1. Real-Time Measurement of Prehensile EMG signals
Master Thesis
Saksit Siriprayoonsak
Supervisor: Marko Vuskovic
Department of Computer Science
San Diego State University
August 24, 2005
Copyright 2005 by Saksit Siriprayoonsak

2. Copyright 2005 by Saksit Siriprayoonsak
Contents
Introduction
EMG Overview
Apparatus for EMG Measurement
Implementation of EMG Capture Program
Experimental Results
Conclusion
Copyright 2005 by Saksit Siriprayoonsak

3. Multifunctional Prosthetic Hand Control
A research in Robotics Laboratory, SDSU
Copyright 2005 by Saksit Siriprayoonsak

4. Copyright 2005 by Saksit Siriprayoonsak
Object of Thesis
Main purpose:
Design and develop hardware and software for measuring surface EMG signals from real human muscles in real-time.
Immediate application:
To control the existing SDSU multifingered robot hand.
Hardware-brings the develop of EMG Amplifier
Software-brings the develop of EMG Capture
Copyright 2005 by Saksit Siriprayoonsak

5. Copyright 2005 by Saksit Siriprayoonsak
EMG Overview
EMG – Electromyography
Electromyography measures the electrical impulses of muscles at rest and during contraction.
Amplitudes of EMG signal range between 0 to 10 mV (peak-to-peak) or 0 to 1.5 mV (rms).
Frequency of EMG signal is between 0 to 500 Hz.
The usable energy of EMG signal is dominant between Hz.
Source:
Copyright 2005 by Saksit Siriprayoonsak

6. Amplification of EMG Signals
Factors to be considered:
Boost signal to TTL standard level (± 5 V.)
Enough gain
Noise/Artifact problem
Filter, stability of electrodes attached to skin, proper grounding
DC offset or bias problem
Bias adjustment
Power consumption
Consume less current
-Enough Gain
Copyright 2005 by Saksit Siriprayoonsak

7. EMG Measurement Stages
Copyright 2005 by Saksit Siriprayoonsak

8. EMG Amplifier: Electrode and Extension
Stereo phone wire with 3 conductors
Positive input to preamplifier
Negative input to preamplifier
Shield as the input of body reference circuit
Velcro strap for securing the electrode to the skin
Copyright 2005 by Saksit Siriprayoonsak

9. EMG Amplifier: Electrode and Extension (cont.)
Plastic piece and snap on for holding electrode elements
Dimension of 1 inch between electrode contacts
4 electrode extensions and 1 body reference extension
Total of 9 electrode contacts
Copyright 2005 by Saksit Siriprayoonsak

10. EMG Amplifier: Power Supply
Dual Supply
Positive Power Supply
Negative Power Supply
Two 9-volt batteries connected in series
Capacitors provide stability of electrical current.
Power Supply Unit Circuit
Copyright 2005 by Saksit Siriprayoonsak

11. EMG Amplifier: Preamplifier
Industry standard instrumentation amplifier op-amp (INA2128)
Accuracy: providing high bandwidth at high gain and output offset current
Differential amplifier circuit with 2 inputs
High gain to boost the EMG signals
Body Reference Circuit or Feed Back (OPA2604)
Copyright 2005 by Saksit Siriprayoonsak

12. EMG Amplifier: Preamplifier (cont.)
BURR-BROWN INA2128 Application Information
Copyright 2005 by Saksit Siriprayoonsak

13. EMG Amplifier: Preamplifier (cont.)
Preamplifier with Body Reference Circuit (1 channel)
Gain Equation:
Find RG at Gain = 1,000:
Find Gain at RG = 22 ohm:
Copyright 2005 by Saksit Siriprayoonsak

14. EMG Amplifier: Averaging Body Reference Circuit
Common body reference circuit for 4 channels
Using summing amplifier circuit and sign changing circuit
Sign Changing Circuit
(Inverting Amplifier Circuit)
Inverting Summing Amplifier Circuit
For independent R1, R2, R3, and R4:
For independent R1, and R2:
For R1= R2= R3= R4:
For R1= R2:
Copyright 2005 by Saksit Siriprayoonsak

15. EMG Amplifier: Average Body Reference Circuit (Cont.)
Common Body Reference Output:
Copyright 2005 by Saksit Siriprayoonsak

