Working principle of touch screen

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 objects, 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 changes in resistance. The principle is the resistance divider voltage in the X direction and the Y direction. Clicking on different points produces different voltages, and then judging the touch point.

Principle of resistive Touch screen

Touch Screens have been widely used in real life, such as automatic deposit/withdrawal machines in banks. There are many types of touch screens, such as ultrasonic touch screens, infrared touch screens, capacitive touch screens, resistive touch screens, etc. Resistive touch screens are electrically low due to their low cost. It can be directly connected to the user's system and used in a large amount. There are several types of resistive touch screens, such as "four-wire", "five-wire" and "eight-wire". The more wires, the higher the accuracy and the less temperature drift, but The basic operation is the same.It is essentially an electronic voltage divider, which converts the physical position of the touch point (X, Y) in the rectangular area into a voltage representing the x coordinate and the y coordinate.

Working principle of Capacitive Touch Screen

Different from 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, the outermost layer It is a thin protective layer of silica glass. 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. .