Skyline Institute of Engineering

SKYLINE INSTITUTE OF ENGINEERING &TECHNOLOGY,

GREATER NOIDA

Affiliated to Uttar Pradesh Technical University, Lucknow (U.P.)

Project Report

On

PERSISTENCE OF VISION DISPLAY

Submitted in the partial fulfillment for the award of degree of

BACHELORS OF TECHNOLOGY

APPLIED ELECTRONICS AND INSTRUMENTATION ENGINEERING

2009-10

SUBMITTED BY:

Akshat Kumar Vaish - 0615335007

Madhav Kumar Sarkar - 0615335032

Harish Chandra Nayak - 0615335027

Loveneesh Rana – 0615335031

ACKNOWLEDGEMENT

We would like to thank everyone who directly or indirectly helped us in completing the project. We would specially like to thank Mr. P.K.Chaturvedi(Dean) and Mr. Tarun Hiteshi for their

guidance and supervising the project throughout the development of the project.

We would also like to every faculty member for their valuable suggestions and guidance.

We would like to thank all our classmates for their constant encouragement, support and valuable suggestions during the development of this project.

CANDIDATE’S DECLARATION

We hereby declare that the project report titled ‘PERSISTENCE OF VISION’ submitted towards the completion of final year major project work in 8th semester of B.Tech (AEI) in Skyline

Institute Of Engineering & Technology, Gr Noida is an authentic record of work carried out under the guidance of Mr. P.K.Chaturvedi Dean(Academics).

Date:- May 2010

Place:- Gr Noida

Akshat Kumar Madhav Kumar Sarkar

0615335007 0615335032

Loveneesh Rana Harish Nayak

0615335031 0615335027

CERTIFICATE

This is to certify that the above declaration made by Mr. Madhav Kumar Sarkar, Mr. Akshat Kumar, Mr. Loveneesh Rana and Mr. Harish Nayak is true to the best of my knowledge and

belief.

Date: May 2010

Place: Gr Noida

Dr. P.K.Chaturvedi

Dean- Academics

EC & AEI Department

Skyline Institute Of Engineering & Technology

Mr. Tarun Hiteshi

Project Guide

Sr – Lecturer

EC & AEI Department

Skyline Institute Of Engineering & Technology

Full Table of Contents

Persistence of Vision Display

ACKNOWLEDGEMENT.................................................................................................................................1

CANDIDATE’S DECLARATION.......................................................................................................................2

CERTIFICATE................................................................................................................................................3

Persistence of Vision Display.......................................................................................................................4

Introduction.................................................................................................................................................9

Conventional Display Devices:...............................................................................................................10

Vision and Goal..........................................................................................................................................12

Concept.....................................................................................................................................................13

THE ANALOGY........................................................................................................................................14

Idea............................................................................................................................................................15

Comparison with Previous Technologies & Implementations...................................................................17

CRT........................................................................................................................................................17

Shadow-mask....................................................................................................................................18

Aperture-grill.....................................................................................................................................18

Slot-mask...........................................................................................................................................18

Dot pitch............................................................................................................................................19

Refresh Rate......................................................................................................................................21

Comparing POV & CRT...........................................................................................................................22

Similarities.........................................................................................................................................22

Differences & Advantages over CRT......................................................................................................23

LCD........................................................................................................................................................24

Specifications of LCD..........................................................................................................................26

Construction & Working of LCD.........................................................................................................27

Comparing POV & LCD...........................................................................................................................29

Similarities.........................................................................................................................................29

Differences and Advantages of POV..................................................................................................30

INGENIOUS DESIGN OF POV..................................................................................................................31

Hardware interfacing.................................................................................................................................32

Block Diagram........................................................................................................................................33

System Components..............................................................................................................................35

System Operation..................................................................................................................................36

Unique System Elements.......................................................................................................................37

Dual Power Supply.............................................................................................................................38

Position Triggering using Interrupts...................................................................................................39

Interfacing with 74HC259..................................................................................................................41

Simplified Flow diagram....................................................................................................................42

Circuit Diagrams........................................................................................................................................44

POV – 1 Board........................................................................................................................................45

Description & Function for POV – 1...................................................................................................46

POV – 2 Board........................................................................................................................................47


POV – 3 Board........................................................................................................................................49


Distribution of Hardware among 3 boards............................................................................................51

Motor....................................................................................................................................................56

Spherical LEDs........................................................................................................................................58

Voltage/Design Current.....................................................................................................................60

Operating Life....................................................................................................................................60

Precautions While Working With LEDs..............................................................................................60

Base.......................................................................................................................................................61

Rotating Platform..................................................................................................................................62

THE CONTENTS..................................................................................................................................62

THE JOINT..........................................................................................................................................62

ASSEMBLY..........................................................................................................................................63

Organization..........................................................................................................................................64

Orientation............................................................................................................................................65

Future Development and Advantages.......................................................................................................66

Future development..............................................................................................................................67

ADVANTAGES........................................................................................................................................68

CHALLENGES IN DESIGN........................................................................................................................71

Table of Figures

Figure 1 Display device in use....................................................................................................................10Figure 2 LCD screens..................................................................................................................................10Figure 3 A CRT display mechanism............................................................................................................10Figure 4 7 – Segment LED display..............................................................................................................11Figure 5 A POV display...............................................................................................................................14Figure 6 CRT...............................................................................................................................................16Figure 7 Dot Pitch in CRT...........................................................................................................................18Figure 8 Refresh Rate................................................................................................................................20Figure 9 LCD cell structure.........................................................................................................................23Figure 10 LCD-Nematic Phase Liquid Crystals............................................................................................24Figure 11 LCD lighting................................................................................................................................24Figure 12 How LCD works..........................................................................................................................27Figure 13 Project Block Diagram................................................................................................................32Figure 14 Dual Power Supply.....................................................................................................................37Figure 15 Position Triggring Mechanism....................................................................................................38Figure 16 IR Sensor....................................................................................................................................38Figure 17 IC 74HC259................................................................................................................................40Figure 18 POV – 1 Board............................................................................................................................44Figure 19 POV – 2 Board............................................................................................................................46Figure 20 POV – 3 Board............................................................................................................................48Figure 22 3D IMAGE OF GLOBE USING 2D ARRAY OF LEDs........................................................................67Figure 23....................................................................................................................................................68Figure 24 DESIGN GENERATED USING 1D ARRAY......................................................................................69

Chapter 1

Chapter 1.....................................................................................................................................................7

Introduction.................................................................................................................................................9

Conventional Display Devices:...............................................................................................................10

Vision and Goal..........................................................................................................................................12

Concept.....................................................................................................................................................13

THE ANALOGY........................................................................................................................................14

Idea............................................................................................................................................................15

Introduction

Display devices have become a day-to-day product now, being used almost everywhere. This particular effect is ascribed to their capability of being used for any image or text and henceforth saving tons of paper.

Like any other technology, these devices have also become more sophisticated and advanced with new circuits and micro-controllers.

But it’s a certain need that every display device employs a screen or maybe a plane of small LEDs as the light source. This seems inevitable because to make a 2-dimensional form, you need a 2-dimensional source.

These display devices are very conventional in their design and mode of construction, but every now and then new applications are being invented in this field. It’s not far when the sci-fi stuff where matter is displayed in thin air without any hardware or screens. Rather, there are technologies in development that are making these concepts reality. Another example is the hologram concept where, 3-d display is generated by using lasers.

We too have tried to develop something which is, as yet, a very unconventional and innately new concept.

In this project report, we try to explain how we designed a display device that employs a 1-dimensional light source (an array of LEDs) to create 2-dimensional images.

Justifying the gist of applied electronics and instrumentation branch, this project demonstrates and involves a direct control of micro-controller over slave latches and operation of LEDs. Furthermore, it also involves a calculated and measured use of instrumentation techniques in operation of the entire assembly.

Conventional Display Devices:

Display devices have been an intimate essence of electronics from very beginning.

There have been a lot of researches and new types of these devices are being made on a regular basis. To demonstrate how our design is innately new and unconventional, here is a brief of conventional display devices.

First of all, these are the early display devices that laid the basics of the designs for new devices.

Cathode ray tube (CRT) - Storage tube

Bi-stable display

Electronic paper

Nixie tube displays

Vector display

Flat panel display

Vacuum fluorescent display (VF)

Light-emitting diode (LED) displays

Electroluminescent display (ELD)

Plasma display panels (PDP)

Liquid crystal display (LCD)

Among these, LED display, LCD and CRT are very common and are part of television display scheme.

Other than these, projectors also constitute quite a different class in modern display devices. Nonetheless, all of these are constantly upgraded to give better quality and a new perspective to this genre of electronics engineering.

Conventional Display Devices

Figure 1 Display device in use.

