Heart sound auscultation is an important means of disease diagnosis. In this paper, we discuss an electronic stethoscope designed by using wireless transmission technology. The electronic stethoscope is based on embedded processor. The data can be transmitted through ZigBee wireless transmission module, and the microphone is used to receive the sound of heartbeat. We can insert a capacitive microphone into the head of its acoustic stethoscope to turn it into a digital stethoscope, so that its sound can be played through headphones. The heart sound signal will be processed and amplified.
Circuit principle:The front-end circuit is used for heart sound signal acquisition and preprocessing. Generally, the effective human heart sound signal frequency is 0 ~ 600Hz. The heart sound auscultation head and MEMS microphone are used to convert the sound generated by heartbeat into an electronic signal. The signal processing circuit consists of three parts, mainly amplification circuit, filter circuit and second amplification circuit. The output from MEMS microphone is a very weak AC small signal, and the amplitude of heart sound signal is about 30-60mv. This size of signal can not meet the requirements of filter module, so the primary amplification processing of signal must be carried out. The primary amplification of signal adopts integrated operation amplifier μ A741。 Due to the low heart frequency rate, all signals with a frequency above 500Hz can be filtered out while amplifying the signal, so as to improve the anti-interference ability of the system. The integrated operational amplifier is still used in this design μ A741 constitutes a suitable low-pass filter circuit. After filtering, the heart sound signal we obtained has been relatively pure, but the size of the signal still can not meet the requirements of the power amplifier. Therefore, it is necessary to amplify the filtered heart sound signal. At this time, the LM386 amplifier is used in the system.