B4R Question MQTT connect to ThingSpeak

[barx]

Hi

Anyone got an example of how to use MQTT to connect and publish to ThingSpeak

I've never used MQTT and things don't seem to be matching up at both ends.

b4r MQTT lib has parameters for:

Port
ClientID

ThingSpeak seems to have:

Username
Password
APIKey
Channel

Here is an example of using Arduino https://uk.mathworks.com/help/thingspeak/use-arduino-client-to-publish-to-a-channel.html

 

[XorAndOr]

https://www.b4x.com/android/forum/threads/sending-data-from-b4a-to-thingstospeak.78300/#post-496227
This link refers to B4A but I think it also works in B4R with the
rHttpUtils2 module.
https://www.b4x.com/android/forum/threads/module-rhttputils2-http-client.74785/#content
sorry but I have not tried

 

[Erel]

You should use Connect2 with MqttConnectOptions to set the user name and password.

 

[barx]

You should use Connect2 with MqttConnectOptions to set the user name and password.

Thanks Erel, I had spotted that shortly before you posted it.
I tried many ways to get this working but each time it failed. After reading the code example I posted I also tried using .getBytes() wondering if it did the same work as
.toCharArray in the example. Still no joy.

After a rather long time and at the point of nearly giving up, I noted that the only thing I hadn't changed was the number of fields I was trying to update. Each time I had been trying to post 8 fields (max allowed for a ThingSpeak Channel.)

I finally got a bite on the line when I reduced the number of fields I was posting to. I tried just one. After a few combinations of the other options, it worked!!!!

So, i then went back to 8 fields........ no worky.

I started back at 1, then worked my way up until it failed. Anyway it failed at anything above 6 fields. I stared at the code tirelessly, trying to see what was different between the 7th and/or 8th fields that would made it fail. Nothing was wrong that I could see. I then began to wonder if it was the actual length of what was being sent, it was the only thing that made sense. So, to increase the buffer I looked for something relating to 'MaxBufferSize' like with async stream. I didn't find anything.

I searched google for an answer and found a pointer in the right direction. The answer was to edit the PubSubClient.h file found under '\Anywhere Software\B4R\Libraries\rMQTT\' and edit the following line

#define MQTT_MAX_PACKET_SIZE 128

Setting the value to 256.

NOTE: your editor needs Admin Priviledges

This now works for all 8 fields!!!!

Working code example to follow as this post is getting a little long with me rambling on, sorry.

 

[barx]

NOTE: the bits in <> are where you insert your own data / keys

Sub Process_Globals

    Private MQTT As MqttClient
    Private MQTTOptions As MqttConnectOptions
    Private tmr0 As Timer
    ...
End Sub

public Sub Start

   tmr0.Initialize("tmr0_tick", 30000) 'tick every 30 seconds
   ...
End Sub

   MQTT.Initialize2(server.Socket.Stream, "mqtt.thingspeak.com", 1883, <ClientID>, "MQTT_MessageArrived", "MQTT_Disconnected")
   MQTTOptions.Initialize(<Username>, <MQTTAPIKey>) 'MQTTAPIKey from Account > My Profile
   If MQTT.Connect2(MQTTOptions) Then
       tmr0.Enabled = True
   Else
       tmr0.Enabled = False
       Log("not connected")
   End If
End Sub

Sub tmr0_Tick
   'publish data
    ...'Code to fill Fields() array with the data to send.
   Log(MQTT.Publish(MQTTHelper.ThingSpeakTopicBuilder(<ChannelID>, <ChannelIDWriteAPIKey>), MQTTHelper.GetPayload))
End Sub

Private Sub MQTT_MessageArrived (Topic As String, Payload() As Byte)
  
End Sub

Private Sub MQTT_Disconnected
  
End Sub

The little helper module look like

public Sub ThingSpeakTopicBuilder(ChannelID As String, ChannelWriteAPIKey As String) As String
    Return JoinStrings(Array As String("channels/", ChannelID, "/publish/", ChannelWriteAPIKey))
End Sub

'returns the payload
public Sub GetPayload() As String
    Return JoinStrings(Array As String("field1=", Fields(0), "&field2=", Fields(1), "&field3=", Fields(2), "&field4=", Fields(3), "&field5=", Fields(4), "&field6=", Fields(5), "&field7=", Fields(6), "&field8=", Fields(7)))
End Sub

Thought I would post this in case it helps someone in future