I. Introduction
At present, there are many anti-theft products on the market, but they are mostly used for car door, window and electronic key control. Although they have a good alarm function, it is difficult to achieve the anti-theft function, so that criminals can take advantage of it. This design is based on the anti-theft control of the vehicle brake system. Through the combination of mechanical, hydraulic and electrical, the four wheels are locked perfectly, thus ensuring the safety of the vehicle.
Second, the system principle
The system principle is shown in Figure 1. According to the command of the remote controller, the controller controls the brake oil circuit through the forward and reverse rotation of the relay drive motor to lock or loosen the wheels to realize the anti-theft function. There is a limit signal when the motor is rotating to prevent over-current phenomenon due to excessive torque; when the remote controller controls the system, the system will automatically issue various voice prompts, especially when the vehicle is driving Voice alarm will be performed for a longer period of time, and the vehicle will be gradually locked after a period of time to slow down the vehicle until it is locked, which can realize remote control of the vehicle; in addition, the system can also check whether the hood is closed or The seat belt detects and issues a voice alarm.
Third, the system's hardware composition
(1) Motor drive main circuit
The system realizes the function of locking and unlocking the wheels by controlling the forward and reverse rotation of the motor, and the realization circuit is shown in FIG. 2. According to the instructions of the controller, LOCK and OPEN control the closing of relays K1 and K2 respectively to realize the forward rotation and reverse rotation of the motor, and then control the wheel brake oil circuit, so as to achieve the purpose of four wheels locking or releasing. Anti-theft function. In order to prevent the motor from over-rotation, limit switches STB1 and STB2 are set to feed back the signal to the controller in real time, so that the system can work stably.
2) The control loop of the system
The principle of the control system is shown in Figure 3.
The controller selects 89C52 single chip microcomputer with 2 counters and 1 timer. The counter T0 is used to calculate the speed of the vehicle, which provides an important basis for the system to perform various controls. The sinusoidal signal of the wheel speed sensor is collected and processed by the single-chip microcomputer after being transformed and shaped by CD4013, so as to determine the current speed of the vehicle.
The open and lock signals from the remote control are amplified by the LM324, which collects and analyzes the MCU and drives the field effect tube for various protection processes to control the main control loop and realize the anti-theft function for the vehicle. At the same time, when carrying out anti-theft control of the vehicle, the system should issue various voice prompts and alarm functions. The single chip computer controls the voice chip API8108A, which stores the various voice signals required in advance in the voice chip and is directly driven by the API8108A when output is needed speaker.
In addition to the basic anti-theft function, the system also integrates other functions, such as the collection of signals such as seat belts, hoods, starters, etc. When various abnormal conditions occur, various alarms can be instantaneously issued until the vehicle stops.
In order to make the system work reliably, the control system uses a hardware watchdog and uses MAX813 to monitor the running status of the single-chip microcomputer in real time. Because the system has a control loop and a main loop, various power supplies are needed. The LM7805 provides 5V power, and the three-terminal adjustable regulator LM317 provides power for the remote control circuit.
Fourth, the software implementation of the system
This system is designed with single chip microcomputer C language, and the program adopts modular design, with strong expansibility and easy reading. After various initializations are performed when the system is powered on, the lock must be cyclically detected and various alarms issued in order to eliminate possible failures in a timely manner.
When there is no fault in the system, the controller controls according to the opening and locking signals of the remote controller and the current opening and locking status, and issues various alarm messages and prompt messages. In the control process, it is processed according to the current vehicle speed, starter status and other information to prompt the driver to drive correctly and safely. The specific control process is shown in Figure 4:
When the system is working, the vehicle may be stolen and work in the locked state. The system must be able to stop the vehicle safely. The partial implementation code is as follows:
5. Anti-interference design of the system
Due to the complex working environment of the vehicle, high requirements are placed on the stability and anti-interference of the system. The signal transmission uses shielded wire to ensure that the wheel speed signal is not disturbed; the pulse signal is shaped in terms of signal reception to eliminate clutter; the electronic components adopt automotive-grade standards and can be suitable for harsh environments; all circuit boards use Dow Corning coatings, with Moisture-proof, anti-corrosion and shock-proof functions, as well as good high-frequency and low-frequency dielectric characteristics, greatly improve the anti-interference performance of the system.
This design not only has good anti-theft performance, but also has an alarm function, and can provide various safety tips to the driver while driving. It is a more advanced intelligent anti-theft system, which has been installed and used in some vehicles. Practice has shown that the system has reasonable design, strong anti-interference and stable operation, and is a reliable and practical anti-theft product.
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