Figure 2 LCD screens.

Figure 3 A CRT display mechanism.

Figure 4 7 – Segment LED display.

Vision and Goal

Our goal is to make a display device that is independent of a display screen. In other words, a display device that employs a single-dimension light source, like a tube-light or an array of LEDs as in our case.

In doing so, we are aiming towards a display which is very much like our science-fiction technologies, i.e. to produce a display in thin air instead of a conventional screen.

This idea leads towards a whole new generation of display device and under proper research, may be extended towards building revolutionary 3-dimensional displays as well.

The idea of creating such type of device is not exactly new, as there are researches going on around the globe. So our idea is also an addition towards this revolution. But, the specialty about this project is that it is dynamic in display. This is due to fact that display depends on motion of the light source along with its direction.

Concept

The basic principle underlying this project is the phenomenon commonly termed as

“PERSISTENCE OF VISION”.

Q. What is “PERSISTENCE OF VISION”?

A. Persistence of vision also known as POV is a commonly-accepted theory which states that the human eye always retains images for a fraction of a second (around 0.04 second). This means that everything we see is a subtle blend of what is happening now and what happened a fraction of a second ago.

In simpler words, it means that retina of human eye has a tendency to capture an image for 0.04 seconds after its been removed. But, as the time interval is very small, we are not fully aware of the effect. If somehow, a series of frames are made to appear in a chromatic order, at fast-enough speed, then we see it not as a slideshow but rather a moving object.

The myth of persistence of vision is the mistaken belief that human perception of motion (brain centered) is the result of persistence of vision (eye centered). The myth was debunked in 1912 by Wertheimer but persists in many citations in many classic and modern film-theory texts.

THE ANALOGY

There is another aspect of the philosophy that makes the understanding of, what we intend to design, pretty much simpler.

This aspect explains how motion was achieved on display devices in earlier days, when digital technology was still developing.

The concept was to show the drawing/picture for every two frames of the film. The run rate would be no less than 24 frames per second (fps). It may be noted that fps is still used as a parameter to measure the clarity of video films.

In this manner, a motion was achieved on screen by changing frames so rapidly that it appears as if the object is actually moving. In reality, it’s simply a fast forward slideshow of still images that were originally clicked in instantaneous real time.

This is what the lexicon definition of term ‘motion picture’ is –

“The display of the images captured on a motion picture

, presented to the eye in very rapid succession

By projection from a special apparatus (a movie projector), with shows some or all of the objects in the

Picture represented in changing positions, producing, by

Persistence of vision, the optical effect of a continuous

Picture in which the objects appear to move as they did in the original scene.”

Although, the theory about POV has some serious doubts over its validation, we have developed a display device that’s based on the same effects.

Idea

The idea that we eventually employed to develop this display device was to move a light source at an incredible fast speed (that is eventually faster than an equivalent speed of 24fps) so as to form a display image.

Hence, instead of using a plane of LEDs or a display screen, we just used a line or a single-dimensional light source. Instead, we implied motion as the second dimension and hence were successful in obtaining a 2-dimensional display just in thin air, rather than using a conventional screen.

In this manner, we used a single-dimensional source to display a two-dimensional image.

This idea can be further explored and a 3-dimensional display might also be made if researched to next level.

But for now, we worked and designed a two-dimensional dynamic display based on persistence-of-vision.

Figure 5 A POV display

Chapter 2

Comparison with Previous Technologies & Implementations...................................................................17

CRT........................................................................................................................................................17

Shadow-mask....................................................................................................................................18

Aperture-grill.....................................................................................................................................18

Slot-mask...........................................................................................................................................18

Dot pitch............................................................................................................................................19

Refresh Rate......................................................................................................................................21

Comparing POV & CRT...........................................................................................................................22

Similarities.........................................................................................................................................22

Differences & Advantages over CRT..................................................................................................23

LCD........................................................................................................................................................24

Specifications of LCD..........................................................................................................................26

Construction & Working of LCD.........................................................................................................27

Comparing POV & LCD...........................................................................................................................29

Similarities.........................................................................................................................................29

Differences and Advantages of POV..................................................................................................30

INGENIOUS DESIGN OF POV..................................................................................................................31

Comparison with Previous Technologies & Implementations

First we will be looking at the constructional difference between CRT and POV. As construction of POV in earlier section here we will be considering only CRT and LCD displays. We start with CRT.

CRT

CRT stands for Cathode Ray Tube. CRTs receive their picture through an analogue cable, and that signal is decoded by the display controller, which handles the internal components of the monitor. CRTs have a distinctive funnel shape. At the very back of a monitor is an electron gun. The electron gun fires electrons towards the front through a vacuum which exists in the tube of the monitor. The gun can also be referred to as a cathode - hence the electrons fired forward are called Cathode Rays. These rays correspond to the red, green and blue channels of the display

At the neck of the funnel-shaped monitor is an anode, which is magnetized according to instructions from the display controller. As electrons pass the anode, they are shunted or pulled in one direction or the other depending on how magnetic the anode is at that time. This moves the electrons towards the correct part of the screen.

Figure 6 CRT

The electrons pass through a mesh, and this mesh defines the individual pixels and resolution on the screen. Electrons that pass through the mesh then hit the phosphor coating which is on the inside of the glass screen. When the particles hit the phosphor, they immediately light up - causing the light to shine through the front of the monitor, thus making up the picture on the screen. There are three differently colored phosphorus for each pixel (known as phosphor triads), and depending on which phosphor the electron hits, that's which color the pixel will light up.

There are three ways to filter the electron beam in order to obtain the correct image on the monitor screen: shadow mask, aperture grill and slot mask. These technologies also impact the sharpness of the monitor's display. Let's take a closer look at these now.

Shadow-mask

A shadow mask is a thin metal screen filled with very small holes. Three electron beams pass through the holes to focus on a single point on a CRT displays' phosphor surface. The shadow mask helps to control the electron beams so that the beams strike the correct phosphor at just the right intensity to create the desired colours and image on the display. The unwanted beams are blocked or "shadowed."

Aperture-grill

Monitors based on the Trinitron technology, which was pioneered by Sony, use an aperture-grill instead of a shadow-mask type of tube. The aperture grill consists of tiny vertical wires. Electron beams pass through the aperture grill to illuminate the phosphor on the faceplate. Most aperture-grill monitors have a flat faceplate and tend to represent a less distorted image over the entire surface of the display than the curved faceplate of a shadow-mask CRT. However, aperture-grill displays are normally more expensive.

Slot-mask

A less-common type of CRT display, a slot-mask tube uses a combination of the shadow-mask and aperture-grill technologies. Rather than the round perforations found in shadow-mask CRT displays, a slot-mask display uses vertically aligned slots. The design creates more brightness through increased electron transmissions combined with the arrangement of the phosphor dots.

Dot pitch

Dot pitch is an indicator of the sharpness of the displayed image. It is measured in millimetres (mm), and a smaller number means a sharper image. How you measure the dot pitch depends on the technology used:In a shadow-mask CRT monitor, you measure dot pitch as the diagonal distance between two like-colored phosphors. Some manufacturers may also cite a horizontal dot pitch, which is the distance between two-like colored phosphors horizontally.

The dot pitch of an aperture-grill monitor is measured by the horizontal distance between two like-colored phosphors. It is also sometimes are called stripe pitch.

Figure 7 Dot Pitch in CRT

The smaller and closer the dots are to one another, the more realistic and detailed the picture appears. When the dots are farther apart, they become noticeable and make the image look grainier. Unfortunately, manufacturers are not always upfront about dot pitch measurements, and you cannot necessarily compare shadow-mask and aperture-grill CRT types, due to the difference in horizontal and vertical measurements.

The dot pitch translates directly to the resolution on the screen. If you were to put a ruler up to the glass and measure an inch, you would see a certain number of dots, depending on the dot pitch. Here is a table that shows the number of dots per square centimeter and per square inch in each of these common dot pitches:

Dot PitchApprox. number ofpixels/cm2

Approx. number ofpixels/in2

.25 mm 1,600 10,000

.26 mm 1,444 9,025

.27 mm 1,369 8,556

.28 mm 1,225 7,656

.31 mm 1,024 6,400

.51 mm 361 2,256

1 mm 100 625

Refresh Rate

In monitors based on CRT technology, the refresh rate is the number of times that the image on the display is drawn each second. If your CRT monitor has a refresh rate of 72 Hertz (Hz), then it cycles through all the pixels from top to bottom 72 times a second. Refresh rates are very important because they control flicker, and you want the refresh rate as high as possible. Too few cycles per second and you will notice a flickering, which can lead to headaches and eye strain.

