Realization of Human-Machine Interface of Car Computer System Based on Windows CE

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Realization of Human-Machine Interface of Car Computer System Based on Windows CE [Copy link]

Abstract: This paper introduces the design and implementation of the human-machine interface of the vehicle computer system based on Windows CE, focusing on the design process and implementation technology of the virtual instrument interface and hybrid power interface, and gives the implementation results of the human-machine interface of the vehicle computer system.
Keywords: Windows CE, vehicle computer human-machine interface

1 Introduction
At present, China's automobile industry is in a period of rapid development. The automobile industry has become one of the important pillar industries for the development of China's national economy. The position of automotive electronics in the automobile industry is becoming more and more important. The digitization, informatization and networking of automotive electronics are the inevitable trend of the technological development of consumer automotive electronics products in the 21st century. However, the application of vehicle-mounted computer systems in automobiles is still in the exploratory stage, lacking a more practical application model that integrates information and network technologies. Windows CE is a 32-bit embedded operating system with preemptive multitasking and powerful communication capabilities. The good graphical user interface provides basic drawing engines, window management, interface event mechanisms, etc. Embedding the Window CE operating system into the vehicle-mounted computer system makes the human-machine interface in the system simple and intuitive, and facilitates the information interaction between the driver and the car.

2 Introduction to Windows CE Operating System
Microsoft Windows CE is a multi-platform, multi-tasking, multi-threaded, scalable 32-bit embedded operating system. It has powerful communication capabilities and is a new strategic operating system product designed by Microsoft specifically for non-PC fields such as information devices, mobile applications, consumer electronics, and embedded applications. It only requires 500KB of RAM to install the entire system. The latest version of the Windows CE kernel only requires 200KB of operating space. Windows CE mainly includes modules such as kernel, persistent storage, graphics and multimedia, inter-process communication, communication services, security services, user interface services, Internet services, and localization support. Windows CE has unique advantages in scalability, portability, and real-time performance. The main features of Windows CE are:
⑴ It has a modular and scalable kernel structure.
⑵ It is suitable for small systems and provides simple, efficient, and complete control methods for low-cost systems with weak computing power.
⑶ It follows the application development specifications of the Windows platform and provides Win32 API, etc.
⑷Flexible memory access mechanism, which enables different types of applications in the system to fully use RAM, ROM and flash memory, and selectively and effectively use the virtual memory, protection and other functions provided by the processor.
⑸Efficient task management scheduling mechanism, with 256-level priority and dynamic priority preemptive scheduling functions.
⑹Support real-time applications.
⑺Provide advanced power management functions.

3 Design of the human-machine interface of the vehicle system
In the display and control of the human-machine interface of the vehicle system, we use a combination of LCD screen and touch screen. This greatly reduces the space occupied by the system in the car. The LCD screen is used to display various information in the car, menu operation, graphic display and touch screen control, providing a good human-machine interface for the vehicle system.
The human-machine interface is designed into four main interfaces: virtual instrument interface, fault diagnosis interface, hybrid interface and video display interface.
The virtual instrument interface mainly displays various signals in the car such as vehicle speed, water temperature, oil level, oil pressure, wheel speed, voltage, etc. And the mileage is calculated using the wheel speed signal for display. In this way, the driver can accurately understand the various basic information during the operation of the vehicle and can make timely judgments on various upcoming situations.
The fault diagnosis interface mainly displays the working status of various components in the car, so that the driver can promptly discover abnormal phenomena during the driving of the vehicle and eliminate various dangerous faults, which is very helpful for the driver's driving safety.
The hybrid interface mainly uses animation to display the various states of energy flow in the car at each moment, including pure battery energy state, pure fuel energy state and mixed energy state.
The video display interface is mainly used when reversing as long as it displays the images transmitted from the camera in real time.
There is a default startup interface and several related display interfaces in the interface design for dynamic display of collected data. The interface is switched by generating corresponding messages through the control button on the window; the control button can be a virtual button on the screen or a key of an actual peripheral or other device that can cause the system to generate corresponding message switching. The startup LOGO interface automatically enters one of the specific display interfaces after displaying for a period of time. The data to be displayed in the display interface is received through the serial port from the in-vehicle signal. The program reception adopts the thread mode. The receiving program works independently as a thread and generates corresponding messages after obtaining the corresponding data. Different messages trigger different areas of the human-machine interface to update the display data. Figure 1 shows the switching of the interface display after startup. Figure 1 Human-machine interface display switching In order to more vividly simulate the swing of the vehicle speed and wheel speed pointer during operation in the virtual instrument interface, we use damping to dynamically display the pointer display and appropriately process the data to be displayed, so that the pointer starts to swing quickly and then slowly reaches the end point when accelerating or decelerating. The display of data is roughly divided into two categories, acceleration and deceleration, which correspond to L1 and L2 of the curve in Figure 2 respectively. L1 is the acceleration curve, and its starting point is not necessarily at zero. During the acceleration process, its function can process the collected data so that it rises faster in the initial stage, which is reflected on the instrument as the pointer swinging faster. When it is about to reach the end of the acceleration, appropriate damping and delay coefficients are added to slow down the pointer swing and gradually stay at the end position. Similarly, when decelerating, the descent speed is slightly faster near the starting point of deceleration, and the descent speed slows down when it is close to the end, gradually tending to the terminal speed. The pointer of the virtual dial appears to drop rapidly and then slowly stabilize at the end. Figure 2 Schematic diagram of instrument damping display

