Touched by Technology

The latest buzz in the mobile world today is the touch screen phone which makes writing emails, sending text messages, surfing the internet and much more seem so easy! It’s literally at your finger tips and can be done by tapping your index finger (or any of the other four). But how exactly does your smartphone know where your finger is on the screen and how to respond to it? The answer may be a little more complex than you've ever imagined.

There are three basic systems that are used to recognize a person's touch:

• Resistive
• Capacitive
• Surface acoustic wave

The resistive system consists of a normal glass panel that is covered with a conductive and a resistive metallic layer. These two layers are held apart by spacers, and a scratch-resistant layer is placed on top of the whole setup. An electrical current runs through the two layers while the monitor is operational. When a user touches the screen, the two layers make contact in that exact spot. The change in the electrical field is noted and the coordinates of the point of contact are calculated by the computer. Once the coordinates are known, a special driver translates the touch into something that the operating system can understand, much as a computer mouse driver translates a mouse's movements into a click or a drag.

In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software. One advantage that the capacitive system has over the resistive system is that it transmits almost 90 percent of the light from the monitor, whereas the resistive system only transmits about 75 percent. This gives the capacitive system a much clearer picture than the resistive system.

On the monitor of a surface acoustic wave system, two transducers (one receiving and one sending) are placed along the x and y axes of the monitor's glass plate. Also placed on the glass are reflectors -- they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity).

Another area in which the systems differ is in which stimuli will register as a touch event. A resistive system registers a touch as long as the two layers make contact, which means that it doesn't matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object -- except hard and small objects like a pen tip.

As far as price is concerned, the resistive system is the cheapest; its clarity is the lowest of the three, and its layers can be damaged by sharp objects. The surface acoustic wave setup is usually the most expensive.

The LG Dare, Samsung Instinct, HTC Touch Diamond and many other phones use the most common of touchscreens built using resistive technology. Apple’s iPhone, the Google Android G1 and BlackBerry Storm all use the more sophisticated capacitive technology. Apple’s slick multi-touch gestures, such as pinching and spreading two fingers to zoom and reduce on-screen objects, are only possible on a capacitive screen.

To summarize the working of touch screens, there are several different technologies that power them, but here are the many things they have in common.

Firstly, almost all touchscreens in use today employ a three-layered system of operating. There is the glass layer, where the user will be touching his finger to the screen in order to implement the gestures he or she wants to perform. Then, underneath the glass layer is where the technology differs, but the technology between the glass layer and the bottom layer is to interpret the finger strokes in one way or another. Finally, the bottom layer of the touchscreen serves as the final point in the relay between your finger and the screen. This bottom layer is responsible for sending information to the device in a form it can understand.

And here is an outline of exactly what happens (in a matter of milliseconds) inside your phone.

1. You touch the screen at a certain place.

2. Depending on the technology, you either disrupt an electrical current or you create a voltage difference, allowing an electrical signal to be generated.

3. A sensor picks up this electrical signal.

4. The original signal is collected by the sensor and sent to the processor in its raw form.

5. The processor interprets the signal as a touch and starts to clean the raw data of any "noise".

6. Once cleaned, the processor then moves on to interpret where on the screen the touch was and determine exact coordinates.

7. These coordinates are sent to the software you're trying to use to determine where the "click" will be.

For something that is relatively complicated, it's amazing how easily it has invaded our everyday lives!