data acquisition board for registration of myoelectric signals

8/13/2019 Data Acquisition Board for Registration of Myoelectric Signals

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Data Acquisition Boardfor Registration ofMyoelectric Signals

Seminario de Mecatrónica



Abstract

Will develop a PCI card (Peripheral Component Interconnect), which functions asa data acquisition system for recording myoelectric signals and in the future toevaluate the improvement of patients with motor disabilities.



Introduction

The development of computer controlled instruments, has allowed measurementautomate processes in various areas.

The result is the occurrence of various communication interfaces such as thecards PIC.

Is develop a data acquisition card that has a PIC communication bus, to obtainregistration, processing and analysis of myoelectric signals.

This card implements an electromyograph, a tool with which to perform studieson the muscle problems.



Electrocardiogram

It consists in the acquisition, recording and analysis of the electrical activitygenerated by nerves and muscles using electrodes (surface, needle orimplanted).

Signals are generated by the exchange of ions through the membranes of themuscle fibers due to muscle contraction.

Muscle cells have an elongated shape and are called fibers, these muscle fibersare arranged in bundles called fascicles that are involved in connective tissue.



Electrocardiogram

It consists in the acquisition, recording andanalysis of the electrical activity generated bynerves and muscles using electrodes (surface,needle or implanted).

Signals are generated by the exchange of ionsthrough the membranes of the muscle fibers

due to muscle contraction.

Muscle cells have an elongated shape and arecalled fibers, these muscle fibers are arrangedin bundles called fascicles that are involved inconnective tissue.



EMG signal characteristics

Spectrum importance 0-500 Hz.

Dominant energy between 50-150 Hz.

The signal acquisition is affected by line noise (60Hz).

Amplitude from 0-60 mV and 0-1.5 mVrms peak.

Action potentials of the muscle have a fixed magnitude.

The EMG signal amplitude varies from microvolts (µV) to a range of lessthan 10 millivolts (mV).



Measurement of the EMG signal

The contraction of the muscle fibers generates electrical activity, measured byelectrodes attached to the skin.

For EMG signal acquisition are requires the correct identification of the involvedmuscle regions.

The collected signals are too weak, so that it is necessary a previous process offiltering and amplification before analysis.

In the EMG signal recording there are drawbacks as environmental noise, noise due tomovement of the electrodes and the crosstalk (interference from the electricalactivity to the muscles next).



Design of a data acquisition system basedon PCI card

Myoelectricsignal

Preamplifiedand filtered

PIC, ADC andMultiplexor

FPGAPC

PIC-FPGACommunication

Data FlowControl

FIFO

PCI Protocol



The first part of the diagram, is the analog input signal, this is preamplified andfiltered due to the signal from the electrodes that is very weak. To digitize theinput signal using an Analog to Digital Converter (ADC) with a resolution of 10 bitby a microcontroller 16F877A.

The system consists of 4 analog channel, if are use the 4 channels the signalsampled is of 10 kHz, with 2 signals are 20 kHz, the signal interpreted by theFPGA in which the digital filters are connected.

Communication between the PIC and the FPGA, followed by the data flow controland FIFO memory, which stores data that reproduce the signal.



Design preamp stage and filtering

Implement a system with a low noise level for myoelectric signal acquisition.

The interference caused by altern current line, unduly fixed electrodes, thuseliminating these effects is important.

Preamplification stage

For this step we use the instrumentation amplifier AD8221 with gain of 500, amplifies

the signals to obtain an appropriate level, must withstand the entry of high DCvoltage , a high common mode rejection (CMRR) and low noise.

Filtering stage

It implements the TL084 integrated circuit that contains four operational amplifiers.Working with low-level signals in noisy.



Band Reject Filter

The band reject filter of VCVS structure (Voltage Controlled Voltage Source), with acutoff frequency of 60 Hz and bandwidth of 6 Hz, to remove the noise produced bystress.

Four these filters in cascaded achieve a -44 dB attenuation.

Low pass filter

Limits the frequency from 0-500 Hz, using a first order filter with a cutoff frequencyof 1 kHz.

High pass filter

Direct component, eliminates the noise, movement of the electrodes and cables.This first order filter has a cutoff frequency of 10 Hz.

Non-Inverting Amplifier

Amplifies the signal again for a profit of 11.



PCB layout

The PCB design of the electronic card consists of four copper layers and three ofdielectric material :

The top and bottom layers contain the components of the card and track routing.The second layer is the earth plane.The third layer is the voltage level.The card is modular and consists of a daughter board containing the FPGA.

The FPGA will be inserted into the card, that count has four connectors. The PCIprotocol is responsible for card-computer communication.

The channels placed around the stage analog produce a grounded shield and reduceinterference from digital circuits.



Firmware and Software Development

The firmware refers to a block of program instructions for specific purposes. It isthe intermediary (interface) between the external commands and electronicdevice.

For programming was used the Quartus II software version 5.0 of Altera and theFPGA card EP2C8Q208C7.

The PIC bus is used as a means of communication between the computer and thecard.



Experimental results

The electrodes were placed, two in the bisep and one neutral of reference to thetendon of the subject.

The signal is taken in a period of 10 seconds, the approach on the oscilloscopewas 20ms.



Conclusions The digital filter stage is in the process of selection and implementation

The acquisition card is a specialized system in the measurement and display ofmyoelectric signals muscle contraction.

The card is designed for use in different applications and not limited only to theFPGA.



References

Data Acquisition Board for Registration of Myoelectric Signals

Authors: C. Martinez-Chiñas, S. Vergara, M. Vargas, F. Reyes, M. A. Vargas, A.Palomino, JM Rodriguez-Lelis

Electronic Science facultas

Robotics Group

Master of Science in Electronics

data acquisition board for registration of myoelectric signals

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