Bookmark and Share

Tuesday, 20 July 2010

how TOUCH-SCREEN works

You must have seen touch screens at ATMs, cellphones, information kiosks .Touch screen based system allows an easy navigation around a GUI based environment.

Tap on the screen twice for double clicks, and drag a figure on the screen to move the cursor .We can do almost everything the mouse does, and do away with the additional device(mouse) leaving only the screen.

So “They’re all the rage, they are the buzzword, they are probably the hottest thing in technological cosmos right now!”Falling price and improved technology has fueled the use of these devices in smaller consumer devices like mobile, Tablet PCs and handheld gaming consoles.

The components

There are four popular touch screen technologies but all of them have three main components.

· Touch sensitive surface

· The controller

· The software driver

LCD Framework LCD Theory

>> The touch sensitive surface is an extremely durable and flexible glass or polymer touch response surface, and this panel is placed over the viewable area of the screen. In most sensors there is an electric signal going across the screen, and a touch on the surface causes change in the signal depending on the touch sensor technology used .This change allows the controller to identify the location of the touch.

>> The controller is a device that acts as the intermediate between the screen and the computer .It interprets the electrical signal of the touch event to digital signal that computer can understand. The controller can be placed with the screen or housed externally.

>> The software driver is an interpreter that converts what signal comes from the controller to information that the operating system can understand.

Touch screen sensor technologies

Resistive touch screens

Resistive touch screens have two glasses or acrylic layers, one of them is coated wit is conducting and other is coated with resistive material. When these layers brought in contact the resistance changes and change is registered and location of touch is calculated.

These are durable and resistant to humidity and liquid spills. But they offer limited clarity, and the surface can be easily damaged by sharp objects.

· Capacitive touch screens

In these devices a glass panel with a coat of charge storing material on its surface .When the panel is touched, a small amount of charge is drawn at the point of contact. Circuit located at each corner of the screen measure the difference in charge and send information to the controller for calculating the position of touch.These are used where the clarity precision is of concern as in laptops and medical imaging

· Acoustic wave touch screens

Touch Screen Acoustic Wave Technology

This newer technology uses ultrasonic waves that pass over the screen . When the panel is touched , there is a change in the frequency of ultrasonic wave and the receiver at end of the panel register this change.

Since only glass is used with no coating, there is nothing that wears out.

Infrared touch screens

Infrared touch screens are primarily used for large displays, banking machines, and in military applications.

Touch Screen Infrared Technology

Infrared touch screens are based on light-beam interruption technology. Instead of an overlay on the surface, a frame surrounds the display. The frame has light sources, or light emitting diodes (LEDs) on one side and light detectors on the opposite side, creating an optical grid across the screen.

When an object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the photo sensors.

Optical touch screen

Touch Screen Optical Technology

Optical touch screen technology is ideal for large LCD and plasma displays up to 100″ diagonal.

Optical touch screen technology uses two line scanning cameras located at the corners of the screen. The cameras track the movement of any object close to the surface by detecting the interruption of an infra-red light source. The light is emitted in a plane across the surface of the screen and can be either active (infra-red LED) or passive (special reflective surfaces).

Dispersive Signal Technology

Dispersive Signal Technology (DST) consists of a chemically-strengthened glass substrate with piezos mounted on each corner, mated to a sophisticated, dedicated controller. The DST Touch System determines the touch position by pinpointing the source of “bending waves” created by finger or stylus contact within the glass substrate. This process of interpreting bending waves within the glass substrate helps eliminate traditional performance issues related to on-screen contaminants and surface damage, and provides fast, accurate touch attributes.

Dispersive Signal Technology (DST)

· Other technologies

The above are the main technologies, there are others as well like strain gauge and Microsoft’s surface technology etc .Through surface computing you can seamlessly synchronize electronic devices that touch its surface.

Advantage and disadvantage

With improvement of technology of touch screens, precise pointing is also possible. Touch screens with glass surface can resist dirt, grease, moisture and also household cleaning agents.

Touch screens have some disadvantages like people with fat fingers may mishit keys , needs to be handle carefully .Touch screens are complex items and unlike keypad there are many things which may go wrong .

Future prospect

Many large companies like Microsoft and Apple have gotten on the touch screen bandwagon, multi touch screens in particular. Apple has patented an “Integrated Sensing Display” wherein display elements are integrated with image sensing elements. If this will put to use, you could have a single device that looked like a monitor for video conferencing, wherein the monitor would be a camera!


  1. Hi,

    After reading your post, I think that its a fresh news for everyone about touch screen and it's work. I am also interested in latest news.

  2. Great information thanks for getting this out there for people like me to read.Lots of good information found right there. Interesting to see how much all those big blogs are making.Thanks for sharing, really cool site....