'Magic' behind the touch screen

The screen of the iPhone, the DS game machine, the coffee table and the computer . help users to drag and drop icons and enter characters right on it without the keyboard developed according to different technologies with features private.

In terms of function, they all aim to feel the force of the finger or the pen click on it, considering what function the impacted position has, corresponding to which software. The difference lies in how the screen detects that impact.

There are 3 common types:

Nintendo DS uses resistive touch screen technology. Photo: Techfresh .

Resistive touchscreen is the most used device because it has the longest and cheapest price. It appears in touch-screen mobile phones (including some cheap Chinese phones), many tablet computers, Nintendo DS game consoles .

At the bottom of this screen is a layer of glass, on which there is a conductive layer and a resistor layer located a very thin distance apart. Above that is the class for users to touch.

So when you press down on the screen, the resistor will touch the conductive layer, changing the current flowing through them and the device can recognize the finger or pen touching it.

This is the cheapest method, but this way cannot support multi-touch (multiple fingers pressing at the same time) because of the limitations of the force-sensing mechanism. In addition, due to the use of multiple layers of materials, this screen is thick, consumes a lot of electricity for lighting and slow reactions.

Capacitive touch technology is applied to iPhone. Photo: Gadget-reviews .

Capacitive touchscreen (capacitive touchscreen) proved more attractive. Previously they were quite expensive but now prices have dropped and appeared in iPhone phones, Dell Latitude XT tablet screens .

Basically, the device has a layer of material on top of the screen surface with electricity flowing through it. Because humans also have magnetism, when touching this screen (assuming finger), it will create electrical variation. By identifying the most noise level on this surface, the device knows where the user is touching.

One can apply multitouch with this technology and due to less physical layer, the screen surface will be brighter. However, based on the interaction between electromagnetic fields, electrical conductivity . so if the user wears gloves, the operation will be difficult. In addition, if you want to use a pen instead of a finger, you must use a dedicated pen.

Surface computer of Microsoft coffee table uses technology
Infrared touch. Photo: Kuanhoong .

Infrared touchscreen (infrared touchscreen) is a loud technology on Microsoft coffee table computers. In theory, the image on its surface is projected from the bottom with infrared light. Below this surface are infrared cameras that can "see" the movement above so that when the light is reflected by the object (such as fingers, pens .), those images are processed and translated into move.

The outstanding advantage of this technique is that it supports very good multi-touch and low cost. However, the system is quite cumbersome and suitable for large devices in large spaces.

In addition, there are many other advanced touch screen technology in the world but not yet widely used. For example, a sound wave system that uses an energy converter and a reflector can detect that the ultrasound being transmitted between them is disconnected (meaning that an object is touching it). This surface without many layers should be 100% bright but dirt flying in the air can affect it.

Sharp (Japan) has also launched a touch-sensitive device using light-sensing technology integrated into the screen. They are sensitive enough to feel the finger to every pixel, increasing the multi-touch capability but, like infrared technology, this technique can be affected because of unwanted light.

Mary Lou Jepsen, an engineer in OLPC's low-cost laptop project, said they are developing a touchscreen based matrix of LCD screens. However, the product does not have the usual plug-and-play form but requires a specially encoded device for compatibility.