PROJECT REPORT ON

LED LIGHT DRIVER

CIRCUIT

SUBMITTED BY-:

NAME ROLL NO

ARBIND KUMAR SG7511

MANISH GAUR SG7525

MANJOT KAUR SG7526

MEENAKSHI SHARMA SG7527

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ACKNOWLEDGEMENT

We feel profound pleasure in bringing out this project report for which we had to go from pillar to post to make it a reality. This project work reflects contributions of many people with whom we had long discussions and without which it would not have been possible. We must first of all, express our heartiest gratitude to respected Mr. Neeraj Sharma (Co-ordinator, Dept. of ECE) for providing us all guidance to complete the project.It would be unfair if we do not mention the invaluable contribution and timely co-operation extended to us by the staff members of our department. And especially we can never forget the most worthy advices given by Mr. Sanjeev Bhatia (senior Technician, Dept of ECE), that would help us the entire lifetime.Last but not the least we express our sincere thanks to the institute SSGPURC, Hoshiarpur, Punjab for providing such a platform for implementing the ideas in our mind.

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SSG Panjab University Regional Centre

Hoshiarpur, Punjab

This is to certify that-:

1. Arbind Kumar2. Manish Gaur3. Manjot Kaur4. Meenakshi Sharma

Studying in ECE Branch have satisfactorily completed the project work on LED LIGHT DRIVER CIRCUIT topic during the academic year 2010-2011.

Project Guide

Asst. Prof. Mr Neeraj Sharma

(Co-ordinator, Dept. of ECE)

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1. Introduction 52. Problem Definition 73. LED Lighting 84. LED(Light Emitting Diodes) 105. Comparison b/w LED lights, CFLs and Light Bulbs 116. ADC 137. PWM 14

8. AVR Microcontrollers 15i. Attiny13 19

9. MOSFETs 2110. Software Used 2411. Block diagram 2612. Circuit Diagram 28

13. Source Code 2914. Future Scope 3115. References 33

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Introduction

To control the brightness of an LED you can vary the power which is sent to the LED, for example using a potentiometer (variable resistor), the more power the LED receives the brighter it is, the less power it receives the dimmer it is. Microcontrollers are digital, meaning they only have two ‘power’ states, on and off. Although it is possible to supply a varying power from a microcontroller (using a Digital to Analog Convertor (DAC)) this usually requires an additional chip. PWM provides the ability to ‘simulate’ varying levels of power by oscillating the output from the microcontroller.

If, over a short duration of time, we turn the LED on for 50% and off for 50%, the LED will appear half as bright since the total light output over the time duration is only half as much as 100% on. The important factor here is the ‘duration’, if we turn the light on and off too slowly the viewer will see the flashing of the LED not

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a constant light output which appears dimmer. The pulsing width (in this case 50%) is the important factor here. By varying (or ‘modulating’) the pulsing width we can effectively control the light output from the LED, hence the term PWM or Pulse Width Modulation.

When using PWM it’s important to consider how slowly we can ‘flash’ the LED so that the viewer does not perceive the oscillation. The eye’s inability to see rapid oscillations of light is caused by our ‘persistence of vision’ which means, in very simple terms, we see the light as on even after it has turned off. This technique is how televisions display a seemingly moving picture which is actually made up of a number of different still frames displayed one after the other very rapidly. The minimum speed of an LED oscillating which can be seen by the human eye varies from person to person. However, for the purposes of this article, we will use a minimum speed of 50Hz, or 50 times per second (the same speed as used by European televisions).

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Problem DefinitionDesign a “LED LIGHT DRIVER CIRCUIT” using ATtiny13. It should perform the following actions:-

1) It should convert the analog voltage from potentiometer into digital.

2) The microcontroller should produce PWM according to the voltage input from potentiometer.

3) It should be able to drive an array of LEDs.

