1ZigBee Technology Introduction With the development of digital communication and computer technology, many short-range wireless communication requirements have been put forward. The network and standardization requirements for wireless technology are gradually appearing in front of people. ZigBee technology is one of them. ZigBee is a short-range, low-complexity, low-power, low-data-rate, low-cost wireless network technology based on the IEEE802.15.4 standard. It is mainly used in various electronic devices with short range and low data transmission rate. Between, thousands of tiny sensors coordinate with each other to achieve communication. ZigBee uses the IEEE 802.15.4 protocol standard released in 2003 as its standard protocol for the physical layer and media access (MAC) layer. The ZigBee Technology Alliance, established in August 2001, provides a unified solution for devices manufactured by different manufacturers to solve their compatibility problems. The network layer of ZigBee technology is developed by the ZigBee Technology Alliance, and the application layer is developed and utilized by users according to their own application needs. There are three different devices in the ZigBee network: a) Reduced power consumption (RFD). In order to reduce power consumption and cost, most nodes in the network are RFDs, called sub-nodes. As the end node of the network, it is responsible for transmitting data to the upper level. b) Full Functional Devices (FFDs), which are responsible for communicating with all sub-nodes under their control, aggregated data, release control or routing information. c) Coordinator, each network has a unique coordinator that is responsible for the management of the entire network. Full-featured devices in the network can act as coordinators, routers, and endpoints, but reduced-function devices can only be used as endpoints. 2 street lights automatically control the working principle of wireless network At present, the problem of low energy utilization rate of traffic lights is widespread in major cities. It is convenient and reliable to use ZigBee technology for street light switch control. Typically, the street light control system includes a microprocessor control system mounted on the street light pole, a control center monitoring system, and a wireless communication system that implements a microprocessor system on the street light pole to communicate with the control center. The system adopts a star wireless network topology to control multiple routes of street lights. There is a coordinator in the system as the monitoring system of the control center. Several FFD devices are used as routing nodes, and RFD devices are used as the end nodes of the system. The network coordinator is responsible for establishing the network and management network, displaying relevant control information, current street lights automatically controlling the condition of the wireless network system, and controlling the state of the entire network power switch. The FFD routing node can be installed next to the road, connected in a string as a relay controller of the wireless node, and can forward the information uploaded by each node of the next level to achieve the purpose of remote control. At the same time it can be used as a microprocessor on the pole to control the opening and closing of the street light. In order to reduce The RFD node is placed at the end of the road as the end node in the system, and it controls its own street light status according to the received wireless signal command. In order to achieve the purpose of energy saving control, a photoresistor is used on both the FFD node and the RFD node to judge the intensity of the light, thereby intelligently controlling the switch of the street light. Hardware and software design of 3 street lights automatic control wireless network The system is a tree-like ZigBee wireless network with routing nodes, which is a wireless network consisting of a coordinator, one or more ZigBee thin functional devices and several routing nodes. Due to the different functions of the devices in the network, there are some differences in the design of the hardware. In this paper, the hardware design of the device is divided into two parts: the coordinator and the full function device. The reduced function device and the full function device use the same solution in hardware. 3.1 Coordinator hardware design In the energy-saving street lamp automatic control wireless network system, the coordinator is equivalent to a main controller. In addition to the function of managing the network, it also needs to display the status of the current network. The hardware part of the coordinator includes a microprocessor (MCU), a ZigBee wireless communication module, a power conversion section, a debug interface, and a serial port section. The serial port and the host computer can be connected to display the status of the entire network. The two switches S1 and S2 are used to control the power switch status of the entire network street lamp. The coordinator device uses wired power supply, and the power conversion circuit makes the input voltage pass through two levels of voltage division. Provides a stable operating voltage. The MCU has two external buttons for controlling the power switch of the entire network. S1 is pressed to turn on the system power, and S2 is pressed to turn off the system power. The MCU in this design uses C8051F020, which is represented by Xinhualong. The MCUs in this series have two enhanced full-duplex Universal Asynchronous Receiver Transmitter (UART), Serial Peripheral Interface (SPI) bus and SMBus/IC. Each serial bus is fully implemented in hardware and can generate interrupts to the CIP-51, so only a small amount of CPU intervention is required. The ZigBee wireless communication module uses the IP-LINK1221-2033 module of Helicomm. The IP-Link1221-2033 module integrates the IEEE802.15.4-compliant RF transceiver (2.4GHz) and SiliconLab's 8051 microprocessor. The IP-Link 1221-2033 module can be used to build a topology including a star, tree or mesh network. The parameter configuration of the IP-Link1221-2033 module before use includes setting the baud rate of the UART, the network node of the module, the node number, etc. The configuration result is saved in the internal non-volatile memory of the module, and then the module enters Data status, preparation of data transmission. Before starting work, set up the ZigBee wireless communication module using Helicom's IP-Link 1221-2X33 configuration tool. In this scenario, the ZigBee module of the coordinator is set as the master node, and each FFD node and the RFD node are placed. The ZigBee module is set as a slave node. 3.2 Hardware Design of FFD Node and RFD Node The difference in functionality between FFD devices and RFD devices is whether they have routing capabilities, so their hardware design is identical. In addition to the power supply and the peripheral portion of the microcontroller, the hardware is identical to the coordinator device. Considering the practicability of the system, FFD equipment and RFD equipment are powered by rechargeable batteries. Due to its low power consumption, ordinary lithium batteries can provide at least 6 months of operating power. On the periphery of the MCU, two LED indicators and a photoresistor have been added. LED1 is used as a power indicator to indicate the switch of the power supply, and LED2 is used to indicate the switch of the street light connected to the node. The photoresistor is used to realize the energy-saving control of the street lamp. It is a special resistor made by the semiconductor photoconductive effect. It is very sensitive to light, and its resistance value can change with the change of external light intensity (shading). It exhibits a high-resistance state when exposed to light; its resistance decreases rapidly when exposed to light. According to the characteristics of the photoresistor, when the power is turned on, when the light is strong, the street light is automatically turned off, and when the light is weak, the street light is automatically turned on, thereby realizing the energy-saving control of the street light. During the process of automatically controlling the wireless network by the energy-saving street lamp, the network coordinator periodically detects whether there is a button press to execute the corresponding power switch command. When the network coordinator is in an idle state, it will listen to the wireless signal in the air to determine whether there is a new node to join the network, and then assign a network address to it. Considering the needs of the site, the coordinator can also control the lighting of a certain section, which is determined by the destination address of the command sent by it. The FFD node is usually in the monitoring state. If the command of the power switch is received, the command is executed, and whether the forwarding is performed, and the switch of the street lamp is determined according to the return value of the photoresistor to reach the intelligent energy-saving control. The function of the RFD node is simpler, just listen and execute commands according to the strength of the light. The communication flow chart of the three devices is shown in Figure 1. 4 Conclusion The level of urbanization in China has been continuously improved, and the schemes and performances of streetlight control have been diversified. With the rapid development of ZigBee wireless technology, the scheme of using wireless networks to control streetlights has gradually attracted people's attention. Due to its flexible networking, convenient control and low cost, the street lighting wireless monitoring system will have a wide application space.
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