In the early days, the license plate was fixed by two common screws and then a protective cap was used on the outside to prevent the screw from being exposed. The screw caps were aluminum, common steel and plastic products. They could only be fastened, they could not be burglar-proof and unloaded. The screwdriver will come off as soon as it is removed, preventing the license plate from being stolen. Most of these license plate anti-theft devices are mechanical. Their commonality is to increase the difficulty of the license plate being dragged, there is no alarm device; there is a license plate alarm device that emits an alarm when the license plate looses or the license plate is removed. It only serves as a warning. If the owner is not at the scene, it will be very difficult to get the alarm information of the stolen license plate. This kind of alarm device does not really alert the owner.
The new smart license plate alarm system based on GSM is based on the single-chip microcomputer as the core controller. It can use the Hall effect digital sensor to sense the looseness of the license plate screw protection cover to carry out on-site alarm and send alarm information to the owner through the existing GSM network. The new smart license plate anti-theft alarm device has the advantages of intelligent, real-time, long-distance communication, simple structure, and easy installation.
1 system principle design
System working principle: There are 2 license plates in the car, each license plate needs to be fixed with 2 screws, so there will be 4 screw protection caps. A small powerful magnet is attached to each screw cap of the fixed license plate in the car. A full-polarity Hall switch is placed inside the shell immediately adjacent to the protective cap. When the cap is not detached, the full-polar Hall switch is opened. When the protective cap of the license plate fixing screw comes off, the Hall switch will Because of the disappearance of the magnetic field, a pulse is generated. When the MCU receives this pulse, the on-site alarm module will issue an alarm sound and the GSM module will call the owner's mobile phone to make an alarm. If the license plate fixing screws have been equipped with mechanical anti-theft screws, the owner will have sufficient time to rush to the scene to avoid the license plate being stolen. Even if the license plate uses ordinary fastening screws, when the first buckle cap comes off, the owner also has Enough time to get to the scene to avoid the theft of the license plate. The block diagram of the new license plate anti-theft alarm device is shown in Figure 1.
2 main hardware design 2.1 sensor module selection and connection circuit
The sensor uses four low-power, high-sensitivity A3212 omnipolar Hall-effect digital sensors. It is a Holzer switch-type sensor manufactured by Allegro Microsystems of the United States. It features low operating voltage and digital latching output. Unlike other Hall-effect switches, as long as there is a north pole or south pole magnetic field with sufficient strength, these devices can be opened without contact, and when there is no magnetic field, the output will be closed, with a solid structure, small size and light weight. Long life, easy installation, low power consumption, high frequency (up to 1MHz), shock resistance, dust-free, etc. Figure 2 shows the link schematic for the omnipolar Hall-effect digital sensor and the AT89C51.
2.2 Sensor Installation
In Fig. 4, a magnet is attached to the screw cap and then the sensor is installed inside the shell. Since the front license plate is installed with a non-ferromagnetic material, the rear license plate is installed with ferromagnetic materials and non-ferromagnetic materials. If the rear license plate is installed in a ferromagnetic material, in order for the sensor to detect the magnetic signal, drill a small hole in the rear shell to ensure that the signal can be detected by the sensor, as shown in Figure 3(a). If it is non-ferrous Magnetic material installation is shown in Figure 3(b).
2.3 Other Hardware Module Design
The central controller module adopts AT89C51 single-chip microcomputer, the display module adopts 12232 LCD screen, and the button module adopts matrix keyboard. In this circuit, the matrix keyboard uses 4x4 matrix keyboard, which uses 4 I/O lines as row lines and 4 I/O lines. Line as a keyboard composed of column lines, at each intersection of row and column lines, set a button, so that the number of buttons in the keyboard is 4x4, this type of determinant keyboard structure can effectively improve the microcontroller system I The utilization of the /O port; on-site alarm module, the use of a 12V drive voltage buzzer; communication module, using the TC35 remote communication module, which can use the GSM network to send alarm information to the owner. The reset circuit of the microcontroller AT89C51 uses a button reset and the clock circuit uses an external oscillator circuit.
3 system software design
In the new smart license plate burglar alarm system program flow chart shown in Figure 4, the main program flow for the initialization of each module - sensor module real-time monitoring a site alarm - LCD display - GSM communication module to send license plate fastening screw off Alarm information.
