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Measuring muscle activation via electric potential, referred to as electromyography (EMG) , has traditionally been used for medical research and diagnosis of neuromuscular disorders. However, with the advent of ever shrinking yet more powerful microcontrollers and integrated circuits, EMG circuits and sensors have found their way into prosthetics, robotics and other control systems. Yet, EMG systems remain expensive and mostly outside the grasp of modern hobbyist.

This instructable will teach you how to make your own muscle sensor / EMG circuit to incorporate into your next project. Use it to control video games, robot arms, exoskeletons, etc.

Click on the video below for a demonstrations on how to hook up and use your EMG circuit board!

You can now also purchase  EMG sensors, kits, cables and electrodes at www.AdvancerTechnologies.com!
Muscle Sensor Kit (now also on SparkFun)
Muscle Sensor Electrodes

Note: This sensor is not intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation treatment, or prevention of disease, in a man or other animals.

About Advancer Technologies 
Advancer Technologies is a company devoted to developing innovative game-changing biomedical and biomechanical technologies and applied sciences. Additionally, Advancer Technologies promotes all forms of interest and learning into biomedical technologies. To help culture and educate future great minds and concepts in the field, they frequently post informative instructions on some of their technologies. For more information, please visit www.AdvancerTechnologies.com .

Step 1: Materials

Click on the links to go to where you can buy items/order free samples.

Circuit Chips

3x TL072 IC Chip  - Free Samples
1x INA106 IC Chip  - Free Samples

Cables and Electrodes
1x EMG Cables   (set of 3)... Note: you could optionally connect the alligator clips directly to the electrodes.
3x EMG Electrodes  

Power
2x 9V Battery
2x 9V battery clips  

Capacitors
• 2x 1.0 uF Tant 
• 1x 0.01 uF Ceramic Disc  
• 1x 1.0 uF Ceramic Disc   

Resistors
• 3x 150 kOhm 1%  
• 2x 1 MOhm 1% 
• 2x 80.6 kOhm 1%  
• 6x 10 kOhm 1%
• 1x 100 kOhm Trimmer 
• 1x 1 kOhm 1%

Misc
• 2x 1N4148 Diode  
Jumper wires
• 3x Alligator clip cables

Optional
• 1x Oscilloscope
• 1x Multimeter

Step 2: POWER SUPPLY

To start things off, you’ll need both a positive and negative voltage power supply. We will make these using two 9V batteries.

Now, everyone knows what a positive voltage power supply is, (e.g. common battery) but how do you go about making a negative voltage power supply?

Common electrical circuit rule of thumb is when you connect two batteries in series (eg positive terminal of battery 1 connected to the negative terminal of battery 2) then measure the voltage from the negative terminal of battery 1 and the positive terminal of battery 2, the measured voltage is equal to the summation of the voltages of battery 1 and battery 2.

For this circuit we want a +9V and a -9V power supplies. If we connect our two 9V batteries in series, we will get a power supply of +18V. So how do we get the -9V from these two?

It might help to think about what voltage actually means… voltage is an electrical potential difference. The keyword here is difference. Voltages are only meaningful in terms of the reference point (or more commonly referred to as ground). A voltage is the electrical potential between this reference point and the point you are measuring. Do you see the answer yet?

We do indeed get a +18V voltage reading if we use battery 1’s negative terminal as the reference point… but what if we choose the connection between battery 1’s positive terminal and battery 2’s negative terminal? If we use this point as our reference or ground, then battery 2’s positive terminals voltage will be +9V and battery 1’s negative terminal will be -9V!

Using your breadboard, 9V batteries and battery clips, connect the battery clip wires as shown. However, for the time being, disconnect the positive terminal of battery 2 and the negative terminal of battery 1. It is good practice to always disconnect your power while you assemble a circuit. At the end of the assembly we will reconnect these wires to power the circuit on. (You could also add switches to do this)


 

Step 3: SIGNAL ACQUISITION

Next, we will work on the signal acquisition phase of your EMG circuit which we will use to measure your body’s nervous system’s electrical impulses used to activate muscle fibers.

