Design of car anti-theft alarm system based on ARM

With the rapid development of China's automobile industry, many families have their own private cars, but the number of garages is far from meeting the demand. Therefore, how to effectively prevent car theft is the most concerned issue for car owners. In recent years, science and technology have developed rapidly, and new car anti-theft equipment combining various new technologies has emerged one after another. As the functions of the current vehicle-mounted system are gradually increasing, the control of the single-chip microcomputer has become increasingly unable to meet the needs. Therefore, the use of embedded technology in automotive electronics will become inevitable.

This paper uses embedded technology to develop a vehicle-mounted anti-theft device, which can enhance the control ability and improve the intelligence of car anti-theft. On the other hand, it reduces the size of the device, improves the flexibility of the application of the device, and also provides expansion space for further enhancing the functions of automotive electronics in the future. Due to limited space, this paper only introduces the hardware circuit.

1 System hardware composition
The system is mainly composed of ARM embedded controller, mobile phone module, wireless remote control module, and car control and status detection module. The car control and status detection module collects vehicle-related data to the ARM embedded controller, and the ARM embedded controller transmits it to the mobile phone module and the wireless remote control module, ultimately achieving the purpose of alarm. The system principle is shown in Figure 1.

1.1 Control Circuit
If a car thief starts the car abnormally and generates vibration, the vibration sensor will transmit the low-level effective signal to LPC2210, and LPC2210 will transmit the information; one to the alarm circuit and the other to TC35. The alarm circuit is mainly composed of an integrated circuit, a speaker and an electronic switch SCR. Among them, the triode or compound tube is a circuit measure commonly used to increase power. It forms an equivalent transistor with a large current amplification factor. The total amplification factor is the product of the amplification factors of these two tubes. SCR is an electronic switch composed of thyristor, capacitor and resistor form a voltage reducer and filter, providing +3~+4 V voltage to IC; IC is an analog sound alarm integrated circuit, the alarm is controlled by SCR, once the car thief presses the wrong password, the battery current enters the anti-theft system in one way, and the other way is when the engine is started and the engine is driven to work, the output voltage of the neutral contact passes through the differential circuit, the thyristor SCR is triggered, and then the voltage is reduced by the resistor, and the voltage is added to the power input end of IC, IC obtains the voltage output alarm signal, which is amplified by the composite tube and drives the speaker to emit a loud alarm sound. In static state, the whole circuit does not consume power. As shown in Figure 2.

1.2 Design of power interface
The working voltage of GSM module is 3.3～5V. In the process of starting connection transmission and logging into the network, the power supply is required to provide a peak current of 2A, and the voltage drop cannot be greater than 400mV. Therefore, the possible voltage drop must be fully considered when designing the power supply of the module. The minimum voltage must be higher than 3V. In addition, during the data transmission process, the voltage fluctuation cannot be greater than 400mV, otherwise, TC35 will think that the voltage is too low and automatically shut down the module. Therefore, the power cord of the circuit should be as short as possible. If the battery clip is used as a backup power supply, the voltage drop caused by the resistance on the connection line between the motherboard and the battery clip must also be considered. In the circuit design, the power supply of the ZIF interface can be separated from other power supplies. The ZIF interface power supply is powered separately. The above requirements must be met. A high-power device with high stability switching power supply can be used.
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1.3 Serial Interface Design
The GSM module and the system processor exchange data via the serial TIU TRS 232 standard serial bus. The high level of all operations is CMOS voltage (2.65 V), so the logic level of the RS 232 conversion chip must be powered by a low voltage (3.3 V), and a 5 V serial port conversion chip cannot be used. In the design, MAX 3238 from MAX Company was selected to achieve data conversion. MAX 3238 is a 3.3 V logic level serial conversion chip produced by MAX Company. It has the same characteristics as the commonly used MAX 232, but the logic level is 3.3 V. The serial communication between the module and the processor fully complies with the universal serial bus standard. The specific hardware interface circuit is shown in Figure 3.

1.4 S1M card interface design
The baseband processor in the GSM module has a complete SIM card interface, which fully complies with the ISO7816 3 standard. When designing the SIM card interface, in order to ensure higher stability, the maximum length of the ZIF connector and the card holder pin should not exceed 200 mm.


Another issue that needs to be considered during design is the ground wire processing of the SIM card. Of course, there are many different methods according to personal design habits and styles. The ultimate goal is to make the SIM card holder have a separate ground. Therefore, a set of filter circuits is formed with 1 inductor and 1 capacitor, and a set is placed on each side of the card holder to form a ring isolation belt, so that the SIM card and the outside maintain a relatively independent ground, and then the module interface ground and the SIM card ground are connected through a wire.

1.5 Wireless remote control module design
The wireless remote control function is implemented using the SRWF-1 module, which is controlled by 89C51. The information received by C51 is sent to the SRWF-1 transmitter module through the serial port, and the SRWF-1 receiver module transmits the received information to the LPC2210 through the serial port.

2 Conclusion
Experimental verification shows that the use of GSM short message-based communication to control the car alarm system can not only greatly improve the communication reliability of the alarm system, but also the communication distance is basically unrestricted, thereby enabling users to monitor the car over a long distance in real time; in addition, the system can also distinguish the urgency of the intrusion, so that users can take measures according to the situation, meet the requirements of car users for car anti-theft, and the system is low-cost and easy to promote.