Pico USB Audio

### Overview
USB audio device. It can output audio to headphone & speaker from a PC via USB.
- It can output audio to headphone & speaker (optional).
- It allows you to control the volume (up/down/mute).
- It can display the L & A audio levels.

How it works


### BOM
- Raspberry pi pico series (pico (RP2040) is sufficient)
- Waveshare Pico-Audio
(Audio expansion Module for Raspberry Pi Pico, headphone and speaker signal output at the same time.)
- OLED SSD1306
- Rotary Encoder KY-040
- M2x10 bolts & nuts (x4) to attach raspberry pi pico.
- M2.5x6 bolts & insert nuts (x4) to attach front panel, back panel.
- QI cable (x10) & pin header or something to branch 3.3v.

### Software
I modified the sample "usb_sound_card" included with the pico-SDK, adding volume control and audio level display functions.
The source code and the built binaries(for pico,RP040) are available on GitHub.