Detecting Apnea with an SPO2 sensor

• When you stop breathing, eventually your blood O2 saturation goes down, and that's generally bad.

• Reading SPO2 and logging it was the obvious thing to do after logging sleep positions.

• But it's actually hard to do for the neophyte EE that I am

• Actually commercial sensors do require a lot of engineering work to be precise.

• Turns out, it's even harder with a cheap SPO2 probe: infrared and red are on the same 2 wires in opposite current direction, and I couldn't get anything out of the photo transistor :(