42 lines
1.5 KiB
Markdown
42 lines
1.5 KiB
Markdown
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---
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tags:
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- micro-controllers
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---
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# MQTT
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_Message Queuing Telemetry Transport_
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Messaging protocol that runs on top of TCP/IP like HTTP. Particularly well
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suited for IoT devices.
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Has publisher/subscriber architecture. Devices publish data to a broker which
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manages topics. Other devices subscribe to those topics. Broker would typically
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run on a server as the central messaging hub.
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MQTT handles connection drops gracefully - if an ESP32 temporarily loses Wi-Fi,
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it can queue messages and send them when reconnected. The protocol uses minimal
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bandwidth (just a few bytes of overhead vs HTTP's much larger headers), which
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means lower power consumption on your ESP32s. MQTT also maintains persistent
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connections rather than creating new ones for each data point, reducing network
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overhead and latency.
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The main Linux client for setting up an MQTT is `mosquitto`.
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There are different **Quality of Service** levels you can use to manage how
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messages are sent and what to do in event of failure:
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- _fire and forget_
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- _acknowledged delivery_
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- _acknowledged only once delivery_
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- _retained message_ (broker remembers last message)
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- _last will and testament_ (automatica notification if device disconnects
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unexpectedly)
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## Example use case
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As an example, my usecase would be to have several ESP32 micro-controllers in
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different rooms publish humidity data to a small computer that acts as broker.
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This computer will also subcribe to the topics belonging to each room e.g
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`bathroom_sensor`, `bedroom_sensor` and store this data in a database.
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