In tropical agricultural regions, accurate estimation of reference evapotranspiration (ET0) remains challenging due to climatic variability, data scarcity, and limitations of empirical models such as FAO-56 Penman–Monteith. To provide the technical basis for future field-based evapotranspiration studies, this study reports the design, construction, and calibration of an automated weighing lysimeter installed at the La Libertad Research Center in Villavicencio, Colombia. The system integrates a galvanized steel tank (1 m3) reconstructed with original soil horizons, an automated sprinkler irrigation system, and a monitoring module based on load cells, soil moisture sensors, a professional weather station, and real-time data transmission powered by a photovoltaic unit. Calibration was performed using incremental load–unload cycles, achieving linear response curves with R2 > 0.99, while soil water retention curves were developed to define irrigation thresholds. The results document the successful construction and integration of the system and show highly linear load-cell responses, also the capacity to provide high-resolution measurements under equatorial conditions, this could reduce methodological uncertainties inherent to model-based approaches. The developed system provides the technical infrastructure required for future evapotranspiration monitoring and comparison with established ET0 estimation methods. Overall, the proposed lysimeter may support future irrigation-management, water-resource assessment, and climate-smart agriculture applications in tropical regions.