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Super Simple Muscle (EMG) Sensor

Measuring your muscles EMG signal usually requires complex electronics. This simple 3 component sensor makes monitoring EMG easy.

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Your muscles generate very small electrical signals that can be monitored with the correct hardware. Usually this involves complex electronics with levels of amplification, low/high pass filtering, notch filtering, complex signal processing, and machine learning.

This amazing technology is great fun to play with, but the complexity of the electronics usually limits makers from experimenting with it. This super simple muscle sensor only requires 3 components to work: An Instrumentation Amplifier (IA), a capacitor, and a diode. You will also need to attach 3 electrodes and power the IA with +5V and -5V.

Muscle (EMG) Sensor

What is EMG?

This section is quite technical. If you don't want to know what EMG is in depth then skip ahead to the next section. All you really need to know is EMG measures very small electrical signals that occur when our muscles move, such moving a finger, clenching a fist, or lifting your arm up.

Electromyography (EMG), which roughly translates to ’electrical muscle recording’, can be used to control a variety of devices. It was originally a medical procedure to analyze muscles and nerve health, but as it grew in popularity it expanded into areas of biomechanics, sports, rehabilitation, and was first used in a commercial prosthetic limb back in the 1980’s. Nowadays it is also used as a human computer/robot/machine interface.

The bulk of the EMG signal can be detected in the 0-500hz frequency band; it is quite a complex signal, and to understand its formation it is important to appreciate where the signal comes from. As you can imagine, it all originates from the brain. The brain initiates the control sequence and passes nerve impulses through the nervous system, similar to the flow of electrical current through a metal wire, the nerves then excite or activate Motor Units(MU), which then control the contraction of the muscle fibres. For very fine low force movements small MU are used, as more force is required, more and larger motor units are recruited to activate the muscle fibres. A single MU produces an Action Potential(AP), which is shown in the image below. Each action potential occurs due to a chemical exchange in the body of potassium (K+) and sodium (Na+) ions.

Muscles create many action potentials during a movement, like moving your arm or closing your hands. This creates a signal similar to the image below, which shows an increase in signal due to different fingers moving.


The Super Simple EMG Circuit

Early Version

Early Prototype Without The Diode

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SAFETY NOTICE

I highly recommend you only use batteries with this circuit. As connecting to mains power can be dangerous without proper isolation.

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The super simple EMG muscle sensor described here will help make it easier for people play with EMG. It uses a ultra simple 3 piece EMG circuit, consisting of an INA128 Instrumentation Amplifier (IA), a capacitor, and a rectifying diode to perform half wave signal rectification (which basically removes all the negative voltage signal so you don't damage your analogue pin on your microcontoller).

The instrumentation amplifier, amplifies differential inputs and subtracts the common mode signal (bascally takes two signals and subtracts what is common in both), which causes noise presented on both channels to be partially suppressed. The super simple EMG circuit uses a capacitors reactive impedance attached to the IA gain pins, which sets a variable frequency dependant gain, thereby only amplifying higher frequencies, and thus creating a similar affect to a high pass filter. The capacitors impedance (which is inversely proportional to the IA amplification) is calculated from below equation

Impedance = 1/(2 ∗ PI ∗ Frequncy ∗ Capactance)

The EMG sensor requires 3 electrodes, a negative, positive and ground, with the positive and negative placed adjacent to each other, and separated by a 1cm gap. These electrodes are placed over the muscle you want to monitor, and the ground electrode placed over a bony area with minimal to no muscle activation. The exact locations of the electrodes can be determined by trial and error. The electrodes used were 30mm diameter, reusable, self-adhesive, and long-term electrodes often found in TENS, EMG and Neuromuscular stimulation applications.

The only other additions you will need to see...

