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COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

COCHIN UNIVERSITY COLLEGE OF ENGINEERING KUTTANADU

MINI PROJECT REPORT

ON

“AUOMATIC TRAFFIC SIGNAL CONTROLLER”

Submitted in partial fullfilment of the requirament for the award of degree of

BACHELOR OF TECHNOLOGY IN

ELECTRONICS & COMMNICATION ENGINEERING

Submitted By

RAKESH KUMAR(ECE,S6) Reg. No:-00600697

DEPARTMENT OF ELECTRONICS & COMMNICATION

COCHIN UNIVERSITY COLLEGE OF ENGINEERING

KUTTANADU,ALAPPUZHA6885045

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COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

COCHIN UNIVERSITY COLLEGE OF ENGINEERING KUTTANADU

DEPARTMENT OF ELECTRONICS & COMMNICATION

CERTIFICATE

This is to certify that the project report on “AUTOMATIC TRAFFIC SIGNAL CONTROLLER” is a bonafide work done by

RAKESH KUMAR(ECE,S6 )

Reg. No:-00600697

During the year2009 in the partial fulfillments of the requirements for the award of the degree of Bachelor of Technology in ELECTRONICS & COMMUNICATION of Cochin University College of Engineering, Kuttanadu during the academic year 2009

Coordinator Project Guide Head of Department

DEPARTMENT OF ELECTRONICS & COMMNICATION

COCHIN UNIVERSITY COLLEGE OF ENGINEERING ,KUTTANADU

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Acknowledgement:-

Dreams never turn to reality unless a lot of effort and hard work is put in to it. And no effort bears fruit in the absence of support and guidance. It takes a lot of effort to work your way through this goal and having someone to guide you and help you is always a blessing. I would like to take this opportunity to thank a few who were closely involved in the completion of this project. Ingenuity and popular guidance are inevitable for successful completion of a project. I am indebted to all sources that helped me in working out this project at each steps of its progress.

First and foremost Mr. Oomen Samuel principal, for granting permission to proceed with the project and providing the necessary facilities/ I sincerely thanks Mrs. Deepa R. the Head of department, Department of Electronics & Communications, for the valuable help provided to me.In particular I extremely grateful to Project coordinator Mrs. Rijimol mathew and Project guide Mrs. Lekshmy Gopal lecture, Department of Electronics & Communication for their valuable suggestion and proper guidance to complete my project. Above all I thank the lord almighty for giving me all the confidence and ability to achieve this dream!

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…DEDICATED TO OUR PARENTS AND TEACHERS

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Automatic traffic signal controller

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ABSTRACT

AUTOMATED TRAFFIC SIGNAL CONTROLLER

This automated traffic signal controller can be made by suitably programming GAL device. Its main features are:- 1. The controller assumes equal traffic density 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 Seconds (or multiples thereof) each.

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CONTENTS: 1. INTRODUCTION

History Technology

2. THE PROJECT

Functional Block Diagram Circuit Diagram PCB Layout Components Used The Situation The solution to the problem

3. THE WORKING

The working of system

4. Description of Major Components

555 Timer-Bistable Multivibrator 7408 IC 7432 IC 7411 IC 7404 IC 74160 IC Resistors &Capacitors Light Emitting Diode

5. Advantages

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Now a days 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.

INTRODUCTION:-

The automatic traffic controller automatically switches on the four way junction for 15 seconds for direction control.

The main circuit components used are 555-Timer and 4-bit binary synchronous counter (74160). 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 different Boolean function of logic gate.

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HIsTORy: 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 January 1869, 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 lights. On 5 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 colors, red and green, and a buzzer, based on the design of James Hoge, to provide a warning for color changes. The design by James Hoge allowed police and fire stations to control the signals in case of emergency. The first four-way, 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 Wolverhampton in 1927.

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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.

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TECHNOLOGy: Optics and lighting:-

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 replacement, 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. • 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 rapidly 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

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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 city's 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, color-changing LEDs are in their infancy and may surpass the multi-color 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).