Figure 8 Refresh Rate

Because your monitor's refresh rate depends on the number of rows it has to scan, it limits the maximum possible resolution. Most monitors support multiple refresh rates. Keep in mind that there is a tradeoff between flicker and resolution, and then pick what works best for you. This is especially important with larger monitors where flicker is more noticeable. Recommendations for refresh rate and resolution include 1280x1024 at 85 Hertz or 1600x1200 at 75 Hertz.

Comparing POV & CRT

Similarities

A display with a higher resolution will be able to reproduce a picture accurately with smoothly varying colours. For a CRT this depends on the nature of the electron beam and me masking of the adjacent pixels. In the POV display the grater resolution of the display means grater proximity of adjacent LED’s.

The picture in CRT display’s like the POV display is actually a series of sequential frames, the rate at which the frames are changed is known as the refresh rate. But the refresh rate means different things in the case of each display. In CRT it means the rate at which the electron gun completes 1 frame, for POV it’s the rpm of the motor.

Differences & Advantages over CRT

Basic and most prominent difference is that the entire method of display is totally different. The most important part of CRT is the electron gun which fires the electrons to the phosphor screen. But in POV we just have LEDs which are indirectly controlled by the uC, no need of a screen.

As the light source is spinning the display seems to be over thin air unlike CRT, the colors are not emitted from a surface. This means that in a POV display you can look through the picture.

CRT have magnetic field to deflect the electron at a proper point at the screen. But in POV nothing like Electric and magnetic field is present.

There is a vacuum present in CRT tube. And if the vacuum condition is disturbed display will not work. Whereas POV can work in vacuum or in air.

Power consumption in POV is very small compared to CRT. Most power consuming part of CRT is the electron gun.

Cost would be an important factor; comparing both POV is comparatively less costly. Because of absence of many components in POV. And the cost of CRT display increases exponentially with the size of screen you buy, but compared to POV where we need just an array of LEDs to display images, cost is very small.

Most important advantage of POV is that the viewing angle is 360 deg. Means the image can be seen from at any angle we want. Whereas in CRT this is not possible the viewing is just in front of the screen. And it is also possible that the images we display are different at one side of viewing than the other side.

The POV display needs radically less number of pixels to produce a higher quality picture.

Pixels in a POV display means LED’S, these led’s inexpensive and abundantly available.

The design enables the POV display to be highly expandable and adaptable.

Unlike today’s TV signals the data signals for POV display are digital in nature hence there is no need for D-A converters at the receiver.

They are not fragile as the gas filled hermetic picture tube of CRT displays.

No high voltage components involved such as the electron gun in CRT, thereby they are safer to handle and design.

LCD

Now we will be discussing about LCD displays. A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). LCs does not emit light directly. LCDs therefore need a light source and are classified as "passive" displays. Some types can use ambient light such as sunlight or room lighting.

Figure 9 LCD cell structure

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are (in most of the cases) perpendicular to each other. With no actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer.

The surfaces of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectional rubbed using, for example, a cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing. Electrodes are made of a transparent conductor called Indium Tin Oxide (ITO).

Figure 10 LCD-Nematic Phase Liquid Crystals

Before applying an electric field, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic device (still the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This reduces the rotation of the polarization of the incident light, and the device appears grey. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray.

Figure 11 LCD lighting

The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). These devices can also be operated between parallel polarizers, in which case the bright and dark states are reversed. The voltage-off dark state in this configuration appears blotchy, however, because of small variations of thickness across the device.

Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).

When a large number of pixels are needed in a display, it is not technically possible to drive each directly since then each pixel would require independent electrodes. Instead, the display is multiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together (typically in columns), and each group gets its own voltage source. On the other side, the electrodes are also grouped (typically in rows), with each group getting a voltage sink. The groups are designed so each pixel has a unique, unshared combination of source and sink. The electronics or the software driving the electronics then turns on sinks in sequence, and drives sources for the pixels of each sink.

Specifications of LCD

Resolution: The horizontal and vertical screen size expressed in pixels (e.g., 1024×768). Unlike CRT monitors, LCD monitors have a native-supported resolution for best display effect.

Dot pitch: The distance between the centers of two adjacent pixels. The smaller the dot pitch size, the less granularity is present, resulting in a sharper image. Dot pitch may be the same both vertically and horizontally, or different (less common).

Viewable size: The size of an LCD panel measured on the diagonal (more specifically known as active display area).

Response time: The minimum time necessary to change a pixel's color or brightness. Response time is also divided into rise and fall time. For LCD monitors, this is measured in btb (black to black) or gtg (gray to gray). These different types of measurements make comparison difficult.[2]

Input lag - a delay between the moment monitor receives the image over display link and the moment the image is displayed. Input lag is caused by internal digital processing such as image scaling, noise

reduction and details enhancement, as well as advanced techniques like frame interpolation. Input lag can measure as high as 3-4 frames (in excess of 67 ms for a 60p/60i signal). Some monitors and TV sets feature a special "gaming mode" which disables most internal processing and sets the display to its native resolution.

Refresh rate: The number of times per second in which the monitor draws the data it is being given. Since activated LCD pixels do not flash on/off between frames, LCD monitors exhibit no refresh-induced flicker, no matter how low the refresh rate.[3] High-end LCD televisions now feature up to 240 Hz refresh rate, which allows advanced digital processing to insert additional interpolated frames to smooth up motion, especially with lower-frame rate 24p material like the Blu-ray disc. However, such high refresh rates may not be supported by pixel response times, and additional processing can introduce considerable input lag.

Matrix type: Active TFT or Passive.

Viewing angle: (coll., more specifically known as viewing direction).

Color support: How many types of colors are supported (coll., more specifically known as color gamut).

Brightness: The amount of light emitted from the display (coll., more specifically known as luminance).

Contrast ratio: The ratio of the intensity of the brightest bright to the darkest dark.

Aspect ratio: The ratio of the width to the height (for example, 4:3, 5:4, 16:9 or 16:10).

Input ports (e.g., DVI, VGA, LVDS, Display Port, or even S-Video and HDMI).

Construction & Working of LCD

To create an LCD, take two pieces of polarized glass. A special polymer that creates microscopic grooves in the surface is rubbed on the side of the glass that does not have the polarizing film on it. The grooves must be in the same direction as the polarizing film. Then add a coating of nematic liquid crystals to one of the filters. The grooves will cause the first layer of molecules to align with the filter's orientation. Then add the second piece of glass with the polarizing film at a right angle to the first piece. Each successive layer of TN molecules will gradually twist until the uppermost layer is at a 90-degree angle to the bottom, matching the polarized glass filters.

As light strikes the first filter, it is polarized. The molecules in each layer then guide the light they receive to the next layer. As the light passes through the liquid crystal layers, the molecules also change the light's plane of vibration to match their own angle. When the light reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final layer of molecules. If the final layer is matched up with the second polarized glass filter, then the light will pass through.

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If we apply an electric charge to liquid crystal molecules, they untwist. When they straighten out, they change the angle of the light passing through them so that it no longer matches the angle of the top polarizing filter. Consequently, no light can pass through that area of the LCD, which makes that area darker than the surrounding areas.

Building a simple LCD is easier than we think. We start with the sandwich of glass and liquid crystals described above and add two transparent electrodes to it.

Figure 12 How LCD works

The LCD needed to do this job is very basic. It has a mirror (A) in back, which makes it reflective. Then, we add a piece of glass (B) with a polarizing film on the bottom side, and a common electrode plane (C) made of indium-tin oxide on top. A common electrode plane covers the entire area of the LCD. Above that is the layer of liquid crystal substance (D). Next comes another piece of glass (E) with an electrode in the shape of the rectangle on the bottom and, on top, another polarizing film (F), at a right angle to the first one.

The electrode is hooked up to a power source like a battery. When there is no current, light entering through the front of the LCD will simply hit the mirror and bounce right back out. But when the battery supplies current to the electrodes, the liquid crystals between the common-plane electrode and the electrode shaped like a rectangle untwist and block the light in that region from passing through. That makes the LCD show the rectangle as a black area.

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Comparing POV & LCD

Similarities

A display with a higher resolution will be able to reproduce a picture accurately with smoothly varying colours. For a CRT this depends on the nature of the electron beam and me masking of the adjacent pixels. In the POV display the grater resolution of the display means grater proximity of adjacent LED’s.

The picture in CRT display’s like the POV display is actually a series of sequential frames, the rate at which the frames are changed is known as the refresh rate. But the refresh rate means different things in the case of each display. In CRT it means the rate at which the electron gun completes 1 frame, for POV it’s the rpm of the motor.

Both displays use digital data as opposed to CRT’s analog signals.

Differences and Advantages of POV

Like CRT’s, LCD’s require a screen in order to display a picture. In the case of LCD’s the screen is a plane of LCD pixels. The POV display isn’t bound by this constraint i.e. it doesn’t need a screen (plane) to display images.

