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Safe and reliable performance of smart password lock works
Nov 19, 2018

Safe and reliable performance of smart password lock works

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 mechanical password lock password and poor security performance, so that the password lock is technically and in performance. Greatly improve one step. With the development of large-scale integrated circuit technology, especially the advent of single-chip microcomputers, there has been a smart password lock with a microprocessor. In addition to the function of electronic password lock, it also introduces functions such as intelligent management and expert analysis system. Therefore, the password lock has high security and reliability, and the application is increasingly widespread. This paper introduces the intelligent password lock with 51 series single chip as the core, and elaborates its working principle, basic function block diagram, key design technology and software workflow.

1 Basic principles and hardware components

The system of smart code locks consists of a smart monitor and an electronic lock. The two are placed off-site, and the smart monitor supplies the power required by the electronic lock and receives the alarm and status information it sends. Here, 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 and composition block diagram of the intelligent monitor

The block diagram of the intelligent monitor is composed of a single chip, a clock, a keyboard, an LCD display, a memory, a demodulator, a line multiplexing and monitoring, an A/D conversion, a buzzer and the like. 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 and receives the alarm information and status information from the electronic lock in a fixed format. For the alarm information, the sound and light alarms are immediately sent through the LCD display and the buzzer; for the status information, it is stored in the memory and compared with the historical state of the electronic lock before this time, and the trend is changed to predict the future. The 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 line.

1.2 The basic principle and composition of electronic locks

The block diagram of the electronic lock, which is also based on the 51 series single chip microcomputer (AT89051), with the corresponding hardware circuit, completes the setting, storage, identification and display of the password, drives the electromagnetic actuator and detects the driving current value, and receives the sensor. The function of alarm signal and data transmission.

The MCU receives the entered 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 three times If it is not correct, the MCU will alarm the intelligent monitor through the communication line. The single-chip microcomputer 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 key technologies

In order to improve the security and reliability of the smart password lock, in addition to the measures taken in the device selection (such as the device with low power consumption and wide temperature range), some key technologies are also adopted in the design.

2.1 Line multiplexing technology

The smart monitor and electronic lock are placed off-site, and the smart monitor supplies the power required by the electronic lock and receives the alarm and status information it sends. If the communication line and the power supply line are separated, it is necessary to increase the number of cable cores and increase the safety hazard. This paper adopts the line multiplexing technology, which uses only one two-core cable to realize the transmission of power and information. The schematic is shown in Figure 3.

At the transmitting end, the electronic lock boosts the modulated data signal through the pulse transformer T and sends it out; at the receiving end, the pulse transformer T steps down the received data signal and sends it to the demodulator to reduce the carrier signal during transmission. Loss in the middle. 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.

Let the carrier frequency fo=400kHz, in order to ensure that most of the signal energy is transmitted to the receiving end, take L=33.7μHC1=0.047μF.

2.2 Current monitoring technology

In order to prevent the artificial destruction of the communication line and the electromagnetic actuator from causing the current flowing through the electromagnetic coil to be excessively burnt due to some reason, the current monitoring technology is adopted in the design of the smart code lock. The current monitor uses the MAX471 current-to-voltage conversion chip from MAXIM. The chip can convert the measured current I into a ground output voltage U, and has the characteristics of large measuring range, high precision, and the output voltage U and the measured current I are proportional. The current monitor output voltage is sent to the A/D converter. The MCU reads the A/D conversion result to know the current change in the line, and finds the abnormality in time by analysis and issues an alarm signal. The principle circuit is shown in Figure 4.

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 Reading the supply current value of the communication line at that time, the three combine to form a data block, wherein 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 communication reliability, this paper 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. 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 less than The threshold value is compared with the same type of data received on the same day, and the larger one is retained. Thus, the data stored every day is the maximum value in the same type of data, and the flowchart thereof is as shown in FIG. 5.

2.4 Intelligent analysis

The intelligent analysis and prediction technology is based on each received data block, compared with the recorded value of the previous similar data, analyzes the magnitude and trend of the current change caused by the operation, finds problems in time, and reports the management personnel. Improve the reliability of the entire system.

3 system software design

The intelligent password lock software 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, an LCD display program, a communication program, an electromagnetic actuator drive and detection program, and a sensor interface program. The modular design method is used 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 system microcontroller, 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 safe. In addition, the smart password lock can be modified in software and hardware to form an intelligent distributed monitoring network, achieving centralized monitoring and management within a certain range, and is widely used in finance, insurance, military and other security fields. Application prospects.