Design and Validation of a Portable AD5933–Based Impedance Analyzer for Smart Agriculture

This paper presents a portable impedance analyzer based on the AD5933 integrated circuit, specifically designed for fruit quality monitoring throughout its entire supply chain. The custom designed system allows to flexibly tune the parameters (i.e. excitation voltage, feedback resistor, settling time) for each AD5933 frequency range from 10Hz to 100kHz, leading to a precise system calibration and consequently, measurement. FruitMeter runs MicroPython on an STM32 microcontroller, allowing ease of development, advanced low-power mode, and both on-demand and scheduled measurements. The system employs Low-Energy Bluetooth and USB communication with a micro SD data storage which, together with its small size (7.5 ×2 ×4cm in volume) and the 300mAh rechargeable battery with USB recharge, increases the system portability and connectivity, critical for smart agriculture on-field applications. The developed portable system is validated by comparing its performance with a benchtop impedance analyzer with both passive components and fruit samples (apple, avocado, banana, mango and tomato). The comparison resulted in an average Root Mean Square Error (RMSE) of 1.0% and 4.3% for the passive components and of 1.36% and 6.8% for the fruit samples, for impedance magnitude and phase, respectively. We finally validated the system for a real use-case regarding the evaluation of banana aging evolution.