The general key switch uses two metal contacts to contact under the action of external force to make electrical conduction, and an electrical circuit is formed to realize the transmission of current. This type of switch key is characterized by simple structure and low price, so it is It is widely used in electrical equipment. But because this type of key switch has mechanical contacts, after a long time, there will be oxidation, poor contact, and the service life is very limited.
For this reason, some electrical equipment also use metal induction buttons, but such buttons still have exposed metal parts and still require direct contact with the human body, which still cannot completely rule out safety hazards and application limitations.
Capacitive touch-sensitive buttons are a new type of button that has been rapidly developed in recent years. It can penetrate several millimeters of insulating materials. It can detect the mobile charge induced by the human body and judge the action of the human finger to identify the "on" and "Off", realizes the button function, completely solves the problems of oxidation and poor contact of ordinary mechanical contact buttons, and greatly improves the service life. At the same time, the button panel can be a flat surface with no gaps, which is easy to clean or even wash. Kitchen appliances (such as induction cookers, microwave ovens) are very suitable for use.
Here we introduce the interface application of TCH683 capacitive touch sensor button chip and single-chip microcomputer. At present, there are many chips with the same function on the market, such as MT8810, etc. The circuit block diagram is as follows:
As can be seen from the above figure, there are almost no external components on the periphery of the touch chip, only a resonant capacitor is needed. The button IC output is connected to the microcontroller through 4 buses. The TCH683 output is the BCD code, which is easy to communicate with the MCU. Bus interface connection, the working voltage range of TCH683 is 2.2-5.5V, the response speed is about 0.2s, and the maximum time limit of the button is about 15s. At the same time, the chip has certain EMC (electromagnetic compatibility) characteristics, and there is no problem in meeting general electrical requirements .
The following picture shows the appearance of a control motherboard PCB designed and produced by our company using capacitive touch sensing buttons.
We use a coil spring style for the metal sensing part of the button, which is fixed on the panel and close to the button panel.The button value can be obtained by just getting your finger around the button, and the single-chip microcomputer can distinguish the button state to realize the control function.
Due to such a sensing structure, some design inconveniences will also occur. In occasions where the panel does not have much space constraints.
The following figure shows the appearance of the component surface of the key board.