4F04_EMG_Lab

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Jan 9, 2024

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Laboratory 2 Introduction to differential amplifiers and design of a bio-instrumentation amplifier for EMG Richard Fanson, Alexandru Patriciu, Hubert de Bruin, Laura Pravato, Zachary DeMelo, Kyle Molinari Scope of the lab 1. Introduce the fundamental properties of differential amplifiers 2. Present the measurement of common mode gain; CMRR; CMR 3. Design a multistage bioinstrumentation amplifier for EMG 4. Acquire EMG data 5. Perform simple analysis of EMG data Before the lab 1. Review the computation of CMRR 2. Download and read the documentation for the instrumentation amplifier LT1920 3. Download and read the documentation for the operational amplifier TLC2274 4. Review the passive and active filters theory (use the 4BD4 cheat sheets if you are not familiar with circuit theory) 5. Review the EMG and muscle fatigue concepts. Do a literature search and find the definitions for isometric contraction and dynamic contraction. 6. Design a multistage bioinstrumentation amplifier for EMG signals. The amplifier should have the following stages : Figure 1: Block diagram of a bioinstrumentation amplifier suitable for EMG measurements 7. Specifications • Note: You are required to use 1% resistors with standard values. • Headstage - Use a differential amplifier LT1920. Gain of 50. • HP Filter & Second Amplification Stage – passive filter, use capacitor value 330 nF and compute proper resistor value. • Low pass filter – use a Sallen - Key topology to implement a second order Tchebyscheff filter with 1dB pass band ripple. Use capacitors C1 = 33nF; C2 = 330nF; verify that C2 value is properly chosen; compute the resistors values. Pre-Lab Tasks:

• Calculate required resistor and capacitor values for each stage of the circuit (see formulas below) and use the list of available resistors to find the closest match • Available resistors in lab: 499ohm 1.00k 1.27k 2.61k 5.49k 10.0k 11.3k 18.7k 22.1k 26.1k 30.1k 36.5k 48.7k 59.0k 66.5k 71.5k 100k 113k 215k 357k 402k 475k 562k 715k Headstage: Using LT1920 differential amplifier Calculate the value of the resistor R G that would result in a gain of 50 Formula: R G = 49.4kΩ/(G – 1), G = Gain = 50 Rg=________ High Pass Filter and 2 nd Amplification Stage: Passive filter. Use 330nF capacitor and compute the proper resistor value to get a cutoff frequency of 10Hz.

R1= ________ Find a pair of resistors that will result in a gain of G=20 for this stage. (Note that this should brings the overall gain to 1000 since 50*20=1000) R2= ________ R3= ________ Low Pass Filter: -Sallen-Key topology -Second order Tchebysheff low pass filter with 1dB passband ripple -Use C1=33nF, C2=330nF You can use the given cheat sheet to find formulas and use the table in the “Active Filter Design” pdf to find the appropriate filter coefficients a1 and b1 ( For a 2 nd order Tchebysheff filter with 1 dB passband ripple: a1=1.3022 and b1=1.5515). Use the formula to calculate the resistor values:

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R1= ________ R2= ________ Have TA confirm resistor and capacitor values During the lab A. Measure the CMRR of the headstage differential amplifier. Do not build the high pass filter, second amplification stage, and low pass filter for this part. 1. Set the input as shown in Figure 1. (Find the signal generator labelled “Gen Out” on the oscilloscope and set it to a sine wave with a frequency of 100Hz and amplitude of 3Vpp). This will be your input common mode voltage (V in CM ). 2. Use the oscilloscope cursors to measure the output (V out CM ) and calculate the common mode gain G CM = V out CM / V in CM . a. Click the “trigger” button, then select “trigger type” and set the source to the input channel (“1” or “2”). Set the trigger type to “edge” and the slope to “rising”. Then press in the trigger knob to set the trigger to 50% of the waveform amplitude b. Adjust the vertical scale of both the input and output channels so that you can see the sine waves (the output channel will be very noisy, but try to take measurements from the middle of the sine wave peaks and troughs) c. Click the “cursors” button, set the source to the channel connected to the output of the headstage (either “1” or “2”). Then select Y1 as the cursor and use the knob beside the cursors button to move the line to the bottom of the output waveform. Then select Y2 as the cursor and use the knob beside the cursor button to move the line to the top of the output waveform. At the bottom of the screen it should show the distance between the cursors (which represents V out CM ) as ΔY(1) or ΔY(2). Use this to calculat e G CM. 3. Calculate the common mode rejection ratio (CMRR = G Diff /G CM , where G Diff =50) and the common mode rejection in decibels (CMR=20log10(CMRR))

Figure 1 : Schematic for measuring the common mode gain B. Build circuit and check gain frequency response 1. Build the designed circuit using the ECE-Biomed Lab. 2. Bypass the second amplification stage so that the overall gain will be 50 to allow a 10 mV p-p test signal from the signal generator). a. Include all other stages. The circuit should be: Headstage (gain of 50), high pass filter (10Hz cutoff frequency), low pass filter (500Hz cutoff frequency). The second amplification stage can be bypassed by removing R3 and replacing R2 with a wire (short circuit) as shown below. 3. Connect the circuit to the signal generator and to the oscilloscope as in Figure 2.

