Commercial pulse oximeters don't always do things exactly this way, but that's more a matter of "secret sauce" than anything else. The principles here are all you really need to understand a basic pulse oximeter. There are more advanced techniques, like Masimo's Rainbow SET, but it's just the same idea with more LEDs.
More interesting to people around here is what the hardware connects to. These things are typically used with patient monitors, those things that display the little charts and go "beep" when your heart beats. Most sensors that connect to a patient monitor are read out by the monitor itself, so a Nihon Kohden and a Mindray monitor might have slightly different sensitivities. It's all handled by manufacturer-designed hardware and manufacturer-controlled software. Not so for SpO2. SpO2 is actually handled by a complete board with firmware purchased from one of the major sensor vendors (usually Nellcor or Masimo). And this board has actual moderately-good security locking down its firmware, and in some cases uses obscure hardware to make it even harder to reverse engineer. Kind of wild!
Commercial pulse oximeters don't always do things exactly this way, but that's more a matter of "secret sauce" than anything else. The principles here are all you really need to understand a basic pulse oximeter. There are more advanced techniques, like Masimo's Rainbow SET, but it's just the same idea with more LEDs.
More interesting to people around here is what the hardware connects to. These things are typically used with patient monitors, those things that display the little charts and go "beep" when your heart beats. Most sensors that connect to a patient monitor are read out by the monitor itself, so a Nihon Kohden and a Mindray monitor might have slightly different sensitivities. It's all handled by manufacturer-designed hardware and manufacturer-controlled software. Not so for SpO2. SpO2 is actually handled by a complete board with firmware purchased from one of the major sensor vendors (usually Nellcor or Masimo). And this board has actual moderately-good security locking down its firmware, and in some cases uses obscure hardware to make it even harder to reverse engineer. Kind of wild!