The point of capacitive touch interface design in mobile devices

Published: 30th December 2011
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Mobile devices, human interface design of products, most have been provided, such as touch screen, virtual buttons for touch operation, which has been non-application of the resistive touch the mainstream, but with high light transmittance, can not produce by repeatedly pressing machine fatigue design of capacitive touch solutions become, the high-end products, man-machine interface technology of choice for ...

Old mobile devices or full screen touch buttons, most adopted mechanical design, for example, Zinc oxide mining key physical design, and full-screen touch function, it resembles the adoption of the design of resistive ITO film form of product integration and development.

In fact, the mechanical operation of the entity keys have lower life, easy water, Titanium dioxide into the dust and other issues, and resistive touch the application of principles of ITO film, but also with mechanical buttons are easy to operate as fatigue problems, switch to new capacitance touch technology, can significantly improve the aforementioned mechanical fatigue and failure phenomena.

Touch response keys with touch screen design of the form

In the past, in the industrial computer, PDA, etc. Magnesia with a touch screen products, LCD modules and more adopted a "resistive" touchscreen design, the type of touch screen most of the screen corresponding to the physical location of the contact touch points coordinate transformation, a common 4,5,7 and 8-wire touch screen design, however, resistive touch screen quite a lot of physical limitations, a shorter life (4-wire resistive touch screen life by approximately 1 million times touch), even ITO with a certain degree of transparency, but in fact will affect the image quality problems.

In contrast, "capacitive" touch-screen design, the screen with up to 97% penetration, allowing the output of the screen itself, the effect is closer to true color, the original resistive touch screen requires touch-point pressure at the tip actuation mechanism for capacitive touch screen for finger pulp is only capacitive effects, contact coordinates can be done to confirm the user contacts the touch screen will be able to confirm the screen last longer, up to 200 million under the touch!

In addition to capacitive touch screen can switch mechanism in addition, new product design, have 11 to switch the capacitive touch capabilities to integrate traditional mechanical buttons. Features capacitive touch buttons, for the use of the body and touch the surface of the capacitor response, Nickel oxide measured changes in key states, simply touch the surface of the electrode plate can be used with touch control IC to design, due to the surface without direct contact with the can determine the capacitance of the pulp reaction, so most of the design will be covered with high-strength plastic surface, so that the touch screen is more durable.

PCT, SCT capacitive touch technology

PCT (ProjectedCapacitiveTouch) projected capacitive touch technology, the touch screen to take the concept of matrix production, PCT panel of ITO touch points in order to improve the SN noise ratio, specially designed for the more etched pattern, to strengthen the finger contacts recognition accuracy.

The SCT (SurfaceCapacitiveTouch) capacitive touch panel, it is a uniform coating of ITO from the four corners of the panel set up a line (respectively, UR, UL, LR, LL ..., etc.), touch-panel Line control IC is connected with the SCT, Neodymium fluoride the touch screen when the user contacts the surface of the pulp, the pulp and because of ITO electrode capacitance change produced by the current changes in 4-pole, through the touch-IC precision conversion resolution, obtained by point contact the corresponding coordinates.

PCT and SCT limit the application of touch solutions

Contact detection analysis because of technical differences between the coordinates, resulting in the PCT and SCT capacitive contact detection mechanism applies a slightly different situation, which, PCT technology, the more practice Multi-touch multi-touch application designed to detect both advantages , while the SCT technology is more suitable for Single-touch function of the low-cost single-touch design.

The touch panel of the SCT production processes must be critical optical coating technology to integrate the terminal module, the industry during this process much more expensive than outsourcing processing methods, Barium titanate this system is the high cost of production caused the problem. The PCT capacitive touch technology works, although relatively simple, but when trying to mass production of a number of technical challenges to be overcome, such as the contact coordinates resolved easily affected by the environment, leading to the sensitivity of touch performance in various panel positions inconsistent, malfunction response, most of these conditions the use of capacitive touch control IC can be improved, has not the major bottleneck in application development.

Compared to PCT technology, although SCT capacitive touch technology also has finger capacitive touch signal is weak, susceptible to interference and other problems, but still within the IC design by controlling mechanism to enhance the touch signal SNR. In addition, SCT capacitive touch screen technology simpler structure than the PCT in the development stage is also relatively easy to upgrade through hardware technology components of SNR. Source:www.mhcocm.com


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