MQTT subscribe retrieves no data back after immediate reply

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Jason Wu
Jason Wu 2021-5-21
评论： Vinod 2021-5-29
Dear Sirs,
I am student in university, new in MQTT, used MQTTlens and MQTT.fx as the client.
Used them to subscribe the public channel "1293177", the channel publish weather data frequently.
But, only got the first record immediately after subscribe, and no more.
If subscribe again, will got the same record again.
I follow the article at https://www.mathworks.com/help/thingspeak/troubleshoot-MQTT-subscribe.html and without mismatch.
Would you kindly help to figure out the problem is?
  2 个评论
Vinod
Vinod 2021-5-25
Do you have multiple clients connected using the same ClientID?
How many concurrent MQTTFx clients do you have using the same MQTT API Key?
Jason Wu
Jason Wu 2021-5-26
One, only one client at the same time. The purpose is to experience about the subscribe effect. Unfortunately, it not work.

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回答（1 个）

Vinod
Vinod 2021-5-27
I just tested the workflow with MQTT.fx and it works fine. Some points to remember:
1) When setting up the connection, set the "Password" to the "MQTT API Key" from your ThingSpeak profile page
2) When subscribing to a channel, the topic must be: channels/<CHANNEL_ID>/subscribe/json/<CHANNEL_READ_API_KEY>
3) Now publish "field1=45" to this channel using this topic: channels/<CHANNEL_ID>/publish/<CHANNEL_WRITE_API_KEY>
For every publish at 15s or slower (with a free license) you should also see that a subscribe message is received.
  2 个评论
Jason Wu
Jason Wu 2021-5-29
Dear Vinod,
Thanks for your suggestion. Since all checked before my issue. Not only MQTT.fx but also MQTTLens are the same. Got the first record immediately, may be the LWT by channel "1293177".
regards,
Vinod
Vinod 2021-5-29
Can you share screenshots of the mqttfx application with your settings. Clearly some misconfiguration as it works perfectly fine for me.

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