Multichannel USB microphone for Raspbery Pi Pico for use in acoustic array beamforming.
This C code and PIO code will accept I2S data from two MEMS microphones and create a USB 2.0 audio microphone source with two channels intially, and expandable to more channels in later versions. The target MCU is the Raspberry Pi RP2040 on the Pico board and the target microphone is the Invensense ICS-43434 MEMS microphone with I2S interface. The code supports the following features:
- USB 2.0 device enumerates as a standard audio class 2.0 isochronous streaming device. No host driver installation is necessary for Windows/Mac/Linux.
- Audio sample rate is fixed at 48000 Hz.
- Data is encoded as PCM samples SE_32 (32 bits per sample).
- Audio volume (gain) is fixed and so volume control must be performed at the host application level.
- MEMS microphone interface is I2S with both outputs interleaved into one data path.
- Target MEMS microphone is Invensense ICS-43434, 24 bits/sample.
- Uses Raspberry Pi Pico RP2040 development board.
- USB enumeration of HID interface providing MCU (environment) temperature and microphone separation distance which are important for acoustic beamforming calculations.
The system can be constructed using a Raspberry Pi Pico development board and two MEMS microphone evaluation boards from Adafruit (Part #6049) as shown in the following diagram.
Connection Diagram for Dual Microphones
- Raspberry Pi Pico/W (RP2040)
- Adafruit #6049 MEMS microphone evaluation board
The code is built using the standard Raspberry Pi Pico SDK and leverages the TinyUSB library for usb functions.
Instructions for installing the Pico development SDK can be found here.
Clone this repo to a new folder in your local system.
mkdir micarray
git clone https://github.com/gregory-whaley/micarray.gitUnfortunately the version of TinyUSB which is automatically included with the Pico SDK has a buffer allocation error in streaming audio. This error has been fixed in version 0.19.0, so we must instead clone the current TinyUSB repository also to a separate folder in your local system.
mkdir tinyusb
git clone https://github.com/hathach/tinyusb.gitThe CMakeLists.txt file in the micarray repo includes a redirection to this updated local TinyUSB folder, and so you must edit the following line to point cmake to your local TinyUSB folder.
set(PICO_TINYUSB_PATH "/home/YOUR_LOCAL_FOLDER/tinyusb")
The code is built from the linux command line as follows:
cd YOUR_LOCAL_FOLDER/micarray
mkdir build
cd build
cmake .. -DBOARD=raspberry_pi_pico
makewhich will produce a *.uf2 binary output file in the build folder. Then follow the standard process to flash the file to the pico by plugging in the pico with the bool_sel button pressed, and copy the uf2 file to the pico folder which is mounted to the system. After flashing, the pico will present both a standard audio streaming USB interface, and an HID interface. The audio function can be tested using any recording application such as Audacity. The hid_test.py script can be used to query the HID functions which returns the pico device temperature and a (hard coded) number representing the physical distance between microphones in the array. In linux HID devices are owned by root by default and thus blocked from user access, so the simplest method to run the python script is to run as root.
A printed circuit board was designed for this system to support two microphones at a fixed spacing which is important for beamforming use. KiCAD PCB files are included herein. In this case the microphone access ports are 390 mm apart.
Custom PCB of two microphone sensor
A mechanical cover for this circuit board was designed and built where almost the entire board is coated in polyurethane to allow for use outdoors for long term sensing.
MicArray sensor with polyurethane coating
A 3D model was designed for the enclosure and was printed in SLS resin to serve as a form for generating a silicone mold. The PCB is then placed in the finished mold and liquid polyurethane is poured in the mold to completely embed the PCB within the polyurethane except for the two small microphone access ports. The microphone ports are angled at 45 degrees from vertical to ensure rainwater will not ingress into the ports. A flat flexible USB cable was chosen to connect the microphone so that the cable may fit under a weather seal such as in a window frame or under a gasket in a sealed enclosure. This allows the host computer to communicate with the microphones from a dry environment.
The MIT License (MIT)
Copyright (C) 2025 The Whaley Group
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.