First, get out your INA106 IC chip (chip A) and insert it into your breadboard as illustrated above. The INA106 is a difference amplifier which will measure and amplify (G=110) the very small voltage differences between the two electrodes you place on your muscle.

Next, grab two 1 M ohm resistors, bend them and then plug them in to your breadboard like the two examples shown. One should connect pins 5 and 6 and the other should bridge pin 1 to your ground rail of your board.

Don’t worry about the other pins of the INA106 for now; we’ll come back to those later.

Step 4: SIGNAL CONDITIONING - Amplification

In this phase, we’re going to take those very small signals measured in the SIGNAL ACQUISITION phase and amplify them.

Let’s start first with two series of amplification; the first will be inverting amplifier with a gain of -15. An inverting amplifier does exactly what it sounds like. It amplifies your signal but also inverts it. You can find more info about inverting amplifiers here

We are going to first build an inverting amplifier with a gain of -15. To do this, we’ll need one of the TL072 chips (chip B), one 150 kOhm resistor and a 10 kOhm resistor. 

Place chip B as the picture indicates. Now use a jumper wire and connect pin 6 of chip A two rows past pin 8 of chip A. Grab one of the 10 kOhm resistors and plug one pin into this row as well. Connect the other pin to pin 6 of chip B. Bend a 150 kOhm resistor and connect one pin to chip B’s pin 6 and the other to pin 7. You can calculate the gain by G=-R2/R1 or in this case G=-150 kOhm / 10 kOhm. (See image 1)

Next, we are going to add a capacitor to AC couple the signal. AC coupling is useful in removing DC error offset in a signal. Read more about AC and DC coupling here

Continuing on, we are going to add an active high pass filter to get rid of any DC offset and low frequency noise. To do this you will need two 150 kOhm resistors and a 0.01uF capacitor. Use a jumper wire and the 0.01 uF capacitor to bridge the center gab of your breadboard as shown. (One end of the jumper wire should be connected to pin 7 of chip B). The 150 kOhm resistor will connect the capacitor you just placed to pin 2 of chip B. Now, bend the 150 kOhm resistor and push it into connect pins 1 & 2. (See image 2)

Also, go ahead and connect chip B’s pin 4 to your -9V rail, pin 8 to your +9V rail, and pins 3 & 5 to your GND rail.

 

Step 5: SIGNAL CONDITIONING - Rectification

In this phase, we will be rectifying the signal using an active full-wave rectifier . Our rectifier will take the negative portion of our signal and turn it positive so the entire signal falls within the positive voltage region. We will use this coupled with a low pass filter to turn our AC signal in to a DC voltage; readying the signal to be passed to a microcontroller.

You will need five of the 10 kOhm resistors, both 1N4148 diodes, and a second TL072 chip. Warning… this will be the most difficult phase to assemble! Pay close attention to the pictures!

First, plug in a TL072 chip (chip C) and connect -9V rail to pin 4, the +9V rail to pin 8 and GND to pin 3, as shown in the first image.

Next, place a 10 kOhm resistor (let’s call it resistor A) connecting pin 1 of the TL072 chip from the amplification phase and plug the other end into the row next to the 0.01uF capacitor’s row. Use a jumper wire to connect this row to pin 2 of the second TL072 chip. The next 10 kOhm resistor we’ll call resistor B. Resistor B’s first pin should be plugged into the row where resistor A’s second pin is plugged in and resistor B’s other pin should be plugged into the row two down. Another 10 kOhm resistor’s (resistor C) first pin should be plugged into the row where resistor A’s second pin terminated (same as resistor B) but the other pin should be plugged into the next immediate row over. (See image #2)

Now get out the two 1N4148 diodes. Diodes are polarized so be sure to pay attention what direction you plug them in! We’ll call these diodes A and B. Plug diode A’s positive end (end with black strip) into pin 1 of chip C and plug the negative end into the row of resistor C’s second pin. Get diode B and plug the NEGATIVE end into pin 1 of chip c and plug the POSITIVE end into the row of resistor B’s second pin. (See image #3)

Next, use two jumper wires to bridge the center gap for resistor C and B’s rows. Use another jumper wire to connect the jumper wire’s row connected to resistor B’s row to pin 5 of chip C. Use another 10 kOhm resistor to connect the jumper wire’s row connected to resistor C’s row to pin 6 of chip C. Finally, use the last 10 kOhm resistor to connect chip C’s pins 6 and 7. (See image #4).

