MQTT Publish

Publish messages to MQTT broker on specified topic

Since R2024a

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  • MQTT publish block

Libraries:
STM32 Microcontroller Blockset / STM32F4xx Based Boards
STM32 Microcontroller Blockset / STM32F7xx Based Boards
STM32 Microcontroller Blockset / STM32H7xx Based Boards

Description

The MQTT Publish block publishes messages from your hardware (publisher) to the Message Queuing Telemetry Transport (MQTT) broker on the specified topic.

The Message port accepts the message to be published to the broker. The Status port outputs the status of the publish request. The string topic/level on the block icon is specified by the Topic parameter.

For more information on MQTT, see Introduction to MQTT.

Note

The MQTT Publish block supports MQTT only over TCP/IP sockets.

Examples

Process ECG Signals Using MQTT on STM32 Processor Boards

Process ECG Signals Using MQTT on STM32 Processor Boards

Use the STM32 Nucleo F767ZI board using STM32™ Microcontroller Blockset to process an ECG signal input from an ECG sensor, extract the heart rate in beats per minutes (BPM), and send the ECG signal and heart rate to the ThingSpeak™ internet of things (IoT) analytics platform service.

Ports

Input

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The message to be published to the MQTT broker, specified as a vector.

Example: [0,3]

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

Output

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The status code issued by the MQTT broker in response to the publish request. If the broker accepts the message for publishing, the port outputs 0. A nonzero output indicates that the broker has rejected the message. A message can be rejected for various reasons, such as an incorrect user name or password or an unacceptable protocol version. For more information on status codes from MQTT brokers, see LWIP error code.

Data Types: int8

Parameters

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Select the MQTT broker service provider that receives, filters, and sends messages to the clients.

  • ThingSpeak — When you specify this option, the MQTT access to your channels is handled by a ThingSpeak™ MQTT broker. To create an MQTT device, follow the steps in Create a ThingSpeak MQTT device (ThingSpeak).

  • Other — Specify this option when the MQTT access to your channels is handled by other MQTT public brokers such as HiveMQ®, Mosquitto™, and so on.

Configure the same MQTT broker properties as in the MQTT.

Programmatic Use

Block Parameter: Broker Service
Type: character vector
Values: 'ThingSpeak'|Others
Default: 'ThingSpeak'

Specify a topic on which the message is to be published. A topic can have a maximum of 128 characters. For information on topics and its structure, see Topics in MQTT.

Programmatic Use

Block Parameter: Topic
Type: character vector
Values: Channels/<channelID>publish|valid channel
Default: Channels/<channelID>publish

Quality of Service (QoS) defines the reliability of the message delivery process in MQTT. MQTT provides three QoS levels for message delivery: QoS 0, QoS 1, and QoS 2. The MQTT broker that you are using might not support the three levels of QoS. For example, ThingSpeak MQTT supports only QoS 0.

Select a QoS level from the list:

  • 0 (At most once): The publisher sends the message to the MQTT broker once. The broker does not send an acknowledgment of the receipt.

  • 1 (At least once): The publisher sends the message to the MQTT broker at least once. The publisher resends the message if it does not receive an acknowledgment from the broker.

  • 2 (Exactly once): The publisher sends the message to the MQTT broker exactly once. The publisher and broker exchange acknowledgments so that the message is received only once.

For more information on QoS levels, see Levels of QoS in MQTT.

Programmatic Use

Block Parameter: QoS
Type: character vector
Values: '0'|'1'|'2'
Default: '0'

The Retain message parameter controls how new subscriptions are handled:

  • on –– When a new subscription is made to a topic, the broker identifies the message in its database with the matching topic name and sends the message immediately.

    Note

    The MQTT broker retains only the last known message published on a topic.

  • off –– When a new subscription is made to a topic, the subscriber must wait until the publisher sends the next message.

    Note

    For example, ThingSpeak MQTT do not support Retain message.

Dependencies

To enable this parameter, set Broker Service to Other.

Programmatic Use

Block Parameter: RetainMsg
Type: character vector
Values: 'off'|'on'
Default: off

Enter the time interval in seconds to publish message(s) to the MQTT broker.

Programmatic Use

Block Parameter: Update interval (seconds)
Type: character vector
Values: '60'|'on'
Default: 60

Version History

Introduced in R2024a

See Also

Blocks

Topics