Skip to main content

Lesson 5 – Wrap-up and theory

Duration: 45 minutes
Target group: individuals, pairs or the whole class

Task: Sum up what you have learned, get to know the theory behind Node-RED and MQTT, and build a small project that ties it all together.

1. What you have achieved​

In the previous lessons, you:

  • prepared the HARDWARIO TOWER kit, paired modules and uploaded firmware,
  • measured various quantities (temperature, orientation, motion),
  • created charts and dashboards in Playground,
  • filtered messages and used conditions,
  • controlled the LED strip and other outputs.

In this lesson, you will connect all this knowledge, understand how it works “under the hood” and try it out in one complete project.

2. What is Node-RED​

Node-RED is a visual environment for “flow-based” programming that is often used in IoT.

  • It is made of nodes that receive, process and send messages.
  • Nodes are connected into flows.
  • A message usually has two important parts:
    • topic: the category or channel of the message
    • payload: the content of the message, for example a number, text or a JSON object
  • Nodes such as Switch, Change, Function or Debug modify messages, filter them or react to them.
  • Playground uses Node-RED to build flows visually, test them and interact with devices.

3. What is MQTT​

MQTT is a messaging protocol that is especially well suited to IoT.

  • The publish / subscribe principle: a device (publisher) sends messages to a certain topic, and other devices (subscribers) subscribe to that topic and receive the messages.
  • The difference from sending directly: the publisher does not know who will receive the message, and the subscriber does not know who sent it.
  • A broker is the server that relays all the messages.
  • Important features:
    • a hierarchy of topics (for example home/room1/temperature)
    • QoS (Quality of Service) levels, for example “delivered at least once” or “delivered exactly once”
    • retained messages: the last message can be stored, and new subscribers receive it as soon as they subscribe
  • Security: authentication, encrypted communication, careful management of keys and tokens.

4. How it all fits together: the architecture​

In a simplified view, a message travels through your projects like this:

  • The sensor module measures and sends the data to HARDWARIO Playground.
  • The HARDWARIO Playground application takes the message that the Radio Dongle received over the radio and publishes it over the MQTT protocol.
  • Node-RED processes the message from MQTT: it can filter it, react to it or pass it on again over MQTT.
  • The broker delivers the messages to everyone who subscribes to them: applications, output modules and dashboards.
  • The outputs react: LEDs, notifications and so on.

5. Final project​

Try the following project:

Task:

  1. Use a sensor (for example a temperature sensor) and a module that detects motion or orientation.

  2. When the temperature exceeds the set threshold and the sensor detects motion or a change in orientation at the same time:

    • the LED strip lights up red,
    • a message appears in HARDWARIO Playground.

  3. Show the current temperature, the motion or orientation status and the LED strip status on a dashboard.

  4. Draw the message flow: the topics, payloads, nodes in Node-RED, and who publishes and subscribes to what.

6. Good practice and pitfalls​

  • Name your topics carefully; clarity pays off.
  • Don’t send data more often than you need to; it saves the network and the device’s resources.
  • Security: never share passwords, tokens or keys, and choose strong passwords and keys.
  • Check what happens in case of an outage or error: what if a message from the sensor does not arrive or the MQTT broker is unavailable?

7. Reflection and sharing​

  • What was the hardest part for you? And the easiest?
  • Which part would you like to explore in more depth (for example how MQTT works, security, databases…)?
  • Share your project or message flow with others and explain how you built it.

Summary ✅​

Congratulations! You have completed the whole course, and you now know the HARDWARIO TOWER kit both in practice and in theory.
You have the basics for your own IoT projects and can keep developing them with your own ideas.