Phew… that is for the rectifying phase! Next is the filter phase.
 

Step 6: SIGNAL CONDITIONING - Smoothing + Amplification

In this last phase of circuit assembly, we will be using an active low-pass filter to filter out the humps of our signal to produce a smooth signal for our microcontroller.

You will need the last TL072 chip (chip D), the two 80.8 kOhm resistors, the 100 kOhm trimmer, the 1 kOhm resistor and the 1.0 uF ceramic disc capacitor.

First, plug in chip D and connect +9V to pin 8, -9V to pin 4, and GND to pins 3 & 5. (image #1).

Now, grab one of the 80.6 kOhm resistors and connect one end to chip C’s pin 7. Connect the other end to chip D’s pin 6. Next grab the other 80.6 kOhm resistor use it to connect chip D’s pin 6 and 7. Do the same thing for the 1.0 uF capacitor. (image #2)

That’s the end of the filter circuit. However, since this is an active filter, there is a side effect of inverting the signal. We will need to invert the signal one more time (and have the ability to amplify it more if desired) using another inverting amplifier circuit with a trimmer configured as a variable resistor.

Use a jumper wire, connected to chip D’s pin 7, and the 1 kOhm resistor to bridge the board’s center gap. Use another jumper wire and connect the 1 kOhm resistor to chip D’s pin 2. Next, place the trimmer one row over with the pins laid out and a jumper wire connecting two of the pins as pictured. Finally, place the last two jumper wires as indicated. (image #3)

By using a screw driver and turning the trimmer, you will be able to adjust the gain of your signal to account for different signal strengths from different muscle groups. Start out with it set pretty low and go up from there (~20 kOhms).

Step 7: Circuit Review

(Optional) If you have an oscilloscope and a wave generator handy, now would be a good time to step through the circuit and test each phase.

If you do not have an oscilloscope handy, go back and review your circuit connections step by step to make sure you have place each component correctly. Pay close attention to the power pins and connections of your chips. If you have these incorrect, you could burn out your chips!

Step 8: Electrode Cables

Next, you'll need to make some changes to the EMG electrode cables since I have been unable to find a vendor who sells the cable's style DIN connector's female compliment.  (if any one has a suggestion please let me know!)

Grab a pair of scissors, wire cutters, wire strippers, pocket knife, etc.... basically anything sharp and strip about a 1/4" of the end of the DIN plug on all three cables (the plug end not the snap end).

Next, clip an alligator cable to each of the wires. We will use these to connect the electrode cables to our breadboard with some jumper wire. You could do as I have done and strip the wire and then solder on terminal pins but it is not necessary and the alligator clips will do fine.

Step 9: Surface Electrodes

For the electrode placement, you will need three surface electrodes.

After determining which muscle group you want to target (for example I will be using my right bicep) and cleaning the skin thoroughly, place one electrode on your skin above the middle of the length of the desired muscle. Let's call this the mid muscle electrode.

Next, place a second electrode at one end of the muscle. We'll call this the end muscle electrode.

Last, place the third electrode on a bony part of your body nearby the muscle group. We'll call this the reference electrode. For example, for the biceps, I am placing the reference electrode on the bony end of my forearm close to my elbow.

Using the snap connections of the electrode cables, snap each cable to each electrode. Make a mental note of which color cable is attached to which electrode.

Step 10: Connecting Electrode Cables

Now you are ready to connect your electrode cables to your circuit. Remember those pins on chip A that we put aside till later?

