium phosphide (AlGaP) Pure green: Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN)
27
Zinc selenide (ZnSe) Blue
450 < λ < 500
2.48 < ΔV <
Indium gallium nitride (InGaN)
3.7
Silicon carbide (SiC) as substrate Silicon (Si) as substrate—under development
Violet
Purple
400 < λ < 450
multiple types
2.76 < ΔV <
Indium gallium nitride (InGaN)
4.0
Dual blue/red LEDs,
2.48 < ΔV <
blue with red phosphor,
3.7
or white with purple plastic
Diamond (235 nm) Boron nitride (215 nm) Ultraviolet
λ <
400
3.1 < ΔV <
Aluminium nitride (AlN) (210 nm)
4.4
Aluminium gallium nitride (AlGaN) Aluminium gallium indium nitride (AlGaInN) — down to 210 nm
Blue with one or two phosphor layers: Pink
multiple types
ΔV ~
yellow with red, orange or pink phosphor
3.3
added afterwards, or white with pink pigment or dye.
White
Broad spectrum
ΔV =
3.5
Blue/UV diode with yellow phosphor
Table- 2
28
4.5.2 Advantages of using LEDs:
LEDs produce more light per watt than incandescent bulbs; this is useful in battery powered or energy-saving devices. LEDs can emit light of an intended colour without the use of colour filters that traditional lighting methods require. This is more efficient and can lower initial costs. When used in applications where dimming is required, LEDs do not change their colour tint as the current passing through them is lowered, unlike incandescent lamps, which turn yellow. LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently or HID lamps that require a long time before restarting. LEDs, being solid state components, are difficult to damage with external shock. Fluorescent and incandescent bulbs are easi ly broken if dropped on the ground. LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, through time to complete failure may be longer. Fluorescent tubes typically are rated at about 30,000 hours, and incandescent light bulbs at 1,000-2,000 hours. LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs. LEDs light up very quickly. A typical red indicator LED will achieve full brightness in microseconds;
LEDs can be very small and are easil y populated onto printed circuit boards.
LEDs do not contain mercury, unlike compact fluorescent lamps.
4.5.3 Disadvantages of using LEDs:
LEDs are currently more expensive. LEDs must be supplied with the correct current. This can involve seies resistors or current-regulated power supplies. LEDs do not approximate a ―point source‖ of light, so cannot be used in applications needing a highly collimated beam.
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4.5.4 Applications of LEDs:
Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning. Illumination where light is reflected from objects to give visual response of these objects. Measuring and interacting with processes involving no human vision. Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light.
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4.6 IC 555 TIMER The 555 timer is one of the most remarkable integrated circuits ever developed. It comes in a single or dual package and even low power emos versions exist ICM7555. Common part numbers are LM555, NE555, LM556, NE556. The 555 timer consists of two voltage comparators, a bi-stable flip flop, a discharge transistor, and a resistor divider network Philips describes their 555 monolithic timing circuit as a "highly stable controller capable of producing accurate time delays, or oscillation. In the time delay mode of operation, the time is precisely controlled by one external resistor and capacitor. For a stable operation as an oscillator, the free running frequency and the duty cycle are both accurately controlled with two external resistors and one capacitor. The circuit may be triggered and reset on falling waveforms, and the output structure can source or sink up to 200mA." The 555 gets its name from the three 5-kOhm resistors used in typical early implementations. The 555 timer is one of the most popular and versatile integrated circuits ever produced. It includes 23 transistors, 2 diodes and 16 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8).
Fig. 9
4.6.1
OPERATING MODES OF 555 TIMER:
The 555 has three operating modes: • ASTABLE MODE: Free Running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms etc. • MONOSTABLE MODE: In this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, bounce free switches, touch switches, Frequency Divider, Capacitance Measurement, Pulse Width Modulation (PWM) etc. • BISTABLE MODE: A Bistable Mode or what is sometimes called a Schmitt Trigger, has two stable states, high and low. Taking the Trigger input low makes the output of the circuit go into the high state. 31
•
555 Timer in ASTABLE operation:
When configured as an oscillator the 555 timer is configured as in figure 2 below. This is the free running mode and the trigger is tied to the threshold pin. At powerup, the capacitor is discharged, holding the trigger low. This triggers the timer, which establishes the capacitor charge path through Ra and Rb. When the capacitor reaches the threshold level of 2/3 Vcc, the output drops low and the discharge transistor turns on. The timing capacitor now discharges through Rb. When the capacitor voltage drops to 1/3 Vcc, the trigger comparator trips, automatically retriggering the timer, creating an oscillator whose frequency is determined by the formula in the figure.
