Chances are pretty good you’ve had a glowing probe clipped to your fingertip or earlobe in some clinic or doctor’s office. If you have, then you’re familiar with pulse oximetry, a cheap and non-invasive test that’s intended to measure how much oxygen your blood is carrying, with the bonus of an accurate count of your pulse rate. You can run down to the local drug store or big box and get a fingertip pulse oximeter for about $25USD, but if you want to learn more about photoplethysmography (PPG), [Rajendra Bhatt]’s open-source pulse oximeter might be a better choice.
PPG is based on the fact that oxygenated and deoxygenated hemoglobin have different optical characteristics. A simple probe with an LED floods your fingertip with IR light, and a photodiode reads the amount of light reflected by the hemoglobin. [Rajendra]’s Easy Pulse Plugin receives and amplifies the signal from the probe and sends it to a header, suitable for Arduino consumption. What you do with the signal from there is up to you – light an LED in time with your heartbeat, plot oxygen saturation as a function of time, or drive a display to show the current pulse and saturation.
We’ve seen some pretty slick DIY pulse oximeters before, and some with a decidedly home-brew feel, but this seems like a good balance between sophisticated design and open source hackability. And don’t forget that IR LEDs can be used for other non-invasive diagnostics too.
If you happened to be wandering the hall of science during MakerFaire NY, you may have noticed a woman walking around with a rather odd boombox strapped around her neck. That was [Sophi Kravitz] with her HeartBeat Boombox. Thankfully [Sophi] lives within driving distance of Makerfaire, and didn’t attempt to get through airport security with her hardware. She started with three medical grade pulse oximeters. These oximeters output a “beep” for every beat of your heart. [Sophi] rolled her own AVR board running Arduino firmware to capture pulses on their way to the oximeter audio transducer. The AVR uses a sound board to convert the pulses into various percussion sounds. The pulse indicators also activate one of three LED strips.
[Sophi’s] biggest frustrations with the hack were the JST connectors on the LIPO batteries powering the entire system. She found that they fell apart rather easily. We’ve used JST connectors in the past with no problem, so we’re guessing she ended up with one of the many knock off connectors out there. [Sophi] tied the entire system together with a custom milled acrylic plate mounted to the front of the boombox.
The final result was very slick. With three people connected to the finger inputs of the pulse oximeters, some complex beats could be formed. We thought we were listening to dubstep when she first walked by. One feature we would like to see implemented would be the ability to record and play back some of the beats created by the boombox.