How to Connect an MQTT Broker to SCADA Cloud

SCADA Cloud subscribes directly to any MQTT broker and turns incoming messages into live dashboard tags — no on-premise server, no VPN into your plant network, and no custom code to write. This guide walks through connecting a broker, mapping payloads to tags, and building your first live dashboard from MQTT data.

Why Connect MQTT to SCADA Cloud

Modbus is built for polling — the master asks, the device answers. MQTT is the opposite: devices publish data whenever it changes, and subscribers (like SCADA Cloud) receive it in real time without asking. This publish/subscribe model fits IIoT sensors, edge gateways, and modern PLCs with native MQTT support far better than polling, especially at scale across many remote sites. Instead of building and maintaining your own MQTT subscriber and dashboard stack, SCADA Cloud does the connection, parsing, storage, alarming, and visualization for you.

Step 1 — Create Your SCADA Cloud Account

Step 2 — Add an MQTT Connection

Step 3 — Subscribe to Topics

Once the broker connection shows Connected, add one or more topic subscriptions.

Step 4 — Map Payload Fields to Tags

SCADA Cloud needs to know which fields inside each MQTT message correspond to which tags on your dashboard.

{
  "device_id": "sensor7",
  "temperature": 68.4,
  "pressure": 4.12,
  "status": "running",
  "ts": "2026-07-09T10:15:00Z"
}

Step 5 — Build a Live Dashboard

Go to Dashboard → Edit Mode and drag widgets onto the canvas — number displays, gauges, trend charts, and status indicators — then bind each widget to an MQTT-mapped tag. Data updates on the dashboard the instant a new MQTT message arrives; there's no polling delay like you'd see with a traditional Modbus dashboard.

Step 6 — Configure Alarms

Go to Alarms → Add Alarm, select an MQTT-mapped tag, and set a threshold condition (above, below, equals). Enable email or SMS notification for critical conditions. You can also create a dedicated alarm rule that fires when the MQTT connection itself drops, so a broker outage doesn't silently freeze your dashboard without anyone noticing.

MQTT + Modbus in the Same Dashboard

Most plants aren't purely MQTT or purely Modbus — a typical setup has legacy PLCs on Modbus TCP alongside newer IIoT sensors publishing over MQTT. SCADA Cloud lets you combine both data sources on the same dashboard, trend chart, and alarm rule set, so your operators get one unified view regardless of how each device communicates. If you're validating a Modbus device before wiring it into the same dashboard, you can simulate it first with a Modbus slave simulator to confirm register values and connectivity without touching production hardware.

Troubleshooting Common Issues

Broker shows "Disconnected"

• Verify the hostname and port — TLS brokers usually use 8883, not 1883.
• Check credentials; some brokers (like AWS IoT Core) require client certificate auth rather than username/password.
• Confirm the broker allows external subscribers — some brokers restrict client IDs or require an allowlist.

Topic subscribed but no tags appear

• Confirm the topic filter actually matches what devices are publishing — use a tool like MQTT Explorer against the same broker to see raw topics first.
• Check that your payload is valid JSON or matches your configured CSV delimiter.

Tags show stale values

• Check the device's publish interval — if it only publishes on change, a stable process may simply not have sent a new message recently.
• Verify the MQTT connection status; a silent reconnect loop can cause missed messages during the outage window.