EMG Controller
An ongoing collaboration with Ezer Longinus. Over the weekend we were able to get consistently solid readings from our EMG (Electromyograph). We rebuilt our circuit with the AD620 instrumentation amplifier and an OP97 operational amplifier using a schematic from The Carleton University Biomedical Engineering Society (view schematic at bottom).
We made an electrode cuff to keep the electrodes secure, especially the body ground placed on the elbow.
Electrode placement - Flexor
We used standard ECG electrodes that have a conductive gel between the metal electrode and your skin. These are one time use / disposable. We plan to switch to reusable electrodes in future builds.
In a basic EMG there are two reference electrodes placed near the muscle and one body ground electrode placed where there are few nerves, typically on non muscular areas or boney protrusions, in this case the elbow.
EMG voltage potentials range between less than 50 μV and up to 20 to 30 mV, depending on where the electrodes are placed. The instrumentation amplifier is what amplifies this signal many times over so that it can be usefully detected and read by the Arduino.
Seen below is our first successful read on the graph. We used Che Wei’s GSR reader to work as a stand in EMG reader, which was way better than trying to make sense of numbers on the serial monitor. -thanks again Che Wei.
Here you can see clear and distinct reads on forearm flexing
Here you can see both forearm activity and less pronounced finger movement.
Great work. One way to minimize noise would be to focus on larger muscle groups. You have about 29 long skinny muscles that live in your arm between your elbow and wrist, so it can be really tricky to isolate just one without getting cross talk from others in the area. Once perfected, you can add this to Noraxon’s list of applications! http://www.noraxon.com