With the improvement of people's living standards, cars have gradually entered ordinary families, and the number of cars in major cities in China has increased year by year. At the same time, car theft and robbing have also become a more serious social problem. Although the application of various types of car anti-theft / alarms to automobiles has solved the problem of automobile safety to a certain extent, with the improvement of thieves, most of the alarms are easy to be destroyed quickly. The way of car alarm is mostly flashing lights and horns. The car owner may not be able to get the alarm, but the surrounding residents are seriously disturbed. In addition, the thieves broke the alarm, and after stealing the car, the appearance was slightly changed, and the car was like a sea of ​​rocks, which could not be traced. In order to solve these problems, this design uses GPS monitoring to track the location of the car. In the case of theft, the GSM SMS module can be used to send the GPS location of the car to the owner or the public security department at any time to speed up the resolution of the case.
Figure 1 System function diagram
System functions This monitor is different from ordinary car anti-theft devices, and does not provide sound and light alarms and car circuit cut-off functions when stolen. It is equivalent to a tracker with an alarm function, using GPS positioning to determine whether the car is stolen. After confirming that the car was stolen, GSM SMS can be used to send the location information of the car to the police at any time. This kind of monitor is a supplement to the general car anti-theft device, it is not easy to be found, it cannot be removed in a short time, and the positioning accuracy is high (about 10m).
The system functions of the entire monitor are shown in Figure 1. The monitor is installed in a hidden place of the car, and usually uses the car battery to supply power. After the car's power is cut off, it can automatically use the battery to independently supply power. The GPS receiving antenna is located outside the car, which is better for receiving signals. The basic mode of operation of the whole monitor is that when the car is driving normally, the monitor is in a power-saving sleep state. When the car stops and the owner leaves, the owner can use the mobile phone to send a text message to the monitor to order it to be in the monitoring state. At this time, the GPS receiving function of the monitor is started, and the position, speed and altitude information sent by the GPS positioning satellite are regularly received, and the static position is marked as a safe position. When the thief destroys the car's general anti-theft system and drives the car away, the position coordinates received by the GPS change, and when the speed and position deviation are greater than the set alarm value. The monitor will automatically send an alarm message to the owner ’s mobile phone, prompting the car to be moved and possibly stolen. When the car owner calls the police, in order to cooperate with the police to find the stolen car, the car owner can send a command to the monitor again, turn on the regular SMS sending function, and send the current car coordinates to the car owner or the alarm center regularly. It can be very convenient to cooperate with the electronic map Find the current car location, you can quickly solve the case. The SD card attached to the system can store information such as the coordinates of the car changes for a long time after the alarm, as evidence for solving the case and finding clues of thieves' associates.
System hardware design In order to realize the monitoring function, the monitor is required to have GPS receiving, GSM short message sending and a large number of data storage functions, and has a certain multi-tasking capability, low cost and small size. The hardware structure of the monitor is shown in Figure 2.
Figure 2 Monitor hardware structure
A suitable main chip will play an important role in the system. The FS7821LQ embedded chip is selected in this monitor. FS7821LQ integrates 8051 core of RISC structure, USB 2.0 controller, transceiver, NAND flash, SD and CF interface controller. The external circuit of the embedded system composed of this chip is simple, powerful, and low in price, which is very in line with the requirements of this design.
The SMS function of the monitor mainly completes the reception of the owner's SMS commands and the transmission of the car's GPS position data. The system uses a mature GSM-RTU SMS module to complete. The module is embedded with a GSM module, 16-bit low-power MSP430 microcontroller control and management, with a core unit for telemetry and remote control, a configurable standard serial port (RS-232C), a standard antenna and a SIM card interface. Insert the purchased mobile phone SIM card into the SMS module, and after completing the system (including service phone number) settings, the serial port of the SMS module and the serial port 1 of the monitor (plus a level conversion chip to make it meet the RS-232C level standard) After connecting, the hardware installation of the SMS module is completed.
