Need help: MQTT Client with Sparkfun AssetTracker (SARA-R5) APIs

[Davefries1966]

Hi all,
I purchased a Sparkfun AssetTracker development kit with MicroMod ESP32 add-on, GNSS antenna and so on.

I’m wondering how to find examples about using MQTT (I would use the onboard LTE modem instead of the Wi-Fi connection, so no "PubSubClient" library ....).

I’ve looked at AssetTracker APIs and tested some examples, all working with my environment (Arduino IDE on Windows 11), but I didn’t find how to correctly use the “MQTT” APIs.

I mean, I’ve written some code which seems to be able to connect (i.e., the connectMQTT() method returns OK) to some public MQTT brokers (e.g., MOSQUITTO, EQMX, etc) but:

• Publish and subscribe methods return errors.
• I didn’t actually understand how/where to use the readMQTT() method.
• I set the command callback, but I don’t understand its purpose (I would use readMQTT() instead to read topic contents).
• How to set a callback to read incoming topics which I’ve subscribed to ?

Please find attached below the code I've written, just to understand where I’m doing wrong...

Thanks in advance for your support! :-)

Best regards
David

MQTT_example.txt

[PaulZC]

Hi David (@Davefries1966 ),

As you've found, we don't have a ready-to-go MQTT example for the SARA-R5. We should add one...

Things that will help are:

• The PointPerfect MQTT example from the u-blox GNSS library. This uses WiFi to establish the MQTT connection, so not directly relevant, but it does walk nicely through the steps needed.

• LTE.h from @mazgch 's fantastic HPG Solution. This does use the SARA-R5 / LARA-R6 and this library to establish the MQTT connection.

I'm leaning towards writing a u-blox GNSS Assist-Now-via-MQTT example, replicating Example12 but using MQTT instead of HTTP. The topic details are here.

It will take me a while to write the example as I have many other tasks I need to complete first.

If you're in a hurry, please work your way through the HPG Solution code. The answer is in there!

Best wishes,
Paul

[Davefries1966]

Thank you Paul for your fast & precious support! :-) I will work on it in the mainwhile as per your suggestions, and look forward to seeing further integrations. Have a great life! Cheers David

[Davefries1966]

Hi, @PaulZC
I am trying the HPG example and started learning how to use your AssetTracker APIs.... both are fantastic softwares indeed (and thank you again so much for the suggestion!).
However I am stuck with MQTT connect, I mean, the call to connectMQTT() method returns 0 (SARA_R5_SUCCESS) but the next call to getMQTTprotocolError() returns error = 13 and errro2 = 34. I am not able to understand those error codes, anyway the state machine of HPG software doesn't advance to "MQTT" state.

Any suggestion would be so much appreciated! -:)

P.S. Another issue: In my software example, I defined a callback for MQTT commands (through setMQTTCommandCallback()), but it is never invoked the one in HPG software...

[PaulZC]

Hi David,

The error codes are hidden in the SARA-R5 AT Command Reference: https://www.u-blox.com/sites/default/files/SARA-R5_ATCommands_UBX-19047455.pdf . Check Section 30 for MQTT and Section A.8.4 for the MQTT error codes.

13 is an MQTT error (from A8). 34 is No Network Service (from A.8.4).

Are you sure you have configured the PSD (Packet Switched Data) connection correctly? Maybe try a Ping test, just to be sure?

Hope this helps,
Paul

[Davefries1966]

I got that error even with the HPG software:

11:20:37.485 -> Setup and connect, AT sequence arrived at step 16 with error 0
11:20:37.524 -> mqtt callback command: 1, result: 0
11:20:37.525 -> protocol error code1: 13, code2: 34

The envolved MQTT command seems to be the "LOGIN", as per enum below:

typedef enum
{
SARA_R5_MQTT_COMMAND_INVALID = -1,
SARA_R5_MQTT_COMMAND_LOGOUT = 0,
SARA_R5_MQTT_COMMAND_LOGIN,
SARA_R5_MQTT_COMMAND_PUBLISH,
SARA_R5_MQTT_COMMAND_PUBLISHFILE,
SARA_R5_MQTT_COMMAND_SUBSCRIBE,
SARA_R5_MQTT_COMMAND_UNSUBSCRIBE,
SARA_R5_MQTT_COMMAND_READ,
SARA_R5_MQTT_COMMAND_RCVMSGFORMAT,
SARA_R5_MQTT_COMMAND_PING,
SARA_R5_MQTT_COMMAND_PUBLISHBINARY,
} SARA_R5_mqtt_command_opcode_t;

I will try a ping and will look to suggested docs...thanks again! :-)

[Davefries1966]

I just ran the Ping example, I inserted "www.google.it" as destination address and didn't get any response...this sounds very strange because the operator seems to be active (VODAFONE ITALY)...for example, the SMS example runs fine.

