The in-vehicle multimedia navigation system is a multimedia system and a navigation system that are embedded and installed in an automobile environment. Compared to handheld personal navigation products (PNDs), in-vehicle multimedia navigation products need to cope with more stringent environmental and performance requirements. First of all, it is more than the working environment temperature requirements of industrial products. Secondly, it is the interference of strong electromagnetic interference such as ignition system and power generation system to the navigation system receiving the weak GPS signal. In addition, the vibration requirements for the product are also a problem. Other environmental factors such as salt spray, humidity, oil pollution, etc., put forward higher requirements for vehicle products.
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Even in harsh environments, the reliability requirements of automotive products need to remain at a fairly high level. Therefore, when designing the system, we need to spend many times more energy and time in terms of reliability, usability, etc. than other household products and general industrial products. An in-vehicle product, after being designed, must be installed in a car, subject to a very lengthy and complicated testing process, especially the long road test, the actual technical and engineering needs, resulting in the chance of new technology and new devices entering the car. Greatly reduced, the speed is much slower than consumption and other areas.
Car audio products, from radios and tape drives to CD players, have undergone decades of gradual improvement and upgrading. When car CDs are just beginning to become popular, in-vehicle products are already facing the pressure and practical need to quickly integrate navigation, Internet, and even mobile computing functions, solid storage and digital compression music, digital sound broadcasting, and digital TV broadcasting. Constantly enter the on-board system.
With the maturity of LCD applications, car audio and video products have entered the era of flat panel display. From the upgrading of the dashboard to the improvement of the content display mode and grades, the demand for display-centric automotive products has been placed in front of us. Among them, navigation products have become the standard components of automobiles, and have become a reality in high-end cars; and the realization in ordinary cars is just around the corner.
Evolution of structural design of car audio products
For a long time, car audio products have been developed on a simple logic control structure. At first, the system mainly supports the radio function. Later, with the tape playback device, such systems do not require load control, and simple logic control can meet the needs. When the CD enters the automotive field, the car audio enters the 4-bit MCU era, the tuning control of the AM/FM radio, the buttons, the display, and the processing of the CD. A 4-bit MCU is sufficient, and this situation lasts for more than ten years. Until today, 4-bit microcontrollers are still the mainstream products on the market.
It is said that the car audio products should also go through the development process of 4, 8 and 16 and then to 32. Just like the development of the technology, the current 8-bit MCU has indeed entered the car audio, but the 8-bit MCU has not yet become The mainstream market in the automotive sector has not yet gained a large share. Under the action of Moore's Law, the acceleration phenomenon of semiconductors and the harsh requirements of reliability and certification of automotive products make 8-bit MCUs still not popular, 16-bit is still rarely used, and our structural design has stepped into 32. An era.
Design Requirements for Vehicle Multimedia Navigation System Based on 32-Bit System
In today's in-vehicle products, we use 32-bit CPU design and face several tricky special requirements:
Low standby power requirements
When the in-vehicle device is in standby, the industry standard has a very low requirement for its actual current consumption.
Fast response problem based on embedded operating system
In the car navigation system using 32-bit CPU, we all need an operating system (OS) to support the work, but any current operating system is a huge thing for the car products, its internal complexity and lengthy The processing process leads to a large gap between the response time of the system and the requirements of the application environment. Solving the problem of rapid response of such embedded systems is a difficult problem and a basic requirement for a vehicle project.
Different format display and touch panel
The LCD display has two different modes, analog and digital, depending on how it is driven. Our system is designed to support two different drive modes. At present, the main application in the car is 6.2, 6.5 or 7 inch LCD screen, most of the resolution is 480 × 234, and a few resolution is 640 × 480.
Ergonomic overall interface design
1) Buttons, remote control and shuttle
The button is always the necessary input device for electronic products. In the design with touch screen, we only keep some basic buttons, such as switch machine, disc, or some buttons for direct switching function. Others should be reflected on the touch screen as much as possible. Flexible display of prompts to achieve.
