The MQTT Publisher example is an MQTT client that connects to the broker identified by the broker address configured in the example at compile time. If the connection succeeds, it is ready to publish the LED state information under the topic "led/state".
The example allows you to disconnect the MQTT client from the broker and then reconnect.
An overview of how the examples could be used is shown in the scenarios below. Scenario 1 is a complex, but possibly a real-time scenario where there are one or more publishers and subscribers. In this scenario, not all MQTT clients (publishers/subscribers) have to be BLE-enabled IPv6 devices. They could as well be computer applications and/or embedded devices, wired or wireless, that use MQTT as the application protocol over the IP stack. This scenario is seen as a superset of possible scenarios.
Scenario 2 shows a possible use case where the nRF52 SoC MQTT publisher is used to send a message to the subscribers that are not BLE MQTT clients, such as computer applications. This scenario is realized when the Mosquitto subscriber application is used to test the publisher application on the nRF52 SoC.
Scenario 3 shows a possible use case where all the MQTT clients are nRF52 devices running MQTT clients, either publisher or subscriber. This scenario is realized when the subscriber and the publisher applications included in this SDK are used to connect to the MQTT broker.
This section summarizes the usage of the nRF52 SoC resources and common modules in the examples, apart from the IoT 6LoWPAN and lwIP stack library.
Module | Inclusion/Usage | Description |
---|---|---|
Timer | 3 | Timer for lwIP, LEDs, and the button module. |
Button | 3 | Buttons are used to control the application. See Button assignments. |
LEDs | 4 | LEDs are used to indicate the application states. See LED assignments. |
Adv Data Encoder | Yes | The device name used is 'MQTTPublisher'. The IPSP Service UUID is included in the UUID list. |
Scheduler | Yes | Scheduler is used for processing stack events. |
<InstallFolder>external/lwip/license.txt
You can find the source code and the project file of the example in the following folder: <InstallFolder>\examples\iot\mqtt\lwip\publisher
LED 1 | LED 2 | Description |
---|---|---|
Blinking | Off | Device advertising as BLE peripheral. |
Off | Blinking | BLE link established, IPv6 interface down. |
On | Off | BLE link established, IPv6 interface up. |
Off | On | MQTT connection is established. |
On | On | Assertion failure in the application. |
LED 3 | LED 4 |
---|---|
Flashes once, if publishing of the LED state failed. | Shows the last successfully published LED state. |
Button | Mapped Action |
---|---|
1 | MQTT Connection Request |
2 | MQTT Publish Topic |
3 | MQTT Disconnection |
The example by default requests a secure connection on MQTT Secure port 8883. In order to disable security for MQTT clients, follow these steps.
Refer to Setting up the Mosquitto MQTT broker for a detailed description of how to set up Mosquitto in various configurations.
Since the example uses security by default, the broker must be set up to use TLS.
This section describes how Mosquitto can be used as a subscriber application to test this example.
See Connecting devices to the router for a list of relevant Linux commands.