The main application and defects of capacitive touch screen
Apr 27, 2018
A capacitive touch screen is a transparent, special metal conductive material applied to the glass surface. When the finger is touched on the metal layer, the capacitance of the contact changes, so that the frequency of the oscillator connected to it changes, and the position of the touch can be determined by measuring the frequency change.
In principle, the capacitive screen uses the human body as an electrode of a capacitor element. When a conductor couples a capacitor with a sufficient capacitance between the conductor and the interlayer ITO working face, the current flowing away is enough to cause the power screen to malfunction. .
The capacitive touch screen is mainly constructed by coating a transparent thin film layer on the resistive screen, and then adding a protective glass outside the conductive layer. The double glass design can completely protect the conductor layer and the sensor.
Capacitive touch screens are coated with elongated electrodes on the four sides of the touch screen to form a low-voltage alternating-current electric field in the conductive body. When touching the screen, due to the human body electric field, a coupling capacitor is formed between the finger and the conductor layer, and the current from the four-sided electrode will flow to the contact, and the current intensity is proportional to the distance from the finger to the electrode, and the controller located behind the touch screen will Calculate the proportion and strength of the current, and accurately calculate the position of the touch point. The double glass of the capacitive touch screen not only protects the conductor and the sensor, but also effectively prevents external environmental factors from affecting the touch screen. Even if the screen is stained with dirt, dust or oil, the capacitive touch screen can still accurately calculate the touch position.
A capacitive touch screen is a transparent, special metal conductive material applied to the glass surface. When the finger is touched on the metal layer, the capacitance of the contact changes, so that the frequency of the oscillator connected to it changes, and the position of the touch can be determined by measuring the frequency change. Since the capacitance varies with temperature, humidity, or grounding conditions, its stability is poor, and drift tends to occur. This kind of touch screen is suitable for the debugging stage of system development.
Defects in capacitive touch screen
The transmittance and clarity of capacitive touch screens are better than those of four-wire resistive screens. Of course, they cannot be compared with surface acoustic wave screens and five-wire resistive screens. The reflective capacitive screen is serious. Moreover, the four-layer capacitive touch screen of the capacitive technology does not have uniform light transmittance for each wavelength of light and there is a problem of color distortion. Due to the reflection of light between layers, the character of the image is also blurred.
In principle, the capacitive screen uses the human body as an electrode of a capacitor element. When a capacitor is coupled between the conductor and the interlayer ITO working surface, a sufficient amount of capacitance is coupled. The current flowing away is sufficient to cause the capacitive screen to malfunction. .
Although the capacitance value is inversely proportional to the distance between the electrodes, it is proportional to the relative area and is also related to the insulation factor of the medium. Therefore, when a large area of the palm power supply ic or a hand-held conductor is brought close to a capacitive screen instead of a touch, it can cause a malfunction of the capacitive screen. In wet weather, this situation is particularly serious, holding the display and palm close to the display. Within 7 cm of rectifier transformer or within 15 cm of the body close to the display can cause the capacitive screen to malfunction. Another disadvantage of the capacitive screen is that it does not respond when it is touched with a gloved hand or with a hand-held object that is not conductive, because of the addition of more insulating mesons.
