MQTT broker and Arduino + Sensors NRF24L01

Question

I am newbie, I have never used MQTT before, so I have some questions. Here is my topology.

I have several sensors (Arduino Pro Mini + NRF24L01) and main server/handler(Arduino Mega + Ethernet Shield or ESP module) to receive/send messages to/from sensor nodes, so all network is build on NRF24L01 (NRF24 Mesh library). But I need to be able to communicate with all these sensors from outside over the internet. Previously I implemented simple socket communication.
I have recently discovered MQTT protocol and it is awesome. I want to implement communication between main server and outside world using it.

1. What part of my topology should implement broker in? I think it should be on the main server (Arduino Mega) but again communication between main server/master server is implemented via NRF24L01 modules and custom protocol.

2. Or in my case is better to use HTTP communication with master server?

Please explain this topic and suggest how to implement this correctly in my case.

Answer 1

The normal topology is sensor nodes publishing topic-data on a MQTT broker. And the broker distributing updates to subscribing clients. The MQTT broker is responsible for several levels of QoS (Quality of Service) such as storing attribute/topic-values (persistence), checking that messages are delivered, etc. Typically the broker runs on a server with disk, multiple network connections, etc.

A possible solution is to send sensor messages to a bridge that translates and publishes the message on the MQTT broker. The sensors may use a simple cheap local wireless network (such as based on NRF24L01) and the bridge would publish over IP (Ethernet, WiFi, etc) to the MQTT broker.

Some sensors/actuators might need configuration/control (alarm thresholds, resolution, etc). In this case they need to subscribe to messages (topic updates) from the MQTT broker. Again the bridge needs to provide the subscription and message translation/routing back to the sensor.

Last, topics naming is a challenge as the bridge should be transparent in the naming structure but still configurable. The bridge configuration (e.g. network address/topic translation) could also be handled as a bridge topic.

Cheers!

Answer 2

You can use a Raspberry Pi as your MQTT server and you can also connect a nRF24L01+ module.