1 The basic principle of the touch screen
The working part of a typical touch screen generally consists of three parts, as shown in Figure 1:
Two transparent resistive conductor layers, an isolation layer between the two conductors, and an electrode. The resistive conductor layer is made of a resistive material such as indium tin oxide (ITO) coated on the substrate, the upper substrate is made of plastic, and the lower layer is made of glass. The barrier layer is a viscous insulating liquid material such as a mylar film. The electrode is made of a material with excellent electrical conductivity (such as silver powder ink), and its electrical conductivity is about 1000 times that of ITO.
When the touch screen is working, the upper and lower conductor layers are equivalent to the resistor network, as shown in Figure 2
When a layer of electrodes is applied with a voltage, a voltage gradient is formed across the network. If there is an external force that causes the upper and lower layers to contact at a certain point, the voltage at the contact point can be measured at another layer where the electrode is not applied with voltage, thereby knowing the coordinates at the contact point. For example, when a voltage is applied to the top electrode (X+, X-), a voltage gradient is formed on the top conductor layer. When an external force is applied to make the upper and lower layers contact at a certain point, the voltage at the contact point can be measured at the bottom layer. Then, based on the distance relationship between the voltage and the electrode (X+), the X coordinate of the place is known. Then, the voltage is switched to the bottom electrode (Y+, Y-), and the voltage at the contact point is measured at the top layer to know the Y coordinate.