Design of automobile center console panel based on capacitive sensing technology

This article introduces the development process of using Cypress's PSoC (Programmable System on Chip) CY8C 21534 series chips in the automotive center console panel. The working principle of the panel and its innovative appearance design are introduced, focusing on the principle of capacitive sensing technology and its advantages in panel control. In addition, the market prospects and commercial value of this center console panel are analyzed.

Background

With the development of automotive electronic technology, there are more and more electronic devices in the car today, and it has become necessary to control and coordinate these electronic devices through the on-board computer. However, the higher the grade of the vehicle, the more electronic devices it will have, and the more complicated the operating system of the on-board computer will be. If each function corresponds to a button, you can imagine how dazzling the car center console will be. In this case, how to make the operation interface simple and practical has become an issue that must be considered. With reference to the operation interface of iPod, we have developed a car center console panel based on capacitive sensing technology, which greatly reduces the number of buttons, has a simple and beautiful appearance, and is interesting to operate.

This car center console panel has the following functions:

1. Record driving data: The driving data on the home page includes driving time, mileage, fuel usage, average fuel usage, and average speed. These data are recorded once for each driving, and users can also review previous records.

2. Display of time and date: This function is integrated on the right side of the screen and is displayed in any interface.

3. Temperature display: Display indoor and outdoor temperatures simultaneously.

4. Multimedia player: This system interface supports MP3 playback, CD playback and radio mode. This part of the function makes extensive use of Cypress capacitive sensing technology to make entertainment more interesting.

5. Air conditioning control: This part includes general control functions, such as temperature control, wind speed control, etc.

Overall system design

System structure and interface design

This system uses the 21534 series chip provided by Cypress, which features an integrated capacitive sensing module CSR, which can be directly configured during use, providing great convenience for designs related to capacitive sensing. This chip has four digital module positions and four analog module positions. Although limited, the main design purpose of this chip is for capacitive sensing control, so it is just right to configure a capacitive sensing module (occupying three digital module positions and one analog module position) and a counter module (occupying one digital module position) required for certain controls on this chip. (If necessary, other modules can also be added using dynamic reallocation technology).

The system block diagram is shown in Figure 1.

Figure 1 System Block Diagram

The display device uses a four-grayscale black and white LCD screen with a resolution of 240×128 pixels. It can be divided into four layers at most without setting a character layer. In this design, two layers of display are used, of which the first layer is the character layer, which can display the 176 letters, numbers, symbols, etc. in the ROM, and the second layer is the picture layer, which can control any point on the display screen to display the desired graphics. The second layer is set to a non-AND relationship with the first layer to achieve the effect of reverse color display when selecting a menu, which is also the method currently widely used in the menu selection of LCD screens such as computers and mobile phones. The backlight of the screen adopts a timed control method, that is, the backlight will turn on 15 seconds after each key is pressed, and the information will still be displayed after 15 seconds, but the backlight will turn off, which can not affect the use and have low power consumption.

The displayed information includes basic information and functional information, which are located in two parts of the screen divided by vertical lines. Basic information includes time, date, indoor and outdoor temperature, etc., which need to be displayed at all times but do not need to be frequently changed and do not require buttons to control. They occupy a fixed position on the right side of the screen and have a certain visual stability. Functional information includes the information display interface of FM, CD, air conditioning, etc. when the equipment is working, which is located on the left side of the screen.

Due to the limitation of the appearance design, the number of buttons is very limited, so the same button must be configured with different control functions in different interfaces to effectively control the system. In the program, each key press will assign a value to the button variable, and how the display is displayed depends not only on the variable button, but also on the current display interface to achieve the correct operation after pressing the button. In addition, the central button has added a long-press function, that is, pressing the central button for more than 1 second will achieve a function different from a single press, so as to expand the function of the button, which is equivalent to increasing the number of buttons.

Capacitive Sensing Principles and Applications

The capacitive sensor module CSR (Capacitive Sensor Relaxation Oscillator) consists of a capacitive sensor array, an analog multiplexer, a capacitive sensor relaxation oscillator and a counter. The schematic diagram of the structure is shown in Figure 2.

Figure 2 Schematic diagram of capacitive sensing module

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Capacitive sensors are usually composed of a capacitor between a copper sheet covering a PCB and the ground. The copper sheet is covered with an insulating material. When a conductor is close to the capacitor, as shown in Figure 3, the capacitance between the copper sheet and the ground will change accordingly. The capacitive sensing relaxation oscillator generates square waves of different frequencies for different capacitors. The pulse width modulation module and the counter calculate the frequency of the output. By detecting the counter value and comparing it with the set threshold, the capacitive sensing switch can be opened and closed intermittently.

