Pulse oximeter design

[moiktran]

Hi,

  I have looked through this forum to find answers for my question, including thread http://forums.ni.com/ni/board/message?board.id=170&message.id=141418&query.id=29185#M141418, but was unsuccessfull so far.

  I'm trying to find the pulse rate by building a pulse oximeter from scratch. I have a continous voltage waveform from the IR receiver and the Red receiver being fed into LabView.

So lets say that I have 2 waves, V-red(t) and V-ir(t)  at any given time(when the patient has his finger between the receiver and transmitter).

 By using V-red(t) and V-ir(t) ,how can I get the pulse wave?

 I am not using a timing circuit alternatively, I'm obtaining these signals from 2 seperate channels constantly. How would go about removing my DC offset?

 Thanks, any help would be much appreciated!

Moik

[Now_With_Underscores]

Hi Moik,

 Thanks for posting!  Can you clarify your question just a bit? Which DAQ device are you using to acquire the analog signal?  Are your inputs connected in Differential mode, Reference Single Ended mode, or NRSE?  I would recommend differential mode, as the DC offset is removed by the DAQ driver (In differential mode two physical channels are used, AIX- and AIX+.  AIX- is subtraction from AIX+ internally to provide the difference between the two RSE channels, which results in a differential measurement).  Is this the DC offset you are referring to?  If this is not what you are referring to, please provide as much information as possible so that we can provide you a more specific answer.

[moiktran]

Hello Knights,

  Unfortunately all the equippment is in my university lab. I can't remember the specifications off the top of my head. I will repost once I have them.

  But in the meantime, I'm trying to figure of if there is a theoritical relationship between V-ir and V-red that will give me the heart pulse wave?

  The DC offset I'm talking about is the DC offset in pulse oximetry, as shown below : 

 

  http://www.oximeter.org/pulseox/principles.htm

  Thanks.

Moik

[Now_With_Underscores]

Hi Moik,

The monitored signal returned bounces in time with the heart beat because the arterial blood vessels expand and contract with each heartbeat.  This should be all you need to determine the heart rate.  I am not an expert with your application, but I would suspect that performing a simple FFT in LabVIEW would easily allow you to isolate and determine the beat frequency.  As far as removing the DC component, this could be done in LabVIEW as well, after the signal is acquired.  

[moiktran]

Hi John,

   The device I'm using to get the voltage signals into LabView is NI BNC-2110. For the Terminal configuration of the DAQ Assistant,I currently have it set to <Let NI-DAQ Choose>.

   I have connected the voltage signal from the IR receiver to AI2 and the Red light receiver to AI3, as floating sources.

[Now_With_Underscores]

Hey Moik,

Are you currently able to read in expected voltages through your DAQ device? 

Since there are many different ways to wire up devices to our DAQ cards, I recommend reading this guide for a general overview on how to configure each type.  Based on your comments thus far, I would guess that you are going to need to use a differential measurement for your configuration.

The BNC-2110 is the breakout device for your card; what card does the 2110 connect to on your machine?  You can easily find this out by opening Measurement and Automation Explorer (Start>Programs>National Instruments>Measurement and Automation).  Once the program opens, expand 'My System,' then expand 'Devices and Interfaces,' and finally expand 'NI-DAQmx Devices.' You should see a list of DAQ devices installed in your computer. 

 Once you have your DAQ hardware configured properly, we have several examples available via our Example Finder.  To view these examples, open LabVIEW, then select Help>Find Examples.  When the Example Finder opens up, click on 'Hardware Input and Output>','DAQmx>','Analog Measurements>','Voltage>','ContAcq&Graph Voltage-Int Clk.'

Hopefully this information gets your DAQ acquisition up and running.  Have a great afternoon!