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).


<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>Hi Gundanium,<br></p><p>I am in the middle of making this circuit. I have<br> just made Stage 1 (Differential amplification using INA106) and Stage 2<br> (15x amplification WITHOUT AC coupling). I tried analyzing the output <br>of these stages using oscilloscope.</p><p>I am seeing that <br>stage 2 output is going to about +-9V. It's like a square wave with some<br> distortion. I am unable to understand this output. As per my <br>understanding, the max output should go to 750mV (muscle output is +-5mV<br> and total amplification in circuit is 150x).<br></p><p>Is <br>the circuit / chip flawed or will AC coupling or the next stages bring <br>the output down ? Do you know what should the output of this stage look <br>like ?</p><p>Thanks</p>
<p>Hey Gundanium, thanks for the amazing DIY.</p><p>I could not find any 1uF Tantalum or 1uF Ceramic Capacitors, my question is pretty dumb, i`m a newbie.</p><p>So could i use 1uF Electrolytic capacitors instead of the Tantalum and Ceramic Capacitors in this circuit ?</p>
<p>Hi i am using IC 741 instead of INA 106. Where do i connect the reference electrode to the circuit. since there is no ground in the circuit.</p>
<p>This is something you're going to have to figure out yourself. Good luck!</p>
<p>hello sir, thank you so much for this tutorial....if we use 6 mid muscle sensors with a mux...the muscle end and body reference sensors will be common to single o/p of mux is this idea works??</p>
<p>Are you trying to measure 6 different muscles with 1 circuit and a mux? It's hard to follow what you're proposing to do. If you are indeed trying this, then my recommended approach would be to put the mux between the signal acquisition phase (step 3) and the Signal Conditioning - Amplification phase (step 4) and you will need a signal acquisition phase for each muscle. The reason for this is that your skin has an extremely high impedance and will cause ghosting effects (aka a trace of the previous input will appear when you switch the mux inputs). The opamp of the signal acquisition phase will act as an impedance buffer and eliminate all ghosting effects.</p>
<p>is it ok sir??</p>
<p>and can u please tell me how much amount of i/p power is required for that??</p><p>like 4 batteries are enough?</p>
<p>can i remove R3 10k? due to internal impedance present in mux?</p>
<p>how to replace the INA106 with INA129-EP since it has no ref pin like connecting to gnd....please help me sir...</p>
<p>This is something you're going to have to figure out yourself. Good luck!</p>
<p>No R3 is part of the first gain phase</p>
<p>I don't think I ever measured how much current this circuit draws but our MyoWare sensor only draws around 12mA. I wouldn't expect this circuit to draw much higher.</p>
<p>Yup pretty much</p>
<p>Hi,</p><p>I am trying to build a human to human interface wherein i control someonelse hand movement by moving my own. Part of it requires making the EMG. I am very poor at electronics.so could you pls clarify some doubts of mine.</p><p>1)with respect to my project, i can stop before the rectification right? cause i am guessing we need the complete signal .</p><p>2)I can use any wires with alligator clips attached to the electrode patch?What exactly is the role of emg recording role.</p><p>the above qs may seem repetitive, but ill be glad if you could clear it</p>
Hi Sarega!<br> <br> 1) It depends on how you are planning to use the EMG. The rectified and integrated signal (envelope) is useful for determining the force the muscle is exerting but you lose the frequency characteristics of the raw signal. The frequency characteristics can tell you what type of muscle fibers are firing but I don't see why you wouldn't be OK using the EMG envelope. The envelope would probably be preferable because it is more easily read by a microcontroller.<br> <br> 2) Yes alligator clips will work fine. What do you mean when you say &quot;role of emg recording role&quot;? I do not understand that part of your question.<br> <br>
<p>Hi Gundanium,</p><p>and first of all thank you very much for you great tutorial!! <br>I was wondering if there are any other solutions for the power supply problem (refering to a negativ voltage-supply), as two 9V blocks are really oversized for my project..</p><p>Since i was planing to use a Arduino-Nano/node-MCU i thought of using something similiar to the LM324-IC (as recommended in this tut <a href="http://gureckislab.org/blog/?p=3027" rel="nofollow"> http://gureckislab.org/blog/?p=3027 </a> ) or a setup as described in this link:</p><p><a href="http://www.instructables.com/id/How-to-create-voltage-using-one-power-supply/" rel="nofollow">www.instructables.com/id/How-to-create-voltage-usi...</a></p><p>With the Arduino only supplying 5V i will get around -5V from both setups; will this be enough to power the system you created or will i run into problems (e.g. amplification of the signal not high enough)?! </p><p>Looking forward for a supply!</p><p>Cheers </p><p>JI</p>
