This article describes the design and implementation process of a module of Pulse Oximetry SpO₂ (Saturation of Hemoglobin with Oxygen As Measured by Pulse Oximetry) by means of the method of light transmittance through a pulsating vascular bed. A digital sensor was used to get the signal which has two light-emitting diodes, a red one in the visible region of the spectrum and another in the infrared together with a photoreceptor. The portion of light which is received by the photoreceptor is transmitted alternately from the red and infrared light, then reconstructed and processed with a dsPIC. Finally it is displayed as a plethysmographic waveform which gives the possibility to determine the percentage of oxygenated hemoglobin in the arteries.