lab7 final project egrb 307

BIOMEDICAL ENGINEERING

VCU School of Engineering

EGRB 307: BIOMEDICAL INSTRUMENTATION

Laboratory No./ Date #7. 11/12/2015Experiment Title Final Project

Name Khade GrantLab Partner’s Name Sarah Tracy, Kelsey Hideshima

Honor Pledge:

"On my honor, I have neither given nor received unauthorized aid on this assignment. Both authors have contributed equally to this work"

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For Official Use Only

Comments: Grade / Score:

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I. INTRODUCTION

The purpose of this lab was to design an ECG circuit and use it to measure the ECG signal from the members of the lab group. Furthermore, the signal was to be amplified to a sufficient level for display and analysis. Through the human ECG signal, the average heart rate in beats per minute (bpm) can be calculated. The lab used the principles explored in previous labs, such as high-pass, and low-pass filters, voltage dividers, and amplifiers.

II. METHODS

Part 1

The purpose of this section was to determine the components of the main amplifier using the equations for the low and high cutoff frequencies, as well as the equation for gain. The main amplifier was designed with a passive high-pass filter and an active low-pass filter. It was designed to have a gain of 70. A low-pass filter attenuates high frequency signals above a cutoff frequency but does not attenuate the frequency response of low-frequency signals below the cutoff frequency. A high-pass filter attenuates low frequency signals below a cutoff frequency but does not attenuate the frequency response of high-frequency signals above the cutoff frequency. The circuit was designed to have a low corner frequency of 0.5 Hz and a high-corner frequency of 100 Hz.

The R1 resistor was calculated with the low corner frequency using the equation: fc1 = 1/(2πR1C1).

The feedback (R3) resistor was calculated with the high corner frequency using the equation: fc2 = 1/(2πR3C2).

The R2 resistor was calculated with a theoretical gain of 70, and using: G = (R3/R2) + 1.

The bias resistor (R4) was calculated using: R4 = R1 – (R2R3)/(R2+R3) ≈ R1.

Part 2

The purpose of this part was to build the main amplifier and test its features. Once the values of the components were determined from part 1, the main amplifier was designed on the breadboard using an AD 741 op amp. (Figure 1.)

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Figure 1. Main Amplifier

The power source was used to supply +4.5V and -4.5V for the circuit. The gain was determined by inputting a signal of 10 Hz with an amplitude of 100mVPP, measuring the output voltage, and using: G = Vo/Vi.

Next, the frequency response for the high-pass filter was determined by slowly decreasing the frequency from 10 Hz to 0.5 Hz and monitoring the output voltage and gain at various intermediate frequencies. The low corner frequency was determined from the resulting frequency response. The frequency response for the low-pass filter was determined by slowly increasing the frequency from 10 Hz to 100 Hz and monitoring the output voltage at various intermediate frequencies. The high corner frequency was determined from the resulting frequency response.

Part 3

The purpose of this part was to determine the components of the pre-amplifier. The RG resistor was calculated with a theoretical gain of 12 and using the equation:

G = (49.4kΩ/RG) + 1.

Both Ra resistors were selected to be 33kΩ. The R0 resistor was determined by using: RG = 2Ra || R0.

Part 4

The purpose of this part was to build the pre-amplifier and test its features. Once the values of the components were determined from part 3, the pre-amplifier was designed on the breadboard using an AD 620 op amp. (Figure 2.)

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Part 5

The purpose of this part was to construct the entire ECG circuit using both the pre-amplifier and the main amplifier. A 100:1 voltage divider was built to reduce the input signal so that a smaller signal could be input into the main amplifier. This way, the output voltage from the main amplifier would not be too high. The reduction ratio was calculated using Vi/Vo:1.

Next, a 100mVpp input signal was input to the full amplifier, and the output voltage was measured. The gain of the entire ECG amplifier was calculated using: G = Vo/Vi-main amp. The reduction ratio was calculated using

After this, the frequency response of the entire ECG amplifier was recorded. The frequency response for the high-pass filter was determined by slowly decreasing the frequency from 10 Hz to 0.5 Hz and monitoring the output voltage and gain at various intermediate frequencies. The low corner frequency was determined from the resulting frequency response. The frequency response for the low-pass filter was determined by slowly increasing the frequency from 10 Hz to 100 Hz and monitoring the output voltage at various intermediate frequencies. The high corner frequency was determined from the resulting frequency response.