There are difficulties with duty cycle here and ‗I‘ will deal with them below. It should also be noted that a minimum value of 3K should be used for Rb.
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Here two signal diodes have been added. This circuit is best used at Vcc= I 5V. Both the trigger and threshold inputs (pins 2 and 6) to the two comparators arc connected together and to the external capacitor. The capacitor charges toward the supply voltage the two resistors Ra and Rh. The discharge pin (7) connected to the internal transistor is connected to the junction of those two resistors. When power is first applied to the circuit, the capacitor will be uncharged, therefore, both the trigger and threshold inputs will be near zero volts. The lower comparator sets the , control flp flop flop causing the output to switch high. That also turns off transistor. That allows the capacitor to begin charging through Ra and Rb. As soon as the charge on the capacitor reaches 2/3 of the supply voltage, the upper comparator will trigger causing the flip-flop to reset. That c output to switch low. Transistor also conducts. The effect of transistor conducting causes res Rb to be connected across the external capacitor. Resistor Rb is effectively connected to ground through internal transistor. The result of that is that the capacitor now begins to discharge through Rb. As soon as the voltage across the capacitor reaches 1/3 of the supply voltage, the lower comparator is triggered. That again causes the control flip-flop to set and the output to go high. Transistor cuts off and again the capacitor begins to charge. That cycle continues to repeat with the capacitor alternately charging and discharging, as the comparators cause the flip-flop to be repeatedly set and reset. The resulting output is a continuous stream of rectangular pulses. The frequency of operation of the astable circuit is dependent upon the values of Ra, Rb, and C. The frequency can be calculated with the formula: f = l/(.693 x C x (Ra + 2 x Rb)) The Frequency f is in Hz, Ra and Rb are in ohms, and C is in farads. The time duration between pulses is known as the 'period’, and usually designated with a 't'. The pulse is on for t l seconds, then off for t2 seconds. The total period (t) is tl +t2. That time interval is related to the frequency by the familiar relationship. f=1/t or t= 1/f The time intervals for the on and off portion of the output depend upon the values of Ra and Rb, The ratio of the time duration when the output pulse is high to the total, period is k nown as the duty-cycle. The duty-cycle can be calculated with the formula: D= (t1)/t = (Ra+Rb) / (Ra+2Rb)
You can calculate t1 and t2 times with the formulas below: tl = 0.693 (Ra+Rb) C t2 = 0.693 (Rb) C
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The 555, when connected, can produce duty-cycles in the range of approximately 55 to 95%. A duty-cycle of 80% means that the output pulse is on or high for 80% of the total period. The duty-cycle can he adjusted by varying the values of Ra and Rb.
