Audio lab

SHRED: (S)ystem for (H)igh-performance (R)eal-time (E)lectric guitar (D)igital effects

If you have any questions, feel free to open Issues & PRs.

WARNING! This project has not been fully tested in long-term production environments and is provided without warranty of any kind. Use at your own risk!

License

This project is licensed under the LGPL-2.1-or-later license.

DO NOT download or clone this project until you have read and agreed to the LICENSE.

TODO

1. plug subboard designs
2. FPGA RTL integration
3. controller firmware

Overview

This project implements an audio system for electric guitars and consists of essential components, including the hardware (core and plug) with Gerber files and schematics, digital logic designs, mechanical designs for the pickguard, and firmware for a low-power microcontroller that provides HMI and system controls.

The TFT screen is not included, which is from Waveshare (Click here) and would be easy to obtain.

Functions

• Audio Record & Playback (SD Card)
• Audio Mixer
• USB Audio Input and Output
• Wireless BLE Real-time Audio Monitor
• Audio Effects (chorus, distortion, EQ...)

Directory

Core

This directory contains PCB designs (KiCad) for the main board, which implements most functions. It includes battery management (TI BQ25601 charger with TPD2S300 for Type-C PD high-voltage fast charging, and TI BQ27720 energy gauge), system microcontroller (WCH CH32X035), FPGA unit (Gowin Tang Primer 25K), and the audio subsystem (ADI/Maxim MAX9850 I2S DAC + onsemi FAN3852 AFE+ADC to PDM, and Skyworks/Silicon Labs Si5351 for clock generation). In addition, this system includes a BLE module (Nordic nRF5340) to provide ultra-low latency LE Audio streaming capability.

The power rails are carefully designed to provide long battery life. The system employs several load switches (MPS MP5095 and Diodes AP2151) and ultra-low quiescent current regulators (TI TPS62743 and TPS7A20), allowing specific components (keys and screen, audio system, flash storage, Bluetooth) to be shut down or set to low-power states.

The dual magnetic pickups are connected via IPEX-4 (some soldering work is required to modify the connection wires), which provides low-noise, pure raw signals.

Plug

This directory contains PCB designs (KiCad) for the plug subboard, which includes an audio jack, microSD slot, USB-C receptacle, charge indicator, and ambient light sensor.

RTL

This directory contains the audio processing logic:

• Core processor
• Audio synthesizer
• FLAC encoder & decoder
• Audio I/O interface
• USB device interface
• I2C device interface
• SD host controller interface

Controller

This directory contains the system controller firmware, which sets up every device, monitors system states, renders the HMI, and reacts to user input events.

LE-Audio

This directory contains the BLE module firmware subproject from a separate repository. It scans, connects, and pairs with earbuds, and then performs real-time audio streaming (LC3). This module acts as a peripheral to the system controller, communicating via a standard AT interface over UART.

Others

Miscellaneous files under the root:

• pickguard.dxf: Pickguard CAD designs.
• logo.jped: Logo of SHRED, generated by Google NanoBanana 2.
• logo.prompt: Prompt of AI gen.

Usage

This section is W.I.P. and will be completed in the future.