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light sensor

Question asked by madhura hegde in #Coffee Room on Oct 30, 2009
madhura hegde
madhura hegde 路 Oct 30, 2009
I am doing a small project, for tht i ned a light sensor ckt. Can anybody suggest me where i can find it. I have got few. But its not reliable m feelin. So plz help me out. Relply sooooon😒 Posted in: #Coffee Room
reachrkata 路 Oct 31, 2009
Rank C2 - EXPERT
Try photodiodes / Phototransistors.

cooltwins 路 Nov 1, 2009
Rank B1 - LEADER
i am not sure about this but will LDR (Light dependent resistor) work
i used it once to find the change in amount of light falling on it
madhura hegde
madhura hegde 路 Nov 1, 2009
thanks a lot frendz......if i face any prob then surely approach again...馃槢
suman.mathad 路 Nov 4, 2009
Rank D3 - MASTER
i am new here.. i am in first sem
eee is realy tough for me .. please tell me how to cop with and also how to do projects[鈥婭MG]
distrito 路 Dec 5, 2009
color sensor project

I am new to eee. We have a color sensor lab project.
Photoresistors, LED diodes, opamps should be used.
Can you please help with its circuit?
cranky 路 Dec 5, 2009
Rank C3 - EXPERT
Use LED in f/b,photodiode(or LDR*) in r/b (don't forget to connect resistors in series with both components)..

connect the voltage across photodiode to one input of op-am and the other input will be a reference(use potentiometers for that)..connect other terminals of op-am to battery terminals(positive and negative)...

Your sensor is ready..depending on whether white or black surface the voltage across photodiode is going to change and hence the output

*LDR are sensitive to atmospheric light so photodiodes will be a better option..however,make sure your photodiodes work well..and there is no biasing in case of LDR's

Any doubt please ask馃榿
electronicsunzz 路 Dec 5, 2009
Rank D3 - MASTER
hi ,
moreover one can increase the sensitivity of the sensor by not letting other light falling on the light dependent resister expect the light we desired to sense.
this gives the accurate change in the resistance with respect to the desired light which we want to sense.
cranky 路 Dec 6, 2009
Rank C3 - EXPERT
the distance between the led and diode should be very less..the angle of cone should be less than equal to six degree for more sensitivity馃榿
distrito 路 Dec 7, 2009
thanks a lot for your assistance friends.
our sensor has to display three detected colors seperately. RGB.
So, does this mean that photoresistors can be used as brightness sensor?
When red light from the LED for example, shines on red and green objects, the light will be reflected more by red object compared to the green object. So can this sensor measure the brightness of the reflected wave and sense that the red object brighter than the green one?

I hope this is a good approach. I need a confirmation from you, please.
It seems thatI will need to use more than one op-amp. How will I calibrate the sensing of the three colors?

Red Green Blue LEDs should turn on when sensing red, green, blue colors respectively.

thanks beforehand

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