16. Copyright 2005 by Saksit Siriprayoonsak
EMG Amplifier: Filter
Suppress noise that has been amplified by the preamplifier
Help to sink any DC current that cause bias to the output
Select particular signal frequency range
Use RC High Pass Filter of 12 Hz
Copyright 2005 by Saksit Siriprayoonsak

17. EMG Amplifier: Filter (cont.)
RC High Pass Filter
Cutoff Frequency of 12Hz
RC High Pass Filter
Cutoff Frequency:
Cutoff Frequency of 12 Hz:
Copyright 2005 by Saksit Siriprayoonsak

18. EMG Amplifier: Amplifier and Bias Adjustment
Provide abilities to amplify and adjust reference level of output signals
Individual amplifier and bias adjustment unit for each channel
Use Non-Inverting circuit for amplifier unit
Use Voltage Follower Offset Adjustment circuit for bias adjustment unit
Provide Gain of 21 times
Provide Offset of ± 9 volts
Copyright 2005 by Saksit Siriprayoonsak

19. EMG Amplifier: Amplifier and Bias Adjustment (cont.)
Non-Inverting Amplifier Circuit
Non-Inverting Output:
Copyright 2005 by Saksit Siriprayoonsak

20. EMG Amplifier: Amplifier and Bias Adjustment (cont.)
Amplifier Circuit with Gain Adjustment
Amplifier Gain:
At :
At :
Copyright 2005 by Saksit Siriprayoonsak

21. EMG Amplifier: Amplifier and Bias Adjustment (cont.)
Case 1: at 0% of
: (
ohms;
volts )
Offset Adjustment for Voltage Follower
Case 2: at 50% of
: (
ohms;
volts )
Output of the circuit:
Case 3: at 100% of
: (
ohms;
volts )
Copyright 2005 by Saksit Siriprayoonsak

22. EMG Amplifier: Amplifier and Bias Adjustment (cont.)
Case 1: at 0% of
: (
ohms;
volts )
Bias Adjustment Circuit
Case 2: at 50% of
: (
ohms;
volts )
Output of the circuit:
Case 3: at 100% of
: (
ohms;
volts )
Copyright 2005 by Saksit Siriprayoonsak

23. Copyright 2005 by Saksit Siriprayoonsak
A/D Interface Card
NI 6220 M-Series Multifunction DAQ
Clock Speed: 8 Hz, up to 1 MHz
Analog Input Resolution: 16 bits
Number of Analog Input Channels: 8
Copyright 2005 by Saksit Siriprayoonsak

24. Final Product Assembly
Netlist,
Circuit designed and tested on breadboard
Schematic created by Multisim8
PCB layout created by Ultiborad7
Copyright 2005 by Saksit Siriprayoonsak

25. Final Product Assembly (cont.)
A schematic diagram is drawn using Multisim8.
Netlist contains all circuit connections.
Netlist is transferred to Ultiboard7 for PCB layout.
PCB is a double layer (top copper layer and bottom copper layer)
Through holes connect between 2 layers.
Netlist is database.
Copyright 2005 by Saksit Siriprayoonsak

26. Final Product Assembly (cont.)
PCB shipped by the manufacturer
Placing the battery on the side, weight balance
Copyright 2005 by Saksit Siriprayoonsak

27. Final Product Assembly (cont.)
PCB after soldering
Copyright 2005 by Saksit Siriprayoonsak

28. Calibration Procedure
Each channel is individually calibrated.
Input is equal to output (100 mV.)
If an arbitrary gain is needed, the output is desired gain value multiplied by input.
Copyright 2005 by Saksit Siriprayoonsak

29. Copyright 2005 by Saksit Siriprayoonsak
EMG Capture
Provides 3 play modes: Real-Time, Record, and Playback mode.
Able to save and open EMG data to/from file.
Display features:
Voltage scales
Time scales
Readout of exact values
Copyright 2005 by Saksit Siriprayoonsak

30. EMG Capture: User Interface
Left side for control. Right side for adjust display
Copyright 2005 by Saksit Siriprayoonsak

