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>hello sir </p><p>can i use electrolyte 1 uf 50v capacitor instead of tantalum and ceramic disk capacitor because in our country 1 uf tantalum and ceramic disk capacitor are not available.plz sir reply me fast</p>
<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>What happened with the high pass filter at the end of the circuit? You show 5 tl0 in the schematic. </p>
<p>Hi, I have trouble understanding the last part of the cirucuit. It is said that a low-pass filter is used in order to smooth the signal and to get rid of the humps which seems weird to me. Could you explain that to me please?</p>
It's actually an integration circuit in this context. It integrates the rectified EMG signal to produced the EMG envelope
<p>Can an integration circuit behave like an envelope detector? </p>
<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>Those battery connections are incorrect. Also, you've set Rg to 10kOhm which gives you a gain of 5.94 (49.4/10+1 = 5.94). The INA106 in this configuration has a gain of 110. If you want the same gain, you'll need to set Rg to 453 Ohms instead of 10 kOhms.</p>
<p>when using 2 batteries of 9V i get around -6 Volts at the output. <br>When i use only one battery of 9V i get around +3 Volts at the output! What could be the problem with the two batteries? </p>
<p>And u used 1uF and 80.6k .l calculated f is 1.9746Hz but its must be 10-500Hz low-hıgh past filter isnt it ? why did u use 1uf and 80.6k ?</p>
<p>You're looking at this from the wrong angle. The 10-500Hz range applies to the raw EMG signal not a rectified signal. This &quot;filter&quot; is actually a simple integration circuit. This is what converts the rectified EMG to the EMG envelope.</p>
<p>ok Thank u very much.</p>
<p>can i Build Electrooculography (EOG) sensor using this circuit</p>
<p>Hello </p><p>What is the total gain ? and I want to use +-12V is there any problem ?</p><p>Thank u</p>
<p>Sir, can i use 1uf 63v electrolytic capacitor in place of the 1uf 50v <br>ceramic capacitor? If yes then how will i know which terminal needs to <br>be connected to which pin?</p>
<p>Thanks a lot for the tutorial. Was able to <br>make this and the output is pretty much same as myoware sensor kit. In <br>India it cost me about 2K. The output voltage to uC is still about 3.8V <br>but adjusting the input voltage takes care of it. I suggest adding a <br>trimmer with your batteries to get the +/- voltage and start with a low <br>voltage (like 10V instead of 18) since it makes it a lot safer with <br>these expensive parts. (Check bottom part of circuit in attached image)</p><p>Nice instructions.</p>
<p>Hey bro from where did you ordered the 80.6k ohm resistor? i couldn't find them anywhere</p>
<p>If you are in India, digikey might not help. I used kitsnspares.com for most of the stuff. However there are few components like 80.6k resistor which are not available anywhere for retail. So i had to order them directly from element14 (kitsnspares' parent site). I ordered 50 pieces (that was the minimum for wholesale order).</p>
<p>I should mention that you don't need exactly 80.6k resistors. Anything around 80k should suffice. The MyoWare uses 82k resistors for example.</p>
<p>sir can i use 1uf 63v electrolytic capacitor in place of the 1uf 50v ceramic capacitor? If yes then how will i know which terminal needs to be connected to which pin?</p>
<p>Good to know that the 82k will work since i have already ordered them. Desperately waiting for the components to come. Thanks again Sir.</p>
I see. in that case you have plenty of options like digibay, robokart or kits spares. there are many other sites from where you can get standard resistors.
<p>i have ordered all the components from the site electronicscomp.com. They have cash on delivery option too. Only the things that i couldn't find there was the 80.6k resistor and the EMG cables and the electrodes. So i had to compensate the 80.6k with the 82k resistor and i am still searching for the EEG/EMG lead cables since they are very less prone to noise compared to the simple copper ones. So did you used the EMG/EEG lead wires or just directly the copper wire attached to an alligator clip?</p>
<p>I am using alligator cables directly connected to electrodes on one end and circuit on the other. </p>
There's links for each component in the Materials section. Digikey is usually our go to vendor for components like that.
