Functions of the Touch Keys
Touch keypad plays the role of keypad. Unlike a keypad, which functions through the on-off switch or metaldome, the touch key detects the change of capacitance and outputs the on-off signal of the switch after processing by the integrated chip of the touch key.
The principle of touch keypad
The following diagram shows the working principle of the touch key. In any two conductive objects between the existence of capacitance, capacitance of the size of the conductive nature of the medium, the size of the pole plate and the conductive nature of the pole plate around the existence of conductive substances, etc. PCB board (or FPC) between the two pieces of exposed copper area is the capacitance of the two poles of the plate, equal to a capacitor. When the human finger close to the PCB, due to the conductivity of the human body, will change the size of the capacitance. The touch key chip detects a significant increase in capacitance and outputs a switching signal.
Key Forms of Touch Keys
Touch keys can be composed of the following types of keys
Single button
Strip keys (including ring keys)
Block keypad
Dimensioning of Touch Keys
Keys can be round, rectangular, oval or any other shape. Rectangular and round are the most common applications.
Touch Key PCB and FPC
Theoretically, touch keys can work on either PCB or FPC. In fact, there are examples of multiple touch buttons on FPCs. The preferred solution is PCB, if because of structural constraints, PCB is really difficult, have no choice but to use FPC, even with FPC, and the touch key chip with the place must be flat, because the chip can not be bent and twisted. As shown in the figure below, FPC and curved surface adhesive co-ordination, the actual processing and assembly is not as reliable as PCB and flat adhesive co-ordination, which leads to a reduction in the reliability of the touch button.