Hi JI!<br><br>This is a very old tutorial and our new sensors don't require the positive/negative power supply and can be powered directly from an Arduino. http://www.advancertechnologies.com/p/shop_3.html<br><br>Setup 1: Voltage inverter<br>The INA106 and TL072 chips need a minimum of +/-5V so you should be fine using an inverter powered via an Arduino 5V supply.<br><br>Setup 2: Voltage divider<br>If you want to use the schematic/chips from this tutorial and a voltage divider, you're going to need at least a 10V power supply to get the minimum required voltage. The INA106 and TL072 chips need a minimum of +/-5V so you can't use a single 9V battery and a voltage divider to do this. <br><br>Setup 3: Use Muscle Sensor v3 schematic<br>You could also build your circuit using our Muscle Sensor v3 schematic. While it is still an older design than the MyoWare, the minimum power supply is +/-3.5V so you would easily be able to make a +/-4.5V supply using a single 9V battery and a voltage divider.
Wanted to know why you used an inverting op amp in step 4 instead of a non inverting one, as well as why you used an inverting lpf instead of a non inverting one?
<p>Please ,I wanna to test the sensor using PC is there any programs I could get </p><p>Thanks again </p>
<p>sir why my sensor value on serial monitor arduino not changed? i dnt know what should i do to fix that ? change position of electrode not effect for me, before electrode i use, sensor value is 150-160, if i place on my muscle just got 180 and not change anymore. </p>
<p>why did we use the 1Mohm resistances, c1 and c2 capacitors and full wave rectifier? I tried to take EMG with INA125 in another circuit without use this parts and it worked(I used only high and low filters). so what is the their profit if i use them too in the circuit?</p>
The full wave rectifier plus the integration circuit is what produce the EMG envelope. If you want the RAW EMG signal you really just need the first phase of this circuit like you said.
<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>
It's complicated :(<br>i haven't any knowledge
<p>the legs are <a href="https://www.google.com.eg/search?q=different&spell=1&sa=X&ved=0ahUKEwjw17i7k8PMAhVIGZoKHdLnC3kQvwUIGCgA" rel="nofollow"><strong><em>different<br><br></em></strong></a></p>
<p>i figured it out bro</p><p>i think this is right </p><p>i am probably wrong</p>
<p>this is what i have done with the AD620 ic</p>
<p>Legs are different but it shouldn't take a rocket scientist to figure out which pins to connect to which legs on the new chip. I'm confident you can figure this one out without my help.</p>
which software?
<p>hi i really appreciate your job. i build sensor and everythings works fine, but i need raw emg signal. i can't see negative portion of signal. Recently i find out that you build sensor with raw signal option. However i would like to finish my job:)</p><p>i saw that you write that is needed to add DC offset, i m not sure how to change project to obtain such result. I'm not very good at electronics but i need this sensor for bigger project, so sorry if it's some trivial job:)</p>
<p>Thanks for showing us how to build an emg, I tried to buy INA106 but as many others, it isn&acute;t available in my country, instead I bought INA126. Do you think it is a good replacement? I already saw both datasheets and the internal resistances in both IC are quite different....</p>
<p>i tried to do as u said but i was not able to make head or tail of it</p>
<p>i have built thid circuit, but i have a problme that the signal it simulate are too small is there any other way to get the signal to be biggger, can i change the low pass filter into a high pass filter?</p>
Depends on what you mean by &quot;too small&quot;. The signal should be able to get up to +9V if you adjust the potentiometer. If you are seeing &lt;2V signals, then there's probably something wrong with the way you built the circuit or your setup in general.
<p>thank you.. </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>Many have already been suggested in previous comments.</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.

About This Instructable




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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