CAFEMEC: Automated Dryer via Arduino--PLC Communication

Resumen

This paper introduces CAFEMEC, an automated drying prototype for raised (African) beds that integrates advanced sensing, control, and actuation through a hybrid Arduino--PLC architecture. An Arduino Nano 33 BLE Sense Rev2 is utilized for real-time monitoring of ambient temperature, relative humidity, and bean moisture content, computing a reference moisture value. This data is transmitted via the Modbus RTU (RS-485) protocol to a Schneider M221 PLC, which executes the control logic. The PLC compares ideal versus actual moisture levels to manage forced ventilation, auxiliary heating, and an automated raking mechanism, incorporating hysteresis and minimum-time constraints for operational stability. The mechanical solution features a stepper-driven raking system (belt-and-pulley transmission with a PVC paddle), a plenum-based airflow duct system, and a foldable frame designed for compatibility with standard African beds. Bench tests validated stable and traceable data acquisition, robust Arduino--PLC communication, and consistent actuator response under safety interlocks. Due to seasonal constraints, corn kernels were employed as a process surrogate during the commissioning phase. The results establish a foundation for real-time solar drying regulation, aiming to enhance moisture uniformity and hygiene compared to traditional manual handling. Future research will focus on scaling the system to 6-meter beds with zoned control, solar-hybrid power integration for resilience, and coffee-specific calibration profiles for natural, parchment, and honey processes.