Touchscreen Technology - I

Well how good it would be when we could control any and everything with just one touch but, halt your imagination that time is too far so, live in present and the present is that touchscreens have just marked their successful commercialized beginning. This article is to give you the slightest idea of how a touchscreen works, more importantly to give a detailed idea of the various touchscreens technologies. To start with let’s describe what a touchscreen means for those who might be reading the term for the first time.

A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus. Touchscreens are common in devices such as game consoles, all-in-one computers, tablet computers, and smartphones.

The History of touchscreen is marked by various individual scientists but not any organization in particular. E. A. Johnson was the first person to have such a vision; he not only published articles on capacitive touchscreens but also worked up ways to build them. Later Bent Stumpe of CERN with the aid of Frank Beck developed the first and only one of its types, the capacitive touch screen. This was the time 1982 when Computers and Mobilephones itself were marking their existence. Thus, without making these devices a complex by introducing the touchscreen technologies it was decided to keep within. But, Hewlett Packard (HP) had something else in mind, the launched the first touchscreen model of PC’s named HP-150 and commercialized it worldwide. It was a great help at Kiosks, Banks, Ticket booths etc. Similar to the PLATO IV system, the touch technology used employed infrared transmitters and receivers mounted around the bezel of its 9" Sony Cathode Ray Tube (CRT), which detected the position of any non-transparent object on the screen. Parallel to it was the beginning of INTERNET which itself spread like virus but also made the technologies acknowledged to the world market.

There are a variety of touchscreen technologies that have different methods of sensing touch which are viz.-

We will now discuss about each but first with the widely used ones.

      

It has two resistive (provides resistance) surfaces made out of Indium-Tin Oxide. These are metallically coated and have insulating spaces. On touching, compression takes place as shown in the above image leading to formation of a closed circuit. This is why gadgets with resistive touchscreens have to be pressed harder so that the contact remains intact and as the movement passes through the insulating spaces it analyses the direction of motion. It is most widely used due to its simple structure.

It again has two types:

1. Matrix (digital):

Striped electrodes on substrates such as glass or plastic face each other

2. Analogue:

Transparent electrodes without any patterning facing each other

Low production costs

There are two Parallel Sheets

If there is no pressure applied – Electronically separated

If applied pressure – Impedancebetween the two sheets is lowered at the touch point.

Top sheet carries a voltage gradient by applying a voltage between the electrodes of top sheet

Bottom sheet serves as a slide in a linear potentiometer.

Linear Potentiometer:
 Linear potentiometers are sensors that produce a resistance output proportional to the displacement or position. Resistance value changes with rotation of screw.

                                  

Electrons move along                                          

Electrons are completely displaced            

Measurement of the touch point resistance is valuable. Value varies depending upon force applied.