Introductionto Touch Screens
The touchscreen interface is the most simple, intuitive, and easiest to learn of all PC input devices. It is fast becoming the interface of choice for a wide variety of applications in
public spaces, businesses, and more.
A touch interface allows users to navigate a computer system by touching icons or links on the screen. With the right software interface, even someone with no computer experience at all can easily use and interact with a touch screen enhanced system.
Touch interface technology has advanced to the point where the hardware is practically plug-an-play for most PC systems, including Windows and Macintosh platforms, without the need for any difficult programming. This means that it can easily be added to existing applications, and new applications can easily be developed.
Why Touchscreen?
Touch is one of the simplest, most instinctive, and universal human actions.
Simplifies the man/machine interface – Because touch input is so simple and natural, touchscreen requires no training and no learning curve.
Durable in harsh conditions – Unlike computer keyboards or mice, touchscreen stands up to punishing environments, so there’s less downtime, fewer mechanical problems, and lower operational costs.
Suitable for all environments – Rugged enough for applications where a keyboard and mouse are not practical, yet attractive enough for uses where appearance is crucial.
Greater accuracy – Clearly defined menus and intuitive touch virtually eliminate operator error.
Smaller footprint – Input device is integrated into the monitor, so no space is wasted.
Response time – Measured in milliseconds (ms), it reflects the screen's speed in reacting to touch. Most screens have response times between 8ms and 20ms; anything slower than 25ms may create problems for users.
Touch contact requirement – Also measured in milliseconds, this denotes the amount of time you must touch the screen before it reacts.
Touch resolution – The screen's ability to recognize touch is measured in total number of points per screen or points per inch (ppi). The higher the resolution, of course, the more accurate the determination of the location touched.
4
Basic Components
A basic touchscreen has three main components: a touch sensor, a controller, and a software driver. The touchscreen is an input device, so it needs to be combined with a display and a PC or other device to make a complete touch input system.
1.Touch Sensor
A touch screen sensor is a clear glass panel with a touch responsive surface. The touch sensor/panel is placed over a display screen so that the responsive area of the panel covers the viewable area of the video screen. There are several different touch sensor technologies on the market today, each using a different method to detect touch input. The sensor generally has an electrical current or signal going through it and touching the screen causes a voltage or signal change. This voltage change is used to determine the location of the touch to the screen.
2.Controller
The controller is a small PC card that connects between the touch sensor and the PC. It takes information from the touch sensor and translates it into information that PC can understand. The controller is usually installed inside the monitor for integrated monitors or it is housed in a plastic case for external touch add-ons/overlays. The controller determines what type of interface/connection you will need on the PC. Integrated touch monitors will have an extra cable connection on the back for the touchscreen. Controllers are available that can connect to a Serial/COM port (PC) or to a USB port (PC or Macintosh). Specialized controllers are also available that work with DVD players and other devices.
3.Software Driver
The driver is a software update for the PC system that allows the touchscreen and computer to work together. It tells the computer's operating system how to interpret the touch event information that is sent from the controller. Most touch screen drivers today are a mouse-emulation type driver. This makes touching the screen the same as clicking your mouse at the same location on the screen. This allows the touchscreen to work with existing software and allows new applications to be developed without the need for touchscreen specific programming. Some equipment such as thin client terminals, DVD players, and specialized computer systems either do not use software drivers or they have their own built-in touch screen driver.
Of course, you will also need a software application that will enable you to develop new or customize existing touch applications to meet your specific requirements.
ji
5
Types of Touch Screens
1. Resistive
2. Surface Acoustic Wave
3. Capacitive
4. Infrared
Resistive
A resistive touch screen typically uses a display overlay consisting of layers, each with a conductive coating on the inner surface. The conductive inner layers are separated by special separator dots, evenly distributed across the active area. Finger pressure causes internal electrical contact at the point of touch, supplying the electronic interface (touch screen controller) with vertical and horizontal analog voltages for digitization.
For CRT applications, resistive touch screens are generally spherical (curved) to match the CRT and minimize parallax. The nature of the material used for curved (spherical) applications limits light throughput such that two options are offered: Polished (clear) or antiglare. The polished choice offers clarity but includes some glare. The antiglare choice will minimize glare, but will also slightly diffuse the light throughput (image). Either choice will demonstrate either more glare (polished) or more light diffusion (antiglare) than associated with typical non-touch screen displays. Despite the tradeoffs, the resistive touch screen technology remains a popular choice, often because it can be operated while wearing gloves (unlike capacitive technology). Note that resistive touch screen materials used for flat panel touch screens are different and demonstrate much better optical clarity (even with antiglare). The resistive technology is far more common for flat panel applications.
Advantages of Resistive
1. High touch resolution and fast response
2. Works with any stylus
3. Not affected by dirt, dust, water, or light
4. Pressure-activated by finger or gloved hand with a very light touch
5. durable hard-coat front surface can be nonglare treated for reflection control or polished for maximum clarity.
Disadvantages
1. Back to the top 75 % clarity
2. Resistive layers can be damaged by a sharp object
6
Capacitive
A capacitive touch screen includes an overlay made of glass with a coating of capacitive (charge storing) material deposited electrically over its surface. Oscillator circuits located at corners of the glass overlay will each measure the capacitance of a person touching the overlay. Each oscillator will vary in frequency according to where a person touches the overlay. A touch screen controller measures the frequency changes to determine the X and Y coordinates of the touch. The X-Y coordinate of the touch is then sent from the controller to the PC serial port.
