BLE Audio: Low-Latency Mobile Sync with nRF54L15

1. Introduction

In this project, we delve into the world of low-latency audio streaming using Bluetooth Low Energy (BLE) Audio. We have designed and built a compact, battery-powered evaluation board (EVM) featuring the powerful nRF54L15 SoC and the nPM1300 power management IC.

The schematics designed in Autodesk Fusion, along with a Bill of Materials (BOM) ready for immediate order from PCBWAY, are also available.

The PCBA quote from PCBWAY is also completed.

These resources make it easy for beginners and first-time developers working with the nRF54L15 to get started. You can download the files in the 'Schematics' section.

The aim is to explore the capabilities of these components, implement a BLE Audio system, and conduct rigorous tests to assess low-latency performance.

This project is aimed for hobbyists, developers, and those interested in exploring Bluetooth Low Energy audio systems.

2.Key Features of this Project:

• Custom Evaluation Board (EVM): A 2-layer PCB design with nRF54L15 and nPM1300, easily accessible for testing and development.

• Battery Powered and Charging: Integrated nPM1300 for battery charging and efficient power management, enabling true mobility.

• Flexible Audio Interface: Includes a standard I2S(or PDM ,PWM) connector for seamless integration with various audio devices.

• Easily Debug Connectors: It can be programmed using the official nRF54L15 DK evaluation board (which I've also already purchased). Additionally, the GPIO debug connector is pin-compatible.

• Multi-Board Synchronization: Designed to perform synchronized low-latency audio tests with multiple boards.

3. Hardware Design

This section details the core components of our custom evaluation board. The nRF54L15 was chosen for its processing power and support for BLE Audio, while the nPM1300 provides a robust power solution that enables battery charging and efficient power delivery for low power consumption.

Please refer to the schematics for details.

• nRF54L15 SoC: We leverage its advanced features, including a high-performance processor and the BLE 5.4 capability, which enables the BLE Audio.
• nPM1300 PMIC: Power management is essential for a portable system. We integrated the nPM1300 for efficient charging and power distribution.
• 2-Layer PCB: The design of this 2-layer PCB is optimized for ease of assembly and reproduction, making it accessible to beginners and other users.
• Battery Charging Circuit: The battery charging circuit is designed around nPM1300, ensuring safe and efficient charging of the portable battery.
• Easily Debug Connectors: It can be programmed using the official nRF54L15 DK evaluation board. Additionally, the GPIO debug connector is pin-compatible.

4. Software Implementation

We chose Zephyr RTOS for this project. It offers scalability and a robust ecosystem for the nRF54L15. This includes Bluetooth stack with BLE Audio support.

We are currently working on coding and configuration.

The codes and other details will be released collectively upon project completion.

• Zephyr RTOS: An open-source RTOS that is well-suited for this kind of embedded system.
• Nordic Semiconductor nRF Connect SDK: This SDK is a very useful tool for developing BLE on a custom board for nRF54L15. We will also introduce practical debugging and usage methods.
• BLE Audio Synchronization: Using the BLE Audio features within the Zephyr RTOS, we create multi-device audio streaming by synchronizing multiple boards.
• Multi-Board Synchronization: The project will also validate the low-latency performance by testing the synchronized performance with multiple boards.

5. Evaluation and Testing

We plan to build the following development environment for evaluation, testing, and project demonstration:

• nRF54L15 DK as a Debugger: We will use the nRF54L15 DK as a debugger to enable effective software development and testing on our custom board. We plan to provide a step-by-step guide that is easy to understand, even for beginners.
• nPM1300 Power Evaluation: We will evaluate the charging and power delivery capabilities of the nPM1300 to ensure that it can effectively manage the low-power needs of the nRF54L15 system.
• BLE Audio Performance: We will conduct a series of tests to BLE Audio quantify low-latency and synchronization performance between our developed multiple boards.

5-1. Pre-Test GPIO with nRF54L15DK

We've purchased an nRF54L15DK for preliminary testing and have started.

We’ve confirmed the ability to control GPIO on any designated pin.

The following is a test video.

We are toggling the GPIO on and off and using a tester to confirm the voltage changes.

5-2. Pre-Test I2S with nRF54L15DK

Additionally, We are also conducting I2S Audio tests as part of my preliminary work.

We've connected the nRF54L15DK to an I2S-to-DAC converter IC (MAX98537A) and am performing speaker output tests.

The program is designed to play a sound when flashed and when the device is reset. The following is a test video.

We've verified that the I2S waveform output is as expected. And checking the waveform using an oscilloscope.

The following is a test video.

This waveform means CH1_3.3V, CH2_BCLK, CH3_DIN, CH4_LRC.

We've confirmed that the clock and data waveforms match the target waveforms.

6. Conclusion and Future Challenges

We would like to express our gratitude for organizing such an attractive contest. We are very eager to be selected as a Contender and move forward with the development of nRF54L15 and BLE Audio.

We appreciate your continued support.