Development Of A Multi-channel Surface Electromyography Acquisition Instrument

Surface electromyography(sEMG)is a time-related graphical record of potential sequences of muscle contractions on the skin surface when the muscle is excited,which collected by surface electrodes.Surface EMG usually contains the physiological state information of the human muscles and nervous system.Surface electromyography plays an important role in human’s basic medical research,physiologic research,pathological analysis,sports science,sports analysis,ergonomics and rehabilitation aids.This paper designs a surface electromyography acquisition instrument based on the STM32 microcontroller.Based on the existing research of the study group,new instrument improved the design of electric circuit,as well as developed an algorithm for sEMG’s end-point detection from measurement signal,and applied an effective algorithm for ECG cancellation which increased the effectiveness of the sEMG evaluation.The main content includes four aspects:1)Hardware Analog Circuit: designed an instrumentation pre-amplifier based on the AD8220 and a right leg driver circuit,in order to suppress the input of the common-mode voltage;designed a filter with the Sallen-Key structure and a notch filter with Fliege structure in order to filter the noise of high-frequency,low-frequency and power-frequency;used AD7682 to convert the s EMG analog signal into digital signal.2)STM32 control program: used SPI peripheral to receive data and used USART peripherals to send data.The data transmission process is dominated by the DMA controller;the Butterworth filter is designed to eliminate high frequency noise and power frequency noise;designed a special communication protocol for the communication with the upper machine.3)The upper machine APP: APP can real-time display the curve of the user’s measurement signal,calculate the signal evaluation index,form the sEMG evaluation report,and archive the user’s information.4)Algorithm application: used the end-point detection algorithm which based on short-term zero-crossing rate and short-term energy to detect the starting and ending points of sEMG,which effectively avoids the error detection caused by ECG interference;the wavelet threshold denoising algorithm and the independent-component-analysis-based denoising algorithm are respectively suppress the ECG interfere in the sEMG;an ECG energy residual ratio index is established to evaluate the effect of ECG suppression.This paper has verified the sEMG acquisition instrument’s performance,and the algorithm based on short-term zero-crossing rate and short-term energy can accurately detect the sEMG end-point.Experimental verification shows that the wavelet threshold denoising algorithm and the independent-component-analysis-based denoising algorithm can effectively suppress ECG interfere.