Currently, there are a large number of unconnected auxiliary subsystems of Supervisory Control and Data Acquisition (SCADA) systems in substations, such as lighting systems, water supply and drainage systems and other small systems, as well as auxiliary heating and moisture removal devices that operate in isolation. These are controlled by relays or programmable Due to its importance to the main substation equipment and cost considerations, the subsystems or devices controlled by the logic controller (Programmable LogicController, PLC) do not realize remote control or monitoring. However, as the substation becomes less manned and unmanned, With the continuous advancement of technology, how to realize remote monitoring of these subsystems or devices at low cost has increasingly become an urgent problem to be solved. The Internet of Things (|nternetOfThings) uses radio frequency identification, infrared sensors, global positioning systems, laser scanners and other information sensing equipment to connect any items to the Internet according to agreed protocols for information exchange and communication to achieve intelligence. A network that can identify, locate, track, monitor, and manage information. It has been widely used in many fields. This article introduces the software and hardware system design and typical application scenarios of a low-cost wireless relay module based on the Zigbee wireless communication protocol of the Internet of Things. Due to its wireless transmission, low cost and self-organizing network advantages, it can well solve the auxiliary subsystem The problem of remote monitoring can also be extended to many fields such as smart homes.
1. Zigbee wireless network
ZigBee is a short-distance wireless communication technology with low power consumption, low transmission rate and simple architecture based on the IEEE802.15.4 protocol. Its application in the field of automatic control is attracting more and more attention from the industry. Zigbee transmission distance can reach 100 meters, the frequency band used is free 2.4GHz, and the transmission rate is 20~250kbps. Compared with various existing wireless communication technologies, ZigBee technology’s low power consumption and low speed are the most suitable standards for sensor networks, which will become the main development direction of Zigbee technology in the future. In addition, Zigbee has the characteristics of low cost, simple structure, and low power consumption, which makes the network composed of Zigbee technology have many advantages such as power saving, reliability, low cost, large capacity, security, and strong self-healing. The mesh network structure based on Zigbee technology is more flexible and free when networking and selecting network paths. Therefore, ZigBee technology has many advantages over the Internet of Things market. 1.1 ZigBee network device types As shown in Figure 1, there are three logical device types in a ZigBee network: c is the coordinator, R is the router, and E is the terminal device. A Zigbee network contains a coordinator node, multiple routers and terminal device nodes. As the organizer of the entire network, the coordinator is the first device of the network. Usually the coordinator selects 1 channel and 1 network identifier (PANID), and then starts the network. During the process of the coordinator starting the network, it can be used to assist in establishing network security and application level binding, allowing the coordinator to automatically transfer after establishing the wireless network. Router type node runs. Each distributed node within the wireless network can operate autonomously. The router performs network management, multi-hop routing and low-power end node management functions. The router node allows specific devices to join its network and participate in the forwarding and control of Mesh network data. At the same time, the router node can have its own node data application. An important function of a router node is to wake up end nodes or subnetworks that have gone dormant due to low power consumption requirements through data. The terminal device does not have specific network responsibilities, it is usually a specific network application link. The battery-powered end node has a hibernation function, and the power consumption is kept to a minimum during hibernation until awakened by a specific router node.
1.2 The ZigBee networking process is shown in Figure 2. The ZigBee network has self-organizing network characteristics. When the coordinator completes the network establishment and the network runs automatically, any node with the same PANID in the network can join the ZigBee network on its own and communicate with other network nodes. communicate
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