4.6.2 PIN CONFIGURATION OF 555 TIMER
Fig 10
•
Pin 1 (Ground):
The ground (or common) pin is the most-negative supply potential of the device, which is normally connected to circuit common (ground) when operated from positive supply voltages. •
Pin 2 (Trigger):
This pin is the input to the lower comparator and is used to set the latch, which in turn causes the output to go high. This is the beginning of the timing sequence in monostable operation. Triggering is accomplished by taking the pin from above to below a voltage level of 1 3 V+ (or, in general, one-half the voltage appearing at pin 5). The action of the trigger input is level-sensitive, allowing slow rate-of-change waveforms, as well as pulses, to be used as trigger sources. The trigger pulse must be of shorter duration than the time interval determined by the external R and C. If this pin is held low longer than that, the output will remain high until the trigger input is 34
driven high again. One precaution that should be observed with the trigger input signal is that it must not remain lower than 1/3 V+ for a period of time longer than the timing cycle. If this is allowed to happen, the timer will re-trigger itself upon termination of the first output pulse. Thus, when the timer is driven in the monostable mode with input pulses longer than the desired output pulse width, the input trigger should
effectively he shortened by differentiation. The minimum-allowable pulse width for triggering is somewhat dependent upon pulse level, but in general if it is greater than the luS (micro-Second), triggering will be reliable. A second precaution with respect to the trigger input concerns storage time; in the lower comparator. This portion of the circuit can exhibit normal turn-off delays of several microseconds after triggering; that is, the latch can still have a trigger input for this period of time after the trigger pulse. In practice, this means the minimum monostablc output pulse width should be in the order of l0uS to prevent possible double triggering due to this effect. The voltage range that can safely be applied to the trigger pin is between V+ and ground, A dc current, termed the trigger current, must also flow from this terminal into the external circuit. This current is typically 500nA (nano-amp) and will define the upper limit of resistance allowable from pin 2 to ground. For an astable configuration operating at V+ = 5 volts, this resistance is 3 Mega-ohm; it can be greater for higher V+ levels.
•
Pin 3 (Output):
The output of the 555 comes from a high-current totem-pole stage made up of transistors Q20 -Q24. Transistors Q21 and Q22 provide drive for source-type loads, and their Darlington connection provides a high-state output voltage about 1.7 volts less than the V+ supply level used. Transistor Q24 provides current-sinking capability for low-state loads referred to V+ (such as typical TTL inputs). Transistor Q24 has a low saturation voltage, which allows it to interface directly, with good noise margin, when driving current-sinking logic. Exact output saturation levels vary markedly with supply voltage, however, for both high and low states. At a V+ of 5 volts, for instance, the low state Vce(sat) is typically 0.25 volts at 5 mA. Operating at 15 volts. however, it can sink 200mA if an output-low voltage level of 2 volts is allowable (power dissipation should be considered in such a case, of course). Highstate level is typically 3.3 volts at V+= 5 volts; 13.3 volts at V+= 15 volts. Both the rise and fall times of the output waveform are quite fast, typical switching times being l00nS. The state of the output pin will always reflect the inverse of the logic state of the latch, and this tact may be seen by examining. Since the latch itself is not directly accessible, this relationship may be best explained in terms of latch-input trigger conditions. To trigger the output to a high condition, the trigger input is momentarily taken from u higher to a lower level. see "Pin 2 - Trigger". This causes the latch to be set and the output to go high. Actuation of the lower comparator is the only manner in which the output can be placed in the high state. The output eau he returned to a low state by causing the threshold to go from a lower to a higher level [see "Pin 6 -Threshold], which resets the latch. The output can also be made to go low by taking the reset to a low state near ground [see "Pin 4 - Reset"), The output
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voltage available at this pin is approximately equal to the Vcc applied to pin 8 minus 1.7V. •
Pin 4 (Reset):
This pin is also used to reset the latch and return the output to a low state. The reset voltage threshold level is 0.7 volt, and a sink current of 0.lmA from this pin is required to reset the device. These levels are relatively independent of operating V+ level; thus the reset input is TTL. compatible for any supply voltage. The reset input is an overriding function; that is, it will t'oree the output to a low state regardless of the state of either of the other inputs. U may thus be used to terminate an output pulse prematurely, to gate oscillations from "on" to "off", ete. Delay time from reset to output is typically on the order of 0.5 uS, and the minimum reset pulse width is 0.5 uS. Neither of these figures is guaranteed, however, and may vary from one manufacturer to another. In short, the reset pin is used to reset the flip-flop that controls the state of output pin 3. The pin is activated when a voltage level anywhere between 0 and 0.4 volt is applied to the pin. The reset pin will force the output to go low no matter what state the other inputs to the flip-flop are in. When not used, it is recommended that the reset input be tied to V+ to avoid any possibility of false resetting. •
