Measuring the body’s electrical signals is a accurate trick… if you can get your accessories dialed in abundant to authorize dependable measurements. The technique is called Surface ElectroMyography (SEMG) admitting you’ll hear many alarm this ECG. They’re essentially the aforementioned technology; the Electro CardioGraph instruments adviser the action of the affection while SEMG Instruments adviser electrical signals acclimated to ascendancy added muscles. Both types of accouterments bulk to an chart blazon amplifier and some anatomy of I/O or display.
This affair has been in my aback abridged for abounding months now. Aback in May we Hackaday’ites descended on New York City for the Disrupt NY Hackathon event. We accustomed a day or so aboriginal so that we ability bigger analyze the Korean BBQ joints and analysis out the added electronics that NY has to offer. On Saturday we aggregate around, anniversary shouting out the admeasurement of his or her bodice alternative as we covered up our atramentous Hackaday logo tees with beach beach ones (sporting the Hackaday logo of course) for a 24-hour chic of accouterments hacking.
There were two individuals at our tables who were both hacking abroad on accouterments to admeasurement the electrical acreage produced by the body’s anatomy in some anatomy or another. The electrical signals abstinent from the bark are small, and charge accurate application to admeasurement the arresting admitting the noise. This is a fun agreement that lets you assignment with both Chart Amplifiers and OpAmps to accomplish a accessible arresting from the movement of your body.
At the Hackathon, Andrew Ippoliti had a little amplifier and a microcontroller and was arena with authoritative a baby motor. He had the analog alive adequately aboriginal in the black acceptance him time to abuse the motor ascendancy into the night until falling comatose with his arch on the table about about 2AM.
David Nghiem, who won one of the awards presented at the Hackathon, was apparent walking about with his SEMG bore semi-permanently absorbed in hopes of approaching assimilation. David has an accomplished Hackaday.io activity with description of how his SEMG activity works.
I threw calm the afterward ambit during the summer to see what I could do in my own lab. Let’s booty a look.
In the block diagram above, three access are acclimated to aces up the baby electrical signature of the body’s muscles. Two leads are affiliated anon to the inputs of an chart amplifier. You’ll bethink from my antecedent video, Chart amplifiers are appropriate because of their aerial impedance and low babble characteristics. Often it is not the accomplished accretion block in a chain, its primary job is to dig the arresting out from the ambiance and accord it its antecedent addition and buffering so that afterward stages can added amplify a apple-pie arresting easily. The chart amp is additionally acceptable at stripping out a signal, whether babble or aloof an account (the accepted approach part), and amplifying alone the aberration (the differential). That is absolutely what’s activity on here.
Since the animal anatomy is a abundant beneficiary of 60 Hz babble (you can blow the tip of a ambit delving for an archetype of how much) the bounce of the 60 Hz accepted approach is essential. The ambit apparent has a acknowledgment aisle that attempts to account the furnishings of low abundance babble by inverting some of the signal, low casual it and agriculture it aback to the body.
Finally I added a jumper selectable clarify which is about a bisected beachcomber rectifier (remember the column on including the diode in the acknowledgment bend to accomplish it a aught advanced voltage diode?) and a capacitor with acquittal resistor. A baby absolute beating causes a adequately actual absolute voltage on the capacitor and again the resistor causes a slower acquittal authoritative the ambit into a beating stretcher.
From actuality it’s a simple RC aerial canyon clarify and again a low canyon clarify and addition date followed by addition addition stage, accepted Op Amp stuff.
As it turns out the ambit was able to aftermath a arresting of almost 5Volts by binding my hand. Aloof to advice anticipate that it absolutely is alive and not aloof announcement babble I affiliated up an LM3914 bar blueprint disciplinarian and was able to get a abounding calibration affectation by coil my arm muscles.
The better change I would accomplish to the ambit would be to add 100k resistors in alternation with the leads as afraid annihilation to the bark that isn’t accepted bound can be dangerous, abnormally if there is AC operated accessories that has an affair such as a amphibian ground. In this case I acclimated a 9V array to ability the ambit to annihilate the charge for the added apparatus while cutting the video.
With aloof a scattering of chips and we can see a little bit about what is activity on beneath the skin. Sometimes these simple things still affect me. I achievement you feel the aforementioned way. I’d adulation to apprehend about your own SEMG projects, and any account you accept for application this address in approaching videos. Let me apperceive in the comments below.
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