Design of lighting monitoring system in ZigBee classroom

With the development of education, the school's hardware investment, campus lighting system is expanding, in bringing brilliant and convenient at the same time, also brought high costs, management difficulties, slow failure reporting and other problems. A set of efficient lighting monitoring system can greatly save manpower and financial resources. Nowadays, the rapid development of wireless communication technology and automatic control technology provides the technical support for the classroom intelligent Lighting control system, which integrates control of each lamp, remote identification of fault lights, measurement and control of various electrical parameters and selection of various controlling strategies.

1 ZigBee Introduction

2009 Jinan Park Bo Park has achieved a small range based on ZigBee street lamp and landscape lamp monitoring, ZigBee digital transmission technology based lighting monitoring system will be the future of lighting monitoring system is a major development direction. ZigBee Digital transmission is a new wireless communication technology with short-distance, low-speed, low-cost and low-complexity, and has been widely used in the field of near-range wireless network. It is a low power wireless personal area network protocol based on the IEEE802.15.4 standard, can operate in the free 2.4 GHz public band, the transmission rate is 100 kbps, the actual transmission distance of a single node is based on the transmit power size and application mode, in the case of no-occlusion can be achieved in the amount of up to a maximum of up to m above. ZigBee can form a high-reliability mesh network, not only self-organizing, but also self-recovery to ensure the overall stability of the system. ZigBee Wireless module implements a strict power management mechanism, mainly by reducing the free and busy transceiver and data transmission frequency to reduce overhead, such as shutdown and sleep mode. The above characteristics, just in line with the discrete distribution of lighting fixtures for the needs of networking.

The ZigBee protocol defines 3 devices, the full-featured device (FFD), the thin-function device (RFD), and the network coordinator device. The function of the controller RFD in the network is usually the end node, cannot communicate with each other directly, can only communicate with the FFD or the coordinator. In addition to the RFD function, FFD is generally used as a network routing node. The network coordinator is actually one of the FFD, but has more computing power and system resources, it acts as the coordinator in the network Formation, is responsible for establishing the network and connecting with other FfD or RfD.

2 System Design

2.1 Network Structure

ZigBee Wireless module network supports three kinds of topologies: Star, tree, mesh type. In the star structure, the Coordinator plays a coordinating role in the center, all nodes only communicate with the coordinator, the other nodes can be FfD or RFD, and there are multiple FfD and RFD in the tree network, the long-distance endpoint can only go through FFD routing to communicate with the coordinator. , there are multiple routing nodes and end nodes in the network structure, any two routing nodes can communicate with each other, and the terminal node can only communicate with the coordinator through the routing node.

Because the environment in the teaching building is relatively complex, the signal occlusion is more, and the spatial stereoscopic features are shown, so the network topology is adopted. In order to ensure the effective connectivity of ZigBee wireless module network, a ZigBee wireless module routing node is placed in a place where communication effect is better in each floor of the staircase, so as to achieve the routing between two floors. With each classroom as a unit, set up a routing node, so as to avoid a classroom failure caused by the entire network paralysis phenomenon, in the distance between the nearest and farthest from the coordinator of the classroom can be set RFD node. To prevent the signal from weakening through the wall, the node module can be installed in the classroom façade, which is extended to connect the sensors and relays of each light group.

Monitoring Center consists of computer and coordinator, with telemetry, remote control, storage and management of data functions, can be the entire teaching building lighting system real-time monitoring. The Coordinator is responsible for establishing, managing and maintaining the network, receiving the information of each routing node, and then sending the data to the computer through the serial port, displaying the real-time situation in the computer terminal and transmitting the control command. The routing node has the functions of terminal control, information acquisition and automatic alarm.

2.2 Hardware Design

The classroom node is mainly composed of ZigBee wireless module, sensor, Relay and expansion/selection circuit, the hardware structure is shown in 1.

