Building a wearable suit that can control things with your muscles

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Maker creates a wearable sensor suit that reads SEMG and uses those muscle signals to control things. 

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When you flex a muscle, it gives off a surface electromyography signal, which is commonly referred to as SEMG. After years of working with circuity designed to read muscle signals, Maker David Nghiem decided to create an SEMG pod that was capable of measuring the level of muscle activation and using those signals to control things.

To accomplish this feat, Nghiem used a combination of an Arduino (ATmega328P) to drive the digital circuitry, a bunch of op amps to read the SEMG signals, a half-wave rectifier to handle the negative aspects of the signals, and LEDs to display the signal levels. In particular, the Maker notes that the primary function of the Arduino is to control the digital potentiometer, as well as to map and output the resulting signals to the LED driver.

The concept initially originated as part of a senior project way back in the late ‘90s, and eventually went on to became the idea behind a startup that unfortunately did not succeed. However, Nghiem did learn from the adventure and offered a tidbit of advice that all Makers can appreciate. He explains, “Still, I learned a ton from that experience. Like who to trust, not to trust, what advice is solid, and what advice is pure crap. In any case, I figure documenting your failures so you learn from them, is far more important than successes.”

At its earliest stage, the basis of the SEMG pod was to apply an opposing force to the arm in order to help prevent muscle deterioration in astronauts while in space. It had been devised in collaboration with the MIT Aero Astro Lab and the Boston University Neuromuscular Research Center. This would then go on to spark another idea after a late night jog in his parent’s neighborhood.

“The SEMG product concept started out in 2009 when I was running down a 3-mile route nearby my parent’s home, and the road in particular is dark at night. There are few street lamps, and cars go down at a limit of 40mph, but let’s be honest, most people don’t give two $#!ts about speed limits. There’s no sidewalk, and barely any shoulder. As I ran, I wondered if I could use the SEMG signal from my legs to control a light pattern to warn oncoming cars with a non patterned light show, like how some animals have vivid colors to ward off potential predators with a show of flair — that also meant they were poisonous,” he writes.

After making use of SEMG signals to control robotics along with the versatile capabilities of Arduino, Nghiem had an initial prototype. Looking ahead to a much prettier, more functional wearable device, he acquired a LilyPad Arduino (ATmega328) — this was before the days of Adafruit FLORA — to route the SEMG data through and then sewed it onto a bicycle jersey. Upon completing this model, he still encountered several problems, including having to integrate the unit make it more compact, making it more flexible and improving its sweat resistance. So, he threw that entire design out.

Back at the drawing board, for the next iteration he tried incorporating a MIL-Spec shielded cable, modifying the electrode placement methods on his sleeve, affixing the backs of the electrodes with velcro and transitioning to a bigger analog pot. Unfortunately, he was still coming across some difficulties, such as random shorts and connection issues, no digital control, and lack of LED lights to indicate signal levels.

And after some more tinkering, he found himself closer to a final product. You can check out Nghiem’s well-detailed project log here, along with the videos showing his project at various stages.