LCD touch screen

LCD touch screen

In fact, the realization principle of the touch screen is roughly the same, and the transparent touch panel is added to the ordinary LCD screen. The types of resistive and capacitive types that we are talking about are divided according to their working principles. At present, the classification of touch screens mainly includes four types: resistive, capacitive, infrared, and surface acoustic wave. In real life, the resistive touch screen is the one we touch most. It has been widely used in mobile phones and portable digital products.

Working principle of resistive touch screen

The resistive touch screen is mainly controlled by pressure sensing. Its composition is a display screen and a resistive thin film screen that fits closely with the display screen. This resistive film screen is usually divided into two layers. One layer is a base layer made of glass or plexiglass, and its surface is coated with a transparent conductive layer; the base layer is pressed with a hardened and scratch-resistant plastic layer that we usually contact directly. There is also a conductive layer inside the plastic layer, and the two conductive layers are separated. When we touch the screen with a finger or other object, the two conductive layers come into contact, and the resistance changes. The controller judges the coordinates of the contact point and performs corresponding operations based on the specific change in resistance.

 Working principle of capacitive touch screen

Unlike resistive touch screens, capacitive touch screens use the current induction of the human body to work. The sensing screen of the capacitive touch screen is a four-layer composite glass screen. The inner surface and interlayer of the glass screen are each coated with a conductive layer, and the outermost layer is a thin layer of silica glass protective layer. When we touch the sensor screen with a finger, the electric field of the human body makes the finger and the surface of the touch screen form a coupling capacitor. For high-frequency current, the capacitor is a direct conductor, so the finger draws 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 these four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position of the touch point by accurately calculating the ratio of these four currents. .

Differentiating touch screens from technical principles can be divided into five basic categories: vector pressure sensing technology touch screens, resistive technology touch screens, capacitive technology touch screens, infrared technology touch screens, surface acoustic wave technology touch screens.

Resistive touch screen. This touch screen uses pressure sensing for control. The main part of the resistive touch screen is a resistive film screen that fits well with the surface of the display. This is a multilayer composite film. It uses a glass or hard plastic plate as the base layer and is coated with a layer of transparent oxide metal (transparent conductive Resistance) conductive layer, covered with a layer of hardened outer surface, smooth and scratch-resistant plastic layer, and 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 for insulation. When a finger touches the screen, the two conductive layers are in contact at the touch point, the resistance changes, signals are generated in the X and Y directions, and then sent to the touch screen controller. The controller detects this contact and calculates the position of (X, Y), and then operates according to the way of simulating a mouse. This is the most basic principle of resistive technology touch screens. The key to resistive touch screens lies in material technology. Commonly used transparent conductive coating materials include: ITO, indium oxide, weak conductors and nickel-gold coatings.

The capacitive touch screen works by using the current induction of the human body. The capacitive touch screen is a four-layer composite glass screen. The inner surface and the interlayer of the glass screen are each coated with a layer of ITO. The outermost layer is a thin layer of silica glass protective layer. The interlayer ITO coating is used as the working surface on the four corners. Lead out four electrodes, the inner ITO is a shielding layer to ensure a good working environment. When a finger touches the metal layer, due to the electric field of the human body, a coupling capacitor is formed between the user and the surface of the touch screen. For high-frequency current, the capacitor is a direct conductor, so the finger draws 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 these four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position of the touch point by accurately calculating the ratio of these four currents. .