> For the complete documentation index, see [llms.txt](https://docs.yudash.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.yudash.com/pf/ct/mqtt.md).
# MQTT
MQTT is a lightweight publish/subscribe protocol widely used for IoT telemetry.
In a typical YuDash installation, the **YuDash device acts as an MQTT client and publisher**. It connects to an MQTT broker and publishes the configured payload to a topic. The broker then makes that data available to the receiving IoT platform or other subscribed MQTT clients.
### MQTT Example
In this example, a YuDash FELYX device will publish two telemetry variables:
* **Temperature**
* **Humidity**
These variables may be acquired from any configured sensor interface, such as **Modbus, analog inputs, or another supported source**. Once available inside the device, they are encoded into a JSON payload and published over MQTT.
For this example, **ThingsBoard Cloud** is used as the receiving IoT platform and MQTT broker.
The target telemetry payload is:
```
{
"Temperature": 29.01,
"Humidity": 67.39
}
```
The complete flow is:
```mermaid
flowchart LR
A["Temperature / Humidity"] --> B["YuDash FELYX"]
B --> C["JSON_FORMAT_10"]
C --> D["ThingsBoard MQTT Broker"]
```
#### Step 1 — Open the MQTT Wizard
From **Cloud Settings**, select **Open MQTT Wizard**.
***
#### Step 2 — Configure Broker & Topics
Enter the connection details supplied by the MQTT broker or IoT platform.
For the ThingsBoard example:
| Setting | Example | Description |
| ------------------- | -------------------------- | ---------------------------------------------------- |
| **Broker Host** | `mqtt.thingsboard.cloud` | MQTT broker hostname or IP address |
| **Port** | `1883` | MQTT broker port |
| **Client ID** | `YuDash_FELYX` | Client identifier used by the YuDash device |
| **Username** | `` | Username or access token required by the broker |
| **Password** | blank | Password, where required |
| **Publish Topic** | `/v1/devices/me/telemetry` | Topic to which telemetry is published |
| **Subscribe Topic** | optional | Topic used where incoming MQTT messages are required |
| **YuDM Topic** | optional | Reserved for YuDash device-management applications |
The current FELYX configuration stores the broker address, port, client name, username, password and publish topic as MQTT settings. mqtt\_thingsboard
> Broker authentication varies between platforms. Some brokers use a username and password, while others use an access token or allow unauthenticated connections.
#### Step 3 — Select MQTT as the Cloud Protocol
Under **Device Settings → Cloud / Network Server**, select:
**Custom Protocol → MQTT**
#### Step 4 — Configure the Payload
MQTT defines **how the data is transported**; the Payload settings define **what data is published**.
For this example, **`JSON_FORMAT_10`** is used to generate a simple JSON key-value payload.
The target payload is:
```
{
"Temperature": 29.01,
"Humidity": 67.39
}
```
Each acquired variable is sent directly as a JSON key-value pair. This is a simple and widely compatible format for MQTT telemetry.
Payload format, timestamp and optional metadata are configured separately under **Cloud Telemetry → Payload**.
### Step 5 — Verify MQTT Telemetry
Once configured, FELYX periodically acquires the configured sensor values, generates the payload and publishes it to the MQTT broker.
In this example, FELYX acquires **Temperature** and **Humidity** as the telemetry variables.
#### Verify with an MQTT Subscriber
An independent MQTT client such as **MQTTX** can also be used to subscribe to a topic and verify the messages available through the MQTT broker.
This is useful during commissioning because it allows the transmitted MQTT payload to be inspected independently of the final IoT application.
> MQTTX is shown here only as an example MQTT subscriber. Any compatible MQTT client may be used.
#### Verify in ThingsBoard
The latest values received by ThingsBoard can be viewed under the device's **Latest telemetry** section.
The received values confirm the complete telemetry path:
**Sensor → FELYX → MQTT Broker → ThingsBoard**
If required, the stored telemetry can also be viewed as a time series.
####
### MQTT Publish Command Equivalent
Conceptually, the YuDash MQTT client performs the same operation as an MQTT publish command: it connects to the configured broker and publishes a payload to the configured topic.
For example:
```
mosquitto_pub \
-h mqtt.thingsboard.cloud \
-p 1883 \
-t v1/devices/me/telemetry \
-u "" \
-m '{"temperature":25}'
```
The corresponding relationship is:
| YuDash MQTT Setting | `mosquitto_pub` option |
| ----------------------- | ---------------------- |
| Broker Host | `-h` |
| Port | `-p` |
| Client ID | `-i` |
| Username / Access Token | `-u` |
| Password | `-P` |
| Publish Topic | `-t` |
| Generated Payload | `-m` |
The supplied ThingsBoard test uses the same broker, port, publish topic and access-token-style username. thingsboard\_mosquito
> **In simple terms, FELYX acts as an automated MQTT publisher:** it continuously acquires sensor data, generates the configured payload and publishes it to the configured MQTT broker.
