Touch-Screen Technologies with Customers and Electronic Devices Interaction

Introduction

Touch screens are favored in recent years since the appearance of the multimedia device such as iPhone, it became quite popular with a series of innovations. It is a trend that touch screens will be gradually replaces the keyboard and mouse in the future, thus the customers and the devices are become more and more close than ever before. The touch screen technology has many types including resistive technology and capacitive technology.

Resistive style

The resistive technology has been in common use for many years for its not expensive price. They are affordable to manufacture and easy to interface.

In resistive-technology sensing, people use a transparent and conductive coating to connect electrodes to two opposite sides of a glass plate. When a voltage is added to the electrodes, the plate acts like a potentiometer. Once a similar, second plate is arranged closely to the first plate with electrodes offset by 90°, and with the coatings facing each other, a 4-wire touch screen is achieved. If the top plate with transparent plastic is deflected by a finger or pen so that the plates touch at the contact point, the x- and y-position of the pressure mark can be determined by comparing the voltages.

Any pen or finger can operate the resistive touch screens because it is pressure sensitive. And it even can be operated with the customer wearing a glove. They have a high electromagnetic interference (EMI) tolerance. However, it is not available to have multi-touch systems.

Capacitive styles

Capacitive technology is gaining in popularity. It must be operated with the following condition: transparent conductor paths made of indium tin oxide (ITO) are applied to a transparent carrier plate mounted behind a glass plate. Touching the glass plate with a finger affects the electrical capacitor field and enables the contact to be detected and measured. There are two fundamentally different approaches used to implement a projected capacitive design. That is the self-capacitance and mutual capacitance.

Self-capacitance

With this design, a clearly defined charge is added to a conductor path. An approaching finger conducts part of the charge to ground. The touch controller will analyze the changing voltage at the conductor path. The ITO conductor paths are arranged in X and Y directions in a diamond pattern (Figure 1).

Figure 1: Functionality and design of a self-capacitance touch screen.

Mutual capacitance

With the mutual; capacitance technology, the coupling capacity of two-crossing conductor paths will be changed by an activating finger. The controller monitors each line one by one and analyzes the voltage curves at the columns (Figure 1). This technology is capable of multitouch; several finger contacts can be detected simultaneously.

Figure 2 Functionality of a mutual-capacitance touch screen.