<p>What is so special about the INA106 IC than the other class of differential amplifier? Is it because of its high gain of 110? Or is there any other reason? </p>
<p>Hi Gundanium,</p><p>I am facing 2 issues with my output voltage.</p><p>1. The minimum voltage (output at 0 muscle exertion) at uC end is going to 1.25V. I think this is due to some mismatch on the circuit but i ma not sure what. Increasing the potentiometer gain makes this go higher and decreasing it makes it go lower. Of course decreasing the gain to solve this problem is not an option. I was thinking of using a voltage shifter however it will only be a hack. I am not sure why this problem is happening.</p><p>2. The maximum voltage at output is saturated at 3.75V. Irrespective of how much gain i increase, the output never goes above 3.75V. I think this is happening due to my supply voltage. Earlier i was using +/-9V directly from battery and output sometimes went over 5V. Today i switched to +/-5V and have been facing this issue ever since.</p><p>I am using a basic op-amp inverter using TL072 and 5V supply from arduino to get +/-5V. I checked through multimeter, my input voltages are steady at +/- 4.88V.</p><p>I see that myoware sensor only requires a 5V supply from arduino and still achieves about 0.2V to 4.8V output. Have you faced these problems before ? Is there something i am missing ? Anything you would suggest to read ?</p><p>Thanks<br></p>
<p>Sir its really damn important. I am building a prosthetic arm as my <br>final year engineering project. I am using this muscle sensor to do it <br>but i have some confusion. </p><p>First one is- In one of your earlier <br>version of the muscle sensor you had used 453k resistor in between pin 1<br> and pin 2 instead of the 150k in case of chip B. Sir, what difference <br>did it make by updating it with a 150k resistor?</p><p>Second one is- <br>In the earlier version you had used a 10k resistor instead of the 1k,why<br> is that? What are the complications that you observed in the earlier <br>version?<br></p>
Hi, I'm a little confused as to which version you're using and what you mean by &quot;earlier version&quot;. The version in this Instructable was our very first version.
<p>actually i found a pdf file same as this- here's the link., maybe someone has manipulated with it -</p><p><a href="https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwitjZS_7_HRAhUDgI8KHZ4ECl4QFggrMAM&url=https%3A%2F%2Fgypsyware.files.wordpress.com%2F2013%2F03%2Fmuscle-emg-sensor-for-a-microcontroller.pdf&usg=AFQjCNH0UDKYq_dUcnl6lg8i1QgcemIE5w&sig2=4ytQYfH2pKPClZVIHNljwA" rel="nofollow">https://www.google.co.in/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;...</a></p><p></p>
<p>Hmm I think we modified the instructions shortly after it was published to consolidate parts (we used to sell a kit for this tutorial). The change from the 453k resistor to 150k resistor changed the gain of that phase from around -3 (453/150=3.02) to -1 (150/150=1). All this difference could be compensated for in the last gain stage but was beneficial because it eliminated 1 part from the BOM.</p>
<p>Thanks Sir,its quite a relief knowing the reason.</p>
<p>Hi, Gundanium! First of all, thank's a lot for this tutorial! My output looks like 0.62, 0.0, 0.0, 0.63, 0.61, 0.0... etc. So... it's clear that I missed something. I don't have tantalum capacitors. They're pretty hard to find. Are they so important to the circuit? Can they change the output values? Thanks for your time!</p>
<p>Ceramic capacitors work just as well as the tantalum. The uF value is important though.</p>
<p>is it possible to use it with a raspberry pi?</p>
<p>Raspberry Pi's don't have analog input pins. I could be wrong about that though. If they do, then this will work.</p>
<p>Does the circuit that filter out the 60Hz/50Hz noise? If so, which portion of the circuit does that?</p><p>From what I understand, there will be an ambient wall outlet noise, due to electromagnetic fields, even if the circuit is powered from a battery</p>
The 60/50 Hz noise gets removed by the high common mode rejection ratio (CMRR) of the instrumentation amplifier. A high CMRR basically removes all signals common to both input lines. This is why braiding the cables is very important; it ensures the 60/50 Hz noise is in the same phase across both input lines.
<p>Hi!</p><p>What apps did you use for mac?</p>
www.processing.org<br><br>You can find the code we used on our Git Hub repository https://github.com/AdvancerTechnologies/MyoWare_MuscleSensor/tree/master/Example%20Code/BarGraph
<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>

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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