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[SOLVED] Photo led and Photo Detector of Specific responsive Frequency

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ismbn

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What can happen if i use LDR instead of Photo diode
 

Audioguru

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What can happen if i use LDR instead of Photo diode
An LDR switches fairly slowly but it can detect light and darkness. Try it like this:
 

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ismbn

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what changes should i have to do in resistors value if i want to run this it 5V

- - - Updated - - -

if you don,t mind, please explain the diagram, i am not able to understand the working of diagram.

and

what changes should i have to do in resistors value if i want to run this it 5V?
 

ismbn

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hello.
i tried your design... but i think there some problem
1. i am not able to see any changes in output.
2. this may be due to the gain is 1. but i connected the resistor of 100K between pin 7 & pin 6. but no result.
3.

i have made this design please tell me is this correct to get the output... i have not included any filter for now, but i seen some waveform yesterday using this design but i think it was some thing else. because i am not getting any clear result now...
 

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Why do you keep changing the opamp and power supply voltage?
The gain of your latest circuit is 11 times and it has a dual polarity supply.
The output of the opamp should go positive or negative depending on the amount of light on the LDR.
 

BradtheRad

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Since you are now taking the sensor input as plain DC, you need to bring the input voltage down near 0V. (The reference is 0V because the inverting input is connected to ground.)

If you adjust values properly, you will get the sensor to provide a signal which stays centered at or near 0V.

Then if you are lucky you will get a few mV or uV signal.

As a result the output will go a few V above and below 0V.

5210086700_1420917615.png


It is important that illumination on the LDR be constant. The only change can come from blood corpuscles in motion.

It will also be tricky to adjust your LED to the proper brightness.

This is all part of experimenting until you get the project working.
 

ismbn

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ok. i will try this also...
one thing i want to conform with you all, please suggest me what will be the proper way to placing
the LED and LDR...

i tried both option...
1. at same plane. i.e. receiver transmitter at same direction. and placing finger on it
2. receiver and Transmitter opposite to each other, covering finger.

and
one more thing
do you think i should apply the pressure while holding or placing finger on the transceiver.
i made this thing using some cloth and paper and 2 sided tape.

IMG_20150112_115156265.jpg IMG_20150112_115205721.jpg

IMG_20150112_115253327.jpg IMG_20150112_115311349.jpg
 
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BradtheRad

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Surprising but true that light penetrates all the way through our thumb! However I believe it reduces the resolution of changes in blood flow, the more flesh you put between led and sensor.

I think the led and sensor should be close together. The only light to reach the sensor, should be indirect light which passes through a few local blood vessels.

They should not be pressed hard against the skin. They should not restrict blood flow.

Several previous threads discuss projects like this. A few of them worked. Try a search on pulsemeter and oximeter.
 

ismbn

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I got this output waveform, Do you think i will get the pulse rate after including a band pass filter of 1Hz to 3Hz. since now its giving 50.xx Hz.
i am using the above LED & LDR pair.
Please refer the images

IMG_20150112_170555.gif
 

BradtheRad

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A filter might help, but it can only help a certain amount.

It will help more if you reduce the 50Hz noise waveform.

Try powering the circuit from batteries. That way you'll have no unwanted supply ripple.

Turn off as many mains-powered lights as you can. Have the least possible light shining on your hand.

Keep your circuit distant from cables and equipment which carry mains current.
 
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Audioguru

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I mentioned the messy wiring might be picking up 50Hz mains hum because many of the wires are too long and are acting like antennas that pick up mains hum. The wires should be short and neat.
 

ismbn

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will it this can work please see the link...


**broken link removed**
 

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The article explains that the differential amplifier cancels the same interference that occurs at each input.
But maybe you should make your previous circuit again but with neat wiring to avoid the interference picked up by the messy wiring.
 

ismbn

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oh.. great news...
its working. you where correct @BradtheRad & @Audioguru
the noise are from the source only the very 1st design worked when i powdered it up using 9V battery & 7805,
i am getting correct & 5v level output...
Thank you all.:thumbsup:
 

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