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									Heart Rate Monitor and Data Acquisition System

                     Bill Leece
                  Sofoklis Nikiforos

                   TA: Ajay Patel
                    June 22, 1999
                                 Project Statement
       We selected this project because we are both interested in biomedical engineering
and analog electronics. This project combines both areas of interests nicely. Secondly,
since we both had hoped to take ECE 314/5, but didn’t have the time to do so during our
studies at the U of I, we felt that this project would give us a good background on most of
the material taught in these courses. Furthermore, in the fall Bill will be working for a
company that makes pacemakers, so this background in biomedical circuits and sensors
will prove to be very useful in that regard.

                                        Project Goals
       For this senior design project, we will build a heart rate monitor and interface it
with a PC via DAQ board. We hope to gain a greater understanding of biomedical
sensors and analog electronics as well as learning more about instrument-computer
interface. We plan to use two different software packages for this project, simulating the
analog circuits (for purposes of optimizing performance) with PSPICE, and writing the
data acquisition programs using LabVIEW.
       Our heart rate monitor will use a sensor to detect a person’s heartbeat. This signal
will then be sent to an ECG amplifier circuit. The output of the amplifier circuit will then
be sent to a DAQ card in a PC. The DAQ will provide the interface between the real
system and the virtual instruments created using LabVIEW. The LabVIEW programs
will display the patient’s heartbeat on a virtual oscilloscope, as well as displaying the
persons heart rate in beats per minute and overall caloric expenditure.
       If time permits, we will also build electronic circuits that will perform the same
functions as the LabVIEW software. We will display the heart pulse on a real (as
opposed to a virtual) oscilloscope as well as using LED displays to display heart rate.
The purpose of actually building these circuits this is twofold. First, it would give us a
chance to learn more about analog electronic circuits, perhaps giving us an opportunity to
use the 555 timer circuit. Furthermore, it will provide an excellent demonstration of the
value of LabVIEW because we suspect that it will be much more difficult to actually
build circuits that calculate heart rate than “building” them with LabVIEW.
                Block Diagram


Sensors   Amplifier                  (Optional)

                        Heart Rate
                         Circuit            Oscilloscope
           Heart rate monitor and data acquisition system

Sensor Inputs
The input to the monitor system is from a human via biopotential sensors. The sensor
detects the patient’s heartbeat by transforming a physical signal from the body into an
electrical signal. This signal is then sent to the ECG amplifier.

ECG/ Instrument amplifier
The purpose of the ECG amplifier is to take our sensor inputs and produce a meaningful
signal. The ECG amplifier removes noise from the signal as well as amplifying it. The
output of the ECG amplifier is then sent to the DAQ board.

National Instruments Data Acquisition Board
The DAQ board takes the analog input signal and sends it to the PC where the heart beat
can be displayed on the computer using LabVIEW software. Furthermore, the DAQ can
also digitize the input signal, which will prove to be useful for the calculation of heart

LabVIEW Software
The last part in the monitor system is the output from a LabVIEW program to a computer
monitor. The program will interface the NI-DAQ by taking the analog input signal and
displaying it in real time on a LabVIEW strip chart. LabVIEW will also use a digitized
version of the input signal to produce a value for heart rate in terms of beats per minute.

Optional System
The optional part of our project consists of making a hardware circuit that performs the
same functions as the LabVIEW software. Displaying the heart pulse will be
straightforward since the output of the ECG amplifier can be connected to an
oscilloscope. In order to display the heart rate (in beats per minute) a complicated
electronic circuit will have to be devised to keep tract of the heart rate and to display this
information on LED’s. A very challanging part of this optional system would be to make
it function properly while using only 9 V batteries. This would probably require more
knowledge of low power electronics than we have. Once again, we will only do this part
of the project if time permits.

