Capacitive touch screens are commonly called "hard screens". For example, iPhones and G1s use such screens. Resistive touch screens are commonly called "soft screens", and are mostly used in Windows Mobile systems.
The capacitive touch screen works by the current sensing of the human body, and the touch screen is composed of a four-layer composite glass screen. When the finger touches the touch screen, since the human body electric field, the user and the surface of the touch screen form a coupling capacitance, for the high frequency current, the capacitance is a direct conductor, and the finger sucks a small current from the contact point. This current flows out from the electrodes on the four corners of the touch screen, and the current flowing through the four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position information of the touch point by accurately calculating the ratio of the four currents. . Capacitive touch screens have the advantages of high sensitivity and easy implementation of multi-touch technology. However, the shortcomings of the capacitive screen are also obvious. The reflective screen of the capacitive screen is severe, and the four-layer composite touch screen of the capacitive technology has uneven transmittance for light of various wavelengths, and there is a problem of color distortion, which is caused by reflection of light between layers. Blurring of image characters. And for mobile phone users, its technical characteristics determine that it can only be operated with fingers (now this shortcoming is actually regarded as an advantage...). The biggest disadvantage of capacitive screens is "floating." Since the capacitance varies with temperature, humidity, or grounding conditions, when the ambient temperature, humidity, and environmental electric field change, the capacitive screen will drift, resulting in inaccurate positioning.
Resistive screen:
The screen part of the resistive touch screen is a multi-layer composite film consisting of a layer of glass or plexiglass as the base layer, and the surface is coated with a transparent conductive layer (ITO film), which is covered with an outer surface and hardened, smooth and scratch-resistant. Plastic layer. Its inner surface is also coated with a layer of ITO, with a number of fine (less than one thousandth of an inch) transparent isolation points between the two conductive layers separating them. When the finger touches the screen, the two layers of ITO come into contact, the resistance changes, the controller calculates the coordinates of the contact point according to the detected resistance change, and then performs the corresponding operation according to the coordinate, so the technique must be applied Go to the screen to get a touch. The resistance screen is divided into four lines and five lines according to the number of lead lines. The outer surface of the five-wire resistive touch screen is a conductive glass rather than a conductive coating layer. This conductive glass has a long life and a high light transmittance. If the ITO coating of the resistive touch screen is too thin, it is easy to be brittle, and the coating is too thick to reduce light transmission and form internal reflection to reduce the definition. Since it is often touched, the surface layer ITO will appear fine cracks or even deformation after a certain period of time, so its life is not long. Resistive touch screens are inexpensive and easy to produce. The four-wire, five-wire, and seven-wire, eight-wire touch screens have made their performance more reliable and improved their optical characteristics.
1 They are all things that are completely severed to the outside world. They are not afraid of dust, water vapor and oil. They can be touched by any object. They can be used to write books and draws. This is because their precision is superior to that of the 3 resistance touch screen. The accuracy of the A/D conversion can easily reach 4096*4096. In comparison, the five-wire resistance is better than the four-wire resistance in the accuracy of the tube identification, but the cost is high, so the price is very high.
(1) Four-wire resistive screen four-wire resistance mimics the two-layer clear metal layer of the skill. When each layer grows 5V constant voltage: one vertical deflection, one degree bias. A total of four cables are required. Features: high resolution, high-speed transmission response. Appearance hardness, eliminating scratches, scratches and chemical disposal. Has a smooth and matte finish. One correction, high stability, never drift.
(2) Five-wire resistance screen Five-wire resistance skill The lower layer of the touch screen puts two biased voltage fields through the fine resistance collection on the conductive surface of the glass. We can easily understand the time-sharing things for the two bias voltage fields. It is added to the uniform surface, and the outer layer of nickel-gold conductive layer is only used as a pure conductor, and the position of the touch point is measured by detecting the X-axis and Y-axis voltage values ​​of the inner ITO snoring point after touch. The inner layer of ITO of the five-wire resistive touch screen requires four leads, the outer layer is only used as one conductor, and the touch screen has five lead wires.
Features: high degree of profiling, high-speed transmission response.
The appearance is high in hardness, eliminating scratches, scratches and chemical disposal.
30 million hits at the same point are still available.
The conductive glass is the medium of the substrate.
One correction, high stability, never drift.
The five-wire resistive touch screen has low price and high requirements for situational requirements. (3) The range of the resistive screen is the same as the four-wire resistive touch screen. Water vapor, which can be touched by any object, can be used to write books and draws, compared to the appropriate industrial control and the use of infinite people in the office. The defect of the resistive touch screen is that the plastic material is applied to the outer layer of the composite film, and it is unclear that the person who is too hard or uses a sharp touch may scratch the entire touch screen and cause scrapping. However, within the limits, scratching only hurts the outer conductive layer. The scratch of the outer conductive layer is not related to the five-wire resistive touch screen, but is fatal to the four-wire resistive touch screen.
Capacitive screen:
(1) Capacitance Skills The touch screen is the application of the current of the human body to stop things. The capacitive touch screen is a four-layer composite glass screen. The inner and outer surfaces and the interlayer of the glass screen are coated with a layer of ITO. The outermost layer is a thin layer of alumina glass maintenance layer. The interlayer ITO coating is used as the surface of the glass. Four electrodes are taken out, and the inner layer of ITO is a barrier layer to manage the fine things.
