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How to Build an Oximeter

An oximeter measures two different things: your pulse and the amount of oxygen present in your blood. Hospital models clip onto your finger; however, using LED lights and a converter chip, it is possible to build an oximeter that shines light through your finger. The light that comes through to the other side will vary with your pulse and with the redness of the blood inside, a sign of oxygen being present.

Things You'll Need

Converter chip/light sensor
AVR microcontroller
Red LED
Computer with serial interface
Infrared LED
Timer counter

Instructions

- 1
  Connect the converter chip to the AVR using one of the AVR's interrupt pins. Attach the red LED to the AVR.
- 2
  Use the AVR to turn on the red LED and let it stay on for 30 seconds, shining through your finger. The converter chip will turn the changes in the red light into comprehensible output for the computer, sending the data to the serial interface on the computer as the light pulses. The installation software for your AVR will accept the data and give you various graphing options, depending on the AVR manufacturer. When the red light is absorbed by redness inside the finger, that means the blood has more oxygen in it.
- 3
  Attach the infrared LED to the AVR, joining the red LED. This light should stay constant, shining through your finger, making your heartbeat changes more visible. Each pulse will correspond to a heartbeat, making your pulse easy to measure. The timer will track each pulse as it comes in from the red and then the infrared LED; when the software gives you a graph of the findings, the timer will serve as the source for the horizontal axis which measures seconds elapsed.

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