Lastly, a 1 Hz cardiac signal was input to the full amplifier with varying input amplitudes of 100mVpp, 200mVpp, and 300mVpp. The output voltage, gain, and calibration parameter from each input signal was measured or determined. The gain was calculated using: G = Vo/Vi-main amp. The calibration parameter was determined using: Calibration parameter = Vo-main-amp/Vi-volt. div.

Part 6

4

Vi (+)

Vo

Vi (-)

AD620

+4.5V

-4.5V

1

2

3

4

7

8

6R

_

+

G

Ref

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Figure 2. Pre-Amplifier

The purpose of this part was to construct a 9V battery power supply. The battery was used to replace the electric power supply during the human experiment. The power supply consisted of the 9V battery, a 4.5V zener diode, 1N5229B, and a resistor Rp of 460 Ω. The power supply circuit provided the full amplifier with a +4.5V, -4.5V supply. The following battery power supply was built on the breadboard. (Figure 3.)

Part 7

The purpose of this part was to build a driven-right-leg circuit using an AD741 op amp, and add it to the full amplifier. The R4 and R5 resistor values were selected to be equivalent to each other and equal to 5.4 MΩ. The full ECG amplifier with the driven-right-leg circuit is shown below in figure 4.

5

+

-

9V Battery

+4.5 V

-4.5 V

0V or ground

Rp

D

1N5229B

Figure 3. Battery Power Supply

Figure 4. Full ECG amplifier with driven-right-leg circuit

Part 8

The purpose of this part was measure the human ECG signal and determine the heart rate. First, a 1 Hz cardiac signal was input to the full amplifier with varying input amplitudes of 100mVpp, 200mVpp, and 300mVpp. The output voltage, gain, and calibration parameter from each input signal was measured or determined. The gain was calculated using: G = Vo/Vi-main amp. The calibration parameter was determined using: Calibration parameter = Vo-main-amp/Vi-volt. div.

Next, three clamps were used for the electrodes. The cardiac signal of each of the three lab members were evaluated. One electrode was placed on the right hand (RR), another was placed on the left hand (LR), and the third one was placed on the left leg (LL). Using the human ECG signal as the input signal, the full ECG amplifier circuit amplified the input so that the signal could be observed. The ECG output signal was observed for 20 seconds in order to find any possible irregularities. The output ECG signal amplitude was measured.

Next, four successive time intervals for the resulting heart beats were measured and the variability was analyzed. The average heart in bpm, as well as the maximum and minimum heart rates were also determined from the signal. Lastly, the ECG signal was observed after the driven-right-leg circuit was disconnected.

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III. RESULTS

Main Amplifier

Component Theoretical/Calculated Measured %Difference/%Error

C1 1µF 1.016 µF 1.60%

R1 318.31 kΩ 313.23 kΩ 1.60%

C2 0.01 µF 0.0099 µF 1%

R2 2.3 kΩ 2.27 kΩ 1.30%

R3 159 kΩ 158 kΩ 0.19%

R4 313 kΩ 312.8 kΩ 0.06%

Table 1. Components of Main Amplifier

All Components were within 5% tolerance.

10 Hz Signal

Name Theoretical/Calculated Measured %Error

Vi 100 mV 105mV 5%

Vo 7.44 V 7.12 V 4.30%

Gain 70.86 67.81 4.30%

Low fc 0.53 Hz 0.48 Hz 9.43%

High fc 100.29 Hz 92 Hz 8.27%

Table 2. Input, Output, and low and high corner frequencies of the Main Amplifier

Low-Pass Filter: Vi = 105mVpp 7

f(hz) Vo Gain

10 7.12 67.80952

20 6.96 66.28571

30 6.8 64.7619

40 6.48 61.71429

50 6.24 59.42857

60 5.84 55.61905

70 5.6 53.33333

80 5.28 50.28571

90 5.12 48.7619

92 5.04 48

94 4.96 47.2381

96 4.88 46.47619

98 4.8 45.71429

100 4.72 44.95238

102 4.6 43.80952

104 4.6 43.80952

106 4.56 43.42857

108 4.52 43.04762

110 4.44 42.28571Table 3. Frequency response of Low-Pass Filter for Main-Amplifier

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Figure 5. Frequency response of low-pass filter

