Help needed! Photodiode does not seem to detect values

Projects General Guidance
1

Hi there, I am quite new to Arduino and i have been using it to work on a project to measure blood oxygen saturation.

I am currently using a SFH213FA(880nm) which is connected to a OP-AMP MCP6002 and into the analog input of Arduino. However, the Serial Monitor value of the input is always 0.00 . This happens for my SFH213 (Red light photodiode) as well.

Attached is the systematic of my circuit. Pin1 and Pin3 are the analog inputs for my IR and Red PD respectively

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2

Your IR LED emitter is the wrong way round. Check it is lighting up by looking at it through a camara.

3

Hi sorry about it but i have changed my configuration of my IR emitter and the values read are still at 0.00. Any ideas?

4

kohjianhao:
Hi sorry about it but i have changed my configuration of my IR emitter and the values read are still at 0.00. Any ideas?

Did you verify that it is emitting, after you changed it?

5

Can you draw a proper schematic showing the op amps as real symbols. They do not look right as you have drawn them. Why are there diodes in line with the sensors?

6

Sorry i am quite new to this schematics thing. Is it better if i link up the circuit, take a picture and post it here?

7

No at this stage it is about as useless as that schematic you posted. Draw a proper one with the op amps circuits showing.

8

Hi, i tried to make a neater schematic and i got the OP amp circuit attached!

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9

Hi,
You do not have you IR Detector biased to operate.
Please look at this example and video.(the video has a schematic of how to bias the detector.

Hope it helps. Tom... :ic

10

Thanks. I would swap over the + and the - inputs on that amplifier as you are asking the output to go more negative than the supply. Which of course it can't do.

11

Hi,
Also google arduino pulse oximeter circuit

Surprising what pops up.

Tom.. :slight_smile:

12

Thank you all so much for the replies! i will try again with the relevant links and changes!

Also, Tom, i did google before posting in the forum :slight_smile: However, i was unable to make sense of some components since i am a newbie!

13

However, i was unable to make sense of some components since i am a newbie!

In that case, you need to learn what those components do and how to use them.