A fraction of the number of pixels is needed in the POV display in order to attain the same resolution as a LCD screen.

As lesser components are needed, the cost of the POV display is lower than a LCD.

Between the basic components, LCD units & LED, Led’s are much cheaper to buy than LCD unit.

LCD’s have a great disadvantage of being notoriously fragile.

The switching time of LED’s (nS) is much lower than that of LCD’s (µS). This means a much higher refresh rate is possible in POV displays.

Power consumption of LED’s displays are low compared to LCD’s.

LCD is a passive device that means that they need an external light source, this light sources should be of v high quality. LED’s do not require an external light source as they themselves are one.

Viewing angle very much limited in LCD, for best viewing person should try to be in front of screen only. But no such constraints are there in POV.

INGENIOUS DESIGN OF POV

After comparison we came to know that POV is very ingenious and robust. But it lacks in certain aspects of color displays of LCD. None the less best advantage is the viewing angle of POV as we have already mentioned it while comparing of POV with LCD and CRT.

We have been talking throughout the project about the 3D implementation of POV. That display would beat LCD and CRT in displaying objects which is not at all possible with LCD and CRT.

POV is ingenious in display image because it is just an array of LEDs which are revolving at a certain speed in circular circumference. The vertical array can be as big in length as we want. The image looks so factual as if it is created out of nowhere because the PCB on which the LED are fixed became invisible because of the rotational speed. And this results in our 360 deg viewing advantage.

Chapter – 3

Hardware interfacing

ContentsHardware interfacing.................................................................................................................................32

Block Diagram........................................................................................................................................33

System Components..............................................................................................................................35

System Operation..................................................................................................................................36

Unique System Elements.......................................................................................................................37

Dual Power Supply.............................................................................................................................38

Position Triggering using Interrupts...................................................................................................39

Interfacing with 74HC259..................................................................................................................41

Simplified Flow diagram....................................................................................................................42

Circuit Diagrams........................................................................................................................................44

POV – 1 Board........................................................................................................................................45


POV – 2 Board........................................................................................................................................47


POV – 3 Board........................................................................................................................................49

Discription & Function for POV – 3....................................................................................................50

Distribution of Hardware among 3 boards............................................................................................51

Block Diagram

Figure 13 Project Block Diagram

Atmega16

Layer1 Slav

e74HC2

9

Layer2 Slav

e74HC

29

Layer2 Slav

e74HC

29

Layer2 Slav

e74HC

29

Layer2 Slav

e74HC

29

The entire system is made up of the following components

Micro controller - Atmega 16/32 Bit-Addressable latch – MM74HC259 Op-Amp – LM398 IR sensor – IR led + IR photodiode pair

The set-up is mounted over a simple dc motor that rotates it at a constant speed. The rotating board is provided power by 9v batteries that are connected to the system through voltage regulating IC’s that change the level of the power supply to the standard that is fit for the system.

The Atmega16 microcontroller houses decent computational power and also satisfies all the memory requirements for our project.

The program procedure reads the information stored in one of the 4 internal memories of the microcontroller, decodes it and provides appropriate signaling to its peripherals to represent the desired message in a unique form on the rotating platform.

System Components

Purchased components,

Microcontroller - Atmega16\32 8-bit Addressable Latch – 74HC259 Dual Op-amp – LM358 Visible-Spectrum spherical led’s Infrared sensor emitters – IR led’s Infrared sensor receiver – IR photo diode Voltage regulator – 7805 220Vac to 32V dc adapter 9V batteries

Salvaged or Improvised components,

Salvaged DC motor Acrylic fibreglass plank as platform Laptop packaging material

For details on the components please refer to Chapter – 4 and Appendix – 2.

System Operation

The operations of the system can be classified into the following,

To retrieve data from its memory. Process the data appropriately and to convey it through proper signalling to its peripherals. Processing various interrupts that may arrive randomly.

All operations are done centrally by the microcontroller except providing the interrupts. On the reception of the interrupt the microcontroller executes an ISR or the interrupt service request. The ISR is a procedure that is to be followed by the microcontroller when it receives a particular interrupt.

The EEPROM memory of the Atmega16 has a word-length of 16 bits or 2 bytes. These pairs of bytes are broken down to bit level, and then they are inserted into a stream of bits that are synchronized with the other operations of the microcontroller. If the microcontroller retrieves conflicting information from its memory it has the ability to choose to display no data.

The system is built around the microcontroller Atmega16, this microcontroller from the Atmel cooperation is available in many flavors that are targeted towards various fields and specific applications. We used the Atmega6L and the Atmega32L for our project.

Atmega16L provides us with the additional feature that these versions of the microcontroller can withstand and maintain decent operation even at v low voltage levels. The Atmega16L has an operational range of

Atmega16/32 – 4.5-5.5V Atmega16L/32L – 2.2-5.5V

This means that the atmega16L can maintain normalcy at 2.2V.

If the voltage falls below the prescribed minimum for the microcontroller then the microcontroller goes into what is called a brown-out.

Unique System Elements

This part of the report will talk about parts that provide the system a platform on which it performs much more advanced functions.

Dual Power Supply Position triggering using interrupts Interfacing with 74HC259

All the above mentioned components integrated on a printed circuit board (PCB) construct a system that can perform all the function as discussed earlier. A complete description of the interfacing and construction of the components has been discussed in this section.

Dual Power Supply

The entire system functions on a 5v power supply this power can be drawn from a single 9V battery, but we used 2 batteries and 2 different 7805 IC’s for each battery.

The use of 2 IC’s for 2 batteries gives the advantage of having independent ripple free power for the sensitive parts of the circuits.

Figure 14 Dual Power Supply

A quick study of the above circuit will reveal that the PCB houses 2, 7805IC’s. The operation of the system involves the v high frequency switching of a large number of LED’s. This means constantly changing loads on the battery. A change in loads causes the change in the current linked to the circuit.

Position Triggering using Interrupts

Figure 15 Position Triggring Mechanism

An interrupt is sent to the microcontroller when it’s sensed by the IR sensor that the distance of the rotating platform from the stationary surface is less than a limit. This triggering distance can be tuned using a potentiometer.

Figure 16 IR Sensor

This part of the system need to have a v constant level of the power supply. The sudden level changes in the power supply lead to erroneous triggering of the sensors. The interrupt is generated by a dual op-amp IC LM398. The IC is used as an open-loop comparator.

This means that the sensor is highly sensitive but is also susceptible to noise and is stable for a small range of inputs.

The heightened sensitivity of the sensor has a drawback that it makes the system extremely sensitive to surrounding temperatures, that means that the sensor has different triggering levels at different temperatures.

As the sensing medium is IR radiations the sensing mechanism is also sensitive towards sunlight. Operation in sunlight will cause the sensor to trigger randomly at all positions.

Interfacing with 74HC259

Figure 17 IC 74HC259

To operate this device as an addressable latch, data is held on the D input, and the address of the latch into which the data is to be entered is held on the A, B, and C inputs.

When ENABLE is taken LOW the data flows through to the addressed output. The data is stored when ENABLE transitions from LOW-to-HIGH. All unaddressed latches will remain unaffected. With enable in the HIGH state the device is deselected, and all latches remain in their previous state, unaffected by changes on the data or address inputs.

In order to operate this IC correctly the following procedure needs to be followed.

1. 1-bit data is held on the D input2. The address of the latch into which the data is to be entered is held on the A, B, and C inputs.3. Enable is taken LOW.4. Enable is taken HIGH5. The o/p of the latch is now independent of the state of the data pin.

Simplified Flow diagram

Start

Initiate EEPROM variable array

Save i th byte into buffer variable

Capture the j th bit

Select the desired Layer2 slave, by placing its address on the

Layer 1 slave.

Select the desired LED connected to slave, by

placing its address on the Layer 2 slave.

Place 1 bit of data on the common DATA line of the

Layer2 slaves

Pull Layer1 slave ENABLE to LOW

A

Pull Layer1 slave DATA to LOW

Pull Layer1 slave DATA to HIGH

Pull Layer1 slave ENABLE to HIGH

STOP

A

Circuit Diagrams

We have divided the system into circuits; these circuits are on 3 different PCB’s connected via ribbon connectors. These boards are placed on the either sides of the rotating acrylic platform and in the center. These 3 boards are as follows,

POV – 1 POV – 2 Master POV – 3

These 3 boards have different functions and are designed differently, the design and the connection diagrams of these boards is shown and discussed in the next section.

