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Touch Screen Technologies Cheat Sheet by

Touch Screen Technoloies
screen     touch     types     technoloies

Introd­uction

Although touch screens may look much the same on the outside, their inner workings can be very different. There are currently five different types of touch screen in use at the moment. Here is a brief guide to them

Resistive

A glass panel is covered with a resistive coating, which is topped by a layer of insula­tion, inters­persed with spacer dots and then covered again by a sheet of polyester which is conductive on the inner side (the side touching the insula­tion). When the polyester outer is touched, it flexes slightly and thus sends an electrical charge to the corres­ponding location on the glass panel. While resistive touch screens had smartphone users grinding their teeth in frustr­ation, they’re great for applic­ations where robustness matters more than respon­siv­eness and so, for example, is the standard choice for ATMs.

Resistive Technology

Surface capacitive

Same basic lines as resistive techno­logy, but the key difference is that instead of a layer of insula­tion, there is a layer of transp­arent electr­odes, which store an electrical charge. When touched by an electrical current, the electrodes discharge and this is converted into an instru­ction. Surface capacitive screens are a big step up in image quality as compared to resistive ones and they’re also less prone to scratches, but they are also more expensive to produce.

Surface Capaci­tiveC

 

Projected Capacitive

An integrated circuit chip is placed into the electrode layer and used to generate a 3D electr­ostatic field. When the screen is touched, the ratio of currents changes and this is measured and used to determine the relevant instru­ction. Projected capacitive screens offer several advantages over surface capacitive screens. Firstly they can be touched by a lightl­y-c­overed finger, which is useful for industries in which people are required to use plastic gloves as standard. Secondly they are much better for processing detailed instru­ctions, they go way beyond pinch and zoom and thirdly, they offer even better image quality. They are, however, even more expensive to produce.

Projected Capacitive

Surface Acoustic Wave

SAW technology uses a grid of ultrasonic waves produced by piezoe­lectric transd­ucers and receivers located on a glass screen. When the screen is touched, by something soft, like a finger, even gloved, the touch is absorbed causing a change in wavelength which can be measured and translated into instru­ctions. The sensit­ivity of SAW technology is both a benefit and a drawback in that it means it is capable of immense respon­siv­eness, but that immense respon­siv­eness means that it is very easy to trigger it inadve­rte­ntly, for example through moisture or dust. SAW technology also offers superb image quality - but at a high price.

SAW Technology

Infrared Touch

Infrared touch screens work similarly to SAW touch screens, except that instead of piezoe­lectric transd­ucers and receivers, they use infrared rays to create the grid and sensors to detect when the infrared beam is interr­upted. While the term infrared may conjure up images of remote controls for indoor use, in actual fact, the robustness of infrared makes it popular for outdoor applic­ations.

Benefits of Infrared techno­logy:

Can be scaled to any size without losing resolution
Calibr­ation stability – no touch point drift
High clarity and light transm­ission
High chemical, scratch, breakage, and liquid resistance
High sealab­ility from dust and liquids
Touch can be activated by anything including finger, gloved hand, or stylus
High durability since a touch is only interr­upting light beams

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