ProjectInfoBox MQTT Broker

Status:	done
Release Date:	July 2018
Initiator:	Martin
Team:	Martin
Tools Used:	Raspberry Pi
Software Used:	MQTTBroker

MQTT Overall

MQTT (Message Queue Telemetry Transport) is a communication protocol with a strong focus on a small data footprint.
Therefore, it is perfect for communication between lightweight devices (such as microcontrollers like the ESP8266). MQTT generally runs on TCP/IP, but there is also an extension (MQTT-SN), which can be used on non-TCP networks. Further information can of course be found on Wikipedia, mqtt.org or - if you require German information - Informatik-Aktuell published a nice introduction article.

Broker

Since MQTT follows a client/server architecture, a central server is needed in order to publish messages and to subscribe to messages. This server is called broker. Since MQTT is an open protocol, multiple implementations exist, which have been compared on GitHub.

Client usage

As mentioned, MQTT is designed to run on a broad variety of devices. As of this, implementations exist for microcontrollers, regular PCs as well as smartphones.
If you want to learn more about topics, messages, subscriptions and QoS, please read this part of the mosquitto documentation.

Libraries

If you want to integrate MQTT in your project, please check the selection of client libraries on GitHub.

Microcontroller

For anything using the Arduino IDE, please use PubSubClient. Martin and Patrick have tried the Adafruit MQTT library as well as the one from the paho project. Both sucked (in different ways, but basically critical things did not work).

Clients with UI

If you want to "just use" MQTT on your device and check the messages in our network, please see this article.
On PCs, we have made good experiences with MQTT.fx, which is a Java based client.
On Android, we have been making good experiences with MyMQTT.

MQTT in the CoMakingSpace

In order to be able to use MQTT in the CoMakingSpace, the Raspberry Pi in the common room runs an instance of mosquitto, which is an open source MQTT broker.

Our implementation runs on the same Raspberry Pi in the common room that also hosts Project:Music Station. Therefore, the hostname is comakingcontroller (having a fixed IP: 192.168.1.2). It offers its services on the standard MQTT port: 1883.

Automated Publishing

Shell

In addition to the broker, the pi in the common room also got the mosquitto-clients package installed. This package mainly provides mosquitto_pub and mosquitto_sub. This means that you can publish messages via the shell. Of course, this can also be automated via a cron job. An example message could be published as follows:
mosquitto_pub -h comakingcontroller -t /CommonRoom/FDD/Text -m "Test"

Python

For python users, the paho-mqtt package was installed. So feel free to use python scripts to publish messages.An example can be found on github. This should work both with Python 2 and Python 3. Of course, it is recommended to use Python 3 for any new scripts!

Users

The following projects use - or will use - the MQTT Broker:

Topics

If you create a new topic, it would be great if you document it here.
Right now, the following topics exist:

Topic	Description
/CommonRoom/FDD/Text	Send text to the FlipDot Display. It will be displayed immediately.
/CommonRoom/FDD/Binary	not implemented yet. Will be used to send binary data directly to the FlipDot Displays. Please note that it will be the senders responsibility to send meaningful data. Anything else will lead to rubbish being displayed.

Project:MQTT Broker

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