1 Introduction
In recent years, GPS navigation and positioning technology is constantly developing, and more and more vehicles are equipped with on-board GPS terminals. Today, vehicle-mounted GPS terminals have become an important part of urban traffic management networks. However, since the user has installed a vehicle-mounted GPS terminal, the lack of friendly human-machine interaction equipment has affected the user's use and the popularization of the vehicle-mounted GPS terminal, which limits the expansion of the functions of the vehicle-mounted GPS terminal product. By installing a Chinese character display terminal, the user can use the car GPS terminal more conveniently, which is convenient for the center to perform dispatch management and make up for the deficiencies of the previous products.
2 The composition of embedded Chinese display
Figure 1 Car GPS system structure diagram
Embedded Hanxian's function is to communicate with GPS vehicle terminals and meter through serial port, receive and process GPS positioning signals sent by GPS vehicle terminal and related operation data sent by meter, and let users show Hanxian through infrared remote control and keys. Set and operate, and then display the corresponding content on the LCD module, and can provide voice services.
The embedded Hanxian consists of the following parts: Hanxian motherboard, LCD module, infrared receiver, buttons, speakers, LEDs and connectors.
3 Mainboard hardware
Figure 2 Hanxian structure diagram
The main board of embedded Chinese display is composed of the following parts: parallel flash, power supply circuit, LCD module interface and drive circuit, serial communication circuit, watchdog power
Road and voice chip and power amplifier circuit.
3.1 MSP430 series MCU
The MSP430 series MCU is a 16-bit MCU developed by TI. Its outstanding feature is ultra-low power consumption, which is very suitable for various occasions with low power requirements. The lowest power consumption is only 1/5 of other flash microprocessors (Flash MCUs). At 3V operating voltage, the current consumption is less than 350uA / MHz, and the standby mode is only 15uA / MHz, with five energy-saving modes. Its 64K program space ensures that it can hold enough code length, and the internal FLASH that can be written during program execution can be used to store important data such as center number, phone number and GPS vehicle terminal settings. The MCU has anti-ESD protection and strong anti-interference ability. Online programming, easy to update the program. The simulator has a simple structure and can be made by itself. The operating temperature range of this series of industrial grade single chip microcomputer is -40 ~ + 85 degrees Celsius, which can meet the requirements of vehicle equipment applications.
3.2 Power supply circuit
In order to be compatible with the 12V and 24V voltages provided by different car batteries, the voltage converter used in the power supply circuit should be able to meet the input voltage between 9V and 36V. Since the vehicle environment is poor and the battery power supply fluctuates greatly, in order to prevent the high current caused by external interference from burning out the internal components, a self-recovery fuse can be connected in series at the power input end. The basic power consumption of this design idea motherboard is about 50mA. When the LCD backlight is lit, the power consumption is about 180mA. Therefore, a self-recovery fuse with a fusing current of 350mA can be selected to meet the requirements. In order to prevent the failure or damage caused by instantaneous pulses such as electrostatic interference, the microprocessor or single-chip microcomputer can be connected in parallel with a TVS tube at the positive input terminal of the power supply. Since the power supply voltage of the car battery is 12V or 24V, it can be selected according to the actual situation .
Figure 3 power supply circuit
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