In 2019, the COVID-19 epidemic began to break out globally, and the number of confirmed cases around the world can be seen on the news every day. How to reduce the chance of exposure to infection and provide effective and accurate diagnosis of infected patients has always been the wish and request of medical staff. Although there are currently Bluetooth wireless electronic stethoscopes on the market, which improves the risk of infection in close contact with patients, the Bluetooth stethoscopes currently on the market can only correspond to a Bluetooth wireless headset or mobile phone, which cannot allow all doctors to hear cardiopulmonary sounds at the same time to discuss the condition. Therefore, this design proposal proposes a Bluetooth low-power Auracast™ broadcast stethoscope, which can

 broadcast auscultation audio signals to unlimited Auracast™ certified Bluetooth headsets or Bluetooth speakers for listening, so that close contact with patients and external noise interference can be avoided, so that medical staff can more safely listen to weak cardiopulmonary sounds to make accurate judgments.         

 This design solution uses Bluetooth low power Broadcast Audio function, allowing an Auracast™ Bluetooth low power transmitter to transmit audio to the receiving range of Auracast™ certified receiving devices to receive and play audio, and the number of receiving devices is unlimited. Bluetooth low power broadcasting introduces the concept of low power Isochronous channels, a key feature for audio transmission. Isochronous channels are designed to synchronize audio streams between different Bluetooth devices to provide a higher quality and more consistent audio experience. Here are some of the advantages of Bluetooth's low power isochronous channels:      

• High quality audio：Isochronous channels offer audio data rates up to 384 kbps for high quality audio.

• Time synchronization: Data is time-stamped at both the source and receiver to ensure playback is synchronized across devices.

• Error correction: Errors in the data are detected and corrected to maintain sound quality.

• Power control: Data is transmitted at a rate that matches the playback rate, minimizing power consumption.

There are two types of Bluetooth low power isochronous channels:

• Connected Isochronous Channels: Channels used for transmission that require two devices to establish a GATT connection.

• Broadcast Isochronous Channels: Use radio to transmit audio. Connected isochronous channels are mainly used in applications such as multi-streaming and sharing, while broadcast isochronous channels are mainly used in applications such as broadcasting.

Figure 1 shows how Auracast™ works. The Auracast™ transmitter sends an Auracast™ broadcast containing broadcast information (share) and provides information about the broadcast (such as name, content, codec configuration, etc.) and one or more streams (such as left and right stereo streams) to Auracast™ assistive devices (such as mobile phones or tablets).

 
Figure 1 How Auracast™ works (Image: Bluetooth Technology Alliance)

 The Auracast™ Assistant uses Bluetooth low-power technology to scan Auracast™ broadcasts and provides users with a user interface that allows them to select any Auracast™ broadcast (sharing) connection, much like selecting a wireless network sharer to connect to on a mobile phone. After the user has selected the Auracast™ broadcast to connect to (share), the Auracast™ auxiliary device provides the Auracast™ receiver (such as headphones, hearing AIDS, etc.) with the necessary information to join the Auracast™ broadcast, and then begins receiving and playing the stream.  

Auscultation head structure

• Stethoscope head: Usually made of metal, it is placed on the patient to collect sounds from within the body. The auscultation head consists of a headset and a diaphragm (see Figure 2).

• Receiver: Used to amplify the collected sound.

Diaphragm: Located between the auscultation head and the receiver, it is used to collect and transmit sound.

Figure 2 Structure entity of auscultation head

Filter and microphone amplification lines

Microphone amplifiers are Power Amplifiers that can be selected specifically for low-loss power supplies and have Automatic Gain Control (AGC) functions, which can automatically adjust the gain to avoid distortion caused by excessive input, and ensure that the output can maintain a certain volume output. In addition, in its basic circuit, a first-order low-pass filter can be added to the output and input terminals to filter out high-frequency noise, which helps to improve the performance in practical applications and ensure the purity and reliability of the output signal.

Bluetooth low power broadcast line

In this design, QCC3086 Bluetooth chip launched by Qualcomm is used as a Bluetooth low-power broadcast transmission platform, and the QCC3086 development board is used in this scheme to facilitate the measurement of post-read signals. This design scheme will use Bluetooth low power LC3 encoding and decoding audio. After the microphone of the design stethoscope head receives the heart-lung sound, it is transmitted to the QCC3086 analog signal input through the microphone amplifier and filter line, and then transmitted to the Bluetooth headset through the QCC3086 Bluetooth wireless broadcasting function, or Bluetooth speakers and other devices for playback and use. Figure 3 is the basic circuit diagram of QCC3086.

• The QCC3086 is a single-chip Bluetooth Audio SoC platform designed to deliver rich functionality in the form of a USB adapter or Line in, bringing the Snapdragon Sound™ technology suite to any source device.

  
  

• The QCC3086 is Qualcomm's S3 Gen 2 Sound platform portfolio, offering Bluetooth 5.4 compliant dual-mode devices that utilize classic Bluetooth and LE audio, as well as Snapdragon Sound capabilities to support source devices.

