RANCANG BANGUN ALAT PENGUKUR SUHU PERMUKAAN AIR TANGKI REAKTOR KARTINI BERBASIS MIKROKONTROLER ESP32 DAN SENSOR DS18B20NIM.: 21106020025Achmad Yogi MustajabauthorThe Kartini Reactor is a TRIGA Mark II research reactor used for research, training, and education. Monitoring the water surface temperature of the Kartini Reactor tank is one of the important aspects in maintaining the operational safety of the reactor. However, the current monitoring system still has limitations, namely it is only active when the reactor is operating and can only be accessed through the control room, making it less flexible for real-time temperature monitoring. This study aims to design, build, and test a water surface temperature measuring instrument for the Kartini Reactor tank based on the ESP32 microcontroller and DS18B20 sensor. The design stage was carried out by creating the schematic circuit design, PCB design, casing design, and software design prior to the building stage. The building stage was carried out by realizing the completed designs, including hardware manufacturing by soldering all electronic components onto the PCB and assembling them into the casing, while software development was carried out by writing the program code using Arduino IDE. The testing stage was carried out by collecting temperature data at the Kartini Reactor tank and processing it by calculating the accuracy and repeatability precision values. The design results include the schematic circuit design, PCB design, casing design, and programming flowchart. The building results include a hardware subsystem consisting of sub-subsystems of the DS18B20 sensor, ESP32 microcontroller, MCP4725, RS485 communication, and TFT ILI9488. The software subsystem consists of sub-subsystems for sensor reading, data processing and transmission to the LCD, RS485 communication, and data transmission to IoT Google Drive. The test results show that the accuracy value obtained is 98.41% and the repeatability precision value is 98.76%. Based on these results, it is concluded that the water surface temperature measuring instrument for the Kartini Reactor tank has been successfully designed, built, and tested.510 Mathematics (Matematika)2026-07-23UIN SUNAN KALIJAGA YOGYAKARTA;FAKULTAS SAINS DAN TEKNOLOGIThesis