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On this page we answer the Frequently Asked Questions.

For each question we list a few options which should solve your issue.
If you still have a problem after trying out all options, post a message on our forum.

Can't upload a new sketch

  • Update to the latest version of the Arduino IDE.
  • For Windows use the installer, not the Windows Store App.
  • Follow the getting started guide to verify you use the correct URL and update your boardfiles to the latest version.
  • Double press the reset button to manually put it into bootloader mode.

My Board isn't replying on AT commands

  • Remove your SIM card.
  • Upload the passthrough sketch.
  • Send the command AT+CFUN=15.
  • Update the u-blox firmware.


You could encounter some issues with the R4XM module and MQTT.
Below are a few option to solve some issues.
Make sure you always have the latest firmware on your module.

eDRX and PSM

Make sure that both eDRX and PSM are disabled as both of these will interfere with the delivery of MQTT packets. To disable these modes use the following commands:


Keep alive pings

Do not use the AT+UMQTTC=8 the command. The keep alive pings are sent automatically. Not only does the ‘8’ command fail to send a keep alive ping, it also seems to mess up the automatic pings. You should set the automatic keep alive period using:



The MQTT example in the R4X library is using the URCs.
If the example hangs on connecting to the MQTT broker, then it's most likely the "URC" issue.

DEBUG output:

Network connected
>> AT+UMQTT=2,"",1883
<< +UMQTT: 2,1
<< OK
<< +UMQTTC: 1,1
<< OK
MQTT failed
Setup done

30 character limit

The Ublox firmware has a 30 character limit, for some services this is an issue since they require a longer username or password.
The 30 character limit is on both the username and password field.

We have developed our own MQTT library, one of the benefits is that you can use longer usernames and passwords.

Connection not stable

We encountered some stability issues with the MQTT build-in the ublox module, therefor we developed our own library.


We have now released an adapter library for Sodaq_MQTT to work with the Sodaq_R4X library.
You will need all three libraries:

This uses a direct MQTT implementation over TCP sockets. The main limitation at this point is the size of the topic payloads which are currently limited to 127 bytes.