Projected Capacitive Touch Technology
Leave a message
Projected Capacitive Touch (PCT) technology is a capacitive technology which allows greater accuracy and flexibility in operations, by etching the conductive layer. An XY array is formed either by etching a single layer to form 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 the pixel grids in LCD displays). Applying voltage to the array creates a grid of capacitors.
How is projected capacitive touch screen structure like?
There are various structures in projected capacitive technology. "One sheet piled-up structure" has X and Y electrodes piled on one sheet. "One sheet two-sided structure" has X and Y electrodes on its surface and backside of one sheet respectively. "Two-sheets-laminated structure" consists of two sheets facing each other with electrodes in between. So, a projected capacitive sensor has X and Y electrodes, and there are several ways to put them together.
Projection capacitance sensing technology can be divided into two types: self capacitance and mutual capacitance.
Self capacitance is also called absolute capacitance. It takes the sensed object as the other electrode of the capacitance. The object induces charge between the sensing electrode and the sensed electrode, and determines the position by detecting the change of the coupling capacitance. However, if it is a single touch, there is only one group of coordinates determined in the x-axis and Y-axis directions through capacitance change, and the combined coordinates are also unique. If there are two touch points on the touch screen and these two points are not in the same X direction or the same y direction, and there are two coordinate projections in the X and Y directions respectively, four coordinates are combined. Obviously, only two coordinates are real, and the other two are commonly known as "ghost points". Therefore, the self capacitive screen cannot realize true multi touch.
The mutual capacitance is also called cross capacitance, which is generated by the coupling of adjacent electrodes. When the sensed object approaches the electric field line from one electrode to the other, the change of the mutual capacitance will be felt. When the transverse electrodes send out excitation signals in turn, all the longitudinal electrodes receive signals at the same time. In this way, the capacitance of the intersection of all the transverse and longitudinal electrodes can be obtained, that is, the capacitance of the two-dimensional plane of the entire touch screen. When human fingers approach, local capacitance will be reduced. According to the two-dimensional capacitance change data of the touch screen, the coordinates of each touch point can be calculated. Therefore, even if there are multiple touch points on the screen, the real coordinates of each touch point can be calculated.
Bringing a finger or conductive stylus close to the sensor’s surface changes the local electrostatic field. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location.
The use of a grid permits a higher resolution vis-a-vis resistive technology, and also allows multi-touch operations. Thus, the PCT’s greater resolution allows operations even without direct contact, such that the conducting layers can be coated with further protective insulating layers, also operating even under screen protectors, or behind weather and vandal-proof glass.
Advantages:
• Touch function operates through customer-installed materials, including vandal-resistant glass up to 18 mm thick.
• Works outdoors - in rain, snow, ice, and dust.
• True flat front surface possible with no bezel.
• Works with fingers, gloved hands or conductive stylus.
• Works even if glass is scratched or broken.
Disadvantages:
• Electronics and sensor construction is more complex, compared to other technologies
• Does not have full stylus independence support
Resistive Technology : Analog 4-wire Resistive, Analog 5-Wire Resistive, Analog 7-wire Resistive, Analog 8-wire Resistive, Features of resistive technology
Capacitive Technology: Surface Capacitive touch technology, Projected Capacitive touch technology
