Car anti-theft system based on GPS and GSM network 2013-07-22 (1)

0 Preface

With the advent of the new era, the automobile has also developed rapidly as an important means of transportation. At the same time, the subsequent car theft has also increased. However, most of the car anti-theft systems on the market currently have certain limitations. Therefore, a network-based anti-theft system with high reliability and security has gradually entered the field of vision. Network-based anti-theft mainly breaks through the limitation of distance, solves the passive anti-theft method of traditional physical anti-theft device, integrates advanced GPS positioning system and GSM communication system module, and uses SMS (short message service) to send and receive text messages to the owner. Two-way communication between users. The interactive, active alarm mode not only informs the owner of the car before it is illegally moved, but also remotely controls the vehicle via the network. This project is a kind of intelligent anti-theft system for the public that is developed by GPS and GSM network and is more reliable and safe.

1 overall system design

The system is mainly composed of GSM module, GPS receiver module, single-chip control circuit, sensor alarm circuit and power supply circuit. The sensor alarm module monitors the abnormal condition of the vehicle; the GPS module is responsible for receiving the positioning data; the single chip control circuit collects, receives and analyzes the GPS positioning data under the condition that the abnormality is detected, and the GSM module sends and receives the short message under the control of the single chip; the power circuit 7805 is The MCU and GPS module provide +5V DC voltage, and the LM2941CS regulates the +5V DC voltage to +4.2V for use by the GSM module.

2 system hardware design

2.1 Sensor section

This system uses Hall switch, vibration sensor, tilt sensor and pyroelectric infrared sensor to monitor different aspects of vehicle body vibration, vehicle body position change and human biological information, and can obtain enough information for car anti-theft. Eliminate the uncertainty of information to the extent and improve the reliability of the alarm.

2.2 GSM part

This system adopts Siemens GSM module TC35i from Germany. The module is RS232 data port, dual frequency (GSM900/GSM1800), and complies with ETSI standards GSM0707 and GSM0705. It contains RF circuitry and baseband, and provides a standard AT command interface for bidirectional transfer of instructions and data, and fault recovery and restart via shutdown or AT commands. Its working voltage is 4.2V, and it will automatically shut down when the module's power supply voltage is lower than 3.3V. Because the module emits a signal with a current maximum of 2A, it is powered by a high-demand power supply. This system uses the voltage regulator chip LM2941CS, which is dedicated to the adjustable switch type high performance microwave circuit, which can provide stable high current and voltage output. The TC35i module pins can be divided into five categories: power supply, SIM card, data input/output, audio interface and control. When using the TC35i module, to put the TC35i into operation, ensure that its start pin IGT plus a low level longer than 100ms.

2.3 GPS section

This system uses SIRF third-generation high-sensitivity leaded GPS receiver module SIRF starIII. The chip is serial communication, baud rate 4800; level data output, format is TTL. With 20 channels, it can track 20 satellite channels at the same time, ensuring the highest receiving sensitivity and positioning accuracy less than 10m. There is a rechargeable battery inside, which can store ephemeris data for quick positioning. The data can be powered off for more than seven days. The module GPS uses a standard MMCX antenna interface for easy connection to a GPS antenna. The data line interface uses a 6-wire connector lead output to facilitate prototyping during product development, and is very simple to use, requiring only three output lines. The output of GPS uses the second pin, which is the serial port TTL level signal, the high level is greater than 2.4V, the low level is less than 0.4V, the output drive capability is 2mA, and can be directly interfaced with the single chip; Six feet, each output a pulse signal of about 0.2V with a width of 10ms for timing; the DC positive power supply is 3.5~5.5V, the first pin is used; the fifth pin is used for the power ground. By default, the GPS receiver module SIRF star III outputs positioning data once per second, usually in the $GPRMC streamlined 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.