ZigBee is an emerging wireless communication technology that has a short distance, low power, low cost and low data rate. The characteristics of smart home are small network transmission data, low, but the network is required, but the network is real-time, the delay is short, the access is convenient, the system is long, and the scalability is strong and the later maintenance is simple. This undoubtedly make ZigBee technology a first choice, because the main application of ZigBee technology is industrial control, electronic equipment and building automation. Its characteristics determine ZigBee technology to meet the needs of smart home systems.
System overall solution
Smart home system networks can be roughly divided into external networks (Internet), internal networks (ZigBee self-network) and home gateways. Among them, the home gateway is a core part that transplanted the BOA server porting on the Tiny6410 development board as a home gateway, which is responsible for the connection and protocol conversion of the home internal network and external network. Here, the internal network is introduced, the internal network here is Zigbee self-assembled network, which uses a tree or star network topology according to the home layout. ZigBee Self-Network includes each terminal node that matches the relay control of various electrical switches, temperature and humidity sensors, and other families need to be monitored, so that remote monitoring functions are reached. From a communication perspective, each node is a terminal that wireless communication is performed through the ZigBee protocol. There is no consideration of different protocol conversion problems in the internal network.
The overall structural block diagram of the smart home system is shown in Figure 1.
Figure 1 Overall Structure of Intelligent Home
2 intelligent home gateway design
The home gateway designed in this article will handle data from the Internet, requiring hardware for home gateways to provide powerful network support, while needing to support TCP / IP protocols, therefore require operating systems to support multitasking. The home gateway is a functional entity that is composed of hardware and software, transplanting the BOA server to the ARM development board as a gateway. BOA is a single task, a small HTTP server, an open source, superior performance, especially suitable for applications in an embedded system, and a home gateway structural diagram is shown in Figure 2.
Figure 2 Structure of Home Gateway
The BOA server is relatively simple. The main steps include: decompression on the development host and cross-compiling, then configure the server, mainly modifying the Boa.conf file, you can transfer it after the configuration is completed, the transplant is successfully installed You can run the BOA server software. Running the BOA server on the built-in embedded platform and serial read-write applications, combined with static web pages and dynamic CGI programs allows commands to reach embedded servers from the web. The CGI technology can realize the call of the web server and serial port reading, thereby reaching data (that is, command) from the webpage to the server to write such a positive process of the Zigbee home internal network through the serial port. After the command is sent to the ZigBee home internal network, read and write the application read the feedback data of ZigBee (mainly the LED status, and the sensor reading), and read the SQLite database stored in the ARM board for later CGI programs. Call and display it on the web.
3 Zigbee Home Internal Network Design
From the perspective of development trends, wireless self-networking is the future development direction of smart home network. ZigBee is an emerging near-distance, low complexity, low power consumption, low data rate, low-cost two-way wireless communication technology. It is a technical proposal between wireless marking techniques and Bluetooth, which is one of the lowest power and cost of technology relative to existing various wireless communication technologies, ZigBee will be one of the lowest power and cost technologies. The scale of intelligent home, that is, the amount of data transmitted in the network is not large, and the node is more equal, and the home internal network topology is used to select the star structure.
The hardware design of the ZigBee node is simpler. This node uses TI's CC2430 chip to integrate the ZigBee RF (RF) front end, memory, and microcontroller on a single chip. It uses an MCU (reinforced 8051) with 128 kB programmable flash memory and 8 kb RAM, further contains ADC, Timer, AES128 Syneric Processor. The data acquisition unit uses a temperature and humidity composite sensor DHT11 containing the calibrated digital signal output.
The software system of the home internal network system is designed with the development environment as the development environment in IAR System's IAR Embedded Work Bench, with TI's Zstack protocol stacks. The ZigBee protocol stack 2006 is based on the IEEE 802.15.4 standard, the protocol's outstanding advantages are: strong networking capacity, wide adaptation, high reliability, good energy saving. Zstack protocol stack consists of a program file and library function that implements different functions of the ZigBee protocol.
4 zigbee protocol
The ZigBee protocol is the foundation of the home network. It can be said to be the core, and its underlying is IEEE 802.15.4, including physical layer and MAC layer. ZigBee works in 3 frequency bands of 868 MHz, 915 MHz and 2.4 GHz, and truly need to care about the network layer and application layer. The main function of the network layer is the routing, the routing algorithm is its core, excellent algorithm can save ZigBee's energy consumption and shorten the delay. The network layer is the application layer, which mainly specifies some functions related to the application, that is, the object of the developer directly deals.
The protocol stack workflow used in this system is shown in Figure 3.
Figure 3 ZigBee Home Internal Network Structure Map
In the intelligent home Zigbee internal self-container, the coordinator is the most critical. It is the "brain" on the smart home system is the home gateway, the next Zigbee self-assembly network other routes and terminal devices, and play a function of wireless interface . As shown in FIG. 3, the coordinator receives the application from the serial port and parses it, parses the command to obtain the terminal address and control command to control, and then send the resolved new control command to the specified terminal node, find The location mode is a point-to-point mode, transmitted by the network address allocated by the coordinator, and the command structure in the ZigBee in the network is shown in Figure 4. After receiving the command, make a corresponding action and feed back its own state to the coordinator, the coordinator will automatically send back to the home gateway through the serial port after receiving the feedback data, which is the embedded server, and is read by the application. The above is the workflow of the Zigbee home internal network.
Figure 4 Command structure
This paper realizes the remote control function of the smart home monitoring system. The entire system architecture is simple, that is, an embedded home gateway and a ZigBee home internal network, which is fully functional, and can increase or decrease the sensor according to the actual situation and personal needs to save costs. Any family provides tailor-made smart home monitoring services. The system can add equipment nodes at any time according to the changes in the home environment, and the installation is convenient, and the user-friendly control of intelligent homes is realized. This technology combines web technology with embedded techniques and expands, and add more features to the sensors of this project, which can also be widely used in various fields in industrial, agriculture and business.
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Source: Wiku Electronic Market Network
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