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Portable EEG Recording Using a Lock-In Amplifier

Portable EEG Recording Using a Lock-In Amplifier. Braden Fong – Matthew Harvey – Kirill Lagoutchev. Project No. 23. Introduction. Current electroencephalography (EEG) technology is large and cumbersome Limits research to a laboratory

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Portable EEG Recording Using a Lock-In Amplifier

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  1. Portable EEG Recording Using a Lock-In Amplifier Braden Fong – Matthew Harvey – KirillLagoutchev Project No. 23

  2. Introduction Current electroencephalography (EEG) technology is large and cumbersome • Limits research to a laboratory Lock-in amplifier for application in brain-computer interfacing (BCI) • Client interested in detecting steady-state visually evoked potentials (SSVEPs) • Lock-in amplifiers can easily detect specific frequencies Objectives • Build a portable EEG recording device

  3. Hardware Overview Portable EEG amplifier Protection from high voltages Common mode rejection Amplify differential signal without saturation Filtering • High-pass for anti-aliasing • Low-pass for DC blocking

  4. Original Design

  5. Design Strategy Initial challenges • Small signal amplification • Product portability • User safety Applicable coursework

  6. Protection Circuit Limits the voltage to the user Protects user from electric shock

  7. Protection Circuit Verified using function generator and oscilloscope Apply voltage to input, measure input and output waveform

  8. Instrumentation Amplifier Rejects common noise generated from the environment Pass differential signals to gain stage

  9. Instrumentation Amplifier Verified using function generator and oscilloscope Apply voltage to input, measure input and output waveform

  10. Gain Stage Amplify EEG signal to readable voltage on the myRIO Filter frequencies above 50Hz

  11. Gain Stage Verified using function generator and oscilloscope Apply voltage to input, measure input and output waveform

  12. Hardware Challenges Noise • Power line noise can be removed with a notch filter Clipping from high gain • Solved by cascading smaller gain amplifiers

  13. Software Overview Implements the lock-in amplifier Reference signals Multiplication Filtering

  14. Reference Signal Phase independent Multiply with input signal

  15. Filtering Low-pass Filter • Extract and output the DC term • Remove the periodic signals • Cutoff Frequency of 0.75 Hz ±0.05 Hz

  16. Software Challenges Reference signal timing Sampling frequency and loop timing Writing speed

  17. Demonstration Video SSVEP Video

  18. Marketability

  19. Marketability Emerging research market Other portable amplifiers • Emotiv Portable BCI • Augmented reality • Advanced functionality for handicapped individuals Long term recording

  20. Finalization before Handover to Customer Minimize the size of PCB • Condense and optimize circuit design Create build multi-channel unit Create user manual Set up wireless capabilities with myRIO • Battery pack • Wirelessly deploy LabVIEW

  21. Safety Issues and Ethics Protection for patients was a key • Voltage and current protection with circuitry • Protects patient from electrical shock Original design of circuitry • Research of the topic ensured original design and properly cited work

  22. Acknowledgements Professor Carney Professor Singer Jamie Norton Rishi Ratan

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