Car alarm system design

With the development of social science and technology and the improvement of people's living standards, cars have gradually entered ordinary families as the most common means of transportation in modern times. The problem of car anti-theft has also aroused people's attention and attention. Cars are usually set in garages or parking lots. The frequency of daily use is that it cannot be installed with a solid safety net like a house. Therefore, to solve the problem of car anti-theft, we should start from the characteristics of the car itself and combine them with modern technology networks. Development and actual needs, design anti-theft alarm solutions and systems that meet the characteristics of the car itself. This system attempts to design a vehicle anti-theft system and simple model based on vibration and positioning sense. The automobile intelligent anti-theft alarm system designed in this paper is composed of shock sensor SW-18020P, single-chip STM32F407ZGT6, GPS positioning module UBLOX-NEO-6M, communication module SIM900A and system power supply. The system can monitor the car in real-time after the car is turned off. When a robbery occurs, the abnormal vibration of the vehicle body triggers the main control chip, and the positioning information obtained by the positioning module is sent to the vehicle owner through the mobile communication network. If the position of the car is abnormal or the owner actively sends a position acquisition instruction, the alarm can also report the position of the car. Thereby, an anti-theft alarm system with abnormal vibration detection and real-time position transmission is realized.

The hardware includes a vibration sensing and recognition module, a positioning module, a communication module, a single-chip microcomputer control module, and a system power supply.

2 hardware design

The hardware includes a vibration sensing and recognition module, a positioning module, a communication module, a single-chip microcomputer control module, and a system power supply.

2.1 Vibration perception recognition module

The vibration perception recognition module is a very important part, which is equivalent to the trigger switch of the entire alarm system. When a car is stolen, the body will inevitably vibrate, and the vibration sensing and recognition module in the car will generate a trigger signal. The sensitivity of the shock sensor is an important factor that determines whether the alarm can be triggered timely and accurately. This module selects SW-18020P as the shock sensor. The vibration perception recognition module uses LM393 as a voltage comparator. When vibration occurs, the shock sensor will output voltage. When the voltage at the reverse end is higher than the non-inverting end, LM393 can output a low level. When the voltage at the reverse end is lower than the non-inverting end, LM393 can output a high level. . Connect a 10K potentiometer to the inverting terminal to adjust the sensitivity of the sensor. When the voltage at the inverting terminal is higher, the sensitivity of the shock sensor is duller, otherwise, the sensitivity is higher.

2.2 Positioning module

The core of the positioning module is UBLOX-NEO-6M. The hardware of the entire GPS positioning system is modularized. Its requirements are mainly to be able to receive GPS signals and to amplify the received signals. At the same time, it provides a complete external interface, which is convenient and intelligent. The connection of instruments and other equipment should be able to effectively control the error and improve the accuracy. The system requires small size, convenient movement, and low power consumption. Only four pins are needed to connect the module and the microcontroller: TXD, RDX, VCC, GND. TXD and RDX are used for serial communication with the microcontroller, and VCC and GND are used to supply power to the module

2.3 Communication module

The communication module uses a high-performance industrial-grade GSM module SIM900A, which has complete functions and rich interfaces and is very small and easy to install. It is very suitable for various fields that require GPRS data services, voice, and SMS. The communication module adopts SMT package form, stable performance, high cost performance, working frequency is 900MHz/1800MHz; carrying RTC backup battery, small size, large capacity, rechargeable, can maintain the long-term power-off operation of RTC; still installed There are a 3.6mm microphone interface and a 3.6mm headphone interface for voice calls; the selection interface is used to select whether the RS232 serial port is connected to the communication port or the debugging port; the RS232 serial port is used to connect the serial port of a PC or industrial computer to achieve control; And this module has all I/O ports led out, which is convenient to use.

2.4 MCU control module

This design directly uses the core board. Its core chip has 114 I/O ports, 4 universal synchronous/asynchronous serial receivers and transmitters, and 2 universal asynchronous transceivers. It meets the requirements of this design and can guarantee GPS and SIM900A modules can be used at the same time.

2.5 System power

This system consists of a power supply circuit composed of AS1117-3.3 and 4 capacitors. The positive voltage regulator AS1117-3.3 contains a current-limiting protection current and a high-temperature overheating protection circuit, which can prevent load short circuit and junction temperature overheating from burning down the device. This kind of voltage regulator The device does not need external compensation components. If the circuit can work normally and stably, the main control chip STM32F407ZGT6 with a working voltage of 2.0V to 3.6V and the communication chip SIM900A with a working voltage of 3.1V to 4.6V must be supplied separately.

3 software design

In daily life, the alarm system is turned off. When the car stops, the alarm is automatically turned on to monitor the car in real-time. When the vehicle body vibrates abnormally, the vibration sensor feels the illegal external force and deforms, and transmits the vibration trigger signal to the main controller; or when the car position and the initial position are initially entered, the main controller can also be transmitted as a trigger Signals to monitor the car in real-time. Once the above two situations occur, the real-time position can be obtained through GPS, and the car’s test position text message can be sent to the owner through the GSM module to determine the specific position of the car. The car owner can also send SMS commands at any time to obtain the latitude and longitude of the car at any time, so as to better ensure the safety of the car.

4 Conclusions and prospects

Automobile intelligent anti-theft alarm system The future automobile anti-theft system will also develop in a more networked and intelligent direction, becoming a typical application scenario of the Internet of Things.

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