Operation of Talkie Toaster and Talkie Radio
1. Impress (this presentation software) executes a script that tells Node-Red to coordinate the conversation between the toaster and radio using MQTT topics to communicate with the toaster and radio.
2. The radio and toaster have a simple arduino/ESP32 sketch that tells an MP3 what to play. The sketch also listens to a MQTT topic and returns the status to another topic.