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LED LIGHTINGA Light Emitting Diode (LED) is a semiconductor device which converts electricity into light. LED lighting has been around since the 1960s, but is just now beginning to appear in the residential market for space lighting. At first white LEDs were only possible by "rainbow" groups of three LEDs -- red, green, and blue -- by controlling the current to each to yield an overall white light. This changed in 1993 when Nichia created a blue indium gallium chip with a phosphor coating that is used to create the wave shift necessary to emit white light from a single diode. This process is much less expensive for the amount of light generated.

Each diode is about 1/4 inch in diameter and uses about ten milliamps to operate at about a tenth of a watt. LEDs are small in size, but can be grouped together for higher intensity applications. LED fixtures require a driver which is analogous to the ballast in fluorescent fixtures. The drivers are typically built into the fixture (like fluorescent ballasts) or they are a plug transformer for portable (plug-in) fixtures. The plug-in transformers allow the fixture to run on standard 120 volt alternating current (AC), with a modest (about 15 to 20 percent) power loss.

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The efficacy of a typical residential application LED is approximately 20 lumens per watt (LPW), though efficacies of up to 100 LPW have been created in laboratory settings. Incandescent bulbs have an efficacy of about 15 LPW and ENERGY STAR® qualified compact fluorescents are about 60 LPW, depending on the wattage and lamp type. Some manufacturers claim efficacies much higher than 20 LPW; make sure to examine system efficacy, which accounts for the power use of all components. In December 2006, the U.S. Department of Energy studied the efficacy of four luminaries. All four fell short of the manufacturers’ claims; the study implies that manufacturers are relying on measurements of how much light an isolated LED produces, rather than how much light an LED luminaire actually delivers.

LEDs are better at placing light in a single direction than incandescent or fluorescent bulbs. Because of their directional output, they have unique design features that can be exploited by clever designs. LED strip lights can be installed under counters, in hallways, and in staircases; concentrated arrays can be used for room lighting. Waterproof, outdoor fixtures are also available. Some manufacturers consider applications such as gardens, walkways, and decorative fixtures outside garage doors to be the most cost-efficient.

LED lights are more rugged and damage-resistant than compact fluorescents and incandescent bulbs. LED lights don't flicker. They are very heat sensitive; excessive heat or inappropriate applications dramatically reduce both light output and lifetime. Uses include:

Task and reading lamps Linear strip lighting (under kitchen cabinets)

Recessed lighting/ceiling cans

Porch/outdoor/landscaping lighting

Art lighting

Night lights

Stair and walkway lighting

Pendants and overhead

Retrofit bulbs for lamps

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LED (LIGHT EMITTING DIODE)

A light-emitting diode (LED) is a semiconductor device that emits visible light when an electric current passes through it. The light is not particularly bright, but in most LEDs it is monochromatic, occurring at a single wavelength. The output from an LED can range from red (at a wavelength of approximately 700 manometers) to blue-violet (about 400 nanometres). Some LEDs emit infrared (IR) energy (830 nanometres or longer); such a device is known as an infrared-emitting diode (IRED).An LED or IRED consists of two elements of processed material called P-type semiconductors and N-type semiconductors. These two elements are placed in direct contact, forming a region called the P-N junction. In this respect, the LED or IRED resembles most other diode types, but there are important differences. The LED or IRED has a transparent package, allowing visible

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or IR energy to pass through. Also, the LED or IRED has a large PN-junction area whose shape is tailored to the application.Benefits of LEDs and IREDs, compared with incandescent and fluorescent illuminating devices, include:

Low power requirement: Most types can be operated with battery power supplies.

High efficiency: Most of the power supplied to an LED or IRED is converted into radiation in the desired form, with minimal heat production.

Long life: When properly installed, an LED or IRED can function for decades.

Typical applications include:

Indicator lights: These can be two-state (i.e., on/off), bar-graph, or alphabetic-numeric readouts.

LCD panel backlighting: Specialized white LEDs are used in flat-panel computer displays.

Comparison Chart LED Lights vs. Incandescent Light Bulbs vs. CFLs

Light Emitting Diodes (LEDs)

Incandescent Light Bulbs

Compact Fluorescents

(CFLs)

Life Span (average)

50,000 hours

1,200 hours 8,000 hours

Watts of electricity

used

6 - 8 watts 60 watts 13-15 watts

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Kilo-watts of Electricity

used 329 KWh/yr. 3285 KWh/yr. 767 KWh/yr.

