Views: 84 Author: Site Editor Publish Time: 2019-09-24 Origin: Site
In the development of door, the door handle has always been an integral part of the door; now, in addition to the door handle, the smart lock gradually appears in the door. In the field of security technology prevention, the electronic password lock with anti-theft alarm function replaces the traditional mechanical password lock, which overcomes the shortcomings of less password and poor security, and now the password lock has improved greatly both in technique and performance.
The system of smart password locks consists of a smart monitor and an electronic lock. The two are placed in different place. The smart monitor supplies the power required by the electronic lock and receives the alarm information and status information sent by the electronic lock. The line multiplexing technology is adopted to share a two-core cable for power supply and information transmission, which improves the reliability and safety of the system.
1.1 The Basic Principle of Intelligent Monitor
The intelligent monitor is composed of a MCU, a clock, a keyboard, a LCD display, a memory, a demodulator, a line multiplexing and monitoring, an A/D conversion, a buzzer and the like. It mainly complete the communication with the electronic lock, intelligent analysis and security monitoring of communication lines.
The intelligent monitor is always in the receiving state, receiving alarm information and status information from the electronic lock in a fixed format. The sound and light alarms are immediately sent through the LCD display and the buzzer if it receive the alarm information. The status information is stored in the memory and compared with the historical state of the electronic lock before at this time, getting the changing trend to predict the future status changes. And the corresponding information is provided to the duty officer through the LCD display for decision making. While the intelligent monitor establishes communication with the electronic lock, the A/D converter monitors the change of the supply current flowing through the communication line in real time, effectively preventing the damage caused by human factors and ensuring the smooth communication.
1.2 The Basic Principle of Electronic Locks
The electronic lock is also based on the 51 series single-chip, equipped with the corresponding hardware circuit to complete the setting, storage, identification and display of the password. It drives the electromagnetic actuator and detects the driving current value, receives the alarm signal sent by the sensor, and transmits the data. And other functions.
The MCU receives the typed code and compares it with the password stored in the EEPROM. If the password is correct, the electromagnetic actuator is unlocked; if the password is incorrect, the operator is allowed to re-enter the password, up to three times. If it is not correct for three times, the MCU will alarm the intelligent monitor through the communication line. The single-chip sends the unlocking operation and the driving current value of the electromagnetic actuator as the status information to the intelligent monitor at this time, and also sends the alarm information received from the sensor interface to the intelligent monitor as the basis of the intelligent analysis.
2.1 Line Multiplexing Technology
Intelligent monitors and electronic locks are placed at different places. If the communication line and the power supply line are separated, it is necessary to increase the number of cable cores, which will increase the safety hazard. In this paper, it adopts the line multiplexing technology, which uses only one two-core cable to realize the transmission of power and information.
At the transmitting interface, the electronic lock boosts the modulated data signal through the pulse transformer and sends it out. At the receiving interface, the pulse transformer steps down the received data signal and sends it to the demodulator to reduce the carrier signal loss during transmission. In order to reduce mutual interference between communication and power supply, the selection of choke coil L and coupling capacitor C should be considered comprehensively.
If we set carrier frequency fo=400kHz, in order to ensure that most of the signal energy is transmitted to the receiving interface, we should take L=33.7μH?C1=0.047μF.
2.2 Current Monitoring Technology
In order to prevent the vandalism for the communication line and prevent the electromagnetic actuator from burning the coil due to excessive current flowing through the electromagnetic coil for some reason, the current monitoring technology is adopted in the design of the intelligent code lock.
2.3 Data Communication and Preprocessing Technology
The intelligent monitor receives the status information sent by the lock (including the opening and closing of the lock, the first password error, the second password error, the third password error, etc.), the current value flowing through the electromagnetic actuator coil, and the power supply current value of the communication line read at this time, and the three datas combine to form a data block, where the operation state occupies 1 byte, the supply current occupies 2 bytes, and the coil current occupies 2 bytes. The intelligent monitor is always in the receiving state during communication with the electronic lock. In order to improve the reliability of communication, it adopts the method of repeated transmission in the communication protocol. The electronic lock repeatedly transmits 5 times for each group of data. After receiving the data, the intelligent monitor corrects the error by using the large number decoding law to ensure the accuracy of data reception. In addition, in order to save memory, pre-processing technology is adopted for the received data, that is, after receiving one data, the data is first compared with the set threshold, and if it is greater than the threshold, an over-limit alarm is issued; if it is less than the threshold, the data is compared with the same type of data received on the same day, and the larger one is retained. In this way, the data stored every day is the maximum value in the same type of data.
2.4 Intelligent Analysis
Intelligent analysis and prediction technology are based on each received data block, compared with the recorded value of the previous similar data, analyze the magnitude and trend of the current change caused by the operation, find problems in time, and report to the management personnel, improving the reliability of the entire system.
The software of intelligent password lock uses the 51 series MCU assembly language to separately program the intelligent monitor and the electronic lock. The intelligent monitor software includes keyboard scanning and LCD display programs, buzzer drivers, clock modification and reading programs, data communication and pre-processing programs, intelligent analysis programs and line monitoring programs. The electronic lock software includes modules such as a keyboard scanning and decoding program, a LCD display program, a communication program, an electromagnetic actuator drive and detection program, and a sensor interface program. We adopts modular design approach in the software design process to facilitate reading, debugging and improvement of the program.
The intelligent password lock fully utilizes the software and hardware resources of the 51 series MCU, and introduces intelligent analysis functions to improve the reliability and security of the system. It is welcomed by users by installing it in a certain type of strongbox. In addition, the intelligent password lock can be modified in software and hardware to form an intelligent distributed monitoring network, achieving centralized monitoring and management within a certain scope, and is widely used in finance, insurance, military and other security fields.
With the development of technology, there will inevitably be more locks, such as new voice locks, face recognition locks, iris locks, and so on. Smart lock door will be more and more popular in life.