Touchscreens

A touchscreen is an intuitive computer input device that works by simply touching the display screen, either by a finger, or with a stylus, rather than typing on a keyboard or pointing with a mouse. Computers with touchscreens have a smaller footprint, and can be mounted in smaller spaces; they have fewer movable parts, and can be sealed. Touchscreens may be built in, or added on. Add-on touchscreens are external frames with a clear see-through touchscreen which mount onto the monitor bezel and have a controller built into their frame. Built-in touchscreens are internal, heavy-duty touchscreens mounted directly onto the CRT tube.

The touchscreen interface – whereby users navigate a computer system by touching icons or links on the screen itself – is the most simple, intuitive, and easiest to learn of all PC input devices and is fast is fast becoming the interface of choice for a wide variety of applications, such as:

• Public Information Systems: Information kiosks, tourism displays, and other electronic displays are used by many people that have little or no computing experience. The user-friendly touchscreen interface can be less intimidating and easier to use than other input devices, especially for novice users, making information accessible to the widest possible audience.
• Restaurant/POS Systems: Time is money, especially in a fast paced restaurant or retail environment. Because touchscreen systems are easy to use, overall training time for new employees can be reduced. And work can get done faster, because employees can simply touch the screen to perform tasks, rather than entering complex key strokes or commands.
• Customer Self-Service: In today’s fast pace world, waiting in line is one of the things that has yet to speed up. Self-service touchscreen terminals can be used to improve customer service at busy stores, fast service restaurants, transportation hubs, and more. Customers can quickly place their own orders or check themselves in or out, saving them time, and decreasing wait times for other customers.
• Control/Automation Systems: The touchscreen interface is useful in systems ranging from industrial process control to home automation. By integrating the input device with the display, valuable workspace can be saved. And with a graphical interface, operators can monitor and control complex operations in real-time by simply touching the screen.
• Computer Based Training: Because the touchscreen 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.

Any touchscreen system comprises the following three basic components;

• a touchscreen sensor panel, that sits above the display and which generates appropriate voltages according to where, precisely, it is touched
• a touchscreen controller, that processes the signals received from the sensor and translates these into touch event data which is passed to the PC’s processor, usually via a serial or USB interface
• a software driver, provides an interface to the PC’s operating system and which translates the touch event data into mouse events, essentially enabling the sensor panel to emulate a mouse.

The first touchscreen was created by adding a transparent surface to a touch-sensitive graphic digitizer, and sizing it to fit a computer monitor. Initially, the purpose was to increase the speed at which data could be entered into a computer. Subsequently, several types of touchscreen technologies have emerged, each with its own advantages and disadvantages that may, or may not, make it suitable for any given application:

Resistive touchscreens respond to the pressure of a finger, a fingernail, or a stylus. They typically comprise a glass or acrylic base that is coated with electrically conductive and resistive layers. The thin layers are separated by invisible separator dots. When operating, an electrical current is constantly flowing through the conductive material. In the absence of a touch, the separator dots prevent the conductive layer from making contact with the resistive layer. When pressure is applied to the screen the layers are pressed together, causing a change in the electrical current. This is detected by the touchscreen controller, which interprets it as a vertical/horizontal coordinate on the screen (x- and y-axes) and registers the appropriate touch event.

Resistive type touchscreens are generally the most affordable. Although clarity is less than with other touchscreen types, they’re durable and able to withstand a variety of harsh environments. This makes them particularly suited for use in POS environments, restaurants, control/automation systems and medical applications.

Infrared touchscreens are based on light-beam interruption technology. Instead of placing a layer on the display surface, a frame surrounds it. The frame assembly is comprised of printed wiring boards on which the opto-electronics are mounted and is concealed behind an IR-transparent bezel. The bezel shields the opto-electronics from the operating environment while allowing the IR beams to pass through. The frame contains light sources – or light-emitting diodes – on one side, and light detectors – or photosensors – on the opposite side. The effect of this is to create an optical grid across the screen. When any object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the photosensors. Based on which photosensors stop receiving the light signals, it is easy to isolate a screen coordinate.

Infrared touch systems are solid state technology and have no moving mechanical parts. As such, they have no physical sensor that can be abraded or worn out with heavy use over time. Furthermore, since they do not require an overlay – which can be broken – they are less vulnerable to vandalism and also extremely tolerant of shock and vibration.

Surface Acoustic Wave technology is one of the most advanced touchscreen types. SAW touchscreens work much like their infrared brethren except that sound waves, not light beams, are cast across the screen by transducers. Two sound waves, one emanating from the left of the screen and another from the top, move across the screen’s surface. The waves continually bounce off reflectors located on all sides of the screen until they reach sensors located on the opposite side from where they originated.

When a finger touches the screen, the waves are absorbed and their rate of travel thus slowed. Since the receivers know how quickly the waves should arrive relative to when they were sent, the resulting delay allows them to determine the x- and y-coordinates of the point of contact and the appropriate touch event to be registered, Unlike other touch-screen technologies, the z-axis (depth) of the touch event can also be calculated; if the screen is touched with more than usual force, the water in the finger absorbs more of the wave’s energy, thereby delaying it more.

Because the panel is all glass and there are no layers that can be worn, Surface Acoustic Wave touchscreens are highly durable and exhibit excellent clarity characteristics. The technology is recommended for public information kiosks, computer based training, or other high traffic indoor environments.

Capacitive touchscreens consist of a glass panel with a capacitive (charge storing) material coating its surface. Unlike resistive touchscreens, where any object can create a touch, they require contact with a bare finger or conductive stylus. When the screen is touched by an appropriate conductive object, current from each corner of the touchscreen is drawn to the point of contact. This causes oscillator circuits located at corners of the screen to vary in frequency depending on where the screen was touched. The resultant frequency changes are measured to determine the x- and y- co-ordinates of the touch event.

Capacitive type touchscreens are very durable, and have a high clarity. They are used in a wide range of applications, from restaurant and POS use to industrial controls and information kiosks.

The table below summarises the principal advantages/disadvantages of each of the described technologies:

• Keyboards
• Ergonomic Keyboards
• Opto-Mechanical mice
• Optical Mice
• Cordless Input Devices
• Laser Mice
• Trackballs
• Joysticks
• Input Device Interfaces
• Touchscreens