　 4 Conclusion
The GSM-based smart license plate anti-theft alarm device has the following features: 1) It can monitor the looseness of the license plate fastening screw in real time; 2) The device can use the existing GSM network to achieve remote alarm; 3) The device uses a single-chip microcomputer as a control High system intelligence; 4) Simple structure, easy installation, low cost, etc. The system has positive significance for the promotion of anti-theft research and development of domestic license plates or related equipment and facilities, and has certain application value.
The new smart license plate alarm system based on GSM is based on the single-chip microcomputer as the core controller. It can use the Hall effect digital sensor to sense the looseness of the license plate screw protection cover to carry out on-site alarm and send alarm information to the owner through the existing GSM network. The new smart license plate anti-theft alarm device has the advantages of intelligent, real-time, long-distance communication, simple structure, and easy installation.
1 system principle design
System working principle: There are 2 license plates in the car, each license plate needs to be fixed with 2 screws, so there will be 4 screw protection caps. A small powerful magnet is attached to each screw cap of the fixed license plate in the car. A full-polarity Hall switch is placed inside the shell immediately adjacent to the protective cap. When the cap is not detached, the full-polar Hall switch is opened. When the protective cap of the license plate fixing screw comes off, the Hall switch will Because of the disappearance of the magnetic field, a pulse is generated. When the MCU receives this pulse, the on-site alarm module will issue an alarm sound and the GSM module will call the owner's mobile phone to make an alarm. If the license plate fixing screws have been equipped with mechanical anti-theft screws, the owner will have sufficient time to rush to the scene to avoid the license plate being stolen. Even if the license plate uses ordinary fastening screws, when the first buckle cap comes off, the owner also has Enough time to get to the scene to avoid the theft of the license plate. The block diagram of the new license plate anti-theft alarm device is shown in Figure 1.
2 main hardware design 2.1 sensor module selection and connection circuit
The sensor uses four low-power, high-sensitivity A3212 omnipolar Hall-effect digital sensors. It is a Holzer switch-type sensor manufactured by Allegro Microsystems of the United States. It features low operating voltage and digital latching output. Unlike other Hall-effect switches, as long as there is a north pole or south pole magnetic field with sufficient strength, these devices can be opened without contact, and when there is no magnetic field, the output will be closed, with a solid structure, small size and light weight. Long life, easy installation, low power consumption, high frequency (up to 1MHz), shock resistance, dust-free, etc. Figure 2 shows the link schematic for the omnipolar Hall-effect digital sensor and the AT89C51.
2.2 Sensor Installation
In Fig. 4, a magnet is attached to the screw cap and then the sensor is installed inside the shell. Since the front license plate is installed with a non-ferromagnetic material, the rear license plate is installed with ferromagnetic materials and non-ferromagnetic materials. If the rear license plate is installed in a ferromagnetic material, in order for the sensor to detect the magnetic signal, drill a small hole in the rear shell to ensure that the signal can be detected by the sensor, as shown in Figure 3(a). If it is non-ferrous Magnetic material installation is shown in Figure 3(b).
2.3 Other Hardware Module Design
The central controller module adopts AT89C51 single-chip microcomputer, the display module adopts 12232 LCD screen, and the button module adopts matrix keyboard. In this circuit, the matrix keyboard uses 4x4 matrix keyboard, which uses 4 I/O lines as row lines and 4 I/O lines. Line as a keyboard composed of column lines, at each intersection of row and column lines, set a button, so that the number of buttons in the keyboard is 4x4, this type of determinant keyboard structure can effectively improve the microcontroller system I The utilization of the /O port; on-site alarm module, the use of a 12V drive voltage buzzer; communication module, using the TC35 remote communication module, which can use the GSM network to send alarm information to the owner. The reset circuit of the microcontroller AT89C51 uses a button reset and the clock circuit uses an external oscillator circuit.
3 system software design
In the new smart license plate burglar alarm system program flow chart shown in Figure 4, the main program flow for the initialization of each module - sensor module real-time monitoring a site alarm - LCD display - GSM communication module to send license plate fastening screw off Alarm information.
　 4 Conclusion
The GSM-based smart license plate anti-theft alarm device has the following features: 1) It can monitor the looseness of the license plate fastening screw in real time; 2) The device can use the existing GSM network to achieve remote alarm; 3) The device uses a single-chip microcomputer as a control High system intelligence; 4) Simple structure, easy installation, low cost, etc. The system has positive significance for the promotion of anti-theft research and development of domestic license plates or related equipment and facilities, and has certain application value.
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