Images in science fiction films often break through the limitations of reality. For example, in the movie minorityreport, Tom Cruise uses a multi touch screen to browse information. Capacitive sensing technology has changed the way we interact with devices. We no longer use simple buttons or switches. We can touch, slide or zoom the data itself on the touch screen to interact with it. The seemingly distant interface in science fiction movies is no longer illusory. In fact, they already exist and are designed for a variety of applications, including cars.

Multi touch sensing is an extension of capacitive sensing, which makes touch technology more intuitive, can detect multiple fingers at the same time and recognize gestures. This paper will introduce the basic principle of capacitive induction and the improvement of capacitive induction technology in automobile application. After introducing the structure and internal operation of multi touch screen / trackpad, the changes brought by multi touch sensing to human machine interface (HMI) will be discussed.

The core of multi touch system is capacitive sensing composed of a pair of adjacent electrodes. When a conductor such as a finger approaches these electrodes, the capacitance between the two electrodes will increase, which can be detected by the microcontroller. In addition, capacitive sensing can also be used for proximity sensing, which does not need to be touched by the sensor and the user’s body. This can be achieved by improving the sensitivity of the sensor.

Application analysis of capacitive induction multi touch in automotive electronics

Capacitive sensing is increasingly used to replace mechanical buttons and knobs. In automotive systems, touch buttons and sliding bars can be used for on-board entertainment, on-off trunk, heating, ventilation & air conditioning control (HVAC), and passive keyless entry sensor (PKE). The number of mechanical parts and grooves (requiring more complex molds, easy access to dust, etc.) is reduced, which improves reliability and reduces system cost.

The touch screen enables the user to directly “touch” the application function of the device, thus reducing the dependence on external buttons. Similarly, on the trackpad, users can also use instinctive actions to interact with the system, such as touch, tap, zoom and drag. There are three main forms of touch screen: single touch, multi touch gesture recognition and multi touch position recognition.

The single touch touch screen is mainly a resistive touch screen, which locates the screen and buttons in the same area. The limitation of resistive single touch screen is that it can only detect one finger on the screen at a time, the gesture recognition ability is limited, the sensor is easy to wear and the performance is poor. These limitations have brought the development of projection capacitor technology, and the multi touch gesture touch screen is based on this principle. The multi touch gesture touch screen does not rely on pressure to detect user interaction. They can also support simultaneous multi touch gesture recognition and tracking to facilitate machine screen and web browsing.

Application analysis of capacitive induction multi touch in automotive electronics

Multi point contact recognition position refers to that the touch sensing surface (trackpad / touch screen) can recognize two or more points on the contact surface at the same time. The user has ten fingers on both hands, and the number will increase when there are multiple passengers on the vehicle. Music browsing, map manipulation, electronic control of the body, such as seat position, are all examples of automotive applications. These are good applications of touch screen.

The trackpad on the car is convenient for the driver to operate systems, such as navigation and audio subsystems, without reaching to the central console. The trackpad can recognize characters without the need for alphanumeric keys. The touch screen is covered with glass and plastic. Below it are two layers of transparent conductors, such as indium tin oxide (ITO), which are separated by insulating materials (see Figure 4). The system of ITO layer forms a capacitance grid. The transparency of the ITO layer is very high, which helps to make the touch screen brighter and easier to read. Since no pressure is required to detect touch, the screen is more durable.

In the track board, there is a similar capacitive sensor structure, but the system has an opaque protective layer, and the simple copper layer is the sensor. Scanning the touch screen sensor can detect any change in sensor capacitance, so as to detect finger touch. Analyzing these data can recognize gestures, finger range and finger motion direction. The system can also drive output devices such as LEDs or control motors.

Capacitive touch screens and track versions that support ten fingers are increasingly used in cars and are used as integrated interfaces by a variety of car systems. The multi touch recognition position sensing system also allows multiple users in the vehicle to access the touch screen at the same time. In addition, automotive network protocols such as can / Lin can integrate distributed electromechanical systems into the central console. This enables the man-machine interface designer to coordinate the operation of various subsystems on the console and create the man-machine interface with a unified style of user interface, which increases flexibility. At the same time, developers can have more design space in appearance and feeling.

Multi touch recognition position sensing can create an intuitive and beautiful display interface, which is more competitive. With the increase of size and processing power, touch screen and trackpad are more and more popular, and they eventually become the choice of automobile interface.


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