Research And Development Of Moisture Content Detector For Tomato Leaves During Flowering Stage Based On Electrical Impedance

China is the country with the largest tomato cultivation area and the largest total production in the world.Excessive or insufficient water had negative effects on the growth and development of tomato plants during the flowering stage.Therefore,it was of great significance to monitor the growth environment of tomato quickly and accurately by detecting the leaf moisture content(LMC)during the flowering stage.At present,the commonly used methods for LMC detection,such as drying,spectroscopy,computer vision,and electrical characteristics,still had drawbacks such as long time consumption,expensive equipment,and significant environmental impact.Electrical impedance spectroscopy(EIS)had the advantages of convenience and low cost.Domestic and foreign scholars had conducted relevant research on the detection method of LMC based on electrical impedance,but the design and research on the detection equipment of tomato LMC during flowering stage based on electrical impedance has not been reported yet.In this article,the changes in impedance spectroscopy of tomato leaves during flowering stage under water scarcity were analyzed,and the applicability of different modeling methods to establish LMC models was explored.By designing the software and hardware system of the detector and further establishing LMC models suitable for different temperatures,a LMC detector based on electrical impedance was developed to achieve real-time and portable detection of tomato LMC during flowering stage.The main research content and conclusions were as follows:(1)The impedance spectroscopy of tomato leaves during flowering stage under water scarcity were analyzed,and the LMC model was established using different modeling methods.The electrical impedance spectroscopy of tomato leaves during flowering stage under different moisture contents was detected,and the influence of reduction of moisture content on the impedance characteristics and equivalent circuit parameters was analyzed.A prediction equation for LMC based on the equivalent circuit parameters of leaf impedance was established.And the LMC models based on different impedance characteristics and different methods were established and compared.The results demonstrated that the overall accuracy of the LMC model based on impedance characteristics combined with random forest was better than that based on partial least square regression(PLSR)and back propagation neural network.And for the convenience of model application,a PLSR model for LMC could be established and applied to the detector.(2)The hardware system of the moisture content detector was designed.Firstly,the overall scheme of the detector was designed,and the impedance measurement scheme with AD5933 as the core was determined.Modules such as AD5933 impedance measurement,DS18B20 temperature measurement,TF card data storage,ESP8266-12F Wi Fi communication,LCD12864 display screen,and lithium battery power supply was selected.Subsequently,a control module with STM32C8T6 as the core was designed and a PCB board was produced.Finally,the shell of the detector with dimensions of 215 mm×125 mm×60 mm and leaf clampe mechanism were designed,and the hardware production of the detector was completed.(3)The software system of moisture content detector was designed.The modular approach was adopted,and the lower computer program,and upper computer program were designed.The lower computer program included impedance measurement,temperature measurement,equivalent circuit parameter fitting,data storage,Wi Fi communication,LCD display,and other programs.The upper computer program included four types of graphical user interfaces.The remote control and data display functions of the detector was realized.and the process of establishing different LMC models and fitting equivalent circuit models based on impedance data was made more simple.(4)The performance of the instrument was tested and the LMC models suitable for different temperatures was established.The detector was used to detect the standard resistance,RC three element circuit model and tomato leaf samples in the frequency range of 1 k Hz～100k Hz,and the measurement error of the detector was evaluated.The results demonstrated that the average relative error of the detector in detecting the impedance modulus of tomato leaves was 5.45%,and the average absolute error of the phase angle was 2.45°.The detector was used to detect the electrical impedance spectroscopy of tomato leaves with different moisture contents during flowering stage at different temperatures.An LMC model containing temperature information was established and the PLSR model established with input T+combination data had the highest accuracy(validation set R~2=0.7292,MAE=0.04360,MAE=3.68%).The self-made moisture content detector was used to detect tomato leaves unrelated to modeling and the average absolute error between the predicted value and the actual value was 3.74%.The detection time was within 4 seconds,indicating that the detector was suitable for real-time detection of tomato LMC during flowering stage.