Build Instructions

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• 1

  Installing MQTT broker on Raspberry Pi

  For this project we use an open source Mosquitto MQTT broker. It is lightweight and is suitable for use on all devices from low power single board computers to full servers.

  Before we start installing, it's a good practice to update the system components first:

  $ sudo apt-get update
  $ sudo apt-get upgrade

  Install Mosquitto broker. Open a terminal and type the following command:

  $ sudo apt-get install mosquitto -y

  Configure Mosquitto broker. Edit config file:

  $ sudo vi /etc/mosquitto/mosquitto.conf

  and add the following lines at the top:

  port 1883allow_anonymous true

  Restart RPi to apply changes:

  $ sudo reboot

  That's it! Our MQTT broker is up and running now!

  NOTE: for the sake of simplicity of this project we are not creating accounts. So anyone within our local network can connect to this MQTT broker without credentials. If you want to add user authentication and make it more secure, there are plenty of tutorials on the internet how to do it.

  Now, we just need to obtain IP address so we can send messages to our Mosquitto broker from other devices in the network:

  Obtain IP address:

  $ hostname -I

  your_RPi_IP_address (e.g. 192.168.1.10)

• 2

  Connect IOT Cricket to RaspberryPi over MQTT

  In this project we use the IOT Cricket WiFi module for a simple sensor to report a temperature every 30 seconds to our system. It will run on a battery so we can stick it anywhere at home or a garden. Later you can use IOT Cricket to build various battery powered sensors, alarms, buttons, switches and connect them too to our RPi MQTT broker out of the box.

  In the first step connect batteries to Cricket.

  Cricket comes with a built-in temperature sensor. We just need to configure it to send temperature value to our MQTT broker by setting the RPi IP address.

  In order to do that open Cricket's configuration panel (see the steps here) and apply the following settings (as shown on the image below, please adjust IP address in "url" box to your RPi)

  Now we can exit from the configuration mode.

  The device is ready! Cricket is already sending data to our MQTT broker every 30 seconds.

• 3

  Inspect MQTT messages

  To view / receive messages sent to our MQTT broker we can use various tools.

  The easiest one might be a command line tool mosquitto_sub. We can install it either on any computer in our network or on our RPi with this command:

  $ sudo apt-get install mosquitto-clients -y

  Now we can execute the following command to listen to ALL topics and messages send via our MQTT broker:

  $ mosquitto_sub -v -h your_RPi_IP_address -p 1883 -t '#'
  ...
  /59A98F494C/device_name MyTemperatureDev
  /59A98F494C/device_sn 59A98F494C
  /59A98F494C/hwc_wake_up 3794
  /59A98F494C/hwc_wifi_enabled 3763
  /59A98F494C/hwc_message_sent 3664
  /59A98F494C/temp 26.0
  /59A98F494C/io1_wake_up 0
  /59A98F494C/rtc_wake_up 1
  ...

  The above is an output example of what IOT Cricket sends to our broker. Among the other data we can see there is a temperature: /59A98F494C/temp 26.0

  The beauty of MQTT is that it allows us to subscribe to only topics which we are interested in. If we want to receive just a temperature, we can subscribe to /59A98F494C/temp topic by using the following command:

  $ mosquitto_sub -h your_RPi_IP_address -t '/59A98F494C/temp'
  ...
  26.1
  26.5
  27.2
  27.6
  ...

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