Working principle of touch screen with five-wire resistance

A uniform electric field is added to the four vertices of the touch screen, such as RT, Rb, LT, and lb, so that the lower layer (indium oxide) ITO glass is filled with a uniform voltage, the upper layer is the receiving signal device. When the pen or finger presses any point on the external side, the controller detects the resistance change and then changes the coordinates at the point where the finger is pressed.
Due to stress sensing, there is no restriction on hands, pencils, and credit cards for touch media, even if you wear gloves.
Touch screen technology relies on controllers. Even some touch screens are a set of controllers. Their Respective positioning principles and controllers determine the reaction speed, reliability, stability, and life of the touch screen.
Types of touch screens
1. Infrared Touch Screen
The principle of the infrared touch screen is very simple. You only need to add a light point to the display frame without adding a coating or connecting the Controller to the screen surface. The infrared emission tube and receiving tube are arranged on the four sides of the frame, forming a red outer network on the screen surface. When you touch a certain point on the screen with your fingers, the system blocks the two infrared rays passing through the position, and the computer can instantly calculate the position of the touch point. The infrared touch screen is not subject to current, voltage and electrostatic interference and is suitable for some harsh environmental conditions. Its main advantage is its low price, easy installation, no need to card or any other controller, it can be used in various levels of computer. However, the frame is added only to the normal screen. during use, the infrared emission tubes and receiver tubes around the frame are easily damaged, and the resolution is low.
2. capacitive touch screen
The capacitive touch screen is constructed by plating a transparent thin film layer on the glass screen and adding a protective glass outside the conductor layer. The dual glass design can completely protect the conductor layer and sensor.
Capacitive touch screens are plated with narrow electrodes on the four sides of the touch screen to form a low voltage AC electric field in the conductive body. When you touch the screen, due to the human electric field, a coupling capacitor will be formed between the finger and the conductor, and the current sent from the four sides of the electrode will flow to the contact, and the current strength is proportional to the distance from the finger to the electrode, the Controller located behind the touch screen will calculate the ratio and strength of the current and accurately calculate the position of the touch point. Capacitive touch screen dual glass not only protects the conductor and sensor, but also effectively prevents external environmental factors from affecting the touch screen, even if the screen is stained with dirt, dust or oil, capacitive touch screen can still accurately calculate the touch position.
3. Resistance Technology Touch Screen
The screen part of the touch screen is a multilayer composite film that works very well with the display surface. A layer of glass or plexiglass serves as the base layer, and the surface is coated with a transparent conductive layer (OTI, indium oxide ), the top is covered with a plastic layer with an external surface hardening and smooth scratch resistance. Its internal surface is also coated with an Oti layer, and there are many small (less than 1 inch) between the two conductive layers) are separated by transparent isolation points. When the finger contacts the screen, there is a contact point in the two layers of Oti conductive layers. Because one of the conductive layers is connected to the 5 V even Voltage Field in the Y axis, the voltage of the detection layer changes from zero to non-zero, after the controller detects the connection, it performs A/D conversion and compares the obtained voltage value with the Y axis of the touch point to obtain the coordinates of the X axis, this is the basic principle of the Resistance Technology touch screen. The resistance screen is divided into four-wire, five-wire, and other multi-wire resistance touch screens based on the number of leads. The a surface of the 5-wire resistive touch screen is conductive glass instead of conductive coating layer. The process of conductive glass greatly improves the life and the light transmittance.
The Oti coating of the resistive touch screen is relatively thin and easily brittle, and the coating is too thick, it will reduce the light transmission and form the inner reflection to reduce the definition. Although Oti adds a thin plastic protective layer, but it is still easy to be damaged by sharp objects. Because it is often touched, the surface Oti may encounter small cracks or even variants after being used for a certain period of time. For example, one of the outer OTI is damaged and broken, as a conductive body, the life of the touch screen is not long. However, the resistive touch screen is not affected by dust, water and dirt.
4. Surface Acoustic Touch Screen
The Touch Screen part of the surface acoustic touch screen can be a plane, spherical or cylindrical glass panel installed in front of the screen of CRT, led, LCD or plasma display. This glass plate is just a pure reinforced glass. Unlike other touch screen technologies, there is no film or covering layer. In the upper left and lower right corner of the glass screen, the vertical and horizontal ultrasonic transmitters are fixed, and the two corresponding ultrasonic receivers are fixed in the upper right corner. The four surroundings of the glass screen are engraved with a 45 ° angle from sparse to dense interval very precise reflection stripes.
The transmitter converts the electrical signal sent by the Controller through the touch screen cable into acoustic energy to transmit to the left side surface, and then the acoustic energy is reflected into an upward uniform surface by a set of precise reflection stripes under the glass plate, the acoustic energy passes through the screen surface, and then the reflection strip on the top is aggregated to the right line and transmitted to the receiving transducer of the x-axis. The receiving transducer changes the returned surface acoustic energy to an electrical signal. When the waveform of the transmitting and receiving signals is not touched, the waveform of the received signal is exactly the same as that of the reference waveform. When the finger or other objects that can absorb or block acoustic energy touch the screen, the sonic energy that flows up through the finger on the X axis is partially absorbed, there is a attenuation gap in the waveform at a certain point in the receiving waveform. The signal of the receiving waveform corresponding to the finger blocks a gap, and the touch coordinate of the GAP location is calculated. The controller analyzes the attenuation of the received signal and determines the X coordinate by the gap position. Then, the Y coordinate of the touch point is determined by the same process on the Y axis. In addition to the X and Y coordinates that can be responded to by the touch screen, the surface acoustic touch screen also responds to the coordinate of the third axis Z axis, that is, the user's touch pressure value. Once the three axes are determined, the controller sends them to the host.
The surface acoustic touch screen is not affected by environmental factors such as temperature and humidity. It has a high resolution, excellent scratch resistance, and long life (50 million failures). The light transmittance is high (92% ), it can maintain a clear and translucent image quality, without drifting, and is most suitable for use in public places. However, after a long period of operation, the induction converter of the surface sensing system will be damaged due to the pressure produced by the sound energy. Generally, wool or leather gloves receive partial acoustic waves, which affects the accuracy of sensing. If the screen surface or fingers that touch the screen are stained with water, oil, dirt or dust, it may also affect its performance, or even stop the system.
Detection and positioning
The touch screen is composed of multiple layers of composite films. The transparency directly affects the visual effect of the touch screen. To measure the transparency of a touch screen, we should not only measure its visual effect, but also include four features: transparency, color distortion, light rejection, and clarity.
Absolute coordinate system. Our traditional mouse is a relative positioning system, which is only related to the coordinates of the previous mouse. The touch screen is an absolute coordinate system, which is essentially different from the relative positioning system. The absolute coordinate system is characterized by the fact that each positioning coordinate has no relationship with the last positioning coordinate, and the data of each touch is converted to the coordinates on the screen by calibration, No matter under what circumstances, the output data of the touch screen coordinates at the same point is stable. However, due to technical principles, the absolute coordinate positioning and inaccurate positioning cannot be ensured for each touch with the same point, which is the biggest concern of the touch screen: drift. For touch screens with good performance, the drift is not very serious.
Transparent performance:
The a surface of the magic touch 5-wire resistive touch screen is conductive glass instead of conductive coating. The process of conductive glass greatly improves its life and improves the light transmittance.
Various touch screen technologies rely on sensors, and even some touch screens are a set of sensors. Their respective positioning principles and their sensors determine the reaction speed, reliability, stability and life of the touch screen.