Modular “Plug-and-Play” Photometer Based on IoT Digital Light Sensors: A DIY Approach for In Situ Analysis

Portable photometers fabricated with low-cost optical components have been developed for a wide range of analytical applications. However, their analytical performance is closely related to the spectral range of the colored solution, as it depends on the detector material used in commercially available digital light sensors. A modular DIY, plug-and-play photometer was designed for quantitative absorbance measurements. Four digital light sensors (BH1750, TSL2591, LTR329, and LTR303) were evaluated for detecting colored solutions. LTR329 and LTR303 were found to provide optimal performance due to their broad spectral coverage, enhancing the device's analytical capabilities. The photometer integrates an LED light source (635 nm) and a microcontroller (Adafruit ESP32-S3), enabling easy operation and data processing. It was employed to determine sulfide concentrations in wastewater using the methylene blue method and urea levels in Automotive SCR fluid samples with the Schiff reaction. The analytical results for sulfide (0.26-3.00 mg L^-1) and urea (0.20-3.00% w/v) were comparable to those obtained by official methods, with detection limits of 0.09 mg L^-1 for sulfide and 0.06% (w/v) for urea. The device's modularity ensures easy component replacement, ensuring longevity and adaptability. With portability, 18-h battery life, and reliability, it is ideal for on-site analyses in remote settings. This study, not previously reported in the literature, presents the photometer as a valuable, sustainable tool for analytical measurements in resource-limited environments.