Design of warehouse intelligent security system based on wireless sensor network

1 Introduction

With the rapid development of sensor technology, embedded computing technology, communication technology, and semiconductor and micro-electromechanical system manufacturing technology, micro sensors with sensing, computing storage and communication capabilities are applied in military, industrial, agricultural and aerospace fields. Wireless network sensors are integrated sensors, actuators, controllers and communication devices. Resource-constrained embedded devices that integrate sensing and drive control capabilities, computing capabilities and communication capabilities. The wireless sensor network composed of these micro sensors can monitor, sense and collect various monitoring object information in the network distribution area in real time, process this information and transmit it to users who need this information. Wireless sensor networks have the characteristics of low price, small size, convenient networking and flexibility. Here, wireless sensor networks are introduced into the security protection system to give full play to the advantages of wireless sensor networks to improve the overall performance of the intelligent warehouse security protection system. The intelligent warehouse security protection system has its own characteristics. Its sensor nodes can be pre-arranged in a targeted manner, so it has a relatively fixed network topology, and network communication and routing protocols also have their own characteristics. Therefore, these issues should be carefully considered when designing the system.

2 Intelligent warehouse security system

Wireless sensor network (WSN) is composed of a large number of cheap micro sensor nodes deployed in the monitoring area, forming a multi-hop self-organizing network system through wireless communication, whose purpose is to collaboratively sense, collect and process the information of the sensed objects in the network coverage area, and send it to the observer. The intelligent warehouse security system network using wireless sensor network technology is composed of infrared sensors, door magnetic switches, temperature sensors, humidity sensors, gas leak sensors, fire smoke sensors, glass breakage sensors and other sensor network nodes. In the security network, a star topology is adopted. Multiple wireless communication modules connected to computers are used as the central nodes of the network. They can communicate with any node in the lower network. The network nodes measure and sample various parameters in the environment, send the collected data to the central node, analyze and process the data and commands sent by the central node, and complete the corresponding operations. Figure 1 shows the overall framework of a single intelligent warehouse security system.

As an extension, the middle node in Figure 1 is used as a small node (a warehouse) to form a wireless sensor network in the entire warehouse area, as shown in Figure 2.

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Sensors play a very important role in the whole system. Commonly used sensors include smoke sensors HIS-07 and NIS-09C for fire detection, temperature sensors TPS-333 and TPS-334, pyroelectric infrared sensors PIS-209S and RE200B for anti-theft alarm, glass breakage sensors BS-02, door magnetic switch sensors FD series, gas sensors MQ-5 and MQ-216 for gas leaks, etc.

3 Design of Wireless Sensor Network Nodes

When designing sensor nodes, miniaturization, scalability and flexibility, stability and security, low cost, etc. need to be considered. The wireless sensor network node of the intelligent warehouse security system is the basic unit and the foundation of the intelligent warehouse security system. The wireless sensor network node must complete the data collection and transmission functions. The power module inside the node is responsible for supplying energy. The battery life determines the node life. Considering scalability and flexibility, commonly used components are selected. The system design adopts modular design, and normal operation is achieved through various functional modules. The sensor node includes modules such as data acquisition, data processing, wireless communication and battery. Figure 3 shows its structure.

3.1 Data processing module

The data processing module is the computing core of the wireless sensor node. All device control, task scheduling, energy calculation and function coordination, communication protocols, data fusion and data dump programs are completed with the support of this module. Therefore, the choice of processor is crucial in the design of sensor nodes. The processor used in sensor network nodes should meet the following requirements as much as possible: small size, high integration, low power consumption and support for sleep mode, as fast as possible, sufficient external general ports and communication interfaces, low cost, and security assurance.

The MSP430 ultra-low power series processors from TI, which are widely used at present, are not only fully functional and highly integrated, but also provide a variety of pin-compatible processors according to the storage capacity, making it easy for developers to smoothly upgrade the system according to the application object. The MSP430F149 processor is used here. The power supply voltage is only 1.8 to 3.6 V, with a 16-bit RISC structure, 125 ns instruction cycle, up to 60 KB Flash ROM and 2 KB RAM. In addition, the device is also equipped with: a 12-bit 200 kS/s MD converter (with built-in sampling and holding), an internal temperature sensor, a 16-bit timer Timer_A/Timer__B with 3 capture/compare registers, 2 serial ports (working in UART or SPI mode), 6 8-bit parallel ports (2 with interrupt capability) and a hardware multiplier. The entire circuit structure is compact and efficient. Its rich addressing methods. Simple kernel instructions. The high processing speed, a large number of registers and data storage give it powerful processing capabilities, and the rich device internal and external interfaces can simplify the entire circuit design, reduce node power consumption and volume, and are very suitable for node design.

