TOUCH SCREEN TECHNOLOGY ABSTRACT

Seminar on

TOUCH SCREEN TECHNOLOGY

Submitted by: Swagata Das (EC-26/08) & Tanmoy Datta (EC-27/08)

A touch screen is an electronic visual display that can detect the presence & location of a touch within the display area. The term generally means touching the display of the device with a finger, hand or other passive devices such as stylus. This technology has two main attributes. First it enables one to interact with what is displayed & secondly it lets one to do so without requiring any intermediate device that would need to be held in the hand. They also play a prominent role in design of digital appliances such as personal digital assistant (PDA), satellite navigation devices, mobile phones, video games etc.

In 1971, the first “Touch Sensor” was developed by Dr. Sam Hurst (founder of Elographics) of University of Kentucky. From 1983, the HP-150 was one of the world’s earliest commercial touchscreen computers which is based on Intel 8088 microprocessor. It did not have a touchscreen in the strict sense instead it has CRT surrounded by infrared transmitter & receiver, which detects the position of any non transparent object on the screen.

There are a variety of touchscreen technologies such as “Resistive”,”Surface Acoustic Wave” (SAW), and “Capacitive”. Different technologies may be used to determine the location of touch by different means. Then location is sent to the controller for processing. As an example, Resistive touchscreen panel is composed of electrically conductive layers separated by narrow gap. When an object presses down on the panel’s outer surface the conductive layers get connected & complete the circuit. Controller then converts the electrical signal into digital X & Y co-ordinate. The SAW technology uses ultrasonic waves that pass over touch screen panel. The Capacitive touchscreen panel consists of an insulator coated with a transparent conductor (such as Indium Tin Oxide ITO).

Touch screen is a developing technology. The development of multipoint touchscreen facilitated the tracking of more fingers than one finger on the screen thus the operations that require more than one finger are possible. These devices also allow multiple users to interact with the touchscreen simultaneously. With the growing field of touchscreen the marginal cost of this technology is decreasing.

But there are some drawbacks of this technology. This technology requires careful handling. Touchscreen suffers from the fingerprints on the display. There are other so many issues also.

There are tremendous applications of touchscreen technology. Public Information Display, ATMs, Ticket Counters, Digital Gaming, Student Registration System are such examples.

Though the touchscreen technology contains some limitations it is still very applicable. It is user friendly, fast accurate, easy to operate. It has been widely accepted & a little modification can replace the concept of mouse & keyboard in near future.

References: 1.John Broz, Ted Dimiropoulos, Alex Schallmo, & Mahreen Younus, Touch screen Technologies.

2. http://en.wikipedia.org/wiki/Touchscreen

3. www.etouchtechnologies.com

4. www.seminarprojects.com

Touch Screen Technology Introduction

INTRODUCTION

A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreen can also sense other passive objects, such as a stylus (it is a small pen shaped instrument that is used to input command to a computing screen).

The touchscreen has two main attributes. First, it enables one to interact directly with what is displayed, rather than indirectly with a cursor controlling device such as a mouse. Secondly, it lets one do so without requiring any intermediate device that would need to be held in the hand. Such displays can be attached to computers, or to networks as terminals. They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDA), satellite navigation devices, mobile phones, and video games.

Touch Screen Technology History

HISTORY

In 1971, the first "Touch Sensor" was developed by Dr. Sam Hurst (founder of Elographics) while he was an instructor at the University of Kentucky. This sensor, called the "Elograph," was patented by The University of Kentucky Research Foundation. The "Elograph" was not transparent like modern touch screens; however, it was a significant milestone in touchscreen technology. In 1974, the first true touch screen incorporating a transparent surface was developed by Sam Hurst and Elographics. In 1977, Elographics developed and patented five-wire resistive technology, the most popular touch screen technology in use today. Touchscreen first gained some visibility with the invention of the computer-assisted learning terminal, which came out in 1975 as part of the PLATO (Programmed Logic for Automated Teaching Operation) project. Touchscreen have subsequently become familiar in everyday life. Companies use touchscreens for kiosk systems in retail and tourist settings point of sale systems, ATMs, and PDAs, where a stylus is sometimes used to manipulate the GUI (Graphical User Interface) and to enter data. The popularity of smart phones, PDAs, portable game consoles and many types of information appliances is driving the demand for, and acceptance of, touchscreen.

