As part of an ongoing project of mine, to build a device which will measure everything, I had a go at assembling some kind of blood oxygen meter. This was sparked when I heard that measuring the oxygen level in blood requires only red and infra-red light- I had both LED’s around, so it was time to head to the workshop and get building!
The device simply relies on the fact that oxygenated and deoxygenated blood absorb red and infrared light in different ratios. By measuring the absorption ratio for a particular person’s blood, one can determine the ratio of oxygenated to deoxygenated blood and hence, how oxygenated it is.
I decided to have a go at making a reflective oximeter, since transmissive oximeters are so intrusive. this means it can be pressed against the skin to get a result, rather than having to be clamped over a finger like the ones used in hospitals. The business end is simply a light sensor adjacent to a red and an infrared LED. An Arduino micro controller makes the whole device work by flashing the red LED, and measuring the light reflected back, then doing the same with the infrared LED, and finding the ratio of the amounts of light reflected.
Annoyingly, since this is a one-of-a-kind machine, there’s no easy way to calibrate it, other than buy a proper Oximeter and comparing- defeating the point of making one. I tried holding my breath to lower the oxygen count; it showed signs of working, but I was also in danger of fainting, so that test was swiftly called off.
Hopefully it will be possible to just do it by finding the actual ratios and using those- it might also be safer…
In any case, I shall let you know how it goes. Come back for the result!
Musings of a Scientist 