Read more »

  • 1 × TS4148 RY Diode
  • 1 × INA128 Amplifier and Linear ICs / Instrumentation Amplifiers
  • 1 × 47uF Capacitor

  • Design Files

    JamesCannan12/18/2015 at 15:10 0 comments

    The super simple muscle sensor Eagle design files have now been uploaded to github.

    https://github.com/Cannonball2134/EMG-Muscle-Sensor

  • SAFETY NOTICE

    JamesCannan12/18/2015 at 11:56 0 comments

    SAFETY NOTICE - Only use batteries.

    This circuit is designed to be super simple to make it easy for people to experiment with EMG. Due to its simplicity the circuit does not include proper isolation, therefore I highly recommend you only use batteries to power your project. As connecting to mains power can be dangerous without proper isolation.

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Discussions

mitchellc_91 wrote 09/04/2017 at 04:18 point

I have built this project but when I connect it to the Arduino and then run the serial plotter, it is just a messy sine wave and doesn't always trigger when I move. 

I am using a TC1044S to give a negative voltage, +6.23v, -5.67v. the TC1044S is using 2 10uF capacitors. 

The INA128 I am using 47uF ceramic capacitor. 

I have been looking at the datasheet and don't know if I should be using a gain resistor instead of the 47uF capacitor. 

thanks

Mitchell 

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Ivan bk wrote 06/26/2017 at 22:58 point

what ina128 is he using, when i went to search for the part there are many variants of the ina128

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Al wrote 04/01/2017 at 16:26 point

Hi James,

Great job!! I'm looking into building a wearable epilepsy monitoring system. Your EMG looks very interesting as many clonic-tonic seizures are accompanied by strong muscular contraction. I want to test EMG is a suitable monitoring system. I'm planning to hook it up with an Espruino WiFi and see how well it does in monitoring seizures.
I have been looking for the components you mentioned but no luck. Looks like you are from the UK as well. Can I ask where did you source the components or can you suggest alternatives?
Thanks!!

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Teaanya wrote 03/28/2017 at 20:41 point

Hi James, can you elaborate a little on how you found the impedance formula? I'm a little confused on that part. 

Thanks! 

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Beyaz wrote 03/28/2017 at 16:54 point

Hi sir, im curious if you have aruino code for this project can you share with us?Cuz something is missing in mind and I couldn't find why it is not working.

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Ryan Garibay wrote 02/27/2017 at 00:44 point

Hi, i'm trying to create your circuit in order to control a prosthetic arm. however i am unable to find the parts on short notice. do you happen to know a store that might sell them in the Los angeles area?

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kartikrana28 wrote 01/27/2017 at 20:43 point

i have done everything as stated above ,  but i couldn't get the smd parts so i didn't got a 47uf ceramic capacitor, neither the diode i used a 47uf electrolytic capacitor instead and also tried a 47pf capacitor ... i used a normal rectifier diode instead and nothing worked ..  can you suggest me any solution or substitution of smd parts ... also i wanted to ask that the reference pin is connected to ground ? because there is no other ground pin only +/- volt pins

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davidmoshal wrote 01/04/2017 at 00:58 point

Hi, just wondering why you chose the INA128, over, say INA132 or 133?

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JamesCannan wrote 01/04/2017 at 21:59 point

It was from another project i found while doing background research, so i thought i would keep using it. It also seemed to have a nice CMRR that i was looking for. The INA132/133 might work, but they are not parts i have tried, therefore additional circuitry may be required.  

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nadzim wrote 12/27/2016 at 07:46 point

hi i would like to ask

where do the ground of the ic


and can i have the circuit diagram

i cant understand the circuit

what kind of capacitor that u used

does it have any polarity on the capacitor

  Are you sure? yes | no

JamesCannan wrote 01/04/2017 at 22:02 point

If you use a battery, the negative terminal would be the GND.

There is a circuit diagram in the description. I am sorry, i don't have any other circuit diagram. 

I use a standard ceramic capacitor with no polarity.   

