Article: Touchscreen technologies in phones

Three types of technologies are used for the manufacturing of mass touchscreen mobile phones: resistive, capacitive and infrared.

Images depicting the different technologies are courtesy of planarembedded.com

Resistive (Pressure sensitive) touchscreen:

As we’ve mentioned above, this is the most widely used touchscreen scheme for the production of mobile phones. It is most common in the Windows Mobile Professional phones, for example HTC TyTN II or HTC Touch Diamond; it is resistant to water and dust, but it is easily scratched and cannot be used with sharp objects. It is represented by three types: 4-wire, 5-wire and 8-wire with the second one being the most used. In contrast to the other types it is composed of three layers, rather than two with the additional layer ensuring greater durability and a much longer life (35 million clicks, instead of 1 million), without impacting the price.

This type of technology works according to the following method: there are small plastic dots (spacer dots) between the two layers, which prevent them from touching if there’s no pressure used. There’s electricity going through each one of the layers and in the event of contact, a chain is formed. The amount of the electricity, passing between the layers is then measured, in order to determine the point of touch. Unfortunately, this method cannot report more than one touch at a time and lets through about 85% of the light, emitted by the screen. The good news is that this is the least expensive from all three types of touchsreen systems we are discussing here (you can read about them later on in this article) and you can use any object to touch it, e.g. a stylus or a finger.




Capacitive (Electrostatic) touchscreen:

Lately, this type of technology has been gaining popularity in the mobile phone industry, its most renowned representatives being Apple’s iPhone and LG PRADA. The smaller market share of phones with such screens is due mostly to their high price, since this is not a cheap method. It has two main subtypes, one of which cannot register more than one touch at a time, while the other, called „MultiTouch” by their creators (Apple and used in iPhone and iPod) can. In addition, despite not being the first to employ it, these two devices made this type of technological method popular.

This system employs just one layer (a grid), covered with an electroconductive material (most often indium tin oxide), providing continuous current with a certain frequency. When touching the screen with an object emitting a constant electric flow, for example a human finger (the human body generates electricity), a change in the current occurs and that’s how the contact point is determined. The pros of this type of technology are that it is scratch, moisture and dust-proof, it lets through about 92% of the light, emitted by the screen and has a very long life (about 225 million clicks). The bad news is that this touchscreen type cannot be activated by contact with inanimate objects (e.g. the gloves that you might be wearing).




Infrared (IR) touchscreen:

The infrared technology is not so popular in mobile phones, compared to the other types, since it is the most expensive one. Therefore, the manufactures themselves do not use it in their touchscreen models. It is divided in two subtypes, heat-sensitive and optical. However, the two types are drastically different from one another in the way they work.

The heat-sensitive subtype is the more widely used one, but it is applied in other components of mobile devices. Such an example are the buttons of Samsung SGH-E900 and Samsung U600, which can only be touched with warm objects (e.g. fingers). Unfortunately, you’ll be unable to operate the phone if your fingers are “frozen”, because of cold weather.

The optical technological method uses infrared beams, which are not visible to the human eye and its only representative among the mobile phones is Neonode N2. It works, using a number of sensors, arranged above and around the screen, forming a grid of invisible beams. If an object (e.g. a finger or a stylus) touches the display, it interrupts the rays in a certain area and thus the touch point is determined. For this system it is not necessary to use physical force and just a gentle touch is enough. 100 % of the light, emitted by the display, is let through and its life depends only on the sensors’ lives, which spans for about 7 years of being constantly lit up. Further on, it is not influenced by dust, moisture or scratches, since actually the display’s glass simply shows the picture, while the sensors above it do the rest. However, a rather big disadvantage of this type of technology is that a strong ambient light can have a negative impact on its productivity and precision.

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