  
  

• The QCC3086 combines Snapdragon Sound and LE Audio to deliver ultra-low latency of less than 20 ms, enabling lag-free wireless audio and a voice backchannel for in-game chat. Latency is further reduced when only game audio is provided.

  
  

• The QCC3086 also offers Snapdragon Sound support via Qualcomm® aptX™ Adaptive and aptX Voice, designed to enable music streaming up to 24-bit 96kHz and ultra-broadband voice hands-free calls.

  
  

• Oems can use the QCC3086 to add Auracast™ broadcast audio capabilities to adapters and adapters for use with source devices such as phones, laptops, TVS, and a variety of other audio devices. The QCC3086 is designed for the emerging Bluetooth® LE Audio audio standard and is designed to support Auracast™ broadcast audio and LE Audio monobook music and voice.

Figure 3 Basic circuit diagram of QCC3086

   This design scheme explores the broadcast function of a Bluetooth low power broadcast stethoscope, which has the unique ability to allow multiple Bluetooth low power receivers to receive a broadcast simultaneously. The left earphone of the Qualcomm QCC5181 Earbud RDP Bluetooth active noise cancellation earphone is placed in the left auricle of the GRAS 45C artificial ear model, as shown in Figure 4. At the same time, the second group of QCC5181 Headset development board with wired headset was placed on the right auricle of the GRAS 45C artificial ear model, as shown in Figure 5.     

Figure4 Qualcomm Earbud RDP(Left)    


Figure5 Qualcomm Earbud RDP(Right)  

         Using the Audio Precision APx500 V8.1 software and Audio Precision APx525B, we set the step frequency scan and set the signal Level to 100mVrms for output. We then measured the RMS Level on the left ear of the Qualcomm QCC5181 Earbud RDP Bluetooth active noise cancellation Headset and the right ear of the QCC5181 Headset development board to see how their output performed. From the test results in Figure 6, we can clearly observe that the output volume of the two objects under test is different because of the different hardware design. However, it is worth noting that despite the difference in volume, the trend of the frequency response curve is similar. This means that at different volume Settings, both devices show consistency in their frequency response.

 
Figure 6 Qualcomm RDP Bluetooth active noise cancelling headset left ear and QCC5181 development board right ear RMS Level output

In addition, the DUT Delay function of the APx 500 software was used to measure the output delay of the left ear of the first test object Qualcomm Earbud RDP and the right ear of the second test object QCC5181 Headset development board, and the results were shown as (Figure 7). Because the product is used as a Bluetooth broadcast stethoscope, it needs to transmit stethoscope Audio accurately, so it is set to High Reliability according to the Basic Audio Profile  (https://www.bluetooth.com/specifications/bap-1-0/). According to the results of multiple measurements, it can be concluded that the delay and specifications between different objects to be measured are almost the same.

 
Figure 7 Delay time of Qualcomm Earbud RDP left ear and QCC5181Headset right ear

We were able to determine that the Bluetooth low power broadcast stethoscope shows a high degree of accuracy in the broadcast function, and can accurately send to each receiver. Pairing Bluetooth headsets not only highlights the potential application of Bluetooth technology in stethoscopes and headphone products, but also emphasizes its advantages in practical operation and functional performance. We can be more confident that Bluetooth technology has a significant contribution to the advancement of modern medical and personal listening devices.

The traditional stethoscope continues to maintain its dominant position in clinical applications, mainly due to its affordability, simplicity of operation and durability. However, its sound quality is limited, and it is easily disturbed by ambient noise, which affects the accuracy of medical diagnosis. The electronic stethoscope, as the modern evolution of the traditional stethoscope, has brought about remarkable improvements. Especially under certain conditions, such as large patients, weak sounds or high noise environments, the electronic stethoscope shows its superiority. This design scheme proposes Bluetooth low power broadcast stethoscope and provides a complete electronic stethoscope solution. This system is not only suitable for medical education and clinical diagnosis, but also has several advantages, including:

It can provide a variety of auscultation modes at the same time, including heart sounds, lung sounds, murmurs, etc., which is convenient for doctors to diagnose.

It can enhance the auscultation volume and improve the auscultation efficiency.

It has data storage and analysis functions for medical research and education.

Low power consumption and fast connections optimize performance and reduce reliance on large batteries.

Bluetooth low power broadcast stethoscope design scheme, as a part of modern medical diagnostic tools, because of its high sound quality, advanced filtering technology, data recording function and remote auscultation capabilities will help improve the efficiency and accuracy of clinical auscultation, and provide doctors with more comprehensive diagnostic information.

►Scene application diagram

►Display board

►Solution block diagram

►Core technology advantage

QCC3086 Performance:

1. Support BT5.4

2. 240MHZ DSP

3. Support Qualcomm® aptX,aptX HD Audio,aptX Adaptive coDEC

4. Support USB Dongle \ Line in

5. Support ADC and DAC maximum sampling rate 96 kHz

►Scheme specification

1. QCC3086 can support traditional Bluetooth BR\EDR\LE Audio, LE Audio Broadcast

2. QCC3086 can support USB Dongle;

3. QCC3086 can support Source devices;

4. QCC3086 supports LE Audio Broadcast;