High-Pass Filter: Vi = 105mVpp

Frequency (hz) Vo (V) Gain10 7.12 67.80952381

9 7.12 67.80952381

8 7.12 67.80952381

7 7.12 67.80952381

6 7.12 67.80952381

5 7.12 67.80952381

4 7.12 67.80952381

3 7.04 67.04761905

2 6.96 66.28571429

1.75 6.88 65.52380952

1.5 6.88 65.52380952

1 6.4 60.95238095

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0.8 6.16 58.66666667

0.6 5.52 52.57142857

0.5 5.12 48.76190476

0.53 5.2 49.52380952

0.48 5.04 48

0.4 4.48 42.66666667

Table 4. Frequency response of High-Pass Filter for Main-Amplifier

Figure 6. Frequency response of high-pass filter

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Pre-Amplifier

Component Theoretical Measured Percent Error

RG 4.491 kΩ 4.485 kΩ 0.13%

Ra-1 33 kΩ 33.02 kΩ 0.06%

Ra-2 33 kΩ 32.79 kΩ 0.64%

2Ra 66 kΩ 65.81 kΩ 0.29%

Ro 4.813 kΩ 4.741 kΩ 1.50%

Gain 12 12.01 0.083%Table 5. Components of Pre-Amplifier

All Components were within 5% tolerance.

10 Hz Signal

Name Theoretical Measured Percent Error

Vi 100 mV 104 mV 4%

Vo 1.27 V 1.22 V 3.94%

Gain 12.21 11.73 3.93%Table 6. Waveform measurements for 10 Hz sinusoidal signal

Signal Vi (%error) Vo (%error) Gain (%error)

0.5 Hz 104 mV (4%) 1.22 V (3.94%) 11.73 (3.93%)

10 Hz 104 mV (4%) 1.22 V (3.94%) 11.73 (3.93%)

20 Hz 104 mV (4%) 1.22 V (3.94%) 11.73 (3.93%)

100 Hz 104 mV (4%) 1.22 V (3.94%) 11.73 (3.93%)

200 Hz 104 mV (4%) 1.22 V (3.94%) 11.73 (3.93%)Table 7. Waveform measurements for sinusoidal signals at varying frequencies

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Cardiac Signal


Vi 100 mV 108 mV 8%

Vo 1.267 V 1.22 V 3.71%

Gain 11.73 11.30 3.67%Table 8. Waveform measurements for cardiac signal

Figure 7. Output of Cardiac Signal with 1 Hz and 100 mVpp

Full Amplifier

Voltage Divider


R100k 100 kΩ 101.96 kΩ 1.96%

R10M 10 MΩ 9.98 MΩ 0.2%

Vin 10V 10.4V 4%

Vout 0.1052V 0.108V 2.78%

Reduction Ratio 98.86:1 96.30:1 2.59%Table 9. Components and Measurements of Voltage Divider

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Vin-voltage divider = 112mV => Vout-voltage divider = 1.16 mV = Vin-main

Vin = 1.16 mV


Vout 923 mV 976 mV 5.74%

Gain 795.4 841.4 5.78%Table 10. Output signal and gain of voltage divider

Low-Pass Filter

Frequency (hz) Vo (V) Gain

10 0.976 841.3793

20 0.932 803.4483

30 0.88 758.6207

40 0.88 758.6207

50 0.86 741.3793

60 0.86 741.3793

70 0.82 706.8966

80 0.8 689.6552

90 0.74 637.931

92 0.74 637.931

94 0.74 637.931

96 0.72 620.6897

98 0.72 620.6897

100 0.72 620.6897

102 0.712 613.7931

104 0.704 606.8966

106 0.696 600

108 0.68 586.2069

110 0.68 586.2069Table 11. Frequency response of low-pass filter for full amplifier

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Figure 8. Frequency response of low-pass filter for Full Amplifier

High-Pass Filter

Frequency (hz) Vo (V) Gain10 0.976 841.37939 1 862.0698 1.01 870.68977 1.01 870.68976 1 862.0695 1 862.0694 0.992 855.17243 0.984 848.27592 0.984 848.2759

1.75 0.976 841.37931.5 0.96 827.5862

1 0.92 793.10340.8 0.88 758.62070.6 0.816 703.44830.5 0.768 662.069

0.53 0.776 668.96550.48 0.744 641.37930.46 0.736 634.48280.44 0.712 613.79310.4 0.688 593.1034

