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Lab 6 Report Coy Coburn & Kevin Bradshaw ECEN 214, Section 506 TA: Amir Tofighi Zavareh Due date: March 25, 2014

Procedure Task 1 –Set up and test the Vernier Heart Monitor ● The first and most delicate part of the Heart Monitor was the NI ELVIS-BTA adapter. This piece was place first carefully and then connected to the 5 Volt power supply. After everything was grounded and the wireless receiver was connected, the circuit was double checked and tested. ● The system used measures heart rate by small bars that are held onto firmly using both hands. This produced a signal on the Tektronix oscilloscope. In order to read the data correctly, three beats of the signal were positioned on the screen and measured by the individual cursors. The frequency, period, number of beats per minute, and peak to peak voltage were measured and recorded in Table 1. Figure 1 is a sample of the signal measured.

Figure 1 Task 2 - Determine the Time Constant of the Signal ● The signal on the Tektronix oscilloscope was then frozen on screen to calculate the peak to peak voltage. Then, the time difference between the two voltage levels were recorded. These values were recorded in Table 2. Figure 2 is a sample of the signal measured.

Figure 2 Task 3 - Build a circuit to mimic the Decay Signal from the Heart Monitor ● The RC circuit in Figure 3 was built using capacitor and resistor values that are similar to the time constant measured by the heartbeat of the student in Task 1. The values of these circuit components are listed in Table 3.

Figure 3: RC Circuit ● In order to complete this circuit, the original signal from the heart monitor was connected to the input of the virtual instrument built in Prelab 6. The output of this virtual instrument was connected to the input of this circuit.

● Probes across the capacitor and the source were used to display two different waveforms on the oscilloscope. The time constant was measured across the capacitor and Table 3 was completed. Figure 4 is a sample of the signal measured.

Figure 4 Task 4 - Compare the Vernier Signal with the mimicked signal ● The original vernier signal was compared on the same screen with the signal created by the RC circuit. Figure 5 is a sample of the signals measured.

Figure 5

Calculations In order to convert from frequency to beats per minute, this simple formula was used: Hertz = BPM / 60 To find the time constant of an RC Circuit, 36.7% of the peak to peak voltage was calculated: V * (0.367) = RC Where RC is the time constant. Building an RC circuit that mimicked the original RC circuit involved working backwards by knowing the time constant. Having only few resistors and capacitors to choose from, these values were multiplied to find a value closest to the original Vernier signal. The percent difference between the RC used and the time constant was determined by: ( RCOriginal - RCConstructed ) / RCOriginal

Discussion During task 1, we saw the transducer signal generated from the heart rate onto the screen, which when compared to the figure given in the lab packet, did match the wanted result. Task 2 saw the calculation of the time constant of said heartbeat signal and recorded. During the tasks 3 and 4, a RC circuit signal was implemented and attempted to mimic the original transducer signal. While the two did have some inconsistencies like peak and period, the two overall did seem to behave similarly. The square function did show some discrepancy though. Conclusion In this lab, we had examined a real life signal and explored some of the parameters of that signal. In order to do this, we were assigned to utilize a Vernier Heart Rate Monitor. This transducer was able to read the frequency of our heartbeats as well as produce a signal that was to be examined in the time domain. At the end of this lab, we are now more familiar with how a signal across time relates to the frequency of a signal. We also observed a signal and utilized a simple RC circuit to approximate the signal coming from the transducer. The experiment revealed how the RC circuit can be made to decay and behave much like a person’s heartbeat. Overall, it was an interesting lab and illustrated the capability of capacitors combined with resistors and the behavior of their respective voltages and currents.