Pulse oximetry measures the relative concentration of arterial oxygenated hemoglobin and reduced hemoglobin. This paper presents the design of a pulse oximeter, which measures the presence of a third substance, carboxyhemoglobin (HbCO), by unfiltered LEDs at 660 nm, 810 nm, and 940 nm. Background information is given on the theory of pulse oximetry. Theoretical approximations and calculations w...