A LED–LED-based photoplethysmography sensor

A high sensitivity, low power and low cost sensor has been developed for photoplethysmography (PPG) measurement. It uses standard light emitting diodes (LEDs) as both light emitter and detector, pulse-based signal conversion techniques instead of the classical analogue-to-digital convertors (ADCs) and a general purpose microcontroller for the implementation of measurement protocol. The main advantages of the proposed approach are that it leads to better spectral sensitivity, increased and adjustable resolution, reduction in cost, dimensions and power consumption, and it avoids the need for expensive and precise operation amplifiers, ADCs and other external components. The basic sensing configuration presented uses only two I/O pins and two LEDs and is capable of detecting the PPG signal from a finger or toe. It is then very simple to extract the vital signs such as heart rate and heart rate variability from such a signal. The basic configuration can easily be expanded to include a pulse oximeter for the determination of oxygen saturation (SpO(2)) by the addition of only two more LEDs. The proposed technique is also suitable for a wide range of other photometric applications.