A device for measuring oxygen saturation includes circuitry configured to measure a first diode voltage at a light emitting diode while applying a first current through the light emitting diode, measure a second diode voltage at the light emitting diode while applying a second current through the light emitting diode, and measure a third diode voltage at a light emitting diode while applying a third current through the light emitting diode. The circuitry is further configured to determine a series resistance based on the first diode voltage, the second diode voltage, and the third diode voltage and 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.