Arthur Gariety, from Sandia National Labs doing his M.ENG here at Cornell, testing the circuit | Ben Madoff, junior electrical engineering major, biomedical engineering minor, hooked up to the EMG |
This project implements a wireless surface electromyograph that displays the signal using a television as an oscilloscope. Electromyography detects the electrical signals that the human body generates to contract muscles. Detecting very low voltages in the milliVolt range on the skin surface is not a trivial task. As shown in figure 1, EMG signals are inherently low frequency signals. The human body is a great antenna and filtering out RF and 60Hz power system noise is essential to observing the EMG signal. The course safety requirement for the final projects required that any human body connection be electrically isolated from the 120V power grid. Thus, the human side of the system must be powered using 9V batteries. Converting the analog EMG signal to digital and transmitting using a wireless transmission protocol was an effective way to electrically isolate the human. The transmitted EMG data was displayed on a television we setup to be a virtual oscilloscope. | |
Figure 1: Example EMG waveforms taken from different parts of a muscle, from C. J. De Luca, 1997, "The use of surface electromyography in biomechanics", Journal of Applied Biomechanics, 13 (2): 135-163. |
Figure 2: Wireless EMG in four steps |
Figure 3: Front end EMG amplifier, encoder, and transceiver |
Figure 4: STK500 to run the ADC and conversion to RS-232 data |
Figure 5: Back end transceiver and decoder with protoboard |
Figure 6: The differential amplifier circuitry. The leftmost chip is the MAX666CPA voltage regulator which converts the 9V battery input into a 5V output used for Vcc for the breadboard. The middle chip is the LM7111 operational amplifier which creates a virtual ground at Vcc/2. The rightmost chip is the INA106 precision gain differential amplifier |
Figure 7: IR transmission circuit |
Figure 8: IR reception circuit |
Figure 9: Top waveform: UART signal going into the MCP2120 encoder/decoder, bottom waveform: IrDA standard signal from the MCP2120 encoder/decoder |
Figure 10: Top waveform: IrDA standard signal going into the IR transceiver, bottom waveform: IrDA standard signal coming out of the IR transceiver |
Figure 11: Top waveform: IrDA standard signal going into the MCP2120 encoder/decoder, bottom waveform: UART signal coming from the MCP2120 encoder/decoder |
Figure 12: Top waveform: Overall UART transmitted 0x0F, bottom waveform: UART received 0x0F |
MCP2120 IrDA Encoder/Decoeder x 2 | SAMPLED |
TI INA106 Diff Amp | SAMPLED |
MAX666 Voltage Regulator x 2 | SAMPLED |
LM7111 Op-Amp | IN LAB |
CRYSTAL OSCILLATORS | IN LAB |
BATTERIES x 2 | IN LAB |
white board x 2 | $12 |
custom PC Board | $ 5 |
Mega32 x 2 | $16 |
ZHX1010 IrDA Trancievers x 2 | $ 7.40 |
Total = | $40.40 |