Pin 5 (Control):
This pin allows direct access to the 2/3 V+ voltage-divider point, the reference level for the upper comparator. It also allows indirect access to the lower comparator, as there is a 2:1 divider (R8 - R9) from this point to the lower-comparator reference input, Q13. Use of this terminal is the option of the user, but it does allow extreme flexibility by permitting modification of the timing period, resetting of the comparator, etc. When the 555 timer is used in a voltage-controlled mode, its voltage- controlled operation ranges from about 1 volt less than v+ down to within 2 volts of ground (although this is not guaranteed). Voltages can be safely applied outside these limits, but they should be confined within the limits of V+ and ground for reliability. By applying a voltage to this pin, it is possible to vary the timing of the device independently of the RC network, the control voltage may be varied from 45 to 90% of the Vcc in the monostable mode, making it possible to control the width of thc output pulse independently of RC. When it is used in the astable mode to control voltage can bevaried from 1.7V to the full Vcc varying the voltage in the astable mode will produce a frequency modulated (FM) output. In the event the control-voltage pin is not used, it is recommended that it be bypassed., to ground, with a capacitor of about 0.01uF (l0nF) tor immunity to noise, since u is a comparator input, This fact is not obvious in many 555 circuits since I have seen many circuits with 'no pin-5' connected to anything, but this is the proper procedure. The small ceramic cap may eliminate false triggering. •
Pin 6 (Threshold):
Pin 6 is one input to she upper comparator (the other being pin 5) and is used to reset the latch. which causes the output to go low. Resetting via this terminal is accomplished by taking the terminal from below to above a voltage level of 2/ 3 V+ (.the normal voltage on pin 5). The action of the threshold pin is level sensitive, allowing 36
slow rate-of-change waveforms. The voltage range that can safely be applied to the threshold pin is between V+ and ground. A dc current, termed the Threshold current, must also flow into this terminal from the external circuit. This current is typically 0.l uA and will define the upper limit of total resistance allowable from pin 6 to V+. For either timing configuration operating at V+ = 5 volts, this resistance is 16 Mega-ohm. For 15 volt operation, the maximum value of resistance is 20 Mega Ohms.
•
Pin 7 (Discharge):
This pin is connected to the open collector of a n-p-n transistor (Q14), the emitter of which goes to ground, so that when the transistor is turned "on", pin 7 is effectively shorted to ground. Usually the timing capacitor is connected between pin 7 and ground and is discharged when the transistor turns "on". The conduction state of this transistor is identical in timing to that of the output stage . It is "on" (low resistance to ground) when the output is low and "off (high resistance to ground) when the output is high. In both the monostable and astable time modes, this transistor switch is used to clamp the appropriate nodes of the timing network to ground. Saturation voltage is typically below l00mV (milli-Volt) for currents of 5 mA or less, and off-state leakage is about 20nA (these parameters are not specified by all manufacturers, however). Maximum collector current is internally limited by design, thereby removing restrictions on capacitor size due to peak pulse-current discharge. In certain applications, this open collector output can be used as an auxiliary output terminal, with current-sinking capability similar to the output (pin 3). • Pin 8 (V+): The V+ pin (also referred to as Vcc) is the positive supply voltage terminal of the 555 timer IC. Supply-voltage operating range for the 555 is +4.5 volts (minimum) to +16 volts (maximum), and it is specified for operation between +5 volts and +15 volts. The device will operate essentially the same over this range of voltages without change in timing period. Actually, the most significant operati onal difference is the output drive capability, which increases for both current and voltage range as the supply voltage is increased. Sensitivity of time interval to supply voltage change is low, typically 0.1% per volt. There are special and military devices available that operate at voltages as high as 18 volts.
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4.7 IC 4017 DECADE COUNTER The IC 4017 is a versatile IC of the CMOS family which has got wide range of applications. Internally it consists of a 10 stage decade counter/divider. When a clock pulse is applied to it externally, its outputs become logic 'hi' and 'lo' sequentially (one after the other). It has got numerous applications, for example in circuits where sequential switching are required and also in decorative ornamental lighting, where the lights are switched on and off sequentially giving it a 'running' effect. 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 l evels are applied to the RESET and ENABLE inputs. The counting action of the 4017 can be understood from the graph below:
Fig. 11
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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 we 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 think of lots of useful applications. Internally, the 4017 contains five bistable subunits. These are interconnected in a pattern known as a Johnson counter. The outputs of the bistables are decoded to give the ten individual outputs.
