DIY EMG Myoware Muscle Sensor Kit

Do you want to activate a sensor by activating a muscle like clenching your jaw or a fist, or maybe raising an eyebrow? This MyoWare Muscle Sensor can make that happen. Makers have used these sensors to monitor teeth clenching and grinding while sleeping and Adafruit has an example project on their site that uses eyebrow muscle to send tweets.

The Myoware circuit has been very well designed and implemented and would be very useful if one wanted to use for muscle-flexing signals to control an external device or detect when someone has used a muscle…so say for instance you wanted to mirror your arm movement with a robotic arm then this is definitely the circuit for the job.

PROJECT 1 – Masseter Sensor Jaw Muscle Activated BioFeedback Sound

I’ll Hack and base my test off of this tutorial:

https://learn.adafruit.com/getting-started-with-myoware-muscle-sensor/about-emg

  • I recommend not having your laptop power cord plugged in. These power cords cause a ton of electrical noise and impacts the quality of the signal being measured.

Possible Advances PROJECT 2 – Lung Capacity Tester

The idea with this circuit is to sense muscle movement when a person breathes in and out and from that correlate lung function.

I’ll Hack and base my test off of this tutorial:

//github.com/AdvancerTechnologies/MyoWare_MuscleSensor/blob/master/Documents/AT-04-001.pdf

The board itself is very simple to setup and use and the instructions are clear and concise.

We’ll attach the red sensor wire and blue sensor wires to electrode pads and put them on my  sternum at either side of my heart.  I attached the black wire to an electrode pad and placed that on my stomach to provide a base reference.  I’m looking to measure my hearts sinus rhythm…and see how sensitive things are.  Here is the test code I’ve written:

(I had both the raw and sig output connected to my arduino analogue inputs A0 and A1)

//test code for Myoware EMG PCB

// variables for input pin from MyoWare PCB
int analogInputSig = A0;
int analogInputRaw =A1;

// variables to store the values
int valueSig = 0;
int valueRaw = 0;

void setup() {

pinMode(analogInputSig, INPUT);
pinMode(analogInputRaw, INPUT);

// begin sending over serial port
Serial.begin(9600);
}

void loop() {

// read the values from the sensor:
valueSig = analogRead(analogInputSig);
valueRaw = analogRead(analogInputRaw);

//print the reading received
Serial.print(valueSig);
Serial.print(“,”);
Serial.print(valueRaw);
Serial.println();

// wait for a bit to not overload the port
delay(10);
}

Here is the serial output graphed for your viewing pleasure:

Here is my wife’s heart rate…apparently I don’t have quite the effect on her I used to!

Here is what happens when the sensors are placed on the abdomen:

The Myoware picks up a good strong electrical signal when sensors are placed close to the heart…but when placed on the abdomen did not really pick up anything I could see correlating to breathing or diaphragm movement.  Either I had my sensors incorrectly placed or the circuit is not sensitive enough for this purpose.  Adjusting the gain potentiometer on the Myoware PCB did change the gain response but didn’t provide the response I was looking for – It was hoped that it would be possible to correlate diaphragm muscle movement with regular breathing.

I did notice that if I activated (flexed) my abdmoninal muscles electrical signals were definitely present and well detected…maybe I don’t use my diaphragm much when I breathe in and out?  I will have to investigate further.


Here is the schematic for the previous version of the device:

//cdn.sparkfun.com/datasheets/Sensors/Biometric/Muscle%20Sensor%20Platinum%20v3.3.pdf

The main integrated circuit is an AD8648 which is a quad operational amplifier.  I suspect the two smaller devices are programmable gain devices for each of the sensor inputs and the rest of the components are associated gain and filtering requirements.

Here is the datasheet for the AD8648

//www.analog.com/media/en/technical-documentation/data-sheets/AD8646_8647_8648.pdf

Here is the datasheet for the devices marked AD A 1V (An AD 628 I think….)

//www.analog.com/media/en/technical-documentation/data-sheets/AD628.pdf

The company (Advancer Technologies) that developed the Myoware PCBs also wrote this instructable which shows how a similar circuit could be developed:

//www.instructables.com/id/Muscle-EMG-Sensor-for-a-Microcontroller/

I have seen similar circuits in the past and believe this is certainly one route to achieving the measurement of electrical signals either from the heart (ECG – ElectroCardioGrapy) or muscle movement (EMG – ElectroMyoGraphy).

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