Hello everyone! I’ve been exploring the MQTT protocol within the Homie convention and came across an interesting challenge regarding non-retained messages. I’d love to share my experience and hopefully gather some insights from the community.
I’ve been using non-retained MQTT messages to handle momentary events, like doorbell presses, as outlined in the Homie documentation. These messages are perfect for such use cases because they don’t persist, ensuring that only active listeners receive them. However, I encountered an issue when trying to make these interactions bi-directional. Specifically, I wanted the system to not only trigger an event but also send a confirmation back, creating a two-way communication channel.
After some research and experimentation, I discovered that while non-retained messages are indeed one-way by nature, achieving bi-directionality isn’t impossible. The key lies in leveraging retained messages for the response. Here’s how I approached it:
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Identify the Use Case: I wanted a doorbell press to notify me via my smart speaker and also receive a confirmation that the notification was sent. This ensures reliability in the communication flow.
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Configure the Trigger: I set up the doorbell sensor to publish a non-retained message on a specific MQTT topic when pressed. This message is picked up by my smart speaker, triggering a notification.
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Implement the Response: To make it bi-directional, I configured the smart speaker to publish a retained message on a different topic once it sends the notification. This retained message acts as an acknowledgment.
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Monitor the Response: On the doorbell sensor side, I added a subscription to the response topic. When the sensor detects the retained acknowledgment message, it knows the notification was successfully sent.
This setup effectively creates a bi-directional communication channel using a combination of non-retained and retained messages. It’s a bit of a workaround, but it works seamlessly!
I’d love to hear how others have tackled similar challenges or if there are more elegant solutions out there. Additionally, I recommend testing this setup thoroughly to ensure both sides of the communication are functioning as expected. Monitoring the MQTT broker and using tools like mosquitto_sub can be invaluable in debugging and confirming the flow of messages.
Happy tinkering, and I hope this helps someone else looking to enhance their MQTT-based projects!