So friends, today I am going to introduce a new series called Evil Genius series! I will start with a DIY(Do It Yourself) EMG circuit.
This project was the result of my work towards the science experiments and demo sections for the OPEN-DAY here at IMSc, Chennai. Representing “computational biology group”, I had to do something interesting. As my previous background was in electronics and also because of my interest in neuroscience, I could not think of any other experiment. I made a low-cost biosignal detector. A biosignal may be signal like EEG (Electroencephalogram or loosely “brain waves”), ECG (Electrocardiogram or “heart waves”) or EMG (Electromyogram or “skeletal muscle waves”). You can find the explanation of these signals elsewhere. I will give a brief idea. But keep in mind that each neuron in the cell is capable of generating an electrical signal and passing them to others. Here we are not talking about those micro-signals, instead focusing on much higher levels like summation of many such signals. A problem here is that neurons are very small (in the range of microns) and there are lots of them. There is a famous analogy: Consider a football stadium full of spectators. The problem is to develop a method to capture the conversation of each and every individual with others in midst of heavy amount of noise. Clearly, we need a microphone near to each of the persons, which is impractical. But if we measure these signals from skin electrodes (surface electrodes) it is like capturing the entire football stadium’s signal using a single microphone in a helicopter which is above the stadium. It, of course, captures some signal. There may not be micro details in it. Keeping this in mind we can go to other details.
Electromyogram
EMG or electromyogram naively means electric signals in muscles. When you decide to move any of your muscle, neurons from your motor cortex sends some electric potential signal to the spinal cord. Then the signal gets transferred to lower motor neurons which in turn connects with the respective muscle. You can see the image below to get a crude idea of the neural network in humans. So brain and spinal cord comprise of CNS(central nervous system) and the other neural network comprises of the peripheral nervous system(PNS).
Source: Wikimedia Commons, License: CC BY 4.0
The EMG circuit
Circuit components
- 9V Battery (2 No.) for powering the circuit
- CRO to visualize the signal
If you don't have a CRO, you can turn your computer into a display too. But on that later.
- INA128 chip from Texas Instruments
This is a nice instrumentation amplifier capable of amplifying very weak signals like EMG.
- breadboard
- resistor (120 ohms)
- wires
- electrodes
- multimeter for checking voltages and connections etc
Circuit Diagram
Output
Do you see spikes when I move my fingers? Those are the EMG signals!
Why is the signal noisy?
The circuit is noisy primarily, because of the 50Hz power pickup and other electromagnetic induction issues. The AC(alternating current supply) current in India has a frequency of 50 Hz and it interferes with the signal. In United States, the power pickup signal would be 60Hz. I can use a filter to remove this signal. In an ideal case to avoid these electromagnetic disturbances, you should use a Faraday Cage.
So enjoy the weekend. I hope you people learned something new today.
About steemSTEM
steemSTEM is an active community which focuses on promoting original, nicely written and informative articles on Science, Technology, Engineering and Mathematics in Steemit. steemSTEM is the best science community I know of in the whole of steemit. So do check out the articles which come in this hashtag #steemSTEM. And also don't forget to join the steemSTEM discord channel: https://discord.gg/BZXkmWw
Besides evil genius series, currently I am writing 2 series:
- Visually Explained! : Focusing on explaining concepts with less math and more physical intuition
- Classical Molecular dynamics: Focusing on teaching and setting up a molecular dynamics simulation of atomic systems.
If you like my content please upvote and resteem it. Below are few of my recent posts, you may find interesting:
- Gradient, Divergence and Curl : Visually Explained!
- The history and mystery of Belousov–Zhabotinsky reaction: Did it violated 2nd law of Thermodynamics?
- Shannon Entropy: Visually Explained!
- Classical Molecular Dynamics Series [Part - 3]: Solving the molecular dynamics equation
Being A SteemStem Member
thank you for the post, friend
wow that is amazing man , would like to read more of your series.
Thank you for the nice comment. I will surely come up with something nice I know for sure. But I think my posts are getting less visible here. steemit will become mature with time I guess. :)
The tags you are using will have a lot of effect on visibility . you are in good care with steemstem , just a matter of time though , also keep an eye on posting time (UTC)
What is the best time?
Nice build, and interesting post. Have you tried to filter the 50Hz? It looks like you have plenty of signal, so it is not necessary. I am interested as using battery power, and still getting noise from the utility implies you may need more than a Faraday Cage ...or a really big one you can walk into. If you just shield the circuit, you will still have your body and the external wires picking up the noise.
It looks like you are already using differential inputs and have plenty of common mode rejection. I have seen some odd cases where single ended worked better, but if the energy is induced, as it appears to be, I would think the way you have it is best. At any rate, as mentioned your signal to noise looks nice, so keep on experimenting.
It has been a while but I have done experiments requiring a Faraday cage big enough to walk into and perform experiments without any external noise :-) --3D
I was not satisfied by my output. I was lazy too. And I was doing electronics after many years. I am thankful for your comments. At certain points I got better outputs. I noticed that even the place I am setting up my experiment matters. May be I should talk to you in discord. 😃
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Thank you @bitgeek . Can you tell me how you pulled out the data. I am interested in knowing.
A great article ! I am writing an article on brain waves and eeg. If you want to review the link here; @emrearar
Who knows, maybe we can do a joint project. :)
Cool. I am interested in brain waves are EEG. If you are in discord we can talk there. :)
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STOPWill share this with my son, he is in the first year of electronics and communication engineering.
Let me suggest something. Ask him to contribute to #steemSTEM . We need quality contributors and active members. steemit is not very popular in India. We need more awareness progammes. I feel personally that when students contribute actively to communities like #steemSTEM it is a win-win scenario. They get incentives, community gets strengthened and his learning process will be more active.
yes and I will show this to him. He has been writing an article as per my suggestion but did not complete it because of his internal exams. It is over today, so will ask him to do it. Thank you so much