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THE

PROJECT

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CIRCUIT DIAGRAM:

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PCB LAYOUT:-

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COMPONENTS REQUIRED:-

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Components

Specification Quantity

1.555 Timer 4.5 to 15 V, 200mA 1 2.Capacitors 10µf,16v

0.1µf 1 1

3.Resistors 240kΩ 270kΩ 470Ω

1 1 18

4.LED Green Red Yellow

10 4 4

5.IC 74160 7432 7404 7411 7408

1 2 1 3 1

6.IC base 8Pin 14Pin 16Pin

1 7 1

6.connector SIP2 SIP3 SIP4

5 2 2

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3. The working of the system:

The corresponding circuit automatically controls the traffic signal during the day as well as nights.

In this system there are one 555 timer and one 74160 synchronous 4 bit counter, which is controlling whole device. Along with there are some electronic equipments like 7404, 7408, 7411 gate, capacitor, resistor, LED (yellow, green, red) etc.

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 seconds (or multiples thereof) each.

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flow of traffic in all possible directions: Fig. above shows the flow of traffic in all permissible directions during the eight time units of 8 seconds each. For the left- and right turning traffic and pedestrians crossing from north to south, south to north, east to west ,and west to east, only green and red signals are used.

TABLE I

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Table I shows the simultaneous states of the signals for all the traffic. Each row represents the status of a signal for 8 seconds. As can be observed from the table, the ratio of green, yellow, and red signals is 16:8:40 (=2:1:5) for the straight moving traffic. For the turning traffic the ratio of green and red signals is 8:56 (=1:7), while for pedestrians crossing the road the ratio of green and red signals is 16:48 (=2:6) In Table II (as well as Table I) X, Y, and Z are used as binary variables to depict the eight states of 8 seconds each. Letters A through H indicate the left and right halves of the roads in four directions as shown in Fig. 1. Two letters with a dash in between indicate the direction of permissible movement from a road. Straight direction is indicated by St, while left and right turns are indicated by Lt and Rt, respectively. The Boolean functions for all the signal conditions are shown in Table II. The left- and the right-turn signals for the traffic have the same state, i.e. both are red or green for the same duration, so their Boolean functions are identical and they should be connected to the same control output. The circuit diagram for realizing these Boolean functions is shown in circuit diagram. Timer 555 (IC1) is wired as an astable multivibrator to generate clock signal for the 4-bit counter 74160 (IC2). The time duration of IC1 can be adjusted by varying the value of resistor R1, resistor R2, or capacitor C2 of the clock circuit. The ‘on’ time duration T is given by the following relationship: T = 0.693C2(R1+R2) IC2 is wired as a 3-bit binary counter by connecting its Q3 output to reset pin 1 via inverter N1. Binary outputs Q2, Q1, and Q0 form variables X, Y, and Z, respectively. These outputs, along with their complimentary outputs X’, Y’, and Z’, Respectively, are used as inputs to the rest of the logic circuit to realize various outputs satisfying Table I. You can simulate various traffic lights Using green, yellow, and red LEDs and feed the outputs of the circuit to respective LEDs via current-limiting resistors of 470 ohms each to check the working of the circuit. Here, for turning traffic and pedestrians crossing the road, only green signal is

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made available. It means that for the remaining period these signals have to be treated as ‘red’ in practice, the outputs of Fig. 2 should be connected to operate high – power bulbs. Further, if a particular signal condition (such as turning signal) is not applicable to a given road, the output of that signal condition should be connected to green signal of the next state (refer Table I).

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The traffic signals can also be controlled manually, if it desired. Any signal state can be established by entering the binary value corresponding to that particular state into the parallel input pins of the 3-bit counter. Similarly, the signal can be reset at any time by providing logic 0 at the reset pin (pin 1) of the counter using an external switch. A software program to verify the functioning of the circuit using a PC is given below. (Source code and executable file will be provided in the next month’s EFY-CD.).

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Generic array logic (GAL Devices)

An innovation of the PAL was the generic array logic device, or GAL, invented by lattice semiconductor in 1985. This device has the same logical properties as the PAL but can be erased and reprogrammed. The GAL was an improvement on the PAL because one device was able to take the place of many PAL devices or could even have functionality not covered by the original range. The GAL is very useful in the prototyping stage of a design, when any bugs in the logic can be corrected by reprogramming. GALs are programmed and reprogrammed using a PAL programmer, or by using the in-circuit programming technique on supporting chips.

Lattice GALs combine CMOS and electrically erasable (E^2) floating gate technology for a high-speed, low-power logic device.

A similar device called a PEEL (programmable electrically erasable logic) was introduced by the International CMOS Technology (ICT) corporation.

