Visible Consumption: Design, Debugging, and Closed-Loop Remote Control of a Low-Cost IoT Prototype for Industrial Energy and Temperature Monitoring Aligned with SDG 12

Low-cost microcontrollers with integrated wireless connectivity have lowered the barrier to instrumented industrial monitoring, yet production adoption remains constrained by memory, cryptographic capacity, and link reliability. This paper documents the design, implementation, systematic debugging, and closed-loop remote control of an industrial monitoring prototype built on an ESP32 microcontroller, simulated on Wokwi, and aligned with SDG 12 (Responsible Consumption and Production). The system integrates simulated voltage and current sensors, an NTC thermistor, threshold-based local alerts, an SSD1306 OLED display, an App Inventor mobile client, an Oracle APEX/ORDS backend, a Groq large-language-model diagnostic layer, and remote sensor activation. Three reproducible platform-level failures an ADC2/Wi-Fi arbitration conflict, progressive heap exhaustion from repeated TLS handshakes, and a persistent TLS handshake timeout against a CDN-fronted endpoint were diagnosed, resolved, and contrasted against peer-reviewed IEEE literature. The final architecture routes all outbound HTTPS traffic through a locally hosted relay to circumvent the simulator's cryptographic limitations, illustrating a practical, literature-grounded mitigation that generalizes to any severely constrained TLS client.