Design and Develop a Portable SPAD Meter using Arduino Nano and Optical Sensing Components

Abstract The study titled “Development and Performance Evaluation of a Low-Cost DIY SPAD Meter for Chlorophyll Estimation” aims to develop an accurate, portable, and cost-effective device for estimating leaf chlorophyll content using optical sensing techniques. The system is based on the principle of differential light transmission through plant leaves using red (~ 650 nm) and infrared (~ 940 nm) wavelengths. A TSL2561 digital light sensor was employed to measure transmitted light intensity, while an Arduino Nano microcontroller was used for data acquisition, processing, and display of SPAD values on an OLED interface. A logarithmic transmittance ratio (R) was computed from the measured intensities to capture the variation in chlorophyll content during measurement. Calibration of the developed device was performed using a standard SPAD-502 chlorophyll meter, and a regression-based approach was adopted to establish the relationship between the measured and reference SPAD values. The calibration model obtained demonstrated a strong correlation, with a coefficient of determination (R²) of 0.8822 and a correlation coefficient of 0.9392. The developed system showed high accuracy, with prediction errors within ± 1 to ± 8 SPAD units, indicating reliable performance comparable to the commercial instrument. The study highlights the effectiveness of integrating low-cost hardware components with microcontroller-based processing for real-time chlorophyll estimation. The developed device provides a scalable, user-friendly, and economical solution for non-destructive plant monitoring. The proposed methodology can be extended to other crops and agricultural applications, supporting precision farming and efficient nutrient management practices.