Optical heart rate sensor

heart rate sensor

hi all,

i'm trying to build a heart rate monitor via finger optical sensor.

Should i be using the transmission or refletion method for pulse oximeter?? any helpful links? advices?

Thanks for all your help. very deeply appreciated.

heart rate sensor circuit

Transmission type would give sensing advantage but it would bring trouble if the person's finger is too thick.

optical heart rate sensor

just simlpy visit this topic all you find



and this

optical pulse sensor

Carrie,

Keep in mind that pulse oximetry is less reliable than EKG.

- Pulse oximetry depends on the thickness of the patient's finger.
- Patient should have no circulation problems in hands and arms.
- Patient should feel warm, because if he's cold, the capillaries in his fingers will contract.

Pulse oximetry works great on healthy engineers, though!

- Nick

optical heart rate monitor

kender said:

Carrie,

Keep in mind that pulse oximetry is less reliable than EKG.

- Pulse oximetry depends on the thickness of the patient's finger.
- Patient should have no circulation problems in hands and arms.
- Patient should feel warm, because if he's cold, the capillaries in his fingers will contract.

Pulse oximetry works great on healthy engineers, though!

- Nick

Click to expand...

Oh well, the major problems with the TRANSMISSION type pulse oximetry are close to what you mention, but in high biomedical enginerring slang they are called "low perfusion" and "motion artefacts" phenomena.

"Low perfusion" problem arises in post traumatic stress situation (after surgery or other trauma) when the periferial blood circulation is greatly reduced. To adress this problem some have to implement REFLECTIVE type pulse oximeter on artery close to the heart (forhead or coratery).

"Motion artefacts" problem arises when the optical path changes due to (surprice) patient motion and the oximeter confuses the venal blood flow with arterial one (the simple optical tickness variations of non-blood carrier tissue influence the RED and IR signals in similar way since their ratio ain't much afected, but if the motion artefact produces venal blood signal which comes inband the arterial signal, there is no way to distinguish between the two). To deal with motion artefacta adaptive filters are used. The measurement is made in at least three wavelenghts, one of them isobestic (the optical transmission don't depend on the oxi hemoglobin but just on the optical tickness) and this isobestic signal is used to estimate the variation in the optical tickness and correct the adaptive coeficcient to minimize the errors from it in the red and ir signals. Take look on the Massimo pattents.


PS :

For an example how to built simple microcontroller based pulse oximeter search texas instruments site (MSP430 pulse oximeter example have both description and full code).

For example of commercial product schematic diagrams and code some should look into the US pattent dadabase of NONIN (fuls description of their finger pulse oximeter) and various NELLCOR pattents.

pulse oximeter schematic

hi carrie,

the requiste of pulse oximetry differs from that of simple pulse counter.

though in priciple method is same but complexity involved in oximetry is each manuf. sectrets as it involes some arithmetic constants , to set for a given value of light detected by photodiode of infra and red led s. i have tried to make one of the pulse counter that is freely available on net by title HEMON pulse monitor
and it worked well. the circuit and the asm file is avilable , if you do not get then email me a request i will sent you ... the oximetry was and is hot topic but
difficult to get ready material to try from net..

optical heart rate monitor circuit

dirana42 said:

hi carrie,

the requiste of pulse oximetry differs from that of simple pulse counter.

though in priciple method is same but complexity involved in oximetry is each manuf. sectrets as it involes some arithmetic constants , to set for a given value of light detected by photodiode of infra and red led s. i have tried to make one of the pulse counter that is freely available on net by title HEMON pulse monitor
and it worked well. the circuit and the asm file is avilable , if you do not get then email me a request i will sent you ... the oximetry was and is hot topic but
difficult to get ready material to try from net..

Click to expand...

Like I pointrd out in my previous post there is A LOT of useful inforrmation on the optical pulse oximetry (including theory, cirquit diagrams and code) in the US patent dadabase.

Simple oximeter design using MSP430 is described here (including schematic diagrams and source code)

**broken link removed**

finger heart rate sensor

i think sound detector is realy suitable for your project. the heart sound is converted to a digital signal, after filtering of course.