POV - 3POV - 1 POV - 2

Acrylic sheet

POV – 1 Board

Figure 18 POV – 1 Board

Name Sign Number74HC259 U2,U3 2

Visible LED - 161Kohm resistance R1 17

LM358 U3 120-pin Ribbon connector J1 1

IR LED - 2IR photodiode - 1

Potentiometer 100K - 11 Mohm R18 1

Description & Function for POV – 1

The POV -1 board is set on the acrylic plank in an upright position it is held into place by a plastic angle on the edge of the board. Of the 2 boards the POV – 1 board is more complex as it involves the only input stream towards the microcontroller.

Out of the 20 circuit’s that the ribbon wire provides the POV – 1 board uses 12. This board also is provided with a separate regulated power supply for the sensor and LM398.

Controls 16 visible spectrum LEDs. Houses 2 IR spectrum LEDs Uses IR receiver to measure the amount of IR light. This is dependent upon the distance of the

reflecting surface from the source of the IR light. Uses LM398 as a comparator to compare the o/p of the sensor to a fixed dc level. The fixed dc level can b changed by tuning a potentiometer. Separate regulated DC supply for sensor related circuitry. Separate DC supply reduces the chance of erroneous firing of the comparator. The o/p of the comparator is connected directly to the INT0 (16) of the microcontroller via the

20 pin ribbon wire. Soldering done on both sides of the board to enable us to fit the circuit in a small area. This is

unconventional as the PCB isn’t made to do this. Tin wire used with a flux core Lead (Pb) soldering wire.

Resistors that were used to load the LED’s were set-up in an unconventional fashion to save PCB area for the rest of the circuit.

POV – 2 Board


The above board contains the following components,

Name Sign Number74HC259 U2,U3 2

Visible LED - 161Kohm resistance R1 16

20-pin Ribbon connector J1 1


The POV -2 board is set on the acrylic plank in an flat position it is held into place by 2 screws on the edge of the board. Of the 2 boards the POV – 2 board is less complex as it only involves controlling the LEDs by the command of the microcontroller.

Out of the 20 circuit’s that the ribbon wire provides the POV – 2 board uses 9. This board is only provided with 1 regulated 5V supply, this supply comes from the same 7805 that provides the supply to the POV – 1 board for the LED’s.

Controls 16 visible spectrum LEDs. Soldering done on both sides of the board to enable us to fit the circuit in a small area. This is

unconventional as the PCB isn’t made to do this. Tin wire used with a flux core Lead (Pb) soldering wire.

Resistors that were used to load the LED’s were set-up in an unconventional fashion to save PCB area for the rest of the circuit.

POV – 3 Board


The above board contains the following components,

Name Sign NumberAtmega16L U1 174HC259 U2 1

20-pin Ribbon connector A,B,C,D 47805 U3,U4 2

9V Battery Connector J5,J6 2


The POV – 3 board is set on the acrylic plank in the middle of the length, above the joint between the plank and the motor axel. Out of all the 3 boards the POV – 3 board is the most complicated as it contains the microcontroller. Designing and the fabrication of this board was the most difficult and the most effort consuming of all the activities.

The board provides 4 20 pin ribbon connectors, each connector can control 2 X 74HC259s, and each layer 2 slave can have 8 LEDs connected to it, which makes 16 Led’s per connector. Therefore the POV – 3 board can control 4 X 16 = 64 LEDs individually.

The board uses 1 74HC259 (Layer1 Slave) to control up to 8 74HC259 (Layer2 Slave). The layer1 slave takes up just 7 pins of the microcontroller; therefore the microcontroller just has to employ 7 pins to control 64 LEDs.

Uses Atmega16L & 74HC259 to control unto 64 LEDs As it contains the microcontroller it contains the intelligence. Provides 4 X 20 pin ribbon connectors. Contains the 2 regulating IC’s that are used to generate 2 regulated voltage sources. The board is connected to 2 X 9V batteries. Out of the 4 ribbon connectors A, B, C & D connector A is special as only it has the ability to

connect a board of the type POV – 1. The other connectors can only connect boards of the POV–2 type.

Soldering done on both sides of the board to enable us to fit the circuit in a small area. This is unconventional as the PCB isn’t made to do this. Tin wire used with a flux core Lead(Pb) soldering wire.

Distribution of Hardware among 3 boards

POV – 1 Board POV – 2 Board

POV – 3 Board

Start

Initiate EEPROM variable array

Save Major th byte into buffer variable

Capture the Minor th bit in Major th byte

Major =Byte no. in EEPROM

Minor=Bit in a byte.

Select the desired LED connected to slave, by

placing its address on the Layer 2 slave.

Place 1 bit of data on the common DATA line of the

Layer2 slaves

Pull Layer1 slave ENABLE to LOW

A

C

D

Microcontroller

Layer1 Slave

Layer2 Slave Layer2 Slave Layer2 Slave Layer2 Slave

YES

NO

Pull Layer1 slave DATA to LOW

Pull Layer1 slave DATA to HIGH

Pull Layer1 slave ENABLE to HIGH

Increment Minor

Is Minor < 8

A

B

C

YES

YES

NO

B

Increment Major

Minor = 0

D

Is Major > EEPlen

?

E

E

Major = 1

Minor = 0

Is Iflag =

1 ?

E

D

Chapter – 4

Motor....................................................................................................................................................56

Spherical LEDs........................................................................................................................................58

Voltage/Design Current.....................................................................................................................60

Operating Life....................................................................................................................................60

Precautions While Working With LEDs..............................................................................................60

Base.......................................................................................................................................................61

Rotating Platform..................................................................................................................................62

THE CONTENTS..................................................................................................................................62

THE JOINT..........................................................................................................................................62

ASSEMBLY..........................................................................................................................................63

Organization..........................................................................................................................................64

Orientation............................................................................................................................................65

Motor

Motor in itself is a very important component of our project. As the appropriate display required a particular speed and stability in motion, it became imperative that we use a motor of specific rating and performance indices.

Main functions that we required our motor to perform are –

As the display depends on high speed switching of LEDs, we require a rotational motion of high rpm values. In our case, the count must be at least 1500 rpm.

Motor must have a strong axel to support and balance the rotating platform. As explained in later text, the micro-controller and other latches are fixed on several PCBs. These PCBs are mounted on a platform which is fixed to the axel of motor.

Along with rpm count, we also require the motor to provide a respectable amount of torque considering the weight of entire assembly that is rotated.

Apart from these features, it is expected that motor can be easily operated with the easily available power source. This means that, it should be of appropriate power rating.

After going through market over some available motors, we eventually found the perfect match in form of a second-hand available at meena bazaar market of old delhi.

Following are the characteristics of our motor –

o DC motor that earlier used to drive rollers in photocopy machineso Rpm count of 1500-1800 rotations per minute, at no-load.o Rated Voltage - 25V DCo Motor is able to provide a respectable amount of torque considering its size and our

requirements.

Although the motor was very much suitable to the project’s requirements, there were some minor problems that we encountered while setup.

The high torque output created a a problem for as the motor was very hard to hold on to one place, this problem however was solved by applying simple mechanical ingenuity.

There was a sharp fall in the rpm of the motor as soon as we applied the indented load on to it, the rpm in the end was less than we would have liked it to be.

Considerations were also made about using stepper motors, but the idea was dropped at an early stage foreseeing the rpm deficiency of a common stepper motor. The use of stepper is not impossible however, a stepper motor will ensure immaculate synchronization between the led’s and there rotation.

An ideal display will constitute of the advantages of the stepper and the rotational speed of the DC motor.

Overcoming these problems by certain mechanical rearrangements, we were able to employ motor successfully in our project.

Spherical LEDsBasically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescent bulbs, they don't have a filament that will burn out, and they don't get especially hot.

Speaking solely in technical terms, light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting.

The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons.

Being used as a primary source of lighting, they come in various shapes and sizes.

But, other than these aspects, LEDs are also categorized on features such as power rating, material used, light output etc.

The LEDs that we used are Spherical in shape and hence are commonly called as spherical LEDs. These are available in many colors but owing to maintain a better view, we chose to use RED color LEDs in our project.

Following are the technical details about LED that we used. Ours belong to the standard brightness type.

http://en.wikipedia.org/wiki/Photon

http://en.wikipedia.org/wiki/Electron_hole

http://en.wikipedia.org/wiki/Carrier_generation_and_recombination

http://en.wikipedia.org/wiki/Electrons

http://en.wikipedia.org/wiki/Semiconductor_diode

http://en.wikipedia.org/wiki/Lighting

http://en.wikipedia.org/wiki/Semiconductor

http://www.howstuffworks.com/light-bulb.htm

A feature of LED’s is their narrow visibility angle for the rotating panel the narrow angle of common LED would prove to be devastating as in the respect to stationary observer the LEDs are moving through a wide range of angle. For the display to work, we want each led to be visible throughout the rotation of the panel.