The HP-150 from 1983 was one of the world's earliest commercial touchscreen computers. It did not have a touchscreen in the strict sense; instead, it had a 9" Cathode Ray Tube (CRT) surrounded by infrared transmitter and receivers, which detected the position of any non transparent object on the screen.

Until recently, most consumer touchscreen could only sense one point of contact at a time, and few have had the capability to sense how hard one is touching. This is starting to change with the commercialization of multi touch technology.

Touchscreens are popular in hospitality, and in heavy industry, as well as kiosks such as museum displays or room automation, where keyboard and mouse systems do not allow a suitably intuitive, rapid, or accurate interaction by the user with the display's content.

Historically, the touchscreen sensor and its accompanying controller-based firmware have been made available by a wide array of after-market system integrator, and not by display, chip, or motherboard manufacturers. Display manufacturers and chip manufacturers worldwide have acknowledged the trend toward acceptance of touchscreen as a highly desirable user interface component and have begun to integrate touchscreen functionality into the fundamental design of their products.

Touch Screen TECHNOLOGIES Page 1

TECHNOLOGIES

There are a variety of touchscreen technologies. They are:-

1. Resistive.

2. Surface Acoustic Wave (SAW).

3. Capacitive.

4. Infrared.

5. Optical imaging.

6. Dispersive Signal Technology (DST).

7. Acoustic Pulse Recognition (APR).

Capacitive technology can further be implemented following through techniques-

a) Surface capacitance.

b) Projected capacitance.

c) Mutual capacitance.

d) Self capacitance.

Different technologies may be used determine the location of touch by different means. Then the location is sent to the controller for processing that particular application.

Now we discuss the working principles of each techniques stated above.

1. Resistive: Resistive touchscreen are composed of two flexible sheets coated with a resistive material and separated by an air gap or microdots. When contact is made to the surface of the touchscreen, the two sheets are pressed together. On these two sheets there are horizontal and vertical lines that when pushed together, register the precise location of the touch. Because the touchscreen senses input from contact with nearly any object (finger, stylus/pen, palm) resistive touchscreen are a type of "passive" technology.

Fig: 1 Operation of Resistive touchscreen technology

For example, during operation of a four-wire touchscreen, a uniform, unidirectional voltage gradient is applied to the first sheet. When the two sheets are pressed together, the second sheet measures the voltage as distance along the first sheet, providing the X coordinate.

When this contact coordinate has been acquired, the uniform voltage gradient is applied to the second sheet to ascertain the Y coordinate. These operations occur within a few milliseconds, registering the exact touch location as contact is made.

Resistive touchscreen typically have high resolution (4096 x 4096 DPI or higher), providing accurate touch control. Because the touchscreen responds to pressure on its surface, contact can be made with a finger or any other pointing device.

2. Surface Acoustic Wave (SAW): Surface Acoustic Wave technology uses ultrasonic waves that pass over the touchscreen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. Surface wave touch screen panels can be damaged by outside elements. Contaminants on the surface can also interfere with the functionality of the touchscreen.

Touch Screen TECHNOLOGIES page 2

Fig: 2 Operation of SAW touchscreen technology

1. Capacitive: A capacitive touchscreen panel is one which consists of an insulator such as glass, coated with a transparent conductor such as Indium Tin Oxide (ITO). As the human body is also a conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance. Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing. These are mentioned below.

a) Surface capacitance:

In this basic technology, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel. As it has no moving parts, it is moderately durable but has limited resolution, is prone to false signals from parasitic capacitive coupling and needs calibration during manufacture. It is therefore most often used in simple applications such as industrial controls and kiosks.

b) Projected capacitance:

Projected Capacitive Touch (PCT) technology is a capacitive technology which permits more accurate and flexible operation, by etching the conductive layer. An X-Y grid is formed either by etching a single layer to form a grid pattern of electrode or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form the grid (comparable to the pixel grid found in many LCD displays).

