A pulse oximetry reading is determined by the difference between two signals. Signal 1 is what we like to call "Red" or your basic LED with light output at about 720 nm, the second signal is what we like to call infer-red or the light from an infra-red transmitter. The two AC signals are put through two sample and hold circuits and the one is subtracted from the other, the resulting signal is directly proportionate to the SPO2 reading. The look up data is usually stored in a chart in the Micro controllers internal or external flash memory (Ususlally external). It will be necessary to strip off the DC and low frequency AC components before doing any calculations, all of which can be done in lab view if you know how using the exsiting filter vi's. The look up table data can be constructed manually by using an SPO2 simulator and recording the raw outputs from the differeance between the hold an capture circuit data and known simulator data once you have sucessfully constructed the labview aplication. I have never tried this, but you may beable to get a calibration chart from the manufacturer for the finger clamp assy. to help get you started.
It will be necessary to initially control the LED and Infra-red outputs to managable and usable levels, adjusting them accordingly before doing any calculations. (Aprox 200 LSB's each) On larger fingers it will be necessary to adjust the gain of the circuit to obtain correct readings. Since you will be using a single pick up device to read both the RED and Infra-red signals, it will be necessary to MUX/Switch between the signals feeding them into separate sample and hold applications in Lab view.
You will have to control the current going through both light sources to achieve the light output needed, which can be done VIA the apropriate Labview DIO Hardware.
Message Edited by doctorhash on 10-18-2005 08:35 AM
Message Edited by doctorhash on 10-18-2005 08:35 AM
