Download Lab-15-datasheet-new

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