Figure 1 Classroom node hardware structure diagram

The ZigBee Wireless module uses CC2530 as the core of the control circuit, which is a system-on-chip solution specifically for 2.4G IEEE 802.15.4, ZigBee, and rf4ce applications, characterized by a strong network node at very low total material cost. Inside the chip, a 8051 microprocessor and high performance RF transceiver are integrated, and modules such as analog-to-digital conversion, ZigBee RF front-end, and timers are integrated. The system's programmable flash memory can be up to 128KB, with multiple operating modes and short changeover times between operating modes to further reduce energy consumption. and a CC2530 only 21 I/O pins, can not achieve the separate control and acquisition of signal requirements, where the expansion/selection of the circuit to achieve the control of multiple lights or signal acquisition. For classrooms with more light, you can assign two or three nodes.

University classroom in class or self-study in the distribution of personnel, and large area, light everywhere under the illumination is not the same, so each lamp is installed body detector and light sensor for ZigBee data acquisition, microprocessor based on the detection of whether someone and natural light illumination to carry out the switch lamp operation. The design of the human body detector and the illumination sensor is not a design priority.

Wireless signal in the teaching building transmission power and receive signal sensitivity requirements, although adjacent two classroom node distance is very close, but in the corner or upper and lower floors of the place CC2530 not necessarily able to meet the communication requirements, to solve this problem, you can CC2530 The CC2591 RF front-end is added to the working circuit to increase the output power and receive sensitivity, thus achieving the purpose of increasing the transmission distance. The CC2591 uses a power amplifier to increase output power and improves reception sensitivity through a low noise amplifier. It is packaged in a 4mmx4mm QFN16 small footprint with modules that integrate high-performance modules such as power amplifiers, low-noise amplifiers, transceiver switches, unbalanced transformers, and logic circuits. CC2530 RF input/output has a high impedance, differential characteristics, in the design of the end node, the use of the Balun antenna cabling method as a non-equilibrium transformer, and the CC2591 inside itself there is a balun structure of the unbalanced transformer and a matching network, which can be achieved CC2591 to CC2530 Seamless interface.

2.3 Software Design

After the system starts, first initializes and builds the ZigBee network by the Coordinator, after the successful establishment, each node will send data from ZigBee to the coordinator, then transfer to the computer, then save in the database, the administrator can switch the light operation according to the actual situation, With the expansion/selection circuit, each lamp can be specified. Under normal circumstances, the system is in automatic control state. Classroom node in every day after the classroom closed into hibernation to reduce power consumption, after the classroom opened into the working state, the microprocessor polling the sensor output of each lamp, according to the light intensity of each lamp and personnel situation to switch the light control. If an alarm occurs, such as the classroom current is too high, then send alarm information to the Monitoring Center for confirmation and maintenance. The node automation diagram is shown in Flowchart 2.

Figure 2 Classroom node automatic control flowchart

The system adopts C/S mode, with Microsoft VisualStudio2010 as the Monitoring software development platform, C # language, database using SQL Server 2008, host computer software main function is to receive the data transmitted by the serial port in real-time and sub-packet, calculation, processing, Display and save, through the response to the administrator instructions, you can control, configure, query the Terminal Light Festival. The host computer main interface 3 is shown,

Figure 3 Classroom Monitoring Interface

The main functions include: Display and monitoring: to achieve the voltage, current, power and other data acquisition in each classroom, can be selected according to the floor, view current power, electricity, alarm or fault, to achieve the control of the switch and single light switch;

Data query: The node configuration information and each classroom status information are kept in the database, convenient for administrators to query historical data, and can form a current, voltage and other electricity reports and running log reports;

Parameter configuration: including correcting the system time, setting the ZigBee node short address and various alarm parameters, after the administrator set the parameters, the system background will be sent through the coordinator to each node. Classroom Monitoring Interface 3 is shown.

3 Conclusion

This system has two significant advantages: first, control is convenient, the monitoring Center can control to specific each lamp, each lamp state can also be displayed in the control center, but also according to the actual needs of Jacquard flexible control scheme to meet the different scene lighting needs. When a node of the communication network fails, the other ZigBee digital transmission module nodes will not be affected, and the fault node can also be manually switched operation; The second is the low cost, only installs two light sensor, for ZigBee data acquisition real-time external illumination, the whole use ZigBee Wireless module communication, without cabling, Easy to install and no communication charges after operation. The system can effectively realize the scientific and efficient control and resource integration of classroom lighting system, and finally realize the goal of energy saving, which has broad application prospect.

Design of lighting monitoring system in ZigBee classroom