Annual Operating

Cost $32.85/year $328.59/year $76.65/year

Contains the TOXIC Mercury

No No

Yes - Mercury is very toxic to your

health and the environment

RoHS Compliant

Yes Yes

No - contains 1mg-5mg of Mercury

and is a major risk to the

environment

Carbon Dioxide

Emissions 451 pounds/year 4500 pounds/year 1051 pounds/year

Sensitivity to low temperatures

None Some

Yes - may not work under negative 10

degrees Fahrenheit or over

120 degrees Fahrenheit

Sensitive to humidity

No Some Yes

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On/off Cycling Switching a CFL

on/off quickly, in a closet for

instance, may decrease the

lifespan of the bulb.

No Effect SomeYes - can reduce

lifespan drastically

Turns on instantly Yes YesNo - takes time to

warm up

Durability

Very Durable - LEDs can handle

jarring and bumping

Not Very Durable - glass or filament can break easily

Not Very Durable - glass can break

easily

Light OutputLight Emitting Diodes (LEDs)

Incandescent Light Bulbs

Compact Fluorescents

(CFLs)

Lumens Watts Watts Watts

450 4-5 40 9-13

800 6-8 60 13-15

1,100 9-13 75 18-25

1,600 16-20 100 23-30

2,600 25-28 150 30-55

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ADC

(ANALOG TO DIGITAL CONVERSION)In our daily life, anything we deal like sound, pressure, voltage or any measurable quantity, are usually in analog form. So what if we want to interface any analog sensor with our digital controllers? There must be something that translate the analog inputs to digital output, and so Analog to digital convertors come to play. Usually we call them ADC (Analog to digital convertor). Before going to learn how to interface an ADC with a controller we first take a look at basic methods of analog to digital conversion. This is a sample of the large number of analog-to-digital conversion methods. The basic principle of operation is to use the comparator principle to determine whether or not to turn on a particular bit of the binary number output. It is typical for an ADC to use a digital-to-analog converter (DAC) to determine one of the inputs to the comparator.

Following are the most used conversion methods:

Digital-Ramp ADC Successive Approximation ADC Flash ADC

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PWM(Pulse Width Modulation)Pulse-width Modulation is achieved with the help of a square wave

whose duty cycle is changed to get a varying voltage output as a result of average value of waveform. Pulse width Modulation or PWM is one of the powerful techniques used in control systems today. They are not only employed in wide range of control application which includes: speed control, power control, measurement and communication.

The basic idea behind PWM implementation on microcontroller is using timers and switching port pin high/low at defined intervals. By changing the Ton time, we can vary the width of square wave keeping same time period of the square wave.

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AVR Microcontrollers

The AVR is a Modified Harvard architecture 8-bit RISC single chip microcontroller. It was developed by Atmel in 1996. Harvard architecture means that the program and data are stored in separate memory spaces which are accessible simultaneously. The AVR was one of the first microcontroller families to use on-chip flash memory for program storage, as opposed to One-Time Programmable ROM, EPROM, or EEPROM used by other microcontrollers at the time. Flash memory is a non-volatile (persistent on power-down) programmable memory.

Low power and high performance AVR microcontrollers can handle demanding 8 and 16-bit applications. With a single cycle instruction RISC CPU, picoPower technology, and a rich feature set, the AVR architecture ensures easy application development and fast code execution combined with the lowest possible power consumption. The well-defined I/O structure limits the need for external components and reduces development cost. A variety of timers, SPIs, UARTs, internal oscillators, pull-up resistors, pulse width modulation, Analog Comparators, ADCs and Watch-Dog Timers are some of the features available for engineers. It is interesting to note that most instructions only take a single clock cycle to execute and there is no internal clock division. Whether you program in C, Pascal or assembly language, the tuned AVR instructions decrease program size and development time. The AVR processor features a real life stack and its instruction set was designed and optimized for use with high level languages - it is easy to program these chips using C. AVR microcontrollers may be programmed using assembly or

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a higher level language. Learning to program it in assembly language is a good idea, as it gives you in depth understanding of the internal operations. A comprehensive collection of application notes also kick-start problematic tasks. Since the introduction of the classic AT90S1200 device with on-chip in-system programmable Flash and EEPROM memory in 1997, today's large AVR microcontroller portfolio consists of devices sharing a single CPU architecture. This makes it easy to find the AVR microcontroller for almost any application.