Table 12. Frequency response of high-pass filter for full amplifier14

Figure 9. Frequency response of high-pass filter for Full Amplifier

Low fc 0.48 Hz 0.44 Hz 8.33%

High fc 92 Hz 106 Hz 15.2%

Table 13. High and low corner frequencies of Full Amplifier

1 Hz Signal; Vi = 100mV


Vi 100 mV 109 mV 9%

Vo 952 mV 920 mV 3.36%Calibration Parameter (mV/mV) 8.734 8.440 3.36%

Table 14. Waveform measurements and Calibration Parameter for 1 Hz Cardiac input signal of 109mV

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Vi 200 mV 210 mV 5%


Table 15. Waveform measurements and Calibration Parameter for 1 Hz Cardiac input signal of 210mV



Vi 300 mV 312 mV 4%


Table 16. Waveform measurements and Calibration Parameter for 1 Hz Cardiac input signal 0f 312mV

Average Calibration Parameter: 8.161 mV/mV.

Power Supply

Component Theoretical ActualPercent Error

Rp 460Ω 454.41Ω 1.22%

Battery 9V 8.73V 3%Table 17. Components of Power Supply

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Driven-Right-Leg Circuit

Component Theoretical ActualPercent Error

R4 5.4 5.443 0.79%

R5 5.4 5.455 1.01%Table 18. Components of Driven-Right-Leg Circuit

Human ECG Signal



Vi 100 mV 110 mV 10%

Vo 961 mV 960 mV 0.10%

Gain 841.4 840.4 0.12%Calibration Parameter (mV/mV) 8.736 8.727 0.10%

Table 19. Waveform measurements and Calibration Parameter for 1 Hz sinusoidal input signal of 110mV with Driven-Right-Leg Circuit



Vi 200 mV 210 mV 5%

Vo 1835 mV 1800 mV 1.91%



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Vi 300 mV 310 mV 4%

Vo 2709 mV 2640 mV 2.54%



Average Gain: 828.6 (1.52% error from 841.4)

Average Calibration Parameter: 8.605 mV/mV.

Figure 10. ECG signal for Khade Grant

Vo = 1.86V

Interval #1 Interval #2 Interval #3 Interval #4

720 ms 840 ms 680 ms 660 msTable 22. Heartbeat intervals for Khade Grant

Average heart rate: 82.8 bpm

Maximum heart rate: 90.9 bpm

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Minimum heart rate: 71.4 bpm

Figure 11. ECG signal for Sarah Tracy

Vo = 0.508V


780 ms 860 ms 840 ms 780 msTable 23. Heartbeat intervals for Sarah Tracy




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Figure 12. ECG signal for Kelsey Hideshima

Vo = 0.720V


664 ms 680 ms 680 ms 660 msTable 24. Heartbeat intervals for Kelsey Hideshima




Figure 13. ECG signal for Khade Grant w/ disconnected driven-right-leg circuit

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IV. DISCUSSION

An electrocardiogram (ECG) is a device used to record the electrical activity of the heart. It uses electrodes placed on the patient’s body and obtains measurements over a period of time. Depolarization of the heart with each beat induces small electrical changes on the skin. The ECG electrodes detect these waves which are then amplified into an observable signal.

Overall, the circuit receives an input signal, which is then amplified into an observable output signal using three amplifiers. The circuit was designed with an experimental gain of 828.6. It consisted of two stages. The first stage, consisting of a pre-amplifier and a driven-right leg circuit was designed to produce a gain of 12. The second stage, consisting of the main amplifier was designed to obtain a gain of 70. The full amplifier was therefore designed to obtain a gain with a value over 800.

The pre-amplifier took the initial waveform as the input signal and amplified it. It then sent the amplified signal as the input signal for the main amplifier. The driven-right leg circuit provided the input from the leg on the electrode, whereas the pre-amplifier provided the input from the electrode on the right arm and the left arm. The main amplifier then took the output signal from the pre-amplifier and used this as its input signal. It amplified this signal to produce the final output cardiac waveform.

All the components used to design the main amplifier were well within a 5% tolerance range. The main amplifier produced a gain of 67.81. This produced a 4.30% error from the theoretical gain value of 70.86. The main amplifier had a low corner frequency, low fc, of 0.48 Hz. This produced a 9.43% error from the theoretical low corner frequency of 0.53 Hz. It had a high corner frequency, high fc, of 92 Hz. This produced an 8.27% error from the theoretical high corner frequency of 100.29 Hz. The main amplifier functioned as expected; there were no major problems encountered in the design of the main amplifier.

