| Summary: | Nutrient monitoring in Micro Indoor Smart Hydroponics (MISH) relies on measuring
electrical conductivity or total dissolved solids to determine the amount of nutrients in a hydroponic
solution. Neither method can distinguish concentrations of individual nutrients. This study presents
the development and testing of a novel spectroscopic sensor system to monitor nitrogen changes
in nutrient solutions for MISH systems. The design phase determined that using an inexpensive
AS7265x Internet of Things (IoT) sensor in a transflective spectroscopic application could effectively
detect small fluctuations in nitrogen concentration. Next, a novel transflective sensor apparatus was
designed and constructed for use in a MISH system experiment, growing lettuce over 30 days. Two
solution tanks of different sizes, 80 L and 40 L, were used in the deployment of the system. Samples
from each tank were analyzed for nitrogen concentration in a laboratory, and multilinear regression
was used to predict the nitrogen concentrations using the AS7265x 18 spectral channels recorded in
the sensor system. Significant results were found for both tanks with an R2 of 0.904 and 0.911 for
the 80 and 40 L tanks, respectively. However, while the use of all wavelengths produced an accurate
model, none of the individual wavelengths were indicative on their own. These findings indicate that
the novel system presented in this study successfully and accurately monitors changes in nitrogen
concentrations for MISH systems, using low cost IoT sensors.
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