myemg monitor

8/11/2019 MyEMG Monitor

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myEMG MonitorIntegrated platform for the measurement of biopotential signals in skeletal

muscle. This technique of electromyography (EMG) is implemented in a circuit board interfaced with the NI myDAQ.

Figure 1 myEMG Monitor

The stimulus for developing this demonstration was to prove that low amplitude EMG signalscould be acquired and displayed, using the NI myDAQ and basic circuit components. This

practical example aims to highlight key concepts related to biopotential theory, basicinstrumentation and a comparison of healthy and unhealthy wave patterns.


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Introduction This document will provide instructions about the development of the myEMG Monitor usingthe NI myDAQ platform. It shows the hardware developed, the LabVIEW application createdand key code.

Project OverviewThe project can be summarised by the following flow chart diagram.

The analogue circuitry is built upon the breadboard and then interfaces with the myDAQ. Thesignals are then transferred through the myDAQ to the laptop/desktop via USB.

Components

Electrodes

In order to pick up the low amplitude surface EMG (sEMG) signals, an appropriate skin-electrode interface is required. This relates to the electrode gel that is required to ensure theimpedance of the skin does not significantly affect the readings obtained. Appropriateelectrodes are shown below. The electrodes chosen were snap connector compatible.

Figure 2 Noraxon disposable self-adhesive Ag-AgCL electrodes

EMG signalacquired throughsurface electrodes

AnalogueCircuitry

myDAQ

Laptop/Desktop


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Electrode Cables

Good quality electrode cables are required to transmit the low voltage potentials from theskin-electrode interface to the analogue circuitry. In this case, snap connectors were used toenable connectivity with the electrodes purchased. These come with male DIN connectors.For integration with the breadboard, these need to be cut. The wires should then be tinned and

placed into the appropriate positions.

Figure 3 Electrode Cables

Analogue Circuitry

The expected values of sEMG signals are in the uV range. For this reason, we need toamplify the signals by with a large gain. An overall gain of 1000 (a culmination of all stagesof the circuit) is required to provide sufficient amplitude for processing and display inLabVIEW.

Figure 4 Breadboard circuit design


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In order to provide a large gain stage upon first receiving the sEMG signal, this circuit uses adifferential amplifier (data sheet can be found here ). This provides a gain of 110. The circuitdiagram is shown below:

Figure 5 Differential Amplifier

Additional gain stages, rectification and filtering use the following IC OpAmp TL072 DualLow-Noise JFET-Input General Purpose Operation Amplifier .

The circuit uses two 9V batteries in series (one as the positive power source and the other asthe negative power source) to power the circuit. This is then reduced to 5V in LabVIEW.

The design of the circuit was copied from an instructables tutorial created by AdvancerTechnologies . This tutorial can be found here . NOTE: This design has not be certified oraccredited by any governing bodies. Users build at their own risk and with no guarantee ofcorrect results. Note that the design does not incorporate the Arduino microcontroller.

LabVIEW Code

sEMG DAQ

To take sEMG readings from the electrodes in LabVIEW, a simple express VI can be used.This express VI can be found in the Biomedical Toolkit.

Figure 6 sEMG Acquisition in LabVIEW
http://www.ti.com/product/tl072http://www.ti.com/product/tl072http://www.ti.com/product/tl072http://www.ti.com/product/tl072http://www.ti.com/product/tl072http://www.ti.com/product/tl072http://www.ti.com/product/tl072http://www.advancertechnologies.com/http://www.advancertechnologies.com/http://www.advancertechnologies.com/http://www.advancertechnologies.com/http://www.instructables.com/id/Muscle-EMG-Sensor-for-a-Microcontroller/http://www.instructables.com/id/Muscle-EMG-Sensor-for-a-Microcontroller/http://www.instructables.com/id/Muscle-EMG-Sensor-for-a-Microcontroller/http://www.instructables.com/id/Muscle-EMG-Sensor-for-a-Microcontroller/http://www.advancertechnologies.com/http://www.advancertechnologies.com/http://www.ti.com/product/tl072http://www.ti.com/product/tl072http://www.ti.com/product/tl072


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This targets the channel AI0 on the myDAQ. Lower level functions are used to produce anRMS value and a frequency spectrogram. This architecture is based on an example found onthe NI Community here . It is based on a shipped example that comes with this toolkit. Thesample rate should vary between 500 - 2000 Hz for the most reliable readings. All other

parameters should remain default.Tab control code tutorial

In order to allow easy navigation between the different pages of the tab control, the followingarchitecture has been used. It is based on an example that can be found here . It uses themaster/slave architecture with a couple of modifications. The top loop deals with commandsreceived from navigation buttons and from the pages of the tab control. The bottom loopdeals with specific processing requirements on each page. This includes displaying imagesand graph indicators.

Figure 7 Master/slave architecture for tab control
https://decibel.ni.com/content/docs/DOC-23510https://decibel.ni.com/content/docs/DOC-23510https://decibel.ni.com/content/docs/DOC-23510https://decibel.ni.com/content/docs/DOC-25835https://decibel.ni.com/content/docs/DOC-25835https://decibel.ni.com/content/docs/DOC-25835https://decibel.ni.com/content/docs/DOC-25835https://decibel.ni.com/content/docs/DOC-23510


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myEMG Monitor Application

Now that we have covered the main aspects that form the project, it is important to look at theapplication itself. The myEMG Monitor application should be used as an interactive tutorialthat reinforces understanding of biopotential theory, basic instrumentation and howLabVIEW can be used for this experiment.

The front panel of the application is shown below.

Figure 8 Front panel of myEMG Monitor

Different pages ofthe tutorial

NavigationButtons

NavigationButtons

NavigationButtons

ApplicationButtons

myemg monitor

Documents