MQTT Broker Guide (HiveMQ Cloud)

MQTT is recommended for device connectivity because it's lightweight and well supported. This guide uses HiveMQ Cloud (free tier available).

If you prefer firebase, skip to the Firebase Guide.

Create HiveMQ Cloud account

• Go to HiveMQ Cloud → Sign up.

• Create a new cluster (free tier). Select region and finish.

Create Credentials

• In the cluster dashboard → Credentials → create a username/password pair for your device(s).

• Copy & Note the credentials:

  • host (e.g., xxxx.hivemq.cloud)

  • port (usually 8883 for TLS, 1883 for non-TLS)

  • username and password

• If using WebSockets, note the ws path (often /mqtt) and use port 8883 or 443 as configured.

Enable WebSocket/TLS as needed

• For device firmware on the web or browser clients, enable WebSocket support. For embedded devices use TLS on 8883.

Topic Naming Convention (recommended)

Use a consistent hierarchical topic scheme:

• Device → Server (device publishes sensor data / state)

  • decentiot/<projectId>/<deviceId>/toServer

• Server → Device (server publishes commands)

  • decentiot/<projectId>/<deviceId>/toDevice

• Optional admin/announce topics:

  • decentiot/<projectId>/broadcast (for broadcast messages)

  • decentiot/<projectId>/<deviceId>/lwt (last will/testament)

Example payloads

• From server to device (command):

  {
    "widget": "led1",
    "type": "boolean",
    "value": 1,
    "ts": 169###  // unix ms timestamp
   }

• From device to server (state update):

  {
  "deviceId": "esp32-01",
  "state": { "led1": 1, "temp": 27.3 },
  "ts": 169###  // unix ms timestamp
  }

Test your broker

• Use the HiveMQ WebSocket client (in HiveMQ Console) or MQTT Explorer / MQTT.fx to test subscribe/publish.

• Subscribe to decentiot/+/+/toDevice and publish a test JSON to see it arrive.