The GAL family includes fourteen distinct product architectures, with a variety of performance levels specified across commercial, industrial, and military (MIL-STD883) operating ranges, to meet the demands of any system logic design

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These GAL products can be segmented into two broad categories:

Base products

Extension products

Base Products - Aimed at providing superior design alternatives to bipolar PLDs, these five architectures replace over 98% of all bipolar PAL devices. The GAL16V8 and GAL20V8 replace forty-two different PAL devices. The GAL22V10, GAL20RA10, and GAL20XV10 round out the base products. These GAL devices meet and, in most cases, beat bipolar PAL performance specifications while consuming significantly lower power and offering higher quality and reliability via Lattice’s electrically reprogrammable E2CMOS technology. High-speed erase times (<100ms) allow the devices to be reprogrammed quickly and efficiently.

Extension Products - These products build upon the Base GAL product features to provide enhanced functionality including innovative architectures (GAL18V10 GAL26CV12, GAL6001/6002), 64mA high output drive (GAL16VP8 & GAL20VP8), “Zero power” operation (GAL16V8Z/ZD & GAL20V8Z/ZD) and In-System Programmability.

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A Product for any System Design Need

Lattice GAL products have the performance, architectural features, low power, and high quality to meet the needs of the most demanding system designs. . Introduction to GAL Device Architectures:-

The GAL 16V8 and GAL 20V8

The GAL16V8 (20-pin) and GAL20V8 (24-pin) provide the highest speed performance available in the PLD market at 3.5 ns and 5.0 ns respectively. CMOS circuitry allows the GAL16V8 and GAL20V8 low power devices to consume just 75mA typical Icc, which represents a 50% savings in power when compared to bipolar counterparts Quarter power versions save even more at 45mAlcc. The GAL16V8 is a 20-pin device which contains eight dedicated input pins and eight I/O pins. The GAL20V8 is a 24-pin version of the 16V8 device with 12 dedicated input pins and eight I/O pins. Their generic architecture provides maximum design flexibility by allowing the Output Logic Macro cell (OLMC) to be configured by the user. An important subset of the many architecture configurations possible with the GAL16V8 and GAL20V8 are the standard PAL architectures. Providing eight OLMCs with eight product terms each, GAL16V8 and GAL20V8 devices are capable of emulating virtually all PAL architectures with full function/fuse map/parametric compatibility.

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Output Logic Macro cell

There are three OLMC configuration modes possible in GAL16V8 and GAL20V8 devices: registered, complex, and simple. You cannot mix modes; all OLMCs are either simple, complex, or registered (in registered mode, the output can be combinational or registered).

The outputs of the AND array are fed into an OLMC, where each output can be individually set to active high or active low, with either combinational (asynchronous) or registered (synchronous) configurations. A common output enable is connected to all registered outputs, or a product term can be used to provide individual output enable control for combinational outputs in the registered mode or combinational outputs in the complex mode. There is no output enable control in the simple mode. The OLMC provides the designer with maximum output flexibility in matching signal requirements, thus providing more functionality than possible with standard PAL devices.

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4. INTEGRaTED CIRCUITs (CHIPs)

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 strip board 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.

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

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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.

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THE 555 TIMER – NE 555 DEsCRIPTION:- The 8-pin 555 timer must be one of the most useful chips ever made. This is a highly stable device for generating accurate time delay or oscillation .With just a few external components it can be used to many circuits, not all of them that involve timing!

A single 555 timer can provide time delay ranging from microseconds to hours whereas counter time can have maximum timing range of days. The 555 can be used with a supply voltage (Vs) in the range 4.5 to 15V (18 V absolute) and can drive load up to 200 mA. Because of wide range of supply voltage, the 555 timer is versatile and easy to use in various applications.

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Inputs of 555 Timer:-

Trigger input: - When <1/3 Vs (‘active low’) this makes the output high (+Vs). It monitors the discharging of the timing capacitor in an astable circuit. It has a high input impedance>2M.

Threshold input: -When > 2/3 Vs (‘active high’) this makes the output low (0V)*.It monitors the charging of the timing capacitor in astable and monostable circuits. It has a high input impedance>10M.

*Providing the trigger input is <1/3 Vs (the trigger inputs overrides the threshold input).

Reset input: -When less than about 0.7 V (‘active low’) this makes the output low (0V), overriding other inputs. When not required it should be connected o + Vs. It has an input impedance of about 10 K.