4.7.1 Pin Configurations of IC 4017 :
As can be from the diagram above, the IC 4017 is a 16 pin dual in line package IC. Pin 1 can be identified from a small depressed circle at the extreme left corner of the IC, or simply one can always remember, the printed side of the IC facing towards you, the pin beginning from the left side of the semi circle notch of every IC is pin 1. Pin configurations of this IC are as follows:
Fig. 12
Pin 1 to pin 7 and pins 8, 9, 10 are all the outputs of the IC. Pin 16 is for the positive supply and pin 8 is ground. Pin 15 is the reset point of the IC. A logic '0' to this pin (or by connecting it to the ground), gives a green signal to the IC, so that it can function. A logic '1' or a positive supply here will bring its proceedings to a stand still and will reset it. At
39
this position pin 3 of the IC4017 stays at logic '1' where as all other outputs are logic 'lo'. Pin 14 is the clock input of the IC 4017. An external clock signal to this point will make a logic '1' to proceed sequentially, beginning from pin 3 and ending at pin 11. The cycle is repeated as long as the clock persists at pin 14. The period of time each output stays logic '1' will depend on the time period of the positive peaks of the clock signal. With the rising edge of every clock pulse, the 'logic 1' will shift from one output to the other serially. Pin 13 is the clock enable point. A logic '1' to this pin will stop the IC 4017 from proceeding and its output will freeze at that instant at the particular output. Even if the clock signal at pin 14 is ON, the output cant shift as long as pin 13 is held at logic'1', therefore this point should be grounded. On the contrary if pin 14 is held at logic'1' and clock signal is applied at pin 1, every falling edge of the pulse will make the outputs to change state sequentially.
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4.8A.C POWER SUPPLY A power supply is a device that supplies electric power to an electrical load. The term is most commonly applied to electric power converters that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (mechanical, chemical, solar) to electrical energy. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source. Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from:
Electrical energy transmission systems. Common examples of this include power supplies that convert AC line voltage to DC voltage. Energy storage devices such as batteries and fuel cells. Electromechanical systems such as generators and alternators. Solar power.
A power supply may be implemented as a discrete, stand-alone device or as an integral device that is hardwired to its load.
Fig. 13
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4.8.1 CIRCUIT DIAGRAM of AC POWER SUPPLY
The above circuit uses 220V A.C as input, a 6V centre tapped, step down transformer for decreasing the high voltage of Alternating current to very low voltage, Bridge rectifier for converting the alternating current into the Direct current and a polar capacitor to store the direct current in it, and thus, gives us the DC output of very low voltage (9-12 V) which is safe for operating circuits with low rating voltage.
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4.9 PRINTED CIRCUIT BOARD (PCB)
Fig. 14
A Printed Circuit Board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non conductive substrate . Alternative names are Printed Wiring Board ( PWB ) , and Etched Wiring Board . A PCB populated with the electronic components is a Printed Circuit Assembly (PCA) , also known as a Printed Circuit Board Assembly (PCBA). PCB is a component made of one or more layers of insulating materials with electrical conductors. The insulator is made of various materials that are based on glass ,ceramics or plastic. PCBs rugged inexpensive and can be highly reliable. The initial cost of the PCB are higher than the either wire- wrapped or point-to-point constructed circuits , but are much cheaper and faster for high- volume production. During manufacturing, the portion of conductors that are not needed are etched off, leaving printed circuit that connect electronic components. Much of the electronics industry‘s PCB design, assembly and quality control needs are set by standards that are published by the IPC Organization. The generic standard for PCB is IPC-2221A. This standard provides rules for manufacturability and quality such as requirement for material properties, criteria for surface plating conductors thickness, component placement, and dimensioning and tolerance rules.
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While routing , the conductor width should be chosen based on selected temperature rise at rated current. The spacing between PC traces is determined by the peak working voltage , type of circuit and safety requirements. Good PCB layout techniques require understanding of effects of non- zero impedance and coupling of the signals.