The software part integrates algorithms to compensate for environmental changes and differences in the physical characteristics of the sensor. It can also identify the identity of buttons, the position of sliders and the position of the two-dimensional touch pad, making the capacitive sensing switch stable.

Figure 3 Capacitive sensing principle

Capacitive sensing is made into a slider in this design. Sliding a finger on it can change a specific amount in a specific interface, such as the volume in multimedia, the air volume in the air conditioning interface, etc. Compared with traditional mechanical switch knobs, the application of capacitive sensing sliders has the advantages of durability, beauty, and easy operation. The driver does not need to accurately aim at the button to adjust, but can make vague adjustments by roughly aiming at the position of the slider.

According to the capacitive sensing principle, the design of the PCB slider is shown in Figure 4.

Figure 4 Capacitive sensing PCB design

Design

Compared with the various center console panels on the market, the design of this center console has a strong visual impact. The gray-white display and control parts are embedded in the black imaginary body, and the black buttons are embedded in the white operation interface, which is in sharp contrast and full of fashion. There are no messy buttons on the entire operation interface. The round touch screen and the surrounding buttons are matched, which is symmetrical and not monotonous. As shown in Figure 5.

Figure 5: Vehicle panel design

Software Design

The software part of this design occupies 8K FLASH capacity. It queries the key input through a main loop and combines it with the current interface to form a task. Software flow chart:

Figure 6 Software system flow

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Advantages and innovations

Simple operation interface

Abandoning the traditional multi-button design, the operation interface consists of only five buttons and a capacitive sensing slider, which can still effectively control the multimedia system including FM radio, multi-disc CD player, DVD player, etc., as well as multiple functions such as car air conditioning, time and date display, indoor and outdoor temperature display and system settings. The five buttons can achieve different control functions under different conditions, and the use will not be affected by the reduction of buttons. Moreover, the buttons are scattered, and the correct operation can be performed as long as their orientation is roughly determined. Compared with the center console full of buttons that also achieve the above functions, the capacitive sensing center console has its incomparable advantages in appearance. The simple operation interface design not only gives people a fresh feeling visually, but also avoids the driver's misoperation caused by too many and too dense buttons, or prolongs the time to find the buttons.

Stylish appearance

Integrating the design elements of iPod into the car center console system is a combination of fashion and technology, which is also the direction that designers have always pursued. The innovative design will change the previous concept of most car center consoles that are more practical, and truly make the car center console into a work of art, giving people a unique feeling.

High integration

Only one Cypress 21534 series chip is used, and its integrated capacitive sensing module is used with the help of a few buttons to control various functions on the vehicle, replacing the traditional multi-button interface with a high degree of integration. In this design, almost all pins of the 21534 series chip are used, and the memory utilization rate is close to 100%, giving full play to the role of this chip. Due to limited conditions, all controls are simulated by liquid crystal. In actual application, pin multiplexing can be used to drive the actuator at the same time, realizing the requirement of replacing multiple chips with one chip. Even if another chip is allocated to control the LCD screen separately in actual application, this design still has a high degree of integration.

Save development time

Using the capacitive sensing module integrated in the Cypress21 series chip to develop an inductive car center console operating system has advantages in terms of time and programming compared to other single-chip microcomputers, and it also saves time and effort. In addition, the modular programming method of the PSoC system is very convenient, and the API functions that can be directly called greatly shorten the chip development time. The advantage of visually configuring the various parameters of the system, module, and pin is that you will not forget the configuration of a certain parameter, and there is no need to remember the register name and the specific meaning of each bit, which also saves time in consulting the manual.

Application of Capacitive Sensing Technology

This is the most distinctive design of this center console. Capacitive sensing control has unparalleled advantages over traditional button control. First, the shape of the slider can be determined arbitrarily, which provides the possibility for a circular sensing area and provides the premise for a beautiful appearance design. Second, the capacitive sensing part is composed of a metal diaphragm on a circuit board, covered with a wear-resistant surface cover, which will not wear out or fail due to excessive pressing times, and its reliability is much better than that of ordinary buttons. Third, the design of the slider can quickly increase or decrease when selecting menus and adjusting some analog quantities (such as volume, air conditioning temperature, wind speed, etc.), without the need to press the button repeatedly, saving operation time. Convenient and fast operation truly meets people's requirements for the control interface. Fourth, the introduction of capacitive sensing technology into the car panel not only reduces the complexity of the car panel mold opening, manufacturing, and assembly due to the reduction of buttons, but also increases the convenience and fun of use - after being tired of the widely used button interface, the slider is indeed interesting and therefore more attractive. Driving pleasure is actually not only provided by traditional car performance, but also the small center console panel can make the driving process pleasant and interesting.