Resistive touch screens are controlled using pressure sensing. The main part is a resistive film screen that is very compatible with the surface of the display. It is a multi-layer composite film with a glass or hard plastic plate as the base layer coated with a transparent metal oxide (ITO). The layer is covered with a layer of externally hardened, smooth and scratch-resistant plastic layer (the inner surface of which is also coated with an ITO coating) with a number of small (approximately 1/1000 inch) transparent spacers between them. The two layers of ITO conductive layer are separated from each other. When the finger touches the screen, the two conductive layers that are normally insulated from each other have a contact at the touch point position, because one conductive layer turns on the 5V uniform voltage field in the Y-axis direction, so that the voltage of the detection layer changes from zero to zero. Non-zero, after the controller detects this turn-on, A/D conversion is performed, and the obtained voltage value is compared with 5V to obtain the Y-axis coordinate of the touch point. Similarly, the coordinates of the X-axis are obtained, which is The most basic principle common to all resistive technology touch screens.
The key to resistive touch screens is material technology. Commonly used transparent conductive coating materials are:
1 ITO, indium oxide, weak conductor, the characteristic is that when the thickness drops below 1800 angstroms (A = 10-10 meters), it will suddenly become transparent, the light transmittance is 80%, and then the light transmittance will decrease. It rises to 80% at a thickness of 300 angstroms. ITO is the main material used in all resistance technology touch screens and capacitive technology touch screens. In fact, the working surface of the resistive and capacitive technology touch screen 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. The outer conductive layer is frequently touched, and the nickel-gold material with good ductility is used for the purpose of prolonging 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 as a working surface of a resistive touch screen because it has high conductivity and the metal is not easy to be very uniform in thickness, and it is not suitable as a voltage distribution layer. Floor.
five-wire resistance touch screen:
The base layer of the five-wire resistive touch screen puts the voltage fields in both directions on the conductive working surface of the glass through the precision resistor network. We can simply understand that the voltage field time-sharing in both directions is added to the same working surface. The outer layer of nickel-gold conductive layer is only used as a pure conductor, and the position of the touch point is measured by a method of detecting the X and Y-axis voltage values of the inner ITO contact point after touch. The inner layer ITO of the five-wire resistive touch screen requires four leads, the outer layer is only used as one conductor, and the touch screen has five lead wires.
Another proprietary technique for a five-wire resistive touch screen is to correct the linearity of the inner ITO through a precision resistor network: the conductive coating may have uneven thickness and uneven voltage distribution.
Resistance screen performance characteristics:
1 They are a working environment completely isolated from the outside world, not afraid of dust, water vapor and oil
2 can be touched with any object, can be used to write and draw, which is their big advantage
3 The accuracy of the resistive touch screen depends only on the accuracy of the A/D conversion, so it can easily reach 4096*4096. In comparison, the five-wire resistance is superior to the four-wire resistance in ensuring the resolution accuracy, but the cost is high. Therefore the price is very high.
Improvements to the five-wire resistive touch screen:
First, the A side of the five-wire resistive touch screen is a conductive glass instead of a conductive coating layer. The process of the conductive glass greatly improves the life of the A surface and can improve the light transmittance.
Secondly, the five-wire resistive touch screen gives the task of the working surface to the long-life A-side, while the B-side is only used as a conductor, and a nickel-gold transparent conductive layer with good ductility and low resistivity is used. Therefore, the B-side Life expectancy is also greatly improved.
Another proprietary technology for five-wire resistive touch screens is to correct the linearity of the A-plane through a precision resistor network: the precision resistor network flows during operation due to the inevitable uneven thickness of the voltage field due to process engineering. Most of the current is passed, so it is possible to compensate for possible linear distortion of the working surface.
The five-wire resistive touch screen is currently the best resistive technology touch screen, and is most suitable for military, medical, and industrial control applications.
four-wire resistance touch screen
The touch screen is attached to the surface of the display and used in conjunction with the display. If the coordinate position of the touch point on the screen can be measured, the intention of the touch person can be known according to the display content or icon 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, as shown in Figure 2. The bottom layer is the base layer made of glass or plexiglass. The top layer is a layer of plastic that is hardened to make it smooth and scratch-resistant. Two layers of metal conductive layers, one above the base layer and the inner surface of the plastic layer, are separated by a plurality of fine transparent isolation points between the two conductive layers. When the finger touches the screen, the two conductive layers are in contact at the touch point. The two metal conductive layers of the touch screen are two working faces of the touch screen, and each end of each working surface is coated with a silver glue, which is called a pair of electrodes of the working surface, if applied on the electrode pairs of one working surface The voltage will form a uniform continuous parallel voltage distribution on the working surface. As shown in FIG. 1, when a certain voltage is applied to the pair of electrodes in the X direction, and no voltage is applied to the pair of electrodes in the Y direction, in the X parallel voltage field, the voltage at the contact can be at Y+ (or Y). -) Reflected on the electrode, the X coordinate value of the contact can be known by measuring the voltage of the Y+ electrode to ground. Similarly, when a 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 known by measuring the voltage of the X+ electrode.