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shiladityachattrrjee54
03-16-2011, 08:54 PM
Hey guys, I am working on a project which involves sensing of colours. Can someone suggest any dedicated IC or any circuit for that?

Coolpratheesh
03-17-2011, 10:10 AM
dude the easiest way of making a colour sensor is a single photodiode/LDR and using a tricoloured LED as a source.
steps involved will be.
1) turn off all LEDs and read the photodiode for ambient light reading
2) turn on one at a time and read the ADC values which will give an approximate value of the R G and the B values. which is the most required for sensing most colours.

shiladityachattrrjee54
03-17-2011, 01:56 PM
ok.....thanx a lot.....but can you suggest how to calibrate the setup....also can u provide a link to any circuit diagram........thanx a lot

Coolpratheesh
03-17-2011, 05:14 PM
dude... i have basically explained the full circuit..... any how no i dont have a circuit all u have to do is bias a photo diode and feed the voltage values to the ADC. and use 3 different LED's connected to any of you digital pins as ur light source. Now when you turn on the red light the amount of light reflected will give you a rough R value and so on and so forth for the Green and the blue as well.... as simple as that...

shiladityachattrrjee54
03-17-2011, 09:00 PM
okay..........i got it.....bt how will i get d percentage of RGB in the object i mean how to measure that???????????

Coolpratheesh
03-17-2011, 10:52 PM
you need to have the materials you want to detect beforehand and take the reading that can be displayed on the LCD and finally the values can be compared in the main program.

shiladityachattrrjee54
03-18-2011, 02:13 PM
i knw bt that reading will give the value of the resistance across the LDR.........how to get the percentage of colours? Isnt there any calibration needed? like some kind of a multiplying factor ????

MohitM
03-18-2011, 04:01 PM
dude the easiest way of making a colour sensor is a single photodiode/LDR and using a tricoloured LED as a source.
steps involved will be.
1) turn off all LEDs and read the photodiode for ambient light reading
2) turn on one at a time and read the ADC values which will give an approximate value of the R G and the B values. which is the most required for sensing most colours.
I am a bit curious... Do you mean to say that a photodiode response to red, green and blue wavelengths will be distinctly different? So much so that you can identify which colour is it?

If yes, can you point me to a credible source - an academic paper or something that says this?

And when you respond, please don't "dude" me!

Coolpratheesh
03-18-2011, 09:42 PM
I am a bit curious... Do you mean to say that a photodiode response to red, green and blue wavelengths will be distinctly different? So much so that you can identify which colour is it?

If yes, can you point me to a credible source - an academic paper or something that says this?

And when you respond, please don't "dude" me!

no not atall
see dis i think it should be self explanatory..
and i dodnt mean to be rude wen i say "dude".... take it easy man...

MohitM
03-18-2011, 10:42 PM
You didn't answer my questions.

Coolpratheesh
03-18-2011, 10:43 PM
http://www.philohome.com/sensors/colorsensor.htm
forgot to paste the link.....

Coolpratheesh
03-18-2011, 10:46 PM
does this answer the question?

debu
03-19-2011, 11:00 PM
@MohitM: While Coolpratheesh's link refers to an LDR based color sensor, I can vouch for a photodiode based solution based on the same principal, if you're looking to read more about this look at USP5229841 (Taranowski et al. '93), it is the same technique used in 100% of all optical fiber modems.

Regards,

Debu :)

allbits
03-26-2011, 12:17 PM
Use Avago sensors. Very small footprint though. Get them soldered or buy the break out board.

The response you can get from different colours are not linear - You need to do some compensations if you need to detect the colours precisely. I would recommend to use a ready made colour sensor it you have the budget. otherwise, use LDRs and green, blue and red filters.

http://www.robotroom.com/ColorSensor.html
might be of some help.