Application of Embedded System Based on GPS Positioning in the Design of Automobile Monitor
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With the improvement of people’s living standards, cars have gradually entered ordinary households, and the number of cars in major cities in China has increased year by year. At the same time, car stolen and robbed have also become a more serious social problem. Although the application of various car anti-theft/alarms in automobiles has solved the safety problems of automobiles to a certain extent, with the improvement of the methods of thieves, most of the alarms are easy to be destroyed quickly. The car alarms are mostly flickering lights and horns. The car owner may not be able to get the alarm, but the surrounding residents are seriously disturbed. In addition, after the thief broke the alarm and stolen the car, the appearance of the car was slightly changed, and the car was like a stone sinking into the ocean and could not be tracked. 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 short message module can be used to send the car’s GPS location to the car owner or the public security department at any time to speed up the speed of solving the case.
Figure 1 System function diagram
System functions
This monitor is different from ordinary car anti-theft devices, and does not provide functions such as sound and light alarm and car circuit cut-off when stolen. It is equivalent to a tracker with alarm function, using GPS positioning to determine whether the car has been stolen. After confirming that the car is stolen, GSM text messages can be used to send the car’s location information 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 function of the whole monitor is shown as in Fig. 1. The monitor is installed in a hidden part of the car, usually powered by the car battery, after the car power is cut off, it can automatically switch to independent battery power supply. The GPS receiving antenna is located outside the car, which is conducive to better signal reception. The basic way the whole monitor works is that when the car is running normally, the monitor is in a power-saving sleep state. When the car stops and the car owner leaves, the car owner can use the mobile phone to send a text message to the monitor, ordering it to be in the monitoring state. At this time, the GPS receiving function of the monitor is turned on, and the position, speed and altitude information sent by the GPS positioning satellites are received regularly, and the stationary position is marked as a safe position at the same time. When a thief destroys the car’s general anti-theft system and drives the car away, the position coordinates received by the GPS will change. 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, reminding that the car has been moved and may be stolen. After 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 timing SMS sending function, and send the current car coordinates to the owner or the alarm center regularly. It is 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 change for a long time after the alarm, as evidence for solving the case and clues to find the thief’s 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 amount of data storage function, and a certain multi-tasking ability, low cost, and small size.
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 meets the requirements of this design very well.
The SMS function of the monitor mainly completes the receipt of the owner’s SMS command and the transmission of the car’s GPS location data. The system selects a mature GSM-RTU SMS module to complete. The module is embedded with a GSM module, 16-bit low-power MSP430 single-chip microcomputer 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 complete the system (including service phone number) settings, then connect the serial port of the SMS module and the serial port 1 of the monitor (plus a level conversion chip to make it comply with 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 uses the MG-30U/R-GPS module and the SiRF second-generation high-performance chip (with 12 channels, up to 12 GPS satellite signals can be received) for comparison and calculation , Can choose speed, position, altitude and other related data, low price, high precision. RS-232C interface can be used for the output of this module, and the serial port 2 of the system main control chip FS7821LQ is used 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 establishing a main USB port on the system using the USB interface.
Figure 3 is the circuit design diagram of the system hardware. FS7821LQ has a complete SD card driver and interface. The system can directly use a 128Mb SD card to connect to it. Utilize the general I/O port PORT2_0～PORT2_3 of FS7821LQ chip to form two serial ports, after adding MAX232 level conversion chip, connect GPS and GSM module respectively. The FS7821LQ chip includes a function and hardware driver from the USB interface. The USB 2.0 interface is reserved in the system for use as a product upgrade. In addition, the system reserves 10 general-purpose I/O ports of FS7821LQ as control ports for subsequent alarm functions.
Figure 3 System hardware circuit design diagram
System software design
Since this monitor includes a variety of more complex functions, it also has burst functions such as SMS sending and receiving and timing tasks such as GPS receiving. In order to better complete the task execution, μC is transplanted in the composed embedded system. /OS-II operating system. As a free source code open real-time embedded operating system, μC/OS-II provides multi-task switching capabilities and interrupts, UART drive and other functions, which can fully meet the requirements of this operating platform.
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