<![CDATA[Abstract Storing corn at high temperatures accelerates quality loss, while blower operation that depends on operators is prone to delays and human error. This study aims to design and test an ESP32-based automatic blower temperature controller integrated with the Internet of Things (IoT) through the MQTT protocol in a simulated corn storage room. The prototype uses a DHT11 sensor for temperature, a capacitive moisture sensor for grain moisture, a relay, a 12 V DC fan, and an I2C LCD; data are displayed locally and sent to an MQTT broker, Node-RED, Firebase Realtime Database, and an MIT App Inventor application. Control is a threshold ON/OFF logic with a 35 °C setpoint that can be changed remotely. The research method is experimental engineering consisting of functional testing, sensor comparison with reference instruments (MX-1200A and Sartorius MA35), actuation logic testing, and network delay and packet loss measurement. Data were analyzed using absolute deviation and relative percentage error. All subsystems worked and data were synchronized across all interfaces. The DHT11 sensor has a mean deviation of −0.82 °C with a mean relative error of 2.54%, the blower switched on and off correctly at the setpoint in all seven test points, the mean network delay was 183.1 ms (Good under TIPHON), and packet loss was 0%. The capacitive moisture sensor has a mean deviation of −10.74 percentage points, so it is unsuitable for absolute measurement without calibration. The prototype can serve as a basis for developing an IoT-based temperature controller for corn storage. Keywords: ESP32; MQTT; Internet of Things; threshold control; corn storage; Node-RED Abstrak Penyimpanan jagung pada suhu tinggi mempercepat penurunan mutu, sedangkan pengoperasian blower yang bergantung pada operator rentan terhadap keterlambatan dan kesalahan manusia. Penelitian ini bertujuan merancang dan menguji purwarupa pengendali suhu blower otomatis berbasis ESP32 yang terintegrasi dengan Internet of Things (IoT) melalui protokol MQTT pada simulasi ruang penyimpanan jagung. Purwarupa menggunakan sensor DHT11 untuk suhu, sensor kelembapan kapasitif untuk kadar air, relay, kipas DC 12 V, dan LCD I2C; data ditampilkan secara lokal serta dikirim ke broker MQTT, Node-RED, Firebase Realtime Database, dan aplikasi MIT App Inventor. Pengendalian memakai logika ambang ON/OFF dengan setpoint 35 °C yang dapat diubah dari jarak jauh. Metode yang digunakan adalah rekayasa eksperimental yang meliputi pengujian fungsional, pembandingan sensor dengan instrumen referensi (MX-1200A dan Sartorius MA35), pengujian logika aktuasi, serta pengukuran delay dan packet loss jaringan. Data dianalisis menggunakan deviasi absolut dan persentase kesalahan relatif. Hasil pengujian menunjukkan seluruh subsistem berfungsi dan data tersinkron pada semua antarmuka. Sensor DHT11 memiliki deviasi rata-rata −0,82 °C dengan galat relatif rata-rata 2,54%, blower menyala dan mati sesuai setpoint pada seluruh tujuh titik uji, delay jaringan rata-rata 183,1 ms (kategori Bagus menurut TIPHON), dan packet loss 0%. Sensor kelembapan kapasitif memiliki deviasi rata-rata −10,74 poin persentase sehingga belum layak untuk pengukuran absolut tanpa kalibrasi. Purwarupa ini dapat menjadi dasar pengembangan pengendali suhu penyimpanan jagung berbasis IoT. Kata kunci: ESP32; MQTT; Internet of Things; kontrol ambang; penyimpanan jagung; Node-RED]]>
