Projected capacitive TP is recently used in mobile phones and other products and has attracted much attention. This method also proposes a variety of good solutions from the structure or working method of the panel. Generally, it can be divided into a wire sensor method suitable for large panels and an ITO Grid method suitable for small panels.
The "metal sensor" method is to detect the vertical (U) and horizontal (F) signals through complex conductive metal wiring with a diameter of about 10 pm between glass and glass or between film and film. Since detection is possible on a 20mm thick glass substrate, it can also be used in outdoor (explosion-proof) environments. It can also be operated on a display installed in a shop window^ In Japan, it is generally used for real estate advertising and used as a set with a projector.
Another method of projected capacitive is the ITO grid method. The technology itself is relatively old. This technology has been developed since more than 20 years ago. Therefore, the related patents have been invalidated. However, due to the low price of the very small sensor 1C chip used for electrostatic touch control recently, the so-called Scanning and multi-touch gestures are loved by consumers.
From the principle point of view, it is the same as the capacitive touchpad of a notebook computer. What makes such a touch panel transparent is the ITO grid projected capacitive touch screen. The X-F electrode is used to detect the current change caused by the capacitance change when the mobile phone is in contact, and the position of the finger is calculated.
More detailed content will not be repeated here, but its working principle has the following two ways.
(1) Self-capacitance detection method
•Using a sensor to detect the increase in capacitance when the finger touches.
•Crosstalk occurs during multi-touch, so it is difficult to display the absolute position.
(2) Mutual capacitance detection method
•Using the two sensors that send and receive signals to detect the reduction of the capacitance on the receiving signal side when the finger touches, this method is more suitable for multi-touch, but there are not too many 1C chips that match.
②iPhone’s touch screen
The iPhone touch screen is also a projected capacitive type, but it has a completely different structure from the above. Figure 2-25 shows the unit structure and coating structure.
The launch of the iPhone, which can achieve multi-touch and support gesture actions, is very impactful, and the high-level sense of the system and the aesthetics of the design are also very good. In order to make it easy to view without degrading the image quality of the display, a lot of efforts have been made to improve the transmittance. Optical connection is also one of them. It has become very common on mobile phones recently, that is, using optical adhesives to fully bond the cover glass on the surface to the touch screen to prevent internal reflections as much as possible.
