diff options
Diffstat (limited to 'assignments/mqtt-with-button/mqtt-with-button.md')
| -rw-r--r-- | assignments/mqtt-with-button/mqtt-with-button.md | 50 |
1 files changed, 27 insertions, 23 deletions
diff --git a/assignments/mqtt-with-button/mqtt-with-button.md b/assignments/mqtt-with-button/mqtt-with-button.md index c825615..30defc8 100644 --- a/assignments/mqtt-with-button/mqtt-with-button.md +++ b/assignments/mqtt-with-button/mqtt-with-button.md @@ -6,6 +6,11 @@ * Publish a message when a button is pressed. * Subscribe to a topic to control the LED +## Preparation + +* Install the *PubSubClient* library. Use the library manager under + *Sketch -> Include library -> Library Manager* to install it. + ## Step 1 Wire up this schematic on the bread board: @@ -16,10 +21,8 @@ Wire up this schematic on the bread board: # Step 2 -* Tip: change upload speed to max. - -* Read button in `loop()`. If the button's state changes, print a - message. +* Read button's value inside `loop()`. If the button's state changes, + print a message. *Note:* reading the button in a busy loop is not really a best practice as it uses lots of energy. Instead use the `attachInterrupt`. @@ -29,34 +32,35 @@ practice as it uses lots of energy. Instead use the `attachInterrupt`. * Connect to the Wi-Fi network * Connect to MQTT broker +See the slides for example code. + # Step 4 -* Publish a message on button press on the topic +* Create a subscription for `ndc/$device-id/#` with HiveMQ's web ui: + http://www.hivemq.com/demos/websocket-client/ +* Publish a message when the button is pressed on the topic `ndc/$device-id/button` # Step 5 (Bonus) -Subscripe to a topic and do something with the led. - -* Subscribe to the topic you're publishing to. - -* Subscribe to the topic `ndc/$device-id/led`. - -* Use the value to for example turn the LED on/off, or change the - LED's blinking pattern. +*Feel free to be creative here.* -## Tips +The other useful half of MQTT is subscribing to topics and reacting to +messages. Here are some example things you can do: -To generate a client id make something with `ESP.getChipId()`{.cpp} +* Subscribe to the topic you're publishing to and change the state of + the LED when the button is pressed. This will give you a very + complicated and brittle way of toggling a LED. -Creating a `String` from a number: +* In `loop` blink the led. Subscribe to another topic (for example + `ndc/$device-id/frequency`), and use the value as a way to control + the blink rate. -* `String(123) => "123"`{.cpp} -* Hex formatted: `String(0x123abc, HEX) => "123abc"`{.cpp} +# Step 6 (Strech goal) -Some APIs require "plain C strings" aka a `char *`{.cpp}. They can be -converted with `String::c_str()`: +Use a last will message to indicate if the device is online or not. -~~~.c++ -char *cStr = myString.c_str(); -~~~ +* When connecting, include a last will message with topic + `ndc/$device-id/online` and payload `0`. +* After a successfull connection, publish a similar message with the + payload `1`. Observe what happens when you unplug the device. |