Name Kyla Jackson, Todd Germeroth, Jake Spooler Date May 5, 2010 Lab 3E Group 3 Experiment Title Project Deliverable 3

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1 Name Kyla Jackson, Todd Germeroth, Jake Spooler Date May 5, 2010 Lab 3E Group 3 Experiment Title Project Deliverable 3 Objective The objective of this project was to design and construct an ECG measurement circuit capable of taking, filtering, and importing ECG waveform measurements into a LabView program. The project was also designed to gain fundamental understanding of ECG measurement output such that basic conclusions and diagnosis can be made from the ECG data obtained Theory An electrocardiogram (ECG) is a graphical tracing of the electric current generated by the heart muscle during a heartbeat. Therefore an ECG provides vital information on the condition and performance of the heart. Electrocardiograms can be produced by placing electrodes at a variety of locations on the body in order to quantify the heart rate being produced at these locations and consequently the overall heart rate of the body. Normally the body s four extremities (two legs and two arms) as well as the chest wall are the most common locations to place ECG electrodes. If four electrodes are attached to the four extremities (left arm (LA), left leg (LL), right arm (RA) and right leg (RL)) then the electrode on the right leg is usually grounded while the voltage drop between any of the other three electrodes is measured. In this experiment only three electrodes will be utilized and the ECG will be measured as the voltage drop from left leg to right arm. A normal ECG will display a pattern of upward and downward measurement deflections, reflecting the alternate contraction of the atria (the two upper chambers) and of the ventricles (the two lower chambers) of the heart. If any deviations or anomalies are detected in the heart rate pattern then the users will know that a heart defect is present. An example of the type of defect analysis that the users are making are to detect any ECG waveform signals that are out of the ordinary. One such abnormality would be ventricular hypertrophy. Ventricular hypertrophy is the enlargement of either of the ventricles. Left ventricular hypertrophy is particularly common in athletes as well as an indicator of hypertension. The distinguishing characteristic of this condition is an inverted ECG waveform spike, also known as a T wave. Equipment In the initial stages of this project a necessary step was to select all hardware components needed to successfully complete the ECG measurement process. As seen below a full listing of the hardware equipment chosen for this experiment as well as the reasons for selecting each component is listed.

2 LabVIEW 9.0 (Student Owned) Data acquisition software used to create a virtual instrument capable of analyzing data input being supplied by adjoining data acquisition system. USB-6009 Data Acquisition Board (Student Owned) - Low cost multifunction data acquisition unit. Selected for its ability to effectively transmit voltage output from circuit board to LabVIEW 9.0 program. Furthermore the capability to supply an adequate amount of resolution for the signal being input to LabVIEW was also desirable. 1 Solderless Breadboard (Student Owned) Utilized to assemble hardware components into a singular system capable of processing and outputting a voltage signal to be input. ECG Lead Wires: 1 Set of 3-Lead ECG Snap Set Lead Wires (Purchased Online) Standard medical equipment currently utilized in conjunction with ECG electrodes to obtain the electric current generated by the heart muscle during a heartbeat. ECG Electrodes: One 30 Pack of Medi-Trace 230 Foam Monitoring ECG Electrodes (Purchased Online) - Standard medical equipment used in conjunction with ECG electrode leads to measure electrical current generated by heartbeat. These ECG electrodes are high performance, cost-effective general monitoring electrodes. 1 LM358N Op-Amp (Student Owned) - A low power dual operational amplifier that required four resistors to set the gain of the amplifier. Chosen for its ability to effectively amplify the signal being transmitted into the circuit by the ECG measurement equipment. The fact that it was already student owned was also a secondary reason for choosing the equipment. Two 9 Volt Batteries (Purchased locally) - Designed for enhanced performance for high drain applications such as transmitters, controllers, or detectors. Chosen for this experiment to provide the offset voltage needed for the op-amp and it s corresponding gain. Two 9 Volt Battery Holders (Purchased Online) Utilized to secure the 9V battery in a project. 2 Friction Lock PCB Headers (Purchased Online) Utilized to serve as an adapter between ECG electrode lead wire probes and the solderless breadboard. Two 10K Fixed Resistors (Student Owned) - A two terminal electronic component that produces a voltage across its terminals that is proportional to the electric current passing through it in accordance with Ohm s Law. Chosen to help supply resistance needed in relation to op-amp gain. Two 100K Ω Resistors (Purchased Online) Similar to the 10K fixed resistors in concept. Also chosen to help supply resistance needed in relation to op-amp gain. Ground wire (Student Owned) Used as a sink for the electric charge.