11:29:11.337 -> SARA-R5 connected!
11:29:11.337 ->
11:29:11.378 -> Connected to: 22210
11:29:11.421 -> Warning: performPDPaction (deactivate profile) failed. Probably because no profile was active.
11:29:11.934 ->
11:29:11.934 -> *** Set the Serial Monitor line ending to Newline ***
11:29:11.934 ->
11:29:11.934 -> Enter the name of the server you want to ping (followed by LF / Newline):

[Davefries1966]

This is the result instead with 8.8.8.8:

11:32:51.341 -> SARA-R5 Example
11:32:51.341 -> Press any key to begin
11:32:53.897 -> SARA-R5 connected!
11:32:53.897 ->
11:32:53.935 -> Connected to: 22210
11:32:53.970 -> Warning: performPDPaction (deactivate profile) failed. Probably because no profile was active.
11:32:54.932 ->
11:32:54.932 -> *** Set the Serial Monitor line ending to Newline ***
11:32:54.932 ->
11:32:54.932 -> Enter the name of the server you want to ping (followed by LF / Newline):
11:33:05.921 ->
11:33:05.921 -> Ping Result: Retry #:1 Ping Size (Bytes):32 Remote Host:"" IP Address:"8.8.8.8" Time To Live (hops):0 Round Trip (ms):-1
11:33:10.943 ->
11:33:10.943 -> Ping Result: Retry #:2 Ping Size (Bytes):32 Remote Host:"" IP Address:"8.8.8.8" Time To Live (hops):0 Round Trip (ms):-1
11:33:15.917 ->
11:33:15.917 -> Ping Result: Retry #:3 Ping Size (Bytes):32 Remote Host:"" IP Address:"8.8.8.8" Time To Live (hops):0 Round Trip (ms):-1
11:33:20.949 ->
11:33:20.949 -> Ping Result: Retry #:4 Ping Size (Bytes):32 Remote Host:"" IP Address:"8.8.8.8" Time To Live (hops):0 Round Trip (ms):-1

[PaulZC]

Check you are following the same steps as Example4 and Example7.

You may need to change:

const mobile_network_operator_t MOBILE_NETWORK_OPERATOR = MNO_GLOBAL;

Try MNO_STD_EUROPE or MNO_SIM_ICCID

[Davefries1966]

ok...the ping example seems to work only with IP addresses and not with URLs, this is the result with the IP of "test.mosquitto.org":

11:38:51.467 -> Ping Result: Retry #:1 Ping Size (Bytes):32 Remote Host:"" IP Address:"91.121.93.94" Time To Live (hops):0 Round Trip (ms):-1
11:38:56.431 ->
11:38:56.431 -> Ping Result: Retry #:2 Ping Size (Bytes):32 Remote Host:"" IP Address:"91.121.93.94" Time To Live (hops):0 Round Trip (ms):-1
11:39:01.455 ->
11:39:01.455 -> Ping Result: Retry #:3 Ping Size (Bytes):32 Remote Host:"" IP Address:"91.121.93.94" Time To Live (hops):0 Round Trip (ms):-1
11:39:06.436 ->
11:39:06.436 -> Ping Result: Retry #:4 Ping Size (Bytes):32 Remote Host:"" IP Address:"91.121.93.94" Time To Live (hops):0 Round Trip (ms):-1

[Davefries1966]

I missed to run ALL the examples, they are very inspiring... this is the output of the Example nr. 4: actually the operator selection is ok, but the actual connection NOT; maybe the SIM (which is not for IoT) is not enabled for data connection outside the cell phone (or maybe I have to enable it before....):

11:45:48.810 -> Press any key scan for networks..
11:45:54.465 -> Scanning for networks...this may take up to 3 minutes
11:45:54.465 ->
11:47:59.099 -> Found 1 operators:
11:47:59.099 -> 1: vodafone IT (22210) - AVAILABLE - LTE
11:47:59.099 -> 2: use automatic selection
11:47:59.099 ->
11:47:59.099 -> Press 1-2 to select an operator.
11:48:07.875 -> Connecting to option 1
11:48:29.903 -> Error connecting to operator. Reset and try again, or try another network.
11:48:29.903 -> Connection info:
11:48:29.903 -> Context ID: APN Name: IP Address:
11:48:31.275 -> RSSI: 18
11:48:31.275 ->

[Davefries1966]

If I remember well, with m-center software the connection was OK.... I have to try again...

[Davefries1966]

I’m beginning to have doubts that the SIM is not enabled for LTE, but only for 4G.... my fault, sorry! :-(

[PaulZC]

That's OK - no worries! I'm in the UK and - in my area - only O2 (Telefonica) provides LTE-M connectivity. It took me a while to discover that - and get the right SIM...!

I'll leave this open until we have our MQTT example ready. If your code can be turned into a 'generic' Arduino code example, please send us a Pull Request and we'll add it. We appreciate it.

Best wishes,
Paul

[Davefries1966]

Very decent of you Paul, I really appreciate your work ! :-)

Cheers
David

[Davefries1966]

Hi @PaulZC

just for the avoidance of any doubt, an usual 4G+ SIM would be suitable for data connection with Sparkfun SARA R5 modem ?
Or, must I purchase a dedicated SIM for IoT ?

Thanks!
David