AVR Features-:The AVR is an 8-bit RISC single-chip microcontroller with Harvard architecture that comes with some standard features such as on-chip program (code) ROM, data RAM, data EEPROM, timers and I/O ports. Most AVRs have some additional features like ADC, PWM, and different kinds of serial interface such as USART, SPI, I2C (TWI), CAN, USB, and so on. The details of the RAM/ROM memory and I/O features of the Mega are given elsewhere on this website.

AVR Microcontroller Program ROM-:In microcontrollers, the ROM is used to store programs and for that reason it is called program or code ROM. Although the AVR has 8M (megabytes) of program (code) ROM space, not all family members come with that much ROM installed. The program ROM size can vary from 1K to 256K at the time of this writing, depending on the family member. The AVR was one of the first microcontrollers to use on-chip Flash memory for program storage. The Flash memory is ideal for fast development because Flash memory can be erased in seconds compared to the 20 minutes or more needed for the UV-EPROM.

AVR Microcontroller Data RAM and EEPROM-:While ROM is used to store program (code), the RAM space is for data storage, The AVR has a maximum of 64K bytes of data RAM space. Not all of the family members come with that much RAM. The data RAM space has three components: general-purpose registers, I/O memory, and internal SRAM, There are 32 general-purpose registers in all of the AVRs, but the SRAM’s size and the I/O memory’s size varies from chip to chip. On the Atmel website, whenever the size of RAM is mentioned the internal SRAM size is meant. The internal SRAM space is used for a

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read/write scratch pad. In AVR, we also have a small amount of EEPROM to store critical data that does not need to be changed very often.

AVR Microcontroller l/O pins-:The AVR can have from 3 to 86 pins for I/O. The number of I/O pins depends on the number of pins in the package itself The number of pins for the AVR package goes from 8 to 100 at this time, In the case of the 3-pin AT90S2323, we have 3 pins for I/O, while in the case of the l00-pin ATmega1280, we can use up to 86 pins for I/O.

AVR Microcontroller Peripherals-:Most of the AVRs come with ADC (analog-to-digital converter), timers, and USART (Universal Synchronous Asynchronous Receiver Transmitter) as standard peripherals. The ADC is 10-bit and the number of ADC channels in AVR chips varies and can be up to 16, depending on the number of pins in the package. The AVR can have up to 6 timers besides the watchdog timer. The USART peripheral allows us to connect the AVR-based system to serial ports such as the COM port of the x86 IBM PC. Most of the AVR family members come with the I2C and SPI buses and some of them have USB or CAN bus as well.

AVR family overview-:AVR can be classified into four groups: Classic, Mega, Tiny, and special purpose.

Classic AVR (AT90Sxxxx)-:This is the original AVR chip, which has been replaced by newer AVR chips.

Mega AVR (ATmegaxxxx)-:These are powerful microcontrollers with more than 120 instructions and lots of different peripheral capabilities, which can be used in different designs. Some of their characteristics are as follows:

Program memory: 4K to 256K bytes Package: 28 to 100 pins

Extensive peripheral set

Extended instruction set; They have rich instruction sets.

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Tiny AVR (ATtinyxxxx)-:As its name indicates, the microcontrollers in this group have less instructions and smaller packages in comparison to mega family. You can design systems with low costs and power consumptions using the Tiny AVRs. Some of their characteristics are as follows:

Program memory: 1Kto SK bytes Package: 8 to 23 pins

Limited peripheral set

Limited instruction set: The instruction sets are limited. For example, some of them do not have the multiply instruction.

