Jinbang Fu, Robert Jackson and Joseph Bardin University of Massachusetts Amherst

UMASS

Student Poster Session

1. Motivation

Health §  The human body needs a very specific balance of oxygen in the blood. Normal

levels are considered to be 95 – 100 percent. §  People need an oximeter that can easily detect their oxygen saturation. What should an Oximeter be like?

§  Non-invasive measurements. §  Convenient and easy to carry.

2.Method

The Pulse Oximetry §  There is a protein, called hemoglobin, in blood red cells. §  When oxygen reacts with hemoglobin, it produces Oxyhemoglobin (HbO2). §  When blood gets in contact with a cell, the hemoglobin releases oxygen and

becomes Deoxyhemoglobin (Hb). §  Oxyhemoglobin and Deoxyhemoglobin has different absorptions to red light

and infrared light. §  Based on these different absorptions, we can build a oximeter to detect the

oxygen saturation.

Pulse Oximeter: Analog Front End

3. System Block Diagram

4. Result and Analysis §  Plot of filter output when measuring the author’s pulse.

Phototransistor Circuit

§  Receive the reflected light from the finger and transfers the light signal into electrical signal

§  The base of the phototransistor receives the light and generates the current that represents the light absorption.

§  The amplifier with high gain converts the current to voltage.

Illuminating LED Circuits §  Consist of one red LED circuit and one

infrared LED circuit. §  These two LEDs played in turn(red LED

played 5s and then infrared LED play 5s) §  Microcontroller sets up high frequency PWM

(Pulse Width Modulation) wave at the base of the transistor. The average light intensity emitted by the LED can be adjusted by controlling the duty cycle of the PWM wave to control the current through the LED.

6. References

§  Santiago Lopez, “Pulse Oximeter Fundamentals and Design", Freescale Semiconductor Application Note, November 2012.

§  Claire M. Lochner, Yasser Khan, Adrien Pierre, and Ana C. Arias, “All-organic Sensor for Pulse Oximetry", Nature Communications, December 2014.

Microcontroller §  Monitors the output of the Phototransistor Circuit. §  Adjusts the currents that pass the LED Circuits by controlling the duty

cycle of the PWM wave set at the base of the transistor to make sure that the output of the phototransistor circuit is in certain range so that the pulse can be detected at the output of the filter.

§  Sample the signal at the output of the bandpass filter. §  Send the sampled signal a computer for further analysis.

Bandpass Filter §  Eliminates the noise out of the range. §  Consists of one low-pass filter and one high-pass filter. §  Pass frequencies: 0.8Hz –– 6Hz.

2.35

2.4

2.45

2.5

2.55

2.6

2.65

0 0.5 1 1.5 2 2.5 3 3.5

Volta

ge (V

)

time (s)

Infrared

2.35

2.4

2.45

2.5

2.55

2.6

2.65

0 0.5 1 1.5 2 2.5 3 3.5

Volta

ge (V

)

time (s)

LED

§  Use FFT on the data, we can see that my heart beat frequency is 1.281/s (76.86/min)

5. Conclusion and Future Works

§  Through the data I have received from my results I can conclude that my design is working

§  Design and build a small PCB version. §  Do further analysis to get the oxygen saturation.