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Pulse Oximeter | Cypress

Block Diagram

Design Considerations

The percentage of arterial blood (or haemoglobin (Hb)) saturated with oxygen to provide anesthesia helps to determine the effectiveness of a patient’s respiratory system, and to diagnose various illnesses. A Pulse Oximeter is a non-invasive device used to measure the percentage of haemoglobin saturated with oxygen and to measure heart rate. This application note describes a Pulse Oximeter, which is useful in medical, sports training, and home appliance applications.

The Pulse Oximeter operation is based on measuring the absorption of red and infrared light that passes through a patient's finger or ear lobe by using light sensors. Haemoglobin that transports oxygen (oxy-haemoglobin) absorbs infrared wavelength (800-940 nm) of light and haemoglobin that does not transport oxygen 

(deoxy-haemoglobin) absorbs visible red wavelength (600-700 nm) of light. Backgrounds such as fluid, tissue, and bone are factored out of the measurement by monitoring the steady state of absorption from bone tissue, venous blood, and arterial blood. LEDs are used as the light source and are sequentially pulsed at a fast rate. During a heartbeat, blood volume increases and the AC component of the photodetector’s current is used to calculate the absorption of oxy and deoxy-haemoglobin. 

The received LED lights are converted to electrical signals by a photodiode and then amplified. PSoC® 3’s inbuilt Trans-impedance Amplifier module can measure currents up to 3 nA is ideal for low current measurements. In addition to this PSoC ® 3’s wide operating voltage range of 0.5V to 5V, low active current of 1mA @ 6 MHz, sleep current of 1µA and hibernate current of 200 nA makes it an ideal choice for a one-chip hand held Pulse Oximeter solution.

Software and Drivers

  • PSoC Creator

    PSoC Creator is a state-of-the-art software development IDE combined with a revolutionary graphical design editor to form a uniquely powerful hardware/software co-design environment.

  • PSoC Designer

    PSoC Designer is the revolutionary Integrated Design Environment (IDE) that you can use to customize PSoC to meet your specific application requirements. PSoC Designer software accelerates system bring-up and time-to-market.