Lab 07_Instrumentation Amplifier

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Pennsylvania State University *

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6484

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Electrical Engineering

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Apr 3, 2024

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BIOMEDE 3702 LAB PROCEDURE: Instrumentation Amplifier Learning Outcomes: Students will be able to…  Build a simple instrumentation amplifier.  Understand the difference between an unfiltered signal coming from the instrumentation amplifier onlye and filtered signal coming from the ekg shield. Materials: 1. Solderless breadboard. 2. Multimeter 3. Wire box 4. Operational Amplifier IC (LMC6484/LM324) 5. Resistors (detailed in procedure) 6. Capacitors (detailed in procedure) 7. 3.5 mm Audio Jack Connector 8. Arduino 9. Power Supply Module (black circuit board w/ breadboard connectors) 10. Oscilloscope a. Two gray lead BNC hook probes. 11. Function generator a. One black lead BNC connector with red/black alligator REMINDER - Setting up your Power Supply: You will be using two sources of power for this lab (unlike past labs). You will be using the 3.3/5 V Power Supply Module and the Arduino. The power supply module will connect to your breadboard and supply +5 V, while the Arduino will supply -5 V (by plugging the GND into the IC and 5V into the breadboards ground). 1. Important Step : It is good practice to always double check that your sources are outputting ± 5V whenever you hook it up to your breadboard. Use a multimeter to verify the output. 1

BIOMEDE 3702 Figure 3: Options for connecting the Arduino and power module. Experiment #1: Connecting the Instrumentation Amplifier 1. Review the Oscilloscope and Function Generator tutorials. You will use the function generator to create signals, and the oscilloscope to measure signals. 2. Build the following voltage divider circuit (Figure 1 – same as in your prelab) that takes a 10Hz sinusoidal input signal of 250mV peak-to-peak (V pp ). NOTE: Set CH1 and CH2 to 10x amplification and adjust the function generator output (-20 dB pressed) Figure 1: Voltage Divider 3. Use the oscilloscope to simultaneously measure Vin+ (channel 1) and Vin- (channel 2) waveforms of your voltage divider. Verify that they match the values you determined in your pre-lab. NOTE: If voltage drops when connected to voltage divider, increase the voltage to match the calculated Vin+ and Vin-. 4. Build the instrumentation amplifier circuit following the schematics on the next page ( Figure 7 ). For this experiment you will be using the Vin+ and Vin- from the voltage divider. This is to ensure your circuit 2

BIOMEDE 3702 is properly connected. Hint: Connect the power supply module first, it will take up some space. Also, your - 5 V will come from the Arduino (connect GND to pin 11 and 5 V to the breadboards ground. This will allow you to supply -5 V to your op amps. 5. Measure the output signal of your amplifier circuit with the oscilloscope. Compare this measurement to the expected output voltage you calculated in the pre-lab. Is it the same? 6. SHOW THE INSTRUMENTATION AMPLIFIER CIRCUIT TO A TA/INSTRUCTOR BEFORE PROCEEDING! Figure 2: Pin diagram for IC LMC6484 Quad Op Amp 3

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BIOMEDE 3702 Figure 3: Instrumentation amplifier circuit schematic for the lab circuit. 4

BIOMEDE 3702 Experiment #2: Acquire your own ECG 1. Did you have an instructor check your circuit from part 1? WARNING: If you don’t have your device wired correctly, you might get an unpleasant shock! Now you will record your ECG from this instrumentation amplifier circuit and compare it to the EKG shield amplifier. You will do this by recording your signal in the oscilloscope coming from both sources. Setting Up the Instrumentation Amplifier 2. Test your circuit-built instrumentation amplifier using the ECG signal from one subject in your lab group, by: a. Turn off and completely remove your function generator, and voltage divider from your circuit . You will be supplying the signal (not the voltage divider). b. Plug the 3.5 mm Audio Jack Connector (red audio jack board) to the board (Figure 4). c. You will only be using the connections tip, ring 1, and ring 2. Tip will connect to Vin+ , Ring1 will connect to Vin- , and Ring2 will connect to GND . 3. Connect electrodes using the Lead I configuration (RA – Blue, LA – Red, RL – GND). Reminder: RA – Right Arm / RL – Right Leg Figure 4: 3.5mm Audio Jack Connector. 4. Connect the oscilloscope probe (either channel) to the instrumentation amplifier output (Pin 1). 5. Save an image of your acquired ECG signal from your oscilloscope. Acquiring a Signal from ECG Shield 6. Disconnect the circuit-built instrumentation amplifier. 7. Connect the EKG using the Arduino ( remember this shield is 3.3 V, not 5 V ). 5

BIOMEDE 3702 8. Use a wire to connect the oscilloscope probe to Output (and another to connect to ground). 9. Save an image of your EKG signal from your oscilloscope. THE POINT This is the culmination of all our efforts in the circuit labs. To finally built the last piece of the puzzle in order to understand signal acquisition on any biopotential-related device. The combination and arrangement of these op amps and resistors allow the instrumentation amplifier to have high input impedance, high common-mode rejection ratio, and low DC offset. Using only these we are able to get the most basic biopotential signals such as ECK and EMG. Learning Outcomes: Students will be able to…  Build a simple instrumentation amplifier.  Understand the difference between an unfiltered and filtered signal. 6

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BIOMEDE 3702 POST LAB: Instrumentation Amplifier 1. Take a screenshot of oscilloscope display of your ECG coming through the instrumentation amplifier . Identify and label each ECG wave in the signal to the best of your ability. (5 points) Note: Make sure units and labels are clear and legible. 2. Take a screenshot of oscilloscope display of your ECG coming through the EKG shield . Identify and label each ECG wave in the signal. (5 points) Note: Make sure units and labels are clear and legible. 3. Compare each ECG output signal. Did you noticed any differences? Any features ( waves or intervals) missing in either of your signal? What do you think might be causing this? Explain Hint: Compare the Instrumentation Amplifier Circuit (Figure 7) with the EKG Shield Circuit (https://cdn.sparkfun.com/datasheets/Sensors/Biometric/AD8232_Heart_Rate_Monitor_v10.pdf ). Do both have capacitors that are filtering, are there multiple stages (or steps) in both? (5 points) 4. What is the overall gain (in dB) of the instrumentation amplifier you built? Use the resistor gain equations in Figure 7 . SHOW YOUR WORK (3 points) 5. If R 1 ( Figure 7 ) is changed to 1kΩ, how will that affect the overall gain? SHOW YOUR WORK 7

BIOMEDE 3702 (2 points) Challenge Question 7: Note: Challenge questions in post-labs are bonus and optional. These questions are designed to be challenging. 1. Set five minutes at the end of this report (with a timer) to catch your breath and reflect on what you have learned. Then give yourself a pat on the back for a job well done! 8