BioAmp EXG Pill

[last updated: 2023-02-20]
(link to:) Crowd Supply
(link to:) gitHub repository
BioAmp projects
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• The BioAmp EXG Pill is a low-noise, high gain instrumentation amplifier module
  designed to be used to amplify and work with the low voltage signals from the human body,
  whether brain waves (EEG), heart rhythms (EKG), muscle contractions (EMG), or eye movements (EOG).
• It started shipping in 2022 from (link to:) Crowd Supply.
  
  
  

  back side
  
  

  front side
  
  

  ECG
  
  

  EEG
  
  

  EOG - vert
  
  

  EOG - horiz

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• Specs:
  Vcc = 5v
  Output nom 5v

• Amplification/Gain:
  Electrical signals from the human body are very low voltage - milli or micro volts.
  In order to work with them, they must be amplified to a range more convenient for typical electronics (typ. 3.3 - 5v)
  The bioAmp board has a nominal gain of 1000x (best guess from sketchy documentation...)

• Signal processing:
  These low level signals tend to be "noisy", or "glitchy".
  In addition, because the gain is so high, "stray" signals from nearby power sources, or even from nearby body parts that tend to act like antennas,
  will add their signals to the total output.
  Signal processing is the hardware and/or software process to clean up the noisy signal so you can clearly see and work with your desired event.

• On-board amplifier and filter stages:
  • Gain:
    As mentioned, the default bioAmp gain is 1000x.
    While this may be sufficient, documentation says connecting a resistor (1603 SMD) on the back of the board at "R1" will increase the gain.
    However I have not found any documentation on resistor values to give whatever gain increase.
  • Filtering:
    There is a configurable, onboard bandpass filter on the BioAmp board.
    R3 and C1 can be added to the board to configure the frequency response of the filter.
    However, as before, I have not found any documentation on R & C values to give whatever filter performance.
    Sent in tech request, and got a response saying values were different for different board versions, so I sent them pictures of my boards.
    Awaiting response.
• Software Signal Processing:
  • There are several Arduino sketches to perform software signal processing: (link to:) gitHub repository
    There are sketches for different filtering modes, different sampling rates, envelope and event detection, and others.

  • (link to:) arduino projecthub FFT

  • https://dsp.stackexchange.com/questions/45345/how-to-correctly-compute-t...
  • https://realpython.com/python-scipy-fft/
  • https://neuraldatascience.io/7-eeg/time_freq.html
  • https://notebook.community/JoseGuzman/myIPythonNotebooks/SignalProcessin...
  • https://github.com/kitschpatrol/Brain
  • https://www.sciencedirect.com/science/article/pii/S2667241321000094
  • https://www.mathworks.com/matlabcentral/answers/605092-fft-of-a-real-tim...

  • https://www.electronics-tutorials.ws/filter/filter_4.html band-pass filter
    https://www.allaboutcircuits.com/textbook/alternating-current/chpt-8/ban...

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