Comparison of working principle between surface and projection capacitance touch
Date:2019-07-31
Touch technology is divided into resistance touch and capacitance touch. Resistance is divided into four wire resistance touch screen and five wire resistance touch screen. Capacitance touch screen is divided into surface capacitance touch screen and projection capacitance touch screen. Is there any difference in the working principle between capacitance touch screen and projection capacitance touch screen
Working principle of surface capacitance screen
The surface capacitance touch screen, that is, because the sensor is in contact with a person to produce a capacitance value, it does not have a capacitance value itself, so it is unable to judge the z-axis information. The finger must touch it to judge the segment coordinates.
The surface of the capacitive screen is coated with transparent conductive layer ITO. The voltage is connected to the four corners, and the charge is distributed on the screen surface to form a uniform electric field. When touching the screen by hand, the human body acts as one pole of the coupling capacitor, and the current gathers from the four corners of the screen to form the other pole of the coupling capacitor. The controller calculates the relative distance from the electricity to the touch position to obtain the coordinate value of the touch. The surface capacitive touch screen can only be touched directly with fingers, while the projected capacitive touch screen can touch through tempered glass!
Working principle of projection capacitive screen
The part of projection capacitance is scanning and positioning. But his sensing principle has to be divided into self capacitance and mutual capacitance. The self capacitance is ITO pattern of X and Y electrodes. There is a parasitic capacitance in the self capacitance, which forms multiple induction unit capacitors in a uniform plane. When the finger contacts, the capacitance change of each induction unit is detected to obtain coordinates. The mutual capacitance is to detect the change of coupling capacitance at the intersection of X and y, Therefore, both of them have the capacitance of multiple sensing units, but they are located by the capacitance change caused by the finger, so they can also distinguish the distance between the finger and the panel, that is, to provide z-axis information. When the finger is only close to the surface of the screen and does not touch, the original capacitance on the X and Y axes can be changed, so it is called projection, even if the user is wearing gloves, Or a 5mm thick glass is pasted on the outside of the sensor.
Projection capacitive screen is a screen using projection capacitive touch technology. The touch screen panel can detect the change of position capacitance when the finger touches it, so as to calculate where the finger is and carry out multi-point touch operation. The common applications of projection capacitive screen in daily life are mobile phone, MP4, digital camera, etc.
