color sensor

[wishfulthinker]

good day...

i have this project that needs to determine the color of a paper... what sensor could you suggest that i could use in this said project... the paper is not so thin and cnt be easily reflected by a light...

can i use LED's...? but how could i use this LED...

 

[Nigel Goodwin]

Think what 'colour' is! - use coloured filters over LDR's/photo-transistors and reflect white light off the paper on to them. Then read the values of the three receivers.

 

[evandude]

I've also seen it done the other way, using red, green, and blue LED's reflected off the paper onto a single LDR. There are issues such as the exact color of each LED not being perfect R/G/B, the light intensities of each not being the same, and the exact angle/distance from each LED to the sensor not being identical, but depending on your application it could be more than good enough.
Accuracy could of course be improved by more careful construction, adjustment of each LED's drive current to better equalize the intensity, and some calibration in software.

 

[Hero999]

Use two RGB LEDs, one for the emitter and one in reverse (acting as a photovoltalic cell) as the reciever.