31. EMG Capture: Main Parameter Subpanel
Working with Real-Time mode and Record mode.
Maximum Buffer Size (Samples per Channel)
Sampling Rate (Hz)
Buffer size has unit in sampler/channel.
Sampling Rate has unit in Hz.
Copyright 2005 by Saksit Siriprayoonsak

32. Copyright 2005 by Saksit Siriprayoonsak
EMG Capture: Play Mode
Copyright 2005 by Saksit Siriprayoonsak

33. EMG Capture: Real-Time Mode
START
Start real time mode
Stop real time mode
Freeze output display for examine interesting segments or save the data
Resume real time mode
Save data in buffer to file
STOP
Pause
Resume
Save
Copyright 2005 by Saksit Siriprayoonsak

34. EMG Capture: Record Mode
Start to Record the signals in specific time range in seconds.
Save the data to file
START
Save
Copyright 2005 by Saksit Siriprayoonsak

35. EMG Capture: Playback Mode
- Open EMG data file (.emg)
Open
Standard window open dialog
Copyright 2005 by Saksit Siriprayoonsak

36. EMG Capture: Voltage Scale
Voltage scale is independent for each channel.
Alternative voltage scales:
200 mV/Div.
500 mV/Div.
1 V/Div.
2.5 V/Div.
5 V/Div.
Copyright 2005 by Saksit Siriprayoonsak

37. EMG Capture: Time Scale
All channels use the same time scale
Alternative time scales:
1 mSec/Div.
5 mSec/Div.
10 mSec/Div.
50 mSec/Div.
100 mSec/Div.
200 mSec/Div.
400 mSec/Div.
Copyright 2005 by Saksit Siriprayoonsak

38. EMG Capture: Time Slider
Scroll time slider to view data from beginning to the end.
The numbers on the left and right corner correspond to the time stamp of the first and the last sample shown on the output display screen.
‘5.416’ is 5 seconds and 416 milliseconds.
Copyright 2005 by Saksit Siriprayoonsak

39. Copyright 2005 by Saksit Siriprayoonsak
EMG Capture: Readout
Read extract value at pink vertical line
Need not to compute the value of scale
Unit: Time (sec) , Voltage (V)
Copyright 2005 by Saksit Siriprayoonsak

40. EMG Capture: Output Display
Displays 4 channels
Voltage: 4 divisions
2 positive divisions
2 negative divisions
Time: 15 divisions
Maximum Display:
±10 volts with 5 volts/Div.
6 seconds with 400 mSec/Div
Copyright 2005 by Saksit Siriprayoonsak

41. EMG Capture: Status Bar
Guide user through the usage
Display important message
eg. Number of samples that went into the buffer.
Copyright 2005 by Saksit Siriprayoonsak

42. Copyright 2005 by Saksit Siriprayoonsak
EMGC Implementation
Developed by using Microsoft Visual C++ tool
GUI developed with MFC (Microsoft Foundation Class) library
Runs on Windows 2000 machine which has A/D interface card installed
A/D Interface Card: Multifunction Data Acquisition (DAQ), M-6220 series from National Instrument Company
Copyright 2005 by Saksit Siriprayoonsak

43. EMGC Implementation: Output Buffer Structure
struct SOutputData {
int output_ii; //Iteration start from 0
double time; //Time stamp in Second
double volt1; //Voltage value for CH1, CH2, CH3, and CH4
double volt2;
double volt1; };
CArray <SOutputData, SOutputData> dumpDataArray;
CArray class from MFC Library used to store input signal data.
CArray can dynamically shrink and grow if necessary.
Copyright 2005 by Saksit Siriprayoonsak

44. EMGC Implementation: Creating Voltages and Time Scales
//For Calculation
double voltScaleSet[5] = {5.0, 2.5, 1.0, 0.5, 0.2}; //unit in volt/div
//For Screen Display
CString voltScaleStrMap[5] = {“5 Volt/Div”, “2.5 Volt/Div”,
“1 Volt/Div”, “500 mVolt/Div”, “200 mVolt/Div”};
Use spin control to select the scales.
Spin control increase/decrease spin value by a specific number of steps.
Use spin value as the index of scale array.
Copyright 2005 by Saksit Siriprayoonsak

