Introduction to touch screen

Introduction to touch screen

The touch screen is also called a touch panel. It is an input device that converts the touch position into coordinate data. According to the detection principle of the touch screen, it is mainly divided into a resistive touch screen and a capacitive touch screen. Relatively speaking, the resistive screen is cheap to make and can adapt to harsher environments, but it only supports single-point touch (only one touch position on the panel can be detected at a time), and a certain amount of pressure is required when touching, which may cause the surface after a long time of use. Wear and tear affects the life; the capacitive screen has the characteristics of supporting multi-touch and high detection accuracy. The capacitive screen detects the touch action through the capacitive effect generated by the conductive object, and can only sense the touch of the conductive object, the humidity is high or the screen surface Water droplets will affect the detection effect of the capacitive screen.

Resistive touch screen detection principle

The resistive touch screen structure is mainly composed of a hard coating on the surface, two ITO layers, spacers and a glass bottom layer. These structural layers are transparent. The entire touch screen is covered on the LCD panel, and the LCD panel can be seen through the touch screen. The surface coating plays a protective role, and the glass bottom layer plays a bearing role. The two ITO layers are the key structure of the touch screen. They are conductive layers coated with indium tin metal oxide. Space points are used between the two ITO layers to separate the two layers. When the surface of the touch screen is pressed, the surface bends so that the upper layer of ITO is in contact with the lower layer of ITO, and the circuit is connected at the contact. The two ends of the two ITO coatings lead to four electrodes, X-, X+, Y-, and Y+. This is the most common four-wire structure of resistive screens. Through these electrodes, the external circuit can apply uniform strength to the two coatings. Electric field or detection voltage. When the touch screen is pressed, the two ITO layers are in contact with each other, dividing the ITO layer into two resistors from the contact, and since the ITO layer is evenly conductive, the size of the two resistors is proportional to the distance between the contact and the two electrodes Using this feature, the coordinates can be detected through the following process, which is the origin of the name of the resistive touch screen.

Capacitive touch screen detection principle

The X-axis electrode and the Y-axis electrode form a capacitor at the intersection, that is, these two groups of electrodes form the two poles of the capacitor. This structure covers the entire capacitive screen, and each capacitive unit has its specific physical location in the touch screen, namely the capacitance The position is its XY coordinate on the touch screen. When detecting the touch coordinates, the first X-axis electrode sends out an excitation signal, and all the Y-axis electrodes receive signals at the same time. By detecting the charging time, the mutual capacitance of each Y-axis and the first X-axis can be detected. , Each X axis sends out excitation signals in turn, repeating the above steps, you can get all the capacitances of the two-dimensional plane of the entire touch screen. When the finger approaches, it will cause the local capacitance to change. According to the obtained two-dimensional data table of the capacitance change of the touch screen, the coordinates of each touch point can be known. Therefore, the capacitive touch screen supports multi-touch.