Control input: -This can be used to adjust the threshold voltage which is set internally to be 2/3 Vs. Usually this function is not required and the control input is connected to 0v with a 0.01 µf capacitor to eliminate noise. It can be left unconnected if noise is not a problem.

The discharge pin: - It is not an input, but it is listed here for convenience. It is connected to 0Vwhen the timer output is high and is used to discharge the timing capacitor ion astable and monostable circuits.

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Output of 555:-

The 555 output (pin 3) can sink and source up to 200mA. This is more than most chips and it is sufficient to supply many output transducers directly, including LEDs (with a resistor in series), low current lamps, piezo transducers, loudspeakers (with a capacitor in series), relay coils (with diode protection) and some motors (with diode protection). The output voltage does not quite reach 0V and + Vs, especially if a large current is flowing.

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Functional block diagram of 555 IC

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SAMPLE GRAPH:

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APPLICATIONS:- Precision timing Pulse generation Sequential timing Time delay generation Pulse width modulation

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Function table

RESET TRIGGER VOLTAGE

THRESHOLD VOLTAGE

OUTPUT DISCHARGE SWITCH

Low irrelevant irrelevant Low On High < 1/3 Vdd irrelevant High Off High > 1/3 Vdd > 2/3 Vdd Low On High > 1/3 Vdd < 2/3 Vdd As previously

established

:-- voltage level shown are nominal

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DESCRIPTION

TEMPERATURE RANGE

ORDER CODE

DWG #

8-Pin Plastic Small Outline (SO) Package

0 to +70 °C

NE555D SOT96-1

8-Pin Plastic Dual In-Line Package (DIP)

0 to +70 °C

NE555N SOT97-1

8-Pin Plastic Small Outline (SO) Package

–40 °C to +85 °C

SA555D SOT96-1

8-Pin Plastic Dual In-Line Package (DIP)

–40 °C to +85 °C

SA555N SOT97-1

8-Pin Plastic Dual In-Line Package (DIP)

–55 °C to +125 °C

SE555CN SOT97-1

ABSOLUTE MAXIMUM RATINGS:--

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SYMBOL PARAMETER RATING UNIT SYMBOL PARAMETER RATING UNIT VCC Supply voltage

SE555 NE555, SE555C, SA555

+18 +16

V V

PD Maximum allowable power dissipation1

600 mW

Tamb Operating ambient temperature range NE555 SA555

0 to +70 –40 to +85 –55 to +125

°C °C °C

Tstg Storage temperature range

–65 to +150 °C

TSOLD Lead soldering temperature (10 sec max)

+230 °C

NOTE:

1. The junction temperature must be kept below 125 °C for the D package and below 150°C for the N package. At ambient temperatures above 25 °C, where this limit would be derated by the following factor

2. D package 160 °C/W

N package 100 °C/W

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7408 IC:-

Quad 2-input AND gates: General description:-- This device contains four independent gates each of which performs the logic AND function.

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7432 IC: QUaD 2-INPUT OR GaTE :

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Absolute maximum ratings:- Supply voltage Input voltage 7 V Operating free air temperature range 0°C to 70 °C Storage temperature range -65°C to +150°C

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7411 IC:-

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FUNCTION TaBLE: y = aBC inputs output A B C Y L L L L L L H L L H L L L H H L H L L L H L H L H H L L H H H H Absolute maximum ratings:- Supply voltage 7 V Input voltage 5.5 V Operating free air temperature range 0°C to 70°C Storage temperature range -65°C to +150°C

The ``Absolute Maximum Ratings'' are those values beyond which the safety of the device cannot be guaranteed. The device should not be operated at these limits. The Parametric values defined in the ``Electrical Characteristics’’ table are not guaranteed at the absolute maximum ratings. The ``Recommended Operating Conditions'' table will define the conditions for actual device operations.

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7404 IC:-

Quad 2-input NOT gates: General description:-- This device contains four independent gates each of which performs the logic NOT function. CONNECTION DIAGRAM:-

FUNCTION TABLE: Y=A’ Inputs (A) Output (Y) L H H L

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Absolute maximum ratings:- Supply voltage 7 V Input voltage 7 V Operating free air temperature range 0°C to 70°C Storage temperature range -65°C to +150°C

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74160 IC:

74160-3 synchronous counters

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74160 synchronous decade counter (standard reset) 74161 synchronous 4-bit counter (standard reset) 74162 synchronous decade counter (synchronous reset) 74163 synchronous 4-bit counter (synchronous reset) These are synchronous counters so their outputs change precisely together on each clock pulse. This is helpful if you need to connect their outputs to logic gates because it avoids the glitches which occur with ripple counters.

