A little light.
A real round trip.

Your dashboard sends a command over the internet. A simulated device receives it and reports its state. The lamp lights up only when that report comes back.

Public test brokerbroker.emqx.io · MQTT over secure WebSocket

ROOM / TOPIC ROOT THIS TAB

A fresh room keeps this demo separate. Use the same room in another tab to share the lamp.

Use your own broker

WEBSOCKET ENDPOINT USERNAME · OPTIONAL PASSWORD · OPTIONAL

Credentials stay in this tab’s memory and go to your selected broker. Reloading clears them. Use WSS; plain WS is available only for a loopback broker on an HTTP development page.

Public broker: synthetic data only. Room names are not passwords; others can read or publish here.

Ready when you are. Connecting starts real network traffic; no installation needed.

CLIENT 01

The dashboard

Not connected

Set the request. The device decides the result.

PowerRequested on

Brightness65%

A quiet glowFull beam

Connect the dashboard to send your first command.

PUBLISHES TO…/command

CLIENT 02 · SIMULATED DEVICE

The lamp

Not connected

CONFIRMED DEVICE STATEAwaiting a report

—

—BRIGHTNESS

A second MQTT connection plays the device. It runs while this tab is open.

REPORTS ON…/state

1 Dashboard→2 MQTT broker→3 Device→4 State comes back

FOLLOW THE MESSAGE

On the wire 0

TIME	ROUTE	TOPIC / PAYLOAD
No messages yet. Connect, then send a little light.

Latest 80 events · QoS 1 · no retained commands or state · the simulator reports state every 5 seconds.

MAKE IT YOURS

One room. More possibilities.

Open another tab as Dashboard only and paste this room. Or let Node-RED join the conversation.

Connect from Node-RED

For the default public broker, use broker.emqx.io, port 8883 with TLS and certificate verification. Leave credentials empty and use a unique client ID. This is a public, synthetic-data demo.

For your own broker, use its separately configured MQTT TCP/TLS endpoint and credentials. Do not infer that endpoint from the browser’s WSS URL.

Subscribe an mqtt in node to …/state and wire it to a Debug node. Connect Inject → Function → mqtt out, with output topic …/command, QoS 1, retain off. The Function creates a fresh command:

msg.payload = JSON.stringify({
  id: msg._msgid,
  sentAt: Date.now(),
  power: true,
  brightness: 80
});
return msg;

The simulator must stay connected in one browser tab. With your own device or flow reporting state, choose Dashboard only. Commands expire after 30 seconds; a matching state report is the application acknowledgement.