[M467 | M487 | M2354] Cellular Communication on Mbed OS and NuMaker IoT Boards

[morgandu]

[For further inquiries, please e-mail to shchen2@nuvoton.com]
[Visit https://www.nuvoton.com/iot_startup for more IoT solutions]

Cellular communication is wireless technology using cellular networks for long-distance data exchange. It relies on infrastructure like base stations and offers wide coverage, reliability, and secure connectivity for IoT devices. So it enables IoT applications with high data rates through LTE and low-power, low-data-rate connectivity with NB-IoT, offering versatility and efficient connectivity options for diverse IoT use cases.

Nuvoton provides two cellular expansion boards for NuMaker-IoT platforms

• RF-EC21A (Click here to Nuvoton Direct) : Quectel EC21 module on board for 3G/4G LTE

  

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• RF-BG96A (Click here to Nuvoton Direct) : Quectel BG96 module on board for NB-IoT

  

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The expansion board is plugged into the Arduino connector on the NuMaker IoT platform. The cellular module is connected to MCU through UART.

Prerequisite

• A NuMaker-IoT-M467 board
  Other NuMaker-IoT boards are also possible but use NuMaker-IoT-M467 for this tutorial.

  

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• A cellular expansion board
  Use RF-EC21A for this tutorial.
• A mini SIM card which has network plan
• Mbed Studio – the development tool
  Register an Mbed OS account to use Mbed tools for free https://os.mbed.com
  Download Mbed Studio and install it https://os.mbed.com/studio

Put SIM card on the back of cellular expansion board. Check the three switches to correct settings.

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Plug the cellular expansion board on NuMaker-IoT board and put on antenna.

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Create a Project

• Run Mbed Studio
• Log in your Mbed account if it asks.
• Click File
• Click Import Program

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• Fill the example link to URL https://os.mbed.com/teams/Nuvoton/code/ ... r-example/
• Click Add Program

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• Active program is “NuMaker-mbed-Cellular-example”
• Use NuMaker-IoT-M467 as example
  • Select target on the pull down menu, use M467 as keyword to find “NuMaker-IoT-M467”, then select it. Or you can
  • Plug the Nu-Link2 USB on NuMaker-IoT-M467 to PC. Mbed Studio will detect it automatically and then select Yes when it ask you to set the device as active.

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View the Code

• Click main.cpp to show the source code
• Get default network interface, it is configure to cellular in mbed_app.json.
• Connect the network.
• If connection success, print IP address and do send and receive test. The test is send a data string to remote server then receive the same data from server.
• Disconnect the network
• End

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Modify Settings for Cellular
The default setting of the example selects GENERIC_AT3GPP driver for cellular module. It is fine for most cases. However, Mbed OS has drivers that supported Quectel EC2X and BG96, we can use them.

• Click mbed_app.json to open it.

  

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• For RF-EC21A

  

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• For RF-BG96A

  

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Build Code

• Click hammer to build code
• After build finish, you get the firmware image file NuMaker-mbed-Cellular-example.bin in the folder.
  
  Windows
  C:\Users\YOUR-ACCOUNT\Mbed Programs\NuMaker-mbed-Cellular-example\BUILD\NUMAKER_IOT_M467\ARMC6
  
  Linux
  ~/Mbed Programs/NuMaker-mbed-Cellular-example/BUILD/NUMAKER_IOT_M467/ARMC6

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Program firmware

• Make sure that no.1 & 2 are ON and no.3 & 4 are OFF of ICESW2 on Nu-Link2-ME

  

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• Plug in USB cable to PC
• A NuMicro MCU drive appears on PC
• Copy NuMaker-mbed-Cellular-example.bin to NuMicro MCU drive to program firmware. Or click “Connect” icon to download firmware and run.

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Open the Terminal

• Mbed Studio automatically open a terminal when a Mbed Enabled board detected.
• Or you can run a terminal tool to open Nu-Link2-ME virtual COM port
• Select baud rate to 115200

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Run it

• Press RESET button on NuMaker-IoT-M467 to run it

  

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• The terminal shows the running messages
  • Establish connection
  • Print IP address when connected
  • TCP connects to remove echo server
  • Send 4 bytes to remove echo server
  • Receive 4 bytes from remote echo server

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That's all.