The greater resolution of PCT allows operation without direct contact, such that the conducting layers can be coated with further protective insulating layers, and operates even under screen protectors, or behind weather and vandal-proof glass. Due to the top layer of a PCT being glass, PCT is a more robust solution versus resistive touch technology. Depending on the implementation, an active or passive stylus can be used instead of or in addition to a finger. There are two types of PCT: Self Capacitance and Mutual Capacitance.

c) Mutual Capacitance:

In mutual capacitive sensors, there is a capacitor at every intersection of each row and each column. A 12-by-16 array, for example, would have 192 independent capacitors. A voltage is applied to the rows or columns. Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field which reduces the mutual capacitance. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location by measuring the voltage in the other axis. Mutual capacitance allows multi touch operation where multiple fingers, palms or stylus can be accurately tracked at the same time.

d) Self Capacitance:

Self capacitance sensors can have the same X-Y grid as mutual capacitance sensors, but the columns and rows operate independently. With self capacitance, the capacitive load of a finger is measured on each column or row electrode by a current meter. This method produces a stronger signal than mutual capacitance, but it is unable to resolve accurately more than one finger, which results in "ghosting", or misplaced location sensing.

Touch Screen TECHNOLOGIES Page 3

1. Infrared: An infrared touchscreen uses an array of X-Y infrared LED and photo detector pairs around the edges of the screen to detect a disruption in the pattern of LED beams. These LED beams cross each other in vertical and horizontal patterns. This helps the sensors pick up the exact location of the touch.

Fig3: Operation of Infrared touchscreen technology
A major benefit of such a system is that it can detect essentially any input including a finger, gloved finger, stylus or pen. Unlike capacitive touchscreen infrared touchscreen do not require any patterning on the glass which increases durability and optical clarity of the overall system.
2. Optical Imaging: This is a relatively modern development in touchscreen technology, in which two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared back lights are placed in the camera's field of view on the other side of the screen. A touch shows up as a shadow and each pair of cameras can then be pinpointed to locate the touch or even measure the size of the touching object. This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for larger units.
3. Dispersive Signal Technology: Introduced in 2002, this system uses sensors to detect the mechanical energy in the glass that occurs due to a touch. Complex algorithms then interpret this information and provide the actual location of the touch. The technology claims to be unaffected by dust and other outside elements, including scratches. Since there is no need for additional elements on screen, it also claims to provide excellent optical clarity. Also, since mechanical vibrations are used to detect a touch event, any object can be used to generate these events, including fingers and stylus. A downside is that after the initial touch the system cannot detect a motionless finger.
4. Acoustic Pulse Recognition: This system, introduced by Tyco International’s Division in 2006, uses piezoelectric transducers located at various positions around the screen to turn the mechanical energy of a touch (vibration) into an electronic signal. The screen hardware then uses an algorithm to determine the location of the touch based on the transducer signals. The touchscreen itself is made of ordinary glass, giving it good durability and optical clarity. It is usually able to function with scratches and dust on the screen with good accuracy. The technology is also well suited to displays that are physically larger. As with the Dispersive Signal Technology system, after the initial touch, a motionless finger cannot be detected. However, for the same reason, the touch recognition is not disrupted by any resting objects.

Touch Screen CONSTRUCTION

CONSTRUCTION

There are several principal ways to build a touchscreen. The key goals are to recognize one or more fingers touching a display, to interpret the command that this represents, and to communicate the command to the appropriate application.

In the most popular techniques, the capacitive or resistive approach, there are typically four layers:

1. Top polyester layer coated with a transparent metallic conductive coating on the bottom.

2. Adhesive spacer.

3. Glass layer coated with a transparent metallic conductive coating on the top.

4. Adhesive layer on the backside of the glass for mounting.

When a user touches the surface, the system records the change in the electrical current that flows through the display.