4.9.1 Materials Conducting layers are typically made of thin copper foil. Insulating materials have the wider scale: phenolic paper, glass fiber and different plastics (poly-eithrothemin) are commonly used. Usually PCB factories use prepregs (pre impregnated), which are a combination of glass fibre mat, non woven material and resin. Copper foil and materials used in the PCB industry are FR-2 (Phenolic Cotton Paper) , FR-3 (Cotton Paper and Epoxy) , FR-4 (Woven Glass and Epoxy) , FR-5 (Woven Glass and Epoxy), FR-6 (Matte Glass and Polyester) , G-10 (Woven Glass and Epoxy) , CEM1 (Cotton Paper and Epoxy) , CEM-2 (Cotton Paper and Epoxy) , CEM-3 (Woven Glass and Epoxy) , CEM-4 (Woven Glass and Epoxy) and CEM -5 (Woven Glass and Polyester).
Procedure of Making PCB: Building PCB in the proper manner is really an art, something that must be practiced and learned through the trial and error. It is not difficult. The main thinks is to remember to take each step slowly and carefully according to the instructions given in making since that everything at it should be before proceeding further. Basic Techniques And Designing of the PCB Layout:4.9.1.1: Introduction:
Printed circuit board making processes are intended for two sees: Making a prototype and for small production runs. User includes design engineers, experimenters as well as students and hobbyists. Instructors are invited to copy these material freely. These are a number of methods for producing a printed circuit board described herein. Read the following synopsis to determine which method best suit your projects. Most likely, you will eventually use more than one of the following methods: 4.9.1.2: The Methods:
The DIRECT ETCH method is usually quickest way to produce one small circuit board. All beginners should try this method. Not recommended when you need to make many boards or for circuit with numerous components.
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4.9.1.3: Etching the Board:
The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides , (creating a ―blank PCB‖) then removing unwanted copper after applying a temporary mask (e.g. By etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex of multiple electroplating steps. 4.9.1.4: Lamination:
Some PCBs have trace layer inside the PCB and are multi-layer PCBs. These are formed by bonding together separately etched thin boards. 4.9.1.5: Tools:
The electronics workbench is an actual place of or with comfortably and conveniently and should be supplied with the compliment of those tools must often must used in the PCB building. Probably the most important device is soldering tool. Other tool which should be at the electronic work bench include a pair of needle nose pliers, diagonal wire cutter, a small knife (blade), an assortment of screw driver , nut driver , few nuts and bolts , electrical tape etc. diagonal wire cutter wick be used to cut away any excess lead length from the copper side of PCB and to cut section of the board after the circuit is complete. The needle nose pliers are most often used to end the wire leads and wrap them in order to form a strong mechanical connection. 4.9.1.6: Drilling:
Holes or vias through a PCB are typically drilled with tiny drikks bit made of solid. The drilling is performed by automated drilling machine with placement controlled by a drill tape or drill file. These computer-generated files are also called numericall y controlled drills (NCD) files. The drill file describe the location and the size of each drilled hole.
When very small vias are required, drilling with mechanical bits is costly because of high rates of wear and breakage. In this case, the vias may be evaporated by lasers. Laser-drilled vias typically have an inferior surface finish inside the hole. These holes are called micro vias. It is also possible with controlled-depth drilling, laser drilling or by pre-drilling the individual sheets of the PCB before lamination, to produce holes that connect only some of the copper layers, rather than passing through the entire board. These holes are called blind vias when they connect internal copper layer to an outer layer or buried vias when they connect two or more internal copper layers and no outer layers. 45
The walls of the holes, for boards with 2 or more layers, are plated with copper to form plated-through holes that electrically connect the conducting layers of the PCB. For multi layer boards those with 4 layers or more, drilling typically produces a smear comprised of the bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process or by plasma-etch.
