Exploring soil moisture sensors

Overview

• In this lesson we are going to connect to a soil moisture sensor.
• The soil moisture sensor is connected to an Arduino MKR 1300 microcontroller (a small computer).
• The data will be transmitted to the LoRa network.
• LoRa is short for Long Range radio communication.
• The data is then sent to The Things Network, which is a community run server that collects data from sensors and makes the data available for download.
• We will download the data to our Raspberry Pi, and in future lessons display that data in a Dashboard using Node-RED.
• All these skills are very important in helping to address Climate Change and general Environmental Sustainability issues the world faces.

Learning Objectives

• Learn how to connect to The Things Network using MQTT using Node-Red
• Learn how to extract specific data from JSON formatted data packets

Connecting to the Things network using Node-RED

• In this lesson we are going to use Node-RED as our main programming tool.
• Node-RED is a block or node based programming language.
• Each block has a discrete function and some blocks can contain Javascript code or be configured in different ways.
• Blocks are connected together using wires.
• Node-RED and the programs on the Raspberry Pi are always being updated, so it’s normally good practise to update our Raspberry Pi on a regular basis.

Updating and Upgrading the Raspberry Pi

• Open the Raspberry Pi Terminal.
• Enter the command sudo apt-get update

• This command will update all the software libraries on the Raspberry Pi, so that if we need to install software the Pi will install the latest software packages.
• Enter the command sudo apt-get full-upgrade -y
• This command will upgrade the entire operating system on the Raspberry Pi.
• The -y option tells the computer to answer Yes to any questions.
• The upgrade will take between 5 and 30 minutes to complete.
• It is always to do this once every month.

Running Node-RED on the Raspberry Pi

• Open the Terminal.
• To start Node-RED enter the command node-red

• The display on your Raspberry Pi will be different, but similar enough.
• When using Node-RED it is important to stop Node-RED when you are shutting down your computer.
• To close Node-RED open a new Terminal window and enter the command node-red-stop
• To re-start Node-RED enter either node-red or node-red-start

• It takes Node-RED approximately 20 seconds to boot up.
• To see the Node-RED interface we need to use a Web Browser.
• Open the default Web Browser on the Raspberry Pi.
• In the Search Bar enter localhost:1880 (or http://localhost:1880)
• The number 1880 represents a Port. Your computer listens and talks on different ports to make communication between devices and systems easier.
• Localhost is an abbreviation for 127.0.0.1 which is a address reserved for the host computer (the Raspberry Pi)

• Node-RED can be installed on Windows, Mac or other Linux machines.
• In a few moments the Node-RED programming environment will be displayed.
• One the left is the Node-RED Pallet containing an assortment of Nodes.
• In the middle is the Node-RED Flow Editor
• On the right are different debugging and system related tools.

Connecting to The Things Network using MQTT

• To download the data generated by our sensor we can use MQTT.
• MQTT is short for Message Queuing Telemetry Transport.
• Using this protocol we can subscribe to newly published data. As soon as new data arrived it is delivered to our device, just like a daily news feed or other subscription.
• To subscribe to our sensor data we need to use a mqtt in node
• Search for the mqtt in node in the pallet on the left and drag it into the Editor Window.

• If the mqtt in node is difficult to find you can enter mqtt in the search bar at the top of the pallet.
• In this example we can see that two results are returned, one for mqtt in and one for mqtt out.

• Note that the mqtt in node has two coloured shapes attached to the node:
  • the red triangle means that the node still needs to be configured
  • the blue circle means that the node need to be Deployed before it will work
• To configure the node, double click on it.
• This will open a Sidebar that will pop out from the right hand side.
• For the Server parameter, we will select Add new mqtt-broker and then click on the Edit tool, which looks like a pencil icon.

• The Edit tool will open up another Sidebar listing the Properties for the mqtt-broker node.
• Enter the following details under the Connection tab:
  • Name – soil-7
  • Server – au1.cloud.thethings.network
  • Port – 1883
  • Protocol – MQTT V3.1.1 (if you don’t see the Protocol parameter you don’t need to change any other settings)
• Now click on the Security tab.

• Enter the following details in the Security tab:
  • Username – whi-soil-7-moisture-mkr-1300@ttn (the username is simply a unique name given to the soil moisture sensor on The Things Network. The name is short for Whittlesea soil moisture sensor #7 running on an Arduino MKR 1300 microcontroller)
  • Password - NNSXS.WL5EA6KF6TWUZCALAIIEWNX7YED4ADI5QQOTK7A.XYRLCUHY6WGY5Z5O6TS7A7UFAACBNY72WIZPAITY6K3LTYLOVZXA (Enter this passwork exactly as shown. This key is generated on The Things Network Console. We will demonstrate this in an upcoming lesson)
• Click on Update to commit these changes.

• Once the Server has been configured there are some other minor configurations in the mqtt in node:
  • Topic - # (the hash symbol # indicates that we are subscribing to all topics)
  • QoS (Quality of Service) – 0 (only zero is supported by Node-RED. Normally higher numbers reflect better error detection)
  • Output – a parsed JSON object (all the data sent from the mqtt in node will be in JSON format. JSON format is similar to a dictionary. There is always an attribute and value pair. For example {colour:blue}. JSON objects are enclosed in curly brackets).
  • Name – soil-7 (this node will be subscribing to data from soil moisture sensor #7)
• Click on Done when finished.