Research on greenhouse environment monitoring system based on wireless sensor network

In daily life, greenhouse planting is already a common example in people's lives. Traditional greenhouse planting is achieved by arranging complex wires and related control equipment in the greenhouse to control the greenhouse environment. This creates obstacles for activities such as fertilizing crops, and the wires may be broken during these activities, which will cause problems for system communication. The use of wireless sensor networks does not require wiring, which avoids the emergence of related problems and meets the requirements for monitoring the greenhouse environment. At the same time, due to the use of wireless sensor network nodes based on CC2431 for design, the requirements of small size, high integration, low power consumption, fast speed and low cost are met when designing wireless sensor network nodes. 1 Overall structure of greenhouse environment monitoring system The overall structure block diagram of the greenhouse environment monitoring system is shown in Figure 1. The network uses sensor measurement nodes and control nodes with simple execution control functions to form a wireless sensor network. The measurement node is used to measure important environmental data such as air temperature, humidity, and light intensity, and the control node (which can perform related control on temperature and humidity control equipment) is used to receive remote control information from the computer in order to properly regulate the greenhouse environmental parameters. The data collected by the measuring node is transmitted along other measuring nodes in a multi-hop manner. During the transmission process, the monitoring data may be processed by multiple measuring nodes. The information reaches the aggregation node after multi-hop routing. The aggregation node uploads the received data directly to the computer. All data are processed by the computer for complex digital signal processing, and the sensor network is configured and managed through the database, and monitoring tasks and monitoring data are released. Finally, these data can also interact with the remote control center through the Internet, thereby realizing remote monitoring of the greenhouse environment.

2 Introduction to CC2431
CC2431 is a product of TI. It is a true system-on-chip based on the ZigBee/IEEE802.15.4 solution for wireless sensor networks. It integrates CC2420 RF transceiver, industrial standard enhanced 8051 MCU core, 128 KB programmable flash memory, 8 KB RAM, precise positioning engine and other rich on-chip resources. It supports hardware debugging and online debugging based on C51 development environment above IAR7.20, providing powerful and flexible development tools. CC2431 is small in size, low in power consumption and high in integration, which is very suitable for the design of wireless sensor network nodes. It can work in 4 working modes, and the conversion time between working modes is short, so it can meet the requirements of ultra-low power consumption system design. 3 Hardware of sensor network nodes Sensor network nodes are composed of sensor measurement nodes, control nodes and aggregation nodes. The measurement node is responsible for collecting surrounding environment information. The collected environmental information reaches the aggregation node after multi-hop routing, and finally reaches the control center through the Internet. The control node is used to receive remote control information from the computer and adjust the greenhouse environmental parameters. 3.1 Measurement node hardware The sensor measurement node consists of a sensor module, a microprocessor module, a wireless communication module, and a power module. Its hardware structure block diagram is shown in Figure 2.

(1) Sensor module. It is composed of different types of sensor chips and has the ability to sense temperature, humidity and light intensity. The temperature and humidity sensor uses the I2C bus digital temperature and humidity sensor SHTll, which has a small size, low energy consumption, a two-wire digital interface, a temperature range of -40℃～85℃, and a relative humidity range of 0%～100%RH. The light intensity sensor uses TSL2550D, whose power consumption can meet the requirements of low-power system design of wireless sensors, and its bus is also easy to interface with CC2431 . (2) Microprocessor module. It uses the 8051 CPU integrated in CC2431. The integrated CPU has 4 different memory spaces: code area, data area, extended data area and special function register area. Different memory spaces are conducive to the separation of code and data, and improve the CPU's access speed to memory. (3) Wireless communication module ① Sensor network nodes consume a lot of energy during communication. Choosing a low-power wireless communication chip will effectively reduce the energy consumption of the communication module. CC2431 is a low-power communication chip that complies with the ZigBee standard. It has the functions of fast wake-up and searching for external devices. It can make the node stay in sleep mode more often and save power consumption. Moreover, its parameters such as channel frequency and power consumption can be flexibly set. The antenna of CC2431 communication module takes into account the requirements of wireless sensor network communication quality and adopts a unipolar antenna. The unipolar antenna requires a "balanced-unbalanced transformer" between the differential output and the antenna. ② The power supply of the wireless sensor network node is a battery-powered system. The battery selected is a lithium battery specially used for mobile phones. In order to make the system work for a long time when powered by batteries, the energy saving of the node should be considered when designing the power module. CC2431 provides 4 power management modes: PM0, PM1, PM2 and PM3. The reasonable use of these 4 modes can effectively reduce the energy consumption of the node. ③ The LED light is used to display the operating status of the sensor node. (4) Power module. Provides energy for other modules. 3.2 Control node The control node consists of a driver module, a microprocessor module, a wireless communication module and a power module. The driver module can perform relevant control on temperature control, humidity control and other equipment. Its hardware structure block diagram is shown in Figure 3.

3.3 Hardware Research of the Aggregation Node
The aggregation node consists of a microprocessor module, a wireless communication module, a memory module, an Ethernet interface module, a serial interface module, and a power module. Its hardware structure block diagram is shown in Figure 4.

