For operational convenience, people use a touch screen instead of a mouse or keyboard. When working, we must first touch the touch screen installed on the front of the monitor with a finger or other object, and then the system locates the selection information input according to the icon or menu position touched by the finger. The touch screen consists of a touch detection component and a touch screen controller; the touch detection component is installed in front of the display screen to detect the touch position of the user and accepts the evacuation of the touch screen controller; and the touch screen controller mainly receives the touch from the touch point detection device. The information is converted into contact coordinates and sent to the CPU. It can also receive commands from the CPU and execute them. This is the basic working principle of Advantech touch screen, Advantech touch screen repair work must understand this principle.
According to the working principle of the touch screen and the medium for transmitting information, we divide the touch screen into four types: resistive, capacitive, infrared, and surface acoustic wave. Each type of touch screen has its own advantages and disadvantages. The various types of touch screens described above are briefly described below:
Resistive touch screens use pressure sensing for control. The main part of the resistive touch screen is a resistive film screen that is very compatible with the display surface. This is a multi-layer composite film with a layer of glass or a hard plastic plate as the base layer, and the surface is coated with a transparent oxide metal (transparent conductive Resistive) conductive layer, covered with a layer of outer surface hardened, smooth rub-resistant plastic layer, its inner surface is also coated with a layer of coating, there are many small (less than 1/1000 inch) transparent between them The isolation point separates the two conductive layers. When the finger touches the screen, the two conductive layers have contact at the touch point, the resistance changes, signals are generated in both the X and Y directions, and are sent to the touch screen controller. The controller detects this contact and calculates the position of (X,Y) and then operates according to the simulated mouse mode. Advantech touchscreen maintenance engineers tell you that this is the most basic principle of resistive touchscreens.
Capacitive touch screens use the body’s current sensing to operate. The capacitive touch screen is a four-layer composite glass screen. The inner surface of the glass screen and the interlayer are respectively coated with ITO, and the outermost layer is a thin layer of alumina glass protective layer. The interlayer ITO coating is used as the working surface, on the four corners. Four electrodes are drawn and the inner ITO is a shield to ensure a good working environment. When the finger touches the metal layer, the user and the touch screen surface are formed with a coupling capacitance due to the body electric field. For the high-frequency current, the capacitance is a direct conductor, and then the finger sucks a small current from the contact point. This current flows 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 calculates the position of the touch point by accurately calculating these four current ratios. . Advantech touch screen maintenance engineers tell you that this is the most basic principle of capacitive touch screen, maintenance work can start from this aspect.
Infrared touch screens use a dense infrared matrix in the X and Y directions to detect and locate the user’s touch. The infrared touch screen has a circuit board frame mounted on the front of the display. The circuit board arranges the infrared transmitting tube and the infrared receiving tube on the four sides of the screen, one by one corresponding to form an infrared matrix that intersects horizontally and vertically. When the user touches the screen, the finger will block two infrared rays passing through the position, and thus the position of the touch point on the screen can be determined. Any touch object can change the infrared on the touch point to achieve touch screen operation. Advantech touch screen maintenance engineers tell you that this is the basic principle of infrared touch screen.
The working principle of the surface acoustic wave touch screen: Take the X-axis transmit transducer in the lower right corner as an example: The transmit transducer converts the electrical signal sent from the controller through the touch screen cable into acoustic energy and transmits it to the left surface, and then from below the glass plate. A set of precise reflection fringes reflect the sound wave energy into an upward uniform surface transmission. The energy of the sound wave passes through the surface of the screen body, and then the reflection fringes on the upper side gather to the right line to transmit to the X-axis receiving transducer. The device converts the returned surface acoustic wave energy into an electrical signal. After the transmitting transducer emits a narrow pulse, the energy of the acoustic wave reaches the receiving transducer through different channels, takes the earliest arrival on the far right, goes to the leftmost, arrives late, and early arriving and late arriving these acoustic energy are stacked into one. With a wider waveform signal, it is not difficult to see that the received signal is a collection of all the energy of the acoustic waves that have been regressed in the X-axis direction along different paths. The distance traveled on the Y-axis is the same, but on the X-axis, the farthest ratio The most recent walked twice the X-axis maximum distance. Therefore, the time axis of this waveform signal reflects the position of each original waveform before superposition, that is, the X-axis coordinate. Transmitting Signals and Receiving Signal Waveforms When there is no touch, the waveform of the received signal is exactly the same as the reference waveform. When a finger or other object capable of absorbing or blocking acoustic energy touches the screen, the energy of the acoustic wave traveling upward along the X-axis through the finger portion is partially absorbed, and the waveform has an attenuation gap in response to the received waveform, that is, at a certain moment in time. Corresponding to the signal received by the finger, the received waveform is attenuated by a gap. The position of the notch is calculated by touching the coordinates. The controller analyzes the attenuation of the received signal and determines the X coordinate from the position of the notch. After the same process on the Y axis, the Y coordinate of the touch point is determined. In addition to the X and Y coordinates that can be responded to by a general touch screen, the surface acoustic wave touch screen also responds to the Z-axis coordinate of the third axis, that is, it can sense the magnitude of the user’s touch pressure. The principle is calculated from the attenuation of the received signal attenuation. Once the three axes have been determined, the controller passes them to the host.