                              Required Performance
The performance that we will require of the finished project is that the system is able to
display Electrocardiograph data (e.g. heart pulse) on a strip chart in LabVIEW and that
heart rate can be calculated and displayed in terms of beats per minute as well. In order
to accomplish this goal, our sensor and ECG amplifier will have to be optimized to meet
minimum performance parameters. Furthermore, there will have to be successful
interfacing between the ECG amplifier and the computer via the DAQ board. Finally, the
LabVIEW programs will have to function properly so that the data can be displayed in a
meaningful manner.
       A few performance parameters are involved in the optimization of the ECG
amplifier circuit. The first stage of our amplifier needs to have low noise and high input
impedance. Optimization calls for minimizing the input bias current. We will be using
the model 411 op amps instead of the more standard 741, since the 411 has lower input
bias current. The common mode rejection ration must also be high for the first stage.
PSPICE will be used to maximize the CMRR as well as obtaining the desired frequency
response specified in Medical Instrumentation by John G. Webster. The gain after the
difference amplifier will have to be approximately 1000 to 4000 .
        For the last stage of the amplifier, we need to optimize the frequency response of
the bandpass filter by selecting appropriate resistor and capacitor values. The frequency
response of the amplifier should have a high corner frequency of 120 Hz to minimize
noise from the muscles. The low corner frequency should be set to 0.05 Hz to obtain the
maximum signal. Once again, obtaining this particular frequency response will be
accomplished by selecting appropriate resistor and capacitor values determined from
PSPICE simulations.
                               Detail of Test Procedures
As discussed, we plan to maximize the amplifier performance by simulating the circuit
with PSPICE. Our amplifier circuit contains a resistor pot that needs to be varied to
maximize CMRR. We will make a plot of CMRR vs. Positive Differential Amplifier
Resistor value (R13 in our circuit included at the end of this proposal) to see which value
maximizes the CMRR. We will also make Bode plots of the frequency response to make
sure that our amplifier has the frequency response that we desire. Our LabVIEW test
procedure will consists of designing and testing subVIs to see if they function properly.
Once the subVIs function properly, they can be assembled in a hierarchical nature into a
high level VI that will measure the heart rate and display ECG data on a graph. Finally,
if time permits, a way to document the projects performance is to compare values
obtained via LabVIEW with those obtained with our hardware circuit that will be
designed if time permits. Obviously, agreement between the software and hardware
versions of the ECG and heart rate monitor would suggest proper performance in both.
  June 17         Bill Leece, Sofoklis Nikiforos: Submit initial proposal.
  June 19         Sofoklis Nikiforos: Study NI-DAQ manual.
                  Bill Leece: Find LabVIEW manuals.

 June 22-          Bill Leece, Sofoklis Nikiforos: Analyze ECG Amplifier
  June 25
                  Sofoklis Nikiforos: Gather all hardware components.
                  Bill Leece: Begin familiarizing with LabVIEW.
 June 23          Bill Leece, Sofoklis Nikiforos: Submit written proposal.
 June 27 -30      Bill Leece, Sofoklis Nikiforos: PSPICE Simulations.
                  Build and refine the hardware.

 June 28-30       Progress check.
  July 1-         Bill Leece, Sofoklis Nikiforos: Complete ECG amplifier; Begin
   July 12         LabVIEW interfacing.
  July 13-20      Bill Leece, Sofoklis Nikiforos: Complete LabVIEW integration
                  and begin testing. Test and compare different sensors
  July 21-28      Bill Leece, Sofoklis Nikiforos: Final debugging and
                  modifications. Add supplementary hardware and software
                  features if time permits.
 July 29          Demo.
 July 30          Oral report.
 August 2         Turn in final report
                                   Cost and Parts
       The only parts that we need to order are the disposable electrodes, HP13951C.
These are disposable, cloth, solid gel, and snap electrodes, with a silver/silver chloride
(Ag/AgCl) sensor, which can be repositioned. We estimate the costs of the case of
electrodes to be about $45 based on market value price. We also plan to use different
sensors (IR, piezoelectric) to determine which type of sensor is most readily able to
detect a heart pulse. The other parts are already available in the lab or shop.


Typical EE entry salary $50,000/year * 1year/240 days * 1 day/8 hours = $26/hour

       $26/hour x 2.5 x 100 hours = $6,500 (per person)
       Total Labor                                            $13,000


       HP13951C electrodes            $45
       Other sensors                  $55
       411 and 741 Op amps            $5
       Resistors, capacitors          $2
       Personal Computer               ---    (available)
       LabVIEW Software                ---    (available)
       PSPICE Software                 ---    (available)
       NI - DAQ                        ---    (available)
       Total Parts                                                $107
       Total Costs                                            $13,107
Tolerance Analysis and Test of Engineering Specifications
       For tolerance analysis and test of Engineering specifications, we will determine
the range of values of the potentiometer (R13 in figure below), which is used to control
the CMRR. Thus we will obtain high and low resistor values for our variable resistor
such that the ECG amplifier circuit still operates in an acceptable manner. The design
will have to be in the range of 47k   5k . We also will vary the resistors and
capacitors responsible for the ECG frequency response to determine minimum and
maximum cutoff frequencies that will still allow the ECG amplifier to function properly.
At this time we really have no idea of what these values will be or of what their variances
can be, but we will be able to determine this after a number of PSPICE simulations as
well as physically varying these parameters in our actual ECG amplifier circuit.

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