HTTP error -304 when using from a Wemos D1 mini | ThingSpeak API | Forum


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HTTP error -304 when using from a Wemos D1 mini
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March 14, 2019
2:13 pm

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March 13, 2019
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I'm kind of a newbie to ESP and ThingSpeak.
During the last few days I managed to set up arduino development IDE, read data from a bme_280 sensor using that Wemos D1 mini, connect it to my local WiFi, send HTTP GET requests to my raspberry and send mails.

But I'm completely lost now as I don't get the connection to Thingspeak to work.
I set up a channel at TS and I'm able to upload data using the URL

But when using the ESP I'll always receive error -304 - regardless whether I try to upload a new value or read an existing one.

Shouldn't be that tough, but ... also searching the Web doesn't help me much.

After the WiFi is connected I'm executing only few commands:

ThingSpeak.setField(1, voltage);
ThingSpeak.writeFields(myChannelNumber, myWriteAPIKey);

I copied the Write API Key out of, same for the Channel Id

What am I missing? Any strange combination of libs which won't work ...

Thanks a lot for your help

March 15, 2019
7:38 am

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March 7, 2017
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I agree, you seem to be doing everything correct.

I assume you are using the api key in the URL when you try it through the web browser:

You wouldn't get a 304 error if you had the wrong API key, but its just one thing to check. Make sure you are using the write API key for your channel and not the user API key.

I am suspecting its a network issue. Do you have the ability to try the same device on another WiFi network?

March 17, 2019
6:51 am

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March 13, 2019
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cstapels said
I am suspecting its a network issue.

I checked using my private WiFi instead of the guest's WiFi - and it worked.
Thanks a lot for that hint, cstapels

I've placed a request at the manufacturer of my FRITZ!Box 7490 as I don't have any setting I know of restricting the guest's WiFi.
In case something helpful is returned, I'll update this topic.

May 2, 2019
3:32 pm
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May 2, 2019
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Hmmm, I have exavtly the same problem and also a Fritz!Box...... did you find a cause for this? Or maybe even a solution?

In my Fritzbox, I found out that having a Internet->Filter->Blacklist with any content causes the ThingSpeak trafic to be blocked. If you make a complete empty blacklist, it works. If you bock then it blocks ThingSpeak.... So I ended up making an unresitricted access profile for my esp modules. But still, the behaviour is very strange and I havent observed it on other devices. I can with my PC connect to thingspeak without problems on the same WiFi. So it seems specific for either ESP32 or the ThingSpeak library for Arduino.

Hoping for a final solution on the ESP/ThingSpeakLib soon.

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