4.9.2 Soldering Soldering is a process of joining together two metallic parts. It is actually a process of function in which an alloy, the solder, with a comparatively low melting point penetrates the surface of the metal being joined and makes a firm joint between them on cooling and solidifying. Before discussing the way of proper soldering, we should know the complete kit of soldering station. 4.9.2.1: Method of Soldering:
Mount components at their appropriate place bend the leads slightly out wants to prevent them from falling out when the board is turned over for soldering. Now cut the leads so that you may solder them easily. Apply a small amount of flux at these components leads with the help of a screwdriver. Now fix the bit or iron with small amount of solder and flow freely at the point and the PCB copper track at the same time. A good solder joint will appear smooth and shiny. If all appear well you may continue to the next solder connections. 4.9.2.2: Tips of Good Soldering:
Use a right type of the soldering iron. A small efficient soldering iron (about 10-25 watt with 1/8 or 1/4 inch tip) is ideal for this work. Keep the hot tip of soldering iron on a piece of metal so excess heat is dissipated. Make sure that connection to the soldered is clean. Wax frayed insulation and other substances cause poor soldering connection. Clean the leads, wires, tags etc before Soldering. Use just enough solder the lead to be soldered. Excess solder can cause short circuit. Use sufficient heat. This is the essence of good soldering. Apply enough heat to the component lead. You are not using heat , if the solder barely melts and forms a round ball flaky solder. A good solder joint will look smooth, shining and spread type. The difference between good and bad soldering just a few seconds extra with a hot iron applied firmly.
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5. WORKING PRINCIPLE
The circuit is self explanatory by its name and can be used to control traffic in public places or to demonstrate traffic parks. The given circuit of the Traffic Light control is a combination of the circuits one is a square wave generator, to provide the pulses and the other is the counter that counts the incoming pulses. Here, the 555 IC works as the square wave generator. The IC is widely used and popular one. It works as astable multivibrator. When the IC receives the supply, the square wave output is available at the pin no. 3 and a regular interval pulse become available continuously. The time interval can be adjusted by varying the preset. The pulse is then fed to the pin no. 14 (input pin) of 4017 IC. This IC is work as a counter IC. 4017 IC is the heart of the circuit, which is a decade counter. This counter has 10 outputs. The diodes are connected to the output of the 4017 IC. Now the Red LED is connected with the first four output of the counter (i.e. Q0- Q3), then straight lane Green LED is connected to the next five output (Q4- Q8) of the counter, whereas the right turn Green LED is connected with the first three output of the counter from which straight lane green LED is connected (i.e. Q4- Q6), the last output of the counter (Q9) is connected with the Yellow LED. Now, the Red LED will glow first, then straight lane as well as right turn Green LED will glow after few seconds the right turn Green LED will be switched off and the straight lane Green LED will remain glow for few seconds. At last, the Yellow LED will glow just for 4-5 seconds then the Red LED will again glow. Thus, the sequence will continue. By changing the value of capacitor, connected at the pin no. 6 and pin no. 2 of the 555 timer IC, as well as by varying the value of 100 Kilo Ohms Preset, the time interval of glowing of lights can be increased or decreased.
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6. ADVANTAGES OF TRAFFIC LIGHTS • Reduction in normal recurring. • Significantly enhanced operational tools congestion to effectively manage traffic incidents. • It improved public transport service. • Reduction in emergency response limes and safer travel. • Improve traffic guidance and traffic flow • Reduce fuel consumption • Increase safety. • They increase the traffic-handling capacity of the intersection • Less cost.
7. DISADVANTAGES OF TRAFFIC LIGHTS
• Excessive delay may be caused. • These unnecessary delay results in significant fuel waste and higher motorist costs. • Disobedience of signals.
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8. APPLICATIONS • Ramp metering. • Timers.
• Fire station or medical emergency entrance. • At the entrance and exit of some car washes. • At the landing-stage of a ferry and aboard the ferry.
9. FUTURE SCOPE 1. We can increase the efficiency by using microprocessors (8086). 2. We can use this as Remote traffic Controller.
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REFERENCES
Malvino and Albert Paul ―Electronics Principles‖, Sixth Edition, 878-895.
R.P. Jain, Modern Digital Electronics, Second Edition, 296-305.
Websites Referred: http:// www.elprocus.com/ic-4017-pin-configuration http:// www.electronic designwork.com http:// www.electronicsforu.com http://www.electronicsclub.info http:// www.wikipedia.com
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APPENDIX- 1 (DATASHEETS) 1.
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