Application of Ethernet Power Technology in Access Control System

Structured cabling is the foundation of all data communication networks today. With the development of many new technologies, data networks are able to provide more and more new applications and services. For example, in places where cabling is inconvenient or the cost of cabling is relatively high, users have begun to consider deploying some network security cameras and other network security devices on the existing Ethernet network architecture.
At present, such new applications have been increasingly accepted by users and have been rapidly developed. All these devices that support new applications require the installation of additional AC power supply devices, especially IP network cameras, access control, etc., which are placed far away from the central computer room, which further increases the cost of the entire network construction. In order to maximize convenience and minimize costs, the Institute of Electrical and Electronics Engineers (IEEE) approved a new Ethernet Power (PoE) standard IEEE 802.3af[1] to ensure that users can use existing structured cabling to provide power for such new application devices.
1 PoE Ethernet Power Supply System
A complete PoE system consists of two parts: the power supply equipment (PSE) and the powered device (PD). The two parts establish information about the connection status, device type, power consumption level, etc. of the powered device PD based on the IEEE802.3af standard, and use this as a basis to control the power supply equipment PSE to supply power to the powered device PD through Ethernet.
The power supply equipment PSE can be an Endspan (Ethernet power supply switch with built-in PoE function) and Midspan (a device with PoE function used between a traditional Ethernet switch and the powered device PD), while the powered device PD is some terminal devices such as wireless LAN AP and IP phone with PoE function.
According to the IEEE 802.3af specification, the connection parameters of the power supply equipment PSE and the powered device PD are shown in Figure 1.

The IEEE 802.3af Ethernet Power Supply standard defines some parameters that must be followed when designing a PoE network:
(1) The operating voltage is generally 48 V DC, but it may be between 44 V DC and 57 V DC, but in any case it cannot exceed 60 V DC;
(2) The maximum current generated by the PSE generally varies between 350 mA and 400 mA. This will ensure that the Ethernet cable will not overheat due to its own impedance;
(3) The above two values ​​make the PSE produce a minimum power output of 15.4 W at its port output. Considering the loss after passing through the Ethernet cable, the maximum power that the powered device PD can receive is 12.95 W.
2 Ethernet Power Supply Working Process
The power supply device PSE is the manager of the entire POE Ethernet power supply process. When the PSE power supply device is deployed in a network, the PoE Ethernet power supply working process is as follows:
(1) Detection process. At the beginning, the PSE device only outputs a small voltage at the port until it detects that the end of the cable is connected to a powered device that supports the IEEE 802.3af standard.
(2) PD device classification. After detecting the powered device PD, the power supply device PSE may classify the PD device and evaluate the power consumption required by the PD device.
(3) Start power supply. During a configurable startup period (generally less than 15 μs), the PSE device starts to power the PD device from a low voltage until it provides a 48 V DC power supply.
(4) Power supply. Provide the PD device with a stable and reliable 48 V DC power to meet the power consumption of the PD device not exceeding 15.4 W.
(5) Power off. If the PD device is physically or electronically removed from the network, the PSE will quickly (generally within 300 ms to 400 ms) stop powering the PD device and start the detection process again to detect whether the cable terminal is connected to the PD device. During the
whole process, some things such as PD device power consumption overload, short circuit, exceeding the power supply load of the PSE, etc. will cause the whole process to be interrupted in the middle and start again from the first step of the detection process.
3 Ethernet Powered Access Control System
As shown in Figure 2, the Ethernet powered access control system consists of a system server, multiple decentralized terminal management computers, network switches, jumpers, access control card reader devices, and electric door locks. The access control card reader device is connected to the switch via Ethernet, which enables plug-and-play network devices without the need for an external power supply, making installation and maintenance easier. The plug-and-play installation method greatly reduces labor costs and enables effective control through online access to the system. When an access control card reader device fails, the system will detect it in time and will not affect the entire system. When a network failure occurs, the access control card reader device can enter an "island state" to operate, reducing the risk of damage and enhancing reliability.