(1) The memory module consists of an AT45DB041 chip produced by Atmel, which is directly connected to the CC2431 SPI input terminal. The chip integrates 2 046 pages × 264 B Flash storage units for storing important historical data of sensors.
(2) In order to provide an Ethernet access channel, DM9161 is used as the physical layer interface of Ethernet in this design. DM9161 is a low-power, high-performance CMOS chip that supports 10 MB/s and 100 MB/s Ethernet transmission. It plays the role of encoding, decoding, inputting and outputting data, so that the aggregation node can be easily connected to the Internet for remote control.
(3) The serial interface module consists of a low-power MAX3232 and a COM mother port. The CC2431 serial port is connected to the MAX3232 for level conversion and communicates with the computer through the COM port.
(4) Since the aggregation node needs to integrate and process the data collected by all the collection nodes and needs to transmit the data to the computer over a long distance, the energy consumption is relatively large. Therefore, its power supply is powered by the conversion from the mains.
(5) The LED light is used to display the running status of the aggregation node.
4 Porting of TinyOS operating system
Embedded operating systems can simplify the development of embedded systems, ensure the stability and reliability of program operation, and facilitate program maintenance and updating. However, since the wireless sensor network node is a small embedded system with very limited hardware resources, it is necessary to efficiently utilize its limited memory, processor and communication module, and minimize system energy consumption and extend the service life of the node. Therefore, traditional embedded operating systems cannot meet its requirements. Based on this, this paper ports the operating system TinyOS developed for the characteristics of wireless sensor networks.
4.1 Introduction to TinyOS
TinyOS is a typical wireless sensor network operating system developed by the University of California, Berkeley. Applications based on TinyOS can be developed using the nesC language. The design goal of TinyOS is small code size, low energy consumption, high concurrency, good robustness, and adaptability to different applications. It adopts lightweight thread technology, event-driven mode, componentized programming, etc., making it an operating system for wireless sensor networks. TinyOS provides Main accessories, as well as perception components, execution components, communication components and hardware abstraction components for certain hardware. Based on these components, users can customize and develop application components, and then connect all components to form the entire application.

4.2 Porting of TinyOS
There are many versions of the TinyOS operating system. The one to be ported is TinyOS 2.0, and the compiler used is Keil. TinyOS 2.0 must work on the Linux platform, and Keil is a Windows software. Therefore, you need to install a software that simulates the Linux development environment on the Windows platform - Cygwin. The following are the specific steps for porting:
(1) Install SmartRF04 Flash Programmer, Keil, Java 1.5 JDK, and Cygwin software;
(2) Download the installation package of the compiler tool required for TinyOS development;
(3) Start Cygwin and install the downloaded compilation tool installation package under Cygwin;
(4) Install TinyOS 2.0.
Unzip the downloaded TinyOS 2.0 installation package and copy the unzipped tinyos-2.0-contrib folder to the Cygwinopt directory. At this time, the TinyOS development environment has been set up. All examples are under tinyos-2.0-contrib/diku/common/apps/. Take BlinkNoTimerTask as an example. In Cygwin, enter: cd/diku/common/apps/BlinkNoTimerTask, then press Enter and enter: make cc2431em. If everything goes well, TinyOS will be compiled to generate the app.hex file. Just burn this file into the microcontroller.
(5) Burning
Plug in the emulator, open the SmartRF04 Flash Programmer software, select the app.hex file under the System-on-Chip tab, and then select "Perform actions" to burn it in sequence. After the burning is successful, TinyOS is successfully ported to CC2431 . 5 Software Design of Sensor Network Nodes The main function of the sensor measurement node is to receive the data collection instructions from the PC, collect data, and then send the collected data through the wireless channel. The function of the aggregation node is to create a wireless network, configure the network node properties, receive the data collected by the sensor measurement node, and then upload it to the computer through the serial port. The sensor measurement node program structure flow chart is shown in Figure 5, and the aggregation node program structure flow chart is shown in Figure 6.

In agricultural production, with the emergence of large-scale operations, many greenhouses may be built. According to the design of the application, a wireless sensor network is built in each greenhouse. Since the environment in the greenhouse is similar, the functions and technologies of the wireless sensor network in each greenhouse are also the same. If all greenhouses are managed uniformly through the computer in the control center, the work efficiency can be greatly improved, making greenhouse management more scientific and control simpler, thereby achieving the ultimate goal of increasing crop yields, improving quality, adjusting growth cycles, and improving economic benefits. The wireless sensor network nodes introduced in this article have the advantages of low power consumption, small size, reliable operation, and easy expansion. The greenhouse environment monitoring solution based on this wireless sensor network will have a good application prospect.
References
[1] Liu Yuying, Shi Wangwang. Design of wireless sensor network based on CC2430 temperature and humidity monitoring [J]. Microcomputer Information, 2009, 25(10):130-131. [2] Li Haosheng, Wang Ruchuan, Sha Chao. Design of wireless sensor network node based on CC2431 [J]. Electronic Engineer, 2008, 34(12):63-67. [3] Zhuang Xiong, Yang Yongming, Ding Wei. Design of wireless sensor network node based on CC2431 [J]. Application of Electronic Technology, 2008, 34(6):98-101. [4] Zhang Baohua, Li Shining, Teng Wenxing, et al. Research and design of greenhouse measurement and control system based on wireless sensor network [J]. Microelectronics and Computer, 2008, 25(5):154-157. [5] Song Baoye, Xu Lin. RF chip CC2431 with positioning engine [J]. Microcontrollers and Embedded Systems Applications, 2007(11):44-46. [6] Wang Shu, Yan Yujie, Hu Fuping, et al. Theory and Application of Wireless Sensor Networks[M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2007.