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Author Topic: Pulse heart sensor?  (Read 2163 times)
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London
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I want to measure someones heartbeat, do you know of any pulse sensors to do this? Ideally i'd like to place a finger on the sensor, rather than wrapping around the finger.

thanks
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I did some minor research into this last night actually. The easiest (althought not the best) solution is to use an IR LED (as bright as possible) to shine through the finger and on the opposite side have an LDR (light dependent resistor) to measure how much of the infrared that passes through. The density of the blood in the finger changes with the heartbeats, so this is what you're supposed to pick up. I've seen some pages describing both the theory + how to build one, but I don't have the bookmarks here at the moment. Let me know if you need them and I'll post them for you. Also, let me know if you manage to build something that works nicely smiley
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London
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I'm not sure about the IR LED solution, it doesn't seem that reliable. Here is one example of that method
http://www.picotech.com/experiments/calculating_heart_rate/index.html
(thanks Adam)

I am trying to find something off the shelf.

Tom Igoe has some information
http://www.tigoe.net/pcomp/resources/archives/elec_supplies/000678.shtml

Linking to OEM products from Polar
http://www.polarusa.com/manufacturers/products/products.asp

and Masimo
http://www.masimo.com/OEM/index.htm

(im still researching)
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I asked a physician relative, and got some further info about the LED IR solution (this applies to all types of "clip-on" solutions).  The main use is to measure oxygen saturation in the blood. It is able to register the pulse, but for rates above 110-120 it's more or less useless, so to get a pulse reading physicians do it manually, i.e. finger to vein and counting the beats over a timespan.
EKG's are much more able in the field of reading heart beats and behaviour, but it's of course way more intrusive than a clip-on, with all them electrodes and such. Finding EKG's off-the-shelf won't come cheap either, from what i've found. And having DIY things run a voltage through your body is usually not a good idea...
I'm going to build the LED IR thing later next week and see how it turns out. Who knows, it might be bad at reading the pulse, but perhaps one could do something fun with haemoglobin oxygen saturation...
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London
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Here are a few off the shelf products
http://store.transducersales.com/tsd200.html
http://www.ufiservingscience.com/DS10201.html
http://www.dolphinmedical.com/210adult.htm

Neither Polar or Masimo do anything like this.

Will you use an IR Led and a light sensor sensitive to IR light? Will you build a signal amplifier circuit?

There is also this Arduino sheild in development, but little info at the moment
http://www.arduino.cc/en/Main/BioSensorsBoard
« Last Edit: August 16, 2006, 06:54:42 am by chris » Logged

London
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Interestingly this page shows the light and sensor on the same side of the finger, not a clasp/holder as the others.

http://e-prolab.com/comlab/sttop/sttop-bm/bm-optical.htm
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Stockholm, Sweden
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Actually you don't need to have the sensor on the opposite side, since the light in the tissue scatters in all directions (with the fluctuating blood pressure in the finger altering the amount of light absorption). I would think it's even better to have the sensor on the same side as the led, or at least have sensor/led on left/right sides of the finger as opposite to top/bottom sides, since you don't have to worry about the finger nail getting in the way. It is after all an extra thick layer the photons have to penetrate.

I'm thinking about butchering this:
http://www.ellos.se/DetailPages/DetailPage.aspx?productId=129782 (Price is approx. €20)
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London
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Do you know which exact type of sensor & led was used here, plus what components are needed to build the amplifying circuit?

http://www.picotech.com/experiments/calculating_heart_rate/index.html
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Quote
Do you know which exact type of sensor & led was used here, plus what components are needed to build the amplifying circuit?

http://www.picotech.com/experiments/calculating_heart_rate/index.html


It gives you the manufacturer and part numbers of the LED and Sensor in the article!

"The light-emitting diode (Siemens SFH487) and the phototransistor (Siemens SFH309FA)..."

And a circuit diagram of the amplifier!!!! With parts listed! What more could you want :-)

Or am I missing something in your question?
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London
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Sorry I am being a complete tool, skimming rather than reading properly.

My main problem is lack of circuit diagram knowledge, knowing what components are needed for amplifier circuit & how to wire them up. About time I learnt.
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Alexandre Quessy
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Hi !
I want to do the same thing.

Maybe a LED and a light sensor. (with a voltage divider) Also, we could use a sound sensor like on this page :

http://www.doctronics.co.uk/voltage.htm

Then, we would need to measure the analog in over time, and record peaks frequency using something like the Metro library. http://www.arduino.cc/playground/Code/Metro

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Alexandre Quessy

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Ok this home made solution isn't going very far.

I have found this for £20 though
http://www.relax-uk.com/product.asp?id=13&sm=14
http://www.bio-medical.com/product_info.cfm?inventory__imodel=6002F

It comes with USB Mini B though, which won't go into a PC and don't think a converter will help.

They say you need this USB Pod for $185
http://www.heartmathstore.com/cgi-bin/category.cgi?item=6002-H&type=store

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Daniel
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Hi

i actually tried to do this a few years ago. The threads above are correct in that the pulse oximeter is the way to go. You can get a box of them on Ebay: they have a proprietary connector that gives you access to the led and a phototransistor.

Now the bad news:

1. You need some pretty sweet, very low noise operational amplifiers to detect the change in the phototransistor. If I remember correctly, a heartbeat caused a 10mv change in the photosensor's value.

2. These pulse oximieters are designed largely for people who are lying in bed and not moving around much! Every time you move your arm around, the blood gets sloshed around in your arm, and influences the signal coming from the phototransistor. Add that blood-sloshing-noise to your 10mv change detector above, and you have got a pretty serious analog and digital  job on your hands. The computerized circuitry that detects the light change in the commercial oximeters filters out such movement anomalies... so you will have to figure out how to do this in yours.  Headache number two.

I never really got it working the way it was supposed to... but if you can, I want the schematic! smiley

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I tried making something like that work, years ago. The IR solution didn't work for me, probably because of the noise level in the preamp.

Finally, I used a small loudspeaker, directly attached to the torso. That proved much easier to filter/amplify and worked very well. The speaker cone was filled with polystyrene, in order to provide a flat surface.

Not sure this will do in your case, but hey, you never know...

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