| The soil temperature and moisture is very important for crop growth and also the main factors of agricultural meteorological observation. It is meaningful for Agricultural production decisions to observe the real-time soil temperature and moisture. More observation of soil temperature and moisture mostly needs to complete in the wild unattended conditions. So measurement system should be with small size, low power consumption characteristics, and transmit and manage result of measurement through some communication network. Soil temperature and moisture which is in different depth has more difference, so It is needed to observe the vertical gradient distribution of soil in agricultural meteorology. In recent years, meteorological department of China has gradually set network of soil temperature and moisture observation on a nation wide scale.Paper designed a kind of soil temperature and moisture gradient survey system which is able to observe continuously and realize data communication function. The system can realize8channels temperature and moisture measurement and be able to arranged in the vertical soil for measuring. System which costs low power consuption can use battery supply. With real-time calendar, system can record the homologous date and time on measurment result. System which has external flash memory can still save measurement data while power down. The system which has a variety of cable and wireless communication function can satisfy different condition of communication requirements, achieving multi-point observing and data management.The system hardware is sperated to digital control board, analog board and RF communication board. The digital control board choose TI company’s low power consumption micro controller MSP430F149as the master MCU,8channels of soil tempreature and moisture analog signal can be digitized by two pieces of24bits A-S type ADC--ADS1256. Because soil temperature and moisture changes relatively slowly and loads’ working time is stagger, we design PMOS switches to control power supply of every load to reduce the system power consuption. The external DS1302real time clock and8Mbit flash memory SST25VF080can save measurement data of each hour when system lost power. Controller which brings serial ports appling electrical level transition chip MAX3232and SN6517B realized RS232and RS485communication interface, meanwhile system which makes use of CAN controller and transceiver expanded CAN bus communication interface which has stronger anti-interference ability. System design a low voltage LCD module for observation of local measurement data; The temperature measurement circuit on analog board is to use MAX494integrated op-amp generate two way dwarf constant flow that act on three-wire PT100and contrast resistance. Through the measurement of the voltage difference between PT100and contrast resistance, System will get the temperature signal. The moisture measurement circuit will divide moisture sensor output signal on the reasonable points and buffer it for ADC conversion; RF communication board intergrate the periphery circuit of ZigBee controller CC2430, and according to the principle RF signal matching up, we build Balun transform circuit between the antenna and CC2430with LC elements to realize the system wireless communication function.System software mainly design the driver of each function module, and transplant μC/OS-Ⅱ real-time kernel to manage the driver. Meanwhile, we make use of Z-Stack to achieve ZigBee wireless network communication function. Finally, we design a PC observation interface matching up the measuring system. |
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