Design of a Noninvasive Pulse Rate Meter

The purpose of this project was to design a noninvasive pulse rate meter. The design team decided to create a four-stage system for identifying the pulse using optical sensors. The first stage is the input, where an infrared LED shines light at a patient's finger while a photodiode receives light on the other end. The change in blood volume in the patient's finger changes the light in the patient's finger, which creates a current across the photodiode. The second stage is the current-to-voltage converter, whereby the current created by the change in light levels effects a change in voltage. This voltage is passed to the third stage, which is filtering, which attenuates the low-frequency DC offset as well as the high-frequency noise. The final stage is amplification, whereby the filtered signal is amplified so that it may be read by other means, such as a microcontroller.