BT40F audio board

BLE Audio Platform - Engineering Project

Custom hardware and firmware platform for prototyping and evaluating Bluetooth Low Energy Audio broadcast transmission.

This repository combines:

• custom PCB design created in KiCad
• firmware applications based on nRF Connect SDK and Zephyr RTOS
• component datasheets used during design and bring-up
• test logs and recorded audio collected during BLE Audio experiments

The platform is built around the BT40F SiP with the Nordic nRF5340 and was used to evaluate LE Audio broadcast transmission based on BIS streams.

System Overview

Main hardware blocks:

• BT40F SiP with Nordic nRF5340
• Nordic nPM13xx PMIC (nPM1304 used in the assembled board as a practical substitute for nPM1300; the main functional difference is reduced battery-charging capability)
• CP2105 USB-UART bridge
• SGTL5000 external audio codec
• USB-C power and debug connectivity
• microphone, line output, and headphone audio connectors

Repository Layout

.
|-- Datasheets/   Component datasheets used during design and bring-up
|-- Firmware/     Zephyr/NCS applications, overlays, and helper modules
|-- Images/       Board photos, PCB renders, and architecture diagrams
|-- KiCad/        Schematic, PCB, project libraries, and Gerber outputs
`-- Tests_data/   Recorded audio samples and test logs

Important subdirectories:

• Firmware/bap_broadcast_source/ BLE Audio broadcast source application
• Firmware/bap_broadcast_sink/ BLE Audio broadcast sink application
• Firmware/codec_test/ codec bring-up and audio-path verification
• Firmware/test_i2c/ I2C and peripheral detection tests
• Firmware/leds_test/ PMIC and LED bring-up
• Firmware/beacon/ BLE beacon baseline application
• Firmware/biblioteki/ shared helper modules such as pmic and i2c_helpers
• KiCad/BT40F_audio_board_smaller/ main KiCad project
• KiCad/Gerber/ exported manufacturing files
• Tests_data/Test_Logs/ logs from lab and real-world experiments
• Tests_data/Recorded_Audio/ captured audio files used during evaluation

Note: some directories inside Firmware/ such as build/, Build_V1/, and MyBoard/ are generated build outputs committed alongside the source tree. They are useful as build records, but they are not the primary source files to edit.

Firmware Summary

The main project flow is built around two applications:

• bap_broadcast_source transmits BLE Audio broadcast streams
• bap_broadcast_sink receives BLE Audio broadcasts and contains project-specific modules for LC3 handling, USB, codec output, and stream reception

Additional applications are included for hardware validation and bring-up:

• codec_test initializes and probes the SGTL5000 path
• test_i2c verifies low-level I2C communication and peripheral presence
• leds_test validates PMIC-related control paths and LED behavior
• beacon provides a minimal BLE reference application

The per-application README.rst files under Firmware/ are based on upstream Zephyr samples. For this repository, the project-specific behavior is defined mainly by the local src/, boards/, *.overlay, prj.conf, and Kconfig* files.

Hardware Design

The hardware project contains:

• schematic and PCB layout files in KiCad/BT40F_audio_board_smaller/
• custom symbol and footprint libraries in KiCad/BT40F_audio_board_smaller/Project libraries/
• generated Gerbers in KiCad/Gerber/BT40F_board_revA.zip
• supporting visual assets in Images/

Some hardware files and library names still refer to nPM1300, while the assembled prototype used nPM1304 because nPM1300 was unavailable at the time. For this project, the devices are treated as near-equivalent except for the weaker charging capability of nPM1304.

Building The Firmware

This repository does not include a full NCS workspace manifest, so builds are expected to run inside an existing nRF Connect SDK environment with west available.

Example commands reconstructed from the committed build artifacts:

west build --pristine --build-dir build/source-custom Firmware/bap_broadcast_source --board nrf5340_audio_dk/nrf5340/cpuapp -- -DEXTRA_CONF_FILE=boards/nrf5340_audio_dk_nrf5340_cpuapp.conf -DCONF_FILE=prj.conf -DEXTRA_DTC_OVERLAY_FILE=Custom_Board.overlay -DDTC_OVERLAY_FILE=app.overlay

west build --pristine --build-dir build/sink-custom Firmware/bap_broadcast_sink --board nrf5340_audio_dk/nrf5340/cpuapp -- -DEXTRA_CONF_FILE=boards/nrf5340_audio_dk_nrf5340_cpuapp.conf -DCONF_FILE=prj.conf -DEXTRA_DTC_OVERLAY_FILE=Custom_Board.overlay -DDTC_OVERLAY_FILE=app.overlay

west build --pristine --build-dir build/codec-test Firmware/codec_test --board nrf5340_audio_dk/nrf5340/cpuapp -- -DCONF_FILE=prj.conf -DDTC_OVERLAY_FILE=nrf5340_audio_dk_nrf5340_cpuapp.overlay

If you build one of the custom configurations, review the local overlays and board configuration files in the target application directory before flashing.

Test Data

Test artifacts are grouped under Tests_data/:

• Test_Logs/01_Lab_Tests/ source and sink logs captured in laboratory conditions
• Test_Logs/02_Real_World_Tests/ logs collected in a more challenging radio environment
• Test_Logs/03_Audio_Transmission_test/ dedicated source and sink logs for audio transmission checks
• Recorded_Audio/ sample WAV captures

Due to memory constraints, logging on the Network Core was disabled. The provided logs come from the Application Core.

Known Limitations

• The SGTL5000 codec could not be fully used in the final tests because the available MCU clocking was insufficient for the intended MCLK configuration
• Network Core logging was disabled because of memory constraints
• Final validation therefore focused on LC3 processing and BLE transmission rather than a fully closed audio path

License

This project is licensed under the terms of the LICENSE file in this repository.