DESIGN AND DEVELOPMENT OF A COST-EFFECTIVE DIGITAL STETHOSCOPE

Abstract

Background: The medical device used for auscultation purpose is known as a stethoscope. There are two types of stethoscopes available in the market; an ordinary or acoustic stethoscope and an electronic or digital stethoscope. The acoustic stethoscope is widely used by physicians due to its cost-effectiveness but it has a poor sound quality especially in the in noisy environment. A digital stethoscope can be used to overcome this problem but due to its expansive nature it is rarely used. The objective of this thesis was to give a better and cost-effective solution. Methodology: An Arduino DUE based digital stethoscope was designed that used the chest-piece of an ordinary stethoscope for detecting the acoustic sounds from the body. A high sensitive studio speech microphone was inserted inside the pipe attached near the end of chest-piece for converting the acoustic sounds into electrical signal. Due to low amplitude, the sounds were amplified by the first low noise operational amplifier. The signal was then passed to a second order Sallen-key low pass antialiasing filter, digitized by built-in 12-bits analog to digital converter (ADC) of Arduino DUE and processed to calculate the beats per minute (BPM) and displayed over a serial TFT graphic LCD. The digital signal was converted to analog signal by means of built-in 12 bits digital to analog converter (DAC) and post-amplified by a low noise power amplifier and fed to the headphones. The device was tested on five subjects in different environmental conditions. The heart sounds were recorded in wav format by Thinkslab one Phonocardiogram software and read in MATLAB. The signal to noise ratio (SNR) was calculated and compared with recorded sounds of a standard commercially available Litmann 3200 digital stethoscope. The beats per minute along with real time heart sounds (S1 and S2) were clearly detected on TFT graphic LCD. The cost analysis of the device was also presented.