Basic Principles of Intelligent Locks

The electronic lock is also based on the 51 series microcontroller (AT89051) as the core, equipped with corresponding hardware circuits, to complete the functions of password setting, storage, recognition and display, driving electromagnetic actuators and detecting their driving current value, receiving alarm signals from sensors, and sending data.

The microcontroller receives the input code and compares it with the password stored in EEPROM. If the password is correct, it drives the electromagnetic actuator to unlock; If the password is incorrect, the operator is allowed to re-enter the password up to three times; If it is not correct three times, the microcontroller will alarm the intelligent monitor through the communication line. The microcontroller sends each unlocking operation and the driving current value of the electromagnetic actuator as status information to the intelligent monitor. At the same time, it also receives alarm information from the sensor interface and sends it to the intelligent monitor as the basis for intelligent analysis.

1. Basic principles and hardware composition

The intelligent password lock system consists of an intelligent monitor and electronic locks. The two are placed in different locations, and the intelligent monitor supplies the power required for the electronic lock and receives the alarm and status information it sends. The line reuse technology is adopted here, which shares a two core cable for power supply and information transmission, improving the reliability and safety of the system.

1.1 Basic principle and composition diagram of intelligent monitor

The composition diagram of an intelligent monitor consists of a microcontroller, clock, keyboard, LCD display, memory, demodulator, line multiplexing and monitoring, A/D conversion, buzzer, and other units. Mainly responsible for communication with electronic locks, intelligent analysis, and safety monitoring of communication lines.

The intelligent monitor is always in a receiving state, receiving alarm and status information from electronic locks in a fixed format. For alarm information, sound and light alarms will be immediately emitted through the LCD display and buzzer; For the status information, it is stored in memory and compared with the historical state of the electronic lock before this time, to obtain the trend of change, predict future state changes, and provide corresponding information to the on duty personnel through the LCD display for decision-making purposes. While establishing communication with electronic locks, the intelligent monitor monitors the real-time changes in the power supply current flowing through the communication line through an A/D converter, effectively preventing damage caused by human factors and ensuring smooth communication lines.

1.2 Basic Principles and Composition Block Diagram of Electronic Locks

The composition diagram of an electronic lock is also based on the 51 series microcontroller (AT89051) as the core, equipped with corresponding hardware circuits, to complete the functions of password setting, storage, recognition and display, driving electromagnetic actuators and detecting their driving current value, receiving alarm signals from sensors, and transmitting data.

The microcontroller receives the input code and compares it with the password stored in EEPROM. If the password is correct, it drives the electromagnetic actuator to unlock; If the password is incorrect, the operator is allowed to re-enter the password up to three times; If it is not correct three times, the microcontroller will alarm the intelligent monitor through the communication line. The microcontroller sends each unlocking operation and the driving current value of the electromagnetic actuator as status information to the intelligent monitor. At the same time, it also receives alarm information from the sensor interface and sends it to the intelligent monitor as the basis for intelligent analysis.

2. Key Technologies

In order to improve the security and reliability of intelligent password locks, this article not only takes measures in device selection (such as using low-power, wide temperature range devices), but also adopts some key technologies in the design.

2.1 Line multiplexing technology

The intelligent monitor and electronic lock are placed in different locations. The intelligent monitor supplies the power required for the electronic lock and receives alarm and status information sent by it. If communication lines and power supply lines are separated, it is inevitable to increase the number of cable cores and increase safety hazards. This article adopts line multiplexing technology, using only one two core cable to achieve power supply and information transmission. The schematic diagram is shown in Figure 3.

At the sending end, the electronic lock boosts the modulated data signal through a pulse transformer T and sends it out; At the receiving end, the pulse transformer T reduces the voltage of the received data signal and sends it to the demodulator to reduce the loss of the carrier signal during transmission. In order to reduce mutual interference between communication and power supply, the selection of choke L and coupling capacitor C should be comprehensively considered.

Assuming the carrier frequency fo=400kHz, in order to ensure that the majority of signal energy is transmitted to the receiving end, L=33.7 μ H and C1=0.047 μ F.

2.2 Current monitoring technology

In order to prevent human damage to communication lines and the electromagnetic actuator from burning out the coil due to excessive current flowing through the electromagnetic coil for some reason, this article adopts current monitoring technology in the design of intelligent password locks. The current monitor adopts the MAX471 current/voltage conversion chip produced by MAXIM company. This chip can convert the measured current I into an output voltage U to ground, and has the characteristics of a large measurement range, high accuracy, and a proportional output voltage U to the measured current I. The output voltage of the current monitor is sent to the A/D converter, and the microcontroller reads the A/D conversion results to obtain the changes in current in the circuit. Through analysis, abnormalities are detected in a timely manner and an alarm signal is issued. The principle circuit is shown in Figure 4.

2.3 Data communication and preprocessing technology

The intelligent monitor receives status information from the lock (including opening, closing, first password error, second password error, third password error, etc.), the current value flowing through the electromagnetic actuator coil, and reads the power supply current value of the communication line at that time. The three are combined to form a data block, where the operation status accounts for 1 byte, the power supply current accounts for 2 bytes, and the coil current accounts for 2 bytes. The intelligent monitor is always in a receiving state during communication with the electronic lock. In order to improve communication reliability, this article adopts a repeated transmission method in the communication protocol. The electronic lock sends each set of data 5 times, and the intelligent monitor receives this set of data and uses the law of large number decoding to correct errors, ensuring the accuracy of data reception. In addition, in order to save memory, preprocessing techniques need to be used for the received data. That is, after receiving each data, the data is first compared with the set threshold value. If it is greater than the threshold value, an over limit alarm will be issued; If it is less than the threshold value, compare the data with the same type of data received on the same day, and retain the larger one. The data stored each day is the maximum value among similar data, as shown in the flowchart.

2.4 Intelligent analysis

Intelligent analysis and prediction technology is based on the data blocks received each time, comparing them with the recorded values of similar data before, analyzing the magnitude and trend of current changes caused by this operation, discovering existing problems in a timely manner, and reporting them to management personnel, thereby improving the reliability of the entire system.

3. System software design

The intelligent password lock software uses 51 series microcontroller assembly language to program the intelligent monitor and electronic lock separately. The intelligent monitor software includes modules such as keyboard scanning and LCD display programs, buzzer driver programs, clock modification and reading programs, data communication and preprocessing programs, intelligent analysis programs, and line monitoring programs. The electronic lock software includes modules such as keyboard scanning and decoding program, LCD display program, communication program, electromagnetic actuator driver and detection program, sensor interface program, etc. In the software design process, modular design methods are adopted to facilitate program reading, debugging, and improvement.

The intelligent password lock fully utilizes the software and hardware resources of the 51 system microcontroller, introduces intelligent analysis functions, and improves the reliability and security of the system. It has been well received by users through installation and use in a certain model of safe. In addition, with slight modifications in software and hardware, intelligent password locks can form an intelligent distributed monitoring network, achieving centralized monitoring and management within a certain range. They have broad application prospects in finance, insurance, military important areas, and other security prevention fields.