When the finger touches the metal layer, the user and the touch screen form a coupling capacitor due to the human body electric field. As for the high frequency current, the capacitor is an indirect conductor, so the finger sucks a small current from the snoring point. This current is discharged from the electrodes on the four corners of the touch screen, and the current flowing through the four electrodes is inversely proportional to the distance between the fingers and the four corners. The controller accurately calculates the ratio of the four currents to obtain the position of the touch point. .
(2) Defect of capacitive touch screen The transmittance and clarity of the capacitive touch screen are superior to those of the four-wire resistive screen, although it is not comparable to the external acoustic wave screen and the five-wire resistive screen. The capacitive screen is very reflective, and the four-layer composite touch screen with capacitive skills has an uneven light transmittance for each wavelength of light, and there is a problem of color distortion. Because the reflection of light between layers also forms the ambiguity of image characters.
The capacitive screen reasonably regards the human body as an electrode of a capacitor component. When a conductor is close to the capacitor with a sufficient capacitance between the ITO surface of the interlayer, the current flowing away is sufficient to cause the wrong action of the capacitive screen. . We know that the capacitance value is proportional to the inter-electrode spacing, but inversely proportional to the absolute area, and also to the dielectric coefficient of the medium. Therefore, when a large area of ​​the palm or hand-held conductor approaches the capacitive screen instead of touching, it can cause the wrong action of the capacitive screen. In a humid climate, this situation is particularly tense, and the hand holding the display, the palm close to the display Within 7 cm or within 15 cm of the body, the malfunction of the capacitive screen can be caused.
Another drawback of capacitive screens is that there is no response when touching a gloved hand or holding a non-conducting object due to the growth of a more insulating medium.
The more important defect of the capacitive screen is drift: when the temperature and humidity change, the electric field changes when the electric field changes, and the city causes the drift of the capacitive screen to form a ban. For example: after the boot, the temperature of the display will rise and drift: when the user touches the screen, the other hand or the body side will drift near the display; the larger object near the capacitive touch screen will move back and drift, and if you touch it, if someone is around The appearance of the screen will also cause drift; the drift of the capacitive screen is due to the lack of talent in the skill. The potential surface (including the user's body) is far away from the capacitive touch screen, but it is much larger than the finger area. They indirectly affect the touch. Determination of status.
In addition, in fact, many linear systems should be non-linear in practice, such as: the difference in body weight is probably the difference between the total amount of current drawn by the difference in finger wetness level, and the change in total current amount and the amount of four divided currents. The transformation of black and white linearity, the four corners of the capacitive touch screen application, the polar coordinate system has no origin on the coordinates, the drift controller can not detect and rectify, and after the completion of 4 A/D, The calculation of the value of the four sub-flows to the X, Y coordinate values ​​of the touch point in the Cartesian coordinate system is huge. Because there is no origin, the drift of the capacitive screen is cumulative, and it is often calibrated at the scene.
First, the indoor visual effects are usually very good.
Second, touch sensitivity
1. Resistive touch screen: It is necessary to use pressure to make contact with each layer of the screen. You can use your fingers (even with gloves), nails, stylus, etc. to operate. Support for stylus is important in the Asian market, where gestures and text recognition are valued.
2, capacitive touch screen: the most subtle contact from the surface of the charged finger can also activate the capacitive sensing system at the bottom of the screen. Non-living objects, nails, and gloves are invalid. Handwriting recognition is more difficult.
Third, the accuracy
1, the resistance touch screen: the accuracy of at least a single display pixel, can be seen with the stylus. It is easy to recognize by hand and helps to operate under the interface of small control elements.
2, capacitive touch screen: theoretical accuracy can reach several pixels, but in fact will be limited by the finger contact area. It is difficult for the user to accurately click on a target of less than 1 cm 2 .
Fourth, the cost
1, the resistance touch screen: very low.
2, capacitive touch screen: different manufacturers of capacitive screen price is 10% to 50% more expensive than the resistance screen. This extra cost doesn't matter to the flagship product, but it may discourage mid-priced phones.
Five, multi-touch feasibility
1. Resistive touch screen: Impossible unless the resilience screen is connected to the machine's circuit.
2, capacitive touch screen: depending on the implementation and software, has been implemented in the G1 technical demonstration and iPhone. The 1.7T version of the G1 is already capable of implementing the multi-touch feature of the browser.
Sixth, damage resistance
1. Resistive touch screen: The fundamental characteristics of the resistive screen determine that the top of the resistive screen is soft and needs to be able to be pressed. This makes the screen very susceptible to scratches. Resistive screens require a protective film and relatively more frequent calibration. An advantageous aspect is that the resistive touch screen device using the plastic layer is generally less susceptible to damage and less prone to breakage.
2, capacitive touch screen: the outer layer can use glass. Although it is not indestructible, and it may break under severe impact, the glass should be better for daily rubbing and smudges.
Seven, clean
1. Resistive touch screen: Since it can be operated with a stylus or nail, it is not easy to leave fingerprints, grease and bacteria on the screen.
2, capacitive touch screen: to use the entire finger to touch, but the outer layer of glass is easier to clean.
Eight, environmental adaptability
1, resistance touch screen: the specific value is not known. However, there is evidence that the Nokia 5800 with a resistive screen can operate at temperatures between -15 ° C and +45 ° C without any humidity requirements.
2, capacitive touch screen: Typical operating temperature between 0 ° and 35 °, requires at least 5% humidity (limited by the working principle).
Nine, the visual effect under the sun
1. Resistive touch screen: Usually bad, the extra screen level reflects a lot of sunlight.
2, capacitive touch screen: still very good.
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