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Touch LCD screen technology and classification

Views: 201     Author: Reshine Display     Publish Time: 2023-08-24      Origin: Site

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Touch LCD screen technology and classification

Touch technology is now widely used in smartphones, tablet computers, and other consumer electronics. Reshine Display explains the technology and classification of touch LCD screens in this article.


Technology for Touch Panels

Touch LCD technology is a new type of human-computer interaction input method that is more intuitive than traditional keyboard and mouse input methods. Touch LCD screens with recognition software can also accept handwriting input.


LCD touch principle

LCD resistive touch technology The use of a resistive screen is the use of a touch LCD screen surface with pressure changes, resulting in screen bump deformation caused by resistance changes to achieve precise positioning of touch LCD technology.


Resistive screen performance has the following characteristics:

① They are completely isolated from the outside world of the working environment, and not afraid of dust, water vapor, and oil.

② can use any object to touch, and can be used to write and draw, which is their greater advantage.

③ The precision of the resistive touch screen only depends on the precision of A/D conversion. So all can easily reach 4096*4096- According to different realization principles, resistive touch LCD screen is divided into two categories: four-wire and five-wire. Surface Acoustic Wave (SAW) type SAW touch LCD is coated by a glass that has transmitting and receiving piezoelectric sensors for the X and Y axes. The controller sends an electrical signal to the transmitting sensor and converts the signal into ultrasonic waves within the surface of the glass. Through an array of reflectors, these waves cover the entire touch LCD screen. The opposite reflector collects and controls these waves to the receiving sensor, which converts them into electrical signals. This process is repeated for each axis. The user absorbs a portion of the propagating waves when he touches them. The received signals corresponding to the X and Y coordinates are compared with the stored digital distribution map to recognize the changes and calculate the coordinates.


The touch LCD is attached to the surface of the monitor and is used in conjunction with the display. Analog electrical signals are generated by touching and converted to digital signals to be calculated by a microprocessor to obtain the coordinates of the touch point, thus obtaining the operator's intent and executing it. Touch LCD screens according to their technical principles can be divided into five categories: vector pressure sensing, resistive, capacitive, infrared, and surface acoustic wave type, of which resistive touch LCD screens in practical applications are used more. Resistive touch LCD screen consists of four layers of transparent thin composition, the bottom is glass or plexiglass composed of grass-roots level, the top is a layer of the outer surface after hardening treatment so that the smooth and scratch-resistant plastic layer, attached to the upper and lower layers of the inner surface of the two layers of the conductive layer of the metal (OTI, Indium Oxide), the two layers of the insulation by the tiny transparent isolation point. When the finger touches the screen, the two conductive layers are in contact at the touch point.


The two metallic conductive layers of the touchscreen are used to measure coordinates in the X- and Y-axis directions, respectively. The conductive layer for X-coordinate measurement leads from the left and right ends to two electrodes, noted as X+ and X-. For Y coordinate measurement of the conductive layer from the upper and lower ends of the two electrodes, noted as Y + and Y -. This is the lead composition of a four-wire resistive touch LCD. When a voltage is applied to a pair of electrodes, a uniform and continuous voltage distribution is formed on that conductive layer. If the X direction of the electrode pair applies a determined voltage, while the Y direction electrode pair does not add voltage, in the X parallel voltage field, the voltage value at the contact can be reflected in the Y + (or Y-) electrode, by measuring the Y + electrode to ground voltage size, you can know the X coordinate value of the contact. Similarly, when the Y electrode pairs of voltage, and X electrode pairs of voltage are not added, by measuring the voltage of the X + electrode, you can know the Y coordinate of the contact.


The five-wire touch LCD is different from the four-wire type. The main difference is that the five-wire touch screen will be one of the four ends of the conductive layer are led out as four electrodes, the other conductive layer is only as a measurement of the conductor output X and Y direction of the voltage, the measurement should be alternately in the X and Y up to the voltage applied.


Classification of touch LCD screen technology

According to the screen surface positioning principle is different, can be divided into acoustic pulse recognition (APR) technology, surface acoustic wave (SAW) technology capacitive touch LCD technology and resistive touch LCD technology infrared/optical technology two categories.


Acoustic Pulse Recognition (APR) technology

Acoustic Pulse Recognition (APR) technology APR consists of a glass display coating or other hard substrate with four piezoelectric sensors mounted on the back. The sensors are mounted on two diagonal corners of the visible area and are connected to the control card via a bent cable. When a user touches the LCD screen, a collision or friction occurs between the finger or stylus and the glass drag, and sound waves are generated. The wave radiation leaves the point of contact and travels to the sensor, generating electrical signals in proportion to the sound waves. These signals are amplified in the control card and then converted into a digital data stream. The data is compared to a pre-stored list of sounds to determine the location of the touch liquid crystal.APR is designed to eliminate environmental influences and external sounds that do not match the stored sound list.


Surface Acoustic Wave (SAW) Technology

SAW (Surface Acoustic Wave) technology The X and Y axes of SAW touch LCDs are made of glass coated with a transmitting and receiving piezoelectric sensor. The controller sends an electrical signal to the transmitting sensor, which converts it into ultrasonic waves on the glass's surface. These waves cover the entire touchscreen with an array of reflectors. The opposite reflector collects and controls these waves, which are then converted into electrical signals by the receiving sensor. This procedure is carried out for each axis. When the user touches the waves, he absorbs a portion of them. To recognize changes and calculate coordinates, the received signals corresponding to the X and Y coordinates are compared with a stored digital distribution map.

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