Design of a low-cost IoT-based data logger for monitoring the palm sugar drying system using ESP32 and Modbus/MQTT conversion

Palm Sugar is made from coconut sap, evaporated and cooled to crystallize to form powder. To obtain palm sugar that is safe to store, the water content needs to be reduced through
controlled drying, usually with a cabinet dryer. Unfortunately, this process may result in nonuniformity of product quality due to non-uniformity of temperature in the drying chamber, so a monitoring system is needed for evaluation. This study aimed to design a low-cost Internet of Things (IoT)-based data logger to monitor the drying temperature of palm sugar in a cabinet dryer. The data logger utilizes an ESP32 microcontroller to access 7-channel temperature data from the NT18B07 sensor module, which can only communicate in the Modbus RTU RS485 protocol, then converts it into Message Queuing Telemetry Transport (MQTT) format. The Adafruit IO cloud platform was selected for the MQTT broker, whose data was then subscribed to by the IoT MQTT panel application and recorded in a Google sheet. A 20x04 I2C LCD and a microSD module were used to display and store data locally. The performance analysis results
show that the designed data logger has a publisher-to-subscriber latency of 353 ms and throughput of 2 kbps. The designed data logger successfully sent data via MQTT, completing more than 97% of the 1440 daily logs with an interval of 1 minute. It also has a measurement accuracy and precision level of above 99%. The details of the specific design and its implementation were described.