To illustrate the use of the MQTT library, we have created two simple Tibbo BASIC applications called "mqtt_publisher" and "mqtt_subscriber".
You can download them here: tibbo.com/programmable/applications.html (scroll to or search for the "MQTT Library Demo" and download mqtt_demo.zip).
In our MQTT demo, the publisher device is monitoring three buttons (Tibbits #38). This is done through the keypad (kp.) object.
The three buttons on the publisher device correspond to the red, yellow, and green LEDs (Tibbits #39) on the subscriber device.
As buttons are pushed and released, the publisher device calls mqtt_publish() with topics "LED/Red", "LED/Green", and "LED/Red". Each topic's data is either 0 for "button released" or 1 for "button pressed". The related code is in the on_kp() event handler.
The subscriber device subscribes to all three topics with a single call to mqtt_sub() and the line "LED/#". This is done once, inside callback_mqtt_connect_ok().
With every notification message received from the server, the subscriber device gets callback_mqtt_notif() invoked. The LEDs are turned on and off inside this functions's body.
Testing the MQTT demo
The demo was designed to run on our TPS3 boards, but you can easily modify it for other devices. The easiest way to get the test hardware is to order "MQTTPublisher" and "MQTTSubscriber" TPS configurations from our website: tibbo.com/store/tps/custom.html.
You can also order all the parts separately:
- On the publisher side:
- On the subscriber side:
MQTT Publisher, based on the TPP3 board, shown without the TPB3 enclosure
MQTT Subscriber, based on the TPP3 board, shown without the TPB3 enclosure
- Install a suitable MQTT server. We suggest HiveMQ (www.hivemq.com):
- Open mqtt_publisher and mqtt_subscriber projects in two separate instances of TIDE, then correct the following in the projects' global.tbh files:
- OWN_IP — assign a suitable unoccupied IP to the publisher and to the subscriber (you know that they will use two different IPs, right?);
- MQTT_SERVER_HOST — set this to the address of the PC on which your run HiveMQ.
- Select your subscriber and publisher devices as debug targets, and run corresponding demo apps on them.
- Press buttons on the publisher to see the LEDs light up on the subscriber.
- If you are running in debug mode you will see a lot of useful debug info printed in the output panes of both TIDE instances.
- You can switch into the release mode to see how fast this works without the debug printing.