Signals

• The electric signal is produced during muscle activation, which is observable through the exchange of ions across the muscle membranes and the electrodes attached on the skin.
• EMG signal is acquired through differential amplification.
• sEMG is usually at the range of 5 - 250 Hz (but the cut-off frequency is suggested at 65 - 180 Hz to avoid strong DC at 60 Hz).

Electrodes

• Ag-AgCl electrodes (pre-gelled) are used in over 80% of surface EMG (sEMG) applications due to its low impedance and high stability
• Placement:
  • Between the motor unit and the tendinous insertion, along the longitudinal midline of the muscle (fig 9 in 1).
  • Electrodes should be only 1-2 cm apart.
  • The reference electrode should be placed far from the EMG detecting surface (i.e., on a neutral tissue) → we use bipolar configuration (fig 13 in 1)

Possible noise to sEMG (see more in 2)

• Ambient noise (radiated EMI, specifically 50-60 Hz)
• Transducer noise (different impedence between the skin and electrode sensor)

Other issues

• Consistency in impedance is critical for the reliability of sEMG measurements (think about our form factor)
• Different kind of biosignals - ECG (heart), EEG (brain), EOG (eye) in 3
• Suggestions of electrode placement 3

Fix bug in RXTX library

• The bug in SerialImp.c causing unnecessary delay (~20ms)
• Modify the sleep time from 20000ms to 2000ms, reducing the delay to ~2ms
• Our ADC sampling rate is 256 Hz (i.e., interval ~3.9ms). The 2ms delay fulfills the system requirement.
• Ref:
  • Bug issue
  • How to compile RxTx: 12
  • Install RxTx on Mac
  • Setup compiler
  • RxTx source code

Initial data collection

Keyu implemented a real-time sEMG data retrieval and visualization using Python.