Connect the reference electrode to the GND rail of your circuit.
Connect the mid muscle electrode to chip A's pin 2
Connect the end electrode to chip A's pin 3

Lastly, we need to add some circuit protection via capacitors. Tanthium capacitors are polarized like the diodes we used earlier. These are easier to tell which is the positive pin and negative pin since one is always marked with a + sign indicating positive pin. Connect one 1.0 uF tant. capacitor between the +9V rail and GND rail, with the positive end connected to the +9V rail. Connect the other 1.0 uF capacitor to the -9V and GND rails, with the positive end connected to the GND rail.

Now you'll ready to power on your circuit!

Step 11: Connecting to a Microcontroller

Before connect your circuit to your microcontroller, you should power on your circuit (by connecting the battery wire's we disconnected earlier) and check the output voltage with a multimeter to make sure it is within your microcontroller's analog input pin's tolerances. To do this, connect the negative multimeter probe to your GND rail and connect the positive probe to pin 1 of chip D. Make sure the voltage measured is less than the max voltage of your input pin!

If you've done that check and everything thing looks fine, use jumper wires to connect pin 1 of chip D to an analog input pin of your microcontroller and your GND rail to the GND pin of your microcontroller.

Congratulations you're done!

Step 12: Arduino Demo

For this demo, we used an Arduino Duemilanove microcontroller hooked up to a PC running Processing visualization software. 

Remember to visit us at www.AdvancerTechnologies.com for kits and fully assembled sensors!

