This document discusses using MQTT (Message Queuing Telemetry Transport) with a Raspberry Pi and Python to connect IoT devices. It provides an overview of MQTT, describes how to implement an MQTT broker using Mosquitto on Docker, and includes Python code examples to publish and subscribe to MQTT topics to control an LED connected to a Raspberry Pi remotely.

1. Martin Christen
FHNW – University of Applied Sciences and Arts Northwestern Switzerland
School of Architecture, Civil Engineering and Geomatics
Institute of Geomatics Engineering
martin.christen@fhnw.ch
@MartinChristen
Getting Started with IoT using a Raspberry Pi and Python
Quelle: http://cloudtimes.org/2013/09/09/introducing-web-3-0-internet-of-things/Quelle: https://www.hifiberry.com/2016/02/the-new-raspberry-pi-3-is-out/

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Quelle: https://www.ncta.com/platform/industry-news/infographic-the-growth-of-the-internet-of-things/

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MQTT (Message Queuing Telemetry Transport)
MQTT provides a lightweight method of carrying out messaging using a
publish/subscribe model. This makes it suitable for “machine to machine”
messaging such as with low power sensors or mobile devices such as phones or
the Raspberry Pi.
MQTT dates back to 1999.
MQTT is:
Open (ISO/IEC PRF 20922)
Lightweight (2 bytes header)
Reliable (QoS/patterns to avoid packet loss)
Simple (TCP based, async, publish/subscribe, payload agnostic)

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How MQTT works
Quelle: https://zoetrope.io/tech-blog/brief-practical-introduction-mqtt-protocol-and-its-application-iot

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XMPP Implementation: Eclipse Mosquitto
• Lightweight server implementation of MQTT written in C
• About 3 MB RAM with 1000 clients connected…
• http://eclipse.org/mosquitto
• Client support for Python 2.x and Python 3.x

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Dockerfile
FROM ubuntu:14.04
ENV DEBIAN_FRONTEND noninteractive
RUN apt-get update
RUN apt-get upgrade -y
RUN apt-get install wget build-essential libwrap0-dev libssl-dev -y
RUN apt-get install python-distutils-extra libc-ares-dev uuid-dev -y
RUN mkdir -p /usr/local/src
WORKDIR /usr/local/src
RUN wget http://mosquitto.org/files/source/mosquitto-1.4.8.tar.gz
RUN tar xvzf ./mosquitto-1.4.8.tar.gz
WORKDIR /usr/local/src/mosquitto-1.4.8
RUN make
RUN make install
RUN adduser --system --disabled-password --disabled-login mosquitto
USER mosquitto
EXPOSE 1883
CMD ["/usr/local/sbin/mosquitto"]
based on: https://hub.docker.com/r/ansi/mosquitto/~/dockerfile
docker build -t test-mosquitto .
docker run -p 1883:1883 test-mosquitto

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Python Client
pip3 install paho-mqtt
Documentation: https://pypi.python.org/pypi/paho-mqtt/
Source: https://github.com/eclipse/paho.mqtt.python

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MQTT: Subscribe
import paho.mqtt.client as mqtt
def on_connect(client, userdata, flags, rc):
print("Connected with result code " + str(rc))
# Subscribing in on_connect() means that if we lose the connection and
# reconnect then subscriptions will be renewed.
client.subscribe("SensorXY/#")
# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
print(msg.topic + " " + str(msg.payload))
client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
host = "192.168.99.100"
print("Connecting to " + host)
client.connect(host, port=1883, keepalive=60)
client.loop_forever()

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MQTT: Publish
import paho.mqtt.client as mqtt
def on_connect(client, userdata, flags, rc):
print("Connected with result code "+str(rc))
# The callback for when a PUBLISH message is received from the server.
# unused for this demo
def on_publish(client, userdata, mid):
pass
client = mqtt.Client()
client.on_connect = on_connect
client.on_publish = on_publish
host = "192.168.99.100"
client.connect(host, port=1883, keepalive=60)
client.loop_start()
topic = "SensorXY"
s = ""
while s != "exit":
s = input("payload >")
client.publish(topic, s)
client.loop_stop()

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Simple example: Remote-control a light from anywhere in the world
In the first example we turn on/off a LED using MQTT. The LED is connected on
GPIO Pin 11 (GPIO 17)
https://ms-iot.github.io/content/en-US/win10/samples/PinMappingsRPi2.htm

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How it works:
Raspberri Pi
MQTT
Broker
Subscribe and wait for command
«light on» or «light off»
Controller
Interface
Send command «light on», «light off», or «get status»
DB
save state
(optional)

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Raspberry Pi Client
import RPi.GPIO as GPIO
import paho.mqtt.client as mqtt
def on_connect(client, userdata, flags, rc):
print("Connected with result code " + str(rc))
# Subscribing in on_connect() means that if we lose the connection and
# reconnect then subscriptions will be renewed.
client.subscribe("Raspberry/#")
# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
s = str(msg.payload, encoding="ascii")
print("retrieved message: " + s)
if s == "lighton":
GPIO.output(LedPin, GPIO.LOW)
elif s == "lightoff":
GPIO.output(LedPin, GPIO.HIGH)
# Initialize GPIO
LedPin = 11 # pin GPIO 17, change if you connect to other pin!
GPIO.setmode(GPIO.BOARD)
GPIO.setup(LedPin, GPIO.OUT)
GPIO.output(LedPin, GPIO.HIGH) # turn off led
# Initialize MQTT
client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
host = "192.168.99.100"
print("Connecting to " + host)
client.connect(host, port=1883, keepalive=60)
client.loop_forever()
sudo pip3 install paho-mqtt

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Control Raspberry Pi
import paho.mqtt.client as mqtt
client = mqtt.Client()
host = "192.168.99.100"
client.connect(host, port=1883,
keepalive=60)
client.loop_start()
topic = "Raspberry"
print("COMMANDS:")
print("0: turn light off")
print("1: turn light on")
print("3: quit application")
s=0
while s!=3:
s = int(input("command >"))
if s == 0:
client.publish(topic, "lightoff")
elif s == 1:
client.publish(topic, "lighton")
elif s == 3:
print("bye")
else:
print("unknown command")
client.loop_stop()

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Questions ?