3M Red Dot electrodes
Alex Lao suggested to try some 3M Red Dot electrodes, and so I got me some of the model 2248-50 (he actually suggested model 2660 but I mixed it up.) They are used for ECG patient monitoring, which is close enough, right?
I connected two of them to EX1 and EX2 on an Electrode Module 3.1 and placed them on the flexor digitorum superficialis muscle (where I place the built-in PsyLink electrodes on most of the other pictures/videos too), and placed a third electrode on the radius bone near the wrist, and connected it to a Vref pin of a Power Module 4.2, which therefore acted as a ground electrode. The electrode module is the one from the previous blog post about the MCP6N11-100 instrumentational amplifier (for no good reason - I should have used INA128 for better comparability).
This is what they look like on my skin:
I recorded the following signals when pressing different fingers onto the table:
The amplitudes of the wavelets were a little disappointing, but perhaps boosting the gain from 501x to 1001x-2001x would help.
The nice surprise was the specificity of the signals. I only saw signals when I actually used that muscle. Unrelated movements like twisting the wrist sometimes produce strong signals with the built-in PsyLink electrodes, but produced no signal with these. There could be many reasons for that:
- The "unwanted" signals may be too weak to be visible against the noise
- There are less mechanical artifacts from electrodes moving around
- The ground electrode is closer to the wrist here, whereas in the default configuration, it's closer to the middle of the bone.
It's good to see that it works, and there's clearly a potential, but I'm not blown away either. Next steps could be:
- increasing the gain
- trying electrodes with better adhesion like the 3M 2660
Note that before attaching the electrodes, I did not shave off hair and did not clean off skin oils with alcohol, but at least I was fresh out the shower. Ok, time to end this post, this is getting weird :).