Hi, I am currently building a DIY EEG circuit using the guide above. This guide is for when there are two inputs. However, how can I modify this so that I can also input two EMG signals too.

It is common knowledge that EEG's carry weak EMG signals with it. My idea is to obtain a clean EMG signal from the source, and also obtain a EEG signal (with the EMG noise) I would use the differential amplifier with both the EEG and clean EMG signal to effectively cancel out the EMG signal and get a more pure EEG signal.

  • \$\begingroup\$ Welcome to EE.SE. Build the same circuit twice. The 2.5 volt floating ground can be shared with several channels. \$\endgroup\$ – user105652 Apr 23 '18 at 2:15
  • \$\begingroup\$ I should let you know that precision EEG machines have lots of expensive parts, and use DSP to extract the alpha waves, etc, from the background noise. \$\endgroup\$ – user105652 Apr 23 '18 at 3:11
  • \$\begingroup\$ @Sparky256 If i build the circuit twice, how can I use the subtraction (common mode) property of differential amplifiers in between EEG and EMG signals to cancel out the EMG noise from the EEG? Also I'm aware there are quite a few effective DSP techniques, but I wish to have a hardware approach for research/experimental purposes \$\endgroup\$ – Nathan Le Apr 24 '18 at 2:47
  • \$\begingroup\$ For 'common' signal return a couple of wires are usually attached to each ear lobe which feeds a instrumentation amp to act as a signal ground for the inputs. \$\endgroup\$ – user105652 Apr 24 '18 at 2:53
  • \$\begingroup\$ I'm still a little unsure what you mean. I'm aiming to use an EMG signal as a signal to the common mode feedback terminal of an EEG amplifier. Doing so could possibly be a better technique of EEG artifact removal because the artifact is removed before saturation and clipping from the EEG amplifiers. \$\endgroup\$ – Nathan Le Apr 24 '18 at 3:05

The problem with the assumption is that EMG signals can be controlled. It can be a couple orders of magnitude higher level in signal strength and there is no precise way to ensure that the EMG signal can be cancelled due to too many reasons to mention including sensing location and contact pressure. Even if you had some adaptive AGC the EEG would still be swamped by possible EMG signals and scalp artifact noise from modulating the galvanic DC charge voltage from motion or pressure changes of the electrodes.

This is why it is done the way it is.

  • proper electrode area prep and attachment
  • Active guarding with CM feedback..
  • and Right Leg RL ground ( mainly for EKG) or equivalent 0V reference point that is convenient on the body.

Conclusion —

Not feasible.

  • \$\begingroup\$ If this is not feasible, I would need to alter the direction of my research thesis. It seems you have quite a bit of experience in this field. Do you have any suggestions on what my topic direction should be, that is somewhat novel, yet possible for a student to accomplish in a small amount of time? Thanks \$\endgroup\$ – Nathan Le Apr 24 '18 at 2:52
  • \$\begingroup\$ I have no idea on your interests nor capability , imotions.com/blog/eeg-cap \$\endgroup\$ – Tony Stewart EE75 Apr 24 '18 at 5:37
  • \$\begingroup\$ Not feasible indeed. Try reading signals from tongue muscles and use ML to interpret them. You will get a lot of noise, but there might be useful patterns. \$\endgroup\$ – Gregory Kornblum Dec 6 '20 at 8:12
  • \$\begingroup\$ I once used temple electrodes to trace lateral eye position which just using differential galvanic skin response with temple skin pressure from the eye motion. Yet I was able to create perfect triangle or asymmetric sawtooth waves sweeping eyes slowly left-right-left , (Watching girls go by) and this is just an AC coupled signal with HPF below 1Hz, during a show and tell festival on Campus in early '70's. I also used bicep/tricep muscles to control a prosthetic hand. There are reliable methods used for EEG, ECG and EMG, so "don't try to reinvent the square wheel with mickey mouse solutions" \$\endgroup\$ – Tony Stewart EE75 Dec 8 '20 at 3:12
  • \$\begingroup\$ My Neurologist used simple electrodes with active guarding for gnd to measure axon muscle velocity on my arm (post arm arterial bypass with neurological inflammation damage to pain conductors. I told him I already knew my muscles were fine what about the pain axon fibre signals? He said he can't measure those. doh. What a waste of time. \$\endgroup\$ – Tony Stewart EE75 Dec 8 '20 at 3:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.