MQTT Interface¶

The MQTT Interface is used to communicate drag&bot with the MQTT broker to exchange JSON messages.

General Notes¶

drag&bot MQTT component includes a MQTT client using QoS level 2 (Quality of service) and supporting MQTT versions 3.1, 3.1.1, and 5.0.

JSON messages are used to communicate the data. They are sent as strings.
When the hyphen is entered "-" in the UserName and/or Password fields then the MQTT client will try to communicate to the broker without any kind of authentication (open broker).
It's highly advisable to use some kind of authentication in the MQTT broker, this can be a userName/Password access or an ACL (Access control list).

Drag&bot MQTT Client¶

Important

Client ID should be unique.

drag&bot acts as a bridge to map the ROS topics data to the MQTT topics and vice versa.
If you would like to allow other clients to control/get the status of the drag&bot programs on your IPC, then you need to activate the flag Allow line controller in the component manger.

Mapping¶

You can configure the mapping functionality in the component manager using the fields ROS to MQTT Topics and MQTT To ROS Topics.

When the hyphen is entered "-" in the Topics names field, then this field will be ignored and no topics will be created.
Any space in the Topics names will be ignored.
You don't need to start with / the topic names in the component topic list.

ROS to MQTT Topics¶

This field is used to map ROS topics to MQTT topics. For multiple topics, write a list of comma separated pairs:

ROS_topic_name : MQTT_topic_name , ROS_topic_name_1 : MQTT_topic_name_1 , etc.

In the example the ROS_topic_name is mapped to MQTT_topic_name.

MQTT To ROS Topics¶

This field is used to map MQTT topics to ROS topics. For multiple topics, write a list of comma separated pairs:

MQTT_topic_name : ROS_topic_name , MQTT_topic_name_1 : ROS_topic_name_1 , ...etc.

In the example the MQTT_topic_name is mapped to ROS_topic_name.

Function Blocks¶

Send Message¶

This function block is used to send JSON string message to MQTT topics (mapped from ROS to MQTT) using its equivalent ROS topic.

	Field name	Data type	Description
Inputs	ROS Topic Name	String	The ROS topic name that is mapped to the required MQTT topic.
	JSON Message	String	The JSON message to be published.
Outputs	-	-	-

Await Message¶

This function block waits until a message is received from specific ROS topic (mapped from MQTT to ROS) and returns the received JSON as string output

	Field name	Data type	Description
Inputs	ROS Topic Name	String	The ROS topic name that is mapped from the required MQTT topic.
Outputs	Received JSON	String	The received JSON message from the MQTT Topic

Start Program¶

This function block starts a drag&bot program at another MQTT client. To use this FNB, the flag Allow line controller must be activated at the another MQTT client.

Important

To start the program remotely, you need to deploy it to the robot system, see section Install Programs for installing programs on the Robot System.

	Field name	Data type	Description
Inputs	Client ID	String	The MQTT client ID of the IPC that contains the program to start.
	Program Name	String	The program name to be started
	Timeout	Float	Timeout in seconds. 0 = wait for ever
Outputs	Success	Boolean	Command executed successfully

Stop Program¶

This function block stops a drag&bot program at another MQTT client. To use this FNB, the flag Allow line controller must be activated at the another MQTT client.

	Field name	Data type	Description
Inputs	Client ID	String	The MQTT client ID of the IPC that contains the program to stop.
	Timeout	Float	Timeout in seconds. 0 = wait for ever
Outputs	Success	Boolean	Command executed successfully

Get Program Status¶

This function block get the drag&bot program status from another MQTT client. To use this FNB, the flag Allow line controller must be activated at the another MQTT client.

	Field name	Data type	Description
Inputs	Client ID	String	The MQTT client ID of the IPC that contains the program to stop.
	Timeout	Float	Timeout in seconds. 0 = wait for ever
Outputs	Running	Boolean	The program is running at the MQTT client
	Stopped by User	Boolean	The program is stopped manually by a user (using MQTT Stop Program function block)
	Finished Correctly	Boolean	The program execution is finished without an error.
	Stopped with Error	Boolean	The program is stopped due to an error

Broker¶

These steps describe the installation of the Mosquitto broker. Alternatively you can set your own broker.

Installation through standard sources¶

The following terminal commands install a broker in your main Ubuntu operating system:

sudo apt-get update sudo apt install mosquitto -y

After the Installation, the mosquitto broker will be immediately launched and also started automatically at the system startup.

The broker IP will be the PC IP where it is installed on. The port number is configured in the mosquitto configuration file (default : 1883).

Configuration¶

Create a file that contains the user name and the password, call it for example pass under the path /etc/mosquitto/ using the command sudo nano /etc/mosquitto/pass. The file should contain the username and password as below. After that save and close the file.
Run the code mosquitto_passwd -U /etc/mosquitto/pass to encrypt the password.
Open the mosquitto configuration file mosquitto.conf under the path /etc/mosquitto/ using the command sudo nano /etc/mosquitto/mosquitto.conf and insert these lines :

listener 1883

allow_anonymous false

password_file /etc/mosquitto/pass

This will configure the mosquitto to accept the connection from a client with a userName and password authentication on port nomber 1883.

Finally restart mosquitto using the command sudo systemctl restart mosquitto