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Author Topic: Arduino based Pulse Oximeter  (Read 2596 times)
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Hello all,
I'm not sure this is in the right section, but I'm stuck on a basic level. I'm trying to make a Pulse Oximeter that will communicate via I2C, and while reading existing projects, I found that someone was able to use a light to frequency converter(https://www.sparkfun.com/products/9768) to make spO2 observations. I currently don't know how to use the frequency that would be outputted by the converter to calculate Blood oxygen content. If anyone could shed some light on this, I might be able to better write the code. Thank you for your help!
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It seems to me that your problem is not about Arduino as such - you need to know how to calculate blood oxygen level from a light level. Is this a conventional use for the sensor? If so, I'd expect the people who supply it to tell you how to interpret the results.
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To make a pulse oximeter, you need to measure light transmission at two wavelengths (not just one), one red and one infrared. I suggest you read up on the theory.
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dc42 is exactly right, both in the tech aspect and in the best to do your own research
to learn what you're trying to do aspect. There should be plenty of info about pulse
oximeters on the web, it's a well-known technology. If you hold your fingers up to
a bright light source, you'll immediately see why it works.





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Yep you use two leds IR and a Red led it works really good the pulse is easy to get
the oxygen level is hard part. I made one using two led's IR and a red one  set the leds to putout there maxim output  with a piece of pvc pipe cut in haft to make like a clip to pace over your finger.

Put to leds on the bottom and the  light-to-frequency converter  on top hooked the output to my scope. It worked better then I figured it would.

here a video I did if you want to see the output its not high-tech but may get you started
Nut's and volts has how to make this better with code for the stamp

* tsl230ROximeter.pdf (303.51 KB - downloaded 53 times.)
« Last Edit: November 19, 2012, 05:42:34 pm by be80be » Logged

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See it good to have stuff all over the net I lost a bunch of good stuff but Google reading heartbeat with a Light to Frequency Converter

And It shows up with the goodies  

Here all you need to know there two pdf's one under the video and one here it's in two parts but it shows how to make this all work.

* TSL230Roximeter2.pdf (153.51 KB - downloaded 49 times.)
« Last Edit: November 20, 2012, 07:11:12 am by be80be » Logged

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See it to have stuff all over the net I lost a bunch of good stuff but Google reading heartbeat with a Light to Frequency Converter

Is that English?  smiley-confuse smiley-razz
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Na it's bad I should read it after I posted I left a lot of words out I do that some time's when I'm thinking faster then I can type. smiley-twist
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I apologize for misrepresenting myself, I've done plenty of research, and understand that I need to use red and infrared light, and understand that the oxygen content is a function of the ratio between the absorbances of the two sources of light because Hb absorbs more red light, and HbO2 absorbs more infrared light. What I don't understand is what parameter the frequency of red/infrared light that has passed through represents, and how I can use it to calculate SpO2
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What I don't understand is what parameter the frequency of red/infrared light that has passed through represents, and how I can use it to calculate SpO2

I haven't done the research you have, but nothing you've said prior to this gives me any reason to think that the frequency represents anything; you're talking about measuring the absorption at two frequencies, both of which are known, and from the two absorption figures you should be able to calculate the O2 saturation by some formula that your research should have given you. Presumably the two frequencies you're using need to be chosen carefully to match the absorption characteristics of Hb and Hb02 so you need to choose the appropriate hardware but once you've done that the frequency is fixed, and is not something you need to measure or derive any values from. It seems to me that what you need to measure is the light intensity, not the frequency.
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Like PeterH says, I don't see that frequency has anything to do with it, what you want to take is
a ratio of analog values. Unless some devices use modulated frequency to drive the Leds, and
bandpass filters to help reject background light, like in TV remotes.

However, the Sparkfun device you mentioned has nothing whatsoever to do with oximetery. The part
where it says "The TSL235R light-to-frequency converter outputs a square wave (50% duty cycle) with
frequency directly proportional to light intensity (irradiance)", the frequency is simply how they are
transferring the intensity information, so it can be read with a digital device rather than an A/D
converter.
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