Projected And Surface Capacitive Touch Technology

Views: 217     Author: Reshine Display     Publish Time: 2024-02-21      Origin: Site

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Projected And Surface Capacitive Touch Technology

1. Projected Capacitive Touch Technology

Projected Capacitive Touch (PCT) technology is a capacitive technology that etches the conductive layer to improve operational accuracy and flexibility. An XY array is created by either etching a single layer to make a grid pattern of electrodes or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form the grid (similar to pixel grids in LCD screens). The voltage applied to the array generates a grid of capacitors.


1.1 What does the projected capacitive touchscreen structure look like?

There are several structures in projected capacitive technology. The "one sheet piled-up structure" consists of X and Y electrodes placed on one sheet."One sheet two-sided structure" has X and Y electrodes on the front and back of one sheet, respectively. The "two-sheets-laminated structure" is made up of two sheets that face each other and are separated by electrodes. A projected capacitive sensor consists of X and Y electrodes, which can be connected in a variety of ways.


Projection capacitance sensing technology is classified into two types: self-capacitance and mutual capacitance.


Self-capacitance is also known as absolute capacitance. It uses the sensed item as the other electrode in the capacitance. The item produces charge between the sensing electrode and the sensed electrode and determines position by measuring the change in coupling capacitance. However, if it is a single touch, capacitance change determines only one group of coordinates in the x and y axes, and the combined coordinates are also unique. If two touch points on the touch screen are not in the same X or Y direction, and there are two coordinate projections in those directions, four coordinates are merged. Only two coordinates are actual, and the other two are referred to as "ghost points". As a result, the self-capacitive screen is unable to support genuine multi-touch.


Mutual capacitance, also known as cross capacitance, is formed by the connection of adjacent electrodes. When the sensed item approaches the electric field line that connects one electrode to the other, the mutual capacitance changes. When the transverse electrodes put out excitation signals sequentially, all of the longitudinal electrodes get signals at the same time. This method yields the capacitance of the intersection of all transverse and longitudinal electrodes, or the capacitance of the full touch screen's two-dimensional plane. When human fingers approach, local capacitance decreases. The two-dimensional capacitance change data of the touch screen can be used to compute the coordinates of each touch point. As a result, even if there are several touchpoints on the screen, the actual coordinates of each touchpoint may be computed.


Bringing a finger or conductive stylus near the sensor's surface alters the nearby electrostatic field. The capacitance shift at each place on the grid can be used to precisely pinpoint the touch location.


In comparison to resistive technology, the use of a grid enables better resolution and multi-touch actions. Thus, the PCT's higher resolution enables activities without direct contact, allowing the conducting layers to be coated with additional protective insulating layers while also operating under screen protectors or behind weather and vandal-proof glass. Click here for 7 Inch Projected Capacitive Touch Screen.


1.2 Advantages:

• Touch function works with customer-installed materials, including vandal-resistant glass up to 18 mm thick.


• Operates outside in rain, snow, ice, and dust.


• A truly flat front surface is feasible without a bezel.


• Operates using fingers, gloved hands, or a conductive stylus.


• Works even when the glass is cracked or shattered.


1.3 Disadvantages:

• Electronics and sensor construction are more difficult than other technologies.


It Does not offer full stylus independence support.


2. Surface-Capacitive Touchscreen Technology

The surface capacitive touch screen detects touch activity on the screen surface using electric field induction. Its panel is made of an evenly coated ITO sheet, with an outgoing line connecting each of its four corners to the controller. During functioning, the touch screen's surface generates a homogeneous electric field. When the grounded object makes contact with the screen surface, the electrode detects the change in charge and determines the coordinates of the touch point.


The surface capacitive touch screen has a long service life and good transmittance, but its resolution is limited and it does not enable multi-point touch. At the moment, it is primarily employed in large-scale outdoor touch panels, such as public information platforms (POI), public service platforms (POS), and other items.


The base glass sheet has a transparent conductive layer, which is then covered with a glass protective coating. Electrodes are put in four corners.


2.1 How does it detect the touch points?

When the same phase voltage is applied to the electrodes in each of the four corners, a homogeneous electric field forms over the entire panel. When a finger contacts the panel, an electrical current flows from the four corners to the finger. To detect the contacted spot, the electrical current ratio flowing from the four corners will be measured. The measured current value will be inversely proportional to the distance between the touch point and the four corners.


2.2 Advantages:

• Surface capacitive technology can detect touch on a sensor surface through glass windows.


• The surface capacitive touch screen can endure grease, dirt, water, and strong chemicals.


• Surface capacitive sensors have a life expectancy of more than 225 million mechanical touches.


• Surface capacitive technology transfers around 90% of the light from the screen.


• Life duration of more than 50 million touches in a single location.


•Surface capacitive sensors provide great resolution and response speed.


2.3 The disadvantages

• Only one contact point is resolvable.


• Only registers the touch of ungloved fingertips or a tethered stylus on a sensor's surface.


• Vulnerable to electromagnetic interference, or erroneous signals emitted by parasitic capacitive screens.


• Severe scratches can disrupt activities in the affected region.

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