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3.2 Wireless Communication Module

The wireless communication module is responsible for wireless communication with other nodes. It exchanges control information and collects data. In addition, the energy consumed by the communication module accounts for a major part of the sensor node, so it is important to consider the working mode and charging energy consumption of the wireless communication module. The modulation mode, data rate, transmission power consumption and operation cycle adopted by the wireless transceiver are all key factors affecting the communication energy consumption. When selecting a wireless transceiver, factors such as power consumption, transmission power, receiving sensitivity, the number of peripheral components required for the transceiver, and the cost of the device should be considered.

The CC2420 wireless transceiver is used here. CC2420 is a 2.4 Hz IEEE 802.15.4 compatible wireless transceiver launched by Chipcon. CC2420 is based on SmartRF03 technology and is produced using 0.18μm CMOS technology with high integration. CC2420 is the first highly integrated industrial RF transceiver that complies with ZigBee technology. Its MAC layer and PHY layer protocols comply with the IEEE 802.15.4 specification and operate in the unlicensed 2.4 GHz frequency band. The short-distance RF transmission system developed using this device has low cost and low power consumption, and is suitable for long-term battery power supply; it also has the characteristics of hardware encryption, security and reliability, flexible networking, and strong anti-destruction, which can provide an ideal solution for sensor network nodes.

4 Signal Acquisition

4.1 Sensor Node Signal Collection

Any object with temperature is constantly radiating infrared rays to the outside world. The surface temperature of the human body is generally 37°C, and most of its radiation energy is concentrated in the 10μm wavelength range. If the infrared radiation of a person is directly irradiated on the pyroelectric infrared sensor, it will also cause temperature changes and output signals, but the detection distance is not far enough. In order to extend the detection distance, an additional optical system is required to collect infrared radiation. Plastic Fresnel lenses are usually used as the focusing system of infrared radiation.

The door magnetic switch sensor is actually a reed switch, which is composed of two metal spring sheets close to each other. The two metal spring sheets are soft magnetic materials. When the reed switch is close to the magnetic field, the metal spring sheets are magnetized, attracting and contacting each other. When the reed switch is far away from the magnetic field, the spring sheets lose their magnetism. Due to the elastic force, the two metal spring sheets separate and send out a signal. When the glass is broken, it will send out a specific sound wave. The glass break sensor mainly alarms based on the sound wave. This method is an auxiliary means to prevent illegal intrusion. Whether to install it depends on the specific situation.

4.2 Fire alarm signal collection

During the combustion of materials, heat (temperature), gas, smoke, flame and other phenomena are generally generated. There are different fire signal detection methods for different phenomena. Ion smoke sensors use the rays generated by radioactive elements and detect the microcurrent generated by air ionization.

At present, most ion smoke sensors adopt single-source dual-chamber operation, that is, one radiation source and two working chambers, namely the reference chamber and the detection chamber. When no smoke enters the detection chamber, the microcurrents of the two chambers remain balanced: when smoke enters the detection chamber, the current of the detection chamber changes. The balance is destroyed, and the sensor sends the detected signal to a positive feedback circuit to generate an alarm.

The temperature sensor detects fire through thermistors and electronic circuits based on the increase in ambient temperature or its rate of change caused by the heat released by the burning of substances.

4.3 Gas alarm signal collection

Liquefied gas (commonly known as coal gas) is a mixture of hydrocarbons with a carbon atom number of 4, and its main component is methane. The use of coal gas sensors can effectively detect whether there is a gas leak and generate an alarm signal.

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5. Software Design of Intelligent Warehouse Security System

The system software design includes two parts: node software and control PC software. The node software is mainly used to collect data, control energy consumption, control node status, etc.

The functions implemented by the control PC software include: receiving data transmitted by the node, displaying and storing it in the host computer through processing subroutines, controlling node power consumption, and real-time dynamic monitoring of the environment. The node software design process is shown in Figure 4, and the control PC software design process is shown in Figure 5.

6 Conclusion

According to the characteristics of wireless sensor networks, a warehouse security system based on wireless sensor networks is designed. The system can monitor the security environment of the entire warehouse in real time. The system is convenient and flexible in networking, easy to upgrade, low-cost, and also suitable for other similar applications. It can effectively monitor a series of unsafe events such as fire alarm, anti-theft, gas leakage, etc. in the warehouse. Once an event threatening safety occurs, the system automatically issues a corresponding alarm. Managers can immediately know and take effective measures to deal with safety accidents urgently to avoid loss of personnel and property. Through the test of a small security system built in a laboratory storage warehouse, the results show that the security system using wireless sensor networks has high security and stability, the system is easy to upgrade, and has broad practical application prospects.