ECE 5030

Electromyograph

Introduction.

In this assignment you will build an Electromyograph (EMG) and force sensor and correlate EMG signals with the force produced by a muscle. Any circuit which you attach to your body must be completely isolated from earth ground and the 110 volt grid. There is a good summary of EMG measurements entitled Important Factors in Surface EMG Measurement by Dr Scott Day.

Procedure

You will need an isolated power supply, an analog signal isolator, a differential amplifier and analog filters.

• A possible differential amplifier circuit. In the schematic, ignore the power supply opamp on the left. The input to the diff-amp has a lowpass filter. The opamp to the right is a highpass filter. The Texas Instruments INA121 is a good, low power diffamp.
• We will use a dc powered, transformer isolated power supply, the Texas Instruments DCP010515, to power the diffamp.
• The analog isolator will be either a Clare LOC110 (see appnote 107) or Vishay IL300 (see appnote 50).

A block diagram is shown below.

Rather than testing the circuit with actual electrodes on the arm, test with this circuit:

The force transducers we will be using are thin film units from AdaFruit. The transducers appear to be a force-dependent resistor.

Assignment

1. Build a circuit based on the block diagram above. You will need to do a fair amount of experimenting. For testing, use a 1 millivolt sine wave applied across the differential amplifier inputs as shown above.
2. Measure the common-mode rejection of your circuit by applying an approximately 1 volt sine wave to both inputs.
3. Build a circuit which will allow you to measure force by measuring the resistance of the thin film sensor.
4. Use the USB-6008 to connect the EMG circuit and force monitor to your computer.
   Write a matlab program to:
   1. Read the EMG output voltage and force monitor about 1000 times/second.
   2. The raw EMG should be preocessed to produce an envelope of activity:
      1. remove the mean value
      2. rectified (absolute value) or squared
      3. smoothed with a lowpass filter which has a time constant comparable to the muscle twitch time.
   3. Make a plot of processed EMG versus time and force versus time over several seconds.
5. Systematically vary the force produced by a muscle and plot the relationship between EMG amplitude and force.

1. Relationship between EMG amplitude and force. How do you interpret this biologically given that each muscle fiber is binary?
2. Observations concerning biological effects, such as electrode position or other effects.