Car anti-theft system based on GPS and GSM network

0 Introduction
    With the advent of the new era, cars have developed rapidly as an important means of transportation. At the same time, the number of car thefts has also increased. However, most of the car anti-theft systems on the market have certain limitations. Therefore, network anti-theft systems with high reliability and security have gradually entered people's field of vision. Network anti-theft mainly breaks through the limitation of distance, solves the passive anti-theft method of traditional physical anti-theft devices, integrates advanced GPS positioning system and GSM communication system module, uses SMS (short message service) to send and receive text messages to car owners, and realizes two-way communication with users. The interactive and active alarm mode can not only notify the owner before the car is illegally moved, but also remotely control the vehicle through the network. This project uses GPS and GSM network to develop a more reliable and safe car intelligent anti-theft system suitable for the public.

1 Overall system design
    The overall system is mainly composed of five parts: GSM module, GPS receiver module, single-chip control circuit, sensor alarm circuit and power supply circuit. The sensor alarm module monitors abnormal conditions of the vehicle; the GPS module is responsible for receiving positioning data; the single-chip control circuit collects, receives and analyzes the GPS positioning data when an abnormality is detected, and the GSM module sends and receives text messages under the control of the single-chip microcomputer; the power supply circuit 7805 provides +5V DC voltage for the single-chip microcomputer and GPS module, and the LM2941CS stabilizes the +5V DC voltage to +4.2V and provides it to the GSM module.

2 System Hardware Design
2.1 Sensor Part
    This system uses devices such as Hall switches, vibration sensors, tilt sensors and pyroelectric infrared sensors to monitor different aspects such as vehicle vibration, vehicle position changes and human biological information. It can obtain sufficient information required for car anti-theft, eliminate information uncertainty to the greatest extent, and improve the reliability of alarms.
2.2 GSM Part
    This system uses the industrial GSM module TC35i from Siemens, Germany. This module is an RS232 data port, dual-band (GSM900/GSM1800), and complies with ETSI standards GSM0707 and GSM0705. It contains radio frequency circuits and basebands, and provides a standard AT command interface to achieve two-way transmission of commands and data, and can achieve fault recovery and restart through shutdown signals or AT commands. Its operating voltage is 4.2V, and the module will automatically shut down when the power supply voltage is lower than 3.3V. Because the maximum current of the module is as high as 2A when transmitting signals, a high-demand power supply is used to power it. This system uses the voltage regulator chip LM2941CS, which is dedicated to adjustable switch-type high-performance microwave circuits and can provide stable high-current voltage output. The TC35i module pins can be divided into five categories: power supply, SIM card, data input/output, audio interface and control, with a total of 40 pins. When using the TC35i module, to put TC35i into working state, ensure that its start pin IGT is added with a low level for more than 100ms.

2.3 GPS part
    This system uses SIRF starIII, the third generation high-sensitivity lead-type GPS receiver module. The chip is serial communication with a baud rate of 4800; the level data output is in TTL format. It has 20 channels, which can track 20 satellite channels at the same time, ensuring the highest receiving sensitivity and making the positioning accuracy less than 10m. It has a rechargeable battery inside, which can save ephemeris data for fast positioning. The data power-off memory time can reach more than seven days. The module GPS uses a standard MMCX antenna interface, which is convenient for connecting the GPS antenna. The data line interface uses a 6-wire connector lead output, which is convenient for making prototypes during product development, and it is very simple to use, only three output lines are needed. The output of GPS uses the second pin, which is a serial port TTL level signal, with a high level greater than 2.4V and a low level less than 0.4V. The output drive capacity is 2mA, and it can be directly interfaced with a single-chip microcomputer; the second signal output uses the sixth pin, and a 10ms width of 0.2V pulse signal is output every second for timing; the DC positive power supply is 3.5~5.5V, using the first pin; the power ground uses the fifth pin. By default, the GPS receiver module SIRF star III outputs positioning data once per second, usually in the $GPRMC simplified data format. The statement format is as follows:
    $GPRMC, <1>, <2>, <3>, <4>, <5>, <6>, <7>, <8>, <9>, <10>, <11>, <12>
    *hh<10-12> is generally not used. Each positioning data starts with "$" and ends with a carriage return. [page]

Figure 3 GPS data receiving flow chart

2.4 Control part
    The control part of this system adopts AT89C52 produced by ATMEL. It is a low-power, high-performance CMOS 8-bit single-chip microcomputer. It contains 8k bvtes Flash read-only program storage unit that can be repeatedly erased and written and 256 bytes of random access data memory unit (RAM). The chip has a built-in 8-bit central processing unit and Flash storage unit. The device is produced using ATMEL's high-density, permanent storage technology and is compatible with the standard MCS-51 instruction system. The AT89C52 single-chip microcomputer is powerful and can be applied to many more complex control systems. This machine has two full-duplex serial communication ports, which meet the conditions of being able to communicate with the GSM module and the GPS module at the same time. Pins 10 and 11 of the single-chip microcomputer communicate with the GSM module. Pins 16 and 17 of the single-chip microcomputer communicate with the GPS module. As shown in Figure 4.

3 AT commands
    The microcontroller can send AT commands to control the GSM module TC35i. Text and PDU modes are commonly used to send text messages. Text mode is mainly used to transmit GPS information. The code for sending and receiving text messages using Text mode is simple and easy to implement, but the disadvantage is that it does not support Chinese text messages; PDU mode is mainly used to send the status and control information of the car. However, it is inconvenient to decode pure English short messages. Therefore, when sending and receiving pure English characters and numeric characters, Text mode is used. PDU mode not only supports Chinese mode, but also can send English text messages.

4 System Setting and Control
    This system is built on the basis of the reliable and mature GSM mobile network, and makes full use of the resources of the GSM mobile network. It uses Chinese short messages to directly display the situation of multiple alarm locations on the user's mobile phone screen, thereby realizing rapid and accurate alarms with strong real-time performance. And minimize the investment in user terminals. In the user terminal, the GSM service network used, the short message special service number, the user's mobile phone number, the type and number of alarm information collection modules, etc. should be set accordingly.

5 Conclusion
    The main innovation of this article is that this anti-theft system integrates GSM and GPS, uses the mobile communication technology of the GSM mobile phone module, combines it with the popular GPS technology today, cooperates with the single-chip control technology, and uses the most intuitive Chinese short message form. It can directly reflect the situation of multiple alarm locations on the mobile phone, completes the design of the car anti-theft positioning system, and realizes the intelligent and safe remote monitoring of vehicles. According to the specific requirements of vehicle intelligent anti-theft, this system can also be upgraded in software and hardware. Because the wireless network technology is used between modules, the confidentiality of this system is increased and the possibility of the system being completely destroyed is reduced. After further improvement, it can be combined with mobile phone positioning system software, which is convenient for users to use and suitable for mass production and popularization and application.