Building a Pulse Oximeter from Scratch

Organizations: Duke University - Biomedical Engineering

Collaborators: N/A

Dates: Spring 2014

Foci: Medical Devices

Synopsis

Biomedical engineering requires a blend of electrical, computer, and biomedical engineering skills. During my Intro to Biomedical Devices class, each student was tasked with building our own pulse oximeter in order to develop and practice all of these skills.

The Work

Building a pulse oximeter first required understanding how the device itself works. And to understand that, you need to understand the basic biological signals upon which the device is based.

It turns out that oxygenated blood reflects more red light than non-oxygenated blood (this is why your veins are blue-ish and your arteries are red). By shining a red light through your fingernail and measuring the amount of red light absorbed by your finger (blood, included), it’s possible to measure (with a great enough degree of accuracy) the percentage of blood that is oxygenated. So, that’s what a pulse oximeter does - shines a light on one end of your finger, and sees how much red light is absorbed on the other end!

I worked in C++ to program the device, and built my own circuits as well. This was tricky, as improper circuitry would cause the device to fail (obviously). Incorrect programming and the results would be far outside expectations (and/or also fail; devices break a lot).

More than anything, the development I did required patience - the patience to work through the many, many bugs that would arise. But in spite of all the unexpected issues I inevitably had to fix, I loved every second of building the device. Fixing problems is immensely satisfying, so in a way, the more bugs I fix (that I didn’t cause intentionally), the more satisfaction I feel. I’m weird like that.

The Outcome

The end result was a working pulse oximeter, as shown below! She’s not the prettiest, but she gets the job done. This project was also one of the first to kindle my interest in medical devices, hardware, and software, and for that, I’m forever grateful.