Design of universal agricultural monitoring system based on MIPS

Introduction
Ubiquitous computing, also known as ubiquitous computing and popular computing, emphasizes ubiquitous computing that is integrated with the environment. In ubiquitous computing, computers disappear from people's sight, and various embedded devices are used as the core of computing. Through sensors and wireless networks, users can obtain and process information at any time, any place, and in any way. The combination of ubiquitous computing and information agriculture has promoted the development of facility agricultural production mode. In this mode, the system summarizes and calculates according to the acquired data, and adjusts the environment of the agricultural production site. This has, to a certain extent, gotten rid of the long-standing excessive dependence of crop growth on the natural environment, making crop growth high-yield, high-efficiency, and high-quality. Its development level reflects the level of agricultural modernization in a country. This paper uses the JZ4755 and PIC32MX4 series processors of the MIPS architecture as the core to develop a data acquisition, analysis, monitoring and early warning system in ubiquitous agriculture. The system realizes the acquisition and calculation of environmental data under low power consumption and small volume conditions, and can analyze and process the acquired data.

1 Overall structure of the system
The whole system consists of two main parts: branch monitoring points and main control terminals. The branch monitoring point uses PIC32MX460 as the processing unit, and the peripheral devices include light sensors, temperature sensors, humidity sensors, etc. Its functions include real-time monitoring and recording of environmental data such as current light intensity, temperature, and humidity. The main control terminal uses the domestic JZ4755 processor as the core, and the peripheral devices include network communication module, SD card storage module, GPRS communication module, etc. Its functions are to integrate the data obtained from each branch monitoring point, give decision-making opinions based on the growth law of crops, and store the data recorded in each stage in the SD card module; the main control terminal also has a built-in Web server. When connected to the network, users can query the current status of the system anywhere. When the crop growth environment is abnormal, the main control terminal can also send warning text messages to users through the GPRS communication module to avoid greater losses. The information exchange between the main control terminal and the branch monitoring point is completed through 433 MHz wireless communication, which not only avoids the cumbersome wiring brought by wired communication, but also has a faster data transmission rate and good stability. The overall structure diagram of the system is shown in Figure 1.

Compared with the currently popular embedded processors, the MIPS processor has the characteristics of low power consumption and high performance.

2 System Hardware Design
The hardware design of the entire system consists of two parts: branch monitoring point hardware design and main control terminal hardware design.
2.1 Branch Monitoring Point Hardware Design
The main task of the branch monitoring point is to complete the collection and transmission of temperature, humidity, and brightness data at each monitoring point. Its working environment is relatively complex, and the stability requirements of the system are also high. Therefore, the PIC32MX460 series chip is used as the main chip. PIC32MX460 is a low-power, high-performance processor based on the MIPS core produced by Microchip. It has an integrated hardware watchdog to ensure that the system can be reset in time when an error occurs. The chip is rich in resources and has complete documentation, which is convenient for development, design and application.
DHT11 is a widely used digital interface temperature and humidity integrated sensor. Its humidity measurement range is 20% to 90%, the temperature measurement range is 0 to 50℃, and the measurement accuracy is 5%, which fully meets the needs of this system. DHT11 adopts a single bus data transmission structure, which is convenient for connection with various MCUs, and the signal transmission distance can reach more than 20 m. In order to accurately collect the current environment temperature, each branch monitoring point uses 3 DHT11 to collect data simultaneously, and then calculates the average value. For the perception of external environment light intensity, the system uses a new single-chip photometric sensor BH1750, which is a single-chip digital light sensor with excellent spectral sensitivity characteristics developed by ROHM to meet the requirements of portable machines. It uses a simple I2C bus interface to connect to the MCU. The hardware schematic diagram of the branch monitoring point is shown in Figure 2.

