A device for measuring oxygen saturation includes circuitry configured to determine a series resistance for a light emitting diode based on a first diode voltage at the light emitting diode for a first current, a second diode voltage at the light emitting diode for a second current, and a third diode voltage at the light emitting diode for a third current. The circuitry is further configured to determine an intensity of a received photonic signal corresponding to an output photonic signal output using the light emitting diode. The circuitry is further configured to determine an oxygen saturation level based on the intensity of the received photonic signal and the series resistance.