The main applications and defects of capacitive touch screen

- Nov 26, 2019-

A capacitive touch screen is a layer of transparent special metal conductive material attached to the surface of the glass. When the finger touches 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.


The capacitive screen uses the human body as an electrode of a capacitor element in principle. When a conductor close to the sandwich ITO working surface couples a sufficient amount of capacitance, the flowing current is sufficient to cause the power screen to malfunction. .


The structure of the capacitive touch screen is mainly a layer of transparent film on the resistive screen, and a protective glass is added outside the conductor layer. The double glass design can completely protect the conductor layer and the sensor.


Capacitive touch screens are coated with narrow electrodes on all sides of the touch screen to form a low-voltage AC electric field in the conductive body. When the screen is touched, due to the electric field of the human body, a coupling capacitance is formed between the finger and the conductor layer. The current from the four electrodes will flow to the contact, and the strength of the current is proportional to the distance from the finger to the electrode. Will calculate the proportion of current and strength to accurately calculate the position of the touch point. The double glass of the capacitive touch screen not only protects the conductors and sensors, but also effectively prevents external environmental factors from affecting the touch screen. Even if the screen is contaminated with dirt, dust or oil, the capacitive touch screen can still accurately calculate the touch position.


Capacitive touch screen is a layer of transparent special metal conductive material pasted on the glass surface. When a finger touches the metal layer, the capacitance of the contact changes, so that the frequency of the oscillator connected to it changes, and the touch position can be determined to obtain information by measuring the frequency change. Because the capacitance changes with temperature, humidity, or ground conditions, its stability is poor, and drift often occurs. This touch screen is suitable for the debugging phase of system development.


的 Defects of capacitive touch screen


Capacitive touch screens have better light transmittance and clarity than four-wire resistive screens, of course, they cannot be compared with surface acoustic wave screens and five-wire resistive screens. Capacitive screens have serious reflections. In addition, the four-layer composite touch screen of capacitive technology has non-uniform transmittance of light at various wavelengths, and there is a problem of color distortion. Due to the reflection of light between the layers, the image characters are blurred.


The capacitive screen uses the human body as an electrode of a capacitor element in principle. When a conductor is close to the sandwich ITO working surface and a sufficient amount of capacitance is coupled, the flowing current is sufficient to cause the capacitive screen to malfunction. .


We know that although the capacitance value is inversely proportional to the distance between the poles, it is directly proportional to the relative area, and it is also related to the dielectric coefficient of the dielectric. Therefore, when a large-area palm power supply IC or a hand-held conductor approaches the capacitive screen instead of touching it, it can cause the capacitive screen to malfunction. This situation is especially serious in humid weather. Within 7 cm of the rectifier transformer or within 15 cm of the body near the display can cause the capacitive screen to malfunction. Another disadvantage of capacitive screens is that they do not respond when touched with a gloved hand or a non-conductive object, because of the addition of a more insulating medium.