The difference between a capacitive screen and a resistive screen

Capacitive touch screen is commonly known as "hard screen", such as iPhone and G1 and other machines use this screen quality, resistive touch screen is commonly known as "soft screen", mostly used in Windows Mobile system mobile phones.

The capacitive touch screen uses the current sensing of the human body to work, and its contact screen is composed of a four-layer composite glass screen. When the finger touches the contact screen, because the human electric field, the user and the surface of the contact screen form a coupling capacitor, for high-frequency currents, the capacitor is a direct conductor, so the finger draws a small current from the contact point. This current flows out of the electrodes on the four corners of the contact screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. Capacitive contact screens have the advantages of high sensitivity and ease of multi-touch technology. However, the shortcomings of the capacitive screen are also obvious, the reflection of the capacitive screen is severe, and the transmittance of the four-layer composite contact screen of the capacitive technology to each wavelength of light is uneven, and there is a problem of color distortion, because the reflection of light between the layers also constitutes the confusion of the picture characters. And for mobile phone users, its technical characteristics determine that it can only be operated with fingers (now this shortcoming is actually used as a place to grow...). )。 The biggest disadvantage of capacitive screen is "drift". Because the capacitance changes with the different temperature, humidity or grounding conditions, when the ambient temperature, humidity and ambient electric field change, it will cause the drift of the capacitive screen, which constitutes inaccurate positioning.

The difference between a capacitive screen and a resistive screen

The difference between a capacitive screen and a resistive screen

The screen part of the resistive touch screen is a multi-layer composite film, which is composed of a layer of glass or plexiglass as the base layer, coated with a transparent conductive layer (ITO film) on the surface, and then covered with a layer of smooth and scratch-resistant plastic layer with a hardened surface. Its inner surface is also coated with an ITO layer, which is separated by a number of tiny (less than thousandths of an inch) transparent barrier between the two conductive layers. When the finger touches the screen, the two layers of ITO produce contact, the resistance changes, the controller calculates the coordinates of the contact point according to the detected resistance change, and then operates accordingly according to this coordinate, so this technology is necessary to apply force to the screen in order to obtain the contact effect. According to the number of lead-out wires, resistive screens are divided into four-wire, five-wire and other types. The surface surface of the five-wire resistive contact screen is conductive glass instead of conductive coating, which has a longer life and higher light transmittance. If the ITO coating of the resistive contact screen is too thin, it will be simple and brittle, and if the coating is too thick, it will reduce light transmission and internal reflection and reduce the clarity. Because it is often touched, the surface ITO will show micro-cracks and even deformation after use, so its life span is not long-lasting. Resistive contact screens are inexpensive and easy to produce. The presentation of four-line, five-line, seven-line and eight-line contact screens makes its performance more reliable, and also improves its optical characteristics.

(1) They are all a kind of operation that is well isolated from the outside world, and are not afraid of dust, water vapor and oil pollution.

(2) They can be used to touch any object and be able to write calligraphy, painting and painting, which is their big advantage

(3) The accuracy of the resistor contact screen only depends on the accuracy of A/D conversion, so it can easily reach 4096*4096 Comparatively speaking, the five-wire resistance is better than the four-wire resistance in ensuring the accuracy of the discrimination rate, but the cost is large, so the price is very high.

(1) Four-wire resistive screen

The two-layer transparent metal layer of the four-wire resistor imitation technology increases the stable voltage of 5V in each layer: one vertical tendency, one degree tendency. A total of four cables are required. Characteristics: High degree of analysis, high-speed transfer reaction. Surface hardness treatment, screening for abrasions, scratches and anti-chemical treatment. It has a smooth and matte finish. A proofreading, high stability, never drifting.

(2) Five-wire resistive screen

The base layer of the five-wire resistance technology contact screen adds the voltage field of the two tendencies to the conductive working surface of the glass through the precision resistance collection, and we can easily understand that the time-sharing operation of the two tendencies is added to the consistent working surface, and the outer nickel-gold conductive layer is only used to see as a pure conductor, and there is a method of detecting the voltage value of the X-axis and Y-axis of the ITO intersection point of the inner layer after contact to measure the position of the contact point. The inner ITO of the five-wire resistive contact screen needs four leads, and the outer layer is only a conductor, and there are a total of 5 lead wires for the contact screen.

Characteristics: high degree of analysis, high-speed transmission reaction.

High surface hardness, screening for abrasions, scratches and anti-chemical treatment.

30 million battles at the same point can still be used.

Conductive glass is the medium of the base material.

A proofreading, high stability, never drifting.

Five-wire resistive contact screens have the disadvantages of low price and high condition requirements.

(3) The scale of the resistive screen

Whether it is a four-wire resistance contact screen or a five-wire resistance contact screen, they are a kind of operation condition that is well isolated from the outside world, not afraid of dust and moisture, it can be used to contact with any object, can be used to write calligraphy, painting and painting, and is more suitable for the use of unlimited people in the field of industrial control and the office. The disadvantage of resistive contact screen cooperation is that the outer layer of the composite film is made of plastic materials, and people who don't know it use too much force or use sharp tools to contact and probably scratch the entire contact screen and cause scrapping. In addition, within the constraints, the scratch will only injure the outer conductive layer, and the scratch of the outer conductive layer is not related to the five-wire resistive contact screen, but is fatal to the four-wire resistive contact screen.