45. EMGC Implementation: Draw Grid for Graph Output
Use CDC class (Class Device-Context object) to draw output on the screen.
The CDC class is a class from the MFC library.
CDC provides various kinds of drawing functions
(working with drawing tool, converting the coordinates, drawing rectangles, drawing circles, drawing text, changing the color)
CDC provides various kinds of drawing functions such as working with drawing tool, converting the coordinate, drawing rectangle, drawing circle, drawing text, or changing the color.
Copyright 2005 by Saksit Siriprayoonsak

46. EMGC Implementation: Draw Grid for Graph Output (cont.)
private:
//Variables for drawing output
int _maxTimeDiv; //Max number of divisions to display on Output-Panel
int _maxVoltDiv; //time axis = 15 divisions
//volt axis = 4 divisions (2 positive Divs)
// (2 negative Divs)
int _ptsPerDiv; //How many points are there in 1 division.
//1 point = 0.1 milimeter
//Default 100 points = 1 division is 1 cm wide
// ** Base on: Display Resolution= 1024 x 768
int _maxDrawPtsX; // _maxTimeDiv*_ptsPerDiv, Max Drawing Point for // time
int _maxDrawPtsY; // _maxTimeDiv*_ptsPerDiv, Max Drawing Point for volt
//Default x=1500, y=400
Copyright 2005 by Saksit Siriprayoonsak

47. EMGC Implementation: Draw Grid for Graph Output (cont.)
Copyright 2005 by Saksit Siriprayoonsak

48. EMGC Implementation: Drawing Graph Output
The output can be drawn by using (x,y) coordinate to specify position to draw.
Function CEMGCDlg::voltToDC()
Function CEMGCDlg::voltToDC()
Copyright 2005 by Saksit Siriprayoonsak

49. EMGC Implementation: Saving Data Buffer To File
File Extension (‘.emg’)
Header line contains
Sampling rate (HZ)
Record time period (sec)
Data speparate by a ‘space’.
Each record separated by a ‘carriage return’ (put in front).
Copyright 2005 by Saksit Siriprayoonsak

50. EMGC Implementation: Read File To Data Buffer
Read header file
Sampling rate -> computes sampling period
Record time period -> verifies the data file (completed or in completed)
Store data in buffer (dumpDataArray)
struct SOutputData {
int output_ii; //Iteration start from 0
double time; //Time stamp in Second
double volt1; //Voltage value for CH1, CH2, CH3, and CH4
double volt2;
double volt1; };
CArray <SOutputData, SOutputData> dumpDataArray;
Copyright 2005 by Saksit Siriprayoonsak

51. Copyright 2005 by Saksit Siriprayoonsak
Results
Our EMG Amplifier
ME3000 Muscle Tester
ME3000-Muscle Tester Manufactured by Maga Electronics Ltd. Displayed by using program VIEW version2.
A comparison of cylindrical grasp recorded from our EMG amplifier and ME3000.
Copyright 2005 by Saksit Siriprayoonsak

52. Copyright 2005 by Saksit Siriprayoonsak
Results (cont.)
Our EMG Amplifier
ME3000 Muscle Tester
ME3000-Muscle Tester Manufactured by Maga Electronics Ltd. Displayed by using program VIEW version2.
A comparison of preshaping of cylindrical grasp recorded from our EMG amplifier and ME3000.
Copyright 2005 by Saksit Siriprayoonsak

53. Copyright 2005 by Saksit Siriprayoonsak
Conclusion
This thesis presents an implementation of EMG amplifier device and EMG Capture program.
Major problems were:
To reduce noise, moving artifacts, system grounding and DC bias.
Problems solved through:
Proper choice of discrete components (resistors, capacitors, and ICs)
Proper design of circuitry
Final implementation of the device using PCB technology
Systematic experimentation with the prototype (implemented on a breadboard)
Extensive testing of the device after implementation and executing final corrections.
Copyright 2005 by Saksit Siriprayoonsak

54. Copyright 2005 by Saksit Siriprayoonsak
Future Work
EMG amplifier
Smaller size of the housing unit.
Eliminate electrode extensions
EMG Capture program
Add print feature
Add properties feature for changing system parameters
Improve drawing ability
Copyright 2005 by Saksit Siriprayoonsak