ENGR337 Lab 2020 Spring
Lab 4
Name: Kurt Emslie
Email: kdemslie@fortlewis.edu

1. Oximeter

2. Introduction
A pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation (SO2). In this lab, we will not be testing SO2, we will be trying to detect a pulse. When blood is pumped to the finger tip, the blood's ability to absorb IR light changes as well. If blood absorbs more IR light, the reflected IR light being received by the receiver will decrease and so the voltage at the Collector (C) terminal will increase. The heart beat rate is the same as the frequency of the voltage pulses from the receiver. A TCRT500 IR sensor in conjunction with a 1NA 128P instrument amplifier to build the oximeter.


3. Materials and Methods
The purpose of this lab was to make a circuit that with a sensor would be able to read a person heat beat and display it on an oscilloscope, similarly to an ECG. As the oximeter receives more or less light the voltage out of the sensor increases and decreases. To build the circuit two 1NA 128 PA Instrument Op Amps. The signal to teh sensor had to pass through a High-Pass filter with a 4.7 mF capacitor and a 68 k resistor. Then the signal had to pass through a Low-Pass filter with a 458 nF capacitor and a 100 k resistor. The signal was then ran through a second 1NA 128 PA Instrument Op Amp. The signal went through one last Op Amp, a 741 and a 1 k resistor to regulate the voltage supplied to the diode. Reference voltage was supplied to the circuit via a 5 V power supply through a zener diode and a 680 ohm resistor. The signal was displayed on the oscilloscope, and plotted in a live graph with Arduino displaying the heart.

4. Results


Figure 1: The peak to peak value of a heat heat signal.



Figure 2: Video of the signal of a persons heart beat.



Figure 3: Video of the LED light on the bread board flashing with a person heart beat.


Figure 2.1: The bread board with the LED light on when light was allowed to hit the sensor.

5. Discussion
The Oximeter that we built in this lab demonstrated how passive filters are used in real world applications. The use of multiple 1NA 128 PA Instrument Op Amps prevented the signal from being attenuated. This lab further demonstrate value and need of being able to filter noise and DC offset when trying to focus on one signal.