LED´s optimum duty cycle in heart rate and oxygen saturation level combinedly measurement device for low power consumption

Heart rate and oxygen saturation level measurement device needs to flash two LEDs alternatively at working mode. These flashing LEDs dominate the power requirement of the whole system. To save power dissipation in the LEDs, the LED drive signals are chopped with a small duty cycle along with high switching frequency. But this small duty cycle lowers the signal SNR and leads to an inaccurate result. So we need to find out an optimum duty cycle which can satisfy both criterions while the device works. This paper made an investigation to find out an optimum duty cycle of LED drive signals which can fulfil not only the low power consumption criterion but also ensures the data accuracy of the device. At first, theoretical design has been given. Then a prototype has been constructed and implemented by which the data accuracy variation at different duty cycle has been checked out. Finally we got the promising result at 5% duty cycle.