Transmit after compressing mono 16㎑ WAV, and play back transmitted on the receiving side

Using STM32 X-Nucleo board with MEMS microphone

[Editor's Note] Generally, when we talk about semiconductors, we tend to think of semiconductors that are familiar to the general public, such as the CPU and memory of computers. On the other hand, MCUs (Micro Controller Units), which are used as core semiconductors for operating electronic products, are semiconductors that are still unfamiliar to the general public, even though they are commonly used in all electronic products that we easily come across. These MCUs have recently been featured in the media due to the semiconductor shortage, and have begun to attract the attention of the general public. Accordingly, this magazine has prepared a place to learn about MCUs through a series of articles by Yuji Kawano, manager at STMicroelectronics, a company specializing in MCU semiconductors.

■ Two-way call demonstration using STM32WB series development board

This time, we will demonstrate two-way voice communication (calling) using Bluetooth® Low Energy (Bluetooth LE) using a development board for the STM32WB series of wireless microcontrollers from STMicroelectronics.

In this demonstration, we successfully achieved simultaneous calls using two sets of STM32 X-Nucleo expansion boards featuring digital MEMS microphones. It is very convenient because it can be done with just one STM32WB.

After compressing mono 16KHz sampling WAV data, it is transmitted via Bluetooth LE and played while transmitting the data on the receiving side.

■ Hardware Preparation

[Required Materials]

- STM32WB Nucleo pack (uses only the MB1355C board included in the pack) x 2 sets

- X-NUCLEO-CCA02M2 (MEMS Microphone Expansion Board) x 2 sets

- PC (Windows 10/7) x 2

- Micro-USB cable x 2

The board to be used this time is the MB1355C board mounted on the STM32WB55 Nucleo Pack (hereinafter referred to as the STM32WB Nucleo board) and the STM32 X-Nucleo microphone expansion board with a microphone, 'X-NUCLEO-CCA02M2' (hereinafter referred to as the MEMS microphone expansion board).

Prepare two sets as they are used for two-way calls. In addition to the board, prepare two PCs with speaker or headphone output for voice confirmation and two USB cables (Micro-USB).

■ Software Preparation

○ Install STM32CubeProgrammer (skip if installation is already complete)

If this is your first time using the STM32 Nucleo board on your PC, install STM32CubeProgrammer (formerly ST Link Utility) to prepare the COM port driver, etc. (STM32CubeProgrammer is not used in this post, but the driver is required).

This tool is required to download software to STM32WB microcontrollers.

Go to the installation file: STM32CubeProgrammer

After unzipping the file, open the executable file and follow the instructions to install. If you have already installed STM32CubeProgrammer, you do not need to do this.

Once the installation is complete, proceed to the next step.

○ Preparing software for operation verification

▶Download the demo program file

Next, download the demo program file.

Go to download: FP-AUD-BVLINKWB1 (skip if you have already completed the download)

When you unpack the downloaded file, a working folder for your integrated development environment is created right away. There are two types of demo program files (binary files) to be used this time, one for Central and one for Peripheral, prepared in the folder below. Check the location of each file.

There is no hardware difference, so it doesn't matter which one you use (just don't download the same program files to both boards).

Save path (example):

" 'Drive:....\STM32CubeFP_BVLINKWB1_Vx.xx\Projects\P-NUCLEO-WB55.NucleoApplications\BLE\BVLCentral\Binary'

" 'Drive:....\STM32CubeFP_BVLINKWB1_Vx.xx\Projects\P-NUCLEO-WB55.NucleoApplications\BLE\BVLPeripheral\Binary'

Make sure each file is included.

File for Central: 「FP-AUD-BVLINKWB1_Central.bin」

File for Peripheral: 「FP-AUD-BVLINKWB1_Peripheral.bin」

○ Connect to PC and download software

When downloading software, set up the board as follows in advance. Also, please note that the settings here will be different when downloading software and running the demo. You can rest assured that even if you make a mistake, the board will not be damaged.

- For jumper JP1*, set the jumper pin to "USB STL"

- Connect the PC and STM32WB Nucleo board to the Micro-USB cable with the "ST-LINK" connector (be careful, there are two Micro-USB connectors)

*Jumper JP1: Jumper for selecting the 5V power supply source of the board.

When you connect the STM32WB Nucleo board to your PC with a USB cable, it will be recognized as a USB memory device named 'NODE_XXXX'. (If this is your first time doing this, driver installation will start first.)

For the two STM32WB Nucleo boards, drag and drop the binary files for Central/Peripheral that you checked earlier onto 'NODE_WB55RG' respectively.

This will complete the software download to your STM32 microcomputer.

Download the first xxx_Central.bin

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