The count advances as the clock input becomes high (on the rising-edge). The decade counters count from 0 to 9 (0000 to 1001 in binary). The 4-bit counters count from 0 to 15 (0000 to 1111 in binary).

For normal operation (counting) the reset, preset, count enable and carry in inputs should all be high. When count enable is low the clock input is ignored and counting stops.

The counter may be preset by placing the desired binary number on the inputs A-D, making the preset input low, and applying a positive pulse to the clock input. The inputs A-D may be left unconnected if not required.

The reset input is active-low so it should be high (+Vs) for normal operation (counting). When low it resets the count to zero (0000, QA-QD low), this happens immediately with the 74160 and 74161 (standard reset), but with the 74162 and 74163 (synchronous reset) the reset occurs on the rising-edge of the clock input.

Counting to less than the maximum (15 or 9) can be achieved by connecting the appropriate output(s) through a NOT or NAND gate to the reset input. For the 74162 and 74163 (synchronous reset) you must use the output(s) representing one less than the reset count you require, e.g. to reset on 7 (counting 0 to 6) use QB (2) and QC (4).

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Connecting synchronous counters in a chain the diagram below shows how to link synchronous counters such as 74160-3, notice how all the clock (CK) inputs are linked. Carry out (CO) is used to feed the carry in (CI) of the next counter. Carry in (CI) of the first 74160-3 counter should be high.

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CaPaCITORs

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.

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

Capacitor values can be very difficult to find because there are many types of capacitor with different labeling systems!

There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.

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Polarised capacitors (large values, 1µF +)

Examples: Circuit symbol:

Electrolytic Capacitors

Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering.

There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.

Tantalum Bead Capacitors

Tantalum bead capacitors are polarised and have low voltage ratings like electrolytic capacitors. They are expensive but very small, so they are used where a large capacitance is needed in a small size.

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Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. However older ones use a colour-code system which has two stripes (for the two digits) and a spot of colour for the number of zeros to give the value in µF. The standard colour code is used, but for the spot, grey is used to mean × 0.01 and white means × 0.1 so that values of less than 10µF can be shown. A third colour stripe near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+) lead is to the right when the spot is facing you: 'when the spot is in sight, the positive is to the right'.

For example: blue, grey, black spot means 68µF For example: blue, grey, white spot means 6.8µF For example: blue, grey, grey spot means 0.68µF

Unpolarised capacitors (small values, up to 1µF)

Examples: Circuit symbol:

Small value capacitors are unpolarised and may be connected either way round. They are not damaged by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the values of these small capacitors because there are many types of them and several different labelling systems!

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Many small value capacitors have their value printed but without a multiplier, so you need to use experience to work out what the multiplier should be!

For example 0.1 means 0.1µF = 100nF.

Sometimes the multiplier is used in place of the decimal point: For example: 4n7 means 4.7nF.

Capacitor Number Code:

A number code is often used on small capacitors where printing is difficult:

• the 1st number is the 1st digit, • the 2nd number is the 2nd digit, • the 3rd number is the number of zeros to give the

capacitance in pF. • Ignore any letters - they just indicate tolerance and voltage

rating.

For example: 102 means 1000pF = 1nF (not 102pF!)

For example: 472J means 4700pF = 4.7nF (J means 5% tolerance).

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Capacitor Colour Code

A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colours should be read like the resistor code, the top three colour bands giving the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating).

For example:

brown, black, orange means 10000pF = 10nF = 0.01µF.

Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band.

For example:

wide red, yellow means 220nF = 0.22µF.

Polystyrene Capacitors

This type is rarely used now. Their value (in pF) is normally printed without units. Polystyrene capacitors can be damaged by heat when soldering (it melts the polystyrene!) so you should use a heat sink (such as a crocodile clip). Clip the heat sink to the lead between the capacitor and the joint.

Real capacitor values (the E3 and E6 series)

You may have noticed that capacitors are not available with every possible value, for example 22µF and 47µF are readily available, but 25µF and 50µF are not!

