LAN connected MQTT nodes

  • I try to rebuild my custom Arduino nodes with MySensors platform. Need some input as I can not recreate all functions I need.

    I have 3 Arduino/ethernet boxes. By removing radio definitions I can make them act as individual gateways with their own root MQTT topic. In essence, they will have 6 digital inputs and 8 outputs/relays (will see how many pins are free at the end).

    1. I selected different MQTT topics for each gateway as they all have NODE_ID 0 (hardcoded by MySensors). How to control/differentiate if all 3 post to the same topic? By sensor ID?

    2. There is no support for MQTT Last Will in MySensors from what I searched... that is a pity. I will probably invent phantom sensor as a heartbeat that will contain a random value, then inspect that on a higher level (NodeRED most likely)

    3. Is there a way to know the MQTT status from inside the node? For example, if my node/gateway loose Ethernet or the MQTT broker is down I want to set relays to a safe state.

    4. Is there a watchdog implemented in the Arduino code by default? I know that Arduino can reset itself if stuck for longer then 8 secs (not getting confirmation message).

    1. I found that I can check like this

    if (_MQTT_client.connected())


  • Mod

    For question 1, use MY_MQTT_CLIENT_ID and/or MY_MQTT_PUBLISH_TOPIC_PREFIX.

  • @mfalkvidd Yes I settled for different MY_MQTT_PUBLISH_TOPIC_PREFIX. per device. but the Client_ID can not be defined for gateway...but that is not a problem now

  • Mod

    @8667 that’s strange. The documentation says

    Set client ID for MQTT connections.

    This define is mandatory for all MQTT client gateways.

    Sonit seems to be for gateways. I have never used it myself though.

  • @mfalkvidd I was talking about MY_NODE_ID As each device will be a gateway with onboard sensors only they all have I think 1 as ID by default and that can not be changed.

    MY_MQTT_CLIENT_ID is different as I create different MQTT user/pass for each device

    For 2. I created a fake sensor that I update with 1 each minute.

    present(99, V_VAR1, "Status");

    Then at the software side (NodeRED) I create additional logic to find out if the device is dead.

  • You don’t need MySensors for a direct connection to MQTT. Just use pubsubclient.

  • @carywin Yes I know. I had my own "firmware" for few years but I want to use something mainstream that will be easier to maintain (by someone else 🙂 ).

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