It should be noted that the PIC32MX460 chip has an I2C bus interface (pins 36 and 37 of the chip respectively), which can be directly connected to other circuit interfaces. Since the electrical characteristics of the I2C bus protocol stipulate that the drain is open, a 10 kΩ pull-up resistor is required here, otherwise the bus will not be able to output a high level. The single bus structure used by DHT11 is relatively simple. The PIC32MX460 chip GPIO is used to simulate the single bus protocol and connect to it. When connecting, a 10 kΩ pull-up resistor is also required to avoid external interference with the signal. [page]

2.2 Hardware Design of Main Control
Terminal The main control terminal uses JZ4755 as the core processing unit, and the external circuits include network interface circuit, SD card storage circuit, 4.3" LCD and 2.4G wireless sensor. JZ4755 is a MIPS architecture processor based on the innovative XBurst dual-core CPU micro-architecture produced by Ingenic, with a main frequency of 360 MHz and supporting multimedia instruction set. It supports a wide range of peripheral types, with 2 I2C bus controllers, 1 SPI controller, 1 I2S controller, 1 RS232 serial port, 2 SD/MMC interfaces, etc. The chip has complete documentation, BSP and technical support. While achieving high performance, the price of this chip is very low, only 20 yuan per 100 pieces, which effectively reduces the cost of the system. JZ4755 is connected to the LCD screen through the RGB interface, and the interface circuit between LCD and JZ4755 is shown in Figure 3.

JZ4755 and SD card are connected through the SD[O] pin on JZ4755. The interface circuit between SD card module and JZ4755 is shown in Figure 4.

Since the JZ4755 chip does not have an integrated network controller, this system uses the 8686 Wi-Fi module launched by MarVell to expand its wireless network connection. The module is connected to the JZ4755 through the SDIO2 interface. Each branch monitoring point is connected to the main control terminal through the LSDRF4717M04/433 MHz wireless module. This module is a high-performance RF transceiver based on TI's RF integrated chip CC1100E. It can be widely used in short-distance wireless communication fields in various occasions. It has the characteristics of small size, low power consumption, long transmission distance, and strong anti-interference ability.

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3 System software design
The system software consists of two parts: branch monitoring point software and main control terminal software.
3.1 Branch monitoring point software design
Each branch monitoring point mainly completes data collection and transmission. After the system completes its own initialization, it will initialize all peripheral devices, including the initialization of the DHT11 temperature and humidity module, the initialization of the BH1750 light sensor module, and the initialization of the LSDRF4717M04. After all peripherals are initialized normally, the branch monitoring point begins to poll each peripheral module
to obtain real-time environmental information, and performs some simple calculations based on this information to determine whether the obtained data is reasonable. If reasonable, it will be recorded in the memory. After each polling is completed, the branch monitoring point will check whether the "transmit" command of the main control terminal is received through the LSDRF4717M04 module. If it is received, the stored environmental data will be sent to the main control terminal, otherwise the next polling will be performed. The software flow of the branch monitoring point is shown in Figure 5.

3.2 Software Design of the Main Control Terminal
Compared with the branch monitoring points, the main control terminal has more functions and the software process is relatively complex. After the system is powered on, the peripherals will be initialized first. After the initialization is successful, the query information will be sent through the LSDRF4717M04 module to obtain the number of branch monitoring points and number them. In the future, query commands will be sent to each branch monitoring point at regular intervals to obtain the current environmental data and store it in the SD card. At the same time, the crop growth curve will be drawn on the screen for user reference. The main control terminal contains a Web server program. When the user wants to view the current situation in a different place, he can choose to log in to the main control terminal from the network to view it. The software process of the main control terminal is shown in Figure 6.

Conclusion
With the continuous improvement of the level of modernization, traditional manual agriculture will gradually be replaced by intelligent facility agriculture. Agricultural producers can use the Internet to obtain data from agricultural production sites at any time and any place, and control them. At the same time, the system will also give agricultural producers certain opinions and suggestions based on past experience data, avoiding losses caused by lack of experience. This system is developed based on the advanced MIPS architecture. It is an attempt to apply ubiquitous technology in intelligent agriculture. It has conducted exploratory research on the promotion of ubiquitous technology in agriculture in the future and has good application prospects.