Overall Design Scheme of Soil Temperature and Humidity Wireless Information Collection and Monitoring System in Greenhouse

In order to achieve energy-saving and environmental-friendly design requirements, the system is designed to use solar power, and data transmission is wireless. This method can eliminate the need for extensive cabling in greenhouses and facilitate the integrated installation and use of lower-level machine modules. The entire greenhouse soil temperature and humidity wireless information acquisition and monitoring system design is divided into two parts of the lower machine and the upper computer. The lower computer is responsible for the collection and display of temperature and humidity, wireless upload, and the control of the solenoid valve and the ventilation motor. The host computer is responsible for the data receiving and recording and the temperature and humidity change curve display task can also wirelessly transmit control parameters to the down machine. The system configuration is shown in Figure 2-1.

2.1 Design Requirements for Wireless Information Collection and Monitoring System of Greenhouse Soil Temperature and Humidity
(l) The soil temperature and humidity recorder transmits the soil temperature and humidity data in a wireless manner. The transmission distance is far away, and the anti-interference ability is stronger.
(2) The use of high-precision and high-protection level temperature and humidity digital sensors, accurate and timely measurement and control of soil temperature and humidity, the system should be easy to install and easy to maintain.
(3) The software design idea is clear, and the modular design scheme is adopted to make full use of system hardware resources to facilitate system software upgrade and maintenance.
(4) The host computer records the temperature and humidity data in time and displays the temperature and humidity changes. The temperature and humidity control parameters can be set by the host computer.
2.2 System design ideas and solutions The overall design concept is: From the actual needs of greenhouse planting, according to the planting crop layout, select the appropriate sensors, temperature measurement modules, data transmission methods, host computer, etc., according to the greenhouse pipe network layout And the specifications of the pipeline, determine the number of specific temperature and humidity sensors and the number of solenoid valves, to achieve an automatic detection and control of greenhouse soil temperature and humidity. This system can be divided into upper computer and lower computer. The lower computer consists of temperature and humidity acquisition module, main control module, wireless communication module, display module and power supply module. The upper computer includes wireless module and serial communication module. , Temperature and humidity curve display module and data storage module. The choice of device in the entire hardware system is mainly the selection of MCU, the selection of temperature and humidity sensors and the selection of wireless communication module; PC software development general development tools such as VB, VC, VFP and Delphi can achieve the upper computer. The function to be completed.
2.2.1 Selection of temperature and humidity sensors In recent years, the design technology of temperature and humidity sensors has made great breakthroughs. Temperature and humidity sensors are moving from single temperature-sensitive and humidity-sensitive components to intelligent, integrated, multi-parameter measurement direction and rapid development, which provides a convenient condition for the development of a new generation of temperature and humidity measurement and control systems. When using conventional temperature-sensitive or humidity-sensitive components for temperature and humidity measurements, a large number of amplification and filtering circuits are required. The design of the circuit is very complicated. Since most of the circuits are nonlinearly output, the application requirements are very high. With the new generation of integrated temperature and humidity sensors, the circuit design can be greatly simplified, and the measurement accuracy and reliability are higher. A new generation of integrated temperature and humidity sensors are available in voltage output or frequency output types, such as the HUM1500, HUM1520, HF3223, and others. They also need to add AD or pulse width test circuit in the application, the application is still more complicated. To this end we chose the latest fully digital integrated temperature and humidity sensor DB170. DB170 uses the world's most advanced temperature and humidity sensors as its core components to ensure that the products have extremely high reliability and excellent long-term stability. The sensor includes a capacitive polymer moisture sensing element and a temperature measurement element made of energy gap material. The sensor is seamlessly connected to a 14-position knife D converter and a serial interface circuit on the same chip. Therefore, the product has excellent quality, high protection level, ultra-fast response, strong anti-interference ability, and high cost-effectiveness. Each sensor chip is calibrated in an extremely accurate humidity chamber. Calibration coefficients are stored programmatically in the OTP memory and used during calibration. The sensor calls these calibration coefficients during the processing of the detection signal. The two-wire serial interface and internal voltage adjustment make peripheral system integration quick and easy. With its small size, extremely high protection performance and extremely low power consumption, the DB170 series has become the first choice for all types of applications.
