Intro
Problem statement
Target Audience
Core Innovation
Basic Block Diagram
Key Features
Power & Battery Strategy
Power Consumption - (approximately)
Current Progress

Published June 25, 2025

Wireless Digital Stethoscope

nRF5340 based portable, energy-efficient, BLE-enabled heart sound capture & streaming for accurate diagnosis & telemedicine.

AdvancedWork in progress640

Base Award

BLE Audio Design Challenge

Things used in this project

Hardware components

Nordic Semiconductor nRF5340 Development Kit

Microphone, Omnidirectional

Texas Instruments OPA2333 op-amp mic pre-amplifier

Texas Instruments OPA365

op-amp for anti aliasing low pass filter

Microchip MCP73833

battery charger

Seeed Studio Polymer Lithium Ion Battery - 2200mAh 3.7V

Flash Memory Card, MicroSD Card

LED (generic)

Nordic Semiconductor nPM1300

Software apps and online services

Nordic Semiconductor nRF Connect SDK

PCBWay PCBA

Story

***It is an ongoing project. I am still developing the firmware and still the hardware design is not completed yet. I am far away from the final development and I know this may not be significant, still I am sharing my work and I'll be updating it from time to time.***

*** If updating is restricted after the deadline, I'll share my work in a separated blog in my profile projects.https://www.hackster.io/sunnyiut/sonicsprint-update-ble-digi-stetho-d8feee***

Intro:

This is a project blog is for the Sonic Sprint BLE Audio Design Challenge.It covers the design, implementation, and evaluation of a BLE-enabled Digital Stethoscope using the Nordic nRF5340 Audio Development Kit. The primary goal is to address the limitations of traditional stethoscopes by introducing wireless, low-latency, high-fidelity heart sound monitoring and sharing.

This project explores the feasibility of capturing low-frequency heart sounds through an analog stethoscope chestpiece and transmitting them wirelessly via Bluetooth LE Audio to BLE headphonesor a smartphone app. The use of Auracast broadcast mode and LC3 codec ensures multi-device connectivity and efficient streaming.

Key goals:

Improve portability, signal quality, and real-time audio monitoring.
Evaluate DSP and power performance of the nRF5340 platform.
Enable real-world telemedicine, training, and clinical diagnosis scenarios

Sample Image

Problem statement:

Traditional stethoscopes are constrained by:

Wired operation and lack of mobility.
No signal processing or amplification.
Inability to transmit or visualize data.
General-purpose earbuds lacking bass response to capture low-frequency heart sounds (S1/S2, murmurs).

A wireless digital stethoscope that overcomes these issues would significantly enhance auscultation quality and utility in clinical and remote health settings.

Target Audience:

Healthcare Professionals like doctors, nurses, and paramedics who require a portable and accurate tool for auscultation.
Remote healthcare services like telemedicine, that need to transmit heart sounds to specialists in real-time.
Medical Researchers and Educators can use it in studying heart sound patterns and abnormalities and teaching auscultation techniques to students.

Core Innovation:

The nRF5340’s dual-core architecture makes it perfect for separate capture, DSP processing and separate interfacing or connectivity.
nPM1100 power management ensure optimal power usage for portable applications which is a major requirement for portable digital stethoscope. I already have a Power Profiler Kit with me, which will be helpful, I believe.
Bluetooth LE Audio enables low-latency, high-quality audio streaming and Auracast™ broadcast for one-to-many communication.
DSP capabilities of the nRF5340 allow for real-time filtering, noise cancellation, and classification of heart sounds.
CS47L63 Audio DSP for testing the driving capability without distortion at lower and higher edge frequency regions.

SystemArchitecture:

The device consists of two main components and an optional App -

Transmitter Unit
Analog Stethoscope Chestpiece with high-sensitivity mic (20 Hz - 1 kHz response)
Preamp + Anti-aliasing filter circuit in a small red box
nRF5340 Audio DK with ADC sampling and DSP filtering
BLE broadcasting via LC3 codec (Mono 16-bit @ 16 kHz)
Receiver Unit
BLE LE Audio-capable headphones or smartphone
Optional second nRF5340 Audio DK for playback test
Optional App
Visualizes heart sounds (waveform, FFT)
Enables switching modes (bell/diaphragm), gain control, recording

Transmitter Unit

Basic Block Diagram

Transmitter Unit Block Diagram

Key Features

Noise Cancellation: Integrated DSP algorithms to filter out ambient noise.
Equalization,Filters and Algorithms: Enhance low-frequency heart sounds for accurate reproduction. Heart sound is combined with Aortic, Mitral and Pulmonic and also Murmurs are there. Selection of frequency with gain helps to classify the abnormalities properly.
Low-Latency Streaming: Synchronized audio playback for real-time diagnosis.
User Interface: Physical buttons for mode selection and a readymade smartphone audio app for visualization.