Colour Code Colour Number Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 White 9

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Why is this? Imagine that you decided to make capacitors every 10µF giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits and capacitors cannot be made with that accuracy.

To produce a sensible range of capacitor values you need to increase the size of the 'step' as the value increases. The standard capacitor values are based on this idea and they form a series which follows the same pattern for every multiple of ten.

The E3 series (3 values for each multiple of ten) 10, 22, 47, ... then it continues 100, 220, 470, 1000, 2200, 4700, 10000 etc. Notice how the step size increases as the value increases (values roughly double each time).

The E6 series (6 values for each multiple of ten) 10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680, 1000 etc. Notice how this is the E3 series with an extra value in the gaps.

The E3 series is the one most frequently used for capacitors because many types cannot be made with very accurate values.

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Variable capacitors

Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = 0.0001µF). The type illustrated usually has trimmers built in (for making small adjustments - see below) as well as the main variable capacitor.

Many variable capacitors have very short spindles which are not suitable for the standard knobs used for variable resistors and rotary switches. It would be wise to check that a suitable knob is available before ordering a variable capacitor.

Variable capacitors are not normally used in timing circuits because their capacitance is too small to be practical and the range of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is necessary to vary the time period.

Variable Capacitor Symbol

Variable Capacitor Photograph © Rapid Electronics

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REsIsTORs

Example: Circuit symbol:

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 colour 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 Resistor Colour Code

Colour Number Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 White 9

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• The fourth band is used to shows the tolerance (precision) of the resistor, this may be ignored for almost all circuits but further details are given below.

4 Band Resistor Color Codes

Resistance 1kΩ

Tolerance ± 10

%

Black

Brown

Red

Orange

Yellow

Green

Blue

Violet

Grey

White

Gold

Silver

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5 Band Resistor Color Codes

Resistance 1kΩ

Tolerance ± 10%

Black

Brown

Red

Orange

Yellow

Green

Blue

Violet

Grey

White

Gold

Silver

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6 Band Resistor Color Codes

Resistance 1kΩ

Tolerance ± 10%

Temperature coefficient

15PPM/°C

Black

Brown

Red

Orange

Yellow

Green

Blue

Violet

Grey

White

Gold

Silver

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This resistor has red (2), violet (7), yellow (4 zeros) and gold bands. So its value is 270000 = 270 k . On circuit diagrams the is usually omitted and the value is written 270K.

Find out how to make your own Resistor Colour Code Calculator

Small value resistors (less than 10 ohm)

The standard colour code cannot show values of less than 10 . To show these small values two special colours are used for the third band: gold which means × 0.1 and silver which means × 0.01. The first and second bands represent the digits as normal.

For example: red, violet, gold bands represent 27 × 0.1 = 2.7 green, blue, silver bands represent 56 × 0.01 = 0.56

Tolerance of resistors (fourth band of colour code)

The tolerance of a resistor is shown by the fourth band of the colour code. Tolerance is the precision of the resistor and it is given as a percentage. For example a 390 resistor with a tolerance of ±10% will have a value within 10% of 390 , between 390 - 39 = 351 and 390 + 39 = 429 (39 is 10% of 390).

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A special colour code is used for the fourth band tolerance: silver ±10%, gold ±5%, red ±2%, brown ±1%. If no fourth band is shown the tolerance is ±20%.

Tolerance may be ignored for almost all circuits because precise resistor values are rarely required.

Resistor shorthand

Resistor values are often written on circuit diagrams using a code system which avoids using a decimal point because it is easy to miss the small dot. Instead the letters R, K and M are used in place of the decimal point. To read the code: replace the letter with a decimal point, then multiply the value by 1000 if the letter was K, or 1000000 if the letter was M. The letter R means multiply by 1.

For example:

560R means 560 2K7 means 2.7 k = 2700 39K means 39 k 1M0 means 1.0 M = 1000 k

Real resistor values (the E6 and E12 series)

You may have noticed that resistors are not available with every possible value, for example 22k and 47k are readily available, but 25k and 50k are not!

Why is this? Imagine that you decided to make resistors every 10 giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable

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in most circuits. In fact it would be difficult to make resistors sufficiently accurate.

To produce a sensible range of resistor values you need to increase the size of the 'step' as the value increases. The standard resistor values are based on this idea and they form a series which follows the same pattern for every multiple of ten.

