Design And Implementation Of Cardiac Function Insusceptibility Detection Device Based On Seismocardiogram

The activity of the heart pumping causes body vibrations synchronously with heartbeat, which is recorded as Seismocardiogram(SCG). Measuring device base on SCG signal can realize insusceptibility monitoring on the mechanical activities of the heart without any sensor attached directly to the human body, but SCG signal is so weak and prone to be jammed that it is difficult to detect. According to the peculiarities, this paper designs and implements cardiac function insusceptibility detection device based on SCG, which is composed of signal acquisition module and signal processing module.Data acquisition module is composed of the sensor circuit, amplifier circuit, filter circuit (including the low-pass, notch and blocking circuits) and power circuit. Sensor circuit is used to get the body vibration signal caused by the activity of the heart pumping. Amplifier circuit consists of the front differential amplifier circuit and main amplifier circuit, the front differential amplifier circuit is used to amplify differential mode signal from sensor output, the output adopts the way of amplifying and flitering step by step, it can obtain the SCG signal after main amplifier circuit and filter circuit composed of low-pass and notch circuit.Signal processing module is composed of CPLD minimum system, analog-to-digital converter(ADC), digital-to-analog converter(DAC), memory part and communication part. SCG signal acquired is converted to digital signal by ADC part, stored by memory part or transformed by communication part. Then transport the result to PC by UART to obtain longer SCG signal, making it facilitate for further analysis and processing. The timing of the entire system is provided by CPLD minimum system. In the module, the paper also used the VHDL to realize digital low-pass filter, to pre-process the SCG signal.To analyze the SCG signal which represents the mechanical activities of the heart can gain the heart rate of the subjects. Using adaptive changeable difference threshold algorithm to extract heart rate of pre-process SCG signal which have minimum computation, is a kind of efficient accurate and rapid IJK location method, achieves real-time heart rate detection.Synchronously acquire ECG signal as the reference of time when monitoring SCG to prove the system. The result shows the system can correctly gain SCG signal, the system can also pre-process, store and upload the signal extracted, and furthermore it can extract the heart rate of the subjects by using adaptive changeable difference threshold algorithm.