Resistive touch screen

Resistive touch screen

The key to resistive touch screens lies in material technology. Commonly used transparent conductive coating materials are:

① ITO, indium oxide, weak electrical conductor, the characteristic is that when the thickness drops below 1800 angstroms (angstroms = 10-10 meters), it suddenly becomes transparent, the light transmittance is 80%, and the light transmittance decreases when it is thinner , When the thickness reaches 300 angstroms, it rises to 80%. ITO is the main material used in all resistive technology touch screens and capacitive technology touch screens. In fact, the working surface of resistive and capacitive technology touch screens is ITO coating.

② Nickel-gold coating, the outer conductive layer of the five-wire resistive touch screen uses a nickel-gold coating material with good ductility. Due to frequent touches, the purpose of using a nickel-gold material with good ductility is to extend the service life. However, the process cost is relatively high. Although the nickel-gold conductive layer has good ductility, it can only be used as a transparent conductor. It is not suitable for the working surface of the resistive touch screen because of its high conductivity and the metal is not easy to be very uniform in thickness. It is not suitable for the voltage distribution layer and can only be used as a probe. Floor.

Four-wire resistive touch screen

The touch screen is attached to the surface of the display and is used in conjunction with the display. If the coordinate position of the touch point on the screen can be measured, the toucher's intention can be obtained according to the display content or icons of the corresponding coordinate point on the display screen. Among them, resistive touch screens are used more in embedded systems. The resistive touch screen is a 4-layer transparent composite film screen. The bottom layer is a base layer made of glass or organic glass. The top layer is a plastic layer whose outer surface is hardened to make it smooth and scratch-resistant. In the middle are two metal conductive layers. On the base layer and the inner surface of the plastic layer, there are many small transparent isolation points between the two conductive layers to separate them. When a finger touches the screen, the two conductive layers touch at the touch point. The two metal conductive layers of the touch screen are the two working surfaces of the touch screen. A silver glue is coated on both ends of each working surface, which is called a pair of electrodes on the working surface. Voltage, a uniform and continuous parallel voltage distribution will be formed on the working surface. When a certain voltage is applied to the electrode pair in the X direction and no voltage is applied to the electrode pair in the Y direction, in the X parallel voltage field, the voltage value at the contact can be reflected on the Y+ (or Y-) electrode , By measuring the voltage of the Y+ electrode to the ground, the X coordinate value of the contact can be known. In the same way, when voltage is applied to the Y electrode pair and no voltage is applied to the X electrode pair, the Y coordinate of the contact can be obtained by measuring the voltage of the X+ electrode.

Five-wire resistive touch screen

The base layer of the five-wire resistive technology touch screen adds the voltage fields in both directions to the conductive working surface of the glass through the precision resistance network. We can simply understand that the voltage fields in the two directions are applied to the same working surface in a time-sharing manner. The outer nickel-gold conductive layer is only used as a pure conductor, and the position of the touch point is measured by the method of time-sharing detection of the X and Y axis voltage values of the inner ITO contact point after touch. The five-wire resistive touch screen requires four leads on the inner layer of ITO, and only one conductor on the outer layer. There are 5 lead wires for the touch screen. Another proprietary technology of the five-wire resistive touch screen is to correct the linearity problem of the inner layer of ITO through a precise resistor network: the uneven thickness of the conductive coating may cause uneven voltage distribution.