Development of a driving recorder based on LPC2362 with GPS function

The car tachograph is a digital electronic recording device that records, stores, and outputs various state information about the vehicle's traveling speed, time, mileage, and related vehicle travel.
The use of the vehicle tachograph has the following effects and social benefits: reducing traffic accidents, improving driving safety, better safeguarding the lives and property of the public and passengers; improving the traffic environment and relieving traffic pressure, regulating driver driving habits, and promoting the driver The process of civilized driving; establish vehicle state data information system to provide legal basis for traffic accidents; standardize the scope of traffic police law enforcement and civilized law enforcement behavior, improve its law enforcement level, efficiency and fairness; safeguard the interests of all parties, record the evidence by the recorder Distinguishing the attribution of the responsibility of the accident can be used as an auxiliary tool for the insurance department to make claims.
Based on the national standards of the vehicle driving recorder and the actual needs of the operating customers, the system adds the functions of the GPS module and the CAN module without increasing the software and hardware resources of the vehicle driving recorder system, so that the vehicle driving recorder has the record GPS data. The function of information; use the management software GIS track playback function to realize the operation vehicle operation route supervision; the CAN interface function is connected with the engine power bus to realize real-time fuel consumption measurement. The realization of this system provides an effective means for commercial vehicle operating companies to monitor and operate vehicles, which can realize the organic combination of operational vehicle safety supervision and operation management.
1 System design The whole system design scheme is combined with the system and function of the vehicle driving recorder, GPS module, CAN module, etc., and is realized by an MCU [1] of ARM7 core.
Figure 1 is a block diagram of the structure of an ARM-based GPS-enabled car tachograph system.

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The MCU uses NPC's ARM series LPC2362 chip, which is based on ARM7 core and has abundant peripheral resources. It is suitable for embedded applications requiring high performance and low power consumption. The USB HOST and isolated RTC functions well meet the design requirements of the car tachograph. The addition of GPS and CAN modules does not require additional system hardware and software resources, and has a good price/performance ratio.
2 System hardware design The hardware design of the system adds GPS and CAN functions on the basis of satisfying the function of the recorder. The power supply design adopts the main input power supply without isolation, adopts EMI processing, and other input and output interfaces associated with the vehicle adopt photoelectric isolation method to meet The electromagnetic compatibility and product cost of the vehicle driving recorder have a good cost performance, so that the product not only meets the requirements of the national standard, but also has a good cost advantage. The power EMI processing and power supply design structure is shown in Figure 2.

The signal acquisition and output module is based on ARM with GPS-enabled car tachograph system and vehicle information interaction module. The information volume includes vehicle speed, engine speed, 10-way switch signal, mileage and alarm. In the signal acquisition design, the operational amplifier is used as the acquisition unit, and the comparator operation principle and method are used to realize the acquisition. This not only ensures high input impedance, does not affect other electronic devices on the vehicle, but also allows the comparator to obtain different comparison voltages by matching different resistors, to meet the level matching of different signals of different models, and the output is realized by photoelectric coupling.
The keyboard adopts 4 buttons, combined with the LCD display module, and uses the Chinese menu to realize the man-machine interface operation. The LCD adopts the ultra-low temperature 12232 dot matrix to meet the complex working conditions of the automobile.
The ISP download is implemented by UART0. Due to the hardware watchdog and low-power function, when the ISP downloads, the jumper shields the hardware watchdog and borrows the system power to supply power to the UART0 transceiver, realizing the online ISP function.
The system design a hardware combination carrier and software data storage method, using small capacity ferroelectric hundreds of millions of times of erasing times to store data with high erasing frequency and as a data buffer, using large-capacity DATAFLASH as the final storage of data, thus Meet system requirements and reduce system costs. The system storage function block diagram is shown in Figure 3.

The system and management software have a large amount of data exchange. In order to facilitate the user to set and upload the lower computer data, the system designs the contact smart card module and the lower computer for data exchange. For the characteristics of large-capacity data and small-capacity data, the smart card module uses two types of cards as data exchange media, one is 128 B 24C01 card, and the IIC data bus is used for data exchange; the other is 4 MB. The AT45DB041 card uses SPI for data exchange. It can realize system data exchange function and save system cost. The smart card has a power management module, and the block diagram is shown in Figure 4.