All the components used to design the pre-amplifier were well within a 5% tolerance range. The pre-amplifier produced a gain of 11.73. This produced a 3.93% error from the theoretical gain value of 12.21. As the frequency of the input signal for the pre-amplifier was varied from 10 Hz to 200 Hz, the output signal of the pre-amplifier remained at a constant value of 1.22V. This showed the robustness of the pre-amplifier. Since heart signals can vary in frequency the pre-amplifier could, therefore, be used to accurately measure signal amplitude regardless of frequency. The pre-amplifier functioned as expected; there were no major problems encountered in the design of the pre-amplifier.

All the components used to design the full amplifier were within a 5% tolerance range. The full amplifier produced an average gain of 828.6. This produced a 1.52% error from the theoretical gain value of 841.4. The full amplifier had a low corner frequency, fc, of 0.44 Hz. This produced an 8.33% error from the theoretical low corner frequency of 0.48 Hz. It had a high corner frequency, fc, of 106 Hz. This

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produced a 15.2% error from the theoretical high corner frequency of 92 Hz. The frequency response was from 0.44 Hz to 106 Hz. It also had an average calibration parameter of 8.605 mV/mV. The full amplifier functioned as expected; there were no major problems encountered in the design of the full amplifier.

The purpose of the voltage divider was to test the gain of the circuit using a small input signal. The input signal needed to be small enough so that the full amplifier did not amplify the signal out of the range that the oscilloscope could detect. The function generator could not input signals small enough, so a 100:1 voltage divider had to be designed to divide the voltage from the function generator and input the small signal to the full amplifier. The voltage divider had a reduction ratio of 96:30:1. This produced a 2.59% error from the theoretical reduction ratio of 98.86:1. The voltage divider functioned as expected; there were no major problems encountered in the design of the voltage divider.

Three ECG electrodes were used in this experiment. One was placed on the right hand, another was placed on the left arm, and the third was placed on the left leg. These produced three leads or vectors along which the relative depolarization of the heart could be measured. The first lead, Lead I, goes from the left arm (LA) to the right arm (RA). The second lead, Lead II, goes from the left leg (LL) to RA. The third lead, Lead III, goes from LL to LA. The depolarization along each lead produces a resultant vector that represents the depolarization of the heart. The black lead was attached to the left arm and was input into pin 3 of the pre-amplifier (AD620). The white lead was attached to the right arm and was input into pin 2 of the pre-amplifier (AD620). The green lead was attached to the left leg and was input between the two Ra resistors of the pre-amplifier (AD620).

The heart rate of normal healthy humans is between 60 and 100 beats per minute (bpm). For Khade Grant, the average heart rate obtained was 82.8 bpm. For Sarah Tracy, the average heart rate obtained was 73.6 bpm. For Kelsey Hideshima the average heart rate obtained was 89.4 bpm. The average heart rates of all three lab members fell within the range of normal healthy heart rates. The heart rate for Khade Grant had the most variability in terms of beat-to-beat intervals. His heart beat ranged from 660 ms to 840ms. The heart rate for Kelsey Hideshima had the least amount of variability in terms of beat-to-beat intervals. Her heart beat ranged from 660 ms to 680ms. The ECG signal of all three lab members was enlarged to over 500 mV. The ECG amplitudes in normal healthy hearts range from 0.5mV to around 2.5 mV.

The calculations for each part are shown on Appendix I.

V. CONCLUSION

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Overall, the lab went as expected. The lab provided a sufficient understanding of how ECGs worked and how to design one. Specifically, the lab provided knowledge of how to design an ECG circuit integrating various components such as a main amplifier, pre-amplifier, and driven-right-leg circuit. When problems are encountered, it is important to recheck the circuit to see if everything is wired correctly, and reread the instructions to see if any crucial steps were omitted. The main amplifier, pre-amplifier, driven-right leg circuit, and other components of the full amplifier worked as expected and provided sufficient results. Furthermore, the full amplifier was designed without any major problems and the results obtained met the requirements that were stated in the lab. Specifically, the full amplifier had a gain over 800, a frequency response approximately between 0.5 Hz and 100 Hz, and was able to acquire the ECG signals from all three members of the lab and enlarge their output signals over 500 mV.

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lab7 final project egrb 307

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