2.2.2 Selection of Wireless Modules Since the beginning of the 21st century, wireless communication technology has grown by leaps and bounds, including various wireless module design and production power consumption as well as the use of FM correction frequency bands and other technologies. There are many technologies currently used in wireless data transmission, such as infrared technology, Bluetooth technology, good technology, GPRS, CDMA and so on.
(l) Infrared communication technology (IrnA)
Infrared communication is the use of infrared data transmission, is a wireless communication technology. Infrared communication technology does not require physical connection, is easy to use and has a low implementation cost, and is therefore widely used in the control of small mobile devices for the exchange of data and electrical equipment, such as between laptops, PDAs, mobile phones or between computers. Data exchange, remote control of televisions, air conditioners, etc., are a variety of everyday applications that have emerged very early. In order to establish a unified infrared data communication standard, the Infrared Data Association (frDA) was established in 1993, and the IrDA 1.0 specification was published in 1994. However, due to the direct characteristics of infrared rays, only line-of-sight transmission can be performed, the effective distance is close, and two infrared communication devices must be aligned, which is particularly unsuitable for transmission obstacles. Due to its poor transmission distance and poor anti-interference ability, it is not suitable for application in this system design.
(2) Bluetooth technology (Bluetooth)
Bluetooth is a radio technology that supports device short-range communications (typically within IOm). Wireless information exchange can be performed between a wide range of devices including mobile phones, PDAs, wireless headsets, laptops, and related peripherals. Utilize / Bluetooth 0 technology, can greatly and simplifies the communication between the mobile communication terminal equipment, can also succeed in simplifying the communication between the apparatus and Internet Internet, thus the data transmission becomes more quickly and efficiently, widen the route for wireless communication "Bluetooth adopts Decentralized network topology and fast frequency hopping and short packet technology, support point-to-point and point-to-multipoint communication, work in the global 2.4GHzISM (histrialseienti6cMe by eal) (ie industrial, scientific, medical) frequency band, its data rate is 1Mbps The use of time division duplex transmission scheme to achieve full-duplex transmission.Bluetooth technology has many advantages such as open technology equipment is compatible with the use of public communications band, but its wireless transmission distance is limited to about 10m, is a fatal weakness, is not suitable Application in wireless greenhouse temperature and humidity information collection.
(3) IEEE8o2.llb (Wi-Fi)
Wi-Fi (wireless Fidelity, wireless compatibility certification), commonly known as wireless broadband, is actually another name of IEEE802.llb. It is an industry term issued by an organization called / Wireless Ethernet Compatibility Alliance (WirelessEthemetcomPatibilltyAlliance, WECA). , Chinese translation / wireless compliance authentication 0. Like Bluetooth, it is a short-range wireless technology used in offices and homes that can support Internet-access radio signals in hundreds of feet. Although in terms of data security, this technology is worse than Bluetooth technology, it is slightly better in terms of radio coverage. The coverage of Wi-Fi is up to about 90 meters. The office will needless to say, and it can be used in smaller buildings. Therefore, Wi-Fi has always been the technology favored by companies to implement their own wireless LANs. Although it has a wide coverage and wide compatibility, its high cost and high technical requirements make this technology difficult to select in general wireless transmission applications.
(4) Micro-power and short-distance wireless communication technology In recent years, micro-power and short-distance wireless RF module design and production technology have made great progress; usually the main circuit of a wireless RF module is integrated in one chip, and the peripheral accessory circuit Few, and the module's small size interface is more UART, SPI, USB and so on. This kind of module generally adopts FSK modulation mode to work in the SIM frequency band to transmit the data in a transparent manner. Users generally can use their own system designs directly as long as they perform simple configuration.