The E6 series (6 values for each multiple of ten, for resistors with 20% tolerance) 10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680, 1000 etc. Notice how the step size increases as the value increases. For this series the step (to the next value) is roughly half the value.

The E12 series (12 values for each multiple of ten, for resistors with 10% tolerance) 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, ... then it continues 100, 120, 150 etc. Notice how this is the E6 series with an extra value in the gaps.

The E12 series is the one most frequently used for resistors. It allows you to choose a value within 10% of the precise value you need. This is sufficiently accurate for almost all projects and it is sensible because most resistors are only accurate to ±10% (called their 'tolerance'). For example a resistor marked 390 could vary by ±10% × 390 = ±39 , so it could be any value between 351 and 429 .

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Variable Resistors

Construction:-

Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermet (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available.

Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment.

Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm.

The resistance and type of track are marked on the body: 4K7 LIN means 4.7 k linear track. 1M LOG means 1 M logarithmic track.

Some variable resistors are designed to be mounted directly on the circuit board, but most are for mounting through a hole drilled in the case containing the circuit with stranded wire connecting their terminals to the circuit board.

Standard Variable Resistor Photograph © Rapid Electronics

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Power Ratings of Resistors:-

Electrical energy is converted to heat when current flows through a resistor. Usually the effect is negligible, but if the resistance is low (or the voltage across the resistor high) a large current may pass making the resistor become noticeably warm. The resistor must be able to withstand the heating effect and resistors have power ratings to show this.

Power ratings of resistors are rarely quoted in parts lists because for most circuits the standard power ratings of 0.25W or 0.5W are suitable. For the rare cases where a higher power is required it should be clearly specified in the parts list, these will be circuits using low value resistors (less than about 300) or high voltages (more than 15V).

The power, P, developed in a resistor is given by:

P = I² × R or P = V² / R

where: P = power developed in the resistor in watts (W) I = current through the resistor in amps (A) R = resistance of the resistor in ohms ( ) V = voltage across the resistor in volts (V)

High power resistors (5W top, 25W bottom)

Photographs © Rapid Electronics

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Examples:

• A 470 resistor with 10V across it, needs a power rating P = V²/R = 10²/470 = 0.21W. In this case a standard 0.25W resistor would be suitable.

• A 27 resistor with 10V across it, needs a power rating P = V²/R = 10²/27 = 3.7W. A high power resistor with a rating of 5W would be suitable.

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LIGHT EMITTING DIODEs (LEDs)

Example: 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 are needed for soldering most LEDs.

Testing an LED

Never connect an LED directly to a battery or power supply! It will be destroyed almost instantly 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

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resistor is suitable for most LEDs if your supply voltage is 12V or less. Remember to connect the LED the correct way round!

For an accurate value please see Calculating an LED resistor value below.

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.

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

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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.

Sizes, Shapes and Viewing angles of LEDs

LEDs are available in a wide variety of sizes and shapes. The 'standard' LED has a round cross-section of 5mm diameter and this is probably the best type for general use, but 3mm round LEDs are also popular.

Round cross-section LEDs are frequently used and they are very easy to install on boxes by drilling a hole of the LED diameter, adding a spot of glue will help to hold the LED if necessary. LED clips are also available to secure LEDs in holes. Other cross-section shapes include square, rectangular and triangular.

As well as a variety of colours, sizes and shapes, LEDs also vary in their viewing angle. This tells you how much the beam of light spreads out. Standard LEDs have a viewing angle of 60° but others have a narrow beam of 30° or less.

Rapid Electronics stock a wide selection of LEDs and their catalogue is a good guide to the range available.

LED Clip

Photograph © Rapid Electronics

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Calculating an LED resistor value

An LED must have a resistor connected in series to limit the current through the LED, otherwise it will burn out almost instantly.

The resistor value, R is given by:

R = (VS - VL) / I

VS = supply voltage VL = LED voltage (usually 2V, but 4V for blue and white LEDs) I = LED current (e.g. 20mA), this must be less than the maximum permitted

If the calculated value is not available choose the nearest standard resistor value which is greater, so that the current will be a little less than you chose. In fact you may wish to choose a greater resistor value to reduce the current (to increase battery life for example) but this will make the LED less bright.

For example

If the supply voltage VS = 9V, and you have a red LED (VL = 2V), requiring a current I = 20mA = 0.020A, R = (9V - 2V) / 0.02A = 350 , so choose 390 (the nearest standard value which is greater).