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mmmsss123456 wrote 04/07/2016 at 15:00 point

Great job, thanks. Unforunatly I cant find INA128 in our city, what are other equvalent ICs for INA128 ?

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JamesCannan wrote 04/13/2016 at 17:02 point

You could give the ina129 a go. I haven't tried it on anything else.

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yhakanusta wrote 01/09/2016 at 12:39 point

what is the best method to make emg caples mr and i have electrodes with conductive gel ? thank you

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JamesCannan wrote 01/09/2016 at 13:03 point

I tend to use alagator cables twisted together, but a better option would be shieled cables. I tend to use these type of electroes: http://www.amazon.co.uk/TensPro-Round-Circle-Electrodes-connector/dp/B00KFLIHN6

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mohammad wrote 01/09/2016 at 01:37 point

great job , can we connect the output to the analog pin of the arduino, i just tried to get data but i couldn't i used two 9 volt batteries and connected the negative of the first and the positive of the second battery and the output to the analog pin of the arduino and i used ina129 but still have no good data , any help i will be grateful , thanks in advance

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JamesCannan wrote 01/09/2016 at 11:12 point

The output can be connected to the anolog pin of an arduino, i have done it before. A lot of EMG devices update around 1000hz, you might not be able to get the same with an arduino, but it is still noticeable when you are contracting and not contracting your muscles. I recommend testing on the bicep muscles, as they have quite a strong signal. 

Do you have an osscilscope you can test it on? 

What sort of electrodes are you using? Dry electrodes tend to be very noisy.

I found that twisting the 3 Electrode cables together helps. Or you could try shielded cables.

Make sure you are using a non polorized capacitor on the gain pins.

  Are you sure? yes | no

mohammad wrote 01/09/2016 at 12:25 point

thank you Mr for quick reply actually i have oscilloscope and also i used normal ECG EMG Electrodes connected to mini jumper caples (another good choice instead jumper caples ?? ) but i used  two positive and negative terminals from two 9 volt   batteries  , do you think the problem  came from here ?

  Are you sure? yes | no

JamesCannan wrote 01/09/2016 at 13:01 point

As long as the INA129 pin 4 reads -9V, and pin 7 reads +9V, it should be ok. I actually use the LTC1046 voltage inverter so that i only need one battery. I also use alligator cables for connecting the INA to the electrodes. Do make sure you have good quality electrodes that stick very well, as the contact is important.

If you want to see more of the EMG signal on the oscilloscope you could remove the diode ( it is only there to help protect a microcontoller from negative voltage). Also if there is a problem with the diode then it would be a good idea to test your setup without it. 

What do you have the ground electrode attached to? In your circuit It should be a common ground connected to a bony part on your body.

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Jose Pedro R. A. Ribeiro wrote 12/18/2015 at 19:30 point

Eu estou tentando comprar ou alugar uma estação de satélite através de transmissão, que querem participar, deixe-me saber é um grande negócio. (Colocar novos equipamentos e ganhar milhões de dólares) dentro da lei.

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JamesCannan wrote 12/18/2015 at 11:44 point

Very interesting. I was looking into trying to determine subcutaneous skin fat using IR LED's to help compensate EMG signals for varying body types. Similar to this https://www.osapublishing.org/view_article.cfm?gotourl=https://www.osapublishing.org/DirectPDFAccess/10A1981B-B5B6-D203-12F5DAB45B8D9C71_194896/josk-13-3-304.pdf?da=1&id=194896&seq=0&mobile=no&org= but unfortunately never got around to actually building a device. I would love to see this technology developed more and see what applications it leads to. Thanks for sending me the link.

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Bruce Land wrote 12/17/2015 at 12:29 point

Safety requires that any circuit you hook to yourself be ground isolated.

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JamesCannan wrote 12/17/2015 at 12:52 point

You are completely right. I have yet to add a safety notice to the project, and recommend you only use this circuit with batteries. As connecting to mains power can be dangerous without proper isolation.

  Are you sure? yes | no

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