We have written about the Quectel RM520N-GL 5G cellular modem before. Back then it was about setting up the software to establish a functioning Internet connection under Linux.

Now there is another article about the modem - but not because everything worked as intended straight away. Rather, this time we want to give you an insight into our daily struggle with and against technology. Because not everything that should work actually works in the end. Even if - as in this case - the electronics have already been used successfully in one way or another.

We took a closer look at the “Waveshare SIM7070G Cat-M/NB-IoT/GPRS HAT” for the Raspberry Pi and put it into operation. We uncovered various pitfalls and describe below how we set up the NB-IoT modem to connect one of our #AMPS nodes to the internet.

• Hardware:
  • Raspberry Pi 4 B
  • Mobilfunk-HAT: Waveshare SIM7070G Cat-M/NB-IoT/GPRS HAT
  • SIM-Karte: Telekom M2M
• Software: Raspbian 12 “Bookworm”

Yesterday, while completing some of our AMPS units with display and Qt application, we encountered an error that caused the application to fail to launch correctly and crash in rare cases. The error looks like this:

Mikroelektronika (MikroE) from Serbia offers within its “Click” ecosystem numerous function modules that can be operated on microcontrollers. One of them is the “CAN SPI Click 3.3V” CAN controller module, which can be connected via the standardized “MikroBus” interface or SPI. To make the connection to a Raspberry Pi 4 work, we added the “Pi 4 Click Shield”.

In this post we will briefly explain how we got the CAN module working in conjunction with the Raspberry Pi 4.

On our odyssey in search of a 5G cellular modem, we have tried several modems from different manufacturers. Unfortunately, the commissioning was not always successful. Sometimes the driver support in the Linux kernel was completely missing - sometimes the control via NetworkManager / ModemManager was buggy or not possible at all.

Easy commissioning and stable operation are important to us. Since we do not want to use the modems on only a few devices, a manual adaptation of the Linux kernel is usually out of the question for us. The effort involved is too great and the consequences for the further life cycle of a product are too unclear. Therefore, the operating system - often a Raspberry Pi OS - should be used in its factory state and without major adjustments, if possible.

Two modems have emerged for us that work “out of the box” in combination with the current Raspberry Pi OS on Debian 11 “Bullseye” basis (kernel 6.1):

Because we had to find out the painful way: The Waveshare IO BASE Module B for the Raspberry Pi CM4 module does not work with the 4" DSI Touch Display from Waveshare - at least not as long as you use a BASE IO board revision < 4.

Only from board version 4 the higher performance DSI1 interface is used instead of the DSI0 interface of the Raspberry CM4 by the IO Base Board.