Step 13: EMG Circuit Schematic

Click the i box in the top left to see a larger version... or go to our website and click on the EMG schematic image .
<p>How much do the meterials fot this cost in total? Is it cheaper than the pre-build myoware muscle sensors?</p>
Well it's not really apples to apples. The MyoWare sensor uses much more advanced circuitry, has built in protection against burning out the ICs, can be powered directly by an Arduino, and the embedded snaps eliminate cables. Electrode cables alone for this tutorial will cost you $5-15 depending on where you order it from. The electrical components cost about $20 from Digikey. However, it would cost you way more to build your own MyoWare than it is to purchase it. That's one reason we started selling the fully assembled versions instead of the kits with just the components packaged together... we were able to get the price of the fully assembled sensors well below the cost of the the component kits.&nbsp;<br> <br> So my two cents is... <ul> <li> <strong>If you want to explore how an EMG circuit works and intend on tweaking/playing around with the internal circuitry</strong>, then you would probably want to build your own using this tutorial. <li> <strong>If you just want a reliable sensor that requires little to no setup and you are more interested in its applications than the circuitry itself,</strong> you're much better off purchasing the MyoWare. </ul>
<p>what programs and code for arduino you used for the data acquisition and the visual representation of the emg signals?, thanks for your time and for your project (:</p>
Hi The sample code can be found on our website: http://www.advancertechnologies.com/p/muscle-sensor-v3.html
<p>Hello</p><p>It's amazing what you done </p><p>It's open the way to alot of projects to be established</p><p>Thanks alot for you and your team</p><p>By the way</p><p>Please, I want the circuit if I used the ad620 instead of ina106</p><p>Cause I haven't any about electronics and I can't find ina106 in my country</p><p>Thanks alot again .</p>
<p>Hi, I would encourage you to try to figure this out on your own first. It shouldn't be too difficult to puzzle out if you read through the AD620 datasheet.</p>
<p>kindly suggest alternate of <a href="http://focus.ti.com/docs/prod/folders/print/ina106.html" rel="nofollow">INA106 IC Chip.???. can i used op amp 741? will it work<br></a></p>
<p>is micro controller is necessary? </p>
The output signal is an analog signal so you need some method to convert it to a digital signal unless you don't plan on interfacing with anything digital (computer, microcontroller, etc). A microcontroller, ADC, DAQ are just a few ways to convert an analog signal to a digital signal.
I haven't study microcontroller, I just want to show my emg signal on oscilloscope directly through circuit... should this circuit works for this
Yes, an oscilloscope will work with this circuit.
<p>hey, nice work. I just wanna know that I am using LM358 instead of TL072 and output i am getting is any random number even if I don't do anything. So i should use TL072 only for this or the problem is something else.</p>
<p>Most general op amps can be used instead of the TL072. Your issues probably lie elsewhere.</p>
Yup I got that as I tried it with TL072 but still I am getting any random number as my output! Thank you for the reply :)
<p>Sir,</p><p>Is the circuit going to work if I change the cut off frequencies of the HPF and the LPF to 20Hz and 150Hz respectively? I need the circuit to pick up signals only for muscle activity in fingers, which the doctors say, lies in the above specified range.</p>
The circuit works for fingers as is. If you want to add more filtering, I would recommend adding it prior to the rectification phase. I would not recommend modifying the LPF frequency as it is acting as an integration circuit not a LPF.
<p>Hi <a href="http://www.instructables.com/member/Gundanium" rel="nofollow">Gundanium</a> , the connection of pins are different ( not same ) in bread board and circuit diagram , which one is true ? </p><p>can i use INA128 in place of INA106 ? </p>
Which pins are you referring to?
please tell me , which one is correct ( Step 11: Connecting to a Microcontroller ) OR ( Step 13: EMG Circuit Schematic )<br><br>can i connect my circuit according to Step 11 ?
<p>I don't understand your question. Step 13 and 11 are the same just represented in a different format.</p>
<p> hi, can you please mail layout of the board (with Proteus), to fadwa.lasswed@gmail.com</p>
<p>Sorry but we don't publish our PCB layouts.</p>
<p>Can you please mail PCB layout of the board, to rovardeakr@gmail.com.</p><p>What is special about EMG electrodes and cables?I find them very costly.</p><p>Is there any cheaper way to replace these electrodes and cables.</p><p>Where can I get AD8226 IC from? </p><p>Thanks alot. Excellent Tutorial. </p>
<p>Sorry but we don't publish our PCB layouts.</p>
<p>I will be needing more than 3 electrodes in my system. So naturally I will be needing more than 1 INA106. But it is exceeding my budget. So i wanted to know if there's a cheaper alternative to the INA106 IC?</p>
<p>AD8236 is not only cheaper but better for EMG applications.</p>
<p>Instead of using wires, is it possible to make this system wireless, especially the microcontroller? And how do i do it?</p>
You can't eliminate the wires going from the electrodes to the circuit but it should be possible to eliminate wires going from the circuit to the microcontroller. In simplest terms, you'll need to send the output through a ADC converter and then a Bluetooth or Wifi transmitter.
<p>Ok! Can you tell me how exactly to make the connection from the circuit to the controller wireless? Could you please provide me the instructions to do it?</p>
<p>You could use a <a href="https://www.adafruit.com/products/2471">Simblee</a> or something <a href="https://www.adafruit.com/products/2471">similar</a>. </p>
