MQTT: Some clients work and other don't

1

I’m uploading data to TTN using a ATMEGA328P (a la Arduino Uno) and RFM95W. The data appears in the TTN Console and also using MQTTLens (Chrome extension). I can’t get either MQTTDash (Android app) or an MQTT client running on ESP8285 to see it though. All the above are using the same broker name, username and password and seem to connect without error.
Can anyone shed any light on this please?

2

You’ll need to find a way to get at the error message produced on failure.

Consider especially issues around port setting, TLS version, validating the server certificate, etc.

3

Thanks for the reply.
I’m not seeing any errors, just no data.
Would an erroneous port setting or server certificate issue still allow me to connect?
The MQTT client I’m using on the ESP8285 works with HiveMQ, so I know the code is OK.

4

You’ll need to figure out how to get debug/status/error messages

Would an erroneous port setting or server certificate issue still allow me to connect?

Any of these would presumably prevent the connection from completing to the point of data flow

Not really, you know it works in one setup, that does not mean it is correctly configured or even capable of working with another.

Consider the reverse of your statement: it’s also known that the TTN MQTT broker works with several clients, so by the logic you just proposed the issue would have to be with your client.

Or more realistically, incompatibility can be incompatibility without needing one side to be inherently “wrong”.

5

I am running two client connections (one shown here), with the same procedures but different parameters.

int test=client_1.subscribe(mqttTopic_1);

returns 1, indicating a successful subscription. It is set up with

client_1.setServer(mqtt_server_1, 1883);
client_1.setCallback(callback_1);

The loop is called within void_loop():

void loop() {
if (!client_1.connected()) {
reconnect_1();
}
client_1.loop();
}

The above works happily with HiveMQ, but TTN doesn’t fire the callback function, hence no error messages.

Consider the reverse of your statement: it’s also known that the TTN MQTT broker works with several clients, so by the logic you just proposed the issue would have to be with your client.

Agreed. This is the essence of the original question.
This approach was intended to be a quick test to get my TTN data into a MySQL database, but I’ve diverted now to option 2 - using http integration to a php script. I think this issue will continue to bug me until I solve it though.