Capacitive touch screen technology works by using the human body's current sensing. 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. Four electrodes, the inner layer of ITO is a shielding layer to ensure a good working environment. When a finger touches the metal layer, a coupling capacitance is formed between the user and the touch screen surface due to the electric field of the human body. For high-frequency current, the capacitance is a direct conductor, so the finger draws a small current from the contact point. This current flows out from the electrodes on the four corners of the touch screen respectively, 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 the four currents. .

Principle overview

To realize multi-touch on capacitive screen, it depends on adding electrodes of mutual capacitance. Simply put, it is to divide the screen into blocks and set up a set of mutual capacitance modules in each area to work independently, so the capacitive screen can work independently. The touch situation of each area is detected, and after processing, multi-touch is simply realized. 

The working principle of capacitive touch screen

Capacitive technology touch panel CTP (Capacity Touch Panel) is to use the human body's current induction to work. The capacitive screen is a four-layer composite glass screen. The inner surface of the glass screen and the interlayer are each coated with a layer of ITO (nano-indium tin metal oxide). The outermost layer is a silica glass protective layer with a thickness of only 0.0015mm, and the interlayer ITO coating As a working surface, four electrodes are drawn from the four corners, and the inner layer of ITO is the screen layer to ensure the working environment. 

When the user touches the capacitive screen, due to the electric field of the human body, a coupling capacitor is formed between the user's finger and the work surface. Because the work surface is connected to a high-frequency signal, the finger absorbs a small current, which flows from the four corners of the screen respectively. In theory, the current flowing through the four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position through precise calculation of the ratio of the four currents. It can reach 99% accuracy and has a response speed of less than 3ms.