Power & Battery Strategy:

Battery Type - Rechargeable Li-ion battery (500mAh).

Charging Method: USB-C for fast charging.

Power Consumption - (approximately):

Transmission Mode: ~20mA.
Standby Mode: ~2mA.
Playback Mode: ~10mA.

Battery Life: 6 to 8 hours of continuous use.

Current Progress:

I am working on the firmware of the transmitter unit right now. A generalized draft is attached, later on I'll share the repository link when it gets final.recorded heart sound in audacity software after processing -

I'll be posting my detailed updates from time to time.

#include <zephyr/kernel.h>
#include <zephyr/drivers/adc.h>
#include <zephyr/device.h>
#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/bluetooth/conn.h>
#include "audio_service.h"

#define ADC_RES 12
#define ADC_CHANNEL 0
#define SAMPLE_BUF_SIZE 128

static const struct device *adc_dev = DEVICE_DT_GET(DT_NODELABEL(adc));
static uint16_t sample_buffer[SAMPLE_BUF_SIZE];

static void bt_connected(struct bt_conn *conn, uint8_t err) {
    if (!err) {
        audio_service_set_conn(conn);
    }
}

BT_CONN_CB_DEFINE(conn_callbacks) = {
    .connected = bt_connected,
};

void start_adc_streaming(void) {
    struct adc_channel_cfg ch_cfg = {
        .gain = ADC_GAIN_1_4,
        .reference = ADC_REF_INTERNAL,
        .acquisition_time = ADC_ACQ_TIME_DEFAULT,
        .channel_id = ADC_CHANNEL,
        .input_positive = NRF_SAADC_INPUT_AIN0,
    };
    adc_channel_setup(adc_dev, &ch_cfg);

    struct adc_sequence seq = {
        .channels = BIT(ADC_CHANNEL),
        .buffer = sample_buffer,
        .buffer_size = sizeof(sample_buffer),
        .resolution = ADC_RES,
    };

    while (1) {
        adc_read(adc_dev, &seq);
        audio_service_send((uint8_t *)sample_buffer, sizeof(sample_buffer));
        k_msleep(20); // ~50 Hz frame rate
    }
}

void main(void) {
    bt_enable(NULL);
    audio_service_init();
    bt_le_adv_start(BT_LE_ADV_CONN_NAME, NULL, 0, NULL, 0);
    start_adc_streaming();
}

#include "audio_service.h"
#include <zephyr/bluetooth/gatt.h>

static struct bt_conn *current_conn;

#define AUDIO_CHRC_UUID BT_UUID_DECLARE_128(0xF0,0x00,0xAA,0x01,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x01)

static uint8_t dummy_data;

BT_GATT_SERVICE_DEFINE(audio_svc,
    BT_GATT_PRIMARY_SERVICE(BT_UUID_DECLARE_128(0xF0,0x00,0xAA,0x00,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x11,0x00)),
    BT_GATT_CHARACTERISTIC(AUDIO_CHRC_UUID, BT_GATT_CHRC_NOTIFY, BT_GATT_PERM_NONE, NULL, NULL, &dummy_data),
);

void audio_service_init(void) {}

void audio_service_send(const uint8_t *data, size_t len) {
    if (current_conn) {
        bt_gatt_notify(NULL, &audio_svc.attrs[1], data, len);
    }
}

void audio_service_set_conn(struct bt_conn *conn) {
    current_conn = conn;
}

Credits

sunnyiut

2 projects • 4 followers

Electronics enthusiast working as a researcher in Biomedical Engineering sector. Graduated in Electrical and Electronics Engineering.

Comments

Awards

Base Award

BLE Audio Design Challenge

Wireless Digital Stethoscope