With the acceleration of urbanization in China and the widespread popularity of the Internet, people are increasingly demanding for home safety [1,2].
Due to the fragmentation and inefficiency of the existing access control system, this topic adopts the form of networking to design the access control system. Through the use of STM32F chip and other equipment, the overall design of a safe, linkage and efficient networked access control system. Entrance guard system is a new type of public safety management system, which integrates computer automatic identification technology and modern safety management measures. It is an effective way to realize safety prevention management at the entrance and exit of residential area, and provides convenience and safety for owners and staff.
Therefore, the development of a linkage, efficient and reliable security system has become an urgent need. This topic focuses on the detailed research and elaboration of the hardware circuit design of the networked access control controller. The networked access controller is used to connect the cell bus or the cell gate to the system bus. Its specific functions include bus isolation, signal forwarding, audio and video channel switching, signal amplification and matching. The unit gates are connected by cascaded networking controllers to form a unified management network. The hardware functions such as communication, information storage, processing and storage of the networked access control controller are realized. With the advantages of strong anti-interference ability, stable operation, low cost and strong linkage, the controller has a wide application space. Connected between the cell bus or the cell gate and the system bus, its functions are bus isolation, signal forwarding and audio channel switching, video channel switching, amplification (bidirectional) and matching. Through the cascade networking controller, the unit gates are connected to form a network to form a unified management of the area. Video signals of cell doors, cell doors and lobby managers are amplified and switched to the video signals in the central corridor and connected directly to the corridor video bus. Video signals from the network bus are amplified and switched to the unit bus video line. Complete the switching of the audio signal (two-way signal) of the unit entrance machine, the district entrance machine, the lobby management machine, the management center machine and the corridor. The signal of the forwarding unit bus is sent to the system bus, and the signal of the system bus is sent to the unit bus. The networked controller, as a channel device, automatically identifies the relevant forwarding signal.
Setting, viewing and address setting of relevant parameters, through the unit gate machine or community gate machine connected with it (without dialing switch). Video gain compensation achieves video gain adjustment or automatic gain adjustment by overlapping cap to select distance (500, 300, 200 m). The networked controller also has two video gain adjustment caps, which correspond to two video channels from host to system bus and from system bus to indoor computer respectively. Adjusting the gain can improve the video transmission distance. That is, the indoor computer should be able to call the lobby management machine; the indoor computer should be able to call the center; the alarm information should be able to report; the center should be able to query the photos. The network controller uses STM32F103RBT6 as the MCU of the controller. With the same series of products have good hardware compatibility, the internal integration of CAN controller, at the same time has 128KB FLASH and 20KB RAM. The three working modes can be freely selected by ISP. The network controller system structure chart is shown in Fig. 1. This design mainly controls other devices through MCU: the camera and other devices provide access control system information to help surveillance personnel improve security level. RS485 bus adopts balanced transmission and differential reception, so it has the ability to suppress common mode interference. RS485 bus network system communication has high reliability [5]. So this section uses RS485 bus. The control unit is mainly the interface circuit of the controller, including 485 interface circuit design and CAN bus interface circuit.
SP3485E is a low-power 485 bus transceiver chip with half-duplex interface chip. Its truth table and pin diagram are shown in Figure 2. Interface circuit: 485 interface circuit uses half-duplex interface chip SP3485E as transceiver chip.
As the bus branch of RS485 communication interface in the corridor, it is connected to the main equipment of RS485 communication to realize mutual data communication and mutual control, including intercommunication, monitoring and other functions. The terminal matching resistance R88 is 120_. It judges whether RS485 bus branch is connected to terminal matching resistance by overlapping JP3. This topic uses CAN interface circuit to replace RS485 bus which is most commonly used in access control system. Compared with RS485 bus, CAN always wants to have better reliability and flexibility, and CAN chip is cheap, simple and reliable technology, performance is better than RS485. To sum up, thermostatic element this topic uses CAN bus [6]. The interface circuit of CAN adopts TJA1051T/3 chip. As the bus branch of the CAN communication interface in the controller, the data communication and control are realized on the main equipment connected to the CAN communication. The terminal matching resistance R89 is 120_. The resistance R93 and R99 in the circuit are current limiting input resistors, which protect TJA1051T/3 with a design resistance of 10. The circuit diagram is shown in Fig. 4. As a vital power supply, this topic uses network control to provide power supply voltage to the whole system through 35V switching power supply, and gets 12V voltage through MC34063 power management chip, which provides working voltage for video amplifier and relay in audio and video control circuit. The power supply for 485 transceiver and CAN transceiver is supplied by 5V voltage obtained from 78M05 power management chip. The latter uses TLV1117-3.
3 power management chip to get 3.3V working voltage to power the CPU.
The peripheral circuit includes crystal oscillator circuit and reset circuit. Crystal oscillator circuit: The grounding capacitance and shunt resistance are different for different crystal oscillator frequencies. This design uses 20 pf capacitance and 105_resistance.
The design circuit is shown in Figure 6. In order to prevent data loss caused by random power outage, the reset circuit of this subject adopts MAX813L watchdog reset chip [7].
In order to prevent the influence of external interference factors, the manual reset pin/mr is pulled up. The level is determined to be stable. The main purpose of this circuit design is to prevent the lack of memory in MCU. Extended FM25CL64,64-bit nonvolatile ferroelectric random access memory.
With SPI fast serial peripheral interface protocol, the maximum bus transmission speed can reach 20M/S, and it has perfect write protection function. EEPROM [8] can be directly replaced in hardware. The main purpose of this part is to prepare for reserve. JTAG interface is used for Flash programming method.
According to the boundary scan function provided by JTAP interface, the JTAP interface timing is simulated by PC parallel interface, and the system program memory is programmed by microprocessor JTAP interface [9].
It is used for in-chip testing and system simulation and debugging. In order to prevent uncertain interference in practical application. We do pull-up and pull-down processing for their signals respectively. The specific circuit diagram design is shown in Figure 9. The controller adopts a topological structure for audio and video. The high frequency transformer is added to the audio processing of the corridor unit and the Internet part to isolate the coupling effect. In order to alleviate the load pressure of MCU, the relay driving circuit is designed by VLN2003A chip. This paper designs an access control system with high efficiency, safety and linkage by means of networking. According to practical experience, the controller uses RS485 bus as communication interface circuit, TJA1051T/3 chip as CAN interface circuit, MC34063 power management chip to improve security, and designs MCU peripheral circuit design and external extended RAM. In addition, JTAG interface is added to Flash programming method.