Intelligent electricity cabinet locks analysis of key technologies

In the field of preventive security technology, electronic anti-theft alarm electricity cabinet locks instead of the traditional mechanical electricity cabinet locks, to overcome the disadvantage of mechanical electrical cabinet locks password less, poor safety performance, the electricity cabinet locks, whether technically and in performance are greatly improved step. With the development of large-scale integrated circuit technology, especially the advent of the single-chip, the microprocessor smart electricity cabinet locks, electronic cabinet locks, it also introduces intelligent management, expert analysis system and other functions, so that the electricity cabinet locks with high security and reliability, the increasingly widespread application. This article describes the 51 series microcontroller as the core smart cabinet locks, elaborated on its working principle, the basic functional block diagram of the key design techniques and software workflow.

??????Basic principles and hardware components

Smart cabinet locks system consists of intelligent monitoring and electronic locks. They are placed in different places, intelligent monitoring supply the power required by electronic locks and receiver send alarm and status information. With a line multiplexing, shared a two-core cable, improve system reliability, security, power supply and transmission of information.

???The basic principles of intelligent monitoring and block diagram

Intelligent monitoring of the block diagram shown in Figure 1, which consists of a single-chip, clock, keyboard, LCD display, memory, demodulator circuit multiplication and monitoring, A / D conversion, the buzzer unit. Mainly to complete with electronic locks between the communications, intelligence analysis and the security of the communication line monitoring function.

Smart Monitor is always in the receiving state, alarm and status information to receive electronic locks to a fixed format. For alarm information, immediately issued by the LCD display and buzzer sound, light alarm; For status information stored in the memory, and electronic locks comparison, the trends in the state before this moment of history to predict the future The change of state, the corresponding information for decision-making by the LCD display to the duty officer. Intelligent monitoring to establish the communication link with the electronic lock at the same time, by the A / D converter real-time monitoring of flow through the communication line of the power supply current variations, to effectively prevent the damage caused by human factors, ensure smooth communication line.

???Basic principles and block diagram of the electronic locks

Electronic locks block diagram is shown in Figure 2, it is 51 series microcontroller (AT89051) as the core, together with the corresponding hardware circuit, complete the password settings, storage, identification and display, to drive electromagnetic actuator and detected drive current value, the alarm signal is sent, the transmission data, and other functions of the receiving sensor.

MCU receives the type code, and compared with the password stored in the EEPROM, if the password is correct, the drive electromagnetic actuator unlock; If the password is incorrect, allows the operator to re-enter the password, can enter up to three times; if three is not correct, the microcontroller through the communication line to the intelligent monitoring alarm. SCM will each unlock and the electromagnetic actuator drive current value as the basis for state information to the intelligent monitoring and alarm information received from the sensor interface is also sent to the intelligent monitoring, as intelligent analysis.

???Key technologies

In order to improve the security of smart electricity cabinet locks, reliability, the addition to the measures (such as the use of low-power, wide temperature range device) in the device selection in the design also incorporates a number of key technologies.

???Line multiplexing

Intelligent monitoring and electronic locks are placed in different places, the intelligent monitoring supply the power required by electronic locks and receiver send alarm and status information. If communication lines and power supply lines separate ways, is bound to increase the number of cable cores, increased security risks. In this paper, the line multiplexing, only a two-core cable, power supply and transmission of information. The principle shown in Figure 3.

In the transmit side, an electronic lock good data signal will be modulated by the pulse transformer T BOOST sent; data signal at the receiving end, the received pulse transformer T Buck evacuation demodulator, in order to reduce the carrier signal during transmission in the loss. In order to reduce the mutual interference between the communication and power supply, the choke coil L, the choice of the coupling capacitor C to comprehensive consideration.

Set the carrier frequency fo = 400kHz, in order to ensure that substantially all the signal energy transmitted to the receiving side, L = 33.7μH ?-C1 = 0.047.

???Current monitoring technology

Burned in order to prevent vandalism of communication lines and the electromagnetic actuator is too large for some reason caused by the current flowing through the solenoid coil of the current monitoring technology used in the design of smart electricity cabinet locks. The current monitor using the current / voltage converter chip MAX471 MAXIM production. The chip can be measured current I translate into output voltage U and the measurement range, high accuracy, output voltage U and the measured is proportional to the current I and other features. Current monitor output voltage sent to the A / D converter, microcontroller by reading the A / D conversion results, informed of current changes in the line, through the analysis to detect anomalies, an alarm signal. The principle of the circuit shown in Figure 4.

???Data communication and pretreatment technology

Intelligent monitoring receiver locks to status information (including the locks open, closed, password wrong the first time, the second time the password is wrong, the third wrong password), flowing through the electromagnetic actuator coil current value, and read the time lines of communication power supply current value, the combination of the three together to form a data block, operating state 1 byte, 2 bytes of the supply current, the coil current is 2 bytes. In the communication process with electronic locks, intelligent monitoring is always in the receiving state. In order to improve the reliability of the communication in the communication protocol using the repeatedly transmitted, electronic locks for each set of data is repeatedly transmitted five times, the intelligent monitoring received after this set of data, the use of the Law of Large Numbers decoding error correction, to ensure that the the accuracy of the data reception. In addition, in order to save memory data to be received pretreatment technology that each receives a data, the data set threshold, if it is greater than the threshold, the issue limit alarm; less than the threshold, then the data with the date received similar data comparing retention greater. Such daily data stored as the maximum value in the same type of data, and its flow chart is shown in Figure 5.

???Intelligent analysis

Intelligent analysis and prediction technology is based on each received data block, record values ??for comparison with previous similar data analysis caused by the size of the current changes and trends, found that there is a problem in a timely manner, and report management, thus improve the reliability of the entire system.

???System Software Design

Smart cabinet locks software uses a 51 series microcontroller assembly language programming for intelligent monitoring and electronic locks. Smart Monitor software includes keyboard scan module and LCD display program, buzzer driver, clock modification and reading programs, data communication with the preprocessor, intelligent analysis procedures and line monitoring procedures. Electrical cabinet locks electronic locks software keyboard scan and decoding procedures, the LCD display program, communication program, the electromagnetic actuator driver and testing procedures, sensor interface program module. Software design process is modular in design, easy-to-program reading, debugging, and improved.

The smart electricity cabinet locks take full advantage of 51 system microcontroller software and hardware resources, the introduction of an intelligent analysis capabilities, improve system reliability and safety. Safe installation in a model, welcomed by the users. In addition, the intelligent electricity cabinet locks little change in terms of hardware and software can constitute an intelligent distributed control network, a range of centralized monitoring and management, in the field of finance, insurance, military areas and other safety precautions has a broad application prospects.