3 Calibration Process Due to the fact that the main components of the hardware setup were the LM358N Op- Amp, two 10K fixed resistors, and two 100K Ω resistors calibration of the hardware circuit created was not as easily attainable. The calibration of hardware experiments such as this experiment can usually be conducted by using instruments such as a potentiometer. But no such equipment was used for the setup in this experiment and thus the only type of calibration utilized for this the ECG measurement process was to theoretically calculate the voltage output of the system given variable specifications. In particular the type of the circuit that was chosen to be built for this experiment was a differential circuit where two voltages would be input, fixed resistors, an operational amplifier, and two nine volt batteries would moderate the op-amp gain signal to be output to the data acquisition system, and then one voltage signal would be output to the DAQ and consequently the LabVIEW program for analysis. After much research from a variety of medical sources it was decided that in this experiment only three electrodes would be utilized and the ECG signal would measured as the differential voltage drop from left leg to right arm, with the ECG electrode attached to the right leg to be used as a grounding source. After further research it was also found that the electrical voltage signal produced in the human body in the ankle area of the right arm was approximately 0.1 mv while the voltage signal produced in the wrist area of the right leg is 1.5 mv. With these voltages in mind and the low power function of the LM358N op-amp realized the team concluded after several trial and error calculations that two 10K fixed resistors as well as two 100K Ω resistors were the best resistors commonly available that could provide a reasonable output voltage. Following this the resolution of the system was also determined to insure that the resolution to be used by the data acquisition unit would be acceptable. Upon performing the calibration and resolution calculations the output voltage was determined to be 0.14 mv and the resolution was found to be mv per step using the 14 bit capability of the USB-6009 data acquisition unit. Seen below as Figure 1 is the schematic of the differential circuit built for this experiment with the particular location of the resistor values outlined. The calculation for nominal calibration of the system as well as resolution of the system is also shown.

4 Figure 1: Schematic of circuit constructed to take ECG data Figure 2: physical wiring of ECG circuit

5 Calibration & Resolution Calculations: Equation Utilized for Differential Circuit Used: Resolution Calculation (14 Bit DAQ): Testing Process & Results In this experiment the users attempted to produce a standardized ECG measurement system so that the resulting LabVIEW program could be used to compare different ECG measurements taken from the same person taken at two separate instances. The first task which the users completed was the design and construction of the previously described hardware system capable of detecting the electrical output produced by heartbeats. Upon completing all of the required connections in the hardware circuit the experiment then proceeded with attaching the three electrodes to the test subject s body at the inner surface of right forearm near the wrist as well as the inner surface of left and right legs near the ankles. The electrodes were then attached to the ECG lead wires and since the friction lock headers never arrived in the mail, the basic copper wires were stuck inside the lead wires and crimped down in order to serve as an interface into the circuit board. The USB-6009 data acquisition unit was then connected to the computer and data acquisition on the accompanying LabVIEW program was be performed. Although good data acquisition did not occur in this experiment what was hoped to have been achieved was to the measurement of several complete ECG cycles in each the test subject. This was desired so that a good comparison of ECG data could be made and the diagnosis of any anomalies be accomplished. The main purpose of the data acquisition unit in this experiment was

6 to filter the measured signal provided by the adjoining circuit and then feed this signal to the LabVIEW program in the computer. The LabVIEW virtual instrument used for this project involved the construction and management of several array structures. Furthermore, the LabVIEW program also supplied an analog processing of the voltage being produced by the heart muscle. This heart muscle force was produced by the exertion of pressure in a complete pumping cycle and was transmitted to the hardware circuit by the accompanying ECG electrodes. Figure 3: voltage readout of ECG device Figure 4: ECG program block diagram System Error Throughout the experiment the measurement and processing errors producing by the system were given special consideration. Due to the fact that no data was actually obtained quantitative system errors were unable to be determined. However it can be speculated on a

7 conceptual level the types of errors that were present in the system and how they contributed to the overall system performance. The first such error would be inaccurate placement of the ECG electrodes. During the course of this experiment it was researched how and where to place the ECG electrodes so that the best possible ECG measurement could be taken. But the taking of ECG data is a practice that requires some level a medical training and therefore it is quite possible that inaccurate placement of these electrodes occurred. Another error that may have occurred is the usage of incorrect values for the fixed resistors in this system. Since the resistors directly affect the performance of the op-amp the use of incorrect values could be very detrimental to the data acquisition process and thus this could be a definite source of error. Due to the delay in shipping of the lock headers, a makeshift solution was to crimp the provided copper wires used in the other homework assignments into the female end of the electrode lead wires. This was not ideal due to the sensitivity of the connection and it also added another transition between two different types of conductors. Conclusion In conclusion, this experiment was a good introductory look into the engineering experience involving mechanical instrumentation. Although the major problem encountered in this experiment, the failure to obtain reasonable ECG data, prevented a quantitative analysis of the project results from taking place several important lessons were learned in the course of this experiment. First, the calibration of an operational amplifier can be somewhat difficult when using a differential circuit. Second, it became quite obvious in the course of this experiment that having a thorough understanding of each instrumentation component utilized is imperative for experiment success. It is surmised that the lack of complete understanding on how the ECG electrodes operated did make the experiment more difficult to complete. Overall the team is content with the outcome of this experiment. While good output data would have been advantageous the team still learned great deal in the course of its research. The lessons learned in this experiment will be beneficial in future engineering work involving mechanical instrumentation.