Develop vehicle anti-theft device based on embedded technology (hardware part)

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

This article uses embedded technology to develop vehicle anti-theft devices. On the one hand, it can enhance the control capability and improve the intelligent degree of automobile anti-theft. On the other hand, the volume of the device is reduced, the flexibility of the device application is improved, and at the same time, it also provides room for expansion to further enhance the functions of automotive electronics in the future. Due to limited space, this article only introduces the hardware circuit.

1 System hardware composition

The system is mainly composed of 4 parts: ARM embedded controller, mobile phone module, wireless remote control module, car control and status detection module. The vehicle 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 to finally achieve the purpose of alarming. The system principle is shown in Figure 1.

1.1 Control circuit

If a car thief starts to vibrate abnormally after starting the car, the vibration sensor will pass the low-level effective signal to the LPC2210, and the LPC2210 will send the information out; one to the alarm circuit and the other to the TC35. The alarm circuit is mainly composed of integrated block, speaker and electronic switch SCR. Among them, the triode or the compound tube is a circuit measure often used to increase power. He constitutes an equivalent transistor with a large current amplification factor, and the total amplification factor is the product of the amplification factors of the two tubes. SCR is an electronic switch composed of thyristor. Capacitor and resistor form a voltage reducer and filter, which provides + 3 ～ + 4 V to IC. IC is a simulated sound alarm integrated circuit. Once the car thief presses the wrong password, the battery current enters the anti-theft system all the way, and the other way is after the engine is started to drive the engine to work. The output voltage of the neutral contact passes through the differential circuit, the thyristor SCR is triggered, and then The resistance is reduced, and the voltage is applied to the power input terminal of the IC. The IC obtains a voltage output alarm signal, which is amplified by the composite tube and urges the speaker to emit a loud alarm sound. While at rest, the entire circuit consumes no power. as shown in picture 2.

1.2 Power interface design

The work of GSM module, the voltage is 3.3 ~ 5 V, and the power supply is required to provide a peak current of 2 A during the process of starting the connection transmission and landing network, and the voltage drop of the voltage cannot be greater than 400 mV. Considering that the voltage may drop. It must be ensured that the minimum voltage is higher than 3 V. In addition, during data transmission, the voltage fluctuation cannot be greater than 400 mV, otherwise, TC35 will consider 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 you use the battery clip as a backup power supply, you must also consider the voltage drop caused by the resistance on the connection between the motherboard and the battery clip. In the circuit design, the power supply of the ZIF interface can be separated from other power supplies. The power supply of the ZIF interface power supply alone must ensure the above requirements. High-power switching power supplies with high stability can be used.

1.3 Serial interface design

GSM module and system processor exchange data through serial TIU TRS 232 standard serial bus. The high level of all operations is CMOS voltage (2.65 V), therefore, the logic level of the RS 232 conversion chip must use low-voltage power supply (3.3 V), and the 5 V serial port conversion chip cannot be used. In the design, MAX 3238 of MAX Company was selected to realize data conversion. The MAX 3238 is a 3.3 V logic level serial conversion chip produced by MAX. It has the same characteristics as the commonly used MAX 232, except that 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 is fully compliant with the ISO7816 3 standard. In the design of 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 handling of the SIM card. Of course, there are many different methods based on personal design habits and styles. The ultimate goal to be achieved is to have a separate ground for the SIM card holder. Therefore, a set of filter circuit is formed with an inductor and a capacitor, and a group is placed on each side of the card holder to form a ring-shaped isolation belt, so that the SIM card and the outside are kept at a relatively independent ground, and then passed through a The wire connects the module interface ground and the SIM card ground.

1.5 Wireless remote control module design

The wireless remote control function is implemented by the SRWF-1 module, which is controlled by 89C51, and sends the information received by C51 to the SRWF-1 transmitting module through the serial port, and the SRWF-1 receiving module transmits the received information to the LPC2210 through the serial port.

2 Conclusion

It has been experimentally verified that the use of a GSM short message-based communication method 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 realizing long-distance real-time monitoring of the car by the user; in addition, the system It can also distinguish the urgency of the intrusion, which is convenient for users to take measures according to the situation to meet the requirements of car users for car anti-theft, and the system is not costly and easy to promote.