4 Implementation of the Human-Machine Interface of the In-Vehicle System
The development environment of the human-machine interface of the in-vehicle computer system adopts eVC4.0 provided by Microsoft, the development system processor adopts Intel's XScale PXA255, and the SDK is customized by Platform Builder4.2. Since there is no multi-document framework in eVC, and we want to display multiple different interfaces, we use a single document to display multiple different forms to switch the forms. We create a single-document application based on CFormView, add several forms and corresponding new view classes based on CFormView, and then realize the dynamic switching of the two forms by adding control codes and menu controls in the main frame class. This method avoids the redundant toolbars, menus, text boxes and other contents on the ordinary WINDOWS window interface, and fully meets the requirements of the human-machine interface.
Figure 3 The hybrid interface adopts an animation display method. The key is to create a bitmap in memory that is the same size as the window area where the animation is displayed, first draw the bitmap with the GDI function, and then display it from the memory at the appropriate time. Because the bitmap has been drawn, unlike the usual programming, it is not displayed while drawing. Therefore, when displaying a frame of graphics, flickering is reduced, thus achieving smooth animation; and the graphics are displayed directly from the memory to the current form, so the speed is also very fast, thus achieving high-speed animation. We first create a new class CPowerBitmap, use the CreateCompatibleBitmap() function to create an area in the memory with the same size as the display interface, then draw the graphics to be displayed in this area of the memory, and finally display it on the screen through BitBlt(). Use the OnTimer() function to display the arrows at different positions at a certain time, so that the dynamic movement of the arrows is achieved. Moreover, when using the OnTimer() function to display at different positions, the original displayed graphics must be removed first, and then the graphics must be drawn at the new position.
In the virtual instrument display interface of Figure 4, the wheel speed and vehicle speed are displayed in the form of dial + pointer. The oil pressure, water temperature and mileage are displayed in the form of Edit box. The oil level and voltage are displayed with a progress bar. In order to avoid the flickering problem of the wheel speed and vehicle speed dials during display, we only refresh the vehicle speed and wheel speed pointers in real time. The method adopted is that if the data to be displayed is the same as the original data, the pointer remains unchanged. Otherwise, we first cover the original pointer with the background color, and then draw the pointer at the new position.
The display of the fault diagnosis interface is shown in Figure 5. The left side shows the general location of the fault in the car, and the right side shows the faulty component, location and fault name. This is conducive to troubleshooting and repairing the fault.

Figure 3 Hybrid interface

Figure 4 Virtual instrument interface

Figure 5 Fault diagnosis interface

4 Conclusion
As the hub of information exchange between people and cars, the human-machine interface must deliver the in-car information to the driver in a real-time, accurate and easy-to-identify manner to achieve the best cooperation between people and cars. The human-machine interface based on the Windows CE operating system can well meet the requirements of the vehicle system, and it will be more and more widely used in vehicle systems.