Homemade Pulse Oximeter Based on 68HC908AB32

The device is based on 68HC908AB32 microcontroller that aims to create a pulse oximeter that will be used to measure arterial blood oxygen saturation and pulse.

A 68HC908AB 32 microcontroller is used to drive the system where the S&H and H-bridge zalaczajacym alternating LEDs are controlled by the waveforms of the 4-output function PWMa through tiny logic circuits. pulses of light brightness are provided by lower transistors.

The project is similar to those in clinics where a small device is put on a finger tip and one side has a light source while the other is a receiver. The parameter can be calculated depending on how much light is absorbed by hemoglobin. There are four buttons used for navigation along with a large 192×64 graphical LCD.

During the usage, the basis of saturation measurement principle is the fact that oxygenated blood, specifically hemoglobin, absorbs different wavelength of a person. The parameter of interest can be calculated using the basis of received signal ratio and the scanned finger with 660nm and 940nm light. The basis of the time lag between the maxima in the curve pletyzmograficznej is use to calculate the heart rate.