After a lot of scouring we were able to find a variant that had a spherical casing that caused the light to be scattered on a wider angle at the cost of lesser brightness. The spherical LEDs also had a moderate switching time as opposed to the low switching time that we would have liked.

Using the spherical LED’s was a gamble that could have proved to be the show stopper but luckily it didn’t cost us that much.

Luminous intensity (Iv) does not represent the total light output from an LED. Both the luminous intensity and the spatial radiation pattern (viewing angle) must be taken into account. If two LEDs have

the same luminous intensity value, the lamp with the larger viewing angle will have the higher total light output.

Voltage/Design CurrentLEDs are current-driven devices, not voltage driven. Although drive current and light output are directly related, exceeding the maximum current rating will produce excessive heat within the LED chip due to excessive power dissipation. The result will be reduced light output and reduced operating life.

LEDs that are designed to operate at a specific voltage contain a built-in current-limiting resistor. Additional circuitry may include a protection diode for AC operation or full-bridge rectifier for bipolar operation. The operating current for a particular voltage is designed to maintain LED reliability over its operating life.

Operating LifeBecause LEDs are solid-state devices they are not subject to catastrophic failure when operated within design parameters. This is another reason as only LEDs are capable of being switched over at such a fast rate as required by our project.

Precautions While Working With LEDs Static electricity and surge damage LEDs. It is recommended to use a wrist band or anti-

electrostatic glove when handling the LEDs. All devices, equipment and machinery must be electrically grounded.

Bending should be performed with the base firmly fixed by means of a jig or radio pliers.

The leads should be formed so they are aligned exactly with the holes on the PC board. This will eliminate any stress on the LEDs.

Solder the LEDs no closer than 3mm from the base of the epoxy resin.

For solder dipping, it may be necessary to fix the LEDs for correct positioning. When doing this, any mechanical stress to the LEDs must be avoided.

When soldering, do not apply any mechanical force to the lead frame while heating.

Base

Base is an assembly of a cardboard case with layers of wooden leaf inside out, to support the lid. This lid has a hole in the centre with a cross-section area equal to that of motor. So, this arrangement is designed to hold motor attached to the base, in a stable position.

Along with motor, platform also provides a storage place for the power adopter. This adopter gets supply from an external source and so, there are wire coming from and to the base. In this scenario, we have to cautious while the motor is moving as there is significant risk of wire being struck with the rotating blades.

As the motor rotates at a high speed, it is natural that it provides a recoil force at its start and jerks while in motion. So, motor has to be attached to the base by some very rigid measures that can make the recoil and jerks bearable. To achieve this, we got a pair of iron angles manufactured (from a local workshop) in shape of alphabet Z. These angles are screwed at their ends and thus provided a strong grip over motor being attached to the base.

Another problem was that being attached to base very rigidly, the assembly as a whole becomes a singe unit. This being the case, there is always a chance that a bump or jolt in motion can knock out the entire assembly. To overcome this problem, we had to introduce some flexibility in the base, so that it can withstand these minor jolts (which were obviously random and accidental). This was achieved by introducing two form based stands for the base assembly. These form stands could provide assembly flexibility in movement and avoid any accidental risks.

Rotating Platform

Rotating platform or panel is that component which actually carries the display and the components that generate it. In this sense, this panel is the most delicate and important part of the hardware section.

This panel is the one that rotates and eventually generates the display. And so, it is but natural that it is connected to the shaft of the motor.

THE CONTENTSThis platform is important not only in terms of its positional aspects but also due to the fact that it carries the most important and delicate parts. These include all the electronic components of the project including the micro-controller and display. There are three PCB boards placed onto this panel.

Two are the display PCBs fixed at two ends. These have LED array and latches to operate them. In the centre is the master PCB that actually controls and monitors the display. This PCB has the microcontroller and slave latch along with communication ports.

In this context, this panel is the most important part of the project and has to handled and protected very carefully. Any mistake on this part can null the entire effort to this point.

THE JOINT Juncture of the motor shaft and this panel is of prime significance. It is so because, rotating at a speed of near about 1500rpm, there is a large amount of centripetal force acting at this point. Add to that, this point also has to hold the central PCB that carries the micro-controller and other latches.

It was obligatory to make this junction strong and congealed. If not done properly, this could prove destructive to the entire project as the PCBs are very delicate and the speed of rotation is extremely high. If joint fails at this point, the components of panel would fly away, causing injuries to the viewers and permanent damage to the project.

To congeal this joint, we used a kind of connecter between motor shaft and the panel. It was done because there is a very significant difference between cross-sectional area of shaft and the base area of panel. To avoid this problem, we introduced a kind of connector that at one end had an hollow section of area almost equal to shaft, and on the second end was large enough to cover width of panel. To ensure proper cementation, we used screws at both the ends.

ASSEMBLY

The assembly is the product of combination of all the hardware components that we have described earlier, in a specific order.

We had to ensure that every part was in its position and interacted with others properly and in manner as it is required to.

So, assembling the project was a delicate and rigorous task. Each connection and joint is specific and crucial. In this aspect, we could not risk ignoring even the minute details. Loose wires, specially the ones from power adopter to external supply were given extra attention. Other than that, there is a necessary requirement of providing a dark background and a white spot on it. This serves as the triggering point, and is specially organized before starting the display.

Another important thing that must be mentioned is that the LEDs and the PCBs on the rotating platform do not have any electrical connections with external power source. In this context, we have to provide two 9 v ac batteries. These must be assembled along with the rotational platform and are attached to the rotational platform with some tape or similar material.

Completing these mentioned steps, we have our project ready to perform. But, before that there are few steps to be mentioned. These are in next chapters. In the mean while, this is how our project now looks like.

Organization

Before the display is started, it must be organized, keeping in mind what are per-requisite conditions.

For instance, placement of triggering spot and adjustment of the I-R sensor is one such thing that must be organized properly as it can distort the display in several manners.

Another such condition is that the 9-v AC batteries must be connected to the PCBs before starting the display. As these are non-rechargeable batteries, they cannot be left switched-on all the time and must be connected before starting the display.

Loose wires should be properly tucked away so that they don’t tangle in the rotational motion on the platform. These are power source to the motor.

Orientation

There are several conditions (external) that may hinder or distort the display.

So, a check on these can make display better and brighter.

These are:-

If possible, the lightning conditions of the surroundings should be kept dim; this makes display appear brighter due to effusive contrast. In otherwise brighter surroundings, display might be fade.

The background should be dark in contrast to a white triggering point. This is necessary to get a starting point in display.

Surrounding temperature must be near about room temperature and should not change rapidly. This effects I-R sensor and may distort display.

Chapter 5

Future Development and Advantages

ContentsFuture Development and Advantages.......................................................................................................69

Future development..............................................................................................................................70

ADVANTAGES........................................................................................................................................71

CHALLENGES IN DESIGN........................................................................................................................74

Future development

As our project uses Atmega 16/32 microcontroller and 74HC259 latches, these components don’t just let us do whatever we want but the design is so expandable in terms of number of LEDs used for display.

We have just used 3 pins from port A and 3 pins from port B of microcontroller for Layer 1 slave. But as we know uC has 4 ports (A, B, C, and D in Atmega 16/32) with 8-pins in each of the ports. If we use all of we have used 2 pins from port B and 3 pins from port A.

Let us considers Layer-1 slaves. Now each of the layer-1 slaves(latch) has 8 outputs ports, so if 2 output port controls 1 Layer-2 slave(latch IC) then each layer-1 slave can control 4 layer-2 slaves making the LEDs numbers to go up to 4*8=32 LEDs indirectly attached to 1 layer-1 slave.

Let us say we control one layer-1 slave from each ports of uC that means we have 4 layer-1 latches. Now number of layer-2 latches will be 4*4=16 latches. Now number of LEDs will go up to 16*8=128 LEDs. This makes our design very versatile and robust.

As our design uses a 1D layer of LEDs array to display 2D messages with 360 deg of viewing angle. The displaying of messaging is linear in development, by that we means our 1D array display 2D messages similarly 2D array of LEDs will be sufficient for displaying 3D images.

The images in 3D will definitely depend on the arrangement of LEDs array and the rotation of LEDs similarly as our project does. The 3D display would have no boundation in the content of images or messages it displays. And the USP of this display would be its viewing angle of 360 deg. It would not possible for any other kind of displays devices such as LCD or CRTs to have such accomplishment.

As LCDs and CRTs just give us a factual 3D images with viewing angle just in front of the screen. This is totally absent if we talk about 3D POV displays. The person can see the image by moving himself/herself around the display device to get the feel of it.

As we have already mentioned 3D would have no boundations in terms of displaying anything from capturing live humans motions to static postures of living and non living objects.

