Touch screen type

1. Capacitive touch screen

The structure of the capacitive touch screen is mainly to plate a transparent film body layer on the glass screen, and then add a protective glass outside the conductor layer. The double glass design can completely protect the conductor layer and the sensor. The capacitive touch screen is plated with long and narrow electrodes on all four sides of the touch screen to form a low-voltage AC electric field in the conductive body. When the user touches the screen, due to the electric field of the human body, a coupling capacitor is formed between the finger and the conductor layer. The current from the four-side electrode will flow to the contact. The current strength is proportional to the distance between the finger and the electrode. The controller located after touching the screen Will calculate the ratio 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 conductors and sensors, but also prevents external environmental factors from affecting the touch screen. Even if the screen is dirty, dust or oil stains, the capacitive touch screen can still accurately calculate the touch position.

2. Resistive technology touch screen

The screen body of the touch screen is a multi-layer composite film that fits well with the surface of the display. A layer of glass or organic glass is used as the base layer, and the surface is coated with a transparent conductive layer (OTI, indium oxide), and an outer surface is covered on it. A hardened, smooth and scratch-resistant plastic layer. Its inner surface is also coated with a layer of OTI. There are many small (less than one thousandth of an inch) transparent isolation points between the two conductive layers to isolate them. When a finger touches the screen, a contact point appears on the two OTI conductive layers. Because one conductive layer is connected to a 5V uniform voltage field in the Y-axis direction, the voltage of the detection layer changes from zero to non-zero. The controller detects this After switching on, perform A/D conversion and compare the voltage value obtained with 5V to obtain the Y-axis coordinate of the touch point, and the X-axis coordinate can be obtained in the same way. This is the most basic principle common to resistive technology touch screens. . Resistive screens are divided into four-wire, five-wire and other multi-wire resistive touch screens according to the number of lead wires. The A-side of the five-wire resistive touch screen is made of conductive glass instead of a conductive coating. The process of conductive glass greatly improves its life and can increase light transmittance. The OTI coating of the resistive touch screen is relatively thin and easy to be brittle. If it is too thick, it will reduce the light transmission and form internal reflection to reduce the clarity. Although a thin plastic protective layer is added outside the OTI, it is still easy to be affected by sharp objects. Damage; and because of being frequently touched, the surface layer OTI will appear small cracks and even deform after a certain period of time. If one of the outer OTI layers is damaged and broken, it will lose its role as a conductor, and the life of the touch screen will not be long. But the resistive touch screen is not affected by dust, water, and dirt.

3. Surface acoustic wave touch screen

The touch screen part of the surface acoustic wave touch screen can be a flat, spherical or cylindrical glass plate, which is installed in front of the CRT, LED, LCD or plasma display screen. This glass plate is just a piece of pure strengthened glass, which is different from other touch screen technologies in that it does not have any film or overlay. The upper left corner and the lower right corner of the glass screen are respectively fixed with vertical and horizontal ultrasonic transmitting transducers, and the upper right corner is fixed with two corresponding ultrasonic receiving transducers. The four peripheries of the glass screen are engraved with very precise reflection stripes with 45° angles ranging from sparse to dense. The transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into sound wave energy and transmits it to the left surface, and then a set of precise reflection stripes under the glass plate reflects the sound wave energy into an upward uniform surface for transmission, and the sound wave energy passes through On the surface of the screen, the reflection fringe on the upper side gathers into a rightward line and propagates to the X-axis receiving transducer. The receiving transducer converts the returned surface acoustic wave energy into electrical signals. The waveform of the transmitted signal and the received signal is exactly the same as the reference waveform when there is no touch. When a finger or other object that can absorb or block sound wave energy touches the screen, the sound wave energy going up on the X axis through the finger part is partially absorbed, reflecting that there is an attenuation gap in the received waveform, that is, the waveform at a certain moment. The received waveform attenuates a notch corresponding to the signal at the part blocked by the finger. The touch coordinate is obtained by calculating the position of the notch. The controller analyzes the attenuation of the received signal and determines the X coordinate from the position of the notch. After that, the same process on the Y axis determines the Y coordinate of the touch point. In addition to the X and Y coordinates that a general touch screen can respond to, the surface acoustic wave touch screen also responds to the third axis Z coordinate, that is, it can sense the magnitude of the user's touch pressure. Once the three axes are determined, the controller transmits them to the host.