Electronic enthusiasts in October "hot touch technology special issue " hot download, how can you lack!
Smartphones and tablets are now everywhere. Businesses and consumers use them a lot, and this year there have been many models of tablets. The touch screen applications that were first introduced to small-sized devices a few years ago are rapidly spreading to large-sized devices. For computing device and electronic device manufacturers, this new market not only represents the latest consumer craze, but it may also indicate a fundamental shift in the way people interact with information and the computing hardware that provides it. The growth of this market has triggered a series of actions by device manufacturers, who are actively transplanting touch screen technology to large-size hardware devices.
Nonetheless, from a small screen and simple touch application to a completely new model that mainly uses hands and fingers to interact with a full-size computer is not necessarily a direct transition. Manufacturers need to reconsider how consumers use touch screens to meet new, more demanding requirements. Most importantly, the transition to larger screens makes multi-touch capabilities indispensable. For example, smaller mobile phone displays can rely on single-finger touch to control and select mobile phone operations. However, although a few finger strokes are sufficient on a 5-inch screen, on a 12-inch or 40-inch device, or when multiple users use both hands to interact simultaneously, how many strokes are needed? What new applications will appear that are popular for large-size devices? How can manufacturers ensure that their devices support these applications?
Basic principles of touch screen technology
The basic principles of today's touch screens are derived from the touch technology of buttons, scroll wheels and sliders that were used early (and are still widely used). Over the years, the use of mechanical switches has continued to decline, and control technologies such as resistive membrane switches, piezoelectric switches, and touch technology based on capacitive sensing have led the development trend.
Resistive touch technology
Resistive touch technology includes a flexible top layer, an insulating spacer and a bottom substrate. A graphic is printed on the upper surface of the top layer, and a conductive graphic using conductive ink of silver or carbon is printed on the lower surface. Corresponding conductive patterns are printed on the substrate. The conductive layers are pressed together through the holes in the separator to form a contact. To form tactile feedback, when the switch action occurs, the metal or plastic dome under the cover layer can be used to make a "click", and the embossing on the top layer can be used to guide the user's finger to each switch's "optimal contact ". Nevertheless, membrane switches still have many disadvantages. First of all, they are not really touch switches. Forming contact requires physical movement and physical pressure.
Similarly, resistive touch screens also contain multiple layers, the most important of which are two thin conductive layers with a small gap. Pressing a certain point on the outer surface of the screen will cause the two metal layers to be connected at this point, which is equivalent to a voltage divider, which will cause the current to change. This change will be recorded as a touch operation and sent To the controller for processing.
Figure 1-Structure of a resistive touch screen
Resistive touch screens are favored by the market because of their low production cost and excellent stylus capabilities, and have many supporters, especially for applications that use Asian characters. However, as multi-touch applications gradually become a trend, resistive technology does not support multi-touch. In addition, due to the need for multiple layers or "stacks" that affect the optical performance, the visibility of the display due to reflection is poor in sunlight, and the brightness of the display is greatly reduced. Due to the need for a soft outer layer to make contact with the stylus (or any object in contact with it), resistive touch screens are also prone to scratches, moisture and dust.
Projected capacitive touch technology
A technology that competes with resistive touch technology uses projected capacitive fields. This technology has quickly won the support of users because it has a hard, "smooth" exterior surface with excellent appearance, and from a practical point of view, it is completely sealed to prevent the intrusion of dust and moisture. In order to meet the needs of consumers, manufacturers have responded quickly. Most manufacturers seem to have regarded capacitive touch technology as the direction of future development. The working principle of this technology is that when an object (such as a finger) approaches or touches the screen surface, the system will measure small changes in capacitance (that is, the ability to hold a charge). Nevertheless, not all capacitive touch screens are the same. Different capacitance-to-digital conversion (CDC) technologies and the spatial arrangement of the electrodes used to collect charge determine the overall performance and functionality that the device can achieve.
In terms of how to arrange and measure capacitance changes in the touch screen, device manufacturers have two basic choices: self capacitance and mutual capacitance. Most early capacitive touch screens relied on self-capacitance, that is, measuring the capacitance change of an entire row or column of electrodes. This method does not pose a problem for single-touch or simple two-touch interactions, but it brings great limitations to more advanced applications, because when the user presses two points, it will cause a position Fuzzy problem. The system can effectively detect two (x) coordinates and two (y) coordinates, but cannot know which (x) and which (y) are a pair. When recognizing touch points, this will result in a "ghost" position, reducing accuracy and performance.
Figure 2-The difference between self capacitance and mutual capacitance
As another solution, the mutual capacitance touch screen uses a set of transceiving electrodes arranged in an orthogonal matrix, so it can measure the intersection of a row of electrodes and a column of electrodes. In this way, the mutual capacitance touch screen can detect each touch operation represented by a specific pair of (x, y) coordinates. For example, a mutual capacitance system can detect two touch points (x1, y3) and (x2, y0), while a self-capacitance system can only detect (x1, x2, y0, y3). (See Figure 2.) Basic CDC technology also affects performance. During the charge acquisition process, the potential of the receiving line remains at zero, and only the charge between the transmitting X and receiving Y electrodes touched by the user is transferred. Other technologies can also do this, but the advantage of CDC is its ability to resist noise and anti-parasitic effects. This capability can increase the flexibility of system design. For example, the sensor IC can be placed on the FPC close to the sensor or on the main circuit board farther away.
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