Dispersive-signal technology which  created in 2002, measures the piezoelectric effect — the voltage generated when mechanical force is applied to a material — that occurs chemically when a strengthened glass substrate is touched.

There are two infrared-based approaches. In one, an array of sensors detects a finger touching or almost touching the display, thereby interrupting light beams projected over the screen. In the other, bottom-mounted internal cameras record screen touches.

In each case, the system determines the intended command based on the controls showing on the screen at the time and the location of the touch.

Touch Screen Technology DEVELOPMENT

DEVELOPMENT

Most touchscreen technology patents were filed during the 1970s and 1980s and have expired. Touchscreen component manufacturing and product design are no longer encumbered by royalties or legalities with regard to patents and the use of touchscreen-enabled displays is widespread.

The development of multipoint touchscreen facilitated the tracking of more than one finger on the screen; thus, operations that require more than one finger are possible. These devices also allow multiple users to interact with the touchscreen simultaneously.

With the growing use of touchscreen, the marginal cost of touchscreen technology is routinely absorbed into the products that incorporate it and is nearly eliminated. Touchscreen now have proven reliability. Thus, touchscreen displays are found today in airplanes, automobiles, gaming consoles, machine control systems, appliances, and handheld display devices including the multi-touch enabled iPhone; the touchscreen market for mobile devices is projected to produce US$ 5 billion in 2009.

The ability to point accurately on the screen itself is also advancing with the emerging screen hybrids.

                      Fig: 04 Multipoint touchscreen

Touch Screen Technology ERGONOMICS & USAGE

· FINGER STRESS: An ergonomic problem of touchscreen is their stress on human fingers when used for more than a few minutes at a time, since significant pressure can be required for certain types of touchscreen. This can be alleviated for some users with the use of a pen or other device to add leverage and more accurate pointing. The introduction of such items can sometimes be problematic, depending on the desired use (e.g. public kiosks such as ATMs).

· FINGER PRINTS: Touchscreen can suffer from the problem of fingerprints on the display. This can be mitigated by the use of materials with optical coating designed to reduce the visible effects of fingerprint oils, such as the oleo phobic coating used in the iPhone, 3G S, or by reducing skin contact by using a fingernail or stylus.

· FINGERNAIL AS STYLUS: These ergonomic issues of direct touch can be bypassed by using a different technique, provided that the user's fingernails are either short or sufficiently long. Rather than pressing with the soft skin of an outstretched fingertip, the finger is curled over, so that the tip of a fingernail can be used instead. The thumb is optionally used to provide support for the finger or for a long fingernail, from underneath. This method does not work on capacitive touch screens.

The fingernail's hard, curved surface contacts the touchscreen at one very small point. Therefore, much less finger pressure is needed, much greater precision is possible (approaching that of a stylus, with a little experience), much less skin oil is smeared onto the screen, and the fingernail can be silently moved across the screen with very little resistance, allowing for selecting text, moving windows, or drawing lines.

The human fingernail consists of keratin which has a hardness and smoothness similar to the tip of a stylus (and so will not typically scratch a touchscreen). Alternately, very short stylus tips are available, which slip right onto the end of a finger; this increases visibility of the contact point with the screen.

· FINGERPRINTS: Touchscreens can suffer from the problem of fingerprints on the display. This can be mitigated by the use of materials with optical coating designed to reduce the visible effects of fingerprint oils, such as the oleo phobic coating used in the iPhone 3G S, or by reducing skin contact by using a fingernail or stylus.

· COMBINED WITH HEPTICS: The user experience with touchscreens without tactile feedback or haptics can be difficult due to latency or other factors. Research from the University of Glasgow Scotland [Brewster, Chohan, and Brown 2007] demonstrates that sample users reduce input errors (20%), increase input speed (20%), and lower their cognitive load (40%) when touchscreens are combined with haptics or tactile feedback, [vs. non-haptic touchscreens].

