04-12-2012, 11:40 AM
DESCRIPTIVE REPORT ON TOUCHSCREENS
DESCRIPTIVE REPORT.docx (Size: 32.92 KB / Downloads: 24)
Two types of touchscreens are: (a)Resistive Touchscreens. (b)Capacitive Touchscreens.
RESISTIVE TOUCHSCREENS:
A resistive touchscreen panel comprises several layers, the most important of which are two thin, transparent electrically-resistive layers separated by a thin space.
These layers face each other, with a thin gap between .The top screen (the screen that is touched) has a coating on the underside surface of the screen.
Just beneath it is a similar resistive layer on top of its substrate. One layer has conductive connections along its sides, the other along top and bottom.
A voltage is passed through one layer, and sensed at the other. When an object, such as a fingertip or stylus tip, presses down on the outer surface, the two layers touch to become connected at that point: The panel then behaves as a pair of voltage dividers, one axis at a time. By rapidly switching between each layer, the position of a pressure on the screen can be read.
Resistive touch screens consist of a glass or acrylic panel that is coated with electrically conductive and resistive layers made with indium tin oxide (ITO) .The thin layers are separated by invisible spacers.
CAPACITIVE TOUSHCSREENS:
A capacitive touchscreen panel consists of an insulator such as glass,coated with a transparent conductor such as indium tin oxide (ITO). As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance.
Different technologies may be used to determine the location of the touch. The location is then sent to the controller for processing.
Advantage:
The largest capacitive display manufacturers continue to develop thinner and more accurate touchscreens, with LCD touchscreens for mobile devices now being produced with 'in-cell' technology that eliminates a layer, by building the capacitors inside the LCD itself. This type of touchscreen reduces the visible distance (within millimetres) between the user's finger and what the user is touching on the screen, creating a more direct contact with the content displayed and enabling taps and gestures to be even more responsive.
Disadvantage:
Unlike a resistive touchscreen, one cannot use a capacitive touchscreen through most types of electrically insulating material, such as gloves; one requires a special capacitive stylus, or a special-application glove with an embroidered patch of conductive thread passing through it and contacting the user's fingertip. This disadvantage especially affects usability in consumer electronics, such as touch tablet PCs and capacitive smartphones in cold weather. In response, there are gloves on the market with one or more fingertips that include conductive material, thus overcoming this limitation.
Working:
A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel. As it has no moving parts, it is moderately durable but has limited resolution, is prone to false signals from parasitic capacitive coupling and needs calibration during manufacture.