A pulse oximeter is a healthcare product that quickly measures the oxygenation of the blood by using light to monitor the state of the hemoglobin. Recently, such products have become smaller and lightweight and sell at lower prices. As a result, besides being used in the treatment of patients in hospitals, they have become popular for home healthcare and everyday health monitoring, including monitoring during strenuous activities such as mountain climbing or physical exercise.
To perform the oxygen measurement, the meter emits red light and infrared light into the blood, and then detects with a sensor the light that passes through the blood. The signal from the sensor is very weak, so an amplifier circuit is used to raise its level, after which an A/D converter reads the amplified signal. A D/A converter is also necessary to modify the strength of the measuring light to compensate for changes in the level of the ambient light.
MCUs in the 78K0R/Lx3, the R8C/Lx and the RL78/L1x Series from Renesas Electronics integrate the on-chip A/D and D/A converters required in pulse oximeters, as well as an LCD drive-control circuit. These on-chip features reduce the number of external components required, making the MCUs ideal choices for pulse oximeter products that must combine compact size and low cost.
System Block Diagram
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