The capacitive screen uses the current of the human body to feel the stoppage. The capacitive contact screen is a four-layer composite glass screen, the inner surface of the glass screen and the interlayer are each coated with a layer of ITO, the outermost layer is a thin layer of silica glass protective layer, the interlayer ITO coating is used as the working surface, four electrodes are drawn out on the four corners, and the inner ITO is the barrier layer to ensure the exquisite operation condition.

When the finger touches the metal layer, because of the electric field of the human body, the user and the surface of the contact screen form a coupling capacitor, which is an indirect conductor for high-frequency currents, so the finger draws a small current from the point of contact. This current divides from the electrodes on the four corners of the contact screen, and the current flowing through these four electrodes is inversely proportional to the interval between the fingers and the four corners, and the controller derives the position of the contact points by precisely planning the four current shares.

(2) Disadvantages of capacitive contact screens

The light transmittance and clarity of the capacitive contact screen are better than those of the four-wire resistive screen, and of course it cannot be compared with the surface acoustic wave screen and the five-wire resistive screen. The reflection of the capacitive screen is tense, and the transmittance of the four-layer composite contact screen of the capacitive technology to each wavelength of light is uneven, and there is a problem of color distortion, because the reflection of light between the layers also constitutes the confusion of the picture characters.

The capacitive screen is used as an electrode of a capacitor element in principle, and when a conductor is close to the mezzanine ITO working surface to couple a capacitance with sufficient capacitance value, the current flowing away is enough to provoke the misbehavior of the capacitive screen. As we know, the capacitance value is, of course, proportional to the interval between the poles, but inversely proportional to the definite area, and is also related to the insulation coefficient of the dielectric. Therefore, when a large area of the palm or the hand-held conductor is close to the capacitive screen instead of touching, it can provoke the misbehavior of the capacitive screen, in a humid climate, this situation is particularly tense, and the hand holding the flasher, the palm of the hand is close to the flasher within 7 cm or the body is close to the flasher within 15 cm can provoke the misbehavior of the capacitive screen.

Another disadvantage of capacitive screens is that they do not react when touched with gloved hands or hand-held non-conductive objects, due to the addition of a more insulating medium.

The more important disadvantage of the capacitive screen is drift: when the temperature and humidity of the condition are changed, and the electric field of the condition is changed, the drift of the capacitive screen will be caused by the city, which constitutes inaccurate. For example, the temperature of the flasher rises after the device is turned on, which will constitute drift: the user touches the screen together with the other hand or the side of the body close to the flasher, and the flasher will drift; The larger object near the left of the capacitive contact screen drifts back after moving, and if someone surrounds you when you touch, it will also cause drifting; The drift of the capacitive screen is due to the lack of technical talent, and the situation potential surface (including the user's body) is of course far away from the capacitive contact screen, but it is much larger than the finger area, which indirectly affects the determination of the contact position.

In addition, in fact, many of the relationships that should be linear are non-linear in practice, such as: the total amount of current sucked by people with different weights and different levels of finger wetness is different, and the change of the total current and the change of the four sub-currents are non-linear, and the self-boundary of the four corners of the capacitive contact screen is said to be the origin of the coordinates, and the controller can not be found and regulated after the drift, and after the completion of the 4 A/D, the value of the four shunts is transferred to the X, The planning process for the Y coordinate value is huge. Because there is no origin, the drift of the capacitive screen is cumulative, and calibration is often required on the job site.

1. Indoor visual function

Both are generally good.

2. Contact sensitivity

1. Resistive touch screen: It is necessary to use pressure to make all layers of the screen contact, and can use fingers (even with gloves), nails, stylus, etc. to operate. Supporting stylus is important in the Asian market, where gesture and text recognition are valued.

2. Capacitive touch screen: The slightest contact from the surface of the charged finger can also activate the capacitive sensing system under the screen. Non-living objects, fingernails, gloves are not effective. Handwriting is more difficult to recognize.

3. Accuracy

1. Resistive touch screen: the accuracy reaches at least a single display pixel, which can be seen when using the stylus. It is easy to read by hand, and it helps to operate in an interface with small control elements. 2. Capacitive touch screen: The theoretical accuracy can reach several pixels, but in fact it will be limited by the contact area of the finger. So much so that it is difficult for users to click on the policy less than 1cm2 accurately.

Fourth, cleaning

1. Resistive touch screen: Because it can be operated with a stylus or fingernails, it is not easy to leave fingerprints, oil stains and bacteria on the screen.

2. Capacitive touch screen: use the whole finger to touch, but the outer layer of glass is easier to clean.

5. Environmental adaptability

1. Resistance touch screen: the specific value is unknown. However, there is evidence that the Nokia 5800 with a resistive screen can operate in temperatures between -15°C and +45°C, and there is no requirement for humidity.

2. Capacitive touch screen: the typical operating temperature is between 0° and 35°, and at least 5% humidity is required (limited by the operating principle).

The difference between a capacitive screen and a resistive screen

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