<p>can we have PCB schematic i would lie to print it also can i use ina 129 instead ina 106.</p><p>thanks </p>
<p>The schematic is on Step 13. INA129 looks like it would be suitable but since I have not used it, I cannot confirm this.</p>
<p>Hi excuse me, i only have the Ad620 instead of the INA i know i can change the resistors and make the G to the same as you are using. my question is can i use the tl074 intead the three of your tl072? thank you for you advise :)</p>
<p>Yes you can.</p>
<p>What type of electrodes work for this? Are there any good reusable ones that can work with it? Thanks</p>
<p>also are there any reusable electrodes that do not require moisture?</p>
<p>We recommend disposable adhesive dry gel electrodes for a couple reasons. </p><p>1) Adhesiveness helps eliminate electrode movement artifacts from your output signal. If you went with a dry contact reusable electrode, you have to pay particular attention to how well you secure it to the skin otherwise every time you move, you'll see large magnitude bumps in your output signal that aren't attributed to muscle activation.</p><p>2) Even with dry contact electrodes, it is recommended to do some amount of skin prep. Dry skin has a significantly high impedance/resistance than moist/wet skin which allows you to measure signals more cleanly with less attenuation.</p><p>3) For dry contact electrodes with no skin prep (aka moisture), you'll need an instrumentation amplifier with an input impedance over 10 GOhms. The <a href="http://www.advancertechnologies.com/p/myoware.html">INA106</a> used here only has an input impedance of 110 kOhms. We use an <a href="http://www.advancertechnologies.com/p/myoware.html">AD8236</a> for our <a href="http://www.advancertechnologies.com/p/myoware.html">MyoWare</a> sensor which has an impedance of 110 GOhm and should be suitable for dry contact no prep applications. Our <a href="http://www.advancertechnologies.com/p/myoware.html">Muscle Sensor v3</a> used an <a href="http://www.advancertechnologies.com/p/myoware.html">AD8226</a> which has an input impedance of 0.4 GOhm which like the INA106 isn't really suitable for those applications.</p>
<p>Hi, </p><p>when the cutoff frequency for high pass and low pass filter was calculated i got values of 106.1 and 1.97 respectively , i didnt understand as to why put a high pass filter first of cutoff frequency 106.1 which allows frequency above 106Hz and then employ a low pass filter with cut of frequency 1.97 HZ which allows frequency only below that!!</p><p>what is the whole point if u filter out it with high pass filter initially?</p><p>and also isn't the range for EMG signal 20-150Hz, please explain </p>
<p>Hi SushmaV!</p><p>This is a very old schematic (published in 2011). For a more recent and advanced one, I would suggest looking at the schematic used for our <a href="https://github.com/AdvancerTechnologies/MuscleSensorV3/blob/master/Documents/Muscle%20Sensor%20v3%20Schematic.pdf">Muscle Sensor v3.</a> Our new MyoWare sensor is even more advanced but we haven't published the schematic publicly yet (patent pending). </p><p>We set the HPF in this design to 106 because we found that was a good frequency for the INA106 for two reasons, 1) it removed the DC offset that can occur due to electrode polarization, and 2) it helped remove any latent 60Hz power line &quot;hum&quot; noise that the INA106 failed to remove. However, this does cut out a good deal of the EMG frequency range but since the rectification and integration phases that come next will completely remove frequency information this isn't as much as a drawback as it might seem on paper. We no longer use this in our MyoWare sensor.</p><p>As for the LPF, it actually isn't a LPF because the signal has been fully rectified by this point. It is actually an integration circuit with a cut off frequency around 2Hz. This phase smooths the rectified signal and produced the EMG &quot;envelope&quot;. We set it to 2Hz because we found this produced the best results w.r.t. signal smoothing and in most applications you won't get muscle activation faster than that (2Hz = 2 full muscle flex/relax cycles per second)</p>
<p>Hi. Can I use MAX4199 instead of INA106? and what adjustments should I make?</p><p>Also with TL072 can I use MAX44263. I can only use MAX products.</p><p>Please. Thanks</p>
Hi <br>I didn't find INA106 So cqn I use AD620 ?
Yes but make sure you set the gain to be equivalent to this circuit.
<p>Many thanks :)</p>
<p>Can we use homemade electrodes from nickel buttons to provide the input for sensor</p>
<p>Hi I'm using your circuit as part of a control mechanism for an exoskeleton. I have made the circuit however I'm getting errors when running the codes for processing and no readings on the graph specifically with the Line 60 in the bar graph processing code: println(Serial.list));. The error is &quot;Type strin[] of the last argument to method println(object...) doesn't exactly match the vararge parameter type. Cast to object[] to confirm the non vararge invocations or pass individual arguments of type object for vararge invocation&quot;</p>
<p>Can we use this circuit for ECG purpose of brain and heart ???</p><p>Please reply me fast</p><p>Thanks</p>
No
<p>I recently made this circuit on a breadboard. But the circuit does not show any output on the Arduino serial plotter when the given Arduino code is used. Can someone please help me out with this? I need to know what could have gone wrong?</p>
<p>Can we connect more than 3 EMG electrodes in this same setup?</p>

About This Instructable

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Bio: Brian Kaminski Owner - Advancer Technologies Brian graduated from North Carolina State University with a BS in Biomedical Engineering with a concentration in Biomechanics in May ... More »
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