Special Purpose AVR-:The ICs of this group can be considered as a subset of other groups, but their special capabilities are made for designing specific applications. Some of the special capabilities are: USB controller, CAN controller, LCD controller, Zigbee, Ethernet controller, FPGA, and advanced PWM.

AVR Product Number Scheme-:The entire product numbers start with AT, which stands for Atmel. Now, look at the number located at the end of the product number, from left to right, and find the biggest number that is a power of 2. This number most probably shows the amount of the Microcontroller’s ROM. For example, in ATmega1280 the biggest power of 2 that we can find is 128; so it has 128K bytes of ROM. In ATtiny44, the amount of memory is 4-K, and so on. Although this rule has a few exceptions such as AT90PWM216, which has 16K of ROM instead of 2K, it works in most of the cases.

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ATtiny 13

The ATtiny13 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATtiny13 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.

Features-:

High Performance, Low Power AVR 8-Bit Microcontroller Advanced RISC Architecture

o 120 Powerful Instructions - Most Single Clock Cycle Execution

o 32 x 8 General Purpose Working Registers

o Fully Static Operation

o Up to 20 MIPS Throughput at 20 MHz

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High Endurance Non-volatile Memory segments

o 1K Bytes of In-System Self-programmable Flash program memory

o 64 Bytes EEPROM

o 64 Bytes Internal SRAM

o Write/Erase Cycles: 10,000 Flash/100,000 EEPROM

o Data retention: 20 years at 85°C/100 years at 25°C

o Programming Lock for Self-Programming Flash & EEPROM Data Security

Peripheral Features

o One 8-bit Timer/Counter with Prescaler and Two PWM Channels

o 4-channel, 10-bit ADC with Internal Voltage Reference

o Programmable Watchdog Timer with Separate On-chip Oscillator

o On-chip Analog Comparator

Special Microcontroller Features

o debugWIRE On-chip Debug System

o In-System Programmable via SPI Port

o External and Internal Interrupt Sources

o Low Power Idle, ADC Noise Reduction, and Power-down Modes

o Enhanced Power-on Reset Circuit

o Programmable Brown-out Detection Circuit

o Internal Calibrated Oscillator

I/O and Packages

o 8-pin PDIP/SOIC: Six Programmable I/O Lines

o 20-pad MLF: Six Programmable I/O Lines

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Operating Voltage:

o 1.8 - 5.5V for ATtiny13V

o 2.7 - 5.5V for ATtiny13

Speed Grade:

o ATtiny13V: 0 - 4 MHz @ 1.8 - 5.5V, 0 - 10 MHz @ 2.7 - 5.5V

o ATtiny13: 0 - 10 MHz @ 2.7 - 5.5V, 0 - 20 MHz @ 4.5 - 5.5V

POWER MOSFET

Unlike the bipolar junction transistor (BJT), the MOSFET device belongs to the unipolar device family, because it uses only the majority carriers in conduction. The development of metaloxide- semiconductor (MOS) technology for microelectronic circuits opened the way for development of the power metal oxide semiconductor field effect transistor (MOSFET) device in 1975. Selecting the most appropriate device for a given application is not an easy task because it requires knowledge about the device characteristics, their unique features, innovation, and engineering design experience. Unlike low-power (signal devices), high-power devices are more complicated in structure, driver design, and their operational i-v characteristics are difficult to understand. This knowledge is very important for power electronics engineers when designing circuits that will make these devices close to ideal. The device symbol for a p- and n-channel enhancement and depletion types are shown in Fig. 6.5. Figure 6.6 shows the i-v characteristics for the n-channel enhancement-type MOSFET. It is the fastest power switching device, with switching frequency >MHz, and with voltage power ratings up to 600 Vand current rating as high as 40 A.

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SOFTWARES USED

1. PROTEUS -:

• ROLE IN THE DESIGN: Proteus proved to be a very handy & easy-to-use tool for the PCB layout process and for circuit designing. Many of its features were utilized leading to an accurate & efficient design. It has Design Error Check & Electrical Rule Check tools which proved to be helpful in the design. It is loaded with a huge component list that is categorized in various libraries for giving simplicity. Placement of components is also very easy & they can be rotated in 360⁰ to customize the design.

