Lab Session 8: IoT with M5Core2

Estimated time: 1.5h (1 session)

1. Working with real hardware

General considerations

In this lab session, an MQTT network will be implemented consisting of two M5Core2 devices connected through a common broker. Within the network, one device will have the role of publisher and will publish to a topic when a button is pressed. The other device will act as a subscriber and, depending on the message received from the publisher, will change the screen color as described below.

• The WiFi network that the devices must connect to will be the local network:
  • SSID: InfInd
  • Password: InfIndMQTT
• As a broker, you can use one of the following options:
  • A public broker such as test.mosquitto.org or mqtt.eclipseprojects.io.
  • A private broker created with mosquitto if you have followed the steps on this page.

Warning

Be careful with names! If you are going to work on a public broker, you must be careful with the client name and topic names: - On the same broker, there cannot be two clients with the same name. - If you use a very generic name on a public broker (e.g., "test" or "topic"), it is very likely that there is another client publishing or subscribing to those topics. In this case, it is advisable to use non-generic names (e.g., using your name) to avoid interfering with other network clients.

Part 1: Publisher

Create a script for M5Core2 (publisher) that does the following:

• If button A (\texttt{M5.BtnA}) is pressed, it publishes the message "Red" to a topic (e.g.: \M5\color).
• If button B (\texttt{M5.BtnB}) is pressed, it publishes the message "Yellow" to a topic (e.g.: \M5\color).
• If button C (\texttt{M5.BtnC}) is pressed, it publishes the message "Green" to a topic (e.g.: \M5\color).

Note

To check if a button has been pressed, you can use the wasReleased() function (e.g., M5.BtnA.wasReleased()).

Part 2: Subscriber

Create a script for M5Core2 (subscriber) that does the following:

• Subscribe to the topic where the other M5Core2 publishes (e.g.: \M5\color)
• The screen changes to the color of the message that has been received. You can use the \texttt{fillScreen() function (e.g., M5.Lcd.fillScreen(RED)).

Part 3: Extension

• On the publisher: The message is not published until button A is pressed for more than one second. That is, the last button that has been pressed (A, B, or C) must be stored, but the message is not sent until button A is pressed for more than one second. You can use the pressedFor() function.
• On the subscriber: If the message is none of the above, the screen turns black.
• On the subscriber: Publish to the topic \confirmacion the message "Message received" when a message has been received and the screen color has been changed. This way, the device will be both subscriber and publisher at the same time.
• On both: Write on the screen of the device acting as publisher the options (e.g.: Press A for "Red", or Message "Red" sent). Write on the screen of the device acting as subscriber the status of received messages (e.g.: Message "Red" received, color changed).

2. Working in simulation

The exercise can be done in simulation following the instructions described on this page