ADVANTAGES

The great advantage of this display would be in medical science. In operations or surgery it can used to display the organ or body part to be display in 3D. And the surgeons can view each of their movements singlehandedly without loving at different LCDs for different angles. This would definitely increase their efficiency and accuracy.

If we human’s beings are capable enough to make a huge display these pins then 5 numbers of layer 1 slaves (latches) can be configured with it. For layer 2 slaves

of size like a theatre screen then. No persons watching a movie in 3D would have worn goggles which they gave you wear it now throughout the screening of the movie/video to experience 3D effects. It would then would be like sitting causally simultaneously not straining our eyes with goggles. And this would just not helpful to the viewer but also to owner also. Because now they just have to give seats to viewer in front of screen only, but with POV the whole 360 deg area will be there and seating capacity would increase many fold. Both will get the benefits.

Below is a picture showing a POV capable of showing 3D images with 360 deg viewing angle.

Figure 21 3D IMAGE OF GLOBE USING 2D ARRAY OF LEDs

Figure 22

(The image shows an 2D array of LEDs on rectangular board, which rotates on high speed motor, thereby displaying a 3D image)

Figure 23 DESIGN GENERATED USING 1D ARRAY

Ultra ORB is a multi-axis three dimensional persistence of vision piece that uses rotation upon two perpendicular axes in tandem with microprocessor control to create visual displays within a three dimensional volumetric space

POV as they uses LEDs there is not much problem of contrast ratio in display. LEDs will just have to switch ON/OFF which give them from 0 brightness to maximum brightness. This is one of the USPs of POV compared to other displays.

CHALLENGES IN DESIGN

The greatest challenge to achieve this kind of technology is precision, color effect and cost effectiveness of POV displays. The cost is very comparable in small size but increases with the size. Because as the size of display increases we require more powerful motor to rotate the display boards.

Secondly the precision of display is important which depends on the size of LEDs and the closeness among themselves. With technology advancement making of small enough LEDs would be possible and the integration of LEDs on PCBs. Like the advancements we have in electronic circuits SCI, MSI, LSI, and ULSI. Similar technology advancement would definitely happen in POV displays.

Finally the color effect. By this we mean POV will have a problem with displaying images in its actual texture. As it is very easy to have display with same color LEDs but to have an actual real nature effect we really need to have an RGB effect similar to those of CRT and LCD. Where these three colors RGB produce every color our human eyes can perceive. As in the previous case this would be possible with technology advancement where a single LED would somehow be capable of displaying RGB colors.

With this kind of digital age waiting for us we cannot stand to wait long. As our curiosity has touched every limit while making this project. Every technology has some shortcomings but it is what we have to overcome.

APPENDIX

ContentsBascom – AVR Family.........................................................................................................................72

Eclipse........................................................................................................................................................73

Utilization of JAVA Classes.................................................................................................................74

74HC259................................................................................................................................................82

Features.............................................................................................................................................82

Pin Diagram.......................................................................................................................................83

Latch Selection Table.........................................................................................................................84

Truth Table........................................................................................................................................84

Logic Diagram....................................................................................................................................85

Absolute Maximum Ratings...............................................................................................................86

Recommended Operating Conditions................................................................................................86

LM358........................................................................................................................................................87

Advantages........................................................................................................................................87

Features.............................................................................................................................................87

Pin Diagram...........................................................................................................................................88

IR Detection Couple...................................................................................................................................89

Basscom Program......................................................................................................................................91

Bascom – AVR Family

Since Atmel's AVR microcontrollers were introduced to the market only a few years ago, they are not so well known as the 8051 controllers. Therefore, this interesting microcontroller family should be described in more detail.

Atmel's AVR microcontrollers use a new RISC architecture which has been developed to take advantage of the semiconductor integration and software capabilities of the 1990's. The resulting microcontrollers offer the highest MIPS/mW capability available in the 8-bit microcontrollers market today.

The architecture of the AVR microcontrollers was designed together with C-language experts to ensure that the hardware and software work hand-in-hand to develop a highly efficient, high-performance code.

To optimize the code size, performance and power consumption, AVR microcontrollers have big register files and fast one-cycle instructions. The family of AVR microcontrollers includes differently equipped controllers - from a simple 8-pin microcontroller up to a high-end microcontroller with a large internal memory. The Harvard architecture addresses memories up to 8 MB directly. The register file is "dual mapped" and can be addressed as part of the on-chip SRAM, whereby fast context switches are possible.

All AVR microcontrollers are based on Atmel's low-power nonvolatile CMOS technology. The on-chip in-system programmable (ISP), downloadable flash memory permits devices on the user's circuit board to be reprogrammed via SPI or with the help of a conventional programming device.

By combining the efficient architecture with the downloadable flash memory on the same chip, the AVR microcontrollers represent an efficient approach to applications in the "Embedded Controller" market.

The AVR microcontrollers make use of a Harvard structure with separate memories and busses for programs and data A flexible interrupt module has its control register in the I/O memory area, too. All interrupts have separate interrupt vectors in an interrupt vector table at the beginning of the program memory. The priority level of each interrupt vector is dependent on its position in the interrupt vector table. The higher the priority of a respective interrupt, the lower is the address of the interrupt vector. All interrupts are maskable and can be enabled or disabled by a Global Interrupt Enable/ Disable.

Eclipse

Eclipse is a multi-language software development environment comprising an integrated development environment (IDE) and an extensible plug-in system. It is written primarily in Java and can be used to develop applications in Java and, by means of the various plug-ins, in other languages as well, including C, C++, COBOL, Python, Perl, PHP, JAVA and others. The IDE is often called Eclipse ADT for Ada, Eclipse CDT for C, Eclipse JDT for Java and Eclipse PDT for PHP.

Eclipse is an open source community, whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle. The Eclipse Foundation is a not-for-profit, member supported corporation that hosts the Eclipse projects and helps cultivate both an open source community and an ecosystem of complementary products and services.

The Eclipse Project was originally created by IBM in November 2001 and supported by a consortium of software vendors. The Eclipse Foundation was created in January 2004 as an independent not-for-profit corporation to act as the steward of the Eclipse community. The independent not-for-profit corporation was created to allow a vendor neutral and open, transparent community to be established around Eclipse. Today, the Eclipse community consists of individuals and organizations from a cross section of the software industry.

The Eclipse Foundation is funded by annual dues from our members and governed by a Board of Directors. Strategic Developers and Strategic Consumers hold seats on this Board, as do representatives elected by Add-in Providers and Open Source committers. The Foundation employs a full-time professional staff to provide services to the community but does not employ the open source developers, called committers, which actually work on the Eclipse projects. Eclipse committers are typically employed by organizations or are independent developers that volunteer their time to work on an open source project.

Utilization of JAVA Classes

The inclusion of JAVA in our project sped up our development and testing phase considerably. All java codes are designed as classes, there are total 5 classes that were created to aid us I the development and the testing process.

The names of the 5 classes are listed below.

POVEventObjects.java BassProgGen.java X16BassProgGen.java POVDemo1.java LineStudyQ1.java

Class POVEventObjects

This is the base class i.e. all other class that are aimed at producing a code in Bascom use this class for their basic functionality. The function of this class is to convert the string provided to it in to actual byte code in hexadecimal form that will be stored in the EEPROM; this data must correctly represent the characters that are wished to be displayed.

These characters include alphabets – 8 bytes

Numbers – Variable, depends on the number

Creating just one class that has the capability to convert all symbols to byte code has its advantages and disadvantages.

AdvantageAny new symbol can be added easily by just updating this class.

Disadvantage This gives rise to a hefty class, which means it’s very long therefore debugging is a cumbersome task. Also being a base class no other class can function without this class.

Class BassProgGen.java

This class uses the underlying classes to generate a Bascom program for 8 uniquely addressable LED’s for just 1 layer of slaves. The addressing of the led starts from 0 to 7 incrementing in the end of each step until 7 is reached, once count reaches 7 it’s bought back to 0.

The layer 1 slave drives 8 eight LED’s by each one of its latch output pins. The program so produced has certain customizable parameters,

Clock frequency of the microcontroller Micro second delay after each step Display String

ImportanceThis step was highly critical as it was the first step in which all the different subroutines of the program worked together to give a coordinated and desired output. This step proved that the hardware components were compatible and were signaling between themselves.

Class POVDemo1.java

This class was the first level of testing resources created, it was used to test the content of the EEPROM it was able to simulate the display of a character in the 8 LED display the only thing required was the hexadecimal bytes that were stored in the EEPROM to represent the characters.

The class worked in 2 steps,

1) To convert hexadecimal bytes into binary bytes to represent each LED by 1 bit.2) To represent each led as ON or OFF in a clear fashion

This class provides background functionality to class POVEventObjects to convert hexadecimal data to binary data. These are some of the screen shots.

