Temperature sensor data visualisation with Node-RED

Overview

This lesson assumes that a temperature sensor is sending data to The Things Network. In this lesson we will use the MQTT protocol to subscribe to data transmission events. We will create a program in Node-RED to subscribe to the data transmissions and to graph the data coming from the sensor using the in-built Dashboard function in Node-RED.

Learning Objectives

• Learn how to subscribe to a MQTT using the Node-RED MQTT-in node
• Learn how to extract specific sensor data using the Node-RED function node.
• Learn how to create a Dashboard in Node-RED to monitor live data.

Subscribe to MQTT

Open Node-RED

• Click on the Raspberry Pi main drop down menu.
• Select Programming > Node-RED

• Node-RED will automatically open the Terminal on the Raspberry Pi.
• It takes approximately ten seconds for Node-RED to initialise itself.

• To actually use Node-RED you need to open the web browser on the Raspberry Pi.
• Click on the default web browser.
• In the search bar enter localhost:1880
• Localhost is the address of the local or host machine.
• In this example the host address is 192.168.1.168, but your computer will have a different address.
• The number at the end of the URL (1880) is the port number for the Node-RED application.
• Different ports are assigned to different applications using HTTP protocols.
• Note - if you are using UFW (uncomplicated firewall) you may need to open this port otherwise Node-RED will not work.

Subscribing to MQTT

• To subscribe to MQTT we need the 'mqtt in node.
• Find the mqtt in node and drag it onto the Flow 1
• You will notice that the node has both a blue circle and a red triangle.
• The red triangle indicates that the node requires further configuration before it will work

Configuring the mqtt in node

• Double click on the mqtt in node.
• In Properties > Server > select Add new mqtt-broker
• Click on the Edit button to the right - which looks like a pencil

• Enter the following details:
  • Properties > Name > pycom-temperature-1
  • Connection > Server > au1.cloud.thethings.network
  • Connection > Port > 1883
  • Leave all other details as shown in the example below.

• Click on the Security tab
• The Username is whi-seedling-1-pycom@ttn
• The Password is NNSXS.Z625CQKKEWAPSQK467JRSAFFYINH7LTHSUC5CYY.MHEVWHKKLPWXQWESSCALZFVHA6EKUNISQH4IVHKAOXYZRMOH6D7A
• If copying these fields from mediawiki or another computer use right mouse button click copy
• Click on the red Add button to commit the changes.

• You will be asked to complete some final configuration settings.

• Update the following fields:
  • Topic # - The hash symbol means subscribe to all topics
  • QoS 0 - quality of service. A value of zero equates to a low quality. Data losses are acceptable.
  • Output a Parsed JSON Object - JSON format output for all data
  • Name pycom-temperature-1
• Then click on Done to commit all the edits.

• The finished mqtt in node should now appear in the main flow window.
• It will still have a blue circle because the flow has not been Deployed.

Add a Debug Node

• Before we Deploy this first flow we will need to add a Debug node.
• Drag a Debug node from the pallet and connect it to the output of the mqtt in node (pycom-temperature-1).

Set the Debug Window

• The Debug node will show us all the JSON data output coming from mqtt in node.
• To see the Debug output click on the Debug messages tab.

• Click on the Deploy button to make the flow active.
• Message should appear indicating that the flow has been successfully Deployed.
• The mqtt in node will also show a green connected status message underneath the node.

Receiving mqtt data

• When data arrives from the temperature sensor (approximately every 30 minutes) it will appear in the Debug window on the right of the screen.
• The data is presented in a compacted form.

• By clicking on the drop down arrows in the message the different sections of the message can be expanded.
• Expand the uplink_message and the decoded_payload to see the sensor data.

Extracting specific sensor data

• We can extract specific sensor data using the Node-RED function node.

Obtaining battery data using the function node

• In this example we will prepare a function node to extract the battery data.
• Drag a function node into the Edit window.

• Then drag a Debug node and wire up all nodes as shown.

Editing the Function node

• Double click on the Function node to bring up the edit window.

• Enter the following code to extract just the battery data.
• Then click on Done to commit the edits.

• The code has been reproduced below.

var time = msg.mytime.concat(" " + (msg.myymd));
var battery; // battery voltage data
var humidity; // humidity data from within the sensor housing
var onewire_temp; // onewire temperature data
var temperature; // temperature data from within the sensor housing

battery = msg.payload.uplink_message.decoded_payload.bat;
humidity = msg.payload.uplink_message.decoded_payload.humid;
onewire_temp = msg.payload.uplink_message.decoded_payload.onewire_temp;
temperature = msg.payload.uplink_message.decoded_payload.temp;

msg.payload = "time=" + String(time) + " "
            + "bat=" + String(battery) + " "
            + "humid=" + String(humidity) + " "
            + "onewire_temp=" + String(onewire_temp) + " "
            + "temp=" + String(temperature);

return msg;

• The complete nodes should appear as in the image below.
• Click on Deploy to make the flow active.

• Click on the Clear log button to clear the Debug window.

• When new messages arrive they can be more clearly seen in the Debug window.
• In this case the voltage of the battery is 4 (4.00 V).

Appendix

• Node-RED code

[
    {
        "id": "79ec9068.0e03",
        "type": "tab",
        "label": "Flow 1",
        "disabled": false,
        "info": ""
    },
    {
        "id": "89fbf612.be32e8",
        "type": "mqtt in",
        "z": "79ec9068.0e03",
        "name": "pycom-temperature-1",
        "topic": "#",
        "qos": "0",
        "datatype": "json",
        "broker": "770475c1.8593ac",
        "nl": false,
        "rap": true,
        "rh": 0,
        "x": 170,
        "y": 100,
        "wires": [
            [
                "4b6b348d.47990c",
                "dbc45c13.5f904"
            ]
        ]
    },
    {
        "id": "4b6b348d.47990c",
        "type": "debug",
        "z": "79ec9068.0e03",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 420,
        "y": 100,
        "wires": []
    },
    {
        "id": "dbc45c13.5f904",
        "type": "function",
        "z": "79ec9068.0e03",
        "name": "battery",
        "func": "var battery; // battery voltage data\nvar humidity; // humidity data from within the sensor housing\nvar soil_temp; // soil temperature data\nvar temperature; // temperature data from within the sensor housing\n\nbattery = msg.payload.uplink_message.decoded_payload.bat;\nhumidity = msg.payload.uplink_message.decoded_payload.humid;\nsoil_temp = msg.payload.uplink_message.decoded_payload.soil;\ntemperature = msg.payload.uplink_message.decoded_payload.temp;\n\nmsg.payload = battery; //only the battery voltage data\n\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 420,
        "y": 180,
        "wires": [
            [
                "a904005e.54aa6"
            ]
        ]
    },
    {
        "id": "a904005e.54aa6",
        "type": "debug",
        "z": "79ec9068.0e03",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 610,
        "y": 160,
        "wires": []
    },
    {
        "id": "770475c1.8593ac",
        "type": "mqtt-broker",
        "name": "pycom-temperature-1",
        "broker": "au1.cloud.thethings.network",
        "port": "1883",
        "clientid": "",
        "usetls": false,
        "protocolVersion": "4",
        "keepalive": "60",
        "cleansession": true,
        "birthTopic": "",
        "birthQos": "0",
        "birthPayload": "",
        "birthMsg": {},
        "closeTopic": "",
        "closeQos": "0",
        "closePayload": "",
        "closeMsg": {},
        "willTopic": "",
        "willQos": "0",
        "willPayload": "",
        "willMsg": {},
        "sessionExpiry": ""
    }
]