The Ethernet-powered access control system can handle all access control card reader control devices in the network globally, and can remotely control access control card reader control devices with different permissions. Therefore, the configuration of the Ethernet-based access control system is a very flexible and economical networking solution.
The Ethernet-powered access control system can have a real-time self-checking function. For typical faults in the system (such as network disconnection), the central workstation and the access control card reader can both provide sound signals and text alarm prompts. When the system is disconnected from the network, the access control card reader at each point can work independently and can record the card swiping door opening information. When the fault is eliminated, the information will be automatically uploaded. The
Ethernet-powered access control card reader provides an RJ-45 standard interface and uses the TCP/IP standard communication protocol. It can be connected to other systems to form a large intelligent management system. In addition, the system can also open the necessary communication protocols for higher-level integration.

4 Access Control Card Reader Hardware Design
The access control controller schematic is shown in Figure 3.

(1) Microprocessor (MPU): The CPU uses a high-speed 8-bit SST89C516 microprocessor, which contains a 32 KB program area, a 256 B RAM area, and an expandable 64 KB external data area.
(2) It has a contactless radio frequency communication interface and supports contactless IC cards (MIFARE ONE, TYPE A) that comply with the ISO14443 international standard; it can also support dual-interface CPU cards based on MIFARE PRO technology.
(3) It has a built-in large-capacity EEPROM memory with a capacity of 16 KB, which can store 1,000 16 B records and can store stored data for more than 10 years.
(4) It has a built-in Ethernet module that supports network protocols such as TCP/IP and is used to achieve long-distance information transmission (data upload, blacklist download, correction time, parameter download, etc.).
(5) The surface of the door controller can be configured with a 128×64 dot matrix LCD (with backlight) that can display 4×8 Chinese characters (or 4×16 characters, numbers) to display date, time, prompt information, card information, door lock status information, etc.
(6) It has an internal hardware power-off protection real-time clock with an error of no more than 60 s/month, and no millennium bug or other time problems such as crossing the year or month.
(7) It supports IEEE802.3af Ethernet power supply.
5 System overall software design
According to the actual situation, an inductive IC card is used to control the entrance and exit, and the door is opened by swiping the card at the entrance. The computer can monitor in real time, making the entrance and exit management convenient, safe and efficient. The system software module diagram is shown in Figure 4.

This system installs a contactless IC card door controller at each entrance, an exit button at the other end of the exit, and an electric lock (electromagnetic lock or electric bolt lock, selected according to the situation) on the door. These devices and the system server, terminal management computer, and network switch form an Ethernet network to form a stable access control management system. The system's door status, user access control permissions, user information, and smart card registration are all completed by the management computer [2-5].
This system not only "intercepts" illegal cards outside the system, but also records and manages the time and access control points of legal personnel passing through the entrances and exits in the system.
5.1 Entry equipment and process
The entrance equipment is a contactless IC card door controller. When the door controller is in working state, it will scan at a certain frequency. When a smart card is detected, it will process the detected information, calculate the data, and execute command operations. If it is legal information, it will be allowed to pass; if it is illegal information, it will be "intercepted", and a buzzer can be used to sound an alarm and upload it to the system.
5.2 Exit equipment and process
The exit equipment is mainly an exit switch. Simple exit control only needs to provide a switch quantity to the controller. When the exit button terminal of the controller receives a switch signal, the controller will change the state of the door lock output terminal of the corresponding door to realize the switch function of the control door.
The benefits of Ethernet power supply in access control system are obvious to users. Since it only needs to install and support one cable instead of two cables, as the number of devices connected to Ethernet increases, there is no need to provide local power for hundreds or thousands of devices, which will greatly reduce deployment costs and simplify its manageability. In addition, Ethernet power supply end devices will only power devices that need power. Only when the devices that need power are connected will there be voltage on the Ethernet cable, thus eliminating the risk of leakage on the line. The application of Ethernet power supply in access control system allows users to integrate new power supply devices on current Ethernet devices and provide 48 V DC power on existing network cables, reducing the total cost of network construction and protecting investment.
References
[1] International Standard IEEE Std 802.3af[S]. 2003.
[2] Philips. MF RC500 Highly Integrated ISO14443A Reader IC[M]. 2002.
[3] KROWCZYK A, KUMAR V. .NET Advanced Network Programming[M]. Translated by Wu Xuchao. Beijing: Tsinghua University Press, 2003.
[4] Philips. P89C60X2_61X2_2DataSheet[M]. 2003.
[5] FINKENZELLER K. Radio Frequency Identification (RFID) Technology - Principles and Applications of Radio Inductive Transponders and Contactless IC Cards[M]. Translated by Chen Dacai. Beijing: Publishing House of Electronics Industry, 2001.