The GPS module mainly completes the reception of car GPS data. The system selects the MG-30U / R-GPS module and uses the second-generation SiRF high-efficiency chip (with 12 channels, which can receive up to 12 GPS satellite signals) for comparison and calculation. , You can choose speed, location, altitude and other related data, the price is low, and the accuracy is high. The output of this module can choose RS-232C interface, and use the serial port 2 of the system main control chip FS7821LQ to connect with the GPS module. Because the amount of data transferred is not large, using the serial port to transfer data can avoid the trouble of using the USB interface to establish the main USB port on the system. Figure 3 shows the circuit design of the system hardware. The FS7821LQ has a complete SD card driver and interface, and the system can directly connect to it using a 128Mb SD card. Use the general-purpose I / O ports PORT2_0 ～ PORT2_3 of the FS7821LQ chip to form two serial ports. After adding the MAX232 level conversion chip, connect the GPS and GSM modules respectively. The FS7821LQ chip includes a function and hardware driver from the USB interface, which is reserved for the USB 2.0 interface in the system as a product upgrade. In addition, the system also reserves 10 general-purpose I / O ports of FS7821LQ as control ports for subsequent alarm functions. 
Figure 3 System hardware circuit design
System software design Because this monitor includes a variety of more complex functions, it also has burst functions such as short message sending and receiving, and GPS receiving and other scheduled tasks. In order to better complete the execution of tasks, in the embedded system composed, The μC / OS-II operating system was transplanted. As a free real-time open source embedded operating system, μC / OS-II provides multi-task switching capability and interrupt, UART driver and other functions, which can fully meet the requirements of this operating platform.
μC / OS-II as a most basic task scheduling kernel, only has the ability to switch tasks, this monitor can be divided into 4 tasks as shown in Table 1 according to its function: the main task has the highest priority (10); SMS The receiving and sending task has the second highest priority (12), which mainly includes the function of receiving short messages (including settings and switch monitors), and the function of sending short messages (send GPS coordinates once every 5s when alarming). The GPS receiving task receives GPS data every 5s and parses its coordinates to determine whether to alarm; the data storage task stores GPS coordinates every 60s after the alarm (128Mb card can save about 1 month of data).
Because the USB device and SD card are used in the monitor, the USB and SD drivers must be mentioned in the software while having a hardware interface. FS7821LQ chip development kit provides USB driver and SD / MMC card driver, including support for standard MMC card commands; embedded 5B command memory; embedded 17B response memory; support 1/4/8 bit data width; support for cards 20MHz clock frequency. In order to save the GPS data to the SD card in the form of a file, there must be a file system compatible with the PC. The monitor successfully transplanted the simplified FAT16 file system and realized the free access of files.
After transplanting OS / II and embedding USB and SD / MMC card drivers, the functions of the application-level software installation system of the monitor are divided into multiple tasks with different priorities. Among them, the main task is used to generate other tasks, and its priority is the highest (10); the GPS receiving task is responsible for controlling the MG-30U / R-GPS module and obtaining the required GPS data from it, which has the second highest priority (12); SMS The receiving and sending task completes the functions of receiving the owner's SMS and sending GPS data, and its priority is again (14); finally, the data storage function completes the function of GPS storage and system settings in the SD card, and its priority is 16. A message queue is established in the program to complete the communication and data exchange between tasks. The software state flow diagram is shown in Figure 4.
Figure 4 Software status flow diagram development and prospect
The design of this embedded car monitor uses a large number of mature technologies and modules. Its application is mainly to issue a warning when the car is stolen and provide accurate car location information after being stolen. It cannot replace the traditional car anti-theft device, but can provide a very practical anti-theft function, which provides fast and accurate search for the stolen car information. With the development of technology, the integration of the controller and the main controller in GPS / GSM will surely become the direction of development, so that the cost and volume can be further reduced. At the same time, the monitor can also be integrated with general car alarms to develop into a more complete system.
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