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Application Report
SLAA274B – November 2005 – Revised February 2012

A Single-Chip Pulsoximeter Design Using the MSP430
Vincent Chan, Steve Underwood ................................................................................. MSP430 Products ABSTRACT This application report discusses the design of non-invasive optical plethysmography also called as pulsoximeter using the MSP430FG437 microcontroller (MCU). The pulsoximeter consists of a peripheral probe combined with the MCU displaying the oxygen saturation and pulse rate on a LCD glass. The same sensor is used for both heart-rate detection and pulsoximetering in this application. The probe is placed on a peripheral point of the body such as a finger tip, ear lobe or the nose. The probe includes two light emitting diodes (LEDs), one in the visible red spectrum (660 nm) and the other in the infrared spectrum (940 nm). The percentage of oxygen in the body is worked by measuring the intensity from each frequency of light after it transmits through the body and then calculating the ratio between these two intensities. This application report uses the MOD-PULSE Pulseoxmeter and Heart-Rate Monitor Using the MSP430FG439 development board by OLIMEX Ltd (http://www.olimex.com/dev/mod-pulse.html). A revised version of this application is described in the application report Revised Pulsoximeter Design Using the MSP430 (SLAA458).

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Introduction
The Pulsoximeter is a medical instrument for monitoring the blood oxygenation of a patient. By measuring the oxygen level and heart rate, the instrument can sound an alarm if these drop below a pre-determined level. This type of monitoring is especially useful for new born infants and during surgery. This application report demonstrates the implementation of a single chip portable pulsoximeter using the ultra low power capability of the MSP430. Because of the high level of analog integration, the external components can be kept to a minimum. Furthermore, by keeping ON