👉 Japanese
This is a project for a USB sound card constructed with a Raspberry Pi Pico microcontroller board.
Hardware schematics and firmware sourcecode are included.
- USB Audio Class 2.0 (Connected by USB 2.0 Full speed)
- 2ch Line in
- 2ch Line out
- 2ch SPDIF in
- 2ch SPDIF out
- 2ch Headphone out
- Maximum resolution is 24bit
- Maximum frequency is 96KHz
In/out USB data streams cannot activate simultaneously at 24-bit/96KHz due to a lack of transfer bandwidth. "Line in" and "SPDIF in" are mixed into one buffer to save USB bandwidth. Each volume can be controlled via a generic USB driver. (Currently, it only supports Windows WinUSB.)
I used KiCad6 to design the schematics.
If you want to view the schematics, Please download KiCad 6 or later.
The hardware design is simple and lacks ingenuity because I am not an electronics expert.
But I designed the schematics with the concept of separating modules by function to facilitate testing and adding other functions.
Electronic components which are used are general and easily obtainable.
The DAC uses PCM5102a and may be easily replaced with any of the PCM510x series. You can choose depending on their availability (although I have never tried this).
The firmware is wrote by C and C++. SPDIF control does not use dedicated hardware and is implemented by the software using one of Pico's features called PIO. It allows running I/O independently of the main processor. Similar to the schematics, the software is also organized by function. Each hardware function is represented as a class in the software.
To build the firmware, you should first install Pico's SDK and CMake. For detailed instructions, please refer to the following resources.
Let's prepare a directory for Cmake setup.
mkdir build
cd build
For standard setup
cmake ..
With tracing log
cmake .. -DLOG=1
'LOG' is passed to tinyusb's debug level. That description is here.
With profiling
cmake .. -DPROFILE=1
To usb device control use TinyUSB. It is included in PicoSDK. TinyUSB for Pico has a problem what memory deallocation of endpoint. Therefore, I prepared a patch for avoiding it. If you encounter to crashing the device in TinyUSB memory allocation, It may resolve by applying the patch to TinyUSB.
The device outputs tracing log to serial port (CDC) owned myself. You can see the contents via serial monitor.
And following commands are usable via serial monitor input.
stats_on
Turn on the output of internal statistics every 0.5 seconds when the LOG is greater than 0.
stats_off
Turn on output of internal stats.
perf
Output measured performance statistics when profiling is enabled.
Unique requests to control internal behaviors from the host device have been implemented in the firmware. If the host OS is Windows, the device requests the installation of the WinUSB driver to the OS through the Microsoft OS Descriptor description. This enables user-mode applications on the host to send requests to the device.
control_uwp is an application to controls the device volumes by using WinUSB via Windows Runtime. To building requires Visual Studio 2022 with C# UWP application development.
- Raspberry Pi Pico Datasheet
- RP2040 Datasheet
- SPECIFICATION OF THE DIGITAL AUDIO INTERFACE (The AES/EBU interface)
- Texas Instruments PCM510xA 2.1 VRMS, 112/106/100 dB Audio Stereo DAC with PLL and 32-bit, 384 kHz PCM Interface
- Texas Instruments PCM1808 Single-Ended, Analog-Input 24-Bit, 96-kHz Stereo ADC
I am not responsible and cannot guarantee any damage or injury that may occur if you decide to undertake this project. Please keep in mind that this is a DIY project.