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projected capacitive touch (multi touch) (PCT)

For touchscreens and multi-touchscreens, there are various methods with which the touch of the screen surface is detected. In the case of capacitive methods, the screen is divided into a capacitive matrix, which is formed from conductive horizontal and vertical stripes.

The conductive strips of a capacitive matrix, these are the driving lines and sense lines, are made of indium tin oxide and are applied to two non-reflective glass panes that are insulated from each other. This matrix responds to touch. As soon as the screen surface is touched, the capacitance between the two conductive strips changes, which has an effect on the signal magnitude. The current flow from the corners of the touch screen to the touch point is proportional to the XY coordinates. The changes in the capacitance values are detected by a controller and converted into the XY coordinates.

Projected Capacitive Touch (PCAP or PCT) gets its name from the fact that the conductive strips are located on the back of the front screen and the touch is projected through the front screen as an electromagnetic field from the outside. The finger or the conductive stylus used for the touch only touches the exterior of the front screen, which is sufficiently protected against wear by appropriate materials.

Principle of PCT touchscreens with drive and sense lines

Principle of PCT touchscreens with drive and sense lines

The conductive matrix strips are made of indium tin oxide( ITO), an inorganic, transparent semiconductor. They are bonded to the back of the front screen and register every touch that causes a capacitive change. The capacitive changes are extremely small and can be a few femto-farads (`10^-15`). In addition, PCT touchscreens are extremely sensitive to electromagnetic interference( EMI), which has a negative effect on larger touchscreens.

PCT technology is extremely robust, it is durable, reliable and requires little maintenance. It is a multi-touch technology that recognizes any number of touch points. PCT touchscreens are used in smartphones, tablets, multimedia players and mobile game consoles. In addition, the technology can be used in a wide variety of environmental conditions in industrial environments, the chemical industry and the food industry. PCT touchscreens are also suitable for kiosk systems and for ATMs.

Englisch: projected capacitive touch (multi touch) - PCT
Updated at: 21.01.2022
#Words: 358
Links: indium (In), matrix, indium (In), arsenic (As), signal
Translations: DE

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