• WORKING WITH Proteus:

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2. AVR STUDIO:

• ROLE IN THE DESIGN: AVR Studio provides IDE for Atmega8 programming & is very easy to use. When starting a new project, simply select the microcontroller you use from the Device Database and the AVR Studio IDE sets all Compilers, Assembler, Linker, and Memory options. Its device database is large which supports many ICs of the AVR family. A HEX file can be created with the help of Studio which is required for burning onto chip. It has a powerful debugging tool which detects most of the errors in the program.

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BLOCK DIAGRAM

The project comprises of Potentiometer, microcontroller board, MOSFET and LED Array. The potentiometer has one scale rotation of 5 volts. The output of the potentiometer is an analog voltage signal. This signal is fed to the microcontroller (Attiny 13). Attiny 13 has an inbuilt analog to digital converter circuitry of 8 bit resolution.

The converted analog to digital signal contains values according to the varying input signal. These digital values are then used to produce a PWM output signal across the output pins of microcontroller. The PWM signal is used is to drive the gate of MOSFET and the intensity of the light is varied according to the PWM signal. The project works on a 12v dc supply.

The microcontroller used is an avr microcontroller from Atmel Corporation. It has inbuilt clock circuitry, a/d converter, watchdog timer, pwm

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POWER

SUPPLY

Potentiometer

Microcontroller MOSFET

LED Array

circuitry and many more useful features in short the microcontroller is one of the most powerful microcontrollers used in industry.

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CIRCUIT DIAGRAM

Power Supply & Main Circuit-:

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SOURCE CODE

.INCLUDE "TN13DEF.INC"

.CSEG

.ORG 0X0000RJMP RESET

.ORG 0x0003CLIRJMP ADC0

.ORG 0x0009RETI

RESET:LDI R31,LOW(RAMEND)OUT SPL,R31LDI R17,$05OUT DDRB,R17LDI R18,$22LDI R19,$CBOUT ADMUX,R18

ADC0:LDI R29,$04OUT PORTB,R29CLCCLZOUT ADCSRA,R19BACK:

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IN R24,ADCSRASBRC R24,4RJMP NEXTRJMP BACKNEXT:IN R23,ADCHSEINOPNOPCLI

PWM:LDI R22,$81LDI R21,$02OUT OCR0A,R23OUT TCCR0A,R22OUT TCCR0B,R21RJMP D1

D1:LDI R20,$02OUT TIMSK0,R20CBR R24,2OUT TIFR0,R24SEILOOP:RJMP LOOP

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FUTURE SCOPE

1. Light Sources For Machine Vision System-: Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used for this purpose, and this is likely to remain one of their major uses until price drops low enough to make signaling and illumination uses more widespread. Barcode scanners are the most common example of machine vision, and many low cost ones use red LEDs instead of lasers. Optical computer mice are also another example of LEDs in machine vision, as it is used to provide an even light source on the surface for the miniature camera within the mouse. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:

The size of the illuminated field is usually comparatively small and machine vision systems are often quite expensive, so the cost of the light source is usually a minor concern. However, it might not be easy to replace a broken light source placed within complex machinery, and here the long service life of LEDs is a benefit.

LED elements tend to be small and can be placed with high density over flat or even-shaped substrates (PCBs etc.) so that bright and homogeneous sources can be designed which direct light from tightly controlled directions on inspected parts. This can often be obtained with small, low-cost lenses and diffusers, helping to achieve high light densities with control over lighting levels and homogeneity. LED sources can be shaped in several configurations (spot lights for reflective illumination; ring lights for coaxial illumination; back lights for contour illumination; linear assemblies; flat, large format panels; dome sources for diffused, omnidirectional illumination).

LEDs can be easily strobed (in the microsecond range and below) and synchronized with imaging. High-power LEDs are available allowing well lit images even with very short light pulses. This is often used to obtain crisp and sharp “still” images of quickly moving parts.

