pulse oximeter

The COVID-19 pandemic has sparked my interest in creating a project or device that can aid in overcoming the virus or helping individuals protect themselves. Initially, I considered developing a DIY ventilator, however, after researching the topic, I found that the commonly available designs were not helpful and the process of creating a functional ventilator would be complex.

As an alternative, I decided to focus on creating a device that can assist in diagnosing or monitoring a person's health status, allowing patients to monitor their health from the comfort of their own home.

That's how the idea of a pulse oximeter came to mind. Pulse oximetry is a non-invasive method for measuring a person's oxygen saturation, which can be done without using needles or taking a blood sample. The readings are typically within 2% accuracy of the more desirable reading of arterial oxygen saturation from arterial blood gas analysis.

Pulse Oximeter

Design thinking process:

After going through the design thinking process,

go to the design thinking process

I began to move forward with the implementation phase.

The main component in the project

the MAX30100 is an integrated pulse oximetry and heart-rate monitor sensor. It combines two LEDs, a photodetector, optimized optics, and low-noise analog signal processing to detect pulse oximetry and heart-rate signals.

the way Pulse Oximeter Works:

Oxygen enters the lungs and then is passed on into blood. The blood carries oxygen to the various organs in our body. The main way oxygen is carried in our blood is through hemoglobin. During a pulse oximetry reading, a small clamp-like device is placed on a finger, earlobe, or toe.

Small beams of light pass through the blood in the finger, measuring the amount of oxygen. It does this by measuring changes in light absorption in oxygenated or deoxygenated blood.

MAX30100 EGC Oximeter sensor - Heart Rate Sensor - RAM Electronicsfor more details click here

0.96" OLED 4pin LCD LED Display Module I2C IIC Communicate - White 128x64 - RAM Electronicsfor more details click here

ATmega328 (Microcontroller - bootloader UNO) - RAM ElectronicsATMega328 32K microcontroller with pre-loaded Arduino UNO bootloader

the circuit on the breadboard

videocompress-051-VID_20210328_134520.mp4

Hardware Connections (Breakoutboard to Arduino):

-5V = 5V (3.3V is allowed)

-GND = GND

-SDA = A4 (or SDA)

-SCL = A5 (or SCL)

-INT = Not connected

it's better to connect the OLED screen to the 3.3 v instead of the 5V .. it's safer

pulse oximeter code.ino

problem : the sensor doesn't work

this problem with the hardware.

As you can see here there are 2 voltage regulators, this will give a constant output of 3.3v, where input can be anything from 1.8 to 5.5v.

Coming to the second regulator, it will give a constant 1.8v output when the input is 3.3v.This regulator is used to power up the max30100 sensing module which required only 1.8v. Up to here, everything is perfect.

The main problem is, with the below-highlighted connection only. as you can see here, there are 3 pull-up resistors. but they are connected to 1.8v to make it pull up. the problem is, our microcontrollers are 3.3v based; so, these pullup resistors are not making SDA and SCL data lines neither pull-up nor pull down.

because of this connection, the data which is sending from the sensor to the microcontroller being corrupted and we are getting error responses as ” Initializing pulse oximeter…FAILED” (or) “Initializing… MAX30100 was not found. Please check the wiring/power”

Since the sensor can’t communicate with the microcontroller, this will never receive a command to read the pulse and oxygen level, thus the red LED will never glow.

the solution: is to connect these pull-up resistors to the 3.3v network.

circuit design

schematic .sch

profile .pdf

board .brd

Design rules

We determine the design rules based on where we fabricate.

Here I fabricate in the Fablab Egypt, so I use its design rules which are :

minimum track width is 0.4 mm
minimum clearance between any wire bad, via is 0.4 mm
the minimum drill is 0.6

drills .pdf

fabrication process

Machine Setup:

1-Imported the bottom PNG files into Fab Modules and

Set the:

- process to PCB Traces 1/64,
- speed to 4 mm/s,
- stock thickness to 1.7,
- tool diameter to 0.4 mm,
- cut depth to 0.1 mm
- number of offsets to 4

2-Use (V Endmill) its for the Traces

2- Imported the Drills PNG files into Fab Modules and

Set the

- process to PCB Outline 1/32.
- speed to 4 mm/s.
- cut depth to 0.6 mm.
- tool diameter to 0.79.
- number of offsets to 1.
- use Ball nose 0.6 endmill for Drilling