Raspberry Pi - MQTT Publish & MQTT Subscribe- Updating Multiple Fields In one MQTT publish request and vice versa

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VISHAL SAWANT 2021-5-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/821095-raspberry-pi-mqtt-publish-mqtt-subscribe-updating-multiple-fields-in-one-mqtt-publish-request-a

编辑： Christopher Stapels 2021-5-17

Hello,

I am working on raspberry pi with MQTT publish block. It is being used with Thingspeak Platform. I understood the example models for publiash and subscribe the fields.

I want to use the MQTT publish and Subscribe block for multiple fields of channel. I am struggling with proper Topic argument for both publish and subscribe blocks.

As I am bengineer, I will be happy to further explain the problem statement if the info given is insufficient.

I used floowing links as refernece but not understood the specific argument.

Publish message to update multiple channel fields simultaneously - MATLAB - MathWorks India

Subscribe to updates from channel feed with MQTT - MATLAB - MathWorks India

Regards

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Christopher Stapels 2021-5-4

In the docs you linked, it lists the topic as

channels/<channelID>/publish/<apikey>

You can get the channel ID from your channel page on the upper left or in the address bar. Your API keys are on the API keys tab.

Does that help?

VISHAL SAWANT 2021-5-6

Hello Christopher Stapels

Thanks for replying. I tried this combination with MQTT publish block. The entry counter is updating but the values are not visible on Channel Field charts.

Input is 1x8 array of uint8 data type.

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Answer 1

Christopher Stapels 2021-5-6

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https://ww2.mathworks.cn/matlabcentral/answers/821095-raspberry-pi-mqtt-publish-mqtt-subscribe-updating-multiple-fields-in-one-mqtt-publish-request-a#answer_693710

Your message needs to be of the form 'field1=value&field2=value2' etc.

If you use the update single field topic instead of the multiple fields topic, you can just send a number.

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VISHAL SAWANT 2021-5-14

What I see is we can give input to MQTT publish block as 1xN array of number only. No string inputs are taken as input. Can you suggest something which can work with MQTT publish and MQTT subscribe block for channle feed.

Christopher Stapels 2021-5-17

编辑：Christopher Stapels 2021-5-17

If you dont need MQTT, you can use the ThingSpeak blocks in the support package for Raspberry pi. This has blocks for the ThingSpeak REST API.

If you want to update miltiple fields in one call, I think the MQTT block will not work for you. Ill submit it as an enhancement request for the block.

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