TI 公司的數字聽診器解決方案是采用TMS320VC5505 DSP醫療開發套件來實現的.主要的元件是捕捉心肺聲音的傳感器,以及聽診的數字化和數字處理,以降低噪音,濾波和放大.此外還包括了心率檢測和心臟缺陷檢測的算法.電源和電池管理是該手提診斷設備的關鍵,主要的設計都采用超低功耗和高效率驅動,以延長電池壽命.本文介紹了數字聽診器總體方框圖, 數字聽診器前端方框圖, 增益為31的前置放大器, 一階低通濾波器,以及TLV320AIC3254方框圖和TMS320VC5505 DSP 與TLV320AIC3254間接口方框圖, 數字聽診器前端板電路圖和材料清單(BOM).

Digital Stethoscope Implementation on the TMS320VC5505 DSP Medical Development Kit (MDK)

The main elements of a Digital Stethoscope are the sensor unit that captures the heart and lung sounds (also known as auscultations), digitization, and digital processing of the auscultations for noise reduction, filtering and amplification. Algorithms for heart rate detection and heart defect detection may also be included. 

Power and Battery Management are key in this ultra-portable diagnostic tool, where key design considerations are ultra-low power consumption and high efficiency driven by the need for extended battery life, and high precision with a fast response time allowing quick determination of the patient’s health status.  Additional requirements may drive the need for recording the auscultations, cabled or wireless interfaces for transmission of the auscultations.  Also, to enable ease of use, features like touch screen control and display backlighting are key to usability of the device.  Adding all these features without significantly increasing power consumption is a huge challenge.  Texas Instruments portfolio of Processors, Instrumentation and Buffer Amplifiers, Power and Battery Management, Audio Codecs, and both wired and wireless interface devices provides the ideal tool box for Digital Stethoscope applications.

The common core subsystems of a Digital Stethoscope are:

Analog Front-End/Sensor Interface and Codec 

Auscultations signal input is amplified and then digitized by the Audio Codec.  Auscultations signal after being digitized and subjected to signal processing, is converted to analog and sent to the stethoscope earpiece.

Low Power Processor 

Processors capable of executing all of the digital stethoscopes signal processing including key functions such as noise reduction, algorithms for heart rate detection, and heart defect detection while maintaining a very low constant current draw from the battery are good fit.  The ability to control interfacing with memory and peripheral devices is also helpful.  Given the nature of the device, processors that can manage the digital display and keyed functions allowing auscultation waveforms to be displayed and manipulated without additional components are ideal.

Data Storage and Transmission

The auscultations can be recorded on MMC/SD card, or on a USB device.  It can also be transmitted via wireless capability such as Bluetooth.

Digital Stethoscope Medical Development Kit

TIs TMS320VC5505 evaluation module together with TIs digital stethoscope analog front-end module make up the new C5505 DS Medical Development Kit (MDK) provides developers access to a development tool set that offers a complete signal chain solution along with software to save months of development time and for portable patient monitoring applications that demand battery efficiency.

 
圖1. 數字聽診器方框圖

A number of emerging medical applications such as electrocardiography (ECG), digital stethoscope, and pulse oximeters, require DSP processing performance at very low power. The TMS320VC5505 digital signal processor (DSP) is ideally suited for such applications. The VC5505 is a member of TIs C5000™ fixed-point DSP platform. To enable the development of a broad range of medical applications on the VC5505, Texas Instruments has developed an MDK based on the VC5505 DSP. A typical medical application includes:

An analog front end, including sensors to pick up signals of interest from the body

Signal processing algorithms for signal conditioning, performing measurements and running analytics on measurements to determine the health condition

User control and interaction, including graphical display of the signal processing results and connectivity to enable remote patient monitoring The MDK is designed to support complete medical applications development. It includes the following elements:

Analog front-end boards (FE boards) specific to the key target medical applications of the VC5505 (ECG, digital stethoscope, pulse oximeter), highlighting the use of the TI analog components for medical applications

VC5505 DSP evaluation module (EVM) main board

Medical applications software including example demonstrations


圖2.VC5505 EVM評估板外形圖

圖3.數字聽診器前端板外形圖

圖4.數字聽診器前端方框圖

The front-end board contains the following stages:

Pre-amplifier

Low pass filter

AC coupling block

Audio codec

Front-end connector

Digital stethoscope analog front-end module can be used with C5505 EVM to make up the C5505 DS MDK that offers a complete signal chain solution along with software

圖5.增益31的前置放大器

圖6.一階低通濾波器

圖7. TLV320AIC3254方框圖


圖8. VC5505 DSP 和TLV320AIC3254間接口方框圖

圖9. 數字聽診器前端板電路圖(1)

圖10. 數字聽診器前端板電路圖(2)

圖11. 數字聽診器前端板電路圖(3)

數字聽診器前端板材料清單(BOM):