Development of an Electronic Stethoscope Using Raspberry

In this study, Raspberry Pi 3B was used to develop an electronic stethoscope by embedding a condenser microphone in the traditional stethoscope head to collect heart and lung sounds. The collected signals pass through amplification and filter circuits, and then the processed signals are transmitted to the Raspberry Pi through audio cables. In addition, a recording system for heart and lung sounds was developed in the graphic user interface on the Raspberry Pi. After recording, the audio file can be directly stored in Raspberry Pi, played on headphones or a small speaker connected to the Raspberry Pi, or transmitted via Bluetooth or Filezilla to a computer for further analyses. The functions of recording audio sounds and playing recorded sounds can help doctors to relieve the pain caused by the long-term use of the traditional stethoscope in the ear. They also improve the inability of recording the heart and lung sounds when using the traditional stethoscope. In this study, we also explored the use of dual microphones for noise reduction. Five kinds of stethoscope heads were developed, and the corresponding audio signals were observed using Fast Fourier Transform (FFT) to analyze their effects on noise reduction. The designed circuit has two modes for collecting sounds depending on the audio source: the heart sound mode or the lung sound mode, and it also has anti-noise mode. After testing, the effect on active noise cancelling proposed in this study is not as good as expected. The frequency of the noise sound changes after passing through the material that the stethoscope surface touches. Various materials cause different variations on frequency received by the microphone, causing incomplete frequency cancellation on noise sound. Based on the testing for passive noise cancelling, the best one, among all the stethoscope heads including one commercial electronic stethoscope, is that the microphone is placed in the stethoscope head and the periphery of the stethoscope head is covered by cork.