Abstract: Due to the increasing number of cars in life, the safety of car license plates has become a concern of many people. The device is more effective than other license plate anti-theft devices. It is monitored by the Hall effect sensor, and the on-site alarm is performed at the first time when the license plate fastening screw protective cap is detached, which serves as a warning function, and simultaneously sends the GSM communication module to the owner's mobile phone in time. The license plate is smashed with information, so that the license plate can be stolen in time. The design background, system principle design and hardware circuit design of the device are described in detail. The system schematic diagram, installation diagram and sensor circuit diagram are given.
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Keywords: single chip microcomputer; intelligent anti-theft; GSM; Hall effect
With the improvement of people's living standards, the number of cars in the city has increased dramatically, which has led to the development of many related industries. However, many lawless elements have also used the idea of ​​stealing license plates to blackmail the owners, which makes the owners very troublesome. It also seriously affected the harmonious development of society.
In the early license plate fixing, the license plate was fixed with two ordinary screws, and then a protective cap was used to prevent the screw from being exposed. The screw protective cap is aluminum, ordinary steel and plastic products, which can only be fastened, can not be used for anti-theft and anti-unloading. The screwdriver will fall off at a glance and it will not prevent 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 smashed, without any alarm device; and the license plate alarm device is to sound the alarm when the license plate is loose or the license plate is taken down. It only serves as a warning. If the owner is not on site, it will be difficult to get the alarm information of the stolen license plate. This kind of alarm device does not really alarm the owner.
The new intelligent license plate alarm system based on GSM is a single-chip microcomputer as the core controller. It can sense the looseness of the license plate screw cover through the Hall effect digital sensor, and perform on-site alarm. It can send alarm information to the owner through the existing GSM network. The new intelligent license plate anti-theft alarm device has the advantages of intelligent, real-time, remote communication, simple structure and convenient installation.
1 system principle design
System working principle: The car has 2 license plates, each license plate needs to be fixed with 2 screws, so there will be 4 screw protective caps, and a small strong magnet is attached to each screw protective cap of the fixed license plate in the car. Place a full-polar Hall switch on the inside of the case against the protective cap. When the cap does not fall off, the all-polar Hall switch is open. When the protective cap of the license plate fixing screw falls off, the Hall switch will A pulse is turned off because the magnetic field disappears. When the MCU receives this pulse, the on-site alarm module will sound an alarm, and the GSM module will dial the owner's mobile phone to alarm. If the license plate fixing screws have been equipped with mechanical anti-theft screws, the owner will have enough time to rush to the scene to avoid the theft of the license plate, even if the license plate uses ordinary fastening screws, when the first buckle cap falls off, the owner also has Sufficient time to get to the scene and 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 all-pole Hall-effect digital sensors. It is a Hall-switched sensor manufactured by Allegro Microsystems, Inc., which features low operating voltage and digital latch output. Unlike other Hall-effect switches, these devices can be turned on and off without contact, and in the absence of a magnetic field, the output is turned off, with a firm structure, small size, and light weight. Long life, easy installation, low power consumption, high frequency (up to 1 MHz), vibration resistance, and no fear of dust. Figure 2 is a schematic diagram of the link between the all-pole 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 mounted in the car casing. Since the front license plate is installed with a non-ferromagnetic material, the rear license plate is installed with a ferromagnetic material or a non-ferromagnetic material. If the rear license plate installation position is ferromagnetic material, in order to detect the magnetic signal, a small through hole is drilled in the rear car casing to ensure that the signal can be detected by the sensor, as shown in Fig. 3(a), if it is non-ferrous The magnetic material is installed as 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. The matrix keyboard in this circuit adopts 4x4 matrix keyboard, which uses 4 I/O lines as the line and 4 I/O. The line is a keyboard composed of column lines. At each intersection of the row and column lines, a button is set, so that the number of buttons in the keyboard is 4x4, and the determinant keyboard structure can effectively improve the I in the single chip system. /O port utilization; field alarm module, using a 12 V drive voltage buzzer; communication module, using the TC35 remote communication module, it can use the GSM network to send alarm information to the owner. The reset circuit of the AT89C51 of the single-chip microcomputer adopts key reset, and the clock circuit adopts an external oscillator circuit.
3 system software design
In the new smart license plate anti-theft alarm system program flow chart shown in Figure 4, the main program flow for the initialization of each module - real-time monitoring of the sensor module - a live alarm - liquid crystal display - GSM communication module to send license plate fastening screws off Alarm information.
4 Conclusion
The GSM-based intelligent license plate anti-theft alarm device has the following characteristics: 1) It can monitor the looseness of the license plate fastening screw in real time; 2) The device can realize the remote alarm by using the existing GSM network; 3) The device uses the single-chip microcomputer as the control The system is intelligent and high; 4) The structure is simple, convenient to install, and low in cost. The system has positive significance for promoting the anti-theft research and development of domestic license plates or related equipment and facilities, and has certain application value.
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