Although the car environment is small, it is also necessary to have a remote control function for the convenience of the rear passengers. From tuning and volume adjustments from the radio era, related products generally need to set one or two knobs using the shuttle technology to quickly and intuitively adjust the volume, etc. In the 32-bit design, we still maintain this style.
2) Touch screen and writing recognition
In recent years, selection and adjustment through touch and drag is a major advancement in electronic product input technology and an important competitive indicator of the saleable performance of a product. In 32-bit systems, we can easily implement these functions through a resistive touch screen.
In the navigation application, it is also necessary to support the writing function. In order to meet the special needs of the car environment, we can also design a wireless handwriting input board using Bluetooth, and install it on the steering wheel to facilitate the driver's operation.
3) Simple and clear operation interface
The design of the human-machine interface is the key to a product design. How to make the product intuitive and simple to operate through careful and careful design is a difficult problem.
A variety of system arousal methods Under the requirements of better ergonomics, the system wakes up from standby in a variety of ways.
Real time clock design
The car needs to provide the user with a real-time clock, and the car audio generally needs to be designed.
Multiple video signal input and disposal methods
Support for foreground and background operations. The front desk is embedded on the console and is mainly used by the driver to display various interactive control information and navigation information. The background output is provided to the rear passengers, mainly to provide multimedia content for the rear passengers to enjoy.
How to communicate with the ECU
In advanced system design, the car audio can communicate with the car's main ECU, displaying some of the main parameters of the car's operation and driving in the display.
Steering wheel controller
The steering wheel controller allows the driver to easily control the equipment. The design is implemented by the ECU. Most of the designed steering wheel is directly connected to the vehicle equipment. We need to develop and implement it according to the target model.
Automatic brightness control
Display products used in automotive applications should have an excellent automatic brightness control device to meet the needs of a rapidly changing lighting environment. To this end, we design an optical sensor in the system, the system automatically adjusts the display indicators of the display according to changes in external illuminance.
System structure design
The block diagram of the system is shown in Figure 1. The system functions that can be added or deleted in this design have the following aspects:
Discless system
For those who love FLASH, the disc is already a redundant and troublesome component. Our design can be easily simplified to a discless system, through the FLASH card and built-in NAND FLASH, USB and other devices as a carrier of digital content.
Single disc CD or DVD
In the basic configuration, we recommend a single disc CD or DVD.
Front replacement disc
If the customer needs to replace the disc before, the 6-disc changer is a better choice, and it is installed inside the fuselage, but the panel design has certain difficulty, and the selection should ensure the cooperation with the space.
Post-displacement disc
Our design supports a rear CD or DVD changer that supports image input and switching of the changer.
AM/FM radio and RDS
In the DTS system, RDS is a choice project. With the powerful functions of the 32-bit CPU, we can realize the functions and needs of various levels of RDS to achieve the function of supporting TMC real-time traffic navigation.
DAB system
In environments where DAB is used in Europe, our system design can support DAB and its corresponding data broadcasting functions through module access.
Bluetooth
As the preferred technology for short-range communication, the application of Bluetooth in the interior of the car is already a must.
Hands-free phone access
First of all, we need to support the hands-free calling function inside the car through Bluetooth, and complete the hands-free calling function through the built-in anti-jamming microphone array and the interior speaker. In the future development, our Bluetooth system will also support Bluetooth rearview mirrors or reversing radars, which will reduce the wiring process and engineering difficulty through wireless technology.
Mobile phone charging power support
Through the USB port, this design can provide charging function for mobile phones that support USB charging.
System process design
A good product, just good circuit and software is not enough, good process design is the key factor to achieve product quantification. In the design of the car multimedia navigation system implemented by 32-bit CPU, we placed the complex navigation and control system and LCD drive system behind the LCD screen, using a double-sided SMT process. The power, audio processing and other modules are placed on the motherboard, using a two-panel single-sided SMT process. The DVD or CD module uses a single PCB process under the movement and is connected to the system via a cable. The whole process design is simple and reliable, the space utilization rate is high, the connection port is small, the processing is convenient, and the pass rate is high.
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