POVDemo1 performs simulation for this surface

Class LineStudyQ1

Like POVDemo1.java this class also was developed for testing content, but unlike POVDemo.java it’s for the surface parallel to the rotational plane. This simulation was more significant as it would replicate distortions in the text.

This is clearly more advanced of the 2 simulation platforms. It was made from the ground up to be self sufficient due to the simulation provided by this platform we were able to identify some crucial problems beforehand and alter our plans appropriately.

LineStudyQ1 performs simulation for this surface

The platform also mimics the fading effect, distortions caused by the difference in length of the paths taken by different led’s. The application is a java servelet that means it can be hosted over the internet, it also means that the servelet inherits all the advantages of java most importantly its platform independence.

74HC259

The MM74HC259 device utilizes advanced silicon-gateCMOS technology to implement an 8-bit addressable latch, designed for general purpose storage applications in digital systems.

The MM74HC259 has a single data input (D), 8 latch outputs (Q1–Q8), 3 address inputs (A, B, and C), a common enable input (G), and a common CLEAR input. To operate this device as an addressable latch, data is held on the D input, and the address of the latch into which the data is to be entered is held on the A, B, and C inputs.

When ENABLE is taken LOW the data flows through to the addressed output. The data is stored when ENABLE transitions from LOW-to-HIGH. All unaddressed latches will remain unaffected. With enable in the HIGH state the device is deselected, and all latches remain in their previous state, unaffected by changes on the data or address inputs.

To eliminate the possibility of entering erroneous data into the latches, the enable should be held HIGH (inactive) while the address lines are changing.

If enable is held HIGH and CLEAR is taken LOW all eight latches are cleared to a LOW state. If enable is LOW all latches except the addressed latch will be cleared. The addressed latch will instead follow the D input, effectively implementing a 3-to-8 line decoder.

Features

Typical propagation delay: 18 ns Wide supply range: 2–6V Low input current: 1 mA maximum Low quiescent current: 80 mA maximum (74HC Series)

Pin Diagram

Latch Selection Table

Select LatchC B A

Latch Addressed

L L L 0L L H 1L H L 2L H H 3H L L 4H L H 5H H L 6H H H 7

Truth Table

Inputs Outputs of the Addressed Latch

Each Other Output

FunctionClear Enable(G*

)H L D Qi0 Addressable LatchH H Qi0 Qi0 MemoryH L D L 8-Line DecoderH H L L Clesr

Logic Diagram

Absolute Maximum Ratings

Supply Voltage (VCC) -0.5 to +7.0VDC Input Voltage (VIN) -1.5 to VCC+1.5V

DC Output Voltage (VOUT) -0.5 to VCC+0.5VPower Dissipation (PD) 600 mW

Recommended Operating Conditions

Supply Voltage (Vcc) 2 6 VDC Input or Output Voltage (Vin,

Vout)0 Vcc V

Operating Temperature Range (Ta)

-40 +85 C

Input Rise or Fall Times Vcc = 2.0V

1000 ns

Input Rise or Fall Times Vcc = 4.5V

500 ns

Input Rise or Fall Times Vcc =6.0V

400 ns

Min Max Units

LM358

The LM358 series consists of two independent, high gain, internally frequency compensated operational amplifiers which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage.

Application areas include transducer amplifiers, dc gain blocks and all the conventional op amp circuits which now can be more easily implemented in single power supply systems. For example, the LM358 series can be directly operated off of the standard +5V power supply voltage which is used in digital systems and will easily provide the required interface electronics without requiring the additional ±15V power supplies.

The LM358 and LM2904 are available in a chip sized package (8-Bump micro SMD) using National’s micro SMD package technology.

Advantages Two internally compensated op amps Eliminates need for dual supplies Allows direct sensing near GND and VOUT also goes to GND Compatible with all forms of logic Power drain suitable for battery operation

Features Available in 8-Bump micro SMD chip sized package, (See AN-1112) Internally frequency compensated for unity gain Large dc voltage gain: 100 dB Wide bandwidth (unity gain): 1 MHz (temperature compensated) Wide power supply range:

o Single supply: 3V to 32Vo or dual supplies: ±1.5V to ±16V

Very low supply current drain (500 μA)—essentially independent of supply voltage Low input offset voltage: 2 mV Input common-mode voltage range includes ground Differential input voltage range equal to the power supply voltage

Large output voltage swing

Pin Diagram

IR Detection Couple

Infrared phototransistors are almost like standard NPN transistors. NPN transistors require a current at the base to allow a large current to flow from the collector to the emitter. The infrared phototransistor operates on the same principle, however the small current is created by infrared light.

Shown below is one infrared phototransistor and one infrared LED. These are available in the easy to use T1 3/4 package.

An IR proximity sensor works by applying a voltage to a pair of IR light emitting diodes (LED’s) which in turn, emit infrared light. This light propagates through the air and once it hits an object it is reflected back towards the sensor. If the object is close, the reflected light will be stronger than if the object is further away.

Appendix – 4

Basscom Program

$regfile = "m32def.dat"

$crystal = 8000000

Config Porta = Output

Config Portb = Output

Config Pind.2 = Input

Config Int0 = Rising

$eeprom

Data &H0 , &H0 , &H0 , &H0 , &H0 , &H0 , &H0 , &H0 '8 PADDING BYTES

Data &H00 , &H3F , &H48 , &H48 , &H48 , &H3F , &H00 'A

Data &H00 , &H7F , &H08 , &H18 , &H24 , &H43 , &H00 'K

Data &H00 , &H32 , &H49 , &H49 , &H49 , &H26 , &H00 'S

Data &H00 , &H7F , &H08 , &H08 , &H08 , &H7F , &H00 'H

Data &H00 , &H3F , &H48 , &H48 , &H48 , &H3F , &H00 'A

Data &H00 , &H40 , &H40 , &H7F , &H40 , &H40 , &H00 'T

Data &H0 , &H0 , &H0 , &H0 , &H0 , &H0 , &H0 , &H0 '8 PADDING BYTES

'Number of bytes = 42

$data

On Int0 Nullpoi

Enable Interrupts

Enable Int0

Dim Iflag As Bit

Iflag = 0

Dim S As Byte

S = &HFF

Dim Bq(58) As Eram Byte At &H0020

Dim Minor1 As Integer , Major1 As Integer , Minor2 As Integer , Major2 As Integer , Buff As Byte , Buff2 As Byte

Minor1 = 0

Major1 = 1

Minor2 = 0

Major2 = 1

Portb.0 = 1

Portb.1 = 1

Portb.3 = 1

Portb.4 = 1

Do

Do

'Print Bin[bq(0)]

Portb.0 = 1

Portb.1 = 1

'Porta = S

S = &HFF

Minor1 = 0

Buff = Bq(major1)

Buff2 = Bq(major2)

Do

Porta.0 = S.0 'For 3rd layer

Porta.1 = S.1

Porta.2 = S.2

'Buff = Bq(major1)

Portb.2 = Buff.minor1 'DATA pin

Porta.3 = 1 'For 2nd layer

Porta.4 = 0 'Latch 1

Porta.5 = 0

Portb.4 = 0 'Toggle ENABLE

Portb.1 = 0 'Toggeling DATA



'Buff2 = Bq(major2)

Portb.2 = Buff2.minor2



Porta.5 = 1




Portb.4 = 1

Decr S


Porta.1 = S.1

Porta.2 = S.2

'Buff = Bq(major1)




Porta.5 = 0





'Buff = Bq(major2)




Porta.5 = 1




Portb.4 = 1

Decr S

Incr Minor1

Incr Minor2

Loop Until Minor1 = 4

'++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Portb.0 = 1

Portb.1 = 1

S = &HFF

'Minor = 4

Do

'Porta = S


Porta.1 = S.1

Porta.2 = S.2

'Buff = Bq(major1)




Porta.5 = 0





'Buff = Bq(major2)




Porta.5 = 1




Portb.4 = 1

Decr S


Porta.1 = S.1

Porta.2 = S.2

'Buff = Bq(major2)

Portb.2 = Buff.minor1

'DATA pin



Porta.5 = 0





'Buff = Bq(major2)




Porta.5 = 1




Portb.4 = 1

Decr S

Incr Minor1

Incr Minor2

Loop Until Minor1 = 8

Minor1 = 0

Minor2 = 0

Incr Major1

Incr Major2

Waitus 100

If Iflag = 1 Then 'INTERRUPT Detection & Action

Reset Iflag

'Gifr = 64

'Enable Interrupts

Major1 = 1

Major2 = 1

End If

Loop Until Major1 > 58

Major1 = 1

Major2 = 1

Loop

End

Nullpoi:

Disable Interrupts

Set Iflag

'Major = 1

Return

Skyline Institute of Engineering

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