LEDs come in several different colors and wavelengths, allowing easy use of the best color for each need, where different color may provide better visibility of features of interest. Having a precisely known spectrum allows tightly matched

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filters to be used to separate informative bandwidth or to reduce disturbing effects of ambient light. LEDs usually operate at comparatively low working temperatures, simplifying heat management and dissipation. This allows using plastic lenses, filters, and diffusers. Waterproof units can also easily be designed, allowing use in harsh or wet environments (food, beverage, oil industries).

2. Lighting-:

With the development of high efficiency and high power LEDs it has become possible to use LEDs in lighting and illumination. Replacement light bulbs have been made, as well as dedicated fixtures and LED lamps. LEDs are used as street lights and in other architectural lighting where color changing is used. The mechanical robustness and long lifetime is used in automotive lighting on cars, motorcycles and on bicycle lights.

LED street lights are employed on poles and in parking garages. In 2007, the Italian village Torraca was the first place to convert its entire illumination system to LEDs.

LEDs are used in aviation lighting. Airbus has used LED lighting in their Airbus A320 Enhanced since 2007, and Boeing plans its use in the 787. LEDs are also being used now in airport and heliport lighting. LED airport fixtures currently include medium-intensity runway lights, runway centerline lights, taxiway centerline & edge lights, guidance signs and obstruction lighting.

LEDs are also suitable for backlighting for LCD televisions and lightweight laptop displays and light source for DLP projectors (SeeLED TV). RGB LEDs raise the color gamut by as much as 45%. Screens for TV and computer displays can be made thinner using LEDs for backlighting.

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LEDs are used increasingly in aquarium lights. Particularly for reef aquariums, LED lights provide an efficient light source with less heat output to help maintain optimal aquarium temperatures. LED-based aquarium fixtures also have the advantage of being manually adjustable to emit a specific color-spectrum for ideal coloration of corals, fish, and invertebrates while optimizing photosynthetically active radiation (PAR) which raises growth and sustainability of photosynthetic life such as corals, anemones, clams, and macroalgae. These fixtures can be electronically programmed to simulate various lighting conditions throughout the day, reflecting phases of the sun and moon for a dynamic reef experience. LED fixtures typically cost up to five times as much as similarly rated fluorescent or high-intensity discharge lighting designed for reef aquariums and are not as high output to date

3. LED Lamps-:

White LED lamps have achieved market dominance in applications where high efficiency is important at low power levels. Some of these applications include flashlights, solar-powered garden or walkway lights, and bicycle lights. Monochromatic (colored) LED lamps are now commercially used for traffic signal lamps, where the ability to emit bright monochromatic light is a desired feature, and in strings of holiday lights.

LED lights have also become very popular in gardening and agriculture by 2010. First used by NASA to grow plants in space, LEDs came into use for home and commercial applications for indoor horticulture (aka grow lights). The wavelengths of light emitted from LED lamps have been specifically tailored to supply light in the spectral range needed for chlorophyll absorption in plants, promoting growth while reducing wastage of energy by emitting minimal light at wavelengths that plants do not require. The red and blue wavelengths of the visible light spectrum are used for photosynthesis, so these are the colors almost always used in LED grow lightpanels. These lights are attractive to indoor growers

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since they use less power than other types for the same light intensity, need no ballasts, and emit much less heat than HID lamps.The reduction in heat allows time between watering cycles to be extended because the plants transpire less under LED grow lights. Due to this change in growth conditions, users of LEDs are advised not to over-water the plants

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REFERENCES

1. Wikipedia - The free encyclopaedia

2. Power Electronics Guide by Keith H. Sueker

3. http://www.atmel.com/

4. http://www.alldatasheet.com/

5. http://www.datasheet4u.com/

6. http://www.howstuffworks.com/led.htm

7. http://www.lc-led.com/articles/ledlights.html

8. http://www.ehow.com

9. http://www.lunaraccents.com/technology-LED-truck-lights-

dimming.html

10.http://www.maxim-ic.com/app-notes/index.mvp/id/4472

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