RF-001 prototype

This is a short post about my main embedded side-project.

Overview

It’s a musical pedal that transmits real-time audio over the air. The purpose is a flexible monitoring solution for professional musicians: sometimes you need to monitor a specific subset of band members during rehearsal, and it would be nice to have such ability without lots of wires.

Features

Universal transceiver module and case design. Modules can be combined into a supermodule (stacked side to side using the 9-pin D-subs):
Real-time low-latency audio, 32-bit 44100 Khz mono channel (stereo in the future).
Full software control over the codec functions, analog mixing for modules connected:
- EQ
- Volume
- Balance
- Other functions
DFU update over the USB.
Desktop software for device management:
Single encoder / push-button control over the OLED screen.
Line / mic input, headphones (single output) / line out (single output)
Inter-module communication: ability to have the first module connected to the laptop as a master module for controlling other modules (to easily change settings)

Details of the prototype / schematics:

STM32F103RCT6 as a core.
AK4954AEN as a codec. Custom module board from the reference schematics:
SSD1306 OLED screen module
Amicom A7190 transceiver module as RF core for audio transmission.
8k-bit EEPROM (from STM, random one)

Early version testing (first successfull full-speed audio transfer):

All together (single module prototype):

Project architecture / parts

DFU Bootloader (standard one)
Firmware:
- HAL part (generated via STM32Cube for faster prototyping)
- FreeRTOS (because of queues and ability to structure the code properly)
- C/C++ mix (generated sources in C, my code in C++)
- RTT for debugging / logging
- Drivers for peripherals (with abstract drivers for easier work with DMA / non-DMA transfers)
- All peripherals configured with DMA (maximum speed)
- Small custom UI framework (rendering based on the Adafruit Driver, to be changed in the future)
- Catch tests with simple mocks for peripherals / interfaces:
UI simulator:
Granular run configurations for the whole project:
CMake as a build system

embedded