Because the glass and the bezel that mounts it to the monitor can be sealed, the touchscreen is both durable and resistant to contaminants like water, dust, dirt, and grease. It can even resist damage from sparks. This makes all capacitive touchscreens ideal for harsh environments like gaming, vending, retail displays, public kiosks, and industrial applications. A capacitive touch screen cannot be activated while wearing most types of gloves (non-conductive).
Advantages
1. High touch resolution
2. High Clarity
3. Not affected by dirt, grease, and moisture
4. Attached pen stylus for precise input
Disadvantages
Back to the top Must be touched by finger- will not work with any non-conductive input
7
SAW (Surface Acoustic Wave)
A SAW touch screen uses a solid glass display overlay for the touch sensor. Two surface acoustic (sound) waves, inaudible to the human ear, are transmitted across the surface of the glass sensor, one for vertical detection and one for horizontal detection. Each wave is spread across the screen by bouncing off reflector arrays along the edges of the overlay. Two receivers detect the waves, one for each axis. Since the velocity of the acoustic wave through glass is known an d the size of the overlay is fixed, the arrival time of the waves at the respective receivers is known. When the user touches the glass surface, the water content of the user's finger absorbs some of the energy of the acoustic wave, weakening it. The controller circuitry measures the time at which the received amplitude dips to determine the X and Y coordinates of the touch location.
In addition to the X and Y coordinates, SAW technology can also provide Z axis (depth) information. The harder the user presses against the screen, the more energy the finger will absorb, and the greater will be the dip in signal strength. The signal strength is then measured by the controller to provide the Z-axis information. Today, few software applications are designed to make use of this feature.
Advantages of SAW
1. High and fast touch resolution
2. No-drift operation, so doesn't need recalibration often
3. Excellent Image Clarity and durability
4. Overlay That Can Be Antiglare-Treated
5. Stable "No-Drift" Operation
Disadvantages
1. Must be touched by finger, gloved hand, or soft-tip stylus. Something hard like a pen won't work
2. Not completely sealable, can be affected by large amounts of dirt, dust, and / or water in the environment.
8
Infrared
The technology utilizes non-visible infrared light, which is transmitted by the highest quality Light Emitting Diodes (LEDs) and detected by very rugged (military spec) Light Receiving Phototransistors (LRPs). Infrared light has a frequency and an intensity that is below the visible light spectrum. Infrared light is also below the frequency and spectrum of night vision goggles (NVGs) used by the military.
The infrared transmitting and receiving diodes are located on opposite sides, facing each other around the periphery of the touch screen, which is mechanically mounted in front of a display (either a CRT monitor, LCD flat panel, or color plasma display). The infrared light impulses travel from side-to-side and top to bottom in front of the touch screen. When the operator touches the screen, it creates a shade for some of the LRPs.
The solid-state electronic controller interpolates the locations of the horizontal and vertical shades and automatically determines the center of the operator's finger. This location is assigned specific coordinates, which are transmitted to the computer via a serial cable, similar to a mouse connecting cable. The driver software program installed in the computer, similar to a mouse driver, then indicates the center of the finger by using an arrow, similar to the arrow that shows the pointing location of a mouse.
Computer activation is generated by "touch down" or "lift off" of the plane. The controller card, with its firmware (imbedded software), is responsible for transmitting the appropriate activation signal, generated by the movement of the operator's finger, to the computer. When the finger touches down, the controller card generates x, y position coordinates as well as a signal similar to that generated by pressing the mouse button. The finger lift-off generates a signal similar to that generated by the release of the mouse button.
9
Technology Comparison Chart
| | Resistive | Capacitive | SAW | Infrared |
Accessibility | Excellent by pressure | Good | Good | Excellent |
| Cursor Stability | Excellent | Good | Good Requires occasional recalibration | Excellent |
| Atmospheric Tolerance | Excellent | Low Will not work properly in moisture and in high humidity | Low Adversely affected by moisture, dirt, dust and noise | Low Adversely affected by moisture, dirt, dust and noise |
Accuracy | Excellent 4096 x 4096 points of accuracy | Good | Excellent | Low Limited by the number of LED's / sensors that can fit in the given area |
Transparency | Good 87.5% Transparency | Excellent Only one extra layer of conductively coated glass | Excellent Only one extra layer of plain glass | Excellent No extra layers (or plain glass if required) |
| Surface Durability | Good 3 Million+ touches | Excellent Conductive coating may wear after time | Excellent | Excellent |
Applications of Touchscreen
Computer Based Training Because the touch screen interface is more user-friendly than other input devices, overall training time for computer novices, and therefore training expense, can be reduced. It can also help to make learning more fun and interactive, which can lead to a more beneficial training experience for both students and educators. | |
| | Assistive Technology The touch screen interface can be beneficial to those that have difficulty using other input devices such as a mouse or keyboard. When used in conjunction with software such as on-screen keyboards, or other assistive technology, they can help make computing resources more available to people that have difficulty using computers. |
| | And many more uses… Other applications include digital jukeboxes, computerized gaming, student registration systems, multimedia software, financial and scientific applications, etc. |
Bibliography
Following websites helped us in gathering above information about ‘Touchscreen’.
