LCD Touch screen For iPhone X12 ProMax

                                                                 How Smartphone Touchscreens Work

We use electronic devices with touch screens every day, such as mobile phones and tablets. Do you know how the touch screen works? How does it know where our fingers are? Why can the mobile phone be used with a film on it, but cannot be used normally with gloves on? At present, most of the touch screens used on the market are capacitive touch screens. To understand how it works, let's first explain what a capacitor is.

In 1745, Mason Brock, a professor at Leiden University in the Netherlands, invented the Leiden bottle to store electric charges. The basic principle of the Leiden bottle is: charge is introduced into the bottle through a conductive metal rod and metal chain, and the inside and outside of the bottle are respectively pasted with metal foil. In this way, the charge is stored in the bottle. We now know that when a positive charge is introduced onto the foil in the bottle, an equal amount of negative charge will be attracted to the outside foil if the outside foil of the bottle is grounded. The positive and negative charges attract each other, but since the glass bottle is an insulator, preventing their neutralization, the charge is stored.

In fact, to store charge, you don't necessarily need a bottle. As long as two conductors that are insulated from each other and close together can play the same role, we call it a capacitor. The simplest capacitor is a parallel plate capacitor. Put two metal plates close to each other, one plate is positively charged and the other negatively charged, due to the attraction between the charges, as long as the two electrodes are not connected through an external circuit, the charge will not run away.

The center of the capacitor is insulated. In theory, current cannot pass through the capacitor. However, in the process of charging and discharging the capacitor, the amount of charge on the plate of the capacitor will change, which can be regarded as the current passing through the capacitor.

When the capacitor is fully charged, even if we disconnect the power supply, the charge on the capacitor will not disappear. However, if we directly connect the two plates of the capacitor with wires, the positive and negative charges will find a path that can be neutralized, so the positive and negative charges will be neutralized through this path, and a counterclockwise current will appear in the circuit , this current is called the discharge current. The discharge current is also instantaneous. After the charge is neutralized, the discharge current disappears.

If the capacitor is charged and discharged repeatedly, the charging current and discharging current will appear repeatedly in the circuit, and the direction of the charging current and the discharging current are opposite. This current is the alternating current we talked about earlier. Now we know that AC can pass through a capacitor.

We know that a test pen can measure whether a wire is charged. Have you ever thought that if you stand on a chair and touch the live wire with the test lead, will the test lead light up? Since people and the earth are conductors, chairs are insulators, and household electricity is alternating current, it can pass through capacitors. Even if you stand on a chair and touch the live wire with a test pencil, the test pencil will still measure, indicating that there is still current passing through the test pencil. and the human body. It's just that the current is relatively small, and the human body doesn't feel anything.

A simple capacitive screen is a four-layer composite glass panel with a layer of ITO material in it. ITO is an indium tin oxide material that is transparent and conductive, making it suitable for making touch screens. When a finger touches a certain part of the screen, it will form a coupling capacitance with the ITO material, changing the capacitance at the contact point. There are wires at the four corners of the screen. Since the alternating current can pass through the capacitor, the current of the four wires will rush to the contacts, and the magnitude of the current is related to the distance to the contacts. The chip inside the mobile phone can analyze the current at the four corners, and the position of the contact can be obtained through calculation.

A more elaborate capacitive screen is a projected capacitive screen. It uses an array of etched ITO layers that are corroded to form multiple horizontal and vertical electrodes. The ITO components of each part also have sensing functions. When a finger touches a certain part, it couples with the array capacitance and changes the electric field on the screen. By analyzing the current change of the electric field through the sensor and the chip, the position of the touch point can be sensed. Compared with the previous four-corner current capacitive screen, this capacitive screen can realize multi-touch and is more widely used.

Human fingers are conductors, so they will affect the capacitive screen, and using an insulating material to touch the capacitive screen will not be able to operate the phone. Mobile phone film can also be used. This is because the finger and the ITO layer do not need to be in contact with each other. There is a glass insulating layer in the middle. The effect of pasting the insulating film is equivalent to a little thicker glass, and the current can still flow through the finger and the screen. The capacitor formed by the conductor. However, if the glove is too thick, the conductor in the screen is too far away from the finger when touching the touch screen, and the capacitance is too small to be sensed by the sensor, so the mobile phone cannot be operated while wearing thick gloves.

In fact, there are many capacitive sensors in life, such as automatic flushing devices and automatic hand dryers that are common in toilets, many of which use capacitive sensing. When the human body approaches or moves away, the capacitance formed by the human body and the device changes, and the sensor senses this change, and the control circuit performs a certain operation.