Touch Screen Technology COMPARISON

COMPARISON BETWEEN VARIOUS TECHNOLOGIES
The following information is supplied by Mass Multimedia Inc., a Colorado-based company selling touch screen technology.

Technology	4-Wire Resistive	Surface Acoustic Wave	5-Wire Resistive	Infrared	Capacitive
Durability	3 yr.	5 yr.	5 yr.	5 yr.	2 yr.
Stability	High	Higher	High	High	Ok
Transparency	Bad	Good	Bad	Good	Ok
Installation	Built-in/On wall	Built-in/On wall	Built-in/On wall	Built-in	On wall
Touch	Anything	Finger/Pen	Anything	Finger/Pen	Conductive
Intense light-resistant	Good	Good	Good	Bad	Bad
Response time	<10ms	10ms	<15ms	<20ms	<15ms
Following speed	Good	Low	Good	Good	Good
Excursion	No	Small	Big	Big	Big
Monitor option	CRT or LCD	CRT or LCD	CRT or LCD	CRT or LCD	CRT or LCD or LED
Water proof	Good	Ok	Good	Ok	Good

          Fig4: Illustration of comparison betweendifferent  touchscreen  technologies.

 

Touch Screen CONTROLLERS 10

TOUCHSCREEN CONTROLLERS

For Resistive: CONTROLLER NAME: VS20UA CONTROLLER .Supply Voltage +5.0V DC, Maximum Current 20mA, Resolution 12-bit.

For SAW: CONTROLLER NAME: 2701RSU CONTROLLER. Supply Voltage: +5V DC, Baud Rate 9600, Touch Resolution 12bit, size independent Conversion Time 10 ms per coordinate set.

For Capacitive: CONTROLLER Name: 5000 RSU SERIAL CONTROLLER Supply Voltage: +5 V DC or +12V, Baud Rate 9600 (default) and 19200 Touch Resolution 12bit, size independent. Conversion Time approximately 15 ms per coordinate set.

Touch Screen APPLICATIONS

The various commercial applications of touchscreen are:-

Public Information Displays, Tourism displays Trade show display, Awareness kiosks Customer Self-Services, General departmental Stores Restaurants ATMs Airline ticket terminals, etc. Other uses, Digital jukeboxes Computerized gaming Student Registration systems, etc.

Touch Screen CONCLUSIONS and References

CONCLUSIONS
Though the Touch screen technology contains some limitations it is user friendly, fast, accurate and easy to operate. In our presentation, we will touch on the history behind touch screen technology while also explaining in detail how the different methods of touch screen technologies work. More specifically, we will spend a considerable amount of time describing the different technologies found in devices that use touch screen. We will also delve into the current commercial applications and practical benefits of touchscreens. Finally, we will comment on the future applications and potentials of touch screen technology.
It has been widely accepted and a little modification can replace the mouse and key board completely in near future….
   
REFERENCE

· Shneiderman, B. (1991). "Touch screens now offer compelling uses". IEEE
Software: pp 93–94, 107
· Potter, R.; Weldon, L. & Shneiderman, B. (1988). "Improving the accuracy of touch screen: An experimental evaluation of three strategies". Proc. CHI'88. Washington, DC: ACM Press. pp. 27–32.
· Sears, A.; Plaisant, C. & Shneiderman, B. (1992). "A new era for high precision touchscreens". In Hartson, R. & Hix, “Advances in Human-Computer Interaction". Ablex, NJ. pp. 1–33.
· Sears, A.; Shneiderman, B. (1991). "High precision touchscreen: Design strategies and comparison with a mouse". Int. J. of Man-Machine Studies.
· John Broz, Ted Dimiropoulos, Alex Schallmo, & Mahreen Younus, "Touch screen Technologies".
· http://en.wikipedia.org/wiki/Touchscreen
· www.etouchtechnologies.com
· www.seminarprojects.com


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