Resistive touch screens have a flexible top layer and a rigid bottom layer separated by insulating dots, with the inside surface of each layer coated with a transparent conductive coating. Voltage applied to the layers produces a gradient across each layer. Pressing the flexible top sheet creates electrical contact between the resistive layers, essentially closing a switch in the circuit.
Touch measurement in 4 Wire resistive touch screen is a 2-step process. The distance along the x-axis at the point of touch is measured by creating a horizontal voltage gradient on the top sheet, with the bottom acting as the return layer. Then a vertical voltage gradient is created on the bottom layer, to measure the y-axis.
The technology and electronics are simple, making 4-wire the cheapest touch screen technology. Any damage to either layer causes the touch screen to stop functioning. This lack of durability means that 4-wire resistive technology may not be ideal for applications like public access kiosks, or on displays larger than 12”.
In this technology, the main electronics are on the glass bottom layer. A uniform voltage is applied to the top layer. A touch causes an electrical contact between the top and bottom layers. Depending on the location of contact, the voltages at the 4 corners of the glass are different.
The 5-wire resistive touch screen is typically more expensive than the 4-wire technology. But the electronics make it possible to use 5-wire for applications up to 22”. In addition, the voltage measurements take place on the rear panel only, making the touch panel system more reliable and less susceptible to damage.
The capacitive touch screen measures the amount of capacitance in each of the touch screen electrodes. By sensing when the capacitance increases, the touch screen can tell when your finger is touching, and through measuring which electrodes have the most capacitance, the touch screen can locate to an accuracy of better than 1/1000th of an inch.
For digital matrix touch screens, the conductive material is patterned into rows and columns in the form of a grid. Each etched layer has a voltage connection. When the layers are pressed together, current will flow through the corresponding row and column where the touch occurs to calculate the position of the touch. The resolution, which is dependent on the number of rows and columns, is far lower than the analog touch screen versions. But the controller electronics are far simpler.