A touchscreen provides the simplest, most direct user interface with a computer. First developed in the 1970s by Elo TouchSystems, touchscreens allow users to just point at what they want to select. Properly programmed, a touchscreen interface can be intuitive, requiring no learning curve for first time users.
According to 3M Touch Systems, the power of touchscreens has been harnessed in a wide variety of applications. For example, airlines use them to simulate aircraft cockpits for pilot training. Realtors use them to allow prospective homebuyers to access full-color images of homes for sale. Greeting card companies use them to let customers create their own one-of-a-kind greeting cards. Touchscreens have found extensive use in restaurants and other commercial establishments to simplify point-of-sale terminals. Medical schools use them to teach student nurses how to respond to crisis situations.
Touchscreens' inherent ruggedness and immunity to contamination suit them for applications on the factory floor for computer-controlled equipment. Touchscreens have also found wide use in stand-alone kiosks for applications such a public information and ticketing. Touchscreens have proven to be essential for handheld computing devices such as PDAs and "pad" computers that are not physically large enough to support a full-sized "QWERTY" keyboard.
The benefits of touchscreen technology include:
- Touchscreens enable first-time users to interface with computers instantly, without any operator training whatsoever.
- Touchscreens virtually eliminate operator errors because users make selections from clearly defined menus.
- Touchscreens eliminate keyboards and mice, which many novice users find intimidating and cumbersome to use.
- Touchscreens are rugged enough to stand up to harsh environments where keyboards and mice can become damaged.
- Touchscreens provide fast access to all types of digital content.
- Touchscreens ensure that no space is wasted because the input device is completely integrated into the monitor.
Touchscreens are not a universal solution for user interfaces. Touchscreens themselves provide no tactile cues so they require the user to be able to see the areas of the screen in order to activate a touch control. Thus visually impaired users will not be able to locate the proper areas of the touchscreen to activate the controls. Further, someone with a physical disability such as spastic paralysis might not be able to activate the touchscreen.
However a touchscreen interface can be beneficial for some handicapped users who 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, touchscreens can make computing resources more available to people who have difficulty using computers because, for example, they cannot grasp and manipulate a mouse.
Touchscreens can be installed on CRTs that are flat, cylindrical, and spherical, or on displays based on electroluminescent (EL), liquid crystal display (LCD), and gas plasma technologies. Many sizes are available, from large, curved units for over-sized monitors to small, flat touchscreens built to fit compact point-of-sale displays and handheld computing devices.
How a Touchscreen System Works
Five basic elements make up a complete touchscreen system:
- The touchscreen itself.
- The touchscreen interfaces with a computer whose display is fitted with the touchscreen.
- A controller drives the touchscreen and converts each touch into X/Y coordinates.
- A software driver, which communicates between the controller card and the computer's operating system.
- Application-development software, which enables developers of touch programs to build their own applications and/or customize existing touch applications.
Resistive touchscreens are the most popular touchscreen in use today. Resistive touchscreens deliver cost-effective, consistent and durable performance in environments where equipment must stand up to contaminants and liquids, such as in restaurants, factories, and hospitals. Disadvantages of resistive touchscreens include only 75% optical transparency and the fact that a sharp object can damage the resistive layers.
A resistive touchscreen consists of a glass panel molded precisely to the shape of a display's face (Figure 1). This underlying glass layer is coated with a transparent, conductive layer of indium tin oxide (ITO) and then covered by a clear, hard-coated sheet of plastic. ITO is a transparent semiconductor that is sputtered onto the touch screen layers. This cover sheet is suspended over the glass by tiny separator dots, each less than one-thousandth of an inch thick. When a user touches the touchscreen, the conductive inner surface of the plastic sheet makes contact with the underlying glass, completing a circuit. The controller senses the contact and computes X/Y coordinates of the touch within a hundredth of a second.
Figure 1: Formed to fit the shape of a display, the resistive touchscreen's underlying glass panel has a coating of uniform resistivity. A polyester cover sheet is lightly suspended over the top of the glass, separated from it by small, transparent insulating dots. The cover sheet has a hard, durable coating on the outer side and a conductive coating on the inner side. (Illustration courtesy of Elo TouchSystems)
Resistive touchscreens come in four- and five-wire versions. The four-wire technology is geared toward hand-held consumer devices while the five-wire technology suits industrial, point-of-sale, and medical applications.
