Problem with the output of a pulse oximeter

• Mar 16, 2009

• #1

nareshbhar

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Hi all,
Actually i am making pulse oximeter as my project.
I am using OPT101 as RED & IR detector, and output of the detector is connected to instrumentation amplifier AD630 as shown in schematic and rest of circuit is connected as shown in schematic.CD 4053 is analog multiplexer which is used to separate out RED & IR detector output signal.
but i am not getting expected result at output point(e.g. Point D,E,F,G),so pls anyone could figure out the problem with circuit,specifically filters.
please give your views,& if any alternate circuits.
Thank You.

 

• Mar 17, 2009

• #2

Audioguru

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pulse oximeter canada

The inputs of the AD620 need a resistance to ground through a patient. The patient needs a negative common-mode feed usually to the right leg which is near the ground voltage. Then the inputs of the AD620 will work.

 

• Mar 17, 2009

• #3

nareshbhar

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shematic cd4053

but my sensor is finger sensor,and it has nothing to do with direct body contacts.
it just transmits the red & ir light which passes through finger and then received by detector.

 

• Mar 17, 2009

• #4

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gnd an ad620

You showed an ECG circuit.
When signal C1 goes high then the ECG output from the instrumentation amplifier is routed to the upper lowpass filter.
When signal C1 goes low then the ECG signal is routed to the lower lowpass filter.

There is no IR nor red detector circuit.

 

• Mar 18, 2009

• #5

nareshbhar

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Re: Pulse Oximeter

how can you say that its ECG circuit?. i think one can not say anything about circuit's application by just watching schematic.
and about analog multiplexer, its used to differentiate red & ir detector output,which is coming from one light detector only.

 

• Mar 18, 2009

• #6

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Pulse Oximeter

Your ECG circuit does not have inputs for an IR detector and a Red detector. Instead it has an instrumentatation amplifier (look on the datasheet of the AD620 for an ECG circuit similar to yours) that has its output switched to 2 identical filters.

Only 1 of the 3 switches in the multiplexer is switched.

 

• Mar 29, 2009

• #7

nareshbhar

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Re: Pulse Oximeter

yes,actually i have taken this circuit from datasheet only,and as i need two differnt filter so as i can get two outputs,one bieng red detector and one being ir detector.
actually problem with the circuit is that it is not filtering out my desired signal which is around .6hz to 1.5hz.so,can you suggest any change in filter design.
Thanks.

 

• Mar 29, 2009

• #8

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Pulse Oximeter

Your schematic does not show an IR detector and a red detector. It just shows part of an ECG circuit with some filters.
The lowpass filters pass frequencies below about 17Hz.

 

• Mar 29, 2009

• #9

nareshbhar

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Re: Pulse Oximeter

yes, I havn't shown the red & ir detector circuit.
I am using one detector with detecting range of 550nm-850nm.
I have connected my detector output to the input of instrumentation amplifier.

 

• Mar 30, 2009

• #10

R

ronydc

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Pulse Oximeter

WHY U EXPECT RESULTS HERE WITHOUT SHOWING THE red and ir DETECTOR CIRCUITS HERE .?

THINK..

 

• Apr 18, 2009

• #11

O

ostik

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Pulse Oximeter

hi im also making a pulse oximeter, if anyone can pls help me with the software pls. upload an example of a program so i know what its expected to look like atleast. im very new 2 this whole design thing n this is my first project. a schemetic would also be nice

 

• Dec 4, 2009

• #12

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arun0289

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Pulse Oximeter

Even im doing a project on pulse oximeter.. Is the ratio R- is jus the ratio of the 2 voltages(red n IR)??? plz do help me...thnks

 

• Aug 4, 2010

• #13

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juliushasan2

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Pulse Oximeter

hi, i'm making a pulse oximeter using msp430f149, any want want to help me?plese send me the code n guide to juliushasan2@gmail.com

Added after 38 minutes:

hi, my name julius..i have project to build up a pulse oximeter using msp430f149, i have build the board n downloader, i have bought the cable probe too..but i don't know how to finish the code and what type of lcd that i should to used...please help me to solve this problem, especially by the code problem..if any one ever build up the same thing like this, please help me to build the one..please answer my question and respond it to my mail at juliushasan2@gmail.com

 

• Aug 30, 2010

• #14

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tshepomatjebe

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Re: Pulse Oximeter

i need help in building a sensor for heart beat using lm358 but i m nt getting the result of pulses

---------- Post added at 10:05 AM ---------- Previous post was at 10:02 AM ----------

i appreciate if you can help me with a working circuit for this design?because i cant get the pulses using led,it just glow steadily it does flash according to pulses