This was part of a project from my circuits lab last year where my partner and I built a basic EMG that could pick up on the electrical signals from my bicep and produce the raw EMG graph up on the Oscilloscope. After we honed in on the biosignal, we built a comparitive ladder using a series of LEDs, the stronger the signal, the more LEDs lit up.
Part 1: Instrumentation Amplifier
Pick up biosignals via electrodes on body
Biopotential amplifier
Human body has a signal of ~60 Hz
120-VAC signal inducted from wiring in the walls
Part 2: Filtering
Design a high pass filter to remove any DC offsets (besides Vcc/2 virtual ground offset)
Non Inverting, cut off 5-30 Hz, gain of 2
Part 3: Envelope Detector
Consists of rectifier and low-pass filter
Rectifier: Half or Full wave
Filter: Active or Passive
Purpose of Envelope: To detect the overall strength of the signal
Part 4: Comparative Ladder
Used when Oscilloscope is not available
Series of voltage dividers accompanied with LED lights
Effective user interface
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