The system uses the TRIMBLE GPS module to implement the GPS function. The TRIMBLE GPS module has serial A and serial B 2 information output channels. The serial port A is directly connected with the serial port 2 of the MCU module to realize the receiving of the positioning information of the MCU module; the serial port B is converted into a standard RS232 level output by the SPX3232 one-way level converting chip, and the positioning information output is reserved for the system. The GPS module is designed with an active antenna and an antenna detection circuit to realize short-circuit, normal, and open-circuit detection of the antenna, and the power management module controls the power of the GPS module. The GPS function block diagram is shown in Figure 5.

The system clock adopts the RTC of the LPC2362 independent power supply. It is powered by the vehicle power supply and the backup battery. The SP609 realizes automatic power switching. When the vehicle power is normal, the vehicle power supply is used. Otherwise, the backup battery power is used. The battery voltage is monitored by the A/D conversion of the LPC2362 and gives a warning that the battery voltage is too low. In addition, SP609 with hardware watchdog function, hardware watchdog and low power coexistence through 74HC01 or gate. When the MCU module control pin output is low, the 74HC01 output is controlled by the SP609 RESET to implement the hardware watchdog; when the MCU module control pin output is high, the 74HC01 output is high, the MCU RESET is high, and the low power MCU is implemented. Not reset. Figure 6 is a functional block diagram of the clock and hardware watchdog.

The CAN module function is realized by the 2-way CAN of the LPC2362, and the CAN function is realized by adding an isolated transceiver. Among them, one way is configured as low-speed CAN, which is connected to the vehicle low-speed CAN bus; the other is configured as high-speed CAN, which is connected to the vehicle high-speed CAN bus. Through the CAN function module system, it can obtain engine information, realize fuel consumption monitoring, and realize low-speed CAN bus on the vehicle. Data exchange with high speed CAN bus.
At present, most recorder systems are designed with a large-capacity transmission protocol, and the mode of the single-chip + USB HOST driver chip is often used. However, this design scheme has the following disadvantages: the cost is too high, the chip with USB HOST function is often expensive, and the peripheral expansion requires more hardware resources, and generally needs to expand RAM to meet complex USB protocol and large-capacity transmission protocol, and cost. Relatively high; the data transmission rate is relatively slow, the main frequency of the selected MCU generally does not exceed 20MHz, and the data exchange efficiency is lower through the communication between the external bus system and the USB HOST interface chip. In addition, the external expansion RAM also occupies system bus resources. When the USB HOST and other accessory hardware are extended, the PCB area is large and the routing is complicated, which makes the system stability lower and debugging inconvenient. The LPC2362 comes with a USB HOST function that solves these shortcomings. It fully satisfies the USB 2.0 protocol, supports full-speed transmission, has DMA transfer mode and power management mode, and has independent 8 KB SRAM. It also has power management and overcurrent. Detection function. The block diagram is shown in Figure 7.

The car drive recorder has a printing function. This design uses an external commercial printer. The power supply uses a switching power supply LM2596, which has a current output capability of 3 A. The interface uses UART0 to realize data recording of the recorder.
3 System software design system software adopts modular design, design corresponding software according to different functional modules, so the system has good cutting performance. Each module software driver is divided into the underlying driver and interface application. The whole embedded software is implemented by the front and back system [2], and the software flow is shown in Figure 8.

According to relevant national laws and regulations, commercial vehicles need to be equipped with vehicle driving recorders to enhance the safety management of vehicle operations. Vehicle operating entities often need to install GPS and CAN functions to realize the monitoring of operating lines and actual fuel consumption. Improve corporate management tools and benefits. Starting from these two aspects, the system realizes the above functions without increasing the hardware and software of the vehicle driving recorder , solves the practical problems faced by the operating company, reduces the use cost of the terminal customer, and thus improves the customer installation of the vehicle driving recorder. The enthusiasm ensures the safety of the operation of the vehicle, improves the operational efficiency, and reduces the operating costs of the operating company.

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