This paper presents a construction of a simple audio-cardiograph based on Doppler effects of a reflected ultrasound waveform and a Cortex-M3 ARM compliant microcontroller applied for analog data acquisition, sampling and digital transmission. This mixed-signal device may be an element of a widely accessible cost effective system for continuous controlling of a patient's heartbeats as well as electronic fetal monitor. It may be used at home in an easy way and the recorded results may be delivered to the medical care staff for an immediate analysis and fast diagnosing. The use of an advanced microcontroller allowed for minimizing the construction complexity, the device size and its cost. The measuring module is supplied directly from USB port of a standard personal computer and it is equipped with a galvanic barrier that ensures the patient's safety. The demodulated analog waveform is sent real time to the computer by the means of isochronous data transmission (USB 2.0 compliant protocol). This data is ready for processing in a computer application that may allow for determining a tempo, both long- and short-term of heartbeats, its stability and other desired parameters.
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