Design Of Soil Temperature And Moisture Sensor And Its Data Acquisition System

The automatic monitoring of soil temperature and humidity can let us understand the soil condition and timely analyze drought or flood situation of soil and the influence on growth and development of crop.It also contributes to transformation of traditional agriculture to modern agriculture,promoting the development of "intelligent agriculture".In addition,according to the determination of soil temperature and humidity,we can timely forecast flood,drought and other natural disasters,which provides help for the protection of ecological environment and construction.This soil temperature and humidity sensor uses MSP430F2272 processor as the core,including the temperature measurement module and humidity measurement module.This paper mainly studies the humidity measurement modules,namely the determination of soil moisture content.Aim at the problems of small measuring range and large error of the present domestic development of soil moisture sensor,we refer to domestic and international data and a large number of document to analyze and summary various determination methods.In the dielectric properties of the soil as the breakthrough point and through the theoretical analysis of the characteristics of the soil dielectric,we find that using dielectric constant to measure soil moisture content is a kind of method with high sensitivity,wide aptation and less affection by the soil physical and chemical characteristics.Experiments than compare methods of the fixed and unfixed frequency in frequency domain,choose the method of fixed frequency.We use the least square method to analysis the data,to study the relationship between moisture content and the output voltage of probe under different frequency.Finally,we respectively choose 90 MHz,40 MHz and 50 MHz signal source when the soil moisture content is 0 to15%,15% to 25% and more than 25%,to broaden the measuring range and improve the measurement precision,further improve the sensor performance.In hardware circuit,the temperature measurement module uses thermistor.Humidity measurement module includes signal source circuit,frequency selective circuit,parallel plate capacitance probe,detection rectifier circuit and voltage amplification circuit.Power supply module uses solar photovoltaic cell,which managed by energy harvesting,charge control circuit,lithium battery protection circuit,voltage regulator circuit and lithium battery.Experimental result shows that the moisture measurement range is 0-60%,with error of ±2% and the temperature range is-40~50 ?,which comply with the design requirement.We develop the sensor with qualitative light material,small volume and good portability,all circuits design on a piece of PCB,and the corrosion resistance of material is strong.The sensor is not easy to damage and can adapt to outdoor use for a long time.In addition,the accuracy,repeatability and stability of this sensor are tested.The results show that the sensor has good accuracy,repeatability and stability,which can achieve real-time measurement of soil temperature and humidity.At last,on the basis of the sensor,wireless sensor data acquisition system is designed.This system uses ZigBee technology with CC2530 single-chip microcomputer as the processing chip,can realize the real-time monitoring of soil temperature and humidity.The user can view the current soil temperature and humidity data on the mobile phone or computer,which realizes the intellectualization of agricultural production.The soil temperature and humidity sensor and its data acquisition system can real-timely monitor the soil temperature and humidity,with high resolution,strong adaptability,low cost and wide application.This system can be widely applied in the field of agricultural production and environmental monitoring.