Pulse Oximeter CMS50D+ File converter and experiments

I’ve been running for a few years and I must admit that one of the things I like the most about it is to keep track of my statistics! I found a cheap device named a Pulse Oximeter model CMS50D+ on ebay that can track the heartbeat as well as the level of oxygen saturation in the blood (SPO2).

Tracking heartbeat is something already pretty standard, but I was curious to see how my saturation would behave when running so I bought the clever device. The device uses proprietary file format (.spoR files) which is in binary. This is not very friendly with the spreadsheets editors. So I did some experiment and found out the binary format was pretty simple. All data are stored in pair of 8bits value like this: [Hearthbeat] [SPO2].

So the resolution is 1 bpm and 1 % respectively and can technically goes up to 255% of oxygen saturation! In practice, the resolution is my less than that when running as the device doesn’t seems to catch up with the shaking and the fast heartbeats.

Most of my capture we only adequate at the beginning of my runs and I could see barely a trend of spo2 reduce and heartbeat increase simultaneously. The device is more designed to record the quality of the sleep so I’m sharing the experiment and the converter in case it helps someone else! https://sourceforge.net/projects/spor-converter/