The Basics of Touch Control

A touch screen allows users to interact with a computer system using one or more fingers, a stylus or other objects.touch control The system recognizes the touch, interprets the command and transmits it to the host computer. In addition, a touchscreen can display information on the system and provide navigation functions.

The most important function of a touch control is its ability to identify a single or multiple touches and translate them into commands that are understood by the host computer.touch control Then, it must determine what actions should be taken based on the type of touch and its location on the screen. In some cases, a touchscreen can also display images and video.

Some touchscreens use resistive or capacitive sensors to detect the presence of a finger.touch control In other cases, a touchscreen may use infrared or ultrasonic technology to identify the position of a finger or other object.

Capacitive touch switches operate on the principle that human skin is electrically conductive. The switch circuitry monitors the surface's baseline capacitance and detects changes in that value. When a conductive object, such as a finger, comes into close proximity to the sensor, the circuitry responds by activating an output, such as a button or a light, to activate the desired function.

The sensors are normally embedded in the glass layer of a touch screen, although they can be bonded directly to the underlying surface. A variety of different materials are used to fabricate the sensing surface. A common choice is a transparent conductive film (TCF), which has the added benefit of being environmentally friendly, as it uses recyclable polyester and minute quantities of copper wire for the sensing layers.

Touch controllers that use a capacitance-change detection system typically have a large number of sensing electrodes arranged in a matrix-like pattern. These electrodes are driven by drive (Tx) and scanned by receiving (Rx) transistors. A single sensor has many possible detection positions, and the system can scan each of these positions by stepping the Tx electrodes and scanning the Rx ones. To avoid ambiguity, the circuitry may apply noise filtering, long-term drift compensation, hysteresis or auto-calibration to ensure that only valid input signals are detected.

A disadvantage of this system is that it cannot detect a motionless finger after the initial touch, and resting objects such as a hand or arm do not interfere with the recognition process. For this reason, some systems are designed to use a "lift-off" strategy, which disables the sensor when a finger leaves the screen.

Infrared-based touch control has been developed to overcome some of the shortcomings of the capacitive-change method, particularly with regard to multi-touch capability. In one approach, an array of sensors detects a finger touching or almost touching the screen and interrupts infrared beams projected over the display. In another, bottom-mounted infrared cameras record the heat of a finger on the touch screen and transfer this information to the host computer. However, these types of touchscreens are expensive and do not give the same feel as a physical button.