Figure 2: Connections for performance evaluation and tuning 4. Check the gain of the circuit for frequencies between DC (1Hz) and 600Hz. a. Press “Wav Gen” and set the input signal to a sine wave with a frequency of 1Hz, amplitude of 10mVpp, and offset of 0V. For now, set the horizontal scale to 200ms/div using the knob labelled “horizontal” and make sure both channels are being displayed (buttons labelled “1” and “2” should both be lit up. If not, press them to turn them on). b. Make sure the oscilloscope is being triggered on the output signal. This can be done by clicking the “trigger” button, then “trigger type”, then setting the source to “1” or “2” depending on which channel is connected to the output. Set the trigger type to “Edge” and the slope to “Rising”. c. Push the trigger knob to set it to 50% of the waveform amplitude. d. Press the “Meas” button to access measurement settings, then select “Clear Meas” followed by “Clear All”. Add a new measurement by selecting the source channel that is connected to the output (“1” or “2”) then select “Ampl” as the type. Press “Add Measurement” and the peak -to-peak amplitude of the output signal will now be displayed at the bottom of the screen. e. Click “Wav Gen” to go back to the wave generator settings. Fill out the table below by setting the signal generator amplitude (Vin) to 10mVpp and adjusting the frequency from 1Hz to 600Hz while recording the peak-to-peak amplitude (Vout). f. When you change the frequency, you may need to re-scale the vertical and horizontal axes for the output channel. This can be done by using the knobs labelled “vertical” for channels “1” and “2” and the knob labelled “horizontal” at the top. 5. Plot gain vs. frequency for signals between 1Hz and 600Hz. Frequency Vin Vout G=Vout/Vin 1Hz 10Hz 50Hz

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100Hz 200Hz 300Hz 400Hz 500Hz 600Hz 1000Hz 1500Hz 2000Hz C. Acquire EMG signal 4. Reconnect the second amplification stage to bring the overall gain to 1000. 5. Add the isolation amplifier at the output of the bioinstrumentation amplifier. 6. Place the two measuring electrodes spaced about 1 inch apart on the belly of the biceps brachii. Place a third ground (reference) electrode on the arm lateral to the measuring electrodes. Refer to the image below:

7. Connect the measuring electrodes to the bio-instrumentation amplifier input. Make sure to twist the leads to minimize 60Hz noise. 8. Plug the DAQ module into the computer and connect the output of the isolation amplifier to the DAQ input AI0. Then open MATLAB and use the "Analog Input Recorder” app to start recording data. 9. Save about 5 sec of EMG data while the muscle is resting. 10. Save about 5 sec of EMG data for a modest isometric contraction. 11. Save about 10 sec of EMG for a series of slow dynamic contractions using a 10 lb barbell. 12. Save about 10 sec of EMG for a series of rapid dynamic contractions using a 5 lb barbell. 13. With your arm in a 90-degree position and wrist supine, begin recording data with no weight (weight of hand and forearm). Then successive weights each 3 seconds, use 5lb, then 10lb, then 15lb, then 20lb. This is to compare EMG magnitude to lifting force. 14. Hold a 15 lb barbell weight in the palm of your hand, keeping arm bent at 90 degrees, with forearm parallel to the ground. Record at least a minute of data to examine the effects of fatigue. 15. If you have time, untwist the electrode leads and repeat one of the previous EMG data collection steps while holding the + and – leads away from each other. + + - gnd

Ensure you have access to all pictures/data collected before leaving the lab (eg: save data to USB, upload to Teams/OneDrive, email it to yourself, etc.) After the lab 1. Prepare a report that includes: – A summary of the design; what does each stage do? Include circuit schematics with values labeled. [2] – A3: Calculate common mode gain, CMRR, and CMR (dB) [3] – B5 : Plot of gain vs frequency. [2] – B5: Explain the shape of the gain vs frequency plot and how it relates to filter stages in the circuit design. [2] – C10 : The time domain and frequency domain plot for an isometric contraction (i.e. The EMG signal vs time and the Fourier transform from 0 to 500 Hz) [3] – C11 : The time domain raw and enveloped data plots (using a 2 Hz low pass filter) and the frequency domain plot for the raw slow dynamic contractions. [4] – C12: The time domain raw and enveloped data plots (using a first the 2 Hz low pass filter and then the 10 Hz LPF) and the frequency domain plot for the raw fast dynamic contractions. Are the frequency domain plots similar for C10, C11 and C12 ? [4] – C13: Break the recording into the sections where the different weights were applied. Rectify each section (abs value) and compute the average magnitude. Plot the relationship between weight vs magnitude. You should have 5 points to plot. Consider no weight as 0 lbs although the magnitude will not be 0. Describe the relationship (positive, negative, linear, exponential, etc.). .). [4] – C14 : Break the minute plus of data into 10 second intervals. Compute the RMS and centroid frequency (MATLAB function) value for each interval and plot over time. Describe any changes you see. [3] – C15: Explain why twisting the electrode leads (wires) reduces 60Hz noise in the signal. [1]

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– Always include your code in your report! Lab reports are due at 11:59 pm 1 week after your lab session, but you must submit a preliminary report 2 days before the due date (the preliminary report will not be marked).