Although many smart locks (such as fingerprint recognition and IC card recognition) have been introduced, these products are for specific fingerprints or valid cards, and can only be used for boxes, cabinets, rooms, etc. with high confidentiality requirements and for individual use. . In addition, the card type IC card is easy to be lost and damaged, and its high cost limits the popularity and promotion of such products to a certain extent.
The electronic password lock has the advantages of high security performance, low cost, low power consumption and simple operation, which makes it more and more important as the role of anti-theft guard. Some existing electronic password locks in the domestic market are developed through the purchase of some product modules, and do not have independent intellectual property rights; some are self-developed, but their power consumption and cost are relatively high, and they do not have wide application value. In order to overcome these shortcomings, from the economical and practical point of view, the single-chip AT89S5l and low-power CMOS E2PROM AT24C02 are used as the main control device and data memory unit, and an electronic password with alarm, real-time monitoring and remote management functions can be designed. lock. The electronic code lock is small in size, easy to develop, low in cost, high in security, and can report the stored historical data of the store to the host computer system in time, realizing real-time network monitoring, and facilitating management personnel to analyze and process data in time.
1 hardware design of electronic password lock The hardware of electronic password lock is composed of core processing module, power management module, execution module and communication module. Its circuit structure is shown in Figure 1.
1.1 Core Processing Module The core processing module is the core of the electronic password lock. It not only processes the information of the password lock, but also manages the stable operation of various programs and controls other modules. The module is mainly composed of single-chip microcomputer and keyboard. , memory, display circuit composition. Among them, the single chip is the core part of the core processing module, and its main task is to cooperate with the software to complete information processing and recording, control the normal operation of other parts of the dispatch, electrical control, password proofreading and modification. From the needs of electronic password lock function, cost performance, program data volume and interface circuit, this paper selects AT89S51 single chip microcomputer of ATMEL as the core of controller. The keyboard circuit is designed in the form of 4&TImes; 4 rows and columns keyboard, which is directly composed of the high and low bytes of the P1 port of the AT89S51.
In the circuit, AT24C02 is selected as the memory of password and unlocking information. This memory is a serial EEFROM with I2C bus interface. Since AT89S51 single chip does not have I2C bus interface, P2.2, P2.3 and AT24C02 of single chip are selected on the circuit. The SCL and SDA lines are connected, and the analog I2C bus interface is implemented on the software. The memory also stores the modified first-level and second-level permission passwords and the specific time of the last 20 unlocks, as well as the information of illegally stealing and setting passwords. The user can conveniently access the keys through the buttons. The connection between the memory and the microcontroller is shown in Figure 2. In view of the functional requirements of the system to implement password input prompts, access to unlock information, time display and other information, and from a low cost, the SMCl602A liquid crystal display module is selected as the display circuit, and its circuit structure is shown in Figure 3.
1.2 Power Management Module This design requires a +5 V DC power supply to power the entire circuit. A voltage regulator is used in the circuit to convert the input DC supply voltage to a voltage of +5 V. In addition, if you only rely on the external DC power supply, there will be problems that cannot be unlocked due to power failure. In order to solve this problem, the automatic switching circuit is added when designing the power management module, so that the battery pack is powered and the external DC power supply is supplied. The method can automatically and automatically switch according to actual needs, so that the electronic password lock can work uninterrupted for a long time. The power supply automatic switching circuit uses the LTC-4414 device. The LTC4414 controls two P-channel insulated gate FETs to realize an automatic switching circuit for efficient or OR operation of two power supplies.
1.3 Execution Module The execution circuit sends a signal through one of the pin lines of the MCU, and is amplified by the triode. The scheme of driving the solenoid valve by the relay to open the lock, the circuit structure is shown in Figure 4. In addition, the alarm circuit is composed of a time base integrated circuit 555 and its auxiliary components. In the case of networking, the alarm signal can be sent to the main controller through the serial port extension network to remind the management personnel.
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