Design of non-invasive visual pulse oximeter based on MSP430 series MCU

A pulse oximeter is a medical device used to monitor a patient's blood oxygen levels. The device measures blood oxygen levels and heart rate and generates an alarm when levels drop below a predetermined threshold. This type of monitoring is extremely useful for newborn babies and during surgical procedures.

The MSP430FG437 microcontroller (MCU) used in the design of the non-invasive visual pulse oximeter combines the peripheral probe with the MCU and uses an LCD glass screen to display the blood oxygen status and pulse rate. The sensor in this application is used for both heart rate detection and pulse oximetry. The probe is placed at a point on the human body, such as a fingertip, earlobe, or nose. The probe contains two light-emitting diodes (LEDs), one in the red visible spectrum (660nm) and the other in the infrared spectrum (940nm). By measuring the intensity of each frequency of light passing through the human body and then calculating the ratio between the two intensities, the human body's blood oxygen percentage can be determined.

The diagram above illustrates a single-chip, portable pulse oximeter implementation using an ultra-low-power MSP430 MCU. The number of external components is kept to a minimum due to the high level of analog integration. Also, power consumption is reduced by keeping the on-time (ONTIme) to a minimum and by cycling the power of the two light sources.