Capacitive Touchscreen Technology
Adding conductive coatings to a clear glass sensor results in an analog capacitive touchscreen. Voltage is applied to the four corners of the screen along an X/Y axis. When the screen is not in use, electrodes spread the voltage, creating a uniform field. When a finger or other conductive instrument touches the screen, the field recognizes a disturbance. The X/Y coordinate of the touch is sent from the controller to the PC's serial or USB port.
Because the glass and the bezel that mounts it to the monitor can be sealed, a capacitive touchscreen is both durable and resistant to contaminants like water, dust, dirt and grease. This suits capacitive touchscreens for harsh environments such as gaming, vending, retail displays, public kiosks and industrial applications.
Infrared Touchscreens Loose Favor
Infrared touchscreens are fabricated by adding a custom bezel to the front of a display utilizing infrared LEDs arrayed along the horizontal and vertical X/Y axes (Figure 2
). A touch breaks the X and Y LED beams, allowing IR sensors to pass this coordinate information to the computer. While infrared was once used extensively, shortcomings of this technology, such as low resolution, parallax problems, and premature touchdown detection, have led developers to employ other touch technologies.
Figure 2: Scanning infrared (IR) technology relies on the interruption of an IR light grid in front of the display screen. The touch frame contains a row of IR-light-emitting diodes (LEDs) and photo-transistors, each mounted on two opposite sides to create a grid of invisible infrared light. (Illustration courtesy of Elo TouchSystems)
Surface Acoustic Wave Technology
Surface acoustic wave (SAW) technology delivers the highest image clarity and durability among all touchscreen technologies. When first introduced in 1987, SAW technology was a major breakthrough because it is the only touchscreen constructed solely of glass, having no plastic layers, conductive coatings, or special CRT bezels. With nothing but glass between the user and an on-screen image, surface wave touchscreens offer unmatched brightness, clarity and durability.
According to Elo TouchSystems, a SAW touchscreen consists of a clear glass overlay formed to match the shape of the display (Figure 3). Each axis on the overlay has a transmitting and receiving piezoelectric transducer and a set of reflector stripes. The touchscreen controller sends a 5 MHz burst to the transmitting transducers, which convert the signal into surface acoustic waves. Surface acoustic waves are mechanical waves that propagate in the surface of materials such as glass. The reflector stripes divert the burst across the face of the overlay. When a finger, gloved hand or soft stylus touches the touchscreen, a portion of the wave is absorbed. The resulting change in the received signal is analyzed by the controller and digitized into X and Y coordinates. A Z-axis level can also determined by measuring how much of the signal was absorbed. Unlike some other technologies, which depend on ratios to determine touch location and thus are prone to drift, SAW is an inherently stable technology offering drift-free performance.
Figure 3: A SAW touchscreen is a glass overlay with transmitting and receiving piezoelectric transducers for both X and Y axes. The durable, scratch-resistant surface continues to work around scratches and contaminants and can be activated by finger, gloved hand, or soft stylus. (Illustration courtesy of Elo TouchSystems)
You can activate both resistive and SAW touchscreens with a gloved hand, a stylus, an artificial limb, or other non-conductive instrument. This is a critical capability not only in public kiosk installations, but in many industrial applications as well. Food handlers, hospital employees, factory personnel, and other workers often wear gloves on the job. Sometimes workers have no choice in the matter. For example, in many states laws are now in effect requiring all food handlers to wear gloves. Both capacitive and SAW touchscreens are more expensive than resistive touchscreens, however.
Elo has developed an advance in SAW touch technology called iTouch. In Elo's new iTouch "touch-on-tube" technology, surface waves are directed onto the CRT surface for touch sensing, eliminating any glass overlay on the CRT and delivering the highest quality image possible. iTouch also enhances durability because the CRT faceplate is several times stronger than a touchscreen overlay.
Touchscreens have carved out solid application niches in public information, industrial control, and point of sale terminals. With the proliferation of handheld computing and communication devices having processors powerful enough to run handwriting-recognition software, touchscreens are expected to find even wider applications.
About the Author
Charles H. Small is a technical editor based in Waltham, MA.