Lab 6: Post-lab
Trey Morris
801006456
ECEN 214-502
(Travis Eubanks)
10/23/2008
Procedure
Task 1: set up and test the Vernier Heart Monitor
1. Connect the adapter to the NI ELVIS board power.
2. Connect the oscilloscope to the adapter.
3. Connect the receiver to the adapter.
4. Record the results in Table 1.
Task 2: Determine the time constant of the signal from task 1
1. Freeze the signal on the oscilloscope.
2. Adjust the oscilloscope to appropriate ranges.
3. Calculate the required data for table 2.
Task 3: Mimic the heart
1. Build a simple RC circuit which has the same time constant as your heartbeat.
2. Connect oscilloscope leads to your circuit.
3. Measure the time constant on the oscilloscope.
4. Record the results in table 3.
Task 4: Compare the signals
1. The oscilloscope now has the heartbeat adapter on channel 1, the NI ELVIS voltage source
on channel 3, and the voltage across the capacitor on channel 3.
2. Adjust oscilloscope to show two periods.
3. Compare the signals.
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Data Tables
Table 1: Tasks 1
Frequency
Period
Table 2: Task 2
Maximum Voltage
Beats per minute
Voltage at 36.7%
Table 3: Task 3
Capacitance Chosen
Resistance Chosen
Time Constant with R and C Chosen
Time Constant Measured
% Difference
2
Peak to Peak Voltage
∆t between the two voltages
Sample Calculations
The only calculation required for this lab was to find the time constant of an RC circuit. I’ll use the
example from the prelab where I had to find a resistance and capacitance to give a 40ms time constant.
𝜏 = 𝑅𝐶
We know that the time constant is 40ms and we need an R and a C. With the constraints on capacitors
available, I chose 𝐶 = 10𝜇𝐹.
40𝑚𝑠 = 𝑅(10𝜇𝐹)
𝑅 = 4000Ω
Discussion
In task one I got to learn the about the time constant my heart has, and how to connect a heartbeat
sensor to anything that can sense a signal. I have a feeling a person’s aerobic health would play a part in
the time constant calculated. In task 2 I figured out the time constant of that heartbeat signal. In task 3 I
created a small RC circuit to mimic the signal that the heartbeat sensor circuit generated. It’s interesting
to see how you can mimic real life with technology. In task 4 I compared the signals generated with the
heartbeat sensor and the model circuit. This step shows the obvious problem with trying to mimic life,
imperfection. You can mimic the time constant and any measurable trigonometric signals, but trying to
mimic the noise is probably impossible.
Conclusion
In conclusion, I liked this lab. It was short and sweet. I got to use my own heart as a part of a circuit! The
circuits were not overly complicated as could have been the case. I would prefer if we didn’t have to use
the NI ELVIS software/hardware. The pre-lab was also very straight forward and applied directly to the
lab.
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