Working out the LED resistor formula using Ohm's law

Ohm's law says that the resistance of the resistor, R = V/I, where: V = voltage across the resistor (= VS - VL in this case) I = the current through the resistor

So R = (VS - VL) / I

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For more information on the calculations please see the Ohm's Law page.

Connecting LEDs in series

If you wish to have several LEDs on at the same time it may be possible to connect them in series. This prolongs battery life by lighting several LEDs with the same current as just one LED.

All the LEDs connected in series pass the same current so it is best if they are all the same type. The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages and use this for VL.

Example calculations: A red, a yellow and a green LED in series need a supply voltage of at least 3 × 2V + 2V = 8V, so a 9V battery would be ideal. VL = 2V + 2V + 2V = 6V (the three LED voltages added up). If the supply voltage VS is 9V and the current I must be 15mA = 0.015A, Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 = 200 , so choose R = 220 (the nearest standard value which is greater).

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Avoid connecting LEDs in parallel!

Connecting several LEDs in parallel with just one resistor shared between them is generally not a good idea.

If the LEDs require slightly different voltages only the lowest voltage LED will light and it may be destroyed by the larger current flowing through it. Although identical LEDs can be successfully connected in parallel with one resistor this rarely offers any useful benefit because resistors are very cheap and the current used is the same as connecting the LEDs individually. If LEDs are in parallel each one should have its own resistor.

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.

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Type Colour

IF max

. VF

typ. VF max.

VR max.

Luminous

intensity

Viewing

angle

Wavelength

Standard Red 30m

A 1.7V 2.1V 5V 5mcd @

10mA 60° 660nm

Standard

Bright red

30mA 2.0V 2.5

V 5V 80mcd @ 10mA 60° 625nm

Standard

Yellow

30mA 2.1V 2.5

V 5V 32mcd @ 10mA 60° 590nm

Standard

Green

25mA 2.2V 2.5

V 5V 32mcd @ 10mA 60° 565nm

High intensit

y Blue 30m

A 4.5V 5.5V 5V 60mcd

@ 20mA 50° 430nm

Super bright Red 30m

A 1.85

V 2.5V 5V 500mcd

@ 20mA 60° 660nm

Low current Red 30m

A 1.7V 2.0V 5V 5mcd @

2mA 60° 625nm

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.

Viewing angle Standard LEDs have a viewing angle of 60°, others emit a narrower beam of about 30°.

Wavelength The peak wavelength of the light emitted, this

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determines the colour of the LED. nm = nanometre.

Flashing LEDs

Flashing LEDs look like ordinary LEDs but they contain an integrated circuit (IC) as well as the LED itself. The IC flashes the LED at a low frequency, typically 3Hz (3 flashes per second). They are designed to be connected directly to a supply, usually 9 - 12V, and no series resistor is required. Their flash frequency is fixed so their use is limited and you may prefer to build your own circuit to flash an ordinary LED, for example our Flashing LED project which uses a 555 astable circuit.

LED Displays

LED displays are packages of many LEDs arranged in a pattern, the most familiar pattern being the 7-segment displays for showing numbers (digits 0-9). The pictures below illustrate some of the popular designs:

Bargraph 7-segment Starburst Dot matrix

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Pin connections of LED displays

There are many types of LED display and a supplier's catalogue should be consulted for the pin connections. The diagram on the right shows an example from the Rapid Electronics catalogue. Like many 7-segment displays, this example is available in two versions: Common Anode (SA) with all the LED anodes connected together and Common Cathode (SC) with all the cathodes connected together. Letters a-g refer to the 7 segments, A/C is the common anode or cathode as appropriate (on 2 pins). Note that some pins are not present (NP) but their position is still numbered.

Pin connections diagram

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ADVANTAGES:

1. Simple and efficient circuit

2. Working requirement is easily met.

3. No instant and direct manual operation is needed.

4. Consumes very small amount of power for operation.

5. It also saves a considerable amount of power.

6. A very practical and low cost device.

7. It can make to work by using solar cell/wind cell for power requirements.

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REFRENCES

1.www.electronics.com 2.www.electronicsforu.com 3.www.google.com 4.www.kpsec.freeuk.com 5. www.wikipedia.org 6.software:-a) pROTEL b)ORCAD