Based on the above discussion, considering the cost and actual demand, we chose the micro-power short-range wireless communication technology chip.
There are many common lamp wireless modules on the market today: CC1000, nRF401, nRf903, nRF905, TH72o11, APC220-43 and others. Combining their respective operating characteristics and the actual needs of system design such as wireless transmission distance, power consumption, interface type, and programming control complexity, we chose the APC220 wireless module.
APC220-43 module is a highly integrated half-duplex micro-power wireless data transmission module, embedded high-speed microcontroller and high-performance RF chip. The innovative use of efficient cyclic interleaving error detection and coding, greatly improve the anti-jamming and sensitivity, can correct 24bits consecutive burst errors, reaching the industry's leading level. PC22o-43 module provides a choice of multiple channels, you can modify the serial port rate, transmit power, RF rate and other parameters online. APC22O-43 module can transparently transmit data of any size, and the user does not need to write complicated setup and transmission programs, while small-volume and wide-voltage operation, long-distance transmission distance, rich and convenient software programming setting function, so that it can be applied and very widely field. APC220-43 module is a new generation of multi-channel embedded wireless data transmission module, it can set a large number of channels, step accuracy is IKhZ, transmit power up to 20mw, and still has low power consumption, volume 37.smlnx18.3Inlnx7 .OInln, very convenient for customers embedded system. APC220-43 coding gain is as high as nearly 3dBm, error correction capability and coding efficiency have reached the leading level in the industry, far higher than general forward error correction coding, anti-burst interference and sensitivity are greatly improved. At the same time, the encoding also includes a reliable error detection capability, which can automatically filter out false and false information and truly realize a transparent connection. Therefore, the wonderful c22o-43 module is particularly suitable for use in harsh environments such as industrial fields and other strong interference. "A comprehensive consideration of the above factors, we chose the APC220 among many wireless comfort modules.
2.3 The choice of keyboard and display circuit Considering the working environment of the entire application system, especially the requirements of brightness and other factors, we chose the digital tube to display the temperature and humidity data. Multi-bit digital display technology has static display and dynamic scan. For example, the static display mode usually occupies more than Mcu's foot pipe, but the display quality is high; the dynamic scan mode occupies less Mcu pin, but the programming control process More complicated. Considering the system's requirements for digital display quality, we have chosen 7415164 for serial and parallel conversion of output fonts, using the 7415138 chip for serial dynamic scanning of the digital tube. This method can save up to 10 ports of Mcu. Only need two port lines to connect 74LS164 to output clocks and fonts respectively. Use 3 port lines as the address line of 74LS138. Use 4 low level output terminals to select 4 digital tubes to complete the display circuit setup. The circuit also reserves the interface for system expansion.Because the upper machine can adopt the wireless way to transfer the working parameters of the lower machine, there is no need to set the parameters in the lower machine, although 4 buttons are set in the lower machine. Its role is not great, but it can be used for future expansion of system functions.
2.4 Selection of Control Modules There are many kinds of control modules that can be used as Mcu, such as ARM, DSP, and MCS series MCUs. However, they all have their own characteristics and special applications. For example, DSP is mainly applied to complex digital signal processing. ARM is mainly used in some advanced embedded applications. The single-chip microcomputer has the features of easy development, abundant interfaces, strong bit control capability, and high reliability. It is very suitable for applications where the processing speed is not high and the system does not have complex arithmetic processing. Combined with the requirements of the system for the controller, the STCI1F32 MCU, which is fully compatible with the popular mesl MCU, was selected. The reason why dsP is not selected is mainly because dsP is mainly used in high-speed data processing and complex algorithm processing. The STC11F32 microcontroller is sufficient to meet the application system that does not require high processing response speed. In the case of a single-chip microcomputer that satisfies the system's requirements for data processing speed and response speed, the preferred data processing unit is definitely a single-chip microcomputer.

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