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Datasheet for Lab 15: Frequency Selective Circuits Name(s): _______________________ Lab Kit: __________ Date: ________________________ Approximate time to complete (to 0.1 hours) :___________ Part 0. Prelab – Watch the lab overview video, and in class Q&A Just do parts 1, 2 and 5 Part 1. Constructing the Heartbeat Detector Circuit Table I. Photocell Voltage Divider Measurements Measurement Condition Voltage at Midpoint of Divider Finger on top of LED/Photocell No Contact with LED/Photocell Table II. Op-amp verification with 3.3k input and 1k feedback resistors Measurement Condition Vin - Voltage at Midpoint of Divider Vout - Voltage at op-amp output Expected Vout (-0.3Vin) Reasonably close? Finger on top of LED/Photocell No Contact with LED/Photocell Table III. Pulse Measurement for each lab partner Subject Name Beats per second Beats per minute 1 Lab 15 Frequency Selective Circuits Screen Capture I. Paste a screen capture here of your WaveForms scope display showing a heartbeat waveform from one of the lab partners above, with the frequency measurement also showing: Photo I. Paste two photos here of your breadboard showing your circuit – a wide view shot and a closeup of your breadboard. Part 2. Adding a Low-Pass Filter Table IV. Description of components used to make the Low-Pass Filter List the value of components and how they are arranged to make a LPF with wo of 20 Rad/sec List components used for your LPF How are these components to be arranged? Calculated wo using nominal values Screen Capture II. Paste a screen capture here of your WaveForms scope display showing a heartbeat waveform from one of the lab partners above, with the frequency measurement also showing: Photo II. Paste a closeup shot of the LPF portion of your circuit here: Part 3. Determining the Overall Frequency Response –SKIP THIS 2 Lab 15 Frequency Selective Circuits Table V. Thevenin Resistance at a-b for Photocell circuit above A Thevenin Model Thevenin Resistance Table VI. System response H(w) System Response for H(w) a) Op-amp circuit b) Low-pass filter c) Product of (a)(b) Table VII. Estimate total H(w) at different frequencies f w = 2pi(f) Calculated |H(w)| Measured |H(w)| - in Part 4 0 Hz 0.1 Hz 1 Hz 2 Hz 3 Hz 10 Hz 100 Hz Plot the magnitude of H(w) – both Calculated and Measured vs f for the data above. Part 4. Measuring the Overall Frequency Response – SKIP THIS Add measured gain to table VII above. Postlab Questions 1. How clean was your signal compared to the photo of the heartbeat waveform provided on the lab handout? 3 Lab 15 Frequency Selective Circuits 2. How steady was the beats per second measurement? How much did it vary from reading to reading? 3. How do filters help with obtaining a clean display of the heartbeat waveform? 4. Did the display improve when you added the LPF to the circuit? 5. How well did the theoretical system response magnitude agree with the measured magnitude at the frequencies you examined? 6. Looking at the amplitude of the heartbeat waveforms from your results above, and the gain of the circuit at 1Hz that you calculated or measured, what do you expect the amplitude is of the voltage coming off the voltage divider? 7. In your own words, how does this circuit show a person’s heartbeat? 8. Can you think of any ways to improve either the circuit itself or the model we are using to understand how it works? Are there any areas that you are unclear about in terms of how the circuit is performing? 4