LCD Touch screen For iPhone 7

                                                         The structure and working principle of capacitive touch screen

The structure of the capacitive touch screen is mainly to coat a transparent film body layer on the glass screen, and then add a protective glass outside the conductor layer. The double glass design can completely protect the conductor layer and the sensor.

The capacitive touch screen is plated with long and narrow electrodes on the four sides of the touch screen, forming a low-voltage AC electric field in the conductor. When touching the screen, due to the electric field of the human body, a coupling capacitance will be formed between the finger and the conductor layer, and the current from the electrodes on the four sides will flow to the contacts, and the current strength is proportional to the distance from the finger to the electrode. The controller behind the touch screen is then It will calculate the proportion and strength of the current, and accurately calculate the position of the touch point. The double glass of the capacitive touch screen can not only protect the conductors and sensors, but also effectively prevent external environmental factors from affecting the touch screen. Even if the screen is stained with dirt, dust or oil stains, the capacitive touch screen can still accurately calculate the touch position.

Since the capacitance varies with the contact area and the dielectric of the medium, its stability is poor, and drift phenomenon often occurs. This kind of touch screen is suitable for the debugging stage of system development.

Capacitive touch screen principle

It 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 coated with a layer of ITO, and 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 ITO is the 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 capacitance is formed between the user and the surface of the touch screen. For high-frequency currents, the capacitance is a direct conductor, so the finger absorbs 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 through accurate calculation of the four current ratios. .