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System master plan
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1. Function introduction
The system consists of three types of equipment: terminal nodes, routers, and network coordinators (gateways). Take the warehouse as the unit to cover the wireless sensor network. The terminal node collects the sensor data and sends it to the network coordinator through the router. The data enters the upper computer for analysis and processing. The node is its own independent collection subsystem, which can complete data collection, data storage and data display functions on the node. The system is based on the principles of high efficiency, low cost, and low power consumption. It is a smart wireless sensor network system based on ensuring accurate data transmission. It is suitable for various warehouses, buildings and home applications.
2. System features
1) Low power consumption. In the low-power standby mode, two AA batteries can support a node to work for 6 to 24 months, or even longer.
2) Low cost. By greatly simplifying the protocol, the requirements for the communication controller are reduced. According to the predictive analysis, using the 8051 8-bit microcontroller to calculate, the sub-function nodes are as few as 4KB of code, and ZigBee is free of protocol patent fees.
3) Low rate. ZigBee works at a communication rate of 250kbps to meet the application requirements of low-rate data transmission.
4) Close range. The transmission range is generally between 10 and 100m, after increasing the RF transmission power, it can also be increased to 100m-1km. This refers to the distance between adjacent nodes. If through the relay of routing and communication between nodes, the transmission distance will be farther.
5) Short time delay. ZigBee’s response speed is relatively fast. Generally, it only takes 15ms to switch from sleep to working state, and it only takes 30ms for nodes to connect to the network, which further saves power.
6) High capacity. ZigBee can adopt star-shaped, sheet-shaped and meshed network structures. One master node can manage several sub-nodes. At most one master node can manage 254 sub-nodes. At the same time, the master node can also be managed by the upper network node, which can form up to 65,000. A large network of nodes.
7) High security. ZigBee provides a three-level security mode, including no security settings, the use of access control lists (ACL) to prevent illegal access to data, and the use of symmetric passwords with advanced encryption standards (AES128) to flexibly determine its security attributes.
8) License-free frequency band. Use direct sequence spread spectrum in the industrial, scientific and medical 2.4GHz (global) (ISM) frequency band.
1. Terminal node
Features
SHT11 is a digital sensor that uses an IIC interface. The module periodically reads out the temperature and humidity data collected by the sensor through the IIC interface, and transmits the temperature and humidity data to the router via RF. If there is sensitive data, it is transmitted to the gateway in real time. The temperature can also be collected in real time by pressing the button and displayed on the LCD. It has a power detection function, and the voltage is lower than 2.3V and an alarm signal is automatically issued to prompt the replacement of the battery. Battery alarm can be wireless alarm or terminal alarm. The node works in the dormant state most of the time, and enters the high-speed working state only when collecting data and transmitting data.
2. Router
Features
Responsible for the communication coordination, routing and link establishment and removal of data in the network. The router works at a high speed for a long time and requires DC power for a long time continuous power supply. It is mainly used as an intermediate link between the network coordinator (gateway) and the terminal node. A power amplifier is added to the RF part of the router to ensure the long-distance communication reliability of the project.
3. Network coordinator (gateway)
Features
Mainly responsible for communication coordination, routing planning, and routing table records. As a gateway, the data in the ZigBee network and the data of the host computer system are exchanged, and the communication is coordinated. The router can choose RS232 interface or TTL to USB interface to connect directly with the upper computer, and send the collected data to the upper computer database or terminal software in real time.
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