Design of an IoT node for in vivo plant communication and sensing

The interrelated issues of climate change, biodiversity loss and the rising demand for food in underdeveloped countries represent a significant challenge that will have far-reaching consequences for generations in the coming centuries. The increased frequency of heavy rainfall and the prevalence of muggy summer days are creating challenging conditions for the survival of certain plant species, which in turn is affecting the social need for food. It is in this context that the field of agritech emerges as a potential driver of improvement in the agricultural production system. This represents the overarching objective and unifying theme that has guided the development of this thesis. The objective of this project is to create a sensor, specifically an electronic board, that is capable of detecting the impedance from the stem of a plant and the water saturation from the soil. The collection of these data allows for the determination of the plant's hydration status and, consequently, possible abiotic stress. The system configuration is designed to be minimally invasive, cost-effective, and energy-efficient, with the capacity to facilitate communication over far distances. The LoRa radiofrequency communication protocol is a widely used standard for the transmission of data packets over long distances in a remote manner. By means of the impedance evaluated by a Tx-Rx (Transmitter-Receiver) pair, it was possible to send a square-wave signal at a known frequency to the plant and then read the return value from the stem. Previous experiments had demonstrated that the impedance modulus increased or decreased as a result of the plant's state of health, depending on its hydration. The process was subdivided into distinct phases. The initial stage of the process entailed the design of the inaugural board, which was tasked with managing the peripherals (the sensors), facilitating communication, and then transmitting packets. In order to achieve this, a microcontroller unit (MCU) supporting the LoRa protocol was employed. The STM32WL5MOC was selected for this purpose, and an ad-hoc PCB (LoRaTo v0d2) was manufactured as electronic control unit and to expose as many GPIOs as possibile. Subsequently, the focus of the project shifted to the design of the "operating arm", the PCB, which was to integrate the impedance sensor together with the commercial WaterMark matric potential sensor (groundwater saturation). The outcome was the creation of a shield, called the "Global Plant Impedance Shield", which integrates sensors to the monitor the plant's physiological condition. Subsequently, a test phase was conducted to ascertain the correct functioning of the boards, initially on an individual basis and then in conjunction with one another. This was followed by a firmware programming phase of the boards, to test the internet of things (IoT) node in precision agricolture applications. The results of the measurements are satisfactory and in line with project expectations.