BREW /descale: Building an Event-Driven Coffee Machine with ESP32, MQTT, and HTCPCP

It started as a joke: a fictitious curl command using the Hyper Text Coffee Pot Control Protocol (HTCPCP - RFC 2324) to trigger a coffee machine cleaning cycle. Then I built it. And it works. In this talk, we’ll walk through how I instrumented a Breville Barista Express with an ESP32 to safely emulate button inputs, expose a playful HTCPCP-inspired interface, and stream real-time telemetry over MQTT. Along the way, we’ll explore how serious engineering concepts—event-driven architecture, state machines, observability, and protocol design—translate surprisingly well into the world of IoT (and espresso). Topics include: - Designing a safe hardware interface without defeating built-in protections - Modeling a physical process (descaling) as an event-driven system - Using MQTT for telemetry, control, and integration with systems like Home Assistant - Building an HTTP façade that translates REST/HTCPCP-like calls into asynchronous device commands - Securing your HTTP façade to prevent your neighbor from flooding your kitchen Whether you're building distributed systems or just love coffee, this talk shows how “toy” projects can become real platforms—and why sometimes the best way to understand architecture is to brew it.