need help with pulse oximeter project

[Siyah]

I have a project : Design a pulse oximeter.

As you know in pulse oximeters, two leds generate two different wavelenght lights; red and infrared. The light passes on finger and reaches photodiode after finger absorbs some light. The amount of light reaches photodiode makes difference in current. Transimpedance circuit changes current to voltage and amplifies and after filtration of signal we'll take it with DAQ (NI USB 6009) and process with labwiev.

We'll work the leds with Analog outputs of DAQ. When red led is open the IR led is closed. Each led has %10 duty cycle. 

When we'll take the signal with DAQ, the signal will be one signal with the components of

1-) when red led is open

2-) when IR led is open

My question is How can we seperate theese signals and get 2 different signal of red and IR. I thought we can do that with time factor. because we'll drive the leds with labwiev and we'll know the time which led is open and when it is open.

I am very new at labwiev. I know this is not a good vi but

I made a "vi" for driving the leds.

I'll apriciate so much if you help me.

Thanks by now.

Osman Onur Erdoğan

Başkent University

Biomedical Engineering

[Alain_S]

I didn't know what a "pulse oximeter" is but Wikipedia teach me a bit 🙂

The vi you posted don't match the description you gave us, so please allow me to ask some questions.

You have two standard electronic components LED's, one emits red light and the other one IR light.

Do you need to drive those led's with the USB 6009 device?

A led needs current to lit not voltage. That current is about 20mA, check datasheet for correct value.

So if you were thinking to drive the led's with "Dev1/ao0" and "Dev1/ao1", this isn't the right way to go, unless I missed something.

You should use two 5V digital outputs, with the correct series resistor the led's will get the current needed.

You talked about 10% duty cycle for each led, but what's the phase between both led's.

Once the complete timing is known, you can program the two digital outputs.

Is there only 1 photodiode the measure the light of both red led and IR led?

The signal from that photodiode is measured by the USB 6009.

There is only one voltage coming out of that sensor, right?

You need a digital triggered acquisition.

Each time a led is driven, you should measure the voltage from the photodiode.

Search the examples for a suitable demo VI and adapt it to your needs.

I think "Acq&Graph Voltage-Int Clk-HW Trig Restarts.vi" is a good place to start as long as you change the trigger from analogue to digital.

[Siyah]

First thanks for your concerne.

Driving the leds are not big deal :D.

The reason I want to use analog outputs of DAQ for driving leds is : using the time domain for separating the signals. duty cycle and phase is optional. Only thing that is important is ; when one led is open the other must be closed. When red led is open We get the signal about Hb consentration and when the IR led is open we get the signal about Hbo2 consentration. There is only one photodiode and gives information about Hb when Red LED is open and about HbO2 when IR LED is open. System works like that. After that I need some formulas but there is some time for that. The things you wrote was true by the way 😄

I tried a simulation with a sine wave(I accept the sine wave as a photodiode output signal).Then I separated the signals. I couldn't aquire the photodiode output signal yet. But after I get it. I think this will work:D

I have attached the vi again with separating parts.

Sorry for my language.

Thanks again

Message Edited by Siyah on 07-26-2009 12:20 PM

[DFGray]

Your VI will not work reliably because there is no synchronization between the different data generation VIs.  Please look at the LabVIEW help for how to synchronize multiple acquisitions.  In short, you need to make sure they all use the same clock.  There are a couple of changes I would recommend:

1. Use waveforms, not single points, for your generation.  This is much more efficient.
2. Use square waves, not sawtooth, if you want the LEDs to go on and off.  This makes it easy to interleave their on periods.
3. Tissue has a lot of scatter.  This will effect the shape of the output signal from the LEDs.  Make sure you separate them enough in time.

And some suggestions for consideration:

1. You do not need to separate the LED signals in time, although that is easiest to understand.  You will probably get better signal to noise if you separate them in frequency (i.e. using sine waves, drive one at 1kHz, the other at 1.7kHz, separate with FFT based analysis).
2. National Instruments has a group dedicated to biomedical applications.  You may consider joining it and posting your questions there.
3. If you have not already done so, run through one of the LabVIEW tutorials.  The time spent doing this will more than make up for itself in the days ahead.  If you can, take some classes.

[rajneojack@yahoo.co.in]

i have bought a pulse oximeter , and i want to interface the readingd to a daq and hence acquire data in labview.

till now what i thought that i connected two wires from the sensors pin and interfaced the data in labview.. but i am getting absurd result.

i dont know how to procedd.

further do tell me if i can buy any blutooth pulse oximeter which can be interfaced with labview.

[johnsold]

This thread was 4 years old. Your question has nothing to do with the topic of the original thread except that it relates to pulse oximetry.

You should start a new thread.

Next, you need to understand how your instrument works. Generally one does not connect a DAQ system to the internal workings of an instrument in an attempt to transfer data to the computer.

Descriptions like "absurd result" do not convey any useful information. You need to specify, quantitatively, numerically, what result you got, what you expected, what errors occurred, and exactly how you had everything connected.  Post your VI with typical data - even if it is absurd - saved as default. We do not have your apparatus and could not duplicate your process so we need your data.

What does Bluetooth have to do with a DAQ-based interface to an instrument?

Lynn