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Connectivity Cheat-Sheet

Wi-Fi → HTTP → MQTT → Home Assistant, on one page. Print me.

The compressed essence of the Connectivity track (Lessons 19–22): the REPORT arrow of SENSE → DECIDE → ACT → REPORT.

Wi-Fi (Lesson 19)

Station mode = join your network (use this). AP mode = be your own hotspot (for setup).
Shape: set STA → WiFi.begin(ssid, pass) → wait for WL_CONNECTED → read WiFi.localIP().
The router gives the gadget an IP address — how other devices reach it.

Gotchas 2.4 GHz only (not 5 GHz) · keep credentials in an uncommitted secrets file · handle reconnects · mind signal/placement.

Request/response: client (browser) asks, server (ESP32) answers.
URLs as commands: /on, /off, /status.
ESP32 as server (host a page) or client (call out to a service). Reach by name with mDNS (name.local).
Limit: you must poll; one-to-one; awkward for a whole home → use MQTT.

Publish/subscribe via a broker. Publish to a topic (home/livingroom/temp); subscribers to that topic receive it.
Publisher & subscriber are decoupled; push-based; many-to-many; lightweight.
ESP32: PubSubClient library — publish() / subscribe(). Know retain & QoS.
Run your own broker (Mosquitto) for privacy. Public brokers = learning only.

Path	How	When
ESPHome	Describe gadget in YAML; it builds firmware; native HA integration + OTA	Easiest — start here
MQTT	ESP32 publishes/subscribes; HA MQTT integration + MQTT Discovery auto-creates entities	Full control / portability

Device becomes an entity → use in automations (e.g. temp > 24°C → fan on).
HA runs locally — private, no cloud needed.