Download Lab 10: Heart Rate Measurement with Reflective

Lab 10:
Heart Rate Measurement
with Reflective Optical
Sensor
Physics 352L Section: 450
Friday, March 27th, 2014
Dr. Hugon
Harris Pharr
I have neither given nor received any unauthorized aid
on this assignment:
Abstract/Introduction:
Lab 10 introduced the TCRT1000 infrared optical sensor and explored its biomedical
applications specifically in measuring the heart rate of a patient. The IC sends out light
through the skin which is then reflected back into the IC; the intensity of the reflected
light is proportional to the blood flowing through a patient’s vein. With each heart beat,
more blood was rushed through the capillaries reflecting back more light which caused
the photoresistor to respond with an increased voltage. The first section of this lab
involved proper construction of the circuit in order to create recognizable heartbeats on
the oscilloscope. In order to do this, two sets of high and low pass filters were constructed
in series. These filters also amplified the signal increasing the gain of the original signal.
LabVIEW was used to calculate the frequency and ultimately the heart rate. The heart
rate was observed on the oscilloscope and LabVIEW simultaneously and compared in
order to validate the circuitry and LabVIEW block diagrams. The recorded heart beats
were found to be 60 bpm and 61 bpm respectively.
Section A: Constructing the Circuit.
In order to construct a circuit to measure a patients heartbeat, a TCRT1000
infrared optical sensor was constructed. In order for the heart beat to be observed on the
oscilloscope, the circuit had to be constructed correctly and contain filters to remove
noise and DC voltage on it. This was done by constructing the circuit according to figure
1 below; this circuit ultimately produced a respectable output for heart beat analysis.
Figure 1: Circuit constructed in part 1 (images provided by http://embeddedlab.com/blog/?p=5508)
The high pass section filtered out the DC voltage while the low pass filtered out the noise
present within the system. Throughout the stages of the high/low pass, the signal was
simultaneously amplified in order to be more easily observed on the oscilloscope (gain at
this point was 750). With the circuit constructed properly, a patient placed his finger on
the sensor in order to register the optical sense fo a heart beat. A sample of the output
observed on the oscilloscope due to the heart beat of the patient is shown below.
Figure 2: Observed Heartbeat on the Oscilloscope::
By analyzing the waveforms produced by the circuit and observed on the oscilloscope,
the heart beat of the patient was able to be measured. In this case the heart beat read
approximately 60 bpm which is the average for a human. The positive peaks observed on
the oscilloscope represent when more light was reflect back due to the pulse of blood
flowing through the capillaries of the patient. The remainder of the lab involved the use
of the software LabVIEW.
B. Reading frequency via the DAQ
In the final section of the lab, LabVIEW was used along with the DAQ to not only upload
the heart beat signal but also determine the frequency at which it was beating using
simple algorithms. The front panel and block diagram of the LabVIEW VI are displayed
below.
Figure 3:
The block diagram shows the analog input is to be continuously read and fed out through
a 1D waveform. This is then read on a waveform chart on the front panel that is identical
to the oscilloscope output observed at the same time. This is then fed into Tone
Measurments VI where the frequency is then calculated and displayed on the front panel.
This simple set up displays not only the waveform but also the calculated frequency. The
frequency is read as the space between the top peaks. The output in this case shows a
frequency of 1.02Hz which displays beats per second. Extrapolating this data results in
61 beats per min, which is very close to the calculated value observed off the
oscilloscope.
Conclusion:
This lab introduced me to alternative methods of measuring one’s heartbeat by using an
optical sensor and then input it through the DAQ into LabVIEW. I gained valuable
practice with more filtering and amplification of a signal with the oscilloscope on average
reading 60-61bpm. This lab incorporated many principles previously learned in past labs
all into one lab report.