Touch screens – you’ve seen them on Apple iPhones, and they pop up in almost any movie set in the future. By freeing us from the keyboard, touch screens are changing the way we interact, not only with computers, but with an ever expanding range of electronic devices.
The first “touch sensor” was developed at the University of Kentucky in 1971. This sensor was not transparent, though, and it took until 1974 for it to evolve into a true, transparent, touch screen.
Used in industry and in commercial settings for the last twenty years, touch screens are now becoming increasingly popular in consumer goods, most visibly in mobile phones and personal computers.
How Touch Screens Work
There are basically three components to a touch screen:
- A clear panel that has some method of sensing a touch event.
- A controller which connects the touch sensor to the computer and translates information from the sensor into a form the computer can understand.
- A software driver which tells the computer how to interpret the touch event information sent from the controller.
In standard touch screens, touching the screen is basically the same as left-clicking a mouse. You can also tap the screen twice to double-click, and drag your finger across the screen to perform drag-and-drop actions.
Types of Touch Screen
There are several different touch screen technologies, each with their own advantages and disadvantages.
In resistive touch screens, the clear panel is composed of two electrically conductive layers separated by a minute gap. When a finger presses against the screen, these two layers come into contact with each other, producing a change in the electric current, and a touch event occurs.
Resistive touch screens are pressure sensitive and so will still work regardless of whether the user is wearing gloves or using an implement such as a pen or stylus. On the downside, they can be damaged by sharp objects and they do not offer high levels of clarity
In this form of touch screen the glass panel is coated with a transparent electrical conductor (indium tin oxide is commonly used). The human body also conducts electricity and so, when a finger touches the screen, the electrical field is disturbed and a touch event occurs. Apple’s iPhone uses this technology
Capacitive screens offer high levels of clarity and durability (as no pressure is necessary), but they will not work if a non-conducting object is used as the touch medium (a plastic pen top, for instance).
In this “optical-touch” system, infrared light emitting diodes (LEDs) are placed on two adjacent edges of the screen and photosensors are placed on the two other edges. In this way a grid of infrared light is created. Any object that touches the screen interrupts this grid and creates a touch event.
The problem with infrared touch screens is that ambient light can interfere with their operation. If external light is too bright the photosensors cannot read the light emitted by the LEDs. They do, however, offer excellent clarity and durability and work with any touch medium, regardless of its conductivity.
Surface Acoustic Wave
Here, ultrasonic waves are sent across the glass panel. When a finger touches the panel the waves are absorbed and a touch can be detected. While offering excellent clarity and “touch-sensitiveness”, these screens can be affected by surface contaminants and will not work when hard objects are used as the touch medium.
Other forms of touch screen include: force panel technology, where the screen is mounted on springs and strain gauges are used to determine where the screen is touched; dispersive signal technology, where sensors measure mechanical vibrations in the screen; optical imaging, where infrared back-lights are used to create shadows on miniature cameras.
Multi-touch – The Next Generation
As previously mentioned, touch screens initially replicated the actions of a left-clicked mouse. Characteristic of this functionality was the limitation of touch screens to sensing only one point of contact at a time. Recently, however, multi-touch functionality has made its way into the consumer market place.
With multi-touch technology the software involved recognizes multiple simultaneous touch points. This allows multi-finger operations and actions such as pinching and stretching. It also enables more than one user at a time to use the same screen.
Perhaps the best known device with multi-touch capability is Apple’s iPhone, but the popularity of the technology has resulted in its integration in an ever-widening range of devices. It can be found, for instance, in HP’s TouchSmart computer (the first widely available touch screen PC), the Microsoft Surface, and the touch pads of certain computers.
The Easiest Interface
Touch screens are among the easiest interfaces to use. Interacting directly with what you see on the screen allows a simpler and more efficient exchange of information. Complex tasks can be reduced to a simple chain of visual interactions that even computer-phobes can follow.
In the realm of assistive technology, they help to make computer-use available to those who are physically unable to use a keyboard or mouse. In education, they provide a user-friendly input device that enhances learning by making it a more enjoyable and interactive experience.
From public information displays to restaurant inventory systems, from industrial automation control to computer gaming, the touch screen, particularly in its multi-touch form, will increasingly become the face electronic devices present to the world.
Check out this video for a fun application of touch screen technology.