Overview

The electronics subsystem captures, amplifies, and conditions electromyographic (EMG) signals from surface electrodes placed on the forearm. The analog front-end includes differential amplification, bandpass filtering, rectification, and envelope extraction—all optimized for low noise and minimal component count.

The INA128 instrumentation amplifier provides high common-mode rejection (%gt 100 dB) to reject 60 Hz line noise and motion artifacts. A two-stage active bandpass filter (10–500 Hz) isolates the EMG spectral content. Full-wave rectification followed by a low-pass envelope filter (~5 Hz cutoff) extracts the amplitude envelope, which the Arduino Nano samples at 500 Hz.

Power for the analog circuitry comes from the Arduino's 5V rail, with local decoupling capacitors to minimize digital switching noise. Total current draw for the analog front-end is ~15 mA.

EMG Analog Front-End Schematic

Schematic showing INA128 differential amplifier, bandpass filter stages, rectifier, and envelope detector.

Design Notes

• •Gain: INA128 configured for ~1000× gain (60 dB). Adjustable via single resistor (R_G).
• •Bandpass filter: 2nd-order Sallen-Key topology. fc_low = 10 Hz, fc_high = 500 Hz.
• •Rectification: Precision full-wave rectifier using TL074 op-amp.
• •Envelope: 1st-order RC low-pass with 5 Hz cutoff for amplitude extraction.
• •Electrode placement: Two active electrodes on flexor digitorum superficialis, one reference on bony prominence (